Hydraulic Closed Circuit Flow Balance via Pump Capacity Control
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Solution Overview
Problem
Conventional hydraulic closed circuit systems face difficulties in maintaining ideal flow rate balance during the extension/retraction of hydraulic cylinder devices due to pump capacity errors or leakage, leading to issues like cavitation and pressure build-up, which affect smooth operation.
Innovation Solution
A hydraulic closed circuit system employing multiple hydraulic pumps with a pump capacity control unit that automatically adjusts the flow rate by detecting operational states and pressures to maintain balance, thereby preventing cavitation and pressure imbalances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a low pressure selecting valve is used to eliminate flow rate imbalance, then the system can handle pressure differences, but hunting of the valve causes difficulty in achieving smooth operation
Solution Approach 1:
The patent removes the low pressure selecting valve from the system and replaces it with a charge circuit that directly connects the rod side of the hydraulic cylinder to the tank. This extraction of the problematic valve eliminates the hunting phenomenon while maintaining the ability to handle flow rate imbalances through the charge circuit's pressure equalization function.
Solution Approach 2:
The patent introduces a charge circuit as an intermediary mechanism between the rod side of the hydraulic cylinder and the tank. This charge circuit acts as a mediator that smoothly equalizes pressure differences without the need for a selecting valve, thereby eliminating hunting and ensuring smooth operation during extension and retraction cycles.
2Device complexity
If pump capacity is fixed based on difference in area between bottom side and rod side, then the system structure is simple, but pump capacity errors or leakage cause flow rate imbalance leading to cavitation or pressure build-up
Solution Approach 1:
The patent makes the pump capacity dynamic by introducing a pump capacity control unit that automatically adjusts the pump's displacement based on detected pressure differences and flow rate imbalances. This transforms the fixed pump capacity system into an adaptive system that maintains optimal flow balance despite wear, leakage, or operational variations, thereby improving reliability without significantly increasing structural complexity.
Solution Approach 2:
The patent implements a feedback mechanism where sensors detect pressure and flow rate conditions, and the pump capacity control unit uses this information to automatically adjust pump capacity. This closed-loop feedback system ensures continuous flow rate balance, preventing cavitation and pressure build-up while maintaining relatively simple system structure through automated control.
3Reliability
If automatic flow rate control is implemented to maintain balance, then flow rate balance is maintained, but the system complexity increases
Solution Approach 1:
The patent implements a self-service control mechanism where the pump capacity control unit automatically detects and corrects flow rate imbalances without requiring external intervention or complex manual control systems. The system monitors its own operational parameters and self-adjusts pump capacity to maintain flow balance, achieving high reliability with minimal added complexity through autonomous operation.
Data Source
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AI summary
Provided is a hydraulic closed circuit system with hydraulic pumps which maintains a well-balanced flow rate by automatically controlling the flow rate, even if an imbalance of a flow rate during extension/retraction of a hydraulic cylinder device is caused by a pump capacity error. In this system, a first hydraulic pump 12 is connected to the hydraulic cylinder device 11 in such a manner that a hydraulic closed circuit is made, a second hydraulic pump 13 is connected at one of paired delivery ports to a bottom side of the hydraulic cylinder device 11 and at the other of the ports to a tank 16, and a prime mover 20 drives the first and second hydraulic pumps 12, 13 and recovers motive power from these pumps. A pump capacity control unit 100 detects a moving direction of the hydraulic cylinder device 11, and a pressure in a lower-thrust side of the device 11, and controls a capacity of the second hydraulic pump 13 so that the flow rate during the extension/retraction of the hydraulic cylinder device becomes balanced between the first and second hydraulic pumps and the hydraulic cylinder device.