Fluid flow arrangement and electronic control device

Abstract

Fluid flow arrangement (1, 15) comprising a preferably adjustable fluid pump device (2), a fluid machine (12) fluidically connected to the fluid pump device (2) and operable in a motor mode and / or in a pump mode, and a return loop which fluidically connects a first fluid port (A) and a second fluid port (B) of the fluid machine (12), wherein the first (A) and the second (B) fluid port are preferably temporarily at different pressure levels, wherein the return loop comprises an adjustable fluid throttle device (21, 22) and a controllable fluid line device (23, 24), wherein the return loop can only be traversed in substantially one direction, characterized in that the adjustable fluid throttle device (21, 22) is a pressure relief valve with an adjustable switching value.which is controlled by means of an electronic control unit (13).

Description

[0001] The invention relates to a fluid flow arrangement comprising a preferably adjustable fluid pump device and a fluid power machine fluidically connected to the fluid pump device and operable in a motor mode and / or a pump mode, as well as a return loop fluidically connecting a first fluid port and a second fluid port of the fluid power machine, wherein the first and second fluid ports are at least temporarily at different pressure levels. The invention further relates to an electronic control device for such a fluid flow arrangement.

[0002] Hydraulic power transmission devices for transferring mechanical energy from one location to another (which typically includes the ability to change certain properties of the mechanical energy, such as rotational speed, torque, and the like) are now used in several technical fields. One example is wind turbines, where an input force originating from a propeller, which exhibits varying rotational speeds and / or drive torques due to changing wind speeds, must be transmitted to an electric generator. However, a constant rotational speed is typically required at the electric generator. Therefore, not only must the location of the mechanical torque be transmitted, but certain properties of the mechanical energy (such as rotational speed) must also be translated.

[0003] Another technical application for hydraulic circuits lies in the propulsion of vehicles, particularly land vehicles. Although some cars and trucks are already powered by hydraulic transmission, its use remains relatively limited, despite the promising characteristics of some hydraulic systems. In contrast, the standard approach is to use hydraulic systems to power specialized vehicles that already utilize hydraulic components to perform their primary function. Since these vehicles already have a sizable hydraulic pump, it is relatively common to use hydraulic energy as a supplementary power source. Examples of such machines include forklifts, excavators, wheel loaders, and similar equipment.

[0004] From a technical standpoint, closed hydraulic fluid circuits are preferred for powering vehicles due to their intrinsic properties. Open hydraulic fluid circuits, on the other hand, are used for other devices, such as hydraulic cylinders, which perform the main functions of forklifts, excavators, wheel loaders, and the like. While it is technically possible to provide a machine that requires an open hydraulic fluid circuit with an additional closed hydraulic fluid circuit, this approach is obviously disadvantageous from an economic point of view.In such a machine, not only is it necessary to provide and maintain a larger number of components, but energy efficiency also decreases due to the resulting increase in weight. For this reason, there is interest in implementing a drive system in combination with an open hydraulic fluid circuit, although this is not necessarily the best starting point.

[0005] The main problem with using open hydraulic fluid circuits is surprisingly not the drive function itself, but rather arises when the vehicle needs to be braked and / or allowed to coast. Here, one is not only faced with the problem of how to generate a braking force for the combined hydraulic pump-hydraulic motor unit connected to the vehicle's wheels, but also with the additional problem of how to prevent cavitation on the intake side of the combined hydraulic pump-hydraulic motor unit under such operating conditions.

[0006] The situation becomes even more problematic if the vehicle is to be able to move in different directions (i.e., forwards and backwards) and, moreover, be able to slow down in these directions (possibility of braking), which, however, is a standard requirement.

[0007] Although various proposals have already been made in the prior art, these have not necessarily been satisfactory so far.

[0008] EP 1 186 783 B1 proposes a regeneration method for a hydraulic system in which the fluid expelled from a first actuator is used to drive a second actuator. Alternatively, it is possible to direct the fluid expelled from one chamber of an actuator into another chamber of the same actuator. As a further alternative, the fluid expelled from an actuator can be directed to a pressure accumulator where it is stored under pressure until it is needed to drive an actuator of the system.

[0009] DE 1 627 617 B1 proposes a hydraulic control system for a stepping movement on forging manipulators for the rapid acceleration of large masses by means of a hydraulic motor, which is simple in design and operates without additional energy input.

[0010] One suggestion was to circumvent the problem by simply providing the braking force through conventional mechanical brakes and preventing cavitation by further supplying pressurized fluid via a standard hydraulic pump. However, it is clear that this is disadvantageous, not only due to the resulting wear on the mechanical brakes, but also because of the reduced energy efficiency of the vehicle.

[0011] For this reason, there is a need for a fluid flow arrangement that can propel and brake a vehicle even when an open hydraulic fluid circuit is used.

[0012] The object of the invention is therefore to propose a fluid flow arrangement comprising an adjustable fluid pump device and a fluid power machine fluidically connected to the fluid pump device, and further comprising a return loop that fluidically connects a first fluid port and a second fluid port of the fluid power machine, wherein the first and second fluid ports are preferably temporarily at different pressure levels, and which is an improvement over similar fluid flow arrangements known in the prior art. A further object of the invention is to propose an electronic control device for controlling a fluid flow arrangement, which is an improvement over electronic control devices known in the prior art.

[0013] The invention solves this problem.

[0014] It is proposed to design a fluid flow arrangement comprising a preferably adjustable fluid pump device, a fluid-driven machine fluidically connected to the fluid pump device and operable in a motor mode and / or a pump mode, and a return loop fluidically connecting a first fluid port and a second fluid port of the fluid-driven machine, wherein the first and second fluid ports of the fluid-driven machine are preferably temporarily at different pressure levels, such that the return loop includes an adjustable fluid throttle device and a controllable fluid line device. The return loop can only be traversed in substantially one direction. Furthermore, the adjustable fluid throttle device is a pressure relief valve with an adjustable switching value, which is controlled by an electronic control unit.Although the fluid pumping device and, in particular, the fluid power machine can, in principle, be of a non-adjustable type (so that one revolution of the machine pumps / consumes essentially the same volume of fluid; minor variations due to certain effects, such as pressure effects, viscosity effects, and the like, can of course occur), it is preferred if at least the fluid pumping device or the fluid power machine, and preferably both the fluid pumping device and the fluid power machine, are of an adjustable type, so that these machines can be adjusted such that one revolution pumps / consumes a variable quantity of fluid (naturally within certain limits). How this adjustability is achieved is arbitrary. In particular, the fluid pumps and / or fluid power machines can be of a type in which the adjustability is achieved by mechanical means.To give an example: Swashplate pumps / swashplate fluid power machines are of a mechanically adjustable type, which is well known in the prior art. However, it is equally possible (and also preferred) for such a fluid pumping device and / or fluid power machine to be of an electrically controlled type. Such electrically controlled types are also well known in the prior art under the name "Digital Displacement Pump®" (DDP) or synthetically commutated hydraulic pump and / or motor (depending on the exact design). Electrically adjustable fluid pumping devices and / or fluid power machines have the advantage that they can be adjusted significantly faster and / or over a wider range, both of which are particularly advantageous when powering a vehicle.In a typical application of the fluid flow arrangement proposed here, the fluid pump device is typically designed to pump only hydraulic fluid, i.e., to increase the pressure of a hydraulic fluid while absorbing mechanical energy (which is typically introduced in the form of a rotary motion, i.e., by means of a torque). Of course, it is also possible for the fluid pump device to be of a combined pump-motor design (although the motor operating mode is typically rarely used, if at all). The fluid pump device is typically connected to a drive device, such as an internal combustion engine, an electric motor, or similar.It should be noted that it is possible for an electric motor or an internal combustion engine to operate at a specific, constant speed, such as the speed of maximum power output, the speed of maximum torque, or the speed of maximum energy efficiency (although it is of course possible that a different speed operating mode may be selected from time to time depending on the current operating requirements), if the fluid pump device (and / or the fluid working machine) is of an adjustable design. Due to the adjustability of the fluid pump device, it is nevertheless possible to change the amount of hydraulic fluid pumped by the fluid pump device.The fluid machine typically has a design that allows it to switch between a motor mode and a pump mode (although a partial motor and partial pump mode may also be considered, such that the fluid machine has different services which are fluidically separated from one another, with some (at least one) of the services operating in a motor mode while at the same time some (at least one) of the services operating in a pump mode). Furthermore, the fluid machine may be of a fixed displacement type or of a variable displacement type (the variable displacement type typically having some advantages in terms of controllability of the fluid flow arrangement).In motor mode, the fluid power machine can actively propel a vehicle if used in such a context. If the vehicle needs to be braked, the fluid power machine is switched to a pump mode, so that pressurized fluid is "consumed" by other components, particularly the adjustable fluid throttle, which will be described in more detail below. This allows for wear-free braking. Typically, the fluid power machine is connected to one or more devices (either directly or via an intermediate mechanical power transmission system, including a gearbox or similar device).For the sake of completeness, it should be noted that it is of course possible to use two or more (adjustable) fluid pumps and / or two or more fluid power machines for the fluid flow arrangement. Depending on the operating mode of the fluid flow arrangement, the first fluid connection is the high-pressure fluid connection and the second fluid connection is the low-pressure fluid connection, or vice versa. If the fluid power machine is operated in motor mode, the high-pressure fluid connection is typically the fluid inlet connection, while the low-pressure connection is the fluid outlet connection. Conversely, if the fluid power machine is operated in pump mode, the high-pressure connection is typically the fluid outlet connection, while the low-pressure connection is typically the fluid inlet connection.It should be noted that, from a mechanical perspective, the first fluid connection may have multiple "mechanical fluid connections," although these different "mechanical fluid connections" constitute a single "logical fluid connection" (the same applies analogously to the second fluid connection). Such a plurality of "mechanical fluid connections" can be interconnected by means of a manifold or similar device. However, it is also possible that the fluid machine has several internal fluid circuits that are separate from one another, for example, to generate different pressure levels or similar. Again, for the sake of completeness, it should be noted that the first and second fluid connections may have the same pressure level at certain times.The most obvious scenario for this occurs when the machine is switched off (for example, when a forklift is parked overnight). Using the return loop, the first and second fluid ports can be selectively "short-circuited." This feature effectively prevents cavitation on the low-pressure side. Otherwise, such cavitation could occur, particularly at the fluid inlet port, when the hydraulic machine is operating in pump mode (which is the case when the vehicle is in freewheeling or braking mode). Of course, this "short-circuit" should not be in place all the time, as this would lead to significant losses of pressurized hydraulic fluid if the hydraulic machine is operating in engine mode while the vehicle is in motion.This would result in a significant energy loss, or the vehicle might even become inoperable. Furthermore, fluid recirculation can also be disadvantageous in other operating modes of the fluid flow arrangement, including certain braking modes. A particularly prominent example of this is the "metering operating mode," which will be described in more detail below. This targeted switching of the recirculation loop can be achieved using the controllable fluid line system proposed here. This controllable fluid line system can be selected from a wide range of devices. In particular, both active and passive controllable fluid line systems are possible.An actively controlled fluid flow device could be a solenoid valve, which is controlled, for example, by an electrical (electronic) controller. However, it is also possible for the controlled fluid flow device to be a passive design, meaning no active control signal needs to be generated. One possible design for such a passively controlled fluid flow device is a check valve or similar. A combination of an actively and passively controlled fluid flow device can also be used. This can be achieved by combining two valves, such as a controlled solenoid valve and a passive check valve, connected in series. Passively controlled fluid flow devices can also be used that additionally feature some form of active override capability.For the sake of completeness, it should be noted that one possible embodiment involves the use of two directional check valves, with the additional and / or alternative inclusion of a single controllable fluid line device of an on / off type in the return loop. It is readily apparent that the controllable fluid line device should be designed, configured, and / or driven such that the return loop is not closed during time intervals when the fluid machine is operating in motor mode (or also in pump mode during special operating modes such as the "metering mode").(that fluid flow through the return loop is not possible), whereas the return loop should generally be "so to speak" short-circuited during time intervals when the fluid machine is operating in a pumping mode (for example, during a coasting mode and / or when braking a vehicle; especially when a "runaway-preventing mode" is used, as described below). The term "so to speak short-circuited" typically refers to a closed fluid loop, with "so to speak" denoting a possible fluid flow obstruction device, where the obstruction of the fluid flow may be comparatively large. However, the obstruction should be sufficiently small to prevent cavitation effects in the fluid machine. A "so to speak short-circuited" operation in the region of "low fluid flow resistance" (i.e.,The fact that the feedback loop is essentially fluidically short-circuited typically results in low braking performance (if any). Such an operating mode can nevertheless be advantageous, for example, to enable freewheeling for a vehicle. If the "essentially short-circuited" state occurs in the region of "high fluid flow resistance," a "true braking mode" for a vehicle can be implemented. This is because the pressure drop at the fluid flow restrictor (where the mechanical energy stored in the form of the fluid's pressure level is converted into thermal energy) acts as a wear-free brake for the fluid-driven machine. The fluid flow restrictor is designed as an adjustable fluid throttle. The adjustability of the adjustable fluid throttle can be selected from a wide range.In particular, it is possible for the adjustable fluid throttle device to be switched between (essentially) two operating modes: a first mode in which there is essentially no fluid flow resistance (during freewheeling or active vehicle propulsion), and a second mode in which a certain fluid flow resistance is present (for example, to implement a "true braking mode" for a vehicle). However, it is preferred if the adjustable fluid throttle device can implement a plurality of different operating states, especially if a continuous range of different "fluid resistance levels" can be achieved. In this way, different braking forces, preferably a continuous range of different braking performance, can be implemented.For the sake of completeness, it should be mentioned again that an operating mode in which the adjustable fluid throttle exerts essentially no fluid flow resistance on the hydraulic fluid flowing through it is important, as otherwise such fluid flow resistance would also be present when the fluid-driven machine is operated in motor mode. This would otherwise lead to significant energy losses, for example, when the vehicle is being propelled. The controllability of the adjustable fluid throttle can be achieved, for example, by means of a throttle device with a flow orifice of variable size. However, other designs are also possible.For example, a device with a tube of a specific diameter could be used, where the "effective length" of the tube (as "seen" by the fluid flowing through it) is changed by "adding or removing" additional loops using switchable valves. However, other designs are also possible.

[0015] It should be mentioned that an embodiment without a feedback loop can also be considered. Instead, one or two fluid return lines can be used, which fluidically connect a first fluid port and / or a second fluid port of the fluid machine to a low-pressure fluid receiving device, wherein at least one adjustable fluid throttle device is provided in at least one of the fluid return lines. The fluid receiving device can be, for example, a fluid inlet port of a fluid pump device or a fluid reservoir. In the case where a fluid reservoir is used, this can optionally be considered a "logical feedback loop".

[0016] It is possible to design the fluid flow arrangement such that the return loop can be traversed in opposite directions, in particular by having at least two adjustable fluid throttle devices and / or at least two controllable fluid line devices. In this way, it is possible to operate the fluid machine in opposite directions (whereas the fluid pump device is normally operated in only one direction; however, it is also conceivable that the fluid pump device could also be operated, at least temporarily, in alternating directions). Using this design, it is possible for a vehicle driven by the fluid flow arrangement proposed here (especially when the wheels are mechanically connected to the fluid machine) to be driven in different directions, i.e.,in a forward direction as well as in a reverse direction. Such a design thus leads to increased functionality of the machine in question. With the design proposed here, using at least two adjustable fluid throttle devices and / or at least two controllable fluid line devices, fluid flow in opposite directions within the feedback loop can be implemented particularly effectively. In particular, a freewheel function and / or a braking mode can be easily implemented in both directions of travel of the vehicle in question when such a design is used.

[0017] In contrast, it is proposed here that the fluid flow arrangement allows the return loop to flow essentially in only one direction. In particular, this design allows the fluid flow arrangement to incorporate a single adjustable fluid throttle and / or a single controllable fluid line within the return loop. This approach reduces the number of hydraulic components, resulting in a more cost-effective, less bulky, and / or lighter design. If bidirectional operation is required, it can be achieved using alternative means, such as a mechanical gearbox, an additional motor for reverse travel, or similar devices. Such a design can still be advantageous, especially in cases where reverse travel is relatively infrequent.

[0018] Another preferred embodiment of the fluid flow arrangement can be implemented if the adjustable fluid pump device and the fluid power machine are connected to each other by means of at least one fluid switching device, in particular such that the output can be selectively connected to at least one of the at least two different fluid connections of the fluid power machine, especially to one of the first and / or second fluid connections of the fluid power machine. Using this embodiment, it is particularly easy to implement operation of the fluid power machine in two different directions. If this is used in conjunction with a drive for a vehicle, forward and reverse movement of the vehicle can be easily achieved.Furthermore, when using the proposed design, it is particularly easy to separate the fluid flow generated by the fluid pumping device from the flow returning from the fluid working machine when the fluid flow arrangement is operated in a drive mode.

[0019] It is further proposed to design the fluid flow arrangement such that it is an open hydraulic fluid circuit. In particular, it is proposed to use the fluid flow arrangement for propulsion purposes, especially for propelling a land vehicle. Using the design proposed here, the fluid flow arrangement can demonstrate its inherent advantages and properties particularly well.

[0020] As mentioned, in the fluid flow arrangement, at least one of the adjustable fluid throttle devices is designed as a pressure relief valve with a preferably adjustable switching value. As previously mentioned, the adjustability of the switching value can be such that two, three, four, or even more—i.e., a multitude of different discrete states—can be realized. However, it is also possible (and usually preferred) for the switching value to be continuously adjustable (within a certain interval). Typically, the adjustability of the switching value (the control of the fluid throttle device in general) is automated. How the input signal is applied is usually irrelevant. For example, the adjustment signal could be applied mechanically, electrically, and / or fluidically (pneumatically, hydraulically).An electrical control signal is usually preferred, as such a signal can be easily generated by an electrical control device (especially an electronic control device). It should be noted, however, that it is of course also possible to apply two or even more control signals, each of which has a certain influence on the position of the adjustable fluid throttle device / the adjustable switching value. The interaction of the individual control signals results in the "final position" / the "final switching value".

[0021] A further preferred design can be implemented if the adjustable fluid throttle is electrically adjustable and / or if it is controlled by a programmable electronic control unit. As mentioned previously, the generated control signal can be a single signal. However, multiple control signals can also act on the fluid throttle. If the fluid throttle is electrically adjustable, it is typically particularly easy to achieve fast and precise control of the adjustable fluid throttle, resulting in typically good control behavior of the fluid flow arrangement. Furthermore, it is typically particularly easy to generate an electrical control signal.As proposed, the control is performed by an electronic control unit, in particular a programmable electronic control unit. A preferred design for this is an electronic microcontroller. In particular, a control unit implemented as a single-board device is preferred. Such devices are readily available and inexpensive in the prior art. To give just one example: a Raspberry Pi® or an Arduino® controller are now available for little money, and these now offer considerable computing power. The electrical control of an electrically adjustable fluid throttle device can be implemented with an electrical coil that exerts a magnetic force on a type of control piston or similar component.It is also possible to use a stepper motor or an electric motor (including rotary and linear motors) to generate movement in a corresponding device. In particular, the size of a passage opening could be changed in an adjustable fluid throttle device.

[0022] Another preferred fluid flow arrangement can be implemented if at least one of the controllable fluid piping devices is a preferably controllable directional valve, in particular a preferably controllable check valve, and / or if at least one of the controllable fluid piping devices exhibits behavior with a defined pressure drop across the fluid piping device, which depends on the fluid flow rate through the fluid piping device. Using such a design, a reliable and cost-effective fluid flow arrangement can be implemented. If the relationship between the pressure drop and the fluid flow rate through the device is known, it is possible to measure (or at least estimate with sufficient accuracy) the fluid flow rate by means of pressure measurements.This information can then be used to measure (or at least to estimate with sufficient accuracy) the speed of the driven device, for example, a vehicle's speed. This information can also be output to various systems. Furthermore, this information can be used internally to determine the precise operating state of the device (e.g., the vehicle), enabling more accurate and refined control of the entire system. The pressure sensors required for this purpose are relatively inexpensive, require little installation space, and are comparatively reliable, especially considering the deterioration of hydraulic oil due to aging.Since the controllable fluid flow system is required anyway, and it is essentially impossible to prevent pressure loss in this system, the pressure drop can be used for a useful purpose. In particular, no additional fluid flow resistances need to be provided in the fluid flow arrangement, resulting in higher energy efficiency and generally better performance of the fluid flow arrangement. When a "preferably controllable directional valve" and / or a "preferably controllable check valve" is highlighted, this can be understood as a type of directional valve / check valve that has a controllable override functionality, i.e., that it can be closed by means of a control signal, regardless of the direction of the pressure drop across the valve.This can be achieved by influencing the directional valve / check valve itself, or by adding an additional component, in particular a controllable valve in series which has a controllable on / off functionality.

[0023] Another preferred embodiment can be achieved if the fluid flow arrangement has at least one pressure measuring device, in particular a plurality of pressure measuring devices, which are preferably arranged in the region of the backflow loop, especially between a fluid connection of the fluid machine and at least one of the adjustable fluid throttle devices and / or between at least two of the adjustable fluid throttle devices and / or at the fluid outlet line of a preferably adjustable fluid pump device. Using such pressure measuring devices makes it possible to obtain a sufficient amount of information to control the behavior of the fluid flow arrangement with sufficient accuracy.In particular, the use of pressure measuring devices allows for the acquisition of a greater amount of information about the volume of fluid pumped by the fluid-driven machine in a freewheeling or braking mode. As mentioned earlier, this information can be used to determine the speed of the respective device, for example, to determine a vehicle's speed. Using this additional input data, the operation of the fluid flow arrangement, especially its braking behavior, can be controlled more precisely. This even makes it possible to simulate the behavior of a conventional mechanical brake or the braking behavior of a dedicated closed hydraulic fluid circuit.When referring to arranging the pressure measuring device (or one of the pressure measuring devices) on the fluid outlet line of a preferably adjustable fluid pumping device, this should primarily be understood in a logical sense. Accordingly, placing the pressure measuring device near and / or adjacent to the fluid pumping device is, of course, possible (and quite often even advantageous, since, due to its proximity to the fluid pumping device, the measured pressure typically better describes the pressure level near the fluid pumping device). However, it can sometimes also be advantageous to arrange the pressure measuring device (or, if applicable, an additional pressure measuring device) adjacent to the fluid outlet port of the preferably adjustable fluid pumping device.

[0024] According to a further aspect of the invention, it is proposed to design an electronic control device for controlling a fluid flow arrangement of the previously described construction such that the fluid flow arrangement comprises at least one fluid working machine, at least one feedback loop fluidically connecting a first fluid port and a second fluid port of the fluid working machine, and at least one adjustable fluid throttle device arranged in the feedback loop such that the electronic control device generates a control signal for at least one of the adjustable fluid throttle devices, such that a defined deceleration force is generated for the fluid working machine. The electronic control device can, in particular, be a microprocessor and / or a single-board controller. As already mentioned, an Arduino® controller or a Raspberry Pi® can be used for this purpose.With the aid of such an electronic control unit, it is possible to emulate the behavior of a conventional mechanical brake for a vehicle that has a hydraulic circuit, particularly an open hydraulic fluid circuit. In particular, a number of different operating modes can be easily implemented using the electronic control unit. The electronic control unit can be a dedicated electronic control unit that serves more or less exclusively for the operation of the fluid flow arrangement. However, the electronic control unit can also be a device that implements several functionalities of the machine for which the fluid flow arrangement is used.In such a case, a sufficient amount of computing power must be provided to perform the calculations required for the operation of the fluid flow arrangement.

[0025] Additionally, a design of the electronic control unit for controlling a fluid flow arrangement is proposed, in which the fluid flow arrangement comprises at least one fluid machine, at least one fluid return line which fluidically connects a first fluid port and / or a second fluid port of a fluid machine to a low-pressure fluid receiving device, and at least one adjustable fluid throttle device which is arranged in the at least one fluid return line such that the electronic control unit generates a control signal for the at least one adjustable fluid throttle device such that a defined deceleration force is generated for the fluid machine. In this way, the advantages and properties described above can be realized in a similar manner.However, these advantages and properties can now be realized for different fluid flow arrangement configurations.

[0026] In particular, the electronic control device may be designed such that at least one sensor signal describing the current state of the fluid flow arrangement is used to generate the control signal. Specifically, pressure data may be used to generate the control signal. Of course, additional and / or alternative sensor signals may also be used to generate the control signal. Pressure data can be obtained, in particular, from pressure measuring devices. The use of such data (with which a fluid flow can even be determined "indirectly") has already been proposed.Furthermore, not only sensor signals from sensors intended more or less exclusively for the operation of the fluid flow arrangement can be used, but also sensor signals from sensors intended for a different purpose (for example, for operating an internal combustion engine that drives the fluid pump device). In addition, other data that is already available (for example, some data values ​​from the existing electronic control unit or from another control device serving a different purpose) can also be used as an input signal.

[0027] It is further proposed to design an electronic control device such that the control signal is generated in such a way that the fluid flow arrangement can be operated in at least one operating mode, which is taken from the group comprising the following operating modes: a method in which the speed of the fluid working machine is controlled by outputting a suitable control signal for controlling the pressure at a fluid output port of the fluid working machine while the fluid working machine is not driven by a fluid pump device; a method in which the speed of the fluid working machine is controlled by outputting a suitable control signal for controlling the pressure at the outlet port of the fluid working machine while the fluid working machine is at least partially driven by a fluid pump device; and a method in which the direction of rotation of the fluid working machine is reversed bythat first the speed of the fluid machine is reduced, and then a fluid switching device is controlled such that the output of the fluid pump device is selectively connected to a different fluid port of the fluid machine. In this context, the use of the term "is controlled" can be understood as "is essentially controlled," meaning that the dominant control characteristic originates from the respective proposed control scheme. However, other influences may still be present, although these typically have a less pronounced or even negligible effect. Using such an embodiment (or a combination thereof), a particularly versatile device can be realized. In particular, freewheeling and braking operation can be implemented.which shows different possible advantageous embodiments. For example, if the fluid machine is not driven by a fluid pump device and the speed of the fluid machine is controlled by outputting a suitable control signal to control the pressure at the output port (i.e., in a case where typically the speed of the fluid machine is controlled by setting a suitable pressure level at the fluid output port of the fluid machine, which in turn is usually done by setting a suitable pressure differential at a fluid throttle device located downstream of the fluid output port of the fluid machine), a particularly energy-efficient,A wear-free braking system can be implemented (no mechanical work is required during operation of the device). If, on the other hand, the fluid-driven machine is controlled by outputting a suitable control signal to regulate the pressure at the output port while the fluid-driven machine is being driven, it is possible to determine the speed of the fluid-driven machine through the speed of the fluid pump device, and thus through the speed of the internal combustion engine (to give an example). This can be advantageous when only a short braking pulse is needed to avoid rapid deceleration and acceleration of the internal combustion engine's speed, which can be inconvenient for the operator of the device. Furthermore, it may be desirable for the operator to have "acoustic feedback" of the driving speed via the internal combustion engine's speed. It should be noted that,Although the fluid pumping device actively pumps to a certain extent, only a small amount of mechanical power is required to drive it. This is because the fluid pumping device does not have to pump against a high pressure; as a result, the required mechanical power input is reduced to increased mechanical friction between the components of the fluid pumping device due to the increased rotational speed. This level of increased mechanical power input is typically acceptable.

[0028] By using a method in which the direction of rotation of the fluid machine is reversed by first slowing down its speed and then controlling a fluid switching device such that the output of a fluid pump is selectively connected to a different fluid port of the fluid machine, the vehicle (to give an example) can exhibit very comfortable behavior (and, for instance, in the case of a forklift where goods could fall off the forks if the forklift accelerates or decelerates rapidly, it is also safe). In particular, very harsh braking can be avoided when reverse gear is engaged while the vehicle is still moving forward.If the fluid switching device were operated in such a way that the output of the fluid pump device is connected to the other fluid port while the vehicle is still moving, this would essentially and unavoidably result in a very strong braking force being applied until the vehicle comes to a complete stop. It is easily understood that such behavior is not exactly desirable.

[0029] Another proposal is to design a fluid flow arrangement, in particular a fluid flow arrangement according to the previous description, in such a way that it has an electronic control device according to the preceding description.

[0030] Another advantageous embodiment can be achieved when the fluid flow arrangement is used as a drive system for a vehicle, particularly a land vehicle. In such a case, the fluid flow arrangement can demonstrate its inherent advantages and properties particularly clearly.

[0031] Further advantages, features and functions of the invention will become apparent from the following detailed description of the invention in conjunction with the accompanying drawings, which show: Fig. 1: the schematic circuit diagram of a first embodiment of a hydraulic drive circuit which uses an open hydraulic fluid circuit; Fig. 2: the first embodiment of a hydraulic drive circuit in a drive mode; Fig. 3: the first embodiment of a hydraulic drive circuit in a runaway-preventing operating mode in which the speed of the drive motor is independent of the speed of the fluid working machine; Fig. 4: a possible control scheme for implementing an operating mode that prevents runaway; Fig. 5: the first embodiment of a hydraulic drive circuit in a metering operating state in which a braking effect is achieved, wherein the speed of the fluid working machine depends on the speed of the drive motor; Fig. 6: a possible control scheme for implementing a metering operating state; Fig. 7: a first embodiment of a hydraulic drive circuit in an aggressive-inverting mode, which should be avoided; Fig. 8: the schematic control circuit of a second embodiment of a hydraulic drive circuit.

[0032] In Fig. Figure 1 is a first embodiment of a hydraulic drive circuit 1, which can be used to drive a vehicle (in particular a vehicle that already uses a hydraulic system, such as a forklift, a wheel loader, an excavator, etc.), shown in the form of a fluid flow diagram. The hydraulic drive circuit 1 shown here is designed such that the vehicle can be moved in two different (opposite) directions, i.e., forward and reverse. Since the circuit is symmetrical, the drive characteristics (maximum speed, torque, etc.) are essentially the same in both directions. This is indeed advantageous for machines such as excavators or forklifts. Furthermore, it can be seen that the hydraulic drive circuit 1 is of the open hydraulic fluid flow type.

[0033] In reality, the output of the main hydraulic pump 2 could also be used for various purposes, such as for hydraulic cylinders to lift the forks of a forklift, to move the bucket of a wheel loader, and the like. Of course, it is also possible that a dedicated pump is used for such "other hydraulic services" (or, if necessary, a main hydraulic pump 2 is used that has several different services, with the different services being used for different hydraulic sub-circuits).

[0034] The main hydraulic pump 2 is driven by a drive motor, which in this case is an internal combustion engine 3 (for example, a diesel engine or a natural gas engine). The torque generated by the internal combustion engine 3 is transmitted to the main hydraulic pump 2 via a drive shaft 4.

[0035] As can also be seen, an auxiliary hydraulic pump 5 is provided. The auxiliary hydraulic pump 5 pumps hydraulic fluid from an oil reservoir 6 (which is typically at ambient pressure) into the low-pressure side 8 of the hydraulic drive circuit 1. Furthermore, the auxiliary hydraulic pump 5 can also serve as a fluid source for other tasks / services (not shown here). In particular, throttle valves can be used to provide different pressure levels for such additional tasks / services and / or for the increased pressure on the low-pressure side 8 of the hydraulic drive circuit 1, especially in the case where a single auxiliary hydraulic pump 5 is used.

[0036] Both the main hydraulic pump 2 and the auxiliary hydraulic pump 5 (or possibly other auxiliary hydraulic pumps, which are not shown here) draw hydraulic oil from the fluid reservoir 6.

[0037] The auxiliary hydraulic pump 5 ensures a minimum pressure so that the relevant fluid lines 26 cannot run dry. Furthermore, a pressure relief valve 9, which responds at low pressure and can be designed as a (slightly) pre-tensioned check valve (as known in the prior art), can limit the pressure in the low-pressure side 8 of the hydraulic drive circuit 1 to a comparatively low pressure (where the pre-tension can be generated by a coil spring or similar device).

[0038] In "realistic designs," the same internal combustion engine 3 is used for both the main hydraulic pump 2 and the auxiliary hydraulic pump 5 (typically, both hydraulic pumps 2 and 5 are connected to the main drive shaft 4). Although it is possible to use two separate hydraulic pumps 2 and 5, the hydraulic pumps 2 and 5 can also be of a design that is "separated from each other by the use of different services," i.e., that they are designed as several independent services within a common pump housing.

[0039] In the embodiment shown here, the auxiliary hydraulic pump 5 is of the fixed displacement pump type; the pumping rate of the auxiliary hydraulic pump 5 is comparatively low; the pressure that the auxiliary hydraulic pump 5 must achieve is also comparatively low, since it only needs to achieve or (slightly) exceed a pressure level that is typical for the low-pressure side 8 of the hydraulic drive circuit 1).

[0040] The main hydraulic pump 2 is of a variable type, for example, a variable displacement hydraulic pump type (e.g., a swashplate pump). Another (typically preferred) embodiment of the variable main hydraulic pump 2, which is used in the present embodiment, is the so-called Digital Displacement Pump® (DDP), also known in the prior art as a synthetically commutated hydraulic pump.

[0041] The pressurized fluid, which is pressurized by the main hydraulic pump 2, is supplied to the high-pressure side 7 of the hydraulic drive circuit 1. By appropriately switching the switchable fluid valves 10, 11 (both of an on / off type), the pressurized fluid can be supplied either to port “A” (via fluid valve 10) or to fluid port “B” (via fluid valve 11) of the fluid-driven machine 12. The fluid-driven machine 12 is a combined fluid motor-fluid pump machine. It can be of a purely mechanical type, or it can be controlled by suitable control signals and / or it can send sensor signals to an electronic control unit 13 via electrical signal lines 14.The electronic control unit 13 is not only connected to the fluid working machine 12 via electrical signal lines 14, but further components of the hydraulic drive circuit 1 are also connected to the electronic control unit 13 via electrical signal lines 14 in order to receive control signals and / or to transmit sensor signals (or other feedback signals) to the electronic control unit 13. In particular, the aforementioned internal combustion engine 3, the main hydraulic pump 2, the fluid valves 10, 11 and the fluid working machine 12 are connected to the electronic control unit 13.

[0042] As can also be seen from the diagram, pressure sensors 16 and 17 are fluidically connected to suitable fluid lines 26 to monitor the pressure in the relevant parts of the hydraulic drive circuit 1. The pressure values ​​measured by the respective pressure sensors 16 and 17 are supplied to the electronic control unit 13. In detail, pressure sensor 16 is located downstream of fluid valve 10, adjacent to port “A” of the hydraulic actuator 12, while pressure sensor 17 is located downstream of fluid valve 11, near port “B” of the hydraulic actuator 12.

[0043] The central section 18 of the hydraulic drive circuit 1 (where the fluid power machine 12 is located) is connected to the low-pressure side 8 by means of a valve combination 19, 20, which is located either on side "A" (right side) or side "B" (left side) of the hydraulic drive circuit 1. Specifically, the valve combination 19 on the right side has an adjustable pressure relief valve 21, which allows fluid flow from the central section 18 towards the low-pressure section 8 of the hydraulic drive circuit 1, provided a corresponding pressure differential is present. The opening pressure of the adjustable pressure relief valve 21 can be adjusted by the electronic control unit 13 via a corresponding electrical signal line 14 by applying a corresponding adjustment signal.Accordingly, the pressure difference between the pressure sensor 16 (hydraulic pressure in the middle section 18, adjacent to the connection “A” of the fluid working machine 12) and the pressure sensor 25 (hydraulic pressure in the low-pressure section 8 of the hydraulic drive circuit 1) can be set to a specific value (of course, typically only if the pressure at pressure sensor 16 is higher than the pressure at pressure sensor 25).

[0044] If the pressure difference reverses (i.e., the pressure at pressure sensor 25 is higher than the pressure at pressure sensor 16), a check valve 23 opens and a fluid flow from the low-pressure part 8 towards the middle part 18 of the hydraulic drive circuit 1 is enabled.

[0045] The valve assembly 20 of the arrangement on the "left side" of the hydraulic drive circuit 1 (adjacent to port "B" of the fluid working machine 12) is designed in a similar manner to the one on the "right side". In particular, the valve assembly 20 has an adjustable pressure relief valve 22 and a check valve 24, the operation and functionality of which are similar to the valve assembly 19 on the "right side", and a detailed description is omitted for the sake of brevity.

[0046] Naturally, the pressure level measured by the pressure sensor 25 on the low-pressure side 8 of the hydraulic drive circuit 1 is also supplied to the electronic control 13 via suitable electrical signal lines 14.

[0047] In Fig. Figure 2 shows a "standard operating situation" of the hydraulic drive circuit 1. In particular, the direction of the fluid flow is indicated by arrows 27 near the relevant hydraulic fluid lines 26. In the example shown, the fluid-driven machine 12 rotates in one direction (for example, in the forward direction of a forklift, if the hydraulic drive circuit 1 is used for such a forklift). If the direction of movement of the fluid-driven machine 12 (and thus of the forklift) needs to be reversed, the fluid flow is reversed by changing the fluid flow such that, essentially, the left side ("B") and the right side ("A") of the hydraulic drive circuit 1 near the fluid-driven machine 12 are exchanged.

[0048] In "standard drive mode", hydraulic fluid is drawn from the fluid reservoir 6 by the main hydraulic pump 2, pressurized, and expelled towards the high-pressure side 7 of the hydraulic drive circuit 1. The fluid valves 10 and 11 are switched such that a fluid connection is established between the high-pressure side 7 and port "A" of the fluid working machine 12 in the central section 18 of the hydraulic drive circuit 1. However, the fluid connection between the high-pressure side 7 and the side of the central section 18 adjacent to fluid port "B" of the fluid working machine 12 is interrupted. Thus, fluid valve 10 is "open" (fluid flow is possible), whereas fluid valve 11 is "closed" (no fluid flow through the valve is possible).

[0049] Since no braking power is required, the adjustable pressure relief valve 22 of the valve assembly 20 on the "left side" (side "B") is set to a mode in which the pressure differential across the valve is 0 (apart from unavoidable residual effects). In fact, setting the pressure differential to essentially 0 is advantageous from an energy point of view, since any pressure differential across the adjustable pressure relief valve 22 would lead to fluid restriction, resulting in reduced energy efficiency of the system.

[0050] Naturally, the adjustable pressure relief valve 21 of the valve assembly 19 on the “right side” (side “A”) is set to its maximum value to prevent a kind of “short circuit”, with the consequence that any fluid flow through the adjustable pressure relief valve 21 is restricted (apart from the possibility of an “emergency pressure release” due to a defect in the arrangement).

[0051] As can be seen from the corresponding arrows 27 adjacent to the hydraulic fluid lines 26, the hydraulic fluid is thus directed via the fluid valve 10 (right side), through the fluid working machine 12 (direction of connection “A” → “B”), through the adjustable pressure relief valve 22 (left side), the pressure relief valve 9 which responds at low pressures back to the fluid reservoir 6.

[0052] Thus, the mechanical energy coming from the combustion engine 3 is converted into pressure energy by the main hydraulic pump 2, which is converted back into mechanical energy by the fluid working machine 12 (whereby the fluid working machine 12 operates as a hydraulic motor in this operating mode).

[0053] This results in a positive torque that accelerates the fluid working machine 12 and the load associated with it (for example, driving a vehicle).

[0054] Apart from minor leakage in the hydraulic drive circuit 1 and its components, the fluid flow through the fluid working machine 12 can be assumed to be identical to the fluid flow through the main hydraulic pump 2. Given a known displacement of the fluid working machine 12, the speed of the fluid working machine 12 (and thus the speed of the load, for example, the speed of a vehicle) can therefore be controlled by controlling the fluid output flow of the main hydraulic pump 2.

[0055] If the amount of fluid pumped by the main hydraulic pump 2 is now reduced to (essentially) 0, the fluid flow behavior is as follows: Fig. 3.

[0056] Due to the shutdown of the main hydraulic pump 2, no more fluid flow is supplied to the fluid working machine 12 (via the main hydraulic pump 2). Ultimately, the fluid valve 10 could also be shut off.

[0057] The problem would now arise that cavitation occurs in the section on side "A" of hydraulic drive circuit 1. Such cavitation must be avoided, as it could seriously damage the components in question, especially the fluid power unit 12. Hydraulic drive circuit 1 is therefore designed to allow fluid return to port "A" of the fluid power unit 12. It should be noted that at this point, the controllable fluid valves 10, 11 and / or the adjustable pressure relief valves 21 and 22 are still in the position corresponding to the situation described in [reference to diagram]. Fig. 2 is shown.

[0058] The result is a "short-circuited" fluid flow that starts at connection "B" (fluid outlet connection of the fluid working machine 12, which now operates as a hydraulic fluid pump), through the "left" adjustable pressure relief valve 22 (pressure differential set to 0), through the "right" check valve 23 (pressure differential at the check valve 23 is also 0) and back to connection "A" (fluid inlet opening) of the fluid working machine 12.

[0059] The relationship between the rotational speed of the internal combustion engine 3 and / or the main hydraulic pump 2 and the rotational speed of the fluid working machine 12 now obviously ends. In particular, the internal combustion engine 3 and / or the main hydraulic pump 2 can idle, while the fluid working machine 12 continues to run at an increased speed (if the hydraulic drive circuit 1 is used to drive a vehicle, the vehicle would still move).

[0060] Such a situation can arise voluntarily (desired operating mode), as is the case with the main hydraulic pump 2 idling while the fluid working machine 12 is in a coasting mode (coasting of a vehicle). However, the situation can also arise involuntarily, as can be the case with a runaway vehicle going downhill.

[0061] Now, some form of braking mechanism must be provided. This is achieved by setting the "left" adjustable pressure relief valve 22 to a specific pressure drop, which corresponds to a specific, desired braking behavior (operating mode to prevent "runaway"). Typically, the "right" adjustable pressure relief valve 21 remains in a position (is set to a position) with a maximum pressure drop (effectively an off position).

[0062] From a control perspective, the situation can be viewed according to Fig. 3 (“Operating mode to prevent runaway”) is recognized by the electronic control 13 via the first condition that P S >P A is (pressure P) B = Pressure at the "left" pressure sensor; side "B", while pressure P A= pressure at the “right” pressure sensor 16 on side “A”). This is easily visible, since the pressure at port “A” of the fluid machine 12 drops to 0 (hopefully not below 0 due to possible cavitation), while, due to the pumping behavior of the fluid machine 12, port “B” is at a certain pressure level (because a certain pressure will always be present due to fluid obstructions and fluid viscosity).

[0063] Another condition for recognizing the situation according to Fig. 3 is the absence of fluid flow through the main hydraulic pump 2 (Q MHP = 0). This can be seen in the control signal of the main hydraulic pump 2.

[0064] To achieve a specific braking behavior of the hydraulic drive circuit 1 (“runaway prevention mode”), the “left” adjustable pressure relief valve 22 must be set to a specific point so that the pressure at fluid port “B” of the fluid work machine 12 reaches a specific point. The fluid work machine 12 then brakes against a pressure differential P. B -P A to work such that the fluid working machine 12 has to perform a certain amount of mechanical work against the difference in pressure levels; this corresponds to a braking power that is performed on the fluid working machine 12 (and possibly a braking power on the vehicle movement if it is used for this purpose).

[0065] One possible control scheme for this is in Fig. 4 shown.

[0066] The input value Pc-ΔP maximum allowable28 is the permissible pressure differential at the "right" check valve 23. Since the check valve 23 (and correspondingly the "other check valve" 24) is selected such that the relationship between the fluid flow through the valve and the pressure differential occurring between the two sides of the valve is known, it is possible to determine the fluid flow through the valve (at least to a good approximation) based on the pressure differential at the valve. This, in turn, is an indicator value for the vehicle speed (if the hydraulic drive circuit 1 is used to drive a vehicle).

[0067] This value is fed (at the negative input) into a comparator 29, where it is compared with the pressure Pc measured at pressure sensor 25, which is connected to the low-pressure side 8 of the hydraulic drive system 1 (and which is fed into the positive input of comparator 29). The output of comparator 29 provides the value P A, setpoint30, namely the “theoretical value” of the pressure P A, as it should be. This will be compared to the actual value of P. A 31 (measured value) is compared to the value actually measured by the "right" pressure sensor 16. This is done by feeding the relevant values ​​into a further comparator 32, whose output signal represents one of the input signals for the electronic control unit 13. The electronic control unit 13 then calculates the value P. PRV 33 which represents the pressure setting value for the pressure relief valve, in this case for the “left” pressure relief valve 22. This in turn is the “main input value” that determines the braking performance of the arrangement.

[0068] In this way, a wear-free brake can be implemented in a simple and efficient manner.

[0069] For the sake of completeness, it should be mentioned that a mechanical brake should of course still be provided for safety reasons.

[0070] Another operating mode that can be implemented with the present arrangement (and which differs from the previously described "walk-through prevention mode") is the so-called "metering mode", which is described in Fig. Figure 5 is shown. Again, the initial position of the fluid valves 10, 11 and the pressure relief valves 21, 22 corresponds to the position shown in Figure 5. Fig. 2.

[0071] However, a braking effect of the hydraulic drive circuit 1 is now to be implemented, whereby a direct relationship between the rotational speed of the main hydraulic pump 2 (and thus, due to the mechanical connection via the drive shaft 4, also that of the internal combustion engine 3) is maintained. The vehicle speed is therefore controlled by a suitable adjustment of the variable main hydraulic pump 2.

[0072] The condition under which “metering” can be used (and how this can be recognized) is identical in one respect to the previously described “runaway prevention mode”, namely in that P B >P AThe fluid working machine 12 operates as a fluid pump and therefore performs mechanical work against the pressure difference, thereby slowing down the vehicle. In contrast to the previously described "operating mode to prevent runaway," the fluid flow rate of the main hydraulic pump 2 differs from 0 (Q). MHP ≠ 0).

[0073] In order to establish a direct relationship between the fluid flow through the fluid machine 12 (and thus the rotational speed of the fluid machine 12) and the fluid flow generated by the main hydraulic pump 2, the pressure in the direction of flow must be measured upstream of the fluid machine 12 (which corresponds to the pressure at the pressure port "A", i.e., P). A,(corresponds) must be maintained at a sufficiently high level not only to prevent cavitation, but also to prevent backflow of the fluid flow, in this case through the "right" check valve 23. This corresponds to the requirement that the pressure P A Viewed in the direction of flow, the pressure upstream of the fluid machine 12 is higher than the pressure Pc on the low-pressure side 8 (measured by means of the pressure sensor 25), i.e., higher than Pc. (The "right" adjustable pressure relief valve 21 is held in a "closed" position, i.e., in a position with maximum pressure differential).

[0074] Although not strictly necessary, the check valves 23, 24 can be designed such that they can be actively closed by means of a control signal, independent of the pressure differential across the respective valve. This can be used as a type of "override functionality." Such functionality can be implemented by arranging a controllable solenoid valve in series with a check valve. However, other designs are also possible.

[0075] A suitable control scheme for this purpose is in Fig. 6 is shown. Now one of the input values ​​of the first comparator 29 is set to ΔP. no circulation 34 changed, i.e. to a position such that the pressure P AAdjacent to the input port “A” of the fluid machine 12, the pressure is maintained at a level higher than Pc on the low-pressure side 8 of the hydraulic drive circuit 1. This is compared to Pc 35 as measured by the pressure sensor 25. In contrast to the previous case, however, the comparator 29 uses both values ​​34 and 35 as a positive input signal. The output 36 of the first comparator 29 is now Pc + ΔP no circulation as a nominal value. This is calculated as in the previous case using the measured value of P. A 31, as measured by the “right” pressure sensor 16, is compared using the comparator 32. This represents the input signal for the electronic control 13, which outputs the nominal pressure value P as an output signal. PRV 33 for the present “left” pressure relief valve 22 is calculated (accordingly, the switching point (“set point”) for this pressure relief valve is changed from the initial 0 position).

[0076] Although in the examples of Fig. 2, Fig. 3 and Fig. 5 where a (for example) forward movement of the vehicle has been shown, it is obvious how a backward movement can be achieved, in a sense, by exchanging the fluid flow between the left and right sides of the fluid working machine 12 and the corresponding hydraulic fluid lines 26, which supply the fluid connections A and B.

[0077] For the sake of completeness, it should be noted that in the case where only a "metering operating mode" is used for braking purposes (as in connection with Fig. 5), and no “runaway prevention mode” is required (as described in connection with Fig. (as described in section 3), it is possible to dispense with the return loop 26 and even the check valves 23, 24. Instead, the fluid outlet ports of the pressure relief valves 21, 22 can simply be connected to the fluid reservoir 6 by means of fluid return lines.

[0078] One potential problem, which still needs to be discussed, is one that occurs if hydraulic drive circuit 1 is switched to a reverse movement mode while the vehicle is still moving forward (or vice versa). This is the problem of "aggressive reversal," which is described in Fig. 7 is shown.

[0079] When the fluid working machine 12 is switched “normally” from a forward mode to a reverse mode, this would mean that the “right” fluid valve 10 would be switched from “on” to “off”, while the “left” fluid valve 11 would be switched from “off” to “on”. Furthermore, the initial switching state for the adjustable pressure relief valves 21, 22 would be assumed, namely a switching state in which the “right” adjustable pressure relief valve 21 would be set to a pressure differential of 0 (starting from “maximum”), while the “left” pressure relief valve 22 would be set to a maximum pressure differential (starting from a pressure differential of 0; essentially a shut-off state of the respective valve except for an “emergency function” if the maximum permissible pressure is exceeded).As can easily be seen, the switching state of the "left" adjustable pressure relief valve 22, in particular, leads to maximum braking power of the hydraulic drive circuit 1. This would result in at least uncomfortable vehicle handling; quite frequently, it would also lead to dangerous handling, since in the case of a forklift, heavy goods could fall from the forks, potentially damaging or destroying the goods and possibly injuring or killing people nearby. This should, of course, be avoided.

[0080] The idea for solving this problem is that the electronic control 13 is programmed in such a way that, in a case where a reversal of direction is ordered, the electronic control 13 is first put either into the “runaway prevention operating state” according to Fig. 3 or into a “dosing mode” according to Fig. 5 shifts, and a braking maneuver is performed. As soon as a complete stop is detected (indicated by an equality of pressures P) A and P B (which can be detected at the fluid connections “A” and “B” of the fluid working machine 12), the “operating state to prevent runaway” or the “metering mode” is terminated and the “standard drive mode”, as described with reference to Fig. The position shown and described in Figure 2 is adopted (in reverse direction). In this way, a smooth transition can be achieved. In particular, it is possible to use moderate braking power for the "deceleration phase" before a reversal of motion begins.

[0081] It should be noted that (some of) the pressure sensors 16, 17, 25 can also be arranged in other positions and / or that some additional pressure sensors can be provided in the hydraulic drive circuit 1. In such a case, the control scheme must be adapted accordingly (in particular, certain modifications to the exemplary embodiment of a control scheme, as shown in Fig. 4 and / or in Fig. 6 is shown, to be carried out).

[0082] The decision as to whether the vehicle has slowed sufficiently (speed approaching zero) to initiate a reverse driving mode can be made using external speed sensors or by means of intrinsic calculations based on the pressure differences and known pressure behavior of one or more of the hydraulic components used, in particular the fluid valves. This possibility is not limited to the embodiment described here.

[0083] Finally, with reference to Fig. Figure 8 shows a second embodiment of a hydraulic drive circuit 15 as a fluid flow diagram. Unlike the previously described embodiment, which allows for a reversal of motion, the embodiment of a hydraulic drive circuit 15 shown here can only be used in one direction (reverse motion, if required, must be achieved by other means). For example, a mechanical transmission could be provided between the fluid machine 12 and the wheels, or small auxiliary electric motors could be used to achieve reverse motion. The embodiment shown here can prove advantageous if either no reverse motion is required at all, or reverse motion is only rarely necessary, so that a few additional components with very small dimensions can be used for such reverse motion.This could be the case, for example, for a normal car, where a reverse movement is rarely used.

[0084] As can be seen from the circuit diagram, no controllable fluid valves are required between the high-pressure side 7 and the central section 18. On the contrary, a simple hydraulic fluid line 26 between the main hydraulic pump 2 and the fluid working machine 12 is sufficient.

[0085] Nevertheless, all three pressure sensors 16, 17, 25 are still in use.

[0086] Between the central section 18 and the low-pressure side 8 of the hydraulic drive circuit 15, only one pressure relief valve 22, namely the former "left" pressure relief valve 22, is used, while on the "right" side only one check valve 23, namely the former "right" check valve 23, is used. The other former "right" pressure relief valve 21 and the former "left" check valve 24 can be omitted.

[0087] As can be seen, the normal drive mode, the operating state to prevent runaway, and the metering mode can all be implemented with the simplified circuit according to the second embodiment of a hydraulic drive circuit 15 if only one direction of movement is required. It is evident that the hydraulic drive circuit 15 can be implemented more easily due to the reduced number of components.

[0088] Due to the great similarity of the two embodiments of hydraulic drive circuits 1, 15, similar reference numerals are used for similar parts. This does not necessarily mean that the corresponding components must be exactly the same in actual embodiments.

[0089] In particular, in the embodiment described here according to Fig. 8. A sufficient supply of hydraulic oil at the fluid inlet port “A” of the fluid working machine 12 during freewheeling operation (or in braking operation), such that cavitation is prevented, can also be achieved by arranging the “right” check valve 23 parallel to the main hydraulic pump 2 (with a suitable opening direction of the check valve). Of course, an additional check valve can also be provided “in addition to the check valve 23” at the location of the main hydraulic pump 2.

[0090] The same idea can be applied analogously to the first embodiment of a hydraulic drive circuit 1, as described with reference to the Fig. 1 and Fig. The example shown and described in section 7 can be applied (and similarly for other embodiments).

[0091] Furthermore, it should be pointed out that in the case where the second embodiment of a hydraulic drive circuit 15 is used according to Fig. Since the pressure relief valve 22 is only used in a drive mode and a "metering operating mode" (i.e., not in an "operating mode to prevent runaway"), the return loop 26 (including the check valve 23) is no longer required and can therefore be omitted. The fluid outlet port of the pressure relief valve 22 can then simply be fluidically connected to the fluid reservoir 6 by means of a fluid return line. Reference symbol list 1 Hydraulic drive circuit 2 Main hydraulic pump 3 Internal combustion engine 4 drive shaft 5 Auxiliary hydraulic pump 6 Fluid reservoir 7 High-pressure side 8 Low-pressure side 9 Low-pressure relief valve 10 Fluid valve (right) 11 Fluid valve (left) 12 Fluid working machine 13 electronic control 14 electrical signal lines 15 Hydraulic drive circuit (second embodiment) 16 Pressure sensor (right) 17 Pressure sensor (left) 18 Middle section 19 Valve combination (right) 20 Valve combination (left) 21 Adjustable pressure relief valve (right) 22 Adjustable pressure relief valve (left) 23 Check valve (right) 24 Check valve (left) 25 Pressure sensor (low pressure side) 26 Hydraulic fluid line 27 Arrow 28 ΔP maximum allowable 29 Comparator 30 P A, set point 31 P A (measured) 32 Comparator 33 P PRV 34 ΔP no circulation 35 P C 36 P C +ΔP allowable

Claims

[1] Fluid flow arrangement (1, 15) comprising a preferably adjustable fluid pump device (2), a fluid working machine (12) fluidically connected to the fluid pump device (2) and operable in a motor operating mode and / or in a pump operating mode, and a return loop which fluidically connects a first fluid connection (A) and a second fluid connection (B) of the fluid working machine (12), wherein the first (A) and the second (B) fluid connection are preferably temporarily at different pressure levels, wherein the return loop comprises an adjustable fluid throttle device (21, 22) and a controllable fluid line device (23, 24), wherein the return loop can only be traversed in substantially one direction, characterized by, that the adjustable fluid throttling device (21, 22) is a pressure relief valve with an adjustable switching value, which is controlled by means of an electronic control device (13). [2] Fluid flow arrangement (1, 15) according to claim 1, characterized by that it has a single adjustable fluid throttle device (22) and / or a single controllable fluid line device (23) in the return loop. [3] Fluid flow arrangement (1, 15) according to claim 1 or 2, characterized by, that the adjustable fluid pump device (2) and the fluid working machine (12) are connected to each other by means of at least one fluid switching device (10, 11), in particular such that the output of the fluid pump device (2) can be selectively connected to at least one of the at least two different fluid connections (A, B) of the fluid working machine (12), in particular to one of the two first (A) and second (B) fluid connections of the fluid working machine (12). [4] Fluid flow arrangement (1, 15) according to one of the preceding claims, characterized by , that the fluid flow arrangement (1, 15) is an open hydraulic fluid circuit, especially for drive purposes. [5] Fluid flow arrangement (1, 15) according to one of the preceding claims, characterized by, that the adjustable fluid throttle device (21, 22) is an electrically adjustable device and / or that the adjustable fluid throttle device is controlled by means of a programmable electronic control device (13). [6] Fluid flow arrangement (1, 15) according to one of the preceding claims, characterized by , that at least one of the controllable fluid line devices (23, 24) is a preferably controllable directional valve, in particular a preferably controllable check valve and / or characterized by , that at least one of the controllable fluid conduit devices (23, 24) exhibits behavior with a certain pressure loss at the fluid conduit device (23, 24), which depends on the fluid flow rate through the fluid conduit device (23, 24). [7] Fluid flow arrangement (1, 15) according to one of the preceding claims, characterized byat least one pressure measuring device (16, 17, 25), in particular by a plurality of pressure measuring devices (16, 17, 25), which are preferably arranged in the feedback loop, particularly preferably between a fluid connection (A, B) of the fluid working machine (12) and at least one of the adjustable fluid throttling devices (21, 22) and / or between at least two of the adjustable fluid throttling devices (21, 22) and / or at the fluid outlet line (26) of the preferably adjustable fluid pump device (2). [8] Electronic control device (13) for controlling a fluid flow arrangement (1, 15) according to one of the preceding claims, wherein the fluid flow arrangement (1, 15) comprises at least one fluid working machine (12), at least one feedback loop which fluidically connects a first fluid port (A) and a second fluid port (B) of a fluid working machine (12), and at least one adjustable fluid throttle device (21, 22) which is arranged in the feedback loop, characterized by , that the electronic control device (13) generates a control signal for the at least one adjustable fluid throttle device (21, 22) such that a certain deceleration force is generated for the fluid working machine (12). [9] Electronic control device (13) for controlling a fluid flow arrangement (1, 15) according to claim 8, wherein the fluid flow arrangement (1, 15) comprises at least one fluid working machine (12), at least one fluid return line which fluidically connects a first fluid port (A) and / or a second fluid port (B) of a fluid working machine (12) to a low-pressure fluid receiving device (2, 6), and at least one adjustable fluid throttle device (21, 22) which is arranged in the at least one fluid return line, characterized by , that the electronic control device (13) generates at least one control signal for the at least one adjustable fluid throttle device (21, 22) such that a defined deceleration force is generated for the fluid working machine (12). [10] Electronic control device (13) according to claim 8 or 9, characterized by, that at least one sensor signal is used to generate the control signal, which describes the current state of the fluid flow arrangement (1, 15), wherein pressure data are used in particular to generate the control signal. [11] Electronic control device (13) according to any one of claims 8 to 10, characterized by , that the control signal is generated in such a way that the fluid flow arrangement (1, 15) can be operated in at least one operating mode taken from the group of operating modes which includes: a method ( Fig. 2, Fig. 3), wherein the speed of the fluid working machine (12) is controlled by outputting a suitable control signal to control the pressure at an output port of the fluid working machine, while the fluid working machine is not driven by a fluid pumping device (2); a method ( Fig. 4, Fig.5), wherein the speed of the fluid working machine (12) is controlled by outputting a suitable control signal to control the pressure at the output port of the fluid working machine, while the fluid working machine is at least partially driven by a fluid pump device (2); and a method wherein the direction of rotation of the fluid working machine (12) is reversed by first reducing the speed of the fluid working machine and then controlling a fluid switching device such that the output of the fluid pump device (2) is selectively connected to a different fluid port of the fluid working machine. [12] Fluid flow arrangement (1, 15), in particular fluid flow arrangement according to one of claims 1 to 7, characterized by an electronic control device (13) according to any one of claims 8 to 11. [13] Fluid flow arrangement (1, 15) according to claim 12, which is used as a drive device for a vehicle, in particular for a land vehicle.

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