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XWD
on Aero versions of the 9-3 Sport Sedan
and SportCombi. |
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APN,
12 June 2007.
Swedish all-wheel-drive specialist
Haldex systems launched the fourth generation of its
limited slip coupling with the all new XWD electronic
limited slip differential in the All-Wheel Drive
versions of the new SAAB 9-3 model, introduced as the
Saab 9-3 XWD for Cross Wheel Drive.
Employed in conjunction with the
Haldex coupling, the electronically controlled add-on
module integrates in the power and control systems of
the longitudinal device, offering a flexible and cost
effective solution for further enhanced vehicle
dynamics. The add-on module can be optionally used in
the vehicle product lines to control the side-to-side
torque distribution, with limited weight and size for
better performance and fuel economy.
“The cooperation with SAAB
Automobile showcases our consistent and continued
commitment to meet the needs of OEM customers through
innovation. The Haldex XWD equips the driver with
improved dynamic safety, broadens the performance scope
of the vehicle and generates superior traction. The new
business consolidates our leading position with European
car manufacturers in the area of controllable and
intelligent systems for All-Wheel Drive” says CEO and
President of the Haldex Group, Joakim Olsson.
Haldex currently supply three of the major OEM groups,
VW AG, Ford Motor Company and General Motors (owner of
Saab Automobile AB, amongst other brands) with
proprietary and advanced systems and solutions for AWD.
Launched to mark Saab's 60th
anniversary, the new Saab 9-3 offers the active,
all-wheel-drive system (Saab XWD) on Aero versions of
the 9-3 Sport Sedan and SportCombi, in combination with
an uprated 280 hp (206 kW), 2.8 V6 turbo engine which
delivers almost 15% more maximum torque (400 Nm). It
comes with a choice of six-speed manual or automatic
transmission.
Manufactured and supplied from a new
Haldex production facility in Guanajuato, Mexico, the
new system includes two innovative features:
- pre-emptive engagement of the rear
wheels to optimize traction at take-off; and,
- an active rear limited-slip differential (eLSD),
allowing variable torque transfer between the rear
wheels.
Saab XWD is a fully automatic,
on-demand system capable of sending up to 100% of
engine torque to the front or rear wheels
whenever necessary. Its operation adds a further sporty
dimension to the driving experience in all road
conditions. Fine balancing of the drive torque between
the front and rear axles raises the threshold at which
ESP throttle and braking interventions are triggered,
providing more scope for closer driver involvement.
The system is governed by its own
electronic control unit, which functions in harness with
the engine, transmission and ABS/ESP control modules.
The hardware consists of a Power Take-off Unit (PTU) in
the front final-drive that transmits engine torque
through a prop-shaft to the Rear Drive Module (RDM).
This incorporates a Torque Transfer Device (TTD) and an
optional electronically-controlled Limited Slip
Differential (eLSD). Both are wet, multi-plate clutch
units from Haldex.
At take-off from rest, the TTD is
initially activated when the clutch plates are forced
together under hydraulic pressure, thereby engaging the
RDM. This pre-emptive function is an improvement in
current technology, which requires the detection of
wheel slip before the TTD is activated. For the driver,
the enhanced functionality gives maximum traction
immediately for smooth, strong acceleration from rest
without the possibility of any initial hesitation.
On the open road, drive torque is
continuously varied between the axles by the control of
a valve in the TTD, which increases or reduces the
pressure on the wet clutch plates. When cornering, Saab
XWD provides enhanced, more finely balanced chassis
dynamics. Data from the vehicle’s ABS/ESP
sensors - measuring wheel speed, yaw rate and steering
angle – is utilized, and careful programming of Saab
XWD enables the application of rear drive to balance
oversteer and understeer characteristics, improving
stability and roadholding.
In highway cruising
conditions, when traction or optimum grip is not an
issue, only 5% to 10% of engine torque is
typically transmitted to the rear wheels. This
helps provide the driver with a measure of greater
stability, while helping to save fuel.
The eLSD option is the first
application of an electronically-controlled, rear
limited slip differential in this segment of the market.
Installed alongside the RDM, it operates via pressurized
clutch plates on a principle similar to the larger TTD.
In icy or wet split-friction conditions, for example, it
uses inputs from the rear wheel speed sensors and can
transfer up to 40% of torque between the drive shafts,
to whichever wheel has more grip.
The eLSD also improves control when
cornering hard or completing a high speed maneuver, such
as a lane change, by momentarily applying more or less
torque to either of the wheels to help the rear of the
car more closely follow the direction of the front
wheels. This yaw damping effect can keep the car better
balanced and more tightly controlled, without requiring
‘outside’ intervention from electronic stability
aides.
Installation of Saab XWD includes the
fitment of a new rear sub-frame to carry the RDM,
revised rear suspension geometry and new wheel hubs for
the drive shafts. The three piece prop-shaft runs
through two bearings with constant velocity joints for
smooth running with minimal ‘wind-up’. Wheelbase and
rear track dimensions are unaltered. Saab XWD will be
available from the beginning of next year. |
