The 12V bus in cars is overwhelmed. What is the future of the 48V bus system?

I remember that in the 1990s, the automotive industry considered replacing the 12V system with a 42V bus power distribution system, but due to the complexity and high cost, the plan failed after more than a decade. Today, under the pressure of global environmental protection, the demand for 48V bus power distribution is becoming more and more obvious, but can 48V mild hybrid become the standard of the future automotive market? Let's see what the industry leaders have to say.

It has become a consensus that future automotive technology will develop in the direction of electrification, but there are still different opinions on which technical route to take. Among the various power forms such as pure electric (EV), hybrid (HEV), plug-in hybrid (PHEV), 48V mild hybrid (MHEV) and heavy hybrid (HEV), as well as fuel cells, which one is most likely to stand out and become the mainstream in the future? We see that the main players in the 48V mild hybrid vehicle (also known as battery-assisted hybrid vehicle) market include Bosch, Continental, Delphi, Valeo, AVL List GmbH, Hitachi Automotive Systems, Schaeffler, Ford, General Motors, Fiat, Chrysler, Toyota Motor, Nissan, Honda, Mercedes-Benz, BMW, Audi, Hyundai Motor, Mitsubishi Motors, Mazda, Subaru, etc. Domestic companies such as Geely, Changan, BAIC, JAC, and Great Wall have plans to produce models equipped with 48V systems. It seems that 48V mild hybrid still has its appeal.

Increased car functionality requires greater power

The 12V electrical system in today's cars can deliver about 300 amps, with peaks of about 600 amps, which is barely enough to power the traction motors and brakes. With all the new power-hungry electronic drives and features on the latest cars, such as electric start-stop, electric steering, electric suspension, electric turbocharging, variable-speed air conditioning, as well as audio systems, heated seats, and headlights that can follow the steering to illuminate dark curves, the traditional 12V distribution bus is overwhelmed, and the need for higher voltage bus distribution is becoming more and more obvious.

12V and 48V electrical system capabilities vary widely

With the advent of autonomous vehicles, systems such as lidar, radar, cameras and ultrasonic sensors that require high-performance graphics processors to collect, interpret, integrate and understand have placed additional demands on the power distribution system. Such processors are very power-hungry and put an additional burden on the traditional automotive 12V distribution bus. Even for vehicles with high autonomy and driver assistance functions (ADAS), today's 12V electrical system is far from providing the energy required for the on-board computer to analyze and process sensor and camera data. Such an on-board computer will consume about one kilowatt to two kilowatts of electricity, which will exhaust the power of the 12V system. Whether the future self-driving car is a hybrid vehicle or a pure electric vehicle, a 48V system is required to withstand high-energy loads.

Stefan Hartung, member of the Bosch Group Board of Management, said: "Many cars and their internal combustion engines are facing transformation as the implementation of emission regulations forces automakers to seek effective ways to reduce carbon emissions from cars. 48V electrical systems are bringing innovation to the automotive industry, and 48V mild hybrids will become the minimum standard in the future automotive market." He said that the market for 48V system solutions is expanding globally, especially in Europe and China. Bosch expects that by 2025, nearly 20% of new cars sold each year in the world will be equipped with 48V systems and supporting batteries.

To this end, Bosch and CATL reached a long-term strategic cooperation agreement and put into production the 48V battery, the core component of the 48V mild hybrid system, according to Bosch's requirements. This cooperation has further expanded the wide application of 48V batteries in many automakers around the world and will also promote 48V mild hybrid vehicles into a reasonable price range.

The New York Times pointed out in 2018 that electric vehicles are not only good for the environment, but also for the user's tendency to consume electricity. Automakers are looking to get rid of the traditional 12V system and turn to the 48V standard to power future cars. Over the past decade or so, automakers have been replacing traditional mechanical drive components such as electric steering racks, electric brake vacuum pumps, and electric water pumps with more efficient electric components.

In fact, some cars already use 48V systems, such as the Porsche Cayenne Hybrid and Bentley Bentayga Hybrid SUV. But while the vast majority of car buyers won’t be able to use them in their cars yet, widespread adoption of the new standard will soon be a reality.

In Europe, especially in most of Volvo's models, it is in a leading position. New models have adopted mild hybrid technology, and the 2021 S90/V90 will add 48V mild hybrid power. 48V standard is used to produce mild hybrid vehicles. Volvo said that 48V mild hybrid can not only improve power, but also optimize fuel consumption. Official data shows that it can save more than 15% of fuel. The introduction of 48V mild hybrid system on Audi A7 and A8 also gave consumers a new understanding of mild hybrid. First, the cost is lower and the burden on consumers and OEMs is less; compared with 12V, the higher voltage also reduces the current and the vehicle is safer. Most importantly, the improvement in fuel economy can be said to be immediate. In actual driving, the 48V mild hybrid system can reduce the vehicle's fuel consumption by 0.7L/100km.

Navigant's forecast shows that in terms of global new car sales in 2025, 48V mild hybrid vehicles may account for 14% of the market share, while gasoline or diesel engines will only account for 65%.

IHS: 48V mild hybrid growth forecast by region

Why does the 48V system appear in the so-called mild hybrid system? There are reasons. First of all, the 48V system can provide 70% of the benefits of a full hybrid vehicle at 30% of the cost.

Secondly, as new cars become more complex and high-tech over time, the new higher power requirements associated with these advances, as well as increasingly stringent emissions regulations, are the reason why 48V power systems are spreading like wildfire. Automakers have added a plethora of new infotainment options as well as driver assistance safety features such as adaptive cruise control, lane keeping assist, blind spot monitoring, etc. In addition, there are heated seats, heated steering wheels, and heated windshields. Needless to say, the standard 12V power system is becoming increasingly weak, and the intervention of the 48V power system helps to meet the demand for more onboard power.

Third, to meet fuel economy and CO2 emissions regulations, especially in the EU and China, 95 g CO2 per kilometer is required by 2021 and 117 g CO2 per kilometer by 2020. The US also needs 54.5 mpg (equivalent to 101 g/km) by 2025. Therefore, HIS predicts that by 2025, the 48V mild hybrid vehicle market will grow 9 times, with 14 million vehicles in production.

What is the disruption of 48V electrical systems?

Karl-Heinz Steinmetz, head of hybrid, electric vehicles and powertrain systems at Texas Instruments (TI), said that the advantages of 48V are first of all increased power and reduced emissions. The progress of automotive power drive architecture from 12V to 48V meets the higher power needs of today's high-energy-consuming vehicles. The increase in power can also make the internal combustion engine run more efficiently, helping manufacturers meet emission regulations more quickly. Automakers are launching mild hybrid vehicles with start-stop technology. This technology allows the engine to be temporarily shut down when the car is coasting, braking or stopping, and then quickly restarted with partial power provided by the new system. Low-end mild hybrid vehicle manufacturers will follow suit this year and adopt this technology. Unlike traditional hybrid vehicles, the motor in mild hybrid vehicles is used to supplement the internal combustion engine and does not power the vehicle alone.

He explained that traditional 12V electrical systems use lead-acid batteries and alternators to provide power for an increasing variety of energy-consuming features, such as interior and exterior lighting, semi-autonomous collision avoidance and lane-keeping safety features, and the hardware and software that provide in-car audio and video. The 48V system can meet these power loads. The energy required to drive the turbocharger, air conditioning compressor, active suspension system, coolant pump, oil pump and power steering pump in a 48V car is provided by the electrical system instead of the crankshaft pulley and belt drive that traditionally powered the internal combustion engine.

How 48V electrical systems support traditional 12V systems

Karl-Heinz pointed out that the transition from a system previously driven by an engine that produces CO2 to a system driven by a 48V electrical system current will allow the use of smaller engines, such as reducing a six-cylinder car to a four-cylinder car, thereby improving fuel efficiency and reducing CO2 emissions. On a technical level, the structural changes required to switch from 12V to 48V are not large.

The second advantage is the recovery of stored energy. The 48V system uses a large-capacity lithium battery and a regenerative braking system. Through regenerative braking or recovery braking, the generator converts the kinetic energy lost when the car decelerates into electrical energy, which is stored in the 48V large-capacity battery and can use the recovered energy to support the electrical device of the internal combustion engine. Karl-Heinz said that through regenerative braking, when the driver changes from stopping to accelerating at a traffic light, the stored energy will be used to propel the vehicle forward, thereby achieving a faster speed than usual. Some 48V electrical systems also shut down the engine when the vehicle is coasting or stopping, thereby improving fuel efficiency and reducing emissions.