JPH07247814A - Variable valve timing mechanism - Google Patents

Abstract

PURPOSE:To effectively reduce by means of a simple means, back lash noise of a variable valve timing mechanism of an internal combustion engine, etc., provided with a helical spline. CONSTITUTION:A bellows 28 and a weight 29 which is installed on the top end thereof are provided in a vibration system having same natural frequency as a constant vibration number, by giving attention to a valve opened/closed by a cam opposing to a valve spring, so that the torque of a cams shaft 2 is fluctuated, a piston 12 performs rebounding operation to support reaction in axial direction which acts on helical splines 12b, 12c when the torque is transferred, and control oil pressure in oil pressure chambers 11, 14 makes pressure pulsation by the constant vibration number. Pressure pulsation in the oil pressure chamber 11 is offset by pressure pulsation whose phase is shifted by 1/2 of a cycle caused when the weight 29 is vibrated by receiving pressure pulsation in the oil pressure chamber 11, and collision is prevented between the helical splines 4b and 12b, and 7a and 12c.

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 for changing the opening / closing timing of valves such as intake valves and exhaust valves used in internal combustion engines.

[0002]

2. Description of the Related Art As disclosed in, for example, Japanese Patent Application Laid-Open No. 3-117604, in an internal combustion engine, power such as a timing belt from a crankshaft is mounted on a shaft of a camshaft that drives an intake valve and an exhaust valve to open and close. The timing pulley, which is rotatably driven by the transmission means, is supported so as to be rotatable relative to each other, and the camshaft side member and the timing pulley side member facing each other in an internal-external relationship and forming an annular gap therebetween are opposed to each other. In each of them, a helical spline having an inclination angle (twisting angle) opposite to each other is formed, and a helical spline that is inserted into a gap between the opposing surfaces and meshes with the helical splines is provided on the inner surface and the outer surface, This piston is controlled in the hydraulic cylinder by balancing the control oil pressure before and after the piston. By moving the shaft in the front-rear direction on the axis, the relative phase of the camshaft with respect to the timing pulley is changed steplessly, and the opening / closing timing of the intake valve and exhaust valve used in the internal combustion engine is changed during operation of the engine. There is known a variable valve timing mechanism which can be freely changed.

In such a variable valve timing mechanism, when the engine is operated at high speed, vibrations in which the teeth of the helical splines meshing with each other are repeatedly collided and separated from each other, causing a backlash noise (or a backlash noise). A noise called rattling noise or tapping noise may occur.

[0004]

It is believed that the direct cause of the backlash noise is the vibrational collision between the teeth of the helical spline, but the inventor who has further investigated the cause. In the variable valve timing mechanism of the type described above, the control hydraulic pressure supporting the hydraulic cylinder may cause pressure pulsation having a constant frequency, and the pressure pulsation causes the hydraulic piston to move. As a result of vibrating the camshaft in the axial direction at a constant frequency with a small amplitude, helical spline teeth formed on the inner and outer surfaces of the hydraulic piston,
We found that a vibrating collision occurred between the teeth of the opponent's helical spline and a backlash sound with a constant frequency was generated.

Generally, the magnitude of the reaction force generated when the cam provided on the camshaft of the internal combustion engine drives the valve fluctuates, so that the torque value of the camshaft also fluctuates finely. In the variable valve timing mechanism, the fluctuating torque is transmitted from the timing pulley to the camshaft via the meshing surfaces of the four helical splines, with the piston in the hydraulic cylinder as a foothold. The influence of the fluctuating torque also appears, and the control oil pressure fluctuates (pulsates) finely. When the pressure pulsation of the control hydraulic pressure matches the natural frequency of the system, resonance occurs and the pressure pulsation becomes strong, so that the pressure pulsation has a specific frequency.

Further, since some backlash (play) is inevitably present between the helical splines formed on the inner and outer surfaces of the piston and the surfaces of the opposing helical splines that mesh with them. Due to the overlapping of these causes, when the engine is rotating at high speed,
The collision and separation between the teeth of the helical splines that are meshed with each other is repeated, and noise called backlash sound (or rattling sound, tapping sound) is generated.

The present invention is based on the above-mentioned consideration and improves the prior art as described above. Therefore, in the variable valve timing mechanism having the helical spline operated by the piston of the hydraulic cylinder, the backlash is reduced. It is an object of the invention to provide a simple solution means having a configuration capable of effectively suppressing sound.

[0008]

As a means for solving the above-mentioned problems, the present invention provides a camshaft provided with a cam for opening and closing a valve, and a rotatably supported on the camshaft. A rotary drive member, a hydraulic cylinder integrated with the rotary drive member, a piston inserted into the hydraulic cylinder and slidable in the axial direction on the camshaft, and the hydraulic cylinder A helical spline formed on the side, a helical spline formed on the side of the camshaft, and a helical spline that is axially movable together with the piston and meshes with the two helical splines at the same time on both the outer and inner surfaces. And a rotation transmission member inserted between the two helical splines, and A vibration system including a weight provided to damp a pressure pulsation having a constant frequency and an elastic member supporting the weight, and two hydraulic chambers defined by the piston in the hydraulic cylinder. And a hydraulic control device for supplying a control hydraulic pressure to the variable valve timing mechanism.

[0009]

The basic operation of the variable valve timing mechanism is the same as the conventional one. When the cam of the camshaft opens and closes valves such as the intake valve and exhaust valve of the internal combustion engine against the valve spring, the torque acting on the camshaft fluctuates periodically, and the varying torque is The axial reaction force acting on the piston that supports one of the pair of meshing helical splines to be transmitted fluctuates, causing the piston to rebound within the backlash between the teeth of the meshing helical splines. , In the hydraulic chambers before and after the piston in the hydraulic cylinder,
Pressure pulsations are generated with a constant frequency determined by the structure.

In the variable valve timing mechanism of the present invention, the variable valve timing mechanism comprises a weight and an elastic member supporting the weight, and has a vibration system having a natural frequency substantially the same as the constant frequency of pressure pulsation in the hydraulic cylinder. Since the weight of the vibration system supported by the elastic member receives the pressure pulsation in the hydraulic cylinder and vibrates at the same frequency, another pressure that is out of phase by one half of the vibration cycle is generated. Generate pulsation in the hydraulic cylinder. These two pressure pulsations cancel each other out in the hydraulic cylinder, so that the pressure pulsations are substantially eliminated and the rebound motion of the piston is suppressed. As a result, the teeth of the helical spline provided on the piston are replaced by the teeth of the other helical spline. It is possible to reduce the backlash sound generated by the collision.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an enlarged view of a main part of a variable valve timing mechanism as a first embodiment of the present invention.
1 shows the entire structure of a variable valve timing mechanism similar to the conventional one, except for the main part of the first embodiment shown in FIG. Before explaining the first embodiment, FIG.
The entire configuration common to the conventional variable valve timing mechanism will be described below.

In FIG. 2, reference numeral 1 denotes a part of a cylinder head of an engine, and a cylinder around the end of a camshaft 2 which is supported inside thereof is a center of a timing pulley 3 in a relatively rotatable manner. The shaped hub portion 3a is loosely fitted. Reference numeral 4 denotes a deep dish-shaped housing which accommodates an actuator portion of the variable valve timing mechanism therein, and a flange portion around the housing is screwed to a disc portion 3b of the timing pulley 3 by several bolts 5. ing. Therefore, the housing 4 can also rotate integrally with the timing pulley 3 along the axis of the camshaft 2. For convenience of assembly, maintenance and inspection, repair, etc., a cap 6 separate from the housing 4 for closing the same is screwed into the central opening of the bottom of the housing 4 which is the left end in FIG. ing.

A gear plate 7 shaped like a gear is integrally attached to the end of the camshaft 2 by a head bolt 8, and the relative position of the gear plate 7 with respect to the camshaft 2 in the rotational direction. Are securely fixed by the positioning pins 9. Further, by fixing the gear plate 7 to the end portion of the cam shaft 2, the hub portion 3a of the timing pulley 3 is restrained, and the axial movement of the timing pulley 3 with respect to the cam shaft 2 is also prevented. However, as described above, the timing pulley 3 is rotatable relative to the cam shaft 2.

The camshaft 2 and the head bolt 8 are provided with hydraulic passages 2a and 8a, which communicate with each other, so as to penetrate through the respective central portions thereof.
Forming a hydraulic passage. First hydraulic passages 2a and 8
The right end of a is closed by the ball 10, but the left end is open to the space 11 in the housing 4, and this space serves as a “advance-side hydraulic chamber” described later.

The timing pulley 3 has a piston 12 which is substantially disc-shaped and has a cylindrical portion integrally formed on its left side surface.
The cylindrical surface of the hydraulic cylinder 4a is loosely fitted on the cylindrical hub portion 3a at the center of the piston so as to be relatively rotatable and axially slidable, and the outer peripheral portion of the piston 12 is formed on the inner surface of the large diameter portion of the housing 4. Is oil-tightly slidingly fitted. A seal ring 17 is inserted in the annular groove of the outer peripheral portion of the piston 12 in order to improve the sealing performance. In this way, the internal space of the housing 4 has two parts, that is, the hydraulic chamber 11 on the advance side which is the left side of the disk part of the piston 12 in FIG. 2 and the hydraulic chamber 14 on the retard side which is the right side of the disk part. Is divided into

Helical splines 12b and 12c are formed on a part of the outer surface and the inner surface of the cylindrical portion 12a of the piston 12, which is the "rotation transmitting member", and each of them has a large number of teeth inclined with respect to the axial direction. However, the teeth of the helical spline 12b and the teeth of the helical spline 12c are inclined in opposite directions. In the illustrated embodiment, the helical spline 12b has a right-hand thread and the helical spline 12c has a left-hand thread. As described above, the helical splines 12b and 12c have opposite inclinations, and they take positive and negative values in the inclination angle with respect to the axial direction of the camshaft 2, that is, in the twist angle, but either of the helical splines 12b or 12c. Since the same operation is performed even when the tooth trace is in the axial direction, the term "helical spline" is simply used in the present invention, but the inclination angle of either one of the helical splines is 0.
Can take the value of.

The helical spline 12b formed on the outer surface of the cylindrical portion 12a of the piston 12 meshes with the helical spline 4b formed on the inner surface of the small diameter portion of the housing 4, and at the same time, the helical spline formed on the inner surface of the cylindrical portion 12a. 12c meshes with a helical spline 7a formed on the outer peripheral surface of the gear plate 7. Therefore, the helical spline 4b on the inner surface of the housing 4 has a right-hand thread inclination angle according to the inclination of the tooth trace of the helical spline 12b of the piston 12, and the helical spline 7a on the outer surface of the gear plate 7 is the helical spline 12c. It has a left-hand thread inclination angle according to the inclination of the tooth trace.

A hydraulic chamber 11 on the advance side, which is a space on the left side of the piston 12 in the housing 4, has a camshaft 2
And the first hydraulic passages 2a and 8a formed in the central portion of the head bolt 8, the hole 2b of the camshaft 2, the annular groove 2
c and the first hydraulic passage 1a formed in the cylinder head 1 of the engine, the hydraulic pressure control valve 18 communicates with the first output opening 18a.

Further, the piston 1 in the housing 4
The hydraulic chamber 14 on the retarded angle side, which is the space on the right side of 2, has a hole 3c in the hub portion 3a of the timing pulley 3 and an annular groove 2d formed in a part of the outer periphery of the camshaft 2 in accordance therewith.
And a second hydraulic passage 2f axially formed at a position deviated from the center of the camshaft 2 through the hole 2e, and the second hydraulic passage 2f is further connected to the hole 2g of the camshaft 2. The second output opening 18b of the hydraulic control valve 18 communicates with the second hydraulic passage 1b formed in the cylinder head 1 of the engine through the annular groove 2h.

The hydraulic control valve 18 is generally called a spool valve because it has a spool 18c. The structure of the hydraulic control valve 18 is well known, so a detailed description thereof will be omitted. Driven solenoid 18
d is a plurality of units formed on the spool 18c as a result of receiving a dither control signal supplied from a well-known electronic control unit (ECU) 19, which is a control unit of the engine, and causing the spool 18c to reciprocate in the axial direction. The land portion is the first output opening portion 18a and the second output opening portion 18
Open and close b for a short time. Then, by changing the ratio of the total time during which the ECU 19 opens the output openings 18a and 18b, the oil pressurized and supplied by the oil pump 20, that is, the lubricating oil of the engine,
It can be distributed in an arbitrary ratio and discharged to the output openings 18a and 18b.

As described above, only one of the output openings 18a or 18b of the hydraulic control valve 18 communicates with the oil pump 20 for a short time, and the hydraulic chamber 11 on the advance side or the retarded side is delayed via the hydraulic passage. Oil is supplied to one of the hydraulic chambers 14 on the corner side, and by repeating this, an arbitrary amount of pressurized oil is supplied to the hydraulic chambers 11 or 14. At the same time as the oil is supplied to one hydraulic chamber, the same amount of oil is supplied from the other hydraulic chamber to the hydraulic control valve 18.
Through the drain passage 21 to the oil pan 22 of the engine. Therefore, the piston 12 is at an intermediate position where the axial forces generated by the control hydraulic pressures of the two hydraulic chambers 11 and 14 become equal, or at the movable range. It will move axially to the end. In the case of the structure shown in the figure, the control hydraulic pressures of the two hydraulic chambers 11 and 14 are the same value in the state where the axial force in the left-right direction is balanced and the piston 12 is stopped at the intermediate position.

When the piston 12 stops at any intermediate position within the movable range, the stop position is determined by the amount of oil remaining in the two hydraulic chambers 11 and 14, respectively. Therefore, by changing the content of the dither control signal generated by the ECU 19, each hydraulic chamber 11, 1
4 can be adjusted by finely adjusting the amount of oil supplied to piston 4.
It becomes possible to freely adjust the stop position of steplessly. Thereby, the opening / closing timing of the intake valve and the exhaust valve of the internal combustion engine can be smoothly changed.

In FIG. 2, 23 is a crankshaft,
Reference numeral 24 is a crank side timing pulley attached to the crankshaft 23, and 25 is a timing pulley 2
4 is a timing belt wound around the timing pulley 3; 26 is a crank angle sensor for detecting the rotation angle of the crankshaft 23; 27 is the camshaft 2;
2 shows a cam angle sensor for detecting the rotation angle of the. The sensors 26 and 27 are specifically magnetic pickups, and each time a protrusion of a rotating member such as a gear attached to the crankshaft 23 or the camshaft 2 generates an electric pulse signal. Therefore, the number is calculated by the ECU 19
By counting at, the rotation angle of each axis can be detected.

In such a variable valve timing mechanism, the rotation of half the rotational speed is transmitted from the crankshaft 23 to the driven side timing pulley 3 by the driving side timing pulley 24 and the timing belt 25. Rotation is helical spline 4b of housing 4
From the helical splines 12b and 12 of the piston 12
It is transmitted to a gear plate 7 having a helical spline 7a via c, and its rotation is transmitted from a positioning pin 9 to a cam shaft 2 to drive a cam (not shown). As a result, valves such as intake valves and exhaust valves open and close intake or exhaust ports formed in the combustion chamber of the internal combustion engine.

The relative phase relationship between the timing pulley 3 and the camshaft 2 can be freely changed by the action of the two pairs of helical splines meshing with each other by moving the piston 12 in the axial direction. As described above, the axial position of the piston 12 controls the amount of oil supplied to the hydraulic chamber 11 on the advance side and the hydraulic chamber 14 on the retard side by the hydraulic control valve 18 operated by a command from the ECU 19. It depends on what you do. The ECU 19 receives the signals generated by the cam angle sensor 27, the crank angle sensor 26, and the like to calculate the cam phase and the rotation speed, and compares them with map data of the optimum cam phase for the operating conditions of the internal combustion engine. A dither control signal is generated to reduce the difference between the actual cam phase and the map data value, and the current supplied to the solenoid 18d of the hydraulic control valve 18 is interrupted.

When the amount of oil in the hydraulic chamber 11 on the advance side increases and the control hydraulic pressure rises due to the action of the hydraulic control valve 18, the piston 12 is pushed to the right in FIG.
Since the cylindrical portion 12a of the piston 12 and the housing 4 are engaged with each other by the right-handed helical splines 12b and 4b, the piston 12 is rotated clockwise with respect to the housing 4 as viewed from the left side of FIG. Also,
Piston 12 and gear plate 7 are helical splines 1
Since they are meshed with each other by 2c and 7a, the gear plate 7 is rotated clockwise with respect to the piston 12 together with the cam shaft 2 by the rightward movement of the piston 12 as described above. In this way, the camshaft 2
The timing of the valve driven by the piston 12
Will be advanced by the amount moved in the axial direction.

On the contrary, when the spool 18c of the hydraulic control valve 18 is moved by the control signal of the ECU 19 and the oil is supplied to the hydraulic chamber 14 on the retard side, the piston 12 is moved leftward and the camshaft is moved. The timing of the valve driven by 2 will be retarded. In this way, the timing pulley 3, and thus the crankshaft 2
The phase of the camshaft 2 with respect to 3 is adjusted steplessly. In the first embodiment shown in FIG. 1 and the second embodiment to be described later shown in FIG. 3 as well, the basic operation described above is not shown in FIG.
This is similar to that of the conventional variable valve timing mechanism shown in FIG.

In the case of an internal combustion engine, the cam nose of a cam (not shown) mounted on the cam shaft 2 reciprocates the valve against the biasing force of the valve spring to open and close the intake or exhaust port. When the valve spring is being compressed to increase the opening of the valve, the valve spring exerts a torque on the camshaft 2 in a direction opposite to the rotational direction of the camshaft 2. On the contrary, when the cam nose is closing the valve, the torque by the valve spring acts in the same direction as the rotation direction of the camshaft 2. As described above, since the cam noses of a large number of cams provided on the camshaft 2 are pushed by the valve spring, the torque acting in the same direction as the rotation direction and the torque acting in the opposite direction are repeatedly reversed on the camshaft 2 periodically. Will work.

The torque that fluctuates in this way is the piston 1
2 as a foothold, 2 pairs of helical splines 4b,
Since it is transmitted from the camshaft 2 to the timing pulley 3 or vice versa through the meshing parts of 12b and 7a, 12c, contact and separation occur oscillatingly repeatedly between the surfaces of the meshing parts of the helical spline, The piston 12 will make a motion that should be called "rebounding motion" during the backlash of the helical spline,
It is considered that this causes a backlash sound as a tapping sound. The cycle or frequency of the rebound motion is mainly determined by the structure of the entire actuator of the variable valve timing mechanism housed in the housing 4, and does not change even if the rotational speed of the camshaft 2 changes.

When a fluctuating torque that causes a backlash sound is transmitted through two pairs of helical splines, the pistons 12 on both sides supporting the piston 12 at a fixed axial position in the hydraulic cylinder 4a. The oil pressure also changes finely (pressure pulsation). The hydraulic system mainly including the hydraulic cylinder 4a and the piston 12 has a natural frequency of pressure pulsation. When the pressure pulsation based on the fluctuation of the transmitted torque matches the natural frequency, resonance occurs and the pulsation becomes stronger. Since it should be, the natural frequency of the hydraulic system is also considered to be one of the factors that determine the constant frequency of the backlash noise.

Therefore, the present invention is intended to suppress the backlash noise by damping the pressure pulsation in the hydraulic system. In the first embodiment, as shown in FIG. 1, the cap 6 of the housing 4 is used. Is provided with a bellows 28 made of a flexible material such as thin steel or stainless steel, a weight 29 is attached to the tip of the bellows 28, and the internal space 30 of the bellows 28 is advanced to the hydraulic chamber 11 on the advance side.
Is in communication with. The space 30 is filled with oil in the hydraulic chamber 11, and due to the rebounding motion of the piston 12, pressure pulsation with a constant frequency is also transmitted, and the volume (or pressure) of the space 30 fluctuates. Although 29 vibrates, the natural frequency determined by the spring constant of the bellows 28, the mass of the weight 29, etc. is designed to match the constant frequency of the pressure pulsation and the rebounding motion of the piston 12.

Since the weight 29 is vibrated by receiving the pressure pulsation of the oil in the hydraulic chamber 11 on the advance side, the weight 29 has another pressure pulsation that is out of phase with one half of the cycle even at the same frequency. Is generated in the hydraulic chamber 11,
These two pressure pulsations cancel each other out, and the pressure pulsations in the hydraulic chamber 11 disappear substantially. As a result, the rebounding motion of the piston 12 in the backlash between the helical spline 12b and the helical spline 4b that mesh with each other and between the helical spline 12c and the helical spline 7a is suppressed, and the backlash noise is also reduced.

FIG. 3 shows a second embodiment of the present invention, in which a disc-shaped weight 31 having a diameter slightly smaller than the inner diameter of the hydraulic cylinder 4a is inserted in the hydraulic chamber 14 on the retard side. It is attached to the piston 12 via a spring 32. In this case as well, the weight 31 determined by the mass of the disk-shaped weight 31, the spring constant of the spring 32, and the like.
Is designed to be equal to the frequency of the rebounding movement of the piston 12, and hence the frequency of the pressure pulsation of the oil in the hydraulic chamber 14.

The weight 31 is vibrated by the pressure pulsation of the oil in the hydraulic chamber 14, so that the weight 3
1 generates another pressure pulsation in the hydraulic chamber 14 with the same frequency and a phase shift of ½ of the cycle. The pressure pulsations in the hydraulic chamber 14 are substantially eliminated by the cancellation of these two pressure pulsations. As a result, the rebounding movement of the piston 12 in the backlash between the teeth of the helical splines that mesh with each other is suppressed, so that the impact when the teeth of the helical splines collide is mitigated and the backlash noise is reduced.

In the illustrated embodiment, the engine oil (lubricating oil) of the engine is used as the hydraulic oil of the hydraulic control system in the variable valve timing mechanism, so the oil pump 2
No. 0 can be used as it is for supplying lubricating oil, but in the present invention, the hydraulic control system of the variable valve timing mechanism is separated from the lubricating oil supply system of the engine and another hydraulic oil and oil pump 20 are used. It goes without saying that an independent hydraulic system may be used.

The camshaft 2 is driven from the crankshaft 23 via the timing pulley 24 on the crank side, the timing belt 25, and the timing pulley 3. The timing belt 25 is a timing chain. Since it may be present, in that case, the sprocket is used as the one corresponding to the timing pulleys 3 and 24. Further, the timing pulley 3 may be a timing gear. Therefore, the timing pulley 3 should generally be called a "rotational drive member" for the variable valve timing mechanism.

[0037]

According to the present invention, the backlash noise of the helical spline can be efficiently reduced by adding a simple vibration mechanism to the variable valve timing mechanism operated by the piston of the hydraulic cylinder having the helical spline. This has the advantage that the cost can be increased only slightly.

[Brief description of drawings]

FIG. 1 is a side sectional view showing a main part of a first embodiment of the present invention.

FIG. 2 is a side view including a partial cross section showing the entire configuration of the variable valve timing mechanism.

FIG. 3 is a side sectional view showing a main part of a second embodiment of the present invention.

[Explanation of symbols]

 2 ... Camshaft 3 ... Timing pulley (rotational drive member) 4 ... Housing 4a ... Hydraulic cylinder 4b ... Helical spline 7 ... Gear plate 7a ... Helical spline 11 ... Advance side hydraulic chamber 12 ... Piston 12a ... Cylinder part of piston ( Rotation transmission member) 12b, 12c ... Helical spline 14 ... Retardation side hydraulic chamber 18 ... Hydraulic control valve 18c ... Spool 18d ... Solenoid 19 ... ECU (control device) 20 ... Oil pump 23 ... Crankshaft 24 ... Crank side timing Pulley 25 ... Timing belt 28 ... Bellows 29 ... Weight 30 ... Space 31 ... Disc-shaped weight 32 ... Spring

Claims (3)

[Claims] 1. A camshaft having a cam for opening and closing a valve, a rotary drive member rotatably supported on the camshaft, and a hydraulic cylinder integrated with the rotary drive member. A piston that is inserted into the hydraulic cylinder and can slide axially on the camshaft; a helical spline formed on the hydraulic cylinder side; and a helical spline formed on the camshaft side; Is movable in the axial direction together with the piston,
A helical spline that meshes with two helical splines at the same time is provided on both the outer surface and the inner surface, and a rotation transmission member inserted between the two helical splines and a pressure pulsation with a constant frequency in the hydraulic cylinder are damped. And a vibration system including an elastic member that supports the weight, and a hydraulic control device that selectively supplies control hydraulic pressure to two hydraulic chambers defined by the piston in the hydraulic cylinder. And a variable valve timing mechanism. 2. The variable valve timing mechanism according to claim 1, wherein the vibration system including a weight and an elastic member supporting the weight is attached to a cap of a housing forming the hydraulic cylinder. . 3. The variable valve timing mechanism according to claim 1, wherein the vibration system including a weight and an elastic member supporting the weight is attached to a piston in the hydraulic cylinder.