The United States takes environmental protection very seriously. Therefore, programs are being implemented in the country’s largest metropolitan areas to convert city buses to cleaner fuels. These programs include the use of hybrid (diesel-electric) buses as well as vehicles running on liquefied gas. Hybrid buses first appeared on the city routes as an experiment back in 1998, and their regular operation began last spring. The starting point was the appearance of Orion-6 buses. Their power units not only emit less toxic substances, but also provide fuel savings compared to vehicles running on natural gas. Fuel consumption is 1% lower in summer and 16% lower in winter (in summer up to 20% of energy is spent on air conditioning drive). During the braking there is an additional charging of batteries, which are located on the roof. The main source of energy are lead-acid batteries that power the electric motors. The diesel engine is used to recharge the batteries and when climbing. The batteries are routinely recharged every six months and have a service life of up to 2.5 years. In addition to all that, hybrid buses accelerate faster due to less transmission losses, are easier to operate, are less noisy, and finally provide smoother braking. Despite the relatively high price of these vehicles ($465,000 on average, while the cost of a similar diesel variant is $290,000), the additional costs should be recouped through fuel savings.
It is no coincidence that a number of city municipalities in the country decided to give preference to hybrid buses over vehicles with engines running on liquefied natural gas. This is due to the fact that gas engines cannot be operated without the use of sophisticated, expensive equipment and specially equipped parks, where there are compressors, inspection boxes and refueling stations. In addition, since September 2000, the U.S. has been using diesel fuel with particularly low sulfur content. In the near future the country will get rid of engines that cause much air pollution, and all buses will be equipped with special filters that trap microscopic particles of soot, which, according to doctors, causes respiratory diseases. That is why it is increasingly common to see bus bodies painted a special color, such as green, or there is a sign on the outside indicating the use of “clean technology”.
Allison Transmissions achieved good results in the battle for ecology in 1989. Three years later the company applied hybrid systems to small models, and in 1999 it completed the second generation of this system for use on intercity buses. Parallel hybrid system Allison Electric Drives, includes two models: EP 40 – for single buses 10-12 m long, and EP 50 – for articulated vehicles 18-24 m long. The design of this device can be higher or lower capacity, which allows to adapt it for installation on buses of different classes. The advantages of the Er system include fuel economy of up to 50 percent, depending on the vehicle’s operating cycle, and a significant reduction in emissions of nitrogen oxide, particulate matter, carbon monoxide, hydrocarbons and carbon dioxide.
If the bus uses an eco-friendly, electronically controlled engine running on low-sulfur fuel, the parallel hybrid system provides economic performance as good as compressed natural gas engines. It also runs quieter than a conventional engine equipped with an automatic transmission. Recently, the company’s specialists have been working on a design that implements the principle of a parallel hybrid system in HUSH mode (low noise and reduced hydrocarbon content). This will make it possible to operate the buses for a long time with practically zero emissions of toxic substances into the environment, moreover, without affecting the service life of the battery.