Electric Power Steering Hysteresis Control for Hunting Prevention
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Solution Overview
Problem
Existing electric power steering apparatuses experience control hunting due to slight fluctuations in electric power near threshold values when determining whether to use an auxiliary power supply, failing to meet the increased power demands of large vehicles.
Innovation Solution
An electric power steering apparatus with a charge-discharge circuit that selectively configures output modes based on required electric power, shifting between using only the main power supply and combining it with an auxiliary power supply, and employing hysteresis to prevent hunting by defining upward and downward threshold values for mode changes, along with PWM control for smooth transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single threshold value is used to determine whether to use the auxiliary power supply, then the control logic is simple, but control hunting occurs due to slight fluctuations in required electric power near the threshold
Solution Approach 1:
The patent applies parameter changes by introducing two different threshold values (first threshold and second threshold) instead of a single threshold. The first threshold is used for determining when to switch from main power supply only to combined power supply, and the second threshold is used for determining when to switch from combined power supply to main power supply only. This parameter differentiation eliminates control hunting by creating a hysteresis effect that prevents rapid switching near the threshold boundary.
2Power
If the auxiliary power supply is used to meet increased power demands of large vehicles, then the power supply capability is improved, but control hunting occurs causing unstable operation
Solution Approach 1:
The patent introduces two distinct threshold parameters (first threshold for upward switching, second threshold for downward switching) to control the auxiliary power supply activation. When required electric power exceeds the first threshold, the auxiliary power supply is activated. When required electric power falls below the second threshold, the auxiliary power supply is deactivated. This dual-threshold parameter strategy prevents control hunting while maintaining the improved power supply capability needed for large vehicles.
3Adaptability or versatility
If the output mode is frequently switched near the threshold value, then the system adapts to power demand changes, but torque variations and instability occur
Solution Approach 1:
The patent uses two different threshold values to create an adaptive switching control system. The first threshold (higher) triggers switching to combined power supply mode when power demand increases. The second threshold (lower) triggers switching back to main power supply only mode when power demand decreases. This parameter differentiation creates a dead zone between the two thresholds where no switching occurs, preventing frequent mode changes and torque variations while still allowing the system to adapt to significant power demand changes.
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
Prevents control hunting by stabilizing the output mode selection, ensuring consistent power supply to the motor and reducing torque variations, thus effectively addressing the power fluctuations and meeting the increased demands of large vehicles.
Implementation Method 1
power is supplied by a in-vehicle battery as a main power supply and also by a capacitor as an auxiliary power supply
Implementation Method 2
selects the second output mode when the electric power required for steering assist in the first output mode becomes equal to or higher than a first threshold value or selects the first output mode when the electric power required for steering assist in the second output mode becomes equal to or lower than a second threshold value that is lower than the first threshold value
Data Source
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AI summary
In an electric power steering apparatus including a charge-discharge circuit 16 that selectively configures a first output mode in which only a main power supply including a battery 9 is used to supply an electric power to a motor 4 or a second output mode in which the main power supply and an auxiliary power supply 14 are used to supply the electric power to the motor 4, and a control circuit 6 that selects the output mode of the charge-discharge circuit 16 according to the electric power required for steering assist, the control circuit 6 selects the second output mode when the electric power required for steering assist in the first output mode becomes equal to or higher than an upward threshold value P1 or selects the first output mode when the electric power required for steering assist in the second output mode becomes equal to or lower than a downward threshold value P2 that is lower than the upward threshold value P1.