Analysis of the automatic start-stop system at idle speed represented by SLK/X3

Many models equipped with the "start-stop system star/stop" were exhibited at the Shanghai Auto Show, including many domestic models, such as the third generation of the Fumeilai. Mercedes-Benz SLK and BMW X3 represent Europe's favor for this technology. It is only a matter of time before this environmentally friendly technology, which has been widely used in Europe, is promoted in China. How does this system work, what are its characteristics, and what help and problems does it bring to us when using cars?

What is the "start-stop system star/stop"

As the name suggests, this system automatically turns off the engine when the vehicle stops temporarily (such as waiting at a red light) while driving. When it is time to continue moving forward, the system automatically restarts the engine.

The system automatically restarts the engine upon learning the driver's intention

Application Background

On March 5 this year, the Hong Kong SAR government reviewed and approved the "Draft Fixed Penalty for Idling Vehicle Engines". According to the regulations, except for exemptions such as buses and hybrid vehicles, vehicles must be turned off after idling for three minutes, otherwise a fixed fine of HK$320 will be imposed. The regulations are expected to take effect in June.

In fact, Hong Kong is not an isolated case. Countries and regions such as the United States, Japan, the United Kingdom, France, Germany, Italy, and Taiwan have already enacted laws to regulate parking and engine shutdown. Idle parking and engine shutdown legislation is becoming a global practice. As for the "start-stop system star/stop". It is equipped in all hybrid models. What's interesting is that academically, vehicles with start-stop systems are classified as "micro-hybrids" because this system can greatly reduce the idling condition of the engine, which is similar to the role played by adding an electric motor.

The start/stop system is the fastest-growing environmental protection technology for automobiles in recent years, and is particularly suitable for stop-and-go urban roads. It is estimated that by 2012, 50% of new cars launched in Europe will be equipped with a start/stop system. According to reports, such a simple system can achieve 15% fuel saving under urban conditions. However, we don't need to pay too much attention to the fuel saving data, after all, the reference values ​​given by each manufacturer are different, and it is also related to the road conditions. In fact, idling stop is to reduce fuel consumption on one hand, but more importantly, it is to reduce emissions. Because the emission quality of the engine under idling conditions will be much worse than that under normal driving conditions.

Some of the models equipped with the "start-stop system star/stop" exhibited at the 2011 Shanghai International Auto Show

BMW X3

Mercedes Benz SKL

Sega's auto-start-stop technology will go into production in the second half of the year

The third generation Fumeilai automatic start-stop version

Usage process introduction

This technology is available on both manual and automatic models. For an example of how it works on manual transmission models, you can refer to the following video.

For models equipped with automatic transmission, the automatic start-stop system works as follows:

If you press the brake pedal directly while driving, the engine will automatically shut down after the vehicle comes to a complete stop for about two seconds. If you keep pressing the brake pedal, the engine will remain off. As soon as you release the brake or turn the steering wheel, the engine will automatically ignite again, and you can immediately press the accelerator to start. The whole process is in D gear.

In order to solve the problem of being too tired from pressing the brake all the time, just turn on the AUTO HOLD electronic handbrake. The engine will only start after lightly pressing the accelerator pedal, and you don't need to keep your right foot on the brake.

Direct injection engines that require a more durable starter are more suitable for applying this technology

The main technical difficulty of automatic start-stop technology lies in the need for a more durable starter and how to reduce the impact during repeated starts. The general starter design allows a large working current to pass, but the use time is very short. Repeated use of the starter can easily cause the starter to overheat and be damaged, so the starter with automatic start-stop function must be much more durable than ordinary starters.

In principle, automatic start-stop is nothing more than turning off the engine and then turning the key to start the engine again. But in fact, it is most important to avoid the startup delay caused by repeated start-stop, because users will experience this firsthand.

From the actual driving situation of X3, there is no delay at all, because the X3 engine starts very quickly in normal conditions. Here, the direct injection engine is the key. Since the direct injection engine can directly atomize gasoline through the injector, it can be started in one working cycle in principle. The general intake pipe injection engine requires the intake air flow to atomize gasoline and then carry it into the cylinder, and the starting time is much slower than direct injection. This fundamentally leads to this type of engine taking a longer time to restart after using the automatic start-stop device. In addition to high power consumption and fuel loss, it also causes discomfort to the passengers in the car.

Direct injection engines are more suitable for automatic start-stop technology

High-quality engine oil must be used

Many questions about the automatic start-stop system have been considered at the beginning of the design. For example, the system will not start when the air conditioner is turned on, the battery power is very low, the temperature outside the car is too high or too low, the pressure in the brake system drops below a certain point, etc. Although the automatic start-stop system has taken many situations into consideration when it was designed, there is one thing we must pay attention to, that is, the use of high-quality engine oil.

The wear of automobile engines in normal driving is very small, because when the engine reaches normal operating temperature, the clearance between parts and oil lubrication are in the most ideal state. On the contrary, during cold start, the clearance between parts is too large, and there is no oil film protection, so the wear accounts for more than 60% of the engine wear.

The starting process accounts for most of the normal engine cylinder wear.

Therefore, repeatedly starting and stopping the engine will inevitably shorten the life of the engine. However, since the engine operating temperature has reached the normal value during the start and stop process, the main factor affecting engine wear is the lubricating oil film.

Different engines are designed with consideration of parameters such as the viscosity of the lubricating oil that they are suitable for. However, domestic users generally do not pay enough attention to engine oil, thinking that it is OK to use any oil that is good enough, and often use cheaper oil. If low-quality oil is used in models equipped with automatic start-stop technology, it will cause great damage to the engine.

After applying automatic start-stop technology, users need to pay more attention to the quality of engine oil

Summarize

As a simple, effective and low-cost energy-saving and emission-reduction technology, automatic start-stop is very popular in Europe, and many domestic manufacturers have followed suit. However, to truly achieve reliable performance and smooth start, it requires support from many aspects, and the starting performance of the engine itself is one of the key and basic issues. Therefore, it is estimated that it will take some time for large-scale application in China.