Grapple Force Limiting Device Protects Prime Mover Arms
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Solution Overview
Problem
Grapple assemblies can transmit excessive hydraulic force to prime mover arms, potentially damaging them when closing around dense loads or solid surfaces, as the arms and associated hydraulics are not designed to handle the necessary force levels.
Innovation Solution
A grapple assembly with a force limiting device, comprising a piston assembly and self-contained fluid circuit, that includes a pressure relief valve to limit the force transferred to the prime mover arms by allowing fluid flow when pressure reaches a predetermined maximum, thereby preventing damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If hydraulic force is increased to close the tines around dense loads, then the grasping force is improved, but the compression force transmitted to the prime mover's arm increases to damaging levels
Solution Approach 1:
A force limiting device is introduced as an intermediary between the hydraulic system and the grapple assembly. This device includes a piston assembly that can rotate between operational and tripped positions, acting as a mediator that allows force transmission during normal operation but limits force when thresholds are exceeded, protecting the prime mover's arm from damaging compression forces.
Solution Approach 2:
The force limiting device changes the operational parameter of force transmission by rotating the piston assembly from an operational position (allowing force transmission) to a tripped position (limiting force transmission) when the closing force reaches a predetermined level. This parameter change enables the system to adaptively control the force transmitted to the arm based on load conditions.
2Force
If the prime mover's arms are designed to handle higher hydraulic forces, then the grasping capability is improved, but the device complexity and cost increase
Solution Approach 1:
Rather than redesigning the prime mover's arms to handle higher forces, a force limiting device is introduced as an intermediary component on the grapple assembly. This approach protects the existing arm structure from excessive forces while maintaining the ability to generate high grasping forces, avoiding the complexity and cost of redesigning the arm structure.
3Device complexity
If mechanical grapples are used without independent hydraulics, then the device complexity is reduced, but the control precision and reliability decrease
Solution Approach 1:
The force limiting device operates autonomously using the existing hydraulic system's pressure. When excessive force is detected, the high pressure automatically causes the piston assembly to rotate to the tripped position, limiting the force without requiring external control signals or additional independent hydraulic systems. This self-service mechanism maintains reliability while keeping the system simple.
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
The force limiting device effectively reduces the pressure on the prime mover arms by allowing the first tine to rotate away from the second tine when excessive force is applied, protecting the arms from damage and maintaining the grip on loads.
Implementation Method 1
The fluid circuit is configured to selectively allow a fluid to flow in a first direction through a relief valve for moving the force limiting device to a tripped position
Implementation Method 2
The fluid circuit is configured to selectively allow a fluid to flow in a second direction through a check valve for returning the force limiting device to an operational position
Implementation Method 3
The force limiting device is biased in the operational position
Data Source
AI summary
A grapple assembly configured to be combined with a prime mover vehicle. The grapple assembly has a first tine configured to rotate relative to a second tine. The first tine is held in a first position by a force limiting device during normal operation. This force limiting device is movable between an operational position and a tripped position, and is biased in the operational position. The force limiting device has a pressure relief valve which opens to allow fluid to flow in a first direction when fluid pressure on the relief valve reaches a predetermined amount. The force limiting device is combined with the first tine so movement of the force limiting device from the operational position to the tripped position causes the first tine to rotate relative from the second tine thereby relieving forces generated by the prime mover's hydraulic system.