“Not all hybrid vehicles use electric motors, batteries and cables. Some vehicles are powered with a combination of pumps, motors, hydraulic fluid pressure accumulator. ”
With fuel prices reaching record high recently, consumers have suffered the pain of fuel outlets, but this is just a stitch, as compared to the pain felt by fleet operators of heavy vehicles.
The trucks that deliver our packages and pick up our trash are a few things from the standpoint of fuel economy. The weight is one. A fully loaded truck covers a range from 6.3 tonnes to more than 31.7 tons and load stop many of these trucks have a fuel burning cycle that requires continuous starts and stops. What further increases its fuel consumption.
Therefore, there should be no surprise to anyone that some of the largest operators of truck fleets have jumped on the side of hybrid vehicles. Federal Express and UPS have added several dozen hybrid electric vehicles to their fleets over the past two years, using a hybrid powertrain supplied by Eaton Corp. Waste Management, the largest garbage hauler, are evaluating a variety of solutions for their hybrid vehicles trucks, according to Lynn Brown, a spokesman for the company.
What may be surprising, however, is the kind of fleet operators like Fed Ex hybrid systems, UPS and Waste Management, are looking for some of their heaviest vehicles. These hybrids do not use electric motors, batteries and cables of the way the Toyota Prius does. Instead propel the vehicle with a combination of motors and high pressure hydraulic pumps, fluid lines and accumulators.
The most radical versions, and efficient fuel use of these hybrid-hydraulic, change the traditional mechanical. In these vehicles, the diesel engine drives a hydraulic pump-motor, which in turn charges a high pressure accumulator, the accumulator in turn sends a pump-motor shaft axial, the rear wheels to propel the vehicle . A tank low pressure reservoir completes the circuit, collecting the liquid to be sent back to the first pump-motor.
As with electric vehicles, hydraulic hybrids also have regenerative braking. During braking events, which are many in a delivery vehicle or a garbage collection truck, the pump-motor charges the high pressure accumulator. The energy stored in the accumulator can be used to reduce the load on the diesel engine when starting the truck again. The stored energy could also allow limited propulsion engine off – for example, when operating the truck inside a building.
To consumers and even some engineers, hydraulics may seem like outdated technology in a world increasingly electronic. However, the hydraulic pump-motors and accumulators can provide a low cost and reliability to apply torque and store energy, that is exactly what hybrid vehicles require. Hydraulics offers a significant power density that exceeds the electrical systems, at least for now. “It looks like hydraulics will make much sense, at least for the wide range of heavy walk,” says John DeCicco, a Ph.D. mechanical engineer automotive is a senior strategist for the Environmental Defense Foundation.
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