Affected by the uniqueness of pure electric vehicles, automobile manufacturers have carried out partial replacement designs on the basis of traditional fuel vehicle air conditioners, replacing the compressor driven by the fuel engine with a compressor directly driven by a DC motor, and corresponding changes in control to complete the air conditioning refrigeration. The current replacement design effect can basically solve the cooling problem of pure electric vehicle air conditioners, but the cooling efficiency needs to be improved.
In the selection of the main components of air conditioners, in addition to compressors and control modes, other main components of pure electric vehicles are still those of fuel-fuel vehicle air conditioners. The condensing equipment mainly uses parallel flow condensers, and the evaporation equipment mainly uses For stacked evaporators, the throttling device is still a thermal expansion valve, and the refrigerant is still R134a.
(1) Composition and function of electric refrigeration system
① The composition of the refrigeration system.
The braking system is mainly composed of an electric compressor, a condenser, a liquid storage dryer, an expansion valve, an evaporator, and a control circuit, as shown in Figure 1. Low-pressure pipeline: from the outlet of the throttle valve to the inlet of the compressor, there is an evaporation box, a low-pressure filling port, and an accumulator along the way. High-pressure pipeline: from the compressor outlet to the throttle valve (expansion valve) inlet, there are compressors, condensers, receiver dryers, high-pressure filling ports, pressure switches, and throttle valves along the way.
Most passenger cars use frequency converters to control high-voltage three-phase motors to drive compressors, so there are independent motor frequency converters, and a belt drive is used between the motor and the compressor. However, cars mostly use integral electric compressors, which have electric motors inside and are generally driven by low voltage 12V.
②Functions of refrigeration system components.
The compressor sucks and compresses the low-temperature, low-pressure gaseous refrigerant into a high-temperature, high-pressure liquid refrigerant to form a temperature difference with the outside air. The condenser dissipates the heat of the high-temperature and high-pressure refrigerant to the surrounding air through the special fan for the condenser or the engine radiator fan, and the refrigerant cools down; the dryer is used to remove the moisture in the refrigerant; the high-pressure filling port is used to add the refrigerant or to The pipeline is used for vacuuming; in the high and low pressure switches, the high pressure switch protects the pipeline, and the low pressure switch protects the compressor; the throttle valve (expansion valve) is a small orifice with variable or fixed cross section to throttle and atomize the high pressure refrigerant. The evaporating box absorbs the heat of the air in the car; under the action of the blower, the evaporating box absorbs the heat in the car, turning the refrigerant into a low-temperature, low-pressure gaseous state; the accumulator is used to store the refrigerant to prevent the refrigerant from the evaporating box from being in a gaseous state The “liquid hammer” compressor; the low-pressure filling port is used to add refrigerant or to vacuum the pipeline.
(2) Working principle
The working principle of a typical electric air-conditioning system is shown in Figure 2.
For pure electric vehicles, there is no engine as the power source of the air-conditioning compressor, nor can it provide the heat source for heating the car air-conditioning in winter, so it is impossible to directly adopt the solution of the traditional car air-conditioning system. For pure electric vehicles, the vehicle has a high-voltage DC power supply. Therefore, the use of an electric heat pump air-conditioning system (the compressor is directly driven by an electric motor) becomes a feasible solution. If the compressor motor of the heat pump air conditioner adopts frequency conversion control technology, and the expansion valve (throttle valve) adopts electronic expansion valve throttling technology, the control will be more precise and more energy-saving.
The automatic air-conditioning system of a traditional fuel vehicle adjusts the outlet air temperature by controlling the opening of the hybrid damper and the fan speed to adjust the air volume, so that the interior temperature of the vehicle is maintained at the set value. As for the heat pump air conditioning system, there is no hot water core to adjust the temperature of the outlet air, but the speed of the compressor can be controlled by the frequency converter. Therefore, its control method is different from the air-conditioning system of traditional fuel vehicles.
In the electric vehicle heat pump air conditioning system, controlling the cooling capacity is mainly achieved by controlling the speed of the compressor. The method of controlling the speed of the compressor: when the temperature of the vehicle compartment is 1°C higher than the set temperature, in order to make the temperature reach the set value as soon as possible, the compressor runs at the maximum speed; if the temperature of the vehicle compartment is 1°C lower than the set temperature, compression The compressor runs at the lowest speed; when the room temperature deviation is -1~1℃, the compressor’s speed is controlled by the fuzzy control algorithm, and the temperature difference between the room temperature and the set value and the change rate of the temperature difference at each sampling time are input. Fuzzy reasoning obtains the speed value of the compressor.
The air volume of the evaporator fan not only affects the refrigeration system, but also has a greater impact on the cabin temperature. If only the evaporator fan is operated at the maximum air volume, not only the noise is relatively large, but also it is not conducive to meeting the comfort requirements of the car cabin. Especially for electric vehicle air-conditioning systems, there is no hot water core to adjust the air outlet temperature, and the volume of the car interior is relatively small. If the temperature of the car room is only controlled by adjusting the speed of the compressor, the temperature inside the car will be relatively easy to fluctuate, which is not conducive to the stability of the system. run. Therefore, the fan is allowed to run at the maximum air volume only when the load in the vehicle compartment is relatively large, and appropriate control strategies should be adopted in other situations to ensure that the temperature in the vehicle compartment is stable at the set temperature. In the initial refrigeration phase, the compressor and evaporator fan run at the maximum speed, which can quickly drop the cabin temperature to the set temperature. When the temperature reaches the set temperature, there is a little overshoot, and the temperature control accuracy is higher. For example, when the compressor drops from the maximum speed of 60min to about 300rmin, by controlling the air volume of the evaporator, the temperature in the cabin can be smoothly dropped to near the set temperature, so that the overshoot of the compressor speed at this time is small.