2009-09-29

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Chassis

Fun to Drive with Excellent Steering Response and Ride Comfort

• Innovative architecture: Compound crank rear axle with Watt’s link
• Mechatronic chassis: FlexRide adaptive suspension with driver-selective settings
• Space-saving convenience: Electric Parking Brake

Rüsselsheim. The chassis on the new Opel Astra has been developed as a mechatronic system that fully integrates mechanical functions and electronic controls. The goal of Opel engineers was to retain the fun-to-drive character of the previous model, while significantly improving its steering response and ride comfort.

While the chassis has the proven McPherson strut layout from the Insignia at the front, it benefits from a major innovation at the rear: Opel engineers are the first in the world to combine a compound crank rear axle with a cleverly positioned Watt’s link, enabling crisp handling and  high comfort. Keeping the advantages of size, weight and overall efficiency of the compound crank rear axle layout over a classical multi-link design, the new architecture with its additional Watt’s link better supports lateral forces on the suspension while cornering. It also makes the car dynamic and agile without compromising on stability and comfort. This innovative architecture has been patented by Opel.

In addition, an adaptive suspension, a rarity in the compact segment, is available in the new Opel Astra. This FlexRide system which first appeared in the Insignia offers the additional option of driver-selected ride control.

Driving dynamics are improved by wider front and rear tracks, which increased by 56 mm and 70 mm respectively. While the wheelbase is 71 mm longer, the proportionately greater increases in track give the car a wider footprint, which contributes to more stable handling and an inherently better road-holding capability. At the same time, it allows ample passenger space inside the cabin and a muscular appearance on the outside.

An increase of 43 percent in torsional stiffness and 10 percent in bending stiffness compared to that of its predecessor also provides the new Astra with a firm base for optimizing its handling and ride capabilities. In addition, it reduces significantly noise, vibration and harshness (NVH).

FlexRide adaptive chassis debuts in the compact class

Opel was the first automobile manufacturer to bring an advanced adaptive damping system to the compact class in 2003 when it introduced its IDS+ in the previous Astra. Now with FlexRide, the brand is the first to offer a new generation of mechatronic chassis system with a full integration of all mechanical functions and electronic controls from the beginning of development, to the segment. FlexRide was launched last year with the Opel Insignia. The electronic brain behind FlexRide is the Driving Mode Control (DMC) module. Using vehicle dynamics information, the DMC constantly monitors prevailing road conditions, vehicle movements and individual driving style, including acceleration, braking and cornering, to optimize chassis behavior. All four dampers, the steering system and the throttle progression are electronically controlled and continuously adapt within milliseconds to the current driving situation, providing optimum balance between performance, comfort fun and safety.

By pressing the relevant button in the center stack, FlexRide also enables drivers to select “Tour” or “Sport” chassis and vehicle settings that match their own driving needs for a particular journey. Thanks to the very wide damper operating window, the system always finds the right answer to daily driving conditions.
 
In the Standard mode, the dampers are continuously adapted to the driving situation, offering the optimal compromise between comfort and efficiency.

The Tour setting provides a perceivable increase in comfort: The dampers are set in a softer mode and the car adopts a smoother ride.

The Sport mode offers a sharper, more connected driving experience. The action of the dampers is stiffened up; the electronic throttle provides a swifter pedal response and the level of power steering assistance is reduced. To underline the effect, the instrument panel illumination changes from white to red. With an automatic transmission, the up-shift points are also raised to a higher engine speed. Last but not least, if fitted, the Adaptive Forward Lighting (AFL+) system reacts even more quickly. As a further refinement, the Sport mode includes a customization menu accessible via the board computer or navigation display, allowing the driver to de-select the Sport setting for the dampers, steering assistance or the throttle response.

Apart from a more rewarding driving experience, FlexRide also offers safety benefits in emergency situations. For example, if an obstacle must be avoided even when the car is in Tour mode, the DMC interprets the information from the various chassis sensors, registers the driver’s swift action on the steering wheel and commands the dampers to stiffen within a millisecond, enhancing the vehicle stability.

The FlexRide system is available as an option in the Enjoy, Sport and Cosmo variants with all engines, except the naturally-aspirated gasoline 1.4 and the 1.3 CDTI units.

Suspension: Innovative rear axle layout with Watt’s link and front McPherson

The chassis layout on the new Opel Astra combines a McPherson front suspension similar to the one on the Insignia and a newly developed compound crank rear axle with a Watt’s link.

This innovative rear suspension layout reduces unwanted noise and vibrations, allows a comfortable ride and improves the vehicle’s handling. Compared to a multi-link axle, it retains all the advantages of the compound crank, yet it is lighter and more compact. It also provides greater wheel camber stiffness, compensates for body roll and keeps constant track width. In addition, it greatly enhances lateral stability.

The Watt’s link is carried on a small cross-member attached to the underbody, just behind the rear wheel center line. It consists of a short, pivoting center link with ball joints at each end, to which the lateral links from the wheels are bolted.

On the road, this link helps the trailing arms resist the impact of lateral loadings and road shocks. The action of the pivot and its links ensures that when a force is applied to either rear wheel, an equal force is simultaneously applied in the opposite direction to the other wheel. This effectively prevents any sideways movement of the axle. Opel engineers estimate that this link absorbs about 80 percent of all lateral loadings on the rear suspension.

An additional advantage of the Watt’s link is that it reduces axle bush loads and therefore allows the use of softer bushings. This is why comfort, road noise and isolation are all greatly improved. Last but not least, the Watt’s link has also enabled an improvement in the geometry of the trailing arms. 

The torsion beam of the compound crank is attached between the trailing links, slightly ahead of the rear wheels. The open, U-shaped profile between the attachment points has now been lengthened and the wall thickness generally increased to provide more roll stiffness. Beams with different wall thickness are fitted to give the required roll steer characteristics in combination with a certain setting of the opening of the U-shaped profile. The perfect adjustment of wall thickness and a certain profile setting defines the wished suspension tuning - more comfortable or sporty or, for instance, adapted to the higher weight of a diesel engine.

The front suspension consists of McPherson struts with de-coupled top mountings that separate the paths of spring and damper loadings. To reduce unsprung weight and assist weight distribution, the combined strut carrier and the lower control arm are made of aluminum; the anti-roll bar is in hollow section steel.

For optimum stability, the L-shaped control arm is attached to the front sub-frame through two bushings. The suspension geometry and the tuning of the bushings are designed to provide both lateral stiffness and longitudinal compliance for excellent handling and good ride comfort. The rearmost bushing of the L-arm is also hydraulically damped for excellent road isolation, helping to prevent vibrations being transmitted into the vehicle structure.

Rebound springs are standard on all Astra vehicles. The rebound spring is integrated into the front strut - therefore not visible from the outside - and adds spring rate to the inside wheel during cornering which adds roll stiffness to the front axle. Body roll is significantly reduced. As the rebound spring does not load the outside wheel, the body roll can be reduced without creating unwanted understeer as would be the case if the front stabilizer bar was increased to achieve the same amount of body roll control. The rebound spring is not compressed during jounce, so there is no negative effect on ride comfort compared to an increased front stabilizer bar.

Space-saving Electric Parking Brake (EPB)

Like in the Opel Insignia, an Electric Parking Brake is available in the new Astra as an option. As well as providing enhanced convenience, this easy-to use Electric Parking Brake also frees up valuable additional storage space in the center console.

To activate the Electric Parking Brake, the driver simply needs to pull up a switch located near the gearshift, instead of a conventional handbrake lever. This sends an electrical signal to actuators clamping the rear brake calipers. The Electric Parking Brake can secure the car on gradients as steep as 30 percent. It is automatically disengaged when the vehicle drives off.

The Electric Parking Brake is offered with the Hill Start Assist (HSA) function, which helps minimize downhill movement of the car and puts less stress on the clutch (and the driver) when taking off on an uphill slope. The HSA briefly maintains pressure on all four brakes to minimize the possibility of the vehicle moving when the driver steps from the brake to the accelerator pedal while engaging the clutch.

Braking and multiple active safety systems

Depending on the performance level of a given version, the dual-circuit braking system of the Astra features one of the two brake disc combinations available. The 15-inch specification uses 276 mm ventilated front discs and 268 mm solid rear discs, clamped by single piston calipers. The 15-inch system is featured on the 1.4, 1.6, 1.4 Turbo and 1.3 CDTI variants. The 16-inch version - on the 1.6 Turbo, 1.7 CDTI and 2.0 CDTI models - has 300 mm ventilated front discs and 292 mm solid rear discs with single piston calipers.

The four-channel ABS (Anti-lock Braking System) is fitted as standard together with the Electronic Brake force Distribution (EBD) which ensures an optimal braking force is applied on both axles for maximum stability under heavy breaking.

The Electronic Stability Control (ESC), including Traction Control (TC), is fitted as standard across the range and offers a high level of active safety. The ESC yaw sensor in the center of the car detects movement around the vertical axis and a sensor on the steering column measures the steering angle being applied. Inputs from these sources are then correlated with the speed of the car. The system is programmed to execute whatever actions will most effectively prevent the loss of control. Depending upon the driving situation, it is possible for braking to be applied via the ESC system to one, two or three wheels at once, or, if necessary, the electronic throttle opening is also reduced.

Other braking functions under ESC direction:

  • Cornering Brake Control (CBC), is activated when the car is braking
    while cornering. Brake pressure is individually varied between all four wheels
    in order to keep the car perfectly stable. 
  • Cornering Torque Control (CTC) prevents the inner wheel from slipping when
    cornering under acceleration, thereby minimizing any understeer tendency.
  • Electronic Drag Torque Control (EDC), keeps the wheels from blocking when
    the throttle is released too quickly or during an abrupt downshift.
  • Brake Assist System (BAS) helps the driver apply optimal braking power in
    emergency braking situations.
  • Hydraulic Brake Fade Assist (HBFA) automatically raises braking pressure
    to compensate for brake fade under repeated applications of heavy braking.
  • Trailer Stability Assist (TSA) is active when an Opel-approved towing hitch is
    fitted. TSA counters any vehicle instability that may occur when towing a trailer
    or caravan by reducing the engine torque and applying brake pressure to
    selected wheels.

Steering: electrical speed sensitive assistance improves feel and saves fuel

The new Opel Astra uses a rack-and-pinion steering system. The speed sensitive assistance is electrically powered by a motor mounted directly on the steering rack as opposed to the base of the steering column.

This architecture ensures improved driver feel when turning the steering wheel. At low speeds, the level of power assistance is increased to minimize steering effort. At higher speeds, assistance is automatically reduced to ensure a high degree of steering feel for the driver. The second important benefit of this system is fuel economy because it does not require an energy-consuming pump and responds directly to the amount of power needed at any speed.

Contact:

Nathalie Van Impe
+ 49 6142 7 66166 (office)
+ 49 151 174 73959 (mobile)
nathalie.van.impe[at]de.opel.com

 

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