基于国六远程排放监控平台获取的385辆重型车实际道路运行数据，参照美国研究低负荷测试循环（low load cycle，LLC）的方法，采用短行程窗口法、分峰拟合等技术分析国内重型车实际道路低负荷工况运行特征及NO_x排放特征。研究发现，我国重型车窗口负荷中位数低于20%，瞬态运行工况超过57%的时间负荷低于20%，而该负荷区间排温偏低，后处理系统催化效率下降，NO_x排放明显偏高，同时，窗口负荷呈现集中于0%~40%的“单峰”分布，和美国重型车负荷分布差异显著。因此，提出平均负荷小于等于13%作为中国重型车低负荷工况窗口上限值，为构建适合国内重型车实际道路运行特征的低负荷工况提供参考。此外，NO_x传感器露点保护策略致使14.60%~23.88%高排放时长数据未纳入监管，需引起重视。

Based on the actual road operation data obtained from China Ⅵ remote emission monitoring platform of 385 heavy-duty vehicles, the low-load operating characteristics and NO_x emission features of China heavy-duty vehicles were analyzed by employing techniques such as the micro-trip window method and peak-by-peak fitting according to the U.S. Low Load Cycle (LLC) methodology. The results reveal that the median window load for heavy-duty vehicles in China is below 20%, and the load that remains below 20% during transient operating conditions accounts for more than 57%. Within the load range, the lower exhaust temperature leads to reduced catalytic efficiency of aftertreatment system and obvious increase of NO_x emissions. Furthermore, the window load distribution demonstrates a "single-peak" pattern concentrated between 0% and 40%, which differs significantly from the load distribution of heavyduty vehicles in the United States. Accordingly, an average load of 13% or less is proposed to be set as the upper limit for the low-load operating conditions window for heavy-duty vehicles in China, which provides a reference for establishing low-load operating conditions that are suited to the actual on-road operating characteristics of domestic heavy-duty vehicles. In addition, the current NO_x sensor dew point protection strategy leads to the exclusion of 14.60% to 23.88% of high-emission operating duration from supervision, necessitating urgent attention.