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BPW Bergische Achsen, DAF Trucks, DAIMLER, HALDEX, IVECO, KNORR-BREMSE, MAN Truck & Bus, MERITOR, SAF-HOLLAND and WABCO
Knowledge on the strength and the operational loads is necessary for the development of durable and reliable products. Linked to the strong cost pressure and the requirement for lightweight construction, the knowledge of the operational loads plays an increasingly major role in the product development. For this reason, the working group Standard Load Spectra for Commercial Vehicle Brakes (CV-Brakes) was established in November 2015 with an objective to derivate a durability standard for the commercial vehicle brakes. The working group consists of ten participants of the commercial vehicle industry and the Institute of Machine Components (University of Stuttgart). The participating companies are BPW Bergische Achsen, DAF Trucks, DAIMLER, HALDEX, IVECO, KNORR-BREMSE, MAN Truck & Bus, MERITOR, SAF-HOLLAND and WABCO. Objectives of the standard are standard load spectra as well as test load spectra for the validation of uniform durability and reliability requirements.
For the development of a standard for the commercial vehicle brakes, a procedure which could be divided into four major parts is used. In part 1 System, Load and Use Case Analysis, the system air brake, the load types on the air brake and its operating modes have to be analysed. In the analysis of the system air brake, a system boundary with input and output parameters have to be defined. For the protection of company specific design, the content of system boundary is treated as a black box for the working group. Determining the operating modes, the challenge for the working group lies in the high diversity of commercial vehicles, which results in a high number of operating modes for the air brake. In part 2 Data Inspection and Test Drives the necessary database has to be determined and compared with the existing database. Gaps in the database have to be closed. Therefore in the working group, measurement runs have to be planned and executed. Data Analysis and Load Spectra Determination is the 3rd part of the procedure. Here the database has to be analysed for the determination of the operating load spectra. Based on the base load spectra, e.g. the vibration load spectra for several road types, the operating load spectra will be determined. Because of the high diversity of commercial vehicles, load spectra for several vehicle types have to be determined for the standard. Part 4 Determination of a Testing Concept starts with the definition of uniform durability and reliability requirements. Depending on these requirements and the operational load spectra, the test paths and the test load spectra have to be defined.
So far, part 1 of the procedure is finished in the working group. The system boundary and the interfaces to the air brake are defined. As relevant load types for the air brake in this standard, the load types are clamping force, braking torque and vibrations were specified. The use case parameters for the description of the air brakes operating modes were determined. The use case parameter space is divided into the three dimensions: vehicle, environment and driver dependent parameters. It is the base for the definition of the necessary data for the standard. Currently, the working group is doing the preliminary work for checking the existing database for the specified load types and operating modes. After this, the next steps in the working group will be the data analysis and the determination of the base load spectra.
Stefan Kemmler, Bernd Bertsche - University of Stuttgart
Tobias Leopold, Jens Fricke - Knorr-Bremse Systeme für Nutzfahrzeuge GmbH
Today's product requirements demand an ever increasing functionality for the same space and usually the same number of components. Thereby, the quality, reliability and robustness of these products should be preserved or even be increased. This target conflict cannot be solved without compromises. The research community between the Institute of Machine Components (IMA), University of Stuttgart, and the Knorr-Bremse Systeme für Nutzfahrzeuge GmbH is seeking for new solutions for these challenges. The new approaches for designing robust and reliable products are being implemented directly in a current development project of an innovative Air Disc Brake (ADB).
With "Systematic Method for Axiomatic Robustness-Testing" (SMART), reliability methods and the basic concept of Robust Design methodology are related to the Taguchi Method. SMART is based on three phases: System, Parameter and Tolerance Design; accordingly, the sample phases of VDA (Association of German Automotives) are used as milestones. In the System Design, SMART focuses on the decreasing complexity according to the functional dependences of the DPs, thus precluding early random failures. In the Parameter Design phase, SMART gives the developer an approach for modeling an adaptive simulation model (SIM-SMART). This model also enables the simulation of random and possible fatigue failures in addition to the nominally robust DPs. In the early stage of product development, reliability predictions are possible. In the iterative Tolerance Design phase, the final tolerance limits for robust and reliable products are defined with consideration of compromises in terms of costs, quality and technical feasibility.
With the application of SMART, a design concept of a new generation of an ADB with less complexity is created. The extensive functions for flexible function studies are modeled with the objective of SIM-SMART. Accordingly to this model, parameter studies for determination of the nominal adjustment levels can be performed and their random and fatigue failures modeled. In conclusion, more accurate reliability test strategies are recommended using the definition of tolerance limits. The cost aspect and technical feasibility are also taken into account.
So far, SMART has not been added to the iterative Tolerance Design phase. With this paper, the method is not only extended to this phase, but also sufficiently validated. In addition, SMART can predict and analyze random failures. With its three coherent and iterative phases, it is an as yet unpublished and unimplemented approach for designing even more robust and reliable products. Robust Design Methodology and reliability methods are fundamental building blocks for products with high quality requirements. SMART presents an approach to support the designing of robust, reliable, highly functional and innovative ADB.
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