Sensorless Vehicle Steering Motor Control via Current Limiting
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Solution Overview
Problem
Existing vehicle steering systems using brushless motors face challenges in sensorless control, particularly in applications like electric power steering, where the absence of a rotation angle sensor disrupts motor control, especially at low speeds or when the sensor fails.
Innovation Solution
A vehicle steering system that employs a control method using a current driving device, control angle computing device, vehicle speed detecting device, steering torque detecting device, and command current value limiting device to manage motor control without a rotation angle sensor, by calculating a control angle and limiting current values based on torque deviations and vehicle speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a rotation angle sensor is used for motor control, then motor control precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent removes the rotation angle sensor from the system and replaces it with a sensorless control mechanism. The control device estimates rotor position by detecting current values during motor startup and using back-EMF detection during operation, thereby eliminating the need for physical sensors while maintaining control functionality.
Solution Approach 2:
The motor system uses its own electrical characteristics (current consumption during startup, back-EMF during rotation) to determine rotor position and speed. The control device leverages the motor's inherent electromagnetic properties to self-diagnose and self-regulate without external sensing components.
2Device complexity
If sensorless drive method is used, then device complexity is reduced, but control reliability deteriorates at low speeds and during rotor stop
Solution Approach 1:
The control device performs preliminary rotor position estimation during motor startup before normal operation begins. By detecting current values in the startup phase and calculating initial rotor position, the system establishes accurate initial conditions that enable reliable sensorless control from the beginning of operation, including low-speed and stopped conditions.
Solution Approach 2:
The control device continuously monitors current values and uses feedback loops to estimate rotor position and speed. By comparing expected current patterns with actual measurements and adjusting control signals accordingly, the system maintains accurate control across all operating conditions without physical sensors.
3Speed
If command current value is not limited, then motor response speed is improved, but system stability deteriorates due to excessive current
Solution Approach 1:
The control device dynamically adjusts the high limit value of command current based on real-time operating conditions including vehicle speed and steering torque. The limiting mechanism is not fixed but adapts to changing system states, allowing maximum current during urgent maneuvers while preventing excessive current during normal operation, thereby maintaining both responsiveness and stability.
Data Source
AI summary
A current increase-decrease amount (ΔIγ*) computed by a command current increase-decrease amount computing unit is added to an immediately preceding value (Iγ*(n−1)) of a command current value (Iγ*) in an adder. The command current value (Iγ*) obtained by the adder is given to a high/low limit limiter. The high/low limit limiter limits the command current value (Iγ*), obtained by the adder, to a value between a low limit value (ξmin (ξmin≧0)) and a high limit value (ξmax (ξmax>ξmin)). A high limit value setting unit obtains the high limit value (ξmax) corresponding to the vehicle speed detected by the vehicle speed sensor, from a vehicle speed-vs.-high limit value map set by a map creating/updating unit, and sets the obtained high limit value (ξmax) in the high/low limit limiter.