US 4,167,163 A · Sensor monitoring apparatus

Abstract

A sensor which determines an operational variable of a system, for example an oxygen sensor of an internal combustion engine, generates a usable output voltage only at the proper elevated temperature. In order to uncouple the control loop from an improperly operating sensor, i.e., a cold sensor, the internal resistance of the sensor is monitored by passing through it a test current and by comparing the resulting voltage drop to a set-point value. Whenever the internal resistance is too high, indicating non-readiness, the control loop is opened and a substitute average output value is supplied to the fuel injection system or to the system driven by the control loop. During normal operation, the sensor is tested periodically with short test pulses to continuously monitor the operational readiness, but the main test current is normally shut off, thereby preventing falsification of the output signal.

Claims14

Dependent claims

A method for turning on and/or off a regulatory means operating with an oxygen sensor which is part of a control loop and which detects a given operational state (actual value) during the mixture preparation for motor vehicles, whereby the sensor requires a period of time which is indeterminable before reaching its operating temperature and full function during the operation of a fuel injection apparatus in which the sensor is disposed in the exhaust gas channel and influences the function of the injection apparatus, which includes one of either the duration of the injection pulses generated the secondary air supply on the exhaust side, the improvement comprising the steps of:

passing a test current through said sensor;
detecting the voltage drop across said sensor due to the passage of said test current;
comparing said voltage drop with a predetermined set-point value;
opening the control loop when said comparison shows that the internal resistance of said sensor is too high;
and
closing the control loop and cutting off said test current when said comparison shows that the internal resistance of said sensor is sufficiently low to provide an adequate control signal to said control loop;
whereby said test current is prevented from falsifying the control signal from said sensor in normal operation.

4 more elements

In an apparatus for turning on and/or off a regulatory means operating with an oxygen sensor which is part of a control loop and which detects a given operational state (actual value) during the mixture preparation for motor vehicles, whereby the sensor requires a period of time which is indeterminable before reaching its operating temperature and full function during the operation of a fuel injection apparatus in which the sensor is disposed in the exhaust gas channel and influences the function of the injection apparatus, which includes one of either the duration of the injection pulses generated or the secondary air supply on the exhaust side, the improvement comprising:

a test circuit for generating a test current to be supplied to said sensor;
comparator means for detecting the relative magnitude of the voltage drop across said sensor due to the passage of said test current;
whereby, when said comparator means indicates that the internal resistance of said sensor is lower than a predetermined limit, said test current is cut off and normal control loop operation is initiated.

Dependencies are inferred from the claim text.

Sensor monitoring apparatus

Life of this patent

Sensor monitoring apparatus

Life of this patent

Abstract

Claims14