726 Bosch VP44 radial plunger type pump

The VP44, Fig. 7.55, is described by Bosch as a high pressure electronically controlled radial plunger type pump. Its housing is divided by a diaphragm into two chambers. One, at fuel lift pump delivery pressure, accommodates the drive shaft and all the components mounted on it. The other, at a much higher pressure, houses the distributor head and shaft. In the base of the pump housing is the device for regulating the timing of the start of injection, together with the pulse valve which influences the timing device by modifying the hydraulic pressure applied to its piston. Mounted on top of the housing is the pump control unit (PCU), which operates in association with the engine electronic control unit (ECU).

With electronic control, response to demands for changes in injection timing is rapid. Therefore, the timing and the rate of delivery of fuel can be matched accurately to the continuously changing requirements. Rapid response solenoids meter the delivery of fuel into the cylinders, so multi-stage injection can be provided. Because the work of pumping the fuel is shared between either two or four radial plungers, the VP44 is inherently more durable and

How Vp44 Injection Pump Works
Fig. 7.55 The Bosch VP44 radial plunger type pump

capable of delivering higher performance than the VE type, with its single axial plunger.

Based on the original Vernon Roosa principle, Section 7.31, this pump is broadly similar to the others described in this chapter, although it differs considerably in detail. Provision can be made for any of the usual types of drive: toothed belt, gear, chain wheel or coupling. The shaft is driven at half engine speed.

Inside the low pressure chamber, the first item on the drive shaft is a spline-driven, vane type transfer pump, termed by Bosch the supply pump. It draws fuel from this chamber and can deliver it at more than 1000 bar to the high pressure chamber around the distributor shaft.

Next to it is a toothed wheel, termed the angular encoder, for indicating directly the rotational speed and angle, or phase, of the pump, and therefore indirectly of the engine crankshaft. Then comes the cam-ring assembly and, finally, the ball type intermediate bearing carrying the rotating assembly in the pump casing. This bearing, and with it the whole assembly on the drive shaft, is retained by a circlip in a groove around the end of the shaft.

The distributor shaft is spigoted into a counterbore in the end of the drive shaft. To keep the overall length of the pump to a minimum, a plate type coupling is employed for transmitting the drive between the two shafts. It resembles a large washer, from which two diametrically opposite lugs extend radially outwards into slots in a flange on the end of the drive shaft. Two slots in its inner periphery, on an axis 90° to that of the lugs, receive pegs extending radially outwards from the periphery of the distributor shaft. The path of the drive is therefore from the drive shaft through the lugs to the plate, and thence through the slots and pegs to the distributor shaft.

Integrally formed on the distributor shaft, immediately beyond the two pegs, is the hub of the radial plunger pump. It houses the diametrically opposed radial plungers of the high pressure pump. Around them is the cam ring, which is retained by a circlip in a groove in the pump casing. The distributor shaft rotates in a sleeve in the distributor head. An extension of this sleeve bears against the hub of the radial plunger pump, and carries the inner race of the previously mentioned ball bearing the outer race of which is clamped between the cam ring and the hydraulic head.

Next to the ball bearing is the diaphragm that separates the high and low pressure chambers in the pump. On the low pressure side, adjacent to the bearing, it is retained by a circlip around the sleeve, and an O-ring seal is interposed between its face remote from the circlip and a shoulder on the sleeve. An O-ring in a groove round the rim of the diaphragm seals it in the distributor head. The high pressure chamber therefore is formed entirely in the distributor head.

The lift pump delivers the fuel from the tank into the chamber to the left of the diaphragm, as viewed in the illustration, whence it passes through a duct to the vane type supply pump. This delivers it at a considerably higher pressure into the chamber to the right of the diaphragm. Thus, all rotating components on the drive shaft are lubricated by fuel at lift pump pressure. In a counterbore in the right-hand end of the distributor shaft is a needle valve, which is actuated by a solenoid in the end of the pump housing. This valve controls the quantity of fuel injected per shot.

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  • selassie
    Does the plunger in the bosch vp44 rotate?
    4 years ago
  • sini
    How a vp44 injection pump works?
    4 years ago
  • alide
    How an injector pump works?
    2 years ago
  • Randy
    How does a bosch vp44 pump work?
    2 years ago

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