METHOD FOR MONITORING A HYDRAULIC SYSTEM

Description

[0001] The invention relates to a method for monitoring a hydraulic system. The preferred application area is hydraulically driven injection molding machines. In principle, however, the invention can be used with any hydraulic system.

[0002] Document DE 10 2019 117 820 A1 discloses a method for monitoring the condition of a hydraulic pump in a hydraulic system of a molding machine, in particular an injection molding machine. The hydraulic pump is connected to a pressure line and is operated at a displacement volume or a rotational speed to provide pressure in the pressure line. The displacement volume or rotational speed of the hydraulic pump is suddenly changed. A condition of the hydraulic pump is determined by analyzing a temporal response of the pressure in the hydraulic pump and / or in the pressure line.

[0003] JP 2020 076223 discloses another known method for monitoring a hydraulic system consisting of several hydraulic components.

[0004] Based on this, the object of the invention is to provide a method for monitoring a hydraulic system consisting of several hydraulic components, in which the condition of all components, in particular all pumps and consumers, can be monitored without additional sensors or with sensors already present in the hydraulic system.

[0005] This problem is solved by the features of claim 1. Advantageous embodiments and further developments can be found in the dependent claims 2 to 11.

[0006] According to a core idea, the present invention is based on the following consideration. A hydraulic system consists of several hydraulic components and usually includes a tank as a source of hydraulic fluid, at least one hydraulic pump driven by a motor, and one or more hydraulic consumers through which the hydraulic fluid delivered by the hydraulic pump flows. Valves are usually also present as additional hydraulic components. The aforementioned hydraulic components are interconnected by means of lines to form a hydraulic system. To monitor the condition of such a hydraulic system, it is necessary to determine the condition of each individual hydraulic component, but at least of the hydraulic pump. In a first step, the at least one hydraulic pump within a hydraulic system is measured, since its leakage affects all downstream hydraulic components.Accordingly, the method according to the invention provides the following step (a): Determination of the leakage of the at least one hydraulic pump as a function of the pressure in the hydraulic pump via predeterminable values ​​of the pressure in the hydraulic pump.

[0007] In a next step (b), subsystems that can be locked from one another are considered. Such a subsystem is formed by the at least one hydraulic pump from step (a) and a hydraulic consumer. The consumer can execute a translational or a rotational movement and thus move an actuator that is operatively connected to this consumer translationally or rotationally. Various known embodiments of a hydraulic cylinder can be considered for generating a translational movement. Various known embodiments of a hydraulic motor can be considered for generating a rotational movement. Depending on how comprehensive the monitoring is to be, individual subsystems that can be locked from one another or all of the subsystems that can be locked from one another can be considered and examined.

[0008] In the next step (c), the leakage of the consumers of the subsystems operated according to step (b) is determined. For this purpose, the difference value is calculated between the leakage of the subsystem with the consumer and the leakage of the at least one hydraulic pump from step (a).

[0009] In the next step (d), the efficiency of the hydraulic system is determined as follows: In step (d1), the efficiency of the hydraulic pump in the subsystems is determined in the current operating state, i.e., at the pressure prevailing at the hydraulic pump during current operation. The operating state can be understood as the combination of a consumer movement at an effective volume flow and the pressure prevailing at the hydraulic pump in the current state. The currently prevailing pressure at the hydraulic pump results from the force that the consumer must apply to generate the movement. "Current" means the time at which step (d1) is executed or the short period of time in which step (d1) is executed.For this purpose, the volume flow actually delivered by the pump, calculated from the leakage from step (a) of this hydraulic pump, is compared to the volume flow requested by the consumer in the subsystem.

[0010] In a step (d2), the efficiency of the consumer or consumers in the current operating state is determined by setting the volume flow actually effective for power conversion (= generation of the movement of the consumers and the connected actuators) at a specific consumer in the operating state in relation to the volume flow actually pumped by the pump and delivered to this consumer in the operating state. The volume flow effective at the consumer in the operating state is determined from the leakages from steps (a) and (c) or by taking these leakages into account. The volume flow actually delivered by the pump to this consumer in the operating state is determined taking into account the leakage of the pump from step (a).

[0011] According to a first embodiment, step (a) can be performed repeatedly at predeterminable times TA, preferably once per day, particularly preferably once per hour. The repetition of step (a) mentioned here ensures that a current history of the hydraulic pump's leakage is always available for subsequent calculations.

[0012] In a further development of the invention, step (b) can be repeated at predeterminable times TB, wherein in a hydraulic system of a cyclically operating machine, in particular an injection molding machine, a press or a machine tool, step (b) is carried out in every n-th cycle, wherein n is preferably less than 10 and particularly preferably n=1.

[0013] In a hydraulic system of a continuously operating machine, in particular in an extruder, step (b) can be repeated in predeterminable time steps ΔT, wherein ΔT is preferably less than 10 minutes, in particular less than 1 minute.

[0014] According to a further embodiment of the invention, a first subsystem with a hydraulic cylinder and a second subsystem with a hydraulic motor can be provided, wherein the two subsystems can be operated sequentially.

[0015] In a further development of the invention, standstill phases can be provided in which the hydraulic system is not operated and the consumers of the hydraulic system are not actuated, wherein step (a) is carried out in one or more such standstill phases.

[0016] In practice, a hydraulic system contains several valves with different functions. These can be purely shut-off valves or purely switching valves. Other valves, such as proportional valves, can also be present. Thus, one or more valves can also be present in one or more of the subsystems. According to one embodiment of the invention, the contribution of these valves can be disregarded or neglected when determining the leakage of the consumer of a subsystem.

[0017] According to an advantageous embodiment of the invention, in a step (d3) the efficiency of one or more, preferably all, of the checked subsystems in the hydraulic system can be determined by relating the actual effective volume flow of a subsystem to the requested volume flow in this subsystem.

[0018] Advantageously, a calculation of the average efficiency of the entire hydraulic system can also be performed. For this purpose, the efficiencies of the subsystems are weighted by the proportional durations of the individual process phases, namely according to η Gesamt = η 1 ⋅ t 1 + η 2 ⋅ t 2 + ⋯ + η n ⋅ t n t Gesamt , where n i the efficiency of a subsystem and ti the duration of operation of the subsystem. The above applies in particular to a hydraulic system of a cyclically operating machine, such as an injection molding machine, a press, or a machine tool. The sum of the individual process phases corresponds to one cycle of the machine, in particular an injection molding cycle.

[0019] In an injection molding machine, subsystems that are cyclically isolated from each other can be observed and monitored, as this corresponds to the operation of the injection molding machine. This results in continuous monitoring of the hydraulic system during operation of the injection molding machine, with measured values ​​(in this case, leakage values ​​and efficiency values) being determined for each injection molding cycle. Furthermore, as mentioned above, an average efficiency of the entire hydraulic system can also be determined.

[0020] The consumer(s) can perform a translational or a rotational movement, or a consumer can be designed in such a way that a translational or a rotational movement can be performed.

[0021] According to the invention, calculations are based solely on existing consumer data and measured actual values ​​of the consumers in their operating state. The available data can be obtained from the relevant consumer data sheets. This can include, among other things, the following data: displacement of the hydraulic motor, area ratio of the hydraulic cylinder, displacement of the pump. The actual values ​​are measured using suitable sensors. These can include, among other things, the following variables: pump speed, pump swivel angle, hydraulic motor speed, and axial speed of the hydraulic cylinder.

[0022] The following definitions may be helpful for understanding the invention and for describing embodiments.

[0023] "Pump leakage" = the volume per unit of time that the pump draws from the tank but does not transfer to a downstream consumer. It is the difference between the drawn-in and discharged flow rates.

[0024] "Leakage of a consumer" = the amount of hydraulic oil delivered by the pump to the consumer per unit of time, but not converted into motion by the consumer. It is the difference between the incoming flow rate and the flow rate converted into motion.

[0025] "Volume flow" = volume pumped per unit of time, for example in liters per minute.

[0026] The invention will be explained below using an embodiment and with reference to the Figures 1 and 2 be described in more detail.

[0027] They show: Figure 1Block diagram of a hydraulic system Figure 2Leakage at the respective operating point of the hydraulic pump.

[0028] The Figure 1shows a block diagram of a hydraulic system with a hydraulic pump 1 – sometimes referred to simply as "pump" below – and two hydraulic consumers, namely a hydraulic cylinder 2 and a hydraulic motor 3. The hydraulic system is supplied with a hydraulic fluid, in particular hydraulic oil, from a tank 4. The hydraulic system further comprises a shut-off valve 5, a proportional valve 6, and a switching valve 7. A motor 8 serves to drive the hydraulic pump 1. A first subsystem is formed by the hydraulic pump 1, shut-off valve 5, switching valve 7, and hydraulic cylinder 2. A second subsystem is formed by the hydraulic pump 1, shut-off valve 5, proportional valve 6, and hydraulic motor 3. Neglecting leaks at the valves 5, 6, and 7, the following subsystems can also be considered: a first subsystem consisting of the hydraulic pump 1 and hydraulic cylinder 2, and a second subsystem consisting of the hydraulic pump 1 and hydraulic motor 3. Step (a) Determine the leakage of the hydraulic pump

[0029] In a first step (a), the leakage of the hydraulic pump in its current state is measured via pressure. For this purpose, hydraulic pump 1 is decoupled from the downstream hydraulic components using the shut-off valve 5.

[0030] The starting point for determining leakage is the pump control concept. According to this control concept, the pump can be specified how much oil it should pump, i.e. a target volume flow can be specified. Because the shut-off valve 5 is closed, the specified oil delivery rate or the target volume flow can only flow out of the hydraulic pump 1 as leakage oil. This creates a certain pressure in the hydraulic pump 1. The more target volume is requested when the valve 5 is closed, the higher the pressure that results. The leakage oil flows back into the tank 4 via a leakage oil line and is therefore not available on the outlet side of the pump 1. The pumped volume flow of oil therefore corresponds to the volume flow of leakage oil. It can therefore be determined at which pressure p which volume flow of leakage oil is present. The target volume flow is continuously increased, preferably in ramp form.Predefined levels can also be reached. At the same time, the resulting pressure and oil temperature values ​​are continuously recorded and recorded. This process is preferably carried out across the entire pressure range that the pump can generate. If the target flow rate is increased in many small steps, and thus also the resulting pressure, a virtually continuous flow of leakage oil occurs across the pump's pressure range. This process is preferably carried out until the pressure limit is reached. pmax of the hydraulic pump or the upper limit of the working range of the hydraulic pump is reached.

[0031] The Figure 2shows the result of such a measurement of a hydraulic pump, namely the percentage leakage at the respective pressure-dependent operating point of the hydraulic pump. Thus, the leakage of the pump, as the supplier for all downstream components, is known and provided as a reference. Due to wear mechanisms during its service life, the leakage of the pump increases over time. The previously described measurement is carried out at preferably defined intervals for each hydraulic pump in the system in order to document a trend over time in a suitable database system and to derive a forecast of the wear progression over future use. Since only target values ​​and measured values ​​that already exist in common hydraulic systems are used, no additional sensors are necessary. The result is the following relationship: Q ist Pumpe = Q soll − Q leck Pumpe

[0032] Since the leak increases over time, step (a) of the method according to the invention only applies to the time being examined. Therefore, step (a) is repeated from time to time, in particular at regular intervals. For example, step (a) can be performed once a day, in particular always at the same time.

[0033] In production using an injection molding machine, the leakage of the subsystems and, consequently, the leakage of the consumers can be continuously determined (from cycle to cycle). This is possible because the subsystems are operated sequentially, thus automatically shutting off. v is in the cylinder as a consumer and N is on the hydraulic motor as a consumer.

[0034] For the calculation of the leakage in steps (b), (c) and (d) the most recent available leakage curve (corresponding to the Figure 2) of the hydraulic pump. Step (b) Determination of subsystem leakage

[0035] In this step, the current leakage of the subsystems that can be isolated from each other is determined. As described above, a first subsystem consisting of hydraulic pump 1 and hydraulic cylinder 2, as well as a second subsystem consisting of hydraulic pump 1 and hydraulic motor 3, can be considered. To determine the leakage, the subsystems are isolated from each other, each subsystem is operated independently, and the leakage is determined in the operating state. (b1) Leakage of the subsystem consisting of a pump and a hydraulic motor

[0036] In the present embodiment, the leakage is determined during the rotation of the hydraulic motor 3. Leakage in valves is neglected. During operation of a hydraulic motor 3, a volume flow from the hydraulic pump 1 is converted into a rotary motion. If the valve 6 upstream of the hydraulic motor 3 is switched, oil flows through the hydraulic motor 3 and drives it.

[0037] The volume flow Q The hydraulic motor 3 can be directly converted into a speed N This is done by interpolating a characteristic curve or by a linear conversion from the pump data sheet. For linear conversion, a displacement V and a maximum speed Nmax The required flow rate of a new hydraulic motor Q should can be used for a speed N thereby in l min can therefore be calculated by linear interpolation: Q soll = N soll ⋅ Q max N max = N soll ⋅ V Schluck 1000

[0038] If a characteristic curve with multiple support points is available, interpolation is performed analogously between the support points of the characteristic curve. If a load is applied to the shaft of the hydraulic motor, this results in a torque that counteracts the rotation of the hydraulic motor. As a result, an oil pressure is established on the input side of the hydraulic motor. p isThis is measured, like the engine speed, using a suitable measuring system. In controlled operation, a speed is usually required to achieve a certain operating state. N should which in the case of a new hydraulic motor is directly converted into the volume flow using formula (2) Q should of this hydraulic motor and which is requested by hydraulic pump 1.

[0039] If wear occurs in the subsystem "pump-hydraulic motor" considered here, which leads to an internal leakage in the pump 1 and / or the hydraulic motor 3, the desired speed N should cannot be reached. Pump 1 cannot be reached due to leakage Q leak pump the requested volume flow Q should not deliver and / or the hydraulic motor 3 may not be able to deliver due to leakage Q leak engine under the applied load, the incoming flow rate can no longer be converted into a sufficient rotational movement. The two leaks Q leak pump and Q leak engine together form the total leakage Q leakTotal of the subsystem consisting of pump 1 and hydraulic motor 3.

[0040] Due to leaks from the pump and hydraulic motor, instead of the specified speed N should a speed N is which is based on the actual effective volume flow Q Engine The actual effective flow rate at the hydraulic motor 3 Q Engine is calculated from the target volume flow of the hydraulic motor 3 according to the above equation (2) minus the leakages at the pump 1 and the hydraulic motor 3 as follows: Q Motor = Q soll − Q leck Pumpe − Q leck Motor

[0041] The leakage of the subsystem consisting of pump and hydraulic motor is calculated from equation (3): Q leck Gesamt = Q leck pumpe + Q leck Motor = Q soll − Q Motor

[0042] The turnover of the volume flow Q Engine into an effective rotation with the speed N is can be described for the hydraulic motor 3 analogously to the above equation (2) as: N ist = Q Motor ⋅ N max Q max

[0043] From these relationships, the total leakage of the pump-hydraulic motor subsystem can finally be determined starting from equation (4) and using equation (5) as follows: Q leck Gesamt = Q soll − N ist ⋅ Q max N max

[0044] In addition to the above explanations, a concrete calculation example is presented below. From the data sheet, it can be seen that the hydraulic motor 3 has a constant geometric displacement volume and thus a displacement volume of V Schluck = 90 cm 3 U Furthermore, the maximum speed N max = 300 U min From this, the maximum volume flow Qmax in l min can be calculated analogously to formula (2): Q max = N max ⋅ V Schlu 1000 = 300 U min ⋅ 90 cm 3 U 1000 = 27 l min

[0045] At a desired speed of N soll = 100 U min The target volume flow required by pump 1 in the new state of the hydraulic motor 3 is calculated according to equation (2) as follows: Q soll = N soll ⋅ Q max N max = 100 U min ⋅ 27 l min 300 U min = 9 l min

[0046] In the operating state, a deviation from the target speed to the actual speed is measured. With the requested flow rate, the hydraulic motor 3 only reaches an actual speed N ist = 80 U min . There is a total leakage in the "pump-hydraulic motor" subsystem, resulting in a lower effective volume flow Q(effective) at the hydraulic motor 3: Q Motor = N ist ⋅ Q max N max = 80 U min ⋅ 27 l min 300 U min = 7 , 2 l min

[0047] According to formula (4) we get: Q leck Gesamt = Q soll − Q Motor = 1 , 8 l min

[0048] At the end of step (b1) the leakage of the subsystem consisting of pump 1 and hydraulic motor 3 for the operating state of a certain desired target speed N should known. (b2) Leakage of the subsystem consisting of a pump and a hydraulic cylinder

[0049] The calculation is largely analogous to the calculations for a hydraulic motor. The only difference is the type of movement being measured. Instead of the speed, N is the speed v isof the piston in the hydraulic cylinder 2. Here, too, there is a conversion factor for determining the volume flow Q, which in this case is described by the diameter of the cylinder and thus the effective area of ​​the piston for the oil (e.g. 4000mm 2< ): v = Q A Zylinder

[0050] Under load, this movement creates a pressure p In this case, if a leak is present, the desired speed is v should not achieved, because the calculation of the required target volume flow Q should analogous to the hydraulic motor with static conversion factors that do not compensate for leakage. For an example requested speed v should from 100 mm s surrendered Q should to Q soll = v soll ⋅ A Zylinder = 100 mm s ⋅ 4000 mm 2 = 400000 mm 3 s

[0051] With 11 = 10 6< mm 3< and 1min = 60s we get: Q soll = 24 l min

[0052] For example, if only one speed v is from 90 mm s reached, the difference can again be attributed to a leak. v is is therefore a result of the effective volume flow Q cylinder . Analogous to formula (3) above, we get: Q Zylinder = Q soll − Q leck Zylinder − Q leck Pumpe

[0053] Analogous to equation (4) above, the total leakage of the subsystem "pump-hydraulic cylinder" is: Q leck Gesamt = Q leck Pumpe + Q leck Zylinder = Q soll − Q Zylinder

[0054] The same applies analogously to formula (5): v ist = Q Zylinder A Zylinder

[0055] The total leakage of the subsystem to the target volume flow Q should and the effective volume flow Q Cylinder from equation (16) as follows: Q leck Gesamt = Q soll − v ist ⋅ A Zylinder = 400000 mm 3 s − 90 mm s ⋅ 4000 mm 2 = 40000 mm 3 s

[0056] This results in a leakage of 2.4 l min .

[0057] At the end of step (b2) the leakage of the subsystem consisting of pump 1 and hydraulic cylinder 3 is known.

[0058] For all subsystems considered, it should be noted that leakage measurement and calculation are only possible for the respective desired operating state ( N should or v should ) and the resulting operating pressure. For a different operating state and therefore for a different operating pressure, the leakage of the subsystems must be recalculated, because the leakage itself depends on the prevailing operating pressure. However, since a characteristic curve for the pump was recorded for several operating pressures in step (a), this is easily possible at any time. The calculation is based solely on existing consumer data and measured actual values ​​of the consumers in the operating state. Step (c) Determine the leakage of each consumer

[0059] This step involves determining the leakage of the consumers of the subsystems operated according to step (b). This is done by calculating the difference between the leakage of the subsystems from step (b) and the leakage of at least one hydraulic pump from step (a). In step (b), the leakages of the two subsystems "pump-hydraulic motor" and "pump-hydraulic cylinder" were compared at a desired operating state with a prevailing pressure. p The leakage of the pump under this pressure p is known from step (a). In step (a), this leakage was recorded for several pressure values ​​or support points. Corresponds p does not exactly correspond to one of the pressure values ​​or support points, the corresponding leakage can be determined by interpolating the support points. The leakage of the consumer of the considered subsystem for the system pressure p can therefore be calculated: Q Verbraucher = Q Gesamt − Q leck Pumpe

[0060] The described method for determining leakage from individual consumers can be applied to any axis downstream of the pump and thus to any consumer downstream of the pump, provided that a rotational speed (consumer = hydraulic motor) or position / speed (consumer = hydraulic cylinder) can be measured and the corresponding displacement (hydraulic motor) or the effective area of ​​the power transmission (hydraulic cylinder) is known. Furthermore, the applied oil pressure p must be measurable. (c1) Leakage of the hydraulic motor

[0061] In the example from (b1), the hydraulic motor 3 demands a volume flow from the hydraulic pump 1 Q soll = 9 l min , whereby an operating pressure of 200 bar is set at the hydraulic pump 1 to deliver this volume flow. At this pressure, a leakage of 15% of the hydraulic pump 1 was measured in step (a) (see Figure 2 ). The hydraulic motor therefore does not receive the required flow rate Q should from 9 l min but only an effective volume flow Q Engine from 7 , 65 l min , corresponding to a leakage of 15% of 9 l min . The leakage of the hydraulic motor 3, which represents the consumer in the subsystem consisting of pump and hydraulic motor, is thus calculated from equation (10) taking into account the total leakage of this subsystem as follows: Q leck Motor = Q leck Gesamt − Q leck pumpe = 1 , 8 l min − 1 , 35 l min = 0 , 45 l min (c2) Leakage of the hydraulic cylinder

[0062] In the example from (b2), the hydraulic cylinder 2 requests a target volume flow of Q soll = 24 l min , whereby an operating pressure of 50 bar is set at the hydraulic pump 1 to deliver this volume flow. At this pressure, a leakage of the hydraulic pump of 5.5% was measured in step (a) (see Figure 2 ). This results in a leakage for the pump of 5.5% of Q should , ie in the amount of 1 , 32 l min . The leakage of hydraulic cylinder 2, which represents the consumer in the subsystem consisting of pump and hydraulic cylinder, is calculated taking into account the total leakage for this subsystem from equation (17) as follows: Q leck Zylinder = Q leck Gesamt − Q leck pumpe = 12 , 4 l min − 1 , 32 l min = 1 , 08 l min Step (d) Determination of the efficiency of the hydraulic system

[0063] The efficiency results from the comparison of the new condition with the actual condition of the respective hydraulic component. In this case, this comparison concerns pump 1, hydraulic cylinder 2 and hydraulic motor 3. First, the volume flow that the consumer (hydraulic motor 3, hydraulic cylinder 1) would have in new condition is determined. For this purpose, the data sheets may contain maximum values ​​or characteristic curves, which can be used to calculate the required volume flow of oil for a corresponding speed of a consumer. For a hydraulic motor, the speed corresponds to the rotational speed. For example, according to the data sheet, in new condition, the hydraulic motor could have a rotation of 300 1 min a volume flow of 40 l min be achieved. It is also conceivable, however, that this data is determined during commissioning of a machine. There, it is calibrated / adjusted in new condition. In this case, the data sheets would not always be necessary. Moreover, even in new condition, there may already be deviations from the data sheets. In the case of a hydraulic cylinder, it is about the actual speed at which the piston is moved. For example, for an area of ​​4000 mm 2< According to the data sheet, in the new condition of the hydraulic cylinder 2 according to formula (19) a speed of 100 mm s at a volume flow of 24 l min In new condition, the actual volume flow Q is the target volume flow Q should . In the actual state, the leaks in the hydraulic system come into play. These leaks are determined as described above. Ultimately, the actual flow rate corresponds to Q is on a component the target volume flow Q shouldthis component minus the leakage volume flow Q leak . The efficiencies of the hydraulic components will be determined in detail below. (d1) Efficiency of the pump in the subsystems

[0064] For this purpose, the actual volume flow calculated from the leakage is used for the individual subsystems Q is pump in relation to the requested volume flow Q should set. Q should In new condition, corresponds to the actual volume flow. (d1.1) Efficiency of the pump in the subsystem with hydraulic motor

[0065] In the example from (b1) the hydraulic motor requests from the hydraulic pump Q soll = 9 l min , whereby an operating pressure of 200 bar is set at the hydraulic pump to deliver this quantity. At this pressure, a leakage of the hydraulic pump of 15% was measured in step (a) (see Figure 2 ). The pump does not deliver the required amount of 9 l min but only 7 , 65 l min . The efficiency can therefore be calculated for a pressure of 200 bar: η Pumpe , 200 bar = Q ist , Pumpe Q soll = 7 , 65 l min 9 l min = 0 , 85 = 85 % (d1.2) Efficiency of the pump in the subsystem with hydraulic cylinder

[0066] In the example from (b2) the cylinder requires a target volume flow of Q soll = 24 l min and a pressure of 50 bar is established. At this operating pressure, the hydraulic pump has a leakage of 5.5%, corresponding to 1.32 l / min. This results in an effective flow rate of Q is pump from 22 , 68 l min . The pump efficiency for this subsystem can therefore be calculated as: η Pumpe , 50 bar = Q ist , Pumpe Q soll = 22 , 68 l min 24 l min = 095 = 95 % (d2) Determination of the efficiency of the consumers in operating condition

[0067] For this purpose, the volume flow actually effective for the power conversion at the consumer Q Consumption in relation to the actual volume flow delivered by the pump to this consumer Q is pump set for the values ​​corresponding to the operating condition under investigation. hydraulic motor

[0068] The hydraulic motor receives in the subsystem of pump and hydraulic motor, as calculated in (c1) does not calculate the amount of 9 l min but only 7 , 65 l min , since the pump already has a leak. In addition, from this finding it was already calculated in (c1) that the leakage of the hydraulic motor is therefore 0 , 45 l min (see equation (18)). Based on the calculated leakages of pump 1 and hydraulic motor 3, it is now possible to determine the efficiency of the hydraulic motor as follows. η hydmot = 1 − Q leck Motor Q soll − Q leck Pumpe = 1 − 0 , 45 l min 9 l min − 1.35 l min = 1 − 0 , 059 = 94 , 1 %

[0069] Alternatively, the efficiency can be calculated from the flow rates. To determine the effective flow rate at the hydraulic motor Q Engine the above equations (5) and (9) apply, ie in the example Q Engine = 7.2 l / min. To determine the actual flow rate of the pump, equation (1) applies, ie in the example from d(1.1) Q ist Pumpe = 7 , 65 l min . Based on this, the efficiency of the hydraulic motor is calculated as follows: η hydmot = Q Motor Q ist Pumpe = 0.941 = 94 , 1 % hydraulic cylinder

[0070] Analogously, the efficiency for hydraulic cylinder 2 in its operating state can be determined: η Zylinder = 1 − Q leck Zylinder Q soll − Q leck Pumpe = 1 − 1 , 08 l min 24 l min − 1.32 l min = 1 − 0 , 048 = 95 , 4 %

[0071] Alternatively, the efficiency can be calculated from the volume flow. To determine the effective volume flow at the hydraulic cylinder Q Cylinder the above equation (16) applies and consequently in the example a value of Q Zylinder = 21 , 6 l min . For the determination of the effective volume flow of the pump, equation (1) applies, ie in the example from d(2.2) Q ist Pumpe = 22 , 68 l min Based on this, the efficiency of the hydraulic cylinder is calculated as follows: η Zylinder = Q Zylinder Q ist Pumpe = 0.954 = 95 , 4 % (d3) Determination of the efficiency of the respective subsystem

[0072] For this purpose, the actual effective volume flow at a consumer in a subsystem is compared to the volume flow requested by that consumer. The requested volume flow Q target corresponds to the actual volume flow in the new state.

[0073] For the subsystem with hydraulic motor: η Gesamt Subsystem Motor = Q Motor Q soll = 7 , 2 l min 9 l min = 0 , 8 = 80 %

[0074] For the hydraulic cylinder subsystem: η Gesamt Subsystem Zylinder = Q Zylinder Q soll = 21 , 6 l min 24 l min = 0 , 9 = 90 % (e) Average efficiency of the overall system

[0075] In a further development of the invention, it can be provided that the average efficiency of the entire hydraulic system is determined for a cyclically operating machine, in particular an injection molding machine. This takes into account how long a subsystem is operated during the injection molding cycle. From this, the average efficiency of the entire system for the set process can be calculated. If, in the example system, the hydraulic motor is operated for 9 seconds per cycle and the cylinder for 1 second, the average efficiency of the entire system is as follows: η Gesamt = η 1 ⋅ t 1 + η 2 ⋅ t 2 + ⋯ + η n ⋅ t n t Gesamt = 9 s ⋅ 80 % + 1 s ⋅ 90 % 10 s = 81 % List of reference symbols

[0076] 1Hydraulic pump 2Hydraulic cylinder 3Hydraulic motor 4Tank 5Shut-off valve 6Proportional valve 7Switching valve 8Drive motor

Claims

1. A method for monitoring a hydraulic system consisting of several hydraulic components, comprising a source of a hydraulic fluid, at least one hydraulic pump and one or more hydraulic consumers, which are flowed through by the hydraulic fluid which is conveyed by the hydraulic pump, wherein the method comprises the following steps: (a) Determining the leakage of the at least one hydraulic pump as a function of the pressure in the hydraulic pump via predeterminable values of the pressure in the hydraulic pump; (b) Operation of one or more, preferably all, hydraulic subsystems of the hydraulic system which can be shut off from one another, and determining of the present leakage of these subsystems in the operating state, wherein a subsystem is formed from the at least one hydraulic pump of step (a) and a consumer, (c) Determining the leakage of the consumers of the subsystems operated according to step (b) by formation of the difference value between the leakage of the at least one hydraulic pump of step (a) and the leakage of the subsystem of step (b) which has the above-mentioned consumer, (d) Determining the efficiency of the components of the hydraulic system according to the steps: (d1) Determining the efficiency of the pump in the subsystems in the operating state, by the volume flow QactualPump actually conveyed by the pump, calculated from the leakage of step (a) in the operating state, being set in relation to the volume flow Qtarget requested in the subsystem by the consumer, (d2) Determining the efficiency of the consumer or consumers in the operating state, by the volume flow Qconsumer actually effective for the force conversion at a particular consumer in the operating state being set in relation to the volume flow Qactual actually conveyed by the pump in the operating state and delivered to this consumer, wherein the volume flow effective at the consumer in the operating state results from the leakages from steps (a) and (c) and the volume flow actually delivered by the pump in the operating state to this consumer results taking into consideration the leakage of the pump from step (a).

2. The method according to Claim 1, characterized in that the step (a) is carried out repeatedly at predeterminable times TA, preferably 1x per day, particularly preferably 1x per hour.

3. The method according to Claim 1 or 2, characterized in that the step (b) is repeated at predeterminable times TB, wherein in the case of a hydraulic system of a cyclically operating machine, in particular an injection moulding machine, a press or a machine tool, the step (b) is carried out in every nth cycle, wherein n is preferably less than 10 and particularly preferably n=1.

4. The method according to Claim 1 or 2, characterized in that in the case of a hydraulic system of a continuously operating machine, in particular an extruder, the step (b) is repeated in predeterminable time steps ΔT, wherein ΔT is preferably less than 10 minutes, in particular less than 1 minute.

5. The method according to one of the preceding claims, characterized in that a first subsystem is provided with a hydraulic cylinder and a second subsystem is provided with a hydraulic motor, and that the two subsystems are operated sequentially.

6. The method according to one of the preceding claims, characterized in that standstill phases are provided in which the hydraulic system is not operated and the consumers of the hydraulic system are not actuated, and that the step (a) is carried out in one or more standstill phases.

7. The method according to one of the preceding claims, characterized in that in one or more subsystems one or more valves are present, and that the proportion of these valves remains unconsidered or respectively is disregarded in the determining of the leakage of the consumer of a subsystem.

8. The method according to one of the preceding claims, characterized in that a determining of the efficiency of one or more, preferably all, of the examined subsystems is carried out in the hydraulic system, by the actually effective volume flow of a subsystem Qconsumer being set in relation to the requested volume flow Qtarget in this subsystem.

9. The method according to Claim 8, characterized in that a calculation of the average efficiency of the total hydraulic system is carried out by the efficiencies of the subsystems being weighted with the proportional durations of the individual process phases, namely according to η Total = η 1 ⋅ t 1 + η 2 ⋅ t 2 + ⋯ + η n ⋅ t n t Total wherein η is the efficiency of a subsystem and t is the duration in which the subsystem is operated.

10. The method according to Claim 9, characterized in that a hydraulic system of a cyclically operating machine is concerned, in particular an injection moulding machine, and that the sum of the individual process phases corresponds to a cycle.

11. The method according to one of the preceding claims, characterized in that the consumer or consumers carry out a translatory or a rotatory movement or respectively are configured such that a translatory or a rotatory movement can be carried out.