JPH0639939B2 - Engine valve gear - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a valve operating system for an engine capable of changing valve lift characteristics according to operating conditions, and more particularly to a valve operating system related to air-fuel ratio control. It is about control.

(Prior Art) In order to improve combustion stability and fuel efficiency by setting the operation characteristics of the intake and exhaust hulls of the engine by suppressing exhaust gas reflow and intake air blowout during a valve overlap period at low speeds. It is desirable to make the overlap amount of intake air and exhaust gas relatively small, and to improve the output at high speed, it is desirable to make the valve lift amount and the valve opening period larger than at low speed.

In order to satisfy such a requirement, at least one of the intake valve and the exhaust valve has a low-speed valve lift characteristic and at least one of a valve opening period and a lift amount larger than the low-speed valve lift characteristic, depending on the operating state. 2. Description of the Related Art A valve operating device in which the valve operation is controlled to be switched according to the high speed valve lift characteristic is conventionally known. For example, actual development 5
In the device disclosed in Japanese Patent Laid-Open No. 7-182205, a low speed type cam giving a low speed valve lift characteristic and a high speed type cam giving a high speed valve lift characteristic are provided for an intake valve or an exhaust valve, and these cams are provided. Further, a high-speed cam abutting member which is slidable at the end of the rocker arm that abuts the valve on the high-speed cam side, and a stopper that prevents the sliding are provided. By controlling the actuator that operates this stopper in accordance with the operating state, the high-speed cam abutment member floats at low speed, the operation of the high-speed cam is not transmitted to the valve, and the valve is operated by the low-speed cam. At high speed, the sliding of the high speed cam contact member is blocked so that the operation of the high speed cam is transmitted to the valve.

By the way, in an engine equipped with a fuel injection device, generally, in an operating range where economical traveling is required, the air-fuel ratio is feedback-controlled according to the output of the O ₂ sensor, and a high load range or a high-speed range where output is required. However, the feedback control is stopped. However, when the above valve operating device is used in this type of engine, there are the following problems.
That is, in the past, the operation of the valve may switch from the low speed valve lift characteristic to the high speed valve lift characteristic even in the operating range where the air-fuel ratio is feedback controlled.
When the valve lift characteristic for high speed is used, the gas blow-through amount increases during the valve overlap period, and when the valve lift characteristic is switched, the intake and exhaust amounts change suddenly, and the feedback control cannot follow this temporarily, which is temporary. The air-fuel ratio shifts. Therefore, torque shock may occur, and emission and fuel efficiency may be deteriorated.

(Object of the Invention) In view of such circumstances, the present invention appropriately controls the valve lift characteristic according to the operating state, maintains good emission and fuel efficiency in a region where the air-fuel ratio is feedback controlled, and reduces torque shock. The present invention provides a valve operating system for an engine.

(Structure of the Invention) According to the present invention, at least one of the intake valve and the exhaust valve has a low-speed valve lift characteristic and at least one of a valve opening period and a lift amount larger than the low-speed valve lift characteristic, according to an operating state. In an engine valve operating system in which valve operation is switched between high-speed valve lift characteristics, the operating range in which the valves operate with the low-speed valve lift characteristics includes an operating range in which the air-fuel ratio is feedback-controlled. A control device is provided for switching the valve lift characteristics at a speed higher than the feedback control operation range.

That is, when the air-fuel ratio is in feedback control, the valve is always operated with the low speed valve lift characteristic so that the valve lift characteristic is not switched during the air-fuel ratio feedback control.

(Embodiment) FIGS. 1 to 4 show an example of a device capable of switching valve lift characteristics, and in the drawings, the case where the invention is applied to an engine having two intake valves per cylinder is shown. In these figures, 1 is a cylinder, 2a and 2b are intake valves installed in the cylinder 1, and the exhaust valve and its drive system are not shown. A low speed cam 3 for giving a low speed valve lift characteristic and a high speed cam 4a, 4b for giving a high speed valve lift characteristic to the intake valves 2a, 2b are arranged on a common camshaft 5. A rocker arm 6 is arranged between the cams 3, 4a, 4b and the intake valves 2a, 2b.

One of the low-speed cam 3 and the high-speed cams 4a and 4b is selectively linked to the valve by a switching mechanism which will be described later. In the figure, the force from the cam acts on the rocker arm 6 in a well-balanced manner. As described above, the low-speed cam 3 is arranged at a position corresponding to the center of the rocker arm 6 substantially in the width direction,
Two high speed type cams 4a and 4b are symmetrically arranged on both sides thereof. The low-speed cam 3 includes the intake valves 2a, 2
The cam nose is formed to be small so that the valve opening period and the lift amount of b are reduced to reduce the overlap amount with the exhaust valve, and the high speed type cams 4a and 4b have a valve opening period and a lift amount that are higher than those of the low speed type cam 3. The cam nose is formed large so that at least one of them is enlarged.

Further, the rocker arm 6 is provided with a switching mechanism that changes the valve lift characteristic by switching the linkage between the cam and the valve. In this embodiment, as the switching mechanism, the rocker arm 6 includes the high speed type cams 3a,
A first arm 7 integrally provided with a pair of left and right arm portions 7a, 7b that abut on 3b and an upper connecting portion 7c, contact portions 8a, 8b for both intake valves 2a, 2b, and a low speed type cam 4 are provided. Second arm 8 integrally provided with abutting portion 8c
And is supported so that the arms 7 and 8 can move relative to each other around the rocker shaft 9, and a plunger 11 for switching the arms 7 and 8 between a connected state and a disconnected state. A selector 10 including a lever member 12 and the like is provided.

Specifically, the selector 10 has the following structure. That is, the guide hole 13 opening toward the upper part of the second arm 8 is formed in the upper part of the first arm 7,
The plunger 11 is movably accommodated in the guide hole 13, and the plunger 11 is biased by the spring 14 in the guide hole 13 so as to come into contact with the second arm 8. The plunger 11 has a small diameter in the middle thereof. Engagement part 1
5 is formed. In addition, on the upper part of the first arm 7,
The lever member 12 is movably supported orthogonal to the plunger 11 in the axial direction of the rocker shaft 9, and the lever member 12 has a plunger insertion hole 16 having a diameter slightly larger than that of the plunger 11 and the engaging portion 15. And a locking hole 17 which is continuous with the plunger insertion hole 16 and has a size corresponding to.

Thus, the locking hole 17 of the lever member 12 is disengaged from the engaging portion 15 of the plunger 11 and the plunger insertion hole 16
When the lever member 12 is moved to the unlocked position where the plunger 11 is inserted into, the relative movement of both arms 7 and 8 is allowed by the sliding of the plunger 11 (at this time, the unconnected state). On the other hand, when the lever member 12 moves to the lock position where the locking hole 17 engages with the engaging portion 15, the plunger 11 is prevented from sliding, and the upper portions of both arms 7 and 8 approach each other. Relative movement in the direction of is blocked (at this time connected state). When the two arms 7 and 8 are disconnected, the first arm 7 accompanying the rotation of the rocker arm 6
Is not transmitted to the second arm 8, the low-speed cam 3
The swing of the second arm 8 according to the rotation of the intake valve 2
When both a and 2b are actuated and both arms 7 and 8 are in the connected state, both arms 7 and 8 integrally swing in response to the rotation of the high speed type cams 4a and 4b, so that the intake valve 2a. , 2b are activated.

The end portion of the lever member 12 projects to the outside of the first arm 7 and is connected to an annular hydraulic actuator 20 rotatably supported around the rocker shaft 9 via an arm 12a of the lever member 12. The actuator 20 moves the lever member 12 toward the lock position when oil is supplied to the hydraulic chamber 21 from an oil pump (not shown) through the oil passage 22, and returns when the oil is relieved. The spring 23 moves the lever member 12 toward the unlocked position. In the oil passage 22, a control valve 26 that controls the supply and discharge of oil to and from the hydraulic chamber 21 of the actuator 20 is provided.

In addition, 27 and 28 are adjusters for adjusting the valve clearance, which are arranged on the second arm 8, and 29 is a cylinder head.

FIG. 5 shows a control system that controls the switching of valve lift characteristics for the valve operating system as described above and performs fuel control for a fuel injection device mounted on the engine. In this figure, reference numeral 30 is a control circuit using a microcomputer or the like, which receives signals for detecting an operating state such as an engine speed detection signal 31 and an intake air amount detection signal 32,
While controlling the actuator 20 of the selector 10 via the control valve 26, it controls the fuel injection valve 34 provided in the intake passage (not shown). Further, in the embodiment shown in the drawing, the engine temperature such as the cooling water temperature is controlled. The detection signal 33 is also used as an input signal, and the EGR valve 35 of the exhaust gas recirculation device is also controlled.
The intake air amount detection signal 32 may be a signal of the output of the air flow meter, the intake negative pressure, the Venturi negative pressure, the back pressure, or the like.

In the control circuit 30, an operating region in which the air-fuel ratio is feedback-controlled based on a signal from an O ₂ sensor (not shown) and an operating region in which the feedback control is not performed are set in advance for the fuel injection device. For the valve system, a low speed lift characteristic region in which the intake valves 2a and 2b are operated by the low speed type cam 3 and a high speed lift characteristic region in which the intake valves 2a and 2b are operated by the high speed type cams 4a and 4b are preset. There is. These areas are set as shown in FIG. That is, the feedback control area is set in a specific area on the relatively low rotation and low load side within the broken line in this figure, and is stored as a map. The low-speed and high-speed lift characteristic regions are the maximum output curve A in the low-speed lift characteristic and the maximum output curve B in the high-speed lift characteristic.
It is set with a boundary line C, which is set so as to deviate to the high rotation side as the load becomes lower, as a reference, based on the intersection point with, and the low speed lift characteristic region is set to include the feedback control region. With this setting, the valve lift characteristics are switched at a speed higher than the feedback control operation range. Such a region can be set by the intake air amount, that is, if a constant intake air amount is set, the boundary line C is obtained, and the lift characteristic is switched with the set value of the intake air amount as a boundary. You can do it like this. Alternatively, the above area may be set by a map based on the engine speed and the load. Further, the low-speed and high-speed lift characteristic regions may be set simply at the boundary of the specific rotation speed on the higher rotation side than the feedback region.

In addition, the EGR that operates the normal operation region and the exhaust gas recirculation device
It is desirable to set the region so as to be included in the low speed lift characteristic region. When the engine temperature is low, the intake valves 2a and 2b are operated with the low-speed lift characteristic regardless of the operating region, or the low-speed lift characteristic region is expanded as shown by the one-dot chain line in FIG. It is desirable to do. The reason why these settings are desirable will be described later.

The control of the fuel injection valve 34 by the control circuit 30 is performed according to the flowchart of FIG.
The process is performed according to the flowchart in the figure.

That is, in the flowchart of FIG. 7, first in steps S ₁ and S ₂ , the engine speed and the intake amount are calculated based on the engine speed detection signal 31 and the intake air amount detection signal 32, and then in step S ₃ . It is determined whether it is in the F / B (feedback control) region. In the F / B region, the feedback correction coefficient Cfb is calculated based on the output of the O ₂ sensor (not shown) in step S ₄ , and the basic pulse width obtained in accordance with the intake air amount and the like in step S _5. Tp
To obtain the injection pulse width T by multiplying by the above feedback correction coefficient Cfb, and in steps S ₆ and S ₇ , the injection pulse of the above injection pulse width T is output to drive the fuel injection valve 34 at the injection timing. To do. In this feedback control, processing such as calculation of the feedback correction coefficient Cfb is performed so that the fuel is gradually increased when the lean state is entered and the fuel is gradually reduced when the rich state is entered. In step S ₈ when it is determined not to be F / B region performs steps S ₅ to S ₇ from the 1 to the feedback correction coefficient Cfb in step S _3, that is the intake air amount without performing feedback control Fuel is supplied according to the requirements.

In the flowchart of FIG. 8, after the intake air amount is calculated in step S ₁₁ , it is determined in step S ₁₂ whether or not it is in the low speed lift characteristic region. This judgment result is YE
If it is S, the actuator 20 is turned off in step S _13.
By setting to F, the selector 10 is operated so that the intake valves 2a and 2b are linked to the low-speed cam 3. If the decision result in the step S ₁₂ is NO, a step S ₁₄
By turning off the actuator 20, the selector 10 is operated so that the intake valves 2a and 2b are linked to the high speed cams 4a and 4b.

By such control, the intake valves 2a and 2b are controlled by the low speed cam 3 in the low speed lift characteristic region shown in FIG.
The exhaust overlap amount is reduced by being operated by, and the blow-in and blow-back of intake air are prevented. As a result, combustibility, fuel efficiency, torque, etc. in the relatively low speed region are improved. On the other hand, in the high speed lift characteristic region, the intake valve 2
The a and 2b are operated by the high speed type cams 4a and 4b to increase the lift amount and the valve opening period, whereby the intake amount is increased and the output is increased on the high speed side.

Further, in the present invention, particularly, the low-speed lift characteristic region includes the air-fuel ratio feedback control region, so that the deviation of the air-fuel ratio during the feedback control is prevented. That is, in the above-described feedback control, the air-fuel ratio is gradually corrected when the intake air amount fluctuates. Therefore, if the lift characteristics of the intake valves 2a and 2b are switched during the feedback control, the intake air intake amount is drastically changed. Fluctuations cause the air-fuel ratio to deviate, resulting in worse fuel efficiency and emissions, and torque shock.However, setting this so that the low-speed lift characteristic area includes feedback control will prevent this situation from occurring. As a result, good fuel economy and emission can be maintained.

Further, if the low-speed lift characteristic region is set to include the normal operating range as described above, good fuel economy, emission, etc. can be maintained in the normal operating range. Further, if the low-speed lift characteristic region includes the EGR region, NOx is reduced by the exhaust gas recirculation device in this region, while in the high-speed lift characteristic region, NOx is increased by the internal EGR due to the increased valve lift amount. Will be reduced. If the low-speed lift characteristic is set or the low-speed lift characteristic region is set to be wide when the engine temperature is low, the warm-up action is promoted by suppressing the internal EGR.

The mechanism for changing the valve lift characteristics by switching the linkage between the cams 3, 4a, 4b and the intake valves 2a, 2b is not limited to the above embodiment, but can be variously changed. For example, as shown in FIG. 9 and FIG. 10, the rocker arm 6 is integrated, and the slidable plunger 41 that abuts the high speed type cams 4a and 4b is provided at the end portion corresponding to the high speed type cams 4a and 4b. By providing the selector 40 having the spring 42 for urging the cams 4a and 4b toward the high speed cams 4a and 4b and the stopper member 43 engaging and disengaging with the plunger 41, the high speed cams 4a and 4b are provided at the ends thereof. May be absorbed and transmitted.

Further, although the case where the invention is applied to the intake valve is shown in the above embodiment, the device of the present invention may be applied to the exhaust valve, and in this case also, the valve overlap amount is changed by changing the lift characteristic of the exhaust valve. Since the exhaust amount and the intake amount fluctuate, the same control as that applied to the intake valve may be performed.

As described above, according to the present invention, the operation of the valve is switched between the low-speed lift characteristic and the high-speed lift characteristic according to the operating state, and the low-speed lift characteristic region includes the air-fuel ratio feedback control region. As described above, since the valve lift characteristics are switched at a speed higher than the feedback control operation range, there is no deviation of the air-fuel ratio due to the switching of the valve lift characteristics during the feedback control, and torque shock is prevented. In addition to being able to prevent it, it is possible to maintain good fuel economy and emission.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a valve train in the device of the present invention, FIG. 2 is a sectional view taken along line II-II of FIG. 1, and FIG.
III-III sectional view of the figure, FIG. 4 is a vertical sectional front view at the rocker shaft position, FIG. 5 is a schematic block diagram of the control system, FIG. 6 is an explanatory view showing the setting of the region, FIG. 7 and FIG. 8 is a flow chart of control, FIG. 9 is a plan view showing another embodiment of the valve train, and FIG. 10 is a sectional view taken along line XX of FIG. 2a, 2b ... Intake valve, 3 ... Low speed type cam, 4a, 4b
... high-speed cam, 6 ... rocker arm, 10, 40 ... selector, 30 ... control circuit, 34 ... fuel injection valve.

Claims (1)

[Claims] 1. A low-speed valve lift characteristic in at least one of an intake valve and an exhaust valve according to an operating state,
In the engine valve operating system in which the valve operation is switched to the high-speed valve lift characteristic in which at least one of the valve opening period and the lift amount is larger than the low-speed valve lift characteristic, the valve is operated with the low-speed valve lift characteristic. An engine valve characterized by being provided with a control device for switching the valve lift characteristic at a speed higher than the feedback control operating range so that the operating range operating includes the feedback control range of the air-fuel ratio. apparatus.