VARIABLE VALVE TIMING APPARATUS

Abstract

A phase adjusting mechanism is engaged with a brake shaft, and adjusts a rotation phase between a crankshaft and a camshaft according to a braking torque acting on a rotor. The rotation phase is adjusted in a predetermined direction when the braking torque is increased. A torque input mechanism inputs a return torque into the phase adjusting mechanism to return the rotation phase in an opposite direction opposite from the predetermined direction. The torque input mechanism increases the return torque corresponding to the rotation phase as an environmental temperature of the variable valve timing apparatus is lowered.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2011-130492 filed on Jun. 10, 2011, the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to a variable valve timing apparatus.

BACKGROUND

A fluid brake device conducts variable control of viscosity of magnetic viscosity fluid by causing a magnetic flux to pass through the magnetic viscosity fluid. The magnetic viscosity fluid is filled in a fluid chamber of a casing, and contacts a brake rotor. Braking torque is provided to the brake rotor of the fluid brake device with comparatively small electric power, so that the fluid brake device is suitably used in a variable valve timing apparatus that controls a relative engine phase between a crankshaft and a camshaft of an engine in accordance with the braking torque.

JP-A-2008-51093 describes a variable valve timing apparatus having a casing, a brake shaft penetrating the casing, and a phase adjusting mechanism engaged with the brake shaft. If the braking torque acting on the brake rotor is increased, the phase adjusting mechanism adjusts the engine phase in a direction advancing the valve timing.

The variable valve timing apparatus further includes an elastic member that inputs a return torque to the phase adjusting mechanism to return the engine phase in a direction retarding the valve timing. The intensity of the return torque corresponds to the engine torque. If the braking torque input into the brake rotor is decreased, the engine phase is returned to the retarding direction by the return torque input from the elastic member. Thus, the engine phase can be controlled in accordance with the braking torque acting on the brake rotor by controlling the viscosity of the magnetic viscosity fluid.

However, as a temperature of the magnetic viscosity fluid is lowered, the viscosity of the magnetic viscosity fluid becomes high. When the environmental temperature of the variable valve timing apparatus is relatively low, for example, immediately after the engine is started, the low-temperature magnetic viscosity fluid has high viscosity, so that the braking torque is increased. Even if the magnetic flux passing through the magnetic viscosity fluid is weakened, it is difficult to retard the valve timing. Thus, at the low-temperature time, it may be difficult to control the engine phase by variably controlling the viscosity of the magnetic viscosity fluid.

If the return torque is increased for the low-temperature time, the return torque remains high when the environmental temperature is raised by the continuous operation of the engine. On the other hand, the braking torque input into the brake rotor is decreased by the lowering in the viscosity of the magnetic viscosity fluid when the environmental temperature is raised. In this case, it is difficult to balance the return torque and the braking torque, so that the engine phase may become unstable in the ordinary temperature time.

SUMMARY

According to an example of the present disclosure, a variable valve timing apparatus that controls valve timing of a valve which is opened and closed by a camshaft driven by torque transmission from a crankshaft in an internal combustion engine includes a case, magnetic viscosity fluid, a control device, a rotor, a phase adjusting mechanism, and a torque input mechanism. The case defines a fluid chamber inside. The magnetic viscosity fluid is kept in the fluid chamber, and has a viscosity variable in accordance with magnetic flux passing through. The control device carries out variable control of the viscosity of the magnetic viscosity fluid by varying the magnetic flux. The rotor has a brake shaft penetrating the case to come into contact with the magnetic viscosity fluid so that the rotor receives a braking torque according to the viscosity of the magnetic viscosity fluid. The phase adjusting mechanism is engaged with the brake shaft at an outside of the case, and adjusts a rotation phase between the crankshaft and the camshaft according to the braking torque acting on the rotor. The rotation phase is adjusted in a predetermined direction when the braking torque is increased. The torque input mechanism inputs a return torque into the phase adjusting mechanism to return the rotation phase in an opposite direction opposite from the predetermined direction. The torque input mechanism increases the return torque corresponding to the rotation phase as an environmental temperature of the variable valve timing apparatus is lowered.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional objects and advantages of the present disclosure will be more readily apparent from the following detailed description when taken together with the accompanying drawings. In which:

FIG. 1 is a schematic sectional view illustrating a variable valve timing apparatus including a fluid brake device according to a first embodiment of the present disclosure;

FIG. 2 is a sectional view taken along a line II-II of FIG. 1;

FIG. 3 is a sectional view taken along a line of FIG. 1;

FIG. 4 is a graph illustrating characteristics of magnetic viscosity fluid of the fluid brake device;

FIG. 5 is a sectional view taken along a line V-V of FIG. 1;

FIG. 6A is a sectional view illustrating a return torque input mechanism of the fluid brake device at a low-temperature time, and FIG. 6B is a sectional view illustrating the return torque input mechanism at an ordinary temperature time;

FIG. 7A is a sectional view illustrating a return torque input mechanism of a fluid brake device according to a second embodiment at a low-temperature time, and FIG. 7B is a sectional view illustrating the return torque input mechanism of the second embodiment at an ordinary temperature time; and

FIG. 8A is a sectional view illustrating a return torque input mechanism of a fluid brake device according to a third embodiment at a low-temperature time, and

FIG. 8B is a sectional view illustrating the return torque input mechanism of the third embodiment at an ordinary temperature time.

DETAILED DESCRIPTION

A plurality of embodiments of the present disclosure are explained referring to drawings. Components and parts corresponding to the components and parts described in the preceding description may be indicated by the same reference number and may not be described redundantly. In a case that only a part of component or part is described, other descriptions for the remaining part of component or part in the other description may be incorporated. The embodiments can be partially combined or partially exchanged in some forms which are clearly specified in the following description. In addition, it should be understood that, unless trouble arises, the embodiments can be partially combined or partially exchanged each other in some forms which are not clearly specified.

First Embodiment

FIG. 1 is a cross-sectional view taken along a line I-I of FIG. 2 and shows a variable valve timing apparatus 1 having a fluid brake device 100 according to a first embodiment. The variable valve timing apparatus 1 is mounted on an engine of a vehicle. The variable valve timing apparatus 1 is installed in a torque transmission train which transmits engine torque to a camshaft 2 from a crankshaft (not shown). The camshaft 2 opens and closes an intake valve (not shown) of the engine through the transmission of the engine torque. The variable valve timing apparatus 1 controls a valve timing of the intake valve.

The variable valve timing apparatus 1 has a control circuit 200 and a phase adjusting mechanism 300 in addition to the fluid brake device 100. The control circuit 200 is a circuit supplying energizing current. The variable valve timing apparatus 1 provides appropriate valve timing for the engine by adjusting an engine phase which is a relative angular phase between the camshaft 2 and the crankshaft.

The fluid brake device 100 is provided with a case 110, a brake rotor 130, a magnetic viscosity fluid 140, a sealing device 160 and a solenoid coil 150.

The case 110 is formed in a hollow shape as a whole. The case 110 has a fixing member 111 and a cover member 112. The fixing member 111 has a cylindrical shape in which outside diameter is changed to form a step, and is made of magnetic materials. The fixing member 111 is fixed to a member of the engine, such as a chain cover (not shown). The cover member 112 has a round disc shape, and is made of magnetic materials. The cover member 112 is arranged to have the same axis as the fixing member 111, and opposes the phase adjusting mechanism 300 through the fixing member 111. The fixing member 111 and the cover member 112 are liquid-tightly tightened to form the case 110 and to define a fluid chamber 114 therebetween.

The rotor 130 includes a shaft 131 and a plate 132 securely fixed each other. The shaft 131 extends in an axis direction, and is made of magnetic materials. The shaft 131 penetrates the fixing member 111 of the case 110 between an inside and an outside of the case 110. One end of the shaft 131 extends to the outside of the case 110, and is engaged with the phase adjusting mechanism 300 at the outside of the case 110. Intermediate part of the shaft 131 is rotatably supported by a bearing 116 defined in the fixing member 111. Since the phase adjusting mechanism 300 receives the engine torque from the crankshaft, the rotor 130 receives a rotating torque in a counterclockwise direction in FIGS. 2 and 3 from the phase adjusting mechanism 300.

As shown in FIG. 1, the annular plate 132 made of magnetic materials is disposed on an outer surface of the shaft 131 and is located on an end portion of the shaft 131 opposite from the phase adjusting mechanism 300. The plate 132 spreads outward in the radial direction, and is accommodated in the fluid chamber 114. In the fluid chamber 114, the plate 132 and the fixing member 111 define a magnetic gap 114a in the axis direction. Similarly, the plate 132 and the cover member 112 define a magnetic gap 114b in the axis direction.

The magnetic viscosity fluid 140 is filled in the fluid chamber 114 having the magnetic gaps 114a and 114b. The magnetic viscosity fluid 140 is a kind of functional fluid. For example, the magnetic viscosity fluid 140 contains magnetic particles which are suspended in non-magnetic base liquid. For example, oil which is the same kind of lubrication oil for the internal combustion engine may be used as the base liquid. A powdered magnetic material such as carbonyl iron etc. may be used as the magnetic particles for the magnetic viscosity fluid 140.

Viscosity of the magnetic viscosity fluid 140 is varied according to a magnetic field intensity applied. In other word, viscosity of the magnetic viscosity fluid 140 is varied according to a magnetic flux density. As shown in FIG. 4, viscosity of the magnetic viscosity fluid 140 is raised according to increase in the magnetic flux density. Therefore, the yield stress is increased in proportion to the viscosity.

As shown in FIG. 1, the sealing device 160 is arranged between the fluid chamber 114 and the bearing 116 in the axis direction of the case 110. The sealing device 160 seals a space between the fixing member 111 of the case 110 and the shaft 131 of the brake rotor 130, thereby restricting the magnetic viscosity fluid 140 from leaking outside of the case 110.

Specifically, the shaft 131 of the brake rotor 130 has a guide rotor 134 continuously extending in the rotation direction. A magnetism sealing sleeve 170 is arranged to surround the outer circumference side of the shaft 131 in the rotation direction. The sealing sleeve 170 has a permanent magnet 171 and a pair of guide yokes 174, 175. A seal gap 180 is defined between the guide yoke 174 and the guide rotor 134 and a seal gap 181 is defined between the guide yoke 175 and the guide rotor 134. The seal gap 180, 181 communicates with the fluid chamber 114.

A magnetic flux generated by the permanent magnet 171 is guided from the guide yoke 174, 175 through the seal gap 180, 181 to the guide rotor 134. The magnetic flux having high density passes through the seal gap 180, 181, and the viscosity of the magnetic viscosity fluid 140 is raised by the high density magnetic flux. Thereby, the magnetic viscosity fluid 140 is caught in a film shape at the seal gap 180, 181, and works as a self-sealing film that restricts the magnetic viscosity fluid 140 from leaking.

The solenoid coil 150 is produced by winding a metal wire on a radial outside surface of a cylindrical bobbin 151. The solenoid coil 150 is disposed on a radial outside part of the plate 132 in a coaxial manner. The solenoid coil 150 is supported in the case 110, and is interposed between the fixing member 111 and the cover member 112 in the axis direction. The solenoid coil 150 is excited by being supplied with electric current, and generates a magnetic flux which passes through the fixing member 111, the magnetic gap 114a, the plate 132, the magnetic gap 114b, and the cover member 112.

When the solenoid coil 150 generates the magnetic flux during counterclockwise rotation of the rotor 130 shown in FIGS. 2 and 3, the magnetic flux passes through the magnetic viscosity fluid 140 of the magnetic gaps 114a and 114b of the fluid chamber 114. The viscosity of the magnetic viscosity fluid 140 is varied by the magnetic flux, and a braking torque is generated between the case 110 and the rotor 130 which come in contact with the magnetic viscosity fluid 140. Therefore, the plate 132 of the rotor 130 receives the braking torque in the clockwise direction in FIGS. 2 and 3, due to the viscosity resistance. As a result, the braking torque according to the viscosity of the magnetic viscosity fluid 140 is applied to the rotor 130 by supplying the magnetic flux from the solenoid coil 150.

The control circuit 200 controls current supplied to the solenoid coil 150. The control circuit 200 is mainly constructed by a microcomputer. The control circuit 200 is disposed separately from the fluid brake device 100. The control circuit 200 is electrically connected with the solenoid coil 150 and a battery 4 arranged in the vehicle. During a stop of the engine, the control circuit 200 turns off a current supply to the solenoid coil 150 in response to a turning off an electric power supply from the battery 4. At this time, the solenoid coil 150 does not generate the magnetic flux, and does not generate the braking torque on the rotor 130.

On the other hand, during an operation of the engine, the control circuit 200 is supplied with the electric power from the battery 4, and controls an amount of current supply to the solenoid coil 150. As a result, the solenoid coil 150 generates a regulated amount of the magnetic flux which passes through the magnetic viscosity fluid 140. At this time, variable control of the viscosity of the magnetic viscosity fluid 140 is carried out. The braking torque applied to the rotor 130 is adjusted by the amount of the current supplied to the solenoid coil 150.

As shown in FIG. 1, the phase adjusting mechanism 300 includes a driving rotor 10, a driven rotor 20, a returning member 30, a planetary carrier 40, and a planetary gear 50.

The driving rotor 10 includes a gear member 12 and a chain wheel 13 which are made of metal. The gear member 12 and the chain wheel 13 are formed in cylindrical shapes and are fastened by screws in a coaxial manner. As shown in FIG. 2, the gear member 12 has a radial inside surface where a driving inner gear 14 is formed. A teeth tip circle has a diameter smaller than that of a teeth bottom circle in the gear 14. As shown in FIG. 1, the chain wheel 13 has a radial outside surface where a plurality of gear teeth 16 is formed. The gear teeth 16 of the chain wheel 13 is engaged with the crankshaft via a timing chain (not shown) and rotated synchronously with the crankshaft. Therefore, the driving rotor 10 is rotated in the counterclockwise direction in FIGS. 2 and 3 in response to the rotation of the crankshaft when the engine torque is transmitted to the chain wheel 13 from the crankshaft through the timing chain.

As shown in FIG. 1, the driven rotor 20 is formed in a cylindrical shape and is arranged in a radial inside of the chain wheel 13 in a coaxial manner. The driven rotor 20 has a connection part 21 on the bottom wall and the connection part 21 is fitted and connected to the camshaft 2 in a coaxial manner using screw. The driven rotor 20 is able to rotate in response to the rotation of the camshaft 2 and is able to have relative rotation relative to the driving rotor 10. The rotation direction of the driven rotor 20 is set in the counterclockwise direction of FIGS. 2 and 3, similarly to the driving rotor 10. The driven rotor 20 is interlocked with the camshaft 2, and is supported to relatively rotate with respect to the driving rotor 10.

As shown in FIG. 3, the driven rotor 20 has a radial inside surface where a driven inner gear 22 is formed. A teeth tip circle has a diameter smaller than that of a teeth bottom circle in the gear 22. The inside diameter of the driven inner gear 22 is set larger than that of the driving inner gear 14, and the number of teeth of the driven inner gear 22 is set greater than the number of teeth of the driving inner gear 14. The driven inner gear 22 is positioned away from the driving inner gear 14 in the axis direction, in a direction opposite from the fluid brake device 100.

As shown in FIG. 1, the returning member 30 consists of a helical torsion metal spring. The returning member 30 is coaxially arranged in an inside of the chain wheel 13. The returning member 30 has one end 31 which is engaged with the chain wheel 13 and the other end 32 which is engaged with the connection part 21. The returning member 30 generates assist torque when the returning member 30 is twisted between the rotors 10 and 20. The assist torque urges and pushes the driven rotor 20 in a retarding direction with respect to the driving rotor 10.

As shown in FIGS. 1-3, the planetary carrier 40 is formed in a cylindrical shape as a whole and is made of metal. The planetary carrier 40 has a radial inside surface where a transfer part 41 which receives the braking torque from the rotor 130 is formed. The transfer part 41 is coaxially arranged with the rotors 10 and 20. The transfer part 41 has a pair of engaging grooves 42 and a connector 43 fitted with the grooves 42. The transfer part 41 of the planetary carrier 40 and the brake shaft 131 are engaged via the connector 43. The planetary carrier 40 is capable of rotating with the brake rotor 130, and is capable of having relative rotation relative to the driving rotor 10. The rotation direction of the planetary carrier 40 is set in the counterclockwise direction in FIGS. 2 and 3 when the engine is active, similarly to the brake rotor 130.

As shown in FIGS. 1-3, the planetary carrier 40 has a supporting portion 46 which supports the planetary gear 50. The supporting portion 46 is located eccentrically with respect to the rotors 10 and 20 and the brake shaft 131, and is coaxially engaged with a center hole 51 of the planetary gear 50 through a planetary bearing 48. The planetary gear 50 is supported by the supporting portion 46 in such a manner as to perform the planetary motion. The planetary gear 50 rotates about an eccentric axis of the supporting portion 46, and also the planetary gear 50 revolves relative to the planetary carrier 40. Thus, when the planetary carrier 40 performs relative rotation with respect to the driving rotor 10 in the revolution direction of the planetary gear 50, the planetary gear 50 performs the planetary motion.

The planetary gear 50 has a radial outside surface formed in a stepped cylindrical shape. The planetary gear 50 has a driving outer gear 52 and a driven outer gear 54 on the radial outside. The driving outer gear 52 is formed on a smaller diameter part of the gear 50, and the driven outer gear 54 is formed on a larger diameter part of the gear 50. The driving outer gear 52 and the driven outer gear 54 are coaxially arranged. The driving outer gear 52 intermeshes with the driving inner gear 14 only at a position where the planetary gear 50 is located by its orbiting motion. The driven outer gear 54 also intermeshes with the driven inner gear 22 only at a position where the planetary gear 50 is located by its orbiting motion. The outside diameter of the driven outer gear 54 is set larger than that of the driving outer gear 52, and the number of teeth of the outer gear 52, 54 is set smaller than the number of teeth of the inner gear 22, 14 by the same number.

The phase adjusting mechanism 300 adjusts the engine phase according to a balance of torques among the braking torque input into the rotor 130, the assist torque of the returning member 30 acting in the opposite direction of the braking torque, and fluctuating torque acting on the camshaft 2 during the operation of the engine.

In a case where the braking torque is adjusted in a constant value in order to enable the rotor 130 to rotate with the drive rotor 10 in the same rotating speed, the planetary carrier 40 does not rotate relatively with respect to the driving inner gear 14. Then, the planetary gear 50 orbits synchronously with both the rotors 10 and 20 without performing relative rotation of the sun-and-planet motion. Therefore, the engine phase is maintained in a constant angular phase.

In a case where the braking torque is increased in order to enable the rotor 130 to rotate at a rotating speed that is slower than that of the drive rotor 10, the planetary carrier 40 relatively rotates in a retarding direction with respect to the driving inner gear 14. Then, the planetary gear 50 itself rotates by the sun-and-planet motion and orbits on the gears 14 and 22. Therefore, the driven rotor 20 is relatively rotated in an advancing direction with respect to the drive rotor 10. Therefore, the engine phase is advanced.

In a case where the braking torque is decreased in order to enable the rotor 130 to rotate at a rotating speed that is higher than that of the drive rotor 10, the planetary carrier 40 relatively rotates in an advancing direction with respect to the driving inner gear 14. Then, the planetary gear 50 itself rotates by the sun-and-planet motion and orbits on the gears 14 and 22. Therefore, the driven rotor 20 is relatively rotated in a retarding direction with respect to the drive rotor 10. Therefore, the engine phase is retarded.

As shown in FIG. 5, a return torque input mechanism 60 is constructed by a thermo sensor element 70 and a holding member 80, in addition to the returning member 30.

As shown in FIG. 1, the returning member 30 is constructed by a wire spirally winded, as a main part 30a. The one end 31 of the returning member 30 is received by the thermo sensor element 70 through a pillar-shaped connection component 31a made of metal materials. The one end 31 of the returning member 30 is extended to the outer circumference side from the main part 30a of the returning member 30. The other end 32 of the returning member 30 is received by a stationary portion 21 through a boss 32a embedded in the stationary portion 21.

The returning member 30 is connected with the phase adjusting mechanism 300. As the engine phase is adjusted in the advancing direction advancing the valve timing, the returning member 30 is twisted at the center axis, so that strong recovery force is acted to the phase adjusting mechanism 300 from the returning member 30. That is, the returning member 30 inputs a return torque corresponding to the engine phase into the phase adjusting mechanism 300, and the return torque causes the engine phase to return in the retarding direction retarding the valve timing.

The thermo sensor element 70 is arranged at periphery side of the returning member 30, and is connected with the returning member 30. The thermo sensor element 70 has a case part 71, a wax 74, a piston 76, and a diaphragm 75, as shown in FIG. 5.

The case part 71 has a cylindrical shape, and is made of metallic material which is excellent in heat conduction, for example. A wax chamber 72 is defined inside of the case part 71. The wax 74 is accommodated in the wax chamber 72. An environmental temperature of the variable valve timing apparatus 1 is transmitted to the wax chamber 72 through the holding member 80 and the case part 71.

The wax 74 is paraffin wax, for example, and is enclosed within the wax chamber 72 of the case part 71. The volume of the wax 74 is decreased, as the temperature of the wax 74 is lowered. The volume of the wax 74 is increased, as the temperature of the wax 74 is raised. The volume of the wax chamber 72 of the case part 71 is varied by the expansion/contraction of the wax 74.

The piston 76 penetrates the case part 71 between the inside and the outside of the case part 71, and is movable relative to the case part 71. The piston 76 has a holding part 78 and a pressure receiving part 77. The holding part 78 is constructed by a portion of the piston 76 located outside of the case part 71, and holds the connection component 31a. Thereby, the piston 76 is connected with the one end 31 of the returning member 30 through the connection component 31a.

The pressure receiving part 77 has a board shape and defines the wax chamber 72 inside of the case part 71. The pressure receiving part 77 displaces the piston 76 in the axis direction of the case part 71 by the pressure received from the wax 74 when the wax 74 has the expansion/contraction. The piston 76 moves relative to the case part 71 by being displaced by the expansion/contraction of the wax 74, so that the piston 76 increases the amount of elastic deformation of the returning member 30 outside of the case part 71.

The diaphragm 75 has a ring shape and is made of rubber material which can be expanded or contracted. The diaphragm 75 is arranged between the outer circumference wall of the pressure receiving part 77 of the piston 76 and the inner circumference wall of the case part 71, and is joined with the outer circumference wall and the inner circumference wall. The diaphragm 75 expands and contracts in response to the displacement of the piston 76, so as to maintain the definition of the wax chamber 72 inside of the case part 71. That is, the diaphragm 75 works as a sealing device, so that the wax 74 is restricted from leaking out of the wax chamber 72.

The holding member 80 has a disc shape and is made of metallic material. The holding member 80 is fixed to the chain wheel 13 by plural fastening components 82. A thermo sensor chamber 81 is defined in the holding member 80, and has a shape corresponding to the thermo sensor element 70. The holding member 80 holds the thermo sensor element 70 in the thermo sensor chamber 81 in the state where the piston 76 can have the displacement.

If the variable valve timing apparatus 1 is left under low-temperature environment in a state where the engine is stopped, the environmental temperature of the variable valve timing apparatus 1 is also lowered with progress of time. The temperature of the magnetic viscosity fluid 140 accommodated in the variable valve timing apparatus 1 is also lowered to the same degree as the environmental temperature. Thereby, the viscosity of the oil, which is the base liquid of the magnetic viscosity fluid 140, is raised as shown in a broken line of FIG. 4.

Therefore, the braking torque which acts on the brake rotor 130 from the magnetic viscosity fluid 140 will increase. In addition, in the inside of the phase adjusting mechanism 300, the viscosity of the lubrication oil is also raised by the lowering in the temperature of the lubrication oil. Therefore, as the environmental temperature of the variable valve timing apparatus 1 is lowered, the torque required to adjust the engine phase in the phase adjusting mechanism 300 is increased.

The return torque input mechanism 60 increases the return torque input into the phase adjusting mechanism 300, as the environmental temperature of the variable valve timing apparatus 1 is lowered. Details of operation of the return torque input mechanism 60 will be explained with reference to FIGS. 6A and 6B.

In low-temperature environment (e.g., about −30° C.) immediately after start-up of the engine, as the environmental temperature of the variable valve timing apparatus 1 is lowered, the temperature of the thermo sensor element 70 is also lowered. Therefore, as shown in FIG. 6A, the wax 74 accommodated in the wax chamber 72 of the thermo sensor element 70 is contracted. At this time, the piston 76 moves to follow the contracted wax 74, so that the piston 76 is displaced in the counterclockwise direction shown in FIG. 6A. The displacement of the piston 76 is transmitted to the returning member 30 through the connection component 31a, therefore the thermo sensor element 70 further increases the amount of elastic deformation of the returning member 30.

Thus, the recovery force of the returning member 30 which acts on the phase adjusting mechanism 300 becomes still stronger, because a set load of the returning member 30 is increased. Therefore, the return torque input into the phase adjusting mechanism 300 is increased by the lowering in the environmental temperature in all the range of the engine phase adjusted with the phase adjusting mechanism 300. Accordingly, the return torque input mechanism 60 increases the return torque input into the phase adjusting mechanism 300, as the environmental temperature of the variable valve timing apparatus 1 is lowered. In addition, the set load of the returning member 30 mentioned above represents a power elastically deforming the returning member 30 in a case where the engine phase has the most retarded phase in the phase adjusting mechanism 300.

When the environmental temperature of the variable valve timing apparatus 1 is raised to an ordinary temperature (e.g., about 130° C.) by continuous operation of the engine, the temperature of the thermo sensor element 70 is also raised. Therefore, the wax 74 accommodated in the wax chamber 72 of the thermo sensor element 70 is expanded, as shown in FIG. 6B. The piston 76 is displaced in the clockwise rotation shown in FIG. 6B by the pressure of the expanding wax 74. The displacement of the piston 76 is transmitted to the returning member 30 through the connection component 31a, therefore the thermo sensor element 70 decreases the amount of elastic deformation of the returning member 30.

Then, because the set load of the returning member 30 decreases, the recovery force of the returning member 30 which acts on the phase adjusting mechanism 300 becomes weak. Thus, the return torque input into the phase adjusting mechanism 300 is decreased by the raising in the environmental temperature in all the range of the engine phase adjusted with the phase adjusting mechanism 300. Accordingly, the return torque input mechanism 60 decreases the return torque input into the phase adjusting mechanism 300, as the environmental temperature of the variable valve timing apparatus 1 is raised.

In the first embodiment, the braking torque input into the brake rotor 130 and the torque required for adjusting the engine phase are assumed to increase due to the lowering in the environmental temperature. At this time, the return torque input mechanism 60 can cause the valve timing to return in the retarding direction by increasing the return torque, while the engine phase is advanced by the increase in the braking torque. That is, even in the low-temperature time, the engine phase can be adjusted by the phase adjusting mechanism 300 through the variable control of the viscosity of the magnetic viscosity fluid 140.

When the environmental temperature of the variable valve timing apparatus 1 becomes to have the ordinary temperature, the braking torque input into the brake rotor 130 from the magnetic viscosity fluid 140 is decreased due to the lowering in the viscosity of the magnetic viscosity fluid 140 in response to the rise in the temperature. At this time, the return torque input mechanism 60 makes it easy to balance the return torque and the braking torque input into the brake rotor 130 by decreasing the return torque input into the phase adjusting mechanism 300. Thus, in the ordinary temperature time, the engine phase can be maintained as stable by the phase adjusting mechanism 300 through the variable control of the viscosity of the magnetic viscosity fluid 140.

According to the first embodiment, the engine phase can be suitable adjusted at the low-temperature time, and the engine phase can be maintained as stable at the ordinary temperature time, due to the variable valve timing apparatus 1.

In addition, according to the first embodiment, the construction of the return torque input mechanism 60 can be simplified using the wax 74 that is contracted as the environmental temperature is lowered and the piston 76 that is displaced by the contraction of the wax 74. Further, the reliability of the return torque input mechanism 60 is raised by the simplification of the return torque input mechanism 60. Therefore, the return torque input mechanism 60 can increase the return torque as the environmental temperature of the variable valve timing apparatus 1 is lowered, with more reliability. Thus, the engine phase can be suitable adjusted at the low-temperature time, and the engine phase can be maintained as stable at the ordinary temperature time, with more reliability.

In the first embodiment, the returning member 30 may correspond to an elastic member. The return torque input mechanism 60 may correspond to a torque input mechanism. The thermo sensor element 70 may correspond to a deformation increasing portion that increases the deformation amount of the elastic member. The wax chamber 72 may correspond to an accommodation chamber. The casing part 71 may correspond to a contraction casing. The wax 74 may correspond to a contraction part. The piston 76 may correspond to a displacement part. The control circuit 200 and the solenoid coil 150 may correspond to a control device that controls the viscosity of the magnetic viscosity fluid. The advancing direction of the valve timing may correspond to a predetermined direction. The retarding direction of the valve timing may correspond to an opposite direction opposite from the predetermined direction.

Second Embodiment

A second embodiment, which is a modification of the first embodiment, will be described with reference to FIGS. 7A and 7B. The thermo sensor element 70 of the second embodiment further includes a coil spring 279. The coil spring 279 is formed by a wire spirally winded around the piston 76, and is made of metallic materials. The coil spring 279 is accommodated in a space opposite from the wax chamber 72 through the pressure receiving part 77 in the state where the coil spring 279 is contracted in the axis direction, in the case part 71. Hereinafter, the space is referred as a spring chamber 273. In the inside of the case part 71, the coil spring 279 biases the pressure receiving part 77 of the piston 76 toward the wax 74.

Operation of the return torque input mechanism 60 with the coil spring 279 will be explained below.

As the environmental temperature of the variable valve timing apparatus 1 is lowered, the wax 74 contracts, and the piston 76 moves to follow the contracted wax 74 so that the piston 76 is displaced in the counterclockwise direction shown in FIG. 7A. Because the coil spring 279 biases the piston 76 toward the wax 74, the piston 76 suitably follows the contracted wax 74 and is displaced with reliability. The displacement of the piston 76 further increases the amount of elastic deformation of the returning member 30, so that the recovery force of the returning member 30 which acts on the phase adjusting mechanism 300 becomes still stronger. Thus, the return torque input mechanism 60 can increase the return torque input into the phase adjusting mechanism 300 certainly, as the environmental temperature of the variable valve timing apparatus 1 is lowered.

Moreover, as shown in FIG. 7B, as the temperature of the variable valve timing apparatus 1 is raised to the ordinary temperature, the wax 74 expands. Thereby, the pressure of the expanding wax 74 displaces the piston 76 in the clockwise rotation by resisting the biasing force of the coil spring 279. The displacement of the piston 76 decreases the amount of elastic deformation of the returning member 30, so that the recovery force of the returning member 30 which acts on the phase adjusting mechanism 300 becomes weak. Thus, as the environmental temperature of the variable valve timing apparatus 1 is raised, the return torque input mechanism 60 can decrease the return torque input into the phase adjusting mechanism 300.

According to the second embodiment, the thermo sensor element 70 has the coil spring 279. Therefore, as the environmental temperature of the variable valve timing apparatus 1 is lowered, the return torque input mechanism 60 increases the return torque with reliability. Thus, the engine phase can be suitably adjusted at the low-temperature time, and the engine phase can be maintained as stable at the ordinary temperature time, due to the variable valve timing apparatus 1.

The coil spring 279 of the second embodiment may correspond to a biasing part.

Third Embodiment

A third embodiment, which is a modification of the second embodiment, will be described with reference to FIGS. 8A and 8B. A thermo sensor element 370 of the third embodiment is arranged at the clockwise direction side of the connection component 31a. In the thermo sensor element 370, arrangement of the wax chamber 72 and the spring chamber 273 is reverse in the axis direction of the case part 71, compared with the thermo sensor element 70 of the first and second embodiments. The wax chamber 72 defined in the case part 71 is located between the holding part 78 and the pressure receiving part 77. Moreover, the spring chamber 273 defined in the case part 71 is located on the clockwise direction side of the pressure receiving part 77, that is separated from the holding part 78. Operation of the return torque input mechanism 60 with the thermo sensor 370 of the third embodiment will be explained below.

When the environmental temperature of the variable valve timing apparatus 1 is lowered, the wax 74 is contracts, and the piston 76 moves to follow the contacted wax 74 so that the piston 76 is displaced in the counterclockwise rotation shown in FIG. 8A, due to the biasing force of the coil spring 279. The displacement of the piston 76 further increases the amount of elastic deformation of the returning member 30, so that the recovering force of the returning member 30 which acts on the phase adjusting mechanism 300 becomes still stronger. Thus, the return torque input mechanism 60 can increase the return torque input into the phase adjusting mechanism 300 certainly, as the environmental temperature of the variable valve timing apparatus 1 is lowered.

Moreover, as shown in FIG. 8B, as the temperature of the variable valve timing apparatus 1 is raised to the ordinary temperature, the wax 74 expands. Thereby, the pressure of the expanding wax 74 displaces the piston 76 in the clockwise rotation by resisting the biasing force of the coil spring 279. The displacement of the piston 76 decreases the amount of elastic deformation of the returning member 30, so that the recovery force of the returning member 30 which acts on the phase adjusting mechanism 300 becomes weak. Thus, as the environmental temperature of the variable valve timing apparatus 1 is raised, the return torque input mechanism 60 can decrease the return torque input into the phase adjusting mechanism 300.

According to the thermo sensor 370 of the third embodiment, the return torque input mechanism 60 can increase or decrease the return torque input into the phase adjusting mechanism 300 so as to respond to the environmental temperature. Therefore, the variable valve timing apparatus 1 of the third embodiment can suitably adjust the engine phase at the low-temperature time, and can maintain the engine phase as stable at the ordinary temperature time.

Other Embodiments

The present disclosure should not be limited to the above embodiments, but may be implemented in other ways without departing from the spirit of the disclosure.

The deformation increasing portion is not limited to the thermo sensor element 70. Alternatively, the deformation increasing portion may be constructed by a temperature detector that detects the environmental temperature of the variable valve timing apparatus 1, and an actuator that is displaced to increase the amount of elastic deformation of the returning member 30 as the temperature detected by the detector is lowered. Furthermore, the elastic member such as the returning member 30 may be omitted. In this case, the variable valve timing apparatus 1 may be equipped with an actuator that increases the return torque as the temperature detected by the detector is lowered, as a torque input mechanism.

Although the present disclosure is applied to the intake valve, the present disclosure may be applied to an apparatus for controlling valve timing of an exhaust valve. In this case, the retarding direction may correspond to a predetermined direction, and the advancing direction may correspond to an opposite direction opposite from the predetermined direction.

The elastic member is not limited to the returning member 30. Alternatively, the elastic member may be a coil spring, plate spring, etc., or may be made of rubber material.

The contraction part is not limited to the wax 74 in semi-solid state. The contraction part may be other component that is contracted as the environmental temperature of the variable valve timing apparatus 1 is lowered. Further, the contraction part may be in a solid state, a liquid state, or a gas state.

More specifically, the contraction part may be a spring made of a shape memory alloy, and the shape of the spring is changed by the temperature. The shape memory alloy may be an alloy of titanium and nickel, for example. The spring made of the shape memory alloy is contracted as the environmental temperature of the variable valve timing apparatus 1 is lowered, and will be recovered into the initial shape as the environmental temperature of the variable valve timing apparatus 1 is raised. In this case, the thermo sensor element corresponding to the deformation increasing portion further increases the amount of elastic deformation of the returning member 30 under low-temperature environment, so that the return torque input into the phase adjusting mechanism 300 from the returning member 30 is made stronger.

Further, the thermo sensor element corresponding to the deformation increasing portion decreases the amount of elastic deformation of the returning member 30 under ordinary temperature environment, so that the return torque input into the phase adjusting mechanism 300 from the returning member 30 is made weak.

In addition, the shape memory alloy may be an alloy using iron as a principal component, and manganese and silicon are mixed into the principal component. Moreover, the spring may have a coil shape, a pan shape or a board shape.

The engine phase may be adjusted according to the braking torque input into the brake rotor 130 due to the cooperation with the brake shaft 131. Although the present disclosure is applied to the intake valve, the present disclosure may be applied to an apparatus for controlling valve timing of an exhaust valve or an apparatus for controlling valve timing of an intake valve and an exhaust valve. Further, the present disclosure may be applied to a variety of apparatuses using the braking torque.

Although the present disclosure has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being within the scope of the present disclosure as defined by the appended claims.

Claims

1. A variable valve timing apparatus that controls valve timing of a valve which is opened and closed by a camshaft driven by torque transmission from a crankshaft in an internal combustion engine, the apparatus comprising:

a case defining a fluid chamber inside;

magnetic viscosity fluid kept in the fluid chamber, the magnetic viscosity fluid having a viscosity variable in accordance with magnetic flux passing through;

a control device which carries out variable control of the viscosity of the magnetic viscosity fluid by varying the magnetic flux;

a rotor having a brake shaft penetrating the case to come into contact with the magnetic viscosity fluid so that the rotor receives a braking torque according to the viscosity of the magnetic viscosity fluid;

a phase adjusting mechanism engaged with the brake shaft at an outside of the case, the phase adjusting mechanism adjusting a rotation phase between the crankshaft and the camshaft according to the braking torque acting on the rotor, the rotation phase being adjusted in a predetermined direction when the braking torque is increased; and

a torque input mechanism inputting a return torque into the phase adjusting mechanism to return the rotation phase in an opposite direction opposite from the predetermined direction, wherein the torque input mechanism increases the return torque corresponding to the rotation phase as an environmental temperature of the variable valve timing apparatus is lowered.

2. The variable valve timing apparatus according to claim 1, wherein

the torque input mechanism has an elastic member connected to the phase adjusting mechanism in a state where the elastic member has an elastic deformation, the elastic member inputting the return torque corresponding to the rotation phase using a recovering force of the elastic member from the elastic deformation, and a deformation increasing portion connected to the elastic member, the deformation increasing portion increasing the return torque by increasing an amount of the elastic deformation of the elastic member as the environmental temperature of the variable valve timing apparatus is lowered.

3. The variable valve timing apparatus according to claim 2, wherein

the deformation increasing portion has a contraction part that is contacted as the environmental temperature of the variable valve timing apparatus is lowered, a contraction casing defining an accommodation chamber that accommodates the contraction part, and a displacement part penetrating the contraction casing, the displacement part increasing the amount of the elastic deformation of the elastic member at outside of the contraction casing by being displaced by the contraction of the contraction part in the accommodation chamber.

4. The variable valve timing apparatus according to claim 3, wherein

the deformation increasing portion further has a biasing part that biases the displacement part toward the contraction part, inside of the contraction casing.