Temperature-compensated exhaust gas recirculation system

摘要

An exhaust gas recirculation (EGR) system (10) includes a proportional solenoid valve (28) that regulates vacuum pressure to a vacuum-actuated EGR valve (12). The proportional solenoid valve (28) includes an inductive coil (30) that generates a magnetic field when energized. An electronic control unit (26) energizes the coil (30) with a fixed-frequency pulse-width modulated signal. The periodic magnetic field drives a ferromagnetic armature valve (44) open and closed - alternately admitting then closing-off a flow of atmospheric-pressure air that is used to alter the vacuum pressure output to the EGR valve (12). The vacuum pressure is dependent upon the amount of current flowing through the coil (30) during each pulse. The resistance of the coil (30) is temperature- dependent and to maintain the current in the coil (30) constant over temperature, the coil (30) is connected in series with a thermistor (48) having a temperature coefficient of resistance that is opposite that of the coil (30). A temperature-stable resistor (50) is connected across the thermistor (48) to modify its temperature-response curve to more closely offset that of the coil (30).