Hydraulic Drive for the Feed Rollers of a Head of a Complete Timber Harvester

Abstract

A hydraulic drive for feed rollers of a head of a complete timber harvester includes two radial piston motors coupled for conjoint rotation to the feed rollers. One radial piston motor has only one displacement volume and the other radial piston motor has two displacement volumes, between which it is possible to switch. A tree trunk clamped between the feed rollers can thus be moved at two speeds. At the higher speed, pressure medium circulates under a control pressure in the second displacement volume of the switchable radial piston motor.

Claims

1. A hydraulic drive for feed rollers of a head of a complete timber harvester, comprising: a first radial piston motor including two ports in operative connection with a first group of cams, and two other ports in operative connection with a second group of cams; and a second radial piston motor, wherein the second group of cams is configured to be deactivated by connecting the two other ports to one another and simultaneously to a control pressure line or to a first control pressure port.

2. The hydraulic drive according to claim 1, wherein: in a first direction of rotation of the first and second radial piston motors, the second radial piston motor is arranged downstream of the first group of cams of the first radial piston motor; in a second direction of rotation of the first and second radial piston motors, the second radial piston motor is arranged upstream of the first group of cams of the first radial piston motor; and the hydraulic drive is bidirectional.

3. The hydraulic drive according to claim 1, wherein the first and second groups of cams are distributed on a common cam ring.

4. The hydraulic drive according to claim 1, further comprising: a speed selector valve, wherein: in a first position of a valve spool of the speed selector valve, the speed selector valve activates the second group of cams by connecting the two other ports to respective main ports of the hydraulic drive; and in a second position of the valve spool, the speed selector valve deactivates the second group of cams by connecting the two other ports to one another and to the control pressure line or to the first control pressure port.

5. The hydraulic drive according to claim 4, wherein: the speed selector valve is a 5/2-way valve; and the valve spool is preloaded into the first position by a first spring and is configured to be moved into the second position by a control pressure of the first control pressure port.

6. The hydraulic drive according to claim 5, wherein: the control pressure line or the first control pressure port is connected via a control pressure branch line to a control pressure space of the speed selector valve, the control pressure space acting counter to the first spring, and configured to be connected via a further control pressure branch line to a second control pressure port of the speed selector valve; and in the second position of the valve spool, the second control pressure port is connected to the two other ports of the second group of cams.

7. The hydraulic drive according to claim 6, further comprising: a shutoff valve arranged in the further control pressure branch line.

8. The hydraulic drive according to claim 7, wherein: in a first shutoff position preloaded by a second spring, the shutoff valve shuts off the second control pressure port of the speed selector valve from the control pressure line or the first control pressure port; and in a second shutoff position configured to be produced by the control pressure, the shutoff valve connects the second control pressure port of the speed selector valve to the control pressure line or the first control pressure port.

9. The hydraulic drive according to claim 4, wherein the valve spool of the speed selector valve is configured to be continuously adjustable.

10. The hydraulic drive according to claim 1, further comprising: a stationary housing, wherein: the first radial piston motor further includes a rotor; the stationary housing is disposed on an outer circumference of the rotor; a first main port of the hydraulic drive and the two other ports of the second group of cams are connected to respective encircling pressure spaces formed between the rotor and the stationary housing.

11. The hydraulic drive according to claim 10, further comprising: a speed selector valve including a valve spool, wherein: in a first position of a valve spool of the speed selector valve, the speed selector valve activates the second group of cams by connecting the two other ports to respective main ports of the hydraulic drive; in a second position of the valve spool, the speed selector valve deactivates the second group of cams by connecting the two other ports to one another and to the control pressure line or to the first control pressure port; and the speed selector valve is arranged in the stationary housing.

12. The hydraulic drive according to claim 11, wherein: the valve spool includes a first neck and a second neck; and in the first position of the valve spool: the encircling pressure space of the first main port of the hydraulic drive is connected via a passage, the first neck, and a further passage to the encircling pressure space of a first other port of the second group of cams; and a second main port of the hydraulic drive is connected to at least one further passage that is connected via the second neck and a further passage to the encircling pressure space of a second other port of the second group of cams.

13. The hydraulic drive according to claim 12, wherein, in the second position of the valve spool, the encircling pressure spaces of the two other ports of the second group of cams are connected to one another via the second neck of the valve spool.

14. The hydraulic drive according to claim 12, further comprising: at least one radial bore arranged in the valve spool in a region of the second neck and configured to connect a control pressure space to the second neck.

15. The hydraulic drive according to claim 14, further comprising: a spool arranged in an interior of the valve spool, wherein: the at least one radial bore is configured to be opened by the spool when a control pressure prevails in the control pressure space; and the at least one radial bore is configured to be closed by the spool when a pressure prevailing in the control pressure space is lower than the control pressure.

16. The hydraulic drive according to claim 1, wherein: each group of cams of the first and second groups of cams is formed on respective cam rings; and the respective cam rings are axially spaced apart.

17. The hydraulic drive according to claim 11, wherein the speed selector valve is arranged in the stationary housing on an outer circumference of the encircling pressure spaces.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] An illustrative embodiment of a drive according to the disclosure for the feed rollers of a head of a complete timber harvester is illustrated in the drawings. The disclosure will now be explained in greater detail with reference to the figures of these drawings.

[0027] In the drawings:

[0028] FIG. 1 shows a circuit diagram of a drive according to the disclosure for the feed rollers of a head of a complete timber harvester according to the illustrative embodiment, and

[0029] FIG. 2 shows a detail of the first radial piston motor of the drive from FIG. 1 in a longitudinal section.

DETAILED DESCRIPTION

[0030] FIG. 1 shows a circuit diagram of a drive according to the disclosure for the feed rollers of a head of a complete timber harvester according to the illustrative embodiment. The drive has a first radial piston motor 1, to the output shaft 2 of which at least one feed roller (not shown) of the head is coupled for conjoint rotation. The drive furthermore has a second radial piston motor 4, on the output shaft 6 of which at least one feed roller (not shown) is likewise provided. By means of these feed rollers, a tree trunk is clamped into the head, allowing it to be sawn off, freed from branches and cut into pieces. By means of these feed rollers, the tree trunk is also moved backward and forward by the head during the two last-mentioned functions.

[0031] The drive has a first main port A and a second main port B, whichdepending on the desired feed direction of the tree trunkcan each be used as a high-pressure and a low-pressure port.

[0032] The first radial piston motor 1 has a housing 8, in which one or two stationary cam rings (not shown), on which two groups 10, 12 of cams are distributed, are arranged, wherein the same number of cams is provided in each group 10, 12. These can be distributed alternately on one cam ring, or each of the two cam rings has the cams of one group 10, 12.

[0033] The first radial piston motor 1 furthermore has a cylinder block, which is coupled for conjoint rotation to the output shaft 2 and on the circumference of which a plurality of cylinders is distributed, in each of which a piston is guided, which is supported via a respective roller on the cams. Each cam has two oppositely sloping flanks, and therefore each cam forms a peak.

[0034] Depending on the desired direction of rotation of the output shaft 2, one of the flanks is a working flank, while the other flank is a return flank. In a first direction of rotation of the first radial piston motor 1, outlet passages, the distribution of which on the circumference of the stationary housing (stator) 8 corresponds to the distribution of the working flanks of the first group 10, are connected to a port A1 of the first group 10, while outlet bores, the distribution of which corresponds to that of the return flanks of the first group 10, are connected to port B1 of the first group 10. In the first direction of rotation of the first radial piston motor 1, outlet passages, the distribution of which corresponds to that of the working flanks of the second group 12, are similarly connected to a port A2 of the second group 12, while outlet bores, the distribution of which corresponds to that of the return flanks of the second group 12, are connected to port B2 of the second group 12.

[0035] A speed selector valve 14 and a shutoff valve 16 are furthermore provided in the housing 8 of the first radial piston motor 1. The speed selector valve 14 is designed as a 5/2-way valve. It is connected directly to the two ports A2, B2 of the second group 12 and furthermore to the two main ports A, B of the drive. Finally, the speed selector valve 14 has a control pressure port X.sub.14. In a first position a of the valve spool 18 of the speed selector valve 14, the first main port A of the drive is connected to the first port A2 of the first group 12, while the second main port B of the drive is connected to the second port B2 of the second group 12. In this case, the control pressure port X.sub.14 of the speed selector valve 14 is shut off. In a second position b of the valve spool 18, the two ports A2, B2 of the second group 12 are connected to one another and furthermore to the control pressure port X.sub.14.

[0036] A control pressure port X.sub.1 is provided on the housing 8 and is connected by a control pressure line 20 and a control pressure branch line 22 to a control pressure space 23, by means of which the valve spool 18 of the speed selector valve 14 can be moved from the first position a to the second position b against the force of a spring 24. The control pressure line 20 furthermore branches into a further control pressure branch line 26, via which the control pressure port X.sub.1 of the housing 8 can be connected to the control pressure port X.sub.14 of the speed selector valve 14.

[0037] The shutoff valve 16 is provided in the control pressure branch line 26 and the valve body of said valve shuts off the control pressure port X.sub.1 of the housing 8 from the control pressure port X.sub.14 of the speed selector valve 14 in a home position preloaded by a spring 28. The shutoff valve 16 opens when the control pressure exceeds the force of the spring 28.

[0038] The main port A of the drive is connected by a branched main line 30 to port A1 of the first group 10, on the one hand, and, in the first position a of the valve spool 18 of the speed selector valve 14, said position being preloaded by the spring 24, to port A2 of the second group 12, on the other hand. The other port B1 of the first group 10 is connected by a connecting line 32 and via the second radial piston motor 4 to the other main port B of the drive. In the position a of the valve spool 18 of the speed selector valve 14, said position being preloaded by the spring 24, the other port B2 of the second group 12 is connected to the other main port B of the drive.

[0039] FIG. 2 shows, in a longitudinal section, part of the housing 8 of the first radial piston motor 1 and a detail of a rotor 2, which is accommodated rotatably therein and is formed integrally with the output shaft 2 (shown in FIG. 1) or coupled for conjoint rotation to said shaft. In this case, the rotor 2 rotates about its longitudinal axis 34.

[0040] Arranged on the outer circumference of the rotor 2 are encircling annular pressure spaces 36, 38, 40, 42 running around in a ring shape, which are formed by depressions in the outer circumference of the rotor 2, on the one hand, and by depressions in an inner circumference of the housing 8, on the other hand. A valve bore 44 of the speed selector valve 14 is formed in the housing 8 on the outer circumference of these pressure spaces 36, 38, 40, 42. The pressure space 36 which forms port B1 of the first group 10 has no connection to this valve bore 44. The pressure space 38 arranged adjacent thereto, which forms port B2 of the second group 12, and the pressure space 40 arranged adjacent thereto, which forms port A2 of the second group 12, and the pressure space 42 arranged adjacent thereto, which is connected to the first main port A of the drive, are each connected by a radial passage (not sectioned in the plane of the drawing) to respective encircling pressure spaces of the speed selector valve 14, which are arranged on the inner circumference of the valve bore 44.

[0041] In FIG. 2, the valve spool 18 of the speed selector valve 14 is furthermore shown in its first position a and, in this position, the pressure space 40 of port A2 of the second group 12 is connected via a first neck 46 to the pressure space 42 of the first main port A of the drive, while, at the same time, the pressure space 38 of port B2 of the second group 12 is connected via a second neck 48 to the second main port B of the drive. The second main port B is formed by a bore routed radially outward from the valve bore 44.

[0042] Arranged at the end of the valve spool 18 is the control pressure space 23, which has a minimum size in the first position a of the valve spool 18, which is shown in FIG. 2. When acted upon by control pressure medium, the valve spool 18 is moved (to the right in FIG. 2), with the result that the two main ports A, B are shut off, while the two inner pressure spaces 38, 40 of the two ports A2, B2 of the second group 12 are connected to one another via the second neck 48.

[0043] A spool 50 is guided in a longitudinal bore in the interior of the valve spool 18. This serves to shut off the second neck 48 from the control pressure space 23 in the first position a of the valve spool 18, which is shown in FIG. 2, and, according to the disclosure, serves to connect the second neck 48 and hence the two ports A2, B2 of the second group 12 to the control pressure space 23 in the second position b of the valve spool 18. For this purpose, a plurality of radial bores 52 are provided on the inner circumference of the second neck 48, said bores being closed by a collar on the spool 50 in the position a of the valve spool 18, which is shown in FIG. 2. When the control pressure space 23 is filled with control pressure medium, the valve spool 18 and furthermore also the spool 50 are moved to the right out of their positions shown in FIG. 2, as a result of which the control pressure space 23 is, according to the disclosure, connected via the radial bores 52 and the second neck 48 to the two ports A2, B2 of the second group 12.

[0044] A disclosure is made of a hydraulic drive having two radial piston motors, which are coupled for conjoint rotation to feed rollers of a harvester head, wherein one radial piston motor has only one displacement volume and the other radial piston motor has two displacement volumes, between which it is possible to switch. A tree trunk clamped between the feed rollers can thus be moved at two speeds. At the higher speed, pressure medium circulates under a control pressure in the second displacement volume of the switchable radial piston motor.

LIST OF REFERENCE SIGNS

[0045] 1 first radial piston motor [0046] 2 output shaft/rotor [0047] 4 second radial piston motor [0048] 6 output shaft [0049] 8 housing [0050] 10 first group of cams [0051] 12 second group of cams [0052] 14 speed selector valve [0053] 16 shutoff valve [0054] 18 valve spool [0055] 20 control pressure line [0056] 22 control pressure branch line [0057] 23 control pressure space [0058] 24 spring [0059] 26 control pressure branch line [0060] 28 spring [0061] 30 main line [0062] 32 connecting line [0063] 34 longitudinal axis [0064] 36 pressure space [0065] 38 pressure space [0066] 40 pressure space [0067] 42 pressure space [0068] 44 valve bore [0069] 46 first neck [0070] 48 second neck [0071] 50 spool [0072] 52 radial bore [0073] A first main port [0074] B second main port [0075] a first position [0076] b second position [0077] A1, B1 port of the first group [0078] A2, B2 port of the second group [0079] X.sub.14 control pressure port of the speed selector valve [0080] X.sub.1 control pressure port of the first radial piston motor