Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of ground fault indication
Reexamination Certificate
1999-04-19
2002-05-28
Sherry, Michael J. (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of ground fault indication
C324S421000, C361S088000, C361S085000
Reexamination Certificate
active
06396282
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to a method and apparatus for testing the ground contact of parts of a networked system.
By way of example, it is known in the field of motor vehicles for a plurality of controllers to be networked in order to allow data to be interchanged between the individual controllers. Owing to the fact that a data protocol is produced, which is sent via one or more lines between the controllers and in which the corresponding data can be entered and read at the appropriate points, it is possible to save a considerable amount of complexity and material in the wiring. Without a data bus a separate cable would be required for each item of information to be interchanged between the respective controllers.
Data are written to and read from the protocol of this data bus by applying a specific voltage level to the line or lines for a specific time period. To do this, it is necessary for these controllers to have a virtually identical reference-ground potential. In the case of a motor vehicle, this is the vehicle ground, with which all the electrical equipment in a motor vehicle makes contact, as an equipotential surface. Networked systems of the type described have become known, for example, as CAN systems.
European patent document EP 0 614 298 A2 discloses a circuit arrangement which is intended to prevent total failure of the entire network if a breakdown in the ground connection or a short to the supply potential occurs on one of the parts in the networked system.
Furthermore, European patent document EP 0 474 907 A1 discloses a method for error identification in a networked system, in which the parts of the networked system are connected to one another in the form of a ring. A wire break at one point in the networked system can be identified in the case of this method by the data originating from one subscriber being sent in both directions. If a receiver receives the data from only one direction, then it is possible to deduce that a wire break is present between the two parts on the path which corresponds to the other direction.
If the ground contact of individual controllers now deteriorates relative to other controllers, disturbances in data transmission can occur since the voltage levels of the individual parts of the networked system are shifted with respect to one another. If the shift is so severe that it is greater than the system tolerance, then there is no longer any certainty that changes in the voltage levels on the data bus can be identified.
One object of the present invention is therefore to identify as early as possible, a deterioration in the ground contact of individual subscribers on a networked system in which data are sent and received via at least one line, with at least one line at each part of the networked system being connected via a resistance arrangement as well as a contact to a common potential of the parts and being connectable via a controllable switch to a further potential.
According to the invention in order to test the ground contact of parts of the networked system, the voltage across the resistance arrangement is compared with a predetermined potential when the line is at one potential in a steady state, and the state of the ground contact of the part is deduced from a comparison of the voltage across the resistance arrangement with the predetermined potential. In this manner, a faulty ground contact can be identified at an early stage, simply and without adversely affecting the ongoing transmission of data. In the case of a CAN network, it is possible to confirm a test of the ground contact by means of the CAN_H line.
According to the invention a method is carried out in which the voltage across the resistance arrangement is compared with a predetermined potential when the line is at one potential in a steady state, the state of the ground contact of the part being deduced from a comparison of the voltage across the resistance arrangement with the predetermined potential.
A faulty ground contact can also advantageously be identified at an early stage in this way using simple means, without adversely affecting the ongoing transmission of data. In the case of CAN network, it is possible to confirm a test of the ground contact by means of the CAN_L line.
In the case of both subjects, a local shift in the voltage owing to a faulty ground contact is compared with the potential on the respective data line. An “average” potential is present on all parts via the connection on the data lines—via the connection at each controller, that is to say each part of the networked system. Any ground fault in an individual subscriber thus has only a minor influence on the potential on the data line. As a consequence of this, in the event of an ground fault in an individual subscriber, a voltage difference is produced across the resistance arrangement, and this voltage difference can be evaluated.
Whenever the controllable switches change over, the potential on the data lines changes at the same time. When such a potential change takes place, overshoots occur which can corrupt the result of any evaluation of the voltage across the resistance arrangement. For this reason, no comparison should take place until the potential on the data line is in a steady state.
Accordingly, in one embodiment of the method according the invention, the potential in the steady state is the common potential. Such a comparison allows ground faults to be detected directly. The comparison when the ground potential on the CAN_H line is in the steady state indicates, advantageously as against a comparison when a VCC potential on the CAN_L line is in the steady state, that more or less undefined voltage losses resulting from the quality of components which are still being used are irrelevant.
In another embodiment of the method according to the invention, the potential in the steady state corresponds to the part-specific potential. In this case as well, undefined voltage losses resulting from the quality of components which are still being used are irrelevant.
In still another embodiment of the method according to the invention, the comparison is carried out with a certain time lag, after which the line is connected, by means of the controllable switches, to a specific potential. The time lag in this case must on the one hand be of such a duration that the steady state is reached, and on the other hand must be of such a duration that the potential has not already switched back again.
In still another embodiment the comparison is carried out within a time window after the switching state of the controllable switches has changed. In this case the time delay which the components experience until the switching process actually takes place is used advantageously. When the state of the transceiver changes, a time period on the order of magnitude of 500 ns passes before the switching process has taken place. The comparison is carried out within this time window, which advantageously ensures that the potential is in a steady state and that the correct potential is present. Thus, the comparison is carried out within the time window while the transceiver is in the “recessive” state.
According to another feature of the invention, the battery voltage which can be detected by the individual subscriber is compared with the battery voltage which can be detected by one or more reference subscribers, and a faulty ground contact is deduced if the discrepancy in the detected battery voltages is above a specific threshold value. This method is suitable for detecting a possibly faulty ground contact independently of the check already described. The locally detected battery voltage is sent, for example as information via the bus, to a further controller which, as a reference, itself determines the battery voltage which can be detected there. If the transmitted value of the battery voltage is lower or higher, a ground fault can be deduced.
It should be noted that a reduction in the locally detected battery voltage can also be caused by a faulty contact
Minuth Juergen
Reeb Max
Schwarz Guenther
Setzer Juergen
Crowell & Moring LLP
Nguyen Trung Q.
Sherry Michael J.
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