JPS62159709A - Valve operation control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To provide a reliable operation with use of a compact motor having a small capacity, by detecting a rotational speed of a motor such as a d.c. motor for driving a lift control cam, and controlling an output voltage to the motor so as to make the detected rotational speed equal to a target rotational speed. CONSTITUTION:A lift characteristic is variable with a stepwise change of a lift control cam 20 in association with a rotation of a control shaft 23 by a motor 26. A battery B as a power source for a driving circuit A of the motor 26 is connected through a DC/DC converter C to the driving circuit A. Further, a rotative speed detecting means D is provided to detect a rotative speed of the motor 26, and a comparing means E is provided to compare the detected rotative speed with a target rotative speed set according to engine operational conditions. According to the comparative result obtained by the comparing means E, the DC/DC converter C is controlled by an output voltage control means F to control an output voltage to the motor 26.

Description

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 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. 5 to 7, for example, has been developed by the present applicant. (Japanese Patent Application Laid-Open No. 60-26109 and JP-A No. 60-2
24909).

To explain this, referring to FIG. 5, 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 rocker arm 13 is brought into fulcrum contact with a lever 15 that 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 a spring seat 15b formed on the lever 15 and the holding member 14 are connected to each other. 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. number,
Hydraulic pressure is supplied from a hydraulic pressure supply passage 18b formed inside the bracket 18 to the hydraulic chamber 19C 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 hexagonal shape and has five substantially flat cam surfaces 20a to 20e of different heights so as to change the lift amount of the intake/exhaust valves 12 in stages.
It 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 200 is fastened to the lower arcuate groove 18c formed in the bracket 18 with bolts 21 on the bracket 18, as shown in FIGS. 6 and 7. It is rotatably held between the upper arcuate grooves 22a formed in the pair of caps 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 in a loose fit state, and the control shaft 23 is inserted into both side portions of each lift control cam 20. A set screw 2 screws one end of each fitted torsion coil spring 24 into the outer peripheral surface of the control shaft 23.
3a, and the other end of the coil spring 24 is fitted into a hole 20i formed in the side wall of the cylindrical portion 20h of the lift control cam 20.

One end of the control shaft 23 is connected to a direct current (DC”) via a joint 25.
) It is connected to a drive shaft 26a of a motor 26 such as a motor or a stepping motor. The motor 26 is driven by a control circuit 27 via a drive circuit 27 based on engine operating conditions such as engine speed and throttle valve opening to rotate the control shaft 23 to a predetermined rotation position. It has become.

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 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 t 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 i of the intake/exhaust valve drive cam 11 to the intake/exhaust valves 12, but the intake/exhaust valve drive cam 11- contacts the rocker arm 13 at the base circle. The initial position of the fulcrum in this state moves to the right side in FIG. 5, 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 by curve Y in FIG. 8, the lift amount 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 rotation of the lift control cam 20 is controlled by the motor 26.
The control shaft 23 and the torsion coil spring 24 are driven by the
It is done through. That is, the control circuit 27 outputs a drive current or pulse set based on a signal corresponding to the engine operating state to the motor 26 via the drive circuit 28.

This drive current or pulse is applied to the drive shaft 26 of the motor 26.
a 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 a large reaction force of the valve spring 29 is applied to the rocker arm 13. It acts on the lift control cam 20 via the lever 15. Therefore, while the lift control cam 20 remains fixed, the torsion coil springs 24 on both sides thereof are replaced, and only the control shaft 23 rotates. Next, after the intake/exhaust valve drive cam 11 rotates and the intake/exhaust valves 12 close,
The contact fulcrum between the rocker arm 13 and the lever 15 is approximately
Since it is located near the top of the exhaust valve 12 and the reaction force of the valve spring 29 disappears, the only force acting on the lift control cam 20 is the weak force of the spring 16 installed between the rocker arm 13 and the lever 15. becomes. Therefore, while the intake/exhaust valve 12 is being lifted, the torque stored in the coil spring 24 can overcome the weak force of the spring 16 and rotate the lift control cam 20.

<Problems to be Solved by the Invention> However, in such a conventional valve control device for an internal combustion engine, the power source for the drive circuit 28 of the motor 26 such as a DC motor or a stepping motor is not derived from the battery voltage. Since the obtained constant voltage was used and the output voltage to the motor 26 was always constant, the control shaft 2
The required drive torque may increase due to an increase in the viscosity of the lubricating oil in the bearings, etc., the motor drive torque may decrease due to an increase in the resistance of the motor windings when the engine is at high temperature, or the required drive torque may increase due to processing variations or aging of various parts. If the rotational speed of the motor 26 becomes slow due to variation or increase in torque, there is a problem in that reliable switching may not be performed.

That is, as the control shaft 23 rotates, the lift control cam 20
By rotating and changing the rocking position of the lever 15, the lift amount and timing of the intake/exhaust valve 12 can be varied, and the rotation angle of the lift control cam 20 and the displacement amount of the lever 15 can be changed as shown in FIG. As shown in Fig. 3, in the setting of each valve lift amount shown in a' to e, the displacement of the lever 15 is set to reach a stable point (O mark), and once in the middle of the switching, it reaches an unstable point ( Since the lift control cam 2 is set to pass through the
If the rotation of the lever 15 becomes slow, the amount of displacement of the lever 15 will often be near an unstable point, and it will often be pushed back when it starts to rise, making it impossible to perform reliable and quick switching, and causing noise. The occurrence was increasing.

Furthermore, if sufficient switching performance is obtained by taking these into consideration, there is a problem in that the motor becomes larger and has a larger capacity.

In view of these conventional problems, the present invention has been developed to ensure proper switching, regardless of increases in the viscosity of lubricating oil at low temperatures, increases in resistance of motor windings at high temperatures, variations in machining accuracy, changes over time, etc. The purpose is to enable reliable switching at high speed.

Therefore, as shown in FIG. 1, the present invention uses a battery as a power source for a drive circuit for a motor such as a DC motor or a stepping motor for driving a lift control cam. D
A rotation speed detection means for detecting the rotation speed of the motor, a comparison means for comparing the detected rotation speed with a target rotation speed, and a D
An output voltage control means for controlling the C/DC converter and controlling the output voltage to the motor is provided.

<Operation> By detecting the actual rotational speed of the motor and controlling the output voltage to the motor so that it is equal to the target rotational speed, reliable switching can be achieved at an appropriate switching speed under any operating conditions. It can be performed.

<Example> An example of the present invention will be described below with reference to FIGS. 2 to 4. However, since the mechanical parts are as shown in FIGS. 5 to 7, their explanation will be omitted.

Referring to FIG. 2, a motor 26 such as a DC motor or a stamping motor drives the control shaft 23 of the lift control cam.
is controlled by a control circuit 27 via a drive circuit 28.

The control circuit 27 includes the CPU 31. RAM32. ROM33
and an input/output interface 34, etc., and sets the lift characteristic according to the engine speed calculated by the signal from the crank angle sensor 35 and the throttle valve opening detected by the signal from the throttle sensor 36, In accordance with this, the motor 26 is driven via the drive circuit 28, and the control shaft 23 is rotated by the motor 26 to a predetermined rotation position. A potentiometer 37 is attached to the motor 26 so that the actual rotation angle is fed back to the control circuit 27.

The drive circuit 28 has a battery 38 as its power source.
connected via a DC converter 39, this DC/DC
Converter 39 converts the battery voltage to a high voltage and provides the output voltage to drive circuit 28 as a power supply voltage.

The output voltage of the DC/DC converter 39 is controlled by a signal from the control circuit 27.

FIG. 3 shows a flowchart of motor drive control and DC/DC converter output voltage control executed by the control circuit 27.

That is, the target is determined from the engine speed calculated from the signal from the crank angle sensor 35 and the throttle valve opening detected from the signal from the throttle sensor 36 in step 1 (denoted as Sl in the figure; the same applies hereinafter). Rotation angle θ. Set.

Next, in step 2, the actual rotation angle θ is detected based on the signal from the potentiometer 37, and in step 3, θ and θ are detected.
. Compare θ〈θ. If so, proceed to step 4 and drive the motor 26 in the forward rotation direction so that θ>θ. If so, proceed to step 5 and drive the motor 26 in the reverse direction. θ
=θ. In this case, the process advances to step 12 and the motor 26 is de-energized.

While the motor 26 is being driven, the rotation speed dθ/dt of the motor 26 is calculated in step 6, and the target dθ/dt is calculated in step 7.
Set. The target dθ/dt is, for example, soft start,
In order to realize a soft stop, it is preferable to set as shown in FIG. Next, in step 8, dθ/dt is set to the target dθ
/dt, and if it is slower than the target, proceed to step 9 and output a corresponding signal to the DC/DC converter 39 to increase the DC/DC converter output voltage to adjust its output voltage. . If it is faster than the target, the process proceeds to step 10, where a corresponding signal is output to the DC/DC converter 39 to reduce the output voltage of the DC/DC converter 39, thereby adjusting the output voltage. If it matches the target, proceed to step 11 and check the current DC.
/Maintains the DC converter output voltage.

Then, steps 2 to 11 are repeated, and it is determined in step 3 that θ=θ. At this point, the driving of the motor 26 is terminated.

It should be noted that the step 6 and the potentiometer 37 correspond to rotational speed detection means, the step 8 corresponds to comparison means, and the steps 9 to 11 correspond to output voltage control means.

<Effects of the Invention> As explained above, according to the present invention, the actual rotational speed of the motor is detected and the output voltage to the motor is controlled so as to reach the target rotational speed. Even though a small motor is used, reliable switching operation can always be obtained and controllability can be improved.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of the present invention, Fig. 2 is a circuit diagram showing an embodiment of the present invention, Fig. 3 is a flowchart of the same as above, and Fig. 4 is a diagram showing an example of the target rotation speed. , FIG. 5 is a longitudinal sectional view of a conventional valve control device, FIG. 6 is a plan view of the same as above, FIG. 7 is a perspective view of the lift control cam portion, and FIG. 8 is a line showing valve lift characteristics. 9 are diagrams showing the relationship between the lift control cam rotation angle and the lever displacement amount. 11... Intake/exhaust valve drive cam 12... Intake/exhaust valve 13... Rocker arm 15... Lever 2
o... Lift control cam 20a-20e... Cam surface 23... Control shaft 24... Torsion coil spring 26... Motor 27... Control circuit 28.
... Drive circuit 37 ... Potentiometer 38
...Battery 39...D C/DC converter Patent applicant Nissan Motor Co., Ltd. Representative Patent attorney Fujio Sasashima Figure 9 Soft control cam 1 time Figure 5 Figure 6

Claims (1)

[Claims] A lever that contacts the rocker arm to form the fulcrum of the rocker arm, and a lift that engages with this lever and changes its swing position to change the fulcrum position of the rocker arm and variably control the lift characteristics of the intake and exhaust valves. In a valve control device for an internal combustion engine, which includes a control cam and a motor that rotates the lift control cam to a predetermined rotation position according to engine operating conditions, a battery is used as a power source for a drive circuit of the motor. A rotational speed detection means for detecting the rotational speed of the motor, a comparison means for comparing the detected rotational speed with a target rotational speed, and a DC/DC converter connected via a converter. A valve train control device for an internal combustion engine, comprising: output voltage control means for controlling a converter to control an output voltage to the motor.