Machine Design

2008 Ford Escape Hybrid

Like most other hybrid vehicles, the 2008 Ford Escape combines a gas engine with an electric motor.

There are no provisions for plugging in the Escape to charge its batteries. Charging is done via engine power and regenerative braking.

The 330-V nickel-metal-hydride battery is under the rear deck where the spare tire usually sits. (The spare is under the vehicle behind the rear bumper.) High-voltage electrical contacts in the battery compartment snap shut when the key is turned, supplying power to the electric drive. The drive battery also has an impact cutoff switch that opens in the event of a crash or other high-g shock.

The gas engine is a 2.3-liter Atkinson-cycle in-line four cylinder that generates 133 hp at 6,000 rpm. Longer power strokes in the Atkinson extract more energy from the burning air-fuel mixture for greater engine efficiency. However, greater efficiency comes at a sacrifice in engine power. The Escape Hybrid augments the engine's lower power with a 70-kW (94-hp) permanent-magnet ac-synchronous electric motor.

Driving the Escape Hybrid breaks down into five distinct phases. The SUV accelerates from a standing start using only the motor. As speed builds, the engine fires up, and draws more power from the gas tank than from the batteries. Any sudden acceleration, such as when passing, activates the motor to give the engine an instantaneous power boost. As the car decelerates and brakes, the motor turns into a generator that restores power to the battery while slowing the vehicle. Finally, as the SUV comes to a stop, the engine shuts down completely. A special gage on the dash monitors power used by the motor (assist mode) and power restored to the battery by regenerative braking (charge mode).

Driving the hybrid wasn’t much different than a standard Escape. Acceleration was brisk with the motor adding more than adequate oomph to pass other vehicles. The electronically controlled continuously variable transmission (eCVT) had no discernible shift points. And the transition from motor to engine and back was barely perceptible.

The ECU adjusts eCVT ratios, along with engine power and rpm, to get the most-efficient operation. For example, traveling under cruise control at 65 mph on flat roads, the engine held a fairly constant 2,500 rpm. But to maintain speed while climbing an overpass sent engine rpm up over 4,000. It dropped to about 1,500 rpm going down the other side while the power meter indicated the SUV was using regenerative braking to control speed.

Four-wheel disc brakes supply extra stopping power and take over entirely when regenerative braking is not effective.

EPA estimates fuel consumption at 34-mpg city and 30-mpg highway, based on the new methods for 2008 vehicles. My short test drive, with mostly highway driving, averaged 29.8 mpg. Base price of the 2008 Escape Hybrid is $25,075. Sticker price of the test vehicle was $29,805.

— Bob Repas

TAGS: Automotive
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