Hydraulic Flow Division Control With Reduced Meter-In Loss
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Solution Overview
Problem
Conventional hydraulic drive systems for construction machines face issues with energy efficiency due to meter-in loss and unstable pressure control, leading to unpleasant shocks and bleed-off losses, especially when transitioning between composite and single actions.
Innovation Solution
A hydraulic drive system with a variable displacement pump, directional control valves, and pressure compensating valves that adjust meter-in opening areas and flow rates based on operation lever inputs, calculating and controlling the set pressure of an unloading valve to minimize bleed-off losses and maintain high energy efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If load sensing control is used to control pump flow rate, then flow rate control is achieved, but meter-in loss increases due to LS differential pressure
Solution Approach 1:
The patent changes the control parameter from LS differential pressure to highest load pressure directly. The pressure compensating valve is controlled to make the downstream pressure equal to the highest load pressure, eliminating the need for LS differential pressure and thereby reducing meter-in loss while maintaining flow rate control capability.
2Loss of energy
If meter-in opening area is increased to reduce LS differential pressure, then energy efficiency improves, but pressure control stability deteriorates
Solution Approach 1:
The patent introduces feedback control where the pressure compensating valve continuously adjusts the meter-in opening area based on the difference between downstream pressure and highest load pressure. This feedback mechanism maintains pressure control stability while allowing the meter-in opening to remain large for reduced energy loss.
3Loss of energy
If unloading valve set pressure is set high to prevent bleed-off loss, then energy efficiency improves, but sudden flow rate changes cause actuator speed shocks
Solution Approach 1:
The patent makes the unloading valve set pressure dynamic by linking it to the highest load pressure through the pressure compensating valve. The set pressure adjusts automatically with load conditions, preventing both excessive bleed-off loss and sudden actuator speed changes, thereby resolving the contradiction between energy efficiency and stability.
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, reduces meter-in loss, and enhances energy efficiency by carefully controlling the unloading valve's set pressure, preventing sudden changes in actuator speed and minimizing bleed-off losses.
Implementation Method 1
a variable displacement hydraulic pump that delivers hydraulic fluid
Implementation Method 2
a plurality of pressure compensating valves arranged in downstream sides of the plurality of directional control valves for controlling pressures in downstream sides of meter-in openings of the plurality of directional control valves such that the pressures in downstream sides of meter-in openings of the plurality of directional control valves becomes equal to the highest load pressure
Implementation Method 3
an unloading valve that discharges the hydraulic fluid of a hydraulic fluid supply line of the hydraulic pump to a tank when a pressure of the hydraulic fluid supply line increases and exceeds a set pressure
Data Source
AI summary
Even where the differential pressure across a directional control valve associated with each actuator is very small, flow dividing control of the plurality of directional control valves can be performed stable, and even where a demanded flow rate suddenly changes at the time of transition from composite action to single action or the like, a sudden change of the flow rate of hydraulic fluid to be supplied to each actuator is prevented to implement superior combined operability. Further, the meter-in loss of the directional control valves can be reduced to implement a high energy efficiency. To this end, a plurality of pressure compensating valves 7a, 7b and 7c for controlling such that the pressure in the downstream side of the meter-in opening of a plurality of directional control valves 6a, 6b and 6c becomes equal to the highest load pressure are individually arranged in the downstream side of meter-in openings of the plurality of directional control valves 6a, 6b and 6c, and demanded flow rates for the directional control valves 6a, 6b and 6c are calculated from input amounts of operation levers. Besides, the meter-in pressure loss of a predetermined directional control valve is calculated from the demanded flow rates for and meter-in opening areas of the directional control valves 6a, 6b and 6c, and the set pressure of the unloading valve 15 is controlled using the value of the meter-in pressure loss.