EP2912309B1 - Method and device for actuating an electrically commutated fluid working machine - Google Patents

Description

The invention relates to a method for controlling a preferably electrically commutated fluid work machine. The invention also relates to a control device for controlling a preferably electrically commutated fluid machine. The invention also relates to a fluid work machine, in particular an electrically commutated fluid work machine.

Fluid machines are now used in technology for a wide variety of fields of application. In general, fluid work machines are used when fluids must be pumped or fluids are used to drive a fluid work machine when it is operated in a motor mode. In this way it is also possible, for example, for mechanical energy to be transported from one location to another with the "interposition" of a fluid circuit.

The term "fluid" can refer to both gases and liquids. It is also possible that the “fluid” is a mixture of gases and liquids. A fluid can also be understood to be a supercritical fluid in which a distinction can no longer be made between the gaseous and the liquid state of aggregation. Moreover, it is also harmless if a liquid and / or a gas carries a certain proportion of solids with it (suspension or smoke).

A first area of application for fluid machines is to increase the pressure level of a fluid, in some cases significantly. Examples of such fluid work machines are air compressors or hydraulic pumps. A fluid can also be used to generate mechanical power, pneumatic motors or hydraulic motors being used as a rule.

A design that is often used for fluid working machines is that one or more working chambers, which have a cyclically varying volume during operation, are used. At least one inlet valve and at least one outlet valve are provided for each working chamber.

In the design most widespread in the prior art to date, the inlet and outlet valves are so-called passive valves. These open when there is a pressure difference in the flow direction, whereas they close when there is a pressure difference against the flow direction. In most cases, the passive valves are also preloaded so that they close automatically in the normal state (for example spring-loaded valves).

If such passive valves are used, for example, in a fluid pump, the structure is such that a fluid inlet valve opens when the volume of the associated working chamber increases. As soon as the volume of the working chamber is reduced again, the fluid inlet valve closes while the fluid outlet valve opens. In this way, fluid is pumped "in one direction" due to the cyclical fluctuations in volume of the working chamber.

In electrically commutated fluid machines, at least one of the passive fluid valves is replaced by an electrically controllable valve. Such fluid work machines are known in the English-speaking world under the term synthetically commutated hydraulic machines or digital displacement pumps. Such electrically commutated fluid machines are for example in the European patent application EP 0 494 236 B1 or in the international patent application WO 91/05163 A1 described.

If, for example, in an electrically commutated hydraulic pump, the passive fluid inlet valve is replaced by an electrically controllable valve, it is possible to leave the inlet valve (initially) in the open position when the working chamber begins to shrink. As a result, the fluid enclosed in the working chamber is conveyed back into the fluid reservoir without performing "real" work. Only when the electrically controllable inlet valve is closed by an electrical control pulse is the fluid still remaining in the working chamber pumped in the direction of a high-pressure line via a passive fluid outlet valve. This special structure makes it possible that the hydraulic oil flow "effectively" pumped by the electrically commutated hydraulic pump can be changed extremely quickly and, in particular, significantly from one pump stroke to the next. This in turn has the advantage that no fluid buffers have to be provided and, as a rule, none Fluid under high pressure has to be drained "unnecessarily" via safety valves. As a result, synthetically commutated hydraulic pumps of this type can in part work significantly more economically than conventional working pumps.

If both the fluid inlet valve and the fluid outlet valve are replaced by electrically controllable valves, a hydraulic motor that can be regulated very quickly can also be implemented.

In order to adapt the fluid flow delivered by an electrically commutated fluid pump (in the case of a fluid motor, the same applies analogously) to the fluid flow currently in demand, different methods and algorithms have been described.

For example, in the European patent application EP 1 537 333 B1 describes a method in which a certain fluid flow is generated by a series of complete pump strokes ("full-stroke pumping modes"), partial pump strokes ("part-stroke pumping modes") and idle pump strokes ("idle-stroke pumping modes "), with the actually requested delivery rate being provided on average. In order to achieve sufficient smoothing, a high-pressure buffer volume is made available, which, however, has a smaller volume than conventional hydraulic pumps. While in EP 1 537 333 B1 the part-load pump strokes are always carried out with a fixed pump volume of around 17%, the method described there in EP 2 246 565 A1 refined. There it is proposed (initially) to allow essentially any partial volumes for the partial pump strokes. Only when the fluid flow speed through the inlet valve becomes too high are certain volume areas excluded in order to avoid noise development or premature wear of the inlet valve and / or the electrically commutated hydraulic pump. Special at the in EP 2 246 565 A1 According to the proposed method, not only the pump quantity of the immediately following working stroke is calculated using a suitable algorithm, but several immediately imminent working strokes are calculated in advance at a certain point in time. This generally improves the quality of the fluid flow generated. In particular, residual pulsations can be suppressed even further.

US 2012/076670 A1 describes a method for operating a fluid working machine in which the volume of the working fluid that is displaced during each cycle of the working chamber volume is selected taking into account the availability of other working chambers. The status of each working chamber is monitored and a working chamber is treated as unavailable if a malfunction is detected. A work chamber can be treated as unavailable if it is assigned to an alternative work function. A fault can be detected in a working chamber by determining whether a measured output parameter of the fluid working machine fulfills at least one acceptable functional criterion, taking into account the previously selected net displacement of the working fluid through a working chamber during a cycle of the working chamber volume.

EP 1 717 446 A2 discloses a pump having a housing having a compression chamber for pressurizing a fluid and a fluid channel for directing the fluid into the compression chamber. A valve is located in the middle of the fluid channel to open and close the fluid channel. A magnetic actuator for actuating the valve is located on a side essentially opposite the compression chamber with respect to the valve. A control element is located between the valve and the solenoid actuator in order to prevent the liquid pressure in the compression chamber from acting on the solenoid drive of the valve.

US 2011/253918 A1 relates to a valve actuator that has a magnetic core with a space and at least one bifurcation branch, at least one variable magnetic field generating device, at least one permanent magnetic field generating device and at least one movable magnetic component, the bifurcation branch defining a first area and a second area of the magnetic core.

Although electrically commutated hydraulic pumps have meanwhile reached a considerable level of development, there is still a need for further improvements. In particular, a current research goal is to make electrically commutated hydraulic pumps even smaller and lighter, to further reduce their acquisition and operating costs and to further reduce their energy requirements - in particular their electrical energy requirements.

The object of the present invention is therefore to propose a method for controlling a fluid working machine which is improved compared to methods known in the prior art for controlling fluid working machines. A further object of the invention is to propose a control device for fluid working machines which is improved over controls for fluid working machines known in the prior art. A further object of the invention is to propose a fluid working machine which has improved properties compared to fluid working machines known in the prior art.

The invention achieves these objectives.

It is proposed a method for controlling a fluid machine, the fluid machine having at least one working chamber with a cyclically varying volume, a high pressure fluid connection, a low pressure fluid connection, at least one electrically controllable valve for the controllable connection of the high pressure fluid connection and / or the low pressure fluid connection to the working chamber, wherein the control of the at least one electrically controllable valve takes place as a function of the fluid requirement and / or the mechanical power requirement, to be carried out in such a way that the control of the at least one electrically controllable valve is at least temporarily additionally dependent on the one for controlling the at least one electrically controllable valve required electrical power takes place, at least one upper electrical power limit is taken into account so that it is not exceeded. In other words, the proposed method can be a method for controlling an electrically commutated fluid machine, with the activation of at least one electrically controllable valve (in particular a fluid inlet valve and / or fluid outlet valve for at least one working chamber) at least temporarily additionally depending on the for the control of the at least one electrically controllable valve required electrical power takes place. In previous developments, when controlling the electrically commutated fluid machine, the main focus was on the most advantageous fluid flow possible (in the case of operation as a hydraulic pump) or the mechanical power generated (in the case of operation as a hydraulic motor). "Side effects" were not considered here. Only in cases in which an unacceptable operating noise and / or an unacceptable increased mechanical wear has occurred due to particularly unfavorable control patterns made "an exception" in this regard. In the meantime, however, the inventors have found, to their own surprise, that electrically commutated hydraulic pumps have now reached a stage of development that the power required for the operation of the electrically controllable fluid valves can sometimes play a considerable role. In order to be able to switch the electrically controllable fluid valves very quickly and precisely, considerable electrical currents are necessary, so that a corresponding electrical output is required to operate the same. Correspondingly, appropriate electrical power, for example in mobile operation (forklifts, vehicles, utility vehicles, excavators and the like) must be made available by appropriately dimensioned generators. An internal combustion engine, for example, is used to drive the generator. The required electrical current can have a not insignificant influence on fuel consumption. In addition, the generator, possibly batteries used for intermediate buffering, and in particular the power electronics used to control the electrically controllable valves must also be dimensioned appropriately large so that (essentially) any desired control pattern can be generated for the electrically controllable valves. The components in question have so far been dimensioned in such a way that it was possible for all electrically controllable valves to be activated at the same time, which made correspondingly generous dimensioning necessary (although in reality safety margins were usually still taken into account). The inventors have found, however, that in normal applications a particularly large proportion of the electrically controllable valves only rarely has to be controlled simultaneously. For this reason, a significant load range of the dimensioning of previous electrically commutated fluid machines is rarely or never used. Accordingly, it is fundamentally possible to be able to dimension the corresponding components smaller, without deficits in the operating behavior or even problems occurring more frequently and / or noticeably in practical applications. It is possible, for example, to dimension the components in such a way that only up to 50%, 60%, 70%, 75%, 80%, 85%, 90% or 95% of the electrically controllable valves can be controlled simultaneously. The corresponding weight and volume savings of the relevant components usually not only have a "direct" influence, but in particular also an "indirect" influence, since, for example, fewer masses are accelerated in mobile operation Need to become. As a result, the electrically commutated fluid machine can possibly even be made smaller overall. In order to be able to realize the undersizing described, the inventors further suggest that when controlling the at least one electrically controllable valve of the fluid machine, the electrical power required for controlling the at least one electrically controllable valve is also taken into account at least at times. Such a consideration can in particular take place to the effect that the control pattern is modified in such a way that certain deviations from the currently required fluid quantity / mechanical power (in particular also temporarily) are tolerated. Alternatively or additionally, it is also possible that a higher residual fluctuation in the amount of fluid generated or the mechanical power and / or, in particular, a higher level of noise or increased wear of the fluid machine is accepted at times. First tests have shown that this usually allows considerable cost reductions, energy savings and space savings with only a slight deterioration in the mode of operation of the electrically commutated fluid machine. In addition, the waste heat generated by the power electronics can also be reduced (which can also affect the dimensioning of heat sinks, fans and the like).

According to a preferred embodiment variant of the method, it is proposed that the at least one upper electrical power limit be at least one hard electrical power limit. A "hard electrical power limit" is to be understood in particular as a value which, at least under normal operating conditions, must not be exceeded under any circumstances. For example, this can be a value which, if exceeded, worsens the control signals to such an extent that that a sufficiently precise and / or reliable control of the electrically controllable valves is no longer possible. This can also include a case in which, for example, control electronics (or parts thereof) break down and initially require a certain time (for example several seconds) before "normal operation" can be resumed. A “soft electrical power limit” is to be understood in particular as a value which may be exceeded under certain operating conditions and / or temporarily (in particular briefly). This can, for example, be an electrical power in which the heat loss occurring in the power semiconductors can no longer (completely) be dissipated, so that the corresponding components would heat up impermissibly over time. However, since these components have a certain heat buffer, briefly exceeding such a performance limit is harmless as long as sufficient time is then made available for the components in question to "recover".

Furthermore, it is proposed to carry out the method in such a way that the at least one upper electrical power limit is at least temporarily and / or at least partially defined by at least part of at least one control device and / or at least temporarily and / or at least partially defined by the electrical power available in the system is. A part of at least one control device can be understood to mean in particular power semiconductors, electrical resistors, capacitors, other temporary energy storage devices and the like. In particular, these can be components that heat up not insignificantly during operation and / or components that conduct electrical energy and / or intermediate buffers. An electrical power available in the system is to be understood in particular as an electrical power that is made available by components located “outside the electrically commutated fluid work machine”. For example, if an electrically commutated fluid machine is installed in a forklift truck, then this can be the electrical power that the forklift truck can provide. This electrical power can change, for example, as a result of the operating conditions of the forklift (for example, power required by lighting equipment, electrical heaters, accumulators with a low charge level, especially after long periods of non-use and / or after a starting process, speed of an internal combustion engine and the like). Of course, the electrical power available in the system is generally also defined by the design of the "overall device". With a temporary energy storage device it is possible, for example, to implement valve actuation cycles over a limited period of time that cannot be implemented in continuous operation. The additional power requirement required for this can be taken from the temporary energy storage device at short notice. After that, however, a certain recovery phase is required for the temporary energy storage device.

Furthermore, it is proposed to carry out the method in such a way that a plurality of electrically controllable valves are controlled and the electrically controllable valves are assigned in particular to different working chambers, the working chambers preferably being arranged out of phase with one another and / or a plurality of working chambers operating in parallel being provided. Especially in such cases it can arise, especially under certain operating conditions, that a larger number of electrically controllable valves have to be activated at the same time (whereby "simultaneously" also means only partially overlapping activation pulses and / or activation pulses that are close together in time but that are separate can be). As already mentioned, initial measurements have shown that such “unfavorable” control cycles occur only rarely and are usually tolerable Deteriorations can be avoided or the resulting deteriorations can be accepted.

One possible embodiment variant of the proposed method consists in that the calculation of the valve activation pattern is carried out using a buffer variable. In this, for example, a fluid request is fed in from work cycle to work cycle per pump cycle on a "credit side". Based on the current value of the buffer variable, a meaningful and at the same time permissible pump stroke is determined and the currently activated pump stroke reduces the buffer variable by the relevant value. This makes it possible in a simple manner for a (partially) suspended value to be "made up" at a later point in time, and thus ultimately to realize the requested amount. The resulting fluctuations are usually sufficiently small that negative effects usually do not occur or only occur at a reasonable cost. Of course, the developments already proposed in the prior art, such as in particular the provision of “prohibited areas” and / or a calculation for a few pump cycles in the future, can also be used for this purpose. Additionally or alternatively, it is possible that in a "critical case" a certain "oversupply" (for example in a pump a pump power of fluid that is higher than the requested amount) is provided by a corresponding valve control pattern, whereby an electrical power limit ( especially a soft and / or a hard electrical power limit) is observed. The "oversupply" can then to a certain extent be "mechanically destroyed" (in the case of a pump, for example, by releasing (high-pressure) fluid through a safety valve or the like. It should be noted that, statistically, it is comparatively seldom necessary to use an "oversupply" Accordingly, with such a design "the bottom line" can result in increased energy efficiency of the overall system.

It is also proposed to carry out the method in such a way that an extrapolation algorithm is used for the value of the buffer variable and / or for the value of the fluid requirement to be expected and / or for the value of the mechanical power requirement to be expected. This allows the method to be carried out even more advantageously. If, for example, it is to be expected that the fluid demand, which is likely to be called up shortly, will increase, the control pattern (in which, among other things, the electrical power required for the control of the electrically controllable valve (s) is also taken into account) can be selected such that as many Boundary conditions are met as well as possible. If, for example (apart from the demand to be expected in the future) there are two different sensible control cycles, then with (presumably) increasing power demand, the variant can be selected with which an increasing power demand can be better satisfied.

Furthermore, it is proposed to carry out the method in such a way that at least the difference between the fluid requirement and / or mechanical power requirement and the amount of fluid actually made available after application of the modification with regard to the electrical power requirement or the actually made available mechanical power is determined and in particular in a Error variable is saved. The error variable can in particular be used to carry out suitable correction mechanisms and, if necessary, to allow correction mechanisms that are "undesirable" per se if it is to be expected that the error variable will otherwise increase too much. It is also possible, however, for the error variable to essentially correspond to the buffer variable already described above or essentially to match it. In any case, with the proposed training, the required Fluid requirement or the required mechanical power requirement can be satisfied better and more precisely.

Furthermore, it is proposed that the method be carried out in such a way that, in particular when a certain value of the error variable is exceeded, special correction methods are used and in particular otherwise impermissible partial pump quantities are permitted. This makes it possible to find a kind of compromise between the most correct fulfillment of the requirements on the one hand and the most advantageous possible operating behavior on the other hand (in particular with regard to wear and / or noise development). If, for example, when using otherwise usual criteria under particularly unfavorable operating conditions, an error would rise too sharply, a (usually comparatively small) increase in operating noise and / or wear of the fluid machine can be accepted instead. This is not necessarily detrimental, since such conditions often occur only rarely and / or for only a short time.

It is also possible to carry out the method in such a way that a plurality of different valve actuation patterns are calculated and stored in advance. With such an embodiment, a comparatively large amount of computing time can flow into the creation of the best possible valve control cycles in order to realize the most advantageous valve control cycles. With electronic memories available today, such valve control patterns can be stored in large quantities inexpensively and with little space requirement. These can then be called up as a function of the fluid requirement and / or the mechanical power requirement. If necessary, interpolation methods between two stored values and the like are also conceivable. It is also possible, however, for a certain number of pump strokes to be calculated "into the future" and the calculated values during the operation of the fluid machine be cached. This can be implemented, for example, by “look ahead” algorithms known per se.

Furthermore, a control device is proposed which is designed and set up in such a way that it at least temporarily carries out a method of the type described above. A control device designed in this way can then have the advantages and properties already described in advance in connection with the previously proposed method, at least in an analogous manner. It is also possible to develop the control device - at least in an analogous manner.

In particular, it is possible for the control device to have at least one electronic storage device, a programmable data processing device, a semiconductor power component and / or a temporary energy storage device. Such control devices have proven to be particularly advantageous in initial tests. A temporary energy storage device can in particular be understood to mean a capacitor and possibly also an accumulator. In the case of a capacitor, a large capacitance is preferably useful, as is the case, for example, with so-called gold cap capacitors. With such a temporary energy storage device, increased electrical power can be called up for a short time, for example, so that more valves can be controlled for a short time than is possible in the long term from the dimensioning of the control device and possibly other components. This can prove beneficial.

Finally, a fluid work machine is also proposed, in particular an electrically commutated fluid work machine, which is designed and set up such that it at least partially carries out a method of the type proposed in advance and / or which has at least one control device of the type described above. The fluid machine can then have the advantages and properties already described in advance in connection with the previously described method and / or the previously described control device, at least in analogy. Furthermore, the fluid machine can be developed further as described above (at least in an analogous manner).

Fig. 1:

ein mögliches Ausführungsbeispiel für eine elektrisch kommutierte Hydraulikpumpe in einer Prinzipskizze;

Fig. 2:

ein Beispiel für ein ungünstiges Ansteuerungsmuster;

Fig. 3:

ein Flussdiagramm für ein denkbares Ausführungsbeispiel eines Verfahrens zur Ansteuerung einer elektrisch kommutierten Hydraulikpumpe.

In the following, the invention is explained in more detail with the aid of advantageous exemplary embodiments and with reference to the accompanying drawings. Show it:

Fig. 1:

a possible embodiment for an electrically commutated hydraulic pump in a schematic diagram;

Fig. 2:

an example of an unfavorable control pattern;

Fig. 3:

a flow diagram for a conceivable embodiment of a method for controlling an electrically commutated hydraulic pump.

In Fig. 1 a conceivable embodiment of an electrically commutated hydraulic pump 1 of the so-called wedding cake type ("wedding cake-type pump") is shown. The hydraulic pump 1 has a total of twelve cylinders 2, 3, which are each arranged at an angular distance of 30 ° from one another. For reasons of space, the cylinders 2, 3 are arranged in different planes, namely in the form of two disks arranged one behind the other, each with six cylinders 2, 3. The two disks made up of cylinders 2, 3 are arranged one after the other in a direction perpendicular to the plane of the drawing. In each disc, the respective cylinders 2, 3 are angularly spaced from one another by 60 °. The two disks are "twisted" against each other by 30 °.

In each of the cylinders 2, 3 there are arranged pistons 4 which are displaceable and rotatable through a certain angle. The bottom 5 of the piston 4 is as Formed sliding sole and is supported on an eccentrically rotating eccentric 6, which is moved around an axis of rotation 7. The upper side 8 of the piston 4 forms a fluid-tight seal with the walls of the piston 4. The up and down movement of the pistons 4 in the cylinders 2, 3 caused by the eccentric 6 results in a cyclically varying volume of the pump chambers 9.

Each cylinder 2, 3 is connected via corresponding hydraulic lines 10 to an electrically controllable valve 11, which in turn is connected to a hydraulic oil reservoir 13. The hydraulic oil reservoir 13 is usually under ambient pressure.

Furthermore, in the exemplary embodiment shown here, each cylinder 2, 3 is connected to a high-pressure collector (not shown here) via hydraulic lines 10 via a passive check valve 12. The high pressure collector can have a high pressure accumulator. However, it is also conceivable that a type of "high-pressure storage function" can be implemented, for example, by means of high-pressure hoses which usually have a certain elasticity. In such a case it is possible that the high-pressure hoses go directly to the hydraulic consumer (for example to a hydraulic motor).

For illustrative reasons, the hydraulic lines 10, the electrically controllable valve 11 and the check valve 12 are shown only once. As a rule, the hydraulic oil reservoir 13 and / or the high-pressure collector is identical for a plurality and / or for all cylinders 2, 3.

The electrically controllable valves 11 are electrically controlled via an electronic controller 14. In particular, the electronic controller 14 can have a memory 15 in which a suitable control program is deposited. The electronic control 14 can either be designed for each electrically controllable valve 11 individually and / or control part or all of the electrically controllable valves 11 of the electrically commutated hydraulic pump 1. If necessary, the electronic controller 14 can also take on other tasks. In particular, the electronic controller 14 is, for example, a single-board computer which has power semiconductor components of corresponding dimensions for controlling the electrically controllable valves 11.

The functioning of an electrically commutated hydraulic pump 1 makes it possible that not only a complete pump chamber volume is "effectively" pumped (that is, it is moved in the direction of the high pressure collector), but also partial or zero strokes are possible.

If the piston 4 in the cylinder 2, 3 moves downwards, the electrically controllable valve 11 is opened by the resulting negative pressure and hydraulic oil is sucked in from the hydraulic oil reservoir 13 via the hydraulic lines 10 and the electrically controllable valve 11 (low pressure valve). If the piston 4 reaches the bottom dead center, the passive suction valve would close automatically in a "classic" hydraulic pump. In the presently illustrated electrically commutated hydraulic pump 1, however, the electrically controllable valve 11 (unless otherwise controlled) initially remains open. As a result, the hydraulic oil is initially pressed back into the hydraulic oil reservoir 13 without load through the electrically controllable valve 11 which is still open (and consequently not pumped in the direction of the high-pressure collector). If the electrically controllable valve 11 is now closed after part of the cylinder travel, a pressure builds up quickly in the pump chamber 9 and the remaining portion of the volume is released via the passive check valve 12 (high pressure valve) "effectively" pumped towards the high pressure collector. The function described corresponds to a partial stroke.

If the electrically controllable valve 11 is closed immediately at the bottom dead center of the cylinder 4, the mode of operation of the electrically commutated hydraulic pump 1 corresponds to a "classic" hydraulic pump (full pump strokes). If, on the other hand, the electrically controllable valve 11 is not closed at all, the electrically commutatable hydraulic pump 1 is in idle mode (idle strokes).

In the currently usual designs of electrically commutated hydraulic pumps, the electrically controllable valve 11 is closed by applying a relatively large current. If, on the other hand, no (or insufficient) current (or electrical voltage) is applied, the electrically controllable valve 11 remains in the open position. (In some cases there are also designs with "inverted" switching logic; in such a case, the present description, in particular the description below, must be adapted accordingly.)

It can be seen that the control pulse for closing the electrically controllable valve 11 occurs later, the lower the volume fraction to be pumped. If, for example, with two cylinders immediately following one another (which are offset by 30 ° from one another, for example) a preceding cylinder is to generate a partial pump stroke and a subsequent cylinder is to generate a full pump stroke, the electrically controllable valves 11 of both cylinders are to be activated simultaneously when the Cylinders running immediately ahead should only generate 93.3% of the volume (180 ° rotation corresponds to 100% pumping power). However, an overlap of different control pulses cannot only occur in exactly one such case (which would presumably not occur too often in reality). Rather, such an overlap can occur significantly more frequently because the signals for closing the electrically controllable valves must be applied over a certain period of time.

If one takes typical values for electrically commutated hydraulic pumps, the required control time is 4 ms. Assuming a hydraulic pump that works at 3000 rpm, the time for a full piston stroke is 20 ms. This can lead to a potential overlap of different activation pulses of 180 ° + 72 °. In extreme cases, a twelve-cylinder pump with the specified values can therefore trigger up to eight cylinders at the same time.

In Fig. 2 this effect is illustrated graphically. In the graph there, the angle of rotation 16 (position of the eccentric 6) is shown along the abscissa. The control currents for the different cylinder numbers 17 (twelve cylinders in total) are shown along the ordinate. The oblique lines 18, 19 that can be seen in the graphic correspond to the course of the respective bottom dead center 18 (start of the hydraulic oil discharge phase; pump chamber volume decreases) or top dead center 19 (end of the liquid discharge phase; pump chamber volume has the minimum value). The times relate to 4 ms activation time and 3000 rpm.

In the Fig. 2 The situation shown occurs when the individual cylinders are acted upon as follows:
Cylinder 1 - 1%, cylinder 2 - 10%, cylinder 3 - 33%, cylinder 4 - 60%, cylinder 5 - 66%, cylinder 6 - 90%, cylinder 7 - 100%, cylinder 8 - 100%, cylinder 9 - 100%, cylinder 10 - 100%, cylinder 11 - 100%, cylinder 12 - 50%. As can be seen from the figure, eight cylinders (namely cylinders 1 to 8 shortly before "180 °") are in fact actuated simultaneously at one point in time. A few activation cycles also follow immediately afterwards, so that the control electronics (electronic control 14) does not have much time to recover.

If the electronic control system 14 is now designed for such a "worst case" scenario, it must be dimensioned in such a way that it can control eight electrically controllable valves 11 at the same time. This is correspondingly expensive and time-consuming. In addition, the electronic controller 14 must have a corresponding size (installation space). The cooling of the electronic controller 14 must also be dimensioned accordingly.

If, on the other hand, one simply "depends" and dimensioned the electronic control system 14 such that, for example, only six control cycles can occur at the same time, the power supply would collapse when the control of the last two cylinders (in the example shown here, cylinders 6 and 8) begins. As a rule, this would mean that not only these two valves could no longer close. In addition, the other valves of cylinders 1 to 5 and 7 would possibly no longer close (completely), because when the actuation of cylinders 6 and 8 begins, these may not yet (completely) close. A further disadvantage would be that the power supply usually collapses in such a way that the electronic control 14 typically needs one to two seconds to recover before it is ready to function again. Such behavior is not tolerable.

In the present case, it is therefore proposed that the electronic control system 14 also take into account the required power requirement when activating the electrically controllable valves 11 and adapt the control cycles accordingly.

For example, if there is a fluid requirement of 35% (in the following it is assumed that a pumping interval between 20% and 80% is "forbidden" so that there is no excessive noise development and / or wear is reduced), this fluid requirement can make sense can be generated by three pump strokes, namely by the sequence 100% - 0% - 5% (105% per three pump strokes = 35% on average).

If the 5% activation of the “last” cylinder would now lead to the maximum output of the electronic control system 14 being exceeded, the last pumping cycle is suspended so that the sequence 100% - 0% - 0% results. This results in an error value of 5% (after the three pump strokes).

This error value is saved and "offset" with the fluid request. If the fluid requirement remains at 35%, a pumping capacity of 36.67% (110% for three cycles) must now be provided in order to compensate for the previous shortfall. This can now be implemented using the 100% - 0% - 10% pumping sequence.

The resulting pump sequence 100% - 0% - 0% - 100% - 0% - 10% now corresponds to the requested average value of 35%.

In Fig. 3 Finally, a schematic flow diagram 20 is also shown, which explains a method for controlling an electrically commutated hydraulic pump 1 in more detail.

In the first step 21, the fluid requirement is read in. In the next step, the read-in fluid requirement is modified taking into account an error parameter (step 22). The error parameter describes the extent to which the requested fluid requirement had to be deviated "in the past". Step 22 therefore (albeit possibly over a somewhat longer period Time periods) on average the actually requested fluid requirement is made available.

Based on the fluid requirement modified in step 22, a control sequence for the electrically controllable valves is calculated (step 23). When calculating the control sequence, the required electrical power requirement is also taken into account. Accordingly, it can happen that a control sequence that is desirable in terms of the fluid requirement cannot be implemented, since this would lead to the maximum electrical power being exceeded.

The valves are controlled with the control sequence obtained in this way (step 24). In parallel with this, in step 23 the error parameter, which describes the deviation between the actually pumped amount of fluid and the amount of fluid requested, is modified - if necessary.

After the control sequence has been sent to the valves, the process (arrow 25) jumps back to the beginning.

Even if the exemplary embodiment relates to a hydraulic pump, it is of course possible that the idea described there is also used for a hydraulic motor or for a combination of hydraulic pump and hydraulic motor.

List of reference symbols:

1.

Electrically commutated hydraulic pump

2.

cylinder

3.

cylinder

4th

piston

5.

bottom

6th

eccentric

7th

Axis of rotation

8th.

Upper side

9.

Pumping chamber

10.

Hydraulic line

11.

Electrically controllable valve

12.

check valve

13.

Hydraulic oil reservoir

14th

Electronic control

15th

Storage

16.

Rotation angle

17th

Cylinder number

18th

Bottom dead center

19th

Top Dead Center

20th

flow chart

21st

Read in fluid requirement

22nd

Modification of fluid requirements

23.

Calculation of the control sequence

24.

Control valve

25th

Return

Claims (12)

1. Method (20) for actuating a fluid working machine (1), the fluid working machine (1) comprising at least one working chamber (9) with a cyclically varying volume, a high pressure fluid connection, a low pressure fluid connection, at least an electrically actuated valve (11) for selectively connecting the high pressure fluid connection and/or the low pressure fluid connection with the working chamber (9), wherein the actuation of the at least one electrically actuated valve (11) depends on the fluid flow requirement (21) and/or the mechanical power requirement, wherein the actuation (23) of the at least one electrically actuated valve (11) depends additionally at least at times on the electrical power requirement for actuating the at least one electrically actuated valve, characterised in that at least an upper electrical power limit is considered (23) in a way that the limit is not exceeded.
2. Method (20) according to claim 1, characterised in that the at least one electrical power limit is at least a hard electrical power limit.
3. Method (20) according to claim 1 or 2, characterised in that the at least one upper electrical power limit is defined at least at times and/or at least in part by at least a part of at least one control device (14) and/or is defined at least at times and/or at least in part by the electrical power that is available in the system.
4. Method (20) according to any of the preceding claims, characterised in that a plurality of electrically actuated valves (11) is actuated, wherein the electrically actuated valves (11) are connected to in particular different working chambers (9), wherein the working chambers (9) are preferably arranged phase shifted with respect to each other and/or a plurality of parallely operating working chambers (9) is provided.
5. Method (20) according to any of the preceding claims, characterised in that the valve actuation pattern is calculated (23) using a buffer variable (22).
6. Method (20) according to claim 5, characterised in that an extrapolation algorithm is used for the value of the buffer variable and/or for the value of the fluid flow requirement to be expected and/or for the value of the mechanical power requirement to be expected.
7. Method (20) according to any of the preceding claims, characterised in that at least the difference between the fluid flow requirement and/or the mechanical power requirement and the actually provided amount of fluid flow and the actually provided mechanical power after applying the modification regarding the electrical power requirement, respectively, is determined (23) and stored in particular in an error variable.
8. Method (20) according to claim 7, characterised in that special correcting methods are used when the error variable exceeds a certain value, in particular correcting methods permitting pumping fractions that are usually prohibited.
9. Method (20) according to any of the preceding claims, characterised in that a plurality of different valve actuation patterns is calculated and stored in advance.
10. Control device (14), comprising a programmable data processing equipment that is designed and arranged in a way that it performs at least at times a method according to any of claims 1 to 9.
11. Control device (14) according to claim 10, characterised by at least an electronic storage means (15), a semiconductor power device and/or a temporal energy storage device.
12. Fluid working machine (1), in particular electrically commutated fluid working machine, that is designed and arranged in a way that it performs at least in part a method (20) according to any of claims 1 to 9 and/or that is characterised by a control device (14) according to claim 10 or 11.

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