TECHNICAL FIELD

The present invention relates to means for determining the charging of a vehicle storage battery, comprising a connection between one pole of the storage battery and the ground contact, which is connected via an electrical conductor to a sensor means.

PRIOR ART

There is a demand for the ability to monitor the charging status in the storage battery of a vehicle. After a number of cold starts, trips with small mileage or with use of energy demanding extra equipment in the vehicle, there is a risk that the effective output of the generator is not sufficient to drive all equipment and simultaneously give enough energy for recharging the storage battery. Fur¬ thermore, an accumulator battery is successively aged, which means that it takes a longer time to recharge it, and that the total accumulator capacity is reduced. Power dissipation may also occur in the generator or other parts of the electric system, so that the output of the generator is reduced or a voltage drop occurs.

Having access to information about the charging status of the battery, the driver of the vehicle will be able to avoid starting problems, e.g. by changing an old battery, by adjustment of the power consumption so that the battery get proper charging or by additional recharging of an temporarily run-down battery.

Known means for determining the charging of a battery does not consider the age of the battery. Besides, they need rather deliberate and expensive sensor means for detection.

TECHNICAL PROBLEM One object of the present invention is therefore to provide a simple and efficient sensor means which can be used for determining the charging status of a storage battery.

THE SOLUTION

This object is achieved according to the invention, in that the sensor means comprises a source of electric power for producing at least one electric current, and at least one current feed unit, wherein values which are deducted from the current flowing through the connection are measured and delivered to the sensor means and are used for determining said charging status.

According to preferable embodiments of the invention, the connection comprises a conductor which connects said bat¬ tery pole to the body or the chassis of the vehicle, and the connection and the conductors which are connected to the sensor means may form a common cabling. Thus the sensor will be simple to integrate in the wiring system of a vehicle.

Preferably, the cabling comprises an un-insulated cabling ground braid with a cable shoe in each of its ends and two insulated conductors, one end of which is connected to the respective cable shoe and wherein the other ends are connectable to the sensor means.

DESCRIPTION OF THE DRAWINGS

One embodiment of the invention will be described in more detail in the following with reference to the attached

drawing, diagrammatically showing a storage battery con¬ nected to a vehicle according to the invention.

PREFERRED EMBODIMENTS

The reference 10 in the drawing designates a storage bat- tery conventionally connected with both its poles 11, 12 to the wiring system of a vehicle via a ground connector 13 and a current connector 14. Each end of the ground con¬ nector 13 is provided with a cable connector 15 and 16 respectively and is mounted with metallic connection by screws to the vehicle body 15, so that it can be used as a return conductor to the battery by the generator and the power consumers in the wiring system, e.g. outer and inner lighting, air-conditioning plant, radio and so on.

The storage battery 10 is used conventionally, to deliver energy to a starter motor for starting a combustion engine and to provide a storage means for the energy consumption, when the output of the generator alone is not sufficient for balancing the energy consumption in the electricity system of the vehicle. The battery 10 is recharged for as long as the voltage is lower in the battery than in the electricity system.

The battery status, i.e. the amount of charge, depends upon several different parameters, e.g. the discharging currency and the pole tension, temperature, capacity and age of the battery. Information of these parameters can according to the invention be obtained by means of a sensor, which is designed as a measuring shunt and comprises the ground connector 13 which is mounted between the body 17 and the battery pole 11. This connector can without any special efforts be devised in such-way that it presents a suitable resistance, for example l mΩ. This resistance can be utilized for measuring the battery current and the tension over the two shunt points, i.e. 15, 16.

For this purpose, an insulated conductor 18, 19 has been connected to each of the cable connectors 15, 16. These conductors connects both shunt points to a central unit 20, preferably comprising a micro processor, current measuring units, a source of constant current for production of at least one current, and an interface unit for adapting the input signals from the sensors, which apart from the measuring shunt 13 may comprise temperature sensors on combustion engine and battery, and an engine speed sensor.

The resistance in the measuring shunt 13 depends for example upon oxidation on the metallic connections of the connectors 15, 16, the body 17 and the battery pole 11. Therefore, the central unit must be updated within certain intervals regarding this parameter, as well as in regard to other parameters concerning battery- and engine tempera¬ ture. For this end, the above described source of constant current is used for measuring the resistance in the conductor 13 during a measuring sequence.

A presentation unit is connected to the central unit 20 via a wiring 21 and is placed at the instrument panel of the vehicle, so that the charging status of the battery 10 can be displayed to the driver. The presentation unit can comprise any type of conventional display means like a pointer, a warning light or similar types of indicator instruments within the field.

The sensor according to the invention can be applied together with the central unit and presentation unit to various types of vehicles, for example passenger cars and lorries, motor cycles and leisure boats.

The invention is not limited to the above described embo¬ diment example and more variations are possible within the scope of the following claims. For example, the conductor

13 may compose an un-insulated braided ground cable or alternatively some form of insulated conductor. Further¬ more, any kind of conductor which connects the car body and the battery pole can be used.