Hydraulic Valve Dithering for Faster Response Under Static Friction
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Solution Overview
Problem
Hydraulic valves in construction machines, such as excavators, experience delays due to static friction, which complicates the control of implement movement as static friction is higher than kinetic friction, requiring more force to initiate movement and causing a lag between user input and actual movement.
Innovation Solution
Dithering of hydraulic valves, where a first and second hydraulic valve are continuously moved back and forth, and their outputs are connected to a main hydraulic valve, allowing a controller to apply hydraulic fluid pressure to mitigate static friction by overcoming it with kinetic friction, thus reducing delays in actuation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If hydraulic fluid pressure is applied to overcome static friction, then the valve component can move, but the delay between user input and movement occurs due to the force required to overcome static friction
Solution Approach 1:
The patent applies dithering, which is a high-frequency mechanical vibration, to the valve component. This vibration continuously breaks the static friction between the valve component and its seating surface, allowing the valve to respond immediately to hydraulic fluid pressure changes without the delay caused by static friction buildup.
Solution Approach 2:
The dithering mechanism applies periodic oscillations to the valve component at a specific frequency. This periodic action prevents static friction from establishing a strong bond, ensuring that the valve component can move promptly when hydraulic pressure is applied, thereby reducing the time delay between user input and actual movement.
2Force
If static friction is overcome by increasing hydraulic fluid pressure, then the valve component moves, but more force is required compared to kinetic friction
Solution Approach 1:
By applying high-frequency vibrations to the valve component, the patent reduces the peak static friction force that must be overcome. The vibration keeps the contact surfaces from fully bonding, allowing the valve to actuate with less hydraulic pressure than would be required without dithering, thereby improving ease of operation.
Solution Approach 2:
The dithering mechanism performs a preliminary action by continuously applying small oscillations that prevent static friction from fully establishing. This preliminary vibration prepares the valve component for smooth actuation, reducing the sudden force requirement when the valve needs to move in response to user input.
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 dithering technique effectively reduces static friction in hydraulic valves, allowing for more immediate and responsive movement of hydraulic cylinders, enhancing control precision and reducing the complexity of user input to machine movement.
Implementation Method 1
This delay is caused, at least in part, by static friction, which prevents immediate movement of a valve component in response to hydraulic fluid pressure urging the component to move. Static friction is the friction occurring between two surfaces that resists movement of the surfaces relative to each other.
Implementation Method 2
As hydraulic fluid pressure urging the component to move increases, static friction is overcome and only kinetic friction remains, which requires less force than static friction to overcome.
Data Source
AI summary
A method and apparatus for dithering hydraulic valves to mitigate static friction (“stiction”) associated with the hydraulic valves. A first hydraulic valve and a second hydraulic valve are dithered to mitigate stiction associated with those valves. The dithering of the first and second hydraulic valves also cause dithering of a main hydraulic valve associated with the first and second hydraulic valves. Accordingly, stiction of three hydraulic valves of a hydraulic system is mitigated.