Claw pump

Abstract

A claw pump includes: a housing; two rotating shafts which are disposed parallel; a pair of rotors respectively fixed to the two rotating shafts; a rotary drive device driving the pair of rotors; and a suction port and discharge ports formed in a partition wall of the housing. The discharge ports are constituted by a first discharge port and a second discharge port. The first discharge port is formed at a position that communicates with an initial stage compression space formed at an initial stage of a compression stroke in a compression space that is formed by joining a first pocket and a second pocket. The claw pump includes an opening/closing mechanism which opens the first discharge port when a pressure of the initial stage compression space reaches a threshold and closes the first discharge port when the pressure does not reach the threshold.

Claims

1. A claw pump comprising: a housing comprising a cylinder having a cross-sectional shape of two partially overlapping circles and a pair of side plates, the housing forming a pump chamber having the cross-sectional shape of the two partially overlapping circles; two rotating shafts which are disposed parallel to each other inside the housing and are synchronously rotated in opposite directions to each other; a pair of rotors which are respectively fixed to the two rotating shafts inside the housing and are provided with hook-shaped claws meshing with each other in a non-contact state; a rotary drive device which is configured to drive the pair of rotors so as to be rotated via the two rotating shafts; a suction port which is formed at the cylinder of the housing and communicates with the pump chamber; discharge ports which are formed at the side plates of the housing which block both end faces of the cylinder in an axial direction of the rotating shafts, the discharge ports configured to communicate with the pump chamber and comprising a first discharge port and a second discharge port, the first discharge port being formed at a position that communicates with an initial stage compression space formed at an initial stage of a compression stroke in a compression space that is formed by joining a first pocket defined by one of the pair of the rotors and the cylinder and the pair of side plates of the housing and a second pocket defined by the other of the pair of rotors and the cylinder and the pair of side plates of the housing, the second discharge port being formed at a position that communicates with an end stage compression space formed at an end stage of the compression stroke in the compression space; a pressure sensor which detects the pressure of the initial stage compression space; a solenoid valve which opens and closes the first discharge port; and a control device which receives a detection value from the pressure sensor and controls operations of the solenoid valve to open the first discharge port when the pressure of the initial stage compression space reaches a threshold of atmospheric pressure or higher and to close the first discharge port when the pressure of the initial stage compression space does not reach the threshold.

2. The claw pump according to claim 1, wherein an opening area of the first discharge port is greater than that of the second discharge port.

3. The claw pump according to claim 1, wherein the first discharge port is disposed at a position that communicates with the initial stage compression space closer to an upstream side in a rotational direction of the pair of rotors than the second discharge port.

4. The claw pump according to claim 1, wherein the suction port is formed at a portion of the cylinder corresponding to the two partially overlapping circles.

5. The claw pump according to claim 1, wherein the suction port is formed at the cylinder at a position that communicates with an inlet pocket in which gas is not compressed.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIGS. 1(A) to 1(H) are front sectional views illustrating a claw pump according to a first embodiment of the present invention in a stroke order.

(2) FIG. 2 is a bottom view of the claw pump.

(3) FIG. 3 is a front sectional view of a claw pump according to a second embodiment of the present invention.

(4) FIG. 4 is a front sectional view of a claw pump according to a third embodiment of the present invention.

(5) FIGS. 5(A) to 5(H) are front sectional views illustrating a claw pump according to the related art in a stroke order.

DESCRIPTION OF EMBODIMENTS

(6) Hereinafter, the present invention will be described in detail using embodiments illustrated in the drawings. Here, the dimensions, materials, shapes, relative arrangements, and the like of components described in the embodiments are not intended to limit the scope of the invention thereto if not particularly defined.

First Embodiment

(7) Next, a claw pump according to a first embodiment of the present invention will be described with reference to FIGS. 1 and 2. In an example in FIGS. 1 and 2, a claw pump 10A according to the embodiment is used as a vacuum pump. A housing 12 that forms a pump chamber therein is included. As illustrated in FIG. 2, the housing 12 is constituted by a cylinder 14 having a cross-sectional shape of two partially overlapping circles, and a pair of side plates 16a and 16b which block both end faces of the cylinder 14. The cylinder 14 is provided with a suction port 18, and the suction port 18 is disposed at a position that communicates with an inlet pocket P.sub.0 in which gas is not compressed. In other words, the cylinder 14 has a shape of two partially overlapping cylinders, and the suction port 18 is formed at a portion where a first cylindrical portion and a second cylindrical portion overlap.

(8) Inside the housing 12, two rotating shafts 20a and 20b are arranged parallel to each other. Inside the housing 12, rotors 22a and 22b are respectively fixed to the rotating shafts 20a and 20b. The rotating shafts 20a and 20b extend toward the outside of the housing 12, and end portions of the rotating shafts 20a and 20b are provided with gears 26a and 26b. The gears 26a and 26b are rotated in the opposite directions to each other at the same speed by an electric motor 28. Therefore, the rotating shafts 20a and 20b are synchronously rotated in opposite directions to each other by the electric motor 28. The rotors 22a and 22b are rotated in the opposite directions to each other at the same speed by the electric motor 28. The rotating shaft 20a and the rotor 22a are accommodated in the first cylindrical portion. The rotating shaft 20b and the rotor 22b are accommodated in the second cylindrical portion.

(9) The rotors 22a and 22b are provided with two claws 24a and two claws 24b which have a hook shape and mesh with each other in a non-contact state (with a fine gap therebetween). The two claws are disposed at opposite positions to each other in the circumferential direction.

(10) The gas g is suctioned into the inlet pocket P.sub.0 from the suction port 18 by the rotation of the rotors 22a and 22b. Next, the inlet pocket P.sub.0 into which the gas g flows is divided into a first pocket P.sub.1 enclosed by the housing 12 and the rotor 22a, and a second pocket P.sub.2 enclosed by the housing 12 and the rotor 22b (see FIG. 1(D)). As the rotors 22a and 22b further rotate, the first pocket P.sub.1 and the second pocket P.sub.2 join such that a compression pocket P is formed (see FIG. 1(F)). Thereafter, the compression pocket P is reduced in size and the gas g is in the compression pocket P is compressed. In a series of stages of such a compression stroke, an initial stage compression space Pe is formed at an initial stage of the compression stroke (see FIG. 1(F)), and an end stage compression space Pc is formed at an end stage of the compression stroke (see FIG. 1(H)).

(11) In the cylinder 14 that forms the circumferential wall of the housing 12, a first discharge port 30 and a second discharge port 32 are formed. In the cylinder 14, the first discharge port 30 and the second discharge port 32 are formed in the first cylindrical portion which is provided with the rotating shaft 20a and the rotor 22a and are formed on the opposite side to the suction port 18 with respect to a plane that passes through the rotating shafts 20a and 20b. The first discharge port 30 is disposed at a position that communicates with the initial stage compression space Pe formed immediately after the first pocket P.sub.1 and the second pocket P.sub.2 join (see FIG. 1(F)). In addition, the first discharge port 30 is disposed at a position that communicates with a region on the upstream side in the rotational direction of the rotor in the initial stage compression space Pe. More specifically, the first discharge port 30 is provided on the upstream side in the rotational direction of the rotor (that is, on the opposite side to the rotating shaft 20b) with respect to a virtual plane which is a virtual plane that passes through the rotating shaft 20a and is perpendicular to the plane that passes through the rotating shafts 20a and 20b (that is, parallel to the axis of the suction port 18). The second discharge port 32 is disposed at a position that communicates with the end stage compression space Pc which is formed in a stroke after the initial stage compression space Pe and has a narrower region than that of the initial stage compression space Pe (see FIG. 1(H)). More specifically, the second discharge port 32 is provided on the downstream side in the rotational direction of the rotor (that is, on the rotating shaft 20b side) with respect to the virtual plane.

(12) As illustrated in FIG. 2, the first discharge port 30 has a rectangular shape with a long side having a length that is close to substantially the entire axial length of the cylinder 14 and a short side directed in the circumferential direction of the cylinder 14. The second discharge port 32 has a circular shape with a small diameter. The first discharge port 30 is formed to have a greater area than that of the second discharge port 32.

(13) In addition, a valve body 34 which opens and closes the first discharge port 30 is provided. One end of a spring member 36 is connected to the rear surface of the valve body 34. The other end of the spring member 36 is connected to a fixed base 38. The spring member 36 is, for example, a compression spring and applies an elastic force to cause the valve body 34 to be biased in such a direction that the first discharge port 30 is closed. The elastic force of the spring member 36 is adjusted such that the first discharge port 30 is opened when the pressure of the initial stage compression space Pe is equal to or higher than the atmospheric pressure and is equal to or higher than a threshold (for example, 1.04 atm) of a value that is approximated by the atmospheric pressure and the first discharge port 30 is closed when the pressure of the initial stage compression space Pe is lower than the threshold.

(14) When the initial stage compression space Pe is reduced in size and the pressure of the initial stage compression space Pe reaches the threshold or higher, the pressure of the initial stage compression space Pe becomes higher than the elastic force of the spring member 36 and presses the valve body 34 such that the first discharge port 30 is opened. Since the first discharge port 30 has a large opening area, the gas is discharged at a high flow rate at a time as the first discharge port 30 is opened. When the gas g is discharged from the first discharge port 30 and the pressure of the initial stage compression space Pe becomes lower than the threshold, the valve body 34 closes the first discharge port 30 by the elastic force of the spring member 36.

(15) As the rotors 22a and 22b further rotate, the initial stage compression space Pe is reduced in size and the end stage compression space Pc is formed. Since the first discharge port 30 is closed, the gas g is discharged from the second discharge port 32 (see FIG. 1(H)).

(16) According to this embodiment, when the pressure of the initial stage compression space Pe becomes higher than the threshold during an operation at a suction pressure of atmospheric pressure, the first discharge port 30 is opened and a large amount of gas g is discharged from the first discharge port 30. Therefore, unnecessary compression of the gas g can be avoided. Therefore, the generation of counter torque applied to the rotors 22a and 22b can be prevented, and the pump power can be reduced. In addition, since the first discharge port 30 has a large opening area, the pressure loss can be reduced, and accordingly, the pump power can also be reduced. Moreover, during an operation at a suction pressure of about the ultimate pressure, the pressure of the initial stage compression space Pe is low and thus the first discharge port 30 is closed. Therefore, the backflow of the outside air to the initial stage compression space Pe can be prevented.

(17) During an operation at a suction pressure of about the ultimate pressure, the claw pump 10A discharges the gas g only from the second discharge port 32. Since the second discharge port 32 has a small opening area, the backflow of the air is less likely to occur. In addition, since the second discharge port 32 is formed in the end stage compression space Pc, a time for which the backflow of the air occurs can be shortened. Therefore, even while the second discharge port 32 is opened, the generation of counter torque can be prevented. In addition, during an operation at about the ultimate pressure, the flow rate of the discharged gas g is low, and the pressure loss can be suppressed. Therefore, even during an operation at about the ultimate pressure, the pump power can be reduced.

(18) In addition, since the first discharge port 30 is disposed at a position that communicates with a region of the initial stage compression space Pe on the upstream side in the rotational direction of the rotor, the first discharge port 30 can be opened early in the initial stage of the compression stroke. Therefore, excessive compression of the gas can be relieved early. Furthermore, since the spring member 36 is used as an opening/closing mechanism of the first discharge port 30, the opening/closing mechanism can be implemented at a low cost.

Second Embodiment

(19) Next, a second embodiment of the present invention will be described with reference to FIG. 3. A claw pump 10B of this embodiment is an example in which a second discharge port 40 is formed in any one of the side plates 16a and 16b. That is, the second discharge port 40 is formed in any one of the side plates 16a and 16b and is disposed at a position that does not communicate with the initial stage compression space Pe and communicates with the end stage compression space Pc. The second discharge port 40 is formed at a position corresponding to any end surface of the first cylindrical portion provided with the rotating shaft 20a and the rotor 22a in the cylinder 14. The shape, size, and the like of the second discharge port 40 are the same as those of the second discharge port 32 of the first embodiment.

(20) According to this embodiment, in addition to the operational effects obtained by the claw pump 10A of the first embodiment, there are advantages that the degree of freedom of disposition of the second discharge port 40 can be increased and the second discharge port 40 can be easily machined. In addition, since the second discharge port 40 is formed in any one of the side plates 16a and 16b and is disposed at a position that does not communicate with the initial stage compression space Pe and communicates with the end stage compression space Pc, the backflow of the air to the pump chamber can be effectively prevented.

Third Embodiment

(21) Next, a third embodiment of the present invention will be described with reference to FIG. 4. A claw pump 10C according to this embodiment is different from that of the second embodiment in the opening/closing mechanism for opening and closing the first discharge port 30. A opening/closing mechanism of this embodiment is constituted by a pressure sensor 50 which detects the pressure of the initial stage compression space Pe, a solenoid valve 52 which opens and closes the first discharge port 30, and a control device 54 which receives a detection value of the pressure sensor 50 and controls operations of the solenoid valve 52 to open the first discharge port 30 when the pressure of the initial stage compression space Pe reaches the threshold and to close the first discharge port 30 when the pressure of the initial stage compression space Pe does not reach the threshold. The other configurations are the same as those of the second embodiment.

(22) In this configuration, the first discharge port 30 can be opened when the pressure of the initial stage compression space Pe reaches the threshold and the first discharge port 30 can be closed when the pressure of the initial stage compression space Pe does not reach the threshold by the control device 54. According to this embodiment, there are advantages that the first discharge port 30 can be accurately opened and closed using the threshold as the reference, and the threshold can be easily changed depending on the change in operational conditions of the claw pump 10C. In addition, the opening/closing mechanism of the third embodiment may be applied to the claw pump 10A of the first embodiment in which the first discharge port 30 and the second discharge port 32 are formed in the cylinder 14.

INDUSTRIAL APPLICABILITY

(23) According to the present invention, a claw pump which can always reduce pump power with simple and low-cost means regardless of operational conditions.

REFERENCE SIGNS LIST

(24) 10A, 10B, 10C CLAW PUMP 12, 102 HOUSING 14 CYLINDER 16a, 16b SIDE PLATE 18, 108 SUCTION PORT 20a, 20b, 110a, 110b ROTATING SHAFT 22a, 22b, 112a, 112b ROTOR 24a, 24b, 114a, 114b CLAW 26a, 26b GEAR 28 ELECTRIC MOTOR 30 FIRST DISCHARGE PORT 32, 40 SECOND DISCHARGE PORT 34 VALVE BODY 36 SPRING MEMBER 38 FIXED BASE 50 PRESSURE SENSOR 52 SOLENOID VALVE 54 CONTROL DEVICE 100 CLAW PUMP 116 DISCHARGE PORT P COMPRESSION POCKET Pe INITIAL STAGE COMPRESSION SPACE Pc END STAGE COMPRESSION SPACE P.sub.0 INLET POCKET P.sub.1 FIRST POCKET P.sub.2 SECOND POCKET g GAS