Electric vehicles

Abstract

This invention provides an electric vehicle that uses a detection method less susceptible to external environmental influences to detect the operation of the safety valve of a battery mounted on the vehicle, thereby suppressing the risk of failure to detect the operation of the battery's safety valve. [Solution] The electric vehicle 1 comprises a plurality of batteries 45 restrained in the stacking direction H by a restraining device 41, and a control unit 20. Each of the plurality of batteries 45 has a safety valve 48. The control unit 20 acquires battery characteristic information for each of the plurality of batteries 45, external environment information, and information on the initial load F0, which is the measured value of the restraining load that restrains the plurality of batteries 45 and is the restraining load when the ignition power is turned on. Based on the battery characteristic information for each of the plurality of batteries 45 and the external environment information, the control unit 20 acquires an estimated load Fes, which is an estimated value of the restraining load that restrains the plurality of batteries 45. Based on the initial load F0 and the estimated load Fes, the control unit 20 detects the opening of the safety valve.

Description

Technical Field

[0001] The present disclosure relates to an electric vehicle.

Background Art

[0002] A large number of batteries are used as the drive source of an electric vehicle. The battery is, for example, a secondary battery such as a lithium-ion battery. When the battery is placed in an abnormal high-temperature environment or overcharged, a large amount of gas is generated inside the battery. The battery is provided with a safety valve that operates to release the gas to the outside when the internal pressure of the battery abnormally rises due to gas or the like. The battery for which the safety valve has operated needs to have its current cut off in order to stop further use. Therefore, a system for detecting the operation of the safety valve has been proposed. International Publication No. 2011 / 101942 (Patent Document 1) discloses a detection system that detects the sound emitted during safe operation and determines the presence or absence of the operation of the safety valve according to the magnitude of the detected sound.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The detection system that determines the presence or absence of the operation of the safety valve according to the magnitude of the detected sound disclosed in International Publication No. 2011 / 101942 may not be able to detect the operation sound of the valve when the opening speed of the valve is small or the noise of the surrounding environment is large. Further, when the safety valve has been opened before the power is turned on, it is impossible to determine whether the safety valve has been opened when the power is turned on.

[0005] This disclosure is made to solve the above-mentioned problems, and its purpose is to provide an electric vehicle that uses a detection method less susceptible to external environmental influences to detect the operation of the safety valve of a battery mounted on the vehicle, thereby suppressing the risk of being unable to detect the operation of the battery's safety valve. [Means for solving the problem]

[0006] An electric vehicle relating to the first aspect of this disclosure comprises a plurality of batteries constrained in the stacking direction by a restraining device and a control unit. Each of the plurality of batteries has a safety valve. The control unit acquires an initial load, which is the actual restraining load of the plurality of batteries and the restraining load when the ignition power is turned on. The control unit acquires an estimated load, which is an estimated value of the restraining load, based on battery characteristic information of the plurality of batteries and external environmental information. The control unit detects the opening of the safety valve based on the estimated load and the initial load. [Effects of the Invention]

[0007] According to the electric vehicle described herein, the operation of the safety valve of the battery mounted on the vehicle can be detected using a detection method that is less susceptible to external environmental influences, thereby suppressing the risk of being unable to detect the operation of the battery's safety valve. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram of an electric vehicle according to an embodiment of the present disclosure. [Figure 2] This is a schematic diagram of a battery pack and energy storage cell according to an embodiment of the present disclosure. [Figure 3] This is a control flow diagram of an electric vehicle according to an embodiment of the present disclosure. [Modes for carrying out the invention]

[0009] Embodiments of this disclosure will be described in detail below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and their descriptions will not be repeated. <Overall configuration of electric vehicles> Figure 1 is a diagram showing a schematic configuration of an electric vehicle according to an embodiment of the present disclosure.

[0010] The electric vehicle 1 is, for example, an electric car. The electric vehicle 1 comprises a motor generator (MG) 11, which is a rotating electric machine, drive wheels 12, a power control unit (PCU) 13, a system main relay (SMR) 14, an ECU 20, an HMI device 30, a battery pack 40, and a monitoring unit 50. The ECU 20 is communicatively connected to the PCU 13, the SMR 14, the HMI device 30, and the monitoring unit 50.

[0011] MG11 is, for example, an embedded permanent magnet synchronous motor (IPM motor) that has both the function of an electric motor and a generator. The output torque of MG11 is transmitted to the drive wheels 12 via a power transmission system that includes a reduction gear and a differential gear.

[0012] When the electric vehicle 1 is braked, the MG11 is driven by the drive wheels 12, and the MG11 operates as a generator. In this way, the MG11 also functions as a braking device that performs regenerative braking, converting the kinetic energy of the electric vehicle 1 into electrical power. The regenerative power generated by the regenerative braking force in the MG11 is stored in the battery pack 40.

[0013] The PCU13 is a power conversion device that converts power bidirectionally between the MG11 and the battery pack 40. The PCU13 includes, for example, an inverter and a converter that operate based on a control signal from the ECU20. When the battery pack 40 is discharged, the converter boosts the voltage supplied from the battery pack 40 and supplies it to the inverter. The inverter converts the DC power supplied from the converter into AC power to drive the MG11. Note that the PCU13 may also be configured without the converter.

[0014] The SMR14 is electrically connected to the power line connecting the battery pack 40 and the PCU 13. When the SMR14 is closed (ON) (i.e., conducting) in response to a control signal from the ECU 20, power can be exchanged between the battery pack 40 and the PCU 13. On the other hand, when the SMR14 is open (OFF) (i.e., disconnected) in response to a control signal from the ECU 20, the electrical connection between the battery pack 40 and the PCU 13 is disconnected.

[0015] The HMI device 15 is mounted on the electric vehicle 1 and displays various information (e.g., map information and video content) on a display screen that is not shown, and also notifies the user of various information (e.g., traffic information and weather information) by voice or other means. The HMI device 15 includes a display with a touch panel and a speaker. The HMI device 15 is configured to notify the user of the electric vehicle 1 of signals corresponding to the output from the ECU 20.

[0016] The ECU 20 includes a processor 21, memory 22, and storage 23. The processor 21 is an arithmetic unit such as a CPU (Central Processing Unit) or MPU (Micro-Processing Unit). The memory 22 is volatile memory (working memory) such as RAM (Random Access Memory). The storage 23 is rewritable non-volatile memory such as flash memory. The storage 23 stores a system program including an OS (Operating System) and a control program including computer-readable code necessary for control calculations. The processor 21 performs various processes by reading the system program and the control program, loading them into memory 22, and executing them. The ECU 20 may be divided into multiple ECUs according to function. Note that the ECU 20 is an example of a "control unit" in this disclosure.

[0017] The battery pack 40 is mounted on the electric vehicle 1. The battery pack 40 has a plurality of energy storage cells 45. The plurality of energy storage cells 45 are electrically connected in series. The energy storage cells 45 are secondary batteries such as nickel-metal hydride batteries or lithium-ion batteries. A secondary battery is, for example, a battery having a liquid electrolyte between a positive electrode and a negative electrode. Note that the energy storage cell 45 is an example of a "battery" in this disclosure.

[0018] Figure 2 shows a schematic perspective view of the battery pack. The battery pack 40 is formed from a restraint device 41, a load cell 44, and a plurality of energy storage cells 45. The restraint device 41 is formed from a pair of end plates 42 and a column member 43. Each of the pair of end plates 42 is positioned at one end and the other end of the plurality of energy storage cells 45 arranged in the stacking direction. The column member 43 connects each of the pair of end plates 42. By the column member 43 connecting the pair of end plates 42, the plurality of energy storage cells 45 are restrained in the stacking direction H. The restraint load that restrains the plurality of energy storage cells 45 in the stacking direction H is measured by the load cell 44. The load cell 44 is positioned between one of the pair of end plates 42 and an energy storage cell 45 adjacent to one of the pair of end plates 42. The load cell 44 is communicated with the monitoring unit 50. The load cell 44 is configured to transmit information on the restraint load acquired by the load cell 44 to the monitoring unit 50.

[0019] Each of the multiple energy storage cells 45 has a cell case 46, an external terminal 47, and a safety valve 48. The cell case 46 is a sealed container formed in the shape of a rectangular parallelepiped. The cell case 46 is made of a metal such as aluminum. The cell case 46 has an electrode body (not shown) inside. The cell case 46 has an outer surface 46a. The external terminal 47 and the safety valve 48 are provided on the outer surface 46a. The safety valve 48 opens when the gas pressure inside the cell case 46 exceeds a certain level. This is called the operation of the safety valve 48. The outer surface 46a on which the safety valve 48 is provided constitutes the internal pressure release surface of the cell case 46. Note that the energy storage cell 45 is an example of the "battery" of this disclosure.

[0020] Referring again to FIG. 1, the monitoring unit 50 has various sensors for detecting the state of each of the plurality of power storage cells 45 (for example, battery temperature, current, current integrated value, and voltage), and the state of the external environment (for example, external air pressure, external air temperature) in which the battery pack 40 is placed. Also, the monitoring unit 50 is formed to be connectable to the load cell 44. The monitoring unit 50 functions also as a BMS (Battery Management System) having a function of acquiring the OCV (Open Circuit Voltage) of each of the plurality of power storage cells 45, a SOC function of estimating the SOC (State Of Charge) of each of the plurality of power storage cells 45, a SOH estimation function of estimating the SOH (State of Health) of each of the plurality of power storage cells 45, and a communication function. The monitoring unit 50 outputs the state, SOC, and SOH of each of the plurality of power storage cells 45 acquired as battery characteristic information to the ECU 20. Also, the monitoring unit 50 outputs the state of the external environment in which the acquired battery pack 40 is placed to the ECU 20 as external environment information. In addition, the monitoring unit 50 outputs the information on the restraint load acquired from the load cell 44 to the ECU 20. <Control Flow of Electric Vehicle> Next, referring to FIG. 3, the control flow of the electric vehicle 1 will be described. In step S10 shown in FIG. 3, the ECU 20 checks whether the ignition power supply of the electric vehicle 1 is ON. If the ignition power supply is ON (Yes in step S10), the process of the ECU 20 proceeds to step S20. If the ignition power supply is not ON (No in step S10), the ECU 20 processes step S10 again.

[0021] In step S20, the ECU 20 acquires the battery characteristic information, external environment information, and information on the initial load F0, which is the restraint load at the time of ignition power supply, of each of the plurality of power storage cells 45 from the monitoring unit 50. The ECU 20 stores the acquired battery characteristic information, external environment information, and information on the initial load F0 in the storage 23. Then, the process of the ECU 20 proceeds to step S30.

[0022] In step S30, the ECU 20 obtains an estimated load Fes based on the battery characteristic information of each of the multiple energy storage cells 45 and the external environment information. The estimated load Fes is the constraint load that the multiple energy storage cells 45 receive from the constraint device 41, as estimated by the ECU 20. The estimation method for the estimated load Fes is described below. When each of the multiple energy storage cells 45 exhibits a predetermined SOC and battery temperature, the ECU 20 pre-stores the constraint load that the load cell 44 will acquire as SOC load data in the storage 23. Also, when each of the multiple energy storage cells 45 exhibits a predetermined SOH and battery temperature, the ECU 20 pre-stores the constraint load that the load cell 44 will acquire as SOH load data in the storage 23. The SOC load data and SOH load data are, for example, experimentally acquired data. The ECU 20 obtains the estimated load Fes based on the battery characteristic information (SOC, battery temperature, SOH, etc.) stored in the storage 23 and the SOC load data and SOH load data. The estimated load Fes may be corrected based on external atmospheric pressure and temperature information included in the external environmental information. After that, the ECU20 proceeds to step S40.

[0023] In step S40, the ECU 20 detects the opening of the safety valve 48 based on the initial load F0 and the estimated load Fes. More specifically, it checks whether the value obtained by multiplying the estimated load Fes by a correction value α is higher than the initial load F0. Here, the correction value α is a value determined by the accuracy of the estimated load Fes. If a highly accurate estimated load Fes can be obtained, the correction value α approximates 1. If the initial load F0 is lower than the value obtained by multiplying the estimated load Fes by the correction value α, it is considered that the internal pressure of at least one of the multiple energy storage cells 45 has been reduced by the opening of the safety valve 48. When at least one safety valve 48 of the multiple energy storage cells 45 is opened, the multiple energy storage cells 45 can no longer obtain the resistance force in the stacking direction H that they receive from the restraint device 41. As a result, the restraint load on the multiple energy storage cells 45 decreases, so the initial load F0, which is the measured value obtained by the load cell 44, becomes smaller than the estimated load Fes. In this way, by comparing the estimated load Fes with the initial load F0, it is possible to detect whether the safety valve 48 was activated before the ignition power was turned on. If the value obtained by multiplying the estimated load Fes by the correction value α is higher than the initial load F0 (Yes in step S40), the ECU 20 proceeds to step S45. If the value obtained by multiplying the estimated load Fes by the correction value α is lower than the initial load F0 (No in step S40), the ECU 20 proceeds to step S70.

[0024] In step S45, the ECU20 checks if the ignition power of electric vehicle 1 is ON. If the ignition power is ON (Yes in step S45), the ECU20 proceeds to step S50. If the ignition power is not ON (No in step S45), the ECU20 terminates its process.

[0025] In step S50, the ECU20 acquires the measured load F1. The measured load F1 is the constraint load acquired by the ECU20 from the load cell 44 via the monitoring unit 50 after step S40. The measured load F1 is, for example, the constraint load during the operation of the electric vehicle 1. After that, the processing of the ECU20 proceeds to step S60.

[0026] In step S60, it is checked whether the value obtained by subtracting the measured load F1 from the initial load F0 is higher than the threshold β. The threshold β is a positive value. If the value obtained by subtracting the measured load F1 from the initial load F0 is higher than the threshold β, it is inferred that, for example, the internal pressure inside the cell case 46 increased due to the temperature rise of the energy storage cell 45 during driving, causing the safety valve 48 to activate and the initial load F0 to become extremely low relative to the measured load F1. If the value obtained by subtracting the measured load F1 from the initial load F0 is higher than the threshold β (Yes in step S60), the ECU 20 proceeds to step S70. If the value obtained by subtracting the measured load F1 from the initial load F0 is not higher than the threshold β (No in step S60), the ECU 20 processes step S45 again and continues to monitor, for example, the operation of the safety valve 48 during driving.

[0027] In step S70, the ECU 20 notifies the user of the electric vehicle 1 that the safety valve 48 of the energy storage cell 45 has opened. More specifically, the ECU 20 transmits a signal to the HMI device 15 indicating that the safety valve 48 of the energy storage cell 45 is open. The HMI device 15 then displays, for example, on a display unit (not shown) that the safety valve 48 of the energy storage cell 45 has opened. After that, the ECU 20 terminates its processing.

[0028] In the embodiments of this disclosure, the ECU 20 detects whether the safety valve 48 has been activated by comparing the estimated load Fes with the initial load F0 when the ignition power is turned on. This makes it possible to detect that at least one safety valve of the multiple energy storage cells 45 has been activated when the ignition power is turned on, even if the safety valve had been activated before the ignition power was turned on. Furthermore, since the initial load F0 and the estimated load Fes are less susceptible to external environmental influences (e.g., noise), the risk of being unable to detect the activation of the safety valve of the energy storage cell 45 can be suppressed.

[0029] In embodiments of this disclosure, a load cell 44 is shown as being located between one of a pair of end plates 42 and an energy storage cell 45 adjacent to one of the pair of end plates 42, but the disclosure is not limited thereto. For example, there may be multiple load cells 44. Also, the load cell 44 may be located between each of the multiple energy storage cells 45.

[0030] In the embodiments of this disclosure, an example is shown in which the ECU 20 detects whether the safety valve 48 has been activated by comparing the initial load F0 with the measured load F1, but the disclosure is not limited thereto. For example, the ECU 20 may store data on time and the measured load F1, and detect whether the safety valve 48 has been activated based on the rate of change of the measured load F1 per unit of time.

[0031] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than by the description of the embodiments above, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of symbols]

[0032] 1 Electric vehicle, 11 MG, 12 Drive wheels, 15 HMI device, 21 Processor, 22 Memory, 23 Storage, 30 HMI device, 40 Battery pack, 41 Restraint device, 42 End plate, 43 Column member, 44 Load cell, 45 Energy storage cell, 46 Cell case, 46a Outer surface, 47 External terminals, 50 Monitoring unit, F0 Initial load, F1 Measured load, Fes Estimated load, α Correction value.

Claims

[Claim 1] The system comprises multiple batteries constrained in the stacking direction by a restraining device, and a control unit. Each of the plurality of batteries has a safety valve The control unit acquires information on the battery characteristics of each of the plurality of batteries, external environmental information, and the actual value of the constraint load that restrains the plurality of batteries, which is the initial load that is the constraint load when the ignition power is turned on. The control unit obtains an estimated load, which is an estimated value of the constraint load that restrains the plurality of batteries, based on the battery characteristic information of each of the plurality of batteries and the external environment information. The control unit detects the opening of the safety valve based on the initial load and the estimated load in an electric vehicle.

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