Zero-Turn Parking Brake Linkage With Cam-Resisted Lever Actuation
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Solution Overview
Problem
Existing zero-turn ride-on mowers face challenges in effectively engaging and disengaging parking brakes through mechanical linkages, particularly when transitioning between driving and braking positions.
Innovation Solution
The design incorporates a brake control linkage system that includes a bell crank, lever connection link, brake connection link, cam, and cam follower, which provides physical resistance to rotate the bell crank during position transitions, ensuring the parking brake is engaged only when manually urged to do so.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mechanical linkages are used to control parking brakes through drive control levers, then the parking brake can be automatically engaged when the lever is in neutral position, but the brake may be inadvertently engaged during normal operation due to lever movement
Solution Approach 1:
A cam mechanism is introduced as an intermediary between the drive control lever and the parking brake linkage. The cam profile is specifically designed to prevent brake engagement during normal lever operation while allowing engagement when the lever is deliberately placed in the outboard position. The cam follower rides along the cam surface, translating lever movement into controlled brake actuation only under specific conditions.
Solution Approach 2:
The cam profile incorporates distinct regions with different geometric properties: a first region that prevents brake engagement during normal operation, a second region that allows engagement when the lever is in the outboard position, and an intermediary region with raised characteristics that provides physical resistance. This local differentiation of cam surface properties enables selective brake engagement based on lever position.
2Ease of operation
If the control lever is made laterally tiltable to the outboard position for easier driver maneuvering, then driver access is improved, but the parking brake linkage may be inadvertently actuated
Solution Approach 1:
The cam profile is designed with localized geometric features that correspond to specific lever positions. The first region accommodates the outboard tilting position for driver access, while the second region and intermediary raised region ensure that brake engagement only occurs when the lever is deliberately positioned in the outboard braking position, not during casual tilting for maneuvering.
Solution Approach 2:
The cam mechanism serves as an intermediary that decouples the lateral tilting motion (used for driver access) from the brake actuation function. The cam follower translates the lever's lateral position into controlled brake engagement only when the lever reaches the specific outboard braking position, preventing inadvertent actuation during normal tilting operations.
3Reliability
If the cam profile includes an intermediary raised region, then physical resistance is provided during lever transition, but the mechanism complexity increases
Solution Approach 1:
The cam mechanism combines multiple functions into a single component: it guides the cam follower through the lever's range of motion, provides physical resistance through the raised intermediary region, and controls brake engagement/disengagement. This merging of functions into one cam profile avoids the need for separate sensors, switches, or complex control systems.
Solution Approach 2:
The raised intermediary region is a localized feature on the cam profile that provides physical resistance only during the transition between braking and driving positions. This localized complexity is confined to a specific region of the cam rather than requiring complex mechanisms throughout the entire linkage system.
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
This solution ensures safe and reliable engagement of the parking brake by requiring manual force to overcome the physical resistance, preventing inadvertent braking and enhancing operational safety.
Implementation Method 1
a cam provided on a first one of either the frame or the bell crank; and a cam follower provided on a second of either the frame or the bell crank at a location adjacent the cam and biased into engagement therewith; wherein a shape profile of the cam of each brake control linkage comprises a first recess... an intermediary region that is disposed between said first and second recesses and is of raised relation thereto within said shape profile so as to, via contact between the cam follower and said intermediary region, impart physical resistance to rotation of the bell crank
Data Source
AI summary
A ride-on zero-turn work machine has two drive control levers longitudinally pivotable for locomotive and steering control, and laterally tiltable inboard and outboard for parking brake control. Two brake control linkages are each connected between one of the levers and one of the parking brakes. Each linkage features a rotatable bell crank, a brake connection link running from the bell crank to the parking brake, and a lever connection link having one end coupled to the bell crank, and another coupled to drive control lever. The bell crank is a flat plate to which the links are coupled at a same common side, and whose outer perimeter includes a cam profile that is engaged by a cam follower to resist movement of the control lever between inboard and outboard positions. The perimeter edge of each bell crank also engages a position detection switch in one of the inboard and positions.