Design and Analysis of a Linkage-Based Wheel-Integrated Drive System

Abstract

Wheel-integrated drive systems incorporate the reducer, driveshaft, and constant velocity (CV) joint into the wheel, thus freeing space in the chassis for the battery. However, affixing the motor to the wheel increases unsprung mass, which negates some of the benefits. A solution is a mechanism that allows transmitting torque via a moving parallel offset, enabling to fix the motor to the chassis and free the wheel rotation with respect to the suspension. This paper analyzes three solutions of this type (Schmidt coupling, geared Watt’s linkage, and CV joint), each implemented in the wheel hub with the same geometry and driven by the same motor. The angular velocity of the output shaft was determined using high-speed video at five vertical offsets of the hub center. Transmission efficiency was evaluated using the stall-torque measurements at the input and output shafts. The efficiency was defined as a ratio of the torque multiplied by the gear ratio, which makes it independent from the rotational speed. The Schmidt coupling reduced the mean value of the output velocity ripple from 71.8% to 50.1%, i.e., improved it by 21.7% or 30.2% relative to the CV joint (p = 0.042). Therefore, its transmission efficiency was not inferior to that of the CV joint (p = 0.56), whereas the geared Watt’s linkage was significantly worse at both counts. This suggests that a link-based mechanism allows for achieving the efficiency of a CV joint while fixing the motor to the chassis, thus decoupling unsprung mass and the motor.