DE2836302A1 - NOTIFICATION AND SHUTDOWN DEVICE - Google Patents

Description

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Patent application

Applicant's The Economy Engine Company 712 Trumbull Avenue, Girard, Ohio 44420, U.S.A.

Title:

Signaling and shutdown device

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Description:

The invention relates to a device for first error reporting and shutdown for an internal combustion engine or the like, which may be arranged remotely from the device can.

Such devices have already been proposed and described several times. Some known devices are electromechanical, others purely electronic, see US Pat. No. 3,965,469 and 3,960,011.

The invention is based on the object of providing a device for first error reporting and stopping in electronic form to create, compared to known devices of this type, improved operating properties, in particular one high operational reliability with low power consumption, a clear error display and a function test option Has.

The device according to the invention with which this object is achieved is characterized in claim 1 and with regard to advantageous embodiments in the subsequent subclaims.

In the device according to the invention, one of the sensor switches changes its state if there is an error on the monitored

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Machine, e.g. a low oil pressure or a excessive coolant temperature. The digital logic circuit then generates a switch-off signal, which is transmitted via the switch-off device or circuit to trigger the switch-off, e.g. electronically or as a relay, which in turn, e.g. short-circuits the ignition system of the internal combustion engine. At the same time, the logic circuit becomes digital Display device controlled, which generates a digital display corresponding to the error that has occurred, and preferably includes the usual BCD seven-segment digit driver, which has a locking clip to fix the output when it is applied a signal of a certain, e.g. low switching value to the latching terminal, this signal defining Switching value is the latching signal generated by the switch-off circuit.

In a preferred embodiment, the shutdown circuit can be shut down or blocked so that a check can be carried out the individual sensor switch is possible without switching off the motor and locking or locking the display device lock. It is furthermore preferably provided that the shutdown circuit receives the shutdown signal generated by the logic circuit into a continuous rest and abstention signal with a slight time delay between the start of the switch-off signal from the logic circuit and the continuous one Rest and stop signal implemented. With a preferred Embodiment of the invention can also include the shutdown circuit be equipped with a delay circuit for generating a signal, which the current flow through the Control of the shutdown switch interrupts.

The device according to the invention for brush error reporting and Shutdown includes a first power supply, which can be, for example, the ignition system, which in the event of a Ignition system with capacitive discharge takes the current from the

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Storage capacitor or in the case of an inductive interrupter ignition system supplies the current from the primary winding. . The first power supply or source feeds the sensor switches, the logic circuit, the display device and the shutdown device during normal operation. The invention The device is further provided with a second voltage source which comprises a battery and for Actuation of the display device in the shutdown circuit after shutdown is used. This ensures that the display device continues to use the number that is assigned to the sensor switch for initial actuation, even after it has been switched off indicates under locking by the shutdown circuit.

The device according to the invention has the advantage that it Consumes very little electricity under all operating conditions, which is why it comes from the self-ignition of the monitored motor and can be fed by a small long-life battery. There is a further advantage of the device according to the invention in that a number which is assigned to the sensor switch from which the first error signal originated from a digital display device is reproduced. Close-1ie the device according to the invention has the advantage that all sensor switches without switching off the associated motor can be checked.

The following is the invention with further advantageous details explained in more detail using schematically illustrated embodiments. In the drawings show:

1 shows a block overview circuit diagram of a signaling and disconnection device according to the invention;

Fig. 2 is a detailed circuit diagram of the sensing switch portion of the device of Fig. 1;

3 shows a detailed circuit diagram of the logic section and the display section the device of Figure 1;

Fig. 4 is a detailed circuit diagram of the first voltage source, the second voltage source and the switch-off circuit of the device according to FIG. 1;

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5 shows a circuit diagram of part of a modified device according to the invention, in which a large number of sensor switches is monitored.

According to FIG. 1, a device for first error reporting and shutdown of an internal combustion engine according to the invention comprises a section 1 with sensor switches and logic elements which provides discrete outputs for each of several actuated sensor switches (ie generation of an error signal). Accordingly, the output of section 1 is a transmission path 2 with several lines. In the particular embodiment described below, the transmission path comprises twelve lines (0-9 and 10, 20) for the transmission of a decimal signal which represents any one of at least twenty sensor switches. During start-up or start-up it is necessary to ignore certain sensing switches (z _o B ', for the oil pressure) generated error signals, and therefore, a timer 3 outputs a disable signal, the specific suppression of the error signals detecting switch is used at the start.

The coding logic section 4 of the device converts the binary decimal signals on the transmission path 2 into binary coded decimal signals (BCD signals). In the exemplary embodiment explained below, the sensor switches, or sensors for short, are assigned the decimal numbers 2 to 21. The transmission path are those numbers to the logic circuit _further} encoding them in BCD. The output transmission path 5 of the logic circuit comprises at least six lines (four for the "ones" and two for the "tens") in the case of a signaling device with twenty sensor switches. The BCD signal is fed to the display section 6 via the transmission path 5. The logic circuit performs other functions. It emits a switch-off signal on line 7 if any sensor switch generates an error signal. The switch-off signal is fed to the switch-off section 8. The logic circuit generates an output signal with the switching value Hull if the timer switched off selected sensor error signals. For this purpose, the timer 3 is connected to the logic section k

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connected via line 9. The logic section generates a switching value 1 as soon as the timer no longer emits a blocking signal and as long as no sensor switch changes its state, i.e. no error signal is generated. So only the feeler, the first has responded to an error is reported (in the event of a shutdown, a number of sensor switches change their state), the display is latched or locked by means of a latching signal which is generated by the switch-off section 8.

The device has two power supply sections. In the preferred embodiment, the first receives power supply or the first power source 10 energy from the ignition, as long as the engine is in operation, and feeds the entire circuit during the operation of the engine. The battery power source 11 supplies power to the display section 6 after being turned off so a digital display is maintained, and to the shutdown section so that the latching signal is maintained.

The display section essentially comprises a square-wave oscillator, two drivers and a two-digit liquid crystal display or LCD display (with one digit for the tens and a place for the ones). An LCD display is preferred because of its very low power consumption.

The shutdown circuit 8 essentially comprises a triggerable one Switch, e.g. a thyristor, a triac or an electromechanical relay, which the ignition of the internal combustion engine short-circuits or connects to ground when its control element is switched through. The shutdown circuit continues to generate a continuous shutdown and latching signal based on a temporary shutdown signal, which is generated by the logic section, wherein the continuous signals can only be terminated by a reset signal.

Fig. 2 shows the mode of operation of the sensor switch section on the basis of only two sensor switches, one of which is during locked from starting and the other is not locked. A

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Sense switch Sq, for example, an oil pressure sensor, usually is a high switching level off, but then a signal S _c low stop level when the oil pressure drops below a certain, just drops as safe respected value. A sensor switch S ^ ₀ , for example a coolant temperature sensor, normally emits a high switching value, but then a signal with a low switching value if the temperature of the coolant becomes too high. Essentially, each sensor has a normally closed contact switch assigned to it, which opens when a fault is detected and thus interrupts the _{voltage V DD present at the output.} To achieve the same function, however, normally open contact switches can also be used without further ado. The timer emits a high switching value during the start-up or start period, whereby the start period can be varied between a few seconds and a few minutes, depending on the application. During normal start-up, Sq outputs a low and S ^ q a high switching value. The high switching value of S ^ q is fed to both the NAND gate 14 with two inputs and the NAND gate 15 with eight inputs. If the other inputs of the NAND gates have a high switching value, their outputs have a low switching value. During the start, the output of the sensor Sq has a low switching value. This is fed to the OR gate 16. A high switching value is fed to the other input of the OR gate 16 from the timer during starting. Since at least one input of the OR element 16 has a high switching value, the output is also a high switching value. The output of the NAND gate 14 has a low switching value, unaffected by the sensor Sq. If after the start S ^ q detects an error and opens, whereby the NAND gates 14 and 15 is supplied with a low switching value, a decimal signal "19" arises at the output of the sensing section, namely a high switching value at the output of the NAND element 15 and a high switching value at the output of the NAND gate 14. If after starting, after the output of timer 3 has gone to a low switching value, the sensor Sq has not yet issued a high switching value (or goes from high to low switching value) , the low switching value fed to the NAND gate 14 results in a decimal signal "9" at the output, ie a high switching value

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value at the output of the NAND element 14. In practice, the sensor switch section comprises 1 sensors to which S ″ to S _{21 is} assigned or assigned. An S ₁ is not allocated for reasons ^v which will be explained later. For the sake of simplicity, only the sensing switches Sq and S ^ g are shown in FIG.

3 shows the coding logic circuit 4 and the display section 6. In the present exemplary embodiment, the sensors Sp to Sq are defined as those which can be blocked by the timer.3 during starting. The sensors S ₁₀ to Sp ₁ are not influenced by the timer 3. The input to the logic section consists mainly of the decimal signal on transmission path 2. The decimal ones signals are converted into binary signals by means of an encoder, which is shown as a single integrated circuit (IC) 19. In practice it is convenient to use a binary coder for eight digits (0-7) plus a quad-OR IC and a NOR IC to form a binary coder with ten digits (0-9). The output of the binary encoder comprises at least four lines (the binary “9” is “1001”). In the present exemplary embodiment, the decimal "tens" do not require a binary coder, since the decimal number "1", represented in binary form, is "01" and the decimal number "2", represented in binary form, is "10". Since the highest number that is assigned to a sensor in the particular embodiment is S ₂₁ , the binary "tens" encoder is superfluous. Sense section 1 outputs a high switching value for sensors 10 to 19 on one line and for sensors 20 to 21 on another line (both lines have a low switching value for sensors 2-9).

With one exception, the BCD outputs are directly supplied to the drivers 23 and 24 in the display section. The binary "One" output line 19a becomes an OR gate 20, too fed. The output of the OR gate 20 is fed to the driver. Therefore, there is a high switching mechanism on line 19a always a high switch value on driver "one" line 24a.

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The following is an explanation of how the logic section outputs the binary-coded decimal number "00" during start-up if the timer outputs a high switching value so that sensors S ₂ to Sq are ignored, and how the logic section outputs a binary-coded decimal number "01", when all sensors are in operation. When starting up, if there are no error signals from the sensors S ^ ₀ to Sp., There is no high switching value on the hold-off signal line 19b, which usually originates from the group selection terminal of the encoder 19. The output of the timer, however, has a high switching value. Therefore, the output of the NOR gate 21 is at a low switching value and so is the input to the binary ones terminal of the driver. Accordingly, the drivers cause output "00" on the two-digit LCD display. When the timer ends the output of the high switching value, the NOR element 21 outputs a high switching value, which leads to the transition of the output of the OR element 20 to a high switching value. Correspondingly, the driver 24 has a high switching value applied to its "one" input line 24a, as a result of which the output "01" is produced on the display. If an error signal is ever emitted by one of the sensing switches, the high switching value originating from the NOR element 21 at the binary one terminal of the driver 24 must be eliminated. This takes place in that the switch-off signal 19b, which is fed to one of the inputs of the NOR element 21, assumes a high switching value and thus brings the output to a low switching value. Correspondingly, the line 24a is controlled exclusively by the "one" output line 19a of the BCD encoder 19 at this point in time.

The drivers or control circuits convert the binary input into a seven-segment LCD display signal on two transmission paths with seven lines each. Each seven-segment display signal is fed to a seven-segment display of the digital display device. A square-wave oscillator 27 supplies the driver 23 and 24 and the digital LCD display 26. Bin signal low switching value, the detent or the "LD terminal of the driver is supplied to 23 and 24, latched or locked _o

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the display of the output at the time of drawing the latching signal is present.

Details of the shutdown 8 and the feed circuits 10 and 11 are described with reference to FIG. The battery feed Circuit 11 comprises a battery 30 and a protective diode 31. The battery only then gives power to the display section 6 and shutdown section 8 when the ignition power supply is no longer able to deliver current. During the operation of the motor, when the power supply is working, the voltage at the cathode of the diode 31 is higher than the battery voltage, which is why the battery cannot deliver any current. The battery only works when the engine is running is switched off, and then delivers 1 mA for about 15 seconds and then only 15 / UA. This is achieved by the fact that the battery only feeds that part of the circuit that does the The display is locked, as is the display itself. It is also achieved in that the current flow to the control terminal of the electronic switch is interrupted in a manner to be explained. Commercially available non-rechargeable lithium batteries have a lifespan of five years under these circumstances, which is why these batteries or similar are used Batteries is being considered.

The power supply, which feeds the various sections of the device for first error reporting and shutdown according to the invention during operation of the motor, comprises a diode 35, a Zener diode 36, a resistor 37 and a capacitor 39 for the supply line Vn-ni>3> 4 as well as a diode 35a, a capacitor 33 and a Zener diode 32 for the supply line V _DD 6, 8. At the input, the power supply 10 is acted upon by the ignition, for example from the storage capacitor of an ignition system with capacitive discharge or the primary winding of an inductive one Breaker ignition system. Since the device is designed for low power consumption at all times, it can also be fed by self-ignition systems, that is to say ignition systems that do not use an additional power source, for example a battery. Such

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Zundsysteme v / earth of direct or alternating current alternators or powered by magneto.

The shutdown section receives the shutdown signal generated by the logic circuit. This signal is generated by the logic circuit when a sensor changes its state. It is a temporary signal in the sense that it must stop after it has been switched off because the logic circuit no longer receives any current after it has been switched off. The shutdown section generates a continuous shutdown and latching signal from the temporary signal received from the logic circuit. This is achieved by means of the NOR element 44 and the inverter 45. The abstention signal is fed to an input of the NOR element. The output of the NOR gate is fed to the inverter. The output of the inverter is fed back to the other input of the NOR element 44 via a resistor. The feedback circuit is connected to ground via a very large resistance. Therefore, during normal operation, if no switch-off signal is received from the logic section, both inputs of the NOR gate are at a low switching value and its output is correspondingly at a high switching value. The output of the NOR gate is fed to the latching clips of the drivers in the display section and holds the drivers in the unlocked state. When a switch-off signal is received, a high switching value is applied to an input of the NOR gate 44, which brings the output to a low switching value. The low switching value at the output is inverted by inverter 45 and fed back to the other input of the NOR gate 44, whereby the output of the NOR gate is locked to the low switching value 44 _e of the output of the NOR gate 44 remains at the low switching value, even if the hold signal received from the logic circuit may no longer be at a high switching value. The latched, low switching value at the output of the NOR element 44 reaches the latching terminal on the drivers in the display section and leads to latching or locking of the digital output in such a way that the number is displayed which corresponds to the sensor switch that responded first, i.e. as first cause an error message

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has leads. To ensure that the number of the reporting error Sensor switch is displayed before the latching signal is applied, a small delay capacitor 46 is between the The input terminal of the NOR element 44, at which the switch-off signal arrives, and ground are connected.

A mechanical reset and test switch 48 is provided to connect the feedback input of the NOR gate 44 via a resistor to ground and thereby the NOR gate 44 and the Unlock inverter 45. The same mechanical switch 48 can be used to switch the input of the NOR gate 44 on To put ground, which receives the switch-off signal, whereby a test condition is brought about. If the switch is in the The various sensor switches can be used in the test position can be checked without switching off the engine and without locking the display. When the switch 48 is in the test position is located, an operator can manually change the state of individual test switches and those assigned to this switch Observe the number as it is shown on the digital display. The above function, the points explained to ground can also be achieved by electronic means.

The main shutdown element of the shutdown circuit of Figure 4 is an electronic switch 50 which is, for example, a Thyristor can act. The thyristor has its cathode connected to ground, while its anode is connected to the ignition system via diodes and if necessary with the electric petrol system connected is. When the thyristor goes from one to the positive outgoing signal is switched through at its control electrode 51, a circuit connection is created for the ignition and the gasoline system to ground, which shuts down the engine. The resistors 52 and 53 and the capacitor 54 act these are common components for switching the control electrode

of the thyristor, which prevent unintentional triggering due to interference signals and restriction processes. The outcome of the Inverter 45 could be connected directly to control electrode 51, since the output of inverter 45 when switched off ins Positive goes. However, the output signal from 45 continues,

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which is why a continuous current consumption via the control electrode of thyristor 50 would take place. Therefore is between the control electrode 51 and the output of the inverter 45 a delayed shutdown circuit with an AND gate 56 inserted. The output of the inverter 45 is fed to an input of the AND gate 56. The output of AND gate 56 is connected to the control electrode 51 of the thyristor 50 via the resistor 52.

A diode 58, a capacitor 59 and a discharge resistor 60 constitute a delay circuit. The capacitor 59 becomes charged during operation of the engine, which is why a signal tapped between the diode 58 and the capacitor 59 leads to a high S-stop value, which is the other input of the AND link 56 is fed. During normal operation, the Output of inverter 45 low switching value. (The output of the delay circuit is at a high switching value.) Correspondingly the output of the AND gate 56 has a low switching value and keeps the thyristor 50 in the non-conductive state via the control electrode. When the inverter 45 has a latched switching signal

outputs, both inputs of the AND gate 56 are at a high switching value, whereby the output also comes to a high switching value and brings the thyristor 50 into the conductive state. After a certain period of time, which depends on the time constants of the resistor 60 and the capacitor 59, is necessary for the safe shutdown of the motor is preferably about 15 seconds, the capacitor 15 is discharged, which is why a lower one Switching value reaches an input terminal of AND gate 56. This in turn leads to the output of AND gate 56 goes to a low switching value and prevents a current draw via the control electrode 51 of the thyristor 50.

It is known to the person skilled in the art that the various links, Inverter, also the BCD encoder and the timer, the oscillator and the LCD driver from various Piers plates can be supplied as integrated circuits. Forner is it is known that various combinations of Verkruifungsg.LieJ.er

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the combinations shown in the exemplary embodiment are functionally equivalent. The table at the end of the description lists various components that are used by the Applicants have been used to produce an actual implementation of the invention.

An alternative embodiment of the reporting device is shown in FIG. In this embodiment, each parallel sensor switch (S ₁₀ -S ₁₇ ; S ₂₀ -S ₂₇ ; S ₃₀ -S ₃₇ ; S ₄₀ -S ₄₇ ) is assigned to an input of a multiplexer 71, 72, 73 or 74, which according to a BCD input connects one of the multiplexer inputs to a common output 71x, 72x, 73x or 7A-X. A suitable multiplexer is the Motorola MC14051. The BCD transmission path for the binary inputs to the multiplexers is controlled by a binary counter 76 which receives its clock from an oscillator divider 77. A suitable binary counter is the Motorola MC1452O. Oscillator 77 can also provide power to operate drivers 84 and 94 and LCD displays 85 and 95. Each multiplexer calls the parallel inputs continuously and sequentially. During startup, the start timer 70 blocks a multiplexer.

If a sensor switch, for example S ^ ₀ , goes to ground, the common output 73x of the assigned multiplexer 73 also goes down. Normally, the output is at a high switching value due to a bias resistor, which is connected to Vjyp, for example, as shown. The low switching value is inverted and reaches the Zabner display via a coding logic from the NAND gates 80, 81 and 82. Driver 84. This encodes this ten-display driver in such a way that, in the example, it causes a three to be displayed on a seven-segment display 85. An output of the coding network 80, 81, 82 which is at a high switching value leads to a high switching value at the output of the OR element 91 due to the manner in which the OR elements 90 and 91 are connected together. This generates a temporary switch-off signal. This signal is fed to the logic element 93 and made possible

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it that the BCD output of the binary counter to the ones display driver got. The switch-off signal is also sent to the binary counter 76 supplied to stop counting.

The NOR gate 121 and the OR gate 120 operate in the same V / eise as was described above for the NOR gate 21 and the OR gate 20; a binary-coded signal is applied which leads to a display "00" during start-up if the timer emits a high switching value, so that the sensors S ₁₀ -S ^ y are ignored, and it becomes binary
encoded decimal signal generated, which leads to a display "01"
leads when all sensors are included in the operation. Of the
The rest of the circuit is designed as shown in FIG. So it turns into a temporary switch-off signal
Latch signal implemented, which causes the driver 84 ,.
94 lock the display that corresponds to the sensor switch that responded first. The latching signal is fed to the logic element 95 for separating the binary counter 76 from the oscillator 77.

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Claims (1)

Patent claims: (ΊΑ apparatus for first error message and stopping an internal combustion engine or the like _o, characterized by a) several sensor switches (1) connected in parallel, which change their state if an error occurs, b) a logic circuit (4), which changes the state of a the sensor switch converts it into a binary digital output that indicates the sensor switch and its status has changed, and which generates a no signal, c) a digital display device (6) which converts the binary digital signal generated by the logic circuit into a digital Playback implements, d) a shutdown device (8) which responds to the shutdown signal with triggering of a shutdown switch and which generates a signal for locking the digital display device, e) a first voltage supply circuit (10) for supplying power the sensing switch, the logic circuit, the display device and the disconnection device during the normal operation, and f) a second voltage supply circuit (11) with öiner Battery for supplying power to the display device and the shut-off device after switching off. 2. Apparatus according to claim 1, characterized by a timer (3) which during starting generates a signal which the logic circuit (4) sends to it prevents the status of one or more sensor switches from being recognized. 909809 / 10U - 2 - 51 215 3. Apparatus according to claim 2, characterized in that the logic circuit (4) is a selected one emits binary digital signal during the start period, another selected binary digital signal after starting, if no error occurs, or a binary digital signal which indicates a sensor switch that has changed its state. 4. Apparatus according to claim 1, 2 or 3, characterized in that the disconnection device (8) to a temporary switch-off signal from the logic circuit (4) by generating a continuous switch-off and Latching signal responds, which can only be terminated by a reset signal. 5ο device according to claim 4, characterized in that the disconnection device (8) a small delay between the start of the temporary switch-off signal generated by the logic circuit (4) and the inserts continuous switch-off and latching signal in such a way that there is sufficient time for the display device (6), display the digital display value, which indicates the sensor switch that has changed its state. 6. Apparatus according to claim 5 _9, characterized in that the disconnection device (8) comprises a triggerable switch with a control element which is excited by the continuous disconnection signal. 7ο device according to claim 6, characterized in that the disconnection device (8) a Delay circuit comprises, which generates a signal shortly after switching off in such a way that the current flow through the Control of the triggerable switch is terminated, - 3 - 51 215 8. Device according to one of claims 4 to 7, characterized characterized in that the disconnection device (8) can be blocked by a test signal in such a way that each Sensor switch can be checked without locking the display device (6) or without shutting it down. 9. Device according to one of claims 2 to 8, characterized in that each sensor switch in a first group of sensor switches connected to one input of a plurality of OR gates, each with two inputs is that each sensing switch in a second group of sensing switches to an input of a plurality of NAND gates of two inputs is connected, so that each sensor switch in the second group is also connected to one of several inputs of a NAND gate with several inputs is connected that the outputs of the OR gates connected to one of the other inputs of the two-input NAND gates, and that the timer to the other Input of all OR gates is connected in such a way that the outputs of all NAND gates have a digital signal in a number system that is higher than binary, which indicates the sensor switch that changes its state, and that the first group of sensing switches produce no outputs during the period during which the timer is on Emits signal. 10. Device according to one of claims 3 to 9, characterized in that the logic circuit (4) a device for converting the outputs of the sensor switches into BCD signals and also a device for generating a Group output signal whenever there is an output from any sensor switch, includes that a NOR element is provided with two inputs to which the timer input and the group selection signal are fed, and that an OR gate with two inputs is provided, to which the output of the NOR gate and the lowest binary terminal the converter are connected in such a way that the logic circuit a BCD "O" during the start period and 309 * 09/1014/4. - 4 - 51 215 issues a BCD "1" during the subsequent period, if no error occurs. 11. Device according to one of claims 4 to 10, characterized in that the disconnection device a NOR element with two inputs, the output of which is connected to an inverter, that the temporary switch-off signal one of the inputs of the NOR gate is fed, and that a feedback circuit from the output of the inverter to the other input of the NOR element runs in such a way that a high temporary abstention signal passes the output of the NOR element latched to a low switching value and the output of the inverter latched to a high switching value. 12. The device according to claim 11, characterized in that through a small capacitor connected to ground, which is connected to the input of the NOR gate, to which the temporary switch-off signal is supplied in such a way that a delay with regard to the generation of the latched Output of the NOR gate is reached. 13. Device according to one of claims 10 to 12, characterized in that the feedback terminal of the NOR element to reset the shutdown circuit Mass can be laid. 14. Device according to one of claims 10 to 13 _f, characterized in that the terminal of the NOR element, which receives the temporary Absehaltsignal, can be connected to ground, such that each sensor switch can be tested without locking the digital display device or without stopping the motor . 15. Device according to one of claims 7 to 14, characterized in that the disconnection device comprises an AND gate with two inputs, one of which is connected to a line, which due to the continuous Switch-off signal assumes a high switching value, 909809 / 10U / 5 - 5 - 51 215 that the output of the AND element to a device for acting on the control element of the switch with a Trigger signal when the output of the AND element assumes a high switching value, that a delay circuit is connected comprises a normally charged capacitor and a discharge resistor in parallel therewith and a Emits a signal with a high switching value when the capacitor is charged and that the output of the delay circuit the other input of the AND gate is fed in such a way that when the capacitor is some time after shutdown or shutdown is discharged, the output of the AND element assumes a low switching value and thereby the flow of current prevented by the control of the switch. 16. Device according to one of claims 2 to 15 »thereby characterized in that each sensing switch in the first group of sensing switches is connected to a first multiplexer is connected that each sensor switch in at least one further group of sensor switches to a multiplexer is connected to at least this one other group it is assigned that a binary counter for outputting binary selected signals to the multiplexer for calling up the sensor switch is provided that the common output of each of the multiplexers to a decoding network for controlling a multi-digit display in the digital display device and for generating a temporary switch-off and latching signal is connected, and that the output of the binary counter also with the digital display according to the temporary Switch-off signal for controlling a one-digit display is linked.