the renewed 4-cylinder engine series for toyota hybrid ... · pdf filethe renewed 4-cylinder...

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Mr. Shouji ADACHI, Mr. Hikomasa HAGIHARA, TOYOTA MOTOR CORPORATION, AICHI JAPAN

The renewed 4-Cylinder Engine Series for Toyota Hybrid System

Die erneuerte 4-Zylindermotorengruppe für das Toyota Hybridsystem

Abstract Reducing CO2 and fuel consumption is one of the major challenges for car makers

nowadays. In 1997, Toyota introduced the world premiere Toyota Hybrid System (THS) as

one of the most effective solutions to improve powertrain efficiency. The THS technology

has been continuously improved to increase its efficiency while being expanded worldwide

as a global technology.

Recently, Toyota has renewed its 4-cylinder engine series for Hybrid Systems to increase

thermal efficiency and to reduce CO2 emissions. In 2009, the 1.8L engine was launched

as first engine of this new series, followed by the 1.5L and 2.5L engines launched in 2011.

This new engine line-up is now integrated in a wide range of B, C and D-segment vehicles.

The new engine series was developed considering the advantages of the base engine

which offers high fuel efficiency and reliability as well as clean exhaust emissions. The

modifications were carried out to optimize the overall benefits when combined with the

Hybrid system. The key technological items implemented in the new engines series are

Cooled EGR system, Electric Water Pump (EWP) and Atkinson cycle. In addition, the

engine friction was significantly reduced to reach a thermal efficiency of nearly 38.5%.

Many parts were common to the base engine in order to keep the same high reliability and

the same integration into the engine compartment of several vehicles.

With the completion of the new engine series, Toyota achieved a big step in improving fuel

consumption and making possible to adapt the system from B to D-segment vehicles. In

the future, Toyota will keep focussing on introducing advanced technologies to contribute

to its environmental vision, which is to offer sustainable mobility.

33. Internationales Wiener Motorensymposium 2012

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Kurzfassung

Die Reduzierung der CO2 Emission und des Kraftstoffverbrauches gehört zu den grossen

Herausforderungen für die Automobilhersteller. 1997 hat Toyota das Toyota Hybrid

System (THS) als einen der effektivsten Ansätze für einen hocheffizienten Antriebsstrang

eingeführt. Die THS Technologie wurde kontinuierlich weiterentwickelt, um den

Wirkungsgrad parallel zur globalen Markteinführung weiter zu verbessern.

Toyota hat die 4-Zylindermotorengruppe für Hybrid Systeme erneuert, um den

thermischen Wirkungsgrad und damit die CO2 Emissionen zu verbessern. 2009 wurde der

1.8L Motor als Erster dieser neuen Motoren eingeführt, gefolgt von den 1.5L and 2.5L

Motoren in 2011. Die neuen Motoren sind in Fahrzeugen des B, C and D-Segmentes

integriert.

Die Entwicklung der neuen Motorengruppe war darauf bedacht, auf den Vorteilen der

Basismotoren wie gutem Kraftstoffverbrauch und hoher Zuverlässigkeit sowie gutem

Abgasverhalten aufzubauen, während die Modifizierungen darauf abzielen, die Vorteile

des Hybridsystems zu optimieren. Die technischen Massnahmen beinhalten ein gekühltes

AGR-System, eine elektrische Wasserpumpe und den Atkinson Zyklus. Dadurch und

durch Reibungsoptimierung konnte ein thermischer Wirkungsgrad von nahezu 39%

erreicht werden. Der mit diesem Konzept erreichte hohe Gleichteilanteil zu den

Basismotoren trägt zu der Zuverlässigkeit des Motors und Integrierbarkeit in den

Motorraum der Zielfahrzeuge bei.

Die neue Motorengruppe Toyotas erlaubt eine deutliche Verbesserung des

Kraftstoffverbrauches und die Einführung des Hybridsystems in einer breiten

Fahrzeugpalette vom B- bis zum D-Segment. Dies ist ein weiter Schritt in Toyota’s

zukunftsorientierter Strategie innovativer Technologien in Richtung nachhaltiger Mobilität.

1. Introduction

1-1. Expansion of Toyota Hybrid System

Toyota Hybrid System (THS) vehicle was launched in 1997. Then it was expanded to

several vehicles and continuously improved to achieve the best fuel consumption in the

world. The THS had quickly become popular thanks to its quality and image of

environment friendly technology thus achieving 1million vehicles sold in 2007, 2million in

2009 and 3million in 2011 as shown in Fig.1.


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0

1000

2000

3000

1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011

Sum

tota

l of

HV

vehic

le(*

1000)

Over 1000,000

Over 2000,000

Over 3000,000

1-2. Fuel consumption of THS

Fig.2 shows THS CO2 performance vs. conventional powertrain systems. THS has

potential to decrease CO2 by approximately 50% compared to a conventional gasoline

automatic transmission (AT) vehicle.

0

50

100

ConventionalGasoline AT

Diesel AT THS(Gasoline)

Inde

x of

CO

2(%

)

Engine efficiency difference

EV drive

Idling stop

Regeneration

City mode/Prius class vehicle

The key merits of THS are the capabilities to perform EV drive, Idling stop and

Regenerative braking. Additionally the thermal efficiency of the engine itself is also

important in the system.

1-3. Requirements for Engine of THS

The main objectives of the THS are to achieve high thermal efficiency and low emission

levels, but also to reduce its cost by expanding the technology globally on many vehicles

complying with each market requirements. Fig.3 shows the thermal efficiency comparison

for each engine type against its hybridized version.

Fig.2 CO2 index comparison of different powertrains

Fig.1 Toyota cumulated vehicle sales with THS technology


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15

25

35

45

ConventionalGasoline

THSGasoline

Diesel (reference)THS Diesel

BoostedGasoline

Best

therm

al e

ffic

iency(

%)

Improved byadopting THS system

Close Diesel by the improvement

From this chart, diesel engine thermal efficiency is the highest, followed by gasoline

engine optimized for Hybrid System, conventional and boosted gasoline. Gasoline engine

for THS can potentially achieve almost same efficiency as diesel engine with some

technological improvements such as, operating point optimization (best BSFC line),

Atkinson cycle and exhaustive low friction items.

0 0.5 1.00.001

0.1

0.01

CO2(Conventional gasoline vehicle=1)

HV Vehicle

Gasoline

Diesel

NO

x(g/

km)

Diesel Euro4

ULEV

SULEV

Regarding exhaust emissions, Fig.4 shows a comparison of CO2 and NOx emissions level

between diesel and gasoline engines In terms of NOx, gasoline engine has much lower

emissions than diesel engine. To further reduce NOx emissions, diesel engines would

require NOx after-treatment like SCR system thus increasing cost and compromising CO2

emissions. However, diesel engine has much lower CO2 than gasoline engine. Gasoline

engine could achieve almost same CO2 level as diesel engine by adopting THS.

0

200

400

600

800

0 20 40 60 80 100LA#4 Time [sec]

Cat

alys

t Tem

pera

ture

[℃

]

CatalystLight-offTemperature

Vehicle Speed

Conventional Vehicle(Less warm-up control)

Hybrid

Rapid Warm-up of Catalyst

Motor Drive

EngineStart

Fig.3 Brake thermal efficiency of different powertrains

Fig.4 NOx vs. CO2 of different powertrains

Fig.5 Improved engine warm-up with THS


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Additionally THS can be further improved to reduce emissions by rapid warm-up of

catalyst as shown in Fig.5 (e.g. vehicle start by motor and acceleration assisted by motor

in cold condition, quick engine start by motor, etc).

Fig.6 shows the cost performance image between each system which is important for

expandability. Gasoline engine for THS could achieve better cost performance by

improving its thermal efficiency with some modifications to adapt THS and lower the cost

(e.g. reduction of unnecessary parts). As a result gasoline has the higher cost / efficiency

benefits when combined with Hybrid System.

Engi

ne t

herm

al e

ffic

iency

system cost

Gasoline for THS(Reference)Diesel for THS

BoostedGasoline

ConventionalGasoline

Good

1-4. Toyota Hybrid System expansion and L4 engine line-up

As mentioned above, Toyota has been expanding Hybrid System with gasoline engine

base. This time, L4 engine line-up has been renewed with displacement changes and

adapted to vehicle from B-segment to D-segment. The changes are shown in Fig.7. In

2007, PRIUS engine (C-segment) has been changed from 1.5L engine “1NZ-FXE” to 1.8L

engine “2ZR-FXE” in order to improve fuel consumption, especially in high speed

conditions. For the new CAMRY (D-segment) produced in 2011, the engine has been

changed from 2.4L “1AZ-FXE” to the new 2.5L engine “2AR-FXE”. In 2012, 1NZ-FXE will

be improved and integrated into AQUA and YARIS HV (B-segment). As a result L4 engine

line-up from B-segment to D-segment vehicle will be renewed.

Veh. System '08 '09 '10 '11 '12 '13

B seg. NZ 1.5L THS3

NZ 1.5L THS2

ZR 1.8L THS3

AZ 2.4L THS2

AR 2.5L THS3

Engine

C seg.

D seg.

2nd PRIUS

from 3rd PRIUS, expand to AURIS HV, CT200h, others

from AQUA, YARIS HV

CAMRY

from New CAMRY

Fig.7 Expansion of gasoline engine based THS to Toyota vehicle line-up

Fig.6 Cost performance of different engines


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2. Aim of new development

2-1. Improvement of Engine for THS

Fig.8 shows comparisons of thermal efficiency and operating line for 1NZ-FXE (second

generation PRIUS) and 2ZR-FXE (third generation PRIUS) engines. The operating line of

THS is on the best thermal efficiency point for each engine speed. Therefore it is important

to improve thermal efficiency around this operating line and our engines for THS have

been changed to Atkinson cycle together with a significant reduction of engine frictions.

Then, further improvement in fuel consumption should focus on the best efficiency

operating line.

230

220

2000 4000 6000

50

00

100

150

Engine speed (rpm)

1NZ-FXE230 g/kWh area

2ZR-FXE230 g/kWh area

230

Tor

que

(Nm

)

1NZ-FXEoperating line

2ZR-FXEoperating line

Low speed

Middle speedHigh speed

Additional friction reduction and heat management (e.g. Electric Water Pump) were also

implemented. These items contribute to a better efficiency in all operating areas by

accessory drive belt elimination and appropriate cooling water control. For middle to high

engine speed area, knocking becomes the major issue. In order to improve it, cooled EGR

system was selected. Thanks to adopting this system, knocking occurrence has been

reduced drastically. It contributes to a better thermal efficiency at middle speed area.

Additionally, stoichiometric operation in all area using cooled EGR system and increased

displacement could improve thermal efficiency at high engine speed.

As shown in Fig.9, best thermal efficiency could be improved to 38.5% on all L4 engine

series. Furthermore the efficiency can still be improved in the future with same direction of

Fig.8 BSFC of 1NZ-FXE engine v.s. 2ZR-FXE engine


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development, and Toyota will continue to develop environmental technology to realize

such a target.

20

25

30

35

40

45

Conv.Gasoline

1NZ-FXE 2ZR-FXE

Best

therm

al e

ffic

iency(

%)

Future

2-2. Utilize base engine technology

In this renewed L4 series engine development, the original technologies of base engine

have been utilized as much as possible. Table 1 shows engine technologies, circle means

common technology and star mark means specific technology for Hybrid System. High

efficiency intake port, roller rocker valve train, long reach spark plug and so on which are

from the original engine have been utilized. Then other specifications have been modified

as less as possible for the Hybrid System. As a result approximately 90% of parts have

been common with base engine. This engine part commonization allowed sharing the

same production line and could offer production flexibility during the fluctuation of

production volume.

High efficiencyintake port

Long reachspark plug

Rollerrocker

High comp.ratio

Resin coatedpiston

Low tensionpiston ring

0W-20oil

Atkinsoncycle

CooledEGR

Electricwater pump

Conv. －－－－ ○ ○ ○ －－－

HV －－－－－－－－－－－－ ☆☆☆☆(13.4) ○○○○ ☆☆☆☆ ○○○○ ☆☆☆☆ ☆☆☆☆ ☆☆☆☆

Conv. ○ ○ ○ － ○ ○ ○ －－－

HV ○○○○ ○○○○ ○○○○ ☆☆☆☆(13) ○○○○ ☆☆☆☆ ○○○○ ☆☆☆☆ ☆☆☆☆ ☆☆☆☆

Conv. ○ ○ ○ － ○ ○ ○ －－－

HV ○○○○ ○○○○ ○○○○ ☆☆☆☆(13) ○○○○ ☆☆☆☆ ○○○○ ☆☆☆☆ ☆☆☆☆ ☆☆☆☆

NZ

ZR

AR

Table 1 Commonization of technologies for each engine

Fig.9 Improvement of Hybrid engine efficiency

○：Common technology ☆：Specific technology for THS


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3. Modification items and their benefits

3-1. EGR system

3-1-1. EGR system outline

The cooled EGR system was adopted to improve fuel efficiency throughout all engine

speeds. Fig.10 shows the configuration of the EGR system. The EGR gas taken from the

exhaust manifold is cooled through a high efficiency water-cooled EGR cooler, and it is

subsequently introduced into each intake port from a chamber inside the intake manifold.

EGR gas chamber(inside intake manifold)

EGR cooler

Pipe to intake chamber

EGR valve

Fig.11 shows the relationships of EGR gas temperature versus brake specific fuel

consumption ratio, and spark timing. By substantially cooling the EGR gas temperature, it

was possible to increase the EGR rate and to advance the spark timing. Consequently, the

fuel consumption was improved. Furthermore, cooling the EGR gas made possible to

introduce EGR gas even during high load conditions. As a result, the anti-knocking

performance was improved and the exhaust gas temperature was lowered. With these

effects, the improvement of thermal efficiency across the whole engine operating area was

achieved. These effects were especially useful for the engine for THS which operates at

higher load conditions than a conventional engine.

From this analysis, the high efficiency EGR cooler was adopted for this 2ZR-FXE with a

high efficiency (approximately 95%) water-cooled heat exchanger cooling the EGR gas to

a temperature close to the temperature of the cooling water. Furthermore 2AR-FXE and

1NZ-FXE had a higher efficiency EGR cooler due to change of core design from “Winglet

type” to “Offset type” (detail will be explained later in this paper).

Fig.10 EGR module integration Fig.11 Effect of EGR gas temperature on spark timing and BSFC

95Nm 2400rpm

Spa

rk ti

min

g (

°CA

)

25

30

35

40

100 150 200 250EGR Cooler　OUT　Temp [℃]

230

226

222

218

BS

FC

(g/

kWh)


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3-1-2. Optimizing EGR and Variable Valve Timing-intelligent (VVT-i)

The VVT-i made it possible to control the intake valve timing. Fig.12 shows the relation

between VVT-i angle and intake valve opening timing on 2ZR-FXE. To maximize fuel

efficiency, this engine has mutual control between intake valve timing and the EGR system

on several driving conditions.

Closing timing102deg. ABDC ~ 61deg. ABDC

VVT-i angle

TDC Opening timing12deg. ATDC ~ 29deg. BTDC

BDC

41 CA°

Intake valve timingat VVT-i angle 41 CA°

Intake valve timingat VVT-i angle 0 CA°

(1) Low load conditions

Fig.13 shows brake specific fuel consumption rates and pumping-loss during low load

conditions plotted against the EGR rate and VVT-i angles. As VVT-i was advanced to an

early closing timing for the intake valve, the pumping loss suppressed by the effect of

Atkinson cycle increased at all EGR rates. Because pumping loss mainly affects low load

conditions, in this situation, increasing the EGR rate is better to improve the fuel efficiency

rather than increasing effective compression ratio by advanced VVT-i.

50

40

30

20

10

020103020100 300

VV

T-i

angl

e (°C

A)

300 290

EGR rate(%)

34

32

3028

2624 22

EGR rate(%)

BSFC (g/kWh) Pumping loss (kPa)

loss areaLow pumping

consumption areaGood fuel

advance

Fig.12 Valve timing of 2ZR-FXE

Fig.13 Effect of EGR rate on BSFC and pumping losses @ 40Nm, 1200rpm


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- 10 -

(2) High load condition

Fig.14 shows fuel consumption rates and spark timing during high load conditions plotted

against the EGR rate and VVT-i angles. In high load conditions, the throttle is almost fully

open, so the ratio of pumping loss is reducing. In this situation, advancing the VVT-i angles

increases the effective compression ratio. This makes it advantageous to increase

indicated work, however, spark timing could not be advanced due to the knocking on the

Atkinson cycle with 13.0 compression ratio. Then by introducing cooled EGR gas,

combustion temperature could be reduced thus allowing earlier spark timing and improved

fuel efficiency.

50

40

30

20

10

020103020100 300

VV

T-i

angl

e (°C

A)

280 270

EGR rate(%) EGR rate(%)

BSFC (g/kWh) Spark timing (°CA)260 250 240

consumption areaGood fuel

timing areaAdvanced spark

0 10 20 30 40

advance

This system with Atkinson cycle successfully improved the minimum fuel consumption and

the expanded area controlled between pumping loss reduction with the introduction of

EGR gas for low load conditions and effective compression ratio increase by advancing

the VVT-i for high load conditions.

(3) High speed condition

The principal characteristic of the EGR system adopted for this engine is that it enables

EGR gas introduction even under high load conditions including maximum power output.

In order to improve fuel efficiency at the points of maximum power output, ensuring high

power output while driving with a stoichiometric air-fuel ratio, the exhaust gas temperature

must be reduced. To solve this problem, EGR gas cooled by the high efficiency EGR

cooler was introduced to reduce exhaust gas temperature.

Fig.15 shows the relationship between power output at points of maximum power output

and volumetric efficiency with and without the EGR system. To control the exhaust gas

Fig.14 Effect of EGR rate on BSFC spark timing @ 80Nm, 1200rpm


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- 11 -

temperature and to protect the catalyst at stoichiometric air-fuel ratio, the air mass must be

reduced by closing the throttle if there is no EGR. Consequently, volumetric efficiency and

power output are reduced. EGR gas introduction improves the power with the following

effects:

• Reduced combustion temperature which reduced exhaust gas temperature

• Reduced maximum compression temperature which prevented early knock

occurrence, allowing spark timing to advance

With these effects, at high speed conditions including maximum power output points, an

optimum balance between high fuel efficiency and high power output was achieved.

Engine speed (rpm)4000 600050003000

Pow

er (

kW)

40

60

80

Pow er

Vol

umet

ric e

ffici

ency

(%

)

10%

Volumetric eff iciency

Power

■ w / EGR● w /o EGR

improv ement

EG

R r

ate

50degThrottle close

EGR ON

Thr

ottle

angl

e (d

eg)

3-1-3. Optimizing EGR and valve opening duration

2AR-FXE has shorter valve opening duration than 2ZR-FXE and earlier intake valve

closing timing. As a consequence, internal EGR could be decreased thus allowing higher

amount of cooled EGR and earlier spark timing due to improvement of knocking. Fig.16

shows the comparison between 260deg and 270deg of opening duration. 260deg of valve

opening duration could reduce fuel consumption ratio compared to 270deg. Therefore, the

smaller valve opening duration was implemented on 2AR-FXE and 1NZ-FXE (but not on

2ZR-FXE).

Fig.15 Effect of EGR on engine volumetric efficiency and power output


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- 12 -

210

215

220

225

230

235

240

65 75 85 95 105

IVC(°ABDC)

Fuel con

sum

ption r

atio(g

/kW

h)

Cam duration 270

Cam duration 260

Improved

3-2. Electric Water Pump (EWP)

3-2-1. Outline of Electric Water Pump

To achieve the objective of improving fuel efficiency using an advanced cooling system, an

EWP and an exhaust heat recirculation device were developed.

Conventional water pumps are operated according to the engine speed, thus requiring

excessive power even in the conditions where flow rates are not so much necessary (e.g.

cold conditions, low load at high rpm). However, by choosing an EWP, it was possible to

optimally control the flow rate of the cooled water according to the demands made by each

of the cooling devices.

Fig.17 and Fig.18 show respectively the design of the EWP and the schematic of the

cooling system. By adopting a flattened compact motor integrated with driver, a size

comparable to a conventional water pump was achieved. Compared to a conventional

water pump, the impeller was inserted to the center shaft fixed to the water pump housing

since the magnet-integrated impeller is rotating.

2AR-FXE 2000rpm, Vacuum 93kPa

Fig.16 BSFC improvement of 2AR-FXE with shorter valve opening


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- 13 -

Center shaft

Impellar

Stator S/A

IN

OUT

3-2-2.Objective of Electric Water Pump

The main six advantages for adopting an EWP are as follows:

• Reduce friction: Eliminate accessory drive belts and mechanical seals

• Efficient water pump energy use: Reduce cooling system water flow resistance and

optimized pumping rate

• Improve heater performance: Optimize cabin heater flow

• Improve fuel efficiency: Control flow rate for appropriate temperature and load

during low and medium load conditions and improve anti-knocking performance in

high load conditions

• Quick engine warm-up: Reduced circulation of cooled water flow rate at low

temperature start-up

• Reduce maintenance: Elimination of accessory drive belts and the water pump seal

3-2-3. Optimize of flow rate and motor size

One of the main challenges to improve the efficiency of the EWP was to reduce the motor

size while keeping required cooling performance and integration constraints. To solve this

issue, all water flow rates from each cooling device were assessed and the water flow

resistance of the whole cooling system was reduced significantly.

The required water flow rate was studied to optimize the engine cooling system. Fig.19

shows the water flow rate ranges in terms of engine reliability, cooling performance and

cabin heating performances. The maximum flow rate on the EWP was determined to

satisfy these requirements.

Fig.17 Electric Water pump design

Fig.18 Cooling system schematic

Engine

Radiator

Thermostat

Heater core

Eliminatedby-pass route

EGR cooler

Heatrecirculationsystem

Electric water pump


- 13 -

- 14 -

2000 600040000

40

80

120

160

Engine speed (rpm)

full load

Flo

w r

ate

(L/m

in)

Mechanical water pump

HeaterMiddle speed climbing

(pattern B)Maximum speed

Unnecessaryarea

Operatingarea

Low speed climbing(pattern A)

Warm upimprov ement

Making good use of simulation techniques, piping arrangements were also optimized. It

was possible to eliminate water by-pass routes from the engine outlet to the thermostat,

reducing pressure drop by parallel layout of the EGR cooler and exhaust heat recirculation

device.

As a result of these improvements, the flow rate was 60% less than conventional water

pump, and the size of the motor was 90% smaller than a motor used for an EWP with a

flow rate equivalent to mechanical water pump. Fig.20 shows the reduction of motor size

and flow rate from the base engine.

Flow rate (L/min)100 2001500

400

800

1600

050

1200

Pow

er c

onsu

mpt

ion

(W)

★

Reduction of motor size

Mechanical w ater pumpBase engine

EWP2ZR-FXE

90%

Reduction of f low60%

Fig.19 Water pump flow requirements for cooling performance

Fig.20 optimized motor size and flow rate


- 14 -

- 15 -

3-2-4. EWP merit to improve fuel consumption

Fig.21 shows the fuel consumption improvements achieved by the EWP. By fully utilizing

the merits of the EWP that have been previously described, 1% to 4% fuel consumption

improvements were confirmed on the engine operating line of this Hybrid System.

Engine speed (rpm)

Tor

que

(Nm

)

2000

6000

4000

0

50

100

150

0

-1% -2%-3%

-4%

-6%

-8%

Engine operating line

Improvement1-4%

3-2-5. Improving engine warming up

The EWP enabled the pump speed to be reduced according to the engine operating

conditions after cold start-up. This successfully shortened the engine warm-up period.

Fig.22 shows the schematic of the exhaust heat recirculation system. This was adopted

with the objective of improving fuel efficiency in cold conditions. The warm-up performance

of the engine and engine coolant was improved by the usage of the exhaust heat, which

was lost in the exhaust gas flow for conventional systems.

Exhaust heat recoveryCatalyst

Engine

Heater core

CoolingchannelFlow path-sw itching

valve

Fig.21 Water pump flow requirements for cooling performance

Fig.23 Improvement of vehicle fuel economy in winter with EWP

Fig.22 Schematic of the exhaust heat recovery system

100

105

115

110

120

95

90Inde

x of

fuel

eco

nom

y (%

)

Previous New(Uninstalled)

New(Installed)

< Test condition >Driv ing cy cle : LA#4 (U.S.)Ambiert temp. : -5deg.CHeater : ON

+19%

+10by Electric Water Pump

etc.

+9%by Heat recirculation

sy stem


- 15 -

- 16 -

As a result, the friction was reduced during the engine warm-up period and especially with

the Hybrid System further fuel consumption improvement was achieved with early engine

stop operations. Fig.23 shows the improvement of vehicle fuel economy in winter. This

new vehicle together with EWP achieved 19% higher fuel economy compared to the

previous vehicle in these given test conditions (LA-4, -5degC ambient temp.).

3-2-6. Structure Sharing of EWP

Table 2 and Fig.24 show each EWP specification and the structure. Several parts have

been shared between each EWP as much as possible to minimize the structure change,

and commonize parts on the production line. As a result, cost reduction could be

maximized.

1NZ-FXE2ZR-FXE

2AR-FXE

160W(13.3V*12A)

200W(13.3V15A)

52kPa*80L/min(69kW)

48kPa*95L/min(76kW)

ShaftStator coreBushOther X XDriver board X XThermal sheetInductor X X

X X

CommonCommon

Common

Common

Common

ENGINE

Pump Input Power

Pump Cooling Power

Stator S/A

Outer Case

Str

uctu

re

Board S/A

Rotor S/A

4. Specification of each engine

4-1. 2ZR-FXE

There were two objectives in developing the new engine for the Hybrid System for C-

segment vehicles. The first was to improve fuel efficiency specifically in practical situations

such as driving at high speed or driving in urban areas in the winter season. The second

was to improve power output capabilities to enable a wider range of THS vehicle types to

be equipped with this engine.

In addition to Atkinson cycle, which is the established concept of engine for THS vehicles,

the following three items were also implemented:

• Increasing displacement

• Cooled EGR

• Electric water pump

Board S/A

Stator shaft

Stator core

BushOuter case

Rotor S/A

Fig.24 EWP parts description

Table 2 EWP parts commonization


- 16 -

- 17 -

4-1-1. Selection of engine displacement

This new system for THS vehicles has been developed with further improvements to fuel

economy during high speed driving. Fig.25 shows the relationship between engine

operating lines, power output and fuel consumption when studied with two engines of

different displacements. Since the majority of the power comes from the engine during the

high speed driving, the engine speed increases with vehicle speed. In the case of 1.5-liter

engine at high speeds the operating line extends outside the minimum fuel consumption

area because of the engine’s power output characteristics. In comparison, by increasing

displacement to 1.8-liters, engine speed is kept lower and the period of acceleration within

the minimum fuel consumption area expanded, thereby fuel economy improvements

during high speed driving can be achieved.

Tor

que

(Nm

)

Engine speed (rpm)

230 g/kWh area

Engine speed (rpm)

Tor

que

(Nm

)

10kW

20kW30kW

10kW

20kW30kW

36504000

40kW40kW

7Nm

1.8 L1.5 L

Fig.26 shows the relationship between power output and brake thermal efficiency for

several displacements. The thermal efficiency improves with increased displacement

because of the reduced s/v (surface area per volume) ratio of combustion chamber and

reduced friction by lower engine speed. However, the thermal efficiency decreases when

operated at light load, because of increased pumping-loss by partial open throttle

operation. This trade-off can be optimized by increasing the amount of driving carried out

by the electric motor. As a result, higher system efficiency in all driving ranges can be

achieved.

The base engine was chosen considering the required power output coverage, the

balance of power output with fuel consumption, and the objective to expand the range of

Hybrid System application to various vehicle types. From this analysis, the engine with

1.8-liter displacement was selected for the THS and for compact vehicles.

Fig.25 Improvement of BSFC and performance by increasing engine displacement


- 17 -

- 18 -

The

rmal

eff

icie

ncy

(%)

30

40

20

0

50

100

0 10 20 30Engine output power (kW)

40 Acc

umul

ated

tim

e (s

ec)

1800cc1500cc1300cc1000cc

Thermal efficiency

Accumulated time

Highway cycle

City cycle

・Atkinson cy cle・Without cooled EGR

4-1-2. Engine specification

The new generation 2ZR-FXE engine was developed on the basis of the 2ZR-FE launched

in 2006. The 2ZR-FE has good fuel efficiency potential by means of such features as roller

rockers to reduce friction, high-efficiency and high-tumble intake ports to improve

combustion, a small diameter M12 spark plug to improve knocking (cooling improvement),

increased rigidity to reduce vibration and noise, and reduced weight with compact design.

Additionally the 2ZR-FXE was improved with modifications that complied with the unique

hybrid system operating condition. Table 3 shows the comparison between the 2ZR-FXE,

the previous 1NZ-FXE engine and the base 2ZR-FE engine.

Engine Type 2ZR-FXE 2ZR-FE 1NZ-FXE

Displacement (cc) 1,797 ← 1,497

Cylinder In-line,4-cylinder ← ←

Bore×Stroke (mm) φ80.5 × 88.3 ← φ75.0 × 84.7

Intake VVT-i Intake&Exhaust

VVT-iIntake VVT-i

Roller rocker drive ← Direct drive

Intake Closed Timing(°CA) 61 ～102 ABDC 30～65 ABDC 72～105 ABDC

Compression Ratio 13 : 1 10 : 1 13 : 1

Maximum Pow er 73kW/5200rpm 100kW/6000rpm 57kW/5000rpm

Maximum Torque 142Nm/4000rpm 175Nm/4400rpm 115Nm/4200rpm

Emission Regulation AT-PZEV ULEV2 AT-PZEV

Atkinson cycle

Cooled EGR Dual VVT-i

Electric w ater pump

Valve Train

Majortechnologies

Atkinson cycle

Fig.26 Relationship between power output and brake thermal efficiency for several engine displacements

Table 3 2ZR-FXE engine specifications comparison


- 18 -

- 19 -

4-1-3. Engine performance

Fig.27 shows engine output performance curves. The 2ZR-FXE achieved 20% or more

torque across all rpm ranges and 28% greater power at maximum engine speed compared

to the previous engine. This is due to the reduced friction and the optimized valve timing in

addition to the benefits of 300cc larger displacement.

2ZR-FXE

1000 2000 3000 4000 60005000Engine speed (rpm)

Pow

er (

kW)

Tor

que

(Nm

)

120

100

80

140

16060

50

40

70

80

28%

1NZ-FXE

4-1-4. Emission

2ZR-FXE took the newly developed emission after-treatment system corresponding to AT-

PZEV which is currently the most stringent emission regulation in the United States. The

exhaust heat recovery system was adopted and the warm-up control strategy was

elaborated to activate the catalytic converter as quickly as possible while controlling the

engine to maximize exhaust gas temperatures. The utilization of the electric motor torque

to drive the vehicle was further optimized.

With these optimizations, the coolant heat storage system that was a key technology to

meet AT-PZEV with the previous PRIUS was not used in the new system. Thus the

emission control system has been simplified. This facilitated the applicability to wider

vehicle variations.

4-2. 2AR-FXE

2AR-FXE for D-segment THS vehicle has been developed utilizing high potential of base

engine “2AR-FE“ which was roller rocker, etc. The specifications are shown in Table 4. In

the case of D-segment vehicles, the development was particular since it aimed at high fuel

economy and performance while keeping clean emissions and good NVH. The key

technical improvements are listed below:

Fig.27 Performance improvement by increasing engine displacement


- 19 -

- 20 -

・ Atkinson cylce

・ Increased engine displacement from 2.4L to 2.5L

・ Cooled EGR system with earlier valve closing timing and high efficiency EGR cooler

・ Electric Water Pump

Engine Type 2AR-FXE 2AR-FE 2AZ-FXE

Displacement (cc) 2,494 ← 2,368


Bore×Stroke (mm) φ90.0 × 98.0 ← φ88.5 × 96.0

Intake VVT-i Intake&Exhaust

VVT-iIntake VVT-i

Roller rocker drive ← Direct drive


Compression Ratio 12.5 : 1 10.4 : 1 12.5 : 1


Maximum Torque 207Nm/4800rpm 235Nm/4100rpm 187Nm/4400rpm

Emission Regulation AT-PZEVAT-PZEVULEV2

AT-PZEV

Atkinson cycle

Cooled EGR Dual VVT-i


Valve Train

Majortechnologies

Atkinson cycle

4-2-1. Engine performance

Intake port design of AR engine has been optimized with CAE to satisfy both high flow rate

and high tumble ratio to achieve high performance and fuel efficient D-segment vehicle.

This engine is currently the best in the world in terms of flow ratio and tumble as shown in

Fig.28. 2AR-FXE utilized the high efficiency intake port enabling stable combustion even at

high EGR rate. Additionally, the 260deg intake valve duration and the optimization of

intake and exhaust manifold ports improved the maximum power by 6% and the middle

speed torque by 20%. Fig.29 shows these performance achievements.

0.5

0.6

Tum ble Ratio

Flow Ratio

A R

AZ

good

0.5

0.6

Tum ble Ratio

Flow Ratio

A R

AZ

good

Fig.28 2AR-FXE engine flow ratio and

tumble ratio against competitors Fig.29 2AR-FXE engine torque and

power improvement

Table 4 2AR-FXE specifications comparison

0 2000 4000 6000Engine Speed (rpm)

Tor

que

(Nm

) Pow

er (

kW)

2AR-FXE

20% Improvement

100

120

200

6% Improvement

150

2AZ-FXE


- 20 -

- 21 -

4-2-2. High efficiency EGR cooler

It is important to increase the efficiency to have increased EGR ratio. Therefore AR engine

had different type of EGR fin type compared to ZR engine type as shown in Table.5. Heat

radiation rate of the Off-set type fin is more efficient by 1.5 times than other type. And the

high efficient fin could offer more compact packaging and reduced cost.

The EGR distribution layout (1-2-4 shape) shown in Fig.30 has been chosen to reduce the

deviation of EGR gas distribution to each port. As a result over 20% of EGR rates could be

possible with stable combustion (see Fig.31 and Fig.32).

TO YO TABaseline

2AR-FXEBaseline

EGR variation(%)

1cyl 2cyl 3cyl 4cyl

0

A rpmB rpmC rpm TO YO TA

Baseline

2AR-FXEBaseline

EGR variation(%)

1cyl 2cyl 3cyl 4cyl

0

A rpmB rpmC rpm

A rpmB rpmC rpm

Also, EGR valve was installed near the intake port to improve EGR rate control and

combustion stability thanks to stable air-fuel ratio when EGR valve was on and off.

As a result, the minimum fuel consumption ratio could achieve 218g/kWh which was top

level in the world and the area of 230g/kWh could be widely expanded compared to the

2AZ-FXE as shown in Fig.33. In CAMRY vehicle, stoichiometric area could be kept until

maximum vehicle speed.

EGRCoolerFin Type

HeatRadiationRate

Wave Winglet

100(Base)

166 313

V6(Current) ZR AR

Off-setEGRCoolerFin Type

HeatRadiationRate

Wave Winglet

100(Base)

166 313

V6(Current) ZR AR

Off-set

EGR Gas Flow

EGR Valve Distribution Passage(1-2-4 Shape)

EGR Gas FlowEGR Gas Flow

EGR Valve Distribution Passage(1-2-4 Shape)

Fig.30 2AR-FXE engine EGR distribution circuit

Fig.32 Mapping of max EGR rate with stable combustion

Fig.31 2AR-FXE engine EGR variation per cylinder

Table 5 Fin design

Engine Speed (rpm)

Eng

ine

Load

(%)

20%

18%

16%


- 21 -

- 22 -

Engine Speed (rpm)

Eng

ine

Load

(%

)

2AR-FXE2AZ-FXE

230g/kWh230g/kWh

4-3. 1NZ-FXE

There are two objectives in developing a new 1NZ-FXE based on previous 1NZ-FXE

developed for C-segment vehicle.

・ Improvement of thermal efficiency

・ Integration in B-segment vehicle

We adopted the following four technologies in addition to Atkinson cycle in order to reach

the above-mentioned objectives.

・ Cooled EGR

・ Electric water pump

・ Low friction timing chain

・ Engine mount design change

A comparison to conventional and previous engine is shown in Table.6.

Engine Type 1NZ-FXE(New ) 1NZ-FE 1NZ-FXE(Previous)

Displacement (cc) 1,497 ← ←


Bore×Stroke (mm) φ75.0 × 84.7 ← ←

Intake VVT-i ← ←

Direct drive ← ←


Compression Ratio 13.4 : 1 10.5 : 1 13.0 : 1


Maximum Torque111Nm

/3600-4400rpm141Nm/4200rpm 115Nm/4200rpm

Emission Regulation SULEV ULEV2 AT-PZEV

Atkinson cycle

Cooled EGR VVT-i


Valve Train

Majortechnologies

Atkinson cycle

Fig.33 2AR-FXE engine BSFC improvement vs. 2AZ-FXE

Table 6 New 1NZ-FXE engine specifications comparison


- 22 -

- 23 -

4-3-1. Adapt to B-segment vehicle

The full length of engine mount bracket is shortened by 20.4mm to fit the engine

compartment size of a B-segment vehicle (Fig.34) and engine layout is optimized for

loading. Maximum engine torque is also optimized for the Hybrid System requirement.

Electric W/P

Shorten20.4mm

Water pumplocation change

4-3-2. Other improvements for better fuel efficiency

1NZ-FXE uses low friction timing chain in addition to above-mentioned items. The plate

shape of chain is changed as shown in Fig.35 to reduce friction by reducing contact area

with chain guide and slipper. Thermal efficiency is improved by changing compression

ratio from 13.0 to 13.4. By adopting these items, the area of minimum specific fuel

consumption is expanded compared with previous engine as shown in Fig.36.

Previous New

Projection

Fig.34 1NZ-FXE engine mount bracket packaging improvement

Fig.35 Low friction timing chain design of 1NZ-FXE engine

Fig.36 BSFC improvement of 1NZ-FXE engine

2000 4000

100

50

1NZ-FXE(Previous)230g/kWh

1NZ-FXE(New)230g/kWh

Engine operating line

Engine Speed (rpm)

Tor

que

(Nm

)


- 23 -

- 24 -

5. Conclusion Toyota has developed innovative L4 engine series for Hybrid System which account for

90% of THS vehicle and cover B to D-segment. This new gasoline engine series achieved

very high fuel efficiency compared to the base engines and were optimally matched to

each vehicle segment to offer the best CO2 and performance compromise.

Knowledge obtained by these technological improvements is the following:

・Thermal efficiency is more than 38.5% in all engines and becomes world’s leading level

by adopting cooled EGR and Electric Water Pump (EWP) in addition to technologies

based on conventional engines for THS.

・Requirements to promote THS to customers is to offer high fuel efficiency and low cost

while complying with emissions regulations. Therefore improving mass-produced

gasoline engines is an effective way to achieve these targets.

・The engine technologies developed for THS are cooled EGR, Atkinson cycle, high

compression ratio and EWP. These technologies are available for conventional gasoline

engine and offer significant fuel consumption reduction potential.

These improvements allow maintaining world’s top level fuel efficiency and to promote

THS to the public and thus contribute to a better world environment. In order for THS to

keep the world’s top level fuel efficiency, Toyota is continuously looking for innovative

solutions to offer environmentally friendly vehicle to customers.

Reference

[1] “Development of new 1.8-Liter Engine for Hybrid Vehicles”

2009 SAE International (Technical Paper Number: 2009-01-1061)

Nobuki Kawamoto, others

[2] “Toyota’s new spark-ignited engine line-up and environmental

Technologies for sustainable mobility”

Aachener Kolloquium Fahrzeug- und Motorentechnik 2008

Masanori Sugiyama, Takeshi Inoue, Fuminori Hosoda


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the renewed 4-cylinder engine series for toyota hybrid ... · pdf filethe renewed 4-cylinder...

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