GB2282092A - Gear shaping machine - Google Patents

Abstract

A gear shaping machine comprises a cutter spindle 5 which is reciprocated axially by a first eccentric drive mechanism 26. The spindle 5 rotates with a guide member 11 which is coupled to a drive ring 14 through helical coupling means 12, 13 and which is reciprocated axially by a second eccentric drive mechanism 28. The respective drive mechanisms 26, 28 comprise eccentrically mounted rotary drive members 25, 27 which drive the spindle 5 and guide member 11 directly. This allows variable helical cuts to be achieved. <IMAGE>

Description

GEAR SHAPING MACHINE The present invention relates to a gear shaping machine for use particularly in the manufacturing of cylindrical gears.

At present, gear shaping machines are mostly capable of cutting straight-toothed cylindrical gears only. When used to cut helical cylindrical gears or small-angle bevel gears, these machines must be equipped with special accessories to serve the purpose.

Otherwise, special gear shaping machines must be used.

In most cases, a special helical gear shaping machine can only cut one kind of helical cylindrical gear of the same helical direction and the same helix angle. In the same way, a gear shaping machine specially for smallangle bevel gear can only process one kind of bevel gear of the same cone angle. However, gear manufacturers, particularly automobile gear manufacturers, frequently need different kinds of special gear shaping machines to produce a range of different gears. This requires large investment and long lead times and manufacturers find it difficult to keep up with the progress and innovations in the field of automobile gear production.

Furthermore, machine manufacturers also find it troublesome to respond to the demands of the automobile gear manufacturers.

Adjustable helical gear shaping mechanisms are known. These mechanisms fall into two categories: the digitally-controlled and the mechanically-controlled.

The first category is represented by Japanese Patent No.

Tekaizhao 62-39115. However, due to high cost and difficulties in developing a digital control system of sufficiently high precision and sensitivity, no satisfactory product has yet been provided to the market.

The second category is represented by U.S. Patent No. 4,606,632. The system disclosed in this patent consists of two crank-lever mechanisms driving respective cutter saddles; the first mechanism drives the cutter spindle to make reciprocal linear movement; the other drives a movable helical guide, arranged within a worm driven ring, to make reciprocal rotational movement. The worm driven gear is linked to the work piece so as to rotate at the same speed as the work piece. The eccentric drive of the helical guide means that as it moves up and down with respect to the drive ring, it will rotate with respect thereto, so giving an additional, or smaller rotation to the cutter spindle which is directly connected to the guide, thereby imparting a helical cut to the gear.In the cutting operation, the eccentricity of the two crank mechanisms is adjusted to give the desired helix angle in the gear.

Again, this system has never been found available in the market. This may be due to helicalline errors introduced by the system.

With reference to Fig. 1 which illustrates the first crank mechanism, as the crank swivels from an angular position OAo over Angle 9 to a new position OA, the eccentricity being el, and the crank lever length 11, a vertical replacement h1 of the cutter results. This is given by:

In the same way, suppose the other crank lever mechanism moves with an eccentricity = ez and lever length = 12 over the same Angle B, this gives a vertical displacement of the movable helical guide = h2. This displacement will be given by:

Supposing that the lead of the movable helical guide is T, when its vertical replacement reaches h2, the main spindle of the cutter should swivel over an angle of T 3 the radian length at the cutter's circle df should be S= #.df.&alpha; = #.df.h2...............4 360 T The combined helix angle at the cutter's reference circle becomes: ss-tan-1 s = - tan #.df. h2...................... 5 h1 T h1

Clearly, as the stroke of the cutter varies from 9 = to 180 , angle p cannot possibly remain a constant; in other words, there exists a helix angle error. The bigger the angle ss, the greater the error, far exceeding the precision allowance for normal gears.For example, Supposing: d1 = 100mm, 11 = 12 = 300mm, T = 600mm e1 = 20mm, e2 = 50mm; When # = 25 (the start cutting point); Then ss1 = 49 36' 46"; When #2 = 155 (the end cutting point); Then ss2 = 52 29' 30".

This shows that the helix angle will differ over the range of rotation of the cutter and that there will therefore be a helix angle error introduced into gears cut on the machine.

The present invention seeks to overcome this problem, and from a first aspect, the invention provides a gear shaping machine comprising: a spindle coupled to a cutter; first eccentric drive means for moving said spindle reciprocably in an axial direction, said spindle being rotatably coupled to rotate with a guide member and constrained so as to be able to move only axially relative to the guide member, said guide member being coupled to a drive ring via helical coupling means; second eccentric drive means for moving said guide member reciprocably in an axial direction; said first and second eccentric drive means each comprising an eccentrically mounted rotary drive member driving directly said spindle and said guide member.

Thus in accordance with the invention, the cutter spindle and the guide member are driven directly by an eccentrically driven member, rather than through a crank lever as in US 4,606,682. This eliminates helix angle errors, as will be seen from the following analysis with reference to Fig. 2 which shows a sliding crank mechanism, in which a block B attached to a rotary arm A slides inside a slide S attached to cutter spindle C which, as the arm A rotates is raised and lowered.

Suppose the eccentricity of the arm A is e. when it moves over an angle o, the main spindle C moves by a vertical displacement h: When a = 0 -90 , then h' = e' (1-cos5); ....,.. 7 When a = 90"-180", then h' = e' [l+sin (8-90 )] ... 8 In the same way, suppose the eccentricity of the eccentric drive of the helical guide is e', then when the eccentric moves over the same angle 9, the guide reaches a vertical displacement h', as follows: When S = 0 -90 , then h=e-e.cos9=e (l-cosa); When a = 90 -180 , then h=e [l+sin (a-90 )].

This leads to the following formula: h' e'(1-cos#)= e'(when#-0-90 )............11 7 e(i-cosO) e h' e'(1+sin(#-90 )) - e' (when0-90-180 ) 12 h e(1+sin(0-900)) e According to the formula 5 above, the helix angle p at the cutter's reference circle is: ss-tan- df . h'=tan-. it. df ff1 13 T h T e Therefore, within the range of S = 0 -180 , the helix angle at the cutter's reference circle will remain a constant during the cutting operation; that is, no error in helix angle will be produced. The formulae further indicate that so long as the diameter d1 of the cutter's reference circle and the stroke T of the spiral rail remain unchanged, the bigger e' is, the bigger e p will be, and vice versa, the smaller is e' , the e smaller will become the angle P. When e' = 0 and p = 0, the machine can cut straight teeth; when e = 0 but e' # o, P = 90", the machine can cut circular teeth.

Therefore, theoretically, the adjustment range for the angle p is infinite.

The helix angle may be easily varied merely by varying the eccentricity of the drive of the helical guide member.

Different forms of eccentric drive means can be envisaged within the scope of the invention. In a simple arrangement the eccentrically mounted drive member engages a drive surface provided on or connected to the spindle or guide member, the eccentrically driven member moving backwards and forwards along the drive surface as it rotates, raising and lowering the drive surface. In one embodiment, the eccentrically mounted drive member may comprise a slide member, for example a block constrained to slide between spaced drive surfaces provided on or connected to the spindle or the guide means. Preferably the slide member has generally parallel sides facing the drive surfaces and is eccentrically and rotatably journaled on a rotating support.The eccentricity of the eccentrically mounted drive member acting on the guide means at least is adjustable, so as to permit variation of the helix angle of the cut. Conveniently, therefore, the drive member may be provided on a carriage adjustably mounted to the rotating support, such as an arm or more preferably a plate, so as to vary the eccentricity of the drive.

In a preferred embodiment, the lines of action of the eccentrically driven members on the spindle and guide members respectively are substantially aligned with each other, generally parallel to and preferably closely adjacent the axis of the spindle. This is advantageous in that it reduces out of line forces on the cutter spindle, so improving the precision of the cut and the life of the cutter bearings, for example.

In a particularly preferred arrangement, the respective eccentric mechanisms lie to one side of the spindle and are arranged generally above one another.

This is a departure from existing arrangements wherein the eccentric mechanisms are arranged generally opposite one another on opposite sides of the spindle. The present arrangement considerably simplifies the transmission system of the machine allows a more compact construction, and facilitates alignment of the lines of action of the respective drive means.

Preferably the spindle is arranged to slide inside the guide member, with respective interengaging axial coupling means, for example axially extending splines and complementary recesses transmitting the rotational drive therebetween. The helical guide member is arranged inside the drive ring, with helical coupling means, for example interengaging helical splines and recesses, to transmit rotational drive therebetween.

In the presently preferred arrangement, the spindle extends downwardly from the guide member and is engaged by the respective eccentrically mounted drive member below the guide member. Also, the guide member preferably has a portion extending above the drive ring which is engaged by its eccentrically driven member.

This is an advantageous arrangement, since it allows more easily the respective eccentric drives to be arranged one above the other, by virtue of introducing a greater spacing therebetween whilst keeping the overall vertical dimension of the machine relatively small.

Preferably the guide member has a shaft portion whose axis is generally aligned with that of the cutter spindle, and which is directly engaged by the eccentrically mounted drive member. This facilitates axial alignment of the respective lines of action of the drives. Most simply, the eccentrically driven members may engage directly in respective collars formed on the spindle and shaft.

As mentioned above, the drive ring is coupled so as to rotate synchronously with the workpiece, which is supported on a work table. In accordance with a further aspect of the invention, the work table is tiltable so as to incline its axis to that of the cutter spindle.

This allows the machine to cut inner or outer teeth of different cone angles, in different directions.

According to a yet further aspect of the invention, the cutter spindle is provided with a relief mechanism whereby the cutter is withdrawn from the workpiece in its upward stroke. Preferably the relief mechanism comprises a relief cam which cooperates with means on or connected to the cutter housing, (which is pivotally mounted) and whose rotation is synchronised with the vertical movement of the cutter. Preferably the cam cooperates with one or a pair of rollers mounted to the cutter housing. Preferably the cam and the roller(s) are formed with a small cone angle. This design allows high speed relief and, further, avoids the defects existing in normal spring-reset relief mechanisms, such as excessive internal stress leading to premature wear of the mechanism, fatigue of the spring and impart vibration.

From a second broad aspect the invention also provides a gear shaping machine comprising: a spindle coupled to a cutter; first eccentric drive means for moving said spindle reciprocably in an axial direction, said spindle being coupled to rotate with a guide member, said guide member being coupled to a drive ring via helical coupling means; second eccentric drive means for moving said guide member reciprocably in an axial direction; said first and second eccentric drive means acting on said spindle and guide means in a generally axial direction.

From a third aspect the invention provides a gear shaping machine comprising: a spindle coupled to a cutter; first eccentric drive means for moving said spindle reciprocably in an axial direction, said spindle being coupled to rotate with a guide member, said guide member being coupled to a drive ring via helical coupling means; second eccentric drive means for moving said guide member reciprocably in an axial direction, said first and second drive means being arranged vertically spaced from one another.

A preferred embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Fig. 1 illustrates a prior art eccentric drive mechanism; Fig. 2 illustrates an eccentric drive as used in accordance with the invention; Fig. 3 shows schematically a machine in accordance with the invention; Fig. 4 shows the cutter drive mechanism of the machine of Fig. 3 in more detail; Fig. 5 shows a vertical sectional view of part of the mechanism of Fig. 4, with the cutter spindle in a raised position; Fig. 6 is a sectional view along line VI-CI of Fig.

5; and Fig. 7 illustrates schematically the relief mechanism of the machine of Fig. 3 in more detail.

Referring firstly to Fig. 3, a gear shaping machine comprises a cutter assembly 1, a work table 2, and a transmission system 3. A workpiece (not shown) is mounted on the work table 2 and a cutter 4 of the cutter of the cutter assembly 1 is moved up and down by an eccentric drive mechanism, while the workpiece and cutter 4 rotate, so as to cut a tooth pattern on the workpiece.

With reference more particularly to Figs. 4 to 6, the cutter assembly 1 comprises a cutter 4 which is mounted on the end of a cutter spindle 5. The cutter spindle 5 comprises a shaft portion 6 and a splined portion 7, the shaft portion being fixed to the splined portion by a nut 8. The splined portion 7 is provided, on its outer surface, with four equispaced spline teeth 9 which extend axially parallel to the axis of the spindle 5. The spline teeth 9 engage in complementary axially extending slots 10 provided on the inner surface of a guide member 11. The guide member 11 is formed on its outer surface with four equispaced helical splines 12. These in turn engage in complementary helical slots 13 formed in the inner surface of an axially fixed drive ring 14.The outer surface of the drive ring 14 is provided with worm gearing 15, for cooperation with a worm shaft 16 of the transmission. As will be described later, the worm shaft 16 rotates the drive ring 14 synchronously with the workpiece.

The guide member 11 has a shaft portion 17 extending from a top surface 18 thereof, the axis of the shaft portion being aligned with that of the shaft portion 6 of cutter spindle 5. The shaft portions 5,17 are formed with respective collars 19,20 defined between annular discs 21,22; 23,24. A rotary drive member of first eccentric drive means 26 in the form of a slide block 25 engages in the collar 19 on the cutter spindle 5 and a rotary drive member of a second eccentric drive means 28 in the form of a slide block 27 engages in the collar 20 on the guide member 11. As will be explained below, the first eccentric drive means 26 controls the vertical movement of the cutter, while the second eccentric drive means controls the helix angle of the cutter.

As can be seen more clearly from Fig. 4, the slide block 25 is in the form of a rectangular block whose upper and lower faces engage slidingly between the discs 22,21 respectively. The block is journaled by a bearing 29 on a first carriage 30 which is adjustably mounted on a slideway 31 to a first rotary drive plate 32. The radial position of the carriage 30 on the drive plate 31 is varied by turning an adjustment screw 33. This will vary the eccentricity of the drive member 25.

Similarly the drive member 27 is in the form of a rectangular block whose upper and lower faces engage slidingly between the discs 24,23 respectively. The block is journaled by a bearing 35 on a second carriage 34 which is adjustably mounted on a slideway 36 to a second rotary drive plate 37. The radial position of the carriage 35 on the drive plate 36 is varied by turning an adjustment screw 38. This will vary the eccentricity of the drive member 27.

It will be seen that the eccentric drive means 26,28 are arranged generally one above the other.

Furthermore, their respective lines of action of the mechanisms on the cutter spindle 5 and helical guide member 11 via the drive members 25,27 respectively are substantially aligned and closely adjacent the common axes of these two components. This reduces out of plane forces on the cutter 4. It will be appreciated that the forces acting on the spindle 5 and the helical guide member 11 will be substantially axial.

The first drive plate 32 and second drive plate 37 are driven at the same speed from motor 39 through gears 40-45, pulley belt 46 and shafts 47,48,49.

The worm gear 15 of the drive ring 14 is driven through a worm shaft 16 mounted on the end of a shaft 50, which is driven by motor 51 through gears 52,53 and drive pulley 54. As mentioned above, the drive ring 14 is rotated synchronously with the workpiece. This is achieved through bevel gears 55,56,57,58, gears 59-62 and a coupling 64, worm shaft 63 and worm gear 65. The workpiece is mounted to a raisable and lowerable table 66 which is rotated by the worm gear 65. A radial feed motor 67 advances the whole work table towards the cutter along a slideway 93 as the cutting operation progresses, to give desired depth of cut. The motor drives a feed screw 68 connected to the work table 2 via a worm shaft 69 and worm gear 70.

The operation of the device as described so far will now be explained. When motor 51 is driven, the drive ring 14 of the cutter mechanism 1 and the table 66 rotate with speeds in a predetermined ratio. For example if the cutter 4 has 30 teeth and it is desired to cut 60 teeth on the workpiece, the ring 14 will rotate twice as quickly as the workpiece. By virtue of the splined connections between the drive ring 14, the helical guide member 11 and the spindle 5, the rotational motion of the drive ring 14 is also transmitted to the cutter 4.

The motor 39 will drive the first and second drive plates 32,37 at the first and second eccentric drive mechanisms 26,28 at the same speed. The first eccentric drive means 26 determines the vertical movement of the cutter 4, in that as the first drive plate 32 rotates, the slide block 25 will execute a circular movement due to its eccentric mounting on the plate 32. As it does, it raises and lowers the spindle 5 through the discs 21,22, and reciprocates laterally between the discs 21,22. It will be clear that the amount of vertical reciprocation of the cutter can be controlled by varying the eccentricity of the slide block 25 through the adjustment screw 33.

The second eccentric drive means 28 acts on the shaft portion 17 of the guide member 11 through the slide block 27. By virtue of its eccentric mounting on the second drive plate 37, it will execute a circular motion, and in so doing will raise and lower the guide member 11 through the discs 23,24. As in the first eccentric drive means, the drive member will also reciprocate laterally between the discs 23,24.

The amount of vertical reciprocating movement of the guide member 11 is varied by varying the eccentricity of the slide block 27 through the adjustment screw 38.

The effect of the vertical reciprocation of the guide member is to introduce a helix angle into the cut.

When the drive member 27 is aligned with the axis of the drive plate 32, there is no reciprocation. In that case, the drive ring 14, the guide member 11 and the cutter spindle 5 rotate as a unit, with the spindle 5 rotating at the same speed as the drive ring 14, and a straight gear tooth will be cut on the workpiece.

However, once the slide block 27 is moved away from the axis of the drive plate 32, the guide member 11 will reciprocate vertically. Due to the interengaging splines 12 and slots 13 between the drive ring 14 and the guide member 11 this vertical movement causes relative rotational movement therebetween, which means that, depending on the direction of eccentricity, the cutter spindle 5, which always rotates at the same speed as the guide member 11, will rotate either slower or faster than the ring 14, and thus slower or faster than the workpiece, which will introduce a helix angle into the cut produced. The size of the helix angle is varied simply by varying the eccentricity of the slide block 27, using the screw adjustment screw 38. The larger the eccentricity, the higher the helix angle will be.

To relieve the stresses on the cutter 4 during its upward stroke, the machine of the invention is provided with a relief mechanism 71, which is shown schematically in detail in Fig. 7. A relief cam 72 is mounted on a shaft 73 which is driven from the gear 43 via shaft 74 gear 75, pulley belt 76, gear 77, shaft 78 and bevel gears 79,80. The cam 72 cooperates with a pair of rollers 81,82 mounted in a housing 83 for the cutter assembly 1. The housing is pivotally mounted at an upper position, by pivots 84. The drive to the eccentric mechanisms 26,28 can accommodate pivotal movement of the cutter assembly 1. The cam 72 and the rollers 81,82 are each formed with a small cone angle, to improve their cooperation.

The rotation of the cam is synchronised with that of the first eccentric drive means, and its profile is such that as the cutter moves vertically upwards, the cam pushes the rollers 80,81 so as to cause the whole housing 83 to swing away from the workpiece about the pivot 84, so disengaging the cutter from the workpiece.

This reduces wear on the cutter mechanism.

The machine in accordance with the invention is also capable of cutting gear teeth with a small cone angle. This achieved through being able to vary the angle of the work table 2 with respect to the cutter 4.

In the preferred embodiments, the work table 2 has a base 85 slidably mounted on slideway 93. The upper surface of the base-85 is provided with a circular guide 86 upon which is mounted an upper part 87 which mounts the workpiece supporting table 66. The upper portion 87 is movable along the circular guide 86 within a range of about 0 + 10 via a gear section 88 and pinion 89, to cut gear teeth with a corresponding cone angle. The coupling 64 rotationally driving the table 66 comprises universal joints 90,91 and a telescopic shaft 92 so as to accommodate tilting of the table 66.

It will be seen from the above description that at least in its preferred embodiments, the invention provides a gear shaping machine which allows a range of internal or external gears, having different helix angles to be easily produced. This is achieved simply by varying the eccentricity of a drive member engaging directly a helical guide member. The cutter is also driven directly by an eccentric mechanism, which eliminates errors in the helix angle produced in known crank-arm mechanisms. The direct drive arrangement also allows the out of axis forces acting on the cutter to be minimised and also facilitates a compact construction.

Furthermore, a relief mechanism is provided which reduces the internal stresses on the relief mechanism and thus improves its stability and working life.

Finally, the invention allows the cutting of gear teeth of different cone angles, by virtue of a tiltable work table arrangement.

Claims (17)

Claims

1. A gear shaping machine comprising: a spindle coupled to a cutter; first eccentric drive means for moving said spindle reciprocably in an axial direction, said spindle being rotatably coupled to rotate with a guide member and constrained so as to move only in an axial direction relative to the guide member, said guide member being coupled to a drive ring via helical coupling means; second eccentric drive means for moving said guide member reciprocably in an axial direction; said first and second eccentric drive means each comprising an eccentrically mounted rotary drive member driving directly said spindle and said guide member.

2. A machine as claimed in claim 1 wherein an or each eccentrically mounted drive member engages a drive surface provided on or coupled to said spindle or guide member respectively, the eccentrically driven member being movable along said surface as it rotates.

3. A machine as claimed in claim 2 wherein said eccentrically mounted drive member slidingly engages said drive surface.

4. A machine as claimed in claim 2 or 3 wherein said eccentrically mounted drive member engages between spaced drive surfaces.

5. A machine as claimed in claim 2, 3 or 4 wherein the eccentrically mounted drive member of at least said second eccentric drive means is adjustably mounted on a rotating support so as to adjust the eccentricity of the drive member.

6. A machine as claimed in claim 5 wherein said eccentrically mounted drive member is journaled on a carriage adjustably mounted to a rotary plate.

7. A machine as claimed in any preceding claim wherein the lines of action of the first and second eccentric drive means on the spindle and guide member respectively are substantially aligned.

8. A machine as claimed in claim 7 wherein said lines of action are closely adjacent the axis of the spindle.

9. A machine as claimed in any preceding claim wherein said first and second eccentric drive means lie to one side of the spindle, generally one above the other.

10. A machine as claimed in any preceding claim wherein said spindle is arranged inside said guide member and extends downwardly therefrom, said first eccentric drive means drivingly engaging a portion of said spindle below said guide member.

11. A machine as claimed in any preceding claim wherein said guide member is arranged inside said driving ring and extends upwardly therefrom, said second eccentric drive means drivingly engaging a portion of said guide means above said drive ring.

12. A machine as claimed in claim 11 wherein said guide member comprises an upwardly extending shaft portion, whose axis is substantially aligned with that of the cutter spindle, said second eccentric drive means drivingly engaging said shaft portion.

13. A machine as claimed in any preceding claim further comprising a work table for mounting a workpiece, the work table being tiltable so as to incline its axis to that of the cutter spindle.

14. A machine as claimed in any preceding claim further comprising a relief mechanism for withdrawing said cutter spindle away from a workpiece in an upward stroke of the spindle.

15. A gear shaping machine comprising: a spindle coupled to a cutter; first eccentric drive means for moving said spindle reciprocably in an axial direction, said spindle being coupled to rotate with a guide member, said guide member being coupled to a drive ring via helical coupling means; second eccentric drive means for moving said guide member reciprocably in an axial direction; said first and second eccentric drive means acting on said spindle and guide means in a generally axial direction.

16. A gear shaping machine comprising: a spindle coupled to a cutter; first eccentric drive means for moving said spindle reciprocably in an axial direction, said spindle being coupled to rotate with a guide member, said guide member being coupled to a drive ring via helical coupling means; second eccentric drive means for moving said guide member reciprocably in an axial direction, said first and second drive means being arranged vertically spaced from one another.

17. A gear shaping machine as claimed in claim 16 wherein said drive means are arranged generally above one another.