A hydrokinetic torque converter has a rotary housing which is connectable to the crankshaft or camshaft of a combustion engine in a motor vehicle to drive the input shaft of the transmission. The housing confines a turbine, a pump, a stator (if necessary) and a lockup clutch between a radially extending wall of the housing and the turbine. A piston of the lockup clutch is movable in the axial direction of the housing and defines a first fluid-filled compartment with the turbine as well as a second fluid-filled compartment with the wall of the housing. The force which is required to engage, to partially disengage or to fully disengage the lockup clutch is reduced by the provision of one or more profiles on the piston and/or on a friction disc of the lockup clutch which extends or extend into the adjacent compartment or compartments to influence the speed of circulation of fluids in the respective compartments and/or the fluid pressures acting upon opposite sides of the piston. This enables a control unit to predictably and reliably change the condition of the lockup clutch (from engaged to partially engaged (slipping) to fully disengaged or in the opposite direction) in response to relatively small changes of fluid pressure in the first or in the second compartment.

BACKGROUND OF THE INVENTION 
The invention relates to improvements in torque converters and, more 
particularly, to improvements in hydrokinetic torque converters which are 
equipped with so-called lockup or bypass clutches. 
A hydrokinetic torque converter normally comprises a rotary housing which 
can be affixed to the output element of a prime mover, such as a 
combustion engine in a motor vehicle. It normally includes a wall 
extending substantially radially of the axis of rotation of the housing 
and disposed between the output element of the prime mover and the turbine 
of the torque converter. The lockup clutch is installed between the 
radially extending wall of the housing and the turbine, as seen in the 
axial direction of the housing. As a rule, the lockup clutch comprises a 
lamella, which constitutes a friction disc, that cooperates with an 
axially movable piston of the lockup clutch. The piston is displaceable in 
directions toward and away from the wall of the housing in response to the 
establishment of a pressure differential between the bodies of hydraulic 
fluid at opposite sides of the piston. Reference may be had, for example, 
to published German patent application Serial No. 38 23 210. Reference may 
also be had to U.S. Pat. No. 4,969,543 granted Nov. 13, 1990 to Macdonald 
for "Slipping Bypass Clutch Construction for a Hydrokinetic Torque 
Converter" and/or to commonly owned Copending patent application Ser. No. 
08/272,920 filed Jul. 8, 1994 by Dieter Otto and Volker Middlemann for 
"Hydrokinetic Torque Converter and Lockup Clutch Therefor". 
OBJECTS OF THE INVENTION 
An object of the invention is to provide a novel and improved hydrokinetic 
torque converter which embodies or is equipped with a lockup clutch or 
bypass clutch and whose lockup clutch can be engaged or disengaged in 
response to the establishment of relatively small pressure differentials 
at the opposite sides of the piston forming part of the lockup clutch. 
Another object of the invention is to provide a novel and improved lockup 
clutch or bypass clutch which can be utilized in or in conjunction with a 
hydrokinetic torque converter and which is designed to ensure an optimal 
transmission of torque under a variety of circumstances of use of the 
torque converter. 
A further object of the invention is to provide a lockup clutch or bypass 
clutch which can be partially or completely engaged or disengaged under a 
wide variety of circumstances of use of the torque converter and in 
response to the action of a fluid which need not be maintained at an 
elevated pressure. 
An additional object of the invention is to provide a lockup clutch which 
can be reliably engaged or disengaged in response to the action of a 
hydraulic fluid whose pressure need not exceed that which is necessary to 
engage or disengage a conventional lockup clutch. 
Still another object of the invention is to provide a lockup clutch which 
is constructed and assembled to ensure the establishment of an optimum 
relationship between the magnitudes of forces furnished by bodies of 
hydraulic fluid acting upon opposite sides of the piston forming part of 
such lockup clutch. 
A further object of the invention is to provide a lockup clutch which can 
be used in or with a hydrokinetic torque converter, and which is 
constructed and assembled in such a way that its operation is not 
adversely affected by the dynamic and/or kinematic behavior of hydraulic 
fluid in the housing of the torque converter. 
Another object of the invention is to provide a lockup clutch which is 
constructed and assembled in such a way that it can take advantage of the 
parameters of bodies of fluid acting upon the axially movable piston of 
the clutch to ensure predictable and reliable disengagement, partial 
engagement or full engagement of the clutch. 
An additional object of the invention is to provide a lockup clutch or 
bypass clutch which is constructed and assembled in such a way that the 
forces acting upon opposite sides of its axially movable piston can be 
accurately and reliably balanced to thus ensure that the piston is not 
acted upon by a resultant force corresponding to the difference between 
the magnitudes of the forces acting upon the opposite sides of the piston. 
Still another object of the invention is to provide a relatively simple and 
inexpensive lockup clutch and a relatively simple and inexpensive 
hydrokinetic torque converter which embodies or cooperates with such 
lockup clutch. 
A further object of the invention is to provide a vehicle, particularly an 
engine-driven motor vehicle, which embodies the above-outlined 
hydrokinetic torque converter and/or the above-outlined lockup clutch. 
Another object of the invention is to provide a novel and improved 
combination of a hydrokinetic torque converter and a lockup clutch which 
can be utilized as a superior substitute for conventional torque 
converter-lockup clutch combinations. 
An additional object of the invention is to provide a novel and improved 
method of combining a lockup clutch with a hydrokinetic torque converter. 
Still another object of the invention is to provide a novel and improved 
method of regulating the operation of the aforementioned combination of a 
lockup clutch and a hydrokinetic torque converter. 
A further object of the invention is to provide a novel and improved 
friction disc for use in the above-outlined lockup clutch. 
Another object of the invention is to provide a novel and improved piston 
or pressure plate for use in the above-outlined lockup clutch. 
An additional object of the invention is to provide a novel and improved 
turbine for use in a hydrokinetic torque converter which embodies or 
cooperates with the aforementioned lockup clutch and can be utilized in 
the power train between the prime mover and one or more driven components 
of a motor vehicle. 
Still another object of the invention is to provide novel and improved 
vibration damping or suppressing means between the output element of the 
lockup clutch and the part or parts receiving torque from the turbine of 
the hydrokinetic torque converter. 
SUMMARY OF THE INVENTION 
One feature of the present invention resides in the provision of a 
hydrokinetic torque converter which comprises a housing rotatable about a 
predetermined axis by an output element (e.g., a rotary camshaft or 
crankshaft) of an engine in a vehicle (particularly a combustion engine in 
a motor vehicle) and defining a chamber for a pressurizable hydraulic 
fluid which is caused to circulate in response to rotation of the output 
element. The housing comprises a wall which extends substantially radially 
of the axis between a rotary turbine of the torque converter and the 
output element of the engine. The torque converter further comprises a 
lockup clutch or bypass clutch which is disposed in the chamber between 
the wall of the housing and the turbine and includes at least one friction 
disc which is rotatable with the turbine, and a piston which is disposed 
between the wall and the turbine. The piston divides the chamber into a 
first compartment adjacent the turbine and a second or further compartment 
adjacent the wall. The piston is movable in the direction of the axis in 
response to the establishment of pressure differentials between the fluids 
in the first and second or further compartments. The lockup clutch is at 
least partially engaged (such term is intended to denote full engagement 
of the clutch as well as an engagement involving at least some slippage 
between the input and output components of the clutch) in response to a 
rise in fluid pressure in the first compartment (e.g., due to axial 
movement of the piston toward the wall to frictionally engage the at least 
one disc with the wall), and the lockup clutch is disengaged in response 
to a rise in fluid pressure in the second or further compartment (e.g., as 
a result of axial movement of the piston away from the wall). The torque 
converter further comprises means for reducing differences developing 
between a lower speed of circulation of fluid in the first compartment and 
a higher speed of circulation of fluid in the second or further 
compartment when the clutch is at least partially disengaged (i.e., when 
the clutch is disengaged or when the clutch is slipping) while the engine 
pulls a load. The aforementioned means for reducing (this term also 
embraces eliminating) differences between the speeds of circulation of 
fluids in the first and second or further compartments can be installed 
only in the first compartment, only in the second or further compartment, 
or in each of the first and second or further compartments. 
At least one of the compartments can be configurated to confine an annular 
layer of hydraulic fluid. 
The means for reducing differences between the speeds of circulation of 
fluids in the first and second or further compartments can further 
constitute, or can be replaced by, mechanical means provided in the second 
or further compartment which serve to at least partially conform the speed 
of circulation of fluid in the further compartment to the rotational speed 
of the turbine while the clutch is at least partially disengaged. 
Furthermore, the means for reducing the differences between the speeds of 
circulation of fluids in the first and second or further compartments 
and/or the means for at least partially conforming the speed of 
circulation of fluid in the further compartment to the rotational speed of 
the turbine can serve as, or can be utilized in addition to, mechanical 
means provided in the second or further compartment which serve to at 
least partially reduce differences which develop between the speeds of 
circulation of the fluids in the first and second or further compartments 
while the clutch is disengaged or while the clutch is slipping. 
The mechanical means for reducing differences that develop between the 
speeds of circulation of fluids in the first and second or further 
compartments while the clutch is disengaged or while the clutch is 
slipping can be disposed between the turbine of the torque converter and 
the piston of the lockup clutch. Alternatively, such mechanical means can 
include one or more components in the first compartment and one or more 
components in the second or further compartment. 
The aforementioned means for reducing differences between the speeds of 
circulation of fluids in the first and second or additional compartments 
and/or the aforementioned means for at least partially conforming the 
speed of circulation of fluid in at least one of the compartment to the 
rotational speed of the turbine can further constitute, or can be provided 
in addition to, means provided in at least one of the first and second or 
further compartments for influencing the fluid in the respective 
compartment or compartments in a sense to reduce differences between 
forces acting upon opposite sides of the piston in the direction of the 
axis which develop while the clutch is slipping and/or while the clutch is 
disengaged. 
Another feature of the invention resides in the provision of a hydrokinetic 
torque converter which comprises a housing rotatable about a predetermined 
axis by an output element of an engine in a vehicle, which housing defines 
a chamber for a pressurizable hydraulic fluid that circulates in response 
to rotation of the output element. The housing has a wall extending at 
least substantially radially of the axis between a rotary turbine of the 
torque converter and the output element of the engine. The torque 
converter further comprises a lockup clutch which is disposed in the 
chamber of the housing and includes at least one friction disc rotatable 
with the housing and a piston disposed between the wall and the turbine, 
which piston divides the chamber into a first compartment adjacent the 
wall of the housing and a further compartment adjacent the turbine and 
being movable in the direction of the axis in response to the 
establishment of pressure differentials between the fluids in the first 
and further compartments. The clutch is at least partially engaged in 
response to a rise in fluid pressure in the first compartment and the 
resulting movement of the piston away from the wall, and the clutch is 
disengaged in response to a rise in fluid pressure in the further 
compartment because this entails a movement of the piston toward the wall. 
The piston urges the at least one disc against the turbine in response to 
a rise in fluid pressure in the first compartment. At least one of the 
first and further compartments confines means for reducing a difference 
between a higher speed of fluid circulation in the further compartment and 
a lower speed of circulation of fluid in the first compartment when the 
engine is coasting and the clutch is disengaged or slipping. 
At least one of the compartments can be configurated to confine an annular 
layer of hydraulic fluid. 
The aforementioned means for reducing differences between the speeds of 
circulation of fluids in the first and further compartments can further 
serve as, or can be utilized in addition to, means provided in the further 
compartment and serving to conform the speed of circulation of hydraulic 
fluid in the further compartment to the rotational speed of the housing 
when the clutch is slipping and/or when the clutch is disengaged. 
The means for reducing differences that develop between the speeds of 
circulation of fluids in the first and further compartments when the 
clutch is slipping and/or when the clutch is disengaged can be installed 
in the further compartment. Such difference reducing means can be 
installed between the piston and the turbine or can include one or more 
parts or components in the first compartment as well as one or more parts 
or components in the further compartment. 
Still further, at least one of the first and further compartments can 
accommodate means for influencing the fluid(s) in the respective 
compartment(s) to reduce differences between forces acting upon opposite 
sides of the piston in the direction of the axis which develop while the 
clutch is disengaged and/or while the clutch is slipping. Such influencing 
means can be provided in addition to, or can form part of or can 
constitute, the aforediscussed means for influencing the speed(s) of 
circulation of fluid(s) in the first compartment and/or in the further 
compartment for the purpose of reducing the differences between the speed 
of circulation of fluid in the first compartment and the speed of 
circulation of fluid in the further compartment when the clutch is 
disengaged and/or when the clutch is slipping. 
A further feature of the invention resides in the provision of a 
hydrokinetic torque converter which comprises a housing rotatable about a 
predetermined axis by an output element of an engine in a vehicle and 
defining a chamber for a pressurizable hydraulic fluid which circulates in 
response to rotation of the output element. The housing has a wall which 
extends at least substantially radially of the axis between a rotary 
turbine of the torque converter and the output element of the engine. The 
torque converter further comprises a lockup clutch, which is disposed in 
the chamber between the wall and the turbine and includes at least one 
friction disc rotatable with the turbine or with the housing, and a piston 
disposed between the wall and the turbine to divide the chamber into a 
first compartment adjacent the turbine and a further compartment adjacent 
the wall. The piston is movable in the direction of the axis in response 
to the establishment of pressure differentials between the fluids in the 
first and further compartments. The clutch is at least partially engaged 
in response to a rise of fluid pressure in one of the first and further 
compartments and the resulting movement of the piston toward the wall or 
toward the turbine, and the clutch is disengaged in response to a rise of 
fluid pressure in the other of the first and further compartments 
entailing a movement of the piston away from the wall or from the turbine. 
The torque converter further includes means provided in at least one of 
the first and further compartments which serve to influence at least one 
of a plurality of different parameters including the speed of circulation 
of fluid in at least one of the first and further compartments and the 
magnitude of forces acting upon the piston in the direction of the axis 
while the clutch is slipping and/or while the clutch is disengaged. 
The at least one friction disc can be provided with at least one friction 
lining and can include a portion extending substantially radially inwardly 
toward the axis beyond the at least one friction lining. 
The turbine can include a set of vanes or blades having radially inner 
portions located at a lesser first distance and radially outer portions 
located at a greater second distance from the axis. The aforementioned 
portion of the at least one disc can extend substantially radially 
inwardly toward the axis to a location at least substantially midway 
between the radially inner and outer portions of the vanes or blades, 
e.g., to a position or location closer to the radially inner portions than 
to the radially outer portions of the vanes or blades. 
The piston is or can constitute an annular piston made of metallic sheet 
material or other suitable material and having a radially inner portion 
located at a lesser first radial distance and a radially outer portion 
located at a greater second radial distance from the axis. The at least 
one disc can overlie at least a major part of the piston between the 
radially inner and outer portions of the piston (as seen in the direction 
of the axis). 
The substantially radially inwardly extending portion of the at least one 
disc is or can be profiled. For example, such a portion of the at least 
one disc can establish one or more paths for the flow of hydraulic fluid 
through the at least one disc radially inwardly of the at least one 
friction lining. 
Furthermore, the aforementioned portion of the at least one disc can be 
provided with at least one vane or blade radially inwardly of the at least 
one friction lining. 
That side of the piston which confronts the turbine can be provided with 
profiles serving to increase the speed of circulation of hydraulic fluid 
about the axis when the engine is in the process of pulling a load. At 
least one of the profiles can resemble or constitute a blade or vane. 
That side of the piston which confronts the wall of the housing can be 
provided with one or more profiles serving to increase the speed of 
circulation of hydraulic fluid about the axis when the engine is coasting. 
The profile or profiles can include or constitute blades or vanes. 
The torque converter further comprises a pump which is adjacent to and 
defines with the turbine an additional fluid containing compartment. Such 
torque converter is preferably further provided with at least one passage 
for the flow of hydraulic fluid between the first compartment and the 
additional compartment. The at least one passage can be provided in, or 
radially inwardly of, a hub of the turbine.

DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring first to FIG. 1, there is shown an apparatus 1 including a 
hydrokinetic torque converter 3 which is driven by an output element 5 
(e.g., a camshaft or a crankshaft) of an internal combustion engine in a 
motor vehicle. The converter comprises a turbine 8 including a hub 25a 
that serves to transmit torque to one or more driven parts, not shown. The 
torque converter 3 further includes a housing 2 which is rotatable about 
an axis X--X and includes a wall 2a extending substantially radially of 
such axis. The housing 2 receives torque from the output element 5 by way 
of a disc-shaped torque transmitting element 6. The torque converter 3 
further comprises a pump (not shown in FIG. 1), an optional stator (not 
shown in FIG. 1) and a lockup clutch or bypass clutch 4 which is confined 
in the chamber of the housing 2 and is installed between the substantially 
radially extending wall 2a and the turbine 8. The radially outer portion 
of the torque transmitting element 6 carries a customary starter gear 7. 
The latter can be mounted on the housing 2 or on the cylindrical 
right-hand portion of the element 6. The output element 5 is bolted or 
otherwise affixed to the radially inner portion of the torque transmitting 
element 6, and the connection between the wall 2a of the housing 2 and the 
torque transmitting element 6 is located radially outwardly of the output 
element 5. 
The aforementioned pump and the optional stator of the torque converter 3 
can be installed in the housing 2 in a manner as disclosed in the 
Copending patent application Ser. No. 08/272,920 of Otto et al. or in U.S. 
Pat. No. 4,993,406 granted Jan. 15, 1985 to Bopp for "Viscous Bypass 
Coupling For Torque Converter". The disclosure of the patent to Bopp is 
incorporated herein by reference. A torque converter including a turbine, 
a pump and a stator is also shown in the aforementioned published German 
patent application No. 38 23 210. 
The radially inwardly extending flange 25 of the turbine 8 carries the 
coaxial hub 25a which is non-rotatably coupled to a shaft 9 constituting 
an output member of the torque from the engine converter 3. The shaft 9 
can be used to transmit torque to a transmission in the motor vehicle by 
way of the output element 5. 
When the lockup clutch 4 is engaged, it transmits torque from the wall 2a 
of the housing 2 to the hub 25a of the turbine 8 by way of a torsional 
vibration damper 10 which is installed to operate in series with the 
clutch 4. The latter comprises a friction disc 17 which is adjacent the 
inner side of the wall 2a and a pressure plate in the form of a piston 20 
which is movable in the directions of the axis X--X, i.e., to the right 
and to the left, as viewed in FIG. 1. At least one side of the disc 17 is 
provided with a friction lining 17a. 
In order to engage the lockup clutch 4, the piston 20 is moved in a 
direction to the left, as viewed in FIG. 1, to urge the friction lining 
17a against the wall 2a and to engage another friction lining 17b on the 
other side of disc 17. When the engine drives its output element 5 while 
the clutch 4 is engaged, the element 5 transmits torque to the shaft 9 by 
way of the element 6, housing wall 2a, disc 17 and damper 10, which damper 
transmits torque to the flange 25 (and hence to the hub 25a) of the 
turbine 8. The damper 10 comprises energy storing elements 11 acting in 
the circumferential direction of the housing 2 to transmit torque to a 
disc 13 which is riveted or otherwise affixed to the flange 25 of the 
turbine 8. The damper 10 absorbs vibratory and/or other stray movements of 
the output element 5 so that such stray movements are not transmitted to 
the hub 25a and the shaft 9. The disc 13 resembles a circular washer and 
is installed between the piston 20 and the turbine 8, as seen in the 
direction of the axis X--X. Portions of the energy storing elements 11 
(e,g., in the form of arcuate coil springs) are received in recesses or 
pockets 12 provided on or carried by the radially outer portion of the 
disc 13. 
The illustrated disc 13 can be replaced by a part (not shown) which 
receives torque from the energy storing elements 11 of the damper 10 and 
transmits torque to the adjacent radially outer portion of the turbine 8, 
i.e., not directly to the flange 25 or to the hub 25a. 
The radially inner portions of the pockets 12 are preferably located 
radially outwardly of or adjacent the radially outer portion of the piston 
20. The pockets 12 of the disc 13 cooperate with complementary pockets 
provided on a washer-like member 14 riveted to the radially outer portion 
of the disc 13. The connection between the disc 13 and the member 14 is 
established radially inwardly of the energy storing elements 11 forming 
part of the damper 10. The pockets 12 of the disc 13 cooperate with the 
pockets of the member 14 to ensure that the arcuate energy storing 
elements 11 of the damper 10 remain in the illustrated positions radially 
outwardly of the piston 20. The pockets of the member 14 and/or the 
pockets 12 of the disc 13 are provided with abutments 15 which are 
adjacent the end convolutions of the energy storing elements 11. These 
energy storing elements are compelled to orbit about the axis X--X when 
the element 5 is driven by the engine and the clutch 4 is engaged because 
the disc 17 is provided with axially parallel legs 16 which engage the 
neighboring end convolutions of the elements 11. The legs 16 can be made 
of one piece with the radially outer portion of the disc 17 or they can 
constitute separately produced parts which are welded or otherwise affixed 
to the radially outer portion of the disc 17. 
The piston 20 is non-rotatably but axially movably coupled to the housing 
2. This piston divides the internal chamber of the housing 2 into a first 
compartment 21 which is adjacent the turbine 8 and a second compartment 22 
which is adjacent the wall 2a. The illustrated piston 20 is a 
substantially circular disc-shaped part which is installed between the 
turbine 8 and the friction disc 17. The compartment 21 contains the disc 
13 and the energy storing elements 11 of the damper 10. The compartment 22 
is sealed from the compartment 21 when the clutch 4 is engaged, i.e., when 
the left-hand friction lining 17a bears against the adjacent inner side of 
the wall 2a and the right-hand lining 17b is engaged by the adjacent side 
of the piston 20. 
Axial movements of the piston 20 in directions to engage or disengage the 
clutch 4 take place in response to the establishment of differentials 
between the pressures of hydraulic fluids which fill the compartments 21 
and 22. The manner in which the pressure of fluids in the compartments 21, 
22 can be regulated by a control unit (not shown) is known and forms no 
part of the present invention. It suffices to say that the piston 20 is 
caused to urge the friction disc 17 against the wall 2a (to thus engage 
the lockup clutch 4) when the pressure of fluid in the compartment 21 
exceeds the pressure of fluid in the compartment 22, and that the clutch 4 
is disengaged in response to a rise of fluid pressure in the compartment 
22 so that the piston 20 is caused to move axially away from the wall 2a. 
The pressure of hydraulic fluid in the compartment 21 can be regulated by 
the aforementioned control unit in such a way that the piston 20 can be 
maintained in one or more axial positions in which the clutch 4 is only 
partially engaged, i.e., the clutch 4 is then operated with a selected 
slip in that the friction linings 17a, 17b of the disc 17 can slide 
relative to the wall 2a and the piston 20 to a selected extent. 
Analogously, the pressure of fluid in the compartment 22 can also be 
regulated in such a way that it suffices to prevent full engagement of the 
clutch 4 but enables the friction disc 17 to slip, to a desired extent, 
relative to the wall 2a and the piston 20. 
The means for non-rotatably coupling the piston 20 to the housing 2 with 
freedom of movement in the direction of the axis X--X includes a 
washer-like annular member 23 which is affixed (e.g., riveted or welded) 
to the inner side of the wall 2a radially inwardly of the adjacent 
friction lining 17a and includes axially parallel male detents or holders 
23a extending into complementary female detents or sockets of the piston 
20. It is also possible to mount the holders 23a or analogous male detents 
of the member 23 in such a way that they engage complementary projections 
or protuberances (such as or analogous to those shown at 20a), as long as 
the cooperating detents of the member 23 and the piston 20 function in a 
manner to prevent the piston 20 from rotating relative to the housing 2 
but ensure that the piston 20 can be moved axially toward and away from 
the wall 2a. Thus, the piston 20 always rotates at the speed of the 
housing 2 and its wall 2a, and the friction disc 17 rotates at the speed 
of the turbine 8. 
The compartments 21, 22 at the opposite sides of the piston 20 are at least 
substantially hydraulically sealed from each other by the piston 20 when 
the lockup clutch 4 is caused to operate with slip. 
When the clutch 4 is disengaged, the pressure of hydraulic fluid in the 
compartment 22 exceeds the pressure of fluid in the compartment 21. The 
radial pressure profile in the compartment 22, which is defined by the 
pressure Pl generated by the pump of the torque converter 3, decreases 
radially inwardly along the left-hand side of the piston. The reduction of 
pressure in a direction radially inwardly from the cylindrical radially 
outer portion of the housing 2, along the left-hand side of the piston 20 
and toward the axis X--X is determined by the portions of hydraulic fluid 
which form or resemble a layer in the compartment 22. Thus, a drop of 
fluid pressure in the compartment 22 in a direction radially inwardly 
toward the axis X--X is less pronounced when the fluid in the compartnnent 
22 is caused to circulate at a relatively low speed but increases in 
response to increasing speed of the layer of hydraulic fluid which 
circulates in the compartment 22 about the axis X--X. This can be 
explained as follows: 
If one assumes that only the fluid particles in the compartment 22 are at a 
standstill while the output element 5 of the engine drives the housing 2, 
there would be no pressure drop in a direction radially inwardly from the 
radially outer portion of the housing 2 (where the pressure equals Pl), 
within the compartment 22 and toward the axis X--X. In other words, the 
pressure of the fluid in the radially inner portion of the compartment 22 
would also equal Pl. When the particles of fluid in the compartment 22 
circulate about the axis X--X, the axial force acting in the compartment 
22 upon the left-hand side of the piston 20, being the resultant of the 
pressure field in the compartment 22, can be increased when the clutch 4 
is disengaged and the vehicle is in the process of pulling a load, by the 
expedient of reducing or lowering the speed of circulatory movement of 
fluid particles in the compartment 22. In the apparatus of FIG. 1, this is 
accomplished by the provision of one or more vanes, blades or wings 33 
which are carried by the friction disc 17 and thus rotate at the speed of 
the turbine 8. When the vehicle is in the process of pulling a load, the 
rotational speed of the turbine 8 is less than the rotational speed of the 
housing 2 and piston 20. 
The just-discussed dynamic and kinematic relationships regarding the 
distribution of fluid pressures in the compartment 21 are also valid for 
the distribution of fluid pressures in the compartment 21 between the 
piston 20 and the turbine 8. Accordingly, and if the aforementioned fluid 
pressure influencing means 33 were omitted, the lockup clutch 4 would 
become engaged in a fully automatic way when the vehicle is in the process 
of pulling a load. Such engagement or closing of the clutch 4 is 
undesirable and is particularly likely to take place when the quantity of 
fluid which is available to engage or disengage the lockup clutch 4 (and 
which is furnished by an externally mounted discrete pump) is so small 
that the pressure differential adapted to be established between the 
compartments 21, 22 by the fluid which is furnished by the discrete pump 
is less than that pressure differential at the opposite sides of the 
piston 20 which is established by the fluid layers in the compartments 21 
and 22 as a result of the aforediscussed fluid pressure drop in a 
direction from the radially outer portion of the housing 2 toward the axis 
X--X. Thus, the lockup clutch 4 would become engaged at an inopportune 
time. In other words, the pressure differentials which develop as a result 
of the circulation of bodies of fluid in the compartments 21, 22 at 
opposite sides of the piston 20 could adversely influence the operation of 
the lockup clutch 4 because the clutch would be automatically engaged at 
an inopportune time. 
Such undesirable operation of the lockup clutch 4 is prevented by the 
simple expedient of employing a friction disc 17 having one or more 
portions 33a extending radially inwardly toward the axis X--X beyond the 
friction linings 17a, 17b and carrying one or more projections 33 which 
can resemble or constitute vanes or blades, e.g., vanes or blades of the 
type known from the art of propellers and blowers. Since the disc 17 
rotates at the speed of the turbine 8, such speed is less than that of the 
piston 20 and housing 2 when the vehicle is pulling a load and the clutch 
4 is disengaged or partially disengaged (slipping). This, in turn, ensures 
that the particles of the (normally viscous) fluid in the compartment 22 
(which is bounded in part by the more rapidly rotating housing wall 2a and 
in part by the piston 20 which rotates at the speed of the housing 2) tend 
to circulate at a higher average speed than the particles of the body of 
fluid in the compartment 21. However, the speed of circulation of the 
fluid particles in the compartment 22 is reduced by the projection or 
projections 33 of the friction disc 17 which rotates at the lower speed of 
the turbine 8. Thus, the interaction between the body of fluid in the 
compartment 22 and the projection or projections 33 is such that the speed 
of circulation of the body of fluid in the compartment 22 is reduced. The 
average speed of circulation of fluid in the compartment 22 when the 
vehicle is in the process of pulling a load is less than if the projection 
or projections 33 of the friction disc 17 were omitted, i.e., if the speed 
of circulation of fluid in the compartment 22 were determined solely by 
the rapidly rotating housing 2 and its wall 2a and by the equally rapidly 
rotating piston 20. The influence of the projection or projections 33 upon 
the speed of circulation of fluid in the compartment 22 is or can be so 
pronounced that, when the clutch 4 is disengaged or when this clutch is 
slipping, the difference between the fluid pressures in the compartments 
21 and 22 is conducive to more predictable and more readily controllable 
engagement, disengagement and partial disengagement (slippage) of the 
lockup clutch 4. 
Similar results can be obtained by providing the radially inwardly 
extending portion or portions 33a of the friction disc 17 with surfaces or 
formations which establish a more pronounced frictional engagement between 
the portion or portions 33a on the one hand and the fluid in the 
compartment 22 on the other hand. Furthermore, the projection(s) 33 and/or 
the friction generating surface or surfaces of the portion or portions 33a 
can be utilized jointly with or can be replaced by holes or recesses in 
the portion or portions 33a; such recesses or holes also reduce the 
average speed of circulation of fluid in the compartment 22 when the 
vehicle embodying the apparatus 1 is in the process of pulling a load. 
This imparts to the friction disc 17 a tendency to reduce the pressure of 
the fluid in the compartment 22 when the lockup clutch 4 is partially 
engaged (slipping) and to increase the fluid pressure in the compartment 
22 when the clutch is disengaged. 
As already mentioned above, the piston 20 is free to move in the direction 
of the axis X--X (either toward or away from the wall 2a) and the piston 
rotates at the speed of the housing 2, namely at a speed which is higher 
than the speed of the friction disc 17, when the clutch 4 is disengaged or 
partially engaged (slipping) while the vehicle is in the process of 
pulling a load. In order to ensure that the opposite sides of the piston 
20 are subjected to the action of fluid-generated forces which at least 
substantially balance each other, at least while the lockup clutch 4 is 
disengaged or partially engaged (such forces are generated by the 
substantially layer-like annular bodies of fluid in the compartments 21 
and 22), it is possible to resort to the aforementioned projection or 
projections 33 (and/or to the aforementioned equivalents of such 
projection or projections) in the compartment 22 as well as to influence 
the speed of circulation of fluid in the compartment 21. For example, such 
influencing can be effected by the portion(s) 20a and/or 20b which form 
part of the piston 20 and extend into the compartment 21 to increase the 
speed of circulation of hydraulic fluid in the compartment 21 when the 
vehicle is in the process of pulling a load and to reduce the speed of 
circulation of fluid in the compartment 21 when the vehicle is coasting. 
The portion or portions 20a and/or 20b can be of one piece with the major 
portion of the piston 20 or they can constitute separately produced parts 
which are affixed (e.g., welded) to the piston. The portion or portions 
20a, 20b (and/or their equivalents) enhance the interaction between the 
piston 20 and the body of hydraulic fluid in the compartment 21. At least 
some of the portions 20a, 20b can extend into the compartment 21 in a 
direction which is parallel to the axis X--X. Depending upon the mode of 
operation of the torque converter 3 during certain stages of operation of 
the vehicle which embodies the apparatus 1, the projection(s) 20a and/or 
20b will tend to increase or to reduce the speed of circulation of 
hydraulic fluid in the compartment, always for the purpose of reducing the 
difference between the pressures of fluid layers confined in the 
compartments 21, 22 and acting upon the respective sides of the piston 20 
in directions parallel to the axis X--X. This, in turn, facilitates the 
task of the control system which is used to change the condition of the 
lockup clutch from a disengaged to a partly engaged and fully engaged 
condition or in the opposite direction. 
When the lockup clutch 4 is partly engaged, i.e., when its friction disc 17 
can slip relative to the wall 2a and piston 20, the compartments 21 and 22 
are practically sealed from each other and the pressure of fluid in the 
compartment 22 is not influenced by the pressure PI of fluid in the 
radially outermost portion of the chamber of the housing 2 and/or by a 
tendency of the fluid in the compartment 21 to reduce its speed of 
circulation starting at the radially outermost part of the compartment 22 
and proceeding toward the axis X--X. At such time (and when the vehicle is 
in the process of pulling a load), the portion or portions 33 (and/or 
their equivalent(s) in the compartment 22) tend to reduce the peripheral 
speed of the body of fluid in the compartment 22 and to thus reduce the 
magnitude of the force which the fluid in the compartment 22 applies to 
the respective side of the piston 20. This, in turn, ensures that the 
partially disengaged (slipping) clutch 4 does not tend to become fully 
disengaged while the vehicle is called upon to pull a load. 
To summarize, the means (20a, 20b) for controlling the speed of circulation 
and the pressure of the fluid in the compartment 21 and/or the means (33, 
33a) for controlling the speed of circulation and the pressure of the 
fluid in the compartment 22 serve to reduce the differences between the 
speeds of circulation of fluid bodies in the compartments 21, 22 when the 
clutch 4 is partially disengaged (slipping) while the vehicle is coasting 
and/or while the vehicle is called upon to pull a load. In the absence of 
such an undertaking or undertakings, the speed of circulation of the fluid 
in the compartment 22 would exceed the speed of circulation of the fluid 
in the compartment 21 because the compartment 22 is bounded by the wall 2a 
of the housing 2 which is driven by the output element 5 of the engine as 
well as by the piston 20 which rotates at the speed of the wall 2, whereas 
the speed of circulation of the fluid in the compartment 21 is determined 
in part by the turbine 8 whose speed is or can be less than the speed of 
the housing 2 and piston 20. 
When the vehicle is in the process of pulling a load, the torque converter 
3 operates in such a way that the output element 5 of the engine drives 
the housing 2 by way of the torque transmitting element 6. The housing 2 
transmits torque to the shaft 9 by way of the lockup clutch 4 and damper 
10 or by way of the pump (not shown), the turbine 8 and the stator (not 
shown). In either event, the hub 25a of the turbine 8 transmits torque to 
the shaft 9 which, in turn, transmits torque to the transmission (not 
shown) in the motor vehicle. 
When the vehicle is coasting, the aforementioned transmission transmits 
torque to the shaft 9 which, in turn, drives the output element 5 of the 
engine through the medium of the partly or fully engaged lockup clutch 4 
and/or by way of the stator, turbine 8 and pump of the torque converter 3. 
In other words, the vehicle is coasting when the operator can remove her 
or his foot from the gas pedal so that the wheels of the motor vehicle 
drive the transmission which drives the shaft 9 and the output element 5 
by way of the partially or fully engaged lockup clutch 4 and/or by way of 
the stator, turbine 8 and pump of the torque converter 3. 
The portion(s) 33a and the projection(s) 33 of the friction disc 17 can be 
said to constitute mechanical means for conforming the speed of 
circulation of the fluid in the compartment 22 to the speed of rotation of 
the turbine 8 when the lockup clutch 4 is disengaged or partially 
disengaged (slipping) and at least while the vehicle is in the process of 
pulling a load. Furthermore, the portion(s) 33a and the projection(s) 33 
can be said to constitute mechanical means for reducing the difference 
between the speeds of circulation of layer-like bodies of hydraulic fluid 
in the compartments 21 and 22 while the vehicle pulls a load and the 
lockup clutch 4 is disengaged or partially disengaged (slipping). 
The projection or projections 20a and/or 20b in the compartment 21 can be 
said to constitute mechanical means also serving to reduce the differences 
between the speeds of circulation of bodies of fluid in the compartments 
21 and 22 when the lockup clutch 4 is disengaged or partially disengaged 
and while the vehicle is in the process of pulling a load. As mentioned 
above, the projection or projections 20a and/or 20b can be utilized in 
addition to or in lieu of the portion(s) 33a and/or projection(s) 33 
and/or their equivalents or vice versa. The projection(s) 20a and/or 20b 
serve to increase the speed of circulation of fluid in the compartment 21 
adjacent to the relatively slowly rotating turbine 8, whereas the 
portion(s) 33a and/or projection(s) 33 (and/or their aforediscussed 
equivalents) serve to reduce the speed of circulation of fluid in the 
compartment 22, i.e., in the compartment which is bounded by the rapidly 
rotating housing 2 and equally rapidly rotating piston 20. Such 
accelerating actions of the projection or projections in the compartment 
21 and decelerating actions of the projections in the compartment 22 are 
effective at least while the lockup clutch 4 is at least partially 
disengaged and while the vehicle pulls a load. Furthermore, and as already 
mentioned above, the projection(s)in the compartment 21 and/or in the 
compartment 22 can serve as a means for balancing or equalizing the forces 
acting upon the respective sides of the piston 20 in the direction of the 
axis X--X when the clutch 4 is at least partially disengaged and while the 
vehicle is in the process of pulling a load. The balancing or equalizing 
action is or can be such that the axial forces which the fluid in the 
compartment 21 applies to the right-hand side of the piston 20 match or at 
least closely approximate the axial forces which the fluid in the 
compartment 22 applies to the left-hand side of the piston 20. 
FIG. 2 shows a portion of a second apparatus 1 including a modified torque 
converter 3 which embodies a modified lockup clutch or bypass clutch 4. 
Those parts of the apparatus 1 of FIG. 2 which are identical with or 
clearly analogous to the corresponding parts of the apparatus 1 of FIG. 1 
are denoted by similar reference characters. The lockup clutch 4 of FIG. 2 
is installed in the chamber of the housing 2 forming part of the torque 
converter 3 and including a wall 2a extending substantially radially of 
the axis X--X between the clutch 4 and the output element 5 of an engine 
in a motor vehicle. The clutch 4 is installed between the wall 2a and the 
turbine 8 of the torque converter 3 and includes an axially movable 
pressure plate or piston 31 and a friction disc 32 disposed between the 
piston 31 and the turbine 8. The disc 32 is disposed in a first 
compartment 36 at one side of the piston 31 and the latter cooperates with 
the wall 2a to define a second compartment 37 which is sealed (by the 
piston 31 ) from the compartment 36 when the clutch 4 is engaged or 
partially engaged (slipping). The turbine 8 of the torque converter 3 
includes a radially inwardly extending flange 25 which is of one piece 
with or is welded or otherwise non-rotatably connected to a hub 25a 
non-rotatably surrounding a portion of a shaft 9 serving to transmit 
torque to or from a transmission (not shown), depending upon whether the 
vehicle embodying the apparatus 1 of FIG. 2 is in the process of pulling a 
load or is coasting. 
When the lockup clutch 4 is engaged, it transmits torque directly between 
the housing 2 and the hub 25a of the turbine 8 because the friction 
linings 32a of the disc 32 are then clamped between the adjacent side of 
the piston 31 and a radially extending plate-like member 35 which is 
riveted and/or otherwise affixed to the flange 25, hub 25a and/or another 
part of the turbine. Actually, the engaged lockup clutch 4 of FIG. 2 
transmits torque to or from the shaft 9 by way of a damper 10 which is or 
can be identical with or analogous to the damper 10 in the torque 
converter of FIG. 1. 
The damper 10 is installed in series with the lockup clutch 4. When the 
output element 5 of the engine drives the housing 2 by way of the torque 
transmitting member 6, the housing drives two discs 13, 14 which, in turn, 
transmit torque to the damper 10. The energy storing elements 11 of the 
damper 10 transmit torque to a disc-shaped carrier 15 for the friction 
disc 32. The disc 32 transmits torque to the torque converter 3, i.e., to 
the hub 25a of the turbine 8 which cooperates with a pump (not shown) and 
(if necessary) with a stator (not shown)in a manner as described and shown 
in the aforediscussed references such as the patent to Bopp. 
The discs 13, 14 are provided with pockets 12 for the energy storing 
elements (such as arcuate coil springs) 11 of the damper 10. The radially 
outermost tubular or cylindrical portion 2b of the housing 2 surrounds and 
is welded to or otherwise non-rotatably connected with the discs 13 and 
14. The pockets 12 of the discs 13, 14 are configurated and located in 
such a way that the energy storing elements 11 of the damper 10 are 
disposed radially outwardly of the friction linings 32a forming part of 
the friction disc 32 and radially outwardly of the piston 31. Otherwise 
stated, the inner radii of curvature of the pockets 12 at least match but 
can exceed the radii of the radially outer portions of the friction 
linings 32a. 
The washer-like discs 13, 14 and the washer-like member 15 cooperate to 
stress the energy storing elements 11 when the turbine 8 is driven by the 
output element 5 of the engine. To this end, the member 15 is provided 
with axially parallel legs 15a which further serve to fix the friction 
disc 32 against movement radially of the axis X--X as well as to transmit 
torque between the disc 32 and the member 15. The illustrated disc 32 
resembles a substantially flat washer with friction lining 32a, 32b formed 
on or affixed to its two sides. When the lockup clutch 4 of FIG. 2 is 
engaged, the friction lining 32a is engaged by the right-hand side of the 
piston 31 and the friction lining 32b is pressed against the member 35, 
i.e., against a portion of the turbine 8. The friction disc 32 cannot 
rotate but can perform limited axial movements relative to the member 15. 
The member 35 includes a radially inwardly extending portion 30 which 
constitutes or includes or is non-rotatably connected to the radially 
extending flange 25 of the turbine 8. 
The compartments 36, 37 are connectable by conduits (not shown) to the 
control unit (not shown) serving to engage, to partially disengage or to 
disengage the lockup clutch 4. Each of these compartments is filled with a 
pressurizable hydraulic fluid, e.g., a viscous or highly viscous fluid. 
When the fluid pressure in the compartment 37 exceeds the fluid pressure 
in the compartment 36, the piston 31 is shifted in the direction of the 
axis X--X toward the turbine 8 to thus engage the lockup clutch 4. 
Inversely, the piston 31 is caused to move toward the wall 2a when the 
pressure of fluid in the compartment 36 exceeds the pressure of fluid in 
the compartment 37; this entails a disengagement of the lockup clutch 4. 
The radially inner portion of the piston 31 is non-rotatably connected to 
the hub 25a of the turbine 8 by a coupling 38 which permits the piston to 
move axially toward or away from the turbine 8. In other words, the 
rotational speed of the piston 31 about the axis X--X always matches the 
rotational speed of the turbine 8 and its hub 25a. On the other hand, the 
friction disc 32 always rotates at the speed of the output element 5 of 
the engine because it is non-rotatably connected to the housing 2 which, 
in turn, is non-rotatably connected to the output element 5 by the 
substantially disc-shaped torque transmitting member 6. In other words, 
the rotational speed of the piston 31 departs or can depart from the 
rotational speed of the friction disc 32 when the lockup clutch 4 is 
disengaged or partially disengaged (slipping). 
When the vehicle is coasting and the lockup clutch 4 is disengaged or 
partially disengaged, the speed of rotation of the turbine 8 (which is 
driven by the shaft 9) exceeds the rotational speed of the housing 2. In 
the absence of any undertakings to the contrary, the speed of circulation 
of fluid in the compartment 36 would considerably depart from the speed of 
circulation of fluid in the compartment 37. Thus, the speed of circulation 
of fluid in the compartment 36 would exceed the speed of circulation of 
fluid in the compartment 37 because the compartment 36 is bounded by the 
turbine 8 and the piston 31, i.e., by two components whose rotational 
speed exceeds the speed of rotation of the housing 2 when the engine is 
coasting. The fluid pressure in the compartment 36 (as compared with fluid 
pressure in the compartment 37) decreases when the lockup clutch 4 is 
disengaged, and this creates problems in connection with the engagement of 
the clutch 4 since a pressure differential between the fluids in the 
compartments 36, 37 already exists before the control system is set to 
reengage the lockup clutch. The problems are particularly acute when the 
control system for the torque converter 3 is designed to engage the lockup 
clutch 4 in response to the establishment of a relatively small pressure 
differential between the bodies of fluid in the compartments 36 and 37. In 
other words, the pressure differential which can be established by the 
control system for the purposes of reengaging the clutch might not be 
sufficient to invariably ensure the engagement of the clutch when such 
engagement is desired or necessary. 
In accordance with a feature of the invention, the friction disc 32 extends 
radially inwardly beyond the friction linings 32a, 32b, and such radially 
inwardly extending portion or portions 33a carry profiles 33, e.g., in the 
form of vanes or blades which are located in the compartment 36 of the 
chamber within the housing 2. When the vehicle is coasting, the rotational 
speed of the friction disc 32 (which shares the angular movements of the 
housing 2) is less than that of the turbine 8 and the piston 31 (the 
latter rotates with the turbine). However, since the profiles 33 rotate at 
the speed of the friction disc 32, i.e., at a speed less than that of the 
piston 31 and member 35 (the parts 31 and 35 are disposed at opposite 
sides of the compartment 36), the profiles 33 reduce the speed of 
circulation of viscous fluid in the compartment 36, i.e., the difference 
between the pressures of fluid bodies in the compartments 36 and 37 is 
reduced due to the provision of the profiles 33 because the profiles 33 
exert a decelerating action upon the fluid in the compartment 36. 
Consequently, the average speed of circulation of fluid in the compartment 
36 is reduced by the profiles 33 when the vehicle is coasting, i.e., when 
the speed of the turbine 8 and piston 31 exceeds the speed of the housing 
2 and friction disc 31. Furthermore, it is necessary to only slightly 
increase the pressure of fluid in the compartment 36 when the lockup 
clutch 4 is to be disengaged and/or maintained in the disengaged condition 
while the vehicle is coasting so that the turbine 8 drives the housing 2 
and the output element 5 of the engine. Stated otherwise, a relatively low 
pressure of fluid in the compartment 36 suffices to maintain the lockup 
clutch 4 in disengaged condition while the vehicle is coasting. 
If the vehicle is used to pull a load and the lockup clutch 4 is 
disengaged, and if the profiles 33 are omitted, the fluid in the 
compartment 36 causes the generation of a force which acts upon the 
right-hand side of the piston 31 in the direction of the axis X--X, i.e., 
toward the wall 2a of the housing 2. In other words, the fluid in the 
compartment 36 then tends to disengage the lockup clutch 4. At such time 
(i.e., when the output element 5 transmits torque to the housing 2), the 
rotational speed of the housing 2 and the friction disc 32 exceeds the 
rotational speed of the piston 31 and turbine 8. The pressure of the fluid 
in the compartment 36 (as seen in a direction from the radially outer 
portion 2b of the housing 2 toward the axis X--X) is then less pronounced 
than in the compartment 37. Thus, the pressure level in the compartment 36 
is higher. This entails the development of a resultant force acting upon 
the piston 31 in a direction from the turbine 8 toward the wall 2a, i.e., 
in a direction to disengage the lockup clutch 4. If the clutch 4 is to be 
reengaged, the pressure of fluid in the compartment 37 must be increased 
by the aforementioned discrete pump in order to reliably overcome the 
elevated pressure of the fluid in the compartment 36. This can be 
accomplished by employing a relatively large discrete fluid pump whose 
energy and space requirements are undesirably large when such a pump is 
used in a motor vehicle. In the absence of a pump which can reliably raise 
the fluid pressure in the compartment 37 to a value sufficient to 
invariably engage the clutch 4, the clutch would remain in the disengaged 
condition. 
The situation is entirely different if the apparatus 1 is constructed in a 
manner as shown in FIG. 2, i.e., if the friction disc 32 is provided with 
one or more radially inwardly extending portions 33a for blades, vanes 
and/or analogous profiles 33. Such profiles raise the speed of circulation 
of the fluid in the compartment 36 because the disc 32 rotates with the 
housing 2 and the speed of the housing exceeds the speed of the piston 31 
and turbine 8 because the vehicle is in the process of pulling a load, 
i.e., the output element 5 of the engine drives the housing 2. As the 
profiles 33 accelerate the fluid in the compartment 36, the pressure of 
the fluid in the compartment 36 (when the clutch 4 is disengaged) 
decreases. This reduces the magnitude of forces acting upon the right-hand 
side of the piston 31 in a direction (toward the wall 2a) to disengage the 
lockup clutch 4. It is even possible to reduce the magnitude of such force 
to zero. Irrespective of whether the pressure of the fluid in the 
compartment 36 is merely reduced or drops to zero, the provision of 
profiles 33 in the compartment 36 ensures that the lockup clutch 4 can be 
reengaged in response to a small or relatively small rise of fluid 
pressure in the compartment 37. 
If the profiles 33 were omitted and the apparatus 1 of FIG. 2 were operated 
in such a way that the vehicle is coasting, the torque converter 3 would 
cause the lockup clutch 4 to become automatically engaged. As already 
explained above, the provision of profiles 33 on the radially inner 
portion or portions 33a of the friction disc 32 at least reduces the 
tendency of the lockup clutch 4 to become automatically engaged when the 
vehicle is coasting. 
The vane- or blade-like profiles 33 on the radially inwardly extending 
portion or portions 33a of the friction disc 32 can be used with or can be 
replaced by other means for influencing the fluid in the compartment 36. 
For example, the portion or portions 33a can be provided with means for 
increasing friction between the disc 32 and the viscous fluid in the 
compartment 36. Furthermore, it is possible to use the profiles 33 and/or 
the friction generating means with or in lieu of recesses (not 
specifically shown) in the portion or portions 33a. All that counts is to 
provide the disc 32 with one or more means or sets of means for ensuring 
that the average speed of circulation of fluid in the compartment 36 is 
reduced when the vehicle is coasting and that the pressure of the fluid in 
the compartment rises when the lockup clutch 4 is disengaged. 
It is equally within the purview of the invention to influence the fluid in 
the compartment 37 in a sense to reduce the pressure differential between 
the hydraulic fluids which fill the compartments 36 and 37. The means for 
influencing the fluid in the compartment 37 can be utilized with or in 
lieu of the aforedescribed means (such as the profiles 33) in the 
compartment 36. FIG. 2 shows that the piston 31 is provided with profiles 
31a, 31b which can constitute vanes or blades and extend into the 
compartment 37. Such profiles can constitute separately produced parts 
which are welded or otherwise secured to the substantially disc-shaped 
main body portion of the piston 31. This main body portion can be made 
(e.g., stamped) from suitable metallic sheet material. 
The profiles 31a, 31b tend to accelerate the fluid in the compartment 37 
when the vehicle is coasting; such an acceleration of the fluid in the 
compartment 37 (due to a more pronounced interaction between the piston 31 
and the fluid in the compartment 37) entails a change (namely a reduction) 
of the pressure differential between the fluids in the compartments 36, 
37. This, in turn, ensures that the condition of the lockup clutch 4 can 
be changed in response to a relatively small rise of fluid pressure in the 
compartment 36 or 37, depending upon whether the lockup clutch is to be 
engaged, partially engaged or disengaged. 
Referring again to FIG. 1, the flange 25 of the turbine 8 is provided with 
one or more holes 24 which establish one or more passages between the 
compartment 21 and a compartment (not specifically shown in FIG. 1) which 
is disposed between the turbine 8 and the pump of the torque converter 3, 
and constitutes a third portion of the internal chamber of the housing 2. 
The hole or holes 24 are provided in the flange 25 radially inwardly of 
the profile or profiles 20a of the piston 20. The hole or holes 24 can be 
provided in addition to or in lieu of one or more holes provided in, or 
radially inwardly of, the hub 25a of the turbine 8 and serve the same 
purpose as the illustrated hole(s), i.e., to establish one or more paths 
or passages for the flow of hydraulic fluid between the compartment 21 and 
the compartment (not shown) between the turbine 8 and the non-illustrated 
pump of the torque converter 3 shown in FIG. 1. The purpose of the hole or 
holes 24 and/or their equivalents is to reduce the difference between the 
pressure of the fluid in the compartment 21 and the compartment between 
the pump and the turbine 8. 
The profiles 33 of the friction discs 17 and 32 share the advantage that 
they bring about an at least substantial identity between the speed of 
circulation of fluid particles in the compartment 22 or 36 on the one hand 
and the compartment 21 or 37 on the other hand. Moreover, the profiles 33 
ensure that the distribution of fluid pressures in the compartment 21 (or 
36) at least approximates the distribution of fluid pressures in the 
compartment 22 (or 37), and this holds true irrespective of whether the 
engine is coasting or is in the process of pulling a load. Otherwise 
stated, the profiles 33 can ensure that, under ideal circumstances, the 
pressure of fluid in the compartment 21 or 36 actually matches the 
pressure of fluid in the compartment 22 or 37, i.e., that a relatively 
small rise of pressure in one of the compartments 21, 22 or 36, 37 (such 
rise of pressure is effected by the aforediscussed discrete pump) suffices 
to change the condition of the lockup clutch from engaged to partially 
disengaged to fully disengaged or in the opposite direction. 
The portion or portions 33a of the friction disc 17 or 32 can extend 
radially inwardly toward the respective axis X--X at least to a location 
substantially midway between the radially innermost and the radially 
outermost portions of the vanes or blades 8a forming part of turbine 8. In 
FIGS. 1 and 2, the portions 33a extend radially inwardly to positions 
closer to the radially innermost portions than to the radially outermost 
portions of the vanes forming part of the turbine 8. In either event, the 
portion or portions 33a of the disc 17 extend radially inwardly beyond the 
friction surfaces 17a and the portion or portions 33a of the disc 32 also 
extend radially inwardly well beyond the radially inner portions of the 
friction linings 32a and 32b. 
It is often desirable and advantageous to select the dimensions of the 
friction disc 17 or 32 (inclusive of its radially inwardly extending 
portion or portions 33a) in such a way that the disc or its radially 
inwardly extending portion overlies the entire piston 20 or 31, as seen in 
the direction of the respective axis X--X. 
An important advantage of the improved torque converter 3 is that the 
pressure of the circulating fluid in the compartment 21 or 36 matches or 
at least rather closely approximates the pressure of the fluid in the 
compartment 22 or 37, irrespective of whether the vehicle is coasting or 
is called upon to pull a load. In other words, small or extremely small 
variations of fluid pressure in the compartment 21 or 22 (FIG. 1) or 36 or 
37 (FIG. 2) suffice to change the condition of the lockup clutch 4. The 
reason is that the lockup clutch 4 is prevented from generating a moment 
of friction not only when the engine is coasting, but also when the 
vehicle is in the process of pulling a load. This is accomplished by 
resorting to the aforediscussed expedient of ensuring that the axial 
forces acting upon the opposite sides of the piston 20 or 31 are at least 
substantially balanced due to the provision of the aforediscussed profiles 
33, 20a, 20b, 31a, 31b and/or analogous expedients. Under ideal 
circumstances, the forces acting upon opposite sides of the piston 20 or 
32 neutralize each other so that axial displacements of the piston 20 or 
31 toward or away from the wall 2a of the respective housing can be 
achieved by slightly increasing the fluid pressure in the compartment 21 
or 22 (FIG. 1) or in the compartment 36 or 37 (FIG. 2). For example, a 
relatively small rise of fluid pressure in the compartment 21 of FIG. 1 is 
necessary to reengage the respective lockup clutch 4, and a relatively 
small rise of fluid pressure in the compartment 37 of FIG. 2 is necessary 
to reengage the respective lockup clutch 4. This holds true irrespective 
of whether the vehicle is coasting or pulling a load. Furthermore, a 
relatively small rise of fluid pressure in the compartment 22 of FIG. 1 or 
in the compartment 36 of FIG. 2 is necessary to disengage the respective 
clutch 4. Such features of the improved torque converter 3 render it 
possible to employ a relatively small discrete pump which causes the fluid 
pressure in the compartment 21 or 22 of FIG. 1 or in the compartment 36 or 
37 of FIG. 2 to rise in order to change the condition of the respective 
lockup clutch 4. 
Another important advantage of the improved torque converter is that it 
contributes to the comfort of the occupant or occupants of the vehicle 
which employs the apparatus 1 of FIG. 1 or 2 or an analogous apparatus. 
The reason is that the transitions between different operating conditions 
of the lockup clutch 4 (from engaged to partially disengaged to fully 
disengaged or in the opposite direction) are smooth because even minor 
changes of fluid pressure in the compartment 21 or 22 of FIG. 1 or the 
compartment 36 or 37 of FIG. 2 suffice to effect a reliable and 
predictable change of the operating condition of the lockup clutch. 
The improved apparatus are susceptible of numerous additional modifications 
without departing from the spirit of the invention. For example, several 
features of the apparatus 1 of FIG. 2 can be incorporated in the apparatus 
1 of FIG. 2 and/or the other way around. Furthermore, it is believed that 
numerous auxiliary features of the torque converter 3 of FIG. 1 and/or of 
the torque converter of FIG. 2 are sufficiently novel and unobvious to 
merit patent protection regardless of the exact nature of the torque 
converter which embodies such features. This applies, for example, to the 
construction and/or configuration and/or dimensioning of the piston 20 or 
31 and/or friction disc 17 or 32. Moreover, the number of friction discs 
can be increased and the number of friction linings on each friction disc 
can be reduced, depending upon the intended use of the improved torque 
converter and its lockup clutch. 
Additional important advantages of the improved apparatus are their 
compactness and simplicity. Thus, by the simple expedient of altering the 
configuration of that portion or those portions of the piston 20 or 31 
which extends or extend into the adjacent compartment 21 or 37, and/or of 
altering the configuration of that portion or those portions of the 
friction disc 17 or 32 which is or which are adjacent the compartment 22 
or 36, one can ensure that the changes in the condition of the lockup 
clutch 4 or an equivalent lockup or bypass clutch can be completed with a 
higher degree of reliability and predictability, and in response to the 
application of lesser forces than in heretofore known torque converters. 
The apparatus of the present invention can be incorporated in heretofore 
known types of motor vehicles to replace conventional torque transmitting 
apparatus employing a hydrokinetic torque converter between the output 
element of a prime mover and the input element of a transmission or 
another unit or assembly in the power train between the prime mover and 
the wheels and/or other driven parts of the vehicle. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of the prior art, fairly constitute essential 
characteristics of the generic and specific aspects of the above-outlined 
contribution to the art and, therefore, such adaptations should and are 
intended to be comprehended within the meaning and range of equivalence of 
the appended claims.