Development of Cummins Turbo Technologies Integrated M²™ Two-Stage systems Architecture using Rotary Turbine Control (RTC) Technology for the Cummins 5.0L V8 Turbo-Diesel Engine

M2 Two-Stage

Cummins Turbo Technologies recently launched a pioneering new Two-Stage turbocharger, the next generation Holset M²™ Two-Stage System with Rotary Turbine Control (RTC) which is Cummins most sophisticated turbocharger to date and delivers high efficiency, excellent driveability and low emissions levels. Successfully developed simultaneously to a major new engine development for Cummins, the ISV 5.0L is a new engine platform for Cummins with its flagship launch on the 2016 Nissan Titan XD pickup truck in North America. This article is a summary of the paper delivered at the 20th Supercharging Conference and highlights some of the system and product development challenges involved in the development of this fully integrated system, specifically looking at the product development challenges of the RTC system. To read the full version of the paper click here. System Engineering Challenges The integrated M²™ system differs from the other turbochargers in the market by its unique architecture and also the complexity of packaging the turbocharger. Due to the physical size of this architecture, the turbochargers most obvious first challenge was to fit or package it in space whilst avoiding surrounding engine components and optimizing for the many potential risks of being in such close proximity to other important engine sub-systems and components. Along with the highly interactive functional requirements, a system thinking mind-set had to be at the core of every team member to achieve program requirements. The project required a high performance team capable with the skills necessary to solve complex problems where both requirements and capabilities were unclear and fuzzy at the outset of the program. The team members had to have the skill and/or tools available to break down critical complex functions into definable functional objectives to execute the project. The full version highlights a few of the more useful system tools used on the journey. Product Development Challenges Nowhere was product development more challenging than in the Rotary Turbine Control (RTC) System, which is a groundbreaking development for the industry. This turbo technology had many new, unique and/or difficult (NUD) functions and components where engineering standard work and traditional computer-aided engineering (CAE) models lacked capability and/or real world usage correlation. This created a greater dependence on the use of a combination of critical thinking, Six Sigma, product and systems engineering tools. The repeating scenario that the team often found itself in can be best visualized using a Mental Model Archetype as shown in Fig 1.


Rotary Turbine Control (RTC) System
The main challenge of this turbocharger development was the RTC system and its many functions required using an actively controlled exhaust-side valve. Figure 2 shows various modes the valve allows. In most if not all conventional automotive sequential two-stage turbo architectures to this point, the state-of-the-art is to use a wastegate style poppet swing valve to achieve the bypassing function between the two turbochargers. For the RTC valve system, it doesnt end here. Not only is it utilized to channel (or bypass) flow between two turbines, but it has the additional functional requirements of an integrated wastegate for the low pressure (LP) turbine as well as exhaust throttling functionality to enable engine warm-up and aftertreatment regeneration. These added functions within a single valve design is something not seen in the industry today and represents a significant breakthrough in exhaust-side valve technology.


However, with the added functionality came significant technical challenges:

  • Design Packaging Constraints another NUD for this system was to attach the actuator for the RTC system not on the turbocharger itself, but on the intake manifold cover. This provided easier access to the actuator for serviceability, but introduced design and product development challenges with respect to tolerance stack-up and variation.
  • Kinematic Challenges the RTC control valve with all of its functionality required over 130 degrees of rotation presenting significant kinematic challenges and no fewer than half a dozen design iterations throughout development.
  • Reliability one challenge often seen with actively controlled turbochargers is the ability of the flow control device to operate reliably in a severe non-lubricated, high temperature diesel exhaust gas environment.
  • Torque Output having sufficient torque available at the actuator (i.e. capability or supply of torque) vs. the torque required to turn the RTC valve (i.e. mechanical system requirement or demand for torque) under all possible scenarios is one of the most challenging elements of developing actively controlled turbocharging systems. Having a positive torque margin is required, therefore solving this challenge involves a delicate blend of design changes to reduce demand whilst ensuring robust supply of torque at all times.

Due to the high degree of system complexity and relative immaturity of advanced computer aided engineering tools, running expensive physical testing often became the most time and cost efficient way to learn about the interactions and product capabilities and iterate on the designs. Developing correlated models was then needed to help drive the validation testing away from hardware toward virtual CAE tools, but often still fell short in capability due to the complex nature of the system.

The full paper also walks through a few more RTC components along with other hardware product development challenges and can be accessed here.

Outlook for the Future
Developing this fully integrated system brought about many system engineering and product development challenges but the end result is one of the most sophisticated turbochargers that Cummins has developed to date, delivering high performance that enables excellent driveability, low emissions and fuel economy. Cummins Turbo Technologies are confident that we have a product that enables Cummins to achieve many successes in the future on this product. Future variants of this technology are already in exploration and Cummins Turbo Technologies hope to utilize the lessons learned on this program and apply them to future opportunities around the globe. To learn more about the Holset M²™ Two-Stage System with RTC and its different modes of operation view our video on YouTube.

Cummins Office Building

Cummins Inc.

Cummins is a global power leader that designs, manufactures, sells and services diesel and alternative fuel engines from 2.8 to 95 liters, diesel and alternative-fueled electrical generator sets from 2.5 to 3,500 kW, as well as related components and technology. Cummins serves its customers through its network of 600 company-owned and independent distributor facilities and more than 7,200 dealer locations in over 190 countries and territories.

Cummins Turbo Technologies launches exhaust throttle valve

Cummins Exhaust Throttle Valve - ETV

A new Exhaust Throttle Valve (ETV) for aftertreatment thermal management and exhaust braking has been developed by Cummins Turbo Technologies (CTT). ETV helps engine manufacturers meet stringent emission requirements.

"With more than 60 years of experience in engine air handling innovation, CTT is uniquely positioned to integrate ETV with engine systems that provide customers with a complete system level solution. Cummins’ knowledge of air handling systems combined with experience in control systems technology has achieved a cost effective, high performing ETV to meet the needs of our customers," commented Matt Franklin, Director – Product Management & Marketing.

Initially, the launch of the ETV was developed for medium-duty engine applications in India and China, and has since grown to Brazil, Europe and Mexico. ETV applications include on-highway truck, transit bus, refuse and tipper trucks. 

The ETV not only helps engine manufacturers meet stringent emission requirements, but also offers flexible design needs. Cummins’ Original Equipment Manufacturers (OEM) have options to configure the product with heat shields, coolant fittings and locator features. Bespoke ETV products can be designed with customized flap diameter for tailored pressure control and unique end connections for easy integration. These flexible design offerings help OEM’s meet their packaging and performance requirements. 

"We have validated the product extensively on more than 130 applications with five different engine families. At the end of 2019, the total field mileage accumulation exceeded ten million kilometers - equivalent to circling the earth 250 times. The extensive engine and vehicle validation pursued by CTT has ensured a reliable and durable product," explained Brett Fathauer, Executive Director, Research & Engineering. 

A modular service strategy was also put in place to allow selected components to be serviced, rather than replacing the entire ETV. Thus, lowering the total cost of ownership. Additionally, CTT has leveraged its global supply chain to minimize product costs and support global market needs. The ETV is currently in production and is available now for customers.

Cummins Office Building

Cummins Inc.

Cummins is a global power leader that designs, manufactures, sells and services diesel and alternative fuel engines from 2.8 to 95 liters, diesel and alternative-fueled electrical generator sets from 2.5 to 3,500 kW, as well as related components and technology. Cummins serves its customers through its network of 600 company-owned and independent distributor facilities and more than 7,200 dealer locations in over 190 countries and territories.

Cummins Turbo Technologies breathes new life into the HE600 Holset Turbocharger

Cummins Holset HE600WG Turbocharger
Cummins Turbo Technologies (CTT) has revitalized the HE600 Turbocharger (pictured) platform

With an all-new compressor stage and turbine housing, the HE600 Holset Turbocharger from Cummins Turbo Technologies (CTT) offers a class-leading product for its customers. 

Strengthening its product catalogue, CTT has revitalized the HE600 platform by delivering significant improvements on performance and durability. By combining years of engineering experience in turbine wheel and impeller design, overall turbocharger efficiency has increased more than four percent while offering a product that is more robust.

"We have used advanced aerodynamic techniques to design a new impeller and compressor housing that offers up to five percent higher efficiency in the flow range of our key customer applications. In addition, a new turbine stage was developed and designed with the benefit of analysis tools that enhance performance, while still optimizing thermal stress and improving fatigue life," explained Charles King-Cox, Compressor and Turbine Stage Director for Cummins Turbo Technologies.

The performance results of the upgraded HE600 have been met with enthusiasm from customers in both on-highway and off-highway applications who describe the Holset product as "class leading."

The turbochargers have increased the flow range to have an overlap with the larger HE800 series. Customers using HE800 can now switch to a more compact HE600 that has increased map-width, higher performance and improved durability to help meet downsizing requirements to save on costs. 

Aerodynamic efficiency is a critical element of turbocharger design and the team at CTT has used the latest design practices to ensure the new product beats the competition and drives value for customers. 

The new product design incorporates aerodynamic efficiency, surpassing the competition with high efficiency and durability. Production for the new HE600 will begin in 2020 and cater to a wide range of customer applications, including on-highway trucks, generators, industrial markets and marine markets. 

"We are continuously working to improve our product line - and the HE600 is no different. This product will exceed performance expectations and provide increased value for our customers across the globe," commented Matt Franklin, Director - Product Management and Marketing at Cummins Turbo Technologies.

Cummins Office Building

Cummins Inc.

Cummins is a global power leader that designs, manufactures, sells and services diesel and alternative fuel engines from 2.8 to 95 liters, diesel and alternative-fueled electrical generator sets from 2.5 to 3,500 kW, as well as related components and technology. Cummins serves its customers through its network of 600 company-owned and independent distributor facilities and more than 7,200 dealer locations in over 190 countries and territories.

Surface Engineering of Turbomachinery Components to Meet Future Industry Trends

Materials Engineer

Novel Solutions for Materials Engineering
Increased demands are being placed upon turbochargers as a result of ever more stringent emissions regulations, a necessity for improved product performance and reliability and a requirement for a wider product operating range. Consequently, a greater level of stress is placed upon the materials from which turbochargers are manufactured. In order to achieve all of the necessary legislation and customer requirements, novel solutions to materials engineering challenges are being developed.

Two such challenges faced by the turbocharger industry are high temperature tribology and the corrosion and erosion environment generated by long route exhaust gas recirculation (LR EGR). Cummins Turbo Technologies has developed innovative materials engineering solutions using surface treatments applied to cost effective substrates, rather than utilising much more expensive, exotic alloys.

High Temperature Tribology
As a consequence of experiencing excessive vane and slot wear whilst in service and experiencing temperatures > 500 °C, a thermochemical diffusion surface engineering solution was developed for variable geometry systems.

Figure 1 - Variable Geometry System


Such technology was generated using a systematic approach to tribological testing and analysis, which was pioneered by Cummins Turbo Technologies as shown in Figure 2. After comprehensive evaluation of the problem using the expertise at Cummins Turbo Technologies, it was determined that during particular operating conditions the conventional uncoated nozzle and shroud plate experienced high levels of abrasive wear and elevated friction forces.

Figure 2 - Cummins Turbo Technologies Approach to Tribological Testing and Analysis

Figure2_Tribilogical_Testing_0.gifIn order to solve the problem, a multi-disciplinary cross functional team at Cummins Turbo Technologies used the relevant customer and regulatory requirements to identify and develop the surface treatment concept. Using cutting-edge techniques, the fundamental mechanical and physical properties of the thermochemical diffusion treatment were determined. Subsequently, the surface treatment was characterised in terms of friction and wear performance using a tribometer, which simulated the variable geometry nozzle to shroud plate interface and associated operating conditions.

The surface treatment was tested on a turbocharger, on both gas stand and engine, with the results correlated to tribometer-based testing to ensure consistency of performance. This approach to the problem ensured that a robust engineering solution was identified and implemented into production; the resultant positive impact on nozzle vane wear performance can be observed in Figure 3.

Figure 3 - Comparison of Wear Performance between Untreated and Surface Treated Nozzle Vanes


Abrasive Wear

Large Wear Volume


Abrasive Wear

Wear Volume

Significantly Decreased

Long Route Exhaust Gas Recirculation
The turbocharger compressor stage, which includes the compressor wheel and cover (Figure 4), is subjected to a corrosive and erosive environment when an engine is operating LR EGR. The chemistry and pH of the condensate present in the compressor stage varies depending on engine operating conditions and the chemistry of the fuel. Furthermore, the architecture of the LR EGR system dictates the density and size of erosive particles to which the compressor stage is subjected.

Figure 4 - Compressor Wheel and Compressor Cover


In order to minimise the wear and corrosion observed on the compressor wheel and cover as a result of interaction with condensate and erosive particles, surface treatments were developed for the two components. Numerous concepts for both components were identified using a multi-disciplinary cross functional team at Cummins Turbo Technologies, using regulatory and customer requirements as a guideline.

Subsequently, the concepts were subjected to numerous in-house tests which were developed using the expertise of Cummins Turbo Technologies:

Mechanical properties
Aerodynamic performance
Corrosion resistance
Erosion performance

Such experiments utilised surface treated test bars and also components in order to correlate the data from fundamental laboratory to turbocharger-based testing. The acquired data was analysed using the expertise of Cummins Turbo Technologies and various advanced techniques, with the results input into a comprehensive scoring matrix in order to select the most appropriate solution for the two respective components.

The process developed for the compressor wheel was of an anodising type, whereas a polymeric coating was developed for the compressor cover. As a result of the research and development work conducted, these technologies have been proven to significantly reduce the wear and corrosion observed on compressor wheels and covers subjected to LR EGR environments. A comparison of untreated and surface treated compressor wheels and covers can be observed in Figure 5.

Figure 5 - Untreated and Treated Compressor Wheels and Covers



Untreated at Top

Treat at Bottom

Experts at Cummins Turbo Technologies are continually developing novel solutions to materials engineering challenges in order to meet customer requirements for more robust and durable products.

Cummins Office Building

Cummins Inc.

Cummins is a global power leader that designs, manufactures, sells and services diesel and alternative fuel engines from 2.8 to 95 liters, diesel and alternative-fueled electrical generator sets from 2.5 to 3,500 kW, as well as related components and technology. Cummins serves its customers through its network of 600 company-owned and independent distributor facilities and more than 7,200 dealer locations in over 190 countries and territories.

The High Temperature Tribological Performance of Turbocharger Wastegate Materials

Engineer Looking at Computer Monitor

This article is a summary of a technical paper delivered at the IMechE 11th International Conference on Turbochargers and Turbocharging.

Tribology within Turbochargers

There are numerous tribological interfaces, commonly termed tribosystems, within a turbocharger. Some of these, such as the rotor bearing system, are lubricated and operate at temperatures less than 200 °C. The variable geometry and wastegate systems (Figures 1 & 2) are examples of high temperature tribological interfaces within a turbocharger which are subject to temperatures between 300°C and 800 °C but are not lubricated.

Figure 1 - Variable Geometry System Figure 2 - Wastegate Assembly




Irrespective of the nature of the tribosystem, it is vital to select the appropriate combination of materials which provide the desired friction and wear behaviour for the interface. For that reason, extensive research and development is conducted on this topic in order to optimise the tribological performance of the system and to determine the reliability and durability of the components when in service.

Tribological Characterisation of High Temperature Materials used within Turbochargers

Within high temperature tribosystems such as the variable geometry and wastegate mechanisms, turbine inlet temperature significantly affects tribological performance. This is because for a given material at high temperature, the rate of oxidation and mechanical properties vary compared to when at room temperature. Therefore, materials which find use within high temperature tribosystems are usually of high cost due to their exotic chemical composition, which is required to provide oxidation stability whilst also affording sufficient mechanical properties, frictional response and wear behaviour. Recently, there has been increased focus on the development of materials that offer a cost reduction yet similar tribological performance compared to the more conventional substrates used at high temperature. As a result, extensive testing and analysis is conducted by Cummins Turbo Technologies in order to understand and validate the capabilities of such materials within turbocharger products. The friction and wear characteristics of high temperature interfaces within a turbocharger are traditionally established through component based experimentation. Using a research and development approach founded on the fundamentals of Materials Science, Cummins Turbo Technologies is able to select preferred material combinations with confidence prior to completion of considerably more expensive and time consuming component based testing.

Fundamental Approach to Tribological Characterisation of Wastegate Materials Wastegate Turbocharger


In this research, a high temperature tribometer was employed in order to simulate the tribological interface between a wastegate shaft and bush within a turbocharger. Such simulation is highly complex and as such, it was essential that Cummins Turbo Technologies utilised their in-house expertise to ensure that the modelled tribosystem was representative of the engineering interface. The extensive knowledge and skill base of engineers at Cummins Turbo Technologies was also used to evaluate test samples from both fundamental and turbocharger-based experiments. Extensive analysis of test samples was conducted using highly complex methods in order to characterise the substrates with regards to surface topography, tribochemistry and wear. This methodology allowed Cummins Turbo Technologies to determine why particular materials and combinations of materials possessed superior performance at specific operating conditions.

A fundamental approach to characterisation of material friction and wear performance has numerous benefits: A significant reduction in cost compared to component-based testing, since test parts do not need to be in component-form Improvement in the efficiency of the product development process, since tribometer-based experimentation is an accelerated test and results can be obtained much faster than traditional component-based validation Reduction in complexity and marked improvements in data quality compared to component-based testing High Temperature Tribological Performance of Wastegate Shaft and Bush Materials Four material combinations were selected for testing based on their suitability for the application in terms of cost, corrosion behaviour and predicted tribological performance (Table 1).

Table 1 - Tribological test substrates


All of the material combinations were subject to fundamental tribological tests which were conducted at 600 °C, 850 °C and 950 °C. The wear performance of the material combinations was determined using an optical measurement technique. Subsequently, the rationale behind why the materials provided the observed performance was determined using high resolution surface analysis techniques and the R&D expertise of Cummins Turbo Technologies in order to characterise the substrates and acquire the greatest possible data quality. Data correlation between tribometer and component-based experiments was successfully conducted in order to ensure that the fundamental tests were relevant and provided the appropriate level of data and confidence prior to conducting much more expensive and complex component-based experiments.

Overview: Materials Science at Cummins Turbo Technologies

This fundamental approach to Materials Science research and development has significantly improved the analysis-led design and testing capabilities of Cummins Turbo Technologies, resulting in the development and delivery of superior technologies to our customers. The analysis-led testing methodology provides greater data quality, improved efficiency of the product development process and reduction in cost of Materials Science research and development. Using the experimental and analytical techniques as described above, Cummins Turbo Technologies is developing high performance material combinations which address the specific requirements for light duty to high horsepower turbocharger applications.

Cummins Office Building

Cummins Inc.

Cummins is a global power leader that designs, manufactures, sells and services diesel and alternative fuel engines from 2.8 to 95 liters, diesel and alternative-fueled electrical generator sets from 2.5 to 3,500 kW, as well as related components and technology. Cummins serves its customers through its network of 600 company-owned and independent distributor facilities and more than 7,200 dealer locations in over 190 countries and territories.

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