Ball Screw Tip Curvature for Piston Wear Reduction
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Solution Overview
Problem
Existing electric braking devices face issues with the wear-out and instability of the contact part between the screw and piston, leading to piston misalignment and damage, which affects the production of brake fluid pressure and the integrity of the braking system.
Innovation Solution
The electric braking device incorporates a driving force transmission mechanism with a nut and screw system, where the screw tip is designed with a convex curved shape to ensure point-by-point contact with a flat piston surface, and includes a regulator to manage piston displacement, enhancing stability and reducing wear-out, while an annular guide seals and guides the piston to prevent axial misalignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional screw and piston contact structure is used, then the device complexity is low, but the reliability deteriorates due to worn-out contact parts causing piston instability
Solution Approach 1:
The screw tip is designed with a convex curved surface instead of a flat or pointed shape. This curved surface contacts the flat abutting face of the piston, creating a point contact that minimizes radial forces and reduces worn-out. The curvature allows the screw to maintain stable abutment to the piston center without causing piston tilt or fall-down, thereby improving reliability while keeping the structural change simple.
2Reliability
If the screw tip is made flat to match the piston surface, then the ease of manufacture is improved, but the reliability deteriorates due to partial contact and increased worn-out
Solution Approach 1:
The screw tip is formed with a convex curved surface that contacts the flat piston abutting face at a point rather than across an area. This point contact concentrates the axial force efficiently and minimizes radial components that cause worn-out. The curved surface can be manufactured through standard machining processes and is more reliable than a flat screw tip that would cause partial contact and increased wear.
3Reliability
If the screw and piston contact area is increased, then the friction increases providing better grip, but the reliability deteriorates due to increased worn-out of the contact part
Solution Approach 1:
The convex curved surface at the screw tip creates a point contact with the flat piston abutting face. This point contact minimizes the contact area and therefore reduces the worn-out of the contact part. The curvature is designed to maintain stable abutment to the piston center without causing radial forces that would increase wear, achieving reliability through minimized substance loss.
Solution Approach 2:
The contact geometry is changed from a conventional flat or broad contact surface to a convex curved surface. This parameter change in the contact geometry reduces the contact area and minimizes the worn-out while maintaining stable abutment. The curved surface shape is optimized to prevent piston tilt and fall-down, ensuring reliable operation with reduced material loss at the contact interface.
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 ensures stable abutment of the screw to the piston, preventing piston fall and wear-out, maintaining brake fluid pressure integrity and extending the lifespan of components like the piston and seal members.
Implementation Method 1
a ball screw structure 80 having a ball screw shaft 80a which is movable in an axial direction and has a tip abutting the second slave piston 88a
Data Source
AI summary
In an electric braking device that produces brake fluid pressure by driving a second slave piston in the axial direction with the driving force by a motor, a driving force transmission mechanism for transferring the driving force by the motor includes a nut that rotates upon reception of the rotational driving force by the motor, and a ball screw shaft which is engaged with the nut and is movable in the axial direction and which abuts the second slave piston. The electric braking device further includes a worn-out reducer for reducing the worn-out of a contact part between the ball screw shaft and the second slave piston.