Power to Spare: Hydraulic Hybrids

COVEr STOrY Jean Van Rensselar/Contributing Editor Power to spare: Hydraulic Hybrids

Already in use in large commercial vehicles, KEY CONCEPTS researchers are close to deploying this • Super-fast charging and technology in passenger vehicles. discharging accumulators make hydraulic hybrids possible. EPA DEVELOPED AND PATENTED HYDrAU- • Hydraulic hybrids are ideal teries). While hydraulic hybrids have LIC HYBrID TECHNOLOGY IN THE 1990s much in common with electric hy- for heavy commercial with the fi rst working hydraulic hybrids, the main difference is that with vehicles and already are in brid vehicle introduced in 2006. It was hydraulic versions energy storage use for refuse and delivery a United Parcel Service diesel delivery takes place in a high-pressure hydrau- trucks. van that used technology developed by lic accumulator rather than a battery. EPA’s National Vehicle and Fuel Emis- Fluid power is stored in accumulators, • Hydraulic hybrids are more sions Laboratory and industry part- just as power is stored in a battery, but ners. This technology has since been unlike hybrids with electric motors, engine effi cient, capture incorporated into commercial vehicles accumulators don’t require rare-earth better braking energy and such as UPS trucks, garbage trucks metals and can have very high charge often have a much cleaner and city buses. EPA currently holds and discharge rates—less than 10 sec- environmental footprint more than 30 patents related to hy- onds. than their electric hybrid draulic hybrids—with more pending. A hydraulic accumulator is a pres- Hydraulic hybrids are based on hy- sure vessel that is used to store poten- counterparts. draulic components (accumulators) tial energy in the form of pressurized rather than electric components (bat- fl uid. This stored energy is a readily

34 • FEBRUARY 2012 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG available source of power that can re- The EPA’s Hydraulic Hybrid Test Vehicles2 spond quickly to changes in system conditions. Accumulators are routine- ly used to absorb shock loads in vehi- EPA, in cooperation with its partners, has successfully installed and tested hydraulic hybrid cle suspension systems and dampen technology in a variety of vehicles. These prototypes have shown tangible results, including high-pressure pulsations in hydraulic fuel economy improvement from 30% to more than 100% over similar conventional vehicles. circuits. They also can serve as a fail- safe in fluid power systems where an Full series HHV in a UPS delivery vehicle. On June 21, 2006, EPA and its partners: Eaton, interruption of power creates a hazard- UPS, Parker, International Truck and Engine Corp., the U.S. Army, FEV, Morgan-Olson and ous loss of machine control. When in- Southwest Research Institute, announced the world’s first series hydraulic hybrid urban stalled in a circuit that requires a vari- delivery vehicle. The vehicle underwent real-world testing by UPS in 2006 and 2007 with the able flow rate, an accumulator can following results: store excess pump capacity until it is needed. This can save energy by mak- • 60%-70% improvement in fuel economy. ing the use of smaller pumps and pow- • A projected 2-3 year payback when produced in high volume. er supplies possible. When it comes to passenger cars, Series Hydraulic Hybrid Yard Hostler. A yard hostler is an off-road truck used to transfer the regenerative braking capabilities of cargo containers at marine ports, rail yards, warehouses and distribution centers. EPA and hydraulic hybrids can significantly its partners created a highly efficient yard hostler using hydraulic hybrid technology with outperform the electric hybrids now the following results: on the market—a feature made possible by the high power density of accu- • Estimated improved fuel efficiency of 50%-60%. mulators and other hydraulic compo- • Reduced maintenance and operation costs. nents. EPA’s hydraulic hybrids typical- • Reduction of emissions and greenhouse gases by over 30%. ly capture 70% or more of the braking energy otherwise lost to heat, while Full series HHV in a Ford Expedition SUV. This hydraulic hybrid demonstrated fuel sav- electric hybrids capture 20% to 25%.1 ings resulting from combining a full series hydraulic hybrid system with a diesel engine. The As a result, there is growing interest prototype was installed in a 2003 Ford Expedition SUV with the following results: in the use of accumulators for power storage, particularly in hydraulic hy- • 85% improvement in fuel economy over a diesel engine. brid vehicle and wind turbine applica- • A less than two-year payback when produced in high volume. tions. These fluid power applications • Expected net lifetime savings from $4,000 to $6,000 from fuel costs and brake create new market opportunities for maintenance. lubricant manufacturers. • Excellent performance.

HOW IT WORKS Parallel HHV in a Ford F-550. This Ford F-550 parallel hydraulic hybrid vehicle was built to There are three main types of hybrid demonstrate the benefits of parallel hydraulic hybrids and to examine the cost-effective- drive trains: parallel, power split and ness of parallel systems with the following results: series (all three types can regenerate braking energy). • Demonstrated the ease of retrofitting trucks with hydraulic hybrid technology. • 20%-30% improvement in fuel economy. 1. A parallel drive uses a pump/ motor to assist the engine, send- Full series HHV in a passenger car test chassis. In the 1990s the Partnership for New ing a high percentage of the Generation of Vehicles was established to help U.S. automakers design a family-sized sedan wheel energy through the me- that could achieve 80 mpg. A team of engineers working at EPA’s National Vehicle and Fuel chanical shaft. The downside is Emissions Laboratory in Ann Arbor, Mich., succeeded in meeting this goal by using a revo- that it doesn’t balance torque lutionary type of hydraulic hybrid (including a small 1.9-liter diesel engine) with the follow- and speed as well as a series ing results: drive. • Attained 80-plus mpg on combined EPA city/highway driving cycles. 1 From: http://www.designnews.com/document. • Accelerated 0-60 mph in eight seconds. asp?doc_id=219518. This figure may be low. • Showed no need for high-end lightweight materials to improve fuel economy. Stelson believes the Toyota Prius captures about • In high volume, the hydraulic components would only add $700 to the base cost of 50% of the braking energy. the vehicle (EPA estimate). 2 From: http://www.epa.gov/oms/technology/

research/demonstration-vehicles.htm#f-550.

(True) Test your knowledge: True or False—Low-speed, heavy-duty bearings found in heavy equipment require high-viscosity oils. 35 2. A series drive transmits engine power to the wheel using hydraulic motors and pumps. The engine operates with an efficient balance of torque and speed, but it doesn’t capitalize on the high efficiency of pure mechanical power transmission through a shaft. 3. The relatively new split drive combines the positive aspects of the series and parallel drive train designs. The main components in a full series hydraulic hybrid vehicle include: • A high-pressure accumulator tank. This stores energy by using hydraulic fluid to compress nitrogen gas inside the tank. For comparison, a standard (non-hydraulic) drive train in a passenger car. • A rear-drive pump/motor. This acts as a motor by converting pressurized hydraulic fluid into rotating power for the wheels. This component also captures braking energy by pumping hydraulic fluid back into the high-pressure accumulator. • A low-pressure reservoir tank. This holds the spent fluid after it has been used by the rear drive pump/motor. • A front engine pump/motor. This creates additional high-pressure fluid needed to drive the vehicle, storing any excess in the high-pressure accumulator tank. Parallel drive system hydraulic hybrid technology in a passenger car. • A hybrid controller. This monitors the driver’s acceleration and braking. It also sends operating commands to the various hybrid system components.3

Kim Stelson, director of the Center for Compact and Efficient Fluid Power (CCE- FP) and professor in the department of mechanical engineering, University of Minne- sota, says, “Advanced controls are essential to fully realizing the potential of a hydraulic hybrid vehicle. The advanced controls are needed to operate the engine efficiently and to decide when the engine should be turned off so that fuel consumption is minimized while also maintaining required perfor- Hydro-mechanical drive system hydraulic hybrid technology in a passen- mance.” ger car. Typically the vehicle’s diesel or gas en- (Illustrations courtesy of the Center for Compact and Efficient Fluid Power) gine powers a hydraulic pump motor, which

3 From http://www.motor.com/newsletters/20110613/WebFiles/ID1_HydraulicHybrids.html.

36 • FEBRUARY 2012 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG charges the accumulator (basically a high-pressure hydraulic fluid storage container). The accumulator drives one or more additional pump motors connected to the wheels. A second (lower pressure) accumulator usually completes the hydraulic circuit. Func- tioning as a motor, the hydraulic drive uses the pressurized fluid to rotate the wheels. Functioning as a pump, the hydraulic drive uses the momentum of the vehicle to repressurize the hydraulic fluid (in essence converting kinetic energy into reusable potential energy). During braking, the wheels’ pump motors reverse themselves and recharge the accumulator in the process. This ‘In terms of energy conservation, the use of accumulators in hydraulic captures energy otherwise lost to heat, hybrid vehicles holds great promise.’ which is also called “regenerative braking.” Designs vary. There might be one pump motor to drive a pair of wheels 1,150 and 2,175 psi. At a flow rate of there are many technical challenges through a differential or, in the case of 102 gallons per minute, it takes about that need to be resolved in order to an all-wheel drive version with inde- five seconds for the fluid to discharge make this approach practical. We are pendent torque, one pump motor per from the accumulator—the energy po- busily working on them.” wheel. Although, hydraulic hybrids tential is impressive. don’t need any electronics to function, Since accumulators are sized to sup- STRAIN ENERGY ACCUMULATOR many do have optional electronic con- plement pump flow, in order to size the While a conventional accumulator trols. accumulator correctly engineers only stores the energy in the compression need to know minimum and maximum of a gas, a strain-energy (elastomeric) THE ACCUMULATOR system pressure and the volume of fluid accumulator stores energy in the elas- STLE-member Paul Michael, research the accumulator needs to deliver. Some tic strain of an elastomer (such as rub- chemist at Milwaukee School of Engi- accumulator manufacturers make cor- ber). “We estimate this approach could neering, says, “In terms of energy con- rect sizing even easier with software- increase the energy storage density by servation, the use of accumulators in enhanced calculators. a factor of five,” Stelson says. hydraulic hybrid vehicles holds great He adds, “We have learned that the promise.” OPEN VERSUS CLOSED characteristics of the open accumula- Because they provide auxiliary ACCUMULATOR tor make it more suitable for energy power during peak periods, hydraulic In a conventional or closed accumula- storage for wind power, and we are accumulators are common in indus- tor, energy can only enter or leave the pursuing that application in the near trial and mobile hydraulic systems. accumulator through the hydraulics. term. With the maturing of open ac- Having the accumulators on board al- The maximum energy is when the gas cumulator technology, it may well be- lows engineers to downsize some of is at its minimum volume. In an open come practical for vehicles. The elas- the other system components such as accumulator, energy can enter or leave tomeric accumulator is a better match motors, reservoirs and pumps by as the accumulator through either the for hydraulic hybrid vehicles at least much as 25%. Designers are looking hydraulics or the pneumatics. The in the near term.” for more ways to use accumulators maximum energy is when the gas is at due to the technology’s demonstrated its maximum volume. ADVANTAGES AND CHALLENGES ability to save energy, reduce operating In a closed accumulator, the pres- Hydraulic hybrids have three basic ad- costs, prolong useful life and handle sure ratio is 3 to 1. In an open accumu- vantages over electric (battery) hy- demanding loads. One of those uses is lator, the pressure ratio is 350 to 1. brids: as a highly efficient energy recovery “These differences mean that the en- and storage device. ergy density of an open accumulator • Much better engine efficiency. A typical accumulator holds 8.5 would be 20 times that of a closed ac- • They operate with the engine gallons of fluid at a pressure between cumulator,” Stelson explains. “But off more frequently.

WWW.STLE.ORG TRIBOLOGY & LUBRICATION TECHNOLOGY FEBRUARY 2012 • 37 and controllers to haul and Key technical hurdles are the noise, vibration and harshness stop—hydraulic systems can do this, electric batteries cannot. issues often associated with hydraulic hybrids. • Better energy management. Hy- draulic hybrids can handle energy flow rates that far exceed • They capture braking energy with purely electric systems. braking requirements. Electric much better. For example, electric hybrid ve- batteries, on the other hand, hicles using typical sodium- must be much bulkier in order “Hydraulic hybrids have one very nickel-chloride batteries would to absorb energy at the rate important advantage over electric hy- be 100% heavier than hydraulic needed for braking. Because of brids—a much higher power density hybrid systems. Systems with this, electric battery systems use than electrics,” Stelson says. “This al- nickel-metal-hydride batteries a battery that can only be par- lows us to create a very powerful drive would be about 95% heavier tially charged by braking (about train in a small package. However, than their hydraulic counter- 15%). This means that much of electric hybrids have the advantage of parts. There are many benefits the spare storage capacity is having higher energy density for stor- to a lighter weight. wasted. Accumulator storage is age. That is, batteries have a much matched exactly to the applica- • Much better power-to-weight ra- higher energy density than accumula- tion. tors, while also having a much lower tio. The heavier the machinery, power density. Our research is de- the more important this advan- • Cost advantage and availability. signed to address the energy density tage. This is part of the reason Hybrid hydraulic systems are gap between accumulators and batter- why hydraulic hybrid systems less expensive than electric hy- ies.” were first introduced into heavy brid systems. Pumps and air According to EPA, in addition to equipment. Heavy vehicles rely storage tanks are inexpensive the fuel savings, the unique energy re- on the high power of hybrid when compared with batteries. covery technology used while braking motors, storage components In the case of retrofitting exist- reduces brake wear by 75%, increasing the net savings substantially. The additional cost for this technology man- ufactured in high volume could be less than 15% of the price of the base vehicle. The bottom line is that at current fuel prices, experts say this technology will pay for itself in 2-3 years. The net lifetime savings over a typical vehicle’s 20-year lifespan would be more than $50,000.4 “Accumulators have an advantage over batteries in that they do not require rare-earth metals and they are capable of very high charge and discharge rates,” Michael says. “An accumulator can be fully charged in less than 10 seconds. Imagine charging your cell phone or laptop that fast.”

Among the many advantages over hybrid electric systems: Heavy vehicles rely on the high power of hybrid motors, storage components and • Lighter weight. Vehicles equipped controllers to haul and stop—hydraulic systems can do this, electric batteries with hydraulic power systems cannot. are much lighter than those

4 From: http://www.epa.gov/otaq/technology/420f06043.htm.

axial) and tangential Helical open gears can transmit what kinds of forces to their shafts when transmitting a load? (Radial, 39 ing vehicles, installing hydrau- mising power. Perry Li, profes- Because of the extremely efficient lic hybrid components requires sor of mechanical engineering regenerative braking capacity, hydrau- only minor adaptations. Electric at the University of Minnesota lic hybrids are a natural fit for heavy hybrid installation can require and co-lead (with Tom Chase) commercial vehicles that deal with replacing the vehicle’s engine of the hydraulic hybrid passen- stop-and-go traffic (commercial deliv- and/or transmission. Also, hy- ger vehicle test bed, explains: ery, refuse trucks, etc.). Another plus draulic hybrid systems have a “Current accumulator technol- is that trucks (as opposed to passenger longer useful life. ogies are not very energy-dense, vehicles) have plenty of room to ac- • Hydraulic accumulators safely and i.e., it takes a large volume to commodate a large accumulator. easily discharge pressure. Some store a certain amount of ener- hydraulic systems automatically gy. In fact, it is 100 times worse THE BOSCH RExROTH HRB than the electric battery in this discharge when the vehicle is One highly innovative hydraulic hy- regard. More compact accumu- turned off. Hydraulic systems brid for commercial vehicles is Bosch lators are needed so that they pose little or no risk of self-igni- Rexroth’s HRB (Hydrostatic Regenera- can fit in passenger cars.” tion, shock or fire. But because tive Braking) system. The first refuse they rely on high voltage/cur- • Unfamiliarity. The system isn’t truck equipped with HRB was intro- rent circuits, hybrid electric sys- any more complex than an elec- duced to the public by Rexroth in Sep- tems can present significant tric hybrid; it’s just that the tember 2008. Commercial production safety issues. components are not mainstream began in October 2010. Right now • Environmental advantage. Most when compared to electric hy- there are HRB equipped vehicles oper- hydraulic hybrid components brids. Electric hybrids also have ating in more than 10 cities. are made of long-lasting readily the advantage of being a proven The system is designed for com- recycled materials. Electric bat- technology in real-world pas- mercial vehicles using conventional teries, by contrast, contain senger vehicles, while hydraulic mechanical drive trains and a combus- highly toxic materials such as hybrids are not there yet. tion engine. It decreases the load on concentrated acid and rare- the brakes during deceleration and the Noise earth metals that are difficult to • . Whereas electric hybrids load on the combustion engine during dispose of safely. can be ghostly quiet, hydraulic acceleration, leading to a considerable hybrids emit a loud (some say reduction in fuel consumption and • Flexible in climate extremes. Hy- annoying) hissing sound. This brake wear. draulic hybrid systems are less is easily solvable by using the The HRB system components, suit- sensitive to extreme climate same methods auto engineers able for refuse trucks with a gross ve- conditions such as moisture, use to muffle engine and hy- hicle weight between 18 tons and 26 heat and cold than their electric draulic steering system noise. tons, are based on serial production counterparts. The high power density that yields high mileage and high performance should make hydraulic hybrid technology perfect for light-duty commercial vehicles and passenger vehicles. With their high regenerative braking capacity, hydraulic hybrid vehicles are already in limited use in applications that require lots of stop- and-go activity (such as urban delivery trucks). However, the goal is to enter the passenger vehicle market, and this will require moving beyond three hurdles:

• Size. Right now the accumulator would have to be larger than the size of most gas tanks. The trick Hydraulic hybrids are a natural fit for heavy commercial vehicles that deal is to develop a more compact with stop-and-go traffic (commercial delivery, refuse trucks, etc.) accumulator without compro-

40 • FEBRUARY 2012 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG components which Rexroth has been producing for years. This ensures good availability, reproducible quality and a In spite of energy density challenges, there are system that should last as long as the vehicle itself. significant efforts underway to implement hydraulic The HRB consists of: hybrid technology in passenger vehicles. • An A4VSO. Variable axial piston unit for pump/motor operation with a displacement of 210 ccm, a maximum power of 233 KW that the HRB continuously runs ing). The 25% savings are based on a and a maximum torque of 1.113 safely, efficiently and comfort- combination of different stop-and-go Nm. Multiplying this by the ably. The goal is to reduce as distances and a waiting period of 30 HRB gearbox ratio, and the rear much work for the driver as seconds after each stop. It also nearly axle ratio would result in a max- possible while at the same time doubles the lifespan of the driving imum brake and acceleration maximizing savings. brake.5 torque of approximately 10.000 • Sensors. Over 10 different sen- Nm on the wheels. ExPANDING INTO NEW MARKETS sors (i.e., pressure, temperature • A gearbox. Three different ratios and speed) ensure that the elec- The future of hydraulic hybrid tech- are available (1-5; 2-2; 3-2), tronic control device is kept up- nology rests on the potential for recon- synchronized for the common to-date on all system condi- ciling improved environmental perfor- rear axle ratios of the truck tions. mance (decreased fuel consumption/ chassis manufacturers to decreased pollution) and cost reduc- achieve the best system efficien- A gearbox connects a hydraulic tion—something researchers have cy and the highest fuel savings. variable axial piston unit to the me- made great strides toward in recent chanical drive train to convert kinetic years. • An accumulator. A high-pressure energy into hydraulic energy when In addition to keeping costs down, bladder accumulator with an in- braking. The axial variable piston unit while improving environmental per- tegrated nitrogen bladder is operates as a pump and converts ki- formance, the key to expanding hy- compressed during braking and netic energy into hydraulic energy by draulic hybrid technology into the relaxed when the vehicle needs loading a hydraulic bladder accumula- passenger vehicle market is to increase to accelerate again. The charg- tor with hydraulic fluid, which brakes energy density (more power in a small- ing pressure is at 120 bar and the vehicle. This process is controlled er design). In fluid power systems, this the maximum pressure at 325 by a proprietary electronic controller is accomplished by increasing the bar. In the current HRB system, along with a hydraulic valve manifold. working pressure of hydraulic systems two bladder accumulators are During acceleration the process is and the efficiency of hydraulic compo- integrated. In both accumula- reversed (pressurized fluid discharges nents without increasing size. tors up to 0,15 KWh can be in a controlled manner from the accu- At the International Fluid Power stored, according to the kinetic mulator and flows back through the Expo in March 2011, Charles L. Gray, energy from braking of 30 km/h variable axial piston unit). The fluid Jr., EPA’s director of Advanced Tech- down to 0 km/h minus all losses flow drives the piston unit, which acts nology Division, reported that the de- (rolling friction, aerodynamic as a motor by giving up its energy to velopment of hydraulic components resistance, etc.). the mechanical drive train and reliev- that reliably perform at 7,000 psi (500 • A valve control block. The hy- ing the existing combustion engine. A bar) would advance the cause of hydraulic control unit of the HRB pressure relief valve and electronic draulic hybrids. With few exceptions, system controls the flow of oil monitoring of all safety relevant sys- most hydraulic components currently and ensures (through a pressure tem and vehicle variables contribute to perform at less than 6,000 psi (400 control valve) that excess pres- the highest level of safety for both pro- bar). As research now stands, this in- sure does not occur in the sys- cesses. crease in working pressure cannot be tem at any given time. In a refuse truck, the HRB system achieved without a substantial (pro- • An electronic controller. The elec- reduces fuel consumption by up to hibitive) increase in hydraulic system tronic control device ensures 25% during collections (or urban driv- weight.

5 http://www.iswa.org/uploads/tx_iswaknowledgebase/Lindzus.pdf.

WWW.STLE.ORG TRIBOLOGY & LUBRICATION TECHNOLOGY FEBRUARY 2012 • 41 PASSENGER VEHICLE RESEARCH The EPA is interested in hybrid ve- including a down-sized diesel engine, In spite of energy density challenges, hicles because they are an economi- variable displacement hydraulic there are significant efforts underway cally attractive technology to reduce pumps and motors, an accumulator, to implement hydraulic hybrid tech- pollutant emissions, fuel consump- sensors, actuators and control elec- nology in passenger vehicles. A proto- tion, oil imports and greenhouse gas tronics. This enables experimentation type BMW 5 Series hydraulic hybrid emissions,” Gray says. “Our analysis with different pump, motor and ener- passenger car has been developed by and test results suggest the series hy- gy storage technologies, including Artemis Intelligent Power in Edin- draulic hybrids offer the highest effi- those developed in complementary burgh, Scotland.6 ciency at the lowest cost when com- CCEFP projects. However, the Gener- In January 2011 the EPA joined pared to other options.” ation 1 vehicle cannot be driven at forces with Chrysler to develop and CCEFP also is looking into the use speeds greater than about 25 mph due adapt hydraulic hybrid technology for of hydraulic hybrid technology in pas- to concerns about vehicle stability. the light-duty auto market, starting senger cars. Its Test Bed 3 focuses on “One lesson is that system architec- with a Caravan (minivan). The goal is power-split design (which combines ture, components, control and expect- for the Caravan, using EPA’s own pat- the positive aspects of the series and ed drive cycles are very important and ented technology, to be a demo vehi- parallel drive train designs). inter-related for overall efficiency and cle. Researchers expect that the hy- The Test Bed 3 team is currently de- performance,” Li says. “For example, draulic hybrid technology will increase veloping two hydraulic hybrid passen- we found that the power-split and par- overall fuel efficiency by 30%-35% on ger vehicles—each offers discrete re- allel hydraulic hybrid architectures, the highway and 60% in the city. This search benefits. The Generation 1 which make use of both mechanical should reduce overall greenhouse gas vehicle was built in-house using the gears and hydraulics for power trans- emissions by 25%.7 platform of an off-road, all-terrain ve- mission, are more efficient than series Gray says that the key technical hicle (a Polaris ATV Ranger). The ve- architecture that uses hydraulics ex- hurdles are the noise, vibration and hicle uses an input-coupled power- clusively, unless one has a super-effi- harshness issues often associated with split architecture and has been cient pump/motors.” hydraulic hybrids. retrofitted with a modular power train The Generation 2 vehicle currently being developed is built on the platform of a pickup truck. It has refined ‘Hydraulic hybrid vehicles have the advantages vehicle dynamics capable of highway of better fuel economy, better performance speeds. Its power train uses a custom- and lower cost compared to built, continuously variable output- electric hybrid vehicles.’ coupled power-split hydraulic transmission developed by Folsom Technologies that will be complement- ed with hydraulic accumulators to en- able hybrid operation. The power train is attractive because it is built as a compact, highly integrated, self-con- tained package. The Generation 2 vehicle will be able to withstand rigorous testing and presents an opportunity for the study of an alternate power-split architecture. Nevertheless, the integrated package prevents changing out the hydraulic pump/motors. Also, since it is not originally designed for hybrid operation, the transmission is not opti- mally sized and presents some control restrictions when operating in hybrid modes. Therefore, the Generation 1 vehicle is being continued despite the

6 Watch the video at: http://www.scienceguy.org/Videos/TabId/57/VideoId/588/42mpg-BMW-5-Series-Hydraulic-Hybrid-Uses-No-Batteries-.aspx. 7 Media release available at: http://yosemite.epa.gov/opa/admpress.nsf/6424ac1caa800aab85257359003f5337/837c1d022dba18448525781d005995be!OpenDocument.

42 • FEBRUARY 2012 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG pending availability of the roadworthy better performance and lower cost opportunities for regenerative braking Generation 2 vehicle. compared to electric hybrid vehicles,” make it a perfect fit. But this is a lim- Stelson explains: “The Gen-1 vehi- Stelson says. “These advantages are ited market. If researchers can reduce cle has been very instructive to us most pronounced in larger vehicles, the physical size of the accumulator since it can be reconfigured as a paral- which are now appearing in the mar- and eliminate or significantly muffle lel, series or power-split hydraulic hy- ketplace. Passenger vehicles are more the noise, this technology holds great brid. This flexibility has allowed us to challenging to compete against since promise for the passenger car market compare the three approaches on a electric vehicles already have a head where the sheer potential for the tech- common platform. Based on what we start. In the passenger vehicle market, nology’s ultra-rapid energy storage and have learned, we have upgraded the the best candidates for hydraulic hy- discharge would be transformative. vehicle considerably in the last year or bridization would be larger vehicles “A main obstacle is the education so. The modularity and flexibility of such as minivans and SUVs.” of the general public. People need to the vehicle allow us to use it to test He adds, “Besides the energy stor- know that electric vehicles are not the new technology developed by CCEFP. age challenge, hydraulic hybrid pas- only—or necessarily the best—ap- The Gen-2 vehicle will allow us to test senger vehicles must be quiet and proach,” Li concludes. the power-split approach on a plat- pleasing to drive. Research is currently form that is much more similar to pro- ongoing to address the packaging, duction vehicles.” noise and driveability characteristics The CCEFP’s ultimate goal will be as hydraulic hybrid technology mi- a Generation 3 vehicle with a true pas- grates to smaller vehicles.” senger vehicle chassis. They plan to begin work on the vehicle sometime THE BOTTOM LINE Jean Van Rensselar heads her own this year.8 Hydraulic hybrid technology has al- communications firm, Smart PR Communications, “Hydraulic hybrid vehicles have ready proven itself in commercial de- in Naperville, Ill. You can reach her at the advantages of better fuel economy, livery trucks and vans where multiple [email protected].

8 For more information, visit: http://www.ccefp.org/research/testbeds/hydraulic-hybrid-passenger-vehicle.

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