Hybrid vehicle and control method for a hybrid vehicle

Abstract

This improves the accuracy of estimating the full charge capacity of batteries installed in hybrid vehicles. [Solution] When the first and second conditions are met, the processor controls the drive system 3 so that the battery 21 is charged by the engine 32 and the SOC transitions to a high SOC range, acquires an SOC-OCV curve while the SOC is in the high SOC range, and updates the SOC-OCV curve stored in memory with the acquired SOC-OCV curve. The first condition is that in the low SOC range, the discrepancy between the amount of SOC change based on the SOC-OCV curve stored in memory and the amount of SOC change based on the integrated current value charged to the battery 21 exceeds a reference amount. The second condition is that the number of transitions of the SOC within the high SOC range or the number of times the high SOC range is reached during a predetermined period is less than a threshold.

Description

Technical Field

[0001] The present disclosure relates to a hybrid vehicle and a method for controlling a hybrid vehicle.

Background Art

[0002] Japanese Unexamined Patent Application Publication No. 2022-149608 (Patent Document 1) discloses a SOC (State Of Charge)-OCV (Open Circuit Voltage) map update system. This system includes a map update unit that can estimate the battery capacity of a battery based on the discharge current measured by a charge-discharge current measurement unit, calculate the open-circuit voltage of the battery based on the voltage of the battery measured by a voltage measurement unit, and update the SOC-OCV map by associating the battery capacity with the open-circuit voltage.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] It is conceivable to estimate the full charge capacity of a battery mounted on a hybrid vehicle based on the SOC-OCV curve. As the deterioration of the battery progresses, the SOC-OCV curve may change. Nevertheless, if the same SOC-OCV curve continues to be used, the estimation accuracy of the full charge capacity of the battery may decrease. Therefore, it is desirable to appropriately update the SOC-OCV curve, thereby improving the estimation accuracy of the full charge capacity of the battery.

[0005] This disclosure was made to solve the above-mentioned problems, and one of the purposes of this disclosure is to improve the accuracy of estimating the full charge capacity of a battery installed in a hybrid vehicle. [Means for solving the problem]

[0006] A hybrid vehicle relating to a certain aspect of this disclosure comprises a drive system, a battery, memory, and a processor. The drive system includes an engine and a motor-generator that operates as a generator when driven by the engine. The battery is rechargeable when driven by the engine. The memory stores a SOC-OCV curve used to estimate the full charge capacity of the battery. The processor controls the drive system and manages the SOC-OCV curve stored in memory. The battery's SOC includes a low SOC region that is above the lower limit SOC and below the boundary SOC, and a high SOC region that is above the boundary SOC and below the upper limit SOC. When the first and second conditions are met, the processor controls the drive system so that the battery is charged by the engine and the SOC transitions to the high SOC region, acquires an SOC-OCV curve while the SOC is in the high SOC region, and updates the SOC-OCV curve stored in memory with the acquired SOC-OCV curve. The first condition is that, in the low SOC range, the difference between the SOC change based on the SOC-OCV curve stored in memory and the SOC change based on the integrated current charged to the battery exceeds a reference amount. The second condition is that, during a predetermined period, the number of transitions within the high SOC range or the number of times the high SOC range is reached is less than a threshold.

[0007] In a control method for a hybrid vehicle relating to another aspect of this disclosure, the hybrid vehicle is equipped with an engine, a motor generator that operates as a generator driven by the engine, and a battery that can be charged by the engine. The hybrid vehicle's memory stores a SOC-OCV curve used to estimate the battery's full charge capacity. The battery's SOC includes a low SOC region that is above the lower limit SOC and below the boundary SOC, and a high SOC region that is above the boundary SOC and below the upper limit SOC. The control method includes the steps of controlling the engine and motor generator so that the battery is charged by the engine and the SOC transitions to the high SOC region when the first and second conditions are met, acquiring the SOC-OCV curve while the SOC is in the high SOC region, and updating the SOC-OCV curve stored in memory with the acquired SOC-OCV curve. The first condition is that, in the low SOC range, the difference between the SOC change based on the SOC-OCV curve stored in memory and the SOC change based on the integrated current value charged to the battery exceeds a reference amount. The second condition is that, during a predetermined period, the number of transitions within the high SOC range or the number of times the high SOC range is reached is less than a threshold. [Effects of the Invention]

[0008] According to this disclosure, the accuracy of estimating the full charge capacity of a battery installed in a hybrid vehicle can be improved. [Brief explanation of the drawing]

[0009] [Figure 1] This is a diagram showing the configuration of a vehicle according to an embodiment. [Figure 2] This diagram illustrates the need to update the SOC-OCV curve. [Figure 3] This is a diagram to explain the first condition. [Figure 4] This flowchart shows the processing procedure for updating the SOC-OCV curve in the embodiment. [Modes for carrying out the invention]

[0010] This embodiment 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.

[0011] [Embodiment] <Vehicle configuration> Figure 1 shows the configuration of a hybrid electric vehicle (HEV) according to an embodiment. The hybrid vehicle 1 is a plug-in hybrid electric vehicle (PHEV) that can charge its battery (external charging) using power supplied from, for example, a charging facility (not shown) located outside the hybrid vehicle 1. However, the hybrid vehicle 1 may also be a normal hybrid vehicle that does not support external charging. The hybrid vehicle 1 includes a battery pack 2, a drive system 3, a charging system 4, and an EVECU (Electric Vehicle Electronic Control Unit) 5.

[0012] The battery pack 2 includes a battery 21, a monitoring unit 22, a system main relay (SMR) 23, and a battery ECU 24. The monitoring unit 22 includes a voltage sensor 221, a current sensor 222, and a temperature sensor 223.

[0013] Battery 21 is a battery pack containing multiple rechargeable batteries. In this example, each rechargeable battery is a lithium-ion battery. However, the rechargeable batteries may also be nickel-metal hydride batteries or solid-state batteries.

[0014] The battery ECU 24 includes a processor 241 such as a CPU (Central Processing Unit), a memory 242 such as a ROM (Read Only Memory) and a RAM (Random Access Memory), and an input / output port (not shown) through which various signals are input and output. Based on the signals received from each sensor, the program stored in the memory 242, and the SOC-OCV curve, the processor 241 manages the battery 21. More specifically, the battery ECU 24 calculates the SOC of the battery 21 and updates (described later) the SOC-OCV curve of the battery 21.

[0015] The drive system 3 includes a power control unit (PCU: Power Control Unit) 31, an engine 32, a first motor generator 33, a second motor generator 34, a power transmission gear 35, and drive wheels 36. By driving the engine 32 as a power source, the first motor generator 33 can generate the charging power of the battery 21.

[0016] The charging system 4 includes an inlet 41, a power conversion device 42, and a charging relay 43.

[0017] Similar to the battery ECU 24, the EV ECU 5 includes a processor 51, a memory 52, and an input / output port (not shown). Based on the signals received from each sensor, the program and map stored in the memory 52, the EV ECU 5 comprehensively controls the hybrid vehicle 1. For example, the EV ECU 5 controls the charging and discharging of the battery 21 by controlling the PCU 31, the engine 32, and / or the power conversion device 42 while cooperating with the battery ECU 24.

[0018] In FIG. 1, the battery ECU 24 and the EV ECU 5 are separately configured, but the battery ECU 24 and the EV ECU 5 may be integrally configured. Hereinafter, to avoid complication of the description, the battery ECU 24 and the EV ECU 5 are comprehensively described as the ECU 6.

[0019] <SOC-OCV curve> FIG. 2 is a diagram for explaining the necessity of updating the SOC-OCV curve. The horizontal axis represents the SOC of the battery 21. The vertical axis represents the OCV of the battery 21. The same applies to FIG. 3 described later.

[0020] In the present embodiment, SOC = 10% is described as the "lower limit SOC", SOC = 50% is described as the "boundary SOC", and SOC = 90% is described as the "upper limit SOC". However, these numerical values are merely illustrative, and the lower limit SOC, the boundary SOC, and the upper limit SOC can be set as appropriate. The battery 21 is usually used between the lower limit SOC and the upper limit SOC. The SOC range between the lower limit SOC and the boundary SOC is described as the "low SOC range", and the SOC range between the boundary SOC and the upper limit SOC is described as the "high SOC range".

[0021] Generally, when the battery deteriorates, the full charge capacity of the battery decreases and the SOC-OCV curve changes. In FIG. 2, for ease of understanding, an example of the SOC-OCV curve of the battery 21 before deterioration is illustrated as an "initial curve", and an example of the SOC-OCV curve of the battery 21 after deterioration is illustrated as a "deteriorated curve". Note that the charge-side SOC-OCV curve used during charging of the battery and the discharge-side SOC-OCV curve used during discharging of the battery may be different from each other. However, in FIG. 2, for simplicity of explanation, a single curve is shown without distinguishing between the charge-side SOC-OCV curve and the discharge-side SOC-OCV curve.

[0022] As the shape of the SOC-OCV curve gradually changes from the initial curve to the deteriorated curve, the ECU 6 updates the SOC-OCV curve stored in the memory (memory 242) of the ECU 6. This process is hereinafter referred to as the "SOC-OCV curve update process". If the SOC of the battery 21 changes significantly from the low SOC range to the high SOC range, the SOC-OCV curve can be acquired and updated over a wide SOC range accordingly.

[0023] However, there may be usage scenarios in which the State of Charge (SOC) of the battery 21 does not change significantly. Specifically, for example, in areas where charging facilities (charging infrastructure) for the hybrid vehicle 1 are not sufficiently developed, external charging of the hybrid vehicle 1 may not be possible for extended periods. As a result, the SOC of the battery 21 may be limited to the low SOC range and may not transition to the high SOC range. In such cases, opportunities to obtain SOC-OCV curves in the low SOC range may be limited, while opportunities to obtain SOC-OCV curves in the high SOC range may not be obtained.

[0024] Therefore, in the SOC-OCV curve update process in this embodiment, if both the first and second conditions described below are met, the ECU 6 uses the engine 32 as a power source to drive the first motor generator 33 as a generator and charges the battery 21 with the generated power.

[0025] <Conditional Check> ≪Condition 1≫ Figure 3 is a diagram illustrating the first condition. The first condition is that, during a predetermined period (e.g., one week, one month), in the low SOC range, the discrepancy between the SOC change amount based on the SOC-OCV curve stored in memory and the SOC change amount based on the integrated current value charged to the battery exceeds a reference amount.

[0026] More specifically, the deviation amount D can be calculated as follows when battery 21 is charged so that its OCV rises from OCV1 to OCV2. Note that "charging" here may include cases where battery 21 is temporarily discharged while its OCV rises from OCV1 to OCV2. ECU6 calculates the change in the state of charge (SOC) of battery 21 using two methods.

[0027] First, the ECU 6 calculates the change in the SOC of the battery 21, ΔSOCa, by referring to the SOC-OCV curve stored in memory. In this example, it is calculated that the SOC of the battery 21 has increased by ΔSOCa from SOC1, which corresponds to OCV1, to SOC2, which corresponds to OCV2 (see equation (1) below). ΔSOCa == SOC2 - SOC1 ... (1)

[0028] Next, the ECU 6 calculates the integrated current ΣI by integrating the current I (the value detected by the current sensor 222) that charges the battery 21 while the OCV of the battery 21 rises from OCV1 to OCV2 over time. Then, the ECU 6 calculates the change in SOC ΔSOCb based on the integrated current ΣI and the full charge capacity C0 (i.e., the initial full charge capacity) assuming that the battery 21 has not deteriorated (see equation (2) below). ΔSOCb = 100 / C0 × ΣI ···(2)

[0029] The ECU6 then calculates the difference (absolute value) between the two SOC change amounts as the deviation amount D (see equation (3) below). D = |ΔSOCa - ΔSOCb| ... (3)

[0030] ECU6 determines that the first condition is met if the deviation amount D exceeds a predetermined reference amount REF.

[0031] ≪Condition 2≫ The second condition is that, during the predetermined period, the number of times the battery 21's SOC transitions within the high SOC range or reaches the high SOC range (hereinafter referred to as "number N") is less than the threshold TH. During the period, if the battery 21's SOC is always within the low SOC range, or if the number of times the battery 21's SOC transitions from the low SOC range to the high SOC range is less than the threshold TH, the ECU 6 determines that the second condition is met.

[0032] <Processing Flow> Figure 4 is a flowchart showing the processing procedure for updating the SOC-OCV curve in the embodiment. This flowchart is called and executed from a main routine (not shown) when predetermined conditions are met (for example, at predetermined intervals). Each step is implemented by software processing by ECU6 (processor 241 and / or processor 51), but may also be implemented by hardware (electrical circuitry) located within ECU6. Hereinafter, each step will be abbreviated as S.

[0033] In S1, ECU6 determines whether the first condition is met. That is, ECU6 determines whether, within a predetermined period, in the low SOC range, the deviation amount D between the SOC change amount ΔSOCa based on the SOC-OCV curve stored in memory and the SOC change amount ΔSOCb based on the current integration amount ΣI exceeds the reference amount REF. If the deviation amount D is less than or equal to the reference amount REF (NO in S1), ECU6 returns processing to the main routine. If the deviation amount D is greater than the reference amount REF (YES in S1), ECU6 proceeds processing to S2.

[0034] In S2, ECU6 determines whether the second condition is met. That is, ECU6 determines whether the number of times N (number of transitions within the high SOC region or number of times reaching the high SOC region) related to the battery 21's SOC is less than the threshold TH within a predetermined period. If the number N is greater than or equal to the threshold TH (NO in S2), ECU6 returns to the main routine. If the number N is less than the threshold TH (YES in S2), ECU6 proceeds to S3. Note that the processing order of S1 and S2 may be reversed.

[0035] In S3, the ECU 6 operates the first motor generator 33 as a generator by driving the engine 32. This forces the battery 21 to charge, and the state of charge (SOC) of the battery 21 rises from the boundary SOC (the initial SOC may be lower or higher than the boundary SOC) to reach the upper limit SOC.

[0036] In S4, the ECU6 obtains the charging-side SOC-OCV curve of the battery 21 in the high SOC range.

[0037] In S5, the ECU 6 operates the first motor generator 33 and the second motor generator 34 as electric motors due to the powered movement of the hybrid vehicle 1, and also operates auxiliary equipment of the hybrid vehicle 1 (such as an air conditioning system, not shown). As a result, the battery 21 is forcibly discharged, and the state of charge (SOC) of the battery 21 drops from the boundary SOC to the lower limit SOC.

[0038] In S6, the ECU6 obtains the discharge-side SOC-OCV curve of the battery 21 in the high SOC range.

[0039] In S7, the ECU6 updates the SOC-OCV curve in the high SOC range using the two curves acquired in S4 and S6, and non-volatilely stores the updated curve in memory.

[0040] As described above, in this embodiment, when the first and second conditions are met, the engine 32 is actively driven to forcibly charge the battery 21, causing the battery 21's State of Charge (SOC) to reach its upper limit. Therefore, the SOC-OCV curve (charging-side SOC-OCV curve) in the high SOC range is acquired, and the SOC-OCV curve stored in memory can be updated using the acquired SOC-OCV curve. As a result, the full charge capacity of the battery 21 is estimated using the SOC-OCV curve that reflects the degradation of the battery 21. Thus, according to this embodiment, the accuracy of estimating the full charge capacity of the battery 21 can be improved.

[0041] Furthermore, in this embodiment, following forced charging of the battery 21, the battery 21 is forcibly discharged by the powered driving or auxiliary operation of the hybrid vehicle 1, causing the battery 21's State of Charge (SOC) to reach the boundary SOC. Therefore, the discharge-side SOC-OCV curve in the high SOC region can be obtained, and the SOC-OCV curve stored in memory can be updated using the obtained SOC-OCV curve. As a result, the full charge capacity of the battery 21 can be estimated using an SOC-OCV curve that reflects the degradation of the battery 21, not only during charging but also during discharging. Thus, according to this embodiment, the accuracy of estimating the full charge capacity of the battery 21 can be further improved.

[0042] 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]

[0043] 1 Hybrid vehicle, 2 Battery pack, 21 Battery, 22 Monitoring unit, 221 Voltage sensor, 222 Current sensor, 223 Temperature sensor, 23 SMR, 24 Battery ECU, 241 Processor, 242 Memory, 3 Drive system, 31 PCU, 32 Engine, 33 First motor generator, 34 Second motor generator, 35 Power transmission gear, 36 Drive wheels, 4 Charging system, 41 Inlet, 42 Power converter, 43 Charging relay, 5 EVECU, 51 Processor, 52 Memory, 6 ECU.

Claims

1. A drive system including an engine and a motor generator that operates as a generator by the drive of the engine, A battery that can be charged by the operation of the aforementioned engine, A memory that stores the SOC (State Of Charge) - OCV (Open Circuit Voltage) curve used to estimate the full charge capacity of the aforementioned battery, The system includes a processor that controls the drive system and manages the SOC-OCV curve stored in the memory, The State of Control (SOC) of the aforementioned battery is The low SOC region is above the lower limit of SOC and below the boundary SOC, This includes a high SOC region that is higher than the boundary SOC and below the upper limit SOC, If the first and second conditions are met, the processor will The drive system is controlled so that the battery is charged by the operation of the engine and the SOC transitions to the high SOC region. While the SOC is within the high SOC region, the SOC-OCV curve is obtained. The acquired SOC-OCV curve is used to update the SOC-OCV curve stored in the memory. The first condition is that, in the low SOC region, the difference between the amount of SOC change based on the SOC-OCV curve stored in the memory and the amount of SOC change based on the integrated current value charged to the battery exceeds a reference amount. The second condition is that the number of transitions of the SOC within the high SOC region or the number of times the SOC region is reached during a predetermined period is less than a threshold value, in the case of a hybrid vehicle.

2. The aforementioned SOC-OCV curve is, The charging-side SOC-OCV curve used when charging the aforementioned battery, This includes the discharge-side SOC-OCV curve used when the battery is discharged, The aforementioned processor, The drive system is controlled by the engine to charge the battery and raise the SOC to the upper limit SOC, and during this time the charging-side SOC-OCV curve is acquired. Subsequently, the drive system is controlled so that the battery is discharged and the SOC drops to the boundary SOC, and during this time the discharge-side SOC-OCV curve is acquired. The hybrid vehicle according to claim 1, wherein the SOC-OCV curve stored in the memory is updated using the acquired charging-side SOC-OCV curve and the discharge-side SOC-OCV curve.

3. The hybrid vehicle according to claim 1 or 2, wherein the processor, when the battery is charged, calculates the difference between the amount of change in SOC calculated from the SOC-OCV curve stored in the memory and the amount of change in SOC calculated from the integrated current value charged to the battery as the deviation amount.

4. The hybrid vehicle according to claim 1, further comprising a charging system for charging the battery with power supplied from outside the hybrid vehicle.

5. A control method for a hybrid vehicle equipped with an engine, a motor generator that operates as a generator driven by the engine, and a battery that can be charged by the engine, The memory of the aforementioned hybrid vehicle stores the SOC-OCV curve used to estimate the full charge capacity of the battery. The State of Control (SOC) of the aforementioned battery is The low SOC region is above the lower limit of SOC and below the boundary SOC, This includes a high SOC region that is higher than the boundary SOC and below the upper limit SOC, The control method described above, when the first and second conditions are met, The steps include controlling the engine and the motor generator so that the battery is charged by the operation of the engine and the SOC transitions to the high SOC region, The steps include: obtaining an SOC-OCV curve while the SOC is within the high SOC region; The process includes the step of updating the SOC-OCV curve stored in the memory using the acquired SOC-OCV curve, The first condition is that, in the low SOC region, the difference between the amount of SOC change based on the SOC-OCV curve stored in the memory and the amount of SOC change based on the integrated current value charged to the battery exceeds a reference amount. A control method for a hybrid vehicle, wherein the second condition is that the number of transitions of the SOC within the high SOC region or the number of times the SOC region is reached during a predetermined period is less than a threshold.

Images