SWASH PLATE ANGLE SENSOR

Abstract

The invention is directed to a swashplate angle sensor (10) for a variable displacement hydraulic unit (1). The hydraulic unit (1) comprising a housing (2), within which a swashplate (3) with a rod shaped feedback-link (12) fixedly attached to the swashplate (3) is arranged pivotable around a swashplate axis (7). The angle sensor (10) comprising a magnet (16) mounted rotatable on a magnet carrier (13), and a sensor (15) for sensing the orientation of the magnet (16). The magnet carrier (13) is located in a control block (14) attached to the housing (2) and is located parallel to the feedback-link (12). The magnet carrier (13) is rotatable around a sensor axis (18) being parallel to the swashplate axis (7). A linkage spring (11) provides a connection between the feedback-link (12) and the magnet carrier (13) such that a pivoting of the swashplate (3) with the feedback-link (12) causes a rotation of the magnet carrier (13).

Claims

1. A swashplate angle sensor for a variable displacement hydraulic unit comprising a pivot-able swashplate with a rod shaped feedback-link attached thereon, the angle sensor comprising a magnet mounted on a magnet carrier rotatable around a sensor axis, and a sensor for sensing the orientation of the magnet, wherein the angle sensor comprises a linkage element providing a mechanical linkage between the feedback-link and the magnet carrier such that a pivoting of the swashplate moves the linkage element via the feedback-link and causes a rotation of the magnet carrier.

2. The swashplate angle sensor of claim 1, wherein the linkage element comprises a spring with a U-shaped elongated hole-section surrounding the feedback-link in a tight slide-able contact therewith, and with two legs, the ends of which are coupled to the magnet carrier.

3. The swashplate angle sensor of claim 1, wherein the linkage element comprises an elongated hole-section surrounding the feedback-link in a tight slide-able contact therewith, and an adjoining leg, the end of which is coupled to the magnet carrier.

4. The swashplate angle sensor of claim 2, wherein the length of the elongated hole-section of the linkage element is greater than the adjoining diameter of the feedback-link.

5. The swashplate angle sensor of claim 1, wherein the ends of the linkage element protruding from the magnet carrier are bent at an angle of at least 90.

6. The swashplate angle sensor of claim 1, wherein the linkage element is a linkage spring of torsional type with a rectangular, round or oval cross-section.

7. The swashplate angle sensor of claim 1, wherein the ends of the linkage element are in slide-able contact with an inner wall of the control block.

8. The swashplate angle sensor of claim 1, wherein the sensor axis and/or the longitudinal axis of the magnet carrier is parallel to the longitudinal axis of feedback-link and/or to the swashplate pivot axis.

9. The swashplate angle sensor of claim 1, wherein the magnet carrier is situated in a housing or in a control block of the hydraulic unit.

10. A control block of a variable displacement hydraulic unit comprising a swashplate angle sensor of claim 1 suitable to be fixed on a housing of the hydraulic unit and suitable to be coupled to a feedback link of the hydraulic unit.

11. The swashplate angle sensor of claim 3, wherein the length of the elongated hole-section of the linkage element is greater than the adjoining diameter of the feedback-link.

12. The swashplate angle sensor of claim 2, wherein the ends of the linkage element protruding from the magnet carrier are bent at an angle of at least 90.

13. The swashplate angle sensor of claim 4, wherein the ends of the linkage element protruding from the magnet carrier are bent at an angle of at least 90.

14. The swashplate angle sensor of claim 2, wherein the linkage element is a linkage spring of torsional type with a rectangular, round or oval cross-section.

15. The swashplate angle sensor of claim 4, wherein the linkage element is a linkage spring of torsional type with a rectangular, round or oval cross-section.

16. The swashplate angle sensor of claim 5, wherein the linkage element is a linkage spring of torsional type with a rectangular, round or oval cross-section.

17. The swashplate angle sensor of claim 2, wherein the ends of the linkage element are in slide-able contact with an inner wall of the control block.

18. The swashplate angle sensor of claim 4, wherein the ends of the linkage element are in slide-able contact with an inner wall of the control block.

19. The swashplate angle sensor of claim 5, wherein the ends of the linkage element are in slide-able contact with an inner wall of the control block.

20. The swashplate angle sensor of claim 6, wherein the ends of the linkage element are in slide-able contact with an inner wall of the control block.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Exemplary embodiments of the invention not limiting the scope of the inventive idea are shown in FIGS. 1 to 5 and will be described in the following.

[0021] FIG. 1 shows a schematic cross-section of a hydraulic unit having a swashplate angle sensor according to an exemplary embodiment of the invention;

[0022] FIG. 2 depicts a detail of the schematic cross-section shown in FIG. 1;

[0023] FIG. 3 depicts a schematic cross-section of a part of the hydraulic unit shown in FIG. 1 according to line A-A indicated in FIG. 2;

[0024] FIG. 4 shows the cross-section according to FIG. 3 with an exemplary used linkage spring in an uncompressed condition,

[0025] FIG. 5 depicts the cross-section of FIG. 4 in a non-neutral operating condition of the hydraulic unit and the exemplary used linkage spring in a compressed condition.

DETAILED DESCRIPTION

[0026] FIG. 1 shows a schematic cross-section of a variable displacement hydraulic unit 1 having a swashplate angle sensor 10 according to an exemplary embodiment of the invention. The hydraulic unit 1 comprises a housing 2 that contains a swashplate 3 supported on a cradle bearing 4 and rotatable about a swashplate pivot axis 5, indicated by a dash-dotted line. The rotation of the swashplate 3 is usually controlled by means of a servo-system 40 using electromagnetic, mechanical or hydraulic actuators. Connected to the swashplate 3 is a feedback link 12 which protrudes into a control block 14 of hydraulic unit 1 and is oriented in such a manner that its longitudinal axis 26 (see FIG. 2) is parallel to the axis of rotation 5 of swashplate 3. The generally rod-shaped feedback link 12 is firmly connected to the swashplate 3 and participates in any rotation of the swashplate 3 thereby returning the angular position of the swashplate 3 with respect to the axis of drive shaft 8. Feedback link 12 interacts with feedback lever 17 connected to the control spool of control unit 30 of hydraulic unit 1. Such a control unit and its functioning for instance is described in DE 10 2004 033 314 B3 and should therefore not be descript in detail here.

[0027] Housing 2 of hydraulic unit 1 also contains a cylinder block 6 with several work pistons 7. Cylinder block 6 is connected to a drive shaft 8 and is rotatable about the axis of drive shaft 8. The drive shaft 8 extends through an enlarged opening 9 in the swashplate 3, permitting a tilting of swashplate 3 relative to drive shaft 8. The ends of the pistons 7 protruding from cylinder block 6 are in slide-able contact with the swashplate 3. By tilting swashplate 3 via servo system 40 triggered by control unit 30 the stroke of pistons 7 is modified, i.e. the displacement of hydraulic unit 1 is changed and therewith the position of feedback link 12 in control block 14. These features and the general functioning of variable displacement hydraulic units 1 are well known such that further detailed description thereof can be omitted here as well.

[0028] In an exemplary embodiment of the invention shown in FIG. 1 hydraulic unit 1 comprises a swashplate angle sensor 10 housed in control block 14 being attached to housing 2 of hydraulic unit 1. The angle sensor 10 comprises a generally rod-shaped magnet carrier 13 supported rotatable about its longitudinal axis 18 in a wall of control block 14. This longitudinal axis 18 is parallel to the longitudinal axis 26 of feedback link 12 which in turn is parallel to pivot axis 5 of swashplate 3. A magnet 16 is firmly affixed to one end of magnet carrier 13 and rotatable therewith. A magnetic rotation sensor 15 is provided on control block 14 directly adjacent to magnet 16. Thereby, any rotation of magnet 16 is sensed by sensor 15 and transformed into an electrical signal that can be utilized by a control system (not shown) associated with hydraulic unit 1 for controlling the operation thereof.

[0029] According to the invention, between feedback link 12 and magnet carrier 13 a linkage is provided by means of a mechanical linkage element 11. In a preferred embodiment of the invention linkage element 11 consists of a linkage spring, generally bent in a hairpin shape, as it will be described in more detail below.

[0030] In the following figures all reference numerals denoting similar constructive features will be retained. Also, linkage element 11 and linkage spring 11 will be used as synonymous terms.

[0031] FIG. 2 shows a detail of the schematic cross-section of hydraulic unit 1 according to FIG. 1. Depicted is a control block 14 with the upper section of feedback link 12 that extends into control block 14. Linkage spring 11 extends from feedback link 12 into a wall section of control block 14 and is connected to magnet carrier 13 mounted rotatable in a wall section of control block 14. Leg 21 of linkage spring 11 is held for instance in a slit in magnet carrier 13 and provide a mechanical connection between magnet carrier 13 and feedback link 12 such that a circular-arc movement of feedback link 12 causes a rotation of magnet carrier 13. On the upper face of magnet carrier 13 a magnet 16 is mounted and rotates with magnet carrier 13 when linkage spring 11 imparts a rotation to magnet carrier 13. On the outside of control block 14 a magnetic rotation sensor 15 is situated opposite magnet 16. Sensor 15 and magnet 16 are separated, e.g. by a non-magnetic membrane that protects magnet 16 and, preferably, also seals the interior of hydraulic unit 1, preventing leakage of hydraulic fluid or entry of dirt.

[0032] FIG. 3 depicts a schematic cross-section of a part of the hydraulic unit shown in FIG. 1 according to line A-A indicated in FIG. 2. The hydraulic unit 1 shown in FIG. 3 is in a neutral operating condition in which the tilt angle of swashplate 3 with respect to the axis of rotation of drive shaft 8 is zero degrees (see FIG. 1).

[0033] As can be seen in FIG. 3 linkage spring 11 has a closed U-shaped section 20, respectively an elongated hole-section 20 that defines an oblong opening that surrounds an axial cross section (see also FIG. 2) of feedback link 12. Two legs 21 of linkage spring 11 are held in a slit 23 in the base of magnet carrier 13. The ends 22 of legs 21 of linkage spring 11 protruding from magnet carrier 13 are bent in the embodiment shown in FIG. 3 at an angle of approximately 90 and are in slide-able contact with inner wall 24 of grove 25 in control block 14. This configuration of linkage spring 11 supports the centring of linkage element 11 on feedback link 12. However, it has the drawback of undesirable friction of the ends 22 of linkage spring 11 on an inner wall 24 of control block 14. In another embodiment it is preferred to bend the ends 22 of the legs 21 of linkage spring 11 at an angle of more than 90, as shown in an exemplary manner in FIGS. 4 and 5, and/or to eliminate any contact between the ends 22 of linkage spring 11 and other parts of hydraulic unit 1 not being the magnet carrier 13.

[0034] FIG. 4 shows the cross-section according to FIG. 3 with a linkage spring 11 used in an exemplary preferred embodiment of the invention in an uncompressed not final assembled condition. In this Figure only one leg 21 of linkage spring 11 is inserted in the slit 23 at the base of magnet carrier 13. Visible is the generally hairpin shape of linkage spring 11 with its closed U-shaped section 20, legs 21 and ends 22. Ends 22 are bent at an angle of more than 90 and serve to fix linkage spring 11 in slot 23 of magnet carrier 13. In this embodiment the ends 22 of linkage spring 11 are not in contact with inner wall 24 of control block 14 and move freely in an grove 25 provided in the inner wall 24 of control block 14 containing also the bore for magnet carrier 13.

[0035] Linkage spring 11 is preferably made of an elastic metal, such as spring steel, and may have a rectangular, round or oval cross-section. However, one can imagine linkage element 11 made of a plastic material, for instance in a reinforced version. In the final assembled state, shown in FIGS. 2, 3 and 5, the U-shaped section 20 of linkage spring 11 is in intimate contact with feedback link 12. The oblong opening provided by the U-shaped section 20 in the linkage element 11 permits a relative motion, i.e. a distance change of feedback link 12 with respect to the axis of the magnet carrier 13. This allows to accommodate the movement of the feedback link 14 on a circular arc centred on the tilt axis 5 of swashplate 3 and indicated in FIG. 5 by a double headed arrow 29 depicting the trajectory of feedback link 12.

[0036] Both sides of the U-shaped section 20 of linkage spring 11 press against the sides of feedback link 12 when both ends 22 of linkage spring 11 are inserted in slit 23 of magnet carrier 13. This ensures a positive contact between feedback link 12 and linkage spring 11 at any time, and enables to compensate for any production inaccuracies or wear of feedback element 12 or linkage spring 11 itself, however, permitting a relatively free movement of feedback link 12 in the direction of the oblong opening 20 provided by the U-shaped section of linkage spring 11. Friction is reduced under operation conditions by the (unavoidable) presence of leakage of hydraulic fluid in the housing 2 of hydraulic unit 1 serving as a lubricant.

[0037] In operation of swashplate angle sensor 10 of the invention any movement of the swashplate 3 is shared by feedback link 11, because the latter is fixedly connected therewith. Thus feedback link 12 moves together with swashplate 3 on a circular arc centred on tilt axis 5 of swashplate 3. This movement imparts a rotation of linkage spring 11 which is transmitted to magnet carrier 13. Thereby, the longitudinal axis 18 of magnet carrier 13 defines the axis of rotation of linkage spring 11. Magnet 16 moves/rotates together with magnet carrier 13 and thus changes the orientation of magnet 16 with respect to the sensing element of magnetic sensor 15, thereby inducing a corresponding signal in sensor 15. This signal provides a measurement value of the actual angle of swashplate 3 relative to a given reference position. This being normally the neutral, i.e. the zero angle position, if, for instance, the swashplate being orthogonal to the axis of driving shaft 8 of hydraulic unit 1, i.e. work pistons 7 do not show any displacement volume.

[0038] FIG. 5 depicts the cross-section of FIG. 4 in a non-neutral operating condition of hydraulic unit 1 and shows the exemplary used linkage spring 11 in a compressed condition. Swashplate 3, of which only a portion is visible in FIG. 5, is displaced relative to its neutral position, depicted in FIGS. 3 and 4. Feedback link 12 has followed this displacement and moved along a circular arc, indicated by the double headed arrow 29. This causes a rotation of linkage spring 11 imparted to magnet carrier 13. It is evident from FIG. 5 that the distance between the centre of feedback link 12 and the axis of rotation 18 of magnet carrier 13 varies as the swashplate 3 tilts, because feedback link 12 moves on a convex arc relative to the fixed axis of rotation 18 of magnet carrier 13. However, the nonlinear response of the magnet angle of rotation versus the tilt angle of swashplate 3 caused by this effect is of a purely geometrical origin that can be compensated readily by the given actual dimensions and distances between the different components of the sensor system.

[0039] In summary, the invention provides a simple and robust sensor system for the determination of a tilt angle of the swashplate in variable displacement hydraulic units. Such sensor systems can be installed also in existing hydraulic units requiring only relative minor modifications and machining. Further, such an inventive angle sensor can be installed also in hydraulic units of the bent axis construction type. Hereby the feedback link is located on the displacement element guiding the displacement of the cylinder block.

[0040] While the present disclosure has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this disclosure may be made without departing from the spirit and scope of the present disclosure.