Research On Improvement Of Braking Performance For Multi-axle Heavy Duty Off-road Vehicle By Theoretical And Experimental Methods

The characteristics of multi-axle heavy duty off-road vehicle (MHDOV), which is usually used as transportation and launch chassis of weapon system, directly influence the transportation and projection of weapon system. Therefore the research and develop for MHDOV to satisfy the requirement of mobile launching of strategic weapon is very necessary. Compared with the ordinary two-axle vehicle, MHDOV has a few new features about the braking ability, such as the complicated air-over-hydraulic (AOH) brake system, many axles and long wheelbases, large vehicle mass moment of inertia and obvious axle load transfer, the applied multi-axle steering and all wheels drive technology. A literature survey shows that only a few studies have investigated the braking dynamics of MHDOV and relatively little research has been performed on AOH brake system. This situation is one of the important reasons that lead the large difference of the vehicle mobility and safety between domestic and developed countries'MHDOVs. It is approved that antilock braking system (ABS) distinctly and effectively improves the vehicle braking ability. According to MHDOV's distinguishing features and taking the advantage of ABS technology, theoretical and experimental study is carried out. The result of the dissertation research shows that MHDOV with ABS achieves so better braking performance that the further relevant need of our country missile system'development could be met. The main contributions of the research include: (1) The fundamental method and procedure that improve the MHDOV's braking ability are put forward. Considering the capability improvement and the economical efficiency at same time, the pneumatic mode is determined as basic ABS control method. For the WS2400 four-axle vehicle as investigated subject, two feasible ABS circuit layouts are proposed. (2) The basic modeling method for the dynamic analysis of multi-axle vehicle with ABS is present. The versatile vehicle dynamic model of multi-axle vehicle is established based the dynamics of rigid bodies. Considering ABS concepts and functions, the versatile ABS multi-axle vehicle mathematical and simulation models are set up. The relevant real vehicle experimental data is compared with the model simulation results. Preliminary results show that for longitudinal emergency braking condition the versatile ABS multi-axle vehicle dynamic model is correct in principle. (3) On the basis of the detailed structure and the law of dynamics, the modeling method for the dynamic characteristic of AOH brake system is put forward. A novel drum model is present based on the structure of the brake and the material characteristics of the lining. In accordance with the significant discovery, that the transient brake pressure is influenced by the braking initial state, the drum model is appropriately modified. While originally developed for the ABS mounting work of MHDOV, the model for pressure transient fluctuations caused by the changes of the braking instructions is built. Then the individual models of other components of the brake system are described in detail, and these models are interfaced to formulate the complete brake system model. The comparison of the digital simulation results and experimental data validate the model. In accordance to the theory of system identification and the working principle of AOH brake system, the experimental data is analyzed further and processed; the identified dynamic model of AOH brake system is set up. The identified model, beneficial to the simulation study for the vehicle control system, accomplishes the ABS multi-axle vehicle dynamic model. (4) The scheme of the WS2400 MHDOV adhesion coefficient is proposed and verified by the ABS multi-axle vehicle dynamic model. Finally, with two determined ABS circuit layouts, the road tests are carried out in turn. The result of experiments shows the optimum ABS circuit layout. A series of road tests in the special field indicates that WS2400 MHDOV mounted ABS by the optimum layout has the better maneuverability and directional stability. The research of the dissertation acquires some achievements in the ABS technique application for four-axle vehicle; the principle method for multi-axle vehicle mounting ABS is verified and has the value of extensive application.