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 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.
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.
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-1ģ 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 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.
COOPERATION BETWEEN 5AT AND DRIVE-BY-WIRE
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.