Abstract:
A reversible double-throw air motor utilizes a moveable cylinder casing to switch between forward and reverse operation. The cylinder casing rotates between its forward and reverse positions in response to movement of an externally accessible actuator, via a front bearing plate rotationally coupled to the cylinder casing. The actuator may be biased to the proper position by reaction forces generated within the motor. In some embodiments, the coupling of the front bearing plate to the cylinder casing allows for the cylinder casing to float, thereby enabling the cylinder casing to self-center about the rotor. In other optional embodiments, the front bearing plate is pressed against the cylinder casing during operation by air pressure. The resulting double-throw air motor is easy to use motor and may be economically produced.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates generally to pneumatically powered hand tools and more specifically to a reversible double-throw air motor for use with such tools. 
     Various pneumatic impulse tools, such as impact wrenches, are powered by reversible rotary vane pneumatic motors. Such motors are required to have a large stall torque in both forward and reverse directions. It is advantageous for such motors to be relatively small in size, since they are generally hand-held by an operator. 
     Most previously known reversible air motors are changed from forward to reverse operation by rerouting the inlet (pressure) and outlet (exhaust) paths at a location remote from the motor package, such as by shuttle spool valves or rotary valves. Such reversing arrangements take up valuable space, making the tool larger, complicate the construction in terms of adding parts and requiring additional labor for assembly, thus increasing the manufacturing cost, and creating tortuous air flow paths, thus reducing efficiency. 
     U.S. Pat. No. 4,822,264 to Kettner discloses a rotary vane air motor/reversal package having five main parts—a housing; a cylinder member; a rotor assembly; a distributor; and a valve plate, each of relatively complicated design and calling for precision manufacture to minimize leaks. In the Kettner device, the supply and exhaust passages leading to and from the cylinder chambers are reversed by changing the rotational position of a rotary valve plate that is positioned between a fixed distributor mounted within the motor casing on a rear side of the valve plate and a fixed cylinder casing on the front side of the valve plate. Although the design of Kettner&#39;s motor improves on some prior art reversible rotary vane motors in terms of size, it has some shortcomings. The distributor has two pressure ports located diametrically opposite each other, each of which is flanked on either side by an exhaust port. The exhaust ports are located very close to the pressure ports, thus presenting an opportunity for blowby of pressure air at the interface between the distributor and the valve plate. That possibility is exacerbated by the fact that the rotatable valve plate interfaces on opposite sides with fixed members with sliding fits. Thus, small tolerance variations can lead to large leaks and reduced efficiency. In addition, the location of the rotary valve plate, upstream from the motor&#39;s cylinder, requires that the actuator for the rotary valve plate (i.e., the part the user touches to switch between forward and reverse) is physically located rearward of the motor&#39;s cylinder. From an ergonomic perspective, this placement of the actuator is somewhat undesirable, as a location closer to the front end of the device would be more easily manipulated by the user under normal gripping circumstances. Further, the position of the valve plate is maintained by a spring/ball detent; avoiding the risk of an unintended rotation of the valve plate during handling of a tool equipped with the motor requires that the detent be quite strong which detracts from a desirable facility of reversal by the user. If the valve plate is rotated inadvertently from a desired position during handling, there is no assurance that it will be moved to the proper position during operation of the tool, and the motor performance may be compromised, resulting in a defective operation, such as a low torque on a fastener. 
     Thus, there remains a need for an improved design of a reversible double-throw air motor. Such a motor should allow for easy use and low production costs. 
     SUMMARY OF THE INVENTION 
     The reversible air motor of the present invention utilizes a moveable cylinder casing disposed within the motor&#39;s housing to switch between forward and reverse operation. The cylinder casing rotates between its forward and reverse positions in response to movement of an externally accessible actuator, the mechanical coupling via a front bearing plate rotationally coupled to the cylinder casing. In preferred embodiments, this actuator is biased to the proper position by reaction forces generated within the motor. In some embodiments, the coupling of the front bearing plate to the cylinder casing allows for the cylinder casing to float, thereby enabling the cylinder casing to self-center about the rotor. In other optional embodiments, the front bearing plate is pressed against the cylinder casing during operation by air pressure. Thus, in preferred embodiments, the present invention provides an easy to use motor that may be economically produced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of one embodiment of a motor according to the present invention. 
     FIG. 2 is a cross-sectional view of the motor of FIG. 1 showing high pressure air flow. 
     FIG. 3 is a cross-sectional view of the motor of FIG. 1, showing exhaust air flow. 
     FIG. 4 is a view of the front of the valve plate. 
     FIG. 5 is a side cross-sectional view, taken along the lines E—E of FIG.  4 . 
     FIG. 6 is a side cross-sectional view, taken along the lines F—F of FIG.  4 . 
     FIG. 7 is a view of the rear of the valve plate. 
     FIG. 8 is a view of the rear of the cylinder casing. 
     FIG. 9 is a side cross-sectional view, taken along the lines H—H of FIG.  8 . 
     FIG. 10 is a partially cut-away side view of the cylinder casing. 
     FIG. 11 is a view of the front of the cylinder casing. 
     FIGS. 12A and 13A are end cross-sectional views taken through the cylinder casing show the motor in the forward and reverse positions, respectively. 
     FIGS. 12B and 13B are schematic diagrams of the parts in the forward and reverse positions, respectively. 
     FIG. 14 is a partial end view of a portion of a cylinder casing of a modified configuration. 
     FIG. 15 is forward facing view of the front bearing plate area with the rotor removed. 
     FIG. 16 is a side cut away view of the front portion of the housing showing the optional air pressure chamber in front of the front bearing plate. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     One embodiment of the reversible double-throw air motor of the present invention is shown in FIG.  1 . The motor includes a housing  20  having a cavity therein. Disposed internal to the housing are the valve plate  60 , the cylinder casing  90 , the rotor  120 , and the front bearing plate  80 . Disposed around the front portion of the housing  20  is the reversing ring  40  for switching the motor  10  between supply of rotational power in a first direction (forward mode) and supply of rotational power in an opposite second direction (reverse mode). 
     Referring to FIGS. 1-3, the housing  20  has a rear portion  22  and a front portion  24  and includes a threaded socket (not shown) for accepting a coupling through which the motor is supplied with pressurized air. The pressurized air is fed to the valve plate  60  via supply passage  26  in housing  20 , and the pressurized air supply is controlled by the trigger lever  52  in a conventional fashion. Two exhaust passages  28 , 30  extend along the sides of the rear portion  22  of the housing  20  to the valve plate  60 , which serves as the end wall of a cavity  32  in the front portion  24  of the housing  20 . A front bearing plate  80  provides the front end wall of the cavity  32 . 
     A tubular cylinder casing  90  (FIGS. 8-11) is received in the cavity  32  for rotation between a forward position and a reverse position, as described in more detail below. The inner surface  96  of the cylinder casing  90  defines a central bore of the cylinder casing  90  where the rotational power for the motor  10  is generated. The inner surface  96  preferably has a uniform, oblong cross section along its axial extent and includes two oppositely located bottom dead center positions (BDC) and top dead center positions (TDC), which correspond to the lines of intersection with the inner surface  96  of two mutually perpendicular planes of symmetry B and D of the inner surface  96  that include the cylinder axis A. The quadrants of the inner surface  96  of the cylinder casing  90  between the lines of intersection are labeled I, II, III, and IV in FIGS. 8,  12 B and  13 B. 
     Two pairs of transfer passages  98  are formed in the wall of the cylinder casing  90  opposite each other in symmetrical relation to the plane T of the top dead center lines TDC. Passages  98  of each pair are symmetrical with respect to the plane B of bottom dead center lines BDC. Each passage  98  opens at a kidney-shaped end port  98   ep  in the back end surface  90   p  of the cylinder casing  90  and opens at a wall port  98   wp  at the inner surface  96  of the cylinder casing  90 . The wall ports  98   wp  may be formed by a round hole bored obliquely to the plane of the TDC lines and parallel to the planes of the BDC lines. The wall ports  98   wp  are closely spaced apart from each other and equidistant from the BDC lines. End ports  98   ep  at the end surface  90  of cylinder casing  90  are kidney-shaped so that the wall thickness of the cylinder casing  90   p  can be kept small and machining is easier to set up for. The passages  98  may optionally have a continuous cross-section corresponding to the kidney-shape of the end ports  98   ep  such that the cylinder casing  90  may be formed by extrusion. The back end surface  90   p  of the cylinder casing  90  abuts the valve plate  60 , while the opposite end of the cylinder casing  90  abuts the front bearing plate  80 . 
     The shape of the oblong bore in the cylinder casing  90  can vary in geometry. Also, as shown in FIG. 14, the bore of a cylinder casing  90  may have concavities  90   c , the curvatures of which are equal to the curvature of the rotor body  120   b . Each concavity  90   c  is flanked by a cusp  90   d . The concavities  90   c  may improve efficiency by reducing blowby at the BDC points where the rotor  120  is in running clearance with the cylinder wall. The concavities  90   c  lengthen the circumferential distance for running of the rotor  120  closely along the wall of the cylinder casing  90  from essentially a line (see FIGS. 12A and 13A) to several degrees of rotation of the rotor  120 . 
     The valve plate  60  (FIGS. 4-7) is received in the housing  20  and secured with a pin or equivalent (not shown) to keep the valve plate  60  from rotating and an O-ring (not shown) at its perimeter to hold pressure supply passage  26 . A pair of oblong pressure passages  66  open at their proximal ends to supply passage  26  (as extended by a central bore in valve plate  60 ) and thus are in fluid communication with the pressurized air supplied to the supply passage  26  when the trigger lever  52  is pressed. The front ends of pressure passages  66  form pressure ports  66   p . A pair of exhaust passages  68  open at their proximal ends to exhaust passages  28 , 30  and at their front ends at exhaust ports  68   p . An axial stepped bore  70  at the center of the valve plate  60  receives a bearing (not shown) by which the proximal end of a rotor  120  is rotatably mounted in the housing. The distal portion of the bore  70  has diametrically opposite notches  74 , the distal ends of which are circumferentially elongated. The purpose of notches  74  is described below. 
     The rotor  120  is carried by a bearing in the valve plate  60  and a bearing in the front bearing plate  80  for rotation about the axis A of the cylinder casing  90 . A circular cylindrical body portion  120   b  of the rotor is received within the cylinder casing  90  with its peripheral surface in close running clearance with the inner surface  96  of the cylinder casing  90  and its end surfaces in close running clearance with the surface of the valve plate  60  and the front bearing plate  80  that define the cavity  32 . The inner surface  96  of the cylinder casing  90 , the surfaces of the end plate  60 , the front bearing plate  80  facing the bore in the cylinder casing  90 , and the peripheral surface of the rotor body  120   b  define two crescent-shaped chambers. 
     The body portion  120   b  of the rotor  120  shown in the drawings has six circumferentially spaced-apart radial slots  124 , each of which extends the full length of the body portion  120   b  and receives a vane  126  for radial sliding displacement (only one vane is shown in the drawings). Segments of the inner surface  96  of the cylinder casing  90  and the rotor body  120   b , the front surface of valve plate  60 , and the proximal surface of front bearing plate  80  between each adjacent pair of vanes  126  define subchambers of the two crescent-shaped chambers. The number of vanes may be varied from four to nine or more, odd numbers being preferred for eliminating what in any case is a small chance of the motor not starting if the rotor  120  should stop with two vanes  126  at bottom dead center. If that were to happen in a motor  10  with an even number of vanes  126 , the user can rotate cylinder casing  90  slightly to reposition the BDC lines relative to the vanes  126  momentarily when starting the motor  10 . 
     The inner edges of the vanes  126  are in radial clearance from the bases of the slots  124  at BDC. Kick-out slots or notches  74  in the valve plate  60  allow pressurized air to flow from the supply passage  26  into the clearance space and bias the vanes  126  outwardly into engagement with the inner surface  96  of the cylinder walls. The kick-out slots  74  are positioned circumferentially to be opposite the initial part of each working stroke of each subchamber of the motor to apply kick-out pressure just after each vane  126  passes BDC. 
     To operate the motor in forward mode, the user moves reversing ring  40  to cause the cylinder casing  90  to rotate to the forward position as shown in FIGS. 12A-12B, as is described further below. The following states and flow paths are set up with the cylinder casing  90  in that position: 
     Quadrant I—Pressure—cylinder end port  98   ep  (kidney-shaped) open to valve plate pressure port  66   p —quadrant I is pressured from end port  98   ep  through the transfer passage to cylinder wall port  98   wp;    
     Quadrant II—Exhaust—cylinder end port  98   ep  (kidney-shaped) open to valve plate exhaust port  68   p —quadrant  11  exhausts from wall port  98   wp  through the transfer passage to  98   ep  and exhausts directly through the exhaust port  68   p  in the valve plate  60 ; 
     Quadrant III—Pressure—cylinder end port  98   ep  (kidney-shaped) open to valve plate pressure port  66   p —quadrant III is pressured from end port  98   ep  through the transfer passage to cylinder wall port  98   wp ; and 
     Quadrant IV—Exhaust—cylinder end port  98   ep  (kidney-shaped) open to valve plate exhaust port  68   p —quadrant IV exhausts from the wall port  98   wp  through transfer passage to  98   ep  and exhausts directly through exhaust port  68   p.    
     When the motor is activated by pressing trigger lever  52 , any vane  126  that is counterclockwise (with respect to the view of FIG. 12) of the BDC line and in quadrant I or III is subjected to pressure, which produces a counterclockwise torque on the rotor  120 . As each vane  126  passes in succession a BDC line and enters quadrant I or III, it becomes subject to pressure and produces torque. As each vane  126  passes a TDC line and enters quadrant II or IV, the subchamber upstream from it is opened to exhaust (see above). Accordingly, all of the subchambers are sequentially subject to pressure and exhaust, thus producing differential pressures across each vane twice in each evolution made by that vane  126 . 
     When the user wants to operate the motor  10  in reverse rotation, the user moves reversing ring  40  to cause the cylinder casing  90  to rotate to the forward position as shown in FIG. 13, as is described further below. As seen in FIG. 13, the states and connections of the quadrants that prevail in the forward mode, as described above and shown in FIG. 12, are reversed such that quadrants II and IV are pressure quadrants and quadrants I and III are exhaust quadrants. Thus, the rotor  120  is driven clockwise with respect to the view of FIG. 13 (counterclockwise as viewed from the rear of the housing  20 ). 
     The general configuration and operation of the rotor  120 , valve plate  60 , and cylinder casing  90  are generally similar to that described in U.S. patent application No. 09/136,301, which is incorporated herein by reference. However, there are several differences between the motor of that application and the present invention, including but not limited to differences between the cylinder casing therein and the cylinder casing  90  of the present invention, that are described further below. 
     One problem of the Ser. No. 09/136,301 design is that the cylinder casing must be tightly constrained within the cavity of the housing, otherwise the rotor will be subject to undue wear. One reason for this is because the arm used to move the cylinder is only at one circumferential position. As the reaction force generated by the rotor and cylinder acts to push the arm against the housing, this in turn causes an unbalanced force to be applied to the cylinder. This unbalanced force tends to skew the cylinder with respect to the rotor. Thus, while the midpoint of the cylinder may be aligned with the rotor, the front and rear ends of the cylinder may not be aligned with the rotor during use. To counter this effect, the cylinder may be tightly constrained in the 09/136,301 housing, thereby minimizing the cylinder&#39;s movement. However, tightly fitting the cylinder within the housing leads to increased production costs to meet the tolerances required. 
     The approach of one aspect of the present invention allows for a greater tolerance fit between the cylinder casing  90  and the housing  20  by providing a balanced resistance to the reaction force torque. While the front face of the cylinder casing  90  preferably abuts the front bearing plate  80 , the cylinder casing  90  is also connected to the front bearing plate  80  by a pair of pins  94 . These pins  94  preferably extend forwardly from the cylinder casing  90  and into opposing radial slots  82  on the rear face of the front bearing plate  80 . See FIG.  15 . The slots  82  should be disposed on opposite sides of the center hole  86  of the front bearing plate  80  through which the output of the rotor  120  is directed and should be just slightly larger in width than the pins  94  such that a sliding fit between the two is established. Further, the pins  94 , and the corresponding radial slots  82 , should be disposed 180° apart. In this way, the reaction force on the cylinder casing  90  acts against two points that are symmetrically disposed about the axis of the cylinder casing  90 , rather than one. Thus, the skewing effect of a single point force application is avoided. Further, the cylinder casing  90  is allowed move with limited relative movement with respect to the front bearing plate  80 , at least generally along the plane of the slots  82 . This action may be referred to as floating. The floating allows the cylinder casing  90  to at least partially self-center about the rotor  120 . 
     In another aspect of the present invention, alone or in combination with the “floating” rotationally moveable cylinder casing  90 , the approach of the present invention utilizes a moveable front bearing plate  80  to help select between forward and reverse. The front bearing plate  80  is positioned within the housing  20  such that it is able to rotate with respect to the housing  20  from a first position to a second position. The rotation of the front bearing plate  80  is controlled by the movement of an actuator  40  that is accessible to the user. Preferably, this actuator  40  takes the form of a reversing ring  40  that is annularly disposed about the housing  20  and connected to the front bearing plate  80  by a tab  46 . Further, the rotation of the front bearing plate  80  is limited by the action of a tab  46  against a slot  42  in the housing  20 . In the embodiment shown in FIG. 15, the tab  46  takes the form of a screw  46  extending inwardly from the reversing ring  40 . The screw  46  extends into a registration hole  84  in the front bearing plate  80 , which may or may not be threaded. To reach the front bearing plate  80 , the screw  46  extends through a slot  42  in the housing. For reference, the housing slot  42  is bounded by first and second slot ends  44 . Thus, the rotation of the front bearing plate  80  is limited by the relative locations of the first and second ends  44  of the housing slot  42 . Preferably, the arc swept by the slot  42  should be such that the tab  46  rests firmly against one end  44  of the slot  42  when the front bearing plate  80  is fully in the forward position and against the opposite end  44  of the slot  42  when the front bearing plate  80  is fully in the reverse position. Preferably, the location of the slot ends  44  allows for more than 45° of rotation, and more particularly between about 50°-55°. As described above, the cylinder casing  90  is joined to the front bearing plate  80  via pins  94  disposed in slots  82  in the front bearing plate  80 . However, it should be noted that two pins  94  are not required for this invention aspect to function; instead, the it is only required that the front bearing plate  80  and the cylinder casing  90  be rotationally coupled. Thus, the joining of the cylinder casing  90  to the front bearing plate  80  may be by any method known in the art, such as by the use of interconnecting pins  94 , gluing, screwing, etc. With this configuration, rotation of the front bearing plate  80  to the first position causes the cylinder casing  90  to assume the forward position; conversely, rotation of the front bearing plate  80  to the second position causes the cylinder casing  90  to assume the reverse position. This arrangement has at least two advantages. First, by relating the reversing ring  40  to the front bearing plate  80 , the reversing ring  40  may be placed farther forward on the housing  20  than with prior designs. As such, the present design allows for the actuator controlling the direction of rotation—in the illustrative example, the reversing ring  40 —to be more conveniently placed for the user. Second, the reaction force acting on the cylinder casing  90 , via the linkage of the front bearing plate  80 , causes the tab  46  to forced against the slot ends  44  when the motor  10  is in operation. The reaction torque on the rotor  120  in both forward and reverse modes is transmitted to tab  46 , forcing it against the slot ends  44  in the housing  20 . Should any frictional drag, vibration, or external handling force move the cylinder casing  90  from the desired or proper position, the reaction pressure forces on the cylinder casing  90  will immediately rotate the cylinder casing  90  until the tab  46  engages the end  44  of the housing slot  42 . Thus, when the motor  10  is operating, the chance of it changing from one mode to the other is small because of the reaction torque; and, when the motor  10  is not operating, any dislocation of the cylinder casing  90  will be immediately corrected by the reaction torque when the motor  10  is started. The tab  46  and housing slot  42  thus provide a simple and effective way to permit changing the direction of operation and maintaining the direction of operation of the motor  10 , once it is selected. 
     In another aspect of the present invention, air pressure may be used to help keep the front bearing plate  80  pressed against the cylinder casing  90 . In some embodiments, the front bearing plate  80  is pressed against the cylinder casing  90  by a spring  102  trapped between the front bearing plate  80  and a more forwardly located bulkhead  104 , such as the bulkhead  104  through which extends the output shaft associated with the rotor  120 . The spring force in such an embodiment should be enough to counter-act the force acting to separate the cylinder casing  90  from the front bearing plate  80  resulting from the presence of pressurized air in the subchambers between the rotor  120  and the cylinder casing  90 . Unfortunately, this spring force also tends to inhibit rotational movement of the front bearing plate  80 , and thus the movement of the cylinder casing  90  between the forward and reverse positions. In some embodiments of the present invention, a lesser spring force is required because air pressure is also used to press the front bearing plate  80  and the cylinder casing  90  together. In such embodiments, a chamber  100  is disposed between the front bearing plate  80  and the aforementioned bulkhead  104 . The chamber  100  may be annular in shape and disposed about, but excluding, the spring  102 . The bulkhead end of the chamber  100  is sealed against air loss by any means known in the art, such as by appropriately placed plugs and O-rings (not shown). In addition, the front bearing plate  80  includes at least one, and preferably two, small orifices  88  that extend through the front bearing plate  80  from the front to the back thereof. The orifices  88  should be fairly small, such as 0.020″ in diameter, and should be aligned with passages  98  of the ylinder casing  90 . While not required in other embodiments, the passages  98  in the ylinder casing  90  in these embodiments should extend the length of the cylinder casing  90  so as to be in fluid communication with the orifice(s)  88 . For these “air clamped” embodiments, when the motor  10  is not activated, the chamber  100  is typically not pressurized and only the action of the spring  102  pushes the front bearing plate  80  against the cylinder casing  90 . Thus, when the motor  10  is not activated, the reversing ring  40 , and therefore the cylinder casing  90 , may be relatively easily moved. However, when the motor  10  is activated, high pressure air flows through one of the passages  98  aligned with the orifices  88 , through the corresponding orifice  88 , and into the chamber  100 , thereby at least partially pressurizing the chamber  100 . Exactly which passage  98  will have the high pressure air will depend on whether the cylinder casing  90  is in the forward position or the reverse position. The high pressure air in the chamber  100  will then act against the front side of the front bearing plate  80  to augment the spring  102  in pushing the rear face of front bearing plate  80  against the cylinder casing  90 . If the second orifice  88  is present, the air in the chamber  100  will also somewhat escape through that orifice  88  to the corresponding passage  98  that is carrying exhaust air. On the other hand, the inclusion of the second orifice  88  allows the chamber  100  to be pressurized regardless of forward or reverse mode of the motor  10 . Conversely, if there is no second orifice  88 , then air losses may be lessened, but dynamic pressurization of the chamber  100  may be limited to only one mode of operation, such as the forward mode. 
     Further, the motor  10  can optionally be provided with some form of spring detent between tab  46  and the housing  20 , primarily to provide a clicking sound that will tell the user that an operating (forward or reverse) position has been attained. Also, the motor  10  may be provided with a governor and/or adjustable torque shut-off mechanism of any suitable type known in the art. In addition, while the illustrative example of the motor  10  discussed above is configured in an “in-line” form, in which the housing  20  is generally cylindrical and is grasped in the hand of the user, the housing  20  may also be in other forms, such as a pistol shape, etc. 
     The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the spirit and essential characteristics of the invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.