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RDCM (Rear Drive Control Module)
The Rear Drive Control Module handles the all wheel drive functionality of the car.
Block diagram RDCM
Transmission
Engine
PTU
PTU
MOTOR
RDCM
(Rear Drive
Control Module)
PUMP
ECU
ACCUMULATOR
TTD
CONTROL
VALVES
OVERFLOW
VALVE *
REAR AXLE TORQUE LIMITER 2700NM
RDM
eLSD
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Power Take-off Unit
PTU
Torque Transfer Device
TTD
Rear Drive Module
RDM
Propshaft
Electronically Controlled
Limited Slip Differential
eLSD
Functional description RDCM
RDCM provides several functions:
• The Control Strategy is during normal driving based on Acceleration capability and
Pre emptive. Acceleration capability is mainly calculated from Engine torque and
driver requested torque. Other Control parts is Slip control, Yaw damping, Braking and
Handbrake
• The Pre emptive functionality adds the possibility to lock both TTD and eLSD
couplings up to fully locked when standing still or driving without any delta speed.
• The eLSD can be used for traction and for Yaw damping during, for example, throttle
of and high side accelerations
• RDCM has a torque based interface to ESC system, The RDCM sends out actual
torques, and the ESC can send torque request back to RDCM for control of TTD and
eLSD, ESC request is always master.
• It is also possible to use the ESC active flag to open the rear drive couplings.
• ABS active flag opens the couplings
Obviously, RDCM controls several units to provide all wheel drive functions. All of these will
be explained below briefly.
Power Take-Off Unit (PTU)
The Power Take-Off Unit is installed at the front axle. It provides torque via connected
propshaft to the rear drive units. PTU is available in two versions due to different
transmissions:
• F40 AF40/55
• X22F
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Torque Transfer Device (TTD)
TTD controls the torque at the rear wheels. It is adjustable from 0..100% clutch state,
maximum torque of the unit is 1000Nm, resulting in 2700Nm on the rear wheels. The unit is
sealed, oil change is not necessary during its life length.
The electronic control unit for the all wheel drive devices, RDCM, is installed at the TTD.
Rear Drive Module (RDM)
RDM transmitts input power to the rear wheels. Output power is split by the differential.
Electronically Controlled Limited Slip Differential (eLSD)
eLSD is an optional device. It provides another clutch, installed at the rear halfshaft leading
to the rear left wheel. eLSD allows to control the slip difference between the rear wheels
continuously between 0..100%. The maximum locking capacity for the eLSD is 1200Nm.
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Connectors and pin assignment RDCM
X1
X2
Battery Positive Voltage
Ground
High Speed GMLAN Serial Data (+) (1)
High Speed GMLAN Serial Data (+) (1)
High Speed GMLAN Serial Data (+) (2)
High Speed GMLAN Serial Data (+) (2)
Serial Data Communication Enable
ECU Housing ground
High Speed GMLAN Serial Data (-) (1)
High Speed GMLAN Serial Data (-) (1)
High Speed GMLAN Serial Data (-) (2)
High Speed GMLAN Serial Data (-) (2)
Rear Drive Motor Control
Rear Drive Motor Return
Limited Slip Diff. valve Control
Limited Slip Diff. Valve Return
Torque transfer device valve Control High
Torque transfer device valve Control Low
53
2
2
A40
B40
C40
D40
1
A40
B40
C40
D40
Pigtail Wire Color
Pigtail Wire Gauge
Terminal Plating
Shield Group
A40
A50
2500
2500
6105
6105
5986
A50
2501
2501
6106
6106
933
987
934
935
Circuit Description
Twist Group & Rate
X1-1
X1-2
X1-3
X1-4
X1-5
X1-6
X1-7
X1-8
X1-9
X1-10
X1-11
X1-12
X2-1
X2-2
X2-3
X2-4
X3-1
X3-2
Minimum Wire
Gauge
Max. Wire
Resistance
Circuit #
internal connection
Cavity
X3
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SADS (Semi-active Damping System)
The semi-active damping system’s purpose is to damp chassis movements caused by
bumpy roads and driving conditions. Its benefits are therefore better ride and handling
capabilities and improved comfort.
Block diagram SADS
3
1
6
2
4
5
1 body acceleration FR
2 body acceleration FL
3 body acceleration R
4 wheel acceleration FR
5 wheel acceleration FL
6 ECU
SADS
Batt
High Speed CAN
Chassis Expansion CAN
Semi-Active
Shock
Absorber
FL
Damping
System
Ground
Shock
Absorber
FR
Body ACC FL
Shock
Absorber
RL
Body ACC FR
Body ACC RL
Shock
Absorber
RR
Wheel ACC FL
Wheel ACC FR
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Functional description SADS
SADS is an electronic damping system that increases driving performance, comfort, and
dynamics by adjusting damping forces optimally for each individual wheel. A control unit
calculates the requisite damping forces within milliseconds and adjusts the dampers. Vehicle
sensors monitor values such as body and wheel acceleration in z-direction, and use them to
generate the ideal damping forces for each individual wheel on a continuous basis.
The benefits of SADS are:
• Enhanced performance thanks to optimized wheel damping
• Enhanced driving comfort and dynamics
• Reduced roll, pitch, and vertical motion
• Continuous adjustment of the dampers in real time
• Better control and handling during lane changes
The ECU of SADS provides some functions which will be explained below.
System mode request
The driver is able to select a different behavior of the vehicles chassis. This driver selection is
processed by the Driving Mode Control 2, DMC II.
The DMC-II is an automatic control algorithm which is not part of the CDC system. This
algorithm sends out the DMC-II status request on the CAN bus.
The CDC system can operate in three different control modes. This is achieved by three
different parameter settings, each of them selectable by the DMC-II status request on the
CAN bus.
Parameter settings:
Mode
Name
1
Comfort
2
Intelligent
3
Sport
(4)*
Demo
Description
Floating body behavior, all adaptive modules are working
Pure Skyhook provides good Body Control and good comfort
Further decreased Body Amplitudes, increased Body accelerations
Extremely firm Damping. * Not used in 65x.
Body stability
The body of the vehicle shall make only small movements (body to wheel displacement,
body vertical speed and body acceleration). SADS reduces the spectral density in the body
resonance frequency range. The SACHS Advanced Skyhook control algorithm is used to
stabilize the body independently from the actual load situation of the car. Therefore the
body vertical speed and the wheel vertical speed are calculated.
Heave, pitch and roll stability by road input
To get a good driving comfort SADS minimizes the heave, roll and pitch movement caused
by road input and independent of various load situations. This is achieved by the SACHS
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Advanced Skyhook control algorithm which allows controlling and tuning all three modal
movements of the car separately.
Body acceleration
The vehicle shall have low body acceleration in all driving situations. SADS improves the
body acceleration spectral density in the seat ride frequency range (3 to 8 Hz). The SACHS
Advanced Skyhook control algorithm is used to get an optimized body acceleration
performance. To guarantee the best possible body acceleration control independently from
the actual load situation of the car, body accelerometers are used to get the most direct
information.
Wheel load variation
To get good stability, self-steering behavior, traction, braking behavior and high possible
lateral acceleration it is essential to minimize the wheel load variation. A wheel acceleration
sensor at each front wheel is used to measure the direct vertical wheel movement. The
SACHS Advanced Skyhook control algorithm minimizes the wheel load variation by
controlling the damping force in an adequate manner.
Brake dive prevention
The function “Brake Dive Prevention” minimizes the diving while braking by intervention of
SADS resulting in a positive influence on braking behavior of the system. By optimization of
the force at center of tire contact on bad roads or gravel an improved contact to the road
will be provided. Customer benefit will be a more comfort oriented braking as the
passengers are not forced to follow the diving. SADS uses the master cylinder brake pressure
for evaluating the tendency of pitching.
Cornering stability
During maneuvers like lane change and cornering with a certain amount of lateral
acceleration SADS will optimize the general roll behavior of the car body. SADS uses the
steering wheel angle sensor signal or lateral acceleration signal from the CAN Bus and the
vehicle speed to calculate the damper setting according the actual driving maneuver.
Brake distance reduction
EBCM can use the measured z-accelerations of the front wheel acceleration sensors of SADS
giving information about the condition or kind of driven road. It can analyze vertical wheel
acceleration values of SADS and the master cylinder pressure to assess the braking status.
By using the additional information of the road condition, EBCM can improve the braking
performance of the car.
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Acceleration performance
During longitudinal accelerating SADS shall improve the pitch behavior of the car body. The
function “Acceleration Performance” shall also assist the driver in improving the traction.
EBCM analyzes vertical wheel acceleration values of SADS and the wheel acceleration
signals to assess the acceleration status.
By using the additional information of the road condition, EBCM improves the acceleration
performance of the car.
Pothole function
By monitoring the wheel acceleration sensors potholes can be detected by SADS. In this case
the damping can be increased in order to improve the wheel control. As a result lateral und
longitudinal traction are optimized.
Reaction to different road surfaces
SADS wants to keep the vehicle behavior regardless of the road quality. Therefore SADS
measures the wheel acceleration and calculates a road quality signal. This signal is used to
influence the system behavior by modifying a set of system parameters continuously.
Vehicle speed dependency
The comfort feeling of the car depends on the vehicle speed. The frequency of the vertical
excitation of the wheel depends on the vehicle speed and the wavelength of the road
unevenness. The input frequency for SADS depends significantly on the vehicle speed.
Therefore it is necessary to adapt the system to the actual driving speed. SADS adapts
many of the tuning parameters continuously to the actual driving speed.
SADS damper control
SADS dampers are controlled by a hydraulic/electromagnetic proportional valve. The
dampers are hydraulically tuned with respect to the softest and firmest setting. The range
between these two corner settings is controlled by the proportional valve. The control is
realized by a current control loop, which provides a constant current according to the
request of the SADS advanced skyhook algorithm. This algorithm updates the nominal
current every 10 ms. The current control loop has to follow this nominal valve as fast as
possible. Therefore it is essential, that high driving speeds of the magnetic valve are
possible. Care must be taken to reach nearly identical rise and fall times for step inputs. The
damping rate of the SADS damper is controlled in an open loop (i.e. current control only, not
damping rate control). This requires a high precision current control with a total deviation of
less than 5%. Below 100 mA an absolute tolerance of +/- 20 mA is required.
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Connectors and pin assignment SADS
12
1819
12
12
3258
3252
12
13
14
15
16
17
3255
1113
1107
1116
1117
A40
58
50mA
50mA
50mA
50mA
50mA
-2A
2A
2A
-2A
2,5A
C20
C20
D20
D20
Pigtail Wire Color
1817
2mA
Pigtail Wire Gauge
12
A20
A20
B20
B20
Terminal Plating
1106
2,5A
-2A
2A
2A
-2A
10mA
2mA
2mA
2mA
2mA
Shield Group
11
Battery Positive Voltage
Right Rear Damping Servo Control
Right Rear Damping Servo Supply Voltage
Left Rear Damping Servo Supply Voltage
Left Rear Damping Servo Control
Serial Data Communication Enable
Rear Accelerometer Signal
Left Front Accelerometer Signal
Right Front Accelerometer Signal
Left Front Wheel Damping Accelerometer
Signal
Right Front Wheel Damping Accelerometer
Signal
Left Front Wheel Accelerometer Voltage
Reference
Right Front Wheel Accelerometer Voltage
Reference
Left Front Accelerometer Voltage Reference
Right Front Accelerometer Voltage
Reference
Rear Accelerometer Voltage Reference
Left Front Damping Servo Control
Left Front Damping Servo Supply Voltage
Right Front Damping Servo Supply Voltage
Right Front Damping Servo Control
Battery Positive Voltage
Twist Group & Rate
A40
1119
1118
1114
1115
5986
3256
3259
3253
1100
Circuit Description
Max. Wire
Resistance
Circuit #
1
2
3
4
5
6
7
8
9
10
Minimum Wire
Gauge
Cavity
X1
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59
-50mA
-50mA
-50mA
10mA
10mA
10mA
10mA
10mA
10mA
10mA
10mA
10mA
10mA
10mA
10mA
E40
F40
F40
E40
G40
H40
H40
G40
Pigtail Wire Color
Pigtail Wire Gauge
3260
3254
3257
2500
2500
2500
2501
2501
2501
NC
6105
6105
6106
6106
NC
-50mA
Terminal Plating
20
20
20
21
22
23
24
25
26
27
28
29
30
31
32
-2,5A
-2,5A
-50mA
Shield Group
1105
Twist Group & Rate
20
GND
GND
Left Front Wheel Damping Accelerometer
Low Reference
Right Front Wheel Damping Accelerometer
Low Reference
Left Front Accelerometer Low Reference
Right Front Accelerometer Low Reference
Rear Accelerometer Low Reference
CAN Termination + (1)
High Speed GMLAN Serial Data (+) (1) Out
High Speed GMLAN Serial Data (+) (1) In
High Speed GMLAN Serial Data (-) (1) In
High Speed GMLAN Serial Data (-) (1) Out
CAN Termination - (1)
CAN Termination + (2)
High Speed GMLAN Serial Data (+) (2) Out
High Speed GMLAN Serial Data (+) (2) In
High Speed GMLAN Serial Data (-) (2) In
High Speed GMLAN Serial Data (-) (2) Out
CAN Termination - (2)
Max. Wire
Resistance
Circuit #
A51
A51
1099
Minimum Wire
Gauge
Cavity
18
19
20
Circuit Description