Auto air conditioning compressor transfer heat from the enclosed space to the outside, or bring heat from the outside into the enclosed space. There will be no heat generation in the process, but only heat transfer.
The electric ac compressor on the electric vehicle is logically managed by the vehicle controller VCU, and its specific implementation forms are various. Here, only a typical form is used to illustrate its detailed working process.
1 Electrical work process
From an electrical point of view, compressor air conditioners are mainly composed of the following parts: air conditioner controller, compressor and thermodynamic system, compressor motor and its controller, communication module, temperature and pressure sensor.
The electrical of the car air conditioner is divided into two parts, the high-voltage part and the low-voltage part. As shown in the figure below, DC+ and DC- are high-voltage power supplies, directly connected to the compressor motor controller
The low-voltage part of the air conditioner is controlled by the VCU. The VCU controls the on and off of the entire air conditioner by controlling the 12V power circuit "air conditioner relay"; transmits command information to the air conditioner controller through the CAN bus to set the target value of the operating temperature; the air conditioner controller feeds back the air conditioner work to the VCU Status information, including the on-off information of the power circuit switch, compressor pressure, and compressor inlet and outlet temperature.
The high-voltage power supply of the air-conditioning compressor comes from the on-board DCDC converter. The air-conditioning controller controls the on and off of the contactor on the power circuit through the contactor trigger port, and then controls the working state of the compressor motor.
The compressor is integrated with the motor and motor controller that power it. The space is relatively small, and electromagnetic interference in the space is often the cause of the malfunction of the controlled motor.
Compressor motors generally use permanent magnet synchronous motors or permanent magnet brushless DC motors. There is no other reason, small size and simple control. The motor speed can be adjusted in a wide range according to needs.
Turn the ignition switch of the electric vehicle to the “ON” position. If the “A/C” switch of the air conditioner is turned on at this time, the air conditioner can start to work.
Cooling and heating capacity adjustment
The air conditioner controller closes the high-pressure circuit contactor, and the compressor enters the working state. Passengers can adjust the temperature in the cabin by adjusting the air volume and temperature setting buttons. The greater the air volume, the more heat is brought into the vehicle compartment from the condenser, and the greater the power of the compressor is required. The greater the difference between the set temperature and the current temperature, the greater the compressor power required.
The air-conditioning controller achieves the purpose of controlling the amount of cooling and heating by controlling the motor speed of the electric compressor. The motor speed is high, the corresponding operating speed of the compressor increases, the refrigerant flow rate increases, and the cooling capacity increases.
2 Physical working process
From a physical point of view, the four essential components of air conditioning include: evaporator, condenser, compressor and expansion valve. The four-way solenoid valve is a switch for switching between cooling mode and heating mode.
The refrigeration mode can be regarded as the air conditioning system. The evaporator is placed in the car interior to allow the refrigerant to evaporate and absorb heat, taking away the indoor heat; the heat is taken to the outdoors through the circulating pipe, and the condenser will condense this part of the heat to release heat. Way, released into the outdoor air.
The refrigerant absorbs heat from the room and becomes a low-pressure gas at room temperature. After being boosted by the compressor, it becomes a high-temperature and high-pressure gas, which flows into the outdoor condenser (the heat exchanger outside the car in the picture). After the heat release process, the gas condenses into a liquid; a high-pressure liquid , Flows into the expansion valve, partially vaporizes and absorbs heat, and the refrigerant turns into low-temperature and low-pressure wet vapor; the wet vapor enters the evaporator in the vehicle compartment and further vaporizes and absorbs heat to form room temperature gas and return to the compressor.
Heating is the reverse process of refrigeration. In a two-way heat pump, it is realized by reversing the solenoid valve. What we see is equivalent to putting the condenser inside the car and the evaporator outside.
However, in practical applications, the compression mechanism heat is rarely used alone. Instead, it borrows other heating equipment to provide a heat source, and then uses the air conditioning system to make the heat flow evenly into the vehicle interior. For example, use PTC electric heating, or use the cooling water of the motor controller to heat.
Post time: Apr-30-2021