Patent Application
20250172131
The invention relates to a method with a hydraulic pressure medium supply arrangement for an open hydraulic circuit according to the preamble of claim 1 and a hydraulic pressure medium supply arrangement according to claim 10.
A hydraulic pressure medium supply arrangement with an adjustable axial piston machine is known from the document EP 3 770 428 A1 from Rexroth. An adjustment cylinder is controlled by a control device, which comprises a cascaded control loop from an external control loop and an inner control loop. The external control loop forms manipulated variables as a function of setpoint and actual values, in particular of a working pressure, a pivot angle or delivery volume and a torque, of the axial piston machine. Prioritizing the smallest of these manipulated variables via a minimum value generator then sets the variable to be adjusted, which is at the upper limit compared to its setpoint value.
However, such a control does not offer the option of limiting a manipulated variable of the external control loop downwards, in particular in the case of system-side limitations in the form of minimum limit values, as prioritization via the minimum value generator only results in an upper limit for the manipulated variables. For example, there can be requirements for the pivot angle of a swashplate of an axial piston machine, such that the swashplate does not fall below a minimum pivot angle and thus a predetermined minimum delivery or displacement volume of the axial piston machine. This ensures, among other things, that a minimum volume flow is always provided for a consumer. In the event that the actual working pressure of an axial piston machine is higher than a predetermined setpoint working pressure, although a predetermined minimum conveyance or displacement volume or a minimum pivot angle of the axial piston machine has already been reached, a pressure controller of the external control loop would provide a negative manipulated variable value for the inner control loop and swivel in the axial piston machine to reduce the pressure. At the same time, a pivot angle controller of the external control loop would output a positive value or zero to swing out the axial piston machine or hold the pivot angle so that the predetermined minimum pivot angle is not undershot. The generic prioritization of the smallest manipulated variable via a minimum value generator would thus select the working pressure as the control variable/variable to be controlled and consequently reduce the pivot angle even further below the predetermined minimum threshold value.
In contrast, the present invention is based on the task of providing a method with a hydraulic pressure medium supply arrangement by means of which a lower limitation/restriction of a hydraulic operating variable, preferably a pivot angle or a displacement volume, a working pressure, or a torque of a hydraulic machine in the form of an axial piston machine, is made possible. Furthermore, a hydraulic pressure medium supply arrangement is to be created that carries out this method.
The first of the problems is solved by a method having the features of claim 1 and the second by a hydraulic pressure medium supply arrangement having the features of patent claim 10. Advantageous configurations and further developments of the respective invention are the subject of dependent claims.
The invention relates to a method with a hydraulic pressure medium supply arrangement for an open hydraulic circuit having a hydraulic machine, preferably an axial piston machine, with an adjusting mechanism which comprises an adjustment cylinder with an adjustment piston for adjusting a displacement volume/delivery volume or a pivot angle of the hydraulic machine and an electrically proportionally controllable (pilot) valve. The valve can be used to control an inflow into and/or an outflow from a control chamber of the adjustment cylinder limited by the adjustment piston. The valve is thereby controlled via an electronic control unit of the hydraulic pressure medium supply arrangement. The method includes the steps of reading a respective actual value and a setpoint value associated therewith of a displacement volume or a pivot angle of the hydraulic machine and/or a working pressure and/or a torque of the hydraulic machine, which can be determined therefrom, into a first external control loop of the control unit and determining a first manipulated variable from a control deviation between the respective actual value and the setpoint value associated therewith via the control unit. The method includes the further steps of determining a setpoint adjustment speed of the displacement volume or pivot angle speed as a function of at least the first manipulated variable or first manipulated variables via the first external control loop of the control unit. According to the invention, the method comprises the steps of reading a respective actual value and a setpoint value associated therewith of the displacement volume or pivot angle and/or the working pressure and/or the torque and determining at least one second manipulated variable from the respective actual value and the associated setpoint value via the control unit, such that the step of determining the setpoint adjustment speed also takes place as a function of the second manipulated variable or manipulated variables.
In other words, the electronic control unit of the hydraulic pressure medium supply arrangement has a first external control loop for hydraulic control variables, preferably for the pivot angle or displacement volume/conveyance volume, the working pressure or the torque of a hydraulic machine, in particular an axial piston machine. This first external control loop has the respective actual values of the hydraulic machine and the setpoint values associated as input variables. The first external control loop determines the first control variables from the individual control deviations/control differences from the difference between the respective setpoint and actual values. In addition, the control unit preferably comprises a second external control loop for the hydraulic operating variables. The second external control loop comprises the respective actual values of the hydraulic machine and the specified/predetermined setpoint values associated therewith as input values. Preferably, these predetermined setpoint values are minimum limit values. The second external control loop of the control unit determines second control variables from the control deviations of these input variables. Preferably, one of these manipulated variables of the two external control loops is then fed to a subordinate inner control loop as a setpoint adjustment speed for the pivot angle or displacement volume of the hydraulic machine. The inner control loop also reads an actual adjustment speed as a derivation of the actual pivot angle or actual displacement volume of the hydraulic machine and carries out a comparison operation between the setpoint and actual adjustment speed. Preferably, the selection of the manipulated variable that is fed to the inner control loop is carried out via a selection unit.
This provides a method with a hydraulic pressure medium supply arrangement by means of which hydraulic operating variables of a hydraulic machine can be restricted/limited downwards in order to comply with corresponding minimum limit values, for example a minimum pressure or a minimum volume flow adjustable via the pivot angle, so that components of a pressure medium supply arrangement are operated in an allowable range.
In a further aspect of the invention, the at least one of the second manipulated variables represent a limitation of the working pressure as a function of a maximum allowable working pressure.
In an advantageous embodiment of the invention, a controller is downstream of the second external control loop of the control unit and the step of limiting the working pressure as a function of the maximum allowable working pressure is carried out via this controller downstream of the second external control loop. Alternatively, the controller for pressure cut-off is designed as the second external control loop of the control unit and the method step of limiting the working pressure as a function of the maximum allowable working pressure is carried out as the second external control loop via this controller.
In other words, the method has an (additional) pressure cut-off step. The corresponding controller is preferably upstream of a further minimum value generator, such that the pressure cut-off function in this embodiment of the electronic control unit has the highest priority. Thus, this arrangement is comparable to a lowest control axis of a hydro-mechanical controller. The controller for pressure cut-off is preferably provided with a separate parameterization and a setpoint value specification in order to enable different dynamics and setpoint values compared to the working pressure controller in the first external control loop. Accordingly, the pressure control dynamics and the pressure cut-off specification as well as the pressure cut-off dynamics are decoupled and separately adjustable from one another.
In a further aspect of the invention, the method comprises a step of prioritizing a smallest of the first manipulated variables via a minimum value generator of the control unit. The step of determining the setpoint adjustment speed is carried out at least as a function of the prioritized, smallest of the first manipulated variables.
In other words, the selection unit of the electronic control unit comprises a determination device, preferably in the form of a minimum value generator. This has the output variables of the first external control loop in the form of the first manipulated variables as input variables. The minimal value generator then prioritizes/selects the manipulated variable with the smallest value as the setpoint adjustment speed. This selection automatically activates only one controller of the first external control loop, which is associated with the control variable prioritized by the minimum value generator. Here, the leading control variable is the manipulated variable whose control deviation is the smallest, and either the pivot angle or the displacement volume, the working pressure or the torque is precisely adjusted, while the two other variables are below their predetermined setpoint value.
With the aid of this selection via the minimum value generator, the control variable whose actual value is at the upper limit compared to its associated setpoint value is ultimately controlled via the first external control loop. For example, the control variable whose actual value is furthest above the corresponding setpoint value is prioritized, as the manipulated variable is therefore the smallest/most negative. An upper limitation of the hydraulic operating variables is thereby achieved.
In a further aspect of the invention, the at least one of the second manipulated variables represent a limitation of a minimum setpoint pivot angle and/or a minimum setpoint displacement volume and/or a minimum setpoint output pressure and/or a minimum setpoint torque.
In a further aspect of the invention, the method comprises a step of prioritizing a largest of the second manipulated variable(s) and the smallest of the first manipulated variables prioritized by the minimal value generator via a maximum value generator of the control unit. The step of determining the setpoint adjustment speed is then carried out as a function of the prioritized, largest variable.
In other words, the selection unit of the electronic control unit comprises a second determination device, preferably in the form of a maximum value generator. This has as input variables the smallest manipulated variable prioritized by the minimum value generator in the form of the setpoint adjustment speed from the first external control loop and the manipulated variables from the second external control loop. The maximum value generator prioritizes the manipulated variable with the largest value from these input variables and outputs the setpoint adjustment speed prioritized on the basis of this MAX selection as the output variable.
Based on the prioritization by the maximum value generator, the control variable that falls below an associated minimum setpoint value is always controlled in the electronic control unit. In the event that all actual sizes of the hydraulic operating variables are greater than the predetermined minimum setpoint values/limit values, the second external control loop outputs the value less than zero for the manipulated variables of the control variables. A comparison is then made between the value less than or equal to zero and the manipulated variable prioritized by the minimum value generator from the first external control loop and the maximum value generator then prioritizes the larger value. This achieves a lower limit of the hydraulic operating quantities of the hydraulic machine, as a control of the hydraulic operating variables that fall below a predetermined minimum setpoint value is prioritized. A pivoting behavior of a hydraulic pump is then defined by the parameterization of the controllers, for example.
In addition, a further selection unit can be connected upstream of the maximum value generator, which blocks the (output) manipulated variables of the second external control loop or withholds them from the maximum value generator in the event that the manipulated variables of the second external control loop assume maximum negative values for all control variables, i.e. if none of the minimum setpoint values have undershot. In such a case, the manipulated variable prioritized by the minimum value generator is always also prioritized by the downstream maximum value generator, as no control via the second external control loop is necessary here.
In a further aspect of the invention, the method comprises a step of reading in an actual adjustment speed and the setpoint adjustment speed determined as a function of at least the first manipulated variable(s) in an internal control loop of the control unit subordinated to the first external control loop.
In a further aspect of the invention, the method comprises a step of limiting the setpoint adjustment speed, which has been determined based on the output variables of both external control loops, as a function of a predetermined maximum setpoint adjustment speed and/or a predetermined minimum setpoint adjustment speed via a controller of the control unit upstream of the inner control loop.
In other words, preferably an additional controller for a limitation/restriction/specification of the setpoint adjustment speed of the pivot angle or displacement volume of a hydraulic machine is downstream of the maximum value generator. In particular, the manipulated variable of the maximum value generator is limited by the additionally predetermined limitation of the adjustment speed upwards and/or downwards, which is preferably adjustable, in order to affect a control dynamics of the pressure medium supply arrangement and to limit the dynamics for the swiveling in and out. This limitation can be a positive or negative maximum of the adjustment speed, for example. The higher the setpoint adjustment speed, the faster the hydraulic machine can swivel out. The dynamics of the hydraulic machine can therefore be overridden externally, independently of a specification of the (first) external control loop, or internally to protect the components. For example, a cavitation, and thus the slowing down of the hydraulic machine dynamics can be avoided, although a higher pivot angle adjustment speed is required in the system in order to adjust the operating variable more quickly.
In the event that the controllers of the (inner and/or external) control loops described above and/or the upstream controller for setpoint adjustment speed limitation and/or the downstream controller for pressure cut-off have at least one controller with an I-portion, the method according to the invention preferably has a step of freezing or reducing the I-portion of the controller(s) with a non-prioritized manipulated variable.
In other words, the controllers of the electronic control unit are preferably designed as PID controllers, the I-portions of which are (partially) reset or frozen when the corresponding controller is not active, i.e. not prioritized by the minimum value generators or the maximum value generator, because another controller or another control variable is dominant. For this reason, after each prioritization step/prioritization process, a minimum or maximum value generator is used to indicate which controller is prioritized in addition to the value of the respective output variable/manipulated variable. Depending on this status message, the corresponding I-portions of the controllers are either activated or deactivated. This prevents a wind-up effect of a controller when prioritizing another controller/control function.
In a further aspect of the invention, in the event that the inner control loop has a control element with an I-portion which is pilot-controlled via a pilot value and whose manipulated variable is limited via a manipulated variable limiter, the method has a step of limiting the I-portion as a function of the pilot control value and the limitation by the manipulated variable limiter via an I-portion limiter.
In other words, in the event that the output variable of a controller with an I-portion, preferably the controller of the inner control loop, is composed of a pilot control/feedforward portion and a controller portion, and the output variable is additionally limited/restricted, the method limits the I-portion of the controller as a function of the pilot control portion, so that a limitation/restriction of the output variable at the (sum) output of the controller is maintained. The controller then only works in up to a saturation in total and has no absolute anti-wind-up limitation. For example, a limitation of the sum output of a piloted controller from pilot portion and (PID) controller portion can be given by a manipulated variable limit. Depending on an operating state of a hydraulic machine, a portion of the manipulated variable is piloted. The difference between the pilot fraction and the manipulated variable limit is thus still available to the (PID) controller. Accordingly, the I-portion of the controller is limited, such that the sum output is not greater than the specification of the manipulated variable limit. The limitation of the I-portion thus results in
This ensures that the controller does not wind up and that there is no additional phase shift or time delay.
In a further aspect of the invention, the method comprises a step of determining a control signal for the valve as a function of a setpoint neutral signal value and an actual signal value via a current controller.
In other words, the output variable/manipulated variable of the inner control loop in the form of a current signal is summed up with a pilot control value of a pilot control device, whereby a neutral flow of the (pilot) valve of the hydraulic pressure medium supply arrangement is pilot-controlled. The resulting setpoint neutral signal value is compared with an actual signal value via a current controller, preferably in the form of a PID controller, whereby a subsequent manipulated variable/control signal is fed to the valve.
The invention further relates to a hydraulic pressure medium supply arrangement for an open hydraulic circuit having a hydraulic machine, an adjusting mechanism, which comprises an adjustment cylinder with an adjustment piston for adjusting a displacement volume or pivot angle of the hydraulic machine and an electrically proportionally controllable (pilot) valve, via which an inflow and/or an outflow is controllable in a control space of the adjustment cylinder limited by the adjustment piston, to apply pressure to the adjustment piston, and with an electronic control unit, which is signal connected to a displacement transducer, a pressure sensor and an actuator of the valve, and which is configured to carry out the method according to the invention.
The present invention will be explained in more detail in the following using advantageous embodiments and with reference to the accompanying figures. The figures are merely schematic in nature and serve solely to understand the invention. It is noted that the features of the individual embodiments can be interchanged with one another and can occur in any combination. Shown are:
The three manipulated variables 18, 22, 26 of the first external control loop 3 formed from control deviations between the setpoint and actual values are fed to a minimum value generator 27, which ensures that only the controller 9, 11 or 13 associated with the setpoint operating point is automatically active. Here, the leading control variable is the manipulated variable whose control deviation is the smallest, and either the pivot angle, the working pressure or the torque is precisely adjusted, while the two other variables are below their predetermined setpoint value. The output variable of the minimum value generator 27 forms a setpoint adjustment speed 29 of the pivot angle, which is fed as the input variable to a maximum value generator 31. The further input variables of the maximum value generator 31 are the output variables or manipulated variables 33, 35, 37 of the respective controllers 39, 40 and 41 of the second external control loop 5. A minimum setpoint pivot angle 43 and the actual pivot angle 16 of the hydraulic machine 10 form the input variables of the controller 39. The controller 40 has a minimum setpoint working pressure 45 and the actual working pressure 21 of the hydraulic machine 10 as input variables, whereas the controller 41 has a minimum setpoint torque 47 and the actual torque of the hydraulic machine 10 as input variables. In this illustrated embodiment of the control unit 1, the controllers 39, 40 and 41 of the second external control loop 5 are also designed in the form of PID control elements. The maximum value generator 31 ensures that only the controller 39, 40 or 41 of the second external control loop 5 or the controller 9, 11 or 13 of the first external control loop 3 prioritized by the minimum value generator 27 is active, which has the manipulated variable with the greatest control deviation. The output variable of the maximum value generator 31 is a setpoint adjustment speed 49 of the pivot angle, which is fed as the input variable to the inner control loop 7. The latter has a control element 51 in the form of a PID element. A further input variable for the control element 51 is an actual adjustment speed 53 of the pivot angle, which results from a time derivation of the actual pivot angle 16. The control element 51 of the inner control loop 7 has a manipulated variable 55 as an output variable in the form of a flow, which is summed up with a pilot control value 57 of a pilot control device 58, whereby a neutral flow of a valve 59 (compare with
Furthermore, the adjusting mechanism 102 includes a cylinder 120. This has an adjustment piston 121 that engages with the swashplate of the axial piston machine 10. The adjustment piston 121 limits a control chamber 122 connected to the pressure line 107. The adjustment piston 121 is acted upon by the pressure medium of the control chamber 122 and spring force of a spring 123, such that it loads the swashplate in the direction of increasing the delivery volume. Furthermore, a pressure sensor 125 is provided, via which the pressure in the pressure line 107 is tapped and reported to the controller 1, wherein the pressure is an actual working pressure 21.
When the pressure medium supply arrangement 100 is in use, the position of the swashplate of the axial piston machine 10 is controlled via the valve 59 and the adjustment piston 116. A conveyed volume flow of the axial piston machine 10 is proportional to the position of the swashplate. The actual working pressure or pump pressure is constantly applied to the adjustment piston 121 or counter-piston biased by the spring 123. When the axial piston machine 10 is not rotating and the adjusting mechanism 102 is depressurized, the swashplate is held in a +100 percent position by the spring 123. When the axial piston machine 10 is driven and the actuator 104 of the valve 59 is de-energized, the swashplate swivels to a zero stroke pressure, as the adjustment piston 116 is pressurized with the pressure medium of the pressure line 107. A balance between an actual working pressure at the adjustment piston 116 and the spring force of the spring 123 is established at a predetermined pressure or pressure range, for example between 8-12 bar. This zero stroke operation is assumed, for example, when the electronics or control unit 1 is de-energized. The valve 59 is controlled via the control unit 1, which is preferably a digital electronics unit, alternatively an analog electronics unit, for example. The control unit 1 processes the required control signals.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2022 200 396.9 | Jan 2022 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2023/050394 | 1/10/2023 | WO |
