The influence of new energy vehicles on automatic transmission is analyzed

2019-12-02
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  I'm afraid most readers will find this topic a little strange. According to the theory, new energy vehicles and automatic gearboxes should coexist peacefully. But in fact, from the traditional vehicle to the new energy vehicle architecture changes a more important link is the transmission. In the traditional sense, the automatic gearbox will become a major shortcoming of the new energy vehicle structure to a large extent because of its structure. Careful readers should also note that a large proportion of new-energy vehicles, especially the more complex plug-in hybrids, do not have automatic transmissions, either dual clutch or CVT. Of course, there are still some automatic transmission tradition, but these cars have the automatic transmission and the traditional automatic transmission is completely different. After all why, wait for author detailed way to come.
  Why the traditional automatic transmission is not suitable for the use of new energy vehicles. To understand the emotional entanglements between automatic transmission and new energy vehicles, we need to start with the structure of automatic transmission and new energy vehicles. So it's easy to see.
  First, the traditional automatic transmission. The main body of traditional automatic transmission is composed of planetary gear mechanism and hydraulic torque converter. Among them, the planetary gear mechanism is responsible for the transmission speed ratio changes, in other words, to determine the transmission gear position. Before the planetary gear, a hydraulic torque converter was used to realize the flexible connection between the traditional system and the engine. From the working principle of hydraulic torque converter, it is not difficult to find that hydraulic torque converter is the transmission of transmission oil through regulating wheel, pump wheel, turbine and other structures to apply power. Simply put, a torque converter transfers power through hydraulic fluid.
  Look at the architecture of new energy vehicles, pure electric vehicles are certainly not in our discussion, because the constant power constant torque output characteristics of pure electric motors do not need gearbox such a device, only a set of reducer is enough to meet the needs of pure electric vehicles. The point here is that the architecture is more complex, the transmission of power is more hybrid and plug-in hybrid models. From the perspective of practical conditions, both hybrid and plug-in hybrid models can provide power independently or work together at the same time. And the power transfer to the wheel on the power path and only one set, that is, the gearbox, transmission shaft, main reducer, half shaft and other parts. Then the problem comes, as the saying goes, a mountain cannot tolerate two tigers, two sets of power output needs to achieve synergy in the place of the gearbox. To be more specific, you need to distribute power at the end of the output from the engine or motor. In a conventional automatic transmission, this position is the position of the torque converter.
  However, from the principle of hydraulic converter, it is not difficult to find that the hydraulic converter through the hydraulic oil transmission of power to ensure the flexible connection, but a feature of hydraulic transmission can not be transferred in the reverse of the problem. Simply put, it's ok for the engine to drive the torque converter to the planet gear, but not for the planet gear to drive the torque converter to the engine, so this is why automatic transmission vehicles are prohibited to glide in neutral. So for hybrid and plug-in hybrid models, one of the working condition of working is the motor and the engine does not work, and when the electric motor to drive the vehicle without the addition of transmission, so in this case, to use motor driver means that the hydraulic torque converter is in a state of inversion, will inevitably lead to hydraulic torque converter. Therefore, from the perspective of vehicle architecture, the traditional automatic transmission is not suitable for hybrid or plug-in hybrid vehicles.
  So, does this mean that automatic transmission will be out of the question with new energy vehicles? Of course not. In general, the industry has several solutions.
  First, the solution can be the power transfer architecture to solve this problem, the typical representative is the zf 8HP automatic transmission. The gearbox is electrically powered by placing the motor behind the torque converter and adding a liquid-cooled clutch called HCC. To a large extent, the transmission of the 8HP gearbox is mainly driven by HCC. In fact, the transmission assembly itself is a hybrid system, because the motor is located in the rear of hydraulic torque converter, so the motor drive sub under the condition of the hydraulic torque converter and engine, and then through the liquid cooling clutch locking speed ratio to achieve electric drive, but trapped in the gearbox arrangement of the space, the power of the motor tend not to be too big, so the structure can only mixed system is weak. However, for the architecture of split-axis plug-in hybrid electric vehicle, this arrangement can completely avoid the inversion of hydraulic torque converter. Therefore, such an architecture is the mainstream configuration mode of plug-in hybrid electric vehicle.
  Second, the architecture to solve the automatic transmission torque converter inversion problem is to place the motor in front of the torque converter. The motor is used as the driving part of the torque converter, and the connection between the torque converter and the engine is realized through the clutch device. There is no drag - back problem with this architecture. However, this architecture is not suitable for the split shaft hybrid power architecture, in which the rear axle is the main power source under the motor driving condition, and this architecture cannot avoid the occurrence of hydraulic converter inversion.
  Third, the solution is much more straightforward, simply abandoning the automatic gearbox and replacing it with a CVT or dual-clutch gearbox. However, this is already the domain of another structure, which is beyond the scope of our discussion today. So I'm not going to talk about that.
  Through analysis, it is not difficult to find that the first problem to be solved when automatic transmission is matched with hybrid and plug-in hybrid models is the inversion problem of hydraulic torque converter. Among them, the architecture that puts the motor behind the hydraulic converter is adopted by most current plug-in hybrid models. In the previous article, the author also said that, thanks to the advantage of the platform layout and performance advantages, points shaft plug-in hybrid system in the future will become the mainstream of plug-in hybrid vehicles structure, so in this case, the motor is located in the structure of hydraulic torque converter rear will more be adopted by new energy vehicles. Therefore, the arrival of the new energy era does not mean that automatic transmission will go far, on the contrary, automatic transmission will continue to play its due role in the new energy era with the characteristics of large torque output.

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