Fluid power transmission system with lock-up clutch

A torque converter wherein a fluid flow established by a pump impeller is fed to rotate a turbine runner, wherein a lock-up clutch to be engaged with and released from a first member integrated with the pump impeller is connected to an annular drive member, and wherein an annular driven member arranged to face the drive member and made rotatable relative to the drive member is connected to a second member integrated with the turbine runner, whereby torque is transmitted between the drive member and the driven member. The torque converter comprises: a plurality of first projections arranged at a circumferentially constant clearance on one of the surfaces of the drive member and the driven member facing each other and having a predetermined circumferential length; a plurality of second projections arranged at a circumferentially constant clearance on the other of the surfaces of the drive member and the driven member facing each other and having a predetermined circumferential length for meshing with the first projections at a radially slight clearance; damper springs arranged between the first projections or the second projections and adapted to be compressed by the first projections and the second projections; and a viscous fluid confined between the first projections and the second projections.

BACKGROUND OF THE INVENTION 
The present invention relates to a fluid power transmission system such as 
a fluid coupling or torque converter for transmitting a torque through a 
fluid such as oil and, more particularly, to a fluid power transmission 
system provided with a lock-up clutch for connecting a drive side member 
and a driven side member directly. 
A lock-up clutch to be mounted in a fluid power transmission system such as 
a torque converter is used to eliminate the power loss in case of 
transmitting the torque through a fluid. For example, a torque converter 
for a vehicle is arranged between the inner surface of a front cover and a 
turbine runner so that the torque may be directly transmitted from the 
front cover to an output shaft by pushing the lock-up clutch into 
engagement with the inner surface of the front cover. If this lock-up 
clutch is engaged, the torque is transmitted not through the fluid so that 
the torque transmission efficiency is substantially 100% without any power 
loss. However, the fluctuations of the engine torque are transmitted as 
they are to the output shaft. In case the fluctuations of the engine 
torque are high, the resultant vibrations are transmitted through the 
output shaft to a drive mechanism such as an automatic transmission to 
establish torsional resonations. As a result, the vibrations are 
transmitted through the mount to the body to vibrate the body panel and 
the floor panel. Then, there arises a defect that the so-called "booming 
noise" is generated in the car compartment. 
In order to eliminate this defect which is caused by engaging such lock-up 
clutch, there has been proposed in the prior art a torque converter 
provided with the following means. 
FIG. 45 shows a torque converter 1 which is provided with a lock-up clutch, 
as disclosed in Japanese Utility Model Laid-Open 157746/1986. A housing 2 
connected to the (not shown) output shaft of the engine is constructed of 
a front cover 2a and the casing of a pump impeller 3. In the housing 2, 
there are disposed a stator 4 and a turbine runner 5. The stator 4 is held 
through a one-way clutch 4a, and the turbine runner 5 is connected to the 
output shaft 6 through a turbine hub 6a. Between the front cover 2a and 
the turbine runner 5, on the other hand, there is arranged a lock-up 
clutch 7. This lock-up clutch 7 is composed of: a disc-shaped driven 
member 8 which is fixed on the turbine hub 6a by means of rivets 13 so 
that it may rotate integrally with the turbine runner 5; and a disc-shaped 
drive member 10 which is arranged between the inner surface of the front 
cover 2a and the driven member 8 and which is interleaved relatively 
rotatably and axially movably on the outer circumference of the turbine 
hub 6a. Moreover, the driven member 8 is provided at its outer 
circumference with damper springs 9 for damping the driven member 8 and 
the drive member 10. The opposed surfaces of the driven member 8 and the 
drive member 10 are formed at their portions close to the center with 
annular projections 8a and 10a which are made so concentric that they can 
be interleaved on each other at a predetermined clearance. These 
projections 8 a and 10a shear the AT oil, which is confined in between, 
when the driven member 8 and the drive member 10 rotate relative to each 
other, so that they establish a resistance acting as a force for 
attenuating the vibrations in the torsional direction. Here is provided a 
viscous attenuation mechanism 11. 
When the running speed increases so that the vehicle state reaches the 
lock-up range, the oil pressure between the front cover 2a and the drive 
member 10 is set at a lower level than that of the oil pressure at the 
side of the turbine runner 5. Then, the drive member 10 is pushed by the 
pressure difference toward the front cover 2a and forced to contact with a 
friction member 12 which is fixed on the inner surface of the front cover 
2a. Then, the lock-up clutch 7 is engaged so that the power is transmitted 
from the housing 2 through the drive member 10 and the damper springs 9 
and further from the driven member 8 to the output shaft 6. If the lock-up 
clutch 7 is thus engaged, a part or most of the rotational torque of the 
engine is mechanically transmitted to the output shaft 6 not through the 
fluid. If the engine torque fluctuates in this state, the damper springs 9 
connecting the drive member 10 and the driven member 8 are tensed or 
compressed in accordance with the input torque. As a result, the 
vibrations caused by the torque fluctuations are reduced by the damper 
springs 9, and the booming noise can be prevented by reducing the spring 
constants of the damper springs 9. 
In the torque converter 1 thus far described, on the other hand, the damper 
springs 9 usually acting as vibration absorbing elements increase the 
vibrations under a special situation having a stepwise change in the input 
torque and may cause the so-called "surging phenomena". However, this 
surging phenomena can be prevented to provide an excellent driving feel at 
a lock-up time, because the viscous attention mechanism 11 arranged in 
parallel with the damper springs 9 acts to suppress the relative rotations 
of the drive member 10 and the driven member 8. 
In the torque converter 1 of the prior art thus far described, however, the 
driven member 8 is provided with the damper springs 9 at its portion 
closer to the outer circumference and with the viscous attenuation 
mechanism 11 at its portion closer to the center. Thus, the torque 
converter 1 has the following problems. 
The damper springs 9 are required to absorb the vibrations caused by the 
high fluctuations of the input torque and is spatially restricted by their 
aforementioned arrangement. In the prior art, therefore, the number of 
damper springs had to be decreased, and their respective spring constants 
also had to be increased. As a result, the vibrations having a relative 
frequency cannot be absorbed so that they are transmitted to the power 
transmission mechanism such as the automatic transmission to cause the 
booming noise. 
One of the causes for generating the booming noise is that the spring 
constants of the damper springs 9 have large spring constants. In order to 
reduce the booming noise, it is conceivable to reduce the spring constants 
of the damper springs 9. In case, however, the spring constants of the 
damper springs 9 are reduced, the relative rotational angle of the drive 
member 10 and the driven member 8, i.e., the torsional angle is increased 
to enlarge the overall compression of the damper springs 9. This makes it 
necessary to increase the number of damper springs 9 or to elongate the 
individual damper springs 9 and accordingly to retain the space therefor. 
In case, on the other hand, the spring constants are decreased, the drive 
member 10 and the driven member 8 are highly twisted relative to each 
other even for a small change in the input torque. After this, the damper 
springs 9 release the energy so that the drive member 10 and the driven 
member 8 are highly twisted relative to each other in the opposite 
directions. As a result, the surging phenomena are liable to occur. Thus, 
it is necessary to enhance the attenuation characteristics of the 
aforementioned viscous attenuation mechanism. 
If the spring constants of the damper springs 9 are thus reduced, the 
structures of the damper mechanism and the viscous attenuation mechanism 
11 have to be accordingly changed from those of the prior art shown in 
FIG. 45. In the existing structure, in which the damper springs 9 are 
circumferentially arranged in one row on the circumference of the driven 
member 8 and which the viscous attenuation mechanism 11 is arranged 
circumferentially inside of the damper springs 9, there are independently 
necessary the space for fitting the numerous damper springs 9, the space 
for the rivets to hold the damper springs 9, and the space for mounting 
the viscous attenuation mechanism 11. It is, however, practically 
difficult to retain such wide spaces in the restricted inside space. After 
all, the restriction on the space makes it impossible to reduce the spring 
constants of the damper springs 9 sufficiently. 
In the aforementioned torque converter 1 of the prior art, the drive member 
10 is so fitted on the outer circumference of the turbine hub 6a as to 
move in the axial direction so that it may engage or release the lock-up 
clutch 7. On the contrary, the driven member 8 for forming the viscous 
attenuation mechanism 11 together with the drive member 10 is fixed 
integrally with the turbine runner 5 on the outer circumference of the 
turbine hub 6a by means of the rivets 13. 
When the lock-up clutch 7 is engaged, the drive member 10 moves toward the 
front cover 2a while leaving the driven member 8 immovable. As a result, 
these two members 10 and 8 are apart from each other to reduce the axial 
overlapped length of the projections 10a and 8a of the viscous attenuation 
mechanism 11. Thus,there arises a problem that the viscous torque to be 
generated drops. 
In the torque converter 1 of the prior art thus far described, moreover, 
the driven member 8 is at its portion closer to the outer circumference 
provided with the damper springs 9 and its portion closer to the center 
with the projections 8a and 10a of the viscous attenuation mechanism 11. 
Since these projections 8a and 10a are formed concentric and annular, 
their relative rotations never fail to establish the viscous torque. Even 
if the springs constants of the damper springs 9 are reduced, for example, 
the vibration attenuation can always be established to prevent the surging 
phenomena. In the aforementioned structure, however, the individual 
projections 8a and 10a are always positioned close to and facing each 
other through the oil. As a result, the fine vibrations having a 
relatively high frequency are transmitted from the drive member 10 to the 
driven member 8 through the individual projections 8a and 10a and the oil 
confined inbetween, thus causing a problem that the booming noise is 
serious. 
On the other hand, the vibration attenuation by the viscous attenuation 
mechanism 11 is established as a result that the viscous fluid or oil is 
caused to absorb the kinetic energy in terms of the thermal energy by 
sharing the oil. In the structure of the prior art, therefore, the energy 
for rotating the drive member 10 and driven member 8 relative to each 
other is partially absorbed at all times. Thus, there arises a 
disadvantage that the energy is unnecessarily consumed to deteriorate the 
fuel economy of the vehicle. 
On the other hand, FIG. 46 shows a torque converter which is provided with 
a lock-up clutch of the prior art, as disclosed in Japanese Utility Model 
Laid-Open No. 28944/1982. This torque converter 14 is constructed to 
include: a drive plate 15 connected to the output shaft of an engine; a 
housing 16 connected to the drive plate 15 by means of bolts; a pump 
impeller 17 integrally formed inside of the housing 16; a stator 19 fixed 
to a stationary shaft through a oneway clutch 18a; a turbine runner 20 
arranged to face the pump impeller 17 across the stator 19; a disc-shaped 
driven member 22 fixed on a hub 21a which is so splined to an output shaft 
21 as to move in the axial direction; and a disc-shaped drive member 24 so 
connected to the driven member 22 as to rotate integrally with the damper 
springs 23 and having its central side so attached to the hub 21a as to 
move in the axial direction. These driven member 22 and drive member 24 
constitute a lock-up clutch 25 for transmitting the torque by engaging the 
circumferential edge of the drive member 24 with the inner surface of the 
front cover 16a of the housing 16. 
In the torque converter 14 thus far described, too, the output torque of 
the engine is transmitted through the drive plate 15 to the housing 16 of 
the torque converter 14 so that the pump impeller 17 integrated with the 
housing 16 is rotated. With the lock-up clutch 25 being released, the 
torque is transmitted from the pump impeller 17 through the AT oil to the 
turbine runner 20 so that the output shaft 21, on which the turbine runner 
20 is fixed through the hub 21a, is rotationally driven. Thus, the torque 
is transmitted through the AT oil so that the vibrations due to the 
fluctuations of the engine torque can be absorbed to provide a 
satisfactory driving feel. 
If, on the other hand, the AT oil in the housing 16 has its pressure 
controlled to bring the circumferential edge of the drive member 24 into 
contact with the inner surface of the front cover 16a so that the lock-up 
clutch 25 is engaged, then the output torque of the engine is transmitted 
from the housing 16 through the drive member 22 and the damper springs 23 
to the drive member 24 and further through the hub 21a to the output shaft 
21. In this case, the torque is transmitted mechanically not through the 
liquid to the output shaft 21. Despite of this direct transmission, the 
vibrations to be caused by the fluctuations of the engine torque or the 
like are absorbed through the tensions or compressions of the damper 
springs 23 so that a satisfactory driving feel can be attained. 
In the torque converter 14 of the prior art shown in FIG. 46, torque to be 
applied to the lock-up clutch 25 is high in case the torque inputted from 
wheels is increased, when the lock-up clutch 25 is engaged, by the 
undulations of the road surface. As a result, the extent of deformation of 
the damper springs 23 may exceed the allowable range. If this deformation 
extent of the damper springs 23 exceeds the allowable range, there arises 
a problem that the torque abruptly rises to cause the shocks. 
If an excessive load is exerted upon the output shaft side (or the wheel 
side) while the lock-up clutch 25 being engaged so that the deformation 
extent frequently exceeds the allowable range, as has been described 
hereinbefore, the overload causes a problem that the lifetimes of the 
springs are shortened. 
Incidentally, the damper mechanism in the torque converter must have a 
capacity for absorbing the maximum input torque anticipated. If the damper 
springs having large spring constants are used to stand the high torque, 
there arise defects that the vibrations cannot be sufficiently reduced and 
that the booming noise is intensified. Thus, the damper mechanism is 
required to increase the spring constants to some extent for its strength 
and to decrease the spring constants for reducing the vibrations. In order 
to satisfy these contradictory requirements, the damper mechanism is 
constructed in the prior art by using several kinds of damper springs 
having different spring constants. 
This structure is exemplified in Japanese Patent Laid-Open No. 252964/1986, 
as will be briefly described in the following. 
As shown in FIGS. 47 and 48, there is mounted in a housing 27 of a torque 
converter 26: a pump impeller 28; a turbine runner 29 arranged to face the 
pump impeller 28; a stator 30 arranged between the pump impeller 28 and 
the turbine runner 29; and a lock-up clutch 31 arranged between a front 
cover 27a and the turbine runner 29. 
This lock-up clutch 31 is composed of a disc-shaped drive member 32 to be 
engaged with and released from the inner surface of the front cover 27a, 
and a disc-shaped driven member 34 arranged to face the drive member 32. 
On the other hand, the driven member 34 is composed of: a first plate 34a 
connected to the outer circumference of the drive member 32; a second 
plate 34b connected to the first plate 34a through first damper springs 
35; and a third plate 34c connected to the second plate 34b through second 
damper springs 36. The third plate 34c is fixed together with the turbine 
runner 29 on a hub 29a which is splined to the output shaft 33 of the 
torque converter 26. Moreover, the aforementioned first damper springs 35 
and second damper springs 36 are given different spring constants such 
that the spring constants of the first damper springs 35 are set at 
smaller values than those of the second damper springs 36. 
In the aforementioned torque converter 26 of the prior art, therefore, the 
first damper springs 35 are tensed or compressed to absorb the torque 
fluctuations, if an input torque in the lock-up state is low, and the 
second damper springs 36 having the larger spring constants are compressed 
to absorb the torque if a high torque is inputted. At a low torque time, 
the angle of torsion of the lock-up clutch 31 for a predetermined torque 
is enlarged. At a high torque time, the angle of torsion of the lock-up 
clutch 31 for the predetermined torque is reduced. Thus, the spring 
characteristics change in the two steps. As a result, the booming noise, 
which is caused by the fluctuations of the engine torque in the ordinary 
running state, can be prevented by the actions of the first damper springs 
35 having the small spring constants. For a high torque inputted 
temporarily, on the other hand, the second damper springs 36 having the 
large spring constants act to prevent the damage. 
The damper mechanism using the damper springs having different spring 
constants is advantageous in that they can stand a high socking torque, 
and is especially effective for a vehicle such as an off-road car, in 
which a high torque is relatively frequently inputted from wheels. Despite 
of these advantages, however, the following disadvantages are invited 
because the spring constants highly change across a predetermined angle of 
torsion. 
In case impact torque is inputted, the damper springs having the smaller 
spring constants are at first compressed abruptly and highly. When the 
angle of torsion then reaches the value for changing the spring constant, 
then the abrupt and high torque is transmitted through the damper 
mechanism. As a result, the torque of the output shaft of the vehicle 
abruptly changes. This change is felt by the rider as such shocks as will 
be caused in case the drive mechanism chatters, and may deteriorate the 
riding comfort and the stability of the vehicle. 
In the aforementioned structure of the prior art, moreover, the spring 
constants are changed abruptly and highly at a predetermined angle of 
torsion. In case high impact torque is inputted from the wheels while the 
vehicle is running on a rough road to compress the damper springs having 
the larger spring constants and to eliminate the input of the torque from 
the wheels, the energy stored in the damper springs having the larger 
spring constants is abruptly released until the changing point of the 
spring constants, i.e., until the angle of torsion comes to the angle at 
which the spring constants change. This is the situation similar to the 
case, in which the input torque is highly changed. These torque 
fluctuations are reduced by the damper springs having the smaller spring 
constants. As a result, the so-called "surging phenomena", in which the 
angle of torsion is repeatedly changed high and slowly, may be caused. 
In the torque converter thus far described, the spring characteristics of 
the damper mechanism of the lock-up clutch is abruptly changed at the 
predetermined angle of torsion, to cause a disadvantage that the shocks or 
the surging phenomena may occur. 
SUMMARY OF THE INVENTION 
A main object of the present invention is to provide a fluid power 
transmission system capable of preventing the booming noise and the 
surging phenomena effectively. 
Another object of the present invention is to provide a fluid power 
transmission system capable of retaining a wide space for arranging the 
damper springs and accordingly using damper springs having small spring 
constants. 
Still another object of the present invention is to provide a fluid power 
transmission system capable of engaging the lock-up clutch at a low 
running speed to improve the fuel economy. 
A further object of the present invention is to provide a fluid power 
transmission system which has viscous attenuation characteristics 
unchanged in accordance with the engaged state of the lock-up clutch. 
A further object of the present invention is to provide a fluid power 
transmission system which has viscous attenuation characteristic changed 
in accordance with the magnitude of the torque inputted. 
A further object of the present invention is to prevent the damage of the 
damper springs due to an overload. 
A further object of the present invention is to provide a fluid power 
transmission system capable of changing the spring characteristics and 
suppressing the surging phenomena. 
According to the present invention, there is provided a fluid power 
transmission system wherein a fluid flow established by a pump impeller is 
fed to rotate a turbine runner, wherein a lock-up clutch to be engaged 
with and released from a first member integrated with the pump impeller is 
connected to an annular drive member, and wherein an annular driven member 
arranged to face the drive member and made rotatable relative to the drive 
member is connected to a second member integrated with the turbine runner, 
whereby a torque is transmitted between the drive member and the driven 
member. The fluid power transmission system comprises: a plurality of 
first projections arranged at a circumferentially constant clearance on 
one of the surfaces of the drive member and the driven member facing each 
other and having a predetermined circumferential length; a plurality of 
second projections arranged at a circumferentially constant clearance on 
the other of the surfaces of the drive member and the driven member facing 
each other and having a predetermined circumferential length for meshing 
with the first projections at a radially slight clearance; damper springs 
arranged between the first projections or the second projections and 
adapted to be compressed by the first projections and the second 
projections; and a viscous fluid confined between the first projections 
and the second projections. 
In the present invention, moreover, the drive member is arranged to get 
close to and apart from the inner surface of the front cover integrated 
with the pump impeller and has a friction member adhered thereto, and the 
driven member is arranged to move back and forth together with the drive 
member. 
In the present invention, still moreover, the drive member and the driven 
member are provided with arcuate projections which are circumferentially 
brought, by the relative rotations thereof, to be fitted on through a 
viscous fluid and released from each other. 
In the present invention, furthermore, the fluid power transmission system 
is provided with a plurality of damper springs having different spring 
constants. 
The above and further objects and novel features of the present invention 
will more fully appear from the following detailed description when the 
same is read with reference to the accompanying drawings. It is to be 
expressly understood, however, that the drawings be for the purpose of 
illustration only and be not intended as a definition of the limits of the 
present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
With reference to FIGS. 1 to 6, a torque converter 40 is constructed to 
have a structure substantially identical to that of the torque converter 
of the prior art, with the exception of a lock-up clutch anism and a 
viscous attenuation mechanism. Specifically, a housing 42 for connecting a 
drive plate attached to the (not shown) output shaft of an engine is 
formed of a front cover 42a and the casing of a pump impeller 43. In this 
housing 42: a turbine runner 44, to which the torque is to be transmitted 
from the pump impeller 43 by means of automatic transmission oil (i.e., At 
oil), is arranged to face the pump impeller 43; and a stator 45 for 
changing the flow direction of the AT oil, which is directed from the 
turbine runner 44 to the pump impeller 43, is arranged between the turbine 
runner 44 and the pump impeller 43. The turbine runner 44 is fixed on a 
hub 46a which is splined to an output shaft 46. On the outer circumference 
of this hub 46a, a generally disc-shaped driven member 47 is splined to 
move in the axial direction. The driven member 47 is interposed between 
the turbine runner 44 and the front cover 42a. Between the driven member 
47 and the front cover 42a, moreover, there is arranged a drive member 48. 
The drive member 48 is formed, as shown in section in FIG. 1, of a 
disc-shaped portion facing the driven member 47 and a cylindrical portion 
extending axially from the outer circumference of the disc-shaped portion. 
The drive member 48 has its cylindrical portion so fitted on the driven 
member 47 that it can move in the axial direction. 
The drive member 48 will be described in more detail in the following. As 
shown in FIG. 2, the surface of the drive member 48 facing the driven 
member 47 is formed with six concentrically arranged annular projections 
48a, 48b, 48c, 48d, 48e and 48f. These annular projections 48a to 48f are 
raised sequentially from the outer circumference and at a predetermined 
spacing. The four grooves between those annular projections 48a to 48f, 
i.e., the four of the five roots except that between the annular 
projections 48d and 48e are formed with stopper projections 49 for the 
damper springs. These stopper projections 49 are so arcuately raised at 
positions quartering the circles as to form part of the individual 
concentric circles. In other words, the annular projections are so 
partially cut out over predetermined lengths to form arcuate notches as to 
leave the stopper projections 49. Moreover, those notches are fitted 
therein with the damper springs, as will be described in the following. 
Specifically, each of the four roots individually formed with the stopper 
projections 49 is fitted therein with eight (i.e., totally thirty two) 
damper springs 50a, 50b, 50c and 50d. These damper springs 50a to 50d are 
given spring constants smaller than those of the damper springs which are 
used for the identical applications in the prior art. The arrangement of 
the damper springs 50a to 50d will be described more specifically with 
reference to FIG. 3. A pair of damper springs 50a to 50d are fitted 
between the circumferentially adjacent stopper projections 49, i.e., in 
each of the notches such that each pair of them sandwich a spacer block 
51. Here, the spacer blocks 51 can be circumferentially moved and are 
provided for preventing the damper springs 50a to 50d from any buckling by 
shortening them individually. Moreover, these damper 
On the other hand, the surface of the driven member 47 facing the drive 
member 48 is formed, as shown in FIG. 4, with a plurality of arcuate push 
projections 52 which are positioned to quarter the circumference and 
shaped to form part of concentric circles. These push projections 52 are 
associated with the aforementioned stopper projections 49 to push and 
compress the damper springs 50a to 50d when the drive member 48 and the 
driven member 47 are turned relative to each other. The push projections 
52 are interleaved between the stopper projections 49 and the annular 
projections 48a to 48f of the drive member 48 while holding slight 
clearances from these projections 49 and 48a to 48f. Incidentally, the 
interleaving states of these projections 49 and 48a to 48f are shown in 
FIG. 5. 
On the other hand, the drive member 48 is supported to have its inner and 
outer circumferences sliding on the driven member 47 such that the sliding 
portions of the inner and outer circumferences of the driven member 47 and 
the drive member 48 are sealed up with X-shaped seals 55. The hollow 
portion sealed up between the driven member 47 and the drive member 48 by 
those X-shaped seals 55 is filled up with highly viscous oil such as 
silicone oil together with a suitable amount of air, thus constituting a 
variable capacity type viscous attenuation mechanism 56. Incidentally, the 
highly viscous oil is injected into holes (shown in FIG. 4), which are 
formed at two positions in the circumferential edge of the driven member 
47. After this, steel balls 58 are press-fitted in the individual holes 
57, and their openings are caulked and shut off. The amount of the highly 
viscous oil to be injected into the viscous attenuation mechanism 56 is 
set to retain a side clearance .DELTA. h between the damper spring 50a, 
for example, and the bottom of the root between the annular projections 
48a and 48b, even in case the maximum pressure to be supposed acts to 
bring the driven member 47 closer to the drive member 48 so that the 
clearance, as indicated at L in FIG. 6, between the driven member 47 and 
the drive member 48 is reduced to the clearance indicated at L1. 
A friction member 59 is adhered to the inner surface of the front cover 
42a. When the drive member 48 is pushed onto the friction member 59, the 
input torque is transmitted to the output shaft 46 through the drive 
member 48, the damper springs 50a to 50d and the driven member 47. Thus, 
here is formed a lock-up clutch 60. 
Incidentally, reference numeral 61 appearing in FIG. 6 designates a sealing 
member for preventing leakage of the oil pressure. This sealing member 61 
is fixed together with the turbine runner 44 to the hub 46a by means of 
rivets 62. On the other hand, numeral 63 appearing in FIG. 4 designates a 
sealing projection, and numeral 64 appearing in FIG. 5 designates a boss. 
Next, the operations of the torque converter 40 thus constructed will be 
described in the following. 
Before the running state of the vehicle reaches the lock-up range, the oil 
is fed to the clearance between the front cover 42a and the drive member 
48 so that the drive member 48 is apart from the friction member 59 
adhered to the inner surface of the front cover 42a, thus establishing a 
state in which the lock-up clutch 60 is released. In this state, the 
torque is transmitted from the pump impeller 43 integrated with the 
housing 42 through the AT oil to the turbine runner 44 and further to the 
output shaft 46. Thus, outside of the lock-up range, the torque 
transmission through the fluid is effected, and the vibrations due to the 
torque fluctuations are cut as a result of the slippage of the torque 
converter 40. 
Moreover, for example, when the vehicle speed increases so that the running 
state of the vehicle reaches the lock-up range, the oil pressure Pa at the 
side of the turbine runner 44 is increased relative to the oil pressure 
between the front cover 42a and the drive member 48. As a result, the 
driven member 47, which is axially movably fitted on the hub 46a, is moved 
toward the front cover 42a (i.e., leftwardly of FIG. 1). 
Since a suitable amount of air is filled together with the highly viscous 
oil between the driven member 47 and the drive member 48, the drive member 
48 is pushed toward the front cover 42a and onto the friction member 59 as 
the driven member 47 moves. In other words, the lock-up clutch 60 is 
engaged. In this case, when the drive member 48 just begins contacting 
with the frictional member 59, the air confined together with the highly 
viscous oil is not compressed yet so that the engaging pressure of the 
lock-up clutch 60 is still low. After this, the driven member 47 is 
further moved to get close to the drive member 48 thereby to compress the 
aforementioned air. Then, the pressure between the drive member 48 and the 
driven member 47 is gradually increased so that the engaging pressure of 
the lock-up clutch 60 is accordingly increased. In other words, the air 
confined together with the highly viscous oil performs the damping action 
so that the engaging pressure of the lock-up clutch 60 is gradually 
increased. 
Since the drive member 48 is thus supported slidably relative to the driven 
member 47, the depth of insertion of the individual projections 48a to 48f 
and 49 of the drive member 48 and the projections 52 are held no less than 
a constant value when the lock-up clutch 60 is engaged, so that a 
predetermined viscous torque is retained. 
With the lock-up clutch 60 being engaged, the drive member 48 rotates 
together with the housing 42. As a result, most of the input torque is 
transmitted from the drive member 48 through the damper springs 50a to 50d 
to the driven member 47 and further to the output shaft 46. In this state, 
the individual damper springs 50a to 50d are under compression according 
to the magnitude of the torque transmitted from the drive member 48 to the 
driven member 47. As a result, the individual damper springs 50a to 50d 
are further compressed or tensioned in the presence of the torque 
fluctuations of the engine, and these extension and shrinkage are effected 
in accordance with the fluctuations of the input torque. In other words, 
the relative turns are caused between the drive member 48 and the driven 
member 47 to reduce the vibrations due to the fluctuations of the input 
torque. Especially in the aforementioned torque converter 40, a sufficient 
space is retained for the damper springs 50a to 50d, and the damper 
springs 50a to 50d used have small spring constants. As a result, the 
torque converter 40 can suppress the transmission of the vibrations of 
relatively high frequency, which might otherwise cause the booming noise. 
This means that the aforementioned torque converter 40 is superior in 
preventing the booming noise to the torque converter of the prior art. 
If, on the other hand, the spring constants of the damper springs 50a to 
50d are reduced, the vibrations of low frequency and large amplitude for 
causing the surging are liable to occur. In the aforementioned torque 
converter 40, however, the relative turns or torsions between the drive 
member 48 and the driven member 47 can be effectively attenuated because 
the projections of the viscous attenuation mechanism 56 are formed even on 
the outer circumferences of the drive member 48 and the driven member 47 
to provide excellent viscous attenuation characteristics. As a result, the 
torque converter 40 is superior in the effect of preventing the surging, 
too. 
These operations will be described in more detail in the following. If the 
engine torque fluctuations are caused with the lock-up clutch 60 being 
engaged, they are transmitted at first to change the rotational speed of 
the drive member 48 so that the push projections 52 formed at the side of 
the driven member 47 compress the individual damper springs 50a to 50d 
between themselves and the stopper projections 49. The operations of the 
viscous attenuation mechanism 56 in this state will be described in the 
following. FIGS. 7A to 7C illustrate the behaviors of the viscous 
attenuation mechanism 56 by using linear models so as to facilitate the 
description. FIG. 7A shows the state, in which the relative turns, i.e., 
torsions between the drive member 48 and the driven member 47 are not 
caused because no torque is applied. In this state, the stopper 
projections 49 and the push projections 52 completely overlap to have a 
"large" overlap length l.sub.1 so that the viscous attenuation torque Ta 
is also "high". On the other hand, FIG. 7B shows a slightly twisted state, 
in which the overlap length l.sub.2 between the stopper projections 49 and 
the push projections 52 is "medium" so that the viscous attenuation torque 
Tb is also "medium". Moreover, FIG. 7C shows a further twisted state, in 
which the overlap length l between the stopper projections 49 and the push 
projections 52 is zero, i.e., l=0 so that the viscous attenuation torque 
T=0. 
In the aforementioned torque converter 40, moreover, many damper springs 
50a to 50d are used by reducing their spring constants. As seen from the 
diagram of FIG. 8A showing the difference in the torsional 
characteristics, an angle of torsion .theta..sub.2 for a constant torque 
is larger than an angle of torsion .theta..sub.1 of the torque converter 
of the prior art. Thus, the angle of torsion is highly changed by small 
torque fluctuations, as schematically shown in FIG. 8B. FIG. 8B 
illustrates an example, in which it is assumed that the angle of torsion 
change at a constant rate from .theta..sub.a to -.theta..sub.b. At point 
P.sub.1, the overlap length l.sub.1 is "large" in the situation of FIG. 7A 
so that the viscous attenuation torque Ta is also "high". At point 
P.sub.2, on the other hand, the overlap length l.sub.2 is "medium" in the 
situation of FIG. 7B so that the viscous attenuation torque Tb is also 
"medium". At point P.sub.3, on the other hand, the overlap length l=0 in 
the situation of FIG. 7C so that the viscous attenuation torque T=0. As a 
result, the viscous attenuation torque changes within the hatched range of 
FIG. 8B to attenuate the vibrations accompanying the torque fluctuations 
so that the surging is effectively prevented. 
Incidentally, it is assumed in FIG. 8B that the changing rate of the angle 
of torsion be constant. As a matter of fact, however, the changing rate of 
the angle of torsion takes its maximum at the point P.sub.1 and gradually 
decreases at the two sides so that the viscous attenuation torque 
resembles the situation shown in FIG. 8C. 
In the aforementioned torque converter 40, moreover, the damper springs 
have the small spring constants but the large angle of torsion to raise an 
effect that the booming noise can be prevented, in addition to the 
following effects. Because of the small spring constants, the angle of 
torsion is large for a low torque. In case the vehicle is driven with the 
torque changing between Ta and Tb, for example, the angle of torsion is 
large, and the viscous attenuation torque is low, as shown in FIG. 8D. 
This is because the aforementioned projections 49 and 52 have a short 
overlap length. In this state, therefore, the vibrations of high frequency 
are hard to transmit through the individual projections 49 and 52 and the 
highly viscous oil so that the booming noise can be prevented. Because of 
the low attenuation, moreover, the energy loss is reduced. Although FIG. 
8D is expressed with an assumption that the angle of torsion change at a 
constant rate, the changing rate of the angle of torsion is varied in 
fact. If this change is considered, FIG. 8D is illustrated as in FIG. 8E. 
As has been described hereinbefore, the aforementioned torque converter 40 
has its viscous attenuation mechanism 56 constructed by forming the 
projections all over the opposed surfaces of the drive member 48 and the 
driven member 47 and accommodating therein the damper springs 50a to 50d. 
These damper springs 50a to 50d can have their spring constants reduced 
but their number increased to enhance the viscous attenuation 
characteristics. 
In the aforementioned torque converter 40, moreover, the force for engaging 
the lock-up clutch 60 can be slowly increased by the elasticity of the air 
which is confined together with the highly viscous oil in the viscous 
attenuation mechanism 56. As a result, it is possible to prevent the 
lock-up shocks. 
In the aforementioned torque converter 40, still moreover, the driven 
member can be moved in the axial direction. When the lock-up clutch 60 is 
engaged, the driven member 47 is moved in the direction to engage the 
lock-up clutch 60, i.e., in the direction to get close to the drive member 
48. As a result, the overlap between the projections 48a to 48f and 49 and 
the projections 52 can be prevented from decreasing to retain 
establishment of the sufficient viscous torque. Thus, a high viscous 
torque can be generated, when the drive member 48 and the driven member 47 
are turned relative to each other by the torque fluctuations of the 
engine, to prevent the surging effectively. 
In the aforementioned torque converter 40, furthermore, the stopper 
projections 49 and the push projections 52 are arcuately formed. If the 
drive member 48 and the driven member 47 are turning relative to each 
other within a predetermined angle range, the surging can be prevented by 
the viscous torque of the highly viscous oil between the aforementioned 
projections 49 and 52. If the angle of relative turns of the drive member 
48 and the driven member 47 exceeds a predetermined value, the 
aforementioned projections 49 and 52 are circumferentially deviated. As a 
result, the transmission of the vibrations through the highly viscous oil 
is suppressed to prevent the booming noise. Thus, the lock-up range can be 
extended to a lower rate without increasing the booming noise, and the 
fuel economy can also be improved. 
FIGS. 9 to 11 show a second embodiment of the present invention, in which 
the shown torque converter has its viscous attenuation characteristics 
improved over those of the aforementioned torque converter of the first 
embodiment. In FIGS. 9 to 11, the portions identical to those shown in 
FIGS. 1 to 6 are designated at the common reference numerals of FIGS. 1 to 
6, and their repeated descriptions will be omitted. 
In FIGS. 9 to 11, the second groove from the outer circumference of the 
drive member 48, i.e., the groove between the annular projections 48b and 
48c is formed, in place of the aforementioned stopper projections 49, with 
two thin annular projections 65 which are narrowly spaced. On the 
contrary, the driven member 47 is formed, in place of the push projections 
52, with three annular projections 66 which are to be interleaved with a 
predetermined clearance in the annular projections 65 of the drive member 
48. Moreover, the viscous attenuation mechanism 56 is constructed by 
injecting the highly viscous oil such as the silicone oil into the hollow 
portion which is sealed up between the drive member 48 and the driven 
member 47. 
In the torque converter 40 shown in FIG. 9, the annular projections 65 of 
the driven member 48 and the annular projections 66 of the driven member 
47 are always in meshing engagement through the highly viscous oil so that 
a high attenuation force can be achieved to prevent the surging without 
fail. Since, moreover, the high impact torque to be applied can be 
absorbed by the viscous attenuation mechanism 56 having excellent 
attenuation characteristics, the damper springs can be prevented from 
being broken. Still moreover, the effect of preventing the booming noise 
is excellent like the aforementioned first embodiment. 
In the first and second embodiments thus far described, the compressions 
and tensions of the damper springs may be suppressed by the highly viscous 
oil because the damper springs are fitted in the hollow portion which is 
filled up with the highly viscous oil. 
The following third and fourth embodiments are improved by separating the 
damper mechanism and the viscous attenuation mechanism completely. 
FIGS. 12 to 16 show a third embodiment of the present invention. Like the 
aforementioned torque converter 40 of the first embodiment, a torque 
converter, as generally designated at 70, is provided, in the housing 42, 
with: the pump impeller 43 made rotatable integrally with the housing 42; 
the turbine runner 44, to which the torque is transmitted from the pump 
impeller 43 through the AT oil; and the stator 45. In the housing 42, 
moreover, there is disposed at the side of the turbine runner 44 a 
disc-shaped driven member 71 which is made rotatable with the turbine 
runner 44 and axially movable on the output shaft 46 through the hub 46a. 
Between the driven member 71 and the front cover 42a of the housing 42, on 
the other hand, there is arranged a drive member 72, which is formed, as 
shown, of a disc portion facing the driven member 71 and a cylindrical 
portion axially extending from the outer circumference of the disc 
portion. Moreover, the drive member 72 is axially slidably supported such 
that its annular projections 72d and 72e have their inner surfaces 
slidably interleaved on a sealing projection 73 and a boss 74, which are 
formed closer to the center of the driven member 71. At the same time, the 
drive member 72 is sealed liquid-tight by an X-shaped sealing member 74a 
which is fitted in the sliding portion of the driven member 71. 
On the other hand, the surface of the driven member 72 facing the driven 
member 71 is formed with concentric annular projections 72a to 72e. 
Stopper projections 75 are so formed between the annular projections 72a 
and 72b, between the annular projections 72b and 72c and between the 
annular projections 72c and 72d that they are positioned to quarter the 
circumference and shaped into arcs forming part of the concentric circles 
(as shown in FIG. 13). In other words, the stopper projections 75 are 
formed by cutting the annular projections partially to predetermined 
lengths to leave annular notches, in which the following damper springs 
are fitted. In the three grooves defined by the stopper projections 75, 
specifically, there are fitted eight for each groove and totally twenty 
four damper springs 76a, 76b and 76c which have smaller spring constants 
than those of the damper springs used for similar applications in the 
prior art. This fitting state will be described more specifically with 
reference to FIG. 14. Each pair of the damper springs 76a, 76b and 76c is 
fitted between the circumferentially adjacent stopper projections 75, 
i.e., in each notch such that the paired springs sandwich spacer blocks 77 
inbetween. Incidentally, these spacer blocks 77 are made circumferentially 
movable like the spacer blocks 51 of the foregoing embodiments and are 
provided for shortening the lengths of the individual damper springs 76a, 
76b and 76c to prevent their buckling. On the other hand, these damper 
springs 76a, 76b and 76c may be given different spring constants. 
In the groove, which is sealed up by the X-shaped sealing member 74a 
between the annular projection 72d and the annular projection 72e closest 
to the center, there are formed four groups each composed of three arcuate 
projections 78, which are positioned on lines joining the stopper 
projections 75 and the center and which are arranged concentrically at a 
predetermined clearance. 
FIG. 15 is a front elevation showing the driven member 71 and taken from 
the side facing the drive member 72. The driven member 71 is formed with 
push projections 79 corresponding to the stopper projections 75. 
Specifically, the push projections 79 are shaped into arcs having 
substantially equal lengths to those of the corresponding stopper 
projections 75. When the drive member 72 and the driven member 71 are 
assembled, as shown in FIG. 16, the push projections 79 are interleaved in 
the grooves between the individual annular projections 72a to 72e and the 
individual stopper projections 75 but at predetermined clearances from the 
corresponding ones of the stopper projections 75. 
The driven member 71 is further formed with three arcuate projections 80 
which are to be interleaved on the three arcuate projections 78 formed on 
the drive member 72. The arcuate projections 80 are positioned 
concentrically with the aforementioned push projections 79, sealing 
projection 73 and boss 74. 
When the driven member 71 is brought into abutment against the drive member 
72 holding the numerous damper springs 76a, 76b and 76c, the push 
projections 79 are individually interleaved between the stopper 
projections 75, and the arcuate projections 80 are interleaved between the 
three arcuate projections 78. Moreover, the sealing projection 73 is held 
liquid-tight in sliding contact with the annular projection 72d, and the 
boss 74 is held liquid-tight in sliding contact with the annular 
projection 72e. Still moreover, a viscous attenuation mechanism 81 is 
constructed by injecting highly viscous oil such as silicone oil into a 
hollow portion which is formed closer to the center and sealed up with the 
sealing member 74a between the drive member 72 and the driven member 71. 
To the inner surface of the front cover 42a of the housing 42, there is 
adhered the friction member 59. If the drive member 72 is pushed onto the 
friction member 59, the input torque is transmitted to the output shaft 46 
through the drive member 72, the damper springs 76a, 76b and 76c and the 
driven member 71. Thus, here is constructed a lock-up clutch 82. 
As has been described hereinbefore, the torque converter 70 shown in FIG. 
12 is constructed such that the viscous attenuation mechanism 81 is 
disposed closer to the center of the driven member 71 and the drive member 
72 by separating the viscous torque generation unit and the damper unit, 
and such that the outer circumferential portion fitting the damper springs 
76a, 76b and 76c is filled up with the AT oil of low viscosity, which also 
fills up the inside of the housing 42. As a result, the frictional 
resistance to the oil when the damper springs 76a, 76b and 76c are 
compressed or tensed is reduced to a lower level than that of the torque 
converter 40 of the first embodiment, in which the whole structure 
including the damper unit is arranged in the highly viscous oil, so that 
the booming noise can be reduced. 
FIGS. 17 to 20 show a fourth embodiment of the present invention, in which 
the shown torque converter has its viscous attenuation mechanism arranged 
at the outer circumference. Like the aforementioned torque converters 40 
and 70 of the aforementioned two embodiments, a torque converter, as 
generally designated at 90, is provided, in the housing 42, with: the pump 
impeller 43 made rotatable integrally with the housing 42; the turbine 
runner 44, to which the torque is transmitted from the pump impeller 43 
through the AT oil; and the stator 45. In the housing 42, moreover, there 
is disposed at the side of the turbine runner 44 a disc-shaped driven 
member 91 which is made rotatable with the turbine runner 44 and axially 
movable on the output shaft 46 through the hub 46a. Between the driven 
member 91 and the front cover 42a of the housing 42, on the other hand, 
there is arranged a drive member 92, which is formed, as shown, of a disc 
portion facing the driven member 91 and a cylindrical portion axially 
extending from the outer circumference of the disc portion. Moreover, the 
drive member 92 is axially slidably supported such that its outermost 
annular projection 92a and next annular projection 92b have their outer 
surfaces slidably interleaved on both a sealing projection 93, which is 
formed closer to the outer circumference of the driven member 91, and the 
outer circumference of the driven member 91. At the same time, the drive 
member 92 is sealed liquid-tight by X-shaped sealing members 94 which are 
fitted in the sliding portion of the driven member 91. 
On the other hand, the surface of the drive member 92 facing the driven 
member 91 is formed with concentric annular projections 92a, 92b, 92c, 92d 
and 92e. Stopper projections 95 are so formed between the annular 
projections 92b and 92c, between the annular projections 92c and 92d and 
between the annular projections 92d and 92e that they are positioned to 
quarter the circumference and shaped into arcs forming part of the 
concentric circles. In other words, the stopper projections 95 are formed 
by cutting the annular projections partially to predetermined lengths to 
leave annular notches, in which the following damper springs are fitted. 
In the three grooves defined by the stopper projections 95, specifically, 
there are fitted eight for each groove and totally twenty four damper 
springs 96a, 96b and 96c which have smaller spring constants than those of 
the damper springs used for similar applications in the prior art. This 
fitting state will be described more specifically with reference to FIG. 
18. Each pair of the damper springs 96a, 96b and 96c is fitted between the 
circumferentially adjacent stopper projections 95, i.e., in each notch 
such that the paired springs sandwich spacer blocks 97 inbetween. 
Incidentally, these spacer blocks 97 are made circumferentially movable 
like the spacer blocks 51 of the foregoing embodiments and are provided 
for shortening the lengths of the individual damper springs 96a, 96b and 
96c to prevent their buckling. on the other hand, these damper springs 
96a, 96b and 96c may be given different spring constants. 
In the groove, which is sealed up by the X-shaped sealing members 94 
between the annular projection 92a and the annular projection 92b, there 
are formed eight groups each composed of three arcuate projections 98, 
which are positioned on lines joining the stopper projections 95 and the 
center and which are arranged concentrically at a predetermined clearance. 
The surface of the driven member 91 facing the drive member 921 is formed 
with push projections 99. These push projections 99 are shaped into arcs 
having substantially equal lengths to those of the corresponding stopper 
projections 95. When the drive member 92 and the driven member 91 are 
assembled, as shown in FIG. 20, the push projections 99 are interleaved in 
the grooves between the individual annular projections 92a to 92e and the 
individual stopper projections 95 but at predetermined clearances from the 
corresponding ones of the stopper projections 95. 
The driven member 91 is further formed with groups each composed of three 
arcuate projections 100, which are to be interleaved on the groups each 
composed of there arcuate projections 98 formed on the drive member 92. 
The arcuate projections 100 are positioned concentrically with the 
aforementioned push projections 99, sealing projection 93 and boss 101. 
When the driven member 91 is brought into abutment against the drive member 
92 holding the numerous damper springs 96a, 96b and 96c, the push 
projections 99 are individually interleaved between the stopper 
projections 95, and the arcuate projections 100 are interleaved between 
the three arcuate projections 98. Moreover, the sealing projection 93 is 
held liquid-tight in sliding contact with the annular projection 92b, and 
the outer circumference of the driven member 91 is held liquid-tight in 
sliding contact with the annular projection 92a. Still moreover, a viscous 
attenuation mechanism 102 is constructed by injecting highly viscous oil 
such as silicone oil into a hollow portion which is formed in the outer 
circumference and sealed up with the sealing members 94 between the drive 
member 92 and the driven member 91. 
To the inner surface of the front cover 42a of the housing 42, there is 
adhered the friction member 59. If the drive member 92 is pushed onto the 
friction member 59, the input torque is transmitted to the output shaft 46 
through the drive member 92, the damper springs 96a, 96b and 96c and the 
driven member 91. Thus, here is constructed a lock-up clutch 103. 
As has been described hereinbefore, the torque converter 90, as shown in 
FIG. 17, has its viscous attenuation mechanism 102 disposed at the outer 
circumference so that it can achieve a higher viscous torque than that of 
the third embodiment and is superior in the action to prevent the surging. 
Here will be described a fifth embodiment of the present invention, in 
which the viscous torque is prominently changed in dependence upon the 
relative angle of rotation (or angle of torsion) of the drive member and 
the driven member. 
A drive member 48A, as shown in FIG. 21, is an improvement over the 
aforementioned drive member 48 shown in FIG. 10. In this improvement, 
stopper projections 49A are made shorter than the stopper projections 49 
of the drive member 48 of FIG. 10. Moreover, the second groove from the 
outer circumference is formed with a plurality of pairs of arcuate 
projections 65A in place of the aforementioned annular projections 65. The 
paired annular projections 65A are formed at a constant spacing in the 
circumferential direction. The remaining structure is identical to that 
shown in FIG. 10, and the shared structural components are designated at 
the common reference numerals in FIG. 21 while their description being 
omitted. 
On the other hand, a driven member 47A, as shown in FIG. 22, is an 
improvement of the aforementioned driven member 47 shown in FIG. 11. The 
driven member 47A is formed with push projections 52A, which are shortened 
to correspond to the stopper projections 49A shown in FIG. 21, and further 
with a plurality of groups each composed of three arcuate projections 66A. 
These arcuate projections 66A are given a substantially equal length to 
that of the arcuate projections 65A and arranged at a constant spacing in 
the circumferential direction. The remaining structure is identical to 
that shown in FIG. 11. 
These drive member 48A and driven member 47A are assembled like the 
foregoing second embodiment, as shown in FIG. 23, to construct the torque 
converter. FIG. 24 is a section showing the state in which the drive 
member 48A and the driven member 47A are assembled. In FIGS. 23 and 24, 
the identical portions to those of FIGS. 6 to 9 and 10 are designated at 
the common reference numerals, and their description will be omitted. 
The operations of the torque converter shown in FIGS. 21 to 24 will be 
described in the following. 
Before the running state of the vehicle reaches the lock-up range, the oil 
is fed to the clearance between the front cover 42a and the drive member 
48A so that the drive member 48A is apart from the friction member 59 
adhered to the inner surface of the front corner 42a, thus establishing a 
state in which the lock-up clutch 60 is released. In this state, the 
torque is transmitted from the pump impeller integrated with the housing 
through the AT oil to the turbine runner 44 and further to the output 
shaft. Thus, outside of the lock-up range, the torque transmission through 
the fluid is effected, and the vibrations due to the torque fluctuations 
are absorbed as a result of the slippage of the torque converter 40. 
Since, in this state, the drive member 48A and the driven member 47A are 
not rotating relative to each other, the relative positions between the 
stopper projections 49A and the push projections 52A and between the 
individual arcuate projections 65A and 66A are fixed, as shown in FIG. 24. 
Moreover, for example, when the vehicle speed increases so that the running 
state of the vehicle reaches the lock-up range, the oil pressure Pa at the 
side of the turbine runner 44 is increased relative to the oil pressure 
between the front cover 42a and the drive member 48A. As a result, the 
driven member 47A is moved toward the front cover 4a (i.e., leftwardly of 
FIG. 23). Since a suitable amount of air is filled together with the 
highly viscous oil between the driven member 47A and the drive member 48A, 
the drive member 48A is pushed toward the front cover 42a and onto the 
friction member 59 as the driven member 47A moves. In other words, the 
lock-up clutch 60 is engaged. In this case, when the drive member 48A just 
begins contacting with the frictional member 59, the air confined together 
with the highly viscous oil is not compressed yet so that the engaging 
pressure of the lock-up clutch 60 is still low. After this, the driven 
member 47A is further moved to get close to the drive member 48A thereby 
to compress the aforementioned air. Then, the pressure between the drive 
member 48A and the driven member 47A is gradually increased so that the 
engaging pressure of the lock-up clutch 60 is accordingly increased. In 
other words, the air confined together with the highly viscous oil 
performs the damping action so that the engaging pressure of the lock-up 
clutch 60 is gradually increased. 
When the lock-up clutch 60 is in complete engagement, the drive member 48A 
rotates integrally with the housing so that the input torque is 
transmitted from the drive member 48A through damper springs 50a, 50c and 
50d to the driven member 47A and further to the output shaft. If, in this 
state, the torque fluctuations of the engine are inputted, for example, 
the driven member 47A mounted on the output shaft and the drive member 48A 
rotate relative to each other so that the angle of their relative 
displacement (as will be called the "angle of torsion") is increased to 
compress the damper springs 50a, 50c and 50d thereby to reduce the 
vibrations. If, moreover, the vehicle is running on a rough road so that 
the torque to be inputted from the wheels is high, the individual damper 
springs 50a, 50c and 50d are also compressed. Specifically, the angle of 
torsion between the drive member 48A and the driven member 47A is further 
increased to reach a predetermined value. Then, the viscous attenuation 
mechanism 56 has its individual arcuate projections 65A and 66A superposed 
radially to establish a shearing resistance due to the highly viscous oil. 
This resistance established by the viscous attenuation mechanism 56 
suppresses the change in the angle of torsion to absorb the input torque 
partially. As a result, the shocks, which might otherwise be increased by 
the abrupt rise in the torque, can be reduced to prevent any overload upon 
the individual damper springs 50a, 50c and 50d. Thus, it is possible to 
prevent the damage of the springs due to the overload and to prevent the 
shortening of the lifetime. 
The positional relations and operations of the individual arcuate 
projections 65A and 66A composing the viscous attenuation mechanism 56 
will be described in connection with the linear models shown in FIGS. 25A 
to 25C. The drive member 48A and the driven member 47A are so assembled in 
phase that they take the state of the linear model of FIG. 25A when the 
individual arcuate projections 65A and 66A are positioned at the angle of 
torsion=0 degrees. 
When the lock-up clutch 60 is engaged, the damper springs 50a, 50c and 50d 
connecting the drive member 48A and the driven member 47A are compressed 
by the torque of the engine so that the torque is transmitted in the 
slightly twisted state (as shown in FIG. 25B). As a result, the vibrations 
to be caused by the torque fluctuations of the engine or the like are 
reduced because the damper springs 50a, 50c and 50d are compressed or 
tensed. 
When a high torque is inputted from the wheels so that the angle of torsion 
between the driven member 47A and the drive member 48A reaches a 
predetermined angle, the arcuate projections 65A individually come into 
engagement with the arcuate projections 66A so that a highly viscous 
attenuation force (as will be called the "viscous torque") is established 
by the shearing resistance of the highly viscous oil. At this time, the 
overlapped length l.sub.3 of the individual arcuate projections 65A and 
66A is changed (as shown in FIG. 25C) in proportion to the magnitude of 
the torque inputted. 
In case, on the other hand, the driven member 47A and the drive member 48A 
are relatively disposed in the opposite directions (or negative 
directions), although not shown, the arcuate projections 65A and 66A begin 
their overlap simultaneously with the establishment of the relative 
displacements so that the viscous torque is established to reduce the 
vibrations instantly. 
In this embodiment, the damper springs 50a, 50c and 50d used are large in 
the number but small in the value of their spring constants. As seen from 
the diagram of FIG. 26A showing the difference in the torsion 
characteristics, the stopper projections 49A and the push projections 52A 
have their interleaving states changed to establish the viscous torque, 
when the damper springs 50a, 50c and 50d are compressed in the present 
embodiment to the angle of torsion .theta..sub.2 (&gt;.theta..sub.1, i.e., 
the angle of torsion of the damper springs used in the prior art). Thus, 
the amount of deformation of the damper spring 50a can be two times as 
large as that of the prior art so that the booming noise can be 
effectively prevented. 
On the other hand, FIG. 26B shows the case, in which the surging phenomena 
occur to cause vibrations between the angles of torsion .theta..sub.a and 
-.theta..sub.c. Here, it is assumed that the angle of torsion .theta. 
taken in the direction to compress the damper spring 50a be increased or 
decreased at a constant rate. With this assumption, the overlapped length 
of the arcuate projections 65A and 66A is at 0 degrees, namely, l=0 in the 
vicinity of point P.sub.4 (at an angle of torsion .theta.=0 degrees). As a 
result, no viscous torque is established but for the viscous torque which 
is generated by the stopper projections 49A and the push projections 52A 
(as indicated at X in FIG. 26B). 
At point P.sub.5, on the other hand, the individual arcuate projections 65A 
and 66A are not overlapped to establish no viscous torque. Nor is 
established the viscous torque by the stopper projections 49A and the push 
projections 52A. 
At point P.sub.6, moreover, the arcuate projections 65A and 66A begin their 
overlapping to generate the viscous torque. When the arcuate projections 
65A and 66A take an overlapped length l.sub.3 at point P.sub.7 (in the 
state, as shown in FIG. 25C), the viscous torque=Td so that the viscous 
attenuation acts in the hatched range Y, as shown in FIG. 26B. 
If the angle of torsion is negative, on the other hand, the individual 
arcuate projections 65A and 66A overlap each other while establish the 
angle of torsion between the driven member 47A and the drive member 48A. 
At point P.sub.8, the viscous torque Te is generated so that the viscous 
attenuation acts in the hatched range Z, as shown in FIG. 26B. 
Incidentally, the increasing or decreasing rate of the angle of torsion 
takes its maximum, when the angle of torsion is in the vicinity of 
{.theta..sub.a +(-.theta..sub.c)}, and is reduced to 0 when the angle of 
torsion is the maximum or minimum. As a matter of fact, as shown in FIG. 
26C, a high viscous attenuation occurs in the hatched ranges Y.sub.1 and 
Z.sub.1 so that the energy is absorbed to prevent the surging. 
Moreover, FIG. 26D shows the torsion characteristics when a torque having a 
high rate of angle of torsion, i.e,. a high torque is inputted in an 
impact manner. Then, the viscous torque is established in the hatched 
ranges. 
When this high impact torque is inputted, the viscous torques to be 
individually generated by the stopper projections 49A, the push 
projections 52A and the arcuate projections 65A and 66A are higher because 
of their high angular rates than those to be generated for preventing the 
surging or the booming noise. As a result, the shocks due to the abrupt 
rise of the torques can be absorbed to prevent the damper springs from 
being damaged by the overload. Thus, the energy is thermally absorbed by 
the viscous attenuation so that the damper springs are protected. As a 
result, the shocks can be reduced to a lower level than those which are 
caused by the spring protection mechanism using the double damper springs 
of the prior art, as could be illustrated by folded line in the spring 
characteristic diagram, so that the damper springs can be protected 
against the overload while retaining an excellent driving feel. 
FIGS. 27 to 31 show a sixth embodiment of the present invention. This sixth 
embodiment is constructed such that the viscous attenuation mechanism 
establishes the viscous torque, when the angle of torsion .theta. is at 0 
degrees, but not temporarily as the angle .theta. increases. 
FIG. 27 shows a drive member 48B in the sixth embodiment, which is improved 
over the drive member 48A shown in FIG. 21. Specifically, the drive member 
48B is formed with a larger number of pairs of shorter arcuate projections 
65B than the projections shown in FIG. 21. The remaining structure is 
similar to that of the drive member 48A shown in FIG. 21. 
FIG. 28 shows a driven member 47B in the sixth embodiment, which is 
improved over the driven member 47A shown in FIG. 22. Specifically, the 
driven member 47B is formed with a plurality of groups each composed of 
three arcuate projections 66B. These arcuate projections 66B are given a 
length equal to that of the projections shown in FIG. 22 and are identical 
in the number to that of the arcuate projections 65B shown in FIG. 27. As 
a result, the circumferential clearance between the arcuate projections 
66B is narrower than that of the projections shown in FIG. 22. The 
remaining structure is identical to that of the driven member 47A shown in 
FIG. 22. 
The drive member 48B shown in FIG. 27 and the driven member 47B shown in 
FIG. 28 are assembled like the aforementioned drive member 48A and driven 
member 47A of the foregoing fifth embodiment, to constitute a torque 
converter. This torque converter has a section identical to that of FIG. 
23 so that its illustration is omitted. FIG. 29 is a section showing the 
state, in which the drive member 48B and the driven member 47B are 
assembled. Incidentally, FIG. 29 shows the state for an angle of torsion=0 
degrees. 
In the torque converter of the sixth embodiment using the drive member 48B 
and driven member 47B thus far described, the drive member 48A and the 
driven member 47A are so assembled in phase that they take the state of 
the linear model of FIG. 30A for the angle of torsion=0 degrees, namely, 
that the individual arcuate projections 65B and 66B are interleaved on 
each other. 
When the lock-up clutch is engaged, the damper springs 50a, 50c and 50d 
connecting the drive member 48B and the driven member 47B are compressed 
so that the torque is transmitted in the slightly twisted state (as shown 
in FIG. 30B). As a result, the torque fluctuations of the engine or the 
like are absorbed because the damper springs 50a, 50c and 50d are 
compressed or tensed. 
When a high torque is inputted from the wheels so that the angle of torsion 
between the driven member 47B and the drive member 48B having a high 
angular rate exceeds a predetermined angle, the arcuate projections 65B 
are individually overlapped with the arcuate projections 66B so that a 
high viscous torque is established by the shearing resistance of the 
highly viscous oil (as shown in FIG. 30C). 
In this embodiment, the damper springs 50a, 50c and 50d used are large in 
the number but small in the value of their spring constants. In case, for 
example, the surging phenomena occurs so that the torque vibrates between 
the angles of torsion .theta..sub.a and -.theta..sub.c, as shown in the 
diagram of the spring characteristics of FIG. 31A, the viscous torque is 
the sum of one, which is caused by the arcuate projections 65B and 66B 
interleaved on each other (as indicated at Z in FIG. 31A) and one, which 
is caused by the stopper projections 49A and the push projections 52A (as 
indicated at X in FIG. 31A), in the vicinity of an origin (for the angle 
of torsion .theta.=0 degrees), if the angle of torsion .theta. of the 
damper spring 50a is increased or decreased at a constant rate. As a 
result, the viscous torque is generated simultaneously with the angle of 
torsion even if this angle is negative. 
Between the angles of torsion .theta..sub.a and .theta..sub.b, moreover, 
the individual arcuate projections 65B and 66B are overlapped so that the 
viscous torque is generated in accordance with the overlapped length. As a 
result, the viscous attenuation acts in the hatched range, as indicated at 
Y in FIG. 31A. 
Incidentally, the increasing or decreasing rate of the angle of torsion is 
not constant but takes its maximum, when the angle of torsion is in the 
vicinity of {.theta.a+(-.theta.c)}, and is reduced to 0 when the angle of 
torsion is the maximum or minimum. As a matter of fact, as shown in FIG. 
31B, a high viscous attenuation occurs in the hatched ranges Y.sub.1 and 
Z.sub.1 so that the energy is absorbed. When a high torque is inputted 
from the wheels, the drive member 48B and the driven member 47B are 
displaced relative to each other to a predetermined extent or more. As a 
result, viscous torque having a magnitude according to the angle of 
torsion is generated to absorb the energy so that the shocks due to the 
abrupt rise of the torque can be absorbed to prevent the overload upon the 
damper springs 50a, 50c and 50d and accordingly the damage of the springs. 
Moreover, the sixth embodiment is effective for preventing the surging 
because higher viscous torque is established in the vicinity of an angle 
of torsion .theta.=0 degrees than that of the foregoing fifth embodiment. 
Here will be described an embodiment which is constructed such that the 
damper mechanism has its spring characteristics changed in two steps. 
FIG. 32 shows a drive member to be used in this seventh embodiment, which 
is improved over the drive member 48A shown in FIG. 21. Specifically, the 
drive member, as indicated at 48C, is provided with four damper springs 
50b in the second groove from the outer circumference, i.e., between the 
annular projections 48b and 48c. These damper springs 50B are 
equidistantly arranged to have their individual two ends supported by a 
pair of short arcuate projections 65C. These arcuate projections 65C are 
given a length to set a central angle .theta..sub.n, and the stopper 
projections 49A are given a length to set a central angle .theta..sub.m. 
Incidentally, the spring constants of the damper springs 50b may be equal 
to or different from those of the other damper springs 50a, 50c and 50d. 
The remaining structure of the drive member 48C is identical to that of 
the drive member 48A shown in FIG. 21, and its description will be omitted 
by designating it at the reference numerals of FIG. 32. 
On the other hand, FIG. 33 shows a driven member to be used in the seventh 
embodiment. This driven member is improved over the driven member 47A 
shown in FIG. 22. The driven member, as indicated at 47C in FIG. 33, is 
formed equidistantly with four damper springs 50b which are arranged on a 
circle having a radius equal to that of the damper springs 50b of the 
driven member 47C shown in FIG. 32. Each of the four damper springs 50b 
has its two ends supported by a pair of three short arcuate projections 
66C. These arcuate projections 66C are given such a length like the 
arcuate projections 65C of the drive member 48C as to set the central 
angle at .theta..sub.n. The remaining structure is identical to that of 
the driven member 47A shown in FIG. 22, and its description will be 
omitted by designating it at the reference numerals in FIG. 33. 
Incidentally, the four damper springs 50b in the drive member 48C and the 
four damper springs 50b in the driven member 47C are offset from each 
other at one half pitch in the circumferential direction. 
These drive member 48C and driven member 47C are assembled in the torque 
converter like the drive member 48A shown in FIG. 21 and the driven member 
47A shown in FIG. 22. The section of this torque converter is identical to 
that of FIG. 1 and will be omitted. FIG. 34 is a section showing the 
state, in which the drive member 48C and the driven member 47C are 
assembled. Incidentally, FIG. 34 shows the state for the angle of torsion 
at 0 degrees, and the clearance between the ends of the arcuate 
projections 65C of the drive member 48C and the ends of the adjoining 
arcuate projections 66C of the driven member 47C is set to give a central 
angle of .theta..sub.l. 
In the torque converter using the drive member 48C and driven member 47C 
thus far described, too, most of the input torque is transmitted, with the 
lock-up clutch being engaged, to the output shaft through the drive member 
48C and the driven member 47C so that the torsional torque is applied 
between those two members 48C and 47C. If the input torque is no more than 
a predetermined torque, the damper springs 50a, 50c and 50d having small 
spring constants are compressed to establish a relative torsion between 
the drive member 48C and the driven member 47C. If the input torque 
further increases, the damper springs 50b are also compressed to prevent 
the overload. As a result, the vibrations are reduced by the damper 
springs 50a, 50c and 50d, if the angle of relative torsion between the 
drive member 48C and the driven member 47C is no more than a predetermined 
value, and the input torque is absorbed by the damper springs 50a, 50c and 
50d if the angle of torsion is no less than a predetermined value. Thus, 
the spring characteristics change in the two stages. 
The operations of those damper springs 50a, 50b, 50c and 50d will be 
described with reference to the schematic diagrams of FIGS. 35A to 35D. 
These Figures are expanded views showing the aforementioned individual 
projections extended linearly. FIG. 35A shows the state, in which no 
torsional torque is applied. In this state, the stopper projections 49A of 
the drive member 48C and the push projections 52A of the driven member 47C 
are completely interleaved on each other, i.e., radially overlapped to 
have the largest overlapped length l.sub.4. On the other hand, the 
individual arcuate projections 65C and 66C are spaced at the maximum 
clearance, as expressed in terms of the value .theta..sub.l of the central 
angle in FIG. 34 and FIG. 35A, i.e., an opening angle .theta..sub.l in the 
assembled state. Moreover, no compressive force higher than that for the 
assembly is applied to any of the damper springs 50a to 50d. 
If the torque is inputted to the torque converter, the torsional torque 
acts upon the damper mechanism so that the drive member 48C and the driven 
member 47C are twisted. FIG. 35B shows the state, in which the damper 
mechanism is twisted until the angle of torsion slightly exceeds the 
central angle .theta..sub.m of the stopper projections 49A. In this state, 
the stop projections 49A and the push projections 52A are 
circumferentially moved relative to each other so that their interleaved 
relations are released. As a result, the damper springs 50a, 50c and 50d 
are compressed by the stopper projections 49A and the push projections 
52A. For a larger angle of torsion, those projections 49A and 52A take an 
overlapped length of "0". In the state of FIG. 35B, on the other hand, the 
angle of torsion does not reach the initial angle .theta..sub.l of the 
individual arcuate projections 65C and 66C yet. As a result, these 
projections 65C and 66C are not radially overlapped. Nor is applied to the 
damper spring 50b a compression force higher than that at the time of the 
initial assembly. 
Those projections 65C and 66C begin to be interleaved on each other when 
the angle of torsion is increased over the initial opening angle 
.theta..sub.l of the arcuate projections 65C and 66C by the high input 
torque. This state is shown in FIG. 35C, in which the arcuate projections 
65C and 66C come into their grooves so that their overlapped length is 
gradually increased. At this time, the damper springs 50b are not 
compressed more than the initial state yet. 
If the angle of torsion exceeds the summed value (.theta..sub.l 
+.theta..sub.n) of the initial opening angle .theta..sub.l of the arcuate 
projections 65C and 66C and the central angle .theta..sub.n for the length 
of the projections 65C and 66C, the mating arcuate projections 65C and 66C 
come out to the opposite sides so that the damper springs 50b are clamped 
and compressed by those projections 65C and 66C. This state is shown in 
FIG. 35D, and the individual projections 65C and 66C have their overlapped 
length l.sub.5 gradually decreased. If the angle of torsion further 
increases to allow the projections 65C and 66C to come out, their 
overlapped length is reduced to "0". 
As has been described hereinbefore, the damper springs 50a, 50c and 50d are 
compressed until the angle of torsion exceeds the value (.theta..sub.l 
+.theta..sub.n), and both the damper springs 50a, 50c and 50d and the 
damper springs 50b are compressed when the angle of torsion exceeds. Thus, 
the spring characteristics of the aforementioned damper mechanism change 
in the two steps. These characteristics are expressed by a line which is 
folded at a point for the angle of torsion of (.theta..sub.l 
+.theta..sub.n), as shown in FIG. 36A. In FIG. 36A, the torque is plotted 
in the characteristic curve against the angle of torsion. Incidentally, 
the point of the angle of (.theta..sub.l +.theta..sub.n) in the 
coordinates will be tentatively called the "changing point". 
Therefore, the spring constants of the damper springs 50a, 50c and 50d are 
so set that the angle of torsion .theta. by the averaged maximum torque of 
the engine inputted to the torque converter may be slightly smaller than 
the changing point. With this setting, the fluctuations of the input 
torque from the engine can be absorbed by the tensions and compressions of 
the drive member 48C to prevent the booming noise which might otherwise be 
generated by the fluctuations of the engine torque. 
In case, moreover, the high impact torque exceeding the averaged maximum 
torque of the engine is inputted from the wheels running on a rough road, 
the damper springs 50b having the larger spring constants also begin to be 
compressed when the angle of torsion exceeds the changing point. As a 
result, the high impact torque is absorbed by the two kinds of damper 
springs 50a, 50c and 50d and damper springs 50b so that the angle of 
torsion cannot grow excessive to prevent the damage of the damper 
mechanism. 
Incidentally, the aforementioned arcuate projections such as the stopper 
projections 49A and the push projections 52A act not only to push and 
compress the damper springs 50a to 50d but also to establish the viscous 
torque. This viscous attenuation will be described in the following. 
The aforementioned arcuate projections establish the viscous torque by 
shearing the highly viscous oil which is confined inbetween. This viscous 
torque has a magnitude inversely proportional to the clearances h.sub.1 
and h.sub.2 between the projections 49A, 65C, 66C and 52A but proportional 
to the overlapped lengths l.sub.4 and l.sub.5 and the velocity difference 
in the shearing direction. 
In the state of FIG. 35A for the angle of torsion of "0 degrees", 
therefore, the overlapped length l.sub.4 between the stopper projections 
49A and the push projections 52A is the maximum so that the viscous torque 
generated by the projections 49A and 52A takes its maximum for the angle 
of torsion of "0 degrees" if the changing rate of the angle of torsion is 
constant. Moreover, these projections 49A and 52A are given a length for 
the central angle .theta..sub.m and are overlapped over the length. If the 
angle of torsion changes in plus and minus directions from the value "0 
degrees", the viscous torque Ta gradually decreases within the range of 
the angle .theta..sub.m. 
In the state of FIG. 35B for the angle of torsion exceeding the value 
.theta..sub.m, none of the arcuate projections is overlapped to establish 
no viscous torque. 
This state continues until the angle of torsion exceeds the value 
.theta..sub.l. After this, the arcuate projections 65C and 66C are 
radially overlapped, as shown in FIG. 35C, so that they establish the 
viscous torque Tb. The overlapped length l.sub.5 of these projections 65C 
and 66C takes its maximum at the changing point and then becomes gradually 
shorter. With a further torsion of the length of the projections 65C and 
66C, i.e., the angle .theta..sub.n from the changing point, the overlapped 
length l.sub.5 decreases to "0" so that the viscous torque Tb also 
decreases to "0". In short, the viscous torque by the arcuate projections 
65C and 66C takes its maximum at the changing point and gradually 
decreases across the changing point within a range of .+-..theta..sub.n. 
As the angle of torsion increases, the relative velocities of the drive 
member 48C and the driven member 47C decrease. As a result, the viscous 
torque Tb by the arcuate projections 65C and 66C is lower than the viscous 
torque Ta by the stopper projections 49A and the push projections 52A. 
The viscous characteristics thus far described are illustrated in the 
diagram of FIG. 36B. The viscous torques Ta and Tb are generated within a 
range of .+-..theta..sub.m around the point of the angle of torsion of "0 
degrees" and within a range of .+-..theta..sub.m around the changing 
point. These viscous torques Ta and Tb decrease the more if the range 
leaves the farther from the point of the angle of torsion of "0 degrees" 
and the changing point. Incidentally, the characteristic diagram of FIG. 
36B is based upon the assumption that the changing rate of the angle of 
torsion for each range be constant. 
The spring characteristics and the viscous attenuation characteristics thus 
far described are illustrated together in FIG. 36C. In the torque 
converter of this embodiment, as seen from FIG. 36C, the viscous 
attenuation occurs within a range of .+-..theta..sub.m around the point of 
the angle of torsion of "0 degrees". Moreover, the damper springs 50a, 50c 
and 50d for reducing the vibrations due to the fluctuations of the engine 
torque have the small spring constants so that the surging phenomena are 
liable to occur. However, the viscous torque to be generated at the 
stopper projections 49A and the push projections 52A acts to suppress the 
relative twisting actions between the drive member 48C and the driven 
member 47C to prevent the surging effectively. 
If, on the other hand, such impact torque as to increase the angle of 
torsion over the changing point is inputted, the input torque disappears 
or abruptly drops so that the damper springs 50a, 50c and 50d and the 
damper springs 50b are tensed to release the energy. Since, however, the 
damper springs 50b have relatively large spring constants, its high 
torsional torque acts until the angle of torsion decreases below the 
changing point. If this angle of torsion is below the changing point, the 
torsional torque disappears. The temporary large torque by the elastic 
energy of the damper springs 50b is similar to a temporary increase of the 
input torque to the torque converter. As a result, there may occur the 
surging phenomena, in which the angle of torsion increases or decreases 
around the changing point, if the damper springs 50b having the large 
spring constants releases the elastic energy. In the torque converter thus 
far described, however, the surging can be effectively prevented because 
the viscous attenuation occurs within a range of .+-..theta..sub.n around 
the changing point, as shown in FIG. 36C. 
Let the case be considered, in which such high impact torque that the angle 
of torsion exceeds the changing point is inputted. At the instant when the 
angle of torsion reaches the value .theta..sub.1, namely, when the angle 
of torsion increases to a value which is smaller by the value 
.theta..sub.n than the changing point for starting the compression of the 
damper springs 50b, the viscous torque Tb by the arcuate projections 65C 
and 66C is generated to act as the resistance to the input torque. Since, 
moreover, the viscous torque Tb gradually increases to the changing point, 
the resultant phenomena are as if the spring characteristics gradually 
change from the state of the angle of torsion .theta..sub.1. As a result, 
the aforementioned torque converter is substantially prevented from any 
abrupt change in the spring characteristics so that neither abrupt change 
of the output shaft torque nor the accompanying shocks are caused to 
improve the riding comfort and stability of the vehicle. 
Incidentally, it is preferable that the angle of .theta. to be established 
by the averaged maximum torque of the engine is smaller than the initial 
opening angle .theta..sub.1 of the arcuate projections 65C and 66C. 
Specifically, the viscous attenuation is caused as a result that the 
kinetic energy is absorbed as the thermal energy by shearing the highly 
viscous oil. If .theta.&lt;.theta..sub.1, therefore, a portion of the engine 
output is hardly absorbed by the attenuation of the arcuate projections 
65C and 66C so that the fuel consumption can be prevented from any 
deterioration. 
Next, an eighth embodiment of the present invention will be described with 
reference to FIGS. 37 to 40. The torque converter of this embodiment is 
improved over the aforementioned seventh embodiment such that the damper 
springs are held only in the drive member. 
This drive member, as designated at 48D in FIG. 37, is arranged at the 
second portion from the outer circumference with six equidistant damper 
springs 50b, each of which has its two ends held by a pair of arcuate 
projections 65C. The remaining structure is identical to that shown in 
FIG. 32, and its description will be omitted by adding the common 
reference numerals to FIG. 37. 
On the other hand, FIG. 38 shows a driven member 47D in the eighth 
embodiment, which is improved over the driven member 47C shown in FIG. 33. 
This driven member 47D is provided with six groups each composed of three 
arcuate projections 66D. These arcuate projections 66D are equidistantly 
arranged to correspond to the arcuate projections 65C of the drive member 
48D. The arcuate projections 66D are given a length to set the central 
angle at .theta..sub.n like the aforementioned arcuate projections 66C. 
Moreover, these arcuate projections 66D are arranged between the 
aforementioned six damper springs 50b. The remaining structure is 
identical to that shown in FIG. 33, and its description will be omitted by 
adding the common reference numerals to FIG. 38. 
These drive member 48D and driven member 47D are assembled to constitute 
the torque converter, as in FIG. 9, and the assembly is shown in section 
in FIG. 39. Incidentally, this section of the torque converter is omitter 
because it is identical to that of FIG. 1. 
In the torque converter thus constructed, the individual damper springs and 
projections act to suppress the vibrations and prevent the surging 
phenomena, as will be described in the following. 
Specifically, FIGS. 40A to 40D are schematic diagrams similar to FIGS. 35A 
to 35D. In the state of FIG. 40A for the angle of torsion of "0 degrees", 
the stopper projections 49A and the push projections 52A are radially 
overlapped all over their length, and the arcuate projections 66D are 
positioned between and apart from the arcuate projections 65C. On the 
other hand, the individual damper springs 50a to 50d are not compressed 
more than before they are assembled. 
FIG. 40B shows the state, in which the angle of torsion increases 
immediately before the torque is inputted to overlap the individual 
arcuate projections 65C and 66D. In this state, the damper springs 50a, 
50c and 50d are compressed by the stopper projections 49A and the push 
projections 52A, and these projections 49A and 52A are prevented from 
coming out of each other to establish no viscous torque. On the contrary, 
the damper springs 50b are not loaded, nor overlapped are the individual 
projections 65C and 66D, so that no viscous torque is established. 
If the angle of torsion further increases, the individual arcuate 
projections 65C and 66D are radially overlapped, as shown in FIG. 40C, to 
establish the viscous torque according to their overlapped length l.sub.5. 
If the angle of torsion exceeds the changing point, i.e., the sum of the 
initial opening angle .theta..sub.1 of the arcuate projections 65C and 66D 
and the central angle .theta..sub.n according to the length of the 
projections 65C and 66D, these projections 65C and 66D begin to compress 
the damper springs 50b so that the viscous torque takes its maximum. If 
this changing point is exceeded, the overlapped length l.sub.5 of these 
projections 65C and 66D becomes short, as shown in FIG. 40D, and the 
damper springs 50b are more compressed to reduce the viscous torque 
gradually. 
In this embodiment, too, the booming noise due to the fluctuations of the 
engine torque can be effectively prevented by reducing the spring 
constants of the damper springs 50a, 50c and 50d. Moreover, the surging 
phenomena to be caused by reducing the spring constants can be prevented 
by the viscous attenuation mechanism 56. Although the spring 
characteristics change in the two steps, high impact torque is partially 
absorbed, if inputted, by the damper springs 50b to prevent the overload, 
and the surging can also be prevented as in the seventh embodiment. In the 
eighth embodiment thus far described, moreover, the assembling efficiency 
can be improved because the damper springs 50b are assembled only in the 
drive member 48D. 
FIGS. 41 to 44 show a ninth embodiment of the present invention. In the 
foregoing seventh and eighth embodiments, the arcuate projections are so 
equidistantly arranged that the viscous torque is generated when the angle 
of torsion exceeds the predetermined angle. In addition to this structure, 
low viscous torque is always established in this ninth embodiment. 
Between the circumferentially adjacent arcuate projections 65C, as shown in 
FIGS. 41 and 42, there are integrally formed thin and arcuate intermediate 
projections 104 for engaging those projections 65C. The arcuate 
projections 66D formed on the driven member 47D are circumferentially 
moved relative to each other while holding the intermediate projections 
104 inbetween at a predetermined clearance. The remaining structure is 
similar to the aforementioned one of the eighth embodiment. The identical 
portions or parts are designated at the common reference numerals, and 
their description will be omitted. 
The arcuate projections 66D are relatively moved in accordance with an 
increase in the angle of torsion according to the input torque from the 
intermediate positions to the one side of the arcuate projections 65C. 
These situations are shown in schematic diagrams in FIGS. 43A to 43D 
similar to FIGS. 40A to 40D. In the states shown in FIGS. 43A and 43B, 
namely, until the arcuate projections 66D are radially overlapped on the 
arcuate projections 65C, the arcuate projections 66D and the intermediate 
projections 104 are circumferentially moved relative to each other to 
establish the viscous torque. Since, however, the intermediate projections 
104 are made thin, the clearances between those projections 66D and 104 
are so wide that the viscous torque generated is low. 
When the arcuate projections 66D come into the clearances between the 
arcuate projections 65C, as shown in FIGS. 43C and 43D, the clearances 
between the two projections 66D and 65C are narrowed because the arcuate 
projections 65C are thick, so that a relatively high viscous torque is 
established until the overlap between the two projections 66D and 65C 
disappears. 
Incidentally, both the actions of the damper springs 50a, 50c and 50d and 
the damper springs 50b and the actions of the stopper projections 49A and 
the push projections 52A are similar to the aforementioned ones of the 
eighth embodiment. 
In the ninth embodiment, as shown in the characteristic diagram of FIG. 44, 
the viscous torque is established by providing the intermediate 
projections 104, even within the range, in which the stopper projections 
49A and the push projections 52A have a central angle no less than 
.theta..sub.m and in which the arcuate projections 65C and 66D have an 
initial opening angle no more than .theta..sub.1. As a result, the viscous 
attenuation is always effected during the run of the vehicle at a rated 
output of the engine, so that an excellent effect for preventing the 
surging phenomena due to the fluctuations of the engine torque can be 
attained. Moreover, it is quite natural that the effects similar to those 
of the eighth embodiment can also be attained. 
In the foregoing individual embodiments, the arcuate projections 65A, 65B, 
65C, 66A, 66B, 66C and 66D are equidistantly arranged in the 
circumferential direction so that the viscous torques may be 
simultaneously established in several portions. If those projections are 
arranged at different clearances, the torsional characteristics of two 
steps can be changed to multiple steps such as three or four steps. If, in 
this case, there is provided a viscous attenuation mechanism which acts in 
the vicinity of the characteristic changing point of each spring, it is 
possible to reduce the shock due to the change in the spring 
characteristics. 
In the foregoing individual embodiments, moreover, the viscous attenuation 
is caused around the angle of torsion, at which the spring characteristics 
change. Despite of this fact, however, the present invention should not be 
limited to those individual embodiments but can be modified such that the 
angular range for the viscous attenuation may be either within a 
predetermined angular range lower than the changing point or within a 
predetermined angular range higher than the changing point. In this 
modification, the changing point may or may not be contained with the 
individual angular ranges. 
The advantages to be obtained by the present invention will be 
synthetically described in the following. 
Since the spaces for the damper springs can be sufficiently retained, 
according to the present invention, it is possible to use the damper 
springs which have small spring constants. As a result, there can be 
attained an excellent effect to prevent the booming noise. In the viscous 
attenuation mechanism, moreover, the projections for applying the shearing 
force to the highly viscous oil are formed substantially all over the 
drive member and the driven member, which face each other, so that high 
attenuation characteristic can be obtained. As a result, according to the 
present invention, there can be attained an excellent effect to preventing 
the surging phenomena which may result from the fact that the spring 
constants of the damper springs are reduced. If the torque converter 
having the lock-up clutch assembled with the damper mechanism of the 
present invention is used in a vehicle, the lock-up clutch can be engaged 
without deteriorating the riding comfort even at a low running speed so 
that the fuel economy can be improved over the prior art. 
According to the present invention, furthermore, the drive member formed 
with the viscous attenuation mechanism is moved together with the drive 
member in a direction to engage the lock-up clutch. When the lock-up 
clutch is to be engaged, the clearance between the drive member and the 
driven member is not enlarged to retain the overlap of the viscous 
attenuation projections in the axial direction, and the stable viscous 
torque can be generated for relative rotations, to effectively attenuate 
the vibrations caused by the fluctuations of the engine torque. 
According to the present invention, furthermore, the projections of the 
viscous attenuation mechanism to be interleaved on each other to establish 
the viscous torque are formed in such relative positions that they are not 
overlapped in the radial direction of the drive member and the driven 
member when the relative angle of rotation of the two members exceeds a 
predetermined value. As a result, the vibrations to be transmitted through 
the viscous attenuation mechanism can be cut by setting the interleaving 
relations of the projections in the booming noise generating range while 
retaining the attenuation in the vicinity of 0 degrees of the relative 
angle of rotation, at which the viscous torque to be generated takes its 
maximum. Thus, it is possible to achieve an excellent effect of preventing 
the surging and to reduce the booming noise in the medium and low speed 
ranges. In the vehicle using the torque converter having the lock-up 
clutch assembled with the damper mechanism of the present invention, the 
lock-up clutch can be engaged without deteriorating the riding comfort 
even at a low speed. Thus, the lock-up range can be drastically extended 
to the low speed side thereby to improve the fuel economy over the prior 
art. 
According to the present invention, furthermore, the arcuate projections of 
the viscous attenuation mechanism are interleaved on each other to 
establish the attenuation when the relative angle of deviation of the 
driven member and the drive member exceeds a predetermined angle. If the 
input torque fluctuates, the viscous torque generated accords to the 
magnitude of the fluctuations to damp the shocks due to the abrupt rise of 
the torque, for example, thereby to effectively reduce the impact torque 
to be applied to the damper springs. Thus, the load to be exerted upon the 
damper springs can be suppressed less than the allowable value to prevent 
the damage of the springs thereby to prevent the shortening of the 
lifetimes of the damper springs. 
According to the present invention, furthermore, the damper mechanism is 
constructed to have its spring characteristics changing with the increase 
in the angle of torsion and to establish the viscous attenuation before or 
after the spring characteristics change. As a result, the surging 
phenomena in the vicinity of the change in the spring characteristics can 
be effectively prevented, even if the impact torque inputted is such that 
the angle of torsion exceeds the angle at which the spring characteristics 
change. Thus, it is possible to improve the riding comfort and the 
stability of the vehicle.