In-wheel Motor Offset for Torque and Clearance
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Solution Overview
Problem
Conventional in-wheel motor drive devices face limitations due to the spatial constraints imposed by the wheel and brake rotor, leading to a small-diameter electric traction unit that cannot generate sufficient driving torque and may interfere with the vehicle body.
Innovation Solution
The in-wheel motor drive device features a motor unit and speed reduction unit positioned to offset perpendicular to the wheel hub bearing unit, with a carrier linked to the vehicle body, allowing for a larger radial dimension of the motor unit by reducing the offset distance from the hub to the motor unit, and includes a stationary shaft and carrier to support the speed reduction unit and motor unit, enhancing torque generation and assembly efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the electric traction unit is disposed in the narrow annular space between the brake rotor and the wheel rim, then the in-wheel motor drive device can be compactly arranged, but the motor radius becomes smaller than the brake rotor radius, resulting in insufficient driving torque
Solution Approach 1:
The patent changes the spatial arrangement from a planar annular configuration to a three-dimensional configuration where the motor axis is offset from the wheel center axis. This dimensional change allows the motor to be positioned in the axial direction rather than being constrained to the radial annular space, thereby increasing the motor radius while maintaining compact overall dimensions.
Solution Approach 2:
The patent introduces asymmetric positioning by offsetting the motor axis from the wheel center axis by a predetermined distance. This asymmetric arrangement creates additional spatial freedom, allowing the motor to have a larger radius without interfering with the brake rotor or wheel rim, thus resolving the contradiction between compact arrangement and sufficient torque generation.
2Stability of the object's composition
If the electric traction unit is disposed radially inside the rim on the outer circumference of the wheel, then the motor can be integrated within the wheel structure, but the motor completely protrudes inward from the wheel, potentially interfering with the vehicle body
Solution Approach 1:
By offsetting the motor axis from the wheel center axis, the motor's position relative to the wheel rim changes asymmetrically. This allows the motor to remain integrated within the wheel structure while its protrusion direction is shifted, reducing the likelihood of interference with the vehicle body by positioning the protruding portion away from the vehicle body interface area.
Solution Approach 2:
The patent applies local quality by selectively positioning the motor at a specific offset location where it can be integrated into the wheel structure while minimizing interference with the vehicle body. The offset distance is carefully selected to optimize the balance between motor integration and clearance from the vehicle body.
3Force
If the offset distance from the hub axis to the motor axis and the distance from the hub axis to the motor outer circumferential surface are set longer than the brake rotor radius, then the motor can be positioned away from the brake rotor, but the overall length from the hub to the motor outer surface increases
Solution Approach 1:
The patent optimizes the offset distance parameter to achieve the best balance between torque generation capability and overall length. By carefully selecting the predetermined offset distance, the motor can generate sufficient torque while minimizing the increase in overall length from the hub to the motor outer surface.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration increases the radial dimension of the motor unit within the limited space, enhancing torque output and preventing interference with the vehicle body, while improving the reliability and assembly efficiency of the speed reduction unit.
Implementation Method 1
a plurality of rolling elements arranged in an annular space between the outer ring and the stationary shaft
Data Source
Figure 1
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AI summary
The wheel hub bearing unit (11) includes an outer ring (12) disposed on an axially (axis O) outer side of the wheel hub bearing unit and coupled to a wheel (W), a stationary shaft (15) passing through a center bore of the outer ring, and a plurality of rolling elements (14) arranged in an annular space between the outer ring and the stationary shaft. A motor unit (21) and speed reduction unit (31) are disposed to offset from an axis of the wheel hub bearing unit in a direction perpendicular to the axis. The motor unit is disposed adjacent to an axially inner end portion (15r) of the stationary shaft. The speed reduction unit includes an output gear (40) coupled to the outer ring, and a rolling bearing (41) provided between the output gear and the stationary shaft to rotatably support the output gear. A carrier (18) is disposed on an axially inner side relative to the wheel hub bearing unit, and secured to the axially inner end portion of the stationary shaft.