GB2333914A - Monitoring operation of switch - Google Patents

Abstract

A switching relay 100, which may operate a fuel injection valve 120 in a vehicle internal combustion engine, has a coil 105 which closes contacts 107 when a controller 110 actuates a control switch 115. When contacts 107 are closed, a capacitor 140 is charged from supply Ubat. When the contacts open, the capacitor discharges through resistors 180,190. If the controller detects a fault, switch 115 is opened. In normal operation, the load is turned off by switch 127, allowing current to flow to capacitor 140 which then acts as a booster when the load is next turned on. The controller 110 monitors the charge and discharge behaviour of the capacitor when the relay is switched on and off so as to detect faulty operation of the contacts 107. The switches 115,125,127,150 may be field effect transistors.

Description

1 2333914 METHOD AND MONITORING MEANS FOR MONITORING SWITCHING MEANS The

present invention relates to a method and monitoring means for monitoring switching means.

A method and a device for functional monitoring of an electrical load are known from DE 40 05 609 (US 5 430 438), in which a resistance-capacitance member distinguishes whether an interruption of a line or a short-circuit to ground is present. The method exploits the fact that different discharge times result for discharge by way of a resistancecapacitance member and a resistance-inductance member. Monitoring of switching means is not provided in the case of this method and device. It is merely monitored whether the connections to the load are free of faults.

There thus remains a need for a method and means for monitoring of switching means, especially a relay.

According to a first aspect of the present invention there is provided a method for monitoring switching means, especially a relay, wherein a capacitor is chargeable from a voltage source by way of the switching means and is discharged by way of discharging means, wherein the functional ability of the switching means is deduced from the state of charge of the capacitor.

Preferably, the switching means comprises a relay, by way of which loads, especially valves which control the admetering of fuel, are supplied with voltage.

For preference, the capacitor is used for drive control of the load.

A fault can be recognised when, during starting, the voltage across the capacitor deviates from an expected value andlor a fault can be recognised when, during the running-on, the voltage across the capacitor does not fall to an expected value within a preset time.

According to a second aspect of the invention there is provided monitoring means for monitoring switching means, especially a relay, with a capacitor which is chargeable from a voltage source by way of the switching means and is discharged by way of discharging 2 means, with means which, starting from the state of charge of the capacitor, recognise the functional ability of the switching means.

In the case of a method exemplifying and monitoring means embodying the invention, a fault in switching means, especially a constantly closed switching means, can be recognised reliably. For this purpose, only a few additional components may be needed. Components already present in an associated circuit may be able to be utilised in particularly advantageous manner.

Examples of the method and embodiments of the monitoring means of the invention will now be more particularly described with reference to the accompanying drawings, in which:

Fig. 1 is a block diagram of monitoring means embodying the invention; and Figs. 2a and 2b are flow charts illustrating steps in methods exemplifying the invention.

Referring now to the drawings there is shown in Fig. 1 monitoring means associated with a load used in a motor vehicle and, as is commonly the case, connected by way of a relay 100 with a supply voltage UBat. It can be provided that several loads together are connected with the supply voltage UBat by way of the relay 100. For reasons of safety, it must be recognised when the switching contact of the relay remains in its closed position. This means that sticking of the relay must be reliably recognised. The circuit incorporates means whereby reliable recognition of a sticking relay is possible. The manner of procedure is not, in fact, restricted to relays and can be used for other switching means.

In the illustrated embodiment, the relay comprises a relay coil 105 and switching means 107, which is denoted in the following as a switching contact 107. The switching contact connects the load 120 with the supply voltage UBat and the coil 105 is connected with ground by way of a relay control switch 115.

The relay control switch 115 is controlled by a drive control signal from a control unit 110, 1 3 By way of the switching contact 107, the supply voltage UBat is present at a high-side switch 125, which is connected in series with the load 120 and a low-side switch 127. This arrangement is chosen only by way of example and merely a low-side switch or merely a high-side switch can be provided.

The junction between the low-side switch 127 and the load 120 is connected by way of a first diode 130 with a first terminal of a capacitor 140. The second terminal of the capacitor 140 is connected to ground. The first terminal of the capacitor 140 is also connected by way of a booster switch 150 with the junction between the load 120 and the high-side switch 125. The low-side switch 127, the high-side switch 125 and the booster switch 150 are also controlled by drive control signals from the control unit 110. The load is supplied with voltage by way of the relay 100, in particular by way of the switching contact 107.

Such a circuit can be used for, for example, the drive control of an electromagnetic valve, i.e. the load 120 is an electromagnetic valve. Such a valve can serve for control of the admetering of fuel, such as the control of fuel injection in an internal combustion engine.

The switching contact 107 also connects the supply voltage UBat with the anode terminal of a diode 160. The cathode of the diode 160 is connected by way of a resistor 170 with the first terminal of the capacitor 140 and with a further resistor 180. The second ten-ninal of the resistor 180 is connected with the control unit 110 and, by way of a resistor 190, with ground.

The switches 115, 125, 127 and 150 are preferably transistors, in particular field effect transistors. The resistors 180 and 170 have higher values than the resistor 190. The resistors 170 and 180, for example, assume values of about 1 megohm and the resistor 190 about 50 kilo-ohms. The capacitor has, for example, a capacitance of 15 microfarads.

In use, depending on different operating parameter magnitudes the control unit 110 determines the drive control signals for action on the different switches 115, 125, 127 and 150. In normal operation, the relay control switch 115 is controlled in such a manner that it frees the current flow. This has the effect that the switching contact 107 is in its closed position. Thus, supply voltage is present across the series connection consisting of the high-side switch 125, the load 120 and the low-side switch 127.

4 If a fault occurs, the control unit 110 passes a signal to the relay control switch 115. The current flow through the coil 105 of the relay 100 is thereby interrupted and the switch 107 passes over into its opened position, so that the load 120 is separated from the supply voltage UBat. A corresponding separation between the supply voltage and the load preferably takes place also when an internal combustion engine, associated with the circuit, is switched off.

The current flow through the load is controlled by drive control of the low-side switch 127 and the high-side switch 125. On opening of the lowside switch 127, the current flow through the load is interrupted, which leads to a high induced voltage across the terminals of the load. This released energy passes by way of the diode 130 into the capacitor 140. There, it is intermediately stored and applied to the load in order to switch this on more rapidly during the next drive control by way of the booster capacitor 150. The capacitor 140 is therefore also a booster capacitor.

The connecting of the switching means 125, 127 and 150 of the load 120, the diode 130 and the capacitor 140 are illustrated merely by way of example. Other circuit arrangements can also be provided, by which energy is stored in a capacitor in order to switch on a load more rapidly.

If the switching contact 107 remains in its closed setting, the load can no longer be separated reliably from the supply voltage in the case of a fault in the region of the lowside switch or of the high-side switch. For this reason, such a fault of the switching contact 107 must be recognised.

The switching contact 107 connects the capacitor 140 with the voltage source UBat. The capacitor is charged by way of the dosed contact 107. The capacitor is discharged by way of the resistors 180 and 190. These resistors can also be termed discharge means. Starting from the charged state of the capacitor, i.e. starting from the voltage across the capacitor 140, the functional capability of the switching contact 107 can be deduced.

As mentioned, the switching contact 107 is connected by way of the diode 160 and a highresistance resistor 170 with the booster capacitor 140. On starting of the engine, the voltage across the capacitor 140 is read in during the initialisation of the control unit 110. If the switching contact operates faultlessly, a booster voltage of about 0 volts is read in by the control unit 110, since the charging time constant is substantially greater than the initialisation phase of the control unit.

With the mentioned values of the resistors, a charging time of about 15 seconds results, whilst the initialising phase of the control device is substantially less than 1 second.

If the relay is defective, the capacitor 140 is then charged to a substantially higher voltage. The forward voltage of the diode 160 is known. Moreover, in the control unit 110, the supply voltage UBat is also known, since this is connected with the supply voltage either by way of a further relay or directly.

Accordingly, a voltage range can be preset, within which a defect of the relay 100 is recognised. The voltage, which is read in by the control unit 110, of the capacitor 140 supplies a statement about the state of the relay 100.

A corresponding procedure is illustrated in Fig. 2a. An interrogation step 200 checks whether the starting operation is present, i.e. whether the control unit 110 is initialised. If this is not the case, the interrogation step 200 is repeated. If this is the case, i.e. the initialisation phase is present, the voltage UC across the capacitor 140 is read in, in a step 210. A subsequent interrogation step 220 checks whether the voltage UC is greater than a value Umin and less than a value Umax. If this is the case, i.e. the voltage UC across the capacitor 140 is in a certain value range, a fault is recognised in a step 230. Otherwise, freedom from faults of the relay 100 is recognised in a step 240. A fault is recognised when, during the starting of the engine, the voltage across the capacitor deviates from its expected value.

In particular, a defect of the relay is recognised when, during the switching-on of the control unit, the voltage across the booster capacitor reaches a certain value more rapidly than expected or when the voltage does not enter a certain value range.

After the switching-off of the control unit 110, the booster capacitor 140 discharges to 0 volts by way of the voltage divider consisting of the resistors 180 and 190. If the discharge voltage is within the tolerance range for recognition of defects and a new start of the control unit takes place, this will lead to a fault recognition although the relay has no defect. Accordingly, it is therefore provided that the running-on, i.e. the switching-off 6 phase, is terminated only when the voltage across the booster capacitor 140 has fallen below the value Umin. In addition, a maximum duration for the running-on is preset by way of the discharge time constant. After this time ST is exceeded, a fault of the relay is recognised. A corresponding procedure is illustrated in Fig. 2b.

A first interrogation step 250 cheeks whether running-on is present. Usually, different checking procedures are run in sequence during the running-on. In addition, ascertained data are filed in suitable storage devices in such a manner that they are available during restarting of the engine. At the end of the running-on, the control unit 110 is separated from the supply voltage UBat.

If this is not the case, the interrogation step 250 is repeated. If a running-on is recognised, i.e. that the relay control switch 115 is controlled in drive in such a manner that the load is separated from the battery voltage UBat, then a step 255 follows. In the step 255, the voltage UC across the capacitor 140 is detected. A subsequent interrogation step 260 checks whether the voltage UC is less than a threshold value. If this is the case, the program ends in a step 265.

If this is not the case, an interrogation step 270 checks whether the time T since recognition of the running-on is greater than a threshold value ST. If this is the case, a fault is recognised in a step 290 and the program ends in a step 295. If the interrogation step 270 recognises that the time T is not greater than the threshold value ST, a time counter determining the time T is increased by the value 1 in step 280. Subsequently, the voltage UC is detected again in the step 255.

With this procedure, faults are recognised during running-on when the voltage across the capacitor does not fall to an expected value within a presettable time. It is particularly advantageous when both procedures are combined.

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Claims (12)

1. A method of monitoring switching means, comprising the steps of causing capacitance means to be charged from a voltage source by way of the switching means and discharged by way of discharging means and of determining the functional capability of the switching means from the state of charge of the capacitance means.

2. A method as claimed in claim 1, wherein the switching means comprises a relay.

3. A method as claimed in claim 1 or claim 2, wherein the switching means is operable to control supply of voltage to a load.

4. A method as claimed in claim 3, wherein the capacitance means is operable to control drive of the load.

5. A method as claimed in any one of the preceding claims, wherein the step of determining comprises recognising a fault in the switching means when, during initial operation of a circuit including the switching means, the voltage across the capacitance means deviates from a predetermined expected value.

6. A method as claimed in any one of the preceding claims, wherein the step of determining comprises recognising a fault in the switching means when, during a switching-off phase of a circuit including the switching means, the voltage across the capacitance means does not fall to a predetermined expected value within a predetermined time.

7. A method as claimed in claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.

8. Monitoring means for monitoring switching means, comprising capacitance means arranged to be chargeable from a voltage source by way of the switching means and dischargeable by way of discharging means, and means for determining the functional capability of the switching means from the state of charge of the capacitance means.

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9. Monitoring means as claimed in claim 8, wherein the switching means comprises a relay.

10. Monitoring means as claimed in claim 8 or claim 9, wherein the switching means is operable to control supply of voltage to a load.

11. Monitoring means as claimed in claim 10, wherein the capacitance means is operable to control drive of the load.

12. Monitoring means substantially as hereinbefore described with reference to the accompanying drawings.

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