Coaxial EV Drive Unit With Planetary Shift Ring Packaging
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Solution Overview
Problem
The challenge is to create a compact drive unit for electric vehicles that positions electric motors close to the wheels, minimizing interference with other vehicle components like the suspension or braking system.
Innovation Solution
A drive unit design featuring a coaxial arrangement of an electric motor, left and right drive shafts, a differential, and a transmission with a carrying structure, planetary gear train, and a shift assembly that allows selective engagement and disengagement of input members without requiring an actuator axially, optimizing axial compactness and reducing conflicts with other vehicle components.
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 less compact and interferes with other vehicle components such as suspension or braking system
Solution Approach 1:
The patent implements nesting by placing the differential inside the transmission housing and mounting the planetary gear train within the transmission assembly. The carrier structure serves as a common mounting platform for both the differential and planetary gear components, creating a nested configuration where smaller components are housed within or attached to larger structural elements, thereby maximizing space utilization and reducing overall drive unit volume.
Solution Approach 2:
The patent merges the differential and planetary gear train into a single integrated transmission assembly. Both components share common structural elements including the carrier structure, housing, and mounting points. The differential carrier and planetary gear carrier are combined into a unified structure that performs both differential function and gear reduction function simultaneously, eliminating the need for separate mounting structures and reducing overall complexity.
2Adaptability or versatility
If an actuator is added to engage and disengage the first input member of the planetary gear train, then gear ratio selection is enabled, but the axial length of the drive unit increases due to the actuator located on the side of the planetary gear train
Solution Approach 1:
The patent resolves the axial space conflict by moving the engagement mechanism from the radial dimension to the axial dimension. The shift ring is positioned axially adjacent to the planetary gear train and engages with the first input member through axial movement rather than radial extension. This allows the actuator to operate in the axial direction within the existing housing space, avoiding the need for additional radial space that would increase the drive unit's axial length.
Solution Approach 2:
The shift ring serves as an intermediary component between the actuator and the first input member of the planetary gear train. The shift ring translates actuator motion into engagement or disengagement of the first input member with the carrier structure. This intermediary mechanism allows for compact actuator placement while maintaining the ability to selectively engage different gear ratios, as the shift ring can be positioned within the existing transmission housing without requiring additional axial space.
Data Source
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AI summary
A drive (20) unit for an electric vehicle (10) comprises an electric motor (24), a differential (30), a transmission (38) and drive shafts (26, 28). The transmission comprises a planetary gear train (52) and a carrying structure (40), 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 (64), comprising a shift ring (66) 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.