Hydraulic Pump and Valve Control for Low-Loss Combined Operation
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Solution Overview
Problem
Conventional hydraulic systems in construction machines face inefficiencies due to meter-in loss and unstable pressure control, leading to energy wastage and operator discomfort from sudden flow rate changes, especially when transitioning between combined and single operations.
Innovation Solution
A hydraulic drive system with a variable displacement pump, directional control valves, and an unloading valve controlled by a sophisticated controller that computes and adjusts flow rates and pressures to minimize meter-in loss and stabilize flow dividing control, even at low differential pressures, thereby preventing energy wastage and operator shocks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the meter-in opening area of the directional control valve is increased to reduce meter-in loss, then energy efficiency is improved, but the differential pressure becomes zero causing unstable pressure control and hunting
Solution Approach 1:
A differential pressure generating valve is introduced as an intermediary component between the hydraulic pump and the directional control valve. This valve artificially generates the necessary differential pressure by creating a controlled pressure drop, allowing the meter-in opening to remain large for energy efficiency while maintaining stable pressure control through the mediator's pressure regulation function.
2Loss of energy
If the differential pressure is reduced to improve energy efficiency, then meter-in loss decreases, but flow dividing control becomes unstable
Solution Approach 1:
The system employs feedback control where a differential pressure detecting valve monitors the actual differential pressure and feeds this information back to the differential pressure generating valve. This feedback mechanism ensures that the differential pressure is maintained at the optimal level for both energy efficiency and stable flow dividing control, automatically adjusting to maintain reliability.
3Loss of energy
If the meter-in opening is enlarged to reduce pressure loss, then energy efficiency improves, but the system can no longer maintain the required differential pressure for control
Solution Approach 1:
The pressure control function is segmented from the flow control function. The differential pressure generating valve handles pressure control by creating a controlled pressure drop, while the directional control valve focuses on flow direction and distribution with its enlarged meter-in opening. This segmentation allows each component to optimize its function without compromise.
4Loss of energy
If the throttle orifice is fully opened to eliminate meter-in loss, then energy efficiency increases, but sudden flow rate changes cause operator discomfort
Solution Approach 1:
The differential pressure generating valve performs preliminary anti-action by maintaining a controlled differential pressure that prevents sudden flow rate changes. This pre-established pressure differential acts as a buffer that smooths out flow transitions, counteracting the potential for sudden changes before they can affect the actuator and cause operator discomfort.
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 stable flow dividing control and high energy efficiency by setting the unloading valve pressure based on meter-in pressure loss, allowing for large meter-in openings and reducing energy wastage and operator discomfort during flow rate changes.
Implementation Method 1
an unloading valve that discharges the hydraulic fluid in a hydraulic fluid supply line of the hydraulic pump to a tank when a pressure in the hydraulic fluid supply line of the hydraulic pump exceeds a set pressure determined by adding at least a target differential pressure to a highest load pressure of the plurality of actuators
Implementation Method 2
a hydraulic drive system comprising: a variable displacement hydraulic pump; a plurality of actuators driven by a hydraulic fluid delivered from the hydraulic pump
Data Source
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AI summary
Flow control over a hydraulic pump and flow dividing control of a plurality of directional control valves associated with actuators can stably be exercised even in a case in which differential pressures across the directional control valves are quite low, an abrupt change in a flow rate of the hydraulic fluid supplied to each actuator is prevented and excellent combined operability is realized even in an abrupt change in a demanded flow rate at a time of transition from a combined operation to a sole operation, and realizing excellent combined operability, and a meter-in loss in each directional control valve is reduced to realize high energy efficiency. Demanded flow rates of the directional control valves are calculated from input amounts of operation levers, openings of flow control valves are controlled using the demanded flow rates, a meter-in pressure loss of a predetermined directional control valve is calculated from the demanded flow rates and meter-in opening areas of the directional control valves, and a set pressure of an unloading valve is controlled using a value of the meter-in pressure loss.