Get Running gear -> Brake system Guide for Audi RS E Tron Gt 4 Door First Generation (2021-2026)

The operating logic from vehicles with conventional drive systems has been used (as on the Audi e-tron):

When the (-) paddle lever is operated, the vehicle is decelerated by shifting down in overrun mode. The Audi e-tron GT decelerates

when the electric motor recuperates energy while it is in generator mode. The driver can increase/reduce the level of recuperation

in stages using the (+) or (-) paddle lever respectively. The menu option for manual recuperation must be set in the MMI to do this.

Two recuperation levels can be selected.

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Four-wheel steering

Four-wheel steering was first used in the Audi Q7 (type 4M). Four-wheel steering is available as optional equipment for the Audi e-

tron GT.

In terms of design (components), functions and servicing requirements, the four-wheel steering system corresponds to that used

on the Audi Q7 (type 4M).

Reference

For further information, please refer to (refer to chapter “Chassis with air suspension and electronic damper control

(adaptive air suspension)”) in SSP 633 “Audi Q7 (type 4M) Chassis.”

The rear axle steering rack also works in the same way as the one on the Audi Q7. The electric motor drives the spindle nut via the

drive belt. The rotational movement of the spindle nut is converted to linear movement of the spindle. The connected track rods

transmit the linear motion to the hub carriers and the wheels are steered in the same direction to the right or left (depending on

the direction of rotation of the electric motor). The system is self-locking due to the transmission ratio and the trapezoidal thread

of the spindle and the spindle nut.

The maximum wheel steering angle on the rear axle is 2.8° (approx. 5° on Audi A8 (type 4N) and Audi Q7 (type 4M)).

Brake system

Overview

Newly developed brake systems are used on the Audi e-tron GT and the RS model. The Audi e-tron GT has conventional brake discs

as standard equipment in conjunction with 6-piston fixed caliper brakes on the front axle and 4-piston fixed caliper brakes on the

rear axle. Brake discs with a tungsten carbide coating (PSCB) are being used on an Audi model for the first time. This brake system

is standard equipment for the Audi RS e-tron GT and is available as optional equipment for the Audi e-tron GT.

Ceramic brakes are available as optional equipment for both e-tron GT models. The brake calipers for the PSCB and ceramic brake

system are available in different colours. The front and rear brakes have separate brake circuits. About 65 % of the braking force is

transmitted at the front axle and about 35 % at the rear axle.

For the first time on an Audi model, the electromechanical parking brake on the rear axle is a drum brake. The brake drum is

formed by the hub of the brake disc. As on other Audi models, the regulating software for the parking brake is in the ESC control

unit.

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To ensure that the requirements that the electric drive system makes of the brake system (brake blending, recuperation etc.) are

met, an electromechanical brake servo is fitted on the Audi e-tron GT in conjunction with a powerful ESC system of generation 9.2.

These systems make autonomous braking maneuvers independent of the driver possible.

The components and dimensions of the brake system may vary from those shown in the overview in some markets in order to con-

form to country-specific regulations.

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Brake system

Type of brakes

Front axle

Rear axle

Conventional brake system

6-piston fixed caliper brakes

4-piston fixed caliper brakes

Standard equipment for Audi e-tron GT

Cast iron brake discs

360 x 30 mm

358 x 28 mm

Steel brake with tungsten carbide coating

6-piston fixed caliper brakes

4-piston fixed caliper brakes

Standard equipment for Audi RS e-tron GT,

optional equipment for Audi e-tron GT

Brake discs with tungsten carbide coating Brake discs with tungsten carbide coating

410 x 38 mm

365 x 28 mm

Special brake pads

Ceramic brake system

10-piston fixed caliper brakes

4-piston fixed caliper brakes

Optional equipment for both models

Ceramic brake discs

420 x 40 mm

Ceramic brake discs

410 x 32 mm

Special brake pads

All four wheels are equipped with brake pad wear detection.

Steel brake with tungsten carbide coating

This brake system is being used on an Audi model for the first time. It was developed by Porsche AG and has already been success-

fully used on some Porsche models. The main difference compared to conventional brake systems is the coating on the friction sur-

faces of the brake discs, which are cast iron composite brake discs. The friction surfaces have two coatings. First, an galvanic nickel

coating of approx. 10 micrometres is applied to the cast iron base plate. This coating is designed to inhibit cracks and provide cor-

rosion resistance. The actual tungsten carbide friction coating of approx. 40 - 200 micrometres is applied to the nickel layer. Tung-

sten carbide is a ceramic material which is added to many different hard metals. It is mainly used in toolmaking for components

and tools which need to be particularly wear-resistant.

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The following characteristics of the brake discs single them out in particular:

›

High corrosion resistance

Because of the high level of recuperation under braking, the hydraulic service brakes are used significantly less than on vehicles

with conventional drive systems. As a result, corrosion resistance is very important, both functionally and from the perspective

of the visual impression given by the vehicle.

›

Large wear resistance

Compared to a conventional brake disc, the service life is approx. 30 % longer.

Better performance

Thanks to the friction torque being built up quickly, the response is better than that of a conventional brake disc. The friction

remains more stable during a braking procedure. As a result, the feared brake fade (a decrease in the braking efficiency at very

high brake temperatures) is reduced significantly.

Specially developed brake pads have been used to be able to make the best use of the positive characteristics of the brake discs.

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Steel brake with tungsten carbide coating – 6-piston fixed

caliper on front axle

Ceramic brake with 10-piston fixed caliper on front axle

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Electromechanical brake servo

Overview

With its electric drive, the normal requirements for achieving the braking function both without recuperation and at different levels

of recuperation also apply to the Audi e-tron GT. Based on previous experience, the driver expects a braking effect which corre-

sponds to the pressure placed on the brake pedal. Depending on the recuperation taking place and the braking power being provi-

ded by the electric drive motor(s), the “remaining” braking effect must be provided by the hydraulic brake system. This is not possi-

ble with a conventional pneumatic brake servo with a fixed ratio of pedal force to piston rod force of the brake master cylinder.

These complex requirements can only be met by an electromechanical brake servo.

The electromechanical brake servo is able to induce brake pressure independently of the driver. When recuperation is taking place,

the hydraulic brake pressure can be restricted to the level required. Alternatively, brake pressure can be generated actively without

being initiated by the driver if other systems request it (e.g. adaptive cruise assist/ACC).

Design and function

This complex module consists of brake servo control unit J539, a two-stage gear drive, an electric motor to drive the gearing, a

distance sensor and the coupling rod which connects to the brake pedal.

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Excepting the gearing technology used, the design and functions of the second generation electromechanical brake servo corre-

spond to those of the systems already in use on other Audi models.

Reference

Further information on how an electromechanical brake servo works can be found in Service TV programme 0413 TV

"A3 Sportback e-tron - Electromechanical Brake Servo".

The brake servo on the Audi e-tron GT works on the basis of a two-stage gear drive driven by an electric motor. The output of the

gear drive is a spindle shaft. When the brake servo is active, the rotational movement of the spindle shaft is converted into a longi-

tudinal movement of the spindle nut on the shaft. The spindle nut is in contact with a thrust piece which moves longitudinally and

passes the force on to a reaction plate. The force initiated by the driver via the brake pedal is also applied to this reaction plate by

the piston rod. The reaction plate operates the piston rod of the brake master cylinder, thereby generating brake pressure. The two

forces work independently of each other. The activation of the electric motor allows brake pressure to be generated even if the

driver does not press the brake pedal. A sensor designed on the principle of redundancy (brake pedal position sender G100, brake

pedal position sender 2 G836) detects the pedal travel initiated by the driver. In doing this, the control unit calculates the braking

torque desired by the driver and the amount of braking assistance required.

If other systems (e.g. deceleration request by the adaptive cruise assist) require that brake pressure be generated autonomously,

control unit J539 receives the message requesting implementation from ABS control unit J104.

Active accumulator VX70 used on the Audi Q7 e-tron and A3 e-tron vehicles is not fitted on the e-tron GT. The accumulator’s func-

tion is assumed by the ESC.

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Run-on – behaviour when terminal 15 is off

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Running gear -> Brake system for Your Audi RS E Tron Gt 4 Door First Generation (2021-2026)

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