Definitions of Tractor Truck 6x4

A 6×4 or 6×4 is a vehicle with three axles, with the drivetrain sending power to the two wheel ends of two of them.It is a form of four-wheel drive but not all-wheel drive.In larger countries such as the US and Australia, it is the most common form of drivetrain for semi-tractors and heavy-duty fixed-chassis cargo trucks; in Europe,4×2 and 6×2 variants are more common.Four-wheel drive, also known as 4×4 (“four by four”) or 4WD, refers to a two-axle vehicle drivetrain that is capable of delivering torque to all wheels simultaneously.It can be full-time or on-demand, and is usually linked through a transfer case, providing an extra output drive shaft and, in many cases, an extra gear range.Four-wheel-drive vehicles that provide torque to both axles are known as "all-wheel drive" (AWD).However, "four-wheel drive" generally refers to a specific set of components and features, as well as intended off-road applications, which generally conforms to modern use of the term.

Definitions

Four-wheel drive systems are developed in many different markets and used on many different vehicle platforms.There is no universally accepted set of terms to describe the various architectures and functions.Terms used by different manufacturers often reflect marketing rather than engineering considerations or significant technical differences between systems.SAE International's standard J1952 recommends only the term "all-wheel drive" with an additional subcategory covering all types of AWD/4WD/4x4 systems on production vehicles.

Design

When the vehicle is going around a curve, the two wheels that are fixed on the same axle (but on opposite axle ends) need to turn at different speeds.The reason is that the wheels on the inside of the curve need to travel a shorter distance in the same amount of time than the wheels on the opposite side.However, if both wheels are connected to the same drive shaft, then they always have to spin at the same relative speed. When cornering, this either forces one of the wheels to slip (if possible) to balance the apparent distance covered, or creates uncomfortable and mechanically stressful wheel hop.To prevent this, the wheels can turn at different speeds using mechanical or hydraulic differentials.This allows one driveshaft to independently drive two output shafts, the ones that go from the differential to the wheels, at different speeds.A differential does this by evenly distributing angular force (in the form of torque) while distributing angular velocity (rotational speed) such that the average of the two output shafts is equal to the average of the differential ring gear.When power is delivered, each axle needs a differential to split the power between the left and right. When power is distributed to all four wheels, a third or "center" differential can be used to distribute power between the front and rear axles.

The system described handles very well, as it adapts to the various forces of motion and distributes them evenly and smoothly, making slippage less likely.However, once it does slip, recovery is difficult.For example, if the left front wheel of a 4WD vehicle spins on icy roads, the spinning wheel will spin faster than the other wheels because that wheel has less traction.Since the differential applies equal torque to each half shaft, the other wheels get less power, even if they have good traction.This problem can occur in both 2WD and 4WD vehicles whenever the driven wheel is placed on a surface with little traction or lifted off the ground.Simple design suitable for 2WD vehicles.This is even more unacceptable for a 4WD vehicle, which has twice as many wheels that lose traction, increasing the likelihood of this happening.4WD vehicles may also be more likely to drive on surfaces with reduced traction.However, since torque is distributed to four wheels rather than two, each wheel receives approximately half the torque of a 2WD vehicle, reducing the possibility of wheel spin.