EP2152489A1

EP2152489A1 - A housing for a gearbox of a device and method

Info

Publication number: EP2152489A1
Application number: EP08733458A
Authority: EP
Inventors: David Leigh Scrimshaw; Benjamin Luke Van Der Linde; Paul Davies; Paul Francis Connor; Paul Miller
Original assignee: Demain Technology Pty Ltd
Current assignee: Demain Technology Pty Ltd
Priority date: 2007-05-09
Filing date: 2008-05-09
Publication date: 2010-02-17
Also published as: EP2152489A4; CN101986780A; WO2008138037A1

Abstract

The invention relates to a housing for a gearbox of a device such as a power tool which may be a drill, a power screwdriver or a cutting tool. The housing includes a first housing portion having an internal surface and an external surface. The internal surface is cooperable with a gear located internally within the housing and the external surface is integrally formed with the internal surface. The housing also includes a second housing portion attached to the external surface of the first housing portion by the application of heat to the second housing portion.

Description

A HOUSING FOR A GEARBOX OF A DEVICE AND METHOD

Field of the Invention

The present invention relates to a housing for a gearbox of a device such as a power tool which may be a drill, a power screwdriver or a cutting tool. The present invention is particularly suitable for use as a housing for a gearbox of a power tool having a functional portion and an overmoulded gripping portion and as a method for production of the housing.

Background

A challenge for tool manufacturers is to be able to provide tools that include components that simultaneously serve a number of purposes. By designing a tool with multi purpose components the number of components used in the tool can be reduced so as to make the tool lighter and easier to use. Another advantage of multi function components is that the amount of materials required to manufacture the tool may be reduced thereby reducing the cost of materials for the manufacturer. Another advantage is that the multi purpose component may involve relatively fewer manufacturing steps and, as a result, lower manufacturing costs. Another challenge is to provide a component that serves a number of purposes of the power tool that would normally be fulfilled by separate components without suffering a reduction in the performance or quality of the power tool.

Some power tools, such as power screwdrivers, include a gearbox that is coupled to an armature of an electric motor and an output shaft of the tool to which a working element, such as a screwdriver bit, may be attached. The gearbox serves to convert rotation of the armature of the motor, which occurs through operation of the power tool, into rotation of the output shaft and the working element attached thereto. The ratio of the gearbox typically results in the output shaft rotating relatively slower than the armature of the motor. By reducing the speed of rotation of the output shaft relative to the armature, the torque of the output shaft is increased relative to the torque originating from the motor. In other words, the gearbox multiplies the motor's torque such that the turning force of the output shaft and the attached working element are increased. This is particularly useful in power screwdrivers where a substantial amount of torque may be required to drive a screw into a workpiece such as a piece of timber.

Existing gearboxes for power screwdrivers have typically taken the form of a discrete component involving a gearbox housing containing gears, a gearbox input shaft and a gearbox output shaft. The gearbox housing is mounted to the screwdriver adjacent to the motor such that the armature and the gearbox input shaft mate together. Then a screwdriver output shaft is mated to the gearbox output shaft and a housing for containing internal components of the power tool is fitted around the gearbox housing, the gearbox input shaft, the armature, the gearbox output shaft and at least a portion of the screwdriver output shaft.

In certain types of gearbox housing, in which an internal surface of the gearbox housing is cooperable with a gear located within the gearbox housing, the shape and configuration of the internal surface is critical to this functionality. Thus, if the shape and configuration of the internal surface of the gearbox housing is altered or deformed then this may adversely affect the ability of the internal surface to cooperate with a gear located within the gearbox housing. For example, the gearbox housing may have a plurality of teeth on its internal surface such that the gearbox housing acts as a ring gear and the gear located within the gearbox housing may be a planet gear which means it is critical to be able to maintain the shape and configuration of the internal surface of the gearbox housing and protect it from deformation in order for it to cooperate properly with the planet gear.

A power tool housing for containing the internal components of the power tool is usually fitted around the gearbox housing to serve the function of shielding moving internal components of the power tool such as the gearbox input shaft, the armature, the gearbox output shaft and at least a portion of the screwdriver output shaft. The power tool housing also acts to prevent the accumulation of foreign matter in the internal components which may affect their movement. The power tool housing also prevents a user from catching their clothing or a part of their body in the moving internal components and suffering an injury. The power tool housing may also act as a means for holding the power tool when in use.

Some power tools may include an overmould on a tool housing for the purposes of reducing the transmission of vibration to the user's hand and/or for providing a gripping surface with improved grip characteristics. In such tool housings, the external surface of the relatively hard tool housing is overmoulded with a resilient material and/or a material with a relatively higher coefficient of friction. The overmoulding operation typically involves placing the formed tool housing into an injection mould and injecting a molten polymer between the mould and the tool housing. The molten polymer is then allowed to cool and cure into a resilient portion on the tool housing that is then removed from the mould for fitment to the power tool.

A problem with overmoulding on formed tool housings, or indeed on any formed polymer object having an internal cavity, has been that the tool housings have tended to be deformed as a result of heat being transferred from the molten polymer to the tool housing during the overmoulding process. This is particularly problematic if it is critical for the shape and configuration of the internal surface of the tool housing not to be altered or deformed. For example, if the tool housing has an internal surface configured to cooperate with a gear located within the tool housing then subjecting the tool housing to an overmoulding process to overmould material to the tool housing may adversely affect the ability of the internal surface to cooperate effectively with a gear located within the tool housing.

A problem with providing a housing for a device, such as a power tool, that doubles as a gearbox housing and an external housing for the device to which an overmould may be applied is that the functionality of the housing as a gearbox housing may be degraded. Summary of the Invention

Accordingly, in one aspect, the present invention provides a housing for a gearbox of a device, the housing including: a first housing portion having an internal surface and an external surface, the internal surface being cooperable with a gear located internally within the housing and the external surface being integrally formed with the internal surface, and a second housing portion attached to the external surface of the first housing portion by the application of heat to the second housing portion.

In one form, the first housing portion is moulded and the second housing portion is overmoulded to the external surface of the first housing portion.

The invention provides a housing for a gearbox of a device, such as a power tool, having a first portion with an internal surface that can cooperate with a gear located within the housing and a second portion, such as a second resilient and/or grippy portion, attached to the first portion by way of the application of heat to the second portion. The invention is particularly advantageous in applications where a single housing is to be used as a gearbox housing and a device housing and where a second housing portion is to be attached to the first housing by the application of heat such as by an overmoulding process. As such, the invention makes it possible to do away with the requirement to have separate gearbox and device housings when an overmoulded portion, such as a resilient and/or grippy overmoulded portion, is to be attached to the device housing by the application of heat to the overmoulded portion. To put it another way, the invention makes it possible to provide a gearbox housing for a device, such as a power tool, that doubles as an external housing for the device to which an overmould is applied without the functionality of the housing as a gearbox housing being degraded. In one form, the internal surface of the first housing portion is shaped to cooperate with the gear. The internal surface of the first housing portion may include a gear engaging portion.

In one form, the internal surface is substantially cylindrical and includes a plurality of teeth projecting inwardly from the cylindrical portion. The internal surface may also radially surround a central axis and the plurality of teeth may be elongated in a direction parallel to the axis.

The above forms of the invention are advantageous in that they may make it possible to provide a gearbox housing having a first housing portion with an internal surface that can mesh with a gear located within the first housing portion such that the gear can rotate about the inside of the first housing portion yet at the same time provide a second housing portion attached to the external surface of the first housing portion by the application of heat to the second housing portion. Accordingly, the first housing portion may function as a ring gear that meshes with a planet gear positioned within the first housing portion as well as have an overmoulded second housing portion attached to the external surface.

In another form, the internal surface of the first housing portion receives and is connected to a separate gear engaging member for engaging with another gear located internally within the housing.

In one form, the separate gear engaging member is a ring gear.

In another form, the second housing portion is injection moulded to the external surface of the first housing portion.

In yet another form, the second housing portion is formed from a resilient material. Such forms of the invention are advantageous in that they may provide a housing for a device, such as a power tool, offering absorption of vibration or shock transmitted from the device to a user's hand.

In another form the second housing portion includes opposte inner and outer surfaces, the inner surface is adhered to the external surface of the first housing portion and the outer surface faces away from the external surface of the first housing portion, the outer surface has a higher coefficient of friction than the external surface of the first housing portion.

Such forms of the invention are advantageous in that they may provide a housing for a device, such as a power tool, offering a more assured grip on the device.

In another form, the external surface of the first housing portion includes a recess for receiving a recess engaging part of the second housing portion. In yet another form, the external surface of the first housing portion is fused with the second housing portion. An advantage of the above forms of the invention is that they may provide a housing for a device having a second housing portion that is firmly and strongly attached to the first housing portion. The resulting housing may also be particularly durable, long lasting and resistant to wear and tear.

In one form, the second housing portion is adapted for gripping the device. In another form, the device is a power tool such as a powered screwdriver. An advantage of these forms of the invention is that they may provide a housing for a gearbox of a power tool, such as a powered screwdriver, that has a gripping surface whereas the power tool may otherwise have incorporated an additional separate component operating as either a gearbox housing or a device housing incorporating a gripping surface. Thus, the resulting power tool device, such as a powered screwdriver, can be produced with less components, using less materials and at a cheaper cost than has hitherto been possible. In another aspect, the present invention provides a method of forming a housing for a gearbox of a device, the method including: forming a first housing portion having an internal surface and an external surface, the internal surface being cooperable with a gear located internally within the housing and the external surface being integrally formed with the internal surface, and attaching a second housing portion to the external surface of the first housing portion by the application of heat to the second housing portion.

The above method is advantageous in that it provides a means of producing a housing for a gearbox of a device having a first portion with an internal surface that can cooperate with a gear located within the housing while at the same time having a second portion, such as a resilient and/or grippy portion, attached to the first portion by way of the application of heat to the second portion. As such the invention makes it possible to do away with separate gearbox and device housings in order to incorporate an overmould portion such as a second resilient and/or grippy overmoulded portion.

In one form of the method, forming the first housing portion includes moulding the first housing portion and attaching the second housing portion to the external surface of the first housing portion includes overmoulding the second housing portion to the external surface of the first housing portion.

In another form, forming the first housing portion includes injecting molten polymer into a first mould cavity and curing the molten polymer to form the first housing portion and attaching the second housing portion to the external surface of the first housing portion includes injecting molten polymer into a second mould cavity wherein the second mould cavity is partially defined by the external surface of the first housing portion.

In another form, the step of forming the internal surface of the first housing portion includes shaping the internal surface to be cooperable with the gear. In another form, the method further includes maintaining the shape of the internal surface of the first housing portion during attachment of the second housing portion to the external surface of the first housing portion.

In another form, maintaining the shape of the internal surface includes supporting the internal surface of the first housing portion.

In Supporting the internal surface of the first housing portion may include positioning a shape maintaining member in abutment with the internal surface. In one form, the shape maintaining member is a mould shaped to form the internal surface of the first housing portion.

An advantage of the above forms of the method is that they may ensure that the internal surface of the first housing portion is not warped or otherwise deformed by the transfer of heat from the second housing portion to the first housing portion as a result of attaching the first housing portion and the second housing portion together.

In one form, the first housing portion and the second housing portion are formed out of polymers and the polymer with which the second housing portion is formed has a higher coefficient of friction than the polymer with which the first housing portion is formed. The second housing portion may be formed from a resilient polymer such as a thermoplastic resin (TPR). Such forms of the invention are advantageous in that they may provide a means of producing a housing for a device, such as a power tool, offering a more assured grip on the device and/or absorption of vibration or shock transmitted from the device to a user's hand.

The external surface of the first housing portion may include a recess and the application of heat to the second housing portion causes a recess engaging portion of the second housing portion to be received within the recess. The application of heat to the second housing portion may also fuse the second housing portion to the external surface of the first housing portion. An advantage of the above forms of the method is that they may result in a housing for a power tool having a second housing portion that is firmly and strongly attached to the first housing portion and that is particularly durable, long lasting and resistant to wear and tear.

Brief Description of the Drawings

It will be convenient to hereinafter describe the invention in greater detail by reference to the accompanying drawings which show a housing for a gearbox of a device in accordance with a preferred form of the invention in which the device is a cordless power screwdriver. The particularity of the drawings and the related detailed description is not to be understood as superseding the generality of the preceding broad description of the invention.

Figure 1 is a perspective view of a cordless power screwdriver incorporating a housing in accordance with a preferred embodiment of the invention.

Figure 2 is a view of a cross section of the power screwdriver of Figure 1.

Figure 3 is a top view of the housing of the screwdriver of Figure 1.

Figure 4 is a view of a cross section of the housing of the screwdriver taken along section line A-A shown in Figure 3.

Figure 5 is a side view of the housing of the screwdriver of Figure 1 incorporating a drive motor and a screwdriver output shaft.

Figure 6 is a view of a cross section of the housing of the screwdriver taken along the section line A-A shown in Figure 5. The housing includes a number of gears located within the housing for transmitting rotation from an armature of the drive motor to the screwdriver output shaft.

Figure 7 is a bottom view of the housing of Figure 1. Figure 8 is a perspective view of the housing of Figure 1.

Figure 9 is a side view of the housing of Figure 1 incorporating the drive motor and screwdriver output shaft shown in Figure 5.

Figure 10 is a perspective view of the housing of Figure 1 incorporating the drive motor and screwdriver output shaft shown in Figure 5.

Figure 1 1 is a view of a cross section of a gearbox for a screwdriver including a housing in accordance with another form of the invention.

Figure 12 is a perspective exploded view of the gearbox and the housing of Figure 1 1.

Detailed Description

Figures 1 and 2 show a cordless power screwdriver 10 incorporating a main body 15 and a housing 20 attached to one end of the main body 15. A screwdriver output shaft 17 projects from the housing 20 and has a hexagonal recess 18 for receiving a hexagonal shaped shaft of a screwdriver bit therein (not shown). The screwdriver 10 includes a power drive in the form of an electric motor 2 located within the meain body 15 and a switch 14 for controlling the flow of electrical power to the motor 2 from electrical power storage means 4 located within the main body 15. The housing 20 is a separate component from the main body 15 of the screwdriver 10.

As shown in Figures 1 to 9, the housing 20 is formed from a first housing portion 27 and a second housing portion 28. The first housing portion 27 has a tapered cylindrical shape extending from one end 25 coupled to the main body 15 of the screwdriver 10 to another end 21 from which the output shaft 17 projects. A cylindrical aperture 22 is formed in the end 21 for the output shaft 17 to pass therethrough. The first housing portion 27 has an internal surface 30 and an external surface 31. The internal surface 30 defines a hollow internal cavity 32. The internal surface 30 has a tapered cylindrical shape and comprises an annular surface portion 35 surrounding the aperture 22, a frustoconical surface portion 36 extending transversely from the annular surface portion 35 to a cylindrical surface portion 37. The cylindrical surface portion 37 has a plurality of elongate teeth 38 that project radially inwardly towards an axis of the cylindrical surface portion 37. The teeth 38 are disposed adjacent each other about the entire cylindrical surface portion 37. The cylindrical surface portion 37 extends to an annular surface portion 39 that extends transversely outwards from the cylindrical surface portion 37. A second cylindrical surface portion 40 extends transversely from the annular surface portion 39. A second annular surface portion 41 extends transversely outwards from the second cylindrical surface portion 40. A third cylindrical surface portion 42 extends transversely from the second annular surface portion 41. The cylindrical surface portions 37, 40, 42 are all parallel. An annular end surface 43 extends transversely outwards from the third cylindrical surface portion 42. The annular end surface 43 is at the end 25 of the first housing portion 27 that is coupled to the main body 15 of the screwdriver 10. The external surface 31 of the first housing portion 27 extends transversely from the annular end surface 43 to the end 21 from which the output shaft 17 projects. The end 21 is comprised of an annular surface extending transversely inwardly from the external surface 31 to the cylindrical aperture 22. The external surface 31 has a curved frustoconical shape.

The first housing portion 27 is preferably injection moulded out of a hard thermoplastic such as PBT - Polybutylene Terephthalate or ABS - acrylonitrile butadiene styrene. However, any other suitable moulding process may be used as can any suitable plastic be used. The material that is used is preferably a hard material as the plurality of elongate teeth 38 that project radially inwardly of the internal cylindrical surface portion 37 should be relatively hard and durable in order to satisfy their functional requirement which is to mesh with teeth 52 of first gears 50 and second gears 60 that are located within the first housing portion 27. The first gears 50 are planetary gears that are each rotatably mounted to a protrusion 53 of a first spindle 54. The elongate teeth 38 that project radially inwardly of the internal cylindrical surface portion 37 act as a ring gear whereby the first gears 50 rotate about the ring gear of the internal cylindrical surface portion 37 while also rotating around their respective protrusion 53 of the first spindle 54. The first spindle 54 has an output shaft engaging portion 56 that abuts the output shaft 17. Accordingly, the first spindle 54 and the first gears 50 act as a bushing or bearing for the output shaft 17 when the output shaft 17 rotates in use.

The second gears 60 are each similarly rotatably mounted to a protrusion 63 from a second spindle 64. The electric motor 2 has an armature 3 extending from the motor 2. Coupled to the armature is a sun gear 6 that rotates along with the armature 3 when the switch 14 is operated to supply electrical power to the motor 2. The sun gear 6 has a plurality of teeth 7 that mesh with teeth 62 of the second gears 60 wherein the second gears 60 act as planet gears. The teeth 62 of the second gears 60 also mesh with the elongate teeth 38 that project radially inwardly of the internal cylindrical surface portion 37. Accordingly, the elongate teeth 38 of the internal cylindrical surface portion 37 act as a ring gear whereby rotation of the sun gear 6 due to operation of the motor 2 and rotation of the armature 3 cause the second planet gears 60 to rotate about the ring gear of the internal cylindrical surface portion 37 while also rotating around their respective protrusion 63 of the second spindle 64. This in turn causes the second spindle 64 to rotate about an axis. The second spindle 64 has a transverse arm portion 66 extending from the protrusions 63 to a base 13 of the output shaft 17. The transverse arm portion 66 is integral with the base 13 of the output shaft 17. Accordingly, operation of the motor 2 causes rotation of the sun gear 6, which in turn causes the rotation of the second planet gears 60, which in turn causes rotation of the second spindle 64 which in turn causes rotation of the output shaft 17.

The sun gear 6, second planet gears 60 and the ring gear of the internal cylindrical surface portion 37 are configured such that the rotational speed of the output shaft 17 is at a predetermined ratio to the rotational speed of the armature 3 of the motor 2. Usually the ratio is such that the output shaft 17 rotates more slowly than the armature 3 at a ration of, say, 2:1 , 3: 1 or any other suitable ratio. In doing so, the torque applied by the motor 2 to the armature 3 is multiplied in the output shaft 17 which enables the output shaft 17 to impart sufficient torque to a screwdriver head placed in the recess 18 to be effective for driving screws into a workpiece such as a piece of timber.

Accordingly, the first housing portion 27 forms a gearbox housing and is functionally involved with the first and second gears 50, 60 within the first housing portion 27. Accordingly, once the first housing portion 27 has been formed it is important that the internal dimensions of the internal cylindrical surface portion 37 with the elongate teeth 38 projecting radially inwardly therefrom remain intact otherwise the gearbox will not function properly or may function with reduced efficiency.

The housing 20 also includes a second housing portion 28 which is attached to the external surface 31 of the first housing portion 27 by the application of heat to the second housing portion 28. In accordance with a preferred form of the invention, the second housing portion 28 is overmoulded onto the external surface 31 of the first housing portion 27 by way of an injection moulding process. This entails providing a thermoplastic and heating the thermoplastic until it becomes molten. The first housing portion 27 is arranged with a mould (not shown) to form a mould cavity therebetween whereby part of the mould cavity is defined by a portion of the first housing portion 27 onto which the second housing portion 28 is to be attached and overlayed. The molten thermoplastic is then injected into the mould. Thus, the second housing portion 28 is formed on the external surface 31 of the first housing portion 27. The second housing portion 28 has an inner surface 75 and an opposite outer surface 76. The inner surface 75 of the second housing portion 28 faces towards the external surface 31 of the first housing portion 27 and the outer surface 76 of the second housing portion 28 faces away from the external surface 31 of the first housing portion 27.

The external surface 31 of the first housing portion 27 includes a recess (not shown) into which a portion of the molten thermoplastic ingresses such that when the thermoplastic cools and cures the portion of the thermoplastic within the recess hardens to form an integrated recess engaging part of the second housing portion 28 to attach the second housing portion 28 to the first housing portion 27. In addition, the inner surface 75 of the second housing portion 28 fuses with the external surface 31 of the first housing portion 27 by the partial melting and miscibility of the first housing portion 27 due to the transfer of heat from the molten thermoplastic when overmoulding the second housing portion 28 to the first housing portion 27. The resulting attachment or bond between the second housing portion 28 and the first housing portion 27 is quite durable, long lasting and resistant to the ingress of fluid and debris.

The thermoplastic of the second housing portion 28 is preferably a softer plastic and has a higher coefficient of friction than that used to form the first housing portion 27. For example, the second housing portion may be formed from a TPR - Thermoplastic resin, a TPE - Thermoplastic elastomer or any other thermopolymer capable of absorbing physical shock, that is relatively soft and flexible and can be moulded into any shape. Accordingly, the outer surface 76 of the resulting second housing portion 28 has a higher coefficient of friction than the external surface 31 of the first housing portion 27 and provides a grippy surface for the housing 20 as well as a means for absorbing some shock and vibration transmitted from the screwdriver 10 to the user's hand. The housing 20 is situated adjacent and near to the output shaft 17 as well as the bit located in the recess 18 in the shaft 17. It is advantageous to have the grippy outer surface 76 in this region because it enables a user to hold and accurately place the bit on the head of a screw and apply a greater amount of force on the screw through the screwdriver 10. Thus, the grippy outer surface 76 enables a user to use the rotation of the output shaft 17 to more effectively drive the screw into the workpiece. The grippy outer surface 76 also helps prevent the user's hand from slipping and being injured. The grippy outer surface 76 also enables the user to ergonomically apply a greater amount of force than would be possible without such a grippy outer surface 76.

Another advantage of the housing 20 is that it houses the gearbox of the screwdriver 10, which is necessarily located adjacent to the output shaft 17, and does away with requiring separate gearbox and screwdriver housings in order to incorporate the resilient and/or grippy overmoulded second housing portion 28. Accordingly, the housing 20 facilitates producing a screwdriver 10 having a gearbox that includes less parts and materials, is cheaper to manufacture, is more efficient to manufacture and assemble, is lighter and that includes an overmoulded portion that, in particularly preferred embodiments, is useful for providing a gripping surface that is grippy and/or that has shock and/or vibration absorbing characteristics.

The method of forming the housing 20 includes injection moulding the first housing portion 27. This involves providing a mould which may be in first and second parts (not shown). The first part is shaped to provide the external surface 31 while the second part is shaped to provide the internal surface 30 of the first housing portion 27. Accordingly, the second part is shaped to provide the plurality of elongate teeth 38 that project radially inwardly of the internal cylindrical surface portion 37 of the internal surface 30. In another possible embodiment, the second part of the mould could be shaped to provide, instead of teeth, a smooth internal cylindrical surface portion 37, or any other desired surface shape, to which could be fitted a separate ring gear made of plastic, metal or any other suitable material. A suitable thermoplastic, such as Polybutylene Terephthalate, is melted and injected into a mould cavity defined as the void volume between the two mould parts. The injection parameters may be: Heat Distortion Temp. 162 degrees (0.45MPa, 6.4mm), 63 degrees (1.8MPa, 6.4mm); Specific Gravity 1.43g/cm³; Mold Shrinkage 1.2-1.4%; Melt Temp. 230-250 degrees. Once the melted plastic is in the mould, it cools to a shape that reflects the form of the cavity, namely the first housing portion 27. The resulting first housing portion 27 is a finished part needing no other work before assembly into the power screwdriver 10. The injection molding machine (not shown) for use with the invention has two basic components: an injection unit to melt and transfer the plastic into the mould (not shown), and a clamp to hold the mould shut against injection pressures and for removal of parts after moulding. The injection unit melts the plastic before it is injected into the mould, then injects the molten plastic at a controlled and predetermined pressure and rate into the mould. The molten plastic enters the mould cavity through passages cut into the mould, called runners. The mould also has passages in it to circulate a coolant, usually water, to chill the hot plastic in predetermined areas. As it cools, the thermoplastic material hardens. After the injection cycle, the clamp gently opens the mold parts. When cooled enough, the mould opens and the first housing portion 27 is removed.

The method of forming the housing 20 also includes attaching the second housing portion 28 to the external surface 31 of the first housing portion 27. This involves a second moulding step which involves placing the first housing portion 27 in a second mould (not shown) to form a second mould cavity therebetween wherein part of the second mould cavity is defined by the portion of the external surface 31 of the first housing portion 27 onto which the second housing portion 28 is to be attached and overlayed. A second molten thermoplastic is then injected into the mould. The external surface 31 of the first housing portion 27 may be formed with a recess (not shown) into which a portion of the second molten thermoplastic ingresses during the second moulding step such that when the second thermoplastic cools and cures the portion of the second thermoplastic that has ingressed into the recess hardens to form an integrated recess engaging part of the second housing portion 28 to enhance the attachment of the second housing portion 28 to the first housing portion 27. In addition, the inner surface 75 of the second housing portion 28 fuses with the external surface 31 of the first housing portion 27 by the partial melting and miscibility of the first housing portion 27 due to the transfer of heat from the molten second thermoplastic when overmoulding the second housing portion 28 to the first housing portion 27. The resulting attachment or bond between the second housing portion 28 and the first housing portion 27 is quite durable, long lasting and resistant to the ingress of fluid and debris.

The method further includes maintaining the shape of the internal surface 30 during the step of overmoulding the second housing portion 28 to the external surface 31 of the first housing portion 27. Any suitable means of maintaining the shape of the internal surface 30 may be utilized such that the heat applied to the second housing portion 28 to attach it to the first housing portion 27 does not result in deforming the internal surface 30. Such means of maintaining the shape of the internal surface 30 may include positioning a shape maintaining member (not shown) in abutment with the internal surface

30. The shape maintaining member may include the second part of the first mould that is shaped to form the internal surface 30 of the first housing portion 27 during the first moulding process. Another means of maintaining the shape of the internal surface 30 may include applying pressure to the internal surface 30 by way of gas or fluid at a pressure that is sufficient to maintian the shape of the internal surface 30 of the first housing portion 27 during the second moulding process.

Figures 1 1 and 12 illustrate a gearbox 80 for a screwdriver including another housing 90 in accordance with the invention. Where like numerals are used herein in relation to the features of the housings 20, 90 disclosed herein then this is an indication of similar features. The housing 90 is formed from a first housing portion 27 and a second housing portion 28. The first housing portion 27 has an internal surface 30 and an external surface 31. The internal surface 30 defines a hollow internal cavity 32. The internal surface 30 has a cylindrical surface portion 37. The cylindrical surface portion 37 has a plurality of elongate teeth 38 that project radially inwardly towards an axis of the cylindrical surface portion 37. The teeth 38 are disposed adjacent each other about the entire cylindrical surface portion 37. The cylindrical surface portion 37 extends to an annular surface portion 39a that extends transversely outwards from the cylindrical surface portion 37. A second cylindrical surface portion 40a extends transversely from the annular surface portion 39a. The cylindrical surface portion 40a extends to an annular surface portion 39 that extends transversely outwards from the cylindrical surface portion 40a. A second cylindrical surface portion 40 extends transversely from the annular surface portion 39. A second annular surface portion 41 extends transversely outwards from the second cylindrical surface portion 40. A third cylindrical surface portion 42 extends transversely from the second annular surface portion 41. The cylindrical surface portions 37, 40a, 40, 42 are all parallel. An annular end surface 43 extends transversely outwards from the third cylindrical surface portion 42. The annular end surface 43 is at an end 25 of the housing 90 for coupling to the main body 15 of the screwdriver 10. The external surface 31 of the first housing portion 27 extends transversely from the annular end surface 43 to an opposite end 21 of the housing 90 from which an output shaft 17 projects. The end 21 is an annular surface extending transversely inwardly from the external surface 31 to a cylindrical aperture 22 through which the output shaft 17 extends. The external surface 31 has a curved frustoconical shape.

The first housing portion 27 is preferably injection moulded out of a hard thermoplastic such as PBT - Polybutylene Terephthalate or ABS - acrylonitrile butadiene styrene. However, any other suitable moulding process may be used as can any suitable plastic be used. The material that is used is preferably a hard material as the plurality of elongate teeth 38 that project radially inwardly of the internal cylindrical surface portion 37 should be relatively hard and durable in order to satisfy their functional requirement which is to mesh with teeth 52 of first gears 50 that are located within the first housing portion 27. The first gears 50 are planetary gears that are each rotatably mounted to a protrusion 53 of a first spindle 54. The elongate teeth 38 that project radially inwardly of the internal cylindrical surface portion 37 act as a ring gear whereby the first gears 50 rotate about the ring gear of the internal cylindrical surface portion 37 while also rotating around their respective protrusion 53 of the first spindle 54. The first spindle 54 has an output shaft portion 56 that connects to the output shaft 17. Accordingly, the first spindle 54 and the first gears 50 act as a bushing or bearing for the output shaft 17 when the output shaft 17 rotates in use.

A set of second gears 60 are also located within the first housing portion

27 and rotatably mounted to a protrusion 63 from a second spindle 64. An armature of an electric motor (not shown) is coupled to a sun gear (not shown) that is connected to and is rotated by the armature when the motor is activated. The sun gear meshes with teeth 62 on the second gears 60 which act as planet gears. A separate gear engaging member in the form of a ring gear 95 is located internally within the housing 90. The ring gear 95 may be made out of metal or any other suitable material and is sized to fit snugly within the space provided between the annular surface portion 39a and the cylindrical surface portion 40a. Accordingly, the ring gear 95 is adjacent to the cylindrical surface portion 37 and the teeth 38 disposed thereon. The ring gear 95 has its own internally oriented teeth 96 disposed about the inner circumference of the ring gear 95. Accordingly, the teeth 96 of the ring gear 95 engage with the teeth 62 of the second gears 60 that are located within the housing 90. In the arrangement disclosed in Figures 1 1 and 12, the teeth 62 of the second gears 60 do not mesh with the elongate teeth 38 that project radially inwardly of the internal cylindrical surface portion 37.

Accordingly, rotation of the armature of the electric motor and the sun gear coupled thereto causes the second planet gears 60 to rotate about the ring gear 95 while also rotating around their respective protrusion 63 of the second spindle 64. This in turn causes the second spindle 64 to rotate about an axis. Accordingly, operation of the motor 2 causes rotation of the sun gear

6, which in turn causes the rotations of the second planet gears 60, which in turn causes rotation of the second spindle 64 which in turn causes rotation of another sun gear 98 extending from the second spindle 64. The sun gear 98 meshes with the first gears 50 such that rotation of the sun gear 98 extending from the second spindle 64 causes rotation of the first gear 50 and thereby causes rotation of the first spindle 54. Rotation of the first spindle 54 causes rotation of the output shaft 17.

Accordingly, the first housing portion 27 forms gearbox housing 90 and is functionally involved with the first gears 50. Also, the first housing portion 27 receives and is connected to a separate gear engaging member in the form of the ring gear 95 for engaging with the second gears 60 located internally within the housing 90. Such an arrangement is advantageous in circumstances where it is appropriate for the first housing portion 27 to functionally interact with some internal gears but not others. For example, some internal gears may rotate at higher speeds for which it might be appropriate to utilize a metal ring gear insert placed within the first housing portion while others might rotate at lower speeds for which the internal surface 37 of the first housing portion 27 might be adequate to provide for functional interaction with those gears. Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such variations and modifications which fall within the spirit and scope.

Future patent applications may be filed in Australia or overseas on the basis of or claiming priority from the present application. It is to be understood that the following provisional claims are provided by way of example only, and are not intended to limit the scope of what may be claimed in any such future application. Features may be added to or omitted from the provisional claims at a later date so as to further define or re-define the invention or inventions.

Claims

The claims defining the invention are as follows:

1. A housing for a gearbox of a device, the housing including:

a first housing portion having an internal surface and an external surface, the internal surface being cooperable with a gear located internally within the housing and the external surface being integrally formed with the internal surface, and

a second housing portion attached to the external surface of the first housing portion by the application of heat to the second housing portion.

2. The housing of claim 1 , wherein the first housing portion is moulded and the second housing portion is overmoulded to the external surface of the first housing portion.

3. The housing of claim 1 or claim 2, wherein the internal surface of the first housing portion is shaped to cooperate with the gear.

4. The housing of any one of the preceding claims, wherein the internal surface of the first housing portion includes a gear engaging portion.

5. The housing of any one of the preceding claims, wherein the internal surface is substantially cylindrical and includes a plurality of teeth projecting inwardly from the cylindrical portion.

6. The housing of claim 4, wherein the internal surface radially surrounds a central axis of the first housing portion and the plurality of teeth are elongated in a direction parallel to the axis.

7. The housing of any one of the preceding claims, wherein the internal surface of the first housing portion receives and is connected to a separate gear engaging member for engaging with another gear located internally within the housing.

8. The housing of claim 7, wherein the separate gear engaging member is a ring gear.

9. The housing of any one of the preceding claims, wherein the second housing portion is injection moulded to the external surface of the first housing portion.

10. The housing of any one of the preceding claims, wherein the second housing portion is formed from a resilient material.

1 1. The housing of any one of the preceding claims, wherein the second housing portion includes opposing inner and outer surfaces, the inner surface is adhered to the external surface of the first housing portion and the outer surface faces away from the external surface of the first housing portion, the outer surface has a higher coefficient of friction than the external surface of the first housing portion.

12. The housing of any one of the preceding claims, wherein the external surface of the first housing portion includes a recess for receiving a recess engaging part of the second housing portion.

13. The housing of any one of the preceding claims, wherein the external surface of the first housing portion is fused with the second housing portion.

14. The housing of any one of the preceding claims, wherein the second housing portion is configured to provide a surface for gripping the device.

15. The housing of any one of the preceding claims, wherein the device is a power tool.

16. The housing of any one of the preceding claims, wherein the device is a powered screwdriver.

17. The housing of any one of the preceding claims, wherein the first housing portion and the second housing portion are formed out of polymers.

18. A method of forming a housing for a gearbox of a device, the method including:

forming a first housing portion having an internal surface and an external surface, the internal surface being cooperable with a gear located internally within the housing and the external surface being integrally formed with the internal surface, and

attaching a second housing portion to the external surface of the first housing portion by the application of heat to the second housing portion.

19. The method of claim 18, wherein forming the first housing portion includes moulding the first housing portion and attaching the second housing portion to the external surface of the first housing portion includes overmoulding the second housing portion to the external surface of the first housing portion.

20. The method of claim 18 or claim 19, wherein forming the first housing portion includes injecting molten polymer into a first mould cavity and curing the molten polymer to form the first housing portion and attaching the second housing portion to the external surface of the first housing portion includes injecting molten polymer into a second mould cavity wherein the second mould cavity is partially defined by the external surface of the first housing portion.

21. The method of any one of claims 18 to 20, wherein forming the internal surface of the first housing portion includes shaping the internal surface to be cooperable with the gear.

22. The method of claim 21 , further including maintaining the shape of the internal surface of the first housing portion during attachment of the second housing portion to the external surface of the first housing portion.

23. The method of claim 22, wherein maintaining the shape of the internal surface includes supporting the internal surface of the first housing portion.

24. The method of claim 22 or claim 23, wherein maintaining the shape of the internal surface of the first housing portion includes positioning a shape maintaining member in abutment with the internal surface.

25. The method of claim 24, wherein the shape maintaining member is a mould shaped to form the internal surface of the first housing portion.

26. The method of any one of claims 15 to 25, wherein the first housing portion and the second housing portion are formed out of polymers and the polymer with which the second housing portion is formed has a higher coefficient of friction than the polymer with which the first housing portion is formed.

27. The method of any one of claims 15 to 26, wherein the second housing portion is formed out of a resilient polymer.

28. The method of any one of claims 15 to 27, wherein the external surface of the first housing portion includes a recess and the application of heat to the second housing portion causes a recess engaging portion of the second housing portion to be received within the recess.

29. The method of any one of any one of claims 15 to 28, wherein the application of heat to the second housing portion fuses the second housing portion to the external surface of the first housing portion.

30. A housing for a gearbox of a device, substantially as herein described with reference to any one of the accompanying drawings of embodiments of the invention.

31. A method of forming a gearbox of a device, substantially as herein described with reference to any one of the accompanying drawings of embodiments of the invention.

32. A power tool including the housing for a gearbox according to any one of the preceding claims.

33. A powered screwdriver including the housing for a gearbox according to any one of the preceding claims.