JPS61191231A - Wire harness fault detector - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (7) Technical details This invention relates to a wire harness failure detection device for an automobile.

A wire harness failure is a disconnection or short circuit in the wire harness. If the wire is disconnected, the electrical equipment installed at one end of the wire harness will not be driven.

If a short circuit occurs, a large current will flow and there is a risk of fire. This is dangerous.

(a) Prior art and its problems Conventionally, measures to prevent vehicle fires due to short circuits in wire harnesses have been taken by improving the quality of fuses and wire harnesses.

It will take some time for the short collar fuse of the wire harness to melt.

A large current flows and the fuse generates heat, but the fuse melts only when too much heat accumulates. .

Furthermore, short circuits may occur intermittently. In this case, even if a large current flows instantaneously, the fuse is cooled down immediately, so no heat is accumulated and the fuse is less likely to blow out.

As a result, vehicle fires sometimes occurred. In other words, apart from fuses, a device is desired that prevents short circuits that generate large currents.

Until now, if you wanted to collect on/off information for each load switch, you had to install a new wire harness for each load to transmit the switch information. Doing so would increase the number of harness circuits, so this was not actually possible.

However, recently, automotive harnesses have been electrically multiplexed or optically multiplexed. Also, AJB (Active
With the adoption of devices such as Junction Boxes, there is a tendency for switch information for various loads to be collected in one place. Therefore, it has become easier to import switch information.

Switch information refers to load on/off information.

(1) Purpose: Detects short-circuits or disconnections in the automobile's wiring harness, warns the driver, or shuts off the breaker to prevent a fire from occurring. It is an object of the invention to provide a device.

2) Configuration The wiring harness of a vehicle branches out for each electrical component that is a load, but from the battery to the branching point there is a single core harness.

□Let electrical components be Ql, Q2,...Qll. When this is off, no current flows to the electrical components. When it is on, the current determined by the electrical equipment is 1, 2, etc.
...In flows. This is called the characteristic current.

Let Xj be the characteristic function of a certain load (electrical component) Qj.

This is 11' when it is on, '0' when it is off,
is a function.

The load switch information is the XjO value. Full load switch information means a set of Xj (Xj). In the past, it was nearly impossible to know (Xj), but modern cars are electrically multiplexed and optically multiplexed, and many load on/off signals are transmitted as serial signals through one or several lines. is given to the signal line. For this reason,
It is becoming easier to know the switch information [Xj) of the full load.

If the total current flowing through the battery is I, then this is ! = ΣIj Xj (1) given by. By the way, I can be measured by providing a current sensor in the part where current flows from the battery to one electric wire.

Then, the measured total current I and ΣI jXj are compared, and if they are equal, it is normal. If the former is large, it is short. If the former is small, you know there is a disconnection.

However, it is difficult to accurately measure the total current I, and there are offsets, etc., so a precise sensor must be used. The cost will be high and adjustment work will also be required.

However, even though it is called a disconnection or a short circuit, it is accompanied by a change in current, so it is not necessary to use a static and comprehensive detection method as shown in equation (1). do not have.

Differentiating equation (1) with time, we get ・j becomes. Since Ij is a constant, the differential is 0.

Now, the time differential of Xj is O if the on/off state of the load does not change at a certain time.

Then, at a certain time, the on/off state changed. Only the load matters. ,.

Equation (2) indicates that when the total current changes, the load has a specific current equal to the amount of change, and the load state has changed.

The time of change is t・, and the difference between the values of 1ε and t−ε is Δ
If we show it by ■, ΔI (t) ni (t'+ g ) −I ('t
-t' ) (8) ΔI (t) =='I'jΔX
j(t) (4")'.Equation (4) shows that when the j-th load Qj changes from off to on (ΔXj = 1'), the total current increases by I,1. It also means that when it changes from on to off (ΔXj=-1), the total current decreases by Ij.

If the total current change is [IjΔXj) for all load changes (ΔXj), it is normal.

However, for a load consisting of an off-to-on change (∆
Even if X=1), if the total current change ΔI is O, this means that the harness connected to the load is disconnected or
This means that the wire is broken inside the load.

Furthermore, for a load consisting of the on-to-off change (Δ
x=-1), if there is no change in the total current I, this is also considered to be a disconnection.

For all loads, when there is no change (ΔX=01) but the total current increases suddenly, this means a short circuit in the wire harness.

Also, if the total current fluctuates repeatedly even though there is no change in load status (Δx=01), this is an intermittent short circuit.

If the total current decreases even though there is no change in the load state (ΔX=01), this means that the wire harness is disconnected.

If the total current changes when there is no change in load status, there are three possibilities: short circuit, intermittent short circuit, and disconnection.

Moreover, which wire harness is abnormal? I don't know that.

If the total current does not change even though the load condition is changing, it is certain that there is a disconnection, and it can be determined which wire harness the disconnection is in. Table 1 shows the relationship between these changes and their determination results.

Table 1 Correspondence table between total current, load state change, and failure The wire harness failure detection device of the present invention will be explained with reference to FIG.

Assume that one end of the battery 7 is grounded, and the terminal is connected to a load (Qj) via a load switch group (X, +). The other end of the load is grounded. The load Qj has a specific current Ij
shall flow.

In addition, a fuse and an ignition switch are connected in series, but are not shown here.

The load switches X1, X2, . . . are either on (X=1) or off (x=0). All load on/off information (Xjl is electrical multiplexed signal,
It is assumed that the optical multiplex signal is provided as a serial signal.

In the middle of the branch wire harness, there are each load, its control circuit, protection circuit, etc., and these attached circuits also require current, but the sum of these currents and load current is calculated as the specific current of that load. Let it be Ij.

A main wire harness connects the battery 7 to the branch wire harnesses.

A current transformer 1 and a breaker 5 are provided in the middle of the main harness 9. The current transformer 1 has a main harness 9 connected to its negative side, and the secondary side is used as a signal line. Although the direct current component is not known, the change in total current ΔI can be detected.

The signal from the current transformer 1 is sent to the current change detection circuit 2 as follows:
amplified. The current change Δ can be positive or negative.

Various load switch signals X1, X2, X3,...
is input by the load switch state detection circuit 3.

Here, the values (0 or 1) of Xl, X2, . . . are stored.

The determination circuit 4 determines the total current change Δ! of the current change detection circuit 2! and the load state change ΔX of the load switch state detection circuit 3 are compared.

When the total current change Δ■ increases or decreases, if the load also turns on and off accordingly, this is normal.

However, if the load condition does not change even though the total current has increased, this is a short circuit.

If the load condition does not change even though the total current has decreased, this indicates a disconnection.

If the load switch changes from off to on without the total current changing, this is an open circuit.

The determination circuit 4 makes such a determination.

Intermittent short circuits can also be determined.

Most strictly, the total current change Δ is correctly determined from the current change detection circuit 2, and this value is held for a certain period of time τ from the time t when this change occurs, while the load switch state detection circuit 3 Input the number j of the switch whose state changed during the time period , (t~ is 10τ) and the amount of change ΔXjIj,
Compare with ΔI using a comparator. The comparison is made instantaneously, and a decision is made based on this result.

When attempting to make such a determination, the current change ΔI is expressed as A/
It is necessary to perform D conversion and use a microcomputer for the determination circuit 4. This is because it is convenient to store and compare the characteristic currents II, I, , . . . .

However, there is no need to make quantitative comparisons like this.
There aren't many.

It is sufficient that the total current change ΔI and the load switch state change ΔX are simultaneous.

For example, a set-reset flip-flop may be operated by a current change ΔA and a state change ΔX. One flip-flop is provided for each positive pulse and negative pulse. The state change (tAX is either faster or slower than the current change ΔI, and this is known in advance.

Set the flip-flop at the faster of ΔI and ΔX,
Reset later.

If the changes in ΔF and ΔX are simultaneous, the flip-flop will be reset immediately. However, ΔI and Δ
If the changes in X are not simultaneous, the flip-flop will not be reset.

By using 7 lip flops for positive pulses and 7 lip flops for negative pulses, it is possible to distinguish between open circuits, short circuits, and intermittent short circuits.

When the determination result is obtained, the short circuit or disconnection is displayed on the short circuit display device 6 which displays or warns that the circuit is disconnected or shorted.

In the case of a short circuit or intermittent short circuit, the breaker 5 may be shut off.

For loads such as motors and horns where the current is not constant, an alternating current component may appear in the current transformer.

However, this can be eliminated by the current change detection circuit 2. The above load will flow a current consisting of the sum of a DC component and a small alternating current component, but by setting a threshold larger than such an alternating current component, a change in current greater than this will be considered a change in ΔI. be. Such a comparison circuit is also useful for cutting noise.

(4) Effects Short circuits and disconnections can be detected without complicating the structure of the wire harness. This is because a current transformer is used.

It can also detect short circuits that cannot be handled by fuses. This is because detection of a short circuit is determined based on load switch information and current change information. This is because current changes can be detected by the current transformer, even if they occur instantaneously.

One device can detect both short circuits and disconnections.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a wire harness failure detection device according to the present invention. 1 ・・・・・・・・・ Current transformer 2 ・・・・・・
...Current change detection circuit 3 ......
Load switch state detection circuit 4 ・・・・・・・・・
Judgment circuit 5 ・・・・・・・・・
Push-force 6 ・・・・・・・・・ Short circuit disconnection indicator 7 ・・・・・・・・・ Battery 8 ・・・・・・・・・ Load invention
Person Nishi 1) Taishin 1) Yutaka
Akira

Claims (1)

[Claims] A breaker 5 and a current transformer 1 are provided in the middle of the main harness 9 that connects the battery 7 and each load, a current change detection circuit 2 that amplifies the output change of the current transformer 1 and generates a signal for a certain period of time, and various types of The load switch status detection circuit 3 receives the on/off signals of the load switches and determines which switch has changed on/off, and the signals from the current change detection circuit 2 and load switch status detection circuit 3 determine whether the switch is normal, disconnected, or shorted. It consists of a determination circuit 4 that determines whether the short circuit is a short circuit or an intermittent short circuit, and a short wire breakage display device 6 that indicates when the short circuit is short or an intermittent short circuit. A wire harness failure detection device featuring: