2005 Acura TL Powertrain - Part 2


Like the previous TL Type-S and the MDX, the TL has a dual-stage intake manifold. Working in concert with VTEC, this manifold improves low-speed torque without sacrificing high rpm power. The manifold is divided into two banks with three cylinders fed by each bank. The powertrain control module (PCM) controls butterfly valves between each bank. At low engine speeds the valves are closed; each separate bank of the manifold is tuned to maximize the resonance effect of the incoming air and increase cylinder filling and the torque through the lower part of the engine's rpm range.

As the engine rpm rises, the resonance effect fades, and the butterfly valves connecting the two banks of the intake manifold open. Now the resonance from individual pressure pulsations is eliminated, and an inertia affect helps the mass of air rushing down each intake passage. This provides more charge than each cylinder would normally ingest, working like mild supercharging to enhance horsepower at high engine speeds. The manifold changeover rpm is set somewhat lower in the rpm range than is the VTEC changeover rpm. This works to smooth and broaden the torque delivery. More than 75 percent of the peak torque is available from 2100 rpm to 6500 rpm.


Optimum ignition spark timing is crucial to engine power and efficiency, and varies based on the engine's load, rpm, temperature and other factors. The powertrain control module (PCM) monitors engine functions to determine the best spark timing. An engine block mounted acoustic detonation-knock sensor "listens" to the engine; based on this input, the PCM retards the ignition timing incrementally to prevent potentially damaging detonation. Platinum-tipped sparkplugs are applied, each with an individual coil unit positioned above in the access bore, and require no service prior to 105,000 miles.


The Programmed Fuel Injection (PGM-FI) system tracks several engine inputs including throttle position, intake air temperature, water temperature, intake manifold pressure, etc. and monitors the exact state of the exhaust gas. Based on these inputs PGM-FI knows when to trigger and how long to keep open the high efficiency multi-hole injectors that deliver fuel to each cylinder.


Like the TSX sports sedan, the TL engine has an advanced Drive-by-Wire Throttle System (DBW) technology that eliminates the need for a conventional throttle cable. With the driver's throttle pedal movements interpreted electronically, the precise relationship between pedal movement and throttle butterfly valve opening can be varied to suit the driving conditions. By altering the amount of "gain" between the pedal and butterfly valve, significant improvements in drivability are possible. DBW also allows the Sequential SportShift automatic transmission and Vehicle Stability Assist (VSA) with traction control to be fully integrated with engine function.

The DBW system monitors various parameters such as pedal position, throttle position, road speed, engine speed and gear position. These inputs are then used to set the moment-to-moment relationship between the pedal position and throttle butterfly opening. In low-speed driving, the system has relatively little gain, so that engine response is smooth and progressive for smooth launches from a standing start. At higher speeds, the gain progressively increases to provide confident acceleration for passing and climbing hills.


To reduce weight and move the engine's to primary catalytic converters as close as possible to the combustion chambers, the TL exhaust manifolds are cast right into the cylinder heads. A 900-cell per-square-inch high efficiency converter mounts directly to the exhaust port of each cylinder head for extremely rapid converter light off after the engine starts. This mounting system has the added benefit of eliminating traditional exhaust header pipes, which saves a total of 17.6 pounds.

To ensure optimum flow and reduce backpressure, a hydroformed 2-into-1 collector pipe carries spent gases down to a 350 cell-per-inch secondary converter under the passenger cabin. The design for the exhaust system downstream of the secondary catalyst, including the dual silencers, further reduces back pressure and is 11 percent lighter than the comparable Type-S arrangement. Because these smaller silencers are easier to package, the rear of the TL has a more refined appearance, finished by dual trapezoidal exhaust outlets that are tightly integrated into the rear fascia.


To develop class-leading power while meeting tight CARB LEV-2/ULEV emissions standards, the TL pushes technology on multiple fronts. It makes more horsepower while creating less exhaust emissions-and is certified to this level of emissions performance for 120,000 miles (20,000 more than required by the current LEV standard).

The cylinder head-mounted close-coupled catalysts ensure very quick light off after engine start up, and a 32-bit RISC microprocessor in the powertrain control module (PCM) boosts computing power. High efficiency multi-hole fuel injectors deliver fuel to each cylinder and direct fuel around the intake valve stem for improved atomization, which helps to further reduce emissions, particularly after starting.

Current CARB* Emission Standards (gram/mi.)

Standard NMOG* CO NOx Vehicle
TLEV @ 100k 0.156 4.200 0.600 -
LEV I LEV @ 100k 0.090 4.200 0.300 '03 3.2 TL Type-S
LEV I ULEV @ 100k 0.055 2.100 0.300 '03 3.2 TL
LEV 2 LEV @ 120k 0.090 4.200 0.070 -
LEV 2 ULEV @ 120k 0.055 2.100 0.070 '05 TL
LEV 2 SULEV @ 150k 0.010 1.000 0.020 -
ZEV 0.0 0.0 0.0 -

*California Air Resources Board
*NMOG = Non Methane Organic Gas


The TL has an inherently smooth-running 60-degree V-angle and a compact, rigid and lightweight die-cast aluminum-alloy block assembly. A rigid forged crankshaft, die-cast accessory mounts, and a stiff, cast aluminum-alloy oil pan also contribute to overall engine smoothness. Both the induction system and the lightweight exhaust system have been tuned to create a refined, sporty engine sound at large throttle openings and high rpm.


With long-lasting components like platinum-tipped spark plugs and a space-saving, self-tensioning serpentine accessory drive belt, the TL is an exceptionally low maintenance automobile. It requires no scheduled maintenance until 105,000 miles, other than periodic inspections and normal fluid and filter replacements. This first tune-up includes water pump inspection, valve adjustment, and replacement of the cam-timing belt and sparkplugs.


The TL has a Maintenance Minder system that automatically monitors the vehicle's unique operating condition to indicate to the driver when maintenance is required. Maintenance alerts are presented when the ignition is first turned on, not while driving (to prevent driver distraction). The system monitors engine operating conditions such as fluid temperatures and engine speed to determine the proper service intervals. The Multi-Info Display (MID) located below the fuel and engine temperature gauges in the instrument cluster indicates the remaining percentage of engine oil life, and then shows service is due with a "wrench" icon. A percentage-based countdown to the next service is displayed when the car is within 15 percent of the end of the service interval. A letter and number code is displayed to indicate the specific type of service that is required. If the service is missed, the MID indicates past-due mileage to express the urgency of the required service to the driver.

The system is designed to eliminate unnecessary maintenance procedures, environmental impact and expenses, while ensuring that important service issues are addressed. In some cases, oil change intervals can extend to a maximum of 10,000 miles, which could spare the owner considerable money and inconvenience over the life of the car. The owner-resettable system monitors all normal service parts and systems, including oil, oil filter, tire rotation, air-cleaner, automatic transmission fluid, spark plugs, timing belt, coolant, brake pads and more.


To further sharpen the enthusiast edge of the TL, it's offered with an available close ratio 6-speed manual transmission. This precise, short-throw unit is designed to take advantage of the high power and torque of the TL engine and give enthusiast drivers maximum control and responsiveness.

This compact transmission is about the same size as a comparable 5-speed manual and is substantially lighter than the TL's Sequential SportShift automatic transmission. It features a high-pressure-cast aluminum-alloy transmission housing to save weight. To further reduce weight and size, special narrow, high-strength steel gears are used, and the shafts are hollow. Close ratio spacing helps provide quicker acceleration by keeping engine revs up close to the power peak. Brass multi-cone synchronizers are used on first through fourth gear with a single-cone synchronizer for reverse to reduce shift load and help ensure smooth, precise shifting. A large gear-teeth contact area helps to reduce gear noise. A reverse lockout feature prevents the transmission from accidentally being shifted into reverse while the car is moving forward.


The TL has a compact clutch unit that's self-adjusting for consistent pedal height, feel and effort throughout its service life. This innovative clutch system automatically takes up the slack between the pressure plate and clutch disc and lowers release loads while maintaining consistent pressure for the diaphragm spring.

To reduce drivetrain shock and limit the torque load on transmission components, the clutch includes a one-way delay orifice (check valve) located in the slave cylinder that restricts return fluid flow during rapid clutch engagement. This makes the clutch engagement more gradual during overly aggressive release.

A dual-mass flywheel helps to reduce noise, cut down the transfer of engine vibration into the cabin and provide increased comfort during shifting. This unit is divided into two flywheels with a torsion spring and viscous damper sandwiched between the two. This design enhances the durability of the synchronizers, reduces vibration and gear rattle and reduces the shift load.


When equipped with the 6-speed manual transmission, the TL features a standard limited-slip differential (LSD). This helical-gear-type LSD enhances traction during acceleration and reduces understeer in high cornering load situations.
A set of helical gears mounted within the ring gear carrier responds to wheel spin at either front wheel by directing torque from the spinning wheel to the wheel with the best traction. This system improves traction when cornering, and when negotiating slippery surfaces or surfaces where traction is uneven from side to side.


To combine the convenience of an automatic transmission with the precise driver-oriented control of a manual, the TL features a 5-speed Sequential SportShift automatic. Five closely spaced ratios help deliver strong acceleration combined with a high level of fuel efficiency at cruising speed. The Drive-by-Wire Throttle System allows the engine and transmission to coordinate their functions electronically, resulting in much quicker and smoother upshifts and downshifts.

When in automatic mode, the transmission incorporates an advanced Grade Logic Control System and Shift Hold control, which work to reduce gear "hunting" and unnecessary shifting.

To cut down on unnecessary shifting when negotiating winding roads, the Sequential SportShift automatic incorporates improved logic called Shift-Hold Control. When the throttle is suddenly released and the brakes are applied, as is the case when decelerating at the entrance of a corner, Shift-Hold Control keeps the transmission in its current (lower) ratio as it negotiates the corner and accelerates out. This feature leaves the chassis undisturbed by excess shifting, and ensures that abundant power is available without a downshift at the exit of the corner.

The 5-speed automatic alters its shift schedule when traveling uphill or downhill to reduce shift frequency, and improve speed control. Throttle position, vehicle speed and acceleration/deceleration are continuously measured, then compared with a map stored in the transmission computer. The Grade Logic Control System then determines when the car is on a hill and automatically adjusts the shift schedule to hold the engine in a lower gear for better climbing power or increased downhill engine braking.

Manual Mode Operation

The Sequential SportShift transmission can be shifted into manual mode by moving the selector lever laterally to a special gate to the left of the "Drive" position. When in the manual gate, a forward push selects a higher gear and a rearward pull selects a lower gear. Special shift logic in manual mode delivers quicker, firmer shifts than in fully automatic mode. An LED display in the instrument panel indicates which gear the transmission is in.

A variety of safety features help protect the engine and drivetrain from damage. The transmission will upshift from first to second automatically if the driver doesn't command an upshift in time. In second, third and fourth, the transmission won't upshift without a command from the driver; the ECU cuts off fuel flow to the engine if there is danger of over-revving the engine. The transmission will upshift itself to prevent engine damage in the rare situation where the fuel cutoff alone is unable to prevent further engine over revving (as could happen on a steep downhill). When downshifting, the transmission won't execute a driver-commanded downshift that would send the engine beyond redline in the lower gear. To prevent lugging away from a stop in a high gear, the Sequential SportShift transmission will automatically downshift to first gear as it comes to a stop, even in manual mode.


The TL benefits from a 5-position shift gate that simplifies the operation of the transmission. It features a quieter linkage and a speed-controlled reverse lockout solenoid to prevent transmission damage. When operated in automatic mode, the transmission lets the driver choose between D (Drive) and L (Low). When moved to the Low position, the transmission downshifts to the lowest possible ratio for the current road speed to provide maximum engine braking. If the vehicle continues to slow, the transmission progressively downshifts to maintain engine braking effect. When it has shifted all the way down to first gear, an upshift back to second gear is automatically available if speed increases, but the transmission won't upshift further unless the driver moves the selector back to the D (Drive) position where normal transmission operation resumes.


The 5-speed Sequential SportShift automatic includes a suitable generation of active lockup torque converter that improves fuel economy while maintaining a high level of drivability. A precise linear solenoid expands the speed and throttle setting range in which lockup can be engaged in the top four gears. This results in a reduction in transmission slippage for an improvement in fuel mileage. The torque converter is now calibrated to offer more progressive acceleration than in the past, coupled with better acceleration at large throttle openings. The efficient Sequential SportShift automatic transmission couples with tall overall gearing to deliver 28 mpg on the highway. City mpg for both transmissions is identical at 20 mpg


With the Drive-by-Wire Throttle System, the function of the engine and transmission can be closely choreographed for faster, smoother shifting. Upshifts from first to second gear, and from second to third gear, are more than 0.3 seconds quicker-a 33 percent or better improvement. In manual mode, driver-commanded downshifts are also more than 0.3 second quicker. Meanwhile, the peak g-or "shift shock"-has been reduced significantly during upshifts and downshifts.

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