European OEMs and suppliers plan to launch 48V hybrid systems after 2016
Automotive World 2015 presentations focus on improvements to fuel economy
European OEMs and suppliers are working to commercialize 48V hybrid systems in 2016 and onward. The hybrid systems are being touted as technologies capable of achieving exceptional cost-performance and significant improvement in fuel economy. Bosch and Valeo both made presentations at the Automotive World 2015 on their respective 48V hybrid systems. The 48V hybrid systems, compared to high-voltage hybrids, are designed to boost or regenerate power from 10-15kW generator motors at lower cost. In addition, the systems reduce electric loss based on high-voltage electrification of heavy energy-consuming electric components such as cooling fans and EPS units. As a result, fuel economy is anticipated to improve fuel economy by 7% to 20%. Also, consideration is being given to the idea of combining various 48V technologies in order to further improve fuel economy. This report gives an outline of the special features of 48V power sources and the 48V hybrid systems under development, based on information provided during the two companies' presentations, .
BOSCH Product Management &Marketing Gasoline Systems
Valeo Research & Development and Marketing Director
Hybrid/Electric Strategy Diector
JSAE Automotive Engineering Exposition 2014: Hybrid systems (Jun. 2014)
Background and needs for 48V systems
Responding to increased power consumption demand arising from electrification of vehicles:
The limit of electrical current that can actually be used in conventional automotive electric systems is said to be 300A, with a limit of 4kW for 14V (12V) systems. Recently, new automobiles are being equipped with more electric power-steering systems instead of conventional hydraulic power-steering systems. In addition, air compressors are starting to be electrified. A greater variety of electrical equipment is increasingly installed on premium cars. As a result, the 4kW or 14V limit has become insufficient to supply power to all the electrical equipment. Michel Forissier, the director of hybrid/electric strategy at Valeo, stated that there is greater need than ever for high-voltage electrification, in order to further advance electrification. When the current limit is raised to 48V, electric current can be lowered and reduce the electric loss, thereby improving fuel economy.
European fuel economy regulations: achieving CO2 emissions target of 95g in 2021:
As of 2015, European fuel economy regulations stipulate that the overall mean value of CO2 emissions of new vehicles per OEM is to be 130g/km or less, i.e., the CO2 value of the NEDC (New European Driving Cycle) official compliance testing in Europe. Furthermore, a decision was made to further reduce that value to 95g/km in 2021. The most fuel-efficient European version of the VW Golf (mounted with a 1.6TDI diesel) is 99g/km, and the European version of the Toyota hybrid Prius achieves 89k/km, just enough to comply with the future regulation. Even though 2021 is still some years away, the 95g/km target is an extremely high hurdle. It will be virtually impossible for premium carmakers to achieve the 95kg/km target by only improving the fuel economy of their gasoline- and diesel-powered engines alone, because their products include SUVs and high-end, luxury vehicles whose fuel economy tend to be low. As a result, achieving the target will require greater electrification and hybridization.
Bosch's 48V hybrid system
The following is an outline of the presentation on Bosch's 48V hybrid system given by Jochen Schaeferling of Product Management & Marketing.
Simple system design
The 48V system is composed of the conventional 14V system as it is, as seen on the right side of the diagram at the right; on the left side, a generator motor and a battery for 48V are added. The two systems are connected by a DC/DC convertor, with a structure designed to enable voltages to be mutually lowered and raised in both directions between the 48V and 14V systems.
Achieving energy regeneration 4-times greater compared to 14V system:
As seen in the graph on the right, compared to conventional 14V lead-acid battery systems, the 48V system can regenerate four times the amount of energy. Based on the presentation made by Mr. Jochen Schaeferling from Bosch, the 48V system regenerates 200Wh of electric power compared to the 50Wh generated by the 14V system in NEDC European compliance testing. Likewise, in Worldwide Harmonized Light-vehicle Test Procedures (WLTC), the 48V system generates over 400Wh of energy, compared to the 100Wh generated by the 14V system.
Improving output of motor for regeneration and boost:
The output of current 14V mild hybrid generators used for regenerative charging is around 3kW. However, the output can be significantly boosted to around 15kW when 48V systems are used. When the motor output reaches a level of 15kW, it is possible for the vehicle to run on all-electric power. According to the explanation given by Mr. Schaeferling, this system will make it possible for the vehicle to run on all-electric power such as creeping at 10km/h, accelerating up to 30km/h, and even cruising at a constant speed of 60km/h.
Components of Bosch's 48V system:
The following are the components of Bosch's 48V hybrid system under development, which were exhibited at international electronics exhibition, the Automotive World 2015 in Japan.
|48V Boost recuperation machine with inverter (BRM)||48V Lithium-ion battery|
|Power conversion unit (PDU) DCDC converter (48V-14V)||ECU Engine control unit|
Four types of 48V systems:
Bosch exhibited four types of 48V systems, which differed in terms of how/where the generator motors were positioned.
(1) ICE mounted: e.g. belt (engine-mounted type) In place of the conventional 14V generator, a 48V/10kW generator motor is mounted to the engine and driven by a belt. This is a less costly solution, requiring only a few redesigns to the base model and no redesigns to the basic architectures of the transmission and engine. Compared to conventional 14V mild hybrids, the level of regeneration and boost was significantly improved by raising the generator motor output to 10kW. However, the engine can not be stopped when the vehicle is traveling on all-electric mode because the motor stays constantly connected to the engine crankshaft by the belt. Nevertheless, even this simple system improves CO2 emissions by 9% to 12%.
(2) Crankshaft mounted: ISG By positioning the generator motor on the crankshaft coaxial, a significantly greater output of up to 15kW per revolution can be achieved. When a clutch is mounted between the engine and the motor, the engine can be stopped depending on the running conditions, making it possible to save energy equivalent to movements of the engine. However, a clutch to serve this purpose was not included in this diagram. This system can improve CO2 emissions by 9% to 13%.
(3) Transmission mounted: eMT, eAMT, eCVT This system drives a 10-15kW generator motor that is mounted on the transmission. There are two candidates being considered for generating power, which are belts and gears. A clutch is mounted between the engine and transmission and when needed, the engine can be stopped to save energy loss. Also, when the engine is stopped, cruising on all-electric power generated by only the motor is possible. This system can improve CO2 emissions by 12% to 19%.
(4) Transmission mounted: eDCT This is basically the same system as (3) above, which is based on eMT, eAMT, and eCVT transmissions, except that this system is married to a DCT. A 48V/15kW generator motor is connected to the driveshaft inside the transmission. A detailed explanation wasn't given, but it seems that the generator motor is mounted to a DCT's odd-number gear shaft, just like the Honda Fit's hybrid i-DCD system. The special feature of the 48V system, compared to the Fit's i-DCD that powers a 22kW motor based on a 173V high voltage system, is that a 15kW motor can be used. This system can improve CO2 emissions by 12% to 19%.
Valeo's 48V hybrid system
Michel Forissier, director of powertrain systems at Valeo, presented Valeo's 48V system, which is outlined below.
STEP1: belt-starter generator type
This system, the simplest of all, consists of a 48V battery and DC/DC convertor. A belt-driven 48V generator motor is mounted to the engine instead of a conventional 14V (12V) alternator. The conventional 14V (12V) electrical system is left intact. The 48V system controls energy recovery and boost, resulting in a combined system, i.e., a system running on conventional 14V (12V) and 48V power.
This system is designed to improve fuel economy in B segment vehicles by 15% in the NEDC, and 12% in the WLTC.
STEP2: gearbox motor generator type (48V beltless)
In this system, the starter, generator, water pump, air compressor and other equipment, which conventionally are connected to and powered by the engine, are being powered by other equipment. For example, the water pump and air compressor are driven by the motor, while the generator motor is driven by the transmission. All-electric cruising powered by the motor alone is possible, even with the engine stopped, by releasing the clutch placed between the engine. The compressor is driven by a 48V motor, and furthermore, the heavy energy-consuming units that conventionally run on 14V(12V) power can be adapted to run on 48V power. One of the benefits of converting to higher voltage systems is improved running efficiency, since loss is reduced by lowering the flow of electric current to even the same level as that of the electric power consumption.
Possibility of improving fuel economy 15% by lowering CO2 levels
According to the presentation given by Michel Forissier using the example of the development and testing of the BWM750, the amount of CO2 emitted from conventional systems was 219g/km, as indicated in the diagram on the right. However, it is believed that belt-driven starter generator systems improve on this by 6.8%; and that the use of electric-powered air compressors in gearbox-driven motor generators improves CO2 emissions by 15.5%.
STEP3：48V hybrid with booster supercharger
This is the same system as STEP2, except that it includes a supercharger. In actual drive tests, this system improved fuel economy by 20% and reduced diesel NOx by 7%. In addition, the company is also developing technology in which a mechanical flywheel KERS system is being combined with a 48V mild hybrid.
Aiming to achieve cost targets that are on par with diesel
Currently, full-hybrid systems cost around EUR 1,800 to build, and as a result, they are still not in widespread use in Europe. Michel Forissier stated that diesel engines cost EUR 800 more than gasoline engines, explaining that the trigger to grow greater market penetration of full-hybrid systems will depend on reducing their cost to the same price range as that of diesel engines. However, the battery accounts for a huge part of the cost of the systems, and even though the technical costs of batteries are dropping, the key to reducing the cost to EUR 800 depends on how much smaller the battery capacity can be downsized as a system.
The future of 48V systems
Michel Forissier of Valeo ended his presentation by talking about the future of the 48V system. He stated that that there is a huge need for the 48V system, adding that 48V electrification and related technology will continue to advance as a solution to respond to the growing increase in heavy energy-consuming onboard electric components and as a solution to eliminate and electrify current belt-driven components such as compressor pumps that rely on engine power. Finally, the 48V system is far superior than high-voltage hybrid systems in terms of cost efficiency when it comes to reducing CO2.
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