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
Acura TL 2006 3.2l SOHC VTEC |
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Jun 5 2005, 06:46 PM
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specialist Group: Membri Posts: 4.583 Joined: 30-May 04 From: Honda World Member No.: 26.577 |
dupa autowrold.com
All Subaru models sold in the U.S. feature the Subaru All-Wheel Driving System. This system consists of several subsystems working in harmony to ensure maximum traction availability without any driver input. Unlike many four-wheel drive or all-wheel drive systems, the Subaru all-wheel drive system consists of power transfer mechanisms that are small enough to fit inside the transmission case. These small components not only hold down weight and power loss, but also ownership costs of Subaru vehicles, as no extra maintenance is required for the system. Subaru all-wheel drive works differently in manual and automatic transmissions. Read on for more technical information. All-Wheel Drive (Automatic Transmission) Active all-wheel drive is a term coined by Subaru to differentiate the all-wheel drive system in the automatic transmission from other "reactive" all-wheel drive systems on the market today. What makes this all-wheel drive system so special is its ability to anticipate traction needs and act before a wheel slips. The mechanism that transfers torque fore and aft is contained within the transmission’s tailshaft. To the casual observer it looks just like a typical hydraulic clutch found in any automatic. The key difference in this clutch pack is its operation. It’s designed to slip according to how much all-wheel drive is needed. When an automatic’s clutch slips, it is due to a malfunction and will eventually burn up. But the multi-plate transfer (MPT) clutch uses a special friction material that easily withstands the friction loads generated during torque transfer. The MPT’s operation is controlled by the Transmission Control Unit (or TCU) and constantly changes dependent on how the vehicle is being driven. To get more all-wheel drive, the TCU increases the hydraulic pressure to the clutch for less slippage. Less all-wheel drive calls for more slip and the TCU reduces the hydraulic pressure to the clutch. Under normal, dry pavement operation torque split is about 90% front and 10% rear. This distribution helps to compensate for the car’s weight distribution and resultant smaller effective rolling diameter of the front tires. As weight transfers to the rear of the vehicle, (i.e., under acceleration), the TCU shifts the torque split more toward the rear wheels. Under hard braking, torque is directed forward. Torque distribution is changed based upon how the vehicle is being driven. Throttle position, gearshift lever position, current gear and other factors combine to influence the TCU and it, in turn, selects a software map that determines how aggressively torque split will be adjusted. Two speed sensors are used by the TCU to detect wheel slippage. One sensor monitors the front axle set, the other the rear axle set. Pre-programmed variables help the TCU differentiate between slipping wheels and normal wheel speed differentials as what occurs when cornering. A speed differential (front-to-rear) of up to 20% signals the TCU that the vehicle is cornering and torque is distributed to the front wheels to help increase traction during the turn. Anything above 20%, however, indicates to the TCU that wheel slippage is occurring and torque is then distributed to the rear wheels. Another feature of the all-wheel drive system is its interaction with the anti-lock brake system. When ABS is engaged, the transmission selects third gear, reducing the unpredictability of engine braking and, thus, reducing the possibility of wheel lock-up. But all four wheels are still connected to the engine through the AWD system and are brought back up to overall vehicle speed quicker and can, therefore, be controlled again sooner. In a two-wheel drive system if the locking wheel isn’t a drive wheel, it can only be brought back up to overall wheel speed by whatever traction exists between it and the road. The quicker a wheel is controlled the better the stopping performance. All-Wheel Drive (Manual Transmission) The 5-speed manual transmission’s all-wheel drive is referred to as a continuous all-wheel drive system. It uses a center differential located inside the transmission case that is controlled by a viscous coupling device. In effect, the center differential is a limited-slip differential. In normal operation, power is distributed equally to the front and rear wheels. Plates are alternately attached to the front and rear output shafts inside the viscous coupling. When a rotational difference occurs between the front and back wheels, the plates inside the viscous housing shear inside the contained fluid (a type of silicone) heating it and causing the fluid to thicken. The thickened fluid causes the plates to transfer torque from those that rotate faster (the slipping wheels) to the plates that rotate slower (the wheels with the best traction). This no-maintenance system is simple, compact and virtually invisible in its operation. The system can distribute torque from a 50:50 torque split for maximum traction to mostly front or rear wheel drive. -------------------- Civic Si 2007 2.0l DOHC iVTEC
Acura TL 2006 3.2l SOHC VTEC |
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