VALVE TIMING CONTROL APPARATUS FOR INTERNAL COMBUSTION ENGINE AND CONTROL METHOD THEREOF

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a valve timing control apparatus for an internal combustion engine, that includes a variable valve timing mechanism that variably sets the opening and closing timing of an engine valve that opens and closes according to a camshaft, by changing the relative rotation phase of the camshaft with respect to a crankshaft, and a lock mechanism that locks the relative rotation phase at a limit phase of the changing range of the relative rotation phase. The invention also relates to a control method of this variable valve control apparatus.

2. Description of Related Art

Internal combustion engines mounted in vehicles such as automobiles often have variable valve timing mechanisms that appropriately change the opening and closing timing (i.e., the valve timing) of an engine valve in order to improve engine output and emissions and the like.

The variable valve timing mechanism includes a housing that is drivingly connected to a crankshaft of an internal combustion engine, and a vane body that is drivingly connected to a camshaft, for example. The housing and the vane body are arranged so as to be able to rotate relative to one another about an axis. Vanes that extend in the radial direction are formed on the vane body. The inside of the housing is divided into an advance side pressure chamber and a retard side pressure chamber by these vanes. Hydraulic fluid that has been pressure-regulated is supplied to each of these pressure chambers. A relative rotation phase of the vane body with respect to the housing, i.e., the relative rotation phase of the camshaft with respect to the crankshaft, is changed to the advance side or the retard side by the hydraulic pressures in the pressure chambers acting on the vanes. More specifically, the relative rotation phase is changed to the advance side by hydraulic fluid being supplied to the advance side pressure chamber and hydraulic fluid being discharged from the retard side pressure chamber. On the other hand, the relative rotation phase is changed to the retard side by hydraulic fluid being discharged from the advance side pressure chamber and hydraulic fluid being supplied to the retard side pressure chamber. The valve timing of the internal combustion engine is changed by changing the relative rotation phase of the camshaft in this way.

Also, Japanese Patent Application Publication No. 2009-156217 (JP-A-2009-156217), for example, describes a valve timing control apparatus that includes a lock mechanism that mechanically locks the relative rotation phase of the camshaft at a predetermined lock phase (i.e., an limit phase on the advance side [maximum advance phase] within the control range and a limit phase on the retard side [maximum retard phase] within the control range). This lock mechanism makes it possible to keep the valve timing of the internal combustion engine at an appropriate timing at engine startup, at which time it is difficult to obtain sufficiently high pressure for the supply pressure of the hydraulic fluid because the rotation speed of the oil pump is low.

This lock mechanism includes, for example, a lock pin that is retractably arranged in a receiving hole formed in the vane body, a recessed portion (i.e., a lock hole) into which a tip end portion of lock pin is inserted, and a spring that urges the lock pin toward the lock hole, and the like. The lock mechanism also has a pressure chamber for releasing the lock (i.e., an unlock pressure chamber). The advance side pressure chamber and the retard side pressure chamber are communicated with this unlock pressure chamber, and some of the hydraulic fluid is supplied into the unlock pressure chamber. The lock pin is urged away from the lock hole by urging force of an amount corresponding to the hydraulic pressure (i.e., the unlock pressure) inside the unlock pressure chamber acting on the lock pin.

In this lock mechanism, the retractable state of the lock pin, i.e., a locked state and an unlocked state in which the locked state is released, is selectively switched according to the magnitude relation between the urging force of the spring and the urging force based on the unlock pressure.

For example, when the engine is stopped by an operating switch being turned off, the valve timing control apparatus continues to operate, and the pressure in the advance side pressure chamber or the retard side pressure chamber increases to change the relative rotation phase of the camshaft to the lock phase. As a result, the relative rotation phase then changes to the lock phase. Then when the unlock pressure drops to equal to or less than a predetermined pressure (i.e., a lock pressure) due to a decrease in the supply pressure of the oil pump following engine stop in this state, the urging force of the spring exceeds the urging force based on the unlock pressure. As a result, the lock pin moves toward the lock hole from the urging force of the spring, and the tip end portion of the lock pin slides into the lock hole. As a result, the lock mechanism becomes locked, thereby restricting relative rotation between the housing and the vane body.

On the other hand, when the internal combustion engine is started and the oil pump starts to operate again, the hydraulic pressure of the hydraulic fluid supplied from the oil pump to the advance side pressure chamber and the retard side pressure chamber gradually increases. When the unlock pressure becomes higher than the predetermined pressure as a result, the urging force based on the unlock pressure becomes greater than the urging force of the spring. As a result, the lock pin the lock pin moves away from the lock hole, such that the tip end portion of the lock pin comes out of the lock hole. As a result, the lock mechanism becomes unlocked, thus enabling the housing and the vane body to rotate relative to one another. Also, when the lock mechanism switches from the locked state to the unlocked state and then the supply pressure of the oil pump rises further, the valve timing changes based on the regulation of the hydraulic pressures in the retard side pressure chamber and the advance side pressure chamber.

When switching the lock mechanism from the unlocked state to the locked state, this switch is preferably performed quickly (i.e., the switching time is preferably short). With the apparatus described above, the switching time is determined by the time that it takes for the relative rotation phase of the camshaft to reach the lock phase, and the time that it takes to decrease the unlock pressure to the predetermined pressure.

Here, with the apparatus described above, the hydraulic pressures in the advance side pressure chamber and the retard side pressure chamber are regulated to change the relative rotation phase of the camshaft at the time that the internal combustion engine is stopped. Therefore, with one of the pressure chambers (more specifically, with the pressure chamber to which hydraulic fluid is supplied when changing the relative rotation phase to the side away from the lock phase), hydraulic fluid is discharged from this pressure chamber, so the hydraulic pressure easily decreases. However, with the other pressure chamber (more specifically, with the pressure chamber to which hydraulic fluid is supplied when changing the relative rotation phase to the side toward the lock phase), hydraulic fluid is supplied to the pressure chamber, so the hydraulic pressure does not easily decrease.

With an apparatus having a structure in which the hydraulic pressure in one of the advance side pressure chamber or the retard side pressure chamber is not easily decreased in this way, the unlock pressure does not easily decrease, so this contributes to preventing a reduction in the switching time. Therefore, with the apparatus described above, there is room for improvement regarding this point.

SUMMARY OF THE INVENTION

In view of the foregoing problem, the invention thus provides a valve timing control apparatus for an internal combustion engine, and control method thereof, that is able to quickly switch a lock mechanism to a locked state.

One aspect of the invention relates to a valve timing control apparatus for an internal combustion engine, that includes a variable valve timing mechanism that changes a relative rotation phase of a camshaft with respect to a crankshaft to a target phase based on hydraulic pressure supplied to an advance side pressure chamber and a retard side pressure chamber, and a lock mechanism that is placed in a locked state in which the relative rotation phase is locked at a limit phase of a changing range of the relative rotation phase when the hydraulic pressure is low, and that is placed in an unlocked state in which the locked state is released when the hydraulic pressure becomes high. This valve timing control apparatus for an internal combustion engine also includes an executing apparatus that is configured to execute, in combination, regulation of the hydraulic pressure in a first mode that changes the relative rotation phase to a side toward the limit phase, and regulation of the hydraulic pressure in a second mode that changes the relative rotation phase to a side away from the limit phase, during a period of time from when a stop operation to stop the internal combustion engine is started until the crankshaft stops rotating.

Another aspect of the invention relates to a control method for a valve timing control apparatus for an internal combustion engine, the valve timing control apparatus including a variable valve timing mechanism that changes a relative rotation phase of a camshaft with respect to a crankshaft to a target phase based on hydraulic pressure supplied to in advance side pressure chamber and a retard side pressure chamber, and a lock mechanism that is placed in a locked state in which the relative rotation phase is locked at a limit phase of a changing range of the relative rotation phase when the hydraulic pressure is low, and that is placed in an unlocked state in which the locked state is released when the hydraulic pressure becomes high. In this control method, regulation of the hydraulic pressure in a first mode that changes the relative rotation phase to a side toward the limit phase, and regulation of the hydraulic pressure in a second mode that changes the relative rotation phase to a side away from the limit phase are executed in combination during a period of time from when a stop operation to stop the internal combustion engine is started until the crankshaft stops rotating.

According to the valve timing control apparatus for an internal combustion engine and the control method of this valve timing control apparatus, when stopping operation of the internal combustion engine, hydraulic fluid is discharged from one of the advance side pressure chamber or the retard side pressure chamber, so as to decrease the hydraulic pressure, when regulating the hydraulic pressure in a first mode in order to change the relative rotation phase of the camshaft to the limit phase. Meanwhile, hydraulic pressure regulation in the second mode that changes the relative rotation phase to the side away from the limit phase is executed such that hydraulic fluid is discharged from the other pressure chamber, i.e., either the advance side pressure chamber or the retard side pressure chamber, and the hydraulic pressure is decreased.

Performing hydraulic pressure regulation in both the first mode and the second mode in this way enables the hydraulic pressure in the advance side pressure chamber and the hydraulic pressure in the retard side pressure chamber to be decreased separately. Therefore, the hydraulic pressures in the advance side pressure chamber and the retard side pressure chamber, and thus the unlock pressure, can be quickly decreased, so the lock mechanism can be quickly switched from the unlocked state to the locked state.

Also, in the valve timing control apparatus described above, the executing apparatus may execute the hydraulic pressure regulation in the first mode until the relative rotation phase reaches the limit phase, and when the relative rotation phase reaches the limit phase, the executing apparatus may execute the hydraulic pressure regulation in the second mode.

With the valve timing control apparatus described above, when operation of the internal combustion engine is stopped, first hydraulic pressure regulation in the first mode is executed and the relative rotation phase of the camshaft is changed to the limit phase. At this time, hydraulic fluid is discharged from one of the advance side pressure chamber or the retard side pressure chamber (more specifically, the pressure chamber to which hydraulic fluid is supplied when changing the relative rotation phase to the side away from the limit phase), such that the hydraulic pressure decreases. Then, when the relative rotation phase of the camshaft reaches the limit phase, hydraulic pressure regulation in the second mode is executed. At this time, the hydraulic pressure in one of the advance side pressure chamber or the retard side pressure chamber is already low from the hydraulic pressure regulation in the first mode before this, so the relative rotation phase of the camshaft will not change to a phase on the side away from the limit phase, and what is more, hydraulic fluid is discharged from the other pressure chamber, either the advance side pressure chamber or the retard side pressure chamber, such that the hydraulic pressure decreases.

In this way, the hydraulic pressures in the pressure chambers can be suitably decreased. That is, the hydraulic pressure in one of the advance side pressure chamber or the retard side pressure chamber is decreased as the relative rotation phase of the camshaft changes to the limit phase, and after the relative rotation phase of the camshaft has reached the maximum retard phase, the hydraulic pressure in the other pressure chamber, either the advance side pressure chamber or the retard side pressure chamber, is decreased while suppressing a change in the relative rotation phase.

Also, in the valve timing control apparatus described above, the executing apparatus may start to execute the hydraulic pressure regulation in the second mode following the start of the stop operation, and when the relative rotation phase changes to a phase on the side away from the limit phase, the executing apparatus may temporarily suspend the hydraulic pressure regulation in the second mode and execute the hydraulic pressure regulation in the first mode.

With the valve timing control apparatus described above, when the relative rotation phase of the camshaft will not change to a phase on the side away from the limit phase, the hydraulic pressure in one of the advance side pressure chamber or the retard side pressure chamber is decreased by regulating the hydraulic pressure in the second mode. Also, when the relative rotation phase of the camshaft will change to a phase on the side away from the limit phase if the hydraulic pressure regulation in the second mode is executed, the hydraulic pressure in the other pressure chamber, either the advance side pressure chamber or the retard side pressure chamber, is decreased by regulating the hydraulic pressure in the first mode. In this way, both the hydraulic pressure in the advance side pressure chamber and the hydraulic pressure in the retard side pressure chamber can be decreased.

Also, in the valve timing control apparatus described above, when a state in which the relative rotation phase does not change to a phase on the side away from the limit phase when the hydraulic pressure regulation in the second mode is executed continues for a predetermined period of time, the executing apparatus may then suspend the hydraulic pressure regulation in the second mode for a predetermined period of time and execute the hydraulic pressure regulation in the first mode.

Even if, through hydraulic pressure regulation in the first mode, the hydraulic pressure in one of the advance side pressure chamber or the retard side pressure chamber (more specifically, the pressure chamber to which hydraulic fluid is supplied when changing the relative rotation phase to the side away from the limit phase) is low enough not to change the relative rotation phase of the camshaft to a phase on the side away from the limit phase, it (i.e., the hydraulic pressure) may not be low enough to enable the lock mechanism to switch to the locked state.

Regarding this, with the valve timing control apparatus described above, after the hydraulic pressure in one of the advance side pressure chamber or the retard side pressure chamber has become low enough to not change the relative rotation phase of the camshaft to a phase on the side away from the limit phase, hydraulic pressure regulation in the first mode and hydraulic pressure regulation in the second mode are alternately executed, thus enabling both the hydraulic pressure in the advance side pressure chamber and the hydraulic pressure in the retard side pressure chamber to be sufficiently decreased.

Also, in the valve timing control apparatus described above, the limit phase may be a limit phase on a retard side for the relative rotation phase, the first mode may be a regulation mode in which hydraulic fluid is discharged from the advance side pressure chamber and hydraulic fluid is supplied to the retard side pressure chamber, and the second mode may be a regulation mode in which hydraulic fluid is supplied to the advance side pressure chamber and hydraulic fluid is discharged from the retard side pressure chamber.

Further, the valve timing control apparatus described above may also include a hydraulic pressure control valve that regulates an amount of hydraulic fluid supplied to the advance side pressure chamber or the retard side pressure chamber according to a duty ratio of a drive signal that is input. Also, the first mode may be obtained by setting the duty ratio to 0% and the second mode may be obtained by setting the duty ratio to 100%.

Also, in the valve timing control apparatus described above, the stop operation may be a stop operation that is in response to an operating switch being operated to stop the operation of the internal combustion engine.

According to the valve timing control apparatus for an internal combustion engine and the control method thereof described above, after the operating switch has been operated to stop the operation of the internal combustion engine, the hydraulic pressures in the advance side pressure chamber and the retard side pressure chamber can be quickly decreased in order to quickly complete the switch of the lock mechanism from the unlocked state to the locked state.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is a schematic view of the structure of a valve timing control apparatus according to a first example embodiment of the invention;

FIG. 2 is a sectional view of the structure of a lock mechanism according to the first example embodiment;

FIG. 3 is another sectional view of the structure of the lock mechanism;

FIG. 4 is a flowchart illustrating a control routine at engine stop according to the first example embodiment;

FIGS. 5A, 5B, 5C, 5D, and 5E are timing charts of an example of the manner in which the control routine at engine stop is executed according to the first example embodiment;

FIG. 6 is a flowchart (part 1) illustrating a control routine at engine stop according to a second example embodiment of the invention;

FIG. 7 is a flowchart (part 2) illustrating the control routine at engine stop; and

FIGS. 8A, 8B, 8C, 8D, and 8E are timing charts of an example of the manner in which the control routine at engine stop is executed according to the second example embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, a valve timing control apparatus according to a first example embodiment of the invention will be described in detail.

FIG. 1 is a view of both the structure of a variable valve timing mechanism related to the valve timing control apparatus of the first example embodiment, and the configuration of a hydraulic circuit of the control apparatus. As shown in FIG. 1, a variable valve timing mechanism 10 has a generally annular housing 12 and a vane body 14 that is housed in the housing 12. The vane body 14 is connected to a camshaft 16 that drives an intake valve, not shown, of an internal combustion engine, in a manner that enables the vane body 14 to rotate together with the camshaft 16. Also, the housing 12 is connected to a cam pulley 18 that rotates in synchronization with a crankshaft, not shown, of the internal combustion engine, in a manner that enables the housing 12 to rotate together with the cam pulley 18. The camshaft 16 rotates clockwise in FIG. 1.

A plurality of vanes 20 that extend in the radial direction (i.e., a direction intersecting the rotation axis of the vane body 14) are provided on the outer periphery of the vane body 14. Also, a plurality of grooves 22 that extend in the circumferential direction of the housing 12 are formed on the inner periphery of the housing 12. Each of the vanes 20 is arranged in a corresponding one of the grooves 22. An advance side pressure chamber 24 and a retard side pressure chamber 26 are formed divided by the vanes 20 inside the grooves 22. In FIG. 1, the two vanes 20 and two grooves 22 are shown, but the numbers of these may be changed as appropriate.

The advance side pressure chamber 24 and the retard side pressure chamber 26 are each connected to a hydraulic pressure control valve 28 via an appropriate fluid passage. Hydraulic fluid delivered from an engine-driven oil pump 30 that is drivingly connected to the crankshaft is supplied to this hydraulic pressure control valve 28. A valve that can regulate the amount of hydraulic fluid supplied to the advance side pressure chamber 24 or the retard side pressure chamber 26 according to a duty ratio of applied voltage may be used as this hydraulic pressure control valve 28. The hydraulic pressure control valve 28 is operated based on the duty ratio of a drive signal input from an electronic control unit (ECU) 32, and supplies hydraulic fluid into the advance side pressure chamber 24 or the retard side pressure chamber 26, or discharges hydraulic fluid from the advance side pressure chamber 24 or the retard side pressure chamber 26. Also, the relative rotation phase of the vanes 20 in the grooves 22 is set to a predetermined phase according to the difference in pressure of hydraulic fluid (i.e., hydraulic pressure) in the advance side pressure chamber 24 and in the retard side pressure chamber 26 formed on both sides of the vanes 20. As a result, the vane body 14 rotates relative to the housing 12, so the relative rotation phase of the camshaft 16 with respect to the cam pulley 18 changes, such that the opening and closing timing (i.e., the valve timing) of the intake valve changes.

The drive signal duty ratio is adjusted within a range of 0% to 100%, inclusive. The hydraulic pressure in each of the pressure chambers 24 and 26 is regulated so that the relative rotation phase more quickly changes to the advance side as the duty ratio nears 100%. Also, the hydraulic pressure in each of the pressure chambers 24 and 26 is regulated so that the relative rotation phase more quickly changes to the retard side as the duty ratio nears 0%.

This kind of valve timing control is performed as described in detail below. Parameters indicative of the engine operating state, such as the rotation phase of the camshaft 16 detected by a cam angle sensor, and the engine speed NE and the rotation phase of the crankshaft detected by a crankshaft angle sensor, are input to the electronic control unit 32.

The electronic control unit 32 computes an appropriate valve timing according to the engine operating state based on these parameters, and calculates a target phase for the relative rotation phase of the camshaft 16 according to the computed appropriate valve timing. The electronic control unit 32 also calculates the current relative rotation phase of the camshaft 16 from the relationship between the rotation phase of the crankshaft and the rotation phase of the camshaft 16.

Then, if the target phase differs from the current phase, the electronic control unit 32 controls the operation of the hydraulic pressure control valve 28 to discharge hydraulic fluid from one of the advance side pressure chamber 24 or the retard side pressure chamber 26, and supply hydraulic fluid to the other. More specifically, when the current relative rotation phase is a phase that is on the retarded side of the target phase, the electronic control unit 32 controls the operation of the hydraulic pressure control valve 28 to supply hydraulic fluid to the advance side pressure chamber 24 and discharge hydraulic fluid from the retard side pressure chamber 26 in order to change the relative rotation phase to the advance side. In this first example embodiment, this kind of hydraulic pressure regulation mode functions as a second mode that changes the relative rotation phase to the side away from a limit phase. On the other hand, if the current relative rotation phase is a phase that is on the advanced side of the target phase, the electronic control unit 32 controls the operation of the hydraulic pressure control valve 28 to discharge hydraulic fluid from the advance side pressure chamber 24 and supply hydraulic fluid to the retard side pressure chamber 26 in order to change the relative rotation phase to the retard side. In this first example embodiment, this kind of hydraulic pressure regulation mode functions as a first mode that changes the relative rotation phase to the side toward the limit phase. The valve timing is adjusted by the vane body 14 rotating relative to the housing 12 according to the difference between the hydraulic pressures in the advance side pressure chamber 24 and the retard side pressure chamber 26 that is created by controlling the operation of the hydraulic pressure control valve 28 in this way.

When the current relative rotation phase comes to match the target phase as a result of regulating the hydraulic pressures in the pressure chambers 24 and 26 in this way, the electronic control unit 32 controls the operation of the hydraulic pressure control valve 28 to stop supplying and discharging hydraulic fluid to and from the advance side pressure chamber 24 and the retard side pressure chamber 26. As a result, the pressures in the advance side pressure chamber 24 and the retard side pressure chamber 26 are kept substantially equal, so the relative rotation phase of the vane body 14 is maintained.

With this variable valve timing mechanism 10, the vane body 14 is able to rotate relative to the housing 12 within a range (a changing range) from a phase in which the vanes 20 abuts against one side wall surface of the grooves 22 to a phase in which the vanes 20 abut against the opposite side wall of the grooves 22. Hereinafter, the relative rotation phase of the camshaft 16 when the vane body 14 has rotated to the most retarded side (i.e., backward in the rotational direction of the camshaft 16) relative to the housing 12, i.e., the control limit phase on the retard side of the changing range, will be referred to as the maximum retard phase. This phase is set as the initial phase when operation of the hydraulic pressure control valve 28 is not being controlled by the electronic control unit 32, i.e., as the phase at engine stop. In contrast, the relative rotation phase of the camshaft 16 when the vane body 14 has rotated to the most advanced side (i.e., forward in the rotational direction of the camshaft 16) relative to the housing 12, i.e., the control limit phase on the advance side of the changing range, will be referred to as the maximum advance phase.

In this way, with the valve timing control apparatus according to the first example embodiment, the relative rotation phase of the camshaft 16 is appropriately changed within a range from the maximum retard phase to the maximum advance phase by regulating the hydraulic pressures in the advance side pressure chamber 24 and the retard side pressure chamber 26 through controlling the operation of the hydraulic pressure control valve 28. The valve timing of the intake valve that is driven open and closed by the rotation of the camshaft 16 can be changed by changing the relative rotation phase of the camshaft 16.

Also, the variable valve timing mechanism 10 according to the first example embodiment is provided with a lock mechanism 34 that restricts the relative rotation of the vane body 14 when the hydraulic pressure is low, such as at engine startup. This lock mechanism 34 will now be described.

A stepped receiving hole 36 that extends parallel to the axial direction of the camshaft 16 is formed in one of the vanes 20. A lock pin 38 is retractably arranged inside this receiving hole 36.

The lock pin 38 moves in the axial direction of the camshaft 16 between the position shown in FIG. 2 and the position shown in FIG. 3, while the outer peripheral surface of the lock pin 38 slides on the inner peripheral surface of the receiving hole 36, as shown by the sectional views of FIGS. 2 and 3. Also, the lock pin 38 is urged toward the housing 12 by a coil spring 40. A stepped portion 38a that has a wide diameter is formed on an end portion of this lock pin 38, and an unlock pressure chamber 42 that is an annular space is formed between this stepped portion 38a and a stepped portion 36a of the receiving hole 36. This unlock pressure chamber 42 is connected to the retard side pressure chamber 26 via a retard side fluid passage 44 formed in the vane 20, such that hydraulic pressure in the retard side pressure chamber 26 can be transmitted to the unlock pressure chamber 42.

Meanwhile, a lock hole 48 that is a recessed portion into which the lock pin 38 can be inserted when the relative rotation phase of the camshaft 16 (i.e., the relative rotation phase of the vane body 14) is the maximum retard phase is formed in the housing 12. As shown in FIG. 2, the vane body 14 is mechanically coupled to the housing 12, and thus relative rotation of the vane body 14 is restricted (i.e., locked), by the tip end portion of the lock pin 38 being inserted into the lock hole 48 from the urging force of the coil spring 40.

The space formed by the lock hole 48 and the tip end portion of the lock pin 38 serves as an unlock pressure chamber 50. This unlock pressure chamber 50 is connected to the advance side pressure chamber 24 via an advance side fluid passage 46 formed in a sliding surface of the vane 20 and the housing 12, such that pressure in the advance side pressure chamber 24 can be transmitted to the unlock pressure chamber 50.

The pressures of the hydraulic fluid in the unlock pressure chambers 42 and 50 act in the direction to disengage the lock pin 38 from the lock hole 48. Therefore, when the internal combustion engine is stopped, the relative rotation phase of the vane body 14 reaches the maximum retard phase. Also, in this state, when the pressures in the advance side pressure chamber 24 and the retard side pressure chamber 26 decrease such that the pressures in the unlock pressure chambers 42 and 50 sufficiently decrease, the lock pin 38 moves by the urging force of the coil spring 40. As a result, the tip end portion of the lock pin 38 becomes inserted into the lock hole 48, as shown in FIG. 2, such that relative rotation of the vane body 14 becomes locked.

The apparatus according to the first example embodiment is provided with an operating switch 52, a battery 54, and a relay 56. The operating switch 52 is operated when the internal combustion engine is started and stopped. The battery 54 is used to supply electric power to various electrical components, and the relay 56 is switched between a state in which electric power is supplied from the battery 54 to the hydraulic pressure control valve 28 and the electronic control unit 32, and a state in which that supply of power is stopped, based on a command signal from the electronic control unit 32.

In the first example embodiment, when the internal combustion engine stops in response to an operation that turns the operating switch 52 off, the relay 56 is operated to keep electric power supplied to the hydraulic pressure control valve 28 and the electronic control unit 32 for a predetermined period of time, and control to operate the hydraulic pressure control valve 28 by the electronic control unit 32 is continued. Also, during the process of stopping the internal combustion engine, operation of the hydraulic pressure control valve 28 is basically controlled so that the relative rotation phase of the camshaft 16 reaches the maximum retard phase. As a result, the relative rotation phase of the camshaft 16 becomes locked at the maximum retard phase by the lock mechanism 34.

On the other hand, when the internal combustion engine is started in response to an operation that turns the operating switch 52 on, the pressure in one or both of the advance side pressure chamber 24 and the retard side pressure chamber 26 is increased. When the hydraulic pressures in the unlock pressure chambers 42 and 50 that are connected to the advance side pressure chamber 24 and the retard side pressure chamber 26 increase sufficiently, the lock pin 38 moves in the direction in which it disengages from the lock hole 48, as shown in FIG. 3, such that the relative rotation becomes unlocked.

In this way, in the first example embodiment, when the hydraulic pressures in the pressure chambers 24 and 26 when the engine is stopped and immediately after the engine is started are low, the relative rotation of the vane body 14 is locked at the maximum retard phase. However, once the oil pump 30 is able to supply enough hydraulic fluid, the relative rotation of the vane body 14 becomes unlocked, such that valve timing control is able to be executed.

In the first example embodiment, when electric power is not supplied to the hydraulic pressure control valve 28 or when a drive signal is not input to the hydraulic pressure control valve 28, the operating state of the hydraulic pressure control valve 28 is one in which the oil pump 30 is communicated with the retard side pressure chamber 26. Therefore, when the hydraulic pressure control valve 28 is not being operated at engine startup, hydraulic fluid is supplied from the oil pump 30 toward the retard side pressure chamber 26, and at this time, pilot pressure is applied in a direction that disengages the lock pin 38 from the lock hole 48. Then, hydraulic fluid is supplied to the advance side pressure chamber 24 by operational control of the hydraulic pressure control valve 28 to reliably apply hydraulic pressure to the unlock pressure chambers 42 and 50 so that the pressure reliably increases and the lock by the lock mechanism 34 is reliably released.

Here, with the valve timing control apparatus in the first example embodiment, the lock mechanism 34 is switched from an unlocked state (i.e., a released state) to a locked state when the internal combustion engine is stopped. The time that it takes for this switch to occur (i.e., the switching time) is preferably short. The reason for this is as follows, for example.

That is, even if the relative rotation phase of the camshaft 16 when the operating switch 52 is turned off is a phase that is on the advance side, the lock mechanism 34 may still be switched to the locked state, so the range of the controllable relative rotation phase immediately before the operating switch 52 is turned off (normally while idling) is wider with a shorter switching time. Thus it may be said that the degree of freedom in setting the control structure of the valve timing control is able to be increased with a shorter switching time. A shorter switching time also enables the lock mechanism 34 to be switched to a locked state earlier after the operating switch 52 is operated, so the supply of power to the hydraulic pressure control valve 28 and the electronic control unit 32 for that switch can also be stopped earlier.

In the first example embodiment, in order to shorten this switching time, instead of controlling the operation of the hydraulic pressure control valve 28 so that the relative rotation phase of the camshaft 16 simply reaches the maximum retard phase during the period of time from after an engine-stop operation to stop the engine is started by an operation to turn the operating switch 52 off until the crankshaft stops rotating, the following control is executed. That is, both operational control of the hydraulic pressure control valve 28 in the first mode (specifically, a mode in which the duty ratio of the drive signal is 0%) that changes the relative rotation phase of the camshaft 16 to the side toward the maximum retard phase, and operational control of the hydraulic pressure control valve 28 in the second mode (specifically, a mode in which the duty ratio of the drive signal is 100%) that changes the relative rotation phase of the camshaft 16 to the side away from the maximum retard phase, are executed in combination.

Accordingly, when the internal combustion engine is stopped and the operation of the hydraulic pressure control valve 28 is controlled in the first mode, hydraulic fluid is discharged from the advance side pressure chamber 24, such that the hydraulic pressure in the advance side pressure chamber 24 decreases. On the other hand, when the internal combustion engine is stopped and the operation of the hydraulic pressure control valve 28 is controlled in the second mode, hydraulic fluid is discharged from the retard side pressure chamber 26, such that the hydraulic pressure in the retard side pressure chamber 26 decreases.

In this way, according to the first example embodiment, the pressure in the advance side pressure chamber 24 and the pressure in the retard side pressure chamber 26 are able to be decreased separately by regulating the hydraulic pressure via operational control of the hydraulic pressure control valve 28 in the first and second modes, respectively. Therefore, when the internal combustion engine is stopped, the pressure in the advance side pressure chamber 24 (i.e., the advance side unlock pressure) and the pressure in the retard side pressure chamber 26 (i.e., the retard side unlock pressure) are able to be decreased more quickly, such that the lock mechanism 34 is switched from the unlocked state to the locked state more quickly, than they are with an apparatus that simply executes operational control of the hydraulic pressure control valve 28 in the first mode.

Hereinafter, a routine related to such operational control of the hydraulic pressure control valve 28 when the engine is stopped (i.e., a control routine at engine stop) will be described in detail with reference to the flowchart in FIG. 4. The routine (i.e., the series of steps) shown in the flowchart is executed by the electronic control unit 32 as an interrupt routine that is executed in predetermined cycles, during a period of time from after the operating switch 52 is turned off to stop the internal combustion engine until a predetermined period of time T1 has passed. In the first example embodiment, this control routine at engine stop is one example of a routine executed by the executing apparatus.

As shown in FIG. 4, in this routine, the duty ratio of the drive signal output to the hydraulic pressure control valve 28 is first set to 0% (step S102) until the relative rotation phase of the camshaft 16 reaches the maximum retard phase (i.e., NO in step S101). That is, at this time, operational control of the hydraulic pressure control valve 28 in the first mode is performed such that hydraulic fluid is discharged from the advance side pressure chamber 24 and hydraulic fluid is supplied to the retard side pressure chamber 26. Here, it is determined that the relative rotation phase of the camshaft 16 has reached the maximum retard phase when the difference between the actual relative rotation phase and the maximum retard phase is less than a predetermined value.

This step is then repeatedly executed until the relative rotation phase of the camshaft 16 reaches the maximum retard phase. When the relative rotation phase of the camshaft 16 reaches the maximum retard phase (i.e., YES in step S101), the duty ratio of the drive signal output to the hydraulic pressure control valve 28 is set to 100% (step S103). That is, at this time, operational control of the hydraulic pressure control valve 28 in the second mode is performed such that hydraulic fluid is supplied to the advance side pressure chamber 24 and hydraulic fluid is discharged from the retard side pressure chamber 26.

Then, operational control of the hydraulic pressure control valve 28 at a drive signal duty ratio of 100% continues to be executed until the duration of this operational control reaches a predetermined period of time T2 (i.e., NO in step S104). This predetermined period of time T2 is obtained by obtaining, in advance, an amount of time sufficient for the hydraulic pressure in the retard side pressure chamber 26 (i.e., the retard side unlock pressure) to fall below a predetermined pressure P1 (i.e., a pressure at which the lock mechanism 34 is able to be unlocked), and storing this time in the electronic control unit 32.

When the duration of operational control of the hydraulic pressure control valve 28 at a drive signal duty ratio of 100% reaches the predetermined period of time T2 YES in step S104), the supply of electric power to the hydraulic pressure control valve 28 is stopped, such that operation of the hydraulic pressure control valve 28 stops (step S105).

Hereinafter, the operation and effects from executing the control routine at engine stop will be described with reference to FIGS. 5A to 5E. FIGS. 5A to 5E are examples of the manner in which the control routine at engine stop is executed. Of FIGS. 5A to 5E, FIG. 5A shows the manner in which electric power is supplied to the electronic control unit 32, FIG. 5B shows the change in the engine speed NE, FIG. 5C shows the change in the relative rotation phase of the camshaft, FIG. 5D shows the change in the unlock pressures, and FIG. 5E shows the change in the drive signal duty ratio.

As shown in FIG. 5A, when the operating switch 52 is turned off in order to stop the internal combustion engine at time t11, electric power continues to be supplied to the electronic control unit 32 from then until the predetermined period of time T1 has passed (i.e., from time t11 to time t16).

Also, because the operational controls of the internal combustion engine, such as fuel injection control and ignition timing control and the like, are stopped at this time, the engine speed NE (FIG. 5B) decreases thereafter, and with this decrease, the supply pressure of the oil pump 30 also gradually decreases.

Furthermore, at this time, the duty ratio (FIG. 5E) of the drive signal input to the hydraulic pressure control valve 28 is set to 0%. Therefore, the hydraulic pressure in the retard side pressure chamber 26 increases, and with this increase, the hydraulic pressure in the unlock pressure chamber 42 (i.e., the retard side unlock pressure (FIG. 5D)) also increases, such that the relative rotation phase of the camshaft 16 (FIG. 5C) changes toward the maximum retard phase. Also at this time, the hydraulic pressure in the advance side pressure chamber 24 decreases, and with this decrease, the hydraulic pressure in the unlock pressure chamber 50 (i.e., the advance side unlock pressure) also decreases. In this way, in the first example embodiment, when the internal combustion engine is stopped, first the relative rotation phase of the camshaft 16 changes toward the maximum retard phase, and with this change, the hydraulic pressure in the advance side pressure chamber 24 decreases.

Then later at time t12, the advance side unlock pressure falls below a predetermined pressure P2 (more specifically, a pressure at which lock mechanism 34 can be switched from an unlocked state to a locked state). Moreover, later at time t13, when the relative rotation phase of the camshaft 16 reaches the maximum retard phase, the duty ratio of the drive signal input to the hydraulic pressure control valve 28 is switched to 100%. As a result, the hydraulic pressure in the retard side pressure chamber 26 decreases, and with this decrease, the hydraulic pressure in the unlock pressure chamber 42 (i.e., the retard side unlock pressure) also decreases.

At this time, hydraulic fluid is supplied to the advance side pressure chamber 24, so the relative rotation phase of the camshaft 16 may change to the advance side unnecessarily. However, the hydraulic pressure in the advance side pressure chamber 24 (i.e., the advance side unlock pressure) is already sufficiently low from the hydraulic pressure regulation in the first mode before this (time t11 to time t13), and the engine speed NE is low, so the supply pressure of the oil pump 30 is low. Therefore, the hydraulic pressure in the advance side pressure chamber 24 will not become that high, so the relative rotation phase of the camshaft 16 will not change to the advance side at this time.

That later at time t14, the retard side unlock pressure falls below the predetermined pressure P1 (more specifically, a hydraulic pressure at which the lock mechanism 34 is able to be switched from the unlocked state to the locked state). That is, at this time, the advance side unlock pressure falls below the predetermined pressure P2 and the retard side unlock pressure falls below the predetermined pressure P1, so the lock pin 38 becomes inserted into the lock hole 48 by the urging force of the coil spring 40 (FIG. 2), such that the lock mechanism 34 becomes locked.

As shown in FIG. 5, later at time t15, when the duration of operational control of the hydraulic pressure control valve 28 at a drive signal duty ratio of 100% reaches the predetermined period of time T2, the supply of electric power to the hydraulic pressure control valve 28 is stopped.

Furthermore, later at time t16, when the amount of time that has passed after the operating switch 52 is turned off reaches the predetermined period of time T1, the supply of electric power to the electronic control unit 32 is turned off. This predetermined period of time T1 is obtained by obtaining, in advance, an amount of time sufficient for the lock mechanism 34 to switch from the unlocked state to the locked state through execution of the control routine at engine stop, based on results from testing or simulation, and storing this time in the electronic control unit 32.

In this way, with the control routine at engine stop according to the first example embodiment, hydraulic pressure regulation in the first mode is executed until the relative rotation phase of the camshaft 16 reaches the maximum retard phase, and when the relative rotation phase reaches the maximum retard phase, hydraulic pressure regulation in the second mode is executed. Therefore, the hydraulic pressures in the pressure chambers 24 and 26 can be suitably decreased. That is, the hydraulic pressure in the advance side pressure chamber 24 is decreased as the relative rotation phase of the camshaft 16 changes to the maximum retard phase, and after the relative rotation phase of the camshaft 16 has reached the maximum retard phase, the hydraulic pressure in the retard side pressure chamber 26 is decreased while suppressing a change in the relative rotation phase. Accordingly, when the internal combustion engine is stopped, the hydraulic pressures in the advance side pressure chamber 24 and the retard side pressure chamber 26, and thus the advance side unlock pressure and the retard side unlock pressure, can both be quickly decreased, so the lock mechanism 34 can quickly be switched from the unlocked state to the locked state.

As described above, according to the first example embodiment, the effects described below can be obtained.

(1) During the period from after the operating switch 52 is turned off until the engine speed NE becomes 0, operational control of the hydraulic pressure control valve 28 in the first mode that changes the relative rotation phase of the camshaft 16 to the side toward the maximum retard phase, and operational control of the hydraulic pressure control valve 28 in the second mode that changes the relative rotation phase of the camshaft 16 to the side away from the maximum retard phase are executed in combination. Therefore, when the internal combustion engine is stopped, the hydraulic pressures in the advance side pressure chamber 24 and the retard side pressure chamber 26, and thus the advance side unlock pressure and the retard side unlock pressure, are able to be decreased more quickly, so the lock mechanism 34 is able to be switched from the unlocked state to the locked state more quickly, than they are with an apparatus that simply executes operational control of the hydraulic pressure control valve 28 in the first mode.

(2) The hydraulic pressure regulation of the advance side pressure chamber 24 and the retard side pressure chamber 26 is performed in the first mode until the relative rotation phase of the camshaft 16 reaches the maximum retard phase, and when the relative rotation phase of the camshaft 16 reaches the maximum retard phase, the hydraulic pressure regulation of the advance side pressure chamber 24 and the retard side pressure chamber 26 is performed in the second mode. Therefore, the hydraulic pressures in the pressure chambers 24 and 26 can be suitably decreased. That is, the hydraulic pressure in the advance side pressure chamber 24 is decreased as the relative rotation phase of the camshaft 16 changes to the maximum retard phase, and after the relative rotation phase of the camshaft 16 has reached the maximum retard phase, the hydraulic pressure in the retard side pressure chamber 26 is decreased while suppressing a change in the relative rotation phase.

(3) After the operating switch 52 is operated to stop the internal combustion engine, the hydraulic pressures in the advance side pressure chamber 24 and the retard side pressure chamber 26 can be quickly decreased in order to quickly complete the switch of the lock mechanism 34 from the unlocked state to the locked state.

Next, a valve timing control apparatus according to the second example embodiment of the invention will be described.

The structures of the variable valve timing mechanism and the lock mechanism provided in the valve timing control apparatus according to the second example embodiment, as well as the structure of the peripheral equipment are the same as those shown in FIGS. 1 to 3 described above, so descriptions of those structures will be omitted. Also, the valve timing control apparatus according to the second example embodiment differs from the valve timing control apparatus according to the first example embodiment only with respect to the procedure for executing the control routine at engine stop.

Hereinafter, the procedure for executing the control routine at engine stop according to the second example embodiment will be described with reference to the flowcharts in FIGS. 6 and 7. The routine (i.e., the series of steps) shown in these flowcharts is executed by the electronic control unit 32 as an interrupt routine that is executed in predetermined cycles, during a period of time from after the operating switch 52 is turned off to stop the internal combustion engine until a predetermined period of time T3 has passed. In the second example embodiment, this control routine at engine stop is one example of a routine executed by the executing apparatus.

As shown in FIG. 6, in this routine, the duty ratio of the drive signal output to the hydraulic pressure control valve 28 is first set to 100% (step S202) when the operating switch 52 is turned off in order to stop the internal combustion engine (i.e., YES in step S201). That is, when the operating switch 52 is turned off, first operational control of the hydraulic pressure control valve 28 in the second mode starts to be executed such that hydraulic fluid is supplied to the advance side pressure chamber 24, and hydraulic fluid is discharged from the retard side pressure chamber 26.

Then, operational control of the hydraulic pressure control valve 28 at a duty ratio of 100% is continued on the condition that condition A and condition B described below are both satisfied (i.e., on the condition that the determinations in all of steps 203 to 205 are YES). Condition A is that the relative rotation phase of the camshaft 16 not change to the advance side after the duty ratio has been set to 100% (step S204). Condition B is that the duration for which the duty ratio is set at 100% be less than a predetermined period of time T4 (such as several tens of milliseconds) (step S205).

When condition A described above is no longer satisfied due to the relative rotation phase of the camshaft 16 changing to the advance side as a result of the duty ratio being set to 100% (i.e., NO in step S204), the duty ratio is switched to 0% (step S206). In this case, operational control of the hydraulic pressure control valve 28 at a duty ratio of 0% is continued until the duration for which the duty ratio is set at 0% reaches a predetermined period of time T5 (such as several tens of milliseconds) (i.e., NO in step S201, NO in step S203, and NO in step S207). Thereafter, this step is repeatedly executed, and when the duration for which the duty ratio is set at 0% becomes equal to or greater than the predetermined period of time T5 (i.e., YES in step S207), the duty ratio is returned to 100% (step S208).

In this way, with this routine, a process is executed in which, when the relative rotation phase of the camshaft 16 changes to the advance side due to the drive signal duty ratio being set to 100%, the duty ratio is temporarily switched to 0% and kept there for the predetermined period of time T2, after which it is returned to 100%. That is, in this case, operational control of the hydraulic pressure control valve 28 in the second mode is temporarily suspended, and operational control of the hydraulic pressure control valve 28 in the first mode is executed such that hydraulic fluid is discharged from the advance side pressure chamber 24 and hydraulic fluid is supplied to the retard side pressure chamber 26.

Then, when the relative rotation phase of the camshaft 16 will no longer change to the advance side even if the drive signal duty ratio is set to 109% (i.e., NO in step S201, YES in step S203, and YES in step S204), it is determined whether the duration for which the duty ratio is set at 100% has reached the predetermined period of time T4 (step S205).

If the duration for which the duty ratio is set at 100% is less than the predetermined period of time T4 (YES in step S205), then operational control of the hydraulic pressure control valve 28 at the duty ratio of 100% is continued. Then when the duration for which the duty ratio is set at 100% reaches the predetermined period of time T4 (i.e., NO in step S205), the duty ratio is switched to 0% (step S206). Then, operational control of the hydraulic pressure control valve 28 at a duty ratio of 0% is continued until the duration for which the duty ratio is set at 0% reaches the predetermined period of time T5 (NO in step S207). When the duration for which the duty ratio is set at 0% becomes equal to or greater than the predetermined period of time T5 (i.e., YES in step S207), the duty ratio is returned to 100% (step S208).

In this way, with this routine, when the relative rotation phase of the camshaft 16 will no longer change to the advance side even if the drive signal duty ratio is set to 100%, operational control of the hydraulic pressure control valve 28 at a duty ratio of 100% for the predetermined period of time T4 and operational control of the hydraulic pressure control valve 28 at a duty ratio of 0% for the predetermined period of time T5 are alternately and repeatedly executed.

Then, as shown in FIG. 7, this operational control of the hydraulic pressure control valve 28 is continued until the time that has passed after the operating switch 52 is turned off reaches a predetermined period of time T6 (i.e., NO in step S209). This predetermined period of time T6 is obtained by obtaining, in advance, an amount of time sufficient for the hydraulic pressure in the advance side pressure chamber 24 (i.e., the advance side unlock pressure) to fall below the predetermined pressure P2 and the hydraulic pressure in the retard side pressure chamber 26 (i.e., the retard side unlock pressure) to fall below the predetermined pressure P1, based on results from testing or simulation, and storing this time in the electronic control unit 32.

Then when the time that has passed after the operating switch 52 is turned off reaches the predetermined period of time T3 (i.e., YES in step S209), the supply of electric power to the hydraulic pressure control valve 28 is stopped such that the hydraulic pressure control valve 28 stops operating (step S210). This predetermined period of time T3 is obtained by obtaining, in advance, an amount of time sufficient for the lock mechanism 34 to switch from the unlocked state to the locked state through execution of the control routine at engine stop according to the second example embodiment, based on results from testing or simulation, and storing this time in the electronic control unit 32.

Hereinafter, the operation and effects from executing the control routine at engine stop according to the second example embodiment will be described with reference to FIGS. 8A to 8E. FIGS. 8A to 8E are examples of the manner in which the control routine at engine stop is executed. Of FIGS. 8A to 8E, FIG. 8A shows the manner in which electric power is supplied to the electronic control unit 32, FIG. 8B shows the change in the engine speed NE, FIG. 8C shows the change in the relative rotation phase of the camshaft, FIG. 8D shows the change in the unlock pressures, and FIG. 8E shows the change in the drive signal duty ratio.

As shown in FIG. 8A, when the operating switch 52 is turned off in order to stop the internal combustion engine at time t21, electric power continues to be supplied to the electronic control unit 32 from then until the predetermined period of time T3 has passed (i.e., from time t21 to time t38).

Also, because the operational controls of the internal combustion engine, such as fuel injection control and ignition timing control and the like, are stopped at time t21, the engine speed NE (FIG. 8B) decreases thereafter, and with this decrease, the supply pressure of the oil pump 30 also gradually decreases.

Furthermore, at time 121, the duty ratio (FIG. 8E) of the drive signal input to the hydraulic pressure control valve 28 is set to 100%. Therefore, the hydraulic pressure in the retard side pressure chamber 26 decreases thereafter, and with this decrease, the hydraulic pressure in the unlock pressure chamber 42 (i.e., the retard side unlock pressure (FIG. 8D)) also decreases. In this way, in the second example embodiment, when the internal combustion engine is stopped, first the hydraulic pressure in the retard side pressure chamber 26, and thus the retard side unlock pressure, is decreased.

Also, at time t21, the operating state of the hydraulic pressure control valve 28 is such that hydraulic fluid is supplied to the advance side pressure chamber 24, so the relative rotation phase of the camshaft 16 (FIG. 8C) may change to the advance side. In this example, the relative rotation phase of the camshaft 16 has actually changed to the advance side (time t21 to t22).

Therefore, at time t22, the drive signal duty ratio is temporarily switched to 0% and remains at 0% for the predetermined period of time T5 (time t22 to t23). Then when the operational control of the hydraulic pressure control valve 28 in which the drive signal duty ratio is 0% has continued for the predetermined period of time T5, the duty ratio is returned to 100% (time t23). Accordingly, the hydraulic pressure in the retard side pressure chamber 26 (i.e., the retard side unlock pressure) is then able to be decreased again.

At time t23, the hydraulic pressure in the advance side pressure chamber 24 decreases due to the operational control of the hydraulic pressure control valve 28 in which the duty ratio is 0% for the predetermined period of time T5 immediately before, and the supply pressure of the oil pump 30 also decreases following a decrease in the engine speed NE. Therefore, the relative rotation phase of the camshaft 16 will no longer change to the advance side when operational control of the hydraulic pressure control valve 28 in the first mode is started at this time. Accordingly, when operational control of the hydraulic pressure control valve 28 at a duty ratio of 100% is started at this time, it will continue for the predetermined period of time T4 (time t23 to t24).

In this way, with this routine, operational control of the hydraulic pressure control valve 28 in the first mode and operational control of the hydraulic pressure control valve 28 in the second mode are executed in combination during the period from when a stop operation to stop the internal combustion engine is started by the operating switch 52 being turned off until the crankshaft stops rotating. Therefore, when the internal combustion engine is stopped, the pressure in the advance side pressure chamber 24 (i.e., the advance side unlock pressure) and the pressure in the retard side pressure chamber 26 (i.e., the retard side unlock pressure) are able to be decreased more quickly, such that the lock mechanism 34 is switched from the unlocked state to the locked state more quickly, than they are with an apparatus that simply executes operational control of the hydraulic pressure control valve 28 in the first mode.

More specifically, with this routine, when the relative rotation phase of the camshaft 16 will not change to the advance side, operational control of the hydraulic pressure control valve 28 in the second mode is executed, such that the hydraulic pressure in the retard side pressure chamber 26 decreases. Also, when the relative rotation phase of the camshaft 16 will change to the advance side if operational control of the hydraulic pressure control valve 28 in the second mode is executed, operational control of the hydraulic pressure control valve 28 in the first mode is executed, such that the hydraulic pressure in the advance side pressure chamber 24 decreases. As a result, both the hydraulic pressure in the advance side pressure chamber 24 and the hydraulic pressure in the retard side pressure chamber 26 will decrease.

At time t24, when operational control of the hydraulic pressure control valve 28 at a duty ratio of 100% continues for the predetermined period of time T4 without the relative rotation phase of the camshaft 16 changing to the advance side, operational control of the hydraulic pressure control valve 28 is then executed in the manner described below. That is, operational control of the hydraulic pressure control valve 28 at a duty ratio of 0% for the predetermined period of time T5 (i.e., times t24 to t26, t28 to t29, . . . , and t34 to t35) and operational control of the hydraulic pressure control valve 28 at a duty ratio of 100% for the predetermined period of time T4 (i.e., times t26 to t28, t29 to t30, . . . , and t35 to t36) are alternately and repeatedly executed. Then at time t25 during the process of executing this operational control of the hydraulic pressure control valve 28, the hydraulic pressure in the advance side pressure chamber 24 (i.e., the advance side unlock pressure) will fall below the predetermined pressure P2, and at time t27, the hydraulic pressure in the retard side pressure chamber 26 (i.e., the retard side unlock pressure) will fall below the predetermined pressure P1.

Here, even if, due to operational control of the hydraulic pressure control valve 28 in the first mode, the hydraulic pressure in the advance side pressure chamber 24 is low enough not to change the relative rotation phase of the camshaft 16 to the advance side, it may not be low enough to enable the lock mechanism 34 to switch to the locked state. In this case, if only operational control of the hydraulic pressure control valve 28 in the second mode continues to be executed, hydraulic fluid will be supplied to the advance side pressure chamber 24, so it may take more time for the hydraulic pressure in the advance side pressure chamber 24 to sufficiently decrease, and thus it may take more time for the lock mechanism 34 to switch from the unlocked state to the locked state.

Regarding this, in the second example embodiment, after the hydraulic pressure in the advance side pressure chamber 24 is low enough to not change the relative rotation phase of the camshaft 16 to the advance side, operational control of the hydraulic pressure control valve 28 in the first mode and operational control of the hydraulic pressure control valve 28 in the second mode are alternately executed. As a result, both the hydraulic pressure in the advance side pressure chamber 24 and the hydraulic pressure in the retard side pressure chamber 26 are able to be sufficiently decreased.

Then at time t37, when the period of time that has passed after the operating switch 52 is turned off reaches the predetermined period of time T6, electric power stops being supplied to the hydraulic pressure control valve 28. Furthermore, later at time t38, when the period of time that has passed after the operating switch 52 is turned off reaches the predetermined period of time T3, electric power stops being supplied to the electronic control unit 32.

As described above, according to the second example embodiment, the effects described in (4) and (5) below are able to be obtained in addition to the effects described in (1) and (3) above.

(4) Operation control of the hydraulic pressure control valve 28 in the second mode starts to be executed as a result of the operating switch 52 being turned off. Also, when the relative rotation phase of the camshaft 16 changes to the advance side, the operation control of the hydraulic pressure control valve 28 in the second mode is temporarily suspended and operational control of the hydraulic pressure control valve 28 in the first mode is executed. Therefore, when the relative rotation phase of the camshaft 16 will not change to the advance side, operational control of the hydraulic pressure control valve 28 in the second mode is executed so that the hydraulic pressure in the retard side pressure chamber 26 can be decreased. Moreover, when the relative rotation phase of the camshaft 16 will change to the advance side if operational control of the hydraulic pressure control valve 28 in the second mode is executed, operational control of the hydraulic pressure control valve 28 in the first mode is executed, such that the hydraulic pressure in the advance side pressure chamber 24 can be decreased. As a result, both the hydraulic pressure in the advance side pressure chamber 24 and the hydraulic pressure in the retard side pressure chamber 26 can be decreased.

(5) After, through operational control of the hydraulic pressure control valve 28 in the first mode, the hydraulic pressure in the advance side pressure chamber 24 becomes low enough not to change the relative rotation phase of the camshaft 16 to the advance side, operational control of the hydraulic pressure control valve 28 in the first mode and operational control of the hydraulic pressure control valve 28 in the second mode are alternately executed. As a result, both the hydraulic pressure in the advance side pressure chamber 24 and the hydraulic pressure in the retard side pressure chamber 26 are able to be decreased sufficiently.

Other Example Embodiments

The example embodiments described above may also be modified as described below. In the first example embodiment described above, the duty ratio of the drive signal input to the hydraulic pressure control valve 28 is set at 0% for the period of time from when the operating switch 52 is turned off until the relative rotation phase of the camshaft 16 reaches the maximum retard phase. Alternatively, however, during this period of time, the target phase may be set at the maximum retard phase. With this structure as well, during this period of time, operational control of the hydraulic pressure control valve 28 in a mode that changes the relative rotation phase of the camshaft 16 to the side toward the maximum retard phase may be executed.

In the first example embodiment, a timing slightly after the timing at which the relative rotation phase of the camshaft 16 reaches the maximum retard phase may be set, for example, a timing at which a predetermined period of time has passed after the relative rotation phase of the camshaft 16 has reached the maximum retard phase or the like may be set, as the timing at which the drive signal duty ratio is switched to 100% after the operating switch 52 is turned off. Also, as long as the relative rotation phase of the camshaft 16 reliably changes to the maximum retard phase by the pressure from the intake valve or the like, a timing before the relative rotation phase of the camshaft 16 reaches the maximum retard phase, for example, a timing at which the relative rotation phase of the camshaft 16 has reached a phase slightly to the advance side of the maximum retard phase or the like, may be set as that timing.

In the first example embodiment, after the drive signal duty ratio is switched to 100%, operational control of the hydraulic pressure control valve 28 at the duty ratio of 100% for a predetermined period of time (<T2) and operational control of the hydraulic pressure control valve 28 at a duty ratio of 0% for a predetermined period of time (<T2) may be alternately and repeatedly executed, instead of keeping the drive signal duty ratio at 100% for the predetermined period of time T2.

In the second example embodiment, step S205 in FIG. 6 may be omitted as long as the hydraulic pressure in the advance side pressure chamber 24 is able to be appropriately decreased. With this structure, the step of alternately and repeatedly executing operational control of the hydraulic pressure control valve 28 at the duty ratio of 100% for the predetermined period of time T4 and operational control of the hydraulic pressure control valve 28 at the duty ratio of 0% for the predetermined period of time T5 when the relative rotation phase of the camshaft 16 will no longer change to the advance side even if operational control of the hydraulic pressure control valve 28 at a duty ratio of 100% is executed may be omitted. In this case, operational control of the hydraulic pressure control valve 28 at the duty ratio of 100% may continue to be executed.

In the foregoing example embodiments, a percent less than 100% may be set instead of setting the drive signal duty ratio to 100% during the period of time from when the operating switch 52 is turned off until the engine speed NE becomes 0. That is, the drive signal duty ratio may be set lower than 100% as long as operational control of the hydraulic pressure control valve 28 in a mode in which hydraulic fluid is supplied to the advance side pressure chamber 24 and hydraulic fluid is discharged from the retard side pressure chamber 26 is able to be executed.

In the foregoing example embodiments, a percent greater than 0% may be set instead of setting the drive signal duty ratio to 0% during the period of time from when the operating switch 52 is turned off until the engine speed NE becomes 0. That is, the drive signal duty ratio may be set higher than 0% as long as operational control of the hydraulic pressure control valve 28 in a mode in which hydraulic fluid is discharged from the advance side pressure chamber 24 and hydraulic fluid is supplied to the retard side pressure chamber 26 is able to be executed.

In the foregoing example embodiments, the predetermined periods of time (i.e., T1 and T2 in the first example embodiment, and T3 to T6 in the second example embodiment) may also be variably set according to the viscosity of the hydraulic fluid or an index value of the viscosity. The temperature of the hydraulic fluid or the temperature of engine coolant or the like may be used as the index value of the viscosity of the hydraulic fluid. Here, if the viscosity of the hydraulic fluid changes due to a change over time or a change in temperature or the like, the rate of decrease in the hydraulic pressure in the advance side pressure chamber 24 and the rate of decrease in the hydraulic pressure in the retard side pressure chamber 26 will also change as a result. Regarding this, according to the structure described above, the control routine at engine stop can be executed in accordance with a change in the rate of decrease that accompanies such a change in the viscosity of the hydraulic fluid, such that the lock mechanism 34 is able to be appropriately switched from the unlocked state to the locked state.

The invention may also be applied to a valve timing control apparatus provided with a lock mechanism that locks the relative rotation phase of a camshaft with respect to a crankshaft, at a limit phase on the advance side of the changing range of the relative rotation phase (i.e., at the maximum advance phase). In this structure, the regulation mode in which hydraulic fluid is discharged from the retard side pressure chamber and hydraulic fluid is supplied to the advance side pressure chamber may be the first mode, and the regulation mode in which hydraulic fluid is supplied to the retard side pressure chamber and hydraulic fluid is discharged from the advance side pressure chamber may be the second mode.

The invention is not limited to a valve timing control apparatus that changes the valve timing of an intake valve, but may also be applied to a valve timing control apparatus that changes the valve timing of an exhaust valve.

VALVE TIMING CONTROL APPARATUS FOR INTERNAL COMBUSTION ENGINE AND CONTROL METHOD THEREOF

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