Lei Feng network press: The author Ye Lei Ray, acting technical engineer.
(Tesla Motors, Via:tocks.org)
Since the listing of the Model S, it has been dismantled by numerous people. It also confirms Tesla’s initial position in the electric vehicle market.
| Powertrain compositionThe Model S powertrain is mainly divided into the following sections:
Power Battery System ESS
AC induction motor Drive Unit
Car Charger Charger
High Voltage Distribution Box HV Junction Box
Heater PTC heater
Air conditioning compressor A/C compressor
DC Converter DCDC
The Model S uses a three-phase AC induction motor and integrates the motor controller, the motor, and the transmission case. In particular, the motor controller is also packaged in a cylindrical shape that corresponds to the motor and looks like a double motor. From the design point of view, high integration and symmetrical appearance. The gearbox in the middle uses a fixed ratio (9.73:1) solution. 85KWh version of the motor peak power 270KW, torque 440Nm.
The charging system supports three charging modes:
1, super charging pile DC fast charge
Super charging pile can directly output 120KW to charge ESS, and it can be filled within one hour.
2, high power wall charging
There are two car chargers under the rear seats, one from the main. The main charger is the default open use, power 10KW, almost 8 hours full. Although the slave charger's hardware is already installed in the car, it requires an additional payment of 18,000 to activate and double the charging capacity. This kind of hardware has already been configured well, and later through the license fee and IBM's server exactly the same way. At present, Tesla has already applied this strategy to power batteries. Actually, more than 70 kWh is installed on the 60th version. The reserved capacity just avoids full discharge, which helps to prolong the battery life. Therefore, it is also a low-cost version. A cost-effective choice.
3, 220V home socket charging
The charging power is about 3kw, and it is fully charged for about 30 hours. By placing the charger on the car, it is possible to use an ordinary household plug to charge the battery even when it is not completely charged.
What's interesting about the thermal management part is that the Model S uses a four-way switching valve to achieve series-parallel switching of the cooling system. The purpose of my analysis is to select the optimal thermal management method based on operating conditions. When the battery needs to be heated at a low temperature, 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 a high temperature, the motor cooling circuit and the battery cooling circuit are connected in parallel, and the two cooling systems independently radiate heat. This type of thermal management is still clever.
Take a look at the PACK before it is disassembled. There are a total of 3 sets of interfaces. They are the low-voltage interface, high-voltage interface, and cooling interface, respectively, and all adopt the quick-insertion scheme. It shows that Tesla fully considered the technical requirements of the battery change mode when designing the battery system. Even though there is very little demand for replacement, the gene has remained. The thick Pin in the high-voltage connector plays a role in positioning on the one hand, and it is also a grounding point. The fine Pin is used to realize the high-voltage interlock function.
A waterproof breathable valve is designed on the top surface of the front of the PACK. The difference in volume size between the gas molecules and the liquid and dust particles allows the gas molecules to pass through, and the liquid and dust cannot pass through, thereby achieving the purpose of waterproof and breathable and avoiding water vapor in the PACK. Internal condensation.
The upper part of the PACK uses a lot of fixing screws, so the white insulating pad is glued to the Pack, which not only plays the role of insulation and fire protection, but also can play a certain waterproof role. The top cover of the PACK is glued to death. Even if all screws are removed, it cannot be opened. I remember that in the hot summer of 14 years, we seven or eight people were "born hard" for an hour before they could be destructively opened. At that time, Tesla felt that the design of the Tesla must be an axe-breaking idea. He did not intend to repair it afterwards. Therefore, there was no manual maintenance switch on the PACK, leaving only one fuse replacement port.
Tesla lower trays use aluminum alloy profiles as the main carrier frame skeleton, and the bottom of the frame is welded with aluminum plates. The dismantling is a 85KWH high version, with two modules stacked on the far right. A large number of explosion-proof valves (a total of 85) are arranged on both sides of the PACK. During the dismantling process, it has been found that PACK always uses isolated insulation plates to separate the high-voltage devices. The way to fix the insulation plates is usually glue. It is difficult to imagine such complexities as using dog's skin plaster to fill patches in the PACK. How the process is carried out during the mass production process. Guessing that the inadequacy of the design at the beginning of the design led to the follow-up can only be done by patching.
BMS is almost completely exposed inside PACK. It may be to reduce weight, but it also brings certain risks.
The water cooling system between Modules uses a parallel structure rather than a series connection . Its purpose is to ensure that the cooling fluid flowing into each Module has a similar temperature .
The high-voltage electrical connections between Modules use a left-right staggered arrangement rather than a simpler connection from the tail to the top of the PACK and back to the tail from the top. The guess is to prevent the formation of large current loops and thus generate strong radiation interference.
The current sampling uses only an ISAscale industrial grade Shunt to communicate with the BMU over the SPI bus. Prior to the standard Roewe E50 A123 power battery solution, it uses shunt and Hall dual backup measures. After all, the current value is an extremely critical parameter in the ESS system.
| Battery Modules
Due to the selection of NCA's batteries , Tesla is far ahead in terms of energy density, and Pack's energy density is higher than that of many models of Cell. The following figure shows the differences between high and low modules. The low module has 10 cells less and the serial number is 6 strings. Therefore, there is not much difference for battery management. It can be seen from the bus board that the color of the part connected to Busbar is obviously different. Here, the surface is plated with nickel to prevent oxidation.
Module heat exchange design Because Tesla selected the 18650 battery will inevitably lead to the Coolant pipe must be designed to be extremely complex, and the battery is firmly fixed in the Module with glue, completely without the possibility of maintenance and ladder utilization. I3 and Volt, which use square batteries, are more convenient for the integration of batteries and cooling systems.
Volt has designed a heat dissipation layer between each cell, making the heat exchange area larger and better. It is speculated that such a scheme may become mainstream in the future.
| Battery Management System BMSThe BMS employs a master-slave architecture. The master controller (BMU) is responsible for functions such as high voltage, insulation detection, high voltage interlock, contactor control, and external communications. The slave controller (BMB) is responsible for cell voltage and temperature detection and reporting to the BMU.
The BMU has master and slave dual MCU designs. The slave MCU can detect the master MCU's working status and obtain the control authority once it is found to be invalid. More humorous is that there is actually a manual reset button on the BMU. When you just saw it, you can't believe that this is an automotive product-level ECU. It's more like a computer motherboard. It is also a bold design to place a pre-charge contactor with an excessively high current directly on the BMU.
The following figure shows the comparison between the BMB monitoring module of Tesla, BMW i3 and A123. The specific parameters are as follows:
The Tesla legend has detected more than 7000 cell voltages. In fact, only 74 cells are tested in parallel in one point. According to legend, the temperature of each cell is monitored. In fact, only 444 cells have two temperature detection points. According to the legend, each battery can be balanced. In fact, the balance current is only 0.1A, which is a good deal for a 230Ah battery. Especially in the redundancy design of voltage monitoring, BMW (preh) adopts LT6801. A123 adopts IC8 for hardware comparison. Once the MCU fails or the communication is abnormal, the alarm can be triggered directly on the hardware. In contrast Tesla is designed more simply. In particular, the use of UART communication instead of CAN is more like an IT company's solution.
| Single Cell Cell 
From the perspective of the Spec provided by Panasonic, the decay rate of the 500cycle is reduced to 68% when the capacity is reduced to the BOL state under the condition of 0.5C charge/1C discharge (100% DOD).
The same is the 1C/1C charging and discharging 150cycle experiment, the comparison of the above figure I3 and Model S battery.
The above several cycle life data is a good example of why the Model S broke through the huge 85 kwh battery in the passenger car . Panasonic 18650 battery has a poor cycle life at a magnification of about 1C. Therefore, high capacity must be adopted to reduce the rate under the same conditions to ensure a longer cycle life; at the same time, a large-capacity battery also ensures that the number of cycles of the vehicle in the entire life cycle is sufficiently small. Calculated according to 100 kilometer power consumption 20KWH, 200,000 kilometers is only 470cycle for 85KWH PACK.
As more battery companies target the standardization and mass production of customized batteries in the automotive field, the advantages of low cost and high consistency of 18650 batteries will quickly disappear, even if Tesla once hoped to win the technical route station through open patents. Seemingly not successful. The openness of patent gimmicks and publicity is more than practical.
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However, in the era when the electric car supply chain was still immature, Tesla was almost always relying on excellent technology integration ideas to “compact†a variety of non-automobile-grade products.
Therefore, it is hard to say that Tesla has done a better job on power batteries than traditional car companies. It would be better to say that Tesla did what they did not dare to do . The complete supply chain system of traditional car companies, long-term accumulation of standards and specifications, and huge market share have all contributed to the promotion of electric vehicles.
Tesla can no longer afford to abandon the automotive supply chain in the selection of industrial-grade products, you can temporarily put Autosar, ISO26262, etc., you can not worry like the traditional car companies go too aggressive in the electric car technology, resulting in a fire Accidents such as loss of control have affected the sales of traditional models. But has Tesla and traditional car companies still enjoyed competitive advantage under this set of historical conditions? I think definitely not.
What should Tesla's core competitiveness be? Battery management software algorithm.
| Tesla's core strengths lies in the underlying technologyPersonally think that battery management technology is not the core strength of Tesla, but the basic technology. Like Lisa PC's core technology introduced by Apple in 1983, it is by no means using a mouse. The 2001 iPod core technology is not based on a 1.8-inch hard disk.
In 2014, the first batch of domestic Tesla had the privilege to participate in the Model S dismantling and was mainly responsible for the Benchmark of the ESS section. It must be said that when the project was completed, the mystical aura and legend of Tesla faded. Just as the US military seized the first MiG 25 fighter jet and was thrilled to explore its strong performance, it did not find that there was a clear and subversive breakthrough in basic technology. It can be said that Tesla is not superior to every detail technology, and even some parts of the design are slightly sloppy (such as the low integration of the ESS system makes the manufacturing process and the late maintenance difficult, more non-automotive components and solutions The risks brought about by the application, etc.) But after integrating all the sub-components that were not perfect in the eyes of the engineers, they still wanted a stunning product.
Tesla's achievements are more accurate in the definition of products than technical core advantages. Why does Japan not have high-performance electric vehicles because it has a strong vehicle manufacturing capability and lithium battery technology?
Because at the time (even now), they did not think that such a product was safe enough and the price was acceptable. Why even after the Tesla's market value has been proven, German car companies are still not slow on the advancement of electric vehicles, because their technical standards to set Tesla products, whether it is design selection or manufacturing process is not mature. As a brand-new automobile company, not possessing a long-term accumulation of knowhow may hit the reef that the former people already knew should avoid, but at the same time, it may also discover the new continent first because it removes the burden of various restrictions.
At present, there are more and more new entrants in the auto industry. You can use the changes in the mobile phone industry in the past 10 years as a reference. During the decline of Nokia, the rise of Apple and Google is not only the competition of enterprise strength, but also the communication industry chain. Competing with the computer software industry chain to compete for mobile phone attributes. If the mobile phone is a communication technology-driven product, then Apple and Google may not necessarily be Nokia's rivals. When the mobile phone becomes a product promoted by the computer and software industry, the supply chain and Apple, which compiles applications for Nokia, and fully interoperates with mobile phones and PCs, Google is not an order of magnitude better than it is natural. How can we have a chance of winning?
In the same way, what do we think of the properties of the car in the future? Is it an excellent vehicle to control performance, or is it an intelligent robot capable of manned movement? The definition of this attribute will determine whether the traditional car companies will continue to occupy supply chain advantages in future production, manufacturing, and sales, or whether high-tech companies with artificial intelligence and cloud computing technologies as core businesses will account for the future industrial supply chain structure. Large proportion.
Therefore, Tesla's technology in the field of power batteries is not only an advantage over traditional car companies, but may be a disadvantage in the future. Instead, drones are their straws to save lives.
| written in the backOnce you look at the product from the engineer's standpoint, you can often uncover the perfection that the company wants to create. After all, the process of product design must be a process of compromise and choice, and companies often try to use concepts such as “not compromise†and “not to be like†(such as some domestic mobile phone companies) and the nature of design in product marketing. Violation.
But when he is a consumer, Tesla is still very attractive to me . The source of its attraction is not the use of advanced or backward technology, but the product quality that surpasses the technology stacking and performance parameters . This temperament is what many people want and other models can not give, I think this It is Tesla's most successful place.
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