Belt Retractor Signal Transmitter Ring Axial Tolerance

The patent replaces the purely magnetic positioning system with a hybrid mechanical-magnetic system. A signal transmitter ring with a stop is mechanically coupled to the shaft via a spring element, providing mechanical pre-positioning that reduces the required magnetic holding force. This substitution allows weaker, more economical magnets to achieve the same sensing reliability.

The spring element acts as an intermediary between the mechanical shaft and the magnetic sensing system. It provides mechanical pre-loading that positions the signal transmitter ring close to the sensor, reducing the air gap and thereby reducing the magnetic field strength requirements while maintaining reliable sensing across tolerance ranges.

The patent introduces dynamic elements (spring and stop) that allow the system to adapt to axial tolerances. The spring provides continuous contact force that maintains the signal transmitter ring's position relative to the sensor despite shaft position variations, while the stop prevents excessive displacement. This dynamic compensation preserves sensing precision without requiring tight shaft tolerances.

The patent changes the system's parameter response to axial displacement by introducing a spring element with specific stiffness characteristics. Instead of a rigid connection that would transmit tolerance variations directly to the sensing interface, the spring filters these variations, maintaining a stable magnetic gap distance despite shaft position changes within the tolerance range.