EP2696075B1 - Gear wheel machine with force sensor in the form of a piezo film - Google Patents

Description

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

From the DE 10 2007 051 352 A1 is a gear machine known. The gear machine includes two gears that mesh with each other in external engagement. The gears are surrounded by a housing which is composed of a main body, a first and a second lid. In the main body of the housing, a low pressure and a high pressure port are provided. When the gear machine is operated as a pump, the gears are, for example, with an electric motor in rotary motion, offset, whereby pressurized fluid, in particular hydraulic oil, flows from the low pressure to the high pressure port. When the gear machine is operated as a motor, the pressure fluid flows from the high pressure to the low pressure port, thereby causing the gears to rotate.

Each gear has two circular cylindrical bearing pin, wherein one of the bearing pins are led out as a drive pin out of the housing. On both sides of the gears is ever a bearing body in which said bearing journals are rotatably mounted. The trunnions are slidably received in the main body in the direction of the rotation axis, being pressed against the side surfaces of the gears by pressurized fluid to effect sealing there.

The main body is provided with a piezo sensor which can measure the pressure of the pressurized fluid inside the housing.

The object of the invention is to provide a gear pump which has a sensor which can directly measure the force which acts on the gears. Next, this sensor should be particularly simple. In addition, the sensor should take up as little space as possible, in particular, the external dimensions of the gear machine should not increase.

According to the independent claim, it is proposed that at least one piezo foil be arranged between the bearing body and the housing. Piezo films are characterized in that they generate an electrical voltage when pressure forces are exerted on them. At the contact surface between the bearing bodies and the housing, the bearing forces are transmitted, which act in the rotary bearing of the gears. The electrical voltage at the piezoelectric film arranged there is thus a measure of the transmitted bearing forces and therefore a measure of the forces acting on the gears. As far as the geometry of the gear machine is known, the pressure of the pressure fluid can be calculated from the electrical voltage across the piezo film.

In the dependent claims advantageous refinements and improvements of the invention are given.

The at least one piezo film may consist of polyvinylidene fluoride, which is polarized. Polarized polyvinylidene fluoride, abbreviated PVDF, has a particularly large piezoelectric effect. This is the greater, the more the material is polarized. Accordingly, the proposed piezo film has a particularly high sensitivity, i. the ratio between the change in the electric voltage and the change in the pressure force acting on the piezo film is particularly large. PVDF moreover has the advantage that it is not chemically attacked by the pressurized fluid, so that the piezo film can be used permanently.

The at least one piezo film may have a thickness between 8 μm and 120 μm. With this thickness, the piezo film can easily between the associated bearing body and the housing are housed without the gear machine for this purpose must be increased compared to the conventional gear machine. At the same time, the piezo film has a sufficient measuring sensitivity.

The at least one piezo film can be provided on both sides with a metal layer. The two metal layers each form an electrode at which the piezo voltage, which represents the measurement signal, can be tapped.

Both metal layers can be completely covered with an associated insulating layer. The piezo film abuts both the bearing body and the housing. Both parts are made of metal, in particular steel, cast iron or aluminum, and are therefore electrically conductive. The proposed insulating layer prevents the measurement signal from being falsified by the fact that electrical charges are discharged to the housing or the bearing body. It should be noted that the piezo film can deliver only extremely small currents. Grounding the metal layer over the housing or bearing body would cause the piezo voltage to collapse immediately.

Both metal layers may be connected to an associated electrical line, which is led out of the housing. About the proposed electrical lines, the piezoelectric film can be connected to an evaluation, which is arranged outside the housing. The evaluation unit is intended to convert the electrical voltage on the piezo film into a meaningful measured value, namely a force value or a pressure value. For this purpose, the evaluation unit is preferably equipped with an analog-to-digital converter and with a programmable digital computer.

The at least one piezo film can be arranged on the side of the low-pressure connection. The low-pressure connection typically has a larger cross-sectional area than the high-pressure connection, so that cavitation does not occur there. The gears are in pressure from the high pressure port in Pressed down direction of the low pressure port, so that a arranged in the region of the low pressure port piezoelectric film is subjected to pressure and thus emits a meaningful measurement signal.

The piezo film can be arranged at the height of the axis of rotation of an associated gear with respect to a Y-axis, which is defined by the line connecting the axes of rotation of two intermeshing gears. The piezo film thus measures only a force component which is aligned transversely to the Y-axis. This can be very accurately converted into the pressure of the pressure fluid. The directed in the direction of the Y-axis force component of the bearing forces is not only caused by the pressure forces, but also by the forces acting in meshing engagement.

The bearing body may be integrally formed, wherein two meshing gears are rotatably mounted in this. The one-piece bearing body prevents from the outset that forces acting in the Y direction are transmitted between the bearing body and the housing, so that the conversion of the measured bearing force to the pressure of the pressure fluid can be performed more easily.

Each gear may be associated with a piezo film. Due to the drive torques acting on the gears, different measured values are to be expected for the different piezo foils. By using a plurality of piezo foils, on the one hand, the driving torques can be determined. On the other hand, the influences of the drive torques in the calculation of the pressure of the pressure fluid can be calculated out.

The housing may have an interior which has a constant cross-sectional shape in the direction of the axes of rotation of the gears, wherein the outer peripheral surface of the at least one bearing body is adapted to said cross-sectional shape, wherein the at least one piezoelectric film is arranged on the outer peripheral surface of the bearing body. This per se known design of the housing and the bearing body is particularly well suited for receiving the piezoelectric film according to the invention, since it can be easily inserted between the bearing body and the housing, where at most slight adjustments to the piezoelectric film must be made.

An information memory containing calibration data for the piezo film may be attached to the housing. The measuring sensitivity of the piezo film according to the invention has a large scattering. In order to obtain accurate measurement results, therefore, the exact relationship between the bearing forces of the gears or the pressure of the pressure fluid and the voltage of the piezo film must be determined by trial and error for each individual gear machine. The results of this calibration are to be stored in the proposed information memory so that they are readily available for later evaluation of the measurement signal. The information store may be, for example, an optical matrix or bar code. However, electronic information stores, for example in the form of an RFID tag, may also be provided. The information memory can also be integrated in the already mentioned evaluation unit, as far as it is mounted on the housing.

Fig. 1

eine Explosionsansicht einer erfindungsgemäßen Zahnradmaschine;

Fig. 2

einen Querschnitt der Zahnradmaschine nach Fig. 1; und

Fig. 3

einen grobschematischen Querschnitt der Piezofolie.

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

Fig. 1

an exploded view of a gear machine according to the invention;

Fig. 2

a cross section of the gear machine after Fig. 1 ; and

Fig. 3

a rough schematic cross section of the piezo film.

Fig. 1 shows an exploded view of a gear machine 10 according to the invention. The gear machine 10 comprises a housing 31; 40; 41, which consists of a main body 31 made of aluminum, at its two opposing front ends 34, a first and a second cover 40; 41 are arranged. The parts 31; 40; 41 are held together by four bolts 44, of which in Fig. 1 only one is shown. The present invention is applicable regardless of the exemplary housing distribution shown for any housing.

In the main body 31 are two mutually mirror-symmetrical bearing body 50 and two gears 12; 13 recorded. The axes of rotation of the gears 12; 13 extend parallel to a longitudinal axis 22. The interior 11, which is enclosed by the main body 31 and the two bearing bodies 50, is substantially fluid-tight to the gears 12; 13 matched, which mesh with each other in external engagement. In particular, the bearing bodies 50 are located on the opposite flat side surfaces 21 of the gears 12; 13, wherein the main body 31 at the tooth tips of the gears 12; 13 is present. The inner peripheral surface of the main body 31 has a constant cross-sectional shape in the longitudinal direction 22, the bearing bodies 50 being adapted to this cross-sectional shape with very little play so as to be slidably received in the main body 31 in the longitudinal direction 22.

The gear 12 is integrally formed with a shaft 14 which passes through the first cover 40 with a drive pin 15 from the housing 31; 40; 41 stands out. In the first cover 40, a radial shaft seal 43 is arranged, which sealingly bears with its sealing lip on the shaft 14, so that there can escape any pressurized fluid. Between the main body 31 and the first and second covers 40; 41 is provided in each case a cover seal 42 in the form of an O-ring made of rubber. The axis 16 and the shaft 14 each form two bearing journals 20, which are rotatably mounted in the two bearing bodies 50 in an associated bearing bore 51. The bearing bore 51 is formed by a separate bushing, so that when the gear machine 10 is running at low speed, no excessive wear on the corresponding plain bearings occurs.

Attention is also drawn to the axial seal 53 and the associated support member 54 on the back of the two bearing body 50. The axial seal 53 is located on the associated first and second cover 40; 41 on. On the opposite side it lies on the support member 54. The axial seal 53 delimits two pressure fields from each other, in each of which the pressure at the high pressure port 33 and the pressure at the low pressure port 32 acts. Thereby, the bearing body 50 slidably received in the main body 31 against the flat side surface of the gears 12; 13 pressed so that a pressure-tight seal is given.

The low and high pressure port 32; 33 are arranged on the main body 31. In the in Fig. 1 As shown delivery state, they are each closed with a separate plug 35, wherein the low pressure port 32 has the larger diameter and thus the larger plug 35.

Fig. 2 shows a cross section of the gear machine 10 after Fig. 1 , wherein the cutting plane passes through the axes of rotation 63 of the two gears. The gap 62 between the bearing body 50 and the main body 31 of the housing is shown greatly exaggerated in order to better identify the position of the piezo film 70 can. In fact, this gap 62 is designed so narrow that almost no pressure fluid under high pressure from the region of the gears can pass through the gap 62, while at the same time the mobility of the bearing body 50 relative to the main body 31 is maintained. In particular, the bearing body 50 lies directly and over the entire area on the piezo film 70, which in turn rests directly and on the entire surface on the main body 31 of the housing.

The Y-axis is defined by the line connecting the axes of rotation 63 of the two gears. The X ₁ and X ₂ axes each extend perpendicular to the Y axis through the axis of rotation 63 of an associated gear. Each gear is associated with a separate piezo film 70, which is arranged in the direction of the Y-axis at the height of the relevant gear. The associated X ₁ or X ₂ axis thus cuts the piezo film 70 in the center. Accordingly, the piezo film 70 measures only in the direction of the X ₁ - or X ₂ axis directed force component of the bearing force 64 of the respective gear. Said bearing force 61 is typically directed from the high pressure port 33 to the low pressure port 32. Since it is mainly caused by the pressure at the high pressure port 33, the one over wide pressure acting on the gear wheels, this pressure can be determined from the voltage on the piezo film 70. The low-pressure connection 32 is raised by its larger cross-sectional area of the high-pressure port 33 to avoid cavitation. The present gear machine is preferably operated as a pump, as shown by the indicated flow directions 61 of the pressurized fluid and the directions of rotation 60 of the tooth edges.

The two piezo films 70 are connected via two electrical lines 71 to an evaluation unit 72, wherein for the sake of clarity, only the electrical lines 71 of the upper piezo film 70 are shown. The evaluation unit 72 includes an analog-to-digital converter, with which the electrical voltage at the associated piezo film 70 is digitized. Furthermore, a programmable digital computer is provided which can calculate a numerical value for the bearing forces of the gears or the pressure of the pressure fluid from the digital measured values determined in this way. For this he uses the calibration data, which are stored in an information memory 74, which is mounted on the housing. By way of example only, an electronic information memory 74 is shown in the present case, which is connected via a cable to the evaluation unit 72. Just as well, a matrix code or an RFID tag can be attached to the housing, the content of which is read once with a suitable reading device and permanently stored in the evaluation unit 72. The evaluation unit 72 is connected to a signal lamp 73, which can indicate, for example, an overload condition of the gear machine 10. An overload condition is given, for example, when the voltage across the piezo foils 70 exceeds a predetermined threshold for at least a predetermined period of time. By the signal lamp 73 is then indicated that the gear machine 10 requires maintenance.

Fig. 3 shows a rough schematic cross section of the piezo film 70. In the uninstalled state, the piezo film 70 is formed in the form of a flat plate, wherein the thickness 81 of the PVDF layer 80, for example, 28 microns. PVDF is the abbreviation for the plastic polyvinylidene fluoride. When installed in the gear machine, the piezo film 70 is elastically bent into the appropriate shape. The Piezo voltages caused thereby are eliminated in the evaluation of the measuring voltage by the evaluation unit. The PVDF layer 80 is provided on both sides with a metal layer 82, to each of which one of the already mentioned electrical lines 71 is connected. The entire piezo foil 70 is surrounded by an insulating layer 83 made of plastic, so that in particular an electrical contact between the metal layers 82 and the housing or the bearing body is excluded.

LIST OF REFERENCE NUMBERS

10

gear machine

11

inner space

12

gear

13

gear

14

wave

15

drive journal

16

axis

20

pivot

21

Side surfaces of a gear

22

longitudinal direction

31

main body

32

Low pressure port

33

High pressure port

34

front end

35

sealing plug

40

first lid

41

second lid

42

cover gasket

43

Radial shaft seal

44

bolts

50

bearing body

51

bearing bore

53

axial seal

54

support element

60

Direction of rotation of the gears

61

Flow direction of the pressure fluid

62

Gap between bearing body and housing

63

Rotary axis of a gear

64

Bearing force exerts a bearing pin on the bearing body

70

piezofoil

71

electrical line

72

evaluation

73

Warning light

74

information store

80

PVDF layer

81

Thickness of the PVDF layer

82

metal layer

83

insulating

Claims (12)

1. Gear wheel machine (10), in particular a pump or a motor, having at least two gear wheels (12; 13) which mesh with one another in external engagement, wherein the at least two gear wheels are surrounded by a housing (31; 40; 41) having a low-pressure and a high-pressure connection (32; 33), wherein each gear wheel (12; 13) has at least one bearing peg (20) which is rotatably mounted in an associated bearing body (50) that is received in the housing (31; 40; 41) such that it can slide along the axis of rotation (63) of the associated gear wheel (12; 13),
   characterized in that at least one piezo film (70) is arranged between the bearing body (50) and the housing (31; 40; 41).
2. Gear wheel machine according to Claim 1, characterized in that the at least one piezo film (70) is made of polyvinylidene fluoride which is polarized.
3. Gear wheel machine according to one of the preceding claims,
   characterized in that the at least one piezo film (70) has a thickness (81) of between 8 µm and 120 µm.
4. Gear wheel machine according to one of the preceding claims,
   characterized in that the at least one piezo film (70) is provided with a metal layer (82) on both sides.
5. Gear wheel machine according to Claim 4,
   characterized in that both metal layers (82) are completely covered with an associated insulation layer (83).
6. Gear wheel machine according to Claim 4 or 5,
   characterized in that the two metal layers (82) are each connected to an associated electric line (71) that leads out of the housing (31; 40; 41).
7. Gear wheel machine according to one of the preceding claims,
   characterized in that the at least one piezo film (70) is arranged on the side of the low-pressure connection (32).
8. Gear wheel machine according to one of the preceding claims,
   characterized in that the piezo film is arranged, with respect to a Y-axis defined by the line connecting the axes of rotation (63) of two gear wheels (12; 13) that are meshed with one another, at the level of the axis of rotation (63) of an associated gear wheel (12; 13).
9. Gear wheel machine according to one of the preceding claims,
   characterized in that the bearing body (50) is of one-piece design, wherein two gear wheels (12; 13) that are meshed with one another are rotatably mounted therein.
10. Gear wheel machine according to one of the preceding claims,
    characterized in that each gear wheel (12; 13) is assigned a piezo film (70).
11. Gear wheel machine according to one of the preceding claims,
    characterized in that the housing (31; 40; 41) has an internal space (11) whose cross-sectional shape is constant in the direction of the axes of rotation (63) of the gear wheels (12; 13), wherein the outer peripheral surface of the at least one bearing body matches said cross sectional shape, wherein the at least one piezo film (70) is arranged on the outer peripheral surface of the bearing body (50).
12. Gear wheel machine according to one of the preceding claims,
    characterized in that an information store (74), containing the calibration data for the piezo film (70), is attached to the housing (31; 40; 41).

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