EV Four-Wheel Drive Torque Control During Disconnector Engagement
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Solution Overview
Problem
The existing systems for electric vehicles struggle with slow engagement of the four-wheel drive mode due to the time required to synchronize the speeds of subsidiary drive wheels, leading to a sense of lag and inconsistency in acceleration, as the disconnector takes around 400-500 ms to engage and synchronization time increases with vehicle speed.
Innovation Solution
A system and method that temporarily release the output limits of both the first and second motors when a driver requested torque exceeds a reference torque, allowing the main drive wheels to operate at maximum torque before the disconnector is engaged, thereby accelerating the engagement process and minimizing lag and acceleration inconsistency by synchronizing subsidiary drive wheels faster.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the disconnector is engaged to drive the subsidiary drive wheels, then four-wheel drive is achieved, but the engagement time is long (400-500 ms) causing lag and acceleration inconsistency
Solution Approach 1:
The system performs preliminary action by temporarily releasing the output limit of the first motor before the disconnector is engaged, allowing the main drive wheels to generate maximum torque in advance. This prepares the drive system for immediate four-wheel drive operation, reducing the perceived lag during the 400-500ms engagement period.
Solution Approach 2:
The controller changes the output parameter of the first motor from a limited state to a maximum torque state by temporarily releasing the output limit. This parameter change allows the main drive wheels to operate at peak performance during the transition period, compensating for the time delay in disconnector engagement.
2Speed
If the output limit of the first motor is increased to maximum torque before disconnector engagement, then acceleration responsiveness is improved, but the motor may exceed its set output limit
Solution Approach 1:
The system applies periodic action by temporarily releasing the output limit for a designated short time period only during the transition phase before disconnector engagement. After the disconnector is engaged and the second motor begins contributing torque, the output limit of the first motor is restored to its original setting, creating a controlled temporary boost rather than a sustained overload.
Solution Approach 2:
The controller dynamically adjusts the output limit parameter of the first motor based on the engagement state of the disconnector. The output limit is temporarily increased only during the specific window before engagement, then dynamically restored afterward, allowing the system to adapt its performance characteristics to the current operational phase.
3Power
If the torque of the second motor is increased rapidly after disconnector engagement, then four-wheel drive torque is achieved faster, but torque inconsistency may occur during the transition
Solution Approach 1:
The controller uses feedback by continuously monitoring the torque output of the second motor and adjusting its increase rate accordingly. The torque is increased at a predetermined slope that ensures it reaches the target level without causing abrupt changes, maintaining smooth transition and torque consistency throughout the engagement process.
Solution Approach 2:
The torque output of the second motor is dynamically adjusted at a controlled rate rather than being instantly maximized. This dynamic approach allows the torque to evolve smoothly from zero to the target level, preventing sudden jumps that would cause inconsistency while still achieving four-wheel drive power efficiently.
Data Source
AI summary
A system and method for controlling switching of an electric vehicle to four-wheel drive are provided. The system includes a first motor connected to main drive wheels and configured to output a first torque, a second motor connected to subsidiary drive wheels and configured to output a second torque, a disconnector mounted on an axle shaft for the subsidiary drive wheels, a driver requested torque detector configured to detect a driver requested torque, and a controller configured to release a set output limit of the first motor for a designated time and simultaneously release a set output limit of the second motor when the driver requested torque is greater than or equal to a reference requested torque, and control the first motor to output a maximum torque exceeding the set output limit to the main drive wheels until the disconnector is engaged.