Hydraulic Hybrid Technology @ UPS

[Don]

Business Week:

ASSISTING THE DIESEL TRUCK ENGINE

"Similar to electric hybrids, hydraulic hybrids draw energy from braking, but are twice as efficient collecting that energy because the braking energy is not wasted by being passed into an electric motor. Instead, this energy is used to power a pump, which transports hydraulic fluid from a low-pressure reservoir to a high-pressure accumulator. As more fluid passes into the accumulator, the pressure grows, eventually being released as energy that is used to directly power the vehicle's driveshaft. "

" This allows the vehicle to move from a stop without taxing the diesel engine, which typically performs poorly while accelerating. Diesel engines are most effective when running at a steady rate, and lose a tremendous amount of efficiency when accelerating; the hydraulic system compensates for this weakness, and lets the diesel engine do its work once it's up to speed. This is especially important for UPS trucks that stop 60 to 70 times per day for deliveries and operate mainly in stop-and-go city traffic, where the hydraulic system can carry most of the burden. "


http://www.businessweek.com/print/bw...116_037066.htm

[427 S/O]

Interesting.....

[Bobcat]

Guys ... very familiar with this technology as I was involved in a system very similar to this one when I was with Parker . The two players in this field were Parker and Eaton . The description is basically correct , but there is a lot more involved as it is all computer controlled and the hydraulic motors/pumps have to be high efficiency piston units . This system performs poorly in a non start stop situation .... the more starts and stops , the better it works . We were surprised as one of the major savings to the user was reduced brake wear , along with reduced fuel usage . On the refuse trucks I was working with , replacing brakes was a major expense . The savings on brake replacement almost equaled the fuel savings . Transmission wear and maintenance was also reduced . Another benefit was a major reduction in noise levels ... in several case , you almost couldn`t hear the trucks ... and pollution was reduced considerably .This technology is a major improvement and I`m surprised it wasn`t adopted years ago as I was working on prototypes two to three years ago . The possible downside was that , back then , it added about $15, 000 to $20,000 per chassis

[Don]

Bobcat, with your familiarity of the technology, could it also be a used in city taxi cabs, such as NYC, with frequent start/stops and braking, or not-applicable to passenger vehicles, space/cost limitations or ?

[Bobcat]

Don ... it could be used , but with current technology it isn`t cost effective. What we found was that the heavier the vehicle the better , as you need the stored energy to recharge the system . Diesels are also "better" as they don`t give 25 + mpg ... try about 3 to 4 mpg for refuse trucks . I would assume about the same for the UPS trucks . It would be difficult to show a payback on a gas car or truck with current technology . As you indicated , space is also a problem as the system components are pretty good size and weight .
Actually , it is really neat . The acceleration an be better then with the engine alone and in some cases we were able to get several start stop cycles before the engine had to be used to recharge the system ... which it did on the longer runs between stops .
Just think of this system as a huge hydrostatic drive with accumulators supplying most of the energy and being recharged by the engine ... the hydraulic motors are a motor / pump combo ... used as a pump as the vehicle decelerates to charge the accumulator and then as a motor to accelerate the vehicle from a stop with the flow from the accumulator.
Good idea , but not really cost effective just yet .