12+12V and 12+48V a modular approach for components and electric architectures.

Transcription

1 12+12V and 12+48V a modular approach for components and electric architectures. Dr. Ing. Olivier COPPIN Abstract Among the various hybridization levels, the volts affordable architecture represents the basic architecture allowing the benefits of hybridization, thanks to the energy recovery during braking. The 12+48V electrical architecture is an easy way to enhance 12+12V functionalities and enter deeper in the hybrid application field. With the extended power field offer by 48V components, more vehicle segments and applications can have more benefits at a still limited over cost. We will illustrate the similar topology of 12+12V and 12V+48V systems and show how complementary functions such as electric supercharger boosting can be added in a modular way. This approach can help to lower the cost of the systems integration in vehicle which can be a significant part of the total system application cost. This can thus contribute to a large application field for mild hybrid systems and by the way contribute to a greater vehicle fleet CO2 reduction. The main hybrid functions impacts on engine emission will be presented. We examine how 48V system can address more efficient hybridization architectures (from P1 to P4) allowing more CO2 emission reduction and see how we can even open the gateway for low cost pure electrical vehicles. We then show how the different hybridization architectures can be addressed in a modular building bloc structure for components. This last level of modularity is an additional lever to lower the hybridization cost. Combining the electrical board net modular predisposition and the field of 48V hybridization would open ways to access further CO2 emission reduction with the best cost ratio. At the end, we will build the general road map of 48V hybridization systems and future vehicle functions. 1 Introduction CO2 reduction for the right cost is one of the main challenges of the next years. As the different car segments have various requirements we will discover the potential of low voltage hybrid systems. These systems offer first level of real hybrid functions. We will illustrate the electric board net evolution based on dual battery architecture

2 and show how complementary functions based on e-clutch can enhance these systems interest. 2 Drivers for electrification It is well known that CO2 regulations are becoming more and more challenging all over the world. Achieving the regulation targets requires a certain degree of electrification / hybridization. Fig 1 illustrates the world CO2 regulation prospective. We can easily notice that worldwide regulations are converging, and so, solutions for CO2 reduction will be global. Figure 1 World CO2 regulation prospective In the same time, the reference drive cycle is changing in many countries. In Europe, NEDC will be replaced by WLTP. This new cycle impacts the cost / CO2 benefit ratio of both existing and new functions addressed by hybridization. In addition of CO2, pollutants regulations will also be enforced in mainly world procedures. The powertrain will then be more effective and cleaner. Hybridization and optimized high level of powertrain control strategies will then be necessary. A well known impediment limiting consumer acceptance of major hybridization of the powertrain is the cost of the system. Cost is also a main driver for system design, as is alignment of technology solution with vehicle platform and customer base. We can observe that depending of the application, the CO2 pressure and cost constraints are different. In general, the premium car segment has a higher CO2 reduction target to achieve, and the hybrid system cost can be more easily supported due to the higher cost of the car. Conversely, for smaller car segments, the cost is more important and an expensive system cannot be afforded by customers. For these car segments, the CO2 target is smaller to meet the regulation target, mainly because these cars are smaller and lighter than the larger and premium cars. For these applications, typically A/B segments, 12V micro hybrid systems are the most affordable solution compatible with CO2 targets [1]. Systems able to lower the CO2 emissions of vehicle and / or enhance performances of smaller powertrain at a lowest added cost are then extremely motivating for car

3 makers. Low voltage hybrid systems are the best ones to meet these antagonist objectives. As fuel consumption reduction objectives are ambitious and managed by regulation, 12V hybrid systems can be completed by 48V ones. These last offer more CO2 emission reduction thanks to the higher power than 12V systems and are also able to address pollutants emission reduction [2] [3]. They are also a mean to offer more comfort. These 48V systems make thus sense for C/D segments. 3 12V and 48V functionalities Energy recovery: This function is the base of all hybridization systems. The goal is to recover the kinetic energy normally lost while braking or decelerating. On lighter vehicles, the energy to be recovered is less than in heavy cars, allowing lower power 12v micro-hybrid systems to be used. The power recovery potential will be limited by the current in components, wiring and connections. On 12V systems, peak power up to 6kW can be achieved. The primary objective after recovering the energy is to use it most effectively, at the highest efficiency. There are two main ways to re-use this energy: Electrical load supplementation: feed the 12v electrical net board Assist propulsion: provide power to the powertrain. Supplement the electrical board net: To directly feed the board net with the energy recovered is typically the most effective approach. It results in the least energy conversion, so the cumulative efficiency is the best. All the energy provided this way has not been produced by the alternator, so the power taken from the engine to drive the alternator can be significantly reduced, or not required in some cases. Propulsion assistance ( torque assist ): Another way to re use the stored energy is to provide power to the powertrain. Thus, the torque required from the engine can be decreased. High speed Extended Stop & Start: This function aims to enlarge the CO2 reduction of the stop and start by anticipating turning the engine off. The engine is then stopped as soon as possible each time the driver puts the gear box in manual position and release the clutch pedal (for a manual transmission), or press the brake pedal (for automated gear box). Coasting: This function is an extension of the extended stop and start and consists to open the drive line as soon as no engine torque is required. The vehicle is then in freewheeling situation without any powertrain drags. In these cases, it is useful to stop the engine to maximize the CO2 impact. This function can be activated very often in real life driving situations. The number of engine stops has a direct consequence on the number of engine restarts. This is higher than in current stop and start function. For coasting, the number of restarts in lifetime is higher than 1 million. This is particularly challenging for reinforced starters components used in some stop and start cycle functions. Valeo has demonstrated that belt e-machines have much more potential to achieve this number of stop and start cycle for coasting with more than 1,2 million cycles. As belt e-machines can also procure quicker and smoother crank, they provide a better vibration and noise behavior at each start of the engine. In addition, the engine starting time is shorter with this kind of machines.

4 2 / g of CO NEDC cycle The engine is thus able to provide torque for traction in a shorter time than with a classical starter. This is also a great advantage for the change of mind situations and so for safety. Fig 2 shows Valeo starter and belt starter-generators (istars 12V and ibsg 48V machines). Figure 2 Valeo starter, istars 12V & ibsg 48V components These different kinds of systems provide numerous mild hybrid functions, offering a panorama of technological solutions to meet a wide range of performance and CO2 emission reduction targets. These systems are thus scalable and allow several cost / CO2 reduction ratios. They also provide a quite range of functionalities. Fig 3 shows relative positioning of main hybrid systems according CO2 gain / cost ratio B - Segment CO 2 saving - /g positioning FULL Hybrid PHEV40 48V Belt Start / Gen n 12+12V Belt Start / Gén CO 2 savings Figure 3 12V and 48V positioning vs. other voltages technologies. The analysis of CO2 gain versus system cost clearly shows that 12V systems addressing hybridization functions are well placed in terms of CO2 reduction and in terms of cost / CO2 gain ratio. From this last point of view they are the best in class. This confirms that 12V micro-hybrid systems are the best solution for vehicle needing a limited CO2 reduction for an affordable cost. 48V systems allow real hybrid functions and more CO2 reduction for a still moderate cost. Boosted hybrid: An alternative way to provide torque to the crankshaft is to use the electrical energy to drive an electric supercharger which can rapidly increase the engine s intake manifold pressure to provide instantaneous reserve torque, while also rapidly increasing the temperature of the exhaust gas. This rapid increase in exhaust enthalpy can be used to dramatically reduce turbo lag in the conventional

5 turbocharger. This additional reserve torque and rapid response can be used to redefine the turbocharger sizing, opening new system optimization possibilities, including downspeeding and downsizing actions to lower CO2. The specific engine power can thus be increased to facilitate engine downsizing, while the additional low speed reserve torque from the electric supercharger can facilitate downspeeding. Furthermore the electrical energy utilized results in a coefficient of performance much greater than one in terms of power output at the crankshaft. For example, 2kW of electrical power consumed by the electric supercharger can provide up to 10kW mechanical power at the crankshaft at low engine speeds. Also as the electric supercharger is only used in transient driving phases at lower engine speeds, it can be provide very effective utilization of the free energy provided from regeneration driving phases. Fig 5 illustrates the energy efficiency comparison between pure electrical boost and electric supercharger boost resulting in the same power level on the crankshaft. Figure 4: Electric supercharger boost efficiency vs. electrical boost The electric supercharger either in 12V or in 48V applications is a gateway to new powertrain adaptation and synthesis. As the electric supercharger can deal with all transient driving phases, it is possible to match the classical turbo ladder in new focus. It is for example possible to optimize the turbo ladder for high engine RPM and thus increase the specific power of the engine. The resulting turbo lag which would normally not be acceptable can then be treated by the electric superchager which has a very short response time. Electric super charger can thus be used in order to increase power and fun to drive, or address extreme downsizing or downspeeding for more CO2 emission reduction. As the electric supercharger is also a way to manage the intake pressure of the air loop in all driving phases, it can also be used for EGR enhancing or scavenging. It can also be used to manage the high loads phases of Diesel engines. Its effect is then to contribute to lower the exhaust gas temperatures and thus reduce NOx

6 emissions [4]. It can thus reduce or replace the SCR system. Fig 5 illustrates the possible uses of the electric supercharger. Fig 5 Electric supercharger uses 4 Enhancement of hybrid functions To enhance the hybrid functions benefits, we can think use predictive behavior of the car linked to the traffic and road situations. We then need to have external data from the vehicle to understand its environment. A first level of road information can be given by GPS. It is then possible to forecast the road profile as slopes, turns, intersections. The first use of this information is to forecast the deceleration phases to optimize the battery feeding and use before the known future deceleration phase. It is even possible to define the optimized point where the driver can release the gas pedal to optimize the deceleration ratio and time and in the same time reduce the use of the mechanical brakes. GPS is a first level of information but it remains theoretical one. It can be useful in real life driving to check and adapt this theoretical information and energy regeneration profile to the real road conditions such as traffic lights state, other vehicles on road, traffic which can modify the place the vehicle has to stop. We can then use the information given by an on board camera to adapt and in real time optimize the GPS information and then optimize a level ahead the energy management of the car. Valeo built such system and demonstrators years ago in the CO2Pilot system. Fig 6 and 7 illustrate the energy regeneration optimization on roundabout and the CO2Pilot Valeo demo car.

7 Fig 6 Deceleration optimization on roundabout for energy regeneration Fig 7 Valeo CO2Pilot demo car. The nest step of hybrid optimization is to be able to optimize all the driving phases of the vehicle. We then need to know all the external context of the driving conditions. By the way, to be able to use the information collected by the sensors of an automated vehicle is really convenient. It becomes the possible to manage all the energy need for the driving, either in classical combustion engine driving phase as hybrid ones. Some dedicated driving phases are then naturally hybrid or pure electric dedicated to manage the electric energy in the best way and in the same time to limit pollution emission, for example in traffic jam, slow motion, parking,.for such driving phases we will see that 48V systems with the right hybrid architecture are convenient. Fig 8 illustrates the last ecruse4you Valeo demo car integrating 360 detection for automated driving and 48V hybrid system able to drive the car in pure electric mode.

8 Fig 8 Valeo ecruise4you demo car. 5 Hybrid architecture Parallel hybrid architectures are usually classified according to the place where the e- motor is placed in the powertrain kinematics. The fig 6 illustrates the widely used hybridization architectures classification. The easiest architecture for low voltages mild hybrid applications is the P1 one with belt electric machines. This architecture requires the less powertrain component modifications which help to limit the cost. But using the belt to transmit the power has some disadvantages. First the belt limits the power to around 10kW, but the main disadvantage is that in P1 architecture the engine is never decoupled from the electric machine. The hybrid system efficiency is thus limited because the energy transfers have always to deal with the engine loses. Some recovered energy is then lost in the engine step. In the same way, some electrical energy used to drive the vehicle is only used to move the engine. Thus, in P1 architecture, even for 48V systems, pure electric driving phases are not interesting from the energy management point of view. P2, P3 and P4 architectures are better placed from the energy flow efficiency. With the power allowed by 48V systems, all the hybrid functions including pure electric driving can be addressed. The CO2 reduction is then higher than for P1 applications. Because these architectures imply more powertrain modifications we can guess they will be used as the next powertrain components generations will come.

9 Figure 6: Hybridization architecture classification 6 Board net evolutions requests Recovering energy requires a storage element, because usually this energy can t be immediately used in same proportions. Thus, it is necessary to have a storage device capable of managing an important energy flow. Classical lead acid batteries aren t able to store and to deliver such energy (cycling effect). A first step of battery improvement consists in using AGM lead battery. For more severe applications it is necessary to use dedicated batteries which have more power and flow capabilities. For applications requiring important current peaks, voltage drops on the net board can be issues. They can induce comfort inconveniences (as radio, light or blower drop off), or even safety problems (as engine control, ESP or steering assistance cutoff during driving phases).to be able to manage such currents needs and to protect the sensitive loads on the board net we have to use a storage device with the right current flow. The challenge of the best compromise is to have all the electrical needs assumed to the lowest cost. One common solution is to use dual battery architecture. One battery takes in charge the high current flow demand for energy recovery or high demand supply as the second one is dedicated to feed the sensitive loads. Figure 7 shows such an electrical architecture. To assume the protection of the sensitive (and / or comfort) loads, the classical board net has to be isolated when either the starter device or the air compressor pulls peak current. That s why a switch can installed between the classical board net branch (safe side) and the other part of the board net. This switch is piloted according to the driving phases, coupling the two board net branches in normal or recovery phases, in order to feed the two batteries by the alternator. The switch is opened to isolate the two board nets when a current in the complementary branch occurs, risking to induce

10 a damageable voltage drop up in the classical one. The need of such a switch is linked to the relative batteries sizing and properties. In some case, the natural current capacity and the internal resistance of the batteries can naturally create a segregation of the two power sources. Figure V electrical architecture 7 Dual battery architectures: a modular view The comparison of 12+12V board net architecture to the 12+48V one shows easily some communality. These two architectures contain two storage devices, each one dedicated to a specific role and a specific components nature. We can also notice that the basic topology of these architectures is the same: two electrical branches, two storage devices and a similar role repartition of each branch. In each case, a storage unit is dedicated to the high current or high power devices. This storage has to be able to feed these components and to be fed in energy regen mode. In common use, the high current demand is relatively short. We can also notice that a quite basic function set can be defined: - Stop & start and the associated device: starter or starter-generator - Regen device: high current alternator or dedicated e-machine - To these basic functions additional features can be added without deeply modifying the architecture: If a function requiring an electric supercharger is wanted (low RPM torque, over torque, EGR pump...), this last can be simply added on the high current branch quite as a plug and play device (from an electrical architecture point of view). For 48V applications, additional comfort devices or chassis control can also be added in the same way [5]. In the 12+12V and 12+48V architectures, a storage device is dedicated to feed the sensitive devices which don t stand current of voltage drop off. Once again, these devices are the same in both cases and can be added on the clean branch on demand. We can thus notice that the 12+12V and 12+48V board net are similarly built. The two branches have the same assignment. The branch isolation and connection is made at the same place by or a switch or a DC/DC. Finally the management energy strategy is similar. We can then predispose a vehicle platform compatible of the two

11 tension applications. It is then imaginable to have some platform applications with 12+12V systems to optimize cost and system customer value. It is also quite easy to replace the generator (or starter-generator), the high current branch battery and the switch by 48V equivalent components and the switch by a DC/DC. The basic electrical architecture of the platform is then vey similar and can be defined to be the same. This interesting modularity of the tension level, components and functions can be put as profit to lower the cost of systems and integration. Fig 8 illustrates the plug and play functions built up and the architecture modularity between 12V+12V and 12V+48V world. Fig 9 illustrates the 48V branch modularity. Fig 8 Functions and architecture modularity

12 Fig 9 48 architecture branch modularity 8 Components modularity In addition to the modular and plug and play building of system functions, it is worth to design the range of a component with a modular thinking in order to lower the cost. It is the basis effect of a design based on platforms. The basis platform blocks can then be re used in many variants of a component. The well known cost effect of platforms can then be used to lower the cost and the development cost of a component. Valeo has based the design of belt e-motors and associated inverters on platforms. The mechanical base of the e-machines rotors and stators are thus designed on the same base for 12V, 48V. The modular building of e-motors is not limited to belt machines. The same machine and inverter topology can be used for e-machines set in gearboxes and on rear driveline. In the same mind, low voltage (under 60V) and high voltage applications can be designed with the same elementary building blocks. The specifications due to the different way to wire the machines are taken into account in the general design. For the inverters, the general design is made compatible with the different basic power module adapted to each voltage level and power. As a result, the general design of the inverter is quite similar for every application. The same electronic base design is used and only the housing is different for air or water/oil cooled version. Fig 10 illustrates the main building block associations to define the range of 12V, 48V, high voltage e-motors for P1, P3 and P4 hybrid architectures.

13 Fig 10: e-machines and inverter building blocks 9 48V: an opportunity for EVs The power of P4 architecture 48V hybrid systems is currently about 20kW. As P4 system includes the e-motor, the differential and the transmission shafts, it is easy to use these components to build the powertrain of an EV. The battery capacity has of course to be adapted to the desired range, but this basic powertrain can be use to motorize some small urban vehicles with a first level of dynamic performances. These components can so be an answer to the double hundred cars of the new Chinese regulation. These vehicles have to be able to reach 100 km/h and a range of 100km. For small and light vehicles, this 48V powertrain is sufficient to match the requirements. Using the 48V modular components is here again a way to lower the cost of dedicated applications. The modular powertrain building can thus have new possibilities and applications. If the vehicle platform allows it, it is even possible to integrate 2 driving axle, one on the front, one on the rear axle to be able to reach about 40kW for the max power available. The car has to be able to integrate the extended battery to feed the two e- motors as for every EVs. This can be done to enhance the car performances or to address bigger economic vehicles. Once more, the modular building extends the basis components possibilities.

14 10 CONCLUSION Hybridization is a necessity for CO2 reduction. However affordable cars do require simpler / cheaper solutions. Extended 12V system ( micro-hybrid ) allows superior fuel economy for best value equation. Those systems, based on belt starter generators, dual battery and electric clutch allow most of hybrid functions from stop and start to boost, regen and coasting. 48V systems are able of more power and so more CO2 reduction for still a moderate cost versus high voltage systems. These systems can be used in P2, P3, P4 hybrid architectures to enhance the powertrain efficiency. A modular building block design is also a way to lower the cost of the components. In addition, a geometrical compatibility from low voltages up to high voltages e-motors and electronics is also a way to propose generic and scalable hybrid systems. The electrical board net architectures are similar between 12+12V and 12V+48V systems and can be a first level of plate forming in order to limit the integration cost. A generic electrical board net architecture topology can then be defined. The tension level can thus be adapted to the vehicle needs and a scalable response for a wide range of vehicle segment is possible. REFERENCES [1]: S.Potteau, Y.Wu, J.Chicot, Y.Jin, P. Masson, F.Boudjemai, P.Maurel, D.Taccoen, K.Surbled, D.Fournigault : 12 Volt electric network evolutions for new functions integration: coasting function, recovery and boost with enhanced electric machines, and support for downsizing/downspeeding with a boosting support., SIA Powertrain, Versailles [2]: T. Schnorbus, J. Schaub, M. Miccio, F. Glados, E. Morra, M. Rasty, J. Ogrzewalla, and S. Potteau: "Mild Hybridisation and Electric Boosting Improving Diesel Emissions and Fuel Efficiency with Premium Performance", 24th Aachen Colloquium Automobile and Engine Technology, [3]: O. Coppin: From 12+12V to 48V: a new road map for hybridization, Engine expo, Stuttgart [4]: J. Schaub, C. Frenken, B. Holderbaum, B. Lindemann (FEV GmbH), P. Griefnow, R. Savelsberg (Lehrstuhl für Verbrennungskraftmaschinen VKA RWTH Aachen), O. Coppin (Valeo) : FEV ECObrid A 48 V Mild Hybrid Concept for Passenger Car Diesel Engines, International Engine Congress, Baden Baden [5]: O. Coppin: From 12+12V to 48V: Extending the hybridization road map, EEHE Electric & electronic Systems in hybrid and Electrical Vehicle and Electrical Energy Management, Bad Boll Autoren / The Authors: Dr.-Ing. Olivier COPPIN, R&D and Innovation Director, Valeo powertrain Cergy (FRANCE).