JPH06159025A - Variable valve system of engine - Google Patents

Abstract

PURPOSE:To suppress the unevenness of the valve lifting amount between cylinders while realizing the position stability of a control cam when it is converted, even though the converting stages of the valve lifting amount are increased. CONSTITUTION:A lever 11 whose one surface is contacted to the rear surface 7a of a locker arm to depress a suction valve against a valve spring 5 following a cam 6 is provided, and one end of the lever 11 is held rotatable with a fulcrum shaft 12, while plural control cams 21 and 22 having a cam crest on the peripheral surface, whose distance from the rotation center is increased step by step when it is slipped in the rotating direction at a specific angle, are provided to the reverse side surfaces 11b and 11c not contacted to the rear surface 7a of the locker arm of the lever 11 opposing respectively, and to increase the distance from the rotation center step by step in the same rotating direction. And when the control cams are rotated a specific angle alternately, plural cams are converted each other so as to contact to the reverse surfaces 11b and 11c.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable valve operating system for gradually changing the lift characteristic of an intake valve or an exhaust valve according to the operating condition of an engine.

[0002]

2. Description of the Related Art As a variable valve operating device of this type, there is one shown in FIG. 5 (see SAE paper 896081).

To explain this, one end of the rocker arm 43 is in contact with the cam 41 rotating in synchronization with the engine and the other end is in contact with the intake valve (or exhaust valve) 42. Are provided in contact with each other. The lever 45 is formed with a fork portion 45a extending downward in the drawing while sandwiching both sides of the rocker arm 43 so as to slide on the rocker shaft 44.
One end of is supported swingably by a hydraulic tappet 46.

The other end of the lever 45 is supported by the control cam 47 in order to switch the swinging position of the lever 45 according to the operating state. Rotatable control cam 4
Four cam ridges having different distances from the center of rotation are formed at a predetermined angle as shown in FIG. 6, and the control cam 47 is rotated step by step at a predetermined angle in the counterclockwise direction in FIG. Then, when the position of the cam crest contacting the lever 45 is switched in the order of "1", "2", "3", "4", the lever 45 approaches the cam 41 in FIG. As one end of the rocker arm 43 is pushed up by the rotation of the cam 41, the rocker arm 43 swings while moving the portion contacting the lever 45 to the left from the point C (start point) in FIG. 5, and the intake valve 42 at the other end. Press down,
As the turning position of the lever 45 moves closer to the cam 41, the above-mentioned starting point moves to the left side in the figure, so that the valve lift amount of the intake valve 42 increases.

[0005]

By the way, in the above device, since the turning position of the lever 45 is determined by the shape and size of the control cam 47 itself, the turning position of the lever 45 is accurate and the valve lift between cylinders is high. The variation in quantity can be suppressed to a small one.

On the other hand, however, when the number of cam ridges is increased, the position stability (sit) of the control cam 47 is increased.
Therefore, the number of stages for switching the valve lift amount cannot be increased.

This is the target position (“1”,
Control cam 4 at “2”, “3” and “4” positions)
This is because, in order to settle down with good response, the cam lift characteristics (FIG. 6) with respect to the cam rotation angle need to be provided with a substantially horizontal portion having a predetermined width W on the left and right with respect to the target position. If the horizontal portion of W is narrowed by increasing the number of stages for switching the valve lift amount, the control cam 4
7 becomes uncomfortable, for example, when instructing to switch the position from "3" to "2", the control cam 47 rushes from the "2" position to the "1" position, and the instructed position is actually changed. The position of may be different.

As described above, when the valve lift amount can be switched only with a small number of stages, the change in the valve lift amount at the time of switching becomes large, and a torque shock occurs.

On the other hand, as in Japanese Patent Laid-Open No. 60-128912, the lever is supported by a reciprocating hydraulic piston instead of the control cam, and the pivot position of the lever is changed by changing the piston stroke. According to this type, the valve lift amount can be switched in a large number of stages. However, in the hydraulic actuator, the accuracy of the pivotal position of the lever is worse than that of the control cam, and due to the poor accuracy, the variation in the valve lift amount between cylinders becomes large.

Therefore, according to the present invention, by alternately rotating a plurality of control cams to change the rotational position of the lever, even if the number of switching stages of the valve lift amount is increased, the position when the control cam is switched is changed. The purpose is to suppress variations in valve lift between cylinders while achieving stability.

[0011]

SUMMARY OF THE INVENTION According to the present invention, a cam that rotates in synchronization with an engine, a rocker arm that follows the cam and pushes down an intake valve or an exhaust valve against a valve spring, and contacts a back surface of the rocker arm. With a lever, a fulcrum shaft that rotatably supports one end of the lever, and a plurality of control cams that have cam peaks on the peripheral surface that gradually increase in distance from the center of rotation with a predetermined angle deviation in one rotation direction. The levers are arranged so as to face the opposite surfaces of the rocker arm which are not in contact with the back surface of the lever, and the distance from the rotation center increases stepwise in the same rotation direction. A plurality of control cams that are alternately replaced when rotating and contact the opposite surface, and a plurality of control cams that are alternately rotated by the predetermined angle. Provided and Chueta.

Further, the control cam which contacts the lever at the position where the valve lift amount is maximum is arranged closest to the fulcrum shaft.

On the other hand, the control cam, which comes into contact with the lever at the rotating position where the valve lift amount is minimized, is arranged farthest from the fulcrum shaft.

[0014]

When the two or more control cams are alternately rotated by a predetermined angle to the side where the distance from the center of rotation increases, the lever rotation position changes stepwise each time the control cam contacting the upper surface of the lever moves alternately. Approaching the cam.

In this case, regarding each control cam, even if the number of cam peaks formed on the peripheral surface is the same as the conventional one, a value obtained by multiplying the number by the number of control cams (actually Is a little less than this) is the number of lever rotation positions. For example, if the number of cam ridges is four, which is the same as the conventional one, by providing two control cams, 4 × 2 (= 8) is approximately the number of lever rotation positions (that is, almost the same as the conventional one). Double). In other words, since the position stability (sit) of the control cam is not deteriorated, even if the number of cam peaks on each control cam remains the same as before, the lever rotation position can be set in multiple stages. Is.

As described above, when the plurality of control cams are alternately rotated by a predetermined angle so that the lever is rotated in a large number of stages, the control cam position is stabilized and the valve lift amount varies among the cylinders. Can be suppressed.

Further, when the control cam contacting the lever at the position where the valve lift amount is maximum is arranged closest to the fulcrum shaft, even if the maximum load acts on the lever, the bending moment applied to the lever is small. The deformation of the lever is prevented.

On the other hand, when the control cam contacting the lever in the rotational position where the valve lift amount is the minimum is arranged farthest from the fulcrum shaft, the minimum valve lift amount is required to have the highest accuracy. At the time of the lift amount, the variation in the valve lift amount is further reduced, which significantly improves the distribution of the air-fuel mixture among the cylinders.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a cylinder head 1 has a pair of intake valves 3 for opening and closing a Siamese type intake port 2.
Is provided and the valve spring 4 is interposed between the valve retainer 5 and the cylinder head 1 to bias the intake valve 3 in the valve closing direction.

A cam 6 that rotates in synchronization with a crankshaft (engine) is provided above the cylinder head 1, and a cam 6 is provided.
There is provided a Y-shaped rocker arm 7 that follows and pushes the intake valve 3 downward in the figure against the valve spring 4.
One end (the right end in the drawing) of the rocker arm 7 that is curved upward in the drawing is connected to the peripheral surface of the cam 6 via a rollable roller follower 8 and the other end (the left end) that is branched into two. Respectively contact the upper end of the intake valve 3 via the hydraulic tappet 9.

In order to change the valve lift amount stepwise, a lever 11 which is swingable around the fulcrum shaft 12 is provided in contact with the rocker arm rear face 7a, and the lever 11 is rotated to be closer to the cam 6. The valve lift amount is increased. When it comes to the lift area of the cam 6, the rocker arm 7
Swings while moving the contact point between its rear surface 7a and the lower surface 11a of the lever 11 to the right side in the drawing to open the intake valve 3 against the valve spring 4.
Is moved from the solid line position to the broken line position (the side closer to the cam 6) in the figure, the lever ratio changes and the intake valve 3 is pushed down more, that is, the valve lift amount increases.

Since not only the valve lift amount but also the valve operating angle (the opening angle of the intake valve 3) is changed at the same time, the center point O of the fulcrum shaft 12 is located on the center axis of the intake valve 3. The fulcrum shaft 12 is provided and is connected to a pin 13 provided at a substantially central position of the rocker arm 7 from both sides (only one side is shown in the figure) via a pair of links 14. Further, in the base circle area of the cam 6, the lever portion in contact with the rocker arm back surface 7a is cylindrical so as to have an arc cross section with a radius R ₁ centered on the point O of the fulcrum shaft 12 and the intake of the hydraulic tappet 9 is increased. The part in contact with the top of the valve is also O
Each of them is formed in a spherical shape so as to have an arc section having a radius R ₂ (R ₂ > R ₁ ) centered on the point.

The fact that the valve operating angle is reduced by rotating the lever 11 away from the cam 6 will now be described with reference to FIG. In FIG. 2, the lever 11 is at the broken line position, and in the base circle area of the cam 6, the point A of the lever lower surface 11a and the point E of the rocker arm back surface 7a are in contact with each other, and the angle is θ in the counterclockwise direction. When the lever 11 is rotated (the lever 11 moves to the position of the solid line), the point C on the lower surface of the lever moves to the point C ′ and contacts the point E, and the point A on the lower surface of the lever moves to the point A ′. At this time, at least the shape of AC on the lower surface of the lever is an arc centered on the point O.

In this state, when the cam 6 reaches the lift area, the entire rocker arm 7 rotates counterclockwise around the point O. As shown in FIG. 1, two points, H point (center point of the pin 13) in the rocker arm and E point on the rocker arm different from this point, rotate about O point (that is, O point).
This is because the point becomes the center of rotation of the rocker arm 7).
With the rotation of the rocker arm 7, the contact point between the rocker arm rear surface 7a and the lever lower surface 11a is C'in FIG.
Move from point A to point A '. At this time, since the hydraulic tappet 9 also rotates integrally with the rocker arm 7, the W point on the hydraulic tappet 9 moves to the W'point and contacts the point V at the upper end of the intake valve (the U point on the hydraulic tappet 9 is U '. However, since the center of the arc forming the lower surface of the hydraulic tappet 9 is point O, the intake valve 3 is not pushed down. That is, when the lever 11 is rotated by the angle of θ toward the side away from the cam 6, the valve operating angle is decreased by θ. Of course, when the lever 11 is in the solid line position in FIG. 2, the valve lift amount is smaller than that in the broken line position. In this way, the lever 11
Both the valve lift amount and the valve operating angle decrease with increasing distance from the cam 6.

By the way, in FIG. 1, the rocker arm rear surface 7a is used to change the rotational position of the lever 11 stepwise.
The lever surface (the upper surface in the figure) on the side opposite to the contact with the control cam 21, facing the lever surface 11b, 11c of each step, is formed in a stepped shape with two steps having a thickness closer to the fulcrum shaft side. 22 is arranged. The tip of the lever 11 (right end in the figure) is attached to the control cam 2 by the spring 23.
It is pressed to the side of 1, 22. Each of the control cams 21 and 22 has four cam ridges whose distance from the center of rotation increases with each deviation of a predetermined angle in one rotation direction (θ ₁ for the control cam 21 and θ ₂ for the control cam 22). Each is formed on the peripheral surface.

Furthermore, two control cams 21 and 2 are provided.
When 2 is alternately rotated by the above-mentioned predetermined angle, the control cams in contact with the lever upper surface are exchanged alternately so that the stepped lever upper surface and the two control cams 2
The dimensions of 1 and 22 are set.

For example, at the top of the cam crest of one of the control cams 21, "0", in order of increasing distance from the center of rotation,
The numbers "2", "4", and "6" are used, and the tops of the cam ridges of the other control cams 22 are "1", "3", "5", and "7" in order of increasing distance from the center of rotation. When the lever 11 is at the position farthest from the cam 6 (initial position) with the “1” cam crest of the control cam 22 in contact with the lever upper surface 11c as shown in FIG. To do. However, there is a clearance between the "0" cam crest of the other control cam 21 and the lever upper surface 11b, and the "0" cam crest and the lever upper surface 1b.
Not in contact with 1b.

From this state, the control cams 21, 22
Consider alternating rotation in the same direction (counterclockwise in the figure).

First, the control cam 21 on _{one side} is θ ₁
Control cam 21 when rotated counterclockwise only
The "2" cam lobes contact the lever upper surface 11b, and the "1" cam lobes move away from the lever upper surface 11c. By switching the cam mountain contacting the upper surface of the lever, the lever 11 is rotated by a predetermined angle toward the side closer to the cam 6.

Next, the other control cam 22 is set to θ ₂
When it is rotated counterclockwise only, the "3" peak is in contact with the lever upper surface 11c, so that the "2" cam peak is located on the lever upper surface 11c.
leave b. The lever 11 moves closer to the cam 6 by the switching of the cam crests.

This time, the control cam 21 on the opposite side
Is rotated counterclockwise by θ ₁ , the "4" cam lobe contacts the lever upper surface 11b, and the "3" cam lobe moves away from the lever upper surface 11c.

The following operations are also the same, and when the two control cams 21 and 22 are alternately rotated by a predetermined angle in this way, the rotation position of the lever changes in a total of seven steps. . This number is 8 obtained by multiplying the number of cam peaks by 4 by the total number of control cams by 2
Is almost equivalent to.

As shown in FIG. 3, the control cam 21 (also for 22) is the control shaft 2
5 is rotatably provided, and is connected to a stopper ring (fixed to the control shaft) 26 via a torsion spring 27. This is a device to prevent the control cam 21 from rolling due to a large valve spring force acting on the control cam 21 even if the control cam 21 is rolled to the adjacent cam mountain in the lift area of the cam 6. In other words, the actuator (DC
By rotating the control shaft 25 by an angle of θ ₁ by the (servo motor) 29, the torsion spring 2
When 7 is twisted and moved to the base circle area of the cam, the control cam 21 is rolled to the command position by utilizing the elastic energy stored in the torsion spring 27.

The operation of this example will now be described.

In FIG. 1, two control cams 2 are provided.
When 1 and 22 rotate in the counterclockwise direction from the state of FIG. 1 alternately by the angles of θ ₁ and θ ₂ , respectively, the turning position of the lever 11 is gradually changed every time the control cam in contact with the upper surface of the lever moves alternately. As it approaches 6, the turning position of the lever 11 changes in 7 steps in total. The valve lift characteristic is set to be almost double that of the conventional one by the total of seven lever rotation positions. Moreover, regarding each control cam, since the number of cam peaks formed on the peripheral surface is only four, which is the same as the conventional one, the positional stability (sit) of the control cam does not deteriorate.

As described above, the plurality of control cams 2
When the rotation position of the lever 11 is set to a large number of stages by alternately rotating 1 and 22 by a predetermined angle, it is possible to suppress the variation in the valve lift amount between the cylinders while stably rotating the control cam. .

Further, in FIG. 1, when the "7" cam crest is in contact with the lever upper surface 11c, the valve lift amount is the maximum, and the maximum load acts on the lever 11. However, the "7" cam crest is the fulcrum shaft 12. Since the lever 11 is provided on the control cam 22 on the side close to the control cam 22 and the lever 11 is supported by the control cam 22, the bending moment applied to the lever 11 can be small and deformation of the lever can be prevented.

FIG. 4 shows another embodiment in which the lever 11 is a cam 6
The cam mountain of "1" that determines the position farthest from (the initial position) is provided not on the side close to the fulcrum shaft 12 but on the control cam 32 far from the fulcrum shaft 12. This is because the position accuracy of the lever 11 is better as the cam ridge contacting the upper surface of the lever is farther from the fulcrum shaft 12, and the best accuracy of the valve lift amount is required when the minimum valve lift amount is required. (That is, when the lever 11 is in the initial position).

In this example, the variation of the valve lift amount can be reduced at the minimum valve lift amount, and thereby the distribution of the air-fuel mixture among the cylinders can be greatly improved as compared with the previous embodiment.

Although the number of control cams is two in the embodiment, three or more control cams can be provided, and in that case, the valve lift characteristic can be further increased. For example, if the number of cam peaks is four and the number of control cams is three, the product of them is 12
However, the number of stages for switching the valve lift amount at that time is almost the same.

[0041]

According to the present invention, a lever, one surface of which is in contact with the back surface of a rocker arm that presses an intake valve or an exhaust valve against a valve spring by following a cam that rotates in synchronization with an engine, has one end as a fulcrum. The rear of the rocker arm of the previous lever has a plurality of control cams that are rotatably supported by a shaft and that have a cam peak on the circumference that gradually increases from the center of rotation with a predetermined angle deviation in one rotation direction. The cams are arranged so as to face the opposite surfaces that do not come into contact with each other, and the distance from the center of rotation increases stepwise in the same rotation direction. To contact with the opposite surface, and the plurality of control cams are alternately rotated by the actuator by the predetermined angle. Even if the Ruburifuto characteristics in many stages,
It is possible to suppress the variation in the valve lift amount between the cylinders while stably rotating the control cam.

Further, since the control cam contacting the lever at the position where the valve lift amount is maximum is arranged closest to the fulcrum shaft, even if the maximum load is applied to the lever, the bending moment applied to the lever is small, and the lever is deformed. Can be prevented.

On the other hand, since the control cam contacting the lever at the pivot position where the valve lift amount is the minimum is arranged farthest from the fulcrum shaft, the minimum valve lift amount required to have the highest valve lift amount accuracy is required. At this time, the variation in the valve lift amount is further reduced, which can further improve the distribution of the air-fuel mixture among the cylinders.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a valve train according to an embodiment of the present invention.

FIG. 2 is likewise an operation explanatory view.

FIG. 3 is a perspective view of the drive mechanism of the control cam.

FIG. 4 is a cross-sectional view of a valve gear according to another embodiment.

FIG. 5 is a front view of a valve train of a conventional example.

FIG. 6 is a characteristic diagram of the control cam lift with respect to the control cam angle.

[Explanation of symbols]

 3 intake valve 4 valve spring 6 cam 7 rocker arm 7a rocker arm rear surface 11 lever 11b, 11c lever upper surface (opposite surface) 12 fulcrum shaft 21,22 control cam 31,32 control cam

Claims (3)

[Claims] 1. A cam that rotates in synchronization with an engine, a rocker arm that follows the cam and pushes down an intake valve or an exhaust valve against a valve spring, a lever that contacts the back surface of the rocker arm, and one end of the lever that rotates. A rocker arm of the lever, comprising a fulcrum shaft movably supported and a plurality of control cams each having a cam mountain on a peripheral surface, the distance from the center of rotation gradually increasing each time a predetermined angle shifts in one rotation direction. They are arranged so as to face the opposite surfaces not in contact with the back surface, respectively, so that the distance from the center of rotation increases stepwise in the same rotation direction, and when they are alternately rotated by the above-mentioned predetermined angle, they are alternately replaced. A plurality of control cams that are in contact with the opposite surface and an actuator that alternately rotates the plurality of control cams by the predetermined angle. A variable valve operating system for an engine. 2. The variable valve operating system for an engine according to claim 1, wherein a control cam that comes into contact with a lever at a position where the valve lift amount is maximized is arranged closest to the fulcrum shaft. 3. The variable valve operating system for an engine according to claim 1, wherein a control cam that contacts a lever at a rotational position where the valve lift amount is minimized is disposed farthest from the fulcrum shaft.