VW Knock detect

[Bernd Felsche]

Stephen Webb tapped away at the keyboard with:

> My project is an '89 VW Cabriolet + a turbocharger.  It's CIS
> injection, not EFI, so I've been somewhat reluctant to bring it
> up.  My focus right now is on the ignition system, which I suppose
> isn't strictly EFI, but I believe is still "on topic" for the
> list.  I want to build an ignition control circuit for the
> vehicle.  It was not originally equipped with a knock sensor, but
> I would like to add one.  

The _easiest_ way to add knock sensing is to use the ignition module
off a K-Jet car with knock sensor.

> I would like to build a circuit that does the following:
> 1. Ignition timing map based on MAP and engine RPM.
> 2. Engine knock detection --> ignition retard.
> 3. Electronic boost control, RPM based
> 4. Idle air stabilizer valve control

That's beginning to sound like a complete ECU.

> Some of this has changed somewhat because my PIC programmer can't deal
> with some of the higher end PICs (I planned on using built in PWM support
> for the IAS valve, and other features made it easy to do multiple things
> at once)

> For now the three issues are:
> 1.  Safely/correctly interfacing the micro with the hall sender.  
> 2.  Safely/correctly interfacing the micro with the [stock] ignition
> control module. 
> 3.  Correctly detecting knock from the knock sensor.

That last one is a tough one.

> I've read the Blue Bosch FI book, and it mentioned engine knock
> producing some frequency.  I believe the Bosch Motronic book said
> that it was typically in the 5kHz range.  One paper I read said

The frequency is largely determined by the bore of the cylinder.

[snap]

> So, I'd like to learn more about engine knock, and in particular
> detecting it with a "Bosch style" knock sensor. 

Look at the HIP9010 data sheet and application notes. They give you
a fair idea of what's required. e.g. knock detection windows.

A large number of SAE papers also deal with knock detection and
characteristics; use the search facility at http://www.sae.org

-- 
 /"\  Bernd Felsche - Innovative Reckoning, Perth, Western Australia
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