2014 Acura RLX and the Realization of Takaburi
What did Yousuke Sekino, large project leader—a.k.a., chief engineer—, for the 2014 Acura RLX set out to deliver when developing the car, which he describes as “Acura’s flagship sedan”?
“Smart Exhilarating Luxury.”
And what exactly does that theme mean?
He says there are three values, or aspects, that are encompassed by that theme:
“The first is ‘Pride and Prestige.’ This feeling is based on a vehicle with luxury, comfort, quietness, and high fuel economy that is right for this class sedan.
“The second is ‘Advanced.’ The many advanced features include the next-generation of AcuraLink, and the all-new ‘Jewel Eye’ headlights with outstanding function and beauty.
“The third and most important value we want to offer our customers is Takaburi. This means exhilarating in Japanese. We achieve this with handling at the will of the driver, nimble powerful acceleration, and styling that is sleek and sophisticated.”
So, how were these achieved?
Keeping Things Exceedingly Quiet.
As this is a car in the luxury category, vault-like silence is key. There are the straight-up countermeasures to keep the car quiet, including an extensive use of acoustic material throughout the car (e.g., carpet back surface, inside the A- and C-pillars, inside trunk lid, floor sills). There is also the use of 4.7-mm thick laminated, sound-insulating glass.
There is an Active Noise Control system that uses microphones to pickup low-frequency noise in the cabin and then a processor to send a reverse phase audio signal to an amplifier that drives the signal through the audio speakers in the door. There is an Active Sound Control system that monitors engine noise. As engine noise doesn’t rise in a linear manner with revs, there are peaks and valleys in the sound pressure levels, so the control system generates same-phase or reverse-phase sounds that are also played through the door speakers so as to even out the sound.
The RLX even has wheels with a noise-reducing design, as there are four resin moldings on the inside of the wheel rim which reduces noise in the air column inside the wheel.
But there are other factors, as well, such as the attention paid to making the vehicle aerodynamic; more than 800 wind tunnel tests were conducted during the development. The aero design not only helps make the cabin quieter, it also contributes to the fuel economy (which we’ll get to below).
Structurally Sound & the Role of Materials
And another contributor to quietness is the basic structure of the vehicle. Compared to the last-generation car, bending rigidity is up 52% and torsional rigidity is up 46%. It is a solid structure. Contributing to this is the extensive use of high-strength steel (HSS). By weight, the vehicle is 55% various grades of HSS, including 2% 340 MPa, 2% 440 MPa, 31% 590 MPa, 6% 780 MPa, 7% 980 MPa, and 7% 1500 MPa.
While on the subject of materials, it is worth noting that there is also an extensive use of aluminum on the RLX. The calculation is that there is a 76.1-lb weight-save by using aluminum vs. steel. For example, the aluminum hood weighs 19.6 lb. less than a comparable steel hood. Other applications of aluminum are for the front and rear bumper beams, floor tunnel bar, steering column hangar beam, and the skins for the front and rear doors.
The door applications lead to the development of a new assembly process because there is a steel inner (for purposes of safety) and Sekino notes that there could be a potential corrosion problem if the traditional welding approach was used to join the aluminum and steel. So instead, the joining is done with a forming process. They call it “3D lock seam.”
The steel inner is first coated with a zinc, aluminum and magnesium plating to resist corrosion. The there is a hemming process that includes a horizontal force to fold the aluminum over onto the steel, then a vertical force to create the seam, locking the two materials in place.
The total weight of the car is 3,393 lb.
Under the Aluminum Hood
There is a 3.5-liter, direct-injection, SOHC i-VTEC V6 engine that produces 310 hp and 272 lb-ft of torque. The previous-generation model has a 3.7-liter, port-injected V6 that produces 300 hp and 271 lb-ft of torque. The new engine is not only more powerful, but it provides better fuel economy: EPA-estimated 20 mpg city and 31 mpg highway, vs. 17/24 mpg (although it should be noted that the previous RL came as an AWD vehicle and the 2014 RLX is FWD.) The engine features electronically controlled Variable Cylinder Management (VCM), which means that it can operate on three cylinders depending on factors including throttle position, vehicle speed, engine speed, and transmission gear selection. The VCM deployment is transparent to the driver, in part because there is a 28-volt Active Control Engine Mount System that counteracts the changes brought on by switching from six cylinders to three and back.
The sort of performance sought while engineering the chassis for the RLX was to provide a setup that would respond to the “will of the driver,” to, as Sekino says, “to provide a synergy between man and machine.” There are multiple elements that contribute to this, with the most notable being “Precision All-Wheel Steer,” (P-AWS), which provides rear-wheel steering. The amount of steering is 1.8 degrees, which is said to be a sufficient amount to improve the handling while not being noticeable by the driver.
Steering & Suspension
P-AWS uses independent electrical actuators, special control arms, and suspension uprights for the rear wheels. An electric control unit is linked to the electric power steering, vehicle stability assist, braking, and engine control systems via a dedicated Control Area Network (CAN). It takes into account measures including steering input, engine speed, road speed, the transmission, throttle piston, brake pressure, yaw rate, and lateral acceleration. As a result, the system provides rear-wheel settings (remember: these are independently actuated, not linked) as required by the situation. So, for example, when braking, there can be toe in of both wheels. When performing sharp, low-speed turns, the rear wheels are out of phase with the front wheels. Accelerating out of a corner, there is toe in to increase yaw, thereby counteracting understeer.
In addition to which, the RLX has a new aluminum front subframe and a new double-wishbone, lower double-joint front suspension. The subframe, which uses die cast front corners (squeeze casting was used for the front corners on the previous-generation car), is 82% more rigid that the previous-generation subframe. In addition to the dual-piston, dual-valve dampers (called “Amplitude Reactive Dampers” and sourced from ZF-Sachs) front and back (the rear suspension is a multi-link design). All of these factors contribute to a ride that is solid without being too stiff.
Sekino: “We believe we have created a unique Acura flagship sedan that is different from competitors. It is a car where every customer can feel exhilaration.”
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