Turbocharger Wastegate Actuator
The wastegate valve opens and closes a passage beside the turbine wheel within the turbocharger housing which allows excess exhaust pressure to bypass the turbine into the downstream exhaust. The ECM controls a bi-directional DC motor and actuator that is connected to the wastegate valve via simple rod and linkage. The ECM supplies a PWM signal on the motor control circuits to control the direction and maintain the position of the wastegate valve. The ECM coverts a serial data signal into a value equal to the relative position of the wastegate valve, which can be observed on a scan tool as percentage and a voltage.
The electronic wastegate actuator addresses the disadvantages inherent with a pressure/vacuum-actuated systems such as position pulsations and leakage. The electric actuator operates the wastegate much faster than the pneumatically actuated system allowing for more precise control of the wastegate in all operating conditions, since valve positioning isn't inhibited by the weight of the actuator spring and transient pressures within the system. The electronic system gives the ECM full authority over the wastegate valve position allowing for complete control over the speed, direction, and position of the valve under transient loads, which increases transient response and significantly reduces turbo lag. The default position of the wastegate is fully open at a learned value represented 0%. When the engine is idling the wastegate remains opened near the learned minimum closed position (0%). On acceleration the ECM commands the wastegate closed to a value learned value represented as 100%, or fully closed, until the desired boost pressure is achieved. During partial load and cruising speeds the ECM modulates the position of the wastegate to maintain boost as desired. This operating characteristic benefits the lag and surge associated with a traditionally actuated wastegate. Precise management of the pressure fluctuations within the turbo and the elimination of valve snap back reduces overall wear and improves fuel efficiency.
The ECM supplies the wastegate actuator with a 5 V reference circuit, a low reference circuit, an ECM embedded H-bridge motor directional control circuit, and an asynchronous signal/serial data circuit. The asynchronous signal means communication is only going from the actuator to the ECM. The wastegate actuator cannot receive data from the ECM over the signal/serial data circuit. The wastegate position sensor provides a signal voltage that changes relative to the position of the wastegate valve. The customized integrated circuit translates the voltage based position information into serial data using the Society of Automotive Engineers (SAE) J2716 Single Edge Nibble Transmission (SENT) protocol. The wastegate position sensor information is transmitted between the actuator and the ECM on the signal/serial data circuit. A DTC will set if the ECM detects a condition with the motor, position control, or circuitry, the wastegate valve will default to open, and boost will be disabled.