Vehicle-Sensitive Sensor Lever Design for Belt Retractor Noise Reduction
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Solution Overview
Problem
Existing vehicle-sensitive sensors for self-locking belt retractors often generate unwanted vibration noise due to their design, which affects the reliability and comfort of seat belt systems during vehicle impacts and rollovers.
Innovation Solution
A vehicle-sensitive sensor with a ball-shaped sensor mass and a sensor lever that includes a locking pawl, a resting pin, and a bearing portion pivot-mounted at a bearing support, where the sensor lever pivots about a pivot axis, engaging the locking pawl when the sensor mass is moved away from the resting pin, reducing rotational mass inertia and noise emissions through a specific arrangement of the center of gravity and pivot axis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a rolling ball mass is used in the vehicle-sensitive sensor, then the sensor can detect acceleration loads and lock the retractor, but it generates undesired vibration noise
Solution Approach 1:
The sensor lever is divided into two separate sections by a vertical plane through the pivot axis: a first section containing the resting pin on one side, and a second section containing the locking pawl and center of gravity on the opposite side. This segmentation isolates the noise-generating ball mass movement from the locking mechanism, allowing the sensor to detect acceleration loads reliably while preventing the transmission of vibration noise to the locking components.
2Measurement precision
If the sensor lever has a long contact area with the ball mass, then the sensor is sensitive to acceleration, but the lever generates more vibration and noise
Solution Approach 1:
The harmful vibration and noise are extracted from the system by separating the ball mass contact function (first section with resting pin) from the locking function (second section with locking pawl). The resting pin provides sufficient acceleration detection sensitivity through its contact with the ball mass, while the locking pawl is positioned in a separate section that does not directly contact the ball mass, thus extracting the noise-generating interaction from the locking mechanism.
3Reliability
If the center of gravity of the sensor lever is not properly positioned, then the locking engagement may be weak, but proper positioning increases rotational mass inertia and oscillations
Solution Approach 1:
The sensor lever employs asymmetric design with its center of gravity deliberately positioned in the second section on the opposite side of the vertical plane from the resting pin. This asymmetric positioning creates an optimal balance: the center of gravity is close enough to the pivot axis to minimize rotational mass inertia and reduce oscillations, while still providing sufficient leverage for the locking pawl to engage strongly with the steering disc during acceleration events.
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 reduces unwanted oscillations and noise emissions, enhances vibrational behavior, and provides a more defined locking characteristic, resulting in a quieter and more reliable self-locking belt retractor with reduced size and cost.
Implementation Method 1
The sensor mass is moved away from the resting pin when subjected to inertial forces
Implementation Method 2
The sensor lever is adapted to pivot about the pivot axis and to engage the locking pawl by force applied to the mass of the sensor lever at its center of gravity
Data Source
Figure 1~2
Figure 3~5
Figure 6~7
AI summary
A vehicle-sensitive sensor (1) for a self-locking belt retractor (20) and a corresponding self-locking belt retractor is suggested, comprising a ball-shaped sensor mass (2), a sensor housing (3) comprising a nest (4), in which the sensor mass (2) is moveable and kept, and a sensor lever (5) comprising a locking pawl (6) which is adapted to engage in a steering disc (21) of the belt retractor (20), a resting pin (7) which protrudes through the nest (4), and a bearing portion (8), wherein the bearing portion (8) of the sensor lever (5) is pivot-mounted at a bearing support (9) of the sensor housing (3) creating a pivot axis (10), wherein the sensor lever (5) is adapted to pivot about the pivot axis (10) and to engage the locking pawl (6) by force applied to the mass of the sensor lever (5) at its center of gravity (11) when the sensor mass (2) is moved away from the resting pin (7).