[YesAuto Electric Vehicle Technology] I believe that friends in the north will have this experience. In the cold winter, the battery of mobile phones or other electrical appliances will consume very fast. This is determined by the physical and chemical characteristics of the battery, and today’s hybrid Most vehicle models use batteries as energy storage units, and they will also face the same problem. So what high-cold tests will the hybrid model go through to verify its performance in cold conditions before it goes on the market? In February of this year, we participated in the alpine test for the Roewe e950 battery performance project. You can see how the engineers performed the alpine test on the battery system. See if the car battery is as cold as the battery of ordinary electrical appliances? (Since the e950 was still in the confidential stage when we tested it, the test vehicle used a regular gasoline version of the body.)

■ The technical structure of e950

Before introducing the alpine test project, it is necessary for us to briefly understand the power system of the Roewe e950, so that we can better understand the operating mode of the car and the importance of our alpine test battery project. Let’s talk about the power system first. Simply put, it can be summarized as “dual-core, triple-core, and eight-mode”. “Dual-core” refers to the e950 equipped with both gasoline engine and electric motor power systems; “three-core” refers to It is equipped with a 1.4TGI turbocharged engine, ISG (Integrated Starter Generator) starter and generator, TM (Traction motor) traction motor three-core power, “eight mode” means that it has 7 drive modes plus charging There are 8 operating modes in total. According to the manufacturer's data, the car has a maximum cruising range of more than 600km, a comprehensive road cruising range of 60km in pure electric mode, and an official comprehensive fuel consumption of 1.7L/100km.

e950 and e550 power parameter table

Model e950 e550
engine 1.4T 1.5L

Maximum engine power (kw/hp)

110/150 80/109

Engine maximum torque (N·m)

235 135
Maximum power of ISG motor (kw/hp) 32/44 23/31
Peak torque of ISG motor (N·m) 150 147
TM motor maximum power (kw/hp) 60/82 44/60
TM motor peak torque (N·m) 318 317

The power structure of e950 and e550 are similar. They both use one engine and two electric motors. The main difference is that e950 uses a 1.4T turbocharged engine, which is superior in performance to the 1.5L naturally aspirated engine used by e550. , The power parameters of the two motors of the e950 are also higher.

In addition to 6 driving modes, e950 also has an idle charging mode and an external charging mode. Combining 8 modes, only the engine only works under high-speed and uniform-speed driving conditions. In other cases, the motor will start. As long as the motor is started, it means that the battery enters the working state. Whether it is accelerating or braking, the battery will not work. Will be idle. To put it bluntly, the two motors are still working in rotation, but the battery is basically always switched between charging and discharging, and the work is not only busy but also very important.

Compared with the current lithium iron phosphate battery used in the e550, the e950 is replaced by a nickel cobalt manganese lithium battery (referred to as a ternary lithium battery). Compared with other types of batteries, it has the characteristics of high energy density and moderate safety. According to manufacturer's data, SAIC's self-developed battery management system BMS has set two data collectors to detect the remaining power with an accuracy of 1%, which is better than the industry average of 8%. (Friends who are interested in SAIC new energy technology can click here to check previous technical articles)

The battery capacity of the e950 is 11.8kWh. If you use a high-voltage charging device to charge it, it can be fully charged in 3 hours. Official data show that it can travel 60 kilometers on pure electric power when fully charged, which can basically meet the needs of most people for commuting to and from get off work a day. In theory, users of e950 may not need gasoline when they are charged once a day. The actual situation is that the six driving modes of the e950 hybrid system are automatically selected by the computer, and the owner cannot specify the pure electric mode. In the daily use of the car, it should be said that there will be engine intervention. Circumstances, so the actual experience of using the car should be very fuel-efficient, but it will not completely burn off the fuel.

After a brief introduction to the hybrid system of the e950, it can be seen that although the battery capacity of the car is not large, it plays a very critical role in the power system, and the battery is basically continuously charged during daily driving. In the discharging operation, these two actions will actually cause the battery to heat up, so when the vehicle is running, the heat dissipation of the battery is more important than the heat preservation.

■ Introduction to e950 battery pack

The battery pack of the e950 is independently designed by SAIC, while the battery cell is provided by the supplier. The battery cell uses a ternary lithium battery. In terms of structure, it meets the requirements of IP67 and is relatively reliable in terms of safety. For the battery pack, safety alone is not enough, but performance can meet the requirements. In order to allow the battery to work at a suitable temperature, the battery pack has a water-cooled heat dissipation system and a thermal pad under the battery module. Cooling plates and cooling pipes take away the excess heat. In terms of heat preservation, it is relatively simple, mainly relying on the heat preservation/flame retardant layer inside the battery pack for heat preservation.

People think that lithium batteries will consume more power in winter because the temperature affects the speed of the battery's chemical reaction. Too low temperature causes the chemical reaction of the lithium battery to be slow, so the discharge current becomes smaller, which directly leads to the usability of the battery. The capacity is reduced. This situation will also appear on the car battery, but due to the e950's operating mode, the battery will be charged/discharged frequently, and the battery temperature will quickly rise to the normal operating temperature.

According to engineers, the temperature of the battery is generally higher after working, and the thicker insulation layer makes it difficult for the battery to cool down, so even in winter, the temperature will not be too low even if it is parked for a few hours. As far as this technical solution is concerned, what needs to be enhanced is the heat dissipation performance of the battery pack, so a water-cooled heat dissipation system is adopted.

■ Introduction to e950's alpine test location and venue

The location of this high-cold test is Heihe, which is on the edge of the subarctic zone, separated from the city of Blagoveshchensk in Russia by only a line of Heilongjiang. The average annual temperature is -1.3-0.4 ℃, and the daily minimum temperature is minus 40. ℃. Due to the severe cold weather here, as well as the road conditions in mountainous areas, lakes and cities, many domestic auto manufacturers choose to conduct alpine tests here. SAIC is also one of the first manufacturers to establish an alpine test center here.

Roewe e950 conducts alpine tests at the Heihe test base of SAIC, where there are test sites with various terrains, three freezer warehouses dedicated to freezing vehicles, and necessary indoor maintenance and charging equipment. When the outdoor temperature does not reach the required temperature, the engineer will drive the car into the freezer for freezing. Let's take a look at what projects will be carried out in the alpine test of hybrid models?

■ Introduction of testers and equipment

Vehicle testing has not always been done by one or two people. Each test requires the cooperation of an entire team. The same is true for the e950's alpine test. At the Heihe test base, we saw that in addition to three battery system testers, there were also engineers from the New Energy Department who were mainly responsible for gearbox calibration, as well as engineers for subjective evaluation and durability testing.

Here is a brief introduction. The CAN in Figure 2 above refers to the (CAN-BUS) bus technology, which is called “Controller Area Network-BUS” in full. This kind of bus network is used in the car. Transmission of various computer data. The calibration software analyzes the condition of the vehicle by reading the sensor data on the vehicle.

The hardware equipment tested is basically the same as the fuel version. It also uses specific instruments to collect vehicle information. At the same time, use INCA and other software to read the data and analyze it. Below we will show the corresponding test data screenshots according to different items. .

■ Introduction of e950 test items

At the end of last month, SAIC conducted a water-soaking experiment on the batteries of its hybrid models in a technical briefing session, so that everyone can see the battery packs that have been soaked in water for a week in the fish tank. In fact, there is no inside. Water shows that the sealing of the battery pack is still reliable. The airtightness alone is not enough, we have to see whether the performance of this battery pack meets the requirements under the high-cold conditions. Since the e950 has been tested in a comprehensive way before, this time it is mainly to verify battery items, so most of the items tested are related to the battery management system (BMS).

● Cold start under extreme cold conditions of -30 degrees Celsius

As mentioned earlier when talking about the structure of the battery pack, the battery is generally difficult to completely cool down, and the requirement for the cold start test is to start the vehicle at -30 degrees Celsius. To let the battery drop to this temperature, it needs to be cold-started. When the ambient temperature reaches -30 degrees Celsius, it will freeze for about 8-10 hours.

Because there are still various road test projects to be done during the day, the cold start is usually arranged in the first project of the day. The vehicle is frozen in the cold storage overnight. After reaching the “freeze through” standard in the engineer’s mouth, the engineer will take a risk. At the risk of being “frozen through”, he entered the freezer for a cold start test.

Of course, the actual operation is not complicated. First, connect the wires and use the computer to read the battery temperature. After reaching the standard of -30 degrees Celsius, the engineer can perform the cold start test. What the engineer has to do is to press the one-key start button to see if the vehicle is successfully started at one time and record various information of the vehicle at the same time.

I have also participated in cold-start tests of other brands before, and there are also cold-start projects, but they are all carried out in an outdoor environment. This is the first time to observe cold-start tests in a cold storage. It gives me the feeling that the cold storage is much colder than the outdoors, and it is prone to fog in the cold storage. Friends who wear glasses can imagine the frosting of the lenses, and the air-conditioning air from the air-conditioning vents around them is blowing “breathingly” around them. After that, the feeling of cold has been strengthened even more.

To be honest, if it is outdoors at -30 degrees Celsius, it is okay to let me stay for half an hour, but in this cold storage, I can't stand it for 5 minutes. In my opinion, the engineers are almost unafraid of the cold. From wiring, starting, collecting data to finally driving the car out, they didn't see them trembling. Afterwards, I asked the engineers whether they were cold or not. In fact, they also felt very cold, but this is a rigorous job for them.

● Monitor changes in battery status during driving

The importance of batteries has already been introduced in the previous article, and how to use these batteries well depends on the battery management system (BMS). The system also has the function of real-time monitoring of each battery cell to ensure the safe and reliable use of the battery. . As mentioned earlier, the battery will continue to charge/discharge during driving, but overcharge and overdischarge will affect the battery life, so BMS is to avoid this situation.

One of the items in this alpine test is to monitor the change of battery power. Here we need to understand the concept of remaining power (SOC), because the performance of the battery pack is determined by the smallest power cell in the battery, similar to the principle of wooden barrels. Therefore, monitoring and controlling the remaining power of the battery is a key function of the BMS. Specific to the actual car environment, what engineers need to verify is whether the SOC change is within a reasonable range and the battery charge/discharge current is within a reasonable range when encountering various extreme car usage conditions in a low temperature environment. Next, we will explain in three situations.

1. Rapid acceleration: Test the discharge capacity of the battery

In the hybrid mode, when the vehicle is fully accelerating, both electric motors need batteries to provide power. At this time, it is necessary to test whether the discharge capacity of the battery can meet the demand. In the actual test, the engineer has been accelerating the vehicle to a speed of 185km/h from a standstill, and the battery can basically maintain a discharge current of more than 130A, which is sufficient to meet the acceleration demand. The BMS current limit system can limit the battery discharge current to no more than 160A, ensuring that the battery will not be shortened or damaged due to over-discharge.

2. Sudden deceleration: test the control of charging current

Sudden deceleration is a situation often encountered in daily cars, which involves the possibility of excessive instantaneous charging current (kinetic energy recovery), which requires engineers to verify the actual value of the car in different environments Is it within the range originally set?

The charging current of the battery is actually related to the kinetic energy recovery of the vehicle. If the speed of the vehicle is higher, the corresponding kinetic energy will be greater, and there will naturally be a greater charging current. Will the charging current exceed the preset value when the vehicle is braking at high speed , Thereby causing overcharge to the battery, which requires engineers to actually verify.

During this test, the engineer increased the vehicle speed to close to 200km/h, then braked with full force, and quickly reduced the vehicle speed to 100km/h to test whether the charging current of the battery would be when the car was braking at high speed. Exceeds the preset range.

From the actual data later, when the vehicle is braking at high speed, the measured battery recovery current continues to be in the range of 150A-100A, which meets the requirements of the BMS, and there is no overcharge.

3. Daily driving

In addition to targeted testing of some extreme driving conditions, engineers also simulate the daily use of ordinary users in their cars and monitor the changes in battery power during daily driving. Today's test engineers recorded daily driving data of 15 kilometers.

As can be seen from the figure, the speed of the car is constantly changing, and it is more consistent with the conditions of the commonly used cars in recent days, and the current has been switching between charge/discharge. The power of the battery has been changing, but it basically fluctuates around 20%. , Which shows that the BMS controls the remaining power in place, can maintain the battery power not too low, and ensure the safety and service life of the battery.

Don't think that the work of engineers can end during the day. In fact, after parking the vehicle, it is the beginning of another work. The data collected during the day must be sorted and analyzed at night, and the vehicle can be adjusted or verified the next day. In fact, this is also a common phenomenon in the automotive industry. After all, the market is fiercely competitive, and manufacturers are speeding up launching new cars. To ensure quality, engineers behind the scenes need to work harder.

■ Summary

Through participating in the high-cold test of Roewe e950, we can conclude that the battery of Roewe e950 can withstand the test of severe cold weather, whether it is a cold start at -30 degrees Celsius or driving in a low temperature environment, the battery The working conditions are basically in line with the design requirements.

In addition, because the Roewe e950 cannot be driven in pure electric mode manually by the driver, the switching of the six driving modes is completely automatically completed by the computer, so we did not test whether the driving range of pure electric mode changes at low temperatures. It can be said that the battery management system will start the engine to charge the battery when the power is low (such as less than 20%), and when the power is sufficient, it will appropriately reduce the intervention of the engine to keep the engine in the most economical operating range. To achieve the best fuel economy. (Photo/text/photograph by Liang Haiwen, the home of the car)