Research On Speed Ratio Control For The Vehicle Equipped With CVT Based On Road Environment

Intelligent control based on driver-vehicle-road is the development direction of theautomatic transmission vehicle. In order to build a complete intelligent control systembased on driver-vehicle-road, the law of the three subsystems’ influence to the automatictransmission has to be sorted out. Road, namely road environment, is the most difficultreal-time parameter to be identified and obtained among the three subsystems, andresearch on automatic speed ratio control based on road environment is an importantarea of the intelligent control. In the step-transmission control area based on roadenvironment, fruitful work has been carried out and some achievement has been made.However, research on continuous variable transmission (CVT) automatic speed ratiocontrol considering road environment factor is introduced not much by the relevantliterature, and there are still some problems to be solved. The Antelope car equippedwith CVT of Changan Auto is the research object in this paper. Theoretical andexperimental studies on complex road, good road, bumpy road, ramp road and lowadhesion road were carried out, in order to optimize vehicle economy under the premiseof satisfying dynamic and safety performance. The main research contents are asfollow:①Numerical models of the engine, hydraulic torque convertor (TC) and CVTwere built by means of testing. The dynamic equations of high adhesion road and lowadhesion road were established using the theory of classical mechanics.②On complex road and good road, the acceleration pedal opening was explainedas the driver demanding power, and the vehicle condition was expressed by demandingpower and vehicle speed. To optimize the transmission efficiency and improve vehicleeconomy, reversely calculate the CVT speed ratio which satisfies the largest value of theproduct of engine efficiency, TC efficiency and CVT efficiency. In the control strategybased on demanding power, best power and economy rules were redefined.③On bumpy road, originally continuously changing CVT speed ratio wasdiscretized into a plurality of gears, to reduce the sensitivity of CVT control system tothrottle opening and vehicle speed, avoiding unnecessary energy loss of CVTelectro-hydraulic system.④On uphill road, based on the power balance equation when the car is in thestable driving state using best economy strategy, the demanding power was determinedconsidering slop factor. Then the integrated control method was found compromising between best power and best economy.⑤On low adhesion road, originally a nonlinear state equation was converted to alinear one using nonlinear state feedback and diffeomorphism mapping, and based onthat a slip rate sliding mode controller was established. Finally, slip rate of the drivingwheel was controlled around the optimum value by comprehensively adjusting throttleopening and CVT speed ratio. The vehicle’s longitudinal acceleration and lateralstability were improved.