By Russ Banham
Every manufacturer seeks to squeeze more out of its machinery: more efficiency, more power, more reliability. For engine manufacturers, this is especially true. “More” is a mandate for their customers in the automotive, aviation and heavy machinery sectors, among others.
Today’s advanced turbochargers help meet these demands. In fact, we’re in the early stages of what’s shaping up to be the “Golden Age of Turbochargers.” The technology may still conjure images of high-performance cars, but increasingly, it’s common in ships, trains, buses and even construction machinery and generators.
First used in the 1920s, turbochargers increase engine horsepower by tapping into the energy that the engine’s own exhaust gases produce. What should go out goes back in — and delivers extra thrust.
This power and efficiency boost is valuable to automakers like General Motors, Volkswagen, Honda and BMW, all of which plan to increase their vehicle fuel economy by 3.7 percent year-over-year between 2022 and 2026. By 2026, the turbocharger market will stand at nearly double what it was in 2018, amounting to $32.4 billion, with more than 20 percent of vehicles running on turbocharged power.
That will include electric vehicles, which are expected to play a pivotal role in decarbonizing transportation. They will benefit from how turbocharging extends the distances they travel between charges, addressing one of consumers’ chief concerns.
Turbochargers That Keep Going … And Going
Future enhancements in reliability and performance will depend on sophisticated methodologies, like those that Mitsubishi Turbocharger, a part of Mitsubishi Heavy Industries (MHI) Group and a top manufacturer of high-quality turbochargers, is currently testing.
At MHI’s testing facilities in Sagamihara and Nagasaki, Japan, the staff performs 100 different tests on turbocharger components. The following five methodologies, in particular, illustrate the state-of-the-art technology and painstaking work needed to ascertain the reliability, functionality and safety of turbocharged engines prior to production.
They tell the evolving story of endurance in modern manufacturing.
Test No. 1: Drive Shaft Motion
Improving longevity begins with setting ambitious goals. For Mitsubishi Turbocharger, the aim is a turbocharger that lasts a minimum of 150,000 miles of driving, with 300,000 miles the optimal target. To increase durability, researchers must find ways to reduce the stress on the turbocharger shaft.
MHI conducts a motion test on the turbocharger components, which is a critical part of a turbocharged noise, vibration and harshness performance. A typical turbocharger has two wheels connected to a common shaft. When in motion, the shaft undergoes vibration and stress that can lead to breakage.
The staff uses sophisticated acoustic testing technology to balance the vibrations evenly across the shaft. “It’s all about the frequency,” says Frank Flores, assistant manager at Mitsubishi Turbocharger and one of the company’s “masters of reliability.” The shaft is “either well-balanced or it’s unbalanced.”
Test No. 2: Thermo Cycling Reliability
In manufacturing, you have to understand the biggest threats to equipment before you can combat them. For instance, every turbocharger suffers from severe temperature fluctuations that affect long-term productive use and lifespan. The turbine housing, the structure that holds together a turbocharger’s components, is particularly vulnerable to such thermodynamic stressors. Different materials — different grades of steel, iron or aluminum, for example — react differently to temperature fluctuations.
MHI engineers test the extent to which the housing materials will maintain their structure under the most severe circumstances. “The target is to see if the material can withstand this cycle and won’t crack, warp or deform,” Flores says.
In one example of many-cycle testing, the team opens up the throttle, revving it up to the maximum for about two minutes, and then lets it fall back to idle for 30 seconds. They repeat this process of cycling up and cycling down for as many as 200 hours to evaluate which materials hold up best.
Test No. 3: Thrust Bearing Endurance
All turbochargers contain highly engineered precision bearings that enable the machinery to operate at high speeds. Along with heat, another threat is friction.
Thrust bearings are static bearings permitting rotation between different parts. Different temperature cycles generate friction, which can interfere with the bearings and compromise turbocharger performance. To combat this, the bearings are lubricated with motor oil. But not every motor oil will do in every case. Each turbocharger is different, requiring a specific volume and oil viscosity to remain maximally functional in the face of various temperature cycles.
To minimize friction, engineers test various types, volumes and viscosities of lubricants and oil additives. The challenge is to adapt these tests to the specific thrust-bearing specifications that an original equipment manufacturer provides. In each case, researchers test a variety of different oil compositions until they discover the optimal lubrication that allows for high-speed efficiency.
Test No. 4: Moment Of Inertia
Vehicle inertia describes the distribution of mass across a vehicle, which affects performance. Rear-engine vehicles, for instance, perform differently than front-engine vehicles. One reason is that the center of mass — the unique point where the weighted relative position of the distributed mass adds up to zero — is different.
An engine performs most efficiently when its mass is evenly distributed around its center of mass. This principle also applies to the wheels inside a turbocharger, such as the compressor wheel and the exhaust gas turbine wheel. They perform best given even distribution.
The MHI staff tests various wheels made of different materials, like titanium aluminide or Inconel (a heat-resistant nickel-chromium-based superalloy), to determine which materials rotate best, completing the most revolutions in a specific period of time.
Test No. 5: Turbine Wheel Burst Containment
As frightening as it sounds, centrifugal forces can shatter the housing of wheels inside a turbocharger. If they do, wheel components can actually penetrate the interior of the vehicle itself and injure its occupants.
So MHI tests to ensure the integrity and reliability of the housing and wheels, particularly those of the high-performance new-generation turbochargers designed to outperform the prior generation.
Researchers simulate a situation in which the wheel shatters from stress, overspeed and other factors, verifying that the housing is capable of containing the wheel. They put different housing materials under extreme conditions to ensure that the containment will hold, thus protecting the passenger.
These five test methodologies represent just the tip of the iceberg. As Flores notes, the teams in various testing facilities — Sagamihara, Nagasaki, the Netherlands — are always striving for frictionless perfection in testing turbocharger reliability, durability and functionality. In that way, they give original equipment manufacturers more of what they’re looking for and, in so doing, pass the ultimate test.
About the author
Russ Banham is a Pulitzer-nominated journalist and best-selling author of the histories of major manufacturers such as Boeing, Ford and Bosch.