Tokyo — They may look like regular 2008 Honda Accord sedans, but the cars seen here are actually engineering mules for chassis and powertrain technologies that will underpin the 2014 Acura RLX luxury sedan.
The first technology is Precision All-Wheel Steering for front-wheel-drive versions of the 2014 Acura RLX. PAWS consists of two electrically adjustable suspension links, one at each rear wheel, that can adjust the alignment of each wheel by up to about two degrees. Steering the rear wheels isn’t a new idea in itself, but while previous systems moved the rear wheels by the same amount, Honda’s PAWS is claimed to the first that can operate the wheels independently on each side, allowing for better control.
PAWS has three primary procedures: Under hard braking, it angles both rear wheels inward slightly (toe in) to improve stability; in normal cornering, the rear wheels are angled opposite to the front wheels to reduce the car’s turning circle (in right turns, the rear wheels point toward the left of the car); and in some high-speed lane-change maneuvers, the rear wheels move in the same direction as the front wheels to improve stability.
We tested an Accord with the system on a 0.8-mile handling loop at Honda’s R&D facilities here in Japan and found it promising. When you enter a corner and add steering input, there’s a miniscule pause before you feel the car tighten its line slightly as the rear wheels add more steering. It produces a sensation of rotation that gives the car a livelier feel than is typical of front-wheel-drive cars. At lower speeds, PAWS makes for easier maneuvering because of the reduced turning circle. PAWS also can correct under- or oversteer by adjusting the line of the rear wheels, which means sometimes PAWS can fix small slides without any need for the brake-based electronic stability control to activate.
Torque-Vectoring Hybrid System
We then had a chance to sample an Accord mule with what Honda calls Sport Hybrid Super Handling All-Wheel Drive (Sport Hybrid SH-AWD), which will be the upgrade powertrain choice on the 2014 Acura RLX. It uses a 3.5-liter V-6 engine and seven-speed dual-clutch transmission, augmented by a 30-kW electric motor/generator, to power the front wheels. A separate pair of 20-kW electric motors powers the rear wheels.
In general, the Sport Hybrid SH-AWD mule behaved like a normal hybrid car. In electric driving, only the rear motors are used. The front motor acts as a starter for the V-6 engine, a generator under braking, and also provides extra torque for hard acceleration. Acceleration was brisk and smooth, although we think Honda is over-promising when it says the setup provides V-8-levels of thrust. The dual-clutch transmission shifts promptly and smoothly, and even blipped the throttle to downshift as we braked for turns — although engineers later confessed that was because the transmission was locked in a sport mode.
The rear motors, meanwhile, provide torque-vectoring during cornering. As shown by a power-flow animation in the car’s head-up display, the outer wheel is overdriven while the inner rear wheel acts as a generator, sapping power and dragging to help turn the car. The goal, like with PAWS, is to provide sharper turning and more lively handling by using the rear wheels to help influence the car’s rotation. It’s quite successful in making the car turn in quickly, although the added weight of the motors and batteries mean the Sport Hybrid SH-AWD mule felt a lot less nimble than the PAWS car.
The torque vectoring still works if the main hybrid battery is depleted because power from “dragging” the inner wheel powers the outer wheel. The function works at all vehicle speeds, even at parking lot speeds. A more powerful version of this powertrain will be used in the 2015 Acura NSX, but it will be reversed so that V-6 powers the rear wheels and the two electric motors power the front wheels.
Honda and Acura hope that the development of these two systems will help imbue new cars, starting with the 2014 RLX, with a sportier driving dynamic that will help them compete with the best German and Japanese luxury cars. We’ll put that to the test in the real world when we drive the Acura RLX sometime next year.