Variable valve timing

Details Variable valve timing Variable valve timing

1992-07-17

1994-07-19

Wolfe, Willis R.

Internal-combustion engines

Poppet valve operating mechanism

With means for varying timing

123 9015, 123 9031, 464 1, 464 2, F01L 134

Patent

active

053298942

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to variable valve timing for an internal combustion engine.
2. Discussion of Prior Art
In an internal combustion engine of the four-stroke (Otto cycle) type the phase of the engine cycle during which the inlet and exhaust valves are open is usually referred to as valve timing and is quoted as the opening and closing angles for both the inlet and exhaust valves before or after the point at which the piston reaches "top dead center" (TDC) or "bottom dead center" (BDC). In a conventional engine these angles are fixed and do not vary over the entire engine speed and load range.
The fixed valve timing is a compromise setting over most of the engine operating range because the dynamic behavior of the gas flows in the cylinder and through the valves varies considerably over the entire range. For this reason the fixed valve timing can only be correct for some required engine performance characteristic (eg. minimum exhaust emissions, maximum power, lowest fuel consumption) at one particular engine speed and load situation and over the rest of the range poorer performance must be accepted.
This behavior of the fixed-valve-timing internal combustion engine has been known almost since its invention but the simplicity of fixed valve timing has led to its retention, with individual engine designs being 8 compromise aimed at some particular performance characteristic in which some desirable characteristics are sacrificed for others; for example an engine design might aim for high output power at high speed at the expense of low speed tractability.
There is a great deal of published information and patents on means of varying the valve timing of an engine. The methods that are described in these vary widely but one group of mechanisms change the valve timing by changing the phase of the camshaft relative to the crankshaft. All of these mechanisms have a source of power separate from the camshaft to effect this variation in phase.


SUMMARY OF THE INVENTION

According to the present invention there is provided an internal combustion engine valve timing system in which the camshaft is driven by means of a mechanism which can permit a limited change in the phase relationship between the engine crankshaft and the camshaft and in which the phase change takes the form of an angular displacement which is compliantly constrained about some nominal angle in such a way that the torque reaction from the camshaft operating the valves results in a change in the instantaneous phase displacement in some desired manner.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial representation of one example of the invention in which the camshaft drive is passed through an epicyclic differential mechanism the reaction-member of which is attached to a device which permits limited movement of the reaction-member and, in addition, a reaction-member locking mechanism is shown.
FIG. 2 shows a particular example of the means of providing compliance and damping in the reaction-member support.


DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In FIG. 1 a camshaft 5 is driven by the engine crankshaft by means of toothed belt 8 and pulley 7 through the input shaft 4. Interposed in this drive is an epicyclic differential-gear 2, the planet gears of which are supported on shafts protruding from the reaction-member 3. The sun gear of the differential 2 is driven by the input shaft 4 which passes through a bearing in the reaction-member 3. Rotation of the sun gear with the input shaft 4 causes the annulus of the differential 2 to rotate in the opposite sense to the input shaft 4 at a speed ratio depending on the number of teeth on the sun gear and the annulus. The torque required to drive the camshaft would cause the reaction-member 3 to rotate in the same sense as the sun gear and this rotation is prevented by the spring-loaded member 1. This spring-loaded member 1 is equipped with damping means which may be varied electromagnetically with solenoid valves 9 and has an oil sup

REFERENCES:
patent: 4305352 (1981-12-01), Oshima et al.
patent: 4577598 (1986-03-01), Ma
patent: 4747375 (1988-05-01), Williams
patent: 5002023 (1991-03-01), Butterfield et al.
patent: 5046460 (1991-09-01), Butterfield et al.
patent: 5056477 (1991-10-01), Linder et al.
patent: 5056478 (1991-10-01), Ma
The Institution of Mechanical Engineers, vol. 186, 23/72, Proceedings 1972 "Variable Valve-Timing Unit Suitable for Internal Combustion Engines" (con't) G. E. Roe, Ma, PhD.

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