Method for determining a regulation limit of a valve, hydraulic machine and travel drive

Abstract

The invention discloses a method for determining at least one adjustment limit of an electrically actuatable first pressure regulating valve from a first actuating current, for which a driven hydraulic machine is provided, the displacement of which can be adjusted by a centrally centered actuating element with pressure surfaces that act against one another, in which a first pressure surface can be loaded by a first pressure regulating valve with a first actuating pressure depending on the first actuating current, wherein a high pressure or an operating variable of the hydraulic machine associated with the high pressure is detected. Furthermore, a hydraulic machine with such a pressure reducing valve and a hydrostatic drive with a hydraulic machine and a hydraulic motor that can be driven by the hydraulic machine are disclosed.

Description

Technical Field

[0001] This invention relates to a method for determining the adjustment limit of a pressure reducing valve according to the invention, a hydraulic press according to the invention, and a hydrostatic travel actuator according to the invention. Background Technology

[0002] For example, a hydrostatic drive system used in a wheel loader has a hydraulic pump that delivers pressurized medium to a hydraulic motor via a working line for travel. The volumetric flow rate of the pressurized medium creates a working pressure or high pressure in the working line. The displacement of the hydraulic pump is adjusted by a double-acting hydraulic cylinder. The chambers of the hydraulic cylinder acting in opposite directions of adjustment can be individually loaded with the operating pressure. The operating pressure in each chamber is regulated by an electro-proportional pressure reducing valve according to the drive current desired by the driver. The valves are subjected to a series of distributed pressures, the effect of which is that the relationship between the drive current and the operating pressure cannot be replicated through the valve series.

[0003] Model-based control of driving drives is becoming increasingly important, requiring an inverse model of this relationship. To ensure that this form of control achieves only a small deviation between rated and actual values, the inverse model used for the valve must be as close as possible to the actual valve.

[0004] Therefore, individualized calibration must be used to determine the characteristics of each valve in the series, consisting of the drive current and the resulting operating pressure, so that the parameters provided in the model can be adjusted individually based on the results. A sensing device for obtaining the operating pressure does not exist for cost reasons, therefore direct valve calibration has not been possible until now. Thus, it is particularly difficult to begin small calibration adjustments at the minimum drive current and to calibrate the maximum operating point at the maximum drive current. The valve adjustment start has not been determined until now because the actuator is pre-tightened by central centering, so the displacement is definitely zero in a stationary state. This pre-tightening must be overcome in order to obtain, for example, a high-pressure response and thus a measurement signal. The important range of the drive current, especially for smooth changes in travel direction, cannot be observed through high pressure in a stationary state. However, using average estimates for this purpose will result in uneven changes in travel direction in a few samples. The adjustment upper limit is determined such that the pump, at the rated power of the travel drive, pivots outward to 100% of the pivot angle against the rotational force acting on the pump related to the load pressure. For this reason, the vehicle must move at a significant speed under full load for a period of time, such as on a test track, which makes the calibration process extremely difficult and costly.

[0005] Document DE 195 246 69A1 illustrates a conventional method for calibration based on vehicle driving behavior. However, as mentioned above, here the entire drivetrain is calibrated, not just the valves, and the range of small drive control currents cannot be calibrated. Summary of the Invention

[0006] Accordingly, the objective of this invention is to create a method for more accurately determining the adjustment limits of a pressure-reducing valve. Another objective is to create a hydraulic press that enables more precise calibration of its control valve. A third objective is to create a hydrostatic drive incorporating such a hydraulic press.

[0007] The corresponding task is solved by a method featuring the features of the present invention, a hydraulic press featuring the features of the present invention, and a driving drive featuring the features of the present invention.

[0008] Advantageous extensions of the invention are described herein.

[0009] According to the method, at least one adjustment limit of the electrically driven first pressure regulating valve, particularly the first pressure reducing valve, is determined or corrected based on the first drive current of the first pressure regulating valve. For this purpose, a hydraulic press, particularly an axial piston pump of swashplate configuration, capable of operating and being driven during pump operation, is provided, wherein the displacement of the hydraulic press can be adjusted in different adjustment directions by an actuator, particularly a hydraulic cylinder, preloaded in the adjustment direction, using opposing pressure surfaces. The hydraulic press is preferably driven at a constant speed during the method. The hydraulic press is preferably reversible and can therefore be adjusted between the zero displacement side and the other side. The first pressure surface in the pressure surface can be loaded with a first operating pressure by the first pressure regulating valve (hereinafter referred to as the first valve) according to the first drive current acting on the first valve. The first drive current corresponds, for example, to the driver's intention along a first travel direction when the first valve is used in a driving actuator. To determine the adjustment limit of the first valve, the high pressure of the hydraulic press or its associated operating parameters are detected. According to the invention, a second pressure surface is loaded with a sufficiently large, constant second operating pressure. Sufficiently large pressure specifically means that the second acting pressure creates high pressure in the corresponding direction or working line. The first drive current then changes from its limit. The first adjustment limit is determined when high pressure caused by the second acting pressure or a measurable first change in the operating parameters is detected. Throughout the process, the hydraulic press is hydraulically locked, in particular. This can be accomplished, for example, by the parking brake of the drive unit or the like.

[0010] The method is therefore based on clamping the actuator between the applied pressures. In this way, the operating point of the actuator is moved out of its preload, and the already minimal first drive current, unlike in the prior art, results in a detectable response of high pressure or operating parameters. The applied pressure here creates a difference that remains constant as long as the adjustment limit is not exceeded. Therefore, initially no change in high pressure or operating parameters is detected, because no change in the force at the actuator occurs. However, as the first drive current changes, due to the shift in the operating point, the adjustment limit of the first valve is quickly exceeded, at which point the first drive current reaches a value that causes a change in the first applied pressure and therefore the force at the actuator. The result is a slight adjustment in displacement, which can then be detected as a change in the adjustment stroke, adjustment angle, and / or high pressure, which remains constant until then. This change is either decreasing or increasing, depending on which limit it originates from. By clamping according to the invention, this response of high pressure or operating parameters can be detected much earlier than in conventional methods, thus enabling the determination of the valve's adjustment limits and therefore characteristic curves with high accuracy and, however, low cost. The valve characteristic curve can therefore be determined from the start of adjustment without measuring the pressure in the adjustment chamber, rendering the expensive sensing devices used for this purpose redundant. Essentially, the quality of driving direction changes is improved in model-based control through the corrections according to the invention.

[0011] In a first variation of the method, the first valve is initially unenergized and the drive current is increased as a variable. The first drive current applied upon detection of high voltage or a change in operating parameters serves as the first adjustment limit, which is also the lower adjustment limit.

[0012] In a first variation of the method, the first valve is fully energized at the beginning, and the first drive current is reduced as a change. The first drive current applied when high voltage or a change in operating parameters is detected serves as the first adjustment limit, which is also the adjustment upper limit.

[0013] In one extended design, two adjustment limits of the first valve are determined. This is preferably accomplished by the step "determining the second adjustment limit when a high pressure or a final change in the operating parameter is detected in the direction of the first operating pressure." This step is preferably performed at the previously mentioned constant second operating pressure and as the first drive current continues to change, i.e., continues to decrease or continue to increase, depending on the change. The final change refers to a situation where, after this final change, the detected high pressure or the detected operating parameter remains constant in subsequent processes, even if the first drive current continues to change. This change in current therefore no longer causes a change in valve behavior, which is equivalent to exceeding the second adjustment limit.

[0014] In another step, the determined adjustment limits are stored.

[0015] In one extended design, in addition to the displacement itself, the operating parameters associated with high pressure are the adjustment stroke or adjustment angle of the actuator or hydraulic press.

[0016] In addition to using a constant high pressure of, for example, 200 bar as the operating parameter detected by the hydraulic press and the method, a pivot angle signal or an adjustment stroke signal can also be used.

[0017] Especially when driving a hydraulic motor over high resistance, this is possible regardless of whether the vehicle is moving. A stationary vehicle is more advantageous here, as disturbances from the surrounding environment are difficult or almost impossible to assess when in motion. However, motion is also reasonable in general, since neither rated volumetric flow rate nor rated power is required, and therefore it will be slow motion accompanied by low power.

[0018] In the extended design scheme where the pivot angle is used as a detected operating parameter and the vehicle is stationary, the high pressure is preferably so high that hydraulic leakage results in a pivot angle of at least 10% to 15% even when the vehicle is stationary. The high pressure here is greater than or equal to approximately 300 bar. The high pressure is so high that the hysteresis in detecting the pivot angle is negligible.

[0019] Therefore, it is preferable to include a stroke or angle sensor, the value of which is entered into the method along with the step "detecting and adjusting stroke or angle". The corresponding explanation also applies to high pressure, therefore the hydraulic press preferably has a pressure sensor for the method step "detecting high pressure on the high-pressure side". If the hydraulic press is driven at a constant speed in an extended design, then the adjustment limits are easily determined.

[0020] In one extended design, a sufficiently constant second acting pressure is provided by a constant pressure source, particularly a hydraulic reservoir.

[0021] In a preferred extended design of the method, a second pressure surface of the second pressure-reducing valve is loaded with a second operating pressure. This arrangement corresponds to the preferred embodiment of the hydraulic press, in which the pressure-reducing valves are assigned to any adjustment direction (travel direction). The adjustment limits of the two pressure-reducing valves are determined by the method in such a way that each pressure-reducing valve to be calibrated is variably energized while the other pressure-reducing valves are constantly energized.

[0022] The hydraulic press according to the invention has an adjustment system that is centrally centered by a pre-tensioned spring and can be adjusted by means of actuators acting on both sides with opposing pressure surfaces. Among these pressure surfaces, a first pressure surface of a first pressure regulating valve of the hydraulic press can be applied with a first operating pressure according to a first drive current, and a second pressure surface of a second pressure regulating valve of the hydraulic press can be applied with a second operating pressure according to a second drive current. A detection device is provided for detecting high pressure, particularly in the working pipeline, or operating parameters of the hydraulic press associated with such high pressure. According to the invention, a control device is provided that can drive the pressure regulating valve, and the control device stores a method according to at least one aspect described above for implementation.

[0023] The hydraulic press is preferably equipped with a device that hydraulically locks the press so that no pressure medium can flow out of the press despite the drive shaft being rotated. This can be, for example, a blind line or a working line that can be shut off on its high-pressure side, or a fluid-connected hydraulic motor whose displacement can be adjusted to zero by a control device or which can be mechanically locked by means of a brake.

[0024] The hydraulic press is preferably locked in such a way that the high pressure affects the displacement adjustment in the direction of its own decrease. This is structurally intended to be achieved by twisting the control panel of the hydraulic press from its central position. The twisting causes the pressure generated by the hydrostatic working chamber of the hydraulic press on the adjusting mechanism of the hydraulic press to be non-zero, and thus results in an adjusting force or adjusting torque in the stated direction, independent of the actuator force.

[0025] The hydrostatic drive includes: a first hydraulic press that operates according to at least one aspect described above; and a second hydraulic press that can be supplied with a pressure medium by the first hydraulic press, which operates as a hydraulic motor and can be connected to, in particular to, the driven structure of the drive. Attached Figure Description

[0026] The following description, with reference to the accompanying drawings, illustrates in more detail one embodiment each of the method according to the invention and the hydraulic press according to the invention for a hydrostatic driving drive.

[0027] Figure 1 A hydraulic press according to the invention for a hydrostatic driving drive is shown according to one embodiment;

[0028] Figure 2 It shows the press Figure 1 The functional relationship of the control device of the hydraulic press; and

[0029] Figure 3 A timeline of the method according to the invention according to one embodiment is shown. Detailed Implementation

[0030] according to Figure 1 The hydraulic press 1, which operates as a hydraulic pump, has an adjustable displacement. In an embodiment, the hydraulic press 1 is designed as an axial piston machine with an adjustable swashplate. The hydraulic press 1 has a drive mechanism 2 and a servo cylinder 4 as an actuator for adjusting its displacement. The actuator is connected to or hinged to the swashplate. The drive mechanism 2 is connected to a drive motor, particularly a diesel engine or electric motor (not shown), via a drive shaft 6 and is driven, particularly, at a constant speed. To operate the servo cylinder 4 and therefore to adjust the displacement, the hydraulic press 1 has pressure regulating valves 12 and 14, designed as pressure reducing valves, for each chamber 8 and 10 of the servo cylinder. The pressure regulating valves can adjust the displacement by applying pressure P as desired by the operator. St The provided pressure medium is adjusted to the corresponding operating pressure p in chambers 8 and 10. a p b The pressure medium is provided by an auxiliary pump 11, which is driven by a drive shaft 6.

[0031] The hydraulic press 2 is designed to be reversible and has two working lines 18 and 20 to which the hydraulic press can supply power. A hydraulic motor is fluidly connected to these working lines and is coupled to a wheel or axle, thus forming a hydrostatic drive system.

[0032] In order to process the driver's intentions, a corresponding drive control current I is used. a I b The pressure reducing valves 12 and 14 are driven and controlled, or more precisely, the electromagnets a and b. The hydraulic press 1 has a control device 16. The method for calibrating the pressure reducing valves 12 and 14, which will be described below, is stored in this control device for implementation.

[0033] For the sake of brevity, further details of the hydraulic press 1 can be omitted, as this is known from the prior art. Particularly relevant here is the applicant's so-called ET-controlled hydraulic press 1. Further description focuses on the methods stored in the control device 16 and capable of being implemented.

[0034] This is based on a possible effective mutual relationship, which first utilizes... Figure 2 This will be explained. Therefore, the driver's intention to enter control device 16 is shown, up to the generated and detectable high pressure. First, according to the rated pivot angle α of hydraulic press 1... soll or rated pressure p soll Or depending on the desired driving direction p Asoll or p Bsoll The driver's intention is then sent to the control unit. This driver's intention is converted into an application pressure p by the inverse model 22 stored in the control unit. asoll or pbsoll The rated value. This rated value is input into the inverse model 22 of the pressure reducing valve 12 or 14, and the corresponding drive current I is calculated through the inverse model. asoll Or I bsoll The current regulator uses a drive current to apply a force to magnet a or b of pressure reducing valve 12 or 14, thereby generating a practically effective pressure p, depending on the mass of model 24 of pressure reducing valve 12 or 14. a or p b This pressure acts on the relevant chamber 8 or 10 of the servo cylinder 4, thereby producing a true and detectable pivot angle α. The pump drive mechanism of the hydraulic press 2 then provides a pressure medium volumetric flow rate Q at a given rotational speed n of the drive shaft 6, which, at a given volume 30, is supplied at a pressure p. A or p B It is generated in the middle.

[0035] Figure 3 The illustration shows current-time and pressure-time plots of an embodiment of a method for determining the lower and upper limits of regulation of pressure reducing valves 12 and 14, where the points represent the characteristic curves of the relevant valves 12 and 14, respectively. This allows for the determination of the lower and upper limits of regulation of the pressure reducing valves 12 and 14. Figure 2 The corresponding inverse model 24 for valves 12 and 14.

[0036] First, the hydraulic press 1 is hydraulically locked, thus preventing any volumetric flow rate Q from flowing out. The adjustment of valve 12 begins at a point where the current I... a Sufficient relative pressure greater than or equal to 0 in chamber 8 as shown in the diagram. However, due to the spring preload at the servo piston, the hydraulic press 1 operates at a pressure p of approximately 5 bar. a High voltage P is used for starting A The system reacts to the high pressure detected by the sensor. Therefore, pressures less than 5 bar cannot be directly detected using traditional methods.

[0037] The proposed correction according to the invention is therefore completed using force compensation at the servo piston of servo cylinder 4. Adjustment should begin at valve 8. Figure 3 Therefore, the second drive current I is used by the control device. b The electromagnet b of valve 10 is energized until a high pressure or working pressure p of, for example, 200 bar is established in pipeline 20 at a rotational speed n. B This work pressure p B The pressure is detected by a pressure sensor. Therefore, an applied pressure p is generated in chamber 10. b .

[0038] The electromagnet a of the pressure reducing valve 12 is then loaded with a slowly increasing first drive current. Here, it is ensured that the minimum current I used to start is...a Adjustment start / adjustment lower limit I, safely positioned below valve 12 alimu Below.

[0039] Once the first drive current I a Large enough to establish the initial working pressure p in chamber 8. a >0 bar, the initial acting pressure p in chamber A a For partial compensation of the second acting pressure p in the second chamber 10 b The force. Hydraulic pump 2 then rotates slightly and the high pressure p B The value drops to <200 bar. This change is monitored and detected, and the configured first drive current is used as the start or lower limit of adjustment for the first pressure reducing valve 12. alimu It is stored in the control device 16. The second pressure reducing valve 14 also adopts an equivalent approach.

[0040] Similarly, force compensation is used to determine the upper limit or lower limit of adjustment for the first pressure reducing valve 12.

[0041] Here, the second pressure reducing valve 14 is also energized in such a way that the high pressure p in pipeline 20... B It is 200 bar. The second drive control current I b Therefore, it remains frozen.

[0042] First drive control current I A The rise now continues. Because chamber 8 now has the first acting pressure p rising. a Therefore, the impact of servo cylinder 4 on displacement becomes smaller and smaller. The result is that the high pressure p in pipeline 20... B The pressure drops to 0 bar. If the first operating pressure p in chamber 8... a If the pressure exceeds the second operating pressure of chamber 10, then the pressure p in pipeline 18 A It has begun to rise.

[0043] At high pressure p in pipeline 18 A The moment when the pressure stops increasing, i.e., the moment when the detection is constant, means that the first pressure reducing valve 12 is fully open, thus exceeding the final adjustment limit or upper adjustment limit I. alimo Therefore, a supply pressure p is applied in chamber 8. St .

[0044] The corresponding drive current I above alimo I blimo The adjustment of valves 12 and 14 is complete, referring to the available supply pressure or operating pressure p. St .

[0045] Maximum available supply pressure or operating pressure pSt Ideally, the high pressure p corresponds to the first and / or second pressure reducing valves 12, 14 being de-energized, and in particular, it can be detected by a high pressure sensor.

[0046] A method for calibrating a pressure-reducing valve in a hydraulic press is disclosed, wherein the valve acts with an applied pressure on one of two opposing chambers of a servo cylinder of the hydraulic press, and the other chamber is loaded with a constant pressure for calibration. The servo cylinder is preloaded in its basic position. At least one adjustment limit of the pressure-reducing valve is determined after compensating for this preload, wherein the preload is compensated by adjusting the drive current of the pressure-reducing valve from a limit outside its adjustment range toward the adjustment range, and storing the current drive current as the adjustment limit once a detected operating parameter associated with the adjustment changes.

[0047] It also discloses: a hydraulic press with such a pressure reducing valve and a control device, the control device having a method stored in the control device for implementation; and a hydrostatic drive having such a hydraulic press and a hydraulic motor that can be driven by the hydraulic press.

[0048] List of reference numerals

[0049] 1. Hydraulic press

[0050] 2. Drive mechanism

[0051] 4 servo cylinders

[0052] 6 drive shafts

[0053] 8 First Chamber

[0054] 10 Second Chamber

[0055] 12 First pressure reducing valve

[0056] 14 Second pressure reducing valve

[0057] 16. Control device

[0058] 18 First working pipeline

[0059] 20 Second working pipeline

[0060] 22. Inverse Model of Hydraulic Press

[0061] 24. Inverse Model of Pressure Reducing Valve

[0062] 26 Current Regulator

[0063] 28 Pump drive mechanism

[0064] 30 Volume

[0065] Ia I asoll First drive current, rated value

[0066] I b I bsoll Second drive current, rated value

[0067] I alimu I blimu Adjusting the lower limit

[0068] I alimo I blimo Adjust the upper limit

[0069] p a p asoll First operating pressure, rated value

[0070] p b p bsoll Second operating pressure, rated value

[0071] α、α soll Adjustment angle, rated value

[0072] p、p soll High voltage, rated value

[0073] p A p Asoll The high voltage on side A, rated value

[0074] p B p Bsoll The high voltage on side B, rated value

[0075] Q. Pressure medium volumetric flow rate

[0076] T-shaped material box

[0077] t time

Claims

1. Used for determining the first drive current (I) a A method for determining at least one adjustment limit of an electrically controllable first pressure reducing valve (12) is provided, for which a driven hydraulic press (1) is provided, the displacement of which can be adjusted by a centrally centered preloaded actuator (4) with mutually opposing pressure surfaces, the pressure surfaces being adjustable according to the first drive current (I a The first pressure reducing valve (12) uses the first operating pressure (p) a The first pressure surface is loaded, where, The method for detecting the operating parameters of a high-pressure or hydraulic press (1) associated with said high pressure is characterized by using a sufficiently large, constant second operating pressure (p). b ) Load the second pressure surface, the first drive control current (I a It then changes from its adjustment limit toward the adjustment range, and when the first change in high voltage or operating parameters is detected, the first adjustment limit is determined.

2. The method according to claim 1, wherein, The first pressure reducing valve (12) is initially not energized and then the first drive current (I) is increased. a ), or wherein the first pressure reducing valve (12) is initially energized to the maximum and then the first drive current (I) is reduced. a ).

3. The method according to claim 1 or 2, wherein a step is performed when a first acting pressure (p) is detected. a When the high pressure or operating parameter changes last in the direction of action, the second adjustment limit is determined.

4. The method according to claim 1 or 2, wherein, The operating parameters are the adjustment stroke or adjustment angle (α) of the actuator or the hydraulic press (1).

5. The method according to claim 1 or 2, wherein, The hydraulic press is driven at a constant rotational speed (n).

6. The method according to claim 1 or 2, wherein, The method is implemented for different rotational speeds (n) and / or high pressures.

7. The method according to claim 1 or 2, wherein, The two pressure surfaces of the first pressure reducing valve can be loaded with a corresponding first operating pressure, and the two pressure surfaces of the second pressure reducing valve can be loaded with a corresponding second operating pressure, and at least one adjustment limit is determined for the two pressure reducing valves (12, 14), wherein, in order to determine, one of the first pressure reducing valve and the second pressure reducing valve is constantly energized and the other is energized variably.

8. A hydraulic press, wherein the displacement of the hydraulic press is pre-tightened with centering in two adjustment directions and the displacement is adjusted in different adjustment directions by means of an actuator (4) with opposing pressure surfaces, wherein, The first pressure surface in the pressure surface can be controlled by the first pressure reducing valve (12) according to the first drive control current (I). a ) using the first acting pressure (p a The second pressure surface in the pressure surface can be controlled by the second pressure reducing valve (14) according to the second drive control current (I). b ) using the second acting pressure (p b The hydraulic press is loaded and equipped with a detection device for detecting high pressure or operating parameters of the hydraulic press associated with the high pressure, characterized by a control device (16) storing the method according to any one of the preceding claims for implementation.

9. The hydraulic press according to claim 8, wherein the hydraulic press is designed such that high pressure acts on the adjustment of the displacement in the direction of its decrease.

10. A hydrostatic drive unit, comprising a hydraulic press (1) according to claim 8 or 9 and another hydraulic press capable of being supplied with a pressure medium by the hydraulic press, the other hydraulic press being capable of operating as a hydraulic motor and being connected to the driven structure of the drive unit.

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