US 3,836,171 · Granted 1974-09-17
The 1974 Seatbelt Lock That Stops You in a Crash
Imagine your seatbelt as a reel. When a car crashes hard, this device spins a gear that instantly locks the reel so the belt can't unwind and let you slide forward. It's an automatic safety catch triggered by the violent motion of an accident.
The plain-English version
What it protects
The claim covers a mechanical locking device built into a seatbelt system that uses synchronized gears and a pawl plate to lock the belt reel during sudden deceleration or impact. What's protected here is the specific synchronization mechanism that aligns the pawl plate with a lock gear mounted on the belt's spool shaft, preventing the belt from extending once the accident forces trigger engagement.
Why it matters
This patent represents an early automated safety innovation in vehicle restraint systems at a time when seatbelts were becoming mandatory. By mechanically locking the belt during a crash rather than relying on the passenger to hold it, the device offered passive protection—a major step toward modern safety features that work without driver input. Tokai Rika was a major supplier to Japanese automakers, so this technology likely equipped vehicles sold worldwide in the mid-1970s.
Real-world use
Every time a driver brakes hard or hits something, the seatbelt locks up to keep you pinned in your seat instead of sliding forward—that's the principle this 1974 design protects.
Original USPTO abstract
A safety belt locking device for use in a vehicle for automatically locking a belt in the event of an accident of the vehicle in order to prevent the passenger fastened by the belt from further injuries, which includes synchromesh means for synchronizing a pawl plate with a lock gear rigidly mounted on a shaft upon which the belt is wound, thereby permitting engagement between the pawl plate and the lock gear for locking the belt.
Patent details
- Publication number
- US 3,836,171
- Filing date
- 1972-07-07
- Grant date
- 1974-09-17
- Assignee
- Tokai Rika Co Ltd
- Inventor(s)
- HAYASHI Y,JA, IWATSUKI M,JA
- CPC class
- B60R22/343
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