Electric Power Steering Motor Temperature Estimation
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Solution Overview
Problem
Conventional electric power steering systems face issues with accurate overheat protection control due to deviations in temperature estimation when the power is turned off and on repeatedly, leading to potential motor overheating and malfunction.
Innovation Solution
The system employs a power self-holding mechanism that continues temperature estimation and control even after the ignition switch is turned off, using a temperature estimation status storage means to store completion flags or temperature stages, allowing for accurate initial value setting when the system is turned back on, ensuring safe overheat protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If power is turned off completely when ignition switch is turned off, then energy consumption is reduced, but temperature estimation accuracy deteriorates due to loss of estimation data
Solution Approach 1:
The system performs preliminary actions by storing temperature estimation completion flags and temperature stage data in storage section 403 before power is completely turned off. This allows the temperature estimation process to be resumed accurately when power is restored, without needing to restart from scratch, thus maintaining estimation accuracy while allowing power to be fully disconnected for energy savings.
Solution Approach 2:
The system creates a copy of the temperature estimation status (completion flags and temperature stages) in storage section 403. This copied data represents the state of temperature estimation at the time of power shutdown, allowing the estimation to be continued or resumed without loss of accuracy when power is restored, effectively decoupling the estimation state from the power supply state.
2Measurement precision
If temperature estimation is continued after power is turned off using power self-holding means, then temperature control accuracy is improved, but energy consumption increases
Solution Approach 1:
The system uses periodic action by implementing power self-holding that activates only during specific periods when temperature estimation is needed. The power self-holding means 402 maintains power to the control unit intermittently during the cooling period after motor operation, rather than continuously, allowing temperature estimation to continue with minimal energy consumption until the estimation is complete or the cooling period expires.
3Duration of action of stationary object
If power self-holding means is used to maintain power after ignition off, then temperature estimation continuity is improved, but device complexity increases
Solution Approach 1:
The system merges the power self-holding function with the existing control unit 401 and storage section 403. The power self-holding means 402 is integrated into the control unit's power management system, sharing hardware resources and control logic. This combining approach extends temperature estimation continuity without adding completely separate systems, thereby limiting the increase in device complexity.
Data Source
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Figure 3A
AI summary
An electric power steering apparatus comprises a motor (20) for providing a steering mechanism with steering assist force and a control unit (40) for controlling the drive current of said motor (20), said electric power steering apparatus comprises said control unit (40): a power self-holding means which can control own power off after power is once turned on by an IG switch (42); a temperature estimation means for estimating a temperature of said motor (20) and performing a temperature control by an estimated temperature; a temperature estimation status storage means, in a case that a temperature estimation processing continues by said power self-holding means, for storing predetermined data indicating a status of said temperature estimation processing in a storage section within said control unit (40) before said temperature estimation means stop; and an initial value setting means, when said IG switch (42) is turned ON again and said temperature estimation means is activated, for setting an initial value of said estimated temperature based on said predetermined data indicating said status of said temperature estimation processing and a predetermined motor temperature estimation offset value. Said temperature estimation status storage means is a temperature stage storage means for storing a temperature stage (ST) to which said estimated temperature belongs in said storage section until said temperature stage (ST) reaches a predetermined stage when said IG switch (42) is turned OFF or a steering assist by said motor (20) ends, and said temperature estimation processing continues by said power self-holing means, and said initial value setting means reads out said motor temperature estimation offset value out of plural preset data and sets the initial value of said estimated temperature based on said temperature stage (ST) when said IG switch (42) is turned ON again and said temperature estimation means is activated.