Acura RL. Manual - part 746

SYSTEM DESCRIPTION

SH-AWD SYSTEM

Outline

This vehicle is equipped with a Super Handling All-wheel Drive (SH-AWD) rear differential system. This
system uses electromagnetic clutches, an acceleration system, and the SH-AWD control unit to control front
to rear torque distribution and independent left to right rear torque distribution. This allows the system to
function both as a limited slip differential and as a torque distribution system to improve standing start
performance, straight-line stability, climbing, and cornering ability.

SH-AWD features include

Rear differential leaks fluid



Fluid level too high.



Clogged breather hose.



Worn or damaged oil seal.



Damaged sealing washer.



Loose mounting bolts or inadequate
sealing.



lower to proper
level



Clean or replace



Replace the oil
seal



Replace the
sealing washer



Recheck torque or
apply sealant

Rear differential screeches,
whines, moans, or squeaks



Fluid level too low.



Incorrect or worn out fluid.



Incorrect tire rolling circumference.



Damaged oil pump.



Add fluid



Drain and fill the
differential



Adjust tire
pressure or
replace tires



Replace the
differential carrier
assembly

Noise during acceleration,
or when accelerating from a
full stop



Incorrect side case clearance.



Incorrect pre-load.



Incorrect of backlash of hypoid gear.



Damaged or chipped gears.



Incorrect tire size (rolling
circumference).



Side case
clearance
adjustment



Pre-load
adjustment



Replace the
differential carrier
assembly



Replace the
differential carrier
assembly

HDS does not communicate
with the SH-AWD control
unit or the vehicle

Troubleshooting the DLC circuit; '05-07
models (see '05-07 MODELS ), '08 model (see
'08 MODEL ).

2007 Acura RL

2005-08 DRIVELINE/AXLES Rear Differential - RL

Friday, June 05, 2009 3:02:18 PM

Page 11



Independent torque distribution to the front and rear wheels, and to the left and right wheels for
neutral handling when cornering.



Controls differential (inside/outside) wheel speed in a turn to increase cornering stability.



Limited slip differential function for better acceleration.

Operation

In a normal turn the radius of the front wheels is shorter that the radius that the rear wheels travel. If the
front and rear wheels are driven at the same speed, full power is not transmitted. The SH-AWD system
monitors the speed of the front wheels and increases the speed of the outside rear wheel proportionally to
accelerate it around the larger radius. This improves stability and steering response. On slippery surfaces
this provides the improved traction of a 4-wheel drive system.

Fig. 9: Direct Electromagnetic Clutch System
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Construction

1. The differential assembly has a conventional hypoid ring and pinion gear set.

2. The acceleration system consists of the high clutch, the one-way clutch/low clutch, the planetary gear

set, and the oil pump. When accelerating straight ahead, the one-way clutch and the low clutch applies
the driving force to the rear wheels. During normal straight ahead driving, only the low clutch applies
driving force to the rear wheels. When turning, the high clutch connects the acceleration planetary
gear to the differential. This speeds up the rear wheels to compensate for the different paths the front
and rear wheels take. When decelerating, the differential drives the oil pump to generate hydraulic

2007 Acura RL

2005-08 DRIVELINE/AXLES Rear Differential - RL

Friday, June 05, 2009 3:02:18 PM

Page 12

pressure.

3. The direct electromagnetic clutch system consists of the coils, the planetary gear sets, and the multi-

plate clutches that are installed in the side cases on either side of the differential carrier. When driving
straight ahead, both rear wheels rotate at the same speed. When turning, current is applied to the
appropriate outside wheel main coil to engage the clutch. The amount of current passed through the
electromagnetic clutch controls the amount of driving force to the outside wheel.

Fig. 10: Cross-Sectional View Of Rear Differential
Courtesy of AMERICAN HONDA MOTOR CO., INC.

SH-AWD 4WD CONTROL SYSTEM

Control System

The SH-AWD control system consists of a SH-AWD control unit, the PCM, the VSA modulator-control
unit, and various sensors and switches that detect the steering angle, the lateral G force, the yaw, and the
vehicle speed. An oil temperature sensor and a speed sensor are located on in the rear differential. The
control units exchange information via the CAN communication lines. The SH-AWD control unit has a self-
diagnostic function. If a malfunction is detected, the SH-AWD control unit turns on the SH-AWD indicator
in the gauge assembly and the system goes into fail-safe mode. When in fail-safe mode, the vehicle disable
the SH-AWD differential. The vehicle defaults to front wheel drive, and the PCM reduces available engine
output.

Driving Force Control

2007 Acura RL

2005-08 DRIVELINE/AXLES Rear Differential - RL

Friday, June 05, 2009 3:02:18 PM

Page 13

The driving force control distributes the power based on the driver's inputs. It distributes torque to the front
and rear wheels based on the throttle opening and the available engine torque output. When turning, torque
is applied to the rear wheels independently based on the lateral G input and the direction of the turn. This
generates an inward yaw movement to help steer the vehicle around the turn.

Feedback Control

In low traction conditions, where a wheel will spin or the vehicle tends to skid, the amount of torque is
distributed to match the traction available.

Fig. 11: SH-AWD 4WD Control System Diagram
Courtesy of AMERICAN HONDA MOTOR CO., INC.

ACCELERATION SYSTEM

Construction

The acceleration system consists of the one-way clutch/low clutch, the high clutch, the planetary gear, and
the oil pump.

2007 Acura RL

2005-08 DRIVELINE/AXLES Rear Differential - RL

Friday, June 05, 2009 3:02:18 PM

Page 14

Content .. 744 745 746 747 ..