How to Know if You Overheat Your Torque Converter

Fluid coupling that transfers rotating ability from a prime mover to a rotating driven load

ZF torque converter cut-away

A torque converter is a blazon of fluid coupling that transfers rotating power from a prime mover, like an internal combustion engine, to a rotating driven load. In a vehicle with an automated manual, the torque converter connects the ability source to the load. Information technology is ordinarily located between the engine'due south flexplate and the transmission. The equivalent location in a manual transmission would exist the mechanical clutch.

The main feature of a torque converter is its ability to increase torque when the output rotational speed is then low that it allows the fluid coming off the curved vanes of the turbine to exist deflected off the stator while it is locked against its i-mode clutch, thus providing the equivalent of a reduction gear. This is a characteristic beyond that of the simple fluid coupling, which can lucifer rotational speed but does not multiply torque and thus reduces power.

Hydraulic systems [edit]

By far the nigh common class of torque converter in automobile transmissions is the hydrokinetic device described in this article. There are as well hydrostatic systems which are widely used in pocket-sized machines such as meaty excavators.

Mechanical systems [edit]

There are also mechanical designs for continuously variable transmissions and these as well have the ability to multiply torque. They include the pendulum-based Constantinesco torque converter, the Lambert friction gearing disk bulldoze transmission and the Variomatic with expanding pulleys and a belt bulldoze.

Usage [edit]

• Automated transmissions on automobiles, such every bit cars, buses, and on/off highway trucks.
• Forwarders and other heavy duty vehicles.
• Marine propulsion systems.
• Industrial power transmission such every bit conveyor drives, almost all mod forklifts, winches, drilling rigs, construction equipment, and railway locomotives.

Office [edit]

Theory of operation [edit]

Torque converter equations of move are governed past Leonhard Euler's eighteenth century turbomachine equation:

${\displaystyle \tau =\sum \left[r\times {\frac {d}{dt}}\left(m\cdot v\right)\correct]}$

The equation expands to include the fifth power of radius; as a consequence, torque converter properties are very dependent on the size of the device.

Torque converter elements [edit]

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

In a torque converter at that place are at to the lowest degree three rotating elements: the impeller, which is mechanically driven past 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 exist prevented from rotating under whatsoever 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 forwards rotation.

Modifications to the basic three element design take been periodically incorporated, specially in applications where higher than normal torque multiplication is required. Nearly usually, these have taken the form of multiple turbines and stators, each set up being designed to produce differing amounts of torque multiplication. For case, the Buick Dynaflow automated transmission was a non-shifting blueprint 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-upwardly clutch to ameliorate cruising power manual efficiency and reduce heat. The application of the clutch locks the turbine to the impeller, causing all ability transmission to exist mechanical, thus eliminating losses associated with fluid drive.

Operational phases [edit]

A torque converter has three stages of operation:

• Stall. The prime mover is applying power to the impeller merely 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 employ the brakes. At stall, the torque converter can produce maximum torque multiplication if sufficient input power is practical (the resulting multiplication is called the stall ratio). The stall phase actually lasts for a cursory period when the load (e.chiliad., vehicle) initially starts to move, as at that place volition exist a very large deviation between pump and turbine speed.
• Acceleration. The load is accelerating merely there nevertheless is a relatively large divergence betwixt impeller and turbine speed. Under this condition, the converter volition produce torque multiplication that is less than what could be achieved under stall conditions. The amount of multiplication will depend upon the bodily difference between pump and turbine speed, as well as various other blueprint factors.
• Coupling. The turbine has reached approximately xc percent of the speed of the impeller. Torque multiplication has essentially ceased and the torque converter is behaving in a fashion similar to a elementary fluid coupling. In modernistic automotive applications, it is usually at this stage of functioning where the lock-up clutch is applied, a procedure that tends to ameliorate fuel efficiency.

The key to the torque converter's ability to multiply torque lies in the stator. In the archetype fluid coupling design, periods of loftier 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 aforementioned condition in a torque converter, the returning fluid will be redirected past the stator then that information technology aids the rotation of the impeller, instead of impeding it. The upshot is that much of the energy in the returning fluid is recovered and added to the free energy existence practical to the impeller past the prime mover. This action causes a substantial increase in the mass of fluid beingness directed to the turbine, producing an increment in output torque. Since the returning fluid is initially traveling in a direction opposite to impeller rotation, the stator volition likewise effort to counter-rotate equally it forces the fluid to modify management, an effect that is prevented by the 1-way stator clutch.

Dissimilar 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 and so the latter can exercise its task. The shape of the blades is important as small variations tin 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-manner clutch. Nonetheless, every bit the torque converter approaches the coupling phase, the free energy and volume of the fluid returning from the turbine will gradually decrease, causing force per unit area on the stator to likewise decrease. One time in the coupling phase, the returning fluid volition contrary direction and now rotate in the direction of the impeller and turbine, an effect which volition attempt to frontwards-rotate the stator. At this point, the stator clutch will release and the impeller, turbine and stator will all (more or less) turn equally a unit.

Unavoidably, some of the fluid'south kinetic free energy will be lost due to friction and turbulence, causing the converter to generate waste material heat (dissipated in many applications past water cooling). This effect, often referred to as pumping loss, will be most pronounced at or near stall weather condition. 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 (equally when a vehicle with an automatic transmission is stopped at a traffic indicate or in traffic congestion while still in gear).

Efficiency and torque multiplication [edit]

A torque converter cannot accomplish 100 percent coupling efficiency. The classic three element torque converter has an efficiency curve that resembles ∩: aught 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 period interference generated by the stator, and as previously mentioned, is commonly overcome past mounting the stator on a one-way clutch.

Even with the benefit of the one-way stator clutch, a converter cannot attain the same level of efficiency in the coupling phase equally an equivalently sized fluid coupling. Some loss is due to the presence of the stator (even though rotating equally part of the assembly), as information technology ever generates some ability-arresting turbulence. Most of the loss, however, is caused by the curved and angled turbine blades, which do not blot kinetic energy from the fluid mass besides equally radially straight blades. Since the turbine blade geometry is a crucial factor in the converter'south power to multiply torque, trade-offs betwixt torque multiplication and coupling efficiency are inevitable. In automotive applications, where steady improvements in fuel economy take been mandated by market forces and government edict, the nearly universal utilise of a lock-up clutch has helped to eliminate the converter from the efficiency equation during cruising functioning.

The maximum amount of torque multiplication produced past 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 about the stall phase of operation. Typical stall torque multiplication ratios range from ane.viii:1 to 2.five:1 for most automotive applications (although multi-chemical element designs as used in the Buick Dynaflow and Chevrolet Turboglide could produce more than). Specialized converters designed for industrial, rail, or heavy marine ability transmission systems are capable of as much every bit 5.0:ane multiplication. By and large speaking, there is a merchandise-off between maximum torque multiplication and efficiency—loftier stall ratio converters tend to be relatively inefficient below the coupling speed, whereas low stall ratio converters tend to provide less possible torque multiplication.

The characteristics of the torque converter must be advisedly matched to the torque curve of the power source and the intended application. Changing the bract geometry of the stator and/or turbine will change the torque-stall characteristics, also as the overall efficiency of the unit. For case, drag racing automatic transmissions frequently use converters modified to produce high stall speeds to improve off-the-line torque, and to become into the power band of the engine more than quickly. Highway vehicles generally employ lower stall torque converters to limit estrus production, and provide a more business 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 set on could be varied in response to changes in engine speed and load. The effect of this was to vary the corporeality 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 bending of attack, increasing torque multiplication at the expense of efficiency.

Some torque converters employ multiple stators and/or multiple turbines to provide a wider range of torque multiplication. Such multiple-element converters are more mutual in industrial environments than in automotive transmissions, simply automotive applications such as Buick'south Triple Turbine Dynaflow and Chevrolet'south Turboglide also existed. The Buick Dynaflow utilized the torque-multiplying characteristics of its planetary gear gear up in conjunction with the torque converter for depression gear and bypassed the beginning turbine, using only the second turbine as vehicle speed increased. The unavoidable trade-off with this arrangement was low efficiency and somewhen these transmissions were discontinued in favor of the more efficient three speed units with a conventional three element torque converter. It is also found that efficiency of torque converter is maximum at very depression speeds.

Lock-up torque converters [edit]

As described to a higher place, impelling losses inside the torque converter reduce efficiency and generate waste heat. In modernistic automotive applications, this problem is commonly avoided by use of a lock-upwardly clutch that physically links the impeller and turbine, effectively changing the converter into a purely mechanical coupling. The result is no slippage, and almost no power loss.

The kickoff automotive application of the lock-up principle was Packard'south Ultramatic manual, 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. This feature was too present in some Borg-Warner transmissions produced during the 1950s. It vicious out of favor in subsequent years due to its extra complexity and cost. In the tardily 1970s lock-upward clutches started to reappear in response to demands for improved fuel economic system, and are now nearly universal in automotive applications.

Capacity and failure modes [edit]

As with a basic fluid coupling the theoretical torque capacity of a converter is proportional to ${\displaystyle r\,Due north^{ii}D^{5}}$ , where ${\displaystyle r}$ is the mass density of the fluid (kg/mⁱⁱⁱ), ${\displaystyle N}$ is the impeller speed (rpm), and ${\displaystyle D}$ is the diameter (k).^[one] 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 (oft through h2o 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 pattern feature that eases the process of inspection and repair, merely adds to the cost of producing the converter.

In loftier 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 fatigued into seams and joints to produce a stronger bail between the blades, hubs and annular ring(south). Because the furnace brazing process creates a small radius at the signal where a blade meets with a hub or annular band, a theoretical subtract in turbulence will occur, resulting in a respective increase in efficiency.

Overloading a converter tin issue 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 impairment to the elastomer seals that retain fluid inside the converter. This volition crusade the unit to leak and eventually finish functioning due to lack of fluid.
• Stator clutch seizure: The inner and outer elements of the one-fashion stator clutch become permanently locked together, thus preventing the stator from rotating during the coupling phase. Most oftentimes, 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 volition showroom very poor efficiency during the coupling phase, and in a motor vehicle, fuel consumption will drastically increase. Converter overheating under such weather will usually occur if connected performance is attempted.
• Stator clutch breakage: A very abrupt awarding of ability 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 ability manual will take place. In an auto, the effect is similar to a astringent example of transmission slippage and the vehicle is all only incapable of moving under its own power.
• Blade deformation and fragmentation: If subjected to precipitous 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 intermission upward into fragments. At the to the lowest degree, 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 loftier RPM may cause the shape of the converter'southward housing to be physically distorted due to internal pressure level and/or the stress imposed by inertia. Nether 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.

Manufacturers [edit]

Electric current [edit]

• Aisin AW, used in automobiles
• Allison Transmission, used in motorcoach, decline, fire, construction, distribution, war machine and specialty applications
• BorgWarner, used in automobiles
• Exedy, used in automobiles
• Isuzu, used in automobiles
• Jatco, used in automobiles
• LuK USA LLC, produces Torque Converters for Ford, GM, Allison Manual, and Hyundai
• Subaru, used in automobiles
• Twin Disc, used in vehicle, marine and oilfield applications
• Valeo, produces Torque converter for Ford, GM, Mazda, Subaru
• Voith turbo transmissions, used in many diesel locomotives and diesel multiple units
• ZF Friedrichshafen, automobiles, forestry machines, popular in city double-decker applications

Past [edit]

• Lysholm-Smith, named later its inventor, Alf Lysholm,^[ii] produced past Leyland Motors and used in buses from 1933-9 and besides some British Runway Derby Lightweight and Ulster Send Authority diesel multiple units
• Mekydro,^[3] used in British Rail Grade 35 Hymek locomotives.
• Packard, used in the Ultramatic automobile transmission system
• Rolls-Royce (Twin Disc), used in some British United Traction diesel multiple units
• Vickers-Coates^[4]

See also [edit]

• Clutch
• Fluid coupling
• Servomechanism
• Torque amplifier
• Transmission (mechanics)
• H2o restriction

References [edit]

1. ^ Hydrodynamic couplings and converters. Automotive Handbook (third ed.). Robert Bosch. 1993. p. 539. ISBN0-8376-0330-7.
2. ^ "Espacenet - Original document". Worldwide.espacenet.com. 1933-03-07. Retrieved 2014-07-21 .
3. ^ "Archived copy". Archived from the original on 2010-03-02. Retrieved 2009-x-31 . {{cite web}}: CS1 maint: archived re-create as title (link)
4. ^ "The Sydney Morning Herald - Google News Annal Search". Archived from the original on 2016-05-12.

External links [edit]

• HowStuffWorks commodity on torque converters
• YouTube video about torque converters

szaboknespolow1961.blogspot.com

Source: https://en.wikipedia.org/wiki/Torque_converter

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