With the introduction of the Mercury Mariner Hybrid, Ford Motor Company added a second hybrid vehicle to its list of clean, highly fuel-efficient vehicles. The Mariner Hybrid uses the same technology initially introduced in the Ford Escape Hybrid allowing it to achieve nearly a 50% increase in fuel economy over its non-hybrid counterpart. The battery powers the vehicle up to 25 mph and works with the gasoline engine under a variety of other driving conditions. During coasting, at stoplights, or at low-speed operation in traffic, the electric portion of the system takes over and the gasoline engine is shut off to conserve fuel and reduce emissions. With this strategy, the Mariner achieves fuel economy estimated at 33 mpg in the city and 29 mpg highway, compared to the Mariner with the 2.3 liter four-cylinder Zetec engine that gets 22 mpg, city and 26 mpg, highway. In addition, the hybrid accelerates like a V-6 and has a driving range of well over 400 miles per tank.
The battery of choice for today's hybrids is nickel metal hydride (NiMH) technology instead of lead acid to reduce the weight, deliver twice the energy, and provide longer life without maintenance. The Mariner Hybrid uses a battery supplied by Sanyo that has 250 NiMH cells. With a nominal 1.2 V per cell, the battery would normally be rated at 300 V. However, Ford calls the unit a 330 V battery. It provides the power for a permanent magnet AC synchronous motor that develops 94 hp at 3,000 rpm to 5,000 rpm.
SPECIAL BATTERY CONSIDERATIONS
NiMH batteries take far more electronics technology to operate properly compared to the simple voltage regulator used with a 12 V lead-acid battery. The NiMH battery requires battery management with controllers and sensor inputs that include voltage, current and temperature to determine battery state of charge (SOC) and life or battery state of health (SOH). In addition, the battery management system has to communicate with the engine control, since the two work together to propel the vehicle and supply power to electrical loads. In the Mariner Hybrid, seven different microprocessor-based control modules manage powertrain-related functions with the vehicle system controller (VSC) making the overall decisions.
The Mariner's NiMH battery pack is housed in a six-inch-thick sealed container, which allows it to be packaged underneath the floor in the cargo area. The battery's location has minimal impact on the cargo space reducing it from 66.2 to 65.5 cubic feet compared to the conventional Mariner. Weight is a different matter. The overall curb weight of the hybrid is 3,787 pounds, about 500 pounds greater than a Mariner with just a four-cylinder engine. The battery's location helps balance weight distribution and lowers the vehicle's center of gravity. To maintain the battery pack's operating temperature within required limits, ventilation air is heated or cooled as necessary.
Similar to other hybrids, the NiMH battery is not the only electrical power source in the Mariner. It still has a 12 V lead-acid battery. The Mariner has a number of additional electric loads that rely on the 12 V battery for power, including electric power-assisted steering (EPAS), power windows, locks and mirrors, as well as front-heated leather seats and heated exterior side mirrors. The Mariner's size allows EPAS operation from 12 V. However, the Mariner's 12 V battery does not have to crank the engine, so its size can be smaller — targeted primarily at handling the key-off loads. To maintain its charge, the 330 V NiMH battery charges the 12 V battery through a single-direction dc-dc converter. Unlike the lead-acid battery, the Mariner's NiMH battery comes with a limited warranty of at least eight years/100,000 miles.