Low-duty Inertia Dynamometer Hydraulic Brake Wear Test Procedures for Vehicles Above 4536 kg (10 000 lb) of GVWR
This Recommended Practice is derived from OEM and tier-1 laboratory tests and applies to two-axle multipurpose passenger vehicles, or trucks with a GVWR above 4536 kg (10 000 pounds) equipped with hydraulic disc or drum service brakes. Before conducting testing for a specific brake sizes or under specific test conditions, review, agree upon, and document with the test requestor any deviations from the test procedure. Also, the applicable criteria for the final test results and wear rates deemed as significantly different require definition, assessment, and proper documentation; especially as this will determine whether or not Method B testing is needed.
This Recommended Practice does not evaluate or quantify other brake system characteristics such as performance, noise, judder, ABS performance, or braking under extreme temperatures or speeds. Minimum performance requirements are not part of this recommended practice. Consistency and margin of pass/fail of the minimum requirements related to wear rates and wear behavior can be assessed as part of the project in coordination with the test requestor.
NOTE: This Recommended Practice uses the unit conversion and rounding techniques from the NIST Special Publication 811. This to ensure the use of standard conversion factors and to determine the appropriate number of significant digits to ensure the Rounding Error (RE) of the converted unit is smaller than or similar to the RE of the original English or Imperial unit.
Certain vehicle applications (like flat-bed recovery vehicles) have driving patterns which are considered light-duty with (a) friction material temperatures remaining under 232.0 °C (450 °F) 2.03 to 2.54 mm (0.08 to 0.1 inch) below the braking surface for at least 90% of the time, and (b) brake applications which require 2690 kPa (390 lbf/in2) or less of hydraulic pressure. This Recommended Practice provides two inertia-dynamometer test procedures, which are repeatable and cost-effective to assess, screen, benchmark, troubleshoot, or fingerprint a given foundation brake regarding low-duty brake wear. The first procedure (or Method A) is a wear versus temperature test from 93.0 to 427.0 °C (200 to 800 °F) to determine if there are potential wear rate issues under low temperature conditions and a low-duty driving cycle. If deemed required after the initial wear versus temperature test (Method A), or upon direct customer request, the second procedure (or Method B) provides an extensive wear test at a constant temperature of 79.0 °C (175 °F) to determine the wear rates and behavior of the friction couple. Data from this Recommended Practice may be combined with other brake system and vehicle characteristics for a comprehensive product characterization program.
Since other wear test procedures cover a different (higher) range of operating temperatures, kinetic energies, and levels, the accelerated wear rate behavior of certain friction materials under low-duty regimes is not properly determined or estimated using test conditions which can affect the transfer layer behavior. The wear test method implemented in this Recommended Practice was derived from prior field testing and correlation investigation. Hence, careful attention was given to not alter the sequence and test conditions which have demonstrated correspondence to the vehicle behavior.
The SAE Truck and Bus Hydraulic Brake Committee considers laboratory test procedures useful in supporting harmonization to improve the overall performance, durability, and safety of motor vehicle braking systems using relevant and cost-effective protocols.
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