Motor vehicle with all-wheel drive, comprising a driven front and rear axle, an internal combustion engine and an electric motor

Abstract

Motor vehicle comprising a driven front axle (2), a driven rear axle (3), an internal combustion engine (4), an automatic transmission (5) coupled thereto, and a switchable torque distribution stage (6) coupled to the automatic transmission (5) and enabling all-wheel drive, which is coupled or can be coupled to the front axle (2) and the rear axle (3), wherein a torque generated by the internal combustion engine (4) can be directed by the torque distribution stage (6) either to the front or the rear axle (2, 3) or distributed to both axles (2, 3), wherein an electric motor (10) is provided which is coupled to the rear axle (3), wherein a torque generated by the electric motor (10) which is applied to the rear axle (3) is applied via the coupling to the torque distribution stage (6) and can additionally be applied by the latter to the front axle (2),and that a freewheel (15) is provided between the automatic transmission (5) and the torque distribution stage (6), by means of which the automatic transmission (5) is decoupled from the torque distribution stage (6) when the internal combustion engine (4) is not running and the axle is driven by the electric motor (10), wherein the torque distribution stage (6) can be switched such that in purely electric operation of the motor vehicle (1) either only the rear axle (3) is driven or the torque supplied by the rear axle (3) to the torque distribution stage (6) is also transmitted proportionally to the front axle (2).

Description

[0001] The invention relates to a motor vehicle, comprising a drivable front axle, a drivable rear axle, an internal combustion engine, an automatic transmission coupled thereto, and a torque distribution stage coupled to the automatic transmission, switchable and enabling all-wheel drive, which is coupled or can be coupled to the front axle and the rear axle, wherein a torque generated by the internal combustion engine can be directed by the torque distribution stage either to the front or the rear axle or distributed over both axles.

[0002] Such a motor vehicle with a conventional drivetrain, into which a conventional automatic transmission, usually also called a multi-step automatic transmission, is engaged, and to which a torque distribution stage, i.e. a switchable all-wheel drive stage, is connected, makes it possible to direct the torque generated by the internal combustion engine and via the automatic transmission, which has seven or eight gear stages, and the downstream torque distribution stage either to just one axle, i.e. either the front axle or the rear axle depending on the drive type, or to the front and rear axles, thus resulting in all-wheel drive. Using the torque distribution stage, the respective proportions directed to the front and rear axles in all-wheel drive operation can be set to be equal or different. This allows the driver to select different drive modes.

[0003] The technological background for the present invention is DE 10 2014 201 355 A1, for example. This document discloses a drive arrangement for a motor vehicle with generator devices, an internal combustion engine, and a main transmission that can be coupled thereto. A transfer case is connected downstream of the main transmission, by means of which the motor vehicle can be driven on multiple axles via the internal combustion engine. This document describes several operating modes, such as an overrun fuel cut-off mode and an engine operating mode, in which the aforementioned components of the motor vehicle are operated in corresponding coupling and operating states to enable highly efficient recuperation of the motor vehicle and energetically advantageous operation of the internal combustion engine.

[0004] A switchable transfer case for distributing a drive torque to two axles of a motor vehicle with all-wheel drive, in which a hybrid drive can be implemented, is known from DE 10 2014 225 337 A1.

[0005] Further prior art in which drive concepts for all-wheel drives are described are AT 007 997 U1 and US 2017 / 0 326 964 A1.

[0006] Motor vehicles are increasingly being equipped with an electric drive, with what is preferably a so-called electric rear axle being provided, i.e. a complete rear axle comprising a differential and an electric motor that directly drives the rear axle. However, the integration of such an electric rear axle is not possible in a motor vehicle with a conventional drivetrain as described above, in which, as explained, the torque distribution stage is connected downstream of the automatic transmission. In order to enable all-wheel drive via the electric rear axle, it must be coupled to the torque distribution stage in order to proportionally direct the torque generated by the electric motor, which is primarily applied to the rear axle, to the front axle so that this is also actively driven.However, since the torque distribution stage is linked to the upstream automatic transmission, with purely electric drive, the automatic transmission driven by the internal combustion engine and the coupled rear axle are connected to the same element of the torque distribution stage, meaning that the automatic transmission is also driven during purely electric driving, i.e., it is dragged along or loaded in the thrust direction. This is because during purely electric driving, the internal combustion engine is not operating. In the best case scenario, this only leads to a drag torque, which represents a loss of power and negatively impacts the electric range. Much more serious, however, is that the transmission is not supplied with lubricant during purely electric driving, since the internal combustion engine is not operating.In a conventional drivetrain of the type described above, the automatic transmission is supplied with lubricant from the internal combustion engine, meaning that the internal combustion engine provides the hydraulic supply and the lubricant is delivered to the transmission with sufficient pressure and in sufficient quantity. However, this lubricant supply is not guaranteed, so that in this case, long journeys can even lead to transmission damage.

[0007] The invention is therefore based on the problem of providing a motor vehicle which is improved compared to the aforementioned.

[0008] To solve this problem, according to the invention, an electric machine is provided in a motor vehicle of the type mentioned at the outset, which is coupled to the rear axle, wherein a torque generated by the electric machine, which is applied to the rear axle, is applied via the coupling to the torque distribution stage and can be applied from there additionally to the front axle, and wherein a freewheel is provided between the automatic transmission and the torque distribution stage, via which freewheel the automatic transmission is decoupled from the torque distribution stage via the electric machine when the internal combustion engine is not running and an axle drive is being provided, wherein the torque distribution stage can be switched in such a way that in purely electric operation of the motor vehicle either only the rear axle is driven or the torque applied by the rear axle to the torque distribution stage is also transmitted proportionally to the front axle.

[0009] The motor vehicle according to the invention features an electric rear axle, in which the electric motor is an integral part of the rear axle, along with the rear axle differential. To fundamentally enable all-wheel drive even in electric mode, the electric motor is permanently coupled to the torque distribution stage. This means that there is a permanent mechanical coupling of the electric motor or its output to a corresponding input element of the torque distribution stage, e.g., via a corresponding cardan shaft that couples the rear axle differential to the torque distribution stage.

[0010] In purely electric mode, only the rear axle can be driven if the switchable torque distribution stage is not switched to all-wheel drive. If all-wheel drive is desired, the torque distribution stage is switched accordingly, and the torque delivered from the rear axle to the torque distribution stage is also proportionally transmitted to the front axle.

[0011] To prevent the automatic transmission from dragging along in the disadvantageous manner described above in both different operating modes, the invention provides a freewheel located between the automatic transmission and the torque distribution stage. This one-way freewheel makes it possible to decouple the automatic transmission from the torque distribution stage in purely electric driving mode. This is because the input element of the torque distribution stage, which is acted upon by the torque coming from the rear axle in electric driving mode, is also coupled to the automatic transmission so that the engine-side torque can be transmitted to the rear axle via the automatic transmission and the torque distribution stage during engine operation.According to the invention, however, this coupling is now guided via the intermediate freewheel, which operates in such a way that it decouples the torque distribution stage from the automatic transmission when the internal combustion engine is not operating or is decoupled from the automatic transmission, so that the rear axle torque applied to the torque distribution stage cannot be guided to the automatic transmission due to the decoupling.

[0012] This decoupling now makes the "electrification" of a conventional drive train possible, as it allows both internal combustion engine operation and electric motor operation without adversely affecting the automatic transmission. In pure internal combustion engine operation, the freewheel has a coupling effect, meaning that the torque from the internal combustion engine is transferred to the torque distribution stage, which, depending on the drive type, is then directed to either the front or rear axle, or to both axles in the case of all-wheel drive. Because the torque is directed via the automatic transmission and the internal combustion engine is operating, a corresponding automatic lubricant supply to the transmission is guaranteed. In pure electric operation, however, the automatic transmission is decoupled, so that it is not dragged along and therefore cannot be damaged due to the lack of lubricant supply.However, in mixed operation, when both the internal combustion engine and the electric motor are operating, the automatic transmission transmits engine-side torque via the coupling freewheel to the torque stage, which also receives the torque generated on the rear axle. The resulting total torque is then distributed via the torque distribution stage in all-wheel drive. Since the internal combustion engine is operating and therefore both delivers torque and operates the hydraulic system, an automatic lubricant supply to the transmission is ensured.

[0013] The freewheel itself, the central component that ensures the situation-dependent coupling, is either a roller type freewheel or a sprag type freewheel. Such a roller type or sprag type freewheel has the corresponding roller type or sprag type on the inner part of the freewheel coupled to the transmission output, while the outer part of the freewheel is coupled to the corresponding input element of the torque distribution stage. In one direction of rotation, the outer part can be rotated relative to the inner part without mechanical coupling; in the other direction of rotation, a corresponding mechanical, torque-stable coupling is established directly.When the internal combustion engine is engaged, i.e., when it delivers torque to the automatic transmission, the transmission output shaft inevitably rotates, and with it the inner freewheel, immediately creating a mechanical coupling to the outer part, and the supplied torque is passed on to the torque distribution stage. In pure internal combustion engine operation, the internal combustion engine torque is the only torque present. In additional electric motor operation, the internal combustion engine torque, together with the electric motor torque, contributes to the total torque, which is then distributed via the torque distribution stage when it is switched accordingly, or acts together with the electric motor torque solely on the driven rear axle.

[0014] The automatic transmission is conveniently coupled to the torque distribution stage via a hollow shaft. For this purpose, the transmission output is coupled to the hollow shaft via a toothed system, which is coupled to an input element of the torque distribution stage via the freewheel. The hollow shaft allows a central, rotationally symmetrical coupling to the input element of the torque distribution stage, for example, an outer disk carrier of a multi-disk clutch, which will be discussed below. The hollow shaft itself is coupled or connected to the inner part of the freewheel, while the outer part of the freewheel is coupled to the input element of the torque distribution stage.

[0015] The input element itself is coupled to an output element within the torque distribution stage, or rather, forms this output element at the output of the distribution stage, via which output element the torque distribution stage is coupled to a propeller shaft connected to the rear axle. The output element therefore transmits the torque generated by the combustion engine to the rear axle when the drive is purely internal combustion engine-side. At the same time, it also acts as an input element for the electric motor torque delivered to the rear axle.

[0016] The torque distribution stage itself is preferably a multi-plate clutch or comprises one. Such a multi-plate clutch, also called a hang-on clutch, allows the front axle to be easily coupled to the rear axle drive. Such a multi-plate clutch typically has at least one outer plate carrier, which represents the input element for the engine-side torque and also for the electric motor-side torque. The multi-plate clutch also includes an inner plate carrier, which is coupled via a shaft to a drive shaft running to the front axle differential, so that the torque to be distributed is transmitted to the front axle via this.Corresponding plates are arranged on the outer plate carrier and the inner plate carrier, which engage with each other, whereby this plate pack can be compressed axially via a suitable actuating means, for example a hydraulic CSC actuator (CSC = Concentric Slave Cylinder), in order to transmit the torque introduced at the input element, i.e. the outer plate carrier, to the inner plate carrier in a frictionally engaged, compressed state.

[0017] This outer disk carrier therefore represents the input element of the torque distribution stage. The disk carrier is coupled to the previously described hollow shaft via the freewheel. A mechanical, rotationally fixed connection is only established when the hollow shaft is actively rotating, and thus when the engine is running. Otherwise, the freewheel acts as a decoupling element. The outer disk carrier itself is further coupled to an output shaft, forming the output element, from which the propeller shaft leading to the rear axle is attached.

[0018] Further advantages and details of the present invention will become apparent from the embodiment described below and from the drawing.

[0019] The figure shows a motor vehicle 1 according to the invention, comprising a drivable front axle 2 and a drivable rear axle 3. Furthermore, an internal combustion engine 4 and an automatic transmission 5 coupled to it, i.e. a stepped automatic transmission having, for example, seven or eight gear stages, are provided.

[0020] Downstream of the automatic transmission 5 is a torque distribution stage 6, via which torque can be directed either only to the front axle 2 or the rear axle 3, depending on the defined drive type of the motor vehicle, or, in the context of an all-wheel drive, to both axles 2, 3. For this purpose, the torque distribution stage 6 is coupled to a front axle differential 7, which will be described in detail below, and via a cardan shaft 8 to a rear axle differential 9, which will also be described in detail below.

[0021] The rear axle 3 itself is an electric rear axle, which has an electric motor 10 as a fixed axle component and a downstream electric motor transmission 11 which is coupled to the differential 9.

[0022] The specific design of the entire drive train enables, on the one hand, a pure combustion engine drive via the rear axle 3 or an combustion engine-driven all-wheel drive via the front axle 2 and the rear axle 3. In addition, a purely electric drive only via the rear axle 3 as well as an all-wheel drive via the rear axle 3 and the front axle 2 are also possible. With a purely electric drive, be it a rear-axle drive or an all-wheel drive, it is ensured in all cases that the automatic transmission 5 is decoupled from the torque distribution stage 6, thus is not dragged along when the internal combustion engine 4 is not operating.To enable this, an output shaft 12 of the automatic transmission 5 is coupled via a gear stage 13 to a hollow shaft 14, which in turn is connected via a freewheel 15, preferably a roller or sprag freewheel, to an input member 16, here in the form of an outer disk carrier 17, of the torque distribution stage 6, designed as a multi-disk clutch 18. The outer disk carrier 17 is connected to an output shaft 19 of the torque distribution stage, which in turn is coupled to the cardan shaft 8, which in turn is coupled to the rear axle differential 9.

[0023] The multi-plate clutch 18 further comprises an inner plate carrier 20. Outer plates 21 are provided axially displaceably on the outer plate carrier 17, and inner plates 22 are provided axially displaceably on the inner plate carrier 20, the axial displacement being represented by the two arrows P. This plate pack can therefore be axially compressed by an actuating means, e.g. a hydraulically operated CSC, and moved against an abutment, so that the plates 21, 22 come into frictional engagement and a torque applied to the rotating outer plate carrier 17 can be transmitted to the inner plate carrier 20.

[0024] The inner disk carrier 20 is coupled to an output shaft 23, which in turn is coupled via a toothed stage 24 to a shaft 25 running to the front axle differential 7, via which the torque, i.e. the drive, is transmitted to the front axle 2.

[0025] The cardan shaft 8 is connected to the rear axle differential 9 as described, so that a torque supplied by the automatic transmission 5 can be transmitted to the rear axle differential 9, via which the rear axle 3 can be driven.

[0026] The electric motor 10, of which the stator 26 and the rotor 27 are indicated here as examples, is connected by its output shaft 28 via a gearing 29 to an intermediate shaft 30, which runs to the actual rear axle transmission 31, which in turn is coupled to the differential 9. This allows the torque generated by the electric motor 10 to be transmitted to the wheels.

[0027] As the figure shows, the automatic transmission 5 as well as the gear stages 13 and 24, the hollow shaft 14, the drive shaft 25, and the differential 27 can be integrated into a compact housing, which is flanged to the internal combustion engine 4 on the one hand, and to which the torque distribution stage 6 is flanged with its housing on the other. Likewise, the electric motor transmission 11 with its gear stage 31 and the rear axle differential 9, as a compact component of the electric rear axle 3, are integrated into a common housing, to which the electric motor 10 and its housing are flanged, resulting in a very compact axle design.

[0028] The central element that enables variable internal combustion engine and electric motor drive with simultaneous all-wheel engagement in conjunction with decoupling of an automatic transmission 5 is the freewheel 15. As described, this is a clamping roller or sprag freewheel. The inner part of the freewheel 15, on which the clamping rollers or sprags are arranged, is connected to the hollow shaft 14, while the outer part of the freewheel 15 is coupled to the input member 16, in this case the outer disk carrier 17. The arrangement is such that the freewheel 15 closes when the hollow shaft 14 is actively driven via the automatic transmission 5 while the internal combustion engine 4 is running. The given torque is transmitted via the outer disk carrier 17 to the output shaft 19 and thus via the cardan shaft 8 to the differential 9, so that the rear axle 3 is driven via the internal combustion engine 4.

[0029] If all-wheel drive is desired, the multi-plate clutch 18 is actuated, the plate pack of outer plates 21 and inner plates 22 is compressed and brought into frictional engagement, so that the torque supplied by the combustion engine is also transmitted to the inner plate carrier 20 and from there via the output shaft 24 and the drive shaft 25 to the front axle differential 7 and via this to the front wheels.

[0030] In pure electric motor mode, i.e. when the internal combustion engine 4 is not running, the torque is generated solely by the electric motor 10 and transmitted via the electric motor transmission 11 to the differential 9 and via this to the rear wheels. Due to the coupling of the propshaft 8 with the differential 9, the propshaft 8 also rotates and, due to its connection to the output shaft 19, the outer disk carrier 17 inevitably also rotates. However, this is decoupled from the stationary hollow shaft 14 via the freewheel 15, i.e. the hollow shaft 14 is not driven via this and thus the automatic transmission 5 is not dragged either. A pure electric motor drive is therefore only possible via the rear axle 3, without the automatic transmission 5 being subjected to overrun load at the same time.

[0031] If all-wheel drive is required with a purely electric drive, it is also easily possible to compress the disk set consisting of outer disks 21 and inner disks 22 axially against the abutment and bring them into frictional engagement, so that the previously stationary inner disk carrier 20 is also driven in rotation. The then branched torque is then transmitted to the front axle 2 via the output shaft 23 and the drive shaft 25. The proportion of the torque applied to the front axle and the torque applied to the rear axle can be adjusted accordingly, similar to a pure internal combustion engine drive.

[0032] However, mixed operation with internal combustion engine drive and electric motor drive is also possible. This means that it is possible to engage the internal combustion engine 4 with electric motor drive, so that it supplies torque to the automatic transmission 5, which transmits the torque via the hollow shaft 14. Because the hollow shaft is actively rotating, a frictional connection automatically occurs within the freewheel 15, meaning that the inner part essentially overtakes the outer part and an additional torque is applied, which is in addition to the torque from the electric motor side. Consequently, there is a total torque from the internal combustion engine side and the electric motor side, which is then applied to the torque distribution stage 6. This can either be branched off to both axles 2, 3, i.e., all-wheel drive is provided. However, it is also conceivable to then only apply the total torque to the rear axle 3.

[0033] The inventive decoupling of the automatic transmission therefore enables purely electric driving, since the transmission of this conventional drive train remains stationary, decoupled via the freewheel 15. This prevents damage to the transmission, which, since the internal combustion engine 4 is not operating, is not actively supplied with lubricant. A further advantage is that the torque of the electric rear axle 3 generally does not pass through the automatic transmission, since even with electric all-wheel drive, it is distributed beforehand via the torque distribution stage 6. This means that the transmission's performance only needs to be designed with reference to the torque delivered by the internal combustion engine 4.The freewheel decoupling according to the invention is also advantageous in terms of efficiency, i.e., drive efficiency, since the automatic transmission is not dragged along with a purely electric drive, which would lead to a relatively high drag torque and thus a reduction in the electric range. Instead, only the freewheel 15 with its outer part needs to be dragged along, which, however, does not result in any significant drag torque.

[0034] Therefore, the inventive design of this drive train or the inventively provided integration of the freewheel 15 between the automatic transmission 5 and the torque distribution stage 6 allows the combination of a conventional drive train comprising an internal combustion engine and a conventional automatic transmission 5 as well as a conventional torque distribution stage with an electric rear axle, without resulting in any disadvantages with regard to the automatic transmission 5.

[0035] In addition, all forward and reverse movements can be realized. During purely forward travel via the internal combustion engine, the freewheel is closed, meaning it engages and the torque is transmitted. Reverse travel via the internal combustion engine is not possible, as the freewheel is open in this case, meaning it is decoupled, even though the hollow shaft 14 rotates. However, since it would rotate in the opposite direction to reverse travel, the freewheel does not engage.

[0036] When the electric motor is used purely for forward drive, the freewheel is engaged, which leads to the decoupling of the automatic transmission, which is not supplied with lubricant, as described in the invention. Reversing via the electric motor is also possible, but in this case, the freewheel is closed due to the reversed rotation direction of the input element of the torque distribution stage, meaning it couples the automatic transmission, which is exceptionally dragged along. However, this is not disadvantageous here, since such reversing only occurs for a very short time and at low speed, thus eliminating any transmission interference.

[0037] In hybrid drive systems that combine both the internal combustion engine and the electric motor, the freewheel is necessarily engaged, as the torque is initiated and transmitted by the internal combustion engine. If reversing is required in hybrid mode, the internal combustion engine is briefly shut down, and reversing is achieved solely by the electric motor.

Claims

[1] Motor vehicle, comprising a drivable front axle (2), a drivable rear axle (3), an internal combustion engine (4), an automatic transmission (5) coupled thereto, and a switchable torque distribution stage (6) coupled to the automatic transmission (5) and enabling all-wheel drive, which is coupled or can be coupled to the front axle (2) and the rear axle (3), wherein a torque generated by the internal combustion engine (4) can be directed by the torque distribution stage (6) either to the front or the rear axle (2, 3) or distributed over both axles (2, 3), wherein an electric machine (10) is provided which is coupled to the rear axle (3), wherein a torque generated by the electric machine (10) which is applied to the rear axle (3) is applied via the coupling to the torque distribution stage (6) and can be applied by the latter additionally to the front axle (2),and that a freewheel (15) is provided between the automatic transmission (5) and the torque distribution stage (6), via which freewheel the automatic transmission (5) is decoupled from the torque distribution stage (6) when the internal combustion engine (4) is not running and an axle drive is via the electric machine (10), wherein the torque distribution stage (6) is switchable in such a way that in a purely electric operation of the motor vehicle (1) either only the rear axle (3) is driven or the torque supplied by the rear axle (3) to the torque distribution stage (6) is also proportionally transmitted to the front axle (2). [2] Motor vehicle according to one of the preceding claims, characterized by that the freewheel (15) is a clamping roller freewheel or a sprag freewheel. [3] Motor vehicle according to claim 1 or 2, characterized bythat a transmission output (12) is coupled via a toothing (13) to a hollow shaft (14) which is coupled via the freewheel (15) to an input member (16) of the torque distribution stage (6). [4] Motor vehicle according to claim 3, characterized by that the input member (16) is coupled to an output member (19) via which the torque distribution stage (6) is coupled to a cardan shaft (8) coupled to the rear axle (3). [5] Motor vehicle according to one of the preceding claims, characterized by that the torque distribution stage (6) is or comprises a multi-plate clutch (18). [6] Motor vehicle according to claim 5 and claim 4, characterized by that the multi-disk clutch (18) has an outer disk carrier (17) which is coupled to the hollow shaft (14) via the freewheel (15) and which is coupled to an output shaft (19) forming the output member.

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