| AFS is the inevitable development demand of automatic-driving, stability control andcomfortable control (variable ratio control) in the future. Based on the consideration ofsecurity, AFS which is adopted the combination of manual control and electromotion to steerhas been used at present. In the area of assisted steering, EPS has developed rapidly andbecome the first choice of small car. Along with the gradual application and transfer tomedium-low-grade automobile of AFS, combination of AFS and EPS will become thedemand of future. Based on this background, the paper did research on AFS, and thecombination control method of AFS add EPS.Both EPS and AFS are independent system, combining them will make an effect oneach other. First, the paper studied EPS system and AFS system dividedly, and then stackedthem and amended the control model according to the infection by each other. AFS can beused to the area of variable ratio operation, active control of driving stability and automaticdrive which will improve cars’ comfortable control and stability. AFS in this paper mainlydeveloped control system according to the demand of variable ratio operation.The main research and achievement of this paper are as follow:(1) The individual EPS system was researched and current colsed-loop control strategiesincluding returnability control algorithm was adopted. Control program was empoldered andassistance characteristics curve was designed and tested on the test-bed in the range of0km/hto95km/h. Moreover, real vehicle experiment of EPS was studied under typical operationcondition. The experiment shows that car with EPS can reduce the burden of drivereffectively and improve steering handiness and returnability. It provided foundation of EPSand AFS combination system’s control model.(2) New AFS system with independent intellectual property was researched anddeveloped. Compared with BMW active steering system, the new AFS system has anintegrative performance with high transmission precision (increase4times), small volume(reduce more than60%) and high efficiency (improve20%).(3) Variable ratio control model which is based on handling comfort and stability wasresearched and presented.(4) The individual AFS system was researched. And according to the demand of AFS’scontrol performance,a double loop controller was designed. And then through adoptingcolsed-loop control method to control AFS motor, a feedback control strategy velocity was、 presented. Moreover, AFS control program was empoldered, simulated and experimented ontest-bed. The experiment shows that the AFS system comes to the meet with handiness in lowspeed and steering precise in high speed. It provided foundation of EPS and AFS combinationsystem’s control model.(5) EPS and AFS combination system was researched by setting up simulation about thetwo stacking independent system. And then comparing with each individual system oncharacteristic, the effect between EPS and AFS was analyzed. Aiming at the problem thatsteering torque of whole system is fluctuating and the torque’s difference between turning leftand right is enlarging during AFS’s intervention, control method about the combinationsystem were studied(EPS has seldom influence on AFS). Furthermore, the control method andstrategy were amended and trimmed and torque colsed-loop control strategy includingreturnability control algorithm was adopted. In addition, sliding mode control algorithm wasused and combination system control software and hardware were empoldered and tested onthe Hardware In-the-loop test bench. The test shows that the combination system can not onlyreduce the burden of driver effectively, but also improve the steering characteristic of thewhole car and enhance control stability and security.(6) Based on establishment of whole car’s7DOF dynamic model, Adams and matlabco-simulation model were set up and verified by simulative experiment. Then, it wascompared with mechanical steering system. The experiment shows that new compositesystem can keep the yaw velocity gain stable in different working condition andcommendably satisfy the request of handiness in low speed and stability in high speed. |
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