Illustration of automobile electric drive system: finally, Tesla driven by gearbox.
Take the best electric car Tesla Model S P85 (hereinafter referred to as Model S) as an example. You can easily win it at first, but you will often lose to your opponent in the middle and late stages. The reason lies in Tesla's matching single-stage gearbox, which makes Tesla always use the first gear to complete the driving from the start to the top speed. This is equivalent to driving a fuel car, starting from the first gear and driving without shifting gears, until the speed is pulled to the red line area, the engine cannot return to the optimal torque output range, and the acceleration power is greatly weakened. Similarly, Tesla &; The potential for further acceleration of ldquo. It is also dragged down by this single-stage gearbox blocking the world one by one, and will be surpassed by opponents in the middle.
Illustration of automobile electric drive system: single-stage gearbox reduces Tesla's endurance potential.
The torque output of the motor brought by the single-stage gearbox can be achieved overnight, and the uninterrupted power output may be beneficial to the starting acceleration, but it is not conducive to the rationality and comfort of the car. Especially Model S, which uses high-speed motor for performance, is equipped with high-speed motor with high power consumption, and the first gear ratio of single-stage gearbox is large, which makes the car cruise at high critical speed, which is unreasonable.
As for how serious the efficiency discount is, you can look at the battery capacity of 47.5 kWh. The best battery life is about 250 kilometers, and the Model S is equipped with a lithium battery pack with a capacity of 85 kWh. It is best to last for about 400 kilometers. Tesla is almost twice as high as Tengshi, but its battery life has not doubled.
Automobile electric drive system diagram: What are the advantages of multi-speed gearbox?
The power output loss of multi-speed gearbox is smaller than that of fixed gear, which can improve the power output efficiency of engine, which is the key for R &:D people to pursue the ultimate gear of gearbox tirelessly. Considering the problems of light weight and large volume, the gearbox does not necessarily increase gears indefinitely. Therefore, if we can match a multi-speed gearbox, reasonable speed ratio range and optimize the timing of motor power explosion, the rationality will be greatly improved, and the continuous acceleration performance will follow.
After talking about the disadvantages of one gear and the advantages of multiple gears, electric vehicle manufacturers are still using single gearbox. Why bother? The key point is that the advantage of single stage is extremely compact structure and much smaller volume than ordinary gearbox. It doesn't need a clutch (the output shaft of the motor is directly connected to the gearbox, not the flywheel of the internal combustion engine), and the electronically controlled gear shifting structure is simpler and more reliable than hydraulic pressure. Single-stage gearbox is widely used because its advantages outweigh its disadvantages, and its key performance has met the current use. This is not to say that manufacturers have given up improving rationality, but there is no time to take care of it at present. GKN has introduced a two-stage gearbox for mass-produced motors. Although the number of gears is not worthy of the name, it is still better than the single-stage gearbox in terms of performance symptoms after the installation and configuration of the BMW i8.
Schematic diagram of automobile electric drive system: first realization &; Ldquo is a lot. Gear, i8 two-stage gearbox
At present, in pure electric vehicles, we haven't seen the multi-stage gearbox. Among the models with plug-in hybrid structure, BMW i8 is the first to install and configure the compact &; Ldquo two. Gearbox.
Most hybrid electric vehicles are basically equipped with clutch structure to avoid the disconnection of electric drive when the motor rotates too fast, but this will affect the performance of power. Bmw i8 is a sports car that pursues power, and the motor accounts for half of the power output. Obviously, it is not suitable for disconnecting the electric drive, but GKN's eAxle gearbox solves this problem, which makes the critical speed of the BMW i8 motor in the second gear lower, so that the whole process is basically that the motor and the gasoline engine drive the car together.
The genius of the gearbox lies in adding extra transmission ratio to the motor, which can improve the acceleration performance of the car and increase the mileage in pure electric mode. JiKane's two-speed eAxle gearbox also reduces the size and weight of the motor and its connecting system. The whole device weighs only 27 kilograms, and its volume is 325 times. 562 & times 13mm, the main parameter of this volume is smaller than that of ZF 9AT gearbox, which is specially designed for horizontal layout and extremely slim. ZF 9AT is 367&; Times; 52 1。 Times4 1 mm BMW i8 has only a narrow lateral gap between the drive shaft and the motor. Rather than saying that the BMW i8 is equipped with an eAxle gearbox, it is not as good as&; Ldquo attached &; Rdquo is more suitable to describe.
Schematic diagram of electric drive system: the future of electric drive system.
I think not only the tall BMW i8, but also Toyota has installed and equipped the ECVT gearbox for its hybrid car. It has no cone and steel belt of traditional CVT, and adopts planetary gear speed change structure. The gearbox not only matches the engine, but also has the function of motor speed change. Now, German auto parts supplier Bosch has stepped up the research and development of multi-speed gearbox for electric vehicles on their behalf. Tesla ecoallen &; Middot Musk is also considering matching a compact and lightweight multi-speed gearbox for Model S in the future.