A transcritical carbon dioxide electric vehicle thermal management system and control method thereof

Abstract

The present invention discloses a transcritical carbon dioxide electric vehicle thermal management system and a control method thereof. In the system, a chiller, an expansion water tank, a battery pack heat exchanger and a water pump are connected in series in sequence; the outlet of the compressor is connected to the a port of a four-way reversing valve, and the b port of the four-way reversing valve is connected in series with the outdoor heat exchanger and the first heat exchange channel of the regenerator, and the pipeline is divided into two paths. One path is connected in sequence to the second electronic expansion valve and the chiller, and then connected to the d port of the four-way reversing valve, and the other path is connected in sequence to the first electronic expansion valve, the indoor heat exchanger, the full-pass expansion valve, and the defrost heat exchanger, and then connected to the d port of the four-way reversing valve; the c port of the four-way reversing valve is connected in series with the gas-liquid separator and the second heat exchange channel of the regenerator, and then connected to the inlet of the compressor. The system provided by the present invention can prevent the low-temperature capacity decay of the battery and can effectively improve the driving mileage of the electric vehicle.

Description

Technical Field

[0001] The present invention belongs to the technical field of transcritical carbon dioxide thermal management, relates to the field of electric vehicle thermal management, and particularly relates to a transcritical carbon dioxide electric vehicle thermal management system and a control method thereof. Background Art

[0002] Electric vehicles do not rely on traditional fossil fuels and have received extensive attention as countries around the world increasingly attach importance to environmental protection and sustainable development concepts. Compared with traditional fuel vehicles, electric vehicles lack sufficient engine waste heat in winter, so an air conditioning system or additional electric heating equipment is required to provide heat for the passenger compartment. Currently, the refrigerant R134a commonly used in electric vehicle thermal management systems has poor heating performance at low temperatures, while the environmentally friendly natural refrigerant CO 2 has excellent thermal performance in low-temperature environments and has gradually become the focus of research.

[0003] Currently, electric vehicles using R134a refrigerant operate in a fresh air mode when starting. Especially in the case of a relatively low winter environment, the heat exchange demand is large. In order to make the temperature inside the vehicle reach a suitable range, it is often necessary to additionally combine an electric heating device on the basis of using a heat pump, resulting in an increase in the power consumption of electric vehicles and seriously affecting the driving range. In addition, the power battery is the only energy source of electric vehicles, and there is a severe capacity attenuation problem in low-temperature environments (specifically exemplified, the battery capacity at -20°C is only 75% of the nominal power). Currently, the method of simultaneously heating the passenger compartment and the battery with a heat pump is generally used to slowly bring the battery to a suitable temperature range. However, this method does not particularly focus on the low-temperature capacity attenuation problem of the battery, wastes part of the battery power, and will also affect the vehicle's driving range to a certain extent.

[0004] In summary, there is an urgent need for a new fast-starting transcritical carbon dioxide electric vehicle thermal management system and a control method thereof. Summary of the Invention

[0005] The purpose of the present invention is to provide a transcritical carbon dioxide electric vehicle thermal management system and a control method thereof to solve one or more of the above-mentioned technical problems. The system provided by the present invention can quickly make the temperature inside the carriage close to the target temperature when the electric vehicle starts, ensure that the battery temperature at startup is within a suitable range, reduce the power consumption while quickly stabilizing the carriage temperature, prevent the low-temperature capacity attenuation of the battery, and can effectively improve the driving range of the electric vehicle.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A transcritical carbon dioxide electric vehicle thermal management system provided by the present invention includes: an expansion tank, a battery pack heat exchanger, a water pump, a compressor, a four-way reversing valve, an outdoor heat exchanger, a regenerator, a first electronic expansion valve, a second electronic expansion valve, a chiller, a gas-liquid separator, an indoor heat exchanger, a full-pass expansion valve, and a defrosting heat exchanger; wherein, the four-way reversing valve is provided with ports a, b, c, and d; the indoor heat exchanger and the defrosting heat exchanger are arranged in an air conditioning box;

[0008] The chiller, the expansion tank, the battery pack heat exchanger, and the water pump are connected in series in sequence to form a coolant circuit in the transcritical carbon dioxide electric vehicle thermal management system; the outlet of the compressor is connected to port a of the four-way reversing valve, and the pipeline after the b port of the four-way reversing valve is connected in series to the outdoor heat exchanger and the first heat exchange channel of the regenerator and then is divided into two paths. One path is connected in sequence to the second electronic expansion valve and the chiller and then is connected to port d of the four-way reversing valve, and the other path is connected in sequence to the first electronic expansion valve, the indoor heat exchanger, the full-pass expansion valve, the defrosting heat exchanger and then is connected to port d of the four-way reversing valve; the c port of the four-way reversing valve is connected in series to the gas-liquid separator and the second heat exchange channel of the regenerator and then is connected to the inlet of the compressor to form a refrigerant circuit in the transcritical carbon dioxide electric vehicle thermal management system;

[0009] Wherein, the four-way reversing valve is used to control the switching of the transcritical carbon dioxide electric vehicle thermal management system between a refrigeration mode and a heating mode.

[0010] A further improvement of the system of the present invention lies in that in the refrigeration mode: the high-temperature and high-pressure steam at the outlet of the compressor enters the outdoor heat exchanger and the first heat exchange channel of the regenerator through the a and b port channels of the four-way reversing valve in sequence to release heat; then the refrigerant is divided into two paths. One path throttles through the second electronic expansion valve and then enters the chiller to absorb the heat of the coolant circuit, and the other path throttles through the first electronic expansion valve and then enters the indoor heat exchanger, the full-pass expansion valve, and the defrosting heat exchanger in sequence to absorb heat. The two paths converge at the outlets of the chiller and the defrosting heat exchanger and then enter the gas-liquid separator and the second heat exchange channel of the regenerator through the d and c port channels of the four-way reversing valve in sequence and then return to the compressor.

[0011] A further improvement of the system of the present invention lies in that in the heating mode: the high-temperature and high-pressure steam at the outlet of the compressor is divided into two paths after passing through the a-d channel of the four-way reversing valve. One path releases heat to the coolant circuit through the chiller, and then enters the second electronic expansion valve for throttling, and the other path releases heat through the defrosting heat exchanger, the full-pass throttle valve, and the indoor heat exchanger in sequence and then enters the first electronic expansion valve for throttling. The two paths converge at the outlets of the first electronic expansion valve and the second electronic expansion valve and then enter the outdoor heat exchanger to absorb heat. Finally, they return to the compressor through the b and c port channels of the four-way reversing valve, the gas-liquid separator, and the second heat exchange channel of the regenerator in sequence.

[0012] A further improvement of the system of the present invention is that it further includes:

[0013] A return air temperature sensor for measuring and obtaining the return air temperature value of the air handling unit;

[0014] A battery temperature sensor for measuring and obtaining the initial battery temperature value;

[0015] A control unit for adjusting the target exhaust pressure based on the proximity of the return air temperature value obtained by the return air temperature sensor to the target temperature value and the change rate of the return air temperature; and for controlling the opening degrees of the first electronic expansion valve and the second electronic expansion valve based on the initial battery temperature value obtained by the battery temperature sensor at startup.

[0016] A control method for a transcritical carbon dioxide electric vehicle thermal management system provided by the present invention includes the following steps:

[0017] After receiving the startup instruction, obtain the initial return air temperature value and the initial battery temperature value;

[0018] Based on the initial return air temperature value, determine the preset exhaust pressure value and the preset exhaust temperature value threshold when the compressor starts; based on the initial battery temperature value, determine the flow rate distribution of the refrigerant passing through the first electronic expansion valve and the second electronic expansion valve;

[0019] The compressor starts at the maximum speed, controls the opening degrees of the first electronic expansion valve and the second electronic expansion valve with the preset exhaust pressure value as the target exhaust pressure value, and obtains the current return air temperature value and the current compressor exhaust temperature value;

[0020] After controlling the air damper of the air handling unit to operate in the fresh air mode for a predetermined time, set the current target exhaust pressure value according to the proximity of the current return air temperature value to the target temperature value and the change rate of the current return air temperature value;

[0021] Based on the comparison between the current compressor exhaust temperature value and the preset exhaust temperature value threshold, end the startup phase.

[0022] A further improvement of the control method of the present invention is that the step of determining the preset exhaust pressure value and the preset exhaust temperature value threshold when the compressor starts based on the initial return air temperature value includes:

[0023] In the refrigeration mode, when T star-up ≥ 45 °C, the preset exhaust pressure value is 12 - 13 MPa, and the preset exhaust temperature threshold is 135 - 145 °C; when 35 ≤ T star-up <45 °C, the preset exhaust pressure value is 11.5 - 12.5 MPa, and the preset exhaust temperature threshold is 125 - 135 °C; when T star-upWhen the temperature is below 35°C, the preset exhaust pressure value is 11 - 12 MPa, and the preset exhaust temperature threshold is 120 - 130°C;

[0024] In the heating mode, when T star-up ≥ 0°C, the preset exhaust pressure value is 8 - 9 MPa, and the preset exhaust temperature threshold is 110 - 120°C; when -20 ≤ T star-up <0°C, the preset exhaust pressure value is 8.5 - 9.5 MPa, and the preset exhaust temperature threshold is 120 - 130°C; when T star-up <-20°C, the preset exhaust pressure value is 9 - 10 MPa, and the preset exhaust temperature threshold is 130 - 140°C;

[0025] Among them, T star-up is the initial return air temperature value.

[0026] A further improvement of the control method of the present invention is that the step of determining the flow rate distribution of the refrigerant passing through the first electronic expansion valve and the second electronic expansion valve based on the initial battery temperature value includes:

[0027] When the initial battery temperature value is lower than 0°C, control the first electronic expansion valve to close so that all the refrigerant passes through the Chiller to release heat for battery heating until the battery temperature value rises to 0°C, and then control the opening degrees of the first electronic expansion valve and the second electronic expansion valve to evenly distribute the refrigerant flow rate;

[0028] When the initial battery temperature value is greater than or equal to 0°C, control the opening degrees of the first electronic expansion valve and the second electronic expansion valve to evenly distribute the refrigerant flow rate.

[0029] A further improvement of the control method of the present invention is that the step of controlling the air damper of the air handling unit to operate in the fresh air mode for a predetermined time and then setting the current target exhaust pressure value according to the proximity of the current return air temperature value to the target temperature value and the change rate of the current return air temperature value includes:

[0030] Obtain the return air temperature value at the pre-designed starting time point of timing, and then record the return air temperature value every timing step τ;

[0031] Calculate the change rate of the current return air temperature value, and the calculation expression is where T current is the currently recorded return air temperature value, and T before is the previously recorded return air temperature value;

[0032] Calculate the proximity of the current return air temperature value to the target temperature value, and the calculation expression is: where T target is the target temperature value of the carriage, and T current is the currently recorded return air temperature value;

[0033] Set the current target exhaust pressure value P according to the percentage ν of the change rate of the current return air temperature value current , and the calculation formula is: In the formula, P star-up is the exhaust pressure value at system startup, ΔP is the minimum adjustment step of the exhaust pressure, and k is the pressure adjustment coefficient determined by experiments.

[0034] A further improvement of the control method of the present invention lies in that the obtaining step of the pre-designed timing start point includes: when the battery temperature value is lower than 0°C at the start of the compressor, 30s after the battery temperature value rises to 0°C is used as the pre-designed timing start point; when the battery temperature value is greater than or equal to 0°C at the start of the compressor, 30s after the start of the compressor is used as the pre-designed timing start point.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The system provided by the present invention adjusts the target exhaust pressure according to the proximity between the return air temperature and the target temperature and the change rate of the return air temperature. Increasing the exhaust pressure at startup can significantly improve the heating capacity in the heating mode and the cooling capacity in the cooling mode of the system, and can quickly make the temperature in the compartment close to the target temperature. In addition, in a low-temperature environment, the system provided by the present invention also preferentially distributes the refrigerant flow to the battery to preferentially increase the battery temperature, can recover part of the battery power, avoid the low-temperature capacity attenuation of the battery, and effectively improve the winter cruising range of the electric vehicle.

[0037] In the present invention, a scheme for the system to operate from the maximum capacity mode to the economy mode at different initial ambient temperatures is given. When the return air temperature in the compartment is relatively close to the target temperature in the compartment, switching to the economy mode can quickly and stably control the temperature in the compartment while reducing the power consumption, and effectively improve the cruising range of the electric vehicle. Brief Description of the Drawings

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following briefly introduces the drawings required for the description of the embodiments or the prior art; obviously, the drawings in the following description are some embodiments of the present invention, and those of ordinary skill in the art can also obtain other drawings based on these drawings without creative efforts.

[0039] Figure 1 is a schematic structural diagram of a transcritical carbon dioxide electric vehicle thermal management system according to an embodiment of the present invention;

[0040] In the figure, 1 is a compressor; 2 is a four-way reversing valve; 3 is an outdoor heat exchanger; 4 is a regenerator; 5 is a first electronic expansion valve; 6 is a second electronic expansion valve; 7 is a Chiller; 8 is a fan; 9 is a gas-liquid separator; 10 is a water pump; 11 is a battery pack heat exchanger; 12 is an expansion tank; 13 is an indoor heat exchanger; 14 is an all-pass expansion valve; 15 is a defrosting heat exchanger; 16 is a first air damper; 17 is a second air damper; 18 is a third air damper; 19 is a return air temperature sensor; 20 is a battery temperature sensor; 21 is a control unit. Detailed implementation manners

[0041] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0042] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily need to be used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0043] The present invention will be further described in detail below in conjunction with the accompanying drawings:

[0044] Please refer to Figure 1 , a transcritical carbon dioxide electric vehicle thermal management system according to an embodiment of the present invention is divided into a coolant circuit and a refrigerant circuit; wherein, the system includes an expansion tank 12, a battery pack heat exchanger 11, a water pump 10, a compressor 1, a four-way reversing valve 2, an outdoor heat exchanger 3, a regenerator 4, a first electronic expansion valve 5, a second electronic expansion valve 6, a Chiller 7 (battery cooler), a gas-liquid separator 9, an indoor heat exchanger 13, an all-pass expansion valve 14 and a defrosting heat exchanger 15;

[0045] In the coolant circuit, the Chiller 7, the expansion tank 12, the battery pack heat exchanger 11 and the water pump 10 are connected in series in sequence.

[0046] In the refrigerant circuit, the outlet of the compressor 1 is connected to port a of the four-way reversing valve 2. The pipeline after the b port of the four-way reversing valve 2 is successively connected in series with the outdoor heat exchanger 3 and the first heat exchange channel of the regenerator 4 and then divided into two paths. One path is successively connected to the second electronic expansion valve 6, the Chiller 7 and then connected to port d of the four-way reversing valve 2. The other path is successively connected to the first electronic expansion valve 5, the indoor heat exchanger 13, the full-pass expansion valve 14, the defrosting heat exchanger 15 and then connected to port d of the four-way reversing valve 2. The c port of the four-way reversing valve 2 is successively connected to the compressor 1 inlet through the gas-liquid separator 9 and the second heat exchange channel of the regenerator 4.

[0047] The indoor heat exchanger 13 and the defrosting heat exchanger 15 are arranged in the air-conditioning box. The air-conditioning box is provided with a blower 8, a first air damper 16, a second air damper 17 and a third air damper 18. Among them, the blower 8 is used to blow air from outside the vehicle or the passenger compartment into the air-conditioning box through the first air damper 16. The second air damper 17 is used to control the on-off of the air passage between the indoor heat exchanger 13 and the defrosting heat exchanger 15. The third air damper 18 is used to let the air in the air-conditioning box out to the passenger compartment.

[0048] In the embodiment of the present invention, the four-way reversing valve 2 can be used to control the quick start of the transcritical carbon dioxide electric vehicle thermal management system to switch between the refrigeration mode and the heating mode. In the refrigeration mode: the high-temperature and high-pressure steam at the outlet of the compressor 1 enters the outdoor heat exchanger 3 and the first heat exchange channel of the regenerator 4 through the a-b channel of the four-way reversing valve 2 in sequence to release heat. Then the refrigerant is divided into two paths. One path enters the Chiller 7 through the throttling of the second electronic expansion valve 6 to absorb the heat of the coolant circuit. The other path enters the indoor heat exchanger 13, the full-pass expansion valve 14 and the defrosting heat exchanger 15 in sequence through the throttling of the first electronic expansion valve 5 to absorb heat. The two paths converge at the outlets of the Chiller 7 and the defrosting heat exchanger 15 and enter the gas-liquid separator 9 and the second heat exchange channel of the regenerator 4 in sequence through the d-c channel of the four-way reversing valve 2 and then return to the compressor 1. In the heating mode: the high-temperature and high-pressure steam at the outlet of the compressor 1 is divided into two paths after passing through the a-d channel of the four-way reversing valve 2. One path releases heat to the coolant circuit through the Chiller 7 and then enters the second electronic expansion valve 6 for throttling. The other path releases heat through the defrosting heat exchanger 15, the full-pass throttle valve and the indoor heat exchanger 13 in sequence and then enters the first electronic expansion valve 5 for throttling. The two paths converge at the outlets of the first electronic expansion valve 5 and the second electronic expansion valve 6 and then enter the outdoor heat exchanger 3 to absorb heat. Finally, they return to the compressor 1 in sequence through the b-c channel of the four-way reversing valve 2, the gas-liquid separator 9 and the second heat exchange channel of the regenerator 4.

[0049] In a specific and explanatory embodiment of the present invention, a compressor 1 is used to input refrigerant in a normal temperature and low pressure state and output refrigerant in a high temperature and high pressure state after compression; a four-way reversing valve 2 is used to realize the switching between the refrigeration mode and the heating mode of the system; wherein, the four-way reversing valve 2 is provided with ports a, b, c, and d. When ports a and b are connected and ports c and d are connected, the system is in the refrigeration mode, and the refrigerant in the high temperature and high pressure state output by the compressor 1 enters the outdoor heat exchanger 3 through the four-way reversing valve 2 to release heat; when ports a and d are connected and ports b and c are connected, the system is in the heating mode, and the refrigerant in the high temperature and high pressure state output by the compressor 1 enters the indoor heat exchanger 13 and the defrosting heat exchanger 15 through the four-way reversing valve 2 to release heat; for the outdoor heat exchanger 3, in the refrigeration mode, the refrigerant flow channel of the outdoor heat exchanger 3 is used to input the refrigerant in the high temperature and high pressure state output by the compressor 1 and output the refrigerant in the normal temperature and high pressure state after heat exchange. The cold flow cold quantity is provided by the outside air in the air flow channel of the outdoor heat exchanger 3; in the heating mode, the refrigerant flow channel in the outdoor heat exchanger 3 is used to input the refrigerant in the low temperature and low pressure state output by the expansion valve and output the refrigerant in the normal temperature and high pressure state after heat exchange. The heat is provided by the outside air in the air flow channel of the outdoor heat exchanger 3; for the regenerator 4, the high-pressure side flow channel in the regenerator 4 is used to exchange heat between the refrigerant in the high temperature and high pressure state and the refrigerant in the low temperature and low pressure state input by the low-pressure side flow channel in the regenerator 4, reducing the temperature before the expansion valve and increasing the suction temperature of the compressor 1 at the same time, playing a role in improving the overall performance of the system; the electronic expansion valve is used to input the refrigerant in the normal temperature and high pressure state and output the refrigerant in the low temperature and low pressure state after throttling; for the Chiller 7 (battery cooler), in the battery cooling mode, the refrigerant flow channel in the heat exchanger is used to input the refrigerant in the low temperature and low pressure state output by the expansion valve, and after exchanging heat with the high-temperature coolant input by the coolant flow channel in the heat exchanger, it outputs, and the coolant flow channel outputs the low-temperature coolant into the battery pack heat exchanger 11 to cool the battery; in the battery heating mode, the refrigerant flow channel in the heat exchanger is used to input the refrigerant in the high temperature and high pressure state output by the compressor 1, and after exchanging heat with the low-temperature coolant input by the coolant flow channel in the heat exchanger, it outputs, and the coolant flow channel outputs the high-temperature coolant into the battery pack heat exchanger 11 to heat the battery; the indoor heat exchanger 13 and the defrosting heat exchanger 15 are arranged in series. In the refrigeration mode, the refrigerant flow channel in the heat exchanger is used to input the refrigerant in the low temperature and low pressure state output by the expansion valve to absorb the heat in the air in the carriage in the air flow channel of the heat exchanger to reduce the temperature of the carriage, and output the refrigerant in the normal temperature and high pressure state after heat exchange; in the heating mode, the refrigerant flow channel in the heat exchanger is used to input the refrigerant in the high temperature and high pressure state output by the compressor 1 to release heat to the air in the carriage in the air flow channel of the heat exchanger to increase the temperature of the carriage, and output the refrigerant in the normal temperature and high pressure state after heat exchange; the gas-liquid separator 9 inputs the refrigerant in the two-phase state and outputs the refrigerant in the gas phase state.

[0050] The system provided by the embodiments of the present invention adjusts the target exhaust pressure according to the proximity between the return air temperature and the target temperature and the change rate of the return air temperature. Increasing the exhaust pressure during startup can significantly improve the heating capacity in the heating mode and the cooling capacity in the cooling mode of the system, and can quickly make the temperature inside the vehicle close to the target temperature. In addition, in a low-temperature environment, the system provided by the present invention also preferentially distributes the refrigerant flow to the battery to preferentially increase the battery temperature, which can restore part of the battery power, avoid the low-temperature capacity attenuation of the battery, and effectively improve the winter cruising range of the electric vehicle.

[0051] In the embodiments of the present invention, it further includes a return air temperature sensor 19, a battery temperature sensor 20, and a control unit 21. Among them, the return air temperature sensor 19 is arranged at the first air damper 16 to measure the real-time return air temperature and return it to the control unit 21. In the rapid startup stage, the control unit 21 controls the opening degrees of the first electronic expansion valve 5 and the second electronic expansion valve 6 according to the proximity between the return air temperature and the target temperature and the change rate of the return air temperature.

[0052] The battery temperature sensor 20 is arranged at the outlet of the battery pack heat exchanger 11 to measure the initial battery temperature at startup and return it to the control unit 21. At startup, the control unit 21 controls the opening degrees of the first electronic expansion valve 5 and the second electronic expansion valve 6 according to the battery temperature value to allocate the passing refrigerant flow ratio.

[0053] In the present invention, a scheme for the system to operate from the maximum capacity mode to the economy mode at different initial ambient temperatures is given. When the return air temperature in the vehicle compartment is relatively close to the target temperature in the vehicle compartment, switching to the economy mode can quickly and stably control the temperature in the compartment while reducing the power consumption, and effectively improve the cruising range of the electric vehicle.

[0054] A control method for a transcritical carbon dioxide electric vehicle thermal management system according to an embodiment of the present invention includes the following steps:

[0055] Step S01: When the thermal management system receives a startup instruction, start the fan at the maximum speed and start the water pump at the maximum power, and read the current battery temperature value and return air temperature value.

[0056] Step S02: Determine the flow distribution of the refrigerant passing through the first electronic expansion valve and the second electronic expansion valve according to the battery temperature value.

[0057] Step S03: Determine the preset exhaust pressure value and the preset exhaust temperature threshold when the compressor starts according to the return air temperature value.

[0058] Step S04: Control the compressor to start at the maximum speed, and at the same time control the opening degrees of the first electronic expansion valve and the second electronic expansion valve with the preset starting exhaust pressure value as the target exhaust pressure value, and read the current return air temperature value and the exhaust temperature value of the compressor.

[0059] Step S05: Control the first air damper to make the system operate in the fresh air mode for a certain period of time, and then set the current target exhaust pressure value according to the proximity of the current return air temperature value to the target temperature value of the compartment and the change rate of the current return air temperature value.

[0060] Step S06: Use the current exhaust temperature value of the compressor as the basis for the end of the quick start phase.

[0061] In an optional embodiment of the present invention, the electronic expansion valve can be used bidirectionally and can be completely closed.

[0062] In an embodiment of the present invention, the step of determining the flow rate distribution of the refrigerant passing through the first electronic expansion valve and the second electronic expansion valve according to the battery temperature value includes:

[0063] When the current battery temperature value is lower than 0°C, control the first electronic expansion valve to close so that all the refrigerant is released through the Chiller to generate heat for battery warming, and when the battery temperature value rises to 0°C, control the opening degrees of the first electronic expansion valve and the second electronic expansion valve to evenly distribute the refrigerant flow rate.

[0064] When the current battery temperature value is greater than or equal to 0°C, control the opening degrees of the first electronic expansion valve and the second electronic expansion valve to evenly distribute the refrigerant flow rate.

[0065] In an embodiment of the present invention, the step of determining the starting target exhaust pressure value and the starting preset exhaust temperature value of the compressor according to the return air temperature value includes:

[0066] Read the return air temperature value T when the fan starts star-up , and determine the starting preset exhaust pressure and the starting preset exhaust temperature threshold according to the starting return air temperature value T star- and the preset initial temperature range.

[0067] In the refrigeration mode, when T star-up ≥45°C, the above-mentioned starting preset pressure value can be 12 - 13 MPa, where the recommended starting preset pressure value is 12.5 MPa, and the above-mentioned starting preset exhaust temperature threshold can be 135 - 145°C, where the recommended starting preset exhaust temperature threshold is 140°C; when 35 ≤ T star-When the temperature is below 45°C, the above-mentioned starting preset pressure value can be 11.5 to 12.5 MPa, and the recommended starting preset pressure value is 12 MPa. The above-mentioned starting preset exhaust temperature threshold can be 125 to 135°C, and the recommended starting preset exhaust temperature threshold is 130°C; when T star-up When the temperature is below 35°C, the above-mentioned starting preset pressure value can be 11 to 12 MPa, and the recommended starting preset pressure value is 11.5 MPa. The above-mentioned starting preset exhaust temperature threshold can be 120 to 130°C, and the recommended starting preset exhaust temperature threshold is 125°C;

[0068] In the heating mode, when T star- ≥0°C, the above-mentioned starting preset pressure value can be 8 to 9 MPa, and the recommended starting preset pressure value is 8.5 MPa. The above-mentioned starting preset exhaust temperature threshold can be 110 to 120°C, and the recommended starting preset exhaust temperature threshold is 115°C; when -20 ≤ T star-up <0°C, the above-mentioned starting preset pressure value can be 8.5 to 9.5 MPa, and the recommended starting preset pressure value is 9 MPa. The above-mentioned starting preset exhaust temperature threshold can be 120 to 130°C, and the recommended starting preset exhaust temperature threshold is 125°C; when T star-up <-20°C, the above-mentioned starting preset pressure value can be 9 to 10 MPa, and the recommended starting preset pressure value is 9.5 MPa. The above-mentioned starting preset exhaust temperature threshold can be 130 to 140°C, and the recommended starting preset exhaust temperature threshold is 135°C.

[0069] In the embodiments of the present invention, setting the current target exhaust pressure value according to the change rate of the current return air temperature value includes:

[0070] Obtain the target temperature value T of the carriage target , when the battery temperature value is lower than 0°C when the compressor starts, use 30 s after the battery temperature value rises to 0°C as the timing starting point. When the battery temperature value is greater than or equal to 0°C when the compressor starts, use 30 s after the compressor starts as the timing starting point, and obtain the return air temperature value at the timing starting point. Thereafter, record the return air temperature value every timing step τ.

[0071] Calculate the change rate of the current return air temperature value according to the following formula: In the formula, T current is the currently recorded return air temperature value, T before is the previously recorded return air temperature value. The unit of the temperature value adopts the international temperature scale. In the refrigeration mode, the return air temperature gradually decreases, and in the heating mode, the return air temperature gradually increases. Therefore, when calculating the change rate of the current return air temperature value, the absolute value of the difference between the two recorded temperature values needs to be taken.

[0072] The proximity between the current return air temperature value and the target temperature value is obtained according to the following formula: In the formula, T target is the target temperature value of the carriage, and T current is the currently recorded return air temperature value. The unit of the temperature value adopts the international temperature scale. In the refrigeration mode, the current return air temperature is higher than the target temperature of the carriage. In the heating mode, the current return air temperature is lower than the target temperature value of the carriage. Therefore, the absolute value of the difference between the current return air temperature value and the target temperature value of the carriage needs to be taken during calculation.

[0073] The current target exhaust pressure value P is set according to the percentage ν of the change rate of the current return air temperature value current , and the calculation formula is:

[0074] In the formula, P star-up is the exhaust pressure value at system startup, ΔP is the minimum adjustment step of the exhaust pressure, and k is the pressure adjustment coefficient determined by experiments.

[0075] When the current compressor exhaust temperature value reaches the startup preset exhaust temperature value, the thermal management system ends the fast startup stage and controls the opening degrees of the first expansion valve and the second expansion valve to enter the economic mode stage with the optimal exhaust pressure calculated according to the current system state parameters as the target exhaust pressure.

[0076] In summary, the embodiments of the present invention disclose a fast-starting transcritical carbon dioxide electric vehicle thermal management system, which is divided into a coolant circuit and a refrigerant circuit, and includes an expansion tank, a battery pack heat exchanger, a water pump, a compressor, a four-way reversing valve, an outdoor heat exchanger, a regenerator, a first electronic expansion valve, a second electronic expansion valve, a chiller, a gas-liquid separator, an indoor heat exchanger, a full-pass expansion valve, and a defrosting heat exchanger. In the coolant circuit, the chiller, the expansion tank, the battery pack heat exchanger, and the water pump are connected in series in sequence. In the refrigerant circuit, the outlet of the compressor is connected to port a of the four-way reversing valve. The pipeline after port b of the four-way reversing valve is connected in series with the outdoor heat exchanger and the first heat exchange channel of the regenerator and then is divided into two paths. One path is sequentially connected to the second electronic expansion valve, the chiller, and then to port d of the four-way reversing valve. The other path is sequentially connected to the first electronic expansion valve, the indoor heat exchanger, the full-pass expansion valve, the defrosting heat exchanger, and then to port d of the four-way reversing valve. Port c of the four-way reversing valve is sequentially connected to the inlet of the compressor through the gas-liquid separator and the second heat exchange channel of the regenerator. The control method provided by the embodiments of the present invention adjusts the target discharge pressure according to the proximity between the return air temperature and the target temperature and the change rate of the return air temperature, and gives a scheme for the system to operate in the maximum capacity mode and then switch to the economic mode at different initial ambient temperatures. It can quickly bring the vehicle interior temperature to a suitable range, ensure the comfort of passengers while saving power consumption during startup. In addition, the present invention also adjusts the refrigerant flow distribution in low-temperature environments to preferentially maintain the battery temperature, avoid the low-temperature capacity attenuation of the battery, and effectively increase the driving range of electric vehicles in winter.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications or equivalent replacements can still be made to the specific embodiments of the present invention. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention shall be covered by the protection scope of the claims of the present invention.

Claims

1. A control method for a transcritical carbon dioxide electric vehicle thermal management system, characterized in that: The transcritical carbon dioxide electric vehicle thermal management system comprises: a compressor (1), a four-way reversing valve (2), an outdoor heat exchanger (3), a regenerator (4), a first electronic expansion valve (5), a second electronic expansion valve (6), a chiller (7), a gas-liquid separator (9), a water pump (10), a battery pack heat exchanger (11), an expansion water tank (12), an indoor heat exchanger (13), a full-pass expansion valve (14) and a defrost heat exchanger (15); wherein the four-way reversing valve (2) is provided with ports a, b, c and d; the indoor heat exchanger (13) and the defrost heat exchanger (15) are arranged in an air conditioning box; the chiller (7), the expansion water tank (12), the battery pack heat exchanger (11) and the water pump (10) are connected in series in sequence to form a coolant circuit in the transcritical carbon dioxide electric vehicle thermal management system; the outlet of the compressor (1) is connected to the four-way reversing valve (2 ), the port b of the four-way reversing valve (2) is connected in series with the outdoor heat exchanger (3) and the first heat exchange channel of the regenerator (4), and the pipeline is divided into two paths. One path is connected in series with the second electronic expansion valve (6) and the chiller (7) and then connected to the port d of the four-way reversing valve (2); the other path is connected in series with the first electronic expansion valve (5), the indoor heat exchanger (13), the full-pass expansion valve (14), the defrost heat exchanger (15) and then connected to the port d of the four-way reversing valve (2); the port c of the four-way reversing valve (2) is connected in series with the gas-liquid separator (9) and the second heat exchange channel of the regenerator (4) and then connected to the inlet of the compressor (1), forming a refrigerant circuit in the transcritical carbon dioxide electric vehicle thermal management system; wherein the four-way reversing valve (2) is used to control the transcritical carbon dioxide electric vehicle thermal management system to switch between a cooling mode and a heating mode; The transcritical carbon dioxide electric vehicle thermal management system further comprises: a return air temperature sensor (19) for measuring and obtaining the return air temperature value of the air conditioning box; a battery temperature sensor (20) for measuring and obtaining the initial battery temperature value; a control unit (21) for adjusting the target exhaust pressure based on the proximity between the return air temperature value obtained by the return air temperature sensor (19) and the target temperature value and the rate of change of the return air temperature; and for controlling the opening of the first electronic expansion valve (5) and the second electronic expansion valve (6) based on the initial battery temperature value obtained by the battery temperature sensor (20) at startup; The control method of the thermal management system of the transcritical carbon dioxide electric vehicle comprises the following steps: After receiving the power-on command, the initial return air temperature value and the initial battery temperature value are obtained; Determine a preset exhaust pressure value and a preset exhaust temperature value threshold when the compressor is started based on the initial return air temperature value; determine a flow distribution of the refrigerant through the first electronic expansion valve and the second electronic expansion valve based on the initial battery temperature value; The compressor is started at the maximum speed, and the openings of the first electronic expansion valve and the second electronic expansion valve are controlled according to the preset exhaust pressure value as the target exhaust pressure value, and the current return air temperature value and the current compressor exhaust temperature value are obtained; After controlling the damper of the air conditioning box to operate in the fresh air mode for a predetermined time, setting the current target exhaust pressure value according to the proximity between the current return air temperature value and the target temperature value and the rate of change of the current return air temperature value; When the current compressor exhaust temperature reaches the preset exhaust temperature value for startup, the thermal management system ends the quick startup phase, controls the opening of the first expansion valve and the second expansion valve to use the optimal exhaust pressure calculated based on the current system state parameters as the target exhaust pressure to enter the economic mode phase.

2. The control method of a transcritical carbon dioxide electric vehicle thermal management system according to claim 1, characterized in that: The step of determining a preset exhaust pressure value and a preset exhaust temperature value threshold when the compressor is started based on the initial return air temperature value comprises: In cooling mode, when ≥45℃, the preset exhaust pressure value is 12~13MPa, and the preset exhaust temperature threshold is 135~145℃; when 35≤ When the temperature is lower than 45℃, the preset exhaust pressure value is 11.5~12.5MPa, and the preset exhaust temperature threshold is 125~135℃; when When the temperature is less than 35℃, the preset exhaust pressure value is 11~12MPa, and the preset exhaust temperature threshold is 120~130℃; In heating mode, when ≥0℃, the preset exhaust pressure value is 8~9MPa, and the preset exhaust temperature threshold is 110~120℃; when -20≤ When the temperature is lower than 0℃, the preset exhaust pressure value is 8.5~9.5MPa, and the preset exhaust temperature threshold is 120~130℃; when When the temperature is less than -20℃, the preset exhaust pressure value is 9~10MPa, and the preset exhaust temperature threshold is 130~140℃; in, is the initial return air temperature value.

3. The control method of a transcritical carbon dioxide electric vehicle thermal management system according to claim 1, characterized in that: The step of determining the flow distribution of the refrigerant through the first electronic expansion valve and the second electronic expansion valve based on the initial battery temperature value comprises: When the initial battery temperature is lower than 0°C, the first electronic expansion valve is controlled to close so that all the refrigerant releases heat through the Chiller to heat the battery. When the battery temperature reaches 0°C, the opening of the first and second electronic expansion valves is controlled to evenly distribute the refrigerant flow. When the initial battery temperature value is greater than or equal to 0° C., the openings of the first electronic expansion valve and the second electronic expansion valve are controlled to evenly distribute the refrigerant flow.

4. The control method of a transcritical carbon dioxide electric vehicle thermal management system according to claim 1, characterized in that: After the damper of the air conditioner is controlled to operate in the fresh air mode for a predetermined time, the step of setting the current target exhaust pressure value according to the proximity between the current return air temperature value and the target temperature value and the change rate of the current return air temperature value comprises: Get the return air temperature value at the preset timing starting point, and then every timing step Record the return air temperature value once; The current return air temperature change rate is calculated and the calculation expression is: ; In the formula, is the currently recorded return air temperature value, is the return air temperature value recorded last time; The calculation expression is as follows: ; In the formula, is the target cabin temperature value, is the currently recorded return air temperature value; According to the percentage of the rate of change of the current return air temperature value Set the current target exhaust pressure value , the calculation expression is: ; In the formula, It is the system startup exhaust pressure value. is the minimum adjustment step of exhaust pressure, is the experimentally determined pressure adjustment factor.

5. The control method of a transcritical carbon dioxide electric vehicle thermal management system according to claim 4, characterized in that: The step of obtaining the preset timing starting point includes: when the battery temperature value is lower than 0°C when the compressor is started, 30 seconds after the battery temperature rises to 0°C is used as the preset timing starting point; when the battery temperature value is greater than or equal to 0°C when the compressor is started, 30 seconds after the compressor is started is used as the preset timing starting point.

6. The control method of a transcritical carbon dioxide electric vehicle thermal management system according to claim 1, characterized in that: In cooling mode: the high-temperature and high-pressure steam at the outlet of the compressor (1) enters the outdoor heat exchanger (3) and the first heat exchange channel of the regenerator (4) in turn through the a and b ports of the four-way reversing valve (2) to release heat; then the refrigerant is divided into two paths, one path passes through the second electronic expansion valve (6) and enters the chiller (7) to absorb heat from the coolant circuit, and the other path passes through the first electronic expansion valve (5) and enters the indoor heat exchanger (13), the full-pass expansion valve (14) and the defrost heat exchanger (15) in turn to absorb heat. The two paths meet at the outlets of the chiller (7) and the defrost heat exchanger (15), pass through the d and c ports of the four-way reversing valve (2), enter the gas-liquid separator (9) and the second heat exchange channel of the regenerator (4) in turn, and then return to the compressor (1).

7. The control method of a transcritical carbon dioxide electric vehicle thermal management system according to claim 1, characterized in that: In heating mode: the high-temperature and high-pressure steam at the outlet of the compressor (1) passes through the ad channel of the four-way reversing valve (2) and is divided into two paths. One path releases heat to the coolant circuit through the chiller (7) and then enters the second electronic expansion valve (6) for throttling. The other path releases heat through the defrost heat exchanger (15), the full-pass throttle valve and the indoor heat exchanger (13) in sequence and then enters the first electronic expansion valve (5) for throttling. The two paths merge at the outlets of the first electronic expansion valve (5) and the second electronic expansion valve (6) and then enter the outdoor heat exchanger (3) to absorb heat. Finally, the steam passes through the b and c port channels of the four-way reversing valve (2), the gas-liquid separator (9) and the second heat exchange channel of the regenerator (4) in sequence and then returns to the compressor (1).

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