Analyze the impact of new energy vehicles on automatic transmissions
Seeing this topic, I am afraid that most readers will find it a little strange. It stands to reason that new energy vehicles and automatic transmissions should be in a peaceful coexistence relationship. Why did the author suddenly talk about this topic. But in fact, the most important part of the change from the traditional vehicle to the new energy vehicle architecture is the gearbox. The traditional automatic transmission will become a major shortcoming affecting the entire vehicle structure of new energy vehicles to a large extent because of its structural relationship. Therefore, careful readers should also find that a large part of new energy vehicles, especially relatively complex plug-in hybrid models, do not use automatic transmissions, either dual clutches or CVTs. Of course, there are also those that continue the tradition of automatic transmissions, but the automatic transmissions on these cars are completely different from the traditional automatic transmissions. Why in the end, wait for the author to elaborate.
Why traditional automatic transmissions are not suitable for new energy vehicles. To understand the emotional entanglement between automatic transmissions and new energy vehicles, we must start with the structure of automatic transmissions and the architecture of new energy vehicles. So it's clear at a glance.
First look at the traditional automatic transmission. The main body of the traditional automatic transmission is composed of a planetary gear mechanism and a hydraulic torque converter. Among them, the planetary gear mechanism is responsible for the change of the speed ratio of the gearbox, in other words, the gear position of the gearbox is determined. Before the planetary gears, a flexible connection between the conventional system and the engine is achieved through a torque converter. From the working principle of the torque converter, it is not difficult to find that the torque converter is a power transmission realized by applying power to the transmission oil through the guide wheel, pump wheel, turbine and other structures. To put it simply, the torque converter transmits power through hydraulic oil.
Let's look at the architecture of new energy vehicles. Of course, pure electric vehicles are not within the scope of our discussion, because the constant power and constant torque output characteristics of pure electric motors do not require a device such as a gearbox at all. demand for electric vehicles. What's going on here are hybrid and plug-in hybrid models with more complex architecture and more power delivery methods. From a practical point of view, the two types of power available in hybrid models and plug-in hybrid models have the ability to provide power independently or work together at the same time. And there is only one set of power paths for the power to be finally transmitted to the wheels, that is, the gearbox, the drive shaft, the final reducer, and the half shaft. Then the problem comes. As the saying goes, one mountain cannot tolerate two tigers. The coordinated output of the two sets of power needs to be coordinated at the gearbox. A more detailed point is that the power needs to be distributed at the end of the output from the engine or the motor. On a conventional automatic transmission, this position is where the torque converter is.
However, from the principle of the torque converter, it is not difficult to find that although the torque converter transmits power through hydraulic oil to ensure a flexible connection, the biggest feature of hydraulic transmission is that it cannot be transmitted in reverse. . To put it simply, it is no problem for the engine to drive the torque converter to the planetary gear, but it will not work if the planetary gear drives the torque converter to the engine, so this is why automatic transmission models are strictly forbidden to slide in neutral. where. So for hybrid or plug-in hybrid vehicles, one of the working conditions is that the motor works but the engine does not work, and the motor does not need a transmission when driving the vehicle. In this case, rashly using the motor to drive It means that the torque converter is in a reversed state, which will inevitably lead to the burning of the torque converter. Therefore, from the perspective of the whole vehicle architecture, the traditional automatic transmission is not suitable for hybrid or plug-in hybrid vehicles.
So, does this mean that automatic transmissions will miss out on new energy vehicles? of course not. Generally speaking, the industry has several solutions.
The first solution can solve this problem on the basis of power transmission, a typical representative is ZF's 8HP automatic transmission. The transmission achieves electric power transmission by placing the electric 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 the HCC. In fact, the gearbox itself is a hybrid system. Since the electric motor is located behind the torque converter, the torque converter and the engine are shorted in the electric motor-driven condition, and then cooled by the liquid. The clutch lock-up ratio realizes electric drive, but due to the arrangement of the gearbox space, the power of the motor is often not too large, so this structure can only be regarded as a weak hybrid system. For the split-shaft plug-in hybrid vehicle architecture, such an arrangement can completely avoid the reversal of the torque converter. Therefore, such an architecture is the more mainstream configuration of plug-in hybrid vehicles at present.
The second architecture to solve the problem of reverse rotation of the automatic transmission torque converter is to place the electric motor before the torque converter. The electric motor appears as the driving part of the torque converter, and the connection between the torque converter and the engine realizes the power transmission through the clutch device. There is also no problem of anti-drag in this structure. However, this architecture is not suitable for the split-shaft hybrid architecture. In this architecture, the rear axle is the main power source under the electric motor driving condition. This architecture cannot avoid the occurrence of the reverse rotation of the torque converter.
The third solution is more simple and rude, directly abandoning the automatic transmission and replacing it with a CVT or a dual-clutch transmission. However, this is already another category of structure, beyond the scope of our discussion today. So not much discussion here.
Through analysis, it is not difficult to find that the first problem to be solved is the reversal of the torque converter in order to match the automatic transmission with the hybrid vehicle and the plug-in hybrid vehicle. Among them, the structure of placing the electric motor behind the torque converter is adopted by most of the current plug-in hybrid models. In the previous article, the author also said that thanks to the advantages of platform layout and performance, the split-shaft plug-in hybrid system will become the mainstream architecture of plug-in hybrid vehicles in the future. Under certain circumstances, the structure of the electric motor behind the torque converter will be more adopted by new energy vehicles. Therefore, the arrival of the new energy era does not mean that the automatic transmission will go far. On the contrary, the automatic transmission will continue to play its due role in the new energy era with the characteristics of large torque output.