Arrangement for operating a hydraulic consumer

Abstract

Arrangement (10) for operating a hydraulic consumer (16), comprising a hydraulic control valve (20) with a main spool valve, a pressure compensation valve and a measuring orifice, wherein a hydraulic volume flow in the direction of hydraulic connections (42) provided for the operation of the hydraulic consumer (16) can be specified by means of the main spool valve, wherein the pressure compensation valve is actuated according to a pressure difference falling at the measuring orifice when the volume flow passes through it, such that it assumes a control position that is at least partially closed when the hydraulic pressure in the direction of the volume flow in front of the measuring orifice is greater than that behind the measuring orifice including a restoring spring force of a spring element that biases the pressure compensation valve into a fully open position.In this case, a sensor arrangement (64) detects the pressure difference and transmits a derived pressure difference value to a control unit (54), whereby the control unit (54) concludes, by evaluating the pressure difference value, that there is a mismatch in the hydraulic supply on the part of the hydraulic control valve (20) if the pressure difference is smaller than a control value given by the restoring spring force.

Description

[0001] The invention relates to an arrangement for operating a hydraulic consumer, comprising a hydraulic control valve with a main spool valve, a pressure compensation valve and a metering orifice, wherein a hydraulic volume flow in the direction of hydraulic connections provided for operating the hydraulic consumer can be predetermined by means of the main spool valve, wherein the pressure compensation valve is controlled in accordance with a pressure difference falling at the metering orifice as the volume flow passes through such that it assumes an at least partially closing control position when the hydraulic pressure in the direction of the volume flow in front of the metering orifice is greater than that behind the metering orifice, including a restoring spring force of a spring element prestressing the pressure compensation valve into a fully open position.

[0002] Typically, such hydraulic control valves are used in agricultural tractors to operate hydraulic actuators that are integrated into an attachment mounted on the agricultural tractor and serve to perform various work functions. These hydraulic actuators are usually hydraulic rotary actuators and / or linear actuators.

[0003] Typically, several hydraulic control valves, often referred to as "control units" or "Selective Control Valves" (SCVs), are combined into a control valve block located at the rear or front of the agricultural tractor. Each of the hydraulic control valves opens into a pair of hydraulic bushings on the connection side, with a first hydraulic bushing forming an inlet and a second hydraulic bushing forming a return for hydraulic fluid. The hydraulic bushings accommodate complementary hydraulic couplers, which create a detachable plug-in connection for operating a respective hydraulic consumer.

[0004] To start up the hydraulic consumer, the valve position of the main spool valve can be specified as desired by the operator via a control terminal provided in the agricultural tractor. The pressure compensation valve included in the hydraulic control valve ensures that a constant flow rate is maintained, corresponding to the valve position of the main spool valve and independent of supply pressure fluctuations.

[0005] Undesirable conditions can occur during operation of the hydraulic consumer. Two different operating situations, A and B, can be distinguished: Operating situation A

[0006] First, there is the possibility that the volume flow requested based on the respective valve position of the main spool valve cannot be achieved due to a simultaneous increased supply demand from other hydraulic consumers that are supplied with hydraulic fluid from the same hydraulic source. This leads to an overall undersupply of the hydraulic consumers and thus, potentially, to corresponding restrictions in the execution of the respective operating or work functions. Operating situation B

[0007] In addition, there are hydraulic consumers in which, by design, no (significant) volume flow flows during operation, ultimately resulting in a hydraulic backpressure, which causes the system pressure built up by a corresponding hydraulic source to reach a maximum value, which in the case of a hydraulic system provided in an agricultural tractor can typically be up to 190 bar. This is particularly true for hydraulic consumers designed as hydraulic linear actuators, in which, by design, a volume flow only flows during the adjustment process until a corresponding end stop is reached.

[0008] A known arrangement is known from WO 92 / 10684 A1.

[0009] In view of this, it is the object of the present invention to further develop an arrangement of the type mentioned at the outset in such a way that it enables the detection of inefficient operating states of a hydraulic supply of a hydraulic consumer.

[0010] This object is achieved by an arrangement for operating a hydraulic consumer having the features of patent claim 1.

[0011] Advantageous further developments of the arrangement according to the invention emerge from the subclaims.

[0012] The arrangement for operating a hydraulic consumer comprises a hydraulic control valve with a main spool valve, a pressure compensation valve and a metering orifice, wherein a hydraulic volume flow in the direction of hydraulic connections provided for operating the hydraulic consumer can be predetermined by means of the main spool valve, wherein the pressure compensation valve is controlled in accordance with a pressure difference falling at the metering orifice as the volume flow passes through such that it assumes an at least partially closing control position when the hydraulic pressure in the direction of the volume flow in front of the metering orifice is greater than that behind the metering orifice, including a restoring spring force of a spring element prestressing the pressure compensation valve into a fully open position.In this case, a sensor arrangement detects the pressure difference and transmits a pressure difference value derived therefrom to a control unit, whereby the control unit concludes, by evaluating the pressure difference value, that there is a mismatch in the hydraulic supply on the part of the hydraulic control valve if the pressure difference is smaller than a control value given by the restoring spring force.

[0013] Such a situation arises when, with the main spool valve open, either no (significant) volume flow flows through the metering orifice toward the hydraulic consumer (operating situation A) or the flow does not reach the volume flow expected based on the respective valve position (operating situation B). In both cases, the pressure drop across the metering orifice and thus the pressure difference detected by the sensor arrangement becomes negligibly small, thus providing a clear and easily evaluated indicator for the occurrence of inefficient operating conditions in the hydraulic supply of the hydraulic consumer in question.

[0014] The restoring spring force generated by the spring element is dimensioned such that the pressure compensation valve reliably assumes its fully open position in a depressurized state. The resulting control value for the differential pressure, which must be achieved to switch the pressure compensation valve from its fully open position to its (at least partially closing) control position, is in the range of 5 to 15 bar.

[0015] The arrangement according to the invention is in particular a component of a higher-level hydraulic system of an agricultural tractor and serves there, among other things, to operate an attachment that can be attached to the agricultural tractor, more precisely a hydraulic consumer provided by the latter to carry out a corresponding work function.

[0016] The sensor arrangement preferably comprises a first pressure sensor and a second pressure sensor, with at least one of the two pressure sensors being integrated into a common valve housing of the hydraulic control valve in a space-saving manner. The sensor signals generated by the pressure sensors can be tapped off via an electrical connector accessible from the outside of the valve housing.

[0017] In principle, it is also conceivable to integrate both pressure sensors into the valve housing. However, in the case of a large number of hydraulic control valves, particularly those combined in a control valve block, unnecessary redundancy can be avoided if the pressure sensor intended to measure the hydraulic pressure upstream of the measuring orifice is assigned to a common supply line serving the hydraulic supply.

[0018] According to the invention, knowledge of the hydraulic supply mismatch resulting from operating situations A or B is used to implement appropriate countermeasures. For this purpose, the main spool valve is closed by the control unit by controlling an electrical actuating device, regardless of a hydraulic demand applied to the hydraulic control valve, particularly resulting from the specification on the operating terminal, until the sensor-detected pressure difference is greater than the control value determined by the restoring spring force, or the main spool valve ultimately assumes a fully closed valve position.

[0019] On the other hand, according to the invention, the control unit opens the main spool valve for testing purposes after a predetermined waiting time has elapsed by controlling the electrical actuating device in accordance with a hydraulic demand applied to the hydraulic control valve, in particular resulting from a specification on an operating terminal. Should the pressure difference again be smaller than the control value determined by the restoring spring force of the spring element of the pressure compensation valve, this indicates that the previously detected mismatch in the hydraulic supply still exists, and the main spool valve is closed again by the control unit by controlling the electrical actuating device until the sensor-detected pressure difference is again greater than the control value determined by the restoring spring force, or the main spool valve ultimately assumes a fully closing valve position.

[0020] Typically, the volume flow is generated by a load-controlled variable-displacement pump, so that the control unit can increase the flow rate by intervening in a pump drive when a sensor detects a swivel angle of the variable-displacement pump, indicating that a maximum displacement has been reached and thus an impending undersupply of the hydraulic consumer. In such a case, it is conceivable that the control unit could increase the flow rate by intervening in the pump drive until the pressure difference detected by the sensor is greater than the control value determined by the restoring spring force of the spring element of the pressure compensation valve.

[0021] Conversely, the control unit can reduce the flow rate of the variable-displacement pump back to a level intended for normal operation as soon as the sensor detects a change in the swivel angle, indicating a decrease in displacement. This ensures that an increase in flow rate, which would lead to increased energy consumption, only occurs for as long as it is actually necessary.

[0022] The pump drive, for example, is a separate motor that can be connected to the variable displacement pump via an intermediate gearbox, the speed of which can be adjusted to change the delivery rate by means of a control unit that communicates with the control unit.

[0023] The inventive arrangement for operating a hydraulic consumer for an implement mounted on an agricultural tractor is described in more detail below with reference to the drawings. Identical reference numerals refer to identical or functionally comparable components. They show: Fig. 1 a schematically illustrated embodiment of the arrangement according to the invention for operating a hydraulic consumer for an agricultural tractor, Fig. 2 a first embodiment of a hydraulic consumer of the arrangement according to the invention according to Fig. 1 included hydraulic control valve, Fig. 3 a second embodiment of an arrangement according to the invention according to Fig. 1 included hydraulic control valve, and Fig. 4 a modification of the Fig. 1 reproduced inventive arrangement.

[0024] Fig. 1shows a schematically illustrated embodiment of the arrangement 10 according to the invention for operating an attachment 14 attached to an agricultural tractor 12, more precisely a hydraulic consumer 16 provided by the latter for carrying out a corresponding work function.

[0025] More precisely, the arrangement 10 is part of a higher-level hydraulic system 18 of the agricultural tractor 12 and comprises a Fig. 2 or Fig. 3 hydraulic control valve 20 shown in detail, which in turn has a main spool valve 22, a pressure compensation valve 24 and a metering orifice 26.

[0026] In accordance with the usual design, the hydraulic system 18 has a supply line 30 fed by a hydraulic high-pressure source 28, a return line 34 leading into a hydraulic reservoir 32, and a load-sensing line 36, wherein the hydraulic high-pressure source 28, designed as a load-controlled variable displacement pump 38, generates a volume flow that can be adjusted in accordance with a pressure feedback signal applied to the load-sensing line 36.

[0027] For example, several hydraulic control valves 20 of identical design are connected in parallel to form a control valve block 40 located in the rear or front area of the agricultural tractor 12. Each of the hydraulic control valves 20 opens into a pair of hydraulic bushings 42 on the connection side, with a first hydraulic bushing 44 forming an inlet and a second hydraulic bushing 46 forming a return for hydraulic fluid. The hydraulic bushings 44, 46 serve to accommodate complementary hydraulic couplers 48, 50, by means of which a detachable plug-in connection can be established for operating the respective associated hydraulic consumer 16.

[0028] To start up the hydraulic consumer 16, the valve position of the main spool valve 22 is specified as desired by the operator via an operating terminal 52 provided in the agricultural tractor 12, which in turn communicates with a microprocessor-controlled control unit 54 for electrically actuating the main spool valve 22. The pressure compensation valve 24 encompassed by the hydraulic control valve 20 ensures that a constant volume flow corresponding to the valve position of the main spool valve 22 is established in the direction of the respective hydraulic consumer 16, independent of supply pressure fluctuations.

[0029] As in Fig. 2 or Fig. 3As can be seen, the hydraulic control valve 20 has three valve positions in the present case: a first and second open valve position 56, 58 corresponding to the two possible flow directions of the volume flow, as well as a closed valve position 60. In addition, a further valve position, not shown, can be present for realizing a so-called floating position in which the two hydraulic bushings 44, 46 communicate freely with one another.

[0030] The pressure compensation valve 24 is controlled in accordance with a pressure difference falling across the metering orifice 26 as the volume flow passes through, such that it assumes an at least partially closing control position when the hydraulic pressure in the direction of the volume flow upstream of the metering orifice 26 is greater than that downstream of the metering orifice 26, including a restoring spring force of a spring element 62 preloading the pressure compensation valve 24 into a fully open position.

[0031] In the control position, the pressure compensation valve 24 attempts to keep the pressure difference across the measuring orifice 26 approximately constant, whereby the pressure difference is determined primarily by the preload built up by means of the spring element 62.

[0032] The restoring spring force generated by the spring element 62 is dimensioned such that the pressure compensation valve 24 reliably assumes its fully open position in a pressureless state. The resulting control value for the differential pressure, which must be achieved to switch the pressure compensation valve 24 from its fully open position to its (at least partially closing) control position, is in the range of 5 to 15 bar.

[0033] Undesirable conditions may occur during operation of the hydraulic consumer 16. Two different operating situations, A and B, can be distinguished: Operating situation A

[0034] First, there is the possibility that the volume flow requested based on the respective valve position of the main spool valve 22 cannot be achieved due to a simultaneous increased supply demand from other hydraulic consumers, which are also supplied with hydraulic fluid by the load-controlled variable displacement pump 38. This leads to an undersupply of the hydraulic consumers as a whole and thus, possibly, to corresponding restrictions in the execution of the respective assigned operating or work functions. Operating situation B

[0035] In addition, there are hydraulic consumers 16 in which, by design, no (significant) volume flow flows during operation, ultimately resulting in a hydraulic backpressure, which causes the system pressure built up by the load-controlled variable displacement pump 38 to reach a maximum value, which in this case can be up to 190 bar. This applies in particular to hydraulic consumers 16 designed as hydraulic linear actuators, in which, by design, a volume flow only flows during the adjustment process until a corresponding end stop is reached.

[0036] As continued in Fig. 1As can be seen, a sensor arrangement 64 detects the pressure difference occurring at the measuring orifice 26 in order to transmit a pressure difference value derived therefrom to the control unit 54. By evaluating the pressure difference value, the control unit 54 concludes that the hydraulic supply is incorrectly adjusted by the hydraulic control valve 20 if the pressure difference is smaller than the control value determined by the restoring spring force.

[0037] Such a condition arises when, with the main spool valve 22 open, either no (significant) volume flow flows through the metering orifice 26 toward the hydraulic consumer 16 (operating situation A) or the volume flow does not reach the volume flow expected based on the respective valve position (operating situation B). In both cases, the pressure drop across the metering orifice 26 and thus the pressure difference detected by the sensor arrangement 64 becomes negligibly small, so that this represents a clear and easily evaluated indicator of the occurrence of inefficient operating conditions of the hydraulic supply to the respective hydraulic consumer 16.

[0038] The sensor arrangement 64 comprises a first pressure sensor 66 and a second pressure sensor 68, wherein the first pressure sensor 66 is provided for detecting the hydraulic pressure in front of the measuring orifice 26 and the second pressure sensor 68 is provided for detecting the hydraulic pressure behind the measuring orifice 26 (in each case relative to the direction of the volume flow). The two pressure sensors 66, 68 are in the case of the Fig. 2 or Fig. 3The illustrated embodiments of the hydraulic control valve 20 are integrated into a common valve housing 70 in a space-saving manner. The sensor signals generated by the pressure sensors 66, 68 are tapped at an electrical connector (not shown) accessible from the outside of the valve housing 70 and transmitted to the control unit 54. The two embodiments differ with regard to the placement of the second pressure sensor 68. This serves to detect either the pressure conditions present on the inlet side or the outlet side of the pressure compensation valve 24.

[0039] Following the two above embodiments, each of the hydraulic control valves 20 is equipped with its own sensor arrangement 64 with two pressure sensors 66, 68. However, in the case of a plurality of hydraulic control valves 20 combined in a control valve block 40, unnecessary redundancy can be avoided if the first pressure sensor 66, which is provided for detecting the hydraulic pressure upstream of the measuring orifice 26, is assigned to a common supply line serving for the hydraulic supply, here the supply line 30. This option is in Fig. 1 indicated by dashed lines.

[0040] Knowledge of the hydraulic supply mismatch resulting from operating situations A or B is used to implement appropriate countermeasures. For this purpose, the main spool valve 22 is closed by the control unit 54 by controlling an electrical actuating device 72, regardless of a hydraulic demand applied to the hydraulic control valve 20, resulting in particular from the specification on the operating terminal 52, until the sensor-detected pressure difference is greater than the control value determined by the restoring spring force or the main spool valve 22 ultimately assumes its fully closing valve position 60.

[0041] In addition, it is provided that the control unit 54 opens the main spool valve 22 for testing purposes after a predetermined waiting time has elapsed by controlling the electrical actuating device 72 in accordance with a hydraulic request applied to the hydraulic control valve 20. If the pressure difference is again smaller than the control value determined by the restoring spring force of the spring element 62 of the pressure compensation valve 24, this indicates that the previously detected mismatch in the hydraulic supply still exists, and the main spool valve 22 is closed again by the control unit 54 by controlling an electrical actuating device 72 until the sensor-detected pressure difference is again greater than the control value determined by the restoring spring force or the main spool valve 22 finally assumes its fully closing valve position 60.

[0042] Fig. 4 shows a modification of the Fig. 1 reproduced arrangement 10, in which a pump drive 74 is provided, which is a separate motor 78 which is drive-connected to the variable displacement pump 38 via an intermediate gear 76 and whose speed can be adjusted to change the delivery rate by means of a control device 80 which communicates with the control unit 54.

[0043] When sensor-based detection of a swivel angle α of the variable displacement pump 38 indicates that a maximum displacement volume has been reached and thus an impending undersupply of the hydraulic consumer 16, the control unit 54 increases the delivery rate by intervening in the pump drive 74. For this purpose, the control unit 54 increases the delivery rate until the pressure difference detected by the two pressure sensors 66, 68 is greater than the control value determined by the restoring spring force of the spring element 62 of the pressure compensation valve 24.

[0044] Conversely, the control unit 54 reduces the delivery capacity of the variable displacement pump 38 back to a level intended for normal operation as soon as it detects through sensors that there is a change in the swivel angle Δα indicating a decrease in the displacement volume.

[0045] The sensory detection of the swivel angle α or the swivel angle change Δα is carried out by means of a swivel angle sensor 82 assigned to the variable displacement pump 38, the sensor signals of which are fed to the control unit 54 for evaluation.

Claims

1. Arrangement for operating a hydraulic consumer, comprising a hydraulic control valve (20) having a main slide valve (22), a pressure compensation valve (24) and an orifice plate (26), wherein, by means of the main slide valve (22), a hydraulic volume flow in the direction of hydraulic connections (42) provided for operation of the hydraulic consumer (16) is able to be defined, wherein the pressure compensation valve (24) is controlled on the basis of a pressure difference that drops at the orifice plate (26) when the volume flow passes through, such that said pressure compensation valve (24) adopts an at least partially closing control position when the hydraulic pressure upstream of the orifice plate (26) in the direction of the volume flow is greater than that downstream of the orifice plate (26), including a restoring spring force of a spring element (62) preloading the pressure compensation valve (24) into a fully open position, wherein a sensor arrangement (64) senses the pressure difference and transmits a pressure difference value derived therefrom to a control unit (54), characterized in that the control unit (54), by evaluating the pressure difference value, extrapolates a mismatch of the hydraulic supply on the part of the hydraulic control valve (20) when the pressure difference is smaller than a control value given by the restoring spring force, wherein the main slide valve (22) is closed by the control unit (54), through actuation of an electric actuating device (72), irrespective of a hydraulic demand at the hydraulic control valve (20) that results in particular from an input at an operator terminal (52), until the pressure difference sensed by sensor means is greater than the control value given by the restoring spring force or until said main slide valve (22) adopts a fully closing valve position (60), wherein the control unit (54) opens the main slide valve (22) for test purposes following a predefined waiting time by actuating the electric actuating device (72) on the basis of a hydraulic demand at the hydraulic control valve (20) that results in particular from an input at an operator terminal (52).

2. Arrangement according to Claim 1, characterized in that the sensor arrangement (64) comprises a first pressure sensor (66) and a second pressure sensor (68), wherein at least one of the two pressure sensors (66, 68) is integrated in a common valve housing (70) of the hydraulic control valve (20).

3. Arrangement according to Claim 2, characterized in that the pressure sensor (66) provided to sense the hydraulic pressure upstream of the orifice plate (26) is assigned to a common feed line (30), used for the hydraulic supply, of a multiplicity of hydraulic control valves (20).

4. Arrangement according to at least one of the preceding claims, characterized in that the volume flow is generated by means of a load-controlled variable displacement pump (38), wherein, when a pivoting angle of the variable displacement pump (38) that indicates the achievement of a maximum displacement volume is detected by sensor means, the control unit (54) increases the delivery rate by acting in a pump drive (74).

5. Arrangement according to Claim 4, wherein the control unit (54) increases the delivery rate by acting in the pump drive (74) until the pressure difference sensed by sensor means is greater than the control value given by the restoring spring force of the spring element (62) of the pressure compensation valve (24).

6. Arrangement according to Claim 5, characterized in that the control unit (54) reduces the delivery rate of the variable displacement pump (38) to a level provided for normal operation as soon it identifies, via sensor means, a change in pivoting angle that indicates a reduction in the displacement volume.

7. Hydraulic system for an agricultural tractor, comprising an arrangement (10) according to at least one of the preceding claims.

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