Simulation Study On The Process Of Air-compressed Engine Auxiliary Brake

Nowadays, the social vehicle demand is growing continuously, and the high speed and security have always been the main focus in automobile field. While long-term used traditional main brake could easily be damaged due to overheat and wear-out, the research and development of auxiliary brake are imperative. Engine auxiliary brake technology doesn’t have the above problems and is a research hotspot in this field.This paper analyzed the working principles, working processes and braking effects of three common engine retarder-engine exhaust brake, engine bleeding retarder and compression release engine retarder in detail. Through in-depth study on the methods of exploring the potential braking ability, the paper proposed a scheme of air-compressed engine auxiliary brake, which contains two engine strokes in a working cycle. A working cycle is divided into four processes which are intake, vacuum pumping, compression and exhaust. After analyzing these processes respectively, it is obvious that the variable valve operation parameters play a decisive role in the braking performance.This paper established and verified an AVL BOOST model based on CY4102BZLQ turbocharged inter-cooled diesel engine. The effects of valve operation parameters on air-compressed braking performance were investigated under different velocities. By evaluating the influence rules of cylinder pressure, intake and exhaust mass flow response to valve operation parameters, this paper presents the influence reason of braking power response to valve operation parameters. The simulation results indicate that-First of all, with the same valve operation parameters, the braking power increases with velocity; secondly, the braking power changes regularly along with the change of valve operation parameters; in addition, there are optimal valve operation parameters corresponding to the maximum braking power under every speed cases and these optimal valve operation parameters change regularly with velocity. The results have a theoretical guidance for the design and match of variable valve system in the future. In order to obtain the best braking effect, the variable valve system should act as following rules with the increase of speed: advancing the intake valve open timing, increasing the intake valve lift, retarding the intake valve closing timing, advancing the exhaust valve open timing, increasing the exhaust valve lift and retarding the exhaust valve closing timing. Comprehensively considering the changes of braking power under each speed, the eclectic optimal valve operation parameters were selected. And the effective braking power and braking efficiency are:1000r/min-51.5kW- 1.526,1900r/min-94.84kW-1.426,2800r/min-114.41kW-1.291. This result fully illustrates that air-compressed engine auxiliary brake has the very good braking potential.