Method for controlling a hydraulic drive system, hydraulic drive system, and work machine

Abstract

The invention relates to a method for controlling a hydraulic drive system which has an adjustable pressure-regulated hydraulic pump (2) which is driven by a motor (4), a valve assembly (10), and a plurality of consumers (12, 14) which are supplied with a pressure medium by the pump (2) via the valve assembly (10), wherein the valve assembly (10) has a load-pressure-limiting device (20) with a controllably adjustable maximum load pressure value. The method comprises the steps of determining (110) the volumetric flow demand for each of the consumers (12, 14); determining (130) a maximum pump pressure value (36) on the basis of the volumetric flow demand (32) of at least one consumer of the plurality of consumers (12, 14), the maximum pump pressure value (36) being lower, in the case of higher volumetric flow demands of the at least one consumer, than in the case of low volumetric flow demands; and controlling (150) the valve assembly (10) in order to set the maximum load pressure value of the load-pressure-limiting device so as to be equal to or lower than the maximum pump pressure value (36) minus a first pressure difference value (48), and / or controlling the pump (2) such that the target pump pressure of a pressure control process for the pump (2) does not exceed the maximum pump pressure value (36).

Description

[0001] R. 414580

[0002] Robert Bosch GmbH

[0003] R.414580 - Tag / kun

[0004] Method for controlling a hydraulic drive system, hydraulic drive system and working machine

[0005] Description

[0006] The present invention relates to a method for controlling a hydraulic drive system, a hydraulic drive system, a working machine, a computing unit and a computer program for carrying out the method.

[0007] Background of the invention

[0008] Machines, such as mobile construction equipment like excavators, loaders, or bulldozers, can have a hydraulic drive system that uses hydraulic actuators (e.g., hydraulic cylinders, hydraulic motors) to move components of the machine, such as boom sections and / or a travel drive. A hydraulic pump, driven by a motor, supplies the hydraulic fluid. Flow-sharing systems can be used to compensate for load pressure differences when multiple components are moving simultaneously, distributing the maximum flow rate available from the pump according to actuation specifications, which are, for example, captured via a user interface. The maximum movement speeds of the hydraulic actuators or the components they move may not be directly determined by the actuation specifications, but rather limited by performance limits or total flow rate limits.

[0009] Disclosure of the invention

[0010] According to the invention, a method for controlling a hydraulic drive system, a hydraulic drive system, a working machine, a computing unit, and an R. 414580

[0011] A computer program for carrying out the method with the features of the independent claims is proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

[0012] The invention employs the measure of determining a maximum pump pressure value as a function of the flow rate requirement of at least one of the several consumers in a hydraulic drive system comprising a pressure-controlled variable displacement hydraulic pump driven by a motor, a valve arrangement, and several consumers supplied with hydraulic fluid by the pump via the valve arrangement, wherein the valve arrangement has a load pressure limiting device with a controllably adjustable maximum load pressure value, wherein the maximum pump pressure value is lower at a higher flow rate requirement of the at least one consumer than at a lower flow rate requirement of the at least one consumer, and controlling the valve arrangement.to set the maximum load pressure value of the load pressure limiting device to be less than or equal to the maximum pump pressure value minus a first pressure differential value, and / or to control the pump so that a setpoint pump pressure of a pressure control of the pump does not exceed the maximum pump pressure value.

[0013] The proposed measure prevents the motor's power and / or torque limits from being exceeded when the target pump pressure rises rapidly and / or to an excessively high value, for example, when an additional consumer with a high load pressure needs to be moved or when a load pressure increase occurs at a consumer. This avoids a sudden reduction in the pump's flow rate, which would occur if the pump pressure rose too high and the motor's power and / or torque limits were exceeded, and the associated uneven movement or slowdown of consumers.

[0014] The at least one consumer can be a single consumer (of the multiple consumers of the hydraulic system) or can include multiple consumers (of the multiple consumers of the hydraulic system), in particular all of them.

[0015] The method is a computer-implemented procedure, carried out in particular by an electronic control, e.g. a control unit, of the hydraulic system. R. 414580

[0016] The load pressure limiting device is designed to restrict the pressure of a hydraulic load pressure signal generated by the valve assembly to a predefined or adjustable pressure value, referred to as the maximum load pressure value. The load pressure limiting device, or the valve assembly, can be controlled so that the maximum load pressure value is set at the load pressure limiting device. The maximum load pressure value is therefore dynamically adjustable and, in particular, not determined by a spring preload or similar mechanism (static).

[0017] The pressure setting on the load pressure limiting device can be implemented by computer using an electronic control system or can be done hydraulically (especially via a hydraulic load pressure line).

[0018] According to one embodiment, the at least one consumer is a predetermined consumer or several predetermined consumers, or the at least one consumer is selected depending on an operating mode and / or an operating point of the hydraulic drive system. An operating point is defined, for example, by flow rate requirements and / or pressure requirements (or load pressures) of the individual consumers and / or by a flow rate delivered by the pump and / or a pump pressure.

[0019] The first pressure differential value, as well as the pressure differential values ​​introduced below (second, third, and fourth), are positive values. The first pressure differential value is chosen, for example, to ensure a sufficient pressure difference across the metering orifices of control valves in the valve assembly.

[0020] According to one embodiment, the method further comprises determining a maximum load pressure value of the consumers, determining a target pump pressure value based on the maximum load pressure value and the maximum pump pressure value, wherein the target pump pressure value is determined in particular as the smaller of the maximum pump pressure value and the maximum load pressure value plus a second pressure differential value (i.e., in particular, either the maximum pump pressure value is used as the target pump pressure value or the maximum load pressure value plus the second pressure differential value is used as the target pump pressure value, whichever is smaller), and carrying out, by means of an electronic control, the pressure regulation of the pump according to the determined R. 414580

[0021] Target pump pressure value. The maximum load pressure value can be measured, for example, using a load pressure sensor on a load pressure line or channel of the valve assembly. Alternatively, a separate load pressure sensor (load-level load pressure sensor) can be provided for each consumer (e.g., on the hydraulic supply line between the valve assembly and the consumer), so that the load pressure of each consumer is measured, with the maximum load pressure value then being the highest of these load pressure measurements. The second pressure differential value can optionally be equal to the first pressure differential value.

[0022] In the case of a hydraulic drive system with pump pressure control based on the load pressure taken from a load pressure line, the activation or control of the load pressure limiting device indirectly limits the target pump pressure by setting the maximum load pressure to less than or equal to the maximum pump pressure minus a first pressure differential value. For example, the pump's hydraulic control is configured to regulate the pump pressure to the load pressure plus the second pressure differential value, perhaps by means of a control valve that regulates the flow of hydraulic fluid to a pump actuator and is pre-tensioned according to the second pressure differential value.Naturally, the load pressure limiting device with the maximum load pressure value can also be combined with a pressure control implemented by an electronic control (computer-implemented) system, which, as described above, regulates the pump pressure to a target pump pressure value.

[0023] According to one embodiment, the method further includes setting the first differential pressure value based on an operating mode of the hydraulic system and / or a machine in which the hydraulic system is installed, or according to an operator input captured via a user interface. This embodiment allows the fine control behavior of the hydraulic system or the machine in which it is used to be influenced.

[0024] According to one embodiment, the method further comprises determining a consumer-specific maximum pressure value for each consumer with a non-zero flow rate requirement, determining a consumer maximum pressure value from the determined consumer-specific maximum pressure values, in particular R. 414580 as the smallest of the consumer-specific maximum pressure values, and controlling the valve arrangement to set the maximum load pressure value of the load pressure limiting device to be equal to the consumer maximum pressure value or equal to the consumer maximum pressure value less a third pressure differential value. Different consumers may have different (consumer-)specific maximum pressure values, which may be stored in a table and / or depend on an operator request and / or an operating mode.In particular, such consumer-specific maximum pressure values ​​can also be due to technical reasons, for example, if individual consumers are only specified or designed for lower pressures (so that, for example, damage can occur at higher pressures). However, this only becomes relevant if their flow rate requirement is not zero; that is, the system can operate at higher pressures in situations where such consumers are not in use. The third pressure differential value can, for example, be in the range of 1 bar to 10 bar and serve as an additional safety margin to ensure that the consumer's maximum pressure value is not reached or exceeded.

[0025] According to one embodiment, determining the maximum pump pressure is further dependent on the maximum consumer pressure, whereby the maximum pump pressure is defined as less than or equal to the maximum consumer pressure plus a fourth pressure differential value. Here, the maximum pump pressure can initially be determined as a preliminary maximum pump pressure without considering the maximum consumer pressure, for example, by means of a diagram as described below. If this preliminary maximum pump pressure is greater than the maximum consumer pressure plus the fourth pressure differential value, the maximum consumer pressure plus the fourth pressure differential value is used as the maximum pump pressure.If this preliminary maximum pump pressure value is equal to or less than the consumer maximum pressure value plus the fourth differential pressure value, the preliminary maximum pump pressure value is used as the maximum pump pressure value. The fourth differential pressure value ensures a pressure drop across the valve assembly. Accordingly, the fourth differential pressure value is, in particular, equal to the first and / or second differential pressure value, or equal to the first differential pressure value plus the third differential pressure value, or equal to the second differential pressure value plus the third differential pressure value. R. 414580.

[0026] According to one embodiment, the method further comprises determining a total volume flow requirement from the volume flow requirements of the consumers (i.e., from the volume flow requirement of at least one consumer or of all consumers), wherein the maximum pump pressure is determined as a function of the total volume flow requirement, the maximum pump pressure being lower for higher total volume flow requirements than for lower total volume flow requirements. In particular, the total volume flow requirement is determined as the sum of the volume flow requirements of the consumers or as a weighted sum of the volume flow requirements of the consumers. In the case of the weighted sum, the consumers for which the weight is not zero constitute the at least one consumer.

[0027] According to one embodiment, the maximum pump pressure is determined by means of a function that depends on the flow rate requirement of at least one consumer or, optionally, on the total flow rate requirement. Starting from a first maximum pump pressure value at a threshold value of the flow rate requirement of the at least one consumer or the total flow rate requirement, the function decreases monotonically or strictly monotonically with increasing flow rate requirement of the at least one consumer or the total flow rate requirement. The decrease of the function from the threshold value can be continuous and / or in steps.For example, the slope can be constant (and therefore negative due to the decrease), or it can start with a relatively high slope that decreases with increasing flow rate demand of the at least one consumer (or total flow rate demand) until it reaches a relatively low slope (flattening slope). Other forms are, of course, possible. In the case of a stepwise decrease, the slope can be understood, for example, as the difference between successive steps or between equally spaced points. The curve can also depend on other variables (besides the flow rate demand of the at least one consumer or the total flow rate demand), such as the maximum load pressure. If the at least one consumer includes multiple consumers, the curve's dependence can differ for each of these consumers.For example, the functional dependency encoded in the figure may differ for different consumers (of at least one consumer). For instance, the first / second maximum pump pressure value and / or the threshold value may differ for different consumers.

[0028] According to one embodiment, the threshold is greater than zero, and the maximum pump pressure is constant below (up to and including) the threshold, equal to the first maximum pump pressure and, in particular, equal to the pump's maximum pressure. In principle, the threshold can be zero. A threshold greater than zero is advantageous because sufficient power is available even with low flow rate requirements, thus enabling a high pump pressure to be achieved or maintained. The threshold might, for example, be in the range of 40% to 90% of the maximum possible pump flow rate (at a given speed), in the range of 50% to 80% of the maximum possible pump flow rate, or in the range of 60% to 70% of the maximum possible pump flow rate.

[0029] According to one embodiment, the pressure decreases from the first maximum pressure value at the threshold value to a second maximum pump pressure value at a maximum pump flow rate, wherein the second maximum pump pressure value is at least 10% or at least 20% below the first maximum pump pressure value and / or wherein the second maximum pump pressure value is greater than or equal to a minimum pump pressure and / or wherein the second maximum pump pressure value is in a range between 50% and 90% of a maximum pump pressure of the pump or in a range between 60% and 75% of the maximum pump pressure of the pump.

[0030] A computing unit according to the invention, e.g. a control unit of a mobile working machine or control unit of a hydraulic system of a working machine, is, in particular in terms of programming, equipped to carry out a method according to the invention.

[0031] A hydraulic drive system according to the invention comprises a pressure-controlled hydraulic pump, a valve arrangement, several consumers supplied with hydraulic fluid by the pump via the valve arrangement, and a computing unit according to the invention, which is configured to control the pump and / or the valve arrangement. The valve arrangement includes a load pressure limiting device with a controllably adjustable maximum load pressure value. In particular, a hydraulic load pressure signal is limited to the maximum load pressure value R. 414580 by means of a pressure limiting valve on a load pressure line. The pressure limiting valve is adjustable, e.g., electromagnetically controllable, so that the maximum load pressure value can be set.

[0032] A machine according to the invention comprises a hydraulic drive system according to the invention and several movable components that are coupled to and driven by the multiple consumers of the hydraulic drive system. The machine is, for example, a mobile machine, such as an excavator or a wheel loader. In particular, the machine is a compact construction machine, such as a compact excavator. The movable components include, for example, booms, boom elements, buckets, forks, travel drives, and the like.

[0033] Implementing a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous, as this incurs particularly low costs, especially if an executing control unit is already available for other tasks. Suitable data carriers for providing the computer program are, in particular, magnetic, optical, and electrical storage media, such as hard drives, flash memory, EEPROMs, DVDs, etc. Downloading a program via computer networks (Internet, intranet, etc.) is also possible.

[0034] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing.

[0035] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0036] The invention is schematically illustrated in the drawing using exemplary embodiments and is described in detail below with reference to the drawing.

[0037] Character description R. 414580

[0038] Figure 1 shows an exemplary hydraulic drive system in which a method according to embodiments of the invention can be applied.

[0039] Figure 2 shows a flowchart of a method for controlling a hydraulic drive system according to an embodiment of the invention.

[0040] Figure 3 illustrates by way of example the dependence of a Maximai pump pressure value and a Maximai load pressure value on a volume flow requirement of at least one consumer.

[0041] Detailed description of the drawing

[0042] Figure 1 shows an exemplary hydraulic drive system in which a method according to embodiments of the invention can be applied. The hydraulic drive system is provided in a working machine, e.g., in a mobile working machine such as an excavator.

[0043] The hydraulic drive system comprises a hydraulic pump 2 and a motor 4 that drives the hydraulic pump 2, for example via a rotationally fixed coupling. The motor 4 is, for example, an internal combustion engine, in particular a diesel engine, or an electric machine. The motor 4 has a power limit and / or a torque limit, which are typically speed-dependent.

[0044] Hydraulic pump 2 is adjustable, meaning it has an adjustable displacement (e.g., specified as a percentage relative to a maximum displacement). The term "displacement" (also referred to as volumetric flow rate, delivery volume, or swashplate angle) denotes the volume of hydraulic fluid (i.e., hydraulic fluid, especially hydraulic oil) delivered per revolution. Hydraulic pump 2 is specifically a swashplate axial piston pump, where the displacement is referred to, for example, as the swashplate angle. The adjustment, i.e., the change in displacement, is achieved, for example, by electromagnetically pilot-operated hydraulic control, meaning the flow of hydraulic fluid to and from an adjustable piston, which effects the adjustment, is controlled by an electromagnetic control valve. Alternatively, a (purely) hydraulic adjustment is also possible, where the flow of hydraulic fluid to and from the adjustable piston is controlled by a hydraulic control pressure, which is... R. 414580

[0045] A control valve or similar device controls, or is controlled. The control pressure is, in particular, a load pressure, whereby the adjustment is carried out such that the output pressure of the hydraulic pump, i.e., the pump pressure, is higher than the load pressure by a certain pressure differential value (offset, for example, the second pressure differential value). For example, the control valve is actuated in opposite directions by the load pressure and the pump pressure, whereby the control valve is preloaded according to the pressure differential value (e.g., by a spring).

[0046] The hydraulic pump 2 delivers hydraulic fluid from a tank connected to a tank port on the hydraulic pump to a pressure line connected to a pressure port on the hydraulic pump. A pump pressure sensor 6 is provided on the pressure line, for example, to measure the pump pressure. The pump pressure sensor 6 transmits pump pressure readings to an electronic control unit 8 (control device or processing unit) of the hydraulic drive system, for example, via an electrical sensor line shown as a dashed line. The electronic control unit 8 is configured, for example, to control the hydraulic pump 2 or to adjust its displacement, whereby the electromagnetic control valve of the electromagnetically piloted, hydraulically adjustable hydraulic pump 2 is controlled by the electronic control unit 8, for example, via an electrical control line shown as a dashed line.The electronic control 8 can in particular implement a pressure control of the hydraulic pump 2 according to a target pump pressure, i.e. the electronic control 8 adjusts the hydraulic pump 2 on the basis of the pump pressure measurements so that the difference between the pump pressure measurements and the target pump pressure is minimized or reduced to zero or regulated.

[0047] The hydraulic drive system has a valve assembly 10 that is connected to the pressure line, i.e., connected via the pressure line to the hydraulic pump 2 or its pressure port. The valve assembly is also connected to the tank. The valve assembly 10 is connected to hydraulic consumers (also referred to simply as consumers) and is configured to control the flow rates of hydraulic fluid from the pressure line or the hydraulic pump to the hydraulic consumers and from the hydraulic consumers to the tank. The valve assembly 10 comprises, for example, several sections or modules that are assembled to form a valve block. The valve assembly 10 (or its sections or modules) includes, for example, electromagnetically adjustable control valves (proportional control valves) by means of which the flow rates of hydraulic fluid to and from the hydraulic consumers can be controlled. The valve assembly 10 (or R.414580 (whose sections or modules) can be controlled, in particular, by the electronic control unit 8 (e.g., via an electrical control line shown as a dashed line). The electronic control unit 8 can, for example, acquire operating signals from a user interface 16 (e.g., a joystick or similar) and, based on these, control the valve arrangement 10. The electronic control unit 8 can determine a flow rate requirement for each consumer, i.e., a flow rate of pressure medium required by the respective consumer to achieve a specific movement or speed of movement. The flow rate requirement can, for example, be determined from the operating signals.

[0048] As examples of hydraulic consumers, a hydraulic cylinder 12 and a hydraulic motor 14 are shown. Of course, more than two hydraulic consumers can also be provided. The hydraulic cylinder 12 serves, for example, to move a component of the machine, such as a boom and a load lifted by it. The hydraulic motor 14 is, for example, provided in a drive system of the machine, i.e., it serves, for example, to drive a wheel or a chain of the machine.

[0049] The valve assembly 10 is designed to detect a load pressure, i.e., the maximum pressure of the hydraulic fluid at the various consumers, e.g., via a load pressure channel or a load pressure line. A load pressure sensor 18 can be provided, which measures the load pressure and transmits load pressure readings to the electronic control unit 8 (e.g., via an electrical sensor line shown as a dashed line). Alternatively or additionally, a hydraulic load pressure line (not shown) can be provided, which is connected to the valve assembly 10 (e.g., to a hydraulic load pressure port on the valve assembly) to transmit the load pressure in hydraulic form to other components, in particular to the hydraulic pump, if it is adjusted (purely) hydraulically, as described above.

[0050] The valve assembly 10 has an adjustable load pressure limiting device 20 by which the detectable load pressure is limited to an adjustable maximum load pressure. The load pressure limiting device 20 is implemented, for example, by an electromagnetically adjustable pressure relief valve that is connected to the load pressure channel (or load pressure line) of the valve assembly 10 and is configured to R. 414580

[0051] Pressure medium is diverted from the load pressure channel as soon as the set maximum load pressure is exceeded (not shown in detail). The maximum load pressure can thus be adjusted by appropriately adjusting this pressure relief valve. The pressure relief valve can additionally be pre-tensioned by a spring or similar device, so that the maximum load pressure can be adjusted above a lower limit (determined by the pre-tension) according to the electromagnetic adjustment. Such a pressure relief valve is, for example, provided in an inlet section of the valve assembly, which can also be connected to the pressure line.

[0052] When several hydraulic consumers are operated simultaneously, the flow rate delivered by hydraulic pump 2 is distributed among the different consumers, specifically according to their respective flow rate requirements. The pump pressure is determined by the load pressure, i.e., the highest pressure requirement of the various consumers. The valve arrangement 10 includes pressure compensators (not shown) which maintain or limit the pressure drop across respective control valves that regulate the flow rates to the consumers, ensuring that the flow rates to the different consumers are independent of their individual pressure requirements.

[0053] If one or more consumers are already being operated or moved, it can happen that if another consumer (e.g., one that was not initially operated) is to be operated or moved, or if the load on a consumer increases, the motor's power or torque limit will be reached or exceeded. Referring to Figure 1, for example, the hydraulic motor 14 can be used in a drive system that requires a medium pressure level, and the hydraulic cylinder 12 can be used to move a boom that requires a relatively high pressure level (e.g., 30% or more above the medium pressure level). If only ferry operation is initially taking place, the pump pressure is at the medium pressure level.If the boom is to be moved additionally in this situation, an increase in pump pressure to the higher pressure level is necessary. This affects the entire delivered volume flow, including the volume flow requirement of the hydraulic motor 14, so that the power or torque required to drive the pump increases significantly and can exceed the motor's power or torque limit. Exceeding the motor's power or torque limit can result in a lower volume flow available to the consumers already in operation (R. 414580), thus reducing their movement or speed (in the example above, the travel speed is reduced). The reduction in the delivered volume flow can occur relatively quickly, e.g.,in the range of a few hundredths of a second, which can lead to erratic and / or dangerous machine behavior, particularly from the operator's perspective. This problem is solved by the present invention, whereby the target pump pressure is limited depending on the flow rate requirement of at least one consumer.

[0054] Figure 2 shows a flowchart of a method for controlling a hydraulic drive system according to an embodiment of the invention. As described by way of example in connection with Figure 1, the hydraulic drive system comprises a pressure-controlled hydraulic pump driven by a motor, a valve arrangement, and several consumers that are supplied with hydraulic fluid by the pump via the valve arrangement. The valve arrangement includes a load pressure limiting device with a controllably adjustable maximum load pressure value.

[0055] In step 110, the respective flow rate requirements for each consumer are determined or recorded. This can be done using control signals from a user interface, which can then be further evaluated or processed, for example, by progressively mapping the control signals to the respective flow rates and / or filtering, and / or similar processes. At least partially automatic determination of the flow rate requirements is also possible. The flow rate requirement of a consumer is the flow rate of pressurized fluid (e.g., specified in liters per minute) that is to be delivered to the consumer; i.e., it can be considered the target flow rate.

[0056] In an optional step 120, a total flow rate requirement is determined from the flow rate requirements of the consumers. The total flow rate requirement is, in particular, the sum of the flow rate requirements of the consumers or a weighted sum of the flow rate requirements of the consumers, where the weights assigned to the consumers in the weighted sum are, for example, predetermined (especially depending on an operating mode of the hydraulic system) or of operating parameters, e.g., pressure requirements or load pressures of the respective R. 414580.

[0057] Consumers are dependent (for example, pressure decreases with increasing pressure demand or increasing load pressure).

[0058] In step 130, a maximum pump pressure value is determined; that is, a pressure value that the pump pressure (the pump's outlet pressure, which can be measured, for example, with a pump pressure sensor) should not exceed. The maximum pump pressure value is determined as a function of the flow rate requirement of at least one of the multiple consumers, such that a higher flow rate requirement from the at least one consumer results in a lower maximum pump pressure value than a lower flow rate requirement from the at least one consumer. In general, the maximum pump pressure value decreases as the flow rate requirement of the at least one consumer increases. An example of determining the maximum pump pressure based on the calculated flow rate is taking into account the maximum available power in the system.If step 120 has been performed and a total flow rate requirement has been determined, the maximum pump pressure can be calculated as a function of this requirement. Specifically, the maximum pump pressure should be lower for higher total flow rates than for lower total flow rates, or more generally, the maximum pump pressure should decrease as the total flow rate requirement increases. This calculation can be based on a function (e.g., defined as a function and / or encoded in a characteristic map) that depends on the flow rate requirement of at least one consumer (or on the total flow rate requirement). This function maps the flow rate requirements of at least one consumer (or the total flow rate requirement) to the maximum pump pressure. The maximum pump pressure or the function itself can optionally depend on other parameters (e.g., specific pressure values).

[0059] In particular, the maximum pump pressure can decrease with increasing flow rate demand of the at least one consumer or, if applicable, with increasing total flow rate demand, especially monotonically or strictly monotonically. As shown exemplified in Figure 3, this decrease can occur, for example, from a threshold value of the flow rate demand of the at least one consumer (or the total flow rate demand), whereby at and below the threshold value, the maximum pump pressure has a constant value, namely a first maximum pump pressure value, which is approximately equal to a maximum delivery pressure of the pump. The decrease R. 414580 then occurs, for example, up to a second maximum pump pressure value at a maximum possible flow rate (adjusting the pump to maximum displacement at a given drive speed).

[0060] In an optional step 140, a target pump pressure or target pump pressure value is determined, whereby this determination is carried out such that the target pump pressure value is less than or equal to the maximum pump pressure value (which was determined in step 130). For example, it is possible to use the maximum pump pressure value itself as the target pump pressure value.

[0061] In an optional step 145, the maximum load pressure of the consumers can also be determined to establish the target pump pressure. This maximum load pressure can be measured, for example, at a load pressure channel or line provided at the valve assembly, where a hydraulic (load) pressure signal, communicating the load pressure of the consumer with the highest load pressure (e.g., tapped via shuttle valves), is present. Alternatively, a load pressure for each of the multiple consumers can be determined from operating signals and / or by means of a respective load pressure sensor, and the highest of these multiple load pressures can then be determined.The target pump pressure is then determined based on the highest load pressure and the maximum pump pressure. Specifically, the target pump pressure is defined as the smaller of the maximum pump pressure and the highest load pressure, plus a second pressure differential value. This second pressure differential ensures a certain pressure difference across the valve arrangement, for example, via metering orifices of pressure compensators. This second pressure differential value can, for example, be in the range of 10 to 20 bar. Determining the target pump pressure based on the load pressure is advantageous for efficiency reasons.

[0062] In step 150, the pump is controlled so that the target pump pressure of the pump's pressure control does not exceed the maximum pump pressure value. Alternatively or additionally, the valve arrangement is controlled to set the maximum load pressure value of the load pressure limiting device to be less than or equal to the maximum pump pressure value minus a first pressure differential value. Generally, the pump's pressure control can be implemented using an electronic control or a hydraulic load pressure control. In the case of electronic control, R. 414580 can be used for this purpose.

[0063] The target pump pressure value, as determined in step 140, is used; that is, the electronic control controls the pump (and / or the motor) so that the pump pressure, measured by a pump pressure sensor, is regulated to the target pump pressure value, step 152. In the case of hydraulic load pressure control (in which the determination of the target pump pressure value can be omitted), a load pressure limiting device of the valve assembly can be actuated, whereby a maximum load pressure value of the load pressure limiting device is set to the maximum pump pressure value minus a first pressure differential value, step 154. The first pressure differential value here corresponds approximately to the pressure differential by which the hydraulic load pressure control regulates the pump pressure above the load pressure (which is, for example, hydraulically tapped from a load pressure line of the valve assembly). The valve assembly is actuated according to the flow rate requirements of the consumers, i.e.,Control values ​​are determined for the valve arrangement or for the control valves included therein, so that the respective volume flow requirements of the consumers are met, and the valve arrangement (or the control valves) is (or are) controlled with the control values.

[0064] In an optional step 160, individual maximum pressure values ​​are determined for consumers with a non-zero flow rate requirement. The individual maximum pressure value for a consumer is, in particular, a pressure that the load pressure of the respective consumer should not exceed. Such a value can be, for example, technically determined and / or dependent on the specific operating situation and / or the operating mode and / or on available power and / or torque. From the determined individual maximum pressure values, a so-called consumer maximum pressure value is calculated, specifically as the smallest of the individual maximum pressure values ​​or using a time function.

[0065] For example (indicated by an arrow between step 160 and step 130), the consumer maximum pressure value can be used in determining the maximum pump pressure value; that is, the maximum pump pressure value can depend not only on the volume flow requirement of the at least one consumer but also on the consumer maximum pressure value. In particular, the maximum pump pressure value can be determined as less than or equal to the consumer maximum pressure value plus a fourth pressure differential value. This fourth pressure differential value represents a certain R. 414580

[0066] The pressure difference is ensured via the valve arrangement, e.g., via metering orifices of pressure balances. The fourth pressure difference value can, for example, be in the range of 10 to 20 bar.

[0067] Alternatively or additionally (indicated by an arrow between step 160 and step 140), the maximum consumer pressure value can be included in the determination of the target pump pressure. Specifically, in step 140, the target pump pressure value is determined such that it is, on the one hand (as already described), less than or equal to the maximum pump pressure value, and on the other hand, less than or equal to the maximum consumer pressure value plus a pressure differential value, which is, in particular, the first pressure differential value or corresponds to it.

[0068] Alternatively or additionally (indicated by an arrow between step 160 and step 150), the consumer maximum pressure value can be used to control the valve arrangement, wherein the maximum load pressure value of the load pressure limiting device of the valve arrangement is set equal to the consumer maximum pressure value or equal to the consumer maximum pressure value less a third pressure differential value.

[0069] Figure 3 illustrates an exemplary dependence of a maximum pump pressure value and a maximum load pressure value on a flow rate requirement of the at least one consumer. A diagram is shown in which the flow rate requirement 32 of the at least one consumer (e.g., in l / min) is plotted along the horizontal axis and the pressure 34 (e.g., in bar) along the vertical axis, whereby the origin of the diagram does not necessarily coincide with the respective zero values ​​of the flow rate requirement of the at least one consumer or the pressure. For example, the flow rate requirement 32 of the at least one consumer is the flow rate requirement of a drive system of a mobile machine.

[0070] Shown is an exemplary curve of the maximum pump pressure value 36, which initially remains constant up to a threshold value 38 of the flow rate requirement 32 of the at least one consumer, equal to a first maximum pump pressure value 40. From the threshold value 38 onwards, the pressure decreases with increasing flow rate requirement 32 of the at least one consumer, e.g., up to a second maximum pump pressure value 42, which is reached when the flow rate requirement 32 of the at least one consumer equals a maximum pump flow rate 44. The maximum pump flow rate 44 R. 414580 can be determined, for example, at a given rotational speed as the product of the rotational speed and the maximum possible displacement of the pump (neglecting leakage). The decrease above the threshold value is, for example, linear. Of course, other forms of decrease are also possible, which are particularly monotonic or strictly monotonic.For example, the course of the performance hyperbola can be modeled on or correspond to it.

[0071] A corresponding maximum load pressure value 46 is shown as a dashed line, to which a load pressure limiting device of the valve arrangement can be set. The maximum load pressure value 46 is, for example, a certain (first) pressure differential value 48 below the maximum pump pressure value 36.

Claims

R. 414580 Claims 1. Method for controlling a hydraulic drive system comprising a pressure-controlled variable displacement hydraulic pump (2) driven by a motor (4), a valve arrangement (10) and several consumers (12, 14) supplied with hydraulic fluid by the pump (2) via the valve arrangement (10), wherein the valve arrangement (10) has a load pressure limiting device (20) with a controllably adjustable maximum load pressure value, the method comprising: Determining (110) a volume flow requirement for each of the consumers (12, 14); Determining (130) a maximum pump pressure value (36) as a function of the volume flow requirement (32) of at least one of the several consumers (12, 14), wherein the maximum pump pressure value (36) is smaller at a higher volume flow requirement (32) of the at least one consumer than at a lower volume flow requirement (32) of the at least one consumer; Control (150) of the valve arrangement (10) to set the maximum load pressure value (46) of the load pressure limiting device (20) as less than or equal to the maximum pump pressure value (36) less a first pressure differential value (48), and / or of the pump (2) so that a setpoint pump pressure of a pressure control of the pump (2) does not exceed the maximum pump pressure value (36).

2. The method according to claim 1, further comprising Determine (145) a maximum load pressure value of the consumers; Determining (140) a target pump pressure value based on the largest load pressure value and the maximum pump pressure value, wherein the target pump pressure value is determined in particular as the smaller of the maximum pump pressure value and the largest load pressure value plus a second pressure differential value; and Performing (152), by means of an electronic control (8), the pressure regulation of the pump (1) according to the determined target pump pressure value.

3. Method according to claim 2, wherein the second pressure difference value is equal to the first pressure difference value (48).

4. Method according to any of the foregoing claims, further comprising R. 414580 Setting the first differential pressure value (48) based on an operating mode of the hydraulic system and / or a machine in which the hydraulic system is installed, or according to an operator input captured via a user interface (16).

5. Method according to any of the foregoing claims, further comprising Determine (160) a consumer-specific maximum pressure value for each of the consumers that has a non-zero volume flow requirement, and determine a consumer maximum pressure value from the determined consumer-specific maximum pressure values, in particular as the smallest of the consumer-specific maximum pressure values; Controlling the valve arrangement to set the maximum load pressure value of the load pressure limiting device to be equal to the consumer maximum pressure value or equal to the consumer maximum pressure value minus a third pressure differential value.

6. Method according to claim 5, wherein the determination (140) of the maximum pump pressure value (36) is further dependent on the consumer maximum pressure value, wherein the maximum pump pressure value (36) is determined to be less than or equal to the consumer maximum pressure value plus a fourth pressure difference value.

7. Method according to any of the preceding claims, wherein the at least one consumer includes one or more predetermined consumers; or wherein the at least one consumer is selected depending on an operating mode and / or an operating point of the hydraulic drive system.

8. A method according to any of the foregoing claims, comprising Determining (120) a total volume flow requirement from the volume flow requirements of the consumers; wherein determining (130) the maximum pump pressure value (36) is carried out as a function of the total volume flow requirement, wherein the maximum pump pressure value (36) is smaller at a higher total volume flow requirement than at a lower total volume flow requirement; R. 414580 wherein in particular the total volume flow requirement is determined as the sum of the volume flow requirements of the consumers (12, 14) or as the weighted sum of the volume flow requirements of the consumers (12, 14).

9. A method according to one of the preceding claims, wherein the determination (140) of the maximum pump pressure value (36) is carried out by means of a mapping which depends on the volume flow requirement (32) of the at least one consumer or, if the features of claim 8 are included, on the total volume flow requirement, wherein the mapping decreases monotonically or strictly monotonically from a threshold value (38) of the volume flow requirement of the at least one consumer or of the total volume flow requirement, starting from a first maximum pump pressure value (40).

10. Method according to claim 9, wherein the threshold value (38) is greater than zero and the maximum pump pressure value (36) below the threshold value (38) is constant and equal to the first maximum pump pressure value (40) and in particular is equal to a maximum pump pressure of the pump (2).

11. Computing unit (8) comprising a processor configured to perform the method according to any of the preceding claims.

12. Hydraulic drive system comprising a pressure-controlled hydraulic pump (2) driven by a motor (4), a valve arrangement (10), several consumers (12, 14) supplied with hydraulic fluid by the pump (2) via the valve arrangement (10), wherein the valve arrangement (10) has a load pressure limiting device (20) with a controllably adjustable maximum load pressure value, further comprising a computing unit (8) according to claim 11, which is in particular configured to control the pump (2) and / or the valve arrangement (10).

13. Working machine, in particular a compact construction machine, comprising a hydraulic drive system according to claim 12 and several movable components which are coupled to and driven by the multiple consumers of the hydraulic drive system. R. 414580 14. Computer program comprising instructions which, when the program is executed by a computing unit, in particular the hydraulic drive system according to claim 11, cause it to execute the method according to one of claims 1 to 10.

15. Computer-readable data carrier on which the computer program according to claim 14 is stored.

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