Engineering 2014 Acura MDX
A key aspect of the development of the 2014 Acura MDX—the third generation of the vehicle, a whole new development for the three-row crossover—is mass reduction. But as Jim Keller, large project leader for the program (i.e., chief engineer), who has been working on the vehicle development since its inception in 2009, explains they worked to reduce mass without adding cost to the vehicle: they avoided doing such things as using “exotic materials.” Yes, they could have gotten to a lower curb weight by using materials other than, by and large, traditional ferrous materials—and they do use some nonferrous, but this use tends to be more judicious rather than across-the-board—but doing so, Keller points out, would have been more costly.
And it’s not like the second generation MDX is particularly chunky in a class that includes vehicles like the Audi Q7, Buick Enclave, and BMW X5. In fact, at 4,500 lb., the 2013 model is lighter than any of those vehicles. But Keller and his crew went at it essentially piece by piece, and reduced the weight of the MDX by 275 lb. The curb weight of a 2013 Q7: 5,192 lb. The curb weight of a 2014 MDX: 4,255 lb.
A delta of 937 lb.
Pretty much everything went on the scale during the development program. “Even little parts,” Keller says, and explains that there is often a tendency for the smaller components in a vehicle to pass through the mesh of what gets serious attention. So what happens is that there is a multitude of parts that receive less rethinking and possible redesign, and given that there is a great number of those parts, an ounce here and an ounce there adds up to excess weight.
“Not everyone does an FEA for every component in a car,” Keller says, adding that this was also the case with the MDX—but then he points out that they actually did more quick finite element analyses (through a program resident in CATIA) on more parts than is generally the norm. The major structures, of course, underwent rigorous analyses as they developed the new platform for the vehicle.
What’s more, they went at the redesign of the components in a way that is certainly out of the mainstream: engineers from one function looked at parts from entirely another area. He cites as an example a bracket used to mount audio components: chassis engineers examined the design and helped reduce the mass of the part. Keller calls the approach “cross pollination.” This was something of an ad hoc approach, not a regimented process. It was largely a case of someone who might have been working on how to support a suspension component looking at how an electronic component was being held in place, which undoubtedly gave rise to questions as to “Why do you do it like that?” But relative informality notwithstanding, Keller says that it helped achieve the goals they were trying to reach.
And as previously indicated, materials played a large role in the weight reduction efforts, as well. And, yes, they do use some materials that don’t have Fe in their chemistry.
The car has a magnesium steering hanger beam that goes across the car from side to side beneath the skin of the instrument panel. It replaces an aluminum structure. The aluminum was light. But this is lighter. What’s more, Keller says the aluminum structure consisted of a variety of extrusions, stampings and castings, some 26 pieces in all, which had to be put in a jig and welded. The magnesium structure consists of three castings that are assembled. One of the three is necessary in order to provide accessibility to the passenger-side airbag for maintenance or repair. (He also notes that this magnesium beam is but the second in Honda production, with the first being for the Honda FCX Clarity hydrogen fuel cell vehicle. In 2012, there were five Claritys moved; there were 50,854 MDXs sold last year.) The weight savings for the magnesium beam vs. the aluminum: 7.5 lb.
While there is the use of aluminum for the hood, engine, and front lower control arms, the use of high-strength steel for the body-in-white is significant: 59% of the total mass compared with 25% for the 2013 MDX. This represents a weight save
of 123 lb.
The materials used for the body-in-white include:
• HSS 340: 4%
• HSS 440: 3%
• HSS 590: 31%
• HSS 980: 14%
• HSS 1500: 7%
As for the remainder:
• Mild steel: 36%
• Magnesium: 2%
• Aluminum: 3%
One interesting aspect of the body-in-white is the front door stiffener rings. Each ring—which makes up the A- and B-pillars, roof rail section, and lower frame area—is a single hot-stamped component. It is thought to be the first such deployment anywhere. The reason behind the ring is to enhance safety.
While on the subject of safety: the 2014 MDX uses the second-generation Advanced Compatibility Engineering (ACE) body structure, which is engineered to provide occupant protection and crash compatibility with other vehicles in frontal crashes through a network of structural body components such that in the event of a collision, there are engineered paths for crash energy management. Keller says that they designed the structure not only to meet present regulations and requirements from non-government agencies (e.g., the Insurance Institute for Highway Safety), but for those that are likely to be in place in the future.
Keller says there were four primary areas that he and his team addressed in developing this all–new platform—and this is the first time that a specific platform has been developed for the MDX, with the previous models being based on the same platform used for the Odyssey minivan: “We wanted it to be safe yet light, sporty yet refined,” he says, adding, “We pushed the boundaries for all four; usually it would be just two or three.”
Under the hood
The 2014 MDX features an i-VTEC 3.5-liter, 24-valve. 60° V6 engine with direct injection and Honda’s Variable Cylinder Management (VCM) technology. This engine has the same architecture as the engine found in the 2014 Acura RLX sedan. The engine in the RLX is the first deployment of direct injection in an Acura vehicle; this is the second.
The 2014 MDX is the first MDX to use VCM, which allows the engine to operate on six or three cylinders, based on engine load. Due to the nature of shutting off cylinders, 28-Volt active control engine mounts and active noise cancelation are deployed to counteract the effects of vibration and noise.
The i-VTEC system—intelligent-Variable Valve Timing and Lift Electronic Control—changes the lift profile, timing and duration of the intake valves predicated on engine operating conditions for purposes of optimizing the performance of the engine, low rpms or high.
The block and heads are aluminum. The block has spin-cast cast iron cylinder liners. The heads feature a “tumble port” design for more homogeneously mixing the air and the fuel for better combustion. Exhaust manifolds are cast into each head to not only reduce weight and parts counts, but to help optimize the location of the close-coupled catalyst.
The transmission is a six-speed automatic with Sequential Sport Shift; the transmission can be controlled by the console mounted shifter or steering wheel-mounted paddles.
For the first time, the MDX is offered with front-wheel drive standard for the simple reason that in many markets, all-wheel drive—even the optional Acura Super Handling All-Wheel Drive—isn’t all that necessary. In addition to which, the front-wheel drive vehicle has an EPA-estimated 20/28/23 (city/highway/combined) mpg fuel economy, which bests the AWD by 2 mpg in the city and 1 mpg on the highway.
Steering and suspension
Even though the 2014 MDX is (comparatively) light, it is also (comparatively) big. It is 193.6-in. long (2-in. longer than the 2013 model), 77.2-in. wide, and 66.7-in. high (both lower and narrower than its predecessor).
The MDX features an electric power steering system—the last one has a hydraulic system—with a larger diameter, one-piece steering shaft (30 mm from 22 mm). The steering system is highly beneficial in both low- and high-speed conditions; the steering ratio is 9% faster than the previous setup. The increased size of the steering shaft reduces vibrations. All of this contributes to improved maneuverability.
The new platform features a new suspension system. In the front, there is a strut-type system with forged-aluminum lower control arms. The rear is a multilink design with a tubular stabilizer bar; its control arms are steel. One interesting aspect of the rear suspension is that it has a compact design and the forward trailing arm that’s used for the 2013 MDX has been eliminated. Consequently, the vehicle’s floor is lowered by 1.8-in. and accessibility to the third row has been improved.
The MDX, which is being produced by Honda Manufacturing of Alabama in Lincoln (where the engines are also manufactured), was styled at the Acura Design Studio in Torrance, California. The theme that the designers pursued was “Executive Aero Sculpture,” which essentially means that they wanted to provide something upscale for the seven-passenger vehicle and to make it as sleek as practical.
The MDX was the first vehicle to be developed using the 40%-scale wind tunnel that Honda operates in Raymond, Ohio.
Because the vehicle is lower (by 1.5 in.) and narrower (by 1.3 in.) compared with the 2013 model, the frontal area is 2% smaller. That and a variety of countermeasures and improvements—from side mirror design to air flow through the engine compartment—results in an 18% improvement in aero efficiency.
Not only does the MDX have an engine that is directly related to the RDX, but it also has a Jewel Eye LED headlight approach similar to the sedan. In this case, each side of the vehicle has an array with five LEDs that are covered by a composite lens and chrome surround. The LEDs not only act as daytime running lights, but the three outer LEDs are used as the low-beam headlamps and the two inner LEDs are the high beams.
Jan Moore, MDX senior product planner, is fairly blunt about the place of the MDX in a market segment that has some capable competitors. Although the MDX was the first seven-passenger luxury crossover back in 2001 (when it received both the North American Truck of the Year and Motor Trend SUV of the Year awards), and while the second-generation (2007) MDX has been well received in the market, that was then, and customers buy now. Things had to change. And they did.
She points out that surveys indicate that people like the package, perform-ance, utility (5,000 lb. towing capacity), and the Super Handling All-Wheel Drive of the second-generation model. But people weren’t so keen on the materials used on the interior, the required steering effort, NVH, and the accessibility and leg room in the third row. And there were, Moore points out, some things that were lacking. Like pushbutton start. Remote start. Parking sensors. And a 2WD model for those in the Sunbelt states.
As indicated, Keller and his team addressed these issues, from the steering to the accessibility. They added the pushbutton start and the sensors. And the 2WD model.
In one regard, one could say that they checked all the boxes. That they ran the analyses and created the spider charts, they made the assessments of where the MDX was in relation to the competitors and the regulations, they made the determinations of where they needed to bring the third-generation model and how they’d get there.
And they did.
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