DE102023103997B3 - Hydraulic system and method for controlling the hydraulic system - Google Patents

Abstract

The invention relates to a hydraulic system (1, 26) for a hydraulic machine (30). The hydraulic system (1, 26) comprises an electrically controllable first fluid switching valve (8) which is fluidically connected to a hydraulic cylinder (2, 28) and a hydraulic pressure accumulator (10) via corresponding fluid lines (7, 9). An electrically controllable pressure regulating valve (15) is provided which is fluidically connected to the hydraulic pressure accumulator (10) via a further electrically controllable fluid switching valve (16) and which connects the hydraulic pressure accumulator (10) optionally to a hydraulic fluid pump (23) or to a hydraulic reservoir (6). An electronic control device (11) can be operated in a pressure compensation mode in which the pressure in the hydraulic cylinder (2, 28) and the pressure in the hydraulic pressure accumulator (10) are balanced; in a vibration damping mode in which the hydraulic cylinder (2, 28) and the hydraulic fluid pressure accumulator (10) are fluidically connected to one another and fluidically separated from the hydraulic fluid pump (23) and the hydraulic reservoir (6); and in a pressure control mode in which the pressure in the hydraulic cylinder (2, 28) is controlled to remain at a defined setpoint based on an operating mode command and a measured pressure at the hydraulic cylinder (2, 28) by adjusting the pressure control valve (15) and the hydraulic switching valves (8, 16) accordingly.

Description

Nowadays, a variety of different work vehicles with an attached tool are used in all kinds of applications. To name just a few examples, such vehicles with attached tools are used in industry, on construction sites, in quarries and in agriculture.

Examples of such machines are skid steer loaders, wheel loaders, telehandlers, telehandlers, tractors and the like. The common feature is that such machines have a vehicle-like construction, i.e. they have a movable chassis (typically with wheels and/or with crawler tracks) to which a hydraulically movable tool is attached. The tool can (and typically is) made up of various subassemblies, which are usually movable relative to one another.

To take the example of a wheel loader, a wheel loader has a pivoting boom arm to which a bucket (i.e. the tool) is attached. The bucket can be tilted in relation to the boom arm. Therefore, by tilting the bucket, goods can be picked up in the bucket so that the goods can be transported to another location (this is done by placing the bucket in a horizontal position, where the horizontal refers to the opening of the bucket). The goods can then be dumped at the destination (by tilting the bucket in a more or less vertical position).

Another example of a tool is a rotary mower attached to a tractor. The rotary mower can be raised or lowered. When the rotary mower is placed in a lowered position, it can mow grass or crops. In a raised position, the mower is not in operation and can be moved to another location. A front boom arm of a tractor can be used to attach such a rotary mower. However, sometimes special attachments/mounting devices (on the front and/or rear of the tractor) are used.

As technology advances, the desire for assistance systems that increase the versatility, comfort and/or safety of the machine grows.

To give an example, for the above-mentioned machines, particularly wheel loaders, so-called "hydraulic hoist damping systems" or "ride control systems" have been proposed, are available on the market and are increasingly in demand by customers. Such ride control systems typically connect a boom lifting/lowering piston (or other suitable device for adjusting the height) to a pressurised hydraulic fluid reservoir, commonly referred to as an accumulator. This can be used to achieve a damping effect when travelling along a path. By using such a hydraulic accumulator, the boom arm and thus the load on the boom arm (e.g. gravel in a bucket or the like) can move up and down easily when driving over potholes or bumps, thus avoiding hard impacts that can not only increase the mechanical wear of the machine, but can also damage the transported goods or lead to spillage of the transported goods. In addition, such impacts are annoying for the operator of the machine, which is certainly an undesirable effect.

Such vibration damping systems are known as such. One such vibration damping system is described, for example, in US patent US9,091,039 B2 This document already addresses a problem associated with vibration damping systems: the problem of pressure equalization between the boom arm hydraulic piston and the accumulator before these parts are fluidically connected. If a fluid connection is established between the respective cylinder chamber and the accumulator without first performing pressure equalization, the pressure difference can lead to an abrupt raising or lowering of the boom arm over a certain distance until the pressures are equalized. To avoid this annoying effect, the US9,091,039 B2 proposes to use a first hydraulic circuit to initially equalize the pressure between the vibration damping control accumulators and the boom arm front cylinder chambers to below a pressure differential threshold when the vibration damping control is activated, and then to use a second hydraulic circuit to establish a low pressure drop connection between the vibration damping control accumulators and the boom arm front cylinder chambers.

In the US Patent US 10,246, 854 B2 a material handling machine, such as a skid steer loader, is proposed that includes an electro-hydraulic control system for controlling fluid flows between a boom lift cylinder, an accumulator, and a hydraulic pump providing a variable system pressure. The electro-hydraulic control system is switchable between a standard or normal mode and a vibration dampening mode. It is configured to charge the accumulator with fluid from the hydraulic pump while simultaneously disconnecting the accumulator from the lift cylinder during operation in the standard mode. It is further configured to disconnect the accumulator from the hydraulic pump while coupling the accumulator to the lift cylinder when in the vibration dampening mode. The accumulator is charged to a maximum output pressure by the hydraulic pump during the standard operating mode and is pressure equalized with the lift cylinder before starting operation in the vibration dampening mode.

Another commonly used driver assistance system for the above tools and machines, in particular for rotary mowers on tractors, is a so-called “pressure relief control” (sometimes also called pressure balancing control, “pressure balancing mode”; or the like). To illustrate how this assistance system works, let us consider the rotary mower for a tractor mentioned above. When driving across a field to mow grass or crops, it is desirable that the mower does not press too hard on the ground or the grass/crops. Therefore, it is desirable to transfer some of the weight from the mower to the tractor. This requires the boom arm or attachment device (or other attachment device) to be raised slightly. Then the boom arm or attachment device takes some of the weight of the front mower up and away from the ground. The operator can set an appropriate pressure set point and the hitch control system can then automatically ensure that this (reduced) pressure on the ground is maintained. This becomes problematic when the vehicle's path is not perfectly level (which is usually the case in most applications). The rotary mower must then be able to move slightly up and down to compensate for the differences in ground surface height. Traditionally this has been achieved by mechanical springs placed between the rotary mower and the boom or hitch. The disadvantage, however, is that mechanical springs, by their nature, cause a variation in the force acting on the ground. In addition, the possible changes in distance that can be compensated with mechanical springs are rather limited.

Therefore, it has already been proposed in the prior art to use a control system for the lifting hydraulics to compensate for surface irregularities. An example of this is described in the European patent application EP 2 524 585 A2 which proposes an arrangement that can compensate for height differences when moving along an uneven lane.

The solutions already known work in principle, but still have shortcomings. In particular, it is always desirable to reduce the complexity of the arrangement. This reduces manufacturing costs, can reduce the required installation space and even increase the reliability and maintenance costs of the machine.

It is therefore an object of the invention to propose a hydraulic system for a hydraulic machine, in particular a hydraulic control system for a hydraulic machine according to the preamble of claim 1, which is improved over the hydraulic systems for hydraulic machines known in the prior art.

It is a further object of the invention to propose a method for controlling a hydraulic system, in particular a method for controlling a hydraulic system according to the preamble of claim 13, which is improved over methods for controlling hydraulic systems according to the prior art.

A hydraulic system according to claim 1 solves this problem.

A method for controlling a hydraulic system according to claim 13 also solves this problem.

A hydraulic system for a hydraulic machine, in particular for a work vehicle, is proposed. The hydraulic system has: a hydraulic cylinder and a hydraulic pressure accumulator; an electrically controllable first fluid switching valve, which is fluidically connected to the hydraulic cylinder on a first side via a first fluid line and fluidly connected to the hydraulic cylinder on a second side via a second fluid line. is fluidically connected to the hydraulic pressure accumulator; a first pressure sensor which is fluidically connected to the first fluid line between the first fluid switching valve and the hydraulic cylinder; an electrically controllable pressure regulating valve which is fluidically connected to the second fluid line on a first side of the pressure regulating valve by means of a third fluid line, and which is fluidically connected on a second side of the pressure regulating valve either to a hydraulic fluid pump for providing pressurized hydraulic fluid or to a hydraulic reservoir in order to be able to drain hydraulic fluid from the second side of the pressure regulating valve; an electrically controllable second fluid switching valve which is arranged in the third fluid line between the second fluid line and the pressure regulating valve; and an electronic control device which reads in at least one operating mode command and at least one measured value of the first pressure sensor and outputs a setpoint for the electrically controllable pressure regulating valve, a setpoint for the electrically controllable first fluid switching valve and a setpoint for the electrically controllable second fluid switching valve. It is proposed to design the hydraulic system such that the electronic control device is designed and configured such that it can be operated in at least one mode selected from the group of operating modes comprising: a pressure compensation mode, a vibration damping mode and a pressure control mode. In the pressure compensation mode, the pressure in the hydraulic cylinder and the pressure in the hydraulic pressure accumulator are balanced. In the vibration damping mode, the hydraulic cylinder and the hydraulic pressure accumulator are fluidically connected to one another and fluidically separated from the hydraulic fluid pump and the hydraulic fluid reservoir. In the pressure control mode, the pressure in the hydraulic cylinder is regulated so that it remains at a certain setpoint.

The hydraulic machine may be a mobile hydraulic machine, in particular a vehicle, in particular a land vehicle (road vehicle and/or off-road vehicle). The vehicle may in particular have wheels and/or tracks.

While typically non-rail wheels/road wheels and/or off-road wheels and/or tires may be used, it is possible that rail vehicle wheels/rail wheels may be used. Particular examples of the hydraulic machine are wheel loaders, bucket wheel loaders, shovel loaders, telehandlers, forklifts, tractors, work vehicles, telehandlers, front loaders and the like. When reference is made to "a" hydraulic cylinder, "a" electrically controllable fluid switching valve or the like (i.e., generally when reference is made to "a" specific part), this may refer to a single one of the respective devices, but also to a plurality of the respective devices, such as two, three, four, five, six, seven, eight, nine, ten or even more such devices (an interval using the aforementioned numbers - including zero and one - as a lower limit and/or as an upper limit may also be used). For example, bucket wheel loaders typically have two boom arm hydraulic cylinders to generate greater lifting forces and/or to avoid unnecessary twisting of the boom arm assembly. A hydraulic accumulator can be any cavity having a sufficiently dimensioned internal volume that can be pressurized, whether it is a dedicated hydraulic accumulator or a "side effect volume" of another device, so to speak. In particular, the accumulator should have an internal volume of typically 0 L, 0.5 L, 1 L, 2 L, 3 L, 4 L, 5 L (lower limit) to 1 L, 2 L, 3 L, 4 L, 5 L, 6 L, 7 L, 8 L, 9 L, 10 L, 12.5 L, 15 L, 17.5 L or 20 L (and possibly even more; upper limit) (L - liters). If several hydraulic pressure accumulators/hydraulic accumulators are provided, the above-mentioned volumes can be divided between several hydraulic pressure accumulators. It is of course possible to use hydraulic pressure accumulators of (at least some) the same size and/or (at least some) different sizes.

When reference is made to electrically controllable fluid switching valves, electrically controllable pressure control valves or the like, this can be understood to mean that the control signal comes from the electronic control device. It is possible that the type of signal remains the same (i.e. it is always an electrical signal), or that it is at least partially changed in one, some, several, a plurality or (essentially) all devices. Therefore, the respective electrically switchable/electrically controllable device can be controlled directly by an applied electrical signal. However, it is also possible that the electrical control signal output by the electronic control device is first converted into a pneumatic control signal, a mechanical control signal or the like. Nevertheless, the respective controlled device continues to be controlled by the electronic control device.

When we talk about a fluid line, we can mean a pipe, a hose, a corrugated hose or a combination of these (e.g. a fluid line that has a pipe-like section and a subsequent hose-like section). Furthermore, the fluid line can also have separate, identical and/or differently designed fluid lines that are arranged parallel to one another.

Typical pressures for the hydraulic arrangement are up to 200 bar, 250 bar, 300 bar, 400 bar or even 500 bar.

The hydraulic fluid pump can be any type of device that can supply pressurized hydraulic fluid. In particular, swash plate pumps, bent axis hydraulic pumps, piston-cylinder hydraulic pumps, swash plate pumps, digital displacement pumps (Digital Displacement ® Pump; also called externally commutated hydraulic pumps, “synthetically commutaded hydraulic pump”) or similar can be used. It is also possible for the respective pump to be able to be switched between pump and motor operation. The delivery volume of the respective pump can also be variable or fixed. Just for the sake of completeness, it should be mentioned that the pressurized fluid can be provided at least partially and/or at least temporarily from a hydraulic fluid pressure accumulator (hydraulic pressure accumulators specially provided for this purpose), so that the hydraulic fluid pump can be operated intermittently.

All designs known in the state of the art (including future embodiments/modifications/refinements thereof) can be used for the fluid switching valves and/or the pressure control valve. The electrical controllability can be realized in particular by magnetic coils/control piston devices for converting the incoming electrical control signal into a mechanical force and/or a mechanical movement. This does not, of course, exclude the possibility of pressure compensation surfaces, mechanical preloading devices (e.g. mechanical preload springs) or the like.

The pressure sensor(s) may be of any type and design known in the art (including future developments). In particular, the measured values may be generated and output in electrical form or at least later converted into electrical form so that the electronic control device can read this measured value. The operating mode command may be entered by an operator as desired.

When referring to a set point for (one of) the electrically controllable fluid switching valves and/or the (at least one) electrically controllable pressure control valve, this may include the possibility of a certain allowable interval around the respective set point. This may be provided to reduce the likelihood of unwanted oscillations, to take mechanical/electrical delays into account, to avoid over-regulation, to allow for a certain hysteresis, or similar.

As already mentioned, in the vibration damping mode, a fluid connection is established between the hydraulic cylinder and the hydraulic accumulator. In particular, such a fluid connection can be realized by a corresponding position of the various switching valves/pressure control valves, in particular by switching the electrically controllable first fluid switching valve to an open position so that a fluid connection is established via the first fluid line and the second fluid line. However, no fluid connection is established between the hydraulic cylinder/hydraulic accumulator and the fluid reservoir/hydraulic fluid storage tank and/or the hydraulic fluid pump. This can be achieved by closing the electrically controllable second fluid switching valve (and possibly the third hydraulic fluid switching valve, which is proposed below).

Additionally or alternatively, the electrically controllable pressure control valve can be switched to a so-called closed position so that no fluid flow through the controllable pressure control valve is possible, i.e. no fluid passage is possible between the first side and the second side of the controllable pressure control valve, in particular between the second fluid line (and possibly the third fluid line) and the hydraulic fluid pump and/or the hydraulic reservoir.

It is understood that the electrically controllable pressure control valve and the electrically controllable second fluid switching valve (if applicable, the electrically controllable third fluid switching valve) can be designed as separate devices and/or as a combined device. For example, an open/closed switching behavior (i.e. the functionality of the electrically controllable second/third fluid switching valve) can be realized by a center position of the control piston of the electrically controllable pressure control valve, which prevents fluid flow through the electrically controllable pressure control valve.

For the sake of completeness, it should be mentioned that it is also possible to additionally or alternatively arrange an electrically controllable (additional) fluid switching valve in the fluid line connecting the electrically controllable pressure control valve to the hydraulic fluid pump and another (additional) electrically controllable fluid switching valve between the electrically controllable pressure control valve and the hydraulic fluid reservoir (so to speak, a fluid switching valve arrangement on the second side of the pressure control valve). However, it is understood that this increases the complexity of the hydraulic control system and is therefore generally not recommended. In certain cases, however, this design can also prove advantageous.

In the aforementioned vibration damping mode (the hydraulic cylinder and the hydraulic pressure accumulator are fluidly connected to each other and fluidly separated from the hydraulic fluid pump and the hydraulic fluid reservoir), a suspension/damping effect can be realized for the tool attached to the boom arm (e.g. a bucket, a fork or similar), for the boom arm and/or for the goods transported by the hydraulic machine. Hard impacts can be avoided so that the mechanical wear acting on the machine (in particular on the parts of the boom arm assembly) can be reduced, which increases the service life of the machine. Also, damage, loss and/or spillage of the transported goods (e.g. gravel transported in the bucket that could fall down; also a pallet that is on the fork of a forklift truck that could fall down) can be at least partially avoided and/or the probability of losing/spilling goods can be reduced.

In the pressure equalization mode mentioned above, the pressure in the hydraulic cylinder and the pressure in the hydraulic accumulator are equalized. The most obvious idea would be to create a fluid connection between the hydraulic cylinder and the hydraulic accumulator. However, this is usually considered disadvantageous, especially when there are large pressure differences between the hydraulic cylinder and the hydraulic accumulator, because it could cause a lifting/lowering movement of the boom arm/attachment actuated by the hydraulic cylinder. Therefore, it is suggested to measure (at least) the pressure on the hydraulic cylinder side (in the first hydraulic fluid line) and adjust the pressure in the hydraulic accumulator to approximately match the pressure in the hydraulic cylinder. This can be done by introducing additional hydraulic fluid into the hydraulic accumulator, thereby increasing its pressure (in particular by establishing fluid communication with the hydraulic fluid pump) and/or by draining hydraulic fluid from the hydraulic accumulator, thereby reducing its pressure (in particular by establishing fluid communication between the hydraulic accumulator and the hydraulic fluid reservoirs). This can be done shortly before a vibration dampening mode is required/requested/switched on. The disadvantage of this approach is that the balancing process takes some time, so there may be some time delay before the vibration dampening mode is actually activated.

Additionally or alternatively, it is possible to perform pressure equalization essentially continuously, so that a vibration damping mode can be established immediately. The typical disadvantage of this approach is that the constant pressurization/depressurization of the accumulator requires a certain amount of energy consumption, which could be considered disadvantageous.

Some approaches “in between” the previously mentioned extremes can also be used. For example, a pressure equalization of the hydraulic pressure accumulator can only take place when the pressures in the hydraulic cylinder and the hydraulic pressure accumulator exceed a certain difference between them. In other words: a pressure equalization is only carried out (and therefore only every now and then) when the two pressures in the hydraulic cylinder and the hydraulic pressure accumulator differ by too great a pressure difference. In this way, the amount of energy required to pressurize/relieve the pressure accumulator can be reduced. Since only one pressure adjustment with a smaller pressure difference is required, this adjustment corresponds to a fine adjustment that requires (significantly) less time, so that the corresponding time delay can usually be tolerated (as a reminder: a developing large pressure difference is reduced by intermittent pressure equalization). It is even possible to dispense with an additional “fine adjustment” of the pressure equalization. The boom arm does move up and down over a certain distance. However, since only a comparatively small pressure difference has to be bridged, this distance is quite short. Additionally or alternatively, a pressure compensation mode can only be triggered if the hydraulic arrangement, the boom arm, the attachment device and/or the tool attached to the boom arm, the attachment device and/or other parts of the hydraulic arrangement are operated in such a way that that it is reasonably likely that a vibration dampening mode could be requested (e.g. by the operator). For example, a vibration dampening mode is typically only useful when - in the case of a bucket wheel loader - the bucket is in a position suitable for picking up goods (horizontal position) and the boom arm is in a slightly raised position.

In the aforementioned pressure compensation mode, the pressure in the hydraulic cylinder is regulated so that it remains at (or close to) a certain setpoint. This can be achieved by establishing a fluid connection between the electrically controllable pressure compensation valve and the hydraulic cylinder. In particular, it is possible to open the first and second fluid switching valve and to control the electrically controllable pressure control valve with a corresponding control signal. According to an embodiment described below, it is also possible to open the third fluid switching valve. In principle, it depends on the specific embodiment whether a fluid connection to the hydraulic pressure accumulator is opened or closed. Establishing such a fluid connection can provide a certain damping effect, which can possibly prevent vibrations or over-control of the system. However, interrupting the fluid connection to the pressure accumulator can lead to faster control behavior of the arrangement.

It is understood that the use of an electrically controllable pressure control valve means that the pressure control behavior of the hydraulic control system is generally particularly fast. In particular, there are no significant delays due to computing times, as can occur with some control systems known in the prior art. In other words: It is not the case that the pressure input signal must first be processed by the electronic control device in order to control a suitably dimensioned fluid connection to the fluid pump and/or the fluid reservoir. Instead, the setpoint is calculated once (and can remain essentially the same as long as no different operator input is detected) and the pressure control valve is controlled accordingly, with the control behavior being such that the electrically controllable pressure control valve (essentially) carries out the control task itself. It is obvious that this control behavior does not require any calculations and therefore the response time is correspondingly short.

It should be noted that it is not excluded that the electronic control device can be operated in even further modes. In fact, this is usually the standard. To give just one example: if the hydraulic control system raises or lowers the boom arm of a hydraulic boom arm arrangement or the hydraulic control system controls a boom arm arrangement so that a bucket is tilted forwards or backwards, the respective process does not fall under the three aforementioned operating modes. Nevertheless, these additional operating modes are absolutely standard operating modes, and such (additional) operating modes are well known in the art. Such additional operating modes are therefore also possible in essentially all realistic embodiments.

It is possible to design the hydraulic system in such a way that the electronic control device is designed and configured such that it can be operated in at least two, preferably in all three operating modes of the aforementioned group of operating modes. This can mean that the electronic control device is designed and configured such that it can be operated in at least two of the aforementioned operating modes: "pressure compensation mode", "vibration damping mode" and "pressure control mode". In particular, it is possible for the electronic control device to be designed and configured such that it can be operated in all three of the aforementioned operating modes. However, by designing and configuring the electronic control device such that it can be operated in two or even three of the aforementioned operating modes, the hydraulic system and thus the hydraulic machine that uses the hydraulic system can become more versatile. In particular, it is possible for the hydraulic system to operate the machine in (at least) a vibration damping mode (possibly including the pressure compensation mode beforehand) and a pressure control mode. It is particularly advantageous that the additional functionality does not come at the expense of a significantly more complicated structure. In particular, the (single) electrically controllable pressure control valve can be used for different purposes, in particular for performing the pressure equalization mode and the pressure control mode. This is an improvement over prior art solutions where two different hydraulic circuits are used, for which consequently two separate electrically controllable pressure control valves must be used. This can be of particular importance since the electrically controllable pressure control valve is typically a rather expensive component. Thus, even if - to give just one example - an additional electrically controllable hydraulic fluid switching valve should be required when using the idea proposed here, this can still be advantageous since an electrically A controllable fluid switching valve is typically simpler in design and less expensive than an electrically controllable pressure control valve.

It is possible to design the hydraulic control system in such a way that an electrically controllable third fluid switching valve is present, which is fluidically connected to the first fluid line on a first side and fluidically connected to the pressure control valve on a second side. This design makes it possible to fluidically isolate the hydraulic pressure accumulator in certain operating modes, while a fluidic connection between the hydraulic cylinder and the electrically controllable pressure control valve remains. This is particularly useful for implementing a pressure control mode. If the pressure accumulator is fluidically separated from the hydraulic cylinder, the pressure control mode can have very fast response times. This can be advantageous at least for certain applications. However, it should be pointed out again that it can be useful to fluidically connect a hydraulic pressure accumulator to the hydraulic cylinder even in pressure control mode. This can reduce or avoid possible vibrations (oscillations) and/or overshoot of the system can be reduced or avoided. It should be noted that a good compromise between the two "extremes" can be achieved if a hydraulic accumulator with a reduced size is fluidly connected to the hydraulic cylinder in pressure control mode. For this purpose, it may be advantageous to provide two or more hydraulic accumulators so that different accumulator volumes can be connected to the respective parts of the hydraulic system depending on the operating mode currently used. For the sake of completeness, it should be mentioned that it is of course possible for the user to request a pressure control mode without hydraulic accumulator, with a small volume hydraulic accumulator and/or with a large volume hydraulic accumulator depending on his needs and/or wishes. "Large volume hydraulic accumulator" can be understood to mean that between 50%, 60%, 70%, 80%, 90% (lower limit) and 60%, 70%, 80% and 90% or 100% of the accumulator volume used in vibration damping mode is used for pressure control mode. Accordingly, a "small volume hydraulic accumulator" can be understood as a volume between 10%, 20%, 30% and 40% (lower limit) and 20%, 30% or 40% of 50% (upper limit) of the volume of the hydraulic accumulator used for the vibration damping mode. For the sake of completeness, it should be mentioned that it is of course possible to use different pressure control modes in the sense that in different pressure control modes different sized accumulator volumes are connected to the hydraulic cylinder.

It is further proposed to design the hydraulic system in such a way that the electronic control device is designed and configured in such a way that the pressure in the hydraulic cylinder is maintained at a defined setpoint value, in particular when the hydraulic system is operated in a pressure control mode. In this way, it is possible for a tool attached to the hydraulic system, in particular to a boom arm, to an attachment device or to a similar device, to be able to contact the ground with a certain, in particular substantially constant, force/pressure, even if significant height differences occur along the machine's track. It should be noted that such a constant weight (including, but not limited to, a reduction in the force associated with the mass of the tool acting on the ground/crop) is a desired behavior for certain tools such as rotary mowers or the like. It should also be noted that the set point of the pressure in the hydraulic cylinder may be different for different operating conditions and/or for different tools attached to the hydraulic system and/or may vary depending on the operator's preferences, to give just a few examples. In any case, it is of course possible for the set point to allow certain variations in the pressure in the hydraulic cylinder in order to avoid overcorrections, oscillations or shock-like reactions of the assembly.

It is further proposed to design the hydraulic system in such a way that the operating mode is selected by an operator and/or by the electronic control device based on input commands given by the operator. In this way, the operating behavior of the hydraulic arrangement can have a high level of acceptance by the operator. In addition, the versatility of the arrangement can be particularly high. It should be noted that it is also possible for the operating mode and/or the setpoint (or other features of the hydraulic circuit) to be set depending on the attached tool, wherein a tool recognition device can be used to automatically recognize the tool attached to the hydraulic system. The control functionality for this can be taken over by the electronic control device. Such an embodiment can be particularly fail-safe and/or convenient for the operator.

Furthermore, it is proposed to design the hydraulic system in such a way that the pressure in the hydraulic accumulator is estimated by the electronic control device based on the settings of the fluid switching valves, the setting of the pressure control valve(s), the measurement data of (at least) the first pressure transducer and/or a time evolution function of the hydraulic control system/hydraulic system. With this approach, it is possible to avoid the need for an additional pressure transducer (in at least one other part of the hydraulic circuit), thus reducing the cost and complexity of the hydraulic system. It should be noted that a reasonably good pressure estimation is sufficient from a practical point of view, although it is insufficient from an academic point of view. As an example, let us consider a pressure equalization before a vibration damping mode: if the two pressures in the boom arm hydraulic cylinder and in the hydraulic accumulator are close to each other, this is sufficient. Although an adjustment error may occur on both sides when switching from pressure compensation mode to vibration damping mode due to an incorrectly calculated pressure level (particularly in the hydraulic accumulator), causing pressure equalization between the hydraulic cylinder and the hydraulic accumulator, resulting in a slight raising or lowering of the boom arm, such a small movement may not be perceived as disturbing or problematic by the operator, or may not be noticed at all by the operator in the case of very small adjustment errors.

In particular, the hydraulic control system can be designed such that the time evolution function is adjusted based on measured operating characteristics of the hydraulic system. These measurements can be made, for example, at the manufacturer's factory (or at a repair shop that can perform a major repair/overhaul) and stored in the electronic control device. Recalibration is then only carried out when a major repair or overhaul of the hydraulic system is carried out. If the size of the hydraulic pressure accumulator is changed, recalibration must of course be carried out. In addition or alternatively, it is also possible that the calibration data is adjusted based on measurements taken during operation of the machine. If, for example, the electronic control device detects a pressure drop or a pressure increase at the first pressure sensor when switching from a pressure compensation mode to a vibration damping mode, this is an indication that the parameters currently used are somewhat faulty and need to be readjusted accordingly. Any methods known from the state of the art can be used for this readjustment. In this embodiment, an increased leakage oil flow due to wear or aging of seals or similar can be taken into account in order not to impair the quality of the correction.

In addition, it is proposed to design the hydraulic control system in such a way that a second pressure sensor is present which is fluidically connected to the second fluid line. In this way, the pressure on both sides (i.e. hydraulic cylinder and hydraulic pressure accumulator) can be measured instead of relying on an - albeit good - estimate of the pressure on one side. This can increase the quality of the control, in particular it can reduce a (small) lifting or lowering movement of the boom arm when changing from the pressure compensation mode to the vibration damping mode. This can clearly be desirable or even necessary for very sensitive goods to be conveyed (e.g. glass bottles, shock-sensitive goods, carbonated drinks) or in areas of application with very small permissible position tolerances or the like. In particular, larger movements of the boom arm at the beginning of a work shift or after a longer break can be avoided, where pressure estimates based on a time development function tend to be comparatively inaccurate.

In addition, it is proposed to design the hydraulic system in such a way that the pressure control valve can be electrically set to a defined pressure, so that the defined set pressure is maintained on one side thereof (typically on the side with the second fluid line/the side with the third fluid line). In particular in a (substantially permanent) pressure equalization operation, the defined set pressure can actually be variable and depend on the pressure on the hydraulic cylinder side. In this way, the pressure in the hydraulic pressure accumulator follows the pressure in the hydraulic cylinder. Depending on the operating conditions, a certain pressure difference between the two sides can be permitted, so that an adjustment of the target pressure can be delayed, such that an adjustment only takes place when a certain pressure difference is reached or exceeded. In this way, energy can be saved. Just for the sake of completeness, it should be mentioned that in this pressure control mode the hydraulic pressure accumulator is fluidically connected to the pressure control valve, while the hydraulic cylinder is fluidically separated from the hydraulic pressure accumulator. In contrast, in the example of the pressure compensation mode, the hydraulic cylinder is fluidly connected to the pressure control valve, and the set pressure is adjusted according to the operator's requirement, depending on the attached tool or depending on speed is set by another consideration. As already mentioned, the hydraulic accumulator may or may not be connected to the hydraulic cylinder/pressure control valve depending on the operating requirements (including the case where only a reduced volume of the accumulator is fluidly connected to the hydraulic cylinder/pressure control valve).

Furthermore, a hydraulic system is proposed which is designed such that the pressure equalization mode is selected shortly before switching on a vibration damping mode and/or a pressure control mode. Additionally or alternatively, it is proposed that the hydraulic control system is designed such that the pressure equalization mode is performed when the hydraulic cylinder is actuated. In this way, pressure equalization can only be performed in situations where a vibration damping mode is subsequently activated or the activation of a vibration damping mode can be expected. Similarly, pressure equalization for the pressure accumulator is only performed when there is a relevant reason for a change in the pressure in the hydraulic pressure accumulator. In this way, unnecessary pressure fluctuations in the hydraulic pressure accumulator can be avoided. This can reduce wear, reduce noise and/or lower the energy consumption of the machine.

Furthermore, it is proposed to design the hydraulic system in such a way that a pressure relief valve and/or a non-return valve is present which is fluidically connected to the third fluid line of the hydraulic system. In this way, damage to the system due to overpressure and/or cavitation can be avoided in a simple and cost-effective manner. It should be clear that damage due to overpressure or cavitation represents a realistic risk during normal operation of the hydraulic system and/or should be avoided. Fluid discharge cannot only be provided towards a hydraulic fluid reservoir at ambient pressure. Additionally and/or alternatively, fluid discharge can be made towards a standby pressure line, wherein the standby pressure line is typically at an intermediate pressure level (i.e. between ambient pressure and the fluid pressure supplied by the hydraulic pump).

Furthermore, it is proposed to design the hydraulic system in such a way that the first fluid line is fluidically connected to a boom arm hydraulic cylinder. In this way, a very simple structure of the hydraulic system can be realized, which can lead to cost advantages. Additionally or alternatively, it is proposed to design the hydraulic system in such a way that a changeover valve arrangement is used so that the first fluid line can be fluidically connected selectively to a hydraulic cylinder of a boom arm (boom arm hydraulic cylinder) and a hydraulic cylinder of an attachment device (attachment device hydraulic cylinder). In this way, the versatility of the hydraulic system can be increased at comparatively low additional costs. This is because changeover valves are readily and inexpensively available on the market.

Furthermore, a method for controlling a hydraulic system is proposed, in which the hydraulic system can be operated selectively in a vibration damping mode and in a pressure control mode, wherein a common pressure control valve is used to implement both the vibration damping mode and the pressure control mode. In particular, the method can be carried out in combination with a hydraulic system according to the previous description. The method can have, at least analogously, the same features and properties as previously described. In addition, the method can also be modified in the sense described above, at least in an analogous manner. Such modifications can have, at least analogously, the same or at least similar features, properties, effects and advantages as previously described.

• 1: eine erste mögliche Ausführungsform eines Hydrauliksystems für ein Arbeitsfahrzeug, das eine Steuervorrichtung zur Durchführung einer Vielzahl von Betriebsmodi aufweist;
• 2: eine zweite mögliche Ausführungsform eines Hydrauliksystems für ein Arbeitsfahrzeug, aufweisend eine Steuervorrichtung zur Durchführung einer Mehrzahl von Betriebmodi;
• 3: ein Arbeitsfahrzeug mit einem hydraulisch betätigten Auslegerarm und einer hydraulisch betätigten Anbringungsvorrichtung.

Further advantages, features and objects of the invention will become apparent from the following detailed description of the invention taken in conjunction with the accompanying drawings, in which:

• 1 : a first possible embodiment of a hydraulic system for a work vehicle, which has a control device for carrying out a plurality of operating modes;
• 2 : a second possible embodiment of a hydraulic system for a work vehicle, comprising a control device for carrying out a plurality of operating modes;
• 3 : a work vehicle with a hydraulically operated boom arm and a hydraulically operated attachment device.

1 shows a possible embodiment of a hydraulic system 1 intended to control a boom assembly 32 of a work vehicle 30 (see 3 ) in a variety of operating modes.

The boom assembly 32 is actuated by a boom arm hydraulic cylinder 2, wherein the lower chamber 3 of the piston 5 of the boom arm hydraulic cylinder 2 is in 1 is used to raise the boom arm 33, while the upper piston chamber 4 is used to lower the piston 5 of the boom arm hydraulic cylinder 2 and thus the boom arm 33 of the boom arm arrangement 32. It should be noted that in the embodiment shown here, for the sake of simplicity, only the lower piston chamber 3 can be filled with pressurized hydraulic fluid. This means that only an upward movement of the boom arm 33 can be actively driven. In contrast, the upper piston chamber 4 is only passively filled with or emptied of hydraulic fluid via the passive fluid line 22 in the direction of the hydraulic fluid reservoir 6 which is under ambient pressure. Of course, an active lowering of the piston 5 of the boom arm hydraulic cylinder 2 can also be realized with the help of a changeover valve or another hydraulic scheme that is known in the prior art and is obvious to the person skilled in the art.

The first fluid line 7 is connected on one side to the lower piston chamber 3 of the boom arm hydraulic cylinder 2. The other side of the first fluid line 7 is connected to the first fluid switching valve 8. At the other end of the first fluid switching valve 8, a second fluid line 9 is connected, which leads to a hydraulic pressure accumulator 10, which is partially filled with hydraulic fluid at different pressure levels. The first fluid switching valve 8 can be switched between two different positions, namely a position in which there is no fluid connection between the first and second fluid lines 7, 9 (as in 1 shown), and a position in which there is a fluid connection between the first and second fluid lines 7, 9. The actuation is controlled by an electronic control device 11 by means of an electrical signal transmitted via one of the different electrical cables 12. It should be noted that, of course, instead of a plurality of electrical cables 12, at least some of the electrical cables 12 can be replaced by a bus system (such as a CAN bus or the like).

Furthermore, a pressure sensor 13 is fluidically connected to the first fluid line 7. The pressure measurement of the pressure sensor 13 is transmitted to the electronic control device 11 via an electrical cable.

A third fluid line 14 branches off from the second fluid line 9 and leads to an electrically controlled pressure control valve 15. As shown in 1 As can be seen, an electrically controllable second hydraulic fluid switching valve 16 is arranged within the third fluid line 14, which divides the third fluid line 14 into parts 14a and 14b. Depending on the position of the second hydraulic fluid switching valve 16, the second fluid switching valve 16 can either establish a fluid flow through the third fluid line 14 or interrupt such a fluid flow (as in 1 Similar to the first hydraulic fluid switching valve 8, the second fluid switching valve 16 can be electrically switched between two switching positions by the electronic control device 11 by means of an electrical signal transmitted via one of the electrical cables 12.

A further fluid line, namely the fourth fluid line 17, connects the first fluid line 7 to the pressure control valve 15. In the fourth fluid line 17, a further fluid switching valve 18, namely the electrically controllable third hydraulic fluid switching valve 18, is arranged so that a fluid flow through the fourth fluid line 17 can either be established or prevented (as in 1 shown). Similar to the third fluid line 14, the third hydraulic fluid switching valve 18 divides the fourth fluid line 17 into parts 17a and 17b. The electrically controllable third fluid switching valve 18 is also controlled by the electronic control device 11 via one of the electrical cables 12.

It should be noted that the fourth fluid line 17 and the electrically controlled third fluid switching valve 18 are optional, which means that a pressure compensation mode, a vibration damping mode and a pressure control mode can be realized even without the third fluid line 17 and the third fluid switching valve 18. Nevertheless, their presence is advantageous because the behavior of the hydraulic system 1 can be improved by them.

The electrically controllable pressure control valve 15 can also be controlled by the electronic control device 11 via one of the electrical cables 12. The pressure control valve 15 can be set to a specific Pressure setpoint can be set. On one of its sides 19, 20, the pressure control valve 15 is connected to the third fluid line 14 (and thus also to the fourth fluid line 17). The pressure control valve 15 is configured such that a defined pressure is maintained on its first side 19 (which is connected to the respective parts 14b, 17b of the third and fourth fluid lines 14, 17), wherein the pressure level can be specifically set by the electrical control signal (and therefore the respective parts 14b, 17b of the third fluid line 14 and the fourth fluid line 17 can be set to a suitable pressure level by the electronic control device 11). In order to keep the pressure on the first side 19 of the pressure control valve 15 at the set level, there is a connection to a high-pressure fluid line 21 and an ambient pressure fluid line 22 on the second side 20 of the pressure control valve 15. The high-pressure fluid line 21 is fed by a hydraulic fluid pump 23, wherein the hydraulic fluid pump 23 can obtain its hydraulic fluid from the hydraulic fluid reservoir 6. The ambient pressure fluid line 22 is directly fluidically connected to the hydraulic fluid reservoir 6. Therefore, by appropriately moving the pressure control valve 15, the pressure on the first side 19 of the pressure control valve 15 can be increased by establishing a fluid connection with the high-pressure fluid line 21; likewise, the fluid pressure on the first side 19 of the pressure control valve 15 can be reduced by a fluid connection with the ambient pressure fluid line 22, whereby fluid can be effectively drained from the first side 19 of the pressure control valve 15.

The hydraulic fluid pump 23 can be electrically controlled by the electronic control device 11 (although in 1 not shown). In addition, the hydraulic fluid pump 23 may be of any suitable type. For example, it may be a variable displacement swash plate pump.

In addition, a safety valve 24 is arranged in the hydraulic system 1. The safety valve 24 is connected to the first side 19 of the pressure control valve 15 via the second part 14b of the third fluid line 14. Furthermore, the safety valve 24 is connected to the ambient pressure fluid line 22. Finally, the safety valve 24 is connected to the intermediate pressure line 25, which is kept at an intermediate pressure level by a suitable device (not shown here).

It should be noted that in 1 In the embodiment of a hydraulic system 1 shown, the pressure in the second fluid line 9/in the hydraulic pressure accumulator 10 cannot be directly measured when the first fluid switching valve 8 and the second fluid switching valve 16 are closed. Therefore, the pressure is estimated by the electronic control device 11 on the basis of the pressure measured by the pressure sensor 13, other parameters programmed into the electronic control device 11 and in particular the time that has elapsed since the hydraulic pressure accumulator 10 was last set to a known pressure level (for example by opening the first fluid switching valve 8, whereby the pressure in the hydraulic pressure accumulator 10 can be measured by the pressure sensor 13). This multi-parameter dependence of the pressure in the hydraulic pressure accumulator 10 can be expressed as a time evolution function that is programmed into the electronic control device 11.

Table 1 shows an overview of the valve settings of the various valves 8, 15, 16 and 18 in the different operating modes from the group of operating modes that includes a pressure compensation mode, a vibration damping mode and a pressure control mode. In particular, in the pressure control mode, the pressure control valve 15 is set to a corresponding pressure level so that a defined pressure is supplied to the boom arm hydraulic cylinder 2 such that the tool attached to the boom arm arrangement 32 presses onto the ground with a desired mechanical force. Table 1 - Valve positions for different operating modes operation mode First switching valve 8 Pressure control valve 15 Second switching valve 16 Third switching valve 18 Pressure equalization mode Off (optional On) Adjust to desired level Out of At Pressure control mode At Adjust to desired level At Out of Vibration damping mode At Out of Out of Out of

Furthermore, in the pressure compensation mode, the pressure level of the pressure control valve 15 is set to a level that corresponds to the desired pressure level in the hydraulic pressure accumulator 10. This can correspond to the pressure measured by the pressure sensor 13, i.e. the pressure in the lower piston chamber 3 of the boom arm hydraulic cylinder 2. The pressure compensation mode can be permanently switched on (in particular when the boom arm assembly 32 is moved) so that the hydraulic pressure accumulator 10 is always at the same pressure level as the lower piston chamber 3 of the boom arm hydraulic cylinder 2.

However, it is also possible to allow a certain maximum pressure difference between the boom arm hydraulic cylinder 2 and the hydraulic pressure accumulator 10 (pressure fluctuations being allowed within the range of the maximum allowable pressure difference). In this way, fewer pressurization and depressurization cycles of the hydraulic pressure accumulator 10 have to be performed, which generally saves energy. Fine adjustment just before the start of a vibration damping mode can be done by initiating a "final" pressure equalization mode before opening the first fluid switching valve 8 (and setting the other valves 15, 16, 18 to a suitable position). Alternatively, it is also possible to simply open the first fluid switching valve 8 (and set the other valves 15, 16, 18 to a suitable position), which can cause some movement of the piston 5 of the boom arm hydraulic cylinder 2 due to the pressure difference between the pressure in the boom arm hydraulic cylinder 2 and the hydraulic pressure accumulator 10. It should be noted that the pressure difference between the boom arm hydraulic cylinder 2 and the hydraulic accumulator 10 is quite small due to the previously described “intermittent pressure equalization mode”, so that either the “final” pressure equalization mode requires little time and/or the movement of the piston 5 of the boom arm hydraulic cylinder 2 is quite small.

Another possibility is to perform a pressure equalization mode just before switching to a vibration damping mode. This is usually the most energy-efficient solution. However, the time delay for adjusting the pressure in the hydraulic pressure accumulator 10 to the pressure in the boom arm hydraulic cylinder 2 can be noticeable. However, depending on the working environment, this can also be tolerable.

2 shows another hydraulic system 26, which is a variant of the hydraulic system 1 according to 1 For the sake of simplicity, identical reference numerals are used for similar parts. The hydraulic system 26 can advantageously be used for a work vehicle 30 according to 3 which includes both a boom arm assembly 32 and an attachment device 36.

As can be seen from a comparison of 1 and 2 As can be seen, the main difference between the two hydraulic systems 1, 26 is the presence of a second pressure sensor 27, which outputs measurement data concerning the pressure level in the second fluid line 9/in the hydraulic pressure accumulator 10 to the electronic control device 11 via another electrical cable 12. Furthermore, not only a boom arm hydraulic cylinder 2 is present, but also an attachment device hydraulic cylinder 28 for actuating an attachment device 36 of a work vehicle 30 (see 3 ). The hydraulic system 26 can be selectively connected to the attachment device hydraulic cylinder 28 or the boom arm hydraulic cylinder 2 by means of a changeover valve arrangement 29, as is known in the art. Thus, depending on the setting of the changeover valve arrangement 29, the hydraulic system 26 can actuate either the boom arm hydraulic cylinder 2 or the attachment device hydraulic cylinder 28. The changeover valve arrangement 29 is also controlled by the electronic control device 11 by means of electrical pulses which are transmitted via electrical lines 12.

The control logic of the hydraulic system 26 is essentially the same as the control logic of the hydraulic system 1. Depending on whether a tool is mounted on the attachment 36 or on the boom arm assembly 32 of the work vehicle 30, the pressure equalization mode, the vibration dampening mode, or the pressure control mode can be performed for either the attachment 36 or the boom arm assembly 32 of the work vehicle 30.

3 shows the basic structure of the work vehicle 30, as it is known as such in the prior art. For this work vehicle 30, a hydraulic system 1 or a hydraulic system 26 (or a variant of such hydraulic systems 1, 26) can advantageously be used.

As in 3 As can be seen, the work vehicle 30 has an operator's cabin 31 in which an operator can sit. The operator can drive the work vehicle 30 and operate the various tools 34, 38.

The work vehicle 30 in the present case has a boom arm arrangement 32 with a pivotable boom arm 33. A tiltable bucket 34 is arranged at one end of the pivotable boom arm 33.

The pivoting boom arm 33 can be operated by means of a boom arm hydraulic cylinder 2 (see hydraulic system 1 in 1 or hydraulic system 26 in 2 ) can be raised or lowered, while the bucket 34 can be tilted by means of the tilting hydraulic piston 35.

On the opposite side of the work vehicle 30, an attachment device 36 is arranged. The attachment device 36 can be operated by means of an attachment device hydraulic cylinder 28 (see hydraulic system 26 of 2 ) can be raised or lowered. A rotary mower 38 is presently mounted on the outer end of the attachment arm 37.

It should be noted that normally only one of the tools 34, 38 is connected to the work vehicle 30. Even if both tools 34, 38 are attached to the work vehicle 30 (which may happen), usually only one of the tools 34, 38 is actively used. Thus, when the rotary mower 38 is used to mow grass or crops, the tiltable bucket 34 is empty. Accordingly, when the tiltable bucket 34 is actively used to shovel goods, the rotary mower 38 is in a passive position and is not driven.

For the sake of completeness, it should be mentioned that it is not only possible for the boom arm arrangement 32 to be arranged at the front of the work vehicle 30. Rather, the boom arrangement 32 can also be arranged at the rear of the work vehicle 30. Furthermore, it is possible for the boom arm arrangement 32 to be arranged on both sides of the work vehicle 30.

Likewise, it is not only possible for the attachment device arrangement 36 to be arranged at the rear of the work vehicle 30. Rather, the attachment device arrangement 36 can also be arranged at the front of the work vehicle 30. Furthermore, it is possible for the attachment device arrangement 36 to be arranged on both sides of the work vehicle 30.

As an additional note, it should also be mentioned that it is also possible for a boom arm assembly 32 and an attachment device 36 to be arranged simultaneously on one (or both) sides of the work vehicle 30 (front and/or rear). Conversely, it is also possible for the work vehicle 30 to have only one (or two or a plurality of) boom arm assemblies 32 and/or only one (or two or a plurality of) attachment devices 36.

It should be noted that any one or a plurality of features of one or more of the presently disclosed detailed embodiments may be used in combination with the general description of the present disclosure.

Claims (13)

Hydraulic system (1, 26) for a hydraulic machine (30), in particular for a work vehicle (30), the hydraulic system (1, 26) comprising: - a hydraulic cylinder (2, 28) and a hydraulic pressure accumulator (10), - an electrically controllable first fluid switching valve (8) which is fluidically connected to the hydraulic cylinder (2, 28) on a first side via a first fluid line (7) and is fluidically connected to the hydraulic pressure accumulator (10) on a second side via a second fluid line (9), - a first pressure sensor (13) which is fluidically connected to the first fluid line (7) between the first fluid switching valve (8) and the hydraulic cylinder (2, 28), - an electrically controllable pressure regulating valve (15) which is fluidically connected to the second fluid line (9) on a first side (19) of the pressure regulating valve (15) via a third fluid line (14), and on a second side (20) of the pressure regulating valve (15) optionally with a hydraulic fluid pump (23) for providing pressurized hydraulic fluid or fluidically connected to a hydraulic reservoir (6) in order to discharge hydraulic fluid on the second side (20) of the pressure control valve (15), - an electrically controllable second fluid switching valve (16) which is arranged in the third fluid line (14) between the second fluid line (9) and the pressure control valve (15), - and an electronic control device (11) which reads in at least one operating mode command and at least one measured value of the first pressure sensor (13) and a setpoint value for the electrically controllable pressure control valve (15), a setpoint value for the electrically controllable first fluid switching valve (8) and a setpoint value for the electrically controllable second fluid switching valve (16), characterized in that the electronic control device (11) is designed and configured such that it can be operated in at least one mode which is selected from the group of operating modes comprising the following: a pressure compensation mode in which the pressure in the hydraulic cylinder (2, 28) and the pressure in the hydraulic pressure accumulator (10) are balanced; a vibration damping mode in which the hydraulic cylinder (2, 28) and the hydraulic pressure accumulator (10) are fluidically connected to one another and fluidically separated from the hydraulic fluid pump (23) and the hydraulic reservoir (6); and a pressure control mode in which the pressure in the hydraulic cylinder (2, 28) is controlled to a defined target value. Hydraulic system (1, 26) according to Claim 1 , characterized in that the electronic control device (11) is designed and arranged such that it can be operated in at least two, preferably in all three operating modes of the group of operating modes. Hydraulic system (1, 26) according to Claim 1 or Claim 2 , especially after Claim 2 , characterized by an electrically controllable third fluid switching valve (18) which is fluidically connected on a first side to the first fluid line (7) and is fluidically connected on a second side to the pressure regulating valve (15). Hydraulic system (1, 26) according to one of the preceding claims, characterized in that the electronic control device (11) is designed and arranged such that the pressure in the hydraulic cylinder (2, 28) is kept at a defined target value, in particular when the hydraulic system (1, 26) is operated in a pressure control mode. Hydraulic system (1, 26) according to one of the preceding claims, characterized in that the operating mode is selected by an operator and/or by the electronic control device (11) on the basis of input commands given by the operator. Hydraulic system (1, 26) according to one of the preceding claims, characterized in that the pressure in the hydraulic pressure accumulator (10) is estimated by the electronic control device (11) on the basis of the settings of the fluid switching valves (8, 16, 18), the setting of the pressure control valve (15), the measurement data of the first pressure sensor (13) and/or a time course function of the hydraulic system (1, 26). Hydraulic system (1, 26) according to Claim 6 , characterized in that the time evolution function is adapted on the basis of measured operating characteristics of the hydraulic system (1, 26). Hydraulic system (1, 26) according to one of the preceding claims, in particular according to one of the Claims 1 until 5 , characterized by a second pressure sensor (27) which is fluidically connected to the second fluid line (14a). Hydraulic system (1, 26) according to one of the preceding claims, characterized in that the pressure control valve (15) is electrically adjustable to a defined pressure, so that the defined set pressure is maintained on one side (19, 20) thereof. Hydraulic system (1, 26) according to one of the preceding claims, characterized in that the pressure compensation mode is selected shortly before switching on a vibration damping mode and/or a pressure control mode and/or characterized in that the pressure compensation mode is carried out when the hydraulic cylinder (2, 28) is actuated. Hydraulic system (1, 26) according to one of the preceding claims, characterized by a pressure relief valve (24) and/or a check valve (24) which is fluidically connected to the third fluid line (14) of the hydraulic system (1, 26). Hydraulic system (1, 26) according to one of the preceding claims, wherein the first fluid line (7) is fluidically connected to a boom arm hydraulic cylinder (2) and/or characterized by a changeover valve arrangement (29) such that the first fluid line (7) is selectively fluidically connected to a boom arm hydraulic cylinder (2) and an attachment device hydraulic cylinder (28). Method for controlling a hydraulic system (1, 26) according to one of the Claims 1 until 12 , characterized in that the hydraulic system (1, 26) is specifically switched to a vibration damping mode dus and can be switched to a pressure control mode, whereby a common pressure control valve is used to realize both the vibration damping mode and the pressure control mode.

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