Method for controlling an adjustable hydraulic machine

Abstract

The invention relates to a method for controlling an adjustable hydraulic machine (2), in particular an adjustable axial piston machine, wherein the hydraulic machine has an adjusting device which is controlled by an electrical control current in order to effect the adjustment of the displacement, in particular of a pivot angle (6), of the hydraulic machine, wherein controller current signal values ​​for the electroproportional valve are determined by a control system in accordance with a control deviation between setpoint values ​​and actual values ​​of at least one controlled variable (110), wherein pressure measurement values ​​of a pressure of the pressure medium delivered by the hydraulic machine and / or displacement measurement values ​​of the displacement of the hydraulic machine are recorded (120), wherein compensated current signal values ​​are determined as a superposition of the controller current signal values ​​with correction current signal values ​​(130), wherein the correction current signal values ​​are determined in such a way thatthat a pulsation of the pressure and / or displacement and / or torque of the hydraulic machine is minimized; and wherein the electroproportional valve is controlled with a current signal as a control current that corresponds to the compensated current signal values ​​(140).,

Description

The present invention relates to a method for controlling an adjustable hydraulic machine and to a computing unit and a computer program for carrying it out.BACKGROUND OF THE INVENTIONMobile work machines, such as excavators, telehandlers, reach stackers and others, have hydraulically driven machine elements, e.g. booms, which are supplied with pressure medium by a hydraulic pump, and / or have a hydraulic travel drive in which a hydraulic pump is coupled to a hydraulic motor via hydraulic lines. Variable displacement hydraulic machines can be used as the hydraulic pump or hydraulic motor. Adjustable hydraulic machines of this type are typically designed as axial piston machines in which pressure medium is conveyed by means of a plurality of pistons which are arranged on a rotating cylinder and which execute a stroke movement during the rotation.Disclosure of the InventionAccording to the invention, a method for controlling an adjustable hydraulic machine and a computing unit and a computer program for carrying it out are proposed having the features of the independent patent claims. Advantageous embodiments are the subject matter of the dependent claims and of the following description.The invention makes use of the measure of actuating an adjustable hydraulic machine (which is in particular an adjustable axial piston machine) which has an adjusting device for adjusting a displacement (in particular a pivot angle) of the hydraulic machine with an electric control current which is obtained as superposition of controller current signal values of a controller with correction current signal values, wherein the correction current signal values are determined such that pulsation of the pressure and / or of the displacement and / or of a torque of the hydraulic machine is minimized. With the proposed measure, pulsation in the hydraulic circuit in which the hydraulic machine is used can be reduced, which leads, for example, to a reduction in noise emissions, a reduction in the excitation of pulsation of the surrounding machine system and a reduction in the component load. Additional design measures, such as the introduction of pre-compression volumes, are not necessary.The expression "superposition" or "superposition" is to be understood in particular in the sense of an addition of the respective current signal values. The term "current signal values" refers to the respective determination and processing by an electronic controller typically being in the form of digital values. The fact that the current signal (which is used as a control current) corresponds to the compensated current signal values should correspondingly mean that the current intensity of the current signal varies according to the compensated current signal values, for example that the current intensity of the current signal is proportional to the compensated current signal value, or that an effective current intensity of the current signal is proportional to the compensated current signal value. The latter can be the case when the control current of the electroproportional valve is given by a PWM signal (PWM: pulse width modulation, also referred to as pulse duration modulation, PWM), wherein an effective current intensity, which is given by the duty cycle of the PWM signal, is then generated in the electromagnetic adjustment mechanism (electromagnet) of the electroproportional valve.According to one embodiment, a pulsation frequency of the pulsation is determined, wherein the correction current signal values comprise compensation signal values with a frequency which is equal to the pulsation frequency or is adapted to the pulsation frequency (e.g. within the scope of an optimum adaptation). The pulsation to be compensated typically has a specific frequency (pulsation frequency), which results from the structure of the hydraulic machine, in particular the displacement coefficient, and the rotational speed thereof during operation. The pulsation frequency could be determined, for example, from the pressure measurement values and / or the displacement measurement values. The compensation signal or the compensation signal values by which it is given is given in particular as an oscillating signal, for example sinusoidal. The frequency of this compensation signal (or of the corresponding cyclical variation of the compensation signal values) is equal to the pulsation frequency. Furthermore, the compensation signal (or the compensation signal values) has an amplitude and a phase. A phase shift may be present between the phase of the compensation signal and a phase of the pulsation.According to one embodiment, the pulsation frequency is determined from a rotational speed of the hydraulic machine and the known displacement number of the hydraulic machine. The pulsation frequency is then in particular the product of the rotational speed with the number of displacers, in the case of the adjustable axial piston unit in particular the number of pistons, or, for example, with an odd number of displacers, twice the product of the rotational speed with the number of pistons. This procedure is expedient since the pulsation frequency is thus independent of measurement values which are influenced by the pulsation, and additional sensor systems on the hydraulic machine can be dispensed with.According to one embodiment, a phase of the pulsation is determined from the pressure measurement values and / or the displacement measurement values, wherein the compensation signal values have a phase shift with respect to the phase of the pulsation, and wherein in particular the phase shift corresponds to half the angular distance between two displacers, in particular pistons, of the hydraulic machine. The phase shift can take into account, for example, a delay between the actuation of the adjustment device (e.g. electroproportional valve) and the adjustment of the displacement effected therewith, i.e. a difference between the actual displacement (corresponding to the displacement measurement values) and a desired displacement.According to one embodiment, an optimum adaptation of an amplitude and / or of the frequency of the compensation signal values is determined in order to minimize the pulsation. This is expedient since the amplitude of the pulsation can be dependent on a respective operating point of the hydraulic machine and / or of the hydraulic circuit in which it is used. An operating point can be given, for example, by specific (setpoint) pressure values and / or (setpoint) displacement values and / or (setpoint) torque values.According to one embodiment, the optimum adaptation of the amplitude and / or frequency of the compensation signal values is determined by varying the amplitude and / or frequency of the compensation signal values during operation and selecting the optimum adaptation of the amplitude and / or frequency of the compensation signal values on the basis of the pressure measurement values and / or the displacement measurement values. According to an alternative or additional embodiment, the optimum adaptation of the amplitude and / or frequency of the compensation signal values is determined during startup of the hydraulic machine and / or of the hydraulic circuit in which the hydraulic machine is used, in particular in a test stand, and / or on the basis of a simulation, wherein the optimum adaptation of the amplitude and / or frequency of the compensation signal values is determined in particular on the basis of operating points of the hydraulic machine and / or of the hydraulic circuit in which the hydraulic machine is used. The advantage of this embodiment is that control units with lower computing power can be used.The adaptation of the amplitude and / or frequency of the compensation signal values can be effected, for example, on the basis of a predetermined or a typical amplitude and / or frequency and / or on the basis of a most recently used amplitude and / or frequency (for example when the operating point changes). The aforementioned possibilities for determining the optimum adaptation of the amplitude and / or frequency of the compensation signal values can also be combined. For example, an adjustment, which was determined during startup in a test bench in particular and / or by means of a simulation, can be stored for different operating points in an electronic controller, for example in the form of a characteristic map, and during operation a variation can take place starting from the adjustment stored for the operating point present during operation, for example within a specific amplitude range and / or frequency range around the stored adjustment. The optimum adaptation of the amplitude and / or frequency can thus be determined in a relatively short time.According to one embodiment, the correction current signal values comprise dither signal values, wherein an optimum adaptation of a frequency of the dither signal values and / or an amplitude of the dither signal values and / or a phase position of the dither signal values is determined in order to minimize the pulsation.The dither signal (corresponding to the dither signal values) is a current signal with a relatively low amplitude (relative to the actual current with which the electroproportional valve is to be adjusted, in particular relative to the regulator current signal or a possible current intensity range thereof), which is superimposed on the current signal with which the electroproportional valve is controlled, in order to avoid an intermittent adjustment of the electroproportional valve on the basis of the so-called "stick slip effect". The dither signal is, for example, a pulse-width-modulated current signal, i.e. the dither signal values correspond to a pulse-width-modulated current signal.According to one embodiment, the frequency and / or the amplitude and / or the phase position of the dither signal values are varied during operation and the optimum adaptation of the frequency and / or the amplitude and / or the phase position of the dither signal values is determined on the basis of the pressure measurement values and / or the displacement measurement values.According to one configuration, the optimum adaptation of the frequency and / or the amplitude and / or the phase position of the dither signal values is determined during startup of the hydraulic machine and / or of the hydraulic circuit in which the hydraulic machine is used, in particular in a test stand, and / or on the basis of a simulation, wherein the optimum adaptation of the frequency and / or the amplitude and / or the phase position of the dither signal values is determined, in particular, on the basis of operating points of the hydraulic machine and / or of the hydraulic circuit in which the hydraulic machine is used.According to one embodiment, the hydraulic machine is used in a hydrostatic circuit.According to one configuration, the hydraulic machine is a hydraulic pump and the pulsation is a pressure pulsation. According to another embodiment, the hydraulic machine is a hydraulic motor and the pulsation is a torque pulsation.A computing unit according to the invention, e.g. a control unit of a mobile working machine in which the hydraulic machine is used, is configured, in particular by programming, to carry out a method according to the invention.The implementation of a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous since this causes particularly low costs, in particular if an executing control device is also used for further tasks and is therefore present in any case. Suitable data carriers for providing the computer program are, in particular, magnetic, optical and electrical memories, such as hard disks, flash memories, EEPROMs, DVDs, among others. Download of a program via computer networks (Internet, intranet, etc.) or mobile radio networks (e.g. 4G, 5G, etc.) is also possible.Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing.It is understood that the features mentioned above and those still to be explained below can be used not only in the respectively specified combination, but also in other combinations or alone, without departing from the scope of the present invention.The invention is schematically illustrated in the drawing on the basis of exemplary embodiments and is described in detail below with reference to the drawing.DESCRIPTION OF THE FIGURESFIG. 1 illustrates the structure of an adjustable hydraulic machine. FIG. 2 illustrates the compensation of a pressure pulsation. FIG. 3 shows a flow diagram of a method according to an exemplary embodiment of the invention.Detailed Description of the DrawingsFIG. 1 illustrates the construction of an adjustable hydraulic machine 2. the hydraulic machine is in particular an axial piston machine of swashplate construction or helical axis construction.The hydraulic machine 2 has a first working connection 20 and a second working connection 22, between which pressure medium (i.e. hydraulic fluid, typically a hydraulic oil) is conveyed. For example, in an open circuit, the first working connection 20 is a high-pressure-side connection and the second working connection 22 is a low-pressure-side connection, wherein in the case that the hydraulic machine is a hydraulic pump or acts as such, pressure medium is conveyed from the second to the first working connection and in the case that the hydraulic machine is a hydraulic motor or acts as such, pressure medium is conveyed from the first to the second working connection. In a closed circuit, a pressure side change is also possible. The hydraulic machine 2 is driven by means of a shaft 8 or drives the shaft 8.The displacement (or stroke volume or displacement volume) of the hydraulic machine 2, i.e. the volume of pressure medium conveyed per revolution, can be adjusted or changed according to a pivot angle 6. The adjustment is effected by means of hydraulic adjusting cylinders 10, 12, wherein the inflow and outflow of pressure medium to or from the adjusting cylinders is controlled by an electroproportional valve 4. The electroproportional valve 4 is adjustable electrically or electromagnetically between different switching positions, in particular continuously adjustable. In this case, an electromagnet, with which the electroproportional valve is adjusted, is actuated or acted upon by an electric control current. The control current is generated, for example, by a control unit 30 (arithmetic unit or electronic controller) of the hydraulic machine or of the hydraulic system in which the hydraulic machine is used. The illustrated arrangement is an example of an adjusting device of an adjustable displacement hydraulic machine. In addition to this electromagnetically pilot-controlled hydraulic adjustment, other adjustment devices are also conceivable which adjust the displacement, for example electro-mechanically.Since the pressure medium is not continuously conveyed by means of displacers, in particular pistons, because of the typical structure of the hydraulic machine, pulsations in the high-pressure-side pressure (in particular in the case of a hydraulic pump) or in the torque (in particular in the case of a hydraulic motor) can occur. The torque is proportional to the product of the pressure difference across the hydraulic machine with displacement, in a known manner. Pulsations can be considered to be variations in the pressure or torque that occur with unchanged (setpoint) pressure change.Furthermore, a pressure sensor 20 and a displacement sensor or pivot angle sensor 22 are provided by way of example, which measure pressure measured values or displacement measured values (or pivot angle measured values) and transmit them to the control unit 30. The pressure sensor 20 measures, in particular, the pressure of the pressure medium at the first working connection 20.The control unit 30 can record the pressure measurement values and / or the displacement measurement values as actual values and, in particular, implement a regulation of the hydraulic machine on the basis thereof. The control can be based, for example, on a control deviation between actual pressure measurement values and a setpoint pressure value and / or a control deviation between actual displacement measurement values and a setpoint displacement value and / or a control deviation between actual torque values and a setpoint torque value, wherein controller current signal values for the electroproportional valve are determined as the control variable by the control. Actual torque values can be determined, for example, from the pressure measurement values and displacement measurement values or can be transmitted by a controller of an electric machine coupled to the shaft. The respective setpoint values can be predefined, for example, by a superordinate controller or a superordinate controller algorithm.According to the invention, provision is made for the regulator current signal values to be superimposed with correction current signal values, i.e. in particular for correction current signal values to be added to regulator current signal values (which relate to identical points in time), in order to determine compensated current signal values. The control current for the actuation of the electroproportional valve is determined in accordance with the compensated current signal values; in particular, a current intensity (which may be effective or averaged, for example in the case of PWM actuation) of the control current is then proportional to the compensated current signal values. By suitable selection of the correction current signal values, pulsations can be avoided or at least reduced. This will be explained below with reference to a hydraulic pump, referred to simply as a pump.The pressure pulsation prevailing on the high-pressure side of the pump can be determined in terms of frequency and amplitude by a pressure sensor located in the hydraulic system. The high-pressure signal should be tapped in an analog manner. Alternatively, the sampling of the pressure signal can be carried out at high frequency (f s >2·f a, according to the Nyquist-Shannon sampling theory; f s: sampling frequency, f a: highest frequency occurring, here f a=2 ·π·k·n, k: number of pistons, n: rotational speed).The angular position of the swivel cradle is detected via a swivel angle sensor. The sensor signal should likewise be detected here in an analogous or alternatively high-frequency manner with f s >2·f a.In the hydraulic system with an electronic pump regulator, a setpoint value for the magnetic current of the pump regulator is determined from the control deviation between actual and setpoint values for pressure, pivot angle or torque. The magnetic current substantially influences the opening behavior of the valve. This in turn has an influence on the pressure in the control chamber of the pump and thus also on the pivot angle of the swashplate. If the current signal of the magnet is changed suitably, the delivery flow of the pump changes accordingly. As a result, influence can be exerted on the volumetric flow pulsation and thus on the pressure pulsation of the pump as a result of the load present in the system.In the operating range of the electromagnetic proportional valve, an increase in the current intensity leads to an increase in the valve piston stroke. The flow area and thus the volume flow over the valve edge increases. Approximately, the following applies: I~F - h - AV, i.e. A v( t)=k·I(t ), in which I is: valve flow, F: opening force, h: valve piston stroke, A V: opening cross section, k 1: proportionality constant.The volume flow over the valve edge Q V is calculated with the pressure difference Δp V present at the valve and the flow rate α D thus as follows:The volumetric flow of the pump is proportional to the product of pivot angle α(t) and rotational speed n(t):The integral of the volume flow over the valve edge is in turn proportional to the pivot angle of the pump:This yields the relationship between the volumetric flow of the pump and the valve supply, which can be divided into the mean value Q(t) and the fluctuation Q̂(t):By introducing a hydraulic capacity C h a relationship is obtained between the pressure at the pump outlet and the delivery flow of the pump:Since the volumetric flow pulsation and the pressure pulsation occur at the piston frequency (f a=2 ·π·k·n), the compensation signal K(t) must correspond to the piston frequency. The amplitude results from the requirement that the volumetric flow pulsation Q̂(t) should disappear. The compensation signal can be impressed in particular by half a piston pitch phase-shifted with respect to the occurring pressure pulsation.Taking into account the control deviation of the pivot angle control loop in the phase shift is advantageous. A phase shift of the actual swivel angle φα,ist compared to the setpoint swivel angle α(t) influences the quality of the pulsation compensation. Accordingly, the deviation K(t)=K(α-Φα,ist) should be taken into account in the calculation of the compensation signal.FIG. 2 illustrates the ideal compensation of a pressure pulsation. The pressure 54 is plotted against the angle of rotation (of the shaft or the revolutions of the hydraulic machine). A pulsation 50 of the pressure is shown, which is present without correction or compensation. Furthermore, a compensation 56 of the pressure is shown, which results from a displacement variation or pivot angle movement, which is caused by the compensation signal in the actuation of the adjusting device, e.g. of the electroproportional valve. Superposition results in a resulting pulsation 58; in this case, in the example shown, the frequency of the compensation signal, the phase shift of the compensation signal and the amplitude of the compensation signal are determined in a suitable manner, such that no pressure variations are present in the resulting pulsation 58, that is to say the case of complete compensation is illustrated.FIG. 3 shows a flow diagram of a method according to an exemplary embodiment of the invention. The method relates to the control of an adjustable hydraulic machine, which is in particular an adjustable axial piston machine and which has an electroproportional valve which is actuated with an electrical control current in order to bring about the adjustment of a displacement of the hydraulic machine (as shown in FIG. 1 ). The method is carried out, for example, by a control unit (arithmetic unit or electronic controller) of the hydraulic machine or of the hydraulic system in which the hydraulic machine is used.In step 110, controller current signal values for the electroproportional valve are determined in accordance with a control deviation between setpoint values and actual values of at least one controlled variable. The controlled variable is in particular the pressure and / or the displacement and / or the torque. The control can be implemented, for example, as a P controller, PI controller or PID controller (P: proportional, I: integral, D: differential).In step 120, pressure measurement values of a pressure of the hydraulic medium delivered by the hydraulic machine and / or displacement measurement values of the displacement of the hydraulic machine are recorded. The pressure measurement values and the displacement measurement values are measured and transmitted by a pressure sensor and a displacement sensor, respectively. A detection or measurement frequency is in particular greater than or equal to twice the pulsation frequency.In step 130, compensated current signal values are determined as superposition of the controller current signal values with correction current signal values, wherein the correction current signal values are determined such that pulsation of the pressure and / or the displacement and / or a torque of the hydraulic machine is minimized.In step 140, the electroproportional valve is actuated with a current signal as control current, which corresponds to the compensated current signal values.

Claims

Method for controlling an adjustable hydraulic machine (2), in particular an adjustable axial piston machine, wherein the hydraulic machine has an adjustment device which is actuated with an electrical control current in order to bring about the adjustment of a displacement, in particular a pivot angle (6), of the hydraulic machine, wherein controller current signal values for the adjustment device are determined (110) by means of a controller in accordance with a control deviation between setpoint values and actual values of at least one controlled variable; wherein pressure measured values of a pressure of the pressure medium conveyed by the hydraulic machine and / or displacement measured values of the displacement of the hydraulic machine are detected (120); wherein compensated current signal values are determined (130) as superposition of the controller current signal values with correction current signal values, wherein the correction current signal values are determined such that pulsation of the pressure and / or the displacement and / or a torque of the hydraulic machine is minimized; and wherein the electroproportional valve is actuated (140) with a current signal as control current corresponding to the compensated current signal values.The method of claim 1, wherein a pulsation frequency of the pulsation (50) is determined; and wherein the correction current signal values comprise compensation signal values having a frequency equal to or matched to the pulsation frequency.Method according to claim 2, wherein the pulsation frequency is determined from a rotational speed of the hydraulic machine (2) and a piston number of the hydraulic machine.Method according to claim 2 or 3, wherein a phase of the pulsation is determined from the pressure measurement values and / or the displacement measurement values; wherein the compensation signal values have a phase shift with respect to the phase of the pulsation; and wherein in particular the phase shift corresponds to half the angular distance between two pistons of the hydraulic machine (2).Method according to claim 4, wherein an optimal adjustment of an amplitude and / or the frequency of the compensation signal values is determined in order to minimize the pulsation.Method according to claim 5, wherein the optimal adjustment of the amplitude and / or frequency of the compensation signal values is determined by varying the amplitude and / or frequency of the compensation signal values during operation and selecting the optimal adjustment of the amplitude and / or frequency of the compensation signal values based on the pressure measurement values and / or the displacement measurement values.Method according to claim 5 or 6, wherein the optimal adaptation of the amplitude and / or frequency of the compensation signal values is determined during startup of the hydraulic machine and / or of the hydraulic circuit in which the hydraulic machine is used, in particular in a test stand, and / or based on a simulation; wherein the optimal adaptation of the amplitude and / or frequency of the compensation signal values is determined in particular depending on operating points of the hydraulic machine (2) and / or of the hydraulic circuit in which the hydraulic machine is used.Method according to one of the preceding claims, wherein the correction current signal values comprise dither signal values; wherein an optimum adaptation of a frequency of the dither signal values and / or an amplitude of the dither signal values and / or a phase position of the dither signal values is determined in order to minimize the pulsation.The method of claim 8, wherein the dither signal values correspond to a pulse width modulated current signal.Method according to claim 8 or 9, wherein the frequency and / or the amplitude and / or the phase position of the dither signal values are varied during operation and the optimum adaptation of the frequency and / or the amplitude and / or the phase position of the dither signal values is determined on the basis of the pressure measurement values and / or the displacement measurement values; and / or wherein the optimum adaptation of the frequency and / or the amplitude and / or the phase position of the dither signal values is determined during startup of the hydraulic machine and / or of the hydraulic circuit in which the hydraulic machine is used, in particular in a test stand, and / or on the basis of a simulation; wherein the optimum adaptation of the frequency and / or the amplitude and / or the phase position of the dither signal values is determined in particular as a function of operating points of the hydraulic machine and / or of the hydraulic circuit in which the hydraulic machine is used.Method according to any of the preceding claims, wherein a detection frequency of the pressure measurement values and / or the displacement measurement values is greater than or equal to twice a pulsation frequency.The method of any preceding claim, wherein the hydraulic machine is a hydraulic pump and the pulsation is a pressure pulsation; or wherein the hydraulic machine is a hydraulic motor and the pulsation is a torque pulsation.A computing unit (30) comprising a processor configured to perform the method of any preceding claim.A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of claims 1 to 12.Computer-readable data medium on which the computer program according to Claim 14 is stored.

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