Hybrid Vehicle Downshift Management via Pre-staged Clutch Control
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Solution Overview
Problem
Hybrid-electric vehicles face challenges in managing downshifts due to limited torque output capacity from the electric motor, leading to delayed engine startup and perceived poor drivability, known as 'torque holes', when transitioning between operating modes.
Innovation Solution
A system with a multispeed transmission and electronic control unit that pre-stages and interrupts downshift sequences by modifying hydraulic pressure to engage and disengage gear sets, using an internal combustion engine to supplement torque once sufficient capacity is achieved, minimizing the duration of 'torque holes'.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the electric motor is used to provide torque during downshift transitions, then the vehicle can maintain torque output, but the limited torque output capacity causes delayed engine startup and perceived poor drivability
Solution Approach 1:
The system pre-stages the downshift sequence by modifying hydraulic pressure to partially disengage the second shift clutch and partially engage the first shift clutch before the actual downshift is needed. This preliminary preparation allows the transmission to be ready for rapid completion of the downshift when torque demand increases, eliminating delays and improving perceived drivability without requiring the electric motor to compensate for power limitations
2Speed
If the downshift shift sequence is completed rapidly, then torque delivery is maintained, but the complex coordination of hydraulic pressure and clutch engagement requires sophisticated control
Solution Approach 1:
The downshift sequence is divided into distinct phases: a pre-staging phase where hydraulic pressure is modified to partially engage/disengage clutches, and a completion phase where the downshift is finalized. The electronic control unit coordinates these phases by controlling the valve body to modify hydraulic pressure at specific times, enabling rapid execution through structured temporal segmentation of the shift process
Solution Approach 2:
The valve body acts as an intermediary component that the electronic control unit uses to modify hydraulic pressure applied to the shift clutches. This intermediary mechanism allows the control unit to precisely regulate the engagement and disengagement of clutches during the downshift sequence, coordinating the complex interactions between hydraulic pressure, clutch engagement, and gear transitions
3Power
If the internal combustion engine is started to supplement torque, then sufficient power is available, but there is a delay before the engine can provide requested torque
Solution Approach 1:
The system starts the internal combustion engine in advance before the downshift is actually needed, during the pre-staging phase. This preliminary engine startup allows the engine to be ready to immediately supplement torque when the downshift completion is commanded, eliminating the delay between engine startup and torque delivery while ensuring sufficient power availability
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 approach reduces the perception of poor drivability by ensuring smoother transitions and minimizing delays in torque delivery during torque-demanding situations, enhancing the responsiveness of hybrid-electric vehicles.
Implementation Method 1
modifying the hydraulic pressure through the valve body to partially disengage the second shift clutch and partially engage the first shift clutch
Implementation Method 2
complete the downshift shift sequence by modifying the hydraulic pressure through the valve body to completely disengage the second gear set from the input shaft with the second shift clutch and completely engage the first gear set and the input shaft with the first shift clutch
Data Source
AI summary
Systems for managing downshifts in hybrid-electric vehicles are disclosed. The systems include a multispeed transmission, an internal combustion engine selectively coupled to the multispeed transmission, an electric motor coupled to the multispeed transmission, and an electronic control unit. The electronic control unit is programmed to evaluate a torque demand, start the internal combustion engine, and pre-stage a downshift shift sequence by partially disengaging a second shift clutch and partially engaging a first shift clutch. The electronic control unit is also programmed to interrupt the downshift shift sequence until a pre-determined torque supplemental event occurs and later complete the downshift shift sequence by modifying the hydraulic pressure through the valve body to completely disengage a second gear set from the input shaft with the second shift clutch and completely engage a first gear set and the input shaft with the first shift clutch.