Calculating Car Brake-Pedal Force for Desired Braking Distance

  • Thread starter johnny_heart
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In summary, a brake pedal force of 100Ibf is needed to generate a friction force that is proportional to the amount of pedal force applied.
  • #1
johnny_heart
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Car brake-pedal force...

Hey all,

im posting because i would like suggestions (preferably with proof) on how a relationship between initial velocity of a car, force to brake pedal and desired braking distance can be formulated. Assuming we know the velocity and the desired braking distance from this initial velocity?

so far i have the equations for forces going through the brake system but only once a foot force is generated.

for example,

biasForce = footforce*Ag

where Ag = mechanical advantage of pedal (found by taking moments about the pedal axis)

biasForce = force transmitted to bias bar.

After this I have pressures generated at master cylinder etc, but id like some references to where I can find a suitable equation to calculate the needed foot force. My idea was to take real tests, and set up a table, but I haven’t managed to get hold of a device which I can strap to my foot, while I am braking in my car!

any help appreciated,

jOn
 
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  • #2
I'm not sure braking force is linear with pedal force anymore, since they are hydraulic or drive-by-wire (not sure if there is much of that), but friction on the brakes is directly proportional to the force between the brake pads and the rotors.
 
  • #3
...

I'm not sure braking force is linear with pedal force anymore, since they are hydraulic or drive-by-wire (not sure if there is much of that), but friction on the brakes is directly proportional to the force between the brake pads and the rotors.

Im ok with the frictional forces for now,

some sources say average foot force is 100Ibf but it seems a bit vague to use just one force measurement.


if anyone has any suggestions for working this out mathematically please let me know,

otherwise my best bet is to try and find a measuring device which can take readings while I am braking and use that data

thanks jOn
 
  • #4
It shouldn't be too difficult to find or make a pressure transducer pad that can fit over the brake pedal. Perhaps an old-style trailer brake controller can be adapted for that purpose. I seem to recall that some of them were proportional (but I'm not sure).
 
  • #5
nearly all cars have power brakes
run off engine vacuum thru a brake booster

if you want real forces you would need to disconnect the vacuum line to the booster SIMPLE AND EAZY BUT THAT KILLS MOST OF THE BRAKEING FORCE
NOTE DONOT TRY THIS ON THE ROAD, MAYBE A EMPTY PARKING LOT
and only at very low speeds BE SAFE
 
  • #6
Good advice, Ray, but I don't know that you'd have to disconnect the boost. Since it's proportional to the pedal pressure, you should be able to compensate for it.
 
  • #7
I don't know - I've driven cars with touchy brakes and "soft" brakes. It seems to me that though it would make sense to make them proportional, but I don't know that they realistically are.
 
  • #8
Maybe. All of mine have been, but it probably depends upon the manufacturer. Also, none of mine had any ABS or other weird stuff.
 
  • #9
...

lol, thanks for the replies,

going a bit off the topic but...

ill probably just use a variety of forces starting at about 100Ibf.

jOn
 

1. How do you calculate the brake-pedal force needed for a desired braking distance?

The formula for calculating brake-pedal force is F = m * a, where F is the force, m is the mass of the car, and a is the deceleration. To determine the deceleration, divide the initial velocity by the stopping distance. Plug these values into the formula to calculate the required brake-pedal force.

2. What factors affect the brake-pedal force needed for a desired braking distance?

The main factors that affect the required brake-pedal force are the mass of the car, the initial velocity, and the coefficient of friction between the brake pads and the wheels. The condition of the brakes and the road surface can also have an impact on the required force.

3. How does the condition of the brakes affect the required brake-pedal force?

If the brakes are worn or damaged, they may not be able to provide enough friction to slow down the car effectively. This means that a higher brake-pedal force may be needed to achieve the desired braking distance.

4. Can the brake-pedal force be manually adjusted in a car?

Yes, most cars have an adjustable brake pedal that can be moved closer or further away from the driver's seat. This can affect the amount of force needed to apply the brakes and can be adjusted for comfort and safety.

5. Is there a minimum or maximum amount of brake-pedal force needed for a desired braking distance?

There is no set minimum or maximum amount of brake-pedal force that is needed for a desired braking distance, as it depends on various factors such as the car's weight, speed, and road conditions. However, it is important to ensure that the brakes are not over or underworked, as this can affect their performance and longevity.

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