Hydraulic Drive System Pressure Compensating Valve Saturation Control
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Solution Overview
Problem
Conventional hydraulic drive systems for construction machines face issues with actuator deceleration or stoppage due to saturation during combined operations with significant load pressure differences, where the pressure compensating valves either restrict or fully close, leading to inadequate hydraulic fluid distribution.
Innovation Solution
A hydraulic drive system with a variable displacement pump and pressure compensating valves that do not fully close at the stroke end, utilizing a pilot primary pressure circuit with separate circuits for specific and non-specific operating devices to manage pilot pressures, ensuring adequate fluid supply to high-load pressure actuators and preventing deceleration or stoppage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pressure compensating valves are configured to fully close at the stroke end in the direction of decreasing opening area, then the differential pressure across flow control valves is kept at a prescribed value, but the actuator on the low load side is decelerated or stopped when saturation occurs during combined operation with great load pressure difference
Solution Approach 1:
The patent changes the parameter of pressure compensating valve closure behavior from full closure to non-full closure at the stroke end. This parameter change allows the valve to maintain a small opening, preventing complete flow restriction and avoiding actuator stoppage during saturation conditions while still maintaining adequate differential pressure control.
2Ease of operation
If pressure compensating valves do not fully close at the stroke end in the direction of decreasing opening area, then the actuator on the low load side is not decelerated or stopped during saturation, but the delivery flow rate is insufficient for the actuator on the high load side when saturation occurs with great load pressure difference
Solution Approach 1:
The patent applies local quality by differentiating the pilot pressure supply for different operating devices. Specific operating devices (those controlling high load pressure actuators) receive full pilot primary pressure, while other operating devices receive reduced pilot primary pressure. This localized differentiation ensures adequate fluid supply to critical actuators while limiting flow to others during saturation.
Solution Approach 2:
The patent segments the pilot primary pressure circuit into two separate circuits: one for specific operating devices and another for other operating devices. This segmentation allows independent pressure control, enabling the system to prioritize hydraulic fluid allocation to high load pressure actuators while maintaining operability of low load pressure actuators.
3Quantity of substance
If the delivery flow rate of the hydraulic pump is increased to supply sufficient fluid to all actuators during combined operation, then the saturation condition is avoided, but the pump size and power consumption increase
Solution Approach 1:
The patent applies partial action by providing full pilot primary pressure only to specific operating devices that control high load pressure actuators, while providing reduced pressure to other devices. This partial differentiation allows the system to allocate hydraulic fluid preferentially to critical actuators during saturation without requiring the pump to deliver excessive flow to all actuators simultaneously, thus avoiding increased power consumption.
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 prevents deceleration or stoppage of both low and high load pressure actuators during saturation, maintaining excellent operability by ensuring necessary hydraulic fluid supply, even under great load pressure differences.
Implementation Method 1
a variable displacement type hydraulic pump (2); a plurality of actuators (5-12) which are driven by hydraulic fluid delivered from the hydraulic pump (2)
Implementation Method 2
a plurality of pressure compensating valves (27a-27h) which respectively control differential pressures across the flow control valves (26a-26h)
Implementation Method 3
Hydraulic drive systems for construction machines such as hydraulic excavators include those controlling the delivery flow rate of the hydraulic pump (main pump) so that the delivery pressure of the hydraulic pump becomes higher than the maximum load pressure of a plurality of actuators by a target differential pressure
Data Source
AI summary
Pressure compensating valves not fully closing at the stroke end are employed, and upon the operator's operation for the traveling, pilot primary pressure is reduced and supplied to remote control valves 34c-34h of non-travel operating devices. Thus, the inflow of the hydraulic fluid into non-travel actuators is suppressed and a necessary amount of hydraulic fluid for travel motors is secured in travel combined operation. Accordingly, when saturation occurs in a construction machine's hydraulic drive system performing the load sensing control due to combined operation with a great load pressure difference between two actuators, deceleration/stoppage of an actuator on the low load pressure side is prevented by preventing full closure of the pressure compensating valve on the low load pressure side, while also preventing deceleration/stoppage of a high load pressure actuator by securing a necessary amount of hydraulic fluid for the high load pressure actuator.