Epicyclic Step-Down Gear With Eccentric Load Path Against Shaft Buckling
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Solution Overview
Problem
Conventional epicyclic reduction gears in electric motor vehicle parking brake actuators are prone to buckling due to mechanical forces applied during braking, which can cause the drive shaft to deform, and they have high mass and cost due to their size and material requirements.
Innovation Solution
An epicyclic reduction gear design featuring a drive shaft with an internal sun gear and external sun gear with internal threading, along with a bearing ring and axial force transmission parts that distribute axial forces, reducing the diameter and mass of the drive shaft and preventing buckling by redirecting forces away from the shaft.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the drive shaft diameter is reduced to decrease mass and cost, then the risk of buckling increases under axial loads during braking
Solution Approach 1:
The patent introduces axial force transmission pieces as intermediary components between the drive shaft and the planet carriers/cylinder. These intermediaries carry the axial compressive loads that would otherwise be borne by the drive shaft, allowing the shaft to be thinner without buckling. The force transmission pieces act as mediators that redistribute the load path away from the vulnerable shaft sections.
Solution Approach 2:
The patent segments the force transmission function by separating the axial load-bearing role from the drive shaft. Instead of the shaft performing both rotation and axial load-bearing functions, the load-bearing function is segmented into dedicated force transmission pieces (such as bearing rings or transmission elements) that handle axial forces independently, allowing the shaft to be optimized for rotation only with reduced diameter.
2Reliability
If the drive shaft diameter is increased to prevent buckling, then the mass and cost of the reducer increase
Solution Approach 1:
The force transmission pieces serve as intermediaries that insert themselves into the load path between the support ring and the moving components (planet carriers and cylinder). By introducing these intermediary elements, the axial compressive forces are redirected through the intermediaries rather than through the drive shaft, enabling the shaft to maintain smaller dimensions while preserving buckling resistance.
Solution Approach 2:
The patent changes the dimensional arrangement of force transmission by introducing radial offsets. The axial force transmission pieces are positioned radially offset from the drive shaft axis, creating an eccentric force path. This dimensional reorganization allows axial forces to be transmitted through a separate radial pathway rather than through the central shaft, decoupling the shaft diameter requirement from the buckling resistance requirement.
3Reliability
If axial force transmission pieces are added to redistribute forces, then the device complexity increases
Solution Approach 1:
The axial force transmission pieces are designed to perform multiple functions simultaneously: they transmit axial forces, support planet carriers or the cylinder, and in some embodiments provide radial support or guide rotation. This multi-functionality reduces the need for separate dedicated components for each function, thereby limiting the increase in overall device complexity while achieving reliable force distribution and buckling prevention.
4Ease of manufacture
If the drive shaft diameter is reduced, then the manufacturing cost decreases, but the structural strength under axial load decreases
Solution Approach 1:
The force transmission pieces act as intermediaries that assume the axial load-bearing function, allowing the drive shaft to be manufactured with a smaller diameter at lower cost. The intermediaries are designed to handle the axial compressive loads that would otherwise require a larger, more expensive shaft, thus achieving cost reduction without sacrificing axial strength.
Solution Approach 2:
The patent changes the structural parameters of the force transmission system by introducing separate force transmission pieces with optimized geometries for axial load bearing. Instead of increasing shaft diameter to improve axial strength, the solution changes the system architecture to use components specifically designed for compression loading, allowing the shaft parameter (diameter) to be reduced while maintaining overall system strength.
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 reduces the risk of drive shaft buckling and minimizes mass and cost by redistributing axial forces, allowing for a smaller diameter and lighter components, thereby enhancing the efficiency and reliability of the brake actuator.
Implementation Method 1
An external thread of the cylinder cooperates with an internal thread formed by an internal toothing 400 of the piston 100 so as to transform the rotation of the planet carrier 300 into a translation of the piston 100 along the longitudinal axis A100
Implementation Method 2
at least one axial force transmission piece interposed between this support ring and the cylinder so as to transmit axial forces exerted on one between the support ring and the cylinder to the other between this support ring and this cylinder
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
The invention relates to an epicyclic step-down gear (1) for an electric parking brake, this step-down gear (1) comprising a drive shaft (3), at least one step-down stage and a cylinder (14) which forms a screw/nut system with an outer planet gear (2) of this step-down gear. This step-down gear (1) comprises at least one axial force transmission component (16, 11) which is positioned between a bearing ring (20) of the drive shaft (3) and the cylinder (14) so as to transmit axial forces applied via either the bearing ring (20) or the cylinder (14) to either this bearing ring (20) or this cylinder (14). Such an axial force transmission component (16, 11) prevents the drive shaft (3) from buckling by defining an axial force transmission path which is radially eccentric.