GB2139283A - A multi-cylinder IC engine operable with at least one ineffective cylinder - Google Patents

Abstract

The rocker arms 8 operating the inlet and exhaust valves of the or each cylinder which is to be ineffective at light loads are movable from a conventional cam 7a to co-operate with a cam 7b which, in the case of the inlet valve, provides permanent closure and which, in the case of the exhaust valve, provides opening when both the inlet valve and the exhaust valve are conventionally open. Thus exhaust gas from the effective cylinder(s) is compressed and expanded in the ineffective cylinder(s). <IMAGE>

Description

SPECIFICATION A multi-cylinder internal combustion engine The present invention relates to a multi-cylinder internal combustion engine which is adapted to keep some of the cylinders thereof inoperative while the remainder are operating when the magnitude of load on the engine decreases.

In a motor vehicle such as an automobile and the like, all cylinders of a multi-cylinder engine must be operated simultaneously to provide a large power output as desired for driving under a heavy load condition. It, however, is often experienced that if all the cylinders are continued to operate simultaneously even after the engine load is reduced, that is, during a partial load condition, each cylinder tends to reduce its charging efficiency, resulting in increased pumping loss and decreased combustion efficiency and fuel economy.

To overcome such shortcomings, several new solutions are already proposed in the art, as described, for instance, in the Japanese Patent Application No. 288770/1975 wherein some cylinders are made inoperative under a partial load condition on the engine, thereby enabling a fuel-air mixture to concentratively enter the rest of cylinders, and thereby providing a consequential improvement in the fuel mileage ratio as a result of increased combustion efficiency and reduced pumping loss. Some cylinders, in such prior art, can be made inoperative by retaining their intake valve and exhaust valve completely closed positions, thereby interrupting further inflow of the fuel-air mixture to the cylinder to cease combustion therein.

However, such a prior art solution is not satisfactory in that because the air left in the inoperative cylinders is repeatedly compressed and expanded every revolution of the engine, the driving torque is subject to a great change while the piston performs the intake and exhaust strokes, although the positive and negative driving torques would be small during the sane strokes enough if the cylinder became operative. This, along with the decreased number of operating cylinders, inevitably causes a problem that the smooth engine rotation is significantly disturbed due to increase in a primary vibrational component as a result of abnormally large variation of the driving torque to be generated from the inoperative cylinder.

It is therefore an object of the present invention to provide a multi-cylinder internal combustion engine which may be operated smoothly under a partially loaded condition.

It is another object of the present invention to provide a multi-cylinder internal combustion engine in which some cylinders are rendered inoperative during the partial load operation, whereby pumping loss is reduced, and an improvement in combustion efficiency and fuel/ mileage ratio is accomplished.

Briefly described, these and other objects of the present invention are accomplished by the provision of a multi-cylinder internal combustion engine comprising at least one cylinder which can be rendered inoperative while the engine is in a partially loaded condition, at least one cylinder which can continue operating regardless of the engine load condition and a controlling means which function during the practical load condition so as to keep the intake valve completely closed and in turn open the exhaust valve on the exhaust stroke and on the intake stroke in the cylinder in the inoperative mode.

In the accompanying drawings: Figure 1 is a diagram of the combustion cycle occurring in a multi-cylinder engine in accordance with the present invention when the engine is in a fully loaded condition; Figure 2 is a diagram similar to Figure 1, but showing conditions occurring in a cylinder that is rendered inoperative; Figure 3 is a plan view of a driving means for the exhaust valve; Figure 4 is a front view of the means shown in Figure 3; Figure 5 is a schematic view showing how intake air and exhaust gas flow when all the cylinders in the multicylinder engine are operated simultaneously; and Figure 6 is a view similar to Figure 5 but showing how intake air and exhaust gas flow when one cylinder is rendered inoperative.

Referring first to Figures 1 and 2, there are shown combustion cycles in a multi-cylinder internal combustion engine having four cylinders in accordance with the present invention.

Figure 1 shows the combustion cycle of the fuel-air mixture in the multi-cylinder engine when the engine is subjected to a heavy load.

Alphabetical references respectively indicate one stroke of each cycle, nanely (a) the expansion stroke, (b) the exhaust stroke, (c) the intake stroke and (d) the compression stroke.

After the intake valve 2 and exhaust valve 3 are closed, the fuel-air mixture in the cylinder 1 is ignited by an ignition plug 4, forcing the piston 5 downwardly on the combustion and expansion strokes. Immediately after the fuel combustion, the exhaust valve 3 is opened for the exhaust stroke, and then the exhaust valve 3 is closed while the intake valve 2 is opened to draw in the fuel-air mixture on the intake stroke. Finally, the intake valve 2 is closed whilst the piston 5 rises for effecting the compression stroke.

On the other hand, there is shown in Figure 2 the cycle of a cylinder in the inoperative mode when the engine is partially loaded. The exrpansion stroke and the exhaust stroke are the same as shown in Figure 1, but the intake stroke is different from the previous description in that as shown in (c), the exhaust valve 3 is opened for re-drawing the burned or combustion gas which was discharged to the exhaust tube. Then, the compression stroke (d) in Figure 2 is effected, wherein the piston 5 is raised upward to compress the combustion gas in the cylinder with the intake valve 2 and the exhaust valve 3 closed.

As shown in Figures 1 and 2, each stroke provides the same operating pattern, that is, Stroke (a) in Figures 1 and 2 both provide positive torque, Stroke (d) in Figures 1 and 2 negative torque and the other strokes smaller torque. This means that the engine can rotate very smoothly even under the partially loaded condition in the same way as the fully loaded condition.

The operating cylinders can provide only a decreased charging efficiency of the fuel-air mixture while the engine is idling or operating under a small load. During idling, for example, the intake air enters the cylinder at an initial pressure of about 40Q mm Hg in negative pressure for suction of about 350 to 400 Hg in absolute pressure (approximately half the atmospheric pressure), and is compressed, burned and expanded. The peak pressure during combustion is about 10 to 1 5 kg/cm2.

The torque change comparable with the peak pressure in the operating cylinder can be easily obtained by compressing the exhaust gas having a pressure close to atmospheric. In addition, as aforementioned, the arrangement in accordance with the present invention can enable the inoperative cylinder to undergo a change in its internal pressure closely as in the operative mode. For instance, in the case of a four-cylinder engine, the compression and expansion strokes can be obtained twice every revolution of the main shaft of the engine even if two cylinders are in the inoperative mode or condition. As a result, according to a predetermined ignition order, the internal pressure in each cylinder increases in the same sequence as that during the four-cylinder operation, whereby increase in the bending vibration of the crank shaft of the engine can be avoided.

Figures 3 and 4 show a construction of the system for controlling the intake valve 2 and the exhaust valve 3, in accordance with load conditions of the engine, according to the present invention, wherein a camshaft 6 is provided with cams 7a and 7b having different profiles adjacent to the cam-shaft, and a rocker arm 8 is provided to come, selectively, into driving contact with either of the cams 7a or 7b. The rocker arm 8 is pivotally mounted on the rocker shaft 9 and can be moved along the rocker shaft 9 in the axial direction through springs 11 and 1 2 by means of a switching ring 10 which is also pivotally mounted on the rocker shaft 9.The movement of the switching ring 10 is controlled by means of a shaft 14 which is linked to an actuator 1 3. A rocker bracket 1 5 is mounted on the rocker shaft 9 which is provided at either side of the rocker arm 8. The shaft 14 is axially slidably held at one of the rocker brackets 1 5. A valve spring 1 6 is provided to urge the exhaust valve 3 upwardly. The cam 7, rocker arm 8, switching ring 10 and springs 11 and 1 2 function as controlling means for switching the operative and inoperative modes of the cylinders.

The function of the arrangement in accordance with the present invention will now be described.

The cams 7a and 7b having different profiles are respectively used for the operation of the exhaust valve 3. The cam 7b has a profile such that it can open the exhaust valve 3 on the exhaust stroke as does the cam 7a and also open the exhaust valve 3 on the intake stroke. The function mentioned above can be also applied to the intake valve 2 except that the profile of the cam 7b for the inoperative mode is in the for of a cam base circle.

While the cam 7a is pivoting the rocker arm 8, movement of the rocker arm is difficult because of the large reaction forces of the valve spring 1 6. In this condition, even if the switching ring 10 moves in the direction of the arrow P according to the actuation of the actuator 1 3, the rocker arm 8 would not move in the same direction only with the spring 1 2 being compressed.

On the contrary, the reaction forces of the valve spring 1 6 against the rocker arm 6 decrease when the end of rocker arm 8 comes into contact with the base circle portion 7 c of the cam 7a. Accordingly, the operation of the actuator 1 3 can move the rocker arm 8 in the direction of the arrow P while compressing the spring 11 for bringing the outer perimeter of the cam 7b into contact with the end of the rocker arm 8. On the other hand, in the case of the rocker arm 8 returning back in the reverse direction of the arrow Q, the rocker arm 8 is set to move when the can 7b reaches the base circle 7c under forces of the spring 11.At this time, if the engine includes four cylinders, the controlling means function to operate two of the intake valves 2 and two of the exhaust valves 3 respectively, while keeping the rest of cylinders inoperative. The intake valve 2 and the exhaust valve 3 of the cylinder that continues operating regardless of the engine load conditions are driven by means of a cam having a single profile. Moreover, the actuator 13 is controlled by "ON" and "OFF" operations of a solenoid.

In such a manner as aforementioned, the rocker arm 8 is moved in the axial direction in response to the operation of actuator 1 3 and corresponding to the magnitude of reaction force of the valve spring 16, and by causing the end of rocker arm 8 to come into selective sliding contact with the two cams 7a or 7b, it becomes possible to close the intake valve 2 and open the exhaust valve 3 on the intake stroke for re-drawing the exhaust gas into the combustion chamber, while compression of the combustion gas is carried out by closing the intake valve 2 and the exhaust valve 3 on the compression stroke, thus producing torque change similar to that in the cylinder in the other normal operation and smoothing the rotation of the engine.In this manner as described above, when the engine is operating under the fully loaded condition; the fuelair mixture is, as show in Figure 5, drawn into the four cylinders through the carburetor 1 7 and the throttle valve 18, burned, expanded and finally discharged through the opened exhaust valve 3 into the catalyst 20 through the exhaust tube 19. The partition wall 21 is provided inside the exhaust tube 19 to separate the adjacent two pairs of cylinders.

Moreover, when the engine is operated under the partially loaded condition, two left-side cylinders are, as shown in Figure 6, rendered inoperative and the burned or combustion gas is draw therein on the intake stroke while the remaining cylinders are performing the same function as shown in Figure 5.

In the foregoing embodiments in accordance with the present invention, four-cylinder engines have been described, however, almost the same effect can be obtained by the six-cylinder engines with three cylinders being rendered inoperative, because the internal pressure change in the cylinders presents the same pattern in both the operative and inoperative modes. Furthermore, igniting sequence of the cylinder is not limited to the embodiment described herein, and is applicable to any conventional combination thereof.

A switching mechanism for the control of the intake valve and the exhaust valve disclosed herein is merely one particular form and may be constructed differently such as hydraulically or electrically driven.

As obvious from the foregoing explanation, the multi-cylinder internal combustion engine in accordance with the present invention makes it possible that only the exhaust valve is operable at the cylinder that is rendered inoperative, and that the burned gas is redrawn from the exhaust passage during the intake stroke and compressed and expanded to develop a torque change similar to that to be produced from the usuai engine operation.

This may reduce the primary vibrational component and thereby smooth the rotation of the engine under the partially loaded condition, while at the same time improving the combustion efficiency and fuel/ mileage ratio as a consequence of the controlled number of operating cylinders.

Claims (5)

1. A multi-cylinder internal combustion engine, comprising at least one cylinder adapted to operate under partially and fully loaded conditions, at least one cylinder being adapted to be inoperative while the rest of cylinders are operating, and controlling means adapted under a partially loaded condition to close the intake valve on the cylinder in the inoperative mode and to open on the exhaust stroke and on the intake stroke the exhaust valve each provided on said same cylinder.

2. A multi-cylinder internal combustion engine as set forth in claim 1, wherein said engine comprises a four-cylinder engine in which two cylinders are rendered inoperative while the rest of cylinders are operating under a partially loaded condition.

3. A multi-cylinder internal combustion engine as set forth in claim 1, wherein said engine comprises a six-cylinder engine in which three cylinders are adapted to be inoperative while the rest of cylinders are operating under a partially- loaded condition.

4. A multi-cylinder internal combustion engine as set forth in any of claims 1 to 3, wherein said controlling means comprises a rocker shaft, a rocker arm pivotally mounted relative to said rocker shaft and slidable in the axial direction of the rocker shaft, said rocker arm being mounted on the valve of said cylinder, and a camshaft including two cams having different profiles, said two cams being selectively in contact with said rocker arm in the fully loaded condition respectively.

5. A multi-cylinder internal combustion engine substantially as described with reference to, and as illustrated in, the accompanying drawings.