Agreed, and I did ponder the name choice when I was hypothesising

I came to the conclusion that they were pots because:

i) that's how they're drawn in the diagram (weakest reason)
ii) there are two shown, which allows for a differential 'sanity' check (as the TPS electronics does).
iii) Something that simply detects movement doesn't provide an absolute position value that is needed to store in memory.

A photointerrupter would be a robust sensor as there's not much to wear out, but I don't see a slick way to represent and store the motion end stop positions. It can only be a pulse count - but from what reference point?

Thinking about it, they might be Hall-effect devices instead of mechanical pots?

 

I have an ME, not an EE background, but as a broader question if you are going through the work of adding multiple potentiometers for comparison checking, how much more expensive would it be to use a stepper motor and the associated controller to make that work, with a microswitch to home with?

 

The set-up would be exactly as it is on the car now - hold the button down to fully open the window - zero the counter (zero now means fully open), then start counting pulses as the window is closed. Once in the fully closed position you now know how many pulses between open and closed and you know the window is fully closed (along with the fully closed count value). After that you just decrement the counter with every pulse as the window is opening and increment the counter with every pulse as the window is closing. To drop the window on door opening, run the motor for a set number of pulses, decrementing the counter as you do it, then do the reverse to close it again.

On fully opening/closing I would imagine the controller would stop the motor just before reaching the fully open/closed position, rather than stalling the motor.

Of course you never know where the window is in absolute terms, just where it should be relative to the original fully open/closed positions - hence why reprogramming it every time the battery is disconnected might be a good idea from a design point of view.

This approach compared to pot(s) would be mechanically much simpler, no gearing needed, no resistance values that change with temperature (which would explain why two pots would be necessary), no A2D converter needed etc. The only way to find out is to take an old window motor apart and have a look.

 

My apologies, I think you're right with this.
Looking at pictures of the mechanism, all the wiring seems to come from the motor, or the gearbox that engages with the winder toothed quadrant. That implies multiple turns needing multi-turn pots or some other gearing down.

Two outputs are needed to determine direction as well as count so that fits, too. The current counter value would represent the current window position and will be valid along with the upper & lower limits while sufficient power is maintained.

Cheers!

 

It doesn't need to sense the direction, just movement - the controller already knows which way the motor is supposed to be turning.

I think we have come up with a very convincing argument as to what the calibration process does.

The window motors are Bosch parts - number 0130821318 (which I think is for the right window) and 0130821317 for the left. I couldn't find any data sheets on them on the internet, so until someone takes one apart this is still speculation unfortunately.