GB2385217A

GB2385217A - Overvoltage protection for a vehicle

Info

Publication number: GB2385217A
Application number: GB0223066A
Authority: GB
Inventors: Rainer Topp
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2001-10-05
Filing date: 2002-10-04
Publication date: 2003-08-13
Anticipated expiration: 2022-10-04
Also published as: GB2385217B; DE10149113B4; FR2830693B1; DE10149113A1; FR2830693A1; GB0223066D0

Abstract

The present invention provides a voltage supply device (1), in particular for a vehicle electrical system, with a protective function for protecting electronic components against overvoltages, to which device a network voltage can be fed from an electrical voltage source (2), with a first and a second output connection (7, 8); with at least one voltage limiting device (3) connected to the electrical voltage source (2) and to the output connections (7, 8), for limiting overvoltages of the network voltage; with a controllable absorber device (4) connected to the output connections (7, 8) for receiving an absorber current; and with an electronic monitoring device (5) that is connected to the voltage source (2) and to the absorber device (4), for measuring voltage values supplied by the voltage source (2) and for generating a control signal for the absorber device (4) based on the measured voltage values. The voltage limiting device (3) may be a zener diode or a power transistor, for example, and the absorber device may be a current sink.

Description

Voltage Supply Device. in particular for a Vehicle Electrical System, with

a Protective Function for Protecting Electrical Components against Overvoltages 5 PRIOR ART

The present invention relates to a voltage supply device, in particular for a vehicle electrical system, with a protective function for protecting electrical components against overvoltages.

Although applicable to circuits in general, the following invention as well as the problem area on which it is based will be discussed with reference to an electrical system installed in a vehicle.

It is generally known that overvoltages are induced directly or indirectly in the case of inductive loads such as coils or the like. Particularly damaging overvoltages are produced for example by a poor contact or a momentary separation of the battery during operation of the generator (load dump). For example, in the vehicle sector overvoltages of up to 80 V may occur in a time o interval of 400 milliseconds with a supply voltage of 12 V. These transient overvoltages may destroy various electronic circuits, for example integrated circuits in the vehicle, if these are not effectively protected against such overvoltages. It is possible to prevent a disruption of the electronic components by overvoltages in the electrical system of a vehicle by configuring the corresponding components in each case corresponding to the maximum occurring voltage peaks. This is however extremely cost-intensive and is not economically viable.

- 2 The problem on which the present invention is based generally consists therefore in providing a voltage supply device that is intended to protect more effectively components configured for a normal operation, against overvoltages of the network voltage of a generator.

Passive diode rectifiers with Zener diodes are suitable for limiting overvoltages produced by the generator to a desired value above the normally adjusted voltage of the vehicle electrical system.

o A disadvantage of this arrangement is the fact that the Zener diode clamp voltage has a large tolerance range and depends to a considerable extent on the temperature of the component. More specifically, a thermal stress on the Zener diodes leads to a rising junction temperature and thus to an increasing breakdown voltage of the diode during operation. In a transition to for example a higher voltage of a vehicle electrical system, for example to a 42 V voltage, as is already planned for large- scale production, these tolerance and temperature dependencies are thus too large for a satisfactory application.

DE 197 10 073 Al describes an overvoltage protection device for protecting o electrical installations against overvoltages, the installation comprising a vehicle electrical system fed by an electrical generator and electrical devices connected thereto, with a voltage limiting device whose threshold lies above the generator rated voltage, a unit being connected at the output side of the generator in parallel to the vehicle electrical system, which unit comprises at least one power branch in parallel to the vehicle electrical system with at least two resistor components, wherein at least one resistor component can be controlled so as to reduce the resistance if the limiting threshold is exceeded.

/ The disadvantage of this arrangement is the fact that, due to the clamping of the load dump voltage exclusively via a separate active voltage limiting module, a complete separation of the rectifier functions and voltage limiting functions occurs in various sub-assemblies, with the result that this system has to be 5 designed in a very complicated and cost-intensive manner in order to buffer the overall load dump excess power. In addition a failure of the module, whether due to the failure of individual module components or due to the separation of one of its connections at the positive or negative terminal, cannot be detected especially in normal operation. Thus, the system cannot be converted to a safe state before o the occurrence of an overvoltage and the risk of a failure of large parts of the vehicle electronics cannot be reduced in the event of an overvoltage.

A further approach is to achieve a load dump voltage limitation by shortcircuiting all three phase connections of the stator windings of the generator to an output capacitor via the upper switching transistors of an inverter when the load drop condition occurs. All the excess power of the generator is thus fed in the event of an overvoltage to the output capacitor. In order to ensure a sufficiently low output voltage ripple in normal operation of the generator, the output capacitor should preferably be designed large. The excess power that is generated accordingly 2 o does not lead to an unallowable voltage rise at the generator output.

However, the disadvantage with this arrangement is that this system can be used only with a sufficiently large output capacitor. Also, for reasons of cost and space efforts are being made to develop generator systems and active rectifier and/or inverter systems without large output capacitors. An enlargement of the output capacitors simply in order to buffer the load dump energy is not sensible for cost reasons.

- 4 ADVANTAGES OF THE INVENTION

The voltage supply device according to the invention with the features of claim l has the advantage compared to the known solutions that the generator components 5 already required for normal operation can be used both for voltage rectification and/or smoothing in normal operation as well as for voltage limitation in the case of load dump interference, and that nevertheless a sufficiently narrowly tolerable load dump voltage limitation is also possible for example for 42 V vehicle electrical systems.

The idea forming the basis of the present invention is that a generator system whose integrated overvoltage limitation capacity is not sufficiently efficient for specific load cases is provided between its direct voltage output connections with at least one additional energy absorber device for receiving specific pulse 5 energies, and this absorber device is connected by at least one signal line to the generator control electronics.

Advantageous developments and improvements of the protection device disclosed in claim l are contained in the subclaims.

According to a preferred development the monitoring device generates a control signal that determines the size of the absorber current.

According to a further preferred development the absorber device has a 2 5 controllable current sink.

- 5 - According to yet a further preferred development the absorber device has a logic control unit connected to the controllable current sink, to which unit the control signal can be transmitted.

According to yet another preferred development the logic control unit transmits a state information message via the absorber current occurring at the absorber device, to the monitoring device to effect a function monitoring.

According to another preferred development the absorber device has an additional o voltage limiting device that is connected to the controllable current sink. This device serves as an additional safety device that becomes operational in the event of a failure and/or an overload of the voltage limitation in the rectifier and/or inverter or in the event of a failure of the control capacity of the current absorber, and constitutes an additional protection for limiting the overvoltages in the vehicle electrical system. Preferably however the value of this voltage limitation should be set sufficiently high so that it is not operational if the voltage limitation in the rectifier and/or inverter is functioning correctly.

According to a further preferred development the monitoring device presets for o the absorber device at specified regular time intervals current values to be adjusted for the function testing.

According to a further preferred development the monitoring device on receiving a negative function state of the absorber device controls the voltage source so as to adopt a defined safety state.

According to a further preferred development the control signal can be transmitted to a control line that is formed as a bidirectional 1-wire control line.

- 6 According to a further preferred development the voltage source is formed as a three-phase alternating current generator.

According to a further preferred development the voltage limiter integrated in the generator is provided as part of a rectifier device.

According to a further preferred development the activation of the current absorber is effected in such a way that the current value preset by the monitoring o device and that is to be adjusted is dependent on the measured current value of the generator output.

According to a further preferred development the voltage limiter integrated in the generator comprises a semiconductor component, for example a Zener diode.

According to a further preferred development the voltage limiter integrated in the generator comprises an output capacitor.

DRAWINGS

One embodiment of the invention is illustrated in the drawing and is described in more detail in the following description.

The sole figure is a schematic representation of a protection device according to one embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

- 7 - The voltage supply device 1 shown in the figure was developed for a vehicle electrical system and has a protective function to protect electronic components against overvoltages.

The reference numeral 2 denotes a conventional three-phase alternating current generator whose three output lines are connected to a rectifier 3, which likewise comprises a conventional voltage limiting device that serves to limit the overvoltage in order to protect the electronic components of a vehicle electrical system to be protected and that is connected to the output connections 7, 8.

Preferably the voltage limiter in the rectifier 3 consists of components already present in the vehicle electrical system, for example rectifier Zener diodes in the case of a passive rectifier or an output capacitor in the case of an active rectifier.

These components absorb as far as possible the load dump energy in the case of an overvoltage and limit the maximum output voltage in the load dump case.

These components should preferably be configured corresponding to the requirements they have to meet in normal operation, i.e. there is no over-

dimensioning on the grounds of overvoltage protection requirements.

The voltage limiter in the rectifier 3 is connected to a monitoring device 5, the electronics of the monitoring device 5 activating, in the event of an overvoltage, the switching states of the corresponding bridge transistors necessary for the voltage limitation in an active rectifier and/or inverter of the voltage limiter. The corresponding components of the voltage limiter thus switch from their normal operation to an overvoltage protection operation and are activated for the overvoltage protection operation.

In each limiting device there may also be used inverters with passive or active overvoltage limitation.

The voltage limiter is for example connected to the three phase connections of the stator windings of the generator 2 via the switching transistors of an inverter or rectifier. The voltage supply device 1 furthermore comprises an absorber device 4 that is preferably indirectly connected to the generator 2 via the output connections 7, 8 o of the rectifier 3 with voltage limiter. The absorber device 4 serves to absorb specific overvoltage energies and accordingly comprises a controllable current sink 41, for example in the form of a power transistor.

The absorber device 4 in addition supports the overvoltage limitation of the rectifier 3, the absorber device 4 preferably being configured as regards its performance so that, in the most unfavourable overvoltage operating state, it can absorb such a load current and/or such an overvoltage energy that is necessary in order to be able to maintain the overvoltage limiting function of the rectifier or inverter of the voltage limiter or the maximum output voltage of the generator 2 in o the event of an overvoltage, below a specified critical value. In this way the maximum permissible voltage of the vehicle electrical system is not exceeded and the electrical components of the vehicle electrical system and the generator 2 are not damaged on account of a voltage pulse that is too high.

The absorber device 4 preferably comprises an internal logic control unit 40 that converts with respect to time and height of the absorber current a control signal transmitted from the monitoring device 5 to the control line 6, and correspondingly controls the current sink 41.

- 9 This logic control unit preferably also transmits back a state information message via the current occurring at the absorber device 4 for the function monitoring at the monitoring device 5. To this end the current is detected at the absorber device 4 and a status notification is transmitted via the control line 6 to the monitoring device 5. The control line 6 is in this connection preferably formed as an additional bidirectional 1-wire control line 6.

The status notification and/or state information message contains for example o information on whether the output current of the absorber device 4 delivers, according to the corresponding presetting, a correct current value or a markedly deviating current value, for example on account of a failure of the power components or on account of a drop of the power connections of the absorber device 4.

The absorber device 4 preferably comprises an additional voltage limiting device 42 that is provided as an additional safety measure to limit the overvoltages in the vehicle electrical system if for example the voltage limiting devices in the rectifier and/or inverter of the current limiter in the rectifier 3 fail and/or are overloaded.

Since the functionality of the voltage limiting device 42 is difficult to check and is provided only to safeguard against the failure of other measures for suppressing load dump overvoltages, it should be dimensioned in such a way that it is not used if the voltage limiting device in the rectifier 3 and the remaining parts of the absorber device 4 are functioning correctly.

As already mentioned above, the absorber device 4 is connected via the additional control line 6 to the monitoring device 5, which latter in turn is formed either as

part of the generator 2 or is at least connected to the latter. The monitoring device 5 executes all the control and monitoring functions of the normal operation of the generator. The monitoring device 5 preferably stores the in each case actual value of the generator output current and/or a corresponding correlation value, for 5 example the control/pulse duty factor of the excitation current. The monitoring device 5 thus measures the voltage rise at the generator output caused by an overvoltage and switches the states of the corresponding transistors in the rectifier 3 that are necessary to effect voltage limitation.

o In the event of a detected overvoltage the monitoring device 5 activates and controls the absorber device 4 so that the latter draws a defined load current between the output terminals of the rectifier 3 and thereby absorbs a defined overvoltage energy. In this connection the load current of the absorber device 4 is preferably preset by the monitoring device 5 depending on the generator output current stored before the occurrence of the overvoltage, and is maintained for a predetermined time and/or until the voltage drops below a defined generator output voltage. The maximum permissible voltage of the vehicle electrical system is thus not exceeded and the components of the system are not damaged due to overvoltage peaks.

For the function monitoring of the absorber device 4, the monitoring device S transmits, preferably at regular intervals, a preset signal of a load current to be applied and checks the status information sent back from the absorber device 4.

In the case of a negative status information report during such a test cycle, the 2 monitoring device 5 can control the electronics of the generator 2 so as to adopt a predetermined safety state. Damage to the electronics of the generator 2 is thus also prevented in the event of a failure of the absorber device 4.

: The present invention provides an efficient, reliable and inexpensive protection device against overvoltages, since the generator components already required for normal operation are utilised both for voltage rectification and/or smoothing in normal operation as well as for voltage limitation in overvoltage operation.

At the same time the additional power absorber device can be suitable scaled down as regards volume and costs depending on the respective application.

Furthermore, the protection device according to the present invention can also be 0 used for example for 42 V vehicle electrical systems since a sufficiently narrowly tolerated overvoltage limitation is possible.

It is also possible to check at regular intervals the overvoltage limiting components in order to avoid extensive consequent damage. Finally, the Is protection device according to the invention also ensures an at least sufficient overvoltage protection in the event of a failure of one of the two parallel activatable protection elements, namely on the one hand the limiting components of the rectifier 3, and on the other hand the components of the absorber device 4.

o Although the present invention has been described hereinbefore with the aid of a preferred embodiment, it is not restricted to the latter but can be modified in many different ways.

Claims

- 12 CLAIMS

1. Voltage supply device (1), in particular for a vehicle electrical system, with a protective function to protect electronic components against overvoltages, to 5 which device a network voltage can be supplied from an electrical voltage source (2), comprising: a first and a second output connection (7, 8); o at least one voltage limiting device (3) connected to the electrical voltage source (2) and to the output connection (7, 8), for limiting overvoltages of the network voltage; a controllable absorber device (4) connected to the output connection (7, 8) for s receiving an absorber current; and an electronic monitoring device (5) that is connected to the voltage source (2) and to the absorber device (4), for measuring voltage values supplied by the voltage source (2) and for generating a control signal for the absorber device (4) based on o the measured voltage values.

2. Device according to claim 1, characterised in that the monitoring device (5) generates a control signal that determines the size of the absorber current.

3. Device according to one of claims 1 and 2, characterized in that the absorber device (4) comprises a controllable current sink (41).

4. Device according to claim 3, characterized in that the absorber device (4) has a logic control unit (40) connected to the controllable current sink (41), to which unit the control signal can be fed.

5 5. Device according to claim 4, characterized in that the logic control unit (40) transmits a state information message via the absorber current adjusted at the absorber device (4), to the monitoring device (5) to effect a function monitoring.

6. Device according to at least one of the preceding claims 3 to S. o characterized in that the absorber device (4) has an additional voltage limiting device (42) that is connected to the controllable current sink (41).

7. Device according to at least one of the preceding claims 5 and 6, characterized in that the monitoring device (5) presets for the absorber device (4) is at specified regular time intervals current values to be adjusted for the function testing.

8. Device according claim 7, characterized in that the monitoring device (S) on detecting a negative function state of the absorber device (4) controls the 2 o voltage source (2) so as to adopt a defined safety state.

9. Device according to at least one of the preceding claims, characterized in that the control signal can be transmitted to a control line (6) that is formed as a bidirectional 1-wire control line.

10. Device according to at least one of the preceding claims, characterized in that the voltage source (2) is formed as a three-phase alternating current generator (2).

11. Device according to claim 10, characterised in that the voltage limiting device (3) is provided as part of a rectifier device.

5

12. Device according to claim 11, characterized in that the monitoring device (5) for an activation of the voltage limiting device (3) based on the measured voltage values is connected to the latter.

13. Device according to at least one of the preceding claims, characterised in 0 that the voltage limiting device (3) comprises a semiconductor component, in particular a Zener diode.

14. Device according to at least one of the preceding claims, characterised in that the voltage limiting device (3) comprises an output capacitor.

15. Device substantially as hereinbefore described with reference to the accompanying drawing.

16. Use of the device according to at least one of claims 1 to 15 in a 42 V o vehicle electrical system.