Webbing Take-Up Device Compact Acceleration Sensor Housing
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Solution Overview
Problem
Existing webbing take-up devices for vehicle seat belts face challenges in reducing size due to the need for bulky mechanisms to accommodate the sliding range of racks during seat back tilting, which complicates the design and increases the overall size of the device.
Innovation Solution
A webbing take-up device design that incorporates a spool for webbing take-up, a locking mechanism, an acceleration sensor with a housing that turns, an elongated coupling member, a tilt detection section with a rotating body, and a coupling member adjusting section, allowing the acceleration sensor to maintain its position relative to the device even when the seat back tilts, thereby reducing the size of the mechanism and its housing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a rack sliding mechanism is used to accommodate seat back tilting, then the acceleration sensor can detect tilt accurately, but the housing becomes bulky due to the large movable range required
Solution Approach 1:
The patent replaces the traditional linear rack sliding mechanism with a rotating body that moves along a curved (arc-shaped) trajectory. The rotating body rotates about a pivot point, and its center moves along an arc path, which naturally accommodates the tilt detection range while requiring significantly less linear space. This curved motion path allows the acceleration sensor to maintain accurate tilt detection without needing a bulky housing to accommodate large linear displacements.
Solution Approach 2:
The invention transitions from one-dimensional linear rack sliding to two-dimensional rotational motion. The rotating body moves in an arc (curved path) rather than along a straight line, effectively utilizing angular displacement to achieve the same tilt detection function. This dimensional change from linear to rotational/curved motion reduces the space required in the direction of movement, thereby reducing housing volume while maintaining detection precision.
2Volume of stationary object
If the acceleration sensor housing is made smaller, then the overall device size is reduced, but the mechanism cannot accommodate the full range of seat back tilting
Solution Approach 1:
The rotating body follows a curved arc path during rotation, which allows it to accommodate a wide range of seat back tilting angles within a compact space. The arc-shaped trajectory naturally provides the necessary movement envelope for full tilting range without requiring a large linear displacement, thus enabling small housing volume while maintaining full adaptability to seat back tilting.
Solution Approach 2:
The mechanism uses dynamic rotational motion of the rotating body about a pivot point, allowing the center of the rotating body to trace an arc path. This dynamic rotational approach provides a compact yet effective solution for accommodating the full range of seat back tilting, as the arc path efficiently packs the movement range into a smaller spatial envelope compared to linear sliding.
3Measurement precision
If a rack and pinion mechanism is used for tilt detection, then the acceleration sensor can be positioned accurately, but the device complexity increases
Solution Approach 1:
The patent extracts and eliminates the pinion gear component from the traditional rack and pinion mechanism. Instead of using a pinion to engage with a rack, the invention uses a rotating body that rotates about a pivot point, with its center moving along an arc path. This extraction of the pinion component simplifies the mechanism while maintaining the ability to accurately position and detect acceleration sensor tilt, thereby reducing device complexity.
Solution Approach 2:
By replacing the linear rack with a rotating body moving along a curved arc path, the invention simplifies the overall mechanism. The curved motion path is achieved through simple rotation about a pivot point, eliminating the need for complex gear engagement between rack and pinion, thus reducing device complexity while preserving positioning accuracy.
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 achieves a reduction in size for the mechanism that couples to seat back tilting and the housing, ensuring the acceleration sensor operates effectively even when the seat back is tilted, without compromising the mechanical integrity or operational efficiency.
Implementation Method 1
an acceleration sensor that includes a housing on which is placed an inertia mass body that actuates the locking mechanism by moving under inertia
Implementation Method 2
an elongated coupling member whose leading end in a length direction is directly or indirectly connected to the housing of the acceleration sensor, and that turns the housing of the acceleration sensor with respect to the take-up device main body by displacing in the length direction
Implementation Method 3
the rotating body winding up thereon the coupling member from the base end side in the length direction of the coupling member by rotating in one direction to pull and move the coupling member towards the base end side
Data Source
AI summary
In a reclining sensor of a webbing take-up device, when a case turns together with a seat back that tilts towards the seat rear, rotation of a pulley is restricted by a pressing tab of an operation plate. Accordingly, when relative rotation of the pulley occurs with respect to the case, a wire is pulled out from another end of a tube, turning a sensor housing of an acceleration sensor. The wire pulled out from the other end of the tube is wound up onto a winding portion that is an outer peripheral portion of the pulley that rotates. Since the pulley that pulls the wire merely rotates about its center of rotation, the inside of the case is sufficient as long as rotation range of the pulley is secured, enabling a reduction in size of the case.