FLUID MACHINE AND METHOD FOR CONTROLLING SUCH A MACHINE

Abstract

Method for controlling a fluid machine actuated by an actuator is provided, wherein the fluid machine comprises, a liner and a piston which together form a chamber and are configured to be in movement one with respect to the other, wherein the actuator comprises, in series: a rotary-shaft motor, a speed-reducing gearbox reducing the speed of the shaft of the motor, a mechanical coupling and a connecting rod. The method can include the steps of: determining the relative position of the piston or of the liner with respect to a critical position when the shaft of the motor is rotating at a first speed, and temporarily increasing the speed of the shaft of the motor according to the relative position of the piston or of the liner with respect to the critical position.

Claims

1. A method for controlling a fluid machine comprising a pump or a compressor for a cryogenic fluid, the fluid machine being connected to an actuator, the fluid machine comprising a liner and a piston which together delimit a fluid compression and expansion chamber, the piston and the liner being configured to be in a back and forth reciprocating movement one with respect to the other between a bottom dead centre as the fluid expands and a top dead centre as the fluid is compressed; the actuator comprising the following elements connected in series: a rotary-shaft motor, a speed-reducing gearbox connected to the shaft of the motor, a mechanical coupling and a connecting rod, the connecting rod being connected to the fluid machine and configured to alternately drive the piston or the liner in a first movement that compresses the fluid and a second movement that expands the fluid, the method comprising the following successive steps: determining a relative position of the piston or of the liner with respect to a reference critical position when the shaft of the motor is rotating at a first speed; and temporarily increasing the rotational speed of the shaft of the motor according to the relative position of the piston or of the liner with respect to the reference critical position, so as to reduce a mechanical shock between the speed-reducing gearbox and the connecting rod at the transition between the fluid-expansion movement and the fluid-compression movement.

2. The method according to claim 1, wherein the step of temporarily increasing the rotational speed of the shaft of the motor occurs when the relative position of the piston or of the liner coincides with or is close to the reference critical position.

3. The method according to claim 1, wherein the step of temporarily increasing the rotational speed of the shaft of the motor extends over a predetermined duration or over a duration that is variable according to the relative position of the piston or of the liner with respect to the reference critical position.

4. The method according to claim 1, wherein the step of determining the relative position of the piston or of the liner with respect to the reference critical position comprises an operation of monitoring the travel of the piston or of the liner during the fluid-compression movement.

5. The method according to claim 1, wherein the step of temporarily increasing the rotational speed of the shaft of the motor accelerates the rotation of the shaft of the motor from the first speed up to a maximum speed greater than the first speed, at a predetermined acceleration.

6. The method according to claim 5, comprising a step of reducing the rotational speed of the shaft of the motor, the step coming after the step of temporarily increasing the rotational speed of the shaft of the motor.

7. The method according to claim 6, wherein the step of reducing the rotational speed of the shaft of the motor decelerates the rotation of the shaft of the motor from the maximum speed down to the first speed, at a predetermined deceleration.

8. The method according to claim 1, wherein the step of determining the relative position of the piston or of the liner with respect to the reference critical position comprises an operation of evaluating the distance of the piston or of the liner with respect to the top dead centre, for example using a position sensor fitted to the fluid machine.

9. The method according to claim 1, wherein the step of determining the relative position of the piston or of the liner with respect to the reference critical position comprises an operation of evaluating a position of the connecting rod with respect to the mechanical coupling, for example using a position sensor fitted to the connecting rod.

10. The method according to claim 1, wherein the step of determining the relative position of the piston or of the liner with respect to the reference critical position comprises an operation of evaluating a position of the shaft of the motor with respect to a housing of the motor, for example using a position sensor.

11. The method according to claim 1, wherein the speed-reducing gearbox comprises at least one gearset made up of at least two toothed components.

12. The method according to claim 1, wherein the step of determining the relative position of the piston or of the liner with respect to the reference critical position comprises an operation of evaluating a position of one of the toothed components with respect to the other of the toothed components of the gearset.

13. The method according to claim 1, wherein the step of temporarily increasing the speed of the shaft of the motor is executed by a variable-frequency drive.

14. The method according to claim 6, wherein the third step of reducing the rotational speed of the shaft of the motor is initiated when the top dead centre is reached.

15. Fluid machine comprising a liner and a piston which together delimit a fluid compression and expansion chamber, the liner and the piston being configured to be in a back and forth reciprocating movement one with respect to the other between a bottom dead centre as the fluid expands in the chamber and a top dead centre as the fluid is compressed in the chamber, the machine further comprising an electronic member equipped with a microprocessor and configured to acquire and process data, as well as an actuator configured to receive an instruction from the electronic member and temporarily increase the speed of travel of the piston or of the liner according to a signal indicative of a relative position of the piston or of the liner with respect to a reference critical position.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the invention and are therefore not to be considered limiting of the invention's scope as it can admit to other equally effective embodiments.

[0035] Further specific features and advantages will become apparent upon reading the description below, which is provided with reference to the following figures, in which:

[0036] FIG. 1 is a schematic view of a fluid machine connected to an actuator, the actuator comprising a motor, a speed-reducing gearbox, a mechanical coupling and a crank connecting rod, the fluid machine comprising a liner and a piston which are configured to be in a relative movement one with respect to the other, the piston being in a top dead centre position.

[0037] FIG. 2 is a schematic view of the machine and of the actuator that are illustrated in FIG. 1, the piston being in a bottom dead centre position.

[0038] FIG. 3 is a partial sectioned view of a detail of the speed-reducing gearbox illustrated in FIG. 1, said gearbox comprising a gearset formed of at least two gear wheels, this figure illustrating the functional clearance there is between two respective teeth of the gear wheels.

[0039] FIG. 4 illustrates the variation in the load registered on the piston during operation of the fluid machine controlled according to a method of the prior art.

[0040] FIG. 5 illustrates the variation in the acceleration on the output side of the speed-reducing gearbox during operation of the machine controlled according to a method of the prior art.

[0041] FIG. 6 illustrates the variation in the speed on the output side of the speed-reducing gearbox during operation of the machine controlled according to a method of the prior art.

[0042] FIG. 7 illustrates the steps of the control method according to the invention.

[0043] FIG. 8 illustrates the variation in the load registered on the piston during operation of the fluid machine controlled according to the method according to the invention.

[0044] FIG. 9 illustrates the variation in the speed on the output side of the speed-reducing gearbox during operation of the fluid machine controlled according to the method according to the invention.

[0045] FIG. 10 illustrates the variation in the acceleration on the output side of the speed-reducing gearbox during operation of the fluid machine controlled according to the method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0046] FIG. 1 and FIG. 2 illustrate a fluid machine 2 connected to an actuator 1.

[0047] The fluid machine 2 comprises a liner 21 and a piston 22 which together form a chamber 23 for the expansion and compression of a fluid. In particular, the piston 22 is configured to be in a back and forth reciprocating movement with respect to the liner 21 between a first extreme position (see FIG. 1) for the admission and expansion of the fluid, and a second extreme position (see FIG. 2) for the expulsion and compression of the fluid. The extreme position for the admission and expansion of the fluid is referred to as bottom dead centre. The extreme position for the compression and expulsion of the fluid is referred to as top dead centre.

[0048] In the example illustrated, the piston 22 is tubular and formed around a fixed component. Furthermore, the piston 22 is positioned inside the liner 21.

[0049] The actuator 1 comprises the following elements connected in series: a motor 11, a speed-reducing gearbox 12, a mechanical coupling 13 and a connecting rod 14.

[0050] In particular, the motor 11 may be of asynchronous type. It comprises a shaft rotating on itself. The shaft has one end connected to the speed-reducing gearbox 12.

[0051] The speed-reducing gearbox 12 comprises a gearset comprising at least two toothed components 121, 122. These are components respectively bearing teeth. These components 121, 122 collaborate in pairs comprising a first toothed component 121 and a second toothed component 122. The teeth of the first toothed component 121 drive the teeth of the second toothed component 122.

[0052] The connecting rod 14 is configured to drive the piston 22 or the liner 21 during a movement of expansion of the fluid in the chamber 23. The connecting rod 14 is also configured to drive the piston 22 or the liner 21 during a movement of compression of the fluid in the chamber 23.

[0053] The action of the connecting rod 14 on the piston 22 introduces a positive nominal load registered on this piston during the fluid-compression movement, followed by a zero load registered during the expansion movement. However, as illustrated in FIG. 4, between the fluid-compression movement and the fluid-expansion movement the piston 22 starts to generate force.

[0054] The load registered on the piston at the transition between the compression movement and the compression movement is due, to a large extent, to a residual pressure in the expansion and compression chamber, which acts on the piston. This load is also due, to a lesser extent, to the inertia of the piston 22.

[0055] At the speed-reducing gearbox 12, the load registered on the piston 22 results in kickback (mechanical shocks) and noise or vibration that exceeds a permissible threshold. This kickback may lead to premature wear of the speed-reducing gearbox 12.

[0056] An analysis of this kickback demonstrates that it is due for example to functional clearances provided between the respective teeth of the toothed components 121, 122 of a gearset of the gearbox 12. The greater the clearances, the greater will be the energy in the kickback at the gearbox 12. An example of such a clearance is illustrated in FIG. 3.

[0057] Analysis of the kickback produced in the speed-reducing gearbox 12 demonstrates that it is associated with a gradual reduction in the speed v on the output side of said gearbox even though the motor 11 is being instructed to maintain a constant speed. This reduction in the speed on the output side of the speed-reducing gearbox is observed during the fluid-compression movement.

[0058] The variation in the speed v on the output side of the speed-reducing gearbox 12 over the course of time t is illustrated in FIG. 5 where three compression/expansion cycles, respectively No. 1, No. 2 and No. 3, are depicted. The cycles No. 1, No. 2 and No. 3 are separated by vertical broken lines.

[0059] For each compression/expansion cycle, the circle indicates the transition from the compression phase to the expansion phase. Notice that there is a reduction in the speed v over a large proportion of the compression phase, followed by an increase in this speed towards the end of the compression phase and the start of the expansion phase, before the speed stabilizes over the rest of the expansion phase. Stated differently, and considering a given cycle, for example cycle No. 2, it will be seen that the speed v on the output side of the gearbox 12 decreases during the compression phase, after a constant rate registered during the expansion phase of a preceding cycle, in this instance cycle No. 1.

[0060] The variation in the speed v on the output side of the speed-reducing gearbox 12 can be represented by a curve of acceleration .

[0061] FIG. 6 illustrates a curve of acceleration for three compression/expansion cycles. The cycles are separated by vertical broken lines. For each cycle, it will be seen that the acceleration is zero over a large proportion of the expansion phase (which means that the speed v is constant during this part of the expansion phase). Furthermore, it will be seen that the acceleration is non-zero, and in particular is negative, over a large proportion of the compression phase (which means that the speed varies by decreasing during this part of the compression phase). Between the end of the expansion phase and the start of the compression phase, it is seen that there is a change in the acceleration characteristic which coincides with the kickback registered in the speed-reducing gearbox 12.

[0062] In order to limit the abovementioned kickback and its associated disadvantages (reduction in speed on the output side of the gearbox), the invention introduces a novel method 200 for controlling the fluid machine 2.

[0063] The method 200 comprises a first step S1 of determining the relative position of the piston 22 or of the liner 21 with respect to a reference critical position Pos_crit. During this step S1, the shaft of the motor 11 is rotating at a first speed. This may be a speed at which the shaft of the motor 11 is instructed to rotate, for example a constant nominal speed v.sub.nom.

[0064] The method 200 also comprises a step S2 of temporarily increasing the rotational speed of the shaft of the motor 11 according to the relative position of the piston 22 or of the liner 21 with respect to the critical position Pos_crit. This temporary increase in the rotational speed of the shaft of the motor 11 makes it possible to reduce a mechanical shock in the speed-reducing gearbox 12 by maintaining contact between the respective teeth of the toothed components 121, 122 of the gearset.

[0065] By reducing the mechanical shock in the speed-reducing gearbox 12, the method 200 makes it possible to keep the rotational speed on the output side of the speed-reducing gearbox 12 substantially constant at the transition between the fluid-expansion movement and the fluid-compression movement. Moreover, by reducing the mechanical shock in the speed-reducing gearbox 12, the method 200 also makes it possible to reduce the shock between the speed-reducing gearbox 12 and the connecting rod 14 at the transition between the fluid-expansion movement and the fluid-compression movement.

[0066] The reference critical position Pos_crit during the fluid-compression movement is a position of the piston 22 or of the liner 21 beyond which the inertia of the fluid machine 2 becomes greater than the inertia of the actuator 1. In other words, the reference critical position Pos_crit is a position of the piston 22 or of the liner 21 beyond which the fluid machine 2 would start to generate force on the actuator 1 if the step S2 were not implemented.

[0067] Advantageously, the step S1 of determining the relative position of the piston 22 or of the liner 21 with respect to the reference critical position Pos_crit comprises an operation S1a of monitoring the travel of the piston 22 or the travel of the liner 21 during the fluid-compression movement.

[0068] Advantageously, the step S1 of determining the relative position of the piston 22 or of the liner 21 with respect to the reference critical position Pos_crit comprises an operation S1b of evaluating the distance of the piston 22 or of the liner 21 with respect to the top dead centre, for example using a position sensor fitted to the fluid machine 2. Such a sensor may be configured to detect the relative position of the piston 22 or of the liner 21 directly or via another element of the fluid machine 2.

[0069] As an alternative or as an addition to the operation S1b, the step S1 of determining the relative position of the piston 22 or of the liner 21 with respect to the reference critical position Pos_crit may comprise an operation S1c of evaluating a position of the connecting rod 14 with respect to the mechanical coupling 13, for example using a position sensor fitted to the connecting rod 14.

[0070] As an alternative or as an addition to the preceding operations S1b, S1c, the step S1 of determining the relative position of the piston 22 or of the liner 21 with respect to a reference critical position Pos_crit may comprise an operation S1d of evaluating a position of the shaft of the motor 11 with respect to a housing of the motor 11, for example using a position sensor fitted to the housing.

[0071] As an alternative or as an addition to the operations S1b, S1c, S1d, the step S1 of determining the relative position of the piston 22 or of the liner 21 with respect to a reference critical position Pos_crit may comprise an operation S1e of evaluating a position of one 121 of the toothed components 121, 122 with respect to the other 122 of the toothed components 121, 122 of the gearset.

[0072] It should be noted that the step S2 of temporarily increasing the rotational speed of the shaft of the motor 11 occurs when the relative position of the piston 22 or of the liner 21 coincides with or is close to the reference critical position Pos_crit. In addition, this step S2 of temporarily increasing the rotational speed of the shaft of the motor 11 extends over a predetermined duration (i.e. a fixed duration) or over a duration that is variable according to the relative position of the piston 22 or of the liner 21 with respect to the reference critical position Pos_crit. Finally, this step S2 of temporarily increasing the speed of the shaft of the motor 11 may be executed by a variable-frequency drive VFD.

[0073] Advantageously, the step S2 of temporarily increasing the rotational speed of the shaft of the motor 11 accelerates the rotation of the shaft of the motor 11 from the first speed v.sub.nom up to a maximum speed v.sub.max greater than the first speed v.sub.nom, at a predetermined acceleration 1. In order to do this, the instruction controlling the rotational speed of the shaft of the motor may for example be increased over the course of a determined duration.

[0074] Advantageously, the method 200 comprises a third step S3 of reducing the rotational speed of the shaft of the motor 11. This step S3 comes after the step S2 of temporarily increasing the rotational speed of the shaft of the motor 1. Furthermore, this step S3 can be initiated as soon as the top dead centre is reached.

[0075] Advantageously, the third step S3 of reducing the rotational speed of the shaft of the motor 11 comprises an operation of decelerating the rotation of the shaft of the motor 11 from the maximum speed v.sub.max attained at the end of step S2 down to the nominal speed v.sub.nom, at a predetermined deceleration 2. In order to do this, the instruction controlling the rotational speed of the shaft of the motor 11 may for example be reduced over the course of a determined duration.

[0076] Advantageously, the actuator 1 may comprise a controller (not illustrated) which is configured to receive, from any one of the position sensors mentioned hereinabove, at least one signal indicative of a position of the piston 22 or of a position of the liner 21. The controller may also be configured to transmit to the variable-frequency drive VFD a command to accelerate or to decelerate the rotation of the shaft of the motor 11.

[0077] The command to accelerate may be based on a signal relating to the relative position of the piston 22 or a signal relating to the relative position of the liner 21. The command to decelerate may be based on a signal indicating that the top dead centre has been reached.

[0078] Also, advantageously, the first step S1 of determining the relative position of the piston 22 or of the liner 21 with respect to the reference critical position Pos_crit may comprise an operation of transmitting a signal relating to the position of the piston 22 or of the liner 21 from any one of the position sensors to the controller.

[0079] The step S2 of temporarily increasing the speed of rotation of the shaft of the motor 11 and the step S3 of reducing the rotational speed of the shaft of the motor 11 may respectively comprise an operation of transmitting a command to accelerate or, respectively, an operation of transmitting a command to decelerate, the rotation of the shaft of the motor 11. This command is transmitted from the controller to the variable-frequency drive VFD.

[0080] The step S2 of temporarily increasing the speed of the shaft of the motor 11 and the consecutive step S3 of reducing the speed of rotation of the shaft of the motor 11 have an impact on the characteristic of the curve of load registered on the piston 22 or on the liner 21, on the characteristic of the curve of speed v on the output side of the speed-reducing gearbox 12 and on the characteristic of the curve of acceleration on the output side of the speed-reducing gearbox 12.

[0081] As illustrated in FIG. 8, at the end of the fluid-compression movement, the fluid machine 2 no longer generates force on the actuator 1. The transition from the compression movement to the expansion movement occurs without any kickback at the speed-reducing gearbox 12.

[0082] Moreover, as illustrated in FIG. 9, the rotational speed v on the output side of the speed-reducing gearbox 12 is generally constant during the course of the expansion movement and during the course of the compression movement. The only variations in the rotational speed v on the output side of the speed-reducing gearbox 12 are those brought about by the increase in the rotational speed of the shaft of the motor 11 (step S2), and those brought about by the reduction in the rotational speed of the shaft of the motor 11 (step S3).

[0083] Finally, as illustrated in FIG. 10, the acceleration on the output side of the speed-reducing gearbox 12 remains zero throughout the compression and expansion phases, the only variations being those introduced in step S2 and in step S3.

[0084] Thus, the acceleration on the output side of the speed-reducing gearbox 12 is no longer experienced as it was in the mode of control according to the prior art. By virtue of the invention, the acceleration is anticipated after evaluating the position of the piston 22 or of the liner 21 with respect to the critical position Pos_crit.

[0085] While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

[0086] The singular forms a, an and the include plural referents, unless the context clearly dictates otherwise.

[0087] Comprising in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of comprising). Comprising as used herein may be replaced by the more limited transitional terms consisting essentially of and consisting of unless otherwise indicated herein.

[0088] Providing in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

[0089] Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

[0090] Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

[0091] All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.