Electric Power Steering Controller Current Recovery
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Solution Overview
Problem
Existing electric power steering devices with redundant inverter circuits face issues of current imbalance during recovery from failures, leading to heat generation imbalances, reduced assist performance, and degraded steering feeling due to unbalanced electromagnetic forces and ripple cancellation.
Innovation Solution
An electric power steering device with two independent inverter circuits and a controller that adjusts target current values for cooperative control after failure recovery, ensuring the sum of currents from both circuits falls within an acceptable range, thereby improving steering feeling and thermal balance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If the target current of the recovering control system is simply gradually increased, then the control continuity is maintained, but the current imbalance between the two inverters continues for a long period, causing heat generation imbalance and reduced assist performance
Solution Approach 1:
The patent dynamically adjusts the target current values of both inverters based on their operational status. When one inverter recovers from failure, its target current is initially set to a smaller value than the final target current, while the other inverter's target current is adjusted accordingly. This parameter change strategy ensures current balance is maintained during the transition period, preventing heat generation imbalance while maintaining control continuity.
Solution Approach 2:
The control system transitions from a static current allocation approach to a dynamic one. The target current values are not fixed but are continuously adjusted based on the operational state of each inverter. This dynamic adjustment allows the system to adapt to changing conditions during recovery, ensuring current balance is maintained throughout the transition from single-inverter to dual-inverter operation.
2Productivity
If the target current of the recovering control system is simply gradually increased, then the control recovery is achieved, but the electromagnetic exciting forces become unbalanced, degrading steering feeling and increasing torque ripple
Solution Approach 1:
The patent implements a two-stage current adjustment strategy. In the first stage, when the recovering inverter is reactivated, its target current is set to a smaller value to maintain balance with the other inverter. In the second stage, after balance is established, the target currents are gradually adjusted to their final values. This parameter change approach ensures smooth control recovery without causing electromagnetic force imbalance that would degrade steering feeling or increase torque ripple.
3Reliability
If one control system recovers from failure while another continues normal control, then system redundancy is utilized, but current imbalance occurs between the two inverters with phase difference, preventing ripple cancellation
Solution Approach 1:
The patent adjusts the target current parameters of both inverters to maintain proper balance during the recovery transition. By setting the recovering inverter's target current to a smaller value initially and coordinating it with the other inverter's current, the system maintains the phase difference relationship necessary for ripple cancellation while avoiding current imbalance that would prevent effective cancellation.
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
The solution enables smooth recovery and cooperative control of electric power steering devices, reducing torque ripple and noise, and maintaining assist performance by balancing currents and electromagnetic forces.
Implementation Method 1
a motor (2), which includes a stator (21) including at least two independent coil winding groups (22, 23)
Data Source
AI summary
In an electric power steering device including a controller, which is configured to carry out feedback control for a motor including independent two coil winding groups and being configured to rotate a steering mechanism of a vehicle, when one of the two groups recovers from a failure that has occurred in the one group while control is continued solely by another group due to the failure, the controller resumes cooperative control by the two groups, and when starting the cooperative control, sets target current values of the one group and the another group to values different from a final target current value based on an actual current value or a target current value of the another group at a time of the recovery, to thereby output respective control amounts for the cooperative control.