JP2015179613A - Vehicle power supply system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently cool a DC-DC converter of a vehicle power supply system.SOLUTION: A high voltage power storage section is connected to a motor generator. A DC-DC converter 12 is disposed between a route to which a low voltage power storage section, having a lower voltage than the high voltage power storage section, is connected, and a route to which a high voltage power storage section is connected. A cooling mechanism cools a high voltage power storage section and a DC-DC converter with the same cooling medium. The cooling mechanism includes: a feed passage 201 of the cooling medium which is disposed on one surface orthogonal to a plurality of gaps of a battery pack; an exhaust passage 214, disposed on the opposite surface, for collecting the cooling medium which was fed to a plurality of gaps 202-213 from the feed passage 201; and a coupling path 205 for feeding the cooling medium from the exhaust passage 214 to the DC-DC converter 12.

Description

  The present invention relates to a vehicle power supply system to be mounted on a vehicle.

  In recent years, mild hybrid vehicles that increase the effects of regeneration and assist with a motor generator using a 48V power supply have attracted attention. Mild hybrid vehicles can be less expensive than strong hybrid vehicles. Generally, the 48V power supply and the existing 12V power supply for auxiliary equipment are electrically connected via a DC-DC converter.

JP 2014-14270 A

  Heat is generated when the voltage is converted by the DC-DC converter. In particular, a large amount of current may flow in an in-vehicle application, and thus a large amount of heat may be generated. Therefore, a cooling mechanism for the DC-DC converter is required, but in a mild hybrid vehicle where low cost is required, the cooling mechanism is also required to be efficient.

  This invention is made | formed in view of such a condition, The objective is to provide the technique which cools the DC-DC converter of a vehicle power supply system efficiently.

  In order to solve the above problems, a vehicle power supply system according to an aspect of the present invention includes a high-voltage power storage unit connected to a motor generator, a path to which a low-voltage power storage unit having a lower voltage than the high-voltage power storage unit is connected, A DC-DC converter provided between a path to which the high-voltage power storage unit is connected, and a cooling mechanism that cools the high-voltage power storage unit and the DC-DC converter with the same cooling medium.

  ADVANTAGE OF THE INVENTION According to this invention, the DC-DC converter of the power supply system for vehicles can be cooled efficiently.

It is a figure for demonstrating the vehicle-mounted electrical storage system which concerns on embodiment of this invention. It is a figure which shows the IV characteristic of a 5 Ah lithium ion battery and a 25 Ah lithium ion battery. It is a figure which shows the IV characteristic of a 25 Ah lithium ion battery. It is a schematic diagram for demonstrating the cooling mechanism of the lithium ion battery of FIG. 1, and a bidirectional | two-way DC-DC converter.

  FIG. 1 is a diagram showing a schematic configuration of an electrical system of a vehicle 100 according to an embodiment of the present invention. In the present embodiment, a mild hybrid type vehicle 100 is assumed. There are two types of hybrid cars: strong hybrid type and mild hybrid type. The strong hybrid type is equipped with a relatively large secondary battery and a motor, and can travel with the energy stored in the secondary battery even when the engine is stopped. The mild hybrid type is equipped with a relatively small secondary battery and a motor, and in principle, does not run when the engine is stopped, and is mainly a power assist type using the energy stored in the secondary battery. The mild hybrid type does not have as much fuel economy as the strong hybrid type, but it has a simple structure and can be configured at a relatively low cost. Generally, the mild hybrid type employs a parallel method. The parallel system is a system in which wheels can be driven by both an engine and a motor. On the other hand, the serial system is a system in which the energy generated by the engine is stored in a secondary battery and the wheels are driven exclusively by a motor.

  A vehicle 100 shown in FIG. 1 includes a power supply system 10, a motor generator 20, a 48V system load 30, a lead battery 40, a 12V system load 50, a starter 60, a second switch S2, and an alternator 70. The power supply system 10 includes a lithium ion battery 11, a first switch S1, a resistor R1, a bidirectional DC-DC converter 12, and a control device 13. The control device 13 includes a voltage / current detection circuit 14, a processing unit 15, a storage unit 16, and a drive circuit 17. The lithium ion battery 11, the motor generator 20, and the 48V system load 30 are connected to the 48V system current path Ph. Lead battery 40, 12V system load 50, starter 60 and alternator 70 are connected to 12V system current path Pl. The bidirectional DC-DC converter 12 is provided between the 12V system current path Pl and the 48V system current path Ph.

  A vehicle 100 shown in FIG. 1 includes an engine (not shown) and a motor generator 20 as power sources. The motor generator 20 integrates a motor and an alternator, and is configured to be able to switch between a power running mode that functions as a motor and a regeneration mode that functions as a generator. The motor generator 20 is composed of a small three-phase AC synchronous motor, for example. In the power running mode, the motor generator 20 rotates based on the power supplied from the lead battery 40 via the lithium ion battery 11 or the bidirectional DC-DC converter 12, and assists the start and acceleration of the vehicle 100. In the low speed region, a mode in which the motor generator 20 can be driven only by the driving force may be set. In the regeneration mode, power is generated by rotation based on the deceleration energy of the vehicle, and the generated power is output to the 48V system current path Ph.

  The alternator 70 generates electric power with engine torque (not shown) and outputs the generated electric power to the 12V system current path Pl. The starter 60 is connected to the 12V system current path Pl through the second switch S2. A relay, IGBT, MOSFET or the like can be used for the second switch S2. The starter 60 is an engine starting motor. When an ignition switch (not shown) is turned on by a driver's operation or when returning from an idling stop state, the second switch S2 is turned on based on a control signal from an ECU (Electronic Control Unit) (not shown). When an engine (not shown) is started, the second switch S2 is turned off.

  Various types of loads (auxiliary machines) are provided in the vehicle 100 in addition to the motor generator 20 and the starter 60. For example, loads such as a headlight, an air conditioner, a defogger, an audio, a meter, a stop lamp, a fog lamp, a winker, a power steering, a power window, and an engine electrical component are provided. In a system in which only a conventional 12V system power supply exists, all loads are connected to the 12V system. On the other hand, in a system in which a 48V system power supply is mounted as in the present embodiment, a load (for example, an air conditioner) with large power consumption can be connected to the 48V system power supply. Thereby, the current value of the load with large power consumption can be reduced. The designer of the vehicle manufacturer can appropriately select whether each of the various loads in the vehicle 100 is connected to the 12V system current path Pl or the 48V system current path Ph. In the present embodiment, a load connected to the 12V system current path Pl is represented as a 12V system load 50, and a load connected to the 48V system current path Ph is represented as a 48V system load 30.

  The lead battery 40 is constituted by six lead battery cells having a representative voltage of 2.0V connected in series, and is a battery mainly for supplying power to the starter 60 and the 12V system load 50.

  The lithium ion battery 11 according to the present embodiment uses an NCM ternary lithium transition metal compound as a positive electrode active material and graphite as a negative electrode active material. The lithium ion battery 11 is configured by connecting twelve or thirteen lithium ion battery cells having a representative voltage of 3.6 to 3.7 V in series.

  The useable voltage range of each lithium ion battery cell is set to 2.0V to 4.3V. Therefore, the operating voltage range of the lithium ion battery 11 when 12 are connected in series is 24.0 to 51.6 V, and the operating voltage range of the lithium ion battery 11 when 13 are connected in series is 26.0 V to 55. .9V. Since the strict insulation process is unnecessary at 60V or less, the upper limit voltage is suppressed to 60V or less. 13 series should be adopted from the viewpoint of increasing electric power during discharging, but 12 series should be adopted from the viewpoint of protecting the lithium ion battery 11 by suppressing the charging voltage. Designers can select as appropriate based on the circumstances of each country. The capacity of the lithium ion battery 11 is designed to be 20 Ah or more, more preferably 25 Ah or more.

  The first switch S1 is connected between the lithium ion battery 11 and the 48V system current path Ph. A relay, IGBT, MOSFET, or the like can be used for the first switch S1. A resistor R 1 is connected in series with the lithium ion battery 11. The resistor R <b> 1 is a shunt resistor for detecting a current flowing through the lithium ion battery 11. A Hall element may be used instead of the resistor R1.

  The voltage / current detection circuit 14 of the control device 13 detects the voltage of each cell of the lithium ion battery 11. The voltage / current detection circuit 14 outputs each detected cell voltage value to the processing unit 15. The voltage / current detection circuit 14 detects the voltage across the resistor R1 and outputs a current value corresponding to the detected voltage across the resistor 15 to the processing unit 15. The voltage / current detection circuit 14 can be configured by an ASIC (Application Specific Integrated Circuit) which is a dedicated custom IC.

  The processing unit 15 executes a process for managing and controlling the lithium ion battery 11 in cooperation with the storage unit 16. The processing unit 15 can be composed of a CPU, and the storage unit 16 can be composed of ROM and RAM. The processing unit 15 can communicate with the ECU via a CAN (Controller Area Network) (not shown).

  The processing unit 15 estimates the SOC of the lithium ion battery 11 based on the voltage value and / or current value detected by the voltage / current detection circuit 14. The SOC can be estimated by, for example, an OCV (Open Circuit Voltage) method or a current integration method. Since these estimation methods are general techniques, their detailed description is omitted.

  The processing unit 15 generates a control signal for controlling on / off of the first switch S1 based on the estimated SOC and / or an instruction signal from the ECU. Further, the processing unit 15 generates a control signal for controlling the operation / stop of the bidirectional DC-DC converter 12 based on the estimated SOC and / or an instruction signal from the ECU. Those control signals are output to the drive circuit 17. The drive circuit 17 is a drive signal for turning on / off the first switch S1 and a drive signal for turning on / off the switching element of the bidirectional DC-DC converter 12 based on the control signal from the processing unit 15. Is generated.

  In this embodiment, a lithium ion battery is used as the 48V power supply. Lithium ion batteries are more vulnerable to overcharge and overdischarge than lead batteries, and need a protection function to prevent them. Lithium ion batteries are generally used in HEV applications with an SOC range of 20-80%. Moreover, in PHEV and EV use, it is common to use in 10 to 95% of range. In the present embodiment, the lithium ion battery 11 is used in an SOC range of 30 to 70% in principle. This avoids overcharging and overdischarging and enables safer operation.

  FIG. 2 is a diagram showing IV characteristics of a 5 Ah lithium ion battery and a 25 Ah lithium ion battery. FIG. 2 (a) shows IV characteristics when discharged from a lithium ion battery for 1 second in an environment of −30 ° C., and FIG. 2 (b) shows 10 seconds from the lithium ion battery in an environment of −30 ° C. The IV characteristics when discharged are shown.

  As described above, in the present embodiment, the lithium ion battery 11 of 20 Ah or more is used. Hereinafter, it is assumed that a 25 Ah lithium ion battery is used. The 50% SOC IV characteristic of a 25 Ah lithium ion battery is approximately equal to the 80% SOC IV characteristic of a 5 Ah lithium ion battery. That is, if SOC of 50% is secured in the 25 Ah lithium ion battery, power corresponding to 80% SOC of the 5 Ah lithium ion battery can be supplied to the load.

  As described above, in this embodiment, the use SOC range of the lithium ion battery 11 is set to 30 to 70% in principle. The energy sufficiently stored by not using the low SOC region is secured as a backup power source for the load connected to the 12V system current path Pl. In particular, it is secured as a backup power source for the starter 60. If the starter 60 cannot be started with the vehicle 100 stopped, it is difficult to start the engine.

  The lower limit set value of the SOC of the lithium ion battery 11 according to the embodiment is set to be equal to or higher than the SOC to be secured as a backup power source for the load connected to the 12V system current path Pl. Specifically, it is set to be equal to or higher than the SOC necessary for operating the starter 60. In the present embodiment, a starter 60 having a power of 3.0 kW necessary for operating for 1 second in an environment of −28 ° C. is used. Therefore, it is necessary to ensure in the lithium ion battery 11 an SOC that can supply power of 3.0 kW or more in an environment of −28 ° C.

  FIG. 3 is a diagram showing IV characteristics of a 25 Ah lithium ion battery. FIG. 3 shows IV characteristics when discharging is performed for 1 second from a state of SOC 30% in an environment of −30 ° C. When the lithium ion battery in this state is discharged at a current of 125 A, the cell voltage becomes 2.0 to 2.5V. In the 12-series configuration, the discharge voltage is 24.0 to 30.0 V, and falls within the range of 24.0 to 51.6 V in the 12-series working voltage range. In the 13-series configuration, the discharge voltage is 26.0 to 32.5 V, and falls within the range of 26.0 V to 55.9 V in the 13-series operating voltage range.

  When discharged in a 12-series configuration with a current of 125 A and a voltage of 24.0 V, 3.0 kW of power can be supplied to the load. In the 13-series configuration, more power can be supplied to the load. Therefore, in this embodiment, the backup power source for operating the starter 60 can be secured in the lithium ion battery 11 by keeping the SOC of the 25 Ah lithium ion battery 11 at 30% or more.

  When the SOC of the lithium ion battery 11 falls below the lower limit set value (30% in the present embodiment), the processing unit 15 generates a control signal for turning off the first switch S1 and outputs the control signal to the drive circuit 17. The drive circuit 17 generates a drive signal for turning off the first switch S1, and supplies the drive signal to the first switch S1. As a result, the first switch S1 is turned off.

  In the above configuration, a large current of 250 A or more may flow through the 48V system current path Ph. In the mild hybrid type, the voltage of the motor generator 20 is lower than in the strong hybrid type, so that a larger current flows than in the strong hybrid type when the load increases. In that case, the heat generation of the bidirectional DC-DC converter 12 and the lithium ion battery 11 also increases. The temperature of the bidirectional DC-DC converter 12 may rise to around 100 ° C. Therefore, a bidirectional DC-DC converter 12 and a cooling device for the lithium ion battery 11 are required.

  In the present embodiment, the lithium ion battery 11 and the bidirectional DC-DC converter 12 are housed and integrated in the same casing, and cooled by the same cooling medium. As a result, the power supply system 10 can be saved in space, and the cost can be reduced by reducing the number of parts. In the present embodiment, it is assumed that the lithium ion battery 11 and the bidirectional DC-DC converter 12 are cooled by an air cooling method.

  FIG. 4 is a schematic diagram for explaining a cooling mechanism of the lithium ion battery 11 and the bidirectional DC-DC converter 12 of FIG. FIG. 4 is a view of the lithium ion battery 11, the bidirectional DC-DC converter 12, and the control device 13 as viewed from above. The lithium ion battery 11 in FIG. 4 is composed of an assembled battery in which a plurality of (13 in FIG. 4) rectangular lithium ion battery cells 111 to 1113 are connected. A separator (not shown) is provided between each of the plurality of lithium ion battery cells 111 to 1113, and air gaps 202 to 213 are secured between the cells. In addition, end plates (not shown) are respectively provided on both end surfaces of the plurality of lithium ion battery cells 111 to 1113 in the arrangement direction, and the plurality of lithium ion battery cells 111 to 1113 are bound from both end surfaces.

  A cooling medium supply path 201 is provided on one surface of the assembled battery orthogonal to the plurality of gaps 202 to 213. The supply path 201 is connected to the blower 200 and feeds the cooling medium flowing from the blower 200 into the plurality of gaps 202 to 213. Thereby, the some lithium ion battery cells 111-1113 are cooled.

  A cooling medium discharge path 214 is provided on the surface opposite to the surface on which the supply path 201 of the assembled battery is provided, which is orthogonal to the plurality of gaps 202 to 213. The discharge path 214 collects the cooling medium sent from the supply path 201 to the plurality of gaps 202 to 213. The temperature of the recovered cooling medium is higher than before being sent into the plurality of gaps 202 to 213 due to the heat of the plurality of lithium ion battery cells 111 to 1113.

  The bidirectional DC-DC converter 12 is disposed on the side where the discharge path 214 of the assembled battery is provided. The bidirectional DC-DC converter 12 is housed in a casing, and an intake port of the casing and an exhaust port of the discharge path 214 of the assembled battery are connected by a connection path 215. The cooling medium recovered from the plurality of gaps 202 to 213 in the discharge path 214 is sent out into the casing of the bidirectional DC-DC converter 12 via the connection path 215. Thereby, the bidirectional DC-DC converter 12 is cooled.

  As described above, the temperature of the bidirectional DC-DC converter 12 may rise up to around 100 ° C. at the maximum. On the other hand, the temperature of the lithium ion battery 11 rises only up to around 70 ° C. at the maximum. The optimum operating temperature range of the bidirectional DC-DC converter 12 varies depending on the model, but is 25 to 75 ° C.

  When the bidirectional DC-DC converter 12 and the lithium ion battery 11 are cooled with the same cooling medium, if the bidirectional DC-DC converter 12 is cooled first, the temperature may rise to a temperature at which the lithium ion battery 11 cannot be sufficiently cooled. There is sex. On the other hand, even if the lithium ion battery 11 is cooled first, it does not rise to a temperature at which the bidirectional DC-DC converter 12 cannot be sufficiently cooled. Based on the above knowledge, in FIG. 4, the path of the cooling medium is designed in the order of the lithium ion battery 11 → the bidirectional DC-DC converter 12.

  The circuit board of the control device 13 is disposed on the side of the surface where the assembled battery supply path 201 is provided. That is, the bidirectional DC-DC converter 12 and the control device 13 are arranged with the lithium ion battery 11 interposed therebetween. The bidirectional DC-DC converter 12 generally has a circuit configuration in which a bridge circuit is provided on the primary side of the insulation transformer, and the bridge circuit includes a plurality of switching elements. The output voltage or output current is controlled by controlling the duty ratios or phase differences of the plurality of switching elements. Switching noise occurs when the plurality of switching elements are switched. This noise may cause the ASIC and CPU in the control device 13 to malfunction.

  In the present embodiment, the lithium ion battery 11 is used as a noise shield by sandwiching the lithium ion battery 11 between them. The influence of noise can be reduced by increasing the distance between the control device 13 and the bidirectional DC-DC converter 12 or providing a dedicated insulation shield between them, but the former leads to an increase in the arrangement space and the latter increases the cost. Leads to.

  As described above, according to the present embodiment, by using the same cooling mechanism for the lithium ion battery 11 and the bidirectional DC-DC converter 12, the power supply system 10 can be saved and the cost can be reduced by reducing the number of parts. Can be planned. In addition, by cooling in the order of the lithium ion battery 11 → the bidirectional DC-DC converter 12, it is possible to prevent the cooling effect from being lost due to an excessive increase in the temperature of the cooling medium. Further, by arranging the control device 13 and the bidirectional DC-DC converter 12 with the lithium ion battery 11 interposed therebetween, the influence of the switching noise generated from the bidirectional DC-DC converter 12 on the control device 13 can be reduced.

  The present invention has been described based on the embodiments. Those skilled in the art will understand that these embodiments are exemplifications, and that various modifications can be made to the combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. By the way.

  In the above-described embodiment, the air-cooling type cooling mechanism has been described. However, the liquid-cooling type cooling mechanism also differs in that a path for cooling in the order of the lithium ion battery 11 → the bidirectional DC-DC converter 12 is provided. There is no.

  In the above-described embodiment, the bidirectional DC-DC converter 12 is arranged on the side of the surface on which the discharge path 214 of the assembled battery is provided. This is an arrangement for shortening the connection path 215, and the arrangement. It is not limited to. For example, the bidirectional DC-DC converter 12 may be arranged on the side of the surface on which the assembled battery supply path 201 is provided. In this case, the circuit board of the control device 13 is disposed on the side where the discharge path 214 for the assembled battery is provided. Even in this arrangement, the lithium ion battery 11 can be utilized as a noise shield.

  Further, in the above-described embodiment, the example in which the 12V lead battery 40 is used as the low voltage power storage unit and the 48V lithium ion battery 11 is used as the high voltage power storage unit has been described. This configuration is an example and is not limited to the configuration. For example, a 36V lithium ion battery may be used for the high-voltage power storage unit. Further, instead of the lithium ion battery, another power storage device such as a nickel metal hydride battery or an electric double layer capacitor may be used for the high voltage power storage unit. Moreover, you may use a 24V lead battery for a low voltage electrical storage part. In addition, instead of the lead battery, other power storage devices such as a nickel metal hydride battery, a lithium ion battery, and an electric double layer capacitor may be used for the low-voltage power storage unit.

  Further, in the vehicle 100 according to the above-described embodiment, a configuration in which the alternator 70 is not provided is also possible. In this case, it is necessary to limit the opportunity of the power generation mode of the motor generator 20 and generate power by the engine torque other than during deceleration. For example, the motor generator is limited to the time of starting and accelerating, and the motor generator 20 generates power with the torque of the engine when the speed change is within a certain range. In this configuration, bidirectional DC-DC converter 12 operates almost always, and lead battery 40 charges the electric power generated by motor generator 20.

  100 vehicle, 10 power supply system, 20 motor generator, 30 48V system load, 40 lead battery, 50 12V system load, 60 starter, 70 alternator, 11 lithium ion battery, 12 bidirectional DC-DC converter, 13 control device, 14 voltage Current detection circuit, 15 processing unit, 16 storage unit, 17 drive circuit, S1 first switch, S2 second switch, R1 resistance, Pl 12V system current path, Ph 48V system current path, 111 to 1113 lithium ion battery cell, 200 Blower, 201 supply path, 202-213 gap, 214 discharge path, 215 connection path.

Claims (6)

A high-voltage power storage unit connected to the motor generator;
A DC-DC converter provided between a path to which a low voltage power storage unit having a lower voltage than the high voltage power storage unit is connected and a path to which the high voltage power storage unit is connected;
A cooling mechanism for cooling the high-voltage power storage unit and the DC-DC converter with the same cooling medium;
A vehicle power supply system comprising: The high-voltage power storage unit is composed of an assembled battery in which a plurality of battery cells are connected,
A gap is provided between the battery cells of the assembled battery,
The cooling mechanism is
A cooling medium supply path provided on one surface orthogonal to the plurality of gaps of the assembled battery, and a discharge for collecting the cooling medium fed from the supply path to the plurality of gaps provided on the opposite surface Road,
A connection path for sending a cooling medium from the discharge path to the DC-DC converter;
The vehicle power supply system according to claim 1, comprising:   3. The vehicle power supply system according to claim 2, wherein the DC-DC converter is arranged on a surface side of the assembled battery where the discharge path is provided. A control device for managing and controlling the high-voltage power storage unit;
The vehicular power supply system according to claim 3, wherein the control device is disposed on a surface side of the assembled battery where the supply path is provided. The low-voltage power storage unit is configured by connecting six lead battery cells having a representative voltage of 2.0 V in series,
The high-voltage power storage unit is configured by twelve lithium-ion battery cells having a representative voltage of 3.6 to 3.7 V connected in series, and a working voltage range is set to 24.0 to 51.6 V. The power supply system for vehicles in any one of Claim 1 to 4. The low-voltage power storage unit is configured by connecting six lead battery cells having a representative voltage of 2.0 V in series,
The high-voltage power storage unit is composed of 13 lithium ion battery cells having a representative voltage of 3.6 to 3.7 V connected in series, and a working voltage range is set to 26.0 to 55.9 V. The power supply system for vehicles in any one of Claim 1 to 4.

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