Development of a range extended electric vehicle powertrain for an integrated energy systems research printed utility vehicle

Development of a range extended electric vehicle powertrain for an integrated energy systems research printed utility vehicle Applied Energy 191 (2017) 99–110 Contents lists available at ScienceDirect[.]

Applied Energy 191 (2017) 99–110 Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy Development of a range-extended electric vehicle powertrain for an integrated energy systems research printed utility vehicle q Paul Chambon ⇑, Scott Curran, Shean Huff, Lonnie Love, Brian Post, Robert Wagner, Roderick Jackson, Johney Green Jr Oak Ridge National Laboratory, Bethel Valley Rd, Oak Ridge, TN 37831, USA h i g h l i g h t s g r a p h i c a l a b s t r a c t  Additive manufacturing plus hardware-in-the-loop speed up vehicle development process  Additive manufacturing shown to provide design flexibility and fast turnaround time  Powertrain integrated and optimized though HIL testing prior to vehicle installation  Printed electric vehicle experiments show range extension with naturalgas genset  Vehicle experiments confirm simulation + HIL + AM process to accelerate vehicle design a r t i c l e i n f o Article history: Received August 2016 Received in revised form January 2017 Accepted 15 January 2017 a b s t r a c t Rapid vehicle and powertrain development has become essential to for the design and implementation of vehicles that meet and exceed the fuel efficiency, cost, and performance targets expected by today’s consumer while keeping pace with reduced development cycle and more frequent product releases Recently, advances in large-scale additive manufacturing have provided the means to bridge hardware-in-the-loop (HIL) experimentation and preproduction mule chassis evaluation This paper details the accelerated development of a printed range-extended electric vehicle (REEV) by Oak Ridge National Laboratory, by paralleling hardware-in-the-loop development of the powertrain with rapid Abbreviations: ABS, acrylonitrile butadiene styrene; AM, additive manufacturing; AMIE, Additive Manufacturing Integrated Energy; APU, auxiliary power unit; BAAM, big area additive manufacturing; BEV, battery electric vehicles; BEVx, Range Extended Battery Electric Vehicle; CAD, computer-aided design; CAN, controller area network; CARB, California Air Resources Board; CNG, compressed natural gas; EPA, Environmental Protection Agency; EREV, extended-range electric vehicles; FEERC, Fuels, Engines and Emissions Research Center; HIL, hardware-in-the-loop; HOV, high occupancy vehicle; HWFET, Highway Fuel Economy Test; ORNL, Oak Ridge National Laboratory; PHEV, plug-in hybrid electric vehicles; PUV, Printed Utility Vehicle; REEV, range-extended electric vehicle; REx, range extender; RLF, road load force; SAE, Society of Automotive Engineers; UDDS, Urban Dynamometer Driving Schedule; VRL, Vehicle Research Laboratory; WOT, wide-open throttle q This manuscript has been authored by UT-Battelle, LLC, under Contract No DE-AC05-00OR22725 with the U.S Department of Energy The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to so, for United States Government purposes The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan) ⇑ Corresponding author E-mail addresses: chambonph@ornl.gov (P Chambon), curransj@ornl.gov (S Curran), lovelj@ornl.gov (L Love), postbk@ornl.gov (B Post), wagnerrm@ornl.gov (R Wagner), jacksonrk@ornl.gov (R Jackson), Johney.Green@nrel.gov (J Green Jr.) National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401, USA http://dx.doi.org/10.1016/j.apenergy.2017.01.045 0306-2619/Ó 2017 The Authors Published by Elsevier Ltd This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) 100 Keywords: Printed vehicle Range extender Additive manufacturing Rapid prototyping Hybrid vehicles Natural gas P Chambon et al / Applied Energy 191 (2017) 99–110 chassis prototyping using big area additive manufacturing (BAAM) BAAM’s ability to accelerate the mule vehicle development from computer-aided design to vehicle build is explored The use of a hardware-inthe-loop laboratory is described as it is applied to the design of a range-extended electric powertrain to be installed in a printed prototype vehicle The integration of the powertrain and the opportunities and challenges it presents are described in this work A comparison of offline simulation, HIL and chassis rolls results is presented to validate the development process Chassis dynamometer results for battery electric and range extender operation are analyzed to show the benefits of the architecture Ó 2017 The Authors Published by Elsevier Ltd This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Introduction The use of additive manufacturing for rapid vehicle prototyping is an emerging field Along with hardware-in-the-loop (HIL), largescale additive manufacturing (AM), or Big Area Additive Manufacturing (BAAM), has recently been shown to have potential use for rapid prototyping of vehicles for evaluation and development purposes AM creates components directly from a computer model using an additive process in which material is added to build a component, as opposed to a subtractive process such as machining, in which material is removed from a billet to manufacture a component AM is well suited for rapid prototyping, as it is extremely flexible and enables the rapid creation of very complex geometries with minimal waste This technology could be transformative in many areas, including the automotive sector A recent paper by Curran et al [1] documents how the use of polymer-composite AM with a BAAM system and a HIL test facility can facilitate the rapid manufacture of lightweight, complex components and impact a broad spectrum of manufacturing industries In that paper, the process to develop a functional battery electric vehicle 3D-printed as a Shelby Cobra replica was described, including vehicle systems simulations, HIL development, and integration of the powertrain into the printed vehicle platform Range-extended electric vehicles (also referred to as extendedrange electric vehicles (EREV) or Range Extended Battery Electric Vehicle (BEVx)) are defined by CARB as ‘‘a vehicle powered predominantly by a zero emission energy storage device, able to drive the vehicle for more than 75 all-electric miles, and also equipped with a backup auxiliary power unit (APU), which does not operate until the energy storage device is fully depleted” It is a subcategory of plug-in hybrid electric vehicles (PHEV) and consists most of the time of a series hybrid architecture Simply stated, they are electric vehicles with an auxiliary power unit (APU) (also known as range extender (REx)) used solely to recharge the ESS and extend the vehicle electric range; the APU internal combustion engine cannot propel the vehicle directly as it does not have a connection to the wheels REx can help alleviate ‘‘range anxiety” compared to battery electric vehicles (BEV) as they can significantly increase the range of the vehicle should a longer trip be required, without burdening the vehicle with extra weight and cost of an oversized ESS In zero-emission vehicle regulation, these definitions become important in the design and marketing of such powertrain architectures For example, recent polices from the California Air Resource Board are driving the design of rangeextended electric vehicles as they can grant their owners access to high occupancy vehicle (HOV) lanes, and provide manufacturers the same credits as BEVs towards California’s zero emissions vehicles (ZEV) mandate [2] To provide a flexible research platform for investigating range extender options for electric powertrains and for integrated energy research, Oak Ridge National Laboratory (ORNL) has partnered with many collaborators through the Additive Manufacturing Integrated Energy (AMIE) project [3] AMIE collaborators have designed and built a functioning printed utility vehicle and printed house, as shown in Fig The underlying key innovative solutions used in the development of AMIE include the following  Advanced Manufacturing: The vehicle and building were 3D printed using ORNL’s BAAM system, demonstrating how 3D printing can get products to market faster than traditional manufacturing techniques  Vehicle Technologies: The vehicle has a hybrid electric powertrain with onboard power generation from natural gas A single engine extends the vehicle’s range and produces power for both vehicle and building Energy flows between the two using fast, efficient level-2 bidirectional wireless power transfer—the world’s first wireless charging technology of its kind [4]  Building Technologies: A team of researchers and architects designed a single-room building to demonstrate new manufacturing and building technologies It incorporates low-cost vacuum-insulated panels into a 3D printed shell that was assembled at Clayton Homes, the nation’s largest manufactured home builder, in a partnership with the University of Tennessee (UT)  Sustainable Electricity: A 3.2 kW solar panel system paired with electric vehicle batteries generates and stores renewable power Advanced building control and power management strategies integrate the various energy systems and enable the building to function as a virtual battery The building charges the vehicle, and the vehicle can provide power to the building The HIL concept is deployed to develop the powertrain and its controls within the same accelerated time frame that is achieved by BAAM to create the vehicle chassis In a larger context, HIL platforms are used to analyze any component or subsystem hardware in a virtual vehicle environment These platforms are valuable for developing controls in a safe, controlled environment where the regular surroundings of the unit under development are simulated using physics-based models [5–7] Typically, a HIL platform consists of a real-time run-time computer running a model of the complete vehicle, except for the component being evaluated in the research test facility Analog and digital signal emulation hardware boards are used to interact with sensors and actuators, and handle the communications the component would experience in a real vehicle With this environment in place, the component being evaluated responds as though it is installed on a vehicle driving under anticipate usage (either real-world conditions or certification drive cycles) In the remainder of this paper, -in-the-loop may be appended to the name of any component characterized on the HIL platform, such as motor, powertrain, or controller The extension of vehicle systems simulations to HIL to a working prototype marks a step forward in rapid controls prototyping [8] The vehicle design, build and validation process can be summarized as shown in Fig Controls were developed offline and refined in the HIL environment In parallel, the chassis was P Chambon et al / Applied Energy 191 (2017) 99–110 101 A comparison of offline simulation, HIL and chassis rolls results is presented to validate the development process Chassis dynamometer results for battery electric operation and range extender operation are analyzed to show the benefits of the architecture Mule vehicle chassis rapid prototyping with BAAM Fig Completed AMIE demo with 3D printed house and 3D printed utility vehicle designed in computer-aided design (CAD) and printed using BAAM The simultaneous nature of both the powertrain and chassis development activities allows significant reduction of the overall vehicle development duration The resulting prototype vehicle, called Printed Utility Vehicle (PUV), is intended to be a flexible research platform [9,10] This means that the vehicle architecture is designed to be modular such that most components can be replaced to investigate different technologies For instance, the APU and battery pack could be substituted with alternative specification units in order to provide researchers with experimental vehicle results after evaluating these units in a laboratory This flexibility comes at the cost of packaging which is not optimized so that different shapes and forms can be accommodated Yet additive manufacturing allows quick iterative designs should packaging of new units require a major chassis modification This paper describes the use of a hardware-in-the-loop laboratory for the design of a range-extended electric powertrain to be implemented in a printed prototype mule BAAM’s ability to accelerate the mule development from computer-aided design to vehicle build is explored The integration of the powertrain and the opportunities and challenges it presents are detailed in this work The following section describes the use of BAAM to print the body and frame of the research vehicle (Fig 3) Details of the use of BAAM for rapid vehicle prototyping were presented in the printed Cobra study by Curran et al [1] The BAAM system used for this project was upgraded from the system used for the Cobra The new Cincinnati Inc BAAM used a new higher capacity (45 kg/ h) extruder on a larger (2.4  6.1  1.8 m) gantry system Other key features include the use of a 7.6 mm diameter nozzle, resulting in a 0.76 mm surface variation Fig shows the BAAM printing the PUV frame The BAAM extruder shown in Fig uses conventional carbon fiber–reinforced pellets from the injection molding industry; these are typically under $5/lb Table gives the characteristics of the extruder shown in Fig Similar to the printed Cobra [1], an acrylonitrile butadiene styrene (ABS) plastic reinforced with carbon fiber was used for the frame and body of the PUV In this relatively new concept, chopped carbon fiber is blended with a thermoplastic Previous experiments had determined that blending carbon fiber with the ABS at higher than 15–20% led to a significant reduction in warping without use of an oven This is described further in a recent study on the effects of adding carbon fiber to ABS [11] Elimination of the oven significantly reduces the energy intensity (i.e., the energy required to manufacture parts) of the manufacturing process Conventional polymer extrusion systems with heated chambers have an energy intensity in excess of 100 kW h/kg This behavior makes the addition of carbon fiber an enabling technology for large printed workpieces and can eliminate the need for additional ovens typically used to prevent warping BAAM’s energy intensity is 1.1 kW h/kg, approximately two orders of magnitude below other polymer Fig Vehicle development process when implementing HIL and 3-D printing technologies 102 P Chambon et al / Applied Energy 191 (2017) 99–110 Fig BAAM system installed at the ORNL manufacturing demonstration facility The design was also driven by the special requirements of 3D printing with the carbon fiber–reinforced ABS polymer For instance, the vehicle frame was designed specifically to ensure that stresses remain below 69 Bar, which is a factor of safety on the inter-laminar strength, (i.e the minimum stress that would cause layer separation and frame failure) Printed structures generally have anisotropic material properties, with the weakest direction being a result of the layer-to-layer adhesion The design incorporated threaded rods that could pass through the layers serving two purposes: providing attachment points for drivetrain components and putting the printed material under compression, thus improving the integrity of the chassis (Fig 6) SolidWorks design software was used for all mechanical modeling As with conventional additive manufacturing, CAD files were transformed to stereolithography (STL) files and entered into a slicing program that transformed the 3D geometry to machine tool path commands The frame was printed in a single process taking approximately 12 h, with the final frame weighing approximately 386 kg This rate is 2500 times above that normally associated with the polymer AM processes In addition to the frame, the skins took approximately h to print, and support structures took approximately h to print Rather than making attempts to light-weight for this case study, components were printed for robustness and workability 2.2 Vehicle build Fig ORNL BAAM printing PUV frame Table BAAM system extruder characteristics Specification Extruder type Fill rate Extruder temperature Bed temperature Single screw 45 kg/h 350 °C 120 °C extrusion AM systems ABS reinforced with carbon fiber shows increased strength and a significant reduction in distortion Additional details on carbon fiber–filled ABS for large-scale printing can be found in Refs [12,13] While the entire frame and body of this vehicle were printed, other components such as the suspension, and powertrain were conventional A similar process was used for the printed Shelby Cobra, in which the front suspension was modified from a commercially available aftermarket suspension kit The rear suspension was modified from a rear-wheel-drive passenger vehicle Modifications to the rear suspension included the addition of shock mounting points and a cradle for the traction motor and gearbox which integrated into space originally occupied by the rear differential All structural modifications to both the front and rear suspensions were made by welding new redesigned carbon steel attachment points An aftermarket brake system was used The frame was designed so that the front suspension would bolt on with the modified suspension pieces There were three general types of printed body parts: (1) the frame, which is the loadbearing structure that integrated the drivetrain, (2) thin skins which were printed for body panels, and (3) skeletal beam structures, which serve as the interface between the skins and the frame The skins were bonded using Valvoline Pliogrip to the skeletal structures, which were then mechanically attached to the frame for ease of removal (Fig 7) HIL development of a hybrid electric vehicle powertrain This section describes the development of the PUV powertrain It relied heavily on the HIL process and was conducted in parallel with the chassis printing and mechanical assembly activities This phase started with simulations for component sizing, performance prediction and controls development, before implementing a HIL environment for the complete powertrain to validate its controls and coordination as if it were already installed in a vehicle 2.1 Mechanical design 3.1 Simulation phase The mechanical design of the vehicle body and frame was created to accommodate the drivetrain, suspension, and battery components already selected during the simulation study described later on in this paper, Fig shows the vehicle chassis and main component layout The simulation study is the first phase of the HIL process During simulation, all components are simulated and represented by a mathematical model The same model is used throughout development, but some components will progressively be replaced with P Chambon et al / Applied Energy 191 (2017) 99–110     Fig Powertrain configuration for PUV real parts as hardware becomes available: they then become ‘‘inthe-loop” with the rest of the simulated environment Autonomie, the system-level modeling environment from Argonne National Laboratory, was selected for this simulation study, whereas a dSPACE platform ran the HIL real-time model Both are based on MathWorks Simulink and therefore provide a seamless transition from pure offline simulation to HIL experiments since the same model is used in both phases without the need for any conversion A series hybrid electric architecture [14] was created and populated with each component’s actual specifications, as shown in Fig 3.1.1 Powertrain component sizing study This model was first used to size components based on vehicle performance requirements determined by the engineering team: 103 Range-extended electric vehicle architecture, 30–40 miles (48-64 km) of all electric range, over 60 mph top speed, and Under 20 s for 0–60 mph Even though in-house AM provides complete control over chassis design and lead time, component selection is restricted by whether products are available off the shelf This is especially true for batteries, because procuring one-off battery packs for prototype vehicles can be very difficult Fortunately, Johnson Controls, Inc offered their 14.2 kW h pack for this project This battery capacity will allow 30 miles or more of all-electric range if the vehicle consumes 300 W h/mile and 70% depletion out of the battery is permitted The pack operates at a nominal voltage of 345 V with a capacity of 41 A h and peak power of 100 kW (continuous power rating of 41.4 kW) To match the battery power, the 90 kW Remy traction motor and 100 kW Reinhart inverter were selected With a top motor speed of 8000 rpm, the motor requires a final drive ratio smaller than 12:1 to achieve a top vehicle speed faster than 60 mph The Borgwarner eGearDrive axle with a final drive ratio of 8.28:1 was chosen APU sizing has been reported for other series hybrid vehicle configurations [15,16] A similar study was conducted for this vehicle The model was run to determine average electrical power consumption on key drive cycles (Urban Dynamometer Driving Schedule (UDDS), Highway Fuel Economy Test (HWFET) and US06 cycle), as well as for steady state speeds for several road grades Fig shows the simulation results and was used to determine the APU size: the target electrical power for the APU was set to 20 kW in order to be able to sustain a highway cycle and cruise speeds of 50 mph on level ground Due to procurement delays with the component originally selected, the team reverted to a commercially off-the-shelf APU with a power limitation of 5.5 kW This sub-optimal initial component selection will be corrected in the future thanks to nature of the PUV’s flexible research platform concept which provides a modular architecture where most components can be replaced to investigate different technologies at the vehicle level 3.1.2 Performance simulation study The sizing study was followed by a performance prediction study The same model was populated with specifications for the selected components and ran over a few predetermined cycles and maneuvers:     0–60 mph wide open throttle acceleration, UDDS drive cycle, representative of city driving, HWFET drive cycle, representative of highway driving, and US06 drive cycle, a more aggressive cycle Fig CAD of printed utility vehicle (left) and frame (right) 104 P Chambon et al / Applied Energy 191 (2017) 99–110 Fig PUV powertrain components before final assembly Fig PUV series hybrid electric Autonomie architecture Fig Vehicle average electrical traction power chart used for APU sizing study Table shows the simulated energy efficiency for the three key drive cycles when operating in all-electric mode Note that the highway cycle consumes significantly more energy than the city cycle due to the large aerodynamic drag coefficient of this utility vehicle causing large high speed losses Acceleration simulations yielded slower-than-expected performance of 25 s to accelerate from to 60 mph due to the limited power available from the battery due to its conservative fusing of 120 A; note that the fuse is capable of larger currents for shorter durations but that feature was not modelled and instead a hard limit was used in the model That limitation was accepted, as it allowed the project to proceed on time thanks to the battery pack being readily available off the shelf The final task performed during the simulation phase was the development, debugging, and optimization of the hybrid electric powertrain control algorithms The off-line environment is ideal to create strategies They can be evaluated quickly over an extended set of experimental conditions because they not have to run in real time This is also a safe debugging environment, as no hardware is involved 3.2 HIL experimentation phase During the HIL experimentation phase, some hardware is being evaluated in the research cell, and some is simulated on a real-time computer so that the real components respond as though they are P Chambon et al / Applied Energy 191 (2017) 99–110 105 Table Simulated energy efficiency modeling results Drive cycle Distance (miles) Energy (W h) Model energy consumption (W h/mile) UDDS HWFET US06 7.47 10.21 7.78 2201.6 4089.5 4087.6 294.8 400.5 525.2 installed in their normal environment, as a vehicle driving on a road The principle is shown in Fig 10 In this case, the unit being evaluated is the whole powertrain (electric traction motor, inverter, battery pack, DC/DC converter, etc.) It is installed in ORNL’s Vehicle System Integration laboratory research cell and subjected to road load conditions generated by a dynamometer The dynamometer is controlled by a real-time computer which runs a model of the vehicle components not physically present in the research cell (e.g., chassis, wheels, final drive axle, driver, speed profiles) The unit being evaluated and the realtime computer interact with each other to create realistic conditions: the powertrain behavior affects the vehicle model, and the vehicle model dictates the control commands out to the powertrain The HIL phase is instrumental in implementing and debugging vehicle communications, which are often transparent in the simulation phase, as model blocks seamlessly exchange floating point variables with consistent units, whereas in the real world, different manufacturers use different units, resolution, and protocols Once interfaces are debugged, control algorithms can be modified and fine-tuned to account for the real-time implementation and limitations that might not have been accounted for by the model Because of this project’s accelerated time frame, once the powertrain achieved full functionality on the HIL system, it was Fig 11 PUV being evaluated on ORNL chassis dynamometer decommissioned for installation in the vehicle Therefore, drive cycle performance was not evaluated in that configuration Only wide-open throttle (WOT) experiments were performed to check powertrain operation under high speeds and loads These tests were completed successfully providing the team with the confirmation that the powertrain was mechanically and electrically ready to be safely installed in the vehicle 3.3 Vehicle integration phase The powertrain system was then installed in the actual vehicle (see Fig 7), allowing for immediate operation, because most integration and controls issues had been identified and resolved during HIL evaluations This reduced the vehicle integration phase to Fig 10 HIL principle diagram 106 P Chambon et al / Applied Energy 191 (2017) 99–110 Fig 12 Brake regeneration event on prototype vehicle on chassis rolls (blue line) and in simulation (dotted red line) (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) mostly wiring and mechanical installation tasks This phase completed the vehicle build The vehicle is now operational and ready for evaluation Chassis dynamometer setup Chassis rolls are an ideal environment to conduct reliable and repeatable vehicle evaluations because of the controlled indoors test conditions and the facility’s ability to emulate the road load experienced by the vehicle when driving outdoors ORNL’s Fuels, Engines and Emissions Research Center (FEERC) Vehicle Research Laboratory (VRL) is equipped with a Burke E Porter 300 hp motor-in-the-middle, two-wheel drive, 48-inch, single roll AC motoring chassis dynamometer The dynamometer meets the requirements of the US Environmental Protection Agency (EPA) specifications for large roll chassis dynamometers The flexible driver’s visual aid and control system facilitate performance of all standard federal drive cycle tests, as well as European, Japanese, or custom cycles The laboratory has been cross checked against independent certification labs, and results are in excellent agreement for fuel economy and vehicle emissions 4.1 Road load determination The forces exerted on a moving vehicle can be broken into three components: (1) forces due to the vehicle’s inertia, (2) gravitational forces due to traversing up or down a grade, and (3) the road load force (RLF) The RLF accounts for the vehicle’s mechanical drag, i.e., its rolling resistance and its aerodynamic drag This force must be derived so that it can be duplicated by the dynamometer, which is a two-step process The Society of Automotive Engineers (SAE) J2263 Standard is used to derive the RLF that a given vehicle experiences under real world conditions Once that is completed, the SAE J2264 Standard is used to replicate the RLF on the dynamometer The range extender PUV was subjected to the road load derivation J2264 coast-down test in the VRL The vehicle was confirmed to be in good working order, with tires filled to 40 psi Normally, per the SAE J2264 Standard, the vehicle is preconditioned by running a double HWFET In order to avoid discharging the vehicle’s battery, a motoring warmup procedure was implemented that approximates the average speed and the same time as a double HWFET test to warm-up the tires, dyno and powertrain This cycle Fig 13 REx APU efficiency as a function of load ramped up to 45 mph by mph/s, and then using an alternating speed from 45–55 mph The same RLF coefficients that were used in the offline simulation were used to develop the set coefficients on the motoring dynamometer for performing model validation These coefficients are not expected to match what the vehicle would experience during SAE Standard J2263 coast downs on the road but instead are part of the rolling laboratory procedure of going from vehicle systems simulations and HIL experiments to chassis dynamometer experiments (Fig 11) 4.2 Instrumentation The vehicle was instrumented with a Hioki power analyzer that measured battery and electric machine current The vehicle controller area network (CAN) bus was accessed to record information reported by key powertrain components such as the battery pack, the electric machine inverter, and the on-board charger Power and energy were calculated using a combination of external instruments (such as the Hioki power analyzer) and self-reported values on the CAN bus Vehicle chassis dynamometer experiments First, the chassis laboratory was used to refine the regenerative braking strategy and further develop controls Then the PUV performed certification drive cycles to measure energy consumption, P Chambon et al / Applied Energy 191 (2017) 99–110 and acceleration performance experiments to characterize 0–60 mph 5.1 Regenerative braking tuning Some noteworthy drivability considerations were found going to full chassis dynamometer experiments on the vehicle, in particular with regenerative braking The model implemented some phase-out strategies so that foundation brakes will progressively take over from regenerative braking at low speeds However, regenerative algorithms were aggressively calibrated to capture as much braking energy back to the battery as possible and would indicate that close to 100% regenerative braking was available However, this ignores drivability issues around the feel of the braking in the actual vehicle During vehicle experiments, some refinement of the regenerative braking strategy was completed to eliminate shudder and improve brake feel This implied limiting motor braking therefore reducing amount of energy recovery to the battery and lowering vehicle energy efficiency This issue was not detected during the simulation phase because the driveline model is not detailed enough to 107 capture resonance phenomenon induced by foundation brakes, for instance gear backlash and shaft stiffness and inertia are not modelled The HIL phase did not help with this issue either because the driveline from the motor to the wheels was not ‘‘in-the-loop”, and it was modelled the same way as in simulation HIL could theoretically capture this issue but it would require a dual dynamometer set-up to have the powertrain and rear differential under test, with each dynamometer emulating a wheel Fig 12 shows the motor torque during a deceleration event at the end of the highway cycle for both the simulation (dotted red line) which tried to maximize brake regeneration, and for the proptotype vehicle tested on chassis rolls (blue line) The experimental torque is much lower than the simulated one; the real vehicle does not regenerate as much braking energy in order to prevent shudder in the driveline 5.2 Range extender characterization For the initial range extender experiments with the PUV rolling laboratory, a Honda EU7000 APU capable of 7.5 kW peak (5.5 kW Fig 14 PUV electrical power consumption as a function of vehicle speed Fig 15 Comparison of instantaneous chassis rolls (blue line) results with simulation results (red line) on HWFET cycle (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) 108 P Chambon et al / Applied Energy 191 (2017) 99–110 Fig 16 Comparison of experimental BEV results with modeling results continuous) was used The APU was converted to natural gas using an aftermarket retrofit kit [17] For the chassis dynamometer experiments, residential natural gas was supplied to the generator instead of using the compressed natural gas (CNG) tanks on board The fuel consumption was calculated using the standard EPA carbon balance method which employs a constant volume sampling system with bagged exhaust emissions over the drive cycle [18] The lower heating value of the residential natural gas was calculated using the component volume percent from the gas chromatograph posted online for the dates used and was calculated to be 49,537 kJ/kg The supplied natural gas was reported to be composed of 92% methane, 7.2% ethane, 0.45% N2, 0.31% propane, and 0.16% CO2, with other minor species Fig 13 shows the generator efficiency as a function of load 5.3 Steady state battery electric vehicle results Fig 17 Comparison of experimental chassis rolls BEV acceleration time with modeling and HIL results The vehicle was subjected to steady-state road loads to characterize its electric energy consumption as a function of speed, with the REx disabled The results are shown in Fig 14 Experimental results match well with simulation results obtained during the sizing study and confirm that less than 20 kW is required to cruise at 50 mph, and the 5.5 kW provided by the APU is adequate to maintain the steady-state speed of 25 mph 5.4 Battery electric vehicle model validation The vehicle was subjected to the same drive cycles and acceleration experiments performed in the offline model environment: UDDS, HWFET, and US06 drive cycles and 0–60 mph wide-open throttle acceleration 5.4.1 BEV drive cycle results The UDDS and HWFET cycles were repeated three times on the chassis rolls setup with the vehicle in its BEV configuration Experimental cycles showed very good repeatability: the coefficient of variance of energy consumption was less than 0.7% on the three experiment replicates Experimental results were then compared with simulation results An example of instantaneous trace comparison is shown in Fig 15: blue traces are simulation results whereas red traces are experimental results collected on the chassis rolls with the prototype vehicle: traces are matching very closely for all variables: vehicle speed, motor torque and battery current Battery energy was also calculated over complete drive cycles for both methods The difference is consistently within 1.5% on all three cycles, as shown in Fig 16 Fig 18 Comparison of HIL results of BEV acceleration time with modeling results The good correlation between the chassis experiment and simulation is a clear indicator of the quality of the model, but it also benefits from the fact that the chassis rolls road load coefficients were calculated from the theoretical model values instead of from experimental coast-down results, which would have most likely yielded different rolling resistance and drag coefficients, which in turn, would have resulted in different vehicle level efficiencies 5.4.2 BEV acceleration experimental results HIL experiments were performed before the prototype vehicle was completed and used an anticipated vehicle weight of 1587 kg (3500 lb) which was lighter than the actual prototype vehicle ended up being (1824 kg (4000 lb)) Therefore HIL WOT P Chambon et al / Applied Energy 191 (2017) 99–110 109 Fig 19 Motor torque limitation at high speed Fig 20 Battery electric vehicle vs range-extended electric vehicle range comparison The same observation can be made during HIL experiments and simulation results as shown in Fig 18 The mismatch on 0–60 mph accelerations can be explained by a torque restriction present on the motor inverter that was not captured by the model Fig 19 shows how the supervisory controller torque command (red line2) is ignored by the motor, which only delivers a lower estimated torque (green trace), resulting in slower accelerations 5.5 Range-extended electric vehicle operation Fig 21 Completed functional PUV manoeuvers cannot be compared to chassis rolls manoeuvers because vehicle weights are different Therefore chassis rolls results are compared individually to simulation results tailored to the correct vehicle mass The correlation between the chassis experiment and the simulation is very good on acceleration maneuvers up to 50 mph (less than 1% error) but not as good for the 0–60 mph maneuver, where the error is 25%, as shown in Fig 17 The PUV was also characterized with its range extender APU activated to recharge the battery pack while the vehicle is driving As explained before, the initial APU installed in the PUV is undersized at 5.5 kW It also relies on an onboard charger to convert alternating current out of the APU into direct current suitable to recharge the battery pack The onboard charger has a power limit of 3.6 kW Therefore, 3.6 kW is the maximum charge rate into the battery while driving with the APU enabled These limitations will be removed in the future thanks to the modular architecture of the PUV which will allow the APU to be upgraded to a larger unit For interpretation of color in Fig 19, the reader is referred to the web version of this article 110 P Chambon et al / Applied Energy 191 (2017) 99–110 The PUV was driven on the chassis rolls following the UDDS and HWFET drive cycles with the APU turned on With an oversized APU, the latter could be controlled to balance the electric traction load, and there should be no depletion out of the battery In this case, because the APU is undersized, it was runs at high maximum rate during the whole cycle which was not sufficient to offset the electric power consumption out of the battery Still battery energy consumption was still reduced by, 58 and 17% respectively, on the city and highway cycles This corresponds to a range increase of 136% or 86 total miles on the city cycle and 21% or 32 total miles on the highway cycle The APU consumes 0.65 L and 0.40 L gasoline equivalent of natural gas during the city cycle and highway cycle respectively Therefore, even a small undersized APU of 3.6 kW can help reduce range anxiety (Fig 20) The APU used in the range-extended electric vehicle presented in this paper is not suggested to be used as an APU option for onroad vehicles that need to meet durability, consumer acceptability, and emissions compliance criteria Instead, the small APU chosen was used to evaluate the use of small range extenders and provide a baseline for future experiments with the printed utility vehicle as a rolling laboratory (see Fig 21) Conclusion This paper demonstrated the combination of big area additive manufacturing and hardware in the loop methodologies which has the potential to speed up the overall vehicle development process by paralleling these rapid prototyping techniques This study did not attempt to quantify the potential acceleration using this approach Further study is needed to establish the correct baseline on which to make any comparison Instead the focus of the paper is to validate this approach leading to the development and experimentation of a hybrid electric powertrain for implementation in a flexible printed vehicle platform A comparison of simulation, HIL and chassis rolls results was provided to demonstrate the accuracy of the methodology which allows to front load the development process before all of the hardware is available for vehicle installation and testing Finally, chassis rolls results of the BEV and range extender configurations allowed by this flexible research platform were presented to show the potential of a small natural gas APU to extend vehicle range, therefore alleviating driver range anxiety Acknowledgments This work was supported by the US Department of Energy’s Office of Energy Efficiency and Renewable Energy Advanced Manufacturing Office under the management of Mark Johnson The authors wish to thank the ORNL leadership team and their colleagues at the Oak Ridge National Laboratory who worked on this project: Steve Whitted, Jimmy Wade, Dean Deter, Larry Moore, John Thomas, Karen Nolen, Kim Askey, Brittany Cramer, Jennifer Palmer, and Ron Graves The authors would also like to acknowl- edge the support of the industry partners who helped make the project possible, including Cincinnati Incorporated and JohnsonControls Inc Special thanks to Rick Spears and Robert Springfield of TruDesign for collaboration on finishing and transporting the PUV References [1] Curran S, Chambon P, Lind R, Love L, et al Big area additive manufacturing and hardware-in-the-loop for rapid vehicle powertrain prototyping: a case study on the development of a 3-D-printed shelby cobra, SAE Technical Paper 201601-0328; 2016, http://dx.doi.org/10.4271/2016-01-0328 [2] California Air Resource Board Zero-Emission Vehicle Standards for 2018 and subsequent Model Year Passenger Cars, Light-Duty Trucks, and Medium-Duty Vehicles [3] Jackson R, Curran S, Chambon P, Ozpineci B, et al Overview of the oak ridge national laboratory advanced manufacturing integrated energy demonstration project: case study of additive manufacturing as a tool to enable rapid innovation in integrated energy systems IMECE2016-66256, Proceedings of the ASME 2016 International Mechanical Engineering Congress and Exposition IMECE2016 [4] Miller JM, Onar OC, Chinthavali M Primary-side power flow control of wireless power transfer for electric vehicle charging IEEE J Emerging Selected Topics Power Electron 2015;3(1):147–62 http://dx.doi.org/10.1109/ JESTPE.2014.2382569 [5] Wagener A, Schulte T, Waeltermann P et al Hardware-in-the-loop test systems for electric motors in advanced powertrain applications SAE Technical Paper 2007-01-0498; 2007 [6] Schuette H, Waeltermann P Hardware-in-the-loop testing of vehicle dynamics controllers – a technical survey SAE Technical Paper 2005-01-1660; 2005 http://dx.doi.org/10.4271/2005-01-1660 [7] He H, Xiong R, Zhao K, Liu Z Energy management strategy research on a hybrid power system by hardware-in-loop experiments Appl Energy 2013;112:1311–7 [8] Chen BC, Wu YY, Tsai HC Design and analysis of power management strategy for range extended electric vehicle using dynamic programming Appl Energy 2014;113:1764–74 [9] Lohse-Busch H, Shidore N, Duoba et al A modular automotive hybrid test bed designed to evaluate various components in the vehicle system SAE Technical Paper 2009-01-1315 http://dx.doi.org/10.4271/2009-01-1315 [10] Venhovens P, Mau R Deep orange – a framework for research, education and collaboration for a sustainable automotive industry SAE Technical Paper 2011-01-1110 http://dx.doi.org/10.4271/2011-01-1110 [11] Love L, Kunc V, Rios O, Duty C, Elliott A, Post B, et al The importance of carbon fiber to polymer additive manufacturing J Mater Res 2014;29(17):1893–8 http://dx.doi.org/10.1557/jmr.2014.212 [12] Tekinalp H et al Highly oriented carbon fiber–polymer composites via additive manufacturing Compos Sci Technol 2014;105:144–50 http://dx.doi.org/10 1016/j.compscitech.2014.10.009, http://www.sciencedirect.com/science/ article/pii/S0266353814003716, ISSN 0266-3538 [13] Love L Utility of big area additive manufacturing (BAAM) for the rapid manufacture of customized electric vehicles 2014 ORNL/TM-2014/607, CRADA/NFE-14-04988 [14] Hu X, Murgovski N, Johannesson L, Egardt B Energy efficiency analysis of a series plug-in hybrid electric bus with different energy management strategies and battery sizes Appl Energy 2013;111:1001–9 [15] Bassett M, et al A study of fuel converter requirements for an extended-range electric vehicle SAE paper 2010-01-0832 [16] Chambon P PHEV Advanced Series Gen-set Development/Demonstration Activity - FY12 Annual Report, ORNL/TM-2012/502 [17] GenConneX Bi-Fuel Honda EU7000 Kit website [18] CFR Pt 600 – FUEL ECONOMY AND GREENHOUSE GAS EXHAUST EMISSIONS OF MOTOR VEHICLES  ... for electric powertrains and for integrated energy research, Oak Ridge National Laboratory (ORNL) has partnered with many collaborators through the Additive Manufacturing Integrated Energy (AMIE)... driver range anxiety Acknowledgments This work was supported by the US Department of Energy? ??s Office of Energy Efficiency and Renewable Energy Advanced Manufacturing Office under the management of. .. manufacturing (AM), or Big Area Additive Manufacturing (BAAM), has recently been shown to have potential use for rapid prototyping of vehicles for evaluation and development purposes AM creates