EE Times Under The Hood - October 8, 2007 - (Page 10) under the hood: FEATURE www.eetimes.com • www.techonline.com in addition to balancing performance and range, tions, along with LED drivers and FETs. Some of the unique design elements of the VX1 stand ensuring cool running even under Death Valley conditions was a primary goal. The solution was to employ out in the software. Take the throttle control on the current-control algorithms to handle battery heating handlebar, for instance. Vectrix engineers could have and clever physical measures such as heat sinks, fins used a conventional mechanical control link. However, and fans (without major current use). The fans, interthey decided to take advantage of the scooter’s electric estingly enough, were implemented without the use of drive motor to function as a generator and charge the battery pack by regenerative braking, and thus conserve computational fluid dynamics but by knowledgeable trial and error by the design team. energy when slowing the vehicle. These heat-handling measures were born in the An Austriamicrosystems absolute rotary magnetic company’s Pink Room—an insulated enclosure where encoder provides a PWM signal of throttle-handle the VX1 demonstrated continuous operation at temposition that the ICM sends to the motor controller peratures of 105°F with simulated cooling flows via the CANbus. To accelerate, the rider twists the over the battery. Dugas noted that it was truly a handlebar grip downward, as with an internalworst-case scenario since not all airflow around the combustion engine. The difference comes when bike was replicated. an upward twist is applied while traveling forward, At the other temperature extreme—winter which puts the powertrain into the “regen” cold—operations and charging were modified. braking mode. Vectrix is While range was down a bit, it came back up The versatility of the electronic throttledeveloping a after a warmup period, Dugas said. And by-wire control architecture allows the eleccharging takes longer because of a battery tric motor to drive the VX1 slowly in reverse hybrid version preheating routine. (Normal charging, on if the upward twist is applied when at a dead stop, which riders find useful when of the electric 120 or 220 V, takes two hours to 80 percent charge and 3.5 hours to full charge.) backing out of tight parking spaces for twoIn another adroit maneuver in handling wheeled vehicles that are at nearly right scooter. adverse conditions, the system will check angles to curbs. switch states (such as the turn and horn The throttle encoder PWM signal is checkswitches) with high-current bursts into them to see if summed for integrity. For safety purposes, the bike turns off in the event of a complete failure, rather than they are closed or open. The reason is that in seacoast having the system rely on the throttle position input by salt air (i.e. such as the Massachusetts south coast), deposits can produce false switch-closed indications if the rider. low current is used. In other examples of hardware/software flexibility, the ICM outputs charging data to the speedometer to Development surprises and the road ahead display “fueling” current (as opposed to mph or kph) When asked if any pleasant surprises fell into place when the bike is plugged in for a battery recharge. during development of the VX1, Dugas said that the The “fuel” gauge function measures and displays amprange went up after production bodywork with tighter hours remaining in the battery. Because the system fit—as well as production weight components—were is not measuring battery charge in μAmp-hours (as available for the bike. with handheld devices), the gauging is relatively easy Looking to future developments of the electric bike and accurate. concept, Vectrix is continuing development on a hybrid version with Parker Hannifin, whose fuel cell would be Safety first used to trickle-charge the battery. The ICM also quarterbacks safety functions and disPerhaps there will be a three-wheeler concept in the plays in conjunction with the motor controller. If the more near term, but with twin, steerable and articulatcharge state is low, or a hot battery condition is detected front wheels rather than a traditional tricycle haved, power is “gracefully degraded” to prolong range or ing a pair of wheels in the rear. The idea would be that allow the battery module(s) to reach an acceptable equilibrium temperature. (For temperature monitoring, in some jurisdictions only a standard driver’s license and not a special motorcycle ticket would be required. there is a sensor on each of the 12 modules in which This arrangement would have greater stability, but the cells are housed.) would still be able to lean in turns with the closely ICM integration makes possible another safety funcspaced front wheels. tion—monitoring turn-signal activation. If a blinker is While the initial cost of the VX1—at around on for a long time, the horn sounds to alert the driver. $11,000—is higher than that of competing gas-engine The blinker is not automatically turned off because the bikes (which run about $7,000), the overall operating switch could end up in the “on,” or thrown, position cost of the VX1 should be less since it doesn’t require when the rider goes to use it again, leaving the bike gasoline or maintenance (except for brake pads), without the signal function in that direction. In discussing the major engineering hurdles faced in Vectrix said. So if you like emission-free, nearly silent running, take a hop on a VX1. ■ development of the VX1, Dugas is quick to note that, 10 Electronic Engineering Times, TechOnline | October 8, 2007 http://www.eetimes.com http://www.techonline.com
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