Control method of non-heat pump vehicle thermal management
system for pure electric vehicles
As pure electric vehicles become more and more popular, many problems in the use process are gradually exposed. The attenuation of driving range in high and low-temperature environments is a major pain point for current users. Compared with traditional fuel vehicles, the main powertrain system of pure electric vehicles (power batteries, motors, controllers, chargers, etc.) has a small operating temperature range, and the working performance is greatly affected by temperature. Too high or too low operating temperature will affect the battery capacity, service life and motor efficiency. Therefore, the battery needs to be reasonably heated in low-temperature environments and appropriately cooled in high-temperature environments to ensure that the battery is always within a reasonable temperature range.
Some pure electric vehicle thermal management systems, especially pure electric vehicle operating models with greater cost pressure, currently mostly use PTC water heaters to heat the passenger compartment and battery pack. This system can effectively meet the thermal management function requirements of the battery pack and passenger compartment. However, due to the high energy consumption of PTC, it seriously affects the driving range of pure electric vehicles in low-temperature environments. The use of heat pump systems will greatly increase costs, so it is very necessary to carry out refined energy management of the vehicle thermal management system. The principle of motor waste heat utilization is that under low-temperature conditions when the water temperature at the motor outlet reaches a certain condition, the coolant heated by the motor waste heat will be heated to the battery circuit through the plate heat exchanger to increase the battery temperature, restore the battery discharge performance, and improve the low-temperature driving ability of electric vehicles.
1 Introduction to non-heat pump vehicle thermal management system
In order to improve the attenuation of the low-temperature driving range of pure electric vehicles, both non-heat pump and heat pump vehicle thermal management systems have been widely adopted. In actual development, the type of vehicle thermal management system can be selected according to the model level and cost performance of pure electric vehicles.
The original vehicle thermal management system studied in this paper is a non-heat pump vehicle thermal management system. The heating function under low-temperature conditions is mainly: using PTC to heat the passenger compartment, the battery thermal management system has no heating function under driving conditions, and the electric drive (including motor) thermal management circuit and the battery thermal management circuit operate independently. This solution can directly convert battery energy into the goals required by users, meet users' needs for driving and passenger compartment heating, and the control system and thermal management circuit are relatively simple and easy to implement. However, since the low-temperature heating requirements of the battery pack under driving conditions are not considered, the capacity of the battery pack itself is greatly attenuated at low temperatures, resulting in a serious attenuation of the driving range under low-temperature conditions, which also has a certain impact on the service life of the battery pack.
In response to the above problems, this paper adds some pipelines and control water valves based on the original vehicle thermal management circuit, connects the water circuits of the electric drive system, battery, and air conditioner at low temperatures, realizes motor waste heat recovery and heating of the battery pack during driving, and implements intelligent control of the passenger compartment and battery temperature, as shown in Figure 1. In addition, a more efficient water heating PTC is used, and its control system is optimized to further improve the low-temperature driving range.
