December 30, 2008 The 2010 Ford Fusion Hybrid includes some significant advances in mass production hybrid automotive technology. Although details released by Ford are technically incomplete many of the features announced to date point to the Fusion being the first to market with a second-generation parallel hybrid.
Due in U.S. showrooms March 2009 at a price $27,270, the Fusion Hybrid's mechanical layout utilizes a fairly conventional parallel hybrid system. A front wheel drive transverse mounted 4 cylinder petrol powered engine with what is effectively a large electric starter motor between the engine and the continuously variable transmission (CVT). Ford has made significant refinements to this system.
The 2.5 Litre 16 valve DOHC Atkinson cycle Duratec engine with 156hp (114Kw) and 135 ft-lb (182Nm). This is mated to a flywheel mounted 106Hp (78Kw) Permanent Magnet AC synchronous (BLDC) 275 Volt electric motor (no torque figure was released) with an electronically controlled CVT, all fairly conventional for a parallel hybrid and similar to the Prius and Camry hybrids. The difference is in the throttle-by-wire aggressive deceleration fuel shut-off and the integration of brake by wire regeneration.
Aggressive deceleration fuel shut-off
The fuel cut-off disables fuel delivery when the driver lifts off the accelerator. However, the engine management doesn't just abruptly disable the injectors. That would cause bumps and hesitation that the occupants of the car would be able to feel. Instead, the control strategy uses engine torque as the control variable. A desired engine torque is calculated based on a combination of driver demand, speed, gear ratio and other variables. When the accelerator is released, the torque is ramped down to zero. The fuel delivery, spark timing and electronic throttle position are determined from the torque demand. This causes the injector pulses to be ramped down so that the overall power delivery is kept smooth and seamless without abrupt changes.
brake-by-wire regeneration
Much like a Toyota Prius the regenerative brake system captures the energy normally lost through friction in braking and stores it. Ford have presumably (no technical data has been released) used brake by wire to increase regeneration capture to nearly 94 percent energy recovery by first delivering full regenerative braking followed by friction brakes during city driving. A simulator brake actuation system dictates brake actuation and delivers improved brake pedal feel compared to the previous generation braking system. It is thought the Fusion Hybrid uses electric actuated wedge brake calipers to achieve integration between regenerative and friction brakes.
The size, weight and presumably the cost of the battery pack has been substantially reduced. The cells are nickel metal hydride supplied by Sanyo. The chemistry has been revised so that each cell now produces 20 percent more power than before. The total number of cells has been reduced by 20 percent keeping the capacity at 1.3 Kw/hr. Improvements to the battery mean that the pack is now 30 percent smaller in volume than the previous generation one pack and weighs 23 percent less. It also means the pack no longer needs its own air conditioning system. Instead, cabin air can be routed through the pack to keep it cool. The pack integration was done by Delphi while Ford engineers handled all the battery management software and electronics internally.
A reduction in cell count means a reduction in the nominal system voltage to 270 V. The reason Ford has reduced the voltage is to improve the efficiency of the power electronics. Higher voltage causes more resistance and heat build up in the switching circuits and lower efficiency. Normally the voltage reduction would mean a corresponding reduction in power for the electric drive system. However, Ford's engineers have added a variable voltage controller (VVC) to the Fusion hybrid that allows the voltage from the battery to be stepped up on demand. During most driving conditions when comparatively little power is needed, the lower voltage increases the efficiency of the electric drive system, while the VVC allows even greater output than the Escape when it's needed for acceleration or heavy regenerative braking.
Another energy saving technology used in the Fusion is Electric Power Assisted Steering (EPAS). This utilizes a steering column mounted electric motor that provides steering power assistance on demand and typically consumes less than 7% of the energy of a conventional hydraulic rack and pinion power steering system.
Not a Plug-In hybrid
All these technical refinements add up to a car capable of traveling at up to 47Mph (75kmh) in EV only mode and with an EPA rating of 41MPG (5.74L/100km). Ford claim a vehicle range of up to 700 miles (1120kms) for in-town driving where maximum regeneration is possible on a single tank of fuel. One area where the 2010 Ford fusion is sadly lacking is that while the Fusion Hybrid provides a standard 110-volt power outlet it is not a plug in hybrid. The 1.3Kw/hr NiMH battery pack is less than 10% the capacity of the Chevy Volt (16Kw/hr) so EV only range is extremely limited and it can not be charged from the grid so even in EV only mode the cars energy is all generated from petrol. Like all parallel hybrid designs the Ford Fusion Hybrid is primarily a conventional petrol power internal combustion engine (ICE) vehicle with what is effectively a large starter motor used to collect energy from regenerative braking which is stored in a small battery pack for power assistance when required. By comparison the Chevy Volt has a series hybrid layout with no direct mechanical connection between the ICE and the wheels is primarily an electric vehicle with an ICE to extend range.
Paul Evans
