Method and device for actuating an electrically commutated fluid working machine

Abstract

The invention relates to a method for actuating an electrically commutated fluid working machine (1), wherein the actuation of the electrically controllable valves (11) of the electrically commutated fluid working machine (1) is effected dependent on the fluid requirement and/or mechanical power requirements. In addition, on actuation of the electrically controlled valves (11) the electrical power required for actuating the electrically controllable valves is taken into account.

Claims

1. A method for actuating a fluid working machine, wherein the fluid working machine has at least one working chamber with a cyclically varying volume, a high-pressure fluid connection, a low-pressure fluid connection, at least one electrically actuable valve for actuably connecting the high-pressure fluid connection or the low-pressure fluid connection to the working chamber, comprising the steps of: actuating the at least one electrically actuable valve depending on a fluid requirement and/or a mechanical power requirement, actuating the at least one electrically actuable valve additionally depending on an electrical power required for actuating the at least one electrically actuable valve, comparing the required electrical power with a soft electrical power limit, a hard electrical power limit or both the soft electrical power limit and the hard electrical power limit, if the required electrical power is compared only to the hard power limit and is greater than the hard power limit, adjusting an actuation cycle of the fluid working machine, if the required electrical power is compared only to the soft power limit and is greater than the soft power limit, actuating the at least one electrically actuable valve, if the required electrical power is compared to both the hard power limit and the soft power limit and is greater than both the hard power limit and the soft power limit, adjusting an actuation cycle of the fluid working machine, if the required electrical power is compared to both the hard power limit and the soft power limit and is greater than the soft electrical power limit and less than or equal to the hard power limit, actuating the at least one electrically actuable valve.

2. The method as claimed in claim 1, wherein the at least one upper electrical power limit is defined by at least one part of at least one control device and/or is defined at least temporarily and/or at least partially by the electrical power which is available in the system.

3. The method as claimed in claim 1, wherein a plurality of electrically actuable valves is actuated, and the electrically actuable valves are associated with different working chambers.

4. The method as claimed in claim 1, wherein a valve actuation pattern is calculated using a buffer variable.

5. The method as claimed in claim 1, wherein an extrapolation algorithm is used for the value of a buffer variable and/or for the value of an expected fluid requirement and/or for the value of an expected mechanical power requirement.

6. The method as claimed in claim 1, wherein at least the difference between the fluid requirement and/or the mechanical power requirement and the quantity of fluid actually available after the application of the modification in respect of the electrical power requirement or the mechanical power actually available is determined and is stored, in an error variable.

7. The method as claimed in claim 1, wherein when a determined value of the error variable is exceeded, correction methods are used.

8. The method as claimed in claim 1, wherein a plurality of different valve actuation patterns is calculated and stored in advance.

9. A control device configured to execute the method as claimed in claim 1.

10. The control device as claimed in claim 9, the control device comprising an electronic memory device, a programmable data-processing device, a semiconductor component and/or a temporary energy storage device.

11. An electrically commutated fluid working machine comprising a control device configured to execute the method as claimed in claim 1.

12. The method as claimed in claim 1, wherein the hard power limit and/or the soft power limit is defined by a control device based on the electrical power which is available in the system.

13. The method as claimed in claim 1, wherein a plurality of electrically actuable valves is actuated, and the electrically actuable valves are associated with different working chambers, wherein a plurality of the working chambers are arranged with a phase offset in relation to one another and/or a plurality of the working chambers which operate in parallel is provided.

14. The method as claimed in claim 2, wherein a plurality of electrically actuable valves is actuated, and the electrically actuable valves are associated with different working chambers, wherein the working chambers are arranged with a phase offset in relation to one another and/or a plurality of working chambers which operate in parallel is provided.

15. The method as claimed in claim 1, wherein a valve actuation pattern is calculated using a buffer variable.

16. The method as claimed in claim 2, wherein a valve actuation pattern is calculated using a buffer variable.

17. The method as claimed in claim 3, wherein a valve actuation pattern is calculated using a buffer variable.

18. The method as claimed in claim 1, wherein the value of a buffer variable is based on an extrapolation algorithm, the value of an expected fluid requirement and/or the value of an expected mechanical power requirement.

19. The method as claimed in claim 2, wherein an extrapolation algorithm is used for the value of a buffer variable and/or for the value of an expected fluid requirement and/or for the value of an expected mechanical power requirement.

20. The method as claimed in claim 3, wherein the working chambers are arranged with a phase offset in relation to one another and/or a plurality of working chambers which operate in parallel is provided.

21. The method as claimed in claim 7, wherein said correction methods comprise permitting otherwise impermissible partial pump quantities.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained in greater detail below using advantageous exemplary embodiments and with reference to the appended drawing, in which:

(2) FIG. 1: shows a basic diagram of one possible exemplary embodiment of an electrically commutated hydraulic pump;

(3) FIG. 2: shows an example of an unfavorable actuation pattern;

(4) FIG. 3: shows a flowchart for a feasible exemplary embodiment of a method for actuating an electrically commutated hydraulic pump.

DETAILED DESCRIPTION

(5) FIG. 1 illustrates one feasible exemplary embodiment of an electrically commutated hydraulic pump 1 of the so-called wedding cake type (wedding cake-type pump). The hydraulic pump 1 has a total of 12 cylinders 2, 3 which are each arranged spaced apart by an angular distance of 30 from one another. For space reasons, the cylinders 2, 3 are arranged in different planes and, specifically, in the form of two disks which are arranged one behind the other and each have six cylinders 2, 3 in this case. The two disks comprising cylinders 2, 3 are arranged in succession in a direction perpendicular to the plane of the drawing in this case. The respective cylinders 2, 3 are each spaced apart in an angular manner through 60 from one another in each disk. The two disks are each rotated through 30 in relation to one another.

(6) Pistons 4 which can each be moved and can each be rotated through a certain angle are arranged in the cylinders 2, 3. The bottom face 5 of the piston 4 is in the form of a sliding sole and is supported on an eccentrically rotating eccentric 6 which is moved around the rotation axis 7. The upper face 8 of the piston 4 forms a fluid-tight closure with the walls of the piston 4. The up-and-down movement of the piston 4, which is caused by the eccentric 6, in the cylinders 2, 3 results in a cyclically varying volume of the pump chambers 9.

(7) Each cylinder 2, 3 is connected to an electrically actuable valve 11, which is connected to a hydraulic oil reservoir 13 for its part, via corresponding hydraulic lines 10. The hydraulic oil reservoir 13 is usually subject to ambient pressure.

(8) Furthermore, each cylinder 2, 3 is connected to a high-pressure collector (not illustrated in the present case) by means of a passive non-return valve 12 via hydraulic lines 10 in the exemplary embodiment illustrated in the present case. In this case, the high-pressure collector can have a high-pressure storage means. However, it is also feasible for a kind of high-pressure storage function to be realized, for example, by high-pressure hoses which usually have a certain degree of elasticity. In a case of this kind, it is possible for the high-pressure hoses to pass directly to the hydraulic load (for example to a hydraulic motor).

(9) For illustrative reasons, the hydraulic lines 10, the electrically actuable valve 11 and the non-return valve 12 are depicted only once. The hydraulic oil reservoir 13 and/or the high-pressure collector are/is generally identical for a plurality of and/or for all of the cylinders 2, 3.

(10) The electrically actuable valves 11 are electrically actuated by means of an electronic controller 14. In particular, the electronic controller 14 can have a memory 15 in which a suitable actuation program is stored. The electronic controller 14 can be designed either individually for each electrically actuable valve 11 and/or actuate a portion of or all of the electrically actuable valves 11 of the electrically commutated hydraulic pump 1. The electronic controller 14 may possibly also perform further tasks. In particular, the electronic controller 14 is, for example, a single-board computer which has power semiconductor components which are correspondingly dimensioned for actuating the electrically actuable valves 11.

(11) The manner of operation of an electrically commutated hydraulic pump 1 allows not only a complete pump chamber volume to be effectively pumped (that is to say to be moved in the direction of the high-pressure collector), but partial strokes or zero strokes are also possible.

(12) If the piston 4 in the cylinder 2, 3 moves downward, the negative pressure produced opens the electrically actuable valve 11 and hydraulic oil is drawn in by suction from the hydraulic oil reservoir 13 via the hydraulic lines 10 and the electrically actuable valve 11 (low-pressure valve). If the piston 4 reaches the bottom dead center, the passive intake valve would automatically close in a classic hydraulic pump. In the case of the electrically commutated hydraulic pump 1 illustrated in the present case however, the electrically actuable valve 11 initially remains open (unless it is actuated in some other way). As a result, the hydraulic oil is initially pushed back into the hydraulic oil reservoir 13 through the still open electrically actuable valve 11, initially without load (and consequently not pumped in the direction of the high-pressure collector). If the electrically actuable valve 11 is now closed after a certain portion of the cylinder path, a pressure builds up rapidly in the pump chamber 9 and the remaining proportion of the volume is effectively pumped in the direction of the high-pressure collector by means of the passive non-return valve 12 (high-pressure valve). The described manner of operation corresponds to a partial stroke.

(13) If the electrically actuable valve 11 is closed immediately at the bottom dead center of the cylinder 4, the manner of operation of the electrically commutated hydraulic pump 1 corresponds to a classic hydraulic pump (full pump strokes). If, however, the electrically actuable valve 11 is not closed at all, the electrically commutable hydraulic pump 1 is in an idling mode (idling strokes).

(14) With the designs of electrically commutated hydraulic pumps which are customary at present, the electrically actuable valve 11 is closed by applying a relatively large current. If, in contrast, no (or an insufficient) current (or electrical voltage) is applied, the electrically actuable valve 11 remains in the open position. (Designs with an inverted switching logic also exist to a certain extent; in a case of this kind, the present description, in particular that illustrated below, should be accordingly adjusted.)

(15) It is clear that the control pulse for closing the electrically actuable valve 11 takes place later the smaller the proportion of volume to be pumped. Therefore, if, for example in the case of two cylinders which immediately follow one behind the other (which are offset, for example, through 30 in relation to one another), a preceding cylinder is intended to generate a partial pump stroke and a following cylinder is intended to generate a full pump stroke, the electrically actuable valves 11 of the two cylinders should be actuated at the same time if the immediately advancing cylinder is intended to generate only a proportion of 93.3% by volume (180 rotation corresponds to 100% pump performance). However, overlapping of different actuation pulses can not only occur in exactly a case of this kind (which presumably would not occur too frequently in reality). Instead, overlapping of this kind can occur considerably more frequently since the signals for closing the electrically actuable valves have to be applied over a certain period of time.

(16) Taking typical values for electrically commutated hydraulic pumps, the required actuation time is 4 ms. Proceeding from a hydraulic pump which operates at 3000 rpm, the duration for a full piston stroke is therefore 20 ms. Therefore, potential overlapping of different actuation pulses of 180+72 can occur. In an extreme case, simultaneous actuation of up to eight cylinders may occur with the indicated values in a twelve-cylinder pump.

(17) FIG. 2 graphically illustrates this effect. In the graph in FIG. 2, the rotation angle 16 (position of the eccentric 6) is illustrated on the abscissa. The actuation currents for the different numbers 17 of cylinders (a total of 12 cylinders) are illustrated on the ordinate. The obliquely running lines 18, 19 shown in the graph correspond to the profile of the respective bottom dead center 18 (beginning of the hydraulic oil ejection phase; pump chamber volume decreases) or the top dead center 19 (end of the liquid ejection phase; pump chamber volume is at the minimum value). The times relate to a 4 ms actuation period and 3000 rpm.

(18) The situation illustrated in FIG. 2 results when the individual cylinders are acted on as follows:

(19) cylinder 11%, cylinder 210%, cylinder 333%, cylinder 460%, cylinder 566%, cylinder 690%, cylinder 7100%, cylinder 8100%, cylinder 9100%, cylinder 10100%, cylinder 11100%, cylinder 1250%. As can be gathered from the figure, eight cylinders are in fact actuated at the same time (specifically cylinders 1 to 8 shortly before 180). Some actuation cycles also immediately follow thereafter, and therefore the actuation electronics system (electronic controller 14) does not have much time to recover.

(20) If the electronic controller 14 is now designed for a worst-case scenario of this kind, it has to be dimensioned in such a way that it can actuate eight electrically actuable valves 11 at the same time. This is correspondingly expensive and complicated. Furthermore, the electronic controller 14 has to have a corresponding size (installation space). Cooling of the electronic controller 14 also has to be correspondingly dimensioned.

(21) If however, it is simply left to chance and the electronic controller 14 is dimensioned in such a way that, for example, only six actuation cycles can be executed at the same time, the current supply would fail at the beginning of the actuation of the last two cylinders (cylinders 6 and 8 in the example illustrated in the present case). This would generally result in not only these two valves no longer being able to close, but furthermore the other valves of the cylinders 1 to 5 and 7 would possibly no longer (fully) close since, for the purpose of starting actuation of the cylinders 6 and 8, these are possibly not yet (fully) closed. A yet further-reaching disadvantage would be that the current supply usually fails in such a way that the electronic controller 14 typically needs one to two seconds recovery time until it is ready to operate again. Behavior of this kind is not tolerable.

(22) It is therefore proposed in the present case for the electronic controller 14 to also take into account the necessary current requirement and to correspondingly adjust the actuation cycles when actuating the electrically actuable valves 11.

(23) If there is, for example, a fluid requirement of 35% (it is assumed below that a pumping interval of between 20% and 80% is forbidden, and therefore there is no excessive development of noise and/or wear is reduced), this fluid requirement can expediently be generated by three pumping strokes, specifically by the sequence 100%-0%-5% (105% for every three pumping strokes=35% on average).

(24) If the 5% actuation of the last cylinder were then to lead to the maximum power of the electronic controller 14 being exceeded, the last pumping cycle is suspended, and therefore the sequence 100%-0%-0% results. This results in an error value of 5% (after the three pumping strokes).

(25) This error value is stored and balanced with the fluid requirement. If the fluid requirement remains at 35%, a pumping capacity of 36.67% (110% in the case of three cycles) has to be produced in order to compensate for the preceding shortfall. This can now be implemented by the pumping sequence 100%-0%-10%.

(26) The resulting pumping sequence 100%-0%-0%-100%-0%-10% now corresponds to the required average value of 35%.

(27) Finally, FIG. 3 further illustrates a schematic flowchart 20 which explains a method for actuating an electrically commutated hydraulic pump 1 in greater detail.

(28) 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 it was necessary to deviate from the demanded fluid requirement in the past. Therefore (albeit possibly over somewhat relatively long periods of time), step 22 provides the actually demanded fluid requirement on average.

(29) An actuation sequence for the electrically actuable valves is calculated based on the fluid requirement modified in step 22 (step 23). The necessary electrical power requirement is also taken into account when calculating the actuation sequence. Accordingly, this may result in an actuation sequence which is desired per se in respect of the fluid requirement not being able to be realized since this would lead to the maximum electrical power being exceeded.

(30) The valves are actuated with the actuation sequence obtained in this way (step 24). In parallel with this, the error parameter, which describes the deviation between the actually pumped quantity of fluid and the demanded quantity of fluid, isif necessarymodified.

(31) After the actuation sequence on the valves has been conducted, the method (arrow 25) returns to the start.

(32) Even though the exemplary embodiment relates to a hydraulic pump, it goes without saying that it is possible for the idea described therein to also be used for a hydraulic motor or for a combination comprising a hydraulic pump and a hydraulic motor.

(33) Although various embodiments of the present invention have been described and shown, the invention is not restricted thereto, but may also be embodied in other ways within the scope of the subject-matter defined in the following claims.