Parking Brake Spindle-Nut Thread Geometry for Lower Wear
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Solution Overview
Problem
Existing nut-spindle systems for parking brake actuating units in motor vehicles face issues with force distribution and wear due to asymmetrical threads, which lead to increased stress and potential microcrack formation, compromising the load-bearing capacity and longevity of the components.
Innovation Solution
Designing the nut-spindle system with symmetrical threads, where the flank angles relative to a radial reference plane are equal, reduces stress concentration and improves force distribution, enhancing the load-bearing capacity and reducing wear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If asymmetrical threads are used in the nut-spindle system, then the load transfer from nut to spindle is improved, but stress concentration and microcrack formation increase, reducing load-bearing capacity and longevity
Solution Approach 1:
The patent applies asymmetry in reverse by using symmetrical thread flanks instead of asymmetrical ones. The thread design features equal flank angles (α = α') on both sides of the thread, creating a symmetrical structure that distributes stresses evenly across the thread roots, preventing stress concentration and microcrack formation while maintaining effective load transfer capability
Solution Approach 2:
The patent changes the geometric parameters of the thread by specifying equal flank angles (α = α' = 30°) and a specific thread pitch relationship (p = d/10 to p = d/15), where d is the nominal diameter of the threaded spindle. These parameter changes optimize the balance between load transfer efficiency and stress distribution, preventing excessive stress concentration at the thread roots
2Force
If asymmetrical threads are used, then force transfer efficiency is improved, but wear increases due to manufacturing tolerances and closing folds
Solution Approach 1:
The patent uses symmetrical thread design (equal flank angles) to eliminate the asymmetric closing fold that occurs in asymmetrical threads during cold forming. This symmetrical approach ensures that manufacturing tolerances do not create uneven stress distributions, thereby reducing wear and improving reliability of the force transfer mechanism
Solution Approach 2:
The patent optimizes the local geometry of the thread by specifying that the flank angles should be between 15° and 45° (preferably 30°), and the thread pitch should be between d/10 and d/15 of the nominal diameter. These localized geometric optimizations ensure uniform stress distribution and reduce wear at the thread contact surfaces
3Productivity
If cold-forming process is used for manufacturing the nut and spindle, then production efficiency and surface finish are improved, but closing folds are created that reduce thread crest load-bearing capacity
Solution Approach 1:
The patent applies symmetrical thread design to minimize the harmful effects of the closing fold created during cold forming. By making the thread symmetrical with equal flank angles, the closing fold is distributed evenly and does not create asymmetric stress concentrations that would significantly reduce load-bearing capacity, thus maintaining both production efficiency and structural integrity
Solution Approach 2:
The patent specifies optimal parameter ranges for the cold-formed thread: flank angles between 15° and 45° (preferably 30°) and pitch between d/10 and d/15 of the nominal diameter. These parameter changes optimize the cold-forming process by minimizing closing fold severity while maintaining thread strength and load-bearing capacity
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 symmetrical thread design improves the load-bearing capacity and reduces wear, maintaining locking forces and operational efficiency while minimizing the negative effects of manufacturing tolerances and closing folds.
Implementation Method 1
The force transfer between the threaded spindle and the nut occurs via the interlocking threads; depending on the load direction, this occurs via the sliding flanks of the threads on the nut and the threaded spindle
Implementation Method 2
the sliding flanks of the threads on the nut and the threaded spindle
Implementation Method 3
A nut-spindle system also has the advantage of being safe even when de-energized, because the self-locking mechanism of the thread, combined with a typically present reduction gear and the drive motor, holds the brake in the locked position
Implementation Method 4
The nut-spindle system technically functions as a screw drive, with the reduction or gear ratio determined by the dimensions of the threaded spindle and the thread pitch
Implementation Method 5
the reduction or gear ratio determined by the dimensions of the threaded spindle and the thread pitch
Data Source
Figure 1
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Figure 4~5
AI summary
An actuating unit for a motor vehicle parking brake comprises a functionally interconnected unit consisting of a drive spindle and a nut, forming an axially length-adjustable element of a linear actuator. The drive spindle has a drive end for connection to an electric drive and a substantially cylindrical spindle section with an external thread. The nut, on the other hand, has a sleeve-shaped central body with an internal thread and a head section designed to act as a pressure piston on a braking element of the parking brake. The central body and head section of the nut, as well as the drive end and spindle section of the drive spindle, can be manufactured as a single piece or joined by force-fit, form-fit, or material-fit connection from two components. The internal and external threads of the actuating unit mesh together in a functional connection, defining a common axial axis of rotation (A).According to the invention, the thread is designed as a symmetrical thread in which the flank angles (α, α') with respect to a radial reference plane (R) perpendicular to the axis of rotation (A) have essentially equal angular magnitudes.