Abstract:
A cushioning system for a pneumatic cylinder powered differential engine door opening and closing device for use in passenger transportation vehicles wherein the cushioning initiation point can be adjusted. This cushioning initiation point is adjusted through the use of a linearly adjustable slider member within the large cylinder. The slider is linearly adjustable through the use of an adjustment screw located outside of the pneumatic cylinder and allows one to adjust the time and the mode of the opening/closing of power doors, without disassembly of the cylinder, and significantly improve the safety of the passenger.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates in general to a pneumatic cylinder powered system for opening and closing a vehicle door and, more particularly, to an adjustable cushioning system for a pneumatic cylinder powered differential engine door opening and closing device for use in passenger transportation vehicles. 
     2. Description of Related Art 
     Pneumatic cylinders have been utilized in mechanical systems to convert compressed air into linear reciprocating movement for opening and closing doors of passenger transportation vehicles. An example of this type of door actuating system is shown in U.S. Pat. No. 3,979,790. 
     Typically, pneumatic cylinders used in this environment consist of a cylindrical chamber, a piston, and two end caps hermetically connected to the cylindrical chamber. The end caps have holes extending therethrough to allow the compressed air to flow into and out of the cylindrical chamber, to cause the piston to move in a linear direction, and to apply either an opening or closing force to the vehicle door. 
     Pneumatic cylinder/differential engine systems have also been designed for opening and closing doors of passenger transportation vehicles. Examples of these systems are shown in U.S. Pat. Nos. 4,231,192; 4,134,231; and 1,557,684. 
     It has been determined in some instances that there is a need to slow the movement of the piston at the end of the stroke when opening and/or closing the door. A known technique for slowing this stroke is by restricting the flow of the exhaust air out of the cylindrical chamber. This is commonly known as cushioning the movement of the piston. 
     A known cushioning system for a pneumatically powered differential engine door opening device is shown schematically in  FIG. 1 . The differential engine includes a housing comprising a large diameter cylinder  1  and a small diameter cylinder  2 , closed at their ends by caps  6  and  7 . A large diameter piston  4  is installed in the large cylinder  1  and a small diameter piston  5  is installed in the small cylinder  2 . A toothed rack  16  is attached to and extends between the large piston  4  and small piston  5 . The toothed rack  16  is engaged with a pinion gear  15 . The pinion gear  15  is, in turn, connected to a shaft  14  which drives the mechanism for closing and opening the vehicle door. Linear movement of pistons  4  and  5  causes linear movement of the toothed rack  16 . This linear movement is converted into rotational movement of the pinion gear  15  and shaft  14  causing opening and/or closing of the vehicle door as viewed in  FIG. 1 , movement of the pistons  4  and  5  to the left causes an opening of the doors and movement of pistons  4  and  5  to the right causes a closing of the doors. 
     As shown in  FIG. 1 , the right outer side of the small cylinder  2  is connected through a hole  19  in the cap  7  to a reservoir of compressed air that constantly applies a positive pressure to the small piston  5 . As shown in schematically in  FIG. 2 , the cap  6 , attached to the outer end of the large cylinder  1 , has a chamber  17  including holes  9  and  10  which are connected through a port yy to a three-way valve, which provides connections to a source of compressed air and to an exhaust. During closing of the doors, hole  9  is connected to a source of pressurized air and exhaust hole  10  is closed. Because the surface area of piston  4  is greater than the surface area of piston  5 , the pistons  4 ,  5  move to the right, rotating the pinion gear  15 /shaft  14  in a counter-clockwise direction. During an opening stroke, holes  9  and  10  are connected to an exhaust, causing the air to flow out of large cylinder  1 . Because the small piston  5  is constantly attached to a source of positive air pressure, the exhausting of the air pressure from within the large cylinder  1  causes the pistons  4 ,  5  connected by toothed rack  16  to move toward the left within the large and small cylinders  1 ,  2 . This movement to the left rotates the pinion gear  15 /shaft  14  in a clockwise direction to initiate opening of the doors. 
     In this design, cushioning at the end of the opening piston stroke occurs through the use of a small hole  11  having a diameter that is substantially smaller than that of opening xx. This hole  11  is located at a side surface of chamber  17  which provides connection to the inside volume of the chamber of the large cylinder  1 . A cylindrical sealing disk  8  is installed between the piston  4  and cap  6  and is supported between two springs  12  and  13 . The leftward movement of the pistons  4 ,  5  causes compression of springs  12  and  13  bringing the disk  8  into contact with a face  17   a  of chamber  17  forming a seal with the chamber face  17   a . Once this seal is achieved, air can no longer exit the chamber of the large cylinder  1  through opening xx into chamber  17  and thus can only exit through hole  11  into chamber  17 . Since the diameter of hole  11  is smaller than the diameter of opening xx, the flow of the air out of the large cylinder  1  is restricted, consequently slowing down the speed of the opening piston stroke movement to the left and achieving a cushioning effect during opening of the doors. 
     U.S. Pat. No. 2,343,316 teaches a pneumatic cylinder/differential engine for power operated doors wherein cushioning occurs near the end of the piston stroke during closing of the doors in order to prevent slamming. In this device, cushioning occurs when a sealing disk contacts with the surface of a cap, causing the exhaust air to flow through a small hole which significantly reduces the rate of flow of the exhaust air from the cylinder housing and decreases the linear speed of the piston. 
     While the concept of cushioning the end of a piston stroke in a door opening or door closing cycle has been documented, a disadvantage of these systems is that cushioning is always initiated at the same point in the movement of the piston (or at the same position of the piston), and because the linear movement of the piston is transferred to the rotational movement of the output shaft and rotation or linear movement of the powered doors, the doors will always begin to slow at the same point in its path. It is difficult and cost prohibitive to disassemble the pneumatic cylinder, remove the existing components of the cushioning system, replace the spring system supporting the sealing disks, and then reassemble the pneumatic cylinder. Furthermore, if one should select the wrong tensioned spring system, then the process of disassembling/reassembling must be repeated. Another disadvantage of these known systems is that it is impossible to finely adjust the cushion initiation point in the broad range of the linear movement of the piston or rotational movement of the output shaft and, respectively, linear or rotational movement of the power doors. 
     SUMMARY OF THE INVENTION 
     It is therefore an aspect of the invention to provide a cushioning system wherein the cushioning initiation point can be adjusted. It is a further aspect of the invention to adjust the time and the mode of the opening/closing of power doors. It is another aspect of the invention to provide a system that allows for fine adjustment of the cushioning initiation point without disassembly of the cylinder. It is still another aspect of the invention to provide a system wherein the cushioning initiation point can be adjusted so that the duration of the cushioning of the piston movement can be adjusted as needed. It is yet another aspect of the invention to provide an adjustable cushioning system wherein adjustment can be accomplished from outside of the cylinder. 
     Accordingly, the present invention is directed to a cushioning system for use with a pneumatic cylinder/differential engine door operator for driving a door between open and closed positions wherein the differential engine includes a large cylinder aligned with a small cylinder and a pair of associated pistons having a rack and pinion assembly connected therebetween and controlled by movement of the associated pistons. The cushioning system includes a large cap for sealing the large cylinder and a slider extending through the large cap and into the large cylinder. The slider is in fluid contact with an interior portion of the large cylinder. At least a first port having a first diameter extends through a first wall portion of the slider. At least a second port having a second diameter smaller than the first diameter extends through a second wall portion of the slider. The second sidewall portion is at a remote location from the first sidewall portion. A valve is associated with the slider for applying fluid through the first and second ports into the large cylinder during a door closing cycle and exhausting fluid through the first and second ports from within the large cylinder during a door opening cycle. A closing device is provided for sealing the slider near the end of a door opening cycle and eliminating the flow of exhaust through the first port so that the flow of exhaust only occurs through the second port and slows the forward movement of the pair of pistons. An adjusting device adjusts the linear extension of the slider into the large cylinder and adjusts the distance between the closing device and the slider for one of increasing and decreasing the amount of time before sealing of the slider occurs to adjust the point at which cushioning occurs during the door opening cycle. 
     The present invention is also directed to an adjustment assembly adapted for use with a cushioning system for a pneumatic cylinder/differential engine door operator. The adjustment assembly includes a cap for sealing a cylinder. A slider is mounted to the cap and into the cylinder. This slider is in fluid contact with an interior portion of the cylinder. A closing device seals the slider near the end of a door opening cycle, preventing the flow of exhaust through a first port so that the flow of exhaust occurs through a second port. This slows the forward movement of at least one piston. An adjusting device adjusts the linear extension of the slider into the cylinder and adjusts the distance between the closing device and the slider for one of increasing and decreasing the amount of time before sealing of the slider occurs to adjust the time at which cushioning occurs during the door opening cycle. This adjusting device includes a screw mounted to the slider and allows for the adjustment of cushioning cycle time without disassembling and/or replacing of parts within the pneumatic cylinder/differential engine door operator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a pneumatic cylinder/differential engine of the prior art; 
         FIG. 2  is a view of the porting arrangement of the large cylinder end cap of the pneumatic cylinder/differential engine shown in  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of the pneumatic cylinder/differential engine according to a first embodiment of the present invention at the start of a door opening cycle; 
         FIG. 4  is a cross-sectional view of the pneumatic cylinder/differential engine of  FIG. 3  at the cushioning initiation point near the end of the door opening cycle; 
         FIG. 5  is a cross-sectional view of the door opening and closing speed adjustment screws of the present invention; 
         FIG. 6  is a perspective view of the pneumatic cylinder/differential engine of the present invention; and 
         FIG. 7  is a cross-sectional view of the pneumatic cylinder/differential engine according to a second embodiment of the present invention at the start of a door opening cycle. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     For purposes of the description hereinafter, the terms “upper”, “lower”, “right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, “lateral”, “longitudinal” and derivatives thereof shall relate to the invention as it is oriented in the drawing figures. However, it is to be understood that the invention may assume various alternative variations, except where expressly specified to the contrary. It is also to be understood that the specific devices illustrated in the attached drawings, and described in the following specification, are simply exemplary embodiments of the invention. Hence, specific dimensions and other physical characteristics related to the embodiments disclosed herein are not to be considered as limiting. 
     Reference is now made to  FIGS. 3 and 4 , which show cross-sectional views of the pneumatic cylinder/differential engine according to a first embodiment of the present invention, generally indicated as  20 , at the start of the door opening cycle and near the end of the door opening cycle where cushioning begins. The pneumatic cylinder/differential engine comprises a large cylinder  22  and a small cylinder  24  which are aligned with one another. A rack and pinion gear mechanism housing  26  is positioned in alignment between the large cylinder  22  and small cylinder  24 . A large piston  28  is contained within the large cylinder  22  and a small piston  30  is contained within the small cylinder  24 . A toothed rack  32  is connected via connecting screws  29   a ,  29   b  between the large piston  28  and small piston  30 . Pinion gear  34  is engaged with toothed rack  32  and is connected to an output shaft  36  such that linear movement of the large piston  28  and small piston  30  results in rotational movement of the pinion gear  34  and output shaft  36  with respect to the toothed rack  32  to cause one of an opening cycle or a closing cycle of the door (not shown). A large cylinder cap  38  is positioned at one end of the large cylinder  22  and a small cylinder cap  40  is positioned at one end of the small cylinder  24 . An opening  42  is provided in the small cylinder cap  40 . This opening  42  is connected to a source of fluid pressure which applies a constant positive pressure of approximately 90-120 psi to the small piston  30 . The large cylinder cap  38  is attached to a three-way valve (not shown) via a fitting  44 . This valve is capable of applying a positive fluid pressure into the large cylinder  22  and against the large piston  28 , thereby forcing the large piston, toothed rack  32  and small piston  30  to move linearly toward the right as shown in  FIG. 3 , and causing the pinion gear  34  to rotate in a counter-clockwise direction to initiate a door closing cycle. When a door opening cycle is desired, the valve allows air to be exhausted from within the large cylinder  22 , thereby allowing the positive fluid pressure applied to the small piston  30  to linearly move the small piston  30 , toothed rack  32  and large piston  28  to the left as shown in  FIG. 4 , and causing the pinion gear  34  to rotate in a clockwise direction, opening the vehicle door. As shown especially in  FIGS. 5 and 6 , the large cylinder cap includes a cushioning speed adjustment screw  46 , a door closing speed adjustment screw  47 , and a door opening speed adjustment screw  48 . Appropriate O-rings  49   a ,  49   b  are provided in the device to achieve fluid tight seals of the individual components in the large cylinder cap  38 . 
     The cushioning system of the invention comprises a cup-shaped slider  50 , having a back wall  52 , a pair of sidewalls  54  and a front opening  56 . The slider  50  is positioned within a cup-shaped aperture  58  in the large cylinder cap  38 . At least a first exhaust port  60 , having a first predetermined diameter, extends through a first wall of the slider  50 . Preferably the first exhaust port  60  extends through the back wall  52  of the slider  50  to exhaust air during the door opening cycle from within the large cylinder  22  into a trap portion  59  of aperture  58  located between a back portion of the slider  50  and the large cap  38  and subsequently out of the device through fitting  44 . More than one first exhaust port  60  may be provided through this back wall  52  of the slider  50 . At least a second exhaust port  62 , having a second predetermined diameter which is smaller than the first predetermined diameter of the first exhaust port  60 , extends through a second wall portion of the slider  50 . This second wall portion preferably comprises one of the pair of sidewalls  54  and is at a remote location from the first sidewall portion. The slider  50  is seated within the aperture  58  such that only a portion of the sidewalls  54  of the slider are contacted by sidewalls  61  of the aperture  58 . Sidewalls  61  do not extend past and/or seal the second exhaust port  62  in the sidewall  54  of the slider  50 . 
     A closing device  64 , typically in the form of a plate, is mounted by a biasing system, generally illustrated as  65 . Preferably, this biasing system  65  comprises a pair of springs  66 ,  68 , between which the closing device  64  is mounted. A first spring  66  has a first end  66   a  associated with and/or secured to cylinder cap  38  and a second end  66   b  secured to the closing device  64 . A second spring  68  includes a first end  68   a  secured to the closing device  64  and a second end  68   b  associated and/or secured to the large piston  28 . This closing device  64  is secured between the first and second springs  66 ,  68  by any well known securing member  70 , such as a screw, post and the like. During an opening cycle, movement of the large piston  28  causes first and second springs  66 ,  68  to compress and bring closing device  64  into contact with the front opening  56  of the slider  50  to initiate a cushioning cycle near the end of the opening cycle piston stroke. 
     The contact of the closing device  64  with the opening  56  of the slider seals this opening  56  against the flow of exhaust air out of the large cylinder  22  through the first exhaust port  60 . The flow of the exhaust air is now limited to escape through the second/smaller exhaust port  62  as this is the only exhaust port in fluid contact with the interior portion of the large cylinder  22 . This sealing of opening  56  significantly slows down the forward movement of the piston stroke near the end of the opening cycle. 
     The slider  50  is attached to an end of a cushioning initiation point adjustment screw  72 . Accordingly, should one require a longer or shorter cushioning cycle, slider  50  may be moved linearly within the large cylinder  22  closer to or farther away from the closing device  64 . This adjustment of the cushioning cycle time/initiation point can occur without disassembling the pneumatic cylinder and without replacing springs  66 ,  68  with springs having different lengths and/or tensions. Additionally, the cushioning initiation point adjustment screw  72  may be readily accessed outside the pneumatic cylinder for easy adjustment and/or fine tuning of the initiation point with respect to closing device  64 . 
     The magnitude of the linear motion of the slider  50  can be up to 50% of the length of the linear stroke of the large piston  28 . Connection between the slider  50  and cushioning initiation point adjustment screw  72  can be made, for example, by a retaining ring  74  mounted on the adjustment screw which enters through a port  76  in the back wall  52  of the slider  50 . 
     The cushioning initiation point is defined by the moment when closing device/plate  64  seals the face or front opening  56  of the slider  50 . This moment can be adjusted by moving the slider  50  along the axis of the pneumatic cylinder so that the closing device  64  will contact the slider front opening  56  earlier in relation to the movement of the piston  28 , or later, at the end of the movement of the piston  28 . This linear adjustment is provided by rotation of the cushion initiation point adjustment screw  72 . In practice, the adjustment of the cushioning initiation point depends on the range of motion of the slider  50 , and cushioning can be adjusted to start at a point between 30 to 90% of the full rotation of the output shaft. The adjustment of the cushioning initiation point enables the field adjustment cycle of the opening/closing of the powered doors without disassembly of the cylinder. 
     The invention can be clarified by an analysis of the air flow and piston movement in different cycles of the cylinder/engine. Opening  42  of the small cylinder  24  is always connected to the source of compressed air (100-120 psi). Fitting  44  connects port  76  to a three-way valve, allowing connection of the port  76  to compressed air or to exhaust (atmospheric pressure) for removing air. 
     During a door closing cycle, port  76  associated with fitting  44  is connected to the source of the compressed air. A ball  78 , as shown in  FIG. 6 , closes a connecting hole  80  of the door opening speed adjustment screw  48  so air can enter into the large cylinder  22  only through the hole  82  of the door closing speed adjustment screw  47 . Compressed air enters into the trap  59  of the cap  38  and flows through the ports  60  of the slider  50  into the cup-shaped portion of the slider. At the beginning of the closing cycle, this cavity of the slider  50  is sealed by the closing device or sealing disk  64  attached to a retainer  84 . The pressure on the sealing disk  64  forces movement of the sealing disk  64  and retainer  84  to the right, opening the front opening cup  56  of the shaped slider  50 , and allowing compressed air to enter into the cavity of the large cylinder  22 . Because of the difference in the diameters of the pistons  28  and  30 , the force acting on piston  28  is greater than the force acting on piston  30 , and as a result pistons  28  and  30 , connected by the rack  32 , move to the right, causing the rotation of the pinion gear  34  in a counter-clockwise direction. The output shaft  36  drives the power door opening/closing mechanism. Rotation of the shaft  36  in a counter-clockwise direction causes closing of the power doors. Air flow into the cylinder, or door closing speed, can be adjusted by rotation of the screw  47 . The movement of the pistons stops when the right side of the piston  28  contacts the surface of the pinion gear housing  26 . 
     The ends of the springs  66  and  68  are attached to the retainer  84 . The opposite end of the spring  66  is located in a cavity  86  of the large cylinder cap  38 , and the opposite end of the spring  68  is located in a cavity  88  of the large piston  28 . This arrangement allows the retainer  84 , and accordingly sealing disk or closing device  64  attached to the retainer  84 , to move between piston  28  and cap  38 . 
     When the piston  28  moves to the right, the retainer  84  also moves to the right, and the gap between sealing disk  64  and opening  56  of the slider  50  increases. However, the movement of the retainer  84  does not exactly follow the movement of the piston  28  because the coefficient of elasticity of spring  66  is greater than the coefficient of elasticity of spring  68 , and because the lengths of springs  66  and  68  are different. 
     During a door opening cycle, port  74  is connected through fitting  44  to the exhaust (atmospheric pressure). The opening cycle consists of two parts: opening without cushioning and opening with cushioning. 
     Opening of the power door without cushioning: When three-way valve connects the port  76  to the exhaust, the pressure gradient causes the ball  78  to move and open the hole  80 , allowing air flow through the cavity to the port  76 . The flow rate through hole  80 , and hence the door opening speed, can be adjusted by screw  48 . The air flows out of the cavity of the large cylinder  22  through the ports  60  in the slider wall into the cavity or trap  59  between slider  50  and cap  38 , and through the holes  80  and  82  to the port  76 . At the same time, air can flow into trap  59  through the small port  62  and a hole  90  of the cushion speed adjustment screw  46 . However, the diameter of the port  62  is substantially less than the diameter of the holes  80  and  82 . Therefore, the flow of the air through the holes  80  and  82  is significantly greater than the flow through the port  62 . As a result, the pressure in the cavity of the large cylinder  22  quickly decreases, causing the force acting on the small piston  30  to exceed the force acting on the large piston  28 , and pistons  30 ,  28  and rack  32  start moving to the left. The linear movement of the rack  32  causes the clockwise rotation of the pinion gear  34  and output shaft  36  and, accordingly, the opening of the doors. The movement of the piston  28  will cause the compression of the spring  68  and will cause the movement of the retainer  84  to the left. The rapid linear motion of pistons  28  and  30  continues until (a) the sealing disk  64  contacts with the front opening  56  of the slider  50  and (b) the force of the spring  68  acting on retainer  84  becomes sufficient to seal front opening  56  of the slider  50  from the cavity of the large cylinder  22 . Because of the decrease in air flow out of the cylinder, the movement of the piston slows and cushioning is initiated. 
     Opening of the power door with cushioning: As described above, the movement of the piston  28  causes the compression of the spring  68  and the sealing of opening  56  of the slider  50 . As a result, the air enters the trap  59  of the cap  38  only through the passage created by the port  62  and hole  90 . The air flow through the hole  90  can be increased or decreased by adjusting screw  46 . Because the flow rate through the ports  62  and  90  is significantly less than the flow rate through the port  60  of the slider  50 , the movement of the piston  28  is significantly slowed or cushioned, which causes the cushioning of the powered doors at the end of the opening cycle. 
     Reference is now made to  FIG. 7 , which shows a cross-sectional view of the pneumatic cylinder/differential engine according to a second embodiment of the invention. In this embodiment, biasing system, generally illustrated as  165 , includes a pair of springs  166 ,  168  between which the closing device  64  is mounted. This mounting is achieved by any well known means such as discussed in detail above with respect to the  FIG. 3  embodiment. In this second embodiment, a first spring  166  includes a first end  166   a , which is located within and supported by the slider  50 . First spring  166  also includes a second end  166   b  which is secured to the closing device  64 . A second spring  168  includes a first end  168   a  secured to closing device  64  and a second end  168   b  associated with and/or secured to the large piston  28 . The slider  50  is attached to the adjustment screw  72  by any well-known attachment means, for example, a nut  95  and a lock-washer  97 . During a door opening cycle, movement of the large piston  28  causes first and second springs  166 ,  168  to compress and bring the closing device  64  into contact with the front opening  56  of the slider  50  to initiate a cushioning cycle near the end of the opening cycle. As discussed in detail above, adjustment screw  72  linearly adjusts the distance between the slider  50  and the closing device  64  to adjust the length of time of the cushioning cycle. This adjustment is readily achieved without the time consuming and costly process of disassembling the pneumatic cylinder and replacing of the first and second springs  166 ,  168  with springs having different lengths and/or tensions. 
     Although the invention has been described in detail for the purpose of illustration based on what is currently considered to be the most practical and preferred embodiments, it is to be understood that such detail is solely for that purpose and that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover modifications and equivalent arrangements that are within the spirit and scope of this description. For example, it is to be understood that the present invention contemplates that, to the extent possible, one or more features of any embodiment can be combined with one or more features of any other embodiment.