Hydraulic cylinder with end position damping

Abstract

A hydraulic cylinder includes a cylinder having axially spaced-apart first and second bores, and a piston having a piston rod and arranged in the cylinder for movement between two end positions and dividing the cylinder into a piston side and a piston-rod side. A hydraulic pump pumps hydraulic oil into the piston side to move the piston from one end position toward the other end position while hydraulic fluid is discharged from the piston-rod side via the first bore and a first outlet line. A throttling device is operably connected to the cylinder to throttle a flow of the hydraulic fluid as the piston moves past and seals the first bore so that hydraulic fluid is discharged via the second bore, thereby reducing a delivery amount of the hydraulic oil and thereby braking and damping a movement of the piston toward the other one of the end positions.

Claims

1. A hydraulic cylinder, comprising: a cylinder having an axially spaced-apart first bore directly connected to a first outlet line and a second bore directly connected to a second outlet line; a piston having a piston rod, said piston being arranged in the cylinder for movement between two end positions and dividing the cylinder into a piston side and a piston-rod side; a hydraulic pump pumping hydraulic oil via an inlet line into the piston side at a preset pressure to move the piston from one of the end positions in a direction toward the other one of the end positions while hydraulic fluid is discharged from the piston-rod side via the first bore and the first outlet line; a mechanical throttling device including a pressure relief valve and a non-return valve, said mechanical throttling device operably connected to the cylinder to throttle a flow of the hydraulic fluid as the piston moves past and seals the first bore so that hydraulic fluid is discharged via the second bore, thereby reducing a delivery amount of the hydraulic oil and thereby braking and damping a movement of the piston toward the other one of the end positions, wherein the pressure relief valve and the non-return valve are arranged on the second outlet line, wherein the piston includes a piston skirt to close the first bore during movement of the piston to one of the end positions, and a piston head to close access to the second bore during movement of the piston to the other one of the end positions in front of the second bore; a guide arranged at the piston-rod side for guiding the piston, wherein the first bore is guided radially outwardly of the cylinder in a region of the piston-rod side; a connection formed as a blind hole in the guide so as to extend parallel to the piston rod and is laterally connected to the second bore in the other of the end positions, wherein the second bore is guided radially outwardly of the cylinder in a region of the piston side via the connection formed as the blind hole, wherein the blind hole is closeable by the piston head in the other end position of the piston, wherein the piston skirt has an outer circular cylindrical surface with which the piston skirt closes the first bore during movement of the piston to the one end position, and wherein the piston head has a flat circular axial end surface with which the piston head closes the blind hole during movement of the piston to the other end position.

2. The hydraulic cylinder of claim 1, further comprising a directional control valve, wherein the pressure relief valve is operatively connected to the hydraulic pump via the first outlet line and the directional control valve.

3. The hydraulic cylinder of claim 2, wherein the non-return valve is configured to force hydraulic fluid to flow through the pressure relief valve, when being discharged from the piston-rod side through the second bore.

4. The hydraulic cylinder of claim 1, wherein the first bore and the second bore are spaced apart by a fixed distance which is designed to correspond to a path the piston travels during a time required by the hydraulic pump to switch from a maximum delivery rate to a minimum delivery rate.

5. The hydraulic cylinder of claim 4, wherein the first bore and the second bore are arranged radially outwardly on the cylinder in a region of the piston-rod side.

6. The hydraulic cylinder of claim 4, further comprising a guide arranged at the piston-rod side for guiding the piston, wherein the first bore is arranged radially outwardly on the cylinder in a region of the piston-rod side, wherein a connection is embedded in the guide so as to extend parallel to the piston rod, said connection being connected to the second bore in the other one of the end positions, said second bore being guided radially outwardly on the cylinder in a region of the piston side via the connection.

7. The hydraulic cylinder of claim 1 constructed as a dump cylinder.

8. A shovel excavator, comprising: a hydraulic cylinder, said hydraulic cylinder comprising a cylinder having an axially spaced-apart first bore directly connected to a first outlet line and a second bore directly connected to a second outlet line, a piston having a piston rod and arranged in the cylinder for movement between two end positions and dividing the cylinder into a piston side and a piston-rod side, a hydraulic pump pumping hydraulic oil via an inlet line into the piston side at a preset pressure to move the piston from one of the end positions in a direction toward the other one of the end positions while hydraulic fluid is discharged from the piston-rod side via the first bore and the first outlet one, and a mechanical throttling device including a pressure relief valve and a non-return valve, said mechanical throttling device operably connected to the cylinder to throttle a flow of the hydraulic fluid as the piston moves past and seals the first bore so that hydraulic fluid is discharged via the second bore, thereby reducing a delivery amount of the hydraulic oil and thereby braking and damping a movement of the piston toward the other one of the end positions, wherein the pressure relief valve and the non-return valve are arranged on the second outlet line, wherein the piston includes a piston skirt to close the first bore during movement of the piston to one of the end positions, and a piston head to close access to the second bore during movement of the piston to the other one of the end positions in front of the second bore; a guide arranged at the piston-rod side for guiding the piston, wherein the first bore is guided radially outwardly of the cylinder in a region of the piston-rod side; a connection formed as a blind hole in the guide so as to extend parallel to the piston rod and is laterally connected to the second bore in the other of the end positions, wherein the second bore is guided radially outwardly of the cylinder in a region of the piston side via the connection formed as the blind hole, wherein the blind hole is closeable by the piston head in the other end position of the piston, wherein the piston skirt has an outer circular cylindrical surface with which the piston skirt doses the first bore during movement of the piston to the one end position, and wherein the piston head has a flat circular axial end surface with which the piston head closes the blind hole during movement of the piston to the other end position.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) In the following, the invention is explained in more detail by way of an exemplary embodiment with reference to the enclosed drawing. The sole FIGURE shows:

(2) FIG. a schematic sectional view through the hydraulic cylinder according to the invention, to which a 4/3 way control valve with a center blocking position with connected hydraulic pump is assigned, which valve is connected to the piston side and the piston rod side of the hydraulic cylinder via lines, wherein a mechanical prethrottling is arranged in the line of the piston rod side which is formed by a pressure relief valve and a non-return valve.

DETAILED CESCRIPTION OF PREFERRED EMBODIMENTS

(3) As shown in the sole Figure, the hydraulic cylinder 10 essentially consists of a cylinder 11 within which a piston 12 is arranged that is connected to a nut 14. The piston 12 is moveable in axial direction, wherein the cylinder 11 is divided by the piston 12 into a piston side 15 and a piston rod side 16. The piston side 15 is sealed against the piston rod side by a gasket 22, which is arranged radially outwardly on the piston 12. The hydraulic oil required to actuate the piston 12 is pumped by a hydraulic pump 17 via inlet- and outlet lines 18 and 19 and 19a through inlet 20 and outlet openings 21, 21a. The piston 12 is guided in a guide 34.

(4) The cylinder 11 is assigned a mechanical pre-throttling 23. Via the mechanical pre-throttling, the hydraulic oil can be discharged on the piston rod side 16 through a first bore 24 during the movement of the piston 12 until the piston 12 closes the first bore 24 with its piston skirt 25. The hydraulic oil is slowly throttled and then discharged through a second bore 26, from where it is conducted to a pressure relief valve 27 as component of the pre-throttling 23. The second bore 26 is provided in the area of the end position 28 at the piston rod side 16 of the hydraulic cylinder 10, where it is connected via a opening 33 to the end position 28. Hereby, the piston 12 may be moved into direct proximity of the end position 28 (with a residual stroke remaining) so that the entire hydraulic oil on the piston rod side 16 can be drained through the outlet opening 21a which is assigned to the second bore 26. The piston head 32 of the piston 12 is hereby moved in front of the second bore 26 with the residual stroke remaining. As a result, access via the opening 33 to the second bore 26 is closed by the piston head 32 so that hydraulic oil is prevented from reaching the second bore.

(5) At a preset pressure the pressure relief valve 27 forces the hydraulic pump 17 into an electronically regulated pressure cut-off function. This means that the hydraulic pump 17 only operates with a low delivery rate on the piston side 15. This means that the pressure remains constant and only the delivery rate changes.

(6) The delivery rate of the hydraulic oil on the piston side 15 is reduced by the pressure cut-off function and the piston 12 thus can be moved into its end position 28 on the piston rod side 16 in a decelerated manner. Hereby the pressure relief valve 27 is connected via the hydraulic line 19 for example with a (4/3) way control valve 30 (with center blocking position) to the hydraulic pump 17.

(7) As the Figure also shows, the first bore 24 is arranged at a distance 29 to the second bore 26. The distance 29 between the first bore 24 and the second bore 26 corresponds to the path the piston 12 travels in the time required by the hydraulic pump 17 to switch from a maximum delivery rate to a minimum delivery rate. The mechanical pre-throttling 23 furthermore has a non-return valve 31. The non-return valve 31 ensures that the hydraulic oil, when flowing out of the opening 21a via the bore 26 into the outlet line 19a, can flow into the pressure relief valve 27 and is not directly pushed into the outlet line 19. In addition, the non-return valve 31 supports the return movement. This means that the non-return valve 31 opens in case of a reversal of flow and enables a pressure-free (i.e. low-loss) filling and return movement of the piston 12 in the cylinder 11. This may be associated with the opening of a flap on a shovel excavator (not shown).