VS-42 es Baugruppe/Group: 32 weltweit Datum/Date:

04/2003
32 01 03 (001)
Update: 02/2007

Active Steering

E60, E61, E63, E64, E70, E81, E87, E90, E91, E92, E93

Introduction

Active Steering is the most recent BMW development in the innovative steering systems sector.
Active Steering varies the steering gear ratio from direct to indirect and vice versa as a function of the vehicle's speed.
[System overview ...]
The benefits of Active Front Steering are:
- direct steering with no more than minimal movements of the steering wheel at the low end of the speed range
- More indirect steering at higher speeds in conjunction with yaw-rate control
Active Steering, including Servotronic, is available as an option (option 217).
Active Steering gives the vehicle an even sportier character.
New for the E70 is the 3rd generation Active Steering:
- Yawing moment compensation has been fully integrated as a function in the Active Steering control unit
- Cumulative steering angle sensor discontinued
- Digital motor-position sensor
- Commissioning exclusively via service function in BMW diagnosis system
On the X5, Active Steering is available for the first time on an all-wheel drive vehicle.
In 03/2007 the actions described for the E70 will also be implemented on the BMW 5-Series. Other model series will
follow later.

Note: On vehicles without active steering.

Option 216 "Servotronic" isnot available without Active Steering.

Note: On BMW 3-Series not with trailer coupling.

Active Steering is not available in conjunction withoption 3AC "Trailer coupling with folding ball head".
SBT Active Steering E60, E61, E63, E64, E70, E81, E87, E90, E91, E92, E93 BMW AG - TIS 07.02.2008 16:13
Issue status (08/2007) Valid only until next DVD is issued Copyright Page - 1 -
 New for the BMW 3-Series was:
- Yaw moment compensation as additional function
- Output stages for the Servotronic valve and the ECO valve are integrated into the Active Steering control unit
- Only 1 DSC sensor (redundant)
New for the BMW 5 and 6-Series from 09/2005 was:
- Active Steering control unit taken from BMW 3-Series
- This allows the Servotronic valve and the ECO valve to be directly actuated by the Active Steering control unit
- Only 1 DSC sensor as on BMW 3-Series

Note: On BMW 5 and 6-Series vehicles without Active Steering from 09/2005.
With option 216 "Servotronic", the body gateway module (KGM) actuates the Servotronic valve.

A conventional steering system inevitably constitutes a compromise:

on the one hand, the steering cannot be too direct as otherwise it would be overly sensitive when the vehicle is
travelling at high speed. On the other hand it is practical to have much more direct steering for manoeuvring at low
speeds and for parking. The new Active Front Steering system is the ideal trade-off. The directness of the steering of a
vehicle fitted with AFS varies with speed.
This results in three major benefits:
- enhanced agility
- enhanced comfort
- enhanced safety

Enhanced agility
Up to about midway through the speed range (about 100 km/h), the directness of the steering means that the
driver perceives the vehicle as more agile and easier to handle. A driver who has to avoid an unexpected
obstacle, say, has much better control, plus significantly enhanced steering precision and less work at the steering
wheel. There is no loss in feedback from the road surface right through the steering wheel.
Enhanced comfort
Current BMW models need more than three full turns of the steering wheel in order for the wheels to describe the
arc from full lock in one direction to full lock in the other.
When the vehicle is travelling at low speed, Active Steering reduces this to less than two full turns of the steering
wheel from lock to lock.
The advantage: The driver's task is easier when turning corners in city traffic or when manoeuvring into parking
slots where space is at a premium. On twisty roads such as mountain passes, moreover, the reduced steering
angle means that the driver's hands remain in the ideal position on the wheel. There is no longer any need for the
driver to feed the wheel through his or her hands, or to cross hands in a tight bend. The multifunction buttons on
the steering wheel and the paddles for the sequential manual transmission (SMG) are always perfectly positioned
relative to the driver's hands, regardless of the driving situation.
Enhanced safety
A completely different set of conditions applies when the vehicle is travelling at high speed:
With the assistance of indirect steering there is increased stability when travelling straight ahead at high speeds
(such as on motorways) compared with conventional steering. At the same time, the yaw-rate control is in the
position to stabilise the vehicle by correcting the steering angle when the vehicle is oversteering.
This supports the Dynamic Stability Control (DSC) function.
Like conventional systems, BMW's Active Front Steering features a steering column with a permanent connection
from the steering wheel to the front wheels. This mechanical link ensures the operability of the steering system at
all times, even in the event of disruption to or the complete failure of the system. The mechanical steering linkage,
what is more, is essential in sustaining the authentic "feeling of steering" as perceived by the driver. True steer-by-
wire systems are intrinsically unable to simulate the realism of this feedback from the road to the driver.

Brief description of components

SBT Active Steering E60, E61, E63, E64, E70, E81, E87, E90, E91, E92, E93 BMW AG - TIS 07.02.2008 16:13
Issue status (08/2007) Valid only until next DVD is issued Copyright Page - 2 -
 The sensors incorporated into the Active Front Steering system are:
- Motor-position sensor
The motor-position sensor registers the rotor position of the electric servomotor. The rotor position is
communicated to the control unit for Active Steering (AL control unit).
The 3rd generation Active Steering includes a digital motor-position sensor.
[more ...]
- Cumulative steering angle sensor and steering angle sensor
The cumulative steering angle sensor captures the steering angle that the Active Steering produces at the
steering box.
As far as its function is concerned, the cumulative steering angle sensor corresponds to the steering angle sensor
in a conventional steering system. The steering angle sensor in the steering column switch cluster registers the
angle to which the driver turns the steering wheel. Both signals are needed by the control unit for Active Steering
(AL control unit).
[more ...]
> From E70 (other model series to follow)
The cumulative steering angle sensor on the X5 is discontinued. Active Steering computes a "virtual" cumulative
steering angle. The virtual cumulative steering angle is derived from the following signals:
- Steering angle sensor signal
- Motor-position sensor signal
[more ...]
The steering angle sensor on the BMW 1 and 3-Series is an optical sensor.
From 09/2005, the BMW 5 and 6-Series also have an optical steering angle sensor.
[more ...]
- DSC sensor
> E60, E61, E63, E64 up to 09/2005:
2 DSC sensors transmit redundant signals capturing the rate of yaw (rotation about the vertical axis) and lateral
acceleration to the AL control unit via the chassis CAN (F-CAN).
[more ...]
> E70, E81, E87, E90, E91, E93, E93
Only 1 DSC sensor is needed for the Active Steering. This DSC sensor transmits redundant signals capturing the
rate of yaw and the lateral acceleration.
[more ...]
> E60, E61, E63, E64 from 09/2005
Only 1 DSC sensor is needed for the Active Steering.
This DSC sensor transmits redundant signals capturing the rate of yaw and the lateral acceleration.
The control units networked for the purposes of AFS are as follows:
- AL: Active Steering control unit
The AL control unit computes the nominal values for the electric servomotor of the planetary gearbox with override
function.
[more ...]
- SZL: Steering Column Switch
The Steering Column Switch provides the steering angle.
- SGM: Safety and gateway module
> E60, E61, E63, E64 up to 09/2005
The safety and gateway module (SGM) drives the ECO valve in the power-steering pump and the Servotronic
valve.
Moreover, the SGM forms the interface between the PT-CAN and the K-CAN (signals for instrument cluster).

SBT Active Steering E60, E61, E63, E64, E70, E81, E87, E90, E91, E92, E93 BMW AG - TIS 07.02.2008 16:13
Issue status (08/2007) Valid only until next DVD is issued Copyright Page - 3 -
 - KGM: Body gateway module
> E60, E61, E63, E64 from 09/2005
The body gateway module (KGM) forms the interface between the PT-CAN and the K-CAN (signals for instrument
cluster).
With option 216 "Servotronic", the KGM actuates the Servotronic valve.
- JBE: Junction box electronics
> E70, E81, E87, E90, E91, E92, E93
The junction box electronics (JBE) forms the interface between the PT-CAN and the K-CAN (signals for
instrument cluster).
Moreover, the AL control unit receives its power supply from the distributor in the junction box.
- DSC: Dynamic Stability Control
The DSC control unit and the AL control unit are interconnected by the F-CAN (chassis CAN). The signals
supplied by the DSC control unit include the road speed signal.
- DME or DDE: digital engine electronics or digital diesel electronics
The engine control sends the signal indicating that the engine is running to the AL control unit via the PT-CAN
bus. The AL control unit notifies the engine control of the approximate drive torque of the power-steering pump.
- CAS: Car access system
The vehicle is authenticated by the AL control unit and the CAS control unit via the K-CAN / PT-CAN (vehicle
identification numbers compared).
Moreover, the CAS control unit transmits the wake-up signal for the PT-CAN.

The following actuators are actuated by the Active Steering:

- Planetary gearbox with override function and electric servomotor
The planetary gearbox with override function uses the electric servomotor to generate the resulting cumulative
steering angle at the front wheels.
[more ...]
- Hydraulic steering with Servotronic valve
The conventional hydraulic steering provides the power-steering assistance.
"Servotronic" (= speed-dependent power-assisted steering) is part of the Active Steering option.
[more ...]
- ECO valve in the power-steering pump
A vehicle fitted with the "Active Steering" option has a controlled-output power-steering pump.
[more ...]
- Warning light and Check Control
The dedicated-function warning light in the instrument cluster lights up to indicate a fault in the Active Steering.
At the same time a Check-Control message is shown in the LCD display. The text for the Check-Control message
can be called up in the Central Information Display (CID).
[more ...]

System functions

The Active Front Steering system comprises the following functions:

- Steering assistance (= Servotronic)
- Variable steering-gear ratio (= Active Steering)
- Yaw-rate control (= damping of dynamic yaw)
A new function will be added in further development leading to the start of series production of the BMW 3-Series:
- Yaw-moment compensation when braking on a road surface with non-uniform traction
In further development from the E70, this function is entirely integrated in the Active Steering control unit (3rd
generation). Further model series to follow.

SBT Active Steering E60, E61, E63, E64, E70, E81, E87, E90, E91, E92, E93 BMW AG - TIS 07.02.2008 16:13
Issue status (08/2007) Valid only until next DVD is issued Copyright Page - 4 -
 Steering assistance
The steering assistance takes the form of conventional hydraulic steering (rack-and-pinion construction).
The speed-dependent steering assistance (= Servotronic) has been available in the E61 series since 03/2004.
E63 and E64 have Servotronic as standard from start of series production. Servotronic has been standard on the
E60 since 03/2005.
Active Steering and Servotronic are co-ordinated. Servotronic is controlled by the AL control unit.
The AL control unit actuates the Servotronic valve and the ECO valve in the power-steering pump via the Safety
and gateway module (SGM). The ECO valve in the power-steering pump regulates the volume flow in the power-
steering pump.
This arrangement means that only the volume flow needed for steering assistance at any given time is actually
provided. In this way, the ECO valve affects the power consumption of the power-steering pump. Fuel
consumption and carbon dioxide emissions (CO 2) from the vehicle's engine are reduced accordingly.

In vehicles without Active Steering, Servotronic is controlled directly by the safety and gateway module (except
BMW 1 and 3-Series).
Clearly, therefore, the steering assistance and AFS are complementary, despite the fact that in terms of function,
the two systems are fully independent of each other.

Variable steering-gear ratio

The variable steering-gear ratio function adapts the steering-gear ratio to the vehicle's road speed.
Steering is direct when the vehicle is moving at low speed. The planetary gearbox with override function
contributes significantly to handling when the vehicle is moving at low speeds and when it is being manoeuvred
into tight parking spaces.
It is not longer necessary for the driver to feed the steering wheel through his or her hands in order to manoeuvre.
When the vehicle is at a standstill, less than 2 complete turns of the steering wheel is all that is needed to move
the wheels from lock to lock.
At high speeds the steering-gear ratio increases. The steering becomes less direct, further improving the
intrinsically high standard of steering systems featured to date in BMW vehicles.
The safety function:
The electric servomotor of the planetary gearbox is limited by an electric servomotor lock that blocks the worm
gear of the planetary gearbox.
The electric servomotor lock is spring-loaded, with the force of the spring countered by the power supply. Any
interruption of the power supply consequently locks the worm gear.
When the planetary gearbox is locked in this way, it ensures that the steering column enables the driver to steer
the vehicle. Under these circumstances, the steering reacts like a conventional, direct, steering gear system.
The purely mechanical steering linkage between the steering wheel and the front wheels is sustained even if the
Active Steering fails.

Yaw-rate control
If the vehicle tends to oversteer, for instance, when cornering, the yaw-rate control can correct the steering angle
on the front wheels. This stabilises the vehicle (with the emphasis on convenience and comfort). In this road
situation, therefore, the Active Steering supports Dynamic Stability Control (DSC).
DSC does not intervene unless the stabilising effect of the steering does not suffice to counteract the tendency to
yaw.

Yaw-moment compensation when braking on a road surface with non-uniform traction

> BMW 1 and 3-Series
Active Steering now has an additional function for driving stabilisation.
With conventional systems, the driver has to actively steer the vehicle in a straight line if the brakes are applied on
a road surface with non-uniform traction levels.
In such situations, the Active Steering performs this active steering intervention, so stabilising the vehicle.

SBT Active Steering E60, E61, E63, E64, E70, E81, E87, E90, E91, E92, E93 BMW AG - TIS 07.02.2008 16:13
Issue status (08/2007) Valid only until next DVD is issued Copyright Page - 5 -
 Compared to pure ABS control, Active Steering with yaw moment compensation shortens the braking distance.
The driving stabilisation function of the Active Steering can be deactivated together with DSC with the DTC button
(when DSC is completely deactivated). Together with the hydraulic power steering, the variable steering-gear ratio
is always active.
> From X5 (3rd generation)
This function is completely integrated in the Active Steering control unit. Other model series will follow later.
Operation

Unlike DSC, which can be switched off by means of the DTC button, Active Steering cannot be deactivated.
Yaw-rate control and yaw-moment compensation are also deactivated when DSC is switched off. The variable steering
gear transmission ratio always remains active.
With the 3rd generation Active Steering, the yaw-rate control remains active when DSC is deactivated.
When DTC is activated, the DSC response thresholds have been widened. Active Steering increasingly assumes the
function of driving stabilisation if the vehicle is oversteered.

Preconditions for activation

Preconditions for activation for Active front Steering are:

- Terminal 15 ON
- Engine running
Steering-wheel position and the position of the steered wheels are synchronised as soon as the engine is running.
This ensures that the positions of the steering wheel and the road wheels match if, for example, the steering wheel was
moved while the vehicle was at a standstill with the ignition switched OFF.

Note: The synchronisation procedure can cause the steering wheel or the vehicle's front wheels to move.
Movements of the steering wheel or the vehicle's front wheels might be perceptible while synchronisation is in
progress.
Synchronisation also occurs while the vehicle is on the move, but the process is extremely slow and virtually
imperceptible.

Notes for service staff

The following information is available for service staff:

- General information: [more ...]
- Diagnosis: [more ...]
- Encoding/programming: ---
Subject to change.

SBT Active Steering E60, E61, E63, E64, E70, E81, E87, E90, E91, E92, E93 BMW AG - TIS 07.02.2008 16:13
Issue status (08/2007) Valid only until next DVD is issued Copyright Page - 6 -