JP4221897B2 - Dual battery mounted vehicle power supply - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a dual battery-mounted vehicle power supply device.
[0002]
[Prior art]
In electric vehicles including hybrid vehicles, the dual power supply system that feeds power from the high-voltage main battery to the motor for driving and from the low-voltage auxiliary battery to low-voltage loads such as air conditioners and lighting devices is diverted to general-purpose machines as low-voltage loads. It is beneficial in that it can be done. Also in ordinary internal-combustion locomotives, high-power transmission such as engine start and engine torque assist is performed from a high-voltage main battery, and a two-battery power supply system that supplies power from a low-voltage auxiliary battery to a low-voltage load is installed as usual. There is momentum.
[0003]
In this dual-power-source vehicle power supply system, when the auxiliary battery has a small capacity and the auxiliary battery capacity is insufficient or when a high-power low-voltage load is driven, the terminal voltage of the low-voltage battery or the step-down DC- Since the output terminal voltage of the DC converter decreases, the transmission control from the high voltage battery to the low voltage battery is performed by controlling the step-down DC-DC converter so as to keep these voltages at a constant level.
[0004]
[Problems to be solved by the invention]
However, in the above-described two-battery-equipped vehicle power supply device, when driving a low-voltage load of high power, the voltage drop of the transmission line from the output terminal of the step-down DC-DC converter to the low-voltage load or the low voltage from the auxiliary battery The voltage drop of the power transmission line to the load increases, and as a result, there is a problem that the illuminance of the low-voltage load, particularly the headlight, decreases.
[0005]
Of course, if the cross-sectional areas of these transmission lines are increased, the above problem can be solved, but it is not easy to increase the area of the low-voltage transmission lines in terms of cost, low-voltage transmission line wiring space, and vehicle weight.
[0006]
The present invention has been made in view of the above-described problems, and is a two-battery-equipped vehicle power source that eliminates problems caused by low-voltage power feeding to low-voltage loads without increasing vehicle manufacturing costs, low-voltage transmission line wiring space, and vehicle weight. The purpose is to provide a device.
[0007]
[Means for Solving the Problems]
Two battery-mounted power supply system for vehicle according to claim 1 includes a high-voltage battery for supplying power to the high 圧負 load, a low voltage battery for supplying power to low 圧負 load, step-down DC powered from the high voltage battery to the low voltage battery A two-battery mounted vehicle power supply device comprising: a DC converter; and a voltage control circuit for controlling an output voltage of the step-down DC-DC converter.
It said voltage control circuit controls the output voltage to a predetermined target value based on the output voltage of the terminal voltage or the step-down DC-DC converter of the low-voltage battery, driving of the headlight as given the low load In this state, after the terminal voltage of the headlight is preferentially controlled to a predetermined target value, the target value is gradually returned to the original value .
[0008]
According to this configuration, it is possible to suppress voltage fluctuation of a predetermined low-voltage load such as a headlamp by using an output voltage control system of an existing step-down DC-DC converter. It is possible to prevent the voltage applied to the low-voltage load from being kept below the preferred range.
[0009]
In addition, when the predetermined low-voltage load is off, the output voltage of the low-voltage battery or the step-down DC-DC converter is controlled to be constant, so that voltage fluctuation of the low-voltage battery can be suppressed and frequent charge state fluctuation can be suppressed. Furthermore, the terminal voltage of the low voltage battery does not deviate from the optimum voltage over a long period of time.
[0012]
In a preferred embodiment, the voltage control circuit, the predetermined voltage of the higher end near the low load than that controls the predetermined target value, the power supply voltage of a predetermined load while avoiding the complication of the circuit scale and the control Problems due to fluctuations can be prevented.
[0013]
In a preferred embodiment, the voltage control circuit controls the terminal voltage of the predetermined low-voltage load to a constant target value Vref, which is the voltage of the transmission line from the predetermined low-voltage load to the low-voltage battery. When the variation amount of the drop is ΔV, Vref + ΔV is set to a value that is maintained in a suitable voltage range of the low-voltage battery. In this way, even when the terminal voltage of the low-voltage load is controlled to the constant target value Vref, the state of the low-voltage battery can always be kept good.
In a preferred aspect, the voltage control circuit performs the priority control when a predetermined high-power low-voltage load and a predetermined low-voltage load are simultaneously driven. As a result, the priority control is performed only when it is really necessary, so that voltage fluctuations of the low-voltage battery can be suppressed, and frequent charge state fluctuations can be further suppressed.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Preferred embodiments of the step-down DC-DC converter device of the present invention will be described with reference to the following examples.
[0019]
[Example 1]
An embodiment of a dual battery-mounted vehicle power supply device of the present invention will be described with reference to the circuit diagram shown in FIG.
(Circuit configuration)
This step-down DC-DC converter device is for voltage-converting power from a main battery 1 for driving energy storage of a hybrid vehicle to an auxiliary battery 2 for feeding auxiliary equipment and a control device. Is a smoothing capacitor, 4 is an inverter circuit formed by bridge connection of four MOS transistors, 5 is a voltage control circuit, 6 is a step-down transformer, 7 is a gate control circuit, and 8 is two rectifier diode elements for full-wave rectification A rectifying circuit 9 is a smoothing circuit including a choke coil 10 and a smoothing capacitor 11. The voltage control circuit 5 performs negative feedback control on the duty ratio of the PWM voltage of the inverter circuit in order to keep the voltage Vi inputted from the outside at a constant value. That is, the voltage control circuit 5 transmits a PWM signal whose duty ratio is adjusted so as to match the input voltage Vi to the target value Vref stored therein to the gate control circuit 7, and the gate control circuit 7 outputs it to a necessary level. And output to the inverter circuit 4 to adjust the duty ratio of the inverter circuit.
[0020]
The main battery 1 applies a high voltage (for example, 300 V) to the positive and negative DC input terminals of the inverter circuit 4 and the smoothing capacitor 3, and the inverter circuit 4 applies a PWM single-phase AC voltage to the transformer 6 at a carrier frequency of, for example, 20 kHz. The transformer 6 has a pair of secondary coils connected in the same direction, the middle point of these secondary coils is grounded, and the other end of both secondary coils is connected to each diode element of the rectifier circuit, The DC voltage rectified by the rectifier circuit 8 is smoothed by the smoothing circuit 9 and then sent to the auxiliary battery 2. The rated voltage of the auxiliary battery 2 is 12V.
[0021]
The operation of the step-down DC-DC converter circuit is well known and will not be described.
[0022]
As shown in FIG. 2, the low-voltage load circuit 20 includes an air-conditioning fan drive motor circuit 22, a headlamp drive circuit 23, and a large number of low-voltage loads fed from a power transmission line 21, and is fed from the auxiliary battery 2. The lower end of each low-pressure load is grounded to the vehicle body. The air conditioning fan drive motor circuit 22 is formed by connecting a motor and a relay (or transistor) for opening and closing the motor in series, and the headlamp drive circuit 23 is connected by connecting a headlamp and a relay (or transistor) for opening and closing the series. Become.
[0023]
Reference numeral 24 denotes an electronic control unit (ECU) for vehicle control, and 25 and 26 are analog switches made of, for example, PMOS transistors. The analog switch 25 selects the terminal voltage of the low voltage battery 2 and sends it to the input terminal of the voltage control circuit 5, and the analog switch 26 selects the terminal voltage of the headlamp drive circuit 23 and sends it to the input terminal of the voltage control circuit 5.
[0024]
The input voltage switching control operation of the voltage control circuit 5 executed by the vehicle control electronic control unit (ECU) 24 will be described below.
[0025]
The vehicle control electronic control unit (ECU) 24 controls opening and closing of the relay (or transistor) of the air conditioning fan drive motor circuit 22 and the relay (or transistor) of the headlamp drive circuit 23 based on an external input signal. At the same time, the analog switch 25 is turned off while the headlamp and the air conditioning fan drive motor are simultaneously turned on, the analog switch 25 is turned on, and the analog switch 25 is turned on while the headlamp and the air conditioning fan drive motor are not turned on simultaneously. Is turned on and the analog switch 25 is turned off.
[0026]
As a result, when both the air conditioning fan drive motor circuit 22 and the headlamp drive circuit 23 are turned on and the voltage drop of the power transmission line 21 between the auxiliary battery 2 and the headlamp drive circuit 23 is large, the headlamp drive circuit Since the terminal voltage of 23 is kept constant, it is possible to prevent the light quantity of the headlamp from fluctuating due to the intermittent operation of the air conditioning fan drive motor and giving the driver an uncomfortable feeling.
[0027]
[Example 2]
Another embodiment will be described below with reference to FIG.
[0028]
In this embodiment, the analog switches 25 and 26 are switched by the voltage of the air conditioning fan drive motor circuit 22 in the low voltage load circuit 20 of the first embodiment shown in FIG. Reference numeral 221 denotes a relay (transistor) of the air conditioning fan drive motor circuit 22, and 222 denotes an air conditioning fan drive motor. Reference numeral 231 denotes a relay (transistor) of the headlamp driving circuit 22, and 232 denotes a headlamp.
[0029]
When the relays 221 and 231 are turned on, the output signal of the AND circuit 27 becomes high level, the analog switch 26 of the multiplexer circuit is turned on, and the analog switch 25 is turned off. In other cases, the analog switch 25 is turned on and the analog switch 26 is turned off. In this way, the input voltage of the voltage control circuit 5 can be switched without going through the electronic control unit (ECU) 24. A similar logical operation may be performed inside the electronic control unit (ECU) 24.
[0030]
[Example 3]
Another embodiment will be described below with reference to FIG.
[0031]
In this embodiment, when the electronic control unit (ECU) 24 drives the air conditioning fan drive motor circuit 22 and the headlamp drive circuit 23 in the low voltage load circuit 20 of the first embodiment shown in FIG. By changing the internal target value Vref by a predetermined value ΔV, the voltage of the power transmission line 21 from the auxiliary battery 2 to the headlamp drive circuit 23 when the air conditioning fan drive motor circuit 22 and the headlamp drive circuit 23 are simultaneously driven. Its feature is to compensate for the descent.
[0032]
Consider a case where the auxiliary battery 2 is near the power transmission line 21 and the air conditioning fan drive motor circuit 22 and the headlamp drive circuit 23 are far from the power transmission line 21 when viewed from the step-down DC-DC converter. In this case, since both the devices 22 and 23 are simultaneously turned on, the terminal voltage of the headlamp driving circuit 23 is reduced by a predetermined value due to the voltage drop of the transmission line 21, so that the voltage control circuit is set to a value substantially equal to the predetermined value. The target value Vref of 5 is increased. As a result, it is possible to prevent a decrease in the amount of light of the headlamp during the drive period of both devices 22 and 23.
[0033]
On the contrary, as viewed from the step-down DC-DC converter, consider the case where the auxiliary battery 2 is located on the power transmission line 21 and the air conditioning fan drive motor circuit 22 and the headlamp drive circuit 23 are located on the power transmission line 21. . In this case, since both the devices 22 and 23 are simultaneously turned on, the terminal voltage of the headlamp driving circuit 23 rises by a predetermined value due to the voltage rise of the power transmission line 21, so that the voltage control circuit is increased by a value substantially equal to the predetermined value. 5 target value Vref is lowered. As a result, it is possible to prevent a decrease in the amount of light of the headlamp during the drive period of both devices 22 and 23.
[0034]
(Modification)
In the above embodiment, the target value Vref of the step-down DC-DC converter is switched while the air-conditioning fan drive motor circuit 22 and the headlamp drive circuit 23 are simultaneously turned on. However, the change in the light quantity of the headlamp is slow. If so, the target value Vref may be gradually returned to the original value after switching the target value Vref by simultaneously turning on both devices using the visual characteristic that it cannot be distinguished. By doing so, it is possible to prevent the terminal voltage of the auxiliary battery 2 from deviating from the optimum voltage over a long period of time.
[0035]
[Example 4]
Another embodiment will be described below with reference to FIG.
[0036]
In this embodiment, the terminal voltage of the headlamp driving circuit 23 is always set to the input voltage Vi to the voltage control circuit 5 in the low voltage load circuit 20 of the first embodiment shown in FIG. The voltage drop of the power transmission line 21 from the auxiliary battery 2 to the headlamp drive circuit 23 is set within a predetermined value.
[0037]
In this way, it is possible to suppress a change in the amount of light of the headlamp without increasing the circuit scale at all.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an embodiment of a dual battery-mounted vehicle power supply device of the present invention.
FIG. 2 is a circuit diagram showing a low voltage load circuit of the apparatus shown in FIG. 1;
FIG. 3 is a circuit diagram showing another embodiment.
FIG. 4 is a circuit diagram showing another embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Main battery 2 Auxiliary battery 4 Inverter circuit 5 Voltage control circuit 6 Step-down transformer 8 Rectifier circuit 9 Smoothing circuit 21 Air-conditioning fan drive motor circuit 22 Headlamp drive circuit 24 Electronic control unit (ECU)

Claims (3)

A high-voltage battery for supplying power to the high 圧負 load,
A low voltage battery for supplying power to low 圧負 load,
A step-down DC-DC converter that feeds power from the high-voltage battery to the low-voltage battery;
A voltage control circuit for controlling the output voltage of the step-down DC-DC converter;
In a two-battery-equipped vehicle power supply device comprising:
It said voltage control circuit controls the output voltage to a predetermined target value based on the output voltage of the terminal voltage or the step-down DC-DC converter of the low-voltage battery, driving of the headlight as given the low load A two-battery-equipped vehicle power supply device characterized in that, in a state, the terminal voltage of the headlight is preferentially controlled to a predetermined target value, and then the target value is gradually returned to the original value . 2. The two-battery-equipped vehicle power supply device according to claim 1, wherein the voltage control circuit controls a voltage in the vicinity of a high end of the predetermined low-voltage load to a predetermined target value. Power supply. In the two-battery mounted vehicle power supply device according to claim 1 or 2 ,
It said voltage control circuit includes two battery-mounted vehicle power supplies, characterized in that performing the priority control at the time of simultaneous driving of said predetermined low pressure load and a predetermined high-power low-voltage load.

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