Brake Pad Insulator Friction Test Apparatus
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Solution Overview
Problem
Existing methods for measuring surface friction of brake pad insulator materials are unsuitable for high-pressure conditions and cannot accurately represent the frictional damping mechanisms under realistic temperature and torque conditions, as they are cumbersome and not representative of the rotational motion and higher pressures found in disk brakes.
Innovation Solution
A test apparatus that includes a rotor with a stator and actuators to apply axially-inward forces, a torque cell to measure torque, and temperature control, allowing for the calculation of the coefficient of effective static friction using the formula μ1 = TBA1 / (reff * FN1), enabling efficient testing of multiple samples under controlled conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If ASTM D 1894-01 standard method is used to measure surface friction of brake pad insulator, then the measurement procedure is simple and standardized, but the test is unsuitable for high-pressure conditions and cannot represent realistic brake operating conditions
Solution Approach 1:
The test apparatus changes the operating parameters from ambient pressure (ASTM standard) to high pressure (10 times higher, simulating brake conditions). The system applies controlled axial loads through the actuator to achieve realistic contact pressures between the brake pad insulator and the piston/caliper finger, making the friction measurement reliable under actual service conditions.
Solution Approach 2:
The test apparatus introduces an intermediary rotating component (rotor with carrier member) that simulates the relative motion between the brake pad insulator and the actuating piston. This intermediary mechanism enables the measurement of friction under rotational conditions while maintaining controlled pressure, bridging the gap between simple standardized testing and complex realistic conditions.
2Reliability
If known friction measurement test rigs for brake linings are used, then the rotational motion and torque measurement are representative of brake applications, but the rigs are bulky and have high rigidity requirements due to large rotational displacement and torque
Solution Approach 1:
The test apparatus segments the brake system into essential components: a simplified rotor with carrier member holding the insulator sample, a separate actuator applying axial force, and a torque cell measuring torque. This segmentation allows each component to be optimized independently, reducing overall bulkiness while maintaining representativeness of the friction measurement.
Solution Approach 2:
The test apparatus applies partial action by focusing only on the critical friction interface between the insulator and the actuator, rather than testing the entire brake assembly. The carrier member and actuator configuration provide sufficient rotational motion and torque measurement for the insulator material testing without requiring the full complexity of a complete brake rig.
3Ease of manufacture
If ASTM D 1894-01 method is used, then the test can be performed at ambient temperature, but it is cumbersome to test at temperatures other than ambient and the plane may be seated while the sled must be held at ambient temperature
Solution Approach 1:
The test apparatus is designed with multi-functionality to handle both ambient and elevated temperature testing. The rotor, carrier member, and actuator configuration can operate in controlled temperature environments, making the system universally applicable to friction measurements under various thermal conditions without requiring separate testing procedures.
Solution Approach 2:
The test apparatus enables self-service temperature control where the rotor and insulator sample can be heated to elevated temperatures while the actuator continuously applies the required axial load and the torque cell measures the friction torque. This self-service capability eliminates the need for complex external temperature maintenance systems required by traditional ASTM methods.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate measurement of surface friction of brake pad insulator materials under conditions simulating actual use, allowing for the evaluation of frictional damping mechanisms and correlation with temperature, suitable for use on a brake dynamometer.
Implementation Method 1
Frictional damping occurs between contacting surfaces that have relative slip. In the brake pad insulator example, the outermost layer of the brake pad insulator is contacted by a brake actuator such as a piston or a caliper finger. Relative slip may occur, resulting in surface friction damping.
Implementation Method 2
The simplest and fundamental representation shown below, is the Coulomb friction model, which relates the total frictional (damping) force (Ff) between contacting bodies, to the net contact force (Fc), through the kinetic coefficient of friction μk.
Implementation Method 3
A stator is configured to operatively support at least one actuator that is operable (i.e., pressurizable) to apply axially-inward force on the damping material.
Implementation Method 4
A rotor is configured to operatively support the damping material for rotation therewith.
Data Source
AI summary
A test apparatus for measuring surface friction of a damping material such as brake pad insulator material includes a rotor configured to support the damping material for rotation therewith, an actuator pressurizable to apply axially-inward force to the damping material and a stator configured to support the actuator. A sensor determines the force applied to the actuator and a torque cell is axially aligned with the rotor for measuring torque of the rotor in relation to force applied to the damping material. The calculation of surface friction of the damping material is possible based on the measured load and torque. A method of measuring surface friction of a brake pad insulator material as well as a method using a brake dynamometer is also presented.