JPS62162710A - Tappet valve control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To improve responsiveness for control in acceleration and deceleration, by changing the angle of a lever abutting against the back of a floating type rocker arm for opening and closing suction and exhaust valves to control a rotating direction of a cam for changing an angle of a lever arbitrarily in controlling a valve opening and closing timing. CONSTITUTION:A suction and exhaust valve opened and closed by a cam through a floating type rocker arm and a lever is disposed at the back of the rocker arm, one end of which being supported by a hydraulic pivot and the other end of which being abutted against a control cam 20. The control cam has a plurality of cam surfaces. An angle of the lever is changed by rotating a shaft 23 by a step motor 26 to change the abutting point of the back of the rocker arm and the lever for controlling an opening and closing timing of a valve 12. A control unit 35 controls the drive of the step motor 26 in accordance with a throttle valve opening 33 an engine r.p.m, In acceleration and deceleration a rotating direction of the shaft 23 is is changed in order to be in direct contact with cam surface, whereby responsiveness is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a valve train control device for an internal combustion engine that variably controls the lift characteristics of intake and exhaust valves according to engine operating conditions.

<Prior Art> As 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 one shown in FIGS. 4 to 6, for example, has been developed by the present applicant. (Japanese Unexamined Patent Publication No. 60-26109 and Japanese Patent Application No. 59-8
(See No. 1052).

To explain this, referring to FIG. 4, 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 S-rocker arm 13 is brought into fulcrum contact with a lever 15 which is supported at one end so as to be swingable by a hydraulic pivot 9 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 swingable manner. and,
Hydraulic pressure is supplied to the hydraulic chamber 19c from a hydraulic pressure supply passage 18b formed inside the bracket through 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.

The lift control cam 20 has a pentagonal shape and has five substantially flat cam surfaces 20a to 20e, each having a different distance from the rotation center axis so as to change the lift i of the intake/exhaust valve 12 in stages.
It also has a hole 20g in the center through which a control shaft 23, which will be described later, is inserted. Further, the cylindrical portion 20h formed to protrude from both ends of the lift control cam 20 is fastened to a lower arc 418c formed on the bracket 18 with bolts 21 on the bracket 18, as shown in FIGS. 5 and 6. An upper arcuate groove 22 formed in a pair of caps 22
It is held freely rotatable between a and a.

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 in a loose fit state, and the control shaft 23 is inserted into both side portions of each lift control cam 20. One end of each fitted torsion coil spring 24 as an elastic member is locked to a stopper 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 based on engine operating conditions such as engine speed and throttle valve opening, and rotates the control shaft 23 to a predetermined rotational position.

28 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 20e having the largest lift amount, the lever 15 is pushed down the most toward 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 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 20a with the smallest lift comes into contact with the lever 15, the end of the lever 15 on the intake/exhaust valve drive cam 11 side 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. 4 compared to when the lever 15 is in contact with the cam surface 20a with the large lift amount, that is, to the side away from the direction in which the fulcrum moves after the lift. As a result,
As shown by the curve Y in FIG. 7, the characteristic is that the riff 1-ffi is small and 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 steering motor 26 . That is, the control circuit 2
7 outputs a drive pulse set based on a signal according to the engine operating state to the stepping motor 26. This drive pulse is applied to the drive shaft 26a of the 7-pin motor 26.
is rotated by a preset angle, and the control shaft 23 is also rotated via the joint 25.

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 11, and the large reaction force of the valve spring 28 is applied to the rocker arm 13. It acts on the lift control cam 20 via the lever 15. Therefore, the lift control cam 20 remains fixed and only the control shaft 23 rotates while twisting the torsion coil springs 24 on both sides thereof. Next, after the intake/exhaust valve drive cam 11 rotates and the intake/exhaust valves 12 close,
The contact fulcrum between the mouth/lug arm 13 and the lever 15 is located approximately above the intake/exhaust valve 12, and the reaction force of the valve spring 28 disappears, so that the lift control cam 20
The only force acting on this is the weak force of the spring 16 attached between the rocker arm 13 and the lever 15. Therefore, the torque stored in the recoil spring 24 during the lift of the intake/exhaust valve 12 can overcome the weak force of the spring 16 and rotate 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 rotational circumference of the adjacent cam surface.

<Problems to be solved by the invention> By the way, in the valve control device of the prior application,
When accelerating from a low load to a high load, the valve lift always increases stepwise from small to large, that is, the lift control cam 20 is rotated clockwise in FIG. During deceleration, the valve lift is controlled to rotate counterclockwise as shown in Fig. 4 so that the valve lift decreases stepwise from large to small.

However, in such a control method, when attempting to switch the cam surface of the lift control cam 20 in a short time during sudden acceleration, the rotation angle required for switching is large, so the rotation speed must be considerably increased. Since the sliding resistance increases accordingly, an actuator such as the stepping motor 26 that has a strong driving torque is required, and furthermore, there is a problem in that the driving loss deteriorates fuel efficiency.

In view of the above-mentioned problems, an object of the present invention is to enable the cam surface to be easily switched in a short time without increasing the driving force of the lift control cam drive actuator during sudden acceleration. do.

Means for Solving Problems> For this reason, the present invention rotates a control shaft connected to a lift control cam via an elastic member to a predetermined rotation position, and adjusts the rotation direction to engine operating conditions. The structure is provided with rotation direction selection means for selecting the rotation direction accordingly.

With this configuration, for example, when switching from the cam surface engagement state with the minimum valve lift to the cam surface with the maximum valve lift during sudden acceleration, the rotation direction selection means adjusts the valve lift 1-4t to the rotation angle of the cam. By selecting the direction of rotation with the largest change, the rotational speed and sliding amount of the cam can be reduced, resulting in a reduction in sliding resistance, which reduces the driving force of the lift control cam, making the drive actuator more compact. and improve fuel efficiency.

(Embodiment) An embodiment of the present invention will be described below with reference to Figs. 1 to 3. Note that the mechanical configurations in Figs. 4 to 6 are the same.

The difference is that in FIG. 1, the signals from the throttle opening sensor 33 that detects the opening of the throttle valve 32 installed in the intake passage 31 of the engine 30, the rotation speed sensor 34 that detects the engine speed, etc. Accordingly, the control circuit 35
It has the function of selecting the direction of rotation of 3.

Specifically, the valve lift, that is, the corresponding switching cam surface, and when switching to the cam surface, the throttle valve opening is determined by the engine speed and the amount of change in the throttle valve opening per time (valve opening speed). The direction of rotation of the control shaft 23 of the stepping motor 2 is determined.
A control signal is output to 6.

This can be done by adding to the control circuit 35 a function of detecting the amount of change in the opening of the throttle valve and a function of selecting the rotation direction of the control shaft 23 in accordance with the function of the earlier application. This can be achieved by adding an internal circuit or by changing the program if the control circuit 35 has a built-in microcomputer.

Next, the valve lift switching control operation by the valve train control device having such a configuration will be explained with reference to FIGS. 2 and 3.

As shown in FIG. 2, during slow acceleration when the opening speed of the throttle valve 32 (corresponding to the slope in the figure) is below a predetermined value, the control circuit 35
The cam surfaces are changed from the cam surface 20a with the minimum valve lift to the cam surfaces 20b, 20c, and 20d so that the valve lift gradually increases.
The valve is then controlled to switch to the cam surface 20e with the maximum valve lift.

During such slow acceleration, the engine speed can follow the increase in the opening of the throttle valve 32 well, so the valve lift is determined only according to the throttle valve opening and the engine speed, as in the steady state, and the control shaft 23 is By selecting a rotation direction that gradually increases the valve lift (clockwise in FIG. 4), smooth and stable operating performance can be ensured.

On the other hand, as shown in FIG. 3, the throttle valve 32
During sudden acceleration, the control circuit 35 detects that the opening speed of the throttle valve 32 has exceeded a predetermined value, and increases the opening speed from the minimum valve lift position to the maximum valve lift position at once. The lift control cam 20 in which the cam surface 20a is engaged is rotated counterclockwise in FIG.
Control is performed to directly switch to 0e.

As a result, the valve lift increases rapidly to cope with an increase in the amount of intake air due to an increase in the opening degree of the throttle valve 32.
Provides quick acceleration performance with good responsiveness.

In this case, since the control is performed so as to directly switch to the adjacent cam surface 20e, the sliding resistance is reduced, making it possible to downsize the stamping motor 26 as an actuator and improve fuel efficiency.

Next, after the opening degree of the throttle valve 32 has settled down to the maximum, normal valve lift control is performed based on the throttle valve opening degree and the engine speed. In this case, since the engine speed N is still small, in order to suppress the decrease in intake air filling efficiency due to pulp overlap, the cam surface 20c with the valve lift in the middle is selected, and the control shaft 23 is rotated counterclockwise in the same figure. Switching is controlled by rotating in the direction.

Thereafter, the cam surfaces 20a and 2oe are sequentially selected and controlled to change over in order to gradually increase the valve lift as the engine speed N increases.

In this embodiment, the control axis 2 is adjusted by taking into account the opening speed of the throttle valve.
In addition to this, the rotation direction is selected by detecting load-related state variables such as accelerator opening (accelerator pedal depression amount), basic injection amount, and intake air flow rate. It is also possible to have a configuration in which

In addition, during deceleration, the control shaft is rotated clockwise from the state of engagement with the cam surface 20e or the cam surface 20d, and switching control is performed so that the cam surface 20a is engaged all at once, resulting in good responsiveness. A decelerated driving state can be obtained.

<Effects of the Invention> As explained above, according to the present invention, since the rotation direction of the control shaft linked to the lift control cam is selected according to the engine operating conditions, the actuator for driving the control shaft can be miniaturized. It is possible to improve various driving performance such as improving responsive acceleration/deceleration performance while improving fuel efficiency.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a valve control device showing an embodiment of the present invention, FIG. 2 is a time chart showing various states of LiI during slow acceleration of the same embodiment, and FIG. 3 is a time chart showing various states of LiI during sudden acceleration. Fig. 4 is a longitudinal sectional view of a conventional valve control device, Fig. 5 is a plan view of the same as above, Fig. 6 is a perspective view of the lift control cam portion, and Fig. 7 is a time chart showing the BMk. FIG. 3 is a diagram showing valve lift characteristics. 11... Intake/exhaust valve drive cam 12... Intake/exhaust valve 13... Rocker arm 15... Lever 2
0... Lift control cam 20a-20e... Cam surface 23... Control shaft 24... Ti recoil spring motor 30... Engine 33... Throttle opening sensor 34... Rotation speed sensor 35 ... Control circuit patent applicant Fujio Sasashima Patent attorney, Nissan Motor Co., Ltd. Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] The curved 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 swingably supported at one end, and the center of rotation is placed at the other end of this lever. By engaging a polygonal lift control cam with multiple cam surfaces at different distances from the shaft and controlling the rotational position of this lift control cam to change the swinging position of the lever, the lever and rocker arm can be The lift characteristics of the intake/exhaust valves are variably controlled by changing the fulcrum position in contact with the lift control cam, and the lift control cam is rotatably attached to the control shaft, and the lift control cam and the control shaft are rotated about the axis. A valve train control device for an internal combustion engine, comprising an actuator that is connected to an actuator via an elastic member having elasticity and rotates the control shaft to a predetermined rotation position according to engine operating conditions,
A valve train control device for an internal combustion engine, characterized in that a rotation direction selection means is provided for selecting a rotation direction in which a control shaft is rotated to the predetermined rotation position according to engine operating conditions.