Internal-combustion engines – Charge forming device – Fuel injection system
Patent
1990-07-30
1991-10-08
Nelli, Raymond A.
Internal-combustion engines
Charge forming device
Fuel injection system
123440, 123489, F02M 5100
Patent
active
050544527
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method and an apparatus for detecting a fault condition of a lambda probe and for taking measures following a fault signal which is emitted when the fault condition is detected.
BACKGROUND OF THE INVENTION
Such methods and apparatus are known, for example, from U.S. Pat. No. 4,528,957 and U.S. Pat. No. 4,742,808. In both methods, it is indirectly investigated whether the monitored probe exhibits a sufficiently high temperature for reliable lambda value measurements. If this is not the case, the probe is considered not to be operationally ready and the lambda value is not closed-loop controlled but open-loop controlled. Only when the operating temperature is sufficiently high and operational readiness is thus detected, the lambda value is adjusted by closed-loop control.
In the method according to U.S. Pat No. 4,528,957, a counter voltage is connected to the probe voltage via a known resistance and it is monitored whether the resulting voltage leaves a predetermined range, that is whether it exceeds a threshold voltage for lambda values for rich mixtures or drops below a threshold voltage for lambda values for lean mixtures. As long as the voltage is still within the range, an absence of operational readiness is detected and thus the lambda value is open-loop controlled. In the method according to U.S. Pat. No. 4,742,808, the internal resistance of the probe is directly measured, which is done with the aid of a known load resistance and two voltage measurements. As soon as the measured value drops below a resistance threshold value, the probe is considered to be ready for operation.
It has been found in actual operation that, in spite of such measures, it happens that the probe is detected as ready for operation due to shunts even though this is not the case. This results in poor closed-loop control performance which results in high pollutant emission and poor driving quality.
The invention is based on the object of specifying a reliable method for detecting such a fault condition of a lambda probe. The invention is furthermore based on the object of specifying an apparatus for carrying out such a method.
SUMMARY OF THE INVENTION
The invention is based on the finding that an unwanted shunt can exist between probe heating voltage and probe voltage. In this case, the heating voltage falsifies the voltage generated by the probe. However, the shunt voltage and thus the falsification do not exist when the probe heater is switched off.
It is particularly simple to determine the shunt voltage when the lambda value does not change. This is the case, in particular, before the internal combustion engine starts and during overrun phases. The difference between the probe voltages measured with the heater switched on and switched off directly provides the shunt voltage. If the difference exceeds a predetermined threshold difference value, the fault signal is output.
If the lambda value continuously changes, it is more difficult to determine whether a shunt is present, particularly when a probe with non-linear performance is used, the probe voltage of which changes greatly with a changing lambda value in the range around lambda=one. If measurements are taken at two successive times, once with the heater switched on and then with the heater switched off and a difference is found between the two measurement values, it is not clear whether this difference is caused by a change in the lambda value or by a shunt or by both. However, this can be established if the switching-off and switching-on is carried out in a pseudo-binary sequence and the measurement values are evaluated by means of a correlation method. If the evaluation shows that an external direct voltage of inadmissible magnitude, which is independent of the respective lambda value, is superposed on the voltage values measured with the heater switched on, the fault signal is output.
Evaluation with the aid of a correlation method is complex but offers the advantage that the amplitude of the shunt voltage can b
REFERENCES:
patent: 4528957 (1985-07-01), Jundt et al.
patent: 4715343 (1987-12-01), Kinoshita
patent: 4724814 (1988-02-01), Mieno et al.
patent: 4724815 (1988-02-01), Mieno et al.
patent: 4742808 (1988-05-01), Blumel et al.
patent: 4780826 (1988-10-01), Nakano et al.
patent: 4797828 (1989-01-01), Suzuki et al.
patent: 4850325 (1989-07-01), Abe et al.
patent: 4951632 (1990-08-01), Yakuwa et al.
patent: 4958611 (1990-09-01), Uchinami et al.
Nelli Raymond A.
Ottesen Walter
Robert & Bosch GmbH
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