Drive system of a mobile work machine

Abstract

The present invention relates to a drive system for a mobile work machine, wherein the drive system comprises a first drive device (1) with a first motor shaft (3), a second drive device (2) with a second motor shaft (4), and a transmission with a first input shaft (5), a second input shaft (6), and an output shaft (16), wherein the first motor shaft (3) is rotationally fixed to the first input shaft (5) of the transmission, and the second motor shaft (4) is rotationally fixed to the second input shaft (6) of the transmission by means of a coupling (18), characterized in that the first input shaft (5) is mechanically operatively connected to the output shaft (16) via a first spur gear stage, wherein the first spur gear stage comprises a first spur gear (7) in rotationally fixed connection with the first input shaft (5) and a third spur gear (13) in rotationally fixed connection with the output shaft (16).wherein the second input shaft (6) is mechanically connected to the output shaft (16) via a second spur gear stage, the second spur gear stage comprising a second spur gear (8) in a rotationally fixed connection with the second input shaft (6) and a fourth spur gear (14) in a rotationally fixed connection with the output shaft (16).

Description

Technical area

[0001] The present invention relates to a drive system for a mobile working machine. State of the art

[0002] The drive systems of mobile machinery often need to meet both high maximum tractive effort and high maximum speed requirements. Electric motors are well-suited for use in such drive systems because they can operate across a wide speed range. However, to meet these requirements, electric motors are frequently used in conjunction with transmissions, typically with two or three gears, as they generally operate with high efficiency only within a limited speed range. Such transmissions enable high tractive effort in a high-ratio gear and high maximum speed in a low-ratio gear.

[0003] Gear changes can occur either with or without an interruption of traction, depending on the transmission. Gear changes with an interruption of traction can be disadvantageous if the mobile machine comes to an unintended stop during the gear change, for example, when the gear change occurs while driving uphill or pulling a heavy load.

[0004] The interruption of traction during gear changes can be avoided by using friction clutches. However, such clutches can cause undesirable power losses and thus reduce the efficiency of the drive. An alternative solution for avoiding the interruption of traction during gear changes is described in German patent application DE 10 2019 214 986 A1. This application describes a drive system for an electric vehicle with a manual transmission, comprising two electric machines, where the second electric machine can be engaged as needed and is available as a drive during the gear-shifting process.

[0005] Existing solutions using manual transmissions have the disadvantage of being technically complex and expensive. Furthermore, they do not adequately address the issue of under what circumstances and in what manner shifting occurs.

[0006] The present invention is based on the objective of finding the most user-friendly method possible for operating a cost-effective and particularly compact drive system that avoids interruptions in traction during operation and meets the above-described requirements regarding maximum traction and maximum travel speed while simultaneously achieving high efficiency. The method should, in particular, offer the advantage of automatic operation, so that no manual shifting is required and the driver can concentrate better on the actual work task. Summary

[0007] The following part of this paragraph serves to explain terms used in this disclosure. If two elements are mechanically connected, these elements are coupled to each other directly or indirectly in such a way that a movement of one element causes a reaction of the other element. A mechanical connection can be established, for example, by a positive-locking or friction-locking connection, or by the meshing of corresponding gear teeth of two elements. Further elements, such as one or more spur gear stages, can be arranged between mechanically connected elements. A connection of two elements via another element can mean that this other element participates in an indirect mechanical connection between the two elements.A connection between two elements via two or more other elements can mean that these additional elements are all involved in an indirect mechanical connection between the two elements. If two elements are connected in a rotationally fixed manner, then these elements are essentially rigidly coupled to each other. A rotationally fixed connection can be a friction-fit connection of elements, in which slippage may occur. Rotationally fixed elements can be integral parts or consist of individual components connected to each other in a rotationally fixed manner.

[0008] According to one embodiment of the present invention, a drive system for a mobile working machine, for example for a wheel loader or an excavator, is provided, wherein the drive system comprises a first drive device with a first motor shaft, a second drive device with a second motor shaft, and a transmission with a first input shaft, a second input shaft, and an output shaft, wherein the first motor shaft is rotationally fixed to the first input shaft of the transmission or can be connected to it, and the second motor shaft can be rotationally fixed to the second input shaft of the transmission by means of a coupling, for example by means of a jaw coupling, characterized in that the first input shaft is mechanically operatively connected to the output shaft via a first spur gear stage.wherein the first spur gear stage comprises a first spur gear in a rotationally fixed connection with the first input shaft and a third spur gear in a rotationally fixed connection with the output shaft, wherein the second input shaft is mechanically operatively connected to the output shaft via a second spur gear stage, wherein the second spur gear stage comprises a second spur gear in a rotationally fixed connection with the second input shaft and a fourth spur gear in a rotationally fixed connection with the output shaft.

[0009] The described embodiment with spur gear drive is advantageous because it enables a very compact, cost-effective and efficient drive system that allows a second drive device to be switched on as needed.

[0010] It is advantageous if the first drive device and / or the second drive device is designed as an electric motor, since electric motors offer high efficiency and their operation is advantageous with regard to pollutant emissions.

[0011] According to one embodiment, the first drive device and / or the second drive device is designed as a hydraulic unit, for example as an axial piston motor. Hydraulic units are advantageous because they have proven themselves in mobile machinery and enable a high power density.

[0012] Preferably, the first motor shaft and the first input shaft of the gearbox are connected to each other in such a rotationally fixed manner that they are formed in one piece.

[0013] Preferably, the first spur gear and the first input shaft are connected to each other in such a rotationally fixed manner that they are formed in one piece.

[0014] Preferably, the second spur gear and the second input shaft are connected to each other in such a rotationally fixed manner that they are formed in one piece.

[0015] Each of the above-described one-piece designs is advantageous in terms of efficiency, cost and compactness of the drive system.

[0016] According to one embodiment of the present invention, a drive system is provided, wherein the first spur gear stage comprises a first intermediate gear in a rotationally fixed connection with a first intermediate shaft, which is rotationally fixed to the first spur gear and the third spur gear. The described intermediate gear in conjunction with the first intermediate shaft is advantageous because it increases the distance between the first input shaft and the output shaft, thus allowing flexibility with regard to the design of the transmission.

[0017] It is advantageous if the first intermediate shaft can be mechanically connected or operatively linked to a power take-off shaft, so that the power of the drive system can be used to power a consumer.

[0018] According to one embodiment of the present invention, a drive system is provided, wherein the second spur gear stage comprises a second intermediate gear in a rotationally fixed connection with a second intermediate shaft, which is rotationally fixed to the second spur gear and the fourth spur gear. The described intermediate gear in conjunction with the second intermediate shaft is advantageous because it increases the distance between the second input shaft and the output shaft, thus allowing flexibility with regard to the design of the transmission.

[0019] It is advantageous if the second intermediate shaft can be mechanically connected or operatively linked to a power take-off shaft, so that power from the drive system can be used to power a consumer.

[0020] It is advantageous if a power take-off shaft is connected to a hydraulic unit, so that power generated by the drive system can be used to drive the hydraulic unit, for example to drive a hydraulic pump that supplies a working device of the mobile machine.

[0021] Preferably, the gear ratio between the second input shaft and the output shaft is greater than the gear ratio between the first input shaft and the output shaft. This facilitates the generation of high torques at the output shaft by means of the second drive device, which is connected to the second input shaft of the transmission. Simultaneously, it facilitates the generation of high output shaft speeds by means of the first drive device, which is connected to the first input shaft of the transmission.

[0022] According to one embodiment of the present invention, a drive system is provided, wherein the coupling is designed as a positive-locking coupling, for example, as a jaw coupling. A positive-locking coupling offers advantages in terms of energy efficiency and robustness. The use of a positive-locking coupling is particularly advantageous when the second drive device is designed as an electric motor, since the use of an electric motor facilitates active synchronization of the shafts that can be connected by the coupling. Such active synchronization simplifies the use of a positive-locking coupling, as no components for passive synchronization are required.

[0023] It is advantageous if the drive system is configured to alternately drive at least one wheel of the mobile machine via the gearbox output shaft. a) only by the first drive device and b) to be driven by the first drive device in combination with the second drive device, preferably via a differential gear. In this way, the drive system enables a high maximum speed, a high maximum tractive force and high energy efficiency.

[0024] According to one embodiment of the present invention, a mobile working machine is provided which has a drive system according to the invention. Brief description of the characters

[0025] The present invention is described with reference to the accompanying figures, where identical reference numerals refer to identical parts and / or to similar parts and / or to corresponding parts of the system. Regarding the figures: Fig. Figure 1 schematically describes the structure of a drive system according to the invention for a mobile working machine in one embodiment of the invention. Fig. Figure 2 schematically describes the arrangement of the spur gears of the transmission for one embodiment of the invention. Fig. Figure 3 schematically describes the arrangement of the spur gears of the transmission for a further embodiment of the invention. Fig. Section 4 schematically describes, for one embodiment, a method according to the invention for operating a drive system using a state diagram. Fig. Section 5 describes, by way of example, the tractive force of the mobile working machine as a function of speed for an embodiment of the invention. Detailed description

[0026] The present invention is described below with reference to certain embodiments as shown in the accompanying figures. However, the present invention is not limited to the specific embodiments described in the following detailed description and shown in the figures; rather, the described embodiments merely illustrate some aspects of the present invention, the scope of which is defined by the claims.

[0027] Further modifications and variations of the present invention are obvious to a person skilled in the art. The present description therefore encompasses all modifications and / or variations of the present invention whose scope of protection is defined by the claims.

[0028] Fig. Figure 1 schematically describes an embodiment of a drive system according to the invention, comprising a first inverter 21, which drives a first electric motor 1, a second inverter 20, which drives a second electric motor 2, and a control unit 22, which is connected to the first inverter 21 and the second inverter 20 via a communication interface. The first inverter 21 determines the current rotational speed of the first motor shaft 3, and the second inverter 20 determines the current rotational speed of the second motor shaft 4, for example, using resolvers. These determined rotational speeds are transmitted to the control unit 22. The current speed of the mobile working machine is calculated in the control unit 22, for example, from the current rotational speed of the first motor shaft 3, from the circumference of a driven wheel of the mobile working machine, and from the known fixed gear ratio between the first motor shaft 3 and the driven wheel axle.The current speed can also be determined by the control unit 22 in other ways, for example, using a speed sensor that may be located on a shaft of the gearbox, or by using a satellite-based navigation system. The control unit 22 is also connected to an input device 23 of the mobile working machine, which includes, for example, a drive pedal with which the operator of the mobile working machine can control the speed and a start button with which the drive can be started. In addition, one or more additional controls may be provided with which the operator can manually request and / or prevent the disconnection and / or engagement of the second electric motor 2, as described in the description of . Fig. 4 will be explained in more detail.

[0029] The first motor shaft 3 of the first electric motor 1 is non-rotatably connected or connectable to the first input shaft 5 of a gearbox, on which a first spur gear 7 is mounted, the first spur gear 7 being integrally formed with the first input shaft 5. The second motor shaft 4 of the second electric motor 2 can be non-rotatably connected to a second input shaft 6 of the gearbox by a first coupling 18, which is controlled by the control unit 22. A second spur gear 8 is mounted on the second input shaft 6, the second spur gear 8 being integrally formed with the second input shaft 6. Preferably, the coupling 18 is positively engaged to achieve good efficiency. A rotary motion of the first spur gear 7 is preferably transmitted via a first intermediate gear 9, which is mounted on a first intermediate gear shaft 11, to the third spur gear 13, which is mounted on the output shaft 16 of the gearbox.The output shaft 16, for example, drives a wheel axle of a mobile machine (not shown) via a differential gear. A rotary motion of the second spur gear 8 is preferably transmitted via a second intermediate gear 10, which is mounted on a second intermediate gear shaft 12, to the fourth spur gear 14, which is mounted on the output shaft 16. It can be provided that the first intermediate gear shaft 11 can be non-rotatably connected to a power take-off (PTO) shaft 17 by means of a second coupling 19, which can drive a consumer 15, for example, a hydraulic pump for a hydraulic working device of the machine. The second coupling 19 can be controlled by the control unit 22 or by other means. Alternatively to the arrangement described above, the PTO shaft 17 can be non-rotatably connected to another shaft of the transmission or be non-rotatably connected to it via a coupling.

[0030] A first gear ratio of the transmission exists between the first input shaft 5 and the output shaft 16. A second gear ratio of the transmission exists between the second input shaft 6 and the output shaft 16. The second gear ratio is preferably selected to be larger than the first gear ratio. In this case, the second input shaft 6 is particularly well-suited for generating high torques at the output shaft 16.

[0031] Fig. Figure 2 schematically describes, for one embodiment of the invention, the arrangement of the spur gears of the transmission from a perspective parallel to the output shaft 16 of the transmission. A rotational movement of the first spur gear 7, which is non-rotatably connected to the first input shaft 5, is transmitted by meshing of corresponding teeth via the first intermediate gear 9 to the third spur gear 13, which is non-rotatably connected to the output shaft 16 of the transmission. A rotational movement of the second spur gear 8, which is non-rotatably connected to the second input shaft 6 of the transmission, is transmitted by meshing of corresponding teeth via the second intermediate gear 10 to the third spur gear 14, which is non-rotatably connected to the output shaft 16.

[0032] Fig. Figure 3 schematically describes, for a further embodiment of the invention which has only one intermediate gear in the transmission, the arrangement of the spur gears of the transmission from a perspective parallel to the output shaft 16 of the transmission. A rotational movement of the first spur gear 7, which is non-rotatably connected to the first input shaft 5, is transmitted by meshing of corresponding teeth via the first intermediate gear 9 to the third spur gear 13, which is non-rotatably connected to the output shaft 16 of the transmission. A rotational movement of the second spur gear 8, which is non-rotatably connected to the second input shaft 6 of the transmission, is transmitted by meshing of corresponding teeth directly to the third spur gear 14, which is non-rotatably connected to the output shaft 16.

[0033] Fig. Figure 4 schematically describes a method according to the invention for one embodiment using a state diagram. The states in this diagram represent states of the drive system. The initial transition 200 in this diagram represents the start of the drive system, for example by means of an input via a start button of the input device 23. This transition 200 causes a transition to state 201.

[0034] In state 201, the control unit 22 actuates the first clutch 18 so that it is closed. In this state 201, the output shaft 16 of the transmission is driven by both the first electric motor 1 and the second electric motor 2. This state 201 is advantageous for driving situations in which high torques at the output shaft 16 of the transmission, and thus high tractive forces of the machine, are required, for example, when filling the bucket of a wheel loader.

[0035] For example, by pressing the accelerator pedal of the input device 23, the operator can increase the speed of the machine. This increase in speed is achieved by the control unit 22 determining a target speed based on the position of the accelerator pedal. This target speed of the machine can be converted into target speeds for the first and second electric motors using the wheel circumference and gear ratios. The target speed of the first electric motor 1 can be transmitted to the first inverter 21, which adjusts the speed of the first electric motor 1 accordingly. The target speed of the second electric motor 2 can be transmitted to the second inverter 20, which adjusts the speed of the second electric motor 2 accordingly.As the speed of the mobile machine increases, the rotational speeds of the first electric motor 1 and the second electric motor 2 also increase. In this embodiment, the rotational speed of the second electric motor 2 is higher than that of the first electric motor 1 because, as described above, the second gear ratio is chosen to be larger than the first gear ratio. Since the efficiency of an electric motor generally decreases at sufficiently high rotational speeds, it is advantageous for efficient operation of the drive system to switch off the second electric motor 2 when a first speed limit is exceeded. This first speed limit of the mobile machine is, for example, a parameter of the control unit 22, which can be appropriately set during commissioning, depending on the technical characteristics of the drive system.Alternatively, the first limit value for the speed can also be provided, for example, by a function in the control unit 22, via an interface of the control unit 22, and / or via an input element of the input device 23.

[0036] The first speed limit is continuously compared by the control unit with the current speed, the determination of which is described above. If the current speed exceeds the first limit, transition 202 can be automatically triggered, causing a transition to state 203. Transition 202 opens the first clutch 18, so that the second electric motor 2 is disconnected from the drive system and can be switched off.

[0037] It may be provided that the activation of the transition 202 can be manually requested by the driver via the input device 23. Such manual activation of the transition 202 can be advantageous in driving situations where only low tractive forces are desired, for example, to avoid loss of traction when the wheels have low grip. Furthermore, it may be provided that the driver can prevent the automatic activation of the transition 202 described above by means of an input via the input device. Such a blocking of the transition can be advantageous in driving situations where the maximum possible tractive force of the mobile work machine is required even at higher speeds.

[0038] As an alternative to a first limit value for speed, a limit value for the rotational speed of the output shaft 16, for the rotational speed of the first input shaft 5, for the rotational speed of the second input shaft 6, or for another shaft of the gearbox can also be used to automatically trigger transition 202, since the speed of the machine being worked can be converted into these quantities using a constant factor.

[0039] In state 203, the first clutch 18 is open, so that only the first electric motor 1 contributes to the drive of the mobile working machine. Preferably, the second electric motor 2 is switched off in this state to save energy. This state is suitable for driving situations in which no large tractive forces are required, for example, when transporting a wheel loader at higher speeds.

[0040] Transition 204 represents the activation of the second electric motor 2 and causes a transition to state 205. This transition can be automatically triggered when the current speed falls below a second limit value, where the second speed limit should expediently not be greater than the first speed limit described above. Alternatively, transition 204 can be manually requested by the driver via the input device 23. Preferably, transition 204 is triggered if the absolute value of the current speed is below a second limit value and the driver simultaneously requests high traction or high speed from the drive system via the input device, for example, by applying sufficient force to the accelerator pedal or by using kick-down.In this way, the drive system operates at high efficiency for as long as possible, and the second electric motor is only engaged when needed. Furthermore, it may be possible for the driver to prevent automatic activation of transition 204 by using the input device. This allows the driver to force the system to remain in state 203 if necessary.

[0041] State 205 represents the synchronization of the second electric motor 2 with the gearbox. Preferably, active synchronization is achieved by actively controlling the second electric motor 2 with the first clutch 18 open. This control can be accomplished by the control unit 22 using the speed of the second input shaft 6 of the gearbox as a reference value for the speed of the second electric motor 2 and transmitting this reference value to the second inverter 20. The second inverter 20 can then adjust the speed of the second electric motor 2 to match the speed of the second input shaft 6 of the gearbox. This active synchronization facilitates the use of a positive-locking clutch, which can be advantageous in terms of energy efficiency. In the active synchronization described above, only the first electric motor 1 contributes to the drive of the mobile machine in state 205.The synchronization of the second electric motor 2 with the gearbox can also be achieved passively via frictional forces, for example if the first clutch 18 is designed as a friction clutch.

[0042] Transition 206 represents the achievement of synchronization between the second electric motor 2 and the gearbox, where the speed of the second electric motor 2 matches the speed of the second input shaft 6 of the gearbox and / or the difference in speeds is within a defined tolerance range. In the case of active synchronization, the first clutch 18 is then automatically closed without load by the control unit 22, and the transition to state 201, described above, takes place.

[0043] Fig.Figure 5 describes, by way of example, the tractive force of the mobile working machine as a function of speed in one embodiment. The horizontal axis 30 indicates the speed of the mobile working machine, and the vertical axis 31 indicates a tractive force.

[0044] The dashed line 32 shows the contribution of the first electric motor 1 to the maximum tractive force, and line 33 shows the contribution of the second electric motor 2, which provides the main contribution at low speeds. Line 34 represents the sum of the contributions of both electric motors. The curves of lines 32 and 33 can be readily adapted to a specific application of a machine by selecting suitable electric motors and appropriate gear ratios. In this example, the first speed threshold at which the second electric motor 2 is disengaged is approximately 29 km / h. At speeds above this threshold, only the first electric motor 1 contributes to the tractive force of the machine.

[0045] The dotted line 36 corresponds to a tractive force that is usually sufficient for operating the machine at medium speed. The difference between lines 34 and 36 in area 35 therefore corresponds to a surplus of tractive force, or rather a surplus of torque from the drive system, which can be used to drive the power take-off shaft 17 without significantly impairing the performance of the drive system.

[0046] While the present invention has been described with reference to the embodiments described above, it is clear to those skilled in the art that it is possible to implement various modifications, variations, and improvements of the present invention in light of the teaching described above and within the scope of the appended claims without deviating from the scope of protection of the invention. In particular, it is possible to use suitable hydraulic units for the drive instead of the first electric motor 1 and / or instead of the second electric motor 2, for example, axial piston motors, which can be driven, for example, by an axial piston pump in conjunction with an internal combustion engine.

[0047] Furthermore, the areas in which experts are likely to be knowledgeable have not been described here in order to avoid unnecessarily obscuring the described invention.

[0048] Accordingly, the invention should not be limited by the specific illustrative embodiments, but only by the scope of protection of the attached claims. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2019 214 986 A1

[0004]

Claims

[1] Drive system of a mobile working machine, wherein the drive system comprises a first drive device (1) with a first motor shaft (3), a second drive device (2) with a second motor shaft (4) and a gearbox with a first input shaft (5), a second input shaft (6) and an output shaft (16), wherein the first motor shaft (3) is non-rotatably connected or connectable to the first input shaft (5) of the gearbox and the second motor shaft (4) is non-rotatably connected to the second input shaft (6) of the gearbox by means of a coupling (18), characterized by, that the first input shaft (5) is mechanically connected to the output shaft (16) via a first spur gear stage, wherein the first spur gear stage comprises a first spur gear (7) in a rotationally fixed connection with the first input shaft (5) and a third spur gear (13) in a rotationally fixed connection with the output shaft (16), wherein the second input shaft (6) is mechanically connected to the output shaft (16) via a second spur gear stage, wherein the second spur gear stage comprises a second spur gear (8) in a rotationally fixed connection with the second input shaft (6) and a fourth spur gear (14) in a rotationally fixed connection with the output shaft (16). [2] Drive system according to claim 1, wherein the first drive device (1) and / or the second drive device (2) is designed as an electric motor. [3] Drive system according to claim 1 or 2, wherein the first drive device (1) and / or the second drive device (2) is designed as a hydraulic unit. [4] Drive system according to one of claims 1 to 3, wherein the first motor shaft (3) and the first input shaft (5) of the transmission are connected to each other in such a rotationally fixed manner that they are formed in one piece. [5] Drive system according to one of claims 1 to 4, wherein the first spur gear (7) and the first input shaft (5) are connected to each other in such a rotationally fixed manner that they are formed in one piece. [6] Drive system according to one of claims 1 to 5, wherein the second spur gear (8) and the second input shaft (6) are connected to each other in such a rotationally fixed manner that they are formed in one piece. [7] Drive system according to one of claims 1 to 6, wherein the first spur gear stage comprises a first intermediate gear (9) in a rotationally fixed connection with a first intermediate shaft (11), which is rotationally fixed to the first spur gear (7) and the third spur gear (13). [8] Drive system according to claim 7, wherein the first intermediate shaft (11) is mechanically connectable or operatively connected to a power take-off shaft (17). [9] Drive system according to one of claims 1 to 8, wherein the second spur gear stage comprises a second intermediate gear (10) in a rotationally fixed connection with a second intermediate shaft (12), which is rotationally fixed to the second spur gear (8) and the fourth spur gear (14). [10] Drive system according to claim 9, wherein the second intermediate shaft (12) is mechanically connectable or operatively connected to a power take-off shaft (17). [11] Drive system according to any one of claims 1 to 10, wherein the gear ratio between the second input shaft (6) and the output shaft (16) is greater than the gear ratio between the first input shaft (5) and the output shaft (16). [12] Drive system according to one of claims 1 to 11, wherein the clutch (18) is designed to be positively engaged. [13] Drive system according to claim 8 or 10, wherein the power take-off (17) is connected to a hydraulic unit so that power generated by the drive system can be used to drive the hydraulic unit. [14] Drive system according to any one of claims 1 to 13, wherein the drive system is configured to alternately drive at least one wheel of the mobile working machine via the output shaft (16) of the transmission a) only by the first drive device (1) and b) to be driven by the first drive device (1) in combination with the second drive device (2). [15] Mobile working machine comprising a drive system according to any one of claims 1 to 14.

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