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Specifying a Brake Caliper
What goes into caliper design from a system level?
Vehicle system calculations will dictate key aspects of the caliper design.
The Systems Engineer will make sure that the specification is safe and legal with regard to brake balance, pedal efforts, thermal capacity, work rates, etc.
These calculations give the Caliper Design Engineer a basic specification that includes:
- Piston hydraulic area
- Disc effective radius
- Pad area
- Pad depth / rubbing path
- Pad coefficient of friction
- Disc friction ring dimensions (outside diameter, inside diameter, thickness, air gap)
- Stiffness
The Caliper Design Engineer will create a caliper that meets these requirements within the wheel package available.
Breaking the requirements down, you have:
1. Available brake torque
- Brake torque (Nm) = k × p × r
- K(dynamic) = piston area × pad friction
- P = maximum working pressure
- R = disc effective radius
2. Disc thermal capacity
Key disc friction ring dimensions will be determined by the System Calculations Engineer to ensure that the thermal mass is sufficient for various energy-creating scenarios, such as single stops, repeated stop fade tests and hill descent.
3. Lining work rate
The pad depth will have been determined through the disc dimensions. A target lining area will be added to this to meet work rate targets. Too high a work rate will result in fade and high wear. Too low a work rate may not allow the material to work efficiently and achieve the desired friction coefficient.
4. Stiffness
Calculations will assume losses for each part of the brake system. These losses contribute to pedal travel. The caliper contributes to this through:
- Pad-to-disc clearance
- Lining material compression
- Caliper housing expansion
Armed with these requirements, the caliper design engineer can start work. It is an iterative process, as what is targeted may not be achievable in the space allowed.
Technical article provided by Alcon Components Ltd. Published by AlconKits with permission.