Electric Vehicle Transmission Downshift Control
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Solution Overview
Problem
The synchromesh type of shifting mechanism in electric vehicle transmissions experiences torque interruption during gear shifting, leading to instability and reduced shifting quality.
Innovation Solution
A method that secures spare torque, generates friction force through a servo clutch, shifts to neutral gear, synchronizes motor speed with the lower gear step, engages the synchronizer, and disengages the servo clutch to prevent torque interruption and improve shifting accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a synchromesh type of shifting mechanism is used to simplify transmission configuration, then device complexity is reduced, but torque interruption occurs during shifting leading to reduced reliability
Solution Approach 1:
The system performs preliminary actions by securing spare torque before shifting begins, and by pre-synchronizing the motor speed with the target gear speed using the secured spare torque. This preliminary preparation ensures that when the actual shifting occurs, the motor is already ready to immediately resume power transmission without interruption, thus maintaining reliability while using a simple synchromesh mechanism.
Solution Approach 2:
The control system acts as an intermediary by introducing a neutral gear state as an intermediate step in the shifting process. The sequence shifts from current gear → neutral → target gear, allowing the synchronizer to disengage and re-engage without direct torque transmission conflicts. This intermediary neutral state resolves the contradiction by enabling smooth transitions in the simple synchromesh mechanism.
2Productivity
If quick shifting is implemented to improve productivity, then shifting time is reduced, but shifting accuracy may be compromised
Solution Approach 1:
The control system continuously monitors motor speed and compares it with the target speed for the desired gear step. Based on this feedback, the controller adjusts the motor torque and controls the synchronizer engagement timing precisely. This feedback mechanism ensures that even during quick shifting, the motor speed is accurately synchronized with the target gear speed, maintaining shifting accuracy while achieving fast transition.
Solution Approach 2:
The system performs preliminary speed synchronization by controlling the motor speed to match the target gear speed before the actual gear engagement occurs. This preliminary action ensures that when the synchronizer engages, the speeds are already matched, enabling both quick shifting and high accuracy without compromise.
3Reliability
If motor torque is reduced to secure spare torque for synchronization, then shifting reliability is improved, but available power during shifting is reduced
Solution Approach 1:
The system employs periodic action by temporarily reducing motor torque only during the brief shifting interval, while maintaining full power output before and after the shift. The control system manages the torque reduction in a time-dependent manner, securing spare torque precisely when needed for synchronization, then immediately restoring full torque once the gear engagement is complete. This periodic torque management ensures shifting reliability without significant impact on overall power availability.
Solution Approach 2:
The system performs preliminary torque management by securing spare torque before the shifting event begins. This preliminary preparation ensures that when shifting occurs, the motor has reserved torque capacity to control the synchronization process smoothly. The spare torque is temporarily utilized only during the shifting interval, then full power is restored, minimizing the impact on overall power availability while ensuring reliable shifting.
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
This method enables stable and reliable downshift control, enhancing shifting quality by allowing quick and accurate gear transitions without torque interruption, thereby improving the commercial value of electric vehicles.
Implementation Method 1
a slip-controlling step of generating a friction force through a servo clutch provided for applying a friction force between an input shaft and a servo driving gear
Data Source
AI summary
A method of controlling an electric vehicle transmission includes: a torque-securing step of securing a predetermined spare torque to be generated by a motor in accordance with a current motor torque when a controller determines that there is a need for downshift from an upper gear step to a lower gear step; a slip-controlling step of generating a friction force through a servo clutch applying a friction force between an input shaft and a servo driving gear of a pair of servo gears; a shifting-to-neutral step of shifting to a neutral gear by disengaging a synchronizer for the upper gear step; a motor-synchronizing step of synchronizing a rotational speed of the motor with a desired speed of a lower gear step using the spare torque of the motor secured in the torque-securing step; a gear-engaging step of engaging a synchronizer for the lower gear step; and a clutch-disengaging step of finishing shifting by disengaging the servo clutch.