Distributor Type Metering A distributor type injection pump generally uses one pumping element to pressurize fuel for all cylinders rather than a single element for each cylinder. Conceptually, it is similar to the distributor on a gasoline engine. Compact, economical pumps are made possible but the engine power is limited by the pump - usually a limit of 25HP to 40HPis produced per cylinder. Wear on the pumping element is accelerated due to the higher duty cycle required of it. High fuel pressure is developed by the pumping element and distributed by a rotor rotating within a hydraulic head to each cylinder in the correct firing sequence. There are two predominant type of distributor pumps, the inlet metered opposed plunger type (Stanadyne, Roosa Master, Lucas CAV,and Bosch), and the Bosch VE type with a sleeve metered rotating and reciprocating pump plunger. Other manufacturers also have distributor pumps but their principles of operation are similar. Opposed Plunger Inlet Metered Pumps
The original distributor injection pump, the Roosa Master, was an opposed plunger inlet metered pump. This type of injection pump used only one metering valve to control the fuel and either two or four opposed plungers to pump the fuel One Component, the distributor rotor, is used to distribute the metered fuel out through the hydraulic head to the injectors. These pumps have a fuel delivery capacity for engines rated between 10-40 hp per cylinder. These pumps can be found on a variety of car and truck engines and some off road and industrial applications. The original Roosa Master Company is now the Diesel Systems Division of Stanadyne Automotive Corporation. Stanadyne Model DB4 and DM4 (four-plunger) and DB2 and DM2 (two-plunger) distributor pumps are highly refined versions of the Roosa Master pump that reflect almost forty years of design evolution and improvement. In 1956, an agreement was signed which allowed Lucas CAV Ltd., of England to produce a pump based on Roosa Master's Model A distributor pump. Lucas CAV designated the original pump the Model DPA, and has continued over the years to manufacture and refine this and another distributor pump, the ROTO-Diesel. Due to their shared heritage, Stanadyne and Lucas CAV pumps are quite similar in basic design and operation. However, there are differences between specific pump models. Opposed Plunger Pump Construction. The Roosa Master, Stanadyne and Lucas CAV pump, are all manufactured according to the original Roosa Master design they are a single pumping cylinder, twin-plunger, distributor pump. This pump is lubricated by the diesel fuel it pumps. Either hydraulic, mechanical or electronic governors can be fitted to the pump. The driveshaft, pumping and distributing rotor, and sliding vane transfer pump are an integral unit. The distributor is driven by the driveshaft that couples the rotor to a drive hub located at the end of the pump housing. The Stanadyne DB4 pump differs in that it incorporates four pumping plungers rather than two.
As with the other pumps, the driveshaft engages the distributor rotor in the hydraulic head. The rotor holds the four pumping plungers. The plungers are actuated simultaneously toward each other by an internal cam ring through rollers and shoes located in slots at the end of the rotor. The number of cam lobes normally equals the number of engine cylinders. The transfer pump is also a positive displacement vane type. It is enclosed in the end cap, which also houses the fuel inlet strainer and transfer pump pressure regulator. The distributor rotor incorporates two charging ports and a single axial bore. One discharge port serves all the outlet ports 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. These pumps usually had their own mechanical governors. The centrifugal force of the weights in their retainer is transmitted through a sleeve to the governor arm and to the metering valve. The metering valve can be closed to shut off fuel by an independently operated shut-off lever. These pumps were used with pintle type injectors fueling indirect injected engines. Components The aluminum alloy pump housing of opposed plunger distributor pumps contain the driveshaft, distributor rotor, transfer pump blades, pumping plungers, internal cam ring, hydraulic head, end plate, adjusting plates, transfer pump, pressure regulator assembly, governor, automatic advance, and metering valve. Driveshaft The driveshaft connects to the engine drive gear and is supported by a bushing or ball bearing. It supports the governor assembly and drives the distributor rotor and transfer pump. The transfer pump consists of two linear blades, it delivers fuel to the metering valve located in the hydraulic head at low pressure. An end plate acts as a cover for the transfer pump. It also provides a fuel inlet to the pump and contains a pressureregulating valve that controls the transfer pump pressure throughout the speed range.
Hydraulic Head The hydraulic head is machined with bores and passages that allow fuel to flow from the transfer pump to the metering valve, from the metering valve to the charging ports, and from the discharging ports to the discharge fittings. On the latest designs, hydraulic heads have been flitted with individual delivery Valves to maintain residual line pressure and eliminate secondary injection. Distributor Rotor The distributor rotor is lap-fitted to the hydraulic head and the governor weight retainer assembly is fastened to its drive end. The plungers are fitted to the rotor and are pushed inward by the rollers and shoes to pump the diesel fuel. The rollers fit into the shoes and contact the cam in a way similar to a cam follower. Adjusting plates are mounted on the rotor and limit the outward travel of the rollers and shoes to control the fuel delivery rate. Cam Ring. A circular cam ring surrounds the rotor base and is located over the shoes and rollers. The number of internal cam lobes equals the number of cylinders. The cam ring forces the plungers toward each other which causes the fuel to be pumped. It can also be rotated back and forth about the rotor to vary the start of injection. Metering valve The metering valve contained in the hydraulic head regulates the volume of fuel entering the rotor. A piston valve is used with hydraulic governors. This valve is spring loaded and controls the fuel according to the valve's axial position. When a mechanical governor is used, the valve is a rotary type, with a slot cut in the periphery. The valve is rotated by the governor arm to regulate fuel injection. It is important to note however that as engine speed increases so too does charging pump pressure. When charging pressure changes it changes the amount of fuel that will flow by the metering valve during a given period of time, so the metering in this type of pump is accomplished through a combination of both metering valve position and charging pump pressure.
Automatic Advance and Governor An automatic advance device is located in the bottom of the pump. A hydraulic piston rotates the cam ring against the direction of pump rotation via the cam advance stud. The cam advance stud threads into the cam and connects it to the cam advance mechanism. The governor weight retainer may be permanently fixed, splined, or bolted to the rotor drive end.
Because the fuel metering mechanism can be affected by vibrations and shocks, the retainer often uses a cushioning device to isolate engine vibration and pulsation from the driveshaft. One end of the governor control arm rests against the thrust sleeve and the other end connects to the governor spring, and to the metering valve via a linkage hook. The control lever is connected to the shut-off lever and the fulcrum lever is connected to the governor spring. Pump Operation and Fuel Flow The operating principles of an opposed plunger pump can be understood more readily by following the fuel circuit during a complete pump cycle. Follow the diagram of fuel flow on the following page. The transfer pump pulls fuel from the fuel tank. The fuel passes through a water separator and secondary fuel filter before reaching the vane type transfer pump. Some systems may use a separate Lift pump to keep the vane type pump supplied, if used, it will be located between the primary and secondary filters. Once through the transfer pump, some of the fuel is bypassed to the transfer pump's suction side through the pressure regulator assembly. Fuel under pressure flows from the pump through passages in the hydraulic head to fill the pump body and to the fuel pressure regulator which bypasses a certain amount of fuel back to the pump inlet. Fuel also flows to the automatic speed advance piston, advance is controlled by transfer pump pressure. Fuel also flows through an annular groove in the hydraulic head, (the head passage), to the inlet metering valve and through a small metered orifice, (the vent wire), to the upper part of the housing then through the housing pressure regulator valve to return to tank. This keeps the upper housing under light positive pressure and prevents ingress of dirt.
The radial position of the metering valve will control how much fuel will pass through it. From the metering valve metered fuel flows to the charging passage in the hydraulic head and from there through the rotors center drilling to the pumping chamber between the plungers. When the plungers are forced together by the cam ring profile the charging passage is no longer in register with the rotor and fuel is forced to travel down the rotor center drilling through the delivery valve to one of the distributor ports in the hydraulic head and on to its attached injector. Leakage fuel from the injector is returned to the tank. As the rotor turns this process is repeated for every engine cylinder.
Later model opposed plunger pumps are computer controlled to varying extents these are known as partial authority systems. Partial Authority Systems are hydro-mechanical systems that have been modified to use computer controls and most were stepping stones toward Full Authority Systems. The pumps are fitted with an electronic governing device that controlled fuel quantity and to a certain extent fuel timing. The timing control window however was extremely short. Low injection pressures and limited control of injection timing meant the writing was on the wall for this type of pump as an on highway injection system when the 1998 emission standards were introduced and they were phased out shortly after in most cases. Bosch has recently introduced an opposed plunger distributor pump the VP44. This pump has been used on the 5.9 Cummins engines in Dodge Ram trucks, (currently these engine are equipped with Common Rail systems), and on many other on and off highway applications.
The VP-44 is a beefed up version of the original opposed plunger style pump with injection pressures of 1,800 Bar or 26,100 PSI and much more precise control over injection timing. These pumps have a solenoid valve that controls the timing of the start of injection and are used in direct injected engines.
As the pumping plungers are being actuated by the cam ring the solenoid will remain open allowing fuel the return to the charging passage until the ECM decides injection should begin. It then energizes the solenoid which seals off the fuels exit route causing pressure to build and injection begins.
VP-44 Solenoid valve (open) above and (closed) at left The ECM has complete control of the injection duration, (within the confines of the limits imposed by the lift of the cam rings lobes), and therefore injected fuel quantity. With high injection pressure, good control of timing and full control of the injected quantity this pump is vastly superior to the electronically controlled Stanadyne pump which boasted pressures of only 750 Bar or 10 to 11,000 PSI. Timing of the injection event can be further altered on the VP-44 by controlling the flow of fuel to the timing advance piston by means of a pulse width modulated pulse valve.
The Bosch VE pump is very similar to the opposed plunger type from outward appearances however the functioning and metering of the pump are quite different. It does accomplish the same end results and that is to use a single pumping element to provide fuel at injection pressures to all of the engine cylinders. The VE has a rotating and reciprocating plunger in the hydraulic head, so the rotor is still used to distribute the fuel.
Pumping in this pump is achieved by driving the base of the rotating plunger, (rotor), over a set of stationary rollers located midway through the pump body.
This causes the rotating plunger to reciprocate in it’s bore pressurizing the fuel in the same way that an in-line pump’s plungers do.
Metering. Metering in the VE pump is accomplished by sleeve metering. The sleeve can be seen in the picture on the right as item 9. The horizontal positioning of this sleeve will vary the effective stroke of the plunger and therefore vary the amount of fuel injected per cycle. The positioning of the sleeve is a product of the driver throttle input and the governor’s spring pressure. As always throttle movement and spring pressure tends to increase fueling while governor weight force tries to limit or reduce fueling.
Fuel Intake (note open fill slot and closed delivery port) Ready to pressurize (note closed fill slot open delivery port) Each time the plunger reciprocates in its bore it will create an injection pulse, (depending on the position of the sleeve), and as it also rotates at the same time it will deliver that pulse to each cylinder in sequence according to the firing order.
Pressurization and delivery Spill occurs when the axial movement of the plunger to the right causes the spill port to go past the control collar or sleeve.
Sleeve Metering is a simple process that has been used by many manufacturers in the past but Caterpillar particularly used this principle quite often. The following diagram shows a sleeve metering system with two cross drillings instead of one but the principle is the same we use the sleeve to alter the plunger effective stroke to control metering
As can be seen in the diagram above the plunger is crossed drilled in two places and a central drilling connects the two cross drillings. The centre drilling also connects to the pumping end of the plunger, (this is not visible on the above diagram), which would be at the top in the diagram above. The sleeve or collar seals the lower cross drilling and the plunger bore seals the top cross drilling. In ‘A’ above the lower cross drilling is uncovered before the top cross drilling is sealed resulting in no effective stroke or no delivery. In ‘B’ the sleeve has been moved up at little resulting in both drillings being covered for a portion of the upward stroke of the plunger giving a short effective stroke or partial delivery. In ‘C’ the sleeve is moved up to almost contact the plunger bore giving the longest effective stroke possible before the lower cross drilling is exposed this results in maximum, (or full), delivery. These pumps also have a hydraulic timing piston controlled by transfer pump pressure that allows a small timing advance related to engine speed. The relative position of all the pump components can be seen at left. Note that the vane pump and the timing piston have been turned sideways so they can be seen more clearly.
Fuel flow in the Bosch VE Fuel is drawn from the tank through a filter or a combination of a water separator and a filter by the positive displacement vane pump and delivered to a pressure regulating valve. Pressure is dependant on the valve setting and rotational speed of the pump. Fuel also acts upon the timing piston and flows through to the main pump housing body excess flow is directed through a valve and back to the tank. The pump body is full of fuel at moderate pressure when the engine is running. Fuel flows through the inlet passage in the hydraulic head and into the high pressure chamber in front of the plunger. The plunger has four inlet slots in a four cylinder application. This pump can be designed fuel up to a six cylinder engine. The plunger is also centre drilled and cross drilled.
As the plunger rotates the inlet slot becomes sealed and the discharge port lines up with one of the discharge passages in the hydraulic head. At the same time the wave plate cams will be rolling over their respective rollers causing the plunger to reciprocate to the right. This action pressurizes the fuel and delivers an injection pulse through a delivery valve to the injector. Pressurization continues until the axial movement of the plunger causes the cross drilling to come out from under they relatively stationary control collar or sleeve at which time pressure spills back into the pump cavity. So precise positioning of the sleeve controls the effective stroke of the plunger and thereby injected fuel quantity. The mechanical governed VE pump has given way to two versions that are electronically controlled and therefore are partial authority systems. These are the VP-29 and 30 pumps which electrical solenoid controlled and the VP-37 which controls the sleeve position using a variable force actuator. The VP 37 is shown at left the rotating solenoid actuator controls the sleeve or control collar position based on a pulse width modulated command from the ECM. This allows the ECM complete control over injected fuel quantity. The ECM also controls the pulse valve at the lower right of the main drawing which controls the timing advance piston position. The VP 37 pump has injection pressures of up to 1,250 bar or 18,500 PSI and can be used with direct injected engines.
The VP29 and 30 are other improvements of the VE pump. These pumps still use a rotating and reciprocating plunger/rotor but the similarities end there.
VP 29/30 In the picture above note that the plunger/rotor has no cross or centre drilling under a control collar or sleeve as the VE pump had. It has a shallow centre drilling to connect the end of the plunger, (pressure chamber), to the distributor port. The timing and duration of injection and therefore fuel quantity is controlled by the
ECM by operating the solenoid valve.
VP 29/30 Hydraulic head As the wave plate or cam plate rotates over the roller ring the plunger reciprocates to the right. During its initial movement it merely displaces fuel back to the charging passage. When the ECM decides injection should begin it energizes the solenoid and traps the fuel in the pressure chamber as this happens the rotor discharge port is lining up with one of the hydraulic head discharge ports and injection begins. Injection continues until the ECM de-energizes the solenoid. The plunger will continue its stroke but the remaining fuel is merely displaced back to the charging passage. This gives the ECM total control over injected fuel quantity and control over timing of injection within the limits of the plunger stroke. Engines with these pumps also have an injector that can sense needle lift and thereby the precise moment of beginning of injection. This tends to negate injection delay which is an inherent problem of all pump line nozzle systems. The ECM merely alters timing to compensate. The VP 29/30 is capable of injection pressures of 1,400 bar or 20,000 PSI and is used with direct injected engines. This pump also has a pulse valve to control the timing advance piston position giving the ECM further control of injection timing. The picture at left shows the pulse valve for a VP44 pump however all three type use the same pulse valve.
