1. Description When the intake air volume (boost pressure) is increased by the turbocharger, the boost compensator increases the maximum fuel injection volume in accordance with the increased intake air volume, in order to maintain optimal combustion conditions and increase the engine output at all times.
2. Construction The boost compensator is installed above the governor of the injection pump. The diaphragm and push rod move up and down by the boost pressure. The push rod has a tapered construction, by which, the control arm is rotated via the connecting pin. This amount of movement becomes tension lever movement distance, and the spill ring movement distance (injection volume).
(1) When the boost pressure is low: The spring pushes the diaphragm upward. The injection volume does not increase because the connecting pin is in contact with the tapered bottom portion of the push rod.
(2) When the boost pressure is high: The diaphragm is pushed by the boost pressure to move the push rod downward. The tension lever is pulled by the control spring. Therefore, the connecting pin moves to the right toward the tapered portion of the push rod, and the control arm also rotates clockwise. The tension lever and control lever rotate counter-clockwise around fulcrum A and move the spill ring to increase the maximum fuel injection volume. (3) When the boost pressure is too high: Normally it is controlled at the area C and D. If the boost pressure rises above the intercept point on the graph, the connecting pin is pushed back to the left by tapered portion B of the push rod, reducing the maximum fuel injection volume. This prevents the boost pressure from rising too high in the case of a failure.