A limited-slip differential (LSD) is a differential type that allows two output shafts to rotate at different speeds but limits the maximum difference between two axes.
In cars, such limited-slip differentials are sometimes used instead of the standard differential, in which they convey certain dynamic advantages, at the expense of greater complexity.
Video Limited-slip differential
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In 1932, Ferdinand Porsche designed the Grand Prix racing car for the Auto Union company. The high design strength causes one of the rear wheels to experience excessive wheel spin at speeds of up to 160 km/h (100 mph). In 1935, Porsche commissioned the ZF engineering firm to design a limited slip differential to improve performance. The ZF "shear pin and cams" became available, and one example was the Type B-70 used during the Second World War in the military VW (KÃÆ'¼belwagen and Schwimmwagen), although technically this was not a slip-limited differential, but the system consisted of two freewheels , which sends all the engine power to the slowest spin of two wheels.
Maps Limited-slip differential
Benefits
The main advantage of the limited-slip differential is shown by considering the case of standard (or "open") differences in off-road or snow situations where one wheel begins to slip. In such cases with standard differentials, the slipped or non-touch wheel will receive most of the power (in the form of low rotation, high rpm rotation), while the touching wheel will remain stationary to the ground. The torque transmitted by the open differential will always be the same on both wheels; if one of the tires is on a slippery surface, the available torque will easily overcome the available traction at very low amounts. For example, the right tire may start spinning immediately after the 70Ã,Â, ¢ t torque? (50 Âμbb) is placed on top of it, as it is on the ice surface. Since the same amount of torque is always felt on both wheels, regardless of the speed at which they are rotated, this means that the wheels with traction can not accept more than 70 Nm of torque, which is much less than necessary to drive a vehicle. Meanwhile, tires on slippery surfaces will only rotate, absorbing all actual power output (which is a function of torque provided all the time), although both wheels provided equal (very low) amount of torque. In this situation, the limited-slip differential prevents excessive power from being allocated to one wheel, and so keeps the two wheels in rotation powered, ensuring that traction will not be limited to wheels that can handle the minimum amount of power. The advantages of LSD in high-powered and rear-wheeled cars were demonstrated during the United States "Muscle-Car" era from the mid-1960s to early 1970s. The car in this era is usually a rear-wheel drive and has no independent suspension for the rear tire (but instead uses a live axle). With the live axle, when high torque is applied through the differential, the traction on the right rear tire is lower because the shaft naturally wants to rotate with the drive shaft torque (but held still by being fitted to the vehicle frame). This creates the term "one wheel peel". Thus, "Muscle-Cars" with LSD or "posi" (positraction) are at a different advantage for their circling counterparts.
The basic principle of operation
Differential automotive limited-slip all contain some basic elements. Firstly, all have a dental gear which, like the open differential, allows the output shaft to rotate at different speeds while maintaining the amount of velocity proportional to the input shaft.
Second, all have a kind of mechanism that implements torque (internal to differential) that rejects the relative motion of the output shaft. In simple terms, this means they have several mechanisms that reject the speed difference between outputs, by creating the opposing torque between the two outputs, or the differential output and housing. There are many mechanisms used to create this resistant torque. This type of limited-slip differential usually gets its name from the design of this resisting mechanism. Examples include LSD viscous and coupling. The number of torque constraints provided by this mechanism varies by design and will be discussed later in the article.
The finite slip differential has a more complex torque separation and should be considered in the case when the output rotates at the same rate and when it rotates at different speeds. The torsion difference between the two axles is called Trq d . (In this work it is called Trq f for torque friction). Trq d is the difference in torque that is sent to the left and right wheels. The amount of Trq d is derived from the slip-limiting mechanism in the differential and possibly the function of the input torque (as in the case of differential gears), or the difference in the output velocity (as in the case of differential thick).
Torque sent to output is:
- Trq 1 = Ã,½ Trq at Ã,½ Trq d for the output slower
- Trq 2 = Ã,½ Trq at - Ã,½ Trq d
When traveling in a straight line, where one wheel begins to slip (and spins faster than wheel by traction), the torque is reduced to the wheels slip ( Trq 2 ) and is given to the wheel which is slower ( Trq 1 ).
In the case when the vehicle is spinning and no wheels are slipping, the inner wheels will rotate more slowly than the outer wheels. In this case the inner wheels will receive more torque than the outer wheels, which can produce understeer.
When both wheels rotate at the same speed, the torque distribution to each wheel is:
- Trq (1 or 2) = Ã,½ Trq within Ã,  ± (< sub>) temporarily
- Trq 1 Trq 2 = Trq at .
This means the maximum torque for the wheels is either statically indeterminate but in the range Ã,½ Trq in Ã,  ± (Ã,½ Trq d ) >.
Type
Some types of LSD are usually used in passenger cars.
- Fixed value
- Torque sensitive
- Sensitive speed
- Electronic controlled
Fixed value
In this differential, the maximum torque difference between the two outputs, Trq d , is a fixed value at any time regardless of the torque input to the differential difference or velocity between the two outputs. Usually this differential uses spring coupling assemblies.
Torque Sensitivity (HLSD)
This type includes a limited-slip differential and a helical gear coupling, cone (alternative clutch type) where the clutch binding strength is a function of the input torque applied to the differential (since the engine implements more torque clutch clutch harder and Trq d decreased).
LSD torque sensing responds to the driveshaft's torque, so the more driveshaft drive torque is present, the harder the clutch, cone or gears are pressed together, and thus the more tightly driven wheels are connected to each other. Some include spring loading to provide some small torque so with little or no torque input (trailing throttle/gearbox in neutral/clutch main distressed) minimum drive wheels are combined. The amount of preload (therefore static coupling) on ​​the coupling or cone is affected by the general conditions (wear and tear) and how dense they are loaded.
Clutch, cone type, or LSD plate
The clutch type has a stack of thin clutches, half of which are coupled to one of the drive shafts, the other half being coupled to the spider gear carrier. The clutch stack may be present on either drive shaft, or just one. If only on one, the remaining drive shaft is connected to the drive shaft gripped through the spider gears. In the cone type the grip is replaced by a pair of cones pressed together reaching the same effect.
One method for creating clamping styles is the use of cam-ramp assembly as used in LSD Salisbury/ramp style. Spider gears are mounted on a pinion pinion shaft that rests on oblique pieces forming a wedged slope. The folded ramp is not always symmetrical. If the ramp is symmetrical, LSD 2 direction. If they see toothed (ie one side of the vertical road), LSD 1 direction. If both sides are tilted, but asymmetric, LSD 1.5 direction. (See discussion 2, 1.5 and 1 below)
The alternative is to use the natural separation power of the gear teeth to load the clutch. An example is the difference center Audi Quattro RS 5 2011.
When the driveshaft input torque tries to change the differential center, the internal pressure ring (adjacent to the clutch pile) is forced to the side by the pinion crossbar which tries to climb the incline, which compresses the clutch pile. The more couplings are compressed, the more wheels are combined. Marriage from the vertical path (80-85 Â in practice to avoid chipping) surfaces in one direction LSD in the overrun does not produce a cam effect or compression coupling coupling accordingly.
2-Directions , 1-Direction, 1.5-Direction
Broadly speaking, there are three torque input states: load, no load, and over run. During load conditions, as stated earlier, the coupling is proportional to the input torque. Without load, the coupling is reduced to a static coupling. Behavior on over runs (especially sudden throttle release) determines whether LSD is 1 way, 1.5 direction, or 2 direction.
The 2-way differential will have the same limiting torque Trq d in both forward and backward directions. This means the differential will provide some degree of restriction under engine braking.
1-way differentials will provide restrictive action in just one direction. When the torque is applied in the opposite direction it behaves like an open differential. In the case of the FWD car it is said to be safer than the 2 way differential. The argument is that if there is no additional clutch on the over run, ie 1-way LSD as soon as the driver lifts the throttle, LSD opens and behaves like a conventional open differential. This is also the best for FWD cars, as it allows the car to ignite throttle releases, instead of plowing ahead.
The 1.5-way differential refers to one where the forward and back limiting torque, Trq d_fwd, d_rev , differs but not equal to zero as in the case of 1-way LSD. This type of differential is common in racing cars where strong limiting torque can help stability under engine braking.
Geared LSD
Differential, torque-sensitive differential-limited mechanical slips use worm gears and spur gears to distribute and differentiate input power between two drive wheels or front and rear axles. This is a completely separate design from the most common spider gear design seen in most automotive applications. When the torque is applied to the gears, they are pushed onto the differential housing wall, creating friction. Friction rejects the relative motion of the output and creates a limiting torque of Trq d .
Unlike other friction-based LSD designs that incorporate a common "open" differential dental spider in combination with a frictionless material that inhibits differentiation, the design of torque sensing is a unique differential type, with a torsional bias attached to the design, not as an addition. in. Torsional bias is applied only when necessary, and does not inhibit differentiation. The result is a non-binding real differential like LSD and locking type, but still provides increased power delivery under many road conditions.
Examples include:
- Torsen T-1 is the original Gleasman differential brand name created by Vernon Gleasman around 1949 (US Pat. 2,559,916 applied in 1949, awarded 1951). The original Gleasman design was sold to The Gleason Works (later named Gleason Corporation), which began marketing it in 1982. The original T-1 model was not compatible with c-clip drive, limiting its use with many cars and pick-up trucks at the time. However, the original Torsen differential was used in racing by Mario Andretti and Paul Newman with great success. All LSD worm gear designs are then derived from the original Gleasman differential. The T-1 is the original equipment in Audi Quattro, Subaru Impreza WRX STI, Toyota Mega Cruiser and AM General HMMWV "Humvee".
- Torsen T-2 is a new Gleasman design circa 1984 (US Patent Application WO1984003745 A1) compatible with c-clip as. The new design, together with the incorporation makes Zexel-Gleason AS increase the availability of Torsen for OEM and aftermarket applications. Variants include the T-2R, which includes a Positraction style coupling package that provides preload for racing purposes; and T-3, double differentials intended for AWD applications. The T-2 is the original equipment in many high-performance cars and pick-up trucks.
- Quaife differentials, sold under the name Automatic Torque Biasing Differential (ATB), are protected by European Pat. 130806A2. The most established Quaife version in Europe and other markets other than the US, provides extensive after-sales support for European and Japanese brand cars, especially front-wheel drive and all-wheel drive applications. Ford Focus RS uses Quaife as the original equipment.
- Eaton Corporation is the latest owner of Truetrac differential, which has been produced secretly for years. The design is similar to the Torsen T-2 (slightly less torque bias), and is an aftermarket part for many US-made solid axles for rear-wheel drive and 4x4 pickup trucks. Truetrac is most commonly used in 4x4 pick-up truck axles intended for off-road use, in combination with central locking and rear differentials. As with all LSD driven designs, Truetrac does not have a negative impact on the steering wheel that most LSD designs and other "lockers" are vulnerable.
Speed ​​sensitivity
The speed-sensitive difference limits the difference in torque between outputs, Trq d , based on the speed difference between the two output shafts. So for the small output difference difference, the differential behavior may be very close to the open differential. When the speed difference increases the torque increase. This results in a different dynamic behavior compared to the sensitive differential torque. The condensed type is generally simpler as it depends on the hydrodynamic friction of the liquid with high viscosity. Silicone-based oils are often used. Here, the cylindrical chamber contains a liquid containing a pile of rotating discs with the normal movement of the output shaft. The inner surface of the chamber is coupled to one of the driveshafts, and the outer part is coupled to the differential carrier. Half of the discs are connected to the inside, the other half is outward, alternating inside/outside in the pile. Differential motion forces the inserted disk to move through the fluid against each other. In some thick coupling when the speed is maintained the liquid will accumulate heat due to friction. This heat will cause the fluid to expand, and expand the coupler causing the discs to be unified resulting in a non-condensed plate being the friction of the plate and a sharp drop in the speed difference. This is known as a hump phenomenon and allows the coupler side to lock gently. Unlike the mechanical type, the delimiter action is much softer and more proportionate to the slip, and easier to overcome the average driver. New Process Gear uses a Ferguson-style thick coupling in some of their transfer cases including those used in Eagle AMC. Viscous LSDs are less efficient than the mechanical type, that is, they "lose" some power. In particular, any sustained load that overheats silicon results in a sudden permanent loss of differential effects. They have the primacy of graceful failure, returning to semi-open differential behavior. Usually a visco-differential that has covered 60,000 miles (97,000 km) or more will function mostly as an open differential. Silicone oil is a factory that is sealed in a separate chamber from the gear oil that surrounds the remaining differential. It can not be used; when the differential behavior deteriorates, the VLSD center must be replaced. Gerotor pump
This limited-slip diffraction differential works by using a motor pump to compress the clutch in a hydraulic way to transfer the torque to a rotating wheel more slowly. The motor pump uses a differential carrier or cage to drive the outer rotor of the pump and axle axle to drive the inner rotor. When there is a difference between the left and right wheel speeds, the pump will suppress the hydraulic fluid that causes the clutch to compress. thereby causing the torque to be transferred to the wheel that spins more slowly. This pump-based system has a lower and upper limit on applied pressure that allows differential work such as conventional or open differential until there is a significant speed difference between the right and left wheels, and internal damping to avoid hysteresis. The newest pumping system has computer-regulated output for more flexibility and no oscillation.
Electronics
Electronic limited slip differential will typically have a bevel gear or a planet similar to an open differential and clutch packs that are similar to differential or differential torque gerotor pump. In electronic units, clamping forces on the clutch are controlled externally by a computer or other controller. This allows control of the differential limiting torque, TRQ d , to be controlled as part of a total management system chassis. An example of this type of differential is the Subaru DCCD used on the 2011 Subaru WRX STi. Another example is the Porsche PSD system used on the Porsche 928. The third example is Saab XWD (Haldex Generation 4) with eLSD, he uses a common hydraulic power network controlled (controlled electronically through the network of the vehicle) to control the longitudinal and transverse torque transfer system XWD. The same Haldex system used in some other Epsilon-based vehicles such as the Cadillac SRX etc.
Electronic systems: brake-based
This system is an alternative to the traditional limited-slip differential. The system utilizes a variety of chassis sensors such as speed sensors, anti-braking sensors (ABS) sensors, accelerometers, and microcomputers to electronically monitor wheel slippage and vehicle motion. When the chassis control system determines the wheel to slip, the computer will apply the brakes to the wheel. The significant difference between the limited slip differential system listed above and this brake-based system, is that the brake-based system does not inherently send a larger torque to the slower wheels, coupled with the use of additional brake friction materials resulting from the use of such systems it if the vehicle is driven in an environment where the brake-based system will be active on a regular basis.
The finite-limited-slip electronics BMW used on the F10 Series 5 is an example of such a system. Another example begins in the first year (1992) production of a redesigned model, and a new Ford Ford Victoria 4.6L V-8 cam model with optional anti-lock brakes. This option is available in 1992 Crown Victoria, onwards; on cars equipped with anti-lock brakes.
- Spool
- Lock the differential
Factory name
In the 1950s and 1960s many manufacturers began to apply brand names to their LSD units. Packard pioneered LSD under the "Twin Traction" brand in 1956, becoming one of the first manufacturers. Other factory names for LSD include:
- Alfa Romeo: Q4, Q2
- Audi: Quattro, Quattro with Differential Sport (rear axle)
- American Motors: Twin-Grip
- Buick: Positive Traction. The Gran Sport model uses the term "Limited-slip (differential)"
- Cadillac: Controlled
- Chevrolet/GMC: Positraction
- Chrysler: A Definite Handbook
- Dana Holding Corporation: Trak-Lok or Powr-Lok
- Ferrari: E-Diff
- Fiat, Lancia: Viscodrive
- Ford: Equa-Lock and Traction-Lok ​​â € <â € <
- Hyundai: HTRAC
- International: Trak-Lok (grip only) or Power-Lok (clutch and lean engagement process)
- Jeep: Trac-Lok (clutch type mechanic), Tru-Lok (gear type mechanic), and Vari-Lok (motor pump), Power Lok
- Lincoln: Directed Power
- Maserati: Tor Equals
- Nissan: GT LSD
- Oldsmobile: Anti-Spin
- Pontiac: Safe-T-Track
- Porsche: PSD (electro-hydraulic mechanical), Porsche Torque Vectoring/Plus (PTV/Plus, electro-mechanical hydraulic brake and brake-based type; only rear axle)
- Saab: Saab XWD eLSD
- Studebaker-Packard Corporation: Twin Traction
- Toyota: LSD
- TVR: Hydratrak
- Yukon Gear & amp; Axle: Duragrip
- Mercedes: ASD, AMG Rear-Axle Differential Lock (active differential on FR-based AMG/S models; pure mechanical variants are also present on certain non-S AMG models)
In popular culture
In the song The Beach Boys' 409 , the lyrics cite a limited-slip difference: "... My four speeds, dual-quad, Positraction 4-0-9 (4-0 -9, 4- 0-9). "
In the 1992 film My Cousin Vinny proof of innocence the two youths accused of murder depended heavily on tire photographs made by cars that had limited slip differentials (which, like Marisa Tomei's character that is famously expressed in Oscar-winning appearance) "is not available on '64 Buick Skylark," the car driven by the defendants. He argues that the evidence proves, no, that the holiday car is the 1963 Pontiac Tempest, which does offer optional Safe-T-Track (Pontiac's Positraction Version) limited-slip differential.
References
External links
- Unlimited slippage differentials explain
Source of the article : Wikipedia
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