Quando le auto hanno guadagnato popolarità per la prima volta, la trazione posteriore (RWD) era il metodo di propulsione preferito. È anche capitato di essere l'unica scelta. Ma la trazione anteriore (FWD) in seguito ha conquistato il mercato principale grazie al suo risparmio di carburante frugale, alla trazione più affidabile, all'imballaggio compatto e alla stabilità.
Oggi, la preferenza si sta spostando ancora una volta su AWD e 4WD a causa della domanda dei consumatori di SUV e CUV. Nonostante mostrino un minore consumo di carburante rispetto alle auto FWD, AWD e 4WD beneficiano di una maggiore trazione e controllo, ma i due possono spesso essere scambiati l'uno per l'altro a causa delle loro somiglianze.
Le moderne tecnologie hanno reso difficile differenziarsi l'un l'altro per la maggior parte, ma comprendere la differenza può significare la differenza tra tornare a casa dopo un lungo viaggio attraverso Moab o chiamare il calvario per salvarti.
Non preoccuparti, come The Drive Il team informativo dedicato di è qui per districare i fili e spiegare tutte le differenze tra AWD e 4WD.
I sistemi AWD e 4WD utilizzano parti diverse. Ecco una rapida suddivisione dei termini, dei nomi e dei componenti correlati.
Un veicolo a trazione integrale utilizza tipicamente un motore, un convertitore di coppia o una frizione, una trasmissione, un differenziale centrale, un pacco frizione, un differenziale posteriore e un differenziale anteriore. Tuttavia, esistono numerosi tipi di sistemi AWD che utilizzano tecnologie uniche, come l'ibrido elettrico e le attrezzature.
Un veicolo a quattro ruote motrici utilizza un motore, un convertitore di coppia o una frizione, una trasmissione, un ripartitore di coppia, un differenziale posteriore e un differenziale anteriore.
Un differenziale è un gruppo di ingranaggi meccanici o elettronici all'interno di una trasmissione che divide la coppia in due alberi o assi di uscita che possono funzionare a velocità diverse. Può anche essere bloccato insieme.
Ad esempio, un differenziale posteriore, collegato all'albero di trasmissione posteriore, consente alle ruote posteriori sinistra e destra di girare a velocità diverse. Un differenziale centrale consente agli alberi di trasmissione anteriore e posteriore di funzionare a velocità diverse, ma offre la possibilità di bloccarli insieme.
Esistono numerosi tipi di differenziali, i più comuni sono aperti, bloccabili o a slittamento limitato.
Sui veicoli AWD e 4WD, una scatola di trasferimento è un meccanismo all'interno di una trasmissione collegata a una trasmissione, un albero di trasmissione anteriore e un albero di trasmissione posteriore. In genere utilizzando ingranaggi, idraulica o una catena all'interno dell'alloggiamento della scatola di trasferimento, la scatola di trasferimento trasmetterà la potenza dalla trasmissione agli alberi di trasmissione per alimentare gli assali anteriore e posteriore consentendo alle ruote anteriori e posteriori di muoversi a velocità diverse.
Sui veicoli 4WD, la scatola di trasferimento può essere azionata manualmente da una leva, un quadrante, un interruttore o un pulsante per inserire diverse impostazioni di marcia. Sui veicoli AWD, il ripartitore di coppia funziona automaticamente senza input.
Un sistema di trazione integrale fornisce potenza a tutte e quattro le ruote del veicolo contemporaneamente per tutto il tempo, ma la quantità di coppia che va a ciascuna ruota varia. A seconda del sistema, una trazione integrale funzionerà normalmente con una polarizzazione anteriore o posteriore. Ad esempio, la Subaru Outback per impostazione predefinita invia l'80 percento della sua coppia all'anteriore e il 20 percento al posteriore. Tuttavia, quando è necessaria la trazione su una o tutte le altre ruote, il sistema incanala la potenza sull'asse che richiede aiuto.
I sistemi a trazione integrale utilizzano un tipo di differenziale centrale (ce ne sono molti) che consente alle ruote anteriori e posteriori di funzionare a velocità diverse. In alcuni esempi, come la Ford Edge, il sistema di trazione integrale consente di disaccoppiare completamente la parte posteriore per consentire la trazione anteriore al 100%.
Trazione integrale con polarizzazione anteriore :Il veicolo devia più coppia alle ruote anteriori rispetto a quelle posteriori.
Trazione integrale posteriore :Il veicolo devia più coppia alle ruote posteriori rispetto alle ruote posteriori.
Lo scopo della trazione integrale è mantenere una trazione ottimale quando viene selezionata manualmente. Un veicolo ha quattro ruote motrici quando gli alberi di trasmissione anteriore e posteriore possono essere bloccati insieme per muoversi alla stessa velocità e inviare la stessa quantità di coppia a tutte e quattro le ruote. La trazione integrale è in genere destinata all'uso fuoristrada e su superfici estremamente scivolose.
Un'auto con 4WD part-time funziona in 2WD a meno che l'auto non venga commutata manualmente o automaticamente elettronicamente su 4WD. Un albero di trasmissione è permanentemente collegato all'alimentazione, mentre l'altro può essere collegato quando necessario. Il 4WD part-time è spesso attivato con un pulsante, un quadrante, una leva o un interruttore all'interno della cabina del veicolo. Questo è il tipo più tradizionale di 4WD e si trova spesso su veicoli 4x4 come SUV e camion simili a Jeep.
Quando un veicolo è in vera trazione integrale, non può guidare normalmente su strade normali perché gli assi anteriore e posteriore non possono funzionare a velocità diverse. Se tentata, l'auto potrebbe iniziare a bloccarsi o rabbrividire, un fenomeno noto come "salto del corvo". Ciò potrebbe danneggiare il veicolo.
Questo è un tipo diverso di AWD part-time. Un'auto con 4 ruote motrici su richiesta funziona a due ruote motrici per impostazione predefinita, ma chiama automaticamente le altre ruote quando è necessaria la trazione.
Un'auto con 4WD a tempo pieno, a volte indicata come 4WD permanente o Auto/Automatic 4WD, invia ugualmente il 25 percento della potenza a ciascuna ruota il 100 percento delle volte. Tuttavia, un pacco frizione o un differenziale centrale consente agli alberi di trasmissione anteriore e posteriore di muoversi a velocità diverse.
Sui veicoli 4x4, in genere è presente un quadrante, una leva, un interruttore o una serie di pulsanti con varie configurazioni di guida. Ciascuna opzione deve essere utilizzata solo nelle specifiche circostanze previste, altrimenti il conducente rischia di danneggiare il veicolo. Di seguito spieghiamo come utilizzare 2H, 4H e 4L.
2H è l'abbreviazione di Two High. Ciò significa che due ruote sono impegnate, tipicamente le ruote posteriori, nella gamma alta. I conducenti dovrebbero utilizzare 2H in condizioni di guida normali su superfici dure.
4H is an abbreviation for Four High. This means four wheels are engaged in a high range gear ratio. Drivers should use 4H when they need extra traction, such as driving on snow or rocky trails, at average speeds of approximately 30-50 mph (check your vehicle’s manual for exact limitations and specifics).
4L is an abbreviation for Four Low. This means four wheels are engaged in a low range gear ratio. Drivers should use 4L in circumstances when maximum traction and torque is needed, such as in deep sand, mud, or snow. It is also suitable for climbing or descending steep inclines with unstable surfaces. 4L allows for slow controlled speed typically less than 15 mph and greatly helps during off-road crawling.
Electric and hybrid AWD systems operate much differently than AWD systems on traditional gas-powered vehicles. On EVs, there’s no engine, transfer cases do not apply, and mechanical linkages are replaced with computer wires. To operate in AWD, the EV must use electric motors to power both the front and rear axles and all four wheels. Here are a few examples of different types of electric all-wheel-drive setups.
The car features two electric motors. One is located on the front axle and the other is located on the rear axle. Differentials on those axles allow the wheels to spin at different speeds. Teslas call this Dual Motor AWD.
The upcoming electric GMC Hummer is rumored to have three electric motors, likely with one upfront and two on the rear. With two motors at the back, the vehicle could control of each of the rear wheels.
Not all electric cars are built the same. Rather than mounting the electric motors directly onto the axles, some electric vehicles use four independent motors built into the hubs of each wheel. Once again, computers can control how much power, negative or positive torque, and slippage occurs at each wheel.
Examples of AWD electric cars :
Hybrids combine a gas motor with some type of electric assistance. Full hybrids pair gas motors with electric motors. All-wheel-drive hybrids typically use the gas engine to power one axle and an electric motor to power the other to achieve control over all four wheels. In some cases such as the Acura NSX, however, a system will use a gas engine and multiple electric motors.
Examples of AWD hybrid cars:
This depends on how much snow is present, as well as the purpose and mission of the drive. Driving down a snowy highway? Think AWD. Driving over a snow-covered mud field? Think 4WD. Read more in How to Drive in the Snow.
Typically, yes, but some modern systems allow the driver to deactivate AWD to use two-wheel drive.
This depends on how the vehicle will be used and the climate it will be driven in.
This is dependent on the buyer’s needs, locale, and budget. The answer is not always yes.
Yes and no, AWD improves traction in slippery conditions, including on ice. But it only helps propel you forward. It won’t help you corner or stop.
Yes, AWD improves traction in slippery conditions, including when it rains.
AWD adds cost, reduces gas mileage, and has complex components that could falter.
Yes, for two reasons:AWD systems require more energy to power more wheels and add weight due to their more complex makeups.
Technically, yes, but traditionally, no. Select systems allow for the front or rear driveshaft to be fully disconnected.
With the proliferation of AWD throughout the industry and its manufacturers’ lineups, each company has slightly different technologies and uses slightly different marketing terms to describe the systems in its vehicles. Here are some of the most common systems and what they mean, as described by the manufacturers themselves.
“SH-AWD uses dynamic torque vectoring to provide more accurate and predictable handling performance in all road conditions.
Up to 70% of engine torque can be sent to the rear wheels as needed, with up to 100% of that torque apportioned to either the left or right wheels. Further, today's SH-AWD can overdrive the outside rear wheels by up to 2.7 percent, creating additional rotational speed that helps "pull" the car through the turn with increased grip and cornering accuracy.”
“Fundamentally, Quattro all-wheel drive for Audi medium and large cars works similarly to previous systems with three differentials. It is mechanically as well as electronically activated, and it distributes torque to wheels based on steering angle sensors, traction and stability control, yaw sensors (measuring how weight shifts left or right around its center of gravity) and wheel sensors.
Default power distribution is 40:60 front to rear, with up to 70% of power to the front wheels or up to 85% of a vehicle’s power to the rear. Additionally, electronic wheel-selective torque control can assist traction across each axle through individual wheel braking. Torque control is provided by an intelligent software function of the stability control.
In S and RS models, the rear Sport differential has the ability to overdrive the inside or outside wheel, or even send almost all power from one rear wheel to the other, in hard cornering, creating more neutral handling. This is known as torque vectoring.”
“With BMW xDrive, intelligent Dynamic Stability Control (DSC) sensors detect the slightest loss of grip, and using an electronically controlled multi-disc clutch, divert the power to the set of wheels that have the best traction, reacting much faster than traditional, hydraulically operated systems. BMW xDrive is a fully variable system that can send almost 100% of the power to either axle, offering instantaneous and effective transfer of engine power.”
“The HTRAC AWD system was developed as a multi-mode system, providing an electronic, variable-torque-split clutch with active torque control between the front and rear axles. The driver-selectable HTRAC Normal, Sport and Smart modes help provide confident control in all weather conditions. The Sport setting gives a more agile feel by sending more available torque to the rear wheels, for a sporty dynamic feel when desired.”
“Available active on-demand all-wheel drive helps provide enhanced driving performance by actively distributing torque between the front and rear wheels depending on road conditions and driver input. The system utilizes electro-hydraulic AWD coupling to precisely activate the multi-plate clutch plate, constantly redistributing the amount of power transferred to the front and rear wheels.
During normal driving, power is distributed according to the drive mode selected. Eco and Smart modes deliver 100 percent power to the front wheels. Comfort and Snow modes deliver 80 percent power to the front wheels and 20 percent to rear. Sport mode splits the power 65-35 percent between front and back. Lock mode delivers power evenly to all four wheels.”
“Mazda’s advanced i-ACTIV AWD system uses sophisticated real-time vehicle dynamics modeling to help predict the available grip at each tire and sends torque to the wheels that can use it best. The system comes into play before the front wheels lose grip, engaging the rear wheels to deliver traction where and when it counts.”
“At its core, the 4MATIC system feeds power to the front axles through a transfer case in the transmission, while a limited-slip differential provides a balance between front and rear. Sensors manage the torque demands of each wheel, resulting in greater traction and acceleration.”
“The compact and weight-optimized all-wheel-drive consists of a power take-off on the front axle transmission, a two-section propeller shaft, and rear axle transmission with an electro-hydraulically regulated hang-on clutch. The intelligent controller of the ALL4 system is interconnected with the Dynamic Stability Control (DSC) and constantly calculates the ideal power distribution ratio between the front and rear wheels. This means that the outstanding engine power is always channeled to the place where it can be most effectively and efficiently translated into driving fun.
In normal driving conditions with the DSC activated, it transmits the drive torque in a brand-typical manner to the front wheels. But if the DSC controller detects a danger of slip on the front wheels, the hang-on clutch will transfer the drive torque to the rear wheels with the aid of an electrohydraulic pump.”
“The new lightweight S-AWC electronically distributes driving torque between the front and rear wheels, along with Active Yaw Control (AYC). The new system offers enhanced tracking performance through cornering, and improves vehicle stability and steering response through the use of a yaw control sensor that precisely controls vehicle yaw rate by applying brake pressure on an inside wheel to pull the vehicle back into line for improved vehicle stability and dynamic composure.
Additionally, a driver-selectable push-button allows drivers to select from four distinct driving modes – the standard Normal mode, enhanced feel in slippery conditions with the Snow setting, maximum control in Lock, and an AWC Eco mode that maximizes fuel efficiency by prioritizing drive to the front wheels and still switches in a split-second to all-wheel drive when multiple sensors determine its necessity.”
“The principle philosophy for any Porsche with active PTM is the same:Enhanced driving dynamics, improved driving safety, and increased traction for an even sportier driving experience. It distributes drive torque between the front and rear axles actively and very quickly.
Permanent monitoring of driving status means PTM can be actively pre-set to respond to different driving situations:For example, sensors continuously monitor the speeds of all four wheels, the longitudinal and lateral acceleration of the vehicle, as well as the steering angle. By evaluating all sensor data, it is possible to adjust the distribution of propulsion force to the front axle as quickly and effectively as possible.”
“The Subaru Symmetrical AWD system is designed to optimize both traction and balance. The entire system lies along the centerline of the vehicle, balancing weight distribution between the two sides to help provide optimal performance and control. The system sends power to all wheels simultaneously for maximum traction and acceleration. In slippery conditions, that power is actively distributed to the wheels with the best traction.”
“The Camry and Avalon AWD system can direct up to 50 percent of engine torque to the rear wheels, in response to acceleration from a start or slippage at the front wheels. Notably, when AWD isn’t needed, such as on long highway stretches, the electromagnetically controlled coupling on the front of the rear-drive axle can disengage the propeller shaft from the differential to prioritize fuel efficiency. The AWD is designed to re-engage in an instant when needed.”
“On all MQB (modular transverse toolkit) models with the 4MOTION all-wheel drive system, power is distributed between front and rear axles on an infinitely variable basis by a multi-plate clutch. Normally, power is mainly transmitted to the front axle, which saves energy. However, in the event of an impending loss of traction, the rear axle is activated in a fraction of a second. This is why 4MOTION is considered to be a permanently engaged four-wheel-drive system.
The distribution of power to all four wheels becomes active before wheelspin occurs. A loss of traction is therefore virtually excluded. There is no fixed distribution of power. Power distribution is continuously adjusted to actual driving conditions. However, should any wheel slip, power is immediately transmitted to the wheels where it is needed.”
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