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Brake Performance—Rubber-Tired Earthmoving Machines (SAE J1473-1999)
This standard defines minimum performance and test criteria for service, secondary, and parking brake systems on self-propelled, rubber-tired earthmoving machines such as loaders, tractors, graders, backhoe loaders, tractor-scrapers, excavators, and dumpers as defined in SAE J1057. It also covers retarders and provides uniform evaluation of braking capability. 🛠️
1. Overview and Scope
SAE J1473 applies to machines identified in SAE J1057. The standard was originally issued in 1984 and updated in 1999 when it was cancelled and superseded by later specifications, but its technical content remains the foundation for brake system design and testing in this category. It specifies brake system components, definitions, and performance requirements for service, secondary, and parking brake systems, as well as retarders used for speed control on grades.
2. Brake Systems and Performance Requirements
All machines must be equipped with three independent brake systems:
- Service Brake System: The primary system used for stopping and holding the machine.
- Secondary Brake System: A system capable of stopping the machine in the event of any single failure in the service brake system.
- Parking Brake System: A system designed to hold the machine stationary in a stopped position.
Brake systems may share common components, but in the event of a failure of any single component (other than a tire), the brake systems must still provide stopping capability meeting the secondary brake system performance requirements. This design insight is critical for engineering robust brake systems: redundancy must be ensured without relying on the same components that could fail simultaneously.
Machine mass for testing is defined as the operating mass including the heaviest combination of equipment approved by the manufacturer, an operator of 75 kg, and the machine fully fueled and serviced. This definition ensures performance testing is conducted under worst-case conditions.
⚠️ Machine Mass Caution: Always verify that the test mass includes the heaviest equipment combination, a 75 kg operator, and full fuel and fluids. Using an incorrect mass can invalidate performance results.
3. Testing and Compliance
Testing must be conducted on a designated test course with surface conditions representing typical usage. The standard specifies accuracy requirements for instruments measuring brake system pressure, machine speed, mass, stopping distance, actuating force, and grade (see Table 1).
| Instrument (Parameter) | Accuracy (Indicated Reading) |
|---|---|
| Brake System Pressure | ±3.0% |
| Machine Speed | ±3.0% |
| Machine Mass | ±2.5% |
| Stopping Distance | ±1.0% |
| Brake Control Actuating Force | ±3.0% |
| Grade | ±1.0% |
Brakes are considered cold if any of the following conditions are met:
- Not actuated in the previous 1 hour (except during burnish or preconditioning).
- Cooled to 100 °C or less when measured on the brake disc or on the outside of the brake drum.
- For totally enclosed brakes (including oil-immersed), the measured temperature on the outside housing is below 50 °C or within manufacturer’s specifications.
🛠️ Cold Brake Definition: Always confirm that brakes meet one of these criteria before testing to ensure baseline performance. Relying solely on the 1-hour rule without temperature checks is a common mistake.
The burnish procedure is used to condition the friction surfaces of the brake(s) before performance testing. The mean deceleration can be calculated from stopping distance using the formula: a = V² / (2L), where V is the initial velocity in m/s and L is the stopping distance in meters. 🔍
Frequently Asked Questions
Q1: What are the minimum performance requirements for service brakes?
While exact numbers are specified in sections 7.6 and 7.7 of the standard, the service brake system must meet minimum stopping distance and mean deceleration criteria defined for the machine’s category. Engineers should refer to the latest version of the standard for current values.
Q2: How to calculate mean deceleration from stopping distance?
Use the formula a = V² / (2L), where V is the initial velocity (m/s) immediately prior to brake actuation, and L is the stopping distance (meters). This average deceleration is used for uniform comparison.
Q3: When are brakes considered cold?
Brakes are considered cold if they have not been actuated for the previous 1 hour (excluding burnish steps), or if their temperature is below 100 °C on the disc/drum (or below 50 °C for the housing of enclosed/oil-immersed brakes). Always verify temperature rather than relying solely on time.
Q4: What is the purpose of the secondary brake system?
The secondary brake system provides stopping capability in the event of a single failure in the service brake system. It is a redundant safety system that must meet its own performance requirements, even if some components are shared between systems.
For engineering teams designing or testing brake systems on rubber-tired earthmoving machines, SAE J1473 provides a comprehensive framework for ensuring safety and performance. Understanding the definitions, testing criteria, and common pitfalls helps avoid costly mistakes and ensures compliance with industry best practices.
