Electric Vehicle Transmission with Hypoid Gearset
Compact electric vehicles require a cost effective and compact solution for the location of the electric motor and the transmission. Yes, even small electric vehicles today require a transmission, if the maximal possible motor efficiency has to be available in the majority of drive conditions. Most of the existing solutions for front wheel driven electric vehicles place the eMotor and the transmission inline between the front wheels. This results in an asymmetric weight distribution as well as motor heat radiation towards one of the two front wheels.
The paper presents a new design concept which utilizes a super reduction hypoid with a ratio between 7 and 15. The hypoid gearset rotates the eMotor away from the limited space between the front wheels and delivers a symmetrical weight distribution as well as a heat radiation away from the wheels. Due to the preferred one stage reduction, the proposed eDrive transmission is very compact and provides multiple possibilities for an optimal vehicle component packaging. The paper will discuss the variety of transmission designs, orientations and locations. The compact design as well as the fact that a one stage transmission minimizes the number of shafts, bearings and gears allows for a cost effective eDrive manufacture.
Design and dimensioning of the transmission and its components was done with the KISSsoft system. In order to utilize a super reduction hypoid gearset for an automotive eDrive, not only the efficiency has to be high, but equally important is a high back driving efficiency. A good back driving efficiency allows recuperating maximal amounts of electrical energy for battery re-charging. To allow the optimization of the back driving efficiency the coefficient CBD (Back Driving Coefficient) is proposed. Furthermore, fundamental changes of the SRH geometry versus conventional hypoid gears had to be developed in order to achieve desirable values for CBD.
Authors: Hermann Stadtfeld and Hanspeter Dinner
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