Transmission is a very broad subject of knowledge.
This article aims to increase readers' understanding of the vehicle transmission structure in the "N-motor dual-voltage, short-distance pure electric long-distance range extender" mode through a very basic popular science introduction.
The vehicle drive system is also called the electric drive automation system.
Electrical drive automation systems are a very mature engineering technology discipline. How can these mature technologies be used to design the drive system of electric vehicles?
First, we need to know what knowledge is required to design a transmission system, and then we need to understand it.
Secondly, a reasonable evaluation standard should be found in the process of technology screening and solution comparison.
Third, consider innovation or continuation based on long-term technological accumulation in practice.
The traditional "N -motor dual-voltage, short-distance pure electric long-distance range extender" system consists of four parts:
1. How does the low-voltage system (50V battery and 35V three-phase motor) drive the vehicle?
2. How the high-voltage system (battery system above 60V) works in conjunction with the low-voltage system to drive the vehicle.
3. How does the range extender system (internal combustion engine) drive the generator motor to generate electricity?
4. How do multi-motor, multi-axle vehicles operate?
If these four questions can be clarified, the vehicle's electronically controlled transmission system can be designed.
Vehicles move because of force—the friction between the vehicle and the ground.
Friction consists of at least five parts: uniform friction, accelerating friction, friction to overcome wind resistance, friction to overcome gravity (climbing and descending slopes), and friction caused by the deformation (thermal deformation, i.e., heat generation) generated when the wheel contacts the road surface.
The electric drive system of a vehicle's electronic control system needs to control these five friction forces.
In vehicle electronic control, the torque of the motor is the reaction force corresponding to the friction force on the ground.
In the design of "N-motor dual-voltage, short-distance pure electric long-distance range extender," the low-voltage system (50V battery) provides three forces: uniform friction, friction to overcome wind resistance, and friction caused by deformation (thermal deformation, i.e., heat generation) from the contact between the wheels and the road surface. The high-voltage system provides two forces: acceleration friction and friction to overcome gravity (climbing and descending slopes). According to simulations and relevant theoretical calculations, under normal road conditions, reasonable 0-100 km/h acceleration (5-13 seconds), and relatively gentle inclines, the power and torque ratio between the low-voltage and high-voltage systems is between 1:2 and 1:5. These simulation calculations are extremely important for determining the motor parameters.
The above describes the characteristics of the electric drive system in vehicle electronic control. Next, let's look at the characteristics of the motor.
For a motor, the power and torque are fixed. Motor power: P = 1.732 × U × I × cosφ; Motor torque: T = 9549 × P / n; Motor power/torque = 9550 * output power / output speed. Torque = 9550 * output power / output speed P = T * n / 9550.
However, even with the same power output, different motors will produce different torques. See Figure 1 below.
Figure 1. Power and torque curves of an 80kW leaf pure electric vehicle motor, built into Motor-CAD.
As shown in Figure 1, when a large motor operates at low power, its torque is at its rated torque. Torque is used to counteract friction. Electric drive loads with starting torque reaching twice the rated motor speed are typically referred to as heavy-load starts.
This motor characteristic can be used to match the electric drive load characteristics of a vehicle's drivetrain.
In the design of "N-motor dual-voltage, short-distance pure electric long-distance range extension", the 50V low-voltage motor is designed as a three-phase asynchronous motor, which has excellent overload characteristics and can provide starting torque of up to 3 times the rated power. This characteristic is utilized for matching.
In the "N-motor dual-voltage" scenario, the vehicle transmission of the Δ-Y connected dual-voltage motor is a single-motor transmission. Because such a motor control system prioritizes minimum cost, it is designed in the simulation as a single gearbox with a fixed transmission ratio, similar to current single-motor transmissions.
In vehicle transmissions with dual motors, three motors, and multiple motors and axles, the control models are quite complex. Let's take a dual-motor system as an example.
Figure 2. Common methods of dual-motor drive.
There are many ways to drive dual motors, and the simulation design of "N motor dual voltage, short-distance pure electric long-distance range extension" appears in a relatively novel way.
I'm still learning about multi-motor, multi-axle vehicle drive systems.
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