| Knock Sensor Box
0 261 201 003
for BMW 745i
The Knock Sensor Box is integrated part of the BMW 745i Motronic Engine
Control System. It can operate only with the Motronic box 0 261 200
013 or 0 261 200 024 and vise wersa. The engine control lines are devided between these two
boxes. For further information of the system schematic diagram and wire harness
connections please see the "Motronic" and "Downloads" sections in our web.
In this section you will find:
* Guidelines how to connect new control line for additional magnetic valve to the boost control system
* Simplified schematic diagram of the knock signal chain inside the knock box.
* Photographs of the connection points inside the knock box.
* Datasheet of ca3080.pdf Operational Transconductance Amplifier (part of the signal chain)
* Datasheet of the lm2902n.pdf Operational Amplifier ( part of the signal chain)
* Binary code of the Intel 8435 Microprocessor program , which is the heart of the knock box. This is for all of you computer specialists who want to know more of how the box operates.
For better understanding of the whole system I recommend that you read/download related info from the "Motronic", "Wastegate" and "Downloads" sections.
The Knock Box
The box is located above the glove compartment.
As I said earlier, the Knock box is integrated part of the Motronic System and it preprocesses following incoming signals before sending the results either to the main Motronic unit or to the magnetic valve (of wastegate):
* From two piezo ceramic knock sensors
* From throttle potentiometer
* From the intake manifold via a air hose. You can see the pressure sensor on the analog part of the knock sensor box PCB. Special note: In the middle of that hose in the engine side ( see this picture) is a special pressure valve. That valve operates properly only in one direction. Sometimes people install it the other way around and then you can's get more than about 2500 RPM's out of the engine.
* From automatic gear box
Installation of extra control line from the knock sensor box
Why do we want to have an extra control line from the knock box? The "Wastegate" section gives you more detailed explanation of different set-up possibilities for the turbo boost and engine protection, but here's the key point:
By having a pure control line directly from the knock sensors we can lower the engine power at any high boost level immediately when knock occurs. The same line can also be used for knock indicator lamp or LED.
Here is the simplified schematic diagram of
the connection (click to enlarge). The resistor in the output of LM2902 is
the middle one between resistors R123 and R105 as shown in the photographs
|Knock sensors are piezo ceramic elements, which provide signal when the engine block vibrates at 5...10 KHz. The signals come to pins 6 and 9 and are first filtered and summed. CD4066 is a CMOS analog switch controlled by the Intel 8435 Microcontroller. First amplification stage is CA3080AE, Operational Transconductance Amplifier, a very sensitive, low power amplifier. The second stage is 1/4 of LM2902 OpAmp, which can provide high output voltage swing. The output of this amplifier is a good point for the new control line. below are pictures of the printed circuit board showing some alternative soldering points.|
This is as far as I have come with the design. As I don't know when I will
have time to finalize the design please feel free to make your own control
system based on this idea/basic work. I know that many of you have been waiting
for this. Treat it like a shareware program; you can use this for yourself,
but leave the commercial utilization to me. If you come up with a good design
let me know and we make it a commercial product together and sell it in my
web pages. If/when I have time to work more on this I will update these pages
accordingly. I am glad to put your inputs here also.
I have one extra knock box for this purpose, which I can loan to someone, who is interested to work on it.
Some design notes:
* I have not measured the output signal from LM2902
* Use fairly high input impedance inverter/magnetic valve driver. That way the signal from LM2902 will not be distorted. We are only interested in the voltage swing anyway, so no current drive capabilities are required.
* Use ground from Motronic wire harness ( see connection/schematic diagrams).
* I assume that there are several different ready made inverters and magnetic valve drivers available from automotive electronics manufacturers. I just have not yet had the time to source those.
In general, the basic concept is fairly simple and straightforward, which any electronic engineer can finalize quite easily.