E-Turbos: The Turbocharger Technology of the Future

The period between pushing your foot to the gas pedal and waiting for the engine to respond with the desired power has always been the Achilles heel of turbochargers. This lag in engine reaction, known colloquially as turbo lag, is what has kept turbochargers from performing optimally. A turbocharger’s purpose is to give more power, higher efficiency, and less lag in power delivery. Engine efficiency is more crucial than ever, prompting the development of smaller engines. However, power requirements are not diminishing, which implies that the displacement loss from tiny designs must be compensated for by other technologies such as turbochargers, which can aid increase power delivery and fuel economy.

What is a turbocharger and how do they work?

First, let’s understand how conventional turbochargers works. Naturally aspirated engines draw air into the combustion chamber by way of a partial vacuum created by the movement of pistons and opened intake valves. Turbochargers help to improve the fuel:air ratio in the combustion chamber and to regulate more precisely the amount of air entering by pushing air under force into the chamber. Exhaust gases from the engine spin a turbine which then powers a compressor by means of a rotating shaft. The compressor pulls in air, compresses it, and pushes air into the cylinders. The downside of turbos is the lag in getting the engine up to speed, from low pressure and low RPM to high pressure and high RPM, needed to spin the turbocharger. Larger turbo compressors cause longer lag, but if the turbo is too small, it will not operate efficiently at high RPM which leads to a shut down to cool. Remember that the turbine is spun up from high temperature exhaust gases, causing temperature management issues for the whole turbocharger.

By using a huge electric motor to operate a larger compressor at low speeds, e-turbos almost eliminate turbo lag. When the revs are high enough, the turbine can take over partially or completely to turn the compressor. This allows for a larger turbocharger, resulting in better power and economy. Furthermore, the electric motor can operate in reverse. By transferring electricity to the car’s battery, residual exhaust gases and the inertia of the turbo’s spinning when the vehicle is slowing down or coasting can be harnessed. This allows for the capture of energy that would otherwise be lost to the exhaust, resulting in increased efficiency and the provision of energy that may subsequently be used to restart the compressor. This effectively converts the electric turbocharger into a generator.

Electric turbocharging technology has been known for a long, but their incorporation into commercial vehicles is a relatively new development. The technology was first utilized in Formula One cars in 2014 as part of the sophisticated hybrid-electric power units, and it is still in use today. These e-turbos, codenamed MGU-H, would work in tandem with regenerative braking technology to boost performance, making them the most efficient combustion engines to date. These technology, like many of the advances created in Formula One, are now making their way into commercial vehicles.

What are the difficulties in e-turbo design?

The creation of an e-turbo is a difficult design task. A compromise must be struck between appropriate compressor, turbine, and electric motor size while minimizing total weight. Because the electric motor spins the compressor at low RPM and pressure, electric turbochargers can be built with a smaller operating range than conventional turbochargers. Turbomachinery design software like AxSTREAM® enables the design, analysis, and optimization of turbocharger components including the compressor and turbine. These tools aid in the design of machines at optimal design points, while the integrated tool is used to create turbine and compressor maps. AxMAP enables an engineer to determine which pressure and rotational speed ranges require the use of an electric motor.

Heat management is a major challenge in turbocharger design due to the high temperature of the exhaust gases utilized to spin the turbine. Because of the harsh working circumstances, special care must be made in the selection of bearings. Current research is focused on the development of spiral groove bearings and ball bearings capable of withstanding strong heat transients and variable loads, which are typical of turbocharger operating circumstances. Complex rotor dynamics difficulties also represent a challenge in turbocharger design and operation. The AxSTREAM Rotor Dynamics and Bearings tool can perform coupled rotor dynamics and bearing analysis. These applications provide information regarding the rotor-bearing-support system, such as static deflection forms, critical speed maps, Campbell diagrams for lateral and torsional analysis, and much more.

Electric turbochargers are the future of turbocharger technology, offering a novel option in the transition to smaller engines without sacrificing power delivery while boosting overall efficiency. Turbo lag can be reduced to almost zero, enhancing vehicle drivability and performance. Many challenges are faced in the design of such systems, but thanks to modern design, optimization, and analysis tools like the AxSTREAM software suite, these challenges can be much more easily overcome, resulting in exciting new turbocharger designs that will help power vehicles for many years to come.

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