SUBARU B9 TRIBECA POWERTRAIN: POWERFUL AND REFINED (2022)

SUBARU B9 TRIBECA POWERTRAIN: POWERFUL AND REFINED
12 April, 2005

CONTACT: Elaine Griffin (905) 568-4959

SAN FRANCISCO, April 10, 2005 - The all-new 2006 Subaru B9 Tribeca progressive sport utility vehicle is powered by a sophisticated 250-horsepower 3.0-litre 6-cylinder boxer engine. The engine is teamed exclusively with a standard electronically controlled 5-speed automatic transmission and Subaru's most advanced version of Symmetrical All-Wheel Drive.

Not only is power output of the Subaru 6-cylinder boxer engine comparable to larger-displacement V6 engines in competitive vehicles, but the engine's specific output of 83.3 hp/litre ranks ahead of many premium 6-cylinder engines in the market today. In addition, the Subaru Boxer engine is exemplary for its quietness and smooth operation.

The B9 Tribeca engine produces 219 lb-ft. of peak torque at 4,200 rpm, with a broad torque curve that delivers the linear power feeling that is characteristic of a higher-displacement engine. Technology contributing to the impressive performance includes Active Valve Control System (AVCS) variable valve timing and Variable Valve Lift System (VVL).

This powerful 6-cylinder uses a new aluminum intake manifold, and Subaru optimized both weight and strength through a program that examined parts down to microscopic detail. The modular camshafts are built up using heat and pressure. Their hollow journals reduce weight, contributing to a significant 40 per cent weight reduction of the entire valve system (compared to using solid camshafts).

The cylinder block uses an optimized rib design for greater strength with less weight. The top piston rings receive a shot-peened treatment for added strength and lower friction. Subaru reduced the number of mounting bolts on the timing chain cover (and added dowels for strength), which helps to reduce engine noise.

Active Valve Control System and Variable Valve Lift System
The engine in the B9 Tribeca employs both Active Valve Control System (AVCS) variable valve timing technology and a Variable Valve Lift System (VVL) technology. This combination results in one of the most advanced valve control systems on the market. Subaru AVCS and VVL vary both cam phasing (intake valve timing) and the amount of lift exerted on the intake valves.

AVCS optimizes the engine's volumetric efficiency throughout the rev band by adjusting intake camshaft timing to employ the ideal intake and exhaust valve overlap under all engine operating conditions. AVCS can rotate the intake camshafts through a range of 35 degrees relative to the crankshaft. The Engine Control Module (ECM) regulates this movement, based on input from various sensors - airflow, engine coolant temperature, throttle position and camshaft position.

The ECM sends an output signal to an oil control valve located at each intake camshaft sprocket. Oil pressure is then varied within "advance" and "retard" chambers inside the AVCS actuator. By referencing computer mappings, the system responds to various driving conditions to provide ideal valve timing for stable engine idling and for optimum torque across the engine speed range.

In response to engine speed and load, VVL varies intake valve lift by hydraulically and mechanically locking the tappet into a higher position by means of a transverse pin. The effect is that of having two separate tappets to act on the camshaft lobe operating the intake valve. Subaru VVL uses three lifter profiles for each intake valve lifter. The low-mid profile boosts air induction speed for greater torque. The high-lift mode decreases induction resistance for higher output.

Variable lift works on one of the two intake valves. At low engine speeds, the two intake valves open at different levels, causing a swirl of air and fuel. At higher speeds, both valves are opened by the same amount. Customers will easily recognize the benefits of having AVCS and VVL: outstanding power and smooth, linear response at all speeds.

The Electronic Throttle Control (ETC) is a drive by wire system that ensures smooth throttle response and also helps to optimize fuel consumption and emissions. The ETC system eliminates the physical linkage between the throttle pedal and the engine. The throttle pedal is connected to an electronic servo-motor that automatically adjusts the engine's throttle plate. All of this is backed up by a complete redundant system for added confidence and reliability.

6-2-1 Exhaust System
The engine's efficiency includes its exhaust system. Individual header pipes for each exhaust port combine into a collector, with the assembly clad in dual-wall stainless steel. The dual-wall design retains heat more effectively to help bring the catalysts up to operating temperature quickly for reduced emissions. There is a separate oxygen sensor for each cylinder bank, also to enhance emission control. Twin rear mufflers help to minimize backpressure for improved engine breathing and efficiency.

5-speed Automatic Transmission with SPORTSHIFT
The 5-speed electronically controlled automatic transmission in the B9 Tribeca is adapted from the Outback 3.0R models. As in those vehicles, the transmission features the SPORTSHIFT control for manual gear shifting when desired. Subaru optimized shifting performance for the B9 Tribeca and also enhanced its performance on hills with new shift control logic.

The Subaru 5-speed electronic direct control automatic transmission employs advanced electronics and adaptive shifting logic. The transmission responds to driver input, selecting shift maps to optimize performance and fuel efficiency under various driving conditions. A lateral-g sensor and cornering logic enable the transmission to choose and hold the appropriate gear when cornering. The transmission helps maintain traction when the vehicle is accelerating away from a corner by calling for more rapid downshifting.

The torque converter uses a multiple-plate lockup clutch with an individual hydraulic circuit for better control. Torque converter lockup occurs in third, fourth and fifth gears - even in manual mode - for optimal fuel efficiency.

The transmission's SPORTSHIFT feature allows intuitive and responsive manual shift control when desired. When the shift handle is in the "Drive" position, the driver can gain manual control by moving it to the left, then pushing either forward to select a higher gear or rearward to select a lower gear.

The 5-speed automatic has been optimized for use in the B9 Tribeca. First, second and third gears and the final drive ratios have been lowered to optimize engine performance in the heavier vehicle, and to account for the larger circumference of the standard 18-inch tires (compared to 17-inch tires on Outback models).

In addition, the shift schedule has been modified for the heavier vehicle, with emphasis on improved performance in hilly terrain. Kickdown points have been optimized, and the transmission now offers a direct fifth-to-third kickdown at low speeds.

The 5-speed automatic transmission features slope control. On inclines, the transmission helps maintain traction by downshifting actively. For enhanced downhill control, the transmission maintains efficient engine braking by holding the most suitable gear. For the B9 Tribeca, the electronic controls now take into account available engine power (which can change with altitude) in addition to road slope when selecting the shift map.

For durability, the final drive gears have been strengthened and both transmission and rear differential fluid capacity are increased for enhanced cooling. The rear differential features larger cooling fins, and the instrument panel includes a rear differential oil temperature warning light. A new phosphate-based Ryubu light coating process for the front and rear differential gears helps to further improve efficiency.

The transmission makes extensive use of aluminum, including the oil pump cover, clutch drums and planetary carrier. At 121 kg (267 pounds), including fluid, the Subaru transmission is one of the lightest 5-speed automatics available. This is even more remarkable considering that the weight includes the All-Wheel Drive transfer gearing and front differential, which are integrated into the transmission case. In the B9 Tribeca, combining the transmission's intermediate and extension cases (containing the VTD All-Wheel Drive centre differential) simplifies assembly and reduces weight by about 0.5 kg (about a pound).

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