CAV Diesel Injection Pump: Components and Operation

CAV Rotary Injection Pump Fundamentals

In CAV rotary injection pumps, fuel is sent from the transfer pump to the hydraulic head at a pressure regulated by a valve. The metering valve precisely controls the fuel flow, which is governed by the throttle position and the speed regulator assembly. The distributor then raises the fuel pressure from the transfer level to the injection pressure, distributing it to the various nozzles.

Fuel Pressure Transfer Mechanism

Under normal operating conditions, the generated pressure causes the control piston to move to the right, against the action of its spring. This pressure is applied to the valve through a conduit from the transfer pump. When the pressure exceeds the limits set by the adjusting screw, regulation holes are uncovered, allowing fuel to pass from the suction side of the transfer pump, thereby regulating the pressure.

Hydraulic Head: Pumping, Dispensing, and Distribution

All these critical actions are performed by the hydraulic head, which is the most important component of the injection pump. During engine operation, as the rotor turns, the filler port opens, allowing fuel to enter the pumping element, which is defined by the pistons. As the engine continues to turn approximately 45 degrees, the projections of the cam ring come into contact with the rollers, compressing the fuel due to the approximation of the pistons. At this precise moment, the ports connected to the injectors align with the output, resulting in the delivery of high-pressure fuel.

Mechanical Speed Regulation System

In this type of pump, the throttle mechanism used for speed regulation is mechanical. In the vehicle, the regulating spring is housed within a sliding sleeve, which connects the control lever to the throttle control, allowing movements of the control lever to be transmitted to the metering valve. Thus, fuel flow can be regulated according to the throttle position.

This adjustment occurs only when the maximum set speed has been reached, and the force exerted on the sliding sleeve by the counterweight exceeds the spring force of the regulator. In this scenario, the lever shifts to the left, and through the connecting rod, the metering valve's position also shifts, reducing fuel flow. When the engine speed is not very high, it causes little effort on the sliding sleeve, which is insufficient to overcome the spring force.

Automatic Injection Advance Mechanism

This type of pump also features an automatic variable speed advance mechanism. When the engine is stationary, the advance chamber lacks spring pressure, causing the ball to shift to the right. This positions the cam ring to create an injection delay.

Once the engine is started, the chamber fills to the transfer pressure for that phase of operation, causing the piston to move to the left. During this movement, the weaker spring is compressed against the sliding stopper, causing a shift of the cam plate, which slightly rotates the cam ring in the opposite direction of the rotor. This action effectively overcomes the initial injection delay. This precise timing adjustment is crucial for the engine operating at idle.