Patent ID: 8079217
Filing Date: 2011-12-20
Classification: F01D,F02C

Abstract:
1. A turbocharger, comprising: a compressor wheel connected to one end of a shaft and disposed in a compressor housing; a turbine wheel connected to an opposite end of the shaft and disposed in a turbine housing having a chamber for receiving exhaust gas from an engine, a nozzle leading from the chamber into the turbine wheel; a center housing connected between the compressor housing and the turbine housing; an array of vanes disposed in the nozzle, each vane being pivotable about a pivot axis of the vane, the vanes being connected to a rotatable unison ring such that rotation of the unison ring causes the vanes to be adjusted in setting angle; a rotatable crank shaft coupled to the unison ring such that rotational movement of the crank shaft causes rotation of the unison ring; and an actuation system coupled with the crank shaft and operable to rotate the crank shaft and hence the unison ring for adjusting setting angles of the vanes, the actuation system comprising: a piston contained in a bore formed in the center housing and reciprocatingly movable in the bore between a fully closed position, a fully open position, and intermediate positions therebetween, the piston including a piston rod; a hydraulic system including hydraulic fluid passages connected to the bore, for supplying pressurized hydraulic fluid to the bore selectively on one side or an opposite side of the piston for causing the piston to move toward the fully open position or toward the fully closed position, respectively, movement of the piston toward the fully open position corresponding to pivoting of the vanes in a predetermined direction; a mechanical linkage coupling the piston rod to the crank shaft and operable to convert reciprocating movement of the piston to rotational movement of the crank shaft; and a spring arranged between the piston and a surface of the bore, the spring being structured and arranged to continuously exert a spring force on the piston toward the fully open position of the piston; wherein the spring has a spring constant and a configuration that are selected to ensure that the spring force is sufficient to hold the piston in a predetermined position corresponding to a predetermined position of the vanes during a start-up of the engine when the hydraulic fluid is substantially unpressurized such that hydraulic fluid force on the piston is substantially zero, and wherein the predetermined position of the piston is intermediate the fully open and fully closed positions, the spring force in the predetermined position being substantially equal and opposite to a total gear train force that must be overcome in order to move the piston from the predetermined position farther toward the fully open position.