POWERTRAIN OVERVIEW
The RL powertrain features a 3.5-liter V-6 engine, VTEC®, a 5-speed automatic with Sequential SportShift, paddle shifters and Grade Logic Control and Super Handling All-Wheel Drive. The crankshaft of the RL is positioned transversely (side to side) instead of longitudinally (front to rear), which allows the RL to be packaged more tightly for better handling agility, without sacrificing interior comfort.
The advanced VTEC® engine develops 290 horsepower and 256 lbs-ft of torque. Fuel economy is 18/26 estimated City/Highway and meets CARB LEV-2 ULEV requirements.
While it is as powerful as some competitive V-8 engines, the high output V-6 in the RL is lightweight for better acceleration and more nimble handling. To put the power to the ground with a high level of efficiency, smoothness and driver control, the RL comes standard with a 5-speed automatic with Sequential SportShift and paddle shifters to allow finger-tip manual operation.
To maximize available traction and to provide exceptional handling balance and responsiveness, the RL comes standard with Super Handling All-Wheel Drive™ (SH-AWD™), the first and only all-wheel drive system that distributes the optimum amount of torque not only between the front and rear wheels but also between the left and right rear wheels. The system's direct yaw control makes the cornering character of the RL exceptionally neutral under power.
POWERTRAIN AT A GLANCE
Engine
- 3.5-liter, SOHC, VTEC® V-6 engine produces 290 horsepower at 6200 rpm and 256 lbs-ft. of torque at 5,000 rpm
- VTEC® (Variable Valve Timing and Lift Electronic Control)
- 11.0:1 Compression ratio
- Two-piece, dual-stage intake manifold
- Direct ignition system and detonation/knock control
- Variable flow exhaust system
- Drive-by-wire throttle system
- Computer-controlled Programmed Fuel Injection (PGM-FI)
- Maintenance Minder System optimizes service intervals
- 100,000 miles or more tune-up interval
Emissions/Fuel Economy
- High flow close-coupled catalytic converters plus under floor catalytic converter
- High capacity 32-bit RISC processor emissions control unit
- Meets CARB LEV-2 ULEV standard
- EPA estimated 18/26 mpg (City/Highway)
Noise, Vibration & Harshness (NVH)
- 60-degree V-angle for inherently smooth operation
- Automatically tensioned, maintenance free serpentine accessory drive
5-speed Automatic with Sequential SportShift, Paddle Shifters and Grade Logic Control
- Quick-response Sequential SportShift allows semi-manual operation
- Steering-wheel mounted manual-mode F1®-style paddle shifters
- Coordination between drive-by-wire throttle system and transmission makes for quicker, smoother shifts
- Wide gear ratio spacing for strong acceleration and good fuel economy
- Advanced shift-hold control limits upshifts during spirited driving
- Advanced Grade Logic Control System reduces gear "hunting" when driving on steep hills
Super Handling All-Wheel Drive™ (SH-AWD™)
- Fully automatic, full-time traction and handling enhancing system
- Distributes torque between the front and rear wheels and between the left and right rear wheels to directly control the yaw moment of the vehicle
- Understeer is reduced when cornering
- Outer wheel capable of being overdriven during cornering by up to five percent
ENGINE ARCHITECTURE
The 3.5-liter VTEC® V-6 in the RL is the most powerful production engine in Acura's history and incorporates many of the refinements and improvements that have been developed in other Acura powerplants. The RL engine has a smooth-firing 60-degree V-angle and compact overall dimensions. Aluminum alloy construction saves weight and improves cooling, while free-breathing VTEC® cylinder heads operate four valves per cylinder.
A high inertia intake system, increased compression ratio, close-coupled catalytic converters and high flow exhaust help make the RL engine the most powerful normally aspirated 6-cylinder engine in its class.
ENGINE BLOCK
The lightweight, heat-treated die-cast aluminum-alloy block has cast-in-place iron cylinder liners. These thin-wall, centrifugal-cast iron liners help reduce the block's overall length and weight. With their rough outer surfaces, these liners bond securely to the surrounding aluminum during the manufacturing process, enhancing liner-to-block rigidity and heat transfer. The block also incorporates a deep-skirt design for rigid crankshaft support and minimized noise and vibration.
CRANKSHAFT / PISTONS / CONNECTING RODS
The forged crankshaft of the RL is equipped with revised counterweights to accommodate the weight of higher compression pistons. With their taller, reinforced crowns, these new pistons raise the compression ratio from 10.0:1 to 11.0:1. Part of the reason this elevated compression ratio is possible is an oil jet system that sprays cooling oil on the underside of the piston crowns to keep temperatures in check. New steel connecting rods are forged in one piece and then the crankshaft ends are broken, creating a lighter and stronger rod with a perfectly fitted bearing cap.
CYLINDER HEADS / VALVES
Like the TL, the RL uses cast alloy single overhead camshaft cylinder heads that incorporate tuned exhaust manifolds as an integral part of the casting. Made of pressure-cast, low-porosity aluminum, these lightweight components improve overall packaging, enhance exhaust flow and allow the optimal positioning of a primary close-coupled catalytic converter on each cylinder bank. To ensure positive sealing, the RL has a three-layer type head gasket like that of the TL. A single Aramid-fiber reinforced belt drives the overhead camshafts. The RL cylinder heads have 36mm diameter intake valves and 30mm diameter exhaust valves.
VTEC® (VARIABLE TIMING AND LIFT ELECTRONIC CONTROL)
Acura VTEC® (Variable Timing and Lift Electronic Control) is a major contributor to the engine's large gains in horsepower and torque. The system operates the 12 intake valves in two distinct modes, so that the operation of the intake valves changes to optimize both volumetric efficiency and combustion of the fuel-air mixture. At low engine speeds, the intake valves have low lift and are open a comparatively short period of time during cylinder filling. At high engine speeds where breathing is critical, the valves switch to high-lift, long duration mode to deliver the best volumetric efficiency. The VTEC™ changeover point is undetectable to the driver and occurs at 4950 rpm.
The RL uses a 3-rocker VTEC® system similar to that of the all-new MDX and TL. This configuration allows each of a given cylinder's intake valves to be controlled by its own low-speed cam lobe, allowing for staggered valve opening and lift. (By comparison, with 2-rocker VTEC, a single low-speed cam lobe controls both intake valves for each cylinder). Better mixing in the cylinders improves both combustion speed and combustion stability. When the engine reaches 4950 rpm, the powertrain control module (PCM) triggers the opening of an electric spool valve that routes pressurized oil to small pistons in the intake valve rocker arms. These pistons slide into position to lock together the three intake rockers in a given cylinder, which then follow a single high-lift, long-duration cam lobe. The intake and exhaust valve timing and duration is unique to the RL.
TWO-PIECE DUAL-STAGE INTAKE MANIFOLD
The RL uses a dual-stage intake manifold that is designed to deliver maximum airflow, to the cylinders. The 2-piece cast-aluminum manifold is also very light and saves the RL 2.6 lbs.
Working in concert with the VTEC® valve train, the induction system significantly boosts torque across the engine's full operating range. Internal passages and two butterfly valves commanded by the powertrain control module provide two distinct modes of operation.
These valves are closed at lower rpm. In this mode, the three cylinders on each bank draw air from only the nearer half of the manifold's internal chamber, or plenum. The volume of the plenum and the length of inlet passages are tuned to maximize the resonance effect, wherein pressure waves are amplified within each half of the intake manifold at certain rpm ranges. The amplified pressure waves significantly increase cylinder filling and the torque produced by the engine throughout the lower part of its rpm band. Funnel-shaped intake ports-similar to those used on racing engines-are built in at the uppermost end of each intake runner to improve airflow.
As the benefits of the resonance effect lessen with rising engine speed, the butterfly valves open at 4000 rpm to interconnect the two halves of the plenum, increasing its volume. An electric motor, commanded by the powertrain control module, controls the connecting butterfly valves. Now each cylinder draws intake air from the full plenum chamber. The inertia of the mass of air rushing down each intake passage helps draw in more charge than each cylinder would normally ingest. This phenomenon is the same effect produced by a low-pressure supercharger. The inertia effect greatly enhances cylinder filling and the torque produced by the engine at higher rpm.
DIRECT IGNITION AND DETONATION/KNOCK CONTROL
The RL power afforded by the 11.0:1 compression ratio is made possible by a powertrain control module (PCM) that monitors engine functions to determine the best spark timing. An engine block mounted acoustic detonation/knock sensor "listens" to the engine; and based on this input, the PCM retards the ignition timing incrementally to prevent potentially damaging detonation. The RL has iridium alloy-tipped sparkplugs, each with a coil unit positioned above it in the access bore.
PROGRAMMED FUEL INJECTION (PGM-FI)
The Programmed Fuel Injection (PGM-FI) system monitors the exact state of the exhaust gas and tracks multiple engine inputs including throttle position, intake air temperature, coolant temperature, intake manifold pressure, etc. Based on these inputs PGM-FI continuously adjusts and optimizes the amount of fuel delivered to each cylinder.
DRIVE-BY-WIRE THROTTLE CONTROL SYSTEM
The RL utilizes a drive-by-wire throttle system that eliminates the need for a conventional throttle cable. The system monitors various parameters like throttle pedal position, throttle valve position, road speed, engine speed and gear position, then adjusts the moment-to-moment relationship between pedal position and throttle opening. By altering the amount of "gain" between the pedal and butterfly valve, significant improvements in drivability and acceleration linearity are possible.
For smooth launches from a standing start the system has relatively little gain, so that engine response is smooth and progressive. At higher speeds, the gain increases to provide responsive acceleration for passing and hill climbing. The Sequential SportShift automatic transmission and Vehicle Stability Assist® (VSA®) with traction control are fully integrated with drive-by-wire.
CLOSE-COUPLED CATALYZERS AND VARIABLE FLOW EXHAUST SYSTEM
The exhaust manifolds of the RL are cast directly into the alloy cylinder heads to reduce weight and to put the engine's two primary catalytic converters as close as possible to the combustion chambers. The 600-cell per-square-inch, high-efficiency converters mount directly to the exhaust port of each cylinder head for extremely rapid converter light off after the engine starts. By eliminating traditional exhaust header pipes, this arrangement results in a significant weight savings.
A hydroformed 2-into-1 collector pipe carries exhaust gases to a single 350 cell-per-inch secondary converter under the passenger cabin. To balance the engine's need for proper exhaust backpressure at low speed and free flow at high speed, the exhaust system incorporates a variable flow rate feature. An exhaust pressure-operated valve in the system has two operating modes. The low speed mode has a flow rate of 130 liters per second; when the engine reaches about 4000 rpm, the exhaust pressure rises enough to open the valve, which increases the flow to 150 liters per second.
EMISSIONS CONTROL
Although the new RL powerplant has made large power advances, it has also gotten much cleaner. It now meets the tough CARB LEV-2/ULEV emissions standards, and is certified to this level of emissions performance for 120,000 miles (20,000 more than required by the current LEV standard).
Many advanced technologies contribute to this emissions performance. The cylinder head-mounted close-coupled catalysts light off quickly after engine start up, and a 32-bit RISC microprocessor in the powertrain control module (PCM) boosts computing power to improve the precision of spark and fuel delivery. Particularly right after startup, better fuel atomization is provided by high-efficiency multi-hole fuel injectors; these deliver fuel to each cylinder and direct fuel around the intake valve stems.
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Current Carb* Emission Standards (gram/mi.) |
||||
| Standard | NMOG* | CO | NOx | Vehicle |
| LEV-I LEV @ 100k | 0.090 | 4.200 | 0.300 | '04 3.5 RL |
| LEV-I ULEV @ 100k | 0.055 | 2.100 | 0.300 | - |
| LEV-2 LEV @ 120k | 0.090 | 4.200 | 0.070 | - |
| LEV-2 ULEV @ 120k | 0.055 | 2.100 | 0.070 | '05-'07 RL |
| LEV-2 SULEV @ 150k | 0.010 | 1.000 | 0.020 | - |
| ZEV | 0.0 | 0.0 | 0.0 | - |
*California Air Resources Board
NOISE, VIBRATION AND HARSHNESS (NVH) CONTROL
With its 60-degree V-angle and compact, rigid and lightweight die-cast aluminum-alloy block assembly, the new RL powerplant is exceptionally smooth. Other factors that reduce noise and vibration are a rigid forged crankshaft, die-cast accessory mounts, and a stiff, cast aluminum-alloy oil pan.
100,000 MILES OR MORE TUNE-UP INTERVALS
The RL requires no scheduled maintenance for 100,000 miles or more, 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.
MAINTENANCE MINDER SYSTEM
To eliminate unnecessary service stops while ensuring that the vehicle is properly maintained, the RL has a Maintenance Minder system that automatically monitors the vehicle's operating condition. When maintenance is required, the driver is alerted via a message on the Multi-information display.
The system monitors operating conditions such as oil and coolant temperature and engine speed to determine the proper service intervals. Depending on the operating conditions, oil change intervals can be extended to a maximum of 10,000 miles, potentially sparing 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 and filter, tire rotation, air-cleaner, automatic transmission fluid, spark plugs, timing belt, coolant, brake pads and more.To prevent driver distraction, maintenance alerts are presented when the ignition is first turned on, not while driving.
5-SPEED AUTOMATIC WITH SEQUENTIAL SPORTSHIFT, PADDLE SHIFTERS AND GRADE LOGIC CONTROL
To maximize acceleration performance, fuel economy and driver control, the RL has a standard 5-speed automatic with Sequential SportShift, paddle shifters and Grade Logic Control. Mechanically related to the extremely compact transmission that made its debut in the 2003 MDX, the RL unit has upgrades and enhancements to suit the greater engine output and higher engine speeds of the RL.
Designed for low maintenance and a high level of durability, the RL transmission requires no scheduled service until 120,000 miles when operated under normal conditions. To provide strong off-the-line acceleration coupled with a relaxed, fuel-efficient cruising rpm, the unit has the widest ratio spread of any 5-speed automatic transmission in the class.
Automatic Mode
The Sequential SportShift transmission can be operated in conventional fully automatic mode via a front center console-mounted gated shifter. When in automatic mode, the transmission incorporates an advanced Grade Logic Control System and Shift Hold Control, both of which work to reduce gear "hunting" and unnecessary shifting.
Shift Hold Control keeps the transmission in its current (lower) ratio when the throttle is quickly released and the brakes are applied (as might be the case when decelerating to enter a corner). Shift Hold Control leaves the chassis undisturbed by excess shifting, ensuring that abundant power is immediately available without a downshift.
Grade Logic Control alters the 5-speed automatic's shift schedule when traveling uphill or downhill, reducing shift frequency, and improving 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; if this is the case, the shift schedule is adjusted to automatically hold the transmission in a lower gear for better climbing power or increased downhill engine braking.
Manual Mode
The Sequential SportShift transmission can be shifted into manual mode by moving the front center console-mounted selector lever laterally to a special gate to the left of the "Drive" position. The RL offers two ways to change gears when in manual mode: either by a push or pull of the shift lever, or via F-1®style paddle shifters mounted on the steering wheel. A digital display in the tachometer face indicates which gear the transmission is in. To heighten control and driver involvement, special shift logic in manual mode delivers quicker, firmer shifts than in fully automatic mode.
To help protect the engine and drivetrain from damage, an array of preventative features are active when the transmission is in manual mode. In second, third and fourth, the logic changes, and the transmission ECU cuts off fuel flow to the engine if there is a possibility of over revving.
In the rare situation where the fuel cutoff alone is unable to prevent engine over revving (as could happen on a steep downhill) the transmission will upshift itself to prevent engine damage. And finally, when downshifting, the transmission won't execute a driver-commanded downshift that would send the engine beyond redline in the lower gear. The
Sequential SportShift transmission will automatically downshift to first gear as the vehicle comes to a stop, to prevent lugging away from a stop in a high gear.
5-POSITION SHIFT GATE
The RL benefits from an innovative 5-position shift gate that simplifies the operation of the transmission. It features a quiet linkage and a speed-controlled reverse lockout solenoid to prevent transmission damage. When operated in automatic mode, the transmission lets the driver choose D (1st through 5th gear) or D3 (1st through 3rd gear). Engine braking can be provided easily by moving from D to the D3 position, downshifting from 5th, 4th or 3rd gear, depending on the vehicle speed.
COOPERATION BETWEEN 5AT AND DRIVE-BY-WIRE
Both shift speed and smoothness are improved by cooperation between the drive-by-wire throttle system and the electronically controlled automatic transmission. The engine can be throttled by the engine management system during upshifts and downshifts, the function of the engine and transmission can be closely choreographed for faster, smoother shifting. As a result, the peak g's (or "shift shock") are reduced significantly during upshifts and downshifts.
SUPER HANDLING ALL-WHEEL DRIVE SYSTEM™
Super Handling All-Wheel Drive™ (SH-AWD™) is an innovative all-wheel drive platform that distributes the optimum amount of torque not only between the front and rear wheels but also between the left and right rear wheels. SH-AWD™ goes a step beyond conventional all-wheel drive by actively controlling the torque delivered to each rear wheel during corning. The result is neutral, accurate steering when cornering under power that front-drive, rear-drive or conventional all-wheel-drive can't equal.
Torque splits are as follows:
- During straight-line cruising and moderate cornering below about half throttle, up to 70 percent of the torque is delivered to the front wheels.
- In full-throttle straight line acceleration, up to 40 percent of the power is sent to the rear axle.
- In hard cornering, up to 70 percent of available torque goes to the rear wheels for enhanced chassis balance. Up to 100 percent of this torque can be applied to the outside rear wheel and that wheel can be overdriven up to five percent by the acceleration device if the situation dictates.
SH-AWD™ ingeniously varies the amount of torque to the left and right rear wheels. When cornering, a planetary gear set overdrives (or accelerates) the rear wheels while individual right and left clutch packs direct torque to either or both rear wheel, faster than the average of the front wheels to dramatically enhance the cornering, steering feel, overall handling and stability of the RL. The result is class leading cornering precision as well as enhanced traction.
Direct Yaw Control System Theory
SH-AWD™ counters understeer under power with the Direct Yaw Control System. Spinning the outside rear wheel faster than the average speed of the two front wheels allows the system to use engine power to yaw the vehicle while turning. By relieving the front tires of some of the work of turning the car, the system reduces understeer and the vehicle stays balanced and controllable. In addition, with the cornering load more evenly distributed between the front and rear tires, the total cornering grip is increased. In conventional cars, cornering is created almost entirely by the steering angle of the front tires; In the RL, cornering is created by steering angle of front tires combined with the extra drive torque supplied by the outside rear tire.
This is a significant advance over conventional drive systems. To deal with high power output, front- or rear-drive systems generally use some type of limited-slip device to maintain traction under power. The linking effect of the inside and outside drive wheels in these systems resists turning, however. This is a factor that works against the front tires as they attempt to turn the car. Conventional AWD systems have a similar linking effect between the inboard and outboard tires and front and rear axles, causing a similar resistance to turning. This is part of the reason why traditional AWD systems typically lack the more nimble feel of the best two-wheel drive systems. By using drive torque to actually help turn the car, the RL can be more responsive, neutral and predictable, while simultaneously offering all of the usual benefits of all-wheel drive.
Electronic Controls and Parameters
The logic and control of SH-AWD is integrated with the RL Engine Electronic Control Unit (ECU), and Vehicle Stability Assist (VSA) ECU. The Engine ECU provides engine rpm, intake manifold pressure, and transmission gear ratio data. The VSA ECU provides data on lateral g, yaw rate, wheel rotation speed and steering angle. The SH-AWD ECU monitors the status of the acceleration device and the right and left Direct Electromagnetic Clutch torque. Traction is calculated based on the information from the engine ECU. During an acceleration situation, lateral g and steering angle are used to set the torque split between the right and left rear wheels. At the same time, this data is used to control the acceleration device.
SH-AWD™ System Layout
SH-AWD™ is a full-time all-wheel drive system that requires no driver interaction for operation. A torque transfer unit is bolted directly to the front-mounted transaxle. Attached to the front wheel differential's ring gear is a helical gear that provides input torque to the transfer unit. A short horizontal shaft and a hypoid gear set within the case turn the propeller shaft ninety degrees and move it to the vehicle center line. A lightweight carbon fiber reinforced composite propeller shaft carries power to the reardrive unit.
The rear drive unit of the RL contains three planetary gear and clutch sets. Torque from the propeller shaft passes through the first clutch/planetary gearset, which is as a unit called the Acceleration device.
Output torque from the Acceleration device is carried a short distance rearward to a hypoid gear that turns the output 90-degrees and drives the rear axle shafts. A matched pair of Direct Electromagnetic Clutch systems, one on each side, send power to each rear wheel. These clutch systems can be controlled as a pair to alter the front/rear torque split; depending on the situation, the rear wheels receive between 30 and 70 percent of the total engine output. The right and left Direct Electromagnetic Clutch systems can also be controlled independently, to allow up to 100 percent of the total rear axle torque to go to only one rear wheel.
Acceleration Device
Positioned at the front of the RL rear drive unit, the Acceleration device typically passes torque rearward to the rear axle at very close to a one-to-one ratio. In cornering, however, the Acceleration device's output shaft spins faster than its input shaft.
The Acceleration assembly uses a compact planetary gearset to achieve its speed increase. Hydraulic actuators operate clutch packs that control the planetary gearset. When the input shaft is locked with the planetary gear carrier, there is no ratio change (this is the straight-line mode). During cornering, the carrier is coupled with the case, and the output shaft speed increases up to five percent. A speed sensor at the hypoid gear, downstream of the Acceleration device provides a feedback loop to the SH-AWD Electronic Control Unit to ensure that the system is working properly.
Direct Electromagnetic Clutch Systems
Located on either side of the hypoid gear that drives the rear axle, two identical Direct Electromagnetic Clutch systems control the amount of drive torque that reaches each rear wheel, and provide limited-slip differential function. An electric coil controls the pressure applied to a clutch, which slows the sun gear in a planetary gearset to modulate the torque that is sent to the wheel. The amount of torque transmitted to each rear wheel can vary continuously, between zero and 100 percent, depending on the conditions.
Under deceleration (throttle closed) while cornering, torque to the outside rear wheel is varied to change from an inward to an outward yaw moment, helping vehicle stability. A search coil sensor allows the ECU to estimate the clutch plate coefficient of friction (which changes with heat,) and then adjusts voltage sent to the electromagnetic coil that controls the clutch to compensate. To ensure that the amount of torque transmitted remains optimized as miles and wear accumulate, a coil provides a feedback loop that the ECU uses to adjust voltage to the electromagnetic clutches to compensate for potential clutch wear.