Parallel Hybrid Transmissions with P2 topology
A P2 parallel hybrid is obtained typically as an add-on to a powershift transmission, an AT or a DCT. This extended layout enables that the electric motor can drive the wheels through all gears of the gearbox, and just like the power path from the internal combustion engine, the electric power path is also uninterrupted during gearshifts.
P2 Hybrid Automatic Transmissions (AT)
The P2 hybridization of an AT can be realized with or without the hydrodynamic torque converter.
The P2 hybridization of an AT can be realized with or without the hydrodynamic torque converter.
Typically for MHEVs with low power electric motors, the hydrodynamic torque converter is kept as starting element and the electric motor with the separating C0 clutch is added between the engine and the torque converter.
Depending on the state of the C0 clutch and the converter lock-up clutch, the hybrid part can realize many operating modes, shown in the figures:
- only the internal combustion engine is driving (either through the torque converter or directly)
- only the electric motor is driving (either through the torque converter or directly)
- the electric motor recuperates during braking
- the engine and the electric motor are both driving (either through the torque converter or directly)
- the engine is driving and charging the battery at the same time (either through the torque converter or directly)
- the engine is charging the battery at vehicle standstill
If the torque of the electric motor is high enough, typically for FHEVs or PHEVs, the torque multiplication of the hydrodynamic torque converter is not needed any more. The torque converter is omitted and its installation space is fully utilized for the electric motor.
The electric functions are equivalent to those of the layout with a torque converter.
Nevertheless, the torque converter is used in an Automatic Transmission (AT) also as the starting clutch, enabling the vehicle to start-off with the internal combustion engine. Since this function is still needed, when the torque converter is omitted, the start-off clutch is realized by an other component, the so-called integrated start-off element. This is indeed not an additional component, rather a new function for one of the existing transmission brakes. The brake used as start-off element is not just engaged or disengaged according to the gearshifts, but has a slipping phase during start-off, just like an MT clutch.
In neutral gear, the transmission actuators are set according to the 1st gear, except for the brake used as start-off element, which is open. During vehicle start-off, the start-off element is smoothly engaged, taking the transmission from neutral to the 1st gear. The slipping phase is different from the clutch slipping of an MT/AMT or DCT in the sense that the slipping does not synchronize the gearbox input speed to the engine speed, but the gearbox output speed to the respective portion of the gearbox input speed.
The figures show one particular way to realize the integrated start-off element.
P2 Hybrid Dual Clutch Transmissions (DCT)
The P2 hybridization of a DCT results in triple-clutch unit: the base dual-clutch unit is extended with the C0 clutch to separate the internal combustion engine from the gearbox.
The additional elements – the electric motor and the C1 clutch – are located between the engine and the dual clutch unit, so that the electric motor is permanently connected to the input of the dual clutch unit.
Depending on the state of the C0 clutch and the dual clutch unit, the hybrid part can realize many operating modes, shown in the figures:
- only the internal combustion engine is driving (in either odd or even gears)
- only the electric motor is driving (in either odd or even gears)
- the electric motor recuperates during braking (in either odd or even gears)
- the engine and the electric motor are both driving (in either odd or even gears)
- the engine is driving and charging the battery at the same time (in either odd or even gears)
- the engine is charging the battery at vehicle standstill
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