Hydraulic Cylinder Fine Pull Control Under Contraction Load
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Solution Overview
Problem
The existing hydraulic drive systems for construction machines, such as hydraulic excavators, face challenges in achieving precise control of the flow rate and action speed of hydraulic cylinders during fine operations, especially when external loads are applied, leading to reduced operability and accuracy in tasks like fine control of the claw tip position or tilting angle.
Innovation Solution
A hydraulic drive system with a bidirectional, variable displacement hydraulic pump and a hydraulic cylinder configuration that includes a discharge flow path and valve, controlled by a controller to manage the flow rate of hydraulic working oil, allowing for precise control of the action speed during fine operations by diverting oil to a discharge path when an external load is applied.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the hydraulic pump operates at small tilting angles to achieve fine control of the work implement position, then the precision of position control is improved, but the leak amount from the hydraulic pump increases and control accuracy decreases
Solution Approach 1:
The hydraulic system is segmented into multiple independent flow paths: a main flow path through the hydraulic pump and a bypass flow path through the flow control valve. This segmentation allows the pump to operate at optimal angles while the bypass path provides precise flow control for fine operations, resolving the contradiction between pump efficiency and control precision.
Solution Approach 2:
The flow control valve acts as an intermediary element that mediates between the hydraulic pump and the hydraulic cylinder. It provides precise flow rate control for fine position adjustments without requiring the pump to operate at small tilting angles, thereby maintaining both pump reliability and position control accuracy.
2Ease of operation
If the control valve divides the hydraulic working oil flow to adjust the flow rate to the hydraulic cylinder, then the flow rate control is improved, but the system complexity increases
Solution Approach 1:
The system dynamically switches between two flow paths based on operational requirements: the main flow path for normal operations and the bypass flow path for fine control operations. This dynamic configuration allows simple flow rate adjustment through the flow control valve without permanently increasing system complexity.
3Use of energy by moving object
If the hydraulic cylinder returns oil to the hydraulic pump at extremely low speeds during fine control operations, then the energy efficiency is improved, but the flow rate control accuracy deteriorates due to increased pump leak amount
Solution Approach 1:
The bypass flow path extracts a portion of the hydraulic oil flow from the main circuit before it reaches the pump. This extracted flow is controlled independently through the flow control valve, allowing precise flow rate control for fine operations while the main circuit maintains optimal pump operation and energy efficiency.
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
This configuration enhances the operability and precision of hydraulic cylinder actions during fine operations by allowing for controlled flow rate adjustments, improving the ability to manage external loads and maintain desired action speeds, even at low flow rates.
Implementation Method 1
a hydraulic pump which is of bidirectional delivery type and bidirectional variable displacement type
Implementation Method 2
controls a flow rate of hydraulic working oil discharged from a first hydraulic working oil chamber of the hydraulic cylinder
Implementation Method 3
a discharge valve which is disposed in the discharge flow path, and controls a flow rate of hydraulic working oil discharged from a first hydraulic working oil chamber of the hydraulic cylinder to the discharge flow path
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A construction machine includes a bidirectionally tiltable type hydraulic pump 2, a hydraulic cylinder 1 having a cap chamber 1e and a rod chamber 1f, a first flow path 11 connecting the hydraulic pump 2 and the cap chamber 1e, a second flow path 12 connecting the hydraulic pump 2 and the rod chamber 1f, a discharge flow path 16 branched from the first flow path 11, a discharge valve 32 that is disposed in the discharge flow path 16 and controls a discharge rate of hydraulic working oil from the cap chamber 1e to the discharge flow path 16, an operation device 54 that instructs an action of the hydraulic cylinder 1, and a controller 56. The controller 56 controls the hydraulic pump 2 and the discharge valve 32 such that at least a part of hydraulic working oil discharged from the cap chamber 1e is discharged to the discharge flow path 16 when an operation amount of the operation device 54 lies within a fine operation region during a pulling action of the hydraulic cylinder 1 in a state that a load is applied in a contraction direction. Accordingly, operability improves during fine operation of the pulling action of the hydraulic cylinder in the state that the load is applied in the contraction direction.