Method and device for monitoring an energy reserve and safety device for a vehicle

Abstract

A method for monitoring an energy reserve for a safety device for a vehicle includes the task of evaluating a change of a voltage present in the energy reserve between a starting value suitable for operating the safety device and a test voltage value suitable for operating the safety device to monitor the energy reserve.

Claims

1. A method for monitoring an energy reserve for a safety device for a vehicle, the method comprising: partially discharging the energy reserve, recharging the energy reserve after the partial discharge, evaluating a period of time of the recharging from a starting value to a test voltage value, wherein the period of time is monitored and evaluated to determine whether the energy reserve is functional.

2. The method of claim 1, wherein the evaluating is carried out repeatedly several times during a driving cycle of the vehicle.

3. The method of claim 1, further comprising: changing the voltage present in the energy reserve between the starting value and the test voltage value to induce the change in voltage.

4. The method of claim 1, wherein the voltage present in the energy reserve is varied between the test voltage value and the starting value.

5. The method of claim 1, wherein during the evaluating, it is evaluated whether the voltage present in the energy reserve, as a result of the change in voltage, reaches the test voltage value within a predetermined period of time.

6. The method of claim 5, wherein the voltage present in the energy reserve is changed to the starting value as soon as the voltage present in the energy reserve, as a result of the change in voltage, reaches the test voltage value within a predetermined period of time.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1a schematically shows a representation of a vehicle, including a device for monitoring the energy reserve according to one exemplary embodiment of the present invention.

(2) FIG. 1b shows a block diagram of one exemplary embodiment of the present invention.

(3) FIG. 1c shows a device for monitoring an energy reserve for a safety device for a vehicle according to one exemplary embodiment of the present invention.

(4) FIG. 2 shows a graphic representation of a voltage present in an energy reserve for a safety device during a monitoring process according to one exemplary embodiment of the present invention.

(5) FIG. 3 shows a graphic representation of the voltage present in a safety device for an energy reserve according to one exemplary embodiment of the present invention.

(6) FIG. 4 shows a graphic representation of the voltage present in a safety device for an energy reserve according to another exemplary embodiment of the present invention.

(7) FIG. 5 shows a flow chart of a method for monitoring an energy reserve for a safety device for a vehicle according to one exemplary embodiment of the present invention.

DETAILED DESCRIPTION

(8) In the following description of exemplary embodiments of the present invention, identical or similar reference numerals are used for elements which are similarly operative and represented in the various figures, so that a repeated description of these elements is omitted.

(9) FIG. 1a schematically shows a representation of a vehicle 100 including a safety device 102, an energy reserve 105 for safety device 102 and a device 108 for monitoring energy reserve 105 according to one exemplary embodiment of the present invention.

(10) A safety device 102 may be an airbag system, which includes, for example, an airbag and a control unit for controlling the at least one airbag. Safety device 102 may, however, also represent another occupant protection system. For example, safety device 102 may, in addition to or as an alternative to an airbag, also include other restraint devices, belt tensioners, roll-bars or the like, and corresponding controls. Energy reserve 105 is connected to safety device 102 and is configured to supply energy to safety device 102 for operating safety device 102 at least during the failure of a main power supply. Device 108 for monitoring is coupled to energy reserve 105 in order to monitor a functional capacity of energy reserve 105. For this purpose, device 108 for monitoring is configured to evaluate a change in voltage in energy reserve 105. In addition, device 108 for monitoring may be configured to carry out the change in voltage in energy reserve 105.

(11) FIG. 1b shows a block diagram of a charge and discharge circuit of an energy reserve 105 according to one exemplary embodiment of the present invention. Energy reserve 105 may be the energy reserve for a safety device of a vehicle shown in FIG. 1a. The circuit includes a converter 110, which is implemented as a DC/DC step-up converter, a charge circuit 115 for energy reserve 105 connected to ground 120 and a discharge circuit 125 for energy reserve 105.

(12) Step-up converter 110 is fed with voltage V.sub.Bat at an input of an on-board battery of the vehicle. An output of step-up converter 110 is connected to integrated charge circuit 115 for energy reserve 105 and supplies a voltage converted from voltage V.sub.Bat to an input of charge circuit 115. An output of charge circuit 115 is connected to a terminal of energy reserve 105. Charge circuit 115 is configured to supply a charge voltage to energy reserve 105 for charging energy reserve 105. Another terminal of energy reserve 105 is connected to ground 120. Positioned parallel to charge circuit 115 is discharge circuit 125 for discharging energy reserve 105. A terminal of circuit 125 for discharging the energy reserve is connected to a node 130. The node is also situated between circuit 115 for charging the energy reserve and a terminal of energy reserve 105. A voltage measurement may be carried out at node 130, where the measurement may be carried out either by an analog/digital converter or by a circuit having fixed comparator thresholds. For example, the measurement may be carried out from the device for monitoring the energy reserve shown in FIG. 1a. Charge circuit 115 and discharge circuit 125 may each include control inputs, via which a charge function of charge circuit 115 and a discharge function of discharge circuit 125 may be controlled. A corresponding control may, for example, be carried out from the device for monitoring the energy reserve.

(13) In the event of a failure of battery voltage V.sub.Bat, the safety device may be operated via energy reserve 105.

(14) An exemplary embodiment of the present invention relating to an airbag system of a vehicle is described below with reference to FIG. 1b. The airbag system includes energy reserve 105. FIG. 1b shows a block diagram of the energy reserve-charge/discharge circuit of the airbag system.

(15) The power supply concepts of the airbag system provide that in the event of a battery separation, i.e., for example, a disconnection in the event of a crash, all system components may at least temporarily also be supplied self-sufficiently from separate energy store 105, in this case an energy reserve capacity. This system state is called self-sufficiency.

(16) With the aid of the integrated charge circuit in the form of DC/DC switch converter 110, including current limiter 115, energy reserve 105 is initially charged to a high voltage level (for example, 33 V) and then serves as a central power source for the entire airbag system self-sufficiently. The capacitance value of energy reserve 105 is initially measured during system start-up, and is evaluated with the aid of software diagnosis in the airbag system. In the event of a defect, i.e., too little energy reserve capacitance, a system error is stored and the driver is informed by the activated airbag warning light. If the defect in the energy reserve capacitance occurs only during the course of the operating cycle, the defect may be handled in the instantaneous cycle with the aid of a diagnosis and an error display. Thus, it is also possible to detect cyclically any errors existing in energy reserve capacitance 105 and to inform the driver when the system availability is affected. The central mechanism of the test is to briefly increase or reduce the voltage present in energy reserve 105 from the nominal value 33 V to a different level and to monitor this process. In the process, the change in voltage is kept low enough so that no other circuit components are disrupted or the period of self-sufficiency is not affected. For example, lowering the voltage in the energy reserve Elko too much would shorten the period of self-sufficiency if the battery disconnection occurs immediately after the start of the test.

(17) FIG. 1c shows a circuit including a device 108 for monitoring an energy reserve 105 for a safety device for a vehicle according to one exemplary embodiment of the present invention. Shown is the arrangement described previously with reference to FIG. 1b, consisting of a converter 110, a charge circuit 115 and a discharge circuit 125. Terminals of the charge circuit 115, the discharge circuit 125 and energy reserve 105 are connected to one another via a shared node 130.

(18) A detection unit 135 is connected to node 130. Detection unit 135 is configured to carry out a voltage measurement at node 130. Thus, detection unit 135 is configured to detect a voltage present in energy reserve 105. Detection unit 135 is configured to supply values of the detected voltage to device 108.

(19) During normal operation, the safety device is supplied by an energy supply with an operating voltage necessary for operating the safety device. Energy reserve 105 is charged by the energy supply during normal operation. In the event of a failure, for example, due to an accident, energy reserve 105 is configured to supply the safety device with the operating voltage necessary for operating the safety device. Energy device 105 is sized in order to supply energy necessary for activating the safety device. Device 108 is configured to monitor whether energy reserve 105 is able to supply sufficient energy for operating the safety device in the event of a failure of the power supply.

(20) For this purpose, device 108 is configured to control charge circuit 115 and discharge circuit 125 in order to effect a change in voltage in energy reserve 105. Device 108 is configured to evaluate the change in voltage detected by detection unit 135 and in response to the evaluation of the change in voltage to decide whether energy reserve 105 is functioning error-free or whether it is defective. If energy reserve 105 is classified as defective, device 108 may then output a warning signal which warns of the defect of energy reserve 105.

(21) Depending on the exemplary embodiment, device 108 is configured to monitor the time or the voltage during a charging operation or alternatively a discharging operation of energy reserve 105 by controlling charge circuit 115 and discharge circuit 125. FIGS. 2 through 4 show voltage curves for corresponding exemplary embodiments of the present invention.

(22) According to one exemplary embodiment of the present invention, described below in greater detail with reference to FIG. 2, charge circuit 115 is deactivated and discharge circuit 125 is activated for monitoring energy reserve 105. Device 108 is configured for evaluating the voltage drop detected by detection unit 135 in energy reserve 105 from the moment of discharge. If within a predefined period from the moment of discharge, the voltage present in energy reserve 105 does not fall below a predefined threshold, energy reserve 105 is detected as adequate. If within the predefined period from the moment of discharge the voltage present in energy reserve 105 drops below the predefined value, device 108 is configured to disconnect discharge circuit 125 from energy reserve 105 and to activate charge circuit 115. In this way, the voltage in energy reserve 105 may be prevented from dropping too low as a result of the monitoring and thereby jeopardizing the operational readiness of the safety device. In such a case, energy reserve 105 is considered to be defective. Device 108 is configured to output a signal for indicating defective energy reserve 105.

(23) Other measures may also be carried out which are intended to ensure that the discharge of energy reserve 105 is suppressed or discontinued as quickly as possible in the event of an imminent airbag release. This may prevent a monitoring of energy reserve 105 from being carried out when an application of energy reserve 105 is imminent. An additional test lock or a termination of the monitoring may be carried out when a battery disconnection is detected. The battery disconnection may be detected with the aid of a V.sub.Bat-low voltage threshold, i.e., when a voltage drops to the V.sub.Bat-low voltage threshold. It is also possible to lock the test of energy reserve 105 as soon as ASIC system trigger-related signals are present, such as the release of the ignition circuits. In addition, the test of energy reserve 105 may not be started by software if initial crash information has been detected in the system, i.e., as soon as the pre-fire or crash algorithm becomes active.

(24) In other exemplary embodiments described in greater detail below with reference to FIGS. 3 and 4, the charging operation is monitored instead of the discharging operation. According to the method described in greater detail below with reference to FIG. 3, a partial discharge of energy reserve 105 initially takes place. The energy reserve is then recharged and a period of time of recharging is evaluated by device 108. For this purpose, the device is configured to disconnect charge circuit 115 from energy reserve 105 and to connect discharge 125 until the operating voltage in energy reserve 105, beginning with a normal operating voltage, reaches a lower threshold. Compliance with the threshold is monitored at node 130 with the aid of detection unit 135 from device 108. Once the lower threshold is reached, device 108 is configured to disconnect discharge circuit 125 from energy reserve 105 and to reactivate charge circuit 115. The subsequent charging operation of energy reserve 105 is carried out until the normal operating voltage value is reached. Device 108 is configured to ascertain and evaluate a period of time of the charging operation. Depending on the period of time, device 108 is configured to decide whether the energy reserve is functional or is defective.

(25) According to a method described in greater detail below with reference to FIG. 4, energy reserve 105, beginning with the normal operating voltage, is initially charged further and subsequently discharged again. In the process, the duration of the charging operation is evaluated by device 108. Instead of the operating voltage, beginning with the normal operating voltage value, first dropping with the aid of discharge circuit 125, it is also possible to increase the operating voltage, starting from normal operation, to an upper threshold value of the operating voltage. For this charging operation, a new setpoint value for the operating voltage or charge voltage to charge circuit 115 is predefined by device 108. A change in voltage at node 130 caused by the charging operation is detected by detection unit 135 and evaluated by device 108. A change in voltage caused as a result of the charging operation and the duration of the charging operation form the basis for calculating the capacitance present in energy reserve 105, which is compared with a setpoint value in device 108. If the capacitance of energy reserve 105 lies below the predefined setpoint value for the capacitance of energy reserve 105, a monitoring signal for a defective energy reserve 105 is then output. Once the upper threshold value for the operating voltage is reached, marking the end of the charging operation, device 108 is configured to output corresponding control signals so that charge circuit 115 is disconnected from energy reserve 105, discharge circuit 125 is connected to energy reserve 105 and the voltage present in energy reserve 105 is again lowered to the value determined for normal operation. Once the value of the operating voltage for normal operation is reached, device 108 is configured to output corresponding control signals so that charge circuit 115 is again connected to energy reserve 105 and discharge circuit 125 is disconnected from energy reserve 105. Thus, the initially prevailing state is reached once again and the monitoring may be cyclically repeated.

(26) By monitoring the energy reserve, it is possible to check a functional capacity of the energy reserve. In particular, it may be checked whether the energy reserve is able to supply sufficient energy for operating the safety device in the event of a failure of the power supply. The monitoring of the energy reserve may be repeated several times during a driving cycle of the vehicle, for example, at predetermined timed intervals.

(27) The driving cycle may correspond to an operating cycle of the vehicle which, in addition to the driving of the vehicle, may also include operation-related stops, such as at a traffic light or in stop-and-go traffic. Thus, the energy reserve may be monitored during the operation of the vehicle and, in particular, as the vehicle is traveling.

(28) FIGS. 2 through 4 show voltage curves of the operating voltage during a monitoring cycle of the energy reserve for a safety device in a vehicle according to different exemplary embodiments of the present invention.

(29) FIG. 2 shows a graphic representation of the voltage present in an energy reserve for a safety device according to one exemplary embodiment of the present invention. The energy reserve may be the energy reserve for a safety device shown in FIGS. 1a, 1b and 1c. Shown is a voltage curve in a Cartesian coordinate system during a monitoring operation of the energy reserve. Represented on the abscissa is time t and on the ordinate is voltage V present in the energy reserve.

(30) Plotted on the ordinate are a starting value V.sub.1 and a test voltage value V.sub.2. Values V.sub.1 and V.sub.2 are indicated as dashed boundary lines in the coordinate system. Two curve profiles 210, 220 show two different voltage curves during a monitoring operation of one exemplary embodiment of the method according to the invention. The voltage has value V.sub.1 up to a point in time t. Value V.sub.1 thus corresponds to a normal operating voltage of the energy reserve. The monitoring operation starts at a point in time t.sub.1. A discharge of the energy reserve starts from the moment in time t.sub.1 on. The discharge is completed at the latest at subsequent point in time t.sub.2.

(31) Voltage curve 210 shows a voltage curve which indicates a defect of the energy reserve. Conversely, voltage curve 220 shows a voltage curve which indicates a correct function of the energy reserve.

(32) Voltage curve 210 extends to point in time t.sub.1 at the level of starting value V.sub.1. At point in time t.sub.1, voltage curve 210 drops sharply and intersects before point in time t.sub.2 the lower threshold value defined by test voltage value V.sub.2 for the voltage present in the energy reserve.

(33) Voltage curve 220 extends to point in time t.sub.1 at the level of starting value V.sub.1. At point in time t.sub.1, voltage curve 220 drops slowly and by point in time t.sub.2 has not reached the lower threshold value defined by test voltage value V.sub.2 for the voltage present in the energy reserve.

(34) The representation of an exemplary embodiment of a monitoring according to the present invention of the voltage existing in the energy reserve for a safety device shown in FIG. 2, shows in the case of voltage curve 210 a test of a defective energy reserve, whereas voltage curve 220 represents a test of a correctly functioning energy reserve. In the exemplary embodiment of a method according to the present invention shown in FIG. 2, the time interval between point in time t.sub.1 and point in time t.sub.2 is defined in advance.

(35) The method shown in FIG. 2 may be described as a method in which starting value V.sub.1 is greater than test voltage value V.sub.2. The voltage drop in the time period between points in time t.sub.1 and t.sub.2 is detected and evaluated. The voltage drop may be induced by deactivating a charge circuit of the energy reserve and activating a discharge circuit of the energy reserve. Thus, the method shown in FIG. 2 may be described as a method in which during the step of evaluating an amount of change in voltage within a predetermined period of time is evaluated.

(36) According to one exemplary embodiment, the voltage in the energy reserve is actively lowered through brief deactivation (for example, 10 ms) of the energy reserve charge circuit and additional switching on of a current-limited charge current source (for example, 5 mA). If in the process a fixed voltage threshold V.sub.2 (for example, 31 V, that is 2 V below nominal value V.sub.1 of 33 V) is not reached within a fixed period, then a complete failure of the energy reserve capacity may be concluded, for example, through disconnection of the Elko or a faulty soldered joint and/or conductor path or contact. In this case, the fixed thresholds V.sub.1, V.sub.2 may be monitored directly in the hardware, for example by comparators, or with the aid of measurements via an ADC.

(37) FIG. 3 shows a graphic representation of voltage present in an energy reserve for a safety device according to one exemplary embodiment of the present invention. The energy reserve may be the energy reserve for a safety device shown in FIGS. 1a, 1b and 1c. Shown is a voltage curve in a Cartesian coordinate system during a monitoring operation of the energy reserve. Represented on the abscissa is time t and on the ordinate is voltage V present in the energy reserve.

(38) Plotted on the ordinate are a starting value V.sub.3 and a test voltage value V.sub.4. Values V.sub.3 and V.sub.4 are indicated as dashed boundary lines in the coordinate system. Two curve profiles 310, 320 show two different voltage curves during a monitoring operation of one exemplary embodiment of the method according to the invention.

(39) Voltage curve 310 shows a voltage curve which indicates a defect of the energy reserve. Conversely, voltage curve 320 shows a voltage curve which indicates a correct function of the energy reserve.

(40) Voltage curve 310 extends to point in time t.sub.3 at the level of starting value V.sub.4, then drops in a straight line until point in time t.sub.4 at the level of starting value V.sub.3. Between point in time t.sub.4 and point in time t.sub.5, voltage curve 310 rises to the level of second operating voltage V.sub.4. Time interval t.sub.1 is defined as the time span between point in time t.sub.4 and point in time t.sub.5. Voltage difference V is defined as the degree of difference between starting value V.sub.3 and test voltage V.sub.4. Second voltage curve 320 extends to point in time t.sub.3 at the level of test voltage value V.sub.4 and then drops in a straight line to point in time t.sub.6 at the level of starting value V.sub.3. Between point in time t.sub.6 and point in time t.sub.7 voltage curve 320 rises to the level of second operating voltage V.sub.4. Time interval t.sub.2 is defined as the time span between point in time t.sub.6 and point in time t.sub.7. In the exemplary embodiment shown in FIG. 3, time difference t.sub.1, t.sub.2 is evaluated in order to draw a conclusion about the functionality of the energy reserve. During the step of evaluating, an increase from lower operating voltage value V.sub.3 to comparatively higher operating voltage value V.sub.4 may be evaluated over time during a charging operation in order to calculate the capacitance of the energy reserve.

(41) The representation of an exemplary embodiment of a monitoring according to the present invention of the voltage present in the energy reserve of a safety device depicted in FIG. 3 shows in the case of voltage curve 310 a test of a defective energy reserve, whereas voltage curve 320 represents a test of a correctly functioning energy reserve. In the exemplary embodiment of a method according to the present invention shown in FIG. 3, the voltage difference between starting value V.sub.3 and test voltage value V.sub.4 is defined in advance.

(42) The method shown in FIG. 3 may be described as a method in which starting value V.sub.3 is smaller than test voltage value V.sub.4. Voltage gain V and the time interval between a first point in time t.sub.4, t.sub.6 and a second point in time t.sub.5, t.sub.6 is detected and evaluated. The voltage drop may be induced prior to the charging operation by deactivating a charge circuit of the energy reserve and activating a discharge current source of the energy reserve. If the lower operating voltage V.sub.3 is reached, it is then reversed, i.e., the discharge current source is deactivated and the charge current circuit is activated. The method shown in FIG. 3 may thus be described as a method in which during the step of evaluating, an amount of time span within a predefined voltage difference is evaluated.

(43) As in the case of the exemplary embodiment shown in FIG. 2, the energy reserve in the exemplary shown in FIG. 3 is discharged during the cyclical test with the aid of the discharge current source. The discharge time, i.e., the time span between t.sub.3 and t.sub.4, and the allowed discharge voltage level V.sub.3 in this case may be adapted for each project and are stored in the control unit software. If the predefined discharge voltage level V.sub.3 has been reached, the voltage in the energy reserve is then charged to nominal value V.sub.4. The charge current used may be programmed according to a project and is very precise. In this case, voltage increase V in the energy reserve during charging is monitored with the aid of ADC measurements and compared to default values. Thus, it is possible to determine the energy reserve capacitance with a high degree of accuracy (C=I*t/U). If the capacitance value ascertained does not meet the required demands, i.e., it is too low, a corresponding error may then be stored and the driver informed.

(44) According to one exemplary embodiment, the discharge from original voltage value V.sub.4 to starting value V.sub.3 occurs solely as a result of leakage currents in the energy reserve. This lasts considerably longer as compared to an active discharge; however, the discharge current source may, if necessary, be omitted. Since only the following charge is measured, the duration of discharge is not important, and discharging may take place without a fixed time period up to threshold V.sub.3.

(45) FIG. 4 shows a graphic representation of the voltage present in an energy reserve for a safety device according to one exemplary embodiment of the present invention. The energy reserve may be the energy reserve for a safety device shown in FIGS. 1a, 1b and 1c. Shown is a voltage curve in a Cartesian coordinate system during a monitoring operation of the energy reserve. Represented on the abscissa is time t and on the ordinate is voltage V present in the energy reserve for a safety device.

(46) Plotted on the ordinate are a starting value V.sub.3 and a test voltage value V.sub.4. Values V.sub.3 and V.sub.4 are indicated as dashed boundary lines in the coordinate system. Two curve profiles 410, 420 show two different voltage curves during a monitoring operation of one exemplary embodiment of the method according to the invention.

(47) Voltage curve 410 shows a voltage curve which indicates a defect of the energy reserve. Conversely, voltage curve 420 shows a voltage curve which indicates a correct function of the energy reserve.

(48) Voltage curve 410 extends to point in time t.sub.8 at the level of starting value V.sub.3, then rises in a straight line until point in time t.sub.9 at the level of starting value V.sub.4. After point in time t.sub.9, voltage curve 410 drops again to the level of first operating voltage V.sub.3. Time interval t.sub.3 is defined as the time span between point in time t.sub.8 and point in time t.sub.9. Voltage difference V is defined as the degree of difference between starting value V.sub.3 and test voltage V.sub.4. Voltage curve 420 extends to point in time t.sub.8 at the level of starting value V.sub.3 then rises in a straight line up to point in time t.sub.10 at the level of test voltage value V.sub.4. After point in time t.sub.10, voltage curve 420 drops again to the level of first operating voltage V.sub.3. Time interval t.sub.4 is defined as the time span between point in time t.sub.8 and point in time t.sub.10. In the exemplary embodiment shown in FIG. 4, time interval t.sub.3, t.sub.4 is measured and, together with predefined voltage difference V, the capacitance contained in the energy reserve is determined. By comparing the capacity determined in this way with a predefined capacitance for the energy reserve, a decision may be made regarding the availability of the energy reserve.

(49) In the exemplary embodiment of the present invention underlying FIG. 4, lower operating voltage V.sub.3 is left at point in time t.sub.8, the lower operating voltage V.sub.3 in this exemplary embodiment corresponding to the operating voltage during normal operation. The control unit shown in FIG. 1c causes the charge voltage to be increased until the voltage present in the energy reserve reaches upper operating voltage V.sub.4. The charging operation is monitored and the time span for the charging operation is ascertained. Based on the time span ascertained in FIG. 4 and the predefined voltage difference, it is possible for the monitoring device to ascertain the capacitance of the energy reserve. At the point in time when the operating voltage reaches upper operating voltage value V.sub.4, the control unit causes the charge circuit to become deactivated and the discharge circuit to become activated until the operating voltage has reached lower operating voltage value V.sub.3. At the point in time at which the operating voltage reaches lower operating voltage value V.sub.3, the discharge circuit is deactivated and the charge circuit is reactivated.

(50) Unlike the exemplary embodiments shown in FIG. 2 and FIG. 3, the energy reserve Elko is not cyclically discharged during testing according to the exemplary embodiment shown in FIG. 4, but charged instead above the nominal value, for example, 33 V. The DC/DC step-up converter which generates the energy reserve voltage is set during the test to a higher setpoint value, for example, 34 V (thus, 1 V above nominal 33 V). The energy reserve Elko is charged to the new setpoint value with a precisely programmed current. The period until the new setpoint value is reached is measured, and from that the energy reserve capacitance (C=I*t/U) is determined and assessed. At the end of the test, the setpoint value of the step-up converter is reset to nominal value V.sub.3, for example, 33 V.

(51) This exemplary embodiment has the advantage that no useable energy is drawn from the Elko, although it should be ensured that a sufficiently safe distance to the clamping voltage of the internal ESD protection (typically: 38 V) is guaranteed.

(52) The cyclical energy reserve monitoring may take place as follows: The test may be carried out and repeated using a software command or be reproduced in hardware in a state machine.

(53) The withdrawal of energy in the exemplary embodiments shown by way of example in FIGS. 2 and 3 is kept to an extreme minimum as a result of short testing times and minimal energy reserve discharges, such that the system availability is not jeopardized and the period of self-sufficiency is not significantly reduced. A slow repetition rate in the range of seconds also ensures that the test has no effects on EMV compatibility or the like.

(54) FIG. 5 shows a flow diagram of a method 500 for monitoring an energy reserve for a safety device for a vehicle according to one exemplary embodiment of the invention introduced. In a step 510 of importing, a voltage, also referred to as a terminal voltage, is read in at the energy reserve. The value representing the voltage, not shown in FIG. 5, may be measured in a measuring step and then, in a step of importing, read in for method 500, or alternatively, in step 510 of importing, the value of the voltage may be read in via an interface. In a step 520 of evaluating, the read-in voltage is evaluated so that conclusions can be drawn about the change in voltage and, at the same time or alternatively, about the time. Based on the evaluation in step 520 of evaluating, a conclusion may be drawn about the energy reserve, such that in a step 530 a monitoring signal may be generated. With the aid of the monitoring signal it is possible, for example, to inform a driver of the vehicle of limited system functionality.

(55) The exemplary embodiments described and shown in the figures are selected merely by way of example. Different exemplary embodiments may be combined fully with one another or with respect to individual features. An exemplary embodiment may also be supplemented by features of another exemplary embodiment. In addition, method steps according to the present invention may be repeated and implemented in a sequence different from that described.