Inductive Speed Sensor Direction Detection via Phase Offset
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Solution Overview
Problem
Existing speed sensors in vehicles face limitations, including temperature constraints, manufacturing cost issues, and a lower speed detection limit, which affect their reliability and adaptability for various applications, particularly in driver assistance systems that require accurate speed detection at all speeds, including standstill.
Innovation Solution
A method utilizing passive inductive speed sensors with a ferromagnetic transmitter element that changes the inductance of a coil, allowing for the detection of speed and direction reversal by analyzing phase offsets between wheel speed sensors on multiple wheels, enabling reliable speed measurement and direction determination without the need for a voltage source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If passive inductive speed sensors are used, then manufacturing cost is reduced and robustness is improved, but a lower speed limit exists below which the induced voltage is too low for reliable evaluation
Solution Approach 1:
The patent changes the evaluation parameter from induced voltage to inductance change detection. By measuring the change in inductance of the coil rather than relying on induced voltage, the system can detect speeds down to standstill, eliminating the lower speed limit while maintaining the passive inductive sensor design.
Solution Approach 2:
The patent replaces the electrical measurement approach (voltage detection) with a magnetic property measurement approach (inductance detection). This substitution allows the sensor to operate effectively at very low speeds where induced voltage is negligible, while maintaining the simplicity and robustness of passive inductive sensors.
2Reliability
If magnetoresistive speed sensors are used, then speed measurement from standstill is enabled, but operating temperature is limited to 150°C-200°C and manufacturing cost increases
Solution Approach 1:
The patent uses passive inductive sensors with simple coil structures instead of complex magnetoresistive elements. These inductive sensors can be manufactured more cheaply and are robust enough for automotive applications, while the inductance-based evaluation method enables standstill detection capability previously only available from expensive magnetoresistive sensors.
Solution Approach 2:
The patent changes the measurement parameter from electrical resistance modulation (magnetoresistive) to magnetic inductance change. This parameter change allows the use of simple coil structures that can operate at higher temperatures while maintaining the ability to detect speeds from standstill.
3Ease of manufacture
If inductive speed sensors are used, then manufacturing cost is reduced and robustness is improved, but direction reversal detection is not possible with a single sensor
Solution Approach 1:
The patent makes the inductive speed sensor system multi-functional by enabling it to perform both speed measurement and direction reversal detection using the same simple inductive sensors. The phase offset evaluation method allows the system to derive directional information without requiring additional sensors or complex hardware modifications.
Solution Approach 2:
The patent uses phase offset as an intermediary parameter to extract direction information. By evaluating the phase relationship between signals from multiple inductive sensors, the system can determine direction reversal without adding complex detection hardware, maintaining manufacturing cost advantages while gaining directional awareness.
4Ease of manufacture
If mass production of magnetoresistive speed sensors is used, then manufacturing cost is reduced, but adaptation to specific vehicle applications is not possible
Solution Approach 1:
The patent changes the evaluation methodology from voltage-based to inductance-based measurement, which simplifies the sensor hardware and enables mass production while maintaining flexibility for application-specific adaptations. The inductance measurement approach works across different vehicle types and sensor configurations without requiring complex application-specific circuitry.
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 provides a cost-effective, robust, and reliable method for detecting speed and direction changes, ensuring accurate operation across a wide range of speeds, including standstill, and supports advanced driver assistance systems by leveraging phase offsets in inductive signals.
Implementation Method 1
a ferromagnetic sensor element which changes the inductance L of the at least one coil
Implementation Method 2
a measuring sensor comprising at least one coil and a ferromagnetic sensor element changing the inductance L of the at least one coil
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
The invention relates to a method for determining a speed between a sensing element comprising at least one coil (3) and a ferromagnetic transmitter element (2) which modifies the inductance (L) of the at least one coil (3), in a vehicle, by means of an inductive speed sensor (1) comprising at least the coil (3) and the ferromagnetic transmitter element (2), according to which a modification of the inductance (L) of the at least one coil (3) is detected and the speed is determined based on the modified inductance (L) of the at least one coil (3), and where an inductive speed sensor (1) is respectively provided, as a wheel speed sensor, for at least two wheels (A, B) of the vehicle. According to the invention, a reversal of the direction of movement of the ferromagnetic transmitter element (2) in relation to the at least one coil (3) or a reversal of the direction of travel of the vehicle from forward travel to rearward travel or from rearward travel to forward travel is identified on the basis of at least one temporal phase shift (∆t1, ∆t2) of the time histories of the inductances (L) detected by means of the wheel speed sensors (1) of the at least two wheels (A, B).