Design and Analysis of Mounting Arrangement of the Rotary Turbine Control (RTC) Drive System

Turbocharger is the turbine driven force induction device widely used in IC engine applications to meet performance and emission requirement. The Rotary Turbine Control (RTC) system is the invention of Cummins in turbotechnology field. The components of system are RTC valve, actuator and RTC linkage. The RTC linkage contains lever arm and spring and it connects actuator shaft and RTC valve shaft. Actuator rotates valve by using linkage. RTC valve manipulates the exhaust gas going in the turbine housing. This valve is actuated by Engine Control Module (ECM) through the actuator. ECM unit sends signal to actuator depending on the road condition and then actuator rotates valve by using RTC linkage. This paper has 2 goals. First is to design bracket to support actuator on turbine housing in the given space claim and validated design of bracket by modal analysis and RVA for given conditions. As all RTC system components are close to turbine housing so they are exposed to high temperature. The actuator and spring are very temperature sensitive. So, second goal is designing of heat shield for actuator and spring and validate these designs by using Steady thermal analysis for given temperature conditions. Keywords— Turbocharger, Turbine Housing (TH), Rotary Turbine Control (RTC), Cause and Effect matrix (CnE), Modal Analysis, Power Spectral Density (PSD)


INTRODUCTION
Cummins Company has many generations of turbocharger. According to recent emission norms, the exhaust gases coming out of engine should be minimum as possible. To meet this condition Cummins introduces RTC system to automobile industry. RTC valve is placed at the inlet manifold of the turbocharger in the turbine housing ss shown in the fig. 1.1. by red dot. This valve manipulates exhaust gases before going into the turbine housing. The components of RTC system are RTC valve, RTC linkage and actuator. RTC valve manipulate the exhaust gas. RTC linkage connects valve shaft and actuator shaft and actuator rotate valve by using RTC linkage. According to road and engine condition, Engine Control Module (ECM) sends signal to actuator, actuator rotate valve through linkage and exhaust gases is manipulated.  [15] General principle of RTC valve is as shown in fig. 1.2. RTC valve controls exhaust gases going in the turbine of turbocharger. Using RTC valve some amount of gas is sent to turbine wheel and some exhaust gas passes straight to the after-treatment system depending on the engine condition. RTC is one of the important inventions in automobile industry that can bypass 100% exhaust gas passes straight to the after-treatment system. The RTC system is close to turbine housing (blue colour body in fig 2.1) and engine so it will exposed to high temperature. High temperature affects the working of actuator and spring so, design the heat shield for both and validate design.. Heat coming to spring and actuator is shown in fig. 2

A. Concept A:
In this concept, the designed bracket can be manufactured from one blank. The lower part of bracket is act as support of actuator and side wall of bracket act as heat shield for actuator and spring. For mounting of bracket on TH, 5 bolts are used. In fig. 3.1, orange part is a bracket this is manufactured from bending process. To protect actuator, actuator should be shield from 3 sides but in this concept the heat shield is for only one side of actuator this is the drawback of concept A.

B. Concept B:
In this concept, the separate heat shield is designed for actuator and spring and bracket for mounting of actuator. Bending process is used for manufacturing of heat shield and bracket. Both bracket and heat shield are mounted on the TH. In fig. 3.2 grey part is heat shield and orange part is bracket. Drawback of concept B is that spring is still exposed to the radiation coming from inlet flange of TH shown by arrows in fig. 3.3.

C. Concept C:
This concept is addition to concept B, the extra heat shield for spring is designed. In fig. 3.4 pink part is heat shield of spring.

IV. CONCEPT SELECTION
Concept selection is the process of evaluation concepts, comparing the relative strengths and weaknesses of the concepts and selecting one concept. The concept is finalized by considering factors like space claim, protection of all components of system, cost and different criteria. Pugh matrix and CnE matrix are used concept finalization.

A. Pugh matrix:
During concept selection, initially concepts are evaluated relative to a baseline product using the Pugh matrix. Pugh matrix compares all concepts with baseline and gives best concept from all. For Pugh matrix used for the concept selection refer Table 1 in Appendix.
After the rating in Pugh matrix, concept C and concept D got same rank. To select best concept from these 2 CnE matrix is used.

B. CnE matrix:
In this matrix, ratings from 1 to 10 are given for the concepts. One more advantage of this matrix is weightage is also given to the criterions, so we can get more accurate result. In a C&E matrix, customer requirements i.e. criteria are ranked by order of importance to the customer. The CnE matrix is shown in Table 2

A. Design of bracket:
The actuator having 1 Kg mass is mounted on bracket and bracket is fixed on TH using 5 bolts. As grade 304 stainless steel have high tensile strength so this material is selected for it. As bracket manufactured by bending procedure so its thickness decided as 3 mm. (as thickness of 3 mm of sheet is widely preferred in Cummins and for manufacturing of sheet having thickness greater than 3 mm, special tools are required which require more cost). The detailed view of bracket is as shown in figure 5.1.  The modal analysis and RVA are performed to check the strength of bracket. Steady thermal analysis is performed to calculate temperature of actuator and spring before and after mounting of heat shield.

Modal Analysis
Modal analysis examines the modal behavior of model. Modal analysis is used to calculate the natural frequencies and mode shapes of model. The analytical frequency of bracket and heat shield for inline engine is given by below equation. Engine speed-3000 rpm Number of cylinders of engine-6 = 330 Hz

Geometry details:
The assembly of following parts is considered for modal analysis as shown in fig. 6.1.
1. Heat shield for spring 2. Bracket 3. Heat shield for actuator 4. Actuator The mass of actuator is 1 kilogram. This mass is acting at CG (Centre of Gravity) of actuator assembly.

Material properties:
The material properties for all components are as shown in table 3.  Heat shield for Actuator 4 4 Actuator 3  5 Face sizing at all contacts 2 The body sizing of various components is as shown in fig.  6.2.

Mode 4
Frequency achieved of mode 4 is 592.65 Hz. In this mode shape there, deformation of bracket in Xdirection and heat shield of actuator in Z-direction occurred but deformation of bracket is maximum. The maximum displacement is dominant in X-direction as shown in fig. 6.8. Where, On X-axis ω/ωn is plotted, where ω is applied frequency and ωn is natural frequency and on Y-Axis is Amplitude plotted.
When ω/ωn is equal to 1 i.e. applied frequency is equal to natural frequency of the system resonance occurs and system vibrates very harshly which may cause failure of it. In order to ensure safe working of the system, the ratio ω/ωn should be either below or above one, i.e. experimental natural frequency should be much below or above the resonant condition. In this case applied frequency is 330 Hz while that obtained from Ansys is 350 Hz, thus ratio of ω/ωn >1 and system is safe. When natural frequency from Ansys is less than calculated frequency then also system is safe, but if there are any changes in operating conditions it is possible that natural frequency may increase and reach resonant condition which is not desirable. Therefore, it is safe to say that natural frequency from Ansys which emulates real world condition during loading and boundary condition must be greater than analytical frequency to ensure safety of the system. Thus, bracket design is safe. To get PSD data, road condition applied to engine and run the engine, the acceleration versus frequency data is plotted.

Boundary condition:
The PSD-G data is taken from the test cell. This PSD data is applied at fixed support shown fig. 6.4 and fig. 6.5.

Results:
The equivalent stress is calculated in RVA analysis. This stress is calculated in 3 direction i.e. X-direction, Y-direction and Z-direction.

a. Equivalent stress generated in X-direction:
The maximum stress is generated in bracket and it is 61.28 MPa is shown in fig. 6.9.

b. Equivalent stress generated in Y-direction:
The maximum stress is occurred in heat shield of actuator and is 79.4 MPa is shown in fig. 6.10.  Analysis of Random Vibration response of the model finite element was conducted on the basis of modal analysis. From the above result, it is clear that maximum stress is generated at bend of bracket and heat shield of actuator. These stresses are generated because of sharp edges. In actual practice, there should not be any sharp edge at bend so, no stress generated in bracket and heat shield. So, this design is safe.

Thermal analysis:
The steady-state thermal analysis is used to calculate the thermal response of system to heat loads depending on the applied thermal conditions. Steady-state thermal analysis assumes a steady-state for all thermal loads and boundary conditions. Steady state means thermal loads are not varying with the time.

Geometry details:
The assembly of following parts is considered for this analysis as shown in fig. 6.12.
1. Turbine housing 2. RTC valve 3. Valve side lever arm 4. Heat shield for spring 5. Actuator side lever arm 6. Bracket 7. Actuator 8. Heat shield for actuator Spring will fit on the extrusion of part number 5 i.e. actuator side lever arm. Temperature of spring will be same as the temperature of extrusion of part number 5 so, spring is not taken in analysis. This is for convenience.

Material properties:
The material properties for all components are as shown in table 5.

Coordinate system:
In this case, global coordinate system is used as coordinate system.

Contact details:
In this case, for all contact bonded contact is selected.

Mesh details:
Element size of all elements used for meshing are listed in table 6. Valve side lever arm 3 4 Heat shield for spring 3 5 Actuator side lever arm  3  6  Bracket  3  7  Actuator  3  8 Heat shield for actuator 3 9 For all face contact 4 The meshing is shown in fig. 6.13.

Boundary condition:
The heat from TH and engine is transferred to RTC system components by 3 modes i.e. conduction, convection and radiation. But radiation mode is dominant over other mode so radiation mode is considered for this analysis. For the radiation following are the boundary conditions.

First condition for actuator-
Emitter source-The radiated surface of turbine housing is shown by blue colored surface as shown in fig. 6.14. The temperature of surface is 77 0 C and emissivity factor is 0.94. Fig. 6.14 Emitter surface of turbine housing Receiver source without heat shield-The receiver surface is actuator is shown by blue colored surface as shown in fig  6.15. The temperature of surface is 77 0 C and emissivity factor is 0.8. Receiver source with heat shield-The receiver surface is heat shield for actuator is shown by blue colored surface as shown in fig 6.16. The temperature of surface is 77 0 C and emissivity factor is 0.8. Second condition for actuator-Emitter source-The high temperature exhaust gases in the outlet of turbine housing radiates lot of heat is shown by blue colored surface as shown in fig. 6.17. The temperature of surface is 675 0 C and emissivity factor is 0.94. Receiver source without heat shield-The receiver surface is actuator is shown by blue colored surface as shown in fig.6.18. The temperature of surface is 675 0 C and emissivity factor is 0.8. Receiver source with heat shield-The receiver surface is heat shield for actuator is shown by blue colored surface as shown in fig. 6.19. The temperature of surface is 675 0 C and emissivity factor is 0.8. Third condition for spring-Emitter source-The radiated surface of turbine housing is shown by blue colored surface as shown in fig. 6.20. The temperature of surface is 77 0 C and emissivity factor is 0.94. Receiver source without heat shield-The receiver surface is spring is shown by blue colored surface as shown in fig. 6.21 Here lower surface of actuator side lever arm is considered as receiver instead of spring surface. The temperature of surface is 77 0 C and emissivity factor is 0.8. Receiver source with heat shield-The receiver surface is heat shield for spring is shown by blue colored surface as shown in fig. 6.22. The temperature of surface is 77 0 C and emissivity factor is 0.8. Forth condition for spring-Emitter source-from the inlet of the turbine housing the high radiation are coming to the spring. The radiated surface of turbine housing is shown by blue colored surface as shown in fig. 6.23. The temperature of surface is 700 0 C and emissivity factor is 0.94. Receiver source without heat shield-The receiver surface is spring is shown by blue colored surface as shown in fig. 6.24.
Here surface of actuator side lever arm is considered as receiver instead of spring surface. The temperature of surface is 700 0 C and emissivity factor is 0.8.  Receiver source with heat shield-The receiver surface is heat shield for spring is shown by blue colored surface as shown in fig. 6.25. The temperature of surface is 700 0 C and emissivity factor is 0.8.    The temperature of spring with heat shield is 80.78 0 C as shown in fig. 6.29. The temperature at the spring is reduced by 163 0 C after installation of heat shield for spring. Conclusion: The heat coming on the actuator and spring is reduced after installation of heat shield. So, working of actuator and spring may not get affected. The design of both heat shields are validated.

VII. CONCLUSION
From this paper it is concluded that, 1. Multiple concepts were developed and based on the result of Pugh and CnE matrix for concept selection; best suitable concept for bracket and heat shield is selected. 2. By comparing the both values it is clear that value obtained from Ansys is greater than analytical value and thus system is safe as there are no chances of occurrence of resonant condition. 3. Also maximum equivalent stresses observed are close to the sharp edge in Ansys but in actual practice there will not be any sharp edge so, there will not be stress in bracket and both heat shield. 4. From steady thermal analysis it can be concluded that heat shield reduces the heat reaching to spring and actuator thus serves its purpose. So, the design of bracket, heat shield of actuator and heat shield of spring are validated and they are safe.