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Simply ingenious ingenious simple:
self-synchronizing hydrodynamic start-up coupling
TurboSyn
Dipl.-Ing. Harald Hoffeld
Head of Technology Department in the Start-up Components product group at
Voith Turbo GmbH & Co. KG in Crailsheim
Special print from antriebstechnik 4/2006
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T
n
E-motor KL 10 / 13
1
Figure 1:Continued development of
75 years of a proven invention:
Voith Turbo fluid coupling with integrated
lock-up clutch, type TurboSyn.
Figure 2:Motor load for different coupling
types having the same size. The characte-
ristic 2a occurs through additional
emptying of the working circuit around the
retaining space 1a (Figure 3) in the delay
chamber 2 (Figure 3).
2
2a
3
2
Basic requirements for fluid
couplings
Typically a fluid coupling is used to
transmit power between a motor
and a driven machine. The charac-
teristic curve of the coupling can be
adapted to suit the requirements.
This provides a proven, easy to
handle, and reliable option for opti-
mizing the drive line.
Direct on line started asynchronous
motors, often preferred because of
their simple construction, can only
be used for a relatively brief start-up
time due to their speed-dependent
current consumption. Start-up ispossible only of relatively small
masses and always leads to loading
of the drive dependent on the
characteristics of the motor. To
overcome these limitations fluid
couplings are commonly used for:
The Fttinger principle on which
hydrodynamic couplings are based
has been known for 100 years.
After the invention in 1905 by
Dr. Hermann Fttinger, it took 25
years before a hydrodynamic
coupling called fluid coupling was
installed in a pumped storage
power station.
For the 100th anniversary of the
Fttinger principle and 75 years of
Voith drive technology, Voith pre-
sents a new hydrodynamic coupling
which eliminates losses and slip atrated operation in an ingeniously
simple way (Figure 1).
When machines are started or
stopped, a slipping transmission
between the motor and the driven
machine is often desired. However
at rated operation a slip-less i.e.
lock-up device is preferred. Up to
now both of these conditions soft
start and synchronous lock-up at
rated operation could not be met
with hydrodynamic couplings.
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Symbols and description
Table: Symbols used.
Figure 3:Hydrodynamic coupling in
different types with nozzle screws.
TVV: design with delay chamber
TVVS: design with delay and annular
chamber
Section drawing
Type TVV
Section drawing
Type TVVS
Nozzle
screw
1b
1c2
1a
3
3
DP Profile diameter
DFriction Friction diameter
F Force
FG Fill level
T Torque
m Mass
n Speed
nP Pump wheel speed
p Contact pressure
q Specific friction consumption
Re Reynolds number
Performance coefficient
Coefficient of friction
* Relative coefficient of friction
Speed ratio
Density
Angular velocity
P Angular velocity of the pump
S Switching angle velocity
Heavy-duty start-up: Soft start of
the motor and subsequent loading
of the driven machine with a
torque somewhat below the pull
out torque of the motor. This
allows the maximum possible
acceleration power of the motor to
be used during the entire start-up
time.
Soft-duty start-up: Soft start of the
motor and subsequent accelera-
tion of the driven machine with
minimum acceleration torque,
which is significantly below the
motor pull out torque during theentire start-up time for the driven
machine.
In both cases the motor is only light-
ly loaded during its acceleration.
After it has reached its rated speed,
the driven machine is accelerated
up to the rated speed, and the
motor is always operating above the
stall speed in the stable nominal
current range.
Options with conventional fluid
couplings
There are various parameters avail-
able to adapt the coupling function
or characteristic to the drive: The
coupling size, the coupling type,
and the fill level, FG. In Figure 2
the load of an electric motor is
shown for differing types of fluid
couplings using the same fill level.
The different primary characteristics
of the fluid coupling are due to the
different chambers. Figure 3:
retaining space 1 (1a, 1b, 1c), delay
chamber 2 and annular chamber 3.
The transmission capability of fluidcoupling is described by the
equation for torque:
T = Dp5
p2 (1)
where the following applies for the
performance coefficient :
= f (geometry, Re, , FG) (2)
With this, the transmitted torque
and slip can be adjusted by chang-
ing the fill level FG. For fluid cou-
plings with delay chambers, the
torque build up can be further ad-
justed over time by changing the
nozzle cross-section using remov-
able nozzle screws (Figure 3).
Based on the principle of operation
of a fluid coupling, a slip between
pump and turbine wheel occurs
during rated torque transmission.
Typically slip is about 3%.
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The lock-up functions close and
open should be self-engaging.
Lock-up should not require any
additional auxiliary power source.
The characteristics should be
input speed independent, to
simplify the engineering.
The installation dimensions of the
existing fluid couplings are to be
retained to offer a drop in
replacement and still offer
compact drive solutions.
The interface connections to
motor and driven machine side
should be retained, so that the
existing connecting technology(connecting coupling, flanges)
can be used.
Working principle
Start-up and TurboSyn lock-up
clutch lead to a centrifugal force
controlled friction clutch, whose
centrifugal bodies rotate at the out-
put speed. To fulfill the requirement
for compactness, a centrifugal
clutch was not just simply coupled
to the fluid coupling, instead, it was
integrated completely. The existing
mass of the turbine wheel is used
as a centrifugal body (Figure 1, red
and blue segments). To do this, the
turbine wheel is now split into mul-
tiple segments. On the inner dia-
meter, all segments receive a pivot
bolt bearing assembly in the coup-ling housing. The segments are
connecting with the hub so that only
one angular motion is possible. This
is minimal and is approximately
1 mm between free running and en-
gaged TurboSyn position. The force
is introduced into the turbine wheel
segments via friction from the shell
of the turbo coupling. The force is
transferred to the hub via the bolt
Requirements for the
TurboSyn
In the following, a lock-up clutch
integrated in the fluid coupling is
shown, which only slightly affects
the essential characteristics of the
fluid coupling. The development
goals for this lock-up clutch were
specified together with the charac-
teristics of the hydrodynamic Voith
coupling:
The machines connected should
be protected as much as possible
for both the heavy-duty start-up as
well as for the soft-duty start-up.
Synchronization should not
reduce the masses to beaccelerated.
There should be no reduction of
the torque transmission.
A stall of the driven machine
should result in load limitation by
disengaging the lock-up and thus
leading to a purely hydrodynamic
torque transmission.
Figure 4:Geometry and applications of
force on the turbine wheel segment.
Figure 5:The effect of spring relief on a
centrifugal body.
-0.4
F
Fmax[1]
0.53
m
m+m
Shifting force
Compensa
for the shi
force loss
to addition
mass
Shifting force reduce
by restoring spring
m
FSpring
Fmax-0.2
0
0.2
0.4
0.6
0.8
1.0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0s
[1]FHub(FG max.)b
FBolt
Fhydro (FG max.)
Fcent
DP Dfriction
FNc
FN
PT
Flift (FG min.)
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connections (Figure 4). Because of
the segmented turbine wheel
design, there is now the opportunity
to use the hydrodynamic peripheral
forces directly to control the
engagement of the clutch.
The torque transmission was
selected so that the turbine wheel
segments are loaded in a trailing
manner by the friction force, when
the motor is operational. This
means that the friction force
supports the clutch disengaging.
Therefore, it is also possible to use
the hydrodynamic peripheral forcefor the disengaging of the clutch.
The hydrodynamic force operates
like the spring of a conventional cen-
trifugal clutch, however with the
advantage that the force becomes
smaller with decreasing slip and
does not act in the engaged state.
This makes it possible to move the
starting point of the engagement to
higher output speeds without in-
creasing the centrifugal body mass,
which would be necessary if con-
tinuously-acting springs were used.
The influence of a continuously acting
spring for moving the engagement
point of a rotating mass is shown in
Figure 5. The spring counteracting
the centrifugal force reduces the
effective engaging force. To
compensate for this loss of engaging
power, an additional mass m is
necessary. The relationship between
the beginning of engagement and the
mass ratios is shown in Figure 6.
Geometry and masses of the tur-
bine wheel segments were matched
with the hydrodynamic peripheral
force so that the reduction of the
hydrodynamic spring leads to a
significant movement of the engage-
ment point. This hydrodynamic
disengagement force, as well as the
trailing of the centrifugal body with
the output speed, results in the
acceleration energy primarily being
applied hydrodynamically, hence
the loading on the friction lining is
very small.
The forces shown in Figure 4cor-
respond to the maximum occurring
forces. The hydraulic force the sum
of the single flow forces applied to
each individual blade.
The speed-dependent force ratios are
shown in Figure 7. The transmittable
torque of the coupling can be calcu-
lated from these force characteristics
and the geometric relationships,along with knowledge of the coeffi-
cient of friction. Figure 8shows the
hydrodynamic torque transmission of
the TurboSyn, and the portion of the
torque transmitted by friction. The
relative coefficient of friction used as
the basis of this calculation is also
indicated.
Figure 6:Dependence of beginning of
shifting on the mass ratios of a spring-
relieved shift coupling.
s
[1]
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0m
m[1]
0.53
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Three turbine wheel versions
In order to implement the clutch
characteristic for different loads
optimally, three different turbine
wheel versions are available:
Version A:
For lower loads, a design in
accordance with Figure 4is
selected. The friction linings can
be found on the side of the
turbine wheel segments which
are leading the links on the hub.
Version B:
For medium loads, the friction
linings are applied on the centerof the segments.
Version C:
For high loads, the friction linings
are also applied on the center of
the segments, however, heavier
turbine wheel segments are used.
The loadings of the friction linings
are similar for all turbine wheel
versions, because not only the
synchronous torque is modified, but
the hydrodynamic torque as well.
The coupling shell without annular
chamber is connected to the pump
wheel and encloses the turbine
wheel so that the operating medium
remains within the working circuit.
In addition to containing the oil, the
shell must accommodate the cen-
trifugal forces of the turbine wheel
segments and also serve as the
contact surface for the friction
linings. This requires the use of aferrous material with sufficient
surface hardness on the friction
surface.
Characteristic curves
The geometric ratios of the lock-up
clutch lead to the same dependence
of torque on profile diameter DPand
on the angular velocity of the out-
put, which is the same as for a
purely hydrodynamic coupling.
Since the coupling series has a simi-
lar design, both geometrically and
hydraulically, the loading of the
TurboSyn can also be shown by the
power coefficient as a specific
characteristic. The following relation-
ship results from equation 1 and 2:
Dp5
p2
T= = f(, FG)
Figure 9 shows the calculated
characteristic for the turbine wheel
version C. The load on the friction
linings is characterized by the
contact pressure and the specific
frictional force.
Figure 7:Speed-dependent force ratios
on the turbine wheel segment.
Figure 8:Torque transmission of the
TurboSyn.
FHydro (FG max)
FHydro (FGmin)
Fcentr.
Flift
nP= 1,500 rpm
F[N]
-40,000
-20,000
0
20,000
40,000
60,000
80,000
100,000
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
[1]
THydro
nP= 1,500 rpm
T[Nm]
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
[1]
*[1]
Ttotal
Tfriction
*
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The power transmitted hydrodyna-
mically and by friction are shown in
Figure 10 for the start-up of a coal
mill. During start-up, a part of the
drive energy is transformed into
heat and stored in the mass of the
TurboSyn. More than 95% of this
heat is generated hydrodynamically.
During operation the coupling is
cooled down to ambient
temperature, because there are no
losses due to slip. This means that
after a system stop, there is a
significantly higher heat capacity
available to restart, compared to aconventional slipping hydrodynamic
coupling.
Example application
The use of this type of coupling is
ideal for drives requiring a soft start,
but which do not require the
characteristics of a fluid coupling
under normal operation. For last 1.5
years, the drive system of a coal
mill at the Frimmersdorf power plant
has been successfully in operation
using a TurboSyn 750 TV-X with an
input power of 450 kW at a speed of
1,480 rpm. Currently a TurboSyn
562 TV is being commissioned on a
coal charging conveyor with an
input power of 108 kW at a speed of
1,480 rpm.
Summary
Using existing fluid coupling
components, a look up clutch can
be integrated into the fluid
coupling without adding additional
parts, simply by modifications to
both the inner wheel and shell.
The turbine wheel was segment-
ed and linked so that it fulfills the
function of an additional centrifu-
gal body.
Force is transmitted from the tur-
bine wheel segments to the hub
via pivot bolts which replace the
previous rigid hub connection.
The coupling shell is used as
friction drum.
The hydrodynamic force is initi-
ated in such a way as this fulfills
the function of a reset spring for
discharge the friction contact.
All other parts of the fluid coupling
remain unchanged.
Figure 9:Calculated characteristic of the
TurboSyn coupling for high load, as well as
for friction contact load.
Figure 10:Portions of the hydrodynamic input power and
centrifugal force coupling friction force dependent on the speed
ratio between input and output. The effect of the synchronous
coupling is implemented starting at a speed ratio of
approximately 0.55.
QHydro
QFriction
Q[W]
0
100,000
200,000
300,000
400,000
500,000
600,000
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
[1]
p
q
Hydro
103 total103
0
2
2.5
3
3.5
4
4.5
5
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
[1]
0.5
1
1.5
103
[1];p[N/mm2];q[W/mm2]
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Voith Turbo GmbH & Co. KG
Start-up Components
Voithstr. 1
74564 Crailsheim, Germany
Tel. +49 7951 32 -409
Fax +49 7951 32 -480
Cr601en,MSW/K&E,05.2007,1000.Dimensionsandillustrationswithoutobligation.Subjecttomodifications.
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