JPH06317636A - Battery current detecting device for vehicle - Google Patents

Abstract

PURPOSE:To reduce the size and cost of a battery current detecting device and to increase the accuracy of the device by detecting an electric current when the battery current is below (above) a designated value by means of a current sensor (from a voltage drop caused by the battery current). CONSTITUTION:The measuring range of a current sensor can be set to only one range for a low current by switching the action of current detecting means 34, 35. In the low current range where detection is shared by the current sensor, the battery voltage is high so that it is not necessary to set the driving voltage of the current sensor low in anticipation of lowering of the battery voltage. Thus, the current sensor can be reduced in its size and cost. When the battery current is below a designated value, starter current is detected by the means 35 by obtaining a current value from differential voltage using the characteristic of an earth cable just before a starter circuit, so that an error caused by resistance value variation in every earth cable and cable resistance value fluctuation due to a temperature change can be removed so as to detect the battery current correctly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current detecting device for a vehicle battery, for example, a current detecting device used in a device for detecting a battery state of a vehicle battery.

[0002]

2. Description of the Related Art A battery state detecting device based on the VI current integration system is known from Japanese Patent Laid-Open No. 4-164269. As a current detecting means used in such a VI current integrating method, there is a current sensor using a hall element. Further, as another battery current detecting means, a means for obtaining the battery current from the potential difference generated at both ends of the earth cable of the battery is disclosed in Japanese Patent Laid-Open No. 62-62.
It is known from the publication of 11184.

[0003]

In the vehicle battery, a current in the range of -100A to -300A flows because the starter is rotated by the battery when the engine is started. Also, in a steady state after the engine is started, -50A to 5A.
A current in the range of 0 A flows. Therefore, the vehicle battery current detection means is required to have two measurement ranges, that is, a measurement range in the range of -100A to -300A and a measurement range in the range of -50A to 50A. Further, the voltage of the vehicle battery drops during starter startup.

When the above current sensor using the Hall element is used as the current detecting means of the vehicle battery having such characteristics, it is necessary to cover two measurement ranges, and the starter is started. Since it is necessary to reduce the drive voltage of the current sensor in consideration of the voltage drop, it becomes difficult to reduce the size of the current sensor and the cost increases.

On the other hand, when the current detecting means for obtaining the battery current from the differential voltage of the earth cable of the battery is used for detecting the battery current, there is a variation in the resistance value among the earth cables, and further, due to the temperature change. Since the resistance value of the ground cable fluctuates, there arises a problem that high detection accuracy cannot be obtained. It is an object of the present invention to make a vehicle battery current detection device small, highly accurate, and low cost.

[0006]

In order to solve the above problems, the present invention provides a first current detecting means for detecting a current when a battery current is a predetermined value or less, and a battery current having a predetermined value. The vehicle battery current detection device is equipped with the second current detection means for detecting the current at the above time from the voltage drop caused by the battery current.

[0007]

According to the above means, the low-current detection of the steady state can be shared by the current sensor, and the large-current detection at engine start-up can be shared by the current detection means obtained from the differential voltage. This allows the current sensor to only share the current detection of one measurement range. Moreover, since the battery voltage is high in the low current region in which the current sensor operates, there is no need to lower the drive voltage of the current sensor in anticipation of a decrease in the battery voltage.

Further, in the current detecting means for obtaining the battery current from the differential voltage, the resistance value of the earth cable is detected during the period when the low current is flowing in the battery immediately before or after the starter current flows, and the correction data is obtained. Seeking
It is possible to correct the detected current value when the engine is started.
As a result, variations in the resistance value of the ground cable and changes in the resistance value due to temperature changes are corrected, so that high-current measurement can be performed with high accuracy during starter rotation.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A vehicle battery current detecting device of the present invention will be described with reference to the drawings. In FIG. 2, 1 is a vehicle battery,
Reference numeral 2 is a vehicle driving engine, 3 is a starter for starting the engine, and as is well known, by turning on a starter switch 4 and supplying electric power from the battery 1 to the starter 3,
The starter 3 rotates and the engine 2 starts. Reference numeral 5 is driven by the engine 2 to charge the battery 1, and also an electric load 8 such as a lamp, a blower motor, a defogger, etc.
It is a generator that supplies electric power to.

Reference numeral 20 is a ground cable for grounding the negative terminal of the battery 1 to the ground. When a battery current flows through the ground cable 20, a voltage drop (differential voltage) is generated across the battery cable. 6 is a current sensor for detecting the battery current flowing through the earth cable 20 by using a Hall element, 7 is a temperature detector for detecting the temperature of the battery 1, 2
1 is a key switch.

A control circuit 9 detects the state of the engine 2, the voltage, current and temperature of the battery 1, controls the rotation speed of the engine 2 and the power generation of the generator 5, and further detects the life of the battery. Is displayed by the display device 10. Details of the control circuit 9 are shown in FIG. The operation of the control circuit 9 is described in the above-mentioned Japanese Patent Application Laid-Open No. 4-164269, so the detailed description of the operation will be omitted here.

The control circuit 9 includes a battery current detector 9a.
Is provided, the value related to the current detected by the current sensor 6 is input from the terminal 11, and the differential voltage of the ground cable 20 is input from the terminals 18 and 19. The battery current detected by the battery current detection unit 9a is the current integration unit 9
d, the discharge characteristic calculation unit 9e, and the power generation control unit 9f. The details of the battery current detector 9a are shown in FIG.

The battery current detected by the current sensor 6 is input from the terminal 11 to the sensor current detecting means 31. The sensor current detection means 31 performs appropriate signal processing on the detected current value and outputs it to the charge / discharge current detection means 34 and the resistance value correction means 33. Further, the sensor current detection means 31 outputs an operation command to the charge / discharge current detection means 34 when the battery current detected by the current sensor 6 is lower than a predetermined value, and the starter current detection means when the battery current is higher than the predetermined value. The operation command is output to 35.

The difference voltage of the earth cable 20 is the terminal 18,
It is inputted from 19 to the differential voltage detecting means 32. The differential voltage detecting means 32 performs appropriate signal processing such as amplification on the detected differential voltage, and the resistance value correcting means 33 and the starter current detecting means 35.
Output to. The resistance value correcting means 33 outputs the correction data obtained by the calculation described later to the starter current detecting means 35.

The charging / discharging current detecting means 34 operates when the battery current is lower than a predetermined value in accordance with a command from the sensor current detecting means 31, and outputs the battery current detected by the current sensor 6. The starter current detecting means 35 operates when the battery current is higher than a predetermined value according to the signal from the sensor current detecting means 31, and calculates the starter current from the differential voltage of the earth cable 20 by a method described later.

The outputs of the charging / discharging current detecting means 34 and the starter current detecting means 35 are inputted to the current integrating section 9d, the discharge characteristic calculating section 9e and the power generation control section 9f of FIG. Here, FIG. 4 shows the relationship between the battery discharge current and the battery voltage when the engine 2 is started. When the starter switch 4 shown in FIG. 2 is turned on, the starter 3 rotates and starts the engine 2. The section B in FIG. 4 is the section in which the starter 3 is rotating.
In the section, a large current is discharged from the battery current, and the battery voltage drops accordingly.

In the section A before the engine 2 is started, the current discharged by the battery 1 is low and the battery voltage is kept high. C after the start of the engine 2 is completed
In the section, the charging current starts to flow from the generator 5 to the battery 1. At this time, the battery current is low and the battery voltage is high. In addition, the battery charging / discharging current is low and the battery voltage is high even when the vehicle is idling or running. Therefore, by setting an appropriate predetermined value, the starter current in the B section and the battery current in the other sections can be distinguished.

Returning to FIG. 1, when the battery current is less than or equal to a predetermined value, the sensor current detecting means 31 causes the charging / discharging current detecting means 3 to operate.
4 is operated to stop the operation of the starter current detecting means 35. As a result, the charging / discharging current detecting means 34 outputs the current detected by the current sensor 6 as the battery current. When the battery current exceeds a predetermined value, the sensor current detection means 31 stops the operation of the charge / discharge current detection means 34,
The starter current detecting means 35 is operated.

Thus, by switching the operations of the current detecting means 34 and 35 depending on the magnitude of the battery current,
The current sensor 6 shares the detection of the battery current only in the steady state where the current value is low. As a result, the current sensor 6 can set its measurement range to only one low current range. Moreover, in the low current range in which the current sensor 6 is responsible for current detection, the battery voltage is kept high, so that a high drive voltage is always obtained when the current sensor 6 operates. Therefore, it is not necessary to set the drive voltage of the current sensor 6 low in anticipation of a decrease in battery voltage. As a result, the current sensor 6 can be downsized and the cost can be reduced.

Next, current detection when the battery current is equal to or higher than a predetermined value will be described. When the battery current exceeds a predetermined value due to the rotation of the starter 3, the sensor current detection means 31 stops the operation of the charge / discharge current detection means 34 and operates the starter current detection means 35. The starter current detecting means 35 calculates the battery current from the difference voltage from the difference voltage detecting means 32 and the correction data from the resistance value correcting means 33 using the characteristics shown in the graph of FIG.

The characteristic shown by the solid line in FIG. 5 shows a standard relationship between the battery current and the differential voltage of the ground cable 20. If the resistance value of the ground cable 20 is the same as the standard value, the current value can be obtained from the difference voltage using the characteristic of this solid line. However, in reality, the resistance value of the ground cable 20 shows a characteristic deviated from the standard characteristic as shown by the broken line in FIG. 5 due to the variation and temperature change for each ground cable.

The resistance value correcting means 33 calculates correction data for the deviation of the characteristic. The operation of the resistance value correcting means 33 will be described with reference to the flowchart of FIG. In step 101, it is determined whether the battery current is a predetermined value or more. If YES, that is, if the starter current is flowing, the routine proceeds to step 106, where the calculation of the correction data is completed. If NO, that is, if the starter current is not flowing, the process proceeds to step 102.

At step 102, the battery current detected by the current sensor 6 is read from the sensor current detection means 31, and at step 103, the differential voltage of the earth cable 20 is read from the differential voltage detection means 32. Then, in step 104, the characteristic due to the resistance value variation at the measurement point indicated by the broken line in FIG. 5 is obtained from the sensor current and the differential voltage. This characteristic accurately represents the relationship between the current value of the ground cable 20 and the differential voltage at the time of the measurement.

The resistance value correcting means 33 calculates correction data by comparing the characteristic due to the resistance value fluctuation and the standard characteristic,
The correction data is stored in the storage unit in step 105, and the process ends in step 106. The above operation is performed every predetermined time, and the correction data is constantly updated. This correction data is used by the starter current detecting means 35 as described below when the battery current becomes equal to or higher than a predetermined value.

The starter current detecting means 35 starts its operation in response to a command from the sensor current detecting means 31 when the battery current exceeds a predetermined value. The starter current detection means 35 calculates a current value from the ground cable differential voltage using the ground cable standard characteristics shown by the solid line in FIG. 5, corrects it by the correction data stored in the resistance value correction means 33, and then the value. Is output as a battery current.

The current accumulator 9d, the discharge characteristic calculator 9e, and the power generation controller 9f of the control circuit 9 shown in FIG. 3 perform processing with the corrected battery current. In the detection of the starter current by the starter current detecting means 35 described above, the current value can be obtained from the difference voltage using the characteristics of the ground cable immediately before the starter rotates three times, so that there are variations in the resistance value of each ground cable, It is possible to accurately detect the battery current, except for an error caused by a change in the resistance value of the ground cable due to a temperature change.

In the above-described example, the correction data by the starter current detecting means 35 immediately before the starter current is detected is used, but the calculation for obtaining the current value from the differential voltage is stored in the buffer. When the difference voltage data is used, it is possible to use the correction data calculated immediately after the starter current flows.

Next, the differential voltage detecting means 32 for detecting the differential voltage of the ground cable 20, which will be described as another example of the resistance value correcting means 33, may generate an offset voltage. In the graph of FIG. 7, the standard characteristics of the battery current and the differential voltage are shown by a solid line, and the broken line shows the characteristics of an actual ground cable measured at a low current. As shown in this graph, the output from the differential voltage detecting means 32 includes an error due to the offset voltage.

In this example, the starter current is obtained more accurately by calculating the error due to the offset voltage as correction data. The operation of obtaining this correction data is shown in FIG.
This will be described with reference to the flowchart of. Step 201
Then, it is determined that the battery current is a predetermined value or more. YES, that is, when the starter current is flowing,
Proceeding to step 209, the creation of correction data is completed. N
When O, that is, when the starter current does not flow, the routine proceeds to step 202.

At step 202, it is judged if the detected battery current is the same as the current value at the time of the previous measurement.
If they are the same, the process proceeds to step 209 to end the creation of the correction data. If they are different, the process proceeds to step 203. In step 203, the battery current from the current sensor 6 is read, and the starter 204 reads the differential voltage of the ground cable 20.

In step 205, the relational expression of the differential voltage shown by the broken line in FIG. 7 is calculated from the battery current and the differential voltage read at a plurality of measurement points. Then, in step 206, the correction value of the resistance value of the ground cable is calculated from the relational expression, the offset error of the differential voltage detecting means is calculated in step 207, and each correction data is stored in the storage unit in step 208.

The starter current detecting means 35 corrects the current value obtained from the differential voltage using the standard characteristics by using these correction data. In this example, when the starter current is calculated, the calculation is performed in consideration of the offset error of the differential voltage detecting means 32 in addition to the fluctuation of the resistance value of the ground cable, so that the current can be detected more accurately.

[0033]

According to the present invention, the vehicle battery current detecting device can be made compact, highly accurate, and low cost.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of a vehicle battery current detection device of the invention.

FIG. 2 is a circuit diagram of a battery state detection device.

FIG. 3 is a circuit diagram of a control circuit used in the battery state detection device.

FIG. 4 is a graph showing battery current and battery voltage during engine start.

FIG. 5 is a first graph showing a relationship between a difference voltage and a current value.

FIG. 6 is a flowchart showing the operation of the first example of the resistance value correction means used in the vehicle battery current detection device of the present invention.

FIG. 7 is a second graph showing the relationship between the difference voltage and the current value.

FIG. 8 is a flowchart showing an operation of a second example of the resistance value correcting means used in the vehicle battery current detecting device of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Vehicle battery 2 ... Engine 3 ... Starter 4 ... Starter switch 5 ... Generator 6 ... Current sensor 9 ... Control circuit 9a ... Battery current detection part 20 ... Ground cable 31 ... Sensor current detection means 32 ... Differential voltage detection means 33 ... resistance correction means 34 ... charge / discharge current detection means 35 ... starter current detection means

Claims (1)

[Claims] 1. A current detecting device for a vehicle battery, comprising: a first current detecting means for detecting a current when a battery current is below a predetermined value by a current sensor; and a current when the battery current is above a predetermined value. A vehicle battery current detecting device comprising a second current detecting means for detecting from a voltage drop caused by a battery current.