This invention relates to methods of operating turbochargers and similar high speed rotating machinery, and to a unique design for a semi-floating bearing apparatus used therein.
Turbochargers are well-known in the prior art and conventionally utilize a turbine wheel and a compressor impeller mounted on a unitary or common shaft. The turbine wheel and compressor are carried within their respective housings and are rotated at high speeds by the shaft.
The operating components of turbochargers and other high speed rotating machinery are subjected to extraordinary forces and destructive vibrations which do not occur in machinery operated at lower speeds. The shafts of turbochargers typically rotate at speeds of 125,000 r.p.m. and above. At such speeds severe destructive vibrations occur as a result of a static inbalance of the shaft and other components. Accordingly, it has been necessary to employ floating or semi-floating bearings in such high speed machinery.
U.S. Pat. No. 3,043,636 describes a floating bearing arrangement in a turbocharger. In the machinery described, the turbocharger shaft is rotatable within a bearing having a generally tubular configuration with a radial flange at one end. The bearing is carried within a sleevelike structure formed in a housing within which the shaft is mounted for rotation. Lubricating oil under a pressure of 30 p.s.i., for example, is continuously introduced into the turbocharger housing and forms a lubricating film between the bearing and the rotating shaft and also between the bearing and the surrounding sleevelike structure of the housing. Ideally, the bearing "floats" within the housing and the shaft "floats" within the bearing. The bearing itself must be restrained from rotation and from moving axially without interfering with its ability to float on the oil film. The oil film dampens vibrations which would otherwise cause instability, particularly at or near the natural frequency of the rotating shaft and components coupled in rotation therewith.
Rotational movement of a floating bearing can be prevented by utilizing a dowel pin which extends parallel to the rotating shaft through an eccentric hole in the flange of the bearing. The ends of the dowel pin are captured by the housing so that the bearing cannot rotate. Alternatively, a pocket may be formed in the housing to receive a bearing flange with an irregular shape.
Axial movement of floating bearings has been limited by a retaining ring mounted in the housing or by bosses protruding from a seal plate. Retaining rings tend to allow excessive longitudinal reciprocation of the floating bearing. The bosses on sealing plates are unsatisfactory if they are in intimate contact with the bearing flange because the minute movement between the sealing plate boss and the bearing flange causes extreme fretting with a subsequent increase in axial play of the bearing.
One solution which has been attempted is to interpose a steel or teflon shim between the protruding boss of the seal plate and the bearing flange. This shim does reduce fretting, but has the undesirable effect of increasing the tolerance stack-up between the parts. That is, the tolerance of manufacture of each of the component parts is cumulative so that the possible maximum end play of the bearing, and therefore the rotating shaft, is increased.
The invention relates to a method of axially restraining movement of a floating bearing carried in a pressurized liquid lubricant in a high speed, rotary machine. As with conventional turbochargers and other high speed machines, the invention employs a shaft which is rotatable within a floating bearing that has a radial flange. The bearing is disposed within a housing and is supplied with liquid lubricant that flows between the shaft and the bearing and between the bearing and the housing. A retainer is provided to act between the housing and the bearing flange to restrain axial movement of the bearing within the housing. The improvement of the invention resides in the interposition of a spring washer between the bearing flange and the retainer so that the spring washer acts upon the bearing and the retainer acts upon the spring washer at a radial displacement from the bearing flange.