| The dominant technique applied to heavy vehicle in the process of continuous retarding and braking is hydraulic retarding.However,this method has shortcomings such as low thermal efficiency,unstable braking torque and long separation time.In this paper the above problems in retarding technology are studied.A new type of hydraulic retarding braking system is designed according to the special requirements of the target vehicle.The main components are selected according to the parameters matching criterion and the related product manuals.In order to analyze and verify the performance of the system,models are built in AMESim,the dynamic characteristics of the braking torque,pressure and flow parameters are analyzed.To verify the reliability and advantages of the proposed system,experiment of hydraulic retarding and braking system are carried out.In order to better the cooperation between the vehicle and retarding braking system,this paper allocates the braking force of the front and rear axle of the vehicle based on the ideal braking force distribution strategy and the requirements of ECE braking regulations.The logic relationship between pure hydraulic braking and machine-hydraulic compound braking are also designed.An integrated model including hydraulic retarding and braking system,vehicle transmission system and its distribution control strategy is established in AMESim.The braking torque,slip rate and fuel consumption of pure hydraulic braking,machine hydraulic compound braking and NEDC condition are studied respectively.The results of this study show that compared with the original vehicle hydraulic retarder,the new hydraulic retarding and braking system is able to run continuously for a long time.Its response speed is faster than the hydraulic retarder.It can provide continuous slow braking torque according to the actual road demand which only related to the braking signal instead of the vehicle speed.So it has better controllability and stability.At the same time,the system can control the wheel slip rate around the steady value by the hydraulic retarding braking distribution strategy.In the NEDC condition,the hydraulic braking accounted for 83% of the total braking ratio which also reduces the fuel consumption and emissions. |
