Sisteme AWD, care e cel mai bun? |
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Sisteme AWD, care e cel mai bun? |
Jun 4 2005, 02:14 PM
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specialist Group: Membri Posts: 4.583 Joined: 30-May 04 From: Honda World Member No.: 26.577 |
In 1980, Audi introduced the world to full-time all-wheel drive to volume-produced passenger cars. It was called quattro. Now in its fourth generation, Audi's quattro® permanent all-wheel drive directs power where and when it's needed. Under ideal conditions power is split 50/50 front to rear. But in extreme cases up to 67% of the engine's power can be directed to a single wheel. The benefits to the driver are safety, performance, power, and control in copious amounts. When cornering, all four wheels of a car must cover varying distances. The task of the center differential is to compensate for the differences between front and rear axles, and to distribute engine power between front and rear wheels. The center differential is the heart of Audi's permanent all-wheel driveline. Depending on the driving situation and road conditions, the system automatically regulates the distribution of power within milliseconds. This takes place by means of either (depending on model) the Torsen; differential, Haldex™ clutch, or hydraulic multi-plate clutch. Influencing parameters in the control process include engine speed and torque, wheel spreads, and longitudinal and lateral acceleration. The division of propulsive power between all four wheels is the basis of the excellent handling and safety of Audi models with quattro. The potential of this drive concept is further optimized by a series of control systems for brake and engine management: The Anti-lock Brake System (ABS) Electronic Brake-force Distribution (EBD) Electronic Differential Lock (EDL) Anti-Slip Regulation (ASR) All of the above assist in increasing traction when accelerating or braking. Furthermore, when cornering, the standard Electronic Stabilization Program (ESP) increases directional stability by comparing target and actual physical driving forces. The locking function of the center differential and the Electronic Differential Lock make sure that an Audi with quattro; all-wheel drive can still pull away with only one wheel able to transfer engine power to the road. Here's how it works: If one of the wheels on an axle loses grip and starts spinning, propulsive power has to be diverted to the other wheel by the axle's differential. Previously, a mechanical differential lock enabled this to take place. Now, the Electronic Differential Lock has replaced the mechanical lock, effectively transferring the excess power of the spinning wheel to the other wheels with better traction. On an Audi with quattro, if both wheels on an axle start spinning, the continuously controlled locking of the center differential ensures that most of the torque is transmitted to the other axle. In this way, propulsion is guaranteed in almost all situations. On an Audi with quattro, if both wheels on an axle start spinning, the continuously controlled locking of the center differential ensures that most ( adica 67%) of the torque is transmitted to the other axle. In this way, propulsion is guaranteed in almost all situations. dupa audiusa.com --------------------------------------------- cineva spunea ca diferenta intre 4motion si quattro este Haldex vs. Torsen. Se pare ca e inexact. Torsen este folosit pentru transmisia de la motoare dispuse longitudinal in timp ce Haldex este folosit pt. motoare dispuse transversal. -------------------- Civic Si 2007 2.0l DOHC iVTEC
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Nov 20 2005, 02:01 PM
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specialist Group: Membri Posts: 584 Joined: 28-June 05 From: Bucuresti Member No.: 50.007 |
Daca ieri mai aveam un dubiu, acum nu mai am niciunul quattro e mult mai performant.
Baiatul asta, pe care l-ai citat tu aici, face ceea ce a facut Nissan mai devreme. Compara cea mai noua versiune AWD de la Subaru cu o versiune mult mai veche de quattro. QUOTE(f1anatic) Originally Posted by RobY
Whereas the quattro has one 2.3:1 bias ratio torsens. If you ever get your front wheels stuck in a low tractive condition the quattro torsens can send a maximum of 2.3 times the force that cause the front wheels to spin. If your front wheels spin at 10lb/ft of torque because you are on ice the maximum your rears will get is 23 lb/ft. The rest of the power will leak out through the front wheels that are stuck. If one set of wheels become completely unloaded the torsens wont work all the power will leak out the unloaded wheels. Tipul ori nu cunoaste modul de functionare al diferentialului torsen, ori e rau intentionat. Problemele aste le avea quattro demult, nici vorba de asa ceva acum. QUOTE(f1anatic) The newest Quattro system uses brakeforce psudo differentials that simply use the brakes and ABS system to apply brake force to bias power side to side. seems like a great idea but unfortunately these brakeforce psudo diffs only work under 25mph. If you use it too much you will overheat the brakes. Dar de EDL nu a auzit? Parca si Golf-ul 3 avea EDL. Si iar e simpatic.... Adica se uzeaza si/sau se incalzesc placutele de frana? Franarea se face doar la pierderea aderentei, energia degajata este nesemnificativa in comparatie cu energia degajata la o franare normala. Daca placutele rezista la franare nici nu se vor incalzi in timpul functionarii diferentialului. Acest sistem se foloseste la multe din masinile off-road adevarate. (Hummer-ul militar, Land Rover etc). Dar repet, acum se folosesc dispozitive elctronice de blocare.
QUOTE(f1anatic) The 5mt subaru is continuous AWD with a 50:50 torque distribution slip limited by a viscous coupling. Brutally effective as it allows each set of wheels to receive an absolute torque split of 50:50 while still allowing each wheel to move independently of each other. Under normal conditions the viscous coupling is stationary and does no work. If one wheel becomes unloaded slip is limited by a viscous coupling differential that works in any condition even if the wheels are completely unloaded.
This system works through differentials slip limited by viscous couplings and works at all speeds. This system is NOT to be confused with a much simpler viscous coupling it is very diffrent. Whereas primary torque transfer in a viscous coupling is through viscous fluid. The primary torque transfer in the Subaru Viscous Copling Locking Differential System is through mechanical differentials whose slip is limited BY viscous differentials. Diferentialele LSD (prin viscocuplaj) au si avantaje si dezavantaje. Cel mai important avantaj fata de torsen este acela al costului, sunt mult mai ieftine datorita simplitatii lor. Ca dezavnataje, ar fi urmatoarele: 1. O intarziere in reactie. Pentru ca ele sa devina eficiente, lichidul trebuie sa se incalzeasca (datorita frecarii cauzata de vitezelor de rotatie diferite). Cu alte cuvinte, roata trebuie sa patineze destul inainde ca diferentialul sa intervina. Este adevarat, ele functioneaza si cand lichidul este rece, dar diferenta de tractiune pe care o indrepta catre o osie sau alta in acest caz nu este foarte mare. In cazul torsen, viteza este mult mai mare. Este necesar ca o roata sa se invarta cu doar 15 grade mai multa decat cealalta si intregul cuplu necesar este indreptat unde trebuie. 2. Dependenta fata de temperatura exterioara. Cu cat este mai rece, cu atat se incalzeste mai greu lichidul. QUOTE Comparison with other types of differentials
Primul exemplu de diferential de pe Subaru, postat de f1anatic Other means are also known for modifying the operative connection between drive axles to provide for the transfer of additional torque to the drive axles collectively. For example, many limited-slip differentials provide for preloading friction clutches to oppose the transfer of torque between drive axles. This frictional pre-load represents a particular minimum magnitude of resistance which must be overcome to permit any relative rotation between drive axles which may interfere with the operation of anti-lock braking systems. Also, since frictional forces are continually active to resist differentiation, the friction clutches tend to wear, resulting in a deterioration of intended differential performance. In contrast to the limited-slip's continuous magnitude of frictional resistance to differentiation, the torque biasing characteristic of the Torsen differential provides for a maximum ratio of torque distributions between drive axles. For instance, as the amount of torque being conveyed by the Torsen differential decreases, the amount of resistance to differentiation also decreases. That is, even though the bias ratio remains relatively constant, a proportional division of a lower magnitude of torque being conveyed by the differential results in a smaller torque difference between drive axles. In braking situations where little or no torque is being conveyed by the differential, a four to one apportionment of torque between drive axles amounts to little or no torque difference between drive axles. Thus, the Torsen differential will not support any appreciable torque 'wind-up' between drive axles during braking and so does not interfere with the operation of anti-lock braking systems. Al doile tip de diferential LSD de pe Subaru, din nou Torsen este mai performant Another known approach to modifying the operative connection between drive axles is to provide for resisting differentiation as a function of the speed difference between drive axles. It has long been appreciated that undesirable wheel slip is associated with very high rates of differentiation. Differentials have been designed using fluid shear friction, which respond to increased rates of differentiation by increasing fluid shear frictional resistance to differentiation. The obvious problem with such 'speed sensitive' differentials is that undesirable wheel slip has already occurred well in advance of its detection. Also, the fluid shear friction designs generally rely on the changes in fluid temperature associated with high differential shear rates to increase resistance to differentiation. However, similar temperature changes may be associated with extended periods of desirable differentiation, or may be influenced by changes in ambient temperature, so that resistance to differentiation may vary throughout ordinary conditions of vehicle use. The bias ratio characteristic of the Torsen differential instantly reacts to unequal traction conditions by delivering an increased amount of torque to the drive wheel having better traction before the other drive wheel exceeds the limit of traction available to that wheel. The bias ratio characteristic also remains substantially constant over a wide range of torque conveyed by the differential, and is not sensitive to changes in ambient temperature or conditions of vehicle use. -------------------- Audi A4 130CP - 2002
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