Section II Principle of controlling and actuating components 1. Intake pressure/temperature sensor (Fig. 1-1) Fig. 1-1 (1) Function: Measure the absolute pressure of the 0.1~0.2bar intake manifold and the temperature of the intake air flow, and provide load information for the engine. (2) Structure and principle: The sensor consists of intake manifold absolute pressure sensor and intake air temperature sensor, which is installed on the pressurizer tank. (3) Intake air pressure sensor: made by a silicon chip. There is a pressure diaphragm on the silicon chip and are 4 piezoelectric resistances on the diaphragm. The 4 piezoelectric resistances build up a wheatstone bridge.
Besides the pressure diaphragm, there is also a signal process circuit on the chip. The silicon chip and a metal housing build up a closed referential space, in which the absolute pressure of the air is approximately zero. Then, a microelectronic mechanical system is established. There is a zero pressure on the active side of the silicon chip and an absolute pressure of the intake manifold on the back side of the chip. The thickness of the silicon chip is only several microns (μm), and the form of the chip will be mechanically changed with the change of the absolute pressure of the intake manifold. Then, the 4 piezoelectric resistances and their resistance values will be also changed.
After treated by the signal process circuit on the chip, the pressure signal, which is linearly related to pressure, will be formed. (4) Intake air temperature sensor: Made by a resistance with negative temperature coefficient (NTC). Similar to water temperature sensor, the resistance value will decrease with the increase of the intake air temperature. The change of the intake air temperature will be supervised and measured by a comparative electric circuit within the ECU. (5) Connection of wiring diagram (Fig. 1-2) Fig. 1-2 22