Official Baja SAE Forums Homepage
Forum Home Forum Home > General > Design Discussion
  New Posts New Posts RSS Feed - Brake line maximum pressure
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

Brake line maximum pressure

 Post Reply Post Reply
Author
Message
buckinghams_pie View Drop Down
Bolt Sorter
Bolt Sorter
Avatar

Joined: Jun/09/2019
Location: us
Status: Offline
Points: 17
Post Options Post Options   Thanks (0) Thanks(0)   Quote buckinghams_pie Quote  Post ReplyReply Direct Link To This Post Topic: Brake line maximum pressure
    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?
Back to Top
Aman2610 View Drop Down
Double Secret Probation
Double Secret Probation


Joined: Apr/07/2016
Location: India
Status: Offline
Points: 6
Post Options Post Options   Thanks (0) Thanks(0)   Quote Aman2610 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/10/2019 at 2:31am
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.
Back to Top
buckinghams_pie View Drop Down
Bolt Sorter
Bolt Sorter
Avatar

Joined: Jun/09/2019
Location: us
Status: Offline
Points: 17
Post Options Post Options   Thanks (0) Thanks(0)   Quote buckinghams_pie Quote  Post ReplyReply Direct Link To This Post Posted: Jun/10/2019 at 7:13am
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
Back to Top
Aman2610 View Drop Down
Double Secret Probation
Double Secret Probation


Joined: Apr/07/2016
Location: India
Status: Offline
Points: 6
Post Options Post Options   Thanks (0) Thanks(0)   Quote Aman2610 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/10/2019 at 1:38pm
What kind of caliper you are using?
No of piston & fixed or floating?
Back to Top
sujandinesh View Drop Down
Baja Godfather
Baja Godfather
Avatar

Joined: Dec/27/2013
Location: Eindhoven
Status: Offline
Points: 458
Post Options Post Options   Thanks (0) Thanks(0)   Quote sujandinesh Quote  Post ReplyReply Direct Link To This Post Posted: Jun/10/2019 at 2:52pm
Originally posted by buckinghams_pie buckinghams_pie wrote:

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?
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. 
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
Back to Top
buckinghams_pie View Drop Down
Bolt Sorter
Bolt Sorter
Avatar

Joined: Jun/09/2019
Location: us
Status: Offline
Points: 17
Post Options Post Options   Thanks (0) Thanks(0)   Quote buckinghams_pie Quote  Post ReplyReply Direct Link To This Post Posted: Jun/10/2019 at 5:14pm
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?
Back to Top
buckinghams_pie View Drop Down
Bolt Sorter
Bolt Sorter
Avatar

Joined: Jun/09/2019
Location: us
Status: Offline
Points: 17
Post Options Post Options   Thanks (0) Thanks(0)   Quote buckinghams_pie Quote  Post ReplyReply Direct Link To This Post Posted: Jun/10/2019 at 5:16pm
As for the caliper, wilwood gp200, 1.23 piston area, 2 pistons each
Back to Top
sujandinesh View Drop Down
Baja Godfather
Baja Godfather
Avatar

Joined: Dec/27/2013
Location: Eindhoven
Status: Offline
Points: 458
Post Options Post Options   Thanks (0) Thanks(0)   Quote sujandinesh Quote  Post ReplyReply Direct Link To This Post Posted: Jun/11/2019 at 6:39am
Originally posted by buckinghams_pie buckinghams_pie wrote:

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?
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?
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
Back to Top
buckinghams_pie View Drop Down
Bolt Sorter
Bolt Sorter
Avatar

Joined: Jun/09/2019
Location: us
Status: Offline
Points: 17
Post Options Post Options   Thanks (0) Thanks(0)   Quote buckinghams_pie Quote  Post ReplyReply Direct Link To This Post Posted: Jun/11/2019 at 7:15am
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
Back to Top
sujandinesh View Drop Down
Baja Godfather
Baja Godfather
Avatar

Joined: Dec/27/2013
Location: Eindhoven
Status: Offline
Points: 458
Post Options Post Options   Thanks (0) Thanks(0)   Quote sujandinesh Quote  Post ReplyReply Direct Link To This Post Posted: Jun/11/2019 at 7:37am
Originally posted by buckinghams_pie buckinghams_pie wrote:

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
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. 
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
Back to Top
RLM View Drop Down
Baja Godfather
Baja Godfather
Avatar

Joined: Nov/15/2012
Location: Hamilton, ON
Status: Offline
Points: 1228
Post Options Post Options   Thanks (0) Thanks(0)   Quote RLM Quote  Post ReplyReply Direct Link To This Post Posted: Jun/11/2019 at 9:38am
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. 
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.
Back to Top
buckinghams_pie View Drop Down
Bolt Sorter
Bolt Sorter
Avatar

Joined: Jun/09/2019
Location: us
Status: Offline
Points: 17
Post Options Post Options   Thanks (0) Thanks(0)   Quote buckinghams_pie Quote  Post ReplyReply Direct Link To This Post Posted: Jun/11/2019 at 6:24pm
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

Back to Top
Aman2610 View Drop Down
Double Secret Probation
Double Secret Probation


Joined: Apr/07/2016
Location: India
Status: Offline
Points: 6
Post Options Post Options   Thanks (0) Thanks(0)   Quote Aman2610 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/12/2019 at 1:25am
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).
Back to Top
buckinghams_pie View Drop Down
Bolt Sorter
Bolt Sorter
Avatar

Joined: Jun/09/2019
Location: us
Status: Offline
Points: 17
Post Options Post Options   Thanks (0) Thanks(0)   Quote buckinghams_pie Quote  Post ReplyReply Direct Link To This Post Posted: Jun/12/2019 at 8:12am
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
Back to Top
RLM View Drop Down
Baja Godfather
Baja Godfather
Avatar

Joined: Nov/15/2012
Location: Hamilton, ON
Status: Offline
Points: 1228
Post Options Post Options   Thanks (0) Thanks(0)   Quote RLM Quote  Post ReplyReply Direct Link To This Post Posted: Jun/12/2019 at 9:05am
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.
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.
Back to Top
buckinghams_pie View Drop Down
Bolt Sorter
Bolt Sorter
Avatar

Joined: Jun/09/2019
Location: us
Status: Offline
Points: 17
Post Options Post Options   Thanks (0) Thanks(0)   Quote buckinghams_pie Quote  Post ReplyReply Direct Link To This Post Posted: Jun/12/2019 at 12:57pm
Thanks for your help
Back to Top
 Post Reply Post Reply
  Share Topic   

Forum Jump Forum Permissions View Drop Down



This page was generated in 0.031 seconds.