JP2006298240A - Power control device for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power control device for a vehicle which can securely control an energy loss due to the conversion of voltage during the supply of power from a high-voltage system to a low-voltage system. <P>SOLUTION: The power control device for the vehicle is provided with a high-voltage battery 10, a low-voltage battery 20, and a DC/DC converter 30 for outputting the voltage which is obtained by performing a step-down conversion of the voltage of the high-voltage system. When the low-voltage system voltage falls below the output voltage of the DC/DC converter 30, the power supply to the load 21, which is a subject to be backed up, is switched from the power supply from the low-voltage battery 20 to the power supply from the high-voltage battery 10 through the medium of the DC/DC converter 30. The DC/DC converter 30 outputs the first output voltage before the action of an engine which causes voltage fluctuations of the low-voltage system, and the first output voltage is smaller than the maximum allowable voltage of the back-up load 21. Then after the action of the engine, the second output voltage is outputted which is smaller than the first output voltage and is slightly larger than the minimum operating voltage of the back-up load 21. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a vehicle power supply control device for performing voltage conversion from a high voltage system to a low voltage system to supply power.

Conventionally, a high-voltage battery and a low-voltage battery for auxiliary equipment have been provided, and power corresponding to the power consumption of the auxiliary equipment can be supplied from the high-voltage battery to the low-voltage system via the DC / DC converter. Power devices are known. (For example, refer to Patent Document 1).
JP 2004-320877 A

  By the way, when supplying power from a high-voltage battery to a low-voltage auxiliary machine, etc., it is necessary to convert the high voltage of the high-voltage battery to a low voltage. Will occur. In this regard, in the above-described prior art, when the low-voltage battery is not in a good state such as a voltage drop or a remaining capacity drop, the DC / DC converter set to a low voltage output to compensate for the shortage of power However, when the power was supplied, the energy loss due to voltage conversion could not be sufficiently suppressed.

  Accordingly, an object of the present invention is to provide a vehicle power supply control device that can reliably suppress energy loss due to voltage conversion when power is supplied from a high voltage system to a low voltage system.

In order to solve the above problems, according to one aspect of the present invention,
A high-voltage power supply,
A low-voltage power supply,
Conversion means for outputting a voltage obtained by stepping down the voltage of the high voltage system,
When the voltage of the low voltage system is lower than the output voltage of the conversion means, the power supply to the low voltage system load is switched from the power supply from the low voltage system power supply to the power supply from the high voltage system power supply via the conversion means. In a vehicle power supply control device,
The conversion means outputs a first output voltage smaller than a maximum allowable voltage of the low voltage system load before the operation of the power source that causes voltage fluctuations in the low voltage system, and after the operation of the power source, the first output voltage is output. A vehicle power supply control device is provided that outputs a second output voltage that is smaller than the output voltage of the low-voltage system load and slightly higher than the minimum operating voltage of the low-voltage system load.

  According to this aspect, the power supply from the high voltage system power supply is adjusted so that the maximum allowable voltage of the low voltage system load is not exceeded before the operation of the power source, so that the low voltage system load is protected. Can do. On the other hand, in the stage after the operation of the power source, the power supply from the high voltage system power supply is adjusted so as not to fall below the minimum operating voltage of the low voltage system load, so that the operating voltage of the low voltage system load is secured. The power supply from the high voltage system power supply is switched to a power supply from the high voltage system power supply at a voltage slightly higher than the minimum operating voltage of the low voltage system load, so that the power supply from the low voltage system power supply continues even if a slight voltage drop occurs. When power is supplied to the voltage system, energy loss due to voltage conversion can be reliably suppressed.

  The low voltage system load may include a backup target load that always requires power supply, and the minimum operating voltage may be the minimum operating voltage of the backup target load. In this case, the operation of a load that needs to be backed up in terms of power supply among the low-voltage system loads can be protected intensively, and the redundancy of power supply can be improved.

  ADVANTAGE OF THE INVENTION According to this invention, when supplying electric power from a high voltage system to a low voltage system, the energy loss by voltage conversion can be suppressed reliably.

  The best mode for carrying out the present invention will be described below with reference to the drawings. FIG. 1 is a system configuration diagram showing an embodiment of a vehicle power supply control device of the present invention. A vehicle equipped with the vehicle power supply control device includes a high voltage system power source 10 (high voltage battery 10), a low voltage system power source 20 (low voltage battery 20), and a high voltage system voltage. A DC / DC converter 30 that performs step-down conversion and outputs, and an electronic control unit (ECU) 40 that controls the DC / DC converter 30 are provided.

  There are cases where a plurality of loads exist on the vehicle but loads of different voltage systems may coexist, and the high voltage battery 10 mainly corresponds to power supply to the high voltage system load 12 that operates at a high voltage system voltage. The low voltage battery 20 mainly corresponds to power supply to a low voltage system load 22 (including a backup target load 21 described later) that operates at a low voltage system voltage. For example, the high voltage battery 10 is a lithium ion battery with a high power density, and the low voltage battery 20 is an inexpensive lead battery with a low power density. What is necessary is just to select the kind of battery according to electric power supply capability. In addition, the load includes a lamp, an audio, an ECU, an electronic component, a solenoid valve, an air conditioner, and other auxiliary devices, but the present invention is not particularly limited to the type of load.

  The ECU 40 includes a plurality of circuit elements such as a microcomputer, a ROM that stores programs, a RAM that temporarily stores data, an input interface, and an output interface as a unit. The ECU 40 outputs a control signal for operating the DC / DC converter 30 and a control signal for operating the relay 26. Further, the ECU 40 detects the charge / discharge current of the low voltage battery 20 by the current sensor 25.

  The DC / DC converter 30 performs step-down conversion from a high voltage system voltage to a low voltage system voltage by a step-down mechanism inside the DC / DC converter 30 such as a transformer, a switching regulator, or a series regulator, and outputs the voltage. The step-down converted output voltage is monitored by a converter control circuit in the DC / DC converter 30 and controlled so that the output voltage becomes constant. The converter control circuit can arbitrarily set the output voltage. By using the step-down conversion function of the DC / DC converter 30, it is possible to supply power to the low voltage system load 22 by the high voltage battery 10 and to charge the low voltage battery 20 by the high voltage battery 10.

  When the DC / DC converter 30 is activated, power can be supplied to the backup target load 21 which is a low voltage system load. When the relay 26 is further turned on, the power supply to the low voltage system load 22 and the low voltage battery 20 are performed. Can be charged.

  The backup target load 21 is a load that always requires power supply. For example, an electric brake system that controls an electric foot brake and an electric parking brake, a Mayday (emergency notification) system that can notify the outside in the event of an accident or failure, and a volatile memory that stores a learning value, an abnormal code, and the like. Electric power is supplied to these loads even when the engine start key is OFF. Accordingly, the electric brake system that is supplied with electric power even when the engine is not started can automatically generate the braking force by the brake actuator regardless of whether or not the driver performs a braking operation. Similarly, the Mayday system and the volatile memory can effectively exhibit their functions when power is always supplied.

  The backup target load 21 has a power supply path via a diode 27 and a power supply path via a diode 28, and the power supply path has a so-called diode OR connection configuration. That is, the circuit including the diodes 27 and 28 has a function of outputting the higher one of the low-voltage system voltage Va and the output voltage Vb of the DC / DC converter 30 to the backup target load 21 side. As apparent from FIG. 1, the backup target load 21 is always supplied with power from the low voltage battery 20 via the diode 27, and from the high voltage battery 30 via the diode 28 and the DC / DC converter 30. Power supply is received. That is, the backup target load 21 has a redundant power supply path.

  The operation of the vehicle power supply control device of the present invention in this embodiment will now be described. The voltage Va of the low voltage system fluctuates due to an increase in current consumption due to the operation of the load of the low voltage system (for example, the operation of the starter 24 that starts the engine that is the power source of the vehicle or the operation of other circuits), It fluctuates due to insufficient capacity of the low voltage battery 20 or poor terminal contact. In particular, since the starter 24 operates with a large amount of power, the voltage Va of the low voltage system tends to fluctuate when the starter 24 operates. Further, even after the operation of the engine, the voltage Va fluctuates due to an increase in the number of loads that start to operate as compared with a static state before the operation of the engine (before the starter 24 operates). Therefore, when the low-voltage system voltage Va, which is easily affected by voltage fluctuations, falls below the output voltage Vb of the DC / DC converter 30, the power supply to the low-voltage system load 22 and the backup target load 21 is from the low-voltage battery 20. The power supply is switched to the power supply from the high voltage battery 10 via the DC / DC converter 30.

  FIG. 2 is a diagram illustrating a voltage state when the engine is started. When the energy of the low-voltage battery 20 is not enough to activate the starter 24 before starting the engine, the engine cannot be started. In that case, the low voltage battery 20 is charged so that the starter 24 can be operated and the engine can be started by supplying power from the high voltage battery 10 via the DC / DC converter 30.

  When the ECU 40 detects that the low voltage system voltage Va is equal to or lower than a predetermined voltage value at which the engine cannot be started before starting the engine, the ECU 40 controls the control signal for turning on the relay 26 and the start time control for operating the DC / DC converter 30. Output a signal. The DC / DC converter 30 (internal converter control circuit) that has received the start-up control signal in the vehicle control device of the present invention has an output voltage smaller than the maximum allowable voltage of the low voltage system load 22 or the backup target load 21. Set to value. For example, when the maximum allowable voltage of the low voltage system load 22 or the backup target load 21 is 15.5V, the DC / DC converter 30 sets the output voltage to 14.5V. With this setting, the DC / DC converter 30 controls 14.5 V to be the upper limit value of the output voltage and not to output any more voltage.

  When the relay 26 is turned on and the DC / DC converter 30 is operated, the potentials Va and Vb are set to the output voltage of the DC / DC converter 30 from Vx (voltage at which the engine cannot be started) as shown in FIG. It rises to 14.5V. That is, in the period A in FIG. 2, the low voltage battery 20 is charged up to 14.5V by the power supply from the high voltage battery 10 via the DC / DC converter 30, and the period in FIG. After B, power supply from the high voltage battery 10 is completed and charging of the low voltage battery 20 is completed. Accordingly, since the output voltage of the DC / DC converter 30 is set so as not to exceed the maximum allowable voltage of the low voltage system load 22 or the backup target load 21, the low voltage system load 22 or the backup target load 21 is protected. be able to. In addition, overcharging of the low voltage battery 20 can be prevented.

  FIG. 3 is a diagram illustrating a voltage state when the voltage of the low voltage battery 20 is lowered. Normally, power is supplied to the low voltage system load 22 and the backup target load 21 by the low voltage battery 20 and the alternator 23. When the low voltage system voltage Va is lower than the output voltage Vb of the DC / DC converter 30, the low voltage The power supply to the system load 22 and the backup target load 21 is switched from the power supply from the low voltage battery 20 to the power supply from the high voltage battery 10 via the DC / DC converter 30.

  When the ECU 40 detects that the voltage Va of the low voltage system is equal to or higher than a predetermined voltage value (for example, a voltage value that does not interfere with the operation of each load), the ECU 40 turns off the relay 26 and a DC / DC converter. An output voltage setting control signal for setting the output voltage of 30 is output. The DC / DC converter 30 (internal converter control circuit) receiving the voltage setting control signal in the vehicle control device of the present invention is smaller than the maximum allowable voltage of the backup target load 21 and slightly less than the minimum operating voltage of the backup target load 21. Set the output voltage to a larger voltage value. For example, when the minimum operating voltage Vy of the backup target load 21 is 10 V, the DC / DC converter 30 sets the output voltage to 10.2 V that is slightly larger than the minimum operating voltage Vy. With this setting, the DC / DC converter 30 always controls the output voltage Vb to be 10.2 V, and controls so as not to output a voltage lower than that.

  As shown in FIG. 3, when an increase in current consumption occurs, the voltage Va, which has been 13 V, gradually drops and may reach 10.2 V of the output voltage Vb of the DC / DC converter 30. The circuit composed of the diodes 27 and 28 has a function of outputting the higher one of the low voltage system voltage Va and the output voltage Vb of the DC / DC converter 30 to the backup target load 21 side. That is, during the period C in which the low voltage system voltage Va is equal to or higher than the output voltage Vb of the DC / DC converter 30, the low voltage battery 20 and the alternator 23 supply power to the backup target load 21, but the low voltage system voltage Va. In a period D during which the output voltage Vb is lower than the output voltage Vb of the DC / DC converter 30, power is supplied from the high voltage battery 10 via the DC / DC converter 30 to the backup target load 21.

  Therefore, since the power supply from the high voltage battery 10 is adjusted so as not to fall below the minimum operating voltage of the backup target load 21, the backup target load 21 can be reliably operated.

  Furthermore, since the power supply from the high voltage battery 10 is switched to a voltage slightly higher than the minimum operating voltage of the load 21 to be backed up, a slight voltage drop (a DC / DC converter in FIG. Even if a voltage drop that does not reach 10.2 V of the output voltage Vb of 30 occurs, the power supply from the low-voltage battery 20 continues and does not switch to the power supply from the high-voltage battery 10. Therefore, when current flows from the high voltage battery 10 to the backup target load 21 via the DC / DC converter 30 and the diode 28, energy is consumed by voltage conversion when power is supplied from the high voltage system to the low voltage system. However, even if a slight voltage drop occurs as described above, no current is supplied to the backup target load 21 via the DC / DC converter 30 and the diode 28, and no power is supplied from the high voltage battery 10. Thereby, it is possible to suppress frequent power supply from the high voltage battery 10 due to a voltage drop, and to reliably suppress energy loss due to voltage conversion when supplying power from the high voltage system to the low voltage system. be able to.

  In other words, in order to suppress frequent occurrence of power supply from the high voltage battery 10 due to a voltage drop, the output voltage Vb of the DC / DC converter 30 is set to be as low as possible with respect to the normal low voltage system voltage Va. Set to be smaller. The output voltage Vb is set in consideration of an assumed voltage drop, energy loss due to voltage conversion when power is supplied from the high voltage system to the low voltage system, and the minimum operating voltage Vy. As a result, the difference between the output voltage Vb and the minimum operating voltage Vy is relatively larger than the difference between the low voltage system voltage Va and the output voltage Vb.

  The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the present invention. Can be added.

  For example, the power supply path is not switched using the diodes 27 and 28, but a switch for monitoring the voltage of Va and Vb is provided, and switching to connect to the higher path of Va and Vb detected by the sensor. A switch may be provided.

1 is a system configuration diagram showing an embodiment of a vehicle power supply control device of the present invention. It is a figure which shows the voltage state at the time of engine starting. 3 is a diagram illustrating a voltage state when the voltage of the low voltage battery 20 is lowered. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 High voltage battery 12 High voltage system load 20 Low voltage battery 21 Backup object load 22 Low voltage system load 26 Relay 30 DC / DC converter

Claims (2)

A high-voltage power supply,
A low-voltage power supply,
Conversion means for outputting a voltage obtained by stepping down the voltage of the high voltage system,
When the voltage of the low voltage system is lower than the output voltage of the conversion means, the power supply to the low voltage system load is switched from the power supply from the low voltage system power supply to the power supply from the high voltage system power supply via the conversion means. In a vehicle power supply control device,
The conversion means outputs a first output voltage smaller than a maximum allowable voltage of the low voltage system load before the operation of the power source that causes voltage fluctuations in the low voltage system, and after the operation of the power source, the first output voltage is output. A vehicle power supply control device that outputs a second output voltage that is smaller than the output voltage of the low-voltage system load and slightly higher than the minimum operating voltage of the low-voltage load. The vehicle power supply control device according to claim 1,
The low-voltage load includes a backup target load that always needs to be supplied with power, and the minimum operating voltage is the minimum operating voltage of the backup target load.

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