Electric Power Steering Control Circuit Battery Failure
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Solution Overview
Problem
Electric power steering apparatuses face a sudden loss of steering assist force when the battery breaks down, leading to an abrupt increase in steering load due to the motor freely drawing power from an auxiliary power supply until it reaches its discharge limit, causing an unpleasant experience for the driver.
Innovation Solution
An electric power steering apparatus with a control circuit that detects battery breakdown and uses the auxiliary power supply to gradually decrease the upper limit of power supplied for steering assist over time, ensuring a smooth transition to zero power, thereby preventing sudden force loss and effectively utilizing stored energy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If the auxiliary power supply is used as backup power source and the motor freely draws power to the power discharge limit, then the steering assist function is maintained as long as possible, but the discharge ends suddenly when the auxiliary power supply reaches the power discharge limit, causing sudden loss of steering assist force
Solution Approach 1:
The patent applies dynamics by making the power supply limit adjustable rather than fixed. The control circuit dynamically adjusts the power supply limit based on the charging state of the auxiliary power supply, transitioning from a static discharge mode to a dynamic control mode that prevents sudden power cutoff while maximizing the use of stored energy.
Solution Approach 2:
The patent implements feedback control by continuously monitoring the charging state of the auxiliary power supply and adjusting the power supply limit accordingly. The control circuit receives feedback about the charge level and modifies the power output limits in real-time, creating a closed-loop control system that prevents sudden discharge termination.
2Power
If the auxiliary power supply is designed to supply stored energy to the motor, then the power discharge limit is reached, but the auxiliary power supply must also maintain the control source voltage, resulting in lower voltage limit and power discharge limit
Solution Approach 1:
The patent segments the power supply function into distinct control modes: a first power supply mode for normal operation with higher power limits, and a second power supply mode for backup operation with adjusted power limits. This segmentation allows the system to optimize power delivery while managing the dual requirements of maintaining control voltage and supplying motor power.
Solution Approach 2:
The patent changes the power supply parameters dynamically based on operating conditions. The control circuit adjusts the power supply limit parameter according to the charging state of the auxiliary power supply, transitioning between different parameter sets to balance the competing demands of control voltage maintenance and motor power delivery.
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 prevents sudden falls in steering assist force by gradually reducing power supply, ensuring a consistent driving experience even after battery failure, effectively utilizing the auxiliary power supply's energy to maintain assist until it is depleted.
Implementation Method 1
an auxiliary power supply (7, 8) connected in series with the battery (6) and adapted to supply electrical energy to the motor (4) in the event of a breakdown of the battery (6)
Implementation Method 2
an auxiliary power supply (7, 8) connected in series with the battery (6) and adapted to supply electrical energy to the motor (4)
Data Source
Figure 1
Figure 2
Figure 3(a)~3(b)
AI summary
An electric power steering apparatus 1 drives a motor 4 to generate a steering assist force according to a steering torque and includes an output circuit 21 for supplying the motor with electric power from at least one of a battery 4 and an auxiliary power supply 7, 8. The electric power steering apparatus has a control circuit 13 which at or after detection of a breakdown of the battery 4, determines a length of time to the end of steering assist (decreasing time t1) based on the amount of energy stored in the auxiliary power supplies 7, 8 and which takes the determined length of time to perform output decreasing control to gradually decrease the upper limit of power supplied for the steering assist to practically zero according to a constant gradient. Thus is provided an electric power steering apparatus which is adapted to prevent a sudden fall of the steering assist force in the event of a battery breakdown while effectively utilizing the available stored energy.