JPH0617618A - Hydraulic control device of variable valve timing mechanism - Google Patents

Abstract

PURPOSE:To secure the rapid operational responsiveness of a variable valve timing mechanism (VVT) and to stabilize the positional control when a ring gear is held at the intermediate position. CONSTITUTION:In a VVT where the valve timing is set variable by driving a ring gear 12 by the hydraulic power, the duty control of a control valve 28 to control the hydraulic pressure to the ring gear is executed based on the duty frequency which is synchronized with the phase inverted relative to the period of the torque fluctuation of a cam shaft 2 to be generated when an air intake valve is opened/closed. Thus, the hydraulic power which is periodically applied to the ring gear is exerted so as to cancel the thrust force to be periodically added to the ring gear caused by the torque fluctuation of the cam shaft, leading to reduction of the resultant force fluctuation. The ring gear is not moved by the thrust force accordingly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable valve timing mechanism driven by hydraulic pressure in order to change the opening / closing timing of an intake valve or an exhaust valve in an internal combustion engine, and more particularly to a hydraulic control device therefor.

[0002]

2. Description of the Related Art Conventionally, as a hydraulically driven type valve control device of this type, one disclosed in, for example, Japanese Patent Application Laid-Open No. 59-120707 is known. In this conventional valve control device, a sleeve (timing pulley) drivingly connected to the crankshaft of the engine is provided at one end of the camshaft, and a ring piston (ring gear) is provided between the timing pulley and the camshaft. Is intervening. At least one of the teeth provided on the inner and outer circumferences of the ring gear is a helical tooth, and the ring gear can rotate relative to the cam shaft by moving in the axial direction. Also, on one end side in the axial direction of the ring gear,
The hydraulic pressure from a hydraulic pump or the like is supplied through an oil passage. Further, a balancing spring is provided on the other end side of the ring gear so as to oppose the hydraulic pressure. Then, hydraulic pressure is applied to one end side of the ring gear, whereby the ring gear is moved in the axial direction against the biasing force of the spring. As a result, the camshaft is twisted with respect to the timing pulley, the phase (rotational phase) of the camshaft and the timing pulley in the rotation direction is changed, and the opening / closing timing of the intake valve or the exhaust valve is changed. The lap is controlled.

In this conventional valve control device, an electromagnetic valve is provided in the middle of the oil passage for controlling the hydraulic pressure acting on the ring gear. Then, the solenoid valve is duty-controlled by a computer based on various drive parameters of the engine. Therefore, by controlling the duty of the solenoid valve, a hydraulic pressure that varies in synchronization with the duty frequency is applied to one end side of the ring gear in the axial direction.

[0004]

However, in the above-described conventional valve control device, when the camshaft is rotationally driven, the reaction force of the periodic torque fluctuation of the camshaft is input to the ring gear. , A cyclic axial fluctuating load (thrust force) was applied to the ring gear. Further, a ring gear having helical teeth has some friction with respect to its axial movement.

Therefore, when the friction of the ring gear is relatively small, there are the following problems. That is,
At both ends of the moving stroke of the ring gear, the biasing force of the spring or the hydraulic pressure is the largest, so that the influence of the periodic thrust force applied to the ring gear is extremely small.
However, when the ring gear is held at the intermediate position by the duty control of the solenoid valve, the position is determined by the balance between the urging force of the spring and the hydraulic pressure. Therefore, in this balanced state, the cyclic thrust force is further applied to the ring gear, and the position control of the ring gear becomes unstable. Therefore, the ring gear may be moved carelessly and the helical teeth may be worn, the oil seal may be worn, or the durability of the mechanism itself may be impaired.

On the other hand, when the friction of the ring gear is relatively large, there are the following problems. That is, the friction of the ring gear exists as a hysteresis with respect to the movement of the ring gear. Therefore, when the hysteresis is large, the responsiveness is affected, especially when the ring gear is moved from the intermediate position. For example, when the hydraulic pressure applied to the ring gear is slightly increased or decreased in order to slightly move the ring gear, the change in the hydraulic pressure may be buried in the hysteresis. Therefore, the start of movement of the ring gear is delayed,
The position control was likely to be non-linear.

The present invention has been made in view of the above-mentioned circumstances, and an object thereof is to change the phase of valve timing in a variable valve timing mechanism for changing valve timing by driving a ring gear by hydraulic pressure. A hydraulic control device for a variable valve timing mechanism that can secure quick actuation responsiveness in the case of maintaining the ring gear at an intermediate position and can stabilize the position control when the ring gear is held at an intermediate position. is there.

[0008]

In order to achieve the above object, according to the present invention, there is provided a camshaft rotatably provided in a cylinder head of an internal combustion engine for opening and closing a valve for intake and exhaust, and a camshaft therefor. A timing pulley that is provided at one end of the camshaft and is drivingly connected to the crankshaft of the internal combustion engine, and at least one of the teeth provided on the inner and outer circumferences is a helical tooth, and is between the camshaft and the timing pulley. While intervening to connect the two,
A ring gear that is rotatable relative to the cam shaft by moving in the axial direction is provided, and by applying hydraulic pressure to the axial end of the ring gear through an oil passage between the cam shaft and the timing pulley, the ring gear moves in the axial direction. A hydraulic control device for a variable valve timing mechanism that applies a twist to a cam shaft by rotating it while moving it. The hydraulic control device is provided in the middle of an oil passage and is opened and closed to control the supply of hydraulic pressure to a ring gear. The control valve includes a control valve and a duty control unit that controls the duty of the control valve based on a duty frequency that is synchronized with a torque fluctuation cycle of the camshaft that occurs when the intake and exhaust valves are opened and closed.

[0009]

According to the above construction, when the timing pulley is rotationally driven in conjunction with the crankshaft, the driving force is transmitted from the timing pulley to the camshaft via the ring gear, and the camshaft is rotationally driven. . Further, the duty control means duty-controls the control valve based on the duty frequency synchronized with the torque fluctuation cycle of the camshaft generated when the intake / exhaust valve is driven to open / close. For this reason, hydraulic pressure is applied to the axial end side of the ring gear through the oil passage with a fluctuation cycle synchronized with the duty frequency.

When the camshaft is rotationally driven, the ring gear is rotated while being axially moved by applying an oil pressure that cyclically fluctuates in accordance with the duty frequency to one end side in the axial direction of the ring gear. Be moved.
As a result, the camshaft is twisted and the phase (rotational phase) in the rotational direction between the camshaft and the timing pulley is changed, and the opening / closing timing of the intake / exhaust valve is changed. Then, when changing the rotational phase of the camshaft in this way, the duty control means duty-controls the control valve based on the duty frequency synchronized in phase with the torque fluctuation cycle of the camshaft. As a result, a cyclic thrust force resulting from the reaction force of the torque fluctuation of the camshaft is applied to the ring gear, and is added to the cyclically changing hydraulic pressure in addition to the hydraulic pressure. Therefore, the resultant force of the hydraulic pressure and the thrust force is applied for the axial movement of the ring gear.

On the other hand, when the ring gear is held at the intermediate position of its moving stroke, the duty control means
The control valve is duty-controlled based on the duty frequency synchronized with the phase that is inverted with respect to the camshaft torque fluctuation cycle. As a result, the hydraulic pressure periodically applied to one end side of the ring gear in the axial direction acts so as to cancel out the thrust force caused by the reaction force of the torque fluctuation of the camshaft, and the ring gear is moved by the influence of the thrust force. There is no such thing.

[0012]

【Example】

(First Embodiment) A first embodiment in which a hydraulic control device for a variable valve timing mechanism according to the present invention is embodied in a gasoline engine will be described in detail below with reference to FIGS.

FIG. 1 is a schematic configuration diagram showing a variable valve timing mechanism (hereinafter simply referred to as "VVT") 1 of this embodiment and a hydraulic control device for driving the VVT 1. The VVT 1 includes a cam shaft 2 for opening and closing valves for intake and exhaust, and the cam shaft 2 is rotatably supported by a cylinder head 3 of an engine (not shown) by a cam journal 2a. In this embodiment, an intake valve and an exhaust valve (not shown) in the engine are opened and closed by separate camshafts, and the camshaft 2 corresponds to the intake valve. A timing pulley 4 is mounted on the tip of the camshaft 2 so as to be rotatable relative to the boss 4a. External teeth 4b are formed on the outer periphery of the timing pulley 4, and a housing recess 4c is formed on one side of the pulley 4 in the axial direction (the left-right direction in the drawing). Further, a cap 5 is tightened and fixed by a bolt 6 at the tip of the cam shaft 2 so as to close the accommodation recess 4c, and
It is locked by a knock pin 7. Further, an outer plate 8 press-fitted and fixed to the timing pulley 4 and an inner plate 9 formed integrally with the cap 5 are provided between the opening end side of the accommodation recess 4 c and the outer periphery of the cap 5.
A well-known viscous coupling (viscus coupling) 10 is provided for cushioning. Furthermore, seal members 11 are interposed between the cap 5 and the outer plate 8 and between the cap 5 and the timing pulley 4, respectively.

A ring gear 12 is interposed between the timing pulley 4 and the camshaft 2 to connect the both 4 and 2. That is, the ring gear 12 is inserted into the housing recess 4c of the timing pulley 4 which is closed by the cap 5.
Is housed. In the ring gear 12, both teeth 12a and 12b provided on the inner and outer circumferences thereof are helical teeth. Also, each tooth 12a, 12b of the ring gear 12
Are meshed with the internal teeth 4d formed on the boss portion 4a of the timing pulley 4 and the internal teeth 5a formed on the inner circumference of the cap 5, respectively. With this configuration, the ring gear 12 is moved in the axial direction, so that the gear 12
Is rotatable relative to the camshaft 2. Furthermore,
The timing pulley 4 is drivingly connected to a crankshaft (not shown) via a timing belt 13 that is wound around its outer teeth 4b.

Therefore, when the power of the crankshaft is transmitted to the timing pulley 4 via the timing belt 13, the timing pulley 4 and the cap 5 connected by the ring gear 12 are integrally rotated, and the camshaft 2 is rotated. It is driven to rotate. At this time, the ring gear 12 is moved in the axial direction, so that the camshaft 2 is twisted with respect to the timing pulley 4. Further, when the camshaft 2 is twisted, rattling caused by backlash of the ring gear 12 is buffered by the action of the viscous coupling 10, and abnormal noise is suppressed.

In order to drive the ring gear 12 by hydraulic pressure, one end in the axial direction of the ring gear 12 in the accommodating recess 4c is a pressurizing chamber 14 into which hydraulic pressure by hydraulic oil is introduced. Similarly, in the accommodation recess 4c, the other end side of the ring gear 12 is a spring chamber 16 for accommodating a balancing spring 15 that opposes its hydraulic pressure. Further, a head oil passage 17 and a shaft oil passage 18 which communicate with each other are formed in the cylinder head 3 and the camshaft 2 in order to supply hydraulic pressure to the pressurizing chamber 14.

On the other hand, in the timing pulley 4 and a part of the cam shaft 2, return oil passages 19 and 20 for leading out the hydraulic oil leaking from the pressurizing chamber 14 to the spring chamber 16 are formed. Further, on one end side of the timing pulley 4, a seal member 21 is interposed between the pulley 4 and the cylinder head 3, and the timing pulley 4,
Cylinder head 3, cam shaft 2 and seal member 21
The space surrounded by is the oil recovery chamber 22. The return oil passages 19 and 20 communicate with the oil recovery chamber 22. Further, below the camshaft 2, an oil return hole 24 for returning the working oil recovered in the oil recovery chamber 22 to the oil pan 23 of the engine is formed in a part of the cylinder head 3.

In this embodiment, each tooth 12 on the inner and outer circumferences is
The friction of the ring gear 12, which is determined by the inclination angles of a and 12b and the like, is set to be relatively small. In this embodiment, engine lubricating oil is used as the hydraulic oil. That is, the oil pump 25, which constitutes one hydraulic circuit for lubricating oil, is driven in conjunction with the engine, whereby the lubricating oil stored in the oil pan 23 is sucked up through the oil filter 26. The main oil passage 2 is provided between the oil pump 25 and the head oil passage 17.
7 is connected, and in the middle of the main oil passage 27,
A solenoid type control valve 28 of three types is provided.
This control valve 28 is duty-controlled, and its characteristics are shown in the graph of FIG. As can be seen from this graph, the control valve 28 is designed such that the hydraulic pressure as an output is proportional to the duty ratio within a certain range of the duty ratio as the input command value. That is, within a certain range of the duty ratio, the hydraulic pressure increases as the duty ratio increases. Then, as the hydraulic pressure controlled by the control valve 28 increases, the rotational phase of the camshaft 2 is advanced.

Therefore, while the oil pump 25 is being driven, the on / off control of the control valve 28 is duty-controlled to periodically open and close the main oil passage 27, so that the lubricating oil discharged from the oil pump 25 operates. A certain hydraulic pressure as oil is supplied to the head oil passage 17. The hydraulic oil supplied to the head oil passage 17 is further introduced into the pressurizing chamber 14 through the shaft oil passage 18. Then, the hydraulic pressure of the hydraulic oil causes the ring gear 12 to be pressed in one axial direction (to the right in the drawing) against the urging force of the spring 15. As a result, the camshaft 2 is twisted, and the rotational phase of the camshaft 2 with respect to the timing pulley 4 is changed. As a result, the opening / closing timing of the intake valve is changed, and the valve overlap between the intake valve and the exhaust valve is changed.

On the other hand, when the control valve 28 is turned off, the supply of hydraulic oil to the head oil passage 17 is cut off. As a result, the hydraulic pressure is released from the pressurizing chamber 14, and the ring gear 12
Is urged by the urging force of the spring 15 in the other axial direction (leftward in the figure) and returned. As a result, an opposite twist is applied to the camshaft 2, and the rotational phase of the camshaft 2 is restored and changed. As a result, the opening / closing timing of the intake valve is changed and the valve overlap is changed. At this time, the hydraulic oil leaking from the pressurizing chamber 14 to the spring chamber 16 is returned to the oil collecting chamber 22 through the return oil passages 19 and 20.
To the oil pan 23 through the oil return hole 24.
Returned to.

In this embodiment, the control valve 28 is an electronic control unit (hereinafter simply referred to as "EC
31) referred to as "U"). The ECU 31 includes a central processing unit (CPU), various memories for preliminarily storing a predetermined control program and the like, temporary storage of the calculation result of the CPU, and the like, and these units, an external input circuit, an external output circuit, etc. It is configured as a theoretical operation circuit connected by.

As various sensors for detecting the operating state of the engine, an air flow meter 32 for detecting the intake air amount Q is provided in the intake passage of the engine (not shown). A cylinder block of the engine is provided with a water temperature sensor 33 that detects the temperature of the cooling water (cooling water temperature) THW. Further, in the vicinity of the camshaft which does not constitute the VVT 1 on the exhaust valve side, the rotation of the crankshaft is detected at predetermined angular intervals from the rotation of the camshaft, and a crank angle signal CAS is obtained for obtaining the engine speed NE. A crank angle sensor 34 for outputting is provided. Furthermore, a cam angle sensor 35 that detects rotation of the camshaft 2 at a predetermined angular interval and outputs it as a cam angle reference signal CBS is provided at the base end of the camshaft 2 that constitutes the VVT 1 on the intake valve side. Has been. The cam angle sensor 35 is provided to calculate an advance value by comparison with the crank angle sensor 34 and to calculate a reference timing for turning on / off the control valve 28. The cam angle sensor 35 includes a timing rotor 36 that is rotated in association with the rotation of the cam shaft 2 and a pickup coil 37. On the outer periphery of the timing rotor 36, a plurality of protrusions 36a matching the number of cam ridges (not shown) on the cam shaft 2 are formed.
These protrusions 36a are arranged so as to match the cycle of torque fluctuations that occur in the camshaft 2 when the intake valve is opened and closed by the cam peaks. In this embodiment, the protrusions 36a are arranged so as to be aligned with the position where the level of torque fluctuation is the lowest. The pickup coil 37 is arranged so as to face each protrusion 36a.
Then, as the timing rotor 36 is rotated in accordance with the rotation of the crankshaft 2, the pickup coil 37 detects the passage of each protrusion 36a, and the cam angle signal CBS is a trigger that matches the position where the torque fluctuation level is minimum. It is designed to be output periodically as a pulse.

In this embodiment, the above-mentioned air flow meter 32, water temperature sensor 33, and
The crank angle sensor 34 and the cam angle sensor 35 are connected to each other. Further, the control valve 28 is connected to the external output circuit of the ECU 31. Then, the ECU 31 executes the VVT
In order to control the valve timing control according to No. 1, the open / close timing of the intake valve is determined according to the engine operating condition at that time based on the output signals from the air flow meter 32 and the sensors 33 to 35, and the control valve 28 is driven appropriately. It is designed to be controlled.

Next, the processing operation for valve timing control executed by the above-mentioned ECU 31 will be described. The flowchart of FIG. 2 shows a “valve timing control routine” executed by the ECU 70,
It is executed by a periodic interrupt every predetermined time while the engine is running.

When the processing shifts to this routine, first, at step 101, the air flow meter 32, the water temperature sensor 33, the crank angle sensor 34, and the cam angle sensor 35.
Intake air amount Q, cooling water temperature T based on each output signal from
The HW, crank angle signal CAS and cam angle signal CBS are read respectively.

Next, at step 102, it is judged if the cooling water temperature THW read this time is higher than a predetermined reference temperature T0. Here, when the cooling water temperature THW is not higher than the reference temperature T0, it is assumed that the engine is not sufficiently warmed up at the time of starting, and the subsequent processing is temporarily terminated.

On the other hand, in step 102, if the cooling water temperature THW is higher than the reference temperature T0, it is assumed that the engine has been sufficiently warmed up and started, and then step 103 is performed.
Then, the process proceeds to step 103 to execute a series of steps 103 to 109.

That is, first, at step 103, the crank angle signal CAS and the cam angle signal C read this time are read.
Based on BS, engine speed NE and camshaft 2
The current advance value θ0 of is calculated.

Next, at step 104, the load equivalent value Q / N of the engine is calculated based on the intake air amount Q read this time and the engine speed NE calculated this time. Then, in step 105, the target advance value θ of the camshaft 2 is calculated based on the engine speed NE and the load equivalent value Q / N calculated this time. As shown in FIG. 4, the calculation of the target advance value θ is performed by the engine speed NE.
And the target advance angle value θ with respect to the load equivalent value Q / N are referenced with reference to a map.

Subsequently, in step 106, a deviation (θ-θ0) of the advance value between the target advance value θ and the current advance value θ0.
Based on this, the duty addition value R of this time is calculated. The calculation of the duty addition value R is performed with reference to a map in which the relationship of the duty addition value R with respect to the advance angle deviation (θ−θ0) is predetermined as shown in FIG.

In step 107, the duty ratio RB obtained last time is added to the duty addition value R obtained this time, and the result is set as the duty ratio RA this time.

Further, in step 108, the energization time R for duty-controlling the control valve 28 based on the engine speed NE and the duty ratio RA obtained this time is used.
Calculate T. The energization time RT is calculated with reference to a map (not shown) in which the relationship between the engine speed NE and the duty ratio RA and the energization time RT is predetermined.

Then, in step 109, the control valve 28 is duty-controlled based on the energization time RT obtained this time. In this embodiment, the energization time RT is output to the solenoid of the control valve 28 based on the duty frequency synchronized with the phase inverted with respect to the cycle of the torque fluctuation generated in the camshaft 2, and the subsequent processing is temporarily terminated.

The processing operation of the valve timing control is executed as described above. Here, the operation of the valve timing control of this embodiment will be described with reference to the time chart of FIG.

This time chart shows the torque fluctuation generated in the camshaft 2, the thrust force in the ring gear 12 caused by the fluctuation, the trigger pulse from the cam angle sensor 35,
Energizing the solenoid of the control valve 28, the ring gear 12
The relationship between the hydraulic pressure and the change in the resultant force of the hydraulic pressure, the spring force, and the thrust force is shown.

As can be seen from this time chart,
The torque fluctuation of the camshaft 2 is periodically generated, and the thrust force of the ring gear 12 resulting from the torque fluctuation is generated in a cycle opposite to the cycle of the torque fluctuation. Then, the solenoid of the control valve 28 starts energization for the energization time RT based on the trigger pulse synchronized with the timing when the thrust force of the ring gear 12 becomes maximum. As a result, the hydraulic pressure applied to the ring gear 12 is
It will fluctuate with a cycle that is the reverse of the cycle of the thrust force.

Therefore, when the control valve 28 is duty-controlled so as to advance the rotation phase of the camshaft 2 to the maximum extent, the maximum hydraulic pressure is supplied to the pressurizing chamber 14, and the ring gear 12 moves to the spring 15. Biasing force (spring force)
It is moved to the right end position in FIG. Further, in order to retard the rotation phase of the camshaft 2 to the maximum, the control valve 28
When is turned off, the hydraulic pressure is not applied to the pressurizing chamber 14, and the ring gear 12 is moved to the left end position in FIG. 1 by the spring force. When the ring gear 12 is moved to the right end position or the left end position in this manner, the oil pressure or the spring force applied to the ring gear 12 is sufficiently large. The position is maintained in a relatively stable state.

On the other hand, when the control valve 28 is duty-controlled so as to advance the rotational phase of the camshaft 2 to a medium degree, the ring gear 12 is driven by the balance between hydraulic pressure and spring force, as shown in FIG. It is held in the middle position of the moving stroke. Then, in this embodiment, the duty control of the control valve 28 is performed based on the duty frequency synchronized with the phase that is inverted with respect to the cycle of the torque fluctuation of the camshaft 2. That is, the ring gear 12
The duty of the control valve 28 is controlled so that the hydraulic pressure applied to the valve fluctuates in a cycle that is the reverse of the cycle of the thrust force. Therefore, the hydraulic pressure periodically applied to the ring gear 12 acts so as to cancel out the thrust forces periodically applied to the ring gear 12 due to the torque fluctuation of the camshaft 2.

Therefore, when the friction of the ring gear 12 is relatively small as in this embodiment, as shown in FIG.
As shown by the solid line in (f), the fluctuation range of the resultant force of the hydraulic pressure, the spring force, and the thrust force acting on the ring gear 12 becomes very small, and the friction width of the ring gear 12 is not exceeded. The action is apparent from comparison with the case where a constant hydraulic pressure is supplied to the ring gear 12 shown by the broken line in the figure. Therefore, the ring gear 12 is not moved by the thrust force caused by the torque fluctuation of the camshaft 2.

As a result, when the ring gear 12 is held at the intermediate position, its position control can be stabilized. Further, as a result, inadvertent movement of the ring gear 12 can be prevented, and as a result, the ring gear 12 can be prevented.
Wear on the helical teeth of, and its oil seal wear,
Alternatively, it is possible to prevent the durability of the ring gear 12 itself from decreasing.

(Second Embodiment) Next, a second embodiment of the hydraulic control device for a variable valve timing mechanism according to the present invention will be described with reference to FIGS. 7 and 8. It should be noted that the configuration of this embodiment is the same as that of the first embodiment, the same components are designated by the same reference numerals, and the description thereof will be omitted. The different points will be mainly described below.

In this embodiment, the inner and outer teeth 12a, 1
The friction in the axial direction of the ring gear 12 determined by the inclination angle of 2b and the like is set to be relatively large. Further, the processing operation of the valve timing control executed by the ECU 31 is different from that of the first embodiment. That is, the flowchart of FIG.
It shows a "valve timing control routine" executed by U70, which is executed by a regular interrupt every predetermined time during the operation of the engine.

In this flowchart, step 2
Since the processing from 01 to step 208 is the same as the processing in the flowchart of FIG. 2 in the first embodiment, a description thereof will be omitted and a different processing of step 209 will be described.

That is, in step 209, the control valve 28 is duty-controlled based on the energization time RT obtained this time. In this embodiment, the energization time RT is output to the solenoid of the control valve 28 based on the duty frequency synchronized in phase with the torque fluctuation cycle of the camshaft 2.
The subsequent process is once ended.

Here, the operation of the valve timing control of this embodiment will be described with reference to the time chart of FIG. 8 according to FIG. As can be seen from this time chart, the torque fluctuation of the camshaft 2 is periodically generated, and the thrust force of the ring gear 12 caused by the torque fluctuation is generated in a cycle that is the reverse of the cycle of the torque fluctuation. Then, the solenoid of the control valve 28 ends the energization for the energization time RT based on the trigger pulse synchronized with the timing when the thrust force of the ring gear 12 becomes maximum. As a result, the hydraulic pressure applied to the ring gear 12 is
It changes with the period of the same phase as the period of the thrust force of 2.

Therefore, when the control valve 28 is duty-controlled to advance the rotational phase of the camshaft 2, hydraulic pressure is supplied to the pressurizing chamber 14, and the ring gear 12 resists the spring force and is shown in FIG. Moved to the right. In this embodiment, the duty control of the control valve 28 is
It is performed based on the duty frequency synchronized in the same phase as the torque fluctuation cycle of the camshaft 2. That is, the control valve 28 is duty-controlled so that the hydraulic pressure applied to the ring gear 12 fluctuates in a cycle having the same phase as the cycle of the thrust force. Therefore, the thrust force caused by the torque fluctuation of the camshaft 2 is applied to the ring gear 12 and added to the hydraulic pressure periodically applied to the ring gear 12.

Therefore, when the friction of the ring gear 12 is relatively large, as in this embodiment, as shown in FIG.
As indicated by the solid line in (f), the resultant force of the hydraulic pressure, the spring force, and the thrust force is applied for the axial movement of the ring gear 12. The fluctuation range of the resultant force is almost the same as the friction width of the ring gear 12. The action is apparent from comparison with the case where a constant hydraulic pressure is supplied to the ring gear 12 shown by the broken line in the figure.

As a result, even if the friction of the ring gear 12 is large, a resultant force sufficient to move the ring gear 12 in the axial direction can be obtained, and the movement response of the ring gear 12 can be improved. For example, even when the hydraulic pressure applied to the ring gear 12 is slightly increased or decreased by the duty control of the control valve 28, the change in the hydraulic pressure is not buried in the hysteresis caused by the friction, and the ring gear 12 is moved quickly. You can Therefore, the position control of the ring gear 12 can be performed in a more linear form, and a quick operation response can be secured when the valve timing is variable by the VVT 1.

The present invention is not limited to the above-described embodiments, but may be implemented as follows with a part of the configuration appropriately changed without departing from the spirit of the invention. (1) In each of the above-described embodiments, the ring gear 12 is moved by supplying hydraulic pressure to one end side in the axial direction of the ring gear 12 by using a hydraulic system of one system. The ring gear may be moved by supplying hydraulic pressure using a hydraulic circuit.

(2) In each of the above-described embodiments, the VVT 1 is provided in which only the opening / closing timing of the intake valve is variable, but the VVT in which only the opening / closing timing of the exhaust valve is variable and the opening / closing timing of both the intake valve and the exhaust valve are provided. It is also possible to provide a VVT that makes each variable.

(3) In each of the above embodiments, the VVT 1 hydraulic control device is embodied in a gasoline engine, but the VVT hydraulic control device may be embodied in a diesel engine.

[0052]

As described above in detail, according to the present invention, in the variable valve timing mechanism for changing the valve timing by hydraulically driving the ring gear, the opening / closing drive is performed to control the hydraulic pressure supply to the ring gear. The control valve is duty-controlled based on a duty frequency synchronized with the torque fluctuation cycle of the camshaft that occurs when the intake / exhaust valve is driven to open and close. Therefore, the cyclic thrust force due to the torque fluctuation of the camshaft is added to the cyclic hydraulic pressure and added to the ring gear. Alternatively, the hydraulic pressure periodically applied in the axial direction of the ring gear acts to cancel the thrust forces periodically applied to the ring gear due to the torque fluctuation of the camshaft. As a result, when the valve timing is variable, a quick actuating response can be secured, and when the ring gear is held at the intermediate position, its position control can be stabilized, which is an excellent effect. .

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a variable valve timing mechanism and a hydraulic control device for driving the same in a first embodiment embodying the present invention.

FIG. 2 is a flowchart showing a “valve timing control routine” executed by an ECU in the first embodiment.

FIG. 3 is a graph showing a characteristic of a duty-controlled control valve in the first embodiment and showing a relationship between a duty ratio and a hydraulic pressure.

FIG. 4 is a map in which a relationship between a target advance angle value and an engine speed and a load equivalent value is predetermined in the first embodiment.

FIG. 5 is a map in which a relationship between a duty addition value and a lead angle deviation between a target lead angle value and a current lead angle value is predetermined in the first embodiment.

FIG. 6 is a diagram showing the torque fluctuation of the camshaft, the thrust force of the ring gear, the trigger pulse of the cam angle sensor, the energization of the solenoid of the control valve, the hydraulic pressure of the ring gear, and the resultant force of the hydraulic pressure, the spring force, and the thrust force in the first embodiment. 5 is a time chart showing the relationship of changes in

FIG. 7 is a schematic diagram of a second embodiment embodying the present invention.
It is a flow chart which shows a "valve timing control routine" performed by CU.

FIG. 8 is a second embodiment of the present invention, in which the camshaft torque variation, the ring gear thrust force, the cam angle sensor trigger pulse, the control valve solenoid energization, the ring gear hydraulic pressure, and the combined hydraulic pressure, spring force, and thrust force. 5 is a time chart showing the relationship of changes in

[Explanation of reference numerals] 2 ... cam shaft, 3 ... cylinder head, 4 ... timing pulley, 12 ... ring gear, 12a, 12b ... teeth, 1
7 ... Head oil passage, 18 ... Shaft oil passage, 27 ... Main oil passage, 28 ... Control valve, 31 ... ECU which constitutes duty control means.

Claims (1)

[Claims] 1. A cam shaft rotatably provided in a cylinder head of an internal combustion engine for opening and closing a valve for intake and exhaust, and a drive shaft connected to a crank shaft of the internal combustion engine provided at one end of the cam shaft. The timing pulley and at least one of the teeth provided on the inner and outer circumferences are helical teeth, which are interposed between the cam shaft and the timing pulley to connect them and to each other by moving in the axial direction. The camshaft and the ring gear rotatable relative to each other are provided, and the ring gear is moved in the axial direction by applying a hydraulic pressure to an axial end side of the ring gear through an oil passage between the camshaft and the timing pulley. A hydraulic control device for a variable valve timing mechanism that applies a twist to the camshaft by rotating the camshaft while rotating. A control valve that is provided in the middle of the oil passage and that is opened / closed to control the supply of hydraulic pressure to the ring gear, and torque fluctuations of the camshaft that occur when the intake / exhaust valve is opened / closed. A hydraulic control device for a variable valve timing mechanism, comprising: a duty control means for controlling the duty of the control valve based on a duty frequency synchronized with a cycle.