Design details

Components


The turbocharger has four main components. The turbine and impeller/compressor wheels are each contained within their own folded conical housing on opposite sides of the third component, the center housing/hub rotating assembly (CHRA).

The housings fitted around the compressor impeller and turbine collect and direct the gas flow through the wheels as they spin. The size and shape can dictate some performance characteristics of the overall turbocharger. The area of the cone to radius from center hub is expressed as a ratio (AR, A/R, or A:R). Often the same basic turbocharger assembly will be available from the manufacturer with multiple AR choices for the turbine housing and sometimes the compressor cover as well. This allows the designer of the engine system to tailor the compromises between performance, response, and efficiency to application or preference. Both housings resemble snail shells, and thus turbochargers are sometimes referred to in slang as snails.

Split-Inlet Exhaust Housings known as "Twin Scroll" permit the exhaust pulses to be grouped (or separated) by cylinder all the way to the turbine. The reason for doing this in keeping the individual package of energy, an exhaust pulse, intact and unmolested by other pulses all the way to the turbine. This in turn can give the turbine a better kick to get it moving. This is specifically usefull in four-cylinder engines. Because a four-cylinder only sees one pulse every 180 degrees of crank rotation, it needs all the energy it can get from each pulse. Keeping them separate and undisturbed will therefore pay back some dividends. 5* (Information from "Maximum Boost" by Corky Bell).

The turbine and impeller wheel sizes also dictate the amount of air or exhaust that can be flowed through the system, and the relative efficiency at which they operate. Generally, the larger the turbine wheel and compressor wheel, the larger the flow capacity. Measurements and shapes can vary, as well as curvature and number of blades on the wheels.

The center hub rotating assembly houses the shaft which connects the compressor impeller and turbine. It also must contain a bearing system to suspend the shaft, allowing it to rotate at very high speed with minimal friction. For instance, in automotive applications the CHRA typically uses a thrust bearing or ball bearing lubricated by a constant supply of pressurized engine oil. The CHRA may also be considered "water cooled" by having an entry and exit point for engine coolant to be cycled. Water cooled models allow engine coolant to be used to keep the lubricating oil cooler, avoiding possible oil coking from the extreme heat found in the turbine.