Pole Piece Design for Steering Torque Waveform Control
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Solution Overview
Problem
Existing vehicle steering systems face challenges in controlling cogging torque, which affects the output torque profile and is not adequately addressed by conventional methods, particularly in variable effort steering actuators, leading to suboptimal performance in maintaining a straight path under various conditions.
Innovation Solution
A method for designing a pole piece in a power assist steering system by selecting the number of inner and outer teeth and optimizing the ratio between tooth tip angles and magnet pole widths to achieve a desired cogging torque shape, incorporating techniques such as tooth profiling and magnetic pole shaping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If conventional methods (skew, dummy notch, shifting) are used to minimize cogging torque, then cogging torque is reduced, but the torque waveform cannot be precisely shaped to achieve desired output torque profile
Solution Approach 1:
The patent applies parameter changes by systematically varying tooth geometry parameters (tip radius, root radius, width, depth) and pole piece parameters (width, depth, arc angle) to shape the cogging torque waveform. This goes beyond conventional binary approaches (skew/notch/shifting) by treating tooth and pole geometry as continuous adjustable parameters that can be optimized to achieve a desired torque profile.
Solution Approach 2:
The patent implements local quality by applying different geometric modifications to specific regions of the teeth and poles. Different portions of the tooth (tip vs. root) and pole piece have different dimensional characteristics, with each region optimized to contribute to the overall torque waveform shaping. This localized geometric tailoring allows precise control over the cogging torque distribution.
2Measurement precision
If the number of teeth and poles is increased to improve torque control, then torque resolution is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent achieves multi-functionality by designing the tooth and pole geometry to simultaneously minimize cogging torque and shape the torque waveform. The same geometric parameters that reduce harmful cogging effects also create the desired torque profile, eliminating the need for separate compensation mechanisms and reducing overall system complexity.
Solution Approach 2:
The patent replaces complex mechanical torque control systems with a geometrically optimized electromagnetic design. By shaping the tooth and pole geometry, the system inherently produces the desired torque waveform without requiring additional mechanical components, sensors, or control algorithms, thereby reducing overall system complexity.
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 the achievement of a nearly constant torque output within the operating range, reducing controller burden and enhancing vehicle stability and park assist capabilities by minimizing cogging torque and reshaping the torque waveform.
Implementation Method 1
due to interactions of a permanent magnet with teeth of a cog, cogging or detent torque is caused
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
A method for designing a pole piece for a power assist steering system, includes: selecting a number of teeth (202), k, for the pole piece where k=n/2 and n represents an even number of poles (206); and selecting a ratio between an angle made by an inner tooth tip and an outer tooth tip, θτp, and an angle made by a magnet pole width, θmp, to provide a desired torque function for the steering system.