Electric Drive Device Current Limit Adjustment for Steering Torque
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional electric drive devices for power steering systems face limitations in maintaining sufficient torque and steering sensation when a motor coil or inverter circuit experiences an abnormality, particularly at reduced operating conditions, leading to inadequate steering performance, especially in large vehicles or low-speed scenarios.
Innovation Solution
The electric drive device and control method involve detecting abnormalities and adjusting the current supply to motor coils, stopping current to non-functional coils while increasing the current limit value for functional coils, thereby enhancing torque stability and heat management, even without spare current margins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the motor drive is kept at 50% overall by driving the normal inverter circuits at 50% or above to suppress severe effects on braking torque due to fault, then the torque output uniformity is improved, but the steering performance becomes insufficient especially in large vehicles or low-speed scenarios
Solution Approach 1:
The patent changes the operating parameters of the normal inverter circuit by increasing the PWM duty ratio beyond 50% to boost the current supply to motor coils. This parameter adjustment allows the system to maintain sufficient torque output for adequate steering performance while operating with only one functional inverter circuit, thus resolving the contradiction between reliability and ease of operation.
2Power
If the current limit value of the normally functioning motor is raised to compensate for torque decrease in the faulty motor, then the total torque output is improved, but the heat generation increases beyond acceptable limits
Solution Approach 1:
The patent dynamically adjusts the current limit value based on the PWM duty ratio. When the PWM duty ratio is increased to boost torque output, the current limit value is correspondingly increased to allow higher current flow. This dynamic adjustment ensures that sufficient torque can be generated while the system actively manages heat generation through coordinated control of multiple parameters.
3Power
If the current to motor coil is increased beyond the original current limit value to maintain torque output, then the steering assist performance is improved, but the motor coil may be damaged due to excessive current
Solution Approach 1:
The patent implements feedback control by continuously monitoring the PWM duty ratio and dynamically adjusting the current limit value accordingly. The control unit receives feedback about the operating conditions and modifies the current limit to allow increased current flow when needed for torque maintenance, while simultaneously ensuring the current remains within safe boundaries to prevent motor coil damage. This closed-loop feedback mechanism resolves the contradiction between power output and component durability.
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 allows for improved torque consistency and reduced torque variation during abnormalities, enhancing steering performance and driver experience by maintaining or increasing current supply to operational coils, thus mitigating the effects of motor coil and inverter circuit faults.
Implementation Method 1
a motor 2 having a rotor 21 and a stator 22, wherein the stator 22 has motor coils 24 of three phases U, V and W
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
Provided is an electric drive device which controls a current supplied to coils during normal operation so as to be less than a current limit value when normal, which is determined from heat generating properties and heat radiating properties of a thermally coupled body that includes the coils and an inverter circuit. When an abnormality in each group or each phase of the coils and the inverter circuit is detected, the supply of current to all phases of a group suffering an abnormality in the coils, or to a phase that is not capable of continuous operation, is stopped or reduced; and the limit value of the current supplied to a coil that is capable of continuous operation is reset to a current limit value in the event of abnormality, which is larger than the current limit value when normal, within the range of improvement of the heat generating properties of the thermally coupled body due to the stopping or reduction of the supply of current.