The difference between real driving emissions of heavy-duty vehicle and the approval emission results of engine bench test was caused mainly by the discrepancy of both test conditions .Taking a LNG-electricity hybrid bus in Guangzhou as the research object ,the operation data such as vehicle speed ,engine speed and torque were collected in real time by PEMS and CAN-bus when the bus ran along a typical bus line .The distribution characteristics of actual working conditions for the bus en-gine were analyzed statistically and compared with those of ETC and WHTC conditions .Due to the power control strategy , speed limit ,bus running rules and so on ,actual operating conditions of this hybrid-bus engine were mainly in the low and mid-dle speed region with a long duration at the small and medium torque ,which was different from the distribution of medium and high speed and torque for ETC set conditions .In addition ,the distribution was also different from that of medium speed and medium and small torque for WHTC set conditions .Compared with ETC ,the characteristic parameters such as average engine speed ,average power and idling ratio for WHTC were more close to those of actual operating conditions in Guangzhou .%重型汽车实际运行排放与发动机排放型式核准台架测试结果间的差异主要在于二者的测试工况不同.以广州市在用的一款LNG-电混合动力公交车为研究对象,在公交线路上开展整车实际道路测试,通过PEMS,CAN总线实时采集测试车辆车速 、发动机转速和扭矩等数据,统计分析该车辆发动机实际工况的分布特征,并与ETC工况和WHTC工况进行比较分析.结果表明,因受动力控制策略 、限速 、公交车运行规律等影响,该混合动力公交车发动机实际运行工况主要分布在中小转速区,在中小扭矩区时间占比较大,不同于排放型式核准发动机台架测试瞬态工况ETC主要分布在中高转速与中高扭矩区,也不同于WHTC工况主要分布在中等转速区 、在中等与偏小的扭矩区分布较均匀.相比于ETC工况,WHTC工况在发动机平均转速 、平均功率和怠速比例等工况特征参数与该公交车发动机实际运行工况较为接近.
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