Study Speed Ratio Control Of CVT Based On Driving Intention

As the current ideal transmission of vehicle, Continuously Variable Transmission(CVT) can achieve the best match of engine-transmission-road environment. CVTcontrol system is the key to realize the best match. CVT speed ratio control is one of thekey technologies of CVT control system impacting on the car power, fuel economy anddriving performance directly. This paper is about the CVT ratio control strategy basedon driver’s intention and different ratio control strategies are formulated on differentcharacteristics of driving conditions including acceleration, overtaking, uphill, coasting,deceleration and parking under the premise of respecting driver’s intention and in orderto improve both economy and power of a CVT vehicle.Contents of this paper are as follows:①Based on kinetic equations of CVT system, the powertrain model is built.According to the characteristics of the engine speed, the optimal power and the besteconomic engine working conditions are determined. On the basis of the formeranalysis, the target ratios on both the optimal power and the best economic model arecalculated.②The effects on CVT ratio due to the throttle opening and small amplitudefluctuations and external resistance ratio change rate are analyzed. In order to improvethe vehicle ride comfort, the maximum rate change of ratio is limited based on therelationship between the ratio change rate and the vehicle acceleration. The driver’sintentions can be divided into acceleration and brake, then acceleration and brakeintention can be identified based on fuzzy reasoning.③Based on the driver’s intentions, the weighted values during the changing andstable throttle phases under optimum power and economy weighting control strategiesare determined. The acceleration intention consists of acceleration, overtaking anduphill. Then the acceleration control strategy is formulated based on the control target ofacceleration intention, the weighted control strategy is used under acceleration condition,the weighted control strategy is revised during the overtaking process in order to shortenresponse time and improve vehicle speed. Under the premise of power during uphill, thebest economical shift points are found.④The brake intention is divided into parking, coasting, downhill speedmaintenance and different control targets are formulated based on different driver’s intentions. According to the ramp value the engine brake torque can be increased timely.The engine target speed is1000rpm during coasting. The CVT ratio is adjusted to keepon the target speed during speed maintenance condition.