Valve timing adjustment system

Abstract

To suppress an actual phase of a relative rotation phase between a housing and a vane rotor from overshooting a target phase after a release of a phase lock mechanism while facilitating the release of the phase lock mechanism even if a working fluid is high in viscosity.SOLUTION: A valve timing adjustment system comprises a valve timing adjustment device (1), a phase lock mechanism (2), a hydraulic pressure control valve (3), an electromagnetic drive part (4) and an electronic control device (5). The electronic control device executes feedback control for adjusting a target current of a current applied to the electromagnetic drive part on the basis of an actual phase and a target phase of a relative rotation phase, also, when holding the relative rotation phase, controls the current applied to the electromagnetic drive part to a holding current, and when releasing a lock pin (50) from a fitting recess (51), executes gradual change control for gradually increasing a current from a current which is smaller than a current which is applied by initial control, and is larger than zero after executing the initial control for applying the target current larger than the holding current to the electromagnetic drive part for a prescribed time.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a valve timing adjusting system that adjusts the opening and closing timing of a valve of an internal combustion engine. [Background technology]

[0002] For example, there is a valve timing adjustment system including a valve timing adjustment device, a phase lock mechanism, a fluid pressure control device, and an electronic control device (see Patent Document 1). The valve timing adjustment device has a housing that rotates together with the drive shaft of the internal combustion engine, and a vane rotor that divides a hydraulic chamber formed inside the housing into an advance hydraulic chamber and a retard hydraulic chamber and rotates together with a driven shaft that drives the valve. The phase lock mechanism is configured such that a lock pin that is reciprocally provided in an accommodation hole formed in the vane rotor fits into a fitting recess formed in the housing, thereby locking the relative rotation between the vane rotor and the housing. The fluid pressure control device includes a hydraulic control valve having a spool and a sleeve, and an electromagnetic drive unit that moves the spool in the axial direction, and supplies hydraulic pressure of hydraulic oil to the hydraulic chamber of the valve timing adjustment device.

[0003] The electronic control device controls the current applied to the electromagnetic drive unit by PWM control with a duty ratio. When releasing the phase lock mechanism, the electronic control device performs an initial control in which a current is applied to the electromagnetic drive unit with a duty ratio of 100% for a predetermined time to move the spool from the initial position, and then performs a gradual control in which a current is applied to the electromagnetic drive unit while gradually increasing the current from a current smaller than the current applied in the initial control and larger than 0, to cause the lock pin to come out of the fitting recess. According to Patent Document 1, the initial control instantaneously applies a large load to the spool from the electromagnetic drive unit, so that even if the hydraulic oil has a high viscosity, the spool can be reliably moved from the initial position and the spool can be changed to a state in which it is easy to slide. Therefore, according to Patent Document 1, the gradual control following the initial control can gradually move the spool to follow the increase in the amount of current applied, and the phase lock mechanism can be reliably released. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2023-20247 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the valve timing adjustment system described in Patent Document 1, the advance hydraulic chamber communicates with a release hydraulic chamber that applies hydraulic pressure to cause the lock pin to come out of the fitting recess. When the phase lock mechanism is released, a current is applied to the electromagnetic drive unit with a duty ratio of 100% in the initial control. For this reason, when the initial control is executed, the hydraulic pressure in the release hydraulic chamber and the advance hydraulic chamber may become excessively high. Therefore, after the lock pin comes out of the fitting recess, the rate of change of the relative rotation phase between the housing and the vane rotor may become excessively high, and the actual phase of the relative rotation phase between the housing and the vane rotor may overshoot the target phase.

[0006] The present invention has been made to solve the above-mentioned problems, and its main object is to make it easier to release a phase lock mechanism in a valve timing adjustment system even when the hydraulic oil is highly viscous, while suppressing the actual phase of the relative rotational phase between the housing and the vane rotor from overshooting the target phase after the phase lock mechanism is released. [Means for solving the problem]

[0007] The first means for solving the above problem is A valve timing adjustment system is provided in a torque transmission system in which torque is transmitted from a drive shaft (7) of an internal combustion engine (6) to a driven shaft (8, 9), and the valve timing adjustment system adjusts opening and closing timing of an intake valve (14) or an exhaust valve (15) that is driven to open and close by rotation of the driven shaft, a valve timing adjusting device (1) including a housing (20) that rotates together with the drive shaft, and a vane rotor (30) that divides a hydraulic chamber formed inside the housing into an advance hydraulic chamber (40) and a retard hydraulic chamber (41) and rotates together with the driven shaft, wherein a relative rotational phase between the housing and the vane rotor is controlled by hydraulic pressure supplied to the advance hydraulic chamber and the retard hydraulic chamber; a phase lock mechanism (2) including: a lock pin (50) reciprocably provided in an accommodation hole (39) formed in the vane rotor; a fitting recess (51) formed in the housing such that a tip of the lock pin can fit therein when the vane rotor and the housing are in a predetermined phase; and a release hydraulic chamber (52) communicating with at least one of the advance hydraulic chamber and the retard hydraulic chamber and applying hydraulic pressure to the lock pin in a direction in which the lock pin comes out of the fitting recess; a sleeve (70) having a plurality of ports (710, 720) communicating with the advance hydraulic chamber and the retard hydraulic chamber via oil passages (37, 38), respectively, and a spool (90) provided reciprocally inside the sleeve and capable of adjusting the opening area of ​​the plurality of ports by changing the axial position thereof, the hydraulic control valve (3) controlling the hydraulic pressure and the supply amount of working oil to the advance hydraulic chamber and the retard hydraulic chamber; an electromagnetic drive unit (4) that is driven in response to an applied amount of current to apply a load to the spool and change the axial position of the spool; and an electronic control device (5) for controlling a current applied to the electromagnetic drive unit, The electronic control device executes feedback control to adjust a target current of the current applied to the electromagnetic drive unit based on the actual phase and the target phase of the relative rotation phase in order to control the relative rotation phase to a target phase, and when maintaining the relative rotation phase, controls the current applied to the electromagnetic drive unit to a holding current. When removing the lock pin from a state in which the tip of the lock pin is fitted into the fitting recess, the electronic control device executes initial control to move the spool from an initial position by applying the target current larger than the holding current to the electromagnetic drive unit for a predetermined time, and then executes gradual-change control to remove the lock pin from the fitting recess by applying a current to the electromagnetic drive unit while gradually increasing the current from a current that is smaller than the current applied in the initial control and larger than zero.

[0008] According to the above configuration, the electronic control device executes feedback control to adjust a target current of the current applied to the electromagnetic drive unit based on the actual phase of the relative rotation phase and the target phase in order to control the relative rotation phase to the target phase. Therefore, when controlling the relative rotation phase to the target phase, the axial position of the spool is changed according to the target current, and the hydraulic pressure and the supply amount of hydraulic oil to the advance hydraulic chamber and the retard hydraulic chamber are controlled by the change in the axial position of the spool. Then, when the relative rotation phase is held, the current applied to the electromagnetic drive unit is controlled to a holding current.

[0009] Here, in the phase lock mechanism, the release hydraulic chamber is connected to at least one of the advance hydraulic chamber and the retard hydraulic chamber. Therefore, when hydraulic pressure is applied to the release hydraulic chamber, hydraulic pressure is also applied to, for example, the advance hydraulic chamber connected to the release hydraulic chamber. Therefore, if an excessively high hydraulic pressure is applied to the release hydraulic chamber when the lock pin is removed from the fitting recess, the hydraulic pressure in the advance chamber becomes excessively higher than the hydraulic pressure corresponding to the target current. As a result, after the lock pin is removed from the fitting recess, the rate of change of the relative rotation phase becomes excessively high, and there is a risk that the actual phase of the relative rotation phase overshoots the target phase.

[0010] In this regard, when the electronic control device causes the lock pin to come out of the fitting recess from a state in which the tip of the lock pin is fitted in the fitting recess, the electronic control device executes an initial control in which the target current larger than the holding current is applied to the electromagnetic drive unit for a predetermined time to move the spool from the initial position. Therefore, by the initial control, a load corresponding to a target current larger than the holding current is instantaneously applied from the electromagnetic drive unit to the spool, even if the hydraulic oil has a high viscosity, the spool can be moved from the initial position and the spool can be changed to a state in which it is easy to slide. Then, by the gradual change control following the initial control, the spool can be gradually moved so as to follow an increase in the amount of current applied, making it easier to release the phase lock mechanism. Moreover, in the initial control, a target current for controlling the relative rotation phase to the target phase is applied to the electromagnetic drive unit, so that it is possible to suppress the actual phase of the relative rotation phase from overshooting the target phase after the lock pin comes out of the fitting recess.

[0011] Furthermore, in the gradual change control, the current is not increased from 0 but is gradually increased from a current greater than 0, thereby eliminating the region where hydraulic pressure is abruptly supplied to either the advance hydraulic chamber or the retard hydraulic chamber, i.e., the region not required for releasing the phase lock mechanism. This prevents the tip of the lock pin from getting caught on the inner wall of the fitting recess, and shortens the time required to release the phase lock mechanism. Therefore, this valve timing control system can unlock the valve timing control device from the phase locked state in a short time, even when the viscosity of the hydraulic oil is high, for example, and can improve start-up performance.

[0012] In a second aspect, the electronic control device adjusts the target current within a range of 60 to 80% of the maximum current that can be applied to the electromagnetic drive unit. With this configuration, in feedback control, when adjusting the target current of the current to be applied to the electromagnetic drive unit based on the actual phase of the relative rotation phase and the target phase, the target current is adjusted within a range of 60 to 80% of the maximum current that can be applied to the electromagnetic drive unit. Therefore, in initial control, when the target current larger than the holding current is applied to the electromagnetic drive unit for a predetermined time, the target current can be set to an appropriate magnitude.

[0013] In the third aspect, the electronic control device controls the current applied to the electromagnetic drive unit by PWM control, and adjusts the target current by the PWM control within a duty ratio range of 30 to 50%. With this configuration, when adjusting the target current of the current applied to the electromagnetic drive unit based on the actual phase of the relative rotation phase and the target phase in the feedback control, the target current is adjusted by the PWM control within a duty ratio range of 30 to 50%. Therefore, when applying the target current larger than the holding current to the electromagnetic drive unit for a predetermined time in the initial control, the target current can be set to an appropriate magnitude.

[0014] In a fourth aspect, when the lock pin is caused to come out of the fitting recess from a state in which the tip of the lock pin is fitted in the fitting recess, the electronic control device calculates the target current to be applied to the electromagnetic drive unit in the initial motion control based on the actual phase of the relative rotation phase and the target phase expected after the lock pin is made to come out of the fitting recess. With this configuration, the target current when controlling the relative rotation phase to the target phase, i.e., the target current to be applied to the electromagnetic drive unit in the initial motion control, can be calculated in advance when the tip of the lock pin is fitted in the fitting recess. [Brief description of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of a valve timing adjustment system according to a first embodiment. [Diagram 2] 1 is a schematic configuration diagram of an internal combustion engine in which a valve timing control system according to a first embodiment is used. [Diagram 3] FIG. 2 is a cross-sectional view taken along line III-III in FIG. [Figure 4] 4 is a cross-sectional view of a phase lock mechanism provided in the valve timing adjusting device. FIG. [Diagram 5] FIG. 2 is a cross-sectional view showing a state in which a spool is in a zero stroke state in the hydraulic control valve. [Figure 6] FIG. 4 is a cross-sectional view of an inner sleeve of the hydraulic control valve. [Figure 7] FIG. 2 is a cross-sectional view showing a state in which a spool is in a full stroke state in the hydraulic control valve. [Figure 8] FIG. 4 is a cross-sectional view showing a state in which a spool is in a holding stroke in the hydraulic control valve. [Figure 9] FIG. 4 is a cross-sectional view showing a state in which a spool is in a holding stroke in the hydraulic control valve. [Figure 10] 1 is a graph showing the relationship between the stroke of a spool or the current value and the opening area of ​​each port or the supply / discharge flow rate of hydraulic oil in a hydraulic control valve. [Figure 11] 1 is a graph showing current supply control when phase lock is released in the conventional technology. [Figure 12] 11 is a graph showing energization control when the phase lock is released in the comparative example. [Figure 13] 11 is a graph showing current supply control when the phase lock is released. [Figure 14] 10 is a flowchart illustrating a control process when a phase lock is released in the second embodiment. [Figure 15] 13 is a graph showing current supply control when the phase lock is released in the second embodiment when the viscosity of the hydraulic oil is lower than a threshold value. [Figure 16] 13 is a flowchart illustrating a control process when a phase lock is released in the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, each embodiment will be described with reference to the drawings. In the following embodiments, the same reference numerals are used to designate the same or equivalent parts, and the description thereof is incorporated herein by reference.

[0017] (First embodiment) DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment will be described with reference to the drawings. A valve timing control system according to the present embodiment is a system that is mounted on a vehicle and adjusts the opening and closing timing of an intake valve or an exhaust valve of an internal combustion engine.

[0018] 1, the valve timing control system includes a valve timing control device 1, a phase lock mechanism 2, a hydraulic control valve 3, an electromagnetic drive unit 4, and an electronic control unit 5. First, each component of the valve timing control system will be described, and then the energization control executed by the electronic control unit 5 will be described.

[0019] <Configuration of valve timing control device 1> As shown in FIG. 2, the valve timing controller 1 is provided in a torque transmission system in which torque is transmitted from a crankshaft 7, which serves as a drive shaft of an internal combustion engine 6, to two camshafts 8 and 9, which serve as driven shafts. In the torque transmission system, a chain 13 is wound around a gear 10 fixed to the crankshaft 7 and two gears 11 and 12 fixed to the camshafts 8 and 9, respectively, to transmit torque from the crankshaft 7 to the two camshafts 8 and 9. One camshaft 8 drives an intake valve 14 to open and close, and the other camshaft 9 drives an exhaust valve 15 to open and close. An arrow R in FIG. 2 indicates the direction of rotation of the chain 13 and the like. The torque transmission system is not limited to a configuration using the chain 13 as shown in FIG. 2, and may be a configuration using a belt.

[0020] In this embodiment, a valve timing adjusting device 1 is provided at the end of a camshaft 8 that drives the intake valve 14 to open and close, and adjusts the opening and closing timing of the intake valve 14. In the following description, for convenience, the camshaft 8 side of the valve timing adjusting device 1 will be referred to as the "rear side" and the opposite side will be referred to as the "front side."

[0021] 1 and 3, the valve timing adjusting device 1 includes a housing 20 and a vane rotor 30. The valve timing adjusting device 1 includes a phase lock mechanism 2 and a hydraulic control valve 3. Note that the hydraulic control valve 3 is omitted in FIG. 3.

[0022] The housing 20 of the valve timing adjusting device 1 of this embodiment is configured by connecting a shoe housing 21 and a rear plate 22 with bolts 23. The shoe housing 21 is formed integrally with an annular peripheral wall 24, a plurality of shoes 25 extending radially inward from the peripheral wall 24, and a front plate 26. A plurality of hydraulic chambers partitioned by the plurality of shoes 25 are formed inside the housing 20. The front plate 26 has a hole 27 in the center thereof for inserting the hydraulic control valve 3. Meanwhile, the rear plate 22 has a hole 28 for passing the camshaft 8. A gear 11 is provided on the outer periphery of the rear plate 22. The chain 13 shown in FIG. 2 is connected to the gear 11. As a result, the housing 20 rotates together with the crankshaft 7 as the drive shaft of the internal combustion engine 6.

[0023] The vane rotor 30 is formed integrally with a cylindrical rotor 31 and a plurality of vanes 32 extending radially outward from the rotor 31. The vane rotor 30 is provided inside the housing 20 so as to be rotatable relative to the housing 20 within a predetermined angular range. A camshaft 8 is fixed to an axial end of the vane rotor 30. The vane rotor 30 and the camshaft 8 are positioned in the circumferential direction by a knock pin 33, and the relative rotation is restricted. Furthermore, the vane rotor 30 and the camshaft 8 are fixed by an outer sleeve 71 of the hydraulic control valve 3. Specifically, the outer sleeve 71 is inserted into a central hole 34 that penetrates the vane rotor 30 in the axial direction at the rotation center of the vane rotor 30. A male thread 72 provided on the outer wall of the outer sleeve 71 is screwed into a female thread 16 provided on the camshaft 8, and a flange 73 provided on the outer wall of the outer sleeve 71 abuts against the vane rotor 30. As a result, the vane rotor 30 and the camshaft 8 are fixed by the outer sleeve 71, and the vane rotor 30 rotates together with the camshaft 8 which serves as a driven shaft of the internal combustion engine 6.

[0024] The vanes 32 of the vane rotor 30 divide a hydraulic chamber formed inside the housing 20 into an advance hydraulic chamber 40 and a retard hydraulic chamber 41. A seal member 35 provided on the radial outside of the vane 32 is in liquid-tight sliding contact with the peripheral wall 24 of the housing 20, and a seal member 36 provided on the radial outside of the rotor 31 is in liquid-tight sliding contact with the shoe 25 of the housing 20. This restricts leakage of hydraulic oil between the advance hydraulic chamber 40 and the retard hydraulic chamber 41.

[0025] The advance hydraulic chamber 40 communicates with the advance oil passage 37 provided in the vane rotor 30. Hydraulic oil is supplied to and discharged from the advance hydraulic chamber 40 via the advance oil passage 37. The retard hydraulic chamber 41 communicates with the retard oil passage 38 provided in the vane rotor 30. Hydraulic oil is supplied to and discharged from the retard hydraulic chamber 41 via the retard oil passage 38.

[0026] When the hydraulic oil supplied to the advance hydraulic chamber 40 becomes higher than the hydraulic oil supplied to the retard hydraulic chamber 41, the vane rotor 30 rotates relative to the housing 20 toward the advance side. Conversely, when the hydraulic oil supplied to the retard hydraulic chamber 41 becomes higher than the hydraulic oil supplied to the advance hydraulic chamber 40, the vane rotor 30 rotates relative to the housing 20 toward the retard side. In general, advance means advancing the opening and closing timing of the intake valve 14 or the exhaust valve 15, and retard means delaying the opening and closing timing of the intake valve 14 or the exhaust valve 15. Arrow D in FIG. 3 indicates the advance direction and retard direction of the vane rotor 30 relative to the housing 20. That is, the valve timing control device 1 can adjust the hydraulic oil supplied to the advance hydraulic chamber 40 and the retard hydraulic chamber 41 to control the housing 20 and the vane rotor 30 to a target rotation phase (target phase) and adjust the opening and closing timing of the intake valve 14.

[0027] <Configuration of phase lock mechanism 2> Next, a description will be given of the configuration of the phase lock mechanism 2. As shown in Figures 1, 3 and 4, the phase lock mechanism 2 of this embodiment has a lock pin 50, a fitting recess 51, a release hydraulic chamber 52, and the like.

[0028] An accommodation hole 39 for accommodating a lock pin 50 is formed (provided) in one of the vanes 32 of the vane rotor 30. A cylindrical tubular member 53 is press-fitted and fixed inside the accommodation hole 39. The lock pin 50 is accommodated inside the tubular member 53 so as to be capable of reciprocating movement in the axial direction.

[0029] The lock pin 50 is formed in a cylindrical shape with a bottom, and has a bottom portion 54 and a cylindrical portion 55. A spring 56 is provided inside the lock pin 50. One end of the spring 56 is engaged with a spring receiver 57 provided on the inner wall of the accommodation hole 39 of the vane 32, and the other end of the spring 56 is engaged with the inner wall of the bottom portion 54 of the lock pin 50. The spring 56 is a compression coil spring, and biases the lock pin 50 toward the rear plate 22.

[0030] On the other hand, the fitting recess 51 is formed (provided) so as to be recessed rearward from the surface 29 of the rear plate 22 of the housing 20 on the hydraulic chamber side. A cylindrical ring member 58 is press-fitted and fixed to the inner wall of the fitting recess 51. The end of the lock pin 50 on the bottom 54 side can be fitted into the radially inner side of the ring member 58. The fitting recess 51 in this embodiment is provided at a position corresponding to the position of the lock pin 50 in a state in which the vane rotor 30 is phase-controlled to the most retarded position with respect to the housing 20. That is, in this embodiment, the fitting phase in which the lock pin 50 and the fitting recess 51 are fitted into each other is the most retarded phase. The fitting of the lock pin 50 and the fitting recess 51 enables the internal combustion engine 6 to start, and prevents the vane rotor 30 and the housing 20 from swinging due to the cam torque acting in the forward and reverse directions from the cam mechanism that drives the intake valve 14 when the hydraulic pressure is low, such as when the internal combustion engine 6 is started, and prevents the generation of a hitting sound.

[0031] A space facing the bottom 54 of the lock pin 50 inside the fitting recess 51 functions as a release hydraulic chamber 52. The release hydraulic chamber 52 is a hydraulic chamber for applying hydraulic pressure to the lock pin 50 in a direction in which the lock pin 50 comes out of the fitting recess 51. The release hydraulic chamber 52 of this embodiment communicates only with the advance hydraulic chamber 40 via an oil passage 59, and does not communicate with the retard hydraulic chamber 41. That is, the phase lock mechanism 2 of this embodiment employs a so-called "single pressure pin mechanism." Therefore, the lock pin 50 of this embodiment engages with the fitting recess 51 when the hydraulic pressure in the advance hydraulic chamber 40 becomes smaller than a pin release pressure Pa described later, with the vane rotor 30 phase-controlled to the most retarded position with respect to the housing 20. In this embodiment, the advance hydraulic chamber 40 connected to the release hydraulic chamber 52 is the hydraulic chamber that increases the hydraulic pressure when the vane rotor 30 and the housing 20 are rotated relative to each other toward the anti-engagement phase that is farthest from the engagement phase (in this embodiment, the most advance phase).

[0032] When the vane rotor 30 is phase-controlled relative to the housing 20 from the most retarded phase to the advanced phase, the phase control is executed after the lock pin 50 is removed from the fitting recess 51 (i.e., after the lock is released). At this time, when the force of the hydraulic pressure supplied to the release hydraulic chamber 52 acting on the axial surface of the lock pin 50 becomes greater than the biasing force of the spring 56 biasing the lock pin 50, the lock pin 50 can be removed from the fitting recess 51 (i.e., unlocked). Here, the relationship of the following formula 1 is satisfied, where Pa is the hydraulic pressure (i.e., the pin release pressure) at which the lock pin 50 can be released from the fitting recess 51, Aa is the area of ​​the surface of the lock pin 50 facing the release hydraulic chamber 52 projected onto an imaginary plane perpendicular to the axis of the lock pin 50, and Fs is the biasing force of the spring 56. Pa = Fs / Aa (Equation 1) That is, when the hydraulic pressure supplied to the release hydraulic chamber 52 becomes equal to or higher than the pin release pressure Pa, and the forces acting on the vane rotor 30 from the advance hydraulic chamber 40 and the retard hydraulic chamber 41 and the cam torque acting on the vane rotor 30 from the camshaft 8 are balanced, the lock pin 50 comes out of the fitting recess 51. Then, in a state where the lock pin 50 comes out of the fitting recess 51 (i.e., in a state where the phase lock mechanism 2 is released), it becomes possible to perform phase control to the advance side. However, if hydraulic pressure is suddenly supplied to the advance hydraulic chamber 40 before the lock pin 50 comes out of the fitting recess 51, a force as shown by the arrow F in FIG. 4 may act on the vane rotor 30. In that case, as shown by the star symbol C in FIG. 4, if the tip of the lock pin 50 gets caught on the inner wall of the fitting recess 51 (specifically, the inner wall of the ring member 58), there is a concern that the phase lock mechanism 2 may not be released. A solution to this problem will be explained later in the section on power supply control by the electronic control device 5.

[0033] <Configuration of hydraulic control valve 3> Next, the configuration of the hydraulic control valve 3 will be described. As shown in Fig. 1, the hydraulic control valve 3 is provided in a central hole 34 that penetrates the rotation center of the vane rotor 30 in the axial direction. The hydraulic control valve 3 has a function of supplying hydraulic oil pumped up from an oil pan 60 by a hydraulic pump 61 to an advance hydraulic chamber 40 and a retard hydraulic chamber 41 (hereinafter referred to as "both hydraulic chambers 40, 41"), and discharging the hydraulic oil discharged from both hydraulic chambers 40, 41 to the outside of the valve timing adjusting device 1.

[0034] 1 and 5, the hydraulic control valve 3 has an outer sleeve 71, an inner sleeve 80, a spool 90, etc. In the following description, the outer sleeve 71 and the inner sleeve 80 may be collectively referred to as "sleeve 70."

[0035] As described above, the outer sleeve 71 fixes the vane rotor 30 and the camshaft 8. Therefore, the outer sleeve 71, the vane rotor 30, and the camshaft 8 are fixed so as not to rotate relative to each other.

[0036] The outer sleeve 71 is formed in a cylindrical shape and has, in order from the front side, an outer retard port 74 and an outer advance port 75. In addition, an annular stopper ring 76 is fixed to an opening on the front side of the outer sleeve 71. On the other hand, an opening 77 on the rear side of the outer sleeve 71 communicates with the hydraulic oil chamber 62 provided in the camshaft 8.

[0037] The inner sleeve 80 is fixed to the inside of the outer sleeve 71. The radially outer outer wall surface of the inner sleeve 80 abuts against the radially inner inner wall surface of the outer sleeve 71. The rear end of the inner sleeve 80 abuts against an outer periphery 79 provided on the outer periphery of a rear opening 77 of the outer sleeve 71. Meanwhile, the axially front end of the inner sleeve 80 abuts against the stopper ring 76. This prevents the inner sleeve 80 and the outer sleeve 71 from being misaligned in the axial direction.

[0038] 5 and 6, the inner sleeve 80 has a hydraulic oil supply chamber 81 that communicates with the hydraulic oil chamber 62 of the camshaft 8. The inner sleeve 80 also has an accommodation chamber 82 that accommodates the spool 90. The hydraulic oil supply chamber 81 and the accommodation chamber 82 are separated by a partition wall 83.

[0039] 6, the inner sleeve 80 has a communication hole 84 communicating with the hydraulic oil supply chamber 81, a communication groove 85 extending axially from the communication hole 84 through the outer wall of the inner sleeve 80, and a through hole 86 penetrating the inner sleeve 80 radially inward from the communication groove 85. The through hole 86 is provided in a region of the inner sleeve 80 corresponding to the accommodation chamber 82.

[0040] Furthermore, the inner sleeve 80 has, in order from the front, an inner retard port 87 and an inner advance port 88 in a region corresponding to the accommodation chamber 82. The inner retard port 87 and the inner advance port 88 are provided at different positions in the circumferential direction of the inner sleeve 80 from the communicating groove 85 and the through hole 86. Furthermore, the through hole 86 is provided at a position midway between the inner retard port 87 and the inner advance port 88 in the axial direction of the inner sleeve 80.

[0041] 5, the inner retard port 87 and the outer retard port 74 are in radial communication with each other, and the inner advance port 88 and the outer advance port 75 are in radial communication with each other. Therefore, in the following description, the outer retard port 74 and the inner retard port 87 are collectively referred to as the "retard port 710," and the outer advance port 75 and the inner advance port 88 are collectively referred to as the "advance port 720." The retard port 710 is in communication with the retard oil passage 38 provided in the vane rotor 30, and the advance port 720 is in communication with the advance oil passage 37 provided in the vane rotor 30.

[0042] The spool 90 is formed in a cylindrical shape with a bottom, and is provided so as to be able to reciprocate in the axial direction in the accommodation chamber 82 of the inner sleeve 80. An outer wall surface on the radial outside of the spool 90 and an inner wall surface on the radial inside of the inner sleeve 80 are in sliding contact with each other.

[0043] A spring 91 is provided between the spool 90 and the partition wall 83. One end of the spring 91 is engaged with a step 92 provided in a part of the inner wall of the spool 90, and the other end of the spring 91 is engaged with the partition wall 83. The spring 91 is a compression coil spring, and biases the spool 90 toward the stopper ring 76. FIG. 5 shows a state in which a front end 93 of the spool 90 abuts against the stopper ring 76. This determines the axial front position of the spool 90. This position of the spool 90 is called the initial position or zero stroke of the spool 90.

[0044] 7, when the spool 90 is pressed from the front side to the rear side by a pressing pin 46 of a solenoid actuator serving as the electromagnetic drive unit 4 described later, the spring 91 is compressed, and a rear end 94 of the spool 90 comes into contact with a stepped surface 89 provided on the outer periphery of the partition wall 83 of the inner sleeve 80. This determines the axial rear position of the spool 90 (i.e., the maximum travel position of the spool 90). This position of the spool 90 is called the maximum travel position or full stroke of the spool 90.

[0045] The hydraulic oil discharge groove 95, the front seal portion 96, the hydraulic oil supply groove 97, and the rear seal portion 98 are provided on the outer wall of the spool 90 from the front side in this order. The hydraulic oil discharge groove 95, the front seal portion 96, the hydraulic oil supply groove 97, and the rear seal portion 98 are all provided continuously in the circumferential direction of the spool 90. The hydraulic oil discharge groove 95 is provided with a hole 99 penetrating in the plate thickness direction. The front seal portion 96 and the rear seal portion 98 are both in liquid-tight sliding contact with the inner wall surface on the radial inside of the inner sleeve 80. The hydraulic oil supply groove 97 is provided at a position where it always communicates with the through hole 86 of the inner sleeve 80 while the spool 90 moves from the zero stroke (i.e., the initial position) to the full stroke (i.e., the maximum movement position). Therefore, the hydraulic oil pumped up from the oil pan 60 by the hydraulic pump 61 is supplied in the following order: hydraulic oil chamber 62 of the camshaft 8 → hydraulic oil supply chamber 81 of the inner sleeve 80 → communication hole 84 → communication groove 85 → through hole 86 → hydraulic oil supply groove 97. In this configuration, the hydraulic control valve 3 changes the axial position of the spool 90 to communicate the hydraulic oil supply groove 97 with the retard port 710 or the advance port 720, thereby making it possible to control the hydraulic pressure and supply amount of the hydraulic oil supplied to both hydraulic chambers 40, 41.

[0046] Next, the supply of hydraulic oil to both hydraulic chambers 40, 41 by the hydraulic control valve 3 and the discharge of hydraulic oil from both hydraulic chambers 40, 41 will be described.

[0047] 5 shows a state in which the spool 90 is in a zero stroke (i.e., initial position) as described above. In this state, the opening area of ​​the retard port 710 opening to the hydraulic oil supply groove 97 is maximized, and the opening area of ​​the advance port 720 opening to the accommodation chamber 82 is maximized. At this time, as shown by the arrow IN, the hydraulic oil pumped up from the oil pan 60 flows through the hydraulic oil supply groove 97 → the retard port 710 → the retard oil passage 38, and is supplied to the retard hydraulic chamber 41. On the other hand, as shown by the arrow OUT, the hydraulic oil in the advance hydraulic chamber 40 flows through the advance oil passage 37 → the advance port 720 → the accommodation chamber 82 → the hole 99 of the hydraulic oil discharge groove 95 → the hole 78 of the stopper ring 76, and is discharged to the oil pan 60.

[0048] 7 shows the state where the spool 90 is in the full stroke (i.e., the maximum movement position) as described above. In this state, the opening area of ​​the advance port 720 opening to the hydraulic oil supply groove 97 is maximized, and the opening area of ​​the retard port 710 opening to the accommodation chamber 82 via the hydraulic oil discharge groove 95 is maximized. At this time, as shown by the arrow IN, the hydraulic oil pumped up from the oil pan 60 flows from the hydraulic oil supply groove 97 to the advance port 720 to the advance oil passage 37, and is supplied to the advance hydraulic chamber 40. On the other hand, as shown by the arrow OUT, the hydraulic oil in the retard hydraulic chamber 41 flows from the retard oil passage 38 to the retard port 710 to the accommodation chamber 82 to the hole 78 of the stopper ring 76, and is discharged to the oil pan 60.

[0049] 8 and 9 show a state in which the spool 90 is between the zero stroke and the full stroke and hydraulic oil is not discharged from either of the hydraulic chambers 40, 41. In this state, it is possible to maintain the relative rotational phase between the housing 20 and the vane rotor 30 of the valve timing control device 1 (hereinafter, sometimes simply referred to as the "relative rotational phase"). The position of the spool 90 of the hydraulic control valve 3 at this time is called the maintained stroke.

[0050] 8 shows a state in which the rear end of the advance port 720 and the rear end of the rear seal portion 98 are aligned. In this state, the advance port 720 is closed by the rear seal portion 98. Therefore, almost no hydraulic oil is discharged from the advance hydraulic chamber 40. On the other hand, the retard port 710 and the hydraulic oil supply groove 97 are in communication. Therefore, as shown by the arrow IN, a relatively small amount of hydraulic oil and hydraulic pressure is supplied from the retard port 710 to the retard hydraulic chamber 41 through the retard oil supply groove 97 and the retard oil passage 38.

[0051] 9 shows a state in which the front end of the retard port 710 and the front end of the front seal portion 96 are aligned. In this state, the retard port 710 is closed by the front seal portion 96. Therefore, almost no hydraulic oil is discharged from the retard hydraulic chamber 41. On the other hand, the advance port 720 and the hydraulic oil supply groove 97 are in communication with each other. Therefore, as shown by the arrow IN, a relatively small amount of hydraulic oil and hydraulic pressure is supplied from the hydraulic oil supply groove 97 to the advance hydraulic chamber 40 through the advance port 720 and the advance oil passage 37. Thus, in the holding stroke state shown in FIGS. 8 to 9, almost no hydraulic oil is discharged from both hydraulic chambers 40, 41, in other words, the amount of hydraulic oil discharged is zero or minimal.

[0052] <Configuration of electromagnetic driving unit 4> As shown in FIG. 1, the electromagnetic drive unit 4 is a solenoid actuator configured as a separate member (separate body) from the hydraulic control valve 3, and is provided on the front side of the hydraulic control valve 3. The electromagnetic drive unit 4 has a main body 45 and a pressing pin 46. The main body 45 includes a solenoid coil, a movable core, and the like, and is attached to a solenoid cover (not shown). The pressing pin 46 protrudes from the main body 45 toward the hydraulic control valve 3. The tip of the pressing pin 46 can abut against and separate from a front end 93 of a spool 90. In the electromagnetic drive unit 4, as the amount of current applied to the main body 45 increases, the pressing force of the pressing pin 46 pressing the spool 90 rearward against the biasing force of the spring 91 increases. The position of the spool 90 is determined by the balance between the load applied to the spool 90 from the pressing pin 46 and the biasing force of the spring 91. Therefore, the electromagnetic drive unit 4 can change the axial position of the spool 90 by axially reciprocating the pressing pin 46 in accordance with the amount of current applied to the main body 45. However, the response speed (i.e., tracking ability) of the axial position change of the spool 90 with respect to the amount of current applied from the electronic control device 5 to the electromagnetic drive unit 4 may vary depending on the viscosity of the hydraulic oil.

[0053] <Configuration of electronic control device 5> The electronic control unit 5 (hereinafter referred to as "ECU") is equipped with a microcomputer including a processor and a memory and its peripheral circuits, and controls the supply of electricity to the electromagnetic drive unit 4 and the like connected to the output side based on a control program stored in the memory. Note that ECU is an abbreviation for Electronic Control Unit. The memory of the ECU is a non-transient tangible storage medium. The ECU performs phase control of the valve timing control device 1 by controlling the current applied to the electromagnetic drive unit 4 according to the operating conditions of the internal combustion engine 6, etc. Specifically, the ECU controls the current applied to the electromagnetic drive unit 4 by PWM control. Note that PWM is an abbreviation for Pulse Width Modulation.

[0054] 10, the relationship between the current value (electric current) applied to the electromagnetic drive unit 4 by the ECU adjusting the duty ratio by PWM control and the flow rate of hydraulic oil supplied to and discharged from the hydraulic control valve 3 to both hydraulic chambers 40, 41 will be described. Note that the graph in Fig. 10 shows a basic state, and may vary depending on the manufacturing tolerances of each component of the valve timing adjustment system, the vehicle installation state, the rotation speed of the internal combustion engine 6, the temperature of the hydraulic oil (oil temperature), the voltage applied to the electromagnetic drive unit 4, etc.

[0055] The horizontal axis of the graph in Fig. 10 indicates the duty ratio (i.e., current value) by the PWM control of the ECU and the stroke amount of the spool 90 that operates in accordance with the duty ratio. When the duty ratio is 0%, the spool 90 has a zero stroke. When the duty ratio is 100%, the spool 90 has a full stroke.

[0056] 10 indicates the opening area of ​​the advance port 720 and the opening area of ​​the retard port 710 of the hydraulic control valve 3, and the flow rate of hydraulic oil supplied to and discharged from the hydraulic control valve 3 to both hydraulic chambers 40, 41. The opening areas of the advance port 720 and the retard port 710 are approximately proportional to the flow rates of hydraulic oil supplied to and discharged from there to both hydraulic chambers 40, 41. Specifically, when the opening area of ​​the advance port 720 is 0, the flow rate of hydraulic oil supplied to or discharged from the advance hydraulic chamber 40 is 0 or a minimum, and as the opening area of ​​the advance port 720 increases, the flow rate of hydraulic oil supplied to or discharged from the advance hydraulic chamber 40 increases. When the opening area of ​​the retard port 710 is 0, the flow rate of hydraulic oil supplied to or discharged from the retard hydraulic chamber 41 is 0 or at a minimum, and as the opening area of ​​the retard port 710 increases, the flow rate of hydraulic oil supplied to or discharged from the retard hydraulic chamber 41 also increases.

[0057] 10 indicates the flow rate of hydraulic oil supplied from the retard port 710 to the retard hydraulic chamber 41, and the dashed line AD indicates the flow rate of hydraulic oil discharged from the advance hydraulic chamber 40 via the advance port 720. On the other hand, the solid line AS indicates the flow rate of hydraulic oil supplied from the advance port 720 to the advance hydraulic chamber 40, and the dashed line RD indicates the flow rate of hydraulic oil discharged from the retard hydraulic chamber 41 via the retard port 710.

[0058] In the graph of Fig. 10, when the duty ratio is 0% and the spool 90 following it is at zero stroke, the flow rate of hydraulic oil supplied from the retard port 710 to the retard hydraulic chamber 41 is maximum, and the flow rate of hydraulic oil discharged from the advance hydraulic chamber 40 via the advance port 720 is also maximum. This state corresponds to the state shown in Fig. 5. At this time, in the valve timing adjusting device 1, the vane rotor 30 is phase-controlled to the retard side relative to the housing 20.

[0059] In the graph of Fig. 10, when the duty ratio is 100% and the spool 90 following it is at full stroke, the flow rate of hydraulic oil supplied from the advance port 720 to the advance hydraulic chamber 40 is maximum, and the flow rate of hydraulic oil discharged from the retard hydraulic chamber 41 via the retard port 710 is also maximum. This state corresponds to the state shown in Fig. 7. At this time, in the valve timing adjusting device 1, the vane rotor 30 is phase-controlled to the advance side relative to the housing 20.

[0060] In the graph of FIG. 10, when the duty ratio is P% to Q% and the spool 90 is in the range of the holding stroke, the amount of hydraulic oil discharged from both hydraulic chambers 40, 41 is 0 or minimum. In detail, the state of the spool 90 where the duty ratio follows P% corresponds to that shown in FIG. 8. At this time, almost no hydraulic oil is discharged from the advance hydraulic chamber 40, and a relatively small amount of hydraulic oil and hydraulic pressure is supplied to the retard hydraulic chamber 41. On the other hand, the state of the spool 90 where the duty ratio follows Q% corresponds to that shown in FIG. 9. At this time, almost no hydraulic oil is discharged from the retard hydraulic chamber 41, and a relatively small amount of hydraulic oil and hydraulic pressure is supplied to the advance hydraulic chamber 40. In the following description, the current value when the ECU sets the duty ratio to P% to Q% and sets the spool 90 to the holding stroke is called the "holding current value." In other words, the holding current value (holding current) is a current value (current) that holds the position of the spool 90 within the range of the holding stroke, and is therefore a current applied to the electromagnetic drive unit 4 when maintaining the relative rotational phase between the housing 20 and the vane rotor 30.

[0061] The range of the duty ratio P% to Q% may vary depending on the manufacturing tolerances of the components of the valve timing control system, the vehicle mounting state, the rotation speed of the internal combustion engine 6, the temperature of the hydraulic oil (oil temperature), the voltage applied to the electromagnetic drive unit 4, etc. For example, in this embodiment, Q% is slightly smaller than 30%. Also, when the duty ratio is set to 100%=1000mA (maximum current), the current value at the duty ratio Q% is slightly smaller than 600mA (60% of the maximum current).

[0062] In this way, the ECU can adjust the flow rates of hydraulic oil supplied to and discharged from both hydraulic chambers 40, 41 by changing the duty ratio to control the current applied to the electromagnetic driver 4, thereby performing phase control of the adjustable valve timing device 1. Furthermore, when starting phase control of the adjustable valve timing device 1, the ECU can control the flow rates of hydraulic oil supplied to and discharged from both hydraulic chambers 40, 41 and the release hydraulic chamber 52 to release the phase lock mechanism 2 (specifically, to cause the lock pin 50 to come out of the fitting recess 51).

[0063] <Electrical control performed by the ECU when phase lock mechanism 2 is released> Next, the power supply control executed by the ECU when the phase lock mechanism 2 is released in the valve timing control system of this embodiment will be described. Before that, however, a problem that occurs when the phase lock mechanism 2 is released will be described.

[0064] In a valve timing control system using a single pressure pin mechanism for the phase lock mechanism 2, when the system is started to perform phase control of the vane rotor 30 from the most retarded phase to the advanced phase, it is required to release the phase lock mechanism 2 and quickly make the vane rotor 30 reach the target phase. However, in a valve timing control system, when the hydraulic oil becomes highly viscous in a low temperature environment or when a high viscosity oil type is used for the hydraulic oil, the following problem may occur. That is, when the hydraulic oil becomes highly viscous, the fluid resistance increases, making it difficult for the spool 90 of the hydraulic control valve 3 to move. Specifically, as shown in FIG. 5, when the phase lock mechanism is locked during the most retarded phase control, the duty ratio is 0% in the current control of the ECU, the spool 90 has a zero stroke, and the front end 93 of the spool 90 abuts against the stopper ring 76. If the spool 90 is moved rearward from that state, a linking force, which is a force in the opposite direction to the above force, acts on the spool 90 and the stopper ring 76. Here, the linking force is a force that occurs in the opposite direction to the traveling direction of the objects when two objects in contact with each other in a fluid attempt to separate, due to a decrease in pressure in the gap at the contact point.

[0065] In general, the linking force Fl of a circular contact area is expressed by the following formula 2, where μ is the viscosity coefficient of the hydraulic oil, V is the moving speed of the object, h is the clearance between the two objects, R is the radius of the object, and πR^2 is the contact area of ​​the two objects. Note that R^2 represents the square of R. Fl=(3 / 2π) · (μV / h^3) · (πR^2)^2 · · (Formula 2) From the above formula 2, it can be seen that as the viscosity coefficient μ of the hydraulic oil adhering to the contact point between the spool 90 and the stopper ring 76 increases, the linking force also increases proportionately. Therefore, when the viscosity of the hydraulic oil becomes high, the spool 90 becomes difficult to start moving. Furthermore, when the viscosity of the hydraulic oil becomes high, the fluid resistance between the seal portions 96, 98 on the radial outside of the spool 90 and the inner wall surface on the radial inside of the inner sleeve 80 also becomes large, making it difficult for the spool 90 to start moving. This causes a problem of an increased delay in the start-up time of the valve timing adjusting device 1.

[0066] In response to this, the ECU of the valve timing adjustment system of the prior art described in Patent Document 1 executes the energization control shown in Fig. 11 when the phase lock mechanism 2 is released. Through this energization control, the ECU applies a current with a predetermined duty ratio to the electromagnetic driver 4 and moves the spool 90 in response to the current, thereby supplying hydraulic oil and hydraulic pressure to each hydraulic chamber of the valve timing adjustment device 1 and causing the lock pin 50 to come out of the fitting recess 51.

[0067] In the graph of FIG. 11, the horizontal axis indicates time, and the vertical axis indicates the duty ratio and current value under PWM control by the ECU.

[0068] At time T1 in FIG. 11, the ECU starts energization control for releasing the phase lock mechanism 2. Between time T1 and time T2, the ECU executes initial control for applying a current to the electromagnetic drive unit 4 at a predetermined current value (for example, a duty ratio of 100%) for a predetermined time. This initial control makes it possible to reliably move the spool 90 from the initial position and change the state of the spool to one in which it is easy to slide, even if the hydraulic oil has a high viscosity. That is, by instantaneously increasing the duty ratio at the start of energization control, it is possible to instantly separate the spool 90 from the stopper ring 76 against the linking force generated at the contact point between the spool 90 and the stopper ring 76 and the fluid resistance between the inner wall of the inner sleeve 80 and the seal portions 96, 98.

[0069] Subsequently, between time T2 and time T3, the ECU executes gradual change control to gradually increase the current value from a current value smaller than the current value applied in the initial control and larger than 0. In this specification, the "current value larger than 0" refers to a current value larger than 0 mA or a current value larger than a duty ratio of 0% (for example, a predetermined value between a current value of 0 mA and 100 mA). This gradual change control makes it possible to remove the lock pin 50 from the fitting recess 51. That is, by gradually increasing the hydraulic pressure and the supply amount of the hydraulic oil from the hydraulic control valve 3 to the advance hydraulic chamber 40, it is possible to increase the hydraulic pressure in the release hydraulic chamber 52 and remove the lock pin 50 from the fitting recess 51 before the torque acting on the lock pin 50 from the vane rotor 30 and the housing 20 becomes excessive. This makes it possible to prevent a malfunction in which the tip of the lock pin 50 gets caught on the inner wall of the fitting recess 51 and the lock cannot be released.

[0070] During the gradual change control from time T2 to time T3, the lock pin 50 comes out of the fitting recess 51. Specifically, the lock pin 50 comes out of the fitting recess 51 when the hydraulic pressure supplied to the release hydraulic chamber 52 during the gradual change control becomes equal to or greater than the pin release pressure and further when the balance between the forces acting on the vane rotor 30 from the advance hydraulic chamber 40 and the retard hydraulic chamber 41 and the cam torque acting on the vane rotor 30 is balanced.

[0071] However, for example, when the internal combustion engine 6 is operated for a certain period of time after starting and the phase lock mechanism 2 is locked again, the temperature of the hydraulic oil becomes high. When the viscosity of the hydraulic oil is low, such as when the temperature of the hydraulic oil is high, the amount of movement of the spool 90 when the initial control is executed may be larger than when the viscosity of the hydraulic oil is high. For more details, in the conventional valve timing adjustment system described in Patent Document 1, the advance hydraulic chamber 40 communicates with the release hydraulic chamber 52 that applies hydraulic pressure to cause the lock pin 50 to come out of the fitting recess 51. When the phase lock mechanism 2 is released, a current is applied to the electromagnetic drive unit 4 with a duty ratio of 100% in the initial control. For this reason, when the initial control is executed, if the viscosity of the hydraulic oil is low, the spool 90 easily moves from the initial position, and the amount of movement of the spool 90 becomes large. As a result, the hydraulic pressure of the release hydraulic chamber 52 and the advance hydraulic chamber 40 may become excessively high. Therefore, after the lock pin 50 comes out of the fitting recess 51, the rate of change of the relative rotational phase between the housing 20 and the vane rotor 30 becomes excessively high, and there is a risk that the actual relative rotational phase overshoots the target phase.

[0072] The ECU of the comparative example executes the energization control shown in FIG. 12 when the phase lock mechanism 2 is released. At time T21 in FIG. 12, the energization control for releasing the phase lock mechanism 2 by the ECU of the comparative example is started. At time T21, the ECU of the comparative example instantaneously switches the duty ratio from 0 to a duty ratio corresponding to a target current value for phase-controlling the vane rotor 30 to the advance side, and thereafter maintains the duty ratio until the vane rotor 30 reaches the target phase. However, in this case, the hydraulic pressure in the advance hydraulic chamber 40 increases sharply from time T21 and is maintained, so that an excessive torque acts on the lock pin 50 from the vane rotor 30 and the housing 20 before the lock pin 50 comes out of the fitting recess 51. Therefore, the tip of the lock pin 50 gets caught on the inner wall of the fitting recess 51, and the phase lock mechanism 2 cannot be released. Therefore, there is a risk that the lock pin 50 cannot be released in the comparative example as well. The target current value is a current value for relatively rotating the vane rotor 30 to the advance angle side and for making the vane rotor 30 reach the target phase, and is therefore a current value greater than the holding current value.

[0073] In this embodiment, the ECU executes feedback control (F / B control) to adjust a target current value (target current) of a current flowing (applied) to the electromagnetic drive unit 4 based on the actual phase and the target phase of the relative rotation phase in order to control the relative rotation phase to the target phase. The actual phase (current actual phase) of the relative rotation phase can be calculated based on, for example, a signal input from a crank angle sensor that detects the rotation angle of the crankshaft 7 and a signal input from a cam angle sensor that detects the rotation angle of the camshaft 8. The target phase of the relative rotation phase is set by a higher-level ECU (higher-level control device) such as an engine ECU (engine control device) based on, for example, the rotation speed, load, temperature, etc. of the internal combustion engine. Then, the electronic control unit 5 (ECU) adjusts the target current value by, for example, PID control or PI control (F / B control) based on the actual phase and the target phase of the relative rotation phase, and sets a duty ratio so that the current flowing to the electromagnetic drive unit 4 becomes the target current value. When adjusting the target current value, the change speed of the relative rotation phase may be taken into consideration. After the current flowing through the electromagnetic drive unit 4 reaches the target current value, the ECU controls the current flowing through the electromagnetic drive unit to a holding current value (holding current) in order to hold the relative rotation phase. Note that the target current value is a current value adjusted based on the actual phase and the target phase of the relative rotation phase, and does not include a current value (such as 950 to 1000 mA) that is targeted in control such as maximally rotating the vane rotor 30 to the advance side relative to the housing 20.

[0074] When the phase lock mechanism 2 is released, the ECU of this embodiment executes the current supply control shown in Fig. 13. In the graph of Fig. 13, the horizontal axis represents time, and the vertical axis represents the current value applied to the electromagnetic drive unit 4 by the PWM control of the ECU.

[0075] At time T31 in FIG. 13, the ECU starts energization control for releasing the phase lock mechanism 2. Between time T31 and time T32, the ECU executes initial control for applying the above target current value to the electromagnetic drive unit 4 for a predetermined time. The period between time T31 and time T32 is, for example, 50 ms. Here, when the ECU causes the lock pin 50 to come out of the fitting recess 51 from a state in which the tip of the lock pin 50 is fitted in the fitting recess 51, the ECU calculates the above target current value to be applied to the electromagnetic drive unit 4 in the initial control based on the actual phase of the relative rotation phase and the target phase assumed after the lock pin 50 is made to come out of the fitting recess 51. The target phase assumed after the lock pin 50 is made to come out of the fitting recess 51 may be calculated based on the current rotation speed, load, temperature, etc. of the internal combustion engine when the tip of the lock pin 50 is fitted in the fitting recess 51, or may be calculated based on the expected rotation speed, load, temperature, etc. of the internal combustion engine. The target current value (target current) is a current value that is optimized (adapted) in advance according to the actual phase and the target phase of the relative rotation phase in order to appropriately control the relative rotation phase to the target phase. The relationship between the actual phase and the target phase of the relative rotation phase and the target current value is acquired in advance based on a test or the like, and is specified, for example, by a map or a calculation formula. For example, when the maximum current that the ECU can apply to the electromagnetic drive unit 4 is set to 1000 mA, the ECU adjusts the target current value in the range of 600 to 800 mA. That is, the ECU adjusts the target current value in the range of 60 to 80% of the maximum current that can be applied to the electromagnetic drive unit 4.

[0076] The ECU sets the duty ratio to a duty ratio corresponding to the target current value so that the current flowing through the electromagnetic drive unit 4 becomes the target current value. In this embodiment, when the target current value is in the range of 600 to 800 mA, the duty ratio corresponding to the target current value is 30 to 50%. That is, the ECU controls the current applied to the electromagnetic drive unit 4 by PWM control, and adjusts the target current value within a duty ratio range of 30 to 50% by PWM control.

[0077] This initial control allows the spool 90 to be moved from the initial position even if the hydraulic oil is highly viscous, making it possible to change the state of the spool 90 to one that is easier to slide. That is, when the current supply control starts, the duty ratio is instantaneously increased to a duty ratio that corresponds to the target current value. This makes it possible to instantly separate the spool 90 from the stopper ring 76 against the linking force generated at the contact point between the spool 90 and the stopper ring 76 and the fluid resistance between the inner wall of the inner sleeve 80 and the seal portions 96, 98.

[0078] Subsequently, between time T32 and time T33, the ECU executes gradual change control to gradually increase the current value from a current value smaller than the current value applied in the initial control and larger than 0. At time T32, the current value at which the gradual change control is started (hereinafter referred to as the "gradual change start current value") is smaller than the current value applied in the initial control and larger than 0. In detail, the gradual change start current value is set to a predetermined current value within the range of the holding current value. Alternatively, the gradual change start current value is set to a predetermined current value smaller than the holding current value and larger than 0. Specifically, the gradual change start current value is preferably a predetermined current value with a duty ratio between 10 and 25%, for example. In addition, when the duty ratio is set to 100%=1000mA, the gradual change start current value is preferably a predetermined current value between 200mA and 500mA, for example.

[0079] 10 may fluctuate due to manufacturing tolerances of the components of the valve timing control system, the vehicle mounting state, the rotation speed of the internal combustion engine 6, the oil temperature, etc. In response to this, by setting the gradual change start current value to a predetermined current value that is smaller than the holding current value and larger than 0, it is possible to ensure that the range of the holding current value is passed through during the gradual change control, even if fluctuations occur in the holding current value. This increases the possibility that the phase lock mechanism 2 can be released regardless of fluctuations in the holding current value.

[0080] This gradual change control makes it possible to remove the lock pin 50 from the fitting recess 51. That is, by gradually increasing the hydraulic pressure and supply amount of hydraulic oil from the hydraulic control valve 3 to the advance hydraulic chamber 40, it is possible to increase the hydraulic pressure in the release hydraulic chamber 52 and remove the lock pin 50 from the fitting recess 51 before the torque acting on the lock pin 50 from the vane rotor 30 and the housing 20 becomes excessive. This makes it possible to prevent a problem in which the tip of the lock pin 50 gets caught on the inner wall of the fitting recess 51, making it impossible to release the lock.

[0081] At time T33, when the current flowing (applied) to the electromagnetic drive unit 4 reaches a target current value, the ECU maintains the current flowing to the electromagnetic drive unit 4 at the target current value. The ECU determines whether the lock pin 50 has been released. This determination is made, for example, by comparing a signal input from a crank angle sensor that detects the rotation angle of the crankshaft 7 with a signal input from a cam angle sensor that detects the rotation angle of the camshaft 8, and judging whether the vane rotor 30 has started to rotate relative to the housing 20. For example, it is assumed that the lock pin 50 has come out of the fitting recess 51 at time T34. Specifically, when the hydraulic pressure supplied to the release hydraulic chamber 52 reaches or exceeds the pin release pressure, and further, the forces acting on the vane rotor 30 from the advance hydraulic chamber 40 and the retard hydraulic chamber 41 and the cam torque acting on the vane rotor 30 are balanced, the lock pin 50 comes out of the fitting recess 51. At time T35, it is determined that the lock pin 50 has come out of the fitting recess 51, and F / B control is started to adjust the target current value based on the actual phase and target phase of the relative rotation phase. Furthermore, when the lock pin 50 comes out of the fitting recess 51, the actual phase of the relative rotation phase (VVT phase) starts to change so as to approach the target phase. Accordingly, the target current value adjusted based on the actual phase and target phase of the relative rotation phase starts to decrease. In particular, as the actual phase of the relative rotation phase approaches the target phase, the target current value decreases so as to approach the holding current value.

[0082] At time T36, when the actual phase of the relative rotation phase coincides with the target phase, the target current value is made equal to the holding current value, thereby holding the relative rotation phase at the target phase.

[0083] Also, for example, suppose that the lock pin 50 comes out of the fitting recess 51 at time T32. Even in this case, the current applied to the electromagnetic drive unit 4 in the initial control is the target current value, so the actual phase of the relative rotation phase approaches the target phase as it is. In other words, the actual phase of the relative rotation phase is prevented from overshooting the target phase. Note that, if the current applied to the electromagnetic drive unit 4 in the initial control is the maximum current (1000 mA) as in the conventional technology described in Patent Document 1, there is a risk that the actual phase of the relative rotation phase overshoots the target phase after the lock pin 50 comes out of the fitting recess 51 at time T32.

[0084] The present embodiment described above in detail has the following advantages.

[0085] When the lock pin 50 is removed from the fitting recess 51 from a state in which the tip of the lock pin 50 is fitted in the fitting recess 51, the ECU (electronic control unit 5) executes initial control to apply a target current larger than the holding current to the electromagnetic drive unit 4 for a predetermined time to move the spool 90 from the initial position. Therefore, by applying a load corresponding to a target current larger than the holding current to the spool 90 from the electromagnetic drive unit 4 instantaneously through the initial control, even if the hydraulic oil has a high viscosity, the spool 90 can be moved from the initial position, and the spool 90 can be changed to a state in which it is easy to slide. Then, by the gradual change control following the initial control, the spool 90 can be gradually moved so as to follow an increase in the amount of current applied, and the phase lock mechanism 2 can be easily released. Moreover, since the target current for controlling the relative rotation phase to the target phase is applied to the electromagnetic drive unit 4 in the initial control, it is possible to suppress the actual phase of the relative rotation phase from overshooting the target phase after the lock pin 50 is removed from the fitting recess 51.

[0086] In gradual change control, the current is not increased from 0, but is gradually increased from a current greater than 0, thereby eliminating the region where hydraulic pressure is abruptly supplied to the advance hydraulic chamber 40, i.e., the region not required for releasing the phase lock mechanism 2. This prevents the tip of the lock pin 50 from getting caught on the inner wall of the fitting recess 51, and shortens the time required to release the phase lock mechanism 2. Therefore, this valve timing adjustment system can unlock the valve timing adjustment device from the phase locked state in a short time to perform phase control, even when the viscosity of the hydraulic oil is high, for example, and improves start-up performance.

[0087] The ECU adjusts the target current (target current value) within a range of 60 to 80% of the maximum current that can be applied to the electromagnetic drive unit 4. With this configuration, in feedback control, when adjusting the target current to be applied to the electromagnetic drive unit 4 based on the actual phase and target phase of the relative rotation phase, the target current is adjusted within a range of 60 to 80% of the maximum current that can be applied to the electromagnetic drive unit 4. Therefore, in initial control, when a target current larger than the holding current is applied to the electromagnetic drive unit 4 for a predetermined time, the target current can be set to an appropriate magnitude.

[0088] The ECU controls the current applied to the electromagnetic drive unit 4 by PWM control, and adjusts the target current by PWM control within a duty ratio range of 30 to 50%. With this configuration, when adjusting the target current of the current applied to the electromagnetic drive unit 4 based on the actual phase and target phase of the relative rotation phase in feedback control, the target current is adjusted by PWM control within a duty ratio range of 30 to 50%. Therefore, when applying a target current larger than the holding current to the electromagnetic drive unit 4 for a predetermined time in initial control, the target current can be set to an appropriate magnitude.

[0089] When the lock pin 50 is removed from the fitting recess 51 from a state in which the tip of the lock pin 50 is fitted in the fitting recess 51, the ECU calculates a target current to be applied to the electromagnetic drive unit 4 in the initial control based on the actual phase of the relative rotation phase and the target phase expected after the lock pin 50 is removed from the fitting recess 51. With this configuration, the target current when controlling the relative rotation phase to the target phase, i.e., the target current to be applied to the electromagnetic drive unit 4 in the initial control, can be calculated in advance when the tip of the lock pin 50 is fitted in the fitting recess 51.

[0090] As shown by the dashed line graph in FIG. 13, if the ECU determines at time T37 that the lock pin 50 has not been released by the first gradual change control, the ECU may execute the second gradual change control from time T37. Then, the ECU determines whether the lock pin 50 has been released. Then, if the ECU determines that the lock pin 50 has been released by the second gradual change control, the ECU rotates the vane rotor 30 to a target phase. If the ECU determines that the lock pin 50 has not been released by the second gradual change control, the ECU may execute the third gradual change control. According to this configuration, after executing the initial control, the ECU repeatedly executes the gradual change control until the tip of the lock pin 50 comes out of the fitting recess 51. This ensures that the phase lock mechanism 2 can be released reliably, and the vane rotor 30 and the housing 20 can be reliably rotated relative to each other to a predetermined target phase.

[0091] Second embodiment The second embodiment will be described. The second embodiment is different from the first embodiment in that the power supply control executed by the ECU when the phase lock mechanism 2 is released is changed, and the rest of the second embodiment is the same as the first embodiment, so only the parts that are different from the first embodiment will be described.

[0092] The ECU provided in the valve timing adjusting system of the second embodiment changes the method of current control in accordance with the viscosity of the hydraulic oil when the phase lock mechanism 2 is released. Hereinafter, the control process executed by the ECU of the second embodiment when the phase lock mechanism 2 is released will be described with reference to the flowchart of FIG.

[0093] In step S10 of Fig. 14, the ECU detects the viscosity of the hydraulic oil. The viscosity of the hydraulic oil may be detected based on the type of the hydraulic oil, may be estimated based on the temperature of the hydraulic oil or the temperature of the engine coolant, or may be detected based on a combination of these.

[0094] Next, in step S11, the ECU compares the viscosity of the hydraulic oil with a predetermined viscosity threshold value stored in the ECU. The predetermined viscosity threshold value is set in advance through experiments or the like as to whether or not the hydraulic oil with that viscosity makes it difficult for the spool 90 to start moving from the initial state (i.e., stroke 0) and whether or not it is necessary to execute initial control, and is stored in the ECU. When the ECU determines that the viscosity of the hydraulic oil is higher than the predetermined viscosity threshold value (i.e., YES in step S11), the ECU proceeds to step S12.

[0095] In step S12, the ECU executes an initial control and a subsequent gradual change control when the phase lock mechanism 2 is released. The current control at this time is substantially the same as that described with reference to the graph in FIG. 13 in the first embodiment.

[0096] In the second embodiment, the time for which the initial control is performed (i.e., the time from time T31 to time T32 shown in FIG. 13) may be changed according to the viscosity of the hydraulic oil. Specifically, the ECU lengthens the time for which the initial control is performed as the viscosity of the hydraulic oil increases. The time for which the initial control is performed is set within a range of 50 to 300 ms, for example. This makes it easier to move the spool 90 from the initial position without lengthening the time for the initial control more than necessary.

[0097] On the other hand, in step S11 described above, when the ECU determines that the viscosity of the hydraulic oil is lower than the predetermined viscosity threshold value (that is, the determination in step S11 is NO), the ECU advances the process to step S13.

[0098] In step S13, the ECU executes gradual change control without executing initial action control when the phase lock mechanism 2 is released. The power supply control at this time is shown in the graph of FIG.

[0099] At time T41 in Fig. 15, the ECU starts energization control for releasing the phase lock mechanism 2. Between time T41 and time T42, the ECU executes gradual change control to gradually increase the current value from a predetermined current value (i.e., gradual change start current value) greater than 0. The gradual change start current value is the same as that described in the first embodiment.

[0100] According to the above configuration, when the viscosity of the hydraulic oil is low and the spool 90 is likely to start moving inside the sleeve 70, the time required to release the phase locking mechanism 2 can be shortened by executing gradual change control without executing initial motion control. Furthermore, since the ease with which the spool 90 and the lock pin 50 start moving varies depending on the viscosity of the hydraulic oil, by changing the time of initial motion control according to the viscosity of the hydraulic oil, the time required to release the phase locking mechanism 2 is not unnecessarily long and the phase locking mechanism 2 can be easily released.

[0101] 15, if the ECU determines that the lock pin 50 has not been released by the first gradual-change control, the ECU may execute a second gradual-change control. Also, if the ECU determines that the lock pin 50 has not been released by the second gradual-change control, the ECU may execute a third gradual-change control.

[0102] Third embodiment The third embodiment will be described. The third embodiment is similar to the first embodiment, etc. in that the power supply control executed by the ECU when the phase lock mechanism 2 is released is changed, but the rest of the third embodiment is the same as the first embodiment, etc. Therefore, only the differences from the first embodiment, etc. will be described.

[0103] The ECU provided in the valve timing adjusting system of the third embodiment changes the method of current control according to the temperature of the hydraulic oil when the phase lock mechanism 2 is released. This is because there is generally a correlation between the temperature of the hydraulic oil and the viscosity of the hydraulic oil. Hereinafter, the control process executed by the ECU of the third embodiment when the phase lock mechanism 2 is released will be described with reference to the flowchart of FIG.

[0104] In step S20 of Fig. 16, the ECU detects the temperature of the hydraulic oil. The temperature of the hydraulic oil may be directly measured by a temperature sensor or the like, or may be estimated from the temperature of the engine coolant.

[0105] Next, in step S21, the ECU compares the temperature of the hydraulic oil with a predetermined temperature threshold stored in the ECU. The predetermined temperature threshold is set in advance by experiments or the like as to whether or not the hydraulic oil at that temperature makes it difficult for the spool 90 to start moving from the initial state (i.e., stroke 0) and whether or not it is necessary to execute initial control, and is stored in the ECU. Note that the predetermined temperature threshold is, for example, a predetermined temperature in the range of 18 to 23°C. When the ECU determines that the temperature of the hydraulic oil is lower than the predetermined temperature threshold (i.e., YES is determined in step S21), the ECU proceeds to step S22.

[0106] In step S22, the ECU executes an initial control and a subsequent gradual change control when the phase lock mechanism 2 is released. The current control at this time is substantially the same as that described with reference to the graph in FIG. 13 in the first embodiment.

[0107] In the third embodiment, the time for which the initial control is performed (i.e., the time from time T31 to time T32 shown in FIG. 13) may be changed according to the temperature of the hydraulic oil. Specifically, the ECU lengthens the time for which the initial control is performed as the temperature of the hydraulic oil decreases. The time for which the initial control is performed is set within a range of 50 to 300 ms, for example. This makes it easier to move the spool 90 from the initial position without lengthening the time for the initial control more than necessary.

[0108] On the other hand, in the above-mentioned step S21, when the ECU determines that the temperature of the hydraulic oil is higher than the predetermined temperature threshold value (that is, the determination in step S21 is NO), the ECU advances the process to step S23.

[0109] In step S23, the ECU executes gradual change control without executing initial action control when the phase lock mechanism 2 is released. The current control at this time is substantially the same as that described with reference to the graph in FIG. 15 in the second embodiment.

[0110] According to the above configuration, when the temperature of the hydraulic oil is high and the spool 90 is likely to start moving inside the sleeve 70, the time required to release the phase lock mechanism 2 can be shortened by executing gradual change control without executing initial action control. Furthermore, the viscosity of the hydraulic oil generally changes depending on the temperature of the hydraulic oil, and the ease with which the spool 90 and the lock pin 50 start moving varies depending on the viscosity of the hydraulic oil. For this reason, by changing the time of initial action control depending on the temperature of the hydraulic oil, the time required to release the phase lock mechanism 2 is not unnecessarily long and the phase lock mechanism 2 can be easily released.

[0111] (Other embodiments) The above-described embodiments can be modified as follows: The same parts as those in the above-described embodiments are denoted by the same reference numerals and the description thereof will be incorporated herein.

[0112] In the above embodiments, the valve timing adjusting device 1 is provided at the end of the camshaft 8 that drives the intake valve 14 to adjust the opening and closing timing of the intake valve 14, but the present invention is not limited thereto. The valve timing adjusting device 1 may be provided at the end of the camshaft 9 that drives the exhaust valve 15 to adjust the opening and closing timing of the exhaust valve 15. In this case, the fitting phase in which the tip of the lock pin 50 fits into the fitting recess 51 is the most advanced phase in which the vane rotor 30 is at the most advanced angle relative to the housing 20. When a one-side pressure pin mechanism is used for the phase lock mechanism 2, the release hydraulic chamber 52 is configured to communicate with the retard hydraulic chamber 41 through an oil passage. Furthermore, the hydraulic control valve 3 is configured to supply hydraulic oil and hydraulic pressure to the advance hydraulic chamber 40 at a zero stroke (i.e., initial position) with a duty ratio of 0%, and to discharge hydraulic oil from the retard hydraulic chamber 41. Moreover, at a full stroke (i.e., maximum movement position) with a duty ratio of 100%, hydraulic pressure is supplied to the retard hydraulic chamber 41, and hydraulic oil is discharged from the advance hydraulic chamber 40. In this manner, the valve timing adjustment system can be applied to either the intake valve 14 or the exhaust valve 15.

[0113] In each of the above embodiments, the hydraulic control valve 3 is arranged in the center of the valve timing adjusting device 1, but the present invention is not limited to this. The hydraulic control valve 3 may be arranged in a position separate from the valve timing adjusting device 1.

[0114] In each of the above embodiments, the hydraulic control valve 3 and the electromagnetic drive unit 4 are configured as separate members, but this is not limiting. The hydraulic control valve 3 and the electromagnetic drive unit 4 may be configured as an integrated unit.

[0115] In each of the above embodiments, the torque transmission system of the internal combustion engine 6 is described as transmitting torque between the drive shaft and the driven shaft by the chain 13 wound around the gear 10 fixed to the drive shaft and the gears 11 and 12 fixed to the driven shaft, but the present invention is not limited to this. Torque may be transmitted between the drive shaft and the driven shaft by a belt wound around a pulley fixed to the drive shaft and a pulley fixed to the driven shaft.

[0116] The duty ratio corresponding to the target current value varies depending on the voltage applied to the electromagnetic drive unit 4. Therefore, even if the target current value is in the range of 600 to 800 mA, the duty ratio corresponding to the target current value may be different from 30 to 50%. Furthermore, the target current value varies depending on the range of the held current value, and the range of the held current value may be changed by learning. Therefore, the target current value may be adjusted to a range different from 60 to 80% of the maximum current, and the duty ratio corresponding to the target current value may change accordingly.

[0117] In the above embodiments, a single-pressure pin mechanism is used for the phase lock mechanism 2, but the present invention is not limited to this. The phase lock mechanism 2 may be a so-called double-pressure pin mechanism in which multiple release hydraulic chambers are formed around the lock pin 50, one of which communicates with the advance hydraulic chamber 40 via an oil passage and the other of which communicates with the retard hydraulic chamber 41 via an oil passage.

[0118] The above-described embodiment and each modified example may be combined to the extent possible. [Explanation of symbols]

[0119] 1...valve timing adjustment device, 2...phase lock mechanism, 3...hydraulic control valve, 4...electromagnetic drive unit, 5...electronic control unit (ECU), 6...internal combustion engine, 14...intake valve, 15...exhaust valve, 20...housing, 30...vane rotor, 39...accommodating hole, 40...advance hydraulic chamber, 41...retard hydraulic chamber, 50...lock pin, 51...fitting recess, 52...release hydraulic chamber, 70...sleeve, 90...spool.

Claims

1. A valve timing adjustment system is provided in a torque transmission system in which torque is transmitted from a drive shaft (7) of an internal combustion engine (6) to a driven shaft (8, 9), and adjusts the opening and closing timing of an intake valve (14) or an exhaust valve (15) that is driven to open and close by rotation of the driven shaft, a valve timing control device (1) including a housing (20) that rotates together with the drive shaft, and a vane rotor (30) that divides a hydraulic chamber formed inside the housing into an advance hydraulic chamber (40) and a retard hydraulic chamber (41) and rotates together with the driven shaft, wherein a relative rotational phase between the housing and the vane rotor is controlled by hydraulic pressure supplied to the advance hydraulic chamber and the retard hydraulic chamber; a phase lock mechanism (2) including: a lock pin (50) reciprocably provided in an accommodation hole (39) formed in the vane rotor; a fitting recess (51) formed in the housing such that a tip of the lock pin can fit therein when the vane rotor and the housing are in a predetermined phase; and a release hydraulic chamber (52) communicating with at least one of the advance hydraulic chamber and the retard hydraulic chamber and applying hydraulic pressure to the lock pin in a direction in which the lock pin comes out of the fitting recess; a sleeve (70) having a plurality of ports (710, 720) communicating with the advance hydraulic chamber and the retard hydraulic chamber via oil passages (37, 38), respectively, and a spool (90) provided reciprocally inside the sleeve and capable of adjusting the opening area of ​​the plurality of ports by changing the axial position, the hydraulic control valve (3) controlling the hydraulic pressure and the supply amount of hydraulic oil to the advance hydraulic chamber and the retard hydraulic chamber; an electromagnetic drive unit (4) that is driven in response to an applied amount of current to apply a load to the spool and change the axial position of the spool; and an electronic control device (5) for controlling a current applied to the electromagnetic drive unit, the electronic control device executes feedback control to adjust a target current of the current applied to the electromagnetic drive unit based on an actual phase and the target phase of the relative rotation phase so as to control the relative rotation phase to a target phase, and when holding the relative rotation phase, controls the current applied to the electromagnetic drive unit to a holding current, and when removing the lock pin from a state in which the tip of the lock pin is fitted into the fitting recess, executes initial action control to move the spool from an initial position by applying the target current larger than the holding current to the electromagnetic drive unit for a predetermined time, and then executes gradual change control to remove the lock pin from the fitting recess by applying a current to the electromagnetic drive unit while gradually increasing the current from a current that is smaller than the current applied in the initial action control and larger than zero.

2. 2. The valve timing control system according to claim 1, wherein the electronic control device adjusts the target current within a range of 60 to 80% of a maximum current that can be applied to the electromagnetic drive portion.

3. 3. The valve timing adjustment system according to claim 1, wherein the electronic control device controls the current applied to the electromagnetic drive unit by PWM control, and adjusts the target current within a duty ratio range of 30 to 50% by the PWM control.

4. 3. The valve timing adjustment system according to claim 1, wherein when the lock pin is caused to come out of the fitting recess from a state in which a tip end of the lock pin is fitted in the fitting recess, the electronic control device calculates the target current to be applied to the electromagnetic drive unit in the initial action control, based on the actual phase of the relative rotation phase and the target phase assumed after the lock pin is caused to come out of the fitting recess.

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