IN ITS QUEST FOR IMPROVED DRIVABILITY AND FUEL ECONOMY FOR THE 2008 TRIBECA, SUBARU COUPLED A HEAVILY REVISED 5-SPEED AUTOMATIC TRANSMISSION WITH THE ALL-NEW 3.6-LITER 6-CYLINDER BOXER ENGINE. THE RESULTS ARE STUNNING!
Advances in electronics help to give today’s Subaru automatic transmissions an edge over their predecessors. As reported in the Summer 2007 issue of Drive, the previous transmission is the foundation for the 2008 model, but changes were major enough to call the 5-speed, electronically controlled automatic transmission “new” – the 2nd Generation 5EAT. (Read about the 2008 Subaru Tribeca in the Summer 2007 Drive.)
BETTER DRIVING PERFORMANCE, IMPROVED FUEL EFFICIENCY
The Subaru 2nd Generation 5EAT resulted from the engineering goals of improving both drivability and fuel economy in conjunction with the new 3.6-liter 6-cylinder engine in the 2008 Tribeca. Although seemingly contradictory, these divergent goals were achieved by a number of modifications.
REDESIGNED TRANSMISSION CONTROL UNIT (TCU): The new TCU has a number of features that improve drivability, including a shift schedule specifically designed for the new 3.6-liter Tribeca engine. The 2008 TCU has a faster microprocessor, providing quicker response and quality shifts. Physically, the TCU is lighter, which contributes to reduced overall vehicle weight and improved fuel economy. (This and other weight reduction measures have resulted in the transmission weighing approximately eight pounds less.)
In addition, the new TCU has several programs that give the driver greater control and provide a quality ride. The transmission control unit works with the engine electronic control unit to “blip” engine speed when the driver manually downshifts with the transmission in Sport mode. Engine speed automatically raises to coincide with road speed in the lower gear, which results in smooth, almost seamless downshifting. Another new feature in Sport mode is automatic downshifting during aggressive braking so the engine can help brake.
Further, the TCU holds the transmission’s gear when cornering. Lateral G-forces are detected throughout the corner. If entering a corner in one gear, the transmission will not shift to the next higher gear, even if the driver lifts off the accelerator pedal. When exiting the turn, the driver can reapply the accelerator without causing a downshift. These capabilities help the driver maintain control throughout a turn without the vehicle’s balance being upset by a gear change, then reapply power for a smooth exit.
On hills, the TCU utilizes new hill logic. When ascending or descending, the TCU can better calculate the optimal gear for a given road condition, resulting in less frequent shifting on hills – uphill or downhill.
REVISED GEAR RATIOS: Closer gear ratios (see comparison chart) make the transmission more compatible with the 3.6-liter engine and help the powertrain accelerate smoother. The final gear ratio remains the same.
OIL PRESSURE CONTROL SYSTEM: Lighter, quicker oil pressure control helps to make the transmission more responsive when downshifting.
REDESIGNED TORQUE CONVERTER: Changes to the fluid characteristics along with less oil in the torque converter contribute to quicker acceleration and engine response during acceleration. Slip lock-up has been added to the 2nd Generation 5EAT, too, improving response. More engine power goes to the driveline with greater efficiency, resulting in improved fuel economy.
SIMPLIFIED MECHANICAL FUNCTIONALITY: Mechanical transmission components that provided functions made unnecessary by the improved functionality of the TCU have been eliminated. This results in reduced power loss due to friction and to the reduced overall weight of the transmission. Both contribute to improved fuel efficiency.
STRENGTHENED FINAL GEAR: Making the transmission’s final gear stronger improves durability.
LARGER TRANSMISSION COOLER: More efficient cooling helps to improve fuel economy and transmission life.
THE PROOF IS IN THE DRIVING
If you’re familiar with the 2006 or 2007 B9 Tribeca, you’ll find the differences between driving it and the new 2008 Tribeca to be significant. The best way to sense the improvements made by the 2nd Generation 5EAT is to get behind the wheel. You’ll experience improved gear changing with greater confidence and control. (The experience is worthwhile even if you’ve never driven a Tribeca before.)
Read what the Drive staff thought about driving the new Tribeca in the Online Exclusive to the 2008 Tribeca article in Summer 2007 Drive at www.drive.subaru.com.