Development of the HighPerformance and HighReliability VG Turbocharger
for Automotive Applications
KATSUYUKI OSAKO* 1
AKIRA SAMATA* 2
SEIICHI IBARAKI* 1

YASUAKI JINNAI* 2
HIROSHI SUZUKI* 2
NORIYUKI HAYASHI* 1

With the tightening of emissions regulations, the turbochargers used to supercharge air into engines are now
essential products for automotive diesel engines. In Europe, where many of the passenger cars on the road arediesel-powered, a new generation of VG (Variable Geometry) turbochargers capable of controlling boost pressurewith a variable nozzle vane on the turbine side is becoming the mainstream. The turbocharger performance has adirect impact on fuel consumption and the variable nozzle mechanism is used in high-temperature unlubricatedenvironments. To respond, Mitsubishi Heavy Industries, Ltd. (MHI) has developed and commercialized a VG turbocharger which meets outstanding standards for performance and reliability.
engine in the turbine to supercharge high-pressure air tothe engine by driving the compressor on the same shaft.
VG turbochargers are a type of turbocharger equipped witha variable nozzle vane mechanism on the turbine side. VG
turbochargers are capable of controlling supercharging
pressure to optimum conditions by adjusting the nozzle
opening according to the engine conditions. The chief benefit of this feature is an effective reduction of the engine's
fuel consumption, as shown in Fig. 1
1.

1. Introduction
With the tightening of emissions regulations in Europe, Japan, and the United States, VG (VariableGeometry) turbochargers have been replacing the conventional turbochargers equipped with waste gate valvesas the standard equipment for diesel engines. Whenoperating at a high level of efficiency, the VG turbocharger improves the fuel consumption and drivabilityof an engine. VG turbochargers use a complicatedTurbine housing

mechanism to drive the nozzle vane in high-temperatureunlubricated environments. As these components areinevitably used in a high pressure range and a wide-flowrate range environment, operation at the turbine blade

VariablenozzleThe variable nozzle
adjusts the level ofturbine throttling.

resonance point cannot be avoided. For this reason,

Nozzlethrottled

there is a stronger demand from the industry for ahigher level of reliability, such as enhancements in thewear resistance of the nozzle drive mechanism and theresonance resistance to the nozzle wake.

Improved Improved
low-speedfueltorque consumption

Turbinemoving blade

To respond to this demand, MHI has developed andcommercialized a new lineup of high-performance andhigh-reliability VG turbochargers for passenger cars,
Table 1
trucks, and buses (T1).

NozzleopenedExhaust gas

Exhaust gas

At low engine speeds =Amount of exhaust gas (Small)At high engine speeds =Amount of exhaust gas (Large)

Fig. 1 Mechanism and effect of the VG turbocharger
The VG turbocharger controls boost pressure to an optimum value bythrottling the nozzle vane during low engine speeds and opening it duringhigh engine speeds.

2. Objective and structure of VG turbochargers
Turbochargers are designed to use exhaust gas from theTable 1 Lineup of VG turbochargers from MHI
VG modelTD03

TF035H

TD04

TD04H

TD05

TD06

TD07

Engine displacement (L)

1.2-1.7

1.6-2.2

2.0-2.8

2.8-3.2

3.2-4.5

4.5-6.0

6.0-8.0 8.0-13.0

Engine output

40-6070-10090-130

130-150 150-180 180-200 200-240 240-350

(kW)

TF08

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 3 (Sep. 2006)*1 Nagasaki Research & Development Center, Technical Headquarters*2 General Machinery & Special Vehicle Headquarters

1Actuator

Nozzle vane
Compressor
wheel

Exhaustmanifold

Nozzle cartridge
VG turbo
Turbine moving blade

Lever plate

Optimized nozzle
vane opening

EGR valve

Crank
Drive ring

Optimized exhaustpressureIntercooler

MountEngine

Vane
Support

Optimized amountof EGR

Fig. 3 Structure of MHI's VG turbocharger
The variable nozzle vane mechanism portion is designed
as a cartridge to eliminate the thermal effect of the turbine housing.

EGR system

Inlet manifold

Turbine housing
Ring
VG nozzle cartridge

Fig. 2 VG turbocharger and EGR
Changes in the nozzle opening and engine exhaust pressure
make it possible to control the amount of EGR.

Turbinemovingblade
Direction ofrotation

Blade inlet

Loss
Circumferential
pressurevariation: Large

Circumferential
pressurevariation: Small

Straight nozzle

Reduction
in loss

Circumferential
direction(direction of rotationof the turbine
moving blade)

Curved nozzle

BladeoutletFig. 4 CFD results for the new-type curved nozzle
MHI has developed a new-type curved nozzle with reduced circumferential
static pressure distortion in the turbine moving blade inlet portion.

Bladeoutlet
Three-dimensional blade

Conventional blade shape

VG turbochargers have been applied over the last several years for the precise control of the EGR (ExhaustGas Recirculation: Recirculation of exhaust gas to theFig. 2intake) systems designed to reduce NOx (Fig.
2)(1). They
are now widely adopted for this purpose. The variablenozzle vane mechanism of MHI's VG turbochargers isstructured as a cartridge to eliminate the thermal effectof the turbine housing and thereby prevent sticking ofFig. 3
the variable nozzle vane (Fig.
3)(2).

New blade shape

Fig. 5 CFD results for the new type turbine moving blade
MHI has developed a new three-dimensional turbine moving bladethat reduces loss by preventing the accumulation of secondary flowat the moving blade outlet.

Further, the aerodynamic moment around the VG
nozzle vane changes according to the nozzle opening. In
the worst case, the opening-and-closing or closing-andopening of the nozzle causes a hysteresis in the boostpressure which hinders the engine control. In addition,
the moment and backlash generated as the nozzle linkmechanism wears leads to an excessive rotation of theVG turbocharger which can result in an excessive boostpressure. These tendencies with the curved nozzle differ from those with straight nozzles. Thus, the pivot
position of the curved nozzle was optimized to enhanceboth controllability and performance.
3.2 High-performance turbine moving blade
Losses in the turbine moving blade are concentrated
in high locations in the suction surface at the blade outlet
due to a secondary flow inside the blade, as shown in theCFD results in Fig. 5(3). In the new-type turbine moving
blade shown in Fig. 5, we were able to reduce losses in
the moving blade by making the blade three-dimensional
to prevent a secondary flow. This new-type turbine moving blade conferred a large effect and improved efficiency
by about 3% in the test of the turbine itself.

3. Performance enhancement
As mentioned previously, the industry now demands
a more highly efficient VG turbocharger to optimize thebenefits on fuel consumption. MHI has developed a highperformance turbine moving blade and also ahigh-performance VG nozzle vane. These are very important components.
3.1 High-performance VG nozzle
Figure 4 shows the curved nozzle developed and theCFD results. Our group changed the VG nozzle vanefrom a conventional straight vane to a curved vane, optimizing the shape to reduce the circumferential pressure
variations at all of the nozzle openings. These modifications also helped to reduce the exciting force of theturbine moving blade during nozzle wake resonance, aphenomenon described later.

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 3 (Sep. 2006)

2LampExample of 2.0L passenger application

Disk : Material A
Mirror Ring : Material B

Turbine efficiency

Turbine efficiency
enhanced by 12 %Ring
Disk: VG turbo of
the latest design: VG turbo of
the conventional design: Target
01 0002 000 3 000 4 000
Engine speed (rpm)

120 m wear
Disk : Material C
Ring : Material B
Bearing TEST FACILITY
16125 000

Original line

DiskRing
TEST PIECE1.18

to link wear. In trucks and buses, a valve is provided forthe down stream of VG turbocharger exhaust, and is used
as an exhaust brake. If the brake is used to close thevalve, the VG turbocharger is placed in an environment
even more susceptible to wear. As the wear of the linkadvances, the precision of the control of the boost pressure and EGR begins to deviate. This is why the everstricter emissions regulations introduced over the last
several years have created a strong demand for reductions in the wear of the nozzle link.
MHI has been improving the wear resistance throughtwo approaches: adopting wear-resistant materials for
the VG linkage and optimizing the shape and dimensionsof the VG linkage.
Wear-resistant materials for the VG link were selectedby a series of tests using the high-temperature wearing
7. Test conditions fortest equipment (4) shown in Fig. 7
the temperature, applied load, and friction speed were
determined based on the conditions of use in the actualunit. More than a dozen combinations of various materials were tested. As shown in Fig. 7, we were able tofind out a material combination that reduced the wear
noticeably compared with the material combinations conventionally used. This material combination is now
adopted for our latest VG turbocharger model.
The Taguchi method was used to optimize the shapeand dimensions of the VG linkage by investigating which
dimensions and shapes for parts were robust against linkwear. Fig. 8 shows the result of our optimization study.
Out of the elements investigated, we found three shapefactors that affected wear. Next, we built a prototype
VG linkage based on this result and confirmed the wearFig
resistance effect in actual tests on the prototype (FigFig.. 9 ).
The designs of the VG turbochargers for trucks and buses
are based on the designs for passenger cars, but withfurther enhancements in the wear resistance of theshapes and structures adopted.

1.14
1.1

Small

1.06

Small

Small

Dimension B

Dimension CL1L3
M
1
M
3
N
1
N
3
O
1
O
3
P
1
P
3
Q
1Q
3
R
1
R
3
S
1S
3
T1
T3
U
1U
3V
1V
3W
1W
31.02
A

3 m wearFig. 7 High-temperature wearing test equipment and test resultsfor optimum materials
Wear-resistant materials for the VG link were tested using the hightemperature wearing test equipment. An optimum material combination
was adopted based on the test results.

Dimension A2
B
1

Wear volume (Nmm/deg)

Fig. 6 Performance of the latest VG turbocharger (TF035H-VG)
The latest VG turbocharger shown on the right has enhanced turbine
efficiency on the engine by 12 %.

1.22

Original line

Design factor
Fig. 8 Optimized shape and dimensions for the VG linkage
The Taguchi method was used to design parts with more robust
dimensions and shapes against link wear.

3.3 Influence on engine performance
Figure 6 shows the TF035H-VG, the VG turbocharger
model most recently developed by our group. The design
combines the high-performance VG nozzle and high-performance turbine moving blade described above. Thismodel is driven by an electrically operated actuator,and has been adopted for use in 2L-class passenger
cars. Dramatic improvements in efficiency, especially atlow engine speeds, lead to equally dramatic improvementsin the fuel consumption and drivability in this model, as
shown in Fig. 6. The TF035H-VG has been well received.

4. Enhanced reliability
As described above, VG turbochargers must operate
in high-temperature unlubricated environments and remain fully workable in a high pressure range and awide-flow-rate range environment. For these reasons,the turbine moving blade is susceptible to inevitabledamage from nozzle linkage wear and nozzle wake resonance. Through the countermeasures shown below, MHI
has improved the VG nozzle linkage by enhancing its
wear resistance and resonance resistance to nozzle
wakes.
4.1 VG link material and shape optimization
As a mechanism used in high-temperatureunlubricated environments and in high-vibration environments in engines, the VG linkage is highly susceptible

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 3 (Sep. 2006)3

(2.0L Passenger:engine endurance)

Conventional type VG: Conventional VG

Noticeable wear
Noticeablewear

Noticeable
Noticeable wear
wear

After shape
optimizationwear
Almost no wear

Amount of wear

: Optimized VG

94 %
Down

92 %
Down

88 %
Down

88 %
DownAlmost no wearwear
0LEVER PLATE DRME PINSLEEVELEVER PIN
Amount of wear after 100-hours of endurance testingFig. 9 Results of durability test on optimally shaped VG turbocharger
The optimal dimensions for a prototype VG linkage were determined based on the Taguchi method and a prototype wasbuilt. Substantial wear reduction was confirmed in the endurance test.

VG nozzle

The resonance stress ofturbine moving blade due tonozzle wake resonance: Large

20Maximumvibrationstress

MEHCANISM OFBLADE VIBRATION161412

Natural frequency ofthe moving blade

10Relative vibration stress ofturbine moving blade based on
FEM analysis

8Turbine moving blade

6Fig. 10 Mechanism of nozzle wake resonance
Pressure variation due to the nozzle wake excites vibrations in theturbine moving blade. Resonance occurs when the moving blade
passes the wake in a cycle that coincides with its natural frequency.

4Full load
VG opening: Small

20

Number of turbine revolutions

4.2 Countermeasures for nozzle wake resonance
VG turbochargers must be capable of operating at anypoint within a high pressure range and a wide-flow-rate
range environment. Inevitably they must operate at
turbine moving blade resonance points within the operation zone. Nozzle wake resonance is the result ofvibrations in the turbine moving blade excited by thepressure distortion conferred by the wake in the nozzle
Fig. 10
wake flow (Fig.
10). The resonance occurs when themoving blade passes the wake in a cycle which coincides
with its own natural frequency.
MHI measures blade resonance stress in actual engines under various operating conditions using VG
turbochargers for trucks and buses. We can enhance theaccuracy of our resonance stress analyses by comparing
Fig. 11 ).
these measurement results with FEM results (Fig.
11This analytical system helps us to estimate blade stressduring nozzle wake resonance and to use our estimations to reduce the exciting force, tune the resonancepoint, and enhance the strength of the moving blade.
Through these improvements, we can protect the turbine moving blade against damages due to nozzle wake

Harmonics

Excitation of the turbine moving
blade due to the nozzle wake

Frequency (Hz)18Example of Truck application

Fig. 11 Comparison between measurements of turbine blade resonancestress and the results of FEM analysis
The turbine blade stress during VG nozzle wake resonance was measured andcompared with the FEM result to enhance the accuracy of our analyses.

resonance. To cope with the resonance points inevitably
encountered within the operation zone, we confirm thevibration resistance strength by operating VG turbochargers under actual engine conditions until theFig. 12
high-cycle fatigue limit is reached (Fig.
12).
4.3 Reliability track records in the market
Figure 13 shows the results of a Weibull analysis carried out to confirm the reliability of the TD03L-VG, theMHI VG turbocharger for passenger cars released commercially in 2003. The B10 life (life based on a failure
probability of 10%) of the TD03L-VG is a travel distanceof 5 million km. If the life of passenger cars is assumed
to be 100 000 km, the failure probability in the market
is 0.025% (250 ppm). This VG turbocharger incorporates
an optimum material combination as a design provision
to handle wear in the VG linkage. The lifetime of MHI's
newer VG turbocharger now being sold commercially isexpected to be even longer.
Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 3 (Sep. 2006)

4

5. Conclusion

Photo of fluorescent penetrant inspection after the turbine
moving blade was rotated 108 times or more at the blade
resonance point

With the tightening of global emissions standards, theconventional turbocharger with the waste gate valve is
rapidly being superseded by a new generation of VG turbochargers with improved fuel efficiency, drivability
improvement, and even EGR control for NOx reduction.
VG turbochargers rely on a complicated mechanism todrive the nozzle vane and have to perform with higher
efficiency and reliability in a wide operation range under conditions of severe use. To respond to these needs,
MHI has developed and commercialized a lineup of VG
turbochargers which perform outstandingly and reliably
not only for passenger cars, but trucks and buses as well.
We hope to improve the performance and reliabilityof our VG turbochargers further in the future and contribute to society through the development ofearth-conscious, low-emission vehicles.

Upper left:
Front face ofthe turbine moving blade
Bottom:Back face ofthe turbine moving blade
Upper right:
Side face ofthe turbine moving blade

References(1) Ebisu, M. et al., Mitsubishi Turbocharger for Lower Pollution Cars, Mitsubishi Heavy Industries Technical Review Vol.
41 No. 1 (2004)(2) Ogita, K. et al., The trend for automotive turbochargers, Journal of the GTSJ Vol.33 No.4 (2005) p.251(3) Osako, K. et al., Study of the Internal Flow of Radial Turbine
Rotating Blades for Automotive Turbochargers, SAE World
Congress (2002)(4) Matsui, A. et al., Improvement of Tribological Properties ofC/C Composites at High Temperatures, TRIBOLOGY TRANSACTIONS Vol.41 (1998) p.124

No damageFig. 12 Turbine moving blade after nozzle wake resonanceendurance test
We induced vibrations of the turbine blade under resonanceconditions in the engine until the material reached its fatigue limit.
Next, we confirmed an abnormality-free condition by an inspection
with fluorescent penetrant.

Example of 1.7 L passenger application

Cumulative failure rate (%)

101.00.025 %3 000 km0.010.001

1 000 km0.0001B10 Life 5 000 000 km
250 ppm at 100 000 km
106.7km=5 000 000km
103104105

Travel distance (km)Fig. 13 In-service (market) reliability of MHI's VG turbocharger for passenger cars
By a Weibull analysis of VG turbochargers now being sold commercially, we confirmed a long lifeand low failure rate of our VG turbocharger.

Katsuyuki Osako

Yasuaki Jinnai

Akira Samata

Hiroshi Suzuki

Seiichi Ibaraki

Noriyuki Hayashi

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 3 (Sep. 2006)5