JPH0968018A - Engine valve gear - Google Patents

Abstract

(57) [Abstract] [Object] An object of the present invention is to obtain several kinds of valve lifts and valve timings by one kind of cam profile to improve engine performance in a wide range of engine operating conditions. Therefore, according to the present invention, a low-speed rocker arm that is swung about the low-speed rocker arm center and a medium-high speed rocker arm that is swung around the middle-high speed rocker arm center are provided, and the rocker arm lever ratio is variable. The rocker arm center for low speed and the rocker arm center for medium and high speed are arranged so as to be deviated, and the arc center of the sliding member for low speed of the low speed rocker arm and the medium and high speed rocker arm for medium and high speed are arranged to vary the valve timing. A plurality of interlocking members that are arranged so as to deviate from the arc center of the sliding member and that engage the low-speed rocker arm and the medium-high speed rocker arm are provided, and these interlocking members are selected according to the engine operating state. The actuating means for actuating automatically is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a valve operating system for an engine, and more particularly to an engine capable of obtaining several types of valve lifts and valve timings by one type of cam profile to improve engine performance in a wide range of engine operating conditions. Related to the valve operating device.

[0002]

2. Description of the Related Art Some vehicle engines are provided with a valve operating device for varying valve lift and valve timing of intake and exhaust valves in order to improve various required functions.

As a form of such a valve operating device, for example, there is a cam profile switching type.

This cam profile switching type valve operating device is provided with a low speed cam and a middle and high speed cam on the cam shaft, the low speed cam rocks the low speed rocker arm, and the middle and high speed cam drives the middle and high speed cams. Rocker arm for rocking, which allows the low speed rocker arm to open and close the intake and exhaust valves at low speed, while
The intake and exhaust valves are opened and closed by the rocker arm for medium and high speed.

As a valve operating system for such an engine,
For example, it is disclosed in JP-A-2-123215. The publication described in this publication opens and closes an intake / exhaust valve by pushing down the intake / exhaust valve by the rotation of a cam of a cam shaft that is interlocked with a crankshaft, and the tip of a sliding rod that slides along a guide. One end of a cam plate whose upper and lower surfaces have different curvatures is attached to the shaft, the cam plate is interposed between the cam and the intake / exhaust valve, and the sliding rod is slid according to the engine speed. is there.

[0006]

However, conventionally, in the valve operating system of the engine, as many cam profiles as the required number of valve lifts are required. Therefore, there are two types of cam profiles for the low speed cam and the medium and high speed cams. Cam profiles are required, and as a result, cam profiles and rocker arms are required for the required number of valve lifts.
In reality, due to the space limitation of the valve operating chamber, only two stages of variable valve lift and variable valve timing can be obtained, and there is a disadvantage that the engine performance cannot be improved in a wide range of engine operating conditions.

[0007]

Therefore, in order to eliminate the above-mentioned inconvenience, the present invention provides a cylinder head of an engine with a cam shaft pivotally supported, and the rotation of the cam of the cam shaft causes a rocker arm to intervene. An engine valve operating device for opening and closing intake and exhaust valves is provided with a low speed rocker arm that is swung around a low speed rocker arm center and a medium and high speed rocker arm that is swung around a middle and high speed rocker arm center. The low-speed rocker arm center and the medium-high speed rocker arm center are arranged so as to be displaced so as to change the lever ratio, and the arc center of the low-speed sliding member of the low-speed rocker arm and the arc center of the low-speed rocker arm so as to change the valve timing. The rocker arm for medium and high speeds is arranged with the center of the arc of the sliding member for medium and high speeds offset from each other, and the rocker arm for low speed and the medium and high speed A plurality of interlocking members operable to engage a Kkaamu provided, characterized in that these interlocking member provided with actuating means for selectively operates in response to engine operating conditions.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention changes the engagement position between a low speed rocker arm and a medium and high speed rocker arm by selectively actuating an interlocking member in accordance with the engine operating state, thereby changing the rocker arm lever ratio. Therefore, it is possible to obtain a plurality of required valve lifts and a plurality of valve timings with one type of cam profile, and thus, in a wide range of engine operating conditions without increasing the number of cam profiles and rocker arms. The engine performance can be improved.

[0009]

Embodiments of the present invention will be described in detail and specifically with reference to the drawings. 1 to 19 show an embodiment of the present invention. In FIG. 1, 2 is a 4-cycle engine, 4 is a cylinder head, 6 is a combustion chamber, 8 is an intake port, 10 is an exhaust port, and 12 is a valve train.

This valve operating device 12 is an intake system valve operating device 12.
-1 and an exhaust system valve operating device 12-2.

In the intake system valve operating device 12-1, an intake cam shaft 14 is axially supported by the cylinder head 4, and an intake cam 16 is provided on the intake cam shaft 14. An intake low speed rocker arm 18 and an intake middle high speed rocker arm 20 that swing by rotation are provided.
An intake valve 22 that reciprocates by swinging the intake low speed rocker arm 18 and the intake high speed rocker arm 20 is provided.

The intake valve 22 is slidably supported by an intake valve guide 24 held by the cylinder head 4.
The intake port 28 formed by the intake valve seat 26 is opened and closed. The intake valve 22 is provided with an intake rocker arm abutting portion 30 and an intake first spring receiving portion 32 on the tip side, and is installed on the intake first spring receiving portion 32 and the cylinder head 4. The intake valve spring 3 is provided between the intake second spring receiving portions 34.
6 is fitted.

As shown in FIG. 2, the low speed intake rocker arm 18 has a base end 18a having a low intake speed rocker arm shaft 38.
It is provided so that it can swing. An intake low speed sliding member 40 that contacts the intake cam 16 and an intake valve low speed contact portion 42 that contacts the intake rocker arm contact portion 30 of the intake valve 22 are provided at the tip end portion 18b of the intake low speed rocker arm 18. There is.

As shown in FIG. 2, the intake mid-high speed rocker arm 20 has a base end portion 20a swingably provided on the mid-intake high speed rocker arm shaft 44 and is arranged in parallel with the low-speed intake rocker arm 18. . An intake arm spring receiving portion 46 is provided at a base end portion 20a of the rocker arm 20 for intake and high speed. At the tip portion 20b of the rocker arm 20 for high intake air speed, a sliding member 48 for high intake air speed is provided in contact with the intake cam 16.

As shown in FIG. 2, the intake low speed rocker arm center 38c, which is the axis of the intake low speed rocker arm shaft 38, is shown.
And the intake-medium-high speed rocker arm shaft center 44c, which is the shaft center of the intake-medium-high speed rocker arm shaft 44, are arranged not on the same axis center but on a biased manner so as to change the rocker arm lever ratio (R). ing.

The intake arm return spring receiving portion 46 provided at the base end portion 20a of the rocker arm 20 for intake and high speed has an intake return spring 52 inserted into an intake return spring holding hole 50 formed in the cylinder head 4. It is locked and provided.

On the side surface of the tip portion 18b of the intake low speed rocker arm 18, the intake low speed rocker arm 18 is provided.
As a plurality of intake interlocking members for engaging the front end portion 20b of the rocker arm 20 for intake and high speed, for example, the intake first interlocking pin 54 (interlocking pin 1) and the second intake interlocking pin 56 (interlocking pin 2). And are provided in parallel.

On the other hand, in the exhaust system valve operating device 12-2, an exhaust cam shaft 58 is pivotally mounted on the cylinder head 4, and an exhaust cam 60 is mounted on the exhaust cam shaft 58.
An exhaust low speed rocker arm 62 and an exhaust medium high speed rocker arm 64 that swing by the rotation of the exhaust cam 60 are provided, and an exhaust valve 66 that reciprocates by the swing of the exhaust low speed rocker arm 62 and the exhaust high speed rocker arm 64 is provided. It is provided.

The exhaust valve 66 is slidably supported by an exhaust valve guide 68 held by the cylinder head 4,
The exhaust port 72 formed by the exhaust valve seat 70 is opened and closed. The exhaust valve 66 is provided with an exhaust rocker arm contact portion 70 on the tip side and an exhaust first spring receiving portion 76, and is installed on the exhaust first spring receiving portion 76 and the cylinder head 4. The exhaust valve spring 8 is provided between the exhaust second spring receiving portions 78.
0 is fitted.

As shown in FIG. 3, the low speed exhaust rocker arm 62 has a base end portion 62a having an exhaust low speed rocker arm shaft 82.
It is provided so that it can swing. An exhaust speed low speed sliding member 84 that contacts the exhaust cam 60 and an exhaust valve low speed contact portion 86 that contacts the exhaust rocker arm contact portion 74 of the exhaust valve 66 are provided at the tip 62b of the exhaust low speed rocker arm 62. There is.

As shown in FIG. 3, the rocker arm 64 for high-speed exhaust air is provided such that its base end portion 64a is swingable on the rocker arm shaft 88 for high-speed exhaust air, and is arranged in parallel with the rocker arm 62 for low speed exhaust. . An exhaust arm spring receiving portion 90 is provided at a base end portion 88a of the rocker arm 88 for high speed during exhaust. At the tip portion 64b of the rocker arm 64 for high speed during exhaust gas, a sliding member 92 for high speed during exhaust gas which is in contact with the exhaust cam 60 is provided.

As shown in FIG. 3, the intake low speed rocker arm center 82c which is the axis of the exhaust low speed rocker arm shaft 82.
And a center 88c of the rocker arm shaft for medium- and high-speed intake, which is the shaft center of the rocker arm shaft 88 for middle-and-intake of intake, is arranged not on the same axis center but in a biased manner so as to change the rocker arm lever ratio (R). ing.

Further, an exhaust arm return spring receiving portion 90 provided at the base end portion 64a of the rocker arm 64 for high speed during exhaust is provided with an exhaust return spring 96 inserted into an exhaust return spring holding hole 94 formed in the cylinder head 4. It is locked and provided.

Further, on the side surface of the tip portion 62b of the low speed exhaust rocker arm 62, the low speed exhaust rocker arm 62 is provided.
And a plurality of exhaust interlocking members for engaging the tip portion 64b of the rocker arm 64 for high speed during exhaust with, for example, an exhaust first interlocking pin 98 (interlocking pin 1) and an exhaust second interlocking pin 100 (interlocking pin 2). And are provided in parallel.

The intake first and second intake interlocking pins 54 and 56 of the intake system valve gear 12-1 and the exhaust first and exhaust second interlocking pins 98 and 100 of the exhaust system valve gear 12-2 are intake low speeds. The rocker arm 18 and the low speed exhaust rocker arm 62 are provided in the same manner, and are actuated by actuating means 120 described later. Therefore, only the intake system valve operating device 12-1 will be described below.

As shown in FIG. 5, in the interlocking mechanism 102 provided with the intake first and intake second interlocking pins 54 and 56, the intake first and second intake interlocking pins 54 and 56 of the intake low speed rocker arm 18 are provided. The first and second intake pin holes 104, 106 formed on the side surface of the tip portion 18 are provided so as to be retractable.

The first intake interlocking pin 54 is the first intake pin hole 1
No. 04 inside the first intake pin hole 104 by the urging force of the intake first spring 112 compressed between the intake first installation groove 108 and the intake second installation protrusion 110 formed on the intake first interlocking pin 54. Is biased to be housed in. Further, the intake second interlocking pin 56 is provided in the intake second pin hole 1
Inside the second intake pin hole 106 by the urging force of the intake second spring 118 compressed between the intake second installation groove 114 formed on the inner surface of 06 and the intake second installation protrusion 116 formed on the intake second interlocking pin 56. Is biased to be housed in. The biasing force of the intake first spring 112 is smaller than the biasing force of the intake second spring 118. Therefore, the relationship between the operating pressure (Pp1) of the intake first interlocking pin 54 and the operating pressure (Pp2) of the intake second interlocking pin 56 is P
p1 <Pp2.

Intake first and second intake interlocking pins 54, 56
Is, for example, selectively actuated by the hydraulic actuating means 120 according to the engine operating state.

In this operating means 120, the intake low-speed rocker arm 18 communicates with the first hydraulic chamber 122 communicating with the intake first pin hole 104 and the first hydraulic chamber 122 via the hydraulic chamber communication passage 124. A second hydraulic chamber 126 and a rocker arm oil passage 128 communicating with the first and second hydraulic chambers 122 and 126 are formed. The rocker arm oil passage 128 communicates with a shaft oil passage 130 formed in the intake low speed rocker arm shaft 38.

The shaft oil passage 130 communicates with the connecting oil passage 132 and the supply oil passage 134 formed in the cylinder head 4. Oil supplied under pressure from an oil pump (not shown) is supplied to the supply oil passage 134 at a pressure (Po).

The supply oil passage 134 is in communication with first and second relief passages 136 and 138. The first relief passage 135 includes a first solenoid valve 140 that opens and closes the first relief passage 136, and a first relief valve (relief valve 1) 142 that opens when a predetermined oil pressure (Pv1) acts. They are provided in sequence. Further, in the second relief passage 138, a second solenoid valve 144 for opening and closing the second relief passage 138,
A second relief valve (relief valve 2) 146 that opens at a pressure (Pv2) larger than the pressure (Pv1) that opens the first relief valve 142 is sequentially provided.

Operating pressure of intake first interlocking pin 54 (Pp
1), the operating pressure (Pp2) of the intake second interlocking pin 56, the pressure of the supplied oil (Po), the valve opening pressure (Pv1) of the first relief valve 142, and the valve opening pressure (Pv) of the second relief valve 146.
The relationship with 2) is Pv1 <Pp1 <P as shown in FIG.
v2 <Pp2 ≦ Po.

First and second solenoid valves 140, 144
Is in contact with the control unit 148. This control unit 148
Is for selectively opening and closing the first and second solenoid valves 140, 144 depending on the engine operating state, that is, low speed, medium speed, and high speed.

Further, the intake low speed rocker arm 18 and the intake high speed rocker arm 20 have an arc center 40 of the intake low speed sliding member 40 so that the valve timing can be varied.
c and the arc center 48c of the intake / high speed sliding member 48 are arranged so as to be offset.

That is, as shown in FIG. 15, the center line C1 connecting the center of the intake low speed sliding member 40 and the center 14c of the intake camshaft 14 is extracted to determine the radius of the arc of the intake low speed sliding member 40. When R, the arc center 40c of the intake low speed sliding member 40 exists on the center line C1. Further, if a centerline C2 connecting the center of the intake-medium-high speed sliding member 48 and the center 14c of the intake camshaft 14 is extracted and the radius of the arc of the intake-medium high-speed sliding member 48 is R, the intake-medium high-speed can be obtained. The arc center 48c of the sliding member 48 exists on the center line C2. The arc center 48c of the intake / high speed sliding member 48 is displaced from the center 14c of the intake camshaft 14 by an angle α in the cam rotation direction.

Alternatively, as shown in FIG. 18, a centerline C1 connecting the center of the intake low speed sliding member 40 and the center 14c of the intake camshaft 14 is extracted to determine the radius of the arc of the intake low speed sliding member 40. When R, the arc center 40c of the intake low speed sliding member 40 exists on the center line C1. Further, the center of the sliding member 48 for high speed during intake and the center 14c of the intake camshaft 14
The center line C2 connecting the and is extracted, and the sliding member for high speed during intake 4
When the radius of the circular arc 8 is R, the sliding member for high speed during intake 4
The arc center 48c of 8 exists on the center line C2. The arc center 48c of the sliding member 48 for high speed during intake
Is displaced from the center 14c of the intake camshaft 14 by an angle α in the counter-cam rotation direction.

Next, the operation of this embodiment will be described.

In the description of the operation of this embodiment, since the intake system valve operating device 12-1 and the exhaust system valve operating device 12-2 have the same structure and function, the intake system valve operating device 12-1 will be described. Only explained.

When the engine 2 is operating at a low speed, as shown in FIG. 6, the first and second solenoid valves 140,
144 is opened by the controller 148,
Since the first and second relief valves 142 and 146 are opened by the pressure (Po) of the supply oil, the pressure of the oil in the supply oil passage 134 is reduced to Pv1. Therefore, at this pressure Pv1, the intake first, intake second Interlocking pins 54, 5
6 does not operate due to the urging force of the intake first and second intake springs 112 and 118.

Therefore, at this low speed, as shown in FIG. 7, during full lift, the intake / high speed rocker arm 20 is in a free state, and the intake valve 22 is pushed by the intake low speed rocker arm 18. At this time, the valve lift is H1.

At this low speed, as shown in FIG. 8, during the base circle, the intake valve 22 closes the intake port 28, and the intake low speed rocker arm center 38c.
And the length between the center 54c of the intake first interlocking pin 54 is A1, and the length between the intake low speed rocker arm center 38c and the circular arc center 40c of the intake low speed sliding member 40 is B1.
The rocker arm lever ratio R1 is R1 = A1 / B1.

When the engine 2 is operating at medium speed, the second solenoid valve 14 is opened by the controller 148 as shown in FIG. 9, but the first solenoid valve 140 is opened by the controller 148. When closed, the second
The relief valve 146 is opened by the pressure (Po) of the supplied oil to reduce the oil pressure to Pv2. As a result, only the intake first interlocking pin 54 operates against the biasing force of the intake first spring 112, and the intake first interlocking pin 54 causes the tip end portion 20 of the high-speed rocker arm 20 during intake to move.
By engaging the lower surface of b, the high speed rocker arm 20 is operated during intake.

Therefore, at a medium speed, as shown in FIG.
Rocker arm 2 for high speed during intake
0 operates the intake low speed rocker arm 18. At this time, the valve lift becomes H2, which is slightly larger than the valve lift H1 at low speed.

At this medium speed, as shown in FIG.
At the time of the base circle, the length between the intake mid-high speed rocker arm center 44c and the center 54c of the intake first interlocking pin 54 is set to A2, and the arc of the intake mid-speed rocker arm center 44c and the intake mid-high speed sliding member 48 is set. Assuming that the length between the centers 48c is B2, the rocker arm lever ratio R2 is R2 = A
It becomes 2 / B2.

Further, when the engine 2 is operating at high speed, as shown in FIG. 12, the first and second solenoid valves 1
Since the control unit 148 closes the valves 40 and 144, the pressure (Po) of the supply oil is higher than the operating pressures (Pp1, Pp2) of the first and second interlocking pins 54 and 56. The two interlocking pins 54 and 56 operate against the biasing forces of the intake first and second intake springs 112 and 118 to engage with the lower surface of the tip end portion 20b of the intake high speed rocker arm 20, thereby lowering the intake low speed rocker arm 18 To operate.

For this reason, at this high speed, as shown in FIG. 13, at the time of full lift, the intake second interlocking pin 56 engages with the lower surface of the tip end portion 20b of the intake high speed rocker arm 20, and this intake high speed rocker arm. 20 is operated. At this time, the valve lift becomes H3 larger than the valve lift H2 at the medium speed.

At this high speed, as shown in FIG. 14, at the time of the base circle, the intake first and second intake interlocking pins 54 and 56 are engaged with the intake high speed rocker arm 20 to center the intake high speed rocker arm. The length between 44c and the center 56c of the second intake interlocking pin 56 is set to A3, and the rocker arm center 44c for intake high speed and the sliding member 4 for high intake speed 4
When the length between the arc centers 48c of 8 is B2, the rocker arm lever ratio R3 is R3 = A3 / B2.

As described above, the exhaust system valve operating device 12-
In No. 2, since the same operation as the intake system valve operating device 12-1 is performed, the description thereof will be omitted here.

As a result, in this embodiment, the intake first and second intake interlocking pins 5 are selected depending on the engine operating condition.
By selectively retracting 4 and 56, the engagement position between the intake low-speed rocker arm 18 and the intake mid-high speed rocker arm 20 changes, and the rocker arm lever ratio changes, so a valve lift can be performed with one type of cam profile. Can be changed.

Further, as shown in FIGS. 13 to 19, when the valve lift is switched by the direction in which the arc center 40c of the intake low speed sliding member 40 and the arc center 48c of the intake high speed sliding member 48 are displaced. , Valve timing changes.
For example, when the valve lift is switched during medium-high speed operation, the arc center 40c of the intake low-speed sliding member 40 and the arc center 48c of the intake medium-high speed sliding member 48 are deviated by an angle α. The low speed rocker arm 18 pushes the intake valve 22, and the intake / medium / high speed rocker arm 20 starts contacting the intake cam 16 with a delay of the crank angle of 2α, and switches from the intersection points a and b of each lift to the valve lift at middle and high speeds. Therefore, the intake valve 22 is closed with a delay of 2α due to the valve lift at low speed. Therefore, as shown in FIG. 17, the valve overlap amount that greatly affects the engine performance,
The closing timing of the intake valve 22 can be changed.

As a result, several kinds of valve lifts can be obtained with one kind of cam profile, and several kinds of valve timings can be obtained with one kind of cam profile. Therefore, valve lifts can be obtained according to engine operating conditions. Since the curve and valve timing can be obtained, the engine performance can be improved in a wide range of engine operating conditions.

Further, if the number of interlocking pins is increased, the number of valve lifts is increased, while it is not necessary to increase the number of rocker arms and cam profiles, the structure is simple, and the number of processing steps can be reduced.

[0053]

As is apparent from the above detailed description, according to the present invention, a low speed rocker arm swung around the low speed rocker arm center and a medium high speed rocker rocked around the middle and high speed rocker arm center. A rocker arm is provided, and the low-speed rocker arm center and the middle-high speed rocker arm center are eccentrically arranged so as to change the rocker arm lever ratio, and the arc of the low-speed rocker arm low-speed sliding member is changed so as to change the valve timing. The center and the arc center of the medium-high speed sliding member for medium-high speed rocker arm are arranged so as to be deviated, and a plurality of interlocking members that operate to engage the low-speed rocker arm and the medium-high speed rocker arm are provided. By providing the operating means for selectively operating the interlocking member according to the engine operating state, the interlocking member can be selectively operated according to the engine operating state. By moving the rocker arm for low speed and the rocker arm for medium and high speed to change the engagement position, it is possible to obtain a plurality of required valve lifts and a plurality of valve timings with one type of cam profile. It can improve engine performance over a wide range of engine operating conditions without increasing the number of profiles or rocker arms.

[Brief description of drawings]

FIG. 1 is a sectional view of an engine.

FIG. 2 is a side view of an intake system valve operating device.

FIG. 3 is a side view of an exhaust system valve operating device.

FIG. 4 is a configuration diagram of an operating means.

5 is an enlarged view of a main part of an interlocking pin portion of FIG.

FIG. 6 is a configuration diagram of actuating means at low speed.

FIG. 7 is a side view of the intake system valve operating device during a full lift at a low speed.

FIG. 8 is a side view of the intake system valve operating device in the base circle at a low speed.

FIG. 9 is a configuration diagram of actuating means at a medium speed.

FIG. 10 is a side view of the intake system valve operating device at the time of full lift at medium speed.

FIG. 11 is a side view of the intake system valve operating device at the time of the base circle at the medium speed.

FIG. 12 is a configuration diagram of actuating means at high speed.

FIG. 13 is a side view of the intake valve operating device during full lift at high speed.

FIG. 14 is a side view of the intake system valve operating device during base circle operation at high speed.

FIG. 15 is a side view of the intake system valve operating device in a state in which the arc center of the sliding member of the medium-high speed rocker arm is displaced in the cam rotation direction.

FIG. 16 is a diagram showing a valve lift when the arc center of the sliding member of the medium-high speed rocker arm is displaced in the cam rotation direction.

FIG. 17 is another diagram showing the valve lift when the arc center of the sliding member of the medium-high speed rocker arm is displaced in the cam rotation direction.

FIG. 18 is a side view of the intake system valve operating device in a state in which the arc center of the sliding member of the medium-high speed rocker arm is displaced in the counter cam rotation direction.

FIG. 19 is a view showing a valve lift when the arc center of the sliding member of the medium-high speed rocker arm is displaced in the anti-cam rotation direction.

[Explanation of symbols]

 2 engine 4 cylinder head 12 valve operating device 14 intake cam shaft 18 intake low speed rocker arm 20 intake medium high speed rocker arm 38 intake low speed rocker arm shaft 40 intake low speed sliding member 44 intake medium high speed rocker arm shaft 48 intake medium high speed slide Moving member 54 Intake first interlocking pin 56 Intake second interlocking pin 120 Actuating means

Claims (1)

[Claims] 1. A valve operating device for an engine, wherein a cam shaft is axially supported by a cylinder head of an engine, and the intake / exhaust valve is opened / closed via a rocker arm by rotation of the cam of the cam shaft. A low-speed rocker arm that is swung around the center and a medium-high speed rocker arm that is swung around the middle-high speed rocker arm center are provided, and the low-speed rocker arm center and the middle-high speed rocker arm center are provided so that the rocker arm lever ratio can be changed. Are arranged so as to be deviated, and the arc center of the low-speed sliding member of the low-speed rocker arm and the arc center of the medium-high-speed sliding member of the medium-high speed rocker arm are deviated so as to vary the valve timing. A plurality of interlocking members that are arranged to operate to engage the low-speed rocker arm and the medium-high speed rocker arm, A valve operating system for an engine, further comprising an operating means for selectively operating the interlocking member according to an engine operating state.