Mazda CX-5 gets Skyactiv treatment

  • 27-Mar-2012 05:01 EDT
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The CX-5 is Mazda’s new, smaller crossover with a Cd of 0.33. Its new suspension geometry provides handling expected of a Mazda.

Mazda’s newest Skyactiv approach to motor vehicle design and engineering has arrived in the form of the five-seat CX-5, a crossover with high fuel economy, historically not the company’s strong suit. The CX-5 is now the fuel economy leader of the non-hybrid compact crossover class, with window sticker U.S. EPA numbers of 26 mpg city/35 mpg highway for a six-speed manual, 26/32 for the six-speed automatic, and 25/31 with AWD. It joins the Mazda3, whose Skyactiv edition is rated at 28/40 mpg.

CX-5 replaces the CX-7, and Mazda identifies the Honda CR-V and Toyota RAV-4 as competitive examples. The CX-7 will be sold for an undefined interval elsewhere, but it’s strictly “clear out stock” in the U.S.

The CX-5 is externally smaller at 178.7 in (4539 mm) in overall length vs. 184.3 in (4681 mm) for the CX-7. It has a smaller four-cylinder engine: the 2.0-L direct injection four is rated at 155 hp (116 kW) and 150 lb·ft (203 N·m) vs. the 2.5-L four of the CX-7, which is rated at 161 hp (120 kW), 161 lb·ft (218 N·m), and just 20/28 mpg. The CX-7 had an optional 2.3 DI turbo rated at 244 hp (182 kW), and the competition has more powerful fours and/or V6 options, so an eventual CX-5 performance engine option would hardly be a surprise.

In an overall comparison with the CX-7, less is more, including base engine performance. The CX-5 body is an average of 40 mm (1.6 in) narrower but has a wide look because of the way the sides are sculpted. Instead of cab forward, the approach is cab pushed rearward to get away from the MPV (multipurpose vehicle) or minivan look. Also, the driver had to be seated closer to the dashboard to reach the touch screen, included on all but the base model. Premium effects: interior materials are largely soft touch, and alloy wheels are standard—17-in with 19-in optional; no steel wheels for the U.S. market.

Weight comparisons are complex. The front-drive CX-5 at 3208-3272 lb (1455-1484 kg) is certainly 220 lb (100 kg) lighter than the CX-7, up to 575 lb (261 kg) less than one AWD version. The body is over 60% high-strength steel and purportedly much stiffer, but Mazda did not provide dynamic torsion numbers for comparison.

The original 195-lb (88-kg) AWD unit was re-engineered for the new model, which not only lowered energy losses 52% but weight by 44% to 109 lb (49 kg)—a savings of 86 lb (39 kg). Weight reduction engineering also followed Mazda’s gram strategy, such as reshaping seat bolt heads to reduce bolt weight by 8 g (0.28 oz) each. And there is a high-temperature plastic water pump impeller with a shroud that is lighter than the previous steel impeller pump and 23% more efficient.

Despite CX-5’s outwardly smaller size, the interior package is bigger: 103.8 ft³ (2939 L) cabin and 34.1 ft³ (966 L) of cargo room vs. the CX-7's 101.7 ft³ (2880 L) and 29.9 ft³ (847 L) volumes, respectively.

The Skyactiv 2.0-L four in the CX-5 has a 13.0:1 compression ratio, highest of any mass production engine ever sold here, and it runs on regular gasoline; the 14.0:1 version in Europe requires premium. It avoids knock with an exhaust manifold that would not fit in the Mazda3 Skyactiv engine compartment, using basic high-performance technology. Ultralong runners help scavenge hot exhaust gases quickly; they’re long enough to prevent pressure pulses from sending hot exhaust back through the still-open exhaust valve of the cylinder next in the firing order, which is just finishing its exhaust stroke. If the hot exhaust mixed with the intake charge, it could cause knock.

In a passenger vehicle, this manifold could result in an emissions problem, as the catalytic converter at the end of the long exhaust manifold delays catalyst warmup. So Mazda retards the ignition timing sufficiently to double exhaust temperature when the engine is first started to quickly heat the catalyst. To prevent misfire, it temporarily delays the second of two fuel injection pulses to produce charge stratification, which stabilizes combustion. The intake camshaft’s electronic timing actuator has a range of 70º. This enables the CX-5 to run open throttle at low-load cruise, with rpm control by valve timing, including delayed intake valve closing for Atkinson/Miller type cycle efficiency. The exhaust camshaft is hydraulically controlled, but just that one means oil pump output at light load can be reduced—another energy saver. That camshaft has an assist spring to reduce pump output needed to overcome inertia.

The CX-5's 2.0-L power rating is the same as the smaller, lighter Mazda3's, so why the higher compression and special exhaust? Answer: the calibration must be for a heavier vehicle, yet it produces more low-end torque than in the Mazda3, and in the CX-5 is surprisingly lively. This keeps the six-speed manual or automatic in higher gears and vehicle running at higher load/lower rpm, also contributing to fuel economy.

The AWD CX-5, capable of up to a 50/50 torque split, doesn’t run purely in 2WD mode. Mazda learned that the four-wheel tire slip losses with some rear wheel traction were always less than the front wheels alone, and the control module operates with a load-speed map to transfer appropriate torque to the rear, most when front slippage is highest, of course. Only with ABS operating is a 2WD mode allowed.

Mazda’s unique idle stop/start system, which stops a piston on compression in an optimum position and uses a precise dose of injected fuel to induce restart, isn’t available in the U.S. yet. U.S. drive cycles don’t provide much credit for it, so it was withheld to enable competitive pricing.

The electric power steering is column-mounted, a packaging necessity for front-drivers, but posed calibration difficulties through all the flex joints to the steering rack. To get Mazda-level handling, the front caster was raised from 3º to 6.5º, which increases feedback. Mazda tilted the control arms so the wheels kick backward in response to road surface inputs and transfer impact to stiffer bushings, which don’t bottom out, but provide linearity, particularly important for hard cornering. In back, the trailing arm pivots were raised to better align the rear suspension with road-surface inputs. This also allowed use of stiffer bushings without hurting ride quality.

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