GB2088959A

GB2088959A - Rotary Positive-displacement Fluid-machine

Info

Publication number: GB2088959A
Application number: GB8121985A
Authority: GB
Original assignee: Atsugi Motor Parts Co Ltd
Current assignee: Hitachi Astemo Ltd
Priority date: 1980-12-09
Filing date: 1981-07-16
Publication date: 1982-06-16
Also published as: DE3147586A1; FR2495700A1

Abstract

In a pump of the sliding-vane type a casing body 19 accommodates a bearing bush 5 for a rotor shaft 6 and defines a working fluid outlet chamber(s) 4 and duct 3, a bore for said bush and the outlet duct being interconnected by a hole(s) 1b to facilitate casting of the body. The working-fluid inlet and outlet ducts and chambers may be arranged so as to balance the pressures on the edges of the vanes 9. The rotor 8 may be retained on the shaft by a deformation-resistant resilient ring, Fig. 14 (not shown). <IMAGE>

Description

SPECIFICATION Vane Pump Background of the Invention 1. Field of the Invention The present invention relates generally to a vane pump, and more specifically to a vane pump improved in such a way that the body thereof is easy to manufacture in casting processes without variation in wall thickness, the structure thereof is simple to assemble without use of side plates, the pump efficiency is high with leakage oil returned to the inlet chamber directly, and the rotor is fixed in position to the rotary shaft by the use of a round snap ring.

2. Description of the Prior Art In a prior-art vane pump, first, the body thereof usually comprises a bushing-fitted bore and an outlet duct disposed separately from each other by a partition; that is, the bushing-fitted bore does not communicate with the outlet duct. Therefore, two different cores are independently required in casting the body, thus causing mismatch of the center positions of the two cores and also variation in wall thickness between the two. In addition to the above, since the discharge passage is so designed as to be smaller in size than the outlet duct, it is very difficult to completely remove casting sand used during the formation of the outlet duct.

Secondly, in the prior-art vane pump, since the vane pump is constructed in such a way that a side plate is used and the side plate is forced against the rotor by a spring, there arises a problem in that rotational friction is inevitably increased and it is necessary to increase horsepower to overcome this energy loss.

Therefore, if the side plate can be omitted, it will be possible to simplify the structure of the vane pump, reduced the number of necessary parts, and improve pump efficiency.

Thirdly, the present invention relates to a leakage-fluid return passage for the vane pump.

The leakage-fluid return passage is a way to return to the inlet side the leakage oil which is flowing out along the drive shaft from the pump chamber of a vane pump.

In the prior-art vane pump, however, since the leakage oil is returned to the inlet duct, there exist various disadvantages such as high energy loss, that is, low pump efficiency, cavitation and noise generation, and increased oil temperature.

Fourthly, the present invention relates to a structure for installing a rotor in position to the shaft of a vane pump in such a way that a snap ring can be fitted to a ring-fitting groove provided for the drive shaft and the end surface of the rotor is retained by the snap ring.

In the prior-art vane pump, since the snap ring is formed in a rectangular shape in cross-section, and is forced against the vertical end surface of the rotor, there are a few problems such as deformation of the snap ring and therefore the snap ring on the rotor can easily slide along the drive shaft.

The respective problems or disadvantages of prior-art vane pump will be described in more detail, where necessary, under Description Of Preferred Embodiments.

Summary of the Invention With these problems in mind therefore, it is the primary object of the present invention to provide a vane pump such that the body thereof is easy to cast without variation in wall thickness and it is easy to thoroughly remove the casting sand used in manufacturing the body of a vane pump by the process of casting from the outlet duct.

To achieve the above-mentioned object, the vane pump according to the present invention comprises the body in which the bushing-fitted bore and the outlet duct communicate with each other by providing a communication hole therebetween.

It is another object of the present invention to provide a vane pump such that it is possible to eliminate rotational friction caused by the conventional side plate spring by avoiding use of a side plate, in order to improve the efficiency of the vane pump and also to decrease the number of necessary parts to simplify the structure of the vane pump.

To achieve the above-mentioned object, the vane pump according to the present invention comprises, in the front body, an inlet duct communicating with the inlet port, an outlet duct communicating with the outlet port, a discharge chamber one end of which communicates with the outlet duct and the other end of which communicates with the contact surface of the cam ring, and two vane back-pressure applied holes one end of the which communicates with the vane-pressure applied groove communicating with the contact surface of the cam ring and the other end of which communicates with the passageway, and, in the rear body, an inlet passageway communicating with the front body inlet passageway through the cam ring inlet passageway and a charge chamber communicating with the contact surface of the cam ring being branched from the inlet duct.

It is a further object of the present invention to provide a high-efficiency vane pump by reducing the energy loss caused by leakage fluid or leakage oil as much as possible in such a way that one end of a leakage-oil-return passage communicates with a clearance between the vane pump body and the drive shaft, and the other end portion of the leakage oil return passage communicates with the charging chamber in order to return the leakage oil to the charging chamber directly.

It is still a further object of the present invention to provide a vane pump in which a snap ring resistant to deformation is used to prevent the rotor from sliding along the drive shaft.

To achieve the present invention, the vane pump according to the present invention comprises a snap ring formed in a circular shape in cross-section and a rotor end surface which is formed so as to contact the snap ring obliquely.

Brief Description of the Drawings The features and advantages of the vane pump according to the present invention will be more clearly appreciated from the following description taken in conjunction with the accompanying drawings in which like reference numerals designate corresponding elements and in which:: Fig. 1 is a cross-sectional view of a prior-art vane pump; Fig. 2 is a cross-sectional view of the front body of the prior-art vane pump of Fig. 1; Fig. 3 is a front view of the prior-art vane pump of Fig. 1; Fig. 4 is a cross-sectional view of the front body of the prior-art vane pump of Fig. 2, taken along the lines IV-lV; Fig. 5 is a cross-sectional view of the front body of the vane pump according to the present invention; Fig. 6 is a cross-sectional view of the front body of the vane pump according to the present invention of Fig. 5, taken along the lines VI--VI; Fig. 7 is a cross-sectional view of the vane pump according to the present invention; Fig. 8 is a front view of the vane pump according to the present invention, as seen in the surface shown by the arrows VIlI-VIlI in Fig. 7;; Fig. 9 is a front view of the vane pump according to the present invention, as seen in the surface shown by the arrows IX-IX in Fig. 7; Fig. 10 is a front view of the vane pump according to the present invention, as seen in the surface shown by the arrows X-X in Fig. 7; Fig. 11 is a cross-sectional view of the vane pump according to the present invention, taken along the line XI-XI in Fig. 10; Fig. 12 is a cross-sectional view of the vane pump according to the present invention, taken along the line XlI-Xll in Fig. 8; Fig. 13 is an enlarged fragmentary crosssectional view of a prior-art snap ring for a vane pump, the position indicated by the circle A in Fig.

1;and Fig. 14 is enlarged fragmentary cross-sectional view of the snap ring for the vane pump according to the present invention, the position indicated by the circle B in Fig. 7.

Detailed Description of the Preferred Embodiments To facilitate understanding of the present invention, a brief reference will be made to a the body of a prior-art vane pump.

As depicted in Fig. 1, the body 1 of a vane pump is provided with a bore 2 formed through the center thereof into which a bushing is pressure-fitted, an outlet duct 3 provided on the outside of the bushing-fitted bore 2, and an discharge passage 4, one end of which communicates with the outlet duct 3 and the other end of which communicates with a contact surface of a cam ring described later. A bushing 5 is pressure-fitted into the bushing-fitted bore 2, and a drive shaft 6 is inserted into the bushing 5.

The drive shaft 6 is rotatably supported by a bearing 7. In addition, the reference numeral 8 denotes a rotor provided at the end of the drive shaft 6, the numeral 9 denotes vanes fixed to the rotor 8, the numeral 10 denotes a cam ring which houses the rotor 8 to which the vanes 9 are fixed, and the numeral 11 denotes a rear body and the cam ring 10 is supported between the rear body 11 and the body 1.

In the vane pump comprising the body 1, the drive shaft 6, the rotor 8, vanes 9, cam ring 10, and the rear body 11, when the rotor 8 is rotated by the drive shaft 6, the vanes 9 fixed to the rotor 8 move in their centrifugal direction while sliding in contact with the inner peripheral surface of the cam ring 10. The change in volume between the respective vanes introduces oil within an oil tank (not shown) into a pump chamber 14 through an inlet port 12 and an inlet duct 13, and the introduced oil is discharged outside through the discharge passage 4 in the body 1, the outlet duct 3, and an outlet port 15.

In the prior-art body of a vane pump, however, as shown in Figs. 2 to 4, since the bushing-fitted bore 2 and the outlet duct 3 are separated by a partition 1 a provided therebetween; in other words, since the bushing-fitted bore 2 does not communicate with the outlet duct 3, there arises a number of problems in manufacturing the body of a vane pump. The basic problems are:- (1) The body of a vane pump is generally manufactured by casting. Since the bushing-fitted bore 2 and the outlet duct 3 are separated in the prior-art body 1 as described hereinabove, two cores for the bushing-fitted bore 2 and the outlet duct 3 are independently required, thus causing mismatch of the center positions of the two cores and variation in wall thickness between the two.

(2) Although the moulding sand for the core forming the outlet duct 3 must be removed through the discharge passage 4 after casting the body of a vane pump, since the discharge passage 4 is so designed as to be smaller in size than the outlet duct 3, it is very difficult to remove the casting sand used for forming the outlet duct 3 completely.

These are the first problems to be solved.

In view of the above description, reference is now made to the attached drawings.

In the embodiment of the body of a vane pump according to the present invention shown in Figs.

5 and 6, a communication hole 1 b is provided on the lower-half side of a partition 1 a to connect the bush-fitting bore 2 to the outlet duct 3. Further, since the bottom surface of the communication hole 1 b is on the same level as that of the outlet duct 3, it is easy to remove the moulding sand for the outlet duct 3 through the communication hole 1 b. Further, in this embodiment, the communication hole 1 b is closed sealingly by the bush 5 pressure-fitted to the bushing-fitted bore 2.

In the body for a vane pump which comprises the bushing-fitted bore 2, the outlet duct 3 provided on the outside of the bushing-fitted bore 2, and a discharge passage 4, one end of which communicated with the outlet duct 3 and the other end of which communicates with the contact surface of the cam ring, as described hereinabove as the present invention, since the bushing-fitted bore 2 communicates with the outlet duct 3 through the communication hole 1 b, the effects are as follows:- (1) Since the core forming the bushing-fitted bore 2 and the core to form the outlet duct 3 are connected to each other by way of the communication hole 1 b when casting the body 1 of a vane pump, it is possible to prevent variation in wall thickness caused by mismatch of the center positions of the two cores.

(2) Since it is possible to remove the moulding sand used for forming the outlet duct 3 through the communication hole 1 b, it is possible to remove the moulding sand easily and thoroughly from the outlet duct 3 as compared with the case where the moulding sand is removed through the discharge passage 4, and further, to inspect the residual moulding sand easily.

Next, there is described hereinbelow the second problem to be solved and the second object of the present invention.

With reference to Figs. 7 to 12, there is explained an embodiment of the vane pump according to the present invention by way of example where the vane pump is used for actuating a power steering device.

In these figures, the reference numeral 1 denotes the body of the vane pump according to the present invention, the numeral 6 denotes a drive shaft so designed as to be rotated by an automotive engine (not shown) through a pulley 16 and a belt 17. The numeral 8 denotes a rotor fixed to the drive shaft 6, which is so designed as to rotate together with the drive shaft 6 by way of serration 32 and fixed to an appropriate position on the drive shaft 6 by a snap-ring 18. The numeral 9 denotes vanes fixed to the rotor 8, which are extendably fitted to the respective throttles 8a arranged radially from the drive shaft 6. The numeral 10 denotes a cam ring to house the rotor 8 to which the vanes 9 are mounted.The cam ring 10 includes two major arc surfaces C1, two minor arc surfaces C2, and two first cam surface C3 and two second cam surfaces C4 connecting the two major and minor arc surfaces to define an elliptical track.

The reference numerals 19 and 11 denote a front body and a rear body respectively which support the cam ring 10 therebetween and form a pump chamber 14 together with the cam ring 10.

The front body 19 is provided with an inlet duct 13 communicating with an inlet port 12, an outlet duct 3 communicating with an outlet port 15, a pair of discharge passages 4 one end of which communicates with the outlet duct 3 and the other end of which communicates with the second cam surfaces C4 of the cam ring 10, a vane back-pressure applied groove 20 and a vane back-pressure applied hole 21, one end of which communicates with the vane back-pressure applied groove 20 and the other end of which communicates with the outlet duct 3.The rear body 11 is provided with another portion of the inlet duct 13 which communicates with the portion of the inlet duct 13 provided for the front body 19 through a third portion of the inlet duct 13 provided for the cam ring 10, and a pair of charging chambers 22 which communicate with the first cam surfaces C3 of the cam ring 10 being branched from the inlet duct 13. Two charging chambers 22 provided for the front body 19 communicate with the two other charging chambers 22 provided for the rear body 11 through the two secondary inlet ducts 13' provided on the cam ring 10. The numeral 23 denotes two leakage-oil return ducts, one end of which communicates with a clearance between the front body 19 and the drive shaft 6 and the other end of which communicates with the two charging chambers 22 on the front body 19.The numeral 24 denotes an oil seal, numeral 25 denotes a bearing device in which the drive shaft 6 is rotatably mounted on the front body 19, numerals 26 and 27 denote O-rings fitted into recessed grooves provided for the cam ring 10 in order to seal the contact surfaces between the cam ring 10 and the front body 19 and between the cam ring 10 and the rear body 11, numeral 28 denotes a locating pin to position the cam ring 10 between the front body 19 and the rear body 11, numeral 29 denotes two pin-fitting holes provided in each of the front body 19 and the rear body 11 for the locating pin 28, numeral 30 denotes a bolt to connect the front body 19 and the rear body 11 with the cam ring 10 disposed therebetween, and the numeral 31 denotes four bolt holes.

Next, there is described the operation of the vane pump thus constructed.

When the drive shaft 6 and the rotor 8 are rotated by the engine for an automotive vehicle by way of the belt 17 and pulley 16, the vanes 9 mounted on the rotor 8 move radially outward due to centrifugal force and slide along the inner peripheral surface of the cam ring 10.

Accordingly, the change in volume between adjacent vanes 9 introduces the oil from an oil tank (not shown) through the intake port 12, the inlet duct 13, and the charge chambers 22 to the pump chamber 14, and next the introduced oil is supplied to the power steering device through the discharge passages 4, the outlet duct 3, the outlet port 15, and a flow control valve (not shown).

When the vanes 9 move radially inward, oil not discharged through the discharging passage 4 becomes slightly pressurized by the decrease in volume between the vanes 9, and is discharged into the outlet duct 3 through the vane backpressure applied groove 20 and the vane backpressure applied hole 21 so that the vanes can move smoothly in that direction. The leakage oil flowing from the pump chamber 14 to the drive shaft 6 is returned directly to the charge chamber 22 through the leakage-oil returning duct 23. This serves to improve the efficiency of the pump, since loss in energy is relatively small compared with the prior-art vane pump where the leakageoil is returned through the inlet duct 13.

As described hereinabove, the vane pump according to the present invention comprises the rotor mounted on the drive shaft, a number of vanes mounted to the rotor, the cam ring to house the rotor to which the vanes are mounted, the front body and the rear body between which the cam ring is sandwiched so as to form a pump chamber. And, further, when the rotor is rotated by way of the drive shaft, the vanes mounted on the rotor move outward in the centrifugal direction while sliding in contact with the inner peripheral surface of the cam ring, and therefore the change in volume between adjacent vanes introduces oil within the oil tank into the pump chamber through the inlet port and the inlet duct and further discharges this introduced oil to the outside through the outlet duct and the outlet port.In this vane pump, since the inlet duct communicating with the inlet port, the outlet duct communicating with the outlet port, the discharge chamber, one end of which communicates with the outlet duct and the other end of which communicates with the contact surface of the cam ring, and the vane back-pressure applied hole, one end of which communicates with the vane back-pressure applied groove and the other end of which communicates with the outlet duct, are provided for the front body, and, additionally, since the inlet duct provided on the front body, including the inlet during provided through the cam ring, and the charge chamber communicating with the contact surface of the cam ring are provided for the rear body so as to provide the function of a side plate, it is possible to eliminate side plates and the spring used for urging the side plate to the rotor, and therefore it is possible to reduce the number of necessary parts in a relatively simple vane pump construction. In addition, since it is possible to eliminate the rotational friction loss produced when the side plate is urged against the rotor by a spring, it is possible to improve pump efficiency.

With reference to Fig. 12, there is explained an embodiment of the ieakage-fluid return duct for the vane pump according to the present invention.

The reference numeral 23 denotes a leakageoil return duct to return the oil flowing along the drive shaft 6 to the inlet side, one end of which communicates with a clearance between the front body 19 and the drive shaft 6 and other end of which communicates with the charge chamber 22 of the front body 19.

Further, the numeral 24 denotes an oil seal, the numeral 25 denotes a bearing to support the drive shaft 6 rotatably, the numerals 26 and 27 denote O-rings mounted on either side of the cam ring 10 to seal the contact surfaces between the cam ring 10, and the front body 19 and the rear body 11, the numeral 28 denotes a locating pin to locate the cam ring 10, and the front body 19 and rear body 11 in position, the numeral 29 denotes pinfitting holes provided for the front body 1 9 and the rear body 11, the numeral 30 denotes bolts to join the front body 19 and rear body 11 with the cam ring 10 disposed therebetween, and the numeral 31 denotes bolt holes Next, there is described the operation of the vane pump thus constructed.

When the drive shaft 6 and the rotor 8 are rotated by an engine for an automotive vehicle through the belt 17 and pulley 16, the vanes 9 mounted on the rotor 8 move radially outward due to centrifugal force and slide along the inner peripheral surface of the cam ring 10.

Accordingly, the change in volume between adjacent vanes 9 introduces oil from an oil tank (not shown) through the inlet port 12, the inlet duct 13, and the charge chambers 22, to the pump chamber 14, and next the introduced oil is supplied to a device such as a power steering cylinder through the discharge passages 4, the outlet port 15, and a flow control valve (not shown). In addition, in this embodiment, the leakage oil flowing along the drive shaft 6 from the pump chamber 14 is returned to the charge chambers 22 of the front body 19 through the leakage oil return passage 23.

As described hereinabove, in the vane pump according to the present invention which comprises the rotor mounted on the drive shaft, a number of vanes mounted to the rotor, the cam ring to house the rotor to which the vanes are mounted, the front body and the rear body between which the cam ring is sandwiched so as to form a pump chamber, and additionally the leakage-oil return duct provided on the body, when the rotor is rotated by way of the drive shaft, the leakage oil flowing along the rotary shaft from the pump chamber is returned to the inlet side through the leakage-oil return duct, since one end of the leakage-oil return duct communicates with the clearance between the body and the drive shaft and the other side of the return passage communicates with the charge chamber in order to return theleakage oil to the charging chamber directly.

Accordingly, in the vane pump according to the present invention, it is possible to reduce energy loss as compared with the case where the leakage oil is returned to the inlet passageway conventionally, that is, to improve the pump efficiency.

Further, it is possible to prevent cavitation and sound noise from being generated and to reduce a rise in oil temperature, since the leakage oil is returned to the charge chamber.

Furthermore, it is possible to design the leakage oil return duct to be shorter as compared with the case where the leakage oil is returned to the inlet passageway, thus reducing the cost of manufacture.

With reference to Figs. 13 and 14, there is explained an embodiment of the snap ring used for the vane pump according to the present invention.

To facilitate understanding of the present invention, a brief reference will be made to a prior-art snap ring.

In the prior-art vane pump, the rotor 8 is installed to the drive shaft 6 by fitting the drive shaft 6 into a shaft-supporting hole provided within the rotor 8 to fix the rotor thereto with serrations 32, and the rotor 2 is positioned at an appropriate position with respect to the drive shaft 6 by fitting a snap ring 18 into a ring groove 6a provided for the drive shaft 6 to press against the end surface 8a of the rotor 8.

In the prior-art construction, however, since the snap ring 18 is formed in a rectangular shape in cross-section, as shown in Fig. 13, and is forced against the vertical end surface 8a of the rotor 8 to prevent the rotor 8 from moving in the axial direction of the drive shaft 6, there are a few faults.The basic problems are:- (1) Since the snap ring 18 is formed in a rectangular shape in cross-section and therefore since a large stress is produced within the snap ring when the snap ring is fitted into the ring groove 6a, it is necessary to design the ring groove 6a to be narrow enough to reduce the bending stress and to prevent the external strain of the snap ring 18. (If the groove 6a is wide, a larger bending moment is applied to the snap ring by the rotor 8.) (2) Since the snap ring 18 is placed in perpendicular contact with the end surface 8a of the rotor 8 and therefore the load applied in the axial direction of the snap ring 18 is directly applied to the side surface of the ring groove 6a, the ring groove 6a is easy to deform.Accordingly, in order to prevent the deformation, it is necessary to provide appropriate heat treatment for the ring groove 6a, for instance, quenching.

(3) The snap ring 18 and the rotor 8 can easily slide along the drive shaft 6, because of the reasons described hereinabove under.(1) and (2).

In view of the above description, reference is now made to Fig. 14, in which there is described an embodiment according to the present invention. In Fig. 14, although an angle of inclination 0 of the end surface 8a of the rotor 8 is formed at 45 degrees, it is unnecessary to set the angle to 45 degrees. In this case, the smaller the angle of inclination, the more the force component of the load applied to the drive shaft through the snap ring 18 can be directed toward the center of the drive shaft 6.

As described hereinabove, in a rotary machine such as a vane pump in which the rotor 8 is designed in such a way that the drive shaft 6 is fitted into the bearing hole provided within the rotor 8 so as to rotate therewith, a snap ring 18 is fitted to the ring groove 6a provided for the drive shaft 6, and the end surface 8a of the rotor 8 is supported by the snap ring 18 to fix the drive shaft 6 in position, since the snap ring 18 is formed in circular shape in cross-section and since the end surface 8a of the rotor 8 brought into contact with the snap ring 1 8 is formed obliquely, the vane pump according to the present invention has the following effects::- (1) Since the snap ring is formed in a circular shape in cross section, it is possible to reduce stress as compared with a rectangular cross section, and therefore it is possible to prevent the external deformation of the snap ring and to increase the depth of the ring groove.

(2) Since the end surface of the rotor with which the snap ring is brought into contact is formed obliquely, a component force applied in the radial direction of the drive shaft is generated in the snap ring, it is possible to reduce the force (load) applied in the axial direction of the drive shaft and therefore it is possible to prevent the ring groove from deforming.

(3) It is possible to prevent the snap ring and the rotor from sliding along the drive shaft easily, because of the reasons described hereinabove.

It will be understood by those skilled in the art that the foregoing description is in terms of preferred embodiments of the present invention wherein various changes and modifications may be made without departing from the spirit and scope of the invention, as set forth in the appended claims.

1-Body, la-Partition, 1 bCommunication hole, 2--Bushing-fitted bore, 3-Outlet duct, 4- Discharge passage, 5-Bushing, 6-Drive shaft, 6aSnap-ring groove, 7-Bearing, 8-Rotor, 9-Vanes, 1 0-Cam ring, 11-Rear body, 12- Inlet port, 13-Inlet duct, 14-Pump chamber, 15-Outlet port, 16-Pulley, 17-Belt, 18- Snap ring 19-Front body, 20-Vane back pressure groove, 21-Vane back-pressure hole, 22-Charge chamber, 23-Leakage-oil return duct, 24-Oil seal, 25-Bearing, 26-0-ring, 27-0-ring, 28-Locating pin, 29-Pin fitting hole, 30-Bolt, 31-Bole hole, 32-Serration.

Claims

1. A vane pump comprising: (a) a front body (19); (b) a rear body (11); (c) a cam ring (10) sandwiched between said front body and said rear body so as to form a pump chamber; (d) a drive shaft (6); (e) a rotor (8) mounted on said drive shaft; (f) a number of vanes (9) mounted to said rotor, said vanes moving radially outward while sliding in contact with the inner peripheral surface of said cam ring when said rotor is rotated, wherein the improvement comprises: said front body (19) having: (a) a bushing-fitted bore (2); (b) an outlet duct (3) provided around the bushing-fitted bore; (c) a discharge chamber (4) one end of which communicates with the outlet duct (3) and the other end of which communicates with the front body surface with which said cam ring is brought into contact; and (d) a communication hole (1b) one end of which communicates with the bushing-fitted bore and the other end of which communicates with the outlet duct, whereby it is possible to cast said front body accurately and easily when manufacturing said front body by the casting process.

2. A vane pump comprising:- (a) a front body (19); (b) a rear body (11); (c) a cam ring (10) sandwiched between said front body and said rear body so as to form a pump chamber; (d) a rotary shaft (6); (e) a rotor (8) mounted on said rotary shaft; (f) a number of vanes (9) mounted to said rotor, said vanes moving radially outward while sliding in contact with the inner peripheral surface of said cam ring when said rotor is rotated, wherein the improvement which comprises: said front body (19) having::- (a) an inlet duct (1 3) communicating with an inlet port (12); (b) an outlet duct (3) communicating with an outlet port (15); (c) a discharge chamber (4) one end of which communicates with the outlet duct (3) and tne other end of which communicates with the front body surface with which said cam ring is brought into contact; (d) a vane back-pressure groove (20) provided on the front body surface with which said cam ring is brought into contact; and (e) a vane back-pressure hole (21), one end of which communicates with the vane backpressure groove and the other end of which communicates with the outlet duct, and further said rear body (11) having: (a) an inlet duct (13) which communicates with the front body inlet duct through the cam ring inlet duct; and (b) a charge chamber (22) being branched from the inlet duct (13) and communicating with the rear body surface with which said cam ring is brought into contact, whereby it is possible to eliminate the rotational friction caused by a conventional side plate spring without use of any side plate.

3. A vane pump comprising: (a) a front body (19); (b)arearbody(11); (c) a cam ring (10) sandwiched between said front body and said rear body so as to form a pump chamber; (d) a drive shaft (6); (e) a rotor (8) mounted on said drive shaft; (f) a number of vanes (9) mounted to said rotor, said vanes moving radially outward while sliding in contact with the inner peripheral surface of said cam ring when said rotor is rotated, wherein the improvement which comprises.

said front body (19) having a leakage-oil return duct (23), one end of which communicates with a clearance between said drive shaft (6) and the bushing-fitted bore (2) of said front body and the other end of which communicates with the charge chamber (22), whereby it is possible to increase the efficiency of the vane pump without generating cavitation and noise and without increasing fluid temperature.

4. A vane pump as set forth in any of claims 1, 2 or 3, which further comprises a round-crosssection snap ring (18) for installing said rotor (8) in position to said drive shaft (6), said round snap ring being fitted to a semi-circular groove (6a) provided near one end surface of said rotary shaft (6) so as to be in contact with one end surface of said rotor (8) with an appropriate contact angle (0) from the axial direction thereof, whereby it is possible to provide a deformation-resistant snap ring.