Study On The Control Method For Vehicle Cornering Stability Based On The Limit Cycle

With the improvement of the condition of road and traffic, the driving velocity of modern vehicles has been greatly increased. At the same time, the number of the traffic accidents caused by vehicles critical cornering and slip also has been increased. Therefore, the increase of the vehicle velocity has brought forward higher demand to the driving safety and steering stability for vehicles. So the new technology called ESP (Electronic Stability Program) has been developed which controlling the steering stability of the vehicle when it runs at high speed.ESP adjusts the running status of the vehicle in real time, makes the vehicle running according to the driver's intention, and reduces the happening rate of traffic accidents caused by the wrong operation made by drivers in critical situations, so as to improve the safe performance of the vehicle.There're two kinds of typical vehicle steering stability control method on abroad: the vehicle steering stability control method based on yaw rate and lateral acceleration control together with the vehicle steering stability control methodbased on β -β phase-plane method. Based on the study about the two methods before, this paper proposes the limit cycle control method on vehicle steering stability. Compared with β -β phase-plane method, it has been confirmed by the limit cycle control method that the ellipse stability region is more sensitive to therunning state of vehicle. The rationality of the ellipse stability region also has been proved by simulation tests.The research work of this paper includes the following contents: 1. Modelling and analysing the vehicle steering stability control method based onyaw rate and lateral acceleration control.The vehicle steering stability control system that constructs in this paper based on yaw rate and lateral acceleration control consists of two parts: the yaw rate control and the lateral acceleration control. At the same time, this paper brings up the rule to judge the state of vehicle, such as neural-steering, understeering or oversteering, also it puts forward the single-wheel and double-wheel brake method. Through the simulation test results, by comparing the brake moment impulse whichthe hydraulic brake system export to four wheels, body side-slip angle, fi-fiphase-plane map and the running track and the running posture of the vehicle when taking the double lane change test, it can be concluded that the action of the double-wheel brake method is smoother and more powerful than the single-wheel brake method. The double-wheel brake method can reduce the driver's steer action, lighten the driver's burden, decrease the yaw moment and the body side-slip angle, make the vehicle running more stable. 2. Modelling and analysing the vehicle steering stability control method based onP - ft phase-plane method.According to the specific function form of the linearity region which has been gained by Shoji Inagaki and so on that analysis on the vehicle dynamic stability incritical cornering with /?-/? phase-plane method, this paper constructs the vehicle steering stability control system based on /? - /? phase-plane method.The vehicle steering stability control method based on yaw rate and lateral acceleration control the yaw rate^ and the lateral acceleration ay chooses theyaw rate^ and the lateral acceleration ay as its state variables, /?-/? phase-planemethod chooses the body side-slip angle /? and the body side-slip angle rate p as itsstate variables. Although the two methods choose different state variables, they reach the same control effect. It has proved the effective of the two methods at the same time. 3. This paper proposes the vehicle steering stability control method based on thef5 — J3 limit cycle method and the/?-^> limit cycle method, and constructscorresponding control logic. Unlike /? - ji phase-plane method, the limit cyclemethod proposes the ellipse stability region, from aspect of control time, the limit cycle method will early correct the current dangerous state of the vehicle, and this makes the limit cycle method consuming less braking energy to take the vehicle back to the stable state. 1) In point of the explanation of the running stable region about vehicle: the twomethods bring up different shape of the stable region, ft — (5 phase-planemethod takes linearity region as its stable region, the limit cycle method considers the ellipse region as that, whose centre is at the origin, and the linearity and the ellipse region contact with each other. That is to say the stableregion /? - f5 phase-plane method brings up covers that which the limit cyclemethod brings up. So the state when the current running state of the vehicle lies in the linearity region but out of the ellipse region has been considered asthe stable state by ft - J3 phase-plane method but as unstable state by the limitcycle method.2) In point of control time: the limit cycle method correct the running state of the vehicle at the initial stage when it getting across the stable region, but theinitial time which P-ftphase-plane method get to control is later than thelimit cycle method.3) In point of control energy: the behavior of early correcting the current dangerous state of the vehicle makes the limit cycle method consuming less braking energy to take the vehicle back to the stable state. As the later the unstable state to be controlled, the farther the vehicle state deviates from the stable region, and then it will take more energy to take the vehicle back to the stable state. The limit case is that if the unstable state to be controlled lag behind a period of time, it may lead the vehicle to the unstable state which can't be taken back. This is why in some cases in the double lane change teststhe vehicle controlled by J3 - J3 phase-plane method get to unstable.4. With the help of the Vehicle Operation Self-organization Simulation VOSS platform developed by our group independently, this paper can simulate and analyse the driver-vehicle-road closed-loop system, on the basis of this also combine with the Virtual Reality, this paper explore the three-dimension visual environment for the driver-vehicle-road closed-loop system. By way of viewing the running status of the virtual vehicle in the environment, we can judge the effectiveness of the model intuitively.5. It can be concluded by the results of simulation test that: with shrink of the control stability region, the body side-slip angle controlled byP - fi phase-plane method and limit cycle method also shows a tendency todiminish;in low speed, the control effects of fi - J3 phase-plane method and limit cycle method are just the same;in high speed, P~ p phase-plane methodis invalid in some cases;the control effects of /? - (5 phase-plane method and limit cycle method are also just the same.