Compared with the traditional automobile thermal management system, the new energy automobile thermal management system is different from it. One is that the management object extends from the cockpit to the battery, electric motor control and other fields, and the other is that its function extends from simple cooling to heat preservation and heating functions. . Therefore, compared with traditional automobiles, new energy automobile thermal management systems have added electronic water pumps, electric compressors, electronic expansion valves or four-way valves, cooling plates, and heating systems (heat pumps or PTC systems).
The heating source of the heating air of the air-conditioning system of a fuel-fuel vehicle is mainly provided by the engine coolant, while the heating system of an electric vehicle is different. The common schemes for the heating of electric vehicle air conditioning systems are as follows:
① Heat pump. The working principle of the electric vehicle heat pump air-conditioning system of the DC brushless motor driven by the transmission belt is shown in the figure. The cooling/heating mode of the air-conditioning system is switched by a four-way reversing valve. The solid arrow indicates the cooling mode, and the dotted arrow indicates the heating mode. In principle, this system is no different from ordinary heat pump air conditioners, but for electric vehicles, it has specially developed a dual-working cavity sliding vane compressor, a DC brushless motor and an inverter control system. Under heat pump conditions, when the system switches from defrosting mode to heating mode, the condensed water on the heat exchanger in the air duct will quickly evaporate, forming frost on the windshield, which affects driving safety.
②PTC electric heater. PTC electric heater is a kind of heater that uses PTC thermistor element as the heat source. PTC thermistors are usually made of semiconductor materials, and its resistance changes sharply with the change of humidity. When the external temperature decreases, the PTC resistance value decreases, and the heat generation increases accordingly. According to the material, it can be divided into ceramic PTC thermistor and organic polymer PTC thermistor. Ceramic PTC thermistor is used for auxiliary electric heater of air conditioner. The PTC thermistor element has the characteristics of increasing or decreasing the resistance value with the change of the ambient temperature, so the PTC heater has the characteristics of energy saving, constant temperature, safety and long service life.
Air conditioning auxiliary electric heaters can be divided into bonded ceramic PTC heaters and metal PTC tubular heaters. The bonded ceramic PTC heater is a heater that bonds multiple ceramic PTC chips and aluminum corrugated heat sinks with high temperature resistant resin glue. It has good heat dissipation and stable electrical performance. Among them, the bonded ceramic PTC heater is divided into the heater surface charged type and the heater surface uncharged type.
The metal PTC tubular heater uses imported nickel-iron alloy wire as the heating material, and the heating tube is inlaid with aluminum fins, which has a very good heat dissipation effect. The heater is equipped with a temperature controller and thermal fuse to make the product safer and more reliable. This kind of heater has the good characteristics of PTC material, and some air conditioners use this kind of heater as auxiliary heating.
③Waste heat + auxiliary PTC. The heat generated by high-power devices (power conversion, drive motors, motor controllers, etc.) is used to exchange heat with the environment in the car. When the heat is insufficient, the auxiliary PTC heater is activated.
The energy consumption of new energy vehicle air conditioners accounts for more than 15% of the energy consumption of the whole vehicle; the PTC thermal resistance heating method consumes a lot of energy, and the heat pump technology has obvious energy-saving effects, which has become an application trend to replace PTC. BMW, Mitsubishi, and Nissan have all begun to adopt electric scroll compressor technology.
PTC electric heater is a kind of heater with automatic temperature control and power saving. It uses PTC thermal ceramic element as the heat source, the corrugated sheet made of aluminum alloy as the radiator, and the heater is formed by bonding and welding.
PTC heater includes PT wind heater and PTC liquid heater. Since the PTC liquid heater can be arranged in the engine room, the existing automobile air conditioning system can be directly used, and it is more widely used in the heating system of electric vehicles.
For pure electric vehicles, PTC wind heating is generally used. This method only needs to replace the traditional automobile air conditioning heater core with a PTC wind heater, and then supplement it with necessary control equipment, which can be directly applied to electric vehicles.
Plug-in hybrid vehicles generally use PTC water heaters. In this way, the traditional car air conditioning heater core is connected in series with the PTC water heater. The liquid heated by the PTC water heater is provided with the air conditioning heater core. The warm air core is heated to increase the temperature of the outlet air and blow it directly into the car to realize the heating function in the car.
However, PTC heating consumes a lot of power batteries during heating in winter, which severely shortens the driving range of electric vehicles. Therefore, many current solutions use heat pump systems to achieve air conditioning heating, and the thermal efficiency can be significantly improved.