9-5 Powertrain


NORCROSS, Ga. - Saab's ultimate 9-5 performance variant, the Aero model, receives a 20-hp power boost, taking peak power to a heady 250 hp - the greatest amount Saab has ever transmitted through the front wheels. The Aero now features a new electronic stability program (ESP) and an improved traction-control system and to help control unwanted wheel spin.

The new top-end power, which accompanies the mid-range performance surge from Saab's 2.3-liter HOT (High-Output Turbo) engine, provides both sedan and wagon Aero models with an even sportier driving experience.

The desired power hike has been made possible by revising Saab's own 32- bit Trionic engine-management system to increase the fuel/air mixture, while winding up the variable-turbo boost pressure to 1.5 bars. With the five-speed manual transmission, torque remains unchanged at 258 lb.-ft., with a 20-second turbo overboost function increasing torque to 273 lb.-ft., to allow decisive and controlled overtaking of other vehicles.

Automatic Aero models, which are now equipped with a new five-speed automatic transmission, also benefit from extra performance. Previously, torque was restricted to 243 lb.-ft. with the older four-speed auto, but the new five-speed auto- gearbox allows full utilization of the Aero engine's 258 lb.-ft. torque reserves for improved mid-range responsiveness.

"We haven't had to make any changes to the engine itself because it was already robust enough to handle this amount of power," explained Bertil Gustafsson, project leader on powertrain for the new 9-5 range. "We've re-calibrated the management system to take greater advantage of the variable-turbo boost on demand. It's something we've tested before, but we were awaiting the opportunity to introduce it. Following the torque upgrades we introduced on the Aero engine last year, it now seemed exactly the right moment for the power upgrade.

"Drivers will notice a difference at the top end and a quicker 0-100km/h (0-62 mph), but I expect the biggest change will be observed by drivers of automatic versions. Now that we have an auto box that can handle 350Nm (258 lb.-ft.), the effects are really startling. So whether customers like to change gears manually, or prefer an auto to shift for them, both sets of owners will notice that the Aero is an even sportier drive." Top speed remains electronically limited to a maximum of 155mph.

New five-speed automatic transmission

To accompany the prodigious torque from the latest Saab 9-5 Aero's HOT engine, there's an optional new automatic gearbox, which will also be available to Saab customers on Linear and Arc models.

The new gearbox, manufactured to Saab's design by Asin AW, is perfectly suited to the more powerful Aero engine. The five-speed automatic makes effortless use of the turbo power, crisply picking up the appropriate power points, while giving all automatic models sportier and smoother performance, more easily taking advantage of Saab's mid-range turbo "rush."

Just as importantly, the gearbox is capable of handling the Aero's high 258 lb.- ft. torque figure. The previous four-speed automatic was limited to 243 lb.-ft. of torque, so drivers opting for the new automatic in combination with the more powerful Aero engine will notice not only a smoother and better-responding automatic but also appreciably more mid-range performance. In fact, Saab will be one of the first European manufacturers to put this much torque through a five-speed automatic in a front-wheel-drive configuration.

Adaptive automatic reconfigures to changing conditions

The automatic constantly monitors its surroundings, adapting performance and shift points to the prevailing conditions. It "knows" when it's in a high-altitude environment for example, or if it's towing a trailer, and it responds accordingly. The transmission will also continue to monitor its own shift quality and will alter shift timings and patterns if it detects any change in its performance or in that of the engine. A high-speed CAN data bus provides the continuous flow of information between engine and transmission to enable this to happen.

"It keeps thinking all the time," explained Saab's powertrain expert, Bengt Wallin. "If the engine is less than perfect at high altitude where the air is less dense, then the gearbox will take care of it. And it continues to monitor its performance throughout the car's working life."

However, the new five-speed automatic transmission isn't driver-adaptive. That's up to the driver to control, with the choice of normal, sport, or winter settings. To choose the sport setting, the driver engages the "S" button located on top of the gearshift handle. In some other applications, the sport mode engages a closer set of ratios by moving the automatic's mapped shift points. Such a solution, though, would fail to optimize the strong mid-range performance that's characteristic of Saab's turbo engines.

Instead, Saab's engineers have engineered a similar result by using an alternative solution. The drive-by-wire throttle becomes more sensitive to the driver's foot pressure - effectively giving him another set of ratios, and providing a sportier response by concentrating the gearbox's best efforts on the engine's mid-range power.

In winter mode, which has a special shift pattern to suit slippery conditions, the engine starts in third gear to ensure a smooth take-off on icy surfaces, and to help minimize wheel spin.

Slipping lock-up clutch gives greater efficiency

The new five-speed automatic transmission also features a clutch within the torque converter. In higher gears this clutch bypasses the torque converter and directly engages the transmission, eliminating some of the frictional losses associated with traditional torque-converter automatics.

"It's good for fuel consumption," Wallin commented, "because with this type of transmission the efficiency is so much better. The gain is 2 percent. But, you couldn't have direct drive all the time, because it would produce an unacceptable feel. So this slipping clutch in lower gears is an excellent combination of responsiveness and efficiency."

The gearbox is a sealed-for-life unit. The automatic transmission fluid, an extremely high-quality mineral oil, has been formulated to last for the life of the car, cutting down on servicing costs and creating less environmental waste. It's also one less worry for the driver.

Wallin concluded, "You should just get in and drive! Enjoy the car and let the auto do the work. It's built to last and last!"

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