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Performance analysis of series and parallel configurations in dual-belt continuously variable transmissions

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Performance Analysis of Series and Parallel Configurations in Dual-belt Continuously Variable Transmissions by Huang Jia Lu M-B1-5450-0 Thesis Supervisor: Prof. Wong Pak Kin Department of Electromechanical Engineering, Faculty of Science and Technology Continuously variable transmission (CVT) is a transmission that can offer an infinite number of gear ratios. It is different from other mechanical transmissions which can only offer a fixed number of gear ratios. A CVT allows for a change in speed ratio without stopping or disengaging the clutch, so that it can achieve a high power transmission efficiency and smooth acceleration. In the past decades, several car manufacturers adopted CVTs for their production cars. However, the exiting CVT is single-belt design which can only be applicable to low-torque passenger cars because of limited torque capacity. To overcome the issue of low-torque capacity, a dual-belt Van Doorne’s CVT and an inline chain CVT have been recently proposed, these two new CVTs could transmit higher torque and offer high transmission efficiency. However, these two CVTs use different configurations. The inline chain CVT connects two single steel chains in series whereas the dual-belt Van Doorne’s CVT connects two steel belts in parallel. Moreover, their control systems are also not the same. At present, little research has ever been done to fully compare the structure and performance of these two new dual-belt CVTs. To decide which of these two structures is of longer endurance, higher torque capacity and efficiency, the author makes a detailed comparison between inline CVT and DBVCVT. The inline CVT is operated by chain and the shift actuator is driven by hydraulic power, both differ from those in DBVCVT. To make a fair comparison between two types of the dual-belt CVTs, this thesis respectively replaces the chain and shifting actuator of inline CVT with the same metal V-belt and servo motor of DBVCVT in modeling. The mathematical models developed in this project include torque capacity, power transmission efficiency, maximum stress of major components, power consumption of actuation system, and slip. The mathematical models for the inline CVT and dual-belt Van Doorne’s CVT are also implemented and analyzed by Matlab. According to the simulation results of both inline CVT and DBVCVT, with regard to maximum torque, DBVCVT excels. When the torque remains the same, the power consumption of actuation system in inline CVT is higher than that of DBVCVT by 30%, the stress of steel ring in inline CVT is also almost 20% lower than that of DBVCVT, and the stress of steel element in inline CVT is almost 50% higher than that of DBVCVT. Comparatively speaking, the life of steel belt of DBVCVT is longer than that of inline CVT. When the input torque of inline CVT ranges from zero to 90Nm, the transmission efficiency of inline CVT is higher than that of DBVCVT by 7% to 18%. As the input torque increases over 90Nm, the efficiency of DBVCVT totally exceeds the efficiency of inline CVT. To conclude, for the light-duty vehicles, inline CVT is a good choice because of its high efficiency in low torque condition, and the DBVCVT is suitable for the heavy-duty vehicles due to its high torque capacity.

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Huang, Jia Lu


Faculty of Science and Technology


Department of Electromechanical Engineering




Automobiles -- Transmission devices, Automatic

Motor vehicles -- Springs and suspension


Wong, Pak Kin

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