Servoless motor

Abstract

A hydraulic piston unit including a rotational group for driving or being driven by a driving shaft, and having a tiltable displacement element for adjusting the displacement volume of the rotational group between a minimum or a maximum displacement, wherein, on t valve segment between a kidney-shaped inlet port and a kidney-shaped outlet port at respective dead end positions of reciprocally moveable working pistons first and second control ports are located in fluid connection with cylinder bores in the cylinder block, for controlling the position of the displacement element. The hydraulic piston unit further includes a control valve with a shiftable control valve spool fluidly connected via a high pressure port to a high pressure side of the hydraulic piston unit. The control valve spool is configured to conduct hydraulic fluid from the high pressure side to one of the first or the second control port.

Claims

1. A Hydraulic piston unit comprising: a rotational group for driving or being driven by a driving shaft, the rotational group comprising a cylinder block with cylinder bores and pistons mounted to be reciprocally moveable in the cylinder bores for conveying hydraulic fluid from a kidney-shaped inlet port to a kidney-shaped outlet port of a valve segment, a displacement element being tiltable with respect to a rotational axis of the driving shaft between a first end position and a second end position for adjusting a displacement volume of the rotational group between a minimum or a maximum displacement, wherein, on the valve segment between the inlet port and the outlet port at respective dead end positions of the reciprocally moveable working pistons, a first control port and a second control port are located in fluid connection with the cylinder bores for controlling the position of the displacement element, wherein the hydraulic piston unit further comprises a control valve with a shiftable control valve spool, the shiftable control valve spool being a two-position valve being shiftable by means of an actuator between only an initial position and a shifted position, the control valve being fluidly connected via a high pressure port to the high pressure side of the hydraulic piston unit being capable to conduct hydraulic fluid from the high pressure side to one of the first and the second control port, wherein, in the initial position, the control valve is configured to conduct the hydraulic fluid under high pressure to the first control port in order to adjust the displacement element to be maintained at the first end position for maintaining the displacement volume at one of the minimum or the maximum displacement and, in the shifted position, the control valve is configured to conduct the hydraulic fluid from the high pressure port to the second control port in order to adjust the position of the displacement element to be maintained at the second end position for maintaining the displacement volume at the other of the minimum or the maximum displacement, wherein the actuator is an electro-mechanical actuator that is controllable by a control unit; and wherein the actuator is configured to shift the control valve spool when a predetermined system parameter is exceeded or underrun.

2. The hydraulic piston unit according to claim 1, wherein the control valve spool is held by a control valve spring in the initial position, in which hydraulic fluid under high pressure can be conducted to the first control port in order to adjust the displacement element into the first end position.

3. The hydraulic piston unit according to claim 2, wherein the hydraulic piston unit is a hydraulic piston unit of the two position construction type.

4. The hydraulic piston unit according to claim 1, wherein the displacement element is held in an initial position by an elastic force generated by a spring.

5. The hydraulic piston unit according to claim 2, further comprising a high pressure selecting valve fluidly connected to both pressure sides of the hydraulic piston unit for supplying hydraulic fluid from the high pressure side to the high-pressure port of the control valve.

6. The hydraulic piston unit according to claim 5, further comprising a low pressure selecting valve fluidly connected to both pressure sides of the hydraulic piston unit for supplying hydraulic fluid from the low pressure side to a low-pressure port of the control valve, wherein the control valve spool is configured to conduct hydraulic fluid under low pressure to the respective other control port of the first and second control port that is not charged by high pressure.

7. Hydraulic piston unit according to claim 1, wherein the control valve further comprises a low pressure port fluidly connected to a charge pressure source of the hydraulic piston unit or to any other system pressure line, wherein the control valve spool is configured to conduct hydraulic fluid under charge pressure or system pressure to the respective other control port of the first and second control port that is not charged by high pressure.

8. The hydraulic piston unit according to claim 1, wherein the hydraulic piston unit is a hydraulic piston unit of the two position construction type.

9. The hydraulic piston unit according to claim 1, further comprising a high pressure selecting valve fluidly connected to both pressure sides of the hydraulic piston unit for supplying hydraulic fluid from the high pressure side to the high-pressure port of the control valve.

10. The hydraulic piston unit according to claim 1, further comprising a low pressure selecting valve fluidly connected to both pressure sides of the hydraulic piston unit for supplying hydraulic fluid from the low pressure side to a low-pressure port of the control valve, wherein the control valve spool is configured to conduct hydraulic fluid under low pressure to the respective other control port of the first and second control port that is not charged by high-pressure.

11. A method for controlling the displacement volume of a rotational group of a hydraulic piston unit comprising a control valve with a two-position shiftable control valve spool shiftable between only an initial position and a shifted position, the control valve being fluidly connected via a high pressure port to the high pressure side of the hydraulic piston unit, and a valve segment with a first control port and a second control port located on the valve segment at respective dead end positions of working pistons reciprocally moveable in cylinder bores of a cylinder block of the rotational group, the method comprising: holding the control valve spool in its initial position to conduct hydraulic fluid from the high pressure side via the control valve to one of the first or second control port, when an initial displacement volume of the rotational group is being maintained, and shifting the control valve spool to the shifted position and holding the control valve spool in the shifted position by means of an actuator for conducting hydraulic fluid under high pressure via the high-pressure port to the respective other control port of the first or second control port, when the displacement volume of the rotational group is to be changed and maintained at a maximum displacement volume, the actuator being an electro-mechanical actuator, wherein shifting the control valve spool includes commanding the actuator via a control unit; and wherein controlling system parameters by means of the control unit and shifting the control valve spool by commanding the actuator via the control unit in case one system parameter is exceeded or underrun.

12. The method according to claim 11, wherein the control valve further comprises a low pressure port and the control valve spool conducts hydraulic fluid from the low pressure side to the respective other one of the first or second control port that is not charged with high pressure.

13. The method according to claim 11, wherein the control valve further comprises a low pressure port and the control valve spool conducts hydraulic fluid from the low pressure side to the respective other one of the first or second control port that is not charged with high pressure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the inventive hydraulic piston unit according to the present disclosure are shown in more detail in the enclosed drawings which do not limit the scope of the present disclosure. All features of the disclosed and illustrated embodiments may be combined in any desired combination with one another within the scope of the present invention. For this purpose it is shown in:

(2) FIG. 1 schematically a first embodiment of an inventive hydraulic piston unit in a first initial position;

(3) FIG. 2 schematically a second embodiment of the inventive hydraulic piston unit with a control valve spool in shifted position;

(4) FIG. 3 schematically a third embodiment of the inventive hydraulic piston unit in a first initial position;

(5) FIG. 4 schematically the embodiment of FIG. 3 with the control valve spool in shifted position; and

(6) FIG. 5 schematically a valve plate adapted according to the invention.

DETAILED DESCRIPTION

(7) In the FIGS. 1 to 5, the present invention is disclosed schematically with the help of a simplified hydraulic piston unit, exemplarily a hydraulic axial piston unit of the swashplate type of construction. The shown embodiments are for simplification reasons only to show the invention in a simple manner and do not to limit the scope of the inventive idea. To the contrary, as mentioned above, the present invention is also applicable on hydraulic axial piston units of the bent axis or the tumbling plate construction type, as well as on radial piston units and vane units. Additionally, in the drawings, like reference numerals refer to like features of the hydraulic piston units of the present application. Accordingly, although certain descriptions may refer only to certain figures and reference numerals, it should be understood that such descriptions might be equally applicable to like reference numerals in other figures.

(8) The hydraulic axial piston unit 1 shown in FIG. 1 comprises a cylinder block 3 in which cylinder bores 5 are located in general parallel to a rotational axis 9 of the cylinder block 3. Working pistons 6 can move reciprocally in these cylinder bores 5 guided by a displacement element 4 according to the invention, which is shown as an exemplary non-turning swashplate in FIG. 1. A skilled person is aware that in bent axis hydraulic axial piston units, the displacement element 4 would be a yoke bending the axis of rotation of the cylinder block with respect to a rotational axis of a drive shaft of the hydraulic axial piston unit.

(9) In the exemplary embodiment of FIG. 1 the displacement element 4 in the form of a swashplate is tiltable around a pivot axis 29 in order to adjust the displacement volume displaced by the working pistons 6 during one revolution of the cylinder block 3. The cylinder bores 5 are fluidly connected via cylinder ports 31 and 32 with a first control port 23 and a second control port 24 on a valve segment 20 located on the lower side of the cylinder block 3, i.e. at the piston bottom side. Valve segment 20 is rotatable fixed with regard to a housing of the hydraulic piston unit and does not turn with cylinder block 3. A driving shaft 8 is attached to cylinder block 3 in a rotatably fixed manner, such that the driving shaft 8 is able to drive or to be driven by cylinder block 3 in a rotatable manner. Depending on which kidney-shaped port of the valve segment 20 forms an inlet port 21 or an outlet port 22 and in which position, i.e. in which angle of tilt the swashplate 4 is oriented, the rotational group 2 of hydraulic piston unit 1 comprising usually at least swashplate 4, working pistons 6, cylinder block 3, driving shaft 8 and valve segment 20, operates as a pump or a motor as well as operates in propel mode or in drag mode. As these details are very well known to a person of ordinary skill in the art, further explanations in this regard are omitted.

(10) For example, the hydrostatic piston unit 1 in FIG. 1 is shown as a hydraulic piston motor in propel mode with an inlet port 21 arranged at the high pressure side 14 of the hydraulic piston unit 1. Correspondingly, outlet port 22 is arranged on the low pressure side 15. Hence, hydraulic fluid under high pressure enters the rotational group 2 at inlet port 21 and presses the working piston 6 towards the swashplate 4, which causes a rotational movement of cylinder block 3. At outlet port 22 hydraulic fluid under low pressure exits the rotational group 2 pressed by swashplate 4 via working pistons 6 and cylinder port 32—not shown in FIG. 1 as the lower working piston 6 is in its lower dead end position, in which in the simplified embodiment in FIG. 1 the cylinder port 32 is aligned with control port 24. The arrangement of the two kidney-shaped ports 21 and 22, as well as the arrangement of the inventive control ports 23 and 24 of the present disclosure, is shown exemplarily in FIG. 5. From FIG. 1 in view of FIG. 5, it may be readily understood that the cylinder block 3 of the hydraulic piston unit 1 in FIG. 1 shows an even number of cylinder bores 5, here four cylinder bores 5, which is a special configuration as frequently an odd number of cylinder bores 5 is used, for instance to enhance a smoother running of the hydraulic piston unit.

(11) In the embodiment of FIG. 1 the swashplate 4 is pushed and held in its tilted or deflected position by hydraulic fluid under high pressure guided from a control valve 10 via first control port 23 to cylinder port 31. This provides for a sufficiently high hydraulic force in cylinder bore 5, which pushes working piston 6 to its upper dead end position and holds it there and, therefore, swashplate 4 is in the maximum deflected/tilted position, as shown in FIG. 1. The hydraulic fluid under high pressure enters the control valve 10 via a high pressure port 11 which is fluidly connected via a high pressure selecting valve 30 to the high pressure side 14. Exemplarily, high pressure selecting valve 30 may be designed as double check valve connected to both pressure sides of the hydraulic piston unit 1.

(12) In the operational state of the hydraulic piston motor 1 according to FIG. 1, control valve 10 with its control valve spool 16 is in a first (initial) position in which control valve 16 conducts hydraulic fluid under high pressure to the first control port 23. Control valve spool 16 is held in this first initial position by means of a control valve spring 17. An actuator 13 is arranged on the opposite side of control valve spool 16, the actuator 13 is controlled by a suitable control unit 100 and is configured to generate a counter force against the elastic force of control valve spring 17 in order to move the control valve spool 16 into a second shifted position. The actuator 13 may be, for example, an electro-mechanical actuator 41, a hydraulic actuator 42, a pneumatic actuator 43 or a combination thereof. In this second shifted position control valve spool 16 is capable of conducting hydraulic fluid under high pressure to the second control port 24, thereby changing the angle of tilt of swashplate 4, as hydraulic fluid under high pressure enters cylinder bore 5 via cylinder port 32 and presses working piston 6 towards the swashplate 4. By this change of the tilt angle of swashplate 4, the stroke of all working pistons 6 is changed and thereby the displacement volume of hydraulic piston unit 1 is also changed. Even though the displacement volume of hydraulic piston unit 1 is changed, the high pressure selecting valve 30 remains in the same position as long as the high-pressure side 14 and low-pressure side 15 do not swap, such that side 15 becomes the high-pressure side and side 14 becomes the low-pressure side.

(13) A switched position of control valve 10 is shown in FIG. 1 with dashed lines, in which the swashplate 4 is at zero position abutting against a stop 33, i.e. the angle of tilt is equal to zero. In this operational condition, the hydraulic piston unit 1 does not show a displacement volume as the swashplate is oriented perpendicular to the rotational axis 9, which means that the working pistons do not perform any stroke as the distance between swashplate and cylinder block seen in direction of the rotational axis is not varying in circumferential direction. Thus, in this state the hydraulic piston unit idles without performing any work.

(14) However, it should be readily understood that the swashplate 4, rather than abutting against stop 33, may instead be tilted to negative angles with respect to the position of FIG. 1, i.e. a deflection of the swashplate 4 contrary to the situation shown in FIG. 1. This would be, for instance, a setting when the hydraulic motor of FIG. 1 would be operated in drag mode, now working as a pump and, for instance, performing a break effect on a hydraulic propel application.

(15) FIG. 2 schematically shows a second embodiment of the inventive hydraulic piston unit with the control valve spool 16 in shifted position. Differing from the embodiment of FIG. 1, the high-pressure side 14 is changed with the low-pressure side 15 in FIG. 2. Assuming that the conveying direction is the same as for the embodiment of FIG. 1, i.e. counter clock-wise, the hydraulic piston unit 1 works as a pump, wherein the pressure present at control port 24 determines the angle of tilt of the swashplate 4 and therewith the displacement volume of the hydraulic piston unit 1, here a hydraulic axial piston pump.

(16) FIG. 3 shows another embodiment of the inventive hydraulic piston unit 1, which differs from the embodiments of FIGS. 1 and 2 in that control valve 10 is a 4-way/2-position valve guiding hydraulic fluid under high pressure to control port 23 and hydraulic fluid under low pressure to the respective other control port 24. This configuration provides for a better lubrication effect at the lower dead end region of the working pistons 6 on the valve segment 20. In order to provide hydraulic fluid under low pressure from the low-pressure side to control valve 10, a low pressure selecting valve 35 is arranged upstream the control valve 10. Low pressure selecting valve 35 is connected to the high pressure side 14 as well as to the low pressure side 15. Thereby the valve spool of low pressure selecting valve 35, e.g. a 3-way/2-position valve is referenced on one front side to high pressure side and on the opposite side to low pressure to ensure that it is always the low pressure side which is connected to a low pressure port 12 of control valve 10. Analogous to the embodiments of FIGS. 1 and 2 a high pressure selecting valve 30 ensures that high pressure port 11 of control valve 10 is connected to the high pressure side 14 of hydraulic piston unit 1.

(17) As can be seen from FIG. 3 the angle of tilt of the swashplate 4 can be changed to the other side, i.e. the leading sign of the angle can be changed from to the respective maximum values in each direction. By doing this, the direction of conveying can be changed, with which the high-pressure side interchanges with the low-pressure side, yet the rotational direction of the hydraulic piston unit 1 remains the same. Additionally, when the conveying direction is maintained, shifting the control valve spool 16 from one position to the other switches the hydraulic piston unit 1 from pump mode to motor mode, and vice versa, as it is preferred for a propel application when changing from propel mode to drag mode. This switched configuration is shown, for example, in FIG. 4.

(18) Additionally FIG. 4 shows another embodiment of the inventive hydraulic piston unit 1, where the hydraulic fluid under a lower pressure than the high pressure is provided for instance by a charge pressure source 40. This enables the preselection of an operational mode at standstill of the hydraulic piston unit 1. For instance, the conveying direction in the case of a hydraulic pump may be selected, simply by shifting the control valve spool 16 in the appropriate position. It should be readily understood that this charge pressure source 40 is interchangeable with any system pressure source 44 providing hydraulic fluid under a lower pressure lower than the pressure at the high pressure side of hydraulic piston unit 1. Furthermore, the pressurized hydraulic fluid guided to one of control ports 23 or 24 improves the lubrication situation on the low pressure area of valve segment 20. As shown in FIG. 5 control ports 23 and 24 are arranged between the kidney-shaped inlet and outlet port 21 and 22 at the respective dead end positions 61 and 62 of the working pistons 6. The circumferential distance between the borders of the kidney-shaped ports 21 and 22 and the borders of the control ports 23 and 24 is preferably less than the double circumferential distance between the borders of the cylinder ports 31. By doing this it can be assured that, in particular with an odd number of cylinder bores, always one cylinder port 31, 32 overlaps with at least one control port 23, 24 to ensure better and quicker reacting control as well as a smother run of the hydraulic piston unit 1.

(19) In summary, with the inventive hydraulic piston unit of the present disclosure, a smaller hydraulic piston unit with a reliable displacement volume control is provided, which eliminates the need of a (external) servo unit. This not only saves costs but also renders the hydraulic piston unit less complex and more reliable as it comprises fewer parts. Also leakage is reduced significantly as less parts are subjected to hydraulic pressure.