Coolant circulation system and vehicle battery temperature raising method

Abstract

To provide a technique capable of suppressing generation of cavitation in a water pump caused by flowing of high-temperature cooling water in a cooling circuit while raising a temperature of a vehicular battery that is being charged by using the cooling water warmed by a cooling target unit.SOLUTION: When a condition of raising a temperature of a battery 12 is satisfied, a circuit state is switched from a first circuit state where a first cooling circuit 10 and a second cooling circuit 20 are disconnected to a second circuit state where the first cooling circuit 10 and the second cooling circuit 20 are connected to form one circuit. The first cooling circuit 10 is a cooling circuit in which a first water pump 13, a chiller 14 and the battery 12 are connected annularly. The second cooling circuit 20 is a cooling circuit in which a second water pump 24, cooling target units 25-27 and a radiator 22 are connected annularly, After switching to the second circuit state, a drive duty of at least one of the first water pump 13 and the second water pump 24 is lowered for a predetermined time.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a cooling water circulation device and a method for raising the temperature of a vehicle battery. [Background technology]

[0002] Patent Document 1 discloses a technology for cooling a battery by circulating coolant between the battery and the radiator using a water pump. This technology places the water pump at a position lower than the battery or at the same height as the battery, preventing the pressure of the coolant flowing out of the battery's coolant outlet from decreasing before it reaches the water pump's intake port. By maintaining the coolant pressure at the water pump's intake port, the occurrence of cavitation within the water pump is suppressed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-107420 A Summary of the Invention [Problem to be solved by the invention]

[0004] When charging a battery, it is sometimes necessary to heat the battery to reduce charging time. One method for heating the battery is to run high-temperature coolant, which has been heated by another unit to be cooled, through the battery. However, the occurrence of cavitation in a water pump is affected not only by pressure but also by water temperature. Specifically, the higher the water temperature, the higher the saturated vapor pressure, so running high-temperature coolant through the circuit makes it more likely that cavitation will occur inside the water pump.

[0005] The present disclosure has been made in view of the above-mentioned problems, and aims to provide a technology that can raise the temperature of a vehicle battery using coolant heated by a unit to be cooled, while suppressing the occurrence of cavitation in a water pump caused by high-temperature coolant flowing through a cooling circuit. [Means for solving the problem]

[0006] The present disclosure provides a coolant circulation device to achieve the above-mentioned object. The coolant circulation device of the present disclosure includes a first cooling circuit, a second cooling circuit, a switching valve, and a control device. The first cooling circuit is a circuit in which a first water pump, a chiller, and a vehicle battery are connected in a circular configuration. The second cooling circuit is a circuit in which a second water pump, a unit to be cooled, and a radiator are connected in a circular configuration. The switching valve is configured to switch the circuit state between a first circuit state in which the first cooling circuit and the second cooling circuit are separated, and a second circuit state in which the first cooling circuit and the second cooling circuit are connected to form a single circuit. The control device controls the first water pump, the second water pump, and the switching valve. When a condition for raising the temperature of the vehicle battery is met, the control device switches the circuit state to the second circuit state using the switching valve. Furthermore, when the circuit state is switched to the second circuit state, the control device reduces the drive duty of at least one of the first water pump and the second water pump for a predetermined time.

[0007] The present disclosure provides a method for heating a vehicle battery to achieve the above-mentioned object. The method for heating a vehicle battery of the present disclosure is a method for heating a vehicle battery in a vehicle equipped with a first cooling circuit and a second cooling circuit. The first cooling circuit is a circuit in which a first water pump, a chiller, and a vehicle battery are connected in a ring. The second cooling circuit is a circuit in which a second water pump, a unit to be cooled, and a radiator are connected in a ring. The method for heating a vehicle battery of the present disclosure includes, upon satisfaction of a condition for heating the vehicle battery, switching a circuit state from a first circuit state in which the first cooling circuit and the second cooling circuit are separated to a second circuit state in which the first cooling circuit and the second cooling circuit are connected to form a single circuit. The method for heating a vehicle battery of the present disclosure also includes, upon switching the circuit state to the second circuit state, reducing the drive duty of at least one of the first water pump and the second water pump for a predetermined time. [Effects of the Invention]

[0008] According to the coolant circulation system and vehicle battery heating method disclosed herein, when the conditions for heating the vehicle battery are met, the first cooling circuit and the second cooling circuit are connected, allowing high-temperature coolant heated by the unit to be cooled to flow to the vehicle battery. This promotes heating of the vehicle battery. The drive duty of at least one of the first water pump and the second water pump is reduced for a predetermined time, thereby reducing the flow rate within the cooling circuit and suppressing pressure loss, thereby suppressing a decrease in pressure at the inlet of the first water pump. This suppresses cavitation within the first water pump due to high-temperature coolant flowing through the cooling circuit. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a conceptual diagram showing a configuration of a coolant circulation device according to an embodiment of the present disclosure, illustrating a first circuit state. [Figure 2] FIG. 4 is a diagram illustrating a second circuit state of the cooling water circulation device according to the embodiment of the present disclosure. [Figure 3]6 is a diagram showing pressures at various positions in a second circuit state before a vehicle battery warming method according to an embodiment of the present disclosure is applied; FIG. [Figure 4] 1 is a diagram illustrating an overview of a method for increasing the temperature of a vehicle battery according to an embodiment of the present disclosure. [Figure 5] 3 is a flowchart illustrating a procedure for a vehicle battery temperature increasing method according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] A coolant circulation system according to an embodiment of the present disclosure is applied to a battery electric vehicle (BEV) equipped with a vehicle battery. The configuration of the coolant circulation system according to an embodiment of the present disclosure will be described below with reference to Figures 1 and 2. Figures 1 and 2 are conceptual diagrams showing the configuration of a coolant circulation system 100 according to an embodiment of the present disclosure.

[0011] As shown in FIG. 1, the coolant circulation system 100 includes two coolant circuits 10 and 20. The first coolant circuit (hereinafter referred to as the first coolant circuit) 10 is a cooling circuit for cooling a battery 12. The battery 12 is typically a lithium-ion battery. Specifically, the battery 12 refers to a battery pack in which multiple battery cells are housed in a case together with an electric circuit. The second coolant circuit (hereinafter referred to as the second coolant circuit) 20 is a cooling circuit for cooling units 25, 26, and 27 other than the battery 12. The units 25, 26, and 27 are typically a power supply unit 25 and a power supply control unit 26 including an inverter, which are heat-generating elements, and an oil cooler 27.

[0012] The first coolant circuit 10 includes a battery (BAT) 12, a water pump ( stThe cooling circuit has a water pump (W / P) 13 and a chiller (CHL) 14 connected in a circular fashion. The cooling water circulation device 100 has two water pumps, so the water pump 13 of the first cooling water circuit 10 is referred to as the first water pump to distinguish between them. By operating the first water pump 13, the cooling water circulates through the first water pump 13, chiller 14, battery 12, and then the first water pump 13 again.

[0013] The second coolant circuit 20 includes a radiator (RDT) 22, a reserve tank (R / T) 23, and a water pump ( nd The cooling circuit is a circularly connected cooling water circuit in which a water supply unit (W / P) 24, an electric power supply unit (ESU) 25, a power control unit (PCU) 26, and an oil cooler (O / L) 27 are connected. The water pump 24 of the second cooling water circuit 20 is called the second water pump to distinguish it from the first water pump 13. By operating the second water pump 24, the cooling water circulates through the second water pump 24, electric power supply unit 25, power control unit 26, oil cooler 27, radiator 22, reserve tank 23, and then back to the second water pump 24 in that order.

[0014] The coolant circulation device 100 includes a five-way valve (VLV) 30. The first coolant circuit 10 and the second coolant circuit 20 are connected to the five-way valve 30. More specifically, five pipes 11a, 11b, 11c, 21a, and 21b are connected to the five-way valve 30. Pipe 11a connects the five-way valve 30 to the coolant inlet of the battery 12. Pipe 11b connects the five-way valve 30 to the coolant outlet of the chiller 14. Pipe 11c bypasses the battery 12 and connects the five-way valve 30 to the coolant inlet of the first water pump 13. Pipe 21a connects the five-way valve 30 to the coolant outlet of the oil cooler 27. Pipe 21b connects the five-way valve 30 to the coolant inlet of the radiator 22.

[0015] The five-way valve 30 is a switching valve that switches the circuit state of the cooling water circulation device 100 by switching the connections between the pipes 11a, 11b, 11c, 21a, and 21b. In the circuit state shown in FIG. 1, the pipes 11a and 11b are connected, and the pipes 21a and 21b are connected, thereby separating the first cooling circuit 10 from the second cooling circuit 20. The circuit state shown in FIG. 1 is referred to as the first circuit state. The first circuit state is selected at least when cooling the batteries 12, and the batteries 12 are cooled by low-temperature cooling water cooled by the chiller 14.

[0016] The coolant circulation system 100 includes a control device (CTR) 40. The control device 40 is an on-board computer, such as an ECU (Electronic Control Unit). The control device 40 includes a processor and a program memory coupled to the processor. The processor may be, for example, a CPU (Central Processing Unit), an FPGA (Field-Programmable Gate Array), an ASIC (Application-Specific Integrated Circuit), or other processing unit. The processor may also be a combination of two or more of the CPU, FPGA, ASIC, or other processing units. The control device 40 controls at least the five-way valve 30, the first water pump 13, and the second water pump 24. The program memory stores a program for causing the control device 40 to execute a temperature-raising method according to this embodiment, which will be described later.

[0017] The five-way valve 30 switches the connections of the pipes in response to instructions from the control device 40. FIG. 2 shows one of the circuit states achieved by instructions from the control device 40 to the five-way valve 30. In the circuit state shown in FIG. 2, pipes 11a and 21a are connected, and pipes 11b and 21b are connected, thereby connecting the first cooling circuit 10 and the second cooling circuit 20 to form a single circuit. The circuit state shown in FIG. 2 is referred to as the second circuit state. In the second circuit state, by operating the first water pump 13 and the second water pump 24, the coolant circulates through the reserve tank 23, the second water pump 24, the power supply unit 25, the power supply control unit 26, the oil cooler 27, the battery 12, the first water pump 13, the chiller 14, the radiator 22, and then back to the reserve tank 23 in that order.

[0018] The second circuit state is selected at least during DC charging of the battery 12. When charging the battery 12, it is necessary to raise the temperature of the battery 12 in order to reduce the charging time of the battery 12. By switching the circuit state to the second circuit state, the coolant that has been heated while passing through the units to be cooled, namely the power supply unit 25, the power supply control unit 26, and the oil cooler 27, flows into the battery 12, and the battery 12 is raised in temperature by receiving heat from the high-temperature coolant.

[0019] Here, Fig. 3 shows examples of pressures at various positions on the cooling circuit when the first water pump 13 and the second water pump 24 are operated in the second circuit state. Fig. 3 shows four examples of different coolant temperatures at the inlet of the first water pump 13. However, in the examples shown in Fig. 3, the temperature increase method according to this embodiment is not applied to the control of the first water pump 13 and the second water pump 24.

[0020] As shown in FIG. 3, the pressure of the cooling water in the cooling circuit is the reference pressure in the reserve tank (R / T) 23, and the pressure in the second water pump (2 ndThe cooling water is then pressurized to a pressure higher than the reference pressure by the first water pump (1W / P) 24. Then, the cooling water flows from the unit to be cooled, such as the power supply unit (ESU) 25, through the five-way valve (VLV) 30 to the battery (BAT) 12, and is then pumped by the first water pump (1 st The pressure loss that occurs during this time causes the cooling water pressure to drop to a level lower than the reference pressure.

[0021] A drop in the coolant pressure at the inlet of first water pump 13 can sometimes lead to cavitation occurring within first water pump 13. The condition for cavitation to occur is when the pressure within first water pump 13 becomes lower than the saturated vapor pressure of the coolant, but the saturated vapor pressure varies depending on the temperature of the coolant. Therefore, it can be said that whether or not cavitation occurs depends on the operating conditions of first water pump 13, which are determined by the temperature and pressure of the coolant.

[0022] Figure 4 is a graph showing the relationship between temperature and saturated vapor pressure. As shown in this graph, saturated vapor pressure increases as the cooling water temperature increases. This means that if the pressure is constant, the higher the temperature, the more likely cavitation will occur, and if the temperature is constant, the lower the pressure, the more likely cavitation will occur.

[0023] Immediately after the circuit state is switched from the first circuit state to the second circuit state, high-temperature coolant heated by the unit to be cooled, such as the power supply unit 25, flows into the first water pump 13. Furthermore, when both the first water pump 13 and the second water pump 24 are operated, the pressure at the inlet of the first water pump 13 drops significantly below the reference pressure due to pressure loss that occurs when the coolant flows through the cooling circuit. Therefore, immediately after the circuit state is switched from the first circuit state to the second circuit state, the first water pump 13 operates under the temperature-pressure condition indicated by point A in the graph of FIG. 4. The temperature-pressure condition indicated by point A is an operating condition under which cavitation can occur.

[0024] One method for suppressing the occurrence of cavitation is to lower the temperature of the coolant, as shown by point D in the graph of Figure 4. By lowering the temperature of the coolant flowing into first water pump 13 and positioning the temperature-pressure condition at the inlet of first water pump 13 on the higher side of the saturated vapor pressure curve, the occurrence of cavitation can be suppressed. However, this method cannot be adopted because it contradicts the purpose of switching the circuit state, which is to increase the temperature of battery 12.

[0025] Another method for suppressing the occurrence of cavitation is to increase the pressure of the coolant, as shown by point B in the graph of FIG. 4. By increasing the pressure at the inlet of first water pump 13 and positioning the temperature-pressure condition at the inlet of first water pump 13 on the higher side of the saturated vapor pressure curve, the occurrence of cavitation can be suppressed. This method does not contradict the purpose of switching the circuit state, which is to increase the temperature of battery 12. This method is adopted as the temperature increase method according to this embodiment.

[0026] In this embodiment, the temperature increase method increases the pressure at the inlet of the first water pump 13 by reducing the pressure loss that occurs when the coolant flows through the cooling circuit. The pressure loss increases with the flow rate of the coolant through the cooling circuit. Therefore, by reducing the drive duty of at least one of the first water pump 13 and the second water pump 24, which circulate the coolant, the flow rate of the coolant can be reduced, thereby reducing the pressure loss. In other words, in the graph of FIG. 4, the operating condition of the first water pump 13 can be shifted from point A to point B.

[0027] The drive duty of at least one of the first water pump 13 and the second water pump 24 only needs to be reduced for a predetermined time after the circuit state is switched. Immediately after the circuit state is switched from the first circuit state to the second circuit state, a mass of high-temperature coolant that has flowed out from the units to be cooled, such as the power supply unit 25, is present in the cooling circuit. However, as time passes, the high-temperature coolant mixes evenly with the low-temperature coolant that was in the first cooling circuit 10, and high-temperature coolant no longer flows into the first water pump 13. In other words, as time passes after the circuit state is switched, the operating condition of the first water pump 13 shifts from point B to point C in the graph in Figure 4.

[0028] After the high-temperature coolant no longer flows into first water pump 13, the reduced drive duty can be increased to its original value. Operating both first water pump 13 and second water pump 24 at their normal drive duties increases the pressure loss that occurs when coolant flows through the cooling circuit, causing the pressure at the inlet of first water pump 13 to drop significantly below the reference pressure. However, because the coolant temperature has already dropped sufficiently, the temperature-pressure condition at the inlet of first water pump 13 is not located on the lower-pressure side of the saturated vapor pressure curve. That is, in the graph of FIG. 4, the operating condition of first water pump 13 can be shifted from point C to point D.

[0029] The time for which the drive duty is temporarily reduced is the time until the coolant temperature at the inlet of the first water pump 13 falls below a threshold value. This time can be a preset fixed time. However, the setting of the fixed time differs depending on whether the drive duty of the water pump to be reduced is the first water pump 13, the second water pump 24, or both. The setting of the fixed time also differs depending on how much the drive duty is reduced. One guideline for the set value of the drive duty is a value that does not completely stop the water pump and that can maintain the flow of coolant in the cooling circuit.

[0030] Alternatively, the temperature of the coolant at the inlet of the first water pump 13 may be measured, and when the measured value falls below a threshold, the drive duty may be increased to its original value. In this case, the time for which the drive duty is temporarily reduced is determined on an ad hoc basis. That is, in the temperature-raising method according to this embodiment, the drive duty of at least one of the first water pump 13 and the second water pump 24 is reduced for a predetermined time, and the predetermined time may be a fixed time or a time determined on an ad hoc basis.

[0031] The above is an outline of the temperature increasing method according to this embodiment. The temperature increasing method according to this embodiment is carried out by the control device 40 in accordance with the procedure shown in the flowchart of FIG.

[0032] In step S1, it is determined whether a condition is met to start raising the temperature of the battery 12. The start of DC charging of the battery 12 is included in the conditions to start raising the temperature of the battery 12. Steps S2 and subsequent steps are not performed until the condition is met.

[0033] Step S2 is performed when the conditions for starting to heat the battery 12 are met. In step S2, the five-way valve 30 is operated to switch the circuit state from a first circuit state in which the first cooling circuit 10 and the second cooling circuit 20 are separated to a second circuit state in which the first cooling circuit 10 and the second cooling circuit 20 are connected to form a single merged circuit.

[0034] After the circuit state is switched by the five-way valve 30, step S3 is performed. In step S3, both the first water pump 13 and the second water pump 24 are operated at the drive duty for normal operation. Normal operation here refers to operation of the coolant circulation device 100 to heat the battery 12. This causes a flow of coolant in the combined circuit where the first cooling circuit 10 and the second cooling circuit 20 are connected together.

[0035] After both the first water pump 13 and the second water pump 24 have been operated, step S4 is performed. In step S4, the drive duty of the first water pump 13 is temporarily reduced for a predetermined period of time. As described above, in order to reduce the flow rate of the coolant and thereby reduce pressure loss, it is possible to reduce the drive duty of either the first water pump 13 or the second water pump 24. However, reducing the drive duty of the first water pump 13 itself, which is the target for cavitation suppression, is more effective in suppressing the occurrence of cavitation.

[0036] Step S5 is performed after a predetermined time has elapsed since the drive duty of the first water pump 13 was reduced. In step S5, the drive duty of the first water pump 13 is restored to the drive duty during normal operation. This promotes the transfer of power from the units to be cooled, such as the power supply unit 25, to the battery 12, accelerating the temperature rise of the battery 12.

[0037] According to the temperature-raising method of this embodiment, which is carried out using the above procedure, when the conditions for raising the temperature of the battery 12 are met, the first cooling circuit 10 and the second cooling circuit 20 are connected, allowing high-temperature coolant heated by a unit to be cooled, such as the power supply unit 25, to flow to the battery 12. This promotes a temperature rise in the battery 12. Then, by temporarily reducing the drive duty of the first water pump 13 for a predetermined period of time, the flow rate in the cooling circuit is reduced, thereby suppressing pressure loss and a decrease in pressure at the inlet of the first water pump 13. This suppresses the occurrence of cavitation in the first water pump 13 due to high-temperature coolant flowing through the circuit. [Explanation of symbols]

[0038] 10 1st cooling water circuit 12 batteries 13 No. 1 water pump 14 Chiller 20 2nd cooling water circuit 22 Radiator 23 Reserve tank 24 Water pump 25 Power Supply Unit 26 Power Control Unit 27 Oil cooler 30 5-way valve 40 Control device 100 Cooling water circulation system

Claims

1. a first cooling circuit in which a first water pump, a chiller, and a vehicle battery are connected in a circular configuration; a second cooling circuit in which a second water pump, a unit to be cooled, and a radiator are connected in a circular manner; a switching valve configured to switch a circuit state between a first circuit state in which the first cooling circuit and the second cooling circuit are separated and a second circuit state in which the first cooling circuit and the second cooling circuit are connected to form a single circuit; a control device that controls the first water pump, the second water pump, and the switching valve, The control device When a condition for increasing the temperature of the vehicle battery is met, the switching valve switches the circuit state to the second circuit state; and reducing the drive duty of at least one of the first water pump and the second water pump for a predetermined time in response to the change of the circuit state to the second circuit state. A cooling water circulation device characterized by:

2. The cooling water circulating device according to claim 1, The control device is configured to reduce the drive duty of at least one of the first water pump and the second water pump for a predetermined time, and then restore the drive duty to the drive duty before the reduction. A cooling water circulation device characterized by:

3. The cooling water circulating device according to claim 1, The switching valve is configured to switch a connection state between the chiller and the vehicle battery in the first cooling circuit and between the unit to be cooled and the radiator in the second cooling circuit so that a coolant outlet of the unit to be cooled and a coolant inlet of the vehicle battery are connected in the second circuit state. A cooling water circulation device characterized by:

4. A method for raising the temperature of a vehicle battery in a vehicle including a first cooling circuit in which a first water pump, a chiller, and a vehicle battery are connected in a circular configuration, and a second cooling circuit in which a second water pump, a unit to be cooled, and a radiator are connected in a circular configuration, when a condition for raising the temperature of the vehicle battery is satisfied, switching the circuit state from a first circuit state in which the first cooling circuit and the second cooling circuit are separated to a second circuit state in which the first cooling circuit and the second cooling circuit are connected to form a single circuit; and reducing the drive duty of at least one of the first water pump and the second water pump for a predetermined time in response to the change of the circuit state to the second circuit state. A method for raising the temperature of a vehicle battery.

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