Valve actuation device for multi-valve-type engine

Abstract: In an engine having three or more inlet valves (5), an inlet camshaft (10) is disposed on a valve seat (5c) side from the phantom axis (12) on which the axes of the inlet valves (5) cross. Engagement is achieved with a slight offset (x) between the inlet camshaft (10) and each lifter (9) driven by the inlet camshaft (10). The inlet valves (5) are driven by rotation of the inlet camshaft (10) through the lifters (9). Such a reduction of height and width of a cylinder is provided.

Description: The present invention relates to a valve actuating device for a multi-valve type engine, comprising three inlet valves disposed on the inside surface of the cylinder bore and a common inlet camshaft for actuating the inlet valves through valve lifters, wherein the axis of the three inlet valves cross on a phantom axis which is in parallel with the axis of the inlet camshaft and wherein the axis of the inlet camshaft is located on the valve seat side from the phantom axis. More specifically the present invention relates to a cylinder head structure of a four stroke engine having a so called dual-cam-type actuation device comprising inlet and exhaust camshafts for actuating the inlet and exhaust valves separately from each other. In recent years internal combustion engines were designed to have the inlet and exhaust valves actuated separately by intake and exhaust camshafts in order to improve the output of a car engine under high speed conditions (see for example JP-A-59-165810). Such DOHC-engines tend to increase the height and the width of the cylinder head of the engine. Therefore, difficulties have arisen to satisfy recent demands for reducing the volume of the engine compartment wherein such an engine is to be disposed. In order to comply with strict demands of compacted engine design disposing the valve actuating elements of three intake valves such that said valve actuating elements can be supported through the cylinder head without effecting the stiffness or rigidity of same DE-A-3524622 comprises a valve actuating device as indicated in the preamble of claim 1 wherein the longitudinal axis of the valve lifter actuating the central intake valve extends laterally offset with respect to the axis of the inlet camshaft. In this way it is possible to acquire an increased wall thickness between adjacent valve lifters of the closely neighboured three inlet valves of said intake arrangement. Moreover, preferably the valve lifters of the side inlet valves are disposed such that their longitudinal axis extends laterally offset to the opposite side with respect to the longitudinal axis of the inlet camshaft. Accordingly it is an objective of the present invention to provide an improved valve actuating structure of the type as indicated above enabling to reduce the overall height of the engine and the width of the cylinder head as much as possible. According to the present invention the afore-indicated objective is performed in that each lifter is disposed eccentrically with respect to the axis of its associated inlet valve such that the axis of the lifters are laterally offset from the axis of the inlet valves and intersect the axis of the inlet camshaft. In this way the axis of the three inlet valves cross on a phantom axis which is in parallel with the axis of the inlet camshaft wherein the axis of the inlet camshaft is located on the valve seat side from such a phantom axis. Accordingly, the height of the engine is lowered. The present invention is explained in greater detail hereinafter by means of a preferred embodiment thereof hereinafter in conjunction with the accompanying drawings, wherein: Figure 1 shows a general layout of a cylinder head of a four stroke engine in cross-sectional view, and Figure 2 is a view showing the relationship between the three inlet valves, the associated valve lifters and the inlet camshaft. In the figures, designated as 1 is a four stroke engine having a combustion chamber 2 defined by a cylinder head 3, a cylinder 4 and a piston 5. Three inlet valves 5 and two exhaust valves 6 are disposed along the inside surface of a cylinder bore 4a of the cylinder head 3, thereby to form a so called semispherical combustion chamber. The reference numeral 7 denotes an inlet passage leading to the combustion chamber 2 through the inlet valves 5 and 8 denotes an exhaust passage leading to the combustion chamber 2 through each exhaust valve 6. These inlet valves 5 and exhaust valves 6 are actuated by a common inlet camshaft 10 and a common exhaust camshaft 11, respectively, through valve lifters 9 each slidably fitted into a guide-hole 3a of the clyinder head 3. Among the above mentioned three inlet valves 5, the both side inlet valves 5a are disposed in parallel with each other and the central inlet valve 5b is disposed obliquely relative to the both side inlet valves 5a with an angle similar to that defined to the axis of the cylinder bore 4a. The axis of these inlet valves 5a, 5b cross at a point on a phantom axis 12 which is in parallel with the axis 10a of the inlet camshaft 10. The axis 10a of the inlet camshaft 10 is located at a position nearer to a valve seat 5c of the inlet valves than the phantom axis 12 is. Thus there is a slight offset X between the axis 10a of the inlet camshaft 10 or, similarly, between the axes of the valve lifters 9 which coincide with the camshaft axis 10a, and the axes of the inlet valves 5a, 5b. The operation of this embodiment will be explained next. When the inlet camshaft 10 is rotated by rotation of a crankshaft, the valve lifters 9 are displaced to push and open the inlet valves 5a, 5b against the reaction force of the valve spring 13 or are moved, while maintaining in contact with the inlet camshaft 10, by the resilient force of the valve spring 13. These operations are quite the same as those in conventional devices. According to the embodiment of the present invention, the inlet camshaft 10 is disposed on the valve seat side from the phantom axis 12 on which the axis of the inlet valves 5a, 5b cross each other. Thus, the engagement is achieved with a slight offset between the inlet camshaft 10 (or the valve lifters 9) and the axis of the inlet valves 5a, 5b. Since the valve lifters 9 have a relatively large diameter and since the area of contact between the valve lifters 9 and the sliding surfaces in the cylinder head 3 is also large it is possible to prevent a large biasing force from acting on the inlet valves 5a, 5b by suitably adjusting the gap inbetween the sliding surfaces. The present invention provides a highly effective valve actuating device for actuating three inlet valves 5a, 5b provided along the cylinder bore 4a of the cylinder head 3 wherein the axes of the three inlet valves 5a, 5b cross on the phantom axis 12 which is in parallel with the axis 10a of the inlet camshaft 10 which, in turn, is located on the side of the valve seat 5c from the phantom axis 12 so that the height of the engine can be lowered and the engine can be accomodated in a relatively small engine compartment.

Claims: A valve actuating device for a multi-valve-type engine, comprising three inlet valves (5) disposed on an inside surface of a cylinder bore, and a common inlet camshaft (10) for actuating the inlet valves (5) through valve lifters (9), wherein the axes of the three inlet valves (5) cross on a phantom axis (12) which is in parallel with the axis (10a) of the inlet camshaft (10) and wherein the axis (10a) of the inlet camshaft (10) is located on the valve seat side from the phantom axis (12), characterised in that, each lifter (9) is disposed eccentrically with respect to the axis of its associated inlet valve (5) such that the axes of the lifters (9) are laterally offset from the axes of the inlet valves (5) and intersect the axis (10a) of the inlet camshaft (10).

Inventors: YAMADA TETSURO, YAMADA, TETSURO
Applicants: YAMAHA MOTOR CO LTD, YAMAHA HATSUDOKI KABUSHIKI KAISHA
Application year: 1988
Main classification: F01L1
IPC codes: F01L1