Hybrid Current Detection in Drive Devices
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Solution Overview
Problem
Conventional drive devices for rotary electric machines face a trade-off between cost and accuracy, with Hall element sensors providing high accuracy but being expensive, and shunt resistors being inexpensive but less accurate and sensitive to temperature, especially in high-temperature environments.
Innovation Solution
A drive device configuration that uses a combination of Hall element sensors for high-accuracy current detection in critical components like the wheel driving rotary electric machine and shunt resistors for less critical components like the alternating-current rotary electric machine, optimizing the ratio of detection periods to control periods for each to balance cost and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Hall element sensors are used for current detection, then measurement precision is improved, but product cost increases
Solution Approach 1:
The patent applies different current detection methods to different rotary electric machines based on their specific requirements. High-precision Hall element sensors are used for the wheel driving rotary electric machine where accuracy is critical, while shunt resistors are used for the alternating-current rotary electric machine where cost is more important and accuracy requirements are lower. This local differentiation resolves the contradiction by matching detection precision to actual needs in each application area.
2Ease of manufacture
If shunt resistors are used for current detection, then product cost is reduced, but measurement precision and temperature stability deteriorate
Solution Approach 1:
The patent strategically places shunt resistors in applications where cost reduction is prioritized and accuracy requirements are less stringent. By using shunt resistors for the alternating-current rotary electric machine rather than Hall element sensors, the patent achieves cost reduction while maintaining sufficient control accuracy for non-critical applications.
Solution Approach 2:
The patent accepts partial degradation in measurement precision for the alternating-current rotary electric machine by using shunt resistors instead of Hall element sensors. This partial action approach allows the system to achieve overall cost reduction while maintaining adequate performance for applications where maximum precision is not essential.
3Ease of manufacture
If shunt resistors are used in high-temperature environments, then product cost is reduced, but reliability deteriorates due to temperature sensitivity
Solution Approach 1:
The patent carefully considers the installation environment when selecting detection methods. For the alternating-current rotary electric machine, the patent determines that shunt resistors can be used even in relatively high-temperature environments because the accuracy requirements are lower and the temperature stability demands are less stringent compared to wheel driving systems.
Solution Approach 2:
The patent accepts the temperature sensitivity limitation of shunt resistors in exchange for significant cost reduction. By using inexpensive shunt resistors in applications where they can function adequately despite temperature effects, the patent achieves cost efficiency while maintaining acceptable reliability for non-critical applications.
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 reduces product costs while maintaining high control accuracy for critical components and tolerating reduced accuracy in less critical components, effectively managing the influence of temperature fluctuations on detection accuracy.
Implementation Method 1
The conventional current sensor used in the drive device generally uses a Hall element as shown in Japanese Patent Application Publication No. 2007-166803
Implementation Method 2
techniques are known in which a shunt resistor provided in an inverter circuit is used to detect the current flowing in the stator coil of each phase of the rotary electric machine
Data Source
AI summary
A drive device that includes a current sensor that detects a current flowing in the wheel driving rotary electric machine; and shunt resistors that detect currents flowing in the respective second switching element units for the corresponding phases between the direct-current power supply and the second switching element units for the respective phases, wherein a ratio of a period during which current detection can be performed by the current sensor to a control period of the first inverter is higher than a ratio of a period during which current detection can be performed by the shunt resistors to a control period of the second inverter.