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With the development of the road industry, heavy-duty vehicles now require additional braking power to fulfill their braking requirements. Auxiliary braking systems, which include a hydraulic retarder and an engine brake, can provide additional braking force in nonemergency braking conditions. A water medium retarder is a new type of hydraulic retarder that can convert the kinetic energy of a vehicle into the thermal energy of coolant. This study introduces a novel auxiliary braking system involving a water medium retarder and an engine brake for heavy-duty vehicles. The specific forces of heavy-duty vehicles and the auxiliary braking system are established. The control logic of the novel auxiliary braking system is assigned, and a main controller is designed to dynamically manage the entire braking process. The main controller includes controllers A and B, which handles the engine brake and water medium retarder, respectively. The heavy-duty vehicles dynamic system model is created using MATLAB/Simulink. Upon performance testing, simulation results show that the designed main controller can effectively and rapidly manage the auxiliary braking system, thus satisfying the braking requirements in any nonemergency braking condition. Even when the slope of a road changes, the main controller can extract dynamical forces as well as acceleration parameters and fulfill the braking requirements of vehicles.

Water medium retarders are auxiliary braking devices which can reduce the vehicle speed by converting the mechanical energy of a driving vehicle to the total energy of the working fluid. These retarders can replace service brakes in nonemergency braking conditions. This study analysed the dynamic and thermodynamic characteristics of water medium retarders. An observer was designed to identify the optimal braking power of the water medium retarder under different braking conditions. The braking process involving the retarder can be divided into three stages. The controller was designed separately at each stage to control the braking torque of the water medium retarder according to braking requirements. A combined dynamic and thermodynamic vehicle model was also constructed with MATLAB/Simulink. The effects of the controller on the vehicle feedback control system were analysed. The results show that the controller equipped with the observer can effectively control the water medium retarder to satisfy the braking requirements of vehicles on the assumption that the coolant circulation is sufficiently radiated. Finally, an experiment was conducted to determine the performance of the controller and to validate the simulation results.

Hydraulic retarders are extensively used in commercial vehicles because of their advantages, such as their large braking torque and long continuous operating hours. In this article, the structure and working principles of hydraulic retarders are introduced, and their dynamic characteristics are analyzed. The theoretical model of a hydraulic retarder is then established based on the dynamic analysis of a vehicle driving downhill. The braking process that involves the hydraulic retarder is divided into three stages. Moreover, the filling ratio controller of the hydraulic retarder is designed by adopting fuzzy control theory to control the braking torque of the vehicle while driving downhill. The vehicle dynamic model and constant-speed control model were then established in the MATLAB/Simulink environment. The simulation results showed that the fuzzy logic controller designed in this study has good constant-torque control and anti-inference performances, which can accurately and immediately produce braking torque to satisfy the braking requirement, thereby enabling the vehicle to drive downhill at a constant speed. As a result, the control strategy designed in this article can lead to significant improvements toward a safe road transport.

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