Key takeaways
Two factors decide the severity level: where the part is mounted on the vehicle (on-board, a specific on-board location, or a specific off-road location) and the expected service environment. Mounting position sets the level; the service environment decides whether extra conditions are needed. Confirm the mounting position first — discussing severity without it is meaningless.
Selecting severity to ISO 16750-3 starts with establishing where the part is mounted and the environment it sees. The same ECU mounted on the body and mounted on the chassis sees very different vibration levels.
1. How ISO 16750-3 classifies its tests
- Mechanical loads: random vibration, mechanical shock, drop and handling
- Climatic loads: temperature, humidity, solar radiation, chemical attack
- Electrical loads: overvoltage, reverse voltage, start voltage drop, short circuit
- Other loads: sealing and ingress protection, connector and terminal tests, chemical exposure
2. Mounting position sets the severity
The standard groups mounting positions into several classes:
On-board: parts mounted on the vehicle such as ECUs, sensors and displays.
In the engine compartment: subject to engine vibration and temperature swings.
Specific position off-road: chassis parts, which see more severe vibration and shock.
Each position maps to a different test procedure and severity parameter in the standard. A part on the body structure sees vehicle-level vibration; a part on the suspension or near the wheel sees wheel-hop-level shock.
3. Random vibration versus mechanical shock
Random vibration
Simulates the continuous random vibration excited by road roughness while driving. The PSD curve shape, the frequency range and the acceleration RMS are the three key parameters. Trucks and construction vehicles, used in harsher conditions, generally see higher vibration levels than passenger cars.
Mechanical shock
Simulates transient large impacts from potholes, speed bumps or a tyre blowout. Shock parameters include the pulse shape (half-sine, trapezoidal), the peak acceleration and the duration. Road impact, engine firing and tyre burst are separate transient conditions that each need coverage.
4. Selection steps
- Confirm the mounting position and whether the part touches the powertrain
- Confirm the vehicle type (passenger car / SUV / truck / construction vehicle) and the service environment
- Select the severity level and test procedure from the standard matrix
- Add or adjust per the OEM corporate standard
- Confirm the test directions, axes (X/Y/Z) and duration
5. Common questions
What if the standard severity and the OEM requirement disagree?
The OEM requirement governs. Corporate standards are usually stricter than the national standard and add provisions aimed at specific failure modes.
The product passed vibration testing, so why does it still fail?
The usual reason is that only function was monitored during the test and no post-test inspection was done (solder joint cross-section, connector latch force). State in the plan which checks are performed before and after the test.
