The working principle of pure electric cars: The structure and configuration of pure electric cars produced by different manufacturers are different, and the working principles of the whole cars will be quite different.
When the power is turned on and the car is driving, the main control ECU receives various information from the gear controller, accelerator pedal and angle sensor, judges and calculates, and sends instructions to the motor controller to control the current that drives the motor forward. At this time, after the battery pack current passes through the emergency switch and the distribution box/relay, one way goes through the motor controller to drive the motor forward to supply the required current, and the other way goes through the DC/DC converter to convert 330V high-voltage direct current into low-voltage 42v, providing Used for EPS (Electric Power Steering System). At the same time, the battery pack is managed by the battery manager, and the instantaneous voltage, current, temperature, and power storage information of the battery pack are transmitted to the battery manager to prevent the battery pack from being damaged by over-discharge or over-temperature. If a leakage occurs, the leakage protector will work. In the event of an emergency such as a short circuit, the protection device (fuse) is blown immediately.
On the basis of pure electric cars, equipped with a small auxiliary generator (range extender) group to prepare for charging the battery when the battery power is insufficient, then it becomes an extended range electric car.
The extended-range electric car is a pure electric car equipped with ground charging and on-board power supply functions (some also classify it as a hybrid car). The loaded battery meets the power needs of daily driving. When the battery power supply capacity is exceeded, the battery pack is charged by other power sources to continue driving the wheels. The battery pack can be charged by a ground charging pile or by an on-board engine. The car operating mode can work in pure electric mode or extended range mode as required.
Range-extended hybrid cars and pure electric cars both use electric motors to drive wheels for driving, but the difference is that there is an additional engine that uses this engine to drive the electric motor to generate electricity to drive the car and charge the battery.
The working mode of extended-range electric cars is very similar to that of plug-in hybrid cars. Both can work in pure electric mode, and the battery pack has an external charging method and an engine charging method. The main difference between extended-range electric cars and plug-in hybrid electric cars: hybrid electric cars basically rely on internal combustion engines to run, and electricity is only a supplement, and they cannot travel too far with pure electricity; while extended-range electric cars are powered by electricity, and the engine is only used for driving. The battery is charged to achieve sufficient driving range.
The typical representative of extended-range electric cars is the Chevrolet Volt (see Figure 1). Although the Volt is equipped with a small engine, its design concept is based on pure electric cars. In the case of sufficient battery power, all the energy to drive the car is provided by the battery. Only when the battery power is insufficient, the engine will be started to charge the battery.
①.Volt power system layout
As shown in Figure 2, the Volt’s power system adopts the front-front drive mode, the charging port is located in the front of the car side, and the T-shaped lithium-ion battery pack is arranged in the middle. The power system consists of two electric motors and an internal combustion engine, which are connected by three sets of clutches and a planetary gear to realize different working modes to meet the needs of driving conditions.
②.Volt working mode
The Volt drive system adopts a coaxial connection, and the motor (can be used as a motor or a generator), planetary gears, and engines are arranged in a straight line, as shown in Figure 3. The more powerful main drive motor MG1 is mechanically connected to the sun gear, the output shaft is mechanically connected to the planet carrier, and the ring gear is connected to different working modes due to the different engagement states of the three clutches: low-speed pure electric mode, low-speed braking energy Feedback mode, low-speed range extension mode, high-speed pure electric mode, high-speed braking energy feedback mode, high-speed range extension mode and parking power generation mode.
(1) Low-speed pure electric mode
As shown in Figure 4, in this mode, the ring gear is locked by the clutch C1, and the clutch C2 and the clutch C3 are both in a disengaged state. The motor MG2 and the engine are separated from the total power, and they do not work. MG1 uses planetary gears to reduce speed and transmits power to the output shaft to drive the wheels. In this mode, the car is driven only by MG1, with a maximum speed of 65km/h.
(2) Low-speed braking energy feedback mode
As shown in Figure 5, in the low-speed pure electric mode, step on the brake pedal and the vehicle enters the braking energy feedback mode. In this mode, the MGI acts as a generator, driven by the wheel energy to generate electricity, and converts the vehicle’s kinetic energy into electrical energy. Store back in the battery.
(3) Low-speed extended range mode
As shown in Figure 6, when the car speed is 40 ~ 80km/h and the battery power is below 35%, the engine starts and enters the low-speed extended range mode. In this mode, clutch C1 and clutch C3 are engaged, and the engine drives MG2 to generate electricity. MG1 obtains electric energy from the battery and MG2 to drive the car.
(4) High-speed pure electric mode
As shown in Figure 7, in this mode, the clutch C1 is disengaged and the clutch C2 is engaged. MG2 is connected with the ring gear of the planetary gear system, and MG1 and MG2 simultaneously drive the car through the planetary gear system. The addition of MG2 reduces the speed requirement of MG1.
(5) High-speed braking capability feedback mode
As shown in Figure 8, similar to the low-speed braking capability feedback mode, the kinetic energy of the car is converted into electrical energy and stored back in the battery. In this mode, C2 is engaged, and MG1 and MG2 generate electricity at the same time to charge the battery.
(6) High-speed extended range mode
As shown in Figure 9, the high-speed extended range mode is activated when the battery power is too low and high-speed driving conditions. In this mode, clutches C2 and C3 are engaged, and C1 is disengaged. The engine and MG1 drive the car together, while the engine drives MG2 to charge the battery.
When a car is in a high-speed driving condition for a long time, only the battery is used as the energy source to output, and the performance of the car cannot meet the power performance requirements of the car. Therefore, the power coupling mechanism of the planetary gear train couples the engine and the motor to power and output power. Therefore, for this model, a more precise statement should be a hybrid model, which is also quite controversial at the beginning of Volt’s design positioning.
(7) Shutdown power generation mode
As shown in Figure 10, when the battery power is low in the parking state, the parking power generation mode is activated. Clutch C3 is engaged, MG1 is closed, and the engine drives MG2 to charge the battery to replenish battery power.
|Low speed||Mode 1 (low-speed pure electric)||Battery|
|Mode 2 (low-speed range extension)||Battery, engine|
|high speed||Mode 3 (High-speed pure electric)||Battery|
|Mode 4 (High-speed extended range)||Battery, engine|
|parking||Mode 5 (Stopping for power generation)||engine|
The working mode of the Chevrolet Volt drive system is shown in Table 1.