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InputTrigger/AudiTrigger (2006-03-16 04:43:08)

Page for the 135-tooth, 3-signal trigger system found on many 5cyl audi engines

Note that for GenBoard/VerThree v3.3 the trigger HW was modified so it can directly use the 3 input signals from the Audi wheels (2 VR crank + 1 HALL cam).

We thought the firmware mod is necessarily complex, but it is not the case. Firmware mod was done in an afternoon, testing and polish is still needed

for this mod is still needed''', and testing of course.

HW mod for a v3.0 .. v3.2

is easy: connect the pullup of secondary LM1815 output to cam-HALL signal instead of direct 5V. Ask for help if this is not clear.

multitooth Audi crankwheels

The old Five cylinder engines with electronically controlled ignition have 2 VR sensors and a hall sender. One of the VR sensors sense the starter gear (135teeth for 5cyl), the other VR sensor sense ONE pin in the flywheel located at 62deg before #1 TDC. This pin is used as a reference. The hall sender is in the distributor, and the hall trigger wheel has ONE slot acting as CAM reference. CAM ref and the Crank pin must overlap each other for the engine to start in the stock application. These engines use a homebrew ignition module with a visible TO-3 transistor in the ignition coil console. (at least the ones I have seen) Igniton computer is made by Hitachi (MAC-xx).

The small spacing between the teeth makes it impossible to synk the engine without the pin in the flywheel.

Signal timing graph from 5-cylinder MC-engine:

audi_mc_trigger.gif

The same type of triggersystem is used on many older Audis, even the Audi V8 had it until it was replaced with the A8. The engines with an even number of cylinders has an 136teeth flywheel to make everything add up.

Solution:

The simplest way to do it is to intercept the signal from the 62BTDC pin after the VR interface. AND it with the hall sender signal from the distributor and pass it on to the AVR secondary-trigger input.

The camsync masks out one of the two crank-home-pulses (for each cam rotation). This way the secondary trigger the AVR sees is timed from crank, but only 1 for each cam-rotation (suitable for 5cyl ign). Effectively a 'cam ref signal' with no slop at all.

135 interrupts per crank-rotation still needed, but the interrupt code is much shorter than for 60-2 wheels, allowing > 20000 RPM:

We thought that 135teeth takes up too much CPU time. After thinking about it, it seems that the multitooth processing code can be bypassed altogether, so the CPU load would be smaller than for 60-2 wheel.

Anyway, we use the tooth pulse after the CAM SYNK pulse direcly. Then we let every 270/5=54th (72deg in cam) signal through and so on.

TODO

The sloppiness seems to be small,see [image1] and [image2]

Configuration

We must start from a coiltype + camsync setup (maybe like MembersPage/MichaelRichards/Projects/NicksGTX don't forget the reset_engphase_after and tooth_twidth.. variables!). Maybe don't even disable primary trigger filter. Just

TODO: assume fire order 53124 because of the actual secondary-trigger pulse phase. This is same as 12453 but from different starting point. Update the tables below to match.

Other Audi triggers:

There is also an other audi trigger arrangement on the older audis that don't have a knock sensing ignition. They only have a 5 slot trigger wheel in the distributor and no crank trigger and a hall sender controlling a auto dwell ignition module. If a few degrees of ignition inaccuracy is acceptable one of these distributors can replace the entire ignition system on the computer controlled cars.

The later models have a standard Motronic triggerwheel and a CAM synk sensor.

Header for easy switch between primary_trig=HALL and 3 signal audi-trigger

For an assembled controller, one wants to avoid too many clamping/unclamping. (assemble/disassemble)

The alubos endplate is very easy to remove, unclamping is not needed. The trigger section can be reached for soldering or measuring with just the alubos endplate removed. However the onboard mounted MAP sensor makes it impossible to reach the connections.

Choices:

I had to apply relatively much hotmelt to prevent the header from shorting on anything (it might take 4..5 minutes of scratching to clean the header when one wants to change it: but at least only the endplate must be removed for it). 3 DIP switches would work for the same too. Are DIP switches acceptable in a car? I would say that they are, I have never heard of problems with the engine management systems that have it. we could make a backup solution with proper smd jumpers too.

See also: