Electric Power Steering Voltage Limiting for Impact Reduction
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Solution Overview
Problem
Existing electric power steering systems face challenges in alleviating impact forces at the time of end contact, leading to reduced durability and uncomfortable steering experiences due to insufficient assist force near maximum steering angles.
Innovation Solution
An electric power steering apparatus with a steering torque detection unit, current command value calculation unit, motor control unit, steering angle detection unit, voltage target value setting unit, motor rotation speed detection unit, and current limiting value setting unit, which sets a voltage target value based on the steering angle and motor output characteristics to limit the current command value, thereby controlling the electric motor's output and reducing impact forces while maintaining a natural steering feel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the steering assist force is increased to improve steering ease, then the steering assist force becomes insufficient near maximum steering angle, but increasing it further causes large impact force at end contact
Solution Approach 1:
The patent applies dynamics by making the voltage target value changeable based on steering angle. The motor control unit dynamically adjusts the voltage target value according to the detected steering angle, allowing the steering assist force to be optimized at different steering positions while preventing excessive impact at end contact.
Solution Approach 2:
The patent changes the voltage target value parameter based on steering angle. By setting different voltage target values at different steering angles, the system optimizes motor output characteristics to provide sufficient assist force during normal steering while limiting impact force at end contact.
2Object-affected harmful factors
If the driving force attenuation starts earlier to reduce impact force, then the steering assist force becomes insufficient in the vicinity of maximum steering angle, but delaying attenuation causes large impact force
Solution Approach 1:
The system dynamically adjusts the voltage target value based on the actual steering angle detected by the steering angle detection unit. This allows the attenuation timing to be optimized for each steering condition, preventing impact force while maintaining sufficient assist force near maximum steering angle.
Solution Approach 2:
The patent uses feedback from the steering angle detection unit to continuously adjust the voltage target value. The motor control unit receives real-time steering angle information and adjusts the motor output accordingly, ensuring optimal balance between assist force and impact reduction.
3Ease of operation
If the steering assist force is maintained high during return from maximum steering angle, then the steering wheel may feel stuck, but reducing it causes insufficient assist force
Solution Approach 1:
The voltage target value is dynamically adjusted based on steering angle during the return motion. As the steering wheel returns from maximum steering angle, the system provides sufficient assist force to prevent sticking sensation while controlling the force to avoid excessive impact.
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
The solution effectively alleviates impact forces at the end contact, enhances steering durability, and provides a smooth, natural steering experience without degrading the steering feel, by setting an upper limit on the current flowing through the electric motor based on its output characteristics.
Implementation Method 1
an electric motor that generates steering assisting torque given to a steering mechanism
Data Source
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AI summary
There is provided an electric power steering apparatus capable of alleviating an impact force at the time of an end contact, while giving natural and smooth steering feeling to a driver without degrading the steering feeling. When steering angle (θs) is equal to or larger than a limit starting steering angle (θst), a voltage target value (Vt) of an electric motor (13) is limited, and an upper limit (current limiting value I_Lim) of a current command value (Iref) is set based on the limited voltage target value (Vt) and the motor rotation speed (N) by use of a motor output characteristic of the electric motor (13). Then, the electric motor (13) is driven and controlled based on a current command value (Iref_Lim) that has been limited with the current command value (I_Lim).