Abstract:
A pneumatic rotary tool has a housing formed primarily from plastic so that the weight and price of the tool are substantially reduced. The air motor is formed for economic assembly while permitting greater structural stability should the housing deflect under an impact. The tool includes a torque selector which controls the amount of pressurized air allowed to enter the air motor, thereby controlling the torque output of the motor. The user may adjust the torque selector to a number of set positions which correspond to discrete torque values. The tool additionally incorporates early and late stage exhaust ports, so that backpressure within the air motor does not slow motor rotation or decrease tool power.

Description:
BACKGROUND OF THE INVENTION 
     This invention generally relates to pneumatic rotary tools and more particularly to an improved pneumatic rotary tool having a plastic housing and a variable torque design for efficient use of pressurized air. 
     The invention is especially concerned with a powered tool that rotates an output shaft with a socket for turning a fastener element such as a bolt or nut. Tools of this type are frequently used in automotive repair and industrial applications. Conventionally, pneumatic rotary tools comprise a metallic outer housing with multiple metallic internal parts. These tools are strong and durable due to their metallic construction, although the all-metal construction makes them both somewhat heavy and costly. Pressurized air flowing through the tool powers tools of this type. As the air expands within the tool, it induces motion of an internal motor, powering the tool. 
     It is an aim of tool manufacturers to provide a pneumatic rotary tool that is as durable as an all-metal tool, but employs portions formed from lighter materials, such as plastic, where appropriate to reduce the weight and cost of the tool. One difficulty in the design of such a tool is the reduced rigidity of plastic as compared with a strong metal, such as steel. For instance, should a plastic tool fall against a hard surface, a metallic air motor inside the tool may shift and become misaligned, or canted, with respect to the housing and the output shaft, rendering the tool unusable. This problem has led tool manufacturers to create complex internal motor casings designed to inhibit the motor from canting in the housing. For example, U.S. Pat. No. 5,346,024 (Geiger et al.) discloses such a motor casing, described as a motor cylinder  15 . This casing is cylindrical in shape, with one closed end that includes multiple parts, such as a back head  26  and bore  27 , extending from the closed end. The cylinder, back head and bore are of unitary construction, making a closed end cylinder significantly more difficult to manufacture. Therefore, these casings are expensive to manufacture, which may mitigate the cost benefit of using lighter and less costly materials, such as plastic, for other parts. As such, a tool formed inexpensively from both lightweight material and metallic parts is desirable. 
     In addition, conventional rotary tools often incorporate mechanisms to regulate torque according to user input. One such tool uses back pressure within the air motor to regulate the torque output. As backpressure within the motor increases, the torque output of the motor decreases. Such a design is inefficient because it uses the maximum flow of pressurized air to power the tool, while operating below its maximum power. At lower torque settings, a large portion of air bypasses the motor for backpressuring the motor, adding no power to the tool. As such, a tool that can more efficiently regulate torque by using less pressurized air is needed. Moreover, a tool that can reduce backpressure in the motor will operate more efficiently, using less air for the same work. 
     Typically air motors incorporate a rotor having a plurality of vanes upon which the pressurized air can react, inducing rotation of the rotor. Pockets of pressurized air are received within compartments defined by adjacent vanes. Conventional rotary tools typically have a single exhaust port in the air motor for exhausting pressurized air from the motor. As each rotor compartment passes the exhaust port, much of the air within the compartment passes through the exhaust port and exits the motor. Any air remaining within the compartment after the compartment passes the exhaust port becomes trapped within the compartment. The volume of the compartment decreases as the compartment nears completion of a motor cycle, and the compartment must compress the air within the compartment for the rotor to continue to rotate. Compressing the air within the compartment (backpressure) reduces the rotational speed of the turning rotor. Backpressure reduces motor efficiency; thus, a pneumatic rotary tool that reduces backpressure losses within the air motor is desirable. 
     SUMMARY OF THE INVENTION 
     Among the several objects and features of the present invention may be noted the provision of a pneumatic rotary tool which weighs and costs less due to a primarily plastic housing; the provision of such a tool having a plastic housing which resists misalignment of internal components under impact; the provision of such a tool which is comfortable to grip; the provision of such a tool having a plastic housing which fixes components without fasteners; the provision of such a pneumatic rotary tool which regulates torque between four discrete levels adjustable by the user; the provision of such a pneumatic rotary tool which throttles pressurized air as it enters the tool to efficiently control torque output of the motor by reducing how much air enters the tool; and the provision such of a pneumatic rotary tool which reduces back pressure within the motor and increases motor efficiency. 
     Generally, a pneumatic rotary tool of the present invention comprises a housing formed substantially from plastic and an air motor disposed within the housing. The tool further comprises a first rigid support of a material more rigid that the plastic housing for engaging the air motor and the housing generally at one end of the motor. A second rigid support of a material more rigid that the plastic housing engages the air motor and the housing generally at an opposite end of the motor. The first and second rigid supports support the air motor from movement and misalignment within the housing. 
     Other objects and features will be in part apparent and in part pointed out hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevation of a pneumatic rotary tool of the present invention; 
     FIG. 2 is a rear elevation of the tool of FIG. 1; 
     FIG. 3 is a section of the tool taken in a plane including line  3 — 3  of FIG. 2; 
     FIG. 3A is an enlarged, fragmentary section of the tool of FIG. 3 showing the grip; 
     FIG. 3B is a side elevation of an inlet cylinder; 
     FIG. 3C is a section of the inlet cylinder taken in a plane including line  3 C— 3 C of FIG. 3B; 
     FIG. 4 is a fragmentary schematic rear elevation with an end cover of the tool removed to reveal internal construction and air flow; 
     FIG. 5 is a rear elevation of a valve body; 
     FIG. 6 is a section of the valve body taken in a plane including line  6 — 6  of FIG. 5; 
     FIG. 7 is a front elevation of a valve member; 
     FIG. 8 is a right side elevation of the valve member of FIG. 7; 
     FIG. 9 is a rear elevation of the end cover with a torque selector positioned to a setting of 1; 
     FIG. 10 is a front elevation of the end cover and partial section of the torque selector of FIG. 9; 
     FIG. 11 is a rear elevation of the end cover with the torque selector positioned to a setting of 2; 
     FIG. 12 is a front elevation of the end cover and partial section of the torque selector of FIG. 11; 
     FIG. 13 is a rear elevation of the end cover with the torque selector positioned to a setting of 3; 
     FIG. 14 is a front elevation of the end cover and partial section of the torque selector of FIG. 13; 
     FIG. 15 is a rear elevation of the end cover with the torque selector positioned to a setting of 4; 
     FIG. 16 is a front elevation of the end cover and partial section of the torque selector of FIG. 15; 
     FIG. 16A is a rear elevation of a support plate of the tool; 
     FIG. 16B is a front elevation of the support plate of FIG. 16A; 
     FIG. 17 is a schematic fragmentary section of the tool taken in the plane including line  17 — 17  of FIG. 1; 
     FIG. 18 is an end view of a support sleeve of the tool; 
     FIG. 19 is a section of the support sleeve taken in the plane including line  19 — 19  of FIG. 18; 
     FIG. 20 is a front elevation of a passaging sleeve; 
     FIG. 21 is a section of the passaging sleeve taken in the plane including line  21 — 21  of FIG. 20; 
     FIG. 22 is a rear elevation of a first end cap; 
     FIG. 23 is a section view of the first end cap taken in the plane including line  23 — 23  of FIG. 22; 
     FIG. 24 is a front elevation of the first end cap; 
     FIG. 25 is a rear elevation of a second end cap; 
     FIG. 26 is a section of the second end cap taken in the plane including line  26 — 26  of FIG. 25; 
     FIG. 27 is a section of the support sleeve and the passaging sleeve taken in the plane including line  27 — 27  of FIG. 28; 
     FIG. 28 is a section of the support sleeve and the passaging sleeve taken in the plane including line  28 — 28  of FIG. 27; and 
     FIG. 29 is a rear elevation of a gasket of the tool. 
     Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings and specifically to FIG. 1, a pneumatic rotary tool of the present invention is generally indicated at  51 . The tool includes a housing  53 , a Maurer Mechanism casing  55  (broadly, a first rigid support) at the front of the housing, an output shaft  57  and an end cover  59  mounted on the rear of the housing  53 . The casing  55  may be considered part of the housing  53 , due to the generally uniform interface between the housing and casing, which creates the appearance of one continuous profile when viewing the tool  51 . The output shaft  57  extends from an front end  63  of the Maurer Mechanism casing  55 . A back end  65  of the Maurer Mechanism casing  55  engages the housing  53 . A gasket  67  (FIGS. 3 and 29) seals the interface between the back end  65  of the Maurer Mechanism casing  55  and the housing  53  to keep lubricating fluids within the tool  51 . The gasket  67  is preferably formed from a fibrous material, such as paper, but may also be formed from rubber, cork, plastic or other any other suitable material. The tool  51  further comprises a grip  71  extending downwardly from the housing  53 , allowing a user to grasp and hold the tool securely. The grip  71  has an additional outer layer  73  of soft material, such as rubber, to cushion and ease pressure on the user&#39;s hand, while increasing friction between the grip  71  and the user, making the tool  51  easier to hold. A trigger  75  extends from the front of the grip  71  for activating the tool  51 . Furthermore, the tool  51  comprises an air inlet  81  for supplying pressurized air to the tool. The air inlet  81  mounts on the lower portion of the grip  71  and receives an air hose (not shown), as is conventional in the industry. 
     Referring now to FIG. 2, the tool  51  additionally includes a rotation selector valve  83  mounted on the rear of the housing  53  for selecting the rotational direction of the output shaft  57 . The rotation selector valve  83  is rotatable within the housing  53  and end cover  59  for altering a flow of compressed air within the tool  51  to control the direction of output shaft  57  rotation. A torque selector  85  mounted on the end cover  59  is rotatable within the end cover for controlling the torque of the tool  51  by throttling the flow of compressed air. In the illustrated embodiment, the torque selector  85  has four discrete positions corresponding to four torque settings. The functioning of the rotation selector valve  83  and the torque selector  85  will be discussed in greater detail below. 
     Additionally, an air exhaust  91  mounts on the lower portion of the grip  71 , adjacent the air inlet  81  (FIG.  3 ). The air exhaust  91  includes a plurality of small holes  93  for diffusing exhaust air as it exits the tool  51 , directing exhaust air away from the user and preventing foreign objects from entering the air exhaust. 
     Turning to the interior workings of the tool  51 , FIG. 3 discloses a side section of the tool. Air flow through the tool  51  is generally indicated by line A. Following the path of line A, pressurized air first enters the tool  51  through the air inlet  81 . The air inlet  81  comprises a fitting  81   a,  a swivel connector  81   b  and an air inlet cylinder  82  through which air passes (FIGS.  3 - 3 C). The plastic housing  53  is formed by a molding process in which plastic in a flowable form surrounds and engages the exterior of the inlet cylinder  82 . The inlet cylinder includes annular grooves  82   a  into which the plastic flows when the housing  53  is formed. When the plastic hardens, the material in the grooves  82   a  forms protrusions  82   b  engaging the air inlet cylinder  82  in the grooves to secure the air inlet  81  in the housing. The housing  53  sufficiently encases the inlet cylinder  82  so that no fastening devices are necessary for holding the inlet cylinder within the housing. The preferred molding process for forming the housing  53  around the air inlet cylinder  82  is a plastic injection molding process that is well known in the relevant art and described in further detail below. 
     The fitting  81   a  mounts the swivel connector  81   b  for pivoting of the swivel connector about the axis of the air inlet  81  via a snap ring  81   c.  Other mounting methods other that a snap ring  81   c,  such as a ball and detent, are also contemplated as within the scope of the present invention. An O-ring  81   d  seals between the fitting  81   c  and the swivel connector  81   b  to inhibit pressurized air entering the air inlet from escaping. The snap ring  81   c  and O-ring  81   d  do not inhibit the rotation of the swivel connector  81   b  on the fitting  81   a.  An upper end of the fitting  81   a  is threaded, as is the lower internal end of the air cylinder  82 . The fitting  81   a  is threaded into the lower end of the inlet cylinder  82  until a flange  81   e  of the fitting abuts the lower end of the inlet cylinder. Another O-ring  81   f  seals between the fitting  81   a  and the inlet cylinder  82  so that air flows through the inlet cylinder to the working parts of the tool. A hex-shaped keyway  82   d  is designed to receive a hex-shaped key (a fragment of which is indicated at  82   e ) for rotating the fitting  81   a  within respect to the air inlet cylinder  82 , thereby engaging the threads  82   c  and threading the fitting fully into the cylinder. The keyway  82   d  and key  82   e  may be formed in any number of matching shapes (e.g., star, square, pentagon, etc.) capable of transferring force from the key to the fitting  81   a.    
     Moreover, the outer layer  73  of soft material, preferably formed from rubber, is overmolded onto the grip  71  after the plastic molding process. The preferred overmolding process forms the outer layer  73  directly on the grip  71 , fusing the outer layer to the surface of the grip and providing a more secure gripping surface for the user. The overmolding process essentially requires the use of a mold slightly larger than the grip  71 , such that the space between the grip and the mold can receive flowable rubber material, which forms the outer layer  73  of the grip, after the rubber cures. Because the rubber outer layer  73  fuses directly to the grip  71 , the layer fits snugly over the grip and requires no further retention means. The snug fit helps the outer layer  73  stay seated against the grip  71  during tool  51  use, so that the user can firmly grip the tool without movement between the grip and the outer layer. 
     After the inlet  81 , the air passes through a tilt valve  95 , which can be opened by pulling the trigger  75  (FIG.  3 ). The detailed construction and operation of the tilt valve  95  will not be discussed here, as the design is well known in the relevant art. The air then passes through the remainder of the inlet  81  until it passes through the rotation selector valve  83  (FIGS.  3  and  4 ). The rotation selector valve  83  comprises two pieces, a valve body  101  (FIGS. 4,  5  and  6 ) fixed in position and a valve member  103  (FIGS. 7 and 8) rotatable within the valve body. The valve body  101  is cylindrical having a first open end  105  for allowing air to enter the rotation selector valve  83 . The valve member  103  directs the flow of air through the valve body  101  and out through either a first side port  107  or a second side port  109 . The valve member  103  has an interior plate  115  rotatable with the valve member for directing the pressurized air. Referring now to FIG. 4, when in a first position, the plate  115  directs air through the first side port  107  and into a first passage  117  for delivering air to an air motor, generally indicated at  119  (FIG. 17) (discussed below), to power the motor and drive the output shaft  57  in the forward direction. When in a second position (shown in phantom in FIG.  4 ), the plate  115  directs air through the second side port  109  and into a second passage  121  for delivering air to the motor  119  to power the motor and drive the output shaft  57  in the reverse direction. The valve body  101  contains an additional top port  127  which allows a secondary air flow through the valve  83  simultaneous with air flow directed through either the first or second passage  117 , 121 . The details of the secondary air flow will be discussed below. 
     The pneumatic rotary tool  51  is of the variety of rotary tools known as an impact wrench. A Maurer Mechanism  131  (FIG.  3 ), contained within the Maurer Mechanism casing  55  and discussed below, converts high speed rotational energy of the air motor  119  into discrete, high torque moments on the output shaft  57 . Because the high torque impacts are limited in duration, an operator can hold the tool  51  while imparting a larger moment on the output shaft  57  than would be possible were the high torque continually applied. Impact tools are useful for high torque applications, such as tightening or loosening a fastener requiring a high torque setting. 
     Once the air passes through the rotation selector valve  83 , the air travels through an air passage toward the air motor  119 . The air passage may be configured with different passages as will now be described in greater detail. First, air passes through either the first or second passage  117 , 121  on its way to the air motor  119 . Air directed through the first passage  117  passes through a torque selector  85  (FIG.  4 ). As discussed previously, the torque selector  85  controls the pressurized air, allowing the user to set a precise output torque for the tool  51 . The end cover  59  mounts on the rear of the housing  53  (FIG.  3 ). Four bolt holes  133  formed in the end cover  59  receive threaded bolts  135  for attaching the end cover  59  and the Maurer Mechanism casing  55  to the housing  53  (FIGS.  3  and  10 ). The bolts  135  fit through the holes  133  in the end cover  59 , pass through elongate bolt channels  137  formed within the housing  53  and fit into threaded holes (not shown) within the Maurer Mechanism casing  55 , clamping the tool components together (FIGS. 2,  4  and  9 ). 
     Referring to FIGS. 9-15, the torque selector  85  rotates within the end cover  59  between four discrete settings. As the selector  85  rotates to each setting, a small protuberance  138  engages one of four notches  139  within the end cover  59 . The protuberance  138  is resiliently formed to extend outward from the selector  85  to engage each notch  139  as the selector rotates. The movement of the protuberance  138  and the increase in force required to move the protuberance from the notch  139  indicates to the user that the selector  85  is positioned for one of the discrete settings. FIGS. 9 and 10 show the first setting, where the flow of air through the first passage  117  is limited to air passing through a fixed orifice  143 . The fixed orifice  143  has a smaller cross-sectional area than the first passage  117 , throttling the air passing through the first passage. The torque selector  85  blocks any additional air from passing through the first passage  117 . The first setting corresponds to the lowest torque output, because the first passage  117  allows a minimum amount of air to pass. Viewing the torque selector  85  from the rear, an arrow indicator  145  on the torque selector indicates a setting of 1. 
     The end cover  59  additionally includes an orientation socket  147  for receiving an orientation pin  149  (FIG.  10 ). The orientation pin extends from the end cover  59  for receiving and orienting tool components with respect to one another. Because of the orientation pin  149 , tool components align and orient properly with respect to one another, ensuring that the tool is assembled and functions properly. Components receiving the orientation pin  149  will be discussed in greater detail below. 
     Turning to FIGS. 11 and 12, the arrow indicator  145  indicates a setting of 2, where a first port  151  of the torque selector  85  is aligned with a lower portion  153  of the first passage  117  and a second, larger port  155  of the torque selector is aligned with an upper portion  157  of the first passage. In this configuration, some air bypasses the fixed orifice  143  and passes to the upper portion  157  of the first passage  117 . More specifically, this air passes through the lower portion  153  of the first passage  117 , the first port  151 , a selector passage  163 , the second port  155  and finally into the upper portion  157  of the first passage. At the same time, air continues to pass through the fixed orifice  143 , as with the first setting. Thus, the total amount of air passing through the first passage  117  to the air motor  119  is the sum of the air passing through the torque selector  85  and the fixed orifice  143 . Like the fixed orifice  143 , the first port  151  controls how much air moves through the first passage  117 , throttling tool power. 
     Referring to FIGS. 13 and 14, the arrow indicator  145  indicates a setting of 3, where the second port  155  of the torque selector  85  is aligned with a lower portion  153  of the first passage  117  and a third, larger port  165  of the torque selector  85  is aligned with an upper portion  157  of the first passage. Again, the total amount of air passing through the first passage  117  is the sum of the air passing through the torque selector  85  and the fixed orifice  143 . Using this selection, the sizes of the second port  155  and the fixed orifice  143  control how much air moves through the first passage  117 , throttling tool power. 
     In the final position (FIGS.  15  and  16 ), the arrow indicator  145  indicates a setting of 4, where the third port  165  of the torque selector  85  is aligned with a lower portion  153  of the first passage  117  and a fourth port  167  of the torque selector, identical in size to the third port, is aligned with an upper portion  157  of the first passage. The total amount of air passing through the first passage  117  is the sum of the air passing through the torque selector  85  and the fixed orifice  143 . Using this selection, the size of the third port  165  and the fixed orifice  143  control how much air moves through the first passage  117 , controlling tool power at a maximum allowable torque in the forward rotational direction. It is contemplated that the torque selector  85  could be formed with a fewer or greater number of ports without departing from the scope of the present invention. 
     Once the pressurized air passes through the first passage  117  and torque selector  85 , it passes through a support plate  168  (broadly, a second rigid support) before entering the air motor  119  (FIGS. 3,  16 A and  16 B). The support plate  168  includes multiple openings  169  for receiving various tool components. Bolt openings  169 A are arranged at the four corners of the support plate for receiving bolts  135 . A rotation selector valve opening  169 B allows the rotation selector valve  83  to pass through the support plate  168 . An orientation opening  169 C passes through the support plate  168  for receiving the orientation pin  149  extending from the orientation socket  147  of the end cover  59 . With the bolts  135 , rotation selector valve  83  and orientation pin  149  passing through the support plate  168 , the end cover  59  and support plate are located in the proper position. Insertion of the orientation pin  149  ensures that the tool components assemble together properly by permitting the components to arrange in a single, correct configuration. Further, air passage openings  169 D are arranged within the support plate  168  to mate with the first or second passages  117 , 121  to allow movement of air from the torque selector  85  to the air motor  119 , as will be discussed in greater detail below. The support plate  168  further includes an outer layer of rubber material  170  on both plate faces for sealing engagement with the end cover  59  and the air motor  119 . When fully assembled, as discussed in greater detail below, the support plate  168  supports the plastic end cover  59  to inhibit it from bending and encouraging uniform support of the motor  119  during tool  51  use. The support plate  168  is preferably formed from steel, although other metallic and non-metallic materials exhibiting strength characteristics adequate to support the plastic end cover  59  are also contemplated as within the scope of the present invention. 
     After passing through the first passage  117 , torque selector  85  and support plate  168 , the pressurized air enters the air motor  119  (FIG.  17 ). As best shown in FIGS. 3 and 17, the air motor  119  includes a cylindrical support sleeve  171 , a passaging sleeve  173 , a rotor  175  having a plurality of vanes  177 , a first end cap  179  and a second end cap  181 . The support sleeve  171  has a first open end  189  and a second open end  191 , so that the passaging sleeve  173  mounts within the support sleeve (FIGS.  27  and  28 ). The first end cap  179  attaches to the first open end  189 , and the second end cap  181  attaches to the second open end  191 . The first and second end caps  179 , 181  are formed separately from the support and passaging sleeves  171 , 173 . The end caps  179 , 181  and sleeves  171 , 173  may be economically manufactured as separate pieces. This design contrasts sharply with prior art designs incorporating cup-like motor housings that combine one end cap and the sleeve into a single part. These prior designs are more expensive to manufacture than the present invention because forming a cylinder having one end closed and machining the inside of the cylinder is more costly than forming and machining an open-ended cylinder. 
     In the present invention, the end caps  179 , 181  engage and support the support and passaging sleeves  171 , 179  against canting with respect to the housing  53  under forces experienced by the tool  51  in use. Three distinct shoulder connections cooperate to rigidly connect the air motor  119 , the Maurer Mechanism casing  55  and the housing  53  (FIG.  3 ). The first end cap  179  has a front external shoulder  193  engageable with a rear internal shoulder  195  of the Maurer Mechanism casing  55 . The engagement of the shoulders  193 , 195  orients the Maurer Mechanism casing  55  and the first end cap  179  so that the two are aligned along their cylindrical axes. In addition, the length of the shoulder  195  helps support the first end cap  179  within the Maurer Mechanism casing  55  to inhibit the two pieces from becoming misaligned should the tool be subjected to a large impact (e.g., if dropped). The first end cap  179  further includes a rear external shoulder  201  engageable with the support sleeve  171  (FIG. 3) and an orientation pin  202  (FIG. 25) having one end received within a hole  202 A (FIG. 26) of the first end cap and an opposite end received within a hole  202 B of the passaging sleeve  173  (FIG.  28 ). Orientation pin  202  orients the first end cap  179  and the passaging sleeve  173  with respect to each other. Because both the first end cap  179  and the passaging sleeve  173  are circular, the orientation pin  202  is advantageous upon assembly to properly orient the two parts. 
     The passaging sleeve  173  is shorter front to rear than the support sleeve  171  so that a front surface  203  of the passaging sleeve  173  is designed for flatwise engagement with a rear surface  205  of the first end cap  179 . The support sleeve  171  extends forward beyond this surface, engaging the rear external shoulder  201  of the first end cap  179  and receiving the orientation pin  149  extending from the support plate  168 , through a hole  207  in the second end cap  181  and into a hole  209  of the passaging sleeve  173 . This shoulder  201  axially aligns the first end cap  179  with the support and passaging sleeves  171 , 173  and inhibits misalignment of the first end cap and the sleeves. The orientation pin  149  orients the support plate  168 , second end cap  181  and passaging sleeve  173 , orienting the parts with respect to one another, much the same as with the pin noted above. Finally, the second end cap  181  includes a front external shoulder  211  for engagement with the support sleeve  171  similar to the rear external shoulder  201  of the first end cap  179 . The four bolts  135  extending from the end cover  59  to the Maurer Mechanism casing  55  compress the internal components of the tool  51 , securely seating the end caps  179 , 181  on the support sleeve  171 . The interaction of the end cover  59 , support plate  168 , housing  53 , support sleeve  171 , passaging sleeve  173 , end caps  179 , 181  and Maurer Mechanism casing  55  create a closed cylinder of considerable rigidity and strength. The multiple interlocking shoulder joints and compressive forces induced by the bolts  135  inhibit the air motor  119  from canting with respect to the housing  53 . The air motor  119  fits snugly within the housing  53 , inhibiting it from canting with respect to the output shaft  57 . 
     The rotor  175  is rotatable within the passaging sleeve  173  (FIGS.  3  and  17 ). The rotor  175  is of unitary cylindrical construction with a support shaft  213  extending from the rear end of the rotor and a splined shaft  215  extending from the front end of the rotor. The splined shaft  215  has a splined portion  221  and a smooth portion  223 . The smooth portion  223  fits within a first ball bearing  225  mounted within the first end cap  179 , while the splined portion  221  extends beyond the first end cap and engages the Maurer Mechanism  131 . The splined portion  221  of the splined shaft  215  fits within a grooved hole  227  of the Maurer Mechanism  131  which fits within the Maurer Mechanism casing  55  (FIG.  3 ). The Maurer Mechanism  131  translates the high-speed rotational energy of the rotor  175  into discrete, high-impact moments on the output shaft  57 . This allows the user to hold the tool  51  while the tool delivers discrete impacts of great force to the output shaft  57 . The Maurer Mechanism  131  is well known to those skilled in the art, so those details will not be included here. 
     The support shaft  213  fits within a second ball bearing  233  mounted within the second end cap  181  (FIG.  3 ). The splined shaft  215  and the support shaft  213  extend generally along a cylindrical axis B of the rotor  175 , and the two sets of ball bearings  225 , 233  allow the rotor to rotate freely within the passaging sleeve  173 . The axis B of the rotor  175  is located eccentrically with respect to the central axis of the passaging sleeve  173  and has a plurality of longitudinal channels  235  that receive vanes  177  (FIG.  17 ). The vanes  177  are formed from lightweight material and fit loosely within the channels  235 , so that the end caps  179 , 181  and passaging sleeve  173  limit movement of the vanes  177  longitudinally of the tool within the air motor  119 . The vanes  177  extend radially outwardly from the rotor  175  when it rotates, to touch the inside of the passaging sleeve  173 . Adjacent vanes  177  create multiple cavities  237  within the motor  119  for receiving compressed air as the rotor  175  rotates. Each cavity  237  is defined by a leading vane  177  and a trailing vane, the leading vane leading the adjacent trailing vane as the rotor  175  rotates. As the cavities  237  pass before an inlet port  245 , compressed air pushes against the leading vane  177 , causing the rotor  175  to rotate. 
     As air travels through the air motor  119 , the rotor  175  turns, causing the air cavities  237  to move through three stages: a power stage, an exhaust stage and a recovery stage (FIG.  17 ). Air moves from the torque selector  85  into an intake manifold  247 . The pressurized air is then forced through the inlet port  245  formed in the intake manifold  247 , allowing air to move into the cavity  237  between the rotor  175  and the passaging sleeve  173 . This begins the power stage. As the pressurized air pushes against the leading vane  177 , the force exerted on the vane causes the rotor  175  to move in the direction indicated by arrow F. As the volume of air expands in the cavity  237 , the rotor  175  rotates, increasing the volume of the space between the vanes  177 . The vanes continue to move outward in their channels  235 , preserving a seal between the vanes and the passaging sleeve  173 . 
     At the end of the power stage, as the volume of the cavity  237  is increasing toward its maximum amount, the leading vane  177  passes a set of early stage exhaust ports  251  in the passaging sleeve  173  and support sleeve  171  (FIGS. 17,  21 ,  27  and  28 ). These ports  251  mark the transition between the power stage and the exhaust stage, allowing expanding air to escape from inside the air motor  119  to an area of lower pressure in interstitial spaces  252  between the air motor and the housing  53 . Air leaving these ports  251  is exhausted from the tool  51 , as discussed below. During an early portion of the exhaust stage, the volume of the cavity  237  is larger than at any other time in the cycle, expanding to a maximum volume and then beginning to decrease as the cavity moves past the bottom of the motor  119 . As the trailing vane  177  passes the early stage exhaust ports  251 , some air remains within the air motor  119  ahead of the trailing vane. As the rotor  175  continues turning, the volume of the cavity  237  decreases, increasing the air pressure within the cavity. Compressing this air creates backpressure within the motor  119 , robbing the spinning rotor  175  of energy, slowing the rotation of the rotor. To alleviate this backpressure buildup within the motor  119 , the end of the exhaust stoke includes a late stage exhaust port  253  which allows the remaining air to escape from the air motor  119  into an exhaust manifold  255 . This exhaust air is then routed out of the tool  51  as discussed below. Passing the late stage exhaust port  253  marks the transition to the third stage of the motor  119 , the recovery stage, where the volume of the cavity  237  is at its smallest. This stage returns the air vane  177  to the beginning of the power stage so that the motor  119  may repeat its cycle. 
     As the rotor  175  rotates, the vanes  177  continually move radially inward and radially outward in their channels  235 , conforming to the passaging sleeve  173  (FIG.  17 ). The rotation of the rotor  175  forces the vanes  177  radially outward as it rotates, but the vanes may be initially reluctant to move radially outward before the rotor has begun turning at a sufficient rate to push them outward as the rotor turns. This problem may be exacerbated by the presence of required lubricants within the air motor  119 . Without the vanes  177  extended from their channels  137 , air may simply pass through the air motor  119  to the early stage exhaust valve  251  without turning the rotor  175  as desired. To counteract this effect, the first end cap  179  (FIGS. 25 and 26) and the second end cap  181  (FIGS. 22-24) each include a vane intake channel  261 . Some pressurized air in the intake manifold  247  passes through these vane intake channels  261  at either end of the air motor  119 . The air moves within the channel  261  behind the vanes  177  to push the vanes out of the channels  235  so that air passing through the motor  119  can press against the extended vanes. The vane intake channels  261  deliver air to each vane  177  as it moves through most of the power stage. The intake channel  261  ends once the vane  177  nears full extension from the channel  235 . After the vane  177  begins moving back inward toward the axis of the rotor  175 , the air behind the vane must escape, so vane outlet channels  263  are formed on the first end cap  179  and the second end cap  181 . These allow the air behind the vane  177  to move through the channel  263  and into the exhaust manifold  255 . The air may then exit the motor  119  in the same manner as the air exiting the late stage exhaust port  253 . 
     Returning to the exhaust air exiting the early stage exhaust port  251 , the air then passes through a pair of orifices (not shown) in the housing  53  which lead to the air exhaust  91  in the grip  71  (FIG.  3 ). Exhaust air exiting the late-stage exhaust port  253  or one of two vane outlet channels  263  and entering the exhaust manifold  255  exits the tool  51  by a different path (FIG.  4 ). This path guides the air through the second passage  121  back toward the rotation selector valve  83 , which diverts it to two symmetrical overflow passages  269  which lead to interstitial spaces  252  between the support sleeve  171  and first end cap  179  and the housing  53  (FIG.  4 ). The remaining exhaust air then travels through these spaces  252  to the pair of orifices and out the air exhaust  91  as with the other exhaust air. 
     Operating in the reverse direction, the tool  51  works substantially the same, except that the air bypasses the torque selector  85 . Air enters the tool  51  through the same air inlet  81 . The rotation selector valve  83  diverts the air to the second passage  121  where the air travels upward through the tool  51  until it enters the exhaust manifold  255 . The air then passes through the late-stage exhaust port  253  and enters the air motor  119  where it reacts on the opposite side of the vanes  177 , thereby applying force to the rotor  175  in the opposite direction. The early-stage exhaust port  251  operates substantially the same as in the forward direction. The vane intake channel  261  and vane outlet channel  263  operate as before, except that they allow air to flow in opposite directions. 
     Typically, pneumatic rotary tools are almost entirely formed from a high strength metal such as steel. These tools are subjected to high stress and loading from proper use plus discrete impacts from being dropped or bumped. Although metal, such as steel, provides adequate strength, a significant drawback of an all-metal construction is the high weight and material cost. The design of the current invention eliminates these problems by forming the tool housing  53  from lightweight and inexpensive plastic. In addition, the design of the support sleeve  171  and the end caps  179 , 181  eliminates the need for machining expensive cup-like parts for the air motor. Such parts were a significant drawback of the prior art. The present invention employs a simple sleeve  171  and end cap  179 , 181  design that can withstand the impact loads of use with parts not requiring elaborate machining techniques as with the prior art. Moreover, the sleeve  171  and end cap  179 , 181  design is resistant to canting within the tool  51  because of the four bolts  135  and shoulder engagements between the parts. 
     The present invention is also directed to a method of assembling the pneumatic rotary tool  51  of the present invention. The tool  51  is designed for easy assembly according to the following method. The method described below is applicable to the tool  51  and its various parts as described above. The air motor  119  is assembled by engaging the rear external shoulder  201  of the first end cap  179  with an end of the support sleeve  171 . The rotor  175  is then seated within the support sleeve  171  so that the splined shaft  215  extends outward through the first end cap  179 . A plurality of vanes  177  are then inserted lengthwise into channels  235  of the rotor  175  for rotation with the rotor inside the sleeve  171 . The second end cap  181  then engages the opposite end of the support sleeve  171  and the support shaft  213  for rotation of the rotor  175  within the sleeve, thereby completing construction of the air motor  119 . The completed air motor  119  is then inserted into the housing  53 . 
     The Maurer Mechanism  131  is then inserted into the Maurer Mechanism casing  55  so that the output shaft  57  of the Maurer Mechanism extends from the casing. The gasket  67  mounts on the back end  65  of the Maurer mechanism casing, and includes four bolt openings  273  for receiving the bolts  135  before they enter the holes of the Maurer Mechanism casing (not shown). The back end  65  of the Maurer Mechanism casing  55  may then be engaged with the housing  53  for connection of the Maurer Mechanism  131  to the splined shaft  215  of the air motor  119 . The Maurer Mechanism  131  will then rotate conjointly with the rotor  175  of the air motor  119 . The support plate  168  and end cover  59  then seat on the rear of the housing  53 , thereby enclosing the air motor  119  within the tool housing. 
     To secure the Maurer Mechanism casing  55 , housing  53 , support plate  168  and end cover  59  together and ensure that the air motor  119  remains properly oriented within the housing, the plurality of bolts  135  are inserted through the end cover, support plate and housing. As described above, these bolts  135  thread into the rigid Maurer Mechanism casing  55 , drawing the support plate  168  and end cover  59  toward the housing  53  and the housing toward the Maurer Mechanism casing. These rigid bolts  135  and the rigid Maurer Mechanism casing  55  compress the tool  51 , including compressing the end caps  179 , 181  and support sleeve  171  of the air motor  119  within the housing  53  to fully seat the end caps onto the support sleeve so that the motor, housing, support plate  168  and end cover  59  cooperate to hold the air motor in proper alignment within the tool. In other words, the air motor  119  is sandwiched between two rigid components, the support plate  168  and the Maurer Mechanism casing  55 . The support plate  168  further supports the plastic end cover  59  to inhibit bending and encouraging uniform motor  119  support during tool  51  use. The method described herein is preferred, although it is contemplated that the method steps may be reordered while remaining within the scope of the present invention. 
     The method preferably comprises another step where the housing  53  is formed by delivering flowable plastic to a mold to form the housing. The flowable plastic enters the mold and surrounds the air inlet  81  of the tool  51 , creating the tool housing  53  with an air inlet cylinder having an interference fit within the housing. As discussed above, the inlet cylinder  81  allows source air to enter the tool  51  for use by the air motor  119 . Other methods of forming a plastic housing  53  around an air inlet cylinder  81  are also contemplated as within the scope of the present invention. The method also preferably comprises a step of overmolding an outer layer  73  of soft material onto a portion of the housing  53  constituting a grip  71 , after the step of molding the housing. 
     In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained. 
     When introducing elements of the present invention or the preferred embodiment(s) thereof, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
     As various changes could be made in the above without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.