Shiftable planetary transmission

A shiftable planetary transmission having a housing, a non-rotatable or rotatable transmission component, a sun gear, a carrier and at least one planet gear mounted on the carrier. A rotatable ring gear is connected to the non-rotatable or rotatable transmission component. The ring gear has an annular surface facing the interior surface of the transmission component and a coupling arrangement is non-rotatably connected to the ring gear and a spring-loaded hydraulic activation mechanism is located within the ring gear to axially move the coupling arrangement.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention is a shiftable planetary transmission having a sun gear, at 
least one planet gear mounted on a carrier, and a rotatable ring gear, 
which can be coupled with a non-rotatable or a rotatable transmission 
component. 
2. Description of the Prior Art 
Planetary transmissions are known in many forms and are used advantageously 
in vehicle drives to achieve multiple stage reductions between a 
high-speed motor and a significantly slower output element, such as a 
vehicle wheel, because they save space. Planetary transmissions are also 
used in construction machines because they are shiftable under load and 
permit relatively high travel speeds during operation over the road. As a 
rule, the desired higher travel speeds cannot be obtained with the 
hydrostatic transmission which is required for operation of the 
construction vehicle at a construction site. 
To obtain the different shift modes, coupling or brake plates are usually 
provided to connect the rotatable components of the planetary transmission 
with other transmission components which may be stationary or rotatable. 
For example, a stationary transmission component may be the transmission 
housing and rotatable transmission components may be the carrier or the 
sun gear of the planetary transmission. 
If a rotatable ring gear is coupled with a rotatable sun gear, a direct 
drive results. Alternatively, rotation of the ring gear may be prevented 
by coupling it with the transmission housing to provide a braking mode. 
With a driven sun gear and a stationary carrier, it is possible to increase 
the torque on the rotatable ring gear. With a driven sun gear and a 
stationary ring gear, i.e., the ring gear is coupled to the transmission 
housing, it is possible to increase the torque on the rotatable carrier. 
These two modes are reduction modes, with the latter variation (output via 
the rotatable carrier) used more frequently. If both the carrier and the 
ring gear are freely rotatable, the planetary transmission is in a 
free-wheeling mode. 
The activation of the coupling or the brake plates is generally 
accomplished hydraulically, which requires significant structural and 
assembly costs. Furthermore, the arrangement for moving the plates 
contributes to the size of the planetary transmission. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a planetary transmission 
having a relatively small size. This object is fulfilled by providing a 
non-positively and/or a positively active coupling which is non-rotatably 
connected to the ring gear. The coupling includes movable plates for 
contacting a rotatable transmission component or a component which is 
non-rotatably connected to it by an activation mechanism located within 
the ring gear. The invention thus consists in locating the activation 
mechanism for the non-rotatable connection of the ring gear with a 
transmission component located inside of the ring gear. This design 
requires less space than prior art planetary transmissions. 
In a first embodiment of the shiftable planetary transmission according to 
the invention, the transmission component is either integral with the 
transmission housing or fixed thereto. The transmission is capable of 
shifting between the free-wheeling mode and reduction operating mode. 
In another embodiment of the invention, a second non-positively and/or 
positively active coupling arrangement is provided on the face of the ring 
gear facing the carrier. The coupling plate can be moved into contact with 
the carrier or with a component connected to the carrier by a second 
activation mechanism disposed within the ring gear. This arrangement 
provides an additional shift capability wherein the ring gear can be 
connected to both the transmission housing and to the carrier to provide a 
braking mode. 
It is advantageous if the activation mechanism for each coupling 
arrangement includes at least one ring groove formed in the ring gear in 
which a spring-loaded axially movable annular piston is located. The 
annular piston has an active piston surface which can be hydraulically 
activated against the spring force. Such an activation mechanism is simple 
to manufacture and has a relatively small number of component parts. 
Additionally, the activation mechanisms of both coupling arrangements can 
be combined. In order to obtain the different shift modes of the shiftable 
planetary transmission, the piston surfaces of the two annular pistons can 
be independently hydraulically activated. The spring force on the annular 
pistons may be achieved, for example, by plate springs. It is also 
possible to form a plurality of holes through the perimeter of the ring 
gear, to connect the ring grooves with each other and to place a spring in 
each hole to push the two annular pistons apart. 
According to a further embodiment of the invention, the transmission 
component consists of an annular brake plate non-rotatably connected to 
the sun gear and extending radially in the region of the ring gear. The 
activation mechanism of the coupling arrangement includes an axial ring 
groove in the ring gear. A spring-loaded annular piston is located in the 
ring groove and is axially movable relative to the brake plate. The 
annular piston has an active piston surface which can be hydraulically 
activated against the spring force. An annular stop plate is non-rotatably 
connected to the ring gear on the side of the brake plate opposite from 
the annular piston. 
In an improvement of the invention, provision is made for a second 
non-positively and/or positively active coupling arrangement which can be 
brought into contact with the ring gear or with a component connected to 
the ring gear by an activation mechanism located outside of the ring gear. 
It is advantageous if the activation mechanism of the second coupling 
arrangement has an axial ring groove in a component fixed to the housing 
and opposing one face of the ring gear. A spring-loaded annular piston is 
located in the ring groove and is axially movable relative to the ring 
gear. The annular piston has an active piston surface located opposite the 
annular stop plate which can be hydraulically activated in opposition to a 
spring force. 
The coupling arrangements in the planetary transmission according to the 
invention can be either positive couplings, such as claw couplings, or 
nonpositive couplings, such as friction couplings. A nonpositive coupling 
is particularly advantageous when a coupling is shiftable under load. 
The invention can be used in many ways independently of the type of drive 
of the planetary transmission. For example, an electric motor can be used 
as the drive. However, it is particularly advantageous when a hydrostatic 
axial piston engine is provided on the input side of the shiftable 
planetary transmission and the shaft of the engine is formed by the sun 
gear. Thus, a hydraulic medium can be introduced from the hydraulic 
circuit to act on the active surfaces of the annular pistons. 
A complete understanding of the invention will be obtained from the 
following description when taken in connection with the accompanying 
drawings wherein like reference characters identify like parts throughout.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The shiftable planetary transmission according to the invention in both 
embodiments shown in the drawings is driven by a hydrostatic swash-plate 
type axial piston engine 1 and may drive a vehicle wheel. 
With reference to FIG. 1 of the drawings, it will be seen that the output 
shaft of axial piston engine 1 is the sun gear 2 of the first stage of a 
two-stage planetary transmission. Planet gears 3 are mounted on a carrier 
4 and are in mesh with a ring gear 5 which rotates on sun gear 2. The 
carrier 4 is non-rotatably connected to a sun gear 6 of the second stage 
of the planetary transmission. The sun gear 6 of the second stage meshes 
with planet gears 7, which rotate in a ring gear 9 formed on the inner 
side of a wheel hub carrier 8 and are mounted on a carrier 10 which serves 
as the output wheel hub 11. A bearing 12 is located between wheel hub 11 
and wheel hub carrier 8. The housing of the transmission is formed by 
wheel hub carrier 8 and the part of the housing of axial piston engine 1 
which serves as a flange. 
Ring gear 5 is rotatably mounted in the transmission housing and has an 
axial ring groove formed on each face. An axially movable annular piston 
13 or 14 is located in each axial ring gear. The axial ring grooves are 
connected to each other by a plurality of axial passages formed in the 
perimeter of the ring gear and a compression spring 15 is located in each 
axial passage. The force of springs 15 push annular pistons 13 and 14 away 
from each other. An active piston surface 16 or 17 is formed on annular 
pistons 13 or 14, respectively, and the space in front of piston surfaces 
16 or 17 is connected by a drilled passageway 18 or 19 in ring gear 5 to 
an annular chamber 20 or 21 which is formed by three spaced sealing rings 
22, 23, and 24 on the external perimeter of the ring gear between the 
external surface of the ring gear and the spaced internal surface of the 
transmission housing. Annular chamber 20, into which passageway 18 opens, 
is located between sealing rings 22 and 23 and annular chamber 21, into 
which passageway 19 opens, is located between sealing rings 23 and 24. 
Each annular chamber 20 and 21 is connected to a pressurized 
hydraulic-medium source. The annular chambers 20 and 21 can be jointly or 
separately filled with a hydraulic medium. The force of the hydraulic 
medium on active piston surfaces 16 and 17 of annular pistons 13 and 14 
axially moves the pistons either jointly or separately against the force 
of spring 15. 
Instead of annular pistons located in the axial ring grooves, it is 
possible to form a plurality of axial holes around the perimeter of the 
ring gear with opposing pistons located therein and a spring located 
between the pistons. However, in this arrangement the delivery of a 
hydraulic medium to the piston surfaces to oppose the spring force is more 
complex. 
Ring gear 5 has axial extensions 5a and 5b on its opposite faces. Each 
axial extension has splines on its internal surface and a plurality of 
non-twistable axially movable annular coupling plates 25a or 25b are 
located on the splines. Annular stop plates 26a and 26b are provided on 
the external side of each coupling plate. Coupling plates 25a or 25b 
prevent rotation of annular pistons 13 or 14 in the ring groove. However, 
if annular pistons 13 and 14 are located in the ring grooves with 
torsional protection, it is possible to dispense with coupling plates 25a 
and 25b. This is particularly true if annular pistons 13 and 14 are 
provided with friction surfaces on the external faces. 
Coupling plate 25a is acted on by annular piston 13 and stop plate 26a acts 
with one or a plurality of coupling plates 27a non-rotatably connected to 
and axially movable with carrier 4. Coupling plate 25b is acted on by 
annular piston 14 and stop plate 26b acts with one or a plurality of 
coupling plates 27b nonrotatably connected to and axially movable with the 
transmission housing. 
In operation, when no pressurized hydraulic medium is present in annular 
chambers 20 and 21, annular pistons 13 and 14 are forced apart by springs 
15 and are in contact with the coupling plates. The ring gear 5 is thus 
fixed relative to both the transmission housing and carrier 4 and the 
shiftable planetary transmission is in the braking mode. When annular 
chamber 20 and passageway 18 are filled with a hydraulic medium under 
pressure which is in contact with piston surface 16 of annular piston 13, 
the annular piston is acted on and carrier 4 is rotatable. The first stage 
of the planetary transmission is now in a reduction mode. When annular 
chamber 21 and passageway 19 are filled with a hydraulic medium under 
pressure which is in contact with piston surface 17 of annular piston 14, 
the annular piston is acted on and ring gear 5 is rotatable in the 
transmission housing. The first stage of the planetary transmission is now 
in a direct drive mode. Reduction thus occurs only by the second stage of 
the planetary transmission. 
When both annular chambers 20 and 21 are filled with a hydraulic medium 
under pressure, both ring gear 5 and carrier 4 are freely rotatable and 
the planetary transmission is in the free-wheeling mode. 
In the embodiment shown in FIG. 2 of the drawings, a transmission according 
to the invention has a ring gear 5 with only one axial ring groove with a 
spring-loaded annular piston 13a located therein. Annular piston 13a 
contacts a coupling plate 25c which is adjacent to a non-rotatable brake 
plate 28 which is axially movable along sun gear 2. Brake plate 28 is 
preferably provided on both sides with friction pads and is held against a 
stop plate 26c by the extension of annular piston 13a. Annular piston 13a 
corresponds to annular piston 13 in FIG. 1 of the drawings, while stop 
plate 26c corresponds to stop plate 26b. Coupling plate 25c corresponds to 
coupling plate 25b of FIG. 1. In both embodiments of the invention, ring 
gear 5 can be coupled with a rotatable transmission component, i.e., 
carrier 4 shown in FIG. 1 of the drawings and sun gear 2 shown in FIG. 2 
of the drawings. 
The operation of ring gear 5 in the transmission housing shown in FIG. 2 of 
the drawings is controlled by a spring-loaded annular piston 14a which 
opposes stop plate 26c. Annular piston 14a is axially movable in a ring 
groove located in transmission housing and cooperates with a non-rotatable 
coupling plate 27b which is axially movable in the transmission housing. 
The function of coupling plate 25c in the embodiment shown in FIG. 2 of 
the drawings is determined by the face of stop plate 26c which is opposite 
from annular piston 14a. In this design, the aforementioned shift modes 
can be obtained. 
In contrast to FIG. 2 of the drawings, annular piston 14a can be located in 
an intermediate flange of the transmission housing instead of in the 
housing of axial piston engine 1. In this modified arrangement, a standard 
axial piston engine can be used. 
While specific embodiments of the invention have been described in detail 
herein, it will be appreciated by those skilled in the art that various 
modifications and alternatives to the embodiments could be developed in 
light of the overall teachings of the disclosure. Accordingly, the 
particular arrangements are illustrative only and are not limiting as to 
the scope of the invention which are to be given the full breadth of the 
appended claims and any and all equivalents thereof.