Then, about three years ago, Davila got to test a new hydraulic hybrid truck: an AutoCar refuse chassis equipped with Parker Hannifin’s Run- Wise E3 Drive.
“I decided to test it in our stop and go urban environment in order to quantify their [fuel saving] statements,” he explains. The truck was tested for 2.5 weeks.
“I would have been happy with the 30% fuel savings they claimed, but attaining 43% on the demo truck was very encouraging,” Davila adds.
As a result, the City of Miami purchased four such hydraulic hybrid trucks and has another two on order.
Even as the fuel savings rolled in, however, there were questions that needed answers. How easy would it be to maintain these hydraulic hybrid vehicles? Would maintenance intervals decrease or increase? Would maintenance costs go up or down?
Solution: First off, Davila says the City of Miami doesn’t have any diesel-electric hybrid trucks in its fleet, so he couldn’t do any direct maintenance cost comparisons. He found the hydraulic hybrid setup required much less maintenance when measured against the city’s diesel-only fleet, which uses automatic transmissions.
“I initially projected brake change cycles on the hybrid at three years versus every four months on a non-hybrid with automatic transmission,” he explains. “In April of this year, we inspected the first hybrid put in service at the City of Miami back in November 2010, and the truck showed minimal brake shoe wear. The projected brake replacement cycle has now been expanded to six years conservatively, not three years as originally expected.
The big savings, of course, comes from burning less fuel. Davila says the demo truck the city’s fleet tested yielded 43% fuel savings as compared to a traditional diesel-only truck with an automatic transmission.
“When we purchased the first hybrid, fuel savings yield for the first month of full operation was 47% and 50% for the second month,” he notes. “It has increased slightly to 51% and maintained that level on average.”
The fuel economy improvements combined with the maintenance savings from the hydraulic hybrid propulsion system significantly shortened the return on investment (ROI) Davila crafted to justify the extra up-front investment.
“Our two newest hydraulic hybrid trucks were purchased without a grant and ROI is projected at less than three years, especially now that we can accurately project the brake change cycle at six years not three,” Davila explains. “Additionally, each truck consumes on average 51% less diesel fuel than a non-hybrid, or 385 gals. versus 785 gals. That is a 400-gal. savings per month per truck.”
In one year’s time, that means one hydraulic hybrid refuse truck saves 4,800 gals. of diesel, with the city’s four hydraulic hybrid refuse vehicles saving a combined 19,200 gals. of diesel per year.
“In the past, if you were able to capture the ROI in five years you had a good product, but less than three years is unheard of,” Davila says.
“Each truck will save the City of Miami $81,000 in brake changes alone during the six-year brake change cycle,” he points out. “It’s too early to determine engine life at this point. However, being that the engine power curve has been remapped to acquire maximum horsepower and torque at a lower rpm indicates that the engine will last much longer by working at a lower range.
“We are also now seeing increased tire life because the physical brakes do not contact the drums until the truck is down to about 5 mph, thus less heat at the wheels is increasing tread life,” he adds.
