New Acura RDX crossover bucks trend with V6 power

  • 29-Mar-2012 12:01 EDT
aei-RDX.JPG

RDX two-seat-row crossover has V6 power and more efficient interior packaging.

The remaking of the Acura lineup is under way, with the introduction of the 2013 RDX two-seat-row crossover and the ILX compact sedan to replace the TSX. Both are entry-luxury models for what are projected to be the highest volume segments through 2017. Acura was the first Japanese luxury brand to be sold in the U.S., and re-establishing a strong position vs. Lexus and Infiniti is its objective as the market recovers.

The RDX engineering package does contain surprises. At a time when some other luxury makes are moving to more four-cylinder engines, the RDX drops the 2.3-L turbo it had been using. The new choice is the 3.5-L V6 rated at 273 hp (204 kW) and 251 lb·ft (340 N·m). It adds 33 hp (25 kW) with just a modest 9.0 lb·ft (12 N·m) drop in peak torque. Further, the V6 is a smoother performer, and the fact that the Lexus RX350 V6 is rated at 270 hp (201 kW) and 248 lb·ft (336 N·m) undoubtedly helped with the decision.

At 183.5 in (4660 mm), the 2013 model is slightly longer than the 2012 model, which measures 182.5 in (4634 mm), but has more passenger room—103.5 vs. 101.4 ft³ (2930 vs. 2870 L)—and more front and rear legroom—42.0 and 38.2 in (1067 and 970 mm) vs. 41.8 and 37.6 in (1062 and 955 mm), respectively.

The increase in length notwithstanding, RDX remains slightly shorter than the Lexus RX, which is 187.8 in (4768 mm) long, and at 129.6 ft³ (3670 L) has about 10 ft³ (283 L) less total interior room, but that is because the cargo area is smaller at 26.1 vs. 40 ft³ (739 vs. 1133 L). However, the tailgate opening width was increased by 6.5 in (165 mm) to 48.8 in (1240 mm), so Acura claims that its smaller area has more accessible space, holding a common selection of six suitcases: two 29-in (737-mm); two 21-in (533-mm), and two 16-in (406-mm) ones. The RDX has a power tailgate, but to minimize intrusion on cargo space, its motor drive is a compact design fitted into the right side D-pillar.

EPA fuel economy is the RDX's strong suit in the class, despite port-fuel instead of direct injection; U.S. EPA numbers are 20 mpg city/28 mpg highway for the front-drive and 19/27 for the AWD model. However, the V6 does have two-stage cylinder deactivation, to four cylinders during highway cruising, to three cylinders in lower-speed cruising. The engine itself was reworked for lower friction. The piston skirts were given a molybdenum disulfide coating, the oil ring a special plating, and the cylinders a “plateau honing,” a process that leaves the cylinder surfaces with a broken-in appearance. A 0W-20 engine oil replaced the previous 5W-20. Installing an alternator pulley one-way clutch permitted a 30% reduction in accessory drive belt tension.

A six-speed automatic replaces the five-speed unit, and that also makes a major contribution to efficiency. Other fuel-economy improvements are from electric power steering and low rolling resistance tires. Further, the wheels are mounted on hubs with lowered-friction bearings and seals. The brake rotors were redesigned to improve cooling and the brake pad mountings were relocated to reduce drag.

The AWD has an intelligent control system that varies torque to the rear wheels—to a maximum of 50% for hard launch and hill climbing (detection logic for 15% grade and above), down to 25% when front wheel slip is detected, to zero for cruising in front-drive. The system is lighter and simpler than the Super Handling system used on higher priced Acura models (MDX, ZDX, and RL).

The RDX gets Motion Adaptive EPS (electric power steering). MA-EPS produces assist force in the appropriate direction to add to the ABS outputs commanded by the Acura electronic stability system.

A major improvement in ride quality—very noticeable in low-medium speed driving on paved secondary roads—was made with 15% softer coil springs and new “amplitude reactive” struts in front and shock absorbers in the rear. Each has an internal rebound spring for anti-roll and a second piston-valve that slides along the primary piston rod. The primary piston is the sole damper for low-amplitude road inputs up to about 10 mm (0.4 in), after which the secondary piston also comes into play. Additionally, each rear shock absorber rubber mount is designed to create two exit paths for road inputs vs. the previous single path.

In other Acura news, the ILX sedan series introduced at the Chicago Auto Show (http://www.sae.org/mags/aei/10595) has since been shown at a drive program with additional and updated technical information.

The line is built on the same platform as the Honda Civic but with interior appointments more befitting its entry-luxury positioning. The ILX is 179.1 in (4947 mm) long overall, 1.6 in (41 mm) longer than the Civic sedan. EPA-spec cabin size actually is slightly smaller than the Civic at 89.3 vs. 94.6 ft³ (2529 vs. 2679 L) because the aero-styled ILX height is lower: 55.6 in (1412 mm) vs. the Civic's height of 56.3 in (1430 mm).

As noted in AEI’s earlier report from the Chicago Auto Show, there are three models in the line: the 2.0-L with five-speed automatic, the 2.4-L with six-speed manual, and the 1.5-L Hybrid.

The 2.0-L is based on the 1.8-L Civic engine, which was stroked 10 mm (0.4 in) to raise displacement. EPA rated at 24 mpg city/35 mpg highway, it is expected to account for 75% of ILX sales.

The 2.4-L was described by Acura as the “pocket rocket” for the entry-luxury line but is anticipated to be just 5% of the sales mix. Fuel economy numbers are 22 mpg city/31 mpg highway.

The 1.5-L Hybrid acceleration assist system, which should deliver the remaining 20% of sales, is almost straight out of the new Civic, with the engine and motor rated at 111 hp (83 kW) and 127 lb·ft (172 N·m). The official fuel economy numbers are 39 mpg city/38 mpg highway. The transmission is the Civic CVT. As does the 2012 Civic, it has a 144-V lithium-ion battery pack, replacing the nickel/metal hydride type. The change reduces weight from 31 kg (68.3 lb) to 22 kg (48.5 lb).

Like the RDX, the ILX line has struts in front and a multilink rear, with the internal rebound spring and amplitude reactive piston valve. And it also incorporates Motion-Adaptive EPS. The sway bar bushings have Teflon liners for reduced friction, which contributes to a smoother ride.

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