Load Holding Valves for Meterless Hydraulic Actuator Control
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Solution Overview
Problem
In meterless hydraulic control circuits, unintended motion can occur when there is a change in load without an operator command, leading to potential load slippage, especially when the pump displacement is zero or the system is turned off.
Innovation Solution
The implementation of load holding valves in the rod and cap side fluid connections, which are controlled by hydraulic pressure differentials to either allow or prevent flow, ensuring the load is held in position when the pump is not commanded or the system is turned off, thereby preventing undesirable movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If meterless hydraulic control circuits are used to control actuator motion by varying pump flow rates, then the system eliminates the need for proportional valves and simplifies control, but unintended load motion and slippage occur when pump displacement is zero or the system is turned off
Solution Approach 1:
The load holding valves are pre-configured in the system to automatically engage when the pump is not operative, preventing load slippage before it can occur. This preliminary protective action ensures that when pump displacement is zero or the system is turned off, the valves are already in position to maintain load position without requiring active control commands.
Solution Approach 2:
Mechanical hydraulic valves are introduced as intermediary components between the pump and the actuator chambers. These valves mediate the fluid flow by automatically opening or closing based on hydraulic pressure differentials, providing a passive safety mechanism that prevents unintended load motion without requiring complex electronic control systems.
2Reliability
If five solenoid valves are used to hold the load in position, then the load can be maintained, but the system complexity increases and more components must be maintained in closed position
Solution Approach 1:
The mechanical hydraulic valves are designed to automatically respond to hydraulic pressure differentials without requiring external control signals. The valves self-regulate their position based on the pressure conditions in the system, eliminating the need for multiple solenoid actuators and reducing system complexity while maintaining reliable load holding capability.
Solution Approach 2:
The system utilizes hydraulic pressure differentials across the mechanical valves to automatically control valve positioning. By leveraging the inherent hydraulic pressure in the system, the valves open or close based on pressure conditions rather than requiring electrical actuation, thereby reducing the number of active components needed.
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 solution effectively prevents unintended load movement by maintaining the load in position even when the pump is not active or the system is turned off, addressing the issue of load slippage and ensuring stability in hydraulic systems.
Implementation Method 1
The first mechanical hydraulic valve is adapted to be disposed in at least one of its first or second positions as a result of a first hydraulic pressure differential applied across the first mechanical hydraulic valve
Implementation Method 2
The second mechanical hydraulic valve is adapted to be disposed in at least one of its first or second positions as a result of a second hydraulic pressure differential applied across the second mechanical hydraulic valve
Data Source
AI summary
First and second mechanical hydraulic valves are disposed between a pump and the cap side chamber of an actuator and the pump and the rod chamber of the pump. The first and second valves are actuated as a result of respective pressure differentials applied across the valves. A controller controls flow from a pump in response to a commanded motion to control movement of the actuator, and cause the valves to open. The valves are disposed in their no-flow positions when the pump is not operative, and when the hydraulic system of off or locked out to hold a load.