Control a trucks ground speed

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#1
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Hi there,

I would like to control trucks ground speed using a microcontroller. There are a lot of sensors on a truck like hall effect sensors, reluctanse sensors e.t.c. that give information in the ECU.
So I would like to make an AVR circuit for control the truck's velocity (ground speed) in order not to exceed a specific preset value (for example 100Km/h).
Is there any way to do this?

Thanks,

Michael.

Michael.

User of:
IAR Embedded Workbench C/C++ Compiler
Altium Designer

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Can you tap into the ECU (diagnostic port or something else) and read what it "thinks" is the ground speed? That would be a lot easier than trying to tie into an existing sensor. This is because the sensors will be managed by the MCU or antiskid unit or what ever and you do not want to mess with those signals.

Jim

 

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I got paid to do exactly what you are describing, so yes there is a way to do it. It is called an intelligent governor and in fact their are many ways to do it depending on the many sensors that can be read from the particular engine you want to control.

Smiley

Last Edited: Sun. Mar 16, 2008 - 03:16 PM
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Hallo guys,

Reading the MCU's data from the diagnostic port there are only fault and trouble codes and some other data like the battery voltage. I also can reset the MIL or reset the trouble codes and some more things.
So personally I don't think that I could do something via this method.

There is a relactanse sensor that read the ground speed and one more that read the engine rpm. Ok, Reading the sin wave from the groun speed I could have enough info about the truck's current speed. My question is that if there is any point that I could control in order to make a close loop for controlling the output (ground speed) reading the input (current ground speed.

I would also like to add another parameter to my question, of how could I also control the rpm of the engine?

Thanks for your time,

Michael

Michael.

User of:
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Altium Designer

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you would change the fuel flow through the throttle as a function data from the speedometer. [Your actual truck may have some other sensors for these functions - this you need to find out]

This is very simple in concept, but harder in implementation since you need to know how to process the incoming data from the speedometer and then generate output to control the throttle. You will need to add data smoothing algorithms and hysteresis.

You would do best by building a device to output fake signals like those coming from the speedometer and accept fake signals from your controller. Then make your controller to work with the fake signals and after you get that fully working, then you attach it to a real engine, where you will find that the real world only loosely mimics what you thought so you will continue tweaking until you get it working properly.

The very first thing you have to do is find out exactly what signals the truck generates that are related to ground speed. Next you need to find out exactly what signals you can generate to control the engine and/or transmission to control that ground speed. You have to have an intimate understanding or that vehicle system before you can even begin.

Smiley

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Hello fellow freaks. Do you all think an aftermarket overspeed warning indicator (using an AVR to read the speed from the OBD and flash a red LED and beep) would sell? There are a few guys like me that hate seeing those flashing blue lights bad enough that I might build one. Think it would sell? I have no idea how to inject a slow down signal into the vehicle... sounds like a job for CAN?

Imagecraft compiler user

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Guys,

Very thanks for you time.
Smiley, according to your last post you say that there is better of read the ground speed from the speedometter's output fake signal than read it out from the ground speed relactanse sensor which is on the truck. I have another idea, of using a velocity sensor that will be on board and will give info to the AVR of the current ground speed when the the truck is going forward or back. So less external cabling.
Doing this the only thing is to control the throttle.
So before asking more questions, I will read and learn about throttles and then I will feel free to ask again.
In any way I will let you know about my research. Who know maybe the idea of using an internal velocity sensor will have good results.

Thank in advance,

Michael.

Michael.

User of:
IAR Embedded Workbench C/C++ Compiler
Altium Designer

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Michael, the thread-title is splendid ! Had to think immediately of "Control a trucks air speed" :lol:

Nard

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I do have one point: if you're going to put something automatic into a truck's speed control, you'd better be absolutely certain that it can *only* fail safe...

Diesel engines are run with the air input wide open, and the speed/torque controlled by the amount of fuel injected - that is, they run lean. These days, a diesel with an ECU will almost certainly be fly-by-wire: no physical connection from the throttle pedal to the engine, but the injectors controlled electronically by the ECU.

Which gives you two ways to speed limit: either you talk to the ECU to tell *it* to stop the injectors (canbus perhaps, or interrupt the throttle pedal signal) or you must tell the injectors directly - interrupt their control pulses.

Either one is tricky... but both *must* be designed so that in the case of failure - any failure, hardware, software, whatever - the engine cannot perform an uncommanded acceleration. Ideally it should fall back to normal operation; acceptably it could fail to a no-fuel (i.e. stopped) situation; but it *must not* fail with any of the injectors stuck open.

(On a petrol 4-stroke engine, engine speed control (usually to prevent mechanical damage from over-revving) is performed by breaking the ignition circuit, since running a petrol engine lean will burn the valves or the piston. The excess fuel will eventually damage the catalytic converter, but...)

You should also consider the legal aspects of your design. Vehicles in the EU are type-approved; your device may take them outside this approval and make it illegal for them to be on the road. Also, an insurance company would consider this a serious change to the specifications and may be reluctant to continue the policy, or to pay out in the case of an accident.

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bobgardner wrote:
Hello fellow freaks. Do you all think an aftermarket overspeed warning indicator (using an AVR to read the speed from the OBD and flash a red LED and beep) would sell? There are a few guys like me that hate seeing those flashing blue lights bad enough that I might build one. Think it would sell? I have no idea how to inject a slow down signal into the vehicle... sounds like a job for CAN?

Hook up a Taser to fire at the driver if the set speed is exceeded?

Smiley

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About 6 years ago I designed a device for my son's Pontiac Fire bird that intercepted the signal from the acceleration pedal. When the pedal got past a certain point, my device took over the shifting of the automatic transmission based on engine RPM. It gained him about a second and a half in the quarter mile.

I don't remember all of the details now, but I'd think a velocity governor wouldn't be too terrible to design.

          |\          +------------+     +----------+
Pedal --->|+\         |            |     |  Engine  |
          |  \        |            |     |          |
          |   +-------+Speed       +---->+Throttle  |
          |  /        |            |     |          |
      +-->|-/         |  Governor  |     |      Tach+---+
      |   |/          |            |     |          |   |
      |               |            |     +----------+   |
      +---------------+Limit       |                    |
                      |            |                    |
                      |        Tach+<-------------------+
                      |            |
                      +------------+

You can avoid reality, for a while.  But you can't avoid the consequences of reality! - C.W. Livingston

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Wow!
Ambitious project. :!:
Some more thoughts for you to ponder:

Vehicles are a harsh environment. Their electrical systems are very noisy, with the potential for lots of high voltage spikes, of both polarity. They are also harsh thermally, humidity wise, and from a vibration / mechanical perspective.

Legal issues noted above, not repeated here, but warrant emphasis.

One of my "other jobs" is with an EMS service. Our jurisdiction has two stretches of 6 lane roads. Over the years there have been several accidents from people "stopping" in the high speed lane. It is always unexpected, and people behind them plow into them.

There are many driver monitoring systems on the market. They use a gps module and record the vehicle's position, speed, date & time, and any other desired data. There was one the size of a USB memory stick in the paper the other day. It is aimed at parents who wish to monitor their chldren's driving behavior.

Why not consider such a "passive" monitorng system. Review the driver's performance. If you have a problem driver, why not monitor their performance, and modify it to meet the company's desired behavior, or terminate the individual? More and more EMS agencies are doing this in the US, and elsewhere. It becomes part of the agency's quality improvement program.

You can reward drivers for good / exceptional performance, or penalize those who do not meet your minimum requirements or show improvement, depending on the mindset of management.

I like this approach much better than a uC potentially failing the throttle control on a semi-trailer, or any vehicle, for that matter.

JC

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The GPS navigators could add a speed limit database and have the pleasant voice chide you that 'Speed is above the local limit'. I thought the insurance companies could give a rate reduction if you had a box with a transponder that would receive local speed limit transmitted from an RFID on the speed limit signs and do something obnoxious like an irritating beeeep and a bright red led. Anyone know how to make some money promoting those two goofy ideas?

Imagecraft compiler user