fuel injection pump addendum

[jeffc280sl]

After adjusting the air fuel ratio of my fip I decided to buy one to learn in more detail how the pump operates.  I thought I would suppliment the work of JA17 with some detailed views of the insides of this incredible fip.  The attached photograph shows a view of the rear on the fip with it's cover removed.  I've identified the main rack adjustment rod, the throttle rod, space cam, stylus and fly weights.  The operation is very, very complex so I'm going to just discuss what happenes when the throttle linkage is moved on the outside of the pump.  Imagine if you can that the engine is idling in neutral.  The flyweights are in and restricted by there springs  (more about that later).  As you step on the gas pedal the throttle linkage inside the pump rotates the space cam up to approx 90 degrees clockwise.  90 degrees clockwise would have the pump at full throttle.  As the space cam rotates because of throttle changes the stylus reads unjulations in the surface of the space cam and directly adjiust the rack and fuel volume to the engine.  To add another layer of complexity to the operation of the stylus and space cam as the rpms increase the space cam is allowed to move towards the rear of the pump and the stylus reads another track so to speak on the space cam.  Working together the space cam, stylus, rack and flyweights are in effect similar to a modern engine management system.  The fly weights help determine engine load by constantly being updated with rpm inputs.  At various load factors the fly weights which are rpm sensative adjust the space cam so that it moves forward or backwards. The throttle rotates the space cam up to 90 degrees cw so the stylus will read a different section of the space cam and adjust the air fuel ratio accordingly.


If any of this is unclear or in error please let me know.

[ja17]

Hello Jeff,

Nice supplimentary information!  Mercedes refers to the cam as the "three dimentional cam". Unlike the lobes on a standard camshaft which are two dimentional.

Yes the rack controls the amount of fuel allowed into the cylinders of the injection pump.  Four inputs control the rack.........Linkage position, engine rpm, engine temperature, and barametric pressure/ altitiude. All interact together through a maze of levers, pivots, springs and such.
Maybe we can add your information (with credits) to the Injection Pump Tour so it can all be found in one place?

As I said in the past,  "these injection pumps are marvels of German Engineering."

[66andBlue]

Jeff,
very informative, thanks!
Is this an early (230SL) pump, or one of the later models?

[jeffc280sl]

Thanks Joe.  They are indeed marvels.  I can't believe the tolerances and interactions of the stylus, 3D cam and various levers springs ...

This pump is a later 22Y pump which I believe is interchangeable with the 24Y pump on my 1970 280SL. 

I'm going to try and take some pics of the baro and wrd control levers.  I now fully understand what JA17 means when he says the baro directly effects the rack.  Maybe some pics will help to explain.

[jeffc280sl]

I just remembered that I had this diagram on my hard disk.  It makes more sense now that I have a pump to look at.  Take the words from my first post along with Joe's and then look at the diagram.

[PnHi]

How much different are the diesel pumps from this era?

[ja17]

Hello,

The diesel injection pumps of the era were very similar in many ways and quite different in others. They were both mechanical. The diesels operated at a much higher pressure over 1,000 psi at the injectors as opposed to the 140psi of the gasoline version of the era.  They both had pistons, plungers, a rack etc.   The rack on the diesel pump was mainly controlled by engine vacuum which is even a factor of the gasoline injection pumps. Many of the major castings and the basic configuration of the two have a striking resemblance.  You can tell that the gasoline injection pump evolved from the earlier diesel pumps.  The original 300SL gasoline injection pumps even were more closely related.  They did have an engine vacuum controlled mixture function.

[awolff280sl]

Jeff, have you thought about somehow adapting a device that would be sensitive to an O2 sensor in place of the barometric compensator?

[jeffc280sl]

Andy,

Do you mean a device that would read afr from and O2 sensor and then adjust the rack where the baro currently does?

[awolff280sl]

Yes. You have demonstrated how we can use modern sensors and computers to TUNE our pumps. So I was wondering what if the BC could be "upgraded" to say a servo device that is dynamically responsive to an o2 sensor, and that would move the rack (on the order of tenths or even hundredths of mm), as required by driving conditions.

[jeffc280sl]

Interesting idea.  Now that my fip is tuned I think I'll let it manage the afr. 

[jeffc280sl]

Here is another picture of the insides of the fip.  This picture shows the location of the barometric compensator and wrd .  It's hard to see from the picture but the baro directly effects the control rack.  I placed red arrows on the control levers impacted by the baro.

[jeffc280sl]

I thought I would post a picture of the space cam.   The varying surface of the  space cam represents the airfuel ratio program which is read by a stylist and transferred to the rack.  The space cam can rotate up to 90 degrees clockwise and is directly controlled by the throttle lever.  The space also moves forwards and backwards as engine rpms go up and down.