Mitsubishi Heavy Industries Technical Review Vol. 56 No. 2 (July 2019)
1Reliability Assessment Technology of Variable Geometry(VG) Turbocharger Nozzle through MBD Analysis inConsideration of Thermal Deformation

ROHIT ARORA*1

HIROYUKI KANAZAWA*2

YOSUKE DANMOTO*3

For passenger vehicle turbochargers, which are one of the products offered by Mitsubishi
Heavy Industries Engine & Turbocharger, Ltd. (MHIET), variable geometry turbochargers(hereinafter referred to as VG turbochargers) are widely adopted as a technology for realizing
both fuel efficiency and power output. A VG turbocharger controls the flow velocity of exhaust gas
to the exhaust turbine blade to enhance the turbocharging effect. The nozzle mechanism, which
controls the flow rate, consists of many components and operates in a high-temperature andnon-lubricated environment. Accordingly, design in consideration of both function and reliability isdifficult.
For the purpose of design that improves the reliability of this mechanism, we developed adynamic behavior evaluation technology that can take into consideration interference and sliding
resistance, in which the thermal deformation of components is added to the conventional MBD
analysis technology considering elastic deformation and vibration response. This paper introduces
an overview of the developed technology.

|1. Introduction
MHIET is trying to improve reliability and performance by making full use of all analysis
techniques for designing turbochargers. In the conventional design of VG turbocharger nozzle
mechanisms, a method of designing the clearance based on the component shape at normal
temperature and evaluating the operability and the damage due to sliding wear to specify
dimensional tolerances was used. Furthermore, a design method to predict thermal deformation in
the operating temperature environment to avoid the risk of functional deterioration due to contact
was also used. In actual operation, since the mechanism operates in a high-temperatureenvironment, it is difficult to evaluate the mechanism using only one-way analysis technique likethe conventional method. Therefore, multiphysics analysis that adds consideration of the influenceof thermal deformation to multibody dynamics (MBD) analysis for predicting the motion andvibration of the mechanism is required.
We have developed a technology that can directly handle the effects of thermal deformation,
which was previously difficult with MBD analysis, and can take into account changes in theclearance and rigidity that change from moment to moment due to thermal deformation by being
coupled with the function of MBD analysis. This report introduces the developed technology.

|2. Overview of MBD and thermal deformation coupled analysis
technology
2.1

Issues to solve

Figure 1 depicts the mechanism and effects of a VG turbocharger, and Figure 2 illustrates
the arrangement and mechanism of a VG turbocharger nozzle. As an example of predicting theoperating behavior of this mechanism, Figure 3 gives the temperature distribution at the time of*1

Machinery Research Department, Research & Innovation Center*2

Chief Staff Manager, Machinery Research Department, Research & Innovation Center*3

Chief Staff Manager, Engineering Department, Turbocharger Division, Mitsubishi Heavy Industries Engine & Turbocharger, Ltd,

Mitsubishi Heavy Industries Technical Review Vol. 56 No. 2 (July 2019)2gas temperature rise (non-steady state) and Figure 4 presents the temperature distribution at thetime of steady gas temperature. As the exhaust gas temperature and flow change during operation,
the temperature distribution changes and the thermal deformation interconnectedly changes.
Considering the change in the clearance of each of the multiple nozzle mechanism components in
response to this change in thermal deformation, a design that maintains the positioning
performance defining the throttling amount of the variable nozzle and avoids the risk of damage
due to contact sliding under any operating condition is required.

Figure 1

Mechanism and effect of the VG turbocharger

Figure 2 VG turbocharger nozzle mechanism

Figure 3 Temperature distribution at thetime of gas temperature rise

2.2Figure 4 Temperature distribution at thetime of steady gas temperature

Development of MBD analysis technology considering thermal deformation

Currently, the mainstream method of predicting thermal deformation is FEM analysis. It isdifficult to couple this method with MBD analysis, which solves an equation of motion configured
by defining constraints between product components, so there were difficulties in considering
thermal deformation in MBD analysis. Responding to this situation, focusing on a method(1) ofmode-decomposing an equation of heat conduction as a differential equation, we developed amethod to analyze and evaluate the thermal deformation and motion of the mechanism
simultaneously by coupling this method with the equation of motion of MBD analysis in joint
research with The University of Iowa(2)(3).
In general, the characteristic equation for the temperature distribution described above can beMitsubishi Heavy Industries Technical Review Vol. 56 No. 2 (July 2019)3

expressed as Equation 1 by coupling it with the equation of motion of the object. In addition,Figure 5 shows the mode (eigen value analysis result) of the temperature distribution of the drivering. By superposing these modes, the deformation caused by the temperature distribution shown in
Figure 3 and Figure 4 is reproduced.
Figure 6 is the estimation result of the thermal deformation of the drive ring and mountusing MBD analysis. The difference in relative deformation between components due to thetemperature distribution causes a contact form distribution. In this way, MBD analysis can predictchanges in clearances and contact conditions between components due to the rotational behavior ofthe drive ring using the deformation and contact conditions as boundary conditions.

Equation 1 Coupling of equation of motion and equation of heat conduction

Figure 5 Drive ring temperature distribution mode (eigen valueanalysis result)

Figure 6 Contact load distribution due to thermal deformation of lower surface of drive
ring and upper surface of mount|3. Prediction of behavior and event occurrence using coupledanalysis
3.1

Prediction of behavior responding to thermal deformation of temperature
distribution at steady gas temperature

The behavior of the nozzle mechanism opening and closing operation was analyzed with thecomponent clearance and the contact state having thermal deformation using the temperature
distribution as the boundary condition shown in Figure 3. Figure 7 presents the result of extracting
the contact load between the drive ring and the mount. The prediction result indicates that thecontact point and load change depending on the drive ring rotation angle (vane opening degree).

Mitsubishi Heavy Industries Technical Review Vol. 56 No. 2 (July 2019)
4

Figure 7 Change in contact load between drive ring inner diameter andmount outer diameter (during gas temperature rise)

3.2

Prediction of behavior responding to thermal deformation of temperature
distribution during gas temperature rise

Next, the behavior of the nozzle mechanism opening and closing operation was analyzed
using the temperature distribution during gas temperature rise as the boundary condition shown inFigure 4. As shown in Figure 8, the prediction result indicates that the strong contact point and themagnitude of load during operation are different compared with the results at steady gas
temperature.

Figure 8 Change in contact load between drive ring and mount (comparison ofloads during gas temperature rise and at steady gas temperature)

3.3

Expected effects of developed analysis method

The influence of temperature distribution on the opening and closing operation of a VG
turbocharger nozzle mechanism is predicted using the developed MBD and thermal deformation
coupled analysis technology. As given in Figure 7 and Figure 8, the prediction result indicated thatthe contact point between components and the magnitude of load change depending on thetemperature distribution and the vane opening degree. Such a response is an event that is difficult tomeasure in testing. An optimal clearance that reduces the risk of damage can be designed byunderstanding the contact points and loads of components under all operating conditions.

Mitsubishi Heavy Industries Technical Review Vol. 56 No. 2 (July 2019)5|4. Conclusion
This report presents examples towards the application of thermal deformation and MBD
coupled analysis technology, which was conventionally difficult, to the design of VG turbocharger
nozzle mechanisms.
By introducing this analysis method that enables the prediction of product performance undera high-temperature environment where the measurement and understanding of actual machineconditions are difficult, highly-reliable product design can be achieved and a reduction in thenumber of prototypes and tests, as well as the prevention of rework, can be expected.

References
(1)
(2)

(3)

A.Heckmann. et. al, FLEXIBLE BODIES WITH THERMOELASTIC PROPERTIES IN MULTIBODYDYNAMICS, MULTIBODY DYNAMICS 2005, ECCOMAS Thematic Conference
Yamashita, H., Arora, R., Kanazawa, H. and Sugiyama, H., 2017, “Development of Reduced Order
Thermomechanical Model Using Floating Frame of Reference Formulation”, Proceedings of ASME
International Conference on Multibody Systems, Nonlinear Dynamics, and Controls (ASMEDETC2017-67317), Cleveland, OH, United States.
Yamashita, H., Arora, R., Kanazawa, H. and Sugiyama, H., 2019, “Reduced-Order ThermomechanicalModeling of Multibody Systems Using Floating Frame of Reference Formulation”, IMechE Journal ofMulti-Body Dynamics, in press (DOI: 10.1177/1464419318810886).