Electric Power Steering Control for Failure-Mode Torque
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Solution Overview
Problem
Conventional electric power steering apparatuses fail to operate optimally when a power converter or winding set fails, as they cannot adjust assist torque based on vehicle speed during a failure, leading to noticeable changes in steering effort and potential overload of remaining components.
Innovation Solution
An electric power steering apparatus with a vehicle speed sensor, torque sensor, motor, reduction gear, and control section that includes power systems with failure detection and power supply stopping mechanisms, allowing for calculation and adjustment of assist current based on pre-defined maps to maintain optimal assist torque even when one power system fails, by setting appropriate current limit values and using maps that account for vehicle speed detection failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the current limit value of the remaining normal power converter is set to a half of the sum of the current limit values before failure, then the electric load of the normal power converter is prevented from becoming excessive, but the assist torque cannot be adjusted based on vehicle speed leading to noticeable changes in steering effort
Solution Approach 1:
The patent applies dynamics by making the current limit value adjustable based on vehicle speed. The control section dynamically changes the current limit value of the remaining normal power converter according to the detected vehicle speed, allowing the system to adapt between different operating conditions (low speed maneuverability vs. high speed stability) rather than using a fixed current limit
Solution Approach 2:
The patent changes the parameter (current limit value) based on another parameter (vehicle speed). By establishing a relationship between vehicle speed and current limit value, the system optimizes the current limit dynamically - using higher current limits at low speeds for better maneuverability and lower current limits at high speeds for stability, thereby maintaining steering effort consistency across different operating conditions
2Device complexity
If conventional electric power steering apparatuses cannot adjust assist torque based on vehicle speed during failure, then the system structure remains simple, but the maneuverability at low speeds and stability at high speeds are compromised
Solution Approach 1:
The control section dynamically adjusts the current limit value based on detected vehicle speed, enabling the system to maintain optimal performance across different speed conditions. This dynamic adjustment mechanism adds complexity but ensures reliable maneuverability at low speeds and stability at high speeds during failure conditions
Solution Approach 2:
The control section serves multiple functions: it detects vehicle speed, determines the appropriate current limit value based on speed, and controls the power converter accordingly. This multi-functional approach integrates speed-responsive control into the failure mode operation, maintaining both maneuverability and stability without requiring separate dedicated systems
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
Enables the provision of necessary assist torque during power converter or winding set failures, preventing excessive load on remaining components and ensuring good maneuverability at low speeds and stability at high speeds, while minimizing heat generation and maintaining system stability.
Implementation Method 1
a motor (80) having a plurality of wiring sets and generating an output torque when supplied with electric power
Implementation Method 2
a reduction gear (89) for reducing a rotational speed of the motor to amplify the output torque of the motor
Data Source
AI summary
The electric power steering apparatus has a plurality of power systems each including an inverter apparatus provided corresponding to a plurality of wiring sets of a motor thereof. The control section calculates the assist current to be supplied to the motor using a one power system failure-state map when the inverter apparatus or its corresponding wiring set of one of the power systems fails, or using a vehicle speed detection failure-state map when there is a failure in detecting the vehicle speed. The assist current limit value in the one power system failure-state map and the assist current limit value in the vehicle speed detection failure-state map are set to the same value.