The engine and gearbox are considered to be the most important technologies in the automotive, even a good gearbox, and it can also make up for the insufficient power of the engine itself, so that the transfer of power is more smooth.
However, most electric cars have no separate transmission. Compared with the internal combustion engine, the motor is different from the nature of power and torque. The internal combustion engine converts the energy generated by the intake-compression-explosion-exhaust stroke into rotation, and transmits it to the wheel through various power transmission devices, and generating energy is complicated, and must pass many mechanical components, so The gearbox is an indispensable component.
When the engine is slowly running, the power and torque are smaller. When the engine speed is increased, a higher power is output. However, due to the output power = torque X speed, the torque will not continue to increase even if the output is increased. Therefore, the internal combustion engine engine typically has an optimum speed of rotation, and the power and torque in this interval can best exert.
However, in the electric vehicle, the maximum torque can be built from the moment from the current through the electric motor. Therefore, the acceleration of pure electric cars is very fierce. Thereafter, the maximum torque gradually draws a downward curve after the number of revolutions reaches the maximum output of the motor.
The important part is “available speed”. The available speed of internal combustion engine based on ordinary passenger cars is: gasoline is 6000 to 7000 rpm, and diesel is 4000 to 5000 rpm.
If the internal combustion engine requires at least 4 shift gears to break through 200 km / h, the electric vehicle can be 1 without the transmission.The speed of 60 to 200 km / h travels. Electric cars can be used without transmissions unless there is a higher speed like a car.
In addition, in pure electric vehicles, the cost of batteries is very high. So now pure electric cars usually use limited space to the battery. To ensure a larger endurance mileage. If you increase the gearbox in the pure electric car, it will increase the cost of the car, and it is not cost-effective for the manufacturer.
Another reason for electric vehicles does not need to use the transmission, it is very efficient. According to the presentation released on the 2017 Electrical and Electronics Engineer (IEEE), the presentation released on the promotion meeting (VPPC), when the electric vehicle increases the two-speed transmission, power consumption (WH / km) is as low as 0.75%, up to only It is 1.5%.
Since the motor itself exhibits a sufficiently high efficiency within any rotation range, the internal combustion engine has the best at a specific speed. Efficiency, if less than or higher, the efficiency will be reduced. 
Most electric vehicles are efficient to 80-90%, so even if the gearbox is added, the additional efficiency improvement effect is slightly negligible.
So, is the gearbox itself is useless? Not! The advantage of equipped with gearbox is to improve performance, Porsche Taycan is the representative.
TAYCAN is equipped with a 2t gearbox. The speed reduction ratio is 15: 1, and it is easy to get greater forces and faster acceleration by utilizing greater torque. When the secondary gearbox is used at a speed of 110 km / h, the maximum speed can be improved by the reduction ratio of 8: 1.
Therefore, when the highest speed of the general electric vehicle is 160km / h, it is difficult to more than 200km / h, and Taycan can reach 25.0km / h. The gearbox plays an important role in improving performance, such as more powerful power and faster speed.
CVT transmission, as an advantage of increasing the endurance mileage of pure electric vehicles, once again attracted people’s attention. 
According to a paper registered in Energies, Switzerland, it is possible to freely change the CVT transmission ratio of the CVT gearbox, which can reduce the energy consumption of electric vehicles to 10-15%. There is a positive impact on the improvement efficiency.
Therefore, some brands have begun to study the technology. Bosch announced an electric drive system called CVT4EV.
According to official news, Bosch CVT4EV gearbox adopts integrated design, and there is no complicated structure such as hydraulic torque converter, planetary gear, clutch, etc. in the traditional transmission. In addition, it can be flexible between broad speed ratios, which can enlarge the vehicle’s starting torque, and reduce the high energy consumption of the motor, low efficiency, while driving at high speed, the motor can be maintained at the most efficient The speed range.
CVT4ev has a module structure integrated with the inverter, the motor, and the CVT transmission, which is to reduce the volume and weight. For vehicle manufacturers, the cost and complexity required for vehicle development and production can be reduced. Due to the modular structure, it can be applied to various models from ordinary passengers to commercial vehicles and sports cars.