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A new combustion pressure
sensor capable of measuring the pressure in a cylinder
of an automobile engine has been developed. Using
the sensor output, the air-fuel ratio in the cylinder
was successfully maintained in the vicinity of the
lean combustion limit. The sensor has been use for
controlling an advanced lean combustion engine for
improvement of fuel consumption efficiency and reduction
of emissions.
The combustion pressure
sensor contains a metal diaphragm, a force transducer
made from Si, and an amplifier. The combustion pressure
is converted to the uniaxial stress thorough the
diaphragm, and then the uniaxial stress is transformed
to the change in resistivity using the piezoresistive
effect of Si. The force transducer is designed to
utilize the piezoresistive coefficient, π63
, for sensing the stress.
The sensor exhibits
excellent performance, including durability and
reliability. Since the fracture load of the force
transducer is 1000N, the whole strength of the sensor
is considered to be sufficient for the actual load,
150-225N. In addition, the sensor output linearly
increases with increasing pressure; the non-linearity
is estimated to be less than 1% of full scale. Consequently,
the sensor is applicable to heavier vehicles and
automatic transmission vehicles.
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