Injection of the fuel will continue as long as both the fill port and spill ports are completely cover by the barrel and sleeve (fig. 5-11).
Injection ends the moment that the spill port starts to edge above the sleeve, releasing the pressure in the plunger and letting fuel escape from the pump back into the housing. Also, at the end of the stroke, the check valve closes to prevent the fuel from flowing back from the injector fuel line (fig. 5-11).
To increase the amount of fuel injected, raise the sleeve through the control shaft and fork so that the sleeve is effectively positioned higher up on the plunger. This means that the spill port will be closed for a longer period of time, as the cam lobe is raising the plunger. Increasing the effective stroke of the plunger (time that both ports are closed) will increase the amount of fuel delivered.
For procedures on removing, replacing, and servicing the injection pumps in a sleeve metering fuel system, refer to the manufacturer's service manual. 5-18
GOVERNOR ACTION. - The governor on a Caterpillar sleeve metering fuel system is a mechanical governor and acts throughout the entire speed range of the engine. The majority of the sleeve metering fuel system uses three springs-a low-idle (inner) spring, a high-idle (outer) spring, and a dashpot spring. When the operator requires more power from the engine, he/she steps on the throttle. This causes the governor control lever to apply pressure that compresses the governor spring and to transfer this motion to the thrust collar. Since governor action from the spring and weight motion is of the back and forth variety, an additional linkage between the injection pumps and the governor transforms this sliding horizontal governor movement from the thrust collar into a rolling motion at the sleeve control shaft. A simple connecting lever commonly known as a bell crank lever accomplishes this action.
The bell crank lever contacts the thrust collar on one end and the governor sleeve control shaft on the other end. The bell crank pivots on a fixed vertical bell crankshaft to gain mechanical advantage through the lever principle. At the sleeve shaft end, it rides in a ball- and-socket joint that holds it in place and minimizes linkage movement. Therefore, any horizontal movement at the governor weight shaft and spring will cause an equally precise movement at the ball-and- socket joint, leading to reposition of the sleeves. If, in this case, the operator has increased the throttle position, the sleeves would be lifted, thereby covering the spill port for a longer overall effective plunger stroke.
As with any mechanical governor, an increase in either the throttle position or load will cause a speed change to the engine. Spring pressure is always trying to increase the fuel delivered to the engine, while centrifugal force of the rotating weights is always trying to decrease the amount of fuel going to the engine. Somewhere within the throttle range, however, a state of balance between these two opposing forces will exist as long as the engine speed is capable of overcoming the load placed on it to keep the spring and weight force in a state of balance.
When the engine is stopped, the action of the governor spring force places the thrust collar and the sleeve control shaft to the full-fuel position; therefore, easier starting is accomplished Once the operator cranks and starts the engine, centrifugal force will cause the flyweights to move outward, which now opposes the spring force, and the thrust collar and spring seat will come together, as they are pushed to a decreased fuel position. When the force of the weights equals the preset force of the spring established by the idle adjusting screw, these forces will be in a state of balance, and the engine will run at a steady idle speed with the throttle at a normal idle position.
Governor action will operate from idle throughout the speed range of the engine. A load stop pin controls the maximum speed of the engine. Rotation of the throttle lever causes the load stop lever to lift the load stop pin until it comes in contact with the stop bar or screw, thereby limiting any more fuel to the engine.
The purpose of the dashpot governor spring is to prevent any surging or irregular speed regulation of the engine by the fact that the piston either pulls fuel into or pushes fuel out of its cylinder through an orifice. The dashpot governor spring force varies with the piston movement, and as the engine load is increased or decreased, fuel is drawn into the piston cylinder through the orifice. This action gives the effect of a high governor spring rate that minimizes speed variations through oscillation during load changes of the engine. At any time the ignition switch is turned off or the governor speed control lever is moved to the OFFContinue Reading