SAAB 9-5 BALANCES HIGH-PERFORMANCE DRIVER CONTROL WITH OPTIMUM RIDE COMFORT
NORCROSS, Ga. - The main objective for the Saab chassis engineers when developing the chassis for the Saab 9-5 was for the driver to stay in control at all times, regardless of the driving situation, the load in the car, or the external conditions, and to combine these typical high-performance Saab driving qualities with unprecedented levels of comfort. The Saab 9-5 conveys clear signals of the car's behavior and balances the best possible directional stability and roadholding with an outstanding ability to absorb bumps smoothly and to ride comfortably over irregular surfaces.
Feedback to the Driver Essential for Safe Driving
As with every Saab, the chassis is designed to transmit the car's balance through the
seat to the driver's hips, located close to the center of gravity of the vehicle where
the car's behavior is easier to sense. This kind of instant feedback then shortens the
driver's reaction time for more immediate control. Stability, responsiveness and
predictability are built into a chassis system that gives the driver plenty of warning
well before any limits are reached. "We wanted the car to handle exceptionally well, even
at the limit of adhesion-smoothly and forgivingly, so that even an average driver would
have a good chance of maintaining control, even in an emergency situation," emphasized
Ekkehard Schwartz, chassis development engineer at Saab. "In engineering terms, we
wanted the car to respond to steering inputs in a linear way, with a linear yaw response
and a linear force feedback through the steering." During the development process, Saab
engineers evaluated ride and handling of a wide range of competitive models in the same
class as the Saab 9-5. "We found on many of these cars that there is still a conflict
between ride and handling characteristics," Schwartz said. "Cars that handled well were
harsh on ride, and those that rode well were too soft or unresponsive in handling. At
Saab, we believe that it is possible to combine the both of best worlds if you take
enough trouble to get the suspension kinematics correct. You can have soft bushings with
good handling if you optimize the stiffness characteristics in the right way-soft in the
longitudinal direction to absorb wheel shocks and stiff in the lateral direction to
control wheel geometry accurately."
Front and Rear Subframes
The Saab 9-5's chassis design introduces isolated front and rear subframes to attenuate
road disturbances more effectively and significantly upgrade the running refinement. The
fully independent suspension includes MacPherson struts for the front suspension, and a
split rear axle with multi-link locating members. The split rear axle features passive
steer characteristics that keep the car on its cornering line at the limit, instead of
causing it to run wide. Spring rates and body mounts were carefully tuned to provide
further insulation from noise, vibration and harshness. The front subframe is a closed
ring of engineered pressings attached to the main body structure via six insulated
bushings around the lower engine bay. Pressed lower wishbones have widely-spaced pivots
that apply toe-correcting geometry for a self-stabilizing effect when braking on road
surfaces with varying degrees of grip on either side. As on other Saab models, a small
negative scrub radius and toe compliant bushings effectively and automatically help to
balance an uneven braking effect. Upper strut mounts use a decoupled dual-path system
that separates spring and damper loads, for better optimization of each mount's
characteristics, improving insulation and thus allowing better control of the ride
characteristics. The coil springs are offset to reduce bending loads in the shock
absorbers for more effective damping during initial suspension movements. An 18-mm
diameter anti-roll bar is mounted on bushes at the rear of the sub-frame and connected to
the struts by vertical links. All the suspension bushes are directionally optimized so
that the chassis is soft longitudinally, to isolate the system better from sharp road
shocks, but stiff laterally for maximum wheel control. The power-assisted steering rack
is also mounted on the rear of the sub-frame so it can operate with short tie rods and
provide very precise wheel control, creating higher levels of response and steering feel.
The steering system is a power-assisted rack-and-pinion type with 2.9 turns from
lock-to-lock. The new multi-link rear suspension is also mounted on a separate subframe,
attached to the rear body structure by four large-volume elastomer bushings. Each wheel
is controlled by three links, two mounted transversely to form the split axle and the
third installed as a longitudinal trailing arm. The two transverse links on each side
pivot on cylindrical bushings mounted on the subframe, while the trailing arm is attached
to the body through similar bushings mounted in rigid brackets. The vertical spacing of
the pivots on the wheel carrier is wider than the spacing at the inboard end, to control
wheel camber on bump and rebound. The geometry of the trailing arm is designed to
provide passive toe-steer in corners, to reduce rear tire slip for more responsive and
secure handling. The transverse links are attached to the wheel carriers by ball joints,
to control wheel camber more precisely throughout the range of suspension travel. The
dimensions, elastomer materials and detail design of the suspension components are all
highly optimized to maximize lateral wheel control and enhance the ride characteristics.
Advanced Braking System with Standard ABS
All versions of the new Saab 9-5 are equipped with disc brakes front and rear with a
diagonally-split hydraulic system and electronically controlled ABS as standard. The
ventilated front disc brakes have a diameter of 11.34 inches (288 mm) and the solid rear
discs have a diameter of 11.26 inches (286 mm). The Bosch 5.3 ABS system is a lightweight
and compact system with four-channel operation triggered by four individual wheel
sensors. It allows high-performance braking to be available even if the electronics
should fail for any reason. This latest generation ABS system incorporates electronic
brake force distribution (EBD) which comes into effect under hard braking before the ABS
is activated, to balance the friction available at each wheel with the braking forces
being applied. It automatically provides the shortest possible stopping distance for the
actual weight and balance of the vehicle and the road surface conditions at the time, by
using the maximum grip available at each wheel independently. The system is controlled by
the integrated ABS controller that compares the rear wheel slip with the front as a
reference point. As soon as significant differences are detected, pressure to the rear
hydraulic system is modulated to provide the most balanced effect without operating the
electric ABS pump, so the driver is unaware that any adjustments are taking place. It
eliminates the need for a rear brake pressure relief valve set at a fixed value, so the
brake balance can be optimized more closely to the theoretical ideal without any risk of
the rear wheels locking too soon. Although EBD provides individual control of each
wheel's braking, the rear valves are interactively linked to prevent any risk of
destabilizing effects.
Integrated Electronic Traction Control System
Saab's advanced electronic Traction Control System (TCS), available only as standard equipment with the 3.0L V-6 engine, helps average drivers maintain control on winter roads by providing a completely seamless and effective slip-correcting system. The system uses the ABS signals from the front wheel sensors to continuously evaluate the degree of wheel slip and acceleration, comparing these signals with similar information from the non-driven rear wheels. If excessive wheel slip is detected at only one front wheel, its brake is applied to transfer engine torque to the other side of the differential, where more grip is available. If both wheels start to spin together, the engine management unit automatically reduces engine torque. TCS optimizes the driving torque automatically and relieves the driver from the difficult task of having to feel for the available grip, especially when making sharp turns or trying to restart on a steep grade. It also helps maintain stability if the driver applies or releases the throttle inappropriately at any time (when driving through a slippery curve, for example). A warning light on the instrument panel illuminates when the traction control is operating, to warn the driver of slippery roads. The TCS system is fully automatic, but includes an off-switch for special circumstances (such as if the driver needs some wheelspin to cut through heavy snow, or when snow chains are fitted). The off-switch will only deactivate the system at low speed (below 40 mph). Unlike some traction control systems on other cars that function only at lower road speeds, Saab's TCS system is functional at all road speeds.
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