Solenoid Valve Control via Dithering for AMT
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Solution Overview
Problem
The existing control methods for solenoid valves in automatic manual transmissions face challenges in achieving high accuracy due to insufficient digital input resolution, which is costly to address by replacing microcontrollers, especially in already marketed transmission control units.
Innovation Solution
A method using dithering, where a main microcontroller adds a high-frequency dithering square wave to the target current, allowing the supporting microcontroller to track the current with increased resolution without requiring additional hardware, thereby enhancing the effective control resolution of solenoid valves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the digital input resolution of the supporting microcontroller is increased to improve current control accuracy, then the manufacturing precision is improved, but the device complexity and cost increase
Solution Approach 1:
The patent applies dithering by superimposing a high-frequency square wave signal on the target current command. This vibration-like signal causes the solenoid valve to oscillate around the target position, preventing static friction from causing the valve to stick. The high-frequency oscillation effectively reduces the impact of friction without requiring higher resolution digital inputs, thus improving control accuracy while maintaining the same microcontroller specifications.
Solution Approach 2:
The patent employs periodic dithering signals with specific frequencies (e.g., 100-1000 Hz) to continuously excite the solenoid valve. This periodic action ensures that the valve remains in a state of minor oscillation, preventing it from settling into a stuck position due to static friction. The periodic nature of the dithering signal allows for predictable and controllable valve behavior without requiring more complex or higher-resolution control hardware.
2Reliability
If dithering is applied to prevent static friction in the solenoid valve, then the reliability is improved, but the position control precision may deteriorate due to oscillations
Solution Approach 1:
The patent uses high-frequency dithering signals that create minor oscillations around the target position rather than large amplitude movements. These small-scale vibrations are sufficient to prevent static friction from causing the valve to stick, while the high frequency ensures the oscillations remain minimal and do not significantly impact the overall position control precision. The valve effectively follows the target trajectory with only minor deviations caused by the dithering.
Solution Approach 2:
The patent carefully selects and adjusts the dithering signal parameters, including frequency (100-1000 Hz) and amplitude, to optimize the balance between preventing static friction and maintaining position control precision. By changing these parameters, the system can adapt to different operating conditions and valve positions, ensuring reliable operation without excessive oscillation that would compromise positioning accuracy.
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 method increases the effective resolution of solenoid valve control beyond the limitations of the digital input resolution, providing more accurate control without the need for replacing microcontrollers, thus being cost-effective and easy to implement.
Implementation Method 1
a solenoid valve (30) provided with a coil (34) to be crossed by a control current (I) variable over time and adapted to drive a spool (32)
Implementation Method 2
the main microcontroller overlaps a dithering square wave, which has a zero mean value and has a high oscillation frequency, to the target current determined according to the target position
Implementation Method 3
a hydraulic servo-control (22) actuated by the solenoid valve (30) and adapted to transmit a force (F) through a hydraulic circuit (21)
Data Source
AI summary
The present subject matter includes a control method to position a solenoid valve using dithering. The control method provides the steps of: determining a target current across the solenoid valve which is expressed in digital form with a given minimum quantization interval, adding a dithering square wave to the target current, controlling the voltage applied to the solenoid valve to cause the current across the solenoid valve to track the target current added to the dithering square wave, jiggling the dithering square wave with a frequency which is a sub-multiple with respect to the maximum variation frequency of the current across the solenoid valve, and varying the amplitude of the dithering square wave.