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SAE J667 Brake Test Code: Inertia Dynamometer Testing for Automotive Brakes
Introduction to SAE J667
This SAE Recommended Practice establishes a uniform laboratory procedure for evaluating performance and wear of automotive brakes and brake drums by inertia dynamometer simulation. The code is applicable to hydraulic, air, or electrically actuated brakes, with appropriate substitutions for electric brakes. It includes methods for torque output and deceleration tests, lining life evaluation, brake characteristics (fade and recovery, noise, chatter, grabbiness), and drum evaluation.
Key Test Procedures and Conditions
The standard defines a series of sequential tests to comprehensively characterize brake performance and wear under simulated vehicle conditions. The key phases are:
| Test Phase | Speed (mph) | Number of Stops | Starting Drum Temperature |
|---|---|---|---|
| Initial Lining Break-In | 40 | Variable (until 80% contact) | 125–150°F (200°F for truck) |
| Effectiveness Tests (Passenger Car) | 30, 50, 70 | At least 5 per speed | Cooled to 125–150°F between stops |
| Fade and Recovery Test (50 mph) | 50 (fade), 30 (recovery) | 10+10 | 125°F before trial; blower cooling continuous |
| Lining Wear Test (Glazing) | 30 | 500 | 200°F |
| Lining Wear Test (Mid) | 40 | 300 | 300°F |
| Lining Wear Test (High Speed) | 60 | 100 | 350°F |
Throughout these tests, the blower air velocity is regulated to 2200 fpm (25 mph) to provide consistent cooling, and dynamometer inertia must be matched to the vehicle’s work load within ±5%.
Instrumentation and Engineering Design Insights
Accurate instrumentation is critical for reliable results. The dynamometer must control speed within ±2% and inertia loading within ±5%. Torque output must be measured directly and via deceleration. Drum temperature is measured by a thermocouple located 0.090 inches from the braking surface. A direct-reading pyrometer can be used for lining temperature observation.
🔍 Design Insight: The drum thermocouple must be placed at 0.090 in from the braking surface, in the center of the brake track, to accurately capture friction interface temperature. Cooling air velocity of 2200 fpm simulates a 25 mph crosswind, ensuring consistent thermal conditions across tests.
⚠️ Common Mistake: Failing to pre-measure lining thickness at multiple points (toe, center, heel) before and after each test phase can invalidate wear data. Similarly, improper drum cleaning with a suitable solvent is essential to avoid contamination.
Frequently Asked Questions
How is brake torque output evaluated?
Torque output is evaluated through effectiveness tests at multiple speeds and line pressures. The results are plotted as torque output vs. brake input, providing characteristic curves for the brake assembly.
How does the dynamometer simulate vehicle conditions?
Vehicle conditions are simulated by matching the dynamometer’s rotating inertia to the work load imposed on the brake in the specific vehicle. Cooling air velocity and stop cycles are calibrated to replicate thermal loads typical of on-road driving.
How is lining wear measured?
Lining thickness is measured at exposed edges of shoes at designated toe, center, and heel points before and after each test phase. The total wear is calculated by subtracting post-test measurements from initial measurements.
What is the purpose of the fade and recovery test?
The fade test assesses brake performance degradation under repeated high-temperature stops, while the recovery test evaluates how quickly the brake regains effectiveness after a cooling period. This is crucial for safety in heavy braking scenarios.
