Power Steering Torque Limiter for Safety Control
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Solution Overview
Problem
Existing electromechanical motor vehicle power steering mechanisms lack a reliable method to limit assistance torque, potentially leading to unsafe operation due to uncontrolled motor torque generation.
Innovation Solution
A logical summer is used to restrict the relationship between input and assistance torque through a transfer function and safety limits, with a diagnostic unit enabling a fail-safe mode to prevent excessive torque, and a limiter ensuring the assistance torque stays within safe parameters, influenced by steering mechanism parameters like driver input torque and vehicle speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a boost curve is used to generate assistance torque based on driver input torque, then steering assist is provided, but the assistance torque may exceed safe limits causing unsafe operation
Solution Approach 1:
The patent applies preliminary anti-action by implementing a limiter that preemptively restricts the assistance torque to predetermined maximum values before excessive torque can be generated. The limiter compares the torque request against predefined limits and blocks any torque exceeding these safety thresholds, preventing unsafe operation before it can occur.
Solution Approach 2:
The patent implements feedback through a diagnostic unit that continuously monitors the operational status of the power steering mechanism. When a malfunction is detected, the diagnostic unit triggers a fail-safe mode that modifies the boost curve or limits the assistance torque, providing real-time feedback control to maintain safe operation conditions.
2Reliability
If hardware limitations are used to impose a maximum torque limit, then safety is improved, but the system complexity and hardware requirements increase
Solution Approach 1:
The patent replaces mechanical/hardware-based torque limiting with an electronic control solution. The limiter is implemented as software logic within the motor controller that electronically restricts the torque request signal, eliminating the need for complex mechanical torque limiting mechanisms while achieving the same safety objective.
Solution Approach 2:
The patent changes the parameter control approach by modifying the torque request parameter through electronic limiting. Instead of physically constraining the motor torque capability, the system changes the commanded torque parameter by comparing it against predefined limits and adjusting it accordingly, achieving safety through parameter management rather than hardware constraints.
3Reliability
If an artificial torque limit is introduced into the boost curve, then safety is improved, but the steering assist performance deteriorates when the limit is reached
Solution Approach 1:
The patent applies dynamics by making the torque limit adaptive rather than static. The fail-safe mode dynamically modifies the boost curve based on diagnostic feedback, allowing the system to optimize steering assist performance under normal conditions while automatically activating torque limiting only when malfunctions are detected, thus balancing performance and safety dynamically.
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 solution effectively limits assistance torque within safe limits, ensuring safe operation by stabilizing the boost curve and activating a fail-safe mode in case of malfunction, thus preventing excessive motor torque and enhancing steering feel and safety.
Implementation Method 1
an electric motor for steering assist... The inverter feeds the motor with sinusoidal motor parameters (current, voltage, magnetic flux) according to a torque request for torque generation
Data Source
AI summary
An electromechanical motor vehicle power steering mechanism for assisting steering of a motor vehicle including an electric motor for steering assist and a torque sensor. The electric motor is configured to apply an assistance torque in response to an output signal from the torque sensor indicative of the input torque applied by a driver of the vehicle to a steering wheel, in which the relationship between the indicated input torque and the assistance torque applied by the motor is defined by a boost curve. A logical summer is used to restrict the relationship between the indicated input torque and the assistance torque within given safety limits.