Closed-Center Hydraulic Pump Control Without Unloading Energy Loss
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Solution Overview
Problem
Existing hydraulic control systems using directional control valves of a closed center type fail to maintain an appropriate discharge flow rate of a hydraulic pump when replicating a virtual negative control system, leading to energy wastage due to low discharge pressure during unloading.
Innovation Solution
A hydraulic control apparatus and method that replicates the negative control system by calculating a virtual bleed amount and adjusting the discharge flow rate of the hydraulic pump based on a virtual negative control pressure, eliminating the need for actual bleed openings and reducing energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an unloading valve is provided to discharge excess flow rate from the hydraulic pump to the tank when the directional control valve is closed, then the pump can be controlled to maintain appropriate pressure, but the discharge pressure becomes close to 0 due to little restriction, causing energy waste
Solution Approach 1:
The patent creates a virtual copy of the negative control system by calculating a virtual bleed amount based on operation amount rather than using physical bleed openings. This virtual model replicates the pressure-flow characteristics needed for negative control without requiring actual restrictive paths that would cause energy loss during unloading.
Solution Approach 2:
The patent replaces the mechanical bleed control system with an electronic calculation and control system. Instead of using physical bleed valves and restrictive passages that create pressure drops and energy waste, the system uses a controller to calculate virtual bleed amounts and control the pump accordingly, substituting mechanical restriction with electronic computation.
2Power
If a virtual bleed opening is set in the control valve with area changed according to operation amount, then pump discharge pressure can be controlled, but a virtual negative control system is not replicated because negative control restriction is not assumed
Solution Approach 1:
The patent changes the parameter representation from physical opening area to calculated virtual bleed amount. By computing the virtual bleed amount as a function of operation amount and assuming a negative control restriction characteristic, the system replicates the negative control behavior through parameter transformation rather than physical geometry changes.
Solution Approach 2:
The patent introduces a controller as an intermediary that calculates the virtual bleed amount based on operation amount and pump discharge pressure. This intermediary computation layer mediates between the operator's input and the pump control, enabling negative control system replication without direct mechanical connection to traditional bleed mechanisms.
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 maintains an appropriate discharge flow rate of the hydraulic pump while reducing energy wastage and eliminating the need for costly bleed lines, enhancing energy conservation and system efficiency.
Implementation Method 1
a hydraulic actuator (11) is connected to the hydraulic pump (1) via a directional control valve (20)
Implementation Method 2
an unloading valve (18), which is connected to a tank (T), is provided between the directional control valve (20) and the hydraulic pump (1)
Data Source
Figure 1
Figure 2
Figure 3~3(C)
AI summary
The present invention is a 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 an unloading valve, which is connected to a tank, is provided between the directional control valve and the hydraulic pump, the hydraulic control apparatus comprising: an unloading valve controlling part; an command value calculating part configured to operate under the situation where the directional control valve is in such a state that the fluid path to the hydraulic actuator is opened, wherein the command value calculating part calculates, based on an operation amount of an operation member for changing a position of the directional control valve and a discharge pressure of the hydraulic pump, a virtual negative control pressure when a negative control system is assumed, and calculates a control command value for the hydraulic pump based on the virtual negative control pressure; and a correcting part configured to operate under the situation where the directional control valve is in such a state that the fluid path to the hydraulic actuator is closed, wherein the correcting part corrects the control command value or a parameter, which is used in calculating the control command value, such that a discharge flow rate of the hydraulic pump is a predetermined flow rate.