Electric Power Steering Control Reducing Torque Fluctuation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional electric power steering systems face issues with increased size, heat generation, and power loss due to the need for current detection, which affects motor output and driver torque stability, and are prone to disturbances like noise and vibrations when current is not detected.
Innovation Solution
An electric power steering control apparatus that calculates motor target torque and applies voltage based on steering torque signals, using phase advance compensation and assist maps to minimize torque fluctuations and disturbances without directly detecting motor current, thereby reducing the need for current sensors and associated components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current detection using resistance is implemented for feedback control, then motor current control precision is improved, but apparatus size increases due to additional interface circuit and resistance element
Solution Approach 1:
The invention extracts and eliminates the current detection function from the control system. Instead of detecting motor current through resistance and interface circuits, the system uses open-loop control based on steering speed and torque signals, removing the need for current sensing hardware and reducing substrate area
Solution Approach 2:
The invention introduces an intermediary approach by using back electromotive force compensation as a mediator between the control input and motor output. Rather than directly measuring current, the system compensates for back EMF effects to achieve accurate current control without direct sensing
2Measurement precision
If resistance is used for current detection, then feedback control is enabled, but heat generation increases requiring larger heat sink
Solution Approach 1:
The invention removes the resistance element from the system entirely, eliminating the source of heat generation. By using open-loop control with back EMF compensation instead of resistance-based current sensing, no power is dissipated as heat in a detection resistor
Solution Approach 2:
The invention replaces the electrical measurement approach (using resistance to detect current) with a computational approach (calculating current based on voltage and back EMF models). This substitution eliminates the physical resistance element that generates heat
3Measurement precision
If resistance is used for current detection, then feedback control is achieved, but power loss increases reducing motor output capability
Solution Approach 1:
The invention extracts and removes the power-consuming current detection function. By eliminating the resistance element used for current sensing, the system removes the continuous power loss associated with maintaining current detection circuitry
Solution Approach 2:
The system uses the motor's own back electromotive force as a natural indicator of current flow. By measuring voltage and calculating current through back EMF compensation, the system makes the motor itself provide the information needed for control without external power-consuming sensors
4Area of stationary object
If current detection is eliminated to reduce heat and size, then apparatus size and heat sink are reduced, but torque fluctuation and disturbances increase affecting driver
Solution Approach 1:
The invention implements a hybrid feedback mechanism. While eliminating direct current sensing, the system uses back EMF compensation to create a virtual feedback loop that continuously adjusts control signals to maintain stable motor torque, preventing fluctuations and disturbances
Solution Approach 2:
The system performs preliminary compensation for back electromotive force effects before they cause torque fluctuations. By calculating and compensating for back EMF in advance based on steering speed and torque signals, the system prevents torque disturbances before they reach the driver
Data Source
AI summary
Provided is an electric power steering control apparatus for an electric power steering system equipped with a torque sensor for detecting a steering torque of the steering system and a motor for generating a torque for assisting the steering torque, including a motor target torque calculation unit for calculating a torque of the motor in response to a steering torque signal from the torque sensor and a motor-applied voltage calculation unit for calculating a voltage applied to the motor in response to a motor target torque signal from the motor target torque calculation unit, in which the motor target torque calculation unit generates the motor target torque signal indicating a motor target torque whose ratio to a steering torque indicated by the steering torque signal is set such that an influence of a torque fluctuation of the motor on a driver becomes equal to or smaller than a predetermined value.