Electric Motor Torque Control via Gearbox Temperature Estimation
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Solution Overview
Problem
In power steering systems, especially electrically operated ones, the steering feel changes with temperature due to the material properties of the gearbox and lubricant, leading to a heavier or stiffer steering experience at low temperatures, which existing methods fail to adequately address by solely adjusting the electric motor's assist torque.
Innovation Solution
A method that uses a temperature sensor to estimate the gearbox temperature, allowing for precise adjustment of the electric motor's torque based on the estimated gearbox temperature and load, without additional sensors, by considering the thermal characteristics and heat transfer between the drive device and gearbox, and adjusting the torque using a factor between 0.8 and 1.2 to compensate for temperature-induced friction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the assist torque is increased at low temperatures to counteract the stiffer steering feel, then the steering feel improves, but the torque adjustment is insufficient because it only considers drive device temperature and not gearbox temperature
Solution Approach 1:
The patent introduces an intermediary approach by using the drive device temperature as a proxy to estimate gearbox temperature through a thermal model, avoiding the need for a direct temperature sensor in the gearbox while still achieving accurate temperature-based torque adjustment
Solution Approach 2:
The patent replaces the mechanical/physical approach of direct temperature sensing with an electronic/software-based thermal model that calculates gearbox temperature based on drive device temperature and operating conditions, enabling precise torque compensation without additional hardware
2Ease of operation
If a temperature sensor is added to directly measure gearbox temperature for precise torque adjustment, then the steering feel control improves, but the device complexity and cost increase
Solution Approach 1:
The patent uses drive device temperature as an intermediary measurement point and employs a thermal model to infer gearbox temperature, eliminating the need for a dedicated gearbox temperature sensor while maintaining accurate temperature-based control
Solution Approach 2:
The system uses its existing temperature sensor and operating data to self-determine the gearbox temperature through thermal modeling, making the system self-sufficient without requiring additional sensing hardware
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 method ensures a consistent steering feel across varying temperatures by precisely compensating for temperature-induced friction, maintaining the steering assistance without influencing other parameters and without the need for additional sensors, thus improving driver experience.
Implementation Method 1
a temperature sensor senses the temperature of the drive device and transmits information about the temperature of the drive device to an evaluation unit
Implementation Method 2
the evaluation unit estimates the temperature of a gearbox based on the temperature of the drive device
Implementation Method 3
by considering the thermal characteristics and heat transfer between the drive device and gearbox
Implementation Method 4
based on the estimated temperature of the gearbox and the load of the gearbox as measured, the temperature-induced friction can be precisely estimated, so that the friction can be exactly compensated
Data Source
AI summary
A method of controlling an electric motor of a drive device of a power steering system, in which a temperature sensor senses the temperature of the drive device and transmits information about the temperature of the drive device to an evaluation unit, the evaluation unit estimates the temperature of a gearbox based on the temperature of the drive device, and, based on the estimated temperature of the gearbox, the evaluation unit adjusts a requested torque of the electric motor.