Electric powertrain for a work vehicle

Abstract

Drive device (8) for a work vehicle, comprising: an electric motor (12) with a motor shaft and a motor housing (16); and a gearbox (10) with a gearbox housing (11); wherein: the gearbox (10) has an output shaft (13) whose axis of rotation is aligned with the axis of rotation of at least one component (14) of a drive shaft (9) of the work vehicle; the output shaft (13) is designed so that the component (14) of the drive shaft (9) can be coupled to it; the gearbox housing (11) and the motor housing (16) are connected to form a single structural unit; the axis of rotation of the drive shaft (9) and the axis of rotation of the motor shaft are parallel to each other; the electric motor (12) is arranged above the drive shaft (9); a braking device (20) is provided which is arranged coaxially to the motor shaft; and wherein the braking device (20) is attached to the motor housing (16).

Description

The invention relates to an electric drive train for a work vehicle, such as a wheel loader, a compact loader, a telescopic loader, a telehandler, a dumper, an excavator or a backhoe loader. Such work vehicles are known. For example, there are wheel loaders with a rigid frame that keeps the two wheel axles parallel to each other. At least one of the wheel axles can be fitted with steerable wheels. All-wheel-steered work vehicles are also known. Wheel loaders with exceptional maneuverability can have a front and rear section, as well as a joint between the front and rear sections to couple them, allowing the front and rear sections to move relative to each other around at least one vertical axis of the vehicle. Because the front and rear sections can thus perform a kind of "articulated" movement relative to each other, these are also referred to as articulated wheel loaders. This articulation between the front and rear sections enables steering and thus cornering, as the wheels or wheel axles on the front and rear sections can be angled relative to each other. To improve off-road capability, it is also known to design the joint in such a way that it allows relative movement between the front and rear sections around the longitudinal axis of the vehicle. This relative movement is also referred to as "oscillation." Such a combined joint is accordingly also called an "articulated oscillating joint." An articulated oscillating joint is known, for example, from DE 101 30 530 C1 or EP 2 218 835 A1. Today, such work vehicles are typically powered by diesel engines. Power transmission from the engine to the chassis is achieved via mechanical, hydrostatic, or hydrodynamic principles. Combinations of these transmission methods are also known. Furthermore, hybrid concepts combining diesel engines and electric drives have already been implemented, employing crankshaft generators or electrifying auxiliary drives. Generating drive power with a diesel engine and subsequently converting that power via hydrostatic or hydrodynamic converters results in high losses and therefore low efficiency. Implementing an electric drivetrain reduces the number of components required for power transmission and eliminates the need for conversion via hydrodynamic or hydrostatic converters. This leads to improved efficiency. From US 2013 / 0 168 166 A1, a drive train is known with an electric motor and a gearbox, in which the electric motor is attached to the gearbox housing with its housing and drives a drive shaft of a work vehicle via the gearbox. CN 2 05 059 171 U also shows an electric motor whose housing is connected to a gearbox housing. DE 40 10 742 C1 describes a spur gear unit for a drive unit of an industrial truck, in which a brake is integrated. A wheel loader with an energy storage unit is known from DE 20 2014 000 738 U1. The invention is based on the objective of providing an electric drive device for a work vehicle and a work vehicle equipped with this drive device. The problem is solved according to the invention by a drive device having the features of claim 1. A work vehicle equipped with the drive device is defined in the dependent claim. Advantageous embodiments of the invention are specified in the dependent claims. A drive device for a work vehicle is equipped with an electric motor with a motor shaft and a motor housing and with a gearbox with a gearbox housing, wherein the gearbox has an output shaft whose axis of rotation is aligned with the axis of rotation of at least one component of a drive shaft of the work vehicle, wherein the output shaft is designed so that the component of the drive shaft can be coupled to it, and wherein the gearbox housing and the motor housing are connected to form a structural unit. The gearbox serves to convert the rotational speed of the motor shaft into a different speed suitable for driving the drive shaft leading to the driven wheels, and thus for propelling the work vehicle. In addition, the gearbox serves to transmit the torque generated by the electric motor to the connectable drive shaft. The drive shaft can be, for example, a driveshaft or a cardan shaft. It is also possible to design the drive shaft as a rigid shaft. However, the drive shaft is not part of the drive system. Rather, the system boundary of the drive system is understood to be the interface between the output shaft of the transmission on the one hand and the drive shaft component that can be coupled to it on the other. Accordingly, the drive shaft component can be, for example, a universal joint or part of a universal joint, to which the driveshaft then connects. The driveshaft, which can be attached to the output shaft of the transmission, should be aligned with the output shaft of the transmission, i.e., essentially coaxial, unless an angular position between parts of the chassis is required, e.g., in an articulated vehicle due to pivoting between the front and rear sections. The output shaft belonging to the gearbox and thus to the drive device can, for example, also carry a gear that is part of the gearbox. The structural unit formed by the engine housing and the transmission housing means that the entire drive system can be implemented as a single unit for the vehicle propulsion. It can, for example, be pre-assembled outside the actual work vehicle and then simply needs to be connected to the work vehicle via appropriate interfaces. One of these interfaces – as already explained above – is located at the system boundary between the output shaft of the transmission and the drive shaft of the work vehicle. Forming the drive system as a single structural unit with the transmission housing and the engine housing allows for a very compact design. Since the gearbox housing and the engine housing form a single structural unit, the entire assembly can be installed in the work vehicle with virtually no stress. No significant forces are transmitted to the outside. In particular, there is no static over-constraint at the bearings (for example, of the engine or gearbox components) and thus no associated stresses. This stress-free state applies primarily when the vehicle is at rest, i.e., with the engine switched off, while stresses can naturally occur during operation due to the additional forces and moments then acting upon it. The gearbox housing can be attached to the engine housing in such a way that the engine housing supports the gearbox housing. The engine housing can be mounted in a designated installation space within the work vehicle via an engine mount. This means that the gearbox housing is attached exclusively to the engine housing, and not to any other components. In particular, the gearbox housing is not mounted in the work vehicle via a corresponding gearbox bearing. Accordingly, the forces are transmitted within the drive unit, i.e., the drive device forming a single assembly. No additional bearing for the transmission within the vehicle is provided. The engine housing forms the sole load-bearing structure. For this purpose, a flange and / or a torque arm can be provided between the gearbox housing and the engine housing. For example, the gearbox housing can be flanged to the engine housing and additionally supported by the torque arm. The torque arm is particularly suitable for supporting the gearbox shaft, located away from the engine, such as the output shaft mentioned above. Since the output shaft is located in the area of ​​the drive shaft of the work vehicle, it must necessarily be spatially separated from the engine, thus exerting a leverage effect on the engine housing. During operation, the torque delivered by the gearbox to the drive shaft must be supported, and this torque can be transferred from the gearbox housing to the engine housing by means of the torque arm.Here too, the gearbox housing does not require any further (additional) support on the structure of the work vehicle. The engine mount can be formed directly on the engine housing, having at least three, and in particular four, bearing points connected to the engine housing via connecting elements, and each bearing point having a vibration decoupling device. This allows the engine mount to be integrated directly into the engine housing, i.e., formed as a single unit with the engine housing. It is also possible to attach the engine mount to the engine housing, in particular to attach it directly. The connecting elements of the engine mount can, for example, also be angled. The engine mount not only supports the weight of the entire assembly, including the engine and transmission, but is also designed to absorb the torque generated during operation. Furthermore, vibration isolation is incorporated to prevent engine vibrations from being transmitted to the rest of the vehicle, and conversely, to prevent vibrations from the vehicle from being transmitted to the electric motor and transmission. Vibration decoupling at the bearing points can be achieved, for example, by using rubber buffers. The bearing points provide another interface between the drive device and the work vehicle. In another embodiment, the engine housing can be attached to the gearbox housing in such a way that the gearbox housing supports the engine housing, with the gearbox housing being secured in a provided installation space in the work vehicle via a gearbox bearing. In this variant, unlike the embodiment described above, the engine housing does not support the gearbox housing and hold the latter in the work vehicle. Instead, the roles are reversed, so that the gearbox housing supports the engine housing and thus the engine in the work vehicle. Appropriate bearing points can also be provided here to design the gearbox mounting accordingly. The axis of rotation of the drive shaft and the axis of rotation of the motor shaft can run parallel to each other when the drive unit is installed in the work vehicle. If the two axes of rotation are parallel, the transmission can be designed as a simple spur gear transmission, eliminating the need for bevel gear stages. This allows for a cost-effective and robust transmission design. The electric motor can be located above the drive shaft. The gearbox can have a drive pinion whose axis of rotation is coaxial with the axis of rotation of the motor shaft. Depending on the design, the drive pinion can even be mounted directly on the motor shaft. In any case, mounting the drive pinion on or coaxially with the motor shaft allows for a very compact design, enabling the gearbox and motor to be integrated as a single unit. A braking device may be provided, arranged coaxially to the motor shaft and attached to the motor housing. In particular, the braking device, arranged in alignment with the motor shaft, may be attached to the motor housing opposite the gearbox, thereby braking the motor shaft. The design of the braking device is known per se. In particular, the braking device can be implemented as a spring-applied brake, in which a spring assembly ensures that the brake is closed when there is no current. The described drive device can be advantageously used in a work vehicle. This work vehicle can be, in particular, a construction machine such as a wheel loader, a telescopic wheel loader, a telehandler, a dumper, an excavator, or a backhoe loader. The work vehicle can have at least two wheel axles, one of which is a front axle and the other a rear axle. Furthermore, the work vehicle has the aforementioned drive shaft, which can extend in a longitudinal direction (main direction of travel) of the work vehicle. As mentioned above, it is possible to mount the work vehicle and the drive unit separately, so that the drive unit is then installed in the work vehicle as a single structural unit. The drive unit can be connected via the aforementioned interfaces, such as the engine mounts and the connection between the transmission output shaft and a corresponding component of the drive shaft. In this work vehicle, the two wheel axles can be rigidly arranged relative to each other, with the drive unit being located in a space selected from the group consisting of the space between the two wheel axles, the space at the front axle, or the space at the rear axle. In this design, the work vehicle can, in particular, have a rigid frame. No change in the angle between the two wheel axles is provided. Rather, the wheels carried by the wheel axles are at least partially adjustable in their angular position to achieve a steering effect. In another design, the work vehicle can be articulated, such that the two wheel axles are arranged to pivot relative to each other. This design incorporates two frames, each supporting one of the wheel axles, which can pivot relative to each other. In particular, the work vehicle can have a front section and a rear section, both of which have a wheel axle and a joint is arranged between the front section and the rear section for coupling the front section to the rear section in such a way that the front section and the rear section are movable relative to each other about at least one vertical axis of the work vehicle. The drive device can be arranged either on the front section or on the rear section. The joint can be implemented as a simple hinge joint or as a so-called hinge-pendulum joint, as already described above in the introductory description. In one embodiment, the previously mentioned electric motor is a drive motor, and an additional electric motor may be provided, which serves as a working motor for driving a hydraulic system. The hydraulic system is specifically designed to supply a lifting device, a loading device, an excavator, a telescopic handler, or a dumper with pressurized hydraulic fluid. The working motor drives, in particular, a hydraulic pump of the hydraulic system. These and other advantages and features of the invention are explained in more detail below with reference to examples and the accompanying figures. The figures show: Fig. 1 a side view of a work vehicle with an electric drive train; Fig. 2 the electric drive train in perspective view; Fig. 3 a rear perspective view of the drive train of Fig. 2 with a braking device; and Fig. 4 a bottom view of the drive train installed in the work vehicle. Fig. 1 shows a side view of a wheel loader used as a work vehicle with its hood open. The wheel loader has a rigid frame 1 to which a front axle 2 and a rear axle 3 are suspended, each of which carries wheels. The wheels are steerable, whereby either only the wheels on the front axle 2, only the wheels on the rear axle 3, or all wheels can be adjusted to generate the steering movement. A lifting device 4 is provided in the front area of ​​the wheel loader, to which a work tool, for example a shovel, can be attached. At the rear of the loader, an upwardly pivoting hood 5 is provided, which, when folded down (not shown in Fig. 1), covers a space containing an electrical energy storage device in the form of a battery 6. The battery 6 has a high capacity and stores the electrical energy required to power the wheel loader, i.e., both for travel and for working. Below a driver's platform 7 is an electric drive device 8 which is suspended from the frame 1. The drive device 8 drives a drive shaft 9 extending longitudinally along the wheel loader, which is designed as a driveshaft or cardan shaft and is accordingly composed of several components. A gearbox 10 belonging to the drive device 8 is located approximately in the middle of the drive shaft 9 and is driven by an electric motor, which is not visible in Fig. 1 because it is concealed by the frame 1, as will be explained later. A front part 9a of the drive shaft 9, extending longitudinally in front of the gearbox 10 (as seen in the direction of travel), delivers the torque supplied by the gearbox 10 to the front axle 2, on which a corresponding front axle gearbox is provided. The other, rear section 9b of the drive shaft 9 extends from the gearbox 10 to the rear axle 3 and transmits the torque to a rear axle gearbox provided on the rear axle 3. In this way, all-wheel drive can be implemented for the wheel loader. Fig. 2 shows the drive device 8 up close in perspective view. Fig. 3 shows the arrangement of Fig. 2, however from the opposite, rear side. Fig. 4 shows the arrangement of Fig. 2 from below in the installed state, in which the drive device 8 is installed in the frame 1 of the wheel loader. Fig. 2 shows that the gearbox 10 comprises a gear stage arranged in and covered by a gearbox housing 11, wherein the smaller gear (drive pinion) not visible in Fig. 2 is mounted on a motor shaft of an electric motor 12 which is hidden in Fig. 2 by housing parts. The larger gear, which is also not visible because it is installed in the gearbox housing 11, is located below the drive pinion and is supported by a shaft element that serves as the output shaft 13 of the gearbox 10. A cardan joint 14 is flanged to each of the two frontal and rearward ends of the output shaft 13. The front part 9a of the drive shaft 9 connects to these cardan joints, pointing to the left in Fig. 2. Correspondingly, the rear part 9b of the output shaft 13 is also connected via a cardan joint. The rear part 9b of the drive shaft 9 leads to a rear axle gearbox 15. Thus, during assembly, the gearbox 10 can be inserted from above or below together with the electric motor 12. The drive shaft 9 can then be easily flanged to the end faces of the output shaft 13 of the gearbox 10 using the two cardan joints 14. The gearbox housing 11 is fully attached to a motor housing 16 of the electric motor 12 and is thus fully supported by the motor housing 16 or the electric motor 12. Since the output shaft 13, located in the area of ​​the gearbox 10 furthest from the motor shaft, has to absorb considerable forces and torques, which are transmitted to the gearbox housing 11 via the bearings in the gearbox 10, this more distant part of the gearbox housing 11 (the lower part in Fig. 2) is additionally connected to the motor housing 16 via a torque support 17. Part of the torque is thus transmitted directly from the gearbox housing 11 to the motor housing 16. Another part of the forces and torques is also transmitted directly to the motor housing 16 via the torque support 17. The torque support 17 can be designed as a flange, bridge, or tab connecting the lower, freestanding area of ​​the gearbox housing 11 to the motor housing 16. The torque support 17 can be formed integrally with the gearbox housing 11 or the motor housing 16, or it can be attached to the two housings 11 and 16 as a separate component. For example, the gearbox housing 11 can be flanged onto the torque support 17, which in turn is connected to the motor housing 16 via a flange, as shown in Fig. 2. The motor housing 16 is fitted with bearing elements 18 in the form of angles. The bearing elements 18 can be integrally connected to the motor housing 16. Alternatively, they can be flanged to the end faces of the motor housing 16, as shown in Fig. 2. In total, four bearing elements 18 are realized in this way, as can be seen from Fig. 2, Fig. 3 to Fig. 4. The four bearing elements 18 are particularly visible in Fig. 4, which shows the underside view. Vibration decoupling elements 19 in the form of rubber buffers are arranged on the bearing elements 18, which in turn can be attached to the frame 1 of the work vehicle. These attachment points of the bearing elements 18 are also referred to as bearing points. The design of the drive unit 8 means that the electric motor 12 alone, with its motor housing 16, absorbs bearing forces that are guided in the frame 1 of the wheel loader. The gearbox 10, in turn, is supported on the motor housing 16 via the gearbox housing 11 and the torque arm 17. Thus, the motor housing 16 forms the load-bearing structure. Fig. 3 shows a braking device 20, which is flanged to the end of the electric motor 12 facing away from the gearbox 10. It acts directly on the motor shaft and can thus bring the electric motor 12 to an immediate standstill. The braking device 20 can, for example, be a spring-applied brake in which, when de-energized, a spring assembly exerts a force on a brake element, which is then pressed against a brake pad. When energized, the braking device 20 is released, allowing the motor shaft of the electric motor 12 to rotate. Since the brake device 20 is also flanged to the motor housing 16, it forms a structural unit with the motor 12, together with the gearbox 10. The entire drive unit, comprising the electric motor 12, the gearbox 10, and the brake assembly 20, is supported solely by the motor housing 16 and thus by the four bearing elements 18. No additional bearing points are provided. This allows the drive unit 8 to be mounted in a virtually stress-free state, without statically indeterminate bearings and therefore without prestressing. From Fig. 2, Fig. 3 to Fig. 4 it can be seen that the drive shaft 9 extends below the electric motor 12. In Fig. 4 a second electric motor can also be seen as working motor 21. The electric motor 12 serves as a drive motor to set the wheels on the front axle 2 and rear axle 3 in motion and to move the wheel loader. The working motor 21, on the other hand, serves to drive a hydraulic pump 22 and thus to generate the hydraulic pressure required for performing work movements. The hydraulic pump 22 is therefore part of a hydraulic system that, for example, serves to lift the lifting device 4 or can also be used to operate other hydraulic tools.

Claims

Drive device (8) for a work vehicle, comprising: an electric motor (12) with a motor shaft and a motor housing (16); and a gearbox (10) with a gearbox housing (11); wherein: the gearbox (10) has an output shaft (13) whose axis of rotation is aligned with the axis of rotation of at least one component (14) of a drive shaft (9) of the work vehicle; the output shaft (13) is designed so that the component (14) of the drive shaft (9) can be coupled to it; the gearbox housing (11) and the motor housing (16) are connected to form a single structural unit; the axis of rotation of the drive shaft (9) and the axis of rotation of the motor shaft are parallel to each other; the electric motor (12) is arranged above the drive shaft (9); a braking device (20) is provided which is arranged coaxially to the motor shaft; and wherein the braking device (20) is attached to the motor housing (16). Drive device according to claim 1, wherein the gearbox housing (11) is attached to the motor housing (16) in such a way that the motor housing (16) supports the gearbox housing (11); and wherein the motor housing (16) can be mounted in a provided installation space in the work vehicle via a motor mounting (18). Drive device according to one of the preceding claims, wherein a flange and / or a torque support (17) is provided between the gearbox housing (11) and the motor housing (16). Drive device according to claim 2 or according to claim 2 and claim 3, wherein - the motor bearing (18) is formed on the motor housing (16); - the motor bearing (18) has at least three, in particular four bearing points which are connected to the motor housing (16) via connecting elements; and wherein - the bearing points each have a vibration decoupling device (19). Drive device according to claim 1, wherein the motor housing (16) is attached to the gearbox housing (11) in such a way that the gearbox housing (11) supports the motor housing (16); and wherein the gearbox housing (11) is attached via a gearbox bearing in a provided installation space in the work vehicle. Drive device according to one of the preceding claims, wherein the transmission has a drive pinion whose axis of rotation is coaxial with the axis of rotation of the motor shaft. Work vehicle with a drive device according to one of the preceding claims, and with at least two wheel axles, wherein one of the wheel axles is a front axle (2) and one of the wheel axles is a rear axle (3); and with a drive shaft (9) extending in the longitudinal direction of the work vehicle. Work vehicle according to claim 7, wherein the two wheel axles (2, 3) are rigidly arranged relative to each other; and wherein the drive device (8) is arranged in a space selected from the group space between the two wheel axles (2, 3), space at the front axle (2), space at the rear axle (3). Work vehicle according to claim 7, wherein the work vehicle is articulated such that the two wheel axles (2, 3) are arranged to pivot relative to each other. A work vehicle according to one of claims 7 to 9, comprising a front carriage and a rear carriage, wherein a joint is arranged between the front carriage and the rear carriage for coupling the front carriage with the rear carriage in such a way that the front carriage and the rear carriage are movable relative to each other about at least one vertical axis of the work vehicle; and wherein the drive device is arranged either on the front carriage or on the rear carriage. Work vehicle according to one of claims 7 to 10, wherein the electric motor (12) is a drive motor; and wherein a further electric motor is provided which serves as a working motor (21) for driving a working hydraulic system.

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