EP2118501B1 - Method for automatically determining the state of a hydraulic aggregate - Google Patents

Description

The invention relates to a method for automatically determining the state of a hydraulic unit for supplying a hydraulic cylinder for performing load strokes.

In DE 10 2004 017979 A1 A method of angularly rotating a part is described in which a hydraulic power unit provides pressure to the hydraulic cylinder of a power wrench. The hydraulic unit is provided with a control device which switches over a control valve as a function of the pressure generated. The pressure increases at each load stroke initially with a higher pitch and then with a lower slope until the end stop of the hydraulic cylinder is reached.

In modern machinery and equipment, it is necessary to perform regular maintenance inspections to identify any errors or impending errors. In such maintenance wear parts are replaced. Usually, the maintenance is carried out at regular time intervals or after a certain number of operating hours of the device. Such an interval-determined definition of maintenance is oriented only to a small extent on the actual workload of the device. Thus, it is disregarded whether the hydraulic implement has performed only light strokes or possibly was operated up to the load limit.

For complex systems that are subject to different load conditions, condition monitoring has been developed in which a condition is determined to avoid system failures. The determined state indicates how far away the monitored system is from a soon to be expected fault or failure. In this way an early detection of creeping system changes and a limitation of the causes is possible. Condition monitoring enables condition-based maintenance of the plant and replaces the previous preventative maintenance, in which the machine was maintained at fixed maintenance intervals. Condition monitoring also offers the option of online status diagnostics.

In DE 102 54 819 A1 a method is described which allows a limit-load-dependent partial deactivation of individual functions of the system components of a vehicle. In this case, the operating data of the monitored and controlled components for determining the component load are recorded. The operating data can be the detection of the switch-on frequency or switch-on time of a pump or of the pump motor in different pressure classes. In addition, the temperature of the hydraulic components can be recorded. The total load is the sum of the loads of all components. With the statement exceeding the permissible load in at least one system component, it is checked whether the system component executes comfort-relevant systems or safety-related functions. For comfort-relevant functions, modifications to the control are carried out, while a reduction of the sensitivity is realized in safety-relevant functions.

JP 59-194215 A describes a method for automatically determining the state of a hydraulic system, in which for a component of the system of pressure and time, a wear-determining index is calculated, wherein together with a wear limit, a degree of wear is determined.

The invention has for its object to provide a method for automatically determining the state of a hydraulic power unit of a power wrench, which allows a realistic state determination.

The inventive method is defined by the patent claim 1. Thereafter, it is envisaged that for Aggregatekomporienten from the pressure and the duration of operation since commissioning each a wear-determining index is calculated that from the index and a set for the component component wear limit each wear is determined and that for the entire unit under the

Wear levels of all aggregate components determines the maximum and from this a total degree of wear is formed.

The magnitude of the resulting pressure provides information about the applied power, from which in connection with the duration of the load stroke, the work or an associated size can be determined. The method thus distinguishes the load strokes according to the resistance that was opposed to them. Therefore, heavy load strokes are rated higher than smooth load strokes.

The inventive method is intended for hydraulic units for operating hydraulic power wrench for tightening screws, nuts and similar rotatable parts. In this case, the pressure which arises during a load stroke depends on the resistance which the part of the rotation to be rotated opposes.

The degree of wear indicates the accumulated workload. This means that, since the last maintenance, all the operations performed on the hydraulic unit will increase the degree of wear, depending on the work done. A heavy-duty hydraulic power unit reaches the upper limit, the wear limit, earlier than a hydraulic power-limited unit, with the same number of operating hours. The degree of wear is a measure of the "exhaustion" of the device. The degree of wear can be used to calculate the number of operating hours still possible until the next maintenance procedure. This calculation is carried out automatically in the control unit of the hydraulic unit. The display of the available operating hours can be called up at the push of a button. When calculating the number of operating hours still available, the average weight of the previous workload will be used as the basis for future work to be carried out.

According to a preferred embodiment of the invention, the time integral of the pressure is formed for the ratio. Here, the area under the pressure curve, which results in the load strokes, evaluated. A simplified embodiment provides that the pressure and the duration of a load stroke are processed as parameters for the determination or further development of the degree of wear.

The pressure and the duration of a load stroke are processed as parameters for the determination or further development of the state variable. This may conveniently be done so that the product of pressure and duration is formed to obtain a load size of the respective load stroke. To this load size of the previous accumulated degree of wear is increased.

Pressure and duration of the load strokes are not necessarily the only parameters that affect the state quantity. For example, the extraction of the state variable can also include the number of load strokes or the temperature of the hydraulic medium. The type of involvement can be done in different ways. For example, each parameter may be weighted.

The signals from sensors which display error messages can also be included in the extraction of the state variable. For example, the frequent exceeding of a limit temperature would lead to an unscheduled increase in the state quantity. It is also possible to measure the operating time of the hydraulic unit below and above a limit temperature. An example of this is: The hydraulic unit has run 50 working hours, 30 hours of which over 50 ° C.

The invention further relates to a hydraulic unit for supplying a hydraulic cylinder for performing load strokes according to claim 7.

The hydraulic power unit can detect and store other monitored parameters such as the number of operating hours from the beginning and last servicing, the product of operating time, current and voltage of the motor as electrical work, the product of operating time of the motor, pressure and volumetric flow as hydraulic work, the product of temperature and time, the current peak value, the voltage peak and / or the minimum voltage value, the temperature peak value, the pressure peak value as well as the product of volume flow and time to determine the accumulated pumped volume.

In addition to the state determination, other functions may be provided, such as a self-test of the hydraulic unit. For this purpose, the two hoses flow and return are connected and the maximum pressure is set to a predetermined value, for. B. 400 bar, set. Due to the elasticity of the tubes sealed at the ends, the pressure builds up linearly with time, according to a reference curve that is recorded or stored. Then it is checked whether the measured Kurzve has the predetermined course of the reference curve.

It also checks the operational readiness of the pressure sensors for forward stroke and return stroke, the flow of current from the motor, the pressure build-up, namely function of the main valve, function of the gear pump, function of the number of pump elements and the pressure relief, namely function of the relief valve.

A diagnostic connector can be plugged into the control unit to read out wear-relevant data or the entire device history. In this way, the state of the unit is available at any time. The fault diagnosis is facilitated because the device caches critical conditions.

It is also possible to connect the control unit to the Internet or to another detention network. Here, for example, the data from the aggregate transmitted daily to a maintenance server. Parameter adjustments can be stored on the maintenance server and automatically programmed at the next diagnosis.

In the following an embodiment of the invention will be explained in more detail with reference to the drawings.

Fig. 1

ein schematisches Ausführungsbeispiel einer Schraubvorrichtung mit einem Hydraulikaggregat und einem Kraftschrauber zum Drehen einer Schraube,

Fig. 2

eine schematische Darstellung des Kraftschraubers, der den Kolbenzylinderantrieb enthält,

Fig. 3

eine Ansicht des gesamten Hydraulikaggregats einschließlich Fernbedienung und Programmiereinheit und

Fig. 4

ein Zeitdiagramm des Druckverlaufs bei mehreren aufeinanderfolgenden Lasthüben.

Show it:

Fig. 1

a schematic embodiment of a screwing device with a hydraulic unit and a power screwdriver for rotating a screw,

Fig. 2

a schematic representation of the power wrench containing the piston cylinder drive,

Fig. 3

a view of the entire hydraulic power unit including remote control and programming unit and

Fig. 4

a time chart of the pressure curve at several successive load strokes.

In the Figures 1 and 2 schematically a power wrench 10 is shown. This has a hydraulic piston-cylinder drive 11 with a hydraulic cylinder 12 and a piston 13 movable therein. The piston is connected to a piston rod 14, and the end of the piston rod engages a lever 15 which engages with a latching pawl 15a on the toothing of a ratchet wheel 17. The ratchet wheel 17 is part of a ring piece 18, which has a socket 19 for inserting a key nut or a screw head to be rotated. By reciprocating movement of the piston 13, the ring piece 18 is rotated, and with this the screw. The Ring piece 18 is mounted in a housing 20 which also contains the piston cylinder drive 11.

The pressure for the piston-cylinder drive 11 is determined by the in Fig. 1 shown hydraulic unit 25 is supplied, which has a positive displacement pump 26, z. B. includes a gear pump, a speed-controlled synchronous motor and a tank. The motor drives the pump 26. The hydraulic unit 25 is connected to a pressure line 28 and a return line 29. These two lines are connected via a control valve 30 to the piston-cylinder drive 11. By switching the control valve 30, the piston 13 can be moved either forward or backward.

For controlling the hydraulic unit 25 and the control valve 30, the control unit 31 is provided. This includes a frequency converter that generates a variable drive frequency for the motor. The control unit 31 thus determines the speed of the pump 26. The pump speed determines the volume flow, which is the pressure line 28 is supplied.

At the pressure line 28, a pressure sensor 32 is provided which measures the hydraulic pressure p in the pressure line. The pressure sensor is connected via a line 33 to the control unit 31.

The hydraulic unit 25 has a housing 35 containing the hydraulic oil. In the housing 35, a pump is housed, which is designed as a submersible pump and the pressure for the hose system 28, 29 generates. It is a volumetric pump of a gear pump or more, distributed pump segments, which are driven by a motor.

At the front end of the housing 35 is an adjustable pressure relief valve 36 and a shoulder 37 for the tubes 28 and 29. There is also the pressure sensor 32 for the pressure line 28 is provided. Another pressure sensor is provided for the return line 29.

The control unit 31 has a housing, in the top of which a display 40 is arranged. The housing is connected to a remote control 41, with which a manual control of the control valve 30 can take place.

Furthermore, the programming unit 42, which forms a user interface with the keyboard and the display, can be connected to the control unit.

FIG. 4 shows the course of the pressure p over the time τ at several successive load strokes of the power wrench. It is the pressure that is measured by the pressure sensor 32.

In FIG. 4 the load strokes LH1 - LH4 of the piston are shown. Each load stroke has an initial section 45, in which a relatively steep increase in pressure takes place to overcome the friction or to reach the state in which the preceding load stroke has been completed. This is followed by a section 46 in which the screw is rotated. At the end of the load stroke, the piston 13 abuts against the front stop of the cylinder ( Fig. 2 ). This creates a steep pressure build-up represented by section 47. By detecting the steep portion 47 of the blocking state is detected at the end of the load stroke. This is followed by a sloping section 48, in which the return stroke of the piston takes place and the pressure p goes back to 0.

In each of the load strokes LH1 - LH4, the initial portion 45 is extended from the previous load stroke until the torque reached at the portion 47 is reached again. Only then begins the section 46, in which the screw is rotated against a rotational resistance.

In one embodiment, the height of the resulting pressure is determined and stored at each load stroke. This is the pressure p of section 47 at the switchover from the load stroke to the return stroke takes place. Here, either the starting point or the end point of the short section 47 can be selected. The level of pressure reached is a parameter for determining the workload. Another parameter for determining the workload is the duration of the load stroke. In this case, the duration from the beginning of the starting section 45 to the end of the section 46 can be evaluated. However, it is also possible to evaluate only the duration of section 46 or to include the duration of section 48, which represents the return stroke. Preferably, the duration of the two sections 45 and 46 is evaluated.

The control unit 31 forms the product of the pressure level and duration of the load stroke and sums the products thus formed from load stroke to load stroke, so that a state variable is obtained which indicates the wear. If this state variable has reached a predetermined value, a maintenance or inspection is due. The difference between the wear limit and the instantaneous value can be displayed to determine the proximity of the upcoming maintenance time.

The described extraction of the state quantity indicating the accumulated workload is not necessarily the sole criterion for determining the time of the next maintenance. Regardless of the accumulated workload, the number of load strokes may represent an alternative or additional criterion. Other criteria, such as As the temperature of the hydraulic medium can be used to perform an emergency shutdown or included in the state determination, for example, by load strokes, in which the temperature exceeds a threshold, receive an additional weighting.

Hereinafter, a second embodiment of the invention will be described, wherein also on the Figures 1 - 4 Reference is made to:

From the actual load of the hydraulic power pack, parameters are calculated that allow conclusions to be drawn about the (wear) condition of individual power unit components. For this purpose, essentially the pressure-time characteristic curve recorded during screwing ( Fig. 4 ), possibly also oil temperature as well as other continuously recorded measurement data.

The pressure-time characteristic curve contains the data relevant to the wear of the unit, regardless of the periphery used for the screw connection (hoses, hydraulic drives, screwdrivers ...) and regardless of the screwdriving cases (torque, frictional torque, inclination ...).

In particular, high pressures, pressure peaks, pressure fluctuations, the volume pumped and the hydraulic power take effect on the wear; In addition, the influence of many of these values changes with the working temperature, which is sufficiently approximated by the oil temperature.

The wear of individual components depends on these parameters differently, so a seal is claimed mainly mechanically under pressure changes, a pump element, however, mainly from the (mechanical and therefore hydraulic) work that it does.

Since a component changes continuously over time with its wear, an integral of these parameters over the course of time gives a good statement about their wear.

mit:
p(τ):  Momentandruck zum Zeitpunkt τ
$\frac{dp\left(\tau \right)}{d\tau }:$

  Ableitung von p(τ) zum Zeitpunkt τ ("Steigung", "Änderung")
q(τ):  Volumenstrom zum Zeitpunkt τ (aus p(τ)) (Baureihenspezifisch zu errechnen)
ϑ(τ):  Öltemperatur zum Zeitpunkt τ
b_0,i,b_1,i,b_2,i,b_3,i,b_4,i :  Komponentenabhängige Gewichtungsfaktoren und Exponenten für die einzelnen KennzahlenTherefore, the characteristic of the wear of an aggregate component K _i determining z _i is calculated since commissioning ( τ = 0) until the time τ as follows: $$z_i=b_{0.i}\cdot \underset{0}{\overset{t}{\int }}p{\left(\tau \right)}^{b_{1.i}}\cdot {\left(\frac{dp\left(\tau \right)}{d\tau }\right)}^{b_{2.i}}\cdot q{\left(\tau \right)}^{b_{3.i}}\cdot \theta {\left(\tau \right)}^{b_{4.i}}\mathit{d\tau }$$

With:
p (τ) : instantaneous pressure at time τ
$\frac{dp\left(\tau \right)}{d\tau }:$

Derivation of p (τ) at time τ ("slope", "change")
q (τ) : volume flow at time τ (from p (τ) ) (to be calculated specifically for the specific model)
θ ( τ ): oil temperature at time τ
b _{0, i} , b _{1, i} , b _{2, i} , b _{3, i} , b _{4, i} : Component-dependent weighting factors and exponents for the individual key figures

ein Verschleißgrad g_i in Prozent ermittelt.For each component K _i , the characteristic number for the wear limit z _{i, 0 is} determined at which maintenance is necessary. Then with each component $${\mathrm{G}}_{\mathrm{i}}=100\%\cdot \frac{z_i}{z_{i.\mathit{0}}}$$

a degree of wear g _i determined in percent.

For the overall aggregate, the maximum degree of wear of all n individual components is decisive, ie $$G=\mathit{Max}\left({\mathit{G}}_{\mathit{i}}\right){|}_{i=\mathit{1}}^n$$

Claims (8)

1. A method for automatically determining the condition of a hydraulic aggregate (25) for powering a power wrench (10) comprising a hydraulic cylinder (12) for performing load strokes by means of a pressurized hydraulic medium,
   characterized in
   that, for a plurality of aggregate components (K_i), a respective wear-indicating characteristic number (z_i) is computed from the pressure (p(τ)) and the duration of operation since start-up, that a respective wear degree (g_i) is determined from said characteristic number and from a wear limit (z_i,0) which has been set for the aggregate component, and that, for the whole aggregate, the maximum $\left(\mathit{max}{\left({\mathit{g}}_{\mathit{i}}\right)|}_{\mathit{i}=\mathit{1}}^{\mathit{n}}\right)$

   

   among the wear degrees (g_i) of all aggregate components is determined and a total wear degree (G) is obtained on the basis of said maximum.
2. The method according to claim 1, characterized in that the characteristic number (z_i) is generated from the time integral of the pressure (p(τ)).
3. The method according to claim 1 or 2, characterized in that the temperature of the hydraulic medium is included into the process of obtaining the characteristic number (z_i).
4. The method according to any one of claims 1 - 3, characterized in that sensors for error messages are provided and that the number of error messages is included into the process of obtaining the characteristic number.
5. The method according to any one of claims 1 - 4, characterized in that, for each load stroke, the product of pressure and duration is computed.
6. The method according to any one of claims 1 - 5, characterized in that the duration of operation of the hydraulic aggregate (25) above and below a limit temperature is measured and evaluated.
7. A hydraulic aggregate for powering a power wrench comprising a hydraulic cylinder (12) for performing load strokes, said hydraulic aggregate comprising a pump (26), a control valve (30), a pressure sensor (32) for measuring the pressure during a load stroke, and a control device (31) including a display means (40),
   characterized in
   that said control device is configured to compute, for a plurality of aggregate components (K_i), a respective wear-indicating characteristic number (z_i) from the pressure (p(τ)) and the duration of operation since start-up, to determine a respective wear degree (g_i) from said characteristic number and from a wear limit (z_i,0) which has been set for the aggregate component, and to determine, for the whole aggregate, the maximum $\left(\mathit{max}{\left({\mathit{g}}_{\mathit{i}}\right)|}_{\mathit{i}=l}^{\mathit{n}}\right)$

   

   among the wear degrees (g_i) of all aggregate components and, therefrom, a total wear degree (G).
8. The hydraulic aggregate according to claim 7, characterized in that said control device (31) is configured in a suitable manner to perform an automatic self-test wherein the pump (26) builds up a pressure whose temporal development can be evaluated for error determination.

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