The start-stop system is too power-hungry. What are the good ways to supply power?

With the increasing acceptance of the start-stop system in the North American automotive market, various manufacturers have begun to consider a series of technologies, such as lithium-ion batteries, supercapacitors, and 48V "light-mixing" systems, to respond to frequent vehicle start-stops, usually as many as daily. More than 20 working conditions. Simply put, the start-stop system works by reducing engine idling and reducing vehicle fuel consumption and emissions.

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Even the most untouchable lead-acid batteries have begun to evolve. Today, the most commonly used conventional batteries in the past few decades are gradually being enhanced by deep-cycling enhanced flooded batteries (EFB) and adsorbed glass fiber separators (Absorbent Glass Mat). , referred to as AGM) battery replaced. Although the rapid spread of electronic components is also a factor, the key reason for this trend is the rise of the start-stop system, which will place higher demands on the fast charge function and service life of the battery.

“Generally speaking, the service life of a larger 12V AGM battery is four times that of a conventional battery, which is very important for the current promotion of the car start-stop system.” Kathi Walker, global director of GM's start-stop system, said, “Lithium The application of ion batteries can become a reality in the near future."

Although lithium-ion batteries may eventually become a major climate, they are currently not suitable for use as the main source of power for vehicle start-up, lighting, and ignition because of their high price. However, lithium-ion batteries can still function outside the power system.

“If you want to consider performance and cost comprehensively, lead-acid batteries and advanced lead-acid batteries are still the most suitable power supply technology for internal combustion engines in the world, and this situation will not change in the next 10 years.” The world's largest supplier of lead-acid batteries Craig Rigby, senior market & technology strategist at Power Controls at Johnson Controls, said, "This means that we can increase the fuel economy of lead-acid batteries by adding technologies such as lithium-ion batteries to support braking kinetics. Recycling and more in-car electric functions."

△ Johnson Controls is continuously increasing the output of AGM batteries to meet the demand for start-stop systems in the North American market.

At present, the start-stop system is the main thrust driving the transformation of the automotive battery field. The US Agang National Laboratory released a research report in 2015 to analyze the impact of the start-stop system on the life of vehicle start-up system components, including batteries. Studies have shown that the service life of traditional flooded lead acid starter batteries is related to many factors, with minimal impact on the number of vehicle starts. In fact, the factors that really affect the battery life are the inability to fully charge the battery when the engine starts and stops frequently, and the excessive discharge of the engine in the stopped state. Due to the influence of the depth of discharge, each time the engine is turned off, the power consumption of the auxiliary equipment in the vehicle has the greatest influence on the service life of the battery, and is also the most direct. If the battery can be fully charged between the two starts of the engine, the above-mentioned power consumption has almost negligible impact on the battery, and it can even be considered that it will not have an impact at all.

In contrast, the results of the Agang National Laboratory show that regardless of the number of engine starts, if the vehicle's battery has not been able to reach full charge, the battery will fail faster. The study also found that because the power output of the alternator is low, the engine can not be effectively charged when the engine is idling, and the charging effect during driving is optimal.

For electrical system designers, powering a frequently re-started engine is only one of the challenges. In order for consumers to accept models with start-stop system, it is very important to ensure that the sound and lighting functions in the car are in a constant state, which requires the "buffering" role played by 12V batteries.

“At startup, the vehicle's electrical system experiences a voltage dip, which causes the interior lighting to dim, etc.,” Walker said. “To ensure the stability of functions such as interior lighting, vehicles can use a variety of technologies to protect In-vehicle components are unaffected by voltage dips, ensuring consumer satisfaction during vehicle start-up. These technologies include dual battery design, DC/DC converters and supercapacitors."

At present, there are a number of models on the market that use dual-battery systems. This design can support a large number of power consumption functions and applications in the car. Since today's vehicles not only use many complex energy-saving technologies, but also apply a variety of safety functions, the design of such dual batteries will become increasingly common.

For example, the 2016 2.5L Chevrolet Mai Rui Bao's start-stop system uses a dual-battery design: one 12V battery is located under the hood and the other is mounted at the rear. The system (in combination with a series solenoid starter for faster start-up speed) is specially calibrated. When the vehicle's internal combustion engine stops working, the second battery can receive signals to immediately take over the auxiliary system power supply load in the vehicle, such as lighting, air conditioning, and sound. , the function of the window and the door lock. In addition, even if the engine stops working, the vehicle's air conditioner can still operate normally, but will switch to low power mode.

△ Basic diagram of the 2.5L Mai Rui Bao start-stop system, where 1 represents the 12V AGM main battery; 2 represents the dual-cell isolation module; 3 represents the 12V AGM auxiliary battery installed at the rear of the vehicle to ensure the balance of the vehicle's counterweight.

“Dual-battery systems can embody their value in many ways, and this design will become more common in the future,” Rigby said. “Two batteries can provide a more stable voltage during start-stop of the vehicle, and can also be advanced. The safety system provides a high level of reliability redundancy. In addition, the design of this dual battery, dual chemistry system is the best balance between performance and cost, providing maximum value to automotive manufacturers and consumers."

Generally speaking, the second battery of the vehicle is mostly 48V system. The system's higher voltage makes it easier to drive the parking camera and integrated sensors. Although the 48V system has many advantages, experts say that the automotive industry may still follow the 12V system in the future. However, Kia released the 2017 Niro Hybrid Utility Vehicle at the 2016 Chicago Auto Show. This CUV is not equipped with a 12V lead-acid battery. Instead, it directly passes the 48V lithium battery pack for the vehicle headlights. Features such as windshield wipers, which are typically supported by traditional 12V lead-acid batteries.

"Higher voltages can reduce the peak current of the system," said Stefano Zanella, commercial development manager at Texas Instruments. "Batteries are very sensitive to the capacity and load current they release during a specific amp hour, making the most of the battery. Features can effectively extend battery life and reduce cable size, thereby reducing costs and reducing weight."

Zanella explained that the 48V system must work with a DC/DC converter or a second 12V battery. This is because the current car uses a lot of very low cost 12V components, and it is difficult for automakers to replace these components with 48V. element.