Why abandon 12V and choose 48V for automotive power supply?

The new generation of Audi A8 models will be equipped with a 48V electrical system to achieve the purpose of saving energy and increasing power. The car will be built on the Volkswagen Group MLBEvo platform. A true technologist should be familiar with the term '48V for cars'. As early as when the new Audi Q7 was released, the mass production application of the 48V system was mentioned. Earlier in 2013, the 'Green Mix' released by BYD also essentially belonged to this category. However, all of these, or 'thunder without rain' after the release, or not introduced to us after mass production, so many people have gradually forgotten this new thing. Since last year, especially some of the displays at the Shanghai Auto Show, people's attention to the 48V system has been reawakened. On the one hand, it is the new high-end Mercedes-Benz S-Class. The plug-in hybrid version will be equipped with a 48V system. It should be no suspense when it comes to us next. On the other hand, independent manufacturers other than BYD are also releasing their own 48V system research and development and investment plans. So why do everyone have to abandon the previous 12V to 48V? Take the air conditioner, for example, when a traditional car is waiting for a red light, the engine is at idle speed, the belt-driven air conditioner compressor can continue to work, and the air conditioner is still cooled. But for cars with start-stop function, they need to switch to electric air-conditioning when waiting for the red light, otherwise the passengers will have to endure the environment without air-conditioning when waiting for the red light or traffic jam. The power of an electric air-conditioning compressor must be at least 2.5kw. If 12V is used for power supply, the grid will be unbearable, and 48V will be no problem. In addition, the 48V side can also supply power to the active suspension, electric power steering, electric heater, etc. 'As more and more high-power electrical appliances are converted from belt drive to electric drive, the high-power electrical appliances on the 48V side will continue to increase. The 48V system car that emerged at the historic moment introduced storage batteries in 1918, and gradually became popular in 1920. At that time, the battery voltage was 6V. Later, with the increase of internal combustion engine displacement and the appearance of high compression ratio internal combustion engines, the 6V system could not meet the demand, so the 12V system was introduced in 1950. By 1988, SAE (Society of Automotive Engineers) proposed The standard voltage was increased to 42V, but due to various restrictions, there were few responders. Later, even with the increase of electrical equipment, the battery could no longer meet the power requirements of the body equipment, the automobile companies adopted the method of cutting off the high-power load. Reduce the load of the battery. The 12V voltage system has basically reached the power output limit after the introduction of the start-stop mechanism. If the light-hybrid system is introduced under the 12V voltage, the power demand is about 10kW~15kW, and the output current of the battery under this voltage is as high as 1000A, obviously does not work. In 2011, Audi, BMW, Daimler, Porsche, Volkswagen jointly launched a 48V system to meet the increasing demand for on-board loads, and more importantly, to meet the strict emission regulations in 2020. And subsequently released 48V system specification LV148. Why is it 48V? Because 60V is a safe voltage, that is to say, as long as the voltage is lower than 60V, no additional safety protection measures are needed. The charging voltage of 48V battery is up to 56V, which is very close to 60V, that is, 48V battery. The voltage is the highest voltage level under the safe voltage. The 48V power system can store more power than the 12V power system. In a car equipped with a start-stop system, the engine can be shut down for a long time, reducing the occurrence of low battery power and frequent engine charging. (If you don’t charge it, you can’t play the engine), so as to avoid wasting too much fuel. Of course, the emergence of the 48V system does not mean that the 12V system has been eliminated, but on the basis of retaining the previous 12V system. A set of 48V system to support weak mixing and mid-mixing systems. In addition, the EU has the most stringent emission regulations. By 2020, fuel consumption per 100 kilometers should be reduced to 4L, and carbon dioxide emissions per kilometer as low as 95g. Obviously relying solely on improving the engine Fuel efficiency is basically an impossible task to achieve the emission target. Hybrid and pure electric vehicles are the best technical routes. Although pure electric vehicles are the goals of vehicles, they cannot be achieved in a large amount in a short period of time due to high costs and battery life issues. Popularity. The 48V architecture standard 48V system consists of three parts: the motor, the lithium-ion battery pack and the DC-DC converter. The 48V system is mounted on the hybrid vehicle, and the 12V-48V-HEV is formed through two DC/DC converters. Electrical system architecture; the electrical architecture of ordinary hybrid vehicles is 12V-HEV mode, through DC/DC The converter directly connects the 12V system and the HEV high voltage system. Compared with the high-voltage hybrid system, the 48V light-hybrid system has a lower cost, but it can achieve most of the energy-saving effects of the high-voltage hybrid system (battery voltage>100V). According to Delphi’s calculations, the 48V light-hybrid system is the cost of the high-voltage light-hybrid system 30% of the energy saving effect of 70% of the high-pressure light mixing system. The advantages of the 48V light hybrid system: 1. The safety voltage is lower than 60V, no additional voltage protection is required, and the cost is lower than the high-voltage hybrid system; 2. Compared with the 12V system, the working current is only 1/4 at the same power. The loss is only 1/16 of the 12V system; 3. Thanks to the electric power assistance of BSG/ISG, the volume of the engine can be further reduced, thereby reducing emissions; 4. The high-load accessories on the traditional engine can be electrically powered, such as air-conditioning compressors and cooling Water pumps, vacuum pumps, etc., reduce the load of the engine, even when the engine is turned off, these devices can work; 5. Raise the working voltage of on-board electrical appliances to 48V, which can further reduce losses and reduce the outer diameter of the wiring harness; 6. Yes Support for higher-power in-vehicle devices. 7. It can be turbo-electric to further improve the efficiency of the engine, and there will be no turbocharger delay; 8. BSG/ISG ignition time is shorter, lower noise and less vibration. 9.48VBeltStarterGenerator (BSG) can easily replace the original 12VBeltStarterGenerator, and it can be matched without major changes in the design.