fluid couplings 3

7/25/2019 Fluid Couplings 3

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ABSTRACT

The subject selected for our mini project is Fluid couplings and

its particulars in turbo transmission used in locomotives. For thisa locomotive manufacturing and assembly unit at Charlapally ,

Hyderabad is selected. As it manufacture locomotives with

hydraulic transmission.

Hydraulic transmission are of two types ; Hydrostatic and hydrodynamic. Hydrodynamic

operates at high flow rate and low pressure while the hydrostatic incorporates low flow rate

and high pressure. The former is chosen for most of the railway applications for the

advantages and maintenance .

tructurally a fluid coupling consists of an impeller on the input shaft or driving shaft and

a runner on output or driven shaft. !mpeller and runner reacts as a turbine. The impeller

accelerates the fluid near its a"is at which the tangential component of absolute velocity is

low near its periphery at which the tangential component of absolute velocity is high.

!n modern age a tor#ue converter is generally a type of fluid coupling used to transfer

rotating power from a prime mover, such as internal combustion engine or electric motor to a

rotating driven load . The $ey characteristic of tor#ue converter is its ability to multiplytor#ue when there is a substantial difference between input and output rotational speeds thus

providing the e#uivalent of a reduction gear. %ngaging the tor#ue convertor by filling it with

oil and for disengaging by draining it.

The company ensures a reliable and effective end product by application of software for the

optimal design of critical components li$e gears ,springs , a"les and bearings.


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CHAPTER 1

INTRODUCTION

A fluid coupling or hydraulic coupling is a hydrodynamic device used to transmit rotating

mechanical power. !t has been used in automobile transmissions as an alternative to a

mechanical clutch. !t also has widespread application in marine and industrial machine

drives, where variable speed operation and controlled start?up without shoc$ loading of the

power transmission system is essential.

The fluid coupling originates from the wor$ of 'r. Hermann F@ttinger, who was the chief

designer at the A1 =ulcan 7or$s in tettin. His patents from >9 covered both fluid

couplings and tor#ue converters.'r Bauer of the =ulcan?7er$e collaborated with %nglish engineer Harold inclair of

Hydraulic Coupling +atents *imited to adapt the F@ttinger coupling to vehicle transmission in

an attempt to mitigate the lurching inclair had e"perienced while riding on *ondon buses

during the >/s. Following inclairs discussions with the *ondon 1eneral )mnibus

Company begun in )ctober >/: and trials on an Associated 'aimler bus chassis +ercy

4artin of 'aimler decided to apply the principle to the 'aimler groups private cars

The first 'iesel locomotives using fluid couplings were also produced in the >5s

Hydrodynamic couplings employ turbo machinery and e"ploit the hydrodynamic forces of a

fluid to transmit power. The basic scheme is composed of a centrifugal pump, a centripetal

turbine and a fi"ed part Dstator2 which ta$es the fluid from the turbine e"it and redirects itinside the pump

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Assuming a steady behaviour, the resultant of the tor#ues applied to the system pump?

turbine?stator must be null. Therefore, one has3

C+ ?CT ? C E ;

where3 C+ is the tor#ue e"erted by the pump impeller on the fluid; CT is the tor#ue e"erted bythe fluid on the turbine blading ; C is the tor#ue e"erted by the fluid on thestator.

From e#uation D.2, it appears that C+ and CT may be different only if there is the stator

between the pump and the turbine. Therefore, hydrodynamic couplings can be divided into

two categories3

Hydrodynamic couplings3there is no stator, therefore C+ E CT .

Hydrodynamic toru! con"!rt!rs3the stator allows the turbine to transmit a tor#uedifferent from the one received by the pump. sually, a tor#ue converter is mounted on the

input side of the transmission gear train and connected to a drive plate. The drive plate is used

to connect the converter to the cran$ shaft flywheel angle of an engine. The tor#ue converter

is filled Dfrom 9 to


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smooth fluid flow. 7hen the impeller is driven by the engine cran$shaft, the fluid is the

impeller rotates with it. 7hen the impeller speed increases, the centrifugal force causes the

fluid to flow toward the turbine. The turbine is located inside the converter case but is notconnected to it. 4any cupped vanes are attached to the turbine, the curvature of the vanes

being opposite from that of the pump vanes. Therefore, when the fluid is thrust from the

pump, it is caught in the cupped vanes of the turbine and tor#ue is transferred to the

transmission shaft, turning it in the same direction of the engine cran$shaft. 7hen automatic

transmissions first came on the scene in the late >5s, the only components were the

impeller and the turbine. This provided a means of transferring tor#ue from the engine to the

transmission and also allowed the vehicle to be stopped while the engine runs at idle.

However, those early fluid couplings had one thing in common3 acceleration was poor. The

engine would labour until the vehicle pic$ed up speed. The problem occurred because the

vanes on the impeller and turbine are curved in the opposite direction to one another. Fluid

coming oG the turbine is thrust against the impeller in a direction opposite to engine rotation.

!n this way, not only is the engine horsepower consumed to pump the fluid initially, but now

it also has to overcome the force of the fluid coming from the turbine. The stator was

introduced to the design to overcome the counterproductive force of fluid coming from the

turbine opposing engine rotation. !t not only overcomes the problem but also has the added

benefit of increasing tor#ue to the impeller. The stator is located between the impeller and the

turbine. !t is mounted on the stator reaction shaft which is fi"ed to the transmission case. The

vanes of the stator catch the fluid as it leaves the turbine runner and redirects it so that it

stri$es the bac$ of the vanes of the impeller, giving the impeller an added boost. The benefit

of this added tor#ue can be as great as 5 to 9. A one?way clutch may be used to allow

the stator to rotate in

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the same direction as the engine cran$shaft. However, if the stator attempts to rotate in the

opposite direction, the one?way clutch loc$s the stator to prevent it from rotating.

Therefore the stator is rotated or loc$ed depending on the direction from which the fluid

stri$es against the vanes.

CHAPTER #

T$PES O% COUP&IN'S

1(Rigid

. leeve coupling

./ Flange coupling

.5 Clamp or split?muff coupling

.6 Tapered shaft loc$

.9 Hirth

#(%l!)i*l!

/. Bush pin Type flange coupling

/./ Beam

/.5 Constant velocity

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/.6 'iaphragm

/.9 'isc

/.: Fluid Coupling

/. 1ear

/./.< 1rid

/.> )ldham

/. -ag joint

/. niversal joint

/./ 4agnetic Coupling

/.5 )thers

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T$PES O% %&UID COUP&IN'S

1( H$DROSTATIC COUP&IN'S

A Hydrostatic Coupling is used for power transmission. nli$e a hydraulic gear motor, they

do not have any mechanical couplings, and all power is transferred via change in static

pressure inside the system components.

The operation of this type of coupling is controlled by modulating the valve which controls

the opening from the high pressure cavity of the gear pumps bac$ to the low pressure portion

of the housing. !f this valve is completely open, then as one shaft, for e"ample the second

shaft which has the central sun gear mounted thereon, is turned relative to the first shaft, then

the gears of the gear pumps in engagement with the sun gear will rotate about their a"es

thereby directing fluid from the low pressure side of the housing through the pumps and bac$

through the open valve to the low pressure side of the housing.

# (H$DROD$NA+IC COUP&IN'S

The operating principle of hydrodynamic couplings is based on the F@ttinger principle3 as opposed to

the direct wor$ing principle, where, for instance, power is transmitted via mechanical couplings,

hydrodynamic couplings transmit power by means of a fluid. ince tor#ue transmission is realied via

a fluid there is almost no wear in comparison to the direct wor$ing principle

Basic !uations

The scheme of an hydrodynamic coupling is shown in figure. The centrifugal pump and the

centripetal turbine are often of pure radial type. The pump increases the total head of the fluid

which is employed by the turbine to provide power to the final user. Apart of the energy of

the pump is dissipated by fluid?dynamic losses inside the pump and the turbine system. From

the energy conservation3

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PP , PT - P./

where ++ , +T , and +7, are the power absorbed by the pump, delivered by the turbine,

and dissipated by losses, respectively. Therefore, one has3

PT 0 PP /

and, since C+ E CT , it follows that wT I w+ , where w indicates the rotational speed.

The difference between the rotational speed of the pump and the turbine is measured by a

non?dimensional parameter called slip3

which has values between ero and one. The hydraulic efficiency of the coupling is

defined as

where v is the speed ratio. The characteristic curves of the coupling are shown in figure ,

where the hydraulic efficiency and the tor#ue ratio

are represented versus

G. !ndicate with and / the inlet and outlet of the pump, respectively and with, 5 and

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CHAPTER

CONSTRUCTION O% %&UID COUP&IN'

The fluid coupling is consisting of three principal parts named !mpellor, -otor and wor$ing

fluid. !mpellor is finned li$e structure and it wor$s as pump in the system. The impellor of

the fluid coupling is directly connected to the prime mover li$e motor or engine by

mechanical means

E)ampl!2Belt drive, gear drive or a mechanical coupling. The impellor is power input

component of the fluid coupling. -otor is also finned li$e structure and it wor$s as a turbine

in the fluid coupling system. The rotor is directly connected to the machine by mechanicalmeans li$e Belt drive, gear drive or a mechanical coupling. The rotor is power output

component of the fluid coupling.

7or$ing fluid of the fluid coupling is the important part of the system. The wor$ing fluid in

the fluid coupling is filled between impellor and rotor which gets energies by rotation of

impellor and converts impellors energy in the $inetic energy of the fluid, this $inetic energy

of the fluid get absorbed while stri$ing on rotor. And by this energy the rotor rotates and

power transmitted to the machine

Two bladed wheels of fluid couplingJ the pump impeller and turbine wheel J enclosed by a

shell. Both wheels are provided with bearings relative to each other. The power is transmitted

virtually without wear, there is no mechanical contact between the power?transmitting parts.A constant amount of operating fluid is in the coupling.

The mechanical energy provided by the drive motor is converted to $inetic energy of the

operating fluid in the connected pump impeller. !n the turbine wheel this $inetic energy is

converted bac$ to mechanical energy.

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CHAPTER 3

.OR4IN' PRINCIP&E

=ariable speed fluid couplings lin$ the drive machine K generally an electric motor K with

the corresponding driven machine. The power is transferred through the fluid energy of the

wor$ing fluid. This fluid flows in an enclosed wor$ing chamber between the pump wheel

Dlin$ed to the input shaft2 and the turbine wheel Dlin$ed to the output shaft2.

Turbo fluid couplings wor$s based on FoettingerLs +rinciple.!ts main components

are two bladed wheels J a pump wheel and a turbine wheel J as well as an outer shell. Both

wheels are positioned relative to each other. )utput is achieved with minimal mechanical

wear as there is no mechanical contact between power?transmitting parts.

The coupling contains a constant #uantity of operating fluid, usually mineral oil. The tor#ue

transmitted by the drive motor is converted into $inetic energy of the operating fluid in the

pump wheel to which the motor is connected. !n the turbine wheel, this $inetic energy is

converted bac$ into mechanical energy. 7hen it comes to the function of the coupling, three

modes are to be noted3

J Standstill2

The total operating fluid is resting statically in the coupling.

J Starting condition2

The pump impeller accelerates the operating fluid with increasing motor speed causing a

circulating flow in the wor$ing chamber. The complete blade chamber of turbine wheel is

flooded, starting to move as a result of the $inetic energy of fluid flow. The coupling

characteristic determines the tor#ue curve during start up.

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J Nominal op!ration2'uring nominal operation only the tor#ue re#uired by the driven machine is transmitted. The

low speed difference between pump impeller and turbine wheel Drated slip2 results in a steady

flow condition in the coupling .Through s$illful coordination of compensating chambers,

such as the delay chamber and the annular chamber shell, the starting performance of the

Turbo Coupling can be regulated.

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CHAPTER 5

%ACTORS IN%&UENCIN' PER%OR+ANCE

1(CENTRI%U'A& &OADIN'2 Fluid coupling has centrifugal loading characteristic in

wor$ing

condition or in other words the power output by fluid coupling is directly dependent on third

power of the -+4, and output tor#ue is proportional to second power of -+4.

#(S&IP: lip is the difference between in input and output speed with respect to input speed.

A fluid coupling cannot develop output tor#ue when the input and output angular velocities

are identical. Hence a fluid coupling cannot achieve percent power transmission

efficiency. 'ue to slippage that will occur in any fluid coupling under load, some power will

always be lost in fluid friction and turbulence, and dissipated as heat.

(C&UTCHIN' AND DEC&UTCHIN'2 Fluid coupling provides soft start to machine.

Fluid coupling has an additional chamber on casing that $nown as delay fill chamber. This

chamber is connected to the circuit of the fluid coupling through some holes .!nitially when

fluid coupling at rest the major #uantity of oil filled inside this chamber and some #uantity of

oil available in circuit. 7hen prime mover shaft starts rotating the less fluid filled inside the

circuit of the fluid coupling. That can supply very less power and the speed of fluid coupling

increases the oil from delay fill chamber gradually comes into the circuit the power output of

the fluid coupling.

3(RISIN' TOR6UE2the fluid coupling allows to prime mover at rated speed and machine

atoverloaded speed. That means the fluid coupling ta$es power constant and by reducing output

speed the tor#ue

increases. The fluid coupling can increase the tor#ue up to / of the rated tor#ue.

5(DIRECTION O% ROTATION:the fluid coupling can be used bidirectional. The impellor

of the fluid coupling is associated with the casing Dhousing2 of the fluid coupling and the

rotor is freely supported on bearing only hence the rotor has less inertia than impellor. The

fluid couplings rotor and impellor can be mounted on vice versa. This is re#uired when the

prime movers starting tor#ue is less and it cannot sustain higher inertia at starting.

7(SET OUTPUT PO.ER2 The fluid coupling can set the output power by varying the

#uantity of oil filled inside the fluid coupling for a fi"ed input power. The #uantity of oil once

filled inside the fluid coupling cannot be change in wor$ing condition; hence the fi"ed

#uantity of oil can transfer a fi" ma"imum power for a particular input power.

8(STA&& SPEED3The stall speed is defined as the highest speed at which the impellor can

rotate when the rotor is loc$ed and ma"imum input power is applied. nder stall conditions

all of the prime movers power would be dissipated in the fluid coupling as heat.

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PROPERTIES O% H$DRAU&IC COUP&IN' %&UID

1(D!nsity2'ensity of the fluid plays a great role in functioning of the fluid coupling. The

power transmission from impellor to rotor transmits through oilLs $inetic energy. The $inetic

energy is dependent on the density of the fluid. Hence the power output of the fluid couplingis dependent on the density of the wor$ing fluid.

#(9iscosity2The property of a fluid that resists the force tending to cause the fluid to flow. !n

the wor$ing condition of the fluid coupling the oil transfer energy in the form of $inetic

energy and the viscosity opposes the motion of the fluid hence it reduces the $inetic energy of

the fluid. For fluid coupling less viscosity of the oil preferred.

(Sp!ci:ic ;!at2 pecific heat of the fluid is the amount of heat re#uired to increase the

temperature by degree centigrade at &T+. !n the wor$ing of fluid coupling heat is generated

inside the fluid coupling that has to dissipate, this heat is dissipated through oil.

3(T;!rmal E)pansion2 Thermal e"pansion of the fluid is the e"pansion of fluid by

increasing the temperature by degree centigrade. !n wor$ing condition of fluid coupling

heat generates and temperature rises hence the thermal e"pansion in the fluid should be as

lower as possible for fluid coupling wor$ing fluid.

5(&u*rication2The !mpellor and rotor are mechanical parts of the fluid coupling and these

are support on shaft by bearing which is re#uired to lubrication. o the fluid coupling fluid

has to be lubrication properties.

.ATER AND ITS PROPERTIES2

7ater is a fluid which is ready and easily available. !t has some properties which ma$es it

feasible for wor$ing fluid for fluid coupling. The properties of the water against conventional

fluid of fluid coupling D!) =1 5/2 are as follows

1(D!nsity2'ensity of the water is .>>/ gmMcc at 6 degree centigrade and density of !)

=1 5/ oil is appro" .

8cal per $g per degree centigrade. 7ater has higher specific heat that show water can be use

as wor$ing fluid in fluid coupling.

3(T;!rmal E)pansion27ater has is 8cal per $g per degree centigrade and .6>.

5(&u*rication:water has very poor lubrication properties. Additional lubrication system is

re#uired when water is used in fluid coupling.

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CHAPTER 8

E


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As we $now above readings the ratio of input speed to output is decrease as the increase of

input speed so as per that we are conclude for our application the at higher speed coupling

output sped higher but that is certain limit that is for general application 6 pole motor drive

the coupling output speed is limited up to 6/ rpm.

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/. 9arious uantity o: :luid =it; sam! sp!!d.

The #uantity re#uired to full the fluid coupling is .:9 litre. But for operation the ma"imum

#uantity re#uired is .9// litre and should be not less than .6:9 litre for this fluid coupling.

*ess fluid inside the fluid coupling creates more slip while higher #uantity ma$es it rigid .

Here the reading ta$es as following specification

)il type3 !) =1 :

fluid couplings 3

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