GB1559492A - Change speed gear boxes - Google Patents

Description

(54) IMPROVEMENTS IN AND RELATING TO CHANGE SPEED GEAR BOXES (71) We, S. R. M. HYDROMEKANIK AB, a Swedish Company, of Box 16, Stockholm Vallingby 1, Sweden, do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement :- The invention relates to a multi-speed planet gear for motive vehicles having only one planet gear carrier carrying a number of planet gears, of which each has gears of at least two diameters, which work together with inner and/or outer gear rings.

The use of such planet gears as step gears in vehicles, especially for passenger cars, trucks and lorries, buses, earth-moving equipments and locomotives is well known.

In order to fulfil the necessary requirements for the applications in question known transmissions are comparatively complicated, comparatively large and expensive to make. Further in the known transmissions of this type, servo-motors are used which are built in to rotating parts for connection of different gear ratios. To control the sealing, filling and emptying of these rotating servo-motors is difficult, especially if the aim is to obtain good quality of the gear changes for the total life of the vehicle and further not to be limited to the use of too low oil pressures.

Especially adverse is the influence of centrifugalpressure on the shaft conditions.

Rotating sealings, normally of the piston ring type, are necessary together with the rotating servo-motors and they are limiting the allowed maximum pressure and require a large, high pressure oil pump for their actuation.

An aim of the invention is to provide a multiple speed planet gear of the type in question for vehicles giving small dimensions and low cost for manufacture simultaneously eliminating the draw-backs described of the known types obtaining stable shift conditions during the life of the transmission, especially as far as influence by the oil pressure level and this without using a large oil pump for high oil pressure.

The aim is reached by using at least 3 central gears in the form of ring or sun gears, of which one is the driving gear while the planet holder forms the driven part and the remaining central gears can be held (stalled) or released by means of friction brakes and further a friction clutch is used between the primary (input) and secondary (output) shafts and is controlled through a lever system from a stationary (non-rotatable) servo-motor.

By driving through a central gear and having a planet gear holder with planet gears with at least two gear diameters on each shaft disposed beside each other, and with which the central gears are meshed, and with friction brakes for holding the central gears, it is possible to obtain suitable gear ratios and further to obtain the brake surfaces on comparatively large diameters, which makes it possible to give them sufficiently high synchronizing capacity when making gear shifts over more than one step. Further since the servo-motors are non-rotatable high oil pressures can be used even with a small capacity servomotor as the leakage can be very low and this is especially important in combination with hydraulic torque converters. In other words as the brake servo-motors are arranged in the stationary casing of the transmission it is easy to have tight seals and because of this also a small high pressure gear pump, especially when filling the servo-motor with low pressure and building up the pressure with a high pressure pump.

With this transmission it is not only possible to have gear steps in one direction of both overdrive and underdrive type and a gear for the opposite driving direction but also to have lock-up direct drive between the input and output side, it is also possible to have a friction clutch directly between the primary gear and the planet gear holder locking up the whole planetary gear with torque transmission through the planet gears. Further, it is also possible to actuate this clutch in a favourable way by a stationary servo-motor i. e. a non-rotatable servo-motor. The actuation of the direct drive clutch is made through lever arms pivotted at one end on the planetary gear carrier and actuating a pressure plate engaging the clutch when the opposite ends of the lever arms are actuated by a servomotor, which through one or two thrust bearings press on the lever arms. By this arrangement the force necessary to engage the clutch is reduced so far that a small stationary piston can be used to create the force and to allow this force to be transmitted to the lever arms through a small, for instance, needle thrust bearings.

In one form of the invention the driving gtar is in mesh on the outside of the largest of the planet gears and the remaining central gears are sun gears. With this arrangement and a suitable selection of gear sizes, suitable gear ratios for a large number of applications are obtained. To operate the lock-up clutch by a stationary servo-motor it is possible to use the sun gear of the smallest dimension as a sleeve transmitting axial thrust from the stationary servo-motor but this can also be made with a separate sleeve to reduce the speed of the thrust bearings.

In another form of the invention the primary gear is a sun gear and the remaining gears in connection with the planet gears are ring gears in gear mesh on the outside of the planet gears. With this arrangement it is possible to obtain essen tially higher gear ratios than in the first example.

In both arrangements it is possible to obtain reverse gear and/'or overdrive gear ratios by adding a gear ring in contact with the remaining not earlier used planet gear sides, which will then be in the first case a ring gear and in the second case a sun gear, which gears then have their own servo-brakes. Whether reverse gear or overdrive is obtained depends on the purpose of the gear used and the diameters of the gears.

With a planet gear having only two gear diameters on each planet gear it is possible to obtain two gear reductions and one reverse, i. e. besides the primary gear there are three different gears possible to hold.

With such an arrangement it may be difficult to obtain the wanted gear ratios, especially in reverse but also the lowest gear may not have a sufficiently high gear ratio. In fact, it may happen that the ratio of the reverse gear is even higher than that of the lower gear and this can only be used in certain applications. Normally, a reverse gear ratio of about the same size as the lowest gear may be wanted. Such reverse gear ratio can be obtained by adding a third gear on each planet gear with a smaller diameter than the other two and a ring gear in mesh with this third gear. If also adding a further sun gear with a friction brake the two gear reductions will be three gear reductions and the reverse, that is besides the primary gear there are then three sun gears with their brakes and one ring gear with its brake where the ring gear gives reverse with high gear ratio.

It is possible to manufacture the planet gears in the planetary gear in question in a favourable way if the gear with the larger diameter is mounted on the gear with smaller diameter using the tooth profile as a spline connection. The large gears must then have their tooth profile simultaneously machined for each set and must be mounted in a certain relationship with the teeth of the inner gear have to be similarly mounted in the gear set.

When making planet gears with three diameters it is normally favourable to have the planet gear of at least the two smaller gears made in one piece and to have a bearing surface between the two smaUer gears and one outside the largest gear. The bearings preferably shall be roll bearings or needle bearings.

As already mentioned, it is possible to have the brakes and the clutch on relatively large diameters making it easy to get suffi- cient large friction surfaces and to avoid too high engaging forces. Under circumstances, it may be possible to make the brakes and the clutch with single discs, which gives favourably low drag losses.

Normally, sintered metal linings are to be used, especially for high H. P.-units and high speed units. Single discs also make it possible to have the servo-motor move only short distances with small oil quantities to fill and empty without to have to use too high fluid pressure.

The drag torque on the brakes and/or the coupling can be widely reduced by using friction discs being sine waved in the direction of rotation with a maximum of 0.2 mm wave height, which will create an air bearing and make unnecessary large lubrication oil quantities.

The invention will be described in detail by way of example with reference to the accompanying drawings: Fig. I Longitudinal section of a first form of the invention having three for ward steps and one reverse gear Fig. la A diagram showing tractive effort and engine speed in different gears in relation to the vehicle speed at one application of the transmission according to Fig. I Fig. 2 Longitudinal section similar to Fig. 1 in another form of the inven tion, also with three gear steps but without reverse gear Fig. 3 One longitudinal section through a further planet gear in accordance with the invention having four for ward gear ratios and one high reverse gear ratio Fig. 3a A diagram for the gear according to Fig. 3 similar to Fig. la Fig. 4 A schematic presentation of the transmission arrangement according to Fig. 1 Fig. 5 A similar presentation of a modi fied form of the transmission according to Fig. 1 and 4 with two reduction gears and direct drive and an overdrive Fig. 6 A schematic presentation of the transmission according to Fig. 2 but with additional overdrive Fig. 7 A modified form of the transmission according to Fig. 6 with reverse gear Fig. 8 A schematic presentation of a variant of the transmission accord ing to Fig. 3 In all the forms of the multiple step planet gears shown in the figures the input shaft is marked with I, the output shaft is marked with O and the transmission casing is marked with H.

The transmission according to Fig. 1 is a 3-speed gear with two reduction ratios in forward direction, direct drive and one reverse ratio. The input shaft I is journalled in the casing H by means of a bearing 10 and the output shaft O is journalled through a bearing 12. Further, the input shaft I is journalled in bearings 14 and 16 inside the hollow output shaft O. A flange 18 on the output shaft O carries on a spline, a planet carrier 20, in which shafts 22 are mounted and on which gears 24 of relatively small diameters are journalled. In the crosssection only one such shaft is shown and another can be seen but there must be normally at least three such shafts. Each such gear 24 carries on splines a gear 26 of larger diameter but with smaller length in such a way that the larger gear only covers a part of the smaller gear, whereby the planet gear has two different gear surfaces.

On the input shaft I a light conical disc 28 is mounted. On a spline connection on the periphery of this disc is mounted a central ring gear 30. The ring gear is in toothed mesh with the larger planet gears 26. A sleeve-formed second central gear 32 is journalled on the output shaft O and constitutes a sun gear in mesh with the larger planet gears 26. A third central gear 34 is journalled on a flange 36 which is splined to the sun gear 32. The gear 32 is in mesh with the smaller of the planet gears. The third central gear 34 carries a flange 38. Further, central gear, viz a ring gear 40 is in mesh on the outside of the smaller planet gears 24.

The flange 38 carries on an outer spline one friction disc for the first disc brake 42 for holding the central sun gear 34 in relation to the casing H. The disc brake 42 is applied by a ring piston 44, which is kept in released position by a Belleville spring 46. In the same way a flange 36 of the sun gear 32 carries a friction disc of a secondary disc brake 48 for connecting the central sun gear 32 to the casing H by actuating the ring piston 50, which is kept in release condition by a Belleville spring 52. The ring pistons 44 and 50 are mounted in cylindrical cavities on the inside of the casing H and the Belleville springs 46,52 are at their inner peripheries axially fixed in the casing.

A third ring piston 54 having a small diameter is also mounted in a cylindrical cavity in the casing H. This piston 54 acts through a first needle thrust bearing 56 on one end of a rotatable and axially movable sleeve journalled on the output shaft O and integral with the sun gear 32, which at its other end acts through a second needle thrust bearing 58 on a ring, which through distance pieces 60 which are axially movable in holes in the flange 18 of the output shaft O. The thrust bearings 56, 58 are shown as needle bearings with relatively short needles. Instead of these bearings other types of bearings can be used, for instance the bearing 56 can be a friction bearing and the bearing 58 an angular contact ball bearing.

The distance pieces 60 transmit movement and pressure from the sleeve 32 to a ring 62. The ring 62 works on a number of radial levers 64, which pass through fulcra cut in a cylindrical part 66 of the planet gear carrier 20 and the lever arm outside the fulcra bear on a ring 68. This ring 68 is one of the side rings in a disc friction clutch 70 between the central ring gear 30 and the planet carrier 20 to obtain direct drive between the input shaft I and the output shaft O. The disc clutch 70 will then be engaged when the servo-piston 54 is actuated and for release of this connection a Belleville type spring 72 acts to move the lever arms to take a radial position, whereby also the needle bearings are kept in contact and the piston 54 is moved towards the right hand position and the disc 68 is moved to the left.

In the casing H is a further cylindrical cavity with a piston 74, by means of which a friction disc mounted on the ring gear 40 forms a disc brake 76 in the casing H.

The friction surfaces of the disc brakes 42,48,76 and of the disc clutch 70 should preferably have sintered metal lingings and the surfaces of the cooperating discs should preferably have in tangential direction a slight sine-form with an amplitude of maximum 0.2 mm and suitably there should be 3 or 4 waves around the circumference of the disc. This arrangement will give an exceptionally low drag torque for the released clutch or brakes especially at high speeds.

By alternative connections of the clutch and the brakes 42,48,70,76 3 forward gear ratios and one reverse are obtained as follows: I. Brake 42 applied: high reduction (e. g. 1.9: 1) II. Brake 48 applied: low gear ratio (e. g. 1.37: 1) lll. Clutch 70 engaged: direct drive (1: 1) R. Brake 76 applied: gear ratio in re verse (e. g. 0.61 : 1) The clutch and the brakes are actuated by stationary servo-motors. The clutch and the brakes have relatively large diameters making them suitable to sustain high torque. The use of the axially movable sun gear 32 to transmit thrust from a stationary servo-piston through a lever system to engage the clutch allows the use of a small diameter servo motor. This means that a small force is transmitted through the rotating bearings and the stationary servomotor itself eliminates the necessity of rotating seals, which in its turn makes it feasible to use high pressure.

Figure la shows in a diagram the primary speed n, and the tractive effort P for different vehicles speeds in the three speed ranges 1, 2 and 3 when using the transmission according to figure 1 in a truck with a FIAT (Registered Trade Mark)- engine of 210 H. P. at 2,000 r. p. m. The vertical lines between the speed lines show shift points at maximum speed in a lower gear to a high gear.

The arrangement shown in figure 2 differs from the one shown in figure 1, mainly because the input member is not a ring gear in mesh on the outside of the planets but a sun gear 78 in mesh on the inside of the planets and, as shown, with the smallest diameter planet gears 80 and further because no reverse ratio can be obtained. The planet gear carrier is journalled in a bearing 82 in the casing H and the input shaft besides being journalled in the casing through a ball bearing is also journalled in the output shaft through a bearing 84.

Also in the arrangement according to figure 2 the planet gears have two diameters, the gears 80 and 86 and the teeth of 80 are utilized as a part of a spline connection to 86.

To obtain the two different gear ratios the larger planet bear 86 is in mesh with a ring gear 88 and the smaller gear 80 meshes with a ring gear 90. The ring gears can alternatively be connected to the casing H by the disc brakes 92,94 by means of the servo pistons 96,98 respectively. A further sun gear 102 is journalled on the input shaft I and carries rotationally fixed thereto a disc 104, which carries the friction disc of the friction clutch 106 to connect the sun gear 102 to the planet gear carrier 108.

This friction clutch is engaged by a servo piston 112 on the input side, which through a thrust needle bearing 114 and a ring 116 engages the clutch by actuating a radial lever system 118, which has radially directed spokes of a Belleville spring 120, which on the outer periphery fulcrums against a stop 122 in the planet carrier and works against a pressure ring 110 having a ring-formed abutment. By means of this lever arm the necessary force from the ring piston 112 is reduced several times. In this case it is possible directly to actuate the lever system and to put the piston on the input side.

With a transmission in accordance with figure 2 are three transmission steps obtained: I. Brake 92 applied : large reduction (for example 2.9: 1) n. Brake 94 applied: lower gear ratio (for example 2.3: 1) III. Clutch 106 engaged: direct drive (1: 1).

Comparing the gear ratios for figures 1 and 2 is found that the arrangement according to figure 2 has much higher gear ratios.

Figure 3 shows a form of the planetary gear which differs from what is shown in figures 1 and 2 basicly, because the planet gears have three different gear sizes, namely, 124,126 and 128. Obviously, it is possible even here to put the largest gear in spline connection to the next largest gear. The different gears of the planets work together with a maximum of five central gears. The largest ring gear meshes with the largest gear on the planet as a driving gear, i. e. an input gear. A further ring gear meshes with the smallest planet gear and three further sun gears can be braked to the casing H. By locking alternatively one of these sun gears or the ring gear three gear ratios are obtained in forward and one in reverse, where the reverse has a compara tively large ratio. Further, even here the direct drive can be used, in other words it is a 4-speed and reverse planetary gear arrangement.

In detail the transmission according to figure 3 has the following design: The short input shaft I drives through a hub 130 a sleeve-formed ring gear 132 in mesh with the gear of the large diameter of the planet gear. The ring gear is also one part of the disc clutch 134 for connecting the ring gear with the planet gear carrier 136 to obtain direct drive between the input shaft I and the planet gear carrier 136, which is attached to the output shaft.

In the lower part of the figure it can be seen that the planet gear carrier 136 consists of two parts and in the upper part it can be seen that each of the parts of the planet gear carrier has roller bearings 138, 140, in which the planet gears are journalled. The inner races of the roller bearings 138, 140 are part of the planet gears where as the outer races are mounted in the planet gear carrier.

Immediately on the output shaft O a first sleeve-formed sun gear 142 is journalled with the left hand end formed as a gear which is in mesh with the largest of the planet gears 124 and, at the opposite end, has a similar gear carrying a friction disc 144, which by means of a piston 146 against the force of the spring 148 and against the abutment 150 connects the friction disc 144 to the casing H. Besides, is The sun gear 142, which is the same as the sun gear 32 of the transmission according to figure 1, is displaced by a servo piston 152 for engaging the friction clutch 134 for engagement of the direct drive. Further, a sleeveformed sun gear 154 is journalled by a plane bearing 156 in the planet gear carrier 136 and at one end thereof is in gear mesh with the planet gear 126. The other end of the sun gear 154 carries and rotationally fixed thereto, a fixed disc 158, which by means of a ring piston 160 against the force of a disc spring 162 is connectable to the casing H. A third sun gear 164 is in gear mesh with the smallest of the planet gears 128 and carries a friction disc 166, which by means of a ring piston 168 is connectable to the casing H against the abutment 172. When the piston is when released, it is forced back by the Belleville spring 170. Finally, a ring gear 176 is in mesh with the smallest of the planet gears; 128 on the outer side and this ring gear is formed with a friction disc 174, which by means of a piston 178 against the abutment 172 is connectable to the casing H. The Belleville spring 180 is connectable to the casing H. The Belleville spring 180 returns to the piston when released.

It will be seen that the friction discs 144, 158,166 and 174 with servo pistons form brakes to connect the sun gears 142,154, 164 and the ring gear 176 with the casing H and together with the direct drive clutch 134 constitute the following gear connections: 1. Brake 144 applied: the biggest reduc tion (for example 3.2: 1) I I. Brake 158 applied: the medium re duction (for example 1.95: 1) in. Brake 166 applied: the smallest re duction (for example 1.31: 1) IV. Friction clutch 134 engaged: direct drive (1 : 1) R. Brake 174 applied: reverse drive (for example 1.8: 1) As can be seen from the drawings the largest planet gear 124 has more than three times the diameter of the smallest planet gear 128, where 124 meshes with ring gear 132 and the planet gear 128 meshes with the ring gear 176. This large difference is necessary to produce a high gear ratio in reverse. Should the difference be used for the gear with only two sizes on the planet gears, i. e. should the middle gear 126 and the sun gear 154 be eliminated, then should the step in gear ration should go directly from 3.2: 1 to 1.32: 1. Such a gear would, for most cases, not be suitable but can very well be of interest for special cases. The shape of the planet gears consisting of three gears and the extra sun gear connectable to the casing for one more gear ratio is, therefore, for most of the applications not necessary if a high gear ratio for reverse is not required.

Figure 3a shows in a diagram similar to figure la the primary speed n, and the tractive effect P over vehicle speeds for the four drives I, II, III and IV for the transmission according to figure 3 when using again in a truck with a FIAT engine of 210 H. P. at 2,000 r. p. m. The vertical lines between the miximum speed points of one gear to the next following higher gear show maximum allowed shift points and also for this maximum reduction necessary in engine speed.

Figure 4 shows again schematically the principle built up of the transmission according to figure 1, where the direct drive clutch 70 is marked with A and the three brakes 76,42 and 48 are marked with B, C and D. The following characteristics will be reached: D: high reduction C: small reduction A: direct drive B: reverse gear Figure 5 shows schematically a modification of the transmission according to figures I and 4 that the large and small planet gears are interchanged, as also the diameters of the central gears are changed.

By this arrangement is the following obtained: D: large reduction C: small reduction A: direct drive B: overdrive Figure 6 shows a transmission according to figure 2 in a schematic way, where the direct drive clutch 106 is marked with A and the brakes 92, 94 are shown with B and C respectively. In contrast to figure 2, a further brake D is forseen to hold the sun gear in gear mesh with the largest of the planet gears (sun gear 102 in figure 2). The following will be obtained: C: large reduction B: small reduction A: direct drive and with the use of the extra brake D: overdrive.

The transmission according to figure 6 differs from the transmission according to figure 5 by a relatively high reduction in the first and second gears and a not very high overdrive, while the transmission in accordance with figure 5 has a useful overdrive in case a relatively small reduction in the first and second gear is allowed.

The arrangement shown schematically in figure 7 corresponds again to figure 6 with the large and small planet gears exchanged and a corresponding change in the central gear diameters. By this arrangement is the following obtained: B: large reduction C: smaller reduction A: direct drive D: reverse gear Figure 8 schematically shows a transmission according to figure 3, with the clutch 134 shown at A and the brakes 174, 166, 158 and 144 are shown at B, C, D and E respectively. The following is then obtained: C: large reduction D: medium reduction E: small reduction A: direct drive B: reverse gear.

In figure 8 is the planet gears are schematically shown as being journalled at one side only, i. e. overhung, which differs from the journalling according to figure 3 and requires increased stiffness of the planet gears.

The use of the diagrammatic arrangements of figures 4-8, depends on the use and the gear ratios required for the application. Further, it is naturally possible to vary the gear ratios by varying the diameters of the gears relatively seen to obtain an optimal result. The multi-speed gear according to the invention can be used alone or in combination with hydrodynamic mechanical transmissions. Especially is the combination with a torque converter having a releasable pump or turbine or with a torque converter utilizing the guide vane in one range rotating in the opposite direction to that of the rotating turbine.

Claims (23)

1. Reference is made to the description and claims of copending Applications 3572/76 (Serial No. 1 559491) and 28965/76 (Serial No. 1 559 493) WHAT WE CLAIM IS :- [. A multi-speed planet gear for vehicles including a casing and one planet gear carrier having two planet gears which mesh solely with inner andjor outer central gears characterised in that the gear comprises at least three central gears of which one constitutes the input gear part whereas the output part is constituted by the planet gear carrier, a servo-motor operated friction brake associated with each of the remaining central gears for connecting the remaining central a rotation with the casing, a friction clutch for introducing direct drive and disposed in the transmission line between the input gear and the planet gear carrier, and a non-rotatable servo motor for controlling engagement and disengagement of the friction clutch.
2. 2. A gear according to claim I wherein the servo motor for controlling the friction clutch operates through a thrust bearing.
3. 3. A gear in accordance with claim I or claim 2 wherein the servo-piston of the servo-motor for the friction clutch operates through a thrust bearing on a pressure ring, from which the engaging force engages the friction clutch through radial lever arms.
4. 4. A gear according to claim 3 wherein the radial lever arms are loaded in the clutch engaging direction by springs, whereby simultaneously the thrust bearings are constantly kept loaded.
5. 5. A gear according to claim 4 wherein the force on the lever arms is obtained by a Belleville spring.
6. 6. A gear according to claims 2-5 wherein the thrust bearings are needle bearings with relatively short needles.
7. 7. A gear in accordance with any of claims 2-5 wherein the thrust bearing is a plane bearing.
8. 8. A gear in accordance with any of the claims 2-7 wherein the input gear is a ring gear and the remaining central gears are sun gears.
9. 9. A gear in accordance with claim 8 wherein the sun gear with the smallest diameter is axially movable to transmit axial engaging force to the direct drive friction clutch.
10. 10. A gear according to claims 3 and 9 including a further needle bearing between the axial movable sun gear and the pressure ring.
11. 11. A gear according to claims 3 and 9 including an angular contact ball bearing between the axial movable sun gear and the pressure ring.
12. 12. A gear in accordance with any one of the claims 2-7 wherein the input central gear is a sun gear and the other central gears are ring gears to obtain a high gear ratio.
13. 13. A gear according to any one of claims I to 7 including a central ring or sun gear in mesh with another gear of the planet gears to obtain reverse or overdrive when connecte to the stationary casing.
14. 14. A gear according to any of the preceding claims wherein the larger diameter planet gears are made as separate gears mounted on the gears with the smaller diameters by using the tooth profile of the smaller gear as a spline connection, wherein at least one tooth of the larger gear has the same angular position as one tooth of the smaller gear and wherein the gears are mounted with the said teeth in the same relative position.
15. 15. A gear according to claim 14 wherein the gears with the smaller diameters are journalled on the planet gear carrier on shafts fixed to the carrier.
16. 16. A gear according to any of the claims I-13 wherein each planet has three gears of different diameters of which the one with the larger diameter is driven by the input gear (a central gear) and the smallest gear is in mesh on the outside with a central ring gear to obtain reverse with high gear ratio.
17. 17. A gear according to claim 16 wherein the planet gear is manufactured in one piece having gear surfaces and bearing surfaces for journalling in the planet gear carrier.
18. 18. A gear according to claim 17 wherein one part of the planet gear is sup- ported on the carrier by a bearing between two of the gears.
19. 19. A gear according to claims 17 or 18 wherein the planet gears are journalled in the planet gear carrier through roller bear- ings providing axial guidance of the gears.
20. 20. A gear according to any of the previous claims wherein the brakes and/or the clutches are made with single discs.
21. 21. A gear according to claim 20 wherein the friction surfaces for the brakes and/or the couplings are of sintered metal.
22. 22. A gear according to claims 20 or 21 wherein the surfaces of the friction discs in the direction of rotation have a sine-form.
23. 23. A gear according to claim 23 wherein the amplitude of the sine-formed waves has a maximum 0.2 mm.