DC-DC converter control device

Abstract

To provide a DC-DC converter control device capable of preventing an auxiliary system from becoming inoperable.SOLUTION: A DC-DC converter control device performs: permitting a DC-DC converter to perform step-down charging for charging a lead-acid battery with electric power charged in the lithium-ion battery (S10), when charging rate of the lithium-ion battery (hereinafter referred to as LiSOC) is equal to or higher than a predetermined value TH (S1); and permitting the DC-DC converter to perform step-down charging (S3) if an engine is in a complete explosion state (S2), when the LiSOC is lower than the predetermined value TH (S1).SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a DC-DC converter control device. [Background technology]

[0002] Conventionally, Patent Document 1 proposes a vehicle equipped with a lithium-ion battery with an output voltage of 48V, a lead battery with an output voltage of 12V, an ISG (Integrated Starter Generator) that generates power by receiving power from the lithium-ion battery, vehicle electrical components that operate by receiving power from the lead battery, and a DC-DC converter that can convert voltage between the lead battery and the lithium-ion battery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-108188 Summary of the Invention [Problem to be solved by the invention]

[0004] In such conventional vehicles, when the state of charge (hereinafter simply referred to as "LiSOC") of the lithium ion battery drops below a predetermined value, the lithium ion battery begins to deteriorate.

[0005] Therefore, in conventional vehicles, when the LiSOC is equal to or greater than a predetermined value, the lead battery can be allowed to be charged with the power stored in the lithium ion battery, thereby preventing the deterioration of the lithium ion battery from progressing.

[0006] However, if the system is configured to allow charging of the lead battery with power stored in the lithium ion battery only when the LiSOC is above a predetermined value, the lead battery will not be charged unless the LiSOC is above the predetermined value.

[0007] Therefore, if the system is configured to allow charging of the lead battery with power stored in the lithium-ion battery only when the LiSOC is above a predetermined value, the output voltage of the lead battery will drop, and the auxiliary system that operates on power supplied from the lead battery may not be able to operate.

[0008] The present invention has been made to solve the above-mentioned problems, and aims to provide a DC-DC converter control device that can prevent the auxiliary system from becoming unable to operate. [Means for solving the problem]

[0009] The DC-DC converter control device according to the present invention is installed in a vehicle having an engine, a motor capable of generating electricity by being driven by the engine, a first battery capable of being charged with the electricity generated by the motor, a second battery that supplies electricity to an auxiliary system, and a DC-DC converter that is configured to charge the second battery with the electricity charged in the first battery, and is configured to permit the DC-DC converter to charge the second battery with the electricity charged in the first battery when the charging rate of the first battery is equal to or higher than a predetermined value, and to permit the DC-DC converter to charge the second battery with the electricity charged in the first battery when the charging rate of the first battery is less than the predetermined value and if the engine is in a full combustion state. [Effects of the Invention]

[0010] The present invention can provide a DC-DC converter control device that can prevent an auxiliary system from becoming unable to operate. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram of a vehicle equipped with a DC-DC converter control device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a block diagram showing peripheral circuits of an ECM that constitutes a DC-DC converter control device according to one embodiment of the present invention. [Figure 3] FIG. 3 is a flowchart showing the DC-DC converter control operation of the DC-DC converter control device according to one embodiment of the present invention. [Figure 4] FIG. 4 is a timing diagram showing an example of the state of each part when the DC-DC converter control device according to one embodiment of the present invention does not execute a DC-DC converter control operation. [Figure 5] FIG. 5 is a timing diagram showing an example of the state of each part when the DC-DC converter control device according to one embodiment of the present invention executes a DC-DC converter control operation. DETAILED DESCRIPTION OF THE INVENTION

[0012] A DC-CDC converter control device according to one embodiment of the present invention is installed in a vehicle including an engine, a motor capable of generating electricity by being driven by the engine, a first battery capable of being charged with the electric power generated by the motor, a second battery that supplies electric power to an auxiliary system, and a DC-CDC converter configured to charge the second battery with the electric power charged in the first battery, and is characterized in that when the charging rate of the first battery is equal to or greater than a predetermined value, the DC-CDC converter is permitted to charge the second battery with the electric power charged in the first battery, and when the charging rate of the first battery is less than the predetermined value and the engine is in a full combustion state, the DC-CDC converter is permitted to charge the second battery with the electric power charged in the first battery. As a result, the DC-CDC converter control device according to one embodiment of the present invention can prevent the auxiliary system from becoming unable to operate. [Example]

[0013] A vehicle equipped with a DC-DC converter control device according to an embodiment of the present invention will be described below with reference to the drawings.

[0014] As shown in FIG. 1, the vehicle 10 includes an engine 20, an ISG 40, a transmission 30, wheels 12, an ECM (Electronic Control Module) 50, and a motor controller 51.

[0015] The engine 20 is formed with a plurality of cylinders. In this embodiment, the engine 20 is configured to perform a series of four strokes for each cylinder, including an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke.

[0016] The engine 20 is provided with a crank angle sensor 27 as an engine rotation speed detector. The crank angle sensor 27 detects the engine rotation speed based on the rotation position of the crankshaft 20A and transmits a detection signal to the ECM 50.

[0017] The transmission 30 changes the speed of the rotation transmitted from the engine 20 and drives the wheels 12 via the drive shaft 11.

[0018] The vehicle 10 is provided with a clutch 31 between the engine 20 and the transmission 30. The clutch 31 is a dry single-plate clutch. The clutch 31 has a flywheel 31A connected to the crankshaft 20A of the engine 20 and a clutch disc 31B connected to the input shaft 30A of the transmission 30.

[0019] The clutch 31 switches to a power transmitting state when the clutch disc 31B is frictionally engaged with the flywheel 31A, and switches to a non-power transmitting state when the clutch disc 31B is separated from the flywheel 31A.

[0020] The vehicle 10 is provided with a differential device 32 between the transmission 30 and the drive shafts 11, and this differential device 32 transmits the rotation transmitted from the transmission 30 to the left and right drive shafts 11 in a manner that allows differential rotation.

[0021] The vehicle 10 is equipped with a starter 26, which, in response to a command from the ECM 50, rotates a flywheel 31A connected to a crankshaft 20A, thereby starting the engine 20 for the first time.

[0022] The ISG 40 is a rotating electric machine that functions as both an electric motor that generates power when supplied with electric power and a generator that generates power using external power. In this way, the ISG 40 is a rotating electric machine that is capable of both regeneration and power running. The torque generated by the ISG 40 (hereinafter also referred to as ISG torque) is positive when the ISG 40 functions as an electric motor and powers, and is negative when the ISG 40 functions as a generator and regenerates.

[0023] The ISG 40 is always connected to the engine 20 via a winding transmission mechanism consisting of a pulley 41, a crank pulley 21, and a belt 42, and transmits power to and from the engine 20. More specifically, the ISG 40 has a rotating shaft 40A, and a pulley 41 is fixed to the rotating shaft 40A.

[0024] A crank pulley 21 is fixed to the other end of the crankshaft 20A of the engine 20. A belt 42 is wound around the crank pulley 21 and a pulley 41. A sprocket and chain may also be used as the winding transmission mechanism.

[0025] The power generated by the ISG 40 is transmitted to the wheels 12 via the crankshaft 20A of the engine 20, the transmission 30, and the drive shaft 11. The rotation of the wheels 12 is transmitted to the ISG 40 via the drive shaft 11, the transmission 30, and the crankshaft 20A of the engine 20, and is used for regenerative power generation in the ISG 40.

[0026] Therefore, the vehicle 10 can run not only by the power of the engine 20, but also by using the power of the ISG 40 to assist the engine 20. Furthermore, the vehicle 10 can run by the power of the ISG 40 while the operation of the engine 20 is stopped.

[0027] In this way, the vehicle 10 forms a parallel hybrid system that can run using at least one of the power of the engine 20 and the power of the ISG 40.

[0028] The torque and rotation speed of the ISG 40 are controlled by a motor controller 51. The motor controller 51 is electrically connected to the ECM 50 and controls the operation of the ISG 40 based on commands from the ECM 50.

[0029] The vehicle 10 includes a lithium ion battery 71 (referred to as LiB in the drawing), a lead battery 72 (referred to as PbB in the drawing), a DC-DC converter 73, and vehicle electrical components 74. The lithium ion battery 71 and the lead battery 72 are rechargeable secondary batteries.

[0030] The number of cells in the lithium-ion battery 71 is set so as to generate an output voltage of approximately 48 V. The number of cells in the lead battery 72 is set so as to generate an output voltage of approximately 12 V. The vehicle electrical components 74 are a collective term for various electrical components that operate at approximately 12 V, such as wipers, headlights, and a car navigation system. In this embodiment, the vehicle electrical components 74, together with the starter 26 and the ECM 50, constitute an auxiliary system.

[0031] The DC-DC converter 73 is electrically connected to the lithium-ion battery 71 and the ISG 40 via a 48V bus 76. The DC-DC converter 73 is also electrically connected to the lead battery 72 and the vehicle electrical components 74 via a 12V bus 77. In this embodiment, the vehicle 10 is equipped with a 48V hybrid system, and the ISG 40 operates at 48V. The DC-DC converter 73 converts voltage between the 48V bus 76 and the 12V bus 77.

[0032] In this embodiment, the ISG 40 operates at a voltage of 48 V, which allows it to generate a larger torque than when operated at a voltage of 12 V. Furthermore, the DC-DC converter 73 can convert 48 V to 12 V, allowing existing electrical components to operate at a voltage of 12 V. Furthermore, the current and heat generated in the 48 V bus 76 and the like can be suppressed, allowing the weight of the 48 V bus 76 and the like to be reduced.

[0033] Furthermore, since the power supply to the ISG 40 can be provided by the lithium ion battery 71 and the power supply to the vehicle electrical components 74 can be provided by the lead battery 72, the capacity of the DC-DC converter 73 can be reduced.

[0034] In this embodiment, the ISG 40 constitutes a motor that can generate electricity when driven by the engine 20. The lithium ion battery 71 constitutes a first battery that can be charged with the power generated by the ISG 40. The lead battery 72 constitutes a second battery that supplies power to the auxiliary system. The DC-DC converter 73 is provided so that the power charged in the lithium ion battery 71 can be charged into the lead battery 72.

[0035] The lithium ion battery 71 is provided with a battery controller 71A, which detects the terminal voltage, ambient temperature, and input / output current of the lithium ion battery 71, and outputs detection signals to the ECM 50.

[0036] The ECM 50 detects the state of charge (hereinafter simply referred to as "LiSOC") of the lithium ion battery 71 based on the terminal voltage, ambient temperature, and input / output current of the lithium ion battery 71. The LiSOC is managed by the ECM 50 within a predetermined management range (for example, a range from 30% to 70%).

[0037] The ECM50 is composed of a computer unit equipped with a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), flash memory for storing backup data, etc., input ports, output ports, and communication ports.

[0038] The ROM of this computer unit stores various constants, various maps, etc., as well as a program for causing the computer unit to function as the ECM 50. That is, the CPU executes the program stored in the ROM using the RAM as a work area, causing the computer unit to function as the ECM 50 in this embodiment.

[0039] 2, various sensors including a crank angle sensor 27 and a Pb current sensor 28 that detects input / output current of a lead battery 72 are connected to an input port of the ECM 50. Various controlled objects including a DC-DC converter 73 are connected to an output port of the ECM 50.

[0040] The communication port of the ECM 50 is connected to various controllers including a battery controller 71A and a motor controller 51. The ECM 50 controls various control targets and various controllers based on information obtained from various sensors and various controllers.

[0041] In this embodiment, the ECM 50 constitutes a DC-DC converter control device. For example, when the LiSOC is equal to or higher than a predetermined value TH, the ECM 50 allows the DC-DC converter 73 to perform step-down charging, which charges the lead battery 72 with the power stored in the lithium ion battery 71.

[0042] The predetermined value TH is set in advance to a value that allows the stopped engine 20 to be started by the ISG 40, with the lower limit being a value that does not cause deterioration of the lithium ion battery 71. During step-down charging, in addition to the power charged in the lithium ion battery 71, the power generated by the ISG 40 driven by the engine 20 is also charged into the lead battery 72.

[0043] In other words, during step-down charging, depending on the terminal voltage of the lithium ion battery 71 and the terminal voltage of the lead battery 72, the lithium ion battery 71 and the lead battery 72 may be charged with power generated by the ISG 40 driven by the engine 20.

[0044] When the LiSOC is less than the predetermined value TH, if the engine 20 is in a complete combustion state, the ECM 50 permits the DC-DC converter 73 to perform step-down charging, and if the engine 20 is not in a complete combustion state, the ECM 50 prohibits the DC-DC converter 73 from performing step-down charging.

[0045] If the engine 20 is operating autonomously, the ECM 50 determines that the engine 20 has reached a complete combustion. For example, if the rotation speed of the engine 20 based on the detection value of the crank angle sensor 27 remains at or above a predetermined speed for a certain period of time or longer, the ECM 50 determines that the engine 20 has reached a complete combustion.

[0046] In this way, even when the LiSOC is less than the predetermined value TH, as long as the engine 20 is fully exploded, the ECM 50 can charge the lead battery 72 with the electricity generated by the ISG 40 driven by the engine 20 without reducing the LiSOC, and therefore allows the DC-DC converter 73 to perform step-down charging.

[0047] The DC-DC converter control operation of the ECM 50 of the vehicle 10 configured as above will be described with reference to the flowchart shown in Figure 3. The DC-DC converter control operation described below is repeatedly executed while the ECM 50 is operating.

[0048] First, in S1, the ECM 50 determines whether the LiSOC is less than a predetermined value TH. If it is determined in S1 that the LiSOC is less than the predetermined value TH, the ECM 50 executes the process of S2. If it is determined in S1 that the LiSOC is not less than the predetermined value TH, the ECM 50 executes the process of S10.

[0049] In S2, the ECM 50 determines whether or not the engine 20 has completely exploded. If it is determined in S2 that the engine 20 has completely exploded, the ECM 50 executes the process of S3. If it is determined in S2 that the engine 20 has not completely exploded, the ECM 50 executes the process of S9.

[0050] In S3, the ECM 50 permits step-down charging by the DC-DC converter 73. After executing the process of S3, the ECM 50 executes the process of S4.

[0051] In S4, the ECM 50 determines whether a predetermined time has elapsed since the complete combustion of the engine 20. If it is determined in S4 that the predetermined time has elapsed since the complete combustion of the engine 20, the ECM 50 executes the process of S5.

[0052] If it is determined in S4 that the predetermined time has not elapsed since the engine 20 achieved complete combustion, the ECM 50 executes the process of S4. That is, if it is determined in S4 that the predetermined time has not elapsed since the engine 20 achieved complete combustion, the ECM 50 enters a state of waiting for the predetermined time to elapse.

[0053] In S5, the ECM 50 determines whether or not the lithium ion battery 71 is being charged. For example, the ECM 50 determines whether or not the lithium ion battery 71 is being charged based on the input / output current of the lithium ion battery 71 detected by the battery controller 71A.

[0054] If it is determined in S5 that the lithium ion battery 71 is being charged, the ECM 50 executes the process of S6. If it is determined in S5 that the lithium ion battery 71 is not being charged, the ECM 50 executes the process of S9.

[0055] In S6, the ECM 50 determines whether the lead battery 72 is being charged. For example, the ECM 50 determines whether the lead battery 72 is being charged based on the input / output current of the lead battery 72 detected by the Pb current sensor 28.

[0056] If it is determined in S6 that the lead battery 72 is being charged, the ECM 50 executes the process of S7. If it is determined in S6 that the lead battery 72 is not being charged, the ECM 50 executes the process of S9.

[0057] In S7, the ECM 50 determines whether the current LiSOC is higher than the LiSOC at the time of complete combustion of the engine 20. If it is determined in S7 that the current LiSOC is higher than the LiSOC at the time of complete combustion of the engine 20, the ECM 50 executes the process of S8. If it is determined in S7 that the current LiSOC is not higher than the LiSOC at the time of complete combustion of the engine 20, the ECM 50 executes the process of S9.

[0058] In S8, the ECM 50 determines whether the LiSOC is equal to or greater than a predetermined value TH. If it is determined in S8 that the LiSOC is equal to or greater than the predetermined value TH, the ECM 50 terminates the DC-DC converter control operation. If it is determined in S8 that the LiSOC is not equal to or greater than the predetermined value TH, the ECM 50 executes the process of S4.

[0059] In S9, the ECM 50 prohibits the DC-DC converter 73 from performing step-down charging. After executing the process of S9, the ECM 50 ends the DC-DC converter control operation. In S10, the ECM 50 permits the DC-DC converter 73 to perform step-down charging. After executing the process of S10, the ECM 50 ends the DC-DC converter control operation.

[0060] FIG. 4 is a timing chart showing the states of various parts of a vehicle that allow charging of the lead battery with power stored in the lithium ion battery only when the LiSOC is equal to or greater than a predetermined value.

[0061] Figure 4 shows, from top to bottom, examples of the engine speed, the terminal voltage of the lead battery (referred to as "Pb battery voltage" in the figure), the charge rate of the lead battery (hereinafter simply referred to as "PbSOC"), the LiSOC, the starter state, whether the engine is fully activated (referred to as "engine fully activated" in the figure), and whether step-down charging is permitted in the DC-DC converter (referred to as "DDC step-down state" in the figure).

[0062] Immediately before time t1 when the starter is activated, PbSOC is such that the engine can be started once, and if the lead battery is not charged immediately after the engine starts, power will not be supplied to the vehicle's electrical components, the ECM will not operate, and the engine will stall, and LiSOC is below the predetermined value TH.

[0063] At time t1, when the starter is activated, the engine speed starts to increase and the voltage across the terminals of the lead battery starts to decrease.

[0064] At time t2, when the engine explodes and the starter stops, the voltage across the lead battery terminals rises temporarily, but then begins to drop due to power consumption by the vehicle's electrical components. Also, as the engine explodes, the LiSOC begins to rise.

[0065] After that, because the LiSOC does not reach the predetermined value TH or higher, step-down charging of the DC-DC converter is not permitted. At time t3, the voltage between the lead battery terminals drops to a level where the ECM cannot operate. As a result, at time t3, the ECM stops and the engine stalls.

[0066] Fig. 5 is a timing chart showing the state of each part of the vehicle in this embodiment. Fig. 5 shows, from top to bottom, examples of the engine rotation speed, the voltage between the terminals of the lead battery 72 (referred to as "Pb battery voltage" in the figure), the state of the lead battery 72 (hereinafter simply referred to as "PbSOC"), the LiSOC, the input / output current of the lead battery 72 (referred to as "Pb battery actual current" in the figure), the input / output current of the lithium ion battery 71 (referred to as "Li battery actual current" in the figure), the state of the starter 26, whether the engine 20 is fully exploded (referred to as "engine fully exploded" in the figure), and whether step-down charging of the DC-DC converter 73 is permitted (referred to as "DDC step-down state" in the figure).

[0067] Immediately before time t11 when the starter is activated, the PbSOC is such that the engine 20 can be started once, and if the lead battery 72 is not charged immediately after the engine 20 is started, power will not be supplied to the auxiliary system, the ECM 50 will not be able to operate, and the engine 20 will stall, and the LiSOC is below the predetermined value TH.

[0068] At time t11, when the starter 26 enters an operating state, the engine speed begins to increase, the input / output current of the lead battery 72 begins to increase toward the discharge side, and the voltage between the terminals of the lead battery 72 begins to decrease.

[0069] At time t12, when the engine 20 explodes completely and the starter is stopped, the DC-DC converter 73 is permitted to perform step-down charging because the engine 20 explodes completely, even if the LiSOC does not reach or exceed the predetermined value TH.

[0070] At time t12, the starter is stopped, so that the input / output current of the lead battery 72 starts to increase toward the charging side, and the voltage between the terminals of the lead battery 72 starts to rise. At time t12, step-down charging is permitted in the DC-DC converter 73, so that the input / output current of the lead battery 72 and the voltage between the terminals of the lead battery 72 are maintained. At time t12, the engine 20 explodes completely, so that the LiSOC starts to rise.

[0071] In this way, even if the LiSOC does not reach or exceed the predetermined value TH, the complete combustion of the engine 20 allows the DC-DC converter 73 to perform step-down charging, so the voltage between the terminals of the lead battery 72 is maintained in a state in which the ECM 50 can operate. Therefore, the ECM 50 does not stop, and the engine 20 does not stall.

[0072] As described above, the DC-DC converter control device of this embodiment allows the DC-DC converter 73 to perform step-down charging if the engine 20 is in a complete explosion when the LiSOC is less than the predetermined value TH, thereby preventing the auxiliary system including the ECM 50 from becoming unable to operate.

[0073] In this embodiment, when the lithium ion battery 71 and the lead battery 72 are charged with electric power generated by the ISG 40 driven by the engine 20 during step-down charging, the lead battery 72 may be charged with priority over the lithium ion battery 71. This configuration allows the auxiliary system, particularly the ECM 50, to continue to operate more reliably.

[0074] While the present invention has been described with reference to an embodiment thereof, it will be apparent that modifications may be made thereto without departing from the scope of the present invention, and the present invention is disclosed with the understanding that equivalents of such modifications are intended to be encompassed within the scope of the appended claims. [Explanation of symbols]

[0075] 10 vehicles 20 Engine 26 Starter (auxiliary system) 40 ISG (motor) 50 ECM (DC-DC converter control device, auxiliary system) 71 Lithium-ion battery (first battery) 72 Lead acid battery (second battery) 73 DC-DC converter 74 Vehicle electrical components (auxiliary systems)

Claims

1. The engine and a motor capable of generating electricity by being driven by the engine; a first battery capable of being charged with power generated by the motor; a second battery that supplies power to the auxiliary system; a DC-DC converter configured to charge the second battery with the power charged in the first battery, When the charging rate of the first battery is equal to or higher than a predetermined value, the DC-DC converter is permitted to charge the second battery with the power charged in the first battery; A DC-DC converter control device characterized in that when the charging rate of the first battery is less than the predetermined value, if the engine is in a full combustion state, the DC-DC converter is permitted to charge the second battery with the power charged in the first battery.

2. 2. The DC-DC converter control device according to claim 1, wherein the output voltage of the first battery is higher than the output voltage of the second battery.

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