Night Latch Pushbar Assembly With Low-Torque Key Unlocking
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Solution Overview
Problem
Existing exit devices with a night latch function require excessive torque to actuate the latch control assembly, which may exceed regulatory requirements and user comfort limits.
Innovation Solution
A pushbar assembly with a slide plate and master cam configuration that limits the rotation of the master cam to a predetermined angular range, allowing the key to unlock the door without actuating the latch control assembly, and instead uses a handle for actuation, reducing the required torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the key is used to retract the latch in conventional exit devices, then the night latch function is achieved, but excessive torque is required to turn the key
Solution Approach 1:
The patent divides the key's rotational movement into two separate functional segments: (1) rotation of the master cam to drive the slide plate for unlocking, and (2) rotation of the latch control assembly for latch retraction. This segmentation allows the key to perform unlocking with minimal torque while the handle performs latch retraction with adequate torque, resolving the contradiction between ease of operation and regulatory compliance.
Solution Approach 2:
The master cam acts as an intermediary mechanism between the key and the locking system. The key rotates the master cam, which then drives the slide plate to unlock the door. This intermediary allows the key to unlock the door without directly actuating the latch control assembly, thereby reducing the torque required on the key while maintaining reliable latch control through the handle.
2Ease of operation
If the key directly actuates the latch control assembly, then the latch can be retracted, but the force required exceeds user comfort limits
Solution Approach 1:
The patent segments the latch retraction function from the key operation. Instead of the key directly actuating the latch control assembly, the system separates unlocking (key rotating master cam) from latch retraction (handle actuating latch control assembly). This segmentation reduces the force required on the key while maintaining adequate force for latch retraction through the handle, with the added complexity of the master cam and slide plate mechanisms.
3Ease of operation
If the master cam rotates through a full 360 degrees, then the mechanism has greater freedom of movement, but the unlocking function cannot be precisely controlled
Solution Approach 1:
The insert is pre-configured with cam surfaces that automatically guide the master cam through the precise angular range needed for unlocking (approximately 90-120 degrees). This preliminary configuration of the cam surfaces ensures that the master cam achieves the exact positioning needed for slide plate movement without requiring full 360-degree rotation, providing precise unlocking control while limiting unnecessary rotation through the inherent geometry of the cam and insert interaction.
Data Source
AI summary
An exemplary pushbar assembly generally includes a mounting assembly, a latch control assembly movably mounted to the mounting assembly, a pushbar operable to actuate the latch control assembly, a master cam rotatably mounted to the mounting assembly, a slide plate, and an insert. The slide plate is slidably mounted to the mounting assembly, and is configured to move between a locking position and an unlocking position in response to rotation of the master cam between a locking orientation and an unlocking orientation. The insert is configured to limit rotation of the master cam to a predetermined angular range less than 360°.