GB2351533A

GB2351533A - Air-driven turbine

Info

Publication number: GB2351533A
Application number: GB0015213A
Authority: GB
Inventors: Shoji Fujii
Original assignee: NTN Corp; NTN Toyo Bearing Co Ltd
Current assignee: NTN Corp
Priority date: 1999-07-01
Filing date: 2000-06-21
Publication date: 2001-01-03
Anticipated expiration: 2020-06-21
Also published as: GB0015213D0; GB2351533B

Abstract

An air-driven turbine (eg. for a machine tool)comprises a shaft 41, and a thrust plate 42<U>b</U>, the latter having recesses 43, formed in a periphery thereof. Turbine nozzles 44, direct compressed air on to the recesses to rotate the thrust plate and shaft. The thrust plate also comprises braking nozzles 65, which are supplied with air via a feed port 66, in a housing portion 48<U>b</U>, and an annular groove 64. The braking nozzles open substantially tangentially along the periphery of the thrust plate and are directed to exert a braking force on the thrust plate. Fixed vanes 67, may be provided with surfaces 69 opposed to the braking nozzles, and the shaft and thrust plate may be supported for rotation by air-bearings. Seals 68 may also be provided. Alternative arrangements for supplying air to the braking nozzles are disclosed, as are air turbines comprising turbine nozzles that are offset or inclined in relation to peripheral recesses in a thrust plate.

Description

2351533

TITLE OF THE INVENTION Air turbine spindle BACK GROUND OF THE INVENTION

The present invention relates to an air turbine spindle and more particularly to an air turbine spindle incorporated into,, for example, a boring machine prec. ision machine tool or electrostatic coating machine wherein the main shaft is noncontact-wise supported by hydrostatic air bearings.

Figs. 16 and 17 show by way of example a conventional air turbine spindle of the type described above using a hydrostatic bearing. This spindle device is of the air turbine driving type; that is, It comprises a plurality of recesses 3 formed in the outer periphery of a thrust plate 2b installed on a main shaft 1, and a plurality of turbine nozzles 4 that tangentially open at positions opposed to the recesses 3, the arrangement being such that compressed air fed from a turbine air feed port 5 through a circumferential turbine air feed passage 6 is blown from the turbine nozzles 4 against radial wall surfaces 7 of the recesses 3 to rotate the main shaft 1. The air that has imparted rotary power to the main shaft 1 is discharged to the outside of a housing 8 through exhaust ports 28 The main shaft 1 is supported in radial and axial direction, by the journal bearing 12 and thrust bearings 15 and 21 for rotation relative to stationary members, such as the housing 8. The two types of bearings 12 and 15, 21 used therein are 1 hydrostatic air bearings that support the main shaft 1 noncontact-wise by the static pressure of compressed air introduced into minute clearances in the journal and thrust bearings.

Further, the air turbine spindle is provided with brake nozzles 24 for imparting a brake force to the main shaft 1 that is rotating in the forward direction, said brake nozzles 24 communicating through an air feed passage 25 with a brake air feed port 26.

When the main shaft 1 is to be braked, the compressed air fed from the brake air feed port 26 is spouted from the brake nozzles 24 via the air feed passage 25 toward the recesses 3 in the thrust plate 2b that is rotating in the f orward direction. This spouted compressed air is blown against wall surfaces 29 at right angles with the radial wall surfaces 7 of the recesses 3 to apply a braking f orce to the main shaft 1 and then discharged from the exhaust parts 28 to the outside of the housing. In addition, at this time, supply of compressed air to rotate the main shaft 1 in the forward direction has been cut off.

Figs. 18 and 19 show another example of a conventional air turbine spindle. The basic arrangement of this air turbine spindle is the same as that of the spindle shown in Figs. 16 and 17, so that like parts are designated by like reference characters to avoid a repetitive description.

This air turbine spindle comprises f orward-rotation recesses 2 3 and brake recesses 30, said recesses 3 and 30 being formed in the outer periphery of the thrust plate 2b and axially arranged side by side in two rows, substantially tangentially-opened turbine nozzles 4 at positions opposed to the recesses 3, and brake nozzles 31 that are formed at positions opposed to the recesses 30 and that open substantially tangentially in a direction opposite to the said turbine nozzles 4.

During the forward rotation of the main shaft 1, thecompresBed air fed from the turbine air feed port 5 is spouted from the turbine nozzles 4 via the annular groove 6 toward the recesses 3 in the thrust plate 2b. This spouted compressed air is blown against the radial wall surfaces 7 of the recesses 3 to impartrotary power to the main shaft 1 and then discharged from the exhaust ports 28 to the outside of the housing.

When the main shaft 1 is to be braked, while the compressed air for rotating the main shaft 1 in the forward direction has been cut off, the compressed air fed from the brake air feed port 32 is spouted from the brake nozzles 31 via the annular groove 33 toward the recesses 30 in the thrust plate 2b that is rotating in the forward direction. This spouted compressed air is blown against the radial wall surf aces 34 of the recesses 30 to impart a brake force to the main shaft 1 and then discharged from the exhaust ports 28 to the outside of the housing.

incidentally, in the case of the air turbine spindle in Figs. 16 and 17 described above, the recesses 3 to serve for forward 3 rotation of the main shaft 1 are utilized for braking purposes. That is, the compressed air spouted from the brake nozzles 24 are blown against the wall surfaces 29 at right angles with the radial wall surfaces 7 in the recesses 3. At this time, since the angle between the direction of spouting of compressed air and the wall surface 29 against which the compressed air is blown is small, there is a problem that the efficiency is low in delivering the brake performance.

Further, because of the construction that makes it necessary to f orm the brake nozzles 24 In the surface in which the turbine nozzles 4 are formed, the brake nozzles 24 must be located at positions where they do not intertere with the turbine nozzles 4, so that it has been dif f icult to secure a suf f icient number of brake nozzles. Because of these problems, it has been dif f icult f or said air turbine spindle to impart a strong brake force.

In contrast thereto, the air turbine spindle shown in Figs. 18 and 19 is constructed such that forward-rotation recesses 3 and brake recesses 30 are arranged side by side in the outer periphery of the thrust plate 2b and compressed air fed from the turbine nozzles 4 and compressed air from the brake nozzles 31 are respectively separately spouted to the recesses 3 and 30. This construction makes it possible to ef f iciently deliver brake perf ormance and to impart a strong brake force s ince it is unnecessary to give consideration to interference with the 4 turbine nozzles 4 in arranging the brake nozzles 31.

However, since this air turbine spindle is constructed such that the radial wall surfaces 34 of the brake recesses 30 formed in the thrust plate 2b are directed opposite to the radial wall surf aces 7 of the f orward-rotation recesses 3, there is a problem that during the f orward rotation of the main shaf t 1, the radial wall surfaces 34 of the brake recesses 30 forms a resistance that lowers the efficiency obtainable during the forward rotation of the main shaft 1.

Fig. 2 0 schematically shows a flow of air in the conventional recess 3, wherein the air blown f rom the turbine nozzle 4 against the recess 3 impinges against the radial wall surface 7 as shown in broken lines, imparting rotary power to the main shaft 1 and then branching into two part's on axially opposite sides for discharge.

However, since the air branch-wise flows in the recess 3 in this manner, there is a tendency for the air to produce turbulence in the vicinity of the branch point (in the vicinity of B in the figure), forming a main cause of energy loss.

As described above, in case of conventional designs, it is dif f icult to improve both the performance of turbine and that of brake, so that there are problems of long acceleration 1 deceleration period and large air consumption of the turbine.

MY OF THE INVENTION Accordingly, the present invention, which has been proposed in consideration of the aforesaid problems g has for its object to provide an air turbine spindle of short acceleration / deceleration period, by ensuring a strong brake force without lowering the efficiency obtainable during the forward rotation of the main shaf t and by improving turbine ef f iciency attained by smoothing the flow of compressed air to reduce energy loss. Further, another object of the present invention is to provide an air turbine spindle having a higher turbine ef f iciency and a higher output power.

As a technical means to achieve said object, the invention provides an airturbine spindle wherein blown against a plurality of recesses formed in the outer periphery of a main shaft is compressed air from a plurality of turbine nozzles disposed in a housing at positions opposed to said recesses, thereby rotating the main shaft, characterized in that a plurality of brake nozzles directed opposite to said turbine nozzles are provided in the main shaft, and a brake air f eed port communicating with said brake nozzles is provided in said housing.

in the present invention, brake nozzles are provided in the main shaf t and compressed air is spouted f rom said brake nozzles in the outer periphery of said main shaft in a direction opposite to the direction of forward rotation, thereby delivering brake 6 performance. This makes it unnecessary to give consideration to interference with turbine nozzles in arranging the brake nozzles, thus making it possible to impart a strong brake force and to realize a construction whose resistance during the f orward rotation of the main shaf t is low as compared with the construction in which the rotating main shaft is provided with brake recesses.

The present invention is applicable to a hydrostatic air bearing including a housing having a plurality of bearing nozzles that open to a journal bearing surface opposed to the outer diameter surface of said main shaft through a journal bearing clearance def ined therebetween and to a thrust bearing surface opposed to the end surf ace of the thrust plate of the main shaf t through a thrust bearing clearance defined therebetween, the main shaft being noncontact-wise supported by feeding compressed air from the bearing nozzles into the bearing clearances.

in addition, in the present invention, it is desirable to provide (1) a construction in which the brake nozzles are disposed in the vicinity of the recesses formed in the main shaft, (2) a construction in which at positions opposed to the brake nozzles there are f ormed surfaces receiving the blowing force of compressed air spouted from said brake nozzles, for example, uneven surfaces such as those including the end surfaces of fixedvanea, and (3) a construction in which a preo sure chamber 7 is f ormed in the main shaft to establish communication between the brake nozzles and the brake air feed port through said pressure chamber. In said (3), it is preferable to provide a construction in which a sealing mechanism for preventing leakage of compressed air f rom the pressure chamber is provided between the pressure chamber of the main shaft and the brake air feed port in the housing, and a construction in which said sealing mechanism is composed of a minute clearance defined between the main shaft and the housing.

According to said invention, brake nozzles are formed in the main shaft and compressed air is spouted from the brake nozzles in the outer periphery of the main shaft in a direction opposite to the direction of forward rotation, thereby delivering brake performance. Therefore, it is unnecessary to give consideration to interference with the turbine nozzles in arranging the brake nozzles, so that it is possible to realize a construction in which a strong brake force can be obtained without decreasing efficiency during the forward rotation of the main shaft and in which the resistance during the forward rotation of the main shaft is low as compared the construction in which the rotating main shaft is formed with brake recesses.

To achieve the objects, the invention provides an arrangement including a main shaft, a bearing for rotatably supporting the main shaf t, a plurality of recesses f ormed in the outer periphery of the main shaft, and a turbine nozzle for blowing compressed 8 air against the recesses to impart rotary power to the main shaft, wherein said turbine nozzle is axially offset with respect to the recesses. Such offset allows the flow of compressed air in the recess to form a single flow, thereby avoiding turbulence attending the branching of flow as in the prior art and hence energy loss attending such turbulence.

in this case, a plurality of turbine nozzles may be disposed with their off set directions made different such that some of the turbine nozzles are on one axial side and the others on the other axial side. At this time, it the amount of offset on one axial side is made equal to that on the other axial side and the number of turbine nozzles on one axial side is made equal to that on the other axial side, then the axial force components acting on the main shaft and produced by the pressure of the compressed air blown against the recesses cancel each other, so that the axial load on the main shaft can be balanced.

Further, if the recesses and turbine nozzles are disposed in double rows and the rows of turbine nozzles are each axially off set toward the side closer to the adjacent row of turbine nozzles, then mutual interference between the air flow fed to one row of recesses and the air flow fed to the other row of recesses is avoided, so that the turbulence of air flow can be further controlled.

In each of the above cases, if the diameter D of the turbine nozzles is not morethan half the axial width X of the recesses, 9 and the amount L of offset of the nozzles with respect to the recesses is not less than half the nozzle diameter D and is not more than half the difference between the axial width X of the recesses and the nozzle diameter D, then the turbulence of air flows in the recesses can be further reduced.

The same function and ef feet as the above can also be attained in an arrangement including a main shaf t, a bearing f or rotatably supporting the main shaft, a plurality of recesses formed in the outer periphery of the main shaft, and a turbine nozzle for blowing compressed air against the recesses to impartrotary power to the main shaf t, wherein said turbine nozzle is inclined with respect to the centerline of recesses.

In each of the above arrangements, the bearing may be composed of a journal bearing that supports the main shaft.radially and noncontact-wise by the static pressure of compressed air introduced into the journal bearing clearance, and a thrust bearing that supports the main shaft in the axial direction and noncontact-wise by the static pressure of compressed air introduced into the thrust bearing clearance.

According to the above invention, the flow of compressed air in the recess forms a single flow. Therefore,, turbulence in flow attendant on the branching and hence energy loss attendant on such turbulence, inherent in the prior art, can be avoided, thus making it possible to ef f iciently impart rotary power to the main shaft.

When the bearings are to be constructed of journal bearing and thrust bearings that are hydrostatic air bearings, compressed air will be used as an air supply to the bearings. Therefore, even when an air turbine is used as a driving source for the spindle, compressed air for the air turbine can be easily obtained by utilizing the compressed air for feeding the bearings Further, the exhaustion for the air turbine and the exhaustion for the bearings can be effected through the common exhaust port, allowing effective use of the space in the housing. An air turbine, which generates almost no heat, is convenient for use as a power source even when a hydrostatic air bearing, which is so small in bearing clearance as to be liable to be influenced by thermal deformation, is used as the bearing as described above. Further, since an air turbine has less mass to be added to a rotary body than an electric motor or the like, high speed rotation can be easily realized by combining it with a hydrostatic air bearing, which is low in bearing loss.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a sectional view of an air turbine spindle according to a first embodiment of the present invention.

Fig. 2 (a) is a sectional view taken along the line A-A in Fig. 1.

Fig. 2 (b) is a sectional view taken along the line B-B in Fig. 1.

11 Fig. 3 is a sectional view showing a second embodiment of the invention.

Fig. 4 (a) is a sectional view taken along the line C-C in Fig.3.

Fig. 4 (b) is a sectional view taken along the line D-D an Fig.3.

Fig. 5 is a sectional view showing a third embodiment of the invention.

Fig. 6 is a sectional view taken along the line E-E in Fig. 5.

Fig. 7 is a sectional view showing a fourth embodiment of the invention.

Fig. 8 is a sectional view taken along the line F-F in Fig. 7.

Fig. 9 is a sectional view of an air turbine driving spindle device according to the present invention.

Fig. 10 is a sectional view taken along the line A-A in Fig. 9.

Fig. 11 is an enlarged sectional view showing the flow of air in a recess in the present inventive device.

Fig. 12 is an enlarged plan view showing another embodiment of the invention.

Fig. 13 is a sectional view showing another embodiment of the invention.

Fig. 14 is an enlarged sectional view showing the flow of 12 air in a recess in the above embodiment.

Fig. 15 is an enlarged sectional view showing another embodiment of the invention.

Fig. 16 is a sectional view showing an example of a conventional air turbine spindle.

Fig. 17 is a sectional view taken along the line G-G in Fig. 16.

Fig. 18 is a sectional view showing another example of a conventional air turbine spindle.

Fig. 19 (a) is a sectional view taken along the line H-H in Fig.

18.

Fig. 19 (b) is a sectional view taken along the line I-I in Fig.

18.

Fig. 20 is an enlarged sectional view showing the flow of an air ciarrent in a recess in the conventional device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Air turbine spindles according to embodiments of the present invention will now be described in detail.

Figs. 1 and 2 (a), (b) show a first embodiment of the invention having a construction in which a main shaft is supported by hydrostatic air bearings. Air turbine spindle in this first embodiment is such that the main shaft 41 is rotated in that 13 blown against a plurality of recesses 43 formed in the outer periphery of the thrust plate 42b of the main shaft 41 is compressed air from turbine nozzles 44 disposed at positions opposed to said recesses 43.

Themain shaft 41 comprises a shaft portion 42a andthethrust plate 42b installed on the end thereof and is supported for rotation relative to a housing 48 by a journal bearing and thrust bearings to be later described. The housing 48 comprises a substantially cylindrical, first housing portion 48a, a circular cover-like second housing portion 48b integrally joined to the end of said first housing portion 48a, a bearing sleeve 49 fixed to the inner diameter of said first housing portion 48a, and a bearing plate 58 fixedto the inner end surface Of said second housing portion 48b.

The inner diameter of the first housing portion 48a has a bearing sleeve 49 fixed therein by a suitable means, such as shrink fitting, press fitting or bonding. This bearing sleeve 49 is formed with a journal bearing 52 having a journal bearing surface 51 opposed to the outer diameter surface of the shaft portion 42a of the main shaft 41 with a minute, journal bearing clea.rance5Odefinedtherebetween, and a thrust bearing 55 having a first thrust bearing surface 54 opposed to the end surface of the thrust plate 42b with a minute, thrust bearing clearance 53 defined therebetween. Further, the bearing sleeve 49 is formed with pluralities of minute, bearing nozzles 56 and 57 14 1 that open to the journal bearing surface 51 and the f irst thrust bearing surface 54.

The inner end surface of the second housing portion 48b has the bearing plate 58 fixed thereto by a suitable means, such as shrink fitting, pressure fitting or bonding. This bearing plate 58 is formed with a thrust bearing 61 having a second thrust bearing surface 60 opposed to the end surface of the thrust plate 42b with a minute, thrust bearing clearance 59 defined therebetween. Further, the bearing plate 58 has a plurality of minute, bearing nozzles 62 formed therein that open to the second thrust bearing surface 60.

Further, the inner diameter of the end of the first housing portion 48a has a fixed ring 63 fixed therein by a suitable means, such as shrink fitting, pressure fitting or bonding. This fixed ring 63 has a plurality of turbine nozzles 44 formed therethrough at positions opposed to the recesses 43 in the thrust plate 42b. The turbine nozzles 44 substantially tangentially open along the outer periphery of the fixed ring 63 and communicate with a turbine air feed port 45 through an annular groove 46 formed in the first housing portion 48a.

On the other hand, the end surface of the trust plate 42b isformed with an annular groove 64 to serve as a pressure chamber and a plurality of brake nozzles 65 for imparting a brake farce, which is directed opposite to said turbine nozzles 44, to the main shaft 41 rotating in the forward direction are formed through to extend in a direction from the annular groove 64 to the outer periphery of the thrust plate 42b. Thebrakenozzles 65 substantially tangentially open along the outer periphery of the thrust plate 42b and communicate with a brake air feed port 66 formed in the second housing portion 48b through the annular groove 64. Further, said f ixed ring 63 has f ixed vanes 67 disposed thereon at positions opposed to the brake nozzles 65 to increase the brake effect. Such fixed vane 67 has an end surface 69 disposed at a position opposed to said brake nozzle 65 and substantially at right angles with a tangential direction in which the brake nozzles 65 open.

To serve as a sealing mechanism for preventing leakage of compressed air from the annular groove 64, clearance seals 68 in the form of minute clearances are formed on the opposite sides of the annular groove 64. The flow resistance provided by the clearances holds the interior of the annular groove 64 under high pressure. Since the clearance seals 68 canbe formed simultaneously with the processing of the second thrust bearing surface 60, it is desirable that they are formed in the same plane as the thrust bearing surface 60. Further, in the case of an air turbine spindle, the clearance seals 68, which are noncontact, are of particularly suitable sealing construction without lowering such characteristics as high speed and high precision.

The radial and axial-wise displacement of the main shaft 16 41 is controlled by compressed air flowing from the bearing nozzles 56, 57, 62 formed in the bearing sleeve 49 and bearing plate58 intothe journal bearing clearance 50 and thrust bearing clearances 53 and 59. The compressed air having flowed into the journal bearing clearance 50 and thrust bearing clearances 53 and 59 is discharged from the end of the shaft portion 42a. directly to the outside of the housing and it is also discharged from exhaust ports 82.

During the forward rotation of the main shaft 41, the compress ed air f ed from the turbine air f eed port 4 5 is spouted from the turbine nozzles 44 of the f ixed ring 63 via the annular groove 46 toward the recesses 43 in the thrust plate 42b. At a position opposed to the turbine nozzle 44, each recess 43 has a radial wall surface 47 substantially at right angles with a tangential direction in which the turbine nozzle 44 opens. The spouted compressed air is blown against the radial wall surface 47 of the recess 43 to impart rotary power to the main shaft 41 and then discharged from the exhaust ports 82 to the outside of the housing.

On the other hand, when the main shaf t 41 is to be braked, the compressed air f ed f rom the brake air f eed port 66 is spouted f rom the brake nozzles 65 via the annular groove 64 in a direction opposite to the direction of forward rotation to impart a brake force to the main shaft 41. This spouted compressed air is blown against the end surfaces 69 of the fixed vanes 67 of the 17 fixed ring 63 to further increase the brake effect and then discharged from the exhaust ports 82 to the outside of the housing via a circumferential groove 70 and exhaust holes 71 in the fixed ring 63. In addition, at this time, supply of compressed air to rotate the main shaft 41 in the forward direction has been cut off.

In this first embodiment, as many exhaust holes 7 1, as many exhaust ports 8 2 and as many f ixed vanes 6 7 for braking purposes as there are the turbine nozzles required for forward rotation are provided inconsideration of space efficiency, and the number of brake nozzles 65 is determined so that it is prime to the number ot tixed vanes 67 within the range of sufficient performance, whereby effects including suppression of vibration are exerted. Further, in this embodiment, it is arranged that compressed air tor braking purposes is fed from one axial end surface of the thrust plate 42b; however, the invention is not limited thereto and it is also possible to provide a construction in which it is f ed from the other axial end surface of the thrust plate 42b or from the outer peripheral surface of the shaft portion 42a. The air turbine spindle in this first embodiment is suitable for use for electrostatic painting and the like where acceleration and deceleration for short periods are required.

Figs. 3and4 (a), (b) show a second embodiment of the invention, wherein the basic arrangement thereof is the same as that of 18 the first embodiment described above [Figs. 1 and 2 (a), (b) j, so that like parts are designated by like reference characters to avoid a repetitive description. What dif fers from the first embodiment is only the absence of the f ixed vanes 67. Even though the fixed vane 67 are absent, it is possible, when the main shaft 41 is to be braked, for compressed air fed from the brake air f eed port 6 6 to impart a brake force to the main shaf t 41 when it is spouted from the brake nozzles 65 via the annular groove 64 in a direction opposite to the direction of forward rotation.

Figs. 5 and 6 show a third embodiment of the invention, wherein parts like those shown in the first embodiment are designated by like reference characters to avoid a repetitive description. In this third embodiment, the end surface of the thrust plate 42b of the main shaft 41 is formed with a pressure chamber 72 that opens to said end surface and a plurality of brake nozzles 73 for imparting a brake force, which is directed opposite to the turbine nozzles 44, to the main shaft 41 rotating in the forward direction are formed through to extend in a direction fromthe pressurechamber 72 to theouter periphery of the shaft portion 42a of the main shaft 41. The brake nozzles 73 communicate through the pressure chamber 72 with the brake air feed port 74 formed in a second housing portion 48b. As in the first and second embodiments, a clearance seal 68 in the form of a minute clearance is f ormed around said pressure chamber

19 72, thus holding the interior of the pressure chamber 72 under high pressure.

When the main shaft 41 is to be braked, compressed air fed f rom the brake air f eed port 74 is spouted f rom the brake nozzles 73 via the pressure chamber 72 in a direction opposite to the direction of forward rotation, thus imparting a brake force tothemain shaft 41. This spouted compressed air is discharged from the exhaust ports 82 in the first housing portion 48a via the exhaust ports 76 formed in the bearing sleeve 49 to the outside of the housing. In addition, at this time, supply of compressed air to rotate the main shaft 41 in the forward direction has been cut off.

In this third embodiment, though the fixed vanes 67 forbraking purposes are not provided, a construction may be provided in which at positions opposed to the brake nozzles 73 in the bearing sleeve 49, surfaces for receiving the blowing force of the compressed air spouted from the brake nozzles 73 r for example, uneven surfaces that perform the same function as that of the fixed vanes 67 used in the first embodiment, are provided. Further, the positions at which the brake nozzles 73 are formed may be any positions besides those shown in the third embodiment, f or example, they may be in the axially middle of the main shaft 41.

Figs. 7 and 8 show a fourth embodiment of the invention, wherein parts like those shown in the third embodiment are designated by like referencecharacters to avoid a repetitive description. The spindle in this fourth embodiment has a construction in which compressed air for braking purposes is radially fed to the main shaft 41. That is, the main shaft 41 is internally formed with a pressure chamber 7 7 andaplurality of brakenozzles 73 for imparting a brake force, which is directed opposite to the turbine nozzles 44, to the main shaf t 41 rotating in the forward direction are formed through to extend in a direction from the pressQre chamber 77 to the outer periphery of the shaft portion 42a of the main shaft 41.

The main shaft 41 is formed with a brake air feed hole 78 communicating with said pressure chamber 77, while the inner diameter surface of the bearing sleeve 49 is formed with an annular groove 79. The brake nozzles 73 communicate with a brake air f eed port 8 0 in the first housing portion 4 Sa through the pressure chamber 77, the brake air feed hole 78 and annular groove 79. The position at which the brake air feed port 80 is formed may be any position in the shaft portion 42a of the main shaft 41 so long as it is a radially directed. As in the case of the f irst through third embodiments, the opposite sides of t he annular groove 79 are formed with clearance seals 81 in the form of minute clearances, thus holding the interior of the pressure chamber 77 under high pressure.

When the main shaf t 41 is to be braked, compressed air fed from the brake air f eed port 8 0 is introduced into the pressure 21 chamber 77 via the annular groove 79 and the brake air feed hole 78 and is spouted from the brake nozzles 73 in a direction opposite to the direction of forward rotation, thus imparting a brake force to the main shaft 41. This spouted compressed air is discharged from the exhaust parts 8 2 in the f irst hOUB ing portion 48a to the outside of the housing via the exhaust ports 76 in the bearing sleeve 49. in addition, at this time, supply of compressed air to rotate the main shaft 41 in the forward direction has been cut off.

Tn addition, in the f irst through third embodiments described above, because of their construction in which compressed air for braking purposes is axially fed, the main shaft 41 can sometimes be subjected to an axial force by the compressed air. In the case where inf luence of such axial f orce is not negligible in view of the specifications of the air turbine spindle, the constrQction in which compressed air for braking purposes is radially fed as in the fourth embodiment is suitable.

Another Embodiment of the present invention will now be described.

As shown in Fig. 9, an air turbine driving spindle according to the present invention is constructed such that a main shaft 41 comprising a shaft portion 42a and a thrust plate 42b installed on the rear end thereof is inserted in the inner peripheral portionof a housing 4 8 and is supported by bearings, forexample, a journal bearing 52 and thrust bearings 55 and 61, which are 22 hydrostatic air bearings, rotatably noncontact-wise in radial and axial directions. The bearings 52 and 55 and 61 may be of other bearing construction than hydrostatic air bearing construction.

The housing 48 is composed of a cylindrical first housing portion 48a, and a second housing portion 48b for closing one end opening therein. The first housing portion 4 Sa comprises a larger diameter portion 48al and a smaller diameter portion M2, said larger and smaller diameter portions having the thrust plate 42b of the main shaft 41 and the shaft portion 42a of the main shaft.4 1, respectively received therein, on their inner diameter sides. The second housing portion 48b Is positioned in opposed relationship to the thrust plate 42b, at which position it covers the opening in the larger diameter portion 48al of the first housing portion 49a.

The first housing portion 48a has a bearing sleeve 49 fixed to the inner peripheral surface thereof. The inner peripheral surface of this bearing sleeve 49 isformedwith a journal bearing surf ace 51 opposed to the outer peripheral surf ace of the ohaf t portion 42a of themain shaf t 41 through a minute, journal bearing clearance def ined therebetween. one end of the bearing sleeve 49 is formed with a flange portion 49a extending around the outer diameter o:Lde,, and the end surface of said f lange portion 49a is formed with a first thrust bearing surface 54 opposed to one end surface of the thrust plate 42b through a minute, 23 thrust bearing clearance def ined therebetween. Further, the portion of the second housing portion 48b opposed to the thrust plate 42b has a bearing plate 58 mounted thereon, and the end surface of said bearing plate SS is formed with a second thrust bearing surf ace 60 opposed to the other endsurf ace of the thrust plate 42b through a minute, thrust bearing clearance def ined therebetween. The journal bearing surface 51 and th e first and second thrust bearing surfaces 54 and 60 are formed with pluraliti-es of minute bearing nozzles 56 and 57, respectively, the arrangement being such that when compressed air is fed to the bearing nozzles 56 and 57 from an air supply (omitted from illustration) through an unillustrated air feed passage, the compressed air is introduced into the journal bearing clearance and the two thrust bearing clearances, and formed in the respective bearing clearances are the journal bearing 52 supporting the shaft portion 42a of the main shaft 41 noncontact-wise in the radial direction and the thrust bearings 55 and 61 supporting the thrust plate 42b of the main shaft 41 noncontact-wise in the opposite axial directions.

The driving system of the main shaf t 41 is the same air turbine driving system as in the conventional spindle device shown in Pigs. 16 and 17. As shown in Fig. 10, a plurality of recesses 43 are formed in the outer peripheral surface of the thrust plate 42b of the main shaft 41, a plurality of turbine nozzles 44 are disposed at positions opposed to the recesses 43, and 24 turbine nozzles 44 blow compressed air tangentially against the recesses 43 in the thrust plate 42b, thereby rotating the main shaft 41. In this embodiment, the turbine nozzles 44 are installed in an annular fixed ring 63 tangentially of the thrust plate 42b, said annular fixed ring 63 being fixed to the inner peripheral surface of the larger diameter portion 48al of the first housing portion 48a. supply of compressed air to the turbine nozzles 44 is ef f ected from an air feed port 45 connected to an unillustrated air supply unit through an annular groove 46 formed in the inner peripheral surface of the larger diameter portion 4Bal opposed to the fixed ring 63. The annular groove 46 may be formed in the outer peripheral surface of the fixed ring 63.

Each recess 43 has axially opposed lateral surface 43a, and a substantIally radially extending wall surface (pressure receiving surface) 47 disposed on one circumferential side thereof and is symmetrically formed on axially opposite sides of the circumferential centerline 0. The pressure receiving surface 47 is a curved surface (e.g., arcuate surface) that is U-shaped In section. The bottom of the recess 43, i.e., the portion 43c extending from the inner diameter end of the pressure receiving surface 47 to the outer peripheral surf ace of the thrust plate 42b is a flat surface that becomes substantially parallel with the direction of the turbine nozzle 44 when the pressure receiving surface 47 is opposed to the turbine nozzle 44.

As shown in Figs. 9 and 11, in the invention, the turbine nozzle 44 is installed at a position that Is axially offset with respect to the recess 43. Such offset allows the flow of compressed air in the recess 43 to form a U-shaped single f low as shown in broken lines in Fig. 11. Theref ore, turbulence in flow (energy loss) as in the prior art attendant on the branching of f low can be avoided, thereby making it possible to ef f iciently impart rotary power to the main shaf t 4 1. The air flow having imparted rotary power to the main shaft 41 is discharged to the outside of the housing 48 through the exhaust ports 82a and 82b, particularly the exhaust port 82a located downstream of said single flow.

in order to further reduce the turbulence in the f low within the recess 43, it is preferable (1) that the diameter D of the turbine nozzle 44 be not more than half the axial width X of the recess 43 [D 5- X 1 2] and (2) that the amount L of offset between the centerline 0 of the recess 43 and the nozzle centerline P of the turbine nozzle 44 be not less than half the nozzle diameter D and not more than half the difference between the axial width X of the recess 43 and the nozzle diameter D [ D 1 2;5 L 2:5 (X - D) / 2]. Further, the of f set direction of the turbine nozzle 44 may be any one of the opposite axial directions and, if structurally possible, may be reverse to the one shown in the figure. Besides this, as shown in Fig.

26 12, the of feet direction of the turbine nozzles 44 (showTi in broken lines) may be made dif f erent between one axial side and the other axial side, in which case, if the amount of off set and the number of turbine nozzles 44 on one axial aide are made equal to those, on the other axial side, then the axial force components acting on pressure receiving surface 47 cancel each other, so that the axial load on the main shaf t 41 can be balanced.

Another embodiment of the invention is shown in Pigs. 13 and 14. in this air turbine spindle,, the recesses 43 are formed in the outer periphery of thrust plate 42b in double rows spaced inaxial direction and the turbine nozzles 44 are correspondingly arranged in double rows, the rest of the arrangement of said spindle being basically the same as shown in Fig. 9 (common members being marked with the same reference numerals to omit a repetitive description). Inthis embodiment also, as in Figs. 9 and 11, the rows of turbine nozzles 44 are axially offset with respect to the corresponding recesses 43 (the amount L of offset being equal for both sides), whereby energy loss of compressed air in the recess 43 can be reduced. At this time, if the double rows of turbine nozzles 44 are each axially of f set toward the side closer to the adjacent row of turbine nozzles, then, as shown in Fig. 14, mutual interference between the air flowing in one recess 43 and the air flowing in the other recess 43 can be suppressed, so that the turbulence in air flow can be controlled to impart rotary power to the main shaft 41

27 more ef f iciently. In this case, if the number of turbine nozzles 44 in each of the two rows is the same, the axial load on the main shaft 41 can be balanced as in the case of Fig. 12.

The above refers to the case where the direction of supply of compressed air (the direction of the nozzle center P) from the turbine nozzle 44 is parallel with the centerline 0 of the recess 43. However, the single flow in the recess 43 can be realized by arranging the nozzle center P inclined with respect to the centerline 0 of the recess 43 as shown in Fig. 15, so that the same effect as described above can also be attained. This arrangement is also applicable to the double-row air turbine spindle shown in Fig. 13f in which case, in order to prevent mutual interference between two flows of air, it is desirable that the direction of inclination of the turbine nozzles 44 be such that the axial spacing between nozzles 44 is reduced on the inner diameter side.

28

Claims

1. An air turbine spindle wherein blown against a plurality of recesses formed in the outer periphery of a main shaft is compressed air from a plurality of turbine nozzles disposed in a housing at positions opposed to said recesses, thereby rotating the main shaft# characterized in that a plurality of brake nozzles directed opposite to said turbine nozzles are provided in the main shaft. and a brake air f eed port communicating with said brake nozzles is provided in said housing.

2. An air turbine spindle as set f orth in Claim 1, wherein said brake nozzles are disposed in the vicinity of the recesses formed in the main shaft.

3. An air turbine spindle asset forth in Claim 1 or 2, wherein formed at positions opposed to said brake nozzles are surfaces for receiving the blowing force of compressed air spouted from the brake nozzles.

4. An air turbine spindle as.set forth in any one of Claims 1 through 3, wherein said main shaft is provided with a pressure chamber, through which the brake nozzles and the brake air f eed port communicate with each other.

5. An air turbine spindle as set forth in Claim 4, wherein a sealing mechanism for preventing leakage of compressed air from the pressure chamber is provided between the pressure chamber of the main shaft and the brake air feed port in the 29 A housing.

6. An air turbine spindle as set forth in Claim 5, wherein said sealing mechanism is a clearance seal in the f orm of minute clearance between said main shaft and said housing.

7. An air turbine spindle comprising a main shaft, a bearing for rotatably supporting the main shaft, a plurality of recesses formed in the outer periphery of the main shaft, and a turbine nozzle for blowing comp:essed air against the recesses to impart rotary power to the main shaft, characterized in that said turbine nozzle is axially off set with respect to the recesses.

8. An air turbine spindle as set forth in claim 7, wherein a plurality of turbine nozzles are disposed with their off set directions made dif f erent such that some of the turbine nozzles are on one axial side and the others on the other axial side.

9. An air turbine spindle as set forth in Claim 7, wherein said recesses and turbine nozzles are disposed in double rows, the rows of turbine nozzles each being axially offset toward the side closer to the adjacent row of turbine nozzles.

10. An air turbine spindle as set forth in any one of claims 7 through 9, wherein the diameter of the turbine nozzles is not more than half the axial width of the recesses, and the amount of offset of the nozzles with respect to the recesses is not less than half the nozzle diameter and is not more than half the difference between the axial width of the recesses and the nozzle diameter.

11. An air turbine spindle including a main shaft, a bearing for rotatably supporting the main shaf t, a plurality of recesses formed In the outer periphery of the main shaft, and a turbine nozzle for blowing compressed air against the recesses to impart rotary power to the main shaft, characterized in that said turbine nozzle is inclined with respect to the centerline of recesses.

12. An air turbine spindle substantially as hereinbefore described with reference to Figs. 1 to 19 of the accompanying drawings.

31

12. An air turbine spindle as set forth in any one of claims 1 through 11, wherein the air turbine spindle including a hous ing having a plurality of bearing nozzles that open to a journal bearing surface opposed to the outer diameter surface of said main shaft through a journal bearing clearance defined therebetween and to a thrust bearing surface opposed to the end surface of the thrust plate of the main shaft through a thrust bearing clearance def ined therebetween, the main shaft being noncontactwise supported by feeding compressed air f rom the bearing nozzles into the bearing clearances.