Method and Apparatus for the Control of Valve Operations in Internal Combustion Engine

The present invention relates to an apparatus for controlling the valves of a four-cycle internal combustion engine. More specifically, the invention relates to a valve control apparatus which renders certain valves inoperative in accordance with the operating conditions of the engine.

In a high-speed four-cycle internal combustion engine, the valve overlap time, that is, the time during which both of the intake and exhaust valves in a cylinder are open is prolonged so that the inertial effect of intake and exhaust gases is utilized to increase the output of the engine. The inertial effect of intake and exhaust gases is useful when the engine is operating at a high speed, but when operating at a low speed, an accompanying reduction in the quantity of the fuel-air mixture introducted into the engine makes the speed thereof insufficient and gives rise to the excess recirculation of exhaust gas. These factors have an adverse effect on combustion, and tend to lower the output of the engine.

There has, therefore, been proposed an engine having a plurality of intake and exhaust valves for each cylinder. When the engine is operating at a low speed, predetermined ones of the intake and exhaust valves are rendered inoperative to increase the flow speed of the fuel-air mixture to thus improve the inertial effect of intake gases and restrict the recirculation of exhaust gas. This engine, however, does not achieve a satisfactory improvement in output during its operation at a medium speed.

In view of these difficulties, it is an object of the invention to provide an internal combustion engine having a maximum output at all engine speeds.

The invention provides an apparatus for the control of valve operations in an internal combustion engine having a plurality of intake and exhaust valves for each cylinder in which a part of each of the intake and exhaust valves are rendered inoperative when the engine is operating at a low speed, all of the intake valves are operated and a part of the exhaust valves rendered inoperative when the engine is operating at a medium speed, and all of the intake and exhaust valves are operated when the engine is operating at a high speed.

FIG. 1 is a graph comparing the output of a four-cycle engine having a plurality of intake and exhaust valves when a part of each of the intake and exhaust valves are placed out of operation (I) and its output obtained when all of the intake and exhaust valves are placed in operation (II);

FIG. 2 is a graph comparing the output characteristics of curves I and II, the output obtained when all of the intake valves are placed in operation and a part of the exhaust valves out of operation (III) and the output obtained when a part of the intake valves are placed out of operation and all of the exhaust valves in operation (IV);

FIG. 3 is a fragmentary side elevational view, partly in section, of the cylinder head of a four-cycle, four-cylinder engine for a two-wheeled motor vehicle showing an intake valve operating mechanism embodying the invention;

FIG. 4 is a fragmentary sectional view taken along a line IV--IV in FIG. 3; and

FIG. 5 is a schematic view showing a mechanism for the hydraulic control of valve operation in the engine.

As stated above, a high speed internal combustion engine having a plurality of intake and exhaust valves provides an improved output if a part of the intake and exhaust valves are placed out of operation when the engine is operating at a low speed. This point will be explained with reference to FIG. 1. FIG. 1 is a graph showing the output P.sub.s of an engine in relation to its speed of rotation N (rpm). Curve I shows the output characteristics obtained by placing a part of each of the intake and exhaust valves out of operation, and curve II shows the output characteristics obtained by placing all of the intake and exhaust valves in operation. As is obvious from a comparison of curves I and II, it is possible to produce an improved output for both low and high speeds of the engine if the operating conditions of curve I are employed when the engine speed is lower than n.sub.0, and those of curve II when the engine speed is n.sub.0 or higher.

An output characteristic curve formed by combining that portion of curve I which corresponds to an engine speed lower than n.sub.0 and that portion of curve II which corresponds to an engine speed of n.sub.0 or higher, however, provides a reduced output at medium speeds, as shown by hatching in FIG. 1. In other words, the engine fails to provide a satisfactory output at medium speeds in the vicinity of n.sub.0.

This is apparently due to the following reasons. If the engine speed increases from a low range to a medium range lower than n.sub.0, the engine fails to receive a sufficient supply of the fuel-air mixture since part of the intake valves are out of operation, despite a greater inertial effect of the intake than when the engine is operating at a low speed. Because the engine is of a high-speed type in which the valve overlap time during which all of the intake and exhaust valves in each cylinder are simultaneously open for a time so as to achieve a maximum output at a high speed, a medium speed range of n.sub.0 or higher is still so low that a relatively large quantity of exhaust gas is recirculated into the fresh fuel-air mixture, thereby lowering its combustibility. Also, the recirculation of hot exhaust gas results in an elevated cylinder temperature and thereby a lower charging efficiency.

It has been discovered that an improved engine output can be obtained in the medium speed range (shown by hatching in FIG. 1) if all of the intake valves are placed in operation so that the inertial effect of the intake is utilized to introduce an increased quantity of the fuel-air mixture, and if a part of the exhaust valves are rendered inoperative to restrict the recirculation of exhaust gas.

FIG. 2 compares curves I and II with a curve III showing the output characteristics obtained by placing all of the intake valves in operation and a part of the exhaust valves out of operation. Curve III lies above curves I and II when the engine speed is in the range of n.sub.1 to n.sub.2 (which corresponds to the hatched area in FIG. 1). In FIG. 2, n.sub.1 is the engine speed at which curve III crosses curve I and n.sub.2 is the engine speed at which it crosses curve II.

Curve IV shows, on the contrary, the output characteristics obtained by placing a part of the intake valves out of operation and all of the exhaust valves in operation. The engine speed n.sub.3 at which curve IV crosses curve I is higher than n.sub.1, while the speed n.sub.4 at which curve IV crosses curve II is lower than n.sub.2. Although curve IV enables an improved output at an engine speed in the range of n.sub.3 to n.sub.4, it is more effective to select curve III since it lies above curve IV in the speed range of n.sub.1 to n.sub.2.

Thus, in accordance with invention, it is possible to obtain smooth output characteristics over the entire range between low and high speeds (1) if curve I, obtained by placing a part of each of the intake and exhaust valves out of operation is selected at an engine speed lower than n.sub.1, (2) if curve III, obtained by placing all of the intake valves in operation and a part of the exhaust valves out of operation, is selected at a speed of n.sub.1 to n.sub.2, and (3) if curve II, obtained by placing all of the intake and exhaust valves in operation, is selected at a speed of n.sub.2 or higher.

The invention will now be described more specifically by way of example with reference to FIGS. 3 to 5.

FIG. 3 is a fragmentary side elevational view, partly in section, of a cylinder head for a four-cycle, four-cylinder engine in a two-wheeled motor vehicle, showing a valve operating mechanism on the intake side of the engine. The valve operating mechanism on the exhaust side is substantially similar in construction to the mechanism on the intake side and will therefore not be described.

The cylinder head 1 has a pair intake ports 3 which are opened and closed by a pair of intake valves 4. Each intake valve 4 is provided with a coiled compression spring 5 which urges the valve 4 in the direction in which it closes the intake port 3.

A cam shaft 6 is rotatably supported by the cylinder head 1 and a cam shaft holder and disposed in a valve operating chamber A surrounded by a cylinder head cover 2. A timing sprocket (not shown) is rotatably carried on one end of the cam shaft 6 and connected by a timing chain to a timing sprocket on a crankshaft.

A hollow rocker arm shaft 7 having an oil passage 8 therein is supported on rocker arm shaft holders 1A and 1B forming an integral part of the cylinder head 1. A pair of rocker arms 9 and 15 are rotatably supported on the rocker arm shaft 7 (see FIG. 3 and FIG. 4, the latter being a fragmentary sectional view taken along the line IV--IV in FIG. 3). The rocker arm 9 has a bearing portion 10 engaging the rocker arm shaft 7, a seat 11 on which a cam 6a on the cam shaft 6 rests slidably, a hydraulic cylinder 12 in which a piston 14 is reciprocatably disposed, and an oil passage 13 connecting the oil passage 8 and the hydraulic cylinder 12. The rocker arm 15 has a bearing portion 16 engaging the rocker arm shaft 7, and a hollow space 17 in which a guide pin 18 urged by a coiled compression spring 19 is slidably disposed.

If the hydraulic cylinder 12 has an elevated oil pressure, the piston 14 advances into the hollow space 17 of the rocker arm 15 and depresses the guide pin 18 upon overcoming the force of the coiled compression spring 19. On the other hand, if the pressure of oil in the hydraulic cylinder 12 remains low, the spring 19 urges the guide pin 18 to bear against the piston 14 and thereby force it to its retracted position within the hydraulic cylinder 12. The coiled compression spring 19 is supported by a retainer 5a.

A mechanism used for the hydraulic control of the valve operation will be described with reference to FIG. 5. In FIG. 5, the suffix E added to some reference numerals indicates components on the exhaust side. For example, 14E denotes a piston for an exhaust valve. The four cylinders are indicated by No. 1 to No. 4.

Lubricating oil is supplied from an oil pan to the cylinder head through an oil strainer 20, an oil pump P and an oil passage 21. Oil is also supplied toward the crankshaft through an oil cleaner 22, a main chamber 24 and oil passages 25. A pressure regulator is shown at 23.

An oil passage 26 is connected to one end of the main chamber 24, and to a hydraulic control valve 27 for the intake valves to which an oil passage 29 is connected. The oil passage 29 is divided into two oil passages 30 and 31. The oil passage 30 is connected to the hydraulic cylinders 12 in the rocker arms 9 for the intake valves in cylinders No. 1 to No. 4, while the oil passage 31 is connected to a hydraulic control valve 32 for the exhaust valves. An oil passage 34, connected to the hydraulic control valve 32, leads to the hydraulic cylinders 12E in the rocker arms 9E for the exhaust valves. Reference numerals 28 and 33 denote return ports for the control valves 27 and 32, respectively.

In the apparatus embodying the invention hereinabove described, the mechanism for the hydraulic control of valve operations operates to place a part of the intake and exhaust valves out of operation or all of them in operation in accordance with the operating condition of the engine as will hereinafter be described.

(1) Low Speed Operation (below n.sub.1):

The hydraulic control valve 27 for the intake valves is placed out of operation (low pressure output), and hence hydraulic oil returns to the oil pan through the return port 28. As no hydraulic oil is supplied to the hydraulic cylinders 12 and 12E, the pistons 14 and 14E stay in their retracted position. The rocker arms 9 and 15 or the rocker arms 9E and 15E are not connected to each other, and only the rocker arms 9 and 9E function to thus keep one of a pair of intake valves and one of a pair of exhaust valves out of operation. This is the position in which the output shown by curve I in FIG. 2 is obtained.

(2) Medium Speed Operation (n.sub.1 to n.sub.2):

The hydraulic control valve 27 for the intake valves is in operation (high pressure output), and hydraulic oil is supplied to the hydraulic cylinders 12 through the oil passages 29 and 30. The piston 14 advances into the hollow space 17 and thereby connects the rocker arms 9 and 15. Both of the rocker arms 9 and 15 then operate, and all of the intake valves are therefore placed in operation.

Although hydraulic oil is also supplied to the hydraulic control valve 32 for the exhaust valves through the oil passages 29 and 31, it returns to the oil pan through the return port 33 as the valve 32 is still closed. No hydraulic oil is therefore supplied to the hydraulic cylinders 12E, and as the rocker arms 9E and 15E are thus not connected, the rocker arm 15E is still in its inoperative position. Therefore, one of the two exhaust valves is out of operation. This is the position in which the output shown by curve III in FIG. 2 is obtained.

(3) High Speed Operation (above n.sub.2):

The hydraulic control valve 27 for the intake valves and the hydraulic control valve 32 for the exhaust valves are both open, and hydraulic oil is supplied to not only the hydraulic cylinder 12, but also the hydraulic cylinder 12E. Therefore, not only the rocker arms 9 and 15, but also the rocker arms 9E and 15E are connected, and hence all of the rocker arms 9, 15, 9E and 15E are in their operative positions so that all of the intake and exhaust valves are placed in operation. This is the position in which the output shown by curve II in FIG. 2 is obtained.

As is evident from the foregoing description, the valve control apparatus of the invention is applicable to an internal combustion engine having a plurality of intake and exhaust valves for each cylinder to place a part of each of the intake and exhaust valve out of operation when the engine is operating at a low speed, place all of the intake valves in operation and a part of the exhaust valves out of operation when the engine is operating at a medium speed, and place all of the intake and exhaust valves in operation when the engine is operating at a high speed, thereby enabling a uniform engine output over the entire range of operation.