CA1217258A - Electro-hydraulic actuating apparatus for a continuously adjustable valve - Google Patents
Electro-hydraulic actuating apparatus for a continuously adjustable valveInfo
- Publication number
- CA1217258A CA1217258A CA000460895A CA460895A CA1217258A CA 1217258 A CA1217258 A CA 1217258A CA 000460895 A CA000460895 A CA 000460895A CA 460895 A CA460895 A CA 460895A CA 1217258 A CA1217258 A CA 1217258A
- Authority
- CA
- Canada
- Prior art keywords
- voltage
- comparator
- amplitude
- error signal
- valve
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
- F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
- F15B21/00—Common features of fluid actuator systems; Fluid-pressure actuator systems or details thereof, not covered by any other group of this subclass
- F15B21/08—Servomotor systems incorporating electrically operated control means
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Physics & Mathematics (AREA)
- Fluid Mechanics (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Magnetically Actuated Valves (AREA)
- Fluid-Pressure Circuits (AREA)
- Feedback Control In General (AREA)
- Servomotors (AREA)
Abstract
Abstract An electro-hydraulic actuating apparatus for a continuously adjustable servo-valve comprises a regulator which delivers an error signal (F3) depending on the regulating departure. Upon exceeding their limiting value, two comparators each associated with one direction of adjustment are caused by the error signal to deliver an output signal for operating a control valve arrangement having magnetic valves. The error signal (F3) is formed by an A.C. voltage with at least one inclined flank, of which the mean value (M) depends on the regulating departure and the half-period is larger than the reaction time of the magnetic valves.
Description
~ 7;~S~
The inven-tion rela-tes to an electro-hydraulic actuating apparatus ~or a continuo~sly adjustable servo-valve o~ whlch the actuating pressure chambers can, with the aid of a respective two-position control valve arrangement having magnetic valves, for each direction of adjustment be either blocked or connected to the pressure side or the low pressure side, comprising a regulator which delivers an error signal depending on the regulating departure of the existing value from the desired value of the valve setting, and comprising two comparators which are each associated with one adjusting direction and, on exceeding their limiting value, are caused ` by the error signal to deliver an output signal for operating .~
the associated control valve arrangement.
In a known actuating appartatus of this kind (DE-OS 26 4~ 768), the two actuating pressure chambers are ._j ~ connected to two diagonal points of a valve bridge of which ,1 the other diagonal points are connected to the pressure supply ~ and container, respectively. The branches of the bridge each ;~ contain a switching valve actuatable by hydrostatic pressure.
c~ 20 The error signal is equal to the regulating departure. When ,~ .
one of the comparators, each provided for one actuating direction ? responds a magnetic valve is de-energised and thereby closed. This results in a drop in the hydrostatic pressure in the case of two opposed bridge valves. The ~: latter open, sothat the valve can be displaced in one actuating direction. By reason of the valve adjustment, the supply of ;~ pressure fluid to a hydraulic motor changes. The motor speed therefore depends on the valve setting.
In operation, it has been found that the movement of the continuously adjustable valve does not take place ~d~
~2~7~
continuously but in steps when a regulating departure is to be compensated. This is disadvantageous, particularl~ when contolling a hydraulic motor because in that case its speed will likewise change in bursts. Even if only small dis-~ placements of the valve caused by unavoidable leakage losses have to be corrected, these will take place in bursts, so that the motor speed cannot be held constant.
The invention is based on the problem of providing an actuating apparatus ofthe aforementioned kind that permits movement o~ the continuously adjustable valve substantially free of jumps.
This problem is solved according to the invention in that the error signal is formed by an A.C. voltage with at least one inclined flank, of which the mean value depends on the regulating departure a~d the half-perlod is larger than the reaction time of the magnetic valves.
~ - The invention is based on the discovery that movement t of the continuously adjustable valve in jumps is accounted for hy the fact that the control valve arrangement has a
The inven-tion rela-tes to an electro-hydraulic actuating apparatus ~or a continuo~sly adjustable servo-valve o~ whlch the actuating pressure chambers can, with the aid of a respective two-position control valve arrangement having magnetic valves, for each direction of adjustment be either blocked or connected to the pressure side or the low pressure side, comprising a regulator which delivers an error signal depending on the regulating departure of the existing value from the desired value of the valve setting, and comprising two comparators which are each associated with one adjusting direction and, on exceeding their limiting value, are caused ` by the error signal to deliver an output signal for operating .~
the associated control valve arrangement.
In a known actuating appartatus of this kind (DE-OS 26 4~ 768), the two actuating pressure chambers are ._j ~ connected to two diagonal points of a valve bridge of which ,1 the other diagonal points are connected to the pressure supply ~ and container, respectively. The branches of the bridge each ;~ contain a switching valve actuatable by hydrostatic pressure.
c~ 20 The error signal is equal to the regulating departure. When ,~ .
one of the comparators, each provided for one actuating direction ? responds a magnetic valve is de-energised and thereby closed. This results in a drop in the hydrostatic pressure in the case of two opposed bridge valves. The ~: latter open, sothat the valve can be displaced in one actuating direction. By reason of the valve adjustment, the supply of ;~ pressure fluid to a hydraulic motor changes. The motor speed therefore depends on the valve setting.
In operation, it has been found that the movement of the continuously adjustable valve does not take place ~d~
~2~7~
continuously but in steps when a regulating departure is to be compensated. This is disadvantageous, particularl~ when contolling a hydraulic motor because in that case its speed will likewise change in bursts. Even if only small dis-~ placements of the valve caused by unavoidable leakage losses have to be corrected, these will take place in bursts, so that the motor speed cannot be held constant.
The invention is based on the problem of providing an actuating apparatus ofthe aforementioned kind that permits movement o~ the continuously adjustable valve substantially free of jumps.
This problem is solved according to the invention in that the error signal is formed by an A.C. voltage with at least one inclined flank, of which the mean value depends on the regulating departure a~d the half-perlod is larger than the reaction time of the magnetic valves.
~ - The invention is based on the discovery that movement t of the continuously adjustable valve in jumps is accounted for hy the fact that the control valve arrangement has a
2~ reaction period ~in the known case about 6 ms for magnetic valve and 2 ms for the bridge valves, i.e. a total 8 ms) and thus the slide of the servo-valve is only stopped with a delay.
By employing the A.C. voltage error signal, the comparators respond much earlier than when the regulating departure exceeds the permissible band width, namely when the amplitude of the A.C. voltage exceeds the comparator limited value.
This has an effect on the servo-valve if the time of exceeding is at least equal to the reaction time of the associated mag-netic valve. Normally, the actuating period is short; it X
5~
terminates during -the same half~period of ~he A.C. voltage.
~ltogether, one obtains operation of the magnetic valves ~ through widely modulated pulses. ~hese lead to a pulsa-ting ,5.~ pressure application of the actuating pressure chambers of -- the servo-valve. However, since the slide of the servo-valve has a comparatively large mass, positioning nevertheless takes place as a uniform movement.
A frequency for the A.C. voltage of 30 to 50 Hz has proved suitable. In particular, it should be about 40 Hz, corresponding to a period of about 25 ms.
Preferably, twice the amplitude of the A.C. voltage ; is no more than somewhat smaller than the difference between the comparator limiting values. This means that small regulat-"~ ing departures will already result in operation of the control ~i.i valve arrangement. The position of the servo-valve can therefore be maintained with a high degree of accuracy whereby one can ' ` `!
~! hold constant for example the rotary speed of a motor controlled `, by the servo-valve~
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Y,``! Another problem with known servo-valves is the presence ~ 20 of hysteresis during positioning. One and the same desired , value results in different positions, depending on from which side the position is reached.
This problem can be entirely or partially solved in that the A.C. voltage has such an amplitude an shape that, with departures of the mean value from -the neutral position by no more than ~12.5~ of the difference between the comparator limiting values, one exceeds at least one limiting value for a longer time than the reaction time of the magnetic valves. Whereas it was hitherto necessary to change the error signal by +50
By employing the A.C. voltage error signal, the comparators respond much earlier than when the regulating departure exceeds the permissible band width, namely when the amplitude of the A.C. voltage exceeds the comparator limited value.
This has an effect on the servo-valve if the time of exceeding is at least equal to the reaction time of the associated mag-netic valve. Normally, the actuating period is short; it X
5~
terminates during -the same half~period of ~he A.C. voltage.
~ltogether, one obtains operation of the magnetic valves ~ through widely modulated pulses. ~hese lead to a pulsa-ting ,5.~ pressure application of the actuating pressure chambers of -- the servo-valve. However, since the slide of the servo-valve has a comparatively large mass, positioning nevertheless takes place as a uniform movement.
A frequency for the A.C. voltage of 30 to 50 Hz has proved suitable. In particular, it should be about 40 Hz, corresponding to a period of about 25 ms.
Preferably, twice the amplitude of the A.C. voltage ; is no more than somewhat smaller than the difference between the comparator limiting values. This means that small regulat-"~ ing departures will already result in operation of the control ~i.i valve arrangement. The position of the servo-valve can therefore be maintained with a high degree of accuracy whereby one can ' ` `!
~! hold constant for example the rotary speed of a motor controlled `, by the servo-valve~
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Y,``! Another problem with known servo-valves is the presence ~ 20 of hysteresis during positioning. One and the same desired , value results in different positions, depending on from which side the position is reached.
This problem can be entirely or partially solved in that the A.C. voltage has such an amplitude an shape that, with departures of the mean value from -the neutral position by no more than ~12.5~ of the difference between the comparator limiting values, one exceeds at least one limiting value for a longer time than the reaction time of the magnetic valves. Whereas it was hitherto necessary to change the error signal by +50
- 3 -of the dif~erence between the comparator limiting values to switch a magnetic valve over, much smaller displacements of the A.C. voltage will now suffice to actuate a magnetic valve, albeit momentarily. Accordingly, since ~he servo-valve can be made to follow the desired value very accurately, it is im~atexial from which side the respective position is reached.
In a preferred embodiment, the A.C. voltage is a triangular voltage of which twice the amplitude is considerably larger than the difference between the comparator limiting values. One can for example attain the condition where at least one of the two magnetic valves is actuated during basic-ally each period. In such a case, the magnetic valves would be alternately actuated in the rest position, so that the servo-valve prac~ically stands still in a predetermined position.
The A.C. voltage may instead be a trapezium voltage of which twice the amplitude substantially corresponds to the .i difference between the comparator limiting values. This ensures ; that the operating signals fed to the magnetic valves are delivered only if they ha~e a particular minimum duration, he magnetic valves are therefore operated less frequently and therefore worn out more slowly.
In particular, the period of constant amplitude should correspond to about the reaction time of the magnetic valves and twice the amplitude should be somewhat smaller than the difference between the comparator limiting values, In this case, an operating pulse is delivered only if it is adequately 2~
long to actuate the magnetic valve. The ~ctuating frequency is correspondingly low.
Preferred examples of the invention will now be described in more detail with reference to the drawing, wherein:-Fig. 1 is a diagrammatic circuit diagram of a servo--valve having an actuating apparatus according to the invention;
Fig. 2 shows a first curve shape for the error signal;
Fig. 3 shows the Fig. 2 error signal. upon positive regulating departure;
Fig. 4 shows the Fig. 2 error signal upon negative regulating departure;
Fig~ 5 shows a modified form of the error signal;
Fig. 6 shows a further modification of the shape of the error signal;
Fig. 7 illustrates time diagrams of the error signal (A), the output signal of a comparator (B), the armature move-ment of the magnetic valve (C)l and the position of a pair of the bridge valves ~D);
Fig. 8 is a diagram of the position of the servo-valve in relation to the desired value and Fig. 9 is a diagram showing the amount of flow to the motor in relation to the desired value.
In the Fig. 1 circuit diagram, a pump 1 feeds pressure medium from a container 2 under atmospheric pressure through a conduit 3 and a servo-valve 4 to a hydraulic operating motor 5 whence the pressure medium returns through the servo-valve
In a preferred embodiment, the A.C. voltage is a triangular voltage of which twice the amplitude is considerably larger than the difference between the comparator limiting values. One can for example attain the condition where at least one of the two magnetic valves is actuated during basic-ally each period. In such a case, the magnetic valves would be alternately actuated in the rest position, so that the servo-valve prac~ically stands still in a predetermined position.
The A.C. voltage may instead be a trapezium voltage of which twice the amplitude substantially corresponds to the .i difference between the comparator limiting values. This ensures ; that the operating signals fed to the magnetic valves are delivered only if they ha~e a particular minimum duration, he magnetic valves are therefore operated less frequently and therefore worn out more slowly.
In particular, the period of constant amplitude should correspond to about the reaction time of the magnetic valves and twice the amplitude should be somewhat smaller than the difference between the comparator limiting values, In this case, an operating pulse is delivered only if it is adequately 2~
long to actuate the magnetic valve. The ~ctuating frequency is correspondingly low.
Preferred examples of the invention will now be described in more detail with reference to the drawing, wherein:-Fig. 1 is a diagrammatic circuit diagram of a servo--valve having an actuating apparatus according to the invention;
Fig. 2 shows a first curve shape for the error signal;
Fig. 3 shows the Fig. 2 error signal. upon positive regulating departure;
Fig. 4 shows the Fig. 2 error signal upon negative regulating departure;
Fig~ 5 shows a modified form of the error signal;
Fig. 6 shows a further modification of the shape of the error signal;
Fig. 7 illustrates time diagrams of the error signal (A), the output signal of a comparator (B), the armature move-ment of the magnetic valve (C)l and the position of a pair of the bridge valves ~D);
Fig. 8 is a diagram of the position of the servo-valve in relation to the desired value and Fig. 9 is a diagram showing the amount of flow to the motor in relation to the desired value.
In the Fig. 1 circuit diagram, a pump 1 feeds pressure medium from a container 2 under atmospheric pressure through a conduit 3 and a servo-valve 4 to a hydraulic operating motor 5 whence the pressure medium returns through the servo-valve
4 and a discharge conduit 6 to the container 2.
~ - 5 -L725i~
The servo-valve has a slide 7. Associated with each of its end faces there is an actuating pressure chamber 8 and 9 in which neutral position springs 10 and 11 are also located. A~utment rings 12 and 13 ensure that each neutral ;, position spring is effective on only one side of the neutral ;' position.
The existing position of the piston 7 is determined with the aid of a measurlng apparatus 14 and delivered to a regulator 16 through a signal line 15. A desired value which - 10 may be predetermined by means of a setting apparatus 17 is led to the regulator through a signal line 18. Also applied to the regulator there is an oscillator 19 which produces an ;l A.C. voltage. Accordingly, an error signal F is delivered through a signal line 20 and depends on the regulating de-parture and this A.C. voltage, as will be explained in more detail later.
Two comparators 21 and 22 compare the error signal ~ with its limiting value. If this limiting value is exceeded `' upwardly at the comparator 21 and downwardly at the comparator,, 20 22, the subse~uent amplifier 23 or 24 delivers an output sig~al Sl or S2 to an associated magnetic valve 25 or 26, respectively. In the present case, the circuitry is such that the magnetic valves are normally energised ! i.e. open, and they become de-energised and closed on the occurrence , of an output signal.
i A valve bridge 27 comprises four bridge valves 28, 29, 30 and 31. The diagonal point 32 is connected by a pressure regulating valve 33 and a conduit 34 to the pressure conduit 3 of pump 1. The diagonal point 35 communicates with ~ - 6 -~ Z~7;~S~
the container 2. The diagonal point 36 leads by way of a conduit 37 to the actuating pressure chamber 8. The diagonal point 3~ leads to the actuating pressure chamber 9 via a conduit 39.
A control pressure conduit 40 leads from the magnetic valve 25 to the servo-elements of the opposed bridge valves 28 and 30. This conduit is connected to the low pressure side by way of a throttle 41. A pressure conduit 42 from the magnetic valve 26 leads to the servo-elements of the opposed bridge valves 29 and 31. This pressure conduit is connected .,, to the low pressure side by way of a throttle 43. When the magnetic va]ves 25,26 are energised and therefore open, the associated pressure conduit 40 and 42 are under pressure and the bridge valves connected thereto are closed~ In contrast, if one or the other magnetic valve closes under the influence of the output signal Sl, S2, the pressure in the pressure conduits 40, 42 decreases by way of the throttle 41, 43. The bridge valves controlled thereby open. T~ith the bridge valve open, pressure medium flows into the one actuating pressure chamber whereas pressure fluid flows out of the other pressure medium chamber to the container 2. This causes displacement of the slide 7.
Figs. 2 to 4 illustrate a flrst embodiment of the error signal F in the form of atriangular voltage F1. This error signal is created by superimposing a mean value M
equal or proportional to the regulating departure and a constant triangular voltage supplied by the oscillator 19.
The amplitude ofthis~triangular vol~age is selected so that the curve in the neutral position of Fig. 2 fits exactly in the window between the limiting values Gl of comparator 21 `` ~2~ZS~
and G2 of comparator 22~ Twlce the amplitude of the triangular voltage is there~ore equal to the di~erence between the com-parator limiting values. The freauency of the error signal Fl is about 40 Hz. The period Tl is therefore about 25 ms.
When a positive regulating departure occurs, as is shown in Fig. 3, the upper peaks of the error signal Fl exceed the upper limiting value Gl, sa that an output signal Sl occurs during the ~ime T2. If this signal is longer than the reaction time of the magnetic valve 25, the latter closes but is immediately thereafter opened again. Similarly, the associated bridge valves 28 and 30 are opened only momentarily. The amount of pressure fluid fed ~o the actuating pressure chamber 8 is correspondingly small. This procedure is possibly repeated several times until the output signal Sl is so short that the magnetic valve 25 will no longer close. Corresponding con-ditions apply to the magnetic valve 26 when there is negative regulating departure as illustrated in Fig. 4~
The error signal F2 Ln Fig. 5 differs from that in Figs. 2 to 4 in that twice the amplitude is considerably larger than the difference between the comparator limiting values Gl and G2. In this way one ensures that already for very small regulating departures the period T2 of the output signal Sl or S2 will be larger than the reaction time of the magnetic valves 25, 26 and consequently there will he immediate correction of the position of the slide 7 for very small regulating departures.
This can result in the two magnetic valves 25 and 26 being alternately actuated in the neutral position, whereby the slide 7 maintains its position. In this way, hysteresis is practically also avoided during positioning of the slide 7.
7;;~5~3 The error signal F3 in Fig. 6 is of trapezium shape.
Twice the amplitude is slightly less than the difference be-tween the comparator limiting values Gl and G2, ~or example smaller by 5 to 20%. Regulating departures between 2.5 and - 10% of this difference will therefore already suffice for the error signal F3 to exceed the one or other limiting value~
The constant section of the amplitude has a duration T3 sub-stantially corresponding to the reaction time of the magnetic valves. The output signals Sl and S2 therefore basically have a period sufficient to bring the magnetic valve to the closed position. Here, again, hysteresis is practically entirely avoided. The number of actuations of the magnetic valves is comparatively low.
In Fig. 7, line A shows how the error signal F3 exceeds the upper limiting value Gl. Line B shows the associated out-put signal Sl formed by the current gaps of the exciter current for the magnetic valve 25. Line C shows the actuating condition of the magnetic valve 25; the magnetic valve follows the output signal with a delay. A reaction time T4 is produced~ Line D
shows the actuating condition of the bridge valves 28 and 30.
Their actuation takes place with further delay relatively to the i magnetic valves. A second reaction period T5 is produced.
In Fig. 8, there is plotted against a desired value voltage Us, which is introduced for the setting apparatus 17, . the position s of the slide which can be displaced out of the neutral position O either into a positive limiting position +Se or into a negative limiting position ~se~ The correspond-ing curve I is practically rectilinear and exhibits no hysteresis.
X _ g _ 7~S~
Fig. 9 shows the amount of pressure fluid Q flowing to the motor 5 against the desired value voltage IJs~ The branch II of the curve applies to operation of the slide 7 in the one direction and the branch III for operation in the other direction. Here, too, the branches of the curves are followed practically without hysteresis there and back. The curve shapes in Figs. 8 and 9 can be achieved with the error signals F2 and F3.
The A.C. voltages may be different from the illustrated shapes, for example, they may be of sawtooth shape or trapezium form and havc flanks of different inclinations.
!
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~ - 5 -L725i~
The servo-valve has a slide 7. Associated with each of its end faces there is an actuating pressure chamber 8 and 9 in which neutral position springs 10 and 11 are also located. A~utment rings 12 and 13 ensure that each neutral ;, position spring is effective on only one side of the neutral ;' position.
The existing position of the piston 7 is determined with the aid of a measurlng apparatus 14 and delivered to a regulator 16 through a signal line 15. A desired value which - 10 may be predetermined by means of a setting apparatus 17 is led to the regulator through a signal line 18. Also applied to the regulator there is an oscillator 19 which produces an ;l A.C. voltage. Accordingly, an error signal F is delivered through a signal line 20 and depends on the regulating de-parture and this A.C. voltage, as will be explained in more detail later.
Two comparators 21 and 22 compare the error signal ~ with its limiting value. If this limiting value is exceeded `' upwardly at the comparator 21 and downwardly at the comparator,, 20 22, the subse~uent amplifier 23 or 24 delivers an output sig~al Sl or S2 to an associated magnetic valve 25 or 26, respectively. In the present case, the circuitry is such that the magnetic valves are normally energised ! i.e. open, and they become de-energised and closed on the occurrence , of an output signal.
i A valve bridge 27 comprises four bridge valves 28, 29, 30 and 31. The diagonal point 32 is connected by a pressure regulating valve 33 and a conduit 34 to the pressure conduit 3 of pump 1. The diagonal point 35 communicates with ~ - 6 -~ Z~7;~S~
the container 2. The diagonal point 36 leads by way of a conduit 37 to the actuating pressure chamber 8. The diagonal point 3~ leads to the actuating pressure chamber 9 via a conduit 39.
A control pressure conduit 40 leads from the magnetic valve 25 to the servo-elements of the opposed bridge valves 28 and 30. This conduit is connected to the low pressure side by way of a throttle 41. A pressure conduit 42 from the magnetic valve 26 leads to the servo-elements of the opposed bridge valves 29 and 31. This pressure conduit is connected .,, to the low pressure side by way of a throttle 43. When the magnetic va]ves 25,26 are energised and therefore open, the associated pressure conduit 40 and 42 are under pressure and the bridge valves connected thereto are closed~ In contrast, if one or the other magnetic valve closes under the influence of the output signal Sl, S2, the pressure in the pressure conduits 40, 42 decreases by way of the throttle 41, 43. The bridge valves controlled thereby open. T~ith the bridge valve open, pressure medium flows into the one actuating pressure chamber whereas pressure fluid flows out of the other pressure medium chamber to the container 2. This causes displacement of the slide 7.
Figs. 2 to 4 illustrate a flrst embodiment of the error signal F in the form of atriangular voltage F1. This error signal is created by superimposing a mean value M
equal or proportional to the regulating departure and a constant triangular voltage supplied by the oscillator 19.
The amplitude ofthis~triangular vol~age is selected so that the curve in the neutral position of Fig. 2 fits exactly in the window between the limiting values Gl of comparator 21 `` ~2~ZS~
and G2 of comparator 22~ Twlce the amplitude of the triangular voltage is there~ore equal to the di~erence between the com-parator limiting values. The freauency of the error signal Fl is about 40 Hz. The period Tl is therefore about 25 ms.
When a positive regulating departure occurs, as is shown in Fig. 3, the upper peaks of the error signal Fl exceed the upper limiting value Gl, sa that an output signal Sl occurs during the ~ime T2. If this signal is longer than the reaction time of the magnetic valve 25, the latter closes but is immediately thereafter opened again. Similarly, the associated bridge valves 28 and 30 are opened only momentarily. The amount of pressure fluid fed ~o the actuating pressure chamber 8 is correspondingly small. This procedure is possibly repeated several times until the output signal Sl is so short that the magnetic valve 25 will no longer close. Corresponding con-ditions apply to the magnetic valve 26 when there is negative regulating departure as illustrated in Fig. 4~
The error signal F2 Ln Fig. 5 differs from that in Figs. 2 to 4 in that twice the amplitude is considerably larger than the difference between the comparator limiting values Gl and G2. In this way one ensures that already for very small regulating departures the period T2 of the output signal Sl or S2 will be larger than the reaction time of the magnetic valves 25, 26 and consequently there will he immediate correction of the position of the slide 7 for very small regulating departures.
This can result in the two magnetic valves 25 and 26 being alternately actuated in the neutral position, whereby the slide 7 maintains its position. In this way, hysteresis is practically also avoided during positioning of the slide 7.
7;;~5~3 The error signal F3 in Fig. 6 is of trapezium shape.
Twice the amplitude is slightly less than the difference be-tween the comparator limiting values Gl and G2, ~or example smaller by 5 to 20%. Regulating departures between 2.5 and - 10% of this difference will therefore already suffice for the error signal F3 to exceed the one or other limiting value~
The constant section of the amplitude has a duration T3 sub-stantially corresponding to the reaction time of the magnetic valves. The output signals Sl and S2 therefore basically have a period sufficient to bring the magnetic valve to the closed position. Here, again, hysteresis is practically entirely avoided. The number of actuations of the magnetic valves is comparatively low.
In Fig. 7, line A shows how the error signal F3 exceeds the upper limiting value Gl. Line B shows the associated out-put signal Sl formed by the current gaps of the exciter current for the magnetic valve 25. Line C shows the actuating condition of the magnetic valve 25; the magnetic valve follows the output signal with a delay. A reaction time T4 is produced~ Line D
shows the actuating condition of the bridge valves 28 and 30.
Their actuation takes place with further delay relatively to the i magnetic valves. A second reaction period T5 is produced.
In Fig. 8, there is plotted against a desired value voltage Us, which is introduced for the setting apparatus 17, . the position s of the slide which can be displaced out of the neutral position O either into a positive limiting position +Se or into a negative limiting position ~se~ The correspond-ing curve I is practically rectilinear and exhibits no hysteresis.
X _ g _ 7~S~
Fig. 9 shows the amount of pressure fluid Q flowing to the motor 5 against the desired value voltage IJs~ The branch II of the curve applies to operation of the slide 7 in the one direction and the branch III for operation in the other direction. Here, too, the branches of the curves are followed practically without hysteresis there and back. The curve shapes in Figs. 8 and 9 can be achieved with the error signals F2 and F3.
The A.C. voltages may be different from the illustrated shapes, for example, they may be of sawtooth shape or trapezium form and havc flanks of different inclinations.
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Claims (7)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An electro-hydraulic actuating apparatus for a continuously adjustable servo-valve having actuating pressure chambers, a source of hydraulic fluid, a two-position control valve arrangement including magnetic valves which can be either blocked or connected to the source of hydraulic fluid, a regulator which delivers an error signal representing the departure of the servo-valve setting from the desired value, two comparators associated one with each adjusting direction, each comparator being responsive to the error signal exceeding its limiting value to deliver an output signal for operating the associated control valve arrange-ment, the error signal (F, F1, F2, F3) being formed by an A.C. voltage having a waveform with at least one sloping side, the mean value (M) of the waveform depending on the value setting departure and the half-period (T1) being longer than the reaction time (T4) of the magnetic valves (25, 26).
2. Apparatus according to claim 1, wherein the frequency of the A.C. voltage is in the range 30 to 50 Hz, preferably about 40 Hz.
3. Apparatus according to claim 1, wherein twice the amplitude of the A.C. voltage does not exceed the difference between the comparator limiting values (G1, G2).
4. Apparatus according to one of claims 1 to 3, wherein the A.C. voltage is of such an amplitude and form that, upon departure of the mean value M from the neutral position by no more than ?12.5% of the difference between the comparator limiting values (G1, G2), at least one limiting value is exceeded for a longer time than the reaction time (T4) of the magnetic valves (25, 26).
5. Apparatus according to one of claims 1 to 3, wherein the A.C. voltage is a triangular voltage of which twice the amplitude exceeds the difference between the comparator limiting values. (Fig. 5).
6. Apparatus according to claim 1, wherein the A.C. voltage is a trapezoidal voltage of which twice the amplitude is substantially the same as the difference between the comparator limiting values. (Fig. 6).
7. Apparatus according to claim 6, wherein the duration (T3) of constant amplitude substantially corresponds to the reaction time (T4) of the magnetic valves (25, 26) and twice the amplitude of the A.C. voltage is smaller than the difference between the comparator limiting values (G1, G2).
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP3329347.3 | 1983-08-13 | ||
| DE3329347A DE3329347C2 (en) | 1983-08-13 | 1983-08-13 | Electro-hydraulic actuation device for a continuously adjustable valve |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1217258A true CA1217258A (en) | 1987-01-27 |
Family
ID=6206513
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000460895A Expired CA1217258A (en) | 1983-08-13 | 1984-08-13 | Electro-hydraulic actuating apparatus for a continuously adjustable valve |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS6055402A (en) |
| CA (1) | CA1217258A (en) |
| DE (1) | DE3329347C2 (en) |
| DK (1) | DK162545C (en) |
| IT (2) | IT8453731V0 (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS63212602A (en) * | 1987-02-26 | 1988-09-05 | Nichirei:Kk | Sorting shelf |
| DE4200312A1 (en) * | 1992-01-09 | 1993-04-01 | Krupp Industrietech | Monitoring pneumatic and hydraulic position controllers - comparing position signals with dynamic reference values for rapid response adjustment. |
| JPH0611001U (en) * | 1992-07-06 | 1994-02-10 | シーケーディ株式会社 | Pressure proportional controller |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5748681B2 (en) * | 1973-02-08 | 1982-10-18 | ||
| DE2429956C3 (en) * | 1974-06-21 | 1979-11-22 | Siemens Ag, 1000 Berlin Und 8000 Muenchen | Control device with a controller and an actuator with at least two constant adjusting speeds |
| DE2645768C2 (en) * | 1976-10-09 | 1983-04-07 | Danfoss A/S, 6430 Nordborg | Electro-hydraulic control device |
| DE2811345C2 (en) * | 1978-03-16 | 1986-12-11 | Knorr-Bremse AG, 8000 München | Pressure regulators for pneumatic pressures, in particular in vehicles |
| JPS5623041A (en) * | 1979-08-03 | 1981-03-04 | Nec Corp | Delay equalizing circuit network |
-
1983
- 1983-08-13 DE DE3329347A patent/DE3329347C2/en not_active Expired
-
1984
- 1984-08-09 DK DK382884A patent/DK162545C/en not_active IP Right Cessation
- 1984-08-13 IT IT8453731U patent/IT8453731V0/en unknown
- 1984-08-13 IT IT67812/84A patent/IT1196737B/en active
- 1984-08-13 CA CA000460895A patent/CA1217258A/en not_active Expired
- 1984-08-13 JP JP59167971A patent/JPS6055402A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| JPS6055402A (en) | 1985-03-30 |
| DK162545C (en) | 1992-04-06 |
| IT8453731V0 (en) | 1984-08-13 |
| DK162545B (en) | 1991-11-11 |
| DE3329347C2 (en) | 1986-10-09 |
| IT1196737B (en) | 1988-11-25 |
| DK382884D0 (en) | 1984-08-09 |
| DE3329347A1 (en) | 1985-02-28 |
| DK382884A (en) | 1985-02-14 |
| IT8467812A1 (en) | 1986-02-13 |
| IT8467812A0 (en) | 1984-08-13 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |