The present invention relates to a chain of the kind used for power transmission purposes including transportation in a conveyor.
A conventional chain used for transmission or transportation purposes has overlapping chain link members or plates that are interconnected by pins that pass through aligned holes in adjacent link members. In roller bush chains opposed inner link plates are connected with opposed pairs of outer link plates by pins about which the inner link plates articulate but to which the outer link plates are fixed by, for example, an interference fit. The opposed inner link plates are joined by a transverse bush that is received in apertures in the plates and through which the connecting pin passes. A roller is rotatably disposed on the bush.
A conventional chain of the kind described above is generally driven by a sprocket and suffers from noise that occurs during meshing of the chain with sprocket teeth. The collision between a chain and sprocket happens rapidly during meshing as a result of what is known as “polygonal effect” or “chordal effect”. These terms describe the uncontrolled and rapid movement of the chain links relative to the sprocket teeth during meshing and unmeshing. The movement arises from the fact that pitch line of the chain comprises a plurality of straight lines or chords that combine to form part of a polygon rather than a circle (as would be the case for a flexible belt). The rapid and uncontrolled movement of the chain links results in them impacting on the sprocket with a high velocity thereby generating significant noise.
Another problem with conventional transmission chains is their tendency to wear as a result of rubbing contact between components of the chain. In particular there is significant wear at the bearing contact surfaces between the chain links and the pins. Wear in chains leads to chain elongation, inefficient power transmission or unmeshing of the chain from the sprockets. Attempts to reduce the tendency to wear include making the bearing contact surfaces smooth and hard and regular lubrication both of which add significant cost to the manufacture and/or running of a chain.
It is an object of the present invention to obviate or mitigate the aforesaid disadvantages.
According to the present invention there is provided a power transmission chain having a longitudinal axis and comprising opposed first link members arranged alternately with opposed second link members along the length of the chain, the first link members interconnecting adjacent second link members in an articulated manner, a clearance defined between adjacent second link members, and a pin disposed in said clearance and extending in a direction transverse to the chain axis, each first link member being fixed to the pin so that it does not rotate relative thereto, each second link member being free to articulate relative to the pin, the first link member defining a first bearing surface extending in a direction transverse to the direction of the longitudinal axis of the chain and each second link member defining a second bearing surface extending in a direction transverse to that of the longitudinal axis of the chain, at least one of the first or second bearing surfaces being arcuate and the first and second bearing surfaces being in engagement with one another to provide an articulating joint in which there is rolling contact between the bearing surfaces during articulation of the links.
The rolling contact between the first and second link members provides a significant reduction in the wear of the chain as it eliminates the rubbing contact between the pin and the link plates.
Each second link member is disposed between adjacent pins.
There are preferably two such first and second bearing surfaces in rolling contact between adjacent pins. The arrangement provides for a chain that has relatively few components and which has two articulating points per chain link pitch. This reduces the polygonal effect and thus the attendant noise.
The first link member may be fixed to said pin by means of a friction fit. Ideally the first link member has an aperture and the periphery of that part of the link member that defines the aperture is a friction fit with the external surface of the pin.
There may be a roller rotatably disposed on the pin.
Each first link member may have two or more parts.
Each first link member comprises a plate having a main portion that extends in a direction along the length of the chain and walls that extend in a direction transverse to chain axis. Each of the walls preferably defines said first bearing surface. Each first link member ideally has two such walls providing a first bearing surface for the second link members on each side of the first link member along the length of the chain.
Each second link member preferably has a central opening. The second bearing surface may be defined by part of the member that defines the opening. In one preferred embodiment the second bearing surface is arcuate and the first bearing surface is planar. However, in an alternative preferred design the second bearing surface is planar and the first bearing surface is arcuate. In a further alternative preferred design both surfaces are arcuate. The arcuate surface (or surfaces) may be symmetrical or asymmetrical.
The first link member may extend on the outside of part of the second link member. In such a design the walls extend inwardly toward the axis of the chain. In an alternative preferred embodiment the main portion of the first link member is disposed in-board of the second link member and the walls extend outwardly of the axis. The walls may have retaining portions that prevent separation of the first and second link members. The retaining portions preferably extend in a plane that is substantially parallel to the plane occupied by the main portion of the first link member.
The first link member may comprise two portions. Preferably a first portion is disposed in-board of the second link members and a second portion extends over the outside of the second link members. One or both portions may have the walls that that define the first bearing surface.
Preferably there is a clearance between the ends of the walls and the inner link members so as to allow for articulation of the second link members.
The ends of second link members ideally have a recess for receipt of the pin. The recess may be of a shape that defines part of a circle.
The chain may be a leaf chain with interleaved strands of first and second link members.
In one possible embodiment opposed second link members are connected to one another. Opposed second link members may be connected by part-cylindrical sections. There is preferably such a section at each end of the second link members.
Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:
Referring now to
A cylindrical roller 14 is rotatably and concentrically mounted on each of the pins 13 and extends transversely between the two sides of the chain.
Adjacent inner link plates 11 on each side of the chain are interconnected by an outer link plate 12 in a manner that allows articulation between them and the inner link plates 11. Each inner link plate 11 is in the form of a frame-like member with two spaced, parallel, straight limbs 11a extending in parallel to the longitudinal axis of the chain and connected at each end by arcuate limbs 11b so as define a central opening 15. The inner periphery of each of the arcuate limbs 11b (facing the opening) defines a bearing surface 16 for engagement with an outer link plate 12. The outer periphery of each limb 11b has a circular sector cut-out 17 that provides space for the pin 13. It is important that there is sufficient clearance between the outer periphery and the pin 13 so that the inner link 11 is free to articulate in the intended manner.
The outer link plate 12 overlaps the ends of adjacent inner link plates 11 and has a central aperture 18 that receives the pin in a friction-fit or interference-fit engagement, although other forms of connection are possible. A wall 19, defined at each end of the outer link plate 12, projects into the central opening 15 in the inner link plates 11 immediately adjacent to the arcuate limbs 11b so as to prevent separation of the inner link plates 11 in the direction of the chain. The length of each wall 19 extends in a direction substantially perpendicular to the straight limbs 11a of the inner link plates and defines an inwardly facing planar bearing surface 20 that faces and bears against the bearing surface 16 of the adjacent inner link plate 11. The walls 19 of each outer link 12 thus serve to carry the load applied to the chain 10.
It will be understood from the described design that the inner link plates 11 are disposed freely between each adjacent pair of pins 13 but are held in position along the length of the chain by the outer link plate 12. In use, the chain meshes with a toothed sprocket in the conventional way. When articulation occurs the bearing surfaces 20, 16 of the outer and inner link plates 12, 11 roll over one another as illustrated in
In view of the central opening 15 of the inner link plate 11, the chain 10 has a lower mass in comparison to a conventional chain. It therefore has the potential for running at higher speeds than currently possible.
A polymer washer or liner (not shown in the figures) may be disposed in a clearance between the end of the roller 14 and the inner link plate 11 to provide damping of any lateral movement of the inner link plate during use.
An alternative design is shown in
In the embodiment of
In
In the embodiment of
The chain illustrated in
It will be appreciated that numerous modifications to the above described design may be made without departing from the scope of the invention as defined in the appended claims. For example, the exact profile of the bearing surface defined on the arcuate limb of the inner or intermediate link plates can take any suitable form. In particular the profile may be asymmetrical so that the amount of articulation of the links when the chain bends in one direction is not the same as that in the other direction. This design can be used in particular in an “anti back bend” chain where full articulation is desirable in one direction for the chain to pass around a sprocket but articulation is prevented in the opposite direction. Furthermore the pin need not be cylindrical as shown in the figures but may take any convenient shape or form.
Number | Date | Country | Kind |
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0329414.7 | Dec 2003 | GB | national |