2009 Ford Escape Hybrid. Click image to enlarge
By Jim Kerr; photos by James Bergeron
With gas prices continually climbing, motorists are looking for ways to save at the pumps. Some of us could drive less or drive smaller vehicles, but for others there is little choice: they need a vehicle that will meet the needs of family and family errands; a hybrid SUV may be the answer.
GM introduced a full size Tahoe hybrid this year and Toyota and Lexus offer the mid-size Highlander and RX400h, but the most popular hybrid SUVs are compact SUV’s like the Saturn Vue and Ford Escape. The regular Escape has been the best selling compact SUV vehicle in a very competitive class for the past five years. Perhaps that is why the current Ford Escape Hybrid is selling so well too.
Last year Ford introduced a new Escape design and many of the benefits of the new body design were incorporated on the 2008 Escape Hybrid. However, the hybrid powertrain didn’t see many changes. Over the past year, Ford engineers concentrated on improving the powertrain to make the 2009 Escape Hybrid an even better vehicle.
2009 Ford Escape Hybrid Electric Drive Assist. Click image to enlarge
To start with, they put a new engine under the hood. A 2.5-litre four-cylinder with variable intake valve timing adds 11 percent more power than the 2008 2.3-litre engine, which increases performance but reduces fuel consumption at the same time. This engine is available on all Escape models, but the Escape Hybrid gets a special version. The Hybrid uses an Atkinson Cycle design in combination with variable valve timing.
The Atkinson Cycle is a modification of the conventional four-stroke engine cycle. On a conventional engine, the intake valve opens as the piston moves down in the cylinder. As the piston starts to move back up, the intake valve closes so the air fuel mixture can be compressed. The piston reaches the top, where the air/fuel mixture is ignited, forcing the piston down on the power stroke. Finally, the piston is pushed back up again with the exhaust valve open to force the burned gases out the tailpipe. This cycle of intake, compression, power and exhaust repeats itself in every cylinder nearly a thousand times a minute at highway cruising speed.
2009 Ford Escape Hybrid Battery Pack (top); 2009 Ford Escape Hybrid Drive information display. Click image to enlarge
The Atkinson cycle changes the intake and compression stroke by changing the timing of the intake valve closing. Instead of closing the intake valve at the end of the intake stroke, the valve is held open much longer. This allows the piston to rise without compressing the gases as much, which reduce pumping losses (the power needed to compress the mixture). As the piston moves further up the compression stroke, the intake valve finally closes to compress the mixture. Variable valve timing helps optimize this at all engine rpm.
Closing the intake valve later would seem to reduce power output, but really only has much effect at lower engine speeds. At higher rpm, there isn’t much time for the air to change direction so effective compression remains high. To help compensate for power losses at low rpm, the engine has higher compression ratios to increase cylinder pressure.
The Atkinson cycle works well when combined with the Hybrid’s electric motors. Electric motors produce strong torque at low rpm to assist the gasoline engine when it is at low rpm. At higher rpm, electric motors don’t have as much torque but the gasoline engine torque is stronger. The two make a good combination.
The Escape Hybrid’s e-CVT transaxle, which utilizes two electric motor/generator units remains largely unchanged as does the 330-volt nickel metal hydride battery pack, but the Escape Hybrid is now programmed to operate on electric only at speeds up to about 60 km/h.
Hybrid technology improvements are coming fast and furious. Much of it will come from improved programming and battery technology, but matching the right gasoline engine and electric motor technology is just as important. The Hybrid is one answer to increased fuel costs.