Internal-combustion engines – Charge forming device – Including cylinder pressure or temperature responsive means
Patent
1996-04-11
1997-08-05
Dolinar, Andrew M.
Internal-combustion engines
Charge forming device
Including cylinder pressure or temperature responsive means
F02D 4114
Patent
active
056532091
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method and system for fuel control in two-stroke engines.
For larger combustion engines in vehicles relatively complicated systems are used in order to reduce emission levels and fuel consumption. A feedback system having a lambda sensor in the exhaust system, is often used. The lambda sensor is used to control that the proper air-fuel ratio is maintained, whereby a three-way catalytic reactor could operate at optimum efficiency.
For smaller and less expensive two-stroke engines, for example used in hand held garden machines, it becomes considerably more difficult to obtain a control system that will not dramatically affect the cost for the propulsion unit. Control systems with lambda sensors are comparatively expensive, and the lambda sensor is sensitive to fuel contamination. The major problem in two-stroke engines is that relatively large mounts of unburned hydrocarbons are exhausted. This is caused by the two-stroke engines having rather simple type of control systems, and often optimised for driveability at the expense of increased content of hydrocarbons in the exhaust. Controlling air-fuel ratios in the lean direction often results in reduction of unburned hydrocarbons in the exhaust. At the same time driveability will decrease when controlling in the lean direction, and the risk for engine damages increases.
In control systems where the control in the lean direction only is made towards the knock limit, in order to reduce emissions, a knocking condition is ceased by increasing the fuel amount. The increase of the fuel amount could in certain operating cases come close to or exceed the amount of fuel that cause a four-stroking condition.
SUMMARY OF THE INVENTION
An object of the invention is to obtain an optimal control of a two-stroke combustion engine as of the amount of fuel supplied. The optimal amount of fuel supplied is adapted to the fuel quality, the temperature of the combustion engine and the condition of the spark plug. Another object is to obtain an adaptive control system for two-stroke engines, which control system on a regular basis could establish feedback reference signals regarding the extreme limits for lean-and rich air-fuel ratios.
Yet another object is that the performance of control of the combustion engine could be based upon feedback information representative for the air-fuel ratio A/F, without using lambda sensors. A cost efficient and inexpensive control system could thus be construed and implemented also for smaller two-stroke engines without increasing the cost dramatically for such engines.
Yet another object is to obtain a reduction of unburned hydrocarbons in the exhaust from two-stroke engines, which also will cause reduction of the fuel consumption, while maintaining driveability at an optimal high level at the prevailing conditions.
The foregoing and other objects are achieved in accordance with the invention by a method for fuel control in two stroke combustion engines which includes supplying an empirically determined fuel amount (F.sub.tab) to the engine dependent on detected engine parameters. This fuel amount is reduced by a reduction (.DELTA.F) in the lean direction of the empirically determined amount of fuel (F.sub.tab) until a knocking condition occurs. This amount of fuel is then stored in memory as a value (M.sub.FK). The fuel amount is then increased by an increase (.DELTA.F+) in the rich direction of the empirically determined amount of fuel (F.sub.tab) until the two stroke engine starts four stroking due to misfire. This value is then stored in memory as a rich limit value (M.sub.F4ST). An adaptive set value (F.sub.korr) is then calculated, which adaptive set value lies at a predetermined level between the rich limit value (M.sub.F4ST) and the lean limit value (M.sub.fk). The adaptive set value (F.sub.korr) is stored in memory and this value compared with the empirically determined amount of fuel (F) and, when a deviation occurs, the empirically determined amount of fuel is corrected proportionally to the deviati
REFERENCES:
patent: 4243009 (1981-01-01), Staerzl
patent: 4964387 (1990-10-01), Hansen
patent: 5174261 (1992-12-01), Fuji et al.
Johansson Hans
Nytomt Jan
Dolinar Andrew M.
Mecel AB
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