Construction Machine Hydraulics for Stable Flow Dividing Control
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Solution Overview
Problem
Conventional hydraulic drive systems in construction machines face inefficiencies due to unstable pressure control and bleed-off losses, leading to reduced energy efficiency and operator discomfort from sudden changes in actuator speed during operation transitions.
Innovation Solution
A hydraulic drive system with a variable displacement pump, directional control valves, flow control valves, and an unloading valve, where a controller computes and adjusts flow rates and differential pressures to maintain stable flow dividing control and minimize bleed-off losses, allowing for large meter-in openings and precise pressure control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the meter-in opening area of the main spool is increased to reduce LS differential pressure, then energy efficiency is improved, but pressure control stability deteriorates due to hunting and instability in pressure compensating valve control
Solution Approach 1:
The patent applies dynamics by making the target differential pressure variable rather than fixed. The control device dynamically adjusts the target differential pressure based on the operating state (single operation vs. combined operation) to optimize both energy efficiency and control stability. During single operation, a smaller target differential pressure reduces meter-in loss, while during combined operation, a larger target differential pressure maintains pressure control stability and prevents hunting.
Solution Approach 2:
The patent changes the parameter of target differential pressure according to different operating conditions. By switching between different target differential pressure values based on whether actuators are operating individually or simultaneously, the system achieves both reduced energy loss during single operation and maintained control stability during combined operation.
2Loss of energy
If the target differential pressure is set to a small value for energy efficiency, then meter-in loss is reduced, but the unloading valve activates prematurely causing bleed-off losses and actuator speed fluctuations
Solution Approach 1:
The system dynamically adjusts the target differential pressure based on the number of operating actuators. When only one actuator operates, a small target differential pressure is used to minimize meter-in loss. When multiple actuators operate simultaneously, the target differential pressure increases, preventing premature unloading valve activation and maintaining reliable actuator speed control.
Solution Approach 2:
The control device monitors the operating state of actuators and adjusts the target differential pressure accordingly. This feedback mechanism ensures that the system responds to changing load conditions, preventing unloading valve activation during combined operation while maintaining energy efficiency during single operation.
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 energy losses, and prevents sudden changes in actuator speed, enhancing operational efficiency and reducing operator shocks.
Implementation Method 1
a hydraulic drive system with a variable displacement pump, directional control valves, flow control valves, and an unloading valve, where a controller computes and adjusts flow rates and differential pressures
Implementation Method 2
supplies hydraulic fluids delivered from one or more hydraulic pumps to a plurality of, that is, two or more actuators through two or more control valves
Implementation Method 3
a variable displacement hydraulic pump
Implementation Method 4
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
Data Source
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.