Cleaner Engine Tech

While the light truck, and in particular the SUV, segment has taken quite a bit of heat in these eco-conscious times, automakers have not necessarily ignored these concerns.

A spate of crossover utility vehicles, many of which are lighter and smaller–dare I say, more carlike than their truck-based predecessors–has been introduced in recent years to provide that SUV look and feel in a smaller package.

However, that trend has in turn spurred the introduction of larger versions to fill the gap–in effect, large SUV-sized models without the step up.

The Ford Flex (made in Oakville, Ont., by the way) is one of these full-sized crossovers, and despite the sense of dj vu that it might give those who went through the last couple of trends in larger vehicles, a quick peek under the hood of the 2010 model reveals that it’s hardly a throwback: it features a direct injection, twin-turbocharged 3.5-litre V-6 engine. (At least, those not outfitted with the standard 3.5 L Duratec 35.)

The 3.5L Ecoboost V-6 produces an estimated 355 horsepower at 5,700 rpm and 350 foot-pounds of torque at 3,500 rpm. Ford says the technology boosts fuel mileage by 20% and reduces emissions by 15%.

The twin parallel turbochargers, which are water-cooled and operate simultaneously, combine with a direct-injection fuel system to produce power. The high-pressure fuel pump operates up to 2,175 psi–more than 35 times the norm seen in a conventional V-6 engine. The high-pressure pump is a cam-driven mechanical pump with a single piston and an electronic valve that controls how much fuel is routed through the fuel rails to the injectors.

As demands on the twin-turbocharged 3.5-litre Ecoboost V-6 engine increase, the control system responds to main tain optimal combustion, timing, and injection duration.

On each stroke, six individual jets spray fuel directly into the combustion chamber, mixing with the incoming air. Bringing the fuel injector right into the combustion chamber means there’s no delay from the time you inject the fuel to when it’s used by the engine.

The fuel injectors are located on the side of the combustion chamber. When the fuel is injected into the cylinder, it evaporates and cools the air that’s been inducted into the cylinder.

The direct injection of fuel into the cylinder also helps provide a well-mixed air-fuel charge, increasing engine efficiency. Direct injection also provides several benefits in terms of fuel burn and lower emissions.

This process also eliminates the risk of fuel wetting the combustion wall as with port fuel injection; intake ports don’t get saturated, and fuel droplets don’t have an opportunity to recombine. It all leads to better, more efficient control of the air-fuel mixture, and more power, lower fuel consumption, and lower emissions are the result.

The simultaneous turbocharger operation paired with the direct-injection system help to virtually eliminate turbo lag, one of the main reasons turbocharger technology has not been more widely used in the past.

The dual-turbocharger setup has several advantages over previous turbocharging systems, including:

• the turbochargers are smaller, resulting in more compact exhaust manifolds that don’t generate as much heat;

• the turbochargers are packaged adjacent to the cylinder block and have improved mounting providing NVH (noise, vibration, harshness) improvements;

• the dual turbochargers spool up more quickly, allowing the 3.5-litre Ecoboost V-6 engine to reach peak torque faster, spinning at approximately 170,000 rpm (by comparison, the redline for the engine is approximately 6,500 rpm);

• two turbochargers operate identically over the speed range of the engine: one is responsible for the left bank of the engine and the other the right bank, producing boost even at low speeds;

• the turbochargers are designed for a life cycle of 10 years; • turbocharger “whoosh” is mitigated by electronically controlled anti-surge valves, which proactively relieve the boost in the intake, which can range up to 12 psi; precise software calibrations manage the pressures in the intake manifold.

Mated to the 3.5-litre Ecoboost V-6 engine is the 6-speed 6F-55 SelectShift automatic transmission, which is dedicated to the twin-turbocharger engine. As with the Ecoboost/Duratec changeout, the transmission shares some specification highlights with the non-Ecoboost drivetrain, such as six speeds and gear ratios, but there are key differences that will be notable down the road should parts replacement be required.

Similarities should not be surprising, though, as the 6F-55 transmission was developed from the 6F-50 transmission specifically to respond to the increased torque demands of the Ecoboost V-6 engine. Upgrades were made to the transmission’s friction material in response to the higher shift energies, and a new torque converter has been optimized for performance and fuel economy.

Additionally, the 6F-55 transmission operates more efficiently. The transmission team was able to reduce the fluid level in the transmission, which in turn reduced weight and drag torque on the system. Upgrades to the transmission’s thermal valve mean the system warms up more quickly, reducing gear-spin losses.

While the Flex is just one vehicle, the approach taken signals a trend toward increasing technology in a largely conventional (read, affordable) approach, while continuing to build the larger vehicles that many consumers still demand. –Andrew Ross

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Ecoboost Versus Duratec

The Ecoboost shares a number of basic specifications with the Duratec: both are 60-degree V6 3.5 litre engines, but they differ in some important ways. The intake manifold on the Ecoboost is a one-piece aluminum component, whereas the Duratec employs a composite split plenum. Also, the pistons on the Ecoboost have a direct injection bowl, not needed on the Duratec. There are likely other subtle differences in the components that will be revealed as these engines become more well known in the aftermarket, but counterpeople should be careful to ensure that they know which 3.5L engine, Duratec or Ecoboost, is under the hood of a vehicle in question.