Fuel Pump Distributor

7/21/2019 Fuel Pump Distributor

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Distributor Type Metering

A distributor type injection pump generally uses onepumping element to pressurize fuel for all cylindersrather than a single element for each cylinder.Conceptually, it is similar to the distributor on agasoline engine. Compact, economical pumps are

made possible but the engine power is limited by thepump - usually a limit of 25HP to 40HPis produced percylinder. Wear on the pumping element is accelerateddue to the higher duty cycle required of it. High fuelpressure is developed by the pumping element anddistributed by a rotor rotating within a hydraulic headto each cylinder in the correct firing sequence. Thereare two predominant type of distributor pumps, theinlet 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 alsohave 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 meteredpump. This type of injection pump used only one metering valve to control the fuel and either two orfour opposed plungers to pump the fuel One Component, the distributor rotor, is used to distribute themetered fuel out through the hydraulic head to the injectors. These pumps have a fuel deliverycapacity for engines rated between 10-40 hp per cylinder. These pumps can be found on a variety ofcar and truck engines and some off road and industrial applications.The original Roosa Master Company is now the Diesel Systems Division of Stanadyne AutomotiveCorporation. 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 yearsof design evolution and improvement.In 1956, an agreement was signed which allowed Lucas CAV Ltd., of England to produce a pumpbased on Roosa Master's Model A distributor pump. Lucas CAV designated the original pump theModel DPA, and has continued over the years to manufacture and refine this and another distributorpump, the ROTO-Diesel. Due to their shared heritage, Stanadyne and Lucas CAV pumps are quitesimilar 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 originalRoosa Master design they are a single pumping cylinder, twin-plunger, distributor pump. This pump islubricated by the diesel fuel it pumps. Either hydraulic, mechanical or electronic governors can befitted to the pump. The driveshaft, pumping and distributing rotor, and sliding vane transfer pump arean integral unit. The distributor is driven by the driveshaft that couples the rotor to a drive hub locatedat 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 rotorholds the four pumping plungers. The plungers are actuated simultaneously toward each other by aninternal cam ring through rollers and shoes located in slots at the end of the rotor. The number of camlobes normally equals the number of engine cylinders.The transfer pump is also a positive displacement vanetype. It is enclosed in the end cap, which also houses thefuel 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 outletports to the injection lines. The hydraulic head contains thebore in which the rotor revolves, the metering valve bore,the charging ports and the head discharge fittings. Thehigh pressure injection lines to the nozzles are fastened tothese discharge fittings.These pumps usually had their own mechanical governors.The centrifugal force of the weights in their retainer istransmitted through a sleeve to the governor arm and tothe metering valve. The metering valve can be closed toshut off fuel by an independently operated shut-off lever.These pumps were used with pintle type injectors fuelingindirect injected engines.

ComponentsThe aluminum alloy pump housing of opposedplunger distributor pumps contain the driveshaft,distributor rotor, transfer pump blades, pumpingplungers, internal cam ring, hydraulic head, endplate, adjusting plates, transfer pump, pressureregulator assembly, governor, automatic advanceand metering valve.

DriveshaftThe driveshaft connects to the engine drive gearand is supported by a bushing or ball bearing. Itsupports the governor assembly and drives thedistributor rotor and transfer pump. The transferpump consists of two linear blades, it delivers fuelto the metering valve located in the hydraulichead at low pressure. An end plate acts as acover for the transfer pump. It also provides a fuelinlet to the pump and contains a pressure-regulating valve that controls the transfer pump

pressure throughout the speed range.



Hydraulic HeadThe hydraulic head is machined withbores and passages that allow fuel toflow from the transfer pump to themetering valve, from the meteringvalve to the charging ports, and fromthe discharging ports to the dischargefittings. On the latest designs,

hydraulic heads have been flitted withindividual delivery Valves to maintainresidual line pressure and eliminatesecondary injection.

Distributor RotorThe distributor rotor is lap-fitted to thehydraulic head and the governorweight retainer assembly is fastened toits drive end. The plungers are fitted tothe rotor and are pushed inward by therollers and shoes to pump the dieselfuel. The rollers fit into the shoes andcontact the cam in a way similar to acam follower. Adjusting plates aremounted on the rotor and limit theoutward travel of the rollers and shoesto control the fuel delivery rate.

Cam Ring. A circular cam ring surrounds the rotor base and islocated over the shoes and rollers. The number ofinternal cam lobes equals the number of cylinders. Thecam ring forces the plungers toward each other whichcauses the fuel to be pumped. It can also be rotatedback and forth about the rotor to vary the start ofinjection.

Metering valveThe meteringvalve containedin the hydraulichead regulatesthe volume of

fuel entering the rotor. A piston valve is used with hydraulicgovernors. This valve is spring loaded and controls the fuelaccording to the valve's axial position. When a mechanicalgovernor is used, the valve is a rotary type, with a slot cut inthe periphery. The valve is rotated by the governor arm toregulate fuel injection. It is important to note however that asengine speed increases so too does charging pumppressure. When charging pressure changes it changes the amount of fuel that will flow by themetering valve during a given period of time, so the metering in this type of pump is accomplishedthrough a combination of both metering valve position and charging pump pressure.



Automatic Advance and Governor An automatic advance device is located in thebottom of the pump. A hydraulic piston rotatesthe cam ring against the direction of pumprotation via the cam advance stud. The camadvance stud threads into the cam andconnects it to the cam advance mechanism.

The governor weight retainer may bepermanently fixed, splined, or bolted to the rotordrive end.

Because the fuel metering mechanism can beaffected by vibrations and shocks, the retainer oftenuses a cushioning device to isolate engine vibrationand pulsation from the driveshaft. One end of thegovernor control arm rests against the thrust sleeveand the other end connects to the governor spring,and to the metering valve via a linkage hook. Thecontrol lever is connected to the shut-off lever andthe fulcrum lever is connected to the governorspring.

Pump Operation and Fuel FlowThe 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 andsecondary fuel filter before reaching the vane type transfer pump. Some systems may use a separateLift pump to keep the vane type pump supplied, if used, it will be located between the primary andsecondary filters.

Once through the transfer pump, some of the fuel is bypassed to the transfer pump's suction sidethrough 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 pumpinlet.

Fuel also flows to the automatic speed advance piston, advance is controlled by transfer pumppressure.

Fuel also flows through an annular groove in the hydraulic head, (the head passage), to the inletmetering valve and through a small metered orifice, (the vent wire), to the upper part of the housingthen through the housing pressure regulator valve to return to tank. This keeps the upper housingunder 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 themetering valve metered fuel flows to the charging passage in the hydraulic head and from therethrough 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 inregister with the rotor and fuel is forced to travel down the rotor center drilling through the deliveryvalve 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 arecomputer controlled to varying extentsthese are known as partial authoritysystems. Partial Authority Systems arehydro-mechanical systems that have beenmodified to use computer controls andmost were stepping stones toward Full

Authority Systems. The pumps are fitted

with an electronic governing device thatcontrolled fuel quantity and to a certainextent fuel timing. The timing controlwindow however was extremely short.Low injection pressures and limitedcontrol of injection timing meant thewriting was on the wall for this type ofpump as an on highway injection systemwhen the 1998 emission standards wereintroduced and they were phased outshortly after in most cases.

Bosch has recently introduced anopposed plunger distributor pump the VP-44. This pump has been used on the 5.9Cummins engines in Dodge Ram trucks,(currently these engine are equipped withCommon Rail systems), and on manyother on and off highway applications.

The VP-44 is a beefed up version of the originalopposed plunger style pump with injectionpressures of 1,800 Bar or 26,100 PSI and muchmore precise control over injection timing. Thesepumps have a solenoid valve that controls thetiming of the start of injection and are used indirect injected engines.



As the pumping plungers are beingactuated by the cam ring thesolenoid will remain open allowingfuel the return to the chargingpassage until the ECM decidesinjection should begin. It thenenergizes the solenoid which seals

off the fuels exit route causingpressure to build and injectionbegins.

VP-44 Solenoid valve (open) above and(closed) at left

The ECM has complete control of the injectionduration, (within the confines of the limits imposed by

the lift of the cam rings lobes), and therefore injectedfuel quantity. With high injection pressure, goodcontrol of timing and full control of the injectedquantity this pump is vastly superior to theelectronically controlled Stanadyne pump whichboasted pressures of only 750 Bar or 10 to 11,000PSI. Timing of the injection event can be furtheraltered on the VP-44 by controlling the flow of fuel tothe timing advance piston by means of a pulse widthmodulated pulse valve.



The Bosch VE pump is very similar to theopposed plunger type from outward appearanceshowever the functioning and metering of thepump are quite different. It does accomplish thesame end results and that is to use a singlepumping element to provide fuel at injectionpressures to all of the engine cylinders.The VE has a rotating and reciprocating plunger

in the hydraulic head, so the rotor is still used todistribute the fuel.

Pumping in this pump is achieved by driving the base ofthe rotating plunger, (rotor), over a set of stationary rollerslocated midway through the pump body.

This causes the rotating plungerto reciprocate in it’s borepressurizing the fuel in thesame way that an in-linepump’s plungers do.



Metering.Metering in the VE pump is accomplished by sleeve metering. The sleeve can be seen in the pictureon the right as item 9.The horizontal positioning of this sleeve will vary theeffective stroke of the plunger and therefore vary theamount of fuel injected per cycle.The positioning of the sleeve is a product of the driverthrottle input and the governor’s spring pressure. As

always throttle movement and spring pressure tends toincrease fueling while governor weight force tries tolimit or reduce fueling.

Fuel Intake (note open fi ll s lot andclosed delivery port)

Ready to pressur ize (note closed fi ll slotopen delivery port)

Each time the plunger reciprocates in its bore it will create an injection pulse, (depending on theposition of the sleeve), and as it also rotates at the same time it will deliver that pulse to each cylinderin sequence according to the firing order.

Pressurization and deliverySpill occurs when the axialmovement of the plunger to the rightcauses the spill port to go past thecontrol col lar or sleeve.



Sleeve Metering is a simple process that has been used by many manufacturers in the past butCaterpillar particularly used this principle quite often. The following diagram shows a sleeve meteringsystem with two cross drillings instead of one but the principle is the same we use the sleeve to alterthe 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 drillingconnects 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 sleeveor 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 noeffective stroke or no delivery.In ‘B’ the sleeve has been moved up at little resulting in both drillings being covered for a portion ofthe 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 alsohave a hydraulictiming pistoncontrolled bytransfer pumppressure thatallows a smalltiming advancerelated to enginespeed.The relative

position of all thepump componentscan be seen atleft. Note that thevane pump andthe timing pistonhave been turnedsideways so theycan be seen moreclearly.



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 thepositive displacement vane pump and delivered to a pressure regulating valve. Pressure isdependant 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 flowis 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 hydraulichead and into the high pressure chamber in front of

the plunger. The plunger has four inlet slots in a fourcylinder application. This pump can be designedfuel up to a six cylinder engine.

The plunger is also centre drilled and cross drilled.



As the plunger rotates the inlet slot becomes sealedand the discharge port lines up with one of thedischarge passages in the hydraulic head. At thesame time the wave plate cams will be rolling overtheir respective rollers causing the plunger toreciprocate to the right. This action pressurizes thefuel and delivers an injection pulse through a deliveryvalve to the injector. Pressurization continues until

the axial movement of the plunger causes the crossdrilling to come out from under they relativelystationary control collar or sleeve at which timepressure spills back into the pump cavity.

So precise positioning of the sleeve controls the effective stroke of the plunger and thereby injectedfuel quantity.

The mechanical governed VE pump has given way to two versions that are electronically controlledand 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 usinga variable force actuator.The VP 37 is shown atleft the rotating solenoidactuator controls thesleeve or control collarposition based on a pulsewidth modulatedcommand from the ECM.This allows the ECMcomplete control over

injected fuel quantity.The ECM also controlsthe pulse valve at thelower right of the maindrawing which controlsthe timing advance pistonposition. The VP 37pump has injectionpressures of up to 1,250bar or 18,500 PSI andcan be used with direct

injected engines.



The VP29 and 30 are other improvements of the VE pump. These pumps still use a rotating andreciprocating 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 orsleeve as the VE pump had.It has a shallow centre drilling to connect the end of the plunger, (pressure chamber), to thedistributor 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. Duringits initial movement it merely displaces fuel back to the charging passage. When the ECM decidesinjection should begin it energizes the solenoid and traps the fuel in the pressure chamber as thishappens the rotor discharge port is lining up with one of the hydraulic head discharge ports andinjection begins.

Injection continues until the ECM de-energizesthe solenoid. The plunger will continue itsstroke but the remaining fuel is merelydisplaced back to the charging passage. Thisgives the ECM total control over injected fuelquantity and control over timing of injectionwithin the limits of the plunger stroke.

Engines with these pumps also have aninjector that can sense needle lift and therebythe precise moment of beginning of injection.This tends to negate injection delay which isan inherent problem of all pump line nozzlesystems. The ECM merely alters timing tocompensate.The VP 29/30 is capable of injection pressures

of 1,400 bar or 20,000 PSI and is used withdirect injected engines.

This pump also has a pulse valve to controlthe timing advance piston position giving theECM further control of injection timing. Thepicture at left shows the pulse valve for a VP-44 pump however all three type use the samepulse valve.

Fuel Pump Distributor

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