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SAE J2747-2019: A Practical Guide to Hydraulic Pump Airborne Noise Bench Testing đ ī¸
SAE J2747-2019 establishes a standardized bench test method for measuring airborne noise from positive displacement hydraulic pumps used in ground vehicle power steering systems. This recommended practice ensures consistent, repeatable sound power measurements across different test labs by specifying pump mounting, operating conditions, instrumentation, and facility requirements. Whether you are a vehicle manufacturer or pump supplier, adhering to J2747 provides a common language for evaluating pump noise performance.
🔍 Engineering Design Insight: The key to accurate noise measurement lies in isolating the pump from extraneous vibrations. The test stand must include a structurally isolated mounting block (e.g., 1.2 cm steel or aluminum) and a belt drive with controlled tension. Use frequency response function (FRF) measurements to verify that the fixture does not introduce resonances in the frequency range of interest.
1. Test Facility and Instrumentation Requirements
The test facility must be a hemi-anechoic room meeting ISO 3745, with a low-frequency cut-off of 250 Hz (200 Hz acceptable for small components). Background noise should be at least 12 dB below the pump noise level. The following table summarizes critical instrumentation specifications:
| Parameter | Specification |
|---|---|
| Microphone Array | 19 microphones in hemispherical arrangement per ISO 3745; 1 m radius preferred (0.5 m radius if low-frequency criteria met) |
| Data Acquisition | 48 kHz sampling rate, Class 1 accuracy (±0.7 dB or ±8%) per IEC 61672 |
| Speed Monitoring | Tachometer for pump speed control and trigger |
| Temperature Sensors | Two thermocouples for component and fluid temperature |
| Pressure Transducers | Static transducers for inlet and outlet pressure; optional dynamic transducers |
The microphone array coordinates are defined in the standard; for example, positions range from (x/r = -0.99, y/r = 0.00, z/r = 0.15) for microphone 1 to (0.00, 0.00, 1.00) for microphone 19. Proper positioning is essential for accurate sound power calculation.
⚠️ Common Mistake: Using a room that is not truly hemi-anechoic can introduce reflections that distort sound power measurements. Always verify that the room meets ISO 3745 qualification criteria and remove any reflective objects from the test cell.
2. Test Procedure and Operating Conditions
Before testing, the hydraulic system must be warmed up until thermal equilibrium is reached and the fluid is de-aerated to prevent cavitation noise. The pump is driven via a belt with specified tension, and the mount fixture is designed to be rigid and isolated from the stand. Key operating parameters to control include:
- Pump speed: monitored by tachometer
- Fluid temperature: typically regulated to a target (often around 50-60°C depending on system)
- Outlet and inlet pressure: set per test plan
- Belt tension: per manufacturer specification
Data is acquired for multiple steady-state operating points. Sound power levels are calculated from the 19 microphone signals and reported in octave or third-octave bands. The standard mandates that background noise must be at least 10 dB below the pump noise. If a facility has a higher cut-off frequency, data below that frequency should not be reported unless clearly identified.
For sweep testing, the tachometer trigger synchronizes data acquisition. Ensure that all instrumentation meets Class 1 accuracy to maintain repeatability.
3. Frequently Asked Questions
- Why is the 19-microphone array necessary? It provides a comprehensive spatial sampling of the sound field, enabling accurate sound power determination as per ISO 3745. The hemispherical arrangement accounts for directivity of the pump noise.
- Can I use a smaller room? The standard specifies hemi-anechoic conditions. A smaller room may suffice if it meets the ISO 3745 qualifications for the frequency range of interest. However, the 1 m radius array requires adequate space.
- How do I ensure my test stand doesn’t contribute noise? Use a silent driveline, journal bearings, and isolate the pump mount. Perform FRF checks to identify fixture resonances. Also verify that motor noise is at least 12 dB below pump noise.
- What if my pump operates at different speeds and pressures? The test can be repeated at multiple operating points. Report sound power at each condition. The standard provides guidelines for reporting formats to ensure comparability.
By following SAE J2747-2019, engineers can rely on a robust, repeatable method for benchmarking hydraulic pump noise. This facilitates design improvements and quality control across the supply chain.
