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1 All-wheel drive
Introduction:
The so-called all-wheel drive, also known as four-wheel drive, front and rear wheels means the car has power. General use 4X4 or 4WD be said that if you see a car marked with the above words, it means that the vehicle has four-wheel drive capabilities.
This overall arrangement, since all wheels are driving wheels, attached full use of all the mass of the car, so the car has a large driving force and to overcome obstacles, the ability to prevent slipping. So, off-road vehicles in general have adopted this overall arrangement. Moreover, since the all-wheel drive car has a large driving force, good acceleration, since the 1980s a number of cars and car travel also have all-wheel drive, a so-called ldquo; sport utility vehicle (SUV) rdquo; , by many American young people, forming quot; 4WDquot; boom. However, all-wheel drive configuration complexity, high cost, fuel consumption when driving on the road is good, big tires and mechanical wear.
two forms:
all-wheel drive can be divided into two types: one is the full-time all-wheel drive, i.e., all the time are all-wheel drive; other one is the short-time all-wheel drive, it can cut off the power of a bridge, in order to reduce fuel consumption and wear, re-use all-wheel drive only when necessary.
in the past only with 4-wheel drive off-road vehicles, off-road vehicles in general, downstream of the transmission with the manual component device, called the front and rear axles of the tube with a drive axle member. Torque transmission output shaft through the component and, respectively, transmitted to the drive axle on the front and rear axles, then the torque is transmitted to the wheels through a drive axle. Now some cars also were using 4-wheel drive system, such as the Audi A4 quattro, the Outlander 4WD version. Now horsepower than the larger car, shifted the center of gravity during acceleration, the weight of the entire vehicle will move to the rear axle, causing the front axle buoyant. Front-wheel drive car even on a good roadIt will slip, 4-wheel drive can prevent this from happening. 4 the drive means
is a constant mesh car, increasing the viscous coupling, eliminating the need for manual component, automatic torque demand assignment in the front wheels. In normal road surface, the drive means 92 the percentage of four engine output torque distribution to the front wheels to the rear wheels 8 percentage distribution; on the slippery road surface, will be at least 40 percent machine engine output torque to the rear wheels; front wheel start to slip, front and rear wheel speed difference causes coupler immediately thickened mucus and lock coupler, such that the propeller shaft transmitting torque to the rear wheels only, until the front, the rear wheel rotation speed difference disappears automatically reply to the original drive form.
drive mode:
Currently, four wheel drive cars have been introduced computer control system, when the front wheel or rear-wheel drive car at any time in accordance with road surface condition power allocation before and after the feedback information wheels, becomes a 4-wheel drive. 4-wheel drive can be broken down into 4 driving modes: full-time drive (Full-Time), driver (Part-Time) when and timely drive (Real-Time) and the time and / timely mixed driving.
Full drive:
(Full-Time): the vehicle is always maintained before and after the 4-wheel drive mode, with the engine output torque is set at 50:50 on the front and rear wheels. Full-time drivers with good driving control and tracking of travel, the disadvantage is more waste oil, the economy is bad.
And when the driving:
(Part-Time): According to the road condition, turning on or off the splitter be varied by the driver driven by two or four-wheel drive mode, which is generally off-road vehicle or 4WD SUV most common drive mode.
advantage is to select a driving mode according to the actual situation, more economical; disadvantage is that the mechanical structure is complicated, the driver should have some experience to master switching timing.
timely drive:
(Real-Time): using timely driven (Real-Time) of the vehicle, which drive mode selector which is controlled by the PC, normal road general rear-wheel drive, If a poor road surface or wheel slip, the computer will automaticallyAnd immediately detected engine output torque assigned to the other two, the state is switched to the 4-wheel drive, simple operation. The disadvantage is that the computer immediate reaction is slow, the lack of driving pleasure.
Principle:
AWD car four-wheel drive system is actually driving force distribution control method, which uses a computer and the continuous improvement of various sensors, continuously determines tire adhesion and dynamic driving intention of the driver of the ground, and actively control the differential state of the automotive differential, the driving force of each wheel balancing, optimizing the performance of the car.
A typical system consists of front and rear wheel AWD cars, sensors, electronic control unit, and a splitter unit for driving a hydraulic composition. Control principle of the control system, the front and rear wheels arranged in asking a wet multi-plate clutch, the vehicle is in motion, computer-controlled hydraulic system using oil pressure, the traveling state of the vehicle to adapt to the driving torque distribution to the front and rear wheels up.
when driving automobiles, computers using the following three kinds of sensor detected vehicle traveling state continues, i.e., the wheel speed sensor 4, the left and right longitudinal vehicle acceleration sensor, an engine speed sensor. Further, with the steering wheel angle sensor, an accelerator pedal opening sensor constantly determines the driver’s driving intention, integrated by predetermined control program. In the AWD systems, front-rear wheel power distribution affects the vehicle driving performance. The front and rear wheels when the vehicle drive power distribution ratio to 0: 100, the steering performance and having high driving performance limit, when the driving force distribution ratio is 50:50, the stability is improved, but the performance and limits the steering with performance degrades. Between the steering performance, stability and ultimate performance to be obtained with good balance, it is necessary to determine the optimal front-rear driving force distribution coefficient, over the distribution coefficients vary according to different road surface, considered in the road pavement allows powerful acceleration the load transfer, to distribute a large driving force to the rear wheels is appropriate. However, in slippery road, when a large driving force distribution to the rear wheels, it will cause oversteer.