DC Motor Hub Unit Split Housing for Heat Dissipation
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Solution Overview
Problem
Existing direct-current motors in hub units for electrically assisted bicycles suffer from overheating and dimensional variations, leading to positional offsets and impaired parallelism of bearings, which strain the rotor support and reduce motor efficiency.
Innovation Solution
A direct-current motor design featuring a motor case with separable first and second cases, cut-away portions, and bulges on the stator for improved heat dissipation and reduced dimensional variations, allowing for increased stator size and efficiency, along with a deceleration mechanism for the rotor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the clad metal plate of the stator is clamped between the pair of end plates of the motor housing, then the stator is retained in the motor housing, but dimensional variations occur in the opposing direction of the end plates due to clamping state variations and thickness errors, resulting in positional offset of the bearings and impaired parallelism
Solution Approach 1:
The motor housing is divided into two separate half-housings (first half-housing and second half-housing) that are joined together. Each half-housing has a bearing disposed on its inner surface, and when joined, the bearings are positioned in parallel relation. This segmentation allows the bearings to be precisely positioned in each half-housing independently, ensuring parallelism without being affected by clamping variations of the stator.
Solution Approach 2:
A joining portion is provided on the outer peripheral surface of the stator that engages with the two half-housings. This joining portion acts as an intermediary element that connects the stator to both half-housings simultaneously, distributing the retention function and preventing dimensional variations from affecting bearing parallelism. The joining portion includes engagement protrusions that fit into engagement grooves on the half-housings, providing stable positioning.
2Reliability
If the stator is clamped between end plates, then the stator is retained, but heat generated by the coils cannot be effectively dissipated
Solution Approach 1:
The traditional end plate clamping structure is replaced by a split housing design where the stator is not clamped between two plates but rather retained by engagement protrusions on the stator that fit into grooves on the half-housings. This extraction of the clamping function allows for better heat dissipation pathways while maintaining retention.
Solution Approach 2:
The retention mechanism is changed from axial clamping (between end plates) to radial engagement (protrusions fitting into grooves on the half-housings). This dimensional change in the retention approach eliminates the need for tight axial clamping, thereby improving heat dissipation in the axial direction while maintaining stator positioning through radial engagement features.
3Ease of manufacture
If the motor case is made as a single piece, then manufacturing is simpler, but heat dissipation from the stator is limited
Solution Approach 1:
The motor case is segmented into two half-housings that can be manufactured separately and then joined together. This segmentation increases the surface area available for heat dissipation and allows for better thermal management. Each half-housing can be independently manufactured with precise bearing positions, and the joining portion on the stator facilitates assembly while maintaining thermal performance.
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
The design effectively prevents overheating and dimensional variations, enhances motor efficiency, and allows for higher output and efficiency by improving air cooling and maintaining stable positional relations within the motor case.
Implementation Method 1
the cut-away portions of the first case and the cut-away portions of the second case cooperatively define a plurality of windows which are provided in a periphery of the motor case in circumferentially generally equidistantly spaced relation
Implementation Method 2
the separation edge of the first case and the separation edge of the second case each have abutment portions not formed with the cut-away portions, the abutment portions of the first case respectively abutting against the abutment portions of the second case
Implementation Method 3
the first case has screw holes which are threadingly engaged with distal end portions of screws inserted through the fixing screw holes of the bulges
Data Source
Figure 1
Figure 2
Figure 3(a)~3(b)
AI summary
In a motor (11), a motor case (16) includes a first case (30) and a second case (31) separable from each other in a direction of an axis of a rotation shaft (22) of a rotor (15). The first case and the second case each have cut-away portions (35, 39) extending parallel to the axis from a separation edge (open side edge (34, 38)) thereof. The separation edges of the first and second cases each have abutment portions (34A, 38A) not formed with the cut-away portions, and the abutment portions of the first case respectively abut against the abutment portions of the second case. The cut-away portions (35, 39) cooperatively define a plurality of windows (43) disposed in a periphery of the motor case. The stator (14) has a plurality of bulges (20) projecting radially outward from a peripheral surface thereof in association with the windows (43). (Fig. 2)