Pneumatic motor and housing assembly

Abstract

A pneumatic motor and housing assembly in which novel means are provided for aligning the pneumatic motor within the housing, said aligning means also providing for the flow of air from one end of the pneumatic motor to the other so that the thrust exerted upon the opposed ends of the rotor shafts of the pneumatic motor is equalized. The aligning means are a pin-like element, a groove on the cylindrical outer periphery of the end plates and tubular liner of the pneumatic motor, the pin-like element being dropped into the groove to hold the end plates and tubular liner from relative rotation with respect to each other, and a tang which cooperates with a slotted flange on one of the end plates of the motor, the tang holding said end plate in alignment within the housing, and the pin-like element holding the other parts of the pneumatic motor in alignment with the end plate engaged by the tang. The slot and the groove are of greater cross-sectional area than the tang and the pin-like element so that air may flow between the housing and the motor from one end to the other to equalize the thrusts on the opposed ends of the rotor shafts.

Description

FIELD OF THE INVENTION

The present invention relates generally to pneumatic motors of the type which may be employed in portable power tools such as, for example, a screw driver, and more particularly, to a novel means for aligning the pneumatic motor within the housing of the portable power tool, the aligning means also providing for the flow of air from opposed ends of the pneumatic motor's rotor shafts so that the thrust exerted on the ends of the rotor shafts is equalized.

BACKGROUND OF THE INVENTION

Pneumatic or air motors of the type generally employed in portable power tools customarily include front and rear end plates, a tubular liner, and a rotor having vanes disposed within the tubular liner and opposed shafts which pass through apertures in the end plates. It is necessary to precisely align the air motor assembly within the cylindrical recess of the housing which receives the air motor in order to properly mate the various air passages of the housing with other air passages of the air motor. It is also necessary to provide for the flow of air from the end of one of the rotor shafts to the opposed end of the other shaft so that the thrust forces exerted upon the opposed ends of the rotor shafts are substantially equalized. If the thrust forces are not equalized, the rotor may rub against the inner face of one or the other of the end plates. Various structures have been employed in the prior art to provide for the alignment of the air motor within the cylindrical recess of the housing, however, the prior art structures have numerous disadvantages. One widely employed system for aligning the various components of the motor within the housing is to provide a longitudinally extending bore through the various components and to insert a pin through the bore, a portion of the pin projecting beyond one of the end plates and being adapted to engage a corresponding bore in the housing adjacent the bottom of the cylindrical recess which receives the air motor. In practice it is very difficult to accurately form such a bore in the various components while maintaining proper alignment of the tool which forms the bore. Additionally, when such an alignment device is utilized it is frequently difficult to disassemble the parts as the pin may become stuck within the corresponding bore. If a gear housing or the like is to be screwed onto the housing about the cylindrical recess, the gear housing including means which engage one of the end plates to hold the air motor in the cylindrical recess, additional problems may occur. Thus, it is possible as the gear housing is being torqued into its final position for it in turn to cause the end plate which it contacts to rotate, either distorting the alignment pin, or, in extreme situations, even shearing the alignment pin. In addition to the aforesaid difficulties, it is also necessary to provide an additional air passage from one end of the motor to the other so that the thrust forces on the ends of the rotor shaft may be equalized.

Alternative approaches have been proposed in various U.S. Patents. U.S. Pat. No. 2,159,232 to Shaff issued May 23, 1939 utilizes an approach somewhat similar to the single bore and pin approach referred to above, however in this design the tubular liner is not bored throughout its entire length and two separate pins are employed. While this overcomes some of the disadvantages of the prior art approach initially referred to above, it is frequently difficult to position one of the pins within the housing bore that receives the pin, and it is also difficult to provide for such a bore in the bottom of the cylindrical recess. Additionally, one or both of the pins may become distorted or sheared when a gear housing, which contacts an end plate, is torqued into its final position. Another approach is shown in U.S. Pat. No. 3,097,571 to Kaman issued July 16, 1963. In this proposal three different alignment means are provided, one of them engaging a rear end plate, another the intermediate tubular liner, and still another engaging the front end plate. The utilization of three separate alignment devices for each of the major components of the pneumatic motor increases the time required to assemble the motor within the housing and is also a somewhat costly approach.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide a novel aligning means for a pneumatic or air motor which is adapted to be disposed within a cylindrical recess of a housing.

More specifically, it is an object of the present invention to provide a novel pneumatic motor design in which means are provided on the front end plate to mate with a corresponding portion in the housing to align the front end plate with the housing, and to provide additional means which interconnect the front end plate, tubular liner, and rear end plate of the pneumatic motor to hold the various components in alignment with each other.

It is also an object of this invention to provide a novel pneumatic motor design in which means are provided to retain the assembled motor components in an aligned subassembly for convenient insertion of the motor subassembly into the housing of a pneumatic tool.

It is another object of the present invention to provide a longitudinally extending groove in the outer periphery of the end plates and tubular liner of a pneumatic motor, the groove receives a pin-like element which holds the various components from rotating with respect to each other, and means on the housing which engages one of the end plates to hold the pneumatic motor assembly in its proper aligned position within the cylindrical recess of the housing.

These and other objects and advantages of the present invention are accomplished by providing a longitudinally extending recess in the outer cylindrical periphery of the front and rear end plates and tubular liner of a pneumatic motor, the recess including a groove, by providing a pin-like element adapted to be dropped into said groove, the pin-like element engaging the sides of the groove to hold the various components of the pneumatic motor from relative rotation with respect to each other, by providing an outwardly extending slotted flange on one of the end plates, and by providing a tang on the housing which engages the slot of the flange to hold the end plate, and thus the other components, in their proper aligned position within the cylindrical recess of the housing. In addition, the cross-sectional area of the recess which receives the pin-like element and the cross-sectional area of the slot which receives the tang are greater than the cross-sectional area of pin-like element or tang received within them so that air may flow from one end of the motor to the other between the cylindrical outer periphery of the pneumatic motor and the cylindrical recess within the housing which receives the motor whereby air thrust forces on the ends of the rotor shafts of the pneumatic motor may be equalized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a portable power tool in which the pneumatic motor and housing assembly of this invention are incorporated.

FIG. 2 is a sectional view through a portion of the portable power tool shown in FIG. 1.

FIG. 3 is an exploded perspective view of the apparatus shown in FIGS. 1 and 2.

FIG. 4 is a top view of various of the components of the pneumatic motor of this invention.

FIG. 5 is a section taken along line 5--5 in FIG. 2.

FIG. 6 is a section taken along line 6--6 in FIG. 4, the alignment tang on the housing being shown in its assembled relationship in broken lines.

FIG. 7 is a right end view of the structure shown in FIG. 4.

FIG. 8 is a perspective view of the housing with a portion being broken away.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following description right-hand and left-hand reference refers to the relative positions as they are shown in FIGS. 1, 2, and 3. Similarly, front and rear reference is determined by viewing the apparatus shown in FIGS. 1, 2, and 3 from the left-hand side.

Referring now to the drawings, the pneumatic motor and housing assembly of this invention may be incorporated in a plurality of tools, and one such tool is shown in FIG. 1, this being an air powered screw driver. The screw driver, which is indicated generally at 10, includes a gear housing 12 and a main housing 14, the main housing having a handle portion 16. A trigger or the like 18 is mounted in the main housing adjacent the handle portion 16 for the purpose of controlling the operation of the screw driver. A pneumatic or air motor, indicated generally at 20 is mounted within a cylindrical recess 22 of the main housing 14. The tool is connected to a source of air under pressure through an air line 24, and the housing 14 has a high pressure air passageway 26 which leads from the air line 24 to control valve 28. The trigger 18 is mounted on the valve stem 29 of the valve, and is normally biased to the left. By moving the trigger to the right the valve 28 is opened permitting air to flow to the air motor 20. The housing is also provided with another high pressure air line or passageway 30 which leads to an arcuate port 32 in the housing. The arcuate port 32 is located at the bottom of the cylindrical recess 22 in the housing 14, and an exhaust arcuate port 34 is also located in the bottom of the recess. The exhaust portion 34 is adapted to discharge exhausted air to the atmosphere through passageway 36. In addition, the housing is also provided with an exhaust cut-out 38 along one side of the cylindrical recess, see FIG. 2, the exhaust recess also being able to discharge air to the atmosphere through a passageway 40.

The air motor 20 includes a tubular liner 42, an apertured right or rear end plate 44, an apertured left or front end plate 46 and a rotor, indicated generally at 48 (FIG. 5), the rotor having a plurality of vanes 50 which are mounted within the tubular liner 42, and right and left-hand opposed shafts 52, 54 which are rotatably journalled in the apertures of the end plates 44, 46. The motor 20 is adapted to be disposed within the cylindrical recess, the right or rear end plate 44 having an end face 45 which abuts against the bottom of the cylindrical recess when the motor is properly positioned within the recess 22, and the front end plate 46 having a radially outwardly extending flange 55 which is disposed adjacent that portion of the housing which surrounds the open end of the cylindrical recess 22. The liner 42, the right end plate 44, and that portion of the front end plate disposed within the cylindrical recess 22 each have a generally cylindrical periphery of the same diameter, the cylindrical periphery of these elements being of approximately the same diameter as the inner periphery of the cylindrical recess 22. The tubular liner 42 is provided with a cylindrical recess 56 that is disposed in an off-center manner from its cylindrical periphery. The rotor 48 and vanes 50 are located concentrically with the outer periphery of the tubular liner, the vanes 50 cooperating with the surface of the recess 56. The tubular liner is also provided with a high pressure bore 58, exhaust bore 60, and exhaust ports 62. As is generally conventional in the air motor art, the rear or right end plate 44 is provided with an inlet port 63 in communication with the arcuate inlet port 32 in the housing 14, the inlet port of the rear end plate also being in communication with the high pressure bore 58. In turn, the high pressure bore 58 is in communication with the inner surface of the liner through a pair of opposed cut-out portions (not shown) as is also conventional. Similarly the low pressure bore 60 is in communication with the interior of the tubular liner through a corresponding pair of opposed cut-out portions to permit the discharge of air through the low pressure bore 60, a discharge port 64 in the rear end plate 44, the arcuate exhaust port 34 in the housing 14, and the passageway 36. The exhaust port 62 in the bottom of the liner also permits additional air to be exhausted through the exahust cut-out 38 and its corresponding passageway 40. The inner faces of both of the end plates are provided with arcuate grooves 65, and internal passageways 66 interconnect these grooves with the ports 63, 64 in the rear end plate 44 and cylindrical cavities in the front end plate. The purpose of the grooves is to provide for the flow of air between the vanes and the rotor to force the vanes 50 outwardly to facilitate start-up, and also to provide for the flow of air between the ends of the rotor and inner faces of the end plates to create an air-film bearing. When the front end plate 46 is assembled next to the liner 42, the cavities in the front end plate should be in line with the bores 58, 60, respectively.

The shafts 52 and 54 of the rotor 48 are journalled in bearings 69 and 95 which are mounted within apertures in the rear and front end plates 44, 46, respectively. The bearings are preferably positioned so that their axes of rotation are concentric with the cylindrical outer periphery of the end plates. The forward or left-hand shaft 54 is splined and engages planet gears 70 of a planetary gear set carried by the gear housing 12, the gear set including a ring gear 71. The carrier of the planetary gear set in turn drives the output member of the screw driver 10. The gear housing 12 includes an internally threaded barrel-shaped portion 72 which is adapted to be screwed about the barrel-shaped portion 74 of the housing 14, the cylindrical recess 22 being formed within the barrel-shaped portion 74.

Novel means are provided for aligning the pneumatic or air motor within the cylindrical recess 22 so that the various passageways, ports and cavities are properly aligned with each other. To this end, longitudinally extending recess means are provided in the cylindrical periphery of the tubular liner 42, the rear end plate 44 and the front end plate 46, the recess means including a slot 80 and a groove 82 formed within the slot 80. When the liner 42 is disposed between the end plates 44, 46, the slots and grooves may be disposed in an axially aligned position wherein they lie parallel to the axis of the circumferential periphery of each of their associated elements and when the recess means 80, 82 are so aligned, the various air passageways in the end plate and liner are properly aligned with each other. Interconnecting structure in the form of a pin-like element 84 is dropped into the groove 82 and when the pin-like element is so disposed in the groove the end plates and intermediate liner will be held from relative rotation with respect to each other. The dimensioning of the slot 80, and pin-like element 84 is such that when the pin-like element is in the groove 82 the entire assembly can be inserted into the cylindrical recess with the cylindrical wall of the recess maintaining the pin-like element 84 in the groove 82. As can best be seen from FIG. 4, the groove 82 terminates between the ends of the front end plate 46. The groove in the rear end plate 44 is of a reduced diameter, and the pin-like element 84 has a reduced diameter end portion 85 which is received in the reduced diameter groove of the rear end plate.

In order to properly align the rear end plate 44 with the arcuate ports 32, 34 in the bottom of the cylindrical recess, aligning means, indicated generally at 86, is provided on the housing. The aligning means engages the front end plate to hold the front end plate in its desired position of rotational alignment. When the front end plate is so held, the rear end plate will also be held in its desired position of rotational alignment with the ports 32, 34 in the housing 14 since the pin-like element interconnects the front end plate, the tubular liner, and the rear end plate. With respect to the aligning means 86, it should be noted that the barrel-shaped portion 74 of the main housing 14 is provided with an outwardly extending tang 88. In addition, the front end plate 46 is provided with a portion which extends outwardly of the cylindrical recess 22 when the pneumatic motor is disposed within the recess, this portion being the radially outwardly extending flange portion 55 which is also provided with a slot 80. When the pneumatic motor is properly assembled within the housing 14 the tang 88 will be disposed within the slot 80 of the flange 55 to hold the assembled pneumatic motor in its properly aligned position within the cylindrical recess 22.

When the tool is assembled the surface 90 of the gear housing will abut against the forward face 92 of the front end plate 46, holding the air motor within the cylindrical recess 22 with the rear face of the rear end plate in abutting relationship with the bottom of the cylindrical recess 22. As the gear housing 12 is torqued or screwed into its final assembled relationship on the housing 14, the frictional contact between the surface 90 and the face 92 imposes rotational forces upon the front end plate 46. However, the interengagement of the tang 88 and slot 80 in flange 55 prohibits such rotational movement, and thus the parts are maintained in their properly aligned positions with respect to each other.

The flow of air from one end of the motor to the other is substantially impeded as the diameter of the cylindrical periphery of the motor 20 is substantially the same as the diameter of the recess 22. However, an additional feature of the present invention is to provide air passage means which extend from one end of the pneumatic motor to the other so that the air pressure exerted upon the ends of rotor shafts will be equalized so that the rotor will run freely within the liner and between the end plates without having one end or the other end of the rotor bearing against one of the inner faces of the end plates. Accordingly, the housing 14 is provided with a chamber 94 in the bottom of the recess. Similarly, there is an air chamber 96 adjacent the forward end of the motor and in communication with the forward end of the front rotor shaft 54. The rear end plate is provided with a channel or groove 98 on its rear surface which is adapted to interconnect the chamber 94 with the slot 80. In this connection it should be noted that the cross-sectional area of the slot 80 and groove 82 is greater than the cross-sectional area of the pin-like element 84 as can best be appreciated from an inspection of FIG. 5. Additionally, the reduced diameter portion 85 of the pin-like element 84 does not interfere with the flow of air from groove 98 to slot 80. Thus, air can flow from the rear chamber 94 toward or from the front chamber 96 along the groove 98 and slot 80. The tang 88 is also so dimensioned that there is a gap between the lower surface 100 of the tang and the bottom of the slot (see FIG. 6) so that air can move into or out of the front chamber 96 through the air passageway between the tang and the bottom of the slot. Thus, the aligning system of this invention is also utilized to provide a convenient way for air to move from one end of the pneumatic motor to the other whereby air pressure on the ends of the rotor shafts is equalized.

During the manufacture of pneumatic tools in accord with this invention, the bearing 69 receives the shaft by a press-fit within its inner race. The further elements of the motor subassembly 20 are mounted and fixed in alignment as previously described. After mounting of the forward bearing 95, a split washer 93 is installed to retain these components in a completed, aligned subassembly as illustrated at FIG. 3. This subassembly greatly simplifies the assembly of the motor into the housing and thus reduces both the time required for assembly and the potential errors which might otherwise occur.

While the preferred structure in which the principles of the present invention have been incorporated is described above, it is to be understood that the invention is not to be limited to the particular details, shown and described above, but that, in fact, widely different means may be employed in the practice of the broader aspects of the invention.

Claims

What is claimed is:

1. A pneumatic motor subassembly adapted for installation in the housing of a portable pneumatic power tool, said subassembly comprising a generally cylindrical rotor member having a plurality of vanes disposed for radial movement therein; a pair of shaft ends extending axially from the ends of said rotor; a tubular liner surrounding said rotor; a pair of front and rear end plates disposed at opposite ends of said liner and said rotor; a pair of anti-friction bearings mounted in the surfaces of said end plates remote from said rotor; means retaining said bearings on said shaft ends of said rotor to hold said end plates, said liner and said rotor in assembled relationship as a separate preassembled motor subassembly; and means retaining said liner and said end plates in predetermined aligned relative positions prior to and during installation of said motor within a power tool housing, said alignment means comprising corresponding grooves entirely contained in the outer peripheries of said liner and of said front and rear end plates, and a retaining pin disposed within all of said grooves and also entirely contained in the outer peripheries of said liner and of said front and rear end plates.

2. The pneumatic motor subassembly as claimed in claim 1, wherein said anti-friction bearings each comprises an outer race mounted in said corresponding end plate, an inner race disposed on said shaft and a plurality of anti-friction rollers disposed between said races; and wherein said means retaining said end plates on said shaft ends comprises a press-fit between one shaft end and one inner race of said pair of bearings; said retaining means further comprising a groove in said other shaft end and a split washer disposed in said groove to retain said inner race of said other bearing.

3. A pneumatic motor and housing assembly comprising:

a pneumatic motor including a cylindrical front and rear end plate, a tubular liner disposed between said end plates, a rotor having a plurality of vanes mounted within the tubular liner, and an interconnecting structure which extends between the front and rear end plates and the tubular liner to hold the front and rear end plates and the tubular liner from relative rotation with respect to each other;

a housing having a generally cylindrical recess closed at one end in which said pneumatic motor is mounted, the rear end plate being disposed adjacent said closed end of the cylindrical recess and the front end plate being disposed in part in the recess adjacent the open end of the cylindrical recess, a portion of the front end plate extending outwardly of the cylindrical recess in the housing;

aligning means functionally separate of said interconnecting structure and on said housing adjacent the open end of the cylindrical recess which engages said portion of the front end plate to hold said front end plate in a position of rotational alignment within the cylindrical recess; and

said portion of the front end plate which extends outwardly of the cylindrical recess comprising a radially outwardly extending flange, said flange being provided with slot means, and wherein said aligning means engages said slot means in said flange.

4. The pneumatic motor housing assembly set forth in claim 3, in which said cylindrical recess is disposed within a barrel shaped portion of the housing, and said aligning means being a tang which extends beyond one end of the barrel-shaped portion adjacent the open end of the cylindrical recess.

5. The pneumatic motor and housing assembly set forth in claim 3, in which each of the front and rear end plates and tubular liner is provided with an outer peripheral groove, and in which said interconnecting structure is a pin-like element lying within all of said grooves.

6. In combination, a housing, a pneumatic motor adapted for mounting in said housing and comprising a tubular liner and front and rear end plates positioned, respectively, at the front and rear ends of said tubular liner, a rotor mounted in said liner, said rotor comprising front and rear shafts extending frontwardly and rearwardly outwardly therefrom, bearing means in said front and rear end plates, respectively, receiving said front and rear shafts, recess means extending across said liner and at least portions of said front and rear end plates, said recess means including a first portion adapted to receive means to interconnect said end plates and said liner, and said recess means including a second portion adapted to permit air flow independently of said interconnecting means and between said front and rear end plate bearing means, whereby the pneumatic forces on said rotor shafts may be equalized to facilitate the rotation of said rotor within said motor when mounted in said housing.

7. The combination of claim 6, said interconnecting means comprising a pin member received in said first portion of said recess, and said second portion of said recess comprising a through recess extending from end to end of said liner and said end plates and located radially outwardly of and overlying said first portion of said recess.

8. The combination of claim 6, and alignment means cooperable with at least one of said end plates to hold said liner, said rotor, said end plates, and said interconnecting means in aligned relationship within said housing, said alignment means being adapted to not interfere with said air flow between said end plates.

9. The combination of claim 8, said liner and said front and rear end plates being of substantially cylindrical external configuration and of substantially the same diameter, the front end of said front end plate being formed with an enlarged flange extending radially outwardly of said common diameter, said first portion of said recess means extending across said liner and at least part way into said front and rear end plates, said second portion of said recess means extending from end to end of said liner and said end plates and across said front end plate flange, and said alignment means comprising a tang portion on said housing positioned radially outwardly of the common diameter of said end plates and said liner and adapted to be received in said second portion of said recess in said flange portion and above said interconnecting means.

10. The combination of claim 6, and holding means cooperable with said shafts and with said interconnecting means to hold said liner, said rotor, and said front and rear end plates into an integral subassembly independently of said housing.

11. The combination of claim 10, said holding means comprising a press fit between one of said rotor shafts and the corresponding end plate bearing means, and said holding means further comprising retaining washer means cooperable with the other of said rotor shafts and the corresponding other of said end plates and its bearing means.

12. A pneumatic motor and housing assembly comprising:

a pneumatic motor including a tubular liner, apertured front and rear end plates disposed to either end of said tubular liner, each of said end plates and liner having a generally cylindrical periphery of the same diameter, a rotor having a plurality of vanes mounted within the tubular liner and opposed shafts rotatably journalled within the apertured end plates, longitudinally extending recess means in each of said end plates and tubular liner and interconnecting structure engagable with said longitudinally extending recess means in each of said end plates and tubular liner to hold the front and rear end plates and tubular liner from relative rotation with respect to each other;

a housing having a cylindrical recess in which said pneumatic motor is mounted, the cylindrical periphery of the end plates and liner being substantially the same diameter as the cylindrical recess in the housing whereby the flow of air between the cylindrical surfaces from the outer end of one of the opposed rotor shafts to the outer end of the other of the opposed rotor shafts is substantially impeded; and

aligning means on the housing which engages the longitudinally extending recess means in one of said end plates to hold said one end plate in a position of rotational alignment within said housing and to prevent rotation of the end plate within the cylindrical recess;

said longitudinally extending recess means having a cross-sectional area greater than each of said interconnecting structure and said aligning means whereby air may flow from the outer end of one of the opposed rotor shafts to the outer end of the other of opposed rotor shafts so that the thrust exerted on the ends of the rotor shafts is substantially equalized.

13. The pneumatic motor and housing assembly set forth in claim 12 wherein said longitudinally extending recess includes a longitudinally extending slot formed in the cylindrical outer periphery of said end plate and tubular liner, and a groove formed within said slot, said interconnecting structure being a pin-like element disposed within said groove, and said aligning means being a tang which engages said slot, there being a gap between the bottom of said slot and said tang.

14. The pneumatic motor and housing assembly set forth in claim 13, wherein the groove in the rear end plate is of reduced diameter, and wherein the pin-like element has a reduced end portion which is disposed within said groove of reduced diameter.

15. A pneumatic motor and housing assembly comprising:

a pneumatic motor including front and rear end plates, a tubular liner disposed between said end plates, a rotor having a plurality of vanes mounted within the tubular liner, each of said end plates and tubular liner having a generally cylindrical periphery of the same diameter, the cylindrical periphery of each of the end plates being provided with a grooved portion which extends longitudinally from one end of the end plate adjacent said tubular liner towards the other end of the end plate, the cylindrical periphery of the tubular liner being provided with a corresponding groove which extends longitudinally from one end of the tubular liner to the other end of the tubular liner, and a pin-like element disposed within all of said grooves to hold the front and rear end plates and the tubular liner from relative rotation with respect to each other;

a housing having a generally cylindrical recess in which said pneumatic motor is mounted, the rear end plate being disposed adjacent the closed end of the cylindrical recess and the front end plate being disposed adjacent the open end of the cylindrical recess;

aligning means on the housing which engages a portion of one of said end plates to hold said one end plate in a position of rotational alignment within the cylindrical recess;

said front end plate being disposed in part in the cylindrical recess, a radially outwardly extending flange on said front end plate being disposed outside of said cylindrical recess, said radially outwardly extending flange being provided with slot means, and said aligning means comprising an outwardly extending tang on the housing received within said slot means.

16. A pneumatic motor and housing assembly comprising:

a pneumatic motor including front and rear end plates, a tubular liner disposed between said end plates, a rotor having a plurality of vanes mounted within the tubular liner, each of said end plates and tubular liner having a generally cylindrical periphery of the same diameter, the cylindrical periphery of each of the end plates being provided with a grooved portion which extends longitudinally from one end of the end plate adjacent said tubular liner towards the other end of the end plate, the cylindrical periphery of the tubular liner being provided with a corresponding groove which extends longitudinally from one end of the tubular liner to the other end of the tubular liner, and a pin-like element disposed within all of said grooves to hold the front and rear end plates and the tubular liner from relative rotation with respect to each other;

a housing having a generally cylindrical recess in which said pneumatic motor is mounted, the rear end plate being disposed adjacent the closed end of the cylindrical recess and the front end plate being disposed adjacent the open end of the cylindrical recess;

aligning means on the housing which engages a portion of one of said end plates to hold said one end plate in a position of rotational alignment within the cylindrical recess;

each of said end plates being apertured, said rotor comprising opposed shafts which extend through said apertures, the cylindrical periphery of the end plates and the tubular liner being of substantially the same diameter as the cylindrical recess in the housing, whereby the flow of air between the cylindrical surfaces from the outer end of one of the opposed rotor shafts to the outer end of the other of the opposed rotor shafts is substantially impeded, and further characterized by the provision of air passage means extending along the outer periphery of the end plates and liner adjacent said pin-like element and the aligning means to provide for the flow of air from the outer end of one shaft end to the outer end of the other shaft end, whereby the thrust exerted on the outer ends of each of the rotor shafts is substantially equalized.

17. The combination of a pneumatic motor and housing assembly comprising:

a pneumatic motor including a tubular liner, apertured front and rear end plates disposed to either end of said tubular liner, each of said end plates and tubular liner having a generally cylindrical periphery of the same diameter, a rotor having a plurality of vanes mounted within the tubular liner and opposed shafts rotatably mounted within said apertured end plates;

a housing having a cylindrical recess in which said pneumatic motor is mounted, the cylindrical periphery of the end plates and tubular liner being substantially the same diameter as the cylindrical recess in the housing, the rear end plate being disposed adjacent the closed end of the cylindrical recess and the front end plate being disposed at least in part in the cylindrical recess adjacent the open end of the cylindrical recess;

wherein the improvement comprises

the cylindrical periphery of each of the end plates being provided with a groove portion which extends longitudinally from the end of the end plate adjacent said tubular liner toward the other end of the end plate, the cylindrical periphery of the tubular liner being provided with a corresponding groove which extends longitudinally from one end of the tubular liner to the other end of the tubular liner, and a pin-like element disposed within all of said grooves to hold the front and rear end plates and the tubular liner from relative rotation with respect to each other;

aligning means on the housing adjacent the open end of the cylindrical recess which engages a portion of the front end plate to hold said front end plate in a position of rotational alignment within the cylindrical recess; and

an air passage adjacent the pin-like element and the aligning means whereby air may flow freely from the outer end of one of the opposed rotor shafts to the outer end of the other of the opposed rotor shafts so that the thrust exerted on the end of the rotor shaft is substantially equalized.