Power supply system for vehicles

Abstract

Vehicle power supply system, comprehensive: an electric motor (2) designed to use the movement of a vehicle (1) to generate electric current and to assist the movement of the vehicle (1); a set of electrical loads (3) that requires a stable supply of electrical current when the vehicle (1) is moving; a first battery (4) which is connected to the electric motor (2) and the set of electrical loads (3) and is designed to supply them with electric current; a second battery (5) connected to the electric motor (2) and the set of electrical loads (3) and designed to supply them with electric current, wherein the second battery (5) is designed to repeat a charge within a shorter period of time than the first battery (4); a first switch (SW1) designed to establish and break a first connection between the first battery (4) and the electric motor (2); a second switch (SW3) designed to establish and break a second connection between the first battery (4) and the set of electrical loads (3); a third switch (SW4) designed to establish and break a third connection between the second battery (5) and the set of electrical loads (3); and a control unit (10) designed to control the first switch (SW1), the second switch (SW3) and the third switch (SW4), wherein the control unit (10) is designed to control the first, second and third switches (SW1, SW3, SW4) such that the first connection is interrupted, one is made from the second and third connections and the other is interrupted from the second and third connections in order to control the electric motor (2) so that it is driven to assist in the movement of the vehicle (1).

Description

GENERAL STATE OF THE TECHNOLOGY Technical field

[0001] This invention relates to power supply systems for vehicles designed to control a state of the power supply in a vehicle concerned. State of the art

[0002] There are vehicle power supply systems, as disclosed in JP 2011-178384A, which include: a combination of secondary cells comprising a lead-acid battery and a lithium-ion battery or a nickel-metal hydride battery, and sets of auxiliary equipment, which are sets of electrical loads connected in parallel to these secondary cells, the system being designed to stabilize the power to the sets of auxiliary equipment connected in parallel. The lithium-ion battery or the nickel-metal hydride battery is connected to a set of auxiliary equipment (as protected loads) that requires a constant stabilized voltage, such as a set of measuring instruments and a vehicle navigation system. The lead-acid battery is connected to a set of auxiliary equipment (as general-purpose loads) designed for temporary services, such as windshield wipers or blowers.

[0003] DE 10 2014 103 551 A1 discloses a power supply system installed in a vehicle. It comprises a rotating machine capable of generating electrical power and starting and assisting an internal combustion engine after starting, a first and a second secondary battery, each electrically connected in parallel to the rotating machine, a switch controller, and a connecting switch on a connecting line between the secondary batteries. The connecting switch is configured to electrically connect and disconnect the second secondary battery and a parallel connection between the first secondary battery and the rotating machine.The switch controller is designed to interrupt the second secondary battery and the parallel connection by controlling the connection switch into a current interruption state during start-up of the internal combustion engine and during delivery support of the internal combustion engine.

[0004] DE 199 55 721 A1 discloses a two-battery system comprising a starter battery and an auxiliary battery, a starter, and electrical consumers, which are divided into start-related consumers and auxiliary consumers, wherein at least one start switch is arranged between the starter and the starter battery. A first, electronically fully blocking switching element is arranged between the starter battery and the start-related consumers, and a second, electrically fully blocking switching element is arranged between the auxiliary battery and the start-related consumers. An element is arranged between the starter battery and the auxiliary battery that prevents current flow from the starter battery to the auxiliary battery and the auxiliary consumers.

[0005] DE 40 28 242 A1 discloses an electrical system for motor vehicles. The electrical system comprises a generator, a starter, a starter battery, and an auxiliary battery for supplying electrical consumers. A connection between the starter battery and the auxiliary battery can be disconnected independently of the driving conditions if otherwise the auxiliary battery would be charged from the starter battery.

[0006] EP 1 137 150 A2 discloses a two-battery system comprising a starter battery and an auxiliary battery for electrical consumers. The electrical consumers are divided into start-related consumers and auxiliary consumers. A switching element is arranged between the starter battery and the start-related consumers, as well as between the auxiliary battery and the start-related consumers. These switching elements enable a battery control unit to alternately assign the start-related consumers to one of the two batteries. The battery control unit is arranged between the starter battery and the start-related consumers and, depending on the operating state, allows current to flow from the auxiliary battery to the starter battery or from the starter battery to the start-related consumers. BRIEF SUMMARY OF THE INVENTION

[0007] The vehicle power supply system disclosed in JP 2011-178 384 A can be used to control a power supply connected to a load consisting of a motor-generator designed to operate as a power generator during regeneration and to drive a rotating shaft during power operation to assist the propulsion of a vehicle. When the motor-generator is used for power control, a combination of a lead-acid battery and a lithium-ion battery or a nickel-metal hydride battery is used to drive the motor-generator, requiring repeated instantaneous use of a large amount of electrical current for power operation to output a current.

[0008] If the lead-acid battery has supplied electrical power for such use, it will be deeply discharged, requiring recharging. Lead-acid batteries have a lower charging efficiency than lithium-ion or nickel-metal hydride batteries, which is why they require a longer charging time. To recharge the lead-acid battery, the alternator must be driven more frequently by the combustion engine, resulting in reduced fuel efficiency.

[0009] Furthermore, when using the lithium-ion battery or the nickel-metal hydride battery to supply electrical current for the execution of an auxiliary control, the lithium-ion battery or the nickel-metal hydride battery may have reached a state of charge in which it is not possible to achieve a stable supply of electrical current from the lithium-ion battery or the nickel-metal hydride battery to protected loads.

[0010] This invention was conceived in light of these problems.

[0011] It is therefore an object of this invention to provide a power supply system for vehicles that is designed to operate electrical loads stably while suppressing a decrease in fuel efficiency.

[0012] According to aspects of this invention, a power supply system for vehicles is provided as a solution to the problems, comprising an electric motor designed to use the movement of a vehicle to generate electric current and to assist the movement of the vehicle, a set of electrical loads requiring a stable supply of electric current when the vehicle is moving, a first battery connected to the electric motor and the set of electrical loads and designed to supply this electric current, a second battery connected to the electric motor and the set of electrical loads and designed to supply this electric current, the second battery being designed to repeat a charge within a shorter period than the first battery, and a first switch designed toto establish and break a first connection between the first battery and the electric motor, a second switch designed to establish and break a second connection between the first battery and the set of electrical loads, a third switch designed to establish and break a third connection between the second battery and the set of electrical loads, and a control unit designed to control the first switch, the second switch, and the third switch, wherein the control unit is designed to control the first, the second, and the third switch such that the first connection is broken, one connection is established from the second and third connections, and the other connection from the second and third connections is broken, in order to control the electric motor to be driven to assist in the movement of the vehicle.

[0013] According to the aspects, for the execution of a support control system, a combination of electric current supplied to the electric motor from the second battery and electric current supplied to the set of electrical loads from the first or second battery can be used, thereby achieving such an adjustment that the set of electrical loads is operated stably while enabling a decrease in fuel efficiency to be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a diagram showing a vehicle which has a vehicle power supply system according to an embodiment of this invention. Fig. Figure 2 is a table showing circuit configurations which include combinations of connections that are made or broken by switches in the power supply system for vehicles according to an embodiment of this invention. Fig. Figure 3 is a diagram that, as a figure showing a power supply system for vehicles according to an embodiment of this invention, shows a circuit configuration when restarting an internal combustion engine. Fig. Figure 4 is a diagram that, as a figure showing a power supply system for vehicles according to an embodiment of this invention, shows a circuit configuration when performing support control at a low charge level of a lithium-ion battery. Fig. Figure 5 is a diagram that, as a figure showing a power supply system for vehicles according to an embodiment of this invention, shows a circuit configuration when performing support control at a high charge level of the lithium-ion battery. DESCRIPTION OF EXECUTION FORMS

[0014] With reference to the drawings, embodiments of this invention will be described. As in Fig. Figure 1 shows a vehicle 1 equipped with a vehicle power supply system according to an embodiment of this invention. The vehicle 1 is constructed to include an internal combustion engine 7, an ISG (an integrated starter-generator) 2 as an electric motor, a set of protected loads 3 as a set of electrical loads, a set of general loads 6, a lead-acid battery 4 as a first battery, and a lithium-ion battery 5 as a second battery.

[0015] The internal combustion engine 7, for example, is a gasoline engine. The internal combustion engine 7 is a four-cylinder engine designed to perform a series of four strokes: an intake stroke, a compression stroke, a power stroke, and an exhaust stroke. During this time, a corresponding piston moves back and forth twice in its assigned cylinder, with ignition occurring between the compression stroke and the power stroke. The internal combustion engine 7 generates a driving force that is used to propel the vehicle.

[0016] The ISG 2 is coupled to the crankshaft of the internal combustion engine 7 using a belt 8. The ISG 2 is designed to generate electrical current while the vehicle 1 is in motion and to assist its movement. In other words, the ISG 2 is designed to function as both a generator and an electric motor. The ISG 2 is also designed to act as a starter for restarting the internal combustion engine 7 from a stopped state.

[0017] The protected load set 3 is a set of electrical loads that require a stable supply of electrical current while vehicle 1 is in motion. Protected load set 3 includes, for example, measuring instruments and a vehicle navigation system.

[0018] The set of general loads 6 is a set of electrical loads that can be used for temporary services and, unlike protected loads 3, does not require a stable power supply. Examples of general loads 6 include windshield wipers or cooling fans.

[0019] The lead-acid battery 4 and the lithium-ion battery 5 are configured as a set of rechargeable secondary cells and are connected to the ISG 2 and the set of protected loads 3 to supply this electrical current. The lithium-ion battery 5 is a battery that can be repeatedly recharged to a higher energy density than the lead-acid battery 4 within a short period of time. Both the lead-acid battery 4 and the lithium-ion battery 5 conform to specifications, including the number of cells and other characteristics, designed to produce an output voltage of 12 V or close to it.

[0020] Furthermore, vehicle 1 has a combination of four switches, namely switch SW1, another switch SW2, another switch SW3, and another switch SW4. The combination of the four switches SW1, SW2, SW3, and SW4 is connected to the lithium-ion battery 5, thereby forming a lithium-ion battery pack 11.

[0021] Switch SW1 is designed to connect and disconnect the lead-acid battery 4 and the ISG 2. In other words, switch SW1 can be electrically controlled to establish (i.e., close) and disconnect (i.e., open) a connection between the lead-acid battery 4 and the ISG 2 (sometimes referred to here as the "first connection"). Switch SW3 is designed to connect and disconnect the lead-acid battery 4 and the set of protected loads 3. In other words, switch SW3 can be electrically controlled to connect (i.e., close) and disconnect (i.e., open) the lead-acid battery 4 and the set of protected loads 3 (sometimes referred to here as the "second connection"). Switch SW4 is designed to connect and disconnect the lithium-ion battery 5 and the set of protected loads 3.In other words, switch SW4 can be electrically controlled to establish (i.e., close) and disconnect (i.e., open) a connection between the lithium-ion battery 5 and the set of protected loads 3 (here sometimes referred to as the "third connection"). Switch SW2 is designed to establish and disconnect a connection between the lithium-ion battery 5 and the ISG 2. Therefore, when at least one of the switches SW3 and SW4 is in a connected state, the set of protected loads 3 is supplied with power from at least one of the lead-acid battery 4 and the lithium-ion battery 5.

[0022] It is noted that the four switches SW1 to SW4 can each be operated in such a way that they close to establish a corresponding connection, and that they open to establish a corresponding disconnection.

[0023] Furthermore, vehicle 1 features an ECU 10 as its control unit. The ECU 10 is designed to control the connections and disconnections of the four switches SW1 to SW4. In other words, the ECU 10 is designed to control each of the four switches SW1 to SW4 so that it closes or opens. The ECU 10 is also designed to perform various control operations, including drive control of the ISG 2 according to the driving state of vehicle 1 and the operating state of the internal combustion engine 7. For example, the ECU 10 is designed for control operations that include: an assistance control to use the drive control of the ISG 2 to assist the vehicle's driving, and an idle stop control, which is performed when a predefined stop condition and a restart condition are met, to automatically stop and restart the internal combustion engine 7.It is noted that the ECU 10, in the idle stop control, is designed to drive the ISG 2 to restart the internal combustion engine when a predefined restart condition is met. Therefore, vehicle 1 is designed to automatically stop or restart the journey when a predefined condition is fulfilled.

[0024] When the support control is activated, ECU 10 controls switch SW1 to be in a disconnected state and switch SW2 to be in a connected state. This makes it possible to suppress decreases in the charge capacity of lead-acid battery 4 and thus prevent decreases in fuel efficiency, since lead-acid battery 4 and ISG 2 are isolated and ISG 2 receives power only from lithium-ion battery 5. Simultaneously, the control is configured so that if either switch SW3 or switch SW4 is in a connected state, the other switch is in a disconnected state. This allows the protected load set 3 to receive power from either lead-acid battery 4 or lithium-ion battery 5. Therefore, the protected load set 3 can receive power regardless of the state of charge of lithium-ion battery 5.In this way, the vehicle power supply system according to the embodiments presented here can operate the set of protected loads 3 stably as an electrical load while suppressing any deterioration in fuel efficiency. Here, the connected state is a state in which one contact of the switch is closed (a closed state), and the disconnected state is a state in which one contact of the switch is open (an open state).

[0025] Furthermore, if the charge capacity of the lithium-ion battery 5 is lower than a predetermined charge capacity when the vehicle 1 is being assisted by the drive control of the ISG 2, the ECU 10 controls switch SW3 to be in a connected state and switch SW4 to be in a disconnected state. This allows electrical current from the lead-acid battery 4 to be supplied to the protected loads 3 when the charge capacity of the lithium-ion battery 5 is low. Therefore, the assistance control can be implemented in such a way as to suppress any deterioration in fuel efficiency while ensuring a stable supply of electrical current to the protected loads 3.

[0026] When the idle stop control is activated and the internal combustion engine 7 is restarted from a stopped state, the ECU 10 controls switch SW1 to be in a connected state, it controls switch SW2 to be in a disconnected state, it controls switch SW3 to be in a disconnected state, and it controls switch SW4 to be in a connected state. This ensures that, for the restart, which requires an instantaneous supply of electrical current exceeding the permissible discharge level of the lithium-ion battery 5, electrical current is supplied from the lead-acid battery 4 to the ISG 2 and electrical current from the lithium-ion battery 5 to the set of protected loads 3. Therefore, the lithium-ion battery 5 can be protected from a deep discharge and a stable electrical current can be supplied to the set of protected loads 3.Furthermore, the restart can be controlled without using a voltage converter, such as a DC-DC converter, and an increase in the overall cost of the system can be suppressed.

[0027] In this way, according to the embodiments presented here, in the power supply system for vehicles, by setting up the ISG 2 and the lead-acid battery 4 via the switch SW1 and setting up the ISG 2 and the lithium-ion battery 5 via the switch SW, it is possible to control the drive of the ISG 2 by using only the current supplied by the lithium-ion battery 5, which has a high energy storage capacity, and the support control can be carried out in such a way that a deterioration in fuel efficiency is suppressed.

[0028] Furthermore, the set of protected loads 3 and the lead-acid battery 4 are configured such that switch SW3 is located between them, and the set of protected loads 3 and the lithium-ion battery 5 are configured such that switch SW4 is located between them. Therefore, current can be supplied to the set of protected loads 3 from the lithium-ion battery 5 when the charge capacity of the lithium-ion battery 5 is high, and current can be supplied to the set of protected loads 3 from the lead-acid battery 4 when the charge capacity of the lithium-ion battery 5 is low. This allows the backup control to be performed even in situations involving a low charge capacity of the lithium-ion battery 5, and ensures a stable supply of electrical current to the set of protected loads 3.

[0029] Furthermore, according to the embodiments presented here, a power supply system for vehicles can be designed, during the implementation of the support control, such that the electrical current supplied to the set of protected loads 3 is always supplied by the lead-acid battery 4, regardless of the charge capacity of the lithium-ion battery. In this case, the ECU 10 can be operatively capable of controlling switch SW1 to be in a disconnected state, switch SW2 to be in a connected state, switch SW3 to be in a connected state, and switch SW4 to be in a disconnected state.This allows the ECU 10 to perform support control to suppress a deterioration in fuel efficiency through simplified control without monitoring the charge capacity of the lithium-ion battery 5 and to supply a stable electrical current to the set of protected loads 3. Furthermore, even if the support control requires a high output power, it is possible to supply a stable electrical current to the set of protected loads 3.

[0030] The following is a description of circuit configurations that are to be adopted by controlling switches SW1 to SW4 in the power supply system for vehicles.

[0031] As from Fig. As can be seen in Figure 2, the ECU 10 in the vehicle power supply system is capable of controlling the four switches SW1 to SW4 to assume each of eleven types of circuit configurations (in particular, a circuit configuration 1, a circuit configuration 2, a circuit configuration 3, a circuit configuration 4, a circuit configuration 5, a circuit configuration 6, a circuit configuration 7, a circuit configuration 8, a circuit configuration 9, a circuit configuration 10 and a circuit configuration 11).

[0032] As in Fig. As shown in Figure 2, circuit configuration 1 is adopted when the vehicle is in a state where charging and discharging of the lithium-ion battery is prohibited. For example, this is a state in a low-temperature environment, which is accompanied by a state where the ISG 2 generates a small amount of current. In circuit configuration 1, switches SW1, SW2, SW3, and SW4 are controlled to be in a connected state, a disconnected state, a connected state, and a disconnected state, respectively. In circuit configuration 1, the lithium-ion battery 5 (shown as Li-battery in the figure) is disconnected from the power supply system to prevent charging and discharging of the lithium-ion battery 5.Furthermore, switches SW1 and SW3 are in their connected state to supply electrical current generated by the ISG 2 or electrical current from the lead-acid battery 4 to the set of protected loads 3. This allows the set of protected loads 3 to operate stably.

[0033] Furthermore, since the dischargeable electrical current of the lithium-ion battery 5 is low in a low-temperature environment, an unstable supply of electrical current to the set of protected loads 3 can occur. Therefore, in circuit configuration 1, the ECU 10 controls the switch SW4 so that it is always in the off state in order to supply a stable electrical current from the lead-acid battery 4 to the set of protected loads 3.

[0034] It is noted that circuit configuration 1 is adopted without restriction to the described example of the low-temperature environment when charging and discharging of the lithium-ion battery 5 is prohibited. In particular, charging and discharging of the lithium-ion battery 5 is also prohibited under high-temperature conditions.

[0035] Circuit configuration 2 is adopted when the vehicle is in a low-temperature environment (1). For example, this is a low-temperature environment where the power generation of the ISG 2 is sufficiently high. Although the set of protected loads 3 may receive insufficient electrical current from the lithium-ion battery 5 in the low-temperature environment because the dischargeable electrical current (the electrical current that can be output) of the lithium-ion battery 5 is low, charging the lithium-ion battery 5 is still possible. Therefore, in circuit configuration 2, switches SW1, SW2, SW3, and SW4 are controlled to be in a disconnected state, a connected state, a disconnected state, and a connected state, respectively.In circuit configuration 2, the lithium-ion battery 5 is charged with electrical current generated by the ISG 2 by bringing switch SW2 into a connected state. Furthermore, since the low-temperature environment (1) is a state in which the lithium-ion battery 5 is charged to a degree that prevents excessive discharge, in circuit configuration 2 electrical current is supplied from the lithium-ion battery 5 to the set of protected loads 3 by bringing switch SW2 into a connected state. This ensures stable operation of the set of protected loads 3.

[0036] Circuit configuration 3 is adopted when the vehicle is in a low-temperature environment (2). For example, this is a low-temperature environment where the amount of power generated by the ISG 2 is sufficiently high, or a state where the lithium-ion battery 5 needs to be charged quickly. In circuit configuration 3, switches SW1, SW2, SW3, and SW4 are controlled to be in a disconnected state, a connected state, a connected state, and a disconnected state, respectively. In circuit configuration 3, the lithium-ion battery 5 is charged with the electrical current generated by the ISG 2 by bringing switch SW2 into a connected state.Furthermore, since the low-temperature environment (2) is a condition in which the lithium-ion battery 5 must be charged quickly, in circuit configuration 3, electrical current from the lead-acid battery 4 is supplied to the set of protected loads 3, while discharge of the lithium-ion battery 5 is avoided by setting switch SW4 to a disconnected state and switch SW3 to a connected state. This ensures stable operation of the set of protected loads 3. Additionally, in circuit configuration 3, the lithium-ion battery 5 can be charged quickly with the electrical current generated by the ISG 2, while electrical current from the lead-acid battery 4 is supplied to the set of protected loads 3.

[0037] Circuit configuration 4 is adopted when the vehicle state is "during regeneration (1)". "During regeneration (1)" is a state in which the ISG 2 performs regenerative power generation. In circuit configuration 4, switches SW1, SW2, SW3, and SW4 are controlled to be in a connected state, a connected state, a disconnected state, and a connected state, respectively. In circuit configuration 4, the electrical current generated by the ISG 2 is supplied to the lead-acid battery 4 and the lithium-ion battery 5 by bringing switches SW1 and SW2 into a connected state, thus efficiently charging the lead-acid battery 4 and the lithium-ion battery 5.Furthermore, since regeneration (1) is a state in which the lithium-ion battery 5 is charged to such a degree that it is not excessively discharged, in circuit configuration 4, electrical current is supplied from the lithium-ion battery 5 to the set of protected loads 3 by bringing the switch SW4 into a connected state. This ensures stable operation of the set of protected loads 3.

[0038] Circuit configuration 5 is adopted when the vehicle state is "during regeneration (2)". "During regeneration (2)" is a state in which the ISG 2 performs regenerative power generation, similar to regeneration (1). In circuit configuration 5, switches SW1, SW2, SW3, and SW4 are controlled to be in a connected state, a connected state, a connected state, and a disconnected state, respectively. In circuit configuration 5, the electrical current generated by the ISG 2 is supplied to the lead-acid battery 4 and the lithium-ion battery 5 by bringing switches SW1 and SW2 into a connected state, thus efficiently charging both batteries.Furthermore, since regeneration (2) is a state in which the lithium-ion battery 5 is not sufficiently charged, in circuit configuration 5 the lithium-ion battery 5 is charged by the ISG 2, and electrical current from the lead-acid battery 4 is supplied to the set of protected loads 3 by setting switch SW3 to a connected state and switch SW4 to a disconnected state. This ensures stable operation of the set of protected loads 3. Additionally, in cases where the lithium-ion battery 5 needs to be charged quickly, switch SW1 can be set to a disconnected state. In this case, the electrical current generated by the ISG 2 can be supplied only to the lithium-ion battery 5.

[0039] Circuit configuration 6 is adopted when the vehicle state is "Restart Time". The restart time is a state in which the internal combustion engine 7 is restarted by driving the ISG 2. In circuit configuration 6, switches SW1, SW2, SW3, and SW4 are controlled to be in a connected state, a disconnected state, a disconnected state, and a connected state, respectively. In circuit configuration 6, switching SW1 to a connected state and switching SW2 to a disconnected state, as shown in Fig. As shown in Figure 3, a large electrical current is supplied from the lead-acid battery 4 to the ISG 2 to drive the ISG 2. Furthermore, by bringing switch SW3 to a disconnected state and bringing switch SW4 to a connected state, electrical current from the lithium-ion battery 5 is supplied to the set of protected loads 3. In other words, at the time of restart, the set of protected loads 3 is operated stably by driving the ISG 2 with the electrical current from the lead-acid battery 4 and supplying electrical current from the lithium-ion battery 5 to the set of protected loads 3. In this way, in circuit configuration 6, a circuit in which the ISG 2 and the lead-acid battery 4 are connected and a circuit in which the set of protected loads 3 and the lithium-ion battery 5 are connected are formed independently of each other. Furthermore, as shown in Figure 3, the ISG 2 is connected to the ISG 2. Fig. Figure 3 shows that the ON state of switches SW1 to SW4 represents a connected state, and the OFF state of switches SW1 to SW4 represents a separate state.

[0040] Circuit configuration 7 is adopted when the vehicle state is "in a charging request phase from the lithium-ion battery (1)." A charging request phase from the lithium-ion battery (1) is a state in which charging the lithium-ion battery 5 has become necessary, unlike during regeneration. In circuit configuration 7, switches SW1, SW2, SW3, and SW4 are controlled to be in a disconnected state, a connected state, a connected state, and a disconnected state, respectively. In circuit configuration 7, the electrical current generated by the ISG 2 is supplied to the lithium-ion battery 5 by bringing switch 2 into a connected state, in order to charge the lithium-ion battery 5.Furthermore, by bringing switch SW4 into a disconnected state and switch SW3 into a connected state, electrical current from the lead-acid battery 4 is supplied to the set of protected loads 3. This ensures stable operation of the set of protected loads 3. Additionally, in circuit configuration 7, by bringing switch SW1 into a disconnected state, the lead-acid battery 4 is discharged from both electrical loads in the set of general loads 6 and the set of protected loads 3. If a reduction in the discharge rate of the lead-acid battery 4 is desired, the ECU 10 preferably controls switch SW3 to be in a disconnected state and controls switch SW4 to be in a connected state to supply electrical current from the lithium-ion battery 5 to the set of protected loads 3 and to charge the lithium-ion battery 5 with the electrical current generated by the ISG 2.In this way, with circuit configuration 7, one of the switches SW3 and SW4 can be in a connected state or in a disconnected state.

[0041] Circuit configuration 8 is adopted when the vehicle state is "in a charging request phase from the lithium-ion battery (2)." The charging request phase from the lithium-ion battery (2) is a state in which, similar to the charging request phase from the lithium-ion battery (1), charging of the lithium-ion battery 5 has become necessary, unlike during regeneration. In circuit configuration 8, switches SW1, SW2, SW3, and SW4 are controlled to be in a connected state, a connected state, a connected state, and a disconnected state, respectively. In circuit configuration 8, the electrical current generated by the ISG 2 is supplied to the lead-acid battery 4 and the lithium-ion battery 5 by bringing switches SW1 and SW2 into a connected state, in order to charge the lead-acid battery 4 and the lithium-ion battery 5 efficiently.Furthermore, by bringing switch SW4 into a disconnected state and switch SW3 into a connected state, electrical current from the lead-acid battery 4 is supplied to the set of protected loads 3. This ensures stable operation of the set of protected loads 3. Additionally, in cases where the state of charge of the lithium-ion battery 5 is lower than a predetermined value, the ECU 10 preferably controls switch SW3 to be in a connected state and controls switch SW4 to be in a disconnected state in order to supply electrical current from the lead-acid battery 4 to the set of protected loads 3.In contrast, when the state of charge of the lithium-ion battery 5 is at or above a predetermined value (in cases where the state of charge is generally sufficient), the ECU 10 preferably controls switch SW3 to be in a disconnected state and controls switch SW4 to be in a connected state in order to supply electrical current from the lithium-ion battery 5 to the set of protected loads 3. Thus, in circuit configuration 8, either switch SW3 or switch SW4 can be in a connected or disconnected state.

[0042] Circuit configuration 9 is adopted when the vehicle state is "a good state of charge of the lead-acid battery and the lithium-ion battery." In circuit configuration 9, switches SW1, SW2, SW3, and SW4 are controlled to be in a disconnected state, a disconnected state, a disconnected state, and a connected state, respectively. In circuit configuration 9, electrical current is supplied to the set of protected loads 3 from the lithium-ion battery 5 by bringing switch SW4 into a connected state. This ensures stable operation of the set of protected loads 3. Since switch SW3 is in a disconnected state, no electrical current is supplied to the set of protected loads 3 from switch SW3.Since, in circuit configuration 9, the lithium-ion battery 5, which can be repeatedly recharged in a short time, is actively used to operate the set of protected loads 3, a period during which the ISG 2 is not used for power generation can be ensured, and the power generation load during the vehicle's driving phase can be reduced, thus improving fuel efficiency. Furthermore, switch SW2 can be in a connected state.

[0043] Circuit configuration 10 is adopted when the vehicle state is "in a support control phase (when the lithium-ion battery charge capacity is low)." In circuit configuration 10, switches SW1, SW2, SW3, and SW4 are controlled to be in a disconnected state, a connected state, a connected state, and a disconnected state, respectively. Since the vehicle state at this time is in a support control phase (when the lithium-ion battery 5 charge level is low), circuit configuration 10 supplies electrical current by bringing switch SW3 into a connected state and bringing switch SW4 into a disconnected state, as shown in Fig. As shown in Figure 4, current is supplied from the lead-acid battery 4 to the set of protected loads 3. Furthermore, by bringing switch SW2 to the connected state, electrical current is supplied from the lithium-ion battery 5 to the ISG 2. Additionally, by bringing switch SW1 to the disconnected state, the lead-acid battery 4 and the ISG 2 are disconnected from each other. Thus, in circuit configuration 10, a circuit in which the ISG 2 and the lithium-ion battery 5 are connected, and a circuit in which the set of protected loads 3 and the lead-acid battery 4 are connected, are formed independently of each other. Since, in circuit configuration 10, the lithium-ion battery 5, which can be repeatedly recharged in a short time, is actively used to drive the ISG 2, the auxiliary control can be performed with a high frequency.Furthermore, the set of protected loads 3 can be operated stably by supplying electrical current from the lead-acid battery 4 to the set of protected loads 3. Furthermore, as in . Fig. Figure 4 shows that the ON state of switches SW1 to SW4 represents a connected state, and the OFF state of switches SW1 to SW4 represents a separate state.

[0044] Circuit configuration 11 is adopted when the vehicle state is "in a support control phase (when the lithium-ion battery's charge capacity is high)." In circuit configuration 11, switches SW1, SW2, SW3, and SW4 are controlled to be in a disconnected state, a connected state, a disconnected state, and a connected state, respectively. The vehicle state at this time is one in which support control is performed when the lithium-ion battery 5 has a high charge level. In circuit configuration 11, as described in Fig. As shown in Figure 5, electrical current is supplied from the lithium-ion battery 5 to the set of protected loads 3 by bringing switch SW3 to a disconnected state and switch SW4 to a connected state, while electrical current from the lithium-ion battery 5 is also supplied to the ISG 2 by bringing switch SW2 to a connected state. Furthermore, the lead-acid battery 4 and the ISG 2 are disconnected from each other by bringing switch SW1 to a disconnected state. Since, in circuit configuration 11, the lithium-ion battery 5, which can be repeatedly recharged in a short time, is actively used to drive the ISG 2, the support control can be performed with a high frequency. Furthermore, the set of protected loads 3 can be operated stably by supplying electrical current from the lithium-ion battery 5 to the set of protected loads 3. Furthermore, as shown in Figure 11, the following applies: Fig.Figure 5 shows that the ON state of switches SW1 to SW4 represents a connected state, and the OFF state of switches SW1 to SW4 represents a separate state.

[0045] Thus, in circuit configurations 10 and 11, a decrease in the charging capacity of the lead-acid battery is suppressed during the implementation of the support control by powering the ISG 2 only with the electrical current from the lithium-ion battery 5, which can be repeatedly recharged in a short time.

[0046] Furthermore, in circuit configurations 10 and 11, when implementing the support control, the set of protected loads 3 is operated stably regardless of the state of charge of the lithium-ion battery 5 by supplying electrical current from the lead-acid battery 4 to the set of protected loads 3 depending on the state of charge of the lithium-ion battery 5.

[0047] As described above, according to the embodiments presented here, the circuit configurations 1 to 11 in the vehicle power supply system are such that either the switch SW3 or the switch SW4 is controlled to be in a connected state, and the set of protected loads 3 can therefore be operated stably.

[0048] The following is a description of the operations and beneficial effects of the power supply system for vehicles according to the embodiments presented here.

[0049] According to the embodiments presented here, the vehicle power supply system includes the switch SW1, which establishes a connection or disconnection between the lead-acid battery 4 and the ISG 2, the switch SW3, which establishes a connection or disconnection between the lead-acid battery 4 and the set of protected loads 3, the switch SW4, which establishes a connection or disconnection between the lithium-ion battery 5 and the set of protected loads 3, and the ECU 10, which controls the connection or disconnection of the switch SW1, the switch SW3, and the switch SW4.

[0050] Furthermore, when assisting the vehicle's movement through a drive control of the ISG 2, the ECU 10 controls switch SW1 so that it is in a disconnected state; and when one of the switches SW3 and SW4 is in a connected state, the ECU 10 controls the other switch so that it is in a disconnected state.

[0051] Thus, during the support control phase, i.e., when the ISG 2 assists the vehicle's operation, a decrease in the charge capacity of the lead-acid battery 4 and a deterioration in fuel efficiency can be suppressed, since the lead-acid battery 4 and the ISG 2 are isolated from each other and electrical current is supplied to the ISG 2 only from the lithium-ion battery 5. Furthermore, electrical current can be supplied to the set of protected loads 3 from either the lead-acid battery 4 or the lithium-ion battery 5. Therefore, electrical current can be supplied to the set of protected loads 3 regardless of the state of charge of the lithium-ion battery 5. As a result, the set of protected loads 3 can be operated stably while a deterioration in fuel efficiency is suppressed.In other words, since the power supply system for vehicles according to the embodiments presented here is equipped with the switch SW3 and the switch SW4, the assistance provided by the ISG 2 during driving assistance can be carried out using a large electrical current from the lithium-ion battery 5, while the supply of the set of protected loads 3 with electrical current is carried out from the lead-acid battery 4.

[0052] Furthermore, the power supply system for vehicles according to the embodiments presented here can have a configuration in which, when the ISG 2 assists the vehicle's movement, at least the lead-acid battery 4 and the ISG 2 are separated from each other, and electrical current is supplied to the ISG 2 only from the lithium-ion battery 5, while electrical current is supplied to the set of protected loads 3 from both the lead-acid battery 4 and the lithium-ion battery 5. That is to say, this invention can also have a configuration in which the lithium-ion battery 5 and the ISG 2 are always connected.

[0053] Furthermore, in the power supply system for vehicles according to the embodiments presented here, when the driving of the vehicle 1 is supported by a drive control of the ISG 2, the ECU 10 controls the switch SW3 so that it is in a connected state, and controls the switch SW4 so that it is in a disconnected state.

[0054] Since this allows electrical current from the lead-acid battery 4 to be supplied to the set of protected loads 3 when the state of charge of the lithium-ion battery 5 is low, the set of protected loads 3 can be operated stably. In other words, since, according to the embodiments presented here, the vehicle power supply system is equipped with the switch SW3 and the switch SW4, electrical current from the lithium-ion battery 5 can be supplied to the set of protected loads 3 when the state of charge of the lithium-ion battery 5 is high, and thus the electrical current from the lithium-ion battery 5 can be used effectively.

[0055] Furthermore, according to the embodiments presented here, the vehicle 1 has in its vehicle power supply system the function of automatically stopping and restarting the internal combustion engine if predetermined conditions are met, and when restarting the internal combustion engine 7 from a stopped state, the ECU 10 controls the switch SW1 so that it is in a connected state, controls the switch SW3 so that it is in a disconnected state, and controls the switch SW4 so that it is in a connected state.

[0056] Since, at the time of restarting the combustion engine 7, electrical current is supplied from the lead-acid battery 4 to the ISG 2 and electrical current from the lithium-ion battery 5 is supplied to the set of protected loads 3, the set of protected loads 3 can be operated stably.In other words, in the vehicle power supply system according to the embodiments presented here, despite the fact that an electric current is instantly required at the time of restarting the combustion engine 7, which exceeds a permissible discharge level of the lithium-ion battery 5, a circuit containing the ISG 2 and the lead-acid battery 4 and a circuit containing the lithium-ion battery 5 and the set of protected loads 3 can be made independent of each other by controlling the switch SW1 and the switch SW3 in order to supply electric current to the ISG 2 from the lead-acid battery 4, and it is therefore possible to eliminate the need to provide a DC-DC converter between the lithium-ion battery 5 and the set of protected loads 3.

[0057] Furthermore, the lithium-ion battery 5 in the power supply system for vehicles according to the embodiments presented here is a battery that can be repeatedly recharged within a shorter time than the lead-acid battery 4.

[0058] Since the vehicle power supply system is thus composed of two types of batteries with different charging characteristics, efficient charging and discharging control can be implemented within the vehicle power supply system. Furthermore, in the vehicle power supply system according to the embodiments presented here, the position of the ISG 2 is such that it is located on the side of the lithium-ion battery 5 instead of on the lead-acid battery 4. This makes it possible to power the ISG 2 exclusively with the electrical current from the lithium-ion battery 5, which has a high energy storage capacity. List of reference symbols 1 vehicle 2 ISG (electric motor) 3 protected loads (set of electrical loads) 4 Lead-acid battery (first battery) 5 Lithium-ion batteries (second battery) 10 ECU (control unit) SW1 switch SW3 switch SW4 switch

Claims

[1] Vehicle power supply system, comprising: an electric motor (2) designed to use the movement of a vehicle (1) to generate electric current and to assist the movement of the vehicle (1); a set of electrical loads (3) that requires a stable supply of electrical current when the vehicle (1) is moving; a first battery (4) which is connected to the electric motor (2) and the set of electrical loads (3) and is designed to supply them with electric current; a second battery (5) connected to the electric motor (2) and the set of electrical loads (3) and designed to supply them with electric current, wherein the second battery (5) is designed to repeat a charge within a shorter period of time than the first battery (4); a first switch (SW1) designed to establish and break a first connection between the first battery (4) and the electric motor (2); a second switch (SW3) designed to establish and break a second connection between the first battery (4) and the set of electrical loads (3); a third switch (SW4) designed to establish and break a third connection between the second battery (5) and the set of electrical loads (3); and a control unit (10) designed to control the first switch (SW1), the second switch (SW3) and the third switch (SW4), wherein the control unit (10) is designed to control the first, second and third switches (SW1, SW3, SW4) such that the first connection is interrupted, one is made from the second and third connections and the other is interrupted from the second and third connections in order to control the electric motor (2) so that it is driven to assist in the movement of the vehicle (1). [2] Power supply system for vehicles according to claim 1, wherein the control unit (10) is designed to establish the second connection and to interrupt the third connection when the second battery (5) has a charge capacity that is lower than a predetermined charge capacity, in order to control the drive of the electric motor (2) in such a way as to assist the driving of the vehicle (1). [3] Power supply system for vehicles according to claim 1 or 2, wherein the vehicle (1) is designed to automatically stop and restart an internal combustion engine (7) when a predetermined condition is met, and the control unit (10) is designed to establish the first connection, break the second connection and establish the third connection in order to restart the internal combustion engine (7) from its stopped state.

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