Patent Publication Number: US-9835031-B2

Title: Reversible pneumatic vane motor

Description:
The invention relates to a reversible pneumatic vane motor having a stator housing with a cylinder, a vane carrying rotor rotatable in the cylinder and forming a clearance seal portion relative to the cylinder wall, wherein the stator housing has air communication ports located at both sides of the clearance seal portion for supplying motive pressure air and scavenging exhaust air from the cylinder at alternative directions of rotation, and a primary outlet is provided at a location diametrically opposite the clearance seal portion for draining exhaust air from the cylinder in both directions of rotation. A directional valve is provided for alternative connection of the air communication ports to a pressure air source and the atmosphere at alternative directions of motor rotation. 
     The above described reversible type of pneumatic vane motor has its primary outlet at an angular location diametrically opposite the clearance seal portion to make the motor operate at equal efficiency in both directions of rotation. In comparison with a vane motor designed for a one way operation with an asymmetrically located primary outlet the efficiency of the reversible motor is considerably lower. This is due to the symmetric location of the primary outlet of the latter, which will cause a slight recompression of the exhaust air that was not able to leave the cylinder through the primary outlet. This recompression causes a reduced power outlet of the reversible type of motor. 
     A further problem with the prior art type of reversible motor is that it tends to generate a higher noise level since there are limited possibilities to optimize the design of the primary outlet. 
     A prior art pneumatic tool is described in U.S. 2007/0217940. This tool is arranged to provide a high torque in a first direction (slackening mode) and a small torque in the opposite direction (tightening mode). A problem with this arrangement is however that is inefficient in the tightening mode. Namely, in most applications it is desired to provide a high torque in both directions. 
     It is an object of the invention to provide an improved reversible pneumatic vane motor having an increased power output and an increased idle speed operation in both directions of rotation. 
     It is a further object of the invention to create a reversible vane motor providing a greater flexibility for noise attenuation by a enabling a balanced exhaust outlet design. 
     It is a still further object of the invention to provide an improved reversible pneumatic vane motor having a stator housing and cylinder provided with air communication ports and a primary outlet symmetrically located relative to the clearance seal portion, and comprising means for preventing recompression of exhaust air. 
     Further objects and advantages of a pneumatic vane motor according to the invention will appear from the following specification and claims. 
    
    
     
       A preferred embodiment of the invention is described below with reference to the accompanying drawings. 
       In the drawings 
         FIG. 1  shows a side view, partly in section, of a reversible vane motor according to the invention in a power nutrunner application. 
         FIG. 2  shows a longitudinal section through a vane motor according to the invention. 
         FIG. 3  shows a cross section along line in  FIG. 2 . 
         FIG. 4 a    shows a rear end view of the motor as shown in  FIG. 2  with the directional valve in one of its operational positions. 
         FIG. 4 b    shows the same end view as in  FIG. 4 a   , but illustrating the directional valve in an alternative operational position. 
         FIG. 5 a    shows a longitudinal section through the motor and illustrates the directional valve in a position wherein one of the air communication ports is connected to the outlet passage whereas one of the auxiliary ports is closed. 
         FIG. 5 b    shows the same view as  FIG. 5 a    but illustrating the directional valve in another position wherein the same air communication port is connected to the pressure air inlet whereas the auxiliary port is open to the outlet passage. 
     
    
    
     The motor shown in the drawing figures is a reversible vane motor comprising the features of the invention. The illustrated motor is incorporated in a pneumatic hand held power nutrunner where a reversible motor is desirable. The motor comprises a stator housing  10  which is formed integral with the nutrunner housing and which has a pressure inlet passage  11  and an exhaust air outlet passage  15 . The inlet passage  11  is controlled by a throttle valve  25  which is maneuverable by a lever  26  supported on the stator housing  10 . Moreover, in the stator housing  10  there is mounted a cylinder  12  with two end walls  13 ,  14 , and a rotor  16  carrying a number of vanes  23   a - e  which define a number of cells  24   a - e . The rotor  16  is rotatable in the cylinder  12  and supported in bearings  17 ,  18  in the end walls  13 ,  14 . In a conventional way the rotor  16  is disposed excentrically relative to the stator housing  10  and forms a clearance seal portion  37  relative to the cylinder  12 . In a way conventional to this type of nutrunners, the rotor  16  is connected to the output end of the nutrunner via reduction gearing  27  and a non-illustrated torque responsive release clutch which is connected to an automatic shut-off valve  34  via rod  35  extending through the rotor centre. 
     In one of the cylinder end wall  13  there is provided two air communication ports  36 ,  19  located at opposite sides of the seal portion  37  and intended for alternative supply of motive air and scavange of exhaust air from the cylinder at alternative directions of rotor rotation. See  FIG. 3 . Diametrically opposite the seal portion  37  the cylinder  11  is provided with a constantly open primary exhaust air outlet  20  comprising a number of openings in the cylinder  12  and communicating with an exhaust chamber  33 . The above described features are well known in prior art reversible vane motors, which means that the symmetrically located air communication ports  36 ,  19  and primary outlet  20  give equal power output and idle speed of the motor in both directions of rotation. 
     A directional valve  21  is rotatively supported at the rear end wall  13  and shiftable between two active positions by a lever  22 . In one of these positions the valve  21  is arranged to duct pressure air from the air inlet passage  11  to one of the air communication ports  36 , and, at the same time, open up the other one of the air communication ports  19  for scavange outlet to the atmosphere via the exhaust air outlet passage  15 . In the other position the directional valve  21  switches the air supply to the other air communication port  19 , whereas the first mentioned air communication port  36  is opened for scavange outlet to the atmosphere. Accordingly, the motor rotation may be altered between alternative directions by the directional valve  21 . 
     A drawback inherent in this type of motor is that when the leading vane  23   a  of one pressurized cells  24   a  on the rotor  16  has passed the primary outlet  20  this cell  24   a  is drained through the primary outlet  20 . However, as the trailing vane  23   b  of this cell  24   a  has passed the primary outlet  20  the cell  24   a  will get smaller in size at continued rotation of the rotor  16 , and the air which has not managed to escape through the primary outlet  20  and which is still entrapped in the cell  24   a  will be recompressed to some extent until the leading vane  23   a  passes the scavange functioning air communication port  19 . This recompression of the entrapped air volume causes a certain resistance to the rotor operation and, hence, an undesirable reduction in power output. 
     In order to avoid such a power loss due to recompression of entrapped exhaust air the motor according to the invention is provided with auxiliary outlet ports  28 ,  29  located at opposite sides of the primary outlet  20  at angular positions between the primary outlet  20  and the air communication ports  36 ,  19 . These auxiliary outlet ports  28 ,  29  comprise two openings each and are individually controlled by the directional valve  21  such that the correct auxiliary outlet port is open for a certain direction of rotation. For that purpose, the directional valve  21  is provided with control members  32   a ,  32   b ,  32   c  which are arranged to alternatively block or uncover not only the air communication ports  36 ,  19  but also the auxiliary outlet ports  28 ,  29  owing to the actual angular position of the valve  21 . 
     For instance, in one of the directional valve  21  positions the auxiliary outlet port  28  which is located at an angular position between the primary outlet  20  and the air communication port  36  is opened to the atmosphere at the same time as the latter is also open to the atmosphere via the exhaust air outlet passage  15 , whereas the other auxiliary outlet port  29  is closed. This means that the angular distance for a travelling cell between the auxiliary outlet port  28  and the scavange point at the air communication port  36  is very short and that recompression of the air entrapped in the cell is substantially avoided. This means a considerably less resistance to the rotor operation and, hence, a higher idle speed and an increased power output. 
     In the other position of the directional valve  21  the auxiliary outlet port  29  located between the primary outlet  20  and the air communication port  19  is opened at the same time as the latter is also open to scavange exhaust air, whereas the auxiliary outlet port  28  is closed. This makes the motor rotate in the opposite direction with the same operational features and power output as in the first described direction. This means that the motor is able to operate with the same operational characteristics in both directions, as in a prior art motor, but at a considerably higher power output and idle speed in both directions. 
     In  FIG. 5 a    the directional valve  21  is illustrated in a position wherein the air communication port  19  is connected to the atmosphere via the outlet passage, whereas the auxiliary outlet port  28  is closed by a control member  32   a  of the valve  21 , and in  FIG. 5 b    the directional valve  21  is illustrated in its opposite position wherein the air communication port  19  is connected to the pressure air inlet passage  11  and the auxiliary outlet port  28  is open to the outlet passage  15 . 
     In operation of the motor in a clockwise rotation the auxiliary outlet port  29  is closed, whereas the auxiliary outlet port  28  is open. During rotation of the rotor  12  drainage of a travelling cell  24   a  starts as before with exhaust air leaving through the primary outlet  20  as the leading vane  23   a  has passed the latter, but before the trailing vane  23   e  has passed the primary outlet  20  the leading vane  23   a  now passes the auxiliary outlet port  28 , which means that the cell  24   a  is still connected to the outlet passage  15  and the atmosphere. Since the distance between the auxiliary outlet port  28  and the scavenging air communication port  19  is very short there will be no closure of the cell  24   a  and consequently no recompression of the exhaust air in the cell. The above operation order is the same for all of the vane defined cells  24   a - e  on the rotor  12 . 
     In the anticlockwise rotation direction of the rotor  12  the auxiliary outlet port  29  is open and the auxiliary outlet port  28  is closed. The leading vane of the cell  24   a  will be vane  23   e , whereas the vane  23   a  will be the trailing vane, and draining of the cell  24   a  starts as the leading vane  23   e  passes the primary outlet  20 . As in the above case, the leading vane  23   e  has reached and passes the open auxiliary outlet port  29  before the trailing vane  23   a  has reached the primary outlet  20 , such that the cell  24   a  will remain connected to the outlet passage  15 . This means that the exhaust air in the cell  24   a  will not be recompressed as the volume of the cell  24   a  diminishes. 
     By the invention it is possible to increase the power of a reversible pneumatic vane motor without increasing the size of the motor. That is particularly important in power tool applications where the overall size and weight of the tool is crucial. 
     It is to be noted that the invention is not limited to the shown and described example but may be freely varied within the scope of the claims. For instance, the exact location and design of the auxiliary outlet ports  28 ,  29  could be varied and adapted to get the most favorable tuning of the motor. Location and size of the auxiliary outlet ports  28 ,  29  may also be varied depending on the number of vanes and cells on the rotor. The fewer the vanes the larger the cells.