The Ford Escape's Full Hybrid System
All hybrid cars have two power sources -- a gasoline engine and an electric motor. They can work together in different ways, however. In so-called "mild" hybrid designs, the gasoline engine is always running, and the electric motor simply augments it, adding a little extra horsepower here and there to save some fuel. But Ford developed a full hybrid system for the Escape.
In a full hybrid system, the gasoline engine and the electric motor can both operate separately, or they can run at the same time. The Escape's hybrid system operates in four phases:
- Start/Stop - When you turn the ignition key of the Escape Hybrid, the electric motor comes to life. The electric motor, in turn, starts the gasoline engine. The car then performs a series of checks to determine if it can switch to electric-only operation: It checks to see if the batteries are charged, if the operating temperatures are okay and if interior climate control settings are in the appropriate range (the air conditioning's maximum setting requires the gasoline engine to run). If everything checks out, the engine will then shut off, leaving the car running under electric-only power. This process only takes a second or two. When you come to a stop in the Escape Hybrid, the gasoline engine actually shuts off. The car runs on electric-only while you're at a stoplight or waiting in line at the drive-thru. Ford put a lot of effort into making the gasoline engine on-off cycles as smooth and seamless as possible, but testers reported a discernible shudder in the vehicle when the engine went on or off. This is common to all hybrid cars.
- Electric Drive - As the Escape Hybrid accelerates from a stop, it does so under electric power. Electric motors are good at generating torque at lower rpm ranges, so they're perfect for this purpose. At about 25 mph, the gasoline engine starts back up. If you're driving in heavy city traffic, you could go all day using only electric power. The electric motor and gasoline engine operate in tandem up to highway cruising speeds.
- Regenerative Braking - Whenever you apply the brakes on a car, the kinetic energy of the car's movement is dissipated as heat. In a hybrid car, the brakes take some of that energy and, using the electric motor as a generator, put power back into the batteries. This is why hybrids actually get better mileage in start/stop city driving than they do on open highways. Every red light recharges the batteries. To maximize the power of regenerative braking, it's important to stop smoothly and gradually. Slamming on the brakes activates the regular anti-lock braking system, and the energy is wasted.
- Electric Assisted Cruising - At highway cruising speeds (roughly 50 to 70 mph or 80 to 110 kph), the gasoline engine does most of the work. It's most efficient at this speed range. But because the Escape Hybrid has a small, four-cylinder engine, it needs a little help when passing. When a speed boost is called for, the electric motor kicks in and adds its horsepower to that of the gasoline engine.
The Escape Hybrid (along with all other hybrid cars) doesn't have the usual transmission, with separate gears for the car to shift into and out of. Instead, the Escape uses an electronically controlled continuously variable transmission (eCVT). On-board computers set the gearing to the optimum setting for fuel efficiency, resulting in a 30 percent increase in efficiency over a conventional transmission, according to Ford engineers.
Next, we'll crunch some numbers and see how the Escape Hybrid measures up.