Taxis Go Green with Hybrid Vehicles

Especially in large cities, taxis often spend a lot of time in stop-and-go traffic, with the emphasis on “stop.” You’d think that advanced technologies would be applied here, and in fact that is taking place with modest sales of hybrid vehicles by major automakers to taxi fleets. As you might gather, though, other automotive suppliers also have this on their agenda.

According to Ricardo US, 10.8 million gallons of gasoline could be saved in New York City alone annually if taxi engines were shut off rather than left idling while stopped. This savings equates to reducing CO2 greenhouse gas emission by 105,000 tons annually.

Ricardo’s answer is a micro hybrid powertrain system it has developed for taxis and small delivery trucks. The system consists of an efficient electric motor-generator that replaces the standard alternator. When the vehicle idles in traffic jams and at stoplights, the micro hybrid system shuts the engine down. Then, when a driver moves his foot from the brake to the accelerator, the electric motor starts the engine instantly and silently.

If this sounds familiar...there’s a reason. This type of operation is the heart of a popular mild hybrid system already marketed by a major automaker, which strives to affordably increase fuel economy and cut emissions through an engine shut-down scenario just like this. Full hybrid systems also incorporate engine shut-off features to increase efficiency.

Ricardo’s system also includes regenerative braking to recoup energy generated during braking. The company says its system, which can be retrofitted to existing vehicles, could be available on the market within two years if sufficient interest is received from potential customers.

The micro hybrid concept recently displayed at the 2007 New York International Auto Show’s “Taxi 07” exposition is a micro hybrid stop-start system for large displacement gasoline engine vehicles, including the Ford Crown Victoria that’s widely used for taxi service. A similar system was demonstrated  on the HyTrans delivery van project in Britain. Here, a team comprised of Ford, Ricardo, Valeo, and Gates produced a micro-hybrid starting with the popular Ford T280 Diesel Ford Transit van. Like the diesel-power delivery van, taxis present a similar high torque, stop-start challenge for a micro hybrid system.

The HyTrans system includes a Valeo 4 kilowatt, 42 volt, belt-driven combined starter/alternator system along with a Valeo 1.5 kilowatt, 14/42 volt DC/DC converter. Electrical energy is stored in an advanced 36 volt lead-acid battery controlled by a Valeo battery management system. The belt-driven, combined starter/alternator is connected to the engine through a Gates-designed Front End Ancillary Drive system. The vehicle’s stop/start and regenerative braking functions are managed by a Ricardo supervisory control system embedded in a production-derived engine management unit. 

Modest regenerative braking is obtained through additional loading of the engine drive belt. The HyTrans demonstrated an over 21 percent reduction in fuel consumption during urban delivery drive cycles. The taxi application is slightly different in the HyTrans with that system concept applied to a gasoline vehicle with an automatic transmission. The taxi concept includes an electric air conditioning system and larger battery to maintain driver and passenger comfort during the vehicle stops.