Seminar Report on

TORQUE CONVERTER

Submitted by

‘AZHAR AHMAD KHAN’

B.TECH (3rd Year)

Under the effective guidance of

Dr. K.M MOEED

2013-2014

DEPARTMENT OF MECHANICAL ENGINEERING

INTEGRAL UNIVERSITY

LUCKNOW

AKNOWLEDGEMENT

For making any seminar or project work needed great support from many

people. Some of them were actual heart and soul of this write up and need

special mention.

I take great pleasure in expressing my gratitude to Dr. K.M Moeed

for his kind guidance all along the way. I give my sincere regards to Mr. P.K

Bharti (HOD) mechanical engineering department for his constant

encouragement. I take this opportunity to thank all the staff member of

mechanical engineering department of INTEGRAL UNIVERSITY for their co-

operation and help during this seminar work.

Last but not least, it goes without saying that I am indebted to a

number of friends and well wisher who have extended their co-operation and

help during the seminar work.

Azhar Ahmad Khan B-tech 3rd year(ME1)

1100116037

This is to certify that seminar entitled

“TORQUE CONVERTER”

Submitted by

AZHAR AHMAD KHAN

Has completed as per requirement of

Integral University

Lucknow

In partial fulfillment of the degree of

BACHELOR OF TECHNOLOGY

(Mechanical engineering Department)

For the academic year

2013-2014

GUIDE H.O.D

(Dr. K .M. MOEED) (Mr. P.K. BHARTI)

ABSTRACT:

Allow the vehicle to come to a complete stop

without stalling the engine

Provide torque multiplication to allow smooth

acceleration from a stop

House a torque converter clutch which will

eliminate torque converter slippage at highway

speed

A torque converter is a type of fluid coupling

There is no direct mechanical link between the

input (engine flywheel) and the output

(transmission input shaft)

The impeller (pump of the torque converter)

forces fluid through the turbine, which forces

the turbine to turn

The turbine is splined to the transmission input

shaft

Introduction

In modern usage, a torque converter is generally a type of fluid coupling (but also being able to multiply torque) that is used to transfer rotating power from a prime mover, such as an internal combustion engine or electric motor, to a rotating driven load. The torque converter normally takes the place of a mechanical clutch in a vehicle with an automatic transmission, allowing the load to be separated from the power source. It is usually located between the engine's flexplate and the transmission.

The key characteristic of a torque converter is its ability to multiply torque when there is a substantial difference between input and output rotational speed, thus providing the equivalent of a reduction gear. Some of these devices are also equipped with a temporary locking mechanism which rigidly binds the engine to the transmission when their speeds are nearly equal, to avoid slippage and a resulting loss of efficiency.

By far the most common form of torque converter in automobile transmissions is the device described here. However, in the 1920s there was also the pendulum-based Constantinesco torque converter. There are also mechanical designs for continuously variable transmissions and these also have the ability to multiply torque, e.g. the Variomatic with expanding pulleys and a belt drive.

Content:

1 Usage 2 Function

o 2.1 Torque converter elements o 2.2 Operational phases o 2.3 Efficiency and torque multiplication o 2.4 Lock-up torque converters o 2.5 Capacity and failure modeso 2.6 Torque Converter Operationo 2.7 Parts of Torque Convertero 2.8 Advantageso 2.9 Disadvantages

3 Manufacturers o 3.1 Current o 3.2 Past

4 References 5 External links

Usage:

Automatic transmissions on automobiles, such as cars, buses, and on/off highway trucks.

Forwarders and other heavy duty vehicles. Marine propulsion systems. Industrial power transmission such as

conveyor drives, almost all modern forklifts, winches, drilling rigs, construction equipment, and railway locomotives.

Function:

Torque converter elements

A fluid coupling is a two element drive that is incapable of multiplying torque, while a torque converter has at least one extra element—the stator—which alters the drive's characteristics during periods of high slippage, producing an increase in output torque.

In a torque converter there are at least three rotating elements: the impeller, which is mechanically driven by the prime mover; the turbine, which drives the load; and the stator, which is interposed between the impeller and turbine so that it can alter oil flow returning from the turbine to the impeller. The classic torque converter design dictates that the stator be prevented from rotating under any condition, hence the term stator. In practice, however, the stator is mounted on an overrunning clutch, which prevents the stator from counter-rotating with respect to the prime mover but allows forward rotation.

Modifications to the basic three element design have been periodically incorporated, especially in applications where higher than normal torque multiplication is required. Most commonly, these have taken the form of multiple turbines and stators, each set being designed to produce differing amounts of torque multiplication. For example, the Buick Dynaflow automatic transmission was a non-shifting design and, under normal conditions, relied solely upon the converter to multiply torque. The Dynaflow used a five element converter to produce the wide range of

torque multiplication needed to propel a heavy vehicle.

Although not strictly a part of classic torque converter design, many automotive converters include a lock-up clutch to improve cruising power transmission efficiency and reduce heat. The application of the clutch locks the turbine to the impeller, causing all power transmission to be mechanical, thus eliminating losses associated with fluid drive.

Operational phases:

A torque converter has three stages of operation:

Stall. The prime mover is applying power to the impeller but the turbine cannot rotate. For example, in an automobile, this stage of operation would occur when the driver has placed the transmission in gear but is preventing the vehicle from moving by continuing to apply the brakes. At stall, the torque converter can produce maximum torque multiplication if sufficient input power is applied (the resulting multiplication is called the stall ratio). The stall phase actually lasts

for a brief period when the load (e.g., vehicle) initially starts to move, as there will be a very large difference between pump and turbine speed.

Acceleration. The load is accelerating but there still is a relatively large difference between impeller and turbine speed. Under this condition, the converter will produce torque multiplication that is less than what could be achieved under stall conditions. The amount of multiplication will depend upon the actual difference between pump and turbine speed, as well as various other design factors.

Coupling. The turbine has reached approximately 90 percent of the speed of the impeller. Torque multiplication has essentially ceased and the torque converter is behaving in a manner similar to a simple fluid coupling. In modern automotive applications, it is usually at this stage of operation where the lock-up clutch is applied, a procedure that tends to improve fuel efficiency.

The key to the torque converter's ability to multiply torque lies in the stator. In the classic fluid coupling design, periods of high slippage

cause the fluid flow returning from the turbine to the impeller to oppose the direction of impeller rotation, leading to a significant loss of efficiency and the generation of considerable waste heat. Under the same condition in a torque converter, the returning fluid will be redirected by the stator so that it aids the rotation of the impeller, instead of impeding it. The result is that much of the energy in the returning fluid is recovered and added to the energy being applied to the impeller by the prime mover. This action causes a substantial increase in the mass of fluid being directed to the turbine, producing an increase in output torque. Since the returning fluid is initially traveling in a direction opposite to impeller rotation, the stator will likewise attempt to counter-rotate as it forces the fluid to change direction, an effect that is prevented by the one-way stator clutch.

Unlike the radially straight blades used in a plain fluid coupling, a torque converter's turbine and stator use angled and curved blades. The blade shape of the stator is what alters the path of the fluid, forcing it to coincide with the impeller rotation. The matching curve of the turbine blades helps to correctly direct the returning fluid to the stator so the latter can do its job. The shape of the

blades is important as minor variations can result in significant changes to the converter's performance.

During the stall and acceleration phases, in which torque multiplication occurs, the stator remains stationary due to the action of its one-way clutch. However, as the torque converter approaches the coupling phase, the energy and volume of the fluid returning from the turbine will gradually decrease, causing pressure on the stator to likewise decrease. Once in the coupling phase, the returning fluid will reverse direction and now rotate in the direction of the impeller and turbine, an effect which will attempt to forward-rotate the stator. At this point, the stator clutch will release and the impeller, turbine and stator will all (more or less) turn as a unit.

Unavoidably, some of the fluid's kinetic energy will be lost due to friction and turbulence, causing the converter to generate waste heat (dissipated in many applications by water cooling). This effect, often referred to as pumping loss, will be most pronounced at or near stall conditions. In modern designs, the blade geometry minimizes oil velocity at low impeller speeds, which allows the turbine to

be stalled for long periods with little danger of overheating.

Efficiency and torque multiplication:

A torque converter cannot achieve 100 percent coupling efficiency. The classic three element torque converter has an efficiency curve that resembles ∩: zero efficiency at stall, generally increasing efficiency during the acceleration phase and low efficiency in the coupling phase. The loss of efficiency as the converter enters the coupling phase is a result of the turbulence and fluid flow interference generated by the stator, and as previously mentioned, is commonly overcome by mounting the stator on a one-way clutch.

Even with the benefit of the one-way stator clutch, a converter cannot achieve the same level of efficiency in the coupling phase as an equivalently sized fluid coupling. Some loss is due to the presence of the stator (even though rotating as part of the assembly), as it always generates some power-absorbing turbulence. Most of the loss, however, is caused by the curved and angled turbine blades, which do not absorb kinetic energy from the fluid mass as well as radially straight

blades. Since the turbine blade geometry is a crucial factor in the converter's ability to multiply torque, trade-offs between torque multiplication and coupling efficiency are inevitable. In automotive applications, where steady improvements in fuel economy have been mandated by market forces and government edict, the nearly universal use of a lock-up clutch has helped to eliminate the converter from the efficiency equation during cruising operation.

The maximum amount of torque multiplication produced by a converter is highly dependent on the size and geometry of the turbine and stator blades, and is generated only when the converter is at or near the stall phase of operation. Typical stall torque multiplication ratios range from 1.8:1 to 2.5:1 for most automotive applications (although multi-element designs as used in the Buick Dynaflow and Chevrolet Turboglide could produce more). Specialized converters designed for industrial, rail, or heavy marine power transmission systems are capable of as much as 5.0:1 multiplication. Generally speaking, there is a trade-off between maximum torque multiplication and efficiency—high stall ratio converters tend to be relatively inefficient below the coupling speed,

whereas low stall ratio converters tend to provide less possible torque multiplication.

While torque multiplication increases the torque delivered to the turbine output shaft, it also increases the slippage within the converter, raising the temperature of the fluid and reducing overall efficiency. For this reason, the characteristics of the torque converter must be carefully matched to the torque curve of the power source and the intended application. Changing the blade geometry of the stator and/or turbine will change the torque-stall characteristics, as well as the overall efficiency of the unit. For example, drag racing automatic transmissions often use converters modified to produce high stall speeds to improve off-the-line torque, and to get into the power band of the engine more quickly. Highway vehicles generally use lower stall torque converters to limit heat production, and provide a more firm feeling to the vehicle's characteristics.

A design feature once found in some General Motors automatic transmissions was the variable-pitch stator, in which the blades' angle of attack could be varied in response to changes in engine speed and load. The effect of this was to vary the amount of torque multiplication produced by the

converter. At the normal angle of attack, the stator caused the converter to produce a moderate amount of multiplication but with a higher level of efficiency. If the driver abruptly opened the throttle, a valve would switch the stator pitch to a different angle of attack, increasing torque multiplication at the expense of efficiency.

Some torque converters use multiple stators and/or multiple turbines to provide a wider range of torque multiplication. Such multiple-element converters are more common in industrial environments than in automotive transmissions, but automotive applications such as Buick's Triple Turbine Dynaflow and Chevrolet's Turboglide also existed. The Buick Dyna flow utilized the torque-multiplying characteristics of its planetary gear set in conjunction with the torque converter for low gear and bypassed the first turbine, using only the second turbine as vehicle speed increased. The unavoidable trade-off with this arrangement was low efficiency and eventually these transmissions were discontinued in favor of the more efficient three speed units with a conventional three element torque converter.

By altering the stator design, stall speed and torque multiplication ratios can be altered

Aftermarket

Stock

Lock-up torque converters :

As described above, impelling losses within the torque converter reduce efficiency and generate waste heat. In modern automotive applications, this problem is commonly avoided by use of a lock-up clutch that physically links the impeller and turbine, effectively changing the converter into a purely mechanical coupling. The result is no slippage, and virtually no power loss.

The first automotive application of the lock-up principle was Packard's Ultramatic transmission, introduced in 1949, which locked up the converter

at cruising speeds, unlocking when the throttle was floored for quick acceleration or as the vehicle slowed down. This feature was also present in some Borg-Warner transmissions produced during the 1950s. It fell out of favor in subsequent years due to its extra complexity and cost. In the late 1970s lock-up clutches started to reappear in response to demands for improved fuel economy, and are now nearly universal in automotive applications.

Capacity and failure modes:

As with a basic fluid coupling the theoretical torque capacity of a converter is proportional to

, where is the mass density of the fluid (kg/m³), is the impeller speed (rpm), and is the diameter(m).[1] In practice, the maximum torque capacity is limited by the mechanical characteristics of the materials used in the converter's components, as well as the ability of the converter to dissipate heat (often through water cooling). As an aid to strength, reliability and economy of production, most automotive converter housings are of welded construction.

Industrial units are usually assembled with bolted housings, a design feature that eases the process of inspection and repair, but adds to the cost of producing the converter.

In high performance, racing and heavy duty commercial converters, the pump and turbine may be further strengthened by a process called furnace brazing, in which molten brass is drawn into seams and joints to produce a stronger bond between the blades, hubs and annular ring(s). Because the furnace brazing process creates a small radius at the point where a blade meets with a hub or annular ring, a theoretical decrease in turbulence will occur, resulting in a corresponding increase in efficiency.

Overloading a converter can result in several failure modes, some of them potentially dangerous in nature:

Overheating : Continuous high levels of slippage may overwhelm the converter's ability to dissipate heat, resulting in damage to the elastomer seals that retain fluid inside the converter. This will cause the unit to leak and eventually stop functioning due to lack of fluid.

Stator clutch seizure : The inner and outer elements of the one-way stator clutch become permanently locked together, thus preventing the stator from rotating during the coupling phase. Most often, seizure is precipitated by severe loading and subsequent distortion of the clutch components. Eventually, galling of the mating parts occurs, which triggers seizure. A converter with a seized stator clutch will exhibit very poor efficiency during the coupling phase, and in a motor vehicle, fuel consumption will drastically increase. Converter overheating under such conditions will usually occur if continued operation is attempted.

Stator clutch breakage : A very abrupt application of power can cause shock loading of the stator clutch, resulting in breakage. If this occurs, the stator will freely counter-rotate in the direction opposite to that of the pump and almost no power transmission will take place. In an automobile, the effect is similar to a severe case of transmission slippage and the vehicle is all but incapable of moving under its own power.

Blade deformation and fragmentation : If subjected to abrupt loading or excessive

heating of the converter, pump and/or turbine blades may be deformed, separated from their hubs and/or annular rings, or may break up into fragments. At the least, such a failure will result in a significant loss of efficiency, producing symptoms similar (although less pronounced) to those accompanying stator clutch failure. In extreme cases, catastrophic destruction of the converter will occur.

Ballooning : Prolonged operation under excessive loading, very abrupt application of load, or operating a torque converter at very high RPM may cause the shape of the converter's housing to be physically distorted due to internal pressure and/or the stress imposed by inertia (centrifugal force). Under extreme conditions, ballooning will cause the converter housing to rupture, resulting in the violent dispersal of hot oil and metal fragments over a wide area.

Torque Converter Operation:

The torque converter is one of the least understood components in an automatic transmission equipped vehicle. I will attempt to explain what it does and how it does it.

The torque converter has a few different functions.

We first need to understand that there is no direct link between the crankshaft and the transmission input shaft (except in the case of a lock up style converter, but we'll talk about that later). This

means that the first function of the converter is to connect the crankshaft and the input shaft so the engine can move the vehicle; this is accomplished through the utilization of a fluidic coupling effect.

The torque converter also replaces the clutch that is required in a manual transmission; this is how an automatic transmission vehicle can come to a stop while still being in gear without stalling the engine.

The torque converter also acts as a torque multiplier, or extra gear ratio, to help the car get moving from a stop. In modern day converters this theoretical ratio is anywhere between 2:1 and 3:1.

Torque converters consist of 4 major components that we need to concern ourselves with for the purpose of explanation.

The first component, which is the driving member, is called the impeller or "pump". It is connected directly to the inside of the converter housing and because the converter is bolted to the flex plate, it is turning anytime that the engine rotates.

The next component, which is the output or driven member, is called the turbine. The transmission's input shaft is splined to it. The turbine is not

physically connected to the to the converter housing and can rotate completely independently of it.

The third component is the stator assembly; its function is to redirect the flow of fluid between the impeller and the turbine, which gives the torque multiplication effect from a standstill.

The final component is the lock up clutch. At highway speeds this clutch can be applied and will provide a direct mechanical link between the crankshaft and input shaft, which will result in 100% efficiency between the engine and transmission. The application of this clutch is usually controlled by the vehicle's computer activating a solenoid in the transmission.

Here's how it all works. For the sake of simplicity, I will use the common analogy of two fans which represent the impeller and the turbine. Let's say that we have two fans facing each other and we turn only one of them on- the other fan will soon begin to move.

The first fan, which is powered, can be thought of as the impeller that is connected to the converter housing. The second fan- the "driven" fan can be likened to the turbine, which has the input shaft

splined to it. If you were to hold the non-powered fan (the turbine) the powered one (the impeller) would still be able to move- this explains how you can pull to a stop without the engine stalling.

Now imagine a third component placed in between the two, which would serve to alter the airflow and cause the powered fan to be able to drive the non-powered fan with a reduction of speed- but also with an increase of force (torque). This is essentially what the stator does.

At a certain point (usually around 30-40 mph), the same speed can be reached between impeller and the turbine (our two fans). The stator, which is attached to a one way clutch, will now begin to turn in conjunction with the other two components and around 90% efficiency between the crank and the input shaft can be achieved.

The remaining 10% slippage between the engine and transmission can be eliminated by connecting the input shaft to the crankshaft through the application of the lock up clutch that was mentioned before. This will tend to lug the engine, so the computer will only command this in higher gears and at highway speeds when there is very little engine load present. The main function of

this clutch is to increase fuel efficiency and reduce the amount of heat that is generated by the torque converter.

Another term that may be unfamiliar is that of a "high stall" torque converter. A high stall converter differs from a stock converter in the sense that the rpm is raised at which the internal converter components- the impeller, the stator and the turbine start to turn together, and hence, stop the torque multiplication phase and begin the coupling phase. The point at which engine rpm will stop climbing with the drive wheels held stationary and the throttle fully opened is referred to as "stall speed".

The idea behind a higher stall torque converter is to allow the engine to rev more freely up to the point where the power band begins, and therefore, enable the vehicle to accelerate from a stop under more power.

This becomes increasingly important when an engine is modified. Engine modifications such as ported heads, bigger cams, bigger turbo (in some cases), bigger intakes, etc. tend to raise the point where the power band begins. For best performance, the stall speed needs to be raised accordingly to work optimally in conjunction with the given vehicle alterations.

In simple terms, for best performance, the stall speed should be raised at least to the point where the torque curve is heading towards its peak. As a rule of thumb, the stall speed should be set to match the rpm at which the engine is making at least 80% of its peak torque for a street driven vehicle.

As you can imagine, a vehicle that can accelerate from a stop with 80% of its peak torque will easily outperform an otherwise identical vehicle that can only launch at 50% of its available torque.

For a performance or "high stall" torque converter to produce maximum gains, it needs to be configured to the specific vehicle in which it will be installed.

Factors such as engine torque and the rpm at which it is greatest, differential gear ratio, vehicle weight, camshaft design, compression ratio, type of induction- forced or naturally aspirated, and a host of other variables all need to be taken into consideration.

Be aware that the "off the shelf" type performance torque converters sold by some manufacturers are very unlikely to be optimized for all vehicles and their unique requirements.

Parts of a Torque Converter:

Housing Hub Impeller Split ring guide Turbine Split ring guide Stator Stator one-way clutch

Torque converter clutch Apply piston

Advantages of Torque Convertor:

Convenience

Torque converters allow a car to start and stop without user intervention. It is this feature that makes an automatic truly "automatic," and the main reason that torque converters are used.

Torque Multiplication

In the moments before full engagement, torque converters act as a sort of

continuously variable transmission. This torque multiplication means that a vehicle so equipped can accelerate faster and smoother than one with a clutch.

Flywheel Effect

Because torque converters are very heavy, they tend to act as a sort of inertial flywheel. This flywheel effect means that vehicles with torque converters have a steadier idle and smoother operation than clutch cars.

Infinite Slippage

To a point, a torque converter can slip almost indefinitely without damage. This compares sharply with a manual

transmission's tendency to burn clutches if allowed to slip too much.

Fluid Reservoir

Torque converters hold several quarts of transmission fluid, and can help to decrease transmission overheating by providing a source of cool fluid when required.

Disadvantage :

Fluid Coupling Problems

When there is a large difference in RPM between the impeller and the turbine in a fluid coupling, the fluid coming off the turbine strikes the impeller opposite the direction of rotation, thus slowing the impeller down (robbing power)

Solution:Fluid Coupling Solutions:

By incorporating a stator into a fluid coupling we can overcome the problem of turbine discharge oil slowing down the impeller

Manufacturers:

Current

Valeo, produces Torque converter for Ford, GM

Allison Transmission, used in bus, refuse, fire, construction, distribution, military and specialty applications

BorgWarner, used in automobiles Subaru, used in automobiles Twin Disc, used in vehicle, marine and oilfield

applications Voith Turbo-Transmissions, used in many

diesel locomotives and diesel multiple units

ZF Friedrichshafen, automobiles, forestry machines, popular in city bus applications

Jatco, used in automobiles Aisin AW, used in automobiles LuK USA LLC, produces Torque Converters

for Ford, GM, Allison, and Hyundai

Past

Lysholm-Smith, named after its inventor, Alf Lysholm, produced by Leyland Motors and used in buses from 1933-9 and also some British Rail Derby Lightweight and Ulster Transport Authority diesel multiple units

Mekydro,[2] used in British Rail Class 35 Hymek locomotives.

Packard, used in the Ultramatic automobile transmission system

Rolls-Royce (Twin Disc), used in some British United Traction diesel multiple units

References:

1.Jump up ^ Hydrodynamic couplings and converters. Automotive Handbook (3rd ed.). Robert Bosch. p. 539. ISBN 0-8376-0330-7.

2.Jump up ^ http://www.intertrains.co.uk/glossary/m/mekydro-transmission.html

3.Wikipedia4.Seminartopics.com

External links

Wikimedia Commons has media related to Torque converters.