Seat Rail Linear Actuator With Cyclic Rack Drive and Low Backlash
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Solution Overview
Problem
Existing linear drives for seat adjustment in motor vehicles face challenges in achieving backlash-free movement and adjustable breaking loads, with limited speed and spatial integration capabilities, which hinder innovative interior designs and safety requirements.
Innovation Solution
A compact linear drive design featuring a rotatable drive shaft with a propulsion element and guide means, allowing for cyclic movement and absorption of transverse forces, enabling high-speed adjustment with integrated components that absorb forces without additional torque, and modular rack housing for adjustable length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a spindle is used to adjust the upper rail, then the linear movement can be achieved, but backlash-free movement is difficult to achieve and manufacturing costs increase
Solution Approach 1:
The drive shaft is segmented into multiple sections (first, second, and third sections) with different functional characteristics. The first section has a larger diameter for high torque transmission, the second section for intermediate functions, and the third section for specific engagement purposes. This segmentation allows each part to be optimized for its specific function, achieving reliable backlash-free movement while simplifying manufacturing of individual components.
Solution Approach 2:
A synchronization element is introduced as an intermediary component between the drive shaft and the rack. This element ensures precise engagement and transmission of motion without backlash, mediating the interaction between rotating and linear components to achieve reliable positioning without requiring complex manufacturing processes.
2Speed
If single-screw linear drives are used, then proven reliability is achieved, but travel speed is limited and cannot be significantly increased
Solution Approach 1:
The drive system employs periodic engagement of drive teeth with the rack through the synchronized rotation of the multi-section drive shaft. This periodic action allows for high-speed operation while maintaining reliability through controlled, repeatable engagement cycles that ensure precise positioning at each phase of the rotation.
Solution Approach 2:
The drive teeth are pre-positioned and pre-loaded on the drive shaft sections before engagement with the rack. This preliminary positioning ensures that when high-speed operation occurs, the engagement is already optimized for both speed and reliability, eliminating the need for slow, cautious engagement that limits single-screw drives.
3Length of moving object
If larger travel distances are achieved, then new spatial concepts are enabled, but components protrude into the room and increase injury sources
Solution Approach 1:
The drive shaft is nested within the rack housing, with the drive shaft sections arranged concentrically and the drive teeth engaging with the rack from within the housing structure. This nesting allows the full travel distance to be achieved while keeping all moving components contained within the safety envelope of the housing, eliminating protruding elements that could cause injury.
Solution Approach 2:
The drive system utilizes the radial dimension within the rack housing to achieve longitudinal travel. By arranging the drive shaft and teeth in a radial configuration that converts rotational motion to linear motion along the longitudinal axis, the system achieves extended travel distances without increasing the longitudinal footprint or creating protruding components.
4Volume of moving object
If the linear drive is made compact, then spatial efficiency is improved, but integrating components without additional torque and absorbing transverse forces becomes complex
Solution Approach 1:
The rack housing serves multiple functions simultaneously: it provides structural support, contains the drive shaft and teeth, absorbs transverse forces through its rigid construction, and prevents torque transmission to stationary components. This multi-functionality achieves compact design without requiring separate components for each function, thereby reducing overall device complexity.
Solution Approach 2:
The drive shaft sections are merged into a single integrated rotational element with varying diameters, combining what could have been separate components into one unified part. This merging reduces the number of interfaces and assembly steps while achieving the compact design needed to contain all components within a small volume.
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 solution achieves almost play-free linear movement with variable breaking loads, high adjustment speed, and compact integration, addressing the limitations of prior art by ensuring safety and spatial efficiency.
Implementation Method 1
The at least one drive element is coupled to the drive shaft in such a way that the drive element follows a cyclical movement upon rotation of the drive shaft about the longitudinal axis, and its drive tooth is pressed into the rack to generate a feed
Implementation Method 2
The at least one guide means forms an abutment counteracting the rack when the at least one drive tooth is pressed into the rack. The guide means absorbs a force or force component resulting from the pressing in of the drive tooth of the at least one drive element, which force acts transversely to the longitudinal axis on the drive element
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The present invention relates to a linear drive (1) having a drive shaft (10) that can rotate about a longitudinal axis (X), at least one propelling element (20) having a propelling tooth (21), a gear rack (30) and at least one guide means (40), the at least one propelling element (20) being coupled to the drive shaft (10) such that during the course of a revolution of the drive shaft (10) about the longitudinal axis (X), the propelling tooth (21) of the element is forced in a cyclical movement (21) into the gear rack (30) in order to produce propelling motion, and the at least one guide means (40) forms a counter-bearing acting in opposition to the gear rack (30), for the at least one propelling element (20), as the propelling tooth (21) of the at least one propelling element (20) is forced into the gear rack (30). The present invention also relates to a longitudinal-adjustment unit and to a motor vehicle.