Don't know how we ever lived so long without ABS.

I do.

ak

 

Thank you guys for your suggestions, the truck doesn't have an ABS system so please tell me how can I get the wheel speed keeping in mind the mounting difficulties I will face when placing each sensor on or around the wheel.

It could be as simple as changing one of your brake rotors. Some cars have a different brake rotor for ABS equipped cars. That type of rotor has a portion of the hub part with notches cast in it for the ABS sensor. Your truck may even have them and you don't know it, so you may want to have a look at them to see.

 

Sure it is.

What is important is how stable the sensor output transition edges are with respect to the angular velocity of the shaft. Even one magnet would be good enough as long as it doesn't wiggle. Using the same math as deriving the frequency of a signal by measuring its period, you easily can get 3-digit resolution of the shaft velocity.

In your example but with only one magnet, 83.6 / 2 = 41.8 Hz = 24 ms. The difference between 60 and 61 mph is 4 us per period, so a 1 MHz, 100 ppm clock is more than twice the precision needed for 100 mph resolution *instantly* (as in only one revolution). But nothing in a car happens instantly, or even in 24 ms. Early systems were analog (!) and used an R-C filter to get a short-term average of the shaft velocity and prevent "hunting".

ak

I didn't consider measuring pulse width to resolve speed. I was stuck thinking about counting pulses and applying time-based averaging.

 

I didn't consider measuring pulse width to resolve speed. I was stuck thinking about counting pulses and applying time-based averaging.

It sounds like you are suffering from a habit. Us analog guys usually work below audio frequency down to DC. One job I did had a high frequency cutoff of 7 Hz. (It was an auto zero circuit for a j-fet audio amp.)

Reiterating AK (I think), cars and trucks have so much inertia that nothing (intentional) about speed change happens quickly. When you're trying to keep the change in speed nearly zero, ten hertz for the entire control loop is more than enough. Detecting 50 or 80 times a second is a good, fat margin of over sampling.

 

Back when I was traveling on business I rented many cars, a good way to get a feel for the status of the art in mid-level car design. Since all of them had various computers sprinkled around, things like the response characteristics of the cruise control were completely programmable by the designers. Some were very "grabby", and effectively stomped on the accelerator when re-engaged from a slow-down. Others were very polite and well controlled. Both did equally well at holding the set speed without wandering around or hunting, so there probably were multiple control loop time constants at work.

ak

 

The cruise control I installed had a loop gain control trimpot that you adjusted while cruising.
Too low a gain setting and it didn't maintain the speed well.
Too high a gain setting and it would start to hunt (speed would vary up and down continuously) at the set speed.

 

Damping is your friend.

ak

 

The cruise control I installed had a loop gain control trimpot that you adjusted while cruising.

I don't remember having that option, but then, I can't remember what I had for lunch 2 days ago.

Some were very "grabby", and effectively stomped on the accelerator when re-engaged from a slow-down. Others were very polite and well controlled.

Now that you mention it, my Ford Aerostar was so grabby that I was careful not to push the "resume" button until I was within 5 MPH of the target speed.

 

Now that you mention it, my Ford Aerostar was so grabby that I was careful not to push the "resume" button until I was within 5 MPH of the target speed.

With a 68000 (ish) thumping away as the engine controller, and multiple, self-adapting control loop time constants merely a matter of a bit more code, I think that is lazy design work.

ak

 

It could be as simple as changing one of your brake rotors. Some cars have a different brake rotor for ABS equipped cars. That type of rotor has a portion of the hub part with notches cast in it for the ABS sensor. Your truck may even have them and you don't know it, so you may want to have a look at them to see.

This is where I was headed when I asked the year, make and model. Many of the trucks switched to ABS but kept their rotor design pretty much the same for a number of years. It would be that easy.
As for cruise control, OEMs have been adapting "fuzzy logic" as they call it so that cruise control systems to not race back to the set position, rather they try to adapt to engine load and rpm and predict what measure must be taken to get back up to speed. Examples would be going downhill or in slippery conditions. You dont want the cruise to take off so they adapt some logic to it to make it safer. Even Class 8 tractors have adapted thus technology.

 

I had an S10 truck that was like that, had the 'reluctor' notches but didn't have ABS. Making one part that will work on both ABS and nonABS only makes sense for the industry, fewer part numbers and less problem in logistics.

 

Is it a rear wheel drive? If so can you use the drive shaft?
I once was involved in a project for the local road works unit concerning a vehicle to paint the lane lines on road surfaces some lanes consist of broken lines, so a set length was required for the paint gun to operate at the correct time as the vehicle traveled.
The front drive shaft where it exits the gearbox was used using a prox sensor.
Max.

 

I know the hall effect sensor is more reliable than IR for speed measurement but is it fast too? Because I need fast and accurate measurements for my system but for hall effect sensor we will get 1 pulse per revolution which will make the measurement slow. So what can I do to make the measurement more fast and accurate? Will attaching more magnets solve my purpose or is there any other solution. Please let me know.

Thank you.

 

Not all Hall sensors require magnets mounted on the rotating part. Many just require a toothed wheel (Must be feromagnetic.) As has been suggested in many replies you can mount a toothed wheel on the wheel hub.

Les.