Experimental Setup to Characterize Shift Time for High Performance Hybrid Transmissions

Abstract

Hybrid vehicles are increasingly common due to fuel efficiency regulations in place worldwide. High performance hybrids have typically been designed with a focus on improving performance, rather than the combination of both performance and efficiency. In order to improve efficiency of high performance cars, new hybrid architectures are necessary. When incorporating an electric motor, careful focus on operational modes allows for removal of certain elements, such as the reverse gear. Additionally, installing an electric motor directly coupled to the transmission without a clutch gives performance benefits, but requires detailed control of motor speed and novel methodology for shifting. In this paper, the design of an experimental setup for the electric drive in a high performance car hybrid transmission is presented. This architecture allows for characterization of synchronizer behavior during two different shifting methodologies. The first methodology is synchronizing a large rotational inertia with a small shaft speed difference (this differs from a gear shift in a traditional transmission with a large speed difference but small inertia). This situation is encountered when coupling an electric motor to the drivetrain, as the inertia of the electric motor is relatively large compared to a transmission layshaft, but the speed difference is small. The second is testing shifting of a synchronizer where dog tooth engagement happens immediately, with no friction cone to match the speed. This type of shifting is possible with precise electric motor speed control, sensing of the dog tooth position, and fast actuation. This methodology eliminates the need for a friction cone in the synchronizers, while maintaining fast gearshifts for performance driving. Our experimental setup for the electric drive in a hybrid transmission will be used to characterize synchronizer performance with these new shifting methodologies. The insights gained from this setup will aid in designing advanced hybrid architectures.