GB2125555A

GB2125555A - Sensing hydraulic systems

Info

Publication number: GB2125555A
Application number: GB08223668A
Authority: GB
Inventors: John Dunbar Kibble
Original assignee: Coal Industry Patents Ltd
Current assignee: Coal Industry Patents Ltd
Priority date: 1982-08-17
Filing date: 1982-08-17
Publication date: 1984-03-07

Abstract

A desired parameter is sensed for a hydraulic circuit having discontinuous load demands. A derived signal indicative of the sensed parameter is fed to processing means 7 adapted to process those portions of the derived signal associated with operational periods when the load demand is applied to the system. Fluid is drawn by a pump 2 from a reservoir and fed to a system including loads 5 and a measurement circuit 6-22 or returned to the reservoir via an unloader valve 3. The fluid pressure is sensed by transducer 6 but a processing means 7 including a comparator 20 disregards the sensed output only if the motor 10 is energised and the sensed pressure is below a predetermined level i.e. due to a discontinuous load. When the pressure falls abnormally low a shut-off device 21 and an alarm 22 are activated. <IMAGE>

Description

SPECIFICATION Sensing hydraulic systems This invention relates to methods of and apparatus for sensing hydraulic systems in orderto determine operational conditions of the systems.

In particular, although not exclusively, the present invention relates to sensing operational conditions of hydraulic systems associated with hydraulic roof supports in underground mines. Frequently, such systems comprise effectively continuously pressurised supplies and discontinuous operational periods when load demands are applied to the systems.

would be simple to sense continuouslythe overall average pressure in a mine roof support hydraulic system with the intention of detecting unsatisfactory conditions. However, such average sensed values tend to be markedly dependent upon the unpredictable proportion oftotaltimetaken up bytheoperational periodswhen load demands are applied to the system. Consequently, such sensing tends to produce unreliable results.

An object of the present invention isto provide methods of and apparatus for sensing hydraulic systems which tendto give useful and reliable indications of selected operational parameters ofthe systems.

According to one aspect ofthe present invention, a method of sensing an operational condition of a hydraulic system having an effective continuous supply of pressurised fluid and atleastonediscontinuous load demand comprises the steps of sensing a desired parameter ofthe system, deriving a signal indicative of the sensed parameter, feeding the derived signal to processing means, and processing portions ofthe derived signal associated with operational periods when the load demand is applied to the system.

Preferably, the desired parameter sensed is the operational pressure ofthe hydraulic system.

Preferably, the processed portions ofthe derived signal are compared with a reference signal indicative of a preselected reference pressure.

Advantageously, the system is shut-offand/or an alarm is activated ifthe processed portions ofthe derived signal indicate an operational pressure below a preselected value.

According to another aspect of the present invention, apparatus for sensing an operational condition of a hydraulic system having an effectively continuous supply of pressurised fluid and at least one discontinuous load demand comprises a sensorforsensing a desired parameter ofthe system and for deriving a signal indicative of the sensed parameter, and processing means adapted to receive the derived signal and to process those portions ofthe derived signals associated with operational periods when the load demand is applied to the system.

Preferably, the sensor is adapted to sense the pressure of the hydraulic system.

Preferably, the processing means comprises comparator means for comparing the processed portions of the derived signal with a reference signal indicative of a preselected reference pressure.

Advantageously, the apparatus comprises means adapted to shut-offthe pressurised supply to the system and/or activate alarm means if the processed portions ofthe derived signal indicate an operational pressure below a preselected value.

Bywayofexample only, one embodimentofthe present invention now will be described with referenceto the accompanying drawings, in which Figure 1 is a hydraulic diagram of a hydraulicsystem including the present invention; and Figure 2(a) and 2(b) indicate variation in a sensed pressure of the system fortwo operational conditions, respectively.

Atypical hydraulic system is shown in Figure 1. It consists of a reservoir (1 ) from which fluid is drawn by a pump (2) driven by an electric motor (10). This pump may be of the type which regulates its output in relation to the demand or, if it is of the fixed output type, when fluid is not required by the system it is returnedtotank by meansofan unloadervalve(3).

Fluid passes to the main system through filter (4) and feeds one or more loads (5) which may befluid-poweroperated machines of any known type. Pressure in the system is measured by a transducer (6) arranged to derive an electric signal indicative ofthe sensed fluid pressure, the derived signal being fed to processing means (7) including comparator means (20). The apparatus also provides means (21) adapted to shut-offthe pressurised supply to the hydraulic system and/or activate alarm means (22).

Normally the loads (5) will be operated in such a way as to create a demand for hydraulic power at some times but not at others. Typically the pressure in the system will vary with time in the manner shown in Figure 2(a). The point (11) indicatesthetime at which electric power is first supplied to the motor (10). The periods during which power is supplied are indicated bythe solid line entitled 'Electric Power' in the Figure.

When such power is not supplied, obviously no pressure is generated in the system. When the pump is operating but during periods when there is no demand forfluid power the pressure will vary between the upper and lower limits 8 and 9 of the pressure regulating means. If this is the unloader valve (3),this valve for example may be closed so asto direct the output ofthe pump solely into the system, until the pressure rises to the level (8) at which the valve will 'cut-off' isolating the system from the pump and diverting the output of the latter backto the reservoir. The pressure will then fall slowly due to leakage in the system until it reaches the lower level (9) at which the unloader valve will cause the pumpto 'cut-in' again. Thus the pressure/time trace is a saw tooth form as shown.

During periods when fluid power working is taking place the pressure will fall to a lower level as shown in two typical periods A and B in Figure 2(a). During these periods the pressure together with the derived signal will fluctuate as determined by the various character The drawing(s) originally filed were informal and the print here reproduced is taken from a later filed formal copy.

istics ofthe system. Usually the pressure will fall belowthe cut-in level (9) to a variable lower level as shown. In a system which is satisfactoryfor its purpose th is lower level will only be slightly lower thanthecut-in preselected level, for example, 80% of that level. This is determined by the comparator means 20 comparing the derived signal with a signal associated with the cut-in reference pressure level. If, however, the operational condition ofthe system is unsatisfactory, this will be indicated by the derived signal indicative ofthe pressure during periods of working falling to a substantially lower level as shown by period Cin Figure 2(b), for example, to 50% of the cut-in level or less. Again the comparator means 20 makes the comparison between the derived signal and the reference signal.

As mentioned previously, the apparatus comprises means (21 ) adapted to shut-offthe system and/or activate alarm means (22) if the processed portions of the derived signal indicate an operational pressure below the preselected value.

Such unsatisfactory performance may be caused by a number of possible faults: the electric motor may be faulty,the pump may have started to fail, its pressure control means may have become faulty, the filter may have become blocked, the conduit connecting the pump assembly unload may have become blocked, leakage may have developed, orthe loads may have altered in such a way asto become excessiveforthe size ofthe pump installed. The monitoring system proposed will detect any of thesefaultsthough itwill not of itself distinguish which one applies.

The difference between satisfactory operational conditions, Figure 2(a), and unsatisfactory ones Figures 2(b), may readily be distinguished by visual examination of a pressure recording. This however requires laborious human intervention.

One embodiment ofthe present invention provides processing means (7) including comparator means 20 whereby the output ofthe transducer (6) is disregarded ifthe electric motor is not energised or ifthe transducer indicates a pressure exceeding a predetermined limit. This limit is chosen to be as close as convenient belowthe lower control limit (9). When these conditions (motor energised, pressue indicated below set level) are fulfilled, however, the processing means is arranged to monitorthe derived signal related to the pressure level. This might be done in the form of a running average with respectto time over intervals of several seconds. The value of this average operational pressure is then an indication ofthe satisfactory or otherwise condition of the whole system.Conveniently, it may be expressed as an index which is the ratio ofthe average pressureto the lower control limit (9).

The processing means may be arranged to display any desired number of readings ofthis kind on request and it may also be arranged to give a warning if the index falls below a preselected limit.

The pressure transducer (6) may be connected to any point in the hydraulic system. Most appropriately, however, it is connected as shown in Figure 1 to the exteme end ofthe system remote from the pump. This enables itto indicate defects due to flow resistance in the line between the pump and the load and to give the most realistic estimate ofthefluid poweractually available atthe load, for it will be noted thatthere is no flow between the load (5) and the transducer (6) and so there is no pressure difference either; therefore the measurement is an accurate one.

The sensing means also is capable of carrying out another control function. If, at any time otherthan during starting of the pump, the electric motor is energised but little orno pressure is registered this must be due to a seriousfault condition. A hose may have burst, for example, orthe pump may be prevented from rotation Such a failure is indicated at 12 in Figure 2(b). The computer means may be programmed to respond immediately, or after a very short interval without waiting for averaging the operational pressure, in such a case, giving an alarm signal and de-energising tha electric motor.

It is to be understoodthatinsteadofa single transducer (6) two or more units may be provided as alternatives in case offailure of one. Ifthis is done it may be desired to install the transducers at different points in the system rather than side by side. The indicative signals derived by the transducers may then be monitored and scrutinised and certain types of failure such as hose orfilter blockage would be identified by an associated consistent difference between the readings.

Claims

1. A method of sensing an operational condition of a hydraulic system having an effectively continuous supply of pressurised fluid andatleastonediscon- tinuous load demand, comprising the steps of sensing a desired parameter ofthe system, deriving a signal indicative of the sensed parameter, feeding the derived signal to processing means, and processing portions ofthe derived signal associated with operational periods when the load demand is applied to the system.

2. A method as claimed in claim 1, wherein the desired parameter sensed is the operational pressure ofthe hydraulic system.

3. A method as claimed in claim 2, in which the processed portions ofthe derived signal are compared with a reference signal indicative of a preselected reference pressure.

4. A method as claimed in claim 3, in which the system is shut-off and/or an alarm is activated if the processed portions ofthe derived signal indicate an operational pressure below a preselected value.

5. Apparatus for sensing an operational condition of a hydraulic system having an effectively continuous supply of pressurised fluid and at least one discontinuous load demand, comprising a sensorforsensing a desired parameter of the system and for deriving a signal indicative ofthe sensed parameter, and processing means adapted to receive the derived signal and to process those portions ofthe derived signals associated with operational periods when the load demand isappliedto the system.

6. Apparatus as claimed in claim 5, in which the sensor is adapted to sense the pressure of the hydraulic system.

7. Apparatus as claimed in claim 6, in which the processing means comprises comparator means for comparing the processed portions ofthe derived signal with a reference signal indicative of a preselected reference pressure.

8. Apparatus as claimed in claim 7, comprising means adapted to shut-offthe pressurised supply to the system and/or activate alarm means if the processed portions ofthe derived signal indicate an operational pressure below a preselected value.

9. A method of sensing an operational condition of a hydraulicsystem,substantially as described herein with reference to the accompanying drawings.

10. Apparatus for sensing an operational condition of a hydrauiic system, substantially as described herein and substantially as shown in the accompanying drawings.