Internal-combustion engines – Charge forming device – Including cylinder pressure or temperature responsive means
Patent
1996-09-17
1998-06-23
Dolinar, Andrew M.
Internal-combustion engines
Charge forming device
Including cylinder pressure or temperature responsive means
73 106, 73116, F02D 4114, G01M 1500
Patent
active
057690499
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method and system for controlling combustion engines, wherein the present air/fuel ratio within the cylinders of the combustion chamber is detected by analyzing the characteristics of the ion current, the ion current being detected via a measuring gap arranged within the combustion chamber.
Lambda sensors are often used in order to obtain closed loop control of stochiometric combustion in combustion engines. A stochiometric combustion is the ideal operation mode for a conventional three-way catalytic converter. The type of lambda sensor used in mass-produced cars has been a so-called narrow-banded lambda sensor, which exhibits a distinct transition of its output signal at a lambda value just below 1.0. This type of narrow-banded lambda sensor is used in order to control the combustion, wherein the control is operated such that the output signal of the lambda sensor switches between a low and high output signal. The order of deviation from the transition point has not been able to be detected by these narrowly-banded lambda sensors, which is the reason why these nanow-banded lambda sensors have not been used in closed loop control of combustion at other air/fuel ratios. An alternative to the narrow-banded lambda sensor is the linear type of lambda sensor, but this sensor is very expensive, at least 10-fold, and could therefore in terms of cost not justify an introduction in mass-produced cars. The linear type of lambda sensor emits an output signal proportional to the present air/fuel ratio, enabling a closed loop control also at lean mixtures in the range .lambda.=1.1-1.4, as well as at richer air/fuel ratios in the range .lambda.=0.8-0.09 or below. An alternative to lambda sensors is shown in U.S. Pat. No. 4,535,740 which employs an ion current sensor in the combustion chamber and where the spark gap of the conventional spark plug is used as a measuring gap enabling detection of the burn duration within the combustion chamber. A parameter representative of the burn duration, and thus the air/fuel ratio, is detected by measuring the length of time the ion current signal is above a predetermined threshold value. At certain operating ranges where the ion current signal exhibits a low accuracy, the closed loop control is based upon the burn duration. The characteristics of the burn duration varies considerably at different operating cases, i.e. load and rpm's, and for that reason alone there is a need for a number of different threshold values to be used for the detection of burn duration, or alternatively of using different weight factors for different load cases.
SUMMARY OF THE INVENTION
An object of the invention is to obtain a simplified and more reliable detection of the present airlfuel ratio within the combustion chamber by detection of the ion current within the combustion chamber and preferably by using the spark plug gap of the combustion chamber as a measuring gap.
Another object is to obtain a method and system for detecting the air/fuel ratio using a simple differentiator circuit or a differentiator algorithm implemented in the software of a micro computer based control unit for the ion Current signal processing, which circuit only needs a measuring window of short duration during the combustion process in order to be able to extract the information necessary for the determination of the air/fuel ratio. The necessary hardware and software for the determination of airlfuel ratio could then be implemented in a cost efficient manner having a low computational load upon the computational capacity of the control system, which, in turn, will release computational capacity for other type of control or control algorithms.
Yet another object is to obtain a method and a system for detecting the airlfuel ratio, which method is less susceptible for operating cases at leaner air/fuel ratios, a so called lean-burn control, at which lean conditions the ion current signal is subjected to large variations between successive combustions in aspects
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Derwent's abstract, No 86-142780/22, week 8622, Abstract Of SU, 1188355 (As KIRG Car Electr (MOAU=), 30 Oct. 1985.
Johansson Thomas
Nytomt Jan
Dolinar Andrew M.
Mecel AB
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