VALVE-EXHAUST 9N5125 - Caterpillar

A rapid reduction in the power output of the generator can cause a rapid increase in the engine speed. The increased engine speed causes the turbocharger to produce boost pressures that are greater than the requirement for the engine operation.Turbocharger surge - In response to the excess pressure in the air inlet system, the flow of air across the turbocharger compressor wheel is reversed. This reversal of the air flow is called a turbocharger surge. During a turbocharger surge, the turbocharger overspeeds temporarily. The result is a greater axial load on the thrust bearing and higher than normal torque on the shaft. The turbocharger surge can result in severe damage to the turbocharger.The compressor bypass group reduces the opportunity for a turbocharger surge.Active BypassThe Electronic Control Module (ECM) monitors the following:
Engine speed
Engine load
Throttle differential pressureThe Electronic Control Module (ECM) monitors the engine speed, engine load, and throttle differential pressure. The ECM responds to these input signals by sending a command signal to actuator . The actuator moves a shaft that is connected to a plate inside bypass valve . The bypass valve opens.The bypass valve is connected before throttle . Tubing is connected from the bypass valve to the inlet for the turbocharger compressor. When the bypass valve is opened, the compressed air/fuel mixture is diverted through the tubing away from the throttle. The result is reduced back pressure that is caused by excessive pressure in the air inlet system.Also, the ECM sends two other command signals. A command to throttle actuator opens the throttle to reduce the resistance that contributes to back pressure. A command to fuel metering valve reduces the fuel supply to reduce the engine speed and the turbocharger speed.The combined effect of these actions reduces the opportunity for a turbocharger surge.The compressor bypass group is also operated during engine shutdown to reduce the opportunity for a turbocharger surge. Also, any air/fuel mixture that may have been trapped in the tubing is purged.The compressor bypass valve is commanded to a wide range of positions. This feature is called active bypass. The ECM uses the input from a differential pressure sensor to determine the pressure drop across the throttle plate. The ECM determines the amount of active bypass that is required to maintain the desired pressure drop across the throttle plate. The ECM sends a command to the actuator for the bypass valve in order for the bypass valve to move to the desired position.