Coaxial EV Drive Unit Layout for Compact Wheel-End Packaging
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Solution Overview
Problem
Existing electric vehicle drive units for heavy-duty vehicles face challenges in achieving compactness without interfering with other vehicle components, such as the suspension or braking system, when positioning electric motors close to the wheels.
Innovation Solution
A drive unit design featuring a coaxially mounted differential and planetary gear train within a carrying structure, with a shift assembly allowing selective engagement and disengagement of input members, reducing the need for axial actuators and optimizing gear ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the electric motor is positioned close to the wheels in an electric axle configuration, then transmission losses are reduced and vehicle performance is improved, but the drive unit becomes bulky and interferes with suspension or braking system components
Solution Approach 1:
The differential and planetary gear train are nested inside the carrying structure, with the carrying structure itself being coaxially mounted around the drive shafts. This nested arrangement allows multiple components to occupy the same radial space, significantly reducing the overall axial volume of the drive unit while maintaining the electric axle configuration's transmission efficiency benefits
Solution Approach 2:
The invention transitions from a traditional longitudinal arrangement of components to a coaxial arrangement around the drive shafts. By organizing components in a radial/coaxial dimension rather than a linear axial dimension, the drive unit achieves compactness in the critical axial direction while maintaining functional performance
2Ease of operation
If a traditional transmission layout is used with axial actuators for gear engagement, then gear shifting is achieved, but the axial space requirement increases and conflicts with other vehicle components
Solution Approach 1:
Instead of using axial actuators that extend outward from the planetary gear train to engage input members, the invention inverts the approach by having the input members selectively engageable with the carrying structure itself. The carrying structure serves as both the mounting structure and the engagement surface, eliminating the need for external axial actuators and reducing axial length
Solution Approach 2:
The carrying structure serves multiple functions simultaneously: it provides structural support for the planetary gear train, acts as a mounting structure for the differential, and serves as an engagement surface for the input members during gear shifting. This multi-functionality eliminates the need for separate axial actuator components
Data Source
AI summary
A drive unit for an electric vehicle comprises an electric motor, a differential, a transmission and drive shafts. The transmission comprises a planetary gear train and a carrying structure, both coaxial with the drive shafts. The differential and the planetary gear train are mounted inside of the carrying structure. The carrying structure is driven by the electric motor and drives the planetary gear train. The transmission comprises a shift assembly, comprising a shift ring coaxially mounted around the carrying structure, axially moveable and rotationally fixed relative to the carrying structure. The shift assembly is configured to cooperate with an input member of the planetary gear train so as to engage or disengage the input member with the carrying structure depending on the axial position of the shift ring relative to the carrying structure.