Self-Study Programme 289 Adaptive cruise control in the Audi A8.pdf

Service.

Adaptive cruise control in the Audi A8

Design and operation

Self Study Programme 289

For internal use only

Adaptive cruise control is a new system

designed to assist drivers and offers a much

wider range of functions than the conven-

tional Tempomat.

Driver convenience is considerably enhanced,

as fewer accelerator and brake pedal opera-

tions are required. Speed restrictions and

safe distances are reliably observed and the

flow of traffic thus better regulated.

Contents

Page

Introduction

Summary of adaptive cruise control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Limits of adaptive cruise control system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Requirements for adaptive cruise control operation. . . . . . . . . . . . . . . . . . . . . . . . 5

Radar basic principles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

System components

General view of vehicle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Distance control sender G259 and distance

control unit J428 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16

Cover for distance control sender . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

System functions

Operation and driver information concept. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

System statuses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Operation and driver information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

System settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Fault displays/deactivation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Mode of operation

General mode of operation of adaptive cruise control . . . . . . . . . . . . . . . . . . . . . 32

Status diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Data flow

System layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36

CAN data exchange . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38

Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Service

Setting of distance control sender . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Special tools. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

The Self Study Programme contains information on design features

and functions.

Attention!

Note!

New!

The Self Study Programme is not intended as a Workshop Manual.

Values given are only intended to help explain the subject matter

and relate to the software version applicable when the SSP was

compiled.

Use should always be made of the latest technical publications

when performing maintenance and repair work.

Introduction

Summary of adaptive cruise control

The basic adaptive cruise control function is

to maintain a driver-selectable distance from

the vehicle in front.

Adaptive cruise control thus represents the

logical next step on from the original cruise

control system.

The distance from and speed of the vehicle in

front are determined by a radar sensor. If the

distance is greater than desired, the vehicle is

accelerated until the required speed input by

the driver is achieved.

If the distance is less than desired, the vehicle

is decelerated by reducing power, changing

gear and if necessary applying the brakes. In

the interests of ride comfort, maximum possi-

ble braking is restricted to approx. 25 % of the

maximum deceleration potential of the brake

system (full braking).

The control action is designed to assist the

driver and thus indirectly contributes to

greater road safety.

In certain traffic situations, active braking by

the driver may still be necessary.

289_002

Limits of adaptive cruise control system

– Adaptive cruise control is designed to

assist the driver and is not a safety system.

It is not a fully autonomous driving system.

– Radar operation is impaired by rain, spray

and slush.

– Tight bends may restrict operation on

account of the limited radar detection

range.

– Adaptive cruise control provides regulation

in a speed range of 30-200 km/h.

– Adaptive cruise control does not react to

stationary objects.

Requirements for adaptive cruise control operation

The following essential information is required for control purposes:

Distance from vehicle in front

289_050

Speed of vehicle in front

289_051

Position of vehicle in front

289_052

If there are several vehicles within the radar detection range at the same time,

the above information is used to select the vehicle to which control is to be related.

289_053

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