HYBRID TECHNOLOGY Eaton’s parallel electric hybrid system. The vehicle’s diesel engine is coupled with Joining forces an electric motor/generator and batter- ies. It maintains a conventional drive- train architecture, such as Eaton’s Fuller UltraShift automated transmission, while A look at the work being done by OEMs and adding the ability to augment engine component suppliers to bring hydraulic and torque with electrical torque (Eaton photo). electric hybrid technology to on-highway trucks. are an inevitable by-product of burning by Michelle EauClaire hydrocarbon fuel. s a consumer, you can make fuel prices for nearly all of the vehicles used changes to your daily lifestyle in these applications is to improve their Electric and hydraulic Ain order to counteract the efficiency, and the best technology avail- There are two different kinds of effects of the rising fuel prices. Those able to do that today is hybrid technology. hybrids, electric and hydraulic. Electric options, however, don’t suit the obli- A hybrid powertrain system reduces hybrids more easily support other on- gations of commercial vehicle users. fuel consumption by blending the power board electronics and have a high energy Refuse has to be picked up, parcels generated by the internal combustion density — best suited to applications that need to be delivered, and the whole engine with power from other stored have a lot of cruising time because they scope of other services still need to be sources of energy on board. And of course, can support longer engine-off operation. provided, regardless of fuel prices. when you reduce fuel consumption, you Electric power is generated by the die- The only practical response to rising also reduce the polluting emissions that sel engine and through regenerative brak- 40 ■ OEM Off-Highway ■ March 2008 ing, which recovers power which would Glenn R. Wendel and Travis W. Jackson, normally be wasted as heat and brake engineers in the Vehicle Systems Research wear. That power is then stored, typically Dept. at Southwest Research Institute in a battery pack, and delivered back to (SwRI) write, “an important characteristic the truck through an electric motor that of nitrogen gas is that as oil is pumped delivers energy back to the drivetrain, or into the high-pressure accumulator dur- to auxiliary power systems on the vehicle ing braking, the gas pressure increases to power equipment or tools. exponentially. Energy is stored as more 2100 While electric hybrids have a high and more fluid is pumped into the accu- Series energy density, hydraulic hybrids have mulator at higher and higher pressures.” a higher power density which provides The stored compressed gas in the accu- Modulating a better power boost for acceleration mulator forces hydraulic fluid through a Control “off the line.” The hydraulic hybrid sys- hydraulic motor to power the wheels. Valves tems work best with intensive stop-and- Other benefits of hydraulic hybrid go applications such as residential refuse systems include the use of less-costly • Hydraulically actuated, single and parallel circuit braking providing pick-up, because of the use of stored ener- components, no battery requirement, modulating output pressures from gy through regenerative braking. and the use of composite material for 600 to 3,500 psi According to NextEnergy, Detroit, MI, a reduced weight and more efficiency (see • Designed for mining haulage vehicles non-profit corporation, a hydraulic hybrid Composites story on page 18). • Easy serviceability and reduced maintenance costs system can recover and use up to 70% of Work is being done to increase the • Smooth modulation at all output the kinetic energy that is captured during maximum operating pressure, currently pressures braking. Hydraulic hybrid vehicles (HHVs) around 5,000 psi to around 7,000 psi. • Externally adjustable for precise reuse stored energy that would normally As accumulators increase in pressure pressure settings be lost during braking in conventional capabilities, a hydraulic hybrid system • Higher flow compared to competitive designs vehicles, creating a cost effective system, will be able to sustain engine-off driving while also eliminating idling and reducing for longer periods of time. engine operation for fuel efficiency. “It is definitely not a question of one Regenerative braking is a process by technology being better than the other. which the hydraulic kinetic energy from Hydraulic and electric hybrids simply have 1100 braking — which pumps low pressure different ‘sweet spot applications,” says Series hydraulic fluid into a high pressure accu- Brad Bohlman, business development Modulating mulator — is stored for future use. As the manager, Advanced Technology, Eaton’s fluid enters the high pressure accumula- Fluid Power Group. “The choice of which Control tor, it compresses nitrogen within the to use in a particular application is highly Valves accumulator, which then pressurizes the dependent on the nature of the applica- • Hydraulically actuated, hydraulic system. The stored energy is tion itself, specifically the duty cycle of the single and tandem circuit braking used for accelerating the vehicle in con- vehicle in question. providing modulating output pressures to max. 3,500 psi junction with, or in place of, the engine. “A key difference between today’s • Ideal for construction equipment and material handling Eatons Hydraulic Launch Assist (HLA) System is a parallel hybrid hydraulic regen- • Smooth modulation at all erative braking system. The HLA system recovers the majority of the energy normally output pressures wasted as heat during braking and uses it to supplement the engine’s • Dampened spools for stable, power during acceleration. HLA delivers 15-30% better noise-free operation fuel economy, provides more torque for • Externally adjustable for precise quicker acceleration and pressure settings shorter cycle times, and • Thoroughly tested to ensure increases brake life superior performance and durability and extends Call 800-873-6361 or visit service www.carlislebrake.com intervals for engine and transmission. Industrial Brake & Friction ■ www.oemoff-highway.com/einquiry.jsp or indicate # 30 on card OEM Off-Highway ■ March 2008 ■ 41 HYBRID TECHNOLOGY Intelligent Hydraulic Drive parallel both utility-boom, and pickup and deliv- hybrid technology from Bosch Rexroth ery applications when equipped with Corp. creates potential for increased a PACCAR PX-6 engine and an Eaton vehicle payload capacity in addition to hybrid power system. other hydraulic hybrid vehicle benefits The Model 335 Hybrid Electric utilizes (Bosch Rexroth photo). components that provide up to a 30-40% in one place for extended periods with improvement in fuel efficiency, when the engine idling to run the bucket and configured for a utility application. These other systems. In that type of applica- fuel savings are realized through both an tion,” Bohlmann says, “you can charge on-road fuel economy gain and an 80% hydraulic and electric hybrids is the dura- the batteries on the way to and from the reduction in engine idling through elec- tion of the power they can supply,” says jobsite, and also capture braking energy, tric operation of the power take-off (PTO) Bohlmann. “Hydraulic systems have high of course. Once on-site you can shut off using the on-board lithium-ion batteries. power density while electric systems have the engine and run the bucket and other Available with a 26,000-lb. GVW rat- high energy density. For example, the systems on battery power until the bat- ing, it can be configured for non-CDL Hydraulic Launch Assist (HLA) system teries need recharging. This could be up (commercial driver’s license) opera- delivers 300 hp from a motor that measures to several hours. At that point, the engine tion with hydraulic brakes for a greater roughly 12 in. by 18 in., but it only does it automatically restarts and fully recharges range of driver options. The integration for a short time, measured in seconds. An the batteries in a few minutes.” of the Eaton Hybrid Drive System and the electric system will deliver less power at 260-hp PACCAR PX-6 engine delivers up any given instant, but do it for an extended Series vs. parallel systems to 860 ft.-lbs. of torque. period of time, measured in minutes. Parallel system design keeps the tra- PACCAR’s other division, Kenworth “So, if you look at vehicle duty cycles, ditional transmission and driveshaft Truck Co., Kirkland, WA, offers a medi- a hydraulic hybrid power system makes a system, and a pump/motor adds and um-duty, hybrid-electric truck for utility lot of sense for a large, heavy vehicle like a subtracts power through the mechanical operations. The Seattle, WA, King County refuse truck that is constantly starting and drive system. A parallel system does not Dept. of Transportation, the first gov- stopping. There, you can capture the brak- keep the ground speed separate from the ernment agency to place the Kenworth ing energy and re-cycle it over and over to engine speed, but it still provides better hybrid into service, uses its Kenworth improve operating efficiency. fuel economy and lower emissions when Class 7 hybrid to maintain traffic signals. “An electric hybrid tends to be ideal compared to traditional drivetrains. The hybrid is equipped with a utility for something like a utility bucket truck Series systems eliminate a traditional bucket atop a 50-ft. boom, which is longer that’s driven to a jobsite and then sits transmission and driveshaft system, allow- than a standard aerial lift. While a non- ing the ground speed and engine speed hybrid utility truck must idle to operate its to be independent of one another. This lift, the hybrid’s lift typically operates on allows the engine to be turned off when electric power, which reduces emissions. not needed, like when stopped or acceler- After just over 5,000 miles of operation, ating, and for the engine to run at its best the hybrid has already achieved a 25% efficiency.