Torsional vibration damper

A torsional vibration damper of the type that incorporates a plurality of radially extending springs in chambers containing damping fluid. The springs flexibly connect an inner hub with an annular outer component comprised of two rings fastened in abutting relation. Opposed recesses in the rings form spring receiving chambers. The outer ends of the springs are clamped either by shims or spring seating wedges acting against the side walls of the recesses, thus eliminating the need for a peripheral clamping ring holding the springs in clamped relation.

TECHNICAL FIELD 
This present invention relates to an improved torsional vibration damping 
mechanism for damping angular oscillation and/or to a coupling mechanism 
for transmitting torque. 
BACKGROUND ART 
There exists a class of torsional vibration dampers of the kind in which 
radially disposed springs in chambers containing damping fluid 
interconnect coaxial inner and outer components which are rotatable 
relative to one another to flex the springs and achieve a damping effect. 
An example of this type of damping is described in U.S. Pat. No. 3,996,767 
to Geislinger. This device comprises a hub integral with an output/input 
shaft. The hub and a clamping ring define therebetween an annular damping 
chamber defined at one end face by a coupling flange and at the other end 
face by a cover plate. Angularly spaced groups of flexible leaf springs 
are arranged in this chamber and extend radially between the hub and the 
clamping ring which locks the leaf springs in position. The leaf springs 
are radially inwardly tapered and a plurality of intermediate wedge-shaped 
elements are arranged between respective groups of leaf springs. The leaf 
spring groups and the wedge-shaped elements are assembled by placing the 
clamping ring around them in tension. 
This type of coupling is expensive because it requires complex assembly of 
many parts which must be premachined to high tolerances. In particular, 
the groups of springs, wedge-shaped elements and clamping ring must all be 
accurately positioned relative to each other and the central hub. This 
type of damper is assembled by placing the wedges, springs and necessary 
shims to form a ring and then placing an outer clamping ring over the 
assembly of individual parts. The clamping ring serves the purpose of 
clamping the outer ends of the springs so it must either be heat shrunk 
onto the periphery of the assembly or incorporate a design which allows it 
to be urged inwardly. Since there are a multiplicity of individual 
components, any inaccuracy will be magnified because of the stack-up of 
tolerances. As a result, the hoop stress of the clamping ring can rise to 
a level where cracking of the ring could occur. 
It is an object of the present invention to obviate or mitigate the 
aforesaid disadvantage. 
DISCLOSURE OF THE INVENTION 
According to the present invention the above objects are achieved by a 
torsional vibration damping or coupling mechanism comprising an inner 
annular element and means forming an outer annular element divided 
radially into two mating rings with facing recesses together defining 
radial spring-receiving slots at the outer ends of which a plurality 
springs are clamped individually without recourse to a common clamping 
ring and extend radially inward to corresponding slots on the inner 
annular element. 
The above and other related objects and features of the invention will be 
apparent from a reading of the following description of the disclosure and 
the novelty thereof pointed out in the appended claims.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring now to FIGS. 1 and 2, a first embodiment of a torsional vibration 
damper comprises an annular hub 1 fixed to a shaft (not shown) received in 
a bore 2. The hub 1 is encircled by an annular outer component 3 
comprising two rings 4, 5 held in mating contact by bolts 6 with heads 7 
and extending through equi-angularly spaced holes into engagement with 
hexagonal nuts 8, the bolt heads 7 and the nuts 8 being located in 
recesses 9, 10 of the rings 5, 4, respectively. The exposed side of the 
ring 5 projects radially inwardly as an integral flange 11 over end face 
1a of the hub 1 and a seal 12 such as an elastomeric o-ring is provided 
between the flange 11 and the hub 1. At the opposite end face 1b of the 
hub 1 the function of the flange 11 is served by a removable annular side 
plate 13 held in position against end face 1b by equi-angularly spaced 
screws 14. A seal 15 is provided between the side plate 13 and the hub 1 
and a further seal 15a is provided between the side plate 13 and the ring 
4. Seals 15, 15a may be formed from elastomeric o-rings. 
The hub 1 has a plurality of radial bores 16 for transmitting engine 
lubricating oil serving as a damping fluid from a central reservoir (not 
shown) to spring chambers 17 in the annular component 3. Each spring 
chamber 17 initially comprises a substantially parallel-sided uniform 
cross-section slot defined partly by a radially extending recess 17a 
formed in the face 4a of ring 4 and partly by a corresponding radially 
extending recess 17b in the confronting face 5a of the ring 5. When the 
two opposed rings 4 and 5 have been assembled to cause end faces 4a and 
5a to abut as illustrated in FIG. 1, the spring chambers 17 are enlarged 
at their radially outer end and extended axially over the full width of 
the annular component 3 to form enlarged slots 18. Preferably slots 18 are 
formed by milling in an axial direction across the rings 4 and 5. By 
milling slots 18 after rings 4 and 5 are in their assembled position, the 
accuracy of the slots 18 is greatly enhanced. 
Each slot 18 receives a pair of spring seating wedges 19 for seating a 
spring 20 having a thickness which tapers radially inwardly and has its 
inner end located in a corresponding outer facing slot 21 in the hub 1. 
Each spring 20 may comprise a single leaf or consist of a pack of two or 
more leaves separated by shims. Illustrated are springs comprising a pair 
of leaves 32 and 33 separated by a shim 34. Shim 34 may be formed from 
material with inherent lubricity and is provided to reduce fretting and 
wear on the opposing faces of the springs during flexing. In addition, 
shim 34 may be sized to eliminate backlash between the inner portion of 
spring 20 and corresponding slot 21. The springs 20 are retained in slots 
18 by retaining clamps 22 attached by screws 23a and 23b to the annular 
periphery of rings 4 and 5, respectively. 
Assembly is carried out by fitting one or more shims (not shown) as needed 
between the spring seating wedges 19 and the enlarged slot 18 sides 18a, 
18b to accurately position the radially inner ends of the springs 20 in 
the hub pockets 21. The shims are sized such that when the springs 17 are 
driven radially inwards, the taper on their outer faces produces a tight 
compression fit of the springs 20, spring seating wedges 19 and shims in 
the slots 18. The small angle of this taper, usually together with the 
lateral location provided at the spring seats by the clamps 22 gives 
improved control of the spring position during fitting thus allowing each 
spring pair to be assembled individually. This makes assembly much easier 
than the complex simultaneous assembly of prior art designs discussed 
above which use a common clamping ring for driving the springs into their 
seats. Because the clamping force for the outer ends of the springs 20 is 
provided by the structure making up the opposed rings 4 and 5, there is no 
need for a peripheral clamping ring that has a critical limit on its hoop 
stress. 
In operation, relative rotation displacement between the annular component 
3 and the hub 1 causes flexing of the springs 20 in their chambers 17. As 
a result, damping fluid flows through clearances 24 between the long edges 
of the springs 20 and the adjacent walls of the chambers 17 to achieve the 
desired damping effect. 
Alternatively, controlled clearances may be provided between the inner 
diameters 4b, 5b of rings 4, 5, respectively, and the outer diameter 2b of 
hub 2 so as to permit flow of damping fluid between adjacent spring 
chambers 17. For the damper shown in FIG. 2, the flow would be from the 
side of spring chamber 17 (at the one o'clock position) to the right of 
the spring 20 that chamber to the side of spring chamber 17 (at the two 
o'clock position) to the left side of the spring in that chamber. 
The radially inner surfaces of the spring seating wedges 19 are convexly 
curved at 19a (FIG. 1) in order to direct radially outwardly flowing 
damping fluid towards the side walls of the chambers 17, past gaps 19b at 
the ends of the wedges 19 and then through small outlet openings 22a to 
the exterior of the damper. The passages 16 are provided to direct a flow 
of fluid through the damper that cools it. In the case of an internal 
combustion engine, lubricating oil which is cooled and filtered is used as 
the fluid. The convex curvature of the seating wedges 19 is provided to 
insure that no dead spaces exist in the damper where sediment entrained in 
the fluid may collect. 
The damper of FIGS. 1 and 2 can be employed in a wide variety of sizes to 
fit different engine applications, although it is preferable that it be 
employed for larger size dampers. The embodiments shown in FIGS. 3-6 show 
dampers that retain common features and benefits but have enhanced 
suitability for smaller sized dampers. 
Referring now to the second embodiment illustrated in FIGS. 3 and 4 the 
torsional vibration damper comprises an annular hub 38 having a bore 40 
which receives a shaft (not shown) whose torsional vibrations are to be 
damped. The hub 38 is encircled by an annular outer component 42 
comprising two rings 44, 46 held in mating contact by bolts 48 with heads 
50 and extending through equi-angularly spaced holes into engagement with 
hexagonal nuts 52, the bolt heads 50 and the nuts 52 being located in 
recesses 54, 56 of the rings 46, 44, respectively. Both rings 44 and 46 
have integral, inwardly extending flanges 58, 60, respectively, that 
embrace opposite end faces of hub 40. Suitable seals 62, such as 
elastomeric o-rings, prevent loss of fluid from chambers internal to the 
torsional vibration damper. 
As is the case with the torsional vibration damper of FIGS. 1 and 2, spring 
chambers 64 each comprise a generally parallel-sided uniform cross-section 
slot defined partly by a radially extending recess 64a in the face 44a of 
ring 44 and a corresponding radially extending recess 64b in the face 46a 
of ring 46. 
However, spring seats 66 are form milled into radially outer ends of the 
slots 64 as shown in FIG. 4a. The spring seats 66 clamp the outer ends of 
springs 68 which may be in unitary form or comprise a pair of leafs 70, 72 
separated by a shim 74. The radially inner ends of springs 68 are received 
in corresponding outer facing slots 75 in hub 38. In this embodiment the 
springs 68 are held in compression between the spring seats 66 through the 
use of suitable shims, when necessary. This allows the elimination of the 
wedges 19 and permits all the springs 68 to be retained by a single outer 
ring 76. It should be noted that ring 76 serves merely to retain and cover 
the outer ends of springs 68. It is not required to provide the clamping 
forces for the springs through hoop stresses as in prior art devices. 
The embodiment of FIGS. 3-4a is intended to be used in 
situations/applications where the damping/coupling mechanism is pre-filled 
with damping fluid and sealed and no provision is made for a continuous 
throughflow of damping fluid. 
In the embodiment of FIGS. 5 and 6 a torsional vibration damper comprises 
an annular hub 80 having an integral inwardly directed flange 82 and holes 
84, only one of which is shown, by which the hub 80 may be mounted to a 
shaft (not shown). The hub 80 is encircled by an annular outer component 
86 comprising two rings 88, 90 held in mating contact by bolts 92 with 
heads 94 and extending through equi-angularly spaced holes into engagement 
with hexagonal nuts 96, the bolt heads 94 and the nuts 96 being located in 
recesses 100, 98 of the rings 90, 88 respectively. The rings 88, 90 are 
maintained on hub 80 by removable annular side plates 102, 104, 
respectively by means of screws 106 threaded into the ends of dowels 108 
extending through the rings 88, 90. 
As is the case with previous embodiments, a plurality of spring chambers 
110 is provided. Each spring chamber 110 comprises a radially extending 
generally parallel-sided uniform cross-section slot defined partly by a 
radially extending recess 110a in the face 88a of ring 88 and a 
corresponding radially extending recess 110b in the face 90a of ring 90. 
However, axially extending tapered spring seats 112 are formed at the 
radially outer end of each spring chamber 110, thereby dispensing with 
wedges. The spring seats 112 may be formed by milling an axially extending 
groove on the periphery of the rings 88, 90 after they are mated together. 
Springs 114 are held in compression between the tapered spring seats 112 
by suitable shims 116. The radially inner ends of springs 114 are received 
in wedge shaped axially extending grooves 115 in the annular hub 80. 
Assembly is carried out by fitting appropriate shims 116 between the 
tapered side faces of the springs 114 and the tapered side faces of the 
spring seats 112. The shims are sized to produce a tight compression fit 
of the springs in the spring seats. This permits elimination of the wedges 
and allows all the springs 114 to be held by a single retaining ring 118 
as in the second embodiment. 
It should be noted that ring 118 serves merely to retain and cover the 
outer ends of springs 114. It is not required to provide the clamping 
forces for holding the springs 114 through hoop stresses as in prior art 
devices. 
Annular side plates 120, 122 are provided on end faces of the rings 88, 90 
respectively so as to close the spring chambers 110 and ring 118 
laterally. The rings 120, 122 are held in position by respective screws 
124, 126. The inner edges 128 of the shims 116 are formed convexly to 
direct damping fluid to gaps 130 formed by sizing the axial length of the 
shims to be slightly less than the dimension of the springs 114 in the 
axially extending direction. The damping fluid flows from the spring 
chamber 110, through gaps 130 to lateral openings 132 thereby keeping the 
spring chambers free of sediment. As an alternative to the lateral 
openings 130 the annular ring 118 may have a similar axial length to the 
shims 116 thereby providing radial outlets 134 for the damping fluid (see 
FIG. 5a). In either case, radial passages 119 in flange 82 provide a 
source of damping fluid to spring chambers 110. 
The springs illustrated for use in the torsional vibration dampers of FIGS. 
1-6 incorporate leaves with a thickness which tapers from their radially 
outer end. Such leaves may be expensive and difficult to manufacture. If 
it is necessary to utilize non-tapered leaves, the spring embodiment of 
FIGS. 7 and 8 may be employed. This embodiment is shown in connection with 
the damper shown in FIGS. 4, but may be employed on any of the other 
dampers described herein. In FIG. 7, the spring chambers 64' have 
positioned in them springs 68' each comprised of flat, substantially 
constant thickness leaves 136, 138. An enlarged, axially directed, slot 
139 is formed at the radially outer end of spring chamber 64'. A pair of 
blocks 141 of appropriate size are positioned on opposite sides of spring 
68' within slot 139 so that spring 68' is clamped or held by the walls of 
slot 139. Leaves 138 are rectangular in plain view as shown in FIG. 8 
while leaves 136 have the same width but incorporate a tapered section 140 
terminating at an inner end 142 short of the length of the rectangular 
leaves 138. A typical spring pack may include two each of leaves 136 and 
138, with leaves 136 being in the center. The advantage of stacking leaves 
in this configuration is that for a given level of stiffness the stress on 
individual springs is reduced. Since the inner ends of leaves 138 are bent 
slightly into grooves 75', any slack between the hub and outer component 
is taken up. The taper on the leaves may be such that the inner edge 142 
is one-fourth of the width of leaf 136 and the taper begins at a point L/4 
where L is equal to the distance from the point at which the taper begins 
to the inner edge of leaf 138. The leaf 136 terminates at a distance L/4 
from the inner edge of leaf 136. 
Although the above description has related to torsional vibration dampers 
it will be appreciated that like constructions may be used in torque 
transmitting coupling mechanisms. In the damping mechanism a shaft, e.g., 
a crankshaft, is connected at one end to the hub. In the case of a 
coupling mechanism the outer component usually is flange connected to a 
shaft to or from which the drive is transmitted through the mechanism by 
an input/output shaft fixed to the hub. 
The throughflow feature for keeping the assembly free from sediment (see 
FIGS. 1 and 2 and FIGS. 5 and 6) has been described in the context of the 
novel torsional vibration damping or coupling mechanism in accordance with 
the present invention. However, it will be appreciated that this feature 
may usefully be incorporated in alternative designs, for example in the 
Geislinger mechanism described in U.S. Pat. No. 3,996,767.