Electric Power Steering Inverter Shielding for Accurate Current Detection
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Solution Overview
Problem
Conventional electric power steering devices with integrated motors and control units face increased noise issues due to PWM driving with large currents and the presence of current detection circuits, which affect noise management.
Innovation Solution
The implementation of an electric power steering device with two sets of independently provided motor windings, each supplied by separate inverter circuits composed of switching elements and control circuits, along with a detection circuit and metal shield walls to block radiation noise near detection terminals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two sets of motor windings and inverter circuits are provided for redundancy, then reliability is improved, but noise emission increases due to PWM driving with large currents
Solution Approach 1:
The control unit is divided into two independent sets, each with its own inverter circuit and motor winding. This segmentation allows independent noise shielding for each set, enabling noise isolation while maintaining redundant functionality for improved reliability.
Solution Approach 2:
A metal shield wall is introduced as an intermediary element between the two inverter circuits. This shield wall blocks electromagnetic noise from one inverter circuit from interfering with the other, reducing noise emission while preserving the redundant system architecture.
2Measurement precision
If detection circuits are provided for monitoring current in each inverter circuit, then measurement precision is improved, but noise interference increases affecting detection accuracy
Solution Approach 1:
The metal shield wall acts as an intermediary protective barrier between the inverter circuits and detection circuits. It blocks electromagnetic noise from the inverter circuits, preventing interference with the detection circuits and thereby maintaining high current detection accuracy.
Solution Approach 2:
The detection circuits are extracted and positioned separately from the main inverter circuit noise sources, with the shield wall providing additional isolation. This separation reduces noise exposure to the sensitive detection circuits while preserving measurement precision.
3Object-generated harmful factors
If shield walls are added to block noise near detection terminals, then noise measures are improved, but device complexity increases
Solution Approach 1:
The metal shield wall serves multiple functions: it blocks electromagnetic noise between the two inverter circuits, protects the detection circuits from noise interference, and can be integrated into the existing control unit structure. This multi-functionality achieves effective noise blocking without proportionally increasing device 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 configuration effectively blocks noise and improves the accuracy of detection signals, enhancing the overall noise management in the electric power steering device.
Implementation Method 1
A shield wall made of metal and for shielding noise emitted by driving of one of the two inverter circuits is provided near the detection terminal of the other inverter circuit
Data Source
AI summary
The electric power steering device includes a motor and a control unit integrated coaxially therewith at an output shaft end of the motor. The motor has two sets of windings independently of each other. The control unit includes two inverter circuits having a plurality of switching elements for supplying currents, and two control circuits for respectively outputting drive signals to the inverter circuits. The inverter circuits are formed by power modules, and have detection terminals for detecting voltages between both ends of shunt resistors for detecting currents. Shield walls for shielding noise are provided to a heatsink for supporting the power modules and control boards forming the control circuits. The shield walls support the control boards.