vehicle rpm based switch- help

[pilottx]

Hi all

Hope this is the right place to ask this type of question??

I'm looking for simple schematic so I can build a simple switching device based upon an engines rpm speed. The rpm signal will be provided by the vehicles ECU.
The purpose would be to control some form of air valve which would be closed upto 3000 rpm ish then open thereafter. If anyone can offer any help it would really be appreciated..


Thanks

Pilottx

[ante]

Hi pilottx,

Welcome to our forum,

Is this for the NO2 valve? ;D
What kind of output do you get from the ECU, pulsetrain or a voltage or something else?

[Tony_Stoynov]

Hi,
if the output is a digital, PWM or Impulse will be better if you use a microcontroler, PIC10 or PIC12. If the output is analog, you can use simple comparator. One another possibilities is useng a Frequency to Voltage convertor, if the output is a Impulse, and comparator after the convertor,but this will be a less accurately, and wil need min. 2 chips. Whit microcontroler you can do this very ease.

[pilottx]

The RPM switch is not for nitrous, it's to put a form of electrical control to a dump valve.
The engine has had a retro supercharger fitted. Engine is a 6 cylinder by the way, the ecu output is digital.

The problem i'm having is that at low speed the high vacuum created by the engine is opening the dump valve, the turbulent air passing through the valve is blowing back onto the airflow meter creating very jerky driving at this speed, ie: fuel mixture is being badly affected.

Stonger springs in the valve help but create a problem further up the rev range where the boost cannot be dumped fast enough.

The idea is to stop the dump valve working upto 3000rpm (if this was adjustable via a pot then even better) then have the electronic controller switch to allow airflow, this switch would control some other form of inline electric valve which would open to allow the dump valve to work in the normal way.



The electronic switching unit would only need to provide enough output to trigger a relay as this would probably be simpler.


I'm really looking for one of you good chaps to be able to provide a schematic and component list as I am not electronic savvy at all really, although adept in vehicle electrical/mechanical.

Thanks in advance for any info or help

Pilottx

[ante]

Hi,
Ok, that makes some sense.
Do you think a relay will be fast enough, I mean when you “step on it” there is not much time before you exceed 3000rpm and the pressure rises rapidly? Perhaps this circuit can be canceled by the kick down maneuver to allow the dump valve to operate normally under this condition. Anyway we need to know more about the digital signal from the ECU, how it is related to the rpm.

[pilottx]

Hi Ante

The boost is relatively low, 8psi at 6600rpm, dont forget because the supercharger is engine driven the the boost rises in a linear fashion, it's not like sudden rush of a turbo. I don't think the reaction time is going to be too much of an issue. The ecu provides a tacho output for the instrument cluster, this is the output I was thinking of using.

I've got a really basic handheld scope, do you need some scope info?

Pilottx

[SM2GXN]

Hi pilottx!

Interesting project, in another thread there is a discussion about a RPM counter using single IC LM2917, inside the IC there is a comparator which can be set to trigger at 3000 rpm (if I undeerstood the data sheet right) and activate the air valve.
Let's see what the output of your ECU will show  :)

[ante]

Hi piloteex,

Must be a well balanced six or perhaps short stroked at that rev range! Anyway, it would help to know the relationship between the ECU output signal and the rpm. You say it’s digital but nothing about  the characteristics of it.