RU2788794C2 - Method for automated control of tightness of pumping unit of hydraulic machines of volumetric action - Google Patents

Abstract

FIELD: control and measuring equipment.

SUBSTANCE: invention relates to the field of control and measuring equipment, namely to a method for automated control of tightness of a pumping unit of hydraulic machines of a volumetric action. The method consists in that a flow meter device is hydraulically connected in series between a drainage hydraulic line of the controlled hydraulic machine and a hydraulic tank. Assessment of tightness of the pumping unit and automatic determination, based on this assessment, of an actually used and residual resource of the hydraulic machine are performed continuously, directly during the operation of the mechanism, by comparison of an actual flow rate value in the drainage hydraulic line with reference values of minimum and maximum flow rate in drainage. The flow meter device is made volumetric with a tachometer on its shaft.

EFFECT: invention is aimed at provision of replacement of a worn hydraulic machine in a planned mode upon the fact of consumption of a full resource of the hydraulic machine, without emergency stop of equipment.

1 cl, 4 dwg, 1 tbl

Description

The claimed invention relates to the field of instrumentation and can be used to control critical parameters, continuously determine the actual technical condition of the pumping unit of hydraulic rotary machines, as well as to determine the actually used and remaining resource directly during the operation of the mechanism.

The real technical condition of the main element of the energy-providing part of the hydraulic system is in most cases estimated only by pressure according to the readings of pressure gauges on the discharge line of the hydraulic pump, while the power N of the hydraulic installation is determined by formula 1:

where N - hydraulic power, [kW]

P - pressure in the discharge hydraulic line, [bar]

Qν - volume flow, [l/min]

Volumetric flow Q _ν determines the speed of movement of the executive link, and in the event of a parametric failure in the form of insufficient speed, diagnostics of the elements of the hydraulic system are performed. During diagnostics, a list of elements is compiled that directly or indirectly affect the occurrence of this failure, which includes possible failures of the hydraulic pump, distribution and control equipment, as well as possible malfunctions of the elements of the executive part. Because the hydraulic pump is the most expensive and complex part of the hydraulic system, and also because other elements cannot be checked without a hydraulic pump, the hydraulic pump is checked last. Due to the absence of volumetric flow control devices on the discharge line, the assessment is made on the basis of signs - vibration, temperature, noise. These diagnostic signs are indirect and not reliable. In case of doubt, a test replacement of the pump is carried out and the result of this replacement is evaluated. As a result of the implementation of this algorithm, the diagnosis of the cause of the failure takes a long time and often with significant material costs (for the purchase of a new pump for a trial test), in some cases, unjustified. In conditions of continuous production, time losses bring significant material losses.

Information about the actual technical condition of the hydraulic machine is determined by calculating according to formula 1, but for this it is necessary to have information about the actual supply Qv _fact. hydraulic pump, which is absent in the vast majority of hydraulic systems.

The main indicator of serviceability and a factor that directly affects the volumetric efficiency of a hydraulic piston rotary machine, and, consequently, the used and remaining resource, is the tightness of the movable joints of the elements of the pumping unit.

Currently, the following methods for diagnosing the tightness of the pumping unit of volumetric hydraulic machines are known:

1. Method No. 1 Comparison of the theoretical and actual flow of a hydraulic pump (G.N. Vasiliev “Repair of pumps and hydraulic equipment”, Ed.: “Mashinostroenie”, 107885, Moscow, B-78, 1 Basmanny per., 3, p. 31, chapter 3. Testing of pumps and hydraulic equipment after repair) is based on determining the technical condition of the hydraulic machine by measuring the actual supply Оν _fact . at the maximum pressure on the pressure hydraulic line of the pump, for which the flow meter is connected hydraulically in series between the discharge channel of the hydraulic machine and the outlet to the hydraulic tank after the load device, and to determine the actual value of the feed coefficient K _{of the feed} (volumetric efficiency) by comparing the actual feed Qv _actual with the theoretical feed Qv _theor. [formula 2), measured on a test bench without load, specified in the technical documentation for this hydraulic machine or calculated using formula 3:

where To _feed - pump feed rate;

Oh _fact. - actual supply, [l/min];

Qv _theop. - theoretical flow, [l/min].

where Qν _theop. - theoretical volume flow, [l/min];

Vg - working volume per 1 revolution, (cm ³ ];

n - shaft speed, (min ^-1 ];

η _ν - volumetric efficiency

The feed coefficient (volume efficiency) of a hydraulic machine (formula 2) describes the tightness of the pumping unit of the hydraulic machine, which consists of cylinder-piston pairs, piston thrust bearings and a distribution unit; for a serviceable hydraulic machine, K _{of the feed} is 0.92-0.98 (depending on the model, displacement, operating pressure, viscosity of the working fluid and the presence of a hydraulic control circuit, the value of K _{of the feed} may vary), while the remaining 2 to 8% Qv _theor. working fluid in the form of a drainage flow Qv _etc. are sent through the drainage hydraulic line to the hydraulic tank.

The criterion for the limiting state of hydraulic pumps according to GOST 13823-78 “Volume hydraulic drives. Displacement pumps and hydraulic motors general technical requirements” is a reduction in the feed rate by no more than 20%, upon reaching which the hydraulic pump must be replaced, because at this boundary, there is a transition of wear from the normal stage to the emergency stage with an avalanche-like development.

The advantage of method No. 1 is the high accuracy of the data obtained. The disadvantages of method number 1 are the following facts:

- assessment of the state by this method can only be carried out on a hydraulic test bench, which requires stopping the mechanism, dismantling the hydraulic machine, transportation to the test bench and testing. This time-consuming work requires good reasons, but in the case of searching for the cause of insufficient working fluid flow parameters, it is based only on suspicions; if the suspicions are not confirmed and there are no grounds for rejecting the pump based on the results of testing on the test bench, the operation is performed in the reverse order, which indicates its inappropriateness due to a significant loss of time;

- thus it is possible to make only diagnostics, but not monitoring;

- not every enterprise has test benches and specialists.

2. Method No. 2 Determining the state of the hydraulic machine by completely disassembling it, measuring the gaps and assessing the condition of the surfaces of the elements of the hermetic movable joints of the pumping unit of the hydraulic machine (X. Exner, R. Freitag, Dr. H. Geis, R. Lang, J. Oppolzer, P. Schwab, E. Sumpf, U. Ostendorff, M. Reik, Bosch Rexroth AG Service Automation Didactics 64711 Erbach Germany "Hydraulic drive. Fundamentals and components. Training course in hydraulics, volume 1, p. 250) .

The advantage of method No. 2 is the possibility of its implementation without a hydraulic test bench.

The disadvantages of method number 2 are the following facts:

- to implement this method, dismantling and complete disassembly of the hydraulic machine is required. The application of this method is complicated by the lack of freely available information about the size of the gaps in the pumping unit in a normal, unworn condition for a particular hydraulic machine, because this information is the intellectual property of the manufacturer;

- the lack of enterprises, as a rule, qualified personnel to carry out such work.

Thus, using existing methods, it is impossible to determine the real current state of a working hydraulic machine at the installation site using methods No. 1 and No. 2. For these reasons, if there is a suspicion of a malfunction or wear of the hydraulic machine, in most cases the hydraulic machine is replaced with a new one if the resource is not fully used, or vice versa, it works beyond the normal resource, which causes an emergency sudden failure of the hydraulic machine with the ingress of destruction products of the pumping unit into the hydraulic system.

The closest analogue in terms of design is the method of automated control of the tightness of the pumping unit of hydraulic machines of positive displacement according to US 5563351 A with the difference that it only describes the determination of exceeding the maximum flow rate in the drainage hydraulic line as a criterion for replacing the hydraulic pump, while the used and remaining resource of the hydraulic machines at the current moment cannot be determined, which does not allow the use of planning methods. As a measuring device, a Venturi nozzle is proposed, the pressure drop across which indicates the flow rate, i.e. a dynamic principle is applied, which is characterized by low accuracy at low flow rates and high hydraulic resistance at high flow rates, which reduces the reliability of the information obtained, and can also harm the tested hydraulic pump in the form of significant resistance in the drainage hydraulic line.

The technical result of the claimed method is the possibility of replacing a worn-out hydraulic machine in a planned mode, after using the full resource of the hydraulic machine, preventing an emergency stop of the equipment.

The specified technical result is achieved in a method for automated control of the tightness of the pumping unit of hydraulic machines of positive displacement, which consists in the fact that the flow meter is connected hydraulically in series between the drainage hydraulic line of the controlled hydraulic machine and the hydraulic tank, while the assessment of the tightness of the pumping unit and automatic determination based on this assessment actually The used and remaining resource of the hydraulic machine is produced continuously, directly during the operation of the mechanism, by comparing the actual flow rate in the drainage hydraulic line with the reference values of the minimum and maximum flow rates to the drainage, while the flow meter is made volumetric with a tachometer on its shaft.

The claimed method for automated control of the tightness of the pumping unit of positive displacement hydraulic machines is illustrated by drawings, which show:

in fig. 1 - the principal location of the flow meter relative to the hydraulic machine;

in fig. 2 - scheme for calculating the value through the annular gap of the gap of the piston pair of the pumping unit of the hydraulic machine;

in fig. 3 - schematic diagram of connection of the flow measuring device to the computer;

in fig. 4 is a diagram of the flow rate in the drainage hydraulic line of the tested hydraulic machine.

The proposed method for automated control of the tightness of the pumping unit of hydraulic machines of positive displacement consists in constant continuous volumetric measurement of the flow rate in the drainage hydraulic line of the hydraulic machine (Fig. 1) directly during the operation of the mechanism using a flow meter 1 installed in the drainage hydraulic line of the controlled hydraulic pump 2 connected to the hydraulic tank 3 is based on the fact of the direct inverse dependence of the value of the effective flow of the hydraulic pump on the amount of leakage into the drainage, as well as on the fact of a significant increase in the flow rate in the drainage hydraulic line due to a decrease in the tightness of the pumping unit, and is described by formula (4):

where Qν _theop. - theoretical supply, l/min.;

Qv _fact. - actual supply, l/min;

Qν _others - flow rate in the drainage hydraulic line, l/min.;

The essence of the invention lies in the fact that as the surfaces of the elements of the hydraulic conjugated pairs of the pumping unit of the hydraulic machine wear out, a significant increase in the gaps in these joints of the pumping unit occurs, which results in an increase in the flow rate through the drainage hydraulic line Qv _etc. . with a simultaneous decrease in the supply Qv _{/ fact} .(see formula 5).

The amount of leakage in laminar motion for a smooth annular gap of constant cross section (Fig. 2) on the example of the gap between the plunger 4 and the sleeve of the piston block 5, based on the distribution disk 6:

where q - leakage, m3/s;

D - plunger diameter, / and;

δ - clearance per side, m (with a concentric plunger arrangement);

g - free fall acceleration;

ν - kinematic viscosity, m ² / s;

l - plunger length, m (contact);

H - pressure drop, m.

Analysis of formula 5 shows that the amount of leakage into the drainage hydraulic line q is proportional to the quadratic dependence on the value of the annular gap 6 of the piston pairs of the pumping unit, which increases the accuracy of the proposed method compared to method No. 1. Since these values are interconnected by the fact that the gaps in the movable tight joints of the pumping unit in the discharge phase connect the discharge line with the internal volume of the crankcase of the hydraulic machine, which, in turn, is connected by a drainage hydraulic line to the hydraulic tank, the flow rate in the drainage hydraulic line can be used as a diagnostic a sign that directly indicates the tightness of the pumping unit. The state is assessed in the maximum loaded state of the hydraulic machine, i.e. at maximum working pressure.

To determine the flow rate, it is proposed to use a flow measuring device made in the form of a volume flow device 7 (Fig. 3) with a tachometer on its shaft.

The readings of the flow meter can be converted into an estimate by the following devices:

1. Visual indicator of the state - the scale of the visual indicator is graduated to display the states "Normal", "Limit", "Faulty", as well as in other terms, symbols or colors that correspond to these concepts in terms of meaning, indicating the normal, limiting and faulty state of the pumping hydraulic machine unit.

2. Electronic status indicator - the readings of the measuring device in the form of an electronic signal from the tachometer 8 on the shaft of the volume flow meter 7 are transmitted through the analog-to-digital converter ADC 9 and processed in the electronic device - built-in microcontroller or external controller 10, recalculated according to formula 6 and transmitted to the computer operator 11, on the working screen of which a special field displays information about the actual current state of the hydraulic machine as a percentage of the remaining resource and / or the states "Normal", "Limit", "Faulty" (Fig. 3).

The determination of the residual resource R (as a percentage of the initial state, %) of the hydraulic machine is carried out according to formula 6:

where Qv _etc . _fact. - the actual measured flow in the drainage hydraulic line of the hydraulic machine;

Qν other _min. . - the minimum (nominal) flow in the drainage hydraulic line, corresponding to 0% wear, is indicated in the technical documentation for the hydraulic machine, or, in the absence of this information in the technical documentation for a specific controlled hydraulic machine, it is calculated from 2 to 8% Qv _meop .

Qν other _max. - the maximum flow rate in the drainage hydraulic line, corresponding to 100% wear, is determined by formula 7:

To display the discrete states of the residual resource R, the ratio of the analog value calculated by formula 6, expressed in%, and the discrete states are placed in the ranges:

- Norm - from 0 to 90%;

- Limit - from 90 to 100%;

- Faulty - more than 100%,

or other close values of the ranges determined from specific conditions.

The advantages of the above method for automated control of the tightness of the pumping unit of positive displacement hydraulic machines are:

1. A flow meter located on the drain line rather than the discharge line operates at lower flow rates (0 to 28% Qv _theor . vs. 100% Qv _theor. ) and pressures (0-2 bar vs. 100% maximum operating pressure) , for this reason, the flow meter has small dimensions, a significantly lower cost, because can be made of polymer and composite materials, and higher reliability;

2. high resource of the flow meter due to relatively low flow, pressure and complete absence of load guarantees high accuracy over the entire resource of the controlled hydraulic machine;

3. ease of implementation and low cost of equipment make it possible to apply the described method for organizing monitoring of hydraulic machines both at the design stage of the hydraulic system and for retrofitting the installed and operating equipment with a monitoring system;

4. the possibility of installing a hydraulic machine on stationary and mobile hydraulic systems, even taking into account the compact design, due to small dimensions;

5. integration of the flow measuring device into the pump housing during its production;

6. the possibility of assessing the condition of the pumping unit of both hydraulic pumps and hydraulic motors, as well as flow dividers based on positive displacement hydraulic machines;

7. high diagnostic accuracy, due to the low flow rate (relative to the pump flow) and the multiple increase in flow rate in the drainage hydraulic line when the pumping unit is worn;

8. the possibility of continuous continuous monitoring of the current state of the pumping unit of the hydraulic machine directly during the operation of the mechanism.

Subject to the requirements of the hydraulic pump manufacturer on the allowable pressure in the drainage hydraulic line in the form of a hydraulic resistance of the flow meter, this device does not affect the operation of the hydraulic pump and the hydraulic system as a whole. The proposed method does not have the disadvantages of diagnostic methods No. 1 and 2.

The described method for automated continuous determination of the residual life of hydraulic reciprocating rotary machines by monitoring the tightness of the pumping unit has passed a practical test on a hydraulic pump A10VSO 71 DR/31R-PPA12N00 Rexroth. This pump is an axial piston adjustable hydraulic machine. According to passport data (RRS 92711/06.09) at n=1500 rpm. and P=0 bar theoretical delivery Qν theor _. \u003d 107 l / min., at maximum pressure P _max. =350 bar theoretical supply Qν _meop .=98 l/min., which means that at the maximum working pressure through the gaps of the pumping unit, the leakage of the working fluid will be 107-98=9 l/min, which is 8.4% Qν _theor ., and is taken as the initial one for assessing the state of the pumping node at 100% of the remaining resource. The measured actual flow rate in the drainage hydraulic line was Qν _dr.min. = 9.2 l / min., which corresponds to the normal state of the pumping unit. Limit value Qν _{other max.} =9.2+0.2×107=30.6 l/min determined by formula 7. The flow rate to the drainage through the control circuit of the hydraulic machine is a constant value, it is not associated with the wear of the pumping unit, it is about 3 l/min for this model . - was not taken into account in the calculations, because does not affect the calculation of the resource. The hydraulic pump is installed on a hydraulic press as part of a pump-accumulator hydraulic drive, the operation mode of the mechanism is continuous around the clock, with periodic pressure fluctuations at the pump outlet from 30 to 320 bar for 2-3 minutes every 3-4 minutes, SHELL TELLUS S2 V68 working fluid, maximum operating temperature 50°C.

Measurement of the actual flow in the drain line over 12 months of operation (table 1) showed an exponential increase in the number of leaks.

Upon reaching the flow rate in the drainage hydroline Qvdr=30 l/min, corresponding to the limit value Qvdr.max. (point A in Fig. 4) at the end of the 12th month of operation, the recommended replacement of the hydraulic pump was made.

Diagnostics of the dismantled hydraulic machine according to method No. 1 - testing on a hydraulic test bench - confirmed the decrease in the effective supply of the pump Оv _fact. up to 78 l/min. at the maximum working pressure, which indicates the presence of critical wear of the elements of the pumping unit.

Diagnostics according to method No. 2 - analysis of the hydraulic machine - confirmed the presence of an increase in the gaps in the piston pairs of the pumping unit due to mechanical friction and abrasive wear up to 0.089-0.095 mm, as well as the presence of damage to the supporting surface of the distribution disk due to mechanical friction, abrasive and cavitation damage up to 0 .35-0.42 mm, which actually indicates the limiting state of the pumping unit of the tested pump.

Thus, the described method is fully confirmed by practical application, tk. the replacement of the worn-out hydraulic machine was carried out as planned, after using the full resource of the hydraulic machine, without allowing an emergency stop of the equipment. Information about the technical condition of the hydraulic machine is reliable, available for evaluation at any time and can be used in the interests of planning equipment repairs.

Claims (1)

A method for automated control of the tightness of the pumping unit of positive displacement hydraulic machines, which consists in the fact that the flow meter is connected hydraulically in series between the drainage hydraulic line of the controlled hydraulic machine and the hydraulic tank, characterized in that the assessment of the tightness of the pumping unit and automatic determination based on this assessment of the actually used and remaining resource The hydraulic machine is produced continuously, directly during the operation of the mechanism, by comparing the actual flow rate in the drainage hydraulic line with the reference values of the minimum and maximum flow rates to the drainage, while the flow meter is made volumetric with a tachometer on its shaft.

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