Planetary Roller Actuator Load Distribution
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Solution Overview
Problem
Conventional electric linear motion actuators, such as those with ball screw or ball-ramp mechanisms, fail to provide sufficient power increase for applications like electric disc brake assemblies without increasing the size of the actuator, and existing solutions with planetary gear speed reduction mechanisms lead to uneven distribution of external thrust loads on planetary rollers, reducing their lifespan.
Innovation Solution
The electric linear motion actuator design features circumferential grooves on planetary rollers aligned with the axial position of the helical rib, supported by thrust bearings, allowing for uniform distribution of external thrust loads by adjusting the axial positions and lengths of these grooves and using spacers between thrust bearings and the carrier to ensure even load distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a planetary gear speed reduction mechanism is added to increase driving force, then the power increase function is improved, but the size of the electric linear motion actuator increases
Solution Approach 1:
The patent merges the motion converter mechanism and speed reduction function into a single integrated planetary roller structure. The planetary rollers simultaneously convert rotary motion to linear motion and provide speed reduction through their engagement with the helical rib, eliminating the need for separate speed reduction mechanisms and maintaining compact size while achieving high power increase (up to 5 times or more).
Solution Approach 2:
The planetary rollers serve multiple functions: they convert rotary motion to linear motion through their engagement with the helical rib, provide speed reduction through their planetary motion, and support thrust loads through their rotational capability. This multi-functionality allows the actuator to achieve high power increase without increasing size.
2Reliability
If thrust bearings are disposed to support planetary rollers during linear motion, then the rotation of planetary rollers is supported, but external thrust loads are distributed unevenly reducing lifespan
Solution Approach 1:
The patent introduces asymmetric spacing between thrust bearings, with different axial distances from the carrier for each thrust bearing. This asymmetric arrangement, combined with appropriately positioned circumferential grooves on planetary rollers, creates uniform load distribution across all planetary rollers during external thrust load application, preventing premature failure while maintaining reliable rotation support.
3Device complexity
If conventional ball screw or ball-ramp mechanisms are used, then the structure is simple, but sufficient power increase cannot be achieved for electric disc brake assemblies
Solution Approach 1:
The patent employs curved helical ribs on the outer ring member that engage with circumferential grooves on planetary rollers. This curved geometry enables the planetary rollers to follow a helical path during rotation, simultaneously achieving motion conversion and significant power increase (5 times or more) while maintaining relative structural simplicity compared to conventional mechanisms.
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 design extends the lifespan of planetary rollers by uniformly distributing external thrust loads, maintaining the compact size and high power increase functionality of the actuator, suitable for electric disc brake assemblies.
Implementation Method 1
the planetary rollers being in frictional contact with the rotary shaft and each having a plurality of circumferential grooves arranged with the same pitch as the pitch of the helical rib and meshing with the helical rib
Data Source
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AI summary
In an electric linear motion actuator, it is proposed to uniformly distribute external thrust loads to respective planetary rollers while the planetary rollers are revolving around a rotary shaft while rotating about their respective axes with a helical rib of an outer ring member in engagement with circumferential grooves of the respective planetary rollers. The planetary rollers (6) have bearing support surfaces (6b) on which thrust bearings (18) are supported, respectively. The distance from the bearing support surface (6b) of each planetary roller (6) to a predetermined reference position of each circumferential groove (6a) of the planetary roller (6) is different from the corresponding distances for the other planetary rollers (6), whereby with the planetary rollers (6) supported by the respective thrust bearings (18), the axial position of each circumferential groove (6a) coincides with the axial position of the portion of the helical rib (5a) of the outer ring member (5) that is engaged in the circumferential groove (6a).