GB1559491A - Change speed gear boxes - Google Patents

Abstract

The epicyclic gear change box has a planet carrier (20), the planet gears (24, 26) of which have at least two axially successive portions of different diameters which mesh exclusively with sun gears (30, 32 and 34, 40 respectively). The sun gear (30) is firmly connected in terms of rotation to the gearbox input shaft (I) while the output shaft (O) is connected to the planet carrier (20). The other sun gears (32, 34, 40) are connected to friction brakes (42, 48, 76) and can be fixed against rotation by servos (50, 44, 74) fixed to the housing. The gearbox has three forward speeds and one reverse speed. The hydraulically activated gearbox avoids concomitantly rotating servomotors and can be shifted with the smallest possible quantities of hydraulic fluid. <IMAGE>

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 multiple-speed gear especially for trucks, lorries and earth-moving equipment. Although for passenger cars and other vehicles with high specific horse power it is generally sufficient together with hydraulic torque converters to have two or three gear steps both for acceleration and climbing and to obtain sufficient engine braking on down-hill running when the torque converter is locked-up, for vehicles with lower specific horse power, it is necessary even if they have lower top speed, to have many gear steps in order that the engine can be used close to maximum H. P. in a very wide speed range and thereby maintain the highest possible average speed, Mechanical gears for such applications are normally synchromesh transmissions designed to give a sufficient number of correctly spaced gear ratios. These transmissions have a number of highly loaded dog clutches with synchronizing arrangements and a release coupling of the friction type to cut-off the torque transmission through the shift periods. Furthermore, and especially in connection with hydrodynamic torque converters, planet gears are also used. Hitherto, such planet gears are in some dimensions larger than the normal synchromesh transmissions and, for reverse gear an additional planet gear is used rendering the dimensions, weights and manufacturing costs of such transmissions very large.

It is an aim of the present invention to provide a multiple speed gear for trucks, lorries and earth-moving equipments, which is simple to manufacture and has relatively small dimensions and a large number of well related gear steps including reverse and which does not need any special main clutch except the power shift arrangements in the gear per se.

According to the present invention there is provided a multiple speed gear suitable for use with motor lorries and earth moving vehicles comprising two serially connected multiple speed planetary gears, each comprising a planet carrier having associated planet gear wheels at least two of which gear wheels are of different diameters and which, in each planetary gear, mesh with at least three internally and/or externally toothed centrally disposed gear wheels, at least one of the centrally disposed wheels in each planetary gear constituting an input member with the planet carriers constituting an output member, each remaining centrally disposed gear wheel having an associated friction brake controlled by a servo motor having a non-rotatable housing.

By driving the planet gear by a central gear and having the planet carrier as an output part in connection with the use of at least two gear diameters on each planet gear and with the central gears in contact it will be possible to make the brakes for the ring gears on a comparatively large diameter, simultaneously using an air bearing effect to reduce the drag torque and giving sufficient surfaces for shift also between gear steps being not near each other. Since all the servo-motors for the brakes are mounted in the casing there are no difficulties to make seals not permitting any leakage, whereby only a small oil quantity is necessary to build up a high pressure. By using this type of planet gear arrangements the necessary reverse gear can also be obtained.

To increase the number of steps in the planet gears and to have a direct drive, in a preferred form of the invention, friction clutches are disposed between the input and the output side of each planet gear and these clutches are actuated by servo-motors in the casing which, through thrust bearings and a lever system engage the friction clutches. This is especially favourable because neither the bearings or the gears are loaded either during clutch engagement or during direct drive which reduces wear on the gear surfaces.

In another preferred form of the invention, the input gear of the first planetary gear considered in the direction of flow of the power in the gear is in mesh with the largest of the planet gears and on the outside of this, i. e. the input gear, there is a ring gear, whereas the input gear in the second planetary gear (to obtain larger gear steps) is a sun gear in gear mesh with the smallest diameter gear of the planet gears. Such a transmission is especially suitable for earthmoving transmissions, because for such applications the steps of the gears at low speeds should be close to each other, whereas at high speeds the gears are used for transport. The forrr. of the planet gears in the two planetary gears shall have two or more gear surfaces of different diameters. The planetary gear system as described may have in a practical form up to 9 forward gear ratios, including the direct drive and also a reverse gear.

For use in a truck or lorry, another form of the invention is preferable, in which the input gears, of the two planetary gears are in mesh with the larger diameter planet gears and are ring gears. In this case, the gear steps in the low speed gears are larger than in the first mentioned form and the steps are smaller at the high speed end and this is mostly required for the trucks and'orries. The number of useful combinations of gear ratios in the two planetary gears together is, due to overlapping, smaller, e. g. only 6. This is, however, normally quite suffi : ient for such applications. A larger number of useful gear steps can, of course, be obtaine (if the planet gears have three instead of two different diameter gear surfaces.

The use of a friction clutch between the input gear and the planet carrier of the primary train and, simultaneously having at each of all other ring and sun gears of the secondary train connectable to the casing by friction brakes at the same time as also the clutch is engaged by a servo-motor in the casing is. In yet another form of the invention the sun gear is utilized to transmit the thrust of the servo-motor to a lever arm system engaging the clutch, whereby the servo-motor works on the sun gear through an axial thrust bearing and where the thrust is-ransmitted from the sun gear to the lever mechanism through a second axial bearing.

In many cases it is necessary to have a high gear ratio in reverse. This is also possible according to the invention by using three gear surfaces of different diameters on the planet gears and a ring gear in gear mesh with the outside of the smallest gear and by, holding this ring gear a high reverse gear, is ratio obtained. It is then also possible to add a further sun gear giving a further gear ratio in the primary gear, which adds three gear ratios to the number of gear ratios mentioned for the different forms of the application.

The invention will now be described in more detail with reference to Examples illustrated in the drawing.

Figure I is an axial section through a first embodiment of a multiple speed gear according to the invention particularly suitable for earth movers, Figure la is a diagram relating to the gear according to Figure 1, representing the tractive force and engine speed for the various gear steps in dependence upon the driving velocity of the vehicle in an earthmover which is also capable of travelling at high velocity between the individual operating sites, Figure 2 is an axial section similar to that of Figure 1 through a different embodiment of the multiple speed gear according to the invention suitable for a motor lorry, Figure 2a is a diagram similar to Figure la relating to Figure 2, Figure 3 is a schematic representation of a modified embodiment of the gear shown in Figure 1, the first planet gear in this case carrying planet wheels having three sections of differing diameters, each meshing with a sun wheel, and Figure 3a is a diagram similar to Figure la corresponding to Figure 3.

In all the embodiments of the multiple speed gear according to the invention illustrated in the drawings, the input shaft is indicated by the reference I, the output shaft by O, an intermediate shaft between the two planet gears by S and the non-rotatable transmission housing, where shown, by H.

In the embodimt nt of the transmission shown in Figure 1, the two shafts I and O are mounted in the housing H by means of ball bearings 10 and 12, respectively, and the input shaft I which extends over almost the whole length of the transmission is centered by means of a roller bearing 16 in a bore in the short output shaft O. The hollow intermediate shaft S encloses the input shaft I over most of its length and its front end is mounted on the input shaft I by means of a needle bearing 14 and its rear end by a friction bearing. The housing H contains two planet gears Pla and Plb which are separated from each other by a housing middle portion Nt formed by a partition and numerus non-rotatable servo motors.

The planet geai Pla on the left will be described first: A radial flange 18 on the intermediate shaft, is splined to carry a planet carrier 20 which has first gear wheels 24 of relatively small diameter mounted on its shafts 22 which are distributed over its circumference. Only one shaft 22 and gear wheel 24 can be seen in the plane of the drawing.

Mounted on each gear wheel 24 is a second gear wheel 26 in positive engagement with gear wheel 24 by means of a splined bore. Gear wheel 26 has a substantially larger diameter but is much shorter than gear wheel 24 so that it leaves a considerable portion of the smaller wheel 24 exposed, thus forming a planet wheel having two sections of differing diameters.

A slightly conical disc 28 is non-rotatably fixed on the input shaft I by splines. The periphery of this disc 28 engages in a form locking manner with the internal teeth of a first central gear wheel 30 which is in the form of a sleeve. The internal teeth which extend over the wh (le length of this gear wheel 30 mesh at their other end with the larger planet wheels 26 for v hich the central wheel 30 thereby forms an external or ring wheel. A second central gear wheel 32 in the form of a sleeve is centered on the intermediate shaft S and meshes as sun wheel with the larger planet wheel section 26. A third central gear wheel 34, which is also in the form of a sleeve, is mounted on a flange disc 36 which has been pushed over the front end of the sun wheel 32 and non-rotatably fixed to it by splines. This central wheel 4 functions as sun wheel meshing with the smaller planet wheel sections 24. The third central wheel 34 also carries a flange disc 38 which is fitted on it by splines. Lastly, a fourth central wheel 40 functions as ring wheel which encloses the small planet wheel section 24 on their outer side and meshes with them.

The flange disc 38 has an external toothing on which it carries the only friction disc 42 of a first disc brake A for fixing the central sun wheel 34 to the housing H. The disc brake A is shifted into engagement by means of a ring pistion 44 which is biassed in the direction of disengagement by a cup spring 46. The flange disc 36 similarly carries the single friction disc 48 of a second disc brake B for fixing the central sun wheel 32 against the housing H by means of a ring pistion 50 which is biassed in the direction of disengagement by a cup spring 52. The ring pistons 44,50 are displaceably mounted in annular cylindrical recesses within the middle portion M of the housing and the cup springs 46,52 bear against axial projections in the interior of the housing.

Another ring piston 54 is arranged on a relatively small diameter in a third annular cylindrical recess within the housing middle portion M. This ring piston 54 acts by way of a first thrust bearing 56 on the sleeve shaped sun wheel 32 which is not only rotatable on but also axially displaceable on the intermediate shaft O. The other end of the sun wheel 32 acts by way of a second thrust bearing 58 on a number of pins 60 which are supported to be axially displaceable in bores formed in the radial flange 18 of the intermediate shafts. In the example illustrated, the thrust bearings 56,58 are needle bearings with relatively short needles but other suitable types of-bearings may equally well be used, in particular the bearing 56 may be a friction bearing and the bearing 58 a deep row ball bearing.

The pins 60 bear axially against a thrust ring 62 which is displaceable on the intermediate The thrust ring 62 engages with the inner ends of numerous radial levers 64 which extend through slots with beaded edges formed in a collar 66 on the planet carrier 20. The shorter lever arms situated radially outside these slots engage in a form locking manner with another thrust ring 68. This thrust ring 68 clamps a friction disc 70 fixed in the ring wheel 30 and thus together with this disc 70 it forms a disc clutch C between the central ring wheel 30 and planet carrier 20 for directly connecting the input shaft I with the intermediate shaft O.

It will be seen that this disc clutch is engaged by pressure acting on the ring piston 54. The clutch is disengaged by means of a cup spring 72 which is attached by screws to the radial levers 64 and tends to swing the levers into a position perpendicular to the axis of the transmission and keeps the thrust bearings constantly under load.

Lastly, the non-rotatable housing H has another annular cylindrical recess containing a piston 74 by means of which a friction disc 76 situated on the external toothing of the ring wheel 40 can be fixed against the non-rotatable housing to form another disc brake D.

The planet gear Plb differs from planet gear Pla mainly in that the input member connected to its input shaft, namely in this case the intermediate shaft S, is not a ring wheel but a sun wheel 78 which meshes with the sections of smaller diameter of the planet wheels.

These planet wheel sections 80 are again formed by relatively long gear wheels which are mounted on shafts 82 of a planet carrier 84 which in turn is attached by screws to a flange on the output shaft O. Gear wheels 86 of larger diameter are pushed over the aforesaid gear wheels 80 and form the larger sections of the planet wheels of gear Plb.

In order to obtain two different reduction ratios from the planet gear Plb, a ring wheel 88 is provided to mesh with the larger planet wheel sections 96 and a ring wheel 90 is provided to mesh with the smaller planet wheel sections 80. The ring wheels 88 and 90 carry friction discs 92 and 94, respectively, by means of which they can be fixed against the transmission housing H by the ring pistons 96 and 98, respectively, to form one-disc brakes E and F.

Another sun wheel 102 is formed by a toothed sleeve mounted on the intermediate shaft S and carries, non rotatably fixed to it, a flange disc 104 which carries the only friction disc 106 of a friction clutch G for clutching the sun wheel 102 to the planet carrier 84 by means of a thrust ring 110. To operate the friction clutch G, a ring piston 112 axially displaceable inside an annular cylinder is provided at the driving end of the housing. This ring piston 112 is capable of axially displacing a thrust ring 116 by way of a thrust bearing 114 designed as a needle bearing. The thrust ring 116 engages the inner ends of radial levers 118 which are formed by inwardly directed spokes extending from a cup spring 120 which bears at its periphery against an abutment 122 in the planet carrier 84 and, radially inwards of this position, engages an annular projection on the thrust ring 110. It is obvious that by this construction the pressure exerted by the ring piston 112 to press the thrust ring 110 against the friction disc of the clutch 106 is greatly remforced. Since in addition, in contrast to the arrangement in the planet gear Pla, the servo motor formed by the ring piston 112 is situated at the driving end of the housing and the sun wheel 102 which is required to be fixed against the planet carrier 84 for direct drive is also situated there, it becomes unnecessary to use a sun wheel as axially displaceable thrust transmission element for operating the direct drive clutch as in the planet gear Pla.

The Table below shows the combinations of any two brakes and/or clutches in engagement at the same time for producing nine forward gears indicated by Roman numerals and one reversing gear R. The second and fourth columns give the transmission ratios of the first and second planet gear, respectively, while the last column shows the overall transmission ratio obtained in the individual gears.

A 1.910: 1 E 3.000 : 1 I 5. 730: 1 A 1.910: 1 F 2.500: 1 II 4.775: 1 B 1.375: 1 E 3.000: 1 III 4.125: 1 B 1.375: 1 F 2.500: 1 IV 3.438: 1 C 1.000: 1 E 3.000: 1 V 3.000: 1 C 1.000: 1 F 2.500: 1 VI 2. 500: 1 B 1.375: 1 G 1.000: 1 VIII 1.375: 1 C 1.000: 1 G 1.000: 1 IX 1.000: 1 D-0.535: 1 E 3.000: 1 R-1.605: 1 Figure la is a diagram representing the variation in the transmission input speed of rotation ni and tractive force P in relation to the velocity of the vehicle in the nine forward gears I to IX when the multiple speed gear according to Figure 1 is used in a heavy motor lorry or earth mover. The vertical lines between the input speed curves give the points at which it is suitable to change gears between the individual forward gears. It can be seen that the revolution speed curves are very close together in the lower gears. This means that when the vehicle is travelling at relatively low speeds and the tractive force is correspondingly high it is possible to operate within a relatively narrow range of input revolution speeds, at which the engine produces its maximum torque. The multiple speed gear shown in Figure 1 is therefore capable of optimally adapting to the different demands of tractive power and travelling velocity encountered in a heavy lorry or an earth remover.

The transmission according to Figure 2, which is mainly intended for motor lorries, comprises two planet gears P2a and P2b which are basically similar in construction and in which, as in the first planet gear Pla of the embodiment according to Figure 1, the input members are formed by external or ring gear wheels which mesh with the sections of larger diameter of the planet wheels. In this case, however, the additional ring wheel which meshes with the planet wheel sections of smaller diameter and can be braked for producing reversing drive, is only provided in the first planet gear P2a.

Furthermore, the arrangement according to Figure 2 contains certain structural alterations compared with Figure 1 but these are immaterial to the invention and the two planet gears Pla and Plb of Figure 2 therefore need not be described in detail. It merely needs to be pointed out that in view of the fact that the arrangement according to Figure 2 is to be used in a heavy motor lorry, the friction brakes and clutches are equipped with multiple discs.

Using a connotation for the brakes and clutches A'and G'analogous to that used in Figure 1, the gear combinations obtainable in practice from the construction according to Figure 2 are shown below: B'2.45: 1 E'2. 15: 1 I 5.27: 1 B'2. 45: 1 F'1. 29: 1 II 3.16: 1 A'1. 00: 1 E'2. 15: 1 III 2.15: 1 C'1. 29: 1 F'1. 29: 1 IV 1.66: 1 A'1.00: 1 F'1.29: 1 V 1.29: 1 A'1. 00: 1 G'1. 00: 1 VI 1.000: 1 D'-1.16: 1 E'2. 15 : 1 R-2.50: 1 The other possible combinations B'-G', C'-E'and C'-G'are not used in practice since B'-G'and C'-E'are too close to A'-E'and B'-F', respectively, while C'-G'in fact produces the same overall reducing ratio as A'-F'. Instead, the effect achieved with the given choice of combinations is that the intermediate shaft is subjected to the minimum of loads at the various reducing steps I to V since the second planet gear P2b always takes part in the reduction and its direct drive clutch G is engaged only in the direct gear VI.

Figure 2a is a diagram again showing the variation in transmission input speed of rotation nl and tractive force P in relation to the travelling velocity at the six forward gears I to VI when using a transmission according to Figure 2 in a motor lorry. The diagram clearly shows the much coarser grading of the engine speed and tractive force in the region of lower travelling velocities compared with the results obtained with the transmission according to Figure 1.

Figure 3 represents schematically a modified embodiment of the transmission of Figure 1.

The difference is that in this case the planet wheels of the first planet gear (on the left in Figure 3) have a third section of smallest diameter which meshes with the second ring wheel designed to be braked by the brake D for reversing gear and with an additional sun wheel designed to be braked by an additional brake Ao. The purpose of this arrangement is to obtain an even higher reducing ratio for reversing and to obtain an additional two extremely high reducing ratios in forward drive, as represented by the revolution curves nlo and n, in Figure 3a. For reversing one obtains a reducing ratio for forward drive are 8.4: 1 and 7.1.

Reference is also made to the description and claims of our copending applications No.

28964 (Serial No. 1559492) and 28965/76 (Serial No. 1559493).

Claims (9)

WHAT WE CLAIM IS :

1. A multiple speed gear suitable for use with motor lorries and earth moving vehicles comprising two serially connected multiple speed planetary gears, each comprising a planet carrier having associated planet gear wheels at least two of which gear wheels are of different diameters and which, in each planetary gear, mesh with at least three internally and/or externally toothed centrally disposed gear wheels, at least one of the centrally disposed wheels in each planetary gear constituting an input member with the planet carriers constituting an output member, each remaining centrally disposed gear wheel having an associated friction brake controlled by a servo motor having a non-rotatable housing.

2. A gear according to claim 1 wherein the planetary gears have at least one friction clutch operable to clutch together a central wheel which preferably constitutes the input member and a planetary carrier.

3. A gear according to claim 2, wherein the friction clutches are adapted to be operated by servo motors supporte on a housing for the gear by at least one thrust bearing.

4. A gear according to claim 3, wherein the servo motor for each friction clutch acts on the appropriate thrust ring via a thrust bearing and wherein the engaging thrust from each thrust ring is transmitted to the friction clutch by way of radial levers mounted outside their fulcra on the appropriate planet carrier.

5. A gear according to one of the preceding claims, wherein the input member of that planetary gear which is the first viewed in the direction of transmission of power through the gear is a ring wheel in mesh with the planet gear wheel of larger diameter and wherein the input member of the second planetary gear is a sun wheel in mesh with the planet gear wheel of smaller diameter for producing a larger reduction ratio.

6. A gear according to one of claims 1 to 4, wherein the input members of both planetary gears are ring wheels in mesh with the planet gear wheel of larger diameter.

7. A gear according to one of the claims 2 to 6, wherein at least one planetary gear includes an axially displaceable sun wheel constituting a thrust transmission member for engaging the friction clutch between the input member and the planet carrier.

8. A gear according to one of the claims 5 to 7, wherein the planet gear wheels of one of the planetary gears (preferably the first planetary gear when viewed in the direction of transmission) has a third planet gear wheel of small diameter which meshes with another and separately braked ring wheel for producing a reverse drive having a high reducing ratio.

9. A gear according to one of the claims 5 to 8, wherein the planet wheels, preferably of the first planetary gear, when viewed in the direction of transmission, inclues a third planet gear wheel of small diameter which meshes with another and separately braked sun gear wheel.