Abstract
This paper examines the benefits of a drivetrain that is able to disengage its propulsion motor from the driveline in an electric vehicle. The drivetrain was developed for an ultra-efficient eco vehicle competing in the Shell 2013 Eco Marathon. Various clutch mechanisms were examined. In spite of the complexity and losses associated with additional bearings and release surfaces, an actuated dog clutch was chosen as it offers superior performance due to the dual capability of freewheeling and regenerative braking that results. Track data from the event is presented along with experimental work that indicates that the clutch mechanism reduces power consumption by more than 35% for a ferrous permanent magnet propulsion motor. Savings were reduced to 5% for a coreless permanent magnet motor coupled to the driveline via an 11:1 straight cut spur gear arrangement. This reduced saving was due to the removal of hysteresis and eddy current losses from the stator. The paper also demonstrates during a competition in which the driver was aware of the energy consumption, the driving style changed when the technological option to free wheel was available. Finally the study was inferred onto a real world application with further experimental and simulation work on the Delta E4 Coupe, a high performance electric sports car. The vehicle uses a ferrous permanent magnet direct drive arrangement, indicated a reduction in power consumption of 10 to 14%. It is hoped that these insights are relevant when considering the development of electric vehicle drivetrains where machine topology and drive cycle will determine the value of a clutch mechanism.
Highlights
As Electric Vehicles (EVs) become smaller and more efficient, idling losses such as those associated with bearings, gear meshes, permanent magnet motor iron losses and windage, become increasingly dominant [1]
This paper explores the value of a clutch mechanism and how it relates to vehicle size and motor topology
The inclusion of a clutch mechanism within a small single seat vehicle resulted in a 35+% reduction in coast losses
Summary
As Electric Vehicles (EVs) become smaller and more efficient, idling losses such as those associated with bearings, gear meshes, permanent magnet motor iron losses and windage, become increasingly dominant [1]. The motivation to disengage the propulsion system from the wheels during a coasting event increases. The benefits of so called “pulse and glide” driving strategies, whereby a vehicle accelerates prior to freewheeling, with respects to conventional IC engines and hybrid electric drivetrains has been demonstrated in [2]. There seems to be little literature regarding the freewheeling performance of electric vehicles and implication on driveline component selection. This paper examines a drivetrain developed for a single seat, battery electric, carbon fibre vehicle weighing 30kg called Peggie. The drivetrain is able to disengage the propulsion motor allowing the vehicle to freewheel during coasting events. The performance of the clutch mechanism within Peggie is compared with the predicted performance on a larger vehicle, the 1000kg Delta E4 coupe based on coast down measurements taken from its drivetrain
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