FW: [Diy_efi] Nitrous Injection system + closed loop control

[Hugh Keir]

I have now spoken to one of the developers at work. He has recommended
the PIC16C773, he has also written me some outline code for the
controller.

http://www.microchip.com/1010/pline/picmicro/category/embctrl/14kbytes/d
evices/16c773/index.htm

It has :-

2 Pulse Width Modulated outputs ( PWM ) - one to control the NOS
solenoid and one to control the fuel solenoid.

A 12 bit Analogue to Digital Converter which is able to be read faster
with less accuracy if required.

It has 6 inputs maximum which should allow for most combinations of
sensors that the engine can offer. The PIC16C774 has 20 channels if more
are needed. The actual time to set the MUX and read a channel is about
20 micro seconds, so with five sensors being read + a few lines of code,
it should be capable of several thousand reads per second.

The principle I will try is:-

The solenoids will only be active when the throttle is between 95% and
100% open.

The NOS solenoid will be activated in line with the Air Flow Meter
output voltage, starting with 20% PWM up to 100% on between 20% and
above 70% of maximum air flow meter voltage.

The Fuel solenoid will react to the output from the wideband Lambdas and
will be settable to track 12.5 to 1 or whatever. The values will set the
PWM % higher than the NOS PWM value when the AFR is less than 12.5 and
the opposite when more than 12.5. If the AFR goes too weak or lean, shut
the NOS down.

Other possible sensor inputs are from MAP, Knock, wheel speed ( cut
solenoids if wheels spin ) or combustion chamber pressure sensors
-mmmmmmm.

I guess the solenoids will be the key to making this thing fly.

Does any one know of some solenoids that would be reliable? I went to a
good tuning shop in Houston last weekend and they felt that although
they sold products from NOS, they were not reliable enough to be Pulse
Modulated even though many of the controllers sold use this method of
control.



Hugh


I have now spent some time researching the available controllers and
have been unable to turn up any devices that will interface with a
Wideband Lambda.

There appears to be a number of controllers that will set the horsepower
based on a time lapse, but nothing that cares about the Air / Fuel
ratio. Given that running lean is one of the major concern of many of
the sites that I visited, I am surprised that nothing exists.

The Diy Telemetry thread is currently talking about microcontrollers
that might work well in this application.

It should be relatively straight forward to link up the outputs from the
following to the A to D inputs:-

Air flow meters
Throttle position
MAP
DIY_EFI wideband

It should be a simple matter to switch mode regulate the NOS and Fuel
coils to whatever combination of airflow throttle, etc you like and have
the input from the DIY_EFI wideband adjusting the timing of the NOS coil
in relation to the Fuel coil to hold a specific A/F ratio.

Anyone see why this should be difficult to do?

Is there a speed of operation of the PIC that would make this hard to
do?

I only have limited experience with 8051 microcontroller and some basic
and assembly language stuff, your comments would be gratefully accepted.

Hugh



I forgot to say, I have a twin DIY_EFI wideband set-up on the car. It
would be good if you could control the nitrous and fuel with a feedback
loop to hold a specific AFR when it is activated.

Hugh

I am about to fit a nitrous injection system to my engine and have been
looking at the Holley NOS Sportsman, individual port, Fogger System to
add 50 to 250 BHP.

Details at
http://www.nosnitrous.com/HiOctn/ProdLine/Products/NOS/foggers.html

Most of the technology seems to be in the jet that disperses the fuel /
NOS.

Are there other things / systems that should be considered?

Hugh Keir


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