Rotor Shaft Form-Fit Gear Mount for Lower-Inertia Brake Booster Motors
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Solution Overview
Problem
Existing electric motors in ancillary units of motor vehicles face challenges with robustness and production costs due to the need for a strong force-fit between the gear wheel and rotor shaft, leading to increased inertia and reduced dynamics.
Innovation Solution
The electric motor design features a rotor shaft with a cylindrical main portion and an assembly portion having a barrel-shaped cross section, allowing for a form-fit with the gear wheel, which reduces stress on the gear wheel and enables a smaller diameter, thus decreasing inertia and increasing dynamics, while also simplifying production and reducing costs by using dissimilar materials and sintering techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a press-fit connection is used between the gear wheel and rotor shaft to ensure strong force transmission, then the robustness of the connection is improved, but the gear wheel requires a robust design leading to increased weight and inertia
Solution Approach 1:
The rotor shaft is divided into two distinct portions: a cylindrical main portion and a barrel-shaped assembly portion. This segmentation allows the gear wheel to be designed with optimized geometry (barrel-shaped cross-section) that provides sufficient connection strength while reducing material usage and weight compared to a fully robust cylindrical design.
Solution Approach 2:
The rotor shaft exhibits local quality variation through its two portions: the cylindrical main portion provides structural support while the barrel-shaped assembly portion specifically optimizes the connection interface with the gear wheel. This localized geometric adaptation allows the gear wheel to achieve necessary strength only where required, reducing overall weight.
2Reliability
If a robust gear wheel design is used to prevent release from the rotor shaft, then the reliability of the connection is improved, but the inertia increases and dynamics are reduced
Solution Approach 1:
By segmenting the rotor shaft into functional portions, the design achieves reliable force transmission at the assembly portion (barrel-shaped interface) without requiring the entire gear wheel structure to be overly robust, thus reducing inertia and improving dynamic response.
Solution Approach 2:
The geometric parameters of the rotor shaft assembly portion are specifically changed to a barrel-shaped cross-section, optimizing the interface geometry for both reliability and weight reduction. This parameter optimization allows sufficient connection strength with minimal material, improving dynamics.
3Force
If a press-fit connection is used between the gear wheel and rotor shaft, then the force transmission capability is improved, but the production complexity and costs increase
Solution Approach 1:
The segmented rotor shaft design with distinct cylindrical and barrel-shaped portions allows for simplified manufacturing processes. The barrel-shaped assembly portion can be produced using standard machining or forming operations, avoiding complex press-fit procedures while maintaining effective force transmission.
Solution Approach 2:
Changing the assembly portion geometry to a barrel-shaped cross-section simplifies the manufacturing process by enabling direct formation of the connection interface, eliminating the need for complex press-fit operations and reducing production complexity and costs.
Data Source
AI summary
An electric motor of an ancillary unit or an auxiliary assembly of a motor vehicle, in particular an electromechanical brake booster, includes a rotor shaft which is disposed along a rotor axis. The rotor shaft includes a cylindrical main portion, which has a round cross-section perpendicular to the rotor axis, and an assembly portion, which adjoins the main portion and has a barrel-shaped cross-section perpendicular to the rotor axis. The barrel-shaped cross-section has two parallel main edges and two convex edges. A gear wheel is positioned on the assembly portion. The gear wheel has a central assembly opening with a barrel-shaped cross-section perpendicularly to the rotor axis. An ancillary unit or auxiliary assembly of a motor vehicle is also provided.