Hybrid Transmission Disconnect Shift Synchronization
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Solution Overview
Problem
Conventional power split hybrid transmissions experience rough shifts due to unsynchronous powertrain disconnect devices, which can block low range gear engagement and limit maximum vehicle speed during gear changes, especially when the vehicle is at standstill or moving.
Innovation Solution
A controller and algorithm that control the speed of the transmission output shaft by coordinating the internal combustion engine and electric motors to ensure smooth shifts by synchronizing the disconnect element, even when the powertrain is disconnected from the wheels, using a high voltage battery system to power the electric motors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If unsynchronous shifting method is used for powertrain disconnect devices, then device complexity is reduced, but shift smoothness deteriorates and low range gear engagement is blocked
Solution Approach 1:
The system changes the control parameter from simple disconnect/engage commands to coordinated torque control. The controller calculates specific torque values for the electric motor and internal combustion engine based on vehicle speed, gear state, and powertrain load, enabling synchronized shifting by precisely controlling the rotational speeds of the disconnect element and transfer case during gear changes.
Solution Approach 2:
The system implements closed-loop feedback control by continuously monitoring vehicle speed, gear state, and powertrain operating conditions. The controller uses this feedback to dynamically adjust torque distribution between the electric motor and internal combustion engine, ensuring the disconnect element and transfer case rotate at matched speeds during shifting operations, thereby achieving smooth synchronized shifts.
2Ease of operation
If synchronized shifting is implemented, then shift smoothness is improved, but device complexity and control complexity increase
Solution Approach 1:
The electric motor serves as an intermediary device between the internal combustion engine and the disconnect element. By introducing this additional actuator, the system can independently control the rotational speed of the disconnect element to match the transfer case speed during shifts, achieving synchronized shifting without requiring direct mechanical coupling or complex mechanical synchronization mechanisms.
Solution Approach 2:
The system performs preliminary speed matching before the actual gear engagement. The controller calculates target rotational speeds for both the disconnect element and transfer case based on the desired gear ratio change, and uses the electric motor to pre-synchronize their speeds before commanding the disconnect element to engage, ensuring smooth shifting without shock or blockage.
3Loss of energy
If powertrain disconnect is maintained during gear shifts, then energy efficiency is improved, but shift synchronization becomes impossible
Solution Approach 1:
The system dynamically adjusts the powertrain connection state during shifting operations. Rather than maintaining a fixed disconnect or connected state, the controller temporarily re-engages the powertrain through the electric motor to enable synchronized shifting, then returns to the efficient disconnected state after the shift is complete. This dynamic transition allows the system to achieve both energy efficiency and shift synchronization.
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
Enables smooth and synchronized gear shifts, allowing engagement of low range gears at higher vehicle speeds and eliminating perceivable bumps, thereby improving the driving experience.
Implementation Method 1
The first electric motor is rotatably coupled to a sun gear of the planetary gear set and provides a first rotatable input to a transmission output shaft. The second electric motor is rotatably coupled to a counter gear that provides a second rotatable input to the transmission output shaft.
Implementation Method 2
The ICE drives an output shaft that is rotatably coupled to a planetary carrier of a planetary gear set.
Implementation Method 3
The first and second electric motors are charged by a high voltage battery system.
Data Source
AI summary
A power split hybrid transmission for a vehicle includes an internal combustion engine (ICE), a first electric motor, a second electric motor, a disconnect element and a controller. The ICE drives an output shaft that is rotatably coupled to a planetary carrier of a planetary gear set. The first electric motor is rotatably coupled to a sun gear of the planetary gear set and provides a first rotatable input to a transmission output shaft. The second electric motor is rotatably coupled to a counter gear that provides a second rotatable input to the transmission output shaft. The disconnect element selectively disconnects rotatable motion from the transmission output shaft to drive wheels. The controller determines whether the ICE, the first electric motor and the second electric motor are disconnected from the drive wheels and commands torque to the first and second electric motors to cooperatively rotate the transmission output shaft.