VALVE TIMING CONTROLLER

Abstract

A valve timing controller has a case which defines a fluid chamber therein. A magnetic viscosity fluid is enclosed in the fluid chamber. The magnetic viscosity fluid including magnetic particles and its viscosity varies according to a magnetic field applied thereto. A coil and a control circuit applies magnetic field to the magnetic viscosity fluid to variably control a viscosity thereof. A brake rotor is rotatably accommodated in the fluid chamber and receives a brake torque from the magnetic viscosity fluid according to the viscosity thereof. A phase adjusting mechanism is connected to the brake rotor for adjusting a relative rotational phase between the crankshaft and the camshaft according to the brake torque. When it is estimated that the engine will be started, the coil is energized to generated heat in the magnetic viscosity fluid.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No.2010-134431 filed on Jun. 11, 2010, the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a valve timing controller which adjusts valve timing of a valve that is opened/closed by a camshaft driven by a torque transmitted from a crankshaft of an internal combustion engine.

BACKGROUND OF THE INVENTION

Conventionally, it is known that a valve timing controller adjusts a relative rotational phase between a crankshaft and a camshaft according to a braking torque generated by an actuator. A valve timing of an intake valve and/or an exhaust valve depends on the above relative rotational phase, which is referred to as an engine-phase. JP-2008-51093A shows such a valve timing controller which adjusts an engine-phase by generating braking torque of a fluid actuator.

Specifically, this valve timing controller has an actuator in which magnetic viscosity fluid is enclosed in a casing. The magnetic viscosity fluid is in contact with a braking rotor. A magnetic field is applied to the magnetic viscosity fluid, whereby a viscosity of the magnetic viscosity fluid is variably controlled. The braking torque is generated on the braking rotor supported by the casing according to the viscosity of the magnetic viscosity fluid. Thus, the engine-phase is adjusted according to the braking torque.

Generally, when temperature of the magnetic viscosity fluid extremely falls, the magnetic viscosity fluid becomes the glass transition condition (solid) in which its viscosity is unstable relative to the magnetic field. Thus, if the magnetic viscosity fluid is brought into the glass transition condition during an engine stop, it is likely that necessary braking torque is not generated at the time the engine is restarted. In such a case, an optimum engine-phase is not obtained and a startability of the engine is deteriorated. An accuracy of the valve timing controller is less ensured.

SUMMARY OF THE INVENTION

The present invention is made in view of the above matters, and it is an object of the present invention to provide a valve timing controller of which reliability is ensured.

According to the present invention, a valve timing controller adjusts a valve timing of a valve opened/closed by a torque transmitted from a crankshaft to a camshaft of an internal combustion engine. The valve timing controller includes: a case defining a fluid chamber therein; and a magnetic viscosity fluid enclosed in the fluid chamber. The magnetic viscosity fluid includes magnetic particles and its viscosity varies according to a magnetic field applied thereto.

The valve timing controller further includes: a viscosity control means for variably controlling a viscosity of the magnetic viscosity fluid by applying a magnetic field to the magnetic viscosity fluid; a brake rotor rotatably accommodated in the fluid chamber and receiving a brake torque from the magnetic viscosity fluid according to the viscosity thereof; a phase adjusting mechanism connected to the brake rotor for adjusting a relative rotational phase between the crankshaft and the camshaft according to the brake torque; and a heating control means for generating a heat in the magnetic viscosity fluid when it is estimated that the internal combustion engine will be started.

When it is estimated that the engine will be started, the coil is energized to generate heat in the magnetic viscosity fluid. Even if the magnetic viscosity fluid is in the glass transition condition, the magnetic viscosity fluid is brought out from the glass transition condition, whereby the variation in viscosity becomes stable according to the applied magnetic field. Consequently, when the engine is started, the viscosity of the magnetic viscosity fluid can be controlled by applying the magnetic field thereto, whereby desired brake torque is inputted into the brake rotor so that the phase adjusting mechanism makes the engine-phase optimal. Therefore, a high reliability of the valve timing controller can be ensured.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention will become more apparent from the following description made with reference to the accompanying drawings, in which like parts are designated by like reference numbers and in which:

FIG. 1 is a cross sectional view showing a valve timing controller according to a first embodiment of the present invention, taken along a line in FIG. 2;

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

FIG. 3 is a cross-sectional view taken along a line in FIG. 1;

FIG. 4 is a characteristics chart for explaining a magnetic viscosity fluid;

FIG. 5 is another characteristics chart for explaining a magnetic viscosity fluid;

FIG. 6A and FIG. 6B are time charts for explaining an energization control according to the first embodiment;

FIG. 7 is a characteristics chart for explaining a heating of the magnetic viscosity fluid according to the first embodiment;

FIG. 8 is a flowchart showing a control flow of an energization control circuit according to the first embodiment;

FIG. 9A and FIG. 9B are time charts for explaining an energization control according to a second embodiment;

FIG. 10A and FIG. 10B are time charts for explaining an energization control according to a third embodiment;

FIG. 11 is a flowchart showing a control flow of an energization control circuit according to a fourth embodiment;

FIG. 12 is a flowchart showing a control flow of an energization control circuit according to a fifth embodiment;

FIG. 13 is a cross sectional view showing a valve timing controller according to a sixth embodiment;

FIG. 14 is a flowchart showing a control flow of an energization control circuit according to a sixth embodiment; and

FIG. 15 is a flowchart showing a control flow of an energization control circuit according to a seventh embodiment;

DETAILED DESCRIPTION OF EMBODIMENTS

Multiple embodiments of the present invention will be described with reference to accompanying drawings. In each embodiment, the same parts and the components are indicated with the same reference numeral and the same description will not be reiterated. Further, each embodiment can be suitably combined.

First Embodiment

FIG. 1 shows a valve timing controller 1 according to a first embodiment of the present invention. The valve timing controller 1 is mounted on a vehicle, and more specifically, the valve timing controller 1 is mounted on a transmission system that transmits an engine torque from a crankshaft (not shown) to a camshaft 2 of an internal combustion engine. In the present embodiment, the camshaft 2 opens and closes an intake valve (not shown) of the internal combustion engine through transmission of the engine torque. The valve timing controller 1 adjusts a valve timing of the intake valve.

As shown in FIGS. 1 to 3, the valve timing controller 1 includes an actuator 100, a current control circuit 200, a phase adjusting mechanism 300 and the like. The valve timing controller 1 adjusts a relative rotational phase between the crankshaft and the camshaft 2 to realize a desired valve timing.

(Actuator 100)

As shown in FIG. 1, the actuator 100 is an electromotive fluid brake which is comprised of a case 110, a brake rotor 130 and a coil 150.

The case 110 is comprised of a fixed member 111 and a cover member 112. The fixed member 111 is annular-shaped and is made of magnetic material. The fixed member is fixed on a chain case (not shown) of the internal combustion engine. The cover member 112 is also made of magnetic material. The cover member 112 and the fixed member 111 define a fluid chamber 114 therebetween.

The brake rotor 130 is made of magnetic material and includes a shaft portion 131 and a rotor portion 132. The shaft portion 131 extends through the fixed member 111 to be connected with the phase adjusting mechanism 300. The other end of the shaft portion 131 is rotatably supported by the cover member 112 through a bearing 115. A middle portion of the shaft portion 131 is supported by the fixed member 111 through a bearing 116. When receiving an engine torque from the phase adjusting mechanism 300, the brake rotor 130 rotates counterclockwise in FIGS. 2 and 3.

The rotor portion 132 is disc-shaped and is accommodated in the fluid chamber 114. A first magnetic gap 114a is defined between the rotor portion 132 and the fixed member 111. A second magnetic gap 114b is defined between the rotor portion 132 and the cover member 112.

The magnetic viscosity fluid 140 is enclosed in the fluid chamber 114. The magnetic viscosity fluid 140 is functional fluid comprised of base-liquid and magnetic particles. The base-liquid is nonmagnetic fluid such as oil. Preferably, the base-liquid is lubrication oil for an engine. The magnetic particles are magnetic powder of carbonyl iron.

As shown in FIG. 4, the magnetic viscosity fluid 140 has characteristics in which its viscosity increases according to an intensity of applied magnetic field. Further, in proportion to the viscosity, its shear yield stress also increases. Further, in a condition where no magnetic field is applied to the magnetic viscosity fluid 140, the base viscosity of the magnetic viscosity fluid 140 is increased along with a decrease in temperature thereof. When the temperature is excessively decreased, the magnetic viscosity fluid 140 becomes the glass transition condition (solid) in which its viscosity is unstable relative to the magnetic field. In the present embodiment, a lower limit temperature “Tl” of the magnetic viscosity fluid 140 is set at “−20° C.”.

A coil 150 is winded around a resin bobbin coaxially to the fixed member 111. When the coil 150 is energized, magnetic field is generated in such a manner that magnetic flux passes through the first magnetic gap 114a, the rotor portion 132, the second magnetic gap 114b, the cover member 112 and the fixed member 111. The generated magnetic field is applied to the magnetic viscosity fluid 140 in the magnetic gaps 114a, 114b, so that its viscosity is varied. Thus, between the case 110 and the brake rotor 130, braking torque is generated to brake the brake rotor 130 in clockwise direction in FIGS. 2 and 3. As above, when the coil 150 is energized to generate the magnetic field which is applied to the magnetic viscosity fluid 140, the braking torque is inputted into the brake rotor 130 according to the viscosity of the magnetic viscosity fluid 140.

As shown in FIG. 1, the resin bobbin 151 is exposed to the first magnetic gap 114a in the fluid chamber 114. The fixed member 111 is also exposed to the first magnetic gap 114a. Thus, even if the coil 150 generates heat when energized, the heat is transferred to the magnetic viscosity fluid 140 in the first magnetic gap 114a through the resin bobbin 151 and the fixed member 111.

(Current Control Circuit 200)

The current control circuit 200 includes a microcomputer and is electrically connected to the coil 150 and a battery 4 of a vehicle. When a specified starting condition “Cw” is established with the engine stopped, the current control circuit 200 receives electricity from the battery 4, whereby the current control circuit 200 is changed from OFF-mode to ON-mode so that the coil 150 can be energized. The starting condition “Cw” is established when a door lock of a vehicle is released, a vehicle door is opened, or a receiver receives a signal from a transmitter of a keyless entry system. If the engine is not started even after a specified time “ST” elapses from changing mode to the ON-mode, the ON-mode is automatically changed to the OFF-mode.

During the On-mode, the current control circuit 200 controls electric current “I” supplied to the coil 150 so that the magnetic field applied to the magnetic viscosity fluid 140 is adjusted. Consequently, according to the applied magnetic field, the viscosity of the magnetic viscosity fluid 140 is variably controlled so that the braking torque to the brake rotor 130 is increased/decreased.

In the present embodiment, the electric current “I” is controlled as shown in FIG. 6A, so that the magnetic flux density “B” applied to the magnetic viscosity fluid 140 is varied before and after the engine is started as shown in FIG. 6B. Specifically, during a period “α” in which the engine is not started, the electric current “I” is controlled in such a manner that the electric current “I” is varied like pulses having low frequency “fα” and an effective electric power in a specified period “RT” is high effective electric power “Wα” around 5 W·s. During a period “β” in which the engine is started, the electric current “I” is controlled in such a manner that the electric current “I” is varied like pulses having high frequency “fβ” and an effective electric power in a specified period “RT” is low electric power “Wβ”.

According to the above energization control, during the period “α”, the magnetic particles in the magnetic viscosity fluid 140 repeatedly perform a movement in which chain-shaped cluster of the magnetic particles is composed and decomposed according to a variation in magnetic flux density “B” as shown in FIG. 6B. As the result, the magnetic viscosity fluid 140 generates heat due to the above movement of the magnetic particles. As shown in FIG. 7, in a case that the applied electric current has low frequency “fα”, such as 2-10 Hz, the magnetic viscosity fluid 140 effectively generates heat. Further, the magnetic viscosity fluid 140 receives heat from the coil 150, so that the temperature of the magnetic viscosity fluid 140 is effectively increased.

During the period “β”, the electric current “I” has high frequency “fβ” around 50 Hz to generate low electric power “Wβ” around 3 W·s. Further, as shown in FIG. 6B, the magnetic flux density “B” is varied according to the frequency “fβ”, the magnetic viscosity fluid 140 receives an agitation action. Thus, the variation in viscosity of the fluid 140 becomes stable with respect to the applied magnetic field, and the desired braking torque can be obtained stably.

It should be noted that the current control circuit 200 controls the energization of other electrical components.

(Phase Adjusting Mechanism 300)

As shown in FIGS. 1 to 3, the phase adjusting mechanism 300 is provided with a driving rotor 10, a driven rotor 20, an assist member 30, a planetary carrier 40 and a planetary gear 50.

The driving rotor 10 is comprised of a gear member 12 and a sprocket member 13, which are coaxially connected with each other by a bolt. The gear member 12 includes a first internal gear 14 on its radially inner peripheral wall. The first internal gear 14 defines an addendum circle located radially inside of a root circle. As shown in FIG. 1, the sprocket member 13 has a plurality of gear tooth 16 on its outer periphery. A timing chain (not shown) is wound around the gear teeth 16 of the sprocket member 13 and a plurality of gear teeth of the crankshaft so that the sprocket member 13 is linked to the crankshaft. When the engine torque is transmitted from the crankshaft to the sprocket member 13 through the timing chain, the driving rotor 10 rotates in accordance with the crankshaft. A rotation direction of the driving rotor 10 is a counterclockwise direction in FIGS. 2 and 3.

As shown in FIGS. 1 and 3, the driven rotor 20 is coaxially arranged in the sprocket member 13. The driven rotor 20 has a connection portion 21 on a bottom wall portion thereof. The connection portion 21 is coaxially coupled with the camshaft 2. This coupling enables the driven rotor 20 to rotate synchronously with the camshaft 2 and to rotate relatively with respect to the driving rotor 10. The rotational direction of the driven rotor 20 corresponds to the counterclockwise direction in FIGS. 2 and 3.

As shown in FIG. 1, the driven rotor 20 includes a second internal gear 22 on its radially inner peripheral wall. The second internal gear 22 defines an addendum circle located radially inside of a root circle. The second internal gear 22 has an inner diameter larger than an inner diameter of the first internal gear 14, and the number of teeth of the second internal gear 22 is greater than the number of teeth of the first internal gear 14. The second internal gear 22 is positioned away from the first internal gear 14 in its axial direction.

The assist member 30 is a torsion coil springs and is coaxially arranged inside of the sprocket member 13. One end 31 of the assist member 30 is engaged with the sprocket member 13, and the other end 32 is engaged with the connection portion 21. The assist member 30 generates assist torque between the driving rotor 10 and the driven rotor 20 so that the driven rotor 20 is biased in a retard direction relative to the driving rotor 10.

The cylindrical planetary carrier 40 has a torque-receiving portion 41 to which the braking torque is transmitted from the brake rotor 130. The torque-receiving portion 41 which is coaxial to the shaft portion 131 includes a pair of grooves 42 with which a joint 43 is engaged. Through the joint 43, the torque-receiving portion 41 is connected to the shaft portion 131. The planetary carrier 40 rotates along with the brake rotor 130 and performs a relative rotation with respect to the driving rotor 10. It should be noted that the planetary carrier 40 and the brake rotor 130 rotate in counterclockwise direction in FIGS. 2 and 3.

As shown in FIGS. 1 to 3, the planetary carrier 40 has a supporting portion 46 which supports the planetary gear 50. The supporting portion 46 is arranged eccentrically with respect to the shaft portion 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 first external gear 52 and a second external gear 54. The first external gear 52 engages with the first internal gear 14. The second external gear 54 engages with the second internal gear 22. The second external gear 54 has an outer diameter larger than that of the first external gear 52. The number of gear teeth of the second external gear 54 and the first external gear 52 is smaller than the number of teeth of the internal gears 22, 14 by the same number of gear teeth.

The above phase adjusting mechanism 300 adjusts the engine-phase according to a balance between the braking torque of the brake rotor 130, the assist torque of the assist member 30 and the variable torque transmitted from the camshaft 2 to the brake rotor 130.

Specifically, when the brake rotor 130 rotates at the same speed as the driving rotor 10, the planetary carrier 40 does not perform a relative rotation with respect to the driving rotor 10. Thus, the planetary gear 50 rotates along with the rotors 10, 20 without performing the planetary motion, so that the engine-phase is maintained.

Meanwhile, when the brake rotor 130 rotates at a lower speed than the driving rotor 10 against the assist torque, the planetary carrier 40 rotates in a retard direction relative to the driving rotor 10. As the result, the planetary gear 50 performs the planetary motion and the driven rotor 20 relatively rotates in the advance direction with respect to the driving rotor 10, so that the engine-phase is advanced.

Meanwhile, when the brake rotor 130 rotates at faster speed than the driving rotor 10, the planetary carrier 40 rotates in the advance direction relative to the driving rotor 10. As the result, the planetary gear 50 performs the planetary motion and the driven gear 20 rotates in the retard direction relative to the driving rotor 10, so that the engine-phase is retarded.

(Control Flow)

Referring to FIG. 8, a control flow which the current control circuit 200 executes will be described hereinafter.

In step S100, the computer determines whether a pre-starting condition “Cs” is established with respect to the engine which is stopped. The pre-starting condition “Cs” includes any event which occurs prior to a starting of the engine.

When the answer is YES in step S100, the procedure proceeds to step S101 in which the computer determines whether an interior of the case 110 is in a low-temperature condition “Sl” in which the temperature of the magnetic viscosity fluid 140 is lower than the lower limit temperature “Tl”.

When the answer is YES in step S101, the procedure proceeds to step S102 in which the coil 150 is energized for the period “α”. Consequently, the coil 150 receives electricity of low frequency “fα”, which generates the high electric power “Wα”. The effective heating of the magnetic viscosity fluid 140 is started.

In step S103, the computer determines whether an engine start command “Os”, such as turning on of an ignition switch, is detected. When the answer is YES in step S103, the procedure proceeds to step S104 in which a cranking of the engine is started and the coil is deenergized. Thus, until the engine is started, the magnetic viscosity fluid 140 has been effectively heated.

In step S105, the coil 150 is started to be energized for the period “β”. Consequently, the coil 150 receives electricity of high frequency “fβ”, which generates the low electric power “Wβ”. In a condition where the magnetic viscosity fluid 140 is agitated and is less heated, the braking torque is generated to adjust the engine-phase.

In step S106, the computer determines whether a complete combustion condition “Ss” of the engine is detected. When the answer is YES in step S106, the present control flow is terminated. Thus, when the engine is started, the magnetic viscosity fluid 140 stably generates the braking torque, so that the stable engine-phase adjustment is achieved.

When the answer is NO in step S101, the procedure proceeds to step S107 in which the computer determines whether the engine start command “Os” is detected. When the answer is YES is step S107, the procedure proceeds to steps S105 and 8106 in which the coil 150 is energized for the period “β”.

According to the above embodiment, even if the magnetic viscosity fluid 140 is in the low-temperature condition “Sl”, the magnetic viscosity fluid 140 is surely heated when it is estimated that the engine will be started. As the result, the viscosity of the magnetic viscosity fluid 140 depends on the applied magnetic field. When the engine is started, the viscosity of the magnetic viscosity fluid 140 less depends on its temperature, so that desired braking torque can be stably inputted into the brake rotor 130. Therefore, since the phase adjusting mechanism 300 connected to the brake rotor 130 optimizes the engine-phase for starting the engine, high reliability of the valve timing controller 1 can be ensured.

In the above first embodiment, the coil 150 and the current control circuit 200 correspond to a viscosity control means of the present invention. Also, the coil 150 and the current circuit 200 correspond to a heating control means of the present invention.

Second Embodiment

As shown in FIGS. 9A and 9B, the second embodiment is a modification of the first embodiment. In an energization control step during the period “α”, which corresponds to step S102 in FIG. 8, alternate electric current having low frequency “fα” is applied to the coil 150 as shown in FIG. 9A. The effective electric power in a specified period “RT” is high effective electric power “Wα”. As the result, as shown in FIG. 9B, the magnetic flux density “B” which varies at low frequency “fα” is applied to the magnetic viscosity fluid 140. The magnetic viscosity fluid 140 generates heat due to the movement of the magnetic particles and receives heat from the coil 150 which generates heat according to the high electric power “Wα”.

During the period “β”, alternate electric current having high frequency “fβ” is applied to the coil 150. The effective electric power in a specified period “RT” is low effective electric power “Wβ”. As the result, the magnetic viscosity fluid less generates heat during the period “β”.

Thus, also in the second embodiment, even if the magnetic viscosity fluid 140 is in the low-temperature condition “Sl”, the magnetic viscosity fluid 140 is surely heated when it is estimated that the engine will be started. When the engine is started, the viscosity of the magnetic viscosity fluid 140 depends on the applied magnetic field. The variation in viscosity becomes stable. Thus, the desired braking torque can be stably inputted into the brake rotor 130. The engine phase which the phase adjusting mechanism 300 adjusts is optimized. A high reliability of the valve timing controller 1 can be ensured.

Third Embodiment

As shown in FIG. 10, a third embodiment is a modification of the first embodiment, During the period “α”, a constant electric current “Iα” is applied to the coil 150, The effective electric power in a specified period “RT” is high effective electric power “Wα”. As the result, as shown in FIG. 10B, the magnetic flux density “B” which is constant is applied to the magnetic viscosity fluid 140. The magnetic viscosity fluid 140 generates heat due to the movement of the magnetic particles and receives heat from the coil 150 which generates heat according to the high electric power “Wα”.

During the period “β”, a constant electric current “Iβ” is applied to the coil 150. The effective electric power in a specified period “RT” is low effective electric power “Wβ”. Thus, the magnetic viscosity fluid 140 less generates heat during the period “β”.

Thus, also in the third embodiment, even if the magnetic viscosity fluid 140 is in the low-temperature condition “Sl”, the magnetic viscosity fluid 140 is surely heated when it is estimated that the engine will be started. When the engine is started, the viscosity of the magnetic viscosity fluid 140 depends on the applied magnetic field. The variation in viscosity becomes stable. Thus, the desired braking torque can be stably inputted into the brake rotor 130. The engine-phase which the phase adjusting mechanism 300 adjusts is optimized. A high reliability of the valve timing controller 1 can be ensured.

Fourth Embodiment

As shown in FIG. 11, a fourth embodiment is a modification of the first embodiment. In a control flow of the fourth embodiment, step S400 and step S401 are included.

Specifically, in step S400, the computer determines whether a temperature of the magnetic viscosity fluid is in a normal-temperature condition “Sn” in which the temperature of the magnetic viscosity fluid 140 is greater than the lower limit temperature “Tl”.

Until the normal-temperature condition “Sn” is detected, the processes in steps S103 and S400 are repeatedly performed, so that the magnetic viscosity fluid 140 effectively generates heat. Meanwhile, when the answer is YES in step S400, the procedure proceeds to step S401 in which the energization in the period “α” is terminated with the engine stopped. Then, the procedure proceeds to step S107 in which the computer determines whether the engine start command “Os” is generated. It should be noted that the specified time “ST” of the current control circuit 200 is suitably varied to avoid a situation where the temperature of the magnetic viscosity fluid 140 becomes lower than the lower-limit temperature “Tl”.

According to the fourth embodiment, from the time when it is estimated that the engine will be started until the time when the temperature of the magnetic viscosity fluid exceeds “Tl”, the magnetic viscosity fluid generates heat therein. Thus, when the engine is started, the viscosity of the magnetic viscosity fluid depends on the applied magnetic field.

Fifth Embodiment

As shown in FIG. 12, a fifth embodiment is a modification of the fourth embodiment. In a control flow of the fifth embodiment, step S500 is included instead of step S400.

Specifically, in step S500, the computer determines whether a specified heat-generating period “HT” has elapsed. It should be noted that the specified heat-generating period “HT” is required for the magnetic viscosity fluid 140 to be brought in the normal-temperature condition “Sn”. The heat-generating period “HT” is previously determined based on the low-frequency “fα” and the high effective electric power “Wα”.

Until the heat-generating period “HT” has elapsed, the processes in steps S103 and S500 are repeatedly performed, so that the magnetic viscosity fluid 140 effectively generates heat. Meanwhile, when the answer is YES in step S500, the procedure proceeds to step S401 in which the energization in the period “α” is terminated with the engine stopped. Then, the procedure proceeds to step S107 in which the computer determines whether the engine start command “Os” is generated.

According to the fifth embodiment, from the time when it is estimated that the engine will be started until the heat-generating period “HT” has passed, the magnetic viscosity fluid generates heat therein. Thus, when the engine is started, the viscosity of the magnetic viscosity fluid depends on the applied magnetic field.

Sixth Embodiment

As shown in FIG. 13, a sixth embodiment is a modification of the first embodiment. An actuator 600 includes the coil 150 and a second coil 650 for generating heat in the magnetic viscosity fluid 140.

Specifically, the second coil 150 is winded around a resin bobbin 651 coaxially to the cover member 112. When the second coil 650 is energized, magnetic field is generated in such a manner that magnetic flux passes through the cover member 112, the second magnetic gap 114b, the rotor portion 132, the first magnetic gap 114a and the fixed member 111. The generated magnetic field is applied to the magnetic viscosity fluid 140 in the magnetic gaps 114a, 114b.

The cover member 112 is exposed to the second magnetic gap 114b. Thus, if the second coil 650 generates heat when energized, the heat is transferred to the magnetic viscosity fluid 140 in the second magnetic gap 114b through the resin bobbin 651 and the cover member 112. In the present embodiment, the cover member 112 is comprised of two bodies 612a, 612b made from magnetic material.

The coil 150 and the second coil 650 are electrically connected to a current control circuit 620. The current control circuit 620 has the same configuration and function as the current control circuit 200 in the first embodiment. Further, the current control circuit 620 can control the energization of the second coil 650 independently from the coil 150.

In a control flow of the sixth embodiment, step S600 is included instead of step S102, as shown in FIG. 14. In step S600, the second coil 650 is energized during the period “α”. Consequently, the second coil 650 receives electricity of low frequency “fα”, which generates the high electric power “Wα”. The effective heating of the magnetic viscosity fluid 140 is started in a similar way of the first embodiment. Until the engine start command “Os” is generated, the magnetic viscosity fluid 140 effectively generates the heat therein.

Thus, also in the sixth embodiment, even if the magnetic viscosity fluid 140 is the glass transition condition, the second coil 650 is energized when it is estimated that the engine will be started, so that the magnetic viscosity fluid 140 surely generates heat therein. When the engine is started, the second coil 650 is surely deenergized. Thus, in step S105, the magnetic viscosity fluid 140 less receives thermal influence. As above, the heat-generation control and the viscosity control of the magnetic viscosity fluid 140 can be suitably executed.

In the above sixth embodiment, the coil 150 and the current control circuit 620 correspond to a viscosity control means of the present invention. Also, the second coil 650 and the current control circuit 620 correspond to a heating control means of the present invention.

Seventh Embodiment

As shown in FIG. 15, a seventh embodiment is a modification of the sixth embodiment. In a control flow of the seventh embodiment, step S700 to step S703 are included.

Specifically, in step S700, the cranking of the engine is started and the energization control of during the period “α” is continued even in the period “β”. Then, the procedure proceeds to step S105.

In step S701, the computer determines whether the engine-phase is changed after performing step S105. A variation in the engine-phase is computed based on output signals from a crank angle sensor (not shown) and a camshaft sensor (not shown). When this variation exceeds the specified quantity “Δθ”, the computer determines that the engine-phase is changed. When the variation in the engine-phase is detected in step S701, the procedure proceeds to step S702 in which the second coil 650 is deenergized. Then, the procedure proceeds to step S106. Thus, until the engine-phase is varied, the magnetic viscosity fluid 140 effectively generates heat therein.

When the engine start command “Os” is detected in step S107, the procedure proceeds to step S703 and step 106. The coil 150 is energized during the period “β”.

According to the seventh embodiment, from the time when it is estimated that the engine will be started until the engine-phase is completely changed, the magnetic viscosity fluid generates heat therein. Thus, when the engine is started, the viscosity of the magnetic viscosity fluid depends on the applied magnetic field.

Other Embodiment

The present invention should not be limited to the disclosure embodiment, but may be implemented in other ways without departing from the sprit of the invention.

Specifically, in the first, second, forth to seventh embodiments, during the period “β”, the effective electric power may be set greater than or equal to the electric power “Wα” while the frequency is changed from “fα” to “fβ”. Also, in the third embodiment, during the period “β”, the effective electric power may be set greater than or equal to the electric power “Wα”.

In the first, second and fourth to seventh embodiments, during the period “α” and the period “β”, the frequency “fα”, “fβ” may be varied directly or indirectly. In the first second and fourth to seventh embodiments, during the period “α” and the period “β”, the frequency of the electric current “I” can be set smaller than or equal to the frequency “fα” while the effective electric power is changed from “Wα” to “Wβ”. In the sixth and seventh embodiments, it may be configured that the magnetic field generated by the second coil 650 is less applied to the magnetic viscosity fluid. In such a case, the frequency of the electric current “I” supplied to the second coil 650 is not necessary to be controlled.

In the control flow of the second, third, sixth, and seventh embodiments, between step S102 and S103 or between step S600 and S103, the processes of steps S400 and S401 in the fourth embodiment may be added. When the normal-temperature condition “Sn” is detected in step S400, the procedure proceeds to step S401 and then proceeds to step S107. Also, in the control flow of the second, third, sixth, and seventh embodiments, between step S102 and S103 or between step S600 and S103, the processes of steps S500 and S401 in the fifth (fourth) embodiment may be added. When it is determined that the heating period “HT” has elapsed in step S500, the procedure proceeds to step S401 and then proceeds to step S107. Furthermore, in the control flow of the sixth and seventh embodiments, the energization control in step S102 of the second embodiment or the third embodiment can be executed in step S600 with respect to the coil 650.

The configuration of the phase adjusting mechanism 300 is suitably variable.

In the first to seventh embodiments, the directions of “advance” and “retard” can be changed therebetween. The present invention is applicable also to a controller which adjusts the valve timing of the exhaust valve, and a controller which adjusts the valve timings of the intake valve and the exhaust valve.

Claims

1. A valve timing controller which adjusts a valve timing of a valve opened/closed by a torque transmitted from a crankshaft to a camshaft of an internal combustion engine, the valve timing controller comprising:

a case defining a fluid chamber therein;

a magnetic viscosity fluid enclosed in the fluid chamber, the magnetic viscosity fluid including magnetic particles, the magnetic viscosity fluid having a viscosity which varies according to a magnetic field applied thereto;

a viscosity control means for variably controlling a viscosity of the magnetic viscosity fluid by applying a magnetic field to the magnetic viscosity fluid;

a brake rotor rotatably accommodated in the fluid chamber and receiving a brake torque from the magnetic viscosity fluid according to the viscosity thereof;

a phase adjusting mechanism connected to the brake rotor for adjusting a relative rotational phase between the crankshaft and the camshaft of the internal combustion engine according to the brake torque which is inputted into the brake rotor; and

a heating control means for generating a heat in the magnetic viscosity fluid when it is estimated that the internal combustion engine will be started.

2. A valve timing controller according to claim 1, wherein

the heating control means starts a heating of the magnetic viscosity fluid to generate heat therein when it is estimated that the internal combustion engine will be started and it is detected that a temperature of the magnetic viscosity fluid is lower than a lower-limit temperature which is required to vary the relative rotational phase.

3. A valve timing controller according to claim 1, wherein

the heating control means includes a coil disposed in the case, and

when the coil is energized, a magnetic field of which intensity is variable is applied to the magnetic viscosity fluid, whereby the magnetic viscosity fluid generates the heat therein.

4. A valve timing controller according to claim 1, wherein

the heating control means includes a coil disposed in the case, and when the coil is energized, the coil generates heat which is transmitted to the magnetic viscosity fluid, whereby the magnetic viscosity fluid is heated.

5. A valve timing controller according to claim 3, wherein

the heating control means energizes the coil to generate a magnetic field which is applied to the magnetic viscosity fluid, whereby the viscosity of the magnetic viscosity fluid is variably controlled.

6. A valve timing controller according to claim 5, wherein

the heating control means sets a first variable frequency of the magnetic field when it is estimated that the engine will be started, and

the heating control means sets a second variable frequency of the magnetic field which is higher than the first variable frequency when the engine is started.

7. A valve timing controller according to claim 5, wherein

the heating control means sets a first electric power supplied to the coil when it is estimated that the engine will be started, and

the heating control means sets a second electric power supplied to the coil, which is lower than the first electric power, when the engine is started.

8. A valve timing controller according to claim 3, wherein

the heating control means further includes a second coil, and

the viscosity control means energizes the second coil to generate a magnetic field which is applied to the magnetic viscosity fluid, whereby the viscosity of the magnetic viscosity fluid is variably controlled.

9. A valve timing controller according to claim 8, wherein

the viscosity control means controls the viscosity of the magnetic viscosity fluid in order to vary the relative rotational phase when the engine is started, and

the heating control means terminates heating of the magnetic viscosity fluid when a variation in the relative rotational phase is detected.

10. A valve timing controller according to claim 1, wherein

the heating control means terminates heating of the magnetic viscosity fluid when it is detected that a temperature of the magnetic viscosity fluid exceeds a lower-limit temperature which is required to vary the relative rotational phase.

11. A valve timing controller according to claim 1, wherein

the heating control means terminates heating of the magnetic viscosity fluid when a specified heating period has elapsed, which is required to increase the temperature of the magnetic viscosity fluid higher than a lower-limit temperature which is required to vary the relative rotational phase.

12. A valve timing controller according to claim 1, wherein

the heating control means terminates heating of the magnetic viscosity fluid when the internal combustion engine is started.