Axial Piston Pump Speed Control Without Mechanical Feedback
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Solution Overview
Problem
Existing hydrostatic axial piston pumps for mobile work machines face challenges in achieving precise speed control with varying loads due to load sensitivity and high parameterization efforts, leading to reduced accuracy and increased costs, especially when using electrically directly controlled or speed-dependent adjustment units.
Innovation Solution
A hydrostatic axial piston pump with an adjustable stroke volume and a learning and adaptation device that refines a model of the current as a function of the requested speed, allowing for precise speed control without the need for mechanical feedback or additional sensors, thereby reducing the complexity of commissioning and enhancing system robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If electrically directly controlled (ET) adjustment units are used for axial piston pumps, then control flexibility is improved, but speed control precision deteriorates under varying loads due to load sensitivity
Solution Approach 1:
The patent implements a feedback mechanism where the actual speed of the hydraulic drive is measured and fed back to the control unit. The control unit compares the actual speed with the requested speed and adjusts the actuating pressure accordingly to compensate for load variations. This closed-loop feedback system resolves the load sensitivity issue of ET-controlled pumps while maintaining control flexibility.
2Measurement precision
If mechanical feedback systems (EP-controlled pumps) are used for speed control, then speed control precision is improved, but system complexity and costs increase due to additional sensors and mechanical feedback components
Solution Approach 1:
The patent replaces complex mechanical feedback systems with an electronically controlled actuating pressure generation system. Instead of using mechanical linkages and sensors to provide feedback, the system uses electronic control units that calculate the required actuating pressure based on requested speed and actual operating conditions. This substitution maintains speed control precision while significantly reducing mechanical complexity.
Solution Approach 2:
The patent introduces an electronic control unit as an intermediary between the speed request input and the actuating pressure generation. This intermediary processes the speed request, determines the appropriate actuating pressure based on stored characteristic curves and actual operating conditions, and controls the pressure control valve accordingly. This intermediary approach simplifies the overall system architecture while maintaining precise control.
3Measurement precision
If feedforward control systems are added to ET-controlled pumps to compensate for disturbances, then speed control accuracy is improved, but parameterization effort and commissioning complexity increase
Solution Approach 1:
The patent performs preliminary characterization of the hydraulic system by storing characteristic curves in the control unit during the commissioning phase. These characteristic curves represent the relationship between actuating pressure, pump displacement, and operating conditions. By pre-storing this information, the system can quickly determine appropriate control parameters during operation without requiring complex real-time calculations or extensive parameterization during commissioning.
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 solution enables robust speed control with varying loads, reducing the need for complex feedback systems and sensors, resulting in high precision, improved driving dynamics, and lower commissioning efforts while maintaining system robustness and accuracy.
Implementation Method 1
a first actuating pressure can be set via a first pressure-reducing valve, on which a first actuating pressure depends on a first current at a first electromagnet of the first pressure-reducing valve
Implementation Method 2
a learning and/or adaptation device, by means of which the model, in particular at least one parameter or characteristic map of the model, can be adapted as a function of the first current and an actual speed, which can be assigned or associated with it
Data Source
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AI summary
A hydrostatic axial piston pump with adjustable displacement for fluidic connection to a hydraulic motor of a hydrostatic drive system in a hydraulic circuit is disclosed. An adjusting unit is provided for adjusting the displacement volume. This unit has an actuating cylinder with a first actuating pressure chamber in which a first actuating pressure can be set via a first pressure reducing valve. This first actuating pressure depends on a first current at a first electromagnet of the first pressure reducing valve. An electronic control device is provided in which a model of the first current is stored as a function of a requested speed. A hydrostatic drive system with the axial piston pump is also disclosed, as well as a method for controlling the axial piston pump and/or the drive system.