Classifications

• • 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
  • F16H1/02—Toothed gearings for conveying rotary motion without gears having orbital motion
  • F16H1/20—Toothed gearings for conveying rotary motion without gears having orbital motion involving more than two intermeshing members
  • F16H1/203—Toothed gearings for conveying rotary motion without gears having orbital motion involving more than two intermeshing members with non-parallel axes

Definitions

• the present invention refers to the field of transmission units .
• the invention was developed with particular regard to a transmission unit with at least two stages having an input shaft and an output shaft inclined with respect to each other and having at least two skew gears .
• transmission units are known for transmitting the motion between two orthogonal axes which employ a reduction gear, in order to produce the inclination between the axes, and a certain number of gears with parallel axes for completing the desired reduction ratio.
• gears which permit the inclination of the axes are "endless worm” gears, "bevel gear pairs” having concurrent axes, and “bevel gear pairs” having skewed axes, or "hypoid bevel gear pairs” .
• transmission units with bevel gear pair, or hypoid bevel gear pair coupled to one or more gear stages with parallel axes, without preclusions about the coupling order, also known as “orthogonal units”
• transmission units having multi-stage endless worm gears also known as combined endless worm units”
• transmission units having endless worm gears with pre-coupling to spur gears with parallel axes are : transmission units with bevel gear pair, or hypoid bevel gear pair, coupled to one or more gear stages with parallel axes, without preclusions about the coupling order, also known as “orthogonal units”; transmission units having multi-stage endless worm gears, also known as combined endless worm units”; transmission units having endless worm gears with pre-coupling to spur gears with parallel axes.
• the principal disadvantage of the endless worm units is the modest output, decreasing as the transmission ratio increases, but also the progressive wear of the crown, generally made of bronze.
• the aim of the present invention is to produce a transmission unit which remedies the disadvantages of the known reduction units while preserving the advantages thereof.
• the invention proposes to provide a transmission unit with contained cost, not bulky, silent in use, and easy to produce, assemble and maintain.
• the subject of the present invention is a transmission unit of the type indicated in the preamble of the present description, in which at least one of the at least two gears is a gear with spur gearwheels.
• the transmission unit has proved to guarantee a high output and the maintenance of performance over time .
• each skew gear apart from contributing to the inclination between the shafts, is also capable of providing a consistent reduction or multiplication of the rotation speed of the shafts, such that the total number of stages required is small .
• a further advantage is the possibility of transmitting high torques, given that the transmission unit is more robust, in fact, the individual skew stages with spur gears have a much greater area of contact between the gearwheels than the skew gears with axes at 90°.
• one of the two shafts, input or output, of the transmission unit lies in a plane substantially orthogonal to the other shaft.
• Experimental results have provided indications of the fact that the best results for output, service life and transmissible power appear to be obtained by inclinations of between around forty and fifty degrees.
• the inclination between the input and output shafts of all the skew gears is selected such that their sum is preferably, though not by way of limitation, substantially equal to ninety degrees, so that the angles of inclination of the input and output shafts of the at least two skew gears are approximately complementary.
• the at least two skew gears have a shaft in common, skewed with respect to both, in order further to reduce the number of stages necessary for obtaining the desired inclination between the input shaft and the output shaft of the transmission unit, and therefore reduce the total dimensions of the transmission unit.
• the reduction gears with skewed axes comprise gearwheels with teeth which have on their flank more material at the periphery than at the centre, proceeding in the direction of the width of the gearwheel.
• a so-called negative crowning of the helix rather than positive is produced, contrary to common usage in the field.
• the production of said teeth not, however, adding to the final cost of the transmission unit, since it can be achieved by means of the common production equipment for gearwheels, but offers the significant advantage of increasing the bearing capacity and the output of the gears, by increasing their contact surface between one tooth and another, particularly under load.
• the skew gears of the transmission unit have shafts all parallel to a common plane. This particular feature permits the manufacture of a reduction unit such that the machining of the seating holes or support seats can be carried out with a single take of the box or casing or a part thereof, in the case where the casing is in several parts .
• Machining may be carried out with a common machine tool, for example a boring machine, in particular even if it is not exclusively of the type with four controlled axes, by aligning the axes of the seating holes or support seats in turn with a spindle axis, positioning that also parallel to the aforesaid common plane, for example by means of rotation of the worktable, and, more generally, relative rotation of the spindle axis and of the casing about an axis perpendicular to the aforesaid common plane.
• a common machine tool for example a boring machine, in particular even if it is not exclusively of the type with four controlled axes, by aligning the axes of the seating holes or support seats in turn with a spindle axis, positioning that also parallel to the aforesaid common plane, for example by means of rotation of the worktable, and, more generally, relative rotation of the spindle axis and of the casing about an axis perpendicular to the aforesaid
• a preferred embodiment of a reduction unit comprises a transmission unit according to one of claims 1 to 7, and, in a variant thereof, said reduction gear comprises a support box for the transmission unit according to claim 8.
• Figure 1 is a three-dimensional view of a reduction unit according to the present invention with two reduction stages and a skew shaft common to the two stages;
• Figure 2 is a three-dimensional view of the gears inside the reduction unit according to the arrow II of Figure
• Figure 3 is a cross-section in a horizontal plane passing through the line III-III of Figure 1.
• the section plane is diametrical to the input shaft of the reduction unit and indicated by III-III in Figure 1;
• Figure 4 is a cross-section in a plane passing through the line IV-IV of Figure 1;
• Figure 5 is a cross-section passing through the line V-V of Figure 1 ;
• Figure 6 is a three-dimensional view of a tooth of a gearwheel according to the present invention, the flanks of which have a negative crowning which for clarity of illustration has been enlarged and exaggerated.
• a reduction unit 10 of the type with gears has a support box or casing 12, preferably, but not by way of limitation, sub-divided into two parts 12a and 12b that can be separated from each other.
• the casing 12 supports the internal gears 15 contained in a chamber 16 produced between the two parts 12a and 12b and has an inlet aperture 14a and an outlet aperture 14b, through which the chamber 16 communicates with the outside.
• an input shaft 18 and an output shaft 20 which extend into the chamber 16 and carry internal gears 15 to which, and from which, they respectively transmit and receive the rotatory motion.
• the input shaft 18 and the output shaft 20 have directions orthogonal to each other, even if their geometric axes may not be incident.
• the input shaft 18 is preferably supported at two points by bearings 22 housed in seats 24 provided in the casing 12.
• a pinion 26 is provided, produced in one piece with the shaft 18 or as a separate part and fixed to the shaft 18 by a known system, for example a shoulder in association with a key or assembly by interference.
• the pinion 26 is a spur gearwheel with teeth having a helical profile and meshes with a spur gearwheel 28 of larger diameter, also with helical teeth and produced in one piece with, or fixed to, an idle shaft 30, skewed with respect to the input shaft 18, for example by means of a key 32 and other .known means.
• the idle shaft 30 is supported by bearings 22, mounted in seats 24 provided in the chamber 16 of the casing 12.
• a second pinion 34 On the idle shaft 30 there is also produced in one piece, or fixed, a second pinion 34, preferably of smaller diameter than the gearwheel 28, which meshes with a second gearwheel 36, made in one piece with, or mounted on, the output shaft 20 so as to entrain the latter in rotation.
• the second pinion 34 and the second gearwheel 36 are also preferably spur gears with helical teeth, while the diameter of the second gearwheel 36 is preferably less than the diameter of the second pinion 34.
• the input and output axes 18 and 20 and the idle shaft 30 are disposed such that their longitudinal axes lie in three planes parallel to one another.
• An expert in the field will be able also to employ a different assembly configuration.
• the longitudinal axes of the input shaft 18 and output shaft 20, if projected onto one of said planes will be inclined with respect to each other by ninety degrees, while with respect to the longitudinal shaft of the idle shaft 30 projected onto the same plane they are preferably inclined by an angle ranging between around thirty and sixty degrees, and more preferably between around forty and fifty degrees.
• the assembled configuration of the input and output shafts 18 and 20 and of the idle shaft 30 is reflected in the arrangement and orientation of the seats 24 of the bearings 22 and of the inlet and outlet apertures 14a and 14b, which have their axes parallel to those of said shafts.
• This skewed arrangement of the axes of the seats 24 and of the inlet and outlet apertures 14a and 14b permits machining of each of the two parts 12a and 12b of the casing 12 in a single "take” by means of, for example, a common boring machine with four controlled axes (for example with a combination of three translations and one rotation of the worktable, for aligning in turn the axis of a seat or aperture with the axis of a spindle) for the production of said seats and apertures.
• coupling means 38 may be employed for the connection of the input shaft 18 to an external drive shaft, for example a cylindrical sleeve may be employed, mounted at the end of the input shaft 18 which projects externally from the outlet aperture 14b of the casing and is firmly secured in rotation to the input shaft 18, for example by means of a key 40 or similar means.
• the sleeve 38 further has means for connection to the external drive shaft, such as for example an axial hole 42 with a longitudinal groove 44 for the insertion of a key.
• the pinions 26 and 34 and the gearwheels 28 and 36 preferably have teeth with negative crowning, for example between 0.02 and 0.05 mm or approximately two hundredths of the modulus, for increasing the contact surface between one tooth and another when meshing with a respective gearwheel or pinion.
• the teeth have on the flank 50 more material at the periphery 52 than at the centre 54 proceeding in the direction L of the width of the gear.
• the input shaft 18 is connected to a drive shaft via the coupling means 38.
• the drive shaft sets in rotation the input shaft 18 and with it the pinion 26.
• the pinion 26 meshing with the gearwheel 28 effects the rotation of the idle shaft 30 at a lower speed than the input shaft 18.
• the second pinion 34 meshing with the second gearwheel 36 of larger diameter effects the rotation of the output shaft at a lower speed than the idle shaft 30.
• a further advantage is provided by the negative crowning, which simulates an adaptation of the teeth generally obtained by means of lapping.
• the contact surfaces are thus well coupled even when it would be technically impossible or uneconomic to carry out lapping.
• the present invention owing to the skew gears, enjoys the advantage of permitting assembly with wide tolerances, unlike the example of bevel gears, and the advantage of permitting reverse motion, therefore finding an application in a wider field than endless worm reduction units.
• the principle of the invention remaining unchanged, the constructional characteristics and the details of production may be course vary widely from what has been described and illustrated, without thereby departing from the scope of the present invention.

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• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Gear Transmission (AREA)
• Gears, Cams (AREA)
• Structure Of Transmissions (AREA)

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Family Cites Families (6)

• 2003
  • 2003-06-12 IT ITBO20030360 patent/ITBO20030360A1/it unknown
• 2004
  • 2004-06-11 EP EP04736676A patent/EP1631755A2/de not_active Ceased
  • 2004-06-11 WO PCT/IB2004/001972 patent/WO2004111492A2/en active Search and Examination

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