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

p0001The invention relates to a method for monitoring a a flowing medium containing system, for example, a lubrication system for a transmission, or the warehouse. Like., In which oil or the means of a pump from a reservoir, swamp. Like., Possibly through cooler , filter, etc., is supplied to the parts to be lubricated as well as to a circuit arrangement for performing the method.

p0002For oil lubricated systems is a quasi-continuous oil supply to the lubrication points, such as bearings and gears of a transmission, is essential. For many, especially non-stationary motion machines, the Olvorratsbehälter often occupies slopes that lead to the outside of Olansaugrohr Olspiegels device, thereby temporarily the oil supply is interrupted. This is for example in mining coal cutting machines in the case where the cutting head and therefore the Schrämgetriebe different layers, for example, occupies 50 ° upwards or downwards and there is a risk that the Schrämgetriebe is not sufficiently supplied with 01 and damaged thereby.

p0003It is known in machine to measure the oil pressure and / or the Oldurchflußmenge in lubrication systems. Often hiebei switches are used, for example, be operated with the oil pressure drops below a certain minimum value and trigger an ad, an alarm or an emergency shutdown. In many vehicles, however, a temporary interruption of the flow of oil can not be avoided and even irrelevant, unless such interruptions occur too frequently and for too long.

p0004Similar problems occur not only in lubrication systems, but also in other systems which contain a flowing medium. Here for example be mentioned: systems, the lubrication and / or promote coolants to the workpieces to machine tools, spray and sprinkler systems for water cooling systems that contain a cooling gas, at best partially liquefied, compressed air systems, systems of medical gases, such as anesthetic gases, contain and promote.

p0005In such systems, a special monitoring the average pressure or the flow rate of the medium is desirable.

p0006The aim of the invention is the discovery of a method which allows such monitoring, in particular the detection of the average lubricating condition of a lubrication system and allows to the problems presented above takes care.

p0007This goal can be achieved by a method of the aforementioned type, wherein the pressure and / or the flow rate of the medium is measured according to the invention and the measured values ​​are compared with predetermined minimum values ​​and an alarm or stop signal is issued, unless the number or duration the positive measurements within a particular measurement interval under a predetermined minimum number or minimum length is.

p0008Although this process tolerated temporary waste of the pressure or of the flow or lubricant failure, however, ensures that an alarm or shutdown signal is output, unless a predeterminable mean, for example, the lubrication state is undershot. By choice of the measurement times determining frequency and the length of the measuring intervals, the process can be adapted to the respective requirements.

p0009Hiebei it is advantageous if the pressure and / or flow rate are periodically measured.

p0010It may also be recommended if the measurement intervals follow one another periodically.

p0011An appropriate circuit arrangement for carrying out the method according to the invention is characterized in that the outputs of a pressure and / or flow sensor are connected via a periodically actuated switch having an input of a comparator, another input dessem a pressure or flow setpoint voltage is supplied and that the output of the comparator and the outputs of the comparators is connected to the input of a counter whose count is periodically downloaded and reset and that a count setpoint is provided for comparing the periodically retrieved count a comparison circuit whose output the alarm or shutdown signal occurs. This circuit requires little effort and can be due to its flexibility in the choice of trigger criteria to use in every conceivable lubrication systems to.

p0012An advantageous development of the said arrangement is characterized in that the pressure and flow sensor associated switches are alternately periodically operable. By this means there is a nested sequence of the pressure and flow signals that can be evaluated together thus.

p0013In a further circuit arrangement for implementing the method according to the invention it is provided that the measurement signals of a pressure sensor and / or a flow sensor through a series resistor are fed to a parallel-RC element and the voltage on the capacitor is supplied to one input of a comparator, at whose other input a setpoint voltage. This quasi-analog circuitry is characterized by low cost, since no counter is required.

p0014Hiebei it is expedient if, for determining the measurement signals of the output of the pressure sensor or the flow sensor is connected via a periodically operable switch to an input of a comparator, a set point voltage is at whose other input.

p0015In another circuit arrangement for performing the method, the invention provides that a pressure switch and / or a flow switch are provided, each having a working and a normally closed contact, connected to the terminal of the make contact to a DC voltage and connected to the terminal of the break contact to ground is and the switching contact piece via the series circuit of a reflection object is connected to a capacitor to ground and d_aß is the voltage on the capacitor to an input of a comparator supplied with a setpoint voltage at whose other input. This variant requires a particularly low circuit complexity and also allows the use of simple switches as pressure or flow sensors.

p0016If you want to use both the pressure and the flow rate of the medium as the delivery of an alarm or Abschaltsignales determining criteria, so it is advantageous if the pressure sensor or switch and the flow sensor or switch each one comparator is assigned and the outputs the comparators are connected to the inputs of a gate, at whose output the alarm or shutdown signal occurs.

p0017The invention together with further advantages and features is explained in the following example wise to hand embodiments, which are illustrated in the drawing. In this FIG. 1 schematically shows a lubrication circuit, Fig. 2 shows a first circuit arrangement according to the invention, Fig. 3 shows a modification of the circuit arrangement of FIG. 2, with measurement and evaluation both of the oil pressure and the oil flow,_Fig. 4 a diagram showing the measurement principle of the circuit arrangements according to Figs. 2 and 3, Fig. 5 shows a further circuit arrangement according to the invention without use of a counter, Fig. 6 a diagram showing the measurement principle to the circuit arrangement of FIG. 5 and FIG. 7 a variant of a circuit arrangement according to the invention, be used in which pressure and flow switch.

p0018According to FIG. 1, a lubrication system an oil reservoir ₁ on, from the means of a pump 2 oil through an oil cooler, an oil filter 3 and 4 the parts to be lubricated is 5, as a gear supplied. At a suitable location, a pressure sensor 6, and a flow sensor 7 is disposed in the closed oil circuit. As is apparent from out below, however, only one of the two sensors can also be provided. If, within the context of the invention of oil, so can this term include any type of lubricant and should not be restricted to "oil". It could also be for example, emulsions for lubrication and cooling in cutting tools.

p0019The circuit arrangement of FIG. 2 shows the pressure sensor 6, which supplies an oil pressure-proportional output signal. In the diagram according to Fig. 4 of the example flow of oil pressure p is plotted against the time t. 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, a DC voltage U_ps supplies. In Fig. 4, this voltage level is indicated by dashed lines.

p0020A clock 11 closes the switch 8 at intervals τ briefly and periodically. Accordingly, whenever pulses occur at the output of the comparator 9, when the output signal of the pressure sensor 6unter the target voltage value,_ps 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 comments received pulses and is scanned 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 the counted pulses occur within the time T. Simultaneously, the counter 12 is again reset so that the pulses of the next measurement period can be summed.

p0021In practice, the sampling time can eg τ s are recognized, so that during a measurement period 100 measurements are performed with 100 ms and the measurement period T by 10. In one particular machine which is connected to the lubrication system, for example, can be tolerated since_ß is 20 measurements of 100 measurements of the oil pressure below the setpoint. If this number within a_Mexceeded dining interval T, is an alarm or a shutdown be issued.

p0022For this purpose, the counter 12, a comparing circuit 1₃ downstream of a count setpoint signal s _zs is supplied. In the comparison circuit 13 of the sampled count is compared with the desired value, for example, the number 20th If the count is above this value, there occurs a signal at the output of the comparator's_aon, which leads to a display and / or triggers an alarm and / or automatically switches off the machine to be lubricated.

p0023Since the oil pressure is not in all cases alone the decisive criterion for proper lubrication, the flow rate of the oil can be monitored in the same way all the time. Also, both the oil pressure and the oil flow by means of circuits of FIG. 2 to be monitored and the corresponding output signals can be combined in a gate, so that each time an alarm occurs, if within a measuring interval a certain number of "negative" Measurements of the oil pressure or the oil flow occur.

p0024The simultaneous control of pressure and flow rate can for example be 3 carried out in a circuit of FIG.. Here, the output signals of a pressure sensor 6 and a flow sensor 7 via two controlled switches 14, 15 according to the first input of two comparators 16, 17, respectively. At the second inputs is each a nominal value voltage source₁8th, ₁9 with setpoint voltages U_ps and U_DSCorresponding to the Mininalwerten of the pressure or the flow rate.

p0025The clock 11 controls the switches 14, 15 periodically, but alternately, so that the sampled values ​​of the output signals from 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 fed to the input of the counter 12th The further evaluation of the signals takes place as described in connection with FIG. 2.

p0026It is understood that U by selecting the setpoint voltages_ps, U_DS, The sampling intervals τ, the measurement interval T and the count set value s_zs an adaptation to the particular operating requirements of the lubrication system in its broadest context is possible.

p0027The circuit of FIG. 5 shows a modification which operates without counter. Again, the output of a pressure sensor 6 (or a flow sensor) via a switch controlled by a clock generator 11 8 is applied to one input of a comparator 9, the other input with a pressure setpoint voltage source 10 (voltage U_ps) connected is.

p0028At the output occur at intervals τ pulses, provided the pressure is above the predetermined level (Up_s) lies. The length t 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, three pulses fail due to a pressure drop after the first three pulses.

p0029The output of comparator 9 is supplied via a resistor Rv a parallel RC network R, C. Unless the pulses occur on a regular basis because of sufficiently high pressure, a steady state is reached, the constant by the average, sawtooth-like voltage across the capacitor C is characterized. The rise of the sawtooth is hiebei except as by the voltage of the pulses, the time constant R by_v, C, the waste by the time constant RC determined. In case of failure of pulses, however, the voltage drops to increase with new impulses occur again. Therefore, when comparing the voltage across capacitor C with a predetermined desired voltage U_S1, Then an accumulation of "negative" pressure measurements are also determined as in the circuits of FIGS. 2 and 3. For this purpose a comparator 21 is provided, the voltage on the RC element R, C is at whose one input and the other input of a reference voltage source 22 (voltage U_S1) connected is. When the voltage drops U_c the capacitor C at the nominal voltage U_S1 appears at the output of the comparator 21 an alarm or shutdown signal s_a on. Here is an adaptation to the respective requirements by selecting the sampling intervals τ, the pulse length t₁, The pressure setpoint voltage Up_S and the target voltage U_S1 possible.

p0030In the circuit of FIG. 7, the evaluation is carried out also without counter, but here are the pressure or flow sensors as for example spring-loaded pressure switch 23 and flow switch 24 is formed. The switches are each equipped with a rest and a working contact, which, otherwise the normally closed contact is closed above a certain oil pressure or above a certain oil flow of work contact.

p0031The connections of the normally open contacts are connected to a DC voltage U, connections of normally closed contacts are connected to ground. The switching contact piece is in each case via a resistor R₁ or R₂ to a capacitor C₁ or C₂ out and the voltage-carrying terminal of the capacitors C₁, C₂ each is connected to the first input of a comparator 25, 26th The second inputs of the comparators 25, 26 are equipped with nominal voltage sources 27, 28 (voltage US₁ or U_S2) connected. The outputs of comparators 25, 26 are at the two inputs of a gate 29, at whose output the alarm or shutdown signal s_a may occur.

p0032As long as the pressure is above the switching value of the switch 23 is located, the voltage across capacitor C is₁ via the resistor R₁ held at the value U. If the pressure drops, the switch 23 and to the voltage across capacitor C₁ decreases according to the time constant R₁C₁ exponentially, since the capacitor C₁ via the resistor R₁ and the normally closed contact of the switch 23 discharges to ground. Once the capacitor voltage U_c below the voltage U_S1 falls, the comparator 21 outputs a signal to the (OR) gate 29; at whose output the alarm or shutdown signal s_a occurs.

p0033Analogously, the same applies 24 downstream circuit for the flow switch. Thus, whenever the signal s_a occur if the pressure and / or the flow rate decrease over time under the value at which the switches 23 and 24 switch. Relevant criteria for submission of the signal s_a here are on the one hand, for example, be fixed by spring voltage switching points of the switches 23 and 24 and on the other hand, the time constants R₁C₁, R₂C₂, The voltage U and the target voltages U_S1 or U_S2, Thus, also this circuit can be adapted to all requirements. In the circuits of FIG. 7 S and it may be appropriate under certain circumstances, temporarily power up the machine via a delay circuit one above the switching level U_S1 or U_S2 lying voltage to the capacitor C, C₁, C₂ to place, since the structure of the oil pressure and the oil flow takes some time and during this time in any case there should be no shutdown.

p0034The inventive method and the derived, described only in examples here circuitry enable the reliable control of a lubrication system, a lot more parameters than just the presence of a certain oil pressure can be used as decision criteria. As already mentioned, the use of the invention is not limited to lubrication systems, but it may extend to many systems that comprise a flowing medium and in which a supply of a particular area should be ensured with a sufficient quantity of this medium.