Hydrostatic Displacement Unit Hysteresis Reduction
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Solution Overview
Problem
Hydraulic machines with variable displacement volume face mechanical hysteresis issues due to friction, leading to inconsistent control volume flow rates and displacement volumes, especially when control signals are ramped up or down, which complicates precise control and adjustment.
Innovation Solution
Incorporating a vibration unit, such as an oscillation exciter, directly attached to the control spool or its mechanical feedback unit, which generates high-frequency oscillations independent of the actuator force, reducing static friction and hysteresis effects by superimposing these oscillations onto the control spool's motion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a control spool is moved by actuators engaging with the same in axial direction, then the control volume flow rate can be adjusted, but friction forces cause mechanical hysteresis leading to inconsistent control
Solution Approach 1:
The patent applies mechanical vibration by superimposing high-frequency oscillations (typically 50-500 Hz) on the control spool motion. This vibration prevents the control spool from settling in static friction zones, ensuring that the control volume flow rate responds consistently to control signals regardless of whether the signal is increasing or decreasing, thereby eliminating hysteresis effects.
Solution Approach 2:
The patent implements periodic action through continuous high-frequency oscillations applied to the control spool. This periodic motion ensures that the control spool is constantly moving through its range of motion, preventing it from getting stuck in dead zones caused by static friction, and ensuring consistent control response throughout the entire control range.
2Reliability
If an oscillation signal is superimposed on the control signal to reduce hysteresis, then friction forces are minimized, but inaccuracies occur in control volume flow rates when the control spool is displaced with pulsing force
Solution Approach 1:
The patent uses mechanical vibration at optimized frequencies (50-500 Hz) that are high enough to minimize friction effects but low enough to avoid creating harmful pulsations in the control volume flow rate. The vibration amplitude is carefully controlled to be sufficient to overcome static friction but small enough not to interfere with the primary control signal.
Solution Approach 2:
The patent optimizes the parameters of the oscillation signal, specifically the frequency (50-500 Hz) and amplitude, to achieve the best balance between hysteresis reduction and control accuracy. By adjusting these parameters, the system minimizes friction effects while avoiding the introduction of harmful pulsations that would degrade control precision.
3Reliability
If dither or PWM signals are used for electric control, then hysteresis can be reduced, but the amplitudes depend on signal height and are not optimal in each control state
Solution Approach 1:
The patent employs mechanical vibration with frequencies in the range of 50-500 Hz, which provides consistent hysteresis reduction across all control states. Unlike dither or PWM signals whose effectiveness varies with signal amplitude, the mechanical vibration approach maintains optimal performance throughout the entire control range, providing greater adaptability to different operating conditions.
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 approach effectively reduces hysteresis and improves the accuracy of displacement volume adjustments in hydraulic machines without altering the existing displacement unit, allowing for simpler retrofitting of existing machines by replacing only the control spool with an inventive one equipped with a vibration unit.
Implementation Method 1
a vibration unit, in particular an oscillation exciter, which by means of excitation forces generates oscillations in the vibration unit
Data Source
AI summary
The invention relates to a displacement unit (1) of a hydraulic machine, for which the hysteresis is reduced. For this purpose, in the control spool (3) and/or at the control spool (3) a mass body (16) and a spring (17) are arranged, which are excited to resonance vibrations. The vibrations are self-excited and sustained by a partial flow rate of the hydraulic fluid which is modulated periodically. The high frequent vibrations are transmitted over the spring (17) onto the associated control spool (3), thereby reducing the friction and hence the hysteresis.