An air-fuel ratio control system for an internal combustion engine includes a LAF sensor and an O2 sensor arranged in an exhaust pipe at respective locations upstream and downstream of a catalytic converter. A desired air-fuel ratio coefficient used in calculating an amount of fuel supplied to the engine is calculated based on operating conditions of the engine, and corrected based on output from the O2 sensor. The air-fuel ratio of a mixture supplied to the engine is feedback-controlled to a stoichiometric air-fuel ratio based on the corrected desired air-fuel ratio coefficient. When the output from the O2 sensor falls within a predetermined range, the desired air-fuel ratio coefficient is not corrected, but held at an immediately preceding value thereof.

Air-fuel ratio control system for internal combustion engines

An air/fuel ratio control system including an oxygen sensor disposed in the exhaust gas to provide a feedback signal. The oxygen sensor is of the solid electrolyte concentration cell type having a heater and is operated with supply of a DC current to the concentration cell to maintain a reference oxygen partial pressure therein. A fuel feed control circuit in this system shifts its closed-loop control function to open-loop aiming at a lower air/fuel ratio if the output of the oxygen sensor continues to indicate that actual air/fuel ratio remains on one side of the intended air/fuel ratio due to breaking of the heater. To prevent the engine from stalling or operating unstably due to excessive increase in the air/fuel ratio before the shift to open-loop control, the system includes means for detecting breaking of the heater and immediately interrupting the current supply to the concentration cell in the oxygen sensor thereby forcing the sensor to put out an output which is indicative of a very high air/fuel ratio and, hence, causes the control circuit to lower the air/fuel ratio before the interruption of the closed-loop control.

System for feedback control of air/fuel ratio in IC engine with means to control current supply to oxygen sensor

An air-fuel (A/F) controller of an internal combustion engine, which computes an average value of a plurality of duty ratios of the voltage supplied to the heater according to the engine speed and the engine load periodically detected during a period from a predetermined moment up to the present, and fixes said average value as the present duty ratio of the voltage to be supplied to the heater, since the A/F ratio sensor is heated not only by the heater but also by exhaust gas The A/F ratio controller smoothes the variation of voltage to be supplied to the heater by applying the computed average value as the present duty ratio of the supply voltage which is to be supplied to the heater Accordingly, even when the driving condition is in high-speed, variation of the temperature borne by the heater is mild and smooth, and thus, the temperature of the oxygen-concentration detecting element does not rise suddenly Furthermore, the A/F ratio controller corrects the above-mentioned present duty ratio of the voltage to be supplied to the heater according to the supply voltage to be supplied to the heater

Air-fuel ratio controller of internal combustion engine

Energization of a heater built in a gas sensor, such as an oxygen sensor, used in an air/fuel ratio control system of an internal combustion engine, is controlled to maintain the temperature of the same within a desired range. The temperature of the heater is calculated using a measured resistance value of the heater, and engine parameters used for estimating a specific engine operating condition. To this end operating state of the engine is first detected to determine whether it is possible to estimate the actual temperature of the heater, and when possible, a reference resistance value of the heater at a reference temperature such as 0° K. or 0° C. is caluclated using estimated heater temperature and a measured resistance value. Once the initial resistance value is obtained, this is used to calculate actual heater temperature using measured resistance value and a predetermined temperature coefficient.

Method and apparatus for controlling heater of a gas sensor

An oxygen concentration detector under a temperature control for an internal combustion engine. An oxygen sensor of a critical current type is held between a gas under test and a reference gas, in the vicinity of which a heater is located for heating up the oxygen sensor in a sensor activating temperature range. A first voltage is applied for a positive bias control to the oxygen sensor during a first period, and a second voltage is applied for a negative bias control thereto during a second period. Electric current flowing through the oxygen sensor is detected during the first period in order to detect the oxygen concentration in the gas under test. The current value is also detected during the second period in order to detect and maintain constant the internal electric resistance of the oxygen sensor by controlling the heater heating output.

Oxygen concentration detector under temperature control

An internal combustion engine with a closed loop air/fuel ratio control utilizes a heated zirconia sensor, the sensor including a resistance heater element connected to receive electric current from the vehicle battery, the sensor having an internal parasitic capacitance and being characterized by a leakage current path between the heater element and the capacitance. The sensor output voltage is sampled by the closed loop control periodically and current is supplied to the heater element only during periods which end a predetermined time before each such sampling so that any charge on the capacitance may discharge before it affects the sampled voltage. Within each period, the current may be duty cycle modulated in response to vehicle battery voltage to maintain a constant average power to the heater element when heat is required.

Internal combustion engine with oxygen sensor heater control

A valve assembly having normally opened and normally closed valves controlled by solenoids to provide various connected and disconnected arrangements in a fluid system. It is particularly useful in a wheel lock control or anti-skid brake system (ABS).

Solenoid valve assembly

Apparatus for sensing the timing of peak combustion pressure in an internal combustion engine includes a capacitive piezoelectric element adapted for flexure in response to variations in combustion chamber pressure and connected in parallel with a first resistance, a constant current generator connected to establish a predetermined voltage across the first resistance and thereby across the piezoelectric element when the capacitance of the latter remains constant, a second resistance, a source of the predetermined voltage, and an operational amplifier effective to compare the voltage across the piezoelectric element with the predetermined voltage and source or sink current through the second resistance to maintain the predetermined voltage across the piezoelectric element. The output voltage of the operational amplifier is an analog of the current through the second resistance and thus of the rate of change of capacitance of the piezoelectric element. The crankshaft angle after ignition at which this voltage crosses the predetermined reference corresponds to the timing of peak combustion pressure. In order to reduce noise in the 6 to 9 kilohertz range, the first and second resistances may be reduced, the second resistance bypassed at high frequencies and the output voltage amplified with low pass filtering.

William J. Ricketts

Papers

Internal combustion engine with oxygen sensor heater control

Solenoid valve assembly

Peak combustion pressure timing detector for internal combustion engine