GB2555854A

GB2555854A - Rack and pinion systems

Info

Publication number: GB2555854A
Application number: GB1619253.6A
Authority: GB
Inventors: Brakes David
Original assignee: Airbus Operations Ltd
Current assignee: Airbus Operations Ltd
Priority date: 2016-11-14
Filing date: 2016-11-14
Publication date: 2018-05-16

Abstract

A rack and pinion system comprising a roller component 10 configured to engage with a toothed component 11. The roller component has first, second and third support members 13a-c, a plurality of first rollers 12a, and a plurality of second rollers 12b. Each first roller has an outer end connected to the first support member and an inner end connected to a first side of the second support member. Each second roller comprises an outer end connected to the third support member and an inner end connected to a second side of the second support member opposite to the first side. Each roller is rotatable about a roller axis perpendicular to the actuation direction. Each second roller may share a common roller axis with a corresponding first roller. Each roller may have a sleeve rotatably mounted on a fixed pin. The ratio of the pin diameter to the axial length of each roller may be greater than 0.5. The support members may be discs. The rack may comprise a slew ring. Also disclosed is a foldable aerodynamic structure (such as the folding aircraft wing-tip of figure 5), and a toothed component configured to engage the abovementioned rack and pinion system.

Description

(54) Title of the Invention: Rack and pinion systems Abstract Title: Double roller rack and pinion system (57) A rack and pinion system comprising a roller component 10 configured to engage with a toothed component 11.

The roller component has first, second and third support members 13a-c, a plurality of first rollers 12a, and a plurality of second rollers 12b. Each first roller has an outer end connected to the first support member and an inner end connected toa first side of the second support member. Each second roller comprises an outer end connected to the third support member and an inner end connected to a second side of the second support member opposite to the first side. Each roller is rotatable about a roller axis perpendicular to the actuation direction. Each second roller may share a common roller axis with a corresponding first roller. Each roller may have a sleeve rotatably mounted on a fixed pin. The ratio of the pin diameter to the axial length of each roller may be greater than 0.5. The support members may be discs. The rack may comprise a slew ring. Also disclosed is a foldable aerodynamic structure (such as the folding aircraft wing-tip of figure 5), and a toothed component configured to engage the abovementioned rack and pinion system.

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Fig. 1 (Prior Art)

Fig. 2a

X

Fig. 2b

23a ²⁴

Fig. 3a

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Fig. 3b

(iii) (ii)

Fig. 4a

(i)

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Fig. 5

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Fig. 7

RACK AND PINION SYSTEMS

TECHNICAL FIELD [0001] The present invention relates to a rack and pinion system comprising a roller component configured to engage with a toothed component such that when the roller component is engaged with the toothed component, rotational movement of one of the roller component and the toothed component drives linear movement along an actuation direction of the other one of the roller component and the toothed component, a toothed component configured to engage with such a roller component, and a foldable aerodynamic structure comprising a roller component and a toothed component.

BACKGROUND [0002] In some known aircraft designs (typically military aircraft) each of the aircraft's wings comprises an outer region which may be folded about a generally chordwise hinge line, between a flight configuration and a ground configuration. Recently, folding wing-tip arrangements have been proposed for commercial airliners which comprise an outer region which folds by rotating about a substantially vertical (or slightly offset from vertical) axis (with reference to the operational orientation of the aircraft). Such arrangements may enable the aircraft to occupy a relatively small space when on the ground, but to still have a relatively large wing span for flight. The movement of the outer region of the wing is typically effected by an actuator.

[0003] The requirements for a folding wing actuator are very demanding. In particular, the actuator is required to handle high loads, and may also be required to stably maintain the outer region of the wing in various different positions, with a high degree of positional accuracy.

SUMMARY [0004] A first aspect of the present invention provides a rack and pinion system comprising a roller component configured to engage with a toothed component such that when the roller component is engaged with the toothed component, rotational movement of one of the roller component and the toothed component drives linear movement along an actuation direction of the other one of the roller component and the toothed component. The roller component comprises a first support member; a second support member; a third support member; a plurality of first rollers; and a plurality of second rollers. Each of the first rollers comprises an outer end connected to the first support member and an inner end connected to a first side of the second support member such that each first roller is rotatable relative to the first and second support members about a roller axis perpendicular to the actuation direction. Each of the second rollers comprises an outer end connected to the third support member and an inner end connected to a second side of the second support member opposite to the first side, such that each second roller is rotatable relative to the second and third support members about a roller axis perpendicular to the actuation direction.

[0005] Optionally, the positions of the second rollers relative to the second side of the second support member correspond to the positions of the first rollers relative to the first side of the second support member, such that each second roller shares a common roller axis with a corresponding first roller.

[0006] Optionally, each roller comprises a sleeve rotatably mounted on a pin fixedly connected to the support member. Optionally, an inner surface of the sleeve and/or an outer surface of the pin comprises a low friction coating.

[0007] Optionally, the ratio of the diameter of the pin to the axial length of each roller is greater than 0.5.

[0008] Optionally, the roller component comprises a roller pinion and the toothed component comprises a toothed rack, wherein each of the first, second and third support members comprises a support disc arranged to rotate about a common pinion axis, and wherein each roller axis is parallel to the pinion axis.

[0009] Optionally, each first roller is mounted at a first predetermined distance from the pinion axis, and at a second predetermined distance from each immediately adjacent first roller, wherein the values of the first predetermined distance and the second predetermined distance are based on the configuration of the toothed component. Optionally, the values of the first predetermined distance and the second predetermined distance are such that, when the roller component is in operation on the toothed component, at least two first rollers are in contact with the toothed component at all times during the operation. Optionally, the toothed rack comprises a slew ring. Optionally, the pitch circle diameter of the roller pinion is less than 70mm.

[0010] Optionally, the roller component comprises a roller rack and the toothed component comprises a pinion. Optionally, the roller rack comprises a slew ring.

[0011] A second aspect of the present invention provides a toothed component configured to engage with a roller component of a rack and pinion system according to the first aspect. The toothed component comprises a first set of teeth configured to engage with the plurality of first rollers, a second set of teeth configured to engage with the plurality of second rollers, and a groove between the first set of teeth and the second set of teeth configured to receive the second support member.

[0012] A third aspect of the present invention provides a foldable aerodynamic structure for an aircraft. The foldable aerodynamic structure comprises an inner region; an outer region moveable relative to the inner region; a roller component fixed to one of the inner region and the outer region; and a toothed component fixed to the other one of the inner region and the outer region and engaged with the roller component. The foldable aerodynamic structure is configured such that movement of the outer region relative to the inner region is driveable by rotational movement of one of the roller component and the toothed component.

[0013] Optionally, the roller component is a roller pinion fixed to the inner region, and the toothed component is a toothed rack fixed to the outer region. Optionally, the roller component is a roller rack fixed to the outer region, and the toothed component is a pinion fixed to the inner region. Optionally, the roller component is a roller component according to the first aspect. Optionally, the inner region comprises a root section of an aircraft wing, the outer region comprises a tip section of an aircraft wing, and the tip section is rotatable relative to the root section.

BRIEF DESCRIPTION OF THE DRAWINGS [0014] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0015] Figure 1 shows a schematic view of a prior art roller pinion;

[0016] Figure 2a is a cross-section through an example roller component engaged with an example toothed component;

[0017] Figure 2b is a schematic perspective view of the example roller component and the example toothed component of Figure 2a;

[0018] Figure 3a is a cross-section through an example roller component;

[0019] Figure 3b is a schematic side-view of part of the example roller component of

Figure 3a engaged with an example toothed component;

[0020] Figure 4a shows schematic views of an example damaged roller component engaged with an example toothed component, in three different relative positions of the roller component and the toothed component;

[0021] Figure 4b shows schematic views of an example roller component engaged with an example damaged toothed component, in three different relative positions of the roller component and the toothed component;

[0022] Figure 5 shows a schematic view of an example aircraft folding wing-tip;

[0023] Figure 6 shows a schematic view of an example aircraft folding wing-tip actuation mechanism comprising an example roller component; and [0024] Figure 7 shows a schematic view of an example aircraft folding wing-tip actuation mechanism comprising a different example roller component.

DETAILED DESCRIPTION [0025] The examples described below relate to rack and pinion systems which include roller components. The use of roller components may reduce or avoid the need to grease the example rack and pinion systems, thereby reducing maintenance overheads and improving reliability as compared with conventional rack and pinion systems. The example rack and pinion systems described herein are suitable for actuating folding wing-tips on aircraft, including commercial airliners.

[0026] Roller pinions are used for high precision linear and rotary actuation in industrial applications such as CNC (computer numeric control) machining gantries, plasma cutting tables and automation gearheads for robotics. Figure 1 shows a prior art roller pinion 1 and rack 2. The roller pinion 1 comprises a pair of discs 3a, 3b that support between them a circumferential series of rollers 4. The profile of the rack 2 is shaped to receive the rollers 4 such that their natural path takes them smoothly up and down the face of each tooth. In contrast to a conventional rack and pinon system (spur gear), the rollers 4 roll rather than slide down the rack teeth. As there is no relative motion between the roller surface and rack, the rack does not require lubrication.

[0027] Known roller pinions such as the one shown in Figure 1 are not intended to handle the relatively high loads associated with actuating an aircraft folding wing-tip. Scalingup a roller pinion and rack system of this design to a point where it is able to handle sufficiently large loads would result in the system being too large and heavy to install on an aircraft wing. It will be appreciated that the space available for a folding wing-tip actuation mechanism is severely constrained by the aerofoil shape of the wing. Furthermore, increasing the diameter of the rollers would require increasing the pitch circle diameter (PCD) of the pinion, which is undesirable as it increases the pinion torque required to support any given rack load. To be useable in a folding wing-tip actuation mechanism, a roller rack and pinion system therefore needs to be relatively lightweight and compact (including having a relatively small pinion PCD) as well as being able to handle high loads (30-60 kN, depending on the architecture of the folding wing). The following example roller rack and pinion systems have novel structures, which enable them to handle high loads whilst having a small pinion PCD and a small overall size.

[0028] The load that a rack and pinion system is able to handle is dependent on the contact area between the rack and the pinion when they are engaged with each other (a larger contact area enables a greater load) and the strength of the gear teeth. In a rack and pinion system in which one of the rack and the pinion comprises a roller component, the load capability is further dependent on the roller journal contact pressure (that between the sleeve and the roller pin), the pin strength and the strength of the pin support in the pinion disks (i.e. bearing strength in the holes). The rack tooth contact area and the roller journal contact area can be increased by increasing the axial length of the rollers and the width of the rack. This improves the rack tooth strength. However; increasing the axial length of the rollers without increasing their diameter reduces their bending strength and their bending stiffness (thereby increasing the pin bending curvature); the latter results in an uneven contact pressure distribution on the roller, which adversely impacts load capability. Increasing the diameter of the rollers increases the roller pin strength and stiffness, lowers the average and peak contact pressure in the roller journal, improves the pin support strength and produces bigger (and therefore stronger) teeth on the rack. However, as mentioned above, increasing the diameter of the rollers has the consequence that the pinion PCD must also increase, which disadvantageously increases the pinion torque required to support any given rack load.

[0029] Examples of the present invention provide a solution which allows the contact area of a roller pinion system to be increased without increasing the roller radius, and therefore without increasing the pinion PCD. In particular, the examples effectively increase the axial length of the roller whilst avoiding the risk of pin bending. This is achieved by dividing each roller axially into two parts, with each part being supported at both ends. Thus the unsupported span of each roller part can be relatively short, to avoid pin bending under high loads, whilst the total axial length of a given roller can be relatively long, to provide a large contact area for reacting large loads.

[0030] Figures 2a and 2b show an example roller component for use in an aircraft folding wing-tip actuation mechanism. The roller component is configured to engage with a toothed component such that when the roller component is engaged with the toothed component, rotational movement of one of the roller component and the toothed component drives linear movement along an actuation direction of the other one of the roller component and the toothed component. The roller component comprises a first support member; a second support member and a third support member. The roller component also comprises a plurality of first rollers and a plurality of second rollers. Each of the first rollers comprises an outer end connected to the first support member and an inner end connected to a first side of the second support member such that each first roller is rotatable relative to the first and second support members about a roller axis perpendicular to the actuation direction. Each of the second rollers comprises an outer end connected to the third support member and an inner end connected to a second side of the second support member opposite to the first side, such that each second roller is rotatable relative to the second and third support members about a roller axis perpendicular to the actuation direction. A toothed component configured to engage with the example roller component comprises a first set of teeth configured to engage with the plurality of first rollers, a second set of teeth configured to engage with the plurality of second rollers, and a groove between the first set of teeth and the second set of teeth configured to receive the second support member.

[0031] In the example of Figures 2a and 2b, the roller component comprises a roller pinion 10 and the toothed component comprises a toothed rack 11. The roller pinion 10 comprises first, second and third support members in the form of first, second and third support discs 13a, 13b and 13c, which are arranged to rotate (as indicated by the arrow in Figure 2b) about a pinion axis X and are coaxial with respect to the pinion axis X. The second support disc 13a is between the first and third support discs 13b, 13c. There are spacer portions between adjacent support discs. The spacer portions have a smaller diameter than the support discs, such that a circumferential groove is formed between the first and second support discs 13a, 13b, and also between the second and third support discs 13b, 13c. The spacer portions may be formed integrally with the support discs, or may be separate components to which the support discs are attached.

[0032] A plurality of first rollers 12a is arranged between the first support disc 13a and the second support disc 13b and plurality of second rollers 12b is arranged between the second support disc 13b and the third support disc 13c. The roller axis Y of each roller 12a, 12b is parallel to the pinion axis X. Each roller comprises a sleeve 15 rotatably mounted on a pin 14 (e.g. in the manner of a journal bearing). In the illustrated example, each pin 14 comprises a low friction coating (such as, e.g., Kamatics KAron or Rexnord Rexlon). This advantageously means that the rollers do not need to be greased or otherwise lubricated, and enables them to carry high loads. In some examples the inner surface of the sleeves 15 comprises a low friction coating, instead of or additionally to the pins 14 comprising a low friction coating. However; alternative examples are possible in which grease is used instead of a low friction coating, or in which each sleeve is replaced by a series of needle rollers arranged circumferentially around the pin.

[0033] The pins 14 may comprise plain pins, bolts or any combination of such components. The pins 14 are fixedly connected to the support discs 13a, 13b, 13c. In some examples the pins 14 may be formed integrally with the support discs 13a, 13b, 13c; however, it is expected that generally the pins 14 will comprise separate components fixedly connected to the support discs. In some examples the pins of a pair of correspondingly positioned first and second rollers 12a, 12b are formed by a single component (e g. a bolt or a plain pin) which passes through a hole in the second support disc 13b. Advantageously, forming the pins of both rollers of a corresponding pair of rollers as a single component means that the forces experienced by that component are balanced during operation of the roller pinon 10. This gives the pins 14 a high strength (as compared to arrangements where individual pins are used for each roller), enabling the roller pinion 10 to handle large loads.

[0034] In the particular example the axial length of each roller is 12mm. It is generally expected that the first rollers 12a will have the same axial length as the second rollers 12b, although that need not necessarily be the case. In the illustrated example, the diameter of each roller 12a, 12b (that is, the outside diameter of the sleeve 15) is 13mm. The contact area between the rack 11 and the pinion 10 depends on the diameter and on the axial length of the rollers 12a, 12b, and affects how much load the roller pinion 10 can handle. A larger contact area enables a larger load to be reacted. On the other hand, the aspect ratio of the diameter to the axial length of each unsupported roller section (in particular, the pin of each roller) affects how much load that roller section can take without risk of excessive bending of the pin 14. The aspect ratio is preferably in the range of 0.5 to 1.0; however ratios outside this range are also possible. In the illustrated example, the aspect ratio of the rollers is relatively low (e.g. as compared to conventional roller pinions known in the art), but the contact area is relatively high, due to providing two coaxial rollers in series. In the illustrated example the thickness of each support disc is 6mm and, the first, second and third support discs 13a, 13b, 13c are all of equal thickness, although that need not necessarily be the case. The thickness of each support disc 13a, 13b, 13c may be as small as possible for a given load handling ability, to minimize the overall size of the rack and pinion system. It will be appreciated that, for any given example, the particular values of the above-mentioned parameters will depend on the particular application of that example.

[0035] The first rollers 12a are arranged in a ring. Each first roller 12a is mounted at a first predetermined distance from the pinion axis X, and at a second predetermined distance from each immediately adjacent first roller. The first and second predetermined distances may, but need not, have different values. The values of the first and second predetermined distances are based on the configuration of the toothed component 11, and will be selected, together with other parameters such as pinion PCD and rack radius (if the rack is curved, as with a slew ring), to be suitable for the intended application of a particular example. For example, the pinion PCD may be selected such that the torque required to support a particular rack load is less than or equal to a particular value. In some examples the values of the first and second predetermined distances are such that, when the roller component is in operation on the toothed component, at least two first rollers 12a (and, therefore, at least two second rollers 12b) are in contact with the toothed rack 11 at all times during the operation. Ensuring that at least two first rollers 12a are in contact with the rack 11 at all times means that the rack and pinion system experiences little or no backlash.

[0036] In the particular example, the positions of the second rollers 12b relative to the second side of the second support disc 13b correspond to the positions of the first rollers 12a relative to the first side of the second support disc 13b. As a result, each second roller 12b is coaxial with (that is, shares a common roller axis with) a corresponding first roller 12a. Additionally, as with the first rollers 12a, each second roller 12b is mounted at the first predetermined distance from the pinion axis X, and at the second predetermined distance from each immediately adjacent second roller. Other examples are possible in which the positions of one or more of the second rollers 12b relative to the second side of the second support disc 13b do not correspond to the positions of any first rollers 12a relative to the first side of the second support disc 13b, such that the one or more second rollers 12b are not coaxial with any first rollers 12a. Such examples may be advantageous for reducing or eliminating backlash and thus increasing the positional accuracy achievable by such example rack and pinion systems.

[0037] The toothed rack 11 comprises a first set of teeth 17a configured to engage with the plurality of first rollers 12a and a second set of teeth 17b configured to engage with the plurality of second rollers 12b. The first set of teeth 17a are aligned with the second set of teeth 17b when the toothed rack 11 is viewed from the side, as in Figure 2b, such that only the first set of teeth 17a is visible in this figure. The width (in a direction parallel to the pinion axis) of the first set of teeth 17a is slightly less than the distance between the first support disc 13a and the second support disc 13b. The width (in a direction parallel to the pinion axis) of the second set of teeth 17b is slightly less than the distance between the second support disc 13b and the third support disc 13c. The tooth widths are preferably as large as possible, whilst still being able to engage with the roller pinion 10, to maximize the contact area between the rack 11 and the roller pinion 10. The toothed rack 11 also comprises a groove (slot) 16 between the first set of teeth 17a and the second set of teeth 17a. The groove 16 is configured to receive part of the second support disc 13b. In some examples the toothed rack may comprise a slew ring. In any given example, the radius of the slew ring may be selected based on the desired load handling ability of the example rack and pinion system.

[0038] Figures 3a and 3b show a further example roller component configured to engage with a toothed component such that when the roller component is engaged with the toothed component, rotational movement of one of the roller component and the toothed component drives linear movement along an actuation direction of the other one of the roller component and the toothed component. Like the roller component of Figures 2a and 2b, the roller component of Figures 3a and 3b comprises a first support member; a second support member and a third support member, as well as a plurality of first rollers and a plurality of second rollers. Each of the first rollers comprises an outer end connected to the first support member and an inner end connected to a first side of the second support member such that each first roller is rotatable relative to the first and second support members about a roller axis perpendicular to the actuation direction. Each of the second rollers comprises an outer end connected to the third support member and an inner end connected to a second side of the second support member opposite to the first side, such that each second roller is rotatable relative to the second and third support members about a roller axis perpendicular to the actuation direction. A toothed component configured to engage with the example roller component comprises a first set of teeth configured to engage with the plurality of first rollers, a second set of teeth configured to engage with the plurality of second rollers, and a groove between the first set of teeth and the second set of teeth configured to receive the second support member.

[0039] In Figures 3a and 3b, the roller component comprises a roller rack 20 and the toothed component comprises a pinion 21 arranged to rotate (as indicated by the arrow in Figure 3b) about a pinion axis X. The roller rack 20 comprises first, second and third support members in the form of first, second and third support beams 23a, 23b and 23c. The second support beam 23a is between the first and third support beams 23b, 23c. There are spacer portions between adjacent support beams. The spacer portions have a smaller width (in the horizontal direction, relative to Figure 3a) than the support beams, such that a groove or slot is formed between the first and second support beams 23a, 23b, and also between the second and third support beams 23b, 23c. The grooves in the roller rack 20 are configured to receive teeth of the pinion 21 when the roller rack 20 and pinion 21 are engaged. The spacer portions may be formed integrally with the support beams, or may be separate components to which the support beams are attached.

[0040] A plurality of first rollers 22a is arranged between the first support beam 23a and the second support beam 23b and plurality of second rollers 22b is arranged between the second support beam 23b and the third support beam 23c. The roller axis Y of each roller 22a, 22b is parallel to the pinion axis X. Each roller comprises a sleeve 25 rotatably mounted on a pin 24 (e.g. in the manner of a journal bearing). The rollers 22a, 22b, the components thereof, and their relative arrangements may have any or all of the same features as the rollers 12a, 12b, and components thereof of the roller pinion 10 described above. Alternative examples are possible in which each sleeve is replaced by a series of needle rollers arranged circumferentially around the pin.

[0041] The support beams 23a, 23b, 23c may each have the same shape, size and configuration. The support beams may be straight or curved. In the particular illustrated example, the thickness (in the direction of the roller axes) of each support beam 23a, 23b, 23c is 6mm andthe first, second and third support beams 23a, 23b, 23c are all of equal thickness, although that need not necessarily be the case. The thickness of each support beam 23 a, 23b, 23c may be as small as possible for a given load handling ability, to minimize the overall size of the rack and pinion system. It will be appreciated that, for any given example, the particular values of the above-mentioned parameters will depend on the particular application of that example.

[0042] As can be seen from Figure 3b, the first rollers 22a are arranged in a line adjacent to an edge of the support beam 23a. Each first roller 22a is mounted at a first predetermined distance H from a lower (with respect to the orientation shown in Figure 3b) edge of the first support beam 23a (and the second support beam 23b), such that the line of first rollers 22a follows the curvature of the support beams. Each first roller 22a is mounted at a second predetermined distance D from each immediately adjacent first roller. The first and second predetermined distances may, but need not, have different values. The values of the first and second predetermined distances are based on the configuration of the toothed component 21, and will be selected, together with other parameters such as pinion PCD and rack radius (if the rack is curved, as with a slew ring), to be suitable for the intended application of a particular example. For example, the pinion PCD may be selected such that the torque required to support a particular rack load is less than or equal to a particular value. In some examples the values of the first and second predetermined distances are such that, when the roller component is in operation on the toothed component, at least two first rollers 22a (and, therefore, at least two second rollers 22b) are in contact with the toothed pinion 21 at all times during the operation. Ensuring that at least two first rollers 22a are in contact with the pinon 21 at all times means that the rack and pinion system experiences little or no backlash.

[0043] In the particular example, the positions of the second rollers 22b relative to the second side of the second support beam 23b correspond to the positions of the first rollers 22a relative to the first side of the second support beam 23b. As a result, each second roller 22b is coaxial with (that is, shares a common roller axis with) a corresponding first roller 22a. Additionally, each second roller 22b is mounted at the first predetermined distance H from the lower edge of the second support beam 23b (and the third support beam 23 c), and at the second predetermined distance D from each immediately adjacent second roller. Other examples are possible in which the positions of one or more of the second rollers 22b relative to the second side of the second support beam 23b do not correspond to the positions of any first rollers 22a relative to the first side of the second support beam 23b, such that the one or more second rollers 22b are not coaxial with any first rollers 22a. Such examples may be advantageous for reducing or eliminating backlash and thus increasing the positional accuracy achievable by such example rack and pinion systems.

[0044] The pinon 21 comprises a first set of teeth 27a configured to engage with the plurality of first rollers 22a and a second set of teeth 27b configured to engage with the plurality of second rollers 12b. The first set of teeth 27a are aligned with the second set of teeth 27b when the toothed pinion 21 is viewed from the side, as in Figure 3b, such that only the first set of teeth 27a is visible in this figure. The width (in a direction parallel to the pinion axis) of the first set of teeth 27a is slightly less than the distance between the first support beam 23a and the second support beam 23b. The width (in a direction parallel to the pinion axis) of the second set of teeth 27b is slightly less than the distance between the second support beam 23b and the third support beam 23c. The tooth widths are preferably as large as possible, whilst still being able to engage with the roller rack 20, to maximize the contact area between the roller rack 20 and the pinion 21. The pinion 21 also comprises a groove (slot) 26 (visible in Figure 3a but not in Figure 3b) between the first set of teeth 27a and the second set of teeth 27a. The groove 26 is configured to receive part of the second support beam 23b.

[0045] Example rack and pinion systems according to the present invention, in which either the rack or the pinion comprises a roller component, may be highly fault-tolerant and therefore very reliable. This is partly because, as discussed above, they do not require regular greasing. However, it is also because the rack and pinion can be configured such that two pinion teeth (in the case of a roller rack) or two pinion rollers (in the case of a roller pinion) are in contact with the rack at all times during operation of the rack and pinion system. As a result, the system may continue to operate if a rack tooth/roller or a pinion tooth/roller is missing or damaged. Figures 4a and 4b illustrate how this is achieved, for a roller pinion with a missing roller, and a rack with a damaged tooth, respectively.

[0046] Figure 4a shows three consecutive relative positions (i), (ii) and (iii) of a clockwise-rotating example roller pinion 40 with a missing roller (as indicated by the gap 42) and a toothed rack 41. The example roller pinion 40 may have any or all of the features of the example roller pinion 10 described above. In the first position (i), the missing roller would have been fully engaged with the rack 41 and would have been able to react loads in both the clockwise and anticlockwise directions. Even with this roller missing, the roller pinion 40 is still able to react both clockwise and anticlockwise loads in this position, because the forward (with respect to the rotation direction) surface of the trailing roller immediately adjacent the gap 42 is in contact with the rack, and the rearward surface of the leading roller immediately adjacent the gap 42 is in contact with the rack. In the second position (i), both the trailing roller and the leading roller are still in contact with the rack, although the surface area of the leading roller in contact with the rack is very small. In the third position (iii) only the trailing roller is in contact with the rack. Thus it can be seen that, even as the roller pinion 40 moves through the positions in which the missing roller would have been engaged with the rack 41, at least one roller is always in contact with the rack. The ability of the roller pinion 40 to drive linear movement of the rack 41 is therefore unaffected.

[0047] Figure 4b illustrates that the same principles apply in the situation in which a roller pinion 43 is engaged with a rack 44 having a damaged tooth 45. In particular, there is always a leading face of a roller in contact with an undamaged tooth at all relative positions of the rack 44 and pinion 43, so that the ability of an example roller pinion according to the invention to drive linear movement of a rack is unaffected by the loss or damage of an individual rack tooth.

[0048] It will therefore be appreciated that the ability of an example roller pinion according to the invention to drive linear movement of a rack is unaffected by the loss or damage of either an individual pinion roller or an individual rack tooth. The same is true in respect of a toothed pinion engaged with an example roller rack according to the invention.

[0049] As mentioned above, example rack and pinion systems in which one of the rack and the pinion comprises a roller component may be advantageously used in aircraft folding wing-tip actuation mechanisms. The implementation of a roller component as part of a folding wing-tip actuation mechanism will now be discussed in detail with reference to Figures 5-7.

[0050] Figure 5 is a perspective top view (relative to an operational orientation of the aircraft) of a foldable aerodynamic structure for an aircraft. The structure comprises an inner region, and an outer region moveable relative to the inner region. In the illustrated example the structure is an aircraft wing 50, the inner region comprises a root section 51 of the wing, and the outer region comprises a tip section 52 of the wing. The tip section 52 is rotatable relative to the root section 51 about an axis Z. The tip section 52 is moveable between a fully extended position (shown in solid lines on Figure 5) and at least one folded position (shown in dashed lines on Figure 5).

[0051] A roller component is fixed to one of the inner region and the outer region and a toothed component is fixed to the other one of the inner region and the outer region and is engaged with the roller component. The foldable aerodynamic structure is configured such that movement of the outer region relative to the inner region is driveable by rotational movement of one of the roller component and the toothed component. For example, the roller component and the toothed component may be comprised in an actuation mechanism for actuating movement of the outer region relative to the inner region. The roller component and the toothed component may together comprise a rack and pinion system.

[0052] Figure 6 shows an example actuation mechanism 60 for the foldable aerodynamic structure of Figure 5. The example actuation mechanism 60 comprises a toothed component in the form of a rack 61. The rack is engaged with a roller component in the form of a roller pinion 62. The rack 61 is fixed to a structural part 65 of the wing tip section 52, and the roller pinion 62 is fixed to a structural part 64 of the wing root section 51.

[0053] Rotation of the roller pinion 62 can be driven by any suitable drive arrangement (e.g. a motor) known in the art. Engagement between the roller pinion 62 and the rack 61 causes rotation of the roller pinion 62 to drive linear (in this case, circumferential with respect to the slew ring) movement of the rack 61. Clockwise rotation of the roller pinion 62 drives anticlockwise movement of the rack 61 (and thereby folding of the wing 50) and anticlockwise rotation of the roller pinion 62 drives clockwise movement of the rack 61 (and thereby extension/unfolding of the wing 50). The teeth of the rack 61 are shaped to engage with the rollers of the roller pinion 62. The engagement of the roller pinion 62 and the rack may have any or all of the features of the engagement of the roller pinon 10 and the rack 11 described above in relation to Figures 2a-b and 4a-b.

[0054] In some examples, the roller pinion 62 is of the same type as the roller pinion 10 described above in relation to Figures 2a and 2b, and may have any or all of the features of that example. It is advantageous for the roller pinion 62 to be of the same type as the roller pinion 10, because of the particular advantages described above which are provided by the roller pinion 10. However; alternative examples are also possible in which the roller pinion is of a conventional roller pinion design, e g. the design shown in Figure 1.

[0055] Figure 7 shows a different example actuation mechanism 70 for the foldable aerodynamic structure of Figure 5. The example actuation mechanism 70 comprises a roller component in the form of a roller rack 71. The roller rack 71 is engaged with a toothed component in the form of a pinion 72. The roller rack 71 is fixed to a structural part 75 of the wing tip section 52, and the pinion 72 is fixed to a structural part 74 of the wing root section

51.

[0056] Rotation of the pinion 72 can be driven by any suitable drive arrangement known in the art. Engagement between the pinion 72 and the roller rack 71 causes rotation of the pinion 72 to drive linear (in this case, circumferential with respect to the slew ring) movement of the roller rack 71. Clockwise rotation of the pinion 72 drives anticlockwise movement of the roller rack 71 (and thereby folding of the wing 50) and anticlockwise rotation of the pinion 72 drives clockwise movement of the roller rack 71 (and thereby extension/unfolding of the wing 50). The teeth of the pinion 72 are shaped to engage with the rollers of the roller rack

71. The engagement of the pinion 72 and the roller rack 71 may have any or all of the features of the engagement of the pinon 21 and the roller rack 20 described above in relation to Figures 3a-b and 4a-b.

[0057] In some examples, the roller rack 71 is of the same type as the roller rack 20 described above in relation to Figures 3a and 3b, and may have any or all of the features of that example. It is advantageous for the roller rack 71 to be of the same type as the roller rack 20, because of the particular advantages described above which are provided by the roller rack

20. However; alternative examples are also possible in which the roller pinion 62 is of a conventional roller rack design.

[0058] Although the particular examples of Figures 5-7 relate to folding wing-tip actuation mechanisms, other examples are possible in which the foldable aerodynamic surface is not a wing.

[0059] It should also be noted that the example roller components described above, although particularly advantageous for use in aircraft foldable aerodynamic surface actuation mechanisms, may also be advantageously used in various other applications which may or may not be related to aircraft. This may particularly be the case for applications in which the space available for the actuation mechanism is constrained, and/or in which the load to be handled by the actuation mechanism is relatively high.

[0060] Although the invention has been described above with reference to one or more preferred examples or embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

Claims

CLAIMS:

1. A rack and pinion system comprising a roller component configured to engage with a toothed component such that when the roller component is engaged with the toothed component, rotational movement of one of the roller component and the toothed component drives linear movement along an actuation direction of the other one of the roller component and the toothed component, the roller component comprising:

a first support member; a second support member; a third support member;

a plurality of first rollers, each comprising an outer end connected to the first support member and an inner end connected to a first side of the second support member such that each first roller is rotatable relative to the first and second support members about a roller axis perpendicular to the actuation direction; and a plurality of second rollers, each comprising an outer end connected to the third support member and an inner end connected to a second side of the second support member opposite to the first side, such that each second roller is rotatable relative to the second and third support members about a roller axis perpendicular to the actuation direction.

2. A rack and pinion system according to claim 2, wherein the positions of the second rollers relative to the second side of the second support member correspond to the positions of the first rollers relative to the first side of the second support member, such that each second roller shares a common roller axis with a corresponding first roller.

3. A rack and pinion system according to any preceding claim, wherein each roller comprises a sleeve rotatably mounted on a pin fixedly connected to the support member.

4. A rack and pinion system according to claim 3, wherein an inner surface of the sleeve and/or an outer surface of the pin comprises a low friction coating.

5. A rack and pinion system according to any preceding claim, wherein the ratio of the diameter of the pin to the axial length of each roller is greater than 0.5.

6. A rack and pinion system according to any preceding claim, wherein the roller component comprises a roller pinion and the toothed component comprises a toothed rack, wherein each of the first, second and third support members comprises a support disc arranged to rotate about a common pinion axis, and wherein each roller axis is parallel to the pinion axis.

7. A rack and pinion system according to claim 6, wherein each first roller is mounted at a first predetermined distance from the pinion axis, and at a second predetermined distance from each immediately adjacent first roller, wherein the values of the first predetermined distance and the second predetermined distance are based on the configuration of the toothed component.

8. A rack and pinion system according to claim 7, wherein the values of the first predetermined distance and the second predetermined distance are such that, when the roller component is in operation on the toothed component, at least two first rollers are in contact with the toothed component at all times during the operation.

9. A rack and pinion system according to any of claims 6 to 8, wherein the toothed rack comprises a slew ring.

10. A rack and pinion system according to any of claims 6 to 9, wherein the pitch circle diameter of the roller pinion is less than 70mm.

11. A rack and pinion system according to any of claims 1 to 4, wherein the roller component comprises a roller rack and the toothed component comprises a pinion.

12. A rack and pinion system according to claim 11, wherein the roller rack comprises a slew ring.

13. A toothed component configured to engage with a roller component of a rack and pinion system according to any of claims 1 to 12, the toothed component comprising a first set of teeth configured to engage with the plurality of first rollers, a second set of teeth configured to engage with the plurality of second rollers, and a groove between the first set of teeth and the second set of teeth configured to receive the second support member.

14. A foldable aerodynamic structure for an aircraft, the foldable aerodynamic structure comprising:

an inner region;

an outer region moveable relative to the inner region; a roller component fixed to one of the inner region and the outer region; and a toothed component fixed to the other one of the inner region and the outer region and engaged with the roller component;

wherein the foldable aerodynamic structure is configured such that movement of the outer region relative to the inner region is driveable by rotational movement of one of the roller component and the toothed component.

15. A foldable aerodynamic structure according to claim 14, wherein the roller component is a roller pinion fixed to the inner region, and the toothed component is a toothed rack fixed to the outer region.

16. A foldable aerodynamic structure according to claim 14, wherein the roller component is a roller rack fixed to the outer region, and the toothed component is a pinion fixed to the inner region.

17. A foldable aerodynamic structure according to claim 14, wherein the roller component is a roller component according to any of claims 1 to 12.

18. A foldable aerodynamic structure according to any of claims 14 to 17, wherein the inner region comprises a root section of an aircraft wing, and the outer region comprises a tip section of an aircraft wing, and wherein the tip section is rotatable relative to the root section.

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