Electric drive and mobile work machine

Abstract

Electric drive for a mobile work machine with a first (10) and a second (12) electric motor, wherein at least one (10) of the electric motors (10, 12) is speed-variable, characterized in that a mechanical summing gearbox (18) with two inputs (28, 30) and one output (32) is provided, via which input torques (M) 10 , M 12 ) to an output torque (M 32 ) are summable, wherein a first (28) of the inputs (28, 30) are rotationally fixed to a first rotor (14) of the first electric motor (10), a second (30) of the inputs (28, 30) are rotationally fixed to a second rotor (16) of the second electric motor (12), and the output (32) is rotationally fixed to a wheel (6) or an axle (8), characterized by a control device (42) in which a first operating range with an output speed (n) is defined. 32 ) equals zero and the output torque (M 32) is provided to be non-zero, in which input speeds (n 10 , n 12 ) are parameterized such that the drive (1) can be operated continuously in the first operating range, wherein one or more operating points are parameterized in the control device (42) in which one of the input speeds is parameterized to zero only if a gradient of the output speed is not equal to zero.

Description

[0001] The invention relates to an electric drive system according to the preamble of claim 1 and a mobile working machine according to claim 11.

[0002] Drive systems for mobile machinery, particularly in the off-highway and material handling sectors, must meet stringent requirements regarding high torque at low speeds or standstill, as well as consistent torque transmission. These sectors require drive systems for equipment such as wheel loaders, telehandlers, reach stackers, and graders. The vast majority of these drive systems are hydrostatic.

[0003] To extend the speed range of the drive system, a mechanical multi-speed transmission can be connected downstream of a hydrostatic drive system. To change the drive system's gear ratio without interrupting the power flow, so-called powershift transmissions are used. This type of vehicle transmission allows the gear ratio to be changed under load, i.e., while driving, without interrupting torque transmission. This allows propulsive forces to be transmitted even during the shifting process, so the vehicle can continue to be pulled or accelerated at a constant speed. Therefore, there are no interruptions in traction or loss of comfort during the shifting process. To achieve this, when shifting gears, one shift element of the previous gear opens while another shift element of the new gear closes.

[0004] Suitable drive systems include, for example, hydrodynamic torque converters or hydrostatic transmissions combined with a powershift transmission. One example is the HVT transmission from Dana Rexroth Transmission Systems.

[0005] The hydrostatic machines or hydraulic motors used in this process have the characteristic that they can continuously generate a high power density and a high drive torque at a driving speed of zero without sustaining damage.

[0006] In principle, the electrification of drive systems is progressing in the aforementioned segments. However, electric drive machines or electric motors generally have a somewhat lower power density compared to the hydraulic variants mentioned above and therefore require more installation space, which is severely limited in mobile technology. This lack of power density is usually compensated for by a higher rotational speed of the electric motors. A disadvantage, however, remains: electric motors are comparatively poor at generating high drive torques at zero or near-zero speeds. At such operating points, for example, the rotor's standstill under load results in a continuous, uninterrupted high current load on only one phase of the n-pole motor and its power electronics.Despite the thermal inertia of the components and their additional cooling, if a certain period of time is exceeded, the electric motor itself or its power electronics can be damaged by overheating.

[0007] The publication DE 691 26 319 T2 discloses a continuously variable, integrated motor and gearbox unit with two inputs.

[0008] Document DE 103 04 610 A1 discloses an arrangement and a method for converting mechanical energy into electrical energy and vice versa.

[0009] In contrast, the invention aims to create an electric drive system for a mobile work machine that is designed to continuously generate a high drive torque at zero speed without sustaining damage. Furthermore, the invention aims to create a mobile work machine equipped with such a drive system.

[0010] This problem is solved by an electric drive system with the features of claim 1, the second by a mobile working machine with the features of claim 11.

[0011] Advantageous further developments of the electric drive system are described in the dependent patent claims.

[0012] An electric drive system for a mobile work machine, in particular for a wheel loader, telehandler, reach stacker, or grader, has a first electric motor and a second electric motor. At least one of these is speed-variable, particularly via a control unit of the drive system, especially for controlling or regulating the travel speed. According to the invention, the drive system also has a mechanical summing gearbox. This gearbox has at least two inputs and one output. Via this gearbox, input torques transmitted from the respective electric motors to the inputs can be summed to form an output torque. For this purpose, a first input is rotationally fixed to a first rotor of the first electric motor, a second input is rotationally fixed to a second rotor of the second electric motor, and the output is rotationally fixed to a wheel or axle of the drive system.The rotationally fixed connection can be configured with or without gearing. Preferably, at least one of the electric motors is operable in both directions of rotation. Preferably, both electric motors are operable in four quadrants. Preferably, at least one of the electric motors is configured as a permanent magnet synchronous motor (PMSM).

[0013] The design with summing gears allows the two electric motors of the drive system to provide an output speed of zero with a non-zero output torque, while their own speeds, the input speeds, can both be non-zero. This protects them against thermal overload, which can occur in conventional electric drive systems when one or both electric motors are stationary with an applied output torque.

[0014] In a preferred further development, the summing gearbox is formed by a planetary gearbox. The planetary gearbox thus provides a compact and practical design for the summing gearbox.

[0015] In this advanced configuration, the output is non-rotatably connected to a planetary gear carrier of the planetary gear set, one of the inputs is non-rotatably connected to a ring gear, and the other input is non-rotatably connected to a sun gear of the planetary gear set. Alternatively, other configurations are of course possible, such as the non-rotatable connection of the output to either the ring gear or the sun gear, or of one of the inputs, for example, to the planetary gear carrier.

[0016] A key feature of the planetary gearbox is its ability to enable operating points or ranges for the drive system where an output speed of zero and a non-zero output torque are possible, while both input speeds are non-zero. This protects electric motors from overload when stationary and subjected to high torque, a specific requirement of mobile machinery, as their rotors undergo continuous pole or phase reversals due to the non-zero input speed. The previously discussed thermal overload caused by a permanently stationary rotor and a simultaneously high-current phase is thus eliminated.

[0017] In a further development, the drive system has a control unit in which a first operating range with an output speed of zero and an output torque of non-zero is provided, and in which input speeds - i.e., speeds of the inputs or the electric motors - are parameterized in such a way that the drive system can be operated continuously in the first operating range.

[0018] In a further training course, for the purpose of continuous operation with zero output speed and non-zero output torque in the first operating range, both input speeds are parameterized to non-zero.

[0019] As explained above, it is advantageous to prevent the electric motors or their power electronics from operating with zero input speed and non-zero input torque, thus protecting them from thermal overload. In a further development, the control unit features a second operating range with a constant output speed, in which both input speeds are parameterized as non-zero. This ensures that even at constant driving speeds (constant output speed), neither electric motor is energized and idling, thereby preventing thermal overload as described above.

[0020] In cases where achieving a desired output speed requires one of the input speeds to be zero and its associated input torque to be non-zero, a further development of the control unit provides one or more parameterized operating points. In these points, one of the input speeds is only parameterized to zero when the gradient of the output speed is non-zero, i.e., when the output speed is accelerating or decelerating. This ensures that the input speed can only reach zero during an acceleration or deceleration process, meaning it can only be zero for a very short period.

[0021] In a further development, an acceleration mode is provided in the control unit, in which one of the input speeds - and thus one speed of one of the electric motors - is constant and the other input speed - and thus the speed of the other electric motor - is parameterized variably to change the output speed.

[0022] In a further development, the control unit includes an inverter that is connected to the electric motors to control or regulate the input speeds and / or input torques and / or the output speed and / or output torque. In particular, the power electronics of the inverter are protected from thermal stress caused by continuous (uninterrupted) current flow on only one phase via the operating ranges and operating points parameterized in the control unit.

[0023] In this advanced version, the drive system is equipped with a primary electrical energy source, which can be, for example, a fuel cell or an electrical storage device such as a battery or battery array. The electric motors can be supplied with electrical energy via this primary energy source. Alternatively, the drive system can have a connection for such a primary electrical energy source.

[0024] Alternatively or additionally, the drive system can have a generator that can supply the electric motors with electrical energy.

[0025] In a further development, the drive system also includes a power engine, in particular an internal combustion engine, for example a diesel engine, by which the generator can be driven, in particular is driven.

[0026] In a further development process, a hydrostatic working device – in particular one of the mobile working machines – can be driven, and in particular driven, by one of the electric motors, especially the one with a constantly parameterized speed. Working devices mentioned here are, in particular, hydraulic machines or hydraulic cylinders, which advantageously exhibit a substantially constant or stationary operating mode.

[0027] A mobile working machine according to the invention, in particular a wheel loader, a reach stacker, a grader or telehandler, has a drive system which is designed according to at least one aspect of the preceding description.

[0028] An embodiment of an electric drive system according to the invention is shown in the drawings. The invention will now be explained in more detail with reference to the figures in these drawings.

[0029] They show Fig. 1 a schematic representation of an embodiment of an electric drive system and Fig. 2 a speed-velocity diagram of the electric drive according to Fig. 1, which is parameterized in the control unit of the drive system.

[0030] According to Fig. 1 has an electric drive 1 two axles 2, 4 each with two wheels 6. The wheels 6 of the respective axles 2, 4 are each connected to each other via a differential 8.

[0031] Furthermore, the electric drive 1 has a first electric motor 10 and a second electric motor 12 with a first rotor shaft 14 and a second rotor shaft 16. The drive 1 has a summing gearbox 18 designed as a planetary gearbox with a sun gear 20, a ring gear 22, and a planet carrier 24 with planet gears 26 (only one of which is shown). The planetary gearbox 18 has a first gearbox input 28, which is rotationally fixed to the first rotor shaft 14, and a second gearbox input 30, which is rotationally fixed to the second rotor shaft 16. The first gearbox input 28 is fixedly connected to a spur gear, which meshes with a gear mounted on a shaft with the sun gear 20. In this way, a reduction is achieved between the first gearbox input 28 and the sun gear 20. The second gearbox input 30 is fixedly connected to a spur gear which engages with an external toothing of the ring gear 22.The planet gears 26 engage with their external teeth with the internal teeth of the ring gear 22 and the external teeth of the sun gear 20. An output 32 of the planetary gear 18 is formed from the planet carrier 24, which is connected by spur gears to a spur gear 34 that acts on a cardan shaft 36 of the drive 1.

[0032] The drive unit 1 also includes a generator 38 driven by an internal combustion engine (diesel, not shown), which is connected to an inverter 40, which in turn is connected to the electric motors 10, 12 for power supply.

[0033] Furthermore, the electric drive 1 has a control unit 42, wherein the inverter 40 is a component of the control unit 42. For controlling and / or regulating an output torque M 32 of output 32, an output speed n 32, of a first input torque M 10 , a first input speed n 10 , a second input torque M 12 and a second input speed n 12 The control unit has a control unit 44 (ECU). This unit stores parameterized speeds and torques for specific operating points and operating ranges, which will be explained later. These operating points and operating ranges are described using the driving operation of a wheel loader as an example. The diagram according to [reference to diagram] is also used for this purpose. Fig. 2.

[0034] To enable the control / regulation of the aforementioned operating parameters of the drive 1, it has speed sensing units 46, 48 and 50, via which the first input speed n 10 , the second input speed n 12 and the output speed n 32detectable and can be transmitted via signal line 52, or 54, 56 to the control unit 44 of the control device 42.

[0035] In a driving operation with a detected output speed n 32 The vehicle (the wheel loader) is moved from a non-zero position according to the driving diagram parameterized in the control unit 44. Fig. 2. The X-axis shows a travel speed v that is proportional to the initial rotational speed n. 32 This means that for the wheel loader, this translates to a maximum speed of approximately 40 kilometers per hour, both in reverse and forward motion.

[0036] It is clearly visible that the second input speed n is used in the control unit 44 to achieve the driving speed v. 12 constant at approximately 8000 revolutions / minute and the first input speed n 10are parameterized variably along a straight line. Since, as mentioned, it is important to avoid a torque being applied for too long at zero rotational speed for electric motors (risk of the aforementioned thermal overload, both of the electric motor and its power electronics), the only operating point X at which the first input speed n 10 = 0 must be set to a driving speed of v x = 8 km / h parameterized in reverse gear. This driving speed value v xThis speed is specifically chosen for wheel loaders because it is known that this type of mobile machine is rarely operated at a stationary speed (constant travel speed) in reverse at this speed. In other words, this speed of the drive 1 is usually achieved in an accelerated or decelerated driving mode and is only rarely maintained at a stationary speed. Furthermore, the output torque M is... 32 comparatively small. The first electric motor 10 thus has the first input speed n x10 = 0 only briefly and also with only low current.

[0037] Let us now assume that the wheel loader plunges its bucket into a pile of heavy bulk material. In doing so, the driving speed is reduced to v = 0. This is clearly visible in the diagram. Fig. 2, that the control unit is parameterized such that the input speeds n 10 and n12 The speeds of the two electric motors 10 and 12 are not equal to zero. In other words, the electric motors 10 and 12 continue to rotate and exhibit rotational speeds despite the vehicle being stationary. 10 , n 12 not equal to zero. This protects them and their power electronics (inverter 40) against the aforementioned thermal overload. At the same time, their input torques M 10 , M 12 via the planetary gear 18 to the output torque M 32 The total amount is summed up. The wheel loader thus presses into the pile of bulk material while standing still and can pick up the desired quantity.

[0038] The operating points x stored in the control device 42 (control unit 44) 10 and operating ranges in connection with the use of the planetary gear 18 for summing the torques M 10 , M 12The shortcoming of electric motors 10 and 12, which requires inverter-driven electric motors to generate high torque at low speeds or zero speed in order to deliver it to the gearbox output 32, is eliminated. Instead, electric motors 10 and 12 deliver their torques M 10 , M 12 at comparatively high speeds, which reduces their thermal stress. The sum of the torques M 10 , M 12 The desired high output torque M is then achieved via gearbox 18. 32 , even at low output speed n 32 , which can even be 0 without damaging the aforementioned components.

[0039] Compared to hydrostatic drive systems with hydraulic machines and powershift transmissions, the drive system according to the invention has an improved efficiency.

[0040] Since the drive system shown does not require a powershift transmission, the drive system has a lower level of technical complexity.

[0041] This means that switching operations are completely eliminated, making operation more convenient and increasing the robustness of the drive.

[0042] Revealed is an electric drive system with two electric motors, a summation gearbox and a control unit that is parameterized in such a way that, despite continuous load torque and standstill, components of the power electronics of the electric motors and the electric motors themselves are protected against overload.

[0043] A mobile work machine with such a drive system has also been revealed. Reference symbol list 1 electric drive 2, 4 axis 6 wheels 8 Differential gears 10 first electric machine 12 second electric machine 14 first rotor shaft 16 second rotor shaft 18 summing gears 20 sun wheel 22 Ring gear 24 planetary gear carriers 26 planetary gear 28 first gearbox input 30 second gearbox input 32 Gearbox output 34 Spur gear 36 Cardan shaft 38 Generator 40 inverters 42 Control unit 44 Electronic Control Unit (ECU) n 10 first input speed n 12 second input speed n 32 Output speed M 10 first input torque M 12 second input torque M 32 Output torque v Driving speed v x Driving speed with n 10 = 0

Claims

[1] Electric drive for a mobile working machine comprising a first (10) and a second (12) electric motor, wherein at least one (10) of the electric motors (10, 12) is speed-variable, characterized by , that a mechanical summing gearbox (18) with two inputs (28, 30) and one output (32) is provided, via which input torques (M 10 , M 12 ) to an output torque (M 32 ) are summable, wherein a first (28) of the inputs (28, 30) is rotationally fixed to a first rotor (14) of the first electric motor (10), a second (30) of the inputs (28, 30) is rotationally fixed to a second rotor (16) of the second electric motor (12) and the output (32) is rotationally fixed to a wheel (6) or an axle (8), characterized by a control device (42) in which a first operating range with an output speed (n 32 ) equals zero and the output torque (M 32) is provided to be non-zero, in which input speeds (n 10 , n 12 ) are parameterized such that the drive (1) can be operated continuously in the first operating range, wherein one or more operating points are parameterized in the control device (42) in which one of the input speeds is parameterized to zero only if a gradient of the output speed is not equal to zero. [2] Drive system according to claim 1, wherein the summing gear (18) is formed by a planetary gear (18). [3] Drive unit according to claim 2, wherein the output (32) is non-rotatably connected to a planet carrier (24) and one (30) of the inputs (28, 30) is non-rotatably connected to a ring gear (22) and the other (28) of the inputs (28, 30) is non-rotatably connected to a sun gear (20). [4] Drive unit according to one of the preceding claims, wherein in the first operating range both input speeds (n 10 , n 12) are parameterized to non-zero. [5] Drive unit according to one of the preceding claims, wherein the control unit (42) has a second operating range with constant output speed (n 32 ) is provided for, in which both input speeds (n 10 , n 12 ) are parameterized to non-zero. [6] Drive system according to one of the preceding claims, wherein an acceleration mode is provided in the control unit (42) in which a (n 12 ) the input speeds (n 10 , n 12 ) constant and the other one (n 10 ) the input speeds (n 10 , n 12 ) is variably parameterized. [7] Drive system according to one of the preceding claims, wherein the control device (42) comprises an inverter (40) which is connected to the electric motors (10, 12) for controlling or regulating the input speeds (n 10 , n 12 ) and / or input torques (M10 , M 12 ) and / or the output speed (n 32 ) and / or the output torque (M 32 ) is connected. [8] Drive system according to one of the preceding claims comprising an electrical primary energy source through which the electric motors can be supplied with electrical energy, or comprising a connection for the electrical primary energy source. [9] Drive system according to one of the preceding claims with a generator (38) via which the electric motors (10, 12) can be supplied with electrical energy. [10] Drive system according to claim 9 comprising a power machine by which the generator (38) can be driven, in particular is driven. [11] Mobile working machine with an electric drive (1) designed according to one of the preceding claims.

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