JPS6123813A - Suction and exhaust valve lift control device for internal-combustion engine - Google Patents

Abstract

PURPOSE:To control twist torque stored in an elastic member to a low value, by a low valve, by a method wherein an elastic member is located between a cam, controlling the lift amount of a valve, and a cam control shaft, and the rotation speed of a cam control shaft is set on a basis of the lift period of a valve. CONSTITUTION:Rotation of a lift control cam 20 causes changing of a fulcrum position allowing a lever to be brought into contact with the back of a locker arm to control lift characteristics of a suction and exhaust valves. The control cam 20 is formed with plural about flat cam surfaces, and a lift amount is shifted in a stepped manner. An elastic member 24 is located between the control cam 20 and a control shaft 23, and the control shaft 23 is rotated depending upon the state of an engine. In a rotation speed, a time, in which rotation is effected by a rotation angle of the adjoining cam surfaces with each other, is set to a value about 2 or more times as long as the lift period of a valve. This, when a cam surface is shifted, enables control of torque, stored in the elastic member 24 during lift of a valve, to a low value, and permits reduction of the output torque of a driving means 26.

Description

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

(Prior art) As an example of a device that variably controls the lift characteristics (opening/closing timing and lift amount) of intake and exhaust valves so that valve overramp, fresh air filling efficiency, etc. are always optimally set, as shown in Fig. 9, for example. (Reference: US Pat. No. 3,413,965).

To explain the outline of this device based on a diagram, the back surface 3a of the rocker arm 3 whose one end is in contact with the intake/exhaust valve drive cam 1 and which is fitted to the stem end of the intake/exhaust valve 2 and is instructed to swing freely. The rear surface 3a is in fulcrum contact with the lever 4 while both ends of the rocker arm 3 swing, thereby transmitting the lift of the intake/exhaust valve drive cam 1 to the intake/exhaust valves 2. In particular, one end of the lever 4 is rotatably supported by the engine body, and the swing position (inclination) of the lever 4 is controlled by a hydraulic actuator or the like to adjust the lift control cam 5 that abuts the other end to the engine operating conditions. The lift characteristic of the intake/exhaust valve 2 is variably controlled by controlling the rotary drive in an appropriate phase accordingly, thereby changing the fulcrum position where the back surface 3a of the rocker arm 3 and the lever 4 contact.

For example, if the lever 4 is pushed down by a large amount by the lift control cam 5, the free end of the lever 4 and the opening/socket arm 3 are close to each other in the base circle state of the intake/exhaust valve drive cam 1, and therefore, , the opening timing of the intake/exhaust valves 2 is advanced and the lift amount becomes large. Conversely, if the amount of depression by the lift control cam 5 is small, the free end of the lever 4 and the rocker arm 3 are separated from each other in the pace circle state of the intake/exhaust valve drive cam 1, and therefore the intake/exhaust valve As the opening timing of the second valve is delayed, the lift it becomes smaller.

<Problems to be Solved by the Invention> However, in such a conventional intake/exhaust valve lift control device, the lift characteristics of the support shaft 5a integrated with the lift control cam 5 are variably controlled by a hydraulic actuator or the like. Due to this configuration, the following problems occurred.

That is, rocker arm 3. The reaction force of the valve spring 6 is applied via the lever 4 to the lift control cam 5 or its support shaft 5a.
(not shown), a frictional force is generated on the contact surface between the lever 4 and the lift control cam 5 or on 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 using the actuator, a large force is required, resulting in an increase in the size of the actuator and an increase in energy loss for control.

In particular, the above problem becomes extremely serious in engines with four or more cylinders in which the reaction force of the valve spring always acts on the lift control cam 5 in any one of the cylinders.

In addition, since the cam surface of the lift control cam 5 has an elliptical shape (or an eccentric circular shape), the lift control cam 5 may be A moment in the rotational direction acts on the cam surface, and the engagement surface between the cam surface and the lever 4 is likely to move, resulting in poor reliability. Moreover, it is necessary to constantly apply a force that opposes the moment. There was also the problem of energy loss.

The present invention has been developed in view of these conventional problems, and uses elastic force to store the necessary minimum rotational driving force of the lift control cam when the intake/exhaust valves are lifted, and allows the lift control cam to rotate when the intake/exhaust valves are not lifted. The driving force can be reduced to the necessary minimum, thereby reducing the size of the driving means and reducing the loss of control energy.In addition, the lift control cam and lever are held in a stable state of engagement, which improves control reliability. An object of the present invention is to provide an intake/exhaust valve lift control device for an internal combustion engine that can maintain improved control performance.

(Means for solving the problem of point B) Therefore, the present invention changes the intake/exhaust valve slope characteristics by rotating the lift control cam as described above and changing the fulcrum position where the lever and the back surface of the rocker arm come into contact. In the control device, the lift control cam is formed with a plurality of substantially flat cam surfaces that change the lift amount of the intake and exhaust valves stepwise in the same rotational direction, and the lift control cam and the lift control cam are rotated. A cam control shaft is connected to the cam control shaft through an elastic member having elasticity around the rotating shaft, and a drive means is provided for driving the cam control shaft by a predetermined amount of rotation according to engine operating conditions, and the drive means is driven by the drive means. The rotation speed of the cam control shaft is set so that the time required for the lift control cam to rotate by the rotation angle of the adjacent cam surfaces is approximately twice or more than the lift period of the intake and exhaust valves. .

With this configuration, even if the elastic member is twisted to the maximum due to the relative rotation between the fixed lift control cam and the rotating cam control shaft when the intake/exhaust valves are lifted, this torsion angle will be smaller than that of the lift control cam adjacent to the lift control cam. Since the rotation angle of the cam surfaces does not exceed the mutual rotation angle between the cam surfaces, it is possible to prevent the elastic member from twisting too much, and when switching the cam surfaces, it is also possible to prevent the lift control cam from rotating too much, thereby stabilizing the switching engagement with the cam surfaces one by one. and be carried out reliably.

(Example> Embodiments of the present invention will be described below based on the drawings.

In FIGS. 1 to 3 showing one embodiment, an intake/exhaust valve drive cam 11 and an intake/exhaust valve 1 rotating in synchronization with the m rotation are shown.
Rocker arm 1 with both ends in contact with the stem end of 2.
3 is provided, and a lever 15 is provided that brings the curved back surface 13a of the rocker arm 13 into fulcrum contact and holds 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 with a small spring constant is interposed between the spring seat 15b formed on the lever 15 and the holding member 14 to bias the rocker arm 13 downward.

Further, the spherical lower end surface of the hydraulic pivot I9, which is fitted and held by a bracket 18 fixed to the cylinder head 17, is in a concave portion 15c formed on the top wall of the other end of the lever 15 on the stem end side of the intake/exhaust valve 12. The lift control cam 20 is fitted into the bracket 18 to support the lever 15 in a freely swinging manner about the fitting part, and the lift control cam 20 is rotatably attached to the bracket 18 as will be described later. The swinging position of the lever 15 is regulated by coming into contact with the top wall of the end portion on the drive cam 11 side.

The hydraulic pivot 19 has an outer cylinder 19 whose lower end surface fits into the concave portion 15C of the lever 15, and whose peripheral surface is slidably inserted into the mounting hole 18a formed in the bracket 18.
a, an inner cylinder 19b that is fitted into the outer cylinder 19a, and a check valve 19d in a hydraulic chamber 19C formed between the two. The inner cylinder 19 is connected from the hydraulic pressure supply passage 18b formed inside the bracket 18.
The pulp clearance is kept constant by supplying hydraulic pressure to the hydraulic chamber 19c through the inside b and the check valve 19d. N The lift control cam 20 has four substantially flat cam surfaces 01 to C on its outer peripheral surface so as to increase the lift amount of the intake/exhaust valves 12 stepwise in the same rotational direction, and The bracket 18 is positioned at a position where the cam surface C1 that minimizes the lift amount with respect to the direction of rotation that reduces the lever 15 engages with the lever 15.
A stopper 20a that engages with a protrusion 18C formed on a part of the
, and has a hole 20b in the center thereof through which a cam control shaft 23 (described later) is inserted. Further, the outer circumferential surface of the cylindrical portion 20c formed to protrude from both sides of the lift control cam 20 is fastened to a lower circular groove 18d formed in the bracket 18 with a port 21 on the bracket 18, as shown in FIG. It is rotatably held between the upper arcuate grooves 22a formed in the pair of caps 22.

Then, some of the cam control shafts 23 are passed through holes 20b formed by penetrating the center of the lift control cams 20 provided in several cylinders, and the cam control shafts 23 are fitted into both sides of each lift control cam 20, respectively. One end of the inserted coil spring 24 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 inserted into a hole formed in the side wall of the cylindrical portion 20c of the lift control cam 20. to lock.

One end of the cam control shaft 23 is connected via a joint 25 to a drive shaft 26a of a stepping motor 26 serving as a drive means. Is the stepping motor 26 M? [1 circuit 27 rotates the cam control shaft 23.

The control circuit 27 is composed of a microcomputer, etc., and selects lever 1 from among cam surfaces 01 to C4 according to engine operating conditions such as engine speed, throttle valve opening, cooling water temperature, intake air flow rate, and intake negative pressure.
5, and when switching from the engaged cam surface to the selected cam surface, the stepping motor 2G is rotated by the rotation angle corresponding to the switching movement to the selected cam surface. The stepping motor 26 is controlled to rotate the cam control shaft 23 by outputting a drive pulse. Here, the driving speed of the stepping motor 26, ie, the rotational speed of the cam control shaft 23, is set as follows.

That is, when the time required for adjacent cam surfaces to rotate by the rotation angle relative to each other is T, the following equation is set so as to hold true.

Here, the right side of the above equation corresponds to twice the lift period of the intake and exhaust valves when the four-stroke engine is idling.

Next, the operation of this embodiment will be explained.

For example, as shown in FIG. 1, when the lift control cam 20 is in contact with the lever 15 at the cam surface C1 with the largest lift amount, the lever 15 is pushed down the most toward the intake/exhaust valve drive cam 11. state. For this reason, the lower surface of the lever 15, which is in fulcrum contact with the back surface 13a of the rocker arm 13, also lowers, and the fulcrum contact point A moves toward the intake/exhaust valve drive cam 11 side and is transmitted to the intake/exhaust valves 12, as shown in FIG. As shown by 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, contacts the lever 15 with the cam surface C2 having a small lift amount, the end of the lever 15 on the intake/exhaust valve drive cam 11 side uses the concave portion 15C as a fulcrum. It rises due to the oscillation, and lever 1
The lower surface 15d of 5 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 valves 12. The initial position of the fulcrum in the state where lever 1
5 moves to the right in FIG. 1 compared to when they are in contact, that is, to the side away from the direction in which the fulcrum moves after the lift.

As a result, as shown by curve Y in FIG. 4, the lift amount is small, 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 01 to C4 into contact with the lever 15, the lift characteristics of the intake/exhaust valves 12 can be changed in stages.

Here, the rotation of the lift control cam 20 is controlled via a cam control shaft 23 and a coil spring 24 by driving a stepping motor 26 in response to a switching signal from a control circuit 27 that detects changes in engine operating conditions and operates. It will be done.

Next, the cam surface switching control operation will be explained with reference to the flowchart shown in FIG.

SL is designed to provide intake/exhaust valve opening/closing characteristics that are optimal for the engine operating conditions detected based on signals such as engine speed, throttle valve opening, cooling water temperature, intake air flow rate, and intake negative pressure. A predetermined cam surface Cx is selected from among the cam surfaces Cl-04.

In S2, it is determined whether the selected cam surface Cx matches the cam surface Ci currently in the engaged state, and if this determination is YES, the current state is maintained, and it is determined that it is NO. In other words, if it is determined that the engaging cam surface should be switched, the process advances to S3.

In S3, the number n i of drive pulses given to the stepping motor 26 is set based on the rotation angle of the lift control cam 20 required for switching movement from the cam surface Ci currently in the engaged state to the cam surface Cx selected in 81.

In S4, the number ni drive pulses set in S2 are output to the stepping motor 26. As a result, the drive shaft 26a of the motor 26 is connected to the cam control shaft 23 via the joint 25.
is rotated by a predetermined angle according to the drive pulse ni.

In S5, the power to the stepping motor 26 is turned off for a short time after a set time has elapsed after the drive pulse is output, and in S6, a weak holding current is applied to the stepping motor 26, and in S7, the cam surface Cx after switching and maintenance is changed to C4. set.

Now, the switching operation of each cylinder will be described with reference to the time chart of FIG. 6 when controlling the switching from the cam surface C1 with the minimum lift amount to the cam surface C3 with the large lift amount.

The intake/exhaust valve 12 is activated at the timing when the cam control shaft 23 rotates.
is not lifted, rocker arm 13 and lever 1
Since the contact fulcrum with 5 is located near the upper part of the intake/exhaust valve 12, the reaction force of the valve spring 28 does not act on the lift control cam 20, and the force acting on the lift control cam 20 is transferred to the rocker arm. Only a weak force is exerted by the spring 16 attached between the lever 13 and the lever 15. Therefore, the lift control cam 20 rotates following the same rotation of the cam control shaft 23 via the coil spring 24.

On the other hand, when the intake/exhaust valves 12 are in lift at the timing when the cam control shaft 23 rotates, the contact fulcrum between the rocker arm 13 and the lever 15 moves toward the intake/exhaust valve drive cam 11. A large reaction force on valve spring 2 causes rocker arm 13. It acts on the lift control cam 20 via the lever 15. Therefore, only the cam control shaft 23 rotates while the lift control cam 20 remains fixed while twisting the coil springs 24 on both sides thereof.

Therefore, when switching from the adjacent cam surface 01 to the force surface C2, the boundary between the cam surfaces C1 and C2 is in line contact engagement with the lever 15, and the reaction force from the lever 15 lifts the surface. If the lift of the intake/exhaust valves 12 is started while the rotational moment generated on the control cam 20 is acting in the opposite direction to the switching direction of the cam surface, the reaction force of the valve spring 28 will cause Cam surface C
3 is returned to the position where it engages in surface contact with the lever 15, and torsional torque is stored in the coil spring 24 accordingly (
part a of Figure 6). Next, when the lift of the intake and exhaust valves is completed, the torsional torque stored in the coil spring 24 causes the lift control cam 20 to rotate to a position where it follows the cam control shaft 23 (section b in FIG. 6).

As the rotation progresses in this way, the rotational moment generated in the lift control cam 20 due to the reaction force from the lever 15 is applied to the cam surface C.
When the lift of the intake/exhaust valve 12 is started at the same stage as the switching direction to 2, the reaction force of the valve spring 28 instantly moves the cam surface C2 to a position where it engages in surface contact with the lever 15. Rotate (section C in Figure 6). As a result,
The lift of the intake/exhaust valve 12 increases due to the switching engagement with the cam surface C2. From cam surface C2 to cam surface C in the same manner.
3 is performed. After the drive pulse output is completed, the stepping motor 26 is continuously energized to support the torsional torque of the coil spring 24 until the last cylinder's four-plane force switching is reliably completed, and then the stepping motor 26 is turned off once.
After releasing the supporting torque as shown in FIG. A small current is applied so that the

In such switching control, the time required to rotate the rotation speed of the cam control shaft 23 by the rotation angle of the adjacent cam surfaces as described above is more than twice the lift period of the intake and exhaust valves (as shown in FIG. 6). In the embodiment shown, the value is set to be sufficiently larger than this value, so that smooth and stable switching control can be performed as described below.

For example, as opposed to the above case, as shown in Figure 7, if the rotational speed of the cam control shaft is set so that the lift period of the intake and exhaust valves is such that the rotation angle of the cam surfaces that are two intervals apart is such that the valves rotate. When the lift of the intake/exhaust valves 12 is started with the rotation of the cam control shaft 23, during the lifting period of the intake/exhaust valves 12, a large force is applied to the coil spring 24 corresponding to the rotation angle between the two cam surfaces. Torsional torque is stored. At the end of the lift, this large torsional torque causes the switch to the next cam surface at once, but due to the large acceleration, the lift control cam 20 rotates to the next cam surface due to momentum due to inertia, resulting in an unstable position. There is a risk that it may become engaged.

Further, since a large torsional torque acts on the coil spring 24, its durability is reduced.

Furthermore, as a drive means for the cam control shaft 23, a device with a large output torque is required, especially the stepping motor 26.
When using this, the increase in torque tends to cause step-out, which reduces reliability.

On the other hand, when the rotational speed of the cam control shaft 23 is set to such a value that the adjacent cam surfaces rotate by the mutual rotation angle in a time approximately twice the lift period of the intake/exhaust valves, the torsional torque of the coil spring 24 is・During the lift period of the exhaust valve, the maximum value is reached in the state shown in FIG.

That is, after the cam control shaft 23 starts rotating, the intake/exhaust valves are lifted when the cam control shaft 23 has rotated by an angle of about 2 times the rotation angle between the adjacent cam surfaces and the boundary point between the cam surfaces is engaged with the lever. The cam control shaft 23 is rotated in the opposite direction to the switching direction by the reaction force from the valve spring 28 and returned to the position where the cam surface and the lever engage before switching.
This is a case where torsional torque is stored in the coil spring 24 due to the rotation of the coil spring 24. In this case, until the lift of the intake/exhaust valve 12 is completed, torsional torque approximately equivalent to the mutual rotation angle of the adjacent cam surfaces is accumulated, and after the lift is completed, the torsional torque is appropriately applied. The cam control shaft 23 rotates at a certain speed, and switching to the adjacent cam surface is performed.

If the start of the lift of the intake/exhaust valve 12 is relatively earlier than in the state shown in FIG. The amount of torsional torque decreases.

On the other hand, if the rotation of the cam control shaft 23 is relatively accelerated from the state shown in FIG. valve spring 28 at the start of the lift.
When the reaction force is received, the cam surface is switched at that point.

Therefore, in the state shown in FIG. 8, the torsional torque stored in the coil spring 24 is maximum.
Since the maximum torsional torque is approximately equivalent to the rotation angle between the adjacent cam surfaces, the lift control cam does not rotate too much during switching and continues to output drive pulses. Also, switching to the cam surface is performed stably and reliably one by one.

Furthermore, since the maximum torsional torque stored in the coil spring 24 can be reduced, durability is improved and wear of the engagement surface between the lift control cam 20 and the lever 15 can be suppressed.

Furthermore, since the output torque of the driving means can be reduced, the size can be reduced, and the occurrence of step-out can also be suppressed, especially when using the stepping motor 26, which has a simple structure and is easy to use.
Improves reliability.

In this embodiment, the rotational speed of the cam control shaft 23 is set based on the lift period of the intake and exhaust valves at idle, so in the normal rotation range other than idle, the maximum torsional torque stored in the coil spring 24 is further reduced. However, stable switching control is performed over the entire rotation range, but it is necessary to detect the engine rotation speed and set the rotation speed of the cam control shaft 23 based on the lift period of the intake and exhaust valves when switching the cam surface. The control speed may be increased according to the engine speed.

<Effects of the Invention> As explained above, according to the present invention, the cam surface of the lift control cam is shaped to include a plurality of protonated cam surfaces, and the lift control cam and the cam control shaft are arranged around the rotation axis. By connecting via an elastic member having elasticity and setting the rotational speed of the cam control shaft based on the lift period of the intake/exhaust valves, the above-mentioned rotational speed during the intake/exhaust valve lifts is achieved when controlling the switching of the cam surface. The torsional torque stored in the elastic member can be minimized, and the cam surfaces can be switched and engaged one by one stably and reliably.

Further, durability can be improved by preventing excessive twisting of the elastic member, and furthermore, the output torque of the cam control shaft driving means can be reduced to achieve miniaturization, and other various features are provided.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view of the main parts of the first embodiment of the present invention, Fig. 2 is a plan view of the main parts of the same embodiment, and Fig. 3 shows how to install the lift control cam of the above embodiment. FIG. 4 is a graph showing the valve lift characteristics of the above embodiment, FIG. 5 is a flowchart showing the cam surface switching control routine of the above embodiment, and FIG. 6 is a flow chart showing the cam surface switching control routine of the above embodiment. Time chart, Figure 7 is a time chart showing the state of the valve lift and torsional torque stored in the coil spring when the rotation speed of the cam control shaft is set high, and Figure 8 is a time chart showing the state of the torsional torque stored in the coil spring when the rotation speed of the cam control shaft is set low. Time chart 1 showing the state of the valve lift of the intake/exhaust valve and the torsional torque of the coil spring when . 11... Intake/exhaust valve drive cam 12... Intake/exhaust valve 13... Rocker arm 15... Louver 20
...Lift control cam 23 River cam control axis 24.
... Coil spring 26 ... Stamping motor 27 ... Control circuit C6 - c4 ... Cam surface patent applicant Nissan Motor Co., Ltd. agent Patent attorney Fujio Sasashima Figure 3 Figure 40 2 Lumph II 4 Figure 5

Claims (1)

[Claims] The curved back surface of the rocker arm, whose ends engage the intake/exhaust valve drive cam and the stem ends of the intake/exhaust valves, is brought into fulcrum contact with a lever that is swingably attached to the engine body along the back surface; By controlling the amount of rotation of a lift control cam engaged with one end of the lever and changing the rocking position of the lever, the fulcrum position where the lever and rocker arm come into contact is changed and the intake/exhaust valves are lifted. In an internal combustion engine intake/exhaust valve lift control device that variably controls characteristics, the lift control cam is formed with a plurality of substantially flat cam surfaces that change the amount of lift of the intake/exhaust valves in stages; A drive in which a control cam and a cam control shaft that rotates the lift control cam are connected via an elastic member having elasticity around the rotation axis, and the cam control shaft is rotated by a predetermined amount depending on engine operating conditions. means is provided, and the time required to rotate the rotation speed of the cam control shaft driven by the drive means by the mutual rotation angle of adjacent cam surfaces of the lift control cams is approximately twice or more than the lift period of the intake/exhaust valves. An intake/exhaust valve lift control device for an internal combustion engine, characterized in that it is set so that: