Rear-Axle Steering Actuator Cage for Pitch-Error-Free Force Transfer
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Solution Overview
Problem
Existing electromechanical actuators for rear-axle steering systems face challenges in achieving operation free from pitch errors, efficient use of installation space, and optimal force and torque transfer, while maintaining manufacturing simplicity.
Innovation Solution
An electromechanical actuator design featuring a threaded spindle surrounded by profiled planets guided in a driven cage, with a nut supported by rolling bearings, and a dual-function cage that acts as both a rotary-linear and rotary-rotary transmission element, utilizing angular contact rolling bearings for radial and axial support, and optionally a belt transmission or spur gear for continuous variable transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If rolling elements are arranged at a fixed predetermined distance with guide rings and ball bearings, then axial force absorption is improved, but device complexity increases
Solution Approach 1:
The patent extracts the axial force absorption function from the rolling element support structure and transfers it to the nut and cage assembly. The rolling elements simply support the spindle radially, while axial forces are absorbed by the nut-cage-brake device connection, simplifying the overall support structure.
Solution Approach 2:
The cage serves multiple functions: it guides the rolling elements, supports the nut, and connects to the brake device. This multi-functionality reduces the need for separate components for each function, thereby reducing overall device complexity while maintaining force absorption capabilities.
2Manufacturing precision
If the cage is non-rotatably connected to the output-side component, then pitch errors are eliminated, but manufacturing precision requirements increase
Solution Approach 1:
The cage acts as an intermediary element between the rolling elements and the output component. Its non-rotatable connection to the output component while being guided by the rolling elements provides a reliable mechanical link that eliminates pitch errors without requiring extremely tight manufacturing tolerances on individual components.
Solution Approach 2:
The system is segmented into distinct functional modules: the rolling elements for radial support, the nut for axial positioning, the cage for guidance and connection, and the brake device for force absorption. This segmentation allows each module to be manufactured and assembled separately, improving ease of manufacture while maintaining precision through the cumulative effect of well-defined interfaces.
3Device complexity
If the cage serves dual function as rotary-linear and rotary-rotary transmission element, then device complexity is reduced, but reliability requirements increase
Solution Approach 1:
The cage is designed as a universal component that performs both rotary-linear transmission (guiding rolling elements that convert rotation to linear motion of the nut) and rotary-rotary transmission (connecting to the output component that rotates with the spindle). This multi-functionality reduces the number of separate transmission elements needed, simplifying the device while the robust design ensures reliability under combined loading conditions.
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 actuator achieves precise linear deflection with reduced friction, allows for simple angular position detection, and efficient force transfer without pitch errors, optimizing the relationship between installation space and transferred forces and torques.
Implementation Method 1
The nut is supported by rolling bearings with respect to the cage
Implementation Method 2
The bearings provided for mounting the nut in the cage are designed as angular contact rolling bearings
Implementation Method 3
a threaded spindle which is surrounded by planets, each having a corresponding profile, i.e., one that engages into the thread of the spindle
Implementation Method 4
the rotation of the relevant part is converted into an axial movement of the other part
Data Source
AI summary
An actuator for rear-axle steering system of a motor vehicle comprises a threaded spindle (2) which is surrounded by planets (21), each provided with a corresponding profiling (8), wherein the planets (21) are guided in a driven cage (13) and, via further profiling (25), contact a nut (4) that surrounds areas of the planets (21) provided with said profiling (8) and is supported with respect to the cage (13) by rolling bearings (14), and wherein the cage (13) is mounted in a housing (20) by means of further rolling bearings (30, 31, 32, 33) and is non-rotatably connected to an output-side component (12, 34) of a further transmission (10, 11, 12).