CLUTCH

Abstract

A clutch is provided with a drive-side rotational body and a driven-side rotational body, which is movable in the axial direction of the drive-side rotational body between a coupled position. The driven-side rotational body has a groove having a helical portion and an annular portion. The clutch also includes an urging member and a pin that is selectively inserted into and retracted from the groove. The clutch moves the driven-side rotational body to the decoupled position against the urging force of the urging member by inserting the pin in the helical portion. The clutch further includes a restricting portion that restricts shifting of the position of the pin from the annular portion to the helical portion when the pin is positioned in the annular portion.

Description

TECHNICAL FIELD

The present disclosure relates to a clutch that switches the state of power transmission from a drive-side rotational body to a driven-side rotational body by switching the coupling state of the driven-side rotational body with respect to the drive-side rotational body.

An engine is known that couples a mechanical pump, which circulates coolant, to the crankshaft through a clutch to operate the pump using rotational force of the crankshaft and disengages the clutch to stop operation of the pump. Clutches for switching the coupling state of the pump with respect to the crankshaft include a clutch having a drive-side rotational body coupled to the crankshaft and a driven-side rotational body, which is rotational relative to the drive-side rotational body. The clutch is maintained in the engaged state by pressing the rotational bodies against each other using magnetic force of magnets.

Such clutches include a clutch described in Patent Document 1. The clutch described in Patent Document 1 includes a coil. To disengage the clutch, energization control is performed on the coil to generate a magnetic field that cancels the aforementioned magnetic force.

PRIOR ART DOCUMENT

Patent Document

Patent Document 1: Japanese Laid-Open Patent Publication No. 2010-203406

SUMMARY OF THE INVENTION

Problems that the Invention is to Solve

In a configuration in which the clutch is maintained in the engaged state by pressing the drive-side rotational body and the driven-side rotational body against each other as described in Patent Document 1, the force needed for such pressing becomes greater as the torque that needs to be transmitted through the clutch, or, in other words, the torque needed by an auxiliary device driven and rotated by the driven-side rotational body, becomes greater. To increase the pressing force, magnets with a greater magnetic force must be employed. This necessitates a larger-sized coil to cancel the magnetic force.

The larger-sized coil enlarges the size of the clutch and increases power consumption. Therefore, the force needed for disengagement is therefore desired to be minimized while ensuring transmission of great torque.

This problem is not restricted to clutches that cancel magnetic force of magnets by generating a magnetic field as in the above-described case. The same problem is generally present in clutches that are disengaged by causing relative movement between a drive-side rotational body and a driven-side rotational body with an actuator, such as clutches that are disengaged using hydraulic pressure.

Accordingly, it is an objective of the present disclosure to provide a clutch that can be disengaged by a small force.

Means for Solving the Problems

To achieve the foregoing objective and in accordance with one aspect of the present invention, a clutch is provided that includes a drive-side rotational body, a driven-side rotational body, an urging member, a groove, a pin, and a restricting portion. The driven-side rotational body is movable in an axial direction of the drive-side rotational body between a coupled position at which the driven-side rotational body is coupled to the drive-side rotational body and a decoupled position at which the driven-side rotational body is decoupled from the drive-side rotational body. The urging member urges the driven-side rotational body from the decoupled position toward the coupled position. The groove is formed in an outer circumferential surface of the driven-side rotational body. The groove has a helical portion that extends about an axis of the driven-side rotational body and an annular portion that is formed continuously from the helical portion and extends over an entire circumference of the driven-side rotational body and perpendicularly to the axial direction. The pin is selectively inserted into and retracted from the groove and restricted from moving in the axial direction. When the pin is in a state inserted in the helical portion and engaged with a side wall of the helical portion, the position of the pin is shifted from the helical portion to the annular portion through rotation of the driven-side rotational body such that the driven-side rotational body is moved to the decoupled position against urging force of the urging member. The restricting portion restricts shifting of the position of the pin from the annular portion to the helical portion when the pin is in a state located in the annular portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a clutch according to a first embodiment;

FIG. 2 is a side view showing the clutch shown in FIG. 1 in a disengaged state;

FIG. 3 is a side view showing the clutch of FIG. 1 in an engaged state;

FIG. 4 is a cross-sectional view illustrating the relationship between a groove of a driven-side rotational body and a stopper member and the configuration of an actuator for operating the stopper member;

FIG. 5 is a side view showing a clutch according to a second embodiment in a disengaged state;

FIG. 6 is a side view showing the clutch illustrated in FIG. 5 in an engaged state;

FIG. 7 is a developed view showing a groove of the clutch of FIG. 5;

FIG. 8 is a side view showing a clutch according to a third embodiment in a disengaged state;

FIG. 9 is a side view showing the clutch illustrated in FIG. 8 in an engaged state;

FIG. 10 is a developed view showing a groove of the clutch of FIG. 8;

FIG. 11 is a developed view showing a groove of a modification of the third embodiment;

FIGS. 12A, 12B, 12C, and 12D are schematic diagrams illustrating change of the state of a clutch according to a fourth embodiment;

FIGS. 13A, 13B, 13C, and 13D are schematic diagrams illustrating change of the state of a clutch according to a fifth embodiment; and

FIG. 14 is a perspective view showing a driven-side rotational body according to another embodiment.

MODES FOR CARRYING OUT THE INVENTION

First Embodiment

A clutch according to a first embodiment will now be described with reference to FIGS. 1 to 4.

A clutch according to a first embodiment switches the state of power transmission from a crankshaft arranged in an engine to a water pump, which circulates coolant of the engine.

As shown in FIG. 1, a clutch 100 of the first embodiment is accommodated in an accommodating portion 310, which is arranged in a housing 300. A substantially cylindrical support member 320 is fitted in the housing 300. An output shaft 210 of the clutch 100 is rotationally supported by the support member 320 through a first bearing 330, which is located at an inner circumferential side of the support member 320.

An impeller 220 of a pump 200 is attached to a distal end portion (a right end portion as viewed in FIG. 1) of the output shaft 210 in a manner rotational integrally with the output shaft 210. A drive-side rotational body 110 is rotationally supported by a proximal end portion (a left end portion as viewed in the drawing) of the output shaft 210 through a second bearing 340. A straight spline 212 is formed in an outer circumferential surface of a portion of the output shaft 210 between the first bearing 330 and the second bearing 340.

With reference to FIG. 1, a driven-side rotational body 120 is arranged between the housing 300 and the drive-side rotational body 110. An engagement portion 121, which is meshed with the straight spline 212 of the output shaft 210, is formed in an inner circumferential surface of the driven-side rotational body 120. This configuration allows the driven-side rotational body 120 to rotate integrally with the output shaft 210 and move in the axial direction of the output shaft 210. In the first embodiment, as represented by the long dashed short dashed lines in FIGS. 1 to 3, the output shaft 210, the drive-side rotational body 110, and the driven-side rotational body 120 are arranged coaxially with one another. Hereinafter, the extending direction of the axis of these components will be referred to as the axial direction.

The driven-side rotational body 120 has an outline including two columns that have different diameters and are joined coaxially with each other. The driven-side rotational body 120 is supported by the output shaft 210 in such an orientation that a large diameter portion 122 is located on the side close to the drive-side rotational body 110 (a left side as viewed in FIG. 1) and a small diameter portion 123 is arranged on the side close to the pump 200 (a right side as viewed in the drawing).

A recess 124 having an opening facing the pump 200 is formed in the small diameter portion 123 of the driven-side rotational body 120. A plurality of accommodating recesses 125 for accommodating urging members 135 are formed in a bottom portion of the recess 124. The accommodating recesses 125 are arranged circumferentially in a manner surrounding the output shaft 210.

Each of the urging members 135 is, for example, a coil spring and accommodated in the corresponding one of the accommodating recesses 125. Each urging member 135 has a distal end secured to a securing projection 211, which projects from the output shaft 210. The urging members 135 are accommodated in the corresponding accommodating recesses 125 each in a compressed state and urge the driven-side rotational body 120 toward the drive-side rotational body 110 (leftward as viewed in FIG. 1).

A plurality of ball accommodating grooves 127 each for accommodating a corresponding one of balls 130 are formed in the large diameter portion 122 of the driven-side rotational body 120 and arranged circumferentially. An arcuate groove 111, which extends over the entire circumference of an inner circumferential surface of the drive-side rotational body 110, is formed in the inner circumferential surface of the drive-side rotational body 110. With reference to FIG. 1, the arcuate groove 111 has an arcuate cross section. Each of the balls 130 is accommodated in the space formed by the corresponding one of the ball accommodating grooves 127 and the arcuate groove 111.

When the driven-side rotational body 120 is arranged at the position illustrated in FIG. 1 after having been moved toward the drive-side rotational body 110 by the urging force of the urging members 135, the drive-side rotational body 110 and the driven-side rotational body 120 are coupled to each other through the balls 130.

Hereinafter, out of axial positions of the driven-side rotational body 120 moving axially along the output shaft 210, the position at which the drive-side rotational body 110 and the driven-side rotational body 120 are coupled to each other, as illustrated in FIG. 1, will be referred to as a coupled position.

A cup-like driven-side pulley 270, which surrounds the clutch 100 accommodated in the accommodating portion 310 of the housing 300, is attached to the drive-side rotational body 110. A drive-side pulley 260 is attached to an end portion of the crankshaft 250 in a manner rotational integrally with the crankshaft 250. The drive-side pulley 260 and the driven-side pulley 270 are coupled to each other through a belt 280, which is looped over the drive-side pulley 260 and the driven-side pulley 270.

As a result, as illustrated in FIG. 1, when the driven-side rotational body 120 is arranged at the coupled position and the drive-side rotational body 110 and the driven-side rotational body 120 are coupled to each other through the balls 130, rotation of the crankshaft 250 is transmitted to the driven-side rotational body 120 and the output shaft 210 via the drive-side pulley 260 and the belt 280. This causes the impeller 220, which rotates integrally with the output shaft 210, to supply coolant out from the pump 200. As represented by the arrows in FIGS. 2 and 3, the drive-side rotational body 110 rotates in a clockwise direction as viewed from the side corresponding to the distal end of the output shaft 210 (the side corresponding to the right end as viewed in FIGS. 2 and 3) toward the drive-side rotational body 110.

Referring to FIGS. 2 and 3, each of the ball accommodating grooves 127, which are formed in the large diameter portion 122 of the driven-side rotational body 120, extends in the axial direction from an end surface of the large diameter portion 122 before being curved and then extends in the rotational direction of the drive-side rotational body 110. A finishing end of each ball accommodating groove 127 forms a holding portion 128.

The depth of each ball accommodating groove 127 becomes smaller in the rotational direction of the drive-side rotational body 110 such that the depth of the holding portion 128 is minimized.

As a result, as illustrated in FIG. 2, when each ball 130 is accommodated in the axially extended portion of the corresponding ball accommodating groove 127, a clearance in which the ball 130 is permitted to rotate, together with the driven-side rotational body 120, with respect to the drive-side rotational body 110 is formed between the ball accommodating groove 127 and the arcuate groove 111 (see FIG. 1) of the drive-side rotational body 110.

In contrast, as illustrated in FIG. 3, when each ball 130 is located in the corresponding holding portion 128 after having been moved in the ball accommodating groove 127, the clearance between the holding portion 128 and the arcuate groove 111 (see FIG. 1) of the drive-side rotational body 110 is small. The ball 130 is thus caught between the driven-side rotational body 120 and the drive-side rotational body 110. This restricts rotation of the ball 130 together with the driven-side rotational body 120 with respect to the drive-side rotational body 110.

In this manner, the balls 130 are non-rotational when the driven-side rotational body 120 is arranged at the coupled position illustrated in FIG. 3. This allows the driven-side rotational body 120 to rotate together with the drive-side rotational body 110. That is, when the driven-side rotational body 120 is located at the coupled position, the balls 130 are caught between the driven-side rotational body 120 and the drive-side rotational body 110 in a non-rotational manner, thus coupling the driven-side rotational body 120 to the drive-side rotational body 110.

In contrast, when the driven-side rotational body 120 is arranged at the position illustrated in FIG. 2, the balls 130 are released from the holding portions 128 and received in the axially extended portions of the corresponding ball accommodating grooves 127. Specifically, a substantially half of each ball 130 is accommodated in the arcuate groove 111 of the drive-side rotational body 110. This restricts axial movement of the ball 130 relative to the drive-side rotational body 110. When each ball 130 is received in the axially extended portion, which has a depth greater than the depth of each holding portion 128, after having been released from the holding portion 128 with a smaller depth, the ball 130 is released from the driven-side rotational body 120 and the drive-side rotational body 110. As a result, the drive-side rotational body 110 and the driven-side rotational body 120 are allowed to rotate relative to each other. That is, the driven-side rotational body 120 is decoupled from the drive-side rotational body 110.

Hereinafter, out of the axial positions of the driven-side rotational body 120 moving axially along the output shaft 210, the position at which the drive-side rotational body 110 and the driven-side rotational body 120 are decoupled from each other as illustrated in FIG. 2 will be referred to as a decoupled position.

As illustrated in FIG. 2, a circumferential groove 400 is formed in an outer circumferential surface of the small diameter portion 123 of the driven-side rotational body 120. The groove 400 includes a helical groove 410 serving as a helical portion extending about the axis in a manner inclined with respect to the axial direction and an annular groove 420 serving as an annular portion extending perpendicular to the axial direction. The helical groove 410 extends in a manner revolving on the outer circumferential surface of the driven-side rotational body 120 by one cycle and inclined such that the helical groove 410 approaches the drive-side rotational body 110 toward the trailing end in the rotational direction of the drive-side rotational body 110. The annular groove 420 is formed continuously from the helical groove 410 and extends over the entire circumference of the outer circumferential surface of the driven-side rotational body 120. The configuration of the groove 400 will be described in detail below.

With reference to FIGS. 2 and 3, the clutch 100 includes a locking member 140 and an actuator 150 for selectively inserting and retracting a pin 141, which is arranged at the distal end of the locking member 140, with respect to the groove 400. The axial position of the locking member 140 is restricted. As illustrated in FIG. 3, the axial position of the locking member 140 is set such that the pin 141 is inserted into a portion of the helical groove 410 of the groove 400 in the vicinity of a starting end 411 when the driven-side rotational body 120 is arranged at the coupled position. If the locking member 140 is operated by the actuator 150 to move toward the driven-side rotational body 120 when the driven-side rotational body 120 is located at the coupled position, the pin 141 is inserted into the portion of the helical groove 410 in the vicinity of the starting end 411. After having been inserted into the helical groove 410, the pin 141 is engaged with a side wall 413 of the helical groove 410, thus locking the driven-side rotational body 120 against the urging force of the urging members 135.

If the pin 141 of the locking member 140 is inserted into the helical groove 410 when the driven-side rotational body 120 is coupled to the drive-side rotational body 110, the driven-side rotational body 120 is rotated with the pin 141 engaged with the side wall 413 of the helical groove 410. Then, while the pin 141 slides on the side wall 413 of the helical groove 410, the driven-side rotational body 120 moves axially from the coupled position toward the decoupled position. When the pin 141 reaches a finishing end 412 of the helical groove 410, the pin 141 is inserted into the annular groove 420 and the driven-side rotational body 120 is switched from the coupled position to the decoupled position. As has been described, the clutch 100 is configured such that, by inserting the pin 141 of the looking member 140 into the groove 400 to engage the pin 141 with the side wall 413 of the helical groove 410, the driven-side rotational body 120 is moved to the decoupled position against the urging force of the urging members 135.

When the drive-side rotational body 110 and the driven-side rotational body 120 are decoupled from each other, torque transmission from the drive-side rotational body 110 to the driven-side rotational body 120 is stopped. However, immediately after such decoupling, the driven-side rotational body 120 is continuously rotated by inertial force. Specifically, when the driven-side rotational body 120 is located at the decoupled position, the pin 141 is inserted in the annular groove 420, which extends over the entire circumference of the driven-side rotational body 120. The driven-side rotational body 120 is thus prohibited from shifting axially. In this state, since torque transmission from the drive-side rotational body 110 to the driven-side rotational body 120 is stopped, the rotational speed of the driven-side rotational body 120 gradually decreases and such rotation eventually stops.

The driven-side rotational body 120 is urged toward the coupled position by the urging force of the urging members 135. Accordingly, to maintain the decoupled state, the pin 141 of the locking member 140 must be maintained in a state inserted in the annular groove 420 of the driven-side rotational body 120. To re-couple the drive-side rotational body 110 and the driven-side rotational body 120 to each other, the pin 141 is retracted from the annular groove 420 of the groove 400 by means of the actuator 150. After the pin 141 is retracted in this manner, the locking member 140 is disengaged from the driven-side rotational body 120 and the driven-side rotational body 120 is moved to the coupled position by the urging force of the urging members 135. As a result, the drive-side rotational body 110 and the driven-side rotational body 120 are returned to the coupled state.

In the groove 400 formed in the outer circumferential surface of the driven-side rotational body 120, the annular groove 420 is formed continuously from the helical groove 410 and extends over the entire circumference of the outer circumferential surface of the driven-side rotational body 120. The groove 400 of the driven-side rotational body 120 thus has a connecting portion at which the annular groove 420 and the helical groove 410 are connected to each other. Therefore, when the pin 141 is inserted in the annular groove 420 such that the driven-side rotational body 120 is located at the decoupled position but the driven-side rotational body 120 is continuously rotated by inertial force, the pin 141 is possibly shifted to the helical groove 410 through the connecting portion between the helical groove 410 and the annular groove 420. To avoid this, the clutch 100 of the first embodiment includes a restricting portion, which restricts such shifting of the pin 141 from the annular groove 420 to the helical groove 410 when the pin 141 is inserted in the annular groove 420.

The restricting portion is configured in the manner described below. That is, in the groove 400, as illustrated in FIGS. 2 to 4, the annular groove 420 has a depth greater than the depth of the helical groove 410. In other words, the bottom surface of the annular groove 420 is located radially inward of the bottom surface of the helical groove 410. The annular groove 420 and the helical groove 410 are thus connected together with a step formed between the annular groove 420 and the helical groove 410. In the first embodiment, the step, which is the side wall 423 of the annular groove 420, functions as the restricting portion.

With reference to FIGS. 2 and 3, the width of the helical groove 410 becomes gradually smaller from the starting end 411 to the finishing end 412. Therefore, when the inserting position of the pin 141, which has been inserted into the portion of the helical groove 410 in the vicinity of the starting end 411, reaches the finishing end 412 of the helical groove 410 as the driven-side rotational body 120 rotates, the pin 141 is pressed by the side wall 413 of the helical groove 410 and thus inserted into the annular groove 420, which has a depth greater than the depth of the helical groove 410.

Further, as illustrated in FIG. 4, the depth of the helical groove 410 becomes gradually greater from the starting end 411 to the finishing end 412. In other words, the radial position of the bottom surface of the helical groove 410 approaches the axis of the driven-side rotational body 120 gradually from the starting end 411 to the finishing end 412. The depth of the annular groove 420 is small at the starting end 421 of the annular groove 420, which corresponds to the finishing end 412 of the helical groove 410, relative to the depths of the other portions in the circumferential direction of the driven-side rotational body 120. The radial distance between the bottom surface of the annular groove 420 and the bottom surface of the helical groove 410 is thus small at the portion corresponding to the finishing end 412 of the helical groove 410 and the starting end 421 of the annular groove 420, relative to other portions. That is, at this portion, the step between the helical groove 410 and the annular groove 420 is relatively small. This attenuates impact applied to the pin 141 when the pin 141 reaches the finishing end 412 of the helical groove 410 and is then inserted into the annular groove 420, which has a depth greater than the depth of the helical groove 410, compared to a case in which the size of the step is set uniform in the circumferential direction. Specifically, the step at the aforementioned portion is set to such a size that the aforementioned impact is attenuated and shifting of the pin 141 from the annular groove 420 to the helical groove 410 is restrained.

The structure of the actuator 150 will now be described.

As illustrated in FIG. 4, the actuator 150 of the first embodiment is an electromagnetic actuator, which is operated through action of a magnetic field generated by energizing a coil 153 accommodated in a first case 152.

The first case 152 has a cylindrical shape having a bottom portion and a fixed core 154 is fixed to the bottom portion. The coil 153 is arranged in the first case 152 to surround the fixed core 154. That is, in the actuator 150, the fixed core 154 and the coil 153 configure an electromagnet. A movable core 155 is movably accommodated in the coil 153 of the first case 152 at a position facing the fixed core 154. The fixed core 154 and the movable core 155 of the first embodiment are both iron cores.

A cylindrical second case 158 is fixed to a distal end portion (a right end portion as viewed in FIG. 4) of the first case 152. A permanent magnet 159 is fixed to an end portion of the second case 158 fixed to the first case 152 in a manner surrounding the movable core 155. As has been described, the movable core 155 is accommodated in the first case 152 such that a proximal end zone (a left end zone as viewed in FIG. 4) of the movable core 155 faces the fixed core 154. A distal end zone (a right end zone as viewed in the drawing) projects outward from the second case 158.

A ring member 160 is attached to the portion of the movable core 155 that is accommodated in the second case 158. A coil spring 161, which has an end secured to the second case 158 and an opposite end secured to the ring member 160, is accommodated in the second case 158 in a compressed state.

The coil spring 161 urges the movable core 155 in the direction in which the movable core 155 projects from the second case 158 (rightward as viewed in FIG. 4). The portion of the movable core 155 that projects from the second case 158 is coupled to the locking member 140 through a fixing pin 162.

The locking member 140 is pivotally coupled to the movable core 155 at the proximal end of the locking member 140 and pivotally supported by a pivot shaft 156. This allows the locking member 140 to pivot about the pivot shaft 156, which is a support point of pivot, when the movable core 155 moves. As a result, as represented by the solid lines in FIG. 4, as the extent of projection of the movable core 155 from the second case 158 is increased by the urging force of the coil spring 161, the pin 141 of the locking member 140 is inserted sequentially into the helical groove 410 and the annular groove 420 of the driven-side rotational body 120.

If the coil 153 is energized in this state, a magnetic field is generated through such energization to magnetize the fixed core 154 and the movable core 155. The movable core 155 is thus attracted to the fixed core 154 against the urging force of the coil spring 161. The direction of the magnetic field generated by the coil 153 at this stage matches with the direction of the magnetic field generated by the permanent magnet 159.

As the movable core 155 is attracted and moved toward the fixed core 154 (leftward as viewed in FIG. 4), the locking member 140 is pivoted clockwise as viewed in FIG. 4 to retract the distal end of the locking member 140 from the groove 400. That is, the actuator 150 retracts the locking member 140 from the groove 400 by attracting the movable core 155 using magnetic force produced through energization of the coil 153.

After the movable core 155 is attracted and moved to a contact position at which the movable core 155 contacts the fixed core 154 (the position represented by the long dashed double-short dashed lines in FIG. 4), the movable core 155 is held in contact with the fixed core 154 by the magnetic force of the permanent magnet 159 even if the energization is stopped afterwards.

In contrast, if the coil 153 is energized by an electric current flowing in the opposite direction to the direction of the electric current for attracting the movable core 155 when the movable core 155 is arranged at the contact position represented by the long dashed double-short dashed lines in FIG. 4, a magnetic field is generated in the opposite direction to the direction of the magnetic field of the permanent magnet 159. This attenuates the attracting force of the permanent magnet 159, and the movable core 155 is separated from the fixed core 154 by the urging force of the coil spring 161. The movable core 155 then moves to the projected position represented by the solid lines in FIG. 4. As the movable core 155 is moved from the contact position to the projected position, the locking member 140 is pivoted counterclockwise as viewed in FIG. 4 and the pin 141 of the locking member 140 is inserted into the groove 400.

When the movable core 155 is located at the projected position at which the movable core 155 is separated from the fixed core 154, the urging force of the coil spring 161 exceeds the attracting force of the permanent magnet 159. As a result, if the coil 153 is energized to separate the movable core 155 from the fixed core 154, the movable core 155 is held at the projected position even after such energization is stopped afterward.

That is, the actuator 150 of the first embodiment is a self-holding type solenoid, which switches the engagement state of the clutch 100 by applying direct electric currents in different directions and thus moving the movable core 155 and does not need the energization to maintain the clutch 100 in either the engaged state or the disengaged state.

Operation of the clutch 100 according to the present embodiment will now be described.

As represented by the long dashed double-short dashed lines in FIG. 4, when the movable core 155 of the actuator 150 is arranged at the contact position, the pin 141 of the locking member 140 is located in the exterior of the groove 400. At this stage, the driven-side rotational body 120 is held at the coupled position by the urging force of the urging members 135 such that the clutch 100 is in the engaged state. That is, the clutch 100 transmits rotation of the drive-side rotational body 110 to the output shaft 210.

If, in this state, the coil 153 of the actuator 150 is energized to generate a magnetic field in the opposite direction to the direction of the magnetic field of the permanent magnet 159, the movable core 155 is moved from the contact position to the projected position represented by the solid lines in FIG. 4 by the urging force of the coil spring 161. This pivots the locking member 140 counterclockwise as viewed in FIG. 4, thus inserting the pin 141 of the locking member 140 into the portion of the helical groove 410 of the groove 400 of the driven-side rotational body in the vicinity of the starting end 411. The driven-side rotational body 120 is thus stopped and held in the state illustrated in FIG. 3.

When the driven-side rotational body 120 is rotated together with the drive-side rotational body 110 with the pin 141 locking the driven-side rotational body 120 and the pin 141 is moved relatively in the helical groove 410, the driven-side rotational body 120 is moved from the coupled position to the decoupled position and thus switched from the state illustrated in FIG. 3 to the state illustrated in FIG. 2. In this manner, the pin 141 is switched to a state inserted in the annular groove 420 and the driven-side rotational body 120 reaches the decoupled position. This stops transmission of rotation of the drive-side rotational body 110 to the driven-side rotational body 120, thus disengaging the clutch 100.

Immediately after the driven-side rotational body 120 and the drive-side rotational body 110 are disengaged from each other, the driven-side rotational body 120 is continuously rotated by inertial force while receiving action of friction force produced between the driven-side rotational body 120 and the pin 141, which is inserted in the annular groove 420 as shown in FIG. 2. When the pin 141 is inserted in the annular groove 420 and the driven-side rotational body 120 is rotating, the pin 141 is engaged with the step in the boundary between the helical groove 410 and the annular groove 420, which is the side wall 423 of the annular groove 420. Therefore, unless the pin 141 is shifted to be retracted from the annular groove 420 and thus move past the step, the pin 141 cannot be shifted into the helical groove 410, so that shifting of the pin 141 from the annular groove 420 into the helical groove 410 is restricted. In this manner, the driven-side rotational body 120 is rotated with the pin 141 of the locking member 140 inserted in the annular groove 420 of the driven-side rotational body 120. The rotational speed of the driven-side rotational body 120 then decreases gradually until the driven-side rotational body 120 eventually stops rotating.

To switch the clutch 100 from the disengaged state to the engaged state, the coil 153 of the actuator 150 is energized to generate a magnetic field in the same direction as the direction of the magnetic field of the permanent magnet 159. The movable core 155 is thus attracted toward the fixed core 154 by magnetic force produced by energization and moved from the projected position represented by the solid lines in FIG. 4 to the contact position represented by the long dashed double-short dashed lines in the drawing. This pivots the locking member 140 clockwise as viewed in FIG. 4, thus fully retracting the pin 141 of the locking member 140 from the groove 400.

After having been released from the locking member 140, the driven-side rotational body 120 is moved to the coupled position by the urging force of the urging members 135. The driven-side rotational body 120 and the drive-side rotational body 110 thus become coupled to each other, switching the clutch 100 to the engaged state.

The above described embodiment provides the following advantages.

(1) In the first embodiment, when the pin 141 of the locking member 140 is inserted in the helical portion of the driven-side rotational body 120, the driven-side rotational body 120 is rotated with the pin 141 engaged with the side wall 413 of the helical portion. This moves the driven-side rotational body 120 from the coupled position to the decoupled position against the urging force of the urging members 135. In this manner, the force needed to disengage the clutch 100 is obtained from the rotational force of the driven-side rotational body 120. As a result, the drive-side rotational body 110 and the driven-side rotational body 120 are disengaged from each other by small force.

(2) In the first embodiment, when the pin 141 is inserted in the annular groove 420, the pin 141 is engaged with the side wall 423 at the step in the boundary between the helical groove 410 and the annular groove 420. Therefore, unless the pin 141 is shifted to be retracted from the annular groove 420 and moves past the step, the pin 141 cannot be shifted to the helical groove 410. That is, when the pin 141 is inserted in the annular groove 420, the side wall 423 at the step in the boundary between the helical groove 410 and the annular groove 420 functions as a restricting portion. This restricts shifting of the pin 141 from the annular groove 420 to the helical groove 410, thus restraining shifting of the driven-side rotational body 120 to the coupled position despite the fact that the pin 141 is maintained in the groove 400.

(3) In the first embodiment, the depth of the annular groove 420 is small in the vicinity of the starting end 421 relative to the depths of the other portions in the circumferential direction of the driven-side rotational body 120. The depth of the helical groove 410 becomes gradually greater from the starting end 411 to the finishing end 412. The step between the finishing end 412 of the helical groove 410 and the starting end 421 of the annular groove 420 is small-sized relative to steps in other portions. This attenuates impact applied to the pin 141 when the pin 141 is moved from the helical groove 410 and inserted into the annular groove 420, the depth of which is greater than the depth of the helical groove 410, compared to a case in which the step between the annular groove 420 and the helical groove 410 is set to a uniform size in the circumferential direction of the driven-side rotational body 120.

Second Embodiment

A clutch according to a second embodiment will now be described with reference to FIGS. 5 to 7.

As illustrated in FIG. 5, a clutch 500 of the second embodiment is different from the first embodiment in terms of the configuration of a groove 520 formed in an outer circumferential surface of a small diameter portion 511 of a driven-side rotational body 510 and the configuration of a pin 560 of a locking member 550. The remainder of the configuration is the same as those of the first embodiment. Thus, like or the same reference numerals are given to those components that are like or the same as the corresponding components of the first embodiment and detailed explanations are omitted.

In the second embodiment, the groove 520 of the driven-side rotational body 510 has a helical groove 530 inclined with respect to the axial direction and an annular groove 540, which is formed continuously from the helical groove 530 and extends over the entire circumference of an outer circumferential surface of the driven-side rotational body 510 and perpendicularly to the axial direction.

With reference to FIGS. 5 to 7, the annular groove 540 has a connecting portion 541, which has a depth equal to the depth of the helical groove 530 and is connected to the helical groove 530, and a non-connecting portion 542, which is disconnected from the helical groove 530. In FIGS. 5 to 7, the boundary between the connecting portion 541 of the annular groove 540 and the helical groove 530 is represented by the long dashed double-short dashed line. The long dashed double-short dashed line representing the boundary coincides with the extended line of a side wall 544 of the non-connecting portion 542 of the annular groove 540.

A protrusion 543, which protrudes from the bottom surface of the annular groove 540 and extends in the extending direction of the annular groove 540, is formed in the annular groove 540. The protrusion 543 is formed over the entire length of the connecting portion 541. The opposite ends of the protrusion 543 are arranged in the non-connecting portion 542. The protrusion 543 of the annular groove 540 has a uniform width and is inclined with respect to the axial direction of the driven-side rotational body 510 by the inclination angle equal to the inclination angle of a side wall 531 of the helical groove 530. As a result, with reference to FIG. 7, the distance from the side wall 531 of the helical groove 530 to the protrusion 543 is a uniform distance d1 in the circumferential direction of the driven-side rotational body 510.

As shown in FIGS. 5 to 7, a recess 561, into which the protrusion 543 can proceed, is formed at the distal end of the pin 560 of the locking member 550. In FIG. 7, states of relative movement of the pin 560 of the locking member 550 in the groove 520 when the driven-side rotational body 510 is in a rotating state are illustrated by way of pins 560 represented by the long dashed double-short dashed lines. In the second embodiment, the protrusion 543, which projects from the bottom surface of the annular groove 540, and the recess 561 of the pin 560 configure a restricting portion.

Referring to FIG. 7, the width d2 of the pin 560 of the locking member 550 is slightly smaller than the distance d1 from the side wall 531 of the helical groove 530 to the protrusion 543. The distance d3 from a starting end of the protrusion 543, which is the end portion of the protrusion 543 that the pin 560 reaches first when the driven-side rotational body 510 is rotated, to the side wall 544 of the annular groove 540 is substantially equal to but slightly greater than the length d4 from the side surface of the pin 560 to the recess 561. The width d5 of the recess 561 is greater than the width d6 of the protrusion 543.

Operation of the present embodiment will now be described.

As illustrated in FIG. 6, when the driven-side rotational body 510 is in a state coupled to the drive-side rotational body 110, the actuator 150 is operated to insert the pin 560 of the locking member 550 into a starting end 532 of the helical groove 530 of the groove 520. This engages the pin 560 with the side wall 531 of the helical groove 530 to locks the driven-side rotational body 120 against the urging force of the urging members 135. Then, as the driven-side rotational body 510 is rotated, the pin 560 is moved relatively in the groove 520 in a circumferential direction while being engaged with the side wall 531 of the helical groove 530. The width d2 of the pin 560 is slightly smaller than the distance d1 from the side wall 531 of the helical groove 530 to the protrusion 543. This restrains interference of the protrusion 543 with movement of the pin 560 when the pin 560 is engaged with the side wall 531 of the helical groove 530 and moved relatively in the groove 520, thus allowing relative movement of the pin 560 in the helical groove 530. The pin 560 thus reaches the annular groove 540 and is then moved relatively in the annular groove 540 of the groove 520 as the driven-side rotational body 510 is rotated. The driven-side rotational body 510 is rotated by inertial force at the decoupled position.

As has been described, the distance d3 from the starting end of the protrusion 543 to the side wall 544 of the annular groove 540 is substantially equal to but slightly greater than the length d4 from the side wall of the pin 560 to the recess 561. The width d5 of the recess 561 is greater than the width d6 of the protrusion 543. Therefore, when the driven-side rotational body 510 is rotated and the pin 560 is moved relatively in the annular groove 540 to reach the starting end of the protrusion 543, which is arranged in the annular groove 540, the protrusion 543 proceeds into the recess 561 and becomes engaged with the recess 561. The protrusion 543 extends in the extending direction of the annular groove 540 and is formed over the entire length of the connecting portion 541. As a result, even if the driven-side rotational body 510 is rotated by inertial force and the pin 560 is moved to the connecting portion 541 of the annular groove 540 such that the pin 560 and the side surface of the groove 520, which is the side wall 544 of the annular groove 540 corresponding to the non-connecting portion 542, become separate from each other, the pin 560 is engaged with the protrusion 543 and thus held in the annular groove 540.

To switch the clutch 500 from the disengaged state to the engaged state, the actuator 150 is operated to retract the pin 560 of the locking member 550 from the annular groove 540 of the groove 520. This also causes disengagement between the recess 561 of the pin 560 and the protrusion 543 of the annular groove 540. By retracting the pin 560 of the locking member 550 from the groove 520 in this manner, the driven-side rotational body 510 is moved to the coupled position by the urging force of the urging members 135. The driven-side rotational body 510 and the drive-side rotational body 110 thus become coupled to each other, switching the clutch 500 to the engaged state.

The second embodiment achieves the following advantage (4) as well as an advantage equivalent to the advantage (1) of the first embodiment.

(4) In the second embodiment, shifting of the pin 560 from the annular groove 540 to the helical groove 530 is restricted unless the pin 560 is shifted to be retracted from the annular groove 540 and the recess 561 of the pin 560 and the protrusion 543 of the annular groove 540 are disengaged from each other. That is, when the pin 560 is inserted in the annular groove 540, the recess 561 of the pin 560 and the protrusion 543 of the annular groove 540 function as a restricting portion. Therefore, since shifting of the pin 560 from the annular groove 540 to the helical groove 530 is restricted, it is possible to restrain shifting of the driven-side rotational body 510 to the coupled position despite the fact that the pin 560 is maintained in the groove 520.

Third Embodiment

A clutch according to a third embodiment will now be described with reference to FIGS. 8 to 10.

As illustrated in FIG. 8, a clutch 600 of the third embodiment is different from the illustrated embodiments in terms of the configuration of a groove 620 formed in an outer circumferential surface of a small diameter portion 611 of a driven-side rotational body 610 and the configuration of a pin 660 of a locking member 650. The remainder of the configuration is the same as those of the first embodiment. Thus, like or the same reference numerals are given to those components that are like or the same as the corresponding components of the first embodiment and detailed explanations are omitted.

In the third embodiment, the groove 620 of the driven-side rotational body 610 has a helical groove 630 inclined with respect to the axial direction and an annular groove 640, which is formed continuously from the helical groove 630 and extends over the entire circumference of an outer circumferential surface of the driven-side rotational body 610 and perpendicularly to the axial direction.

As illustrated in FIGS. 8 to 10, the annular groove 640 has a connecting portion 641, which has a depth equal to the depth of the helical groove 630 and is connected directly to the helical groove 630, and a non-connecting portion 642, which is not connected directly to the helical groove 630. In FIGS. 8 to 10, the boundary between the connecting portion 641 of the annular groove 640 and the helical groove 630 is represented by the long dashed double-short dashed line. The long dashed double-short dashed line representing the boundary coincides with the extended line of a side wall 644 of the non-connecting portion 642 of the annular groove 640.

A recessed groove 643, which extends in the extending direction of the annular groove 640, is formed in the annular groove 640. Specifically, the recessed groove 643 extends in a direction perpendicular to the axial direction of the driven-side rotational body 610. Also, the recessed groove 643 extends over the entire length of the annular groove 640. That is, the recessed groove 643 is formed over the entire circumference of the outer circumferential surface of the driven-side rotational body 610.

With reference to FIGS. 8 to 10, a projection 661, which can be inserted into the recessed groove 643, projects from the distal end of the pin 660 of the locking member 650. In FIG. 10, states of relative movement of the pin 660 of the locking member 650 in the groove 620 when the driven-side rotational body 610 is in a rotating state are illustrated by pins 660 represented by the long dashed double-short dashed lines. In the third embodiment, the recessed groove 643, which is formed in the bottom surface of the annular groove 640, and the projection 661 of the pin 660 configure a restricting portion.

Referring to FIG. 10, the length d1 from the side surface of the pin 660 of the locking member 650 to the projection 661 is substantially equal to but slightly greater than the distance d2 from the side wall 644 of the annular groove 640 to the recessed groove 643. The width d3 of the projection 661 of the pin 660 is smaller than the width d4 of the recessed groove 643 of the annular groove 640.

Operation of the present embodiment will now be described.

As illustrated in FIG. 9, when the driven-side rotational body 610 is in a state coupled to the drive-side rotational body 110, the actuator 150 is operated to insert the pin 660 of the locking member 650 into a starting end 632 of the helical groove 630 of the groove 620. This engages the pin 660 with a side wall 631 of the helical groove 630 to lock the driven-side rotational body 120 against the urging force of the urging members 135. Then, as the driven-side rotational body 610 is rotated, the pin 660 is moved relatively in the groove 620 in a circumferential direction while being engaged with the side wall 631 of the helical groove 630. The pin 660 thus reaches the annular groove 640 and the driven-side rotational body 610 is moved to a decoupled position and rotated by inertial force. As a result, with reference to FIG. 8, the pin 660 is switched to a state moving relatively in the annular groove 640.

As has been described, the length d1 from the side surface of the pin 660 of the locking member 650 to the projection 661 is substantially equal to but slightly greater than the distance d2 from the side wall 644 of the annular groove 640 to the recessed groove 643. The width d3 of the projection 661 of the pin 660 is smaller than the width d4 of the recessed groove 643 of the annular groove 640. Therefore, when the driven-side rotational body 610 is rotated and the pin 660 is moved relatively in the annular groove 640, the projection 661 of the pin 660 proceeds into the recessed groove 643, which is formed in the annular groove 640, and becomes engaged with the recessed groove 643. The recessed groove 643 extends in the extending direction of the annular groove 640 and is formed over the entire length of the annular groove 640. As a result, even if the driven-side rotational body 610 is rotated by inertial force and the pin 660 is moved to the connecting portion 641 of the annular groove 640 such that the pin 660 and the side surface of the groove 620, which is the side wall 644 of the annular groove 640 corresponding to the non-connecting portion 642, become separate from each other, the projection 661 of the pin 660 is engaged with the recessed groove 643. The pin 660 is thus maintained in the annular groove 640.

To switch the clutch 600 from the disengaged state to the engaged state, the actuator 150 is operated to retract the pin 660 of the locking member 650 from the annular groove 640 of the groove 620. This also causes retraction of the projection 661 of the pin 660 from the recessed groove 643 of the annular groove 640, thus disengaging the projection 661 of the pin 660 and the recessed groove 643 of the annular groove 640 from each other. The driven-side rotational body 510 is then moved to the coupled position by the urging force of the urging members 135. As a result, the driven-side rotational body 510 and the drive-side rotational body 110 become coupled to each other, thus switching the clutch 500 to the engaged state.

The third embodiment achieves the following advantage (5) as well as an advantage equivalent to the advantage (1) of the first embodiment.

(5) In the third embodiment, shifting of the pin 660 from the annular groove 640 to the helical groove 630 is restricted unless the pin 660 is shifted to be retracted from the annular groove 640 and the recessed groove 643 and the projection 661 of the pin 660 are disengaged from each other. That is, when the pin 660 is inserted in the annular groove 640, the recessed groove 643 and the projection 661 of the pin 660 function as a restricting portion. As a result, since shifting of the pin 660 from the annular groove 640 to the helical groove 630 is restricted, it is possible to restrain shifting of the driven-side rotational body 610 to the coupled position despite the fact that the pin 660 is maintained in the recessed groove 643.

Modification of Third Embodiment

As illustrated in FIG. 11, the present modification is different from the third embodiment in terms of the configuration of a helical groove 680 of a groove 670 of the driven-side rotational body. Specifically, in the modification, a recessed groove 681, which extends in the extending direction of the helical groove 680, is formed also in the helical groove 680. The recessed groove 681 of the helical groove 680 is connected to the recessed groove 643 of the annular groove 640.

If the actuator 150 is operated to insert the pin 660 of the locking member 650 into the helical groove 630 of the groove 620 when the driven-side rotational body 610 is in a state coupled to the drive-side rotational body 110, the pin 660 becomes engaged with the side wall 631 of the helical groove 630. Also, the projection 661 of the pin 660 proceeds into the recessed groove 681 of the helical groove 680 and becomes engaged with the recessed groove 681. Then, when the driven-side rotational body is rotated and the pin 660 is moved relatively in the helical groove 630, engagement between the projection 661 and the recessed groove 681 is maintained. In this state, where such engagement is maintained, the pin 660 reaches the annular groove 640. Therefore, after the pin reaches the annular groove 640, the projection 661 proceeds into the recessed groove 643 of the annular groove 640 through the connecting portion between the recessed groove 681 of the helical groove 680 and the recessed groove 643 of the annular groove 640. That is, the recessed groove 681 of the helical groove 680 guides the projection 661 of the pin 660 into the recessed groove 643 of the annular groove 640.

Also in this embodiment, the recessed groove 643 extends in the extending direction of the annular groove 640 and is formed over the entire length of the annular groove 640. As a result, even if the driven-side rotational body 610 is rotated by inertial force and the pin 660 is moved to the connecting portion 641 of the annular groove 640 such that the pin 660 and the side surface of the groove 620 become separate from each other, the projection 661 of the pin 660 is engaged with the recessed groove 643. The pin 660 is thus maintained in the annular groove 640.

The remainder of the configuration, the operation, and the advantages of the present modification are the same as those of the third embodiment.

Fourth Embodiment

A clutch according to a fourth embodiment will now be described with reference to FIG. 12.

As illustrated in FIG. 12, a clutch 700 of the fourth embodiment is different from the illustrated embodiments in terms of the configuration of a driven-side rotational body 710 and the configuration of a locking member 750. The remainder of the configuration is the same as those of the first embodiment. Thus, like or the same reference numerals are given to those components that are like or the same as the corresponding components of the first embodiment and detailed explanations are omitted. Position change of each ball 130 in the corresponding ball accommodating groove 127 caused by axial shifting of the driven-side rotational body 710 and switching between the engaged state and the disengaged state caused by such position change happen in the same manners as the first embodiment. Accordingly, illustration of the balls 130 and the ball accommodating grooves 127 are omitted in FIG. 12.

As illustrated in FIG. 12, a groove 720 of a small diameter portion 711 of the driven-side rotational body 710 includes a helical groove 730 inclined with respect to the axial direction and an annular groove 740, which is formed continuously from the helical groove 730 and extends over the entire circumference of an outer circumferential surface of the driven-side rotational body 710 and perpendicularly to the axial direction. The annular groove 740 of the groove 720 has a depth equal to the depth of the helical groove 730. In FIG. 12, the boundary between a connecting portion of the annular groove 740, which is connected directly to the helical groove 730, and the helical groove 730 is represented by the long dashed double-short dashed line.

A flange 770 projects from the outer circumferential surface of the driven-side rotational body 710 and extends over the entire circumference of the outer circumferential surface of the driven-side rotational body 710. Specifically, the flange 770 is arranged on an outer circumferential surface of the small diameter portion 711 of the driven-side rotational body 710. That is, the flange 770 is formed at a right side as viewed in FIG. 12A with respect to a groove 720 in the outer circumferential surface of the driven-side rotational body. The flange 770 extends perpendicular to the axial direction of the driven-side rotational body 710 and parallel to the annular groove 740.

The locking member 750 includes a pin 760, which is inserted into the groove 720 of the driven-side rotational body 710, and a one-way locking portion 780, which selectively proceeds and retreats with respect to the driven-side rotational body 710 as the pin 760 is inserted into or retracted from the groove 720. In the fourth embodiment, the one-way locking portion 780 and the flange 770 of the driven-side rotational body 710 configure a restricting portion.

The one-way locking portion 780 includes an engagement member 781 and an elastic member 785, which urges the engagement member 781 toward the driven-side rotational body 710. The elastic member 785 is configured by, for example, a coil spring. The one-way locking portion 780 is located at the same side with respect to the pin 760 as the side at which the flange 770 is arranged with respect to the groove 720 (the right side as viewed in FIG. 12A).

The right surface of the flange 770 as viewed in FIG. 12A is referred to as a first surface 771 and the left surface of the flange 770 as viewed in the drawing is referred to as a second surface 772. The right surface of the engagement member 781 as viewed in FIG. 12A is referred to as a first surface 782 and the left surface of the engagement member 781 as viewed in the drawing is referred to as a second surface 783. The right surface of the pin 760 as viewed in FIG. 12A is referred to as a first surface 761. In this case, the distances between the respective surfaces and the shapes of the surfaces 782, 783 of the engagement member 781 are defined as follows.

As illustrated in FIG. 12A, in the locking member 750, the distance d1 from the first surface 761 of the pin 760 to the second surface 783 of the engagement member 781 is substantially equal to but slightly greater than the distance d2 from a side wall 732 at a starting end 731 of the helical groove 730 to the first surface 771 of the flange 770. The distance d3 from the first surface 761 of the pin 760 of the locking member 750 to the first surface 782 of the engagement member 781 is substantially equal to but slightly smaller than the distance d4 from a side wall 741 of the annular groove 740 (the position represented by the long dashed double-short dashed line in the connecting portion of the annular groove 740) to the second surface 772 of the flange 770. In the engagement member 781, the distal end of the first surface 782 is a corner and the distal end of the second surface 783 is a chamfered round surface. That is, the second surface 783 is inclined such that the first surface 782 approaches the first surface 782 in a distal direction. In other words, the distal end of the engagement member 781 is inclined and becomes gradually smaller in size.

Accordingly, when the driven-side rotational body 710 is in a coupled state and the pin 760 is inserted in the starting end 731 of the helical groove 730 of the groove 720 as illustrated in FIG. 12B, the second surface 783 of the engagement member 781 is in contact with the first surface 771 of the flange 770. The second surface 783 of the engagement member 781, which contacts the flange 770 at this stage, has the inclined distal end as has been described. Also, referring to FIG. 12D, when the pin 760 is inserted in the annular groove 740 of the groove 720, the engagement member 781 is in contact with the second surface 772 of the flange 770. The distal end of the first surface 782 of the engagement member 781, which contacts the flange 770 at this stage, is the corner as has been described.

Operation of the present embodiment will now be described.

Referring to FIG. 12A, the driven-side rotational body 710 is located at a coupled position and the driven-side rotational body 710 is in a state coupled to the drive-side rotational body 110. In this state, by operating the actuator 150 to insert the pin 760 of the locking member 750 into the helical groove 730 of the groove 720, the state illustrated in. FIG. 12B is brought about. In this manner, the pin 760 is engaged with a side wall 732 of the helical groove 730, thus locking the driven-side rotational body 120 against the urging force of the urging members 135. Then, as the driven-side rotational body 710 is rotated, the pin 760 is moved relatively in the groove 720 in a circumferential direction while being engaged with the side wall 732 of the helical groove 730. The driven-side rotational body 710 is thus shifted from the coupled position to a decoupled position.

As the driven-side rotational body 710 is shifted to the decoupled position, the position of the pin 760 in the groove 720 is shifted relatively in a direction from the helical groove 730 toward the annular groove 740. Correspondingly, the engagement member 781, which is fixed to the locking member 750 together with the pin 760, is shifted relative to the driven-side rotational body 710. As illustrated in FIG. 123, when the pin 760 is inserted in the starting end 731 of the helical groove 730 of the groove 720, the engagement member 781 faces the first surface 771 of the flange 770. The second surface 783 of the engagement member 781, which faces the flange 770, has the inclined distal end. That is, the surface by which the engagement member 781 contacts the flange 770 when the driven-side rotational body 710 is shifted from the coupled position to the decoupled position is inclined. Therefore, when the driven-side rotational body 710 is moved from the coupled position to the decoupled position, the flange 770 and the engagement member 781 contact each other, as illustrated in FIG. 12C, to cause the force for pressing the engagement member 781 back against the urging force of the elastic member 785 such that the engagement member 781 moves past the flange 770. In this manner, when the pin 760 is inserted in the helical groove 730 of the groove 720, movement of the driven-side rotational body 710 from the coupled position to the decoupled position is permitted despite the fact that the engagement member 781 is in contact with the flange 770.

Then, as illustrated in FIG. 12D, when the driven-side rotational body 710 is rotated by inertial force at the decoupled position and the pin 760 is moved relatively in the annular groove 740, the engagement member 781 faces the first surface 771 of the flange 770. As has been described, the first surface 782 of the engagement member 781 contacts the flange 770 in this state and the distal end of the first surface 782 is the corner. Therefore, when the pin 760 is moved relatively in the annular groove 740 of the groove 720, the engagement member 781 is prevented from being pressed back by the flange 770 against the urging force of the elastic member 785, and engagement between the engagement member 781 and the flange 770 is thus maintained. In this manner, movement of the driven-side rotational body 710 from the decoupled position to the coupled position is restricted. That is, even when the driven-side rotational body 710 is arranged at the decoupled position and rotated by inertial force and, in this state, the pin 760 is moved to the connecting portion of the annular groove 740 to separate the pin 760 from the side surface of the groove 720 (the side wall 741 of the annular groove 740), the one-way locking portion 780 restricts shifting of the driven-side rotational body 710. The pin 760 is thus held in the annular groove 740.

To switch the clutch 700 from the disengaged state to the engaged state, the actuator 150 is operated to retract the pin 760 of the locking member 750 from the annular groove 740 of the groove 720. This also causes disengagement between the engagement member 781 and the flange 770. The driven-side rotational body 710 is thus moved to the coupled position by the urging force of the urging members 135. As a result, the driven-side rotational body 710 and the drive-side rotational body 110 become coupled to each other, thus switching the clutch 700 to the engaged state.

The fourth embodiment achieves the following advantage (6) as well as an advantage equivalent to the advantage (1) of the first embodiment.

(6) Unless the pin 760 is shifted to be retracted from the annular groove 740 to disengage the flange 770 and the one-way locking portion 780 from each other, the pin 760 is not shifted from the annular groove 740 to the helical groove 730. That is, the flange 770 and the one-way locking portion 780 function as a restricting portion. This restricts shifting of the pin 760 from the annular groove 740 to the helical groove 730 when the pin 760 is inserted in the annular groove 740. As a result, it is possible to restrain shifting of the driven-side rotational body 710 to the coupled position despite the fact that the pin 760 is maintained in the groove 720.

Fifth Embodiment

A clutch according to a fifth embodiment will now be described.

As illustrated in FIG. 13, a clutch 800 of the fifth embodiment is different from the fourth embodiment in terms of the configuration of the locking member 750. The remainder of the configuration is the same as those of the first embodiment. Thus, like or the same reference numerals are given to those components that are like or the same as the corresponding components of the first embodiment and detailed explanations are omitted. The fifth embodiment is the same as the first embodiment in terms of position change of each ball 130 in the corresponding ball accommodating groove 127 caused by axial shifting of the driven-side rotational body 710 and switching between the engaged state and the disengaged state caused by such position change. Accordingly, illustration of the balls 130 and the ball accommodating grooves 127 is omitted also in FIG. 13.

With reference to FIG. 13, the driven-side rotational body 710 of the fifth embodiment is configured identically with the driven-side rotational body 710 of the fourth embodiment. The flange 770 is formed in the driven-side rotational body 710.

A locking member 850 includes a pin 860, which is inserted into the groove 720 of the driven-side rotational body 710, and a one-way locking portion 880, which selectively proceeds and retreats with respect to the driven-side rotational body 710 as the pin 860 is inserted into or retracted from the groove 720. In the fifth embodiment, the one-way locking portion 880 and the flange 770 of the driven-side rotational body 710 configure a restricting portion.

The one-way locking portion 880 includes an engagement member 881, a pivot shaft 885 through which the engagement member 881 is pivotally supported by the locking member 850, and a restricting member 888, which restricts pivot of the engagement member 881 in a certain direction (a leftward direction in FIG. 13A). As illustrated in FIG. 13A, a state in which the distal end of the engagement member 881 projects toward the driven-side rotational body 710 is defined as a reference position of the engagement member 881. The restricting member 888 restricts tilting of the engagement member 881 in a specific direction from the reference position and permits tilting of the engagement member 881 in another direction (a rightward direction in FIG. 13A) from the reference position.

The right surface of the flange 770 as viewed in FIG. 13A is referred to as the first surface 771 and the left surface of the flange 770 as viewed in the drawing is referred to as the second surface 772. The right surface of the engagement member 881 as viewed in FIG. 13A and the left surface of the engagement member 881 as viewed in the drawing when the engagement member 881 is arranged at the reference position are referred to as a first surface 882 and a second surface 883, respectively. The right surface of the pin 860 as viewed in FIG. 13A is referred to as a first surface 861.

In this case, the distances between the respective surfaces are defined as follows.

As illustrated in FIG. 13A, in the locking member 850, the distance d1 from the first surface 861 of the pin 860 to the second surface 883 of the engagement member 881 is substantially equal to but slightly greater than the distance d2 from the side wall 732 of the helical groove 730 at the starting end 731 to the first surface 771 of the flange 770. The distance d3 from the first surface 861 of the pin 860 of the locking member 850 to the first surface 882 of the engagement member 881 is substantially equal to but slightly smaller than the length d4 from the side wall 741 of the annular groove 740 (the position represented by the long dashed double-short dashed line corresponding to the boundary position between the annular groove 740 and the helical groove 730 in the connecting portion of the annular groove 740) to the second surface 772 of the flange 770.

Accordingly, when the driven-side rotational body 710 is in a coupled state and the pin 860 is inserted in the starting end 731 of the helical groove 730 of the groove 720 as illustrated in FIG. 13B, the second surface 883 of the engagement member 881 is in contact with the first surface 771 of the flange 770. Also, as illustrated in FIG. 13D, when the pin 860 is arranged in the annular groove 740 of the groove 720, the engagement member 881 is in contact with the second surface 772 of the flange 770.

Operation of the present embodiment will now be described.

Referring to FIG. 13A, the driven-side rotational body 710 is located at a coupled position and the driven-side rotational body 710 is in a state coupled to the drive-side rotational body 110. In this state, by operating the actuator 150 to insert the pin 860 of the locking member 850 into the starting end 731 of the helical groove 730 of the groove 720, the state illustrated in FIG. 13B is brought about. In this manner, the pin 860 is engaged with the side wall 732 of the helical groove 730, thus locking the driven-side rotational body 120 against the urging force of the urging members 135. Then, as the driven-side rotational body 710 is rotated, the pin 860 is moved relatively in the groove 720 in a circumferential direction while being engaged with the side wall 732 of the helical groove 730. The driven-side rotational body 710 is thus shifted from the coupled position to a decoupled position.

As the driven-side rotational body 710 is shifted to the decoupled position, the position of the pin 860 in the groove 720 is shifted relatively in a direction from the helical groove 730 toward the annular groove 740. Correspondingly, the engagement member 881, which is fixed to the locking member 850 together with the pin 860, is shifted relative to the driven-side rotational body 710. As illustrated in FIG. 13B, when the pin 860 is inserted in the starting end 731 of the helical groove 730, the engagement member 881 is in contact with the first surface 771 of the flange 770. The engagement member 881 is permitted to tilt in the certain direction (the rightward direction as viewed in FIGS. 13) from the reference position, at which the engagement member 881 contacts the flange 770. Therefore, when the driven-side rotational body 710 is moved from the coupled position to the decoupled position, the engagement member 881 contacts the flange 770 and tilts, thus moves past the flange 770, as illustrated in FIG. 13C. In this manner, when the pin 860 is inserted in the starting end 731 of the helical groove 730, movement of the driven-side rotational body 710 from the coupled position to the decoupled position is permitted despite the fact that the engagement member 881 is in contact with the flange 770.

Then, as illustrated in FIG. 13D, when the driven-side rotational body 710 is rotated by inertial force at the decoupled position and the pin 860 is moved relatively in the annular groove 740, the engagement member 881 faces the second surface 772 of the flange 770 and the first surface 882 of the engagement member 881 contacts and becomes engaged with the second surface 772 of the flange 770. When the pin 860 is moved relatively in the annular groove 740 of the groove 720, tilting of the engagement member 881 in the certain direction (the leftward direction as viewed in FIG. 13D) is restricted by the restricting member 888. The engagement member 881 is thus prevented from tilting even if the urging force of the urging members 135 acts on the driven-side rotational body 710 such that the engagement member 881 is pressed by the flange 770. As a result, the engagement member 881 is held at the reference position, thus maintaining engagement between the engagement member 881 and the flange 770. This restricts movement of the driven-side rotational body 710 from the decoupled position to the coupled position. That is, even when the driven-side rotational body 710 is arranged at the decoupled position and rotated by inertial force and, in this state, the pin 860 is moved to the connecting portion of the annular groove 740 such that the pin 860 becomes separate from the side surface of the groove 720 (the side wall 741 of the annular groove 740), the one-way locking portion 880 restricts shifting of the driven-side rotational body 710. The pin 860 is thus held in the annular groove 740.

To switch the clutch 800 from the disengaged state to the engaged state, the actuator 150 is operated to retract the pin 860 of the locking member 850 from the annular groove 740 of the groove 720. This also causes disengagement between the engagement member 881 and the flange 770. The driven-side rotational body 710 is thus moved to the coupled position by the urging force of the urging members 135. As a result, the driven-side rotational body 710 and the drive-side rotational body 110 become coupled to each other, thus switching the clutch 800 to the engaged state.

The fifth embodiment achieves advantages equivalent to the advantage (1) of the first embodiment and the advantage (6) of the fourth embodiment.

The clutch according to the present disclosure is not restricted to the configurations illustrated in the above-described embodiments but may be embodied in, for example, the forms described below, which are modifications of the embodiments.

In the first embodiment, the depth of the annular groove 420 is small in the vicinity of the starting end 421 relative to the depths of the other portions in the circumferential direction of the driven-side rotational body 120. The depth of the helical groove 410 becomes gradually greater from the starting end 411 to the finishing end 412. However, the depth of the annular groove or the depth of the helical groove may be uniform in the circumferential direction. That is, the step between the annular groove and the helical groove may be set to a uniform size in the circumferential direction of the driven-side rotational body 120.

In the second embodiment, the protrusion is formed over the entire length of the connecting portion of the groove. The opposite ends of the protrusion reach the non-connecting portion. However, if the protrusion is formed at least over the entire length of the connecting portion of the groove, shifting of the pin into the helical groove can be restrained by engaging the protrusion with the recess of the pin over the entire length of the connecting portion. The opposite ends of the protrusion thus do not necessarily have to reach the non-connecting portion. For example, only one of the end portions may reach the non-connecting portion. Alternatively, the length of the protrusion may be equal to the length of the connecting portion such that neither end portion reaches the non-connecting portion. Further, as long as shifting of the pin from the annular groove into the helical groove is restrained and disengagement of the clutch is restrained, the protrusion does not necessarily have to extend over the entire length of the connecting portion. For example, the protrusion may be provided in a portion of the connecting portion of the groove.

In the third embodiment and its modification, the recessed groove is formed over the entire length of the annular groove. However, the recessed groove only has to be formed at least over the entire length of the connecting portion of the annular groove. That is, if the protrusion is formed at least over the entire length of the connecting portion, shifting from the annular groove into the helical groove is restrained. Further, if shifting of the pin from the annular groove into the helical groove is restrained and disengagement of the clutch is restrained, the recessed groove may be formed in a portion of the connecting portion.

In the fourth and fifth embodiments, the flange is formed over the entire circumference of the outer circumferential surface of the driven-side rotational body. However, if shifting of the pin from the annular groove into the helical groove is restrained and disengagement of the clutch is restrained, the flange does not necessarily have to extend over the entire circumference but may be arranged in a portion of the outer circumferential surface to extend in the circumferential direction of the driven-side rotational body.

The number of the urging members may be modified as needed. For example, a single urging member may be employed to urge the driven-side rotational body.

Any suitable urging member may be employed as long as the urging member urges the driven-side rotational body toward the coupled position. The urging member is thus not restricted to the aforementioned compression coil spring. For example, a tension spring for pulling the driven-side rotational body toward the coupled position may be employed as the urging member.

The actuator is not restricted to the self-holding type solenoid but may be, for example, a solenoid having a locking member that is inserted into a groove only when a coil is energized. In this configuration, the clutch is disengaged only when the coil is energized. The clutch is thus maintained in the engaged state if the coil cannot be energized. As a result, even when the actuator fails to operate normally, the pump can be operated.

The actuator is not restricted to a solenoid. That is, any other suitable actuator than the solenoid, such as a hydraulic type actuator, may be used to selectively insert and retract the locking member. Also in this case, the clutch is disengaged through engagement between a groove of the driven-side rotational body and the locking member. The force needed to disengage the clutch is thus obtained from rotational force of the driven-side rotational body. As a result, disengagement is carried out by small force.

The clutch is not restricted to the configuration in which drive force is transmitted through the balls. The clutch may be a pressing type clutch.

For example, opposed surfaces of the driven-side rotational body and the drive-side rotational body may be parallel tapered surfaces each inclined with respect to the axial direction. The tapered surfaces serve as pressing surfaces. By moving the driven-side rotational body in the axial direction and pressing the pressing surfaces against each other, the driven-side rotational body and the drive-side rotational body are coupled to each other.

In the clutch of each of the illustrated embodiments, the shapes of the components are not restricted particularly to the shapes of the illustrated embodiments, as long as the operation illustrated for each embodiment is ensured. For example, as illustrated in FIG. 14, ball accommodating grooves 927 may be formed in a large diameter portion 922 of a driven-side rotational body 910 and recesses 928 may be formed by lightening portions that lack the ball accommodating grooves 927. This decreases the weight of the driven-side rotational body 910 and thus reduces the inertial force caused by the driven-side rotational body 910. As a result, when the driven-side rotational body 910 reaches a decoupled position, rotation of the driven-side rotational body 910 quickly stops.

In each of the illustrated embodiments, the clutch switches the state of power transmission from the crankshaft to the pump. However, the clutch according to the present disclosure may be employed as a clutch arranged between other auxiliary devices, such as a compressor or an oil pump, and the crankshaft. Also, the clutch according to the present disclosure is not restricted to the clutch for switching the state of power transmission from the crankshaft but may be used as a clutch for switching the state of power transmission from other drive sources.

Claims

1. A clutch comprising:

a drive-side rotational body;

a driven-side rotational body movable in an axial direction of the drive-side rotational body between a coupled position at which the driven-side rotational body is coupled to the drive-side rotational body and a decoupled position at which the driven-side rotational body is decoupled from the drive-side rotational body;

an urging member that urges the driven-side rotational body from the decoupled position toward the coupled position;

a groove formed in an outer circumferential surface of the driven-side rotational body, wherein the groove has a helical portion that extends about an axis of the driven-side rotational body and an annular portion that is formed continuously from the helical portion and extends over an entire circumference of the driven-side rotational body and perpendicularly to the axial direction;

a pin that is selectively inserted into and retracted from the groove and restricted from moving in the axial direction, wherein, when the pin is in a state inserted in the helical portion and engaged with a side wall of the helical portion, the position of the pin is shifted from the helical portion to the annular portion through rotation of the driven-side rotational body such that the driven-side rotational body is moved to the decoupled position against urging force of the urging member; and

a restricting portion that restricts shifting of the position of the pin from the annular portion to the helical portion when the pin is in a state located in the annular portion.

2. The clutch according to claim 1, wherein

the helical portion is a helical groove,

the annular portion is an annular groove having a depth greater than the depth of the helical groove,

the groove includes a step in a connecting portion by which the helical groove and the annular groove are connected to each other, and

a side wall of the step functions as the restricting portion.

3. The clutch according to claim 1, wherein

the helical portion is a helical groove,

the annular portion is an annular groove including a connecting portion connected to the helical groove, and

the restricting portion includes a protrusion and a recess, wherein the protrusion projects from a bottom surface of the annular groove and extends at least over an entire length of the connecting portion in the extending direction of the annular groove, and the recess is formed at a distal end of the pin and becomes engaged with the protrusion when the pin is arranged in the connecting portion.

4. The clutch according to claim 1, wherein

the helical portion is a helical groove,

the annular portion is an annular groove including a connecting portion connected to the helical groove, and

the restricting portion includes a recessed groove and a projection, wherein the recessed groove is formed in a bottom surface of the annular groove and extends at least over an entire length of the connecting portion in the extending direction of the annular groove, and the projection projects from a distal end of the pin and becomes engaged with the recessed groove when the pin is arranged in the connecting portion.