Electric Motor Position Detection with SPI and PWM Signal Switching
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Solution Overview
Problem
Existing methods for determining and controlling the position of an electric motor in a clutch actuation system, particularly with sensors outside the axis of rotation, face challenges in achieving high position resolution without requiring extensive construction space or being cost-effective, especially when using small magnetic transmitter rings with limited curvature of the magnetic field.
Innovation Solution
The method employs a serial peripheral interface (SPI) protocol for short transmission distances and pulse width modulation (PWM) signals for longer distances, allowing precise transmission of the rotor's position using a single sensor system, with a microprocessor analyzing both signals to ensure accurate commutation and error detection through comparison of absolute and incremental positions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple sensors are used to achieve high position resolution, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent segments the position measurement function into two distinct parts: (1) an absolute position sensor that provides the base position information, and (2) an incremental encoder that provides high-resolution position changes. This segmentation allows each component to be optimized for its specific function, achieving high overall measurement precision without requiring multiple high-complexity sensors.
Solution Approach 2:
The patent merges two different measurement approaches (absolute positioning and incremental encoding) into a single integrated system. The absolute sensor provides a reference frame while the incremental encoder captures fine position changes, and their outputs are combined through coordinate transformation to achieve high-resolution position measurement with simpler individual components.
2Device complexity
If a small diameter magnetic transmitter ring is used, then device complexity is reduced, but measurement precision deteriorates due to insufficient magnetic field curvature
Solution Approach 1:
The patent introduces an intermediary computational process (coordinate transformation) that mediates between the absolute position data from the sensor and the incremental position data from the encoder. This computational intermediary allows the system to achieve high measurement precision without requiring a large magnetic transmitter ring, as the mathematical transformation compensates for the limited physical curvature.
Solution Approach 2:
The patent changes the parameter of position representation from direct magnetic field curvature measurement to a computed value derived from coordinate transformation of absolute and incremental position data. This parameter change allows accurate position measurement with a small diameter magnetic transmitter ring, as the computational approach replaces the need for large physical curvature.
3Measurement precision
If SPI protocol is used for position signal transmission, then measurement precision is maintained, but reliability deteriorates due to susceptibility to interference over longer distances
Solution Approach 1:
The patent implements a dynamic signal transmission strategy where the system automatically selects between SPI protocol and PWM signal transmission based on the transmission distance. For short distances, SPI protocol is used to maintain high measurement precision. For longer distances, the system dynamically switches to PWM transmission which is more reliable and less susceptible to interference, thus adapting the transmission method to the specific operational conditions.
Solution Approach 2:
The patent changes the transmission parameter (signal type) based on transmission distance. The system monitors the distance between the sensor and analysis unit, and accordingly changes the signal transmission parameter from SPI protocol (for short distances) to PWM signal (for longer distances). This parameter change ensures both measurement precision and transmission reliability under different operational 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 enables reliable and precise determination of the electric motor's position with a simple construction, reducing costs and interference susceptibility, while ensuring accurate commutation and robust error validation.
Implementation Method 1
a magnetic transmitter ring is non-rotatably connected to the rotor of the electric motor, for example on a shaft end (on-axis), while the sensor system that senses the magnetic transmitter ring is attached, for example, to the stator (off-axis)
Data Source
AI summary
The invention relates to a method for determining and/or controlling a position of an electric motor, in particular in a clutch actuation system of a motor vehicle, wherein the position of a rotor of the electric motor is picked up by a sensor system situated on a stator of the electric motor outside an axis of rotation of the electric motor, and the position signal picked up by the sensor system is analyzed by an analysis unit. In a method in which the rotor position is detected with a high level of certainty, the position signal is transmitted to the analysis unit depending on a transmission distance between the sensor system and the analysis unit by means of an SPI protocol signal for short transmission distances, and/or by means of a PWM signal for longer transmission distances.