State-of-charge measuring device, state-of-charge measuring program, battery pack, and saddled vehicle

Abstract

The invention aims to provide a state of charge measuring device achieving good measurement accuracy in a battery with a large energy capacity and with a small placement space. Such a state of charge measuring device (1) is connected to a lithium-ion battery (2) and measures the state of charge of said battery (2).If the initial state of charge at the start of previous charges is higher than a predetermined state of charge, the state of charge acquisition unit (13) of the measuring device obtains the state of charge of said battery (2) by referring to the lithium corrective characteristic whose state of charge index has been increased over a determined voltage range of the voltage-state of charge characteristic, and decreases the magnitude of the increase in said state of charge index of said lithium corrective characteristic if said degree of deterioration of said battery (2) is higher than a reference degree of advancement compared to the case where said degree of deterioration is lower. Figure for abstract: Figure 1.

Description

Title of the invention: State of charge measuring device, state of charge measuring program, battery pack, and saddled vehicle Technical field

[0001] The present invention relates to a state-of-charge measuring device, a state-of-charge measuring program, a battery pack, and a saddled vehicle. Prior art

[0002] For example, patent document 1 discloses a battery pack of a saddled vehicle. The battery pack of patent document 1 has multiple batteries and a control unit using a battery management controller. The control unit detects the voltage of the batteries and measures the state of charge of the batteries from the detected voltage. The control unit controls charging and discharging based on the state of charge. Prior technical documentation Patent documents

[0003] Patent Document 1: Unexamined Published Patent Application No. 2013-232280

[0004] Disclosure of the Invention Problems that the invention attempts to solve

[0005] For example, the battery used to drive a charging device such as a saddle vehicle may require a large power capacity and a small placement space (see paragraph

[0005] of patent document 1). In addition, the state of charge of the battery is an index closely related to the amount of electric power that can actually be continuously supplied to a charging device for example. For this reason, it may be necessary to have good accuracy in measuring the state of charge. The present invention aims to achieve good accuracy in measuring the state of charge in a battery with a large energy capacity and a small placement space. Ways to solve problems

[0006] A battery pack having lithium-ion storage batteries can be used, for example, as a traction battery of a saddled vehicle. Lithium-ion storage batteries have, for example, a larger energy capacity per unit volume and a smaller placement space compared to nickel-metal hydride storage batteries. In addition, lithium-ion storage batteries are not subject to the so-called memory effect, unlike Nickel-metal hydride batteries. For example, on a web page explaining the characteristics of lithium-ion batteries (https: / / www.eco-hatsu.com / battery / faq / 26 / ), it is written that "in principle, the memory effect does not occur in lithium-ion batteries." If the memory effect does not occur, it is possible to obtain the state of charge from the measured voltage, for example by referring to a previously prepared single voltage-state of charge characteristic.

[0007] However, after checking the measurement accuracy of the state of charge under different charging and discharging conditions for different characteristics of lithium-ion storage batteries, the present inventor found that the measurement accuracy of the state of charge may decrease. After further checks on lithium-ion storage batteries, the present inventor found that if the initial state of charge at the start of previous charges is higher than a reference state of charge, the measurement accuracy of the state of charge decreases because the voltage as a function of the state of charge decreases over a certain range, compared to the opposite case. Furthermore, after further checks, the present inventor found that the voltage drop as a function of the state of charge is less as the deterioration degree of lithium-ion storage batteries progresses, even if the aforementioned initial state of charge is higher than the reference state of charge. The present invention has been completed based on the knowledge described above.

[0008] To achieve the above objective, the vehicle has the following configuration according to one embodiment of the present invention: (1) A state of charge measuring device connected to a lithium-ion battery and measuring the state of charge of said lithium-ion battery; said state of charge measuring device has: - a voltage measuring unit which measures the battery voltage of said lithium-ion battery; - a characteristic memory unit which stores a voltage-state of charge characteristic expressing a characteristic of said lithium-ion battery; - a state of charge acquisition unit which obtains the state of charge of said lithium-ion battery from said battery voltage measured by said voltage measuring unit, with reference to said voltage-state of charge characteristic; - a historical memory unit storing the initial state of charge, which is the state of charge at the start of past charges of said lithium-ion battery; - and a unit for acquiring a degree of deterioration of said lithium-ion battery. Said unit for acquiring the state of charge: - obtains the state of charge of said lithium-ion battery by referring to a lithium correction characteristic, the state of charge index of which has been increased for said lithium-ion battery over a determined voltage range of said voltage-state of charge characteristic, if said initial state of charge at the start of previous charges is higher than a predetermined state of charge; - decreases the importance of the increase in said state of charge index of said lithium corrective characteristic, if said degree of deterioration of said lithium-ion battery is greater than a reference degree of progress, compared to the case where said degree of deterioration is lower.

[0009] According to the state of charge measuring device (1), if the initial state of charge at the start of previous charges is higher than a predetermined state of charge, the state of charge acquisition unit obtains the state of charge of the lithium-ion battery by referring to the lithium corrective characteristic whose state of charge index has been increased over a determined voltage range of the voltage-state of charge characteristic, and decreases the amount of increase in the lithium corrective characteristic if the degree of deterioration of the lithium-ion battery is higher than a reference advancement degree compared to the case where the degree of deterioration is lower.For this reason, it is possible to obtain good accuracy of the state of charge measurement during the possible use period of the lithium-ion battery, even if the state of charge over a certain voltage range of the voltage-state of charge characteristic decreases when charging and discharging are repeated, and even if a lithium-ion battery with a high degree of deterioration is used and the magnitude of the aforementioned decrease is reduced. Therefore, it is possible to obtain good accuracy of the state of charge measurement in a lithium-ion accumulator with a large energy capacity and a small placement space.

[0010] The state of charge measuring device is always electrically connected to the lithium-ion storage battery. The state of charge measuring device is, for example, a battery management system (BMS) or a battery management controller (BMC), which is installed on the battery pack having lithium-ion batteries, and which controls the charging and discharging of the lithium-ion batteries. However, the state of charge measuring device is not particularly limited, and it may be, for example, a state of charge display device which displays the measured state of charge. Furthermore, the state of charge measuring device may be located remotely from the lithium-ion battery.

[0011] A lithium-ion battery is a battery that performs charging and discharging by transferring lithium-ion. A lithium-ion battery is a rechargeable battery. A lithium-ion battery has, for example, a positive electrode containing lithium oxide. A lithium-ion battery has, for example, a negative electrode containing lithium. In addition, a lithium-ion battery has, for example, a negative electrode containing silicon-based materials. If a lithium-ion battery has an electrode containing silicon-based materials, the capacity increases. However, in this case, the state of charge over a given voltage range tends to increase more easily, if the initial state of charge at the start of previous charges is higher than the reference state of charge. For this reason, the measurement accuracy of the state of charge is likely to decrease when referring to the voltage-state of charge characteristic. However, it is possible to achieve good measurement accuracy by decreasing the magnitude of the increase in the lithium corrective characteristic when the degree of deterioration is greater than a reference degree of advancement while referring to the lithium corrective characteristic.

[0012] The battery voltage is, for example, the voltage of a battery having several lithium-ion storage cells connected in series. However, the battery voltage is not particularly limited, and it can be the voltage of one lithium-ion storage cell for example. Furthermore, the battery voltage is, for example, a closed-circuit voltage. More precisely, the battery voltage can be obtained, for example, by correcting the voltage during discharge according to the discharge current. In this case, an accurate state of charge can be obtained even during operation of a charging device. However, the battery voltage is not limited to this and can be, for example, the voltage when the charging circuit is open.

[0013] The state of charge acquisition unit obtains the state of charge of the lithium-ion battery by referring to the lithium corrective characteristic, after, for example, two consecutive charges that start at an initial state of charge higher than the predetermined state of charge, and decreases the amount of increase in the lithium corrective characteristic if the degree of deterioration is higher than the reference degree of advancement. However, there should be, as a condition, several charges previously starting with an initial state of charge higher than a predetermined state of charge, for example, three or more.The state of charge acquisition unit can obtain the state of charge of the lithium-ion battery by referring to the lithium correction characteristic, after, for example, ten or more consecutive charges that start at an initial state of charge higher than the predetermined state of charge, and can decrease the amount of increase in the lithium correction characteristic if the degree of deterioration is higher than the reference degree of advancement.

[0014] The voltage-state-of-charge characteristic is a characteristic describing the relationship between the battery voltage and its state of charge. More concretely, the characteristics are characteristic map data. The voltage-state-of-charge characteristic is the relationship between, for example, the reference characteristics of the state of charge and the voltage of the battery after being charged to from a state of charge below a predetermined state of charge. The voltage-state of charge characteristic is, for example, a characteristic referenced after the battery has been charged from a state of charge below a predetermined state of charge. The voltage-state of charge characteristic is, for example, stored in the characteristic memory unit as a characteristic acquired based on the results of previous measurements of the same type of battery as the target battery to be measured. The voltage-state of charge characteristic may be, for example, a characteristic obtained based on previous results of the target battery to be measured. The lithium patch characteristic is, for example, the voltage-state of charge characteristic that describes the relationship between the state of charge and the voltage of the battery after being charged from a state of charge above a predetermined state of charge.A portion of the voltage-state-of-charge characteristics is corrected with the lithium correction characteristic. With the lithium correction characteristic, the state-of-charge index over a specified voltage range is increased compared to the case where the voltage-state-of-charge characteristic is not corrected. The magnitude of the increase in the state-of-charge index of the lithium correction characteristic can be gradually reduced if the degree of deterioration is greater than the reference degree of advancement. Furthermore, the magnitude of this increase can be reduced little by little as the degree of deterioration increases. The lithium correction characteristic is, for example, stored in the characteristic memory unit as characteristic map data acquired on the basis of the results of previous measurements of the same type of battery as the target battery to be measured.However, the lithium correction characteristic may be a correction formula or a correction data map applied to correct the reference result for part of the voltage-state-of-charge characteristic. In addition, several sets of voltage-state-of-charge characteristics can be stored depending on the degree of battery deterioration. In this case, it is possible to refer to the voltage-state-of-charge characteristic that is a function of the degree of deterioration of the target battery to be measured. In addition, the lithium correction characteristic can also be formed based on each set of voltage-state-of-charge characteristics. Moreover, for some of the sets of voltage-state-of-charge characteristics, it is not necessary to form a lithium correction characteristic because there is practically no change. The determined voltage range is set, for example, to a range lower than the voltage-state-of-charge function equal to half of a full charge.The determined voltage range is defined, for example, to a range below the state-of-charge voltage between 5% and 25%, for the voltage-state-of-charge characteristic. In . In this case, it is easier to respond to changes in the characteristics of the lithium-ion battery having electrodes containing silicon-based materials.

[0015] The degree of deterioration expresses the amount of use of a lithium-ion battery between the start of its use and the end of its lifetime. A low degree of deterioration is said to be when the degree of deterioration is less than the reference degree of advancement. When the degree of deterioration is greater than the reference degree of advancement, reducing the magnitude of the increase in the lithium corrective characteristic compared to the case where the degree of deterioration is low may mean, for example, that the magnitude of the increase in the lithium corrective characteristic decreases as the degree of deterioration increases.As a result of reducing the magnitude of the increase in the lithium corrective characteristic compared to the case where the degree of deterioration is low, the state of charge index over a determined voltage range of the lithium corrective characteristic is equal to or greater than the index of the voltage-state of charge characteristic before its increase, and is for example a predetermined number of charge / discharge cycles from the end of use. The reference degree of progress is the deterioration degree reference defined from the start of use to the end of life. Concretely, the reference degree of progress is defined according to the type of lithium-ion battery.

[0016] According to one embodiment of the present invention, the vehicle can adopt the following configuration:

[0017] (2) Device for measuring the state of charge in (1), in which said state of charge acquisition unit decreases the magnitude of the increase in said state of charge index of said lithium corrective characteristic, if said initial state of charge at the start of the previous charge is lower than said predetermined state of charge.

[0018] If the initial state of charge at the start of the previous charge is lower than the predetermined state of charge, the voltage drop depending on the state of charge over a determined voltage range of the voltage-state of charge characteristic of the lithium-ion battery is attenuated. According to embodiment (2), since the magnitude of the increase in the lithium correction characteristic decreases if the initial state of charge at the start of the previous charge is lower than the predetermined state of charge, it is possible to obtain good measurement accuracy of the state of charge of the lithium-ion battery even in this case.

[0019] (3) Device for measuring the state of charge in (1) or (2), in which said unit acquisition of the degree of deterioration obtains, as the degree of deterioration, the cumulative charge of said lithium-ion battery, the cumulative discharge of said battery lithium-ion, the capacity of said lithium-ion battery, the internal resistance of said lithium-ion battery, or each voltage deviation of said lithium-ion battery.

[0020] According to embodiment (3), it is possible to indirectly and easily obtain the degree of deterioration of the lithium-ion battery.

[0021] (4) Device for measuring the state of charge mentioned in one of the modes of achievements (1) to (3), in which said predetermined state of charge is set between 20% and 50% of a full charge.

[0022] According to embodiment (4), it is possible to obtain good state of charge measurement accuracy for a lithium-ion battery whose voltage as a function of the state of charge decreases over a certain voltage range if charging starts from a predetermined range.

[0023] (5) Device for measuring the state of charge of one of the embodiments (1) to (4), having a discharge prevention unit which prohibits the discharge of a lithium-ion battery, if the state of charge obtained by said state of charge acquisition unit is lower than a minimum state of charge value.

[0024] According to embodiment (5), if the state of charge is lower than a minimum state of charge value, the reduction of the usage time of the lithium-ion battery is prevented because the discharging of the lithium-ion battery is prohibited. And it is possible to prevent the reduction of the usage time while discharging the lithium-ion battery to the maximum limit because the state of charge is accurately obtained by referring to the lithium correction characteristic.

[0025] (6) Battery pack having a device for measuring the state of charge of one of the modes of embodiments (1) to (5), and said lithium-ion battery connected to said state of charge measuring device.

[0026] According to the embodiment (6), it is possible to increase the actual charging and discharging capacity of the lithium-ion battery by achieving better measurement accuracy of the state of charge of the lithium-ion battery having a large energy capacity and a small placement space, compared with the case without the present configuration.

[0027] (7) Saddled vehicle equipped with a battery pack of embodiment (6), a motor receiving electrical power from said battery pack, and a wheel driven by said motor.

[0028] According to embodiment (7), it is possible to reduce the size of the saddled vehicle equipped with a battery pack having a large energy capacity, because it is possible to increase the actual charging and discharging capacity of the lithium-ion battery.

[0029] A saddled vehicle is a vehicle on which a driver sits astride a saddle. Examples of saddled vehicles include: scooters, mopeds, off-road motorcycles, and road motorcycles, for example. Furthermore, a saddled vehicle is not limited to two-wheeled motor vehicles and can be, for example, a three-wheeled motor vehicle or an all-terrain vehicle (ATV). A three-wheeled motor vehicle can have two front wheels and one rear wheel, or one front wheel and two rear wheels. The steering of a saddled vehicle is carried out by transferring the rider's weight. For this reason, the saddled vehicle must be compact and lightweight. In addition, it is preferable for the vehicle to be configured to be able to turn in an inclined position. A vehicle configured to turn in an inclined position is configured to turn in an inclined position towards the center of the curve. The vehicle configured to turn in an inclined position thus resists the centrifugal force exerted on the vehicle during a turn.Examples of vehicles configured to turn in an inclined position include saddle vehicles configured to turn in an inclined position (e.g., two-wheeled motor vehicles, three-wheeled motor vehicles). Since agility is required in a vehicle configured to turn in an inclined position, it is essential that it be compact and lightweight.

[0030] (8) State of charge measurement program that performs the measurement operation of the state of charge of said lithium-ion battery on a computer installed in the state of charge measuring device connected to a lithium-ion battery; said state of charge measuring program performs: - a voltage measuring function which measures the battery voltage of said lithium-ion battery; - a characteristics memory function which stores a voltage-state of charge characteristic expressing a characteristic of said lithium-ion battery; - a state of charge acquisition function which obtains the state of charge of said lithium-ion battery from said battery voltage measured by said voltage measurement function, with reference to said voltage-state of charge characteristic; - a historical memory function storing the initial state of charge, which is the state of charge at the start of past charges of said lithium-ion battery; - and a function for acquiring a degree of deterioration of said lithium-ion battery. Said state of charge acquisition function, as such: - obtains the state of charge of said lithium-ion battery by referring to a lithium corrective characteristic, the state of charge index of which has been increased for said lithium-ion battery over a determined voltage range of said voltage-state of charge characteristic, if said initial state of charge at the start of previous charges is higher than a predetermined state of charge; - and reduces the importance of the increase in said state of charge index of said lithium corrective characteristic, if said degree of deterioration of said lithium-ion battery is greater than a reference degree of progress, compared to the case where said degree of deterioration is lower.

[0031] According to embodiment (8), it is possible to increase the actual charge and discharge capacity of a lithium-ion battery.

[0032] The technical terms used in this specification are used only to define specific examples and are not intended to limit the invention. The terms "and / or" as used herein include any combination of one or more related listed components. When used herein, the use of the terms "including, having," "including, comprising," or "having" and variations thereof identifies the presence of the described features, processes, operations, elements, components, and / or their equivalents, but may include one or more steps, movements, elements, components, and / or groups thereof. When used herein, the terms "installed," "connected," "coupled," and / or their equivalents are used broadly, and encompass both direct and indirect installation, connection, and coupling.Furthermore, the terms "connected" and "coupled" are not limited to physical or mechanical connections or couplings, and may include direct or indirect electrical connections or couplings. Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meanings as those generally understood by those skilled in the art to which the invention pertains. Terms as defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the relevant technology and this disclosure, and will not be interpreted in an ideal or overly formal manner unless explicitly defined herein. In describing the present invention, it is understood that a number of techniques and methods are disclosed.Each of these techniques has individual advantages and each can also be used in conjunction with one or more, or even all, of the other techniques disclosed. Therefore, for the sake of clarity, the present description refrains from unnecessarily repeating all possible combinations of the various steps. Nevertheless, the description should be read with the understanding that all such combinations fall within the scope of the present invention. The present description describes a novel state-of-charge measuring device, a state-of-charge measuring program, a battery pack, and a saddled vehicle. In the following description, by way of illustration, a number of specific details are given to enable a complete understanding of the invention. However, it It is clear to those skilled in the art that the present invention can be embodied without these particular details. The present disclosure is to be considered as an example of the present invention and is not intended to limit the present invention to any specific embodiment indicated by the following drawings or explanations. Effects of the invention

[0033] According to the present invention, it is possible to provide a state-of-charge measuring device achieving good state-of-charge measuring accuracy of a battery having a large energy capacity and a small placement space, a state-of-charge measuring program, a battery pack, and a saddled vehicle.

[0034] Brief description of the drawings [Fig.l]: Figure describing the battery system comprising a device for measuring the state of charge according to one embodiment. [Fig.2]: Graph showing the voltage-state of charge characteristic of an example of a state of charge measuring device shown in [Fig.l]. [Fig.3]: Block diagram showing a different example of a state of charge measuring device shown in [Fig.l]. [Fig.4]: Block diagram showing a different example of a state of charge measuring device shown in [Fig.l]. Embodiments of the invention

[0035] [Fig.l] is a figure describing the battery system including a state of charge measuring device according to one embodiment. Part (a) of [Fig.l] is a block diagram showing the schematic configuration of the battery system having a state of charge measuring device. Part (b) of [Fig.l] is a block diagram showing the functional configuration of the state of charge measuring device. Part (c) of [Fig.l] is a programming flowchart describing the operation of the state of charge measuring device. Part (d) of [Fig.l] is a graph showing the voltage-state of charge characteristic when the degree of deterioration is low. Part (e) of [Fig.l] is a graph showing the voltage-state of charge characteristic when the degree of deterioration is high.

[0036] The battery system S shown in [Fig.l] serves as a power source supplying an external electrical device with electrical energy. The battery system S can be supplied and charged with electrical energy from an external source. The battery system S has a state of charge measuring device 1 and a lithium-ion battery 2. The lithium-ion battery 2 consists of several cells connected in series. The lithium-ion battery 2 has, for example, an electrode containing silicon-based materials.

[0037] The state of charge measuring device 1 is connected to the lithium-ion battery 2 and measures the state of charge of the lithium-ion battery 2. The state of charge measuring device 1 produces a signal expressing the measured state of charge. The state-of-charge measuring device 1 is a computer having a processor 101 and a memory 102. The state-of-charge measuring program 103 is stored in the memory 102. The processor 101 performs each function of the state-of-charge measuring device 1 by executing the state-of-charge measuring program 103. Each type of data such as the voltage-state-of-charge characteristic data 104 is stored in the memory 102.

[0038] The state of charge measuring device 1 has a voltage measuring unit 11, a characteristics memory unit 12, a state of charge acquisition unit 13, a history memory unit 14, and a deterioration degree acquisition unit 15. The voltage measurement unit 11, the state of charge acquisition unit 13, and the deterioration degree acquisition unit 15 are configured by the processor 101 which executes the state of charge measurement program 103. Furthermore, the characteristics memory unit 12 and the history memory unit 14 are configured by the memory 102 and the processor 101 which executes the state of charge measurement program 103. By executing the state-of-charge measurement program 103, the processor 101 realizes the state-of-charge measurement function of the state-of-charge measurement device 1, the voltage measurement function of the voltage measurement unit 11, the characteristic memory function of the characteristic memory unit 12, the state-of-charge acquisition function of the state-of-charge acquisition unit 13, the historical memory function of the historical memory unit 14, and the deterioration degree acquisition function of the deterioration degree acquisition unit 15, described below.

[0039] The voltage measuring unit 11 measures the battery voltage of the lithium-ion battery 2. The voltage measuring unit 11 measures, for example, the battery voltage with an analog / digital converter, not shown, installed on the state of charge measuring device 1.

[0040] The historical memory unit 14 stores the initial state of charge which is the state of charge at the start of previous charges of the lithium-ion battery 2. The historical memory unit 14 stores the initial state of charge over several previous periods. More specifically, the historical memory unit 14 stores at least the number of times the state of charge at the start of charging of the lithium-ion battery 2 was higher than the predetermined state of charge C1 (part (d) of [Fig.l]) consecutively over the most recent period.

[0041] The deterioration degree acquisition unit 15 obtains the deterioration degree of the lithium-ion battery 2. The deterioration degree acquisition unit 15 obtains as the deterioration degree, for example, the cumulative charging current or the cumulative discharging current since the start of the first use of the lithium-ion battery 2.

[0042] The characteristic memory unit 12 stores the voltage-state-of-charge characteristic Qa. More concretely, the voltage-state-of-charge characteristic Qa is data that represents the relationship between the voltage and the state of charge of the lithium-ion battery 2. More precisely, the voltage-state-of-charge characteristic Qa is map data that has associated the voltage and the state of charge of the lithium-ion battery 2. The solid line of parts (d) and (e) of [Fig.l] indicates the voltage-state-of-charge characteristic Qa of the lithium-ion battery 2. The solid line of part (e) of [Fig.l] shows the voltage-state-of-charge characteristic Qa where the degree of deterioration is higher than the state of the characteristic indicated in part (d), i.e., where the deterioration situation is more advanced. The vertical axis of parts (d) and (e) of [Fig.l] represents the battery voltage. The horizontal axis represents the amount of electrical energy discharged from a fully charged state to an end-of-discharge state. The horizontal axis also indicates the state of charge of the lithium-ion battery 2. The state of charge of a fully charged state is 100%, and the state of charge of an end-of-discharge state is 0%. The state of charge decreases as the amount of electrical energy discharged increases. Therefore, on the horizontal axis of parts (d) and (e) of [Fig.l], the index of the amount of electrical energy discharged, i.e., the value of the amount of electrical energy discharged, is higher on the right. In contrast, the value of the index of the state of charge is higher on the left. The battery voltage of the lithium-ion battery 2 varies depending on the state of charge. Specifically, the lithium-ion battery 2 has a voltage-state of charge characteristic Qa in which the battery voltage decreases as the state of charge decreases. In addition, the solid line in parts (d) and (e) of [Fig.l] shows the voltage-state of charge characteristic Qa of the lithium-ion battery 2 when the initial state of charge at the beginning of the previous charge of the lithium-ion battery 2 is lower than the predetermined state of charge CL. The dotted line indicates the lithium corrective characteristic Qb whose state of charge index has been increased over a determined voltage range Vr.

[0043] The voltage-state-of-charge characteristic Qa and the lithium correction characteristic Qb are stored in the characteristic memory unit 12. The voltage-state-of-charge characteristic Qa stored in the characteristic memory 12 is, for example, an average characteristic obtained from previous measurements on the same type of battery as lithium-ion battery 2. However, the voltage-state-of-charge characteristic Qa and the lithium patch characteristic Qb may be characteristics obtained from measurements of the lithium-ion battery 2 itself during its manufacture or use. In addition, the characteristic memory unit 12 stores the voltage-state-of-charge characteristic Qa in the initial state, shown in part (d) of [Fig. 1], and the voltage-state-of-charge characteristic Qa in a state having a high degree of deterioration, shown in part (e) of [Fig. 1]. The characteristic memory unit 12 can store, as the voltage-state-of-charge characteristic Qa, more than three voltage-state-of-charge characteristics Qa corresponding to each stage of the degree of deterioration, and is not limited to the two characteristics shown in [Fig. 1].

[0044] The state-of-charge acquisition unit 13 obtains the state-of-charge of the lithium-ion battery 2 from the battery voltage measured with the voltage measurement unit 11, by referring to the voltage-state-of-charge characteristic (e.g., Qa in part (d) of [Fig.l]) stored in the characteristic memory unit 12. However, the state of charge acquisition unit 13 obtains the state of charge of the lithium-ion battery 2 by referring to the lithium corrective characteristic Qb, if the initial state of charge during previous charges is higher than the predetermined state of charge CL. The lithium corrective characteristic Qb is a characteristic whose state of charge index has been increased over a determined voltage range Vr of the voltage-state of charge characteristic Qa. Furthermore, the state of charge acquisition unit 13 obtains the state of charge of the lithium-ion battery 2 by referring to the lithium corrective characteristic Qb whose amount of increase in the state of charge index has decreased over the determined voltage range Vr, if the degree of deterioration of the lithium-ion battery 2 is higher than the reference degree of advancement Dl, as shown in part (e) of [Fig.l].

[0045] An example of operation of the state of charge measuring device 1 is also explained with reference to the programming flowchart of part (c) of [Fig.l]. In the state-of-charge measuring device 1, the function of each unit shown in part (b) of [Fig.l] is implemented by the processor 101 which executes the state-of-charge measuring program 103. The operation of each step is repeated.

[0046] The voltage measuring unit 11 measures the battery voltage of the lithium-ion battery 2 (SI 1). The state of charge of the lithium-ion battery 2 is obtained on the basis of the voltage measured at the time the voltage was measured.

[0047] The deterioration degree acquisition unit 15 obtains the deterioration degree of the lithium-ion battery 2 (S 12).

[0048] The state of charge acquisition unit 13 determines whether the previous charge of the lithium-ion battery 2 started from a high state of charge (S13). More specifically, the state of charge acquisition unit 13 determines whether the initial state of charge at the start of previous charges is higher than the predetermined state of charge CL or not. The initial state of charge at the start of past charges is stored in the history memory unit 14. The state of charge acquisition unit 13 obtains the initial state of charge at the start of previous charges from the history memory unit 14. The state of charge acquisition unit 13 obtains the state of charge of the lithium-ion battery 2 from the battery voltage (S15), referring to the voltage-state of charge characteristic Qa, if the initial state of charge during previous charges is lower than the predetermined state of charge Cl (No in step S13).

[0049] The state of charge acquisition unit 13 corrects the voltage-state of charge characteristic Qa into the lithium correction characteristic Qb (S 14), if the initial state of charge at the start of the previous charges is higher than the predetermined state of charge (yes in step S13). The state of charge acquisition unit 13 obtains the state of charge of the lithium-ion battery 2 from the battery voltage, by referring to the lithium correction characteristic Qb. In the lithium correction characteristic Qb, the state of charge index has been increased over a determined voltage range Vr of the voltage-state of charge characteristic Qa. Parts (d) and (e) of [Fig.l] schematically show examples of histories H1 and H2 of the state of charge evolution that accompany the charging and discharging of the lithium-ion battery 2. The histories H1 and H2 show the evolution of several consecutive starts of the charge when the state of charge is higher than the predetermined state of charge Cl (i.e. to the left of Cl on the graph), followed immediately by a discharge until the state of charge is zero. In cases such as histories H1 and H2, the state-of-charge acquisition unit 13 corrects the voltage-state-of-charge characteristic Qa into the lithium correction characteristic Qb (S 14), and obtains the state-of-charge of the lithium-ion battery 2 (S 15) from the battery voltage, referring to the lithium correction characteristic Qb.

[0050] Furthermore, the reference of the number of times the initial state of charge is greater than the predetermined state of charge C1, and which is determined in step S13 above, differs depending on the type of lithium-ion battery 2. This number can be set between 2 and 20 times for example.

[0051] The state of charge acquisition unit 13 decreases the magnitude of the increase in the state of charge index over a determined voltage range Vr of the lithium corrective characteristic Qb, if the degree of deterioration of the lithium-ion battery 2 is greater than the reference degree of advancement Dl. More specifically, the state of charge acquisition unit 13 decreases the magnitude of the increase in the state of charge index over a determined voltage range Vr of the lithium corrective characteristic Qb (part (e) of [Fig.l]), compared to the case where the degree of deterioration is less than the reference degree of advancement Dl (part (d) of [Fig.l]). The state of charge acquisition unit 13 obtains the state of charge of the lithium-ion battery 2 (step S15) by referring to the lithium correction characteristic Qb of which the magnitude of the increase in the state of charge index has been reduced.

[0052] According to the inventors' research, it has been discovered that, if the initial state of charge at the beginning of previous charges is higher than the reference state of charge, a lithium-ion battery 2 has its state-of-charge voltage decrease over a part of the range of the voltage-state-of-charge characteristic Qa, compared to the opposite case. In other words, some lithium-ion batteries 2 have a voltage-dependent state of charge that increases over a part of the range of the voltage-state-of-charge characteristic Qa. For example, a lithium-ion battery 2 having a negative electrode containing silicon-based materials has a strong tendency to the above. Furthermore, the state-of-charge voltage decrease is less, even if the aforementioned initial state of charge is higher than the reference state of charge, when the degree of deterioration of the lithium-ion battery 2 progresses.In other words, the magnitude of the state of charge increase as a function of voltage decreases over part of the range.

[0053] According to the present embodiment, if the initial state of charge at the start of previous charges is higher than a predetermined state of charge C1, the state of charge acquisition unit 13 obtains the state of charge of the lithium-ion battery 2 by referring to the lithium corrective characteristic Qb whose state of charge index has been increased over a determined voltage range, and obtains the state of charge by referring to the lithium corrective characteristic Qb whose amount of increase in the state of charge index is reduced, if the degree of deterioration of the lithium-ion battery 2 is higher than a reference advancement degree D1, compared to the case where the degree of deterioration is lower, as shown in part (e) of [Fig.l].For this reason, it is possible to obtain good accuracy, even if the state of charge over a given voltage range Vr of the voltage-state of charge characteristic Qa decreases when charging is repeated from an initial state of charge higher than the reference state of charge, and even if a lithium-battery is used. ion 2 with a high degree of deterioration and the magnitude of the aforementioned decrease is reduced. Therefore, it is possible to achieve good state of charge measurement accuracy in a lithium-ion 2 battery with a large energy capacity and a small placement space.

[0054] [Fig. 2] is a graph showing the voltage-state of charge characteristic of an exemplary state of charge measuring device shown in [Fig. 1].

[0055] [Fig. 2] shows an example of a history H3 of the state of charge evolution that accompanies the charging and discharging of the lithium-ion battery 2. According to the history H3, the initial state of charge Ca at the start of the previous charging is lower than the predetermined state of charge CL. In this case, the state of charge acquisition unit 13 can decrease the magnitude of the increase in the state of charge index of the lithium corrective characteristic Qb, compared to the magnitude of the increase in the lithium corrective characteristic Qb shown in part (d) of [Fig. 1].

[0056] If the initial state of charge Ca at the start of the previous charge is lower than the predetermined state of charge Cl, the voltage drop as a function of the state of charge over a determined voltage range Vr of the characteristic of the lithium-ion accumulator 2 is attenuated. In the example described in [Fig. 2], it is possible to obtain good measurement accuracy of the state of charge by reducing the magnitude of the increase in the lithium corrective characteristic Qb, if the initial state of charge Ca at the start of the previous charge is lower than the predetermined state of charge CL

[0057] Furthermore, it has been explained that the deterioration degree acquisition unit 15 of the state of charge measuring device shown in [Fig.l] obtains the cumulative charge or the cumulative discharge as the deterioration degree. However, the index obtained by the deterioration degree acquisition unit 15 is not limited to these. The deterioration degree acquisition unit 15 may, in one example, obtain the cumulative charge, the cumulative discharge, the internal resistance, the battery capacity, or the voltage deviation. In addition, the deterioration degree acquisition unit 15 may obtain a combination of these. The internal resistance can be obtained, for example, from the current and voltage by measuring the current and voltage during charging or discharging of the lithium-ion battery 2. The battery capacity can be obtained using a previously measured relative characteristic, for example from the fully charged voltage. The fully charged state is detected as a state in which the charging current hardly flows even when a charging voltage is applied. The voltage deviation can be obtained, for example, as the difference between the maximum voltage and the minimum voltage detected for each cell of the lithium-ion battery 2.

[0058] According to the above-mentioned examples of indices, it is possible to obtain an accurate degree of deterioration of the lithium-ion battery 2, using an index that is easy to obtain depending on the type of system.

[0059] [Fig.3] is a block diagram showing a different example of a state of charge measuring device shown in [Fig.l]. The state-of-charge measuring device 1 can be configured with a battery pack P as well as a lithium-ion battery 2. In other words, the battery pack P has a state-of-charge measuring device 1 and a lithium-ion battery 2.

[0060] Furthermore, the state of charge measuring device 1 may be equipped with a discharge prevention unit 105 which prevents the lithium-ion battery 2 from being discharged. The discharge prevention unit 105 prevents the lithium-ion battery 2 from being discharged if the state of charge obtained by the state of charge acquisition unit 13 is lower than a minimum state of charge value. For example, a lower limit at which the usage time of the lithium-ion battery 2 is likely to be maintained may be set as the minimum state of charge value. The minimum state of charge value is set, for example, between 1% and 9% relative to a full charge.

[0061] If the state of charge of the lithium-ion battery 2 is lower than the minimum state of charge value during the discharging of the lithium-ion battery 2, the discharging is prohibited. Therefore, it is difficult for the state of charge of the lithium-ion battery 2 to fall below the minimum state of charge value. Therefore, the reduction of the use time of the lithium-ion battery 2 is prevented. And it is possible to prevent the reduction of the use time while discharging the lithium-ion battery 2 to the maximum limit because the state of charge is accurately obtained by referring to the lithium correction characteristic Qb.

[0062] Furthermore, in the example shown in [Fig.3], it is possible to increase the actual charge and discharge capacity as a battery pack P by achieving better measurement accuracy of the state of charge of the lithium-ion battery 2, compared to a battery pack not having this configuration for example.

[0063] [Fig.4] is a block diagram showing a different example of a state of charge measuring device shown in [Fig.l]. The state-of-charge measuring device 1 can be installed on a saddled vehicle 3, as shown in [Fig. 4]. The saddled vehicle 3 has a battery pack P, a motor 4, and a wheel 5. The saddled vehicle 3 moves by rotating the wheel 5. The wheel 5 is driven by the motor 4. The motor 4 is supplied with electrical energy by the battery pack P.

[0064] In the saddle vehicle 3 of [Fig.4], it is possible to reduce the size of the saddle vehicle 3 equipped with a battery pack P having a large energy capacity, because it is possible to increase the actual charge and discharge capacity of the lithium-ion battery 2. Legend

[0065] 1: Device for measuring the state of charge 2: Lithium-ion accumulator battery 3: Saddled vehicle 4: Engine 5: Wheel 11: Unit of measurement for voltage 12: Characteristics memory unit 13: State of charge acquisition unit 14: Historical Memory Unit 15: Unit of acquisition of the degree of deterioration 103: State of charge measurement program 105: Discharge Prohibition Unit Cl: predetermined state of charge DI: Reference degree of progress P: Battery pack Qa: Voltage-state-of-charge characteristic Qb: Lithium corrective characteristic Vr: Determined voltage range

Claims

Claims

1. A state-of-charge measuring device (1) connected to a lithium-ion battery (2) and measuring the state of charge of said lithium-ion battery (2); said state-of-charge measuring device (1) has: - a voltage measuring unit (11) which measures the battery voltage of said lithium-ion battery (2); - a characteristic memory unit (12) which stores a voltage-state-of-charge characteristic expressing a characteristic of said lithium-ion battery (2); - a state-of-charge acquiring unit (13) which obtains the state of charge of said lithium-ion battery (2) from said battery voltage measured by said voltage measuring unit, with reference to said voltage-state-of-charge characteristic; - a history memory unit (14) storing the initial state of charge, which is the state of charge at the beginning of past charges of said lithium-ion battery (2);- and a unit for acquiring a degree of deterioration (15) of said lithium-ion battery (2); said state of charge acquisition unit: - obtains the state of charge of said lithium-ion battery (2) by referring to a lithium corrective characteristic, the state of charge index of which has been increased for said lithium-ion battery (2) over a determined voltage range of said voltage-state of charge characteristic, if said initial state of charge at the start of previous charges is higher than a predetermined state of charge; - decreases the magnitude of the increase in said state of charge index of said lithium corrective characteristic, if said degree of deterioration of said lithium-ion battery is higher than a reference degree of advancement, compared to the case where said degree of deterioration is lower.;

2. A state of charge measuring device (1) according to claim 1, wherein said state of charge acquisition unit (13) decreases the magnitude of the increase in said state of charge index of said lithium corrective characteristic, if said initial state of charge at the start of the previous charge is lower than said predetermined state of charge.

3. A state-of-charge measuring device (1) according to claim 1 or 2, wherein said deterioration degree acquisition unit (15) obtains, as the deterioration degree, the cumulative charge of said lithium-ion battery (2), the cumulative discharge of said lithium-ion battery (2), the capacity of said lithium-ion battery (2), the internal resistance of said lithium-ion battery (2), or each voltage deviation of said lithium-ion battery (2).

4. A state of charge measuring device (1) according to one of claims 1 to 3, wherein said predetermined state of charge is set between 20% and 50% of a full charge.

5. A state of charge measuring device (1) according to one of claims 1 to 4, having a discharge prevention unit (105) which prevents the discharge of a lithium-ion battery (2), if the state of charge obtained by said state of charge acquisition unit is lower than a minimum state of charge value.

6. Battery pack (P) having a state of charge measuring device (1) according to one of claims 1 to 5, and said lithium-ion battery (2) connected to said state of charge measuring device (1).

7. A saddled vehicle (3) equipped with a battery pack (P) according to claim 6, a motor (4) receiving electrical power from said battery pack, and a wheel (5) driven by said motor.

8. A state-of-charge measurement program that performs the operation of measuring the state of charge of a lithium-ion battery (2) on a computer installed in the state-of-charge measurement device connected to said lithium-ion battery (2); said state-of-charge measurement program performs: - a voltage measurement function (S11) that measures the battery voltage of said lithium-ion battery (2); - a characteristic memory function (12) that stores a voltage-state-of-charge characteristic expressing a characteristic of said lithium-ion battery (2); - a state-of-charge acquisition function (S15) that obtains the state of charge of said lithium-ion battery (2) from said battery voltage measured by said voltage measurement function, with reference to said voltage-state-of-charge characteristic; - a historical memory function (14) storing the initial state of charge, which is the state of charge at the start of past charges of said lithium-ion battery (2); - and a function for acquiring a degree of deterioration (S 12) of said lithium-ion battery (2); said state of charge acquisition function (S 15), as such: - obtains the state of charge of said lithium-ion battery (2) by referring to a lithium corrective characteristic, the state of charge index of which has been increased for said lithium-ion battery (2) over a determined voltage range of said voltage-state of charge characteristic, if said initial state of charge at the start of previous charges is higher than a predetermined state of charge; - and decreases the importance of the increase in said state of charge index of said lithium corrective characteristic, if said degree of deterioration of said lithium-ion battery (2) is greater than a reference degree of progress, compared to the case where said degree of deterioration is lower.

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