Bosch Endorses LMS Test.Lab for Vibration Qualification Testing

The performance and durability of Bosch gasoline injection systems inherently determine the operation and reliability of automotive engines. To make sure these injection assemblies operate as planned and last their full lifetime, Bosch extensively tests these parts under extreme circumstances. Key equipment are four LMS environmental testing systems, which Bosch uses in combination with shaker systems to perform dynamic vibration measurements. Recently, Bosch upgraded all eight-channel environmental testing systems to LMS Test.Lab and LMS SCADAS III, providing higher degrees of testing productivity and flexibility for its automotive qualification tests. In addition to improved functionality, Bosch also takes advantage of LMS Test.Lab’s excellent user interface and networked data collection, to furthermore respond to its specific reporting requirements.

To keep its leading market position well into the future, Bosch is currently working on advancing the progressive development of its range of Gasoline Direct Injection (GDI) systems. These injection systems work with high-pressure valves that inject fuel at any given time directly into the combustion chambers. Their programmable microprocessors enable an accurate calculation of every single combustion cycle, providing precise adjustments in response to varying operating conditions and specific driver characteristics. Increased computation power allows engineers to integrate additional engine management functions, including knock control, boost pressure control of turbo chargers, throttle valve actuation and speed control. In addition, injectors with multiple aperture nozzles and other new injection advances, including Fuel Stratified Injection (FSI), further optimize engine performance characteristics. Overall, these modern injection systems are advantageous in many ways, as they increase driving pleasure and reduce fuel consumption and carbon dioxide emissions.

The new generation of GDI systems basically consists of a high-pressure pump (HDP5), high-pressure injectors (HDEV4/5) and a high-pressure fuel rail, as the mechanical components. To realize optimal durability performance of these parts, engineers are requested to design components and systems that are fail-safe – but at the same time not over-designed. Parts being repeatedly subjected to load cycles well below the material’s static failure load may potentially damage this material and subsequently initiate cracks. Inadequate durability engineering may also lead to parts that are too heavy or too expensive. All components of a vehicle’s injection system assembly, including injectors, pump, rail, valves and throttle device must withstand excessive and long-lasting vibrations, and some of them must also resist extreme and varying climatic and pressure conditions. Therefore, Bosch performs extensive operational tests and qualification measurements, for flawless operation throughout the entire lifecycle.

Already in the early nineties, Bosch used LMS CADA-X and HP Paragon systems to perform operational durability tests and qualification measurements on fuel injection systems. A typical test setup consisted of an injection system locked on a shaker in a climatic chamber. Under high pressure and at high temperature, the gasoline was supplied to the injector, while vibration levels on several points on the structure were measured. Recently, as part of a broader investment strategy, Bosch replaced all its environmental test software and hardware at multiple locations in Germany. The reason for this decision was the age of the testing equipment, which exceeded ten years. Although the systems were still running smoothly, the increased maintenance costs and upcoming obsolescence of the HP Paragon calibration service lead to the replacement.

The new environmental test systems consist of LMS SCADAS 310 and 316 front-end hardware and the LMS Test.Lab Environmental software portfolio for automotive testing, containing random vibration control, sine control, sine dwell and sine-on-random. In addition to the functionality offered by the previous systems, each of Bosch’s four systems is capable of controlling sine-on-random excitation schedules. This is of particular importance since requests for sine-on-random tests are becoming more frequent and related ISO test regulations are underway. Compared to the test requirements that apply to aerospace markets, with large test specimens and huge channel counts, eight-channel test setups are often the preferred choice of automotive manufacturers. Each of these channels can be freely allocated for use as a measurement or vibration control channel. A LAN network allows gathering the acquired data from different distributed measurement test setups and storing this mass of information on a central network location, which securely manages the data while adhering to a project-oriented approach. 

An environmental measurement sequence at Bosch typically occurs in three consecutive steps, each focusing on measurements in one specific direction (three orthogonal axes). After these initial measurements, which serve as references for qualification tests to be executed later on, the tested specimens are subjected to severe durability testing. During these tests, separate injectors or larger assemblies, for example an intake manifold including an injector rail and control unit, are exhaustively tested by vibration (on shaker), climatic (in chamber) and operational load at the same time. Bosch’s extensive range of durability tests includes both operational as well as non-operational test setups. Full-operational tests carry serious risks for fire hazards, especially when danger of fuel leakage exists.

Bosch engineers also perform durability shaker tests on fuel rail assemblies to check whether bending modes and stresses have the potential to cause damage, and dwell tests to make sure whether cracks have been initiated or not.

After these durability tests, the specimens are subjected again to vibration qualification measurements, which are performed exactly the same way as the baseline measurements performed earlier on. In case the results of baseline and final measurements show differences, the performed durability tests have generated fatigue in the structure of one or more of the tested components. In such cases, further testing is required to distinguish the components that suffered most and to trace to what extent their durability performance is affected. In some cases, destructive tests are executed to find out precisely when components break down.

Testing flexibility is key to Bosch, because automotive OEM’s pass on their own specific testing requirements, which are to some extent based on their own testing practices and experience. The first task Bosch engineers perform is tailoring the test in such a way that it fits the purpose of the requested performance specifications. Test tailoring involves the specification of test types, test loads, test profiles and the duration of tests. Since Bosch is strongly committed to the quality of its high-pressure injection system equipment and all formal responsibilities arising from a supplier role, it may decide to execute modified or additional tests to make sure GDI’s will operate as planned. Bosch additionally leverages its own yearlong expertise, and uses the outcome of specific vehicle measurements to further fine-tune the internal Bosch-proprietary specifications to which new components and assemblies have to comply.