End position detection of a variable hydraulic machine

Abstract

The invention relates to a method and a device for determining of at least one end position of a displacement element of an adjustable hydraulic machine, in particular of the axial piston type, shiftable or displaceable between two ends position a by means of a displacement unit between a first end position and a second end position. According to the invention the determination of having reached an end position of displacement takes place by means of a measurement circuit, whose electrical characteristics are changed jumpily when an end position is reached. This is done by connecting a partial branch of the measuring circuit with earth, when a moveable element comes into electric contact with a limit stop assigned to the corresponding end position.

Claims

1. A method for determining of at least one end position of a displacement element of a hydraulic machine displaceable or shiftable between two end positions, the hydraulic machine being variable in its displacement or conveying volume by means of the displacement element, wherein an electric contact between the displacement element and an electric component of an electric measuring circuit is established, when the end position is reached by the displacement element; the method comprising a step of determining that the end position is reached based on an analyzed change of electrical parameters of the measuring circuit induced by the electrical contact.

2. The method according to claim 1, wherein the electric components comprise a resistance, a capacity or an inductivity.

3. The method according to claim 1, wherein one of the captured parameters is the resistance of the measuring circuit or the current flowing in the measuring circuit.

4. The method according to claim 1, wherein the measuring circuit is a resonant circuit, whose frequency or amplitude is captured.

5. A variable hydraulic machine whose displacement or conveying volume is adjustable by means of a displacement element of a displacement unit, the displacement element displaceable between a first end position and a second end position, wherein the hydraulic machine comprises electrical components forming part of an electrical measuring circuit and are assigned to at least one of both end positions, such that an electrical contact between the electrical components arranged in a machine housing of the hydraulic machine and the displacement element can be established, if the displacement element reaches one of the two end positions.

6. The hydraulic machine according to claim 5, wherein the displacement element comprises electrical components, which can be brought in contact with the electrical components in the machine housing or with a voltage conducting line of the measuring circuit.

7. The hydraulic machine according to claim 5, wherein the hydraulic machine comprises a solenoid, with which the displacement element of the displacement unit is actuable, wherein the solenoid is part of the measuring circuit.

8. The hydraulic machine according to claim 5, wherein the hydraulic machine comprises an electronic control unit, by means of which the current through the solenoid can be set and monitored.

9. The hydraulic machine according to claim 5, wherein the hydraulic machine comprises at least one adjusting screw for determining one of the two end positions of the displacement element, and that a first contact of an electrical component is arranged isolated from a mechanical contact area of the adjustment screw, wherein the contact area can be contacted electrically conductive by the displacement element when the end position is reached.

10. The hydraulic machine according to claim 5, wherein a second contact of the electrical component is connected electrically conductive to the measuring circuit.

11. The hydraulic machine according to claim 5, wherein the electric component is a resistor, a condensator or an inductor.

12. The hydraulic machine according to claim 5, wherein the electric component is a resistor, which is connected electrically parallel to the solenoid in at least one end position of the displacement element.

13. The hydraulic machine according to claim 5, wherein a line, which connects the power source of the measuring circuit with an electrical component, runs via a light emitting electric component, in particular a light emitting diode.

14. The method according to claim 2, wherein one of the captured parameters is the resistance of the measuring circuit or the current flowing in the measuring circuit.

15. The method according to claim 2, wherein the measuring circuit is a resonant circuit, whose frequency or amplitude is captured.

16. The hydraulic machine according to claim 6, wherein the hydraulic machine comprises a solenoid, with which the displacement element of the displacement unit is actuable, wherein the solenoid is part of the measuring circuit.

17. The hydraulic machine according to claim 6, wherein the hydraulic machine comprises an electronic control unit, by means of which the current through the solenoid can be set and monitored.

18. The hydraulic machine according to claim 7, wherein the hydraulic machine comprises an electronic control unit, by means of which the current through the solenoid can be set and monitored.

19. The hydraulic machine according to claim 6, wherein the hydraulic machine comprises at least one adjusting screw for determining one of the two end positions of the displacement element, and that a first contact of an electrical component is arranged isolated from a mechanical contact area of the adjustment screw, wherein the contact area can be contacted electrically conductive by the displacement element when the end position is reached.

20. The hydraulic machine according to claim 7, wherein the hydraulic machine comprises at least one adjusting screw for determining one of the two end positions of the displacement element, and that a first contact of an electrical component is arranged isolated from a mechanical contact area of the adjustment screw, wherein the contact area can be contacted electrically conductive by the displacement element when the end position is reached.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, the invention is explained with the help of embodiments depicted in the Figures. In the depicted embodiments the invention is shown only in the example of a hydraulic machine of the bent axis-type. However, the inventive idea also encompasses hydraulic machines of the swash plate-type, whose displacement element is a swash plate. Needless to say that the inventive idea is also applicable in variable radial piston machines, so this type of hydraulic machine is also encompassed by the inventive idea. The Figures show the following:

(2) FIG. 1 shows a part of a section view of a hydraulic machine according to the state of the art;

(3) FIG. 2 shows a detail view of one embodiment of the invention;

(4) FIG. 3 shows a detail view of a further embodiment of the invention; and

(5) FIG. 4 shows a modification of the embodiment according to FIG. 2.

DETAILED DESCRIPTION

(6) In FIG. 1 shows a detailed view of a variable hydraulic machine 1 of the axial piston type according to the invention in a section view. In a machine housing 2, of which only a small part is shown, a cylinder block 3 is arranged on a yoke 4 for example being a displacement element 4 for hydraulic machines of the bent axis type. The non-shown pistons in the cylinder block 3 are operated in the known manner by a rotating drive mechanism or are driving a driving shaft, according to whether a pump or motor operation of the hydraulic machine is intended. These details are known to a person skilled in the art, such that further explanations hereto are renounced.

(7) Yoke 4 is mounted in housing 2 jointly displaceable with cylinder block 3, wherein the corresponding end positions of displacement are given by adjusting screws 5 or by other fixed or adjustable parts of the hydraulic machine. In FIG. 1 only one adjusting screw 5 is shown exemplarily. Here, the screw is assigned to a minimum angle of displacement. When reaching this minimum angle, a first end portion 15 of the yoke 4 contacts a front face of the adjustment screw 5 thus forming an limit stop 6. It is self-evident that such an adjustment screw can also be assigned to the maximum angle of displacement of yoke 4, against which the second end portion 16 of yoke 4 abuts. In this embodiment yoke 4 plays the role of a displacement element 4.

(8) The displacement of yoke 4 together with cylinder block 3 is effected by means of a displacement unit 7, whose casing 8 is firmly attached to machine housing 2 of hydraulic machine 1. In casing 8 of displacement unit 7 a displacement spool 9 is arranged movable longitudinally. The displacement of displacement spool 9 is controlled by solenoid 10 acting on a control spool. The control spool (not shown) controls in common way fluid flow rates which act on displacement spool 9 and determine its position. Here, a spring 11 is used as a mechanic return. Displacement spool 9 acts via a rod serving as a carrier for yoke 4 of hydraulic machine 1. Thus, an axial displacement of displacement spool 9 leads to a correspondent displacement of yoke 4 and therewith of cylinder block 3. In this manner the displacement or the conveying volume of the cylinders in the cylinder block 3 is adjusted. The control of solenoid spool 10, which is commonly realized as proportional magnet, i.e. its supply with current is done by a not shown electronic control unit with which the hydraulic machine 1 is operated.

(9) According to FIG. 1, as an example, Casing 8 of displacement unit 7 is provided with an end cap 13 serving as an limit stop 14, for example for the maximum displacement of the displacement spool 9. Hence, this limit stop 14 defines the maximum displacement position of yoke 4. Therefore, limit stop 14 can take over the function of an limit stop 6 formed by displacement screw 5. Needless to say that for a person skilled in the art, an analog minimum or maximum displacement position of yoke 4 at limit stop 14 is encompassed by the inventive idea as well.

(10) FIG. 2 shows an inventive hydraulic machine in a partial section view according to FIG. 1. In the following Figures all reference signs are maintained for the denomination of equal structural features. The general structure and way of operation of the hydraulic machine 1 corresponds to the details given by means of FIG. 1.

(11) In FIG. 2 the inventive measuring circuit 20 is shown comprising a current or power source 22. The power source 22 is part of a non-shown electronic control unit of hydraulic machine 1 and, for example, serves as power supply of solenoid 10, with which it is operatively connected via lines 23a, 23b. Therefore, solenoid 10 forms part of measuring circuit 20. One of line 23a or 23b is connected to earth, which, for example, is formed by the general earth of hydraulic machine 1. Hereby, one can assume that hydraulic machine 1 consists of metal, hence, being electrical conductive. Earth 26 may be formed by the earth of a not shown electronic control unit for hydraulic machine 1 as well, for example, formed by an inlet pin of a microcontroller for fault monitoring.

(12) The other part of measuring circuit 20 is built according to the invention by a further line 23c and, for example, by resistors 27a and 27b being connectable to ground 26 parallel to solenoid 10. Resistor 27a is assigned to adjustment screw 5; Resistor 27b to yoke 4. Resistor 27a and the corresponding line 23 are mounted electrically isolated within adjustment screw 5, wherein part 29 of line 23c ends at front face 17 of adjustment screw 5 serving as an limit stop 6. This part 29 of line 23c forms a contact area 30 on front face 17 being electrically isolated from the rest of front face 17. The first end portion 15 of yoke 4 assigned to adjustment screw 5 also shows a contact surface capable to establish electrically conductive contact with contact area 30 of adjustment screw 5. This case occurs if yoke 4 is at the opposite limit stop, for instance in the position of the lowest or biggest displacement, i.e. if end portion 15 of yoke 4 contacts limit stop 6 arranged on front face 17 of adjustment screw 5. In this position a partial current of current or power source 22 is connected via lines 23c, 29 and the resistors 27a and 27c to earth 26. Resistor 27c however can be formed by the reduced conductivity of the material of hydraulic machine 1 such that a separate discrete resistor 27c can be omitted.

(13) If the electrical contact between the contact areas of yoke 4 and the adjustment screw 5 is closed, as descript already above, a partial current of measuring circuit 20 flows through solenoid 10 and a further partial current flows through the branch of measuring circuit 20 which is built by the lines 23c and 29 and the resistors 27a and 27b to earth 26. This can be identified by a jumpy change in the resistance of measuring circuit 20 in the moment the contact is closed. This change of resistance can be seen for example by a change of current or voltage in the measuring circuit and can be detected by the electronic control unit of the hydraulic machine. Thus, its occurrence is a secure indication that yoke 4 has reached one of its end positions of displacement.

(14) By the selection of the resistors 27a and 27b it should be considered that the partial current flowing over the same is significantly lower than the current flowing over solenoid 10. Otherwise, with the closed contact between contact area 30 of adjustment screw 5 and the yoke 4, a non-admissible high reduction of current flowing through the solenoid 10 would occur and would lead to a jumpy and undesired change of the displacement angle of yoke 4.

(15) In implementation of the invention it is further possible to substitute resistors 27a and 27b by capacitors and/or inductivities. Thereby, the change of parameters of the measuring circuit 20 occurring by contact of the adjustment screw 5 with yoke 4 can, for example, detected by a change in frequency or amplitude in the resonant circuit.

(16) In FIG. 3 a further embodiment of the invention is shown, wherein similar parts are denominated with the same reference signs as in FIGS. 1 and 2. As described above, one branch of the measuring circuit 20 is built by magnet coil 10 and lines 23a and 23b connected to the current or voltage source 22. The other branch of measuring circuit 20 leads over line 23c and over resistors 28a and 28b to earth 26. Here, the resistor 28a is arranged in end cap 13 of displacement element 7, wherein its outlet contact is conducted electrically isolated to a contact area 18 of limit stop 14 arranged in end cap 13. As shown in FIG. 3, contact area 19 faces contact area 18 in the end position of displacement spool 9, wherein both contact areas 18, 19 are connected electrically conductive. From contact area 19 in displacement spool 9 an isolated line 31 leads over resistance 28b to earth 26. In this embodiment displacement spool 9 functions as displacement element 4. As displacement spool 9 is coupled via rod 12 with yoke 4, the end position of displacement spool 9 corresponds in a functional way to the end position of yoke 4, and, hence, to the one of cylinder block 3.

(17) In FIG. 3 limit stop 14 is depicted as a fixed stopper arranged in end cap 13 or formed by the same. Naturally, this stopper 14 can be adjustable by implementation of the invention. This eventually permits a vernier adjustment of the designated end position of displacement unit 4 and, thus, of cylinder block 3. As can be seen easily by a person skilled in the art, at this limit stop 14 the maximum as well as the minimum angle of displacement of the axial piston machine, i.e. the maximum or the minimum displacement or conveying volume is reached.

(18) The embodiment according to FIG. 4 corresponds in structure and function to the one of FIG. 2. However, it differs therefrom by the arrangement of a light emitting diode (LED) 32 or another lighting device arranged in line 23c connecting the power source 22 of measuring circuit 20 with electrical component 27a. Light emitting diode 32 lights if a contact between electrical component 27a and ground 26 is established and indicates that displacement element 4 has reached the end position. Hence, light emitting diode 32 serves as an optical indicator. It is obvious that line 23, only shown schematically in FIGS. 1 to 4, can be conducted through the working machine such that light emitting diode 32 may be arranged for example in an indication area of the electronic control unit of the hydraulic machine. Commonly, the electronic control unit is a separate assembling group of the hydraulic machine being connected with the same via electric lines. For the present explanation of the inventive idea and for simplification reasons only, it is assumed that the electronic control unit is arranged on the hydraulic machine.

(19) The way of operation of this embodiment of the invention is as follows: In a position of displacement spool 9 between the end positions of its displacement no electric conductive contact between the contact areas 18 and 19 in the end cap 13 and in the displacement spool 9 is established. Thus, no current flows through line 23c and through resistors 28a and 28b. However, if the displacement spool reaches the end position, which is shown in FIG. 3, the contact areas 18 and 19 at limit stop 14 and at displacement spool 9 contact each other such that a current via resistors 28a and 28b flows to earth 26. The caused jumpy change of the situation in the measuring circuit 20 serves for detecting that the displacement spool 9 has reached the end position and, thus, also yoke 4 of the hydraulic machine 1 coupled with displacement spool 9.

(20) In modification of the invention a modification of the conditions in measuring circuit 20 can consist also therein that at the beginning of a take-off of displacement element 4 from its end position, current through the electrical component or through the electrical components stops flowing, as the contact to earth is interrupted. The jumpy reduction of current or of the total resistance in the measuring circuit 20 then constitutes an indication in such regard that the designated end position is left. Such a signal can be used also by the electronic control unit of hydraulic machine 1. This case, for example, occurs if the current in the solenoid is raised continuously in a ramp-like manner beginning at zero current. As the displacement spool commonly starts with a movement only, if the solenoid current reaches a predetermined minimum value, this value has to be reached in order that the displacement spool 9 or the displacement element 4 takes off from the limit stop (contact) and, thereby, interrupting the partial current in that branch of measuring circuit 20. Thus, the inventive method is suitable to indicate the reaching as well as the departure from an end position of displacement elements 4, 9.

(21) As displacement spool 9 preferably consists of metal and is connected electrically conductive via casing 8 or other parts with the overall earth of hydraulic machine 1, in realization of the invention, it is possible to waive resistance 28b and to bring contact area 18 at stopper 14 directly into contact with the facing front face of displacement spool 9. In this case the modification of displacement unit 7 is limited to the end cap 13 only, which has to be provided with a resistor 28a, a contact area 18 at stopper 14 and with a line 23c. The corresponding electrically conductive contact areas 18 and 19 are preferably designed such that they are elevated with regard to the surrounding surface. This guarantees a reliable electric contact if the two contact areas facing each other came into contact.

(22) In implementation of the invention, at least for a person skilled in the relevant art, it is possible without more to combine the two embodiments mentioned above in one hydraulic machine 1. Here, for example, one of both end positions of displacement of displacement element 4, e.g. the yoke 4, in which end portion 15 of yoke 4 abuts against front face 17 of adjustment screw 5 (c.f. FIG. 2), is detected by means of a measuring circuit 20, for example the one according to FIG. 2. The other end position of displacement shown in FIG. 3, corresponding to the other extreme displacement of yoke 4, can be determined, for example, by means of a measuring circuit 20 according to FIG. 3.

(23) Thus, the invention provides with a simple and reliable method for detecting that a displacement element of an adjustable hydraulic machine, e.g. of an axial piston type, has reached an end position of displacement, as well provides with a design of a hydraulic machine suitable for carrying out the method.

(24) 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.