Experimental Investigation And Analysis On Cavitation Of Hydraulic Retarder

As a brake assist, hydraulic retarder is widely used in diesel locomotive, heavy truck and military vehicle. It can improve driving safety and braking safety of cars. Cavitation will occur in hydraulic retarder when vehicle is getting faster and heavier, which will result in performance depreciation, vibration and noise, reducing the stability and working life of braking system, affecting the running safety. It is very important to grasp cavitation rule of hydraulic retarder to guarantee driving safety. This paper studied the difference on cavitation at performance, internal flow, vibration, noise and pressure pulsation, and let out monitoring plan on cavitation. The main contents and results are as followed:(1) The significance of monitoring on cavitation of hydraulic retarder and the usual monitoring method on cavitation are summarized. The research status of fluid drive from home and abroad are introduced.(2) The theory of cavitation, cavitation vibration, cavitation noise and cavitation pressure pulsation are introduced. The basic knowledge and usual analysis method of vibration, noise and pressure pulsation are summarized.(3) Multi signal experiment test stand is built, achieved the synchronous measurement of signal on performance, internal flow, vibration, noise and pressure pulsation at different filling ratios in 800~1200rpm and 0.01~0.1MPa. Result shows that retarding torque reduced with the decrease of filling ratios, and retarding torque enlarged with the increased of rotate speed at a certain initial pressure. Besides, the influence of pressure change on retarding torque is small without cavitation, while retarding torque decreases with pressure dropped with cavitation.(4) Define cavitation of hydraulic retarder first with performance and high-speed photography. The change rate of no-cavitation is less than 2.0%. The change rate of cavitation inception is between 2.0% and 5.0%. The change rate of serious-cavitation is greater than 5.0%. High-speed photography experiment shows that cavitation first occurs in suction of pump impeller. The volume of bubble increases and fills the whole passageway when pressure dropped. Vibration acceleration differs in cavitation stage, especially in 2000-3000 Hz and 3000-4000 Hz. It is biggest in no-cavitation, second in serious-cavitation and least in cavitation inception. Sound pressure level differs in cavitation stage, especially in 2000-4000 Hz and 5000-6400 Hz. It’s relationship of size is the same to vibration acceleration. Pressure pulsation differs in cavitation stage, especially in 4APF and BPF. It is biggest in no-cavitation, second in cavitation inception and least in serious-cavitation.(5) Analysize quantitatively on cavitation charaterstic signal to ensure threshold value of different signals. Use 3σ theory to confirm threshold value of vibration and noise on cavitation. Threshold value of vibiration is 94.5dB in 2000-3000 Hz, and 89 dB in 4000-5000 Hz. Threshold value of noise is 97 dB in 2000-3000 Hz, and 78 d B in 4000-5000 Hz. Use the ratio meathod to confirm threshold value of pressure pulsation. Threshold value of pressure pulsation is 1.9 in 4APF, and 2.3 in BPF. Finally, change parallel side blade to 15° slant blade to verify the rationality on threshold value confirming meathod of this paper.