The present invention relates to a bearing device for a scroll type compressor. 
In, for example, U.S. Pat.  No.  4,065,279, a scroll-type compressor is proposed which includes a wrap revolving scroll composed of an end plate and a wrap formed along an involute curve or a curve approximating an involute curve and standing upright from the end plate, and a stationary scroll having a construction similar to the revolving scroll but additionally provided with a discharge port.  The revolving scroll and the stationary scroll are assembled together with their wraps mating with each other, and are housed by a housing having a suction port.  An Oldham's ring prevents the revolving scroll from rotating around its own axis and is provided between the revolving scroll and the housing or between the revolving scroll and the stationary scroll.  In operation, the revolving scroll is driven by a crankshaft to revolve in such a manner as not to make apparent rotation around its own axis, so that the volume of a chamber formed between two scrolls is continuously changed to cause a pumping action to displace a fluid in the chamber. 
Another known type of scroll compressor incorporates a vertical crankshaft provided with a balance weight between the crank portion and the shaft portion of the crankshaft.  In this scroll compressor, the crank portion of the crank shaft is received by a first bearing provided in the revolving scroll, while the shaft portions of the crankshaft are supported by two bearings, i.e. a second bearing and a third bearing, provided on the frame of the compressor.  In addition, an intermediate chamber, accommodating the balance weight, is defined between the revolving scroll and the frame, and is maintained at a pressure intermediate between the discharge pressure and the suction pressure. 
In this type of scroll compressor, the crank portion of the crankshaft has a diameter smaller than that of the shaft portion, in order to comply with a demand for reducing an impact which is generated in the eccentric crank portion at the time of start up of the compressor and the demand for reduction in size of the compressor as a whole.  In operation, discharge gas pressure is applied to the upper end surface of the crank portion of the crankshaft and the lower end surface of the shaft portion of the crankshaft.  Since the crank portion has a diameter smaller than that of the shaft portion the upward axial force applied to the crankshaft exceeds the downward axial force applied to the same.  Consequently, a heavy load is applied to a thrust bearing which is formed as a unit with the first bearing and contacted by the upper end surface of the balance weight, often resulting in a rapid wear or, in the worst case, a seizure of the thrust bearing.