Ford's approach to hybrid technology has some similarities with that of Toyota's Synergy system, however there are some key differences.
In the Escape application, Ford has decided to use an Aktinson-cycle four-cylinder as well as active battery cooling. Ford also integrates their high voltage hybrid components into the transaxle, which simplifies the engine compartment and helps prevent damage. The battery life and power is increased by using the auxiliary battery cooling system. The Aktinson-cycle engine offers improved fuel economy, while sacrificing low-end power. This sacrifice is well matched with the instant power available from the electric traction motor.
There are actually two electric motors in the Escape Hybrid. One 70 kW traction motor and one 45 kw generator/motor both contribute to the hybrid's powertrain. How this system works is actually pretty amazing. I will try my best to relay it to you accurately. The schematic below will show you the relationship of the hybrid's components. The planetary gearset is crucial to the operation of the entire system. Its simplicity is quite elegant.
The system has three modes, Electric vehicle mode, positive split mode, and negative split mode. There is also an idle charge mode, but that does not contribute to the vehicle's direct motivation.
In electric vehicle mode, the traction motor draws energy from the batteries to propel the car without using the gasoline engine. At this point, the gasoline engine is off. When in this mode, energy is also collected when the vehicle is slowing down. This regenerative braking is done in the other modes as well. The diagram below shows how the regenerative braking torque contributes to the vehicle's deceleration effort.
In positive split mode, the gasoline engine is on and works in concert with the traction and generator motors to power the vehicle at moderate speeds or loads. In this mode, the generator is producing energy from the gasoline engine's output. This energy can be used to charge the batteries or power the traction motor. The traction motor also contributes to the Escape's motivation.
During high speed or high load situations, the system operates in negative split mode. In this mode all three power plants are contributing to the vehicle's movement in some way or another. The generator motor operates to reduce the gasoline engine speed required while the traction motor operates as a generator to provide power to the generator motor.
The electrically controlled CVT or eCVT does not have the belts and chains typically found in other CVTs. Instead
the motors and planetary gear set work in harmony to operate in the most efficient manner possible. The planetary gear
set allows the contribution of the gasoline and generator motor to vary depending on the situation.
So what do we think of all this? It all works very seamlessly. In fact, the shutdown and start up of the motor is hardly noticeable unless you're watching for it. The power delivery is smooth, and there is a surprising amount of power available. Off the line, it is not that fast but once you are moving the entire hybrid powertrain can accelerate the Escape briskly. The Hybrid information screen will give you a diagram of what mode the system is running in, but if you're not paying attention to the system it operates fine on its own.
The sensation of driving a hybrid is a different from what most people experience in normal cars. Hearing the whine of the electric during assist or regeneration is strange at first, but then becomes a novel reminder that you're driving a hybrid. Of course, you can't really hear it with the radio on, but roll down the windows and turn off the radio. Then you can experience the eeriness of rolling way from a stop light with the engine off as well as the other audible indications of the hybrid's operation. This car would be great for the kid who lives at home and wants to avoid getting caught on those late night returns. No need to turn the engine and the lights off to coast in with stealth. Just stop a safe distance away, let the engine stop, and cruise in under 25 mph in the silent EV mode. How useful this would've been in our youth!
We did have a couple complaints. With any CVT transmission, you have to contend with engine noise. The engine noise
is really only a problem when accelerating, and is simply off-putting to the uninitiated. The other complaint is with
the air conditioning when the engine shuts off. The AC simply does not cool when the gasoline engine is off, in EV mode
or when you are idle. You can prevent this engine shut down with the AC set to Max AC, but that defeats the purpose of
having a hybrid. The AC compressor should probably be driven by another electric motor to keep the passenger
compartment cool. Ford has openly told us they have made a substantial effort to improve this problem in the 2006
models. Ford has also made some tweaks to the rest of the hybrid system to make it operate even smoother.
Based on what we've seen so far, we look forward to this power system finding its way into other Ford products. We could see where such a system would help give the Five Hundred more power or give Volvo a competitor to the Lexus RX400h in an XC90 Hybrid.
Also, look for an upcoming podcast where we interview Tom Gee with Ford's Hybrid team.