Method for Calibrating a Pivot Angle Sensor, Control Means, and Propulsion or Working Machine

Abstract

A method is for calibrating a pivot angle sensor of a hydraulic machine of a propulsion or working machine. A control device is configured to operationally control the hydraulic machine. The control device is also configured to process a sensor signal from the pivot angle sensor. The pivot angle sensor is calibrated, preferably in an automated manner, via the control device.

Claims

1. A method for calibrating a pivot angle sensor of a hydraulic machine of a propulsion or working machine, comprising: controlling the hydraulic machine with a control device; and processing a sensor signal of the pivot angle sensor, with the control device; and calibrating the pivot angle sensor with the control device.

2. The method according to claim 1, wherein the control device performs the calibration of the pivot angle sensor during normal operation of the propulsion or working machine, at a start-up of the propulsion or working machine and/or at intervals.

3. The method according to claim 1, wherein the control device calibrates the pivot angle sensor based on characteristic, pre-specified, and/or intended operating states of the propulsion or working machine.

4. The method according to claim 1, wherein the hydraulic machine is installed as intended in or on the propulsion or working machine.

5. The method according to claim 1, wherein the pivot angle sensor transfers to the control device a pivot-angle-dependent sensor signal, from a the sensor value of which the control device with an assigned pivot angle forms a respective pair of values from the sensor value of the sensor signal and the pivot angle.

6. The method according to claim 5, wherein, calibrating the pivot angle sensor comprises: controlling a state of the hydraulic machine with the control device, the state of the hydraulic machine defined by a design-related pivot angle, a design-related pressure or a design-related pressure-medium volume flow of the hydraulic machine, and assigning the detected sensor value to the pivot angle with the control device.

7. The method according to claim 6, wherein: the design-related pivot angle is a maximum pivot angle of the hydraulic machine or a minimum pivot angle of the hydraulic machine and/or the design-related pressure or the design-related pressure-medium volume flow characterizes an internal leakage of the hydraulic machine.

8. The method according to claim 6, wherein, calibrating the pivot angle sensor comprises: controlling at least two states with the control device, so that at least two value pairs are formed by the control device, and further value pairs are interpolated or extrapolated, and/or controlling the at least two states with the control device and determining further value pairs via a calculation rule.

9. The method according to claim 8, further comprising: controlling the state with the control device over a pre-specified period of time and averaging sensor values of the sensor signal captured in the pre-specified period of time so that an averaged sensor value is determined; and forming at least one of the value pairs with the averaged sensor value using the control device.

10. The method according to claim 8, further comprising: forming at least one of the value pairs, using the control device, with the sensor value captured when the control device controls the state, if when the sensor value is within a predetermined interval.

11. The method according to claim 5, wherein, before the calibrating, the control device assigns to a respective pivot angle a respective nominal value or a respective sensor value determined in a previous calibration of the pivot angle sensor.

12. A control device for a hydraulic machine of a propulsion or working machine, comprising: a pivot angle sensor for the hydraulic machine, wherein the hydraulic machine is controlled with the control device, and a sensor signal of the pivot angle sensor is processed by the control device, wherein the control device is configured to calibrate the pivot angle sensor.

13. The control device according to claim 12, further comprising: a proportional valve, wherein to adjust the pivot angle, the control device is configured to actuate the proportional valve, and wherein a control chamber of an actuating cylinder of the hydraulic machine is acted upon with pressure medium based on a position of the proportional valve, wherein an actuating piston of the actuating cylinder is subjected to the pressure medium via the control chamber, and wherein the pivot angle of the hydraulic machine is changed via the actuating piston.

14. The control device according to claim 12, wherein the control device is included in a propulsion or working machine.

Description

[0041] Preferred exemplary embodiments of the invention are explained in more detail below with reference to schematic drawings. In the drawings:

[0042] FIG. 1 shows a hydraulic pressure-medium supply arrangement,

[0043] FIG. 2A and FIG. 2B in each case are a diagram showing the course of different measured values during the capture of a sensor value which can be assigned to a maximum pivot angle, and

[0044] FIG. 3A, FIG. 3B, in each case are a diagram that shows the course of different measured values during the capture of a sensor value which can be assigned to a minimum pivot angle.

[0045] FIG. 1 shows a hydraulic pressure-medium supply arrangement 1 which has a hydraulic machine in the form of an axial piston machine 2. This has a pivoting cradle for adjusting a delivery volume. The axial piston machine 2 can be used not only as a pump, but also as a motor. Thus, for example, the pivoting cradle is pivotable. It is also conceivable to design and use the axial piston machine 2 only as a pump. The axial piston machine 2 is driven via a drive shaft 4, which can be driven, for example, by an internal combustion engine, such as a diesel unit. Furthermore, a proportional valve 6 is provided, the valve slide of which can be controlled in an electrically proportional manner via an actuator 8. The proportional valve 6 is provided for controlling the axial piston machine 2. A control variable 10 is fed to the actuator 8 by a control means 12. The valve slide of the proportional valve 6 is acted upon in the direction of a basic position by a spring force of a valve spring 14. The spring force acts counter to the actuator force of the actuator 8.

[0046] The axial piston machine 2 is connected on the output side to a pressure line 16.

[0047] Via this line, the axial piston machine 2 can be connected, for example, to a main control valve or a valve block. Via the main control valve or the valve block, the pressure-medium supply can be controlled between the axial piston machine 2 and one or more consumers. A control line 18 branches off from the pressure line 16 and is connected to a pressure connector P of the proportional valve 6. Furthermore, the proportional valve 6 has a tank connector T which is connected to a tank via a tank line 19. In addition, the proportional valve 6 has a working connector A, which is connected to a control chamber 20 of an actuating cylinder 22. The control chamber 20 is thereby delimited by an actuating piston 24 of the actuating cylinder 22. The pivoting cradle of the axial piston machine 2 can be adjusted via the actuating piston 24, so that a pivot angle of the axial piston machine 2 can be changed.

[0048] Furthermore, the hydraulic pressure-medium supply arrangement 1 has a pivot angle sensor 26. A sensor signal 28 captured by the pivot angle sensor 26 is forwarded to the control means 12. The control means 12 is configured such that, from the captured sensor signal 28, it can determine a pivot angle of the axial piston machine 2. The control means 12 can have stored, for example, a characteristic curve, e.g., in a storage medium, wherein the characteristic curve assigns individual sensor values of the sensor signal to the respective pivot angle in order to form value pairs.

[0049] Furthermore, a pressure sensor 30 is provided, which picks up a pressure in the pressure line 16 and reports it to the control means 16, wherein the pressure is an actual output pressure 32.

[0050] In the basic position of the valve slide of the proportional valve 6, the pressure connector P is connected to the working connector A, and the tank connector T is shut off. When the actuator force of the actuator 8 is applied to the valve slide, the valve slide, starting from its basic position, is moved in the direction of switching positions in which the pressure connector P is blocked, and the working connector A is connected to the tank connector T. In the basic position of the valve slide of the proportional valve 6, the actuating piston 24 is thus acted upon by pressure medium from the pressure line 16. Furthermore, a cylinder 34 is provided which has an actuating piston 36 that acts on the pivoting cradle of the axial piston machine 2. The actuating piston 36 delimits a control chamber 38 which is connected to the pressure line 16. Via pressure medium of the control chamber 38 and via the spring force of a spring 40, the actuating piston 36 is acted upon in such a way that it loads the pivoting cradle in the direction of an increase in the delivery volume, i.e., an increase in the pivot angle.

[0051] During a calibration of the pivot angle sensor 26, i.e., when a sensor value is captured which can be assigned to the minimum or maximum pivot angle, the control means 12 controls the proportional valve 6 via the actuator 8.

[0052] For example, during the capture of a sensor value which can be assigned to the minimum pivot angle, the control means can control the proportional valve 6 via the actuator 8 in such a way that the actual output pressure 32, which is measured via the pressure sensor 30, is a pre-specified pressure, e.g., 20 bar, when the pressure line 16 is closed. This means that the valve block or the main control valve with which the pressure line 16 is fluidically connected are blocked.

[0053] When the axial piston machine 2 is not rotating, and there is no pressure in the pressure line 16, the pivoting cradle is held by the spring 40 in a position in which a pivot angle can be approximately 100%. For this reason, a calibration, in which a sensor value is captured which can be assigned to the pivot angle, can preferably take place at the start-up of a working machine 42, which comprises the hydraulic pressure-medium supply arrangement 1. In order to ensure that the pivot angle of the axial piston machine 2 is at 100%, the actuator 8 of the proportional valve 6 can be controlled such that the pressure connector P of the proportional valve 6 is not connected to the working connector A. The actuating piston 36 of the cylinder 34 is then subjected to pressure from the pressure line 16 and from the spring force of the spring 40, while the actuating piston 24 is not acted upon by pressure from the pressure line 16. For this reason, the pivoting cradle of the axial piston machine 2 pivots to 100%.

[0054] FIG. 2a shows a diagram in which measured values captured during calibration, wherein a sensor value is to be captured which can be assigned to the maximum pivot angle, are to be recorded over time. The diagram in FIG. 2a shows a motor speed 44 which corresponds to a rotational speed of the drive shaft 4, which is shown in FIG. 1. Furthermore, the actual output pressure 32 is recorded over time, which, in FIG. 1a, is captured by the pressure sensor 30. Furthermore, a pivot angle 46 of the axial piston machine 2 of FIG. 1 is recorded, wherein the pivot angle 46 is a value which determines the control means 12 of FIG. 1 before calibration of the pivot angle sensor 26 (see FIG. 1) has taken place. Furthermore, a calibrated pivot angle 48 is plotted, wherein this is the pivot angle determined by the control means 12 of FIG. 1 after a calibration has taken place.

[0055] FIG. 2b shows the sensor signal 28 recorded by the pivot angle sensor 26.

[0056] At a time To, a motor driving the drive shaft 4 is started, and in this way the speed 44 of the drive shaft 4 increases from 0 rpm to approximately 950 rpm over the entire recorded time period that is shown in the diagram. If the motor is started at time To, the axial piston machine 2 begins to convey volume, and the actual output pressure 32 in the pressure line 16 begins to rise. The actual output pressure 32 does not rise linearly, but periodically, since, at low revolutions of the drive shaft 4, the piston frequency is visible when the actual output pressure 32 rises. This means that a piston stroke of the axial piston machine 2 generates a corresponding pressure increase of the actual output pressure 32. Furthermore, the pivot angle 46 captured by the control means 12, which is determined before calibration, is 100%. The pivot angle 46 can correspond, for example, to a nominal value of production. That is to say, the measured values shown here can be recorded, for example, during an initial calibration, and the pivot angle 46 can be a pre-specified value which is not determined during a calibration, but which has been pre-specified during production. An initial calibration can take place when a propulsion or working machine is started up for the first time. The calibration is started at time T1. This is defined by the actual output pressure 32, which is captured by the pressure sensor 30, that reaches 20 bar, since it can be assumed that the axial piston machine 2 can be controlled at this point in time via the control means 12, which controls the proportional valve 6. That is to say, at time T1, it can be assumed that the pivot angle is 100%. It can be seen that the pivot angle 48 calibrated by the control means 12 is somewhat smaller at the start of calibration at time T1 than the pivot angle 46 determined by the control means 12 before calibration. Calibration is finished at time T2. At time T2, the actuator 8 of the proportional valve 6 is controlled via the control means 12 in such a way that a pivot angle of the axial piston machine 2 becomes smaller, so that the motor that drives the drive shaft 4 does not overload. Since, during calibration, the axial piston machine 2 conveys with a maximum pivot angle against a closed main control valve or a closed valve block, the actual output pressure 32 can increase quickly and markedly, so that the motor can no longer rotate the drive shaft 4.

[0057] For this reason, it is advantageous if the time period, i.e., the time from T.sub.1 to T.sub.2, is only very short. For example, a time period of T.sub.1 to T.sub.2 can be 80-140 milliseconds, wherein the pivot angle sensor 26 can record approximately one value per millisecond, for example. The sensor signal recorded by the pivot angle sensor 26 is shown in FIG. 2b. From T.sub.1 to T.sub.2, the sensor signal 28 is virtually constant, wherein sensor values fluctuate within a range of approximately 665 to 675 mV. In order to compensate for this fluctuation, the sensor values of the sensor signal 28, which are recorded in the time period from T.sub.1 to T.sub.2, can preferably be averaged. Furthermore, it can be seen in FIG. 2b that the sensor signal 28 may fluctuate within the range from T.sub.0 to T.sub.1, since the control pressure is still not present in this time period, and therefore the pivoting cradle of the hydraulic machine can also fluctuate slightly. Furthermore, in the time period from T.sub.0 to T.sub.1, it is possible that drops in the voltage supply of the control means can occur—in particular, severe drops. For the reasons mentioned above, it is possible that, during an initial phase of ignition, which takes place at time T.sub.0, the sensor signal cannot be reliably evaluated. It is therefore advantageous to start the calibration at T.sub.1. It can also be seen from FIGS. 2a and 2b that the sensor signal 28 behaves inversely proportionally to the pivot angle 46, 48. This means that the larger the sensor signal 28, the smaller the pivot angle 46, 48 assigned by the control means 12.

[0058] FIG. 3a shows various measured values during the calibration of the pivot angle sensor 26, wherein a sensor value is to be captured which can be assigned to the minimum pivot angle. In this example, the minimum pivot angle is defined as the pivot angle at which an actual output pressure 32, which is shown in FIG. 1, is approximately 20 bar against a closed valve—for example, the closed main control valve or the closed valve block. The actual output pressure 32 should be approximately 20 bar against a closed valve, so that an internal leakage can be compensated for, and a control pressure in the pressure line 16 (see FIG. 1) can be maintained. This value is a reference value, which provides sufficient accuracy for calibrating the pivot angle sensor. In FIG. 3a, the sensor signal 28, which is captured by the pivot angle sensor 26 of FIG. 1, is recorded. Since this signal fluctuates very strongly, a filtered sensor signal 50 is also determined and is shown in FIG. 3a by comparison. Furthermore, the pivot angle 46 determined from the sensor signal 28 by the control means 12 (see FIG. 1) is plotted. In FIG. 3b, the actual output pressure 32 is plotted over time.

[0059] It can be seen in FIG. 3a that, when the actual output pressure 32 at the beginning of the measurement up to a time To is 20 bar, the filtered sensor signal 50 (see FIG. 3a) is essentially constant and does not oscillate strongly. The pivot angle sensor 46 determined in the time period is approximately 1%. At time To, the actuator 8 of the proportional valve 6 is controlled via the control means 12 such that the pivot angle of the pump becomes smaller, and thus the actual output pressure 32, which is applied to the pressure line 16, lies within the range of 5 to 10 bar. In this period from T.sub.0 to T.sub.1, the actual output pressure 32 oscillates between 5 to 10 bar, and the sensor signal 28, and thus even the filtered sensor signal 50 (see FIG. 3a), fluctuates more strongly up to time To compared with the sensor signal 28 and the filtered sensor signal 50. For this reason, the pivot angle 46 shown in FIG. 3a also varies within a range of 0% to 2%. Since this fluctuation is very strong, it is difficult to carry out the calibration. If the axial piston machine 2 is controlled via the control means 12 in such a way that the pivot angle is very small, the detected sensor value 28 will fluctuate, and therefore this state will not be suitable for calibration. It is therefore advantageous if the calibration is carried out when the actual output pressure is adjusted to approximately 20 bar. Subsequent to time T1, the proportional valve 6 is controlled via the control means 12 in such a way that the actual output pressure 32 is re-adjusted to approximately 20 bar. As is also shown in the time period up to To, the filtered sensor signal 50 is virtually constant as soon as the pressure 32 has been regulated to approximately 20 bar, and this state is therefore very well-suited for a calibration.

LIST OF REFERENCE SIGNS

[0060] 1 Hydraulic pressure-medium supply arrangement

[0061] 2 Axial piston machine

[0062] 4 Drive shaft

[0063] 6 Proportional valve

[0064] 8 Actuator

[0065] 10 Control variable

[0066] 12 Control means

[0067] 14 Spring

[0068] 16 Pressure line

[0069] 18 Control line

[0070] 19 Tank line

[0071] 20 Control chamber

[0072] 22 Actuating cylinder

[0073] 24 Actuating piston

[0074] 26 Pivot angle sensor

[0075] 28 Sensor signal

[0076] 30 Pressure sensor

[0077] 32 Actual output pressure

[0078] 34 Cylinder

[0079] 36 Actuating piston

[0080] 38 Control chamber

[0081] 40 Spring

[0082] 42 Working machine

[0083] 44 Motor speed

[0084] 46 Pivot angle

[0085] 48 Calibrated pivot angle

[0086] 50 Filtered sensor signal