With all the emphasis on improved fuel economy, energy conservation, environmental protection and enhanced vehicle functionality, commercial truck and component manufacturers have been busy developing “green” technologies. Chief among these are hybrid and alternative fuel vehicles.
Alternative fuels refer to all fuels that can replace diesel and gasoline. A hybrid vehicle, basically, is one that uses two or more distinct power sources to directly or indirectly provide propulsion power.
A key benefit of hybrids is that they cut down on fuel use by letting the engine stay at idle during initial vehicle acceleration, having the hybrid system accelerate the load. With reduced engine run time, there is lower exhaust emission.
Depending on the application, hybrid truck users can experience an improvement of 30 to 35 percent in fuel economy compared to a traditional diesel engine powered truck in a stop-and-go city delivery operation.
Hybrids provide other benefits as well. Along with extending engine life, hybrid systems assist in deceleration through regenerative braking, reducing brake wear for less maintenance and lower life cycle costs. There also is less noise, as well as enhanced customer image by going “green.”
Hybrid technologies are being successfully used in all classes of vehicles, from automobiles to heavy-duty trucks. A number of commercial truck builders offer a range of production model hybrids.
Electric hybrids
One of the more common types of hybrid systems is the parallel-type diesel-electric. It combines an engine with a combination electric motor/generator and high-capacity batteries to augment engine torque with electrical motor torque.
Advanced powertrain controls monitor driving conditions and automatically select the ideal power mode, smoothly switching among electric-only, combined diesel and electric, and diesel-only power modes.
The hybrid drive system recovers energy normally lost during braking and stores this energy in the hybrid system’s batteries. During the next vehicle launch cycle, this electric energy is pulled from the batteries and supplied to the hybrid motor, which converts the electric energy to torque and horsepower. When blended with engine torque, the stored energy is used to improve fuel economy and vehicle performance.
The main components of a parallel electric hybrid drive system are the diesel engine; hybrid drive unit (HDU) — electric motor and automated manual transmission; power electronics carrier (battery box); motor inverter controller; hybrid cooling system; and DC/DC converter and battery charger.
Among the truck manufacturers currently offering a range of hybrid electric drive trucks are Freightliner, International, Kenworth and Peterbilt with Eaton systems, and Volvo Group (parent company of Mack Trucks, Nissan Diesel, Renault Trucks and Volvo Trucks), which recently introduced its fourth-generation hybrid technology solution based on a concept known as I-SAM (Integrated Starter, Alternator Motor).
In November, Recaptured Energy Technologies unveiled a new hydraulic braking and propulsion system that can be retrofit to existing commercial vehicles to provide the same benefits as new hybrid vehicles.
Hydraulic hybrids
Hydraulic hybrid systems are particularly good candidates for trucks operating in stop-and-go duty cycles. These systems capture and store energy during braking and then re-use it to accelerate the vehicle during the next vehicle launch phase. The process continues over and over again.
Along with improving efficiency and reducing fuel consumption, hydraulic hybrids also reduce wear on the engine and brakes, and help lower overall maintenance cost.
Hydraulic pump motors and hydraulic storage tanks are used to recover and store energy, similar to what is done with electric motors and batteries in hybrid electric vehicles. This allows the engine to run at speeds that are most efficient, rather than ramping up in lower gears as happens with a conventional transmission, which is where inefficiencies can occur.
Electric hybrids generally provide smaller amounts of power for longer durations of time. Hydraulic hybrids provide greater amounts of power for shorter periods of time.
Series hydraulic
Another form of hybrid power is the series hybrid hydraulic system. This replaces the conventional transmission and driveline with a hybrid hydraulic powertrain that transfers energy from the engine to the drive wheels through fluid power.
The engine operates at a “sweet spot” of fuel consumption, facilitated by the continuously variable transmission (CVT) functionality of the series hybrid hydraulic system and by regenerative braking.
Here again, hydraulic pump motors and storage tanks are used to recover and store energy. Fuel economy improvements between 50 and 70 percent have been demonstrated.
Renewable fuels
The Volvo Group has been a leader in developing CO2-neutral vehicles powered by fuels produced from renewable raw materials, which unlike fossil fuels, can be produced and burned with reduced or near zero net contribution of carbon dioxide to the atmosphere.
Volvo is adapting the diesel engine to run on a wide range of renewable fuels. Under evaluation are biodiesel, synthetic diesel, DME (dimethylether), methanol/ethanol, biogas, biogas plus biodiesel, and hydrogen plus biogas.
Of late, liquefied natural gas (LNG) is emerging as an alternative clean, high-performance fuel. A fuel derived from natural gas, the LNG is cooled to a liquid and stored under pressure in the truck fuel tanks.
Kenworth, Peterbilt and Sterling have LNG models that use Westport Innovations’ LNG fuel system technology adapted for Cummins diesel engines.
Westport Innovations is a leading supplier of proprietary solutions that allow engines to operate on clean-burning fuels such as LNG, compressed natural gas (CNG), hydrogen and renewable biofuels.
In addition to running cleaner, LNG engines can save money as natural gas costs about 25 to 40 percent less per gallon than conventional diesel. Furthermore, LNG-powered trucks achieve similar miles-per-gallon rates compared to an equivalent diesel engine.
Value proposition
Green technologies have been proven and are reliable. However, there is a cost premium for the advantages and benefits they provide.
Eaton, on its Web site, has a hybrid power systems value calculator that can be used to compare the estimated return on an initial investment in a hybrid powertrain with a non-hybrid powertrain.
As time passes, the cost for technology decreases. Volume production also will drive costs down to achieve an acceptable return on investment.
In the meantime, federal, state and local governments, as well as vehicle manufacturers and others, offer various financial incentives to offset the cost of this new technology.
Keep in mind, the early adopters of any new technology gain significant competitive business advantages. BI