# Patent

## Title
Hydrostatic-mechanical transmission

## Abstract

A hydrostatic-mechanical transmission with a radial piston motor (1) which has a crankshaft (2) that drives a spur gear (7) and the crankshaft (2) is rotatably mounted at three bearing points (12, 13, 14).

## Background
This application claims priority from German patent application serial no. 10 2006 043 290.8 filed Sep. 14, 2006.
FIELD OF THE INVENTION
The invention relates to a hydrostatic-mechanical transmission.
BACKGROUND OF THE INVENTION
DE 10 2004 023 631 A1 discloses a hydrostatic-mechanical transmission with a radial piston motor with a crankshaft, the crankshaft driving a spur gear which is actively connected with another spur gear and powers the drive output.
Transmissions of this type are used for example in working machines such as wheel loaders.
The purpose of the present invention is to provide a hydrostatic-mechanical transmission with improved efficiency.
SUMMARY OF THE INVENTION
According to the invention, the hydrostatic-mechanical transmission comprises at least one radial piston engine having a crankshaft that drives a spur gear. The crankshaft is mounted on three bearing points, whereby the dimensions of the crankshaft can be such that at the maximum permissible deflection under load, the structural space available need not change. Preferably, one bearing point is located between the spur gear and the eccentric portion of the crankshaft and the other two bearing points are respectively in the area of the crankshaft's ends.
In a further embodiment of the invention the spur gear has spiral toothing and the two bearings, close to the eccentric portion of the crankshaft, are conical roller bearings, whereby the conical roller bearing located in the area of the pressure medium inlet to the cylinders produces an axial force component that opposes the hydraulic force in the area of the pressure medium distributor, so that the distortion of the housing portion in which the pressure medium inlets are located is reduced. Since the spur gear has bearing points on both sides, the radial force produced by the co-operation of the spur gears is transferred directly to the transmission housing, and this too reduces the distortion of the crankshaft under load. Since the pressure medium distributor is connected with the crankshaft via a connecting shaft, this reduction of the crankshaft's distortion also reduces the radial movement of the pressure medium distributor.
In another embodiment of the invention the transmission housing consists of three transmission housing portions:
a first housing portion in which the spur gears and the first bearing point in the area of the spur gear are located,
a second housing portion, which forms the middle bearing point between the spur gear and the eccentric part of the crankshaft, and
a third housing portion, which holds the third bearing point and contains the pressure medium inlets.
Connected to the third housing portion is a valve housing that contains the pressure medium distributor and the pressure medium connections and other valves, this structure makes it possible for the first and second housing portions to provide a lubricant space within which the spur gears are arranged, the second and third housing portions to provide a lubricant space in which the main components of the radial piston motor are arranged, and the valve housing to hold the valve components.
Preferably, the lubricant space containing the spur gears and the lubricant space containing the radial piston motor are sealed to be fluid-tight relative to one another.
Preferably, the cylinders of the radial piston motor are mounted both in the housing portion to which the valve housing is connected, and in the housing portion that separates the radial piston motor from the spur gear transmission.
In a further embodiment the spur gear actively connected with the crankshaft drives another spur gear, which powers the drive output, which has either two output flanges, one at each end of the drive output shaft, or one output flange and a bevel pinion, in order to incorporate the hydrostatic-mechanical transmission either between the front and rear axles of the vehicle, so as to drive the front and rear axles, or to incorporate it directly on the rear axle, so that the other axle is driven by the remaining drive flange via a Cardan shaft.



BRIEF DESCRIPTION OF THE DRAWINGS
Other features emerge from the description of the figures, in which:
FIG. 1 is a sectional view through the hydrostatic-mechanical transmission with a radial piston motor;
FIG. 2 is a sectional view through the radial piston motor of the hydrostatic-mechanical transmission in FIG. 1;
FIG. 3 is a sectional view through a hydrostatic-mechanical transmission with two radial piston motors;
FIG. 4 is a sectional view through the radial piston motors of the hydrostatic-mechanical transmission in FIG. 3;
FIG. 5 is a sectional view through the other radial piston motor of the hydrostatic-mechanical transmission in FIG. 3;
FIG. 6 is a hydraulic layout of the hydrostatic-mechanical transmission of FIG. 1; and
FIG. 7 is another hydraulic layout of the hydrostatic-mechanical transmission of FIG. 3.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a hydraulic radial piston motor 1 with a crankshaft 2 having an eccentric section 3 with a cylinder 4, which is mounted on one side in the third housing portion 5 and the second housing portion 6. The crankshaft 2 is connected in a rotationally fixed manner to a first spur gear 7. The first spur gear 7 is actively connected with a second spur gear 8, which drives a drive output shaft 9. If the driveshaft 9 has a pinion 10 and an output flange 11, the hydrostatic-mechanical transmission can be incorporated directly on a drive axle, but the drive output shaft 9 can also be fitted on each side with an output flange 11, so that the hydrostatic-mechanical transmission can be arranged between the drive axles.
Preferably, the first spur gear 7 and the second spur gear 8 are made with spiral toothing. The crankshaft 2 is mounted on a first bearing 12, a second bearing 13 and a third bearing 14. The first bearing 12 is located in the first housing portion 15 and forms the first bearing point. The second bearing 13 is located between the spur gear 7 and the eccentric section 3 in the second housing portion 6 and forms the second bearing point. For this, the second housing portion 6 has a housing wall 16. The third bearing 14 is located in the third housing portion 5 and forms the third bearing point. Via a connecting shaft 17, which can also be made integrally with the crankshaft 2, the latter drives a pressure medium distributor 18. Thanks to the special mounting of the crankshaft 2 its distortion under load is reduced, and this also improves the function of the pressure medium distributor 18. The pressure medium distributor 18 is located in a valve housing 19, which also contains the valves and main connections needed for the pressure medium supply 20. Together with the second housing portion 6, the first housing portion 15 forms a lubricant space 21 which is sealed relative to the space 22 by a seal 23 thus preventing leakage of pressure fluid between them. This enables different lubricants to be used in the spaces 21 and 22. The valves in the valve housing and any leakage from the radial piston motor 1 flow into the space 22 and pass from there, via a line (not shown) and a cooler, into an external lubricant reservoir. The cylinder 4 has bearing trunnions 24 by means of which the cylinder 4 is mounted and able to rotate, and which are in active connection with a rotation angle sensor, by means of which the ballast volume of the hydraulic motor can be determined. This signal serves as a control magnitude to enable appropriate regulation of the ballast volume of the hydraulic motor. The second spur gear 8 is shielded by a shield 25 in order to reduce splashing losses when the second spur gear 8 is rotating. The shield 25 is preferably made in two parts, and both can be made from a plastic, for example a polyamide. The shield 25 has at least one projection, 26 which engages in a recess 27 to fix the position of the shield 25. The two individual parts of the shield 25 are plugged together in the axial direction and are in contact with the first housing portion 16 and the second housing portion 6 in the axial direction, so that the shield 25 remains closed. The bearing trunnions 24 have surfaces (not shown) extending in the axial direction, which prevent hydraulic pressure from building up between the blind-hole bore in the second housing portion 6 or in the third housing portion 5 and the bearing trunnion 24, which would push the second housing portion 6 and the third housing portion 5 apart.
FIG. 2 shows the radial piston motor 1 has a crankshaft 2 whose eccentric section 3 moves pistons 28 in the cylinders 4.
FIG. 3 shows the hydrostatic-mechanical transmission in FIG. 3 differs from the hydrostatic-mechanical transmission in FIG. 1, in that there are two radial piston motors, each radial piston motor driving a spur gear in active connection with spur gears arranged on a drive output shaft 9. The first radial piston motor 1 drives the first spur gear 7, which is in active connection with the second spur gear 8 and which drives the drive output shaft 9. The second radial piston motor 29 (not shown) drives a third spur gear 30 (not shown), which is in active connection with a fourth spur gear 31 that drives the drive output shaft 9.
FIG. 4 shows the first radial piston motor 1 and the second radial piston motor 29 are in active connection with the drive output shaft 9.
FIG. 5 shows the second radial piston motor 29 drives the fourth spur gear 31 via the third spur gear 30, and thereby the drive output shaft 9.
FIG. 6 shows the first spur gear 7 and the second spur gear 8 are located within the space 21. In the space 22 are arranged the radial piston motor 1 and its stroke volume adjustment device 32. The valve housing 19 accommodates the 4/2 proportional valve 33 for adjusting the stroke volume, the two-way valve 34 and the flushing valve 35 with its associated pressure limiting valve 36. The valve housing 19 also contains the connections 20 for the main pressure medium supply. The valves in the valve housing 19 are vented through the line 37 leading to the space 22 and from there, through the line 38 and the cooler 39 into a pressure medium reservoir 40. Thus, the radial piston motor 1 is cooled sufficiently and the hydrostatic-mechanical drive has only a small number of connections.
FIG. 7 shows the first radial piston motor 1 with its stroke volume adjustment device 32 and the second radial piston motor 29 with its stroke volume adjustment device 41 are in the space 22, and the spur gears 7, 8, 30 and 31 are in the space 21. The valve housing 19 also has a cut-off valve 42 by means of which the first radial piston motor 1 can be fully connected to the space 22, whereby the said radial piston motor 1, when its stroke volume is adjusted to zero, can be operated at very high speed since it is completely separate from the high-pressure inlet and heat losses can be dissipated through the connection with the space 22. Accordingly, it is no longer necessary to arrange a cut-off clutch between the first radial piston motor 1 and the first spur gear 7.
INDEXES


    1 Radial piston motor
    2 Crankshaft
    3 Eccentric section
    4 Cylinder
    5 Third housing portion
    6 Second housing portion
    7 First spur gear
    8 Second spur gear
    9 Drive output shaft
    10 Pinion
    11 Drive output flange
    12 First bearing
    13 Second bearing
    14 Third bearing
    15 First housing portion
    16 Housing wall
    17 Connection shaft
    18 Pressure medium distributor
    19 Valve housing
    20 Connections
    21 Space
    22 Space
    23 Seal
    24 Trunnions
    25 Shield
    26 Projection
    27 Recess
    28 Piston
    29 Second radial piston motors
    30 Third spur gear
    31 Fourth spur gear
    32 Stroke volume adjustment device
    33 4/2 proportional valve
    34 Two-way valve
    35 Flushing valve
    36 Pressure-limiting valve
    37 Line
    38 Line
    39 Cooler
    40 Pressure medium reservoir
    41 Stroke volume adjustment device
    42 Cut-off valve

## Claims

1. A hydrostatic-mechanical transmission comprising:
at least one radial piston motor (1) comprising a crankshaft (2) with an eccentric section (3), the crankshaft (2) driving a spur gear (7) and being mounted by first and second bearings (12, 13);
wherein the crankshaft (2) is rotatably supported by at least the first and the second bearings (12, 13) and a third bearing (14), the second bearing (13) is located between the spur gear (7) and the eccentric section (3) such that the eccentric section (3), the second bearing (13) and the spur gear (7) are all located between the first bearing (12) and the third bearing (14), and
the transmission has a housing comprising first, second and third transmission housing portions (5, 6, 15), the spur gear (7) and the first bearing (12) are arranged within the first housing portion (15), the second bearing (13), located between the spur gear (7) and the eccentric section (3), is supported by the second housing portion (6), and the third bearing (14) is supported by the third housing portion (5).

2. The hydrostatic-mechanical transmission according to claim 1, wherein the second bearing (13) and the third bearing (14) are conical roller bearings.

3. The hydrostatic-mechanical transmission according to claim 1, wherein the first bearing (12) is a cylindrical roller bearing which is remote from the radial piston motor (1).

4. The hydrostatic-mechanical transmission according to 1, wherein the second housing portion (6) has a housing wall (16), positioned between the eccentric section (3) and the spur gear (7), which supports the first bearing (13) and cylinders (4) of the radial piston motor (1).

5. The hydrostatic-mechanical transmission according to claim 4, wherein the third housing portion (5) is connected to a valve housing (19) and contains pressure medium inlets for the cylinders (4) of the radial piston motor (1).

6. The hydrostatic-mechanical transmission according to claim 1, wherein the first housing portion (15) and the second housing portion (6) form a first lubricant space (21), the second housing portion (6) and the third housing portion (5) form a second lubricant space (22), and the first lubricant space (21) and the second lubricant space (22) are separated from one another by a fluid-tight seal (23).

7. The hydrostatic-mechanical transmission according to claim 1, wherein the spur gear (7) has spiral exterior toothing.

8. The hydrostatic-mechanical transmission according to claim 1, wherein the third bearing (14), located in the third housing portion (5), produces an axial force that opposes a hydraulic force acting upon the third housing portion (5) via a pressure medium distribution (18).

9. The hydrostatic-mechanical transmission according to claim 4, wherein a rotation angle sensor co-operates with mountings of the cylinder (24) to facilitate determining a ballast volume of the radial piston motor (1) during operation of the radial piston motor (1).

10. The hydrostatic-mechanical transmission according to claim 4, wherein a rotation angle sensor co-operates with trunnions (24) of the cylinder (4) to facilitate determining a ballast volume of the radial piston motor (1) during operation of the radial piston motor (1).