Brake line maximum pressure |
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buckinghams_pie
Bolt Sorter Joined: Jun/09/2019 Location: us Status: Offline Points: 21 |
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Posted: Jun/09/2019 at 8:40am |
I am using 100 lbf as the desired force to lock wheels, and 450 lbf as the maximum load case the system will see in terms of driver force onto the pedal. the components i find (master cylinders, calipers) have rated pressures of 1200 psi, so to ensure the system doesn't exceed the pressure limit during maximum load, i would be using 266.67 psi (1200*100/450) to lock the wheels, which isn't close to enough, How do I avoid breaking the components through excess pressure?
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Aman2610
Double Secret Probation Joined: Apr/07/2016 Location: India Status: Offline Points: 8 |
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Hi, you can go for larger disc diameter as it will provide you the required braking torque with reduced brake line pressure.
Also you can search for much more strength components for front wheel as it is will have major load transfer while braking and you can reduced the pressure of rear line via brake biasing. |
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buckinghams_pie
Bolt Sorter Joined: Jun/09/2019 Location: us Status: Offline Points: 21 |
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Unfortunately, we are already at around the limit in size for rotors, and I could try to find stronger calipers, but the pressure ceiling for all components seems to be 1500 psi
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Aman2610
Double Secret Probation Joined: Apr/07/2016 Location: India Status: Offline Points: 8 |
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What kind of caliper you are using?
No of piston & fixed or floating? |
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sujandinesh
Baja Godfather Joined: Dec/27/2013 Location: Enschede Status: Offline Points: 494 |
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The rated line pressure for any master cylinder is very high (just like in your case) and you will never exceed it with the nominal driver force onto the pedal. There seems to be a lapse in your calculations, please note that the line pressure is the force/area and your maximum driver pedal force (and multiplied by pedal ratio) divided by the area of the master cylinder will never exceed 1200 psi.
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RVCE BAJA: 2011-2015
General Motors: 2015-2016 Tyre Testing - University Racing Eindhoven: 2016-2017 Tyre Dynamics - TASS International: 2017-2018 Tyre Engineer - Apollo Vredestein The Netherlands |
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buckinghams_pie
Bolt Sorter Joined: Jun/09/2019 Location: us Status: Offline Points: 21 |
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So my equations
Maximum driver force: 450 lbf Master cylinder area: 0.31 square inches Pedal ratio: 3 450*3/0.31=4355 psi 124*3/0.31=1200 psi So a definitely achievable force of 124 lbf would match the maximum pressure the calipers are rated for Am I wrong somewhere? |
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buckinghams_pie
Bolt Sorter Joined: Jun/09/2019 Location: us Status: Offline Points: 21 |
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As for the caliper, wilwood gp200, 1.23 piston area, 2 pistons each
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sujandinesh
Baja Godfather Joined: Dec/27/2013 Location: Enschede Status: Offline Points: 494 |
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This seems too low. What is your master cylinder piston diameter? Also, there is nothing wrong with your maximum driver force, but however, have you measured whether a driver can generate that force in your car?
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RVCE BAJA: 2011-2015
General Motors: 2015-2016 Tyre Testing - University Racing Eindhoven: 2016-2017 Tyre Dynamics - TASS International: 2017-2018 Tyre Engineer - Apollo Vredestein The Netherlands |
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buckinghams_pie
Bolt Sorter Joined: Jun/09/2019 Location: us Status: Offline Points: 21 |
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The bore size is 5/8, the area is listed as 0.31
We use a tm1 The driver force is a value that fsae suggests, I’m working on validating it in the coming weeks, but I’ve seen it listed by multiple sources |
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sujandinesh
Baja Godfather Joined: Dec/27/2013 Location: Enschede Status: Offline Points: 494 |
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Its been a while since I have looked at MC specifications, now I recall that this is pretty standard. Assuming all other calculations are fine, I think you have to re-evaluate your pedal force. 450lbf is about 2000N, which is very high. Also, you have to understand that there are components in your car which come with fixed dimensions and hence you have to work backwards, making compromises where they are feasible.
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RVCE BAJA: 2011-2015
General Motors: 2015-2016 Tyre Testing - University Racing Eindhoven: 2016-2017 Tyre Dynamics - TASS International: 2017-2018 Tyre Engineer - Apollo Vredestein The Netherlands |
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RLM
Baja Godfather Joined: Nov/15/2012 Location: Hamilton, ON Status: Offline Points: 1258 |
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Couple things here,
1) validate your drivers input force PRIOR to using it in a cal otherwise the calc is useless. 2) most brake system components can easily withstand 3000PSI which is significantly higher than your max 1200psi. you said that this pressure was a max for the calipers, however looking at all the documentation available on wilwood's site for the GP200, a max pressure is nowhere to be found. If this is a max pressure for your master cylinder, I would suggest looking at a different master. 3) calculate out the brake torque required to stop your car, and then the line pressure required from there. there is no point arbitrarily picking a line pressure and input force/pedal ratio if you do not know how much brake torque you need to produce. you are currently working backwards.
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McMaster Baja Racing (09-Dec 2015)
Team Captain 2012-2015 Suspension Lead 2015-2016 All spoonfeed PM requests will be billed at $10 USD per reply, payable via paypal. |
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buckinghams_pie
Bolt Sorter Joined: Jun/09/2019 Location: us Status: Offline Points: 21 |
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1) the torque requirement i calculated was 6325 lbf-in (worst case possible, 11.5 inch wheel radius, 550lbf car and driver, 1 coefficient of friction)
2) the 1200psi limit is listed on a warning document that comes with the caliper |
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Aman2610
Double Secret Probation Joined: Apr/07/2016 Location: India Status: Offline Points: 8 |
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You have calculated the torque based on total vehicle weight. In actual it will be shared by 4 wheel based on the dynamic weight transfer. So your actual torque on every wheel will be 1/4 of the calculated value(assuming equal load on both axles).
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buckinghams_pie
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Sure, I’m accounting for that in my later calculations. In the rear we only use one caliper, and when the car is pushed from the front in the static test, it will see almost all of the load, as a safety factor I use all of the load
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RLM
Baja Godfather Joined: Nov/15/2012 Location: Hamilton, ON Status: Offline Points: 1258 |
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If these are the restraints and safety factors you are designing to, then you will need to resize your calipers to different bores, and you will likely need to increase your rotor diameter. you could also choose different calipers of similar size that can handle higher pressures. another thing you could look at is mounting your caliper internal to the rotor. this will allow you to increase rotor diameter within the same envelope of area.
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McMaster Baja Racing (09-Dec 2015)
Team Captain 2012-2015 Suspension Lead 2015-2016 All spoonfeed PM requests will be billed at $10 USD per reply, payable via paypal. |
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buckinghams_pie
Bolt Sorter Joined: Jun/09/2019 Location: us Status: Offline Points: 21 |
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Thanks for your help
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