FR2831272A1 - Detection of a short circuit in a dual voltage motor vehicle electrical network, by summation of the earth voltages in the high voltage network, with a non-zero total value taken to indicate a short circuit - Google Patents

Abstract

Method for detection of a short circuit in a motor vehicle dual-voltage network according to which currents in each of the high voltage network (A) branches (I1-I3) are measured. Connected to the high voltage network are an electric motor (1), battery (2), high voltage loads (3) and a DC-DC converter (4). If the sum of the measured earth currents is not zero a short-circuit is assumed to have occurred. An Independent claim is made for a device for measuring the total currents flowing in the high voltage section of a motor vehicle electrical network that comprises a current sensor (C3) positioned at a point in which all the earth currents of the loads are combined to form a total earth current (I4). A short circuit is assumed to have occurred if the total earth current is not equal to zero. The electric motor considered is an alternator or a combined alternator starter motor.

Description

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 The invention relates to methods and devices for detecting a resistive short circuit in an electrical network for a motor vehicle.

 The increase in electrical energy needs of new on-board electrical equipment means that the traditional 14 volt energy production system is reaching its limits. The electrical energy that must be available in the vehicle is constantly increasing. One solution is to switch from a network voltage of 14 volts to a network voltage of 42 volts. However, this transition cannot take place instantaneously. Indeed, many consumers must always be supplied with a voltage of 14 volts, such as filament signal lights for example.

Thus, it is necessary to make the 2 electrical networks coexist, respectively 12 volts and 42 volts within the same motor vehicle.

 The invention also relates to dual voltage networks of the 42 volt / 12 volt type.

 The alternator which delivers energy to the electrical network of the motor vehicle transforms mechanical energy into electrical energy when the armature is formed by the stator to operate as an electric generator. When the armature is formed by the rotor, this alternator constitutes an electric motor and transforms electrical energy into mechanical energy. Thus, the alternator can be reversible, its rotor possibly constituting an armature as mentioned above in certain situations to form a motor vehicle alternator-starter making it possible to start the motor of the motor vehicle.

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 The invention applies to the electrical networks of motor vehicles powered by a conventional alternator. It also applies to starter alternators.

 This alternator-starter can be integrated into the clutch and thus be secured axially in rotation with the crankshaft of the internal combustion engine of the motor vehicle. By way of example, reference will be made to the electric machine described in document FR 2,782, 355.

 This alternator-starter can also be separated from the crankshaft. In this case, this electric machine is constituted by a conventional alternator, integral in rotation with the drive belt integral in rotation with an output shaft of the internal combustion engine. For more details, see document FR 2,807, 231.

 Motor vehicles are subject to constant vibration during operation. These vibrations can induce short circuits between 2 wires or between a wire and a conductive part of the vehicle due to wear of the wire insulation. These short circuits are generally resistive. Indeed, the short-circuit current does not exceed a few tens of amps and therefore does not blow the protection fuses. However, these resistive short-circuits can cause the wire to heat up by the Joule effect, which can lead to the fire of the motor vehicle.

 One solution would be to use for the insulating sheath of the wire, a material which has a melting point included in a very low temperature range. So the short circuit quickly becomes straightforward

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 which causes the immediate protection fuse to blow. However, this solution has the disadvantage of being expensive.

 The object of the invention is therefore to overcome this drawback, in a simple and economical manner.

 It therefore relates to a method for detecting a short circuit in a motor vehicle electrical network comprising a dual-voltage network in which the currents flowing in each of the branches of the high-voltage electrical network to which the electric machine, high-voltage battery, high-voltage electric consumers and a DC / DC converter characterized in that the mass current of all the high-voltage consumers connected at a single point is measured and considered to be there is a short circuit if the sum of the currents is not zero.

 Consequently, an economical short-circuit detection method system is obtained since the consumption of the high-voltage charges is only carried out by a single measurement.

 This method has in one embodiment the following characteristic according to which the detection of a short circuit is detected if the absolute value of the sum of the currents is equal to a low non-zero current which corresponds to the margin of error due to the imprecision of current dedicated measurement devices.

 The invention also relates to a device for detecting a short circuit in a motor vehicle electrical network comprising a dual-voltage network, in which on the high-voltage network are

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 connected, the electric machine, a high voltage battery, a DC / DC converter and high voltage loads characterized in that all the masses of the high voltage loads are connected at a single point to a current sensor to measure the total mass current of all these consumers.

 Consequently, an economical short-circuit detection system is obtained because the connection of all the ground wires of the high-voltage consumers are all located under the engine cover of the motor vehicle. Another advantage is that this detection device requires the addition of only one additional current sensor.

 This device can advantageously be supplemented by one or more of the following characteristics: - the current sensor is a hall effect sensor.

- the current sensor is connected to a control box (Cl, C2, C4, CM).

- the electric machine is an alternator.

- the electric machine is an alternator-starter.

Other object, characteristics and advantages of the invention will emerge from the following description, given solely by way of example, and made with reference to the appended drawing in which - Figure 1 is a diagram which describes an exemplary embodiment of the 'invention
As illustrated in FIG. 1, an electrical machine 1 of the alternator or alternator-starter type is connected to an electrical network A of the 42 volt type. On this network, are connected in particular a battery 2

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 of 42 volts, loads 3 operating at a voltage of 42 volts and a converter 4 of the DC / DC type. By way of nonlimiting example, the 42 volt loads may consist of an additional device for heating the passenger compartment, wiping motors, a device for controlling electromagnetic valves, an electric power steering, etc.

 The electric machine 1, depending on whether it operates in alternator mode or in alternator-starter mode respectively supplies or receives to / from the electrical network A an electric current of intensity Il.

 Battery 2 of 42 volts, can receive a charging current 12, or, if consumers need, supply a current 12.

 A 3 DC / DC converter, for supplying the secondary network B with 12 volts receives a current 13 which makes it possible both to supply the DC / DC converter as well as to supply the current necessary for the low voltage network B of 12 Volt.

 On this secondary network B are connected a 12 volt battery 6 which can receive a charging current or supply energy to supply the low voltage loads 5.

 This low voltage battery can also supply energy to the high voltage network via the DC / DC converter which in this case will supply current 13 to the high voltage network.

 According to the invention the masses of the high-voltage equipment, connected to the network A of 42 volts, are connected at a single point. This ground connection point can be made at terminal B-of high-voltage battery 2 or at the body

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 of the motor vehicle. A current 14 then passes through this ground wire which connects the masses of all the high voltage electrical consumers.

 To detect the presence of an electrical short circuit in the network, in the context of the present invention, it is necessary to measure all the currents flowing in the different branches of the electrical network.

 Thus, to measure each of the currents Il, 12, 13 and 14, a current sensor is used such as for example a hall effect sensor. Each of the branches of the high voltage network, through which the currents Il, 12, 13 and 14 flow, has a current sensor C1, C2, C3 and C4.

 These various current sensors are connected to a computer such as for example a motor control computer CM to which it communicates the value of the measured current.

 The computer then performs the summation of all these currents 11 + 12 + 13 + 14. If the result of this summation is zero, this indicates that there is no current leakage.

 Advantageously, to overcome the margins of error due to the imprecision of the current sensors, it may be considered that there is a current leak if the absolute value of 11 + 12 + 13 + 14 is greater than 5 amps. This value is given for information only and must be assessed according to the imprecision of the current measurement sensors.

 In practice, the currents associated with the electric machine, the battery and the DC / DC converter are already known. Thus, high voltage batteries are

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 provided with an electronic box generally called Battery Management System which is able to measure the battery current 12. These Battery Management systems are capable of performing several functions such as for example the automatic disconnection of the battery, the measurement of the charging current.

 Likewise, the alternator and the DC / DC converter contain electronics capable of measuring and communicating respectively the currents Il and 13 which pass through their connection points to the electrical network.

 Advantageously, all of these electronic boxes are connected to a multiplex network of the VAN or CAN type, for example, as well as the engine control box.

So there is no need to pull additional wires
In a multiplexed architecture, it is no longer necessary, to measure the currents 11, 12 and 13, to use specific current sensors as described above, these measurements being carried out by their associated multifunction boxes. It is therefore no longer necessary to use individual current sensors Cl, C2 and C4.

 To measure current 14, an economical solution according to the invention consists in connecting all the masses of consumers of the high voltage network A. By the architecture of motor vehicles, all these high voltage consumers are placed under the engine hood or in an environment extremely close to it. Thus, to connect all the ground wires of high voltage consumers, it will be necessary to connect the ground wires of short length being

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 given that these high voltage consumers are all close to each other.

 Obviously, it is possible to transpose these current measurements to the low voltage network B to detect short-circuits on this network. However, the implementation of this measure in the low voltage network B would require the use of ground wires of great length. Indeed, these low-voltage consumers are generally distributed at the four corners of the vehicle, such as for example the traffic lights.

 The present invention therefore provides a very particular advantage for the detection of short circuits in the context of a dual-voltage network. Indeed, by limiting itself to the measurement of the currents which flow on the high voltage network A, an effective solution is obtained at low cost. In fact, existing electronic boxes are used which are possibly connected to a multiplex network associated with a measurement of the ground current of the high voltage loads 14 which requires low cost implementation thanks to their close location.

 With this method, it is thus possible to detect short circuits between 42-volt and 12-volt networks as well as between 42-volt networks and ground by the additional addition of a single additional current sensor mounted on the point that connects all the masses of high voltage consumers connected to each other by a cable having an economically acceptable length of wire in the field of the automotive industry.

 The ground wire which connects all high voltage consumers can be connected to the chassis

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 the automobile. In this case, it is necessary to use a current sensor, for example a hall effect which will itself be connected to any electronic control unit, for example by a wired link or by the Can network.

 If the sum of the currents 11 + 12 + 13 + 14 is not zero or the absolute value of this sum is greater than a value representative of the tolerable measurement error of the currents, then the box which is responsible for detecting this short circuit can, for example, to avoid vehicle fire, issue an order via the multiplex network, to the box which manages the battery. These boxes generally include a switch which automatically disconnects the battery. Thus, when a short circuit is detected, an order to disconnect the high voltage battery can be given, thereby protecting the vehicle from a possible fire.

 This invention is of particular interest in the case of high voltage networks of the 42 volt type which have greater consequences than on a low voltage network of the 12 volt type in the event of a short circuit.

Claims (7)

1. Method for detecting a short circuit in a motor vehicle electrical network comprising a dual-voltage network, according to which the currents (II, 12, 13) passing through each of the branches of the high-voltage electrical network ( A) to which the electric machine (1) is connected the high voltage battery (2) and high voltage electric consumers (3) and a DC / DC converter (4) characterized in that the ground current (14) is measured ) of all high voltage consumers (4) connected at a single point and that it is considered that there is a short circuit if the sum of the currents 11 + 12 + 13 + 14 is not zero.  2. Method for detecting a short circuit in a motor vehicle electrical network according to claim 1 characterized in that the detection of a short circuit is detected if the sum of the currents 11 + 12 + 13 + 14 is equal to a low non-zero current which corresponds to the margin of error due to the imprecision of the current dedicated measurement devices Il, 12, 13 and 14.  3. Device for detecting a short circuit in a motor vehicle electrical network comprising a dual-voltage network (A, B), in which on the high-voltage network (A) are connected, the electrical machine (1) , a high voltage battery (2), a DC / DC converter (4) and high voltage loads (3) characterized in that all the masses of the high voltage loads (3) are connected at a single point to a <Desc / Clms Page number 11>  current sensor (C3) for measuring the total ground current (14) of all these consumers.  4. Device for detecting a short circuit in a motor vehicle electrical network according to claim 3 characterized in that the current sensor is a hall effect sensor.  5. Device for detecting a short circuit in a motor vehicle electrical network according to claim 3 characterized in that the current sensor is connected to a control box (Cl, C2, C4, CM).  6. Device for detecting a short circuit in an electrical network of a motor vehicle according to claim 1 characterized in that the electric machine (1) is an alternator.  7. Device for detecting a short circuit in an electrical network of a motor vehicle according to claim 1 characterized in that the electric machine (1) is an alternator-starter.