JPS62279216A - Controlling method for suction and exhaust valve lift in tappet valve controller of internal combustion engine - Google Patents

Abstract

PURPOSE:To decrease the beat sound in the shift of cam by controlling the rotation speed of a multi stage cam for varying the inclination of a lever when being shifted from the cam face of a small lifting quantity side to that of a large lifting quantity side in a tappet valve device for supporting the back face of a rocker arm float ingly moved by the lever having a cam face. CONSTITUTION:The back face of the rocker arm 13 abutted at its end to a cam 11 and at the other end to a valve 12 and floatingly moved is supported by the lever 15 abutting at its end to a multi stage control cam 20 and at the other end to the back face of the rocker arm. The rotation of the control cam 20 varies the inclination of the lever 15 for changing the timing to open and close a suction and exhaust valve 12 due to the change of the fulcrum of the rocker arm. The rotation speed of the cam must be controlled so as to become slow in the former half and rapid in the latter half when the control cam 20 is shifted from the cam face on the small lifting quantity side to that on the large lifting quantity side. Since the rotation speed in the former half is slow, the rotation quantity of the lift control cam when releaved from the reaction force after completion of valve lifting can be regulated in smaller quantity.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a valve control device for an internal combustion engine that variably controls the lift characteristics of intake and exhaust valves according to engine operating conditions. The present invention relates to a control method for reducing tapping noise during switching control.

<Prior Art> Examples of valve control devices for internal combustion engines that variably control the lift characteristics of intake and exhaust valves according to engine operating conditions include those shown in FIGS. 1986-22
(See No. 4909).

To explain this, referring to FIG. 7, a rocker arm 13 is provided with both ends abutting the intake/exhaust valve drive cam 11 that rotates in synchronization with engine rotation and the stem end of the intake/exhaust valve 12. The curved back surface 13a of the loser arm 13 is brought into fulcrum contact with a lever 15 which is swingably supported at one end by a hydraulic pivot 19, which will be described later. Further, the lever 15 holds a shaft 13b protruding from both side walls of the rocker arm 13 in a groove 15a via a holding member 14, and there is a space between a spring seat 15b formed on the lever 15 and the holding member 14. A spring 16 with a small spring constant is interposed to bias the rocker arm 13 downward.

The hydraulic pivot 19 includes an outer cylinder 19a that is slidably inserted into a mounting hole 18a formed in a bracket 18 attached to the cylinder head, and an inner cylinder 19b that is fitted into the outer cylinder 19a. , and a check valve 19d is provided in a hydraulic chamber 19c formed between the two. and,
The hemispherical lower end of the outer cylinder 19a fits into a recess 15c on the upper surface of one end of the lever 15 on the stem end side of the intake/exhaust valve 12, supporting the lever 15 in a freely swinging manner. and,
Hydraulic pressure is supplied from a hydraulic pressure supply passage 18b formed inside the bracket 18 to the hydraulic chamber 19c via the inside of the inner cylinder 19b and the check valve 19d to keep the valve clearance constant.

In addition, a lift control cam 20 rotatably attached to the bracket 18 as described later engages with the upper surface of the other end of the lever 15 on the intake/exhaust valve drive cam 11 side.
The swing position of 5 is regulated.

Does the lift control cam 20 have different heights so as to change the lift amount of the intake/exhaust valves 12 in stages? M number of cam surfaces 20a
~20e, and a control shaft 23, which will be described later, in the center.
It has a hole 20g through which it is inserted. Further, the cylindrical portion 20h formed to protrude from both ends of the lift control cam 20 is fastened to the lower arc 418C formed on the bracket 18 with bolts 21 on the bracket 18, as shown in FIGS. 9 and 10. It is held freely rotatably between the upper arcuate groove 22a formed in the pair of camps 22.

Then, one control shaft 23 is inserted into the hole 20g formed by penetrating the center of the lift control cam 20 provided in several cylinders, with a gap between the control shaft 23 and the both sides of each lift control cam 20. One end of each fitted coil spring 24 as an elastic member is locked to a set screw 23a screwed into the outer peripheral surface of the control shaft 23, and the other end of the coil spring 24 is connected to the cylindrical portion 20h of the lift control cam 20.
It is locked by fitting into a hole 20i formed in the side wall.

One end of the control shaft 23 is connected via a joint 25 to a drive shaft 26a of a stepping motor 26 as an actuator. The stepping motor 26 is driven by a control circuit 27 via a drive circuit 28 based on engine operating conditions such as engine speed and throttle valve opening.
is rotated to a predetermined rotation position.

29 is a valve spring.

To explain the operation, when the lift control cam 20 is in contact with the lever 15 with the cam surface 20a having the largest lift amount, the lever 15 is pushed down the most towards the intake/exhaust valve drive cam 11 side. For this reason, the rocker arm 13
The lower surface of the lever 15, which is in fulcrum contact with the back surface 13a of the lever 15, also lowers, and the fulcrum contact point A moves toward the intake/exhaust valve drive cam 11 while being transmitted to the intake/exhaust valves 12, as shown by the curve X in FIG. The lift amount is large, and the valve opening timing is early and the valve closing timing is late.

On the other hand, when the lift control cam 20 is rotated so that, for example, the cam surface 20e with the smallest lift i contacts the lever 15, the end of the intake/exhaust valve drive cam 11 of the lever 15 uses the concave portion 15c as a fulcrum. The lower surface of the lever 15 also retreats upward as a result of the swinging motion.

The lower surface of the lever 15 serves as a fulcrum for the rocker arm 13 to transmit the lift of the intake/exhaust valve drive cam 11 to the intake/exhaust valves 12, but the intake/exhaust valve drive cam 11 is in contact with the rocker arm 13 at the base circle. The initial position of the fulcrum in this state moves to the right in FIG. 8, that is, to the side away from the direction in which the fulcrum moves after the lift, compared to when the lever 15 is in contact with the cam surface 20a with the large lift amount. As a result,
As shown in the song vAY in Fig. 11, the lift amount is small,
In addition, the valve opening timing is delayed and the valve closing timing is advanced.

In this way, by rotating the lift control cam 20 and bringing any of the cam surfaces 20a to 20e into contact with the lever 15, the lift characteristics of the intake/exhaust valves 12 can be changed in stages.

Here, the lift control cam 20 is rotated via a control shaft 23 and a torsion coil spring 24 by driving a stepping motor 26 . That is, the control circuit 2
7 supplies a drive pulse set based on a signal corresponding to engine operating conditions to the stepping motor 2 via a drive circuit 28.
Output to 6. This drive pulse is the stepping motor 2
6 is rotated by a preset angle, thereby rotating the control shaft 23.

Now, at the timing when the control shaft 23 rotates, the intake/exhaust valve 1
2 is in lift, the rocker arm 13
The contact fulcrum between the lever 15 and the lever 15 has moved toward the intake/exhaust valve drive cam ll side, and the large reaction force of the pulp spring 29 is applied to the rocker arm 13. It acts on the lift control cam 20 via the lever 15. Therefore, only the control shaft 23 rotates while the lift control cam 20 remains fixed and the coil springs 24 on both sides thereof rotate. Next, after the suction/exhaust valve drive cam 11 rotates and the suction/exhaust valves 12 are closed, the contact fulcrum between the rocker arm 13 and the lever 15 is located approximately above the suction/exhaust valves 12, and the pulp Since the reaction force of the spring 29 disappears, the lift control cam 2
The only force acting on 0 is the weak force of the spring 16 attached between the rocker arm 13 and the lever 15.

Therefore, the torque stored in the torsion coil spring 24 while the intake/exhaust valve 12 is lifted is transferred to the spring 16.
The lift control cam 20 can be rotated by overcoming the weak force of the lift control cam 20. Therefore, the output required from the stepping motor 26 is small enough to twist the torsion coil spring 24 by the rotation angle of the adjacent cam surface.

<Problems to be Solved by the Invention> Incidentally, in such a conventional valve control device for an internal combustion engine, the switching speed of the lift control cam 20 is controlled to rotate at a substantially constant speed. However, there was a problem in that a loud tapping sound was generated when switching in the direction of increasing the valve lift amount.

This will be explained using FIG. 12. FIG. 12 shows the rotation angle of the control shaft 23 and the lift control cam 20 when the valve lift amount is controlled to increase under certain engine operating conditions.
The rotation angle of the lever 15, the vertical position of the lever 15, the daily vibration acceleration of the bracket and throat, and the magnitude of the valve lift of the intake/exhaust valve 12 are shown.

As shown in the figure, when the rotation of the control shaft 23 is controlled at a constant speed, the lift control cam 20 is integrated with the control shaft 23 because no reaction force is generated by the valve spring 28 when the intake/exhaust valve 12 is lifted. Although it rotates, in the valve lift section, the reaction force of the valve spring 28 initially returns it to the lower stage (small valve lift) side.

On the other hand, the control shaft 23 further increases the amount of rotation and the return angle of the lift control cam 20 increases, so at the end of the valve lift (timing X), the lift control cam 20 rotates vigorously and overshoots greatly. As a result, the lever 15 is also pushed downward. Although the lift control cam 20 is then returned to its original position by the cam of the spring 24, the lever 15 and the lift control cam 20 remain pushed down because the friction of the contact surface with the hydraulic pivot throat 19 is large. A clearance is created between the lever 15 and the lift control cam 20 at the start of the next valve lift, resulting in a spike-like peak of vibration acceleration and generation of a tapping sound.

The present invention has been made in view of these conventional problems, and an object of the present invention is to provide a control method that reduces the occurrence of tapping noise during valve lift l-ff1 increase switching control.

Therefore, in the present invention, the cam surface that engages with the lever of the lift control cam is changed from the cam surface on the small lift amount side to the cam surface on the large lift amount side. When rotating a control shaft by an actuator, the rotation speed is controlled to be slow in the first half and fast in the second half.

(Function) As a result, during the first half of switching control, the rotation speed of the control shaft is slow, so the amount of rotation of the control shaft and lift control cam is small, and the amount of rotation of the lift control cam when released from the reaction force at the end of the valve lift is reduced. Can be kept small.

When moving to the latter half, the rotational speed of the control shaft increases, and together with the control shaft, the lift control cam can be rotated all at once to the upper stage.

Therefore, it is possible to prevent the lever from falling too far downward, and it is possible to prevent the generation of loud hitting sounds without creating a clearance between the lever and the lift control cam.

<Example> An embodiment of the present invention will be described below.

The configuration of the valve control device is as shown in FIGS. 8 to 10, but the lift control cam 20 has a profile as shown in FIG. 4. That is, the lift control cam 20 has multiple stages (here, the lift amount L
Stable cam surface (lift-footrest) C1~ of +~L4 4 stages)
C4, and as it rotates, the lift amount changes stepwise and smoothly as shown in FIG. In addition, as shown in Fig. 3, during valve lift switching operation, the lift control cam 20 receives a stable (+) moment mainly on the lower stage, and also receives a (-) moment to prevent it from falling on the lower stage. It is made in

In the present invention, the control circuit 27 controls the stepping motor 2.
6 to rotate the control shaft 23, in particular, the cam surface of the lift control cam 20 that engages with the lever 15 is rotated in a direction that changes from a cam surface with a small lift amount to a cam surface with a large lift amount. When moving, as shown in the timing chart in FIG. 1, the first half of the rotation angle of the control shaft 23, about 173, is slowed down, and the second half, about 273, is controlled fast. This is done by changing the cycle of the drive pulses to the stepping motor 26.

To explain with reference to FIG. 1, in the first half, the rotation speed of the control shaft 23 is slowed down, so the control shaft 23 is rotated before the valve lift starts.
3 and the amount of rotation of the control cam 20 that rotates together with this is small, and the amount of rotation of the lift control cam 20 when released from the reaction force of the valve spring 28 at the end of the valve lift can be kept small.

When the rotation amount of the control shaft 23 further increases and shifts to the second half, the rotation speed of the control shaft 23 increases, and together with the control shaft 23, the lift control cam 20 is suddenly engaged by the cam surface with a large lift amount to the lever 15. Rotate until. At this time, since the tear coil spring 24 is twisted, overshoot does not occur.

Therefore, the lever 15 does not fall too far downward, and no clearance is created between the lever 15 and the engaging cam surface of the lift control cam 20, so that it is possible to prevent the generation of loud hitting sounds.

On the other hand, the rotation start timing of the control shaft 23 is
The fact that the tapping noise can be eliminated even when the timing is not synchronized with the opening/closing timing of No. 2 will be explained with reference to FIG. 2 (starting later than the valve lift) and FIG. 3 (starting ahead of the valve lift).

In FIG. 2, the valve lift starts when the lift control cam 20 does not fully rotate with respect to the rotation of the control shaft 23, but the lift control cam 20 is moved between the cam surfaces on the way to the upper stage. The protruding portion between the valves remains engaged with the lever 15, and the valve lift ends without falling significantly to the lower stage, and the valve smoothly engages with the upper stage, so no hitting sound is generated.

Furthermore, as shown in Fig. 3, if the rotation start of the control shaft 23 is on the advance side, the initial rotation speed of the valve lift control cam 20 at the lower stage increases a little, so when the control shaft 23 is rotated, the lift is controlled. ′
A20 overshoots a little, but the amount is small.
The clearance generated between the lever 15 and the lever 15 is also small, and the level of the hitting sound can be suppressed to an extremely low level that cannot be discerned.

In addition, in order to obtain the above effect at all rotation speeds, it may be necessary to change the rotational speed of the control shaft 23 approximately in proportion to the engine rotation speed at the time of valve lift switching. This is possible depending on the ability of the actuator (stepping motor in this embodiment).

However, in reality, in the high-pressure region of the engine, other engine noise levels are so high that the knocking sound is drowned out and becomes less noticeable.On the other hand, in the low-speed region, even if there is clearance between the lift control cam and the lever, Since the opening/closing speed of the intake/exhaust valves 12 is slow, the tapping sound cannot be discerned, so it is not necessarily necessary to make it strictly proportional to the engine speed.

Furthermore, as shown in Fig. 6, a DC servo motor is used as the actuator instead of a stepping motor, and the rotational position of the control shaft is detected by a potentiometer.
After comparing with the command value, PID (
The gain value (proportional, integral, differential) is determined, and a duty current is output to a DC servometer to perform feedback position control.

<Effects of the Invention> As explained above, according to the present invention, when controlling the lift amount of the intake/exhaust valve in the increasing direction, the rotational speed of the control shaft is controlled to be slow in the first half and fast in the second half, so that the rotation speed of the control shaft is slowed in the first half and fast in the second half. During lift switching operation, the amount by which the lift control cam is returned to the lower stage due to the reaction force of the valve spring is significantly reduced, thereby almost eliminating the clearance between the lift control cam and the lever due to overshoot of the lift control cam. Therefore, it is possible to significantly reduce the tapping noise generated when changing the valve lift.

[Brief explanation of drawings]

1 to 3 are diagrams showing the characteristics of each part at the control start timing during control by the control method according to the first embodiment of the present invention, and FIG. 4 is a diagram showing the profile of the lift control cam of the same embodiment. FIG. 5 is a diagram showing the characteristics of the lift amount with respect to the rotation angle of the lift control cam, FIG. 6 is a diagram showing an outline of the second embodiment of the present invention, and FIG. ,
Diagrams showing the control characteristics of the same example, FIGS. 8 to 10, are as follows:
A vertical cross-sectional view, a plan view, and a perspective view of the vicinity of the lift control cam of a valve control device common to the conventional example and the first embodiment;
Figure 1 is a diagram showing an example of valve lift characteristics of intake/exhaust valves.
FIG. 12 is a diagram showing the characteristics of each part when controlled by a conventional control method. 11... Intake/exhaust valve drive cam 12... Intake/exhaust valve 13... Rocker arm 15... Lever 2
0...Lift control cam 26...Stepping motor 27...Control circuit 2nd...Drive circuit Patent applicant Nissan Motor Co., Ltd. Agent Patent attorney Fujio Sasashima Figure 1 Figure 6 Fr To 1 Go 4 Ya Kanoyu Figure 8 Figure 9 Figure 10 Kunun 7A Section 12

Claims (1)

[Claims] The back surface of the rocker arm that engages the intake/exhaust valve drive cam and the intake/exhaust valve is brought into fulcrum contact with a lever that is supported to swing freely at one end. By engaging a lift control cam having a cam surface of - The lift characteristics of the exhaust valve are variably controlled, the lift control cam is rotatably attached to the control shaft, the lift control cam and the control shaft are connected via an elastic member, and the control shaft is In a valve control device for an internal combustion engine, which is provided with an actuator that rotates to a predetermined rotational position depending on engine operating conditions, the cam surface that engages with the lever of the lift control cam is set from the cam surface on the smaller lift amount side. A valve train control device for an internal combustion engine, characterized in that when the actuator rotates the control shaft so as to change the cam surface to a larger lift amount side, the rotation speed is controlled to be slow in the first half and fast in the second half. Intake/exhaust valve lift control method.