Hydraulic Drive System Variable Restrictor Valve Flow Control
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Solution Overview
Problem
In hydraulic drive systems for construction machines, the flow rate supplied to travel hydraulic motors is affected by variations in traveling load and changes in pump delivery pressure during fine operations, leading to unfavorable operability when the travel control lever is operated in a range less than half stroke.
Innovation Solution
A hydraulic drive system with a variable displacement main pump, flow control valves, pressure compensation valves, and a pump control unit that maintains a target differential pressure higher than the maximum load pressure, ensuring consistent flow rates and reduced energy loss, while allowing the opening area of the travel flow control valve to adjust according to the operating mode to minimize the impact of load and pressure variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the opening area of the travel flow control valve is increased to reduce energy loss and improve energy efficiency during traveling operation, then energy efficiency is improved, but the flow rate supplied to travel hydraulic motors becomes overly sensitive to variations in traveling load and changes in pump delivery pressure during fine operations
Solution Approach 1:
The patent applies dynamics by making the opening area of the travel flow control valve variable rather than fixed. The control system dynamically adjusts the opening area based on operating conditions: during high-speed traveling operation, a larger opening area is used to reduce energy loss, while during fine operations at low speeds, the opening area is reduced to improve flow rate stability and operability. This dynamic adjustment resolves the contradiction between energy efficiency and ease of operation.
Solution Approach 2:
The patent changes the parameter of the opening area of the travel flow control valve according to different operating modes. By varying this parameter based on whether the machine is in high-speed travel mode or fine operation mode, the system optimizes both energy efficiency and operability for different working conditions, resolving the technical contradiction between these two features.
2Loss of energy
If the target differential pressure of load sensing control is reduced during traveling operation to improve energy efficiency, then energy efficiency is improved, but the flow rate control precision deteriorates during fine operations
Solution Approach 1:
The system dynamically changes the target differential pressure parameter based on operating conditions. During high-speed traveling operation, a lower target differential pressure is applied to reduce energy loss. During fine operations, the target differential pressure is increased to improve flow rate control precision. This dynamic parameter adjustment resolves the contradiction between energy efficiency and control precision.
Solution Approach 2:
The patent applies parameter changes by adjusting the target differential pressure of load sensing control according to the operating mode. The control system switches between different target differential pressure values to optimize both energy efficiency during travel and flow rate control precision during fine operations, resolving the technical contradiction between these two requirements.
3Speed
If the opening area of the travel flow control valve is set large for high-speed travel, then travel speed is maintained, but the system becomes unstable during low-speed fine operations
Solution Approach 1:
The patent applies dynamics by making the opening area of the travel flow control valve adaptable to different speed requirements. During high-speed travel, a large opening area maintains travel speed, while during low-speed fine operations, the opening area is reduced to stabilize flow rate and improve operability. This dynamic adjustment resolves the contradiction between speed and stability.
Data Source
AI summary
An object of the invention is to achieve a travel speed known in the art during travelling operation, improve energy efficiency by reducing energy loss, and obtain favorable travel operability less susceptible to effects from variations in a travel load and changes in a pump delivery pressure when travelling operation is performed through operation of a travel lever over a half stroke range or less. A variable restrictor valve 80 is disposed in parallel with a flow sensing valve 50 of an engine speed sensing valve unit 13. A travel pilot pressure is adapted to act in an opening direction of the variable restrictor valve 80. The variable restrictor valve 80 is set to have a continuously increasing opening area from a full closure to a maximum with an increasing travel pilot pressure. Travel flow control valves 6d and 6e have an opening area that allows a predetermined flow rate QT required for traveling to be obtained even when a target LS differential pressure is decreased to a second specified value Pa3 when the travel lever is fully operated. In a first half of a spool stroke, the travel flow control valves 6d and 6e have an opening area approximate to an opening area of comparative example 1.