Oil supply system for valves in an internal combustion engine
The present invention relates to an oil supply system for overhead valves in an internal combustion engine that includes an interlinking mechanism operatively connecting the cam of a camshaft and the head of a valve with a hydraulic tappet for continually maintaining contact with the valve head, wherein the oil supply system is effective in supplying operating oil to the hydraulic tappet and lubricating oil to the other components. 
     In a typical conventional oil supply system, as shown in FIGS. 2 and 3, for the overhead valve operating mechanism of an internal combustion engine, an oil supply passage 31 is provided in an engine cylinder head 1 and communicates with the outlet port of an oil pump 32 (shown diagrammatically). The oil supply passage 31 is connected to operating oil passages 30 communicating with each of the hydraulic tappets 12 and a lubricating oil passage 40 communicating with the bore 16a defined in a rocker arm shaft 16 on which a plurality of rocker arms 15 are supported. The rocker arm shaft 16 has oil holes 41 defined therein to provide communication between the bore 16a and the bearing bore 15a of each of the rocker arms 15. 
     Generally, in the prior conventional systems shown in FIGS. 2 and 3, the rocker armshaft 16 is pushed laterally to one side under forces imposed by the camshaft 7 and the hydraulic tappets 12 on the rocker arms 15. Therefore, there is a tendancy for a gap or clearance to be produced on the other side between the rocker arm shaft 16 and a portion of the bore 42 in the cylinder head 1 which supports the shaft 16. Therefore, the conventional oil supply system has a drawback in that when oil is delivered from the lubricating oil passage 40 into the bore 16a of the rocker arm shaft 16, a considerable amount of oil tends to leak from the gap formed between bore 42 and rocker shaft 16. As a consequence, the capacity of the oil pump 32 has to be greater than would otherwise be required for lubrication purposes just to make up for such oil leakage. 
     In view of the aforesaid problem, it is an object of the present invention to provide an oil supply device which suppresses leakage of the lubricating oil supplied to the bearing holes of rocker arms, thereby reducing the required capability of the oil pump used. To achieve this object, the present invention is characterized in that the oil supply passage communicating with the outlet port of the oil pump of the engine is connected to an oil reservoir chamber of the hydraulic tappet, and an interlinking mechanism has oil holes defined therein for communicating the oil reservoir chamber with the bearing hole of each rocker arm. 
     A further object of this invention is to provide an oil supply system wherein oil is supplied under pressure from the oil pump via the oil supply passage to the oil reservoir chamber of the hydraulic tappet as operating oil to the hydraulic tappet and also partly as lubricating oil to the bearing hole of the rocker arm through oil holes in the interlinking mechanism. The joints between members of the interlinking mechanism are held in contact under pressure by both the lifting action of the cam and the projecting movement of the hydraulic tappet. Therefore, any leakage of lubricating oil from the joints is extremely small. 
    
    
     Referring now to the drawings wherein a preferred embodiment is illustrated: 
     FIG. 1 is a fragmentary sectional end view of the cylinder head portion of an internal combustion engine with overhead valves and illustrating the preferred embodiment oil supply system of the present invention. 
     FIG. 2 is a fragmentary sectional end view similar to FIG. 1 but illustrating a conventional oil supply system. 
     FIG. 3 is a sectional plan view taken substantially on the line III--III in FIG. 2 illustrating the conventional oil suoply system. 
    
    
     The preferred embodiment of the present invention will hereinafter be described with reference to FIG. 1. An internal combustion engine includes a cylinder head 1 having combustion chambers 2 and intake and exhaust ports 3i, 3e which open into each of the combustion chambers 2. The intake and exhaust ports 3i, 3e can be opened and closed by respective intake and exhaust valves 4i, 4e. 
     The intake and exhaust valves 4i, 4e are axially slidably supported by valve guides 5i, 5e, respectively, in the cylinder head 1, and are normally urged to the closed position by valve springs 6i, 6e, respectively. 
     A single camshaft 7 operatively coupled to a crankshaft (not shown) is disposed substantially above the intake valves 4i. The camshaft 7 is rotatably supported by bearing caps 9 fastened by bolts 8 to the cylinder head 1. The camshaft 7 has intake cams 7i and exhaust cams 7e corresponding to the intake and exhaust valves 4i, 4e, respectively, with first cam followers 10i interposed between the intake cams 7i and the head or upper ends of the intake valves 4i. Each of the first cam followers 10i has an end pivotally supported by a first hydraulic tappet 12i mounted in a support hole 11i defined in the cylinder head 1. 
     Second cam followers 10e each have a side surface at their intermediate portions held in engagement with the exhaust cams 7e on the side of the camshaft 7 which is directed toward the exhaust valves 7e. Each of the second cam followers 10e has an opposite side surface having an upper end coupled through an interlinking mechanism 13 with the respective exhaust valve 4e and a lower end pivotally supported by a second hydraulic tappet 12e mounted in another support hole 11e defined in the cylinder head 1. 
     Each of the interlinking mechanisms 13 comprises a pusher rod 14 having one end engaging the upper end of the opposite side surface of one of the second cam followers 10e, and the other end engaging the bell-crank-shaped rocker arm 15 that in turn engages the head or upper end of one of the exhaust valves 4e. The rocker arms 15 are pivotally supported by a rocker arm shaft 16 in the cylinder head 1. 
     The first hydraulic tappets 12i are structurally identical to the second hydraulic tappets 12e and therefore only the construction of the second hydraulic tappets 12e will be described below. 
     Each of the hydraulic tappets 12e is principally comprised of a cylinder 17 and a plunger 19 held in slidable engagement with the inner peripheral surface of the cylinder 17 and defining a hydraulic pressure chamber 18. The cylinder 17 is fitted in one of the support holes 11e of the cylinder head 1. The plunger 19 has an outer spherical operating end 19a slidably engaging in a spherical recess 20 defined in the lower end of one of the cam followers 10e. 
     The plunger 19 has an internal oil reservoir chamber 21 and a valve hole 22 by which the oil reservoir chamber 21 communicates with the hydraulic pressure chamber 18. The oil reservoir chamber 21 communicates with an operating oil passage 30 defined in the cylinder head 1 through an oil hole 23 defined in the side wall of the plunger 19 and an oil hole 24 in the side wall of the cylinder 17. There is an operating oil passage 30 branched from the common oil supply passage 31 to each of the hydraulic tappets 12e which are arranged in a row normal to the sheet of FIG. 1. The oil supply passage 31 and the operating oil passages 30 are defined in the cylinder head 1 and the oil supply passage 31 is connected to the outlet port of an oil pump 32 (shown diagrammatically as a circle) of the engine. During operation of the engine, therefore, the oil reservoir chamber 21 of each of the hydraulic tappets 12e is filled with pressurized oil discharged from the oil pump 32. 
     In the inner end of the plunger 19, there is fitted a hat-shaped valve cage 26 accommodating therein a ball-shaped check valve 27 for opening and closing the valve hole 22 and a spring 28 for normally urging the check valve 27 to close the valve hole 22. The check valve 27 is opened when the oil pressure in the hydraulic pressure chamber 18 is lowered, and closed when the oil pressure therein is increased. The hydraulic pressure chamber 18 houses therein a pusher spring 29 for normally biasing the plunger 19 in a direction to project from the cylinder 17. 
     The plunger 19, the second cam follower 10e, the pusher rod 14, and the rocker arm 15 have oil holes 33, 34, 35, 36, respectively, which are interconnected at the joints where the plunger 19, the second cam follower 10e, the pusher rod 14, and the rocker arm 15 are operatively coupled. Thus, the oil reservoir chamber 21 in the second hydraulic tappet 12e is continually in communication with the bearing hole 15a of the rocker arm 15 via these oil holes 33 through 35. 
     The operation of the oil supply system of this invention will now be described. While the engine is in operation, the camshaft 7 is rotated by the crankshaft through a timing transmission device (not shown). When the engine initiates an intake stroke, the raised portion of the intake cam 7i pushes the first cam follower 10i which is pivoted about the first hydraulic tappet 12i toward the intake valve 4i. The intake valve 4i is now opened against the resilient force of the valve spring 6i to introduce an air-fuel mixture through the intake port 3i into the combustion chamber 2. 
     As the engine starts an exhaust stroke, the raised portion of the exhaust cam 7e pushes the second cam follower 10e. The second cam follower 10e is pivoted about the second hydraulic tappet 12e to push the pusher rod 14, thereby swinging the rocker arm 15 toward the exhaust valve 4e. The exhaust valve 4e is now opened against the resilient force of the valve spring 6e to discharge the exhaust gas from the combustion chamber 2 into an exhaust port 3e. 
     The first and second hydraulic tappets 12i, 12e operate in the same manner. Operation of the second hydraulic tappet 12e is as follows: When the cam 7e lifts the cam follower 10e, the cam follower 10e imposes a pushing force on the plunger 19. Since the check valve 27 remains closed at this time, a hydraulic pressure builds up in the hydraulic pressure chamber 18 to enable the plunger 19 to rigidly support the end of the cam follower 10e. As a result, the cam follower 10e is pivoted about the operating end 19a to push the pusher rod 14. During this time, oil in the hydraulic pressure chamber 18 leaks in a small quantity from a sliding clearance gap between the cylinder 17 and the plunger 19. 
     When the cam follower 10e is released from the lifting action of the cam 7e, the plunger 19 is forced by the pusher spring 29 to project outwardly until the slipper surface of the cam follower 10e engages the cam 7e. As the hydraulic pressure in the hydraulic pressure chamber 18 is lowered during the projecting movement of the plunger 19 under the resiliency of the pusher spring 29, the check valve 27 is opened to permit oil to be supplied from the oil reservoir 21 through the valve hole 23 into the hydraulic pressure chamber 18 for thereby making up for the oil leakage that has occurred from the hydraulic pressure chamber 18 during actuation of valve 4e as described above. Thus, any potential gaps associated with the valve operating mechanism, i.e., gaps at the joints between the members from the cam 7e to the valve 4e are eliminated. 
     Oil supplied under pressure from the oil pump 32 via the oil supply passage 31 and the operating oil passage 30 into the oil reservoir chamber 21 of the second hydraulic tappet 12e during engine operation is also supplied as operating oil into the hydraulic pressure chamber 18 from time to time. Part of the supplied oil is delivered from the oil reservoir chamber 21 successively to the oil holes 33, 34, 35, 36 for lubricating the junctions between the plunger 19, the second cam follower 10e, the pusher rod 14, and the rocker arm 15, and then delivered from the oil hole 36 to the bearing hole 15a of the rocker arm 15 to lubricate the surfaces of the rocker arm 15 and the rocker arm shaft 16 which pivot relative to each other. During this time, the joints between the plunger 19, the second cam follower 10e, the pusher rod 14, and the rocker arm 15 are held under pressure by the lifting action of the cam 7e and the resiliency of the pusher spring 29, so that any leakage of lubricating oil from those joints is extremely small. 
     According to the present invention, as described above, part of the oil supplied from the oil supply passage into the oil reservoir chamber of the hydraulic tappet is delivered as lubricating oil to the bearing hole of the rocker arm through the oil holes defined in the interlinking mechanism. Oil leakage from the joints of the interlinking mechanism which are held under pressure at all times is extremely small but adequate for the joints of the interlinking mechanism as well as the bearing hole of the rocker arm to be effectively lubricated. Consequently, the capability of the oil pump used can be minimized. Moreover, since the oil leakage is small, a desired hydraulic pressure can be maintained in the oil reservoir chamber for stabilized operation of the hydraulic tappet.