The present invention relates to a valve actuating apparatus for an internal combustion engine. More particularly, the invention relates to a valve actuating apparatus which is capable of selectively disabling valves of the engine. This invention finds particular application in motorcycle engines.
To obtain an improved operating efficiency over a wide range of engine speeds, engines have been developed having multiple intake and exhaust valves for each cylinder. For instance, in an engine having two intake and two exhaust valves for each cylinder, for low and medium engine speeds, one of the intake and one of the exhaust valves may be disabled, while all four valves are enabled for higher engine speeds. Of course, a valve actuating apparatus must be provided to selectively actuate the valves.
FIG. 1 shows a cross section of a part of a conventional valve actuating apparatus utilizing an oil pressure actuator 5 for selectively disabling the intake and exhaust valves. In this valve actuating apparatus, a pair of rocker arms 3 and 4 are adjacently mounted on a rocker arm shaft 2, the latter being fixedly mounted to a cylinder head 1. One of the rocker arms 3 is directly driven by a cam shaft, and the other rocker arm 4 is selectively engageable with the rocker arm 3 to thereby selectively enable the valve associated with the rocker arm 4. The actuator 5 is a reciprocation type, constructed such that a shaft pin 5a slidably mounted in the rocker arm 3 is pushed by pressurized oil to protrude into the rocker arm 4. A pressure oil chamber 5b receiving the shift pin 5a is communicated through an oil path 5c with an oil path 5d provided in the rocker arm shaft 2. An engaging hole 5e sized receiving the shift pin 5a therein is provided at a position of the rocker arm 4 opposing the pressure oil chamber 5b. There is provided in the engaging hole 5e a return pin 5f for urging the shift pin 5a back into the pressure oil chamber 5b and an elastic member 5g for urging the return pin 5f toward the rocker arm 3.
In operation, when the engine is driven at a high speed, operating oil at a predetermined pressure is supplied into the oil path 5d from an oil supply apparatus (not shown) to thereby energize the actuator and couple the rocker arms 3 and 4.
In most conventional actuator systems, oil paths are provided in members adjacent to the actuator (the rocker arm 3 and the rocker arm shaft 2, etc. in the abovedescribed actuator) to provide paths for supplying operating oil as lubricating oil for other engine components. Specifically, interlinked portions of the members forming the oil paths and the sliding portion of the actuator are constructed so as to allow the operating oil to be leaked slightly therefrom.
If the engine has been operated at a low speed for a long period, and hence the actuator is not supplied with operating oil for a long period, air tends to leak into the oil paths from the sliding and the interlinked portions. If the air leaked into the oil paths remains until the actuator is activated, the responsiveness of the actuator may be low. Namely, in the above-described valve actuating apparatus, for example, the moving speed of the shift pin 5a is made lower so that the edge portion of the shift pin 5a is likely to collide with the edge portion of the inlet of the engaging hole 5e thus making it difficult to smoothly activate the actuator to couple the rocker arm 4 to the rocker arm 3.
To overcome this drawback, it has been proposed to provide an oil pump for exclusive use by the actuator adjacent to the actuator so as to shorten the time required for the operating oil to reach the actuator from the oil pump. However, in this case, the size of the engine is unavoidably increased due to the provision of the oil pump near the actuator, and further a transmission mechanism for exclusive use for driving the oil pump is required, thereby making the oil supply apparatus expensive.
A typical example of the conventional valve actuating apparatus installed on an engine is shown in FIG. 3. There is provided, in a cylinder head a at the top of the engine disposed almost at the center of a body having a front and a rear wheel, a valve actuator d operated by pressurized oil and having an oil pressure chamber c. Operating oil is supplied to the oil pressure chamber c from a control valve b, whereby the intake and exhaust valves e of the engine are selectively activated. The conventional control valve includes a spool valve j for selectively opening a control path f, an oil supply path g and an oil return path h provided in a valve housing i having a control path communicating with the oil pressure chamber c. The oil supply path g communicates with an oil pressure source and the oil exhaust path h communicates with an oil ejecting opening.
In this type of control valve, the height of an opening end of the oil exhaust path h, that is, the height of the oil ejecting opening, is of particular importance. If the oil ejecting opening is disposed relatively lower, the oil in the path h is likely to undesirably flow out through the oil ejecting opening, while if it is disposed relatively higher, the resistance of the oil path from the control path to the oil ejecting opening becomes higher so that the responsiveness of the control apparatus is lowered. Further, the control valve must be positioned by taking into consideration the tilt angle thereof when the motorcycle is held up by its kickstand.
The control valve b is generally disposed along a horizontal line parallel to the crankshaft of the engine in the valve casing i as shown in FIG. 3. Thus, the control valve b is subjected to the vibration of the engine, which may cause the state of the control valve b to change states unintentionally. Namely, for example, a four-cycle, four-cylinder in-line engine generally vibrates not only in a vertical direction, but also in a horizontal direction (the direction parallel to the crankshaft) with an amplitude almost half that in the vertical direction. In order to prevent such erroneous changeover operations of the intake and exhaust valves, it has been unfavorably required to increase the elasticity of a spring or the magnetic force of an operating solenoid associated with the control valve.