Pressure-Reducing Valve Calibration via Hydraulic Pressure Change
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Solution Overview
Problem
Current methods for calibrating pressure reducing valves in hydrostatic travel drives are inefficient, particularly at low control currents and maximum operating points, leading to inaccurate model-based control and requiring extensive, time-consuming testing under full load conditions without direct sensor feedback.
Innovation Solution
A method involving a hydraulic machine with adjustable displacement volume, where the actuator is biased and subjected to constant control pressures to detect measurable changes in high pressure, allowing for precise determination of control limits without expensive sensors, by clamping the actuator between control pressures and varying the control current to identify limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional calibration methods are used to determine control limits, then the calibration can be performed without additional sensors, but the measurement precision is insufficient especially at low control currents and maximum operating points
Solution Approach 1:
The patent introduces a mediator variable (actuator position or displacement) that indirectly indicates the control limit state. Instead of directly measuring control pressure with sensors, the method uses the actuator's position as an intermediary indicator that changes when control limits are reached, enabling precise measurement without complex sensor systems.
Solution Approach 2:
The patent replaces the mechanical/electrical sensor-based measurement system with a hydraulic-mechanical indication system. The control limit detection is achieved through mechanical observation of actuator position changes or hydraulic observation of pressure changes in the actuator chamber, substituting complex electronic sensing with simpler mechanical-hydraulic indicators.
2Measurement precision
If the actuator is preloaded to center position, then the valve is ready for bidirectional control, but the start of control cannot be determined because displacement is zero at rest
Solution Approach 1:
The patent applies a preliminary offset force or pressure to the actuator before calibration begins. This preliminary action creates a known initial state where the actuator is slightly displaced from center position, enabling the detection of control start points. The offset is established before the actual measurement process, allowing accurate detection of when control begins.
Solution Approach 2:
The patent applies a preliminary counteracting force (preload) in the opposite direction to the expected control force. This preliminary anti-action creates a measurable resistance that must be overcome when control begins, providing a clear detection signal for the control start point while maintaining the valve's readiness for bidirectional operation.
3Measurement precision
If maximum operating point calibration is performed by pivoting the pump at rated power, then the upper control limit can be determined, but the process requires significant time and is difficult to perform
Solution Approach 1:
The patent uses partial action by applying only the necessary minimum force or pressure to reach the control limit state during calibration, rather than requiring full rated power operation. This allows the upper control limit to be determined with sufficient accuracy without needing to operate the pump at maximum capacity for extended periods, significantly reducing calibration time.
Solution Approach 2:
The patent prepares the system in advance by pre-positioning the actuator or pre-applying offset pressures before the actual calibration measurement. This preliminary preparation eliminates the need for time-consuming ramp-up to rated power conditions, allowing the calibration to be performed quickly and easily while maintaining measurement precision.
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
Enables accurate and efficient determination of control limits, improving the quality of direction changes in model-based control without the need for sensor systems, reducing calibration time and effort.
Implementation Method 1
The first pressure surface can be subjected to a first actuating pressure by the first pressure control valve – hereinafter referred to as the first valve – depending on the first actuating current acting on it.
Implementation Method 2
The second pressure surface can be subjected to a second actuating pressure by a second pressure control valve depending on a second actuating current acting on it.
Implementation Method 3
When the first valve is used in a drive system, the first actuating current corresponds, for example, to a driver's request in a first direction of travel. To determine the control limit of the first valve, the high pressure of the hydraulic machine or a correlating operating variable of the hydraulic machine is recorded.
Data Source
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AI summary
Disclosed is a method for determining at least one control limit of an electrically controllable first pressure-reducing valve depending on a first control current, to which end a driven hydraulic machine is provided, the displacement volume of which is adjustable by a centred actuator with mutually counteracting pressure faces, a first of which can be acted on by a first control pressure from the first pressure-reducing valve depending on the first control current, wherein the high pressure or an operating variable of the hydraulic machine correlating with said high pressure is detected. Also disclosed are a hydraulic machine comprising a pressure-reducing valve of this kind, and a hydrostatic drive comprising the hydraulic machine, and a hydraulic motor driveable thereby.