Since the Model S was launched, it seems to have been dismantled countless times, which also confirms Tesla's benchmark position in the early stage of the electric vehicle market. (TeslaMotors, Via: stocks.org) Powertrain composition Model S powertrain is mainly divided into the following parts: 1. Power battery system ESS2. AC induction motor DriveUnit3. On-board charger Charger4. High-voltage distribution box HVJunctionBox5. Heater PTCheater6. Air conditioning compressor A/Ccompressor7. DC converter DCDCModelS uses a three-phase AC induction motor and integrates the motor controller, motor and transmission box into one. In particular, the motor controller is also packaged in a cylindrical shape, corresponding to the motor, and looks like a dual motor. From the design point of view, it is highly integrated and symmetrical. The middle transmission box adopts a fixed speed ratio (9.73:1) solution. The 85KWh version of the motor has a peak power of 270KW and a torque of 440Nm. The charging system supports three charging methods: 1. Super charging pile DC fast charging. The super charging pile can directly output 120KW to charge the ESS, which can be fully charged within an hour. 2. High-power wall-mounted charging There are two car chargers under the rear seats, one master and one slave. The main charger is open for use by default, with a power of 10KW and can be fully charged in about 8 hours. Although the hardware of the slave charger is already installed on the car, it requires an additional payment of 18,000 to activate it, which can double the charging capacity. This kind of hardware has already been configured, and the charging method through license is the same as that of IBM servers. Currently, Tesla has applied this strategy to power batteries. The 60 version actually contains more than 70 kilowatt-hours of electricity. The reserved capacity is just enough to avoid being fully discharged, which helps extend the battery life, so it is also a good idea to buy the low-end version. There are cost-effective options. 3. The charging power of 220V household socket is about 3kw, and it takes about 30 hours to fully charge. Put the charger in the car and you can use ordinary household plugs to charge even in places where there is no charging infrastructure. The interesting part of the thermal management part is that Model S uses a four-way switching valve to realize series-parallel switching of the cooling system. The purpose of my analysis is mainly to select the optimal thermal management method according to the working conditions. When the battery needs to be heated at low temperatures, the motor cooling circuit is connected in series with the battery cooling circuit, so that the motor heats the battery. When the power battery is at high temperature, the motor cooling circuit and the battery cooling circuit are connected in parallel, and the two cooling systems dissipate heat independently. This thermal management method is quite clever. Battery PACK Let’s take a look at the PACK before disassembly. There are a total of 3 sets of external interfaces. They are low-voltage interface, high-voltage interface, and cooling interface, and all adopt quick-plug solutions. This shows that Tesla fully considered the technical requirements of the battery swap mode when designing the battery pack system. Even though there is rarely a need for battery swap now, this gene has always been retained. The thicker Pin in the high-voltage connector plays a positioning role and is also a grounding point. The thinner Pin is used to implement the high-voltage interlock function. A waterproof and breathable valve is designed on the top surface of the front of the PACK. It takes advantage of the difference in volume between gas molecules and liquid and dust particles to allow gas molecules to pass through, but liquid and dust cannot pass through, thereby achieving the purpose of waterproofing and breathability and preventing water vapor from entering the PACK. Internal condensation. There are a lot of fixing screws used in the upper part of the PACK, so the white insulating pad is glued to the Pack. In addition to playing the role of insulation and fire protection, it can also play a certain waterproof role. The upper cover of the PACK is tightly glued and cannot be opened even if all the screws are removed. I remember that in the hot summer of 2014, seven or eight of us "struggled hard and pried it apart" for an hour before we were able to destructively pry it open. At that time, I felt that Tesla must have had the idea of breaking the ax and sinking the ship when designing, and had no plan for subsequent maintenance, so naturally there was no manual maintenance switch on the PACK, and only a fuse replacement port was left. The Tesla lower tray uses aluminum alloy profiles as the main load-bearing frame frame, and a whole aluminum plate is welded to the bottom of the frame. What was disassembled was an 85KWH high-end version, with two more modules stacked on the far right. A large number of explosion-proof valves (85 in total) are arranged on both sides of the PACK. During the disassembly process, I found that scattered insulating boards are always used to separate high-voltage components in the PACK. The way to fix the insulating boards is usually glue, such as using dog-skin plaster to fill the PACK with patches. It is hard to imagine that it is so complicated. How the process works during mass production. It is speculated that insufficient consideration at the beginning of the design resulted in the subsequent helpless patching. The BMS is almost completely exposed inside the PACK, perhaps to reduce weight, but it also brings certain risks. The water cooling system between modules adopts a parallel structure instead of being connected in series. The purpose is to ensure that the coolant flowing into each module has a similar temperature. The high-voltage electrical connections between modules are arranged in a staggered left and right arrangement, rather than a relatively simple connection method from the tail to the top of the PACK, and then from the top back to the tail. The guess is that it is to prevent the formation of large current loops and strong radiation interference. Current sampling only uses an ISAscale industrial-grade Shunt to communicate with the BMU through the SPI bus. The previous benchmark solution for the A123 power battery on the Roewe E50 used shunt and Hall dual backup measures. After all, the current value is an extremely critical parameter in the ESS system. Because the battery module uses NCA cells, Tesla is far ahead in terms of energy density. The energy density of the Pack is much higher than that of the Cell of many models. The picture below shows the difference between the high-end and low-end modules. The low-end module has 10 fewer cells each, and the number of series connections is still 6, so there is not much difference in terms of battery management. It can be seen from the manifold that the color of the part connected to the Busbar is obviously different. The surface here is nickel plated to prevent oxidation. In the module heat exchange design, because Tesla chose the 18650 battery, the Coolantpipe must be designed to be extremely complex, and the battery is firmly fixed in the module with glue, making it completely impossible to repair and use it step by step. The I3 and Volt that use prismatic batteries are more convenient for the integration of battery cells and cooling systems. Volt designed a heat dissipation layer between each cell to make the heat exchange area larger and more effective. It is speculated that this solution may become mainstream in the future. The battery management system BMSBMS adopts a master-slave architecture. The master controller (BMU) is responsible for high voltage, insulation detection, high-voltage interlocking, contactor control, external communication and other functions. The slave controller (BMB) is responsible for cell voltage and temperature detection and reporting to the BMU. The BMU has a primary and secondary MCU design. The secondary MCU can detect the working status of the primary MCU and obtain control authority once its failure is discovered. What's more humorous is that there is a manual reset button on the BMU. When I first saw it, I couldn't believe that it was an automotive product-grade ECU, more like a computer motherboard. Moreover, it is also a bold design to place the precharge contactor for excessive current directly on the BMU. The picture below is a comparison of the module monitoring BMBs of Tesla, BMWi3, and A123. The specific parameters are as follows:

　　It is said that Tesla detected the voltage of more than 7,000 batteries, but in fact it only connected 74 batteries in parallel to detect one point. It is said that Tesla monitored the temperature of each cell, but in fact, the 444 batteries only had two temperature detection points. It is said to be able to balance each battery, but in fact the balancing current is only 0.1A, which is a drop in the bucket for a 230Ah battery. Especially in the redundant design of voltage monitoring, BMW (preh) uses LT6801 and A123 uses IC8 for hardware comparison. Once the MCU fails or communication is abnormal, the alarm can be triggered directly on the hardware. In comparison, Tesla has a simpler design. Especially the use of UART communication instead of CAN is more like an IT company's solution. According to the Spec provided by Panasonic, the capacity of the single cell Cell drops to 68% of the BOL state after 500 cycles under the conditions of 0.5C charge/1C discharge (100% DOD), and the attenuation is relatively serious. It is also a 1C/1C charging and discharging experiment of 150 cycles. The picture above compares the I3 and Model S batteries. The above cycle life data illustrates well why Model S is a breakthrough in installing such a huge 85kwh battery in a passenger car. Because the cycle life of Panasonic 18650 battery is very poor at a rate of about 1C. Therefore, high capacity must be used to reduce the rate under the same working conditions to ensure a longer cycle life; at the same time, large-capacity batteries also ensure that the number of cycles of the vehicle during the entire life cycle is small enough. Calculated based on the power consumption of 20KWH per 100 kilometers, 200,000 kilometers is only 470 cycles for the 85KWH PACK. As more battery companies standardize and mass-produce customized batteries for the automotive field, the advantages of low cost and high consistency of 18650 batteries will quickly disappear. Even if Tesla once hoped to win over technical lines by opening patents, It doesn't seem to be successful. Open patent gimmicks and publicity effects are greater than practical significance. However, in an era when the electric vehicle supply chain was still immature, Tesla almost relied on its excellent technology integration ideas to "cobble" together a variety of non-automotive-grade options to create a product of generational significance. So if we insist on saying that Tesla is better than traditional car companies in terms of power batteries, it would be better to say that Tesla has done something they dare not do. The comprehensive supply chain system, long-term accumulation of standards and regulations, and huge market share of traditional car companies have become a burden when it comes to promoting electric vehicles. Tesla can give up the automotive supply chain and select industrial-grade products without any burden. It can temporarily put aside Autosar, ISO26262, etc., and it does not have to worry like traditional car companies about going too radical in electric vehicle technology and causing fires. , loss of control and other accidents, which affected the sales of traditional models. But will the competitive advantage between Tesla and traditional car companies still be the solution under this set of historical conditions? I guess not. So what should be Tesla’s core competitiveness? Battery management software algorithm. Tesla's core advantage lies in basic technology. I personally believe that battery management technology is not Tesla's core advantage, but basic technology. Just like the core technology of the Lisa PC launched by Apple in 1983 did not lie in the use of a mouse, the core technology of the iPod in 2001 did not lie in the 1.8-inch hard drive. In 2014, I was lucky enough to participate in the disassembly of the Model S when the first batch of Teslas were launched in China, and was mainly responsible for the Benchmark of the ESS part. I have to say that when the project was completed, the mysterious aura and legend of Tesla faded a lot in my mind. Just like when the US military captured the first MiG-25 fighter jet, it was so excited that it wanted to find out the details of its powerful performance. However, it found no obvious disruptive breakthrough in basic technology. It can be said that Tesla is not superior in terms of every detailed technology, and even the design of some parts is slightly sloppy (for example, the low integration of the ESS system makes the manufacturing process and later maintenance difficult, and there are many non-automotive grade parts and solutions. risks brought by the application, etc.), but after integrating all the sub-components that are not perfect in the eyes of engineers, a stunning product is still ready to come out. Tesla's achievements are more about accurate grasp of product definition rather than core advantages in technology. Why has Japan, which has both strong vehicle manufacturing capabilities and lithium battery technology, no high-performance electric vehicles? Because at the time (and probably even now) they simply did not believe that such a product was safe enough and that the price was acceptable. Why, even after proving Tesla's market value, are German car companies still slow to promote electric vehicles? Because applying their technical standards to Tesla's products, whether it is design selection or manufacturing technology, is simply not enough. Mature. As a brand-new automobile company without long-term knowledge accumulation, it may hit the rocks that predecessors have long known to avoid, but at the same time, it may also be the first to discover a new continent by unloading the burden of various restrictions. At present, there are more and more new entrants in the automobile industry. We can take the changes in the mobile phone industry in the past 10 years as a reference. During this period, the decline of Nokia and the rise of Apple and Google are not only competitions in terms of corporate strength, but also competition in the communications industry chain. Competition with the computer software industry chain for mobile phone attributes. If mobile phones are still products driven by communication technology, then Apple and Google may not necessarily be Nokia's rivals. But when mobile phones become products driven by the computer and software industries, then the supply chain for writing Apps for Nokia and fully interoperating mobile phones and PCs will be the same as Apple, Naturally, Google is not in the same order of magnitude, so how can it have a chance of winning? In the same way, let’s imagine what the attributes of future cars will be? Is it a vehicle with excellent handling performance, or an intelligent robot that can carry people around? The definition of this attribute will determine whether traditional car companies will still occupy the supply chain advantage in future production, manufacturing, and sales, or whether high-tech companies with artificial intelligence and cloud computing technology as their core businesses will occupy a larger share of the future industrial supply chain structure. Large proportion. Therefore, Tesla's technology in the field of power batteries is not only not an advantage compared to traditional car companies, but may actually become a disadvantage in the future. On the contrary, driverless driving is its life-saving straw. As written below, once you look at the product from the perspective of an engineer, you can often reveal the perfection that the company wants to create. After all, the process of product design must be a process of compromise and trade-offs, and companies often try to use concepts such as "no compromise" and "no compromise" in product marketing (such as some domestic mobile phone companies), which is inconsistent with the essence of design. Contradictory. But when I am a consumer, Tesla still has a strong appeal to me. The source of its appeal does not lie in the use of advanced or backward technology, but in the product's temperament that is above the technology stack and performance parameters. This temperament is what many people want but cannot be given by other models. I think this This is probably Tesla’s most successful place.

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