Zero Lash Torque Transfer Joint for Bus Doors
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Solution Overview
Problem
Conventional systems for opening and closing bus doors experience undesirable lash or lost motion due to tolerances in the shaft and hub connections, making them difficult to assemble and service, and can lead to post-welding corrosion issues.
Innovation Solution
A torque transfer system with a shaft and hub configuration that uses a fastener to draw flats on the shaft and hub together, forming a zero lash joint, which is easy to manufacture and service using common tools and techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If interference or press fit joint is used to join shaft and hub, then lash is eliminated, but assembly difficulty increases and servicing is inhibited
Solution Approach 1:
The joint is segmented into modular components (shaft, hub, fastener) that can be independently assembled and disassembled. The fastener acts as a separate element that connects the shaft and hub through threaded engagement, allowing the joint to be built in stages rather than requiring complex interference fitting operations.
Solution Approach 2:
The fastener serves as an intermediary element between the shaft and hub. Instead of directly joining the shaft and hub through press fit or welding, the fastener mediates the connection by threading into the shaft and engaging the hub, eliminating lash while maintaining ease of assembly and servicing.
2Reliability
If welded joint is used to join shaft and hub, then lash is eliminated, but heat generation creates undesirable effects and corrosion protection impacts nearby structures
Solution Approach 1:
The mechanical fastening system (threaded fastener) replaces the thermal joining process (welding). Instead of using heat to join the shaft and hub, the invention uses mechanical threading and clamping forces to eliminate lash and create a rigid connection, thereby avoiding all heat-related harmful effects and corrosion issues associated with welded joints.
3Ease of operation
If tolerances are built into shaft and hub connection for assembly, then assembly is facilitated, but lash or lost motion occurs during rotation
Solution Approach 1:
The fastener is installed and tightened before the shaft and hub are subjected to operational loads. This preliminary action of pre-tensioning the fastener ensures that the flats are drawn together with sufficient force to eliminate lash, while the tolerances in the connection allow for straightforward assembly without requiring precision fitting.
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
Enables torque transfer with zero lash or lost motion, is cost-effective, and simplifies assembly and disassembly, reducing the risk of corrosion and maintenance challenges.
Implementation Method 1
a fastener extending through the through bore in the hub and into the threaded bore in the shaft. Rotation of the fastener draws the flat on the hub towards the flat on the shaft
Implementation Method 2
a fastener extending through the threaded through bore in the hub and engaging the radially outer surface of the shaft diametrically opposite the flat on the radially outer surface of the shaft. Rotation of the fastener urges the flat on the hub towards the flat on the shaft
Data Source
AI summary
A system for transferring torque with zero lash from a driver to a driven object is provided. The system includes a shaft disposed about a rotational axis and a hub defining a bore that receives the shaft. The shaft and hub are each configured for coupling to one of the driver and driven object. The shaft defines a flat on a radially outer surface and the hub defines a flat on a radially inner surface opposing the flat in the shaft. In one embodiment, the shaft includes a threaded bore and the hub includes an aligned through bore. Rotation of a threaded fastener in the bores draws the flat into engagement. In another embodiment, the hub includes a threaded through bore. Rotation of a fastener extending through the bore and engaging the shaft diametrically opposite the flats urges the flats into engagement.