Power supply for vehicles

Abstract

Vehicle power supply, which includes the following: - a first power supply system (21) comprising a power generator (18) and a first storage unit (20) connected to the power generator (18); - a second power supply system (27) comprising an electrical load (26) with a lower upper limit voltage than the power generator (18) and a second storage unit (22) connected to the electrical load (26); - a switch (31) provided between the first power supply system (21) and the second power supply system (27) and switchable between a connected state in which the first power supply system (21) and the second power supply system (27) are connected and a disconnected state in which the first power supply system (21) and the second power supply system (27) are disconnected; and - a power supply control unit (32) configured to switch the switch (31) to the connected state or to the disconnected state, wherein, when the switch (31) is in the disconnected state, the generating voltage of the current generator (18) is specified as being higher than the upper limit voltage of the electrical load (26), and when the switch (31) is in the connected state, the generating voltage of the current generator (18) is specified as being at or below the upper limit voltage of the electrical load (26), wherein the switch (31) is switched to the disconnect state during vehicle deceleration, and wherein, even when the vehicle slows down, if the state of charge (SOCm) of the first storage unit (20) deviates from a predetermined range (M3) defined by a first predetermined value (M1) and a second predetermined value (M2), the power supply control unit (32) is designed to prevent the switch (31) from being disconnected.

Description

[0001] The present invention relates to a vehicle power supply that is installed in a vehicle.

[0002] In a conventional vehicle, the electrical devices are typically powered by a lead-acid battery. Although a lead-acid battery can ensure high storage capacity, the battery is rapidly degraded by charging and discharging. For this reason, in a vehicle equipped with a lead-acid battery, the charging and discharging of the lead-acid battery is prevented by constantly running an alternator (power generator) to generate electricity. However, if the alternator is constantly running, the engine load increases, resulting in a reduction in fuel efficiency.

[0003] To solve this problem, a vehicle has been proposed that includes a lithium-ion battery in addition to a lead-acid battery, wherein the generated voltage of an alternator is controlled to zero during acceleration and increased during deceleration (see, for example, Japanese Unexamined Patent Application Publication JP 2004-225649 A). By controlling the alternator in this manner, thereby preventing an increase in engine load, the vehicle's fuel efficiency can be improved. It should be noted that when power generation by the alternator stops, the electrical devices are supplied with power from the lithium-ion battery, preventing the lead-acid battery from discharging.

[0004] However, in the vehicle described in Japanese Unexamined Patent Application Publication JP 2004-225649 A, the electrical devices are connected to the alternator's power system, making it impossible to significantly increase the alternator's generation voltage. In other words, the generation voltage cannot be set above an upper limit voltage of the electrical devices, and therefore it is difficult to ensure a sufficient degree of regeneration in the alternator during deceleration.

[0005] If a sufficient degree of regeneration cannot be ensured during deceleration, the alternator must be operated to generate power at times other than deceleration, which consequently increases the engine load and leads to a reduction in fuel efficiency.

[0006] US 2005 / 0 093 370 A1 discloses a power supply device for a motor vehicle, comprising a motor generator, an inverter for driving the motor generator, a battery, and a capacitor made of an electrical double layer. The capacitor is directly connected to a DC voltage side of the inverter, and the battery is connected in parallel with the capacitor via a first switching unit. When the engine is started, the energy stored in the capacitor is used, and the switching unit is switched off to disconnect the battery from the engine starting process.

[0007] DE 10 2008 031 964 A1 discloses a switching control unit for controlling the transmission of power in a vehicle from at least one starter-generator or a supercapacitor bank to / from at least one service battery or a plurality of electrical devices. A switching device selectively connects / disconnects at least the starter-generator or the supercapacitor bank to / from at least the service battery or the plurality of electrical devices. The switching control device is configured to measure a voltage across the supercapacitor bank to generate a bank voltage signal, measure a voltage across the service battery to generate an service voltage signal, and control the switching device to connect / disconnect at least the starter-generator or the supercapacitor bank to / from at least the service battery or the plurality of electrical devices in response to the voltage signals.

[0008] DE 103 05 939 A1 and DE 103 13 081 A1 each disclose an on-board electrical system for a motor vehicle. The system comprises a generator, a starter, an energy storage device, at least one on-board electrical system, a battery, and a DC / DC converter between the energy storage device and the on-board electrical system, as well as a switch for disconnecting the on-board electrical system from the generator. The generator is directly connected to the energy storage device. The switch is opened at the start of recuperation and remains open until the voltage of the energy storage device has been reduced to approximately the on-board electrical system voltage. During this time, the DC / DC converter, together with the battery if necessary, takes over the on-board electrical system supply.

[0009] The object of the present invention is to improve the fuel efficiency of a vehicle by increasing a regeneration amount of a power generator.

[0010] This object is achieved according to the invention by a vehicle power supply having the features of claim 1. An advantageous further development is specified in subclaim 2.

[0011] By switching the switch provided between the first power system and the second power system to the disconnected state according to the present invention, the generation voltage of the power generator can be increased, so that the regeneration rate of the power generator can be increased. In this way, the power generator can be actively stopped, and consequently, the fuel efficiency of the vehicle can be improved.

[0012] The invention and further developments of the invention are explained in more detail below with reference to the drawings illustrating exemplary embodiments. The drawings show: Fig. 1 is a schematic diagram for explaining the configuration of a vehicle equipped with a power supply according to an embodiment of the present invention; Fig. 2 a diagram explaining control states of a switch; Fig. 3 is a diagram illustrating power supply states of the vehicle power supply; Fig. 4A and Fig. 4B illustrations for explaining power supply states of the vehicle power supply; Fig. 5 is a diagram for explaining a relationship between a switch control performed on the switch and a regeneration control of the alternator; Fig. 6A and Fig. 6B are diagrams for explaining power supply states of the vehicle power supply during engine starting; Fig. 7 is a schematic diagram illustrating the configuration of a vehicle with a power supply according to a further embodiment of the present invention; and Fig. 8 is a schematic diagram for explaining the configuration of a vehicle with a power supply according to yet another embodiment of the present invention.

[0013] In the following, embodiments of the present invention are described in detail with reference to the drawings. Fig. 1 shows a schematic diagram to explain the design of a vehicle 11 with a vehicle power supply 10 according to an embodiment of the present invention. As in Fig. As shown in Figure 1, the vehicle 11 includes an engine 12 and a transmission 13. Drive wheels 16 are coupled to an output shaft 14 of the transmission 13 via a differential mechanism 15. Furthermore, a starter motor 17 is attached to the engine 12.

[0014] Furthermore, an alternator 18 serving as a power generator is coupled to the engine 12 via a drive belt 19. It should be noted that the vehicle 11 shown in the drawing is a so-called micro-hybrid vehicle in which a low-voltage regeneration system using the alternator 18 is installed.

[0015] When the operation applied to an accelerator pedal is released and the vehicle thus decelerates, the alternator 18 is operated to generate electricity, so that the kinetic energy of the vehicle 11 is actively converted into electrical energy and stored. When the accelerator pedal is depressed so that the vehicle accelerates or travels at a constant speed, power generation by the alternator 18 is stopped, resulting in a reduction in engine load. By controlling the alternator 18 in this way so that the engine load does not increase, the fuel efficiency of the vehicle 11 is improved.

[0016] To improve the fuel efficiency of the vehicle 11, it is important to stop the operation of the alternator 18 for power generation during acceleration and constant-speed cruising, as mentioned above. However, in a conventional vehicle that includes only a lead-acid battery as a storage unit, it is difficult to stop the operation of the alternator 18 for power generation to prevent deterioration of the lead-acid battery caused by charging and discharging. To solve this problem, a lithium-ion battery or the like with high resistance to deterioration by charging and discharging can be used as the storage unit, but the use of a lithium-ion battery results in an increase in the cost of the storage unit.

[0017] The storage unit installed in the vehicle 11 therefore requires sufficient storage capacity to drive the starter motor 17 after the vehicle has been unused for a predetermined period of time (e.g., three months). However, since the cost of a lithium-ion battery per unit of storage capacity is high, ensuring the necessary storage capacity requires high expenditures for the storage unit. To avoid these higher costs for the storage unit, the vehicle power supply 10 according to the present embodiment is configured as follows.

[0018] The design of the vehicle power supply 10 is described below. The vehicle power supply 10 is provided with a main battery 20, which serves as the first storage unit. Furthermore, the starter motor 17 and the alternator 18 are connected to the main battery 20. The main battery 20, the starter motor 17, and the alternator 18 together form a first power supply system 21. It should be noted that the permissible voltage range of the main battery 20 and the alternator 18, which form the first power supply system 21, is specified between approximately 12 V and 18 V.

[0019] In other words, an upper limit voltage for controlling the main battery 20 and the alternator 18 is set at 18 V. Furthermore, a storage unit with low charge / discharge resistance and higher cycle characteristics is used as the main battery 20. A rocking-chair type storage unit, such as a lithium-ion battery, a lithium-ion capacitor, an electric double-layer capacitor, and a nickel-hydrogen battery, can be cited as examples of this type of storage unit.

[0020] It should be noted here that a rocking-chair type storage device is a storage device that is charged and discharged when lithium ions, hydrogen ions, or the like move back and forth between electrodes. With the storage mechanism of a rocking-chair type storage device, no changes (dissolution and deposition) occur in the physical structure of the electrodes, and for this reason, a rocking-chair type storage device has low charge / discharge resistance and better cycling characteristics.

[0021] The vehicle power supply 10 is provided with an auxiliary battery 22 serving as a second storage unit. Electrical devices 26, such as a headlight 23, an ignition coil 24, and an electronic control unit 25, are connected to the auxiliary battery 22 as an electrical load. The auxiliary battery 22 and the electrical devices 26 together form a second power supply system 27. It should be noted that a permissible voltage range of the auxiliary battery 22 forming the second power supply system 27 and the electrical devices is specified between approximately 12 V and 15 V.

[0022] In other words, an upper limit voltage for controlling the auxiliary battery 22 and the electrical devices 26 is set at 15 V. Furthermore, a storage unit with a predetermined storage capacity is used as the auxiliary battery 22. The storage capacity of the auxiliary battery 22 is set taking into account a starting power after the vehicle has been idle for a predetermined period of time. A so-called backup storage unit, such as a lead-acid battery, which is inexpensive and has a high storage capacity, can be cited as an example of this type of storage unit.

[0023] It should be noted here that a reserve storage unit is a storage unit that is charged and discharged when ions dissolve in an electrolyte made of the metal of an electrode or the like and the ions in the electrolyte are deposited on an electrode as a metal or the like.

[0024] In a storage mechanism of a reserve-type storage unit, changes (dissolution and deposition) occur in the physical structure of the electrodes, and therefore, a reserve storage unit has a higher charge / discharge resistance and poorer cycling characteristics compared to a rocking-chair type storage unit.

[0025] The auxiliary battery 22 is not limited to a reserve storage unit, and as long as the predetermined storage capacity can be ensured in a cost-effective manner, a rocking chair type storage unit may be used as the auxiliary battery 22.

[0026] Furthermore, a switch 31, such as an n-channel FET, is provided in a power line 30 connecting the first power supply system 21 and the second power supply system 27. When the switch 31 is switched to a connected state, the first power supply system 21 and the second power supply system 27 can be electrically connected to each other. On the other hand, when the switch 31 is switched to a disconnected state, the first power supply system 21 and the second power supply system 27 can be electrically disconnected.

[0027] To perform switch control on the switch 31, the vehicle power supply 10 is provided with a power supply control unit (switch control device) 32. The power supply control unit 32 is constituted by a CPU for executing a program, a ROM for storing the program, etc., a RAM for temporarily storing data, an input / output terminal connected to various sensors and actuators, etc.

[0028] The sensors connected to the power supply control unit 32 include an accelerator opening sensor 33 for detecting an operation state of the accelerator pedal, a vehicle speed sensor 34 for detecting a vehicle speed, a voltage sensor 35 for detecting the voltage of the main battery 20, a current sensor 36 for detecting a current of the main battery 20, a temperature sensor 37 for detecting a temperature of the main battery 20, a voltage sensor 38 for detecting the voltage of the auxiliary battery 22, and a current sensor 39 for detecting a current of the auxiliary battery 22.

[0029] The switch control performed by the power supply control unit 32 is described below. Fig. Fig. 2 shows a view for explaining control states of the switch 31, and Fig. 3 shows a view for explaining power supply states of the vehicle power supply 10. Fig. 3 illustrates a state in which the accelerator pedal is depressed so that vehicle acceleration or constant speed running occurs, or in other words, a state in which regeneration control of the alternator 18 is stopped.

[0030] Furthermore, the Fig. 4A and Fig. 4B Views for explaining power supply states of the vehicle power supply 10. The Fig. 4A and Fig. 4B, a state in which the depressed state of the accelerator pedal is released, so that there is a vehicle deceleration, or in other words, a state in which a regeneration control of the alternator 18 is executed. It should be noted that in the Fig. 3 to 4B the power supply states are illustrated by black arrows.

[0031] If, according to the representations in the Fig. 2 and Fig. 3, when the accelerator pedal is depressed (accelerator ON), the power supply control unit (power generation control device) 32 sets a target generation current of the alternator 18 to "0", so that the alternator 18 stops power generation. At this time, the switch 31 is maintained in the connection state (ON) by the power supply control unit 32, so that the main battery 20 and the auxiliary battery 22 are connected to the electrical devices 26.

[0032] A voltage range in which the storage capacity of the main battery 20 can be exerted is made larger than a voltage range in which the storage capacity of the auxiliary battery 22 can be exerted, and therefore, power is primarily supplied from the main battery 20 to the electrical devices 26, while power supply from the auxiliary battery 22 is suppressed.

[0033] It should be noted that as the states of charge SOCm and SOCs, which indicate a storage ratio of the main battery 20 and the auxiliary battery 22, decrease, the alternator 18 may be operated to generate power depending on the conditions, as shown in Fig. 3 is represented in the form of an arrow drawn in dashed lines.

[0034] When the accelerator pedal is released (gas OFF), the power supply control unit 32 outputs the power as shown in Fig. 2, the target generation current of the alternator 18 is set depending on the vehicle speed, so that the alternator 18 sets a generation voltage to achieve the target generation current. During this regeneration control of the alternator 18, it is important to increase the regeneration amount (power generation amount) achieved by the alternator 18, and therefore, the power supply control unit 32 switches the switch 31 from the connection state (ON) to the disconnection state (OFF) depending on the charge states SOCm and SOCs of the main battery 20 and the auxiliary battery 22.

[0035] As in Fig. As shown in Fig. 4A, when the switch 31 is maintained in the connected state, the first power supply system 21 and the second power supply system 27 remain electrically connected. Therefore, to protect the second power supply system 27, whose upper limit voltage is 15 V, the generation voltage of the alternator 18 must be suppressed to or below 15 V.

[0036] On the other hand, when the switch 31 is switched from the connection state to the disconnection state as shown in Fig. As shown in Figure 4B, the first power supply system 21 and the second power supply system 27 are electrically isolated from each other. Thus, the alternator 18 and the main battery 20 are disconnected from the second power supply system 27, and the generation voltage of the alternator 18 can thereby be set above the upper limit voltage (15 V) of the second power supply system 27.

[0037] By switching switch 31 to the disconnected state, the generation voltage of alternator 18 can be increased, and consequently, the regeneration rate can be significantly increased. Furthermore, since the charging resistance of main battery 20, which is formed by a rocking-chair type storage unit, is low, energy can be absorbed at a high current (e.g., 200 A).

[0038] Generated power, which increases with increasing generation voltage, can thus be stored in the main battery 20 without loss. It should be noted that despite the disconnected switch 31, power is supplied to the electrical devices 26 from the auxiliary battery 22, so that the electrical devices 26 can operate normally.

[0039] As described above, by providing the first power supply system 21 constituted by the main battery 20 and the alternator 18 and the second power supply system 27 constituted by the auxiliary battery 22 and the electrical devices 26, and by providing the switch 31 between the first power supply system 21 and the second power supply system 27, the regeneration amount of the alternator 18 during deceleration can be significantly increased.

[0040] Thus, the main battery 20 can be sufficiently charged during deceleration, and the alternator 18 can be stopped or deactivated during acceleration and constant-speed running. As a result, the engine load can be reduced, enabling an improvement in the fuel efficiency of the vehicle 11. Furthermore, by increasing the generation voltage without relying solely on the charging resistance of the main battery 20, as described above, the regeneration rate of the alternator 18 during deceleration can be increased.

[0041] Thus, there is less need to increase the number of parallel main batteries 20 formed by lithium-ion batteries or the like to thereby reduce the charging resistance, and thus the design storage capacity can be reduced, so that a smaller size and reduced cost of the vehicle power supply 10 can be realized.

[0042] It should be noted that the storage capacity of the main battery 20 is specified to be lower than the storage capacity of the auxiliary battery 22. Furthermore, by deactivating the alternator 18 during acceleration, the engine load can be reduced, so that improvements in the acceleration performance of the vehicle 11 can be achieved.

[0043] Furthermore, by providing the auxiliary battery 22 with a secured, predetermined storage capacity, favorable starting performance can be achieved after the vehicle has been idle for a predetermined period of time. Furthermore, by using a backup storage unit, such as a lead-acid battery, which is inexpensive and has a high storage capacity, as the auxiliary battery 22, an increase in the cost of the vehicle power supply 10 can be avoided.

[0044] Furthermore, as described above, when the regeneration control of the alternator 18 is stopped, the switch 31 is placed in the connected state, so that power is supplied from the main battery 20 to the electrical devices 26, and consequently, charging and discharging of the auxiliary battery 22 can be avoided. Thus, even when a backup storage battery, which suffers deterioration due to frequent charging and discharging, is used as the auxiliary battery 22, deterioration of the auxiliary battery 22 can be avoided.

[0045] It should be noted that the main battery 20, which is formed by a rocking chair type storage unit, has a favorable cycle characteristic and thus is not subject to rapid deterioration even if it is frequently charged and discharged.

[0046] In addition, the storage capacity of the auxiliary battery 22 provided as a backup device with a separate switch can be reduced compared to a conventional battery, and thus even if the main battery 20 and the auxiliary battery 22 are provided in combination, the size thereof can be kept equal to the size of a conventional battery.

[0047] This allows the vehicle power supply 10 to be installed in an engine compartment similar to that of a conventional vehicle with only a lead-acid battery. Consequently, the vehicle power supply 10 according to the present invention can be installed without significant modifications to the vehicle body structure.

[0048] Furthermore, in the vehicle power supply 10, the main battery 20 with a high voltage range (approximately 12 V to 18 V) in which the storage capacity can be exerted and the auxiliary battery 22 with a low voltage range (approximately 11 V to 12.8 V) in which the storage capacity can be exerted are provided in parallel.

[0049] Thus, even when a lead-acid battery is used as the auxiliary battery 22, the usable storage capacity (effective storage capacity) can be greatly increased without discharging the lead-acid battery compared to a conventional vehicle using only a lead-acid battery. Furthermore, by connecting the main battery 20 and the auxiliary battery 22 in parallel, the total electrical resistance of the batteries can be reduced, and consequently, the voltage applied to the electrical devices 26 can be stabilized.

[0050] The switch control performed on the switch 31 and the regeneration control of the alternator 18 are described in detail below. Fig. 5 is a view for explaining a relationship between the switch control performed on the switch 31 and the regeneration control of the alternator 18.

[0051] It should be noted that a terminal voltage, an open circuit voltage and a charging current as shown in Fig. 5 denotes a terminal voltage and an open circuit voltage of the main battery 20 and a charging current applied to the main battery 20.

[0052] Furthermore, Fig. 5, a state in which the accelerator pedal depression is released, so that deceleration occurs, or in other words, a state in which regeneration control is performed by the alternator 18. First, the power supply control unit 32 calculates the state of charge SOCm of the main battery 20 based on the voltage, current, and temperature of the main battery 20. Furthermore, the power supply control unit 32 calculates the state of charge SOCs of the auxiliary battery 22 based on the voltage and current of the auxiliary battery 22.

[0053] As in Fig. As shown in FIG. 5, when the state of charge SOCm of the main battery 20 drops below a predetermined value M1 (symbol α), the switch 31 is maintained in the connected state by the power supply control unit 32. As the state of charge SOCm decreases, the open-circuit voltage of the main battery 20 is low, and thus a predetermined target generation current (e.g., 200 A) can be achieved without increasing the generation voltage to 15 V.

[0054] In other words, the predetermined value M1 is set in advance based on experiments and simulations so that the predetermined target generation current can be achieved within a generation voltage range lower than 15 V. If the required generation current can be achieved in this way without disconnecting the switch 31, charging and discharging of the auxiliary battery 22 is avoided, and thus the alternator 18 is driven to generate power while the switch 31 remains connected. Note that when a lead-acid storage battery is used as the auxiliary battery 22, the generation voltage is preferably controlled to a value equal to or higher than 12.8 V to prevent deterioration due to excessive discharge.

[0055] When the state of charge SOCm of the main battery 20 exceeds the predetermined value M1 in a state where the state of charge SOCs of the auxiliary battery 22 exceeds a predetermined value S1 (symbol β), the power supply control unit 32 switches the switch 31 to the disconnected state. Thus, in a state where the terminal voltage of the main battery 20 exceeds 15 V due to an increase in the state of charge SOCm, the switch 31 is switched to the disconnected state.

[0056] In this way, the generation voltage can be increased to a value equal to or higher than 15 V, and consequently, the predetermined target generation current (e.g., 200 A) can be ensured. Furthermore, power is supplied to the electrical devices 26 from the auxiliary battery 22 while the switch 31 is disconnected, and thus the switch 31 is disconnected after checking the state of charge SOC of the auxiliary battery 22. Specifically, the power supply control unit 32 prohibits disconnection of the switch when the state of charge SOC is less than the predetermined value S1.

[0057] It should be noted that the predetermined value S2 is set in advance on the basis of experiments and simulations such that sufficient power can be supplied to the electrical devices 26 from the auxiliary battery 22.

[0058] When the main battery 20 is charged to a point where the state of charge SOCm exceeds a predetermined value M2 (symbol γ), the power supply control unit 32 switches the switch 31 back to the connected state. When the state of charge SOCm exceeds the predetermined value M2, the open-circuit voltage of the main battery 20 reaches the upper limit voltage of 15 V of the electrical devices 26, and if power generation continues at 15 V or above, the open-circuit voltage of the main battery 20 rises above 15 V, that is, the upper limit voltage of the electrical devices 26.

[0059] In other words, if the generation voltage continues to increase, the open-circuit voltage of the main battery 20 exceeds 15 V, and therefore, in order to prevent damage caused by the application of excessive voltage to the electrical devices 26, the switch 31 is brought into the connection state to return the generation voltage of the alternator 18 to 15 V. Note that the predetermined value M2 is a state of charge SOC of the main battery 20, which corresponds to the upper limit voltage of the electrical devices 26, which is predetermined in advance based on the specifications of the electrical devices 26.

[0060] Thus, when the state of charge SOCm of the main battery 20 falls below the predetermined value M1 or exceeds the predetermined value M2, the switch 31 is controlled to the connected state. In other words, if the state of charge SOCm deviates from a range M3 defined by the predetermined values ​​M1 and M2 by the power supply control unit 32, the disconnection of the switch 31 is prohibited.

[0061] As described above, when the switch 31 is disconnected, the generation voltage is increased to a value of 18 V, ie, the upper limit voltage of the first power supply system 21, and as a result, the terminal voltage of the main battery 20 also increases to 18 V. However, the open circuit voltage of the main battery 20 is designed to remain below 15 V, ie, the upper limit voltage of the second power supply system 27, even in this case.

[0062] Therefore, the open-circuit voltage of the main battery 20 is also controlled to a value below 15 V when the generation voltage is increased in conjunction with the disconnection of the switch 31. The switch 31 can thus be safely switched from the disconnection state to the connection state. Note that the upper limit voltage of the first power supply system 21, i.e., 18 V, is set based on a test voltage (18 V) used in a withstand voltage test performed on the electrical equipment 26.

[0063] Thus, even in the case that the switch 31 is mistakenly brought into the connection state when the generation voltage is increased to 18 V, damage to the electrical devices 26 can be avoided.

[0064] When switching the switch 31 to the disconnected state during the determination of the states of charge SOCm and SOCs, a determination can also be made regarding a disconnection history of the switch 31 during the current regeneration window. Specifically, the switch 31 is allowed to be disconnected only once during a single regeneration window after the accelerator pedal depression state is released. As a result, a rapid sequence of operations in which the switch 31 is repeatedly switched between the disconnected state and the connected state can be prevented.

[0065] It should be noted that the state of charge SOCm of the main battery 20 is calculated by a method in which a state of charge SOCc is calculated based on an integrated value of a charging and discharging current and a state of charge SOCv is calculated based on an estimated open-circuit voltage, and then the state of charge SOCm is calculated by weighted synthesis of the states of charge SOCc and SOCv (see, for example, Japanese Unexamined Patent Application Publication JP-A-2005-201743).

[0066] Furthermore, the state of charge SOC of the auxiliary battery 22 is calculated by integrating the charging current and a discharging current. It goes without saying that the methods for calculating the states of charge SOCm and SOCs are not limited to the methods described above, and other calculation methods may also be used.

[0067] The following describes the power supply states of the vehicle power supply 10 during the engine start-up process. Fig. 6A and Fig. 6B show views for explaining power supply states of the vehicle power supply 10 during engine start. It should be noted that in the Fig. 6A and Fig. 6B, the power supply states are illustrated by black arrows. For example, if the outside air temperature is higher than 0 °C, switch 31 is switched to the disconnected state during engine starting.

[0068] As in Fig. As shown in Fig. 6A, with the switch 31 in the disconnected state, power is supplied to the starter motor 17 from the main battery 20, and power is supplied to the electrical devices 26 from the auxiliary battery 22. Thus, in an environment where the engine 12 can be easily started, the starter motor 17 is driven using only power from the main battery 20. This can prevent a reduction in the voltage of the auxiliary battery 22 due to a high starting current.

[0069] As a result, the occurrence of a momentary power failure can be avoided in the electrical devices (e.g., a navigation device and lighting devices such as a headlight) with a high lower limit voltage compared to electrical devices (control units related to the driving process, such as an ECU (engine control unit) and a TCU (transmission control unit)) with a low lower limit voltage.

[0070] When the outside air temperature is equal to or lower than, for example, 0 °C, the switch 31 is switched to the connection state during the engine start process. As shown in Fig. 6B, with the switch 31 in the connected state, power is supplied to the starter motor 17 and the electrical devices 26 from both the main battery 20 and the auxiliary battery 22.

[0071] Thus, in an environment where starting the engine 12 is not easily possible, the starter motor 17 is driven using power from both the main battery 20 and the auxiliary battery 22. It should be noted that power is supplied to the electrical devices 26 from the auxiliary battery 22 regardless of the control state of the switch 31, as shown in the Fig. 6A and Fig. 6B. This can prevent an instantaneous voltage drop that occurs when a large current is supplied to the starter motor 17, and consequently, a failure of the control system during engine start-up can be avoided.

[0072] In the following, vehicle power supplies 40 and 50 according to further embodiments of the present invention are described. Fig. 7 and Fig. 8 show schematic representations for explaining the configuration of vehicles 41 and 51 having the vehicle power supplies 40 and 50 according to further embodiments of the present invention.

[0073] It should be noted that in the Fig. 7 and Fig. 8 identical reference numerals are used for components that correspond to the Fig. 1, whereby a repetition of the description of these components is omitted. As in Fig. 7, in the vehicle power supply 40, a switch 42 is provided at a location for disconnecting the main battery 20 from the first power supply system 21.

[0074] By providing the switch 42 on a positive electrode line 43 of the main battery 20 in this manner, the main battery 20 can be disconnected from the vehicle power supply 40 when an abnormality occurs in the main battery 20. Thus, the vehicle 41 can be activated using the auxiliary battery 22 without the abnormal main battery 20 operating. As a result, the safety of the vehicle 41 can be improved.

[0075] As in Fig.As shown in Figure 8, the vehicle power supply 50 includes a switch unit 52 on the power line 30, which connects the first power supply system 21 and the second power supply system 27. The switch unit 52 is formed by a plurality of switches 53 connected in parallel.

[0076] Furthermore, the plurality of switches 53 constituting the switch unit 52 are switched between the connected state and the disconnected state at an identical time. Furthermore, the switch unit 52 is also equipped with a voltage sensor 54 for detecting a potential difference before and after the switch. The power supply control unit 32 determines the presence of a defect in the switch unit 52 by comparing a voltage signal from the voltage sensor 54 with a predetermined determination value.

[0077] Specifically, the power supply control unit 32 defines the determination value as the voltage drop that occurs when all switches 53 are normally connected, and determines whether or not an actual voltage drop deviates from the determination value. If the actual voltage drop is higher than the determination value, the power supply control unit 32 determines that an internal resistance of the switch unit 52 is high, or, in other words, that an abnormality has occurred in which all switches 53 are not normally connected.

[0078] An abnormality in the switch unit 52 causes a sharp voltage drop to occur in the switch unit 52, and therefore, the abnormality determination is preferably performed when power is supplied to the starter motor 17 from the auxiliary battery 22. By detecting the presence of an abnormality in the switch unit 52 during engine start in this way, the presence of an abnormality in the switch unit 52 can be detected before the vehicle travels, and thus, measures such as displaying a warning light can be taken before the vehicle travels, enabling improvement in the safety of the vehicle 51.

[0079] The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the invention. For example, in the drawings, the present invention is applied to vehicles 11, 41, and 51 that have only the engine 12 as a power source. However, the present invention is not limited thereto, but can also be applied to a hybrid vehicle that has the engine 12 and an electric motor as power sources.

[0080] The present invention can be used particularly effectively in a vehicle with high energy or power consumption. For example, in a vehicle with so-called idle stops, in which the engine is automatically stopped under predetermined conditions, the starter motor 17 must be frequently started, and therefore the present invention can be applied extremely effectively.

[0081] Furthermore, in the above description, when the alternator 18 is operated to generate electricity, the target generation current is set depending on the vehicle speed. However, the present invention is not limited to this, and the target generation current may also be set based on other information. Furthermore, in the drawings, the alternator 18 and the starter motor 17 are provided separately, but an electric motor having both the functions of the alternator 18 and the starter motor 17 may be provided instead.

[0082] It should be noted that the allowable voltage range of the first power supply system 21 is specified in the above description as being between approximately 12 V and 18 V, but is not limited thereto. Similarly, the allowable voltage range of the second power supply system 27 is also specified as being between approximately 12 V and 15 V, but is not limited thereto. List of reference symbols 10 Power supply 11 vehicles 12 Engine 13 gearboxes 14 Output shaft 15 Differential mechanism 16 drive wheels 17 Starter motor 18 Alternator 19 drive belts 20 Main battery 21 first power supply system 22 Additional battery 23 headlights 24 ignition coil 25 electronic control unit 26 electrical equipment 27 second power supply system 30 power line 31 switches 32 Power supply control unit 33 Accelerator pedal opening sensor 34 Vehicle speed sensor 35 Voltage sensor 36 Current sensor 37 Temperature sensor 38 Voltage sensor 39 Current sensor 40 Power supply 41 vehicles 42 switches 43 positive electrode lead 50 Power supply 51 vehicles 52 Switch unit 53 switches 54 Voltage sensor

Claims

[1] Vehicle power supply comprising: - a first power supply system (21) including a power generator (18) and a first storage unit (20) connected to the power generator (18); - a second power supply system (27) including an electrical load (26) having a lower upper limit voltage than the power generator (18) and a second storage unit (22) connected to the electrical load (26); - a switch (31) provided between the first power supply system (21) and the second power supply system (27) and switchable between a connection state in which the first power supply system (21) and the second power supply system (27) are connected and a disconnection state in which the first power supply system (21) and the second power supply system (27) are disconnected; and - a power supply control unit (32) which is designed to switch the switch (31) into the connection state or into the disconnection state, wherein, when the switch (31) is switched to the disconnected state, a generation voltage of the power generator (18) is set higher than the upper limit voltage of the electrical load (26), and when the switch (31) is switched to the connected state, the generation voltage of the power generator (18) is set at or below the upper limit voltage of the electrical load (26), wherein the switch (31) is switched to the disconnected state during vehicle deceleration, and wherein, even during vehicle deceleration, when the state of charge (SOCm) of the first storage unit (20) deviates from a predetermined range (M3) defined by a first predetermined value (M1) and a second predetermined value (M2), the power supply control unit (32) is configured to prevent the switch (31) from being disconnected. [2] Vehicle power supply according to claim 1, wherein, during vehicle deceleration, when the state of charge (SOCm) of the first storage unit (20) falls below the first predetermined value (M1), the power supply control unit (32) is designed to keep the switch (31) in the connected state, and wherein, during vehicle deceleration, when the first storage unit (20) is charged to a point where the state of charge (SOCm) exceeds the second predetermined value (M2), the power supply control unit (32) is configured to switch the switch (31) back to the connected state.

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