Multi-Mode Powertrain Shift Control via Three Degrees of Freedom
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Solution Overview
Problem
Existing multi-mode powertrain systems face challenges in smoothly shifting between EVT modes while maintaining constant engine speed, leading to noticeable shifts and inefficiencies, particularly during transitions from EV drive mode to engine-on operation at moderate to high vehicle speeds.
Innovation Solution
A powertrain system with a multi-mode transmission that employs a control scheme allowing three degrees of freedom during transmission shifts, synchronizing the speed of the second torque machine and engine to achieve a preferred output speed, and activating the oncoming clutch to manage torque output, enabling smooth transitions between EVT modes without changing engine speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If synchronous activation of oncoming clutch is used to control transmission output torque during shift, then torque control is improved, but shift time becomes long and engine speed changes are noticeable to operator
Solution Approach 1:
The system preemptively transitions to the three degrees of freedom operating mode before the actual clutch engagement, allowing speed synchronization to occur in advance. This preliminary action enables the oncoming clutch to be activated more quickly without causing torque disruption, as the speed matching has already been accomplished during the transitional mode.
Solution Approach 2:
The system dynamically adjusts the operating mode from two degrees of freedom to three degrees of freedom during the shift process. This dynamic transition allows flexible control of multiple speed variables simultaneously, enabling both rapid clutch engagement and smooth engine speed management without the constraints of fixed operating modes.
2Productivity
If engine speed is changed during shift to synchronize transmission ratio, then shift execution is achieved, but vehicle operator perceives noticeable shifts
Solution Approach 1:
The system changes the operational parameters by introducing a third degree of freedom that decouples engine speed from transmission ratio synchronization. Instead of changing engine speed to achieve the desired transmission ratio, the system maintains engine speed and uses the additional speed variable to accomplish the ratio change, thereby eliminating perceptible shifts while maintaining productivity.
3Adaptability or versatility
If transition from EV drive mode to engine-on operation occurs at moderate to high vehicle speeds, then operational flexibility is improved, but shift smoothness deteriorates due to required maximum torque from first torque machine
Solution Approach 1:
The system segments the torque management function across three independent torque-generative devices (engine, first torque machine, second torque machine). This segmentation allows the torque requirements to be distributed and managed independently, enabling smooth transitions at high speeds by coordinating the contribution of each device rather than relying on a single torque machine to provide all required torque.
Solution Approach 2:
The system employs multiple torque-generative devices that can each independently provide torque to the transmission. This multi-functionality allows flexible distribution of torque demands during mode transitions, enabling smooth shifts by having multiple devices share the torque burden rather than requiring one device to handle the entire torque requirement alone.
Data Source
AI summary
A method for operating a powertrain system includes executing a transmission shift between an initial electrically-variable transmission (EVT) range and a target EVT range. The transmission shift includes transitioning to operating with three speed degrees of freedom including controlling speed of a second torque machine to synchronize speed of an oncoming clutch associated with the target EVT range and coincidentally controlling speeds of a first torque machine and an engine to achieve a preferred speed of the output member of the transmission. The transmission shift further includes controlling torque output from the first torque machine in response to an output torque request, and activating the oncoming clutch upon synchronizing the speed of the oncoming clutch. Subsequent to the transmission shift, the powertrain system is operated in the target EVT range.