Reliability Allocation Study On Motor-transmission Integrated Driving System Of FCV

Fuel cell vehicle (FCV), one typical kind of new energy vehicle, means a lot tosolve the severe energy and environmental problems and to realize the transformation ofautomotive energy and power in the21st century. In China, the developments of FCV inpower, fuel economy, and noise performance have reached the international level. Thecore technologies in developing FCV and its key components have been basicallymastered by domestic enterprises and researchers. FCV was put into demonstrationoperation during the2008Beijing Olympic Games and2010Shanghai World Expo,and great advantages were emerged in energy conservation and emissions reduction.However, severe reliability problems of FCV were also exposed during itsdemonstration operation. It’s urgent to conduct reliability study on FCV and improve itsreliability. The electric drive system is the key component of FCV which differs fromthat of the traditional vehicles. It’s significant to improve the electric drive system’sreliability and it will make great contribution for improving the whole FCV’s reliability.In this paper, closely combined with National Hi-Tech Development Plan Key Program(863)“Research and development of fuel cell vehicle power system technologyplatform”, study of reliability allocation theories and methods are conducted around thedevelopment process of FCV. Considering that FCV’s functional component system ismuch more complex than in traditional vehicles, this paper mainly focused on thereliability allocation method of electric driving unit of FCV.In order to allocate the reliability index for electric driving unit of FCV, thereliability requirement should be cleared in the first place. So, in this paper, the wholevehicle reliability of FCV was studied firstly to make the reliability requirement ofelectric driving unit totally clear. And then, the reliability index of electric driving unitof FCV was allocated to the subunits of the electric driving unit to make the designrequirements of these subunits clear.In this paper, a new reliability allocation method based on the Fuzzy OrderedWeighted Averaging (Fuzzy-OWA) was proposed though the comprehensive researchand analysis to the existing several reliability allocation methods. This new methodincludes the system reliability allocation method based on the Fuzzy-OWA andsubsystem reliability allocation method based on the Fuzzy-OWA. And these twomethods were applied to the whole FCV and electric driving unit to gain reasonablereliability allocation results respectively. The specific implementation steps of the Fuzzy Ordered Weighted Averaging(Fuzzy-OWA) method used in systems are as follows: the contrast matrixes wereconstructed and computed based on fuzzy theory firstly; then gained the reliabilityallocation results by OWA method.The specific implementation steps of the Fuzzy Ordered Weighted Averaging(Fuzzy-OWA) method used in subsystems are as follows: first, the structure character ofFCV electric drive unit (motor-reducer coupling system) was analysed and theallocation weighted indicators were calculated based on Equal Reliability Allocationmethod and AGREE Reliability Allocation method respectively; then, the allocationweighted indicators were also calculated based on System Function Realized ReliabilityAllocation method and System Failure Criticality Reliability Allocation methodrespectively; finally, the OWA of all the allocation weighted indicators werecalculated and the reliability allocation results were gained.The reliability allocation method based on the Fuzzy-OWA takes full considerationof the fuzziness during the allocation process of reliability indexes, overcomes theshortcomings of the existing reliability allocation methods. According to the realreliability allocation process of the whole FCV and electric driving unit of FCV, morereasonable and accurate reliability allocation results are verified by using this method,and it can be seen that the proposed method can have better engineering practicalvalue.To meet the reliability requirement for whole FCV, Mean Time Between Failures(MTBF) up to4000kilometer, reliability allocation process was applied to FCV electricdrive unit and system reliability allocation technology of electric drive unit was formedin this paper. The work completed in this paper is significant for improving reliability ofFCV electric drive unit and supporting the next-generation FCV’s development inreliability and durability.