Electric Power Steering Inverter Layout for Noise-Shielded Current Detection
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Solution Overview
Problem
Conventional electric power steering devices with integrated motors and control units face challenges in noise reduction, particularly with the increased noise sources from PWM driving and minute current detection circuits.
Innovation Solution
The implementation of metal shield walls near detection terminals to block radiation noise, improving signal accuracy and reducing noise interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two sets of motor windings and PWM drive circuits are provided for redundancy, then reliability is improved, but noise sources are increased
Solution Approach 1:
The control unit is segmented into separate functional regions: a first region housing the PWM drive circuit for one motor winding set, and a second region housing the PWM drive circuit for the other motor winding set. This spatial segmentation isolates noise sources from sensitive detection circuits, allowing redundancy to be maintained while managing noise through physical separation.
Solution Approach 2:
Different regions of the control unit are assigned different functional qualities: power-driven regions (PWM circuits) are separated from sensitive regions (detection circuits). The detection terminals for minute current detection are positioned in regions away from PWM switching noise, creating local quality differences that protect sensitive measurements while maintaining system redundancy.
2Device complexity
If detection terminals are positioned near PWM drive circuits, then device complexity is reduced, but measurement precision deteriorates due to noise interference
Solution Approach 1:
The control unit is divided into distinct functional zones: a first region containing the PWM drive circuit and a second region containing the detection terminals for minute current detection. This segmentation ensures that detection terminals are not positioned near PWM switching noise sources, maintaining measurement precision while keeping the overall device structure manageable through systematic zoning.
Solution Approach 2:
The control unit implements local quality differentiation by creating noise-sensitive regions (for detection terminals) and noise-generating regions (for PWM circuits). The detection terminals are specifically positioned in regions with low electromagnetic interference, ensuring high measurement precision without requiring overly complex shielding or routing arrangements.
3Volume of moving object
If power supply circuit portion is provided separately from control unit, then size reduction is achieved, but noise shielding becomes more difficult
Solution Approach 1:
The control unit is segmented into functional regions with the PWM drive circuits and detection terminals positioned in separate zones. This internal segmentation provides noise shielding benefits by isolating sensitive detection circuits from power switching noise, while the overall compact integration maintains size efficiency. The segmentation occurs at the circuit board level rather than requiring separate physical housings.
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 solution effectively blocks noise and enhances the accuracy of detection signals, improving the overall noise management in electric power steering devices.
Implementation Method 1
shield walls made of metal are provided near the detection terminals against radiation noise from one of noise sources
Data Source
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AI summary
The electric power steering device includes a motor (2) and a control unit (1) integrated coaxially therewith at an output shaft end of the motor (2). The motor has two sets of windings (24a, 24b) independently of each other. The control unit (1) includes two inverter circuits (3a, 3b) having a plurality of switching elements for supplying currents, and two control circuits for respectively outputting drive signals to the inverter circuits (3a, 3b). The inverter circuits (3a, 3b) are formed by power modules (50a, 50b), and have detection terminals for detecting voltages between both ends of shunt resistors (33U, 33V, 33W) for detecting currents. Shield walls (41h, 41k) for shielding noise are provided to a heatsink (41) for supporting the power modules (50a, 50b) and control boards (4a, 4b) forming the control circuits. The shield walls support the control boards (4a, 4b).