Patent Publication Number: US-7594466-B2

Title: Actuator with a protective sleeve for a piston

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to the field of hydraulic or pneumatic actuators. More specifically, it concerns a protective sleeve for hydraulic or pneumatic actuator. 
   BACKGROUND OF THE INVENTION 
   Hydraulic and pneumatic actuators are well known in the art. Indeed, a conventional hydraulic or pneumatic actuator normally consists of a hollow cylinder and a piston able to fit sealingly therein and adapted to translate relative to the cylinder in an axial direction between an open position and a closed position. The piston sealingly engages the inner surface of the cylinder so as to create a chamber whose volume varies with the position of the piston. A pressurized fluid can be supplied to, or withdrawn from, the chamber in order to force and change in the chamber&#39;s volume and thereby change the position of the piston relative to the cylinder. 
   A common use for such an actuator is as a hydraulic actuator for heavy machinery, such as a grapple, an excavator or the like. Such heavy machinery run large gasoline or diesel powered engines to power hydraulic pumps, which in turn pressurise hydraulic fluid. This machinery often comprises large mechanical arms, or booms, driven by externally mounted hydraulic actuators. When the actuator is extended, the piston is exposed to an environment where it is vulnerable to damage which could compromise the functioning of the hydraulic actuator. In addition, the piston may simply become dirty as unwanted contaminants, metallic dust particles for example, are deposited on the surface of the piston. Repeated contraction and expansion of the actuator can cause these contaminants to enter into the chamber thereby damaging the piston seal and the inner surface of the cylinder. Both such aspects of exposure have a detrimental effect on the functioning of the actuator and can lead to actuator failure. 
   The following U.S. and Canadian patents disclose prior art devices for protecting actuator pistons. 
   U.S. Pat. No. 4,936,193, issued Jun. 26, 1990 to STOLL, describes a protective device comprising a series of cylindrical guard sections operable to protect a piston rod when in an open position. The first of the series of guard sections is fixed to the extremity of the cylinder from which protrudes the piston rod, and the last of the series is fixed to the outer extremity of the piston rod itself. The sections decrease in diameter in a telescopic manner, such that they may be stowed in an overlapping arrangement, one inside another, in a closed position and extended together in an open position. Each guard section comprises an inwardly extending flange at its outer extremity and an outwardly extending flange at its inner extremity. In use, the inwardly extending flange engages the outwardly extending flange of the next guard so as to prevent the complete drawing apart of the individual guard sections in the open position. However, this design is relatively complex comprising a number of sliding elements and engagements. 
   U.S. Pat. No. 5,386,652 issued to RAMUN, U.S. Pat. No. 6,843,005 issued to CLAPPER, U.S. Pat. No. 5,152,351 issued to RIEGER and Canadian patent No. 1,176,915 issued to MARTIN all disclose actuator protection devices for heavy machinery wherein a piston protector is attached to an outside extremity of a piston rod and is operable to cover at least portion of the exposed piston rod when the cylinder is in an open position. 
   However, while each of these devices may aid in protecting a piston rod in an exposed open position, there is still a continued need for an improved actuator for heavy machinery that overcomes at least some of the above-mentioned disadvantages. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide an improved actuator for heavy machinery. 
   According to a first aspect, that object is achieved with an actuator for heavy machinery including a cylinder, a piston and a protective sleeve. The cylinder forms a chamber for receiving a fluid, and includes an external flange extending radially and outwardly from the cylinder. The piston is operable to translate axially relative to the cylinder between an open position and a closed position, and includes a first extremity positioned outside the cylinder and a second extremity positioned within the chamber. The second extremity sealingly engages the chamber. The protective sleeve is movable with the piston and protects the same in the open position. The protective sleeve is also operable to overlap at least a portion of the cylinder in the closed position. The protective sleeve further includes an internal flange extending radially and inwardly from the protective sleeve. The internal flange is positioned for abutting the external flange when the piston is in the open position. This abutment limits the axial translation of the piston out of the cylinder. 
   As can be appreciated, the protective sleeve of the present design not only protects the piston cylinder when exposed, but it also advantageously provides a simple and relatively inexpensive construction which allows a limitation of the translation of the piston out of the cylinder. Indeed, thanks to the internal flange which cooperates with the external flange on the cylinder, the piston is prevented from falling out of the cylinder. This additional functionality advantageously simplifies the overall design of the hydraulic actuator and provides additional structural integrity and operability. 
   For the sake of clarity of the following description, it is worth mentioning that as discussed herein the expansion and contraction of the actuator will be described from the frame of reference of a fixed cylinder wherein the actuator expands in a forward direction and retracts in a rearward direction. In addition, as used herein the open position refers to the most forward position or expanded position of the piston where the volume of the chamber is at its maximum, and similarly the closed position refers to the most rearward position or retracted position of the piston where the chamber of the cylinder is at its minimum. Also for a sake of clarity, the first and second extremities of the piston and cylinder, will be referred to as the front and rear extremities respectively. 
   In accordance with a first preferred variant, the piston comprises an engagement portion at the front extremity for engagement with a driven article, the protective sleeve having a first end attached to the engagement portion. The first end will also be referred to as the front end. 
   Preferably, the engagement portion comprises a fixture for receiving a pin connection, and the protective sleeve comprises an axial flange extending from the front end, the axial flange engaging the fixture, thereby retaining the protective sleeve to the piston. 
   In accordance with another preferred variant, the protective sleeve comprises a first end wall extending radially at the first end thereof, the first end wall comprising a first aperture for receipt of the piston. More preferably, the protective sleeve comprises a second end wall extending radially at a second end of the sleeve, the second end wall having an aperture for passage of the cylinder. The second end, the first and second end walls, the first and second apertures will similarly be referred to as the rear end, the front and rear end walls, and the front and rear apertures, respectively. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and advantages of the invention will become apparent upon reading the following description and upon referring to the drawings in which: 
       FIGS. 1A and 1B  are side views of a portion of a grapple provided with an actuator according to a preferred embodiment of the present invention, the actuator being shown in a closed position in  FIG. 1A  and in an open position in  FIG. 1B . 
       FIG. 2  is a perspective view of the actuator of the previous Figures in an open position. 
       FIG. 3  is a cross-sectional side view of the actuator shown in  FIG. 2 . 
       FIG. 4  is a side view of the actuator of  FIG. 2  in a semi-open position, and with one half of the protective sleeve not illustrated. 
       FIG. 5  is a bottom view of the actuator shown in  FIG. 4 . 
   

   While the invention will be described in conjunction with an example embodiment, it will be understood that this is not intended to limit the scope of the invention to such an embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included as defined in the appended claims. 
   DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
   In the following description, similar features in the drawings are given similar reference numerals, and in order to lighten the figures, some elements may not be referred to in some figures if they were already identified in a precedent figure. 
   Referring to  FIGS. 1A and 1B , there is shown generally a portion of a grapple for handling scrap and the like. The grapple has a shaft  15  and a plurality of grapple tines  13  pivotally fixed to the end of the shaft  15 , although for clarity only one tine  13  is shown here. By means of the actuator  10  which interconnects the grapple tine  13  to the shaft  15 , the grapple tine  13  can be pivoted between a retracted position, as seen in  FIG. 1A , and a gripping position, as seen in  FIG. 1B . As is common, pressurised hydraulic fluid is supplied to the actuator  10  in order to drive its expansion and contraction. 
   As will be apparent to one of ordinary skill in the art, such an actuator  10  can be provided to actuate many other hydraulically or pneumatically driven components associated with heavy machinery, such as grapple tines  13  and the like. Such equally suitable applications will therefore not be discussed further herein. 
   Referring now to  FIGS. 2 to 5 , the actuator  10  according to a preferred embodiment of the invention comprises a cylinder  12 , a piston  14  and a protective sleeve  16 . The piston  14  and sleeve  16  are operable to slide axially in unison with respect to the cylinder  12  between the open position, as seen in  FIGS. 1B ,  2  and  3 , and the closed position, as seen in  FIG. 1A . The hollow interior of cylinder  12  receives the piston  14  for forming an inner chamber  18 . In operation, the actuator  10  extends and contracts as fluid is either supplied or removed therefrom. 
   The piston  14  has a front extremity  20  which extends outside of the cylinder  12  through an entry end  28  of the cylinder  12 , and a rear extremity  22  located within the chamber  18  which sealingly engages the inner surface  24  of the cylinder  12  at a sealing engagement  19 . At the front extremity  20  is an engaging portion  34  adapted for engagement with a driven article such as a tine  13  of the grapple shown in  FIGS. 1A and 1   b . A rear engaging portion  35  is also provided at the rear end  37  of the cylinder  12  in order to connect the actuator  10  to a corresponding component of a grapple such as the shaft  15  in  FIGS. 1A  and  1 B. In the preferred embodiment illustrated, both engagement portions  34  and  35  are provided with a hole  36  for pivotally connecting the driven article to the piston  14 , or the cylinder  12  to the shaft  15 , by means of a pivot rod  39 . 
   The axial position of the piston  14  with respect to the cylinder  12  is defined by the closed volume of the chamber  18 . In use, hydraulic fluid is fed into the chamber  18  thereby expanding it and forcing the piston  14  outwards. Alternatively, hydraulic fluid may be removed from the chamber  18  thereby decreasing its volume and forcing the piston  14  inwards. 
   In addition, and as will be apparent to one of ordinary skill in the art, a secondary chamber may further be provided within the cylinder  12  located on the opposite side of the sealing engagement  19  to the chamber  18 . Formed within the cylinder  12 , around the piston  14  and between the engagement  19  and the entry end  28 , such a secondary chamber can be used in conjunction with the chamber  18  to axially translate the piston  14 . As is well known in the art and will not be discussed further herein, a pair of opposed chambers work together by feeding fluid into one, while removing fluid from the other, and vice versa in order displace the piston by the application of both positive and negative pressure in both directions of motion. 
   The protective sleeve  16  is provided for protecting the exterior surface of the piston  14  from any unwanted and potentially damaging debris or impact. The protective sleeve  16  comprises opposite front and rear ends  32  and  46 , the front end  32  being proximate the front extremity  20  of the piston  14 . An axial flange  38  extends axially outward from the front end  32  and attaches to the engaging portion  34  of the piston  14 . This attachment is firm and enables the sleeve  16  to follow the motion of the piston  14 , in other words to move in synchronism with the piston  14 . With the specific reference to  FIG. 5  illustrating the actuator  10  with half of the protective sleeve  16  removed, the protective sleeve  16  preferably comprises a first axially extending flange  38  as shown and an equivalent second flange  38  extending axially from the removed half of the sleeve  18 . Combined, the pair of axially extending flanges  38  are operable to sandwich the engaging portion  34  of the piston  14 . 
   In the closed position, the protective sleeve  16  overlaps at least a portion of the cylinder  12 , preferably the whole length of the cylinder  12 , as shown in  FIG. 1A . The piston  14  and the cylinder  12  are preferably substantially the same length such that the travel of the piston  14  may be maximized. Preferably, the protective sleeve  16  is operable to cover the entirety of the outer surface of the piston  14  when in the open position, as shown in  FIGS. 1B and 3 . However, it is to be noted that other arrangements whereby the protective sleeve  16  covers only a portion of the cylinder  12  are well within the scope of the invention. The protective sleeve  16  is of a larger diameter than the cylinder  12  such that it may envelop the cylinder  12  in, for example, a semi-contracted position as seen in  FIGS. 4 and 5 . 
   Further provided on the cylinder  12  is an external flange  26  extending radially and outwardly from the cylinder  12 . Preferably, the external flange  26  is located proximate the entry end  28  of the cylinder  12 . The protective sleeve  16  further comprises a corresponding internal flange  30  extending radially and inwardly and that is positioned for abutting the external flange  26  of the cylinder  12  when the piston  14  is in the open position. Preferably, the internal flange  30  is located at the rear end  46  of the protective sleeve  16 . This abutment of the external and internal flanges  26  and  30  creates a mechanical stop limiting the axial translation of the piston  14  out of the cylinder  12 . Preferably, the external flange  26  of the cylinder  12  is a collar surrounding the majority of the circumference of the cylinder  12 , although it will be noted that other embodiments are well within the scope of the present invention. 
   While the surface of the protective sleeve  16  protects the piston  14  from a direct impact, the exterior surface of the piston  14  cannot be entirely sealed from airborne debris and contaminants. A front end wall  40  is provided at the front end  32  of the protective sleeve  16  for shielding the interior of the protective sleeve  16  against the entry of such debris and contaminants. The front end wall  40  comprises an aperture  42  through which the piston  14  passes. In the preferred embodiment illustrated, the internal flange  30  also functions as a rear end wall in that it not only abuts the external flange  26  but it also functions to block the entry of a majority of the airborne debris and contaminants. Preferably, the external flange  36  further comprises a collar  44  having an aperture  48  for closely surrounding the sleeve  16  and allowing it to pass around the cylinder  12  as the sleeve  16  translates between the open and closed positions. 
   Because the front and rear end wall  40  and the collar  44  are provided primarily for limiting the entry of potentially damaging airborne particles, they do not need to be built as robustly as the external and internal flanges  26  and  30  which provide mechanical stopping for the actuator  10 . 
   The dimension of the rear aperture  48  of the sleeve  16  is necessarily larger than the outer diameter of the cylinder  12  so that the sleeve  16  may move without unwanted contact and frictional interference between the rear end wall  44  and the outer surface of the cylinder  12  during expansion and contraction of the actuator  10 . The dimension of the rear aperture  48  is therefore preferably as close to the diameter of the cylinder  12  as possible so as to minimise the entry of debris and contaminants inside the protective sleeve  16 , while allowing the sleeve  16  and the cylinder  12  to move freely. 
   The protective sleeve  16  is preferably formed of two formed pieces of sheet metal  52  attached together at flanges  54 , on opposite sides of the apparatus  10 . 
   As being now better appreciated, the present invention is an improvement and presents several advantages over other related devices known in the prior art. Indeed, the present invention is particularly advantageous in that it provides a protective sleeve  16  operable to both protect the exposed piston  14  from damage and contamination when the actuator  10  is in an open position, and it limits the travel of the piston  14  within the cylinder  12 . This advantageous second operability removes the necessity of a mechanical stop within the cylinder  12  as in conventional actuators by placing it outside the cylinder over a larger area, thereby enhancing the structural integrity and simplifying the construction of the actuator  10 . Such simplifying in turn lowers the cost of production and increases the durability and robustness of the actuator  10 . 
   The above description of a preferred embodiment of the present invention should not be read in a limitative manner as refinements and variations are possible without departing from the spirit of the invention. The scope of the invention is defined in the appended claims and their equivalents.