DE102021201409A1 - Displacement machine with displacement volume measuring device - Google Patents

Abstract

The invention relates to a displacement machine (10) which defines a displacement volume which can be adjusted by moving an adjusting element (20), an actuator (30) being provided, by means of which the adjusting element (20) can be moved. According to the invention, a force sensor (40 ) and a measuring spring (60), wherein the measuring spring (60) has a first and an opposite second end (61; 62), the first end (61) of the measuring spring (60) being stationary on a housing (16) of the displacement machine (10; 10'), wherein the second end of the measuring spring (60) is coupled in motion to the actuating element (20), the force sensor (60) being connected to the measuring spring (60) in such a way that the measuring spring (60) has a exerts a force that can be measured by the force sensor (40) on the force sensor (40), so that the displacement volume of the displacement machine (10; 10') can be determined using a measured value of the force sensor (40).

Description

The invention relates to a displacement machine according to the preamble of claim 1.

From the DE 10 2010 045 539 A1 a displacement machine in the form of an axial piston machine in a swash plate design is known. This comprises an actuating element in the form of a pivotable swash plate, the displacement volume of the displacement machine being dependent on the position of the actuating element. Its position can be adjusted by means of an actuator, which includes a hydraulic cylinder. A rotation angle sensor is also provided, with which the pivoted position of the actuating element can be measured. The corresponding measured value is used, for example, as part of a pressure control of the hydraulic drive system in which the displacement machine is installed.

An advantage of the present invention is that displacement volume measurement can be performed more easily and at lower cost.

According to claim 1 it is proposed that a force sensor and a measuring spring be provided, the measuring spring having a first end and an opposite second end, the first end of the measuring spring being arranged in a stationary manner on a housing of the displacement machine, the second end of the measuring spring being connected to the Actuating element is coupled in motion, the force sensor being connected to the measuring spring in such a way that the measuring spring exerts a force that can be measured by the force sensor on the force sensor, so that the displacement volume of the displacement machine can be determined using a measured value of the force sensor. The positive-displacement machine can be an axial piston machine of swashplate design, with the actuating element being a pivotable swashplate. The positive-displacement machine can be an axial piston machine with a bent-axis design, with the actuating element being a displaceable distribution plate. The displacement machine can be a radial piston machine, with the adjusting element being an adjusting ring which surrounds the rotor and can be displaced transversely to the axis of rotation of the rotor. The positive-displacement machine can be a vane cell machine, with the adjusting element being an adjusting ring which surrounds the rotor and can be displaced transversely to the axis of rotation of the rotor. The displacement volume of the displacement machine is preferably determined using the measured value of the force sensor. The displacement machine can be operated either as a pump or as a motor.

Advantageous developments and improvements of the invention are specified in the dependent claims.

It can be provided that the force sensor is connected to the first end of the measuring spring. The first end of the measuring spring is arranged in a stationary manner on the housing. The force sensor can thus be fastened there in a particularly simple manner. A connection cable of the force sensor can be routed in a fixed position on the housing so that there is no risk of breakage during operation. During operation of the displacement machine, there are fewer vibrations in the area of the housing than on the actuating element. A disturbance of the force measurement caused by the vibrations is correspondingly lower.

Provision can be made for the measuring spring to be a compression spring which is installed between the force sensor and the actuating element, so that a compressive force of the measuring spring presses the force sensor against the housing of the displacement machine, the compressive force mentioned being supported on the actuating element. The compression spring is preferably under compressive stress in every position of the actuating element. This means that the force sensor can be held at the desired installation location solely by the compressive force of the measuring spring. The assembly of the force sensor is simple and inexpensive.

It can be provided that the force sensor comprises at least one bending beam with a first and a second end, the first end of the bending beam being arranged essentially stationary with respect to the housing of the displacement machine, the first end of the measuring spring being connected to the second end of the bending beam is, wherein the at least one bending beam is provided with a strain gauge, wherein said measured value of the force sensor is dependent on the strain condition of the at least one strain gauge. Such a force sensor is particularly simple and inexpensive. It can easily be installed between the first end of the range spring and the housing.

Provision can be made for the actuating element to be displaceable in the region of the second end of the measuring spring along a travel path, with the measuring spring being arranged essentially parallel to the travel path, so that a force of the measuring spring prestresses the actuating element in the direction of an end position. The adjustment path is preferably straight or curved in a circle. In the second case, the compression spring preferably extends at most over 20% of the total circumference of the corresponding full circle. With this design, a high measuring accuracy can be achieved with a small measuring spring.

It can be provided that at least one restoring spring is connected in parallel with the measuring spring, with only the measuring spring exerting a force on the force sensor, with the restoring spring prestressing the actuating element in the direction of an end position. In this way, the rigidity and the preload of the measuring spring and the return spring can be optimally adapted to the respective function. As a result, a particularly high measurement accuracy can be achieved. The first and second compression springs preferably act in the direction of the same end position.

It can be provided that the measuring spring is a helical spring. The return spring is preferably also a helical spring. A coil spring is particularly inexpensive and durable.

It can be provided that the at least one bending beam is formed by a one-piece measuring part made of metal, the measuring part comprising an inner frame which is surrounded by an outer frame, the at least one bending beam being arranged between the inner and outer frames, wherein the measuring spring is supported on one of the two frames, inner frame or outer frame, with the other frame, outer frame or inner frame, being arranged in a stationary manner with respect to the housing of the displacement machine. Such a force sensor can be installed in a particularly simple manner between the measuring spring and the housing. At the same time, this design can also be used within the pressure chamber of an actuating cylinder, because the pressure of the hydraulic fluid essentially does not affect the measurement result. The inner and outer frames and the at least one bending beam are preferably arranged essentially in one plane.

Provision can be made for the force sensor to comprise a plurality of bending beams, with the corresponding strain gauges being interconnected in the manner of a measuring bridge. As a result, a particularly high measurement accuracy can be achieved. Temperature changes have little influence on the measurement result. The measuring bridge is also known as a Wheatstone bridge (https://de.wikipedia.org/wiki/Wheatstonesche_Messbr%C3%BCcke).

Provision can be made for the at least one strain gauge to be connected to an assigned analog/digital converter, which is part of an evaluation device, with the evaluation device being set up to determine a dimension for the displacement volume of the displacement machine from the corresponding digital value. The specified number can be specified in relation to a physical unit of measurement (eg cm ³ ). It can also be considered to use a metric that can assume values between 0 and 1 or -1 and +1, with +1 or -1 representing a maximum displacement volume in relation to one of the two opposite directions of adjustment. The evaluation device preferably includes a programmable digital computer.

Provision can be made for the displacement machine to be designed as an axial piston machine with a swash plate design, with the actuating element being formed by a swash plate which can be pivoted with respect to a pivot axis, with the actuator comprising at least one hydraulic actuating cylinder.

It goes without saying that the features mentioned above and those still to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention.

• 1 einen Querschnitt einer Verdrängermaschine gemäß einer ersten Ausführungsform der Erfindung;
• 2 einen Querschnitt einer Verdrängermaschine gemäß einer zweiten Ausführungsform der Erfindung; und
• 3 eine perspektivische Ansicht des Kraftsensors mit der zugeordneten Auswertevorrichtung.

The invention is explained in more detail below with reference to the accompanying drawings. It shows:

• 1 a cross section of a displacement machine according to a first embodiment of the invention;
• 2 a cross section of a displacement machine according to a second embodiment of the invention; and
• 3 a perspective view of the force sensor with the associated evaluation device.

1 shows a cross section of a positive displacement machine 10 according to a first embodiment of the invention. The positive-displacement machine 10 is designed, for example, as an axial piston machine in a swashplate design, with the present invention being usable for any hydrostatic positive-displacement machine with an adjustable displacement volume, ie for example also for radial-piston machines or vane-cell machines.

The displacement machine 10 has a housing 16 in which a drive shaft 12 is rotatably mounted with respect to an axis of rotation 11 . The drive shaft 12 protrudes from the housing 16, where it can be brought into rotary drive connection, for example, with an electric motor or an internal combustion engine. Within the housing 16, the drive shaft 12 is surrounded by a cylinder drum 13, in which a plurality of working pistons 14 are accommodated so as to be displaceable in the direction of the axis of rotation 11. The cylinder drum 13 is non-rotatably connected to the drive shaft 12, for example via splines. The mutually identical working col Ben 14 are preferably arranged uniformly distributed around the axis of rotation 11, wherein they are each supported via a hydrostatic sliding shoe 15 on an actuating element 20 in the form of the so-called swash plate. The actuating element 20 is mounted in the housing 16 so that it can pivot with respect to the pivot axis 21 . The pivot axis 21 preferably runs perpendicularly to the axis of rotation 11. As in the present case, it can be arranged at a distance from the axis of rotation 11, and it can also intersect the axis of rotation 11. It should be noted here that the adjusting element 20 can also be linearly displaceable, as is the case, for example, with the adjusting ring of a vane cell machine.

An actuator 30 is also provided, with the aid of which the actuating element 20 can be pivoted with respect to the pivot axis 21 in order to adjust the displacement volume of the displacement machine 10 . The actuator 30 is designed in the form of a hydraulic actuating cylinder 31, the movable piston of which presses against the actuating element 20 via a sliding shoe. The immovable element of the adjusting cylinder 31 is firmly connected to the housing 16 .

A restoring spring 22 is also provided, which is arranged approximately in alignment with the actuating cylinder 31, the actuating cylinder 31 and the restoring spring 22 being arranged on opposite sides of the actuating element 20 so that their compressive forces act in opposite directions. In the pressureless state of the displacement machine 10, the restoring spring 22 causes the displacement volume to be adjusted toward the maximum displacement volume. If the displacement machine 10 is under pressure, additional hydrostatic forces act in the same direction because the pivot axis 21 is arranged at a distance from the axis of rotation 11 . However, this fact is of secondary importance for the present invention.

In the first embodiment of the invention, the return spring 22 also forms the measuring spring 60; 60a. Between the housing 16 and the range spring 60; 60a, i.e. at the first end 61 of the measuring spring 60, is the in 3 Force sensor 40 shown in more detail installed, so that the compressive force of the measuring spring 60; 60a can be measured with the force sensor 40. The compressive force mentioned is approximately proportional to the position of the actuating element 20 and thus to the displacement volume of the displacement machine 10. Insofar as the corresponding relationship is non-linear, it can be easily described by a mathematical formula or by a table of values, in which case it can be used as part of the determination of the dimension ( No. 72 in 3 ) can be taken into account.

The measuring spring 60; 60a or the restoring spring 22 is designed here as a compression spring in the form of a helical spring. The second end of the measuring spring 60 opposite the first end; 60a is present directly on the actuating element 20, where there is a to the measuring spring 60; 60a adapted centering recess is provided on the actuating element 20.

2 shows a cross section of a positive displacement machine 10' according to a second embodiment of the invention. The displacement machine 10' is also designed as an axial piston machine with a swash plate design. In contrast to the first embodiment 1 the displacement volume of which can be adjusted beyond the displacement volume of zero, so that the direction of flow through the displacement machine 10' can be reversed simply by adjusting the displacement volume while the direction of rotation of the drive remains the same. In the present case, the actuator comprises two single-acting hydraulic actuating cylinders 31, which act in opposite directions on the actuating element 20 in the form of the pivotable swash plate. In the second embodiment, the pivot axis of the actuating element 20 intersects the axis of rotation 11. The in 2 upper actuating cylinder 31 is provided with a return spring 22 which biases the actuating element 20 to a maximum displacement volume.

In the second embodiment of the displacement machine 10 ′, the measuring spring 60 is designed separately from the restoring spring 22 . As a result, the measuring spring 60 and the associated force sensor 40 can be arranged much more flexibly within the displacement machine. In 2 are three different possible arrangements of the range spring 60b; 60c; 60d drawn. Although it is conceivable to use several measuring springs 60 at the same time in order to increase the measuring accuracy, for cost reasons it is preferred to use only one of the three measuring spring 60 arrangements shown.

All three arrangements of the measuring spring 60 have in common that the force sensor 40 is arranged at the first end of the measuring spring 60 fixed to the housing. In this way, a connection cable that is stationary with respect to the housing 16 can be used for the force sensor 40, which is easy to assemble and is not exposed to any risk of breakage during operation. Furthermore, the vibrations of the displacement machine 10' occurring during operation are less strong on the housing 16 than on the actuating element 20, so that a higher measurement accuracy can be achieved.

In all three variants, the measuring spring is 60b; 60c; 60d designed as a compression spring, being designed as a helical spring. the inside 3 The force sensor 40 shown in more detail is between the measuring spring 60b; 60c; 60d and the housing 16, the compressive force of the measuring spring 60b; 60c; 60d is supported directly on the force sensor 40.

The measuring spring 60b, together with the associated force sensor 40, is in the pressure chamber of the 2 upper adjusting cylinder 31 arranged. Its second end is supported on the movable element of this actuating cylinder 31, so that it is coupled to the actuating element 20 for movement. An advantage of the in 3 The force sensor shown is that the pressure of the hydraulic fluid in the pressure chamber mentioned does not exert a total force on the force sensor 40 that would cause a deformation of the bending beam (No. 43 in 3 ) causes.

The measuring spring 60d is arranged analogously to the measuring spring 60b, but in the in 2 lower adjusting cylinder 31.

The measuring spring 60b is analogous to the return spring of the first embodiment 1 arranged. Preferably, the range springs 60b; 60c; 60d has a significantly lower stiffness than the restoring spring 22. The advantage of the second embodiment is precisely that the two stiffnesses mentioned can be selected essentially independently of one another, so that they can be optimally adapted to the relevant function (restoring, force measurement). The same applies to the bias of said springs 60b; 60c; 60d; 22

3 shows a perspective view of the force sensor 40 with the associated evaluation device 70. The force sensor 40 is both in the first embodiment 1 as well as in the second embodiment 2 usable.

The force sensor 40 includes a measuring part 45, which is formed in one piece from metal, preferably from spring steel. The measuring part 45 has an outer frame 47, which in the present case is designed as a closed ring. The outer frame 47 is preferably designed in such a way that the associated measuring spring can rest directly there. Furthermore, the measuring part 45 comprises an inner frame 46 which is arranged inside the outer frame 47 . The measuring part is supported on the housing of the displacement machine via the inner frame 46 . The outer and inner frames 47; 46 are preferably arranged essentially in one plane. In order for the measuring part 45 to be sufficiently movable in itself, another part can be permanently attached to the inner frame 46, for example riveted, which rests directly on the housing of the displacement machine. Said part thus causes a distance between the measuring part 45 and the housing.

The present measuring part 45 comprises a single bending beam 43 which is integrally connected both to the inner frame 46 and to the outer frame 47 . In the present case, the measuring part 45 is stamped out of sheet metal, so that the bending beam 43 is designed in the manner of a flat plate with a constant thickness. The area of the bending beam 43 where the highest strains occur is thus formed by a comparatively large area on which a strain gauge 44 (https://de.wikipedia.org/wiki/Dehnungsmessstreifen) can be attached without any problems. It is conceivable that several bending beams are provided between the inner and the outer frame 46; 47 are connected in parallel. It is conceivable that several strain gauges 44 are provided, which are arranged at different points of the measuring part 45 . These are preferably interconnected as a measuring bridge so that temperature changes have little effect on the measurement result. A foil gauge can be used, which encompasses the entire measuring bridge with a plurality of strain gauges, with the individual strain gauges being oriented differently, if desired.

The evaluation device 70 includes an analog/digital converter 71, a programmable digital computer and a voltage source. The voltage source is connected to the strain gauges, in particular the measuring bridge, on the input side, with the analog/digital converter 71 being connected to the strain gauges 44 or the measuring bridge on the output side. It uses it to measure a voltage that depends on the force of the measuring spring and converts it into a digital value. This digital value is converted into a dimension 72 by means of the programmable digital computer. The force-displacement characteristic of the range spring is taken into account. The programmable digital computer preferably implements a digital filter, with which disturbances that change over time are filtered out of the named digital value, which also changes over time.

Reference List

10

positive displacement machine (first embodiment)

10'

positive displacement machine (second embodiment)

11

axis of rotation

12

drive shaft

13

cylinder drum

14

working piston

15

Sliding shoe on the working piston

16

Housing

20

actuator

21

pivot axis

22

return spring

30

actuator

31

adjusting cylinder

40

force sensor

41

first end of the bending beam

42

second end of the bending beam

43

bending beam

44

strain gauges

45

measuring part

46

inner frame

47

outer frame

60

range spring

60a

range spring

60b

range spring

60c

range spring

60d

range spring

61

first end of the range spring

62

second end of the range spring

70

evaluation device

71

analog to digital converter

72

measure

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102010045539 A1 [0002]

Claims (11)

Displacement machine (10; 10') which defines a displacement volume which can be adjusted by moving an adjusting element (20), an actuator (30) being provided, by means of which the adjusting element (20) can be adjusted, characterized in that a force sensor ( 40) and a measuring spring (60) are provided, the measuring spring (60) having a first and an opposite second end (61; 62), the first end (61) of the measuring spring (60) being fixed in place on a housing (16) of the positive-displacement machine (10; 10'), the second end of the measuring spring (60) being coupled for movement to the actuating element (20), the force sensor (40) being connected to the measuring spring (60) in such a way that the measuring spring (60 ) exerts a force that can be measured by the force sensor (40) on the force sensor (40), so that the displacement volume of the displacement machine (10; 10') can be determined using a measured value of the force sensor (40). displacement machine (10; 10'). claim 1 , wherein the force sensor (40) is connected to the first end (61) of the measuring spring (60). displacement machine (10; 10'). claim 2 , wherein the measuring spring (60) is a compression spring, which is installed between the force sensor (40) and the actuating element (20), so that a compressive force of the measuring spring (60) forces the force sensor (40) against the housing (16) of the displacement machine ( 10; 10'), said compressive force being supported on the actuating element (20). Displacement machine (10; 10') according to one of the preceding claims, wherein the force sensor (40) comprises at least one bending beam (43) with a first and a second end (41; 42), the first end (41) of the bending beam (43 ) is arranged essentially stationary with respect to the housing (16) of the displacement machine (10; 10'), the first end (61) of the measuring spring (60) being connected to the second end (42) of the bending beam (43), the at least one bending beam (43) is each provided with a strain gauge (44), said measured value of the force sensor (40) depending on the strain condition of the at least one strain gauge (44). Displacement machine (10; 10') according to one of the preceding claims, wherein the actuating element (20) can be displaced along a travel path in the region of the second end (62) of the measuring spring (60), the measuring spring (60) being arranged essentially parallel to the travel path is, so that a force of the measuring spring (60) biases the actuating element (20) in the direction of an end position. Displacement machine (10') according to one of the preceding claims, wherein at least one restoring spring (22) is connected in parallel with the measuring spring (60), with only the measuring spring (60) exerting a force on the force sensor (40), with the restoring spring (22) biases the actuating element (20) in the direction of an end position. Positive displacement machine (10; 10') according to any one of the preceding claims, wherein the measuring spring (60) is a coil spring. Displacement machine (10; 10') according to one of the preceding claims, wherein the at least one bending beam (43) is formed by a one-piece measuring part (45) made of metal, wherein the measuring part (45) comprises an inner frame (46) which is connected to an outer frame (47), the at least one bending beam (43) being arranged between the inner and outer frame (46; 47), the measuring spring (60) being attached to one of the two frames, inner frame (46) or outer frame (47 ), is supported, wherein the other frame, outer frame (47) or inner frame (46), is arranged stationary with respect to its housing (16) of the displacement machine (10; 10'). Displacement machine (10; 10') according to one of the preceding claims, wherein the force sensor comprises a plurality of bending beams (43), the corresponding strain gauges (44) being interconnected in the manner of a measuring bridge. Displacement machine (10; 10') according to one of the preceding claims, wherein the at least one strain gauge (44) is connected to an associated analog-to-digital converter (71), which is part of an evaluation device (70), the evaluation device (70) being is set up to determine a measure (72) for the displacement volume of the displacement machine (10; 10') from the corresponding digital value. Displacement machine according to one of the preceding claims, wherein the displacement machine (10; 10') is designed as an axial piston machine with a swash plate design, the actuating element (20) being formed by a swash plate which can be pivoted with respect to a pivot axis (21), the actuator (30) having at least one hydraulic actuating cylinder (31).

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