JPH0242109A - Valve mechanism for internal combustion engine - Google Patents

Abstract

PURPOSE:To aim at reduction of a shocking sound at the time of switching by approaching the initial portions of a lift curve with regard to a valve opening direction in the cam profile of a plurality of valve tappet cams, in a valve mechanism providing a switching device for changing a valve operation timing by stages. CONSTITUTION:Cams 3a, 3b for a low speed having a cam profile formed by a base circle portion B1 and a high level portion L1 having a relatively small lift, and a cam for high speed having a cam profile formed by a base circle portion B2 and a high level portion L2 having a large lift along a wide angle compared with the cams 3a, 3b for a low speed, are integrally formed. Intake valves 1a, 1b are opened/closed by the rotation of the respective cams 3a, 3b, 4 via the first - the third rocker arms 5-7 capable of being freely engaged and disengaged each other by a connecting device 14. In this case, the initial portions of the lift curve with regard to a valve opening direction in the can profiles of the respective cams 3a, 3b, 4 are approached to be formed each other.

Description

[Detailed Description of the Invention] [Object of the Invention] <Industrial Application Field> The present invention relates to a valve mechanism that opens and closes an intake port or an exhaust port of a combustion chamber, and particularly relates to a valve mechanism that opens and closes an intake port or an exhaust port of a combustion chamber. The present invention relates to a valve operating mechanism for an internal combustion engine equipped with a switching device for changing valve operating timing in stages.

<Prior Art> In order to supply the air-fuel mixture to the combustion chamber and discharge combustion gas at predetermined timings, the combustion chamber of a four-cycle internal combustion engine is equipped with an intake valve and an exhaust valve. Both of these valves are normally biased in the valve closing direction by a valve spring provided so as to surround the valve stem.

Furthermore, both of these valves are forcibly pushed against the biasing force of the valve spring mentioned above by a cam that is integrally installed on a camshaft that is connected and driven from the engine's crankshaft using a belt or boob. It is notched so that it can be opened.

On the other hand, in order to improve the filling efficiency of the air-fuel mixture into the combustion chamber over a wide rotational speed range, various techniques have been proposed in which the timing of valve operation is changed according to the rotational speed of the engine. As such a valve operation timing switching device, in Japanese Patent Application Laid-Open No. 63-16111 by the present applicant, a low-speed cam having a shape corresponding to the low-speed rotational speed range of the engine and a cam having a shape corresponding to the high-speed rotational speed range of the engine are disclosed. A high-speed cam having a corresponding shape is integrally formed on a camshaft that is rotationally driven in synchronization with the rotation of the engine, and at the same time, one tongue is in contact with the low-speed cam and one of the intake valves or the exhaust valve is in contact with the other. The 10th lever arm and the 20th arm that comes into contact with the other intake valve or exhaust valve
A state in which the claw arm and a 30th claw arm that is in sliding contact with the high-speed cam are adjacent to each other and pivotally supported on a rocker shaft so as to be movable relative angles, and each of these first to third rocker arms are integrally connected. A valve operation timing switching device for an internal combustion engine has been proposed in which the first to thirtieth rocker arms are provided with a connecting means that enables switching between a state that allows relative angular displacement between each rocker arm. ing.

On the other hand, the lift of the valve relative to the rotation angle of the cam is known to be an important factor that determines the operating characteristics of the engine.
A head curve representing the rate of change in the valve head with respect to the rotation angle of the cam is generally determined based on a quadratic function. In the case of a plurality of cams having different cam profiles corresponding to the rotational speed range of the engine as described above, the lift curves of the cams are generally similar to each other.

<Problems to be Solved by the Invention> Incidentally, in a valve mechanism having a plurality of cams each having a different lift curve depending on the engine rotational speed range, the switching operation of the connecting means is performed by This is done in a state where the cam slipper of the rocker arm is in sliding contact with the portion, that is, in a region where the rocker arm is not performing its rocking movement.

However, due to the influence of inertia, hydraulic responsiveness, friction, etc., the valve lift may start before the switching operation of the connecting means is incomplete when switching from high speed to low speed.

If the switching operation is achieved after the rocker arm starts swinging with the high-speed cam, the rocker arm will suddenly be marked on the low-speed cam, producing a shocking sound.

The present invention has been made to solve these difficulties, and its main purpose is to prevent the cam and rocker arm from interfering if the release operation of the coupling means is incomplete when switching from high speed to low speed. An object of the present invention is to provide a valve operating mechanism for an internal combustion engine, which is equipped with an improved valve operation timing switching device so as to be able to alleviate the tapping noise that occurs during the operation.

[Structure of the Invention] <Means for Solving the Problems> According to the present invention, a plurality of rotating cams whose cam profiles are set corresponding to the rotational speed range of the engine, and a combustion chamber are provided. a valve that is installed in the intake port or exhaust boat of the valve and is normally biased to close by a spring means and is driven to open by the cam; and a valve that is installed in the intake port or exhaust boat of A valve operating mechanism for an internal combustion engine having a plurality of transmission members and a switching means for selectively switching between coupling and non-coupling of these transmission parts, wherein the valve opening direction in the cam profile of the plurality of cams is disclosed. This is achieved by providing a valve operating mechanism for an internal combustion engine, which is characterized in that the initial portions of the head curves of the two are made close to each other.

<Operation> By doing this, the lift heights of the high-speed and low-speed image cams at the initial stage in the valve opening direction become values that are close to each other. Therefore, even if the connecting means is not able to operate completely in the inner part of the base and operates after the valve lift starts, the difference in head height at the initial stage of the head curve is small, so the difference in head height is small at the initial stage of the head curve. Shock is suppressed.

<Embodiments> Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIGS. 1 to 4, a pair of intake valves 1a and 1b are provided in the internal combustion engine body (not shown). These intake valves 1a, 1b are connected to a pair of low-speed cams 3a, 3a, 3a, 3b, which are integrally provided on a camshaft 2, which is driven synchronously at half the speed of a crankshaft (not shown), and which have a generally egg-shaped cross section. 3
b, a single high-speed cam 4, and these cams 3a, 3b,
4 as a transmission member to perform a rocking motion.
The opening and closing operations are performed by working with the 30th claw arms 5 to 7. Additionally, this internal combustion engine is equipped with a pair of exhaust valves (not shown), which are driven to open and close in substantially the same configuration as the intake valves 1a and 1b described above.
Hereinafter, only the intake valve side will be explained.

The first to thirtieth hook arms 5 to 7 are rotatably supported adjacent to each other by a rocker shaft 8 that is fixed below the cam shaft 2 in parallel to the cam fi2. Of these, the first and thirtieth lever arms 5 and 7 have basically the same shape, their bases are pivotally supported by the rocker shaft 8, and their respective free ends extend above the intake valves 1a and 1b. It's being served. Also, these double-ended Tsuka Arms 5 and 7"!
l In the Da section, tappet screws 9a and 9b that come into contact with the upper ends of the intake valves 1a and 1b are threaded so that they can move forward and backward, respectively, and the tappet screws 9a and 9b are prevented from loosening by lock nuts 10a and 10b. has been done.

The 20th claw arm 6 is connected to the first and 30th claw arms 5 and 30.
7 and is pivotally supported by a rocker shaft 8. This 20th
The lever arm 6 connects both intake valves 1a and 1 from the rocker shaft 8.
1b, and as clearly shown in FIG. 4, a cam slipper 6a is formed on the upper surface of the cam slipper 6a for slidingly contacting the high-speed cam 4, and a cam slipper 6a is formed on the lower surface of the end of the cam slipper 6a. The upper end surface of the lifter 12 placed on the stand is in contact with the guide hole 11a formed in the cylinder head 11.

The lifter 12 has a cylindrical shape with a bottom, and the diameter of the bottom wall thereof is reduced, and accordingly, a stepped portion 12a is formed inside. Inside the lifter 12, there is a small diameter spring 13a with a relatively small spring constant and a large diameter spring 13b with a relatively large spring constant.
2b is held in place and contracted. This allows the second
The zero tension arm 6 is elastically biased so that its cam slipper 6a is always in sliding contact with the high speed cam 4.

As mentioned above, the cam fl12 is rotatably supported above the engine body, and the low speed cams 3a and 3b
and a high-speed cam 4 are integrally connected. As clearly shown in Figures 1 and 2, the low speed cam 3a.
3b is formed in a cam profile suitable for the low speed rotation range of the engine, which is composed of a base inner part B1 which is basically a perfect circle and a high part L1 which has a relatively small lift.
・Touch the outer circumferential surfaces of the cam slippers 5a and 7a formed on the upper surfaces of the 30th hook arms 5 and 7, respectively.
It is designed to be The high-speed cam 4 also includes a base inner portion B2, which is basically a perfect circle, and a low-speed cam 3a.
The cam slipper 6a of the 20th lug arm 6 has a cam profile suitable for the high-speed rotation range of the engine, which is composed of a high-ranking part 2 that has a large lift over a wider angle than the cam slipper 3b. The outer circumferential surface is in contact. Note that the lifter 12 is not shown in FIGS. 1 to 3.

Each of these rocker arms 5 to 7 can be swung together by a connecting device 14, which will be described later, and which is installed in a hole drilled through the center of each rocker arm 5 to 7 and parallel to the rocker shaft 8. It is possible to selectively switch between the state and the state where relative displacement is possible.

On the other hand, a retainer 15a is provided at the upper part of each intake valve 1a, 1b.
- 15b are provided respectively. At the same time, between the retainers 15a and 15b and the engine body, a valve spring 1 surrounding the stem portion of each intake valve 1a and 1b is installed.
6a and 16b are interposed, respectively, and are used to elastically bias each intake valve 1a and 1b in the normally closed direction, that is, upward in FIG. 2.

As clearly shown in Figures 1 and 3, the 10th lug arm 5
A first guide hole 17 that opens toward the 20th hook arm 6 is bored in parallel to the rocker shirt 1-8. A reduced diameter portion 18 is formed on the bottom side of the first guide hole 17, and a stepped portion 19 is formed accordingly, and a through hole 20 is further formed in the bottom wall of the first guide hole 17. The 20th lever arm 6 has the first arm of the 10th lever arm 5.
A second guide hole 21 communicating with the guide hole 17 is drilled through both sides thereof.

A third guide hole 22 communicating with the second guide hole 21 is bored in the 30th claw arm 7 . Similar to the first guide hole 17, the bottom side of the third guide hole 22 has a stepped portion 23.
and a small diameter portion 24 are formed.

Inside these first to third guide holes 17, 21, and 22, there is a first hole that can be moved between a position where the 30th claw arm 7 and the 20th claw arm 6 are connected and a position where they are released.
A piston 25, a second piston 26 that is movable between a position where the 20th lever arm 6 and the 10th lever arm 5 are connected and a position where the connection is released, and both pistons 25 and 26.
A stopper 27 that defines the moving distance of both pistons 2
A coil spring 28 is attached to the coil spring 28 which always resiliently urges the coils 5 and 26 toward the disconnection position.

The first piston 25 is located between the third guide hole 22 and the second guide hole 21, so that a hydraulic chamber 29 is defined between the bottom surface of the third guide hole 22 and the end surface of the first piston 25. There is. Further, a lubricating oil passage 30 is bored in the rocker shaft 8 and communicates with a hydraulic pressure supply device (not shown). An oil passage 31 bored to communicate with the hydraulic chamber 29 of the 30th lever arm 7 and a rocker shaft 8
The lubricating oil supplied from the lubricating oil passage 30 can always be introduced into the hydraulic chamber 29 through the communication hole 32 bored in the peripheral wall of It is like that.

The axial dimension of the first piston 25 is such that when one end thereof comes into contact with the stepped portion 23 in the third guide hole 22, the other end does not protrude from the side surface of the 30th claw arm 7 facing the 20th claw arm 6. It is set.

The second piston 26 has an axial dimension equal to the entire length of the second guide hole 21 and is configured to fit in the second guide hole 21 and the first guide hole 17 in a sliding manner.

The stopper 27 has a disc portion 27a formed at its Da to slide into the first guide hole 17, and a guide rod 27b inserted into the n-through hole 20 at its other end. Further, between the disk portion 27a of the stopper 27 and the bottom of the small diameter portion 18 of the first guide hole 17, the coil spring 2 described above is provided surrounding the guide rod 27b.
8 has been reduced. This coil spring 28 is connected to the hydraulic chamber 2
When the hydraulic pressure acting on 9 reaches a predetermined value or more, it is bent.

Next, the operating procedure of the apparatus described above will be explained.

In the middle and low speed range of the engine, the oil pressure in the lubricating oil passage 30 is maintained at a low pressure by closing a control valve (not separately shown). Then, due to the urging force of the coil spring 28, each piston 25, 26 is aligned in each guide hole 21, 22, respectively, as shown in FIG. be.

When the coupling device 14 is in the uncoupled state, the rotation of the camshaft 2 causes the first and third rocker arms 5 to
・7 swings in response to sliding contact with each low-speed cam 3a, 3b, and each intake valve 1a, 1b delays its closing timing and advances its closing timing, and also reduces the amount of lift. Each is driven to open and close. At this time, the 20th lever arm 6 swings due to its contact with the high-speed cam 4, but this swinging action has no effect on the operation of both intake valves 1a and 1b.

When operating the engine at high speed, by opening the control valve, the lubricating oil passage 30, the communication hole 32 of the rocker shaft 8,
and the coupling device 1 via the oil passage 31 of the 30th hook arm 7.
High pressure oil pressure is supplied to the hydraulic chamber 29 of No. 4. As a result, as shown in FIG. and move to the 10th arm 5 side. As a result, the first and second pistons 25 and 26 move together until the disk portion 27a of the stopper 27 comes into contact with the stepped portion 19, and the first piston 25 connects the 30th lever arm 7 and the 20th lever arm 6. , the 20th claw arm 6 and the 10th claw arm 5 are connected by the second piston 26.

As described above, each rocker arm 5 to 7 is connected to the coupling device 1.
4, the oscillation ω of the 20th claw arm 6 circumferentially surrounding the high-speed cam 4 is the largest, so the first and 30th claw arms 5 and 7 are
It swings together with the zero tension arm 6. Therefore, both intake valves 1a
- 1b is driven to open and close at the same time by making the valve closing timing earlier and later according to the cam profile of the high-speed cam 4, and by increasing the lift amount.

Now, as can be seen from the above description, in the valve train in the above embodiment, the double-ended lock arms are connected by the piston moving across the guide holes of the adjacent rocker arms. Therefore, the coupling device 14 is operated in a state in which the cam slippers 5a to 7a of each rocker arm 5 to 7 are in circumferential contact with the inner base portions B1 and B2 of each cam 3a, 3b, and 4. However, the hydraulic response was delayed,
Due to the inertia lag of the piston, the valve lift may start before the release operation is completed. In such a case, if the connection between each rocker arm can be maintained until it reaches the inner part of the base again, no actual damage will occur. However, if the release operation is achieved after the high-speed cam 4 starts lifting the valve, the first and 30th rocker arms 5 - Since there is a gap between the cam slippers 5a and 7a of No. 7 and the low-speed cams 3a and 3b by the lift difference between the low-speed cams 3a and 3b and the high-speed cam 4, the valve spring 16a
- The first and 30th lever arms 5 and 7 are struck against the low-speed cams 3'a and 3b by the urging force of 16b, producing an impact sound and at the same time, the behavior of the valve becomes discontinuous.

In view of this, in the present invention, as shown in FIG. It is said that By doing this, the lift difference d between the low-speed cams 3a and 3b and the high-speed cam 4 at the same cam rotation angle can be reduced, and the coupling device 14 can be released after the Yoshiba valve lift starts. In this case, the impact can be suppressed to a relatively low level.

It has been empirically confirmed that such a delay in the operation of the coupling device is more likely to occur in the early stages of the valve opening direction. Therefore, by appropriately setting the head curve in the region from the buffer section of the head curve to the point where the curve inflects, it is possible to deal with the problem without affecting the actual valve timing. can.

Note that the present invention is not limited to the structure of the coupling device shown in the above embodiment, but can be equally applied to a valve mechanism having a plurality of cams formed with different profiles for each corresponding rotation speed range, if necessary. Regarding the structure of other parts, various modifications can be made.

[Effects of the Invention] As described above, according to the present invention, it is possible to alleviate the impact noise that occurs when switching from a high-speed cam to a low-speed cam when the switching operation is incomplete. Factors that increase operating noise and decrease durability can be effectively eliminated.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway top view showing a valve mechanism having a valve operating state switching device constructed according to the present invention during high-speed operation. FIG. 2 is a partially cut away side view. FIG. 3 is a sectional view taken along the line m--■ in FIG. 2, showing the state of low-speed operation. Fig. 4 is a sectional view taken along the line IV-IV in Fig. 3. Fig. 5 shows an example of the lift curve. 1a, 1b... Intake valve 2... Camshaft 3a. 3b・
...Low speed cam 4...High speed cam 5...10th lever arm 6
...20th Tsuka Arm 7...30th Tsuka Arm 5a
・6a, 7a...Cam slipper 8...Rocker shaft 9a, 9b...Tappet screws 10a, 10b...Lock nut 11...Cylinder head 11a...Guide hole 12.
...Lifter 12a...Step part 12b...Retainer 13a...Small diameter spring 13b...Large diameter spring
14... Connecting device 15a, 15b... Retainer

Claims (2)

[Claims] (1) A plurality of rotating cams whose cam profiles are set according to the rotational speed range of the engine, and which are installed at the intake port or exhaust port of the combustion chamber and are normally biased to close by a spring means, and the cams A valve that is driven to open, a plurality of transmission members corresponding to each of the plurality of cams to impart the lift of the cam to the valve, and a switching means that selectively switches connection/disconnection between these transmission members. A valve operating mechanism for an internal combustion engine, characterized in that initial portions of lift curves in the valve opening direction in the cam profiles of the plurality of cams are made close to each other. . (2) The valve mechanism for an internal combustion engine according to claim 1, wherein the initial portion is a portion of the lift curve from the end point of the buffer section to the vicinity of an inflection point.