AS/TS Magnet Arrangement for Electric Power Steering Ripple
Solution Overview
Problem
Existing electric power steering systems experience torque ripple due to magnetic disturbances between angle sensors and torque sensors, leading to faulty steering assist calculations and uncomfortable driving experiences.
Innovation Solution
The electric power steering apparatus optimizes the arrangement of angle sensors and torque sensors by pre-assembling and calibrating their magnets, determining the zero crossing point of the envelope curve, and adjusting mechanical components to minimize the influence of sensor magnets, thereby reducing torque ripple and improving steering accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If angle sensors and torque sensors are placed close together to save space, then device compactness is improved, but magnetic field interference between sensors increases causing torque ripple
Solution Approach 1:
A magnetic shield is introduced as an intermediary component between the angle sensor and torque sensor. This shield blocks or redirects magnetic field lines, preventing the multi-pole ring magnet's magnetic field from directly interfering with the angle sensor's measurement. The shield acts as a mediator that allows the sensors to remain close together while eliminating the harmful magnetic interference.
Solution Approach 2:
The harmful magnetic field influence is extracted or separated from the sensor measurement path by using the magnetic shield to redirect field lines away from the angle sensor. This effectively removes the interference component while maintaining the compact sensor arrangement.
2Measurement precision
If multi-pole ring magnet and two-pole magnets are positioned close for signal measurement, then measurement precision is improved, but magnetic disturbance between magnets increases causing faulty steering assist calculation
Solution Approach 1:
The magnetic shield serves as a mediator that selectively blocks magnetic field lines from reaching the angle sensor while allowing the measurement function to operate. It creates a magnetic field boundary that protects the angle sensor from the multi-pole ring magnet's interference.
Solution Approach 2:
The magnetic shield provides localized magnetic field management, creating different magnetic field environments in different spatial zones. The area around the angle sensor is protected from interference, while the multi-pole ring magnet continues to function normally in its own zone.
3Manufacturing precision
If gears and magnets are assembled with tight tolerances to reduce play, then manufacturing precision is improved, but assembly complexity and cost increase
Solution Approach 1:
The magnetic shield is pre-assembled with the angle sensor or gear assembly in a preliminary assembly step. This preliminary action establishes the correct spatial relationship and tolerance requirements before final assembly, making the overall manufacturing process more manageable and reducing the complexity of achieving tight tolerances in the final assembly.
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 torque ripple, enhances steering precision, and provides a more comfortable driving experience by minimizing unwanted assist torque, especially at the neutral steering position.
Implementation Method 1
AS measures the magnetic field, wherein the torque sensor detects the strength of the magnetic field deriving from the multi-pole ring magnet
Implementation Method 2
In each of the two small gears a two-pole permanent magnet is arranged, providing magnetic signal for angle sensors placed very close to the multi-pole ring magnet of a torque sensor unit (TSU)
Data Source
AI summary
A power steering apparatus assists steering of a vehicle by conferring torque generated by an electric motor to a steering mechanism. The apparatus includes a steering column with linked upper and lower steering shafts. An angle sensor (AS) includes a gear and magnet to measure the steering shaft angle. A torque sensor (TS) measures the relative shift angle between the upper and lower steering shaft and includes a multi-pole ring magnet and a magnetic flux conductor. The TS and AS are arranged such that the AS magnet influences the TS measurement creating a steering shaft angle depending error signal. The steering mechanism is arranged such that a zero crossing of an envelope curve of the error signal is given for the neutral position of the steering apparatus or a range of the steering position in which the steering angle is less than a threshold angle limit.