VANE-TYPE AIR MOTOR AND AIR TOOL PROVIDED WITH VANE-TYPE AIR MOTOR

Abstract

 Provided are a vane air motor capable of starting driving even more reliably even with low-pressure compressed air and an air tool having the vane air motor. A vane air motor (12, 112, 212) has a rotor (40, 140, 240) which is provided on an outer peripheral surface (40b, 140b, 240b) thereof with cut-out portions (44, 144, 244) for promoting vane pushing-out action which intersect vane accommodating grooves (40a, 140a, 240a) at a position of a predetermined depth from the outer peripheral surface (40b, 140b, 240b).

Description

Technical Field:

[0001] The present invention relates to a vane air motor and an air tool having a vane air motor.

Background Art:

[0002] A vane air motor usable as a driving device for an air-driven polishing machine or the like has, as disclosed, for example, in Patent Literature 1, a housing having a rotor accommodating chamber with a circular cylindrical inner peripheral surface, a rotor rotatably retained in the rotor accommodating chamber such that the rotational center axis of the rotor is eccentric with respect to the rotor accommodating chamber, and a plurality of vanes slidably disposed in respective vane accommodating grooves provided on the outer peripheral surface of the rotor. The housing is provided with an air supply port and an air discharge port which open into the rotor accommodating chamber. When compressed air flows from the air supply port toward the air discharge port in one direction around the rotor in the rotor accommodating chamber, the compressed air acts on the vanes projecting outward from the outer peripheral surface of the rotor, thus rotationally driving the rotor.

Citation List:

Patent Literature:

[0003] Patent Literature 1:
Japanese Patent Application Publication No. 2010-159689

Summary of Invention:

Technical Problem:

[0004] In the above-described vane air motor, however, a start-up failure may occur in which the rotor fails to rotate even when compressed air is supplied thereto. The cause of the start-up failure may be as follows. When the rotor is being driven to rotate at high speed by compressed air, the vanes are urged to be displaced outward by receiving a large centrifugal force and therefore rotate with the rotor, with the outer edges of the vanes being kept in contact with the inner peripheral surface of the housing. The inner peripheral surface of the housing is set eccentric with respect to the outer peripheral surface of the rotor, so that the vanes are displaced in such a manner as to reciprocate in the radial direction between a position where the vanes are completely pushed in the vane accommodating grooves and a position where the vanes are greatly pushed out from the vane accommodating grooves. In this regard, however, when the supply of compressed air is stopped to stop the drive of the vane air motor, the rotational speed of the rotor gradually slows downs, and the centrifugal force that the vanes receive gradually decreases correspondingly. Accordingly, when the vanes have been completely pushed into the vane accommodating grooves by the inner peripheral surface of the housing, the vanes may remain in the state of being accommodated in the vane accommodating grooves without projecting outward from the pushed-in positions even if the rotation of the rotor continues. If compressed air is supplied to drive the vane air motor again in this state, the compressed air cannot act on the vanes effectively, resulting in a start-up failure in which the rotor fails to rotate.

[0005] The present invention has been made in view of the above-described assumption of the cause, and an object of the present invention is to provide a vane air motor capable of starting driving even more reliably and an air tool having such a vane air motor.

Solution to Problem:

[0006] The present invention provides a vane air motor comprising: a housing having a rotor accommodating chamber with a circular cylindrical inner peripheral surface; a rotor retained in the rotor accommodating chamber rotatably about a rotational center axis parallel to a center axis of the inner peripheral surface, the rotor having a vane accommodating groove extending inward from an outer peripheral surface thereof and in parallel to the rotational center axis; and a vane slidably disposed in the vane accommodating groove. Compressed air is supplied from an air supply port opening on the inner peripheral surface and passed around the rotor in one direction before being discharged from an air discharge port located at a position circumferentially spaced from the air supply port, so that the compressed air acts on the vane to rotationally drive the rotor. In the vane air motor, the rotor has a cut-out portion for promoting vane pushing-out action which is provided on the outer peripheral surface to intersect the vane accommodating groove.

[0007] We carried out an experiment in which a conventional vane air motor likely to suffer a start-up failure as stated above was provided with the above-described cut-out portion for promoting vane pushing-out action. As a result, a clear improvement was observed in the start-up failure rate. The reason for the improvement has not yet been clarified, but it is conceivable that, when supplied, compressed air can easily flow into the vane accommodating groove through the cut-out portion for promoting vane pushing-out action, and this increases the pressure in the vane accommodating groove, resulting in an increase in the pressure difference between the pressure in the vane accommodating groove and the pressure in the space outside the vane where compressed air is flowing at high speed, thereby allowing the vane to be easily displaced outward of the rotor.

[0008] Preferably, the cut-out portion may be provided to intersect only a rear side of the vane accommodating groove in the rotational direction of the rotor when driven to rotate.

[0009] With the above-described structure, the cut-out portion is located on the upstream side of the flow of compressed air in the housing; therefore, compressed air can flow into the vane accommodating groove even more easily.

[0010] Preferably, the cut-out portion may be provided at a position spaced from the air supply port in the direction of the rotational center axis.

[0011] Specifically, the air supply port may be provided at a central position of the inner peripheral surface in the direction of the rotational center axis, and the cut-out portion may be provided to intersect the opposite ends of the vane accommodating groove in the direction of the rotational center axis.

[0012] Alternatively, the cut-out portion may be provided to intersect a central position of the vane accommodating groove in the direction of the rotational center axis.

[0013] Alternatively, the cut-out portion may comprise a plurality of grooves extending in the circumferential direction of the outer peripheral surface of the rotor and spaced from each other in the direction of the rotational center axis.

[0014] In addition, the present invention provides an air tool comprising: the above-described vane air motor; a tool body retaining the vane air motor; and a driven part drivably connected to the vane air motor.

[0015] Embodiments of a vane air motor and air tool according to the present invention will be explained below on the basis of the accompanying drawings.

Brief Description of Drawings:

[0016] 

Fig. 1 is a sectional view of a pneumatic polishing machine having a vane air motor according to an embodiment of the present invention.

Fig. 2 is a sectional view of the vane air motor taken along the line A-A in Fig. 1.

Fig. 3 is a sectional view of the vane air motor taken along the line B-B in Fig. 1.

Fig. 4 is an exploded perspective view of a rotor and vanes of the vane air motor according to the embodiment of the present invention.

Fig. 5 is an exploded perspective view of a rotor and vanes of a vane air motor according to another embodiment of the present invention.

Fig. 6 is an exploded perspective view of a rotor and vanes of a vane air motor according to still another embodiment of the present invention.

Description of Embodiments:

[0017] As shown in Fig. 1, a pneumatic polishing machine 10 according to an embodiment of the present invention has a vane air motor 12, a tool body 14 retaining the vane air motor 12, and an abrasive holding member 18 drivably connected to the vane air motor 12 and holding an abrasive material 16 at a distal end bottom surface 18b thereof. The tool body 14 is provided with a compressed-air supply path 20 extending from a rear end 14a thereof to the vane air motor 12, and a valve member 22 disposed halfway in the compressed-air supply path 20. In the state shown in Fig. 1, the valve member 22 is sealingly engaged with a valve seat 23 provided in the compressed-air supply path 20 to close the compressed-air supply path 20. The tool body 14 further has an operating lever 24 pivotably attached thereto to open and close the valve member 22. The operating lever 24 is equipped with a safety lock 26. In the state shown in Fig. 1, the safety lock 26 is engaged with the tool body 14 to lock the operating lever 24 from being pivoted toward the tool body 14. To drive the polishing machine 10, an operating part 26a of the safety lock 26 is pushed forward to rotate the safety lock 26 counterclockwise as seen in the figure so that the safety lock 26 is disengaged from the tool body 14. Thereafter, the operating lever 24 is pivoted toward the tool body 14. Consequently, a valve operating shaft 28 projecting from the tool body 14 is pushed in by the operating lever 24, causing the valve member 22 to be tilted. When the valve member 22 is tilted, the sealing engagement between the valve member 22 and the valve seat 23 is canceled. As a result, the compressed-air supply path 20 which has been closed so far opens to allow compressed air to be supplied to the vane air motor 12. Thus, the vane air motor 12 is driven to rotate by the compressed air. The abrasive holding member 18, which is drivably connected to a rotary drive shaft 30 of the vane air motor 12, is retained by a bearing 32 so that the abrasive holding member 18 is rotatable about an eccentric axis E which is eccentric with respect to a rotational center axis R of the vane air motor 12. In addition, a sliding engagement projection 34 located on a top portion 18a of the abrasive holding member 18 is slidingly engaged by a sliding retaining portion 36 of the tool body 14 so that the sliding engagement projection 34 is allowed to move in a longitudinal direction (left-right direction as seen in the figure) but restrained from moving in a lateral direction (depth direction as seen in the figure). Accordingly, when the vane air motor 12 is driven to rotate, the abrasive holding member 18 is driven so that the abrasive material 16 attached to the distal end bottom surface 18b performs a reciprocating elliptical motion in a plane perpendicularly intersecting the rotational center axis R. The polishing machine 10 is an air tool configured to polish a member to be polished by pressing the abrasive material 16, which moves in a reciprocating elliptical motion as stated above, against the member to be polished.

[0018] The vane air motor 12 disposed in the tool body 14 of the polishing machine 10 has, as shown in Figs. 1 to 4, a housing 38 having a rotor accommodating chamber 38b with a circular cylindrical inner peripheral surface 38a, a rotor 40 rotatably retained in the rotor accommodating chamber 38b, and vanes 42 slidably disposed in respective vane accommodating grooves 40a formed in the rotor 40. A center axis C of the inner peripheral surface 38a, which defines the rotor accommodating chamber 38b, and the rotational center axis R of the rotor 40 are parallel to each other at respective positions eccentric with respect to each other (Figs. 2 and 3). As shown in Fig. 4, there are four vane accommodating grooves 40a provided on an outer peripheral surface 40b of the rotor 40, being equally spaced from each other in the circumferential direction of the outer peripheral surface 40b. Each vane accommodating groove 40a extends on the outer peripheral surface 40b in parallel to the rotational center axis R of the rotor 40 and also extends inward from the outer peripheral surface 40b toward the rotational center axis R. In addition, the outer peripheral surface 40b of the rotor 40 is provided with cut-out portions 44 for promoting vane pushing-out action at the opposite ends of each vane accommodating groove 40a. The cut-out portions 44 intersect the associated vane accommodating groove 40a at a predetermined depth from the outer peripheral surface 40b. More specifically, each cut-out portion 44 has a cut plane perpendicularly intersecting the associated vane accommodating groove 40a over a length approximately equal to one-fifth of the length of the rotor 40 in the direction of the rotational center axis R. The cut-out portions 44 are provided only at the rear side of each vane accommodating groove 40a as viewed in the rotational direction of the rotor 40 when driven to rotate (i.e. only at the upstream side of the flow of compressed air). The vane 42 disposed in each vane accommodating groove 40a has an outer surface 42a facing radially outward of the rotor 40, and an inner surface 42b facing radially inward of the rotor 40, and is radially slidable between a position where the vane 42 is pushed into the vane accommodating groove 40a by the inner peripheral surface 38a of the rotor accommodating chamber 38b, as in the case of the vane 42 located at the upper position as seen in Fig. 2, and a position where the vane 42 is projected from the vane accommodating groove 40a outward of the outer peripheral surface 40b of the rotor 40 to contact the inner peripheral surface 38a of the housing 38 by the centrifugal force due to the rotation of the rotor 40, as in the case of the other vanes 42 in Fig. 2. The housing 38 is provided with an air supply port 38c (Fig. 2) opening on the inner peripheral surface 38a at a central position in the axial direction thereof to receive compressed air, and air discharge ports 38d (Fig. 3) opening on the inner peripheral surface 38a at respective positions near the axially opposite ends of the housing 38 to discharge compressed air, so that compressed air supplied from the compressed-air supply path 20 through the air supply port 38c flows in one direction (clockwise as seen in Figs. 2 and 3) through a space 46 between the inner peripheral surface 38a of the housing 38 and the outer peripheral surface 40b of the rotor 40 and flows out of the vane air motor 12 from the air discharge ports 38d before being discharged through a compressed-air discharge path 48. In the process of flowing through the housing 38 from the air supply port 38c toward the air discharge ports 38d, compressed air collides against side surfaces 42c of the vanes 42 projecting outward from the vane accommodating grooves 40a of the rotor 40 and pushes these vanes 42, thereby driving the rotor 40 to rotate.

[0019] Table 1 below shows the results of an experiment carried out to compare between a grinding machine having a conventional vane air motor and a grinding machine having the vane air motor 12 of the present invention in terms of the frequency of occurrence of a start-up failure in each of the grinding machines at various pressures of compressed air used. The experiment was carried out by repeating start and stop operations 100 times for each grinding machine having the above-described vane air motor and counting the number of times at which the vane air motor failed to start. The grinding machines used in the experiment were the same except that one vane air motor had the cut-out portions 44 and the other vane air motor had no cut-out portions 44. As will be understood from Table 1, the grinding machine having the vane air motor 12 according to the present invention showed a great improvement in the start-up failure rate over the grinding machine having the conventional vane air motor at any air pressure.

[Table 1]

Air pressure [MPa]	Number of times of start-up failure (out of 100)
	Conventional vane air motor (without cut-out portions)	Vane air motor of present invention (with cut-out portions)
0.1	54	4
0.2	37	3
0.3	12	1
0.6	3	0

[0020] In a vane air motor 112 according to another embodiment, as shown in Fig. 5, cut-out portions 144 provided in a rotor 140 are disposed so that each cut-out portion 144 intersects the central position of the associated vane accommodating groove 140a. The cut-out portion 144 forms an arcuate surface gradually becoming shallower as the distance from the center of the rotor 140 in the direction of the rotational center axis R increases toward the opposite ends of the rotor 140. It should be noted that the cut-out portion 144 is configured not to intersect either of the opposite end portions of the vane accommodating groove 140a.

[0021] In a vane air motor 212 according to still another embodiment, as shown in Fig. 6, cut-out portions 244 provided in a rotor 240 are formed as grooves of rectangular section extending in the circumferential direction of an outer peripheral surface 240b of the rotor 240. The groove-shaped cut-out portions 244 are provided to extend circumferentially and contiguously around the outer peripheral surface 240b of the rotor 240 while crossing vane accommodating grooves 240a. In addition, the cut-out portions 244 are provided such that three groove-shaped cut-out portions extend parallel to each other and are equally spaced from each other in the direction of the rotational center axis R of the rotor 240.

[0022] We carried out an experiment to compare between a grinding machine which was different from that used in the experiment shown in Table 1 above and which had a conventional vane air motor without cut-out portions and grinding machines respectively having the vane air motors 12, 112 and 212 of the present invention shown in Figs. 4 to 6 in terms of the frequency of occurrence of a start-up failure in the grinding machines. As a result, with the conventional vane air motor, the start-up failure occurred 28 times out of 100 trials. In contrast, with the vane air motor 12, shown in Fig. 4, the start-up failure occurred 2 times out of 100 trials. With the vane air motor 112, shown in Fig. 5, the start-up failure occurred 16 times out of 100 trials, and with the vane air motor 212, shown in Fig. 6, the start-up failure occurred 2 times out of 100 trials. In other words, the vane air motors 12, 112 and 212 according to all the embodiments of the present invention showed an improvement in the start-up failure rate over the conventional vane air motor. In particular, a significant improvement effect was observed with the vane air motor 12, shown in Fig. 4, which has the cut-out portions 44 provided at both ends of the rotor 40, and the vane air motor 212, shown in Fig. 6, which has the cut-out portions 244 provided in the form of three grooves extending in the circumferential direction of the rotor 240. All the vane air motors used in this experiment had a structure in which the air supply port 38c is provided at a central position in the axial direction of the housing 38, and the air discharge ports 38d are provided at respective positions near the axially opposite ends of the housing 38.

[0023] In the vane air motors 12, 112 and 212 according to the present invention, the cut-out portions 44, 144 and 244 are provided on the outer peripheral surfaces 40b, 140b and 240b of the rotors 40, 140 and 240 so as to intersect the vane accommodating grooves 40a, 140a and 240a, respectively. It is therefore conceivable that it is easier for compressed air to flow into the vane accommodating grooves 40a, 140a and 240a than in the conventional vane air motor without cut-out portions. Accordingly, it is conceivable that, in the vane accommodating grooves 40a, 140a and 240a, the pressure in the space at the inner side of each of the vanes 42, 142 and 242 increases, resulting in an increase in the pressure difference between the inner side of each of the vanes 42, 142 and 242 and the outer side thereof where compressed air is flowing at high speed and, consequently, the vanes 42, 142 and 242 are easily displaced outward of the rotors 40, 140 and 240. In other words, it is conceivable that, in the vane air motors 12, 112 and 212 according to the present invention, even if the vanes 42, 142 and 242 are completely pushed in the vane accommodating grooves 40a, 140a and 240a, the vanes 42, 142 and 242 can be easily displaced outward by the action of compressed air; therefore, the frequency of occurrence of a start-up failure is lower than in the conventional vane air motor.

[0024] Although in the above-described embodiments, the vane accommodating grooves 40a, 140a and 240a are provided so as to extend radially toward the respective centers of the rotors 40, 140 and 240, the vane accommodating grooves 40a, 140a and 240a may extend in a direction different from the radial direction. Further, the number of vane accommodating grooves 40a, 140a and 240a and vanes 42, 142 and 242 may be set to any desired value. Although the present invention has been explained above with regard to the polishing machine 10, in which a driven part that is driven by the vane air motor 12, 112 or 212 is the abrasive holding member 18, as one embodiment of an air tool having the vane air motor 12, 112 or 212, the present invention is also applicable to other air tools, such as a grinding machine, a drill, etc., by replacing the driven part with other elements.

List of Reference Signs:

[0025] Polishing machine 10; vane air motor 12; tool body 14; rear end 14a; abrasive material 16; abrasive holding member 18; top portion 18a; distal end bottom surface 18b; compressed-air supply path 20; valve member 22; valve seat 23; operating lever 24; safety lock 26; operating part 26a; valve operating shaft 28; rotary drive shaft 30; bearing 32; sliding engagement projection 34; sliding retaining portion 36; housing 38; inner peripheral surface 38a; rotor accommodating chamber 38b; air supply port 38c; air discharge ports 38d; rotor 40; vane accommodating grooves 40a; outer peripheral surface 40b; vanes 42; outer surface 42a; inner surface 42b; side surfaces 42c; cut-out portions 44; space 46; compressed-air discharge path 48; vane air motor 112; rotor 140; vane accommodating grooves 140a; vanes 142; cut-out portions 144; vane air motor 212; rotor 240; vane accommodating grooves 240a; outer peripheral surface 240b; vanes 242; cut-out portions 244; rotational center axis R; eccentric axis E; center axis C.

Claims

1. A vane air motor comprising:

a housing having a rotor accommodating chamber with a circular cylindrical inner peripheral surface;

a rotor retained in the rotor accommodating chamber rotatably about a rotational center axis parallel to a center axis of the inner peripheral surface, the rotor having a vane accommodating groove extending inward from an outer peripheral surface thereof and in parallel to the rotational center axis; and

a vane slidably disposed in the vane accommodating groove;

wherein compressed air is supplied from an air supply port opening on the inner peripheral surface and passed around the rotor in one direction before being discharged from an air discharge port located at a position circumferentially spaced from the air supply port, so that the compressed air acts on the vane to rotationally drive the rotor;

wherein the rotor has a cut-out portion for promoting vane pushing-out action which is provided on the outer peripheral surface to intersect the vane accommodating groove.

2. The vane air motor of claim 1, wherein the cut-out portion is provided to intersect only a rear side of the vane accommodating groove in a rotational direction of the rotor when driven to rotate.

3. The vane air motor of claim 2, wherein the cut-out portion is provided at a position spaced from the air supply port in a direction of the rotational center axis.

4. The vane air motor of claim 3, wherein the air supply port is provided at a central position of the inner peripheral surface in the direction of the rotational center axis, and the cut-out portion is provided to intersect opposite ends of the vane accommodating groove in the direction of the rotational center axis.

5. The vane air motor of claim 2, wherein the cut-out portion is provided to intersect a central position of the vane accommodating groove in the direction of the rotational center axis.

6. The vane air motor of claim 1, wherein the cut-out portion comprises a plurality of grooves extending in a circumferential direction of the outer peripheral surface of the rotor and spaced from each other in a direction of the rotational center axis.

7. An air tool comprising:

the vane air motor of any one of claims 1 to 6;

a tool body retaining the vane air motor; and

a driven part drivably connected to the vane air motor.

Amended claims

Amended claims under Art. 19.1 PCT

1. A vane air motor comprising:

a housing having a rotor accommodating chamber with a circular cylindrical inner peripheral surface;

a rotor retained in the rotor accommodating chamber rotatably about a rotational center axis parallel to a center axis of the inner peripheral surface, the rotor having a vane accommodating groove defined by an elongated opening formed on an outer peripheral surface of the rotor to extend parallel to the rotational center axis between opposite end surfaces of the rotor, the vane accommodating groove being further defined by a front side surface and a rear side surface which extend radially inward from a front edge and a rear edge, respectively, of the opening, as viewed in a rotational direction of the rotor, and a bottom surface extending between the front side surface and the rear side surface at a position spaced radially inward from the outer peripheral surface of the rotor; and

a vane slidably disposed in the vane accommodating groove;

wherein compressed air is supplied from an air supply port opening on the inner peripheral surface and passed around the rotor in one direction before being discharged from an air discharge port located at a position circumferentially spaced from the air supply port, so that the compressed air acts on the vane to rotationally drive the rotor;

wherein the air supply port is provided at a central position of the inner peripheral surface in a direction of the center axis;

the rotor having a cut-out portion for promoting vane pushing-out action which is provided on the outer peripheral surface to intersect the vane accommodating groove at a position spaced from the bottom surface of the vane accommodating groove, the cut-out portion being one cut-out portion for promoting vane pushing-out action selected from a group consisting of: (a) a cut-out portion for promoting vane pushing-out action which is defined by cut-out surfaces extending rearward in the rotational direction from the rear side surface of the vane accommodating groove to intersect the outer peripheral surface at opposite ends, respectively, of the rotor in the direction of the rotational center axis; (b) a cut-out portion for promoting vane pushing-out action comprising a plurality of grooves extending in a circumferential direction of the outer peripheral surface of the rotor and spaced from each other in the direction of the rotational center axis; and (c) a cut-out portion for promoting vane pushing-out action defined by a cut-out surface intersecting the rear side surface of the vane accommodating groove along an arcuate line which extends from a central position of the rotor in the direction of the rotational center axis to near opposite ends of the rotor, the arcuate line becoming closer to the outer surface as a distance from the central position increases toward the opposite ends, the cut-out surface further extending rearward in the rotational direction to intersect the outer peripheral surface.

2. The vane air motor of claim 1, wherein the cut-out surfaces defining the cut-out portion (a) for promoting vane pushing-out action intersect the end surfaces, respectively, of the rotor.

3. The vane air motor of claim 1, wherein the cut-out surfaces defining the cut-out portion (a) for promoting vane pushing-out action perpendicularly intersect the rear side surface of the vane accommodating groove.

4. The vane air motor of any one of claims 1 to 3, wherein the cut-out surfaces defining the cut-out portion (a) for promoting vane pushing-out action each intersect the vane accommodating groove over a width approximately equal to one-fifth of a length of the rotor in the direction of the axis.

5. The vane air motor of claim 1, wherein the cut-out portion (b) for promoting vane pushing-out action has three of the grooves located respectively at a central position of the rotor in the direction of the rotational center axis and positions spaced from the central position toward the opposite ends.

6. The vane air motor of claim 5, wherein the grooves of the cut-out portion (b) for promoting vane pushing-out action each extend over an entire circumference of the rotor, and there are provided a plurality of the vane accommodating grooves spaced from each other in the circumferential direction to divide each of the grooves of the cut-out portion into a plurality of arcuate grooves.

7. An air tool comprising:

the vane air motor of any one of claims 1 to 6;

a tool body retaining the vane air motor; and

a driven part drivably connected to the vane air motor.

Drawing