Electrically operated axle drive train

Abstract

The invention relates to an electrically operable axle drive train (1) for a motor vehicle (2), having an electric machine (3) which is drivingly connected to a wet-running transmission arrangement (4) which is arranged in a transmission housing which comprises a transmission sump arranged at the bottom with respect to a line of action of the earth's gravity, in which a hydraulic fluid collects during operation of the axle drive train (1), which hydraulic fluid serves in a hydraulic system to supply the electric machine (3) and the wet-running transmission arrangement (4). In order to improve the functionality of the electrically operated axle drive train (1), in particular with regard to its cooling and / or lubrication, at least one additional reservoir for the hydraulic fluid is provided, which is arranged in the transmission housing above the transmission sump with respect to the line of action of the earth's gravity, can be pressurised by means of a hydraulic pump and is sufficiently large to hold a minimum amount of hydraulic fluid required to supply the electric machine (3) and the wet-running transmission arrangement (4).

Description

The invention relates to an electrically operable axle drive train for a motor vehicle, having an electric machine which is drivingly connected to a wet-running transmission arrangement which is arranged in a transmission housing which comprises a transmission sump which is arranged at the bottom with respect to a line of action of a gravity force and in which, during operation of the axle drive train, hydraulic fluid which serves in a hydraulic system for supplying the electric machine and the wet-running transmission arrangement collects.Electric motors are increasingly used for the drive in motor vehicles in order to create alternatives to internal combustion engines that require fossil fuels. In order to improve the suitability of electric drives for all days and in addition to be able to offer users the usual riding comfort, considerable efforts have already been made.A detailed illustration of an electric drive is given in an article of the journal ATZ 113. Vol. 05 / 2011, pages 360-365 of Erik Schneider, Frank Fickl, Bernd Cebulski and Jens Liebold, with the title: High-integration and Flexible Electric Drive Unit for E-vehicles, which certainly forms the closest prior art. In this article, a drive unit for an axle of a vehicle is described, which drive unit comprises an electric motor which is arranged concentrically and coaxially with a bevel gear differential, wherein a shiftable 2-gear planetary gear set is arranged in the power train between electric motor and bevel gear differential, which is also positioned coaxially with the electric motor or the bevel gear differential or spur gear differential. The drive unit is of very compact construction and, owing to the shiftable 2-gear planetary gear set, allows a good compromise between climbing capability, acceleration and energy consumption. Drive units of this type are also referred to as E-axles or electrically operable drive train.From DE 10 2010 048 837 A1, such a drive device with at least one electric motor and at least one planetary differential drivable with a rotor of the electric motor is known, wherein the planetary differential has at least one planet carrier operatively connected to a rotor of the electric motor, first planetary gears and second planetary gears rotatably mounted on the planetary carrier, as well as a first sun gear and a second sun gear, each of which is operatively connected to an output shaft of the planetary differential. The first planetary gears mesh with the first sun gear and each of the second planetary gears mesh with the second sun gear and with one of the first planetary gears. Furthermore, the sun gears are arranged coaxially with a rotation axis of the rotor.In order to ensure the operation and durability of such vehicle transmissions, corresponding oiling or lubrication of toothings and bearings within a planetary transmission must be ensured. From the prior art, there are various approaches to doing this, including, among other things, oil guide plates and / or oil bores which are intended to form a defined oil path for a lubricating oil. In a passively oiled transmission running in an oil bath, the oil is distributed in the transmission by the rotating components, such as planetary stage, gear wheels, etc. Depending on the oil level, the components are partly covered with oil. The oil is then slid on via oil guide plates and / or oil bores to the bearings and / or to the toothing (tooth engagement). Depending on the operating point (low rotational speeds, downhill travel / downhill travel, cornering, etc.), oil level in the transmission, arrangement and / or design of the transmission components, a sufficient oil supply of bearings and toothings is not ensured.Thus, for example, due to driving dynamics situations, such as acceleration, braking or cornering, it can happen that oil which is located in a reservoir of the axle drive train is excited and is conveyed via an overflow into the transmission region for extraction, which can lead to undesired planetary losses in the planetary transmission.German laid-open specification DE 10 2015 221 901 A1 discloses a delivery device for delivering oil from an oil sump to a consumer of an internal combustion engine or of a transmission of a motor vehicle, having an oil pump which can be driven by a mechanical direct drive and by a connectable electric drive, wherein the oil pump has two components which can be moved relative to one another for delivering the oil with a rotor and a rotor part which surrounds the rotor, and the mechanical direct drive is connected to a first of the components which can be moved relative to one another and the connectable electric drive is connected to a second of the components which can be moved relative to one another, wherein a housing has a jacket section open on one side with a large internal cross section for the introduction of the components of the oil pump, and wherein the housing has a housing base or housing cover with a constriction section with a comparatively small internal cross section, and wherein a sealing ring for separating the pressure side of the oil pump from a suction side is arranged at the constriction section.The object of the invention is to improve an electrically operable axle drive train according to the preamble of claim 1 functionally, in particular with regard to its cooling and / or lubrication.The object is achieved in an electrically operable axle drive train for a motor vehicle, having an electric machine which is connected in terms of drive to a wet-running transmission arrangement which is arranged in a transmission housing which comprises a transmission sump arranged at the bottom with respect to a line of action of a gravity force, in which sump, during operation of the axle drive train, a hydraulic fluid which serves in a hydraulic system for supplying the electric machine and the wet-running transmission arrangement is collected, in that at least one additional reservoir for the hydraulic fluid is provided which is arranged above the transmission sump with respect to the line of action of the gravity force in the transmission housing and which reservoir is capable of being pressurized by means of a hydraulic pump and is sufficiently large to accommodate a minimum amount of hydraulic fluid required for supplying the electric machine and the wet-running transmission arrangement. The transmission housing preferably additionally serves to receive the wet-running transmission arrangement for receiving at least one component of the electric machine. The transmission housing can also be combined with a machine housing of the electric machine. The hydraulic fluid may be hydraulic oil. However, it could also be water. The hydraulic fluid extracted from the sump can advantageously be cooled in a corresponding circuit, for example with the aid of a heat exchanger. A pump in the circuit serves, for example, to suck out the hydraulic fluid. During operation of the axle drive train, it has been found that the hydraulic fluid foams in the sump in an undesirable manner. This foaming, also referred to as oil foaming, can result in a wet chamber in the transmission housing being flooded with hydraulic fluid in such a way that a required cooling and / or lubrication function is no longer ensured or is no longer sufficiently ensured. Moreover, foaming results in the heat capacity of the hydraulic fluid being reduced. A higher oil level in the wet chamber of the transmission housing can additionally lead to splashing losses. Moreover, hydraulic fluid can undesirably leak out, for example, via a vent. To represent the additional reservoir in the transmission housing, considerable structural and production-related complexity is deliberately accepted. The additional reservoir advantageously reduces the overall installation space required for the electrically operable axle drive train. In addition, the efficiency during operation of the electrically operable axle drive train can be maximized. This is achieved, among other things, by the fact that undesirable splashing losses can be reduced because the transmission sump can be reduced in size. This advantageously ensures that the moving components become less planar in the oil. Of course, a plurality of additional reservoirs for the hydraulic fluid can also be provided. It is then advantageous, for example, if an applied hydraulic pump is designed in multiple stages. With the single-stage or multistage hydraulic pump, the hydraulic fluid is conveyed from the transmission sump counter to the action of the gravity force of the earth into the at least one additional reservoir. The minimum hydraulic fluid quantity is approximately one third of a volume flow delivered by the hydraulic pump. At a volume flow of ten liters per minute, for example, an oil quantity of two and a half to three and a half liters is recommended. Depending on the design of the hydraulic system and the electric axle drive train, an oil quantity in the order of magnitude of one quarter of the volume flow delivered by the hydraulic pump may also be sufficient. The transmission arrangement may comprise a planetary transmission as described at the beginning. The design of the transmission arrangement is not, however, limited to such a planetary transmission. The transmission arrangement can also comprise a spur gear transmission. The transmission arrangement can generally comprise different types of transmission.A preferred exemplary embodiment of the electrically operable axle drive train is characterized in that the hydraulic pump in the transmission housing is hydraulically connected between the transmission sump and the additional reservoir. With the additional reservoir, a line system is advantageously enlarged on a pressure side of a cooling and / or lubrication circuit in the hydraulic system.A further preferred exemplary embodiment of the electrically operable axle drive train is characterized in that a nonreturn valve is connected upstream of the additional reservoir in the transmission housing, which nonreturn valve prevents the additional reservoir from running out or idling. The check valve leads to lower losses especially in a decoupled state of the E-axle of the motor vehicle. Since idling of the additional reservoir and, if appropriate, of a heat exchanger connected to the additional reservoir is prevented, the hydraulic fluid level in the transmission sump is advantageously lower than in the case of conventional E-axles. This then provides the advantage, for example, that a gear wheel which travels along in the uncoupled state of the electric machine, in particular a so-called finaldrive wheel, causes significantly lower churning losses.A further preferred exemplary embodiment of the electrically operable axle drive train is characterized in that the additional reservoir in the transmission housing is followed by a heat exchanger which represents a fluidic resistance for the hydraulic fluid from the additional reservoir. Both the electric machine and the transmission arrangement can thus be supplied with sufficient pressurized oil.A further preferred exemplary embodiment of the electrically operable axle drive train is characterized in that the additional reservoir is primary-formed in the transmission housing. The additional reservoir is realized in a primary shape in a transmission housing body, for example. A corresponding cavity for the representation of the additional reservoir can be open on at least one side of the transmission housing body. The cavity, which serves to form the additional reservoir in the transmission housing body, can also be open on two sides. For closing the at least one open side of the cavity, which serves to form the additional reservoir, a correspondingly shaped transmission housing cover can be used.A further preferred exemplary embodiment of the electrically operable axle drive train is characterized in that a valve arrangement is integrated into the transmission housing. The valve arrangement comprises, for example, valves which ensure a supply of lubricating and / or cooling points in the transmission housing or in the axle drive train as required. A receiving space for receiving the valve arrangement is advantageously also molded in the transmission housing.A further preferred exemplary embodiment of the electrically operable axle drive train is characterized in that, in addition to the additional reservoir, a pressure accumulator is arranged in the transmission housing. The pressure accumulator is arranged, for example, in the additional reservoir. The pressure accumulator can, however, also be arranged in front of or behind the additional reservoir. The pressure accumulator advantageously serves to smooth out undesired pressure peaks or to delay a pump start-up. The pressure accumulator is advantageously likewise accommodated in a primary-molded cavity of the transmission housing.A further preferred exemplary embodiment of the electrically operable axle drive train is characterized in that, in addition to the additional reservoir, a pressure compensation element is arranged in the transmission housing. The pressure compensation element may comprise, for example, a spring-biased piston. The pressure compensation element enables, for example, a more frequent deactivation of the hydraulic pump. If necessary, the pressure compensation element and / or the above-described pressure accumulator also enables pulsating operation of the hydraulic pump. The pressure equalization element is advantageously likewise accommodated in a primary-molded cavity of the transmission housing.A further preferred exemplary embodiment of the electrically operable axle drive train is characterized in that, in addition to the additional reservoir, a defoaming device is arranged in the transmission housing. The defoaming device is especially advantageously integrated into the additional reservoir. The defoaming device may comprise, for example, a labyrinth-like guide structure for the hydraulic fluid in the additional reservoir. Air can thereby be advantageously separated from foamed hydraulic fluid.The invention further relates to a transmission housing, a hydraulic pump, a nonreturn valve, a heat exchanger, a valve arrangement, a pressure accumulator, a pressure compensation element and / or a defoaming device for an electrical axle drive train described above. The parts mentioned can be purchased separately.Further advantages, features and details of the invention will become apparent from the following description, in which various exemplary embodiments are described in detail with reference to the drawing. The following are shown: FIG. 1 shows a motor vehicle having an electric axle drive train in a schematic block switching view; FIG. 2 shows a schematic illustration of a hydraulic system for supplying an electric machine and a wet-running transmission arrangement of the electric axle drive train from FIG. 1 ; FIG. 3 shows a perspective and partially transparent illustration of a transmission housing into which the hydraulic system illustrated in FIG. 2 is integrated; and FIG. 4 shows a similar illustration as in FIG. 3 from another perspective.FIG. 1 shows an electrically operable axle drive train 1 in a motor vehicle 2, comprising an electric machine 3 and a transmission arrangement 4 coupled to the electric machine 3, which forms a structural unit with the electric machine 3. The transmission arrangement 4 comprises a wet-running planetary transmission 5 with an internally toothed ring gear 6, as is also outlined in FIG. 2.The electric machine 3 and the wet-running transmission arrangement 4 of the electrically operable axle drive train 1 illustrated in FIG. 1 are incorporated into a hydraulic system 12, which is schematically illustrated in FIG. 2. The hydraulic system 12 comprises a transmission sump 11 for a hydraulic fluid. The hydraulic fluid is, for example, oil or water. For the sake of simplicity, the hydraulic fluid is usually referred to below as oil.The oil contained in the transmission sump 11 is suctioned off via a hydraulic pump 15. The oil extracted from the transmission sump 11 is conveyed by the hydraulic pump 15 via a check valve 16 into an additional reservoir 14, which, with respect to the line of action of a gravity force, which is indicated in FIG. 3 by an arrow 13, is arranged above the transmission sump 11.The transmission sump 11 is arranged at the lowest point of the hydraulic system 12 with respect to the line of action of the gravity force, which is designated by 13 in FIG. 3. This ensures that oil can always be drawn in from the transmission sump 11 by means of the hydraulic pump 15. The additional reservoir 14 intentionally increases a line arrangement of the hydraulic system 12 indicated only by arrows on a pressure side of a cooling and / or lubrication circuit shown with the hydraulic system 12.The check valve 16 is disposed between the hydraulic pump 15 and the auxiliary reservoir 14. The optional check valve 16 advantageously prevents the additional reservoir 14 from idling.The nonreturn valve 16 provides, inter alia, the advantage that, in the operation of the electrically operable axle drive train, which is also referred to simply as an E-axle for short, the hydraulic pump 15 ideally does not have to be operated when the E-axle is decoupled from the drive. Energy for operating the hydraulic pump 15 can thus be saved.In this case, the nonreturn valve 16 prevents the additional reservoir 14 and a downstream heat exchanger 17 from idling. A final gear wheel, which travels along in the uncoupled state of the E-axis and is also referred to as final drive wheel, then causes lower churning losses.The heat exchanger 17 is connected downstream of the additional reservoir 14 in the hydraulic system 12. Two horizontal arrows 24, 25 indicate that the hydraulic fluid in the heat exchanger 17 is cooled via a cooling circuit. The electric machine 3 and the wet-running transmission arrangement 4 are connected downstream of the heat exchanger 17 in the hydraulic system 12. The electric machine 3 and the wet running transmission arrangement 4 are connected in parallel in the hydraulic system 12.FIGS. 3 and 4 show a transmission housing 10 in perspective and partially transparently at various viewing angles. The transmission housing 10 comprises the wet-running transmission arrangement 4 and, depending on the embodiment, advantageously also the electric machine 3 or at least one component of the electric machine 3.The transmission housing 10 comprises a housing body 18, in which both the transmission sump 11 and the additional reservoir 14 are advantageously integrated. The housing body 18 is formed in a primary shape, preferably by casting. To simplify production, the additional reservoir 14 is accommodated in a cavity 26 which is provided with a draft angle. The draft angle is realized, for example, in that the cavity 26 in FIG. 3 narrows to the left.The transmission sump 11, the hydraulic pump 15 and the check valve 16 are only symbolically indicated in FIG. 3. Likewise symbolically indicated in FIGS. 3 and 4 are a valve arrangement 19, a pressure accumulator 20, a pressure compensation element 21 and a defoaming device 22. Thus, a multifunctional housing body 18 of the transmission housing 10 that can be produced cost-effectively is created.List of reference characters1 Axle drive train 2 Motor vehicle 3 Electric machine 4 Transmission arrangement 5 Planetary transmission 10 Transmission housing 11 Transmission sump 12 Hydraulic system 13 Gravity force 14 Additional reservoir 15 Hydraulic pump 16 Nonreturn valve 17 Heat exchanger 18 Housing body 19 Valve arrangement 20 Pressure accumulator 21 Pressure compensation element 22 Defoaming device 23 Primary-formed cavity 24 Arrow 25 Arrow 26 CavityReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2010 048 837 A1

[0004] DE 10 2015 221 901 A1

[0007] Cited Non-Patent LiteratureJournal ATZ 113. Vol. 05 / 2011, pages 360-365 of Erik Schneider, Frank Fickl, Bernd Cebulski and

[0003]

Claims

Electrically operable axle drive train (1) for a motor vehicle (2), having an electric machine (3) which is connected in terms of drive to a wet-running transmission arrangement (4) which is arranged in a transmission housing (10) which comprises a transmission sump (11) arranged at the bottom with respect to a line of action of a gravity force (13), in which hydraulic fluid collects during operation of the axle drive train (1), which hydraulic fluid is used in a hydraulic system (12) for supplying the electric machine (3) and the wet-running transmission arrangement (4), characterized in that at least one additional reservoir (14) for the hydraulic fluid is provided in the transmission housing (10) above the transmission sump (11) with respect to the line of action of the gravity force (13), which reservoir can be pressurized by means of a hydraulic pump (15) and is sufficiently large, to take in a minimum amount of hydraulic fluid required for supplying the electric machine (3) and the wet-running transmission arrangement (4).Electrically operable axle drive train according to Claim 1, characterized in that the hydraulic pump (15) in the transmission housing (10) is hydraulically connected between the transmission sump (11) and the additional reservoir (14).Electrically operable axle drive train according to one of the preceding claims, characterized in that the additional reservoir (14) in the transmission housing (10) is preceded by a nonreturn valve (16) which prevents the additional reservoir (14) from running out or idling.Electrically operable axle drive train according to one of the preceding claims, characterized in that the additional reservoir (14) in the transmission housing (10) is followed by a heat exchanger (17) which represents a fluidic resistance for the hydraulic fluid from the additional reservoir (14).Electrically operable axle drive train according to one of the preceding claims, characterized in that the additional reservoir (14) is rough-formed in the transmission housing (10).Electrically operable axle drive train according to one of the preceding claims, characterized in that a valve arrangement (19) is integrated into the transmission housing (10).Electrically operable axle drive train according to one of the preceding claims, characterized in that, in addition to the additional reservoir (14), a pressure accumulator (20) is arranged in the transmission housing (10).Electrically operable axle drive train according to one of the preceding claims, characterized in that, in addition to the additional reservoir (14), a pressure compensation element (21) is arranged in the transmission housing (10).Electrically operable axle drive train according to one of the preceding claims, characterized in that, in addition to the additional reservoir (14), a defoaming device (22) is arranged in the transmission housing (10).Transmission housing (10), hydraulic pump (15), nonreturn valve (16), heat exchanger (17), valve arrangement (19), pressure accumulator (20), pressure compensation element (21) and / or defoaming device (22) for an electric axle drive train (1) according to one of the preceding claims.

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