Research On Traction/Brake Integrated Control Algorithm For Commercial Vehicle

Active safety control systems play an important role in vehicle safety, more and more safety systems are appeared to ensure the occupants'safety. Active safety systems such as antilock braking system, traction control system, electronic brake distribution is the standard configuration for new cars or trucks. Antilock braking system can identify the slip ration of the wheels when braking on low friction road or applying panic brake on high friction road, ABS can regulate brake pressure to an appropriate level and keep the wheels from locking, meanwhile vehicle directional stability and maneuverability are improved. Traction control system can detect the slip ratio of the driven wheels when staring the vehicle and can control driven torque when the wheel slip ration exceed a threshold, so the vehicle can accelerate well , the directional stability and steering performance are enhanced. Electronic brake distribution system can distribute brake force of front/rear wheels in an ideal way, and keep the vehicle away from side slip because of great slip ratio in rear wheels.Active safety control system domestic is worse than that of foreign, especially for commercial vehicles, so there are many advantages to do some research on active safety for commercial vehicles. In this paper much work has been done on control algorithm of ABS, TCS and EBD, and integrated the three system into an integrated control system, that is traction and braking force integration control system.Different practical control algorithms for different control condition are developed and many tests have been done to validate the control algorithms, test results show that the algorithms are effectiveness and practicality.Main content of this dissertation are shown as below:1. Study on the control algorithm of ABSAccording to the different characteristics of the roads and braking conditions, divided into the typical condition control of the anti-lock control and confirm the total control strategy of the ABS, impose different controls to different conditions.①The accuracy of the reference speed has a major impact to the ABS control strategy, this paper presents a simple but stable estimation algorithm of the reference speed that can improve the ABS control effect;②The boost pressure manner of ABS has significant impact on the control effect, this paper presents an adaptive control method with the acceleration of wheel and vehicle as the main parameters, and divides the process of increasing pressure into three grade;③When the vehicle brakes on the rough road, the wheels may vibrate because of the road surface excitation, the dramatic changes of the wheels's acceleration causes the decrease of the control effects of the ABS and even worse get invalid, besides, the vibration of transmission system can also stimulate the vibration of the wheels so that cause the bad impact to the ABS control, this paper proposes an identify method to the above two kinds of vibration and a pressure control method to suppress vibration;④In the braking process, the change of adhesion of the road may change from low to high or the converse, resulting in the wheel locking or insufficient braking force. With the analysis of the wheel dynamic characteristics in the process of road adhesion jump, proposes an identify method of high to low adhesion jump or low to high adhesion jump of the road surface, on the base of identification, respectively use the methods of wheel slip integral and compare between wheel acceleration integral average and corresponding threshold, further proposes the pressure control method in the transition process;⑤Aim to the three kinds of the vehicle coming into separate adhesion of the road surface, proposes different identification and pressure control strategies to suppress the direction instability phenomenon due to different braking forces on the both sides;⑥For the situation of understeer and oversteer in steering brake, proposes steering brake control strategy of ABS;⑦Because of some braking conditions occur more then ABS emergency braking, and less use of braking force distribution control to the commercial vehicles, proposes EBD control strategy based on the slip rate error, which contains judged logic of permission to enter and force to quit, state control logic and pressure control logic. Propose a reduced-pressure suspension control of EBD based on the change of vehicle speed and slip rate.2. Research on Traction control algorithmElectronic control engine, automatic transmission and CAN network of vehicle are included in the researching vehicle model, this paper establishs TCS overall control strategy and control algorithm.①In order to improve the stability of this algorithm and prevent that drive roller transfer caused by shift falsely triggers TCS control, the communication between integrated controller and transmission controller is used to overcome false triggering. When TCS is informed that transmission is in the normal shift, TCS control are not performed.②To settle the collision when shift and TCS control act on engine at the same time, coordinated control algorithm is proposed. Engine is controlled by transmission in the process of shifting control, and is controlled by TCS control after shift.③Engine torque control of the TCS is phased; composite control of engine torque is offered based on feedforward control of vehicle resistance estimation and feedback control of slip error; adaptive control strategy of engine torque under different conditions is proposed.④To coordinate driving wheel brake and engine torque control, brake torque is translated into the equivalent engine torque, and is included in objectives torque of engine control under different conditions, so that the purpose is achieved which is to ensure acceleration capacity, maintain vehicle stability and reduce fuel consumption.⑤When TCS is in control, it is proposed to execute active upshift control of transmission under the low adhesion conditions, to prevent dramatic changes of driving force from causing vehicle instability. Therefore, a smooth start of vehicle is realized, taking into account the stability of the vehicle turning.⑥Three kinds of the driving wheel braking control strategies are proposed: differential braking control;cornering stability braking control and the first circulation control. When the vehicle have a Turning traveling on the road with low adhesion, it is allowed that the slip level and duration of the driving wheel could be less than straight-line running, so the turning control threshold is reduced. In order to prevent the vehicle instability lead by additional yaw torque, and no longer uses differential braking control, and prevent additional yaw torque of the vehicle instability, the two driving wheels choose a low control mode, meanwhile, differential braking control is no longer used.⑦Based on the brake pressure estimation, the brake temperature estimation algorithm and pressure control algorithm for temperature suppression are proposed, in order to restraint the brake overheating caused by Continuous brake. According to the estimated brake pressure, the current temperature of the brake is calculated, and thus the maximum allowed pressure of follow-up brake is decided. By allowing the brake pressure reducing with increasing temperature, when the temperature reaches its limit, it will not allow brake control. The brake overheating problems can be solved in this way.3. Implementation of integrated control system①In connection with Characteristics of commercial vehicle air brake system, the hardware components and functions of the traction and braking force integration control system is researched;②Both the control algorithm of TCS and cornering brake of ABS are usedto enhance vehicle stability during acceleration, and the integrated control algorithm is realized.③Based on the study of the application layer protocol SAEJ1939 , the specific coordination method of integrated control system, engine control system and automatic transmission control system is proposed.4. The research of traction and braking force integrated control algorithm testing of real vehicleFor a certain type of commercial vehicle,A number of tests in real road environment are performed to verify the control algorithm of the integrated control system.Reference to ABS regulations, a variety of road test under different conditions are performed, results show that in the typical condition, such as even high and low adhesion surface, split adhesion road, jump of the road surface and turning, the better control effect is obtained. In the even high and low and split adhesion road, the start acceleration on TCS control is tested, results show that the vehicle's acceleration capacity has significantly improved, and coordinated control of the engine, transmission and driving wheel brake is accomplished. Combined brake and drive test is performed, results show that, when the vehicle starts, TCS controls the stability of the vehicle starting; when the vehicle reaches a certain speed, ABS controls the stability of the vehicle braking. In the entire process control, TCS and ABS have to play a control role, and have a smooth transition without interference, those prove the control algorithms have a good compatibility.