Internal-combustion engines – Charge forming device – Including exhaust gas condition responsive means
Patent
1991-05-22
1992-06-09
Wolfe, Willis R.
Internal-combustion engines
Charge forming device
Including exhaust gas condition responsive means
F02D 4114, G01N 2750, G01R 19165
Patent
active
051197880
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method for determining at least one threshold voltage for a lambda-one control comprising a lambda probe which is connected in opposition to a voltage which essentially corresponds to the desired switching voltage. In addition, the invention relates to a arrangement for carrying out such a method.
BACKGROUND OF THE INVENTION
From U.S. Pat. No. 4,528,957 a configuration for detecting the voltage of the lambda probe is known which utilizes a counter-voltage source, the voltage of which is connected in opposition to that of the lambda probe. Two threshold voltages are referred to the counter voltage, namely an upper threshold voltage U.sub.O and a lower threshold voltage U.sub.U. The counter voltage is, for example, 450 mV and the threshold voltages are separated therefrom by 50 mV upwards or downwards, respectively. If the measured voltage reaches one of the two thresholds, the system switches from open-loop to closed-loop control.
In closed-loop control operation, control is effected in the direction of lean as long as the voltage measured is above a switch-over threshold voltage and control is effected in the direction of rich if it is below this voltage. As a rule, the switch-over threshold voltage is close to the counter voltage, for example 10 mV above it.
In the case of the example mentioned, the counter voltage is therefore 450 mV, the upper switch-on threshold voltage 500 mV, the lower switch-on threshold voltage 400 mV and the switch-over threshold voltage 460 mV. Each voltage value is permanently associated with a digital value. In the case of the example, these are assumed to be the values 130, 143, 117 and 132, respectively.
In order to be able to set the voltage values accurately, a high-precision reference voltage source is used, that is, not the conventional voltage stabilizer which supplies, among others, the usual logic voltage of +5V for electronic components. The voltage of the reference voltage source is divided by means of high-precision constant-temperature resistors in such a manner that the desired counter voltage is accurately obtained. The threshold voltages are referred to this accurately set counter voltage. In addition to the calibration with the aid of the precise resistors, a software calibration can also be effected so that the predetermined digital value for the counter voltage is accurately obtained.
SUMMARY OF THE INVENTION
The invention is based on the object of being able to manage without the high-precision reference voltage source and without high-precision resistors. A method and an arrangement will be provided for this.
The method according to the invention is characterized in that the counter voltage is measured and threshold voltages are referred to the measured counter voltage. If the measured counter voltage is, for example, 460 mV instead of 450 mV, the upper switch-on threshold voltage U.sub.O is set to 510 mV instead of 500 mV. It is noted that, strictly speaking, it is not known whether the counter voltage is 455 mV or 465 mV since, of course, a high-precision reference voltage source for comparison is lacking. However, it is not important to know this precisely, either, since other voltages of importance, for example the switch-on threshold voltages, are, of course, referred to the measured voltage. This ensures that, for example, the two switch-on threshold voltages are always symmetrical with respect to the counter voltage independently of what the precise value of the counter voltage is. To obtain the value for the upper switch-on threshold voltage, 13 units are basically added, for example, to the digital value of the measured counter voltage or 13 units are subtracted in order to obtain the lower switch-on threshold voltage. Correspondingly, other spacings or even unsymmetrical spacings can be set.
Apart from the switch-on threshold voltages, the switch-over threshold voltage is also advantageously referred to the measured voltage.
Due to the fact that threshold voltages are referred to the measure
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Fritz Adolf
Rein Christian
Zimmermann Jurgen
Ottesen Walter
Robert & Bosch GmbH
Wolfe Willis R.
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