PLC Programming for a Supermileage car

Alright, I'm a 1st time user/programmer/see-er, of a PLC. I'm programming a PLC to run a Supermileage car. If you don't know what a Supermileage car is, it's a car, or a glorified go-kart, that runs on 1 gal. of gas or alcohol or some other type of flameable liquid, and what ever car gets the most mileage out of 1 gal. of gas, that car wins. The engines are Briggs & Straton engines...can be any size, shape, color, anything...you name it. Ok, on to the fun stuff.

What I need the PLC to do is monitor how fast the supermileage car goes. Once the car reaches a speed of 30mph, the PLC would shut the motor off. And once it would get to a speed of anything LESS than 30, for example...25mph, the PLC needs to turn the motor back on. Now my questions are: how would I program the PLC to do this? is there a certain mode I need to use? Is this even possible?

Thanks for all of your help.

I think it's possible.

The things to keep in mind with the setup:
-Supply voltage of the PLC
-High speed counter input on the PLC or encoder card.
-High speed puls divice like a proximity switch

The way I would start with the project.
Determin where to put the detecting divice. FOr intance on the ax that isn't powerd by the motor.
Then dicide what fit's. A metal gear wheel and a small procimity switch. Or an encoder. Depending on your buget.
Then determin the revolutions of the gear wheel or encoder at 30 mph. If you know those you know what the frequenty of the counter input you should have.

When you are on this point write the results on this form and I and probably all the rest will try to help you out.

Jurgen

If you do not need super resolution on the speed calculation, you could probably use any of the small micro PLC's with a prox switch picking up a flag attached to an axle. Count the times the flag goes by the prox and divide by the elapsed time to get a frequency.

For instance

If you have an 18" diameter tire, then the circumfrence is c=56.549".

30 mi/hr is v=528 in/sec. v/c=9.337 Hz or one revolution every 107 miliseconds. If you make your flag so that the prox sees it for 1/2 a ref and doesn't see it for the other half rev then you have an on time of 54 msec and an off time of 54 msec. So you need a scan time faster than half of that or faster than 27 msec. Round down to 20 msec is using a standard input. This seems a resonable scan requirement for a micro plc with a program as simple as you would require.

If you need more accuracy, many of the micro plc's have a built in high speed counter which would allow you to use more lobes on your target for better speed resolution or even to hook up an encoder. These will have special functions within the plc software to calculate the frequency of the signal for you and thus the speed.

There are also built in comparison instructions which will allow you to set up your hi speed cut out and low speed re-start so I would say that definately yes, this is not only possible but right up the alley of a small plc.

Just curious, what kind of PLC? What kind of motor, electric, or gas-driven?

This may be beyond you at the moment but, not knowing what sort of technical assistance you might have, I'll throw something out.

Will there be any need or use for an operator interface? Nothing fancy here, just something to allow adjusting your setpoints on the fly (it can get to be a real pain connecting and editing constantly for small program/parameter changes). At a minimum, I'd include some switches either on a display or discrete types to allow the setpoint changes.

Depending on the PLC and the display, this could also be harnessed to give other information if needed, for instance, (calculated) fuel/battery remaining or distance traveled.

.02

SupermileagePLC_Newb

I would respectfully suggest that cutting your engine is not the best way to increase your milage. In fact this may decrase your milage by quite a bit.

If anything goes, try fuel injection, and/or, water/alchol injection.

A Paxton type blower can be made from an old anti-pollution air pump used to inject air into the exhaust sysetm on cars. These can make great superchargers for small engines.

The engine will get maximum milage from running at a constant speed & load. If you cut your engine and dont disengae the clutch then the engine will drag the car down defeating the purpose. An overrunning clutch would disengage the engine from the rest of the powertrain when coasting. Doug-P provided me this link on an earlier thread regarding a Sprague Clutch: http://www.renoldusa.com/renold/clutches/sprag/general.html

If your engine has a centrifugal clutch, which is common with small engines, than that may do it for you.

Narrow wheels, hard tires, effecient burn, good arrowdynamics, and very conservative driving will get you the most mileage.

Additionally if you can get access to one, tune your engine for the lowest hydrocarbon content using an exhaust gas analizer. In the best of circunsatances this would be done on a dyno so that you could measure the NOx Hco and Co with the engine under the expected load, and within the expected RPM range etc...

Setup a governor to maintain your engine rpms at the most effient speed. When you apply full throttle the governor will do the rest.

I dont think a PLC is your answer here.

Best of luck.

Mike.

I think Mike's interested in joining the competition!...

One question... How are you planning on powering the PLC? Do the rules allow the use of a battery?...

Even though the battery will not be directly powering the vehicle, it is power NOT generated by the engine...

beerchug

-Eric

Doug-P: I do believe the PLC is a DLo5 D05D-DD I do believe and the motor is an gas motor. The only operate interface is go and stop.

Eric Nelson: Yes, we can use battery.

I forgot to mention something when I posted. We can't modify the engine one bit. The only thing we can put on is an electric starter and a few other misc. things. My group is running in the stock class which basically means we can't touch the motor itself(valves, bore it out, better header, etc.)out of the box. And if you guys think that a PLC won't work, please tell me now as we only have 4 more weeks of this class. Thanks for your help guys.

PLC will work.

It will take you some time to set up and program. And afcourse the testing also takes a few momentsssssssssssss.

Only start on working with the PLC when you really think cutting the engine and starting again will result in saving fuel.

I think it won't do any good. You need extra fuel when increasing the speed back to the setpoint.
When you would try to keep the speed at a same level you will get the best milleage I think.
But i'm all but an expert in this field.

If only experience with my own car. When I drive on the motorway at the same speed I can drive up to 950 km on a tank.
When traffic is bussy an you need to brake a lot I will end up with a total of 750-800 km a tank (same amount of liters).

SupermileagePLC_Newb,

Trust me, I've been there and have done that. I also was a NIASE (now ASE) Certified Master Mechanic, (I let my cirtificate expire a few years ago), and spent some time in the racing game (SCCA Trans AM). I ran a 302 naturally asperated Chevy in a Monza back in the late 70s. Better milage ment less pit time, which could enable a slower car to place.

Cutting your engine and starting it up again will severly worsen your milage!

I would suggest you drop the whole idea, and save the weight of the battery, and PLC etc..

Things to consider:

1) Consider the use of an overunning clutch in the drivetrain to prevent your engine from slowing the car during coasting.

2) Super-Tune your engine for maximum burn efficenty at the expected aggerate rpm and load. Find somebody with an Exhaust Gas Analizer so that you can measure the Hydrocarbon content of the exhaust. Hydrocarbons are unburnt fuel molecules. Adjust the carb, and spark timeing to get the most from your burn. Throw away the manual regarding these settings and look at the exhaust gas analizer to tell you whats happening in the combustion process. A scope may be handy but it wont tell you the end result, like the exhaust gas analizer will.

3) Closely maintain a constant speed/rpm to be maintained at the most effient RPM for the engine. Keep your throttle in the most efficent position for your best burn. Do not close your throttle to coast as this will pour more raw gas through your engine, causing worse milage. Your engine will achive more efficenty with the throttle open enough to avoid a rich fuel/air mixtre.

The ability of your driver to maintain the speed of the car in the most efficet rpm/load range for the most complete combustion will decide the "race".

Dinners ready, so I gota go.