Why is it necessary to distribute power and torque in this way? Tesla is also painstaking, which is related to the dynamics of the car. Here is a concept:
"weighttransfer" weight transfer - refers to the acceleration of the vehicle, due to the inertial force, the load of the front wheel will be reduced, the wheel adhesion will decrease, the load of the rear wheel will increase, the adhesion of the wheel will increase, equivalent The weight is transferred from the front wheel to the rear wheel.
When the weight transfer phenomenon of the acceleration process occurs, the force given by the front wheels is not only inefficient, but the wheels are slippery, the rear wheels have a strong adhesion, and the power should be more distributed to the rear wheels. In response to this phenomenon, Tesla allocated more torque to the rear motor as the main motor, so that the effective combined torque of the two motors is much larger than the average distribution.
The Tesla engineers also did a more in-depth study. The two motors are not only different in power, but also have different torque speed characteristics. As shown in the figure below: the main motor is a typical transverse torque transverse power curve, while the auxiliary motor's torque is basically flat, which can be considered as a torque source. The purpose of this is to make the two motors differentiate and complement each other.
Those who have done the design of the drive motor for vehicles have the same experience: it is easy to pursue the climbing torque alone, and it is easy to pursue high-speed performance alone. It is not easy to pursue two performances simultaneously in one motor. And also to control costs.
The high-speed power of the motor for the vehicle is limited by the battery voltage, and the torque will decay rapidly with the speed, also called “torque drop”. We want to make the high-speed power higher, we must reduce the torque coefficient of the motor, but in this case, the low-speed current will become larger, and the torque will not be generated. This is what motor people often say: "The contradiction between low speed and high speed."
Tesla's differentiated primary and secondary motor solutions are equivalent to decoupling this problem. The main motor is made into an ordinary motor, and it can be designed according to the low-speed climbing. The auxiliary motor is made into a high-speed non-weakening magnetic motor, which has two advantages: 1 the torque does not change with the rotational speed, the power increases linearly with the rotational speed, 2 because the torque is small, and the problem of large low-speed current is not considered. In this way, the auxiliary motor can compensate for the problem of high-speed torque drop of the main motor and can compensate some acceleration torque. The torque envelope synthesized by the two motors is greater than the torque envelope of one motor. Not only that, but the cost is much smaller than the two identical motors:
The high-speed performance of a combination of two different types of motors with different characteristics is better than the combination of two identical motors. This is because the weakness of ordinary motor motors is that the output capability is significantly reduced due to voltage constraints at high speeds. The constant torque motor can compensate the weakness of the ordinary motor with the least cost, which is called complementary complementarity.
To sum up, the Tesla dual-motor design is able to achieve excellent performance, on the one hand, the battery and motor power match. On the other hand, the optimal distribution of torque is made for the dynamic characteristics of the vehicle during acceleration. And through the differential design of the front and rear motors, an equivalent synthetic motor with better performance is obtained, which can be said to be both a system solution and a component solution. This is the Tesla dual motor technology solution I gave.
