Abstract:
In a power transmission utilizing a bushingless roller chain, the inner links of the chain have chain guide-contacting backs that have a convex arcuate shape, and the outer links are shaped so that they do not contact the chain guides. The rollers are wider than the sprocket teeth that they engage, and widthwise gaps between the ends of the rollers and the outer link plates allow the inner link plates to move in the widthwise direction. The gap between the inner surfaces of the rollers and the outer surfaces of the connecting pins of the chain is larger than the gap between the inner surfaces of the holes in the inner link plates and the outer surfaces of the connecting pins that extend through them.

Description:
[0001]    This application claims priority on the basis of Japanese Patent Application No. 2011-182451, filed on Aug. 24, 2011, the disclosure of which is hereby incorporated by reference. 
       FIELD OF THE INVENTION 
       [0002]    This invention relates to a chain transmission having a bushingless roller chain including rollers directly supported by connecting pins which connect outer and inner link plates. The chain transmission apparatus has utility in automobiles, industrial machinery, conveyors and other machinery. 
       BACKGROUND OF THE INVENTION 
       [0003]    In known chain transmissions including a bushingless roller chain engaged with sprockets, the chain is composed of outer and inner link plates, connecting pins and rollers. Pairs of inner link plates and pairs of outer link plates are disposed in an alternating, overlapping arrangement along the direction of travel of the chain. The pins are fixed to the outer link plates and extend through pin holes in the inner link plates and through the rollers in such a way that the inner link plates can articulate relative to the outer link plates and the rollers can rotate on the pins. Teeth on the sprockets engage with the rollers. A chain transmission using a bushingless roller chain is described Japanese patent application 1991-0349922, laid open under no. Hei 5-164196 on Jun. 29, 1993. A similar bushingless roller chain, having sets of multiple link plates in widthwise rows, is described in Japanese patent Application No. 1999-0310336, laid-open under No. 2001-124149 on May 8, 2001. 
         [0004]    Unlike conventional roller chains, these roller chains have no bushings fixed to inner link plates and interposed between rollers and connecting pins. The rollers therefore contact the connecting pins directly. A large impact force acts on the rollers, the connecting pins, and the inner link plates when the rollers start to engage a sprocket tooth, reducing the durability of the rollers, the connecting pins and the inner link plates and generating excessive noise. 
         [0005]    If the chain transmission incorporating a bushingless roller chain includes chain guides, an additional problem arises. If the outer and inner link plates of the chain conform to the surface of the chain guide the contact area between the chain and the guide becomes large, and results in a high frictional loss increases and decreased power transmission efficiency. 
         [0006]    Accordingly, there is a need for a chain transmission utilizing a bushingless roller chain, in which the inner link plates, connecting pins and rollers have improved durability, in which power transmission efficiency is improved, and in which noise generated as the rollers engage sprocket teeth is reduced. 
       SUMMARY OF THE INVENTION 
       [0007]    The chain transmission according to the invention comprises a bushingless chain, a plurality of sprockets, and a pair of chain guides. The chain, which is in the form of an endless loop, comprises pairs of outer link plates, pairs of inner link plates disposed between the pairs of outer link plates, connecting pins, and rollers. The sprockets have sprocket teeth that engage with the rollers of the chain so that the chain travels along a direction of travel around the sprockets. The guides include a movable guide operated by a tensioner, and a stationary guide. Both guides have sliding contact surfaces on which the chain slides as the chain travels around the sprockets. The pairs of inner link plates and the pairs of outer link plates are arranged in alternating sequence, and linked together articulably by the connecting pins. The connecting pins are fixed to the outer link plates and extend through holes in the inner link plates, which are directly supported by, and rotatable on, the connecting pins. The chain is lubricated by oil from an oil supply. One of the rollers is rotatable on each connecting pin and a film of said oil is disposed between the outer circumferential surface of each connecting pin and the inner circumferential surface of the roller thereon. 
         [0008]    The link plates have back surfaces which face toward the outside of said endless loop, and only the inner link plates come into contact with the sliding-contact surfaces of the guides, by contact between parts of the back surfaces of the inner link plates and the sliding contact surfaces of the guides. The parts of the back surfaces of the inner link plates that come into contact with the sliding contact surfaces of the guides are in the form of convex arcs having axes transverse to the direction of travel of the chain. 
         [0009]    In the chain transmission an oil film is produced between the outer circumferential surfaces of each connecting pin and the inner circumferential surface of the surrounding roller, and only the inner link plates, the backs of which are in the form of convex arcs, come into sliding contact with the guides. Therefore, the contact area between chain and the guide is reduced, frictional loss is reduced, and power transmission efficiency of the chain transmission is improved. 
         [0010]    Oscillation of the inner link plates resulting from friction between the link plates and the guide surfaces is absorbed by radial gaps between the connecting pins and the holes in the inner link plates through which the connecting pins extend. Therefore, whereas there oscillation of link plates causes oscillation in the thickness of the oil film between the bushings and the rollers in a roller chain having bushings fixed to the inner link plates, it is possible to suppress this oscillation in the thickness of the oil film in the chain according to the invention. Consequently, it is possible to stabilize the impact-reducing effect of the oil film, i.e., to reduce the impact applied by the sprocket teeth to the rollers and the connecting pins, when the rollers start to engage the sprocket teeth, to reduce noise, and to achieve improvements in the durability of the rollers and the connecting pins, and in the overall durability of the chain. 
         [0011]    Because the inner link plates oscillate, the contact regions between the inner link plates and the guides, and between the connecting pins and the holes in the inner link plates, are less concentrated. 
         [0012]    The durability of the inner link plates and the overall durability of the chain can be further improved by making the thickness of the inner link plates larger than the thickness of the outer link plates, so that wear is still further suppressed. 
         [0013]    In another aspect of the invention, the width of the rollers is greater than the maximum width of the sprocket teeth, and widthwise gaps are formed between the ends of the rollers and the outer link plates. These gaps being sufficiently large to allow movement of the inner link plates in the direction of the width of the chain. By allowing widthwise movement of the inner link plates, it is possible to reduce the impact caused by the collision of the inner link plates and the sprocket teeth, and to reduce the noise and wear caused by the collisions. 
         [0014]    In still another aspect of the invention, the inner diameter of the rollers is larger than the inner diameter of said holes in the inner link plates. The smaller radial gap between the inner link plate and the connecting pin suppresses flow of oil held between a roller and an inner link plate through the radial gap. Therefore, the formation of the oil film between the roller and the connecting pin, and the increase of its thickness, are accelerated, and the effect the oil film in reducing the impact on the roller and the connecting pin when the roller starts to engage with the sprocket tooth is enhanced. Accordingly, it is possible to reduce the noise generated when the roller starts to engage with the sprocket tooth and to improve the durability of the roller and the connecting pin. 
         [0015]    Further features of the invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a schematic front elevational view of an engine timing drive incorporating a chain transmission according to the invention; 
           [0017]      FIG. 2  is an exploded perspective view of a part of a bushingless roller chain according to the invention; 
           [0018]      FIG. 3  is a fragmentary side elevational view showing a part of the chain in sliding contact with a chain guide; 
           [0019]      FIG. 4  is a sectional view of the part of the chain shown in  FIG. 3 , taken on a surface defined by the connecting pin axes; 
           [0020]      FIG. 5  is a sectional view taken on a section plane V-V in  FIG. 4 , illustrating engagement of the chain with a sprocket; and 
           [0021]      FIG. 6  is an enlarged sectional view taken on section plane VI-VI in  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0022]    As shown in  FIG. 1 , the timing drive  100  of an engine  1  is located inside a timing drive cover  2  and includes a bushingless roller chain C having, as shown in  FIGS. 2-4 , a plurality of rollers  150  respectively rotatable on, and directly supported by, a connecting pins  140 . Each of sprockets  101  has a plurality of sprocket teeth  102  ( FIG. 5 ) which engage with the rollers  150 . The chain C is an endless chain in the form of a loop and is in sliding engagement with two chain guides  110 . 
         [0023]    The sprockets include a driving sprocket  103  on and driven by a crankshaft  10 , and a pair of driven sprockets  104  and  105  on valve-operating camshafts  11  and  12 , respectively. 
         [0024]    The chain guides  110  include a movable chain guide  111 , on the slack side C 1  of the chain C that travels from sprocket  103  toward sprocket  104 , and a stationary chain guide  116 , on the tension side C 2  of the chain that travels from sprocket  105  toward sprocket  103 . 
         [0025]    A chain tensioner assembly  111  includes a tensioner  112  that exerts a biasing force for applying tension to the traveling chain C, and a guide lever  113 , pivoted on pin  5  and biased by the tensioner  112  so that it presses against the chain. 
         [0026]    The stationary chain guide  116  comprises stationary guide member  117 , supported in fixed relation to the engine by a pair of supports  6  provided on the engine block. 
         [0027]    The guide lever  113  and the stationary guide member  117  have surfaces  114  and  118  respectively, in sliding contact with the chain C. 
         [0028]    The chain transmission  100  is disposed within an enclosed, oil-tight space  3  formed by the engine block and the timing chain cover  2 . The chain C, the sprocket teeth, the sliding contact surfaces of the guides, and other engine components within the space  3  are lubricated by oil supplied from the engine oil pump (not shown). One or more oil jets (not shown) can be used to direct oil to the regions that contact each other movably, e.g., the regions in which the rollers contact the teeth of the sprockets and the regions in which the chain comes into sliding contact with the guides. 
         [0029]    As shown in  FIGS. 2 through 4 , the chain C includes a plurality of sets of outer link plates  120  that face each other in pairs while being spaced from each other in the direction of the width of the chain. The chain also includes sets inner link plates  130  that face each other in pairs, the plates of each pair also being spaced from each other in the direction of the width of the chain. The pairs of inner link plates  130  are arranged in alternating relationship with the pairs of outer link plates  120 , and connecting pins  140 , press-fit into pin holes  126  in the outer link plates extend rotatably through holes  136  in the inner link plates, thereby holding the element so the chain together while allowing articulation of the chain. Each of the pins  140  extends through a roller  150  disposed between a pair of inner link plates  130 . 
         [0030]    The traveling direction of the chain is the direction in which the chain C moves as it engages with sprockets  103 - 105  in  FIG. 1 , and the chain width direction is the direction parallel with the axes Lc of the connecting pins  140  about which the chain bends as the inner link plates  130  articulate with respect to the outer plates  120  as shown in  FIG. 3 . The chain width direction is also parallel to the axes of rotation of the sprockets  103 - 105 . Radial and circumferential directions are directions defined with reference to axes Lc of the connecting pins  140 . 
         [0031]    Each of the outer link plates  120  has an outer circumferential surface  121  symmetrical about a reference line Lp extending perpendicularly through pin axes Lc. Circumferential surface  121  includes an inner surface  122  facing toward the inside of the loop formed by the chain and an opposite back surface  123  facing toward the outside of the loop. The chain height direction is a direction orthogonal to the reference line Lp when seen from the side. 
         [0032]    As shown in  FIG. 3 , the back surface  123  faces toward the sliding contact surfaces  114  and  118  of the chain guides. The inner surface  122  is located on the side opposite from the back surface  123 , i.e., on the side facing the sprockets. The inner surface  122  and the back surface  123  have straight flat portions  124  parallel to the reference line Lp. 
         [0033]    Each outer link plate  120  is provided with a pair of pin holes  126  separated from each other along the direction of chain travel. As shown in  FIG. 4 , opposite end portions  141  and  142  of each connecting pin  140  are press-fit to the pin holes  126  in the outer link plates, and fill the pin holes in such a way as to prevent oil from flowing though the pin holes. As an alternative to press-fitting, the connecting pins can be welded or otherwise fixed to the outer link plates. 
         [0034]    Each inner link plate  130  has an outer circumferential surface  131  symmetrical about a reference line Lp. The outer circumferential surface includes an inner surface  132  facing the sprockets and an opposite back surface  133  that faces the guides. 
         [0035]    Each inner link plate  130  is provided with a pair of circular through holes  136  separated from each other along the direction of chain travel. Connecting pins  140  fit loosely through these holes. The connecting pins  140  support the inner link plates  130  directly, and the inner link plates are rotatable relative to the outer plates  120  about axes Lc. 
         [0036]    As shown in  FIG. 6 , a radial gap R 1  is formed between the outer circumferential surface of each pin and the inner surface  137  of the through hole  136 . 
         [0037]    The thickness of the inner link plates  130  is preferably larger than the thickness of the outer link plate  120 , as shown in  FIGS. 4 and 5 . 
         [0038]    As shown in  FIGS. 3 and 5 , the height of the inner link plate  130  is greater than the height of the outer plate  120  so that the back surface  133  and the inner surface  132  of the inner link plate  130  project in the chain height direction beyond the back surface  123  and the inner surface  122  of the outer plate  120  respectively when the pairs of the outer link plates  120  and the pair of inner link plates  130  are connected by the connecting pins  140 . Therefore, only the inner link plates  130  of the chain C, contact the sliding contact surfaces  114  and  118  of the chain guides. The back surface  133  of each inner link plate  130  has a single contact portion  134  that comes into sliding contact with surfaces  114  and  118  of the guides. This contact portion  134  is only a part of the back surface  133 , and is in the form of a convex arc having an axis perpendicular to the direction of chain travel and parallel to the axes of the connecting pins. The arc is generally circular in shape but can be a composite arc having a varying radius of curvature. 
         [0039]    As shown in  FIG. 4 , each of the connecting pins  140  has a constant outer diameter at least within the range in which the roller  150  and the pair of inner link plates  130  are movable by in the chain width direction. 
         [0040]    In the assembly of the chain, as shown in  FIG. 2 , end portions  141  ( FIG. 4 ) of a pair of connecting pins  140  are press-fit into the pair of pin holes  126  of an outer link plate  120 A. Each connecting pin  140  is then inserted sequentially through an inner link plate  130 A, a roller  150 , and another inner link plate  130 . End portions  142  ( FIG. 4 ) of the respective connecting pins  140  are press-fit into pin holes  126  of an outer link plate  120 B which is opposite to and paired with outer link plate  120 A. The chain C can be assembled efficiently from one side in the chain width direction. 
         [0041]    As shown in  FIGS. 5 and 6 , widthwise gaps A 1  exist between the outer link plates  120  and the inner link plates  130  and widthwise gaps A 2  are produced between the inner link plates  120  and the roller  150 . These gaps allow the inner link plates  130  and the roller  150  to move in the chain width direction even though the outer link plates  120  are connected to inner link plates  130  by a connecting pin  140 . Both gaps A 1  and A 2  are between the outer link plates  120  and the roller  150 . 
         [0042]    As shown in  FIG. 5 , the roller  150  has a roller width Wr which is larger than the maximum width Ws of a sprocket tooth  102 . 
         [0043]    As shown in  FIG. 6 , the inner diameter Dr of the roller  150 , defined by an inner circumferential surface  157 , is larger than the diameter Db of the through hole  136  of the inner link plate  130 . The inner diameter Dr and the hole diameter Db are both larger than the outer diameter Dp of the connecting pin  140  defined by its outer circumferential surface  147 . Moreover, diameter Dr is larger than diameter Db. Therefore the width E 2  of the radial gap R 2  between the inner circumferential surface  157  of the roller  150  and the outer circumferential surface  147  of the connecting pin  140  is greater than the width E 1  of the radial gap R 1  between the outer circumferential surface  147  of the connecting pin and the inner circumferential surface  137  of the through hole in the inner link plate. The radial widths E 1  and E 2  are the radial widths of the gaps R 1  and R 2  when the roller  150 , the through hole  136  and the connecting pin  140  are coaxial. 
         [0044]    An oil film F is formed by oil supplied from an oil supply to the chain transmission chamber  3  ( FIG. 1 ) in the radial gap R 2  between the outer circumferential surface  147  of the connecting pin  140  and the inner circumferential surface  157  of the roller  150 . 
         [0045]    As a result of variation of the frictional force between the contact portion  134  and the sliding contact surfaces  114  and  118  as an inner link plate comes into contact with and departs from the sliding contact surface, and as a result of variations in chain tension, the inner link plate  130  oscillates within a range restricted by the connecting pins. As the inner link plate oscillates, the radial gap R 1  of the inner link plate  130  oscillates around a connecting pin  140 . 
         [0046]    When the link radial gap R 1  is reduced, part of the oil held in the gap is pushed outward in the chain width direction and enters the radial gap R 2 , thus increasing the amount of oil forming the oil film F. 
         [0047]    Because of the convex shape of the back surface  133  of the inner link plate, the contact area between the back surface  133  of the inner link plate  130  and the sliding-contact surfaces  114  and  118  of the chain guide  110  is reduced. Moreover, the outer plate  120  does not contact the sliding-contact surfaces  114  and  118  at all. Accordingly, frictional loss is reduced, and the power transmission efficiency of the chain transmission can be improved. 
         [0048]    The oscillation of the inner link plate  130  that would otherwise be transmitted to the connecting pin  140  is absorbed by the radial gap R 1  between the connecting pin  140  and the through hole  136  because the connecting pin  140  is loosely fitted through the through hole  136 . Therefore, compared to the oscillation of a thickness of an oil film between a bushing and a roller in a roller chain having bushings fixed to its inner link plates, it is possible to achieve a greater suppression of the oscillation of the thickness of the oil film F between the connecting pin  140  and the roller  150 . Moreover, it is possible to stabilize the impact reducing effect brought about by the oil film F, i.e., the impact applied by the sprocket teeth to the rollers and the connecting pins when the rollers starts to engage with the sprocket teeth. As a result, it is possible to reduce the noise otherwise caused by the impact of the sprocket teeth and the rollers, and to improve the durability of the rollers and the connecting pins, and the overall durability of the chain. 
         [0049]    Because the inner link plate  130  oscillates when the contact portion  134  slides on sliding contact surfaces  114  and  118 , the region where the contact portion  134  contacts surfaces  114  and  118 , and the region where the connecting pin  140  contacts the inner surface  137  of the through hole  136 , are dispersed. Therefore, it is possible to suppress the wear of surface  137  which would occur if the contact regions were concentrated. 
         [0050]    Where the thickness of the inner link plate  130  is larger than the thickness of the outer plate  120  wear is suppressed still further, and it is possible to realizes further improvements in the durability of the inner link plates  130  and the connecting pins  140 , and to improve the overall durability of the chain. 
         [0051]    The roller width Wr is larger the maximum tooth width Ws of the sprocket tooth  102  and widthwise gaps in which the inner link plates  130  are movable in the chain width direction are produced between the outer link plates  120  and the roller  150 . Because the roller width Wr is larger than the maximum tooth width Ws, it is possible to suppress collision between the sprocket tooth  102  and inner link plates  130 , and to suppress wear of the inner link plates  130 . 
         [0052]    Because widthwise gaps A 1  and A 2 , in which the inner link plates  130  are movable in the chain width direction, are produced between the outer link plates  120  and the roller  150 , it is possible to alleviate the impact caused by the collision of the inner link plate  130  and a sprocket tooth  102 , and to reduce the noise and wear caused by the collision. 
         [0053]    Because the inner diameter Dr of the roller  150  is larger than the diameter Db of the through hole  136 , while the outer circumferential surface  147  of the connecting pin  140  has a uniform outer diameter Dp, flow of oil held between the roller  150  and the inner link plate  130  to the outer plate  120  through gap R 1  is suppressed. On the other hand, oil can more readily flow into the radial gap R 2  between the connecting pin  140  and the roller  150 . Therefore, the formation of the oil film F and the increase of its thickness are accelerated. It then becomes possible to enhance the effect the oil film F in reducing the impact acting on the rollers  150  and the connecting pins  140  when a roller  150  begins to engage a sprocket tooth  102 . Accordingly, it is possible to reduce the noise generated when a roller  150  starts to engage the sprocket tooth  102  and to improve the durability of the rollers and the connecting pins. 
         [0054]    In addition, because the hole in the outer link plate to which the connecting pin  140  is secured is oil-tight, oil is prevented from flowing to the outside of the outer link plate along the connecting pin. As a result, oil held between the roller  150  and the inner link plates  130  can be utilized for forming the oil film F more efficiently. 
         [0055]    In a modified configuration of the chain, the back surface  133  of the inner link plate  130  may have other configurations that contact sliding contact surfaces  114  and  118  of the guides in a manner similarly to the manner in which contact portion  134  contacts the guide surfaces. Moreover, the outer circumferential surfaces  121  and  131  of the respective link plates need not be symmetrical about the reference lines Lp. 
         [0056]    The chain transmission apparatus of the invention can be utilized not only in automobile engines but as a power transmission apparatus in industrial machinery, conveyors and various other kinds of machinery.