Speed Sensor for Transport Trailer

Most heavy transport vehicles operate with 24 volts, though there are some 12 volt systems around.

Depending on the type of trailer, be it a Pantech, Refrigerated, Cattle Crate, Container Skel, or other variation. With applications being Semi, A double, B double or Road train perhaps you could use a GPS to determin road speed, or just simply a tone ring on one of the wheels. Bearing in mind that there are a lot of trailers now with ABS braking systems, perhaps getting the speed pulses from that may be viable.

Bear in mind most modern heavy transport vehicles are quite sophisticated and you will need to be mindfull that some systems may not behave as intended if not given the utmost respect with regards to add on equipment.

My Twopence worth.

Thanks for your input. I definitely do not wish to get involved with the complex electronics of the vehicles that is why I will develop a stand alone system. It is bad enough that I will be tapping into the electrical system for power and the air system however I should be able to do so with out creating any issues. The power unit is where you find 24 volts for starter but they have a series parallel switch to drop the rest of the vehicle to 12 volt. Regards

I've only been involved with heavy transport for the past 30 years in relation to providing technical support with communication and data systems.

Even today 12volt systems are the exception rather than the rule at least in Australia. It's no biggy, a 24/12volt invertor sorts it out quickly. Though if you are designing a system you would use a switchmode regulator that had a 40Volt head room (something like a LM2596) then your covered for both.

The last truck I saw with a series parallel switch was an old leyland about 20 years ago. I'm told there is the odd Mercedes Benz coach with it and I have seen the odd N12 Volvo which was 12 Volt, but that was 12 Volts through out.

The last big system rollout I was involved with was the Pioneer/Hanson Concrete Status Automator rollout, the fleet included Mack, International(IVECO) Acco's, White, Kenworth, Izusu, all of them 24 volt.

With freight work I've installed Radio/Data/GPS tracking systems into Renault/Mack, Mercedes Benz Actros, Hino, Izusu, Kenworths, Freightliner Argosy, Sterling, Scania, Volvo, Nissan UD, Toyota to name a few, they all have been 24 volt systems.

Interfacing with the vehicles various systems can be done but not in a hamfisted way (like what most auto elecs try to do). Getting the pulses from the Speedometer is easy enough as long as you buffer it and don't load the circuit too much. Same goes for the Tachometer signal.

Now you don't mention a specific vehicle, whether it is a on/off road, or farm, local or interstate transport. So I can only offer you the most general of advice. That's what happens here on CR4, the better the detail you give the better the responses are. I realise that you may have "patent" issues to contend with as well and are trying to keep things close to your chest. You can always send a pm to likely suspects to keep it off the open forum...

Thanks for the interest but the issue is not 24 volt vs 12 volt that can be controlled. In Canada all trailers are 12 volt and yes the 24 volt with the series parallel switch died out some time ago. All tractors from according to my fleet manager are 12 volt in North America with possible exceptions. Any comments on a device to actuate a solenoid valve at low speed would still be appreciated. Looks at this time like the Doppler radar items are most common followed by a laser system.

What is the soleniod going to actuate?

Do you want it to switch "on" everytime the vehicle travels at or below a given speed or when actually stopped?

Does it matter if the vehicle is travelling forward or reverse?

Does it have to do it everytime the vehicle slows below 20km or only at the end of the journey? I could imagine if the vehicle was in heavy traffic that it may not be good thing for this to be going on and off randomly. There are some manouvres that are low speed i.e. driving onto weigh bridges, or into worksites/high pedestrian areas, that this may be problematic too.

Once the solenoid is switched on what mechanism/logic is required to switch it off?

Is the switching off of the solenoid a manual function or automatic?

You could, put a tone ring (ala ABS braking) on one of the trailer wheels (or if it has ABS then add an additional sensor for your device), using a proximity sensor. Count the pulses from the sensor in a PIC like PIC16F88 (which has a frequency counter input) Tell the PIC that when the pulse count is below "x" then turn on the Solenoid. Which you would do by instructing the PIC to hold one of its pins high, that pin would then either switch on a switch on a transistor, which then drove a larger transistor (ala 2N3055) or maybe a switching FET, or a ULN200X that inturn turned on the solenoid.

Alternatively you could use a GPS engine, which continually outputs the speed information to (again) a PIC via serial data connection. The PIC looks at the data stream for the nominal speed value. Once the PIC sees the desired value it then switches on the Solenoid.

Does that help?

Solenoid activates an air cylinder Needs to work forward and reverse any time below set speed NO problem going on and off in heavy traffic. It could be set with a timer circuit to keep it on for a set period of time or any time speed is low. I am of the opinion that we will need a logic circuit. The cylinder is to activate a aerodynamic device that works best as low to the roadway as possible within reason but to raise up in rough terrain. Such as curbs, loading ramps, possible construction sites, Crossing sidewalks on driveways.

Ok, I'm going to introduce you to a new concept, Functional Safety.

I'd like to suggest to you that rather than have the cylinder activate to raise the "curtain" at low speed, you tackle the logic like this, once the vehicle is travelling over 40kmh then it lowers the curtain. Aero dynamic devices are really only effective at highway speeds (over 80kmh) any way.

Make the default that the curtain "fails safe" in the retracted state. This means that if the power or air fails then truck is not stranded because the curtain is down.

I had another thought, that if this is a Pantech type trailer, one way you could do this is with a pitot tube sensor. With this sensor mounted on the leading edge of the roof of the trailer, it measures speed by the differential pressure of air flowing over and through it. This provides a air signal that could activate a switch to turn on your air solenoid at over a given speed. The neat thing is that it would be mostly fool proof and have a minimum of parts, most off the shelf. The only power required would be for the solenoid.

I will look into our suggestions ,,,thanks.

Hi Roy,

Further to Tobugrynbaks thoughts, if the pitot tube works out, it should be possible to use a pneumatic signal booster relay, to give an air signal to a air pilot operated spring return valve, this would do away with electrics completely. You did however mention the possible need for a timer circuit, which, if required, might swing the cost of control back towards electric.

Best of luck,

John

Just wondering if the pitot tube sensor performance or accuracy won't be affected by windy, dusty and /or muddy road conditions that may be encountered along the way?

Those were my thoughts especially if sitting some time. Aircraft are plagued with insects finding homes in them and nesting. Also slow speed and wind as well as cross winds may create some havoc. I am getting more info on the radar systems at this point. Hard to do it off the wheels but maybe off the cogs in the brake drum that is used if they have anti skid braking system. That would be cheep all I need is a prox switch or sensor but dirt and ice may be an issue. More research but thanks.