DRIVE ARRANGEMENT OF A WORK MACHINE TO BE DRIVED WITH A VARIABLY ADJUSTABLE SPEED AND METHOD FOR OPERATING THE DRIVE ARRANGEMENT

Description

[0001] The invention relates to a drive assembly of a work machine for driving the work machine at a variably adjustable speed. Furthermore, the invention relates to a method for operating the drive assembly.

[0002] Practical applications are known in which a working machine, such as a compressor or a pump, must be operated at a variably adjustable speed. For this purpose, either electric motors with frequency converters are used as drive units, or a gearbox with a hydraulically or electrically driven superposition branch is used, which can provide a variable transmission ratio within the required range. Both of these practical options for driving a working machine with variably adjustable speed are complex and expensive; medium-voltage frequency converters are necessary due to the high power required for the drive task.

[0003] DE 10 2015 006 084 A1 discloses a drive arrangement of a work machine for driving the work machine at a variably adjustable speed, wherein the drive arrangement comprises, in addition to the work machine, a differential gear and two drive units. A first drive unit is coupled to a first element of the differential gear. The work machine is coupled to a second element of the differential gear. A second drive unit is coupled to a third element of the differential gear, the speed of which can be superimposed on a speed dependent on the speed of the first drive unit. The first drive unit or the second drive unit can be driven at a variably adjustable speed. This drive arrangement allows a work machine to be driven at a variably adjustable speed using simple and cost-effective means.

[0004] WO 2016 / 172742 A1 relates to a drive train with a drive shaft, a working machine, with a drive machine and a differential system with an epicyclic gear system with three input and output drives, wherein one output drive can be connected to the drive shaft, a first drive drive can be connected to the drive machine and a second drive drive can be connected to the differential gear system, wherein the drive drive can be connected simultaneously to the other drive drive or to the output drive.

[0005] There is a need to create a drive assembly for a work machine driven at a variably adjustable speed, preferably a drive assembly in which the drive assembly can be easily and safely ramped up to a rated speed. Preferably, the goal is to prevent excessive inrush current from being generated when connecting a non-speed-adjustable drive unit to the power grid, which could lead to either grid disruptions or overheating during startup.

[0006] Based on this, the present invention seeks to create a novel drive arrangement and a method for operating the drive arrangement. This object is achieved by a drive arrangement for a work machine to be driven at a variably adjustable speed according to claim 1. The method for operating the drive arrangement is defined in claim 17.

[0007] According to the invention, the drive arrangement comprises a differential gear, a first drive unit coupled to a first element of the differential gear, a working machine coupled to a second element of the differential gear, and a second drive unit coupled to a third element of the differential gear, the speed of which can be superimposed on a speed dependent on the speed of the first drive unit. The first drive unit or the second drive unit can be driven at a variably adjustable speed.

[0008] According to the invention, the drive arrangement further comprises an auxiliary transmission stage and a shifting element interacting with the auxiliary transmission stage. When the shifting element is closed, the auxiliary transmission stage transmits the load and the rotational speeds of the first drive unit and the second drive unit are coupled depending on at least one ratio of the auxiliary transmission stage. When the shifting element is open, the auxiliary transmission stage is load-free and decouples the rotational speeds of the first drive unit and the second drive unit. The drive arrangement can advantageously be easily and reliably ramped up to nominal speed via the auxiliary transmission stage by utilizing the speed variability of the second drive unit.

[0009] Preferably, the switching element is a self-switching, i.e. self-closing and self-opening, switching element such as a freewheel or a synchronous clutch. Thus, when the first drive unit is brought up to its rated speed during start-up, and then when the speed of the second drive unit reaches a safety-relevant overspeed, the switching element can close automatically and prevent a safety-critical failure of the drive arrangement. If the speed of the first drive unit is greater than the speed of the second drive unit, the switching element opens automatically. If a control device of the second drive unit fails and its speed, taking into account the ratio of the auxiliary transmission stage, becomes higher than that of the first drive unit, the switching element closes automatically.By using a self-switching switching element, a control unit can be dispensed with and safety-critical protection can be ensured simply and reliably by using mechanical components.

[0010] Alternatively, the switching element can also be an actively switching switching element such as a multi-plate clutch.

[0011] The auxiliary gear stage can be designed as an auxiliary planetary gear set. This is structurally simple and preferred.

[0012] In one embodiment, the switching element in the closed state either couples the second drive unit in a rotationally fixed manner to an element of the auxiliary transmission stage or another element of the auxiliary transmission stage in a rotationally fixed manner to the first element or the second element of the differential gear.

[0013] When the switching element is closed, the differential gear can no longer be operated as such; the differential gear then has a fixed gear ratio.

[0014] According to the invention, the switching element, in the closed state, couples the second drive unit in a rotationally fixed manner to an element of the auxiliary transmission stage, wherein another element of the auxiliary transmission stage is permanently coupled in a rotationally fixed manner to the first element of the differential gear together with the first drive unit.

[0015] According to the invention, it is alternatively provided that the second drive unit is permanently coupled in a rotationally fixed manner to an element of the auxiliary transmission stage, wherein the switching element, in the closed state, couples another element of the auxiliary transmission stage in a rotationally fixed manner to the first element of the differential gear.

[0016] These two advantageous embodiments of the invention are particularly preferred. When the shift element is closed, the speed of the first drive unit, which is accelerated to nominal speed with the aid of the second drive unit, depends exclusively on the ratio of the auxiliary transmission stage, in addition to the speed of the second drive unit.

[0017] The ratio of the auxiliary transmission stage is preferably selected so that the first drive unit reaches its rated speed at the maximum speed of the second drive unit.

[0018] Preferred developments of the invention will become apparent from the dependent claims and the following description. Exemplary embodiments of the invention are explained in more detail, without being limited thereto, with reference to the drawings. Herein: Fig. 1: a block diagram of a first drive arrangement, which is not part of the invention; Fig. 2: a block diagram of a second drive arrangement, which is not part of the invention; Fig. 3: a block diagram of a third drive arrangement according to the invention.

[0019] The invention relates to a drive arrangement of a working machine to be driven at a variably adjustable speed, wherein the working machine can be, for example, a compressor or a pump.

[0020] Fig. 1 shows a first preferred embodiment of such a drive arrangement, which is not part of the invention, with a differential gear 1, a first drive unit 2, a second drive unit 3 and a work machine 4. The first drive unit 2 is also referred to as the main drive unit and the second drive unit 3 is also referred to as the superposition drive unit. These drive units 2, 3 are each preferably electric machines. In the preferred embodiment shown, the differential gear 1 has a first planetary gear set 5 with a sun gear 5a and at least two planet gears 5b, wherein the planet gears 5b mesh with the sun gear 5a of the first planetary gear set 5. The differential gear 1 further has a second planetary gear set 6 with a sun gear 6a and at least two planet gears 6b, wherein the planet gears 6b mesh with the sun gear 6a.Two planetary gears 5b, 6b of each of the two planetary gear sets 5, 6 are arranged on a respective common planetary shaft 7, so that each of the planetary shafts 7 is rotationally fixedly coupled to a planetary gear 5b of the first planetary gear set 5 and a planetary gear 6b ​​of the second planetary gear set 6. In the differential gear 1 of the . Fig. 1 the planetary shafts 7 are rotatably mounted in a planetary carrier 8, wherein the planetary carrier 8 is rotatably mounted in a rotationally fixed housing 9 not shown in detail, preferably via plain bearings not shown.

[0021] In the first drive arrangement, the first drive unit 2, which is referred to as the main engine, is coupled to a first element of the differential gear 1, in such a way that the first drive unit 2 is permanently, directly and non-rotatably coupled to the first element of the differential gear 1 via a shaft 10, wherein in the embodiment of the Fig. 1 This first element of the differential gear 1, to which the first drive unit 2 is coupled, is the sun gear 5a of the first planetary gear set 5.

[0022] It should be noted that the first planetary gear set 5 can also have a ring gear instead of the sun gear 5a, in which case the first drive unit 2 is coupled via the shaft 10 to the ring gear of the first planetary gear set 5, which then meshes radially outwardly with the planet gears 5b.

[0023] The working machine 4 is coupled to a second element of the differential gear 1, namely according to Fig. 1 such that the working machine 4 is permanently, directly and rotationally fixedly coupled to the sun gear 6a of the second planetary gear set 6 via a shaft 11.

[0024] The second drive unit 3 engages a third element of the differential gear 1. In the illustrated embodiment, this third element of the differential gear 1, on which the second drive unit 3 engages, is the planet carrier 8 of the differential gear 1. The planet carrier 8 is therefore driven via the second drive unit 3, whose speed or drive power is superimposed on the speed or drive power of the first drive unit 2. The first drive unit 2 is preferably driven at a fixed or constant speed, whereas the second drive unit 3 is preferably driven at a variable speed.Thus, when the first drive unit 2 is running at a constant speed, a speed dependent on the speed of the first drive unit 2 can be continuously superimposed by the second drive unit 3 in order to set a variable speed on the working machine 4.

[0025] In addition to the differential gear 1, the two drive units 2, 3, and the working machine 4, the drive arrangement has an auxiliary gear stage 12 and a shifting element 13 that interacts with the auxiliary gear stage 12. When the shifting element 13 is closed, the auxiliary gear stage 12 transmits the load, and the speeds of the first drive unit 2 and the second drive unit 3 are coupled, depending on the ratio of the auxiliary gear stage 12.

[0026] Then, when the switching element 13 is closed, the speeds of the two drive units 2 and 3 are in a fixed ratio. The driven machine 4 then also assumes a speed that still depends on the speed of the drive units 2 and 3. If only the second drive unit 3 is supplied with electrical power, the speed of the second drive unit 3 determines all other speeds of the drive arrangement—the second drive unit 3 then drives the drive arrangement alone.

[0027] If, however, the switching element 13 is open, the auxiliary transmission stage 12 is load-free and the speeds of the first drive unit 2 and the second drive unit 3 are decoupled. The second drive unit 3 then only provides the overlapping portion of power and speed.

[0028] In the closed state, the switching element 13 therefore acts as a lock for the differential gear 1, blocking one degree of freedom of the differential gear 1. This is used in particular for starting up the drive arrangement, starting from a stationary first drive unit 2, in order to bring the first drive unit 2 to its rated speed starting from the second drive unit 3.

[0029] When the first drive unit 2 is started up in this way, starting from the second drive unit 3 with the switching element 13 closed, the first drive unit 2 is de-energized; only after the rated speed of the first drive unit 2 has been reached is the first drive unit 2 energized and then the switching element 13 opened.

[0030] The auxiliary gear stage 12 has a sun gear 12a, planet gears 12b, and a ring gear 12c. The planet gears 12b are rotatably mounted on a planet carrier 14.

[0031] In Fig. 1 an element of the auxiliary gear stage 12, namely the sun gear 12a, together with the first drive unit 2, permanently, directly and non-rotatably engages the shaft 10 and thus the first element of the differential gear 1, in Fig. 1 on the sun gear 5a of the first planetary gear set 5 of the differential gear 1.

[0032] Then, when the switching element 13 is closed, it couples in Fig. 1 the second drive unit 3 is connected in a rotationally fixed manner to a second element of the auxiliary transmission stage 12, namely in Fig. 1 to the planet carrier 14.

[0033] In the example of Fig. 1 Accordingly, the first drive unit 2 drives the sun gear 6a via the sun gear 5a and the planetary shafts 7, and the driven machine 4 via the sun gear 6a. During regular operation, a speed can be superimposed on the speed on the shaft 11, which speed depends on the speed of the first drive unit 2, via the rotatably mounted planetary carrier 8 of the differential gear 1, in order to set a variable speed on the driven machine 4.

[0034] During normal operation, namely when the first drive unit 2 is operating at its rated speed, the switching element 13 is open. However, in order to start up the drive arrangement, in particular starting from a state in which the first drive unit 2 is stationary, the switching element 13 is closed and the second drive unit 3 is coupled or connected in a rotationally fixed manner to the auxiliary gear stage 12 and to the shaft 10 via the switching element 13. This blocks one degree of freedom of the differential gear 1 and enables the second drive unit 3 to start up the drive arrangement up to the rated speed of the first drive unit 2, which is de-energized during start-up. The gear ratio of the auxiliary gear stage 12 is selected such that the first drive unit 2 reaches its rated speed at the maximum speed of the second drive unit 3.

[0035] The shifting element 13 can be a friction-engaging shifting element in the form of a friction clutch, such as a multi-disk clutch, or a positive-locking shifting element in the form of a dog clutch. If the shifting element 13 is designed as a friction clutch, it can assume the function of a brake for the second drive unit 3 if the latter fails during operation.

[0036] Particularly preferred is a design in which the switching element 13 is designed as a self-closing and self-opening switching element 13, in particular as a freewheel or synchronous clutch, in which torque can be transmitted exclusively in one direction of rotation. This ensures that the switching element 13 closes automatically when the drive arrangement is started up, as well as in the event of a safety-critical failure of the second drive unit 3 during operation. If the speed of the first drive unit 2 is greater than the speed of the second drive unit 3, the switching element 13 opens automatically, and regular superimposed operation can begin.

[0037] As soon as the speed of the first drive unit 2 reaches its nominal speed, which is already running at its nominal speed when switched on without a voltage peak, driven by the second drive unit 3, the switching element 13 can be opened.

[0038] This is achieved with a preferably self-shifting design of the shifting element 13 by reducing the speed of the second drive unit 3 relative to that of the first drive unit 2—taking into account the gear ratio of the auxiliary gear stage 12, which is preferably designed as an auxiliary planetary gear set—or, in the case of a shift clutch, by disengaging the clutch. However, the self-shifting design of the shifting element 13 as a synchronous clutch or freewheel is preferred.

[0039] The switching element 13 remains open throughout normal operation, i.e., when the first drive unit 2 is running at its rated speed. When using a self-switching switching element 13, no safety-relevant control unit is required. Safety-critical functions can be provided by mechanical components, namely by the automatically closing switching element 13. No actuator is required to lock the differential gear 1. The locking of the differential gear 1 occurs automatically. No actuator is required to unlock the differential gear 1 either. When the speed of the first drive unit 2 is greater than the speed of the second drive unit 3, the switching element 13 opens automatically. The auxiliary planetary gear set 12 always rotates at the speed of the first drive unit 2.

[0040] Fig. 2 shows a modification of the drive arrangement, which is not part of the invention, in which the second drive unit 3 is permanently and rotationally fixedly coupled to an element of the auxiliary transmission stage 12, namely to the planet carrier 14. Via the switching element 13, in Fig. 2 the sun gear 12a of the planetary gear set 12 is connected in a rotationally fixed manner to the first element of the differential gear 1, namely in Fig. 2 to the sun gear 5a of the first planetary gear set 5 of the differential gear 1. In Fig. 2 The switching element 13 is therefore connected between the sun gear 12a and the shaft 10. The auxiliary planetary gear set 12 always rotates at the speed of the second drive unit 3.

[0041] An embodiment of a drive arrangement according to the invention shows Fig. 3 While in Fig. 1 and 2 the ring gear 12c of the auxiliary gear stage 12 is permanently connected to the housing 9, is in Fig. 3 provided that the switching element 13 is connected between the housing 9 and the ring gear 12c of the auxiliary transmission stage 12. In Fig. 3 The sun gear 12a of the auxiliary transmission stage 12 is permanently coupled to the shaft 10 in a rotationally fixed manner, and the electric motor 3 is permanently coupled to the planetary carrier 14 of the auxiliary transmission stage 12. The rotational speeds of the components of the auxiliary planetary gear set 12 assume rotational speeds determined by those of the two drive units 2, 3.

[0042] By closing the switching element 13, the ring gear 12c of the auxiliary transmission stage 12 is coupled to the housing 9 in order to restrict a degree of freedom of the differential gear 1 and to use the second transmission unit 3 to start up the first drive unit 2, wherein for this purpose load is then transmitted via the auxiliary transmission stage 12, starting from the second transmission unit 3 in the direction of the first transmission unit 2.

[0043] The examples of the Fig. 1 bis 3 is that an element of the auxiliary gear stage 12 is either permanently (see Fig. 1 , 3 ) or switchable (see Fig. 2 ) is coupled to the second drive unit 3.

[0044] In contrast, it is also possible for the auxiliary gear stage 12 to interact with the shaft 11 to which the working machine 4 engages, either in such a way that an element of the auxiliary gear stage 12 is either permanently coupled to the shaft 11 in a rotationally fixed manner or switchably. The second drive unit 3, together with the auxiliary gear stage, can be relocated to the other side of the differential gear 1, along which the shaft 11 runs. The second drive unit 3 and the auxiliary gear stage 12 can also be arranged on different sides of the differential gear 1.

[0045] The invention allows the drive arrangement to be started up via the second drive unit 3 until the first drive unit 2 has reached its rated speed. Thus, only the second drive unit 3 requires a converter. A starting aid on the first drive unit 2 is eliminated. When the switching element 13 closes automatically, a safety-relevant control device for controlling the switching element 13 can be dispensed with.

[0046] This is achieved by using preferably a synchronous clutch or a freewheel, which automatically closes and opens to start up the drive arrangement.

[0047] The invention further relates to a method for operating the drive arrangement according to the invention. To start the drive arrangement, the switching element 13 is closed, preferably automatically. The still de-energized, first drive unit 2 is then accelerated to its rated speed via the second drive unit 3 with the switching element 13 closed, and the auxiliary gear stage 12 transmits speed to the first drive unit 2. When the rated speed is reached at the first drive unit 2, the first drive unit 2 is first energized, and then the switching element 13 is opened. The speed of the second drive unit 3 is reduced, and the switching element 13 is opened, preferably automatically.

[0048] When designing the second drive unit 3, care should be taken to ensure that the driven machine 4 develops an application-specific start-up torque that is proportional to its speed in a known manner. This torque, or the required power, must be provided reliably by the second drive unit 3, albeit only briefly, until the first drive unit 2 is energized. List of reference symbols

[0049] 1Differential gear 2First drive unit 3Second drive unit 4Drive machine 5First planetary gear set 5aSun gear 5bPlanetary gear 6Second planetary gear set 6aSun gear 6bPlanetary gear 7Planetary shaft 8Planetary carrier 9Housing 10Shaft 11Shaft 12Auxiliary gear stage 12aSun gear 12bPlanetary gear 12cRing gear 13Shift element 14Planetary carrier

Claims

1. A drive arrangement of a working machine (4) which is to be driven at a variably adjustable rotational speed, wherein the drive arrangement comprises a differential gear (1), wherein the drive arrangement comprises a first drive unit (2) which is coupled to a first element of the differential gear (1), wherein the drive arrangement comprises a working machine (4) which is coupled to a second element of the differential gear (1), wherein the drive arrangement comprises a second drive unit (3) which is coupled to a third element of the differential gear (1), wherein the rotational speed of the second drive unit (3) can be superimposed on a rotational speed which is dependent on the rotational speed of the first drive unit (2), wherein the first drive unit (2) or the second drive unit (2) can be driven at a variably adjustable rotational speed, wherein the drive arrangement comprises an auxiliary gear stage (12) and a switching element (13) which cooperates with the auxiliary gear stage (12), wherein, when the switching element (13) is closed, the auxiliary gear stage (12) is load-transmitting and the rotational speeds of the first drive unit (2) and the second drive unit (3) are coupled as a function of at least one transmission ratio of the auxiliary gear stage (12), and wherein, when the switching element (13) is open, the auxiliary gear stage (12) is load-free and the rotational speeds of the first drive unit (2) and the second drive unit (3) are decoupled; characterised in that the second drive unit (3) is permanently coupled to an element of the auxiliary gear stage (12) in a rotationally fixed manner, and another element of the auxiliary gear stage (12), together with the first drive unit (2), is permanently coupled to the first element of the differential gear (1) in a rotationally fixed manner, or another element of the auxiliary gear stage (12), together with the working machine (4), is permanently coupled to the second element of the differential gear (1) in a rotationally fixed manner, and the switching element (13), when the switching element (13) is in the closed state, couples another element of the auxiliary gear stage (12) to a housing.

2. The drive arrangement according to claim 1, characterised in that the auxiliary gear stage (12) is designed as an auxiliary planetary gear set .

3. The drive arrangement according to claim 1 or 2, characterised in that the switching element (13) is a freewheel or a synchronous clutch.

4. The drive arrangement according to any one of claims 1 to 3, characterised in that the switching element (13) switches automatically, that is, it closes and opens automatically.

5. The drive arrangement according to claim 1 or 2, characterised in that the switching element (13) is a frictionally engaging clutch.

6. The drive arrangement according to any one of claims 1 to 5, characterised in that, in the closed state, the switching element (13) either couples the second drive unit (3) to an element of the auxiliary gear stage (12) in a rotationally fixed manner, or couples another element of the auxiliary gear stage (12) to the first element or to the second element of the differential gear (1) in a rotationally fixed manner.

7. The drive arrangement according to any one of claims 1 to 6, characterised in that the differential gear (1) comprises a first planetary gear set (5) to which the first drive unit (2) is coupled, the differential gear (1) comprises a second planetary gear set (6) to which the working machine (4) is coupled, the first planetary gear set (5) and the second planetary gear set (6) each comprise planet gears (5b, 6b) which are arranged on at least two common planetary shafts (7) which are supported in a planet carrier (8); the planet carrier (8) is rotatably supported in a housing (9) and can be driven by the second drive unit (3).

8. The drive arrangement according to claim 7, characterised in that the first planetary gear set (5) comprises a sun gear (5a) to which the first drive unit (2) is coupled, wherein the sun gear (5a) of the first planetary gear set (5) meshes with the planet gears (5b) of the first planetary gear set (5), which planet gears (5b) of the first planetary gear set (5) are arranged on the planetary shafts (7), or the first planetary gear set (5) comprises a ring gear to which the first drive unit (3) is coupled, wherein the ring gear of the first planetary gear set (5) meshes with the planet gears (5b) of the first planetary gear set (5), which planet gears (5b) of the first planetary gear set (5) are arranged on the planetary shafts (7).

9. The drive arrangement according to claim 7 or 8, characterised in that the second planetary gear set (6) comprises a sun gear (6a) to which the working machine (4) is coupled, wherein the sun gear (6a) of the second planetary gear set (6) meshes with the planet gears (6b) of the second planetary gear set (6) arranged on the planetary shafts (7).

10. The drive arrangement according to any one of claims 1 to 9, characterised in that the first drive unit (2) can be driven at a constant rotational speed and the second drive unit (3) can be driven at a variable rotational speed.

11. A method of operating a drive arrangement according to any one of claims 1 to 10, comprising the following steps: to start the drive arrangement, the switching element (13) is closed and the first drive unit (2), which is still de-energised, is run up to its rated rotational speed via the second drive unit (3), when the rated rotational speed is reached on the first drive unit (2), the first drive unit (2) is energised and the switching element (13) is opened.