Motor Vehicle Door Latch Third Lever Engagement
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Solution Overview
Problem
Conventional motor-vehicle door latch devices face difficulties in determining an unsteady engagement state, where the door is stuck due to reduced weatherstrip counterforce or freezing, leading to unclear operational states.
Innovation Solution
The motor-vehicle door latch device incorporates a ratchet with a pawl and a third latch lever that engages with a third engagement portion on the latch, allowing the door to be stopped in a determinable half-open state when an unsteady engagement occurs, enabling easy identification of the unsteady state by visual inspection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the door latch device uses only a latch and pawl mechanism, then the structure is simple, but it is impossible to determine whether an unsteady engagement state had occurred
Solution Approach 1:
The patent uses visual position changes of the third latch lever to indicate the engagement state. When the third latch lever is positioned at the third latch position (engaged with third engagement portion), it visually indicates that an unsteady engagement state had occurred. This allows occupants to determine the engagement state by watching the appearance position of the third latch lever without adding complex electronic sensors or indicators.
2Ease of operation
If the door is pushed by weatherstrip counterforce to open, then the door can be opened normally, but when weatherstrip counterforce is reduced or door is adhered, the door cannot be pushed out and remains in closing position making unsteady state undetectable
Solution Approach 1:
The third latch lever is designed to engage with the third engagement portion on the latch as a preliminary action when the latch rotates to the third latch position during an unsteady engagement state. This preliminary engagement occurs before the door can be fully opened or closed, and it creates a visible intermediate position that indicates the unsteady state has occurred, regardless of whether the door ultimately opens or remains closed due to weatherstrip counterforce issues.
3Ease of operation
If the latch is allowed to rotate freely to open position, then the door can open completely, but in unsteady engagement state the door may open unexpectedly when operated with large force
Solution Approach 1:
The patent segments the latch rotation path into distinct positions with different engagement states: the third latch position (where third latch lever engages), the half-latched position, and the fully-latched position. By providing the third latch position as an intermediate stop with a dedicated blocking mechanism (third latch lever), the system prevents the latch from rotating freely to the open position when in an unsteady engagement state, thereby improving door closing stability while maintaining the ability to open when properly engaged.
Data Source
AI summary
A motor-vehicle door latch device includes: a main body; a latch that engages with a striker on a vehicle body side when a door is closed, and is capable of moving from an open position to a fully-latched position; a ratchet provided with a pawl that blocks the latch from rotating to an opening direction by respectively engaging with a half-latched engagement portion and a fully-latched engagement portion of the latch; and a third latch lever that engages with a third engagement portion provided on the latch when the latch is in a third latch position between a half-latched position and the open position of the latch so that the third latch lever is capable of blocking the latch from rotating in the opening direction from the third latch position.