Piloted Spool Valve Control for Stable Forestry Head Positioning
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Solution Overview
Problem
Existing hydraulic proportional valve systems for work vehicles, such as feller bunchers, experience unstable responses due to dynamic and variable loads, leading to oscillations and inefficient control of spool position and output, particularly during forestry operations.
Innovation Solution
The implementation of a method using a piloted spool valve with two proportional pilot valves, where a command control signal and a reaction control signal are applied concurrently to the first and second proportional pilot valves, respectively, to stabilize and precisely control the spool movement, independent of system temperatures and loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional hydraulic proportional valve system is used, then the system structure is simple, but the spool position control is unstable and oscillates under dynamic loads
Solution Approach 1:
The control valve is divided into a main spool valve and separate pilot valves. The pilot valves are further segmented into multiple independent pilot valves, each controlled by separate command signals. This segmentation allows independent control of different aspects of the spool movement, improving stability while maintaining manageable system complexity.
Solution Approach 2:
Reaction control signals are generated based on the spool position and applied to the pilot valves. This feedback mechanism counteracts oscillations and stabilizes the spool position by continuously adjusting the control signals in response to the actual system state, resolving the stability issue without requiring complete system redesign.
2Speed
If conventional proportional valve control is used, then the control system is simple, but the response speed is slow and oscillations occur under variable loads
Solution Approach 1:
Command control signals are generated in advance based on the desired spool position and applied to the pilot valves before the main spool moves. This preliminary action allows the system to anticipate and prepare for position changes, improving response speed while the modular pilot valve structure keeps the added complexity manageable.
Solution Approach 2:
The control system uses dynamic command signals that are continuously adjusted based on real-time spool position and load conditions. The reaction control signals dynamically respond to changing loads, enabling fast and stable response without requiring an overly complex fixed-structure system.
3Measurement precision
If conventional valve control is used, then the system is easy to operate, but the control precision is insufficient under dynamic conditions
Solution Approach 1:
Different pilot valves are assigned different local control functions with specific command signals tailored to their roles. This local quality approach allows precise control of specific spool position aspects while keeping each pilot valve's control logic relatively simple, balancing precision with ease of operation.
Solution Approach 2:
The control system adjusts command signal parameters (amplitude, frequency, phase) based on spool position and load conditions to optimize control precision. These parameter changes are implemented through the pilot valves, achieving high precision without requiring a completely complex control architecture.
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 approach provides faster and more stable control of the spool position and output, resulting in smoother and more accurate operation of the work machine, improving timber harvesting efficiency by reducing oscillations and enhancing control dynamics.
Implementation Method 1
a first and a second proportional pilot valve operatively connected to the spool valve... applying the command control signal to the first proportional pilot valve to actuate the first proportional pilot valve to move the spool... applying the reaction control signal to the second proportional pilot valve to actuate the second proportional pilot valve to move the spool
Data Source
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AI summary
A work machine to cut timber including a control system, a felling head (118), a hydraulic motor (201) configured to adjust the position of the felling head, and a spool valve (216) operatively connected to the hydraulic motor, the spool valve being configured to move the felling head responsively through operation of the hydraulic motor. A machine controller (202) coupled to the operator controller and the spool valve executes stored program instructions to generate a first control signal responsive to an operator control signal provided by the operator controller, generate a second control signal as a function of the generated first control signal, adjust a position of the spool of the spool valve in response to a concurrent receipt of the first control signal and the second control signal by the first proportional control valve (228) and the second proportional control (230) valve to move the felling head through operation of the hydraulic motor.