Fault current recognition circuitry

Details Fault current recognition circuitry Fault current recognition circuitry

1998-03-05

1999-06-01

Gaffin, Jeffrey

Electricity: electrical systems and devices

Safety and protection of systems and devices

With specific quantity comparison means

361 87, 361 86, 361191, H02H 318

Patent

active

059093480

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention relates to a circuitry which is used for detecting a fault current on the supply line of an electronic circuit and which is equipped with an auxiliary voltage source and a potential monitor for determining and analyzing the potential prevailing on the supply line during a testing period.
German patent application No. 42 42 177 discloses a circuitry of this type which is used to monitor a large number of valve coils and their associated final stages. For fault current detection, an auxiliary voltage source is connected to the common supply line for the valve coils by way of a high-ohmic resistor, and the potential on the supply line is measured and analyzed. Before this action, the connection of the supply line to the supply source, i.e., the vehicle battery, was interrupted by way of a semiconductor relay. The associated potential monitor is connected by way of a high-ohmic voltage divider. When a shunt circuit or a leakage current from the supply line to the supply source or to ground occurs, the potential on the supply line will vary.
An object of the present invention is to provide a circuitry of this type which has a high degree of accuracy, sensitiveness and reliability in the detection of fault currents, which also includes leakage currents, and, in addition, can be realized with comparatively little effort. A simple and, hence, low-cost measuring apparatus for monitoring the potential on the supply line is deemed sufficient.


SUMMARY OF THE INVENTION

It has been found that this object can be achieved by the design of a circuitry with the special feature that the installation of a current source, which is rated for a maximally allowed current and preferably includes two anti-parallel single current sources, prevents response of the monitoring means as long as the fault current is within the range of predefined limit values, however, that even when the limit values are only slightly exceeded, a very apparent and, therefore, easily assessable potential variation on the supply line is caused during the testing period.
In a preferred aspect of the present invention, two single current sources responding to fault currents in opposite directions are used, whereby it is ensured that fault currents, or shunt circuits, from the supply line to the positive pole of the supply source and to ground are detected.
The circuitry of the present invention is especially appropriate, for example, for monitoring the valve coils and the associated electronic circuits of a controlled brake system, wherein the coils are connected to the supply voltage by way of a common supply line and a common relay. In a brake system of this type, the detection of a fault current must be ensured with a high degree of reliability because the control must be deactivated in a case of malfunction in order to keep the brake system in function. Therefore, the application is critical with respect to safety.
Further features, advantages and possible applications of the present invention can be seen in the following description of an embodiment, making reference to the accompanying drawings.


BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings,
FIG. 1 is a schematically simplified view of the generally electrical components of a circuitry of the present invention.
FIG. 2 is a wiring diagram of a monitoring circuit on the basis of the circuitry of FIG. 1.
FIG. 3 is a diagram in which the signal variation is plotted as a function of the fault current in a circuitry of FIG. 1 or FIG. 2.
FIG. 4 is the basic circuit of a potential monitor for the circuitries of FIG. 1 or FIG. 2.
FIG. 5 is a diagrammatic view of a part of an integrated circuit for realizing current sources for the circuitry of FIG. 1 or FIG. 2.
FIG. 6 is a variation of the circuit in FIG. 5 in the same illustration as in FIG. 5.


DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is used to illustrate the basic operation of the circuitry of the present invention. L1, L2, Ln designate valve coils comprised in the hydraulic valves of an auto

REFERENCES:
patent: 5638247 (1997-06-01), Loreck et al.

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