New steel-intensive Mazda CX-9 sheds mass, debuts new turbo system

  • 24-May-2016 05:07 EDT
LEAD image 2016 Mazda CX9.jpg

Other than its aluminum hood, the 2016 CX-9's structure and exterior panels are in various steel alloys. Finally Mazda has arrived at a handsome exterior design language that doesn't resemble origami.

For a mainstream unibody SUV, the 2016 Mazda CX-9 pulls off a neat trick—it adds premium content and features while losing weight compared with its predecessor. The design and engineering solutions behind this achievement go beyond expectations for vehicles in this segment and include first use of an all-new turbocharged 4-cylinder direct injection gasoline engine with cooled EGR.

For the second-generation CX9, Mazda planners and engineers knew they had to raise their game significantly because of the improved quality and content of the competition, notably the Toyota Highlander and Honda Pilot.

The changes start with a shift away from the previous CD3 platform shared with former partner Ford. The new seven-passenger CX-9 adopts the same large-Skyactiv platform used by the Mazda3 and Mazda6 sedans, as well as the CX-5 compact crossover. (A small-Skyactiv platform is dedicated to the CX-3 and smaller non-U.S. market models).

At 199.4 in (5065 mm) long, the new CX-9 is 1.2 in (30 mm) shorter than its predecessor, but its wheelbase has been stretched 2.2 in (55 mm), providing more passenger leg room and easier entry and egress to the rear compartment.

Contributing to the new model’s more distinctive and better proportioned design are reduced overhangs—2.3 in (59 mm) shorter in front and 1 in (25 mm) shorter in the rear. In addition, the A-pillars are moved 3.9 in (100 mm) rearward. This lengthens the hood and adds a touch of sporty “Kodo design” visual drama.

Shunning aluminum for high-strength steel

The other big change is a switch from Ford’s 3.7-L V6 to Mazda’s first use of a turbocharged version of its Skyactiv 2.5-L four-cylinder—the sole powertrain offering for CX-9 and rare among three-row crossovers with available V6s. But according to Mazda vehicle development engineer Dave Coleman, both platform and powertrain changes bring significant weight reductions—198 lb (90 kg) total in the front-drive version and 287 lb (130 kg) in AWD models. Nearly half of that reduction comes from the powertrain switch.

“We improved the strength-to-weight ratio without resorting to materials other than high strength steel,” Coleman told Automotive Engineering. While the car’s hood is aluminum, the development team “shied away from more extensive use of aluminum because of its high cost in Japan,” he explained.

The weight savings in turn allowed Mazda to increase use of NVH dampening material—53 lb (24 kg) in the CX-9, compared to 5 lb (2.23 kg) in the CX-5. Combined with the use of acoustic glass (window thickness is increased to 4.8 mm/1.9 in), the changes reduce interior noise levels by a claimed 12%. The quiet cabin environment was one of the most impressive aspects of our recent test drive.

Equally notable is the powertrain transformation. Shifting to a 4-cylinder-only strategy is potentially risky in a segment where buyers are conditioned to expect a V6 option, but Mazda’s research found that “in real world conditions consumers are less concerned with 0-60 mph times than they are with drivability at lower engine speeds,” Coleman noted.

High compression and cooled EGR

This data drove development and tuning of the Skyactiv turbo four, with the focus on torque and low-rpm responsiveness. Addressing the traditional drawback of turbo lag, Mazda engineers developed a new “dynamic pressure” turbocharger system. This design locates the turbo just one inch from the engine block, connected with a novel 4-into-3 exhaust manifold that pairs the output of cylinders two and three.

At low rpm the exhaust is routing through separate smaller ports to accelerate the gas pressure and spin up the turbocharger faster to its maximum boost of 1.2 bar (17.4 psi). At higher rpm, valves open to allow exhaust flow through the three larger ports. Pairing the center ports encourages better exhaust gas scavenging, thus raising the knock limit and allowing for a high compression ratio.

At 10.5:1, this ratio is one of the highest of any production car turbocharged engine, and is enabled in part by use of a cooled exhaust gas recirculation (EGR) system. Mazda’s EGR design lowers exhaust gas temperatures by as much as 212° F (100° C), using EGR rates up to 15%.

According to Coleman, the EGR system does not benefit the CX-9 fuel economy rating in the EPA test cycle, which he said is “very gentle” on throttle application. The U.S. EPA test masks the typical disadvantage of small displacement turbo engines, which can consume excessive fuel under full throttle usage. But in real world driving conditions, consumers will experience better mileage with the Skyactiv turbo engine because of its high compression ratio efficiency and performance gains.

As it is, the engine produces a claimed 310 lb·ft (420 N·m) at just 2000 rpm. Claimed power is 250 hp at 5000 rpm on 93-octane fuel and 227 hp on 87 octane. EPA fuel economy figures are 22/28 city/highway mpg for the fwd CX-9 and 21/27 mpg for the AWD versions.

Bucking the industry trend to 8- or 9-speed automatic transmissions, the CX-9 makes do with a 6-speed unit. According to Coleman, its ratio spread is well matched to the engine’s torque characteristics and avoids the “ratio hunting” issue that has afflicted some transmissions with more gears.

Inside, the new CX-9 adopts and expands on the range of infotainment and driver-aid features found in the CX-5. The flagship CUV also offers greater use of upscale materials including, for the first time for Mazda, aluminum, real wood and Napa-quality leather trim. The latter is featured in the new range-topping Signature edition, which sits above the Grand Touring version and starts at $44,015. The base CX-9 Sport model starts at $31,520.

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