| During a hundred years of vehicle history, people have benefited much from the convenience and pleasure in living and manufacturing, at the same time suffered from the energy crisis and environment pollution delivered by vehicles. Energy and environment problems have already drew worldwide attentions and became the main obstacle of vehicle development. Accordingly, to develop a kind of energy-saving or new energy car is the only feasible way to solve the problems. HEV, which is the most appropriate member with current technologies in the green energy car family, can decrease the fuel consuming and emission effectively. Vehicle giants have promoted out their characteristic productions sequentially. In domestic, some R&D activities on HEVs have proceeded, as well as a large number of representative research projects have been completed. Under the push of which, domestic HEV techniques have been developed by leaps and bounds. Driveline is one of the key technologies in HEV research. Currently, control of power coupling and transmission has been raised well enough on abroad, yet very few deep studies started in domestic. The dissertation bases on Coupled by Planetary Gears Hybrid Electric Vehicle with Continuously Variable Transmission (H-CVT) developed by Hunan Changfeng Motor Co.Ltd., focusing on the control of power coupler and CVT ratio. Planetary gears have two degrees of freedom, which will fitful for the"Two input-single output"requirement of HEV. Through the control of clutches and brakes in power coupler, 10 working modes would be achieved conveniently with the vehicles'smoothness and dynamics fulfilled. With the CVT ratio adjusting function, H-CVT will make the power unit work under the economic rotation speed of current load (above the"Optimal Operation Line, OOL"), consume less energy in traction mode, recover more energy in regenerative braking mode and accordingly will increase the fuel economy of HEV. Computer simulation will proceed helping verify the power coupler control strategy, CVT ratio control strategy as well as H-CVT vehicle control strategy. Finally the consummate control strategy will be loaded to H-CVT model vehicle for road test.1. Control Strategy of Planetary Gears Power CouplerMath model is established based on the dynamics of planetary gears system, using of which H-CVT power delivering route and the components'motion relationship is analyzed to determine the engaging/separating status of clutches and brakes in power coupler under every working modes. A fuzzy control strategy is proposed ensuring that the switching process synthetically considers the driver's intention and vehicle operating status based on the mode switching requirement of HEV. Subsequently, a simulation model of planetary gears is set up with MATLAB/Simulink software for the off-line simulation of typical working mode. The results illustrate that the fuzzy control strategy of clutches and brakes in power coupler would diminish about 0.5 seconds of switching and reduce more than 50% of slipping friction work. The control strategy of planetary gears power coupler offers a reference for future problems on switching impact for HEV.2. Control Strategy of Ratio for H-CVTThe CVT ratio control includes target ratio determination and ratio tracking algorithm. Target ratio is decided by rotation-load of power unit. H-CVT has 10 working modes, each of which differs in rotation-load characteristic on the different working status of power unit. Accordingly, target ratio of H-CVT is determined with different working modes.a).Target ratio under engine driving mode. Engine power plays the major role under the engine driving mode, motor assisting mode and engine driving-and-generating mode. Because engine fuel consuming rates under different load is different and the motor run efficiency is relatively high, the target ratio of the three working modes are decided according to the engine's rotation-load characteristic to ensure that engine always working above the"OOL"during the three modes, which would lead to a minimum fuel consuming for engine. Motors here work for assisting or generating. b).Target ratio under motor driving mode. In H-CVT, motor is located before CVT, which makes the possibility that under motor driving mode motor works on the most efficient rotation speed under current load through the regulating of CVT (motor works above the"OOL"). As the CVT target ratio could conform to motor's optimal driving operation line. The control target is to make the motor deliver the same driving power while consuming less energy.c).Target ratio under regenerative braking mode. In regenerating mode, H-CVT could also take use of the rotation speed regulating function of CVT and the motor works on the most efficient rotation speed under current braking load(motor works above the"OOL"). CVT regulating could recovery more energy under regenerative braking mode. It can be showed in the following two aspects: 1.Under the same braking condition, power generating efficient is higher and more energy would be recovered for the motor's working on the optimum rotation speed under current braking load. 2.Speed regulating of CVT could make H-CVT maintain motor's rotation speed for generating when the vehicle velocity is very low, which could accordingly prolong the range and time of regenerative braking and recover more energy.Target ratio of other working mode would be the largest CVT ratio to ensure the vehicle could get the largest torque for driving.H-CVT has three target ratios. When the working mode switches, the rotation speed-load character alters accordingly which might lead the jump of target speed. To make the real CVT ratio follow the target ratio closely and overcome the jumping impact caused by mode switching, an improved PID tracking algorithm is designed in this dissertation. By applying this algorithm, H-CVT could track the target ratio as a common CVT, as well the overshot and hysteretic caused by jump of target ratio could be eliminated.Control strategy of H-CVT ratio provides several target ratios in a HEV to fit the requirement of all kinds of rotation speed-load character of power unit under different working modes, tracks the target ratio with the ratio tracking algorithm and makes a further enhancing of HEV fuel economy. It provides a valuable reference for the future controlling research of HEV with CVT.3. Simulation of H-CVT Control StrategyTo optimize and verify the control strategy of planetary coupler and ratio for H-CVT, the dissertation sets up the computer simulation model which takes the utility of CRUISE software to establish the whole vehicle model and the model of H-CVT control strategy including the planetary coupler control strategy and H-CVT ratio Control strategy is based on MATLAB/Simulink. After the co-simulation of vehicle model and control strategy model, results show that control strategy of power coupler could guarantee the smooth of power transmission for every mode of H-CVT and satisfy the requirement of dynamics and smoothness when switching; CVT ratio control strategy can make the power unit work above the"OOL", with which H-CVT reduces 28% fuel compare with traditional vehicle; under regenerative braking mode, the equivalent braking torque according with the driver demand, which prolongs the regenerative range and time, thus recover much more energy.4. Road Test of H-CVTAfter verifying the control strategy of power coupler and ratio for H-CVT, it should be downloaded to the controller of H-CVT for the road test of controlling performance. Experiment would be divided into three groups: controlling performance of typical working mode of power coupler and ratio; controlling performance of typical switching mode of power coupler; tracking performance of target ratio based on typical cycling. The result shows that the strategy of power coupler could control the engaging/separating status of clutches and brakes according to the requirement of working mode. The ratio tracking algorithm in this dissertation could make the real ratio of H-CVT catch up with the target ratio quickly.
|
PDF Full Text Request