VALVE ACTUATING DEVICE FOR MULTI VALVE-TYPE ENGINE

Abstract: In an engine having three or more inlet valves, said inlet valves (3) are disposed along the periphery of the cylinder. Said inlet valves having a long distance between the valve seat and the axis of the camshaft are arranged so that their cams (9a) have a large base circle diameter, valves having a long valve stem need not to be used and the length of valves are equalized.

Description: A valve actuating device for a multi-intake valve type engine comprising an inlet camshaft for operating at least three intake valves each of said intake valves cooperating with an associated valve seat and being actuated by an associated cam, the distance between the camshaft axis and the valve seat for at least one valve being larger than the distance for another valve, depending on the position of the intake valves along the periphery of the cylinder head. An engine having three or more inlet valves disposed on an inside periphery of a cylinder is known from JP 59-165, 810 and the applicant's US-A-4 624 222 which underlies the preamble portion of Claim 1. In an engine of the above-mentioned type, however, the top surface of a combustion chamber is formed as flat as possible in order to increase a compression ratio. For this reason, the inlet valve positioned at the center differs from the other two valves disposed in both sides thereof not only in a crossed angle to the axis of an exhaust valve but also in a length between the valve seat and the axis of the camshaft. As a result, it is unavoidable to prepare inlet valves whose valve stems have different lengths from each other. This causes a useless increase in inertial mass of the inlet valves and, in addition, it brings about a problem that the production cost is increased due to the increase of the kinds or parts. The present invention has as its object the solving of the above problems, the prevention or useless increase of inertial mass of an inlet valve and the achievement of making the inlet valves more equal to each other. A valve actuating device for a multi-intake valve type engine comprising an inlet camshaft for operating at least three intake valves each of said intake valves cooperating with an associated valve seat and being actuated by an associated cam, the distance between the camshaft axis and the valve seat for at least one valve being larger than the distance for another valve, depending on the position of the intake valves along the periphery of the cylinder head. The diameter of the base circle of the cam of the inlet camshaft which corresponds to said at least one intake valve for which said distance is greater than that of another cam corresponding to another valve for which said distance is shorter and that all intake valves have the same length. Preferred embodiments of the present invention are laid down in the sub-claims. Since, of the inlet valves disposed along the periphery of the cylinder, those having a long distance between the valve seat and the axis of the camshaft are arranged so that their cams have a large base circle diameter, valves having a long valve stem need not to be used and the lengths of valves can be equalized. The drawings illustrate an embodiment of the present invention, in which Figure 1 is a cross-sectional view of a four-stroke engine; Figure 2 is a cross-section taken along the line II-III; and Figure 3 is a cross-section taken along the line III-III. The present invention will be explained below with reference to an embodiment illustrated in the drawings. In the drawings, the reference numeral 1 denotes a four-stroke engine, or so-called multivalve-type engine, in which the total number of inlet valves and exhaust valves disposed on the top of a combustion chamber 2 is three or more. In the illustrated case, there are provided three inlet valves 3 and two exhaust valves 4. The combustion chamber 2 is defined by a cylinder 5, a cylinder head 6 and a piston 7. An electrode of a sparking plug 8 is disposed on the center of the top surface. Designated as 9 is an inlet camshaft for opening and closing the inlet valves 3 through lifters 10 and as 11 is an exhaust camshaft for opening and closing the exhaust valves 4 through lifters 12. The two exhaust valves 4 are disposed in parallel with each other. The three inlet valves 3 are disposed along the inside periphry of the cylinder 5. The two inlet valves located on both sides correspond to outer cams 9a and 9a through lifters 10 and are oriented with the same tilt angle, whereas the other valve located at the center corresponds to a center cam 9b and is oriented at an angle similar to the axis of the cylinder. The inlet camshaft 9 is driven by a crank shaft (not shown) through a timing chain 16 and a sprocket 15 provided on the shaft of the inlet camshaft 9. Designated as 9c is a journal portion for the inlet camshaft 9 and as 17 a bearing cap. Thus, the distance between the axis of the inlet camshaft 9 and the valve seat of each valve, namely the necessary length of the valve is longer in the valves located on both sides than that located at the center. However, since the diameter of the base circle of the cam corresponding to each of the two valves located on both sides is made larger than that corresponding to the other valve, the lengths required for these valves can be made equal to each other. As described in the foregoing, in the present invention, the diameter of the base circle of the cam of a valve, in which the length between the axis of the camshaft and the valve seat is large, is set to be large so that the required lengths of the valves can be made equal to each other, the valves and the lifters can be common to each other in spite of the irregularity in the length between the axis of the camshaft and the valve seats of the three poppet valves disposed on the inside periphery of the cylinder. Thus, there is obtained an effect that an increase in kinds of the parts can be avoided.

Claims: A valve actuating device for a multi-intake valve type engine comprising an inlet camshaft (9) for operating at least three intake valves (3) each of said intake valves (3) cooperating with an associated valve seat and being actuated by an associated cam (9A, 9B), the distance between the camshaft axis and the valve seat for at least one valve being larger than the distance for another valve, depending on the position of the intake valves (3) along the periphery of the cylinder head, characterized in that , the diameter of the base circle of the cam (9A) of the inlet camshaft (9) which corresponds to said at least one intake valve (3) for which said distance is larger, is greater than that of another cam (9B) corresponding to another valve (3) for which said distance is shorter and that all intake valves (3) have the same length. A valve actuating device as claimed in Claim 1, wherein three intake valves (3) are provided and each cam (9A, 9B) of the inlet camshaft (9) engage a lifter of the associated intake valve (3), wherein the diameter of the base circle of the outer cams (9A) actuating the side intake valves (3) is greater than the diameter of the base circle of the centre cam (9B) actuating the associated centre intake valve (3). A valve actuating device as claimed in Claims 1 or 2, wherein the cams (9A, 9B) of the inlet camshaft (9) are designed to have the same lift.

Inventors: YAMADA, TETSURO
Applicants: YAMAHA HATSUDOKI KABUSHIKI KAISHA
Application year: 1988
Main classification: F01L1
IPC codes: F02F1, F01L1