JPH0545762Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a valve control device for an internal combustion engine that variably controls the lift characteristics of an intake valve according to engine operating conditions.

<Prior Art> As a valve control device for an internal combustion engine that variably controls the lift characteristics of an intake valve according to engine operating conditions, the applicant has proposed, for example, those shown in FIGS. 6 to 8. (See Japanese Patent Application Laid-Open No. 60-26109 and Japanese Patent Application No. 59-81052).

To explain this, referring to FIG. 6, the intake valve drive cam 11 rotates in synchronization with engine rotation.
A rocker arm 13 is provided with both ends of the rocker arm 13 in contact with the stem end of the intake valve 12, and the curved back surface 13a of the rocker arm 13 is swingably supported at one end by a hydraulic pivot 19, which will be described later. The fulcrum is in contact with the lever 15. Further, the lever 15 holds the shaft 13b protruding from both side walls of the rocker arm 13 in the groove 15a via the holding member 14, and there is a space between the 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 fitted into the inner cylinder 9a, and
A check valve 19d is provided in a hydraulic chamber 19c formed between the two. The hemispherical lower end of the outer cylinder 19a is fitted into a recess 15c on the upper surface of one end of the lever 15 on the stem end side of the intake valve 12, supporting the lever 15 in a freely swingable manner. 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 valve drive cam 11 side, thereby regulating the swinging position of the lever 15. are doing.

The lift control cam 20 has a hexagonal shape and is attached to the intake valve 1.
It 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 amount of 2 in stages, and has a hole 20g in the center through which a control shaft 23, which will be described later, is inserted. ing. Further, the cylindrical portion 20h formed to protrude from both ends of the lift control cam 20 is fastened to the lower arcuate groove 18c formed in the bracket 18 with a bolt 21 on the bracket 18, as shown in FIGS. 7 and 8. 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 a hole 20g formed by penetrating the center of the lift control cam 20 provided with several cylinders in a loose fit state.
A torsion coil spring 2 as an elastic member is inserted into both sides of each lift control cam 20 of No. 3.
One end of the coil spring 24 is engaged with 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 engaged with a cylindrical portion 20h of the lift control cam 20.
It is fitted and locked 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. Stepping motor 2
6 is driven by a control 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.

28 is a valve spring.

To explain the operation, when the lift control cam 20 is in contact with the lever 15 at the cam surface 20e having the largest lift amount, the lever 15 is pushed down the most towards the intake valve drive cam 11 side. Therefore, 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
while moving toward the intake valve drive cam 11 side, the intake valve 12
As shown by curve X in FIG. 9, 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 which has the smallest lift amount contacts the lever 15, the end of the lever 15 on the intake valve drive cam 11 side rises due to the swinging motion with the recess 15c as the fulcrum, and the underside of the lever 15 also retreats upward.

The lower surface of the lever 15 serves as a fulcrum for the rocker arm 13 to transmit the lift of the intake valve drive cam 11 to the intake valve 12, but the initial position of the fulcrum is when the intake valve drive cam 11 is in contact with the rocker arm 13 at the base circle. However, the cam surface 20 with the large lift amount
Compared to when the lever 15 is in contact at point e, it moves to the right side in FIG. 6, 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. 9, 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, any one of the cam surfaces 20a to 20e is attached to the lever 15.
By bringing the valve into contact with the intake valve 12, the lift characteristics of the intake valve 12 can be changed stepwise.

Here, the lift control cam 20 is rotated by a stepping motor 26 via a control shaft 23 and a torsion coil spring 24.
That is, the control circuit 27 outputs a drive pulse set to the stepping motor 26 based on a signal corresponding to the engine operating state. This driving pulse is
The drive shaft 26a of the stepping 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, in the cylinder where the intake valve 12 is being lifted, the contact fulcrum between the rocker arm 13 and the lever 15 has moved toward the intake valve drive cam 11 side, and the valve spring 28 is A large reaction force is caused by the rock arm 13 and the lever 1.
5 to the lift control cam 20. 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 valve drive cam 11 rotates and the intake valve 12 closes, the contact fulcrum between the rocker arm 13 and the lever 15 is located approximately above the intake valve 12, and the reaction force of the valve spring 28 is As a result, the only force acting on the lift control cam 20 is the weak force of the spring 16 mounted between the rocker arm 13 and the lever 15. Therefore, the torque stored in the torsion coil spring 24 during the lift of the intake 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 rotation angle of the adjacent cam surface.

<Problems to be solved by the invention> By the way, when starting a normal engine, the mixture ratio is enriched using a choke valve or the like to increase the amount of fuel vaporized in order to improve startability. At this time, the vaporization property worsened, so good starting performance could not be expected.

In addition, in the structure of the prior application example, it has already been possible to improve starting performance by using the cam surface with the minimum lift amount during starting to reduce friction caused by valve drive and increasing cranking speed. It has been proposed (see Japanese Patent Application No. 59-142182).

However, in this case, if a cam surface with a small lift amount is used, as shown in Figure 9, the intake valve opening timing will be delayed but the closing timing will be advanced, resulting in the intake valve being closed considerably earlier than bottom dead center. Therefore, the effective compression ratio decreases significantly and the top dead center pressure decreases, and the top dead center temperature also decreases, worsening the evaporation property, which impairs the effect of improving startability. was.

This invention was developed in view of the above-mentioned circumstances, and by improving the lift characteristics of the intake valve according to the operating conditions, it increases the compression temperature and improves vaporization during startup, and ensures intake air filling efficiency after startup. The purpose is to provide good drivability.

<Means for solving the problem> For this reason, the present invention includes means for variably controlling the lift amount and opening/closing timing of the intake valve, while
A cranking detection means detects cranking of the engine, and during cranking, the lift amount of the intake valve is small and the opening timing is delayed until near the bottom dead center.
The configuration includes valve operation switching control means that increases the lift amount of the intake valve and advances the opening timing after cranking is completed.

<Function> With such a configuration, during cranking, the lift amount of the intake valve is reduced, so the initial temperature of the air sucked into the cylinder increases due to throttling friction when passing through the intake valve, and the opening timing also increases. Since intake is performed near the bottom dead center at both the closing timing and the actual compression ratio does not decrease, the top dead center temperature also rises, which improves the vaporization of the fuel in the cylinder and improves starting performance. do. Further, by reducing the lift amount, friction is reduced and cranking speed is increased, which further improves startability.

<Example> Hereinafter, an example of the present invention will be described based on the drawings.

The configuration of the means for variably controlling the lift amount of the intake valve shown in FIGS. 6 to 8 is the same, and hereinafter the same components as in FIGS. 6 to 8 are given the same reference numerals. and explain.

In FIG. 1 showing the overall configuration, a rotation speed sensor 31 for detecting the rotation speed of an engine 30 is provided as engine cranking detection means, and an intake passage 3
A throttle valve opening sensor 34 for detecting the opening of a throttle valve 33 interposed in the throttle valve 2 and a water temperature sensor 35 for detecting the engine cooling water temperature are provided, and detection signals from these sensors are input to a control circuit 36.

These sensors and control circuit 36 constitute a valve operation switching means.

On the other hand, means for variably controlling the opening/closing timing of the intake valve 12 is constituted by means for controlling the rotational phase of the intake valve drive cam 11.

That is, as shown in FIG.
A timing pulley 38 is connected to one end of the camshaft 37, which has a toothed timing belt 39 interlocked with an engine crankshaft (not shown). Further, a phase control device 40 for controlling the rotational phase of the drive cam 11 is incorporated in a connecting portion (fixed portion) between the timing pulley 38 and the camshaft 37.

The phase control device 40 freely slides and reciprocates within an annular cylinder 38A formed within the timing pulley 38 to create a hydraulic chamber 41 within the cylinder 38A.
an annular piston 42 that defines an annular piston 42; a slider 44 that contacts this piston 42 and slides along the camshaft 37 against the biasing force of a coil spring 43 due to the reciprocating motion of the piston 42; and a stopper member 45 that restricts the movement via a coil spring 43. As shown in FIG. 3, the slider 44 has a spiral female spline 44A formed on the inner surface of its hollow portion, and has a flange portion 44B at one end thereof, on which the piston 42 comes into contact, and the other end thereof. Projections 44C are respectively formed to be slidably supported in a groove 38B formed in the inner wall of the cylinder 38A. Further, as shown in FIG. 3, a spiral male spline 37A is formed at one end of the camshaft 37, and this male spline 37A connects to the female spline 44 of the slider 44.
It is designed to mesh with A.

In FIG. 2, reference numeral 46 denotes a hydraulic passage formed within the camshaft 37 and the timing pulley 38. One end of this hydraulic passage 46 communicates with the hydraulic chamber 41, and the other end communicates with an external hydraulic pressure supply passage 47. are doing. The other end of this hydraulic supply passage 47 is
One passage 47A is for oil pump 4
8, the other passage 47B is connected to the hydraulic control valve 49,
They are connected to each other. The hydraulic control valve 49 controls the hydraulic pressure supplied from the oil pump 48 to the hydraulic chamber 41 by the control rotation 36 according to engine operating conditions such as engine speed, throttle valve opening, and cooling water temperature. In addition,
Reference numeral 50 denotes a presser bolt for fixing the stopper member 45 to the end surface of the camshaft 37.

Next, the action will be explained.

When the rotation speed sensor 31 detects the rotation speed during cranking which is lower than the rotation speed during idling, and the water temperature sensor 35 detects that the cooling water temperature is below a predetermined value, the control circuit 36 detects a low temperature start. In response to the command, the stepping motor 26 moves to the cam surface 20a with the minimum valve lift amount.
the control shaft 23 until it engages with the end of the lever 15.
Rotate. On the other hand, the hydraulic control valve 49 is actuated to guide the oil discharged from the oil pump 38 to the hydraulic chamber 41, thereby moving the slider 44 to the left in the figure as shown in the lower half of FIG. As a result, the camshaft 37 rotates in one direction via the female spline 44A and the male spline 37A, the rotational phase of the drive cam 11 moves to the delayed side, and the opening timing of the intake valve 12 is controlled to near the bottom dead center. be done.

As a result, the lift characteristic of the intake valve 12 becomes as shown by the solid line in FIG. If the lift characteristics of the intake valve 12 during cranking are set in this way, the intake valve 12 will move when the piston reaches near the bottom dead center during the intake stroke and the negative pressure inside the cylinder becomes sufficiently large.
2 opens and intake begins. At this time, since the intake air rapidly passes through the narrow opening of the intake valve 12 whose lift amount is controlled to be small, a large throttling friction is generated, and the intake air that has absorbed the generated frictional heat is drawn into the cylinder.

That is, part of the work done by the downward movement of the piston is converted into frictional heat of the intake air, and this heat is absorbed by the intake air.

By delaying the intake start time and increasing the throttle friction in this way, the negative pressure inside the cylinder reaches its maximum before bottom dead center, as shown in Figure 5, and this negative pressure has a normal valve lift characteristic (dashed line). However, the closing timing of the intake valve 12 is set at a predetermined time after the bottom dead center, which is approximately the same as that for normal lift characteristics, and the cranking speed is low. As a result, the pressure had recovered sufficiently to slightly exceed atmospheric pressure by the time it closed.

That is, the intake air temperature temporarily decreases due to the pressure decrease due to expansion, but this is offset by the temperature increase due to the subsequent pressure increase.

Therefore, when the intake valve 12 closes and compression begins, the initial temperature of the intake air has increased by the amount of frictional heat absorbed, and the compression ratio is also approximately the same as the normal lift characteristic. The dead point temperature also increases significantly.

As a result of this increase in the intake air temperature within the cylinder, the vaporization of the fuel improves and it becomes easier to ignite, making it possible to significantly improve startability at low temperatures.

Additionally, by reducing the lift amount, the friction in driving the intake valve is reduced, which increases the cranking speed and accelerates the temperature rise in the cylinder, improving startability in this respect as well.

On the other hand, after starting, the engine speed, throttle valve opening,
Based on load conditions such as water temperature, a cam surface with a lift amount suitable for operating conditions is selected, and the stepping motor 26 is driven to perform switching control. Further, the oil pressure control valve 49 controls the oil pressure in the oil pressure chamber 41 by relieving part or all of the oil discharged from the oil pump 48 to the low pressure source (tank) side, thereby reducing the control oil pressure compared to when cranking. to move the slider 44 to the right as shown in the upper half of FIG. As a result, the rotational phase of the drive cam 11 is advanced, and, for example, when the cam surface with the maximum lift amount is selected, the opening timing of the intake valve 12 is advanced to near the top dead center as shown by the chain line in FIG.

As a result, intake characteristics suitable for the operating conditions can be obtained, and output and exhaust emission characteristics can be appropriately controlled.

In this embodiment, the valve lift amount is switched in multiple stages, but it may be switched in two stages, one at startup and the other, or it may be continuously variable in a stepless manner.

In particular, in the case of two stages, a configuration may be adopted in which two types of drive cams are formed, one for cranking and another for cranking, and each cam profile is selectively switched by having a different lift amount and opening/closing timing.

<Effects of the invention> As explained above, according to the invention, the lift amount of the intake valve is reduced during cranking, and the opening timing is controlled near the bottom dead center, so that the throttling friction when the intake valve passes through is reduced. The vaporization of the fuel is improved by absorbing the heat generated by the engine and raising the temperature of the intake air inside the cylinder, which makes it possible to significantly improve low-temperature startability. On the other hand, after cranking is completed, by increasing the lift amount of the intake valve and advancing the opening timing, it is possible to ensure good output, fuel efficiency, and exhaust emission performance.

[Brief explanation of the drawing]

Fig. 1 is an overall configuration diagram of a valve control device showing one embodiment of the present invention, Fig. 2 is a cross-sectional view of the cam rotational phase control device portion of the same embodiment, and Fig. 3 shows the slider and An exploded perspective view showing the end of the camshaft; FIG. 4 is a diagram showing the lift characteristics of the intake and exhaust valves of the same embodiment;
Figure 5 is a diagram showing the cylinder pressure characteristics as well.
FIG. 6 is a longitudinal sectional view of a conventional valve control device;
FIG. 7 is a plan view of the same as above, FIG. 8 is a perspective view of the lift control cam portion, and FIG. 9 is a line diagram showing the intake valve lift characteristics of the above. 11...Intake valve drive cam, 12...Intake valve, 1
3...Rotsuka arm, 15...Lever, 20...
Lift control cam, 20a to 20e...cam surface, 2
3...Control shaft, 24...Torsion coil spring,
26... Stepping motor, 30... Engine, 3
1... Rotation speed sensor, 36... Control circuit.

Claims (1)

[Scope of utility model registration request] It is equipped with a means for variably controlling the lift amount and opening/closing timing of the intake valve, and a cranking detection means for detecting cranking of the engine, and a means for reducing the lift amount of the intake valve during cranking and adjusting the opening timing. Valve operation control for an internal combustion engine, characterized in that it is provided with a valve operation switching control means that controls the valve operation to be delayed until near bottom dead center, and after completion of cranking, increases the lift amount of the intake valve and advances the opening timing. Device.