JPS59147279A - Battery capacity meter for electric vehicle - Google Patents

Abstract

PURPOSE:To enable indication of residual capacity of a battery based on a discharge rate by calculating it based on a open voltage-to-discharge rate characteristic after a terminal voltage of the battery is measured. CONSTITUTION:A push button 9 is turned ON at the time to and a switch 7 is closed to let discharge current flow to a dummy fixed load 8 from a battery 6. During the closure thereof, the terminal voltage of the battery 6 lowers by a fixed value. When the push button 9 is turned OFF and the switch 7 is opened, the voltage returns to he open voltage plotting a smooth transient characteristic curve because of effect of an internal resistance, namely, discharge rate. Here, when a time tau is selected appropriately, the terminal voltage V is almost regarded as the open voltage of the battery 6 after a fixed time tau from the opening time t1 of the switch 7. This voltage is read by a microcomputer 12 to calculate the discharge rate based on a data of the open voltage-to-discharge rate in an ROM of a memory 12c. Thus, a residual capacity of the battery 6 corresponding to the discharge rate is indicated on a display unit 16.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides
The present invention relates to a battery capacity meter for electric vehicles that displays the remaining capacity of a battery.

As a conventional battery capacity meter for electric vehicles, there is one shown in FIG. 1, for example. This battery capacity meter is
It is a so-called ampere hour meter, and the battery 1. Current sensor such as shunt 2゜load 3. It is composed of an integrator 4 and a display meter 5, and the current sensor 2 outputs a voltage corresponding to the discharge current flowing through the load 3. The integrator 4 accumulates this detected voltage, and the integrated value is displayed on the display meter. This is what is displayed in 5. If the pointer 5a of the display meter 50 is adjusted to full scale when the battery 1 is fully charged, the pointer 5a will display the remaining capacity of the battery 1 as the battery 1 discharges.

However, in general, the capacity of the battery 1 in a fully charged state tends to decrease over its lifespan (repetition of charging and discharging) K, and self-discharge occurs. In this case, as the battery 1 is used for many years, the pointer 5a will indicate a higher value than the actual residual capacity value. Therefore,
The conventional capacitance meter described above lacks reliability as a capacitance meter. Furthermore, since this battery capacity meter uses a current sensor such as a shunt, it has the drawbacks of being large and expensive.

The present invention has been made by focusing on such conventional drawbacks, and includes a circuit in which a constant load is connected to a battery via an on-off switch, and a circuit that connects the battery with a constant load after a certain period of time from the time when the on-off switch is opened. means for measuring the terminal voltage of the battery; a calculation device that reads the terminal voltage and calculates a discharge rate based on a pre-stored open circuit voltage versus discharge rate characteristic of the battery; and a residual capacity of the battery corresponding to the discharge rate. It is an object of the present invention to provide a battery capacity meter for an electric vehicle that can accurately display the remaining capacity without any trouble even when the capacity of the battery decreases, self-discharges, etc. purpose.

First, a residual capacity measuring method implemented in the electric vehicle battery capacity meter according to the present invention will be described.

Figure 2 is a graph of discharge current vs. terminal voltage characteristics using the discharge rate of a general battery as a parameter, and Figure 3 is a graph of discharge rate vs. open voltage characteristics and discharge rate vs. internal resistance of a general battery. It is a graph of characteristics.

As is clear from Figure 2, the terminal voltage of a battery varies depending on the discharge rate even at a specific discharge current value, but the terminal voltage when the discharge current value is zero (when the terminals are opened), that is, the open circuit voltage. decreases as the discharge rate increases. This relationship is shown in the discharge rate vs. open circuit voltage characteristics shown in FIG. Therefore, the remaining capacity of the battery can be determined by first measuring the open circuit voltage and calculating the discharge rate based on the discharge rate vs. open circuit voltage characteristic shown in FIG. 3 from the measured open circuit voltage. Note that the difference between the fully charged state and the discharge rate (%) can be regarded as the residual capacity.

The discharge rate vs. open circuit voltage characteristic shown in FIG. 3 is a characteristic that includes capacity reduction due to battery life, self-discharge, etc.

Therefore, it can be said that the residual capacity obtained by the above measurement method is highly reliable.

An embodiment of an automobile battery capacity meter according to the present invention will be described below.

FIG. 4 is a circuit diagram of an embodiment of an automobile battery capacity meter according to the present invention.

Reference numeral 6 denotes a battery whose residual capacity is to be measured, and a gummy constant load 8 is connected to this gauge 6 via an on-off switch 7. It constitutes a circuit. The open/close switch 7 is opened and closed in conjunction with the push button 9. Reference numeral 10 denotes a voltmeter for measuring the terminal voltage of the battery 6, and the measured terminal voltage is supplied to the microcomputer 12 via the switch 11 in a manner to be described later. 13 is a one-shot multivibrator, 14 is an ID clock oscillator, and 15 is a counter, and the output of the counter 15 controls the opening and closing of the r-to switch 11.

The microcomputer 12 has an input/output unit (Ilo) 12
a, a micro arithmetic unit 12b, and a storage section 12e such as ROM and RAM. 16 is a display device that displays the remaining capacity of the battery 6.

Next, the operation of the above embodiment will be explained.

First, as shown in FIG. 5(A), at time t. Press button 9
When turned on, the open/close switch 7 is closed, and a discharge current flows from the battery 6 to the dummy constant load 8. During the closing time of the open/close switch 7, the terminal voltage of the battery 6 decreases by a constant value. .

(See Figure 5(B)). Next, at time ti, push button 9
When the switch is turned off, the on/off switch 7 opens to stop discharging, but the terminal voltage of the battery 6 changes as shown in FIG. 5(B) due to the influence of the internal resistance of the battery 6, that is, the discharge rate. It gradually returns to the open circuit voltage with a smooth transient characteristic curve. Here, if the time τ is selected appropriately, the open/close switch 7
The opening time of t! Terminal voltage v2 after a certain period of time τ
can be regarded as approximately the open circuit voltage of the battery 6.

Next, as shown in FIGS. 5(C) and 5(D), a trigger is applied to the fall of the signal from push button 9 at time t,
One-shot multivibrator 13 outputs pulses. In response to this pulse, the clock oscillator 14 generates a clock pulse (see FIG. 5(g)).

Then, the counter 15 counts the clock pulses and outputs a clock pulse when a certain number (five in this embodiment) corresponding to the time τ is reached (see FIG. 5(G)).

This A? As a result, the dart switch 11 is controlled to close (see FIG. 5(G)). That is, the dirt switch 11 is closed at a time τ from the opening time tl of the open/close switch 7. At this time t + τ, the 6th
As shown in the figure, the terminal voltage Vτ of the battery 6 measured by the voltmeter 10 (which can be considered as an open circuit voltage) is read into the microprocessing unit 12b via the input/output section 12a of the microcomputer 120. Read terminal voltage v
T is temporarily stored in the RAM of the storage unit 12c, and the discharge rate corresponding to the measurement terminal voltage Vτ is calculated based on the open circuit voltage vs. discharge rate characteristic (see FIG. 3) stored in advance in the ROM of the storage unit 12c. This value is also stored in the RAM of the storage unit 12c. Then, the remaining capacity of the battery 6 corresponding to this discharge rate is displayed on the display device 16.

This residual capacity display is maintained at the time point t1i when the on-off switch 7 is closed during the next measurement. That is, at the time t1 when the open/close switch 7 is closed, a clear signal is supplied from the push button 9 to the micro arithmetic unit 12b of the microcomputer 12, and thereby the previously measured terminal voltage Vτ and discharge stored in the RAM of the storage section 12c are The rate is eliminated (see Figure 6).

In this way, this embodiment measures the terminal voltage Vτ, which can be regarded as the open-circuit voltage of the battery 1, and automatically calculates the discharge rate based on this value to display the remaining capacity of the battery 6. Even if the capacity of the battery 6 itself decreases due to use, self-discharge, etc., the remaining capacity can be accurately measured without any problems.

Further, there is no need to use a large and expensive current sensor such as a shunt, and for example, the microcomputer 12 can also be used as a microcomputer for controlling the drive motor of an electric vehicle.

In the above embodiment, the time τ is set so that the terminal voltage ■τ of the battery 6 at time tl+τ can be regarded as the open circuit voltage (for example, in the case of an electric forklift battery, a dummy constant load of 300 A is used). and τ
It is also possible to calculate the discharge rate after calculating the corresponding open circuit voltage based on the terminal voltage Vτ using the microcomputer 12 (set to 3 seconds). Also,
When operating an electric vehicle, turn on pushbutton 9 periodically.
By turning it off, it is also possible to monitor the remaining capacity of the battery 6 one after another.

FIG. 7 is a circuit diagram showing another embodiment of the gummy constant load in the electric vehicle battery capacity meter according to the present invention.

A dummy constant load 8 is connected to the notoutlet 6 via an on/off switch 7. This dummy constant load 8 is an idle rotation load of the drive motor 81 of the electric vehicle.

That is, when the push button 9 is turned on, the open/close switch 7 is closed, and the release signal issued from the push button 9 operates the shift latch 82, which closes the drive motor 81 and the rotating main shaft 83.
is disconnected, and the drive motor 81 rotates idly. At this time, since the idle rotation load of the drive motor 81 is constant, the same effect as if the dummy constant load 8 was connected to the battery 6 can be obtained.

According to this embodiment, the dummy constant load 8 does not need to be particularly resistant to the capacity measuring circuit of the battery 6, and there are advantages that the number of parts is small and the manufacturing cost is low.

As explained above, according to the present invention, by measuring the terminal voltage of the battery, the discharge rate is automatically calculated based on the open circuit voltage vs. discharge rate characteristic and the residual capacity is displayed. The displayed residual capacity is accurate and reliable even when the battery itself decreases in capacity and self-discharges due to its lifespan, and there is no need to use large and expensive current sensors. This has the excellent effect of being able to utilize a microcomputer for controlling the drive motor.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing an example of a conventional electric vehicle battery capacity meter, Figure 2 is a graph showing discharge current vs. terminal voltage characteristics with the discharge rate of a general battery as a parameter, and Figure 3 is a graph of a general battery. FIG. 4 is a circuit diagram showing an embodiment of the electric vehicle battery capacity meter according to the present invention, and FIGS. G) is a time chart diagram showing the operation of the same embodiment, FIG. 6 is a flow chart diagram showing the operation of the same embodiment, and FIG. 7 is a dummy constant load in the battery capacity meter for an electric vehicle according to the present invention. FIG. 3 is a circuit diagram showing another embodiment of the invention. 6... Battery, 7... Open/close switch, 8... Dummy constant load, 9... Push button, 10... Voltmeter, 11...
...Dart switch, 12...Microcomputer, 12a...Input/output section, 12b...Micro arithmetic unit, 12c...Storage section, 13...One-shot multivibrator, 14...Clock oscillator , 15...
- Counter, 16... Display device, 81... Drive motor, 82... Clutch, 83... Rotating main shaft. Figure 1 Figure 2 Figure 3 Figure 5 -433- Figure 6

Claims (1)

[Claims] a circuit in which a dummy constant load is connected to the battery via an on-off switch; a means for measuring the terminal voltage of the battery after a certain period of time from when the on-off switch is opened; and a means for reading the terminal voltage and storing it in advance. A battery capacity meter for an electric vehicle, comprising a calculation device that calculates a discharge rate based on the open circuit voltage versus discharge rate characteristic of the battery, and a device that displays the remaining capacity of the battery corresponding to the discharge rate.