GB2098817A

GB2098817A - Current generation system

Info

Publication number: GB2098817A
Application number: GB8208456A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1981-05-16
Filing date: 1982-03-23
Publication date: 1982-11-24
Also published as: GB2098817B; FR2506089B3; JPS57196840A; DE3119551A1; FR2506089A1

Abstract

A current-generation system having an electrical generator with controllable excitation (not shown) and with over-voltage protection (Zener diode ZD) connected to its battery-charging terminal B + includes a monitor (AV) for indicating via the charging pilot lamp (AL) failure of the over-voltage protection. A system of this kind is particularly suitable for motor vehicles. <IMAGE>

Description

SPECIFICATION Current generation system The invention relates to a current generating system comprising a generator, such as an alternator with rectified output, connectible to a battery, the generator having a voltage regulator for controlling the excitation.

Circuit arrangements for protecting vehicle electrical systems have been known for a long time. Systems of this kind generally include a Zener diode which is short-circuited when the voltage of the electrical system exceeds a predetermined upper value. The generator is thereby de-energized. Circuit arrangements are also known which indicate this shortcircuit to the user of the system by, for example, a light-emitting diode (German Patent Specification (Offenlegungsschrift) No. 28 41 544). However, circuit arrangements of this kind require additional components for indicating the short-circuiting of the Zener diode. It is impossible to obtain information as to whether the over-voltage protection can be effective or whether it might have failed.

Devices are also known which isolate the voltage regulator and/or the rectifiers of the generator from the electrical system if the battery is connected with incorrect polarity.

The present invention resides in a currentgeneration system having an electrical generator having controllable excitation and having an output connectible to a battery, a voltage regulator for controlling the excitation, a charging pilot lamp for indicating the operating state, a device for protection against overvoltage of the generator, a device for protection against the effect of a connection of the battery with incorrect polarity, and a monitor for indicating failure of the device for protection against over-voltage and/or failure of the device for protection against incorrect polarity, the device for protection against over-voltage being a series combination which comprises a fuse and a Zener diode and which is connected in parallel with the said generator output and the device for protection against incorrect polarity being a series combination comprising a fuse and a diode which is forward-biassed during normal operation, the two protective devices being connected in series with the use of one and the same fuse, and the monitor having a first control input terminal which is connected to the junction between the two protective circuits a second control input terminal which is connected to an operating switch and a switching output terminal which is connected to a pilot lamp.

This has the advantage that the over-voltage protective device and the device for protection against connection with incorrect polarity, are combined in a simple manner.

It is more particularly advantageous for the response of one of the two protective devices to be indicating by the charging pilot lamp provided in the system. Furthermore, it is highly advantageous for effective information to be given as to whether one and/or the other of the two protective devices is still effective or whether it has failed. The simple construction and the ready possibility of connection to existing systems are advantageous.

The invention is further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a circuit diagram of a currentgeneration system having a voltage regulator, a generator, a vehicle electrical system and two protective devices, Figure 2 is a circuit diagram of a system of this kind but having a device for detecting faults, and Figure 3 is a circuit diagram showing the combined protective devices.

Fig. 1 shows a current-generation system for a mechanically propelled vehicle and having a generator GEN and a voltage regulator SR. The generator GEN is in the form of a three-phase alternator which comprises, in a known manner, a rotating e,scitation winding EW, a stationary three-phase winding PW, and a rectifier assembly GR which is connected to the output of the three-phase winding PW and which has six main current diodes HD and three excitation current diodes ED. The voltage regulator SR is a conventional voltage regulator and its circuit components, other than its output transistor, have therefore not been shown. The output transistor is connected in series with the excitation winding EW of the generator GEN by way of a brush holder BH.A battery SA and a switch 5W leading to loads V1 are connected to the terminal B + of the main current diodes HD.

One terminal of a pilot lamp AL is connected to an output D + of the excitation diodes ED.

The other terminal 1 5 of the pilot lamp AL is connected to the output terminal B + by way of an operating switch ZS (the ignition switch in the case of a petrol engine) and to further loads V2 by way of a switch SW2.

Further modules are included in this known current-generation system and are intended to protect the system against damage which could be caused by an over-voltage or by connection of the battery with incorrect polarity. In addition, a monitor AV is provided. A terminal A2 of the monitor AV is connected to the terminal B + of the generator, a terminal B2 is connected to the terminal 1 5 of the pilot lamp AL, a terminal C is connected to one end (facing the generator terminal D +) of the pilot lamp AL, and a terminal M is connected to earth (the vehicle chassis).A protective diode D1 for protecting the monitor AV from over voltage or connection of the battery with reverse polarity is connected between one terminal (facing the generator terminal D +) of the pilot lamp AL and the terminal D + itself, and a protective resistor R1 is connected across the series combination comprising the diode D1 and the pilot lamp AL.

The connection of the monitor AV is somewhat simplified in the current generator of Fig. 2 which includes a device FA for indicating faults. in a system of this kind, one terminal of the pilot lamp AL, serving as a charging pilot lamp, is connected to the device FA for indicating faults. The protective diode D1 and the protective resistor R1 of Fig. 1 are not required. The current-generation system of Fig. 2 is otherwise wired in substantially the same manner as the currentgeneration system of Fig. 1.

Fig. 3 shows details of the invention. As already mentioned, the terminal A2 of the monitor AV is connected to the positive pole B + of the battery SA. A series combination comprising a fuse SB, a forward-biassed diode D2 and a reverse-biased Zener diode ZD is connected between the terminal A2 and the chassis terminal M. The diode D2 protects the Zener diode ZD in that a current of virtually unlimited value is prevented from flowing in the forward direction of the Zener diode in the event of the battery SA being connected with incorrect polarity. The monitor AV includes a control transistor T1 and a switching transistor T2.The base of the control transistor T1 is connected by way of a leakage resistor R4 to the emitter, connected to the chassis M, of the control transistor T1, the base of the transistor T1 at the same time being connected by way of a resistor R3 to the junction Al between the diode D2 and the Zener diode ZD. The collector terminal B1 of the control transistor T1 is connected to the base of the switching transistor T2 whose emitter is also connected to the chassis M. The collector terminal B1 of the control transistor T1 is connected by way of a resistor R2 to the connection terminal B2 of the monitor AV, and the terminal B2 is connected to the terminal 1 5 of the charging pilot lamp AL.As already described, the collector terminal C of the switching transistor T2 is connected to that end of the charging pilot lamp AL which leads to the excitation diode terminal D + .

During normal operation, the positive potential of the battery SA is essentially applied to the terminal Al by way of the fuse SI and the diode D2. The control transisitor T1 is conductive, and consequently the collector terminal B1 is approximately at the potential of the chassis M. The switching transistor T2 is thus non-conductive. In the event of a high current surge (during which the Zener diode ZD limits the voltage applied to the terminal Al) or in the event of a short-circuit of the Zener diode ZD, the previously determined admissible i2t value is exceeded and the fuse SI melts.

Consequently, there is no longer any control current available on the terminal Al, and the control transistor T1 is blocked. As a result of the blocking of the control transistor T1, current flows into the switching transistor T2 by way of the resistor R2 and the terminal B1, and the switching transistor T2 becomes conductive. The charging pilot lamp AL lights up.

Hence, by virtue of the preferred embodiment of the invention, the charging pilot lamp AL already provided indicates whether the device for protection against over-voltage (SI, ZD) and/or the device for protection against connection with incorrect polarity (SI, D2) is defective.

If a hybrid regulator SR without a fault indicator FA is used, the protective diode D1 has to be connected between the charging pilot lamp AL and the terminal D + as shown in Fig. 1. In order to ensure reliable preexcitation in the event of failure of the over-voltage protection (SI, ZD), it is advisable to connect the resistor R1 in parallel with the series combination comprising the charging pilot lamp AL and the diode Dl. The two circuit elements D1 and R1 are not required when a hybrid regulator SR is used in conjunction with a fault indicator FR, as shown in Fig. 2.

Claims

1. A current-generation system having an electrical generator having controllable excitation and having an output connectible to a battery, a voltage regulator for controlling the excitation, a charging pilot lamp for indicating the operating state, a device for protection against over-voltage of the generator, a device for protection against the effect of connection of the battery with incorrect polarity, and a monitor for indicating failure of the device for protection against over-voltage and/or failure of the device for protection against incorrect polarity, the device for protection against over-voltage being a series combination which comprises a fuse and a Zener diode and which is connected in parallel with the said generator output, and the device for protection against incorrect polarity being a series combination comprising a fuse and a diode which is forward-biassed during normal operation, the two protective devices being connected in series with the use of a one and the same fuse, and the monitor having a first control input terminal which is connected to the junction between the two protective circuits a second control input terminal which is connected to an operating switch and a switching output terminal which is connected to a pilot lamp.

2. A system as claimed in claim 1, in which the charging pilot lamp is used as the pilot lamp.

3. A system as claimed in claim 2, in which the output switching terminal and the charging pilot lamp are connected to that terminal of the excitation winding which is connected to the rectifier assembly.

4. A system as claimed in claim 3, in which a protective diode is connected between the output switching terminal of the excitation winding which is connected to the rectifier assembly, and a protective resistor is connected between the operating switch and that terminal of the excitation winding which is connected to the rectifier assembly.

5. A system as claimed in any preceding claim, in which the monitor includes a control transistor and a switching transistor, the control terminal of the control transistor being connected to the first control input terminal the control of the switching transistor being connected to the output terminal of the control transistor and (by way of a further component if required) to the second control input terminal, and the output terminal of the switching transistor being the switching output terminal.

6. A current-generation system constructed and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.