JP7464440B2 - Vehicle Power System - Google Patents

Description

The present invention relates to a power supply system for a vehicle.

Patent Document 1 describes an example of a vehicle power supply system that includes a main battery, an auxiliary battery, a DC-DC converter that adjusts and outputs the DC voltage of the main battery, and an auxiliary power line that is a power line to which on-board auxiliary equipment is connected. In this system, the output voltage of the DC-DC converter can be input to the auxiliary equipment via the auxiliary power line, and the voltage of the auxiliary battery can be input to the auxiliary equipment via the auxiliary power line.

The above system includes a discharge circuit. When the regulated voltage, which is the output voltage of the DC-DC converter, becomes less than the voltage of the auxiliary battery, or when the voltage of the auxiliary power line becomes less than the voltage of the second battery, the discharge circuit becomes conductive. When the discharge circuit becomes conductive, the voltage of the auxiliary battery is input to the auxiliary power line via the discharge circuit. On the other hand, when the discharge circuit is not conductive, the voltage of the auxiliary battery is not input to the auxiliary power line.

The above system further includes a charging circuit. The charging circuit has a switching element arranged in parallel with the discharge circuit. When the remaining capacity of the auxiliary battery is greater than the determined capacity, the switching element is kept off. On the other hand, when the remaining capacity of the auxiliary battery falls below the determined capacity, the switching element is repeatedly turned on and off. This operation of the switching element reduces the regulated voltage, and the reduced regulated voltage is input to the auxiliary battery. As a result, the auxiliary battery is charged.

JP 2018-113814 A

When the discharge circuit is in a state where electricity can be conducted as described above, the auxiliary battery's voltage is input to the auxiliary equipment via the discharge circuit and the auxiliary power line, so that the remaining capacity of the auxiliary battery gradually decreases. Then, when the remaining capacity falls below the determination capacity, the switching element of the charging circuit is repeatedly turned on and off. When the switching element is turned on in this way, the current that passed through the discharge circuit flows to the charging circuit side instead of the auxiliary equipment side.

A vehicle power supply system for solving the above problem includes a first battery, a second battery capable of charging and discharging, a DC-DC converter that adjusts the magnitude of the DC voltage of the first battery and outputs it, an auxiliary power line that is a power line connecting an on-board auxiliary device and the DC-DC converter, and an electric circuit arranged between the auxiliary power line and the second battery, which allows current to flow from the second battery side to the auxiliary power line side when the voltage of the auxiliary power line is lower than the voltage of the second battery, a charging circuit having a switch arranged in parallel with the discharge circuit and repeatedly turning on and off the switch to step down the output voltage of the DC-DC converter and input it to the second battery, and a control device that maintains the switch in an off state when current flows from the second battery side to the auxiliary power line side in the discharge circuit.

According to the above configuration, when the voltage of the auxiliary power line is lower than the voltage of the second battery, a current flows from the second battery side to the auxiliary power line side in the discharge circuit, so the switch of the charging circuit is kept off. This makes it possible to prevent the current that flows from the second battery side to the auxiliary power line side in the discharge circuit from flowing to the switch side.

When the discharge circuit does not allow current to flow from the second battery to the auxiliary power line, the switch of the charging circuit is allowed to be turned on. Therefore, in the charging circuit, the output voltage of the DCDC converter can be stepped down by repeatedly turning the switch on and off. The stepped-down voltage can be input to the second battery to charge it.

1 is a schematic diagram showing a vehicle power supply system according to an embodiment; 4 is a flowchart illustrating a flow of processing executed by a control device of the vehicle power supply system. 4 is a flowchart illustrating the flow of processing executed by the control device.

An embodiment of a vehicle power supply system will be described below with reference to Figures 1 to 3. In the following description, the vehicle power supply system will be simply referred to as the "power supply system."
As shown in Fig. 1, a power supply system 10 of this embodiment includes a first battery 11 which is a main battery for driving a vehicle, a second battery 12 which is a power supply for auxiliary equipment, and a DC-DC converter 13 which steps down and outputs the voltage of the first battery 11. The first battery 11 and the second battery 12 are each configured to be capable of charging and discharging. The voltage output from the DC-DC converter 13 is referred to as a "regulated voltage Vdc."

A system main relay 15 is provided on the high-voltage line 14, which is a power line connecting the first battery 11 and the DCDC converter 13. The system main relay 15 is in a conductive state when the vehicle's driving switch is on. When the system main relay 15 is in a conductive state, electricity can flow between the first battery 11 and the DCDC converter 13. An inverter 16 is connected to the high-voltage line 14 on the DCDC converter 13 side of the system main relay 15. The inverter 16 converts the DC voltage of the first battery 11 into an AC voltage. When the AC voltage generated by the inverter 16 in this manner is input to the motor generator 100 for driving the vehicle, the motor generator 100 is driven.

An auxiliary power line 17 is connected to the output side of the DCDC converter 13. The auxiliary power line 17 is a power line to which the on-board auxiliary devices 110 are connected. Examples of the auxiliary devices include an electric power steering device and a power window device.

A fuse 19 and an auxiliary relay 20 are provided on the low-voltage line 18, which is a power line connected to the second battery 12. The auxiliary relay 20 is in a conductive state when the vehicle driving switch is on. When the auxiliary relay 20 is in a conductive state, electricity can be passed between the second battery 12 and a discharge circuit 23 and a charge circuit 24 described later. The fuse 19 is disposed between the auxiliary relay 20 and the second battery 12. A Zener diode 21 is connected to the opposite side of the low-voltage line 18 to the fuse 19 across the auxiliary relay 20. One end of the Zener diode 21 is connected to the low-voltage line 18, while the other end of the Zener diode 21 is connected to ground. By disposing the Zener diode 21 in this manner, it is possible to prevent the voltage of the low-voltage line 18 from becoming too high when the second battery 12 is charged.

The power supply system 10 includes, as electric circuits connected to the auxiliary power line 17 , a high voltage suppression circuit 22 , a discharge circuit 23 , and a charge circuit 24 .
If the connection point of the auxiliary power line 17 with the auxiliary 110 is designated as an auxiliary connection point 17a, the discharge circuit 23 is connected to the portion of the auxiliary power line 17 opposite the DCDC converter 13 across the auxiliary connection point 17a.

The discharge circuit 23 has a discharge power line 31, which is a power line connecting the auxiliary power line 17 and the low voltage line 18, and a first switching element 32 is provided on the discharge power line 31. In this embodiment, a MOSFET is used as the first switching element 32. Therefore, the first switching element 32 has a parasitic diode 32a. This parasitic diode 32a allows current to flow from the low voltage line 18 side to the auxiliary power line 17 side, but does not allow current to flow from the auxiliary power line 17 side to the low voltage line 18 side.

The discharge circuit 23 has a discharge control IC 33 that outputs a signal to the gate of the first switching element 32. The discharge control IC 33 is configured to detect the voltage of the portion of the auxiliary power line 17 that is connected to the first switching element 32 and the voltage of the portion of the low-voltage line 18 that is connected to the first switching element 32. In other words, the discharge control IC 33 can detect the regulated voltage Vdc of the DCDC converter 13 and the voltage Vbt of the second battery 12.

The charging circuit 24 has a charging power line 41, which is a power line that connects the auxiliary power line 17 and the low-voltage line 18. The charging power line 41 is connected to the auxiliary power line 17 between the connection with the discharge circuit 23 and the connection with the high-voltage suppression circuit 22 described below. The charging power line 41 is also connected to the low-voltage line 18 between the connection with the Zener diode 21 and the connection with the discharge circuit 23. In other words, the charging power line 41 can be said to be a power line that bypasses the first switching element 32 of the discharge circuit 23.

The charging power line 41 is provided with a second switching element 42, which is an example of a switch. In this embodiment, a MOSFET is used as the second switching element 42. Therefore, the second switching element 42 has a parasitic diode 42a. This parasitic diode 42a allows current to flow from the low voltage line 18 to the auxiliary power line 17, but does not allow current to flow from the auxiliary power line 17 to the low voltage line 18.

In addition, a reactor 43 is arranged between the connection part of the charging power line 41 with the low voltage line 18 and the second switching element 42. A capacitance 45 is provided on a power line 44 that connects the part of the charging power line 41 between the second switching element 42 and the reactor 43 and the ground. A power line 46 is connected to the part of the power line 44 between the connection point with the charging power line 41 and the capacitance 45. One end of the power line 46 is connected to the power line 44, while the other end of the power line 46 is connected to the ground. A third switching element 47 is provided on this power line 46. In this embodiment, a MOSFET is used as the third switching element 47. For this reason, the third switching element 47 has a parasitic diode 47a. This parasitic diode 47a allows current to flow from the ground side to the power line 44 side, but does not allow current to flow from the power line 44 side to the ground side.

The charging circuit 24 has a charging control IC 48 that inputs signals to the gate of the second switching element 42 and the gate of the third switching element 47. That is, the input from the charging control IC can control the on/off of the second switching element 42 and the on/off of the third switching element 47.

The high voltage suppression circuit 22 is a circuit for suppressing the voltage of the auxiliary power line 17 from becoming too high. The high voltage suppression circuit 22 is connected between the connection part of the auxiliary power line 17 with the charging power line 41 of the charging circuit 24 and the auxiliary connection point 17a. The high voltage suppression circuit 22 has a suppression circuit line 61, which is a power line that connects the connection point with the auxiliary power line 17 and ground. A resistor 62 and a Zener diode 63 are provided on this suppression circuit line 61. More specifically, the Zener diode 63 is disposed between the resistor 62 and ground. The midpoint 61a between the resistor 62 and the Zener diode 63 on the suppression circuit line 61 is connected to the gate of the first switching element 32 of the discharge circuit 23.

Next, the control device 80 of the power supply system 10 will be described.
Detection signals are input to the control device 80 from various sensors. Examples of the sensors include a first voltage sensor 81 and a second voltage sensor 82. The first voltage sensor 81 detects an auxiliary voltage Va, which is the voltage of the auxiliary power line 17, and outputs a signal corresponding to the detection result as a detection signal. The second voltage sensor 82 detects a voltage Vbt of the second battery 12, and outputs a signal corresponding to the detection result as a detection signal.

The control device 80 controls the on/off of the first switching element 32 by outputting a command to the discharge control IC 33. The control device 80 also controls the on/off of the second switching element 42 and the on/off of the third switching element 47 by outputting a command to the charge control IC 48.

Next, a charging process for charging the second battery 12 by controlling the charging circuit 24 will be described.
A command to operate the charging circuit 24 is output from the control device 80 to the charging control IC 48. Then, the second switching element 42 is repeatedly turned on and off, thereby lowering the regulated voltage Vdc of the DCDC converter 13. Specifically, the second switching element 42 and the third switching element 47 are alternately turned on and off. If the regulated voltage Vdc lowered by the operation of the charging circuit 24 is set as the charging voltage Vc, the charging voltage Vc is input to the second battery 12. As a result, the second battery 12 is charged.

Next, with reference to FIG. 2, a flow of a series of processes repeatedly executed by the control device 80 when the second battery 12 is charged will be described.
In the first step S11, it is determined whether the auxiliary voltage Va is lower than the voltage Vbt of the second battery 12. The first switching element 32 has a parasitic diode 32a. Therefore, when the auxiliary voltage Va is lower than the voltage Vbt of the second battery 12, the discharge circuit 23 allows current to flow from the second battery 12 side to the auxiliary power line 17 side. That is, a current flows from the second battery 12 side to the auxiliary power line 17 side through the parasitic diode 32a of the first switching element 32. Therefore, when the auxiliary voltage Va is lower than the voltage Vbt of the second battery 12 (S11: YES), the process proceeds to the next step S12.

In step S12, the charging circuit 24 remains stopped. That is, the second switching element 42 of the charging circuit 24 remains off. As a result, when a current flows from the second battery 12 side to the auxiliary power line 17 side in the discharge circuit 23, the second switching element 42 remains off. Then, the series of processes is temporarily terminated.

On the other hand, in step S11, if the auxiliary voltage Va is equal to or higher than the voltage Vbt of the second battery 12 (NO), the second switching element 42 is not kept off and the series of processes is temporarily terminated. If the auxiliary voltage Va is equal to or higher than the voltage Vbt of the second battery 12, no current flows from the second battery 12 to the auxiliary power line 17 through the parasitic diode 32a of the first switching element 32. In this case, the discharge circuit 23 does not allow current to flow from the second battery 12 to the auxiliary power line 17, so the operation of the charging circuit 24 is not stopped. In other words, the charging process is allowed to be executed.

Next, referring to FIG. 3, we will explain the flow of a series of processes that are repeatedly executed by the control device 80 when driving the auxiliary device 110 by power supply from the first battery 11 or the second battery 12.

In the first step S21, it is determined whether the auxiliary voltage Va is lower than the voltage Vbt of the second battery 12. The first switching element 32 has a parasitic diode 32a. Therefore, when the auxiliary voltage Va is lower than the voltage Vbt of the second battery 12, the discharge circuit 23 allows current to flow from the second battery 12 to the auxiliary power line 17. That is, a current flows from the second battery 12 to the auxiliary power line 17 through the parasitic diode 32a of the first switching element 32. In addition, when the auxiliary voltage Va is lower than the voltage Vbt of the second battery 12, the regulated voltage Vdc may be lower than the voltage Vbt of the second battery 12. When the auxiliary 110 is driven under such circumstances, the first switching element 32 may be turned on to input the voltage Vbt of the second battery 12 to the auxiliary 110. When the first switching element 32 is on in this manner, a current flows from the second battery 12 to the auxiliary power line 17 in the discharge circuit 23. Therefore, if the auxiliary voltage Va is lower than the voltage Vbt of the second battery 12 (S21: YES), the process proceeds to the next step S22.

In step S22, the charging circuit 24 remains stopped. That is, the second switching element 42 of the charging circuit 24 remains off. As a result, when a current flows from the second battery 12 side to the auxiliary power line 17 side in the discharge circuit 23, the second switching element 42 remains off. Then, the series of processes is temporarily terminated.

On the other hand, in step S21, if the auxiliary voltage Va is equal to or higher than the voltage Vbt of the second battery 12 (NO), the process proceeds to the next step S23. If the auxiliary voltage Va is equal to or higher than the voltage Vbt of the second battery 12, no current flows from the second battery 12 to the auxiliary power line 17 through the parasitic diode 32a of the first switching element 32. Furthermore, when the auxiliary 110 is driven under such circumstances, the first switching element 32 is not turned on. That is, the discharge circuit 23 does not allow current to flow from the second battery 12 to the auxiliary power line 17.

In step S23, it is determined whether the remaining capacity SOC of the second battery 12 is less than the judgment capacity SOCTh. The remaining capacity SOC of the second battery 12 can be derived based on the voltage Vbt of the second battery 12, the current flowing through the low-voltage line 18, and the temperature of the second battery 12. The judgment capacity SOCTh is set so that it can be determined whether or not the charging process needs to be executed based on the remaining capacity SOC. If the remaining capacity SOC is less than the judgment capacity SOCTh, it is deemed that the charging process needs to be executed. On the other hand, if the remaining capacity SOC is equal to or greater than the judgment capacity SOCTh, it is deemed that the charging process does not yet need to be executed. Therefore, if the remaining capacity SOC is less than the judgment capacity SOCTh (S23: YES), the process proceeds to the next step S24. In step S24, the charging process starts to be executed. Then, the process ends.

On the other hand, if the remaining capacity SOC of the second battery 12 is equal to or greater than the determination capacity SOCTh in step S23 (NO), the series of processes is temporarily terminated without starting the charging process.

Next, the operation and effects of this embodiment will be described.
When the auxiliary voltage Va, which is the voltage of the auxiliary power line 17, is lower than the voltage Vbt of the second battery 12, a current flows from the second battery 12 side to the auxiliary power line 17 side via the parasitic diode 32a of the first switching element 32. When the discharge circuit 23 allows a current to flow from the second battery 12 side to the auxiliary power line 17 side in this manner, the second switching element 42 of the charging circuit 24 is maintained in an off state. Therefore, when a current flows from the second battery 12 side to the auxiliary power line 17 side via the discharge circuit 23, it is possible to suppress the current that has flowed through the discharge circuit 23 from flowing to the second switching element 42 side rather than to the auxiliary 110 side.

If no current flows from the second battery 12 to the auxiliary power line 17 in the discharge circuit 23, the charging process is started when the remaining capacity SOC of the second battery 12 falls below the judgment capacity SOCTh. When the charging process is being executed, the regulated voltage Vdc is stepped down by repeatedly turning on and off the second switching element 42 in the charging circuit 24. The second battery 12 can be charged by inputting the voltage stepped down by the charging circuit 24 to the second battery 12 in this manner.

The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other to the extent that no technical contradiction occurs.
The discharge power line 31 may be provided with a switch other than the first switching element 32 as long as it can allow or block current flow. For example, if a switch other than a MOSFET is provided in the discharge power line 31, the parasitic diode 32a or something equivalent to the parasitic diode 32a is not provided in the discharge circuit 23. Therefore, when the auxiliary voltage Va is lower than the voltage Vbt of the second battery 12, it is preferable to turn on the switch provided in the discharge power line 31 so that a current flows from the second battery 12 side to the auxiliary power line 17 side via the switch.

The switch may be a relay contact.
The switch provided in the charging power line 41 may be anything other than the second switching element 42 (MOSFET) as long as it can allow or cut off the passage of electricity. For example, the charging power line 41 may be provided with a relay contact instead of the second switching element 42.

- The power line 46 may be provided with a switch other than the third switching element 47 (MOSFET) as long as it can allow or block the passage of electricity. For example, the power line 46 may be provided with a relay contact instead of the third switching element 47.

The regulated voltage Vdc output from the DC-DC converter 13 may become lower than the voltage Vbt of the second battery 12. When driving the auxiliary device 110 in such a case, the first switching element 32 of the discharge circuit 23 may be turned on, and the auxiliary device 110 may be driven by power supply from the second battery 12. In this case, since a current flows from the second battery 12 side to the auxiliary power line 17 side in the discharge circuit 23, it is preferable to keep the second switching element 42 of the charging circuit 24 off.

-Some of the auxiliary devices 110 generate regenerative power. When regenerative power is generated by such auxiliary devices 110, the auxiliary voltage Va increases. When the auxiliary voltage Va increases, a current flows through the high voltage suppression circuit 22, and a current may flow from the high voltage suppression circuit 22 to the gate of the first switching element 32. That is, a signal may be input from the high voltage suppression circuit 22 to the gate of the first switching element 32, turning the first switching element 32 on. In this way, even when the first switching element 32 is turned on, the second switching element 42 of the charging circuit 24 may be kept off.

The control device 80 may have any one of the following configurations (a) to (c).
(a) The control device 80 includes one or more processors that execute various processes according to a computer program. The processor includes a CPU and memory such as RAM and ROM. The memory stores program codes or instructions that are configured to cause the CPU to execute processes. Memory, i.e., computer-readable media, includes any available media that can be accessed by a general-purpose or special-purpose computer.
(b) The control device 80 includes one or more dedicated hardware circuits for executing various processes. Examples of the dedicated hardware circuits include application specific integrated circuits, i.e., ASIC and FPGA. ASIC is an abbreviation for "Application Specific Integrated Circuit" and FPGA is an abbreviation for "Field Programmable Gate Array."
(c) The control device 80 includes a processor that executes some of the various processes in accordance with a computer program, and a dedicated hardware circuit that executes the remaining processes among the various processes.

REFERENCE SIGNS LIST 10 power supply system 11 first battery 12 second battery 13 DCDC converter 17 auxiliary power line 23 discharge circuit 24 charging circuit 42 second switching element 80 control device 110 auxiliary

Claims (1)

A first battery;
A second battery capable of being charged and discharged;
a DC-DC converter that adjusts the magnitude of the DC voltage of the first battery and outputs the adjusted voltage;
an auxiliary power line that is a power line connecting an on-vehicle auxiliary and the DCDC converter;
a discharge circuit, which is an electric circuit disposed between the auxiliary power line and the second battery, and which allows a current to flow from the second battery side to the auxiliary power line side when a voltage of the auxiliary power line is lower than a voltage of the second battery;
a charging circuit having a switch provided in parallel with the discharge circuit, and repeatedly turning on and off the switch to step down the output voltage of the DC-DC converter and input the step-down output voltage to the second battery;
a control device that maintains the switch in an off state when a current flows from the second battery side to the auxiliary power line side in the discharge circuit.