Hybrid cars

1. Introduction

Hybrid cars

Cars with more than one source of acceleration.
Currently, the term HEV (Hybrid Electric Vehicle) is used for a solution that combines an internal combustion engine (ICE) with one or more electric motors as a source of accelerating force.
Energy storage devices are a fuel tank and an electric battery.
Two basic HEV structures:

serial,
parallel.

2. Types of hybrid drives

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

2.1. Serial hybrid drive

1 – ICE

2 – fuel tank

3 – electric machine (generator)

4 – electric machine (motor)

5 – power inverter

6 – battery

Serial connection of acceleration force sources.
The series arrangement consists of an internal combustion engine (ICE) and a pair of electrical machines.
The internal combustion engine (ICE) is not mechanically coupled to the axle.
The electric machine (3) works as a generator.
All power flow to the axle is realized through an electric machine (4).
The electric machine (4) is working

as a motor in drive mode, energy is taken from the traction battery and ICE,
as a generator during braking, the traction battery is charged,
as ICE starter.

Drive mode

Brake mode

ICE can be operated at the optimal efficiency point:

$P_1 = M_1 ω_1$ = konst. = $argmax⁡[(η_1 = f(M_1, ω_1)]$ .

ICE is not mechanically coupled to the axle → many installation options in the car.
Low power transfer efficiency from ICE to wheel (large number of conversions).

Example

Maximum efficiency $η_{max} = \max(η_1 η_3 η_5 η_4 ) = 0,35\cdot0,96\cdot0,98\cdot0,96 = 0,32$

Applications

Buses in city traffic, ie. stop & go driving style on a known route.
Range extenders - practically BEV, emergency driving after discharging the battery.

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

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}

2.3. Split-power hybrid drive

1 – ICE

2 – fuel tank

3 – planetary gear

4 – electric machine (motor)

5 – power inverter

6 – battery

7 – electric machine (generator)

It combines both configurations, serial and parallel.
1x ICE (1), 2x electric machine (4) and (7)
The variant in Fig. 3 shows the connection by means of a planetary gear (3).
The variant in Fig. 3 with a planetary gearbox and a 2nd electric machine (7) makes it possible to realize a continuously variable transmission between the axle and the ICE (1), similarly to CVT gearboxes.
There are a number of modes, e.g.

the internal combustion engine (ICE) (1) can drive the vehicle independently, as well as a purely electric drive,
part of the power of the internal combustion engine can drive the axle and the rest can recharge the battery at the same time.

There system disposes by several degrees of freedom, requiring sophisticated management strategies to optimize efficiency.

Split-power hybrid drive with planetary gearbox without clutch

Toyota Hybrid System

Opel Ampera/Chevrolet Volt - drive with multiple clutches

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

https://www.youtube.com

https://www.chevrolet.com}

3. Degrees of vehicle electrification

_{Doppelbauer, M.: Antriebstechnik für die E-Mobilität, Springer 2012}

3.1. Micro hybrid

Start & stop + ESM (Energy Smart Management)
Turns off ICE when standing
Uses a 12 V battery (usually Pb)
Reduce fuel consumption with ESM

The 12 V battery supplies the car's consumption even when the engine is running, the alternator is unloaded => reduction of fuel consumption.
The 12 V battery is recharged when

braking,
in the area of maximum ICE efficiency.

The electric machine does not contribute to the driving torque.

3.2. Mild hybrid (MHEV)

ICE is the dominant drive
Electric drive powered by 48 V battery (Li or Ni-MH technology)

Battery 48 V (Li), DC-DC converter, battery 12 V (Pb)

Electric motor: power usually max. 15 - 20 kW

It is auxiliary system, it increases power and torque of the whole drive.
It helps compensate problematic areas of the ICE efficiency map.
It compensates torque generation delays from ICE.

It does not allow a purely electric driving.
Recuperation

MHEV Honda IMA

Ford Puma

Hyundai Tucson

Hyundai Tucson

Battery Lion 48 V, 0,44 kWh
On-board battery 12 V, charging via DC/DC converter
Electric motor P = 12 kW, M = 55 Nm

_{https://www.ford.com

https://www.honda.com

https://www.hyundai.com}

3.3. MHEV types according to location of electric motor

P0 - Electric machine is connected to ICE only via a V-belt

Electric machine of 12 V replaced by machine of 48 V
ICE torque boost, recuperation, start & stop
Cannot be mechanically separated from ICE.
Electric driving is not possible.
E.g. Audi A8 48V MHEV, mainstream technology, great benefit (CO₂ / km) at low integration costs

P1 - Electric machine on ICE's output (couplted to crankshaft)

ICE torque boost, recuperation, start & stop
Higher power and torque than P0 (not limited by belt slip torque)
Cannot be mechanically separated from ICE, same speed.
Higher integration costs, problematic cooling, narrow installation space
E.g. 2009 Honda Insight

P2 - Electric machine on input of gearbox

Electric machine mechanically separated from ICE (clutch)
Electric machine of same speed as ICE (or higher)
Increased recuperation possibilities
Possibility of purely electric driving (P2, P3, P4), do not allow start & stop

P3 - Electric machine on output of gearbox

Electric machine mechanically separated from ICE
The speed is a multiple of the wheel speed.
Higher recuperation efficiency (P3 and P4)

P4 - Electric machine is coupled to axle or placed on the wheel

Electric machine mechanically separated from ICE
Possibility of independent wheel drive
Axle split hybrid topology option (ICE front axle, rear electric motor)

3.4. Full hybrid (FHEV)

Batteries of relatively high capacity (Lithium or Ni-MH)

Several kWh or several tens of kWh

Voltage: several hundreds of Volts
Traction battery 200 - 400 V (Li), DC-DC converter, battery 12 V (Pb)
Electric motor power: several tens of kW

Increases power and torque of the whole drive.
Helps cover problematic areas of the ICE efficiency map.
Covers torque generation delays from ICE.

Purely electric driving

Driving range: several km or several tens of km

Recuperation

The battery is not being charged from an external power supply.

Toyota Prius 2. generation (FHEV)

_{https://global.toyota.com}

3.5. Plug-in hybrid (PHEV)

High capacity of the battery (Lithium or Ni-MH)

Several kWh or several tens of kWh

Voltage: several hundreds of Volts

Traction battery of 200 - 400 V (Li), DC-DC converter, on-board battery of 12 V (Pb)

Electric machine power: several tens or several hundrets of kW

It drives the vehicle independently.
Increases power and torque.
Helps cover problematic areas of the ICE efficiency map.
Covers torque generation delays from ICE.

Purely electric driving

Driving range: several tens of km

Recuperation
Battery recharging by

external power supply (dominant)
recuperation

Škoda Superb iv (PHEV)

Škoda Superb iv (PHEV)

ICE: 1395 ccm, 115 kW, 250 Nm
E-motor: PMSM, 85 kW, 330 Nm
Traction battery: 13 kWh

_{https://www.skoda-auto.cz}

3.6. Range extender (REEV)

Similar to pure electric vehicles (BEV)

The electric motor is the main drive, power of several tens or hundreds of kW
Traction batteries of several tens of kWh, driving range of hundreds of km
Charging from an external power supply (dominant) and by recuperation

ICE for emergency use only

Low power
Driving at limited speed

Often a serial hybrid

Audi A1 e-tron

Audi A1 e-tron

ICE: Wankel, 254 ccm
E-motor: 45 (75) kW
Trakční baterie: 380 V, 12 kWh

BMW i3 range extender

BMW i3 range extender

ICE: 650 ccm, 25 kW
E-motor: PMSM, 125 - 137 kW
Trakční baterie: 18 - 38 kWh

_{https://www.bmw.com

https://www.autorevue.cz}

3.7. Battery electric vehicle

Traction battery of high capacity (dominant Lithium technology)

Several tens of kWh
Voltage: hundreds of V

Typically 400 V (Li), DC-DC converter, 12 V battery (Pb)

Electric motor power: several tens (several hundreds) of kW

The only drive of the vehicle
Purely electric driving only

Driving range of several hundreds of km
Recuperation
Battery charging

from external power supply (dominant)
by recuperation

VW E-Golf (BEV)

VW E-Golf (BEV)

E-motor: PMSM, 100 kW, 290 Nm
Traction battery: 35,8 kWh

_{https://www.volkswagen.de}

Website:	Moodle ZČU
Kurs:	KEV/EMB Elektromobilita - podklady k výuce
Buch:	Hybrid cars

Gedruckt von:	Nepřihlášený host
Datum:	Montag, 9. November 2026, 00:02

Beschreibung

Inhaltsverzeichnis

1. Introduction

2. Types of hybrid drives

2.1. Serial hybrid drive

2.2. Parallel hybrid drive

2.3. Split-power hybrid drive

3. Degrees of vehicle electrification

3.1. Micro hybrid

3.2. Mild hybrid (MHEV)

3.3. MHEV types according to location of electric motor

3.4. Full hybrid (FHEV)

3.5. Plug-in hybrid (PHEV)

3.6. Range extender (REEV)

3.7. Battery electric vehicle