WO2010116125A1 - A gearbox and a driving assembly therefor - Google Patents

A gearbox and a driving assembly therefor Download PDF

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Publication number
WO2010116125A1
WO2010116125A1 PCT/GB2010/000652 GB2010000652W WO2010116125A1 WO 2010116125 A1 WO2010116125 A1 WO 2010116125A1 GB 2010000652 W GB2010000652 W GB 2010000652W WO 2010116125 A1 WO2010116125 A1 WO 2010116125A1
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WO
WIPO (PCT)
Prior art keywords
gear
housing
teeth
internally toothed
adjuster
Prior art date
Application number
PCT/GB2010/000652
Other languages
French (fr)
Inventor
Neil Adcock
Patrick Adcock
Original Assignee
H.R. Adcock Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by H.R. Adcock Limited filed Critical H.R. Adcock Limited
Publication of WO2010116125A1 publication Critical patent/WO2010116125A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60N—SEATS SPECIALLY ADAPTED FOR VEHICLES; VEHICLE PASSENGER ACCOMMODATION NOT OTHERWISE PROVIDED FOR
    • B60N2/00—Seats specially adapted for vehicles; Arrangement or mounting of seats in vehicles
    • B60N2/02—Seats specially adapted for vehicles; Arrangement or mounting of seats in vehicles the seat or part thereof being movable, e.g. adjustable
    • B60N2/04—Seats specially adapted for vehicles; Arrangement or mounting of seats in vehicles the seat or part thereof being movable, e.g. adjustable the whole seat being movable
    • B60N2/16—Seats specially adapted for vehicles; Arrangement or mounting of seats in vehicles the seat or part thereof being movable, e.g. adjustable the whole seat being movable height-adjustable
    • B60N2/1635—Seats specially adapted for vehicles; Arrangement or mounting of seats in vehicles the seat or part thereof being movable, e.g. adjustable the whole seat being movable height-adjustable characterised by the drive mechanism
    • B60N2/1655—Cycloidal or planetary mechanism
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60N—SEATS SPECIALLY ADAPTED FOR VEHICLES; VEHICLE PASSENGER ACCOMMODATION NOT OTHERWISE PROVIDED FOR
    • B60N2/00—Seats specially adapted for vehicles; Arrangement or mounting of seats in vehicles
    • B60N2/02—Seats specially adapted for vehicles; Arrangement or mounting of seats in vehicles the seat or part thereof being movable, e.g. adjustable
    • B60N2/0224—Non-manual adjustments, e.g. with electrical operation
    • B60N2/02246—Electric motors therefor
    • B60N2/02253—Electric motors therefor characterised by the transmission between the electric motor and the seat or seat parts
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60N—SEATS SPECIALLY ADAPTED FOR VEHICLES; VEHICLE PASSENGER ACCOMMODATION NOT OTHERWISE PROVIDED FOR
    • B60N2/00—Seats specially adapted for vehicles; Arrangement or mounting of seats in vehicles
    • B60N2/02—Seats specially adapted for vehicles; Arrangement or mounting of seats in vehicles the seat or part thereof being movable, e.g. adjustable
    • B60N2/04—Seats specially adapted for vehicles; Arrangement or mounting of seats in vehicles the seat or part thereof being movable, e.g. adjustable the whole seat being movable
    • B60N2/16—Seats specially adapted for vehicles; Arrangement or mounting of seats in vehicles the seat or part thereof being movable, e.g. adjustable the whole seat being movable height-adjustable
    • B60N2/1635—Seats specially adapted for vehicles; Arrangement or mounting of seats in vehicles the seat or part thereof being movable, e.g. adjustable the whole seat being movable height-adjustable characterised by the drive mechanism
    • B60N2/165—Gear wheel driven mechanism
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16H—GEARING
    • F16H1/00—Toothed gearings for conveying rotary motion
    • F16H1/28—Toothed gearings for conveying rotary motion with gears having orbital motion
    • F16H1/32—Toothed gearings for conveying rotary motion with gears having orbital motion in which the central axis of the gearing lies inside the periphery of an orbital gear

Definitions

  • the present invention relates to a gearbox suitable for use in a car seat height adjustment mechanism, a drive assembly therefor, and a method of manufacturing the same.
  • Gearboxes and associated driving assemblies suitable for use in car seat height adjustment mechanisms must be small to be installed in a standard fixing arrangement, but should provide a high reduction ratio.
  • gearboxes must be able to withstand relatively large crash loading forces and torques.
  • US 7,235,020 describes three embodiments of step down gear trains suited for use in a vehicle seat adjustment mechanism.
  • Each comprises an annular gear mounted on an eccentric provided on an output shaft, the eccentric having an axis of symmetry displaced from the axis of rotation of the output shaft.
  • the rotation of the eccentric causes the annular gearwheel to translate in a plane perpendicular to the axis of rotation of the output shaft.
  • the annular gear has a set of external teeth and also a set of internal teeth.
  • One of the sets of teeth engages a static toothed rack connected to the housing whilst the other engages a toothed rack provided by an output gear attached to an output shaft.
  • US 6,491,601 discloses an eccentric gear mechanism having an annular gear mounted on an eccentric on an input shaft .
  • the annular gear is provided with only one set of teeth which engage the teeth of an output gear.
  • a slot is provided in the annular gear and an arm formed integrally with a pinion gear is positioned in the slot.
  • the pinion gear is supported on a spindle mounted on a housing part and has external teeth meshing with teeth of the input shaft .
  • Only one eccentric is provided and the annular gear has only one set of gear teeth, an internal set.
  • US 6,280,359 discloses an eccentric gear drive with an input shaft having an eccentric element and an annular gear mounted on the eccentric element.
  • the annular gear has a set of internal teeth engaging external teeth on an output gear.
  • a lug or a pair of lugs are provided on the annular gear, which slide in one or a pair of slots in a fixed housing cap.
  • One eccentric element is provided and the annular gear has only one set of gear teeth.
  • US 6,453,772 discloses an eccentric gear drive with an input shaft having an eccentric element with an annular gear mounted thereon.
  • the annular gear has a set of internal teeth which engage external teeth of an output gear.
  • a pair of pegs are provided on the annular gear which extends into sockets in a flexible housing part. The housing part flexes to allow eccentric motion of the annular gear. Only one eccentric element is provided and the annular gear has only one set of gear teeth.
  • a gearbox according to claim 1 there is provided a gearbox according to claim 1. According to a second aspect of the present invention, there is provided a gearbox according to claim 7.
  • the present invention provides a gearbox with compact dimensions, which is self -locking and which provides a high reduction ratio.
  • Figure 1 shows a cross sectional view of a first embodiment of a gearbox in accordance with the present invention
  • Figure 2 shows a cut away perspective view of the gearbox of Figure 1, including a drive assembly
  • FIG 3 shows another cut away perspective view of the gearbox of Figure 1;
  • Figure 4 shows a perspective view of an input shaft forming part of an embodiment of the present invention
  • Figure 5 shows a perspective view of an output pinion forming part of an embodiment of the present invention
  • Figure 6a shows a perspective view of a first side of a fixed internal gear forming part of an embodiment of the present invention
  • Figure 6b shows a perspective view of a second side of the fixed internal gear of Figure 6a;
  • Figure 7 shows a perspective view of a drive ring forming part of an embodiment of the present invention
  • Figure 8 shows a perspective view of a bush assembly forming part of an embodiment of the present invention
  • Figure 9 shows a perspective view of an orbiting gear forming part of an embodiment of the present invention.
  • Figure 10 shows a schematic view of a drive assembly for use in an embodiment of the present invention
  • Figure 11a shows a perspective view of an adjuster body forming part of the drive assembly of Figure 10;
  • Figure lib shows an end view of the adjuster body of Figure
  • Figure 12a shows a perspective view of an adjuster housing forming part of the drive assembly of Figure 10;
  • Figure 12b shows an end view of the adjuster housing of
  • Figure 1 depicts a gearbox comprising: an input shaft 10; a fixed internal gear 30; an output pinion 50; an orbiting gear 70; a housing 90; a drive ring 110; and a bush assembly 130.
  • the input shaft 10 comprises an input portion 12, a first eccentric lobe 14, a second eccentric lobe 16, and an output portion 18.
  • the input shaft 10 is driven to rotate about rotational axis X (which is parallel to the longitudinal axis of the cam shaft 10) by a drive assembly (not shown in Figure 1) .
  • the input portion 12 has a circular cross-section (in a plane perpendicular to the rotational axis X) with a centre that lies on the rotational axis X and is formed with splines 12a for attachment to the drive assembly, and a journal portion 12b for rotation within the bush assembly 130.
  • the output portion 18 has a circular cross-section (in a plane perpendicular to the rotational axis X) with a centre that lies on the rotational axis X.
  • Each of the two eccentric lobes 14, 16 has a circular cross- section (in a plane perpendicular to the rotational axis X) with an axis of symmetry that is off-set from the rotational axis X.
  • the lobe 16 has a cross-sectional diameter greater than that of the output portion 18, and the lobe 14 has a cross-sectional diameter- greater than that of the lobe 16.
  • a fixed internal gear 30, shown in Figures 6a and 6b comprises a bore 32, a tubular boss 32a, a pair of lugs 34 formed on and extending from a circular first flat side face 30a, and a set of N internal teeth 36 extending annularly away from a circular second flat side face 30b.
  • the input shaft 10 is inserted in the bore 32 so that the fixed internal gear 30 is rotatably mounted on the first eccentric lobe 14.
  • the fixed internal gear 30 is free to rotate relative to the input shaft 10.
  • the pair of lugs 34 protrude from the first side 30a of the fixed internal gear 30, and lie on a common diameter extending across the first side face 30a.
  • the lugs 34 each comprise two sides having straight edges which are parallel to the diameter on which they lie.
  • the pair of lugs 34 are arranged to slide in a corresponding pair of slots 114 formed in drive ring 110, as will be discussed below.
  • N can be any suitable number, however, in this embodiment N is equal to 22.
  • the tubular boss 32a protrudes from the first side face 30a of the fixed internal gear 30, so as to maximise the length of the bore 32 to thereby ensure that the fixed internal gear 30 does not tilt relative to the axis of the eccentric lobe 14, (i.e. to ensure that the axis of the bore 32 coincides with the axis of the eccentric lobe 14 of the input shaft 10 about which the fixed internal gear 30 rotates) .
  • Figure 5 depicts the output pinion 50, which comprises a set of output teeth 52, a set of M radially inward facing teeth 54, a ring portion 56, a bore 58, a tubular boss 58a, and an annular abutment surface 59.
  • the output teeth 52 provide meshing engagement of the output pinion 50 with an external apparatus to be driven (not shown) .
  • the set of M radially inward facing teeth 54 are formed on the inside surface of the ring portion 56.
  • the input shaft 10 is inserted in the bore 58 so that the output pinion 50 is rotatably mounted on the output portion 18. The output pinion 50 is free to rotate relative to the input shaft 10.
  • the radially outermost surface of ring portion 56 and the abutment surface 59 abut against the housing 90, and rotate relative thereto and so they, and the corresponding abutting internal surfaces of the housing 90, must be machined to a high accuracy to reduce friction therebetween and minimise radial free play.
  • the tubular boss 58a protrudes from the output pinion 50, so as to maximise the length of the bore 58 to thereby ensure that the output pinion 50 does not tilt relative to the axis of the output portion 18, (i.e. to ensure that the axis of the bore 58 coincides with the axis of the output portion 18 of the input shaft 10 about which the output pinion 50 rotates) .
  • Figure 9 depicts the orbiting gear 70, which comprises a first set of teeth 72, a second set of teeth 74, a bore 75, a divider 76, and cavities 78.
  • the first set of teeth 72 and the second set of teeth 74 are external teeth which face radially outwards to mesh, respectively, with the radially inward facing internal teeth 54 of the output pinion 50 and the radially inward facing internal teeth 36 of the fixed internal gear 30.
  • Both first and second sets of teeth 72, 74 have the same number of teeth, L.
  • L is equal to 20.
  • the tooth geometry of the teeth differs between the first and second sets 72, 74. This is necessary in order to ensure involute interaction between the external teeth 72, 74 of the orbiting gear 70 and the internal teeth of the output pinion 50 and of the fixed internal gear 30 with which they mesh.
  • the first and second sets of teeth 72, 74 are separated by a divider 76 in the form of an annular wall.
  • the divider 76 strengthens the teeth 72, 74. This is particularly beneficial for resisting crash loading.
  • the input shaft 10 is inserted in the bore 75 so that the orbiting gear 70 is rotatably mounted on the second eccentric lobe 16.
  • the orbiting gear 70 is free to rotate relative to the input shaft 10.
  • a plurality of cavities 78 are formed in the orbiting gear 70 to reduce the amount of material required to form the orbiting gear 70.
  • the drive ring 110 comprises a pair of slots 114 formed on a first side face 110a, and a pair of lugs 118 formed on a second side face 100b.
  • the drive ring 110 is located surrounding the tubular boss 32a of the fixed internal gear 30 with the first face 110a facing the first side face 30a of the fixed internal gear 30.
  • the drive ring 110 has an internal radius which is greater than the external radius of the tubular boss 32a of the fixed internal gear 30, to thereby allow translational motion of the drive ring 110 in a plane perpendicular to the axis of rotation X, relative to the fixed internal gear 30.
  • the drive ring 110 has an external radius which is less than the internal radius of the housing 90 at the position along rotational axis X at which it is located, to thereby allow translational motion of the drive ring 110 in a plane perpendicular to the axis of rotation X, relative to the housing 90.
  • the pair of slots 114 lie on a common diameter extending across the drive ring 110.
  • the slots 114 each comprise two sides having straight edges which are parallel to the diameter on which they lie.
  • the drive ring 110 is oriented so that the straight edges of the slots 114 are parallel to the straight edges of the pair of lugs 34 formed in the fixed internal gear 30.
  • Each of the pair of lugs 34 is inserted in a corresponding one of the pair of slots 114 such that the drive ring 110 and the fixed internal gear 30 may slide relative to each other in the direction of the straight edges of the slots 114. Relative rotation between the drive ring 110 and fixed internal gear 30 and relative translation other than along the direction of the straight edges of the slots 114 is prevented.
  • the pair of lugs 118 lie on a diameter of the drive ring 110 that is not parallel to the diameter on which the slots 114 lie, i.e. there is an angle > 0° between the two diameters.
  • the lugs 118 lie on a diameter that is perpendicular to the diameter on which the slots 114 lie.
  • the lugs 118 each comprise two sides having straight edges which are parallel to the diameter on which they lie.
  • the pair of lugs 114 are arranged to slide in and relative to a corresponding pair of slots 138 formed in a bush assembly 130, as will be discussed below.
  • the bush assembly 130 comprises a bush 132 having a central generally circular section 131, a circular cross-section bore 134 through a centre of the section 131, attachment arms 136 extending radially out from the central section 131, and a pair of slots 138.
  • the input shaft 10 is inserted through the bore 134 to locate the bush assembly 130 on the journal portion 12b of the input shaft 10.
  • the input shaft 10 is free to rotate relative to the bush assembly 130.
  • the bush assembly 130 is attached to the housing 90 by the attachment arms 136, thus preventing relative movement (translation or rotation) therebetween.
  • the pair of slots 138 lie on a common diameter extending across the central section 131 of the bush 132.
  • the slots 138 each comprise two sides having straight edges which are parallel to the diameter on which they lie.
  • the drive ring 110 is oriented so that the straight edges of the lugs 118 are parallel to the straight edges of the pair of slots 138 formed in the bush assembly. Each of the pair of lugs 118 is inserted in a corresponding one of the pair of slots 138 such that the drive ring 110 may slide relative to the bush assembly 130 in the direction of the straight edges of the slots 138.
  • the drive ring 110 is restricted so that it may move only along a single line (collinear with a diameter of the input portion 12 of the cam shaft 10) relative to the housing 90.
  • the fixed internal gear 30 may move relative to the drive ring 110 in the direction of the straight edges of the slots 114 of the drive ring 110, and this direction is perpendicular to the direction that the drive ring 110 may move relative to the housing 90, the fixed internal gear 30 is therefore able to translate, relative to the housing 90, in the plane perpendicular to the rotational axis of the input shaft 10.
  • the fixed internal gear 30 cannot rotate relative to the housing 90.
  • Figure 10 shows a drive assembly 300, suitable for driving the cam shaft 10 of the above-described gearbox.
  • the drive assembly 300 comprises an electric motor 302, a drive assembly housing 304, attachment means 305, a gear 310, a worm gear 320, an adjuster body 330, and an adjuster housing 340.
  • the drive assembly housing 304 is fixed to the housing 90 via attachment means 305.
  • the drive assembly housing 304 comprises a cylindrical section 304a through which the worm gear 320 extends.
  • the worm gear 320 is driven by the output shaft 350 of electric motor 302.
  • the gear 310 is provided with a bore having radially inward facing splines 310a for meshing with splines 12a of the input shaft 10, so that worm wheel 310 and cam shaft 10 rotate together.
  • the worm wheel 310 is further provided with a set of teeth, which are arranged to be driven by the screw thread of worm gear 320.
  • Figure 11a depicts the adjuster body 330, which comprises a main body 334, a first socket 338, a second socket (not shown in Figure 11a, but visible in Figure 10 as the bore into which the output shaft 350 of the electric motor 302 extends) and a divider wall 336 dividing the two sockets and providing end faces for the sockets.
  • An annular shoulder 332 extends radially outward, from one end of the main body 334 (see Figure lla) .
  • the adjuster body 330 is inserted into the cylindrical section 304a of the drive assembly housing 304 and oriented such that the shoulder 332 is closest to the electric motor 302.
  • the adjuster body 330 is located so that the second socket is penetrated by the end of the output shaft 350 of the electric motor 302.
  • the end of the output shaft 350 abuts with a thrust face provided by the divider wall 336.
  • the first socket 338 has a hexagonal cross-section which enables the adjuster body 330 to be engaged and rotated by a suitable tool of a corresponding cross-section.
  • Figure 12a depicts the adjuster housing 340, which comprises a cylindrical portion 341, an annular castellated shoulder 342 at one end, an abutment end face 344 and a bore 346.
  • the bore 346 of the adjuster housing 340 closely fits over the main body 334 of the adjuster body 330, whilst the abutment end face 344 of the adjuster housing 340 abuts against the shoulder 332 of adjuster body 330.
  • the outer surface of the main body 334 of the adjuster body 330 and the inner surface of the bore 346 of the adjuster housing 340 are each formed with inter-engaging lobes 334a, 346a.
  • the cylindrical portion 341 of the adjuster housing 340 is provided with an external male screw thread (not shown) which screws into a corresponding internal female screw thread (not shown) formed on the inside of the end of the cylindrical section 304a of the drive assembly housing 304.
  • the castellated shoulder 342 of adjuster housing 340 forms lugs 342a which enable the adjuster housing 340 to be rotated by a suitable tool with features of a corresponding shape.
  • the adjuster housing can thus be screwed into place in the drive assembly housing 304.
  • the adjuster body 330 and the adjuster housing 340 lock in place in drive assembly housing 304, and together determine the amount of axial movement available to shaft 350, as will be explained below.
  • the gear 310 is provided with a resiliently compressible protrusion 311 (see Figure 2) which engages a facing surface of the drive assembly housing 304 and provides a clearance between the drive assembly housing 304 and the majority of the facing surface of the gear 310. This reduces the effect of friction between the worm wheel 310 and the drive assembly housing 304.
  • the surface of the drive assembly housing 304 facing the gear 310 may also have a resiliently compressible protruding thrust face, to take up clearance in the assembly.
  • the gear 310 slides over and engages the splines 12b of the input shaft 10 so that the gear 310 and input shaft 10 rotate together.
  • the gear 310 forms part of a stack of components mounted on the cam shaft 10 and the attachment of the drive assembly 300 applies an axial force to the stack of components, thereby forcing the stacked components mounted on the input shaft 10 to abut one another with minimal clearance therebetween. Resultant frictional effects are minimal, since only the output pinion 50 has large surfaces in contact with the housing 90, and the output pinion 50 rotates very slowly.
  • a gear must have sufficient length in an axial direction (as compared with the gear radius) to prevent tilt relative to the rotational axis.
  • the gears are arranged axially with minimal clearance therebetween and thus are collectively prevented from tipping. Therefore, they can be formed with as large a radius as possible (subject to the constraints of the space available to a car seat height adjustment mechanism) and without a large dimension in the axial direction. The total axial dimension of the gearbox can therefore be kept small.
  • Figure 2 depicts the gearbox in combination with the drive assembly 300.
  • the electric motor 302 drives the worm gear 320 via output shaft 350.
  • the worm gear 320 drives the gear 310.
  • the gear 310 is mounted on the input shaft 10 such that splines 12b prevent relative rotation therebetween. Therefore, the electric motor 302 of the drive assembly 300 drives the input shaft 10 to rotate relative to housing 90.
  • the axes of symmetry of the circular cross-sections of the first and second eccentric lobes 14, 16 travel in respective circular paths about the axis of rotation X of the input shaft 10.
  • the fixed internal gear 30 is prevented from rotation, but able to translate in a plane perpendicular to axis of rotation X, relative to the housing 90.
  • the fixed internal gear 30 therefore translates in the plane in the circular path defined by the motion of the centre of the first eccentric lobe 14.
  • the orbiting gear 70 is mounted on the second eccentric lobe 16 and consequently travels in the circular path defined by the motion of the centre of the second eccentric lobe 16.
  • the orbiting gear 70 Since the orbiting gear 70 is free to rotate about input shaft 10 and the second set of teeth 74 of the orbiting gear 70 mesh with the inward facing teeth 36 of the fixed internal gear 30, the orbiting gear 70 rolls without slip about a circular path within the fixed internal gear 30. Thus, the orbiting gear 70 rotates relative to the housing 90.
  • the output pinion 50 is free to rotate about the output portion 18 of the input shaft 10, and is therefore not driven directly thereby. However, since the first set of teeth 72 of the orbiting gear 70 mesh with the inward facing teeth 54 of the output pinion 50, the rotation of the orbiting gear 70 drives the output pinion to rotate. Thus the output pinion 50 rotates relative to the housing 90.
  • the orbiting gear 70 rolls once around the circular path within the fixed internal gear 30 and the orbiting gear 70 rolls along the N internal teeth of the gear 30 (sometimes calling "swash motion") .
  • the orbiting gear 70 therefore meshes with N teeth of the fixed internal gear 30.
  • the orbiting gear 70 meshes with M teeth of the output pinion 50, with the orbiting gear 70 rolling along the M teeth (sometimes called "swash motion") .
  • the output pinion 50 therefore advances M- N teeth for every revolution of the input shaft 10. Therefore, in this embodiment, the output pinion 50 advances by one tooth for each revolution of the input shaft 10 (that is, the output pinion 50 rotates once for every 23 revolutions of the input shaft 10) .
  • the fixed internal gear 30 it is necessary for the fixed internal gear 30 to move translationally in a plane perpendicular to axis of rotation X, on the circular path defined by the motion of the centre of the first eccentric lobe 14, in order to allow involute meshing of the second set of teeth 74 of the orbiting gear 70 with the internal teeth 36 of the fixed internal gear 30.
  • the eccentric motion of the fixed internal gear 30 provides a velocity ratio which varies, as between the input shaft 10 and the output pinion 50, over each revolution of the input shaft 10. Conventionally, such variation is considered undesirable. However, this variation will be so minor (e.g. 2.4%) to not attract the attention of a user of a car seat adjustment mechanism.
  • the construction of the gearbox ensures that the only large surfaces between which significant frictional effects may occur are the abutting surfaces of the output pinion 50 and the housing 90. Accordingly, it is only the abutting surfaces of these two components that must be machined to a high accuracy with good surface finishes.
  • the orbiting gear 70 can be formed by a known powder metallurgy technique, wherein a powder is compressed in a die and then heated in a furnace.
  • a powder is compressed in a die and then heated in a furnace.
  • Such a technique allows orbiting gear 70 to be formed with cavities 78 to thereby reduce the amount of material used in the manufacture of the gearbox.
  • the geometry of the teeth 72, 74 of the orbiting gear 70 is dictated by the teeth of the gears with which they mesh.
  • the design parameter of the depth of the teeth 72, 74 may be modified to control the strength of the teeth 72, 74.
  • the orbiting gear 70 form a fine blank, e.g. of 6mm thickness medium carbon steel .
  • a bore would be reamed in the blank and then a gear form rolled on the external surface of the blank, with the pre-reamed bore and to set the centre of the rolled gear form.
  • the resulting gear would be simple in design.
  • the electric motor 302 is a standard commercially available motor. Normally, the output shaft 350 of such motors is provided with a degree of freedom to move axially. It is desirable to be able to control the amount of axial movement available to the shaft. In the present embodiment, this is done as follows:
  • the adjuster body 330 is inserted into the adjuster housing 340 such that the bore 346 of the adjuster housing 340 passes axially over the main body 334 of the adjuster body 330. Owing to the lobes 334a, 346a, formed on the outer surface of the main body 334 of the adjuster body 330 and on the inner surface of the bore 346 of the adjuster housing 340, the adjuster body 330 cannot freely rotate relative to the adjuster housing 340.
  • the adjuster housing 340 is then screwed into the end of the cylindrical section 304a of the drive assembly housing 304, such that the adjuster body 330 and adjuster housing 340 are together inserted into the cylindrical section 304a of the drive assembly housing 304, until the divider wall 336 abuts against the end of the output shaft 350 of the electric motor 302.
  • Adjuster housing 340 is screwed into the drive assembly housing 304, so that the resulting axial motion forces the end of the output shaft 350 to move axially towards the electric motor 302.
  • This is done using a tool which fits with features 342a of the end part 342.
  • a tool would have a "torque trip". That is, it would be configured to provide no more than a desired maximum torque, so as not to damage the apparatus .
  • the adjuster housing 340 is then unscrewed a pre-determined distance, which corresponds with the desired amount of axial movement of the output shaft 350 of the electric motor 302. Finally, the adjuster housing 340 is held in place by a first tool which fits with lugs 342a of the shoulder 342, whilst a second tool, which fits into the hexagonal first bore 338 of the adjuster body 330, applies a large torque to rotate the adjuster body 330 within the static adjuster housing 340. The lobes 334a, 346a are deformed by this large torque and the adjuster housing 340 is forced outwards to thereby lock the housing 340 in place within the internal thread formed inside the end of the cylindrical section 304a of the drive assembly housing 304.
  • the drive ring 110 comprises slots 114 which fit with lugs 34 on the fixed internal gear 30, and lugs 118 which fit with slots 138 in the bush assembly 130
  • the inter- fitting slots and lugs could be provided on either the drive ring 110 or the fixed internal gear 30, and similarly the inter-fitting slots and lugs could be provided on either the drive ring 110 or the bush assembly 130.
  • the arrangement described above, in which slots 138 are provided on the bush assembly 130 is preferable, since the bush assembly may be formed more easily, as a pressed plate .
  • the fixed internal gear 30, drive ring 110, and bush assembly 130 of other embodiments of the invention may be provided with any number of features, so long as they restrict the motion between the neighbouring components to be linear.
  • the two sets of teeth 72, 74 of the orbiting gear 70 have the same number of teeth
  • the first and second sets 72, 74 may be formed with a different number of teeth, in which case, the fixed internal gear 30, and the output pinion 50 need not have a different number of internal teeth 36, 54.
  • the gear assembly referred to above is often termed hypocyclic gearing.
  • the gear assembly provides a 500:1 step down between input speed and output speed in a compact robust gearbox.
  • the meshing involute gear forms on the output pinion 50, the orbiting gear 70 and the fixed internal gear 30 will have undercuts which means that they cannot be assembled by radial motion into engagement, but must be assembled by axial motion into engagement.
  • This axial engagement is permitted by the design described above, in particular the stepped design of the input shaft 10.
  • the gear form on the worm gear 320 is preferably a cold rolled translational gear form, so that it has a good surface finish.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Aviation & Aerospace Engineering (AREA)
  • Transportation (AREA)
  • Retarders (AREA)
  • Chairs For Special Purposes, Such As Reclining Chairs (AREA)

Abstract

The present invention relates to a gearbox suitable for use in a car seat height adjustment mechanism, a drive assembly therefor, and a method of manufacturing the same. The gearbox, comprises: a housing (90); an input shaft (10) comprising an input portion (12), an output portion (18), a first eccentric lobe (14), and a second eccentric lobe (16); a first internally toothed gear (30) rotatably mounted on the first eccentric lobe (14); an internally toothed output gear (54), rotatably mounted on the output portion (18) of the input shaft (10); and an externally toothed orbiting gear (70) rotatably mounted on the second eccentric lobe (16) and arranged to mesh with both the first internally toothed gear (30) and the internally toothed output gear (54); wherein: the first internal toothed gear (30) has a first number of teeth different from a second number of teeth of the internally toothed output gear (30); and a locating means (110) prevents rotation of the first internally toothed gear (30) relative to the housing, whilst allowing translational movement of the first internally toothed gear (30) in a plane perpendicular to a rotational axis of the input shaft (10).

Description

A gearbox and a driving assembly therefor
The present invention relates to a gearbox suitable for use in a car seat height adjustment mechanism, a drive assembly therefor, and a method of manufacturing the same.
Gearboxes and associated driving assemblies suitable for use in car seat height adjustment mechanisms must be small to be installed in a standard fixing arrangement, but should provide a high reduction ratio.
Additionally, gearboxes must be able to withstand relatively large crash loading forces and torques.
US 7,235,020 describes three embodiments of step down gear trains suited for use in a vehicle seat adjustment mechanism. In all embodiments there are two eccentric gear stages. Each comprises an annular gear mounted on an eccentric provided on an output shaft, the eccentric having an axis of symmetry displaced from the axis of rotation of the output shaft. The rotation of the eccentric causes the annular gearwheel to translate in a plane perpendicular to the axis of rotation of the output shaft. The annular gear has a set of external teeth and also a set of internal teeth. One of the sets of teeth engages a static toothed rack connected to the housing whilst the other engages a toothed rack provided by an output gear attached to an output shaft. Only one eccentric is provided in the arrangement and the annular gear always has both a set of external teeth and a set of internal teeth. US 6,491,601 discloses an eccentric gear mechanism having an annular gear mounted on an eccentric on an input shaft . The annular gear is provided with only one set of teeth which engage the teeth of an output gear. A slot is provided in the annular gear and an arm formed integrally with a pinion gear is positioned in the slot. The pinion gear is supported on a spindle mounted on a housing part and has external teeth meshing with teeth of the input shaft . Only one eccentric is provided and the annular gear has only one set of gear teeth, an internal set.
US 6,280,359 discloses an eccentric gear drive with an input shaft having an eccentric element and an annular gear mounted on the eccentric element. The annular gear has a set of internal teeth engaging external teeth on an output gear. A lug or a pair of lugs are provided on the annular gear, which slide in one or a pair of slots in a fixed housing cap. One eccentric element is provided and the annular gear has only one set of gear teeth.
US 6,453,772 discloses an eccentric gear drive with an input shaft having an eccentric element with an annular gear mounted thereon. The annular gear has a set of internal teeth which engage external teeth of an output gear. A pair of pegs are provided on the annular gear which extends into sockets in a flexible housing part. The housing part flexes to allow eccentric motion of the annular gear. Only one eccentric element is provided and the annular gear has only one set of gear teeth.
According to a first aspect of the present invention, there is provided a gearbox according to claim 1. According to a second aspect of the present invention, there is provided a gearbox according to claim 7.
According to a third aspect of the present invention, there is provided an assembly of a gearbox according to claim 12.
According to a fourth aspect of the present invention, there is provided a method of manufacturing an assembly of gearbox according to claim 13.
The present invention provides a gearbox with compact dimensions, which is self -locking and which provides a high reduction ratio.
The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
Figure 1 shows a cross sectional view of a first embodiment of a gearbox in accordance with the present invention; Figure 2 shows a cut away perspective view of the gearbox of Figure 1, including a drive assembly;
Figure 3 shows another cut away perspective view of the gearbox of Figure 1;
Figure 4 shows a perspective view of an input shaft forming part of an embodiment of the present invention; Figure 5 shows a perspective view of an output pinion forming part of an embodiment of the present invention; Figure 6a shows a perspective view of a first side of a fixed internal gear forming part of an embodiment of the present invention; Figure 6b shows a perspective view of a second side of the fixed internal gear of Figure 6a;
Figure 7 shows a perspective view of a drive ring forming part of an embodiment of the present invention; Figure 8 shows a perspective view of a bush assembly forming part of an embodiment of the present invention;
Figure 9 shows a perspective view of an orbiting gear forming part of an embodiment of the present invention;
Figure 10 shows a schematic view of a drive assembly for use in an embodiment of the present invention;
Figure 11a shows a perspective view of an adjuster body forming part of the drive assembly of Figure 10;
Figure lib shows an end view of the adjuster body of Figure
11a; Figure 12a shows a perspective view of an adjuster housing forming part of the drive assembly of Figure 10; and
Figure 12b shows an end view of the adjuster housing of
Figure 12a.
Figure 1 depicts a gearbox comprising: an input shaft 10; a fixed internal gear 30; an output pinion 50; an orbiting gear 70; a housing 90; a drive ring 110; and a bush assembly 130.
As shown in Figure 4, the input shaft 10 comprises an input portion 12, a first eccentric lobe 14, a second eccentric lobe 16, and an output portion 18.
The input shaft 10 is driven to rotate about rotational axis X (which is parallel to the longitudinal axis of the cam shaft 10) by a drive assembly (not shown in Figure 1) . The input portion 12 has a circular cross-section (in a plane perpendicular to the rotational axis X) with a centre that lies on the rotational axis X and is formed with splines 12a for attachment to the drive assembly, and a journal portion 12b for rotation within the bush assembly 130.
The output portion 18 has a circular cross-section (in a plane perpendicular to the rotational axis X) with a centre that lies on the rotational axis X.
Each of the two eccentric lobes 14, 16 has a circular cross- section (in a plane perpendicular to the rotational axis X) with an axis of symmetry that is off-set from the rotational axis X. The lobe 16 has a cross-sectional diameter greater than that of the output portion 18, and the lobe 14 has a cross-sectional diameter- greater than that of the lobe 16.
A fixed internal gear 30, shown in Figures 6a and 6b, comprises a bore 32, a tubular boss 32a, a pair of lugs 34 formed on and extending from a circular first flat side face 30a, and a set of N internal teeth 36 extending annularly away from a circular second flat side face 30b.
The input shaft 10 is inserted in the bore 32 so that the fixed internal gear 30 is rotatably mounted on the first eccentric lobe 14. The fixed internal gear 30 is free to rotate relative to the input shaft 10.
The pair of lugs 34 protrude from the first side 30a of the fixed internal gear 30, and lie on a common diameter extending across the first side face 30a. The lugs 34 each comprise two sides having straight edges which are parallel to the diameter on which they lie. The pair of lugs 34 are arranged to slide in a corresponding pair of slots 114 formed in drive ring 110, as will be discussed below.
On the second side 30b of the fixed internal gear is formed a ring having a set of N radially inward facing internal teeth 36. N can be any suitable number, however, in this embodiment N is equal to 22.
As can be seen in Figure 6a, the tubular boss 32a protrudes from the first side face 30a of the fixed internal gear 30, so as to maximise the length of the bore 32 to thereby ensure that the fixed internal gear 30 does not tilt relative to the axis of the eccentric lobe 14, (i.e. to ensure that the axis of the bore 32 coincides with the axis of the eccentric lobe 14 of the input shaft 10 about which the fixed internal gear 30 rotates) .
Figure 5 depicts the output pinion 50, which comprises a set of output teeth 52, a set of M radially inward facing teeth 54, a ring portion 56, a bore 58, a tubular boss 58a, and an annular abutment surface 59.
The output teeth 52 provide meshing engagement of the output pinion 50 with an external apparatus to be driven (not shown) .
The set of M radially inward facing teeth 54 are formed on the inside surface of the ring portion 56. M can be any number greater than N, however, in this embodiment M is equal to N+l, i.e. M=23. The input shaft 10 is inserted in the bore 58 so that the output pinion 50 is rotatably mounted on the output portion 18. The output pinion 50 is free to rotate relative to the input shaft 10.
The radially outermost surface of ring portion 56 and the abutment surface 59 abut against the housing 90, and rotate relative thereto and so they, and the corresponding abutting internal surfaces of the housing 90, must be machined to a high accuracy to reduce friction therebetween and minimise radial free play.
As can be seen in Figure 5, the tubular boss 58a protrudes from the output pinion 50, so as to maximise the length of the bore 58 to thereby ensure that the output pinion 50 does not tilt relative to the axis of the output portion 18, (i.e. to ensure that the axis of the bore 58 coincides with the axis of the output portion 18 of the input shaft 10 about which the output pinion 50 rotates) .
Figure 9 depicts the orbiting gear 70, which comprises a first set of teeth 72, a second set of teeth 74, a bore 75, a divider 76, and cavities 78.
The first set of teeth 72 and the second set of teeth 74 are external teeth which face radially outwards to mesh, respectively, with the radially inward facing internal teeth 54 of the output pinion 50 and the radially inward facing internal teeth 36 of the fixed internal gear 30.
Both first and second sets of teeth 72, 74 have the same number of teeth, L. In this embodiment, L is equal to 20. Owing to the different number of radially inward facing teeth of the output pinion 50 and of the fixed internal gear 30, the tooth geometry of the teeth differs between the first and second sets 72, 74. This is necessary in order to ensure involute interaction between the external teeth 72, 74 of the orbiting gear 70 and the internal teeth of the output pinion 50 and of the fixed internal gear 30 with which they mesh.
The first and second sets of teeth 72, 74 are separated by a divider 76 in the form of an annular wall. The divider 76 strengthens the teeth 72, 74. This is particularly beneficial for resisting crash loading.
The input shaft 10 is inserted in the bore 75 so that the orbiting gear 70 is rotatably mounted on the second eccentric lobe 16. The orbiting gear 70 is free to rotate relative to the input shaft 10.
A plurality of cavities 78 are formed in the orbiting gear 70 to reduce the amount of material required to form the orbiting gear 70.
As can be seen in Figure 7, the drive ring 110 comprises a pair of slots 114 formed on a first side face 110a, and a pair of lugs 118 formed on a second side face 100b.
The drive ring 110 is located surrounding the tubular boss 32a of the fixed internal gear 30 with the first face 110a facing the first side face 30a of the fixed internal gear 30. - S -
The drive ring 110 has an internal radius which is greater than the external radius of the tubular boss 32a of the fixed internal gear 30, to thereby allow translational motion of the drive ring 110 in a plane perpendicular to the axis of rotation X, relative to the fixed internal gear 30.
The drive ring 110 has an external radius which is less than the internal radius of the housing 90 at the position along rotational axis X at which it is located, to thereby allow translational motion of the drive ring 110 in a plane perpendicular to the axis of rotation X, relative to the housing 90.
The pair of slots 114 lie on a common diameter extending across the drive ring 110. The slots 114 each comprise two sides having straight edges which are parallel to the diameter on which they lie.
The drive ring 110 is oriented so that the straight edges of the slots 114 are parallel to the straight edges of the pair of lugs 34 formed in the fixed internal gear 30. Each of the pair of lugs 34 is inserted in a corresponding one of the pair of slots 114 such that the drive ring 110 and the fixed internal gear 30 may slide relative to each other in the direction of the straight edges of the slots 114. Relative rotation between the drive ring 110 and fixed internal gear 30 and relative translation other than along the direction of the straight edges of the slots 114 is prevented.
The pair of lugs 118 lie on a diameter of the drive ring 110 that is not parallel to the diameter on which the slots 114 lie, i.e. there is an angle > 0° between the two diameters. In this embodiment, the lugs 118 lie on a diameter that is perpendicular to the diameter on which the slots 114 lie. The lugs 118 each comprise two sides having straight edges which are parallel to the diameter on which they lie. The pair of lugs 114 are arranged to slide in and relative to a corresponding pair of slots 138 formed in a bush assembly 130, as will be discussed below.
The bush assembly 130, depicted in Figure 8, comprises a bush 132 having a central generally circular section 131, a circular cross-section bore 134 through a centre of the section 131, attachment arms 136 extending radially out from the central section 131, and a pair of slots 138.
The input shaft 10 is inserted through the bore 134 to locate the bush assembly 130 on the journal portion 12b of the input shaft 10. The input shaft 10 is free to rotate relative to the bush assembly 130.
The bush assembly 130 is attached to the housing 90 by the attachment arms 136, thus preventing relative movement (translation or rotation) therebetween.
The pair of slots 138 lie on a common diameter extending across the central section 131 of the bush 132. The slots 138 each comprise two sides having straight edges which are parallel to the diameter on which they lie.
The drive ring 110 is oriented so that the straight edges of the lugs 118 are parallel to the straight edges of the pair of slots 138 formed in the bush assembly. Each of the pair of lugs 118 is inserted in a corresponding one of the pair of slots 138 such that the drive ring 110 may slide relative to the bush assembly 130 in the direction of the straight edges of the slots 138.
Since the bush assembly 130 is fixed relative to the housing 90, the drive ring 110 is restricted so that it may move only along a single line (collinear with a diameter of the input portion 12 of the cam shaft 10) relative to the housing 90.
Since the fixed internal gear 30 may move relative to the drive ring 110 in the direction of the straight edges of the slots 114 of the drive ring 110, and this direction is perpendicular to the direction that the drive ring 110 may move relative to the housing 90, the fixed internal gear 30 is therefore able to translate, relative to the housing 90, in the plane perpendicular to the rotational axis of the input shaft 10. The fixed internal gear 30 cannot rotate relative to the housing 90.
Figure 10 shows a drive assembly 300, suitable for driving the cam shaft 10 of the above-described gearbox.
The drive assembly 300 comprises an electric motor 302, a drive assembly housing 304, attachment means 305, a gear 310, a worm gear 320, an adjuster body 330, and an adjuster housing 340.
The drive assembly housing 304 is fixed to the housing 90 via attachment means 305. The drive assembly housing 304 comprises a cylindrical section 304a through which the worm gear 320 extends.
The worm gear 320 is driven by the output shaft 350 of electric motor 302.
The gear 310 is provided with a bore having radially inward facing splines 310a for meshing with splines 12a of the input shaft 10, so that worm wheel 310 and cam shaft 10 rotate together. The worm wheel 310 is further provided with a set of teeth, which are arranged to be driven by the screw thread of worm gear 320.
Figure 11a depicts the adjuster body 330, which comprises a main body 334, a first socket 338, a second socket (not shown in Figure 11a, but visible in Figure 10 as the bore into which the output shaft 350 of the electric motor 302 extends) and a divider wall 336 dividing the two sockets and providing end faces for the sockets.
An annular shoulder 332 extends radially outward, from one end of the main body 334 (see Figure lla) .
The adjuster body 330 is inserted into the cylindrical section 304a of the drive assembly housing 304 and oriented such that the shoulder 332 is closest to the electric motor 302.
The adjuster body 330 is located so that the second socket is penetrated by the end of the output shaft 350 of the electric motor 302. The end of the output shaft 350 abuts with a thrust face provided by the divider wall 336. The first socket 338 has a hexagonal cross-section which enables the adjuster body 330 to be engaged and rotated by a suitable tool of a corresponding cross-section.
Figure 12a depicts the adjuster housing 340, which comprises a cylindrical portion 341, an annular castellated shoulder 342 at one end, an abutment end face 344 and a bore 346.
The bore 346 of the adjuster housing 340 closely fits over the main body 334 of the adjuster body 330, whilst the abutment end face 344 of the adjuster housing 340 abuts against the shoulder 332 of adjuster body 330.
As can be seen in Figures lib and 12b, the outer surface of the main body 334 of the adjuster body 330 and the inner surface of the bore 346 of the adjuster housing 340 are each formed with inter-engaging lobes 334a, 346a.
The cylindrical portion 341 of the adjuster housing 340 is provided with an external male screw thread (not shown) which screws into a corresponding internal female screw thread (not shown) formed on the inside of the end of the cylindrical section 304a of the drive assembly housing 304.
The castellated shoulder 342 of adjuster housing 340 forms lugs 342a which enable the adjuster housing 340 to be rotated by a suitable tool with features of a corresponding shape. The adjuster housing can thus be screwed into place in the drive assembly housing 304. The adjuster body 330 and the adjuster housing 340 lock in place in drive assembly housing 304, and together determine the amount of axial movement available to shaft 350, as will be explained below.
The gear 310 is provided with a resiliently compressible protrusion 311 (see Figure 2) which engages a facing surface of the drive assembly housing 304 and provides a clearance between the drive assembly housing 304 and the majority of the facing surface of the gear 310. This reduces the effect of friction between the worm wheel 310 and the drive assembly housing 304. In preferred embodiments, the surface of the drive assembly housing 304 facing the gear 310 may also have a resiliently compressible protruding thrust face, to take up clearance in the assembly.
When the drive assembly 300 is installed on the gearbox, the gear 310 slides over and engages the splines 12b of the input shaft 10 so that the gear 310 and input shaft 10 rotate together.
The gear 310 forms part of a stack of components mounted on the cam shaft 10 and the attachment of the drive assembly 300 applies an axial force to the stack of components, thereby forcing the stacked components mounted on the input shaft 10 to abut one another with minimal clearance therebetween. Resultant frictional effects are minimal, since only the output pinion 50 has large surfaces in contact with the housing 90, and the output pinion 50 rotates very slowly. Conventionally, a gear must have sufficient length in an axial direction (as compared with the gear radius) to prevent tilt relative to the rotational axis. Advantageously, in the above-described embodiment, the gears are arranged axially with minimal clearance therebetween and thus are collectively prevented from tipping. Therefore, they can be formed with as large a radius as possible (subject to the constraints of the space available to a car seat height adjustment mechanism) and without a large dimension in the axial direction. The total axial dimension of the gearbox can therefore be kept small.
Figure 2 depicts the gearbox in combination with the drive assembly 300. The electric motor 302 drives the worm gear 320 via output shaft 350. The worm gear 320 drives the gear 310. The gear 310 is mounted on the input shaft 10 such that splines 12b prevent relative rotation therebetween. Therefore, the electric motor 302 of the drive assembly 300 drives the input shaft 10 to rotate relative to housing 90.
As the input shaft 10 rotates, the axes of symmetry of the circular cross-sections of the first and second eccentric lobes 14, 16 travel in respective circular paths about the axis of rotation X of the input shaft 10.
The fixed internal gear 30 is prevented from rotation, but able to translate in a plane perpendicular to axis of rotation X, relative to the housing 90. The fixed internal gear 30 therefore translates in the plane in the circular path defined by the motion of the centre of the first eccentric lobe 14. The orbiting gear 70 is mounted on the second eccentric lobe 16 and consequently travels in the circular path defined by the motion of the centre of the second eccentric lobe 16.
Since the orbiting gear 70 is free to rotate about input shaft 10 and the second set of teeth 74 of the orbiting gear 70 mesh with the inward facing teeth 36 of the fixed internal gear 30, the orbiting gear 70 rolls without slip about a circular path within the fixed internal gear 30. Thus, the orbiting gear 70 rotates relative to the housing 90.
The output pinion 50 is free to rotate about the output portion 18 of the input shaft 10, and is therefore not driven directly thereby. However, since the first set of teeth 72 of the orbiting gear 70 mesh with the inward facing teeth 54 of the output pinion 50, the rotation of the orbiting gear 70 drives the output pinion to rotate. Thus the output pinion 50 rotates relative to the housing 90.
For each revolution of the input shaft 10, the orbiting gear 70 rolls once around the circular path within the fixed internal gear 30 and the orbiting gear 70 rolls along the N internal teeth of the gear 30 (sometimes calling "swash motion") . The orbiting gear 70 therefore meshes with N teeth of the fixed internal gear 30. Equally, for each revolution of the input shaft 10, the orbiting gear 70 meshes with M teeth of the output pinion 50, with the orbiting gear 70 rolling along the M teeth (sometimes called "swash motion") . The output pinion 50 therefore advances M- N teeth for every revolution of the input shaft 10. Therefore, in this embodiment, the output pinion 50 advances by one tooth for each revolution of the input shaft 10 (that is, the output pinion 50 rotates once for every 23 revolutions of the input shaft 10) .
In the above embodiment, it is necessary for the fixed internal gear 30 to move translationally in a plane perpendicular to axis of rotation X, on the circular path defined by the motion of the centre of the first eccentric lobe 14, in order to allow involute meshing of the second set of teeth 74 of the orbiting gear 70 with the internal teeth 36 of the fixed internal gear 30.
The eccentric motion of the fixed internal gear 30 provides a velocity ratio which varies, as between the input shaft 10 and the output pinion 50, over each revolution of the input shaft 10. Conventionally, such variation is considered undesirable. However, this variation will be so minor (e.g. 2.4%) to not attract the attention of a user of a car seat adjustment mechanism.
Advantageously, the construction of the gearbox ensures that the only large surfaces between which significant frictional effects may occur are the abutting surfaces of the output pinion 50 and the housing 90. Accordingly, it is only the abutting surfaces of these two components that must be machined to a high accuracy with good surface finishes.
Additionally, the bore 58 of the output pinion 50 supports one end of the input shaft 10 so that a further journalled bearing surface is unnecessary, thus providing a gearbox that is compact in the axial direction. The orbiting gear 70 can be formed by a known powder metallurgy technique, wherein a powder is compressed in a die and then heated in a furnace. Advantageously, such a technique allows orbiting gear 70 to be formed with cavities 78 to thereby reduce the amount of material used in the manufacture of the gearbox. The geometry of the teeth 72, 74 of the orbiting gear 70 is dictated by the teeth of the gears with which they mesh. The design parameter of the depth of the teeth 72, 74 may be modified to control the strength of the teeth 72, 74.
Alternatively it is possible to make the orbiting gear 70 form a fine blank, e.g. of 6mm thickness medium carbon steel . A bore would be reamed in the blank and then a gear form rolled on the external surface of the blank, with the pre-reamed bore and to set the centre of the rolled gear form. This would be suited to an application in which a sample gear form is provided whereon the orbiting gear, suitable for meshing with both the teeth 54 of output pinion 50 and the teeth 36 of internal gear 30, rather than two separate gear forms as previously disclosed. The resulting gear would be simple in design.
The electric motor 302 is a standard commercially available motor. Normally, the output shaft 350 of such motors is provided with a degree of freedom to move axially. It is desirable to be able to control the amount of axial movement available to the shaft. In the present embodiment, this is done as follows:
Firstly, the adjuster body 330 is inserted into the adjuster housing 340 such that the bore 346 of the adjuster housing 340 passes axially over the main body 334 of the adjuster body 330. Owing to the lobes 334a, 346a, formed on the outer surface of the main body 334 of the adjuster body 330 and on the inner surface of the bore 346 of the adjuster housing 340, the adjuster body 330 cannot freely rotate relative to the adjuster housing 340.
The adjuster housing 340 is then screwed into the end of the cylindrical section 304a of the drive assembly housing 304, such that the adjuster body 330 and adjuster housing 340 are together inserted into the cylindrical section 304a of the drive assembly housing 304, until the divider wall 336 abuts against the end of the output shaft 350 of the electric motor 302.
Adjuster housing 340 is screwed into the drive assembly housing 304, so that the resulting axial motion forces the end of the output shaft 350 to move axially towards the electric motor 302. This is done using a tool which fits with features 342a of the end part 342. Preferably, such a tool would have a "torque trip". That is, it would be configured to provide no more than a desired maximum torque, so as not to damage the apparatus .
When the output shaft 350 has moved to the maximum extent of available axial movement, the output shaft 350 is no longer free to move axially.
The adjuster housing 340 is then unscrewed a pre-determined distance, which corresponds with the desired amount of axial movement of the output shaft 350 of the electric motor 302. Finally, the adjuster housing 340 is held in place by a first tool which fits with lugs 342a of the shoulder 342, whilst a second tool, which fits into the hexagonal first bore 338 of the adjuster body 330, applies a large torque to rotate the adjuster body 330 within the static adjuster housing 340. The lobes 334a, 346a are deformed by this large torque and the adjuster housing 340 is forced outwards to thereby lock the housing 340 in place within the internal thread formed inside the end of the cylindrical section 304a of the drive assembly housing 304.
Although in the gearbox described above, the drive ring 110 comprises slots 114 which fit with lugs 34 on the fixed internal gear 30, and lugs 118 which fit with slots 138 in the bush assembly 130, the skilled person would appreciate that the inter- fitting slots and lugs could be provided on either the drive ring 110 or the fixed internal gear 30, and similarly the inter-fitting slots and lugs could be provided on either the drive ring 110 or the bush assembly 130. However, the arrangement described above, in which slots 138 are provided on the bush assembly 130 is preferable, since the bush assembly may be formed more easily, as a pressed plate .
Furthermore, although the features of the slots and lugs described above are formed in pairs, the fixed internal gear 30, drive ring 110, and bush assembly 130 of other embodiments of the invention may be provided with any number of features, so long as they restrict the motion between the neighbouring components to be linear. Although in the embodiment described above, the two sets of teeth 72, 74 of the orbiting gear 70 have the same number of teeth, the first and second sets 72, 74 may be formed with a different number of teeth, in which case, the fixed internal gear 30, and the output pinion 50 need not have a different number of internal teeth 36, 54.
The gear assembly referred to above is often termed hypocyclic gearing. The gear assembly provides a 500:1 step down between input speed and output speed in a compact robust gearbox.
It is possible that the meshing involute gear forms on the output pinion 50, the orbiting gear 70 and the fixed internal gear 30 will have undercuts which means that they cannot be assembled by radial motion into engagement, but must be assembled by axial motion into engagement. This axial engagement is permitted by the design described above, in particular the stepped design of the input shaft 10.
The gear form on the worm gear 320 is preferably a cold rolled translational gear form, so that it has a good surface finish.

Claims

1. A gearbox, comprising: a housing; an input shaft comprising an input portion, an output portion, a first eccentric lobe, and a second eccentric lobe; a first internally toothed gear rotatably mounted on the first eccentric lobe; an internally toothed output gear, rotatably mounted on the output portion of the cam shaft; and an externally toothed orbiting gear rotatably mounted on the second eccentric lobe and arranged to mesh with both the first internally toothed gear and the internally toothed output gear; wherein: the first internal toothed gear has a first number of teeth different from a second number of teeth of the internally toothed output gear; and a locating means prevents rotation of the first internally toothed gear relative to the housing, whilst allowing translational movement of the first internally toothed gear in a plane perpendicular to a rotational axis of the input shaft .
2. A gearbox according to claim 1, wherein the orbiting gear is formed with a first set of teeth for meshing with the first internally toothed gear and a second set of teeth for meshing with the internally toothed output gear.
3. A gearbox according to claim 2, wherein the first set of teeth of the orbiting gear have first tooth geometries different to second tooth geometries of the second set of teeth of the orbiting gear.
4. A gearbox according to any one of claims 1 to 3, wherein: the locating means comprises a first drive ring provided with one or more first slots on a first side; the first internally toothed gear is provided with one or more lugs for insertion into the slots of the first drive ring; and the slots and lugs are configured and arranged to allow translational relative movement between the first drive ring and the first internally toothed gear.
5. A gearbox according to any one of claims 1 to 3 , wherein: the locating means comprises a first drive ring provided with one or more lugs on a first side; the first internally toothed gear is provided with one or more slots for receiving the lugs of the first drive ring; and the slots and the lugs are configured and arranged to allow translational relative movement between the first drive ring and the first internally toothed gear.
6. A gearbox according to any one of claims 1 to 5 wherein: the first eccentric lobe has a circular cross-section of a first diameter with an axis of symmetry spaced apart from the axis of rotation of the input shaft; the first internally toothed gear has a central bore of a cross-section which matches the cross-section of the first eccentric lobe; the second eccentric lobe has a circular cross-section of a second diameter smaller than the first diameter with an axis of symmetry spaced apart from the axis of rotation of the input shaft; and the externally toothed orbiting gear has a central bore of a cross-section which matches the cross-section of the second eccentric lobe.
7. A gearbox, comprising: a housing; an input shaft comprising an input portion, an output portion, a first eccentric lobe, and a second eccentric lobe; a first internally toothed gear rotatably mounted on the first eccentric lobe; an internally toothed output gear, rotatably mounted on the output portion of the cam shaft; and an externally toothed orbiting gear rotatably mounted on the second eccentric lobe and arranged to mesh with both the first internal gear and the second internal gear; wherein: the orbiting gear is formed with a first set of teeth for meshing with the first internally toothed gear and a second set of teeth for meshing with the internally toothed output gear; and the first set of teeth of the orbiting gear has a number of teeth different from a number of teeth of the second set of teeth of the orbiting gear; and a locating means prevents rotation of the first internal gear relative to the housing, whilst allowing translational movement of the first internal gear in a plane perpendicular to a rotational axis of the input shaft.
8. A gearbox according to claim 7, wherein the first set of teeth of the orbiting gear have tooth geometries different to tooth geometries of the second set of teeth of the orbiting gear.
9. A gearbox according to claim 7 or 8, wherein: the locating means comprises a first drive ring provided with one or more first slots on a first side; the first internally toothed gear is provided with one or more lugs for insertion into the slots of the first drive ring; and the slots and lugs are configured and arranged to allow translational relative movement between the first drive ring and the first internal gear.
10. A gearbox according to claim 7 or 8, wherein: the locating means comprises a first drive ring provided with one or more lugs on a first side; the first internally toothed gear is provided with one or more slots for receiving the lugs of the first drive ring; and the slots and the lugs are configured and arranged to allow translational relative movement between the first drive ring and the first internal gear.
11. A gearbox according to according to any one of claims 7 to 10 wherein: the first eccentric lobe has a circular cross-section of a first diameter with an axis of symmetry spaced apart from the axis of rotation of the input shaft; - I S -
the first internally toothed gear has a central bore of a cross-section which matches the cross-section of the first eccentric lobe; the second eccentric lobe has a circular cross-section of a second diameter smaller than the first diameter with, an axis of symmetry spaced apart from the axis of rotation of the input shaft ; and the externally toothed orbiting gear has a central bore of a cross-section which matches the cross-section of the second eccentric lobe.
12. An assembly of a gearbox as claimed in any one of the preceding claims with an electric motor; wherein the electric motor has an output shaft; the housing has a cylindrical part having a female thread on the internal surface thereof; an adjuster body, which has a shoulder protruding radially outwards therefrom, abuts against an end of the output shaft; and an adjuster housing, having a male thread on the external surface thereof is screwed into the female thread of the cylindrical part of the housing, with the adjuster housing abutting the shoulder of the adjuster body.
13. A method of manufacturing the assembly of claim 12, comprising the steps of:
(a) providing the electric motor with an output shaft that is free to move axially within the electric motor by a first amount; (b) attaching the electric motor to the drive assembly housing; (c) inserting the adjuster body with the radially protruding shoulder into the adjuster housing until the radially protruding shoulder abuts against the adjuster housing; (d) screwing the male thread of the adjuster housing into the female thread of the cylindrical part until the adjuster body abuts the end of the output shaft;
(e) screwing the adjuster housing further into the drive assembly housing to thereby move the output shaft of the electric motor in the axial direction until the object is no longer free to move axially; and
(f) then unscrewing the adjuster housing a predetermined axial distance until the output shaft is free to move axially by a chosen second amount.
14. A method according to claim 13, wherein step (e) comprises : applying a torque to the adjuster housing, the torque being sufficient to move the output shaft axially; and when the torque applied to the adjuster housing required to move the shaft axially is greater than a predetermined maximum torque, removing the torque from the adjuster housing.
15. A method according to claim 13 or claim 14, wherein: the adjuster body is provided with lobes on the outer surface thereof; and the adjuster housing is provided with lobes on the internal surface thereof, further comprising the step of: (g) rotating the adjuster body relative to the adjuster housing to force the adjuster housing radially outwards to deform inter-engaging lobes of the adjuster housing and the adjuster body and thereby to lock the adjuster body and the adjuster housing in position within the housing.
16. An assembly of gearbox and electric motor substantially as herebefore described with reference to and as shown in the accompanying drawings .
PCT/GB2010/000652 2009-04-06 2010-04-01 A gearbox and a driving assembly therefor WO2010116125A1 (en)

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GB0905974A GB2469280A (en) 2009-04-06 2009-04-06 A gearbox for a car seat height adjustment mechanism
GB0905974.2 2009-04-06

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WO2017035327A1 (en) * 2015-08-25 2017-03-02 Fisher & Company, Incorporated Single-stage gear reduction output mechanism with a locking fork providing anti-back drive capability for automotive seat adjuster drives
US10024392B2 (en) 2015-08-25 2018-07-17 Fisher & Company, Incorporated Single-stage gear reduction output mechanism having a locking gear with pin receiving guide holes and anti-back drive capability for automotive seat adjuster drives
US10195975B2 (en) 2016-01-19 2019-02-05 Fisher & Company, Incorporated Gear assembly for a seat adjuster
CN110395149A (en) * 2019-08-30 2019-11-01 湖北航嘉麦格纳座椅***有限公司 A kind of automotive seat and its height adjuster
US10843591B2 (en) 2016-01-19 2020-11-24 Fisher & Company, Incorporated Gear assembly for a seat adjuster
US10953772B2 (en) 2016-09-08 2021-03-23 Fisher & Company, Incorporated Open architecture power length adjuster assembly for a vehicle seat and method of manufacturing the same
US11273506B2 (en) 2016-09-08 2022-03-15 Fisher & Company, Incorporated Open architecture power length adjuster assembly for a vehicle seat and method of manufacturing the same
US11485255B2 (en) 2020-05-01 2022-11-01 Fisher & Company, Incorporated Gearbox for vehicle seat adjustment mechanism
US11529892B2 (en) 2020-05-01 2022-12-20 Fisher & Company, Incorporated Gearbox for vehicle seat adjustment mechanism
US11584261B2 (en) 2019-01-09 2023-02-21 Fisher & Company, Incorporated Power seat track assembly
US11760233B2 (en) 2019-02-20 2023-09-19 Fisher & Company, Incorporated Ultra-compact power length adjuster with anti-back drive capability and pinion-rack output for a vehicle seat
US11766956B2 (en) 2016-09-08 2023-09-26 Fisher & Company, Incorporated Open architecture power length adjuster assembly for a vehicle seat and method of manufacturing the same

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FR2975054B1 (en) * 2011-05-13 2014-05-16 Faurecia Sieges Automobile MOTORIZED ARTICULATION FOR VEHICLE SEAT
CN103089955B (en) * 2011-10-27 2015-11-25 比亚迪股份有限公司 A kind of speed change gear
DE102016101732A1 (en) * 2016-02-01 2017-08-03 Igor Lier Mechanical transmission gear
CN105546052A (en) * 2016-02-05 2016-05-04 秦皇岛博硕光电设备股份有限公司 Roller oscillating tooth gear reducer
CN107461482B (en) * 2016-06-02 2021-03-19 广东肇庆爱龙威机电有限公司 Gearbox assembly and headrest driver comprising same
DE112019003566B4 (en) 2018-07-13 2022-06-15 Denso Corporation Speed reducer and engine with speed reducer

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Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9902295B2 (en) 2015-08-25 2018-02-27 Fisher & Company, Incorporated Single-stage gear reduction output mechanism with a locking fork providing anti-back drive capability for automotive seat adjuster drives
US10024392B2 (en) 2015-08-25 2018-07-17 Fisher & Company, Incorporated Single-stage gear reduction output mechanism having a locking gear with pin receiving guide holes and anti-back drive capability for automotive seat adjuster drives
WO2017035327A1 (en) * 2015-08-25 2017-03-02 Fisher & Company, Incorporated Single-stage gear reduction output mechanism with a locking fork providing anti-back drive capability for automotive seat adjuster drives
US10195975B2 (en) 2016-01-19 2019-02-05 Fisher & Company, Incorporated Gear assembly for a seat adjuster
US10843591B2 (en) 2016-01-19 2020-11-24 Fisher & Company, Incorporated Gear assembly for a seat adjuster
US11766956B2 (en) 2016-09-08 2023-09-26 Fisher & Company, Incorporated Open architecture power length adjuster assembly for a vehicle seat and method of manufacturing the same
US10953772B2 (en) 2016-09-08 2021-03-23 Fisher & Company, Incorporated Open architecture power length adjuster assembly for a vehicle seat and method of manufacturing the same
US11273506B2 (en) 2016-09-08 2022-03-15 Fisher & Company, Incorporated Open architecture power length adjuster assembly for a vehicle seat and method of manufacturing the same
US11584261B2 (en) 2019-01-09 2023-02-21 Fisher & Company, Incorporated Power seat track assembly
US11760233B2 (en) 2019-02-20 2023-09-19 Fisher & Company, Incorporated Ultra-compact power length adjuster with anti-back drive capability and pinion-rack output for a vehicle seat
WO2021037114A1 (en) * 2019-08-30 2021-03-04 湖北航嘉麦格纳座椅***有限公司 Vehicle seat and height adjuster thereof
CN110395149A (en) * 2019-08-30 2019-11-01 湖北航嘉麦格纳座椅***有限公司 A kind of automotive seat and its height adjuster
US11529892B2 (en) 2020-05-01 2022-12-20 Fisher & Company, Incorporated Gearbox for vehicle seat adjustment mechanism
US11485255B2 (en) 2020-05-01 2022-11-01 Fisher & Company, Incorporated Gearbox for vehicle seat adjustment mechanism

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