Electrohydraulic Valve Calibration via Differential Pressure Sensing
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Solution Overview
Problem
Existing electrohydraulic valve calibration methods lack stability and repeatability, especially for systems with electronically controlled displacement pumps, due to sensitivity to manufacturing variations, machining tolerances, and environmental factors, making it difficult to accurately determine the cracking point and cracking current.
Innovation Solution
A calibration method that involves opening and stalling the electrohydraulic system, equalizing pressures, and incrementally increasing the valve control current to determine the calibration orifice size by monitoring downstream pressure, using a combination of coarse and finer calibration steps to achieve precise calibration, even for pumps with electronically controlled displacement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the valve start of flow point is determined by observing pump output pressure in a load sensing hydraulic pump system, then the cracking point can be identified, but this method cannot be used for pumps with electronically controlled displacement and lacks stability and repeatability
Solution Approach 1:
The patent introduces a differential pressure sensor as an intermediary measurement device that directly senses the pressure difference across the electrohydraulic valve. This mediator enables accurate cracking point detection without relying on pump type-specific behaviors, making the calibration method universally applicable to both load sensing and electronically controlled displacement pumps while maintaining high measurement precision
Solution Approach 2:
The patent replaces the indirect mechanical observation method (monitoring pump output pressure changes) with a direct electronic sensing approach (differential pressure sensor across the valve). This substitution eliminates the dependency on pump mechanical characteristics, enabling the calibration method to work with electronically controlled displacement pumps that do not exhibit the same pressure response behaviors as load sensing pumps
2Ease of manufacture
If the cracking point is determined using manufacturing tolerance-based methods, then calibration can be performed, but the results are sensitive to manufacturing variations, machining tolerances, and environmental factors reducing stability
Solution Approach 1:
The patent implements a feedback-based calibration method where the differential pressure sensor continuously monitors the actual pressure difference across the valve during calibration. The system adjusts the valve control current based on the measured pressure feedback, allowing the calibration to adapt to actual valve characteristics rather than relying on predetermined manufacturing tolerance ranges. This feedback mechanism ensures high reliability and repeatability by using real-time measurement data to determine the precise cracking point for each individual valve
Solution Approach 2:
The calibration method enables each valve to self-calibrate by using its own actual performance characteristics measured during the calibration process. The differential pressure sensor captures the valve's unique cracking behavior, and the system automatically determines the calibration parameters based on these self-measured data, eliminating dependency on generic manufacturing tolerance specifications and environmental assumptions
3Measurement precision
If the valve calibration accounts for manufacturing variations and environmental factors, then accuracy can be improved, but the calibration process becomes more complex
Solution Approach 1:
The patent extracts the pressure differential measurement function from the complex pump system behavior and isolates it to a dedicated differential pressure sensor positioned directly across the electrohydraulic valve. This extraction simplifies the calibration system by focusing measurement on the valve itself rather than the entire hydraulic system, reducing complexity while maintaining the ability to account for manufacturing variations and environmental factors through direct valve performance measurement
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 method provides a stable and repeatable calibration of the electrohydraulic valve, reducing the impact of manufacturing tolerances and environmental factors, and allows for accurate determination of the calibration orifice size, enhancing the precision of the valve control characteristic.
Implementation Method 1
the current that is driven to the valve control solenoid will either directly or indirectly displace the valve spool
Implementation Method 2
increasing pressure on the upstream side of the electrohydraulic valve to an increased pressure using the pump
Implementation Method 3
finding a calibration valve control current that provides a calibration orifice size through the electrohydraulic valve by monitoring pressure on the downstream side
Data Source
AI summary
A valve calibration system and method is disclosed for an electrohydraulic valve having upstream and downstream sides. A valve current controls the valve orifice size connecting the upstream and downstream sides. The calibration method includes opening the valve, stalling the system to prevent volume changes, and closing the valve with substantially equalized upstream and downstream pressures; then increasing upstream pressure, and finding a calibration current that provides a calibration orifice size through the valve by monitoring downstream pressure. Finding a calibration current can include stepping through valve control currents, sensing downstream pressures, and calculating step orifice sizes until the calculated step orifice size is greater than or equal to the calibration orifice size. Finding a calibration current can include performing a coarse calibration followed by a finer calibration. An offset can be calculated for a valve characteristic relating valve control current to valve orifice size.