JPH076473B2 - Engine with variable valve lift characteristics - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine with a valve lift characteristic varying device capable of changing the valve lift characteristic according to operating conditions, and particularly to controlling ignition timing in such an engine. It is about.

(Prior Art) To set combustion characteristics of an engine and exhaust valves, and to improve combustion stability and fuel efficiency by controlling exhaust gas backflow 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 requirements, 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 above-mentioned overlap amount is larger than the low-speed valve lift characteristic according to operating conditions. A valve operating device in which the operation of the valve is switch-controlled has been conventionally known (for example, Japanese Utility Model Laid-Open No. 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 the intake valve or the exhaust valve, 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.

However, in the case of this type of conventional engine, when the low-speed valve lift characteristic with the small overlap amount and the high-speed valve lift characteristic with the large overlap amount are used, the so-called internal EGR during the overlap period is used.
As the combustion state (combustion speed, etc.) also changes with the change of, etc., the ignition timing deviates from the optimum value,
There was a risk that the knock resistance, output, etc. would not be sufficiently improved.

(Object of the invention) In view of such circumstances, the present invention can appropriately adjust the ignition timing according to the change of the overlap amount due to the change of the valve lift characteristic, and improve the knock resistance, the output and the like. An engine with a variable valve lift characteristic device is provided.

(Structure of the Invention) According to the present invention, 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 the operating state. In an engine with a variable valve lift characteristic device in which the valve operation can be switched between the two, the advance ratio of the ignition timing in the operating region of the above-mentioned valve lift characteristic for high speed is calculated as follows. Ignition timing control means for increasing the angle ratio is provided.

In other words, when the valve lift characteristic for high speed is used, the combustion speed decreases as the internal EGR amount increases compared to when the valve lift characteristic for low speed is used. It is configured to increase the ratio.

(Embodiment) FIGS. 1 to 4 show an example of a variable lift characteristic varying device, which is applied to an engine having two intake valves per cylinder. 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 cam shaft 5. A rocker arm 6 is arranged between the cams 3, 4a, 4b and the intake valves 2a, 2b.

One of the low speed type cam 3 and the high speed type cams 4a, 4b is selectively linked to the valve by a switching mechanism which will be described later, and 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 type cam 3 is arranged at a position substantially corresponding to the center of the rocker arm 6 in the width direction, and the two high speed type cams 4a and 4b are symmetrically arranged on both sides thereof. The low speed cam 3 has a small cam nose so that the intake valve 2a, 2b has a short valve opening period and a small lift amount to reduce the overlap amount with the exhaust valve, and the high speed cams 4a, 4b are low speed type cams. The cam nose is formed larger than the cam 3 so that at least one of the valve opening period and the lift amount is made larger.

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 both high speed type cams 3a and 3b.
A pair of left and right arm portions 7a, 7b that come into contact with the first arm 7 integrally provided with an upper connecting portion 7c, and both intake valves 2
It is divided into a second arm 8 integrally provided with contact portions 8a, 8b for contacting a, 2b and contact portion 8c for contact with the low-speed cam 4, and these arms 7, 8 are relatively arranged around the rocker shaft 9. A plunger 11 that is supported so as to be movable and that switches both 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 second arm 8 is provided above the first arm 7.
A guide hole 13 opening toward the upper part of the is formed, the plunger 11 is movably accommodated in the guide hole 13,
The plunger 11 is biased by a spring 14 in a guide hole 13 so as to come into contact with the second arm 8, and a small-diameter engaging portion 15 is formed in the middle of the plunger 11. The lever member 12 is provided on the upper part of the first arm 7.
Is movably supported orthogonally 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 a locking hole 17 connected to the plunger insertion hole 16 and having a size corresponding to the engagement portion 15 are formed.

In this way, the locking hole 17 of the lever member 12 becomes
When the lever member 12 moves to the unlocked position in which the plunger 11 is inserted into the plunger insertion hole 16 after being disengaged from the engaging portion 15, the sliding of the plunger 11 is allowed, so that the arms 7 and 8 Relative movement is allowed (non-connected state at this time), and 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, sliding of the plunger 11 is blocked. As a result, relative movement of the upper portions of both arms 7 and 8 in the directions approaching each other is prevented (at this time, the connected state). And both arms 7,8 above
Is disconnected, the swing of the first arm 7 due to the rotation of the rocker arm 6 is not transmitted to the second arm 8, so that the swing of the second arm 8 according to the rotation of the low-speed cam 3 causes When the intake valves 2a, 2b are operated and both arms 7, 8 are in the connected state, both arms 7, 8 swing integrally as the high-speed cams 4a, 4b rotate and intake The valves 2a and 2b are operated.

The end of the lever member 12 projects to the outside of the first arm 7 and is connected to the annular hydraulic actuator 20 rotatably supported around the rocker shaft 9 via the arm 12a of the lever member 12. , This actuator 20
The oil passage from the oil pump (not shown)
When the oil is supplied via 22 the lever member 12 is moved toward the lock position, and when the oil is relieved, the return spring 23 moves the lever member 12 toward the unlock position. ing. In the oil passage 22, a control valve 24 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 arranged on the second arm 8, and 29 is a cylinder head.

FIG. 5 shows a control system for controlling the switching of the valve lift characteristic for the valve operating system as described above and controlling the ignition timing for the ignition device 34 of the engine. In the figure, 30 is a control circuit using a microcomputer or the like, which receives an engine speed detection signal 31 and an intake air amount detection signal 32 and outputs a signal for controlling the actuator 20 of the selector 10 to the control valve 24. The ignition timing control signal is output to the ignition device 34. 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.

The control circuit 30 controls the valve lift characteristics of the valve operating system in accordance with the operating state, and determines, for example, a set value of the intake air amount in advance, and when the detected value of the intake air amount is smaller than the set value. Controls the intake valves 2a, 2b to be linked to the low speed type cam 3, and controls the intake valves 2a, 2b to be linked to the high speed type cams 4a, 4b when the detected value becomes larger than the set value. is doing. For the ignition device 34, the engine speed and the intake air amount are respectively adjusted for low speed (when the low speed valve lift characteristic is used) and for high speed (when the high speed valve lift characteristic is used). The ignition timing is stored in advance as a map, and the ignition timing based on the high speed map is set to a larger advance angle ratio than the ignition timing based on the low speed map. Then, by performing control according to the flowchart shown in FIG. 6, it functions as ignition timing control means.

To explain the control of the ignition timing shown in the flowchart of FIG. 6, first, in step S _1, S ₂ calculates the engine speed and the intake air amount, "low speed in the low speed valve lift characteristic (in the figure at the step S ₃ Abbreviated as "lift characteristic"). Then, the ignition timing Tig determination in step S ₃ are in step S _4, if YES
Is read from the low speed map, and if the determination result is NO, the ignition timing Tig is read from the high speed map in step S ₅ . Next, in steps S ₆ and S ₇ , an ignition pulse is output at the ignition timing.

According to the engine having the above valve operating system, control, and correction means, the intake valves 2a and 2b are operated with the low-speed valve lift characteristic in the low-speed low-load operating region, and in the high-speed high-load operating region. By operating the intake valves 2a and 2b with the high-speed valve lift characteristic, the intake introduction condition is adjusted to suit the operating condition, and the ignition timing is appropriately adjusted according to such a change in the valve lift characteristic. Controlled. In other words, when the low-speed valve lift characteristic with a small valve overlap amount is used, combustion is promoted due to a decrease in the internal EGR amount (EGR amount due to blowback of exhaust gas), so the required ignition timing at this time The advance rate of the ignition timing is reduced so that the ignition timings match, and thus knocking due to excessive advance of the ignition timing is prevented. Also, when the valve lift characteristic for high speed with a large valve overlap amount is used, the combustion speed decreases due to the increase of the internal EGR amount,
By advancing the ignition timing, the advance rate of the ignition timing is increased and adjusted to the required ignition timing, so that the output reduction or the like due to the advance of the ignition timing is prevented.

In the above embodiment, the ignition timing is controlled depending on whether the valve lift characteristic is for high speed or low speed, but in addition to such control, the delay in switching the valve lift characteristic is considered. Then, the ignition timing may be controlled after a predetermined time has elapsed from the output of the switching signal. When switching the valve lift characteristic, the ignition timing is changed so as to mitigate the torque shock, and for example, when switching from the high speed valve lift characteristic to the low speed valve lift characteristic,
When the ignition timing is gradually changed to switch from the low speed valve lift characteristic to the high speed valve lift characteristic, the ignition timing is once shifted to the retard angle side or the like and then changed to the timing according to the valve lift characteristic. Correction may be performed.

Further, although the switching of the valve lift characteristic is controlled according to the intake air amount in the above-mentioned embodiment, the present invention is not limited to this, and may be controlled only by the engine speed, for example.

Further, the structure of the valve lift characteristic varying device is not limited to the above-mentioned embodiment, but can be variously modified. For example, as shown in FIGS. 7 and 8, the rocker arm 6 is integrated, and the high speed type cams 4a, 4b are attached to the ends corresponding to the high speed type cams 4a, 4b.
A selector 40 including a slidable plunger 41 that abuts against the spring 41, a spring 42 that biases the plunger 41 toward the high-speed cams 4a and 4b, and a stopper member 43 that engages and disengages with the plunger 41.
By providing, the operation of the high speed type cams 4a and 4b may be absorbed and transmitted at this end.

Further, in the above embodiment, the case where it is applied to the intake valve is shown, but 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 combustion state changes with this, the same control as that applied to the intake valve may be performed.

(Effects of the Invention) As described above, according to the present invention, the valve operation is changed to the low-speed valve lift characteristic in which the overlap amount of intake and exhaust is small and the high-speed valve lift characteristic in which the overlap amount is large according to the operating state. In the engine designed to be switched, the advance ratio of the ignition timing in the operating region of the high-speed valve lift characteristic is made larger than the advance ratio of the ignition timing in the operating region of the low-speed valve lift characteristic. It is possible to adjust the ignition timing corresponding to the change in the firing state accompanying the change in the overlap amount due to the change, such as knock resistance in the low speed side operating range, output in the high speed side operating range, etc. It can be improved.

[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 a control system, FIG. 6 is a control flowchart, and FIG. 8 is a plan view showing the embodiment of FIG. 8 and FIG. 8 is a sectional view taken along the line VIII-VIII in FIG. 2a, 2b ... intake valve, 3 ... low speed type cam, 4a, 4b ... high speed type cam, 6 ... rocker arm, 10, 40 ... selector, 30 ... control circuit (ignition timing control means), 34 …
… Ignition device.

Claims (1)

[Claims] 1. A valve operation according to a low speed valve lift characteristic in which an intake air and exhaust gas overlap amount is 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. In an engine with a variable valve lift characteristic that allows switching, the advance ratio of the ignition timing in the operating range of the valve lift characteristic for high speed is higher than the advance ratio of the ignition timing in the operating range of the valve lift characteristic for low speed. An engine with a valve lift characteristic varying device, characterized in that ignition timing control means for enlarging is provided.