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To detect an air-fuel ratio in wide range is very important to control the automotive engines with low fuel consumption and low exhaust emissions. Although the application of zirconia electrolyte for this purpose has been proposed by the authors several years ago, there remained several problems due to the contamination of gas diffusion apertures which are exposed to the exhaust gas environment. Here the behavior of ions transported in zirconia electrolyte have been analyzed to optimize the structure and characteristics, and to guarantee the long life operation of sensor. Gas contents and their reactions in combustion process under the wide range air-fuel ratio have been analyzed, and these results were reflected to the analysis of ion transportation in zirconia electrolyte. Experimental results supported the analytical results, and they showed the possibilities of long life operation of zirconia air-fuel ratio sensor utilizing ion transportation phenomena.

This report describes the development of an air fuel ratio sensor with a linear voltage output, and its signal processing module that is able to calibrate the sensor output function on the measuring point of the 20.9% oxygen concentration in atmospheric air and the zero diffusion current at stoichiometry as the reference. This sensing system is effective when applied to air fuel ratio PID feed back engine control and it is able to realize the reduction of initial variability of sensors, interchangeability of sensors, and long term output change of the sensor.

Emissions tests were performed to study the operating characteristics of a wide range air/fuel ratio (AFR) sensor in closed loop control. The AFR sensor used here has an output voltage with respect to AFR that is linear and can be characterized by a fourth order polynomial function. For this study the output signal of the AFR sensor was fed into a General Control Unit (GCU). The GCU converted this analog input signal into a square wave similar to a lambda sensor. The output from the GCU was fed into the Engine Control Unit (ECU) of the 3.8L, V6 test engine to control the engine A/F ratio. Emissions tests were conducted in closed loop mode under steady state and transient condition. Emissions of HC, CO and NOx using the AFR sensor will be shown. Results of these tests showed that the AFR sensor allowed for precise control of the AFR at the stoichiometric point (λ = 1.0).

A hot-wire air flow sensor which can directly measure the intake air mass flow has been developed, and a microprocessor based engine control system using the sensor has been designed. The sensing probe of the sensor is formed from a small wire-wound resistor, and installed in the bypass of the intake passage. The sensor requires a good signal processing method under pulsating flow conditions because of its quick response. New control technologies were examined for the prototype engine control system, using the sensor, as applied to a 4 cycle, 4 cylinder engine. The air-to-fuel ratio, ignition timing, and EGR rate are controlled to their optimum values by a microprocessor which processes signals of this sensor and of other sensors indicating the engine operating conditions. The results of engine performance tests show that the output power, fuel economy and exhaust emissions are improved significantly in comparison with other fuel management systems.

This paper describes the design and operation of a thick-film zirconia air-fuel ratio sensor with a heater. This sensor is composed of two zirconia plate cells, a stoichiometric cell and a lean cell, laminated on the platinum heater. It is fabricated as one body using a thick-film process. The pair of cells has a gas diffusion chamber and a slit type gas diffusion aperture. The sensing principle is based on the rate-determining diffusion of oxygen molecules at the gas diffusion aperture. By using an oxygen pumping phenomenon, air-fuel ratios of the stoichiometric and lean regions can be detected. As this sensor is heated to a high constant temperature, it has sufficient accuracy without any additional temperature compensation. Its starting time is short and response time is very quick.

The detection range of an air-fuel ratio sensor is expanded in the rich A/F region. Using a simulation technique, the limiting cause of the detection range in the rich A/F region is identified as insufficient combustion rates of CO and H2 with O2 on the electrode, which prevent realization of a limited diffusion state which is necessary to detect the air-fuel ratio. Applying an improved diffusion layer to decrease the diffusion rates and an improved electrode to increase the combustion rates, it is demonstrated that the detection limit can be expanded to λ=0.6 while that of a conventional sensor is λ=0.8.

This paper describes the sensing principle of a new air-fuel ratio sensor, which has the ability to detect air-fuel ratios in rich, stoichiometric and lean ranges. The sensing part is composed of a gas diffusion layer and a zirconia solid electrolyte with a pair of electrodes which function as an anode and a cathode. The anode and the cathode electrodes are exposed to the atmosphere and the exhaust gas, respectively. To obtain the bidirectional pumping current between the two electrodes, the potential of the cathode is held to a constant value higher than the electronic circuit ground. The electromotive force induced between the two electrodes is forcibly controlled to a constant value by the electronic circuit. In this composition, three ranges of air-fuel ratio can be detected by the amount of pumping current.

The oxygen ion conductive solid electrolyte cell served as a device for measuring the combustibles content and the oxygen content of an exhaust gas. The cell is comprised of a tubular electrolyte, two opposed electrodes and a porous diffusion layer located on the outer electrode surface. The sensor is employed to measure both rich and lean air fuel ratio through the use of an electronic circuit pumping the oxygen ions to achieve a constant voltage between the electrodes. The wide range detecting capability makes it particularly attractive for air fuel ratio control applications associated with the internal combustion engine. The result of the performance tests are as follows, Detecting range (air excess ratio λ) : 0.8 - “∞ Step response time constant (63%) : 200ms Warm up time. - less than 80 sec at 20°C We found in the durability test concerned with the heat cycle and contamination that if initial aging treatment is applied the output variation ratio (. λ/λ) is limited with in : 5%.