Jak funguje AWD (visco) [EN]

Kulaté velké předokolky/AWD
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#1 Jak funguje AWD (visco) [EN]

Příspěvek od Drtic »

Prevzato z VolvoXC.com:

HOW Volvo 'S first generation AWD [98-03] works


Engine power can be diverted to rear wheels through a transfer differential located adjacent to the transmission. Power can be split to either the front or rear wheels in varying amounts as road conditions dictate and without driver intervention.

Further downstream in the driveline resides the main component that handles engine power transfer, the viscous clutch. In simple terms it is a type of turbine in which power that normally drives the front wheels is instantly transferred to the rear wheels to help maintain optimum vehicle traction. It is the key to Volvo 's AWD system.

The viscous clutch normally allows 95 percent of the engine power to remain directed to the front wheels and five percent to the rear wheels under conventional driving conditions. But as soon as a wheel slip is detected, the viscous clutch adjusts torque distribution to all wheels and when necessary, can transfer up to 95 percent of the engine power to the rear wheels. This all takes place in milliseconds--well before a driver would be capable of making such a decision. No special technical or driving skills are required to operate the all-wheel drive mode. The entire action is completely transparent to the driver. In fact, the action is similar to what occurs in an automatic transmission.

SYSTEM MECHANICS:

Transfer Differential
Volvo 's transmission has been modified and extended to include a compact transfer differential. The power is transferred between the transmission's differential housing and bevel gear's tubular shaft via a splined joint. The bevel gear's wheel and pinion and the final drive have the same numerical ratio between the front and rear wheel. At the rear edge of the transfer differential there is a drive shaft which leads to the rear wheels. This shaft has CV joints at the front and rear and a U-joint in the center, where the intermediate bearing is situated. The drive shaft runs through the standard floor tunnel which permits the installation of the system with only a few minor modifications.

Viscous Coupling
The viscous coupling, which is located ahead of the rear differential, appears as a long tube filled with silicone oil and contains a large number of discs. The viscous clutch is designed to use the silicon oil's viscosity to transfer power via the discs to the rear wheels when the front wheels start to spin. Every other disc is connected to the front wheel part of the shaft and the alternating discs are connected to the rear differential. When the discs revolve at a different rate the silicone oil in which the discs rotate becomes more viscous and thus increases the pressure. As this pressure increases, torque is transferred to the rear wheels. If the viscous coupling is subjected to intensive slipping, the silicone oil and discs become very hot. At this point, the coupling locks-up to prevent any slippage.

Freewheel Unit
Volvo has also engineered into the drive line system a freewheel component. This unit disengages the rear drive during braking and/or coasting help ensure optimum braking performance. With this feature, the ABS braking system does not need modification. Another refinement, when it comes to this freewheel, is that it also has a lock-up function. This means that Volvo 's AWD system is always in four-wheel driven when it reverses.

Rear Drive Unit
The rear drive unit is similar to the one used for the S90N90 series, but uses coil springs rather than a mono-leaf composite spring. The choice of this unit, rather than engineering a completely new one, is a clever bit of engineering. The drive unit was fitted with minor modifications, required virtually no re-engineering, and created only minor changes in manufacturing, which means that all the good characteristics S90N90 are transplanted into this vehicle. And this also turns out to be a very cost effective solution to a potentially tricky problem. The axle housing assembly consists of two sections of cast aluminum bolted together. This assembly houses the drive unit and Multi-link rear suspension, shock absorbers, and anti-roll bar. This independent rear suspension unit mounts into the S70 and V70 chassis without major modifications or loss of interior cargo space. The rear drive unit delivers a high degree of rear wheel traction while providing excellent road noise isolation, passenger comfort, and driving pleasure.

FRONT AND REAR TRACTION CONTROL

Volvo engineers have also incorporated a locking differential for the rear axle drive unit, and Traction Control System (TRACS) for the front drive unit to help ensure that the correct amount of power is distributed as needed at low speeds. The locking rear differential senses minute differences in rear wheels rotational speed and at speeds less than 25 mph automatically locks both rear wheels to transfer engine power to help maintain traction. TRACS, based on an ABS feed back system, is designed to work at speeds of less than 25 mph and is especially useful in helping to prevent front wheel spin at vehicle launch. Both these systems, locking rear differential and front wheel TRACS, working together help to prevent wheel spin, thereby helping to ensure maximum take-off traction control on most slippery road surfaces.
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Volvo XC70, B5244T3, AW50/51, 170kW(ard), 2002 Obrázek
Volvo 964, B280E, AW71, 125kW, 1991, diplomat, jeste vetsi plna palba Obrázek
Volvo 744, B200E, M47, 85kW, 1991, diplomat - Bushovka, plna palba
Volvo 244, B19A, 1983 - v renovaci

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#2 Jak funguje AWD (visco) [EN]

Příspěvek od Drtic »

This is what VIDA says about the first AWD system fitted to V70 XC 1998- 2003


The AW 50-42 is an electronically-controlled four-speed automatic transmission with torque converter lock-up of the three highest gears. Because the transmission is controlled by an electronic control module gear-shifting can be controlled to allow the correct gear to be selected for driving conditions, engine load, driver's wishes, speed, etc. This yields good fuel economy combined with top-class performance and increased comfort by ensuring smoother shifts and lower noise levels.
A control module receives information about the selected gear and driving mode setting required. Together with signals from a number of sensors describing the running conditions of the car, this information is processed by the control module, which calculates optimum shifting and lock-up engagement points, depending on the driving mode selected. The control module then controls shifting and lock-up engagement by acting on the transmission hydraulic system. The control module also affects the quality of gear-changing by instantaneously modifying the hydraulic line pressure when shift is made.
The transmission's electronic control system receives continuous information from a number of sensors, as well as from the engine control system. Unlike a transmission with just a hydraulic control system, this enables the control system to adapt to extremely small changes in operating conditions and to control the various transmission functions so that the correct gear is always selected in accordance with the driving mode selected by the driver.
To facilitate fault-tracing, the control module has a built-in on-board diagnostic system (OBD II system) which records any faults in the control system and transmission, these can be read off via the data link connector (DLC).

The gearbox itself is controlled with the TCM but the AWD and viscous coupling has no diagnose and is not electronically controlled.

Be very aware of not using wheels with more than 10% tyre circumference since this will wear the coupling severely ending up in a FWD vehicle in the end and a very expensive repair. The 1998 and 1999 had some problems with the rear differential and also the propshaft is prone to have bearing failure therefore alot of V70 XC is sold as front wheel drive only nowadays since the prop shaft must be bought as a complete part from Volvo. You can hand it in to a mechanical workshop and change only the support bearing in case it fails.
_________________
Volvo XC70, B5244T3, AW50/51, 170kW(ard), 2002 Obrázek
Volvo 964, B280E, AW71, 125kW, 1991, diplomat, jeste vetsi plna palba Obrázek
Volvo 744, B200E, M47, 85kW, 1991, diplomat - Bushovka, plna palba
Volvo 244, B19A, 1983 - v renovaci

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#3 Jak funguje AWD (visco) [EN]

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_________________
V 70 B5244 T5, AWD, MY 07' HILTON TUNING stage 3 + úpravy
V 70 B5244 S2 2.4L, MY 01' stage 2, LPG

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#4 Jak funguje AWD (visco) [EN]

Příspěvek od Urvanej »

Todle ale neni rozdíl mezi haldexem a viskačkou, ale zadní diferák a elektroniky řízení prokluzu kol. Oba systémy "jen" připojujou zadek různými způsoby, nicméně bez pomoci čehokoliv jinýho by se z válců na jednom kole každé nápravy nedostaly.
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745, D24, M47, 1990, Kája; 945, B230FT, AW71, 1995, Jaruna; V70, D5, M56, 2004, Bertík; 944, B230FT, M46, 1991, Blex; XC90 V8, 2004; 142, B20A, M40, 1970 ex; S40, 1.8, m3p, 1997 :764, B280F, AW71, 1988, Tomasssovka;244, D24, M47, 1990, Blu; XC90 V8, 2005, Mastodont; V40, B4204S, M5P, 1996.

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#5 Jak funguje AWD (visco) [EN]

Příspěvek od peter cz »

No p80 awd mají v zadním difu uzávěrku (g80), stejně jako krabice, tam by to šlo. Docela by mě zajímalo jestli jí zachovali i v P2 (pro ty už ve vidě není rozkres, jen celý dif jako jeden díl).
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´96 850 R, B5234T5, AW50-42LE, Elotec E85 | ´89 760 GLE, D24TIC, ZF4HP22 Obrázek | ´97 940 Turbo, B230FK, M90, LPG Obrázek
Volvo diagnostika k dispozici.

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#6 Jak funguje AWD (visco) [EN]

Příspěvek od Urvanej »

Takže P80 AWD (visko) by se nerozjela v konfiguraci jedinýho předního kola s trakcí, ale kdyby to bylo zadní, tak se rozjede :-D
_________________
745, D24, M47, 1990, Kája; 945, B230FT, AW71, 1995, Jaruna; V70, D5, M56, 2004, Bertík; 944, B230FT, M46, 1991, Blex; XC90 V8, 2004; 142, B20A, M40, 1970 ex; S40, 1.8, m3p, 1997 :764, B280F, AW71, 1988, Tomasssovka;244, D24, M47, 1990, Blu; XC90 V8, 2005, Mastodont; V40, B4204S, M5P, 1996.

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#7 Jak funguje AWD (visco) [EN]

Příspěvek od Ykka »

Na P2 už je to nahrazeno elektronickou uzávěrkou v rámci STC, DSTC. Je to jednodušší, i když ten účinek na rozjezd na kluzkém povrchu je podle mých zkušeností přinejmenším sporný. Začíná to účinkovat totiž až při určitých otáčkách, kdy už se třeba na uježděném sněhu ztratí adheze úplně.
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