Usage:
Fuel Injection Pump Components
Fuel Injection Pump Components
The fuel injection pump is a totally enclosed and pressurized system. The pump sends the correct amount of high pressure fuel through injection nozzles, to individual cylinders at the correct time (near end of compression stroke). The injection pump meters (measures) amount of fuel delivered to the nozzles. This action controls engine speed by the governor setting or position of the accelerator or throttle control.
The fuel lines to the fuel injectors are equal lengths. This ensures even pressure and correct injection timing at each nozzle.
During operation, extra fuel, which is used as a coolant and a lubricant for pump parts that move, is circulated through the pump housing and returned to the tank. Return lines also remove any air trapped in the nozzles or pump housing.
The main rotating components are drive shaft (1), distributor rotor (7), transfer pump blades (5), and governor (11).
The drive shaft engages the distributor rotor in the hydraulic head. The drive end of distributor rotor incorporates two pumping plungers (10).
The pumping plungers are actuated toward each other simultaneously by an internal cam ring (8) through rollers and shoes which are carried in slots at the drive end of distributor rotor.
The transfer pump at the rear of the distributor rotor is of the positive displacement vane type and is enclosed in the end cap. The end cap also houses the fuel inlet strainer and transfer pump pressure regulator. Transfer pump pressure is automatically compensated for viscosity effects due to temperature changes and various fuel grades.
The distributor rotor incorporates two charging ports and a single axial bore with one discharge port to serve all head outlets to the injection lines. The hydraulic head contains the bore in which the rotor revolves, the metering valve bore, the charging ports, and the head discharge fittings. The high pressure injection lines to the nozzles are fastened to these discharge fittings.
The fuel injection pump contains a mechanical governor. The centrifugal force of the governor weights in the retainer is transmitted through a sleeve to the governor arm and through a positive linkage to the metering valve.
The automatic speed advance is a hydraulic mechanism which advances or retards the beginning of fuel delivery from the pump.
Fuel Flow
Fuel Flow Diagram
The operating principles of the pump can be understood better by following the fuel circuit during a complete pump cycle.
Fuel is drawn from fuel tank (1) through filters (2) into transfer pump (3) inlet through the inlet filter screen by the vane-type fuel transfer pump. Some fuel is bypassed through pressure regulator assembly (4) to suction side.
Fuel under transfer pump pressure flows through the center of the transfer pump rotor, past the rotor retainers into a circular groove on the rotor. It then flows through a connecting passage in head (5) to automatic advance (6) and up through a radial passage and then through a connecting passage to metering valve (7). The radial position of the metering valve, controlled by governor (8), regulates flow of the fuel into radial charging passage (9) which incorporates the head charging ports.
As the rotor revolves, the two rotor inlet passages register with the charging ports in the hydraulic head, allowing fuel to flow into the pumping chamber. With further rotation, the inlet passages move out of registry and the discharge port of the rotor registers with one of the head outlets. While the discharge port is opened, the rollers contact the cam lobes forcing pump plungers (10) together. Fuel trapped between the pumping plungers is then pressurized and delivered by nozzle (11) to the combustion chamber.
The fuel injection pump is self lubricating. As fuel at transfer pump pressure reaches the charging ports, slots on the rotor shank allow fuel and any entrapped air to glow into pump housing cavity (12).
An air vent passage in the hydraulic head connects the outlet side of the transfer pump with the pump housing. Vent wire assembly (13) allows air and some fuel to be bled back to the fuel tank through the return line. The bypass fills the housing, lubricators the internal components, cools and carries off any small air bubbles. The pump operates with the housing completely full of fuel. There are no dead air spaces within the pump.
Transfer Pump
The positive displacement vane type fuel transfer pump consists of a stationary liner and spring-loaded blades which are carried in slots in the rotor. Because the inside diameter of the liner is eccentric to the rotor axis, rotation causes the blades to move in the rotor slots. This blade movement changes the volume between the blade segments.
Transfer Pump Operation
Transfer pump output volume and pressure increases as pump speed increases. Because displacement and pressure of the transfer pump can exceed injection requirements, some of the fuel is recirculated by means of the transfer pump regulator to the inlet side of the transfer pump.
Radial movement causes a volume increase in the quadrant between blades 1 and 2 (a). In this position, the quadrant is aligned with a kidney-shaped inlet slot (3) in the top portion of the regulator assembly. The increasing volume causes fuel to be pulled through the inlet fitting and filter screen into the transfer pump liner. Volume between the two blades continues to increase until blade 2 passes out of alignment with the regulator slot. At this point, rotor (5) has reached a position where outward movement of blades 1 and 2 is negligible and volume is not changing (b). The fuel between the blades is being carried to the bottom of the transfer pump liner (4).
As blade 1 passes the edge of the kidney-shaped outlet slot (6) in the lower portion of the regulator assembly (c), the liner, whose inside diameter is eccentric to the rotor, compresses blades 1 and 2 inward (a). The volume between the blades is reduced and pressurized fuel is delivered through the slot of the regulator assembly, through the transfer pump, through the rotor, past the rotor retainers, and into a channel on the rotor leading to the hydraulic head passages. Volume between blades continues to decrease, pressurizing the fuel in the quadrant, until blade 2 passes the slot in the regulator assembly.
Regulator Assembly Operation
Regulator Assembly Operation
The illustration shows the operation of the pressure regulating piston while the pump is running. Fuel output from the discharge side of the transfer pump forces the piston in the regulator against the regulating spring. As flow increases, the regulating spring is compressed until the edge of the regulating position starts to uncover the regulating slot "A" (a).
Because fuel pressure on the piston is opposed by the regulating spring, the delivery pressure of the transfer pump is controlled by he spring rate and size of the regulating slot "A". Therefore, pressure increases with speed. A high pressure relief slot is incorporated in some regulators as part of the regulating slot "A" to prevent excessively high transfer pump pressure.
Viscosity Compensation
The transfer pump works equally well with different grades of diesel fuel and varying temperatures, both of which effect fuel viscosity. A unique and simple feature of the regulating system offsets pressure changes caused by viscosity difference. Located in the spring adjusting plug is a thin plate incorporating a sharp-edged orifice. The orifice allows fuel leakage past the piston to return to the inlet side of the pump. Flow through a short orifice is virtually unaffected by viscosity changes. The biasing pressure exerted against the back side of the piston is determined by the leakage through the clearance between the piston and regulator bore, and the pressure drop through the sharp-edged orifice. With cold or viscous fuels, very little leakage occurs past the piston. The additional force on the back side of the piston from the viscous fuel pressure is slight. With hot or light fuels, leakage past the piston increases. Fuel pressure in the spring cavity increases also, since flow past the piston must equal the flow through the orifice. Pressure rises due to increased piston leakage and pressure rises to force more fuel through the orifice. This variation in piston position compensates for the leakage which would occur with thin fuels, and design pressures are maintained over a broad range of viscosity changes.
Charging and Discharging
Charging Cycle
Charging Cycle Diagram
As the rotor revolves, the two inlet passages (1) in the rotor align with ports of the circular charging passage (4). Fuel under pressure from transfer pump (2), controlled by the opening of metering valve (3), flows into the pumping chamber forcing plungers (5) apart.
The plungers move outward a distance proportionate to the amount of fuel required for injection on the following stroke. If only a small quantity of fuel enters the pumping chamber, as at idling, the plungers move out a short distance. Maximum plunger travel and consequently maximum fuel delivery is limited by leaf spring (6), which contacts the edge of roller shoes (7). Only when the engine is operating at full load will the plungers move to the most outward position. While the angled inlet passages in the rotor are in alignment with the ports in the circular charging passage, the rotor discharge port is not in alignment with a head outlet, and the rollers are off the cam lobes.
Discharge Cycle
Discharge Cycle Diagram
As the rotor continues to revolve, the inlet passages move out of alignment with the charging port. The rotor discharge port opens to one of the head outlets. The rollers contact cam lobes (1), forcing the shoes in against the plungers, and high-pressure pumping begins.
Beginning of injection varies according to load (volume of charging fuel), even though rollers may always strike the cam (2) at the same position. Further rotation of the rotor moves the rollers up the cam lobe ramps pushing the plungers inward. During the discharge stroke, the fuel trapped between the plungers flows through the axial passage of the rotor and discharge port (3) to the injection line. Delivery to the injection line continues until the rollers pass the innermost point on the cam lobe and begin to move outward. The pressure in the axial passage is then reduced, allowing the nozzle to close. This is the end of delivery.
Delivery Valve
Delivery Valve Operation
The delivery valve rapidly decreases injection line pressure after injection to a predetermined value lower that of the nozzle closing pressure. This reduction in pressure permits the nozzle valve to return rapidly to its seat, achieving sharp delivery cut-off and preventing improperly atomized fuel from entering the combustion chamber.
The delivery valve operates in a bore in the center of the distributor rotor. The valve requires no seat, only a stop to limit travel. Sealing is accomplished by the close clearance between the valve and the bore into which it fits. Since the same delivery valve performs the function of retraction for each injection line, the result is a smooth running engine at all loads and speeds.
When injection starts, the fuel pressure moves the delivery valve slightly out of its bore and adds the volume of its displacement, section "A" to the delivery valve spring chamber. Since the discharge port is already opened to a head outlet, the retraction volume and plunger displacement volume are delivered under high pressure to the node. Delivery ends when the pressure on the plunger side of the delivery valve is quickly reduced, due to the cam rollers passing the highest point on the cam lobe.
After this, the rotor discharge port closes completely and a residual injection line pressure is maintained. The delivery valve is only required to seal while the discharge port is opened. After the port is closed, residual line pressures are maintained by the seal of the close-fitting head and rotor.
Return Oil Circuit
Return Oil Circuit
Fuel under transfer pump pressure is discharged into a vent passage in the hydraulic head. Flow through the passage is restricted by a vent wire assembly to prevent excessive return oil and undue pressure loss. The amount of return oil is controlled by the size of wire used in the vent wire assembly. For example, the smaller the wire, the greater the flow. The vent wire assembly is available in several sizes in order to meet the return oil quantities called for on the specification. This assembly is accessible by removing only the governor cover. The vent passage is located behind the metering valve bore and connects with a short vertical passage containing the vent wire assembly and leads to the governor compartment.
Should a small quantity of air enter the transfer pump, it immediately passes to the vent passage as shown. Air and a small amount of fuel then flow from the housing to the fuel tank through the return line.
Housing pressure is maintained by a spring-loaded ballcheck return fitting in the governor cover of the pump.
Mechanical All-Speed Governor
Mechanical All-Speed Governor
The governor shaft serves the purpose of maintaining the desired engine speed within the operating range under various load settings.
In the mechanical governor, the movement of weights (1) acting against the governor thrust rotates metering valve (2) by means of governor arm (3) and linkage hook (4). This rotation varies the alignment of the metering valve opening to the passage from the transfer pump, thereby controlling the quantity of fuel to the plungers. The governor derives its energy from weights (1) pivoting in weight retainer (5). Centrifugal force tips weights (1) outward. This moves the governor thrust sleeve (6) against the governor arm (3). Governor arm (3) pivots on the knife edge of pivot shaft (7) and through a simple, positive linkage, rotates the metering valve. The force of the weights against the governor arm is balanced by governor spring (8) force, which is controlled by the manually positioned throttle lever and vehicle linkage for the desired engine speed.
When speed increases due to a load reduction, the resultant increase in centrifugal force of the weights rotates the metering valve clockwise to reduce fuel. This limits the speed increase (within the operating range) to a value determined by governor spring rate and setting of the throttle.
When the load on the engine is increased, the speed tends to reduce. The lower speed reduces the force generated by the weights permitting the spring force to rotate the metering valve in the counterclockwise direction to increase fuel. The speed of the engine at any point within the operating range is dependent upon the combination of load on the engine an the governor spring rate and setting as established by the throttle position. A low idle spring (9) is provided for more sensitive regulation when weight energy is low in the low end speed range. The limits of throttle travel are set by adjusting screws for proper low idle and high idle positions.
A light tension spring on the linkage assembly takes up any slack in the linkage joints and also allows the shutoff mechanism to close the metering valve without having to overcome the governor spring force. Only a very light force is required to rotate the metering valve to the closed position.
Automatic Advanced-Speed Response
Automatic Advanced-Speed Response
The governor design permits the use of a simple, direct acting hydraulic mechanism, powered by fuel pressure from the transfer pump, to rotate the cam slightly and vary delivery timing. The advance mechanism advances or retards start of fuel delivery in response to engine speed changes. In most injection systems, the actual beginning of delivery of fuel at the nozzle will start later (in engine degrees of rotation) as the speed increases.
Compensating inherent injection lag improves high speed performance of the engine. Starting delivery of fuel to the nozzle earlier when the engine is operating at higher speeds insures that combustion takes place when the piston is in its most effective position to produce optimum power with minimum specific fuel consumption and minimum smoke.
The advance pistons, located in a bore in the housing, engage the cam advance screw and move the cam (when fuel pressure moves the power piston) opposite the direction of rotor rotation. Fuel under transfer pump pressure is fed through a drilled passage in the hydraulic head which aligns with the bore of the head locating screw. Fuel is then directed past the spring-loaded ballcheck in the bore of the head locating screw. It then enters the slot on the outside diameter of the screw which aligns with a drilled passage in the housing leading to the power piston side of the automatic advance assembly.
A slot around the power piston plug and a drilled passage allow the fuel to enter the advance piston bore. Fuel pressure against the piston must overcome the opposing spring force plus the dynamic injection loading on the cam in order to change the cam position. The spring-loaded ballcheck in the bore of the head locating screw prevents the normal tendency of the cam to return to the retard position during injection by trapping the fuel in the piston chamber. When engine speed decreases, the hydraulic pressure is reduced and the spring returns the cam to a retarded position in proportion to the reduction in speed. The fuel in the piston chamber is allowed to bleed off through a control orifice located below the ballcheck valve in the head locating screw.
At low speeds, because transfer pump pressure is comparatively low, the cam remains in the retarded position. When engine speed increases, transfer pump pressure rises and moves the piston in the advanced direction. Advance piston movement is related to speed. Total movement of the cam is limited by the piston length.
A "trimmer screw' is provided to adjust advanced spring preload which controls start of cam movement. It can be incorporated at either side of the advance mechanism and may be adjusted on the test bench while running.