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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

startup.components@voith.comwww.startup-components.com

Cr601en,MSW/K&E,05.2007,1000.Dimensionsandillustrationswithoutobligation.Subjecttomodifications.