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This paper presents a novel Power Take Off system, using a Continuously Variable Transmission for power levels up to 45 kW. The system, intended for driving auxiliary equipment on distribution trucks, is developed in order to comply with new restrictions concerning exterior noise, fuel consumption and emissions as well as to improve the performance of the driven equipment.

By using the ability to shift to high overdrive ratios, a CVT equipped vehicle can outperform the fuel economy of its counterpart with conventional automatic transmission. A further signi cant reduction of fuel consumption can be obtained by reducing transmission power loss. The main sources of power loss are well known to be losses inside the V-belt variator and losses caused by driving the hydraulic pump. Signi - cant reduction of these losses will increase the attractiveness of the V-belt type CVT. This paper rst analyses the most important loss contributions present in a reference transmission and how they depend on actuation and control properties, like pump driving power, over-clamping and variator slip. Based on this analysis, actuation and control improvements will be proposed. The effciency increase is presented, that can be expected when the hydraulic pump is replaced by a servo-electromechanical actuation system, and when variator slip control is introduced.

Historically slip in a CVT was regarded as destructive. The reason for this was that slip was not controllable and since it is unstable always resulted in damage to the variator. Recent publications suggest that limited amounts of slip in a pushbelt type variator can be allowed [6]. This opens the door to other strategies for lowering the powerconsumption of CVT's. Not only can slip be used for optimizing variator efficiency [1], actuation efficiency can also be greatly improved. If the safety margin is eliminated, the clamping force can be reduced by more than 25%. This can be directly translated into a 25% decrease in actuation power. Shifting behaviour is also influenced by slip [3]. This effect can be used to greatly reduce the power needed for fast shifting during emergency stopping, tip-shifting and kickdown actions. Using this strategy the force needed for shifting is reduced, and with it the power needed from the actuation system is reduced.

Apart from enabling continuous ratio change under load, the Continuously Variable Transmission (CVT) offers, between limits, the ability to choose engine rotational speed independently of vehicle speed. Here lies a potential efficiency benefit, because the engine can operate more fuel efficiently. There are unfortunately considerable power losses within the CVT itself, causing many CVT equipped cars to be less fuel-efficient than cars with a manual transmission. The internal losses are caused for a substantial part by the CVT’s hydraulic actuation. An electromechanical CVT pulley actuation system was designed to overcome the hydraulic power loss and hence improve CVT efficiency. Spindles are driven from the fixed world through epicyclic gearings by electric motors that are placed outside the transmission housing in a cool environment. A mechanical link between the adjustment mechanisms on the two shafts provides energy exchange, thus lowering shifting power demand and actuator size.

This paper concentrates on the design and construction aspects of a transmission for a mid-class passenger car with internal combustion engine. The transmission, consisting of a Continuously Variable Transmission (CVT) with a Van Doorne V-belt, a planetary gear set and a compact steel flywheel is used to prove the concept of mechanical torque assist. The design goal is to obtain a proof of concept transmission with maximal efficiency, using proven transmission technology. With the developed so-called Zero Inertia CVT, the fuel economy of the car is improved by operating the engine at its fuel optimal operating line. To achieve a good vehicle acceleration response, the flywheel assists the powertrain mechanically. Low-cost transmission technology is used to upgrade the CVT design (gears, bearings and a steel rotor). The test results, regarding the functionality and the efficiency of the transmission, will be available in due time.

In this paper, gear ratios of a two-speed transmission system are optimized for an electric passenger car. Quasi static system models, including the vehicle model, the motor, the battery, the transmission system, and drive cycles are established in MATLAB/Simulink at first. Specifically, since the regenerative braking capability of the motor is affected by the SoC of battery and motors torque limitation in real time, the dynamical variation of the regenerative brake efficiency is considered in this study. To obtain the optimal gear ratios, iterations are carried out through Nelder-Mead algorithm under constraints in MATLAB/Simulink. During the optimization process, the motor efficiency is observed along with the drive cycle, and the gear shift strategy is determined based on the vehicle velocity and acceleration demand. Simulation results show that the electric motor works in a relative high efficiency range during the whole drive cycle.

For analysis, control design and testing of an electromechanically actuated metal V-belt type CVT, a simulation model is built. Due to its complexity and nonlinear behavior, this model is not suitable for control design. To use control design techniques like H1 or μ-synthesis, linear transfer functions from all inputs to all outputs must be known. Using approximate realization techniques, step responses simulated with the model are analyzed. In this way, a linearized state-space representation of the system is obtained. The transfer functions show resonances around 8−10 [Hz], depending on the CVT ratio. Using MIMO-control, closed loop bandwidths that could be obtained are up to 10 [Hz] for ratio control and 15 [Hz] for slip control.