Workshop Manual

Chapter Two Principle of Electronic Fuel Injection System
I. Overhaul of System Components
1. Intake Air Temperature Pressure Sensor
1.1 Function of the sensor:
Detect air intake pressure and temperature in air intake manifold, which will be provided to
ECU as main load signal of engine; ECU will calculate injection pulse-width based on this signal.
1.2 Principle of the sensor:
Intake air temperature pressure sensor is a sensor that integrates an intake air pressure sensor
and an intake air temperature sensor. Absolute pressure sensor element of intake manifold is
composed of a silicon chip. A pressure diaphragm is etched on the silicon chip. On the pressure
diaphragm, there are 4 piezo-resistances, which serve as strain sensors and constitute a Wheatstone
bridge. In addition to this pressure diaphragm, a signal processing circuit is also integrated on the
silicon chip. The silicon chip and a metal housing constitute a closed reference, where the absolute
pressure of the gas inside approaches to zero. Thus, a micro-electronic mechanical system is
formed. The active face of the silicon chip stands a pressure close to zero, while its back face stands
the pending measuring intake manifold absolute pressure introduced by a connecting pipe. The
thickness of the silicon chip is merely several µm, so the absolute pressure change in intake manifold
will bring mechanical deformation to the silicon chip. The 4 piezo-resistances will accordingly
deform and their resistances also change. The voltage signal in linear relation to the pressure is
formed after process by the signal processing circuit on the silicon chip. The intake temperature
sensor element is a negative temperature coefficient (NTC) resistance, which will change with the
intake temperature. This sensor sends out a voltage indicating the intake temperature change to the
controller.
Cross-section view for sensor of air absolute pressure and temperature in intake manifold
1 Gasket 2 Stainless Steel Sleeve 3 PCB Board 4 Sensing Element 5 Housing 6 Pressure Bracket 7 Soldering 8
Bonded With Bonding Agent
进气压力温度传感
器
Intake air temperature
pressure sensor