Internal-combustion engines – Engine speed regulator – Engine speed reduction by fuel cutoff
Patent
1996-02-26
1998-01-20
Argenbright, Tony M.
Internal-combustion engines
Engine speed regulator
Engine speed reduction by fuel cutoff
123436, 123438, F02D 4114
Patent
active
057091935
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The subject invention concerns a method and a device for controlling the supply of fuel and/or air to an internal combustion engine in its fuel supply section, such as the carburettor or the fuel-injection system, to ensure that its mixture ratio is automatically adjusted to the desired level in response to different operational conditions.
BACKGROUND OF THE INVENTION
In all internal combustion engines the air/fuel ratio is of utmost importance for the engine function. Usually the air/fuel ratio is referred to as the A/F-ratio, A and F signifying respectively air and fuel. In order to achieve a satisfactory combination of low fuel consumption, low fuel emissions, good runability and high efficiency the A/F-ratio must be maintained within comparatively narrow limits, compare FIG. 3. An A/F-ratio slightly on the lean side of the optimum position of efficiency is that usually sought after. The requirements that exhaust emissions from combustion engines be kept low are becoming increasingly stricter. In the case of car engines these requirements have led to the use of exhaust catalysers and to the use of devices of a kind known as lambda probes, to control the A/F-ratio. Such special transducers, i.e. oxygen sensors or lambda probes, are positioned in the car exhaust system. In this position they are able to detect the efficiency of the combustion and the results derived from the measurements made by the probe can be used in a control system to control the mixture ratio to provide a good result. The results from the oxygen sensor (lambda probe) is fed back to the fuel control system, eliminating the need for any further transducers.
However, the sensor or the probe requires a reference having completely pure oxygen, which is a situation that it is practically impossible to achieve in some engines, for instance the motors of power saws. In addition, control systems fitted with lambda probes are bulky and heavy while at the same time such systems are expensive and complicated and proned to entail operational safety problems in many applications. For instance, in a power saw, a system of this kind would result in increased size and weight as well as a drastic rise in costs and possibly also cause operational safety problems. The operational safety problems arise primarily because of the sensitivity of the unit and its wiring. This means that in the case of consumer products, such as power saws, lawn mowers, and similar products, this technology is difficult to use for mounting reasons and also for cost--efficiency and operational--safety reasons. Expected future legislation with respect to CO-emissions from small motors may make it difficult to use manually adjusted carburetors. Given the manufacturing tolerances that could be achieved in the case of carburetors it is impossible, with the use of fixed nozzles in the carburetors, to meet these legal requirements and at the same time guarantee the user good runability in all combinations of air-pressures and temperatures, different fuel qualities and so on. The desired mixture ratio, the A/F-ratio, is affected by many factors. From the Swedish Published Patent Application No. 468 998 is known a method and a device for controlling the carburetor of an internal combustion engine. This prior art control system comprises two regulating circuits. A first control unit essentially continuously affects an adjustment means to ensure that the mixture ratio is adjusted in response to a previously known rotational-speed dependency with respect to the mixture ratio, whereby the latter will be given a modified rotational-speed dependency. This means that the carburetor curve is corrected and such correction is an absolute requirement in the control operation.
However, to use two separate regulating ciruits to control the A/F-ratio naturally entails considerably complications and costs while at the same time it increases the error risks in comparison with the use of one single regulating circuit. However, it has been considered necessary to use two regulating
REFERENCES:
patent: 4368707 (1983-01-01), Leshner et al.
patent: 4442815 (1984-04-01), Ninomiya
patent: 4829963 (1989-05-01), Oblaender et al.
patent: 5345912 (1994-09-01), Svensson et al.
Petersson Ulf Johan
Svensson Ulf Malte
Aktiebolaget Electrolux
Argenbright Tony M.
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