Potentials and possible applications of mechanical energy recuperation systems in vehicles

Transcription

1 Potentials and possible applications of mechanical energy recuperation systems in vehicles Dipl.-Ing.(FH) Helmut Kastler, ECS Magna Powertrain, Engineering Center Steyr, Austria Paper presentation at the conference 8. Internationales CTI Symposium Innovative Fahrzeug-Getriebe 1. / 2. December 2009 in Berlin

2 8 th International CTI Symposium - Innovative Automotive Transmissions, Dec. 1 st / 2 nd, 2009 Potentials and possible application of mechanical energy recuperation systems in vehicles Dipl.-Ing.(FH) Helmut Kastler, ECS Design Engineer Drivetrain Engineering Magna Powertrain, Engineering Center Steyr, Austria Abstract A hybrid system comprises a co-operation of two different propulsion units in one vehicle. Usually this term is used for a combination of an internal combustion engine with one or more electric machines. The storage of electric energy in the vehicle needs accumulators. The downside is that these accumulators are very expensive and quite heavy. These two aspects were the motivation to work out the potentials of mechanical energy recuperation systems (MERS). For this reason the function of an electric hybrid system is substituted by mechanical energy recuperation systems and the potential of these systems is determined. Firstly a benchmark vehicle has been defined. The vehicle has been chosen due to its availability with an electric hybrid drive train and also with a conventional drive train with a gasoline engine. Mathematic models of the mechanical energy recuperation systems have been created. Standardized driving cycles have been used to compare and dimension the main components of the different systems. Two systems have been worked out in detail, one with a flywheel and one with a hydraulic storage system.

3 8 th International CTI Symposium - Innovative Automotive Transmissions, Dec. 1 st / 2 nd, Introduction In the automotive industry the term "hybrid system" is used for a combination of an internal combustion engine with one or more electric machines. Complex electrical systems are necessary to store electric energy in the vehicle. Electric hybrid systems require at least following components (slide 3): Motor Battery pack Power electronics The downside is that these components cause higher production costs and increase the vehicle weight significantly. The high voltage used for electric hybrid systems is an important safety feature. Furthermore capacity losses of batteries over the lifetime, the so called fading, is a disadvantage of electric hybrid systems. These issues are the reason to search for a mechanical energy recuperation system capable to replace the electrical hybrid system. To determine the potential of fuel consumption reduction of a vehicle, the function of an electric hybrid system has to be substituted by the combination of an engine with a mechanical energy recuperation system (MERS). The specific power and specific energy of different energy storage systems are shown in the Ragone-diagram [2] (slide 4). The diagram shows that hydraulics and flywheel systems are able to provide high specific power. Batteries feature higher specific energy but lower specific power. Especially for recuperation higher specific power is helpful to realize recuperation systems with low storage weight. It also shows that hydraulics and flywheels are not suitable to work as traction batteries and power vehicles for longer distances exclusively (without engine running). In the systematic approach of a recuperation system six phases have been performed (see slide 5): Definition of a benchmark vehicle Design of a system architecture Generate mathematic models Dimensioning of components Simulation of driving cycles Results and evaluation of recuperation systems in driving conditions

4 8 th International CTI Symposium - Innovative Automotive Transmissions, Dec. 1 st / 2 nd, 2009 The potential of energy recuperation depends significantly on the driving cycle (slide 6). The entire energy is defined by the consumption and the energy density of the fuel used. This energy is reduced by engine losses. The energy provided by the engine is split into drive train losses, drag losses and losses caused by rolling resistance. The energy spent on braking can be recuperated. The amount of energy to be recuperated is 17.9 % in NEDC [1]. 2 Definition of a benchmark vehicle The first step is to find a benchmark vehicle with an electric hybrid system (see slide 7). The base vehicle should be available with an electric hybrid system as well as with a conventional drive train with a gasoline engine. The electric hybrid system has to fulfil following functions: Recuperation Boosting Start- stop To comply with these requirements a Honda Civic was defined as benchmark [3][4]. This car is available with an electric hybrid drive train and with gasoline engine alone. The Honda Civic hybrid is graded as a mild hybrid vehicle. 3 Hydraulic recuperation system (H-MERS) Slide 8 shows the system architecture of a hydraulic energy recuperation system (H-MERS). The main components of H-MERS are: Gear set with clutch Axial piston pump/motor High pressure accumulators Oil tank ECU Valve block On Slide 9 important points which has to be considered for dimensioning of the system components are listed. Slide 10 shows specifications of H-MERS for different driving cycles. Slide 11 shows published systems which operate similar as the described H-MERS [5][6][7].

5 8 th International CTI Symposium - Innovative Automotive Transmissions, Dec. 1 st / 2 nd, Recuperation system with flywheel (F-MERS) Slide 12 shows the system architecture of an energy recuperation system based on a flywheel (F-MERS). The main components of F-MERS are: Gear set with clutch Variator Planetary gear Flywheel ECU On Slide 13 important points which has to be considered for dimensioning of the system components are listed [1]. Slide 14 shows specifications of F-MERS for different driving cycles. The gyro effect has to be considered for non stationary flywheel concepts (slide 15). An unintended torque is generated for the driven vehicle every time the motion direction changes. The graph shows the gyro torque of a vehicle versus the vehicle speed and the turn radius [1]. This torque appears with a flywheel running at maximum speed ( rpm). In longitudinal alignment of the flywheel the gyro torque causes a pitching motion of the vehicle which is different in right or left hand turns. Slide 16 shows published systems which operate similar as the described F-MERS. Except the system of Flybrid Systems the flywheel has no mechanical connection to the transmission [8][9][10]. 5 Simulation of recuperation systems in driving cycles To determine the average fuel consumption of vehicles with MERS the systems have been simulated in three different driving cycles (see slide 17). The vehicle data of the Honda Civic 1.4 have been calibrated in the driving simulation tool FASI to achieve the same values for max. speed, acceleration and average consumption in the NEDC as the manufacturer s data. The system weight of the MERS has been added to the mass of the base vehicle. MERS have been optimized to achieve the best improvement in fuel consumption in the driving cycles. Following functions have been considered in the simulations: Recuperation Boosting

6 8 th International CTI Symposium - Innovative Automotive Transmissions, Dec. 1 st / 2 nd, 2009 Start-stop Disengaged engine in coasting mode 5.1 Simulation of NEDC Slide 18 shows the graph of the NEDC cycle which is used for the evaluation of average fuel consumption in Europe. Slide 19 shows H-MERS and F-MERS behaviours in the driving cycle. For H-MERS the graph shows the system pressure (red line) and the gas volume in the pressure accumulators (blue line) during the simulation. The average fuel consumption of the base vehicle including the additional system mass of 145 kg is 6,14 l/100km. With recuperation, start-stop and disengaged engine in coasting mode the average consumption decreases to 4,71 l/100km. This is an improvement of 23,3 %. For F-MERS the graph shows the flywheel speed (red line) during the simulation. The average fuel consumption of the base vehicle including the additional system mass of 40 kg is 5,96 l/100km. With recuperation, start-stop and disengaged engine in coasting mode the average consumption decreases to 4,63 l/100km. This is an improvement of 22,3 %. The average consumption of the benchmark vehicle (Honda Civic Hybrid) is 4,6 l/100km [4]. 5.2 Simulation of FTP 75 Slide 20 shows the graph of the FTP75 cycle which is used for the evaluation of average fuel consumption in US. Slide 21 shows H-MERS and F-MERS behaviours in the driving cycle. For H-MERS the graph shows the system pressure (red line) and the gas volume in the pressure accumulators (blue line) during the simulation. The average fuel consumption of the base vehicle including the additional system mass of 91 kg is 6,08 l/100km. With recuperation, start-stop and disengaged engine in coasting mode the average consumption decreases to 4,6 l/100km. This is an improvement of 24,4 %. For F-MERS the graph shows the flywheel speed (red line) during the simulation. The average fuel consumption of the base vehicle including the additional system mass of 34,5 kg is 5,98 l/100km. With recuperation, start-stop and disengaged engine in coasting mode the average consumption decreases to 4,46 l/100km. This is an improvement of 25,4 %.

7 8 th International CTI Symposium - Innovative Automotive Transmissions, Dec. 1 st / 2 nd, Simulation of ECS Steyr Loop Slide 22 shows the graph of the ECS Steyr Loop. This cycle was recorded with a differential GPS and includes altitude differences as well. The ECS Steyr Loop represents an urban driving cycle with highway sections. It was recorded under real driving conditions. Slide 23 shows H-MERS and F-MERS behaviours in the driving cycle. For H-MERS the graph shows the system pressure (red line) and the gas volume in the pressure accumulators (blue line) during the simulation. The average fuel consumption of the base vehicle including the additional system mass of 119 kg is 6,3 l/100km. With recuperation, start-stop and disengaged engine in coasting mode the average consumption decreases to 4,22 l/100km. This is an improvement of 33 %. For F-MERS the graph shows the flywheel speed (red line) during the simulation. The average fuel consumption of the base vehicle including the additional system mass of 38 kg is 6,1 l/100km. With recuperation, start-stop and disengaged engine in coasting mode the average consumption decreases to 4,11 l/100km. This is an improvement of 32,6 %.

8 8 th International CTI Symposium - Innovative Automotive Transmissions, Dec. 1 st / 2 nd, Summary Benefits of mechanical energy recuperation systems are (see slide 24): The analyzed MERS show a similar reduction in fuel consumption during the simulated driving cycles as the benchmark vehicle. Estimated costs for mechanical recuperation systems are much lower than for electric hybrid systems. ECS favours F-MERS for passenger car applications. The main advantages are the low system weight and a maintenance free design. Especially in comparison with electric hybrid systems the constant energy capacity over lifetime without fading is beneficial. Flywheels are not able to store energy for long periods. For instance during parking short term energy fading is caused by friction losses. In this situation the stored energy may still be used for auxiliary drives. ECS favours H-MERS for heavy vehicles such as trucks. The higher system weight can be compensated by synergies with auxiliary drives or hydraulic equipment used in the vehicle already. As for all hydraulic systems the oil has to be serviced. In comparison with electric hybrid systems the energy capacity of the high pressure accumulators has practically no fading tendencies. An intelligent integration in the power train in combination with a sophisticated control technology MERS show potentials to achieve mild hybrid's fuel economy.

9 8 th International CTI Symposium - Innovative Automotive Transmissions, Dec. 1 st / 2 nd, 2009 References [1] Helmut Kastler, Diploma Thesis, Potentialabschätzung und mögliche Anwendung mechanischer Technologien zur Energierekuperation im Kfz im Vergleich zu bekannten elektrischen Systemen, [2] Guzzella, L. & Sciarretta, A., Vehicle Propulsion Systems: Introduction to Modeling and Optimization, Ausg., o.o., 2007, S [3] Honda Austria GmbH, Technische Daten, Brochure Honda Civic, 2008, S [4] Honda Motor Europe (North) GmbH, Technische Daten, Brochure Honda Civic Hybrid, 2008, S [5] Eaton Corporation, Hydraulic Launch Assist, , [6] Lightning Hybrids, , [7] Bosch Rexroth, Deutschland, , [8] Flybrid Systems LLP, , [9] Williams Hybrid Power Limited, , [10] Compact Dynamics, ,

10 Potentials and possible application of mechanical energy recuperation systems in vehicles Dipl.-Ing.(FH) Helmut Kastler, ECS Design Engineer Drivetrain Engineering Magna Powertrain, Engineering Center Steyr, Austria MPT ECS Kastler H. 8. International CTI Symposium - Innovative Automotive Transmissions Berlin, Dec Contents 1. Introduction 2. Definition of a benchmark vehicle 3. Hydraulic recuperation system 4. Recuperation system with flywheel 5. Simulation of recuperation systems in driving cycles 1. Simulation of NEDC 2. Simulation of FTP Simulation of ECS Steyr Loop 6. Summary MPT ECS Kastler H. 8. International CTI Symposium - Innovative Automotive Transmissions Berlin, Dec

11 1. Introduction Hybrid = commonly engine + motor Additional components (at least) Motor Battery pack Power electronics Disadvantages Expensive Additional mass High voltage Capacity loss (fading) MPT ECS Kastler H. 8. International CTI Symposium - Innovative Automotive Transmissions Berlin, Dec Introduction Ragone diagram MPT ECS Kastler H. 8. International CTI Symposium - Innovative Automotive Transmissions Berlin, Dec

12 1. Introduction MPT ECS Kastler H. 8. International CTI Symposium - Innovative Automotive Transmissions Berlin, Dec Introduction Potential of energy recuperation (e.g. NEDC) 100% Energy (density Gasoline 95 octane Wh/kg) η engine 22,6% Engine losses 77,4% 100% Energy engine Braking 17,9% Rolling resistance 32,8% Drag 39,4% Drive train losses 9,9% MPT ECS Kastler H. 8. International CTI Symposium - Innovative Automotive Transmissions Berlin, Dec

13 2. Definition of a benchmark vehicle Requirements for benchmark vehicle Following functions have to be enabled Recuperation Boosting Start-stop Availability with hybrid drive and conventional propulsion system 2009 Honda Civic Specifications Honda Civic Gasoline 1.4 Hybrid Max. power engine 73 kw 70 kw Max. torque engine 127 Nm 123 Nm Max. power motor - 15 kw Max. torque motor Nm Combined consumption acc. 1999/100/EG1 5,9 l/100km 4,6 l/100km Vmax 177 km/h 185 km/h Acceleration km/h 13 s 12,1 s Kerb weight 1257 kg 1368 kg Tires 195/65 R 15 85H MPT ECS Kastler H. 8. International CTI Symposium - Innovative Automotive Transmissions Berlin, Dec Hydraulic recuperation system (H-MERS) System architecture H-MERS Gear set Clutch Oil pump/motor High pressure accumulator Oil tank Engine Transmission ECU Valve block MPT ECS Kastler H. 8. International CTI Symposium - Innovative Automotive Transmissions Berlin, Dec

14 3. Hydraulic recuperation system (H-MERS) Dimensioning Energy capacity of pressure accumulators ~ energy of strongest deceleration in driving cycle Combined hydraulic motor/pump Continuously variable axial piston pump/motor Brake power during cycle ~ peak power of axial piston pump max. permissible speed of max. speed in driving cycle Definition of min. and max. system pressure to achieve required brake/propulsion torque in all driving conditions MPT ECS Kastler H. 8. International CTI Symposium - Innovative Automotive Transmissions Berlin, Dec Hydraulic recuperation system (H-MERS) Specifications for cycle optimated systems MPT ECS Kastler H. 8. International CTI Symposium - Innovative Automotive Transmissions Berlin, Dec

15 3. Hydraulic recuperation system (H-MERS) Published systems MPT ECS Kastler H. 8. International CTI Symposium - Innovative Automotive Transmissions Berlin, Dec Recuperation system with flywheel (F-MERS) System architecture F-MERS Clutch Gear set Variator Planetary gear Flywheel ECU Engine Transmission MPT ECS Kastler H. 8. International CTI Symposium - Innovative Automotive Transmissions Berlin, Dec

16 4. Recuperation system with flywheel (F-MERS) Dimensioning Flywheel speed < min -1 Circumferential speed <330 m/s Step up drive Continuously variable transmission Variator ratio spread = 6.0 Planetary gear set Energy capacity of flywheel ~ energy of strongest deceleration in driving cycle MPT ECS Kastler H. 8. International CTI Symposium - Innovative Automotive Transmissions Berlin, Dec Recuperation system with flywheel (F-MERS) Specifications for cycle optimated systems MPT ECS Kastler H. 8. International CTI Symposium - Innovative Automotive Transmissions Berlin, Dec

17 4. Recuperation system with flywheel (F-MERS) Gyro effect Max. 120 Nm at 5 m turn radius (µ=1,0) Max. 45 Nm at 30 m turn radius (µ=1,0) MPT ECS Kastler H. 8. International CTI Symposium - Innovative Automotive Transmissions Berlin, Dec Recuperation system with flywheel (F-MERS) Published systems MPT ECS Kastler H. 8. International CTI Symposium - Innovative Automotive Transmissions Berlin, Dec

18 5. Simulation of MERS in driving cycles Calibration of vehicle data in driving simulation tool Simulation with base vehicle mass of Civic system weight System modified to achieve best cycle consumption Energy state of storage at cycle start = energy at cycle end Simulation with driving simulation tool FASI 8.0 NEDC FTP75 ECS Steyr Loop Considered functions Recuperation Boosting Start-stop Disengaged engine in coasting mode MPT ECS Kastler H. 8. International CTI Symposium - Innovative Automotive Transmissions Berlin, Dec Simulation of NEDC Distance: [km] Average speed: 33.6 [km/h] MPT ECS Kastler H. 8. International CTI Symposium - Innovative Automotive Transmissions Berlin, Dec

19 5.1 Simulation of NEDC without H-MERS: 6.14 l/100km with H-MERS: 4.71 l/100km % without F-MERS: 5.96 l/100km with F-MERS: 4.63 l/100km % Honda Civic Hybrid (benchmark): 4.6 l/100km MPT ECS Kastler H. 8. International CTI Symposium - Innovative Automotive Transmissions Berlin, Dec Simulation of FTP 75 Distance: [km] Average speed: 36.6 [km/h] MPT ECS Kastler H. 8. International CTI Symposium - Innovative Automotive Transmissions Berlin, Dec

20 5.2 Simulation of FTP 75 without H-MERS: 6.08 l/100km with H-MERS: 4.6 l/100km % without F-MERS: 5.98 l/100km with F-MERS: 4.46 l/100km % MPT ECS Kastler H. 8. International CTI Symposium - Innovative Automotive Transmissions Berlin, Dec Simulation of ECS Steyr Loop Distance: Average speed: [km] [km/h] MPT ECS Kastler H. 8. International CTI Symposium - Innovative Automotive Transmissions Berlin, Dec

21 5.3 Simulation of ECS Steyr Loop without H-MERS: 6.3 l/100km with H-MERS: 4.22 l/100km -33 % without F-MERS: 6.1 l/100km with F-MERS: 4.11 l/100km % MPT ECS Kastler H. 8. International CTI Symposium - Innovative Automotive Transmissions Berlin, Dec Summary F-MERS For passenger cars Low system weight Maintenance free No long term capacity fading Short term energy fading H-MERS For heavy vehicles High system weight Low maintenance Synergies with auxiliary drives/hydraulic equipments No capacity fading MERS show potentials to achieve mild hybrid s fuel economy MPT ECS Kastler H. 8. International CTI Symposium - Innovative Automotive Transmissions Berlin, Dec

22 Thank you for your attention! Dipl.-Ing.(FH) H. Kastler