Rear Caster Steering Assist via Hydraulic Turn Bias
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Solution Overview
Problem
The existing steering arrangements for work machines with rear caster wheels face challenges in control due to high turn resistance, leading to slow reaction times and difficulty in maneuverability, especially at higher speeds, due to friction and inertia, which is exacerbated by low tire inflation pressures and the absence of the cutting platform.
Innovation Solution
A turn assist arrangement is introduced, featuring a steering assembly with an output gear, a steering assist valve, and a transfer gear that biases the caster wheel assembly during turns, allowing for improved control by selectively operating turn assist cylinders and reducing turn resistance through a hydraulic steering circuit with a proportional valve that adjusts fluid flow based on speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If low tire inflation pressures are used to improve ride quality, then ride quality is improved, but turn resistance increases
Solution Approach 1:
A hydraulic turn assist system acts as an intermediary mechanism between the operator's steering input and the caster wheels. The system uses hydraulic pressure to generate assistive force that counteracts the increased turn resistance caused by low tire inflation pressures, allowing the caster wheels to turn more easily without compromising ride quality.
2Ease of operation
If the cutting platform is removed to improve maneuverability, then maneuverability is improved, but turn resistance increases due to reduced weight on casters
Solution Approach 1:
The hydraulic turn assist system serves as a mediator that compensates for the reduced weight on caster wheels when the cutting platform is removed. By providing hydraulic assist force, the system maintains adequate turning capability despite the lower normal force on the casters, which would otherwise reduce friction and make steering uncontrollable.
3Force
If hydraulic pressure is increased to overcome turn resistance, then turn resistance is overcome, but reaction time increases due to inertia
Solution Approach 1:
The hydraulic turn assist system performs preliminary action by pre-charging the hydraulic circuit and maintaining pressure readiness. When steering input is detected, the system immediately directs hydraulic flow to assist cylinders, providing instant assistive force that overcomes caster turn resistance without delay, thus reducing the machine's reaction time to steering commands.
4Force
If steering assist is added to reduce turn resistance, then turn resistance is reduced, but device complexity increases
Solution Approach 1:
The steering assist valve is designed to perform multiple functions: it controls hydraulic flow to turn assist cylinders for reducing caster turn resistance, and simultaneously integrates with the existing hydrostatic steering circuitry. This multi-functionality allows the system to reduce turn resistance without proportionally increasing complexity, as the valve leverages existing hydraulic infrastructure.
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 solution enhances the controllability of work machines by reducing turn resistance and improving reaction times, enabling better agility at higher speeds while maintaining maneuverability at lower speeds without sacrificing existing system performance.
Implementation Method 1
hydraulic pressure builds in one drive wheel circuit to increase speed and is reduced in the other drive wheel circuit to lower the speed
Implementation Method 2
Turn resistance of the caster wheels results from friction in the pivot of the caster assembly and friction between the castered wheels and the ground
Implementation Method 3
The transfer gear directly interconnects the output gear with the input gear. The transfer gear includes a first set of peripheral teeth enmeshed with the output gear and a second set of peripheral teeth enmeshed with the input gear
Data Source
AI summary
A steering arrangement for a work machine includes a frame, at least one caster wheel assembly carried by the frame, at least one turn assist cylinder, and a turn assist arrangement. Each turn assist cylinder is coupled between the frame and a corresponding caster wheel assembly. The turn assist arrangement includes a steering assembly, a steering assist valve and a transfer gear. The steering assembly includes an output gear which is positionable dependent upon an operator commanded degree of turn. The output gear has exterior teeth. The steering assist valve is configured to selectively operate at least one turn assist cylinder and thereby bias a corresponding caster wheel assembly during an operator commanded turn. The steering assist valve includes an input gear with exterior teeth. The transfer gear includes a first set of peripheral teeth enmeshed with the output gear and a second set of peripheral teeth enmeshed with the input gear. The transfer gear pivots about a common pivot point. The first set of peripheral teeth and the second set of peripheral teeth are each at a common radius from the common pivot point on opposite sides of the transfer gear.