Claw pump with relief space

Abstract

In a pump chamber (12), a male rotor (20) having claw portions and a female rotor (24) having recesses into which the claw portions enter are secured to rotating shafts (18a and 18b), respectively. The female rotor is provided with hollows on an upstream side in the rotational direction of the female rotor relative to a plane L containing the rotating shafts. For the hollows, the disposed position, size and configuration are selected so that a compression pocket P and a discharge opening remain in communication with each other through the hollow throughout the time from when the compression pocket stops communicating with the discharge opening and separates from the discharge opening until the compression pocket gradually reduces to disappear, and so that the hollow stops communicating with the discharge opening at the same time as the compression pocket disappears.

Claims

1. A claw pump having a pair of mutually parallel rotating shafts rotating in opposite directions to each other, a pair of rotors secured to the pair of rotating shafts, respectively, the pair of rotors including a first rotor having a claw portion projecting in a radial direction and a second rotor having a recess into which the claw portion enters, a pump chamber accommodating the pair of rotors, a suction opening formed in the pump chamber on one side of a plane containing axes of the pair of rotating shafts, and a discharge opening formed in the pump chamber on an other side of the plane, the claw pump comprising: a relief space formed by a hollow provided in an opposing surface of the recess of the second rotor which faces the claw portion of the first rotor, the hollow extending across the entire thickness of the second rotor, the relief space communicating with a compression pocket formed between the claw portion of the first rotor and the recess of the second rotor when the compression pocket separates from the discharge opening, so that a compressed gas remaining in the compression pocket is allowed to escape into the relief space.

2. The claw pump of claim 1, wherein: the hollow extends to a surface of the second rotor that faces the discharge opening, and the relief space formed by the hollow communicates with the discharge opening and the compression pocket when the compression pocket separates from the discharge opening and until the compression pocket disappears due to the rotation of the first and second rotor.

3. The claw pump of claim 2, wherein the hollow is disposed so as to separate from the discharge opening at a same time that the compression pocket disappears due to the rotation of the first and second rotor.

4. The claw pump of claim 1, wherein the hollow is disposed so as to remain in communication with the compression pocket throughout time from when the compression pocket separates from the discharge opening until the compression pocket disappears due to the rotation of the first and second rotor.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a front sectional view of a claw pump according to a first embodiment of the apparatus of the present invention.

(2) FIG. 2A is a front view of a female rotor of the claw pump according to the first embodiment, and FIG. 2B is a perspective view of the female rotor of the claw pump according to the first embodiment.

(3) FIG. 3A is an enlarged view of part B in FIG. 1, and FIG. 3B is an enlarged view of part B after a compression pocket has disappeared.

(4) FIG. 4A is a front view showing a modification of the female rotor of the first embodiment, and FIG. 4B is a perspective view showing the modification of the female rotor of the first embodiment.

(5) FIG. 5 is a front sectional view of a claw pump according to a second embodiment of the apparatus of the present invention.

(6) FIG. 6 is a perspective view of a pump chamber of the claw pump according to the second embodiment.

(7) FIG. 7A is an enlarged view of part C in FIG. 1, and FIG. 7B is an enlarged view of part C after a compression pocket has disappeared.

(8) FIG. 8 is a front view of a conventional claw pump, of which: FIG. 8A to 8D show the rotation of rotors in time series; and FIG. 8E is an enlarged view of part A in FIG. 8D.

DESCRIPTION OF EMBODIMENTS

(9) The present invention will be explained below in detail by using embodiments shown in the accompanying drawings. It should, however, be noted that the dimensions, materials, shape, relative dispositions, and so forth of the constituent components described in the following embodiments do not limit the scope of the present invention to themselves alone, unless specifically indicated otherwise.

First Embodiment

(10) A first embodiment in which the claw pump of the present invention is applied to an oil-free vacuum pump will be explained with reference to FIGS. 1 to 3. In FIG. 1, a claw pump 10A of this embodiment has as pump chamber 12 comprising an outer peripheral wall 14 having an inner surface with a sectional configuration defined by two mutually overlapping circles. The pump chamber 12 further comprises two (front and rear) side walls 16 juxtaposed to the outer peripheral wall 14 (front side wall is not shown in the figure). Two rotating shafts 18a and 18b extend in parallel to each other through bores provided in the front and rear side walls 16. The rotating shaft 18a has as male rotor 20 secured thereto. The male rotor 20 has two radially projecting claw portions 22a and 22b. The rotating shaft 18b has a female rotor 24 secured thereto. The female rotor 24 has recesses 26a and 26b into which the claw portions 22a and 22b enter, respectively.

(11) A suction opening 28 is provided on one side of a plane L containing the axes of the rotating shafts 18a and 18b, and a discharge opening 30 is provided on the other side of the plane L. On the discharge opening side of the plane L, a compression pocket P is formed being surrounded by the mutually opposing surfaces of the claw portion 22a or 22b of the male rotor 20 and the recess 26a or 26b of the female rotor 24 and the outer peripheral wall 14, together with the side walls 16. As the male and female rotors 20 and 24 rotate in the directions of the arrows, respectively, the volume of the compression pocket P decreases progressively, and the gas in the compression pocket P is compressed correspondingly. Then, the discharge opening 30 is opened, and the gas in the compression pocket P is discharged through the discharge opening 30.

(12) FIGS. 2A and 2b show the structure of the female rotor 24 in this embodiment. The female rotor 24 has a recess 26a into which the claw portion 22a of the male rotor 20 enters, and a recess 26b into which the claw portion 22b of the male rotor 20 enters. In addition, the female rotor 24 has a hollow 32a provided in an opposing surface of the recess 26a that faces the claw portion 22a, and a hollow 32b in an opposing surface of the recess 26b that faces the claw portion 22b. The hollows 32a and 32b are provided upstream in the rotational direction a of the female rotor 24 relative to the plane L containing the axes of the rotating shafts 18a and 18b. The hollows 32a and 32b are formed in an arcuate configuration over the whole range of the female rotor 24 in the plate thickness direction of the female rotor 24. The arcuate configuration facilitates the hollow machining process using a cutting drill.

(13) For the hollows 32a and 32b, the disposed position, size and configuration are selected so that the hollows 32a and 32b each provide communication between the compression pocket P and the discharge opening 30 in the final stage of the compression process and during the period from the time when the compression pocket P stops communicating with the discharge opening 30 and separates from the discharge opening 30 until the compression pocket P gradually reduces to disappear. Further, the disposed position, size and configuration of the hollows 32a and 32b are selected so that the hollows 32a and 32b each stop communicating with the discharge opening 30 and separate from the discharge opening 30 at the same time as the compression pocket P disappears.

(14) FIGS. 1 and 3(A) correspond to FIGS. 8(D) and (E), respectively, in terms of the rotor operation timing, which show the final stage of the compression process of the compression pocket P. In the final stage of the compression process, the compression pocket P having reduced in volume separates from the discharge opening 30. In this embodiment, however, because the hollow 32b is provided, the compression pocket P is in communication with the discharge opening 30 through the hollow 32b while the compression pocket P remains. Therefore, the gas in the compression pocket P can escape into the discharge opening 30 through the hollow 32b as the volume of the compression pocket P decreases. Accordingly, there will be no occurrence of over-compression in the compression pocket P.

(15) FIG. 3(B) shows the instant when the compression pocket P has disappeared immediately after the state shown in FIG. 3(A). At the same time as the compression pocket P disappears, the hollow 32b and the discharge opening 30 separate from each other. For the hollow 32a also, the disposed position, size and configuration are selected so that the hollow 32a has the same function as the hollow 32b.

(16) According to this embodiment, because the hollows 32a and 32b are provided, the compression pocket P remains in communication with the discharge opening 30 through the hollow 32a or 32b in the final stage of the compression process while the compression pocket P remains between the mutually opposing surfaces of the claw portion 22a or 22b of the male rotor 20 and the recess 26a or 26b of the female rotor 24. Therefore, there will be no occurrence of over-compression in the compression pocket P. Accordingly, it is possible to suppress pulsation caused by over-compression and to suppress vibration and noise caused by pulsation. It is also possible to suppress power loss due to as reaction force generated by over-compression.

(17) In addition, because the hollows 32a and 32b are disposed on the upstream side relative to the plane L in the rotational direction of the female rotor 24, it is possible to suppress the gas over-compressed in the compression pocket P from flowing into a pocket in the pump chamber 12 at a side thereof closer to the suction opening 28. Accordingly, deterioration in ultimate pressure can be suppressed. It is also possible to suppress thermal expansion of the rotors due to the heat of compression generated by over-compression. Consequently, it is possible to prevent wear of the sliding portions of the rotors.

(18) In addition, because the hollow 32a or 32b and the discharge opening 30 separate from each other at the same time as the compression pocket P disappears, there is no possibility of the discharged gas flowing back from the discharge opening 30 into the subsequent compression pocket. Accordingly, it is possible to prevent a reduction in pump efficiency of the vacuum pump.

(19) FIGS. 4A and 4B show a modification of the hollows provided in the female rotor 24. In this modification, quadrangular hollows 34a and 34b are provided. The disposed positions of the hollows 34a and 34b are the same as the hollows 32a and 32b in the first embodiment. The modification also provides the same functions and advantages as the first embodiment.

Second Embodiment

(20) Next, a second embodiment of the present invention will be explained with reference to FIGS. 5 to 7. In this embodiment also, the claw pump is applied to an oil-free vacuum pump as in the case of the first embodiment. The same parts or members as those of the first embodiment are denoted by the same reference signs as used in the first embodiment, and an explanation of the same parts or members is omitted because of redundancy. In a claw pump 10B of this embodiment, a hollow 36 is provided in the inner surface of the side wall 16 at a position upstream of the plane L in the rotational direction of the female rotor 24, i.e. at a position in the area between the rotating shafts 18a and 18b closer to the discharge opening 30 than the plane L. The hollow 36 has a circular outer periphery and a spherical curved surface. Such a configuration facilitates machining using a cutting drill.

(21) FIG. 6 shows the pump chamber 12 at the claw pump 10B according to this embodiment. The pump chamber 12 has the same structure as the pump chamber 12 in the first embodiment. In FIG. 6, the front side wall is omitted. The side wall 16 is provided with bores 38a and 38b through which the rotating shafts 18a and 18b extend, respectively.

(22) For the hollow 36, the position, size and configuration are selected so that the hollow 36 remains in communication with the compression pocket P in the final stage of the compression process and during the period from the time when the compression pocket P, which remains between the mutually opposing surfaces of the claw portion 22a or 22b of the male rotor 20 and the recess 26a or 26b of the female rotor 24, separates from the discharge opening 30 until the compression pocket P disappears. In addition, the position, size and configuration of the hollow 36 are selected so that the whole area of the hollow 36 is closed by the female rotor 24 at the same time as the compression pocket P disappears.

(23) FIG. 7(A) corresponds to FIG. 3(A) in terms of the operation timing of the male and female rotors 20 and 24. When the compression pocket P decreases in volume and separates from the discharge opening 30 in the final stage of the compression process, the compression pocket P is in communication with the hollow 36. This state continues until the compression pocket P disappears. Therefore, the gas in the compression pocket P can escape into the hollow 36. Accordingly, over-compression in the compression pocket P can be reduced.

(24) FIG. 7(B) shows timing at which the compression pocket P disappears immediately after FIG. 7(A). The hollow 36 is closed by the female rotor 24 at the same time as the compression pocket P disappears. Therefore, it is possible to suppress the discharged gas from flowing back from the discharge opening 30 into another compression pocket through the hollow 36. Accordingly, it is possible to suppress reduction in pump efficiency of the claw pump 10B as a vacuum pump.

(25) Although the above-described first and second embodiments are examples in which the claw pump of the present invention is applied to a vacuum pump, the present invention is also applicable to a claw pump for compression.

INDUSTRIAL APPLICABILITY

(26) According to the present invention, it is possible to reduce over-compression in a compression pocket formed between rotors by simple and low-cost means and to suppress problems due to over-compression.