Timing chain snubber

An engine timing chain snubber comprises a pair of guide shoes fixedly supported on the engine block and extending in line-to-line nondeflecting contact with the inner sides of unsupported chain portions between drive and driven sprockets. The guide shoes prevent movement of the chain runs inwardly of their tensioned positions and thus prevent chain oscillation or vibration.

BACKGROUND OF THE INVENTION 
It is well known in the art to utilize a chain, either of the link or 
silent type, to connect sprockets on the crankshaft and camshaft of an 
engine to drive the camshaft and its associated valve gear. In many such 
applications it has been found desirable to prevent or damp out vibrations 
in the chain runs, the unsupported portions between the sprockets, by 
providing some sort of snubbing or tensioning arrangement. Known 
arrangements include systems wherein a movable shoe is yieldingly urged 
into engagement with the slack side of the chain. In some cases, a fixed 
snubbing shoe is also provided in position to contact the tensioned or 
driving side of the chain. Such arrangements have been effective in 
snubbing chain vibrations and taking up slack that may exist or develop in 
the timing chain; however, such arrangements apply some load to the chain 
which is in turn added to the load already carried by the sprockets in 
driving the camshaft. This loading of the chain increases the driving 
forces and may noticeably increase wear on the sprockets, as well as the 
tensioning device itself. In addition, such snubbing arrangements may be 
complex and involve substantial cost to manufacture, install and maintain. 
SUMMARY OF THE INVENTION 
The present invention provides a simplified engine timing chain snubber 
which is relatively inexpensive to manufacture and install, is less 
subject to wear than conventional arrangements and accomplishes the 
purpose of preventing chain vibration without loading the chain so as to 
contribute to chain or sprocket wear. These and other features of the 
invention will be more fully understood from the following description of 
a preferred embodiment taken together with the accompanying drawing.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT 
In the drawing, numeral 10 generally indicates an internal combustion 
engine of largely conventional construction and having a frame or cylinder 
block 12 in which are rotatably supported in spaced parallel relation a 
crankshaft 14 and a camshaft 16. Sprockets 18 and 20 are provided on the 
ends of the crankshaft and camshaft, respectively, and are engaged by a 
timing chain 22 which drivingly interconnects the crankshaft 14 with the 
camshaft and relates them in predetermined fashion so that in a 
four-stroke cycle engine of the type shown, the camshaft rotates at a 
speed one-half the speed of the crankshaft. 
The timing chain extends around both sprockets and between them in 
conventional fashion so that at any particular moment of time the chain 
has a first supported portion 24 engaging the drive sprocket 18, a second 
supported portion 26 engaging the driven sprocket 20 and first and second 
runs or unsupported portions 28, 30 which extend between the peripheries 
of the drive and driven sprockets. As is common in such drive chains where 
the unsupported portions or runs are of substantial length, undesirable 
vibration is likely to occur in the chain runs, causing increased wear and 
possible damage to the chain and sprockets if some means of snubbing, 
damping or otherwise preventing such vibration is not provided. 
The present invention provides the needed chain snubbing function by means 
of a snubber member generally indicated by numeral 32. Snubber 32 includes 
a formed sheet metal base portion 34 having a flat center section 36 with 
upturned upper and lower edges 38, 40, respectively, arranged to stiffen 
the center section. 
Openings 42, 44 are provided in the center section to receive bolts or 
other fasteners, not shown, for securing the center section against the 
front face of the engine frame 12. Opening 44 is formed in part by an 
extending wall portion 46 which is adapted to be received in a suitable 
counterbored recess of the engine frame or block to properly position the 
snubber member upon assembly. 
The opposite sides of the snubber member are provided with upstanding wall 
portions 48, 50 formed integrally with the center section and upper and 
lower edges. Portions 48, 50 in turn support individual nonmetallic guide 
shoes 52, 54 respectively, which are secured to the outer faces of the 
wall portions 48, 50. 
The outer surfaces of the guide shoes 52, 54 extend in line-to-line 
nondeflecting contact with the opposed inner sides of the chain runs or 
unsupported portions 28, 30 over most of their length when they are in 
their tensioned positions. If desired, a slightly angled lead-in ramp 56 
may be provided at the end of the shoe 52 from which the chain moves from 
the drive sprocket into engagement with the shoe in order to provide for a 
smooth engagement of the chain with the surface of the shoe. 
In operation, rotation of the crankshaft and camshaft sprockets are in 
clockwise direction as viewed in drawing FIGS. 1 and 2. Thus, the 
direction of chain movement is upwardly in run 28 and downwardly in run 
30, with run 30 carrying the driving load and normally being tensioned and 
run 28 being the slack side of the chain. 
Because of the tension, run 30 is normally held relatively straight and in 
line-to-line contact with its guide shoe 54. Vibration which might 
otherwise be set up in this run is prevented by the shoe 54 which allows 
only outward movement of the chain run from its nominal tensioned drive 
position and does not permit any movement inward thereof. Thus, 
oscillation of chain run 30 in a vibrating motion is not possible. 
Chain run 28, being the slack side, is of course free to move outwardly 
from the position of its guide shoe 52. However, in actual practice it is 
found that the tendency of the slack side of the chain is to be carried 
inwardly somewhat by the drive sprocket and to try to move in an inward 
direction. This tendency is prevented by the presence of guide shoe 52, 
the lead-in ramp 56 of which guides entering portions of the chain off of 
the adjacent drive sprocket and onto the surface of the shoe. 
Oscillation or vibration of the slack side 28 of the chain is prevented as 
effectively as vibration of the taut side. Since the chain cannot move 
inwardly from its straight line tensioned position, the freedom to move 
outwardly does not result in generating vibrational problems. Thus, both 
runs or unsupported portions of the timing chain are effectively damped or 
snubbed so that vibration problems do not occur in the timing chain 
system. 
Because of the line-to-line nondeflecting contact positioning of the guide 
shoes with the chain runs, the chain snubber of the present invention does 
not place any side loading on either of the chain runs. Rather, it merely 
passively prevents movement inwardly from their tensioned positions of the 
chain unsupported portions. Thus, except for light friction caused by 
unloaded rubbing of the chain links against the guide shoes, the snubber 
does not increase the drive loading on the chain sprockets. Accordingly, 
it has little or no effect on their wear life, except as it increases such 
life by avoiding damaging vibration effects in the chain itself. 
Thus, the present invention provides a simple, inexpensively manufactured 
and easily installed chain snubbing device which effectively prevents 
chain vibrations and increases component life without adding to drive 
loading or other problems. Any suitable materials may be used for the 
various parts of the snubber. In a preferred embodiment it utilizes a 
bracket or base portion formed of steel with guide shoes molded thereon 
and formed from a nylon base material, preferably containing molybdenum 
disulfide, one form of which is available commercially under the tradename 
Nylatron. 
While the invention has been described by reference to a specific 
embodiment, it should be understood that numerous changes could be made 
without departing from the inventive concepts disclosed. Accordingly, the 
invention is not intended to be limited except by the language of the 
following claims.