Abstract:
A tensioning device for producing tension in a chain, including a hydraulic tensioner, a tensioner arm, a lever arm and a pin member. The tensioner causes the tensioner arm to pivot at one end. The lever arm is positioned with a part toward the hydraulic tensioner. The pin member is fitted in a fixed wall and also has one end inserted in a hole in part of the lever arm.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation of the U.S. Application Ser. No. 12/999,358 filed on Dec. 16, 2010. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a tensioning device for producing tension in a chain, and more specifically it relates to an improved structure for increasing the pressing force on the chain as the chain undergoes greater elongation. 
       BACKGROUND 
       [0003]    Various systems have been used in the past as tensioning devices for producing tension in chains. For example, the tensioning device shown in  FIG. 1  of Japanese Unexamined Utility Model Application Publication S52-34377 consists of a cam plate having a cam surface which abuts the chain, and a spring which latches on the cam plate and causes the cam plate to turn so that the cam surface runs into the chain when the chain undergoes elongation. 
         [0004]    Furthermore, the tensioning device shown in  FIGS. 1 and 2  of Japanese Unexamined Utility Model Application Publication S52-99478 consists of a tensioner arm on which the chain slides, a cam plate having a cam surface which abuts the back surface of the tensioner arm, and a spring which causes the cam plate to turn so that the cam surface runs into the back surface of the tensioner arm when the chain undergoes elongation. 
         [0005]    However, with the tensioning devices disclosed in the publications mentioned above, when the cam surface runs into the chain or tensioner arm during chain elongation, the amount of elastic deformation of the spring decreases, and therefore the spring force decreases. Consequently, the pressing force from the spring which acts on the chain through the cam is also reduced. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention has been devised in view of the situation that has existed until now, and the issue which the present invention aims to resolve is that of providing a tensioning device with which it is possible to increase the pressing force on the chain as the chain undergoes greater elongation. 
         [0007]    The tensioning device according to a preferred embodiment of the invention of claim  1  is provided with: a tensioner arm which has a chain sliding surface and in which a through-hole is formed at a free end which can pivot about a pivoting end; a hydraulic tensioner which acts on the free end of the tensioner arm so that the tensioner arm pivots about the pivoting end; a lever arm having a boss part which is rotatably supported in the through-hole at the free end and comprises a pin insertion hole at a position which is offset from the center of the through-hole, said lever arm also having a lever part which is integrally provided with the boss part at one end of the boss part and which extends from the boss part toward the hydraulic tensioner with the tip end of a piston of the hydraulic tensioner in abutment against it; and a pin of which one end is fitted in a fixed wall around the tensioner arm, and of which the other end is inserted into the pin insertion hole of the boss part of the lever arm. When the piston of the hydraulic tensioner extends, the lever arm pivots about the pin, whereby the amount of pushing by the free end of the tensioner arm into the chain is increased. 
         [0008]    The piston of the hydraulic tensioner extends when slack is produced in the chain as it travels. This being so, the lever part is driven by the piston, whereby the boss part of the lever arm pivots about the pin while rotating inside the through-hole at the free end of the tensioner arm. In this instance, the pin is provided offset from the center of the through-hole at the free end of the tensioner arm (that is to say it is eccentric), and therefore the boss part of the lever arm projects toward the chain as the boss part pivots about the pin, and by means of this the free end of the tensioner arm is moved toward the chain by way of the through-hole at the free end of the tensioner arm. As a result, the amount of pushing by the free end of the tensioner arm into the chain is increased. 
         [0009]    In this case, the pressing force which acts on the lever part of the lever arm depends on the hydraulic pressure of the hydraulic tensioner, and therefore this pressing force does not change according to the projection of the piston of the hydraulic tensioner, and it can be kept constant. Accordingly, a constant pressing force always acts on the lever part of the lever arm during operation, and consequently the pressing force which the free end of the tensioner arm exerts toward the chain increases as the amount of projection of the piston of the hydraulic tensioner increases, leading to an increase in the amount of pushing by the free end of the tensioner arm into the chain. 
         [0010]    One end of the pin is fixed to the fixed wall, while the other end is rotatably supported in the pin insertion hole of the boss part. If the piston of the hydraulic tensioner extends in this case, when the boss part of the lever arm rotates inside the through-hole at the free end of the tensioner arm, the boss part rotates while sliding about the outer peripheral surface at that other end of the pin. A long hole can be formed at the pivoting end of the tensioner arm, and the pivoting end is pivotably supported on the fixed wall by way of a pin which is inserted into the long hole. When the boss part of the lever arm has pivoted about the pin in this case, the boss part moves a certain amount toward the pivoting end of the tensioner arm or away from the pivoting end thereof, as a result of which the pivoting end of the tensioner arm moves a certain amount, but this amount of movement can be absorbed at this time because the long hole is formed at the pivoting end. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a schematic front view of a timing chain system in which the tensioning device according to an exemplary embodiment of the present invention is employed; 
           [0012]      FIG. 2  shows a state in which the chain in the timing chain system ( FIG. 1 ) is elongated; 
           [0013]      FIG. 3  is a view in cross section along the line III-III; and 
           [0014]      FIG. 4  illustrates the operation of the lever arm, with (a) showing the state of the chain before elongation, and (b) showing the state of the chain after elongation. 
       
    
    
     ADVANTAGES OF THE INVENTION 
       [0015]    As described above, a through-hole is formed at the free end of the tensioner arm with the boss part of the lever arm being provided so as to be able to rotate inside the through-hole, and the pin insertion hole is formed in the boss part at a position which is offset from the center of the through-hole; one end of the pin is fitted in the surrounding fixed wall, while the other end is inserted into the pin insertion hole, and the lever arm is provided with a lever part which extends from the boss part as far as the hydraulic tensioner and which is abutted by the tip end of the piston of the hydraulic tensioner, and therefore when the piston of the hydraulic tensioner extends, the boss part of the lever arm pivots about the pin while rotating inside the through-hole at the free end of the tensioner arm, whereby the boss part of the lever arm projects toward the chain and the amount of pushing by the free end of the tensioner arm into the chain is increased. 
         [0016]    In this case, the pressing force which acts on the lever part of the lever arm depends on the hydraulic pressure of the hydraulic tensioner, and therefore this pressing force does not change according to the projection of the piston of the hydraulic tensioner, and it can be kept constant. Consequently, the pressing force which the free end of the tensioner arm exerts toward the chain can be increased as the amount of projection of the piston of the hydraulic tensioner increases (and therefore as chain elongation increases), leading to an increase in the amount of pushing by the free end of the tensioner arm into the chain. 
       DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]      FIGS. 1 to 4  illustrate the tensioning device according to an exemplary embodiment of the present invention, where  FIG. 1  is a schematic front view of a timing chain system in which the tensioning device according to this exemplary embodiment is employed.  FIG. 2  shows a state in which the chain in the timing chain system ( FIG. 1 ) is elongated.  FIG. 3  is a view in cross section along the line III-III; and  FIG. 4  illustrates the operation of the lever arm, with (a) showing the state of the chain before elongation, and (b) showing the state of the chain after elongation. 
         [0018]    As shown in  FIGS. 1 and 2 , this timing chain system  100  is provided with a crank sprocket  101  which is mounted on a crankshaft of an engine; cam sprockets  102 ,  103  which are mounted on a camshaft; and a timing chain  104  which is wound around the sprockets  101 ,  102 ,  103 . It should be noted that the arrows in the figure denote the direction of rotation of the sprockets. 
         [0019]    A tensioning device  1  is provided at the slack side span of the timing chain  104 . The tensioning device  1  is provided with: a tensioner arm  2  having a pivoting end  20  and a free end  21  which can pivot about said pivoting end, and having a chain sliding surface  2   a  on which the chain  104  slides; a hydraulic tensioner  3  which acts on the free end  21  of the tensioner arm  2  so as to cause the tensioner arm  2  to pivot about the pivoting end  20 ; and a lever arm  4  which is joined to the free end  21  of the tensioner arm  2 . 
         [0020]    As shown in  FIG. 3 , a through-hole  21   a  is formed at the free end  21  of the tensioner arm  2 . Meanwhile, the lever arm  4  has a cylindrical boss part  40 , and a lever part  41  which is provided as a single piece with the boss part  40  at one end of the boss part  40  (the left-hand end in  FIG. 3 ) and extends from the boss part  40  up to the hydraulic tensioner  3  (see  FIGS. 1 and 2 ), and the boss part  40  is rotatably supported in the through-hole  21   a  at the free end  21  of the tensioner arm  2 . 
         [0021]    The boss part  40  has a pin insertion hole  40   a  at a position which is upwardly offset from a center line C L  of the through-hole  21   a  (see the center line C LP )). Meanwhile, one end of a pin  5  is fixed in a fixed wall (the cylinder block, for example) surrounding the tensioner arm  2 , and the other end of the pin  5  is inserted into the pin insertion hole  40   a  of the boss part  40  of the lever arm  4 . The boss part  40  can rotate about the pin  5 . 
         [0022]    A recessed surface  41   a  is formed in the lever part  41  of the lever arm  4 , and the tip end of a piston  3   a  of the hydraulic tensioner  3  is in abutment with the recessed surface  41   a . 
         [0023]    Furthermore, a long hole  20   a  is formed at the pivoting end  20  of the tensioner arm  2 , and the pivoting end  20  is pivotably supported on the fixed wall such as the cylinder block by way of a pin  25  which is inserted into the long hole  20   a.    
         [0024]    The operational effects of this exemplary embodiment will be described next. 
         [0025]    As shown in  FIGS. 1 and 4(   a ), in a state before the timing chain  104  is elongated by wear, the pressing force which acts on the lever part  41  of the lever arm  4  from the piston  3   a  of the hydraulic tensioner  3  is designated F 1 . By means of this pressing force F 1 , the lever part  41  and boss part  40  attempt to rotate counterclockwise in the figure about the pin  5 . As a result, the boss part  40  of the lever arm  4  presses the free end  21  of the tensioner arm  2  toward the chain, by way of the through-hole  21   a  at the free end  21 . At this point, the opposing force which acts on the free end  21  from the chain is designated F 2 . Furthermore, the distance between the line on which the pressing force F 1  acts and the center Op of the pin  5  is designated L 1 , and the distance between the line on which the pressing force F 2  acts and the center O P  of the pin  5  is designated L 2 . 
         [0026]    Here, the moment balance equation for the center O P  of the pin  5  is established in the following manner: 
         [0000]    
       
      
       F 
       1 
       ·L 
       1 
       =F 
       2 
       ·L 
       2  
      
     
         [0000]    and solving this for F 2 , 
         [0000]        F   2   =F   1   ·L   1   /L   2    (1)
 
         [0027]    Next, when the timing chain  104  is elongated by wear, as shown in  FIG. 2 , the piston  3   a  of the hydraulic tensioner  3  extends to press the lever part  41  of the lever arm  4 , and the lever part  41  pivots counterclockwise in the figure. By means of this, the boss part  40  of the lever arm  4  pivots about the pin  5  and projects toward the chain (the right-hand side in the figure—see  FIG. 4(   b )). As a result, the amount of pushing by the free end  21  of the tensioner arm  2  into the chain increases (see the increased amount of pushing T in  FIG. 2) . 
         [0028]    At this point, as shown in  FIG. 4(   b ), the pressing force which acts on the lever part  41  of the lever arm  4  from the piston  3   a  of the hydraulic tensioner  3  stays as F 1 , provided that the hydraulic pressure supplied to the hydraulic tensioner  3  is constant. Here, if the distance between the line on which the pressing force F 1  acts and the center O P  of the pin  5  is designated L 1 ′, the lever part  41  pivots about the center O P  of the pin  5 , and therefore L 1 ′=L 1 . Furthermore, when the opposing force which acts on the free end  21  from the chain, due to the fact that the boss part  40  of the lever arm  4  presses the free end  21  of the tensioner arm  2  toward the chain, is designated F 2 ′, and the distance between the line on which the force F 2 ′ acts and the center O P  of the pin  5  is designated L 2 ′, the moment balance equation relating to the center O P  of the pin  5  is as follows: 
         [0000]        F   1   ·L   1   ′=F   2   ′·L   2 ′
 
         [0000]    here, L 1 ′=L 1  and therefore 
         [0000]        F   1   ·L   1   =F   2   ·L   2 ′
 
         [0000]    and solving this for F 2 ′, 
         [0000]        F   2   ′=F   1   ·L   1   /L   2 ′  (2)
 
         [0029]    When we compare the right-hand side of equations (1) and (2), L 2 ′&lt;L 2 , and therefore F 2 ′&gt;F 2 . 
         [0030]    In this way, the pressing force exerted by the free end  21  of the tensioner arm  2  toward the chain increases as the amount of projection of the piston of the hydraulic tensioner  3  increases, leading to an increase in the amount of pushing by the free end  21  of the tensioner arm  2  into the chain. 
         [0031]    When the chain operates initially without any wear, the pressing force on the chain need not be great, and if it is too great, the chain is subjected to wear, and wear of the chain sliding surface of the tensioner arm is promoted. 
         [0032]    In the exemplary embodiment described above, when the chain is worn, the boss part of the lever arm projects toward the chain, whereby the pressing force on the chain can be increased, and therefore when the chain operates initially without any wear, it is possible to reduce the pressing force on the chain by reducing the hydraulic pressure of the hydraulic tensioner. By means of this, wear of the chain when it runs initially can be reduced, and the engine fuel consumption can be improved. 
         [0033]    While the invention has been described in connection with one or more embodiments, it is to be understood that the specific mechanisms and techniques which have been described are merely illustrative of the principles of the invention, numerous modifications may be made to the methods and apparatus described without departing from the spirit and scope of the invention as defined by the appended claims.