Hydraulic Closed-Circuit Control for Stable Cylinder Retraction
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Solution Overview
Problem
In construction machines with hydraulic closed circuits, the contraction action of single rod hydraulic cylinders is not stabilized due to excessive back pressure in the cap chamber when the rod assist action is initiated, leading to potential instability in cylinder contraction.
Innovation Solution
A construction machine with a bidirectionally tiltable variable displacement pump, a unidirectionally tiltable variable displacement pump, a flushing valve, pressure sensors, and a controller that manages the pumps and valves to control the rod assist action based on pressure differentials, disabling the rod assist when the differential pressure is below a threshold to prevent excessive cap pressure increase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If rod assist action is started early to speed up cylinder contraction, then contraction speed is improved, but cap chamber pressure increases excessively causing instability
Solution Approach 1:
The controller determines whether to enable rod assist action in advance by evaluating the differential pressure between rod chamber and cap chamber before actually enabling the action. This preliminary assessment prevents excessive cap chamber pressure increase by only enabling rod assist when differential pressure exceeds the flushing valve setting pressure, thus maintaining contraction stability while allowing speed improvement when conditions are favorable.
Solution Approach 2:
The system continuously monitors the differential pressure between rod chamber and cap chamber and uses this feedback to control the rod assist selector valve. When differential pressure exceeds the flushing valve setting pressure, the rod assist is enabled; otherwise it remains disabled. This feedback mechanism dynamically adjusts the rod assist action based on real-time pressure conditions, resolving the contradiction between contraction speed and stability.
2Stability of the object's composition
If rod assist action is disabled to prevent excessive cap pressure, then pressure stability is improved, but cylinder contraction speed decreases
Solution Approach 1:
The rod assist selector valve dynamically switches between enabled and disabled states based on real-time differential pressure conditions. The system transitions from a static rod assist configuration to a dynamic one where the rod assist action is automatically adjusted according to pressure differential thresholds, allowing the system to optimize both pressure stability and contraction speed under different operating conditions.
Solution Approach 2:
The system changes the operational parameter of rod assist action (enabled/disabled state) based on the differential pressure parameter. By monitoring differential pressure and switching the rod assist state accordingly, the system adapts to varying pressure conditions, maintaining cap chamber pressure stability while enabling speed enhancement when pressure conditions permit.
3Loss of energy
If flushing valve is used to return surplus fluid, then energy efficiency is improved, but rod assist timing becomes critical for stable operation
Solution Approach 1:
The flushing valve automatically activates when differential pressure exceeds its setting pressure, eliminating the need for complex timing control of rod assist action. The system self-regulates by using the pressure differential itself to trigger the flushing mechanism, thereby reducing energy loss while simplifying operational control. The rod assist timing becomes less critical because the flushing valve provides automatic pressure management.
Solution Approach 2:
The flushing valve acts as an intermediary between the cap chamber and rod chamber, automatically managing surplus fluid return when pressure differential conditions are met. This intermediary mechanism decouples the direct relationship between rod assist timing and pressure stability, allowing energy-efficient operation while reducing the criticality of precise rod assist timing control.
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 allows for stable contraction action of the single rod hydraulic cylinder by preventing excessive cap pressure increase and ensuring efficient fluid flow, thereby stabilizing the cylinder's contraction speed.
Implementation Method 1
a hydraulic closed circuit in which a hydraulic actuator is driven directly by a hydraulic pump
Implementation Method 2
the hydraulic pump delivers only a flow rate required by the hydraulic actuator
Implementation Method 3
a cap pressure sensor that detects a pressure of the cap chamber; a rod pressure sensor that detects a pressure of the rod chamber
Data Source
Figure 1
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Figure 3
AI summary
A construction machine is provided which includes a hydraulic closed circuit in which a single rod hydraulic cylinder is driven directly by a bidirectionally tiltable variable displacement pump and can stably speed up the contraction action of the single rod hydraulic cylinder. In the case where a contraction action of a hydraulic cylinder 10 is instructed through an operation lever 30, when a differential pressure obtained by subtracting the pressure of a cap chamber 10a from the pressure of a rod chamber 10b is equal to or lower than a first threshold value α set to a level equal to or higher than a selection setting pressure of a flushing valve 14, a controller 20 closes a rod side selector valve 12b to disable rod assist action for supplying hydraulic fluid from a second hydraulic pump 8 to the rod chamber, and when the differential pressure is higher than the first threshold value, the controller 20 opens the rod side selector valve to enable the rod assist action.