Spring-Guided Worm Reducer for Backlash and Impact Noise
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Solution Overview
Problem
Conventional worm reducers in electric power steering systems experience unwanted noise and impact sounds due to the displacement of the worm teeth and wheel teeth caused by asymmetric engaging reaction forces, leading to collisions and vibrations.
Innovation Solution
A worm reducer design with a first spring biasing the tip end portion of the worm in a first direction and a second spring supporting it in a second direction, aligning the displacement angles of the engaging reaction forces to minimize collisions and stabilize the engaging state, using a combination of leaf springs with nonlinear spring characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a gap is provided around the entire circumference between the holder and the worm accommodating portion to enable radial displacement of the worm tip end portion, then the worm can move toward and away from the worm wheel to suppress backlash and teeth rattling noise, but the worm can also move in unintended directions causing collisions and impact sounds
Solution Approach 1:
The patent introduces guide portions as intermediary elements that mediate between the holder and the worm accommodating portion. These guide portions allow the worm to displace radially toward and away from the worm wheel while constraining movement in other directions, thus preventing collisions and impact sounds while maintaining backlash suppression functionality
Solution Approach 2:
The patent segments the gap provision into specific regions by introducing guide portions that create controlled displacement paths. Instead of a completely open circumferential gap, the structure is divided into guided regions that permit radial movement while blocking lateral movement, thereby preventing harmful collisions
2Reliability
If the worm tip end portion is allowed to displace freely in radial direction to accommodate engaging reaction forces, then the worm can adapt to dimensional and assembly errors, but asymmetric engaging reaction forces cause unstable engagement and impact sounds
Solution Approach 1:
The guide portions act as intermediaries that stabilize the worm's displacement behavior. They ensure that the worm moves smoothly in the radial direction to accommodate engaging reaction forces while preventing asymmetric movements that would cause impact sounds and unstable engagement
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 design effectively reduces engaging reaction forces and suppresses impact sounds by stabilizing the worm teeth and wheel teeth engagement, ensuring smoother operation and reduced noise.
Implementation Method 1
a first spring (112) formed of a torsion coil spring is provided between the holder (111) and the worm accommodating portion (105). The first spring (112) is elastically deformed, and an elastic restoring force of the first spring (112) biases the tip end portion of the worm (103) toward the worm wheel (102) side
Implementation Method 2
a second spring (113) made of a leaf spring is provided between the outer circumferential surface of the holder (111) and the inner circumferential surface of the worm accommodating portion (105). The second spring (113) suppresses momentum of the tip end portion of the worm (103) when the tip end portion moves in the second direction
Data Source
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AI summary
[Problem] To provide a worm reducer capable of effectively suppressing an impact sound generated when an engaging reaction force applied to a worm decreases, causing worm teeth and wheel teeth to collide with each other. [Solution] When viewed from a third direction, which is an axial direction of a worm accommodating portion 8, an angle formed between a direction in which an engaging reaction force Fl increases, causing a tip end portion of a worm 4 to displace away from a worm wheel 3, and a direction in which an engaging reaction force F1 decreases, causing the tip end portion of the worm 4 to displace back to the side of the worm wheel 3, is within a range of ±10°.