By Jim Marotta
At 100 horsepower per liter, GMβs newer turbocharged 1.4L has the power of a larger engine but retains the efficiency of a small-displacement four-cylinder in most driving conditions. Courtesy GM
Β
A naturally aspirated automobile engine uses the downward stroke of a piston to create an area of low pressure in order to draw air into the cylinder through the intake valves. Because the pressure in the atmosphere is no more than 14.7 psi, there is a limit to the amount of airflow entering the combustion chamber.
A turbocharged engine uses a radial fan pump driven by the engineβs exhaust that consists of a turbine and a compressor on a shared shaft. The turbine converts exhaust gases exiting the engine into rotational force, which is used to drive a compressor which draws in ambient air and pumps it at high pressure into the intake manifold to improve the engineβs volumetric efficiency. This results in a greater mass of air entering the cylinders on each intake stroke.
There are four main components to a turbocharger: the housing, the impeller/turbine wheels, the center hub and the bypass.
The size and shape of the housings fitted around the impeller and turbine affect performance,Β response, and efficiency. Courtesy Borg-Warner
Β
The size and shape of the housings fitted around the impeller and turbine dictate the performance characteristics of the overall turbocharger. This allows the designer of the engine system to tailor the compromises between performance, response, and efficiency to application or preference.
The impeller and turbine wheel sizes also dictate the amount of air or exhaust that can be flowed through the system. Generally, the larger the turbine and compressor wheels, the larger the flow capacity. The shape, curvature and number of blades on the wheels allow infinite variability in design to tailor a turbocharger to a given engine.
Water-cooled bearings, such as the one shown, allow engine coolant to keep the lubricating oil cooler, avoiding possible oil coking from the extreme heat found in the turbine. Courtesy Borg-Warner
Β
The center hub connects the compressor impeller and turbine and uses a bearing lubricated by a constant supply of pressurized engine oil. While the engine oil cools some systems, the preferred method is to use engine coolant to keep the lubricating oil cooler, avoiding possible oil coking from the extreme heat found in the turbine.
Turbos use a bypass or wastegate to prevent over-pressurizing the system. At a specific boost pressure, a bypass feeds part of the exhaust gas flow around the turbine. The wastegate which opens or closes the bypass is usually operated by a spring-loaded diaphragm in response to the boost pressure.
There are several tips to maintaining and servicing turbochargers:
Planning to service or repair your vehicle? Chilton can help! Access procedures, specifications, tips, and more at http://www.ChiltonDIY.com/.
A muscle car enthusiast and drag racer, Jim Marotta is a freelance automotive writer with more than 20 years experience in the automotive industry. |