When it comes to heat pump air conditioning, whether we start with the traditional joint venture brand electric vehicle or the product of the new force. This technology has been deployed on a large scale in the new pure electric models that have been on the market in the past two years. Even in a sense, as the subject said, the market of more than 200,000 yuan has basically achieved standard allocation. Looking back at the efforts made by major OEMs in the thermal management of electric vehicles, from the perspective of the technical development path of heat pump air conditioning technology, it is an inevitable trend for the technical side to further solve the problem of mileage anxiety.
The main and secondary contradictions of the "mileage anxiety" problem
In the process of the development of the entire electric vehicle industry, the solution of "mileage anxiety" can be divided into two stages. Different problems are also faced at different stages.
- From the beginning of the popularization of pure electric vehicles to 2020, the pure electric vehicle products on the market mainly solve the main contradiction of "range anxiety". That is, the problem of insufficient basic battery life in the whole scene. The problem of insufficient basic endurance actually involves two main aspects. The first is the insufficient energy density of the battery pack, followed by the cost of the power battery. These two main problems led to the early birth of pure electric vehicles, a large number of products and their basic endurance can only achieve 300-400 kilometers. Such a battery life, even in the ideal environment, is difficult to meet the user's full-scenario usage needs. In this process, it has undergone the gradual optimization of the structural design of the battery pack, the migration of the battery technology route (from the mainstream lithium iron phosphate battery to the ternary lithium battery to obtain higher energy density) and the cost of the power battery has decreased. Finally, around 2020, the cruising range of mainstream pure electric vehicles was increased to about 600 kilometers, and the basic level of basic endurance and fuel vehicle products was achieved to solve this problem.
Power battery price trends Source: bloomberg
- After solving the main contradiction of mileage anxiety, it is necessary to solve the problem of "mileage anxiety" in some scenarios of pure electric vehicle products one by one, which is a secondary contradiction. Among these scene-based deficiencies, the decline in winter battery life is the most prominent one. The power battery is actually the same as people, the cold day does not want to move, limited by the chemical characteristics of the battery, the winter temperature is low, the battery activity is reduced, which makes the actual available energy decline. Although the decline in available energy is a reversible process, when the temperature rises, the available energy of the battery will naturally rise, but in the process of recovering the battery temperature, a lot of energy is also consumed. At the same time, in the low temperature scenario, a huge demand for heating in the driver's compartment is generated. Compared with internal combustion engine cars, because electric vehicles do not have enough energy heat sources for occupants to use, heating air conditioners in winter also consumes a lot of energy. The loss of these two energies makes electric vehicles consume significantly more electricity in winter than in summer, which brings about the problem of range anxiety. The heat pump air conditioner is the solution to the problem of winter endurance at the level of vehicle thermal management.
Schematic diagram of metal element migration during battery charge and discharge
PTC air conditioning with heat pump
Although fuel vehicles also face the problem of increasing energy consumption in winter, electric vehicles are more sensitive. This is because the fuel vehicle heats the crew compartment in the winter, which is actually wasted. In the working process of the fuel vehicle, 60%-70% of the energy is wasted in the form of heat, and when the power system is rapidly heated up to the optimal operating temperature range, there will be a large amount of useless heat that can be supplied to the crew compartment. Only about 10% of the energy of electric vehicles is converted into heat. Compared with 60%-70% of fuel cars, this 10% is already very rare, and if you do not use heat pump air conditioning, even this precious 10% can not be used. In the absence of a heat pump air conditioner, the solution is heated by PTC.
The so-called PTC is the Positive Temperature Coefficient, in fact, the principle is very simple, that is, the current generates heat. PTC heaters use a positive temperature coefficient material, commonly by directly heating the coolant. The resistance of a positive temperature coefficient material increases as the response temperature increases, limiting the current.
But even so, the ratio of the amount of refrigeration (heat) generated in the refrigeration (heat) cycle in the air conditioner to the power consumed by the refrigeration (heat) is called the maximum value of the heating efficiency ratio COP is not more than 1, that is to say, 1KW of electricity can produce up to 1KW of heat.
Heat pump air conditioning breaks the inherent thinking of generating heat with energy, and the "porter" who lets energy do heat uses the laws of thermodynamics to carry the low temperature heat from the outside to the relatively high temperature passenger compartment. Because the heat pump air conditioner uses the thermodynamic principle of evaporative heat absorption and liquefaction exothermic heat, the use of low boiling point refrigerant to bring heat from the environment into the passenger compartment, the heat obtained by the passenger cabin is the sum of the power consumed and the absorbed low heat energy, so its heating coefficient COP ((absorbed low heat energy + consumption of electrical energy) / consumption of electrical energy) must be greater than 1. The efficiency of the heat pump can usually reach 200-400%, which greatly improves the energy conversion efficiency.
Schematic diagram of two heat transfers for heat pump air conditioners
Heat pump air conditioning progression
Although it is the same as heat pump air conditioning, the solution of heat pump air conditioning will be different for different products and market positioning. For products that are more cost-conscious, single-air-source heat pumps are the most preliminary solution. An air-source heat pump is actually heated by the heat exchange of heat absorbed from the air by the refrigerant. Like some non-luxury brands use air source heat pumps, if the external temperature is too low, the difference between the refrigerant evaporation temperature and the ambient temperature is too small, and the heat absorbed is relatively small. Therefore, in the low temperature environment, the efficiency of the heat pump is much smaller. This makes the system operating window of the air source heat pump usually greater than -10 °C, at which PTC heating is still required. But even so, we can see that in the case of using heat pumps, the heating power drops significantly.
On the basis of a single air source heat pump. It is the integrated heat system, which is also the heat pump air conditioning system used in LYRIQ and some other products. The integrated thermal system is characterized by connecting the air conditioning system with the battery assembly and motor assembly to manage the heat on the whole vehicle. In this way, in the cold temperature of winter, it is possible to make full use of natural energy (air), motor and battery preheating for heating, improving efficiency while reducing costs. The risk of frosting in the system is also avoided.
Eight-way valve design
In an integrated thermal system, the control strategy of the system in different environments and the thermal management system path on the hardware are the keys to improving the experience. There is an integrated thermal system that uses a device called an octa-way valve on the back of the coolant house to control the movement of the stepper motor by adjusting the position of the valve so that the coolant flows in different systems, heats or cools the system.
Eight-way valve three-dimensional structure
The BEV3 integrated thermal system used by LYRIQ also integrates the crew compartment system, battery system thermal management system, motor thermal management system, and electrically controlled thermal management system through system integration design. The heating mode of bevHEAT further improves the heat utilization efficiency of the crew compartment in the case of waste heat and no waste heat in the motor battery:
- When there is waste heat in the motor battery: The system handles the heat of the battery and the motor and heats the passenger compartment. At the same time, the system stores the charging pile electrical energy conversion heat energy in the system battery and waterway, which can support the heating of the passenger compartment of short-distance travel for 1-2 hours.
- When there is no waste heat in the motor battery, the system absorbs external heat through the waterway, and the system carries the waterway heat and heats the crew compartment.
LYRIQ Battery System
The optimization of range anxiety for pure electric vehicle models has begun to transition to the optimization stage of scenario by scene. For many OEMs, in terms of thermal management, more resource integration needs to be considered. In the entire pure electric vehicle thermal management system, the crew cabin air conditioning system is only one part of it, and the integrated heat system realizes the heat management of the crew cabin air conditioning system and the motor electronic control thermal management system and the battery heat management system, thereby improving the heat utilization efficiency of the whole vehicle, reducing power consumption, and improving the mileage. The follow-up development ideas will develop in the direction of higher system integration, lower degree of system development, and further improvement of comfort in multiple scenarios of the system.
Compared with the solution of a single air source heat pump, LYRIQ's heat pump air conditioner also realizes the integration of the crew compartment air conditioning system and the entire thermal management system based on the BEV3 integrated heat system, and the same function as the model Y thermal system can already be achieved from the perspective of scene function. In this case, we are also looking forward to the subsequent experience of the integrated thermal system of the LYRIQ real car. I think it won't be long before we get it.