Electrical system for motor vehicles

An electrical system (1) for motor vehicles, with a generator (6) and with double batteries (3,7), one of them a starting battery (3) and the other a consumer battery (7), has a charging regulator (9) between the generator and the starting battery. The charging regulator (9) is arranged between the batteries (3,7) and separates them and can regulate the magnitude of the charging current to the starting battery (3).

TECHNICAL DOMAIN
 The present invention relates to an electrical system with double
 batteries, particularly for motor vehicles.
 STATE OF THE ART
 A practice known from, for example, DE 40 28 242 A1 is the use of double
 batteries in an electrical system for motor vehicles. In such cases, the
 starting battery and the starter motor form a starting battery side, while
 the generator, consumer battery and other consumers form a consumer
 battery side. A problem with this type of electrical system is that of
 simply and safely separating the two battery sides so that the starting
 battery is always kept well charged. Another problem with known solutions
 is that they often use relays which, like cables and contact devices, have
 to be amply dimensioned in order to cope with the currents which occur
 during charging.
 OBJECT OF THE INVENTION
 The invention has the object of providing an electrical system which
 constitutes a simple, inexpensive and reliable solution for separating the
 two batteries. A further object is to ensure that the starting battery is
 kept as well charged as possible.
 SUMMARY OF THE INVENTION
 The object of the invention is achieved by executing the aforeside
 electrical system by providing a charging regulator.
 The chosen location of the charging regulator creates a simple separation
 of the batteries, while current regulation to the starting battery creates
 the possibility of moderate charging currents which permit relatively thin
 conductors and connections.
 Further providing the charging regulator with transistors of a special type
 creates the possibility of safe supply of current from each battery to an
 engine control unit which is essential for the operation of the engine.

DESCRIPTION OF A PREFERRED EMBODIMENT
 An electrical system 1 (in FIG. 1) intended for a motor vehicle includes
 not only a starting battery side 2 with a starting battery 3 and a starter
 motor 4 but also a consumer side 5 with a generator 6, a consumer battery
 7 and a number of consumers here represented by a consumer 8. As used
 herein, the term "consumer" means a device in the car which uses
 electrical energy. Between the starting battery side 2 and the consumer
 battery side 5 there is a charging regulator 9 which controls the current
 between the two sides. An engine control device 10 is connected to the
 charging regulator 9 and receives via the latter its power supplied either
 from the starting battery side 2 or from the consumer battery side 5, as
 will be described in more detail further on. The charging regulator 9 is
 connected to the electrical system 1 via conductors 11, 12 and 13.
 As may be seen in more detail in FIG. 2, there is in the charging regulator
 9 an electronic control device 14 with connections 15, 16 and 17. Two
 transistors T1 and T2 are each connected respectively to connections 15
 and 16 and receive their control signals from the control device 14. In
 conductor 11 there is, after transistor T2, a measuring device 18 with a
 current shunt 19 for measuring the strength of the current in the
 conductor 11. The control device 14 receives via the conductor 17 a signal
 representing the measured strength of the current.
 In the embodiment depicted, the two transistors T1 and T2 are MOSFET
 transistors (enrichment type, N-channel) and are connected together by
 common D-electrodes in the conductor 13. The respective diodes D1 and D2
 built into the two transistors are directed towards one another and can
 both allow current to pass to conductor 13.
 Operation is as follows:
 In inactive states of the electrical system 1, the starting battery side 2
 and the consumer battery side 5 are kept separate by the fact that
 transistors T1 and T2 block contact between conductors 11 and 12. Despite
 this, the engine control device 10 can nevertheless be supplied with
 current from whichever of the batters 3 and 7 has the higher voltage. This
 takes place via diodes D1 and D2. Starting can thus take place even if the
 consumer battery 7 is completely uncharged.
 In active states of the electrical system 1, when the engine is running and
 the generator 6 is charging, transistor T1 turns on in order to reduce the
 power losses in the transistor. This is achieved by diode D1 in the
 transistor being bypassed and the current passing through the transistor
 instead. When the generator begins to charge, transistor T2 is turned on
 slowly by the control device 14. This means that the powerful current peak
 created when the generator begins to charge is eliminated and the maximum
 strength of current to the starting battery in conductor 11 can be limited
 to a desired level. When the strength of current has decreased
 sufficiently and the starting batteries 3 is charged, the control device
 14 disconnects the current to the starting battery by turning off
 transistors T1 and T2. This reduces the water consumption in the starting
 battery.
 Transistor T2 is controlled analogously (i.e., by applying an analog signal
 thereto from the engine control unit 14 via the conductor 16) in order to
 achieve the graduated current regulation referred to. The control of
 transistor T1 may, however, be analog or digital by applying either analog
 or digital signals thereto from the engine control unit 14 via the
 conductor 15.
 And advantage of the electrical system 1 according to the invention is that
 the vehicle will continue to travel even if the control device 14 ceases
 to function. Although the charging of the starting battery 3 ceases when
 transistor 2 cannot be turned on, but this malfunction can be indicated to
 the driver so that the fault can be rectified.
 The resulting strength of current in conductor 11 may be adjusted as
 necessary by suitable choice of transistors T1 and T2 and by suitable
 control of them.