Open Loop Electrohydraulic Pressure Compensation
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Solution Overview
Problem
Existing hydraulic systems for equipment like backhoe-loaders face challenges in precisely controlling the flow of pressurized fluid to hydraulic actuators, particularly with variable displacement pumps, which can lead to undesirable velocity increases in actuators due to pressure variations, and lack affordable and versatile control solutions.
Innovation Solution
A hydraulic system that uses a microcomputer-based controller to derive and apply flow coefficients to control valves, incorporating a bypass valve and throttling valve to manage fluid flow based on operator commands, load values, and pressure values, ensuring precise control and pressure compensation without the need for additional pressure compensators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a variable displacement pump is used to provide fluid flow for hydraulic actuators, then the system efficiency is improved by matching pump output to demand, but the actuator velocity becomes unstable and exceeds commanded values due to pressure variations
Solution Approach 1:
The patent implements pressure feedback through load sense lines that continuously monitor supply pressure and actuator pressure. This feedback is used by the controller to dynamically adjust pump displacement and control valve positioning, compensating for pressure variations and maintaining stable actuator velocity despite the variable nature of the pump output
Solution Approach 2:
The system dynamically changes operating parameters including pump displacement, control valve flow coefficients, and bypass valve opening positions based on real-time pressure conditions. The controller adjusts these parameters to maintain consistent actuator flow rates even as supply pressure fluctuates with varying pump displacement
2Measurement precision
If electrical signal control of variable displacement pumps is implemented, then control precision is improved, but the system cost increases due to expensive specialized pumps
Solution Approach 1:
The patent introduces a microcomputer-based controller as an intermediary between the electrical command signals and the hydraulic pump. This controller processes electrical signals and generates appropriate control signals for the pump and control valves, enabling precise control of standard pumps without requiring expensive electrohydraulic pumps with built-in electronic control
Solution Approach 2:
The system replaces direct electrohydraulic pump control with a separate electronic control system that uses standard hydraulic components. The microcomputer controller substitutes for complex electrohydraulic pump mechanisms, allowing the use of conventional, more affordable pumps while maintaining high control precision through software-based control algorithms
3Stability of the object's composition
If pressure compensation valves are added to maintain constant flow, then actuator velocity stability is improved, but the device complexity increases
Solution Approach 1:
The patent makes the controller multi-functional by having it perform both pump displacement control and control valve positioning functions. The same microcomputer system that manages pump operation also calculates and commands control valve positions based on pressure feedback, eliminating the need for separate pressure compensation hardware and reducing overall system complexity
Solution Approach 2:
The system implements self-service pressure compensation where the controller automatically adjusts control valve positions and pump displacement in response to pressure variations without external intervention. The load sense lines provide automatic feedback that triggers controller responses, making the system self-regulating and reducing the need for additional passive compensation components
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
The system achieves precise control of hydraulic functions, maintaining consistent flow rates and preventing velocity excesses, while being cost-effective and adaptable to various machine sizes, thus enhancing operational efficiency and reducing the need for expensive, specialized pumps.
Implementation Method 1
a pump that draws fluid from a tank and provides the fluid under pressure to an outlet
Implementation Method 2
Each combination of an actuator and a control valve assembly is part of a hydraulic function
Implementation Method 3
The hydraulic actuators 16-19, 28 and 29 are cylinder-piston assemblies
Data Source
AI summary
A hydraulic system has a pump that furnishes pressurized fluid to a supply node connected to a plurality of functions. Each function includes hydraulic actuator and a control valve assembly through which fluid flows both from the supply node to the hydraulic actuator and from the hydraulic actuator to a return line. A control method involves receiving a plurality of commands, each designating desired operation of a function. Each command is separately used to derive a flow value designating an amount of flow for the respective function, a load value indicating a load magnitude related to the respective function, and a pressure value denoting a supply pressure for the respective function. Then, the control valve assembly for each given hydraulic function is operated in response to the flow and load values for that function and in response to the pressure value that is greatest among the plurality of functions.