Shift By Wire System Research And Design Base On Functional Safety

With the development of automobile technology and consumers' requirements for comfort performance are increasing,the technology application of replacing human power by electronic and electrical is becoming more and more common.Shift by wire system is a product of this era.But from simple and reliable mechanical components to a series of complex electronic and electrical components,the risk of the whole system increases without doubt,so how to ensure the safety of the system has become a hot topic.To achieve the system functional safety,we perform the full life cycle functional safety during the Shift by wire system development,in this paper the author emphersize the following point:First,identify the risk point.This paper based on ISO 26262-2018 and SAE J2980-2018 two standards,identify the functionality of the Shift by Wire system.Derived the system malfunction from functionality by HAZOP.According to the vehicle architecture,got the vehicle level mulfunction behavior from the system malfunction,and at the end,got the hazard which is the risk point.Second,quantify the risk.This paper focuses on quantization of the risk evaluation in vehicle level which is the weakness in domestic functional safety design.First specify the research scope of Shift by Wire system,and then analyze the hazards,and define the situation.According to the hazard events,calculate the Severity,Exposure,Controllability and the Fault Tolerance Time Interval detail.This paper aim at ‘the vehicle unintended back driving in stationary state' safety goal,calculated the above parameters.Finally,define the fault handling time interval through the Hazard Matrix Test.Based on the S,E and C,evaluate the risk and get the quantitative risk,which defined as ASIL.Third,reduce the risk to an acceptable level.To avoid or mitigate the systematic failure and random hardware failure effects on the vehicle,ensure the Functional safety achieved,this paper implements Fault Tree Analysis,derives the failure rate requirements of each element,calculates the cut sets,and derives the functional safety requirements for Shift by Wire system based on the cut sets,designed the concept of functional safety,and then verifies the completeness and correctness of the requirements by the qualitative analysis method of FMEA-MSR.Due to the responsibility,the system phase,software phase and hardware phase were developed by suppliers.In order to reduce risks,we performed the audit and assessment in five milestones,which were not described in this paper,to ensure the supplier's development process the technical satisfied the requirement from ISO 26262.Finally,validate the risk has been reduced to the acceptable level.According to the functional safety requirements,the author performed safety validation.This paper just describe one safety goal,which defined as “the vehicle unintended back driving in stationary state”.The test result indicated that,the normal driver could stop the car in around 1.9m without any safety mechanism.In contrast,the driver could stop the car with in 0.1m with the safety mechanisms designed in functional safety actives,which was much lower than the accept criteria 0.5m.Based on this result,we can confirmed that the previously evaluated class of controllability and the Fault Handle Time Interval were appropriate,and the design achieved functional safety.