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Technical background of rotary distributor diesel fuel injection pump

Posted on 3/24/2016 11:24:13 AM

An external view of a typical pump is shown in Fig. 1 and an internal section in Fig. 2 .The main rotating components are the drive shaft (1), distributor rotor (2), transfer pump blades (5), and governor components (11).The drive shaft engages the distributor rotor in the hydraulic head. The drive end of the rotor incorporates two pumping plungers.

 

 
The plungers are actuated toward each other simultaneously by an internal cam ring through rollers and shoes which are carried in slots at the drive end of the rotor. The number of cam lobes normally equals the number of engine cylinders.
 
The transfer pump at the rear of the rotor is the postive 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 both 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 tubings. The hydraulic head contains the bore in which the rotor revolves, the metering valve bore, the charging ports and the head outlet fittings. The high pressure injection tubings leading to the nozzles are fastened to these fittings
 
 
Distributor pumps contain their own mechanical governor capable of close speed regulation. Both all-speed and min-max types are available. The centrifugal force of the weights in their retainer is transmitted through a sleeve to the governor arm and through a linkage to the metering valve. The metering valve can be closed to shut off fuel through the linkage by an independently operated shut-off lever.
 
The automatic speed advance is a hydraulic mechanism which advances or retards the beginning of fuel delivery from the pump. This can respond to speed alone, or to a combination of speed and load changes. A more detailed description of each pump area will be covered in the following pages.
 
Transfer pump pressure regulation
Refer to Fig. 3 for the following description. Filtered, low pressure fuel from an overhead tank or a lift pump passes through the transfer pump inlet screen. This vane-type pump consists of a stationary liner and four spring loaded blades,which are carried in the rotor slots. Excess fuel is recirculated to the transfer pump inlet by means of the pressure regulator piston, spring,and ported sleeve. Fuel pressure from the transfer pump forces the piston in the regulator sleeve against the spring. The pressure curve is controlled by the pump displacement, spring rate and preload, and regulating slot configuration. Therefore, pressure increases with speed.
 
The transfer pump operates consistently over a wide viscosity range determined by different grades of diesel fuels and also when affected by varying temperatures. A thin plate incorporating a sharp-edged orifice is located in the spring adjusting plug. Flow through an orifice of this type is virtually unaffected by viscosity changes. An additional biasing pressure is exerted against the spring side of the piston and is determined by the linear flow around the regulating piston and the flow through the orifice. With cold or viscous fuels a reduced flow occurs through the piston and sleeve clearance, and the additional biasing pressure is slight. With hot or low viscosity fuels the clearance flow increases and the pressure within the spring chamber increases. The regulating spring and higher biasing pressure forces combine to control the slot area. This control maintains a nearly constant transfer pump pressure over a broad range of fuel viscosities and thus maintains stable automatic advance operation over various fuel types and temperatures.
 
Hydraulic head and rotor – Fig. 4 shows an exploded view of the rotor and the pumping plungers. The cam rollers contact the inner surface of the cam ring form and push the plungers toward each other for injection. The shoes act as tappets between the rollers and plungers.
 
Refer to Fig. 5. As the rotor revolves, its two inlet passages register with the charging annulus ports in the hydraulic head. Transfer pump fuel controlled by the metering valve opening, flow into the pumping chamber forcing the plungers apart. The plungers move outward for a distance proportional to the amount of fuel required for the next injection stroke. If only a small amount is admitted, as at idling, the plungers move out a short distance. If half-load is required,approximately half the pumping chamber is filled. This process is known as inlet metering.
 
Full-load delivery is controlled by the maximum plunger travel. This plunger travel is limited by the leaf spring as it is contacted by the edge of the shoes.
 
Refer to Fig. 6. The leaf spring contacts two points near the outer ends of the rotor. As the adjusting screw is turned inward, the center of the leaf spring moves in and its ends extend outward. This increases the maximum plunger travel. Turning the adjusting screw out has the reverse effect. The adjustment set point is retained by the screw head-to-leaf spring friction and the coating material on the screw threads.
 
As the rotor continues to revolve (Fig. 7),the inlet ports move out of registry and the rotor discharge port indexes with one of the head outlets. The rollers then contact opposing cam lobes which force the shoes inward against the plungers. At this point high pressure pumping begins. Further rotation of the rotor moves the rollers along the cam ramps forcing the plungers together. During the discharge stroke the fuel between the plungers is displaced into the axial passage of the rotor through the delivery valve to the discharge port. The pressurized fuel then passes through the outlet fitting, enters the injection tubing and opens the nozzle. Delivery continues until the rollers travel over the cam noses and begin to move outwardly. The pressure in the axial passage is then reduced, allowing the nozzle to close.

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