Wells Engineered Products

Good Vibrations: How Vibration Testing Differs for Automotive, Power Sports and Heavy Equipment


Engineers call it “shake-and-bake” testing for a good reason: that’s exactly what happens. Electronic components are subjected to vibration and temperature extremes exceeding what they should ever see in service. If they still perform afterward the designs are considered fit for purpose. If not, it’s back to the workstation for a redesign.

Vibration testing like this is core to the product development process at Wells Engineered Products. It demonstrates that design and manufacturing together can create components that will withstand conditions harsher than anything they should see in the field.

The challenge, from a development perspective, is that those fields differ significantly. If on-road automotive applications are the baseline, power sport and heavy-duty diverge significantly, but in opposite directions. Vibration test regimens must be tailored accordingly if they’re to represent real-world conditions.

At the Heart of Design Validation

Engineers enjoy reducing complex ideas to simple expressions, hence the phrase, “shake-and-bake.” While summarizing what happens, this glosses over the intricate details.

Vibration testing, which is done in conjunction with thermal cycling, verifies that an electronic component can endure the conditions it will see in the vehicle. It reveals any faults in circuit board design and manufacture and weaknesses in interfaces between mating parts. Temperature adds the influence of differential expansion. As such, vibration testing is a key aspect of design and product validation.

Vibration Testing Methods

Components under test are mounted on a vibration table. This is equipped with actuators to provide oscillation in two, sometimes three, axes. For added “bake,” the table is placed in an oven or climate-controlled chamber.

Test regimens must reflect the expected operating environment. The primary consideration is the nature of excitation: sinusoidal or random.

A sinusoidal excitation is one with a regular forcing frequency. Pistons and valves are good examples of sources of such vibration. Random vibrations are those from outside of the vehicle, such as impacts with potholes.

Sinusoidal excitation takes three forms. There’s the sine sweep where the component is subjected to a range of frequencies. This identifies particular resonant frequencies. Sine dwell excitation is done at those resonant frequencies, and then there’s sine-on-random, which combines sinusoidal and random excitation.

Vibration Test Specifications

Testing has little value unless it’s done in a standardized and reproducible manner. Some vehicle manufacturers have their internal standards – GMW3172 is an example – but these mostly derive from IEC 60068-2.

GMW3172, based on IEC 60068-2, includes vibration profiles, given in terms of acceleration and frequency. These relate to where in the vehicle the electronic component will be mounted. Engine components see primarily sinusoidal excitation. Those elsewhere experience more random vibration, although the severity depends on whether they are in a sprung (cabin) or unsprung (wheel end) location.

An alternative to standard test profiles is to use data obtained directly from the vehicle. In this case, the installation location is instrumented for vibration data capture in three axes. This results in Peak Spectral Density (PSD) plots that are subsequently fed into the “shake-and-bake” test apparatus.

Applications Drive Vibration Testing Details

Vibration testing is intended to verify the durability of the component in the intended application. Thus, it’s essential to know application parameters like target vehicle, mounting location, intended use, terrain and speed.

For general automotive applications – on-road use – the vibration environment is well understood. Engine-mounted components will experience primarily sinusoidal excitation along with a known range of temperatures. Those in the cabin or in unsprung parts of the vehicle will see a preponderance of random vibrations.

In power sport applications, engines run at higher RPMs. This pushes up the range of frequencies at which sinusoidal vibration testing is done. Temperatures may also be higher. A strong emphasis on minimizing unsprung mass means most random vibration is at moderate levels.

Engines in heavy equipment run slower than those in automotive applications and are often diesels. Thus, while excitation frequencies are lower, displacements may be greater. Sprung areas, (the cabin) are usually well isolated from vibration, but unsprung electronic components could be exposed to significant impacts.

Testing for Durability

Engines and vehicles are harsh environments for electronic components. Vibration and temperature changes will quickly reveal any defects in design or manufacture.

Vibration testing with temperature cycling is a core part of the supplier test plan used in the Analysis/Development/Validation process. While engineers casually refer to it as, “shake-and-bake” it’s a complex activity that requires thorough preparation and organization.

Vibration testing must reflect worst-case conditions, and that requires detailed knowledge of the application. Power sport and heavy equipment applications present complex challenges that differ significantly from on-road automotive usage: the component designer and manufacturer will take this into account throughout the development process.