Fundamental limitations to no-jerk gearshifts of multi-speed transmission architectures in electric vehicles

TL;DR

This paper establishes fundamental theoretical limits on achieving jerk-free gear shifts in multi-speed electric vehicle transmissions, highlighting the impact of actuator saturation and transmission design choices.

Contribution

It introduces three theorems defining the fundamental limitations to no-jerk gear shifts caused by motor or actuator saturation, and compares different transmission architectures including one-way clutches and planetary gearsets.

Findings

One-way clutches increase the likelihood of gearshift jerk due to motor saturation.

Planetary gearsets influence gearshift dynamics and no-jerk limitations.

Theoretical tools are provided for early-stage transmission architecture comparison.

Abstract

Multi-speed transmissions can enhance the performance and reduce the overall cost of an electric vehicle, but they also introduce a challenge: avoiding gearshift jerk, which may sometimes prove to be impossible in the presence of motor and clutch saturation. In this article, we introduce three theorems that explicitly define the fundamental limitations to no-jerk gearshifts resulting from motor or actuator saturation. We compare gearshifts that consist of transferring transmission torque from one friction clutch to another, to the case in which one of the clutches is a one-way clutch. We show that systems with a one-way clutch are more prone to motor saturation, causing gearshift jerk to be more often inevitable. We also study the influence of planetary gearsets on the gearshift dynamical trajectories, and expose the impact on the no-jerk limitations. This work offers tools to compare transmission architectures during the conceptual design phase of a new electric vehicle.