GB2225874A

GB2225874A - Controlling pressure pump

Info

Publication number: GB2225874A
Application number: GB8922829A
Authority: GB
Inventors: Heinz-Theo Gaertner; Friedrich Neuhaus; Hans-Dieter Roehling; Josef Schriek
Original assignee: Hella KGaA Huek and Co
Current assignee: Hella GmbH and Co KGaA
Priority date: 1988-10-11
Filing date: 1989-10-10
Publication date: 1990-06-13
Anticipated expiration: 2009-10-10
Also published as: GB8922829D0; DE3834485C2; DE3834485A1; FR2637702B1; GB2225874B; FR2637702A1

Description

1 CONTROLLING AND MONITORING A PRESSURE GENERATING DEVICE The invention

relates to a method and to a device for controlling and monitoring the operating condition of a pressure generating device, particularly for central locking systems which can be operated by means of pressure medium in motor vehicles.

German Offenlegungsschrift 3400945 discloses a device for carrying out a method of this type in which a pump is driven by an electric motor which is electrically connected to control electronics when at least one switch connected to the control electronics is operated, in order to generate a positive and/or negative pressure in a predetermined fixed or variable volume which can be connected to the pump, and the electric motor is switched off by the control electronics when a predetermined positive and/or negative pressure is reached. In this arrangement, a central locking system of a motor vehicle has one or several control switches which are connected to control electronics. The electric motor connected to the control electronics is switched on in accordance with the position of the control switches. In this way, the direction of running of the electric motor can be reversed.

The electric motor is effectively connected to a pump which can generate a positive and/or negative pressure in a pressure line system. The pressure line 2 system has actuating elements which can be operated by means of a pressure medium and which carry out an actuating process when a predetermined pressure is reached in the pressure line system. In order to ensure that all actuating elements which can be operated by the pressure medium have carried out an actuating process when a positive and/or negative pressure is generated, a pressure switch is connected to the pressure conductor system and is electrically connected to the control electronics. The pressure switch is set to a predetermined positive pressure and a predetermined negative pressure and outputs a control signal to the control electronics when one of the set pressures has been-reached. The electric motor is switched off by the control electronics on the basis of such a control signal which indicates that all actuating elements have carried out an actuating process.

There is the disadvantage with this arrangement that the pressure switch, which indicates when the electric motor can be switched off, cannot be produced inexpensively, particularly if it has to switch with high accuracy both with a predetermined positive pressure and with a predetermined negative pressure. It is furthermore found to be disadvantageous that automatic circuit board fitting is frequently not possible with an advantageous arrangement of the pressure switch on a circuit board of the control electronics and thus separate assembly of the pressure switch is required. In this connection, the disadvantage exists that even with a preliminary setting of 1 3 the pressure switch having been effected for achieving a high switching accuracy, additional setting is required after the pressure switch has been mounted, which increases the costs.

The invention is based on the object of creating a method and a device for carrying out the method which can be mounted and produced simply and inexpensively and reliably controls and monitors the operating condition of a pressure generating system without using a pressure switch.

In accordance with one aspect of the present invention there is provided a method for controlling and monitoring the operating condition of a pressure generating device, in which a pump is driven by an electric motor which is connected to electronic control means when at least one switch connected to the control means is operated, in order to generate a positive and/or negative pressure in a space connected to the pump and the electric motor is switched off by the control means when a predetermined pressure value is reached, with each switching-on of the pump by the control means a measure of the current taken by the electric motor is evaluated and the motor is switched off in dependence thereon.

It is of advantage that a measure of the current taken by the electric motor is evaluated with each switching-on of the pump of the pressure generating device by the control means because it is possible to achieve reliable monitoring of the operating condition of a pressure generating system simply and inexpensively since k 4 the current measured is a measure of the pressure built up by the pump in the pressure generating system. In this connection, it is particularly advantageous that the motor is switched off in dependence on the current measured and evaluated because the operating condition of a pressure generating system is thus controlled in a simple and inexpensive manner since the pump is controlled by the electronic means for switching-off the pump with a predetermined positive and/or negative pressure without using an elaborate pressure switch which may be difficult to mount.

It is particularly advantageous that the measured current is evaluated at a predetermined or determinable time after the switching-on of the pump because this achieves greater accuracy since the start-up current for a pump which rises steeply after the pressure generating device has been taken into operation is excluded from the evaluation and only the relatively flat linearly rising current characteristic need be evaluated as a measure of the pressure built up in the pressure generating device.

If the time is determined by continuously determining the slope of the current/time curve after the switch-on or a switch-over of the pump, the advantage is obtained that the time at which the evaluation begins, that is to say whenever a steep rise of a start-up current changes to a flatter linear pump current, is simply and reliably determined. It is particularly advantageous that the evaluation consists of forming a difference between the current measured at the predetermined or determinable time and the current measured after this time and that the pump is switched off when a predetermined or predeterminable difference has been reached because this simple formation of a difference predetermines a reliable measure of the pressure built up in the pressure generating system and thus a reliable switching-off of the pump is achieved when a predetermined positive and/or negative pressure has been reached in a pressure generating device and tolerances of the electric motor and of the pump are compensated.

The same advantage is achieved if the evaluation lies in forming a quotient between the current measured at the predetermined or determinable time and the current measured after this time and that the pump is switched off when a predetermined or predeterminable quotient has been reached.

Due to the fact that at least one difference or one quotient is stored in a microcomputer which is a part of the electronic control means, the advantage is obtained that the switching-off time of the pump is determined in a simple and inexpensive manner.

It is advantageous that the times which are needed for reaching the predetermined or predeterminable difference or the quotient are stored in the microcomputer because thus, on the one hand, in the event of a possible malfunction in the pressure generating device, it is possible to resort to a time stored in the microcomputer for switching-off the pump and, on the other hand, changes 6 in the pressure generating devices due to ageing or due to external influences can be taken into consideration in that the pump is switched off after these stored times or the quotient to be reached or the difference to be reached for 5 switching-off is changed in the microcomputer.

Due to the fact that a stored time Is replaced by a newly determined time, the advantage is obtained that changes in the pressure generating device can be taken into consideration in a simple and inexpensive manner.

In this connection, it is of advantage that a stored time is replaced by a new time only when a predetermined number of new times has been determined and these times have been averaged because thus possibly wrong individual measurements cannot, or at least not decisively, influence the control of the pressure generating device.

It is advantageous that the times for generating a positive pressure and a negative pressure are separately stored because thus an adaptation to different situations of pressure generating devices is achieved which are due to the fact that the times for generating a predetermined positive pressure and a predetermined negative pressure differ by a factor.

Discontinuities in the current/time variation which are generated by the switching of actuating elements which can be operated by pressure medium, due to voltage dips in the supply voltage or due to fast switch-over of -the pump, can be taken into consideration in operation, giving the advantage that the reliability in control of the 1 7 pressure generating device is increased because errors in the analysis of the measured current are avoided in the case of discontinuities in the current/time curve which are generated by voltage dips in the supply voltage or by fast 5 switch-over of the pump.

In the case of discontinuities due to the switching of actuating elements which can be operated by pressure medium, the advantage is obtained that these discontinuities enable the switching of actuating elements to be determined which can be included in the evaluation and thus increases the reliability in operating the pressure generating device.

It is of advantage if the switching positions of control switches of actuating elements which can be operated by pressure medium are interrogated and evaluated since thus the reliability in monitoring and controlling the pressure generating device is increased.

It is advantageous in this connection that the pump is switched off after a predetermined safety time has elapsed because the pump is thus switched off in the event of a possible effect in the pressure generating device which prevents components of the pressure generating device being otherwise destroyed.

In the device for carrying out the method according to the invention, a sensing resistor is arranged in the electrical connection of the motor to the voltage source and a first terminal in the connection between the electric motor and the sensing resistor is connected to a 8 first input of a microcomputer of the control means.

It is of advantage that a sensing resistor is arranged in the electrically conductive connection of the electric motor with the negative pole or the positive pole of the voltage source because a current or a voltage which corresponds to the current taken by the electric motor of the pump during its operation can thus be measured in a simple manner and because this ensures simple mountability and producibility. In this connection, it is particularly advantageous that a first terminal is arranged in the connection between the electric motor and the sensing resistor and is connected to a first input of a microcomputer of the control electronics because a reliable monitoring and controlling of the operating condition of the pressure generating device is thus achieved in a simple and inexpensive manner because the microcomputer is supplied with a signal which provides a measure of the pressure generated in the pressure generating device without having to use an elaborate pressure switch which is difficult to mount, for determining a predetermined positive and/or negative pressure.

It is advantageous to connect the first terminal to the first input of the microcomputer via an amplifying circuit arrangement because an amplified signal increases the reliability of the evaluation and thus the reliability in the operation of the device.

If the amplifying circuit arrangement is constructed in such a manner that the first terminal is z 9 connected to the non-inverting input of a first operational amplifier and that the output of the first operational amplifier, on the one hand, is connected to the first input of the microcomputer and, on the other hand, via a first resistor to the inverting input of the first operational amplifier which is connected via a second resistor to the negative pole of the voltage source, the advantage is obtained that the signal which can be picked up at the first terminal can be amplified in a simple and inexpensive manner which increases the reliability in the operation of the device.

It is advantageous also if the amplifying circuit arrangement is connected to the first input of the microcomputer via a subtracting circuit arrangement because this increases the reliability in the operation of the device because thus only the signal voltage range used for the evaluation is taken into account.

Preferably, the subtracting circuit arrangement is constructed in such a manner that the output of the first operational amplifier is connected via a third resistor, on the one hand, to the non-inverting input of a second operational amplifier and, on the other hand, via a fourth resistor to the negative pole of the voltage source, that the output of the second operational amplifier is connected, on the one hand, to the first input of the microcomputer and, on the other hand, via a fifth resistor to the inverting input of the second operational amplifier, and that the inverting input of the second operational amplifier is connected via a sixth resistor to a second terminal. The advantage can then be obtained that, when this subtracting circuit is used, the first input of the microcomputer can be set, with a suitable signal present at the second terminal, to a predeterminable signal level for a time which can be predetermined by the microcomputer so that, for example, a steeply rising start-up current of the electric motor when the pump is taken into operation is not taken into consideration for the signal evaluation but only the relatively flat linearly rising pump current that follows, thereby providing an accurate measure of the positive and/or negative pressure generated by the pump in the pressure generating device.

It is advantageous in this connection that the second terminal is connected, on the one hand, via a seventh resistor to a third output of the microcomputer and, on the other hand, is connected to a second input of the microcomputer and via a first capacitor to the negative pole of the voltage source because the second terminal is thus supplied with a signal via the third output of the microcomputer and the timing section which is formed by the seventh resistor and the first capacitor, which signal generates a predetermined signal level at the first input of the microcomputer and because the signal present at the second terminal is measured via the second input of the microcomputer as a result of which an accurate control of the signal level at the first input of the microcomputer is achieved.

11 If the second terminal is connected, on the one hand, via an eighth resistor to the positive pole of the voltage source and, on the other hand, via a ninth resistor to the negative pole of the voltage source, the advantage is obtained that the second terminal is supplied in a simple and inexpensive manner with a signal by means of which the signal level at the first input of the microcomputer is set to a predetermined signal level via a period which can be predetermined or determined by the microcomputer.

It is of advantage that the first terminal is connected via a tenth resistor to the non-inverting input of the first operational amplifier and this input is connected via a second capacitor to the negative pole of the voltage source because possible interference present in the signal picked up at the first terminal can thereby be suppressed so as not to influence disadvantageously the measurement and analysis by the microcomputer.

If the microcomputer is connected to a supply voltage regulator, the advantage is obtained that the voltage supply of the microcomputer is largely independent of voltage fluctuations of the voltage source.

It is an advantage if the microcomputer has a timing section by means of which the pump is switched off after a time which can be predetermined by the timing section which is required in the event of a possible defect in the pressure generating device in order to prevent destruction of components of the pressure generating 12 device.

By way of example, in the text which follows the method according to the invention and a device for carrying out the method are described in greater detail with 5 reference to the accompanying drawings, in which:

Fig. 1 shows a circuit arrangement of a device for carrying out the method according to the invention, and Fig. 2 shows a detail of a circuit arrangement for carrying out the method within a modified embodiment.

In the circuit arrangement of Fig. 1, to supply microcomputer (MR) with the voltage generated by voltage source (B), the positive pole of the voltage source is connected via a resistor (W11) to input (E3) of the microcomputer (MR). Since the microcomputer (MR) needs a predetermined voltage, for example about 5 volts, it is connected to a supply voltage regulator (VR) which additionally has a reset output (R) for generating a resetting of the microcomputer, for example when the pressure generating device is brought into operation, or in the event of an inadmissible drop of the supply voltage from the supply voltage regulator. The supply voltage regulator (VR) is connected, on the one hand, to the positive pole of the voltage source (B) and, on the other hand, to the negative pole of the voltage source (B). The microcomputer (MR) is also electrically connected to the negative pole of the voltage source (B).

To be able to supply the microcomputer (MR) with control signals from control switches, not shown here, 13 which are arranged, for example, in actuating elements which can be operated by a pressure medium or are constructed as lock switches, the microcomputer has a number of inputs (E4,E5,E6,...) which are indicated by way of example here and which are connected to the control switches via resistors (Wl2,Wl3,Wl4, which are used for circuit matching.

For generating a positive and/or negative pressure in a pressure line system which contains actuating elements which can be operated by pressure medium, the pressure generating device has a pump, not shown here, which is operatively connected to an electric motor (E). The electric motor can be switched on by the microcomputer (MR) in dependence on control signals present at the inputs (E4,E5,E6,...). In the embodiment here shown by way of example, the direction of running of the electric motor can also be reversed.

To drive the motor in a first direction, the microcomputer (MR) has a first output (Al) which is connected to the base of a first bipolar transistor (Tl). The emitter of the first bipolar transistor (Tl) is connected to the negative pole of the voltage source (B). The collector of the first bipolar transistor (Tl) is connected to a first relay (Rl). When the electric motor (E) is to run in the first direction the bipolar transistor (Tl) is switched into the conducting state via the output (Al) of the microcomputer (MR), as a result of which the relay (Rl) connects a second armature (N2) of the electric 14 motor (E) to the positive pole of the voltage source (B). At the same time, the first armature (N1) of the electric motor is connected to the negative pole of the voltage source.

To drive the electric motor in the other direction of running, the microcomputer has a second output (A2) which is electrically conductively connected to the base of a second bipolar transistor (T2). The emitter of the second bipolar transistor (T2) is connected to the negative pole of the voltage source (B), and the collector is connected to a second relay (R2). With an appropriate signal from the control switches, the second bipolar transistor (T2) is switched into the conducting state via the second output (A2) of the microcomputer, as a result of which the second relay (R2) connects the first armature (N1) of the electric motor to the positive pole of the voltage source (B). The second armature of the motor is then electrically conductively connected to the negative pole of the voltage source.

To achieve accurate reversal of the direction of running of the electric motor, the first bipolar transistor (T1) and the second bipolar transistor (T2) are switched in accordance with the control signals present via the first output (A1) and the second output (A2) of the microcomputer (MR) either both simultaneously into the cut-off state or alternatively successively into the conducting state.

For measuring a voltage which is a measure of the current taken by the electric motor (E) during its operation, which in turn is a measure of the positive and/or negative pressure built up in the pressure line system, the electric motor is connected via a sensing resistor (M) to the negative pole of the voltage source (B). In this arrangement, the sensing resistor is alternatively connected to the first armature (N1) or the second armature (N2) of the electric motor. In the connection between the electric motor (E) and the sensing resistor (M), a first terminal (K1) is arranged which is electrically conductively connected to a first input (E1) of the microcomputer (MR) so that a voltage is present at the first input which is a measure of the current taken by the electric motor. It is thus possible for the electric motor to be switched off by the microcomputer (MR) when the measured voltage corresponds to a current which ensures that all actuating elements in the pressure line system which can be operated by pressure medium have carried out a switching process.

To suppress interference in the voltage which can be picked up at the first terminal (K1), the terminal is connected via a resistor (W10), on the one hand, to the first input (E1) of the microcomputer (MR) and, on the other hand, to the negative pole of the voltage source (B) via a second capacitor (C2).

In order to achieve an amplification and thus a higher accuracy in the analysis of the voltage which can be picked up at the first terminal (K1), the resistor (W10) and the second capacitor (C2) are connected to a non- 1 16 inverting input of a first operational amplifier (OPI). The output of the amplifier (OP1) is connected, on the one hand, to the first input (El) of the microcomputer (MR) and, on the other hand, via a resistor (Wl) to the inverting input of the amplifier which is also connected to the negative pole of the voltage source (B) via a resistor (W2).

To achieve accurate and precise measurement and analysis of the voltage or of the current, a subtracting circuit is arranged in the connection between the output of the first operational amplifier (OP1) and the first input (El) of the microcomputer (MR). In this arrangement, the output of the amplifier (OPl) is connected via a resistor (W3), on the one hand, to a non-inverting input of a second operational amplifier (OP2) and, on the other hand, via a resistor (W4) to the negative pole of the voltage source (B). The output of the second operational amplifier (OP2) is connected to the first input (El) of the microcomputer (MR) and via a resistor (W5) to the inverting input of the amplifier (OP2) which is also connected to a second terminal (K2) via a resistor (W6).

So that the steeply rising start-up current during a switching-on of the electric motor (E) is not taken into consideration in the analysis, that is to say only the flatter linearly rising pump current, which is a measure of the pressure built up by the pump in the pressure line system, is included in the analysis, the first input (El) of the microcomputer (MR) is held at a 7 17 predetermined signal level, which is here about 0 volts by way of example, up to a predetermined or determinable time after the switching- on of the electric motor (E). For this purpose, a voltage is generated at the second terminal (K2) via a third output (A3) of the microcomputer (MR), which voltage has the effect that the first input (El) of the microcomputer (MR) is held at the predetermined signal level in dependence on the signal present at the noninverting input of the second operational amplifier (OP2).

After the predeterminable or determinable time, the voltage at the second terminal (K2) is held at the value which is present at the second terminal at the predetermined or determinable time. The result is that a greater range or a greater accuracy is obtained for the analysis of the voltage which is a measure of the pressure built up in the pressure line system. With regard to this, the third output (A3) can be the output of a digital converter and is electrically conductively connected via a resistor (W7), on the one hand, to the second terminal (K2) and, on the other hand, via capacitor (Cl) to the negative pole of the voltage source (B). The resistor (W7) and the capacitor (Cl) in this arrangement act as a timing section by which a signal suitable for driving the second operational amplifier (OP2) can be formed via the digital third output (A3) of the microcomputer (MR) at the second terminal (K2). To achieve a precise and accurate control of the voltage present at the second terminal (K2), the second terminal (K2) is connected to a second input (E2) of the 18 microcomputer (MR). Thus, the voltage at the terminal (K2) is measured via this second input (E2) of the microcomputer and analysed for controlling and driving the third output (A3).

Fig. 2 shows a circuit section of a modified embodiment in which the second terminal (K2) is connected, on the one hand, via a resistor (W8) to the positive pole of the voltage source (B) and, on the other hand, via a resistor (W9) to the negative pole of the voltage source (B), in order to generate at the second terminal a voltage which is dependent on the voltage which can be picked up at the first terminal (K1). This is possible since the amplitude of the voltage of the voltage source (B) is changed when the electric motor (E) is switched on.

In order to save costs and achieve a simple construction of the device, the first operational amplifier (OP1) and the second operational amplifier (OP2) can be combined in one housing. In another embodiment, the output of the first operational amplifier (OP1) can be directly connected to the first input of the microcomputer if the accuracy of monitoring and controlling the pressure generating device in the analysis by the microcomputer meets all necessary requirements.

In another illustrative embodiment, the first terminal (K1) can also be directly connected to the first input (E1) of the microcomputer (MR) which achieves a simple and inexpensive variant which is practicable if all requirements for analysis accuracy have been met.

1.

19 The sensing resistor (M) can be constructed as a low-resistance ribbon resistor which is arranged inexpensively and simply with all other components of the circuit arrangement on one circuit board. However, the sensing resistor can also be constructed as a lowresistance wire bridge which is similarly arranged on a single circuit board.

The waiting time between the switching-on of the electric motor (E) and the start of analysis can be about 150 milliseconds in this example. However, this time can be selected to be shorter or longer depending on the conditions predetermined by the pressure generating device.

In the text which follows, different method sequences employing the circuit of Fig. 1 are described in greater detail.

When the electric (E) is switched on by the microcomputer (MR) due to control signals present at the microcomputer from control switches, one of the two armatures (N1,N2) is connected to the positive pole of the voltage source (B) depending on the required direction of running of the electric motor. The current taken by the motor during its start-up is measured via the sensing resistor (M). For this purpose, a voltage signal corresponding to the current taken is supplied to the microcomputer for measurement and analysis. During the start-up of the electric motor, the current risessteeply. This rise can be the result, for example, of having to overcome friction losses in the pump and in the pressure line system. At a fixed or variable time after the switching-on of the pump, the current rise becomes flatter and extends linearly. The analysis of the measured current or of the measured voltage begins at this time or with a predetermined safety margin from this time.

In order to increase the reliability of the monitoring and controlling operations of the pressure generating device, the rate of change of the current rise can also be continuously determined so that the change in the rates of change and thus the time at which the analysis is to begin is precisely determined.

In this arrangement, the analysis can be effected in two different ways. In a first type of analysis, the instantaneous value of the current is measured and stored at the predetermined or determined time. Thereupon, a difference is continuously formed between the continuously measured value of the current and the current measured at the predetermined or determined time. If a predetermined or predeterminable difference is reached which can be stored in the microcomputer and which ensures that a positive and/or negative pressure was generated in the pressure line system which guarantees that all actuating elements which can be operated by pressure medium have carried out an actuating process, the electric motor is switched off by the microcomputer.

in a second type of analysis, the instantaneous value of the current is also measured and stored at the predetermined or determinable time. Thereupon, a quotient 1 21 is continuously formed between the current measured at the predetermined or determinable time and the current measured after this time. If a predetermined or predeterminable quotient is reached which can be stored in the microcomputer, the electric motor is switched off.

To achieve high reliability in the monitoring and controlling of the pressure generating device, the voltage which can be picked up at the first terminal (Kl) is amplified by an amplification circuit arrangement which contains a first operational amplifier (OP1). Since the possible measuring range of the microcomputer for the voltage present at the first input (El) is limited, the first operational amplifier (OP1) can be followed by a subtracting circuit arrangement by means of which it is achieved that the voltage at the first input (El) is held at a predetermined voltage level, which is 0 volts in this example, up to the predetermined or determinable time. For this purpose, the second operational amplifier (OP2) is supplied via the second terminal (K2) with a voltage which generates the required voltage level at the output of the second operational amplifier (OP2). To achieve this, the microcomputer (MR) measures the voltage present up to the predetermined or determinable time via the first input (El) and activates the third output (A3) as soon as the voltage at the first input (El) does not correspond to the required predetermined voltage level. If the third output (A3) is a digital output as in this example, it is required that a timing section is provided as a result of which a voltage 22 of the required magnitude can be generated at the second terminal (K2). The voltage at the second terminal is advantageously controlled by the fact that the second terminal is connected to a second input (E2) of the microcomputer (MR) which measures the voltage at the terminal and supplies it to the microcomputer for controlling the third output (A3). When the predetermined or determinable time Is reached from which a difference or a quotient is formed, the voltage value present at the second terminal to this time is held constant via the third output (A3).

To increase the reliability in monitoring and controlling the pressure generating device, the times needed for reaching the predetermined difference or the predetermined quotient can be stored in the microcomputer. If a precise analysis of the current taken by the electric motor is prevented by interference which can be, for example, voltage dips or can be generated by fast successive reversal of the direction of running of the electric motor and other transient effects, the motor is switched off after the stored times have elapsed. To be able to take into consideration changes in the pressure generating device, a stored time is replaced by a newly determined time. To prevent individual possible wrong measurements from disadvantageously influencing the reliability in the operation of the pressure generating device, a stored time can only be replaced by a new time when a predetermined number of new times has been 1 Z! If 1 - 23 determined and these times have been averaged. Since the times in the generation of a positive pressure and of a negative pressure can differ, it can be provided that different times are stored for the generation of negative pressure and positive pressure.

If the rate of change of the current variation is continuously determined, interference such as due to voltage dips or due to fast reversal of the direction of running of the electric motor is detected and compensated in that the forming of the difference or of the quotient is interrupted and recommenced or continued after the interference.

In this continuous determination of the rate of change of current variation the advantage is obtained that during an actuating process of an actuating element of the pressure line system, a pressure change occurs in this system which has an effect on the current consumption of the electric motor and which can be measured and analysed as a discontinuity in the current variation. It is thus possible to measure the actuating processes of actuating elements and utilize these for an analysis by the microcomputer which can increase the reliability in the operation of the pressure generating device.

Switching positions of control switches which are connected to the actuating elements which can be operated by pressure medium can be additionally sampled and subjected to an analysis by the microcomputer. The microcomputer can also contain a timing section which t 24 predetermines a safety margin after the expiry of which the electric motor is switched off to prevent components of this device from being destroyed in the case of a defect of the pressure generating device.

If there is no continuous determination of the rate of change of the current variation, the electric motor is switched off after a stored time If interference is present such as, for example, voltage dips or a fast reversal of the direction of running of the electric motor.

In another illustrative example, the microcomputer calculates, when an interference of the type mentioned occurs, the voltage to be generated at the second terminal (K2) so that the interference present can be compensated for. Interference of this type can also be compensated for if the electric motor is switched off with each interference occurring during the operation of the motor and the pressure line system is vented via the pump or via a valve arranged in the system and the pump is only switched on again when atmospheric pressure is present in the system.

K In 1

Claims

1. Method for controlling and monitoring the operating condition of a pressure generating device, in which a pump is driven by an electric motor which is connected to electronic control means when at least one switch connected to the control means is operated, In order to generate a positive and/or negative pressure in a space connected to the pump and the electric motor is switched off by the control means when a predetermined pressure value is reached, with each switching-on of the pump by the control means a measure of the current taken by the electric motor is evaluated and the motor is switched off in dependence thereon.

is

2. Method according to claim 1, wherein the evaluation of the current is effected at a predetermined or determinable time after switching on the pump.

3. Method according to claim 2, wherein the determination of said time is effected in that the rate of change of the current/time slope curve after the switch-on or switch-over of the pump is monitored.

4. - Method according to claim 3, wherein discontinuities in the current/time curve, which are generated by transient effects, are taken into consideration in the evaluation.

1 26

5. Method according to any one of claims 2 to 4, wherein the evaluation comprises forming a difference between the current measured at the predetermined or determinable time and the current measured after the time, 5 the pump being switched off when a predetermined or predeterminable difference has been reached.

6. Method according to any one of claims 2 to 4, wherein the evaluation comprises forming a quotient between the current measured at the predetermined or determinable time and the current measured after said time, the pump being switched off when a predetermined or predeterminable quotient has been reached.

7. Method according to claim 5 or claim 6, wherein at least one difference or one quotient is stored in a microcomputer which is part of the control means.

8. Method according to claim 7, wherein the times needed for reaching the predetermined or predeterminable difference or the quotient are stored in the microcomputer.

9. Method according to claim 8, wherein a stored 20 time is replaced by a newly determined time.

10. Method according to claim 8, wherein a stored time is only replaced by a new time when a predetermined A 1 27 number of new times has been determined and these times have been averaged.

11. Method according to any one of claims 8 to 10, wherein respective times for the generation of positive and negative pressures are separately stored.

12. Method according to any one of the preceding claims wherein switching positions of control switches of actuating elements which can be operated by pressure medium are interrogated and analysed.

13. Method according to any one of the preceding claims, wherein the pump is switched off after the expiry of a predetermined safety time.

14. Device for controlling and monitoring the operating condition of a pressure generating device, comprising one or r6ore control switches which are connected to electronic control means for an electric motor to connect said motor with opposite poles of a voltage source to operate a pump for generating positive and/or negative pressures in a pressure line system connected to the pump, with actuating elements in the pressure line system to be operated by pressure medium, a sensing resistor being arranged in the electrical connection of the electric motor to the voltage source and a first terminal in the connection between the electric motor and the sensing r kS 28 resistor being connected to a first input of a microcomputer of the control means.

15. Device according to claim 14, wherein the first terminal is connected to the first input of the microcomputer via an amplification circuit arrangement.

16. Device according to claim 15, wherein the amplification circuit arrangement is constructed in such a manner that the first terminal is electrically conductively connected to the non-inverting input of a first operational amplifier and that the output of the first operational amplifier is connected, on the one hand, to said first input of the microcomputer and, on the other hand, via a first resistor to the inverting input of the first operational amplifier which is connected to the negative pole of the voltage source via a second resistor.

17. Device according to claim 16, wherein the amplification circuit arrangement is connected via a subtracting circuit arrangement to said first input of the microcomputer.

18. Device according to claim 17, wherein the subtracting circuit arrangement is constructed in such a manner that the output of the first operational amplifier is connected via a third resistor, on the one hand, to the non-inverting input of a second operational amplifier and, It 29 on the other hand, via a fourth resistor to the negative pole of the voltage source, the output of the second operational amplifier being connected, on the one hand, to the first input of the microcomputer and, on the other hand, via a fifth resistor to the inverting input of the second operational amplifier and the inverting input of the second operational amplifier being connected to a second terminal via a sixth resistor.

19. Device according to claim 18, wherein the second terminal is connected, on the one hand, via a seventh resistor to a third output of the microcomputer and, on the other hand, to a second input of the microcomputer and to the negative pole of the voltage source via a first capacitor.

20. Device according to claim 18, wherein the second terminal is connected, on the one hand, via an eighth resistor to the positive pole of the voltage source and, on the other hand, via a ninth resistor to the negative pole of the voltage source.

21. Device according to any one of claims 18 to 20, wherein the first terminal is connected via a tenth resistor to the non-inverting input of the first operational amplifier and this input is connected to the negative pole of the voltage source via a second capacitor.

1.

22. Device according to any one of claims 14 to 21, wherein the microcomputer is electrically conductively connected to a supply voltage regulator.

23. Device according to any one of claims 14 to 22, 5 wherein the microcomputer has.a timing section.

24. Method of controlling and monitoring the operational condition of a pressure generating device, substantially as described herein with reference to the accompanying drawings.

25. Method according to any one of claims 1 to 13 or 24 for operating a central locking system of a motor vehicle by means of a pressure generating device.

26. Device for controlling and monitoring the operational condition of a pressure generating device, constructed and arranged for use and operation substantially as described herein with reference to the accompanying drawings.

27. Device according to any one of claims 14 to 23 or 26 for operating a central locking system of a motor - vehicle by means of a pressure generating device.

Published 1990 WThe Patent Office.State House. 6671 High Holborn.London WC1R4TP. Further copies maybe obtainedfrom7T!e Patent Office Sales Branch. St Mary Cray. Orpington. Kent BR5 3RD- Printed by Multiplex techniques 1Td. St Mary Cray. Kent. Con- 1'87