Braking force calculation 2

[grounder758]

How do I convert an engineering callout of "must having braking force of 0.6g with pedal force of no more than 80 lbs" into a measurable force (ideally in newtons) that I can use to measure on a chassis dynameter (aka rolling road) in a production environment? We normally just check braking force go/no go; however, we are looking to check a brake bias between front and back and want to get a more meaningful number from the engineering callout.

I have the vehicle weight + CG, rolling road roller diameter, and am working on getting the coefficient of friction for both the tire and rolling road roller surface.

 

[NormPeterson]

Knowing such things as brake pedal ratio, master and wheel cylinder diameters, mean radii of the various disc swept areas, and wheel rolling radii would probably help.

Actually, it's not a bad little problem to throw into a spreadsheet.


Norm

 

[SwinnyGG]

F = M*A

.6 g of acceleration will result from a force equivalent to 60% of the vehicle's mass.

 

[grounder758]

Thanks! jgKRI - I'm concerned that the callout is for stopping the vehicle in road conditions, while the test will be conducted when the vehicle is static. In that case I think what I'm looking for is the force that can be generated by each wheel on rollers - I think I can pull all those variables and go from there. We can take a few known good units (that pass the 0.6g test in field conditions) and back in to a required force that the brakes have to generate.

 

[SwinnyGG]

You know that to meet .6 G of acceleration, the forces at each contact patch must, at minimum, sum to 60% of vehicle mass. The mass of your dyno rollers is a known, so by recording the amount of time it takes for the car's braking system to stop the rollers from a known speed, you can determine very easily if the braking system is capable of your requirement. Unless you need to know the actual forces on the individual parts, you don't need to do a deep dive into the hydraulics.

The only major variable that the dyno test won't account for is weight transfer- when you apply the brakes on the dyno, you will get no (or at least much less than in real-world conditions) weight transfer between the front and rear axles.