Hybrid cars: Parallel hybrid drive

2. Types of hybrid drives

2.2. Parallel hybrid drive

1 – ICE

2 – Fuel tank

3 – Electric machine

4 – Coupling

5 – Power inverter

6 – Battery

Parallel connection of acceleration force sources.
The internal combustion engine (ICE) (1) is mechanically coupled to the axle.
Each of the drives, i.e. the internal combustion engine (ICE) (1) and the electric motor (2), can drive the axle independently.
Alternatively, both motors can drive the vehicle at the same time → the sum of the powers allows to minimize the individual machines (i.e. ICE and electric motor).
Many possibilities of parallel connection implementation (on separate axle, on shaft (according to location P0-P4), with planetary gearbox, etc.).
The electric machine (3) is working

as a motor when powered by a traction battery (6),
as a generator when recharging the traction battery (6),
alternatively as ICE starter.

Drive mode

$P_k = P_6 + P_1 = U_6 I_6 + M_1 ω_1 = (M_1 + M_3) ω_1$ , alternatively $M_1 ω_1+M_3 ω_3$
$P_1 = 0$ , $P_k = M_3 ω_3 = P_6 = U_6 I_6$
$P_6 = 0$ , $P_k = M_1 ω_1 = P_1$

Brake mode

$-P_k = (-M_1 -M_3)ω_1 = -P_6 -P_1 = U_6 (-I_6) -M_1 ω_1$ , alternatively $-M_1 ω_1-M_3 ω_3$
$P_1 = 0$ , $-P_k = -M_3 ω_3 = -P_6 = U_6(-I_6)$
$P_6 = 0$ , $P_3 = 0$ , $P_k = -M_1 ω_1 = -P_1$

Drive mode and charging

$P_k = P_1 -P_6 = (M_1-M_3)ω_1 = M_1 ω_1 - U_6 I_6$ , alternatively $M_1 ω_1-M_3 ω_3$

ICE cannot be operated only at the optimal efficiency point.
There is an ICE-axle connection → fewer losses than with a series hybrid drive.

Applications

Wide use in a variety of vehicles, including hybrid passenger cars (mild hybrid, full hybrid, plug-in hybrid).

The electric drive increases the efficiency of the drive with ICE, especially when accelerating and braking using recuperation (suitable for urban traffic).
When driving over very long distances, the battery gradually discharges and the drive is provided only by ICE → loss of electric motor power (3).

_{Bosch Automotive Electrics and Automotive Electronics: System
Components, Networking and Hybrid Drive, Robert Bosch GmbH, Springer
2007, ISBN 978-3-658-01783-5}