JPH066886B2 - Intake and exhaust valve lift control device for multi-cylinder internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an intake / exhaust valve lift control device for a multi-cylinder internal combustion engine that variably controls lift characteristics of intake / exhaust valves according to engine operating conditions.

<Prior Art> A device for variably controlling the lift characteristics (opening / closing timing and lift amount) of intake / exhaust valves so that the valve overlap, the fresh air charging efficiency, etc. are always set optimally is shown in, for example, FIG. (Reference: US Pat. No. 3,413,965)
issue).

The outline of this will be described with reference to the drawings. One end of the rocker arm 3 comes into contact with the intake / exhaust valve drive cam 1 and is fitted to the stem end of the intake / exhaust valve 2 so that the rear surface 3a of the rocker arm 3 that is freely rocked is indicated. The back surface 3a is curved, and both ends of the rocker arm 3 swing while the back surface 3a is in contact with the lever 4 as a fulcrum, whereby the lift of the intake / exhaust valve drive cam 1 is transmitted to the intake / exhaust valve 2. In particular, one end of the lever 4 is swingably supported by the engine body, and the lift control cam 5 that abuts the swing position (tilt) of the lever 4 on the other end is controlled by a hydraulic actuator or the like to meet the engine operating conditions. Therefore, the lift characteristic of the intake / exhaust valve 2 is variably controlled by changing the fulcrum position where the back surface 3a of the rocker arm 3 and the lever 4 come into contact with each other by rotationally driving the rocker arm 3 to an appropriate phase.

For example, if the amount by which the lever 4 is pushed down by the lift control cam 5 is large, the free end of the lever 4 and the rocker arm 3 are close to each other in the base circle state of the intake / exhaust valve drive cam 1, and therefore, The lift amount increases as the opening timing of the exhaust valve 2 advances. Conversely, the lift control cam 5
If the amount of pushing down is small, the intake / exhaust valve drive cam 1
In the base circle state, the free end of the lever 4 and the rocker arm 3 are separated from each other, so that the valve opening timing of the intake / exhaust valve 2 is delayed and the lift amount is reduced.

However, in such a conventional intake / exhaust valve lift control device, since the lift characteristic of the support shaft 5a integrated with the lift control cam 5 is variably controlled by a hydraulic actuator or the like, Was causing problems.

That is, the reaction force of the valve spring 6 via the rocker arm 3 and the lever 4 causes the lift control cam 5 or its support shaft 5a.
Therefore, a frictional force is generated on the contact surface between the lever 4 and the lift control cam 5 or the sliding surface between the support shaft 5a and the support shaft member, and the actuator overcomes these frictional forces. Since it is necessary to rotate the lift control cam 5 by means of this, a large force is required, resulting in an increase in the size of the actuator and an increase in energy loss for control.

Especially, in the engine of four cylinders or more in which the reaction force of the valve spring always acts on the lift control cam 5 in any of the cylinders, the above problem becomes extremely large.

Further, since the cam surface of the lift control cam 5 has an elliptical shape (or an eccentric shape), the lift control cam 5 is deviated due to the deviation between the direction of the reaction force from the lever 4 and the center of the rotation axis of the lift control cam 5. Since a moment in the rotational direction acts on the engaging surface of the cam surface and the lever 4 is apt to move, the reliability is poor, and it is necessary to always apply a force that opposes the moment. Had a problem of causing energy loss.

In view of the above problems, the applicant of the present application has a configuration in which the lift characteristics can be switched in multiple stages, and the lift control cam and the control shaft that rotationally drives the cam are rotated relative to each other by a predetermined amount around an axis via an elastic member. There has been proposed a lift control device having a structure in which the lift control device is connected as possible (see Japanese Patent Laid-Open No. 60-26109).

In this cylinder, the lift control cam does not rotate in the cylinder in which the intake / exhaust valve is being lifted when switching the lift characteristics, but only the control shaft rotates and the elastic member twists to accumulate the rotational force. Is rotated and the characteristics are switched. As a result, the driving force of the actuator for driving the control shaft can be reduced.

<Problems to be Solved by the Invention> However, even in the case where the lift characteristics are switched during the non-lift period of the intake / exhaust valve (the base circle period of the intake / exhaust valve drive cam) as described above, There was such a problem. That is, when the lift control cam is switched in two or more steps, the control shaft is driven to rotate by an amount corresponding to the switching lift by an actuator such as a stepping motor in response to the switching signal, so that the control shaft is not rotated in the cylinder in the non-lift period. While the target lift characteristics can be switched to the target without delay, the lift characteristics cannot be switched at all during the lift period, and there is a state where the cylinders are operated with intake / exhaust valve lift characteristics that differ by two or more stages at the same time. Therefore, drivability at the time of switching may be deteriorated.

The present invention has been made in view of these problems.
An object of the present invention is to provide an intake / exhaust valve lift control device for a multi-cylinder internal combustion engine, which can prevent the lift characteristics from being greatly different between the cylinders when switching the lift characteristics of the exhaust valve to reliably prevent deterioration of drivability. And

<Means for Solving the Problems> Therefore, the present invention has a variable mechanism capable of switching the lift characteristics of the intake / exhaust valve in multiple stages, and during the non-lift period of the intake / exhaust valve for each cylinder. In an intake / exhaust valve lift control device for a multi-cylinder internal combustion engine in which the lift characteristics are switchable, the selecting means for selecting one lift characteristic from the multi-stage lift characteristics based on the engine operating conditions, and the lift characteristics are Drive means for switching the variable mechanism until the lift characteristics match the selected lift characteristic, and during the switching operation, the lift characteristics of all the cylinders are set to 1
Control means for controlling the drive means so as to start switching to the next lift characteristic after waiting for the stage switching.

<Operation> When the lift characteristics are switched in two or more stages, with this configuration, the switching to the next lift characteristic is started after waiting for all the cylinders to be switched in one step, so that two or more cylinders simultaneously have two or more stages. Lift characteristics do not differ, and deterioration of driving characteristics can be prevented.

<Example> Hereinafter, an example of the present invention is described based on a drawing.

In FIG. 1 showing an embodiment, a rocker arm 13 is provided by contacting both ends with an intake / exhaust valve drive cam 11 that rotates in synchronization with engine rotation and a stem end of the intake / exhaust valve 12. A lever 15 is provided for supporting the curved back surface 13a of the rocker arm 13 as a fulcrum contact and for holding the shaft 13b protruding from both side walls of the rocker arm 13 in the groove 15a via the holding member 14. A spring 16 having a small spring constant is interposed between the spring seat 15b formed on the lever 15 and the holding member 14 to urge the rocker arm 13 downward.

Further, the spherical lower end surface of the hydraulic pivot 19 fitted and held in the bracket 18 fixed to the cylinder head 17 has a concave portion 15c formed in the top wall of the other end of the lever 15 on the intake / exhaust valve 12 stem end side. The lever 15 around the fitting part.
And a lift control cam 20 which is attached to the bracket 18 so as to freely swing, and which is attached to the bracket 18 to rotate freely as described later.
Contacts the top wall of the end of the lever 15 on the intake / exhaust valve drive cam 11 side to regulate the swing position of the lever 15.

The lower end surface of the hydraulic pivot 19 is a recess 15 of the lever 15.
an outer cylinder 19a which fits into the outer peripheral surface of the bracket 18 and whose peripheral surface is slidably inserted into a mounting hole 18a formed in the bracket 18;
The internal cylinder 19b is inserted into the internal cylinder 19a, and a check valve 19d is provided in a hydraulic chamber 19c formed between them. Then, from the hydraulic pressure supply passage 18b formed inside the bracket 18 to the inside of the inner cylinder 19b and the check valve 19b.
Hydraulic pressure is supplied to the hydraulic chamber 19c via d to keep the valve clearance constant.

The lift control cam 20 has six substantially flat cam surfaces C _{1 on the} outer peripheral surface so as to change the lift amount of the intake / exhaust valve 12 stepwise.
To C ₆ and has a cam control shaft 23 to be described later in the center thereof.
It has a hole 20a for inserting. The outer peripheral surface of the cylindrical portion 20b formed so as to project from both sides of the lift control cam 20 has a lower arc groove 18c formed on the bracket 18 and a bolt on the bracket 18 as shown in FIGS. It is rotatably held between the upper arc groove 22a formed in the pair of caps 22 fastened by 21.

Then, one cam control shaft 23 is passed through a hole 20a formed through the central portion of the lift control cam 20 provided in several cylinders,
One end of a coil spring 24 fitted into each side of each lift control cam 20 of the cam control shaft 23 is locked to a set screw 23a screwed into the outer wall of the cam control shaft 23, and the other end of the coil spring 24 is lifted. The control cam 20 is fitted and locked in a hole formed in the side wall of the cylindrical portion 20b of the control cam 20.

One end of the cam control shaft 23 is connected via a joint 25 to a drive shaft 26a of a stepping motor 26 as a driving means. The stepping motor 26 rotates the cam control shaft 23 by a control circuit 27 as a control means.

Here, the control circuit 27 is composed of a microcomputer or the like, and is included in the cam surfaces C _{1 to} C ₆ according to the engine operating conditions such as the engine speed, the throttle valve opening, the cooling water temperature, the intake air flow rate, and the suction negative pressure. To select the cam surface that engages with the lever 15, and when switching from the engaged cam surface to the selected cam surface, the stepping motor is rotated by the rotation angle corresponding to the switching movement to the adjacent cam surface.
After outputting the drive pulse to 26 to rotate the cam control shaft 23, wait for the lift control cams 20 of all the cylinders to switch to the adjacent cam surface, and then switch to the next adjacent cam surface. The stepping motor 26 is controlled to start (details will be described later). 28 is a valve spring.

Next, a series of operations of this embodiment will be described.

In FIG. 1, when the lift control cam 20 is in contact with the lever 15 on the cam surface C ₁ having the largest lift amount, the lever 15 is most pushed down toward the intake / exhaust valve drive cam 11 side. For this reason, the lower surface of the lever 15 that is in fulcrum contact with the rear surface 13a of the rocker arm 13 also lowers, and the fulcrum contact point A is transmitted to the intake / exhaust valve 12 while moving to the intake / exhaust valve drive cam 11 side, and as shown in FIG. As shown by the curve X, 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 rotates and, for example, the cam surface C ₅ having a small lift amount is brought into contact with the lever 15,
The end of the lever 15 on the intake / exhaust valve drive cam 11 side is a recess 15c.
Is raised by swinging around the fulcrum, and the lower surface 15d of the lever 15
Also retreats upward.

The lower surface 15d 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 valve 12, but the intake / exhaust valve drive cam 11 contacts the rocker arm 13 with the base circle. The initial position of the fulcrum in this state moves to the right side in FIG. 1, that is, to the side away from the direction in which the fulcrum moves after the lift, as compared to when the lever 15 is in contact with the cam surface C ₁ having the large lift amount. . As a result, as shown by the curve Y in FIG. 5, the lift amount is small, the valve opening timing is delayed, and the valve closing timing is advanced.

In this way, the lift control cam 20 is rotated to rotate the cam surface C
By abutting one of ₁ -C ₆ the lever 15, it is possible to stepwise change the lift characteristics of the intake and exhaust valves 12.

Here, the rotation of the lift control cam 20 is performed via the cam control shaft 23 and the coil spring 24 by driving the stepping motor 26 according to a signal from the control circuit 27.

The control operation will be described with reference to the flowcharts of FIGS. 5 and 6 and the time chart of FIG.

FIG. 5 shows a routine for starting the cam surface switching control.

In S1, the intake / exhaust valve opening / closing characteristics most suitable for the engine operating conditions detected based on signals such as engine speed, throttle valve opening, cooling water temperature, intake air flow rate, intake negative pressure, etc. are obtained. A predetermined cam surface Cx is selected from the cam surfaces C _{1 to} C ₆ .

In S2, it is determined whether or not the selected cam surface Cx matches the currently engaged cam surface Ci. If this determination is YES, the current state is maintained, and if NO, that is, If it is determined that the engagement cam surface should be switched, the process proceeds to S3.

In S3, during the period from the start of the switching movement to the adjacent cam surface to the start of the switching movement to the next cam surface (B
Whether or not it is in the USY state) is determined by the BUSY / FLAG set in the cam surface switching control routine described later. In the BUSY state where BUSY / FLAG is 1, it waits until the switching control operation is completed.
When the USY state is released and BUSY / FLAG becomes 0, the process proceeds to S4 to start the cam surface switching control.

FIG. 6 shows a cam surface switching control routine.

That is, in S11, BUSY.FLAG is set to 1, and then in S12, the adjacent cam surface (C _{i + 1} or the adjacent cam surface Ci closer to the cam surface Cx selected in S1 from the currently engaged cam surface Ci). The driving pulse number ni given to the stepping motor 26 is set from the rotation angle of the lift control cam 20 required for the switching movement to C _i-1 ).

In S13, a driving current is output to the stepping motor 26, and at the same time, a driving pulse of several ni set in S12 is output to the stepping motor 26 (a, a in FIG. 7).
b). As a result, the cam control shaft 23 rotates through the drive shaft 26a of the motor 26 and the joint 25 by an angle corresponding to the drive pulse ni (c in FIG. 7).

In this case, the cylinders in which the intake / exhaust valve 12 is not lifted at the timing when the cam control shaft 23 rotates (# 2, # 3 and # 3 in FIG. 7).
In the (# 4 cylinder), the contact fulcrum between the rocker arm 13 and the lever 15 is located substantially above the intake / exhaust valve 12, so that the reaction force of the valve spring 28 does not act on the lift control cam 20. The force acting on the lift control cam 20 is a spring mounted between the rocker arm 13 and the lever 15.
There are only 16 weak forces. Therefore, the lift control cam 20 rotates following the rotation of the cam control shaft 23 via the coil spring 24, and the cam surface adjacent to the cam surface Ci engages with the lever 15 (d in FIG. 7).

On the other hand, the cylinder in which the intake / exhaust valve 12 is being lifted at the timing when the cam control shaft 23 rotates (# 1 cylinder in the example of FIG. 7).
, The contact fulcrum between the rocker arm 13 and the lever 15 moves to the intake / exhaust valve drive cam 11 side, so a large reaction force of the valve spring 28 acts on the lift control cam 20 via the rocker arm 13 and the lever 15. To do. Therefore, while the lift control cam 20 is fixed, the coil springs 24 on both sides of the lift control cam 20 are twisted, and only the cam control shaft 23 rotates (seventh).
E) in the figure. After the driving pulse is output, the stepping motor 26 continues to be energized for the set time t ₁ . During this time, when the intake / exhaust valve drive cam 11 of the cylinder whose lift control cam 20 is in the fixed state rotates and the intake / exhaust valve 12 closes, the intake / exhaust valve
12 During the lift, the torque stored in the coil spring 24 overcomes the weak force of the spring 16 to rotate the lift control cam 20 (f in FIG. 7).

Here, the time required for the rotation of the lift control cam 20 depends on the moment of inertia of the lift control cam 20 and the coil spring 24.
Since it is determined by the spring constant and the frictional force and is not influenced by the engine speed, it is possible to perform constant and good switching control.

The reason why the stepping motor 26 is continuously energized is to hold the torque stored in the coil spring 24.

In this way, the lift control cams 20 of all the cylinders are rotated and the switching movement between the adjacent cam surfaces is completed, and when the set time t ₁ has elapsed, the stepping motor is moved to S14.
The power supply to 26 is turned OFF, and the OFF state is set for a set time t ₂
Hold. This is to set the output torque of the stepping motor 26 to 0 even when a so-called step-out phenomenon occurs in which the drive pulse number ni given to the stepping motor 26 and the angle at which the stepping motor 26 actually rotates deviate from each other. Lift control cam 20 by the urging force of spring 16
This is because the substantially flat cam surface of (1) is automatically corrected to the position where it engages with the lever 15 in a stable state.

In S16, the current engagement cam surface switched as described above is set to Ci, and BUSY.FLAG is set to 0 in S17.

At S18, the current engagement cam surface Ci is the selected cam surface C
It is determined whether or not x matches, and if they do not match, the flow from S11 to S17 is repeated to perform switching control to the next adjacent cam surface.

When the engagement cam surface Ci coincides with the selected cam surface Cx by the above operation, the switching control is stopped, and the process proceeds to S19, in which the current supplied to the stepping motor 26 is necessary to stabilize the engagement state of the cam surface. The current consumption is reduced by reducing the current to as small as possible.

As described above, conventionally, when the lift control cam is directly driven by the cam control shaft during the lift of the intake / exhaust valve, a strong torque that overcomes the reaction force of the valve spring is required. By storing torque in the spring 24, the lift control cam 20 can be rotated while the intake / exhaust valve 12 is closed, and after the switching control to the adjacent cam surface is completed, the lift control cam 20 is moved to the next adjacent cam surface. Due to the stepwise control of switching control, the output required for the stepping motor 26 is small enough to be twisted by the rotation angle to the cam surface adjacent to the coil spring 24. Therefore, the stepping motor 26 may be of small size and small capacity, and the engine power loss for control may be small, which leads to improvement of fuel consumption. Further, it is possible to suppress the occurrence of step-out of the stepping motor 26 as the output torque is reduced.

The effect of reducing the control force as described above becomes more remarkable as the number of cylinders increases.

Then, by making the cam surface substantially flat, the engagement state can be stably maintained, and the coil spring 24 is prevented from being excessively twisted during the switching control, and the durability can be improved, and
It is possible to reliably prevent the lift control cam 20 from excessively rotating and engaging with the intermediate portion between the cam surfaces.

Further, in the present embodiment, since the stepping motor is used as the drive means for the cam control shaft, there is an advantage that the electronic control can be easily performed with a compact structure, but the drive means is not limited to this, and a hydraulic actuator is used to switch the hydraulic circuit. It goes without saying that the present invention can also be applied to those controlled by.

It should be noted that even if the lift characteristics of all the cylinders are detected to be switched by one stage, the lift characteristics of each cylinder (the currently engaged cam surface) is detected even in the most basic configuration. Of course good things. Further, the lift characteristic switching control according to the present invention is not limited to the application to the hardware configuration of the present embodiment, and if the lift characteristic switching is performed during the non-lift period of the intake / exhaust valve. Good.

<Effects of the Invention> As described above, according to the present invention, since the switching of the lift characteristics of all the cylinders is completed step by step and the switching of the next lift characteristics is started, the two cylinders are simultaneously operated. It is possible to reliably prevent the lift characteristics from being different in more than one stage, and thus to prevent deterioration in drivability.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of an essential part of an embodiment of the present invention, FIG. 2 is a plan view of an essential part of the same embodiment, and FIG. 3 is an exploded perspective view showing a method for mounting a lift control cam of the same embodiment. 4 is a graph showing the valve lift characteristic of the above embodiment, FIG. 5 is a flowchart showing a routine for starting the cam switching control of the above embodiment, and FIG. 6 is a flowchart showing a cam surface switching control routine of the above embodiment. FIG. 7 is a time chart showing signals and operation switching states of various parts of the above embodiment, and FIG. 8 is a vertical sectional view showing an example of a conventional intake / exhaust valve lift control device for an internal combustion engine. 11 ... intake / exhaust valve drive cam, 12 ... intake / exhaust valve, 13 ... rocker arm, 15 ... lever, 20 ... lift control cam, 23 ... cam control shaft, 24 ... coil spring, 26 ... stepping motor, 27 ... control circuit , C _{1 to} C ₆ ... Cam surface

Front Page Continuation (72) Inventor Hiroto Bito 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd. (56) Reference JP-A-60-26109 (JP, A)

Claims (1)

[Claims] 1. A variable mechanism capable of switching the lift characteristics of intake / exhaust valves in multiple stages and capable of switching the lift characteristics for each cylinder during a non-lift period of the intake / exhaust valves. In an intake / exhaust valve lift control device for a cylinder internal combustion engine, selection means for selecting one lift characteristic from multistage lift characteristics based on engine operating conditions, and the variable until the lift characteristics match the selected lift characteristic. A drive means for switching the mechanism, and during the switching operation, the lift characteristics of all the cylinders are 1
An intake / exhaust valve lift control device for a multi-cylinder internal combustion engine, comprising: a control means for controlling the drive means so as to start switching to the next lift characteristic after waiting for the stage switching.