Battery charging management system for a vehicle

Abstract

Battery charging management system for a vehicle having two batteries (6, 30) with different charging characteristics, wherein the battery charging management system comprises: a load control section (51) configured to control the level of electrical load applied to at least one of the two batteries (6, 30); and a connecting switch (34) that enables or interrupts an electrical connection between the two batteries (6, 30), wherein, in the case of a requirement for electrical connection between the two batteries (6, 30), the load control section (51) enables electrical connection between the two batteries (6, 30) after the level of electrical load has been gradually varied until the difference in battery voltage between the two batteries (6, 30) becomes less than the specified value.

Description

[Technical field]

[0001] The present invention relates to a battery charging management system for a vehicle. [Previous state of the art]

[0002] A vehicle incorporating a hybrid powertrain has a traction battery or battery pack that is used in an electric vehicle (EV) mode and has at least one power supply battery to supply power to electrical loads. Two different types of batteries can be used to supply power to the loads.

[0003] JP 2014-033 571 A discloses a system that includes two different types of batteries to supply current to electrical loads and that includes a connecting switch provided to interrupt an electrical connection between the batteries.

[0004] EP 2 950 419 A1 generally discloses a control system for a power supply comprising a plurality of voltage sources. The voltage is adjusted either by charging, through the supply of electrical energy from a power generator to a storage battery with the lowest output voltage among a plurality of storage batteries, or by discharging, through the supply of electrical energy from a storage battery with the highest output voltage among the plurality of storage batteries to a load circuit connected to the storage battery with the highest output voltage.

[0005] US 2007 / 0102212A1 discloses a system for controlling the supply of electrical energy to electrical / electronic consumers or loads installed in a motor vehicle. In particular, an electrical energy supply system is disclosed for supplying predetermined consumers without priority and predetermined consumers with priority, the energy supply of which can be reduced and / or delayed or interrupted. [Brief description of the invention][Technical problem]

[0006] In the power supply system described in JP 2014-033 571 A, when the connecting switch interrupts the electrical connection between the power supply batteries to allow each battery to provide an isolated power supply to its associated loads, there is a difference in terminal voltage (or battery voltage) between the batteries. Because of this difference, an abrupt change in battery voltage occurs when the electrical connection between the batteries is re-established while the connecting switch is in the "on" state.

[0007] Since the power supply to the loads changes when the battery voltage abruptly changes, there will be a change in the brightness of the lights and a change in the noise of the fan(s). Sometimes such changes can cause a feeling of discomfort for a vehicle occupant.

[0008] One object of the present invention is to reduce changes in brightness during lighting and changes in the noise of a fan (or fans) powered by a battery, in order to reduce a feeling of discomfort that may arise for a vehicle occupant. [Solution to the problem]

[0009] According to one aspect, a battery charging management system is provided for a vehicle having two batteries with different charging characteristics, wherein the battery charging management system comprises: a load control section configured to control the level of electrical load applied to at least one of the two batteries; and a connection switch that enables or disables an electrical connection between the two batteries, wherein, in the event of a request for electrical connection between the two batteries, when a difference in the battery voltage between the two batteries is not less than a predetermined value, the load control section enables the electrical connection between the two batteries after the level of electrical load has been gradually varied until the difference in the battery voltage between the two batteries becomes less than the predetermined value. [Advantageous effect of the invention]

[0010] According to the present invention, a battery charging management system is provided which is able to reduce a feeling of discomfort that may arise for a vehicle occupant. [Brief description of the drawings] Fig. Figure 1 is a diagram of a vehicle representing a battery charging management system; Fig. Figure 2 is a flowchart that represents an algorithm for battery connection processes; Fig. Figure 3 is a flowchart that represents an algorithm for a battery charging process; Fig. Figure 4 is a diagram of a time sequence representing battery connection processes; Fig. Figure 5 is a diagram of a time sequence representing a battery charging process. [Description of one embodiment (of embodiments)]

[0011] With reference to the attached drawings, a vehicle equipped with a battery charging management system is described.

[0012] As in Fig. As shown in Figure 1, a vehicle 1 includes an internal combustion engine 2, an integrated starter generator (ISG) 3, general loads 4, critical loads 5, a lead-acid battery 6, a battery pack 7, and an internal combustion engine control module (ECM) 8.

[0013] The internal combustion engine 2 is designed with multiple cylinders. In this example, the internal combustion engine 2 is a four-stroke engine, meaning that four piston strokes are necessary to complete one cycle. The cycle comprises four distinct processes: intake stroke, compression stroke, power stroke, and exhaust stroke.

[0014] The ISG 3 is connected to an output shaft of the internal combustion engine 2 via a belt or similar device. When current is supplied, the ISG 3 functions as an electric motor, and it also functions as a generator, producing current when torque is applied from the drive wheel(s) or the internal combustion engine 2.

[0015] General loads 4 are electrical loads that allow fluctuations in the supply of an electric current. These general loads 4 include, for example, a blower fan 10; a radiator fan 11 that cools the coolant for the internal combustion engine 2; an electric water pump 12 that circulates the coolant in the internal combustion engine 2; an electric vacuum pump 13 that creates a vacuum used to provide power assistance for a braking system; and interior lighting 14.

[0016] Important loads 5 are electrical loads that require a stable supply of electrical current. Examples of important loads 5 include a navigation system 20; an audio system 21; a measuring instrument (or instruments) 22; a control panel 23 for a vehicle air conditioning system; a vehicle headlight 24; a steering angle sensor 25; and an on-board camera 16.

[0017] The lead-acid battery 6 is a rechargeable secondary battery with a voltage of 12 volts. The lead-acid battery 6 is connected to the general loads 4 to continuously supply them with an electrical current. The lead-acid battery 6 supplies an electrical current to the ISG 3 when the ISG 3 is to function as an electric motor, and it is recharged by the ISG 3 when the ISG 3 is to function as a generator.

[0018] The battery pack 7 includes a lithium-ion battery 30; switches 31, 32 and 33, a connecting switch 34; and a battery management system (BMS) 35. The battery pack 7 has an input end 36 and an output end 37.

[0019] The input end 36 is connected via a fuse 38 to the general loads 4 and the lead-acid battery 6. The output end 37 is connected to the critical loads 5. The output end 37 includes a first terminal 37a, a second terminal 37b, and a third terminal 37c. The first terminal 37a is enabled for connection to the critical loads 5 when switch 31 is in the on state. The second terminal 37b is enabled for connection to the critical loads 5 when switch 32 is in the on state, provided that switch 31 is in the on state. The third terminal 37c is enabled for connection to the critical loads 5 when switch 33 is in the on state, provided that switch 31 is in the on state.

[0020] The lithium-ion battery 30 is a rechargeable secondary battery with a voltage of 12 volts. Vehicle 1 is equipped with a motor-generator (not shown). A second battery, providing electrical current for the motor-generator, is another lithium-ion battery with a voltage of 100 volts.

[0021] In the following description, the lead-acid battery 6 and the lithium-ion battery 30 are also referred to as "two batteries". The lithium-ion battery 30 has a voltage sensor 39.

[0022] Under the control of the BMS 35, the switch 31 is set to the on or off state. When the switch 31 is in the off state, the lithium-ion battery 30 is completely disconnected from the input end 36 and the output end 37. When the switch 31 is in the on state, the lithium-ion battery 30 is connected to both the input end 36 and the output end 37.

[0023] Under the control of the BMS 35, the switch 32 is set to the on or off state in response to the state of an accessory switch 40, which is simply referred to as "ACC" in the following description. When the switch 31 or the switch 32 is in the off state, the lithium-ion battery 30 is completely disconnected from the second terminal 37b.

[0024] When switches 31 and 32 are in the ON state, the lithium-ion battery 30 is connected to the second terminal 37b, which allows the supply of current to that portion of the important loads 5 which is to be activated when the ACC 40 is in the ON state.

[0025] Under the control of the BMS 35, the switch 33 is set to the on or off state in response to the state of an ignition switch 41, which is simply referred to as "IG" in the following description. When the switch 31 or the switch 33 is in the off state, the lithium-ion battery 30 is completely disconnected from the third terminal 37c.

[0026] When switches 31 and 33 are in the ON state, the lithium-ion battery 30 is connected to the third terminal 37c, which allows current to be supplied to that proportion of the important loads that needs to be activated when IG 41 is in the ON state.

[0027] The connecting switch 34 enables or interrupts an electrical connection between the two batteries 6 and 30, which have different charging characteristics. Under the control of the BMS 35, the connecting switch 34 is set to the on or off state in response to instructions from the ECM 8.

[0028] When switch 31 or connecting switch 34 is in the off state, the lead-acid battery 6 and the lithium-ion battery 30 are completely disconnected. When switch 31 and connecting switch 34 are in the on state, the lead-acid battery 6 and the lithium-ion battery 30 are connected in parallel. The following example explains how switch 31 is normally in the on state.

[0029] In the present example, the BMS 35 consists of a computer unit that includes a central processing unit (CPU), random access memory (RAM), read-only memory (ROM), flash memory for data backup, input ports and output ports.

[0030] The ROM of this computer unit stores programs, along with various constants and characteristic maps, to enable the computer unit to function as the BMS 35. In other words, it makes the computer unit function as the BMS 35 by allowing the CPU to execute programs stored in the ROM, using the RAM as a working area.

[0031] The BMS 35 communicates with other control units, such as the ECM 8, via a local area network (LAN) that meets Controller Area Network (CAN) or FlexRay standards and is connected to a network module.

[0032] In the present example, the BMS 35 controls the switching on / off between the on state and the off state of each of the switches 31, 32 and 33 and the connecting switch 34 in response to the states of the ACC 40 and the IG 41 and the instructions from the ECM 8.

[0033] In the present example, the ECM 8 consists of a computer unit that includes a CPU, RAM, ROM, flash memory for data backup, input ports and output ports.

[0034] The ROM of this computer unit stores programs, along with various constants and characteristic maps, to enable the computer unit to function as the ECM 8. In other words, it makes the computer unit function as the ECM 8 by allowing the CPU to execute programs stored in the ROM, using the RAM as a workspace. The ECM 8 communicates bidirectionally with other control units, such as the BMS 35, via LAN connected to the network module.

[0035] In this example, sensors provided for the internal combustion engine 2 and the ISG 3 are connected to the input terminals of the ECM 8. The output terminals of the ECM 8 are connected to each section of the internal combustion engine 2 and to each of the objects to be controlled, such as the ISG 3 and the general loads.

[0036] The ECM 8 controls the various objects to be controlled and the other control units, such as the BMS 35, based on information it receives from various sensors and the other control units, such as the BMS 35.

[0037] In the present example, the ECM 8 acts as a voltage sensor 50 that detects a terminal voltage of the lead-acid battery 6, as well as a load control section 51 that controls the amount of load applied to each of the two batteries.

[0038] In the event that an electrical connection between the two batteries 6 and 30 is required, the ECM 8 enables the electrical connection between the two batteries 6 and 30, provided that the difference in battery voltage (i.e., terminal voltage) between the two batteries 6 and 30 is not less than a predefined value THv. This is achieved by gradually varying the electrical load until the difference in battery voltage between the two batteries 6 and 30 becomes less than the predefined value THv. The predefined value THv is determined experimentally.

[0039] In electric vehicle (EV) mode, when vehicle 1 is powered solely by the motor-generator, the combustion engine 2 is switched off, and the electrical connection between the two batteries 6 and 30 is interrupted. During this operating time, the lead-acid battery 6 provides power only for the general loads 4, and the lithium-ion battery 30 provides power only for the critical loads 5.

[0040] The process of establishing an electrical connection between the two batteries 6 and 30, and the process of recharging the battery by operating the ISG 3, are automated when the combustion engine 3 is restarted by factors such as a drop in remaining battery capacity, the need to operate a vehicle air conditioning system, and the need for warm-up. If the difference in battery voltage between the two batteries 6 and 30 is not less than the specified value THv, the ECM 8 gradually increases the electrical load applied to the battery with the higher voltage, in order to bring its voltage closer to that of the other battery.The ECM 8 increases the electrical load at a gradual rate that falls within a range where the driver experiences a barely noticeable effect. This range is pre-programmed into the ECM 8's ROM.

[0041] The ECM 8 determines, for example, whether the difference in battery voltage between a detection value of voltage sensor 50 and a detection value of voltage sensor 39 is not less than the preset value THv, that is, whether the difference in battery voltage between the two batteries 6 and 30 is not less than the preset value THv. The ECM 8 increases the electrical load applied to the lead-acid battery 6 by gradually varying the degree of activation of the general loads 4, such as the radiator fan 11, the electric water pump 12, and the electric vacuum pump 13, until the difference in battery voltage between the two batteries 6 and 30 becomes less than the preset value THv.

[0042] The ECM 8 instructs the BMS 35 to turn the connecting switch 34 into the ON state at a time when the difference in battery voltage between the two batteries 6 and 30 becomes smaller than the specified value THv.

[0043] The ECM 8 acts as a power generation control section 52, which controls the power generation torque of the ISG 3. The ECM 8 periodically changes the rate at which the power generation torque varies, while maintaining the rate of increase within a predetermined range of values, when the ISG 3 is caused to generate power.

[0044] After the electrical connection between the two batteries 6 and 30 is established, the batteries 6 and 30 are charged with a current generated by the ISG 3. The ECM 8 increases the current generation torque by periodically combining a time period when the rate of change is low with a time period when the rate of change is high, until the battery voltage of the lead-acid battery 6 and that of the lithium-ion battery 30 reach their target values. The ECM 8 varies the level of electrical load at a gradual rate that falls within a range where the driver of the vehicle experiences a barely perceptible effect. This range is pre-stored in the ROM of the ECM 8.

[0045] The ECM 8, for example, periodically increases the power generation torque of the ISG 3 by dividing each time period into a first sub-period T1 and a second sub-period T2. The second sub-period T2 is longer than the first sub-period T1.

[0046] The ECM 8 controls the rate of increase such that the power generation torque of the ISG 3 is increased by a first rate of increase d1 during the first sub-period T1 and by a second rate of increase during the second sub-period T2. The second rate of increase T2 is lower than the first rate of increase T1. The first sub-period T1, the second sub-period T2, the first rate of increase d1, and the second rate of increase d2 are predefined values.

[0047] Referring to Fig. Section 2 describes the operation of the battery charging management system for enabling or interrupting the electrical connection between the lead-acid battery 6 and the lithium-ion battery 30. The operation described below is repeated until the process of connecting the two batteries 6 and 30 is complete after the combustion engine 2 has been restarted.

[0048] Step S1 determines whether the difference in battery voltage between the two batteries 6 and 30 is less than the specified value THv, i.e., whether (V Pb - V Li ) ≥ THv is or is not, where V Pb The battery voltage of the lead-acid battery 6, which is detected by the voltage sensor 50, and V LiThe battery voltage of the lithium-ion battery 30 is detected by the voltage sensor 39. This determination can be carried out by the ECM 8.

[0049] If, at step S1, it is determined that V Pb - V Li If the value is not less than THv, then the algorithm advances to step S2. If, at step S1, V Pb - V Li If THv is smaller than THv, then the algorithm advances to step S3.

[0050] In step S2, an electrical load applied to (or carried by) the lead-acid battery 6 is increased. After step S2, the algorithm returns to step S1. In step S3, an electrical connection between the two batteries 6 and 30 is established. The increase in electrical load and the electrical connection can be controlled by the ECM 8.

[0051] Referring to Fig. Section 3 describes the processes of the battery charging management system with regard to a charging operation. The execution of the operation described below is repeated until the battery charging process is complete, after the electrical connection between the two batteries 6 and 30 has been established.

[0052] Step S11 triggers ISG 3 to start generating electricity if it is not currently generating any. After step S11, the algorithm proceeds to step S12. The processes performed in step S11 can be carried out by ECM 8.

[0053] Step S12 determines whether the current state exists during the first sub-period T1. If step S12 determines that the current state exists during the first sub-period T1, the algorithm proceeds to step S13. If step S12 determines that the current state does not exist during the first sub-period T1 (or in other words, if the current state exists during a second sub-period T2, where T1 < T2), the algorithm proceeds to step S14. This determination can be performed by the ECM 8.

[0054] In step S13, the power generation torque is increased by the ISG 3 with a first rate of increase d1. After step S13, the algorithm returns to its initial state. In step S14, the power generation torque is increased by the ISG 3 with a second rate of increase d2, where d2 < d1. After step S14, the algorithm returns to its initial state.

[0055] The internal resistance of the lithium-ion battery 30 is lower than that of the lead-acid battery 6, so the former has a higher charging power than the latter. Thus, the charging of the lithium-ion battery 30 is completed before the charging of the lead-acid battery 6 is completed when the batteries 30 and 6 are connected.

[0056] Therefore, when it is determined that charging of the lithium-ion battery 30 is complete, the ECM 8 instructs the BMS 35 to switch the connection switch 34 to the off state. When charging of the lead-acid battery 6 is complete, the ISG 3 is subsequently instructed to stop power generation.

[0057] Referring to Fig. 4 further describes the operation of the battery charging management system for enabling or interrupting the electrical connection between the lead-acid battery 6 and the lithium-ion battery 30.

[0058] At time t1, the combustion engine 2 is shut down and the vehicle 1 is powered solely by the engine generator. Then, at time t2, it is determined that at least one of the lead-acid battery 6 and one of the lithium-ion battery 30 require recharging, and immediately after time t2, the measure of the general load 4 is varied in steps to account for the difference in battery voltage between the two batteries 6 and 30, i.e., V1. Pb - V Li , to reduce it so that it becomes smaller than the specified value THv.

[0059] At time t3, the combustion engine 2 is started. At time t4, the voltage difference between the two batteries 6 and 30 becomes smaller than the predetermined value THv. BMS 35 is instructed by ECM 8 to switch the connection switch 34 to the ON state to enable the electrical connection between the lead-acid battery 6 and the lithium-ion battery 30.

[0060] Referring to Fig. Section 5 describes the processes related to the charging process of the battery charging management system.

[0061] At time t4, the lead-acid battery 6 and the lithium-ion battery 30 are connected. Charging of the lead-acid battery 6 and the lithium-ion battery 30 begins at time t5. Until time t6 after time t5, i.e., until the first sub-period T1 has elapsed, the ISG 3 is caused to increase the power generation torque at the first rate of increase d1. Until time t7 after time t6, i.e., until the second sub-period T2 has elapsed, the ISG 3 is caused to increase the power generation torque at the second rate of increase d2.

[0062] Until time t8 after time t7, i.e., until the first sub-period T1 has elapsed, the ISG 3 is caused to increase the power generation torque at the first rate of increase d1. Until time t9 after time t8, i.e., until the second sub-period T2 has elapsed, the ISG 3 is caused to increase the power generation torque at the second rate of increase d2.

[0063] As described, the power generation torque of the ISG 3 is periodically varied, keeping the rate of increase within the specified range. Once the charging of the lithium-ion battery 30 is complete, the connecting switch 34 is then switched to the off state. Once the charging of the lead-acid battery 6 is complete, the ISG 3 is then instructed to stop power generation.

[0064] As can be seen from the foregoing description, the present embodiment prevents rapid changes in the voltage applied to the electrical loads when the two batteries 6 and 30 are connected. Therefore, this reduces changes in lighting brightness and fan noise, thus minimizing any potential discomfort experienced by the vehicle occupant.

[0065] Furthermore, in the present embodiment, the level of power generation can reach the target level in a shorter time because the power generation torque is increased, with the rate of increase being changed periodically.

[0066] Furthermore, changes in lighting brightness and fan noise can be reduced to such an extent that the vehicle occupant does not feel such changes.

[0067] In the present example, the embodiment is described under the assumption that V Pb higher than V Li is. If V Pb lower than V Li The battery voltage of the lead-acid battery, i.e. V, is... Pb , increased by the ECM 8 by increasing the control level generated by the ISG 3.

[0068] In the present example, the ISG is used as a power generator. The embodiment can use an alternator or the like as such a power generator. [Description of reference symbols] 1 hybrid electric vehicle 3 integrated starter generator (ISG) (generator) 4 general load (electrical load) 6 Lead-acid battery (battery) 34 connecting switches 39 Voltage sensor 50 voltage sensor 51 Load Control Section 52 Power generation control section

Claims

[1] Battery charging management system for a vehicle having two batteries (6, 30) with different charging characteristics, wherein the battery charging management system comprises: a load control section (51) configured to control the level of electrical load applied to at least one of the two batteries (6, 30); and a connecting switch (34) that enables or interrupts an electrical connection between the two batteries (6, 30), wherein, in the case of a requirement for electrical connection between the two batteries (6, 30), the load control section (51) enables electrical connection between the two batteries (6, 30) after the level of electrical load has been gradually varied until the difference in battery voltage between the two batteries (6, 30) becomes less than the specified value. [2] Battery charging management system according to claim 1, further comprising: a power generator (3); and a power generation control section (52) configured to control the power generation torque through the power generator (3), wherein the power generation control section (52) periodically varies the power generation torque, the rate of increase being kept within the specified range in the event of a demand for power generation by the power generator (3).

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