Variable valve timing

Details Variable valve timing Variable valve timing

1993-12-15

1994-11-08

Cross, E. Rollins

Internal-combustion engines

Poppet valve operating mechanism

With means for varying timing

123 9031, 74568R, 464 1, F01L 134, F16D 310

Patent

active

053617363

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 centre" (TDC) or "bottom dead centre" (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 behaviour 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 (e.g. 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 behaviour 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 a 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. Some of these are concerned with altering the phase of the camshaft with respect to the crankshaft but these suffer the disadvantage that advancing or retarding the opening of a valve has the same effect on the closing of that valve. For example advancing the opening of an inlet valve to increase the overlap with the exhaust valve for better cylinder scavenging at higher engine speeds results in that inlet valve closing earlier so limiting the fuel charge available.


SUMMARY OF THE INVENTION

According to the present invention there is provided a system for controlling the opening and closing of the inlet and/or exhaust valves of an internal combustion engine having one or more cylinders said system including means of controlling in a variable manner the rotational phase of the valve operating means with respect to the phase of the engine output shaft such that the instantaneous phase of the valve operating means changes in a predetermined cycle of advance and retard about some nominal value during any one complete cycle of one valve operation and in which system the amplitude of said phase change may be altered whilst the engine is operating so permitting a change in the valve open-time or phase of opening for any given engine speed and said system including means of ensuring that only one valve opening is affected by any one cycle of advance and retard of the valve operating means characterized by the valve operating means being divided into appropriate sections such that the number of valves controlled and the phase relationship between sequential operations of the valves controlled by any one section ensures that there is no overlap in sequential valve operations on any section of the valve operating means.


BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying
FIG. 1, shows a particular example of the invention; and
FIG. 2 shows a simplified model for the purposes of explanation of the invention;
FIGS. 3 to 9 inclusive show various details of mechanisms applying to the invention;
FIG. 10 shows a computer generated graph of the operation of the particular example;
FIG. 11 shows one means of applying the invention to one camshaft of a four cylinder engine; and
FIG. 12 shows a means of including a hydraulic actuator in a coaxial arrangement of the invention such as that shown in FIG. 1.




REFERENCES:
patent: 1757046 (1930-05-01), Horine
patent: 4305352 (1981-12-01), Oshima et al.
patent: 4498352 (1985-02-01), Hedelin
patent: 4694789 (1987-09-01), Frost
patent: 4747375 (1988-05-01), Williams
patent: 4917058 (1990-04-01), Nelson et al.
patent: 5105679 (1992-04-01), Voigt
patent: 5136887 (1992-08-01), Elrod et al.
C. Gray; A Review of Variable Engine Valve; SAE Technical Paper Series; Internation Congress and Exposition Feb. 29-Mar. 4, 1988; p. 7; FIG. 10.
T. Dresner & P. Barkan; A Review and Classification of Variable Valve Timing Mechanisms; International Congress & Exposition Feb. 27-Mar. 3, 1989; pp. 5, 6, 11 & 12.
Proceedings of the Institution of Mechanical Engineers, vol. 186, No. 23, 1972, London pp. 301-306; G. E. Roe: Variable Valve-Timing Unit Suitable . . . .

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