Closed-Center Hydraulic Pump Control Using Virtual Negative Pressure
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Solution Overview
Problem
Existing hydraulic control systems for construction machines with closed center type directional control valves do not effectively replicate a negative control system, leading to inconsistent actuator speeds with varying loads, as they lack a virtual negative control system.
Innovation Solution
A virtual bleed system is implemented using a controller to replicate the characteristics of an open center type negative control system by calculating a virtual bleed amount and adjusting the pump discharge pressure, allowing for accurate control of hydraulic actuators based on load conditions without actual bleeding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a directional control valve of closed center type is used without a virtual negative control system, then the hydraulic circuit structure is simplified, but the actuator speed consistency under varying loads deteriorates
Solution Approach 1:
The patent creates a virtual copy of the negative control system by calculating a virtual bleed amount based on operation amount and replicate negative control characteristics through software control of the variable throttle valve, eliminating the need for physical bleed lines while maintaining actuator speed consistency under varying loads
Solution Approach 2:
The patent replaces the mechanical negative control system (with physical bleed lines and restrictions) with an electronic control system that uses sensors, a controller, and variable throttle valves to achieve the same control effect, thereby simplifying the hydraulic circuit structure while maintaining reliability
2Reliability
If a virtual bleed system is implemented to replicate negative control characteristics, then actuator speed consistency under varying loads is improved, but control system complexity increases
Solution Approach 1:
The variable throttle valve serves multiple functions: it controls the bypass flow rate to maintain pressure equalization and simultaneously replicates the negative control characteristics when combined with the virtual bleed amount calculation, reducing the need for separate dedicated components
Solution Approach 2:
The controller acts as an intermediary that processes operation amount signals, calculates virtual bleed amounts, and controls the variable throttle valve positioning, thereby coordinating the complex interactions between different system components without requiring direct mechanical connections
3Loss of energy
If bleed lines and negative control restrictions are eliminated, then energy loss is reduced and costs are decreased, but the ability to maintain negative control characteristics is lost
Solution Approach 1:
The patent calculates a virtual bleed amount that replicates the flow characteristics of a physical bleed line, allowing the system to maintain negative control characteristics through software control without the energy losses associated with physical bleed lines
Solution Approach 2:
The patent dynamically adjusts the variable throttle valve opening based on the calculated virtual bleed amount and operation amount, changing the flow rate parameter to maintain pressure equalization and negative control characteristics without the energy waste of continuous bleeding
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 enhances energy conservation, reduces costs by eliminating the need for bleed lines, and allows for precise control of hydraulic actuators, improving the consistency of actuator speeds with varying loads.
Implementation Method 1
a hydraulic actuator (200) is connected to the hydraulic pump (11) via a directional control valve (20)
Implementation Method 2
A variable throttle valve and a pressure adjusting valve are disposed in a bypass line branched from a pump supply line for controlling an outlet pressure of the variable throttle valve
Implementation Method 3
pressure adjusting valves control outlet pressures of variable throttle portions of directional control valves of closed center type to be kept substantially equal to a maximum load pressure detected by a detecting line
Data Source
Figure 1
Figure 2
Figure 3(A)~3(C)
AI summary
The present invention is hydraulic control apparatus that controls a hydraulic pump in a construction machine in which a hydraulic actuator is connected to the hydraulic pump via a directional control valve of a closed center type, and in which a position of the directional control valve is changed according to an operation amount of an operation member, the hydraulic control apparatus comprising a virtual negative control pressure calculating part configured to calculate, based on the operation amount of the operation member and a discharge pressure of the hydraulic pump, a virtual negative control pressure when a negative control system is assumed; and a part configured to calculate a control command value for the hydraulic pump based on the virtual negative control pressure.