Centrifugal clutch

A centrifugal coupling with fly elements pressable against the internal surface of a friction drum contact to spring biasing forces wherein the fly elements each include at least two concentric partial weights mutually connected by radially-acting compression springs. The radial stroke of the inner partial weight or weights is limited by a primary side stop, so that from a specific predetermined speed any further increase in the centrifugal force from the inner partial weight directly acting upon the outer partial weight is prevented. The partial weights are further provided with check ramps, inclined in the circumferential direction, for a driver pin mounted on the primary side in order to give the torque curve of the coupling an optimum configuration. In some embodiments the check ramp on the outer partial weight may be replaced by a lever mounted on the primary side which transforms the force generated by the inner partial weight into a centripetal force acting upon the outer partial weight.

BACKGROUND AND SUMMARY OF THE INVENTION 
The invention relates generally to centrifugal couplings and, more 
particularly, to such couplings arranged as starting couplings to precede 
an automatic motor vehicle transmission, or installed as bridging 
couplings in a hydrodynamic torque converter. 
It is possible in such couplings for vehicles, during a kick-dwn operation 
and the associated speed jumps, for example, for jolts to occur which may 
interfere considerably with riding comfort and possibly even damage 
components. These jolts or torque surges are attributable to the fact 
that, at high rotary speeds, the torque transmission capacity of the 
centrifugal coupling is a multiple of the engine torque and it is 
therefore impossible for a moderating speed slip to occur. If such a 
coupling were dimensioned so that it can just transmit the engine torque 
at high speeds, then at low speeds and high torques it would always 
operate in the slip range, which would result in considerable wear. 
It is already known, from German Offenlegungsschrift (published unexamined 
patent application) No. 2,913,694, to divide the fly weight element of 
centrifugal couplings into two partial weights mutually connected by a 
spring, and to associate a primary side stop with the inner partial 
weight. Then, with increasing rotary speed, the inner partial weight 
contacts the stop so that with further increasing rotary speed only the 
outer partial weigh is effective as a source additional contact pressure. 
This results in a flattening of the centrifugal coupling torque curve (as 
shown in FIG. 7a) from the speed at which the inner partial weight 
contacts the stop (point A in FIG. 7a). However, torque surges during 
starting and shifting operations are nevertheless left out of 
consideration and not compensated for. 
An object of the present invention is to provide a centrifugal coupling in 
which the torque curve can be influenced by starting and shifting 
operations as well as changes in the rotary speed, and which is 
particularly capable of reducing torque surges. 
This and other objects of the present invention are attained in the 
provision of a centrifugal coupling with fly elements pressable against 
the internal surface of a friction drum counter to spring biasing forces 
wherein the fly elements each include at least two concentric partial 
weights mutually connected by radially-acting compression springs. The 
radial stroke of the inner partial weight or weights is limited by a 
primary side stop, so that from a specific primary speed any further 
increase in the centrifugal force from the inner partial weight directly 
acting upon the outer partial weight is prevented. The partial weights are 
further provided with check ramps, inclined in the circumferential 
direction, for a driver pin mounted on the primary side in order to give 
the torque curve of the coupling an optimum configuration. In some 
embodiments the check ramp on the outer partial weight may be replaced by 
a lever mounted on the primary side which transforms the force generated 
by the inner partial weight into a centripetal force acting upon the outer 
partial weight. 
Other objects, features, and advantages of the present invention will 
become more apparent from the following description when taken with the 
accompanying drawings(s) which show, for purposes of illustration only, an 
embodiment/several embodiments in accordance with the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS 
As may be seen from FIGS. 1-4, the fly weight element means consists of two 
fly element parts or partial weights 1 and 2 which are separated in the 
axial direction and exhibit a movement play S in the radial direction. 
Outer partial weight 1 has a U-shaped cross-section with extending arm 
members 3 and 3'. Internal annular collars 4 and 4' are formed on arm 
members 3 and 3', respectively. The outer cylindrical surface of partial 
weight 1 carries friction lining 13. Inner partial weight 2 is formed so 
as to have an approximately T-shaped cross-section with external annular 
collars 5 and 5' which can be braced against collars 4 and 4', 
respectively, of partial weight 1. The outer partial weight thus encloses 
the inner partial weight in U-shape, considered in axial section. This 
arrangement is particularly preferred because it is economical of space, 
and in this case, due to the annular collars, there is a possibility of 
providing the connecting resilient means, such as compression springs, 
with a desired adjustable tension, as described later. 
Inner partial weight 2 can be moved in the radial direction and in the 
circumferential direction relative to outer partial weight 1. This 
mobility is restricted in that radially arranged spring elements 
(compression springs) 6 establish a tensioning force between the fly 
element parts and bias them apart. Spring elements 6 are mounted in 
depressions 7 on outer partial weight 1 and in bores 8 of inner partial 
weight 2. The tensioning force of spring elements 6, can for example, be 
adjusted by set screws 9. However, it is also sufficient, after the 
assembly of the spring elements between the inner and outer partial 
weights, to close bores 8 and tension the spring elements radially by 
means of pressed-in cylindrical pieces 10, for example. 
Bores 8 are enlarged to a greater diameter 11 in the upper region of inner 
partial weight 2. As a result of this, by exerting a circumferential force 
proportional to the lateral resiliency of spring elements 6, the inner 
partial weight can be displaced within certain limits in the 
circumferential direction relative to outer partial weight 1. 
As FIG. 1 further shows, either or both outer partial weight 1 (illustrated 
on the right) or inner partial weight 2 (illustrated on the left) is 
formed with a pan-like depression 12 at its ends. These depressions serve 
for fixing return springs 23 of the fly element. The return springs 
function to determine the engagement speed of the centrifugal coupling. 
Orifices 14 and 15 are also machined into the partial weights in 
corresponding positions. They serve to accommodate the drive elements for 
the fly element and also for the circumferential force between the driving 
part and the driven part of the centrifugal coupling which results from 
the torque to be transmitted. 
FIG. 3 shows the fly element according to FIG. 1 as it is installed in 
driver ring 16 of a centrifugal coupling. A plurality of such fly elements 
can be present in a single couplin assembly according to the present 
invention. The principle of operation is that return springs 23, braced 
outwardly in driver ring 16, press the fly element radially inwards. Only 
at rotary speeds for which the centrifugal force of the fly element is 
greater than the spring force of the return springs does the fly element 
move radially outwards to overcome movement play S and come into abutment 
against friction drum 17. If the rotary speed is increased further, both 
the transmissible centrifugal force of inner partial weight 2 and that of 
outer partial weight 1, and therefore, via friction lining 13 and the 
corresponding friction drum radius, the transmissible torque of the 
centrifugal coupling, increase. 
If the rotary speed is increased until the tensioning force of compression 
springs 6 is exceeded by the centrifugal force of inner partial weight 2, 
then inner partial weight 2 moves radially towards outer partial weight 1. 
The force on the springs produced due to this movement is transmitted 
directly to outer partial weight 1 and is added to the centrifugal force 
of the outer partial weight. According to the rotary speed, this movement 
of inner partial weight 2 can occur until the inner part of orifice 14 
abuts the primary side radial stop, which, in this case for example, is 
bolt-shaped driver 18 mounted firmly in driver ring 16. 
From this moment onwards, despite increases in rotary speed, no further 
additional centrifugal force of inner partial weight 2 can be transmitted 
to outer partial weight 1. The force acting from inner partial weight 2 
upon outer partial weight 1 now remains constant, and only the 
transmissible centrifugal force of outer partial weight 1 continues to 
increase with increasing rotary speed to increase the transmissible torque 
of the centrifugal coupling. This relationship of the coupling torque with 
respect to the motor torque is illustrated diagramaticly in FIG. 7a. It 
has been found that the flattening of the coupling torque curve in this 
case is the greater, the smaller the mass of the outer partial weight 
relative to that of the inner partial weight. 
During this process, due to the circumferential force, the entire fly 
element can move towards driver 18 in the circumferential direction, 
namely until a lateral side of orifice 14 comes to abut the driver. The 
torque can therefore then be transmitted from driver ring 16 through 
driver 18, the fly element and friction lining 13 to friction drum 17. 
During that phase of operation before the driver is contacted by a lateral 
side of orifice 14, torque transmission occurs via the lateral deflection 
of the return springs 23 mounted in the driver ring, and therefore a soft 
engagement is ensured. 
The resilient means for establishing tensioning force between the inner and 
outer partial weights is not restricted in the present invention to the 
use of cylindrical helicoidal springs, for example, as shown in FIG. 1. 
Cup spring arrangements or rubber springs (elastomers) or other known 
means may also be employed. In another embodiment of the present 
invention, shown in cross-sectional detail in FIG. 9, one or more 
appropriately dimensioned, thin-walled tubular pieces or tubular sections 
206 are employed as tubular springs between inner partial weight 202 and 
outer partial weight 201. 
Up to this point in the description of the present invention, the 
principles of operation of the present centrifugal coupling resemble that 
of the coupling known from German Offenlegungsschrift No. 2,913,694. 
However, unlike that prior reference, the present invention further 
provides self-intensifying and/or self-attenuating devices arranged in the 
form of inclined check ramps on at least one partial weight. For this 
purpose, one or more recesses are arranged on the relevant partial weight, 
which each enclose a primary side driver in the circumferential direction 
and are provided with check ramps inclined in the direction of rotation. 
It has been found to be particularly advantageous in some embodiments of 
the present invention for the primary side radial stop to also assume the 
function of the driver. 
In FIGS. 1 and 4, these check ramps are shown, for example, machined into 
orifices 14 and 15 of partial weights 2 and 1, respectively, as bevels. If 
orifice 14 of inner partial weight 2 is provided with a ramp or bevel 19 
at the top side thereof, and if that partial weight is displaced 
counter-clockwise due to the circumferential force, then, as a result of 
the wedge effect caused by the engagement of driver 18 with bevel 19, an 
intensification occurs of the radial components of the torque which is 
transmitted, via the compression springs present between the partial 
weights, to outer partial weight 1 and thus causes a stiffer torque 
characteristic. This relationship of coupling torque with respect to motor 
torque is illustrated diagramaticly in FIG. 7b. The servo effect of bevel 
19 and driver 18 is limited if, as explained earlier, the lateral side of 
orifice 14 comes into abutment against the driver 18 such that the driver 
now acts as a stop to further motion of the inner partial weight. 
The present invention also provides attenuation of the transmission 
capacity of the coupling by having a bevel 20 on the lower side of orifice 
15 of the outer partial weight. Bevel 20 comes into engagement with driver 
18 when both the circumferential force and also the circumferential 
movement are greater than required for abutment of driver 18 and bevel 19 
of the inner partial weight. This is the case when compression springs 6 
permit relative circumferential movement between the fly element parts. 
For this reason, in preferred embodiments of the present invention the 
lower line of engagement of bevel 20 is placed closer to the pivot point 
of the centrifugal coupling than the lower line of engagement of orifice 
14. In this manner, a torque surge can be dissipated, for example, because 
the coupling commences to slip briefly due to the attenuation. This 
relationship of coupling torque with respect to motor torque is 
illustrated diagramaticly in FIG. 7c. 
Bolts employed as drivers 18 are, for example, provided with movable 
sleeves 21 and 22 in order to reduce friction, as shown in FIG. 4. 
Further, where such a centrifugal coupling is used for only one direction 
of rotation, then it is sufficient to provide ramps on bevels extending to 
only one lateral side of the orifices. However, where it is used with both 
directions of rotation, then it has been found to be advantageous to 
provide bevels to both lateral sides of the orifices in conformity with 
the action of the circumferential forces. For example, as shown in FIGS. 1 
and 3, orifice 15 is provided with bevel 20 extending to the right lateral 
side and bevel 20' extending to the left lateral side. 
In the case of a centrifugal coupling according to the present invention 
installed in a motor vehicle torque converter, it has been found to be 
advantageous, for example, to associate both the positive or intensifying 
bevel and the negative or attenuating bevel with the directions 
corresponding to operation in traction. On the other hand, association of 
the attenuating bevel alone is sufficient for operation of such a torque 
converter in thrust. Further, due to the division of the fly element into 
two partial weights, these bevels can be distributed between the two 
partial weights in a particularly advantageous and functionally favorable 
manner. For example, an intensifying bevel can be associated with the 
inner partial weight in order to increase the starting torque, and two 
attenuating bevels associated with the outer partial weight in order to 
absorb higher torque surges by brief slipping of the coupling. 
Although the present invention has been described and illustrated above 
only with respect to a two piece fly element, it is specifically 
comtemplated that the fly element may be formed from a plurality of 
concentric partial weights if the installation space so permits and the 
operating characteristics so demand. Also, other means may be employed as 
a stop for the inner fly element parts. For example, the spring housing 
for the return spring or grooves turned on the circumference of the 
partial weights which correspond to projections in the driver ring can be 
formed so as to function as such a stop. 
Due to the extremely differently shaped torque curves, defined by M=f (n) 
where n is the rotational speed of the motor, of prime movers, and 
particularly those of internal-combustion engines, in certain cases it may 
not be advisable to adapt a given centrifugal coupling to some of the 
above-described features of the present invention. In such cases the 
advantages of the present invention are achieved by additional features. 
In particular, the inner partial weight, after overcoming the radial 
movement play, influences in the centrifugal direction one or more levers 
mounted on the primary side of the driver ring. One arm of one or each of 
these levers forms the primary side stop. The force at the other end of 
the levers influences, in the centripetal direction, the outer partial 
weight, which is abutted by the other arm or arms, so that a rising, 
constant or falling torque transmission characteristic can be generated 
depending upon the mass proportions of the fly element parts and in 
conformity with the lever transmission ratio after the abutment of the 
levers and further increase of the rotary speed. 
Here again the transmission capacity of this embodiment of the present 
invention in the lower speed range can further be increased and better 
surge moderation achieved if the inner partial weight is provided with at 
least one intensifying check ramp or bevel. Such an arrangement is 
illustrated in FIGS. 5 and 6. Inner partial weight 102 has a T-shaped 
cross-section and is inserted into outer partial weight 101 in the 
circumferential direction. Inner partial weight 102 is tensioned to the 
outer partial weight by resilient means, such as spring elements 106. 
These spring elements are supported by pressure pieces 109 (set screws, 
for example) in inner partial weight 102 and in bores 107 of outer partial 
weight 101. 
The fly element is set into a U-shaped driver ring 116. Levers 125 are 
mounted on bolts forming driver 118 which are pressed into the sides of 
driver ring 116. Before the fly element is inserted into the driver ring, 
the levers are inserted laterally into corresponding recesses 126 and 127 
of the fly element parts, and the sleeves 122 are pushed in between the 
levers. The levers are shaped so that lever ends 130, located farther out 
in the circumferential direction, are braced against annular collar 128 
and 128' of inner partial weight 102. Lever ends 131, also located farther 
in the circumferential direction, are braced against annular collar 129 
and 129' of outer partial weight 101. In the rest condition of the 
centrifugal coupling, a definite movement play is provided between the 
annular collars and the lever end. The levers can, in some embodiments of 
the present invention, be fit to rotate through 180.degree. in the plane 
of the drawing if the annular collars are appropriately shaped. 
The entire fly element is braced in both the radial direction and in the 
circumferential direction at the outer ends by return springs (not shown), 
as in the above-described embodiments illustrated in FIGS. 1 and 4. 
When the centrifugal coupling of the present invention shown in FIG. 5 is 
set in rotation, the entire fly element moves radially outwards when the 
centrifugal force exceeds the force of the return springs. Torque 
transmission occurs when lining outer contour 113 touches the cylinder 
drum (not shown). From this moment on outer partial weight 101 cannot 
execute any further radial movement. When the rotary speed is increased 
further, inner partial weight 102 continues to move farther radially 
outwards and transmits its centrifugal force through inner tensioning 
means 106 to outer partial weight 101. Due to the circumferential force 
produced by friction lining 113, circumferential movement is typically 
executed simultaneously. This movement is braced by the return springs. In 
the example illustrated in FIG. 5, for a clockwise rotation of the driver 
ring, the fly element moves counter-clockwise relative to the latter. 
When the torque exceeds that which can be transmitted by the return 
springs, bevel 119 comes into contact with sleeves 122 of driver 118 and 
causes an increased radial movement of the inner partial weight, and 
therefore, a greater radial force by tensioning means 106. 
Radial movement occurs until annular collars 128 and 128' of inner partial 
weight 102 lever abuts the lever ends 130 and other lever ends 131 are 
braced against annular collars 129 and 129' of outer partial weight 101. 
Any further centrifugally directed radial movement or radial force from 
inner partial weight 102 therefore causes a centripetally directed force 
action through the levers upon outer partial weight 101. 
In this manner a rising, constant or even falling torque characteristic 
(M=f(n)) can be generated depending upon the choice of the mass proportion 
of the inner to the outer fly element part, and of the lever ratio and 
mass proportions of lever ends 130 and 131, whereby extremely good 
adaptation to the characteristics of prime movers is achieved. 
FIGS. 8a-c show various torque curves (M=f(n)) for the same examplary fly 
element depending upon proportion of the mass of the inner fly element 
part, mi, to that of the outer fly element part, m.sub.a, specifically, 
coupling torque curves are illustrated for where m.sub.i /m.sub.a =1, 
m.sub.i /m.sub.a =1, and m.sub.i /m.sub.a =1 in FIGS. 8a-c, respectively. 
The advantageous torque surge moderation provided by the present invention 
is believed to be due to the fact that any additional positive torque 
variation which is greater than the maximum transmissible torque of the 
coupling associated with sudden or instantaneous speed is dissipated via 
the servo device (bevel) and the lever action. 
As the embodiments of the present invention explained above show, it has 
been possible to fulfill the high desiderata for modern propulsion systems 
by utilising the principle of a fly element divided concentrically into a 
plurality of parts provided with check ramps or levers and mutually 
connected by resilient tensioning means. 
In addition to the examples illustrated with bipartite fly elements, the 
present invention includes multiple divided fly elements, in which the 
individual fly element parts come into contact consecutively by different 
movement plays. Further, fly element parts can also be connected among 
themselves, by clamps or by collar bolts, etc., for example, in order to 
absorb the internal tensioning forces. 
Although the present invention has been described and illustrated in 
detail, it is to be clearly understood that the same is by way of 
illustration and example only, and is not to be taken by way of 
limitation. The spirit and scope of the present invention are to be 
limited only by the terms of the appended claims.