Hydraulic machine

Abstract

A hydraulic machine having a variable intake volume/pump capacity includes working spaces (8) disposed in a cylinder (2), each of the working spaces (8) being limited by a piston (6) and a cylinder bore (4) in which the piston (6) is accommodated. The pistons (6) are supported on a reciprocating element (14) that rotates relative to the pistons (6), and therefore when the cylinder (2) rotates relative to the pistons (6), the pistons (6) undergo a displacement that determines the volume of the working spaces (8) which can be connected to high pressure and low pressure, to a control unit for actuating the valves (16, 22) as a function of the displacement of the particular piston (6), and to an angle-of-rotation sensor (36). The angle-of-rotation sensor (36) has a Gray code track (60) and an incremental track (58), to each of which at least one sensor (72, 74) is assigned.

Description

CROSS-REFERENCE

The invention described and claimed hereinbelow is also described in DE 102009049354.9, filed Oct. 14, 2009. This German Patent Application, whose subject matter is incorporated here by reference, provides the basis for a claim of priority of invention under 35 U.S.C. 119 (a)-(d).

BACKGROUND OF THE INVENTION

The invention relates generally to a hydraulic machine. More specifically, the present invention relates to a hydraulic machine having a variable intake volume/pump capacity, the rotational angle position of which is detected using an angle-of-rotation sensor that includes a Gray code track and an incremental track

Valve-controlled hydraulic machines of that type are known, for example, from EP 1 537 333 B1. That publication describes a hydraulic machine of an axial-piston design or a radial-piston design, which can be operated, in principle, as a motor or a pump, it being possible to adjust the pump capacity or intake volume in a nearly stepless manner via valve control. In one embodiment that is described, the hydraulic machine is designed as an axial piston machine, wherein a large number of pistons disposed in a cylinder is supported on a rotatably supported swash plate. Via the assigned cylinder chamber, each piston limits a working space which can be connected to a pressure-medium inlet or a pressure-medium outlet via a low-pressure side valve and a high-pressure side valve.

According to the known solution, the two valves are designed as electrically releasable or blockable non-return valves which can be controlled using the pump control unit and are operated in the particular working space in the “full mode”, “partial mode”, or “idle mode”. As a result, the pump capacity or intake volume can be adjusted from a maximum value to 0 in a nearly stepless manner. Using the control unit, the valves are controlled according to a control algorithm to minimize the pulsations of the total displacement (pump) or the total intake volumetric flow (motor). The volumetric flow rate is often adjusted using phase-angle control, but can also be adjusted using phase-section control or phase cut-out control.

Hydraulic machines of that type are also known, for example, from WO 2008/012577 A2, WO 2008/012586 A1, or WO 2004/025122 A1. In all of these hydraulic machines, the valves are controlled for example as a function of the displacement of the particular piston, which, in turn, depends on the angle of rotation of a drive shaft or output shaft which, by way of example, in the case of an axial piston machine, is operatively connected to the above-mentioned swash plate.

According to the known solutions, the angle of rotation or the rotational speed is measured using angle-of-rotation sensors, in the case of which a sensor is operatively connected to an incremental track. That is, according to these solutions, a track is formed, for example, on the outer circumference of the drive/output shaft or the rotating cylinder, the track being embodied as recesses in a regular formation, similar to a gear wheel, and generating a sensor signal during rotation, for example, by changing a magnetic field, the sensor signal being used to determine the relative rotational angle position. The track is often also provided with an identification that can be used to detect a reference position. The disadvantage of these solutions is that the level of accuracy and resolution that can be achieved does not fulfill the requirements for the control of a hydraulic machine (DDU) according to the invention. Furthermore, the sensors often operate using optical procedures, making it practically impossible to situate them in the medium to be pumped.
A further disadvantage is that up to one revolution must be completed to detect the reference position when using this incremental angle-of-rotation measurement procedure.

SUMMARY OF THE INVENTION

In contrast, the object of the invention is to create a hydraulic machine, in the case of which the rotational angle position of a rotating component, for example, a cylinder drum or a drive shaft or output shaft, can be detected with high accuracy.

According to the invention, the hydraulic machine is designed as a DDU (Digital Displacement Unit) and comprises a large number of working spaces disposed in a cylinder, each working space being limited by a piston and a cylinder bore in which the piston is accommodated. The pistons are supported on a reciprocating element that can move relative to the pistons, and therefore the pistons are displaced in the cylinder bore due to the motion of the cylinder relative to the reciprocating element that supports the pistons. Each working space can be connected to high pressure or low pressure via high-pressure valves or low-pressure valves, respectively. The hydraulic machine has a control unit for selectively actuating these valves, and an angle-of-rotation sensor for detecting the rotational angle position of the cylinder or the reciprocating element. According to the invention, the angle-of-rotation sensor is designed to include a Gray code track and an incremental track, to each of which a sensor is assigned.

The use of a conventional incremental track and an additional Gray code track enables the absolute angle of rotation to be detected with a high level of accuracy. This angle-of-rotation sensor does not require referencing, in contrast to the incremental sensors described initially. The design according to the invention therefore makes it possible to detect the rotational angle position and, therefore, the displacement of the particular piston in an extremely exact manner, and to control the low-pressure valves and high-pressure valves as a function of this position and the desired pump capacity/intake volume.

According to an embodiment of the invention, the tracks are located on the circumference of a base body, and the sensors of the angle-of-rotation sensor are distributed accordingly along this circumferential section.

The angle-of-rotation sensor can have a compact design when the two tracks are offset in the axial direction. The assigned sensors are then situated accordingly.

To improve the resolution of the rotational angle measurement, a plurality of sensors can be assigned to one track. According to a specific embodiment, five sensors are assigned to the Gray code track, and one sensor is assigned to the incremental track.

According to a variant of the invention, the incremental track is provided with more track sections than is the Gray code track. A variant having 72 track sections of the incremental track and 36 track sections of the Gray code track has proven suitable; the ratio of track sections is therefore preferably 2:1.

In the case of a hydraulic machine, the base body on which the tracks are located is supported on a drive shaft or output shaft of the hydraulic machine. Basically, however, the two tracks can also be formed directly on the rotating component.

The sensors can be accommodated in a separate holder on the housing side, being inserted in a corresponding recess in the housing.

The design of the hydraulic machine is particularly simple when the two tracks are situated in the pressure medium.

It has proven effective in particular to use magnetic angle-of-rotation sensors instead of optical sensors. Magnetic sensors of that type can be designed e.g. according to the Hall Effect or, generally speaking, as magnetostatic sensors.

In the case in which the tracks run in the pressure medium, it is preferable to seal the sensors against the pressure medium.

In the case of an embodiment having a very simple design, the base body on which the tracks are located is fastened to an end section of the drive shaft or output shaft, and is covered by a housing cover.

The hydraulic machine can be of an axial-piston design or a radial-piston design.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention is explained in greater detail below with reference to schematic drawings. They show:

FIG. 1 a highly schematicized depiction to explain the operating method of a valve-controlled hydraulic machine having a digitally variable intake volume/pump capacity (DDU);

FIG. 2 a detailed depiction of an angle-of-rotation sensor of the hydraulic machine shown in FIG. 1, and

FIG. 3 tracks of the angle-of-rotation sensor depicted in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, the operating method of a valve-controlled hydraulic machine 1 having a digitally adjustable pump capacity/intake volume (DDU) will be explained with reference to FIG. 1. In the embodiment shown, hydraulic machine 1 is designed as an axial piston machine in swash plate design, wherein FIG. 1 shows a highly schematicized variant. Only the essential components that are required to understand the invention will be explained in the following. Reference is made to the above-described prior art for more detailed designs. In the description that follows, hydraulic machine 1 is operated as a hydraulic motor, although the descriptions of the hydraulic motor basically likewise apply to a pump having a variable pump capacity. As mentioned initially, the hydraulic machine is in no way limited to the axial-piston design.

According to the schematic depiction shown in FIG. 1, hydraulic machine 1 includes a cylinder drum 2, in which a large number of cylinder bores 4 is formed, each of which contains an axially displaceable piston 6. Together with cylinder bore 4, each piston 6 limits a working space 8, the volume of which is dependent on the displacement of piston 6. Each piston 6 bears via a piston shoe 10 against a slanted swash plate that is connected to output shaft 12. Control curve 14 formed by the rotation of the swash plate is shown in the depiction in FIG. 1; control curve 14 shows how the piston displacement and, therefore, the volume of particular working space 8 are dependent on the angle of rotation. As shown on the right in FIG. 1, each working space 8 is connected via an inlet valve 16 to a supply line 18 that is common to all working spaces 8, and to which a system pressure or high pressure is applied. This high pressure can be created e.g. using a pump 20.

Moreover, each working space 8 is connected via a drain valve 22 to a low-pressure side drain line 24, which is likewise common to all working spaces 8, and which leads into a tank 26.

As explained initially, drain valves 22 and inlet valves 16 are designed as electrically releasable and blockable non-return valves in the embodiment shown. In its home position shown, inlet valve 16 is preloaded into a closed position via a not-shown spring, and can be moved into an open position by applying current to a solenoid actuator 28, thereby allowing the pressure medium to flow out of inlet line 18 into particular working space 8. In its home position shown, drain valve 22 is preloaded into an open position using a spring. By supplying current to solenoid actuator 30, drain valve 22 is moved into a blocking position in which pressure medium cannot flow out of working space 8. Solenoid actuator 28, 30 is activated by a control unit 34 which is used to set the above-described modes (full mode, partial mode, idle mode), and therefore the intake volume of the hydraulic motor is approximately steplessly adjustable, wherein pulsation can also be reduced to a minimum by activating valves 16, 22 in a suitable manner. According to the invention, valves 16, 22 are activated depending on the rotational angle of output shaft 12, the rotational angle being detected using an angle-of-rotation sensor 36 and reported via a signal line to control unit 34. In principle, other characteristic data of the hydraulic machine such as the torque acting on output shaft 12, the intake volume of hydraulic motor 1, or the angle of rotation of the swash plate can be taken into account, of course, in the activation of valves 16, 22.

Cylinder drum 2, the swash plate, and output shaft 12 connected thereto are supported in a housing 38 of hydraulic machine 1. FIG. 2 shows an end-face end section of housing 38, in which output shaft 12 is supported via a not-shown bearing system. A bearing cover 42 is placed on end face 40—which is shown in FIG. 2—of housing 38. A stepped end section of output shaft 12 enters a recess 44 of bearing cover 42, where it is covered by a sealing bushing 46.

An axially projecting hub section 47, on which an annular base body 48 is placed, is formed on above-mentioned stepped end section of output shaft 12. The fit between hub section 47 and base body 48 is designed with a high level of accuracy, thereby ensuring that base body 48 is centered exactly. The rotational angle positioning of base body 48 relative to hub section 46 of output shaft 12 is ensured by using one or more location pins 50 and fastening screws 52 which preferably lie on a common partial circle and extend through base body 48 and a region of output shaft 12 in an axially parallel manner.

A Gray code track carrier and an incremental track carrier 54, 56 are fastened to base body 48, the axial extension of said track carriers being substantially less than that of base body 48. Gray code track carrier 54 is supported in the region of the end face of base body 48 located at the bottom in FIG. 2, and incremental track carrier 56 is supported in the region of the upper end face of base body 48, and therefore the end faces of the base body and respective track carrier 54, 56 are approximately aligned. An incremental track 58 and a Gray code track 60 are formed on the circumferential surfaces of the two code tracks 54, 56.

The design of tracks 58, 60 will be explained with reference to FIG. 3. FIG. 3 shows the design of incremental track 58 and Gray code track 60. Incremental track 58 is subdivided into a total of 72 track sections 62, each having the same width, and each representing, in alternation, the number (bit) “0” or “1”.

Gray code track 60 shown at the bottom in FIG. 3 is subdivided into 36 track sections 64; particular Gray code sections 66, 68, 70, etc. are obtained by designing these track sections accordingly, wherein the light track sections stand for the number “0”, and the track sections marked with an “X” stand for the number “1”, for instance. Therefore, when output shaft 12 rotates, incremental track 58 delivers an increment having a resolution of 6°, while Gray code track 60 results in a resolution of 12°. By evaluating these two signals jointly, accuracy can be increased further depending on the algorithm that is used. Gray code track 60 is selected such that only one bit ever changes for sensor 72 when it is rotated by one track section 64.

Individual code tracks 62, 64 of incremental track 58 or Gray code track 60 can be magnetized differently to depict the information “0” or “1”, or they can be composed of a material that changes a magnetic field. As shown in FIG. 3, five sensors 72 are assigned to Gray code track 60, and therefore a 5-bit code can be read by evaluating the sensor signals. Only one sensor 74 for reading a 1-bit code is assigned to incremental track 58. It is characteristic of a Gray code for adjacent code words read by five sensors 72 to differ from each other by a single track section 64. Sensors 74, 72 are located in a holder 76 which is inserted into an annular recess 78 in housing 38 in a non-positive or form-fit manner. In the embodiment shown, holder 76 has a two-pieced design, including an inner ring 80 and an outer ring 82 enclosing inner ring 80 in sections; sensors 72, 74 are supported between inner ring 80 and outer ring 82. According to FIG. 3, the five sensors 72 of Gray code track 60 are distributed evenly along the outer circumference of Gray code track 60, and therefore the angular distance between adjacent sensors 72 is 72°.

A unique feature of hydraulic machine 1 is that tracks 58, 60 run in a pressure medium chamber filled with pressure medium. The optical sensors that are typically used could not be used in variants of that type, or only with difficulty, and therefore the use of magnetic sensors is preferred. Sensors 72, 74 are therefore designed such that they detect a change in a magnetic field induced by the rotation of tracks 58, 60, and the corresponding signals can be used to calculate the absolute rotational angle position.

Since sensors 72, 74 are relatively sensitive, holder 76 is sealed against pressure medium chamber 84 using suitable sealing rings 86, 88. Outer ring 78 of holder 76 is preferably held in housing 38 in a form-fit manner.

In deviation from the embodiment described above, a plurality of sensors 74 can be assigned to incremental track 58. It is also possible, in principle, to sample Gray code track 60 using another number of sensors 72 in order to adapt the accuracy to the particular application.

The advantage of the design described above is high accuracy with adapted resolution. The rotational speed sensor can be used in the pressure medium, and installation is very easy since housing 38 can be accessed from the end face. Furthermore, the solution according to the invention is characterized by an extremely compact design; by using incremental track 58, Gray code track 60, and a relatively large number of sensors, the angle of rotation can be detected very exactly, the signal transit time is short, and the signals are easily evaluated.

Since the two tracks 58, 60 are situated on one carrier (base body 48, code carriers 54, 56), the sensor system can be positioned in a very flexible manner, and retrofitting can be easily performed.

Disclosed herein is a hydraulic machine having a variable intake volume/pump capacity, the rotational angle position of which is detected using an angle-of-rotation sensor that includes a Gray code track and an incremental track.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.

While the invention has been illustrated and described as embodied in a hydraulic machine having a variable intake volume/pump capacity, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.

LIST OF REFERENCE CHARACTERS

• 1 Hydraulic machine
• 2 Cylinder drum
• 4 Cylinder bore
• 6 Piston
• 8 Working space
• 10 Piston shoe
• 12 Output shaft
• 14 Control curve
• 16 Inlet valve
• 18 Supply line
• 20 Pump
• 22 Drain valve
• 24 Drain line
• 26 Solenoid actuator
• 30 Solenoid actuator
• 34 Control unit
• 36 Rotational-speed sensor
• 38 Housing
• 40 End face
• 42 Bearing cover
• 44 Receptacle
• 46 Sealing bushing
• 47 Hub section
• 48 Base body
• 50 Location pin
• 52 Fastening screw
• 54 Gray code track carrier
• 56 Incremental track carrier
• 58 Incremental track
• 60 Gray code track
• 62 Track section
• 64 Track section
• 66 Gray code section
• 68 Gray code section
• 70 Gray code section
• 72 Sensor
• 74 Sensor
• 76 Holder
• 78 Annular receptacle
• 80 Inner ring
• 82 Outer ring
• 84 Pressure medium chamber

Claims

1. A hydraulic machine having a variable intake volume/pump capacity, comprising:

a cylinder (2);

at least one piston (6);

a plurality of working spaces (8) disposed in the cylinder (2), each of the working spaces (8) being limited by the at least one piston (6) and at least one cylinder bore (4) in which the at least one piston (6) is accommodated;

a reciprocating element (14), wherein the pistons (6) are supported directly or indirectly on the reciprocating element (14), wherein said reciprocating element (14) is configured to rotate relative to the at least one piston (6), such that when the cylinder (2) rotates relative to the at least one piston (6), the at least one piston (6) undergoes a displacement that determines the volume of the working spaces (8);

a control unit;

high-pressure valves and low-pressure valves (16, 22), wherein said working spaces (8) are connected via said high-pressure valves and low-pressure valves (16, 22) to high pressure and low pressure, and to the control unit, wherein said control unit is configured to actuate the valves (16, 22) as a function of a displacement of one of said at least one piston (6);

an angle-of-rotation sensor (36), wherein said working spaces (8) are further connected to said angle-of-rotation sensor (36), wherein said angle-of-rotation sensor is configured to detect the rotational angle position of a rotating component (2, 14), wherein the angle-of-rotation sensor (36) has a Gray code track (60) and an incremental track (58), wherein at least one sensor (72, 74) is assigned to each of said Gray code track (60) and said incremental track (58).

2. The hydraulic machine according to claim 1, wherein the Gray code track and the incremental track (58, 60) are located on a circumference of a base body (48), and the sensors (72, 74) are distributed along the circumference.

3. The hydraulic machine according to claim 2, wherein the Gray code track and the incremental track (58, 60) are offset in an axial direction.

4. The hydraulic machine according to claim 3, wherein a plurality of sensors (74, 72) is assigned to one track (58, 60).

5. The hydraulic machine according to claim 4, wherein five sensors (72) are assigned to the Gray code track (60), and one sensor (74) is assigned to the incremental track (58).

6. The hydraulic machine according to claim 1, wherein the incremental track (58) has 72 track sections (62), and the Gray code track has 36 track sections (64).

7. The hydraulic machine according to claim 4, wherein the Gray code track (60) is selected such that a total of only one bit ever changes for the sensor (72) assigned to said Gray code track (6) when rotated by a track section.

8. The hydraulic machine according to claim 1, wherein the base body (48) is fastened to a drive shaft or output shaft (12).

9. The hydraulic machine according to claim 8, wherein the sensors (72, 74) are accommodated on a housing side in a holder (76).

10. The hydraulic machine according to claim 1, wherein the Gray code track (60) and the incremental track (58) run in the pressure medium.

11. The hydraulic machine according to claim 1, wherein the angle-of-rotation sensor is a magnetic sensor.

12. The hydraulic machine according to claim 9, wherein the holder (76) is sealed against a pressure medium.

13. The hydraulic machine according to claim 8, wherein the base body (48) is has an end face, wherein said base body (48) is fastened on the end face to the drive shaft or output shaft (12) and is covered by a housing cover (42).

14. The hydraulic machine according to claim 1, wherein said hydraulic machine has an axial-piston design or a radial-piston design.