Flexible Worm Shaft Coupler for EPS Gearbox Assembly Alignment
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Solution Overview
Problem
The assembly of conventional worm and wheel gearbox assemblies for electric power steering systems is hindered by misalignment issues during assembly, which can lead to damage or require replacement of parts due to the rigid nature of the two-part coupler, causing assembly delays or failures.
Innovation Solution
A flexible coupler with a thin, undulating membrane connects the worm shaft to the motor power take off, allowing for self-alignment and relative axial and radial movement, while maintaining high resistance to torsional loads, thus preventing clashing and facilitating torque transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a rigid two-part coupler is used to connect the motor shaft to the worm shaft, then torque transfer is efficient, but misalignment during assembly can cause damage or require replacement of parts
Solution Approach 1:
The coupler employs a flexible membrane instead of a rigid structure, allowing dynamic adjustment during assembly to accommodate misalignment while maintaining torque transfer capability. The membrane's flexibility enables self-alignment between the motor shaft and worm shaft, preventing damage during assembly.
Solution Approach 2:
A thin flexible membrane forms the core of the coupler, replacing rigid connecting parts. This membrane can deform to accommodate alignment variations during assembly while still effectively transferring torque from the motor shaft to the worm shaft, eliminating the need for precise alignment procedures.
2Stability of the object's composition
If a rigid two-part coupler is used, then structural stability is maintained, but misalignment can lead to clashing and damage requiring part replacement
Solution Approach 1:
The flexible membrane provides dynamic compliance that absorbs misalignment stresses during assembly, preventing clashing and damage while maintaining structural integrity for torque transfer. This dynamic property ensures reliable assembly even when alignment is not perfect.
3Ease of operation
If the coupler allows freedom of movement to prevent misalignment damage, then assembly is easier, but rotational play or hysteresis may be felt by the driver
Solution Approach 1:
The thin flexible membrane provides just enough compliance to accommodate assembly misalignment while maintaining sufficient stiffness to prevent excessive rotational play during operation. The membrane's properties are optimized to allow movement only during assembly, not during normal steering operation.
Solution Approach 2:
The coupler design changes the flexibility parameter spatially and temporally - allowing flexibility during assembly to prevent damage, while maintaining rigidity during operation to eliminate rotational play. The membrane's effective stiffness changes based on the operational state.
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 flexible coupler enables smooth assembly by allowing for radial and axial offset, preventing misalignment and damage, while maintaining torque transfer efficiency and reducing rotational play or hysteresis felt by the driver.
Implementation Method 1
a flexible membrane that connects the first hub part to the second hub part, the flexible membrane providing a primary path for the transfer of torque from the first hub part to the second hub part
Data Source
AI summary
A gearbox assembly for power take off from an electric motor of an electric power assisted steering apparatus comprising a gearbox housing which houses a worm shaft and a gear wheel, is disclosed. The worm shaft incorporates one or more external helical worm teeth. A main bearing assembly supports the worm shaft at an end closest to the motor. A tail bearing assembly supports the worm shaft at an end furthest from the motor, in which at least the tail bearing assembly is free to move relative to the housing through a limited range of motion that enables the worm shaft to move radially away from the axis of the wheel gear. The gearbox assembly further comprises a flexible coupler which connects the worm shaft at the main bearing end to a power take off from the motor so as to transfer torque from the motor to the worm shaft. The flexible coupler comprises a first hub part providing a connection to the worm shaft, a second hub part providing a connection to the power take off from the motor, and a flexible membrane that connects the first hub part to the second hub part. The flexible membrane provides a primary path for the transfer of torque from the first hub part to the second hub part.