JPH05244701A - Ground fault detecting circuit for feeder in motor vehicle - Google Patents

Abstract

PURPOSE:To make it possible to detect ground fault positively without feeding short circuit current by interrupting between a feeder and the body of vehicle through a capacitor while furthermore detecting variation of impedance due to ground fault. CONSTITUTION:The ground fault detecting circuit comprises a network(C1, C2, R1, Rx1, Rx2) having impedance variable upon occurrence of ground fault and including capacitors(C1, C2) for interrupting between feeders(B1, B2) in DC sense, and impedance variation detecting circuits (1, 2) for detecting variation of impedance in the network thereby detecting occurrence of ground fault.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground fault detection circuit for detecting a ground fault of a power supply line wired in an electric vehicle.

[0002]

2. Description of the Related Art In an electric vehicle, a power supply line called a boss or a bus bar having a relatively high voltage of about 100 to 300 volt is laid in order to supply a large amount of electric power to an electric motor. Unlike the low-voltage power supply line of about 12 volt used in conventional gasoline engine cars, the power supply line laid inside this vehicle body is electrically connected to the power supply line of both positive and negative polarities. Insulation is desirable. In this way, if both power supply lines of both polarities are completely insulated from the vehicle body, even if a ground fault occurs in which the electrical insulation of the power supply line of one polarity collapses, the positive and negative polarities are immediately There is no short circuit between power lines. That is, a short circuit occurs between the power supply lines with the vehicle body interposed only when both of the bipolar power supply lines are grounded.

However, when the bipolar power supply line is completely insulated from the vehicle body as described above, even if a ground fault occurs in one of the power supply lines, there is no change in current or voltage. There is a problem that it cannot be detected. Therefore, conventionally, a high-resistance resistor is connected between one power supply line and the vehicle body, and a minute short-circuit current that flows when a ground fault occurs in the other power supply line and the accompanying change in voltage A configuration for detecting is considered.

[0004]

SUMMARY OF THE INVENTION In the above conventional configuration,
Both power supply lines are not completely insulated from the vehicle body, and even if they are minute, the short-circuit current actually flows,
It's hard to say the best way. Therefore, an object of the present invention is to realize a simple and inexpensive circuit for surely detecting a ground fault of a power supply line without actually flowing a short circuit current.

[0005]

SUMMARY OF THE INVENTION A ground fault detection circuit of the present invention includes a circuit network which includes a capacitor for direct current cutoff between a power supply line and a vehicle body, and whose impedance changes with the occurrence of a ground drop. An impedance change detection circuit that detects the occurrence of a ground fault by detecting the change in impedance that has occurred in the circuit network.

[0006]

In the ground fault detection circuit of the present invention, the capacitor between the power supply line and the vehicle body is completely cut off in terms of direct current and the change in impedance due to the ground fault is detected. Without fail, the landslide can be reliably detected.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram showing the structure of a ground fault detection circuit according to an embodiment of the present invention together with a power supply line to be detected,
It is composed of an oscillation circuit 1 and a frequency change detection circuit 2. BATT is a storage battery, B ₁ is a positive power supply line connected to the positive electrode of the storage battery, B ₂ is a negative power supply line connected to the negative electrode of the storage battery, and the ground point is a point at the same potential as the vehicle body. It is shown that. In addition, the resistor R _x1 shown by the dotted line,
R _x2 is a variable resistor that simulates the presence or absence of a ground fault between the power supply lines B ₁ and B ₂ and the ground point, and has a sufficiently large value before the ground fault occurs, and after the ground fault occurs. Is a small value.

The oscillator circuit 1 comprises an operational amplifier OP, capacitors C ₁ and C ₂ , and resistors R ₁ , Ra and Rb. That is, the inverting input terminal of the operational amplifier OP is connected to the feed line B ₁ through the capacitor C ₂ is grounded via a capacitor C _1, the non-inverting input terminal is grounded via the resistor Rb .. Further, resistors R ₁ and Ra are connected between the output terminal of the operational amplifier OP and the inverting / non-inverting input terminals, respectively. This oscillator circuit 1 has a capacitance value c _{1 of} capacitors C ₁ and C ₂ ,
at an oscillation frequency determined by the c ₂ and the resistance value r ₁ of the resistor R ₁ generates a square wave.

Before the ground fault occurs in the feeder line B ₁ or B ₂ , the resistance values of the variable resistors R _x1 and R _x2 are sufficiently large.
The oscillation circuit 1 oscillates at an oscillation frequency equal to the reciprocal of 2r ₁ c ₁ without being affected by the capacitor C ₁ connected to the power supply line B ₁ . When a ground fault occurs in the power feed line B ₁ and the resistance value of the variable resistor R _x1 decreases, the capacitor C ₂
The oscillation frequency of the oscillation circuit 1 changes according to the capacitance value of. The oscillation frequency decreases to a value equal to the reciprocal of 2r ₁ (c ₁ + c ₂ ) as the value of the ground drop resistance at the time of occurrence of the ground fault decreases.

[0010] Considering that the internal resistance of the battery BATT is sufficiently small, similarly to the case where a ground fault in the power supply line B ₂ occurs and the resistance value r _x2 of the variable resistor R _x2 decreases, the capacitor C ₂ The oscillating frequency of the oscillating circuit 1 decreases due to the capacitance value of.

The frequency change detection circuit 2 includes the power supply line B ₁
Alternatively, a change in the oscillation frequency of the oscillation circuit 1 due to the ground fault of B ₂ is detected and a ground fault detection signal is output. This ground fault detection signal is sent to, for example, a control micro computer to display a ground fault alarm on the dashboard, or to interrupt the power supply circuit as necessary.

[0012] As described above, since between the feed line B ₁ and a ground point (vehicle body) is cut off direct current by the capacitor C ₁ and C _2, earth both the feed line B ₁ and B ₂ Short-circuit current does not flow until a fault occurs. And the power supply line B
₁ and for immediately ground落検detection signal when either one ground fault occurs in the B ₂ is output, unless the power supply lines B ₁ and B ₂ is extremely rare that a ground fault is simultaneously or one after another, the short-circuit Sufficient time is available to take measures to avoid the occurrence.

In the above, the configuration in which the change in the oscillation frequency is caused by the change in the impedance of the circuit network due to the landfall and the change is detected is illustrated. However, it is also possible to adopt an impedance bridge type configuration in which a change in the impedance of the circuit network due to a ground fault is detected by the amplitude of the current or voltage.

[0014]

As described in detail above, in the ground fault detection circuit of the present invention, the power supply line and the vehicle body are completely cut off from each other in a direct current manner by a capacitor so that a change in impedance due to a ground fault is prevented. Since the detection is performed, the effect of reliably detecting the ground fault can be achieved without applying a short-circuit current and with a simple and inexpensive configuration.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a ground fault detection circuit for a power supply line in an electric vehicle according to an embodiment of the present invention, together with a power supply line to be detected and the like.

[Explanation of symbols]

1 Oscillation circuit 2 Frequency change detection circuit B _1, B ₂ Feed line BATT Storage battery C ₁ , C ₂ Capacitor connected between feed line and ground point (vehicle body)

[Procedure amendment]

[Submission date] November 25, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 2

[Correction method] Added

[Correction content]

2 is a circuit diagram showing an example of a configuration of a frequency change detection circuit 2 of FIG.

Claims (2)

[Claims] 1. A circuit for detecting a ground fault of a power supply line to be electrically insulated from a vehicle body of an electric vehicle to the vehicle body, wherein the capacitor cuts off the direct current between the power supply line and the vehicle body. And an impedance change detection circuit that detects the occurrence of the ground fault by detecting a change in the impedance generated in the circuit network. A ground fault detection circuit for a power supply line in an electric vehicle. 2. The impedance change detection circuit according to claim 1, wherein the impedance change detection circuit includes an oscillation circuit whose oscillation frequency changes according to the change of the impedance, and a frequency change detection circuit which detects a change in the oscillation frequency of the oscillation circuit. A ground fault detection circuit for a power supply line in an electric vehicle, comprising: