Abstract:
The communication between at least one of the pump inlets opening in at least two housing cavities and the suction chamber can be interrupted by a first valve means for prohibiting fluid compression in at least one of the housing cavities associated with the at least one pump inlet. At least one of the front and rear side blocks is formed with at least two passage means at locations corresponding to different ones of the cavities for introducing compressed fluid into back pressure chambers formed in the rotor. The communication between at least one of the passage means and the suction chamber can be interrupted by a second valve means. A control means actuates the second valve means so as to interrupt the communication between the at least one passage means and the suction chamber at the same time of establishment of the communication between the at least one pump inlet and the suction chamber, to thereby reduce the back pressure acting upon vanes moving in the above at least one housing cavity while the fluid compression in the same housing cavity is prohibited.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to variable capacity vane compressors, and more particularly to a vane compressor of this kind which is capable of controlling the back pressure acting upon vanes in response to operating conditions of the compressor. 
     Vane compressors of the type which is capable of varying the capacity thereof and adapted for use in air conditioning systems such as car coolers generally have a plurality of housing cavities defined between the pump housing and the rotor received therein. For reduced capacity operation, at least one of the housing cavities is kept disconnected from the suction chamber to prohibit fluid compression in the at least one housing cavity. Variable capacity vane compressors of this kind have been disclosed e.g. in Japanese Provisional Patent Publications (Kokai) Nos. 56-138489, 57-153982, and 57-102596. 
     In such vane compressors, vanes are radially slidably fitted in slits formed in the rotor within the pump housing and are pushed radially outward by a centrifugal force produced by the rotation of the rotor and the pressure of compressed fluid introduced as back pressure into back pressure chambers formed in the rotor through gaps between the rotor and the side blocks of the pump housing as well as gaps between the vanes and the slits so as to have their radially outer ends in sliding and urging contact with the camming inner peripheral surface of the pump housing. 
     However, in such a vane compressor having a plurality of housing cavities, the back pressure chambers communicating with respective vanes in the housing cavities are communicated with each other by means of an annular groove formed in the rotor, as disclosed e.g. in Japanese Provisional Patent Publication No. 57-153982 referred to above. Consequently, even when the fluid compression is prohibited in part of the housing cavities, part of the compressed fluid is introduced into back pressure chambers corresponding to vanes moving in the housing cavity in which the fluid compression is prohibited, so that the vanes moving in the above housing cavity are urged against the camming inner peripheral surface of the pump housing with a large urging pressure. This results in large power loss of the compressor as well as in a great amount of wear of the pump housing and the vanes. No solution to this problem has been provided by any of the aforementioned publications. 
     SUMMARY OF THE INVENTION 
     It is the object of the invention to provide a variable capacity vane compressor which is capable of reducing the back pressure acting upon vanes moving in part of the housing cavities in which fluid compression is prohibited, to thereby largely reduce the power loss of the compressor as well as prevent wear of the vanes and the pump housing. 
     The present invention provides a variable capacity vane compressor of the type having at least two housing cavities defined between the pump housing and the rotor, at least two pump inlets opening in different ones of the housing cavities, and first valve means for selectively establishing and interrupting communication between at least one of the pump inlets and the suction chamber. 
     The vane compressor according to the invention is characterized by the following: 
     At least two passage means are formed in at least one of the front and rear side blocks forming part of the pump housing at locations corresponding to different ones of the above cavities and separated from each other, for supplying back pressure chambers formed in the rotor with compressed fluid as back pressure from respective ones of the cavities. 
     At least one communication means is formed in the above at least one side block for communicating at least one of the above passage means corresponding to the above at least one pump inlet with the suction chamber. This communication can be selectively established and interrupted by second valve means. 
     Control means for controlling the first valve means and the second valve means is adapted to cause the first valve means to interrupt the communication between the at least one pump inlet and the suction chamber, and at the same time cause the second valve means to establish communication between the at least one passage means and the suction chamber by way of the communication means, thereby reducing the pressure of compressed fluid supplied to the back pressure chambers by way of the at least one passage means. 
     The above and other objects, features and advantages of the invention will be more apparent from the ensuing detailed description taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal sectional view of a variable capacity vane compressor according to an embodiment of the invention; 
     FIG. 2 is a transverse cross-sectional view taken along line II--II in FIG. 1; 
     FIG. 3 is a longitudinal sectional view of the same compressor during full capacity operation, taken along line III--III in FIG. 2; and 
     FIG. 4 is a view similar to FIG. 3, showing the compressor during half capacity operation. 
    
    
     DETAILED DESCRIPTION 
     The invention will now be described in detail with reference to the drawings illustrating an embodiment thereof. 
     In the drawings, a vane compressor 1 comprises a front head 2, a casing 3 secured to the front head 2, a cylinder 4 disposed within the casing 3 and having an endless camming inner peripheral surface 4a with an ellipsoidal cross section, and front and rear side blocks 5 and 6 secured to opposite ends of the cylinder 4. The cylinder 4 and the side blocks 5, 6 cooperate to form a pump housing. A rotor 8 is rotatably received within the pump housing and journalled by a rotary shaft 7 rotatably supportedly extending through the front side block 5. The rotor 8 has its outer peripheral surface formed therein with four slits 8a circumferentially arranged at equal intervals, and as many vanes 10 are radially slidably fitted in their respective slits 8a. The rotor 8 has its interior formed with axially extending back pressure chambers 14 communicating with radially inner ends of their respective slits 8a. Opposite ends of each of the back pressure chambers open in opposite ends of the rotor 8. 
     Two housing cavities 18 and 19 are defined between inner surfaces of the pump housing and the outer peripheral surface of the rotor 8. An inner end face 5a of the front side block 5 is formed therein with two generally semicircular grooves 5b and 5c disposed along the same circumference as the back pressure chambers 14 to serve as passages communicating their respective back pressure chambers 14 with each other. The grooves 5b, 5c are arranged separately from each other at locations diametrically opposite with respect to the rotary shaft 7 and corresponding in circumferential position to their respective housing cavities 18, 19. To be specific, they circumferentially extend about the rotary shaft 7 through a predetermined circumferential angle (e.g. 180 degrees), with their mutually opposed ends 5b&#39;, 5c&#39;; 5b&#34;, 5c&#34; separated from each other. Each of the grooves 5b, 5c can communicate its two adjacent back pressure chambers 14 with each other while the latter move along the former, and both open in a clearance 30 between opposed end faces of the rotor 8 and the front side block 5. 
     The housing cavities 18, 19 communicate, on one hand, with respective pump inlets 4b and 4c formed in the wall of the cylinder 4, and on the other hand, with pump outlets 4d and 4e formed in the same wall and provided with discharge valves 20 and 21, respectively. As shown in FIGS. 3 and 4, the pump inlets 4b, 4c are communicated with a suction chamber 22 defined in the front head 2 by inner surfaces thereof and an outer end face of the front side block 5, by way of respective through holes 5d and 5e formed in the front side block 5, while the pump outlets 4d, 4e can be communicated with a discharge pressure chamber 23 defined within the casing 3 by inner surfaces thereof and outer surfaces of the pump housing, through their respective discharge valves 20, 21. 
     As shown in FIGS. 3 and 4, the outer end face of the front side block 5 facing the suction chamber 22 is formed therein with a blind hole 5f at a predetermined circumferential location corresponding to the groove 5b, and a small communication bore 5g is obliquely formed through the side block 5 and communicates the above blind hole 5f with the groove 5b. 
     Electromagnetic valves 25 and 26 are mounted in the front head 2 and disposed opposite the respective holes 5d, 5f in the side block 5 in such a manner that the valve body 25a of the electromagnetic valve 25 is in axial alignment with the hole 5d for closing same, while the valve body 26a of the electromagnetic valve 26 is slidably fitted in the hole 5f. Lead wires 15 and 16 extend to the outside from the solenoids 25b and 26b of the valves 25, 26 through holes 2a and 2b formed through the front head 2, for connection to an electromagnetic valve-control circuit 17. The control circuit 17 controls the energization of the electromagnetic valves 25, 26 in response to the rotational speed Ne of an engine associated with the compressor and/or the discharge refrigerant temperature Tr. 
     The valve body 25a of the electromagnetic valve 25 is disposed for displacement toward the hole 5d by the force of a spring 25c to block the hole 5d when the solenoid 25b is deenergized, and for displacement away from the hole 5d against the force of the spring 25c by electromagnetic force produced by the solenoid 25b to open the hole 5d for communication between the pump inlet 4b and the suction chamber 22 when the solenoid 25b is energized. The valve body 26a of the electromagnetic valve 26 is disposed to be held at the bottom of the blind hole 5f by the force of a spring 26c disposed in the central opening of the solenoid 26b when the latter is deenergized, whereby the bore 5g is opened to communicate the groove 5b with the suction chamber 22 (FIG. 4), while when the solenoid 26b is energized, it is displaced away from the bottom of the blind hole 5f against the force of the spring 26c due to electromagnetic force produced by the solenoid 26b, whereby an end of the communication bore 5g opening in the blind hole 5f is blocked by the outer peripheral surface of the valve body 26a to thereby interrupt the communication between the groove 5b and the suction chamber 22 (FIG. 3). In the latter position, the electromagnetic valve 26 has its stopper 26d brought into urging contact with the solenoid 26c. 
     The suction chamber 22 is communicated with a refrigerant circuit of an air conditioning system, not shown, by way of the interior of a suction connector 28 mounted on the front head 2, while the discharge pressure chamber 23 is communicated with the same circuit by way of the interior of a discharge connector 29. 
     With the above arrangement, to operate the compressor with full capacity, as shown in FIG. 3, the control circuit 17 energizes the electromagnetic valve 25 to cause displacement of the valve body 25a away from the hole 5d to open same 5d to establish the communication between the suction chamber 22 and the pump inlet 4b in the cylinder 4, and at the same time energize the electromagnetic valve 26 to cause displacement of the valve body 26a toward the solenoid 26b to close the communication bore 5g to interrupt the communication between the suction chamber 22 and the groove 5b in the front side block 5. Thus, the two housing cavities 18, 19 are communicated with the suction chamber 22 by way of their respective pump inlets 4b, 4c to be supplied with suction refrigerant. In this position, as the rotor 8 is rotated in the counterclockwise direction as indicated by the arrow A in FIG. 2, the suction refrigerant drawn into the housing cavities 18, 19 is compressed by vanes 10 moving together with the rotor 8, and forcively opens the discharge valves 20, 21 to be discharged into the discharge pressure chamber 23 through the pump outlets 4d, 4e. 
     Part of the refrigerant compressed in the housing cavities 18, 19 is forced to travel through a fine gap between opposed end faces of the front side block 5 and the rotor 8 into the respective grooves 5b, 5c in the side block 5, and then travels into the back pressure chambers 14 to increase the pressure therein to thereby obtain sufficient back pressure acting upon the vanes 10 to urge their radially outer ends against the camming inner peripheral surface of the cylinder 4. Another part of the refrigerant compressed in the housing cavities 18, 19 is forced to travel through fine gaps between the vanes 10 and their respective slits 8a into the back pressure chambers 14 to also contribute to the increase of the back pressure. The vanes 10 are positively held in sliding and urging contact with the camming inner peripheral surface 4a of the cylinder 4 by centrifugal force produced in themselves due to the rotation of the rotor, in addition to the above back pressure. 
     To operate the compressor with half capacity, as shown in FIG. 4, the control circuit 17 deenergizes the electromagnetic valve 25 to have its valve body 25a close the hole 5d in the front side block 5 whereby the associated pump inlet 4a becomes disconnected from the suction chamber 22, and at the same time the control circuit 17 deenergizes the electromagnetic valve 26 to have its valve body 26a displaced as far as the bottom of the blind hole 5f to open the communication bore 5g whereby the communication between the groove 5b and the suction chamber 22 becomes established. 
     In this position, no suction refrigerant is supplied from the suction chamber 22 to the housing cavity 18 but the other housing cavity 19 alone is supplied with suction refrigerant from the suction chamber 22 through the hole 5e and the pump inlet 4c. 
     On this occasion, as the rotor 8 rotates in the counterclockwise direction indicated by the arrow A in FIG. 2, a refrigerant compressing action takes place in the housing cavity 19 which is supplied with suction refrigerant, during its compression stroke, whereas no such action takes place in the other housing cavity 18 which is not supplied with suction refrigerant. The refrigerant compressed in the cavity 19 is discharged through the pump outlet 4e into the discharge pressure chamber 23 in the same manner as previously stated. At the same time, part of the refrigerant compressed in the cavity 19 is forced to travel into the associated groove 5c through a gap between a lower half of the end face of the rotor 8 closer to the cavity 19 as viewed in FIG. 2 and the opposed inner end face of the front side block 5, and then flow into back pressure chambers 14 as the latter move therealong to positively hold the radially outer ends of the vanes 10 in sliding and urging contact with the camming inner peripheral surface 4a of the cylinder 4 in the same manner as previously stated. Another part of the refrigerant compressed in the housing cavity 19 also flows through gaps between the associated vanes 10 and their slits 8a into the associated back pressure chambers 14 to obtain required back pressure. Due to this sufficient back pressure and centrifugal force produced in the vanes themselves, refrigerant compression is effected in the housing cavity 19 in a positive and stable manner. 
     On the other hand, on this occasion, no refrigerant compressing action takes place in the other housing cavity 18. Since on this occasion the groove 5b associated with the cavity 18 is communicated with the suction chamber 22 as previously noted, the pressure in the groove 5b is substantially equal to that in the suction chamber 22. Further, since the grooves 5b, 5c are separated from each other as previously noted and shown in FIG. 2, the compressed refrigerant under high pressure supplied to the groove 5c will not flow into the groove 5b. Therefore, low pressure prevails in the back pressure chambers 14 communicating with the grooves 8a in which are fitted vanes 10 moving in the housing cavity 18 on the upper half side in FIG. 2. Consequently, vanes 10 are free from large back pressure while they are travelling in the cavity 18 so that they have their radially outer ends in sliding contact with the camming inner peripheral surface 4a of the cylinder 4 with a small urging pressure corresponding to centrifugal force produced in themselves alone. 
     That is, during half capacity operation wherein the housing cavity 18 is held in a non-compressive state, while the vanes 10 are travelling in the cavity 18 in a non-compressive state, they are held in urging contact with the camming inner peripheral surface 4a of the cylinder 4 with a small urging pressure corresponding to the centrifugal force alone, whereas while the vanes 10 are travelling in the cavity 19 during normal compression stroke thereof, they are positively held in urging contact with the surface 4a with a large urging pressure corresponding to the sum of sufficient back pressure and centrifugal force. 
     As stated above, according to the invention, the back pressure acting upon the vanes can be controlled in different manners appropriate, respectively, to full capacity operation and half capacity operation of the compressor, thereby enabling the compressor to fully exhibit the fluid compressing function during full capacity operation, while reducing the power loss during half capacity operation. 
     Although the foregoing embodiment is directed to a vane compressor having two housing cavities, the invention is not limited to such type compressor but may be applied to other vane compressors having other numbers of housing cavities. Also, although in the embodiment means 5d, 25 for establishing and interrupting the communication between part of the housing cavities and the suction chamber and means 5f, 5g, 26 for controlling the communication between the groove 5b and the suction chamber are both provided on the side of the front side block 5 alone, one or both of such means may be provided at both of the side blocks 5, 6 or at the side block 6 alone. 
     Obviously many other modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.