JPH0641726B2 - Engine valve gear - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an engine valve operating system capable of changing valve lift characteristics in accordance with operating conditions, and more particularly to countermeasures during acceleration.

(Prior Art) In order to improve combustion stability and fuel efficiency by setting the operation characteristics of the intake and exhaust valves of the engine by suppressing exhaust blowback and intake blowout during the valve overlap period at low speed. 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 meet such requirements, depending on the operating condition, the low-speed valve lift characteristic that the intake and exhaust overlap amount is small and the high-speed valve opening characteristic or the lift amount that is larger than the low-speed valve lift characteristic are high speed. 2. Description of the Related Art A valve operating device in which the valve operation is controlled to be switched according to the valve lift characteristic for a vehicle has been conventionally known (for example, the actual opening 57).
-182205). In this conventional device, a low-speed cam that gives a low-speed valve lift characteristic and a high-speed cam that gives a high-speed valve lift characteristic are provided for an intake valve or an exhaust pipe, and a rocker arm that abuts on these cam and valve. Is equipped with a slidable high-speed cam contact member and a stopper for preventing the sliding. 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 the conventional device of this type, the valve lift characteristic is simply switched according to the engine speed or the engine speed and the engine load, etc., and each operating range of the low speed valve lift characteristic and the high speed valve lift characteristic is changed. Is only set to a fixed value, but this has the following problems. That is, when driving in urban areas, driving is mainly performed in the low-speed valve lift characteristic region, which improves fuel efficiency and emission in a steady operation state, but acceleration is performed in such an operating region. In such a case, the combustion temperature rises, so that the generation of NOx is not always sufficiently controlled, and thus the emission may not be good. Therefore,
As a countermeasure against this, it is conceivable to increase the EGR amount by the exhaust gas recirculation device, but in that case, combustion may become unstable in the low speed range, and the driving feeling may be deteriorated.

It should be noted that Japanese Patent Application No. 59-212467 (Japanese Patent Application Laid-Open No. 61-62167)
In Japanese Patent Laid-Open No.-93215), a valve lift characteristic can be changed by controlling an oil leak amount from an orifice provided in a hydraulic lash adjuster with a solenoid valve, and the solenoid valve is controlled according to an operating state. By doing so, the valve lift characteristics are changed between high speed and low speed so that the valve opening period is increased at high speed, and at the time of acceleration, the same valve lift characteristics as at high speed are shown. There is.
However, if the high-speed valve lift characteristic is used in a region where the intake air amount is extremely small even during acceleration, the combustion stability may be deteriorated.

(Object of the Invention) In view of such circumstances, the present invention can appropriately adjust the valve lift characteristic according to the operating state, and
In particular, the present invention provides a valve operating system for an engine capable of suppressing generation of NOx during acceleration in urban driving, maintaining good emission during urban driving, stabilizing combustion, and improving driving feeling. Is.

(Structure of the Invention) The present invention provides a low-speed valve lift characteristic in which the amount of overlap between intake air and exhaust gas is small, and a high-speed valve lift characteristic in which the amount of overlap is larger than the low-speed valve lift characteristic, according to the operating state. A valve operating system for an engine in which valve operation is switched to a low speed valve lift in an operating region where the intake air amount is smaller than a preset set value of the intake air amount. In the operating region where the intake air amount is larger than the set value, the control means has a valve lift characteristic for high speed, the acceleration detection means for detecting the acceleration state, and the above set value during acceleration based on the acceleration detection. It is provided with a correction unit that corrects to a low intake air amount side and switches the valve lift characteristics at the corrected set value as a boundary.

That is, at the time of acceleration, the operating region having the high-speed valve lift characteristic with the large overlap amount is expanded to the low intake air amount side.

(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 or a lift amount that is higher than that 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 is provided with the high speed type cams 4a,
A first arm 7 integrally provided with a pair of left and right arm portions 7a and 7b and an upper connecting portion 7c that abut on 4b, contact portions 8a and 8b to both intake valves 2a and 2b, and a low speed type cam 3 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 both arms 7 and 8 are disconnected, the swing of the first arm 7 accompanying the rotation of the high speed cams 4a and 4b is not transmitted to the second arm 8 and the low speed cam 3 rotates. When the intake valves 2a and 2b are actuated by the swing of the second arm 8 in response to the movement of the second arm 8 and the arms 7 and 8 are in the connected state, the high speed cams 4a and 4b rotate in response to the rotation of the arms 7. The intake valves 2a and 2b are operated by swinging 8 integrally.

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. A control valve 24 is provided in the oil passage 22 to control the supply and discharge of oil to the hydraulic chamber 21 of the actuator 20.

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 for controlling switching of valve lift characteristics for the above valve operating system. In the figure, reference numeral 30 is a control circuit using a microcomputer or the like, which includes an intake air amount detection signal 31 based on the output of an air flow meter and a throttle opening detection signal 32 for detecting the opening of a throttle valve in the intake passage. Receiving the control valve 24
The actuator 20 of the selector 10 is controlled via the. The intake air amount detection signal 31 may be converted from a signal of intake negative pressure, venturi negative pressure, back pressure, or the like. The control circuit 30 stores a set value of the intake air amount in advance and controls the valve lift characteristic with the set value as a boundary, acceleration detecting means for detecting an acceleration state, and the set value at the time of acceleration. And a correction means for correcting to the low intake air amount side.

In FIG. 6, the horizontal axis represents the engine speed, and the vertical axis represents the average effective pressure. The low-speed lift characteristic region (operating region considered to be the low-speed valve lift characteristic) and the high-speed lift characteristic region (high-speed valve lift characteristic Operating range). In this figure, A is the maximum output curve when the low-speed valve lift characteristic is used, B is the maximum output curve when the high-speed valve lift characteristic is used, C is the boundary line between the above two regions, and this boundary line C is the intake air. This boundary line C is set so as to pass through the intersection of the maximum output curves A and B, which corresponds to the set value of the amount. A two-dot chain line C'indicates a boundary line for switching the valve lift characteristic during acceleration, and corresponds to a value obtained by correcting the set value of the intake air amount to the low intake air amount side by a fixed amount.

The control of the valve lift characteristic by the control circuit 30 and the correction at the time of acceleration are performed as shown in the flowchart of FIG.

That is, the intake air amount detection signal 31 and the throttle opening detection signal 32 are input in step S ₁ , and next, in step S ₂ , it is determined whether the rate of change dθ / dt of the throttle opening is larger than a predetermined value α. It is determined whether or not the vehicle is in an accelerated state. In Step S ₃ when not in an accelerating state based on the normal region setting, the low-speed lift by examining whether the amount of intake air is smaller than the set value corresponding to the boundary line C indicated by the solid line in FIG. 6 Check whether it is a characteristic region. Then, if the low-speed lift characteristic region, and controls the low-speed valve lift characteristic in step S _4, i.e. outputs a signal for controlling the selector 10 to associated intake valves 2a, 2b are low-speed cam 3, Further, if the high-speed lift characteristic region, and controls the high-speed valve lift characteristic in step S _5, i.e. the intake valves 2a, 2
selector 1 so that b is linked to high speed type cams 4a and 4b
A signal for controlling 0 is output.

Further, when it is determined that the acceleration state in step S ₂ in step S _6, the value corresponding to the sixth boundary line for the time of acceleration indicated by the two-dot chain line in FIG C 'as a reference, inhalation It is determined whether the amount of air is smaller than this. Then, if the determination is YES, the process proceeds to step S ₄ , and the low speed valve lift characteristic is set, and if the determination is NO, step S 4 is performed.
Moving to ₅ , the valve lift characteristic for high speed is set.

According to this valve gear, when the steady operation is performed in the low speed lift characteristic region where the intake air amount is equal to or less than the set value, the intake valves 2a and 2b are operated by the low speed type cam 3 to exceed the exhaust valve. The amount of lap is reduced to prevent blow-in and blow-back of intake air, thereby improving combustibility, torque, fuel consumption, etc. in such a region. On the other hand, when the intake air amount is in the high speed lift characteristic region of the set value or more, the intake valves 2a and 2b are operated by the high speed type cams 4a and 4b to increase the lift amount and the valve opening period. The quantity is increased and the output is increased.

Further, at the time of acceleration, a value (corresponding to the line C ′ in FIG. 6) obtained by correcting the set value (corresponding to the boundary line C in FIG. 6) to the low intake air amount side is used for switching the valve lift characteristic. The border. In the region where the intake air amount is smaller than the corrected value, the NOx generation due to the increase of the combustion temperature as described later is small even during acceleration, so that the low-speed valve lift characteristic is used to secure the combustion stability. , If the intake air amount becomes larger than the above corrected value during acceleration,
Even within the low speed lift characteristic region during normal operation, the intake valves 2a, 2b are operated by the high speed cams 4a, 4b to increase the amount of overlap with the exhaust valve, thereby reducing NOx. That is, generally, when acceleration is performed, the combustion temperature rises and NOx easily occurs,
As described above, when the overlap amount of the intake and exhaust valves during acceleration is increased, the amount of internal EGR (EGR due to blowback of exhaust gas to the intake system during the overlap period) increases, which increases the combustion temperature. It is suppressed and NOx is reduced. Further, by increasing the internal EGR amount in this way, the amount of external EGR (exhaust gas recirculation by the exhaust gas recirculation device) can be reduced or made unnecessary. According to the external EGR, it is difficult to improve the distribution of the recirculated gas to each cylinder and the mixing with the intake air, and combustion tends to become unstable, whereas the internal EG
According to R, mixing of intake air is favorably performed, and since the EGR amount is reduced during steady operation in the low speed lift characteristic region, combustion stability is improved.

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. 8 and FIG. 9, the rocker arm 6 is integrated, and at the ends corresponding to the high speed type cams 4a and 4b,
Selector comprising a slidable blanker 41 that contacts the high-speed cams 4a and 4b, a spring 42 that urges the slantable blanker 41 toward the high-speed cams 4a and 4b, and a stopper member 43 that engages and disengages with the plunger 41. By providing 40, the operation of the high speed type cams 4a and 4b may be absorbed and transmitted at this end.

Further, although the case where the invention is applied to the intake valve is shown in the above-mentioned 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. Therefore, the same control as that applied to the intake valve may be performed.

(Effects of the Invention) As described above, the present invention switches between the low-speed valve lift characteristic and the high-speed valve lift characteristic with a predetermined set value of the intake air amount as a boundary, and lowers the set value during acceleration. Since the region for high-speed valve lift characteristics is expanded to the low intake air amount side by correcting to the intake air amount side, during acceleration, the overlap amount of intake air and exhaust gas is increased in the above expanded region. Becomes larger and the internal EGR causes N
It is possible to prevent the generation of Ox, to control emissions during urban driving satisfactorily, and to improve combustion stability and driving feeling even when compared with the case of external EGR. it can.

[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 drawing, 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, and FIG. 7 is control FIG. 8 is a plan view showing another embodiment of the valve train,
FIG. 9 is a sectional view taken along line IX-IX in FIG. 2a, 2b ... intake valve, 3 ... low speed type cam, 4a,
4b ... High-speed cam, 6 ... rocker arm, 10,4
0 ... selector, 30 ... control circuit.

Claims (1)

[Claims] 1. A valve operation according to a low speed valve lift characteristic in which the intake and exhaust overlap amounts are small and a high speed valve lift characteristic in which the overlap amount is larger than the low speed valve lift characteristic according to an operating state. Is a valve operating device for an engine, in which a low speed valve lift characteristic is set in an operating region in which the intake air amount is smaller than the preset set value of the intake air amount. In the operating region where the intake air amount is larger than the set value, the control means having the high speed valve lift characteristic, the acceleration detection means for detecting the acceleration state, and the acceleration detection based on the acceleration detection, the above set value is set to the low intake air amount during acceleration. A valve operating device for an engine, comprising: a correction unit for correcting the valve lift characteristic when the correction value is set to the side, and the valve lift characteristic is switched at the corrected setting value as a boundary.