Research On Simulation Of Active Safety Control Of Tractor-Semitrailer Based On Differential Braking

With the rapid development of Chinese economy, the tractor-semitrailer has become the optimal vehicle in the term of Zone Service and Drop & Poll Transport. It raises transporting efficiency greatly, however, its driving stability becomes the bottleneck of the development of transportation. Therefore, the purpose of this paper is to search after the active control method of tractor-semitrailer in order to improve its driving stability.The active safety of tractor-semitrailer has been studied on early in the 1960s in some developed countries. In China, however, it's still in the beginning stage. By tracing the international trend, the research focuses on this field, and has made some accomplishment as follows:In the first place, it is the study to tractor single vehicle. By reviewing the previous research, several reasons of stability loss of single tractor have been raised. The tractor has three axles—the first is steering axle, the others are driving shafts which have been treated as a lumped one. The two-DOF reference model has been made based on it, and tire cornering stiff has been considered as a variable in order to make the tracing of reference model more precise. LQR was chose to produce the optimum compensate yaw moment to correct the vehicle path based on the bias of yaw rate and lateral acceleration respective. The allocation strategy of braking moment can allocate the braking moment to unique wheel at particular moment, which is the differential brake. At the same time, the PD controller can regulate the longitudinal slip ratio of brake wheel to make it works at optimum slip ratio nearby to obtain maximum brake force.In the second place, the stability of tractor-semitrailer has been put into two categories—yaw stability and roll stability. Further three normal stability loss situations, which are rollover, trailer swing, and jack-knifing, have been come up with. This work extends previous tractor-trailer stability research from roll stability or yaw stability to roll-yaw stability, moreover, the object of the research has been set up that is'enhance the tractor-trailer stability by reducing the occurrence of three stability loss.'What's more, it is the study to yaw-roll stability of tractor-trailer based on that of tractor. A three-axle plane reference model, whose state variables are yaw rate, lateral acceleration, articulate angle and articulate angle rate, has been modeling by simplifying the axles of tractor-trailer and by expanding it, the six-axle plane reference model can be got, whose number of axles is equal to actual vehicle. The precision of this model has been verified through the actual vehicle model in the software of TruckSim. Because tractor-trailer is articulated by tractor and trailer with the fifth wheel flexibly, the control is much more complicated than that of tractor. The control must be accurate and coordinate, or the result will be terrible. The controlled variables are yaw rate, lateral acceleration and hitch articulation angle. Because there are related between the yaw rate and lateral acceleration of tractor and that of trailer, it uses tractor's parameters when producing optimum braking moment with LQR method and determining whether it is unstable. In view of the trait of the tractor-trailer itself, it needs very big brake moment to keep stable when sharp cornering. As a result, it can lead to blocking of steering axle which is not permit. So, as to tractor-trailer, one-sided brake was chose as the control strategy based on the differential brake. The combination control to tractor and trailer which used to be a lot difference is the innovative points in this paper.At last, tractor's control strategy has been stimulated with the Fishhook, one typical condition, at the high and low coefficient of adhesion. Two typical conditions, Fishhook and Double Lane Change, have been selected to simulate tractor-trailer at high and low adhesion coefficient too. From the simulation result we can conclude that the yaw-roll stability of tractor and tractor-trailer has improved fruitfully after applying the differential brake and it also releases the driving tension of driver.