2005 Acura RL Powertrain Part 2


The RL power boost afforded by the new 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; 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.


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.


Like the NSX supercar and other Acura models, the RL utilizes a drive-by-wire throttle system that eliminates the need for a conventional throttle cable. The DBW 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.


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.


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.

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 '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 RL
LEV-2 SULEV @ 150k 0.010 1.000 0.020 -
ZEV 0.0 0.0 0.0 -

*California Air Resources Board

'04/'05 RL Emissions Comparison (gram/mi.)

Vehicle/Standard NMOG* CO NOx Certification mileage
'04 3.5 RL
0.090 4.200 0.300 100,000
'05 RL
0.055 2.100 0.070 120,000
'05 RL improvement
over '04 3.5 RL
39% 50% 77% 20%

*NMOG = Non Methane Organic Gas


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.


The RL 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.


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.


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 2005 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. 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.


The new RL benefits from a new 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.


Both shift speed and smoothness have been improved by cooperation between the new Drive-by-Wire Throttle System and the electronically controlled automatic transmission. Now that 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™ (SH-AWD™) is the first and only 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 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 outer 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 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. Then the 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 set 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 rear drive unit.

The rear drive unit of the RL, unlike the MDX, 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 side of the vehicle.

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