Brammo Empulse R | First Ride

eBike Fun, Now With Gears

By Aaron Frank, Photography by Kevin Wing

HARD PARTS

BRAMMO EMPULSE R
Under the Skin of the World’s Most Advanced Electric Motorcycle

MOTOR
The Empulse motor is designed by Brammo and built by Parker-Hannifin in New Ulm, MN. Essentially a scaled-down version of what’s in Brammo’s 170-mph electric superbike that won the 2012 TTXGP World Championship at Daytona, the permanent-magnet AC motor uses a samarium-cobalt magnet and is liquid cooled—a first for a production electric bike. It produces 40 kilowatts of energy at 8200 rpm—equivalent to 54 horsepower—with a peak torque rating of 60.5 lb.-ft. that remains constant from 4500 through 8200 rpm. A Sevcon Gen 4 digital motor controller moderates the power supply with Advanced Flux Vector control—shades of Back to the Future—to smoothly channel power from battery to motor.

BATTERY
The Empulse carries Brammo’s latest BPM 15/90 lithium-ion battery: a 103.2-volt battery that delivers 90 amp-hours storage and a nominal battery capacity of 9.3 kilowatt-hours. The battery pack is constructed from 252 individual pouch cells grouped in seven modules. The individual cells are rectangular, with each presenting a large, flat surface that can be heated or cooled via heat-transfer plates running through the module extrusions. Very cold temperatures can decrease charging efficacy of lithium-ion batteries, and these heat transfer plates can bring the battery modules up to a temperature that allow full-rate charging even if the bike is stored outside in below-freezing temperatures, which Brammo says is crucial for customer satisfaction.

CONTROLS
A Hall-effect electronic throttle (ride-by-wire) allows Brammo to offer two power modes: Sport mode delivers 10 percent more peak power, and reaches peak output 25 percent sooner than Normal mode. Regenerative braking effect, which uses deceleration forces to recharge the battery and also mimics a gas engine’s compression-braking for a more familiar riding experience, is reduced in Normal mode for a smoother ride at low speeds around the city. A handlebar-mounted switch changes modes. The Empulse also incorporates an on-board diagnostics system that service techs can access directly by connecting a laptop to the bike. Alternately, the bike owner can download files from a USB drive located under the seat and e-mail these to the dealer for diagnostic purposes.

CHARGING SYSTEM
The Empulse is charged using a SAE-standard J1772 connector that’s included with the bike, which feeds into a 3 kW on-board charger and DC-DC converter. This is the same charging interface used on electric cars like the Nissan Leaf and Chevy Volt, so Empulse owners can take advantage of the ever-increasing number of public charging stations being installed across the United States. Using a Level 1 power supply (single-phase 120-volt, like most household outlets), it takes 8 hours to fully charge the depleted battery; connecting to a Level 2 power supply (split-phase 240-volt, like most dedicated charging stations) reduces that charging interval to 3.5 hours. The charging connector, which looks remarkably like a gas pump nozzle, plugs into an outlet under what would be the gas cap on a conventional fuel tank.

TRANSMISSION
Brammo’s super-compact, six-speed Integrated Electric Transmission (IET) was developed in partnership with SMRE Engineering of Perugia, Italy. This so-called “mechatronic propulsion unit” is a small feat of engineering, combining electronic propulsion with a mechanical transmission that uses a conventional wet, multi-plate clutch and gear mechanisms. Sophisticated software and a dedicated electronic control system vary power supply and engine response according to gear position to more closely mimic the dynamic riding feel of an internal-combustion engine. Brammo originally envisioned a four-speed transmission, but settled on six ratios to reduce stress on the motor and control system. Generating torque from an electric motor requires precise tracking of the rotor position, which proved difficult when the rotor was forced to make bigger speed jumps from gear to gear. Six closely spaced ratios make it easier to track rotor position more precisely, reducing the risk of a controller fault. For packaging reasons, neutral is located between second and third gears, but since you hardly ever use neutral on this bike—the electric motor is essentially in neutral any time you’re off throttle, including at a stop—this unusual layout is mostly a non-issue. The transmission adds a service requirement to an otherwise maintenance-free drivetrain—its oil needs to be changed every 3000 miles, but because it only holds one liter and the closed system requires no filter, this is a quick and easy task.

CHASSIS:
Accossato in Italy fabricates the aluminum E-Beam frame, tubular-steel subframe, and tubular-steel swingarm. Making enough room for a large battery pack is always challenging on eBikes, and adding a transmission here ate up even more available space. Brammo’s solution was to widen the frame by 2 inches (compared to the original, direct-drive Empulse prototype) to make enough space for the BPM battery. The remainder of the chassis components are premium European parts befitting a $19,000 sportbike, including radial-mount Brembo brakes, Marchesini wheels, a Marzocchi fork, and Sachs rear shock (the latter two components both fully adjustable on the R-version).

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