GB2119853A

GB2119853A - Four-cylinder I.C. engine operable with two effective cylinders

Info

Publication number: GB2119853A
Application number: GB08312442A
Authority: GB
Inventors: Shunichi Aoyama; Yasuo Nakajima
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1982-05-07
Filing date: 1983-05-06
Publication date: 1983-11-23
Also published as: GB8312442D0; DE3316446A1; GB2119853B

Abstract

Two cylinders 2, 3 are effective during light and heavy load conditions on the engine and two cylinders 1, 4 are ineffective during light load conditions on the engine. During light load conditions the inlet and/or exhaust valves or an additional inlet valve (28, Fig. 11) of each cylinder 1 and 4 are opened only for a period around B.D.C. of each stroke, e.g. 30 to 60 DEG on either side of B.D.C., to provide a charge in the cylinder which is compressed and expanded, whereby the forces transmitted to the crankshaft from each of the pistons 1 to 4 are equivalent. <IMAGE>

Description

SPECIFICATION Four-cylinder internal combustion engine The invention relates to an improvement of a multi-cylinder internal combustion engine wherein part of the cylinders are rendered inoperative during light load operation of the engine.

In general, the fuel consumption rate of an internal combustion engine is improved when the engine is operated at its heavy load condition. In view of this, an improved multi-cylinder internal combustion engine was developed as disclosed in Japanese Patent Application No. 28770/1975, wherein some of the cylinders in a multi-cylinder engine are rendered inoperative during light load conditions while the remainder of the cylinders are rendered operative under relatively heavier load conditions on the engine, thereby improving the whole fuel consumption rate during light load conditions.

Conventionally there are two methods for halting the operation of a given number of cylinders in a multicylinder engine during the operation of the engine. One method is terminating the fuel supply and the other method is restricting the opening motion of intake valves and/or exhaust valves in the cylinders. According to the latter method, during the reciprocating motion of the engine and, accordingly the compression and expansion of the gas contained in the cylinders, the blow-by gas enters the crankcase and consequently the pressure in the inoperative cylinders is gradually decreased, thereby considerably reducing the smoothness of rotary motion of the engine.

Figure 1(A) shows the change of pulsation in pressure in the cylinders (Pl-P4) of an in-line four-cylinder engine where the intake and exhaust strokes of the cylinders Nos. 2 and 3 are halted.

As shown in Figure 1, initially the peak values (dotted line) of the cylinder pressures P2 and P3 are about half the P1 and P4 of the operative cylinders, respectively. However, a continued inoperative condition would result in the relatively, smoothed or faded pressure change in pressure as shown by solid lines in Figure 1. The operative cylinders (&num;1 and &num;4) have their peak pressure every 720 degrees of the crank angle when the other cylinders (&num;2 and &num;3) are in their inoperative condition, the respective peak pressures of the cylinders being 360 degrees out of phase with respect to each other.

Consequently, the conventional four-cylinder engine has a large peak combustion pressure every 360 degrees of the crank angle when two cylinders are inoperative as compared with a peak pressure every 1 80 degrees of the crank angle where all (four) cylinders are ordinarily in their operative condition. Thus, when the engine is in a cylinder-in-part operating mode (two cylinders operative and two cylinders inoperative), the engine does not operate smoothly.

According to the conventional internal combustion engine described in the Japanese Official Gazette of the Patent Laid-open No.

38639/1982, the cylinder pressure is prevented from lowering by opening the intake valve or the exhaust valve in the neighbourhood of the bottom dead centre (which is hereinafter called B D C while top dead centre is called T D C) of the respective inoperative cylinders, the object of which is, however, to prevent oil from entering the inoperative cylinders. In addition, the object is realized in a six-cylinder engine.

Accordingly, the object of this invention is to provide a mechanism for preventing the deterioration of the smooth rotation of an engine in a cylinder-in-part operating mode. It should be noted that the mechanism according to the present invention is effectively applied to a fourcylinder engine and has no effect on a six-cylinder engine.

The reason why the mechanism cannot be applied to a six-cylinder engine will be explained herebelow.

When half the number of the six-cylinders (cylinders No. 1, 2 and 3, or No. 4, 5 and 6) are rendered inoperative and air is supplementarily supplied to the cylinders during the inoperative period, the inoperative cylinders No. 4, 5 and 6, for example, raise the pressure P4, P5 and P6 in the cylinders No. 4, 5 and 6, and their phases are differentiated 120 and their peak pressure does not overlap with each other.

Additionally, as shown in Fig. 1 B, any one of the compression peaks in the inoperative cylinders is overlapped with a combustion pressure peak of the operative cylinder, resulting in large variations in output torque and pulsations.

As apparent from the foregoing, the object of the cylinder-in-part operation carried out conventionally in a multi-cylinder engine is to prevent oil from overflowing at every cylinder and not to make the operation of the engine smooth by preventing an unbalanced condition of the whole cylinders.

An object of the present invention is to provide an improvement in a four-cylinder internal combustion engine, in which a pressure drop in a cylinder due to the cylinder-in-part operating mode of the engine is prevented so as to always obtain a stable and smooth operation of the engine.

These and other objects of the present invention are accomplished by the provision of a four-cylinder internal combustion engine with a valve mechanism for closing and opening the valves on two cylinders in the inoperative mode in the neighbourhood of the B D C position during the cylinder-in-part operation mode of the engine.

In the accompanying drawings: Figure 1(A) is a graph showing the pressure change of the inoperative cylinders and the operative cylinders in a conventional in-line fourcylinder engine.

Figure 1(B) is another graph showing the pressure change of three inoperative cylinders and the three operative cylinders in an in-line sixcylinder engine, Figure 2 is a plan view of the valve operating mechanism for an intake valve or an exhaust valve for changing-over the opening operation of the valve, Figure 3 is a sectional view of the valve operating mechanism, Figure 4 shows a structure of the control system provided with the valve operating mechanism for the in-line four-cylinder engine, Figure 5 is a plan view of the essential part of the control system shown in Figure 4, Figure 6 shows diagrammatically an opening time graph of an exhaust valve, Figure 7 shows an illustrative view of the exhaust and intake valves of a given cylinder as a function of the intake, compression, combustion and exhaust modes of the cylinder, and as a function of the inoperative and operative conditions of the cylinder, Figure 8 is a diagram showing the change of pressure in the cylinders at the inoperative mode and the operative mode, Figure 9 is a valve timing graph of the intake and exhaust valves, Figure 10 shows another embodiment of the valve operating mechanism according to this invention, and Figure 11 (a, b) shows an illustrative view of the valves of a given cylinder in the inoperative and operative modes as a function of the different modes of the cylinder for the embodiment shown in Figure 10.

When the intake and exhaust valves on two cylinders namely Nos. 1 and 4 or Nos. 2 and 3 cylinders, respectively, are closed in the operation of their pistons in the same phase in the fourcylinder engine, effective compression is attained in the cylinders at the operative or inoperative mode simultaneously every 360 degrees of the crank angle and at a phase shifted 180 degrees from that of the cylinder at the operative mode, making the total of these peak values substantially the same as the combustion peak values of one of the cylinders at the operative mode as shown in Figure 1(A). The smoothness of the operation as in the four-cylinder engine is maintained in the twin-cylinder engine if the compression mode is securely accomplished.

According to the present invention, the effective compression mentioned above can be obtained by providing the inoperative cylinders with a valve mechanism for opening the valves of the cylinders during the inoperative period approximately symmetrically with respect to the B D C and around the B D C (at the original intake BDC or expansion BDC) in order to supplement for the drop of pressure in the cylinder at the inoperative mode. The drop of pressure due to the continuation of the operation of the engine in a cylinder-in-part mode of operation is prevented by a small volume of gas supply in the neighbourhood of B D C.

This invention will be explained with reference to a preferred embodiment shown in the accompanying drawings.

It is noted that various kinds of change-over mechanisms for intake valves and exhaust valves have been proposed. One example of a conventional change-over mechanism will be explained with reference to the drawings of Figures 2 and 3.

In this invention, by a valve timing change-over means for intake and exhaust valves on two cylinders of the four-cylinder engine, the cylinders are put in the inoperative mode thereby closing completely the exhaust valve during the inoperative period and slightly lifting the intake valve in the neighbourhood of the B D C as previously explained, in which the pistons are at the same phase.

Figure 2 shows partly the mechanism according to the present invention, where a cylinder head 1, an intake valve 2, a rocker arm 3, brackets 5A and 5B for fixing the rocker shaft 4 to the cylinder head 1 and a camshaft 6 are shown.

A first cam 6A is formed on the camshaft 6 and is provided with an operation profile to open and close the intake valve 2, in co-operation with a valve spring 2A, through the rocker arm 3 during the operative intake stroke. A second cam 6B is formed next io the cam 6A on the shaft 6 to open the intake valve 2 in the neighbourhood of B D C of the piston.

The rocker arm 3 is pivotally supported with respect to the rocker shaft 4 and in addition axially movably between the brackets 5A and 5B.

A change-over ring 7 is mounted on the rocker shaft 4 so as to slide axially along the shaft 4 between the rocker arm 3 and one of the brackets 5A. The longitudinal position of the rocker arm 3 on the rocker shaft 4 is determined in accordance with the tension balance between a first spring 8A placed between the change-over ring 7 and the rocker arm 3 and a second spring 8B placed between the rocker arm 3 and the other bracket 5B.

The change-over ring 7 mentioned above is driven or made to slide along the rocker shaft 4 by an actuator 10 consisting of a solenoid, a hydraulic cylinder or the like, via a rod 9.

When the engine operates, the rocker arm 3 is positioned as shown in Figure 2 so as to move the intake valve 2 according to the profile on the first cam 6A. When the actuator 10 moves the change-over ring 7 toward the bracket 5B along the rocker shaft 4, the springs 8A and 8B are compressed and simultaneously the rocker arm 3 is pushed and moves towards the bracket 5B.

Consequently, a follower portion 3A of the rocker arm 3 is transferred onto the second cam 6B, while the follower portion 3A is positioned in the base circle portion of the first cam 6A. The second cam 6B has a profile giving a small lift to the intake valve 2 when the respective piston is in its B D C position.

The exhaust valve (not shown in Figures 2 and 3) has a mechanism similar to the one for the intake valve 2, wherein a second cam corresponding to the second cam 68 has a true circle of the same diameter as the base circle portion formed on the cam 6A. As a result, when the actuator 10 operates in accordance with the engine operative conditions such that the intake valve 2 is controlled so as to only lift a small distance and also the exhaust valve is controlled so as to be fully closed, the intake and exhaust operation of the inoperative cylinder can be controlled.

Figure 4 shows an example of a control system for an in-line four-cylinder split engine, in which the first cylinder &num;1 and a fourth cylinder &num;4 are in the inoperative mode and the second cylinder &num;2 and the third cylinder #3 are in the operative mode.

In operation of the split engine control system shown in Figure 4, the load condition on the engine is detected with a control circuit 1 7 in accordance with signals outputted from a load sensor 1 6 operatively connected to an accelerator pedal 1 5. When it is in the preset light load range, the operation of the valves on the cylinders &num;1, &num;4 is stopped by means of the actuator 10 as previously described, Furthermore, electrical switches 1 9A and 20A are placed in series with the ignition leads 19 and 20, each having one end thereof connected to a distributor 1 8 and the other end thereof to the respective ignition plugs in the cylinders 1 and 4.

The opening and closing operation of the switches 1 9a, 20a is controlled by the control circuit 1 7 thereby determining if electrical power is supplied to the respective spark plugs.

Accordingly, the firing of the spark plugs (not shown) can be controlled according to the load conditions on the engine.

In consequence, the operating conditions, namely the operative or inoperative mode of the cylinders of an engine can be controlled. A battery 21, an ignition switch 22, and an ignition coil 23 are shown in Figure 4.

Figure 5 illustrates the overall structure of the valve operation timing mechanism partly shown in Figure 2 and installed on a cylinder head 1.

In the valve operation timing mechanism shown, the profile of the cam 6B is so formed as to open the intake valve 2 for the time duration corresponding to the amount up to about 30 to 60 degrees of the crank angle respectively before and after the B D C position (that is, about 60 to 1 20 degrees in total) during non-operation of the cylinders, in other words, to start the opening of the intake valve 2 in the range up to about 30 to 60 degrees before B D C, and to close the valve in the range up to about 30 to 60 degrees after B D C as illustrated in Fig. 6.

In accordance with the structure described above, the intake valve 2 is opened and the cylinders &num;1 and &num;4 intake new air every time an intake stroke starts even when the exhaust valve 29 is closed.

If compressed gas is blown into the crankcase during a rising motion of a piston 28, a volume of new air corresponding to the gas volume which is lost as blow-by gas is supplied to the cylinder during the next cycle and consequently suitable sufficient compression is always kept as shown in Figure 8. As already noted, the maximum pressure in the cylinders &num;1 and &num;4 during the inoperative mode of operation is made about half that of the pressure in the operative cylinders &num;2 and &num;3, and the air in the inoperative cylinders is naturally compressed through the compression strokes and the exhaust strokes as usual.

Then the air pressure in the inoperative cylinders and the compressed air are integrated to attain or make full use of approximately the same torque as that of the operative cylinders &num;2 and &num;3.

In other words, the engine will experience the peak vaiue of combustion pressure or the pressure change corresponding to the peak value every 1 80 degrees of the crank angle.

Furthermore, the pressure in the inoperative cylinders &num;1 and &num;4 is made the same as that of the intake passage 25 (see Figure 4) and the input rate of intake air equally changes at the inoperative cylinders &num;1 and &num;4 and at the operative cylinders &num;2 and &num;3 in accordance with the load change in the cylinder-in-part operation mode.

As a result, a very smooth operation without any change in torque and rotation can be attained in the engine for all modes of operation. It is preferable that the opening period of the intake valve 2 of the cylinders during their inoperative mode of operation is distributed in the range up to about 30 to 60 degrees respectively before and after the B D C position, the reason of which will be understood from the following: First of all, in order to ensure a sufficient supply of air corresponding to the air loss or blow-by air during non-operation, it is necessary to obtain at least about 60 degrees of the valve opening period in view of the lift distance of the valve. If the lift distance is to small, unevenness in valve gap results in a difference between the cylinders in intake filling rate, which results in vibration and rotation fluctuations of the engine.Accordingly, it is necessary to prevent the phenomena mentioned above from occurring as well as to provide the entry of sufficient air. Furthermore, some pumping loss is generated when the valve opening period is deviated or shifted from the centre towards the expansion stroke or the compression stroke. For example, when the valve is set so as to open for a period of 90 degrees after B D C, approximately 50% of the air contained in the cylinder flows backward and is lost, and consequently the desired compression pressure is not attained. Also, it is necessary to consume disadvantageously some energy to expand the gas in the cylinder before the expansion stroke ends, generating a torque loss.

On the contrary, when the valve opening period is set at an angle of 90 degrees before the B D C position, an increased pumping loss may be generated because the pressure in the cylinder is lost during the expansion stroke and consequently the energy utilized during the previous expansion stroke is wasted in part.

These pumping losses increase the fuel consumption rate of the engine and the essential purpose of controlling the engine cylinder-in-part mode of operation is lost.

Another disadvantage is generated when the valve opening period is too long, thereby decreasing the intake filling rate and resulting in insufficient compression pressure. Accordingly, it is preferable to set the valve opening period in the region of 60 to 120 degrees centered symmetrically with the B D C position.

Though this invention has been explained in reference to an in-line four-cylinder engine, the same effect can be obtained when a V-type fourcylinder engine is employed, wherein the combustion interval is 1 80 degrees of the crank angle when all cylinders operate and 360 degrees when two cylinders operate.

As described above, in a four-cylinder engine, wherein the intake valves and/or the exhaust valve on two cylinders of the same phase are placed under an inoperative mode during light load conditions on the engine, which is herein referred to as cylinder-in-part mode of operation of the engine, the intake valves of the inoperative cylinders are controlled so that they are opened for a period up to about 30 to 60 degrees on either side of the respective B D C position of the respective inoperative cylinders during their inoperative mode of operation, thereby ensuring that a sufficient supply of air corresponding to the blow-by gas is inputed to the inoperative cylinders during the cylinder-in-part mode of operation and keeping a sufficient compression pressure in the inoperative cylinders.

In the case of the exhaust valve, the period or range should be broadened to about 90 degrees respectively before and after the B D C position.

Thus, smooth operation of the engine during the cylinder-in-part mode of operation can be effectively accomplished. As can be seen in Figure 9, graph (a) shows the opening condition of the exhaust valves and the intake valves during the effective operation, and graph (b) shows the opening condition of the valves on the inoperative cylinders (#1, #4). It is apparent that various valve mechanisms other than in the above embodiment can be used in this invention. Graphs (c) and (d) show the opening conditions of other exhaust and intake valves adapted to open in the neighbourhood of the respective B D C position and are respectively placed on the cylinders in the inoperative mode.

The intake valve and the exhaust valve shown in the graph (c) open at only the positions near the B D C position of the piston to overlap one another. The graph (d) shows the intake valve and the exhaust valve to be alternately opened in the neighbourhood of the B D C position wherein the valve opening is made in reverse order for the cylinders #1 and #4.

Figure 10 and 11 show another embodiment of the present invention. As shown in Figure 10, the valve mechanism has a third valve device 26 fixed therein, together with the conventional intake valve and exhaust valve. The third valve 26 is operatively controlled by a supplement cam 6C formed on a cam shaft 6 through a rocker arm 27 exclusively used for the cam 6C without any relation to the effective or the inoperative conditions of the cylinder.

In the condition of effective operation, the third valve 26 intakes mixed gas together with the intake valve 2 as seen in Figure 11 (a) and in the inoperative condition, it opens independently to keep suitable compression pressure in the cylinders as shown in Figure 11(b). It is apparent that the third valve 26 opens in the range of about 60 to 120 degrees in the neighbourhood of the B D C position as explained in reference to the embodiment above.

Claims

1. A four-cylinder internal combustion engine comprising: two cylinders which are operated during light and heavy load conditions on the engine, two cylinders which are inoperative during said light load condition on the engine, a valve mechanism for said inoperative cylinders which operates during said light load condition on the engine, a control means for controlling said valve mechanism to supply each inoperative cylinder with an amount of air during a valve opening period which is around the bottom dead centre position of said inoperative cylinder.

2. A four-cylinder internal combustion engine as claimed in claim 1, wherein said valve opening period is provided approximately symmetrically with respect to said bottom dead centre position.

3. A four-cylinder internal combustion engine as claimed in claim 1 , wherein said valve mechanism comprises an exhaust valve and a cam for said exhaust valve, which operates during non-operation of said cylinder.

4. A four-cylinder internal combustion engine as claimed in claim 1, wherein said valve mechanism comprises an intake valve and a cam for said intake valve, which operates during nonoperation of said cylinder.

5. A four-cylinder internal combustion engine as claimed in claim 1, wherein said valve mechanism comprises an intake valve, an exahust valve, and cams for said intake and exhaust valves which operate during non-operation of said cylinders.

6. A four-cylinder internal combustion engine as claimed in claim 1, wherein said valve mechanism comprises a third valve and a cam for said third valve which operates during nonoperation of said cylinder.

7. A four-cylinder internal combustion engine as claimed in claim 3, wherein said valve opening period is provided in the range up to about 90 degrees respectively before and after the bottom dead centre position of the piston movement.

8. A four-cylinder internal combustion engine as claimed in claim 4, wherein said valve opening period is provided in the range between about 30 to 60 degrees respectively before and after the bottom dead centre position of the piston movement.

9. A four-cylinder internal combustion engine as claimed in claim 5, wherein said valve opening period for said intake valve is provided in the range between about 30 to 60 degrees respectively before and after the bottom dead centre position rotation and said valve opening period for said exhaust valve is provided in the range up to about 90 degrees of the bottom dead centre position.

10. A four-cylinder internal combustion engine as claimed in claim 6, wherein said valve opening period is provided in the range between about 30 to 60 degrees before and after the bottom dead centre position of the piston movement.

11. A four-cylinder internal combustion engine substantially as described with reference to, and as illustrated in Figs. 2 to 5, or Fig. 10 of the accompanying drawings.