Gearbox and method of manufacture

Abstract

An epicyclic gear system comprising a sun gear (10 fig.1); a gear carrier 24 that is mounted concentrically with the sun gear and comprises radially extending carrier arms (26 fig. 3); a planet gear 2

Description

25 10 24 Field

[0001] This invention relates to gearboxes and their manufacture. In particular, the invention relates to epicyclic gearboxes and methods of manufacturing epicyclic gearboxes. Background

[0002] Gearboxes, such as epicyclic gearboxes, can find uses in many industrial installations. For example. Such gearboxes are used in industrial actuators such as valve actuators where the rotary motion of an electric motor is used to drive a valve to open or close. Because the loads on the drive can vary from valve to valve depending on size and other requirements, it is usually the case that a gearbox is needed between the motor and the valve to modify the torque and speed characteristic of the drive applied to the valve.

[0003] Typically, a manufacturer will have a number of different gearbox designs available for customers to select according to their needs. As a practical matter, this means selecting the gearbox with the closest properties to those required and typically results in the selected gearbox being over-specified for any particular use for reliability and safety.

[0004] To date it has not been possible to provide sufficient flexibility in gearbox design to be optimised for all uses. The development of additive manufacturing processes offers an opportunity for bespoke gearbox designs to be produced quickly and cheaply. However, production of separate components means that assembly still remains a challenge.

[0005] This invention seeks to provide a gearbox design that is suitable for additive manufacturing with less assembly required, and a process for manufacturing that allows relatively easy control of the manufacturing process to match the design of the gearbox with user requirements. The invention seeks to address problems that can arise due to the use of additive manufacturing processes. 25 10 24 Summary

[0006] A first aspect of the invention comprises an epicyclic gearbox, comprising an input shaft, an output shaft, and an epicyclic gear system connected between the input shaft and the output shaft; wherein the epicyclic gear system comprises: a sun gear; a gear carrier that is mounted concentrically with the sun gear and comprises radially extending carrier arms; a planet gear mounted at the end of each carrier arm so as to engage the sun gear; a ring gear that extends around and engages the planet gears and is concentric with the sun gear; and a housing enclosing the sun gear, gear carrier, the planet gears, and the ring gear, wherein the housing comprises a side wall that extends around the outside of the sun gear and axial end walls closing the ends of the side wall; wherein each carrier arm has one or more apertures extending axially through the arm; and the housing comprises apertures in the end walls and in the side wall providing communication between the inside and outside of the housing.

[0007] A second aspect of the invention provides a method of manufacturing the gearbox, comprising selective laser sintering input shaft, the output shaft, the sun gear, gear carrier, the planet gears, the ring gear, and the housing as a single component.

[0008] The apertures allow the removal of unsintered material from the interior of the housing though the apertures following selective laser sintering.

[0009] Each planet gear can be mounted on a respective arm by means of a shaft in a bearing, and each shaft has axial grooves extending along its outer surface. This can also allow unsintered material to be removed from bearing surfaces. 25 10 24

[0010] The housing can be a single piece construction.

[0011] The method can comprise determining maximum external dimensions for the gearbox; determining torque and speed input and output parameters; calculating the size and number of teeth for the sun gear, planet gears, and ring gear necessary to provide the torque and speed input and output parameters; and controlling the selective laser sintering to provide the sun gear, planet gears, and ring gear having the calculated sizes and number of teeth.

[0012] There is also disclosed a method of manufacturing an epicyclic gearbox, comprising an input shaft; an output shaft; and an epicyclic gear system connected between the input shaft and the output shaft, comprising a sun gear; a gear carrier that is mounted concentrically with the sun gear and comprises radially extending carrier arms; a planet gear mounted at the end of each carrier arm so as to engage the sun gear; a ring gear that extends around and engages the planet gears and is concentric with the sun gear; and a housing enclosing the sun gear, gear carrier, the planet gears, and the ring gear; wherein the method comprises determining maximum external dimensions for the gearbox; determining torque and speed input and output parameters; calculating the size and number of teeth for the sun gear, planet gears, and ring gear necessary to provide the torque and speed input and output parameters; and controlling a manufacturing process to provide the sun gear, planet gears, and ring gear having the calculated sizes and number of teeth.

[0013] Further aspects of the invention are described below in relation to the drawings. Description of the Drawings

[0014] Figure 1 shows the basic components of an epicyclic gearbox.

[0015] Figure 2 shows an epicyclic gearbox according to an embodiment of the invention.

[0016] Figure 3 shows detail of the epicyclic gearbox shown in Figure 2. Detailed Description 25 10 24

[0017] The basic components of an epicyclic gear arrangement are shown in Figure 1. A sun gear 10 is mounted at the centre of the gear arrangement. A gear carrier 12 is mounted concentrically with the sun gear 10. The gear carrier 12 comprises a number of arms (in this case three arms are shown) extending radially from the centre of the gear carrier 12 and a planet gear 14 is mounted at the end of each arm. Teeth on the planet gears 14 engage teeth on the sun gear 10. A ring gear 16 surrounds the planet gear 14 and teeth on the inner surface of the ring gear 16 engage the teeth on the planet gears 14. In an epicyclic gearbox, an input shaft (not shown) is connected to one of the sun gear, gear carrier, or ring gear, and an output shaft (not shown) is connected to one or other of those to which the input shaft is not connected. For example, an input shaft could be connected to the sun gear and an output shaft could be connected to the ring gear.

[0018] Figures 2 and 3 show an embodiment of an epicyclic gearbox according to an embodiment of the invention that can be made by an additive manufacturing process. The gearbox comprises a sun gear 20 connected to an input shaft 22.

[0019] A gear carrier 24 is mounted concentrically with the sun gear 20. The gear carrier 24 has three arms 26 extending in a radial direction. A planet gear 28 is mounted at the end of each arm 26 by means of a shaft 30 that is located in a bore 32 at the end of the arm 26. The shaft 30 has a series of axial grooves 34 in its outer surface. Apertures 36, 38 are provide in each arm 26 and between the arms 26.

[0020] A ring gear 40 is mounted around the outside of the planet gears 28 concentrically with the sun gear 20, the inwardly projecting teeth of the ring gear 40 engaging the teeth on the planet gears 28. The teeth on the sun gear 20, planet gears 28, and ring gear 40 are dimensioned such that there is a relatively large backlash 42. [0021 ] An output shaft 44 is connected to the gear carrier 24.

[0022] A single-piece housing 46 encloses the components described above. The housing includes a circular side wall 48 that extends around the outside of the ring gear 40, and axial end walls 50 extending across the ends of the side wall 25 10 24 48. The side wall 48 has a series of through apertures 52 so that the inside and outside of the housing 46 are in communication. Further through apertures 54 are provided in the end walls 50. At least some of the apertures 54 in the end wall 50 correspond to the size and shape of the apertures in the gear carrier 24.

[0023] The gearbox shown in Figure 2 and 3 can be made by an additive manufacturing process such as selective laser sintering (SLS). SLS produces solid structures by sintering a shape within a volume of powered material such as nylon or polyamide. At the end of the SLS process, a certain amount of unsintered powder will remain. If this remains within the gearbox described above, it can lead to failures by jamming between moving parts or by increasing friction and abrasion as parts move next to each other. By providing the apertures in the gear carrier 24 and housing 46, the grooves 34 in the planet gear shafts 30, and the backlash 42 between the ger teeth, there is sufficient interconnected space of a suitable size that any remaining powdered material can flow out of the housing 46. The use of SLS means that the gearbox can be manufactured as a single component and parts such as the housing 46 can be of single-piece construction, making assembly simpler.

[0024] The use of an additive manufacturing process is suitable for a parameterised process. In such a process, parameters of the gearbox such as maximum external dimensions, torque and speed input and output parameters are determined. From these parameters, the size and number of teeth for the sun gear, planet gears, and ring gear necessary to provide the torque and speed input and output parameters can be calculated and the manufacturing process controlled to provide the sun gear, planet gears, and ring gear having the calculated sizes and number of teeth. Therefore, the design of each gearbox can be optimised for its intended use.

[0025] Further changes can be made within the scope of the invention.

Claims

25 10 241. An epicyclic gearbox, comprising:an input shaft;an output shaft; andan epicyclic gear system connected between the input shaft and the output shaft, comprising:a sun gear;a gear carrier that is mounted concentrically with the sun gear and comprises radially extending carrier arms;a planet gear mounted at the end of each carrier arm so as to engage the sun gear;a ring gear that extends around and engages the planet gears and is concentric with the sun gear; anda housing enclosing the sun gear, gear carrier, the planet gears, and the ring gear, wherein the housing comprises a side wall that extends around the outside of the sun gear and axial end walls closing the ends of the side wall;whereineach carrier arm has one or more apertures extending axially through the arm; andthe housing comprises apertures in the end walls and in the side wall providing communication between the inside and outside of the housing.25 10 242. An epicyclic gearbox as claimed in claim 1, wherein each planet gear is mounted on a respective arm by means of a shaft in a bearing, and each shaft has axial grooves extending along its outer surface.

3. An epicyclic gearbox as claimed in claim 1 or 2, wherein the housing is a single piece construction.

4. A method of manufacturing a gearbox as claimed in claim 1, 2, or 3, comprising selective laser sintering input shaft, the output shaft, the sun gear, gear carrier, the planet gears, the ring gear, and the housing as a single component.

5. A method as claimed in claim 4, comprising removing unsintered material from the interior of the housing though the apertures following selective laser sintering.

6. A method as claimed in claim 4 or 5, comprising:determining maximum external dimensions for the gearbox;determining torque and speed input and output parameters;calculating the size and number of teeth for the sun gear, planet gears, and ring gear necessary to provide the torque and speed input and output parameters; andcontrolling the selective laser sintering to provide the sun gear, planet gears, and ring gear having the calculated sizes and number of teeth.

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