Vehicle battery system

Abstract

This invention provides an on-board battery system. In this system, the battery temperature is prevented from exceeding its operating limit. When the battery temperature (T) is high, the battery's output power (Wout) is limited to suppress temperature rise. When three conditions are met—an external gas temperature above a predetermined temperature, a vehicle driving load above a predetermined driving load, and a battery cooling device operating load above a predetermined operating load—the battery's output power is limited using a high-load output limit value (Wrh) that is lower than the normal output limit value (Wrn) and above a second lower power limit temperature (Tr2) below the normal first power limit temperature (Tr1).

Description

Technical Field

[0001] This invention relates to an on-board battery system for supplying power to an electric motor that drives a vehicle, and particularly to battery cooling. Background Technology

[0002] Electric vehicles, which are driven by electric motors, are known. Electric vehicles include battery-powered electric vehicles that are driven solely by an electric motor, and hybrid electric vehicles that are driven by both an electric motor and a motor. Electric vehicles are equipped with a battery that supplies power to the electric motor that drives the vehicle. The battery has a defined upper operating temperature for protection. A known technique limits the output power from the battery to suppress temperature rise and prevent it from exceeding the upper operating temperature when the battery temperature approaches the upper operating temperature. Patent Document 1 discloses a technique for changing the battery temperature that limits the start of power output based on the depth of discharge, i.e., the value obtained by subtracting the current charge from the charge level at full capacity.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 11-224697 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] When the vehicle is traveling at high speeds or under heavy driving loads, and the external air temperature is high, the battery cooling device that cools the battery is also under heavy operating load. Even with output limiting, the battery temperature may still reach the upper limit of its operating temperature.

[0008] Methods for solving problems

[0009] The vehicle-mounted battery system of the present invention includes: an on-board battery supplying power to an electric motor that drives the vehicle; a battery cooling device for cooling the battery; a battery temperature sensor for detecting the battery temperature; an external gas temperature sensor for detecting the external gas temperature; a driving load sensor for detecting the driving load of the vehicle; a cooling load acquirer for acquiring the operating load of the battery cooling device; and a battery control device for controlling the input and output power of the battery, and limiting the output power from the battery when the battery temperature is above a predetermined lower power limit temperature. The lower power limit temperature is a first lower power limit temperature when at least one of three conditions is not met, and a second lower power limit temperature, lower than the first lower power limit temperature, is a temperature lower than the first lower power limit temperature when all three conditions are met. The three conditions are: the external gas temperature is above a predetermined temperature, the vehicle driving load is above a predetermined driving load, and the operating load of the battery cooling device is above a predetermined operating load.

[0010] In situations where battery temperature is prone to rise, suppressing battery heat generation from a lower battery temperature prevents the battery temperature from reaching its operating limit. Furthermore, when the battery cooling device operates under low load and has sufficient cooling capacity, not imposing battery output limits can suppress the frequency of output limiting.

[0011] Furthermore, in the aforementioned vehicle battery system, the battery cooling device may include: a liquid cooling device that uses coolant circulating in the battery and heat exchanger for cooling; and a refrigeration circulation device that uses a refrigeration circulation cooling medium to cool the coolant in the liquid cooling device via the heat exchanger. By combining the liquid cooling device and the refrigeration circulation device to form the battery cooling device, the battery can be cooled efficiently and powerfully.

[0012] Furthermore, in the aforementioned vehicle battery system, the cooling load acquisition device can obtain the operating load status of the battery cooling device based on at least one of the flow rate of the coolant in the liquid cooling device and the rotational speed of the compressor that compresses the cooling medium of the refrigeration cycle device.

[0013] Furthermore, in the aforementioned vehicle battery system, the refrigeration cycle unit can be an air conditioning unit that cools the passenger compartment of the vehicle. By sharing a portion of the battery cooling unit with the passenger compartment air conditioning unit, the unit becomes smaller and its vehicle-mountability is improved. Moreover, if the operating load of the battery cooling unit is determined based on the compressor speed, then even when the battery cooling unit operates under high load due to passenger compartment cooling, battery output can be limited at a lower temperature.

[0014] Furthermore, in the aforementioned vehicle battery system, the driving load acquisition unit may include a vehicle speed sensor that detects the vehicle's speed and calculates the vehicle's driving load based on the detected speed. At higher speeds, the battery generates more heat; limiting the battery's power output can suppress the rise in battery temperature.

[0015] Furthermore, in the aforementioned vehicle battery system, the driving load acquisition unit may include an accelerometer sensor that detects the amount of operation of the accelerometer actuator, and calculates the vehicle's driving load based on the detected amount of operation of the accelerometer actuator. When the amount of accelerometer operation is large, the battery generates more heat; in this case, limiting the battery's output power can suppress the rise in battery temperature.

[0016] Furthermore, in the aforementioned vehicle battery system, the driving load acquisition unit can include a vehicle speed sensor that detects the vehicle's driving speed and an accelerometer sensor that detects the amount of operation of the accelerometer actuator. The driving load is calculated based on the detected vehicle speed and the detected amount of operation of the accelerometer actuator. By calculating the driving load based on both the vehicle speed and the amount of accelerometer operation, the driving load can be calculated with higher accuracy.

[0017] Furthermore, in the aforementioned vehicle battery system, it is possible for the battery control device to set the output power below the output power when at least one of the three conditions is not met, provided that the battery temperature is above the second power limit lower limit temperature, when the three conditions are met.

[0018] Furthermore, based on the aforementioned vehicle battery system, it is possible for the battery control device, when the three conditions are met and the battery temperature is above the second lower limit temperature, to continuously reduce the output power as the battery temperature rises. This can suppress the sharp drop in vehicle driving force that accompanies the rise in battery temperature.

[0019] Invention Effects

[0020] It can suppress the rise in battery temperature when the battery temperature is more likely to rise than usual, and prevent the battery temperature from exceeding the upper limit of the operating temperature. Attached Figure Description

[0021] Figure 1 This is a schematic diagram illustrating the general structure of an on-board battery system according to an embodiment.

[0022] Figure 2 This is a graph showing the characteristics of the battery's output power.

[0023] Figure 3This is a flowchart illustrating the control process for limiting the battery's output. Detailed Implementation

[0024] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1 This is a diagram showing a schematic structure of the battery system 10 installed in the vehicle according to this embodiment. Figure 1 The diagram also shows an electric motor (M) 12 that is powered by the battery system 10 and drives the vehicle. Furthermore, the electric motor 12 functions as a generator during vehicle braking. The vehicle can be either a battery-powered electric vehicle driven solely by the electric motor, or a hybrid electric vehicle driven by both an electric motor and an engine.

[0025] The battery system 10 includes a battery 14, which supplies power generated from discharging the battery 14 to the motor 12 via a converter 16, and charges the battery 14 with power generated by the motor 12 via the converter 16. The battery system 10 includes a battery control device 18, which controls the converter 16 to control the power supplied to the motor 12 and the power regenerated from the motor 12.

[0026] The battery system 10 includes a battery cooling device 20 for cooling the battery 14. The battery cooling device 20 includes a liquid cooling device 24 for cooling the battery 14 by means of coolant circulating in the battery 14 and the heat exchanger 22, and a refrigeration circulation device 26 for cooling the coolant of the liquid cooling device 24 via the heat exchanger 22 by means of a refrigeration circulation cooling medium.

[0027] The liquid cooling device 24 includes a coolant flow path 28 that connects the battery 14 and the heat exchanger 22 in a ring and supplies coolant, and a coolant pump (P) 30 disposed on the coolant flow path 28 and circulates the coolant. The coolant pump 30 is an electric pump, and its speed is controlled by the battery control device 18. By controlling the speed of the coolant pump 30, the flow rate of the coolant flowing in the coolant flow path 28 can be controlled. Furthermore, when the pump motor driving the coolant pump 30 is a PWM-controlled motor, the speed of the coolant pump 30 is controlled by controlling the duty cycle of the power supplied to the pump motor.

[0028] The refrigeration circulation unit 26 includes a compressor (C) 32 for compressing the cooling medium, a condenser 34 for condensing the compressed cooling medium, an evaporator 36 for evaporating the condensed cooling medium that expands again through an expansion valve 35, and an annular cooling medium flow path 38 connecting these components in a ring for supplying the cooling medium. Furthermore, the refrigeration circulation unit 26 has a bypass cooling medium flow path 40 relative to the annular cooling medium flow path 38, which bypasses the evaporator 36. An expansion valve 41 and a heat exchanger 22 of a liquid cooling device 24 located downstream of the expansion valve 41 are provided on the bypass cooling medium flow path 40. In the heat exchanger 22, the coolant of the liquid cooling device 24 is cooled by the cooling medium of the refrigeration circulation unit 26. The refrigeration circulation unit 26 can also be an air conditioning device for cooling the passenger compartment (not shown) of a vehicle. By supplying air around the evaporator 36 to cool the air, and then supplying the cooled air to the passenger compartment, the passenger compartment can be cooled. The compressor 32 controls its speed through the air conditioning control device 42, and controls the cooling capacity of the passenger compartment and the cooling capacity of the coolant in the heat exchanger 22 by controlling the speed.

[0029] The battery control device 18 manages the temperature of the battery 14. A battery temperature sensor 44 is provided on the battery 14 to detect its temperature. The battery control device 18 controls the battery cooling device 20 based on the battery temperature detected by the battery temperature sensor 44. When the battery temperature increases, the battery control device 18 increases the speed of the coolant pump 30, thereby increasing the coolant flow rate and improving the cooling capacity of the liquid cooling device 24. Furthermore, the battery control device 18 increases the speed of the compressor 32 via the air conditioning control device 42 as needed, further improving the cooling capacity of the refrigeration cycle device 26. By improving the cooling capacity of the refrigeration cycle device 26, the coolant can be further cooled in the heat exchanger 22.

[0030] The battery control device 18 controls the power output from and input to the battery 14 based on the detected battery temperature. Specifically, the battery control device 18 controls the input and output power of the battery 14 by controlling the converter 16. When the battery temperature exceeds the upper limit temperature for use of the battery 14, the battery control device 18 stops the use of the battery 14. In order to prevent the battery 14 from becoming unusable due to a rise in battery temperature, the battery control device 18 limits the input and output power of the battery 14 when the battery temperature approaches the upper limit temperature, thereby suppressing the rise in battery temperature.

[0031] The battery system 10 includes a cooling load acquirer 46, which acquires the current cooling capacity of the battery cooling device 20, i.e., the operating load involved in cooling (hereinafter referred to as cooling load). The cooling load acquirer 46 acquires the cooling load based on at least one of the flow rate of the cooling water in the liquid cooling device 24 and the rotational speed of the compressor 32 in the refrigeration cycle device 26. When the flow rate of the cooling water in the liquid cooling device 24 is high, it can be considered that the battery 14 must be further cooled, which is a state with a high cooling load. Furthermore, when the rotational speed of the compressor 32 is high, it can be considered that the cooling water in the liquid cooling device 24 must be further cooled, resulting in a high cooling load. In addition, when the refrigeration cycle device 26 also serves as an air conditioning device for the passenger compartment, the temperature inside the passenger compartment is higher when the rotational speed of the compressor 32 is higher, which is also a state with a high cooling load for the refrigeration cycle device 26.

[0032] The cooling load acquirer 46 can also calculate the flow rate of the coolant in the liquid cooling unit 24 based on the rotational speed of the coolant pump 30. To detect the rotational speed of the coolant pump 30, a speed sensor can be installed to detect the rotational speed of the coolant pump 30 and the rotating part of the pump motor that drives the coolant pump 30. Furthermore, the rotational speed of the coolant pump 30 can also be obtained based on the current supplied to the pump motor that drives the coolant pump. For example, when the pump motor is controlled by PWM control, the rotational speed of the coolant pump 30 can be obtained based on the current duty cycle. Moreover, the rotational speed of the coolant pump 30 can also be calculated based on the control command from the battery control device 18 that controls the rotational speed of the coolant pump 30. Additionally, a flow meter can be installed on the coolant flow path 28 to obtain the flow rate of the coolant in the liquid cooling unit 24.

[0033] The cooling load acquirer 46 can also acquire the speed of the compressor 32 from a speed sensor that detects the speed of the rotating part of the compressor 32. Alternatively, it can acquire the speed based on control commands from the air conditioning control unit 42 to the compressor 32.

[0034] The battery system 10 includes an external gas temperature sensor 48 that detects the temperature of the external gas surrounding the vehicle. The battery control unit 18 controls the cooling capacity of the battery cooling device 20 based on the external gas temperature detected by the external gas temperature sensor 48. When the external gas temperature is high, there is a tendency for the battery temperature to rise, and the battery control unit 18 increases the cooling capacity of the battery control unit 18.

[0035] The battery system 10 includes a driving load acquirer 50 for obtaining the driving load status of the vehicle. The driving load acquirer 50 includes at least one of a vehicle speed sensor 52 that detects the vehicle's speed and an accelerator sensor 54 that detects the amount of operation of a control such as the accelerator pedal operated by the driver. The driving load acquirer 50 is set to have a higher driving load when the vehicle speed is higher and when the accelerator operation is higher. Furthermore, the driving load can also be determined relative to a combination of vehicle speed and accelerator operation. For example, even when the vehicle speed is low but the accelerator operation is high, conditions with a high driving load, such as driving uphill or towing a trailer, are considered.

[0036] The battery control unit 18 includes a processing unit that operates according to a predetermined program and processes information. The cooling load acquirer 46 may also include sensors that convert physical quantities such as flow rate and rotational speed into electrical signals, and a processing unit that calculates the cooling load based on the electrical signals from these sensors. The driving load acquirer 50 may also include sensors that convert physical quantities such as vehicle speed and accelerator operation into electrical signals, and a processing unit that calculates the driving load based on the electrical signals from these sensors. The processing units of the battery control unit 18, cooling load acquirer 46, and driving load acquirer 50 can also be implemented by a single processing unit executing programs corresponding to each device and acquirer.

[0037] Figure 2This is a graph showing the relationship between battery temperature T and the output power Wout of battery 14. The output power Wout of battery 14 is controlled to a constant upper limit value Wmax or lower within a range where battery temperature T is not high. Within a range where battery temperature is high, the output power Wout of battery 14 is controlled to be below output limit values ​​Wrn and Wrh, which are lower than the upper limit value Wmax. If the battery temperature T is above the upper operating temperature Tu, it is 0. During the rise of battery temperature T, the temperature rise is suppressed by limiting the output power Wout before reaching the upper operating temperature Tu. When the battery temperature T reaches the lower limit values ​​Tr1 and Tr2 (lower power limit temperatures Tr1 and Tr2) of the temperature range for output limiting, the output limit values ​​Wrn and Wrh are applied to control the output power Wout below the output limit values ​​Wrn and Wrh. The two output limit values ​​Wrn and Wrh are selected based on the driving load, the external gas temperature, and the operating load (cooling load) of the battery cooling device 20 during cooling. When the driving load is high and the external air temperature is high, as well as the cooling load is high, the battery temperature may rise suddenly. In this case, an output limit value Wrh that further suppresses the temperature rise is selected compared to the normal output limit value Wrn. Hereinafter, the output limit value Wrn will be referred to as the normal output limit value Wrn, and the output limit value Wrh will be referred to as the high load output limit value Wrh.

[0038] Normal output limiting is implemented when the battery temperature T is above the first power limit lower limit temperature Tr1. The normal output limit value Wrn decreases progressively from the first power limit lower limit temperature Tr1 towards the upper limit temperature Tu. Furthermore, the normal output limit value Wrn slopes more sharply at the points connecting the flat sections of the steps; therefore, when the output power Wout is high, the output power Wout may sometimes drop sharply when the normal output limit is applied.

[0039] The high-load output limit value Wrh is applied as described above during high-load conditions where the battery temperature T may suddenly rise. The high-load output limit is executed when the battery temperature T is above the second lower power limit temperature Tr2, which is lower than the first power limit lower limit temperature Tr1. The high-load output limit value Wrh decreases continuously and without step change relative to the rise in battery temperature T, moving towards the upper operating temperature Tu. Furthermore, within the temperature range above the second lower power limit temperature Tr2, the high-load output limit value Wrh is below the upper limit of output power Wmax and the normal output limit value Wrn. Although the battery temperature T is lower than normal, output limiting is still applied, thereby further suppressing the output power Wout as the battery temperature T rises, preventing the battery temperature T from reaching the upper operating temperature Tu. Moreover, the high-load output limit value Wrh decreases slowly relative to the rise in battery temperature T, thus preventing a sudden decrease in output power Wout.

[0040] Figure 3 This is a flowchart involving the limitation of the output power from battery 14. First, it is determined whether the driving load is large (S100). The driving load is obtained based on at least one of vehicle speed and accelerator operation amount. When the vehicle speed is high, the output of motor 12 is large in order to overcome driving resistance, and the output power Wout of battery 14 is also large. Therefore, the heat generated by battery 14 also increases. Furthermore, when the accelerator operation amount is large, the driver demands a greater output from motor 12, the output power Wout of battery 14 increases, and the heat generated by battery 14 also increases. When the driving load is obtained based on both vehicle speed and accelerator operation amount, a more precise judgment can be made. Even when the vehicle speed is low, when driving uphill or towing a trailer, a large driving force is required, the driver depresses the accelerator pedal, and the accelerator operation amount increases. Furthermore, the output of motor 12 increases, and the heat generated by battery 14 also increases. In this case, although the driving speed is low, it is preferable to apply the output limit value Wrh for high load. When the driving speed is, for example, 140 km / h or higher, it is determined that the driving load is large. Furthermore, when the accelerator operation amount is, for example, 5 / 8 or more, it is determined that the driving load is large. When the driving load is small, the normal output limit value Wrn is applied (step S108).

[0041] When it is determined that the driving load is high, the next step is to determine whether the external air temperature is high (S102). When the external air temperature is high, the temperature around the battery 14 also increases, so less heat is dissipated from the battery 14 to the atmosphere, and the battery temperature is prone to rise. When the external air temperature is, for example, above 40°C, it is determined that the external air temperature is high. When the external air temperature is low, the normal output limit value Wrn is applied (step S108).

[0042] When it is determined that the external gas temperature is high, the operating load (cooling load) involved in cooling the battery cooling device 20 is then assessed. The cooling load is determined based on at least one of the coolant flow rate of the liquid cooling device 24 and the rotational speed of the compressor 32 of the refrigeration cycle device 26. A large cooling load is determined when the coolant flow rate is above a predetermined value, or when the compressor rotational speed is above a predetermined value. Specifically, a large cooling load is determined when the duty cycle of the current driving the pump motor of the coolant pump 30, corresponding to the coolant flow rate, is, for example, 60% or more (the maximum duty cycle is 85%). Furthermore, a large cooling load is determined when the compressor rotational speed is, for example, 60% or more of its maximum speed. When the coolant flow rate is high, there is less margin for increasing the flow rate, resulting in less remaining capacity corresponding to a further increase in battery temperature. Furthermore, when the compressor rotational speed is high, the remaining capacity of the refrigeration cycle device 26 corresponding to a further increase in battery temperature is relatively small. Therefore, when the coolant flow rate is high and the compressor speed of 32 is high, the cooling capacity of the battery cooling device 20 is less than expected. In this case, it is preferable to use the output limit value Wrh under high load.

[0043] Furthermore, when the refrigeration cycle unit 26 also functions as an air conditioning device for cooling the passenger compartment, the compressor 32 speed may increase due to the temperature of the passenger compartment and cooling requirements based on the passengers' needs. When the compressor 32 speed increases due to the cooling requirements of the passenger compartment, i.e., when the cooling load of the refrigeration cycle unit 26 increases, although there is a cooling requirement for the battery 14, the corresponding remaining capacity decreases. Therefore, in this case, it is preferable to apply the high-load output limit value Wrh. When the cooling load of the battery cooling unit 20 is low, the normal output limit value Wrn (S108) is applied; when the cooling load is high, the high-load output limit value Wrh (S106) is applied.

[0044] Under conditions where the battery temperature is prone to rise, the output limit is initiated earlier than usual during the temperature rise of battery 14, i.e., when the battery temperature is lower, thereby preventing the battery temperature from reaching the upper limit temperature Tu. Furthermore, when the cooling capacity of the battery cooling device 20 is sufficient, the output limit is set to the normal level, thereby reducing the frequency of output limiting.

[0045] Explanation of reference numerals in the attached figures

[0046] 10 Battery System (On-board Battery System), 12 Electric Motor, 14 Battery, 16 Converter, 18 Battery Control Unit, 20 Battery Cooling Unit, 22 Heat Exchanger, 24 Liquid Cooling Unit, 26 Refrigeration Circulation Unit (Air Conditioning Unit), 28 Coolant Flow Path, 30 Coolant Pump, 32 Compressor, 34 Condenser, 35, 41 Expansion Valve, 36 Evaporator, 38 Annular Cooling Medium Flow Path, 40 Bypass Cooling Medium Flow Path, 42 Air Conditioning Control Unit, 44 Battery Temperature Sensor, 46 Cooling Load Acquisition Unit, 48 External Gas Temperature Sensor, 50 Driving Load Acquisition Unit, 52 Vehicle Speed ​​Sensor, 54 Accelerator Sensor, T Battery Temperature, Tr1 First Power Limit Lower Limit Temperature, Tr2 Second Power Limit Lower Limit Temperature, Tu Upper Limit Temperature, Wmax Upper Limit Value of Output Power, Wout Battery Output Power, Wrh Output Limit Value under High Load, Wrn Output Limit Value under Normal Condition.

Claims

1. A vehicle-mounted battery system, comprising: The vehicle's battery supplies power to the electric motor that drives the vehicle. A battery cooling device for cooling the battery; A battery temperature sensor is used to detect the temperature of the battery. An external gas temperature sensor detects the temperature of the external gas. A driving load acquisition device acquires the driving load of the vehicle; Cooling load acquisition device, which acquires the operating load of the battery cooling device; as well as A battery control device controls the input and output power of the battery, and limits the output power from the battery when the battery temperature is above a predetermined lower limit temperature for power consumption. The lower limit temperature for power supply is a first lower limit temperature for power supply when at least one of the three conditions is not met, and a second lower limit temperature for power supply that is lower than the first lower limit temperature for power supply when all three conditions are met. The three conditions are: the external gas temperature is above a predetermined temperature, the vehicle's driving load is above a predetermined driving load, and the battery cooling device's operating load is above a predetermined operating load.

2. The vehicle battery system according to claim 1, wherein, The battery cooling device includes: A liquid cooling device is used to cool the battery and the heat exchanger; and A refrigeration circulation device uses a refrigeration circulation cooling medium to cool the coolant of the liquid cooling device via the heat exchanger.

3. The vehicle battery system according to claim 2, wherein, The cooling load acquisition device obtains the operating load status of the battery cooling device based on at least one of the flow rate of the coolant in the liquid cooling device and the rotational speed of the compressor that compresses the cooling medium of the refrigeration cycle device.

4. The vehicle battery system according to claim 2, wherein, The refrigeration circulation device is an air conditioning device for cooling the passenger compartment of the vehicle.

5. The vehicle battery system according to claim 1, wherein, The driving load acquisition device includes a vehicle speed sensor that detects the vehicle's driving speed and calculates the vehicle's driving load based on the detected vehicle's driving speed.

6. The vehicle battery system according to claim 1, wherein, The driving load acquisition device includes an accelerometer sensor that detects the amount of operation of the accelerometer actuator, and calculates the driving load of the vehicle based on the detected amount of operation of the accelerometer actuator.

7. The vehicle battery system according to claim 1, wherein, The driving load acquisition device includes a vehicle speed sensor for detecting the vehicle's driving speed and an accelerometer sensor for detecting the amount of operation of the accelerometer control component. The driving load of the vehicle is calculated based on the detected vehicle speed and the detected amount of operation of the accelerometer control component.

8. The vehicle battery system according to any one of claims 1 to 7, wherein, When the three conditions are met, and the battery temperature is above the second power limit lower temperature, the battery control device sets the output power to be below the output power when at least one of the three conditions is not met.

9. The vehicle battery system according to claim 8, wherein, When the three conditions are met, the battery control device causes the output power to continuously decrease as the battery temperature rises when the battery temperature is above the second power limit lower temperature.

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