SE541982C2 - Method of presetting a planetary gear train - Google Patents

Abstract

The present disclosure relates to a method of presetting a planetary gear train (1), said planetary gear train comprising a sun gear (3), at least two beveloid planet gears (5) and a ring gear (7), wherein said at least two planet gears (5) being arranged to rotate about a respective gear shaft (13) and each of said planet gears (5) being displaceable in the axial direction of the gear shaft (13).The method comprises operating the planetary gear train (1) at a torque load, applying, while the planetary gear train is operated at said torque load, a similar axial force (F) to each of the planet gears (5) in their respective axial directions, thereby forcing each of the planet gears (5) to stabilize in an axial normal position, and axially locking the planet gears (5).

Description

METHOD OF PRESETTING A PLANETARY GEAR TRAIN Technical field The present disclosure relates to a method of presetting a planetary gear train.

Background Planetary gear trains are used in various systems. For instance, planetary gear trains often employ three or more planet gears that connect to a ring wheel at separate locations to convey power.

One problem with gear trains of the initially mentioned type is that they require components with high tolerances and often must be considerably over-dimensioned compared to what would be needed in an ideal realisation. Therefore gear trains of the initially mentioned type are often expensive.

WO 2016/140618 discloses a planetary gear train with beveloid planetary gears that are axially movable. The planetary gear train is provided with an equalizing arrangement, that interconnects the planetary gears, such that they are subjected to a similar force of application in their respective axial directions. In this arrangement, the load will be more or less evenly distributed between the planet gears. Tolerances can then be less demanding.

However, such a planetary gear train may be considered costly and bulky.

Summary One object of the present disclosure is therefore to provide a method of presetting a planetary gear train such that the planetary gear train can be less costly and/or less bulky, and still have a considerable capacity in terms of transferred power.

This and other objects that will be apparent from the following summary and description are achieved by a method according to the appended claims.

According to one aspect of the present disclosure there is provided a method of presetting a planetary gear train, said planetary gear train comprising a sun gear, at least two beveloid planet gears and a ring gear, wherein said at least two planet gears being arranged to rotate about a respective gear shaft and each of said planet gears being displaceable in the axial direction of the gear shaft, said method comprising operating the planetary gear train at a torque load, applying, while the planetary gear train is operated at said torque load, a similar axial force to each of the planet gears in their respective axial directions, thereby forcing each of the planet gears to stabilize in an axial normal position, and axially locking the planet gears.

The axial forces are thus applied as the gears of the planetary gear train are rotated with a torque load. The planetary gear train may be rotated with the planet gears axially loaded this way until no backlash is present.

Hence, the presetting is carried out while the gear train is operated, preferably at a low torque load, and serves to stabilize the planet gears in individual axial positions. Since the presetting is carried out while the gear train is operated, individual axial normal positions that works over a full rotation of each gear of the planetary gear train are achieved. Thanks to the presetting of the planetary gear train, the load will be more or less evenly distributed between the planetary gears in normal operation of the preset planetary gear train. This method thus enables the planet gears of the planetary gear train to operate with an even load distribution, which increases the capacity of a given gear train, such that it can be used to transfer more power. Alternatively, tolerances can be less demanding. The result is a more efficient and/or less expensive planetary gear train. Furthermore, a very space-efficient solution is enabled, since no load distribution device is needed once the planetary gear train has been preset. A preset planetary gear train may thus be installed in an application without the need of a separate force equalizing device, such as a hydraulic, a pneumatic or a mechanical force balancing device.

Especially, the method is thus advantageous in situations where no hydraulic system is available and where there is complicated to connect a hydraulic system, e.g. in hub reduction gears in heavy vehicles.

The planet gears may be locked in their respective stabilized axial normal positions. Alternatively, a further stabilization operation, in which the planetary gear train is operated in an opposite direction while the axial forces are applied to the planet gears, may be performed before locking the planet gears. Then, each planet gear may be locked in a position between two stabilized axial normal positions.

According to one embodiment an equal axial force is applied to each of the planet gears while the planetary gear train is operated at said torque load.

According to one embodiment the method comprises replacing the sun gear used to stabilize the planet gears with a sun gear having a smaller gear tooth thickness. The sun gear used to stabilize the planetary gears in axial normal positions is thus replaced by a sun gear that provides a predetermined backlash. In this way, a desired backlash may be set in a very easy manner. Then, the sun gear used during the stabilization operation, i.e. the operation in which axial forces are applied to the planet gears as the planetary gear is operated, works as a dummy sun gear and may thus be used to preset several planetary gear trains.

According to one embodiment, the method comprises replacing the ring gear used to stabilize the planet gears with a ring gear that provides a predetermined backlash. In this way, a desired backlash may be set in a very easy manner. Then, the ring gear used during the stabilization operation works as a dummy ring gear which may be used to preset several planetary gear trains.

Hence, the method may comprise replacing the sun gear used to stabilize the planet gears with a sun gear that provides a predetermined backlash and/or replacing the ring gear used to stabilize the planet gears with a ring gear that provides a predetermined backlash.

The axial forces are preferably applied by force application devices.

According to one embodiment at least one of said force application devices comprises a set screw. Then, the magnitude of the applied force may be controlled by monitoring the tightening torque of the set screw. Hence, this embodiment has the advantage that the applied force may be monitored in an easy and reliable manner.

According to one embodiment at least one of said force application devices comprises a force applicator in the form of a fluid, preferably a compressible fluid. This embodiment has the advantage that the load distribution between the planet gears may be even further improved, since such a compressible fluid enables a resilient locking of the planetary gear.

According to one embodiment the planetary gear train comprises at least four beveloid planet gears. As all planet gears will carry equal load after the presetting it is preferable to use as many planet gears as the space admits.

According to one embodiment the planetary gear train comprises at least six beveloid planet gears.

According to one embodiment the planetary gear train comprises a beveloid sun gear and a beveloid ring gear.

The planet gears may be subjected to said axial forces during a predetermined number of revolutions of operation of the planetary gear train, such as 10-30 revolutions of operation, until the axial positions of all planet gears are stabilized.

According to one embodiment the planet gears are locked in the respective stabilized axial normal positions.

According to one embodiment the planetary gear train is operated, with the planet gears axially loaded, in both directions of operation. The planetary gear train may thus be preset to be loaded in both directions of operation.

If the planetary gear train is intended to, in operation, be loaded equally in both directions of rotation, the planetary gear train is operated in both directions with the planet gears axially loaded until no backlash is present. If the respective planet gears then have different axial normal positions depending on the direction of rotation, the planet wheels may be locked in a position between the measured axial extreme values, i.e. in a position between two stabilized positions.

These and other aspects of the invention will be apparent from and elucidated with reference to the claims and the embodiments described hereinafter.

Brief description of the drawings The invention will hereafter be described in more detail and with reference to the appended schematic drawings.

Fig. 1 illustrates a planetary gear train.

Fig. 2 shows a sectioned view of the planetary gear train shown in Fig 1.

Fig. 3 shows a partly sectioned view of the planetary gear train shown in Fig. 1 and illustrates a method according to a first embodiment of the present disclosure.

Fig. 4 shows a partly sectioned view of a planetary gear train and illustrates a method according to an alternative embodiment of the present disclosure.

Detailed description of Preferred Embodiments Fig. 1 shows a schematic front view of a planetary gear train 1. The planetary gear train 1 comprises a central driving pinion 3, also referred to as sun gear 3, four planet gears 5 and an outer ring gear 7. The central driving pinion 3 is mounted on a shaft 4, illustrated in Fig. 2, which constitutes an input/input shaft of the planetary gear train 1. The planetary gear train 1 may have an outer casing (not shown) that may be attached to a structure to provide a stationary reference point with regard to the operation of the planetary gear train 1.

The four planetary gears 5 are arranged with 90° spacing, although different angular spacings are possible, and attached to a common planet carrier 9, illustrated in Fig. 2.

The centrally located driving pinion 3 meshes with each planet gear 5. Each of the planet gears 5 further mesh, at different locations, with the outer ring gear 7. Either the planet carrier 9 or the ring gear 7 is kept fixed with regard to the reference of the planetary gear train 1, which means that the other part (the ring wheel or the planet carrier) will be driven by the driving pinion 3 but at a much lower angular speed and constitutes the output of the planetary gear train 1. Of course, the gear may be reversed, such that the driving pinion is instead driven.

As best illustrated in Fig. 2, which shows a schematic cross section of the planetary gear train 1 of Fig. 1, each of the central driving pinion 3, the planet gears 5 and the ring gear 7 is a beveloid gear.

Now referring to Fig. 2, each planet gear 5 is rotatably mounted by means of bearings 11 on a planet shaft 13. Each planetary shaft 13 is axially movable, as illustrated by arrows D in Fig. 2. Each planet gear 5 is mounted on its planet shaft 13 so as to move axially together therewith when the planet shaft 13 is displaced. A force applicator device 15 is connected to each of the planet shafts 13. For instance, as illustrated in Fig. 2, a force applicator in the form of a set screw 17, which is supported by the planet carrier 9 and arranged to abut the planet shaft 13, may be used.

The force applicator devices 15 may be used to apply axial forces to each of the planet shafts 13, which results in that axial forces are applied to each of the planet gears 5, as will be described hereinafter. Also, each force applicator device 15 may be used to lock a planet shaft 13, and thereby the planet gear 5 that is mounted thereon, in an axial position.

Flence, each each planetary gear 5 is mounted on a planet shaft 13 and can be displaced in that axis’ axial direction by a force application device 15.

A method of presetting a planetary gear train according to the present disclosure comprises a stabilization operation in which, while the planetary gear train is operated with a torque load in the main direction of rotation, a similar axial force is applied to each of the planet gears in their respective axial directions. The stabilization operation causes each of the planet gears of the planetary gear train to stabilize in an individual axial normal position, which may be an adjusted position compared to the initial position. The axial forces are applied until all meshing gears come into backlash-free contact with each other. For instance, 15-35 revolutions of operation may be sufficient to reach a state in which all planet gears of the planetary gear train have stabilized in such a normal axial position.

After the stabilization operation, the planet gears may be locked in their respective stabilized axial normal positions. Prior to locking the planetary gears in their respective stabilized axial normal positions, the rotation of the planetary gear train may be stopped.

If the planetary gear train is intended to, in operation, be loaded equally in both directions of rotation, the planetary gear train is operated in both directions with the planet gears axially loaded until no backlash is present. Hence, the stabilization operation then comprises operation of the planetary gear train in both directions of operation. If the respective planet gears then have different axial normal positions depending on the direction of rotation, the planet gears are fixed in a position between the measured axial extreme values.

The planet gears may be locked in their respective stabilized axial normal positions, or in a position between two measured axial extreme values, by means of locking means, such as, e.g., set screws or locking rings.

Then, the planetary gear train is preset to operate with an even load distribution between the planetary gears and without backlash.

Alternatively, when the gear train is intended to be used in applications where backlash is desired, a predetermined backlash may be set, e.g. by means of set screws or locking rings.

Optionally, in a subsequent step, a predetermined backlash may thus be set. Such a predetermined backlash may be set by displacing each of the planet gears a similar distance in the axial direction, e.g. by means of set screws or locking rings. Alternatively, such a predetermined backlash may be set by replacing the sun gear, which then only serves as a dummy sun gear during the stabilization process, with a slightly smaller sun gear with slightly less gear tooth thickness and/or by replacing the ring gear with a ring gear that provides a predetermined backlash. The difference in gear tooth thickness between the dummy sun gear and the sun gear intended to be used in operation, if only the sun gear is replaced, is determined based on the desired backlash. Hence, the difference in gear tooth thickness between the dummy sun gear and the sun gear intended to be used in operation corresponds to the desired backlash in the planetary gear train. Hence, such a dummy sun gear and/or dummy ring gear is/are thus used only in the stabilization operation and may thus be used for presetting several planetary gear trains.

With reference to Fig. 3, a method according to an embodiment of the present disclosure will be described hereinafter.

As illustrated by arrow R in Fig. 3, the planetary gear train 1 is operated at a low torque load in the main direction of rotation. As the gears 3, 5, 7 of the planetary gear train 1 are rotated, an equal axial force is applied to each of the planetary gears 5, as illustrated by arrows F in Fig. 3. The axial forces F are applied by means of a respective set screw 17. Each set screw 17 is supported by the planet carrier 9 and connected to a planetary shaft 13 such that an axial force F can be applied thereto by turning the set screw 17. The force F applied to the planetary shaft 13 is transferred to the planet gear 5 that is mounted thereon. Hence, by tightening a set screw 17, an axial force F is applied to a planet gear 5 via the planet shaft 13 on which the planet gear 5 is mounted.

As the gears 3, 5, 7 of the planetary gear train 1 are rotated with a torque load, a similar or equal axial force F is thus applied to each of the planet gears 5 by a respective force applicator device 15. The applied axial forces F act to stabilize each planet gear 5 in an axial normal position. To secure that an equal, or at least similar, force is applied to each of the planet gears 5 during the stabilization operation, in which the gears 3, 5, 7 of the planetary gear train are rotated with a torque load, each of the set screws 17 is tightened with an equal torque. To control the stabilization operation, the tightening torque of each of the set screws 17 is thus monitored. The axial forces F are applied until all meshing gears come into backlash-free contact with each other. Then, each planet gear 5 has stabilized in an axial normal position. During the stabilization operation, the planet gears 5 may move axially differently, as illustrated by arrows D1 and D2 in Fig. 3.

As mentioned hereinbefore, the stabilization operation causes each of the planet gears 5 of the planetary gear train to stabilize in an individual axial normal position. In this embodiment, in which set screws 17 are used to apply the axial forces to the planet gears, the planet gears 5 are locked in their respective stabilized axial normal position by the force applicator devices 15 themselves. Flence, the planet gears 5 are maintained in their respective normal axial positions, or adjusted positions, by the force application devices, i.e. by means of the set screws 17. If, as illustrated in Fig. 3, the axial forces is applied by means of set screws 17, the planet gears 5 will thus remain in their stabilized positions after the stabilization operation without further action. Flence, locking of planetary gears is then carried out in the stabilization operation and with the force application devices 15. In this embodiment there is thus no need for separate locking devices.

According to an embodiment of the method of the present disclosure, a planetary gear train with beveloid planetary gears may thus be preset by applying a similar axial force to each of the planet gears in their respective axial directions as the gears of the planetary gear train are rotated. The presetting, which involves stabilization of the planetary gears of the planetary gear train, may be carried out while the planetary gear train is operated at low load, i.e. at low torque.

In many applications, such as in vehicle applications, a predetermined backlash is often desired. In such applications, a predetermined backlash may be set after the stabilization operation and before the planetary gears are axially locked. For instance, a predetermined backlash may be set by displacing each of the planet gears a similar distance in the axial direction, e.g. by turning set screws equally or by using locking rings.

By using beveloid gears and making sure that they are loaded axially with the same force during the stabilization operation, the planetary gear may thus be preset to provide for a more or less exactly even load distribution when used in normal operation in an application.

Fig. 4 serves to illustrate a method according to an alternative embodiment of the present disclosure. Essentially all features disclosed in the first embodiment are also present in the second embodiment. Having mentioned this, the description will focus on explaining the differing features.

The method according to this embodiment differs in that the force application devices 15 includes valve arrangements 19 instead of set screws. The valve arrangements 19 are configured such that an axial force may be applied by means of a force applicator in the form of a fluid. Preferably, a compressible fluid is used in order to achieve some flexibility.

It is realized by a person skilled in the art that features from various embodiments disclosed herein may be combined with one another in order to provide further alternative embodiments.

The illustrated planetary gear trains comprises four planet gears. Four planetary gears will be considered preferred in some applications. It it however appreciated that a different number of planetary gears, such as e.g. six planetary gears, may be preferred in other embodiments.

Claims (11)

1. Method of presetting a planetary gear train (1), said planetary gear train comprising a sun gear (3), at least two beveloid planet gears (5) and a ring gear (7), wherein said at least two planet gears (5) being arranged to rotate about a respective gear shaft (13) and each of said planet gears (5) being displaceable in the axial direction of the gear shaft (13), said method comprising: operating the planetary gear train (1) at a torque load, applying, while the planetary gear train is operated at said torque load, a similar axial force (F) to each of the planet gears (5) in their respective axial directions, thereby forcing each of the planet gears (5) to stabilize in an axial normal position, and axially locking the planet gears (5).

2. Method according to claim 1, wherein an equal axial force (F) is applied to each of the planet gears (5) while the planetary gear train is operated at said torque load.

3. Method according to any of the preceding claims, further comprising replacing the sun gear (3) used to stabilize the planet gears (5) with a sun gear having a smaller gear tooth thickness.

4. Method according to any of the preceding claims, further comprising replacing the ring gear (7) used to stabilize the planet gears (5) with a ring gear that provides a predetermined backlash.

5. Method according to any of the preceding claims, wherein said axial forces (F) are applied by force application devices (15, 17, 19).

6. Method according to claim 5, wherein at least one of said force application devices (15) comprises a set screw (17).

7. Method according to claim 5, wherein at least one of said force application devices (15, 19) comprises a force applicator in the form of a fluid, preferably a compressible fluid.

8. Method according to any of the preceding claims, wherein said planetary gear train (1) comprises at least four beveloid planet gears (5).

9. Method according to any of the preceding claims, wherein the planetary gears (5) are subjected to said axial forces (F) during a predetermined number of revolutions, preferably 10-30 revolutions, until the axial positions of all planet gears (5) are stabilized.

10. Method according to any of the preceding claims, wherein the planet gears (5) are locked in the respective stabilized axial normal positions.

11. Method according to any of the preceding claims, wherein the planetary gear train is operated in both directions of operation.