A device for controlling torques arising in a mechanical system

Abstract

A device for controlling torques arising in a mechanical system, comprising: first and second terminals couplable respectively with first and second parts of the mechanical system; coupled to the first terminal, a housing enclosing a chamber for containing a fluid; coupled to the second terminal, a shaft rotatably coupled to the housing; a rotor coupled to the shaft; and a fluid path coupled to the chamber; wherein the device is configured such that, when in use: the fluid is caused to flow along the fluid path in response to relative rotational motion between the first and second terminals, thereby generating an inertial force due to the mass of the fluid, and the inertial force causes equal and opposite inertance torques to be applied at the first and second terminals respectively, the inertance torques being torques whose magnitude are substantially proportional to the relative rotational acceleration between the first and second terminals.

Description

[0001] A DEVICE FOR CONTROLLING TORQUES ARISING IN A MECHANICAL SYSTEM

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to the field and art of mechanical systems, and in particular to devices for controlling torques arising in a mechanical system.

[0004] BACKGROUND

[0005] It is known to skilled persons in the art that mechanical systems may be represented by an analogous electrical system — this is known as the mobility analogy. Doing so may be advantageous in that the theory and analytical techniques developed to analyse electrical systems may be leveraged for the purposes of developing mechanical systems to implement any desired passive behaviour.

[0006] It was known that the mobility analogy was incomplete — while the mass element may be seen as analogous to capacitance, the mass element has only one freely movable terminal, and so is only analogous to grounded capacitors; there was no mechanical analogy for capacitance in the case of ungrounded capacitors. This led Malcolm Smith to develop the mechanical parameter of inertance; a generalised mechanical parameter analogous to capacitance which is applicable to both grounded and ungrounded capacitors.

[0007] Further to this, Smith invented a mechanical device capable of exhibiting inertance; the inerter. The inerter comprises two independently movable terminals coupled together in such a way that, in response to relative motion between the terminals, equal and opposite forces are produced at the terminals, these forces being substantially proportional to the relative acceleration between the terminals.

[0008] To achieve the aforementioned application of force within the inerter, the terminals may be coupled via mechanical means and / or hydraulic means. The most straightforward mechanical embodiment may comprise a rack and pinion mechanism mechanically linked to a geared flywheel whose gearing and moment of inertia may be chosen to give a specified inertance value. Variations have been developed to improve performance and reliability using mechanisms like ball screws and planetary gear systems.

[0009] Using hydraulic means may result in an inerter comprising fewer moving parts. Such hydraulic means may comprise a housing enclosing a chamber (such as a piston cylinder) and piston whose head divides the chamber into two chamber volumes. A fluid path may connect the two chamber volumes together to form a closed fluid system. The housing and the piston rod may act as the device terminals, and their relative motion may drive a working fluid through the path.

[0010] Heretofore, inerters have been developed for use in a range of applications, such as vehicle suspension and vibration isolation. However, there is a desire to apply the inertance principle to a yet wider range of applications. The present invention has been developed to fulfil this desire.

[0011] SUMMARY OF INVENTION

[0012] In a first aspect, a device for controlling torques arising in a mechanical system is provided in claim 1.

[0013] Further respective aspects and features of the present invention are defined in the appended claims.

[0014] BRIEF DESCRIPTION OF DRAWINGS

[0015] Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

[0016] • Figure 1 schematically illustrates a device according to embodiments of the present invention;

[0017] • Figure 2 schematically illustrates a coupling according to embodiments of the present invention; • Figure 3 schematically illustrates a device according to embodiments of the present invention;

[0018] • Figure 4 schematically illustrates a device according to embodiments of the present invention;

[0019] • Figure 5 schematically illustrates a device according to embodiments of the present invention;

[0020] • Figure 6 schematically illustrates a device according to embodiments of the present invention; and

[0021] • Figure 7 schematically illustrates a device according to embodiments of the present invention.

[0022] DETAILED DESCRIPTION

[0023] A device for controlling torques arising in a mechanical system is disclosed. In the following description, a number of specific details are presented in order to provide a thorough understanding of the embodiments of the present invention. It will be apparent, however, to a person skilled in the art that these specific details need not be employed to practice the present invention. Conversely, specific details known to the person skilled in the art are omitted for the purposes of clarity where appropriate.

[0024] Turning now to Figure 1 , in embodiments of the present invention, device 1 for controlling torques arising in a mechanical system comprises: first and second terminals 2a, 2b couplable respectively with first and second parts of the mechanical system; coupled to first terminal 2a, housing 3 enclosing chamber 4 for containing a fluid; coupled to second terminal 2b, shaft 5 rotatably coupled to housing 3; rotor 6 coupled to shaft 5 (via coupling 5a, for example); and fluid path 7 coupled to chamber 4; wherein device 1 is configured such that, when in use: the fluid is caused to flow along fluid path 7 in response to relative rotational motion between first and second terminals 2a, 2b, thereby generating an inertial force due to the mass of the fluid, and the inertial force causes equal and opposite inertance torques to be applied at first and second terminals 2a, 2b respectively, the inertance torques being torques whose magnitude are substantially proportional to the relative rotational (for example, angular) acceleration between first and second terminals 2a, 2b.

[0025] As mentioned previously, there is a desire in the art to utilise the inertance principle in a wider range of the applications. The present invention fulfils this desire by providing a hydraulic (that is, fluid-based) rotational inerter that imparts respective torques (the rotational analogue to forces) on terminals 2a, 2b, these torques being equal, opposite, substantially proportional to the relative rotational acceleration between the two terminals, and acting along a common axis of rotation. As with the piston-cylinder hydraulic inerter, the inertance of the present invention arises by way of driving the fluid from chamber 4 into fluid path 7, and vice versa.

[0026] Unlike known fluid inerters, which typically apply equal and opposite translational forces on the two terminals along a common line of action, the present invention enables the fluid inertance principle to be extended towards rotational applications, such as passive control of torsional vibrations in drive shafts, rotating machinery, and the like. Notably, the present invention may be utilised in drilling applications, where the interaction between drill-bit and rock (such as bedrock) typically includes highly variable and uncertain torsional resistance.

[0027] The inventors envisage two main groups of embodiments of the present invention, each of which shall be discussed herein.

[0028] The first group of embodiments, which shall be described later herein with reference to Figures 1 and 2, shall be referred to as “unlimited travel inerters”. Unlimited travel inerters facilitate an arbitrarily large angular displacement (exceeding a full revolution, for example) between terminals 2a, 2b. This is achieved by exploiting the fact that rotational displacement is periodic in nature, unlike translational displacement.

[0029] The second group of embodiments, which shall be described later herein with reference to Figures 3 to 7, shall be referred to as “limited travel inerters”. Limited travel inerters facilitate angular displacement within a predefined range (typically less than a full revolution).

[0030] However, both groups of embodiments share common features, which shall be discussed first with reference to Figure 1 .

[0031] Common Features

[0032] Turning back to Figure 1 , device 1 may be coupled to first and second parts of a mechanical system when in use, this coupling being achieved via first and second terminals 2a, 2b. As will be appreciated, the present invention is not limited to a specific type of means employed to couple a given terminal and a given part of the mechanical system. Examples of such means may take the form of adhesives, fixings (such as nuts and bolts, screws, rivets or the like), welding, bearings, ball joints, universal couplings, or the like.

[0033] To make use of the inertance principle, the first and second parts to which the inerter is coupled are preferably rotatable relative to each other along a common axis of rotation. This is so that the relative motion between the first and second parts results in relative rotational acceleration between first and second terminals 2a, 2b, and thus the application of inertance torques onto first and second terminals 2a, 2b.

[0034] Housing 3 is coupled to first terminal 2a, and shaft 5 is coupled to second terminal 2b. As will be appreciated, the present invention is not limited to a specific type of means employed to couple first and second terminals 2a, 2b with housing 3 and shaft 5 respectively. Examples of such means were mentioned previously.

[0035] To simply manufacture, first terminal 2a and housing 3 may optionally be formed as a monolithic part, and / or second terminal 2b and shaft 5 may be formed as a monolithic part. Hence more generally, the first terminal 2a may comprise housing 3, and / or the second terminal 2b may comprise shaft 5.

[0036] Shaft 5 is rotatably coupled to housing 3. This is to say that shaft 5 is coupled to the housing in such a manner so as to permit the rotation of shaft 5. As will be appreciated, shaft 5 should be allowed to rotate in order that rotor 6 (which is coupled to shaft 5) also rotate, and thereby drive the fluid when in use.

[0037] As will be appreciated, the present invention is not limited to a specific type of means employed for enabling shaft 5 to be rotatably coupled to housing 3. Examples of such means may take the form of bearings, a gearbox, the application of oil, grease or lubricant onto the contacting portions of shaft 5 and housing 3, or the like, or indeed any combination of the preceding.

[0038] As mentioned previously, rotor 6 is coupled to shaft 5 (via coupling 5a, for example). It should be noted that rotor 6 and shaft 5 should be coupled in such a way that the rotation of shaft 5 causes rotation of rotor 6 in order that rotor 6 drives the fluid when in use. As will be appreciated, the present invention is not limited to a specific type of means (such as coupling 5a) employed to couple rotor 6 to shaft 5. Examples of such means were mentioned previously. Further examples include universal couplings, flexible shafts, hypocycloidal gearing (which shall be discussed later herein), or the like. To simply manufacture of limited travel inerters, rotor 6 and shaft 5 may optionally be formed as a monolithic part.

[0039] Housing 3 provides an enclosed space (that is, chamber 4) within which rotor 6 may reside. As will be appreciated, while rotation of rotor 6 drives the fluid, chamber 4 (provided by housing 3) directs the driven fluid towards fluid path 7.

[0040] Fluid path 7 is coupled to chamber 4. As will be appreciated, fluid path 7 enables the fluid to enter and exit chamber 4 when being driven by rotor 6. It is this flow of the fluid from chamber 4 along fluid path 7 (and vice versa) which generates the inertial force for applying inertance torques on first and second terminals 2a, 2b.

[0041] As will be appreciated, the present invention is not limited to a specific type of means employed for coupling fluid path 7 to chamber 4. Examples of such means may take the form of seals, gaskets, hose barbs, fittings such as elbows or tees, a plug and socket (or other male-female connector) arrangement. To reduce the form factor of device 1 , at least a part of fluid path 7 may optionally be disposed on housing 3. For example, fluid path 7 may be disposed on an exterior surface of housing 3. Alternatively, at least a part of fluid path 7 may be disposed within housing 3. For example, fluid path may be disposed within a wall of housing 3 (as shown in Figure 1).

[0042] Alternatively or in addition, as another way to reduce the form factor of device 1 , at least a part of fluid path 7 may optionally comprise a helical tube (as shown in Figure 1).

[0043] To vary the amount of inertance of device 1 , device 1 may comprise a plurality of fluid paths 7 forming a network, and a valve for directing the fluid along one of the fluid paths 7 of the network. For example, the fluid paths 7 may be of differing lengths, and / or may be coupled in series or parallel. Indeed, the valve may even be operable to change a series coupling of fluid paths 7 into a parallel one, or vice versa. It will be appreciated that the amount of inertance generated by the flow of fluid along fluid path 7 is dependent upon the properties of the fluid path (effective length and / or cross-sectional area, or the like). Thus, by operating the valve to cause fluid to flow along a different fluid path 7 of the network, the amount of inertance provided by device 1 may be adjusted.

[0044] To enhance portability and versatility of device 1 , fluid path 7 and chamber 4 may optionally form a closed fluid cycle. This is to say that fluid path 7 and chamber 4 may be coupled in such in a way that, when in use, a fixed volume of fluid is retained within device 1 . For example, the fluid path may comprise a pipe or tube, and both ends of the pipe or tube may be coupled to chamber 4. This may be seen in Figure 1 , where helical tube 7 is coupled to chamber 4 such that a closed loop is formed, thus preventing a part of the fixed volume of fluid within device 1 from exiting — or any other fluid from entering — device 1 when in use.

[0045] Alternatively, fluid path 7 and chamber 4 may form an open fluid cycle. This is to say that fluid path 7 and chamber 4 may be coupled in such in a way that, when in use, fluid may enter or exit device 1 . For example, the fluid path may comprise a pipe or tube, and one end of the pipe or tube may be coupled to chamber 4, and the other end may be open to the outside. Moreover, a hole or port may be coupled chamber 4 to the outside. When in use, rotor 6 may cause the fluid in chamber 4 to exit device 1 via the pipe or tube, and simultaneously draw in fluid via the port or hole.

[0046] Such an arrangement may be beneficial in applications where device 1 may be submersed in a fluid, and so can make use of this fluid to provide the appropriate inertance. For example, in the case of downhole drilling in a well, downhole tools (such as drills) are typically powered by a fluid known as mud. Mud is forced along a drillstring (which is typically in the shape of a pipe) and into a drill which comprises a rotor attached to a drill bit. The mud impinges on the rotor (thus rotating the drill bit) and exits the drill to lubricate the drill bit and rock being drilled. This mud flows up through the well to the surface, where fragments of rock are separated out from the mud before forcing the mud back down the drillstring. By having a open fluid cycle, device 1 may further use the surface-bound mud flow to provide the appropriate inertance. In this case, the port / hole and pipe / tube may comprise a filter to prevent the ingress of rock fragments into device 1 , which may otherwise damage device 1 .

[0047] In any case, device 1 is configured such that, when in use, the fluid is caused to flow along fluid path 7 in response to relative rotational motion between the first and second terminals 2a, 2b. As will be appreciated, this relative rotational motion causes relative rotational motion between shaft 5 and housing 3, and thus rotation of rotor 6 relative to chamber 4, which drives the fluid along fluid path 7.

[0048] The fluid flow generates an inertial force due to the mass of the fluid (that is, due to Newton’s Second Law of Motion), and the inertial force causes equal and opposite inertance torques to be applied at first and second terminals 2a, 2b respectively, the inertance torques being torques whose magnitude are substantially proportional to the relative rotational acceleration between the first and second terminals.

[0049] Device 1 may additionally provide torsional damping due to the use of fluid within device 1. As will be appreciated, most fluids possess viscosity, which may be thought of as the fluid’s resistance to flow. When a fluid flows, internal frictional forces arise within the fluid, with more viscous fluids generating greater internal frictional forces. As will be appreciated, a fluid’s viscosity may be exploited for the purposes of damping. A typical example of a viscous damper is the dashpot, where the damping force provided is substantially proportional to the relative translational velocity between the two terminals (coupled to the dashpot’s housing and piston head respectively). The proportionality constant (that is, the damping coefficient) is based on the fluid’s viscosity.

[0050] Thus, while device 1 provides inertance torques that are substantially proportional to the relative acceleration between first and second terminals 2a, 2b, it may additionally provide damping torques that are dependent upon the relative velocity between first and second terminals 2a, 2b.

[0051] Hence more generally, device 1 may optionally be configured such that, when in use, the fluid is caused to flow along fluid path 7 in response to relative rotational motion between first and second terminals 2a, 2b, thereby generating a frictional force due to the viscosity of the fluid, and the frictional force causes equal and opposite damping torques to be applied at first and second terminals 2a, 2b respectively, the damping torques being torques whose magnitude are dependent upon the relative rotational velocity between first and second terminals 2a, 2b.

[0052] A relationship between the torques applied at first and second terminals 2a, 2b due to inertance and damping may be expressed below in equation 1 :

[0053] 2T = B(02- 0X) + C(02- 0X) Equation 1

[0054] Where 2T is the magnitude of the sum of the equal and opposite torques applied to first and second terminals 2a, 2b, the constant B is the inertance, C is the viscous damping coefficient (in the case of linear damping) or the non-linear viscous damping function, 02- is the relative rotational acceleration between the first and second terminals 2a, 2b, and 02- is the relative rotational velocity between the first and second terminals 2a, 2b. It will be appreciated that the quantities B(02- 0i) and c(02- 0i) thus represent the inertance torques and damping torques, respectively.

[0055] It should be noted that equation 1 may be applicable in the case where parallel inertance and damping are provided by device 1 , this parallel damping component arising from the flow of fluid through fluid path 7. It is entirely within the remit of persons skilled in the art to derive other equations which describe the relationship between the torques applied between first and second terminals 2a, 2b and the inertance and damping torques generated in the case where series damping arises in device 1.

[0056] Series damping may arise within device 1 by configuring rotor 6 and / or the interior surface of housing 3 such that a clearance arises therebetween (that is, such that rotor 6 does not contact the interior surface of housing 3). In this way, some of the fluid within chamber 4 may flow through this clearance as rotor 6 rotates relative to housing 3, thus generating frictional forces within chamber 4, thereby providing a series damping component.

[0057] Series spring resistance may also arise within device 1. As will be appreciated, “spring resistance” here refers to the resistance which elastic materials / components (such as springs or other elastically resilient members) exhibit when deformed (as described by Hooke’s law). Such series spring resistance may arise within device 1 by configuring features such as rotor 6 and / or housing 3 such that they exhibit a degree of flexibility, and thus may elastically deform when in use. The elastic deformation of such features results in a spring resistance arising within the features, thereby providing a series spring resistance component.

[0058] Unlimited Travel Inerters

[0059] As mentioned previously, unlimited travel inerters facilitate an arbitrarily large angular displacement (exceeding a full revolution, for example) between terminals 2a, 2b. This is achieved by exploiting the fact that rotational displacement is periodic in nature, unlike translational displacement. In light of this, unlimited travel inerters may be suitable for applications such as vibration control in turbines (such as wind turbines), power transmissions, gimbals, differentials, or other mechanical devices / systems where angular displacements exceeding a full revolution during operation are expected.

[0060] To behave as an unlimited travel inerter, rotor 6 and interior surface 3a should be configured so as to form a fluid pump within chamber 4, with rotor 6 acting as the pump’s rotor and interior surface 3a acting as the pump’s stator. Moreover, such a pump should be able to displace a volume of fluid that is substantially proportional to a given angular displacement of rotor 6, and also be back-drivable such that displacement of the fluid within device 1 causes an angular displacement of rotor 6.

[0061] As will be appreciated, back-drivability is ability of a device to interchange driven and driving components, the thereby obtain the device’s input from its output. In the case of device 1 , the pump formed by rotor 6 and interior surface 3a, a driving operation may be thought of as rotating rotor 6 and interior surface 3a relative to each other (the input thus being rotational motion) in order to cause the fluid to flow from chamber 4 into fluid path 7 (the output thus being fluid flow). In light of this, back-driving device 1 would be the flowing of fluid into chamber 4 from fluid path 7 to do work on rotor 6, and thereby cause relative rotation to occur between rotor 6 and interior surface 3a.

[0062] Optionally, device 1 may be operable in a bi-directional manner, with rotor 6 being able to rotate clockwise and anti-clockwise relative to interior surface 3a. This may be advantageous for vibration control as vibrations are typically oscillatory motions, with the direction of motion changing periodically.

[0063] As will be appreciated, the substantial proportionality of volumetric fluid displacement to angular rotor displacement enables the substantial proportionality of the inertance torques applied at first and second terminals 2a, 2b to the relative rotational acceleration therebetween, that is, the ability of device 1 to provide inertance. Hence more generally, in embodiments of the present invention where device 1 is an unlimited travel inerter, rotor 6 and interior surface 3a of housing 3 may form a back-drivable fluid pump configured such that, when in use, a volumetric displacement of the fluid is substantially proportional to an angular displacement of rotor 6.

[0064] An example of a pump that meets the above criteria is a progressing cavity pump (also known as a progressive cavity pump or Moineau pump). As will be appreciated, the present invention is not limited to progressing cavity pumps; other types of fluid pump fulfilling the above criteria may be used or devised for use in device 1 .

[0065] Turning now to Figure 2, in the case where a progressing cavity pump is formed by rotor 6 and interior surface 3a, rotor 6 may optionally be coupled to shaft 5 (not shown) such that, when in use: rotation of shaft 5 about an axis of rotation of shaft 5 (axis of rotation 10) causes rotation of rotor 6 about an axis of rotation of rotor 6 (axis of rotation 11), and axis of rotation 11 of rotor 6 follows path 14 enclosing axis of rotation 10 of shaft 5.

[0066] A non-limiting example of such a coupling between rotor 6 and shaft 5 may take the form of a planet gear engaged with a ring gear, as seen in Figure 2. For example, device 1 may comprise: ring gear 12 coupled to interior surface 3a of the housing 3; engaged with ring gear 12, a planet gear 13 coupled to rotor 6; and a crank (not shown) coupled between the shaft 5 (not shown) and rotor 6.

[0067] As will be appreciated the crank may be any mechanical component that facilitates an eccentric coupling between shaft 5 and rotor 6 such that axis of rotation 11 follows path 14 enclosing axis of rotation 10 (the eccentricity defining a radius of path 14, for example).

[0068] Preferably, the crank may comprise a thrust bearing for withstanding axial load arising along axis of rotation 10 of shaft 5, these axial loads arising due to the flow of fluid within chamber 4 towards fluid path 7, for example. For example, shaft 5 may be coupled to the bore of the shaft washer of the thrust bearing, and the housing washer of the thrust bearing may be coupled to housing 3. Moreover, rotor 6 may be rotatably coupled to the shaft washer such that an eccentricity or offset arises between axis of rotation 11 and axis of rotation 10. In this way, the shaft washer of the thrust bearing may act as a crank.

[0069] As will be appreciated, the present invention is not limited to thrust bearings; other types of crank for coupling between the shaft 5 and rotor 6 may be used or devised for use in device 1.

[0070] Indeed, the present invention is not limited to using a ring gear and planet gear arrangement to couple rotor 6 and shaft 5 such that axis of rotation 11 of rotor 6 follows path 14 enclosing axis of rotation 10 of shaft 5; other types of couplings between these features may be used or devised for use in device 1.

[0071] In any case, coupling rotor 6 and shaft 5 such that axis of rotation 11 of rotor 6 follows path 14 enclosing axis of rotation 10 of shaft 5 may be beneficial in the case where rotor 6 and interior surface 3a of housing 3 are configured so as to not contact each other. In such case, the rotational behaviour of rotor 6 defined by way of the aforementioned coupling may help to ensure that a substantially constant clearance is maintained between rotor 6 and interior surface 3a as rotor 6 rotates within housing 3. As mentioned previously, providing such a clearance has the effect of providing a series damping component within device 1 .

[0072] Limited Travel Inerters

[0073] As mentioned previously, limited travel inerters facilitate angular displacement within a predefined range (typically less than a full revolution).

[0074] In light of this, limited travel inerters may be suitable for applications such as vibration control in power transmissions, drillstrings, driveshafts, building foundations, or other devices where limited amounts of angular displacement. A further example application of limited travel inerters may be the control of resonant frequencies in an electromechanical machine (to mitigate or alleviate subsynchronous resonance, for example). Turning now to Figure 3, in embodiments of the present invention where device 1 is a limited travel inerter, rotor 6 may comprise paddle 6a, and device 1 may comprise baffle 8 coupled to and extending from interior surface 3a of housing 3 towards an axis of rotation of rotor 6.

[0075] As will be appreciated, baffle 8 obstructs the motion of paddle 6a such that paddle 6a (and thus rotor 6 and shaft 5) cannot complete a full revolution. In other words the angular range through which rotor 6 may be displaced is predefined by the presence of baffle 8.

[0076] As will be appreciated, the present invention is not limited to a specific type of means employed to couple baffle 8 with interior surface 3a. Examples of such means have been discussed previously. To simplify manufacture, baffle 8 and housing 3 may be formed as a monolithic part.

[0077] As will be appreciated, the ends of fluid path 7 may be coupled to chamber 4 in any position the skilled person sees fit. However, it should be noted that the placement of the couplings between the ends of fluid path 7 and chamber 4 may further limit the useful angular displacement of rotor 6.

[0078] While baffle 8 physically restricts the angular displacement of rotor 6, the angular displacement between the chamber-to-fluid-path couplings define the angular displacement through which rotor 6 may rotate to provide inertance. Alternatively put, in order for the rotation to rotor 6 to provide inertance, paddle 6a should reside within the sector formed between the axis of rotation of rotor 6 and the chamber- to-fluid-path couplings. This sector defines the range of useful angular displacement of rotor 6, as rotation of rotor 6 cannot reliably drive fluid along fluid path 7 (via one of the ends) if paddle 6a falls outside of this sector.

[0079] Given this, a preferable arrangement may be to couple the ends of fluid path 7 proximate to either side of baffle 8 so that the difference between physical and useful ranges of angular displacement of rotor 6 may be minimised. This arrangement may be seen in Figure 3. Hence more generally, baffle 8 may comprise first and second major baffle surfaces (that is, the surfaces of baffle 8 which are perpendicular to the radial direction in which baffle 8 extends), and first end 7a of fluid path 7 may be coupled to chamber 4 at a first position relative to interior surface 3a of housing 3, the first position being closer to the first major baffle surface than to the second major baffle surface, and second end 7b of fluid path 7 may be coupled to chamber 4 at a second position relative to interior surface 3a of housing 3, the second position being closer the second baffle major surface than to the first major baffle surface.

[0080] More preferably, first end 7a may be coupled to the first major baffle surface, and / or second end 7b is coupled to the second major baffle surface. This arrangement may further minimise (or even eliminate) the difference between physical and useful ranges of angular displacement of rotor 6. This arrangement may be seen in Figure 4, where a plurality of baffles 8 and paddles 6a are disposed within chamber 4. As seen in Figure 4, each baffle 8 comprises first and second ends 7a, 7b, where first end 7a is coupled to a first major baffle surface, and second end 7b is coupled to a second major baffle surface. It will be appreciated that limited travel inerters comprising a plurality of baffles 8 and a plurality of paddles 6a fall within the scope of the present invention.

[0081] Where embodiments of the present invention comprise a plurality of baffles 8 and a plurality of paddles 6a, it will be appreciated that a network of fluid paths 7 may be formed.

[0082] Figure 4 provides a non-limiting example of such a fluid path network, where each baffle 8 may comprise respective first and second ends 7a, 7b coupled thereto, with each first end 7a coupled together in parallel, and each second end 7b coupled together in parallel. Moreover, a further length of pipe or tube (the helical tube in Figure 4) may be coupled such that one end of the length of pipe or tube is coupled in parallel to the group of first ends 7a, and the other end of the length of pipe or tube is coupled in parallel to the group of second ends 7b.

[0083] As will be appreciated, fluid path networks configured in series are also contemplated within the scope of the present invention. Moreover, multiple separate fluid paths are also contemplated within the scope of the present invention. Indeed, combinations of the above arrangements are also contemplated within the scope of the present invention.

[0084] As will be appreciated, different fluid path network configurations may cause different amounts of inertial (and optionally frictional) forces to be generated within the flowing fluid, and thus different amounts of inertance (and optionally damping) provided by device 1 . By using one or more valves in the fluid path network, the network configuration may be adapted on-the-fly in order to provide the appropriate amount of inertance (and optionally damping) for a given application. For example, operating a given valve may result in a given branch of the network being closed off so that fluid cannot flow along it, or may increase the flow resistance along the given branch. Optionally, the use of variable orifices or shim stacks may be employed to control a series damping component due to direct flow between fluid paths 7 and chambers 4.

[0085] Optionally, and turning now to Figure 5, fluid path 7 may be disposed within rotor 6. This may be advantageous, as having fluid path 7 reside within rotor 6 may reduce the form factor of device 1 , as fluid path 7 is contained within housing 3 of device 1 .

[0086] To enable fluid communication between fluid path 7 (within rotor 6) and chamber 4, first and second ends 7a, 7b of fluid path 7 may be coupled to rotor 6. As will be appreciated from the above discussion concerning useful ranges of angular displacement of rotor 6, a preferable arrangement may be to couple first and second ends 7a, 7b of fluid path 7 proximate to either side of paddle 6a so that the difference between physical and useful ranges of angular displacement of rotor 6 may be minimised.

[0087] Hence more generally, paddle 6a may comprise first and second major paddle surfaces (that is, the surfaces of paddle 6a which are perpendicular to the radial direction in which paddle extends from the axis of rotation of rotor 6 towards interior surface 3a of housing 3), and first end 7a of fluid path 7 may be coupled to chamber 4 at a first position relative to rotor 6, the first position being closer to the first major paddle surface than to the second major paddle surface, and second end 7b of fluid path 7 may be coupled to chamber 4 at a second position relative to rotor 6, the second position being closer the second paddle major surface than to the first major paddle surface.

[0088] More preferably, first end 7a may be coupled to the first major paddle surface, and / or second end 7b may be coupled to the second major paddle surface (as seen in Figure 5). This arrangement may further minimise (or even eliminate) the difference between physical and useful ranges of angular displacement of rotor 6.

[0089] In any case, and turning now to Figure 6, rotor 6 may be coupled to housing 3 via elastically resilient member 9. As will be appreciated, by including elastically resilient member 9, further torsional resistance to relative motion between first and second terminals 2a, 2b may be provide, this further torsional resistance being substantially proportional to the relative rotational (that is, angular) displacement between first and second terminals 2a, 2b (Hooke’s Law). This further torsional resistance shall be hereafter referred to as a spring torque.

[0090] This spring torque may be beneficial in that it may reduce the frequency / likelihood of a limited travel inerter “bottoming out” when in use. Bottoming out occurs when paddle 6a and baffle 8 contact each other. Spring torque may also be beneficial in that it may facilitate steady state torque transmission between the first and second parts of the mechanical system to which device 1 is coupled.

[0091] A relationship between the torques applied at first and second terminals 2a, 2b due to inertance, damping and elastic deformation may be expressed below in equation 2: Equation 2

[0092] Where 2T is the magnitude of the sum of the equal and opposite torques applied to first and second terminals 2a, 2b, the constant B is the inertance, C is the viscous damping coefficient (in the case of linear damping) or the non-linear viscous damping function, k is the spring constant (in the case of linear spring forces) or the non-linear spring force function, 02> isthe relative rotational acceleration between the first and second terminals 2a, 2b, 02- is the relative rotational velocity between the first and second terminals 2a, 2b, and 02- is the relative rotational (that is, angular) displacement between the first and second terminals 2a, 2b. It will be appreciated that the quantities B(02- 0i), C(o2- 0X) and fc(02- thus represent the inertance torques, damping torques and spring torques, respectively.

[0093] It should be noted that equation 2 may be applicable in the case where parallel inertance, damping and spring resistance are provided by device 1 , the parallel damping component arising from the flow of fluid through fluid path 7, and the parallel spring resistance being provided from elastically resilient member 9 coupled between rotor 6 and housing 3. It is entirely within the remit of persons skilled in the art to derive other equations which describe the relationship between the torques applied between first and second terminals 2a, 2b and the inertance, damping and spring torques generated in the case where series damping and / or series spring resistance arises in device 1. Series spring resistance may arise by configuring paddle 6a and / or baffle 8 such that they exhibit a degree of flexibility, as mentioned previously.

[0094] As will be appreciated, the present invention is not limited to a specific type of elastically resilient member 9, or how such member is coupled between rotor 6 and housing 3. Examples of elastically resilient member 9 include spiral torsion springs (as seen in Figure 6), helical springs and / or leaf springs (coupled between a paddle major surface and a baffle major surface, for example), torsion bars, and the like.

[0095] As another example, and turning now to Figure 7, elastically resilient member 9 may optionally be a torsion bar. In particular, the torsion bar may be coupled between housing 3 and rotor 6 via a hollow shaft in rotor 6. Alternatively put, rotor 6 may optionally comprise a hollow shaft, elastically resilient member may optionally be a torsion bar within the hollow shaft, wherein a first end of the torsion bar is coupled to an interior surface of the hollow shaft, and a second end of the torsion bar is coupled to interior surface 3a of housing 3; and paddle 6a is coupled to the hollow shaft.

[0096] Further optionally, the hollow shaft of rotor 6 may be configured so as to form part of a second fluid path when in use. For example, the hollow interior of rotor 6 may extend through housing 3, thereby providing a through-hole in device 1 which may facilitate a second fluid flow. Turning to Figure 7, alternatively, shaft 5 and housing 3 may be provided with one or more holes to facilitate fluid communication between shaft 5 and housing 3 via the hollow shaft of rotor 6.

[0097] This second fluid path may be particularly beneficial in drillstrings. For example, a first drillstring segment may be coupled to first terminal 2a, and a second drillstring segment may be coupled to second terminal 2b. When in use, mud flows in a downhole direction along the first drillstring segment, passes through the second fluid path (comprising the hollow shaft of rotor 6) and into the second drillstring segment.

[0098] After rotating the drill bit and providing lubrication to the bit-rock interface, the mud flows in an uphole direction outside of the drillstring but within the drilling well. As seen in Figure 7, fluid path 7 may also (but not necessarily) form an open fluid cycle (as mentioned previously). More specifically, the fluid path has an open end 7c and a port 7d, respectively coupled to a helical tube and chamber 4. This way, some of mud flowing in the uphole direction may be used by device 1 to provide inertance, and thus control torsional vibrations occurring in the drillstring during use. More specifically, some of this mud may enter chamber 4 via port 7d or enter the helical tube via open end 7c.

[0099] As will be appreciated, this second fluid path may be provided without having a torsion bar within it. For example, where embodiments of the present invention do not comprise elastically resilient member 9 (or comprise another type of elastically resilient member 9 that is not a torsion bar), rotor 6 may optionally comprise a hollow shaft, which may be configured so as to form part of a second fluid path when in use. In any case, such a hollow shaft may also be beneficial in providing a path through which conduits carrying electrical power / signals may be laid; rather than using a commutator or external attachments, the conduits may simply pass through the hollow shaft, and thus through device 1. As will be appreciated, unlimited travel inerters may also comprise hollow shafts in rotor 6.

[0100] In any case, it will be appreciated that paddle 6a may be offset from baffle 8 by a predefine amount such that, paddle 6a lies closer to a first major baffle surface than to the second major baffle surface (or even abutting the first major baffle surface). This predefined offset may be advantageous in that it may counteract a persistent angular displacement which may arises between first and second terminals 2a, 2b of device 1 during operation. This offset may result in paddle 6a moving to a time-averaged position within chamber 4 that is approximately equidistant from the first and second major baffle surfaces, thereby reducing the likelihood / frequency of bottoming out during operation.

[0101] As will be appreciated, this initial offsetting of paddle 6a with respect to baffle 8 may also be achieved in the case where baffle 8 is rotatably coupled to interior surface 3a of housing 3 — first and second terminals 2a, 2b may be rotated relative to each other (thereby defining the initial offset) prior to coupling with a mechanical system. The same may be said of embodiments where baffle 8 is fixed to interior surface 3a. Other ways to define the initial offset are via alignment of rotor 6 with shaft 5, spring loading rotor 6 such that paddle 6a is biased towards one of the major baffle surfaces, and the like.

[0102] Hence more generally, baffle 8 may comprise first and second major baffle surfaces; and when not in use (for example, prior to use), paddle 6a lies within chamber 4 at a position that is closer to the first major baffle surface than to the second major baffle surface.

[0103] The foregoing discussion discloses and describes merely exemplary embodiments of the present invention. As will be understood by those skilled in the art, the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the disclosure of the present invention is intended to be illustrative, but not limiting of the scope of the invention, as well as other claims. The disclosure, including any readily discernible variants of the teachings herein, defines, in part, the scope of the foregoing claim terminology such that no inventive subject matter is dedicated to the public.

Claims

CLAIMS1. A device for controlling torques arising in a mechanical system, comprising: first and second terminals couplable respectively with first and second parts of the mechanical system; coupled to the first terminal, a housing enclosing a chamber for containing a fluid; coupled to the second terminal, a shaft rotatably coupled to the housing; a rotor coupled to the shaft; and a fluid path coupled to the chamber; wherein the device is configured such that, when in use: the fluid is caused to flow along the fluid path in response to relative rotational motion between the first and second terminals, thereby generating an inertial force due to the mass of the fluid, and the inertial force causes equal and opposite inertance torques to be applied at the first and second terminals respectively, the inertance torques being torques whose magnitude are substantially proportional to the relative rotational acceleration between the first and second terminals.

2. A device according to claim 1 , wherein the rotor and an interior surface of the housing form a back-drivable fluid pump configured such that, when in use, a volumetric displacement of the fluid is substantially proportional to an angular displacement of the rotor.

3. A device according to claim 2, wherein the fluid pump is a progressing cavity pump.

4. A device according to claim 3, wherein the rotor is coupled to the shaft such that, when in use: rotation of the shaft about an axis of rotation of the shaft causes rotation of the rotor about an axis of rotation of the rotor, and the axis of rotation of the rotor follows a path enclosing the axis of rotation of the shaft.

5. A device according to claim 4, comprising: a ring gear coupled to the interior surface of the housing; engaged with the ring gear, a planet gear coupled to the rotor; and a crank coupled between the shaft and the rotor.

6. A device according to claim 5, wherein the crank comprises a thrust bearing for withstanding loads arising along the axis of rotation of the shaft.

7. A device according to claim 1 , wherein: the rotor comprises a paddle; the device comprises a baffle coupled to and extending from an interior surface of the housing towards an axis of rotation of the rotor.

8. A device according to claim 7, wherein: the baffle comprises first and second major baffle surfaces; and a first end of the fluid path is coupled to the chamber at a first position relative to an interior surface of the housing, the first position being closer to the first major baffle surface than to the second major baffle surface, and a second end of the fluid path is coupled to the chamber at a second position relative to an interior surface of the housing, the second position being closer to the second baffle major surface than to the first major baffle surface.

9. A device according to claim 8, wherein the first end is coupled to the first major baffle surface, and / or the second end is coupled to the second major baffle surface.

10. A device according to claim 7 or claim 8, wherein: the paddle comprises first and second major paddle surfaces; and a first end of the fluid path is coupled to the chamber at a first position relative to the rotor, the first position being closer to the than to the second major paddle surface, and a second end of the fluid path may be coupled to the chamber at a second position relative to the rotor, the second position being closer the second paddle major surface than to the first major paddle surface.

11. A device according to claim 10, wherein the first end is coupled to the first major paddle surface, and the second end is coupled to the second major paddle surface.

12. A device according to any one of claims 7 to 11 , wherein the rotor is coupled to the housing via an elastically resilient member.

13. A device according to claim 12, wherein the elastically resilient member is one of a spiral torsion spring, a helical spring, a leaf spring and a torsion bar.

14. A device according to claim 12, wherein: the rotor comprises a hollow shaft; the elastically resilient member is a torsion bar within the hollow shaft, wherein a first end of the torsion bar is coupled to an interior surface of the hollow shaft, and a second end of the torsion bar is coupled to an interior surface of the housing; and the paddle is coupled to the hollow shaft.

15. A device according to claim 14, wherein the hollow shaft is configured so as to form part of a second fluid path when in use.

16. A device according to any one of claims 7 to 15, wherein: the baffle comprises first and second major baffle surfaces; and when not in use, the paddle lies within the chamber at a position that is closer to the first major baffle surface than to the second major baffle surface.

17. A device according to any preceding claim, wherein at least a part of the fluid path is disposed on or within the housing.

18. A device according to any preceding claim, wherein at least a part of the fluid path comprises a helical tube.

19. A device according to any preceding claim, wherein the fluid path comprises a valve for controlling the flow of the fluid along the fluid path.

20. A device according to any preceding claim, wherein the fluid path and the chamber form a closed fluid cycle.

21. A device according to any one of claims 1 to 19, wherein the fluid path and the chamber form an open fluid cycle.

22. A device according to any preceding claim, wherein the device is configured such that, when in use: the fluid is caused to flow along the fluid path in response to relative rotational motion between the first and second terminals, thereby generating a frictional force due to the viscosity of the fluid, and the frictional force causes equal and opposite damping torques to be applied at the first and second terminals respectively, the damping torques being torques whose magnitude are dependent upon the relative rotational velocity between the first and second terminals.

23. A device according to any preceding claim, wherein the first terminal comprises the housing, and / or the second terminal comprises the shaft.

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