2019 Acura RDX brings world’s-first chassis tech

The all-new 2019 Acura RDX brings world’s-first chassis tech, new five-link suspension, and gen-4 SH-AWD
Few words are as inspiring to an engineering team as “all-new.” For the 2019 Acura RDX, the engineers behind the compact SUV’s third-generation had a host of all-new to manage, including a dedicated platform, five-link rear suspension, torque-vectoring driveline and infotainment interface. Though the turbocharged engine/10-speed transmission combo have recently appeared in other products, the RDX is the first all-wheel-drive (AWD) application.
 
That “all-new” enthusiasm is likely tempered when the vehicle being replaced is not only one of the company’s most popular, but most profitable. The RDX has been the compact-lux-SUV segment’s top nameplate since 2006, with sales topping 50K/year for the last three years. Not only are compact SUVs one of the market’s fastest-growing segments, but near-luxury examples are some of the most important for any automaker’s bottom line.
 
New platform, new direction
The 2019 RDX is the first vehicle in the Acura line to represent the rebirth of the company’s “precision crafted performance” marketing tagline, and is the best template yet for future Acura models in terms of performance direction and design. This shift was heralded by two recent Acura concepts, the Precision Concept (exterior) and Precision Cockpit (interior/HMI).
 
The RDX’s edgier styling is a direct reflection of those concepts, which was handled by the Acura Design Studio in Los Angeles. The rest of its redux was also managed stateside, mostly in Ohio: Development was centered at Honda R&D Americas in Raymond; manufacturing of the new RDX will continue in East Liberty; the turbocharged engine is sourced from the Anna engine plant; and its new AWD system from the Russels Point transmission plant. The 10-speed transmission is sourced from Honda’s facility in Tallapoosa, Georgia.
 
World’s-first door-ring structure
The biggest news on the 2019 RDX must be its all-new platform, which sees an increase in the use of high-strength steels (now 60%), aided by 37 meters of structural adhesive. Passenger interior volume in both seating rows along with cargo volume have increased, and the wheelbase has been stretched 2.6-inches. Standard is a truly expansive panoramic sunroof. Despite the volume/dimensional gains and additional openings, the new chassis sees some impressive stiffness gains, thanks to two key innovations.
 
The first is a hot-stamped inner and outer front-door-ring structure, a world-first technology Acura debuted at this year’s SAE WCX. The new door-ring system adds significant structural rigidity, and is key in meeting safety targets, including IIHS’s small-overlap frontal crash test. The second is the new “rear double-ring” construction, designed to anchor a new five-link rear suspension while still improving cargo volume.
 
Stephen Frey, engineering development lead on the all-new RDX, explained this utility vs. agility challenge in the lux-CUV segment. “People are buying them because they offer a certain level of capacity, but they also want them to handle dynamically,” Frey said. “We want to maximize the size of the tailgate opening, but that's counterproductive when you're trying to make a rigid structure.”
 
The RDX solution is a new, rear double-chassis-ring structure to create multiple connected load paths. This includes Y-shaped members that connect forward to the new ultra-stiff door-ring system, as well as multiple paths beneath the rear load floor. The spare tire has been moved underneath the vehicle, but multiple storage compartments remain beneath the flat floor.
 
The results for the all-new chassis is a 38.3% gain in global body rigidity (with gains of 125% in some locations), and fitting-point stiffness increased 52.8%. These rigidity gains did not come at the expense of mass, as body-in-white weight dropped 9 kg (19.8 lb). With a significantly stiffer body as a base, the team was able implement an all-new rear suspension.
 
Five-link: more knobs to turn
The current RDX uses a MacPherson-strut front suspension and trailing-arm design in the rear. For the 2019 RDX, the MacPherson setup remains up front, but chassis dynamics lead Jed Aston said they were eager to take advantage of the new, stiffer body structure to debut an all-new five-link rear suspension with a dedicated subframe. “When we looked at it from a performance perspective, it was evident to us that we had to do something to separate the compromise between ride and handling in the rear of the car, and you get a little bit of that compromise with a trailing arm.”
 
The new five-link suspension setup features forged-aluminum control arms, high-strength steel connecting links, and far fewer compromises. “When you have the five-link, you can separate those tuning items,” Aston explained. “You can tune in really nice vertical mechanical compliances to get good ride, but you can put in really high lateral stiffness to get the great line trace—very intuitive output from your input.”
 
“You also have much more freedom to design in proper mechanical kinematics. Meaning, as the wheel strokes, you can get your toe-in more accurately than you can with a trailing arm. You can have perfect bump toe curves. You can have perfect vertical curves. There’s just more knobs to turn, and more freedom to get it right.”
 
Metrics on the new suspension are impressive, including a 125%-gain in tire-patch lateral stiffness. On the road, the back end feels transparent, and fully connected to the chassis. “When you have the trailing arm bolted to the body, and the lower arms bolted to the subframe, you're juggling the relative motions between different bodies. But when it all goes through the subframe, you're not having a conflict between body motions and subframe motions.”
 
Turbo, 10-speed, SH-AWD
The 2019 RDX provides a single powertrain option, in either front-, or all-wheel drive. Replacing the sonorous 3.5-liter V-6 is Honda’s new 2.0-L turbo four-cylinder engine. The direct-injected, 16-valve DOHC VTEC powerplant is SAE rated at 272 hp and 280 lb·ft (380 N·m) and paired exclusively to the segment’s only 10-speed automatic transmission. Compared to the outgoing 3.5-liter V6, the turbo-4 delivers 40% more low-end torque (a boon for drivability), but some may miss the silken snarl of the V-6.
 
Based on the ripper of a motor that originally debuted in the Honda Civic Type R (306 hp), the RDX version takes its cue from the more civilly tuned “Step-2” version in the Honda Accord. “The Step-2 became more refined by changing things like the turbocharger, and we added balance shafts,” explained Chris Kipfer, powertrain lead on the new RDX. “Exclusive changes for the RDX were in flow for both intake and exhaust, to make sure we get the performance that we need, and ECU tuning for premium fuel—recommended but not required.”
 
The powerband is packed with low-end torque (the 280 lb·ft peak starts at just 1600 rpm), and for those opting for AWD, that grunt is routed through a torque-vectoring Super Handling All-Wheel Drive (SH-AWD) system. This fourth-generation of SH-AWD has seen significant upgrades, including a 40% increase in rear-wheel-torque capacity. “We have increased the output capability from around 2200 total N·m to 3000 N·m,” Kipfer explained. “There's a lot more torque coming back, and we've made it more responsive through exclusive software tuning.”
 
The Gen-4 RDX setup (based on 3rd-gen systems in the MDX and TLX), ups the rear-overdriven percentage from 2.7% to 2.9%, and 70% of available torque can now be sent rearward, with 100% of that torque distributable to either rear wheel. “It starts off with a natural torque distribution based on weight distribution—60% to the front wheels, 40% to the rear—and light acceleration maintains that,” Kipfer explained. “The purpose is to maintain as much ground contact and traction force as possible, which the system directs based off of actual weight transfer and acceleration rate.”
 
To handle the additional torque, the rear diff’s clutch packs are larger in diameter and there are more of them. “In the current RDX there's 20 per side and now there's 22,” Kipfer said. “We’ve been able to package them closer together, and the hydraulic system and electronics have gotten more efficient, so we’ve kept the profile and weight essentially the same, but with higher capacity.”
 
Also new to RDX is the standard Integrated Dynamics System, which provides four different drive modes (Snow, Comfort, Sport and Sport+) to alter the RDX’s on road personality. The modes affect the drive-by-wire throttle, transmission shift map, electric power steering, traction control, Active Sound Control and (if so equipped), the active dampers and torque vectoring. On the road, the characteristics of each mode are easily discernable, and provide a wide range of personalities for the new RDX, from mellow cruiser to autocrosser.
 
Bountiful tech suite
The 2019 RDX is also the first application of Acura’s new True Touchpad Interface, a new infotainment control that combines a center console-mounted touchpad with a 10.2-in (259-mm) display mounted high on the dash. Acura is using what it calls “absolute positioning” for the touchpad, and claims it’s the world's-first use in a driving environment.
 
The setup uses two “zones” on the touchpad to match the screen display, and it can even understand written text input. Once used to the somewhat organic mapping and feedback of the touchpad surface compared to what happens on the screen, the system becomes quite intuitive, and Acura may be on to something. The media system is Apple CarPlay compatible, with Android Auto support on the way.
 
Standard on the new RDX is Acura’s suite of safety tech, which includes forward collision warning with emergency braking, lane-keep assist, adaptive cruise, and road departure mitigation. A new audio system features 16 speakers, including four mounted effectively in the ceiling, genuinely meriting the “Studio 3D” moniker. An available color head-up display provides info (including nav, phone, and audio data) with useful clarity and minimal distraction.
 
Future of performance
Acura has ladled an impressive amount of engineering prowess on the 2019 RDX, and its continued sales success is probable considering the host of new tech and features arrive with no change in pricing for comparably equipped trims. With Acura announcing in January that Type-S performance models and a new turbocharged 3.5-L V-6 are in the pipeline, it’s also likely the RDX engineering team will soon have further cause to leverage its all-new platform. Continue reading »
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