Method for monitoring the operability of a lambda sensor
AssigneeSiemens Aktiengesellschaft
InventorsGerd Rösel, Hong Zhang
Life of this patent
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Abstract
A method of monitoring the dynamic operability of a lambda sensor (monitor sensor), disposed in the exhaust gas stream of an internal combustion engine downstream of a catalytic converter. Once the engine operating state of overrun fuel cutoff is detected, the rich/lean switching time of the monitor sensor disposed downstream of the catalytic converter is ascertained and weighted as a function of the air flow rate (LMM) in the intake conduit. By comparing the mean value of the thus-obtained switching time with a limit value and ensuing evaluation, the operability of the monitor sensor is diagnosed. Operability is assured if the switching time is below the limit value. Other diagnostic criteria are formed by evaluating the signal level of the monitor sensor.
Claims15
In a method for monitoring the operability of a lambda sensor disposed downstream from a catalytic converter of an internal combustion engine for providing an output signal, the method which comprises the steps of:
- determining when the internal combustion engine is operating in a state of overrun fuel cutoff;
- determining, during the state of overrun fuel cutoff of the internal combustion engine, at least one switching time of the lambda sensor disposed downstream from the catalytic converter of the internal combustion engine by measuring the output signal of the lambda sensor disposed downstream from the catalytic converter;
- and
- normalizing the switching time with a factor, the factor determined as a function of an air flow rate delivered to the engine;
- and
- determining the operability of the lambda sensor disposed downstream from the catalytic converter by comparing the normalized switching time with a limit value.
In a method for monitoring the operability of a lambda sensor disposed downstream from a catalytic converter of an internal combustion engine for providing an output signal, the method which comprises the steps of:
- determining when the internal combustion engine is operating in a state of overrun fuel cutoff;
- detecting, during the state of overrun fuel cutoff of the internal combustion engine, the output signal of the lambda sensor disposed downstream from the catalytic converter of the internal combustion engine;
- and
- if the output signal exceeds a diagnostic threshold value;
- then
- determining at least one switching time of the lambda sensor disposed downstream from the catalytic converter by measuring the output signal of the lambda sensor disposed downstream from the catalytic converter;
- normalizing the switching time with a factor, the factor determined as a function of an air flow rate delivered to the internal combustion engine;
- and
- determining the operability of the lambda sensor disposed downstream from the catalytic converter by comparing the normalized switching time with a limit value.
In a method for monitoring the operability of a lambda sensor disposed downstream from a catalytic converter of an internal combustion engine for providing an output signal, the method which comprises the steps of:
- determining when the internal combustion engine is operating in a state of overrun fuel cutoff;
- determining, during the state of overrun fuel cutoff of the internal combustion engine, at least a predetermined number of switching times of the lambda sensor disposed downstream from the catalytic converter of the internal combustion engine by measuring the output signal of the lambda sensor disposed downstream from the catalytic converter;
- normalizing at least the predetermined number of switching times with a factor, the factor determined as a function of an air flow rate delivered to the internal combustion engine;
- calculating a mean value from the normalized predetermined number of switching times;
- and
- determining the operability of the lambda sensor by comparing the mean value with a limit value.
In a method for monitoring the operability of a lambda sensor disposed downstream from a catalytic converter of an internal combustion engine for providing an output signal, the method which comprises the steps of:
- determining when the internal combustion engine is operating in a state of overrun fuel cutoff;
- detecting, during the state of overrun fuel cutoff of the internal combustion engine, the output signal of the lambda sensor disposed downstream from the catalytic converter of the internal combustion engine;
- and
- if the output signal exceeds a diagnostic threshold value, then:
- determining at least a predetermined number of switching times of the lambda sensor disposed downstream from the catalytic converter by measuring the output signal of the lambda sensor disposed downstream from the catalytic converter;
- normalizing at least the predetermined number of switching times with a factor, the factor determined as a function of an air flow rate delivered to the internal combustion engine;
- calculating a mean value from the normalized predetermined number of switching times;
- and
- determining the operability of the lambda sensor by comparing the mean value with a limit value.
In a method for monitoring the operability of a lambda sensor disposed downstream from a catalytic converter of an internal combustion engine for providing an output signal, the method which comprises the steps of:
- determining when the internal combustion engine is operating in a state of overrun fuel cutoff;
- determining, during the state of overrun fuel cutoff of the internal combustion engine, at least one switching time of the lambda sensor disposed downstream from the catalytic converter of the internal combustion engine by measuring the output signal of the lambda sensor disposed downstream from the catalytic converter;
- and
- discontinuing determining the switching time if it is determined that the internal combustion engine has exited the state of overrun fuel cutoff.
In a method for monitoring the operability of a lambda sensor disposed downstream from a catalytic converter of an internal combustion engine for providing an output signal, the method which comprises the steps of:
- determining when the internal combustion engine is operating in a state of overrun fuel cutoff;
- monitoring the output signal of the lambda sensor disposed downstream from the catalytic converter of the internal combustion engine upon entering an overrun fuel cutoff phase and upon leaving the overrun fuel phase;
- and
- determining that the lambda sensor is defective if an implausible course of the output signal occurs.
Dependencies are inferred from the claim text.