Analysis of transient pressure pulsation during hydraulic retarder starting process

Hydraulic retarder is a highly efficient auxiliary brake device in vehicle transmission system. Compared with traditional vehicle braking systems, it can improve braking and transmission thereby improving safety in driving. Being able to independently design and manufacture hydraulic retarders is therefore essential to safeguarding development of vehicle industry for a country. The internal pressure pulsation in the hydraulic retarder is one of important factors that could cause vibrations and noise in a vehicle, while there is limited study on how the transient pressure pulsation changes responsively to the impeller angle and liquid filling rate in the transmission system. The purpose of this paper is to bridge this gap by presenting the results of an experiment study on the impact of the impeller angle and charging rate on transient pressure pulsation in a hydraulic retarder during its starting process. We compared three blade inclination angles: 60°, 75° and 90°, and five liquid filling rate: 60%, 70%, 80%, 90% and 100%, and conducted the experiments in a transient pressure pulsation test system equipped with an INV3020 data acquisition system. The test system included a frequency converter, a drive motor, a hydraulic retarder, a high frequency dynamic pressure sensor, a torque speed collector and a booster pump. During the test, the motor speed was adjusted by the inverter, and the liquid filling rate was adjusted by the inlet ball valve and the outlet ball valve in the hydraulic reducer as well as the booster pump to control water-filling of the hydraulic reducer cavity. The amplitude of the pressure pulsation at the axial frequency and the leaf frequency was analyzed to elucidate the effect of the impeller angle and the liquid filling rate. The results showed that the peaks of the pressure pulsation in the hydraulic retarder under different blade inclination angles occurred below 200 Hz, and the pressure pulsation mainly occurred at the leaf frequency and increased with the blade inclination. The pressure pulsation under different liquid filling rate mainly occurred at the leaf frequency. The amplitude of the pressure pulsation decreased as the charging rate increased from 60% to 90%, and then increased steadily when the charging rate further increased from 90% to 100%. Reducing the impeller angle and maintaining the charging rate at 70%-90% can therefore effectively reduce the pressure pulsation. The results presented in this paper unravel the impact of the impeller angle and charging rate on transient pressure pulsation in the hydraulic retarder, and have important implications for optimal design of low-vibration and low-noisy hydraulic retarders.