The rollers run inside a movable ring containing the lobes and whose angular position is controlled by the timing plunger (piston).Reading the streams on this and other forums, it seems that about the only two things we know for sure about the BOSCH VP44 is that they cost a bunch of money and, if you dont run a FASS Titanium, theyre gonna burn up.The VP44 sticky on this forum gives a lot of information about what the VP44 does, but precious little on how it does it.
Several years ago, I decided there must be more to them than this. I have also carefully read and filtered information from a number of forums. Information taken from Mopar1973mans actual tear down of a VP44 and his accompanying photos and discussions were very helpful. There is an outstanding, detailed description of VP44 internal operation on YouTube. Unfortunately, the audio is in Spanish, but it pretty well backs up my description of its operation. Although the VP44 is a precision device manufactured to extremely close tolerances, its not a magic box and the basic mechanics that allow it to accomplish its job are easily understood; its the control system that makes it more like rocket science. There is a lot more detail to the operation of VP44 than I cover here, but here are the basics: The Bosch VP44 is an electronically actuated, solenoid needle valve controlled radial piston Distributor Fuel-Injection pump. Low Pressure Stage: Internal feed pump (vane pump), Pressure Regulator, Accumulation Chamber, and Overflow Valve. High Pressure Stage: Radial Piston (plunger) High Pressure Pump, Distributor Shaft, Solenoid Valve, and Delivery Valve. Timing Control: Angular encoder, Timing Ring, Timing Piston and Timing Control Valve (TCV) 4. Electronic Control Unit (also called the PCM (Pump Control Module)). ![]() I bought my truck new in the autumn of 2002 and it is going on 187000 miles and 13 years; others have gone a lot more than that. Here we go: The High-Pressure Pump: The rotating parts of the VP44 are gear driven at camshaft speed (12 engine crankshaft speed). It is mechanically fused so that anything that locks up the distribution head will not destroy the drive gears. The VP44 uses a 3 roller (cam followers)6 lobe cam ring (one lobe for each cylinder) cam-driven radial piston high- pressure pump to compress fuel to a pressure sufficient to open a fuel injector. All three rollers (arranged 120 degrees apart radially) are cammed in at the same time, compressing fuel by use of cam followers and pistons (Plungers) in a central compression chamber (Plunger Chamber). This pump can raise pressure to as high as 1500 bar (21,750 PSI). ![]() This distributor shaft contains passages that determine where the fuel comes and goes in the distributer head and which cylinder will be fueled. The sequence of the VP44 outlet is consecutive in a rotating manner (A-B-C-D-E-F); the sequence of the cylinders that the fuel goes to is determined by the piping arrangement from the VP44 output (153624). One revolution of the distributor shaft delivers fuel to each of the six injectors (two revolutions of the engine crankshaft (four stroke engine)).
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