Abstract:
An axial flow power tool turbine motor for operation with an elastic fluid, like pressured air, includes a housing ( 12 ), a rotor ( 11 ) rotatively journalled in the housing ( 12 ) and formed in one piece with drive blades ( 24 ) arranged in axially spaced circumferential rows (C, A, C, E, G, I, K), and a stator ( 10 ) in the form of a tubular body ( 22 ) which is immovably supported in the housing ( 12 ) and which carries internal guide vanes ( 23 ) arranged in circumferential rows (B, D, F, H, J), wherein the tubular stator body ( 22 ) is divided into three longitudinal sections ( 22   a   , 22   b   , 22   c ) with which the guide vanes ( 23 ) are integrally formed, and a retainer ( 27, 29 ) for fixing and mounting the longitudinal sections ( 22   a   , 22   b   , 22   c ) in accurately defined relative positions to form the tubular stator body ( 22 ).

Description:
This invention relates to an axial flow turbine machine for operation with an elastic fluid. 
     In particular, the invention concerns an axial flow turbine machine comprising two or more expansion or compression stages, i.e. having a rotor carrying drive blades arranged in two or more axially spaced circumferential rows and a stator carrying guide vanes arranged in one or more circumferential rows, wherein each one of the rows of guide vanes is disposed between two adjacent rows of drive blades. 
     BACKGROUND OF THE INVENTION 
     In prior art, it is well known to produce multi-stage turbine machines by forming both the rotor and the stator in a number of sections to be assembled into a complete rotor and a complete stator. In bigger turbines, the guide vanes are formed as separate parts for mounting in rows in the stator, and the stator is divided into two longitudinal halves to be put together around the rotor, whereby the guide vane rows are introduced between the drive blade rows. 
     However, when producing small size turbines having a diameter of only 30-40 mm, it is not practically possible to use separate guide vanes in the stator. The radial size of the guide vanes in the high pressure stage may be as small as a fraction of a millimeter. Such small vanes have to be formed integral with the stator by machining or molding. 
     In British Patent No. 1 287 850, there is described a small size two-stage turbine in which the rotor is formed in one piece, including two rows of drive blades. Since the drive blades extend from an outer cylindrical surface, there is no problem machining them from the rotor body. The stator of this known turbine comprises one row of guide vanes which is located between the drive blade rows and which is formed by two semicircular ring elements provided with guide vanes on their outside. This means that the guide vanes are easily machinable from the outer surface of the ring elements. 
     On the other hand, this prior art guide vane arrangement means that the turbine is rather complicated as it comprises not only separate ring elements to form the stator but also separate sleeve elements for accomplishing an axial clamping of the ring elements in the housing. This also means that there is a nonfavourable air flow path through the turbine, because the guide vanes have a bigger radial extent than the drive blades for enabling the axial clamping of the stator ring elements. Thus, the air flow path is locally enlarged in the stator, which causes an undesirable turbulent air flow therethrough. 
     OBJECT OF THE INVENTION 
     The primary object of the invention is to accomplish an axial flow turbine machine having two or more expansion or compression stages and which is inexpensive and easy both to manufacture and to assemble and which is suitable for production in small sizes. 
     A preferred embodiment of the invention is below described in detail with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a longitudinal section through a turbine according to the invention. 
     FIG. 2 shows a cross section along line II—II in FIG.  1 . 
     FIG. 3 illustrates a machining process in which the guide vanes of a stator section are formed by milling. 
     FIG. 4 shows, on a larger scale, a fraction of the longitudinal section in FIG.  1 . 
    
    
     DETAILED DESCRIPTION 
     The turbine illustrated in the drawing figures is a six stage pneumatic motor comprising a stator  10 , a rotor  11  and a cylindrical housing  12 . The stator  10  is immovably secured in the housing  12 , whereas the rotor  11  is rotatively journalled in the housing  12  by means of two roller bearings  13 ,  14 . The rotor  11  also comprises a splined output end  15  for connection to a reduction gearing (not shown). 
     The housing  12  comprises a forward section  16  and a rear section  17  which are rigidly interconnected by a thread connection  18 . A pressure air inlet passage  19  extends coaxially through the rear housing section  17 , and a number of parallel air exhaust passages  20  in the rear section  17  communicate with a tubular exhaust chamber  21  formed between the forward housing section  16  inner wall and the stator  10 . The air flow through the turbine is illustrated by arrows in FIG.  1 . 
     The stator  10  comprises a tubular body or sleeve  22  carrying inwardly directed guide vanes  23  which are arranged in five axially spaced circumferential rows B, D, F, H, and J, whereas the rotor  11  is provided with drive blades  24  arranged in six axially spaced circumferential rows A, C, E, G, I, and K. See FIG.  1 . In a common manner, the drive blades  24  and the guide vanes  23  are disposed in alternating positions, viewed in the direction of the motive pressure air flow through the turbine. This means that between adjacent rows of drive blades  24  there is a row of guide vanes  23  for linking the pressure air flow into an optimum direction before entering the next row of drive blades  24 . 
     In the drawings, the reference numerals of the drive blades  24  and the guide vanes  23  are combined with the reference letters of the circumferential rows A, C, E, G, I, and K and B, D, F, H, and J, respectively, in which they are arranged. 
     In order to simplify this specification, however, these suffix letters are omitted in the text, which means that all the drive blades are simply referred to as  24  and all the guide vanes are referred to as  23 . Apart from the differences in size, all of the drive blades  24  have the same functional features. All of the guide vanes  23  also have the same functional features. 
     The stator  10  further comprises a forward mounting sleeve  27 , forming an outer support for the sleeve  22 , and a rear cup shaped nozzle piece  28 . The latter has a forwardly directed tubular skirt portion  29  for radial support of the sleeve  22  and a rear air inlet portion  30 . This portion is formed with an air inlet opening  31  communicating at its one end with the air inlet passage  19  and at its other end with radially directed air feed passages  32 . These air feed passages  32  communicate motive pressure air from the inlet portion  30  to a number of air nozzles  33  by which the motive high speed air flow through the turbine is generated. The nozzle piece  28  also comprises a socket  34  forming a support for the rear rotor bearing  14 . 
     At its front end, the stator  10  also comprises a ring element  35  which forms a radial as well as an axial support for the mounting sleeve  27 . The ring element  35  is formed with a number of exhaust openings  36  communicating with the exhaust chamber  21 . 
     The motor turbine illustrated in the drawings is intended to be produced in small dimensions, i.e. having a rotor diameter from about 30-40 mm. Accordingly, the rotor drive blades  24  as well as the guide vanes  23  on the stator sleeve  22  are of such small sizes that it is not possible to produce them as separate details for mounting on the respective carrier. Instead, the drive blades  24  and the guide vanes  23  are machined out as integrated parts of the rotor  11  and the stator sleeve  22 , respectively. Since the drive blades  24  are located on the outer surface of the rotor body  11 , there is no problem to carry out the necessary machining work, for instance by a shank end mill. 
     However, to be able to form the guide vanes  23  on the inside of the stator sleeve  22 , the latter is divided into three separate shells  22   a ,  22   b  and  22   c . See FIG.  2 . These shells are divided along three cylinder generatrices located at 120 degrees intervals, which means that each shell has a circumferential extent of 120 degrees. 
     As the turbine is assembled, the shells  22   a ,  22   b  and  22   c  are kept together in a fixed radial relationship by the forward mounting sleeve  27  and the tubular skirt portion  29  of the nozzle piece  28 . The mounting sleeve  27  and the skirt portion  29  surround the shells  22   a ,  22   b ,  22   c  with a tight fit such that the positions of the shells  22   a ,  22   b  and  22   c  are accurately defined so as to form the tubular sleeve body  22 . The stator shells  22   a ,  22   b  and  22   c  are secured relative to the housing  12  by axial clamping between a shoulder  38  on the forward mounting sleeve  27  and a shoulder  39  on the nozzle piece skirt portion  29 . The clamping force is obtained by the thread connection  18  between the two housing sections  16  and  17 . 
     Scattering of the detail dimensions within the production tolerances is compensated for by a Belleville-type spring washer  37  which is disposed in the socket  34  behind the rear bearing  14  to ensure a correct axial load on the rotor bearings. 
     In FIG.3, there is illustrated a machining situation wherein one of the stator shells  22   a  is firmly clamped against a part cylindrical surface of a fixture  40 , and a milling spindle  41  fitted with a shank end mill  42  is in a position for machining a guide vane at the longitudinal edge of the shell. The shell is clamped in this position by means of screws  43 ,  44  and clamp rules  45 ,  46  carried on the fixture. This illustrated machining situation intends to show that machining of the guide vanes close to the edges of a stator shell would not be possible with a 180 degree two part divided stator. Each shell has to have a circumferential extent well below 180 degrees to give access to a machining tool. 
     As illustrated in FIG. 4, the extreme free ends of the drive blades  24  and guide vanes  23  form clearance seals with cylindrical surfaces  50  and  51  on the stator  10  and the rotor  11 , respectively. The drive blades  24  in each circumferential row A, C, E, G, I, and K cooperate sealingly with a corresponding cylindrical surface  50  on the stator  10 . It is to be noted that the drive blade and sealing surface reference numerals in FIGS. 1 and 4 are provided with the suffix letter of the corresponding circumferential row. 
     In the same way, the extreme free ends of the guide vanes  23  in each circumferential row B, D, F, H, and J cooperate sealingly with a cylindrical surface  51  on the rotor  11 . The reference numerals of the guide vanes and sealing surface in the drawing figures are provided with the suffix letter of the corresponding circumferential row. Although, the last three stages only of the turbine are shown in FIG. 4, i.e. the drive blade rows G, I and K and the guide vane rows F,H, and J, the clearance seal arrangement with cylindrical sealing surfaces  50  and  51  on the stator  10  and the rotor  11 , respectively, is similar in all turbine stages. 
     By having the drive blades  24  and guide vanes  23  form clearance seals together with cylindrical surfaces  50  and  51 , respectively, there is obtained the advantage of allowing a certain axial adjustment of the rotor  11  relative to the stator  10  without influencing on the clearance seals. 
     It is to be noted that the embodiments of the invention are not limited to the shown and described example but can be freely varied within the scope of the claims. 
     For example, the circumferential extent of the stator shells does not have to be exactly the same. The important thing is that the guide vanes  23  are formed in one piece with and on the inside of the tubular stator body formed by the shells. To enable this, the tubular body  22  has to be divided into three or more sections or shells each having a circumferential extent well below 180 degrees. 
     In an alternative embodiment of the invention the stator shells  22   a ,  22   b ,  22   c  are fixed and mounted relative to each other by joints engaging external flanges located at the longitudinal edges of the shells. This method for fixing and mounting the stator shells is well known per se at bigger two-part turbine stators.