By their design, four independent suspension arms correspond to the front axle Audi A8. Due to the arrangement of four transverse levers, it is achieved that the influence of the drive is practically not felt in the control.
The three figures show where the - imaginary - left axis is located (arrow) at different wheel turns. Especially important is the position of the axle with steered wheels in the neutral position of the wheels. In this case, it is almost exactly in the center of the wheel.
The front-wheel drive Audi A4 has a so-called linkage rear axle. It basically consists of two tubular trailing arms that are connected by a torsionally plastic V-profile.
The Audi A4 quattro has a so-called double wishbone axle at the rear, in the center of which is the rear-wheel drive.
Front axle
With four independent front axle suspension arms in Audi, each wheel is controlled by four aluminum wishbones. The two upper transverse arms are fixed to the structure by means of rubber-metal bearings and are connected to the wheel support by ball heads with reduced friction. Both lower wishbones (one by one - carrier and driving levers) mounted on the subframe by means of a rubber-metal bearing, and each of them is connected to the wheel support with a ball head with reduced friction. A gas-filled shock absorber and a coil spring are connected to a suspension strut. The suspension strut does not take over the task of steering the wheels. An additional spring made of cellular polyurethane, in combination with a buffer spring in the shock absorbers, provides a comfortable interception of strong body vibrations on the front axle.
The independent suspension arms are located in such a way that they are largely smoothed out by raising the front of the car at the beginning of the movement and lowering it during braking. To reduce the longitudinal movements of the axle, the inner bearing of the drive arm is hydraulically damped. A tubular stabilizer bar fixed to the subframe, which is connected to the carrier arm via a connecting rod, reduces body roll when cornering.
Through the use of aluminum in the various axle parts and structural configuration, and through the use of high strength materials in the springs, the costly suspension structure could be kept low in weight. The positive properties of the front suspension with four independent suspension arms form a block with steerable wheels that runs almost vertically through the center of the wheel. By steerable wheel block, the engineer means the intended line around which the wheel moves when the rudder is moved. A steerable wheel unit close to the wheel center has great advantages, since in front-wheel drive, in addition to the forces applied to turn the wheel, the driving forces are also transmitted, which are again applied in the center of the wheel. The shorter the distance between the steering axle and the wheel centre, the shorter the arm and the less interference there is in steering.
With a front axle with four independent suspension arms in the A4, the influence of drive forces on steering is almost eliminated, since the distance between the axle with steerable wheels and the center of the wheel is very small - it is only 10 mm.
Rear axle in front-wheel drive vehicles
A known linkage rear axle consists of two flexurally rigid and torsionally rigid tubular trailing arms connected by a torsionally plastic, flexurally rigid V-shaped transverse profile. An additional stabilizer is welded to the ends of the trailing arms. This results in a high lateral stiffness of the axle and outstanding track stability. This rear axle needs to be re-adjusted in many details. At the same time, the priority goal is to increase comfort and stability of movement, reduce noise and reduce weight.
The design of the rear axle with mated levers makes it behave like a rear axle with trailing arms when both wheels are simultaneously compressed, and when the spring suspension telescopic strut is alternately compressed, it behaves like a diagonal lever of an independent suspension of the rear axle.
Rear axle of Quattro models
The Audi A4 quattro models are equipped with double wishbones for independent wheel suspension, including elastic supports for the rear wheels. Upper wishbones located above the wheels provide the possibility of building a large trunk.
The guiding wheel suspension system is provided by two triangular wishbones with an additional rod link on each side. Shock absorbers and coil springs are combined to save space in the suspension struts.
Brake system with ABS
The standard fifth-generation anti-lock system with electronic brake force distribution EBV ensures high braking stability in a wide range of driving conditions and eliminates the need for a mechanical brake force regulator. Since the ABS electronic control has a much more sensitive response than the mechanical brake force regulator, a much larger adjustment range is used. In order to ensure driving stability also when braking when cornering, the proportion of braking force on the rear axle must be reduced. EBV detects by means of the ABS speed sensors whether the Audi A4 is driving straight ahead or is cornering. When cornering, the brake pressure on the rear wheels is reduced. Thanks to this, the rear wheels can give maximum lateral force.
Electronic differential lock EDS
EDS is installed as standard on all A4 quattro models and is included in the special package of front-wheel drive models with four-cylinder engines with a displacement of 1.8 liters.
With the electronic differential lock EDS in all-wheel drive models, it is a targeted friction clutch of up to three wheels, in front-wheel drive vehicles it is one wheel. This ensures maximum traction when starting off under extreme conditions, such as slippery roads.
Electronic wheel slip control ASR
In front-wheel drive A4 models with 2.6 and 2.8 liter V6 engines, electronic wheel slip control ASR is offered as a special equipment for improving traction, which also has all the functions of EDS. While the EDS includes a targeted frictional clutch to improve traction, the electronic wheel slip control ASR provides additional intervention in the engine management when required. The point of electronic wheel slip control is to avoid front wheel spin no matter how much throttle the driver gives.
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