Planetary Roller Actuator for Electric Brake Systems
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Solution Overview
Problem
Existing electric linear motion actuators face challenges in providing sufficient driving force without increasing size, and smooth linear motion guidance is hindered by lateral moments and complex manufacturing processes, especially when used in electric brake systems.
Innovation Solution
An electric linear motion actuator design featuring a rotary shaft, outer race member, carrier with support pins, and planetary rollers, where the carrier is axially immovable and the outer race member is rotationally fixed and axially movable, with an elastic member biasing the rollers against the rotary shaft to prevent preload and facilitate smooth linear motion guidance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a separate speed reducer such as a planetary gear speed reducer is added to increase the driving force, then the driving force is sufficiently increased, but the size of the entire electric linear motion actuator increases
Solution Approach 1:
The patent combines the motion converter mechanism and the speed reducer into a single integrated planetary roller mechanism. The planetary rollers simultaneously perform motion conversion and provide mechanical advantage through their engagement with the helical rib on the rotary shaft, eliminating the need for a separate speed reducer while maintaining compact size
Solution Approach 2:
The planetary rollers serve multiple functions: they convert rotary motion to linear motion, provide mechanical advantage through their interaction with the helical rib, and act as the speed reduction mechanism all in one component. This multi-functionality allows the actuator to achieve sufficient driving force without additional components that would increase size
2Volume of moving object
If the carrier or linear motion member is made relatively short in the axial direction to maintain compact size, then the actuator remains compact, but a lateral moment from the braking member hampers smooth linear motion
Solution Approach 1:
The patent inverts the traditional design by making the outer race member axially movable instead of the carrier, and by providing a long-guidance linear motion member that extends through the outer race member. This inversion allows the linear motion member to be guided over a long axial distance even when the overall actuator remains compact, enabling smooth linear motion despite lateral moments from the braking member
3Reliability
If negative gaps are used to apply preload to planetary rollers for stable torque transmission, then torque transmission is stable, but the manufacturing process becomes complex and costly
Solution Approach 1:
The patent extracts the preload application function from the gap design and implements it through a dedicated elastic member (such as a spring) that actively applies preload to the planetary rollers. This eliminates the need for complex negative gap configurations and high-precision surface finishing, simplifying the manufacturing process while maintaining stable torque transmission
Solution Approach 2:
The elastic member acts as an intermediary component that mediates between the planetary rollers and the rotary shaft, providing the necessary preload force to ensure stable torque transmission. This intermediary approach simplifies the interface design and reduces manufacturing complexity compared to direct gap-based preload 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 allows for stable torque transmission and smooth linear motion guidance even under lateral moments, reducing manufacturing complexity and cost, while maintaining a compact size suitable for electric brake systems.
Implementation Method 1
an elastic member biasing the planetary rollers against a radially outer surface of the rotary shaft
Implementation Method 2
a helical rib is formed on the radially inner surface of the outer race member, and wherein each of the planetary rollers has, on a radially outer surface thereof, a plurality of circumferential grooves which are arranged at the same pitch as the helical rib and in which the helical rib is engaged
Data Source
AI summary
In an electric linear motion actuator for transmitting torque of a rotary shaft (4) to planetary rollers (7) and thus to a linearly driven output member constituted by an outer race member (5), axial movement of a carrier (6) supporting the planetary rollers (7) is restricted, and the outer race member (5) is axially slidably fitted in a radially inner surface of a cylindrical portion (1a) of a housing (1) and is rotationally fixedly coupled to an object to be driven via keys (25) The planetary rollers (7) have their radially inner surfaces rotatably supported on respective support pins (6c) of the carrier (6), and are radially inwardly biased by radial compression ring springs (21) wound around the support pins (6c) so as to envelop the support pins. The planetary rollers (7) are thus pressed against the radially outer surface of the rotary shaft (4).