This article shall explore the characteristics of hydro-mechanical transmission in power shift. Based on the double brakes overlapping, the adjustment of the displacement ratio of variable-displacement hydraulic component is considered, and then a new full power shift method is proposed. Models respectively for speed, torque, and power in the power shift process are built. The ideal power shift timing is deduced, with the ratio between speed of fixed-displacement hydraulic component and input speed being the criterion. By combining theoretical analysis and experimental studies, it shows that in power shift process by regulating the displacement ratio of variable-displacement hydraulic component, the interchange between high- and low-pressure sides in closed hydraulic circuit can be completed, and power transition can be thus realized. A new full power shift method is put forward, in which the shift process is divided into five stages: current range, prior stable stage, power transition stage, post stable stage, and target range. Experiments on full power shift process prove that the full power shift method is not only feasible but also can remove the rotational speed fluctuation in power shift process and realize normal full power transmission of output power.

A hydromechanical variable transmission (HMT) has advantages of continuous variation and high efficiency. So it is one of the ideal transmissions of heavy vehicles. The continuous speed varying process involves speed governing in range and range shift. Integrated control strategy of the HMT is proposed in this paper. The algorithm of the asymmetric saturated incremental proportional integral derivative (PID) speed control strategy in range and range shift conditions are derived. And this paper presents the range shift logic and range shift control strategies. A controller model is built in Matlab Simulink and cosimulated with the model of vehicle equipped with a two-range HMT. The HMT prototype hardware-in-the-loop simulation (HILS) platform of the integrated control strategy is built. The HILS results show that the range shift process is smooth and speed fluctuation does not happen. In the throttle stable stage, the engine speed is adjusted to the near optimal speed, and its change rules are in accordance with simulation results. The integrated control strategy is reasonable.

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In order to improve the fuel economy of vehicles, based on the automated mechanical transmission (AMT), a plug-in hybrid electric vehicle (PHEV) hybrid transmission for low-end multi-purpose vehicles (MPVs) is developed. To obtain the statistics of the best-selling models, we took several best-selling models in the Chinese market as the research object to study the relationship between power demand, energy demand, weight, and cost. The power requirements and energy requirements of PHEVs are decoupled. According to the decoupled theory, a single-motor parallel scheme based on the AMT is adopted to develop a PHEV hybrid transmission. In the distribution of engine and motor power, the engine just needs to meet the vehicle’s constant driving power, and the backup power can be provided by the motor, which means we can use an engine with a smaller power rating. The energy of short-distance travel is mainly provided by the motor, which can make full use of the battery, reducing the fuel consumption. The energy of long-distance travel is mainly provided by the engine, which can reduce the need for battery capacity. The working modes of the electrified mechanical transmission (EMT) are proposed, using P3 as the basic working mode and setting the P2 mode at the same time, and the gear ratios are designed. Based on the above basic scheme, two rounds of prototype development and assembling prototype vehicles for testing are carried out for the front-engine-front-drive (FF) layout. The test results show that the vehicle’s economy has been improved compared to the unmodified vehicle, and the fuel-saving rate of 100 kilometers has been achieved at 35.18%. The prototype development and the vehicle matching verify the effectiveness of the new configuration based on AMT.