Hydraulic Valve Dithering to Mitigate Stiction Delays
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Solution Overview
Problem
Hydraulic valves in construction machines experience delays due to static friction, making control of implement movement complex and confusing, as static friction requires more force to overcome than kinetic friction, leading to a lag between user input and valve actuation.
Innovation Solution
Dithering of hydraulic valves is implemented by applying continuous back-and-forth motion to produce periodically varying hydraulic fluid pressures, which reduces static friction by causing the main hydraulic valve to dither, allowing actuation with pressures lower than those required to actuate the cylinder, thereby mitigating stiction and improving responsiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hydraulic fluid pressure is increased to overcome static friction, then the valve component can be actuated, but the response time is delayed and control becomes complex
Solution Approach 1:
The patent applies a dither signal (high-frequency low-amplitude oscillation) to the valve spool to induce continuous small movements. This vibration prevents the spool from settling into a static position where friction would lock it, thereby eliminating the delay between hydraulic pressure application and valve actuation while maintaining precise control
Solution Approach 2:
The dither signal provides periodic oscillatory motion to the valve spool through the solenoid actuator. This continuous periodic action keeps the spool in a state of motion rather than static equilibrium, ensuring that static friction is constantly overcome and the valve responds immediately to control signals
2Ease of operation
If dithering is applied to reduce static friction, then responsiveness is improved, but device complexity increases due to additional control signals
Solution Approach 1:
The dither function is integrated into the existing solenoid actuator that already controls the valve. The same solenoid that actuates the valve based on control signals also receives the dither signal, combining two functions into a single component and avoiding the need for separate dithering hardware
Solution Approach 2:
The control system generates and applies the dither signal through the existing solenoid actuator without requiring external dedicated dithering equipment. The system uses its own existing components to provide the friction-reducing dither function, eliminating the need for additional complex external control systems
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, allowing for immediate and precise control of hydraulic cylinder movement, enhancing user input responsiveness and simplifying the control of construction machine implements.
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
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
Figure 1A~1B
Figure 2
Figure 3
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.