POWER SPLIT TRANSMISSION

[0001]

[0002]

[0003]

[0004] The Invention concerns a power split transmission according to the preamble
of claim 1 to be specified below.

[0005]

[0006] Power split transmissions of this kind have one hydrostatic power branch and
one mechanical power branch, which are summed via a summation gear in order to
drive an output means.

[0007] The hydrostatic-mechanical transmission with power split disclosed in DE 28
54 375 A1 has two shift ranges, and the continuously variable control of the
transmission is carried out by means of the hydrostatic power branch.

[0008]

[0009] The invention has as an object the creation of a power split transmission with
at least two operating ranges, wherein at least two operating ranges are available in one forward travel direction and in one reverse travel direction, and the transmission is characterized by a simple control of the hydrostatic power branch.

[0010] The object is attained with a power split transmission of the specified kind,
which has the characteristic features of the main claim.

[0011] The power split transmission has one hydrostatic power branch and one
mechanical power branch, which are summed In a summation gear. A reversing gear, by means of which the direction of rotation of the transmission input shaft can be reversed depending on the desired direction of travel, is connected upstream of the summation gear.

[0012] The summation gear is preferably configured as a planetary gear set for use
with the power split transmission in a working machine, for example, a wheel loader, wherein the outer central gear of the planetary gear set Is operatively connected to the output shaft of the reversing gear, the sun gear of the planetary gear set is
operatively connected to the first hydrostatic unit, and the planetary gear carrier of
the planetary gear set is operatively connected to a downstream gear shifting
mechanism. The gear shifting mechanism is configured herein as a spur gear unit,
whereby the axle offset needed for the wheel loader can be obtained in this
combination.

[0013] in one embodiment of the invention, a first clutch for forward travel is
arranged in the reversing gear coaxially with respect to the input shaft of the power split transmission and the planetary gear set, the gear shifting mechanism and the clutch for reverse travel are arranged outside of the input shaft of the power split transmission, that is, not coaxial thereto. The second hydn3Static unit is operatively connected to the planetary gear carrier of the summation gear, either directly or via a spur gear stage, and is arranged preferably next to the first hydrostatic unit. The first and second hydrostatic units have a common component, by means of which the displacements of the first and of second hydrostatic units can be adjusted simultaneously, wherein the first and second hydrostatic units are configured as hydrostatic units in a transverse axis design. The displacements of the first and of the second hydrostatic unit are configured such that In the first operating mode of the power split transmission with rotating input shaft and stopped output shaft, the common component adjusts the first and the second hydrostatic units in such a way that the first hydrostatic unit, which is operatively connected to the sun gear is adjusted to zero displacement, and the second hydrostatic unit, which is directly connected in operative connection to the planetary gear carrier, is adjusted to its maximum displacement. In a second mode of operation of the power split transmission at maximum possible rotational speed of the output drive, the displacement of the first hydrostatic unit is adjusted to its maximum displacement, and the displacement of the second hydrostatic unit is adjusted to zero displacement, whereby that the total power Is transferred purely mechanically. If the standard transmission Is to be shifted from a first gear to a second gear, then the two gear clutches are actuated to engage, wherein at least one of these gear clutches Is kept in a slip mode until the load has been transferred from the one gear clutch to the other gear clutch, wherein the gear ratio, that is, the displacement, is reduced during this transfer via the common component by the progressive ratio between the first and the second gear. The power split transmission can be shifted without Interruption of reactive force by means of this procedure during range shifting.

[0014]

[0015] Additional features are disclosed in the description of the figures. In the
figures:

[0016] Fig. 1 shows a kinematic diagram of a power split transmission with the
working pump arranged coaxial with respect to the input shaft; and

[0017] Fig. 2 shows a power split transmission with the working pump not arranged
coaxially with respect to the input shaft.

[0018]

[0019] Fig. 1:

[0020] A drive engine 1 drives the input shaft 2 of the power split transmission. The
input shaft 2 is connected in a rotationally fixed manner to the spur gear 3. The spur gear 3 is operatively connected to the spur gear 4, wherein the clutch for forward travel 5 and the clutch for reverse travel 6 and the spur gear 3 and the spur gear 4 form the reversing unit 7. The spur gear 8, which can be connected to the spur gear 4 via the clutch for reverse travel 6, and the spur gear 9, which can be connected to the spur gear 3 via the clutch for forwards travel 5, are operatively connected to the spur gear 10. The spur gear 10 is connected in a rotationally fixed manner to the outer central gear 11 of the planetary gear set 12. The planetary gear set 12 forms the summation gear for the mechanical power branching and the hydrostatic power branch. The inner central gear 13 of the planetary gear set 12 is connected in a rotationally fixed manner to the first hydrostatic unit 14, The planetary gear carrier 15 is connected in a rotationally fixed manner to the spur gear 16. The spur gear 16 Is operatively connected to the spur gear 17, wherein the spur gear 17 is connected in a rotationally fixed manner to the second hydrostatic unit 18 and the gear clutch 19 for the second gear of the reduction gear 20. The spur gear 17 is operatively connected to spur gear 21, which can be connected to spur gear 23 via the gear clutch 22. The spur gear 17 can be connected to spur gear 24 via the gear clutch

19. The spur gear 24 is operatively connected to spur gear 23. The spur gear 23 drives the spur gear 25 and the latter drives in turn the output drive 26. The first hydrostatic unit 14 and the second hydrostatic unit 18 are configured as hydrostatic units in a transverse axis design, wherein the displacements can be adjusted via a common component 27 and the hydrostatic units 14 and 18 are arranged adjacent to each other. A working pump 28, as well as a feed and lubrication pressure pump 29, is arranged coaxially with respect to the input shaft 2. For startup in forward travel direction with rotating input shaft 2, the clutch for forward travel 5 is engaged, the clutch for reverse travel 6 is open, the gear clutch 19 is disengaged, and the gear clutch 22 is engaged. The first hydrostatic unit 14 is adjusted to zero displacement and the second hydrostatic unit 18 is adjusted to its maximum displacement. In this situation, the output drive 26 is at standstill, if the common component 27 is now adjusted, then the first hydrostatic unit 14 is adjusted from its zero displacement and pumps pressurizing medium to the second hydrostatic unit 16, which is connected to the first hydrostatic unit 14 in a closed circuit. The output drive 26 begins to rotate. At the maximum possible adjustment of the common component 27, the first hydrostatic unit 14 Is at its maximum displacement and the second hydrostatic unit 18 Is at zero displacement. The total power is transferred herein exclusively via the mechanical power branch to the output drive 26. if the second gear is to be selected, then the gear clutch 19 Is likewise operated in an engaging direction toward the engaged gear clutch 22, wherein either the gear clutch 19 or the gear clutch 22 or both gear clutches are kept In a slip mode until the common component 27, the first hydrostatic unit 14, and the second hydrostatic unit 18 are adjusted in such a manner that the displacements and thus the rotational speed of the hydrostatic units 14 and 18 are adapted to the new gear ratio. The gear clutch 22 is subsequently fully disengaged and the gear clutch 19 is fully engaged. The input drive can now be further modified in its output speed by adjusting the common component 27.

[0021] Fig. 2:

[0022] This figure differs from Fig. 1 exclusively in that the working pump 28 and the
feed and lubrication pressure pump 29 are in drive connection with the spur gear 4, whereby the working pump 28 and the feed and lubrication pressure pump 29 can
be configured with a smaller displacement, since the rotational speed of the spur gear 4 is greater than the rotational speed of the spur gear 3. It is also possible to only connect the working pump 28 to the spur gear 4 and the feed pump 29 to the input shaft 2, or the working pump 28 to the input shaft 2 and the feed pump 29 to the spur gear 4.

List of Reference Numerals
1 Engine
2 Input shaft
3 Spur gear
4 Spur gear
5 Clutch for forward travel
6 Clutch for reverse travel
7 Reversing unit
8 Spur gear
9 Spur gear
10 Spur gear
11 Outer central gear
12 Planetary gear set
13 Inner central gear
14 First hydrostatic unit
15 Planetary gear carrier
16 Spur gear
17 Spur gear
18 Second hydrostatic unit
19 Gear clutch
20 Reduction gear
21 Spur gear
22 Gear clutch
23 Spur gear
24 Spur gear
25 Spur gear
26 Output drive
27 Common component
28 Working pump
29 Feed pump

Patent Claims

1. A power split transmission with a hydrostatic branch and a mechanical branch, which are summed via a summation gear (12), having at least two driving ranges in one forward driving direction and at least two operating ranges in one reverse travel direction, characterized in that the hydrostatic branch has a first hydrostatic unit (14) and a second hydrostatic unit (18), whose displacements can be adjusted via a common component (27), wherein the common component (27) Is connected to the first and to the second hydrostatic units (14,19).

2. The power split transmission of claim 1, characterized in that the summation gear (12) consists of a planetary gear set, whose inner central gear (13) is connected to the first hydrostatic unit (14) and whose outer central gear (11) can be driven by an engine (1), and the second hydrostatic unit (18) Is operatively connected to a planetary gear carrier (15).

3. The power split transmission of claim 1, characterized in that a reversing gear (7) is arranged in the power flow between an engine (1) and the summation gear (12).

4. The power split transmission of claim 1, characterized in that a gear shifting mechanism (20) is arranged between the summation gear (12) and an output drive (26).

5. The power split transmission of claim 4, characterized In that a planetary gear earner (15) of the summation gear (12) can be connected to the output drive (26) via a first reduction stage of the gear shifting mechanism (20) in a first gear, and the planetary gear carrier (15) of the summation gear (12) can be connected to the output drive (26) via a second reduction stage of the gear shifting mechanism (20) in a second gear.

6. The power split transmission of claim 1, characterized in that the first hydrostatic unit (14) is adjusted to zero displacement and is second hydrostatic unit (18) is adjusted to maximum displacement while the input shaft (2) rotates and the output drive (26) is at standstill.

7. The power spilt transmission of claim 1, characterized in that the first hydrostatic unit (14) is adjusted to its maximum displacement and the second hydrostatic unit (18) is adjusted to zero displacement while the input shaft (2) rotates and the output drive (26) rotates at its maximum possible speed.

8. The power split transmission of claim 1, characterized in that a hydraulic working pump (28) is arranged concentrically with respect to the input shaft (2) of the power split transmission and is operatively connected to the input shaft (2).

9. The power split transmission of claim 1, characterized in that a hydraulic working pump (28) is arranged concentrically with respect to a travel direction clutch (6) of the power split transmission and is operatively connected to an output drive (4) of the travel direction clutch (6).

10. The power split transmission of claim 1, characterized in that a travel direction clutch forward travel (5) is arranged concentrically with respect to the input shaft (2).