Abstract:
The invention concerns a chain for a chain transmission with chain links coupled by a parellel chain pins, each chain link having at least one link plate, the chain pins forming pivot axes for the link plates at a pitch distance whereby a chain link axis perpendicularly intersects the two pivot axes, said link plates having towards at least one end side of the link plate a cam surface for supporting the link plate on a cylindrical support surfaces of a sprocket wheel with a pitch angle. In accordance with the invention the cam surface ends in a convex curved plane with near the end side an increasing slope angle with the link axis whereby the slppe angle increases to at least half of the pitch angle or to at least seven degrees.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation of pending International patent application PCT/EP2006/070159, filed Dec. 22, 2006, which designates the United States and claims priority from European patent application no. 05112684.5, filed Dec. 22, 2005, the content of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention concerns a chain for a chain transmission with chain links coupled by parallel chain pins, each chain link having at least one link plate, the chain pins forming pivot axes for the link plates at a pitch distance whereby a chain link axis perpendicularly intersects the two pivot axes, the link plates having a cam surface for supporting the link plate on a cylindrical support surfaces of a sprocket wheel with a pitch angle. 
       BACKGROUND OF THE INVENTION 
       [0003]    Such a chain for a chain transmission is known from WO03093700. The disadvantage of the known transmission is that leaving out the straight guide that supports the cam surfaces of the chain links before being supported by the cylindrical support surface, for instance in order to save costs, can cause wear on the corners of the cam surfaces. This wear is caused by the impact of the edge of the cam surface at the end of the chain link on the cylindrical support where the impact can create a too high stress level in the material. 
         [0004]    In order to reduce the wear of the cam surface of the link plate the chain transmission includes a cam surface, the cam surface ends in a convex curved plane with near the end side an increasing slope angle with the link axis whereby the slope angle increases to at least half of the pitch angle or to at least seven degrees. At the location of the impact between a link plate and the cylindrical support surface the cam surface and the cylindrical support surface are parallel. As a consequence of the construction the area where the cam surface first impacts on the cylindrical support surface is limited to the area which makes an angle between zero and fifteen degrees with a line perpendicular to the path of the pitch axes of a link plate when it approaches the cylindrical support surface. The tangent to the cam surface at the impact location is parallel to the tangent on the cylindrical support surface and for this reason the location of the first impact on the cam surface is determined by the tangent of the cam surface. At the moment of impact the path of the pin axis is more or less parallel to the link axis and the surface of the impact area on the link plate makes an angle between zero and fifteen degrees with the link axis. By having the link plate in accordance with the chain for a chain transmission with chain links coupled by parallel chain pins, each chain link having at least one link plate, the chain pins forming pivot axes for the link plates at a pitch distance whereby a chain link axis perpendicularly intersects the two pivot axes, said link plates having towards at least one end side of the link plate a cam surface for supporting the link plate on a cylindrical support surfaces of a sprocket wheel with a pitch angle, characterized in that the cam surface ends in a convex curved plane with near the end side an increasing slope angle with the link axis whereby the slope angle increases to at least half of the pitch angle or to at least seven degrees, the curvature radius of the impact area of the cam surface is increased considerably whereby this does not lead to diminishing of the support the cam surface gives to the link plate so that an increase in the chordal movement of the chain is avoided. This increase of curvature radius leads to a strong reduction in the Hertz&#39; contact stress so that excessive stress and deformation of the link plate is avoided. 
       SUMMARY OF THE INVENTION 
       [0005]    In accordance with an embodiment the chain comprises a convex curved plane ( 27 ) that has a radius of curvature (Rc) that is equal to or larger than half of a distance (d) from the chain link axis ( 13 ) to the cam surface ( 15 ). Making the radius of curvature approximately a quarter to half of the width of a link plate makes the radius at the location of impact significantly larger than the fillet radius so that the Hertz&#39; contact stress is substantially reduced. 
         [0006]    In accordance with an embodiment the chain&#39;s radius of curvature (Rc) is at least twice the distance (d) from the chain link axis ( 13 ) to the cam surface ( 15 ). This leads to a further increase of the radius at the location of impact and to further reduction of the Hertz&#39; contact stress. 
         [0007]    In accordance with an embodiment the chain&#39;s cam surface ( 15 ) ends in a corner with the second leg of the corner forming an end side ( 16 ) of the link plate ( 12 ;  26 ;  28 ;  29 ;  33 ). In this way the cam surface sup-ports the link plate directly at its end, whereby due to the convex shape of the cam surface the link plate does not collide with its corner on the cylindrical support surface. 
         [0008]    In accordance with an embodiment the chain&#39;s cam surface ( 15 ) ends in a rounded corner with a fillet radius (Rf), which fillet radius preferably is at least 0.5-1.5 mm. In this way in stamping tools used for making the link plates sharp corners can be avoided so that tool life is increased. 
         [0009]    In accordance with an embodiment the chain comprises cam surfaces ( 15 ) near the different pivot axes ( 6 ) that have different lengths. In this way the link plates are made asymmetrical, so improving the support of the link plates in the area where the chain links move towards a sprocket wheel, whereby it is accepted that an increase in the chordal action occurs in the area where the chain links move from a sprocket wheel. 
         [0010]    In accordance with an embodiment the chain comprises a cam surface ( 15 ) that is for a part of its length parallel to the chain link axis ( 13 ). This makes sure that the pin axes follow a straight path when approaching the sprocket wheel. 
         [0011]    In accordance with an embodiment the chain comprises each chain link that has at least two link plates ( 12 ;  26 ;  28 ;  29 ;  33 ) that are separated by a chain bush ( 1 ) near each pivot axis ( 6 ). In this way the chain links can be supported in a more stable way. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0012]    The invention is now explained by describing several embodiments of the invention using a drawing. In the drawing: 
           [0013]      FIG. 1  shows a section of a sprocket wheel with a chain, 
           [0014]      FIG. 2  shows a side view of the sprocket wheel and the chain of  FIG. 1 ; 
           [0015]      FIG. 3  shows a partial top view of the sprocket wheel and the chain of  FIGS. 1 and 2 ; 
           [0016]      FIG. 4  shows an outside contour of an embodiment of a chain link; 
           [0017]      FIG. 5  shows a schematic side view of a sprocket wheel with a chain having the chain links of  FIG. 4 ; 
           [0018]      FIG. 6  shows an outside contour of a first embodiment of a chain link according to the invention; 
           [0019]      FIG. 7  shows a schematic side view of a sprocket wheel with a chain having the chain links of  FIG. 6 ; 
           [0020]      FIG. 8  shows an outside contour of a second embodiment of a chain link according to the invention; 
           [0021]      FIG. 9  shows a schematic side view of a sprocket wheel with a chain having the chain links of  FIG. 8 ; 
           [0022]      FIG. 10  shows an outside contour of a third embodiment of a chain link according to the invention; 
           [0023]      FIG. 11  shows a schematic side view of a sprocket wheel with a chain having the chain links of  FIG. 10 ; 
           [0024]      FIG. 12  shows a side view of a fourth embodiment of a chain link according to the invention; and 
           [0025]      FIG. 13  shows a schematic side view of a sprocket wheel with a chain having the chain links of  FIG. 12 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]      FIGS. 1 ,  2  and  3  show a chain  3  engaged with a sprocket wheel  9 . The sprocket wheel  9  can rotate around a sprocket wheel axis  10  and is provided with sprocket teeth  7 . The sprocket wheel  9  has at both sides of the sprocket teeth  7  a support surface  8  which supports the chain  3 . The chain  3  is provided with inner link plates  2 . Between two inner link plates  2  there are two chain bushes  1  and together the inner link plates  2  and the chain bushes  1  form an inner link. This type of chain is called a bush chain. Two inner links are connected by two outer link plates  4  using chain pins  5  whereby the inner link and the outer link plates  4  can pivot around a pin axis  6 . The distance between two pin axes  6  is a pitch p. The sprocket wheel  9  has a number of sprocket teeth  7  which engage with the chain bushes  1  so that the pin axes  6  when positioned around the sprocket wheel  9  are on a pitch circle  20  with a pitch circle radius R pc . The inner link plates  2  and the outer link plates  4  are supported on the support surface  8  that has a support surface radius R ss . 
         [0027]    In the situation that the sprocket wheel  9  is part of a chain transmission the pin axes  6  follow a pin axis path  11 . Around the sprocket wheel  9  this pin axis path  11  follows the pitch circle  20  and between two sprocket wheels the pin axes  6  follow a line L that is parallel to the tangent line connecting the pitch circles of the sprocket wheels in the chain transmission. 
         [0028]    For a skilled man it will be clear that the chain  3 , which in the shown embodiment is formed by a single line of chain bushes  1 , can also be executed two or three lines of chain bushes  1 . Such chains are known as duplex chains and triplex chains, whereby the sprocket wheels  9  are designed accordingly. For maintaining the chain links in a straight line without torsion in the chain  3  and in order to limit the stress in the chain pins  5  in these types of chain the link plates  2  and  4  are supported by support surfaces  8  on both sides of the chain bush  1 . 
         [0029]      FIG. 4  shows an outer circumference of a link plate  12 . The link plate  12  can be used as inner link plate  2  or as outer link plate  4  and has in its longitudinal direction a chain link axis  13  which intersects the pin axes  6 . At the end of a longitudinal side  14  the link plate  12  has a cam surface  15 . Near the end of the link plate  12  the cam surface  15  is more or less parallel to the chain link axis  13  so that the pin axis  6  follows a more or less straight path when the cam surface  15  of the link plate  12  is supported on the support surface  8  of the sprocket wheel  9  (see hereafter) . The link plate  12  ends in an end side  16  and the corner between the cam surface  15  and the end side  16  is rounded by a fillet with a fillet radius R f  and a centre  23  of the fillet radius . In the shown embodiment all four corners of the link plate  12  have a cam surface  15 . However if the chain  3  is used in a chain transmission with two sprocket wheels it is possible to provide only one longitudinal side  14  at both ends with cam surfaces  15  and if the chain  3  moves only in one direction one cam surface  15  will suffice. 
         [0030]    The link plate  12  of the disclosed embodiment has a fillet radius R f  which is a consequence of the production method of the link plate  12 . In the situation that the link plate  12  is punched with a punching die the fillet radius R f  determines the wear that occurs in this tool. For practical purposes the fillet radius R f  might be approximately 0.5 to 1.5 mm.  FIG. 4  shows a link plate  12  with a pitch of 8 mm with a fillet radius Rf of 0.5 mm. 
         [0031]      FIG. 5  shows in more detail how the chain  3  with chain links  12  contacts the sprocket wheel  9 . The  FIG. 5  shows the situation where a chain link A with the outer link plate  4 , shown in the figure at the left side, moves in a direction V towards the sprocket wheel  9 . On the side away from the sprocket wheel  9 , its trailing side, the chain link A is connected to a chain link that is free from the sprocket wheel  9  and on the other side, its leading side, the chain link A is connected to a chain link B by the inner link plate  2 . The cam surface  15  of chain link B is supported by the support surface  8  so that its leading side pin axis  6  is at a position P 3  approximately on the pitch circle  20 . 
         [0032]    During its movement in the direction V the leading pin axis  6  of chain link B has more or less followed the pitch circle  20  along a curve  19 . This curve  19  starts at a tangent point P 2  which is approximately where a tangent line L to the pitch circles of two sprocket wheels coupled by the chain  3  ends on the pitch circle  20 . Due to the tension in the chain  3  the trailing pivot axis  6  of chain link B, which is also the leading pivot axis  6  of chain link A, has followed a curve  17  from the tangent line L in the direction of the support surface  8 . The curve  17  is parallel to the curve  19  due to the same vertical position of the leading pin  6  and the trailing pin  6  of chain link B and this causes the chain link A to move towards the support surface  8  until the cam surface  15  of the chain link plate  4  touches the support surface in a point of impact S. The common pivot axis  6  of the chain links A and B is then in position P 1 . When the chain links A and B move further in the direction V, the common axis  6  moves along a curve  18  towards the line L that is tangent to the pitch circles. The curve  18  is more or less parallel to the pitch circle  20 . The support of the cam surface  15  of the link plates on the support surface  8  limits the chordal movement perpendicular to line L of the chain  3  between two sprocket wheels, in this case the maximum chordal movement near the sprocket wheel  9  is indicated as a chordal stroke a. It will be clear that the shape of cam surface  15  influences the paths  18  and  19  of the pin axis  6  so that they will slightly differ from the pitch circle  20  in order to maintain constant speed of the pin axes  6  along line L and when moving around the sprocket wheel  9 . This is disclosed in WO 03093700. 
         [0033]    The point of impact S on the support surface  8  has a radial  21  from the sprocket wheel axis  10  and the tangent point P 2  has a radial  22  from the sprocket wheel axis  10 . The radial  21  and the radial  22  form an angle α 1 . On the chain link the point of impact S has a perpendicular  25  on the surface of the chain link. The perpendicular  25  makes an angle α 2  with a line  24  perpendicular to the chain link axis  13 . As the impact takes place on the surface of the fillet the centre  23  of the fillet radius is on the perpendicular  25 . Due to the situation that at the moment of impact the chain link axis  13  is more or less perpendicular to the radial  22 , the angle α 1  and the angle α 2  are more or less equal. If the number of chain links that can be fitted around the sprocket wheel  9  is z, then the pitch angle y is equal to 360 degrees divided by z. It appeared that the angle α 1  is smaller than half of the pitch angle γ, and in most situations the angle α 1  is smaller than seven to twelve degrees. 
         [0034]    The fillet radius Rf is preferably as small as possible in order to have the cam surface  15  as large as possible towards the end side  16  of the link plate  12  in order to reduce the chordal stroke a. However a smaller fillet radius R f  increases the Hertz&#39; contact stress at the point of impact S so that at higher speeds of the chain  3  or at higher axial chain forces plastic deformation or wear of the link plates might occur. Such deformation or wear leads to increased noise, vibration and reduced life time of the chain transmission and must be avoided. In order to reduce the risk of plastic deformation the radius at the point of impact S is increased. The Hertz&#39; contact stress is proportional to the reciprocal value of the square root of the radius. Therefore de-formation and wear decrease significantly with a limited increase in the radius at the location of contact. It has been found that the increased radius has to be applied over an angle that includes the angle α 1  but need not to be much more so that the reduction of the cam surface  15  is limited and the chordal stroke a hardly increases. 
         [0035]      FIG. 6  shows an embodiment of the invention whereby the outer circumference of a link plate  26  has an additional curve as compared to the link plate  12 . Towards the end side  16  the cam surface  15  which is more or less parallel with the chain link axis  13  forms a curve  27  with a curve radius R c  and at the end of the curve  27  the cam surface ends as a fillet with the fillet radius Rf towards the end side  16  of the link plate  26 . The curve  27  is tangent to the cam surface  15  and forms an increasing angle with the chain link axis  13  and has a slope angle β. The maximum value of the slope angle β is approximately half the pitch angle y and generally larger than seven degrees. In the direction perpendicular to the chain link axis  13  the distance from the pin axis  6  to the surface of the cam surface  15  is a distance d. Preferably the curve radius R c  is equal to or larger than half of the distance d so that it is significantly larger than the fillet radius R f . By doing this the Hertz&#39; contact stress is acceptable. In this embodiment the curve  27  is shown as a part of a circle with radius R c . It is also possible that the curve has another shape as long as it has a curvature radius that is at least equal to the curve radius R c . 
         [0036]      FIG. 7  shows in a similar way as  FIG. 5  the moment of impact of the chain link A on the support surface  8 , whereby the chain  3  now has the link plates  26  as shown in  FIG. 6 . The perpendicular  25  to the surface at the point of impact S makes an angle α 2  with the perpendicular to the chain link axis  13 . As this angle is smaller than the angle β the surface at the point of impact S has a radius R c  and the centre of the fillet radius  23  is in regard to the perpendicular  25  towards the end side  16  of the link. The radius R c  at the point of impact S is sufficient to avoid high Hertz&#39; contact stress at the impact point S. Due to the limited angle β the chordal stroke a has hardly increased. 
         [0037]      FIG. 8  shows an embodiment of the invention whereby the outer circumference of a link plate  28  has an additional curve as compared to the link plate  12  in a similar way as in the embodiment of  FIG. 6  and whereby there is no fillet connecting the curve  27  to the end side  16  of the link. Leaving out the fillet is possible when the link plates  28  are produced according an adapted process known to a skilled man, for instance sequential punching of the longitudinal and end sides of the link plate  28 . Such a process might slightly increase production costs but has the advantage that the chordal stroke a is further reduced. 
         [0038]      FIG. 9  shows the moment of impact of the chain link A on the support surface  8 , whereby the chain  3  has the link plates  28  as shown in  FIG. 8 . Due to the avoidance of the fillet the chordal stroke a is further reduced compared to the chordal stroke shown in  FIG. 7  with the radius R c  at the point of impact S being similar. 
         [0039]      FIG. 10  shows an embodiment of the invention whereby the outer circumference of a link plate  29  has an additional curve with a radius which is equal or larger than R c  ending in a fillet as in the link plate  26 . In order to reduce the chordal stroke the link plate  29  has an increased length of the cam surface  15  on a leading side  30  of the link plate  29  and a reduced length of the cam surface  15  on a trailing side  31 . This means that the link plate  29  is asymmetric. A consequence of the link plate  29  being asymmetric is that the chordal stroke a is reduced only in one movement direction V and that in the opposite movement direction the chain will have a chordal stroke a that is slightly increased but substantially smaller than that of a chain transmission without cam surface  15 . In a situation whereby the sprocket wheels rotate only in one direction this stronger chordal movement is in a part of the chain transmission where the chain links move away from the sprocket wheel and where no impact occurs. At that location the tension in the chain is low so that the stronger chordal movement does not lead to a noticeable increase of noise and unacceptable wear and vibrations. 
         [0040]    In the earlier described link plates  12 ,  26 ,  28  and  29 , see  FIGS. 4 ,  6 ,  8  and  10 , the end sides  16  are near the chain link axis  13  curved with a radius R 1  and continue towards the longitudinal sides  14  as a tangent to this radius R 1  which makes an angle equal to half of the pitch angle γ with the perpendicular  24  on the chain link axis  13 . The direction of this tangent is indicated with line  32  in  FIG. 10 . The radius R 1  is slightly smaller than half the pitch p. In this way there is a clearance between the link plates near the chain link axis  13  and the link plates  12 ,  26 ,  28  do not touch each other when positioned around the sprocket wheel  9 . In order to get this same result with the link plate  29  the leading side  30  makes an angle with the perpendicular  24  which is an addendum angle δ smaller than half of the pitch angle γ and the trailing side  31  makes an angle with the perpendicular  24  which is an addendum angle δ larger than half of the pitch angle γ. Near the cam surface  15  the leading side  30  ends with a fillet with radius R f  and curve  27  in similar way as shown in  FIG. 6 . Near the cam surface  15  the trailing side  31  ends with a fillet with radius R f  and there is no need for a curve  27  as the chain will only move in direction V. 
         [0041]      FIG. 11  shows the moment of impact of the chain link A on the support surface  8 , whereby the chain  3  has the link plates  29  as shown in  FIG. 10 . Due to the asymmetry the chordal stroke a is further reduced compared to the chordal stroke as shown in  FIG. 7  whereby the radius R c  at the point of impact S is similar. 
         [0042]      FIG. 12  shows a further embodiment of the invention. An asymmetric link plate  33  is more or less similar to the link plate  26  except that it has a pitch p′ which is the length of the pitch p of the earlier shown embodiments plus an additional length that is approximately equal to the pitch of link plate  26  p and the same width so that the maximum transmission force in the chain is more or less equal using half the number of chain links and the same sprocket wheel  9 . Also the support surface  8  and the number of sprocket teeth  7  of the sprocket wheel  9  are more or less similar, whereby only every other tooth is used. The same effect can also be obtained by using a sprocket wheel with a reduced number of teeth. The distance between the leading side  30  and the leading pin axis  6  is also increased with the pitch of the link plate  26  p. The distance between the trailing side  31  and the trailing pin axis  6  is not changed. Towards the leading side  30  the cam surface  15  ends in the curve  27  and the fillet with radius R f , towards the trailing side  31  the cam surface  15  ends with the fillet R f . 
         [0043]      FIG. 13  shows a chain  3  with link plates  33  shaped as described in  FIG. 12 . Due to the use of the asymmetric shape of the link plates  33  the chordal stroke a is small, thereby making cost saving possible due to the reduced number of chain pins  6  and chain bushes  1  without increase in chordal stroke, wear, noise and vibrations. 
         [0044]    In the discussed embodiments sprocket wheels  9  with sprocket teeth  7  are shown. It will be clear that in order to reduce the chordal movement on the sprocket wheels only the support surface  8  is essential. In situations where wheels are used as guide wheels without teeth the same reduction in chordal movement is obtained using the support surface  8  and the cam surface  15  on the chain links. 
         [0045]    The above embodiments explain the invention using the example of a bush chain. The design of the link plates that cooperate with a cylindrical support on the sprocket wheel can be used for other types of chains as well, such as roller chains, Fleyer chains and Gall chains and also for chains working with sprockets without teeth or having a single inner link plate and two outer link plates.