Ford Gives 2009 Escape and Mariner Hybrids a Mid-Term Boost; Electric Drive Now Up to 40 mph

27 June 2008

The 2009 Escape Hybrid.

Ford has given its 2009 Escape and Mariner models a new engine—a new 2.5-liter four-cylinder engine with intake variable cam timing (i-VCT) for enhanced fuel economy and performance. (Earlier post.) This basic engine platform carries over to the hybrid models of the Escape and Mariner, with adaptation for the Atkinson Cycle. This marks Ford’s first engine to incorporate variable valve timing on a engine applied in a hybrid powertrain.

In addition to the other fuel-efficiency measures inherited from the basic 2009 Escape/Mariner platform such as improved aerodynamics, the hybrid versions also feature an entirely new braking system—a major endeavor, according to Gil Portalatin, Ford’s Hybrid System Applications Manager—and a refinement in the operating strategy that boosts the maximum speed for all-electric drive up to 40 mph.

Simple comparison of Otto and Atkinson cycles. Click to enlarge. Source: Ford

The 2.5L I-4. The Hybrid 2.5L utilizes an Atkinson cycle producing 153 hp (114 kW), a 20 hp improvement over the 2008MY 2.3 liter engine. The total hybrid system offers a net 177 hp (132 kW), up 22 hp over the 2008MY. The 2009 Hybrid performs with the same city cycle fuel efficiency as the 2008 (34 mpg US), improves highway fuel efficiency by 1 mpg to 31 mpg in the front wheel drive version; and offers improved performance—a 1.5-second reduction in 0-60 mph acceleration time to 10.3 seconds.

Comparison of the torque and efficiency of Otto and Atkinson cycles. Click to enlarge. Source: Ford

The Atkinson cycle features a compression stroke that is shorter than the power stroke, achieved by leaving the intake valve open longer. This effectively allows the gases to expand more than they are compressed and thus the gas does more work per stroke than in the Otto Cycle. By getting more work out of a given amount of gas, the efficiency of the engine is improved.

Converting to the Atkinson cycle yields a 7 – 8% improvement in engine efficiency, according to Ford, but the tradeoff is a reduction of engine torque especially at the low end, due to less gas being burned in the cylinder. In a hybrid configuration, however, an electric motor can compensate for the reduced low-end torque.

Ford used the Atkinson cycle implemented through delayed intake valve closing on its earlier hybrid models as well. But where the earlier models had a fixed delay, the use of the i-VCT system allows Ford to optimize the cycle further at different points across the engine range.

The Atkinson cycle puts the vehicle in the sweet spot for brake specific fuel consumption—in the most fuel efficient band possible...The i-VCT allows us to further enhance it, to tweak it for a few different rpm ranges. The i-VCT makes the mechanism a little bit better, and we can rephase the cam to further maximize it at different ends of the spectrum.

—Gil Portalatin

A new engine processor that exploits the i-VCT enables nearly imperceptible transitions between gas and electric vehicle mode. The i-VCT phases in the amount of torque to smooth in the transition between gas and electric. The hybrid models also feature a new powertrain damping system to reduce vibrations and feedback to the driver and other vehicle occupants.

Other key new elements of the engine design include intake and exhaust manifolds, camshafts, pistons and bore size. The powertrain also incorporates electronic throttle control (ETC). This technology replaces the manual linkage between accelerator and throttle with a control unit that calculates the optimal throttle position from a number of sensors. ETC is a form of the state-of-the-art, drive-by-wire technology.

Ford will also use the new 2.5L-based hybrid powertrain in the upcoming Milan hybrid, to be revealed later this year, although that vehicle will feature the company’s second-generation battery pack, Portalatin said.

Operating strategy. Based on feedback from customers, Ford rewrote the operating strategy to enable the hybrid to drive in all electric mode at speeds up to 40 mph. This is done without a change in the NIMH battery pack itself, or in the basic state of charge operating window of the pack. It is also accomplished in a fuel consumption neutral manner—in other words, the additional charge draw from the battery is achieved in such a way that it doesn’t trigger additional charge sustaining work from the engine. The new braking system also supports the new strategy.

(Portalatin said that Ford engineers were working on an SAE paper describing the optimization of the strategy.)

Braking system. The new brake system simulates a more conventional brake system for the user. Compared to the first-generation electro-hydraulic system, the new system delivers a more seamless transition from electric regenerative braking system to traditional braking operation. A new brake pedal sensor is at the heart of the improvements. The new system allows for further fine-tuning of the capture of regenerative braking energy.

Other aspects. Electric Power Assist Steering (EPAS) is featured on both the standard and hybrid models of Escape and Mariner. EPAS replaces the traditional hydraulic power steering pump. Because it operates only when required for steering assistance, it contributes to lower fuel consumption than the hydraulic pump, which operated constantly during engine operation.

The 2009 Escape and Mariner feature new seats that include soy-based foam. Seat fabrics made from post-industrial 100% recycled materials are also offered. All 2009 Escape and Mariner hybrid models feature a standard 110V AC power outlet.

Through May 2008, Ford has sold a combined 76,120 units of the Escape and Mariner hybrids since the first introduction of the Escape Hybrid in October 2004. Combined sales for January-May 2008 are down 13% compared to the same period in 2007, to 9,510 units.