BOLT 2152900 - Caterpillar

A rapid reduction in the generator's power output 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. This places 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.
Illustration 1 g00926843
Flow of the compressed air/fuel mixture during activation of the compressor bypass group (50 Hz arrangement)
(1) Actuator for the bypass valve
(2) Bypass valve
(3) Throttle
(4) Throttle actuator
(5) Fuel metering valve The master Electronic Control Module (ECM) monitors the engine speed. The ECM responds to a rapid increase in the engine speed by sending a command signal to actuator (1). This causes the actuator to move a shaft that is connected to a plate inside bypass valve (2). The bypass valve opens.The bypass valve is connected before throttle (3). 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. This reduces the back pressure that is caused by excessive pressure in the air inlet system.Note: The bypass valve for the 60 Hz arrangement is connected to two sets of tubing: one set of tubing is connected to the inlet for the right turbocharger and the other set of tubing is connected to the inlet for the left turbocharger.Additionally, the ECM sends two other command signals. A command to throttle actuator (4) opens the throttle