Vehicle Downhill Speed Planning For Commercial Vehicles Based On Vehicle Mass Identification

Long downhills are the most frequent area of traffic accidents in mountain areas.Continuous braking is usually used to keep the vehicle speed in the safe speed when the commercial vehicle drives on the long downhill in mountain areas.Commercial vehicles’ drivers often adjust the braking vehicle speed based on their driving experience and their visual perception.Commercial vehicle speed is mainly affected by slope grade,commercial vehicle mass and other influence factors during the downhill process.All these influence factors increase the difficulty of the driving operation for the commercial vehicles’ drivers.In this thesis,the aim of the research is the control of the commercial vehicle speed on the long downhill in mountain areas.The dynamic commercial vehicle mass is identified in real time during the downhill process.A safe vehicle speed planning method for commercial vehicle on the downhill is proposed according to the vehicle longitudinal dynamics,combined with the slope information and the temperature limit of commercial vehicle’s brake drum.The safe vehicle speed planning method has a great significance for commercial vehicles when they are driven on the long downhills in mountain areas.This research mainly studies on the design of the safe vehicle speed planning,the calculation of the commercial vehicle engine brake force,the temperature properties of the brake drum and the online identification of the commercial vehicle mass.The vehicle test is conducted to verify the feasibility of the dynamic commercial vehicle mass identification during the downhill process and validity of the safe vehicle speed planning model.Aimed at the braking safety of the commercial vehicle on long downhill,this research conducts the safe vehicle speed planning using the vehicle and the slope parameters as input and using the temperature limit of the brake drum as constraint.The calculation model of the engine brake force is established.And from the matching calculation,the only engine braking could be used when the slope grade is 3%~4%.Through the temperature properties analysis of the brake drum,the research finds that the lower the uniform braking speed is,the larger the braking force is,leading to the temperature increase of the brake drum.What’s more,the increase of the commercial vehicle mass and the slope grade also rise the brake drum’s temperature.Then,the safe vehicle speed and the initial slide slope length are analyzed based on different commercial vehicle mass and initial vehicle speed,aiming at the slope grade of 5%~9%.After this,the safe vehicle speed planning method is confirmed in middle and large slope grade.The commercial vehicle mass identification model is built according to the functional principle of commercial vehicle on the downhill combined with recursive least square method.The commercial vehicle mass identification is the most accurate when the sampling frequency for the vehicle speed is 20 Hz through the comparison of different sampling frequency for the vehicle speed.The accuracy is 96.16%,which validate the feasibility of the commercial vehicle mass identification model.The vehicle tests are carried out based on commercial vehicle mass identification model and safe vehicle speed planning model.The test results show that,the identification accuracy of the test vehicle mass is 95.19%.The identification accuracy means that the commercial vehicle mass identification model is feasible.The vehicle tests are stopped at 3453 m,3486m and 3438 m respectively after using the safe vehicle speed planning because the temperature of the brake drum exceeds 180℃.But the brake drum temperature could be maintained beside the temperature limit when the test vehicle reaches the bottom of slope from the brake drum temperature rise trend.The safety of the commercial vehicle on the long downhill could be ensured.