This week, the city of Ann Arbor, MI began deploying four of the first 25 trucks equipped with an Eaton Corporation hydraulic launch assist system. Ann Arbor mayor John Hieftje and Clean Energy Coalition executive director Sean Reed presented one of the new recycling trucks at the city's Wheeler service center.
The hydraulic launch assist (HLA) system operates on a principal similar to other hydraulic hybrid systems we've seen. A pair of accumulators store energy captured during braking and release it during acceleration. The HLA is a parallel hybrid with a hydraulic pump motor connected to the drive-shaft through an electronically controlled transfer case clutch.
The system was actually originally developed at the EPA national laboratory in Ann Arbor. Engineers employed there are encouraged to come up with new ideas and patent them. The technology is then shared with privately owned companies for commercialization. Eaton is one of several companies developing hydraulic hybrid technology variants, including series hybrids. The Eaton HLA was first seen on the 2002 Ford F350 Tonka concept and Ford has been evaluating it for use in big pickups and vans, although no production variants have been announced yet.
HLA cuts fuel consumption of the trucks by about 15-20 percent in this type of application that includes frequent starts and stops. The four trucks are expected to save $73,000 in fuel costs over their 10 year useful life, along with $26,500 in reduced maintenance costs. These trucks make an average of about 1,000 stops a day and conventional versions require new brakes every three months or so. The HLA-equipped versions recapture about 75 percent of the kinetic energy of braking and only require brake maintenance once a year. The payback time for the extra initial cost is estimated at two to three years. Future versions could reduce operating and acquisition costs further through the use downsized engines and transmissions.