Screw-type fluid machine

Abstract

A vacuum pump includes rotary shafts connected to a pair of screw-type rotors, respectively, and a pair of shaft retainers extending in the housing. Each shaft retainer supports the corresponding rotary shaft by means of a proximal bearing portion and a distal bearing portion. Each pair of the proximal and distal bearing portions are fixed in the axial direction with respect to the corresponding rotary shaft and shaft retainer. Lubricant oil is stored in an oil storage space in a gear case attached to the housing. A cooling water passage through which cooling water to cool the lubricant oil passes is formed in the gear case. A controller controls the flow rate of the cooling fluid, so that the temperature of the lubricant oil in the oil storage space is kept constant. With this configuration, when the bearing portions are fixed in the axial direction with respect to the rotary shafts and the shaft retainers, it is possible to prevent load from being applied to the bearing portions in the axial direction.

1 . A screw-type fluid machine, comprising:
 a housing;   a pair of screw-type rotors accommodated in the housing and meshed with each other;   a pair of rotary shafts each coaxially coupled to one of the rotors, each rotary shaft having an end portion protruding from the housing;   a pair of cylindrical shaft retainers extending in the housing, each shaft retainer having a first end portion and a second end portion, and having a through hole into which one of the rotary shafts is inserted;   first bearing portions each mounted in the through hole at one of the first end portions;   second bearing portions each mounted in the through hole at one of the second end portions, each pair of the first and second bearing portions rotatably supporting the corresponding rotary shaft with respect to the shaft retainer, and each pair of the first and second bearing portions being fixed in the axial direction with respect to the corresponding rotary shaft and the corresponding shaft retainer;   synchronous gears each provided at the end portion of one of the rotary shafts protruding from the housing;   a gear case in which the synchronous gears are accommodated, the gear case defining an oil storage space capable of storing lubricant oil and being connected to the housing,   a cooling portion for cooling the lubricant oil by using a cooling fluid; and   and   a control portion for controlling the flow rate of the cooling fluid so that the temperature of the lubricant oil in the oil storage space is kept constant.   
   
   
       2 . The screw-type fluid machine according to  claim 1 , wherein the first and second bearing portions are each composed of a combination of at least two roller bearings. 
   
   
       3 . The screw-type fluid machine according to  claim 2 , wherein the roller bearings include angular ball bearings. 
   
   
       4 . The screw-type fluid machine according to  claim 1 , wherein the cooling portion includes a cooling water passage extending in the gear case so as to permit passage of the cooling fluid. 
   
   
       5 . The screw-type fluid machine according to  claim 1 , further including oil feed portions each driven by one of the rotary shafts so that the shaft retainers and the rotary shafts are cooled by using lubricant oil in the oil storage space. 
   
   
       6 . The screw-type fluid machine according to  claim 5 , wherein a space is provided between the inner circumferential surface of each shaft retainer and the outer circumferential surface of the corresponding rotary shaft, an oil feed passage having an inlet opening to the end portion of the rotary shaft and an outlet communicating with the space is formed at each rotary shaft, wherein the oil feed portion is a pump provided at the end portion of each of the rotary shafts, and the pump supplies lubricant oil existing in the oil storage space to the inlet of the oil feed passage of the corresponding rotary shaft. 
   
   
       7 . The screw-type fluid machine according to  claim 1 , further comprising a flow rate changing portion for controlling the flow rate of the cooling fluid and a temperature sensor provided in the oil storage space for detecting the temperature of the lubricant oil, wherein the control portion controls the flow late changing portion in accordance with the temperature detected by the temperature sensor.