Installation and Design Problems Associated with the Automotive Turbocharger 790313
The projected high volume use of turbochargers on automobiles has presented the designer with two formidable problems - cost and mounting flexibility. The cost of an automotive turbocharger has to be less than that of a comparable unit for a diesel engine - without any sacrifice in reliability. In order to maintain the cost, the manufacturer is forced into designing one basic unit to be used in numerous applications. Therefore, the successful marketing of an automotive turbocharger will depend very heavily upon the mounting versatility designed into the basic unit.
The design of the Schwitzer S6 automotive turbocharger was initiated with severe economic guidelines and mounting versatility being paramount in the design philosophy. In order to meet the design goals, a number of unique items had to be considered and incorporated into the turbocharger. The current design can be mounted from within four degrees of horizontal to within ten degrees of vertical. The bearing housing is sandwiched between the compressor end flange plate and the turbine housing with retention by three cross bolts located at 120 degree intervals. This arrangement allows the gravity oil drain to be rotated within the intervals between the bolts. The bearing system was simplified by using a free floating non-rotatable sleeve bearing with axial thrust capability to replace the Schwitzer rotating journal with a separate thrust bearing. The wastegate system is comprised of a rotary valve actuated by a remote boost-controlled spring-loaded diaphragm. The rotary valve concept allows the turbine to be bypassed to avoid any increase in the engine back pressure as a result of the presence of the turbocharger at high cruising speeds. The rotary valve also has the advantage of a positive self-cleaning feature and minimizes the close tolerance machining compared to a more conventional pop-off valve arrangement. The control mechanism for the wastegate is located remote from the turbine housing which allows the use of less expensive parts since they do not have to endure a hot corrosive environment. The relative merits of carburetor pressurization versus suction will also be discussed.