PTC Technology in New Energy Vehicles
Compared with the traditional automotive thermal management system, the difference between the new energy vehicle thermal management system is that the management object extends from the cockpit to the battery, motor electronic control and other fields, and the second is that its function extends from simple cooling to heat preservation and heating functions . Therefore, compared with traditional vehicles, the thermal management system of new energy vehicles adds electronic water pumps, electric compressors, electronic expansion valves or four-way valves, cooling plates and heating systems (heat pumps or PTC systems), etc. New Energy Vehicle Air Conditioning System Solution.
The warm air heat source of the fuel vehicle air conditioning system is mainly provided by the engine coolant, but the heating system of the electric vehicle is different. Common schemes for electric vehicle air conditioning system heating are as follows:
① heat pump. The working principle of the electric vehicle heat pump air conditioning system driven by the DC brushless motor is shown in the figure. The cooling/heating mode of the air conditioning system is switched by the four-way reversing valve, the solid arrow indicates the cooling condition, and the dotted arrow indicates the heating condition. In principle, the system is no different from ordinary heat pump air conditioners, but it is used in electric vehicles, and it has specially developed a dual-cavity sliding vane compressor, DC brushless motor and inverter control system. Under the heat pump working condition, when the system changes from the defrosting mode to the heating mode, the condensed water on the heat exchanger in the air duct will evaporate rapidly, and frost will form on the windshield, affecting driving safety.
②PTC electric heater. PTC electric heater is a kind of heater that uses PTC thermistor element as heat source. PTC thermistor is usually made of semiconductor material, its resistance changes sharply with the change of humidity, when the outside temperature drops, the resistance value of PTC decreases, and the calorific value will increase accordingly. According to the material, it can be divided into ceramic PTC thermistor and organic polymer PTC thermistor. For air conditioning auxiliary electric heaters are ceramic PTC thermistors. Because the PTC thermistor element has the change characteristic that its resistance value increases or decreases 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 in which multiple ceramic PTC chips and aluminum corrugated heat sinks are bonded together 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 a charged type on the surface of the heater and an uncharged type on the surface of the heater.
The metal PTC tubular heater uses imported nickel-iron alloy wire as the heating material, and the heating tube is inlaid with aluminum heat sinks, and its heat dissipation effect is very good. The heater is equipped with a temperature controller and a thermal fuse to make the product safer and more reliable. This kind of heater has good characteristics of PTC material, and some air conditioners use this kind of heater as auxiliary heating.
③Residual heat + auxiliary PTC. Use the heat generated when high-power devices (power conversion, drive motor, motor controller, etc.) work to exchange heat with the environment in the car. When the heat is insufficient, the auxiliary PTC heater is activated.
The energy consumption of air-conditioning in new energy vehicles 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. Foreign BMW, Mitsubishi, and Nissan have all begun to adopt the technology of electric scroll compressors. At present, some models in China are also adopting them, but the current technical level is still at the level of stand-alone compressors.
For heat pump technology, further increasing the power density and lowering the minimum operating temperature are the focus of the next research and development, as well as an important means of energy saving.
