DE102020206343A1 - Procedure for calibrating an electro-proportional adjustable proportional valve - Google Patents

Abstract

The invention relates to a method for calibrating a proportional valve arranged in a hydraulic system and adjustable in proportion to a control signal of an electronic control device with regard to an offset of the control signal at an operating point with a predetermined pressure difference and a predetermined volume flow via the proportional valve. Via the continuous valve, pressure fluid can be supplied to a hydraulic consumer from the pressure connection of a hydraulic pump, the size of which can be measured in displacement and whose pump pressure is controllable ; 2) Acquisition of a value at least for the stroke volume of the hydraulic pump; 3) Changing, in particular increasing, the control signal of the continuous valve from an initial control signal until a difference between the current pump volume flow and the pump volume flow given when the flow cross-section of the continuous valve is closed is detected 4) Determination of the offset of the control signal by comparing the control signal of the proportional valve detected when the specified volume flow is reached with a theoretical control signal.

Description

The invention relates to a method for calibrating a proportional valve that can be adjusted proportionally to a control signal of an electronic control device with regard to an offset of the control signal at an operating point with a predetermined pressure difference and a predetermined volume flow via the proportional valve. Such a continuous valve can usually be actuated directly electrically or electrohydraulically with the aid of a proportional solenoid. After installation, for example on a mobile work machine such as an excavator, pressure fluid can be fed to a hydraulic consumer via such a proportional valve during operation from the pressure connection of a hydraulic pump, the size of which is adjustable and the pump pressure is adjustable.

Electro-proportional adjustable proportional valves have a manufacturing-related scatter in the characteristic curve of the flow cross-section to the electrical current through the proportional electromagnet. The series spread of the proportional valves usually consists of an essentially constant offset of the control signal. This means that for a desired flow cross-section, the control signal is smaller or larger than a theoretical value by a fixed amount. It is known to measure the manufactured proportional valves to compensate for the manufacturing variance and to store the characteristics of the proportional valves controlled by an electronic control device in the control device. Alternatively, the continuous valves are set in production in order to reduce the variance. Both approaches involve a lot of effort. In addition, the control unit and the proportional valves controlled by it are permanently assigned to one another. This makes it difficult to replace a proportional valve at a later date.

The effort for taking into account the spread or narrowing of the spread itself can be avoided or at least reduced and the subsequent replacement of a proportional valve can be simplified if the control unit itself detects how large the offset of the control signal of the respective proportional valve is within the spread and the individual characteristic of the Proportional valve generated and saved.

A procedure for this is from the US 2017 262 001 A1 known. It is proposed there to allow a certain delivery rate of the hydraulic pump to flow first via a calibration nozzle with a known flow cross-section to a tank and then with the calibration nozzle closed via the continuous valve and to change the control signal for the continuous valve until the pressure drop across the continuous valve is as large as is above the calibration nozzle beforehand. The pump pressure and thus the pressure upstream of the calibration nozzle is recorded by a pressure sensor. With the same flow rate and the same pressure drop, the flow cross-section of the continuous valve is then just as large as the flow cross-section of the calibration nozzle, so that an operating point with a specific value of the control signal and a specific value of the flow cross-section assigned to it is known. If the course of the valve characteristic is known per se except for an offset, the valve characteristic is shifted so that the operating point lies on it.

For the implementation of the US 2017 262 001 A1 known method, a calibration nozzle is necessary. This means an increased effort even if the calibration nozzle is integrated into a continuously adjustable bypass valve which is present in the hydraulic system and via which pressure medium can flow from the pressure connection of the hydraulic pump to the tank. According to the US 2017 262 001 A1 Such a bypass valve has a rest position which is assumed under the action of a compression spring and in which there is a calibrated flow cross section used as a calibration nozzle from the pressure connection of the hydraulic pump to the tank. With the aid of a proportional solenoid, the bypass valve can be moved from the rest position via a position in which it is closed and there is no flow cross-section from the hydraulic pump to the tank, into positions in which flow cross-sections of different sizes are set. This means that the proportional solenoid is energized when the bypass valve is in the closed position. If you wanted the bypass valve to be in a normally closed position, you would need a second electromagnet, by means of which the bypass valve would be brought into the position in which the calibrated flow cross-section is open.

The invention is therefore based on the object of specifying a method with which a continuous valve can be calibrated in a simple manner within the hydraulic system, of which it is a component, by the electronic control unit.

This object is achieved for a continuous valve which is arranged within the hydraulic system described at the beginning by a method with the method steps according to the invention.

Accordingly, the pump pressure is regulated to a preset pressure when the proportional valve is closed. A value is recorded at least for the stroke volume of the hydraulic pump. This can also take place in that a control signal for an adjusting device of the hydraulic pump, from which the stroke volume is obtained, is recorded and thus the stroke volume per se is not known, or at least not exactly known. Axial piston pumps are usually used as hydraulic pumps today Swashplate or bent axis construction used. With these, the stroke volume is given by the swivel angle of the swash plate or the swivel angle of the cylinder drum, taking into account the size and number of the axial pistons. The control signal of the continuous valve is changed from an initial control signal until a difference between the current pump volume flow and the pump volume flow given when the continuous valve is closed is detected.

The method according to the invention can be developed further in an advantageous manner.

In principle, it is conceivable to begin with a high initial control signal, that is to say a high start current and thus a wide open continuous valve, and to reduce the control signal until the hydraulic pump delivers the specified volume flow. Particularly preferably, however, the control signal of the continuous valve is increased by an initial control signal in which the continuous valve is closed. As long as the proportional valve is still closed despite an increase in the control signal, the delivery rate of the hydraulic pump does not change. As soon as the proportional valve begins to open, a volume flow can flow through the proportional valve. The pressure regulation leads to the fact that the stroke volume of the hydraulic pump is increased so that the preset pressure is maintained. The control signal for the proportional valve is increased further until a difference corresponding to the specified volume flow between the current pump volume flow given by the current stroke volume and the current speed of the hydraulic pump and the pump volume flow given by the stroke volume and the speed of the hydraulic pump before the opening of a flow cross section of the proportional valve is reached. The volume flow flowing through the continuous valve is thus equal to the change in the volume flow conveyed by the hydraulic pump. This change in the volume flow can be determined very precisely compared to the absolute size of the volume flow, even if the volume flow conveyed by the hydraulic pump when the continuous valve is opened and the current volume flow are inaccurately determined. An inaccuracy in the same direction and by at least approximately the same amount does not affect the difference. Thus, the determination of the volume flow flowing through the proportional valve is possible without additional mechanical effort. Finally, the offset of the control signal is determined by comparing the control signal of the proportional valve detected when the specified volume flow is reached with a theoretical control signal. The individual process steps are carried out automatically by the electronic control unit after a start signal, with the individual process steps being carried out automatically by the electronic control unit in a very short time in the region of one second, at least from the start of the opening of the continuous valve.

In principle, it is conceivable that the adjusting and regulating device of the hydraulic pump comprises an optionally also adjustable pressure regulator, to which the pump pressure is hydraulically fed back for pressure regulation. It seems simpler, however, if the pump pressure can be recorded by a pressure sensor whose electrical output signal is used to regulate the pump pressure to the set pressure by the electronic control unit or by electronics built directly onto the hydraulic pump, so-called on-board electronics.

It can be provided that the stroke volume of the hydraulic pump is detected by a stroke volume sensor with an electrical output signal and is thus fed back electrically. Then the supply and discharge of pressure fluid to an adjusting piston arrangement of the hydraulic pump can be done via a simple electrically controlled directional valve, for example via a proportionally adjustable directional valve with three hydraulic connections the stroke volume detected by the stroke volume sensor results. If the desired stroke volume is present, the directional control valve is in a control position in which a valve connection connected to an actuating chamber of the actuating piston arrangement is blocked from a pressure connection and from a tank connection with a small positive or negative overlap. After a shift from the control position, pressure fluid flows to or from the control chamber and the stroke volume changes.

The stroke volume of the hydraulic pump can also be adjusted proportionally to an electrical pump control signal. One then speaks of an electro-proportional (EP) control, in which the position of an element that determines the stroke volume of the hydraulic pump, for example the swash plate, is fed back via a feedback spring as a force on the valve piston of a control valve. A proportional electromagnet, the force of which depends on the level of the current flowing through it, acts on the valve piston against the force of the feedback spring. If the spring force is just as great as the magnetic force, the control valve is in a control position in which, apart from the replacement of leakage, pressurized fluid neither flows into an actuating chamber nor flows out of the actuating chamber. The stroke volume of the hydraulic pump does not change. The magnetic force is changed by changing the force generated by the electromagnet If the current flowing through is increased or decreased, the equilibrium of forces on the valve piston is disturbed and the valve piston is moved out of the control position. Pressurized fluid flows to or from the actuating chamber, the swash plate changes its position until there is again a balance between the force of the feedback spring, which changes with the position of the swash plate, and the magnetic force. With an EP control, the achievement of the specific difference between the current pump volume flow and the pump volume flow before the opening of the flow cross-section can be determined using a value of the pump control signal, which is calculated using the value of the pump control signal before the increase in the stroke volume and the specified specific pump volume flow difference . The pump control signal is the electric current flowing through the proportional solenoid.

The continuous valve is preferably a valve with exactly two connections, so its function is an adjustable throttle valve.

In principle, it is conceivable that the speed of the hydraulic pump changes while the method is being carried out. Then the pump volume flow at the beginning of the opening of the proportional valve results from the stroke volume present at this moment and from the speed present at this moment. The current pump volume flow during the increase in the control signal of the proportional valve results from the current stroke volume and the current speed, so that if the speed changes, the pump volume flow would have to be calculated continuously until the specified difference between the current pump volume flow and that at the beginning of the opening of the proportional valve was available Pump volume flow is reached.

If, on the other hand, the speed of the hydraulic pump is at least approximately constant during the change in the control signal for the proportional valve, a value of the stroke volume can be calculated with this speed, at which the specified difference in the pump volume flows and thus the specified value of the volume flow flowing through the continuous valve reaches will. You only have to look at the value of the stroke volume and not continuously calculate a volume flow. This value of the stroke volume can therefore be determined from the value of the stroke volume and from the value of the speed during method steps one and two.

The method is possible without a special design of the hydraulic system if three pressurized fluids flow to the hydraulic consumer while the method step is being carried out, the load pressure of the hydraulic consumer being known or assessable. Then no additional valve is necessary through which the amount of pressure fluid flowing through the continuous valve can flow to the tank. For example, the stick and bucket of the equipment of an excavator can hang freely during calibration of the associated proportional valves so that the load pressure is zero. This means that the pressure difference across the proportional valve is equal to the set pressure. A certain amount of pressurized fluid flows to the arm cylinder and the bucket cylinder during the calibration process, so that their position and thus also the load pressure change somewhat. However, the process can take place very quickly, so that the amount of pressurized fluid flowing in is small. The pressure difference is only included in the volume flow with its root. The boom can rest on the ground via the handle and the bucket while the procedure is being carried out,

It is also conceivable to measure the load pressure and to set the specified pressure to which the hydraulic pump is regulated by a specified difference above the load pressure.

The hydraulic consumers on mobile work machines, for whose control the proportional valves to be calibrated are primarily provided, are usually double-acting hydraulic cylinders. Then, in addition to the continuous valve, there is also a main control valve for each hydraulic cylinder, with which the direction of movement of the hydraulic consumer can be controlled, but volume flow throttling is also possible. The main control valve has two consumer connections which are fluidically connected to the hydraulic consumer, a supply connection which is fluidically connected to the continuous valve, and a tank connection. It is now particularly advantageous if, during method steps one to three, the lower-load side of the hydraulic consumer is fluidically connected to the continuous valve via the main control valve. The method can then be performed in a situation in which the pressure on the opposite side of a hydraulic cylinder from the load side is zero or near zero.

The hydraulic system, within which the continuous valve to be calibrated is arranged, can also comprise a continuously adjustable bypass valve with which a flow cross section between the pressure connection of the hydraulic pump and a tank can be controlled. As a result, even if the main control valve is one with a closed center position, load sensitivity can be obtained in accordance with a type of control of a hydraulic consumer referred to as positive control. In a neutral position, a defined amount of pressurized fluid (eg 30 l / min) flows from the hydraulic pump via the bypass valve to the tank. Becomes a hydraulic When the consumer is actuated, the main control valve, the proportional valve and the bypass valve are actuated and their valve pistons are shifted proportionally to the level of the actuation signal. This reduces the flow cross-section of the bypass valve and at the same time opens a flow cross-section on the main control valve and on the continuous valve. At the same time, the pump swings out proportionally. As soon as the pump pressure is greater than the load pressure, oil flows to the consumer. It is advantageous if the bypass valve is open during method steps one to three. It is set to such a flow cross-section that is constant during the calibration that the pump pressure can be regulated to the preset pressure during method steps one to three by the delivery rate of the hydraulic pump. Too large a flow cross-section of the bypass valve would lead to the default pressure not being reached even at the maximum stroke volume of the hydraulic pump.

A hydraulic system with a continuous valve to be calibrated and various diagrams with time profiles of electrical currents, flow cross-sections, pump pressure and delivery rate of the hydraulic pump while an example of a method according to the invention is being carried out are shown in the drawings. The invention will now be explained in more detail with the aid of these drawings.

• 1 ein Schaltbild des vereinfacht nur mit einem Hydraulikzylinder und entsprechenden Ventilen dargestellten hydraulischen Systems, wobei sich dieses in einem Ausgangszustand befindet,
• 2 das Schaltbild einer in dem hydraulischen System gemäß 1 einsetzbaren Verstellpumpe mit einer elektroproportionalen Einstellung des Hubvolumens,
• 3 drei Graphen mit der Darstellung verschiedener Größen am Stetigventil, nämlich der vorgegebenen Druckdifferenz, des elektrischen Stroms, mit der ein Elektromagnet des zu kalibrierenden Stetigventils angesteuert wird, und des durch das Stetigventil hindurchfließende Volumenstroms über die Zeit, in der das erfindungsgemäße Verfahren durchgeführt wird,
• 4 vier Graphen mit der Darstellung zusätzlicher Größen in einem Ausgangszustand und in aufeinanderfolgenden Abschnitten der Zeit, in der das erfindungsgemäße Verfahren durchgeführt wird,
• 5 das Schaltbild nach 1 in einem Zustand während eines ersten Zeitabschnitts bei der Durchführung des Verfahrens zur Kalibrierung,
• 6 das Schaltbild nach 1 in einem Zustand während eines zweiten Zeitabschnitt bei der Durchführung des Verfahrens zur Kalibrierung,
• 7 das Schaltbild nach 1 in einem Zustand während eines dritten Zeitabschnitt bei der Durchführung des Verfahrens zur Kalibrierung und
• 8 das Schaltbild einer in dem hydraulischen System gemäß 1 einsetzbaren Verstellpumpe, bei der das eingestellte Hubvolumen durch einen Schwenkwinkelsensor erfassbar ist.

Show it

• 1 a circuit diagram of the hydraulic system shown in simplified form with only one hydraulic cylinder and corresponding valves, this being in an initial state,
• 2 the circuit diagram of one in the hydraulic system according to 1 usable variable displacement pump with an electro-proportional setting of the stroke volume,
• 3 three graphs showing various variables on the continuous valve, namely the specified pressure difference, the electrical current with which an electromagnet of the continuous valve to be calibrated is controlled, and the volume flow flowing through the continuous valve over the time in which the method according to the invention is carried out,
• 4th four graphs showing additional variables in an initial state and in successive sections of the time in which the method according to the invention is carried out,
• 5 the circuit diagram according to 1 in a state during a first time segment when performing the calibration method,
• 6th the circuit diagram according to 1 in a state during a second time segment when performing the calibration method,
• 7th the circuit diagram according to 1 in a state during a third time segment when the method for calibration and
• 8th the circuit diagram of one in the hydraulic system according to 1 usable variable displacement pump, in which the set stroke volume can be detected by a swivel angle sensor.

The hydraulic system according to 1 comprises a double-acting hydraulic cylinder designed as a differential cylinder 15th which is used, for example, to move a component of an excavator arm and which has a cylinder housing 16 has, the interior of which is a piston 17th , one side of which is a piston rod 18th protrudes into a cylinder space remote from the piston rod 19th and into a cylinder space on the piston rod side 20th divides.

The hydraulic system according to 1 furthermore comprises a device with the aid of an adjustment device 24 Hydraulic pump adjustable on one side in its stroke volume between a minimum value and a maximum value 25th , which is designed as an axial piston pump in swashplate design and which can be driven, for example, by a diesel engine. From the hydraulic pump 25th are the hydraulic cylinder 15th and usually other hydraulic cylinders or hydraulic motors (not shown) that can be supplied with pressurized fluid either individually or at the same time. The hydraulic pump 25th sucks from a tank 26th Pressure fluid and is there via a pressure connection 27 into a pump line 28 away. The speed of the hydraulic pump 25th is from a speed sensor 23 recorded.

The inflow and outflow of pressurized fluid to and from the hydraulic cylinder 15th is controlled by a valve arrangement, the individual valves of which form a valve disc 29 are summarized, which can be assembled with other valve disks of the same or similar structure to form a control block. The valve assembly includes a main valve 30th , with which the direction in which the piston rod is 18th of the hydraulic cylinder 15th is moved, is set and a consumer connection 31 , the one with the cylinder space 19th of the hydraulic cylinder 15th is fluidically connected, a consumer connection 32 , the one with the cylinder space 20th of the hydraulic cylinder is fluidically connected, a pump connection 33 , the one from the hydraulic pump 25th Pressure fluid can be supplied, and two tank connections 34 has, of which pressurized fluid into the tank 26th can drain. A control slide of the main valve, not shown in detail 30th takes under the action of two return springs 35 one in 1 drawn Middle position in which the connections of the main valve are blocked against each other. This is why one speaks of a valve disc with a locked center position (closed-center control disc). The spool is with the help of two by one proportional solenoid each 36 adjustable pressure control valves from the middle position to one or the other side continuously adjustable in proportion to a control signal. When moving in one direction, the consumer connection 31 and thus the cylinder space 19th to the pump connection 33 and the consumer connection 32 and thus the cylinder space 20th to a tank connection 34 opened out, so that pressure fluid conveyed by the hydraulic pump enters the cylinder space 19th flow in and pressure fluid from the cylinder space 20th to the tank 26th can flow away. When the control spool is moved out of the middle position in the opposite direction, the consumer connection 32 and thus the cylinder space 20th to the pump connection 33 and the consumer connection 31 and thus the cylinder space 20th to a tank connection 34 opened out, so that pressure fluid conveyed by the hydraulic pump enters the cylinder space 20th flow in and pressure fluid from the cylinder space 19th to the tank 26th can flow away.

Between the pressure connection 27 the hydraulic pump 25th and the pump connection 33 of the main valve 30th is a proportional valve that can be adjusted proportionally to a control signal 40 with two working connections 41 and 42 arranged, with an input port 41 with the pump line 28 and an output port 42 with the pump connection 33 of the main valve 30th are fluidically connected. Under the action of a return spring 43 takes the proportional valve 40 a rest position in which the two working connections are blocked from each other. The proportional valve 40 is continuously adjustable from the rest position up to a maximally open position. When adjusting from the rest position, the flow cross-section through the proportional valve increases up to a maximum value. The adjustment takes place electro-hydraulically with the help of a proportional solenoid 44 adjustable pilot valve, so that the flow area of the proportional valve 40 ultimately from the signal with which the proportional solenoid 44 is controlled, and therefore depends on the electric current flowing through the proportional electromagnet. The proportional valve 40 also serves as a load holding valve and closes when the pressure at its connection 42 higher than the pressure at the connection 41 , i.e. higher than the pump pressure in the pump line 28 is.

To the pump line 28 is a continuously adjustable bypass valve 50 connected, via the pressure fluid from the pump line 28 straight to the tank 26th can drain. Under the action of a return spring 51 takes the bypass valve 50 a rest position in which a maximum flow cross-section between the pump line 28 and the tank 26th is open. The bypass valve 50 can be adjusted from the rest position with a steadily decreasing flow cross-section into a closed position in which no pressure fluid can flow from the pump line to the tank via the bypass valve. A proportional solenoid is used for adjustment 52 .

The pressure in the pump line is measured by a pressure sensor 54 recorded.

With an electrical input device 55 the direction and the speed with which the piston and the piston rod of the hydraulic cylinder should move can be specified. The electrical signals from the input device 55 are via an electrical line 56 an electronic control unit 57 supplied with a microcontroller, which also has an electrical line 53 from the speed sensor 23 receives an electrical signal indicating the speed of the hydraulic pump 25th represented, and via an electrical line 58 from the pressure sensor 54 receives an electrical signal indicating the pressure in the pump line 28 , i.e. represents the pump pressure. The two proportional electromagnets 36 of the main valve 30th , the proportional solenoid 44 of the proportional valve 40 , the proportional solenoid 52 of the bypass valve 50 and a proportional solenoid 59 the adjustment device 24 for adjusting the stroke volume of the hydraulic pump 25th are via electrical lines 61 , 62 , 63 , 64 and 65 with the electronic control unit 57 and are connected by this depending on the signals from the input device 55 , the condition of the hydraulic system and the initiation of a procedure for calibrating the proportional valve 40 energized.

The stroke volume of the hydraulic pump 25th is through the in 2 Adjusting device shown in more detail 24 designed according to an electro-proportional (EP) control with superimposed maximum pressure control. Taking into account the signals from the pressure sensor 54 however, it is also possible to regulate a pressure below the maximum pressure. The adjustment device 24 includes an actuating piston 73 , which can be moved in a straight line and an actuating chamber 74 limited, which -controlled by two control valves - flow pressure medium and can be displaced from the pressure medium via the control valves. The control piston 73 is under the action of the in the actuating chamber 74 prevailing pressure on a swash plate 75 on and tried the swashplate 75 to be adjusted in the direction of a reduction in the stroke volume.

The swash plate acts in the opposite direction 75 a return spring 76 that differ from what is shown in the circuit diagram 2 shown, not directly on the setting piston 73 , but, on the swash plate 75 attacks. An attack by the counter spring on the actuating piston would make a positive connection between the actuating piston and the swash plate necessary in both directions of adjustment.

On a flange surface of the pump housing indicated by dash-dotted lines 77 is a control valve that functions as a pressure regulator 78 built up, the one control piston 79 for regulation, more precisely to limit the pump pressure. The control piston 79 is from an adjustable control spring 80 urged in the direction of a rest position, which in 2 is shown, and continuously adjustable from the rest position. With the housing, which is not specified, it represents a proportionally adjustable 3/2-way valve.

The control valve 78 has a pressure connection P, a control connection A and a tank connection T in a mounting surface with which it rests on the flange surface. The pressure connection P is via a bore inside the pump housing 77 with one to the pressure connection 27 the hydraulic pump 25th leading high pressure channel fluidically connected. The tank connection is via a bore inside the pump housing with the interior of the pump housing 77 and connected to the tank via a leakage connection of the pump housing in a manner not shown in detail. The control connection A is via a bore in the pump housing 77 connected to the actuating chamber bore in which the actuating piston 73 is slidably guided. The control valve 78 can supply pressure medium from pressure port P directly to the control chamber via control port A. 74 Supply or drain pressure medium from the actuating chamber to tank connection T.

The control piston 79 of the pressure regulator 78 is against the rule pen 80 acted upon by the pump pressure.

In the rest position of the pressure regulator 78 its control port A is connected to the tank port T so that the counter spring 76 Pressure medium from the actuating chamber 74 can be displaced. This increases the stroke volume of the variable displacement pump. If the pump pressure is so high that it is the pressure equivalent of the control spring 80 exceeds the control piston 79 of the pressure regulator 78 moved from its rest position, so that the pressure regulator of the actuating chamber 74 from the pressure connection 27 the hydraulic pump 25th forth pressure fluid can be supplied and the stroke volume of the hydraulic pump is reduced.

From control port A of the pressure regulator 78 the fluid path does not lead directly into the actuating chamber 74 . Rather, there is still a through the proportional electromagnet in this fluid path 59 proportionally operable control valve 81 inserted, which is used as an installation cartridge in the actuating chamber bore and the actuating chamber 74 on the setting piston 73 opposite side limited. The control valve 81 , also known casually as EP regulator, has a pressure connection that connects directly to the high pressure side of the hydraulic pump 25th is connected, an indifferent connection, which is connected to the control connection A of the pressure regulator 78 is connected and an actuating chamber connection that connects to the actuating chamber 74 connected is. A control piston 82 of the control valve 81 is controlled by the force of a between the control piston 82 and the actuating piston 73 clamped feedback spring 83 acted upon in the direction of a rest position in which the control chamber connection with the pressure connection of the control valve 81 connected is. The force of the feedback spring depends on the position of the actuating piston 73 and thus on the position of the swash plate 75 away. The proportional solenoid 59 is capable of the control piston 82 against the feedback spring 83 to move into positions in which the control chamber connection with the indifferent connection and further via the control connection A of the pressure regulator 78 is connected to the pressure port P or to the tank port T of the pressure regulator. Opposite the one in the actuating chamber 74 The pressure applied is the control piston 82 pressure balanced. The pressure prevailing in the actuating chamber therefore does not exert any resulting force on the control piston 82 the end. This takes a control position when the feedback spring 83 The force exerted is the same as the force of the proportional solenoid 59 is. Because the one from the feedback spring 83 force exerted by the position of the swashplate 75 depends, is thus proportional to that by the proportional solenoid 59 flowing current a certain swivel angle of the swash plate 75 regulated. Through the control valve 81 is therefore an electro-proportional adjustment of the hydraulic pump 25th realized.

In the case of the 2 The variant of an electro-proportional adjustment shown has the control valve 81 a third position to which it comes in the event of a loss of control signal. The hydraulic pump is set to maximum stroke volume in the event of a loss of control signal.

Through the three graphs de 3 is an exemplary characteristic deviation of the proportional valve 40 compared to a theoretical characteristic curve. The top graph shows a pressure that is present across the continuous valve over time, for which a certain value, namely an operating point pressure of, for example, 50 bar is specified. According to the middle graph, the control signal for the proportional valve 40 , namely the one by the proportional solenoid 44 flowing electrical current, ramped up over time. The bottom graph shows a theoretical volume flow with a dashed line and with a continuous line the actual volume flow through the proportional valve 40 shown how it results during the ramp-like increase in the electrical current. In addition, an operating point volume flow of, for example, 10 l / min is shown. Theoretically, at the specified operating point pressure, the operating point volume flow at time T1 should be achieved by the proportional solenoid 44 flowing nominal current 11 can be achieved. The proportional valve opens due to manufacturing-related deviations 40 only later, the working point volume flow is therefore only reached at a later point in time T2 when the current value 12 is higher than the current value 11. The difference between the current value 12 and the current value 11 is the current offset, which is created in the hydraulic system by the electronic control unit 57 individually for the respective proportional valve 40 is determined by the calibration process according to the invention.

In 4th the top graph shows the current generated by the proportional electromagnet in an initial state a and during various sections b, c, d and e of a calibration process 44 of the proportional valve 40 , the proportional solenoid 52 of the bypass valve 50 , the proportional solenoid 59 the adjustment device 24 and one of the proportional electromagnets 36 on the main valve 30th flows. The curves are provided with the same reference numbers as the proportional electromagnet that is energized accordingly. The second graph from the top shows the pump volume flow in the initial state a and during the calibration sections b to e. The third graph from the top shows the flow areas of the valves 30th , 40 and 50 in the initial state and in the various calibration sections. The curves are given the same reference numerals as the corresponding valve. The dashed line indicates the theoretical flow cross-section of the proportional valve 40 . And finally, the bottom graph shows the pump pressure in the initial state and during the calibration process, in the present case the pump pressure during the calibration process is equal to the operating point pressure and is regulated. It is advantageous if the speed of the hydraulic pump is adjusted during the calibration process 25th is kept constant. This is assumed in the following.

In the initial state a, which is shown in 1 is shown, the hydraulic system is in a standby mode. The hydraulic pump 25th generates a standby volume flow, which results from the energization of the proportional solenoid 59 and the over the open bypass valve 50 in the tank 26th flows. According to the top graph of the 4th is the proportional solenoid 52 the bypass valve is already charged with a certain current. The proportional valve 40 is closed, according to the top graph of 4th However, even a small current flows through the proportional solenoid 44 of the proportional valve 40 . The main valve 30th is in its middle position. For the hydraulic pump 25th no pressure control is active. The pump pressure results from the standby volume flow of the hydraulic pump 25th and the flow area of the bypass valve 50 .

The calibration process begins in section b. The bypass valve 50 is achieved by a higher current supply to the proportional solenoid that is kept constant over the further sections 52 set to such a smaller flow cross-section that in the pump line 28 the operating point pressure to be regulated can be achieved. The hydraulic pump 25th is made with the help of the pressure sensor 54 and the electronic control unit 57 and its adjustment device 24 pressure-regulated to the specified operating point pressure, the proportional solenoid 59 is applied with an increased electrical current I1 _pump compared to the output section a. This current value I1 _pump is generated by the electronic control unit 57 saved. A proportional solenoid 36 of the main valve 30th is fully energized and remains fully energized during the calibration process, so that the proportional valve 40 to the hydraulic cylinder 15th there is an open fluidic connection.

In section b of the calibration process, all of the flow from the hydraulic pump 25th generated volume flow via the bypass valve 50 to the tank 26th away.

Starting from a minimum current supply, in section c of the calibration process, the proportional solenoid is used 44 of the proportional valve 40 flowing electric current slowly increases as this in 6th due to the increasing lightning over the proportional valve 40 is indicated. From the third graph from the top of the 4th it can be seen that during section c the proportional valve 40 is not open yet. Therefore, the volume flow of the hydraulic pump is in section c 25th the same as in section b, as well as from the second graph from the top of the 4th emerges. The pump volume flow continues to flow through the bypass valve 50 to the tank 26th away.

Section d of the calibration process begins when on the proportional solenoid 44 of the proportional valve 40 a current value has been reached at which the proportional valve begins to open. From this point in time, a volume flow can flow out of the pump line 28 via the proportional valve 40 and via the main valve, which is already open from the beginning of section b 30th to the hydraulic cylinder 15th flow. Since now both via the bypass valve 50 as well as via the proportional valve 40 If pressure fluid flows out of the pump line, the stroke volume of the hydraulic pump becomes due to the pressure regulation 25th increased so that the operating point pressure in the pump line is maintained. The larger the one by the proportional solenoid 44 flowing current, the greater the flow cross-section in the continuous valve 40 , the greater the volume flow of the hydraulic pump and the greater that through the proportional solenoid 59 the EP regulation 24 Electric current flowing through the hydraulic pump, which is necessary to generate the volume flow. The one via the bypass valve 50 The volume flow flowing to the tank does not change because the flow cross-section of the bypass valve and the pump pressure do not change.

From the speed of the hydraulic pump and the stored current value I1 _{pump it} can now be calculated how large a current value I2 _pump is at which the working point volume flow through the proportional valve 40 flows. It is particularly advantageous if the relationship between the stroke volume and the current through the proportional solenoid 59 represents a linear relationship. Then the necessary change in stroke volume is independent of the absolute stroke volume. Now there is the relationship between the working point volume flow through the proportional valve 40 and the necessary change in the electrical current to the hydraulic pump 25th is known, based on an unknown or imprecise pump volume flow in sections b and c of the calibration process, the one via the continuous valve 40 flowing working point volume flow corresponding volume flow change of the hydraulic pump and thus the working volume flow can be determined very precisely. To determine the operating point volume flow, only knowledge of the change in the pump volume flow is necessary, whereas the absolute size of the volume flow in sections b and c of the calibration process does not have to be known.

As soon as now with the further increase of the proportional solenoid 44 of the rising valve 40 flowing electrical current at the pump the current value I2 _{pump is} reached, the last section e of the calibration process begins. The control unit 57 , knows that the working point volume flow is now over the proportional valve 40 flows. The control unit 57 also knows how high the proportional solenoid is 44 of the proportional valve 40 electrical current flowing at the point in time at which the operating point volume flow through the proportional valve 40 flows, and stores this current as current value 12. The difference between the current value 12 and the current value 11, at which theoretically at the given working point pressure the working point volume flow through the proportional valve 40 should flow is the current offset. This is in the control unit 57 stored and the manufacturing-related deviation of a single proportional valve 40 corrected from the theoretical characteristic curve by applying the current offset to the proportional solenoid for each 44 of the proportional valve 40 The control signal to be given is added to the theoretical control signal, taking into account the sign of the current offset.

It is advantageous for the method if the load pressure is as low as possible and significantly lower than the operating point pressure so that a volume flow can flow to the hydraulic consumer. With the help of the main valve, the cylinder chamber with the lower load can be selected for the influx of pressurized fluid during the calibration process. It is particularly advantageous to know the load pressure, for example by measuring or estimating from a known position of the kinematics. The regulated pump pressure can then be increased by the load pressure compared to a value at zero load pressure, so that a pressure difference corresponding to the operating point pressure is present across the continuous valve.

It is conceivable that the bypass valve 50 to keep it closed during the calibration process. However, most hydraulic pumps have a mechanical stop for a minimal stroke volume. In the initial state of section a according to 4th The standby volume flow resulting from this minimum stroke volume and the speed of the hydraulic pump can flow off to the tank with little loss and a pressure below a maximum pressure can be regulated in sections b and c.

A variable displacement pump with EP control is not absolutely necessary for calibration of a valve according to the invention. Other adjustment devices are also possible.

So shows the 8th a hydraulic pump in axial piston design, in which the stroke volume and in particular a change in stroke volume is determined with the aid of a swivel angle sensor.

In the 8th Adjusting device shown 24 for adjusting the swashplate 75 the variable displacement pump 25th includes a single-acting actuating piston 86 , with which the swash plate can be pivoted in the sense of a reduction in the inclination and thus a reduction in the stroke volume, and a single-acting opposing piston 87 that together with a feather 88 the swash plate can pivot in the sense of an increase in the inclination and thus an increase in the stroke volume and its effective area is smaller than the effective area of the actuating piston 86 . One the opposed piston 87 surrounding opposing chamber 89 is permanently connected to the pressure connection 27 the variable displacement pump 25th connected so that the opposed piston is acted upon by the pump pressure.

The inflow and outflow of hydraulic oil to and from an actuating chamber 90 into which the actuating piston 86 immersed is considered proportional by one adjustable 3/2 way valve designed control valve 91 controlled, the one pressure connection 92 , the one with the pressure connection 27 the variable displacement pump is connected, and a tank connection 93 that is connected to the inside of the pump housing 77 and above with the tank 26th is fluidically connected. The control valve 91 finally has a control chamber connection 94 , which is fluidically connected to the actuating chamber 90 connected is. In a rest position, the control valve 91 under the action of a compression spring 95 occupies, there is a large flow cross-section between the actuating chamber connection 94 and the tank connection 93 . By a proportional solenoid 96 can the control valve 91 depending on the magnitude of the solenoid current against the force of the compression spring 95 can be moved differently from the rest position. At a certain height by the proportional solenoid 96 Flowing electrical current is taken by a control piston (not shown) of the control valve 91 a control position in which the control chamber connection 94 with a small negative overlap against the pressure connection 92 and against the tank connection 93 is largely cordoned off. In the control position, only the small leakage flow flowing out of the control chamber is replaced. The inclination of the swashplate 75 and thus the displacement of the variable displacement pump 25th do not change. Then through the proportional solenoid 96 Flowing current is therefore also referred to as neutral current.

Is the by the proportional solenoid 96 The pressure spring is able to reduce the flowing electrical current compared to the neutral current 95 to move the control piston from the control position into a position in which the control chamber connection 94 to the tank connection 93 is open. The size of the flow cross-section depends on the difference between the neutral current and the instantaneous current. It can now be removed from the actuating chamber 90 Hydraulic oil via the actuating chamber connection 94 and the tank connection 93 be displaced, so that the inclination of the swash plate 75 is enlarged. Is the by the proportional solenoid 96 If the electric current flowing increases compared to the neutral current, the proportional solenoid is able to move the control piston from the control position into a position in which the control chamber connection 94 to the pressure connection 92 is open. The size of the flow cross-section depends on the difference between the instantaneous current and the neutral current. It can now be the actuating chamber 90 from the pressure connection 27 the variable displacement pump 25th flow in from hydraulic oil, so that the inclination of the swash plate 75 is reduced.

With the variable displacement pump 25th according to 8th becomes the swivel angle of the swashplate 75 and thus the stroke volume through a swivel angle sensor serving as a stroke volume sensor 97 which sends an electrical output signal to the electronic control unit 57 gives away. This compares the output signal of the swivel angle sensor corresponding to the actual value of the swivel angle 97 with a setpoint and controls the control valve 91 depending on the difference between the setpoint and the actual value of the swivel angle.

Also with the variable displacement pump according to 8th is a pressure sensor for recording the pump pressure 54 provided with the control unit 57 connected is. This enables the pump pressure to be regulated. With the help of the signals from the swivel angle sensor 97 can be via the proportional valve 40 flowing operating point volume flow can be recorded quite precisely, so that also with a hydraulic pump according to 8th the calibration method according to the invention can be carried out.

List of reference symbols

15th

Hydraulic cylinder

16

Cylinder housing from 15

17th

Piston of 15

18th

Piston rod from 15

19th

Cylinder space away from the piston rod of 15

20th

Piston rod side cylinder space of 15

23

Speed sensor

24

Adjusting device

25th

Hydraulic pump 25

26th

tank

27

Pressure connection from 25

28

Pump line

29

Valve disc

30th

Main valve

31

Consumer connection from 30

32

Consumer connection from 30

33

Pump connection from 30

34

Tank connection from 30

35

Return spring

36

Proportional solenoid

40

Proportional valve

41

Working connection of 40

42

Working connection of 40

43

Return spring

44

Proportional solenoid

50

Bypass valve

51

Return spring from 50

52

Proportional solenoid of 50

53

electrical line

54

Pressure sensor

55

electrical input device

56

electrical line

57

electronic control unit

58

electrical line

59

Proportional solenoid on 25

61

electrical line

62

electrical line

63

electrical line

64

electrical line

65

electrical line

73

Control piston

74

Control chamber

75

Swash plate from 25

76

Return spring

77

Pump housing

78

Control valve

79

Control piston from 78

80

Rule spring from 78

81

Control valve

82

Control piston from 81

83

Feedback spring

86

Control piston

87

Opposed piston

88

feather

89

Opposing chamber

90

Control chamber

91

Control valve

92

Pressure connection from 91

93

Tank connection from 91

94

Actuating chamber connection from 91

95

Compression spring on 91

96

Proportional electromagnet of 91

97

Swivel angle sensor

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• US 2017262001 A1 [0004, 0005]

Claims (12)

Method for calibrating a proportional valve (40) which is arranged in a hydraulic system and can be adjusted proportionally to a control signal of an electronic control device (57) with regard to an offset of the control signal at an operating point with a predetermined pressure difference and a predetermined volume flow via the proportional valve (40), wherein, via the continuous valve (40), pressurized fluid from the pressure connection of a hydraulic pump (25), whose stroke volume can be measured in terms of its size is adjustable and whose pump pressure can be regulated, can be fed to a hydraulic consumer (15), with the following process steps: 1) Regulation of the pump pressure to a preset pressure with the continuous valve (40) closed; 2) acquisition of a value at least for the stroke volume of the hydraulic pump (25); 3) changing the control signal of the continuous valve (40) from an initial control signal until a difference between the current pump volume flow and the pump volume flow given when the continuous valve (40) is closed is detected; 4) Determination of the offset of the control signal by comparing the control signal of the proportional valve (40) detected when the specified volume flow is reached with a theoretical control signal. Procedure according to Claim 1 , wherein during method step three, the control signal of the proportional valve (40) is increased from an initial control signal in which the proportional valve (40) is closed until a difference between the current pump volume flow and that before the opening of a flow cross-section corresponds to the specified volume flow Proportional valve (40) given pump volume flow is detected. Procedure according to Claim 1 or 2 , the pump pressure being detectable by a pressure sensor (54), the electrical output signal of which is used to regulate the pump pressure to the preset pressure. Procedure according to Claim 1 , 2 or 3 , the stroke volume of the hydraulic pump (25) being detected by a stroke volume sensor (97). Procedure according to Claim 4 , the stroke volume of the hydraulic pump (25) being adjustable by supplying and removing pressure fluid to and from an adjusting device (24) via an electrically controlled directional valve (91) and the control signal for the directional valve (91) being the difference between a desired one Stroke volume and the stroke volume detected by the stroke volume sensor (97) results. Procedure according to Claim 3 or 4th , the stroke volume of the hydraulic pump (25) being adjustable proportionally to an electrical pump control signal, and the achievement of the specific difference between the current pump volume flow and the pump volume flow before the opening of the flow cross-section is determined using a value of the pump control signal, which is determined using the value of the pump control signal is calculated before increasing the stroke volume and the predetermined specific pump volume flow difference. Method according to one of the preceding claims, wherein the continuous valve (40) is a valve with exactly two connections. Method according to one of the preceding claims, the speed of the hydraulic pump (25) being at least approximately constant during the change in the control signal for the proportional valve (40) and the stroke volume at which the determined difference between the pump volume flows is obtained from the value of the stroke volume and is determined from the value of the speed during process steps one and two. Method according to one of the preceding claims, wherein three pressurized fluids flow to the hydraulic consumer (15) during the method step and the load pressure of the hydraulic consumer (15) is known or can be estimated. Procedure according to Claim 9 , wherein the preset pressure to which the hydraulic pump (25) is regulated is a preset difference above the load pressure. Method according to one of the preceding claims, wherein the hydraulic consumer (15) is a double-acting hydraulic consumer, in particular a double-acting hydraulic cylinder, and the direction of movement of the hydraulic consumer can be controlled by a main control valve (30), which has two consumer connections (31, 32) which are fluidly connected to the hydraulic consumer are connected, a supply connection (33) which is fluidly connected to the continuous valve (40), and a tank connection (34) and wherein at least during process steps one to three, the load-lower side of the hydraulic consumer (15) via the Main control valve (30) is fluidically connected to the proportional valve (40). A method according to any preceding claim, wherein the hydraulic system comprises a continuously adjustable bypass valve (50) with which a flow cross-section between the pressure connection (27) of the hydraulic pump (25) and a tank (26) can be controlled, and wherein the bypass valve (50) is open during method steps one to three and is set to such a flow cross-section that during method steps one to three the pump pressure can be regulated to the preset pressure by the delivery rate of the hydraulic pump (25).

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