Camshaft for multi-valve internal combustion engine

Details Camshaft for multi-valve internal combustion engine Camshaft for multi-valve internal combustion engine

1992-03-30

1993-06-01

Cross, E. Rollins

Internal-combustion engines

Poppet valve operating mechanism

Rod

123 9022, 74567, F01L 104, F01L 126

Patent

active

052150488

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The invention relates to a camshaft for a multi-valve internal combustion engine of the type having at least two adjacent inlet and/or two exhaust valves per cylinder.


BACKGROUND OF THE INVENTION

It is has already been proposed to design the valve drive train in an internal combustion having multiple valves to allow the primary and secondary valves to have different events. An example of a camshaft which allows two inlet valves to have different events is shown EP-A-0 319 956. It has furthermore been suggested to vary the phase of the secondary valve in relation to the primary valve in dependence upon engine operating conditions.
In the prior art, the event timing of each valve has been selected or controlled with a view to determining the charging of the engine, the aim often being to improve the volumetric efficiency by maximising the mass of the intake charge. As a result, in the prior art, where a primary valve and a secondary valve have different events, the difference has been a major one affecting either the durations or the relative phasing of the events.
The present invention is not, by contrast, concerned with controlling the charging of the engine cylinders and relates to engines in which the primary and secondary valves have substantially the same event timing and duration, the purpose of providing two valves being only to increase the combined valve skirt area and the through flow cross section of the valves when they are open.
The invention is instead concerned with the noise emitted from an engine. In any engine, the valve mechanism is a source of noise and this problem is accentuated in a multi-valve engine since there are more valves to operate.


OBJECT OF THE INVENTION

The invention seeks to reduce valve train noise in an engine having multiple inlet and/or exhaust valves in which the secondary valves and primary valves are operated with substantially the same event phase and duration


SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a camshaft for operating the primary and secondary inlet or exhaust valves of an internal combustion engine having multiple valves in each cylinder, the camshaft having cams of substantially the same cam profile and phase for operating the primary and secondary valves of each cylinder, characterised in that at least the trailing ramps of the cams are offset by between 1.degree. and 3.degree. relative to one another.
In one embodiment of the invention, both the leading and the trailing ramps are offset in the same direction so that the cams are identical in profile but phase shifted relative to one another by between 1.degree. and 3.degree..
In an alternative embodiment of the invention, the leading ramps may be in phase with one another and only the trailing ramps offset, so that one cam has an event duration slightly longer than the other.
It will be noticed that the offset of 1.degree. to 3.degree. is too small to have any serious effect on the charging of the cylinder but, as will be explained below, it results in a marked reduction in the noise emitted by the valve train.
It should be pointed out briefly that valve train noise has several causes. In particular, one may distinguish between two excitations mechanisms, which are herein termed impulse excitation and force excitation. Impulse excitation consists of impulses which occur on valve opening, valve closing and following loss of contact between valve train components. Force excitation is caused by varying inertial forces, valve train oscillations, or the jerk occurring on a transition between hydrodynamic lubrication and metallic contact.
Generally, impulse excitation is the predominant source of noise at low and medium engine speeds and force excitation is predominant at high speed. If valve bounce occurs, impulse excitation can again in some cases again become predominant at very high engine speeds.
In the present invention, impulse excitation during valve closing is reduced by the staggering the impulses from the two valves. In prac

REFERENCES:
patent: 4852527 (1989-08-01), Beardmore et al.
patent: 4878462 (1989-11-01), Kurisu et al.

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