Injection pump

Drivbiwire · February 19th, 2003, 09:53

A question was asked the other day and I replied to it, after rereading it I thought posting it in the 101 section would be a good way to find the post with a forum search for new members under the header of "Injection Pump".

Enjoy!

Information is relevant for the A3/B4 and also the A4 TDI using the VE series injection pump. PD motors replace this pump with more advanced individual pump injector units.

Inside the TDI injection pump there is a "Cam Plate" that is turned by the pumps timing belt pulley. The cam plate is also turning a small "Plunger", these two assemblies rotate in unison. The rotating plunger is mounted to a stationary plate or "Roller Ring" that has four rollers that provide the contours for the spinning cam plate to follow and cause the plunger to extend in and out on. The cam plate contours are what determines how far the plunger slides in and out of the fuel compression chamber and the size of the contours are what can vary from year to year effectively determining how hight the fuel pressures can reach. Since the roller ring assembly (fig 2) is "mostly" stationary the compression of the small amounts of fuel can occur at exactly the same time. The caviate to this is that the roller ring assembly can be rotated slightly clockwise or counter clockwise effectively adjusting when the compression of the fuel actually occurs without having to integrate a complex system for injection timing.

The looming question is how do you control the quantity of fuel ie speed of the motor? The above describes how you effectively create fuel pressure and adjust timing but the next key is the "Fuel Collar" (Fig 7). The fuel collar is a simple ring that the plunger slides through during each and every injection stroke. In the plunger there is an elongated hole (figure 5, top) that when uncovered allows all remaining fuel in the compression chamber to be vented back into the internal body of the pump effectively ending the fuel delivery for that cylinder. This means that all unused fuel is simply vented internally without having to flow to and from each injector. The injectors ONLY recieve what is needed and the fuel collar is what directly determines engine speed and power output.

So internally you have an oscilating and rotating plunger that aligns with the four or in some cases 5 or even 6 outlet ports depending on the pump layout. In the case of the VW ALH TDI, with every complete horizontal stroke of the plunger, the plunger itself rotates 90 degrees. This means that it goes from start point to full extension and back as it rotates a complete 90 degrees of rotation. With one full 360 degrees of rotation the plunger will actuate 4 complete injection events while varying timing and injection quantity on each and every stroke.

The collar is controlled by an electrical servo that receives its control signal from the cars ECU. The computer looks at all engine sensors and determines when and how much fuel to inject.

On each injector there are fuel return lines. Since the insides of the injectors are not perfect there is sometimes some fuel that is leaked internally. Rather than allowing that fuel to remain in the injector Bosch allows for a return line to return that fuel back to the cars fuel filter where it is recirculated, filtered and eventually burned in the engine.

The pump can be described as having 2 seperate pumps. The first is often described as a "Low Stage Vane type pump" This provides "Head Pressure" to make the fuel push its way into the plunger chamber fast enough not to allow cavitation of the plunger. The pressure of the pump is around around 100 psi. When the plunger compresses the fuel the pressures can reach as high as 19,000 psi at the fuel nozzle.

Hope that helps.

DB

[ February 20, 2003, 08:24: Message edited by: Drivbiwire ]

gern_blanston · February 19th, 2003, 20:03

Cool techno stuff. That's one of the things I love about this car: Useful technology instead of technology for technology's sake, like so many manufacturers purvey.
Ahhhh, to be in the Flight Levels.

Drivbiwire · February 19th, 2003, 20:06

Salem huh! I am going to be in PDX this weekend and I will have some time to meet up on Saturday. Drop me an email if your interested in meeting up.

DB

LanduytG · February 20th, 2003, 02:51

Pete
The control collar is fig 7. Youhave fig 4.

Greg

Drivbiwire · February 20th, 2003, 08:23

Good catch! Thanks [img]images/icons/grin.gif[/img]

DB

gdr703 · February 20th, 2003, 09:02

Most interesting, Thank you.
I think I got it.
The fuel pump plunger always travels the same distance, it is the collar that determines when the plunger is pressurising fuel. So on over-run the collar completely uncovers, and the plunger just moves through its cycle without pressurising anything. So the pump is not pressurising fuel unecessarily.
The fuel return line from the injectors is merely for injector leakage, so the flow will be very small.
The timing of the fuel injection on small throttle openings will be slightly advanced when compared to a large throttle demand. Unless this is compensated for by the ECU by adjusting the start of injection cycle.
The other obvious observation is the importance of adequate lubrication in this fine piece of engineering.
once again, thanks for the detail

dzljet · February 20th, 2003, 09:38

Pete,
good write up, thanks.

This BTW folks is something we need to see more of that harkens back to "Old Skool" tdiclub and is a welcome site from all the bickering that has gone on entirely too long and degenerated the value of this board.

Huzah, Pete!!!

Perhaps, we could get someone else with time and energy to write up how "tuning boxes" come into play and their pro's and con's.
Just make sure it maintains the same quality. [img]images/icons/wink.gif[/img]

TDIRookie · February 21st, 2003, 07:35

FWIW, the whole Bosch VE manual (66 pages) that this came from is available from SAE's website (www.sae.org/ do a search for Bosch VE) in a PDF download for $14.95 US. I actually downloaded it this morning to use on my Dodge Cummins truck, wasn't sure that it was the same pump as the VW. IMHO, for $14.95, you can't beat it. Everything anyone wants to know about the way that the pump works should be in here. I used to write this stuff for a living and I would really recommend it.

Joe

gern_blanston · February 21st, 2003, 11:41

drivbiwire. Sorry, been in Florida all week. Gotta' fly this weekend, too, or maybe we could hook up. Howw do I contact you via e-mail

Drivbiwire · March 26th, 2003, 08:09

Drivbiwire · November 17th, 2003, 20:03

Thought I would refresh this thread

DB

Growler · December 22nd, 2003, 16:45

WOW, you learn something new every day.

Thank you drivebywire for writing this up for all to learn from.

Aaron

Birdman · December 22nd, 2003, 18:25

[ QUOTE ]
The fuel return line from the injectors is merely for injector leakage, so the flow will be very small.

[/ QUOTE ] Not that small if the hose breaks or more likely rots it will soak the engine very fast. changing return line every 3-4 years is a good idea. When i got my PP205 injectors set up on installing them I must have hit the injector on the end with the rubber boot and a day or so later stopping at a light there was what looked like steam coming from under the hood, the leak was spraying out a pin hole about 2 feet. sure makes a mess.

Drivbiwire · July 7th, 2004, 21:54

Bump this too the top

DB

Kiwi_ME · July 8th, 2004, 22:44

So here's a question. I wonder if wear debris from the "Low Stage Vane type pump" would cause eventual damage to the high pressure pump?

I'm not seeing the exact fuel flow path but perhaps there is a small filter in there somewhere.