Method for monitoring a system with a flowing medium, for example a lubricating system, and device for performing the method

(54) METHOD OF MONITORING A SYSTEM CONTAINING A FLOWING MEDIUM, FOR EXAMPLE A LUBRICATION SYSTEM AND CIRCUIT ARRANGEMENT FOR PRACTICING THE METHOD (57) Circuitry for monitoring a system containing a flowing medium, for example a lubrication system for a transmission, for bearings or the like which oil by means of a pump from a reservoir, sump or the like., Where appropriate, via cooler, filter, etc., is supplied to the parts to be lubricated.

A possible circuit arrangement for monitoring is characterized in that the output of a pressure and / or flow sensor (6,7) via a respective periodically actuated switch (8,14,15) with an input of each of a comparator (9,16,17 ) are connected to the other input of a Dnjck- or flow rate setpoint voltage (U pg, U og) is fed and that the

Output of the comparator (9) or via a gate (20), the outputs of the comparators (16, 17) connected to the input of a counter (12) is or whose counter reading is periodically retrievable and resettable and that for the comparison of periodically retrieved counter reading with a counter reading setpoint value (S _z ), a comparison circuit (13) is provided at the output of the alarm or shutdown signal (S _) occurs.

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No. 391 014

The invention relates to a circuit arrangement for monitoring a system containing a flowing medium, for example, a lubrication system for a transmission, for bearings od. Like., In which oil by means of a pump from a reservoir, sump od. Like., Where appropriate, via cooler, filter, etc., is supplied to the parts to be lubricated, with pressure and / or flow sensors, which are adapted to output signals in response to the pressure and / or the flow rate and a counter whose count periodically is retrievable and resettable and is set up to count the signals over a predeterminable period of time, which falls below a likewise predeterminable number value an alarm or shutdown signal occurs

In oil-lubricated systems, a quasi-continuous supply of oil to be lubricated Stel len, such as. As the bearings and gears of a transmission, essential. In many, especially non-stationary machines, the oil reservoir often takes inclined positions, which cause the Ölansaugrohr outside the oil level device, which is temporarily the supply of oil is interrupted. This is z. B. in mining at Schrämmaschinen the case where the cutting head and thus the Schrämgetriebe different positions, eg. B. 50 ° upwards or downwards and there is a risk that the cutting gear is not sufficiently supplied with oil and thereby damaged.

It is known in mechanical engineering to measure the oil pressure and / or the oil flow rate in lubrication systems. Often hiebei switches are used, the z. B. be actuated when the oil pressure drops below a certain minimum value and trigger a display, an alarm or an emergency shutdown. In many machines, however, a temporary interruption of the oil flow is unavoidable and also irrelevant, unless such interruptions occur too often and too long.

In connection with lubricant systems and their (monitoring is in GB-PS 2,153,570 a monitoring by means of a control circuit disclosed, which in particular prevents a shutdown of the system during startup, wherein the working pressure is not yet established

DE-OS 1 965 386 relates to a lubricant system in which a longer lasting, too low lubricant supply is to be prevented, but short-term interruptions of the lubricant flow should be tolerated.

The lubrication system according to DE-OS 2 054 822 is set in a similar manner as the previously mentioned Vorhalt the goal that the system to be lubricated in a lubricant failure should not be turned off in any case, so it does not often lead to unnecessary stoppages

Similar problems occur not only in lubrication systems, but also in other systems containing a flowing medium. Here are z. B. mentions: systems that promote lubrication and / or cooling emulsions to the workpieces in machine tools, spray and sprinkler systems for water, cooling systems containing a cooling gas, at most partially liquefied, compressed air systems, systems containing medical gases, eg. As anesthetic gases, contain and promote.

In such systems, special monitoring of the average pressure or flow rate of the medium is desirable

The aim of the invention is to provide a circuit arrangement which serves such a monitoring in particular enables the detection of the average lubrication state of a lubrication system and takes into account the problem described above.

This goal can be achieved with a circuit arrangement of the type mentioned, in which according to the invention the outputs of a pressure and / or flow sensor are each connected via a periodically actuated switch to an input of each comparator whose other input a pressure or Durchflußsollwert- Voltage is supplied and the output of the comparator or via a gate, the outputs of the comparators is connected to the input of a counter or are. This circuit requires little effort and allows because of their flexibility in the choice of triggering criteria for use in all conceivable lubrication systems.

An advantageous development of said circuit arrangement is characterized in that in the presence of both a pressure sensor and a flow sensor provided for between these sensors and the inputs of the comparators associated switches are push-pull actuated. This results in a nested sequence of pressure and flow signals, which can thus be evaluated together.

In a further circuit arrangement according to the invention it is provided that for determining the derived from the pressure sensor or the flow sensor measuring signal, the output of the pressure sensor or the flow sensor is connected via a periodically actuated switch with an input of a comparator, At the other input, a setpoint voltage is applied and that the measurement signal of the pressure sensor or the flow sensor thus obtained via a series resistor is supplied to a parallel RC element This quasi-analog circuit is characterized by little effort, since no counter is required in another circuit arrangement provided according to the invention that a pressure switch and / or a flow switch are provided as sensors, each have a working and a normally closed contact, wherein above predetermined values ​​of the pressure or the flow rate of the normally open contact, otherwise the normally closed, is closed, that the connection of the normally open contact to a DC voltage and the terminal of the normally closed contact is connected to ground and that Changeover contact via a resistor with both the

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Capacitor connected to ground as well as connected to one input of a comparator. This variant requires a particularly low circuit complexity and also allows the use of simple switches as pressure or flow sensors.

If one wants to use both the pressure and the flow rate of the medium as the output of an alarm or 5 Abschaltsignal determining criteria, it is useful if the comparison of the measured signals or the capacitor voltages with setpoints, the outputs of these comparators with the inputs of a

Gates are connected, at the output of the alarm or shutdown signal occurs.

The invention together with its further advantages and features is explained in more detail below by way of example embodiments, which are illustrated in the drawing. 2 shows a first circuit arrangement according to the invention, FIG. 3 shows a modification of the circuit arrangement according to FIG. 2 with measurement and evaluation of both the oil pressure and the oil flow rate, FIG. 4 5 shows a further circuit arrangement according to the invention, without the use of a counter, FIG. 6 shows in a diagram the measuring principle to the circuit arrangement according to FIG. 5 and FIG. 7 a Variant of a

Circuit arrangement according to the invention, in which pressure and flow switches are used.

According to Fig. 1, a lubrication system to an oil reservoir (1), from which by means of a pump (2) oil via an oil cooler (3) and an oil filter (4) to be lubricated parts (5), z. B. a transmission is supplied. At a suitable point in the closed oil circuit, a pressure sensor (6) and a flow sensor (7) is arranged. As can be seen from the following, however, only one of the two can

Sensors be provided. When referring to oil in the context of the invention, this term may include any type of lubricant and is not intended to be limited to oil. It could also be z. B. emulsions for lubrication and cooling in cutting tools.

The circuit of Fig. 2 shows the pressure sensor (6) which provides an output signal proportional to the oil pressure. In the diagram of FIG. 4, the example course of the oil pressure (p) in

Dependent on the time (t) plotted. The output of the pressure sensor (6) is fed via a controlled, preferably electronic switch (8) to an input of a comparator (9). The other input of the comparator (9) is connected to a setpoint voltage source (10) having a DC voltage (U_nB). In Fig. 4, this voltage level is shown in dashed lines.

A timer (11) closes the switch (8) at intervals (τ) for a short time and periodically. Accordingly, pulses appear at the output of the comparator (9) whenever the output signal of the pressure sensor (6) drops below the desired voltage value (Up_S) lies. These pulses are detected by a counter (12) which is connected downstream of the comparator (9). The counter (12) counts over a measurement interval (T) all pulses received and is queried at the end of this interval by a pulse of the clock (11), so that at the output of the counter (12) the total number of counted within the time (T) pulses occurs. At the same time the counter (12) is reset, so that the pulses of the next measurement period can be summed up.

In practice, for. B. the sampling time (τ) with 100 ms and the measuring period (T) are set at 10 s, so that within a measurement period 100 measurements are performed. For example, for a given machine connected to the lubrication system, it can be tolerated that for 20 measurements of the 100 measurements, the oil pressure is below the set point. If this number is exceeded within a measuring interval (T), an alarm or a shutdown signal should be issued.

For this purpose, the counter (12) is followed by a comparison circuit (13), which is also a counter reading Sollwertsignal (s_zs) is supplied. In the comparison circuit (13), the requested counter reading is compared with the setpoint value, for example the number (20). If the counter reading is above this setpoint value, a signal appears at the output of the comparison circuit (see FIG_a), which leads to an indication and / or triggers an alarm and / or automatically shuts off the machine to be lubricated.

Since oil pressure alone is not always the most important criterion for proper lubrication, the flow rate of the oil can be constantly monitored in the same way. Also, both the oil pressure and the oil flow by means of circuits of FIG. 2 be monitored and the corresponding output signals are linked in a gate, so that an alarm signal occurs whenever a certain number of negative measurements of the oil pressure or the Öldurchflußmenge occur within a measuring interval.

The simultaneous monitoring of pressure and flow rate can, for. B. in a circuit of FIG. 3 are performed. Here, the output signals of a pressure sensor (6) and a flow sensor (7) via two controlled switches (14), (15) depending on the first input of two comparators (16), (17) supplied. At each of the second inputs is a setpoint voltage source (18), (19) with setpoint voltages (U__B) and pb (Uj) §), which correspond to the minimum values ​​of the pressure or the flow rate.

The clock (11) controls the switches (14), (15) periodically, but alternately, so that the sampled values ​​of the outputs of the sensors (6) and (7) are time-interleaved. The outputs of the comparators are connected to the inputs of a gate (20) whose output is applied to the input of the counter (12). The further evaluation of the signals takes place as described in connection with FIG. 2.

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It is understood that by selecting the setpoint voltages (Up_G), (Upg), the sampling intervals (τ), the measuring interval (T) and the counter reading setpoint (s_2S) adaptation to the respective operating requirements of the lubrication system is possible in the widest possible range.

The circuit of Fig. 5 shows a modification which operates without counter. Again, the output of a pressure sensor (6) (or a flow sensor) via one of a clock (11) controlled switch (8) to an input of a comparator (9) supplied to the other input to a pressure setpoint voltage source (10) (voltage (U_nc)) connected is.

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Pulses occur at the output at a distance (τ), provided the pressure above the predetermined level (Up_G) lies. The length (tj) of these pulses is determined by the closing time of the switch (8) and must remain constant during the measurement. In the diagram of Fig. 6, these pulses are shown, wherein three pulses fail due to a pressure drop after the first three pulses.

The output of the comparator (9) is connected via a resistor (R_y) is supplied to a parallel RC element (R, C). Since the pulses occur regularly due to sufficiently high pressure, a stationary state is achieved which is characterized by an average, constant sawtooth voltage across the capacitor (C). The rise of the sawtooth is here, except by the voltage of the pulses, by the time constant (R_y, C), the decay determined by the time constant (RC). In the event of failure of pulses, however, the voltage decreases to increase again when new pulses occur. Therefore, if the voltage across the capacitor (C) is compared with a predetermined setpoint voltage (Ugj), an accumulation of negative pressure measurements can also be determined, as in the case of the circuits according to FIGS. 2 and 3. For this purpose, a comparator (21) is provided, at one input of which the voltage at the RC element (R), (C) is located and whose other input is connected to a desired voltage source (22) (voltage (Ugj)). When the voltage drops (U_c) at the capacitor (C) below the setpoint voltage (Ugj) occurs at the output of the comparator (21) an alarm or shutdown signal (s_a) on. Again, an adaptation to the respective requirements by selecting the sampling intervals τ, the pulse length (tj), the pressure setpoint voltage (Upg) and the desired voltage (Ugj) is possible.

In the circuit of FIG. 7, the evaluation is also without counter, but here are the pressure or flow sensors as z. B. spring-loaded pressure switch (23) or flow switch (24) is formed. The switches are each equipped with a rest and a working contact, above a certain oil pressure or above a certain oil flow rate of the normally open contact, otherwise the normally closed contact is closed.

The terminals of the normally open contacts are connected to a DC voltage (U), the terminals of the normally closed contacts are connected to ground. The change-over contact piece is in each case connected via a resistor (Rj) or (R₂) to a capacitor (Cj) or (C₂) and the live connection of the capacitors (Cj), (C₂) is each connected to the first input of a comparator (25), (26). The second inputs of the comparators (25), (26) are connected to nominal voltage sources (27), (28) (voltage (Ugp or (Ug₂)) connected. The outputs of the comparators (25), (26) are located at the two inputs of a gate (29), at whose output the alarm or shutdown signal (s_a) can occur.

As long as the pressure is above the switching value of the switch (23), the voltage across the capacitor (Cj) is maintained at the value (U) via the resistor (Rj). When the pressure drops, the switch (23) toggles and the voltage across the capacitor (Cj) decreases exponentially according to the time constant (RjCj), as the capacitor (Cp) via the resistor (Rp) and the normally closed contact of the switch (23) to ground discharges. As soon as the capacitor voltage (U_c) falls below the voltage (Ugj), the comparator (25) outputs a signal to the (OR) gate (29), at whose output the alarm or shutdown signal (s_a) occurs.

The same applies mutatis mutandis to the flow switch (24) downstream circuit. Thus, always the signal (s_a) occur when the pressure and / or the flow rate decrease over a longer time below the value at which the switch (23) or (24) switch over. Relevant criteria for the delivery of the signal (s_fl) are here on the one hand, the z. B. by spring tension switchable switching points of the switches (23) and (24) and on the other hand, the time constants (RjCp, (R₂C₂), the voltage (U) and the desired voltages (U_§1) or (U_S2). Thus, this circuit can be adapted to all requirements. In the circuits of FIGS. 5 and 7, it may be appropriate, when switching on the machine via a delay circuit temporarily above the switching level (Ugj) or (Ug₂) to the capacitor (C), (Cj), (C₂), since the construction of the oil pressure and the Öldurchflußmenge requires a certain amount of time and in any case should be no shutdown during this time.

The inventive method and the derived therefrom, described here only by way of examples circuit arrangements allow the reliable control of a lubrication system, wherein substantially

-4Nr. 391 014 more than just the presence of a particular oil pressure can be used as decision criteria. As already mentioned, the use of the invention is not limited to lubrication systems, but it can extend to many systems that contain a flowing medium and in which a supply of a certain area with a sufficient amount of this medium should be ensured.