Patent Publication Number: US-6663366-B2

Title: Compressor having cooling passage integrally formed therein

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims benefit of priority of Japanese Patent Application No. 2001-146504 filed on May 16, 2001, the content of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a compressor for compressing fluid, the compressor having a male-rotor and a female rotor engaging with each other. The present invention is applicable to compressors such as a screw-type compressor and a roots-type compressor. 
     2. Description of Related Art 
     In a compressor having a pair of rotors and a driving mechanism for driving the pair of rotors in synchronism with each other, a gear housing containing the driving mechanism therein is connected to a rotor housing containing the rotors therein. In case an inlet port for introducing fluid is formed in the rotor housing at a position close to the driving mechanism contained in the gear housing, lubricant in the gear housing tends to leak into the rotor housing due to a negative pressure developed in the rotor housing at a vicinity of the driving mechanism through a bearing supporting the driving mechanism. To avoid such a problem, the inlet port may be formed at a position far from the driving mechanism and the outlet port at a position close to the driving mechanism. In this manner, a positive pressure is developed in the rotor housing at a vicinity of the driving mechanism, and thereby leakage of the lubricant in the gear housing into the rotor housing can be avoided. 
     In this structure, however, the compressed fluid at a high temperature flows out from the outlet port formed at a vicinity of the driving mechanism. Therefore, the heat of the compressed fluid is transferred to the driving mechanism, and thereby the driving mechanism is heated to a high temperature. Accordingly, the driving mechanism has to be made to be durable to a high temperature. This results in a high manufacturing cost of the driving mechanism. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved compressor having the outlet port formed at a vicinity of the driving mechanism, in which the driving mechanism and other components are effectively cooled, and temperature of the compressed fluid delivered from the outlet port is lowered at the same time. 
     The compressor is composed of a pair of rotors rotating in engagement with each other and a driving mechanism for driving the pair of rotors. The pair of rotors is disposed in a rotor chamber formed in a rotor housing, and the driving mechanism constituted by plural gears is disposed in a gear chamber formed in a gear housing. The rotor chamber and the gear chamber are separated from each other by a separating wall of the rotor housing. Lubricant for lubricating the driving mechanism is encapsulated in the gear chamber. An inlet port for introducing fluid such as air into the rotor chamber is formed in the rotor housing at a position remote from the driving mechanism, while an outlet port for delivering compressed fluid at a high temperature is formed in the rotor housing at a position close to the driving mechanism. 
     The pair of rotors is rotated by a rotational torque transferred from a driving shaft via the driving mechanism. According to rotation of the pair of rotors, fluid is introduced into the rotor chamber from the inlet port and compressed therein, and the compressed fluid is delivered from the output port. 
     A first cooling water passage through which cooling water of an internal combustion engine circulates is formed in the gear housing at its bottom portion. The first passage is positioned at a vicinity of the outlet port. The lubricant in the gear chamber is effectively cooled by the cooling water flowing through the first cooling water passage, and thereby the driving mechanism and bearings supporting rotor shafts are cooled by the lubricant. The compressed fluid at a high temperature delivered from the outlet port is cooled by the cooling water at the same time. 
     A second cooling water passage communicating with the first cooling water passage may be additionally formed around the bearings fixed to the separating wall for supporting the rotor shafts. The bearings heated to a high temperature by the compressed fluid in the rotor chamber is effectively cooled by cooling water flowing through the second passage. Further, a third cooling water passage communicating with the first passage through the second passage may be formed at a bottom portion of the rotor housing, so that the compressed fluid in the rotor chamber is further cooled by the cooling water. Further, a communicating passage connecting a bearing hole containing the bearings therein and the gear chamber may be formed through the rotor housing to sufficiently supply lubricant in the gear chamber to the bearing hole. 
     According to the present invention, the driving mechanism in the gear chamber, the bearings supporting the rotor shafts and the compressed fluid in the rotor chamber are effectively cooled, and thereby durability of the compressor is improved. The cooling water passage or passages can be formed in the housings in an inexpensive manner. 
     Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiments described below with reference to the following drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view showing a compressor as a first embodiment of the present invention; 
     FIG. 2 is a cross-sectional view showing the same compressor as shown in FIG. 1, taken along line II—II of FIG. 1; 
     FIG. 3 is a perspective view showing a pair of rotors used in the compressor; 
     FIG. 4 is a cross-sectional view showing a compressor as a second embodiment of the present invention; 
     FIG. 5 is a cross-sectional view showing a compressor as a third embodiment of the present invention; 
     FIG. 6 is a cross-sectional view showing cooling water passages formed in the compressor shown in FIG. 5, taken along line VI—VI of FIG. 5; and 
     FIG. 7 is a cross-sectional view showing a compressor as a fourth embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first embodiment of the present invention will be described with reference to FIGS. 1-3. For an explanation purpose, a left side of FIGS. 1 and 2 is referred to as a front side of the compressor, while a right side thereof is referred to as a rear side of the compressor. The compressor is composed of a pair of rotors  1 ,  2  and a driving mechanism  3  for driving the pair of rotors, both contained in a casing  4 . The casing  4  consists of a gear housing  6 , a rotor housing  7  and an end cover  8 , all firmly connected by through-bolts (not shown) or the like. A gear chamber  9  is formed in the gear housing  6 , and the driving mechanism  3  is disposed in the gear chamber  9 . Lubricant such as engine oil is also encapsulated in the gear chamber  9  so that the lubricant is splashed to gears constituting the driving mechanism. The rotor housing  7  forms a rotor chamber  10  in which the pair of rotors  1 ,  2  are contained. As shown in FIG. 3, the pair of rotors  1 ,  2  consists of a male-rotor  1  and a female rotor  2  engaging with each other, both having plural screw blades. In FIG. 1, both the male-rotor shaft  14  and the female-rotor shaft  20  are shown in an overlapping situation, while both rotor shafts ( 14 ,  20 ) are shown in parallel in FIG.  2 . 
     Now, referring to FIGS. 1 and 2 together, the structure of the compressor will be described in detail. A driving shaft  5  is rotatably supported by a pair of bearings  11 ,  12  fixed in the gear housing  6 . An oil seal  13  is provided outside the bearing  11  to prevent lubricant supplied to both bearings  11 ,  12  from flowing out from the gear housing  6 . The male-rotor shaft  14  is supported by a pair of bearings  15  and  16 . The bearing  15  is fixed to a separating wall  17  of the rotor housing  7  which separates the rotor chamber  10  from the gear chamber  9 , while the bearing  16  is fixed to the end cover  8 . An oil seal  18  for preventing lubricant supplied to the bearing  15  from leaking to the rotor chamber  10  is disposed in the separating wall  17 . Another oil seal  19  is disposed in the end cover  8  next to the bearing  16  to prevent lubricant leakage into the rotor chamber  10 . The female-rotor shaft  20  is supported by a pair of bearings  21  and  22 . The bearing  21  is fixed to the separating wall  17  while the bearing  22  is fixed to the end cover  8 . Oil seals  23  and  24  are disposed in the separating wall  17  and the end cover  8 , respectively, to prevent lubricant leakage from the bearings  21 ,  22  into the rotor chamber  10 . 
     A rotational torque of the driving shaft  5  is transferred to the male-rotor shaft  14  and the female-rotor shaft  20  through the driving mechanism  3 . The driving mechanism  3  includes four gears, a first gear  31 , a second gear  32 , a third gear  33  and a fourth gear  34 . The rotational torque of the driving shaft  5  is transferred to the male rotor shaft  14  via the first gear  31  fixed to the driving shaft  5  and the second gear  32  fixed to the male-rotor shaft  14 . The rotational torque of the male rotor shaft  14  is transferred to the female-rotor shaft  20  via the third gear  33  fixed to the male-rotor shaft  14  and the fourth gear  34  fixed to the female-rotor shaft  20 . The third gear  33  and the fourth gear  34  constitute timing gears for rotating the female-rotor shaft  20  in synchronism with the male-rotor shaft  14 . 
     The first rotor  1  and the second rotor  2 , each having plural screw blades, are shown in FIG.  3 . When the both rotors  1 ,  2  rotate in engagement with each other, fluid such as air is introduced into the rotor chamber  10  through an inlet port  35  formed in the rotor housing  7  at the front side (at a position remote from the driving mechanism  3 ). The introduced fluid is compressed in the rotor chamber  10  and moves from the front side to the rear side. The compressed fluid is delivered from an outlet port  36  formed in the rotor housing  7  at its bottom rear side (at a position close to the driving mechanism  3 ) at a predetermined rotational angle of the pair of rotors  1 ,  2 . 
     As shown in FIG. 1, a cooling water passage  37  is formed in the gear housing  6  and partly in the separating wall  17 . The cooling water passage  37  is connected to an engine-cooling water passage, so that the cooling water circulates through the cooling water passage  37 . An O-ring  38  is disposed on a surface connecting the gear housing  6  and the rotor housing  7  to prevent cooling water leakage. The cooling water passage  37  is formed so that it is positioned at a bottom portion of the compressor when the compressor is mounted on a predetermined position. Heat of the lubricant staying at a bottom portion of the gear chamber  9  is transferred to the cooling water flowing through the cooling water passage  37 . 
     Since the cooling passage  37  is located close to the bottom of the gear chamber  9  where the lubricant stays, the heat exchange between the lubricant and the cooling water is efficiently performed. The driving mechanism  3  is cooled by the cooled lubricant which is splashed to the gears of the driving mechanism according to the rotation thereof. Further, since the outlet port  36  is positioned close to the cooling water passage  37 , the compressed fluid having a high temperature flowing out of the outlet port  36  is cooled by the cooling water. Cooling the outlet air also contributes lowering the temperature in the gear chamber  9 . 
     In the first embodiment described above, the driving mechanism  3  disposed in the gear chamber  9  is effectively cooled by simply forming the cooling water passage  37  at the bottom portion of the gear housing  6 , even though the outlet port  36  delivering the compressed fluid at a high temperature is formed close to the driving mechanism  3 . Accordingly, a temperature-durability requirement for the driving mechanism  3  is alleviated thereby to reduce its manufacturing cost. In addition, the temperature of the compressed air delivered from the outlet port  36  is lowered at the same time. 
     A second embodiment of the present invention will be described with reference to FIG.  4 . In this embodiment, a second cooling water passage  41  is additionally formed between the rotor housing  7  and the gear housing  6  around the bearings  15 ,  21 . Other structures are the same as those of the first embodiment. At the rear side of the rotor housing  7 , a groove  44  and an end wall  42  are formed. On the other hand, a circumferential surface  43  are formed in the gear housing  6 . The second cooling water passage  41  is formed by the groove  44 , the end wall  42  and the circumferential surface  43  and is connected to the cooling water passage  37  so that the cooling water circulates through the cooling water passage  37  and the second cooling water passage  41 . O-rings  45 ,  46  are disposed at portions connecting the rotor housing  7  and the gear housing  6  to prevent water leakage from the second cooling water passage  41 . The second cooling water passage  41  forms an oval passage surrounding the bearing  15  supporting the male-rotor shaft  14  and the other bearing  21  supporting the female-rotor shaft  20 . 
     The bearings  15 ,  21 , temperature of which becomes high due to the compressed fluid at a high temperature, are effectively cooled down by the cooling water flowing through the second cooling water passage  41 . Accordingly, the bearings  15 ,  21  are properly lubricated by preventing lubricant evaporation, and the oil seals  18 ,  23  disposed at a vicinity of the bearings  15 ,  21  are protected from an excessive temperature rise. Further, the temperature of the compressed air delivered from the outlet port  36  is lowered because the separating wall  17  of the rotor housing  7  is also cooled down by the cooling water flowing through the second cooling water passage  41 . 
     Referring to FIGS. 5 and 6, a third embodiment of the present invention will be described. In this embodiment, a third cooling water passage  51  surrounding at least a part of the outlet port  36  is formed in the rotor housing  7  in addition to the cooling water passages  37  and  41 . Other structures are the same as those of the second embodiment described above. The third cooling water passage  51  is connected to the cooling water passage  37  via the second cooling water passage  41 . As shown in FIG. 6, in which a cross-sectional view taken along line VI—VI of FIG. 5 is shown, the third cooling water passage  51  is formed around the outlet port  36  in the bottom portion of the rotor housing  7 . The compressed fluid at a high temperature delivered from the outlet port  36  is further cooled down by the cooling water flowing through the third passage  51 . 
     A fourth embodiment of the present invention will be described with reference to FIG.  7 . In this embodiment, cooling fins  61  are formed on the groove  44  of the second cooling water passage  41  and other cooling fins  62  are formed on an inner wall of the gear chamber  9 . Further, a communicating passage  63  connecting an upper portion of the gear chamber  9  and the bearing hole containing the bearings  15 ,  21  is formed. Other structures are the same as those of the third embodiment described above. 
     The cooling fins  61  are formed not to interfere with the cooling water flow in the second cooling water passage  41 . The bearings  15 ,  21  held in the separating wall  17  and the rotor housing  7  are effectively cooled by the cooling water flowing through the second cooling water passage  41  having the cooling fins  61 . The cooling fins  62  are aligned along an oval path facing two gears  33  and  34 , which constitute the timing gears. The surface area of the inner wall facing the gears  33 ,  34  is increased by the cooling fins  62 . Since the lubricant splashed from the bottom of the gear chamber  9  hits the cooling fins  62  and flows through spaces between the cooling fins  62 , the lubricant is effectively cooled down thereby to cool the driving mechanism  3  in the gear chamber  6 . 
     Since the bearing hole holding the bearings  15 ,  21  communicates with the gear chamber  9  through the communicating passage  63 , the lubricant is sufficiently supplied to the bearings  15 ,  21 . The bearings  15 ,  21  which are heated to a high temperature by the compressed fluid in the rotor chamber  10  are effectively cooled down by the lubricant supplied thereto. 
     Though the present invention is applied to the compressor for compressing fluid such as air in the foregoing embodiments, it may be applied to other compressors for compressing gases such as hydrogen. Though the present invention is applied to the screw-type compressor in the foregoing embodiments, it may be applied to other compressors such as a roots-type compressor. 
     While the present invention has been shown and described with reference to the foregoing preferred embodiments, it will be apparent to those skilled in the art that changes in form and detail may be made therein without departing from the scope of the invention as defined in the appended claims.