Valve operating system for an automotive engine
BACKGROUND OF THE INVENTION 
     The present invention relates to a valve mechanism for an automotive engine. 
     In order to improve combustion in an entire range of engine speed, a multiple-valve type engine, each cylinder of which has two or more intake valves is known. In a low engine speed range, one of the intake valves of each cylinder is held in closed state. Various valve stopping means are proposed. Japanese patent Laid Open No. 57-86512 discloses a valve stopping device mounted in a rocker arm, and Japanese patent Laid Open No. 57-188715 discloses a rocker arm device comprising high speed rocker arm and low speed rocker arm. However, these devices are complicated in construction and large in size. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a valve stopping device which is simplified in construction and small in size. 
     According to the present invention, there is provided a valve operating system for an automotive engine having two or more intake valves for one cylinder, a camshaft having cams for operating the intake valves. The system comprises one of the cams being rotatably and axially slidably mounted on the camshaft, clutch means for engaging the slidable cam with the camshaft at a predetermined angular position, shifting means for axially shifting the slidable cam to engage the cam with the camshaft by the clutch means. 
     In an aspect of the present invention, the clutch means includes an eccentric conical hole formed in the cam and an eccentric conical portion formed on the camshaft, and the shifting means comprises a hydraulic cylinder formed between the cam and the camshaft to form an oil chamber, and a spring for urging the cam to the oil chamber. 
     The other objects and features of this invention will be apparently understood from the following description with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a sectional view of a cylinder head in which a device according to the present invention is mounted; 
     FIG. 2 is a sectional view taken along a line II--II of FIG. 1; 
     FIG. 3 is an enlarged view of a part of FIG. 1; and 
     FIG. 4 is an enlarged view showing a cam and a camshaft. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 and 2, there is shown a cylinder head H for two cylinders, each having two intake valves 10 and 10a and one exhaust valve 15. A camshaft 1 comprises a pair of shafts which are relatively positioned by a pin 13 and connected by a journal member 4. 
     On the camshaft 1, cams 2 for the exhaust valves 15 and cams 3&#39; for the intake valves 10a are integrally formed. Cams 3 for the intake valves 10 are rotatably and axially slidably mounted on the camshaft 1. Since both the cams 3 for adjacent cylinders are symmetrical and are the same in construction, only one cam and a device about the cam will be described hereinafter. 
     Referring to FIG. 3, the cam 3 has a cylindrical portion 3a at one side adjacent the journal member 4. The cylindrical portion 3a is rotatably and slidably engaged mounted on a cylindrical projection 4a of the journal member 4 to form an oil chamber 5. The cam 3 further has an eccentric conical hole 3b at the other side thereof. The center C of eccentric conical hole 3b is deviated Δt from the center of the axis 0 of the cam 3 as shown in FIG. 4. The camshaft 1 has an eccentric conical portion 1a corresponding to the conical hole 3b. 
     A coil spring 7 is disposed between the side of the cam 3 and a retainer 6 mounted on the camshaft 1 to urge the cam toward the chamber 5. The chamber 5 is communicated with an oil pump (not shown) through a solenoid operated control valve 12 (FIG. 2). As shown in FIG. 2, the cam 3 engages with a rocker arm 9 engaging with a stem of intake valve 10 and with a hydraulic lash adjuster 8. 
     In a low engine speed range, oil in the chamber 5 is drained through the control valve 12, so that the cam 3 is shifted to the journal member 4. As a result, the cam 3 is disengaged from the conical portion 1a of the camshaft 1. Thus, the cam 3 is not rotated by the camshaft 1, so that the intake valve 10a is not opened. Accordingly, only intake valve 10 is operated by the cam 3&#39;. 
     In a high engine speed range, oil is supplied to the chamber 5 by operating the control valve 12, so that the cam 3 is pushed to the conical portion 1a. However, the cam 3 can not be shifted to the conical portion 1a unless the phase of the cam 3 coincides with that of the camshaft 1. When both the phases coincide with each other (namely the center of conical hole 3b coincides with that of the conical portion 1a), the cam 3 is shifted to engage with the conical portion 1a. Thus, the cam 3 is rotated by the camshaft 1 to operate the the intake valve 10. 
     Although the above described system is provided with eccentric engaging clutch means comprising the conical hole 3b and conical portion 1a, another clutch means such as a dog clutch engaging at a pre-determined angular position can be employed. 
     While the presently referred embodiment of the present invention has been shown and described, it is to be understood that this disclosure is for the purpose of illustration and that various changes and modifications may be made without departing from the spirit and scope of the invention as set forth in the appended claim.