Research On The Assist-steering Method With Skid Steering Mode For Distributed-drive Articulated Steering Vehicle With Hydraulic Steering Mode

Articulated steering vehicles(ASVs),the particular engineering equipment,Have good maneuverability and tractability in poor road and narrow space conditions.They are always used in the mining,construction,forest,and agricultural industry.When each wheel of ASVs is equipped with the in-wheel motor,it can be called distributed-driver articulated steering vehicles(DASVs).The DASVs can realize the independent control for ASVs,and shows the significant advantages than ASVs in structural simplification and stable driving,which is the development direction of ASVs in the future.The DASVs use the hydraulic steering mode to be the steering method.Its structure comprise front and rear frame connected by an articulation joint and two hydraulic struts.In the steering process,the two struts are driven by pump of hydraulic system,and the vehicle will turn following the control of steering wheel with the coupling effects of articulation joint and struts.But due to the high load of the DASVs,the influence of pressure of outlet chamber,and the compressible of the oil,it is easy to cause the high pressure level,the low energy efficiency,and poor stability in hydraulic steering process.And it is not conducive to improving the security,economy,and stability of DAVs.Therefore,in order to solve these problems,this paper make the DASVs as the objective vehicle,and take full advantage of its independent driving method to study the coupling control strategy between skid steering and hydraulic steering mode.With the discussions of the optimal distribution of differential driving forces in the front and rear parts of the vehicle,and the assistance stability control method,the DASVs can work more efficient and intelligentized than before.Considering the inaccurate model of existing researches,the nonlinear dynamic model of DASVs is established,which includes the dynamic model of hydraulic steering system,the analytical model for vehicle posture based on the principle of least resistance,and the 12-DOF dynamic vehicle model.The characteristics of DASVs during hydraulic steering process are discussed in the modeling process.And the simulation model are built in the MATLAB/Simulink.Field test are implemented under the path-changing and steady-state steering driving cycle.The data in the field test is used to compare with the simulation,which can be implemented to verify the model above.Base on the simulation model and the data from field test,the characteristics of the hydraulic pressure and the effective steering forces,and the influence of the vehicle stability during steering process are analyzed quantitative.Meanwhile,the methods of improving the performance for DASVs by changing the input pressure of hydraulic steering system are discussed.And the impacts on the vehicle steering process are shown in this paper.Correspondingly,the assist-steering method with skid steering mode for DASVs is proposed to reduce the influence of different input pressure during hydraulic steering process.With the decoupling analyses of skid steering mode and hydraulic steering mode for DASVs,the strategy of coupling control of these two steering mode are designed with the reference of the original hydraulic steering process.Meanwhile,the optimal distribution and the slip regulation control methods based on the sliding mode control algorithm are applied on the forces control of each wheel.With the limitation of maximum driving forces of in-wheel motor,the capability of the assist-steering with skid steering mode for DASVs is studied.The simulation are always implemented to verify the discussion above.And the results show that the assist-steering methods with skid steering mode can reduce the hydraulic steering pressure about 45%,and improve the energy efficiency about 10%?15%without changing the steering process for DASVs.When the limitation of the driving forces of in-wheel motor is released,the skid steering mode can replace the hydraulic steering mode for DASVs completely.Therefore,simplifying the hydraulic pump,accumulator for DASVs,the steering system with connectivity steering unit(CSU)are designed to realize the skid steering control for DASVs individually.Moreover,making the magnetic valve to replace the steering unit,the steering system with connectivity steering cylinder(CSC)is also designed for DASVs.With the development of control strategies,the simulation of the discussions above is conducted.And the results show that the energy efficiency of CSU and CSC can be improved about 20%?30%and 30%-50%,respectively compared with the hydraulic steering process for DASVs.In order to improve the vehicle stability during steering process and steady driving process,the assistance control method based on the MPC algorithm are designed.With the reference of linear 2-DOF dynamic vehicle model,the simulation of the stability control effect is implement in MATLAB/Simulink.The results show that the assistance control methods can decrease the instability time of steering process about 30%?55%,and reduce the oscillation amplitude and period of external interference about 30%-55%and 20%?45%,respectively.In addition,the stability control effect for the DASVs under CSU and CSC control method is better than that of the hydraulic steering control process.Its performance is improved about 25%?30%.