Transmission

A transmission includes a first shaft, and a second shaft, and a shifting group arranged between the first and second shafts. The shifting group is configured such that a mechanical power transmitted via the first shaft is transmitted to the second shaft via a first power path or a second power path which is coupled-in or coupled-out. The first power path is designed as a forward gear and the second power path is designed as a reverse gear. The forward gear includes a different transmission ratio in magnitude from the reverse gear. The shifting group includes a summation planetary stage, where the mechanical power of the power paths is transmitted thereby to the second shaft.

RELATED APPLICATIONS

This application claims priority to German Patent Application Ser. No. 102019210847.4, filed Jul. 22, 2019, the disclosure of which is hereby incorporated by reference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to a transmission, and in particular to a transmission having a first and a second shaft and a shifting group which is arranged between the shafts.

BACKGROUND

Transmissions having a shifting group are known in principle from the prior art and serve for implementing at least one forward gear and at least one reverse gear. Generally, further shifting groups are arranged upstream and downstream of this shifting group so that a plurality of different gears may be produced, where the gears differing from one another in terms of the transmission ratio thereof, however, in order to be able to ensure load changes which are as small as possible during the shifting process.

In agricultural machines, however, it is frequently required to provide a specific crawler gear which permits very slow travel speeds. In the case of vehicles, a crawler gear serves for slow travel without a slipping clutch being required. Typical fields of use are, for example, when working in rough terrain, when transporting heavy loads or also when working in agriculture. Thus, agricultural machines frequently have a crawler gear, speeds of considerably less than 1 km/h being able to be achieved thereby and, for example, slow field work being possible thereby.

The crawler gear was generally achieved via a separate gear stage which has a transmission ratio in the region of 10. This accordingly requires additional spur gear sets with a plurality of shafts and gearwheels, as well as an additional shifting shaft, whereby the transmission as a whole is of large constructional size and at the same time the production costs may rise significantly relative to a transmission without a crawler gear.

Overall, therefore, conventional transmissions which have a crawler gear are worthy of improvement so that a transmission which provides a crawler gear is characterized by a smaller design and by lower production costs relative to the conventional transmissions.

This object is achieved by a transmission as disclosed herein, wherein according to the present disclosure the shifting group has a summation planetary stage, the mechanical power of the power paths being able to be transmitted thereby to the second shaft.

SUMMARY

In the present disclosure, a transmission may include a shifting group having a summation planetary stage, where the mechanical power of the power paths are able to be transmitted thereby to the second shaft.

Planetary stages consist of a plurality of planetary units which are arranged coaxially to one another and which are rotatable relative to one another. These planetary units may be a sun gear, a planet carrier or a ring gear. The sun gear is arranged centrally in the planetary stage and accordingly is only able to carry out a rotational movement around itself. A plurality of planet gears are arranged on this sun gear and which in turn are connected to one another via a common planet carrier. Accordingly, the planets may perform, on the one hand, a rotation around one another and, on the other hand, a rotation around the sun gear. A ring gear may then be attached to the planets. Accordingly, both the ring gear as well as the planet carrier and the sun gear have a common rotational axis. As a result, it is possible to combine together the rotational movements of the first power path and the second power path.

According to the present disclosure, the first and the second power paths differ from one another such that the first power path is configured as a forward gear and the second power path is configured as a reverse gear, so that both power paths have an opposing rotational direction. If both power paths are now combined together via the summation planetary stage, this results in the rotational movements being equalized to a large extent, wherein a slight rotation furthermore begins either in the forward direction or in the reverse direction, however, due to the different transmission ratio in the two power paths. By a careful choice of transmission ratios, therefore, according to the present disclosure it is possible to configure a crawler gear which is solely based on the coupling of the forward gear and the reverse gear without further components, for example, additional spur gear stages being required. For implementing the crawler gear it may be necessary that both the first and the second power paths are in a coupled-in state. In this context “coupled-in” means that a torque or a power may be transmitted via the corresponding power path. This is generally carried out by actuating shifting devices in the form of clutches, wherein a shifting device is provided in each power path, the corresponding power path then being able to be coupled-in or coupled-out thereby.

The summation planetary stage also comprises a shifting device which is designed either such that the first and the second power paths are able to be directly coupled together or such that one respective power path is able to be coupled to an output path of the summation planetary stage, wherein the output path is connected to the second shaft. Such a shifting device is required so that normal forward travel or reverse travel is also possible instead of the crawler gear. If, for example, the two power paths are coupled together in the summation planetary stage, this results in the planetary units which are connected to the power paths performing the same rotational movement and thus no relative movement is present between the individual planetary units. Accordingly, no transmission may be carried out via the summation planetary stage so that, as a result, the torque is directly transmitted from the corresponding power path to the output path.

In this case, and in particular for forward travel, the first power path is coupled-in and the shifting device of the summation planetary stage is actuated. The second power path, however, is not coupled-in. Accordingly, in the case of reverse travel or when engaging the reverse gear, the first power path may be coupled-out and the second power path may be coupled-in, while the shifting device of the planetary stage is also actuated.

The manner in which the two planetary units of the first and the second power paths may be blocked relative to one another substantially depends on how the shifting device is configured. Particularly suitable in this case are claw clutches, multi-disk clutches or synchronization units. Multi-disk clutches have the advantage that the rotational speeds of the first and the second power paths may be equalized when actuating the clutch, while the transmission continues to be under load. This is permitted by the multi-disk clutch consisting of a radially internal multi-disk shaft and a radially external multi-disk carrier. Both the multi-disk shaft and the multi-disk carrier have radially protruding disks which are forced against one another axially when the clutch is actuated, so that a frictional connection is produced between the multi-disk carrier and the multi-disk shaft. In such an embodiment, the multi-disk carrier and the multi-disk shaft are connected in each case to one of the power paths and in each case to one of the planetary units of the summation planetary stage.

In contrast to a multi-disk clutch, while a synchronization unit may effect an equalization of the rotational movements, this is not possible under load. In a synchronization unit, in a similar manner to a multi-disk clutch, two rotatable shafts which are arranged coaxially to one another are brought into contact on the front face by a synchronization ring, wherein the synchronization ring forms a frictional connection between the individual shafts and results in a synchronization of the rotational speeds. In a similar manner to the multi-disk clutch, the shafts are respectively connected to one of the power paths and one of the planetary units of the summation planetary stage.

In contrast to a multi-disk clutch and a synchronization unit, a synchronization of the rotational speed is not possible by a claw clutch. Thus, in order to actuate this clutch, initially the transmission has to be brought to a standstill, wherein the claw clutch may only be actuated at a standstill.

As already described above, the summation planetary stage may be configured differently, wherein at least two planetary units which are arranged coaxially to one another are provided for connecting the individual power paths. In particular, the planetary units are configured as a sun gear and as a planet carrier, wherein the planet carrier circulates around the sun gear by a plurality of individual planets. For the configuration of the output path, the summation planetary stage has a second planet carrier, wherein the planet carriers are directly coupled together and wherein the second planet carrier is connected to the second shaft. The connection to the second shaft may be carried out either directly or indirectly via a second sun gear which is driven via the second planet carrier.

According to a variant, the first or the second power path is formed in each case by a shaft arrangement, the first or second power path being connected to the summation planetary stage either directly or by incorporating a spur gear set, and wherein the shaft arrangement in each case has a shifting device, the shaft arrangement being able to be coupled-in or coupled-out thereby. By such a spur gear set a specific transmission ratio may be set within the respective power path. For example, in the case of a gearwheel pair of the spur gear stage, the coupling-in or coupling-out of the corresponding power path may be implemented by at least one of the gearwheels being arranged on a coaxial shaft portion which is arranged coaxially to a shaft, wherein the coaxial shaft portion may be connected to the internal shaft by means of a clutch.

Alternatively, the first and the second power paths may also be formed by a power-branching planetary stage.

The shifting group may also have a third power path, wherein the third power path is configured as a forward gear or as a reverse gear and has a different transmission ratio from the first power path in the case of a forward gear or from the second power path in the case of a reverse gear.

Moreover, the shifting group may also have a second summation planetary stage, wherein both summation planetary stages are connected to the first and the second power paths.

Corresponding reference numerals are used to indicate corresponding parts in the drawings.

DETAILED DESCRIPTION

FIG. 1shows a basic sketch or schematic of a transmission according to the present disclosure with a first shaft1and a second shaft2, wherein a shifting group3is arranged between the shafts. The shifting group3is configured such that a mechanical power introduced via the first shaft1is branched into a first power path4and into a second power path5, wherein the first power path4is configured as a forward gear (FWD) and the second power path5is configured as a reverse gear (RWD).

A clutch or other shifting device6,7is additionally provided in each of the power paths4,5, where the respective power path4,5is able to be coupled-in or coupled-out thereby.

The two power paths are then combined in a summation planetary stage8, so that the mechanical power may be transmitted to the second shaft2. According to the embodiment ofFIG. 1, a shifting device9is also provided. Here, the two power paths4,5are able to be coupled together thereby upstream of, or directly in, the summation planetary stage8.

FIGS. 2 and 3show possible embodiments wherein the second power path is connected via a spur gear set to the summation planetary stage8, while the first power path4directly transitions into the summation planetary stage8.

The spur gear set consists of a first gearwheel set10and a second gearwheel set11, wherein the first gearwheel set10has two gearwheels in engagement with one another and the second gearwheel set11has three gearwheels in engagement with one another, a reversal of the rotational direction being achieved thereby. An auxiliary shaft12is also provided between the first gearwheel set10and the second gearwheel set11, the auxiliary shaft12connecting together the two gearwheel sets10,11. The shifting device7is implemented as a multi-disk clutch, the first gearwheel set10being able to be coupled thereby to the auxiliary shaft12.

A shifting device6is also provided in the first power path4as a multi-disk clutch which couples the first shaft1directly to a multi-disk shaft13. This multi-disk shaft is part of the shifting device9of the summation planetary stage8. The multi-disk carrier14is directly connected to the gearwheel set11. Thus, the two power paths4,5may be coupled together via the shifting device9, wherein this is only possible or expedient when one of the two power paths is decoupled in order to permit a forward gear or a reverse gear (FWD, RWD).

The multi-disk shaft13is thus directly connected to the sun gear15of the summation planet shaft and the multi-disk carrier14is directly connected to the first planet carrier16of the summation planetary stage8.

The summation planetary stage8also has a second sun gear17which is connected to the second shaft2and which is connected via a second planet carrier18to the first planet carrier16of the summation planetary stage8.

According toFIG. 3, instead of a multi-disk clutch, the shifting device9is formed via a synchronization unit, wherein the remaining components remain the same.

FIG. 4shows an alternative embodiment of the shifting group according toFIG. 2, wherein the first power path and the second power path are formed by a power-branching planetary stage19. In this case, the first shaft1may be coupled again directly to the multi-disk shaft13via the shifting device6, wherein a planet carrier20is also driven via the first shaft1, the planet carrier20being connected to the multi-disk carrier14. By shifting the shifting device7, a ring gear21of the power-branching planetary stage19is connected directly to the housing22and this results in a reversal of the rotational direction of the planet carrier20and, as a result, in a reverse gear.

FIG. 5shows an alternative embodiment according toFIG. 4, wherein a third power path4″ is now provided in addition to the first power path4′ and the second power path5, the third power path4″ also being configured as a forward gear (FWD2) in a similar manner to the power path4′.

FIGS. 6 and 7shows the shifting group3having a second summation planetary stage8′, wherein both summation planetary stages8,8′ are connected to the first and the second power paths4,5.