Abstract:
A pulley assembly operable in connection with a tensioner assembly is provided for tensioning a belt. The pulley assembly includes one or more elements for sealing the pulley to protect the pulley assembly in harsh environments. For instance, the pulley assembly may include one or more shields for protecting the pulley from contaminants entering the interior of the pulley assembly that can lead to premature failure.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the field of devices for tensioning belts. In particular the present invention relates to an improved belt tensioner adapted for use in harsh environments. More specifically, the present invention provides a belt tensioner having a pulley with features that protect against contamination and wear in harsh operating environments. 
     BACKGROUND 
     Belts are used in a variety of applications to transmit power. During use, the belt may tend to elongate due to the tensile forces on the belt. The elongation slackens the belts, which leads to slippage, so that the belt does not transmit the power as efficiently. 
     To reduce the detrimental effects of belt elongation, tensioners are commonly used to reduce the slack so that a belt continues to efficiently transfer power even as the belt elongates. Specifically, a pulley attached to a tensioner engages the belt. The tensioner biases the pulley into engagement with the belt to reduce the slack. Although tensioners are effective in eliminating the slack, the known tensioners may face premature failure when operating in harsh environments. 
     SUMMARY OF THE INVENTION 
     In order to overcome the problems associated with premature failure of tensioner assemblies operating in harsh environments, the present invention provides a tensioner assembly adapted to reduce the effects of the environment. Specifically, a pulley assembly is provided, which is operable in connection with a tensioner operable to tension a belt. The tensioner includes an arm and a biasing element for biasing the arm. 
     The pulley is configured to engage a belt, and has a bore that has an inner opening and an outer opening. The pulley also includes a bearing connected with the bore of the pulley. An outer shield encloses the outer opening of the pulley bore to seal the outer opening to impede migration of contaminants through the outer opening. Optionally, the pulley also includes an inner shield for impeding migration of contaminants through the inner opening of the pulley bore. Further, the inner shield optionally includes a flange extending radially outwardly to overlap the inner opening of the bore. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The foregoing summary and the following detailed description of the preferred embodiments of the present invention will be best understood when read in conjunction with the appended drawings, in which: 
         FIG. 1  is a partially exploded perspective view of a tensioner assembly with a sealed pulley; 
         FIG. 2  is an exploded perspective view of the sealed pulley illustrated in  FIG. 1 ; 
         FIG. 3  is a sectional view of the sealed pulley illustrated in  FIG. 2 ; and 
         FIG. 4  is a sectional view of the tensioner assembly with sealed pulley illustrated in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the figures in general, a tensioner assembly with sealed pulley is designated generally  10 . The assembly  10  includes a tensioner  20  and a pulley assembly  30  mounted on the tensioner. The tensioner  20  is operable to bias the pulley assembly  30  toward a belt to tension the belt. 
     Referring to  FIGS. 1 and 4 , the tensioner  20  is illustrated as a rotary tensioner. The tensioner  20  includes a housing  22  for housing a biasing element  23 , such as a spring. An arm  26  attached to the housing  22  projects away from the housing. In the present instance, the arm is integrally formed with the housing. However, the arm may be releasably connectable with the housing in other applications. 
     The biasing element  23  in the housing provides a biasing force to bias the arm  26 . Since the tensioner  20  is a rotary tensioner, the biasing force tends to rotate the arm  26 . The details of a rotary tensioner that are operable in the tensioner assembly  10  is provided in U.S. patent application Ser. No. 11/560,608, filed Nov. 16, 2006. The details of patent application Ser. No. 11/560,608 are incorporated herein be reference. Alternatively, the tensioner  20  may be a linear tensioner, in which the biasing element (s) provide a radial force directed radially outwardly from the housing. 
     As shown in  FIG. 1 , the tensioner  20  has a central axis  25  and the arm  26  rotates about the central axis. Spaced apart from the central axis  25  adjacent a distal end of the arm  26  is a mounting hole  28  for mounting the pulley assembly to the arm. In the present instance, the mounting hole is a through hole that is not threaded. However, the mounting hole  28  may be threaded and/or a blind hole as well. 
     As shown in  FIG. 4 , the pulley assembly  30  is attached to the distal end of the tensioner arm  26 . A mounting bolt  80  extends through the pulley assembly  30  and through the mounting hole  28 . In the present instance, a connector in the form of a nut  82  engages the bolt  80  to attach the pulley to the tensioner arm  26 . Alternatively, as mentioned above, the mounting hole  28  may be a threaded hole, and the mounting bolt  80  may threadedly engage the mounting hole to connect the pulley assembly  30  to the tensioner arm  80 . 
     Referring now to  FIGS. 2 and 3 , the details of the pulley assembly  30  will be described in greater detail. The pulley assembly  30  includes a pulley  35  that is configured to engage a belt to be tensioned. The pulley  35  includes a central hub  39  and a pair of flanges projecting outwardly from the hub  39  to form a v-groove  37  for engaging the belt B to be tensioned. 
     The central hub  39  of the pulley  35  includes a cavity  40  that forms a central bore. The cavity  40  is configured to received sealed bearing  45 . In the present instance, the bearings  45  are ball bearings. The cavity  40  is open at both the inner end and the outer end of the pulley  35 . However, a flange  41  adjacent the inner end of the pulley projects radially inwardly to form a reduced diameter opening. As shown in  FIG. 3 , the bearing  45  abuts the flange  41 , so that the flange retains the bearing within the cavity. 
     The outer end of the cavity has a diameter that is larger than the diameter of the bearing so that the bearing can be inserted into the cavity through the outer opening. Additionally, a notch or shoulder is formed adjacent the outer end of the cavity to cooperate with a retainer to retain the bearing in the pulley. Specifically, as shown in  FIG. 3 , a bearing retainer  47  partially covers the outer opening of the cavity  40  to retain the bearing. The retainer  47  includes a central opening for providing access to the bore of the pulley  35 . Additionally, the retainer  47  includes a protrusion, such as an annular protrusion  48  that seats against the bearing  45  to retain the bearing in place. 
     Although the pulley  35  may be formed of a variety of materials, such as aluminum or other metal, in the present instance, the pulley is molded from reinforced nylon. The retainer  47  is also formed of reinforced nylon, and is fixedly attached to the pulley  35 . 
     The pulley assembly also includes one or more sealing elements to seal the pulley to impede contaminants from entering the cavity. Specifically, the pulley assembly  30  includes one or more elements for sealing the inner and/or outer ends of the bore of the pulley  35 . In the present instance, the pulley assembly includes an outer shield  50  and an inner shield  70 . 
     The details of the outer shield  50  are most clearly seen with reference to  FIGS. 1 and 4 . The outer shield  50  is a cup-shaped element that provides a cap to enclose the outer opening of the pulley  35 . Specifically, the outer shield  50  is a generally cylindrically-shaped cup with a circumferential flange  52  that extends radially outwardly from the outer surface of the cup. The inner edge of the cup fits within the opening of the retainer  47 , and the flange  52  overlaps the retainer to enclose the opening. In the present instance, the outer shield  50  forms a snap fit connection with the retainer  47  so that the outer shield substantially seals the outer end of the pulley to impede contaminants from entering the pulley cavity  40 . For instance, the outer shield may be formed of a reinforced nylon similar to the material used to form the pulley and/or retainer, and the inner edge of the shield may flare outwardly to form a circumferential rib that cooperates with the edge of the opening in the retainer  47  to form a snap fit. 
     The details of the inner shield  70  are most clearly seen with reference to  FIGS. 2-4 . The inner shield  70  is positioned to shield the inner opening of the pulley (i.e. the side of the pulley that confronts the arm  26  of the tensioner  20 ). The inner shield  70  includes a generally cylindrical body  72  and a circumferential flange  74  that projects radially outwardly from the body. In the present instance, the body  72  of the shield  70  projects into the inner opening of the pulley, so that the distal end of the body is adjacent to or abutting the bearing  45 . The flange  74  may be configured in a variety of shapes, and in the present instance, is a tapered flange, having a generally flat surface opposing the inner face of the pulley and having an angled surface on the side opposing the tensioner arm  26 . 
     The inner shield  70  is mounted on a mounting hub  60  that projects into the pulley. The inner hub  60  has a base  62  and a reduced diameter tip  64 . The tip  64  projects into the bearing  45  and in the present instance, the tip projects into the bearing substantially the entire width of the bearing. The body  72  of the inner shield  70  is mounted onto the base  62  of the mounting hub  60 . 
     In the present instance, the shield is rigidly connected to the pulley so that the spacing between the inner shield and the pulley is substantially fixed. More specifically, the inner shield  70  is rigidly fixed to the mounting hub  60 , which is rigidly fixed to the bearing  45 . In the present instance, the inner shield  70  is fixedly adhered to the mounting hub  60 . Additionally, in the present instance, the mounting hub is formed of metal, such as aluminum, and is press fit into the bearing to form a substantially rigid interference fit. 
     As shown in  FIG. 4 , the pulley assembly  30  is connected to the tensioner arm  26  by a bolt  80 . The bolt  80  extends through a bore in the mounting hub, and through the tensioner arm. The nut  82  on the backside of the tensioner arm threadedly engages the bolt to tighten the bolt against the mounting hub  60 . In this way, the bolt tightens against the mounting hub so that the mounting hub and the attached inner shield  70  are fixed relative to the tensioner arm. 
     The details of construction of the tensioner assembly  20  are provided in U.S. application Ser. No. 11/560,608, and the details of construction for the pulley assembly  30  are now provided. Referring to  FIGS. 2-4 , the pulley assembly  30  is assembled by inserting the bearing  45  into the cavity  40  of the pulley  35 . Preferably, the bearing  45  is sized to form a friction fit or interference fit with the cavity  40 , so that the outer race of the bearing is fixed relative to the pulley  35 . After the bearing is inserted into the cavity, the bearing retainer is connected to the pulley to partially enclose the outward end of the pulley. The bearing retainer  47  may be connected to the pulley in a variety of ways, such as by welding or adhesive. In the present instance, both the bearing retainer and the pulley  35  are formed from reinforced plastic, and are connected by welding the two together. 
     Next, the inner shield  70  is connected with the mounting hub  60 . For instance, the inner shield  70  may be formed of a plastic, such as reinforced plastic, and it may be press fit onto the mounting hub to form an interference fit. Alternatively, the inner shield may be connected to the mounting hub  60  by an adhesive. 
     After the inner shield is attached to the mounting hub, the mounting hub is connected with the bearing  45 . Specifically, in the present instance, the mounting hub  60  is formed of metal, such as aluminum, and the mounting hub is press fit into the bearing so that the mounting hub forms an interference fit with the inner race of the bearing. 
     The mounting hub  60  and inner shield  70  are formed so that they substantially enclose the inner end of the pulley. Specifically, the inner shield  70  is positioned on the mounting hub so that the gap between the face of the pulley and the opposing face of the inner shield is small enough to impede the migration of contaminants into the interior of the cavity, while providing sufficient clearance to allow the pulley to rotate relative to the inner shield without interference. To provide the appropriate gap, the gap between the inner shield and the face of the pulley is less than half the thickness of the inner shield, and in the present instance is less than ¼ the thickness of the inner shield. Similarly, the body  72  of the inner shield is configured to provide a gap between the inner shield and the bore of the pulley created by the inner flange  41 . Again, the gap is configured to impede migration of contaminants into the interior of the pulley while providing sufficient clearance to allow the pulley to rotate relative to the body  72  of the inner shield. To provide the appropriate gap, the gap between the inner shield and the face of the pulley is less than half the thickness of the inner shield, and in the present instance is less than ¼ the thickness of the inner shield. 
     To attach the pulley assembly to the tensioner, the bolt  80  is inserted through the outer end of the pulley, through the mounting hub  60  and through the mounting hole  28  in the tensioner arm  26 . The nut  82  is then tightened to tighten the bolt head down against the mounting hub  60 . In this way, the mounting hub is fixedly connected to the tensioner arm. 
     After the pulley assembly  35  is connected to the tensioner arm  26 , the outer shield  50  is connected to the pulley  35 . Specifically, the outer shield  50  is snapped onto the bearing retainer  47  to form a releasable snap fit with the pulley  35 . In this way, the outer shield  50  encloses the outer end of the pulley during use, but can be easily removed to remove the pulley assembly from the tensioner arm if desired. For instance, to remove the pulley assembly  30  from the tensioner, the outer shield  50  can be pried off the pulley to expose the mounting bolt  80 . The pulley assembly can then be removed from the bolt by unthreading the nut from the bolt. 
     It will be recognized by those skilled in the art that changes or modifications may be made to the above-described embodiments without departing from the broad inventive concepts of the invention. For instance, in the embodiment above, the pulley assembly  30  includes a bearing retainer  47  connected to the pulley, and an outer shield  50  that connects with the bearing retainer. Alternatively, the bearing retainer could be molded together with the outer shield to create a single element for enclosing the outer end of the pulley  35 . Similarly, although the inner shield  70  and mounting hub are described as being formed of two elements that are then connected, the inner shield and mounting hub may be formed as a unitary elements that is then connected with the pulley  35 . Additionally, although the pulley assembly has been illustrated as including a pair of shield, in some applications it may be desirable or necessary to use a single shield, such as the outer shield  50 . It should therefore be understood that this invention is not limited to the particular embodiments described herein, but is intended to include all changes and modifications that are within the scope and spirit of the invention as set forth in the claims.