Hydraulic Drive Control With Pump-Valve Split for Precise Positioning
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Solution Overview
Problem
Existing electrohydraulic axles face issues with insufficient stiffness, inaccurate positioning dynamics, and varying resonant frequency when using rotational speed as a manipulated variable, and they suffer from power losses, nonlinear characteristics, and varying resonant frequency when using a valve as a manipulated variable.
Innovation Solution
The proposed method connects an electrohydraulic axle to a tank via a pump of variable rotational speed and a proportional valve, utilizing a model-based control that swaps inputs and outputs in an inverse system model to set a setpoint value for the braking force on the piston, thereby achieving precise position control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If rotational speed of the pump is used as manipulated variable, then position control is achieved, but stiffness of the hydraulic drive is insufficient
Solution Approach 1:
The control system is segmented into two independent parts: a proportional valve for stiffness control and a variable displacement pump for energy-efficient power delivery. This segmentation allows each component to optimize its function without compromising the other.
Solution Approach 2:
A proportional valve is introduced as an intermediary component between the pump and hydraulic consumer. This valve acts as a mediator that maintains high stiffness by controlling fluid flow, while the pump operates independently to deliver power efficiently.
2Measurement precision
If rotational speed of the pump is used as manipulated variable, then position control is achieved, but positioning dynamics are inaccurate
Solution Approach 1:
The control functions are segmented: the proportional valve handles dynamic positioning responses while the variable displacement pump handles power delivery. This division allows accurate positioning dynamics through the valve while maintaining energy efficiency through the pump's variable displacement capability.
3Measurement precision
If valve position is used to change volumetric flow, then position control is achieved, but power losses occur due to pressure drop
Solution Approach 1:
The variable displacement pump dynamically adjusts its delivery volume based on actual system requirements rather than using fixed displacement with throttling. This dynamic adaptation eliminates the need for continuous pressure drops across the valve, significantly reducing power losses while maintaining position control accuracy.
4Measurement precision
If valve position is used to change volumetric flow, then position control is achieved, but resonant frequency varies
Solution Approach 1:
Instead of using the valve to control flow (which causes varying resonant frequency), the invention inverts the approach: the variable displacement pump directly controls delivery volume, and the valve is used only for stiffness maintenance. This inversion stabilizes the hydraulic system's resonant frequency while achieving accurate position control.
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 enhances the stiffness and energy efficiency of the hydraulic drive, allows for quick and accurate responses during operation, and enables dynamic control of the valve, significantly reducing response time and improving overall system controllability.
Implementation Method 1
a pump (which is operated as a rule by means of an electric motor or drive) and a hydraulic cylinder
Implementation Method 2
a valve for changing the volumetric flow of the hydraulic liquid into the cylinder or out of the cylinder
Data Source
AI summary
The disclosure relates to a method for operating a hydraulic drive which comprises a hydraulic consumer with a positionable piston in a cylinder which is connected to a tank at one connection via a pump of variable rotational speed and at another connection via a proportional valve, wherein a position of the piston is controlled using a model-based control in which a rotational speed of the pump is used as a manipulated variable and in which a position of the proportional valve is preset.