Abstract
A sensor arrangement for indirect detection of a torque of a rotatably mounted shaft includes a sensor with at least one sensor element arranged in the surroundings of a bearing of the shaft. The bearing is linked to a supporting structure. The sensor element is configured to detect a proportion of a bearing force acting in a predetermined direction. The torque of the shaft is configured to be calculated from the acting proportion of the bearing force. The sensor has at least one sensor body with an outer contour that supports a corresponding sensor element and is pressed into a receiving hole. The sensor element has a predetermined distance and a predetermined angle to the bearing.
Claims
1. A sensor arrangement for indirect detection of a torque of a rotatably mounted shaft, comprising: a sensor that includes at least one sensor element arranged in the surroundings of a bearing of the shaft, the bearing linked to a supporting structure, the sensor element configured to detect a proportion of a bearing force acting in a predetermined direction, the torque of the shaft configured to be calculated from the acting proportion of the bearing force, wherein the sensor has at least one sensor body with an outer contour, the sensor body supporting a corresponding sensor element and being pressed into a receiving hole, and wherein the sensor element is at a predetermined distance and a predetermined angle relative to the bearing.
2. The sensor arrangement as claimed in claim 1, wherein the receiving hole for the corresponding sensor body is defined by the supporting structure.
3. The sensor arrangement as claimed in claim 1, wherein the sensor element is accommodated in a housing, the housing having an outer contour that is pressed into a receiving hole defined by the supporting structure.
4. The sensor arrangement as claimed in claim 3, wherein the pressed-in outer contour of the housing has at least one recess.
5. The sensor arrangement as claimed in claim 3, wherein the receiving hole for the sensor body is defined in a support structure of the housing, and wherein the housing transmits the acting proportion of the bearing force via the supporting structure to the sensor body.
6. The sensor arrangement as claimed in claim 1, wherein the at least one sensor element is implemented as a piezoresistive sensor element configured using thin layer technology and has a metallic base, to which an insulating layer and a functional layer of piezoresistive materials are applied, and wherein the functional layer has four resistor structures that are wired up to form a Wheatstone bridge.
7. The sensor arrangement as claimed in claim 1, wherein the sensor comprises at least two sensor elements, arranged at different positions in the surroundings of the bearing.
8. The sensor arrangement as claimed in claim 7, wherein the at least two sensor elements have different detection directions and detect proportions of the acting bearing force acting in different directions.
9. The sensor arrangement as claimed in claim 8, wherein the detection directions of two adjacent sensor elements extend substantially perpendicularly to each other.
10. The sensor arrangement as claimed in claim 1, wherein the sensor comprises at least one evaluation electronics unit connected electrically to at least one sensor element.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 shows a schematic illustration of a plurality of shafts and gears to illustrate the occurrence of bearing forces which can be detected by exemplary embodiments of the sensor arrangement according to the invention for indirect detection of a torque of a rotatably mounted shaft.
[0018] FIG. 2 shows a schematic illustration of a first exemplary embodiment of a sensor arrangement according to the invention for indirect detection of a torque of a rotatably mounted shaft.
[0019] FIG. 3 shows a sectional illustration of the sensor arrangement according to the invention from FIG. 2.
[0020] FIG. 4 shows a schematic illustration of a second exemplary embodiment of a sensor arrangement according to the invention for indirect detection of a torque of a rotatably mounted shaft.
[0021] FIG. 5 shows a plan view of a receiving hole for a sensor body of a sensor element which can be used in exemplary embodiments of the sensor arrangement according to the invention for indirect detection of a torque of a rotatably mounted shaft.
[0022] FIG. 6 shows a plan view of an exemplary embodiment of a sensor body having a sensor element which can be used in exemplary embodiments of the sensor arrangement according to the invention for indirect detection of a torque of a rotatably mounted shaft and can be pressed into the receiving hole from FIG. 5.
[0023] FIG. 7 shows a sectional illustration of the receiving hole from FIG. 5 and a sectional illustration of the sensor body from FIG. 6 before the operation of pressing the sensor body into the receiving hole.
[0024] FIG. 8 shows a plan view of an exemplary embodiment of a sensor element which can be used in exemplary embodiments of the sensor arrangement according to the invention for indirect detection of a torque of a rotatably mounted shaft.
[0025] FIG. 9 shows a sectional illustration of the sensor element from FIG. 3.
[0026] FIG. 10 shows a schematic illustration of a third exemplary embodiment of a sensor arrangement according to the invention for indirect detection of a torque of a rotatably mounted shaft.
[0027] FIG. 11 shows a sectional illustration of the sensor arrangement according to the invention from FIG. 10.
[0028] FIG. 12 shows a schematic plan view of an exemplary embodiment of a sensor for a sensor arrangement according to the invention for indirect detection of a torque of a rotatably mounted shaft.
[0029] FIG. 13 shows a schematic sectional illustration of a fourth exemplary embodiment of a sensor arrangement according to the invention for indirect detection of a torque of a rotatably mounted shaft.
[0030] FIG. 14 shows a schematic sectional illustration of a fifth exemplary embodiment of a sensor arrangement according to the invention for indirect detection of a torque of a rotatably mounted shaft.
EMBODIMENTS OF THE INVENTION
[0031] FIG. 1 serves to illustrate the occurrence of bearing forces. FIG. 1 shows multiple shafts W1, W2, W3, which are connected to one another by gears Z1, Z2, Z3. The arrangement serves to transmit a first torque M1 from a first shaft W1 via a second torque M2 of a second shaft W2 to a third shaft W3, which has a third torque M3. This is carried out by the gears Z1 and Z3 connected to the shafts W1, W3 via an intermediate gear Z2, which is connected to the second shaft W2. Here, two forces act on a bearing of the second shaft W2. Firstly, a force F.sub.12 or F.sub.21 acting at the point of contact between the first gear Z1 and the second gear Z2 also acts on the bearing of the second shaft W2, since the second gear Z2 is supported there via the second shaft W2. Secondly, the force F.sub.32 or F.sub.23 acting between the third gear Z3 and the second gear Z2 must be absorbed by the bearing. From the addition of these two forces F.sub.L2 and F.sub.32 the result is the bearing force F.sub.L2 acting overall on the bearing of the second shaft W2. The bearing absorbs this force F.sub.l2 and passes it on to the surrounding structure. The resultant material stresses within this structure lead to material strains, which are proportional to the bearing force F.sub.L2 and thus proportional to the torque M2. For this purpose, a hole B1 is introduced into the structure 3 surrounding the bearing 7, which hole is compressed by the force F.sub.L2 illustrated in FIG. 1, according to the dashed illustration B2. These material stresses can be detected by means of a piezoresistive sensor element. Finally, by means of a suitable evaluation electronics unit, the torque M2 is determined therefrom.
[0032] As can be seen from FIGS. 2 to 14, illustrated exemplary embodiments of a sensor arrangement 1, LA, 1B, 1C, 1D according to the invention for indirect detection of a torque of a rotatably mounted shaft 5 each comprise a sensor 10, 10A, 10B, 10C, 10D, which comprises at least one sensor element 30 arranged in the surroundings of a bearing 7 of the shaft 5, said bearing being linked to a supporting structure 3, which sensor element detects a proportion of a bearing force F.sub.L acting in a predetermined direction, from which force the torque of the shaft 5 can be calculated. According to the invention, the sensor 10, 10A, 10B, 10C, 10D has at least one sensor body 20 with an outer contour 24, which sensor body supports a corresponding sensor element 30 and is pressed into a receiving hole 12, 52.1, wherein the sensor element 30 is at predefined distance and a predefined angle relative to the bearing 7.
[0033] As can be seen further from FIGS. 2 and 3, the illustrated first exemplary embodiment of the sensor arrangement 1 according to the invention has a sensor element 30, which is pressed into a receiving hole 12 of the supporting structure 3. In a way analogous to the hole B1 in FIG. 1, the receiving hole 12 in FIGS. 2 and 3 is also compressed in accordance with the force F.sub.L shown. In a first design variant, the sensor element 30 is pressed directly into the supporting structure 3 via the sensor body 20. In a second design variant, the sensor element 30 is pressed via the sensor body 20 into a support structure 52 of a sensor housing 50, 50A, which is in turn pressed into the receiving hole 12. In both cases, the compression is transmitted to the sensor element 30 and can be detected and evaluated by the latter.
[0034] The precise relationship between the output signal from the sensor element 30 and the bearing force F.sub.L proportional to the torque depends critically on the positioning of the sensor element 30. This places certain requirements on the position and manufacturing tolerances but also opens up high degrees of freedom in the application. Thus, for example, with a sensor design conceived once, greater torques can also be measured if the sensor element 30 is merely placed at a somewhat greater distance from the shaft 5 than previously or at a different angle relative to the direction of the bearing force F.sub.L. As can be seen further from FIG. 4, multiple sensor elements 30 can also be placed around the bearing 7, in order thus, for example, to monitor the direction of the bearing force F.sub.L of the shaft 5 under changing conditions.
[0035] As can be seen further from FIG. 4, the sensor 10A in the second exemplary embodiment of the sensor arrangement 1A according to the invention has multiple sensor elements 30. Here, a first sensor element 30 is arranged underneath the bearing 7 in the illustration and detects a proportion of the bearing force F.sub.L that acts downward. A second sensor element 30 is arranged on the left beside the bearing 7 in the illustration and detects a proportion of the bearing force F.sub.L that acts to the left. A third sensor element 30 is arranged above the bearing 7 in the illustration and detects a proportion of the bearing force F.sub.L that acts upward. A fourth sensor element 30 is arranged on the right beside the bearing 7 in the illustration and detects a proportion of the bearing force F.sub.L that acts to the right. From the detected proportions of the force, magnitude and direction of the acting bearing force can be determined. In addition, interference variables, such as transverse forces, on the bearing 7 can be eliminated, or a redundant signal can be generated.
[0036] As can further be seen from FIGS. 5 to 9, the sensor element 30 has a sensor body 20 made of steel, which has a highly precise outer contour 24 produced by turning, for example, which outer contour is suitable to be pressed into a correspondingly shaped inner contour 14 of the receiving hole 12, 52.1. In order to make the pressing-in operation easier, an insertion bevel 16, 26 can be formed respectively on the edge of the receiving hole 12, 52.1 and on the edge that is to be inserted of the sensor body 20. Underneath the highly precise round outer contour 24 there is a contour of any desired shape which can be used as a stop 22 during the pressing-in operation. In the exemplary embodiment illustrated, the contour is formed as a hexagon. Following the joining or pressing-in, the sensor element 30 can also be secured additionally by one or more spot welds.
[0037] On the steel sensor body 20 there is a thin layer which is composed at least of an insulating layer 33 (e.g. silicon oxide) and a functional layer 32. Piezoresistive materials, such as NiCr alloys, platinum, polysilicon, titanium oxynitride and so on can be used as functional layer 32. At least four resistors 34 are structured from the functional layer 32 by means of suitable methods such as, for example, wet etching, dry etching, laser ablation and so on, and are wired up to form a Wheatstone bridge. The resistor structures 34 are typically implemented in the form of meanders and arranged in such a way that they are sensitive in pairs to strains in spatial directions which are perpendicular to one another. Feed lines 36 to the bridge and contact-making surfaces 38 can be implemented in the plane of the functional layer 32 or in an additional metallization plane. In addition, the functional layer 32 can be protected by a passivation layer (e.g. silicon nitride) or other measures (e.g. gel coating).
[0038] As can be seen from FIGS. 10 and 11, the sensor 10B in the illustrated third exemplary embodiment of the sensor arrangement 1B according to the invention has a sensor element 30, the sensor body 20 of which is pressed directly into the receiving hole 12 of the supporting structure 3. In addition, the sensor 10B in the illustrated exemplary embodiment has no dedicated housing. The protection of the sensor elements 30 and an associated evaluation electronics unit 40 against environmental influences is ensured by the transmission housing, for example, which here also comprises the supporting structure 3. The protection of the sensor element 30 and of the evaluation electronics unit 40 against oil spray or abrasion can be carried out by means of a protective gel or a protective cap. The sensor element 30 is pressed via its sensor body 20 into the transmission housing or the supporting structure 3 within the transmission, in the vicinity of the bearing 7. Following the joining or pressing-in, the sensor element it can be secured additionally by one or more spot welds. The sensor element 30 detects the material strains arising on account of the bearing forces and converts said strains by means of the bridge circuit formed from resistor structures 34 into an output voltage. The sensor element 30 is connected, for example via wire bonding, to internal contact points 48 of a circuit board 42, on which there is a suitable evaluation circuit 44, which, for example, is implemented as an ASIC (application specific integrated circuit). The evaluation circuit 44 evaluates the bridge voltage and provides an output signal proportional to the torque in the form of a voltage (e.g. 0-5 V), a current (e.g. 4-20 mA) or in digital form. This signal can be picked up at external contact points 46, for example, by means of cables that are soldered on or plugged on. The power supply of the entire sensor 10B is likewise provided via these external contact points 48. Via the cables, the signal can be led to the outside or passed on to a control device likewise integrated in the transmission housing.
[0039] As can be seen from FIGS. 12 to 14, the sensor element 30 in the illustrated exemplary embodiments has a housing 50, 50A. The housing 50, 50A offers many advantages during application. In its press-in area, the housing 50, 50A is configured in such a way that lateral compressions are transmitted to the sensor element 30. The sensor element 30 is pressed via the sensor body 20 into a receiving hole 52.1 in a support structure 52 which runs radially relative to this part of the housing 50, 50A and therefore in the direction of the external force F.sub.L. Following the joining or pressing-in, the sensor element 30 can additionally be secured by one or more spot welds.
[0040] In the area of the sensor element 30 and the support structure 52, the housing 50, 50A has a highly precise external contour 54, which is suitable for being pressed into a correspondingly configured receiving hole 12 of the supporting structure 3. The force-fitting connection produced in this way ensures that the compressions arising on account of the bearing force F.sub.L are transmitted via the sensor housing 50, 50A to the sensor body 20 and thus to the sensor element 30. As can be seen further from FIG. 14, the outer contour 54A the sensor housing 50A in the illustrated exemplary embodiment has multiple recesses 54.1 in the area of the sensor element 30, in order to achieve central introduction of the force F.sub.L onto the sensor element 30.
[0041] As can be seen further from FIGS. 13 and 14, there is relative freedom in the configuration of the rest of the housing 50, 50A. Care must merely be taken that no further forces are coupled into the signal path via the sensor housing 50, 50A, since this would lead to undesired cross-sensitivity of the sensor arrangement 1C, 1D. This is best achieved if there are no further points of contact between the sensor housing 50, 50A and other components. An introduction of force via the cabling is likewise to be avoided. As can be seen further from FIGS. 13 and 14, the housing 50, 50A in the illustrated exemplary embodiments is essentially composed of a steel sleeve, which is closed off on one side by a cover 56 and on the other side by a connector 58. Together with a suitable connector, such a construction can also be implemented in a hermetically sealed manner, so that use directly in the transmission oil becomes possible. The sensor element 30 converts the material strains into an output voltage in a way analogous to the exemplary embodiments already described, by means of the bridge circuit formed from the resistor structures 34. The signal evaluation is carried out in a manner analogous to the exemplary embodiments already described. In contrast to the third exemplary embodiment, in which the circuit board 42 is arranged substantially parallel to the supporting structure 3, in the fourth and fifth exemplary embodiment the circuit board 42A with the evaluation circuit 44A is arranged at right angles to the supporting structure 3 and within the housing 50, 50A. In a way analogous to the third exemplary embodiment, the sensor element 30 is, for example, connected electrically to internal contact points 48A, for example by wire bonding. The output signal from the evaluation circuit 44A can be output via the external contact points 46A and the connector 58.
[0042] Exemplary embodiments of the present invention provide a sensor arrangement for indirect detection of a torque of a rotatably mounted shaft which arrangement, advantageously, can be used everywhere where economical detection of the torque of drive shafts is required.
