Friday, June 26, 2009

Sizing up the Ford Fusion Hybrid

Dropping an electric bus motor and a Ford 9" differential into a modern mid-sized sedan is no easy task. While we're waiting on delivery of our conversion vehicle (locked in, will finally get here in two weeks), we're doing everything possible to prepare the new drivetrain outside of the vehicle.

So while Kevin is bench-testing the motor and controller system, Matt has been gettting the drivetrain components together that will connect from the motor to the wheels, and he's had an amazing find in picking out a differential that has exactly the gearing we need.

Electric motors can spin at high RPM (ours goes to 12,000) and have a very broad torque range; our vehicle will only need one gear ratio to reach 100mph. To match this speed with the top speed of our motor, we need a gear ratio of 7.3:1. The Ford 9" differential has a huge aftermarket following among the rock-crawler crowd and there are a few companies that make very low gearing for it. Luckily, the lowest one we've been able to find is 7.3:1, exactly what we need. This means we can drive the motor directly to the differential, eliminating the need for a high-speed gear reducer (an expensive piece of equipment that would have otherwise needed to have custom made).

To double check that all of the components will fit before we order them, we took a couple of measurements off of a 2010 Ford Fusion Hybrid (Ford is donating us a Mercury Milan Hybrid, but they're the same vehicle mechanically). We have a few options for fitting the motor and differential into the car; they will be in a T-shape, so the motor will be sitting in the car longitudinally. The motor with the differential coupled to it will have a length of 90cm. The distance from the center of the front axle to the radiator is 65cm, too short for the system. We'll need to connect the differential to the front wheels, with the motor sitting behind it.

However, this mounting also leads to a few other problems: we need to get by the steering rack, a few subframe mounts, and make room for the motor in the exhaust tunnel. Fortunately, the tunnel is already relatively large. We also have plenty of interior room in the car's center console location to enlarge the tunnel with no visual modifications to the vehicle interior. This may also mean connecting the motor to the differential with a CV joint at an angle to not disturb the steering rack; we will find out for sure once we remove the drivetrain. Until then, we're looking to order the differential, gearing and an IRS center housing with CV style ends.

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