Internal-combustion engines – Charge forming device – Fuel injection system
Patent
1990-04-30
1991-08-06
Wolfe, Willis R.
Internal-combustion engines
Charge forming device
Fuel injection system
F02D 4114
Patent
active
050368192
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a control system for controlling the air/fuel ratio in an internal combustion engine to an air ratio lambda to be maintained. The control system has an oxygen probe (lambda probe) which is exposed to the exhaust gas of the internal combustion engine and the output voltage of the probe, which represents a measure of the air ratio lambda, changes essentially abruptly in the region of lambda=1.
If a three-way catalytic converter is used for reducing the main pollutant components (NOx, HC, CO) of an internal combustion engine, it is necessary for its optimal efficiency, that is to achieve a maximum conversion rate, that a stoichiometric air/fuel mixture (lambda=1), or at least an air ratio lambda which moves in a certain region around lambda=1 (lambda window), is maintained. In the known control systems, the jump-like response of the output voltage of the lambda probe at the transition from the rich region (.lambda.<1) to the lean region (.lambda.>1) and at the transition from the lean region (.lambda.>1) to the rich region (.lambda.<1) is evaluated for mixture control, that is, not the value of lambda itself. In this case, the values for the injection time, which are stored in a characteristic field as a function of the speed and load (throttle flap position) of the internal combustion engine, are corrected by means of a two-position control multiplicatively using a correction factor. Usually, a two-position controller with PI action is used for continuous correction of the correction factor. Due to the jump characteristic of the output voltage in the region of lambda=1 and due to existing dead times (transport time of the mixture from the injection valves through the internal combustion engine to the lambda probek, response time of the probe), a control oscillation occurs for the correction factor. The required air ratio lambda can thus only be maintained on average. The amplitude and frequency of this control oscillation significantly influences the exhaust gas emission. An increase in the amplitude of the control oscillation leads to the air ratio lambda temporarily moving outside the lambda window, thereby resulting in a drastic increase in the harmful components of the exhaust gases.
BACKGROUND OF THE INVENTION
From U.S. Pat. No. 4,594,984, a control system is known in which a control device with constant control action is arranged for controlling in the lean region (preferably around lambda=1.2). Since the probe output signal has a relatively small increase in this region, a greater control accuracy is achieved with the continuous-action control device than with the usual two-position control. In the above U.S. Pat. Pat. application, it is also stated that this continuous-action control device cannot be used for a lambda=1 control, since the lambda probe has a steep voltage jump at lambda=1 and, as a result, the control device would always be at the lean or rich limit.
U.S. Pat. No. 4,601,276 discloses a method and apparatus for controlling the air/fuel mixture of an internal combustion engine by means of oxygen probes. The probes are mounted in respective combustion chambers of the engine. This arrangement affords the advantage that the direct measurement of the result of combustion makes possible a very rapid response of the control. The duration of detection of the components of the air/fuel mixture metered to the engine can be considerably reduced. In addition, extreme conditions such as too rich or too lean can be detected after a few cycles of the particular cylinder in question and an appropriate response can be made. The entire engine can be monitored and the measuring results from cylinder to cylinder can be evaluated serially in the ignition sequence. In addition to this, the invention of U.S. Pat. No. 4,601,276 permits the simultaneous monitoring of each individual cylinder. This affords the advantage that variations from cylinder to cylidner in the composition of the mixture can be eliminated. Signals of oxygen probes which are
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Peter Cornelius
Plapp Gunther
Raff Lothar
Schnaibel Eberhard
Westerdorf Michael
Ottesen Walter
Robert & Bosch GmbH
Wolfe Willis R.
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