Motor vehicle with axle housing

Abstract

The invention relates to a motor vehicle (1) with at least one electric motor (3) arranged in an axle housing (2) for driving the motor vehicle (1). What is essential to the invention is - that a vent line (5) is provided for venting the axle housing (2) by means of negative pressure, - that the vent line (5) is connected via at least one oil separator (6) to a vacuum generating device (7) for generating a vacuum that vents the axle housing (2). This is intended to reduce air friction loss from parts rotating in the axle housing (2).

Description

The present invention relates to a motor vehicle having an electric motor arranged in an axle housing for driving the motor vehicle, according to the preamble of claim 1.US 2010 / 0 079 946 A1 discloses a motor vehicle of the generic type having at least one electric motor for driving the motor vehicle, said electric motor being arranged in an axle housing. In this case, ambient air can be supplied via an air duct to the electric motors arranged in the axle housing and the latter can thereby be cooled. The cooling air can be discharged again into the environment via a vent opening.DE 10 2014 202 233 A1 discloses a motor vehicle having at least one electric motor for driving the motor vehicle.DE 10 2019 103 877 A1 discloses a pump device for lowering the internal pressure in a transmission, equipped with a suction line which leads from a suction point on a connection side to a discharge point on a discharge side, a pump for generating negative pressure at the suction point, a pump drive for driving the pump, an oil separator which is connected upstream or downstream of the pump in the suction line and separates oil contained in the suction flow and returns it to the connection side via a return line.DE 10 2012 111 017 A1 discloses a device for cooling an axle differential of a motor vehicle, comprising an air guide plate for guiding the air flow under the motor vehicle. In order to be able to ensure optimal cooling of the axle differential and at the same time not to increase a coefficient of flow resistance of the motor vehicle, the air guide plate is fastened to the axle differential in such a way that an intrinsic movement of the axle differential brings about an adjustment of the air circuit board.DE 10 2012 203 541 A1 discloses a device for venting and venting an axle housing of a motor vehicle having at least one filter membrane for separating the emerging and entering air from contained liquid, wherein the filter membrane is arranged in a replaceable manner in a filter housing fastened to the axle housing and, in addition, the filter housing has an axle housing-side connection and a surrounding-side connection. This is intended to make it possible to create a device for venting and venting an axle housing, which is cost-effective and at the same time functionally reliable.DE 10 2016 218 774 A1 discloses a motor vehicle having a motor vehicle transmission housing with an oil housing interior which is designed to accommodate an oil-lubricated component and has a ventilation opening which is connected to a ventilation line with a hollow venting body in a fluid-conducting manner.DE 11 2008 003 585 T5 discloses an axle arrangement with a carrier housing arrangement with a carrier housing which defines a chamber with an opening. A differential housing is further provided in the chamber and is rotatably mounted on the carrier housing about a first axis. Heat can be discharged from the carrier housing arrangement via an air duct.JP 2008 128 338 A discloses a control device for an oil level within a transmission housing of a motor vehicle, wherein the control device is controlled as a function of a dynamic pressure generated by a relative wind.In general, in the case of components arranged in the axle housing, for example a differential or electric motors, it is true that these have a poorer efficiency the greater their friction losses.The present invention therefore concerns the problem of specifying an improved or at least one alternative embodiment for a motor vehicle of the generic type, by means of which in particular friction losses can be reduced in an environmentally friendly manner.This problem is solved according to the invention by the subject matter of independent claim 1. Advantageous embodiments are the subject of the dependent claims.The present invention is based on the general idea of generating a negative pressure in an axle housing of an electrically driven motor vehicle and thereby significantly reducing air friction losses of parts rotating in the axle housing, such as regions of an electric motor, which are dependent on the air density of the air surrounding this rotating part. In order to prevent undesired oil mist separation from the axle housing via a venting line into the environment, at least one oil separator, in particular an oil mist separator, is additionally arranged in the venting line, for example a baffle with an oil mist collecting fleece arranged accordingly thereon or an oil mist centrifugal separator or a simple oil mist separating fleece, whereby the friction reduction can additionally be achieved in an environmentally friendly manner, since undesired oil discharge is reliably avoided, at least however minimized. The motor vehicle according to the invention is electrically driven and has at least one electric motor arranged in the axle housing for driving the motor vehicle. According to the invention, a venting line for venting this axle housing by means of reduced pressure is now provided, wherein the axle housing is preferably connected to the environment exclusively via this venting line. In addition, an oil separator and a vacuum generating device for generating the vacuum venting the axle housing are arranged in the region of the venting line. If an interior of the axle housing is connected to the environment exclusively via the venting line, no air can flow in when a negative pressure is generated via the venting line, which would entail a reduction in the negative pressure and thus higher air friction losses. By providing at least one oil separator in the venting line, an undesired oil mist discharge into the environment can additionally be reliably prevented, at least reduced. The oil separator is preferably arranged between the axle housing and the vacuum generating device.In an embodiment not falling under the invention, the vacuum generating device is designed as an electric fan. Such an electric fan offers the great advantage that it can be activated independently of a travel speed of the motor vehicle, so that even at low speeds, the air pressure in the axle housing can be significantly reduced and thus the air friction losses of the parts rotating therein, for example of the electric motor or of a differential, can also be reduced. Such fans are not only cost-effective, but can also be viewed with respect to a required installation space, so that such a fan can be arranged without problems at locations provided for this purpose in the course of the venting line.According to a first alternative embodiment of the invention, the negative pressure generating device is designed as a diffuser, in particular as a rear diffuser. In this case, a driving-speed-dependent and thus dynamic negative pressure is produced via the negative pressure generating device designed as a diffuser, which negative pressure is proportional to the vehicle speed, which is particularly advantageous since the air friction losses of the parts rotating in the axle housing likewise increase with increasing rotational speed, which in turn correlates with an increasing vehicle speed. At comparatively high vehicle speeds, the vacuum generating device designed as a diffuser thus offers the great advantage that a comparatively large vacuum is generated, which significantly reduces the air pressure in the associated axle housing and thus also significantly reduces the air friction losses of the parts rotating therein. At lower vehicle speeds, at which the parts rotating in the axle housing, for example an electric motor, also have lower rotational speeds, the air friction losses of these rotating parts are in any case lower, so that here too a lower negative pressure dependent on the vehicle speed is sufficient. By generating the negative pressure by means of a diffuser, a negative pressure arising under the motor vehicle during driving can be used to evacuate the axle housing and thus also minimize the air friction losses. It is particularly advantageous here that such a diffuser does not have to be electrically wired and is also maintenance-free.In a further advantageous embodiment of the motor vehicle according to the invention, the latter has a front axle housing with at least one electric motor arranged therein and a rear axle housing with at least one electric motor arranged therein, wherein both axle housings are connected to the venting line. In this case, the motor vehicle is thus designed with four-wheel drive, usually all-wheel drive, wherein both venting of the front axle housing and venting of the rear axle housing can take place by the vacuum generating device arranged in the venting line. This makes it possible to reduce the air friction loss of both the front axle housing rotating parts and the rear axle housing rotating parts.Expediently, an oil separator is arranged in the venting line both in the region of the front axle housing and in the region of the rear axle housing. This offers the great advantage that the two oil separators can be made smaller and can thus be used in construction gaps previously present on the underbody.According to a further alternative embodiment of the invention, the ventilation line ends at a vehicle rear or at a rear underbody. In this region, a rear diffuser is usually also arranged, which ensures an increasing negative pressure under the motor vehicle with an increasing travel speed and thus an improved traction. The negative pressure arising in this case can be used for venting the at least one axle housing and thus for reducing the air friction losses of parts rotating in the axle housing.In a further preferred embodiment of the motor vehicle according to the invention, the venting line is formed from plastic, in particular from fiber-reinforced plastic, or from metal. In particular, a design made of plastic, for example of carbon fiber-reinforced plastic, offers both a firm and weight-optimized design, wherein analogously a venting line made of metal, for example of a light metal such as aluminum, is also possible. However, if the motor vehicle according to the invention is driven by electric motor, exhaust pipes are not arranged on its underbody, as was usual hitherto in motor vehicles driven by internal combustion engines, so that a thermal load is dispensed with, which would possibly prevent a venting line made of plastic.According to a further alternative embodiment of the invention, the ventilation line is at least partially incorporated into an underbody of the motor vehicle. This makes it possible to achieve a hidden and protected and aerodynamically optimized arrangement of the ventilation line in the underbody of the motor vehicle according to the invention, as a result of which both a road clearance is increased and a visually appealing accommodation of the ventilation line is made possible. By the at least partial integration of the ventilation line into the underbody of the motor vehicle, a comparatively smooth underbody can additionally be created, which can additionally be covered with an underbody plate, for example, and is thus aerodynamically optimized.In a further particularly preferred embodiment of the motor vehicle according to the invention, the axle housing is connected to an environment exclusively via the vent line. As a result, it is possible, by suctioning air via the venting line, to reduce the air pressure in the axle housing and thereby generate a negative pressure which likewise minimizes the air friction losses during the rotation of the parts in the axle housing. Alternatively, it is of course also conceivable that a supply air line also leads into the axle housing, wherein the supply air line is designed such that although air flows in via the latter on account of the negative pressure generated in the axle housing by means of the negative pressure generating device, only so much that negative pressure reducing air friction losses of the rotating parts remains in the axle housing despite all. This supply air line advantageously allows cooling of the components arranged in the axle housing, for example electric motors, wherein the power thereof can be increased by cooling these electric motors by means of the ambient air flowing in via the supply air line.Further important features and advantages of the invention are evident from the dependent claims, from the drawing and from the associated description of the figures with reference to the drawing.It is understood that the features mentioned above and those still to be explained below can be connected not only in the respectively specified combination, but also in other combinations or alone, without departing from the scope of the invention. The above-mentioned components of a superordinate unit, such as a device, a device or an arrangement, which are designated separately, can form separate components or components of this unit or can be integral regions or sections of this unit, even if this is illustrated differently in the drawings.A preferred exemplary embodiment of the invention is illustrated in the drawing and is explained in more detail in the following description, wherein the same reference numerals refer to the same or similar or functionally the same components.The single FIG. 1 shows a highly schematic view of a motor vehicle according to the invention.According to FIG. 1, a motor vehicle 1 according to the invention has at least one electric motor 3 arranged in an axle housing 2 for driving the motor vehicle 1. In the present case, the motor vehicle 1 according to the invention has both a front axle housing 2 a, as seen in the direction of travel 4, with an electric motor 3 aand a rear axle housing 2 b, as seen in the direction of travel 4, with an associated electric motor 3 b. Furthermore, a venting line 5 for venting the axle housing 2, 2 a, 2 bby means of reduced pressure is provided, wherein the venting line 5 is connected via at least one oil separator 6, 6 a, 6 bto a reduced pressure generating device 7 for generating the reduced pressure venting the axle housing 2, 2 a, 2 b.In the present case, an oil separator 6 ais arranged in the venting line 5 both in the region of the front axle housing 2 a, as seen in the direction of travel 4, and in the case of the rear axle housing 2 b, as seen in the direction of travel 4.The axle housing 2, 2 a, 2 bis preferably connected to the environment exclusively via the vent line 5, so that when the vacuum generating device 7 is active, a vacuum reducing air friction losses of the rotating parts in the axle housing 2, 2 a, 2 bcan be generated comparatively easily. Alternatively, it is of course also conceivable for the respective axle housing 2, 2 a, 2 bto also have an inlet air line, not shown, via which air can be sucked into the respective axle housing 2, 2 a, 2 bwhen a corresponding negative pressure is generated and the electric motor 3, 3 a, 3 barranged therein or further components can thereby be cooled. However, it is important that more air is suctioned out of the axle housing 2, 2 a, 2 bvia the vacuum generating device 7 than can flow out of the environment via the supply air line, since otherwise an effective generation of a vacuum is not possible.Such an oil separator 6, 6 a, 6 bmay be equipped, for example, as a baffle plate, in particular covered with a corresponding nonwoven, but alternatively also as a so-called labyrinth oil separator.According to a first alternative embodiment of the invention, the vacuum generating device 7 is designed as a diffuser 8, in particular as a rear diffuser, in accordance with FIG. 1, but can alternatively also be designed as an electric fan 9. A design of the vacuum generation device 7 as a diffuser 8 offers the great advantage that a driving speed-dependent vacuum generation without further electrically operated components is possible as a result.In principle, the parts rotating in the respective axle housing 2, 2 a, 2 b, for example of the electric motor 3, 3 a, 3 b, have increasingly higher air friction losses with increasing rotational speed, wherein these air friction losses are dependent on the air density of the surrounding air. By venting or even ideally evacuating the axle housings 2, 2 a, 2 b, the parts rotating in the axle housing 2 can rotate almost without air friction loss, whereby the efficiency of the motor vehicle 1 according to the invention can be significantly increased. If the vacuum required for this is generated by a vacuum product device 7 designed as a diffuser 8, the vacuum generated can be increased in proportion to the increasing travel speed, as a result of which a particularly effective reduction of the air friction losses, which are made possible by parts rotating in the axle housing 2, 2 a, 2 b, since these rotating parts also have increasingly high air friction losses with increasing rotational speed, i.e. higher travel speed.According to an embodiment not falling under the invention, the vacuum generating device 7 can also be designed, for example, as an electric fan 9 shown only with a broken line according to FIG. 1, which offers the great advantage that such an electric fan 9 can be controlled individually, for example with a control device, and is thereby capable of also generating a vacuum in the respective axle housings 2, 2 a, 2 bdependently of the travel speed of the motor vehicle 1. Since fans 9 of this type usually not only have a compact construction but are also cost-effective, this represents an attractive alternative. In comparison, however, the vacuum generating device 7 designed as a diffuser 8 does not require any electrical components or any electrical wiring and is also maintenance-free, as a result of which an embodiment which is not only light in weight, but also cost-effective and maintenance-free can be provided.The ventilation line 5 leads centrally through the motor vehicle 1 according to the invention in accordance with FIG. 1, wherein an arrangement on an underbody 10 is alternatively also conceivable. According to a further alternative embodiment of the invention, the ventilation line 5 is let into a correspondingly complementary receptacle on the underbody 10 of the motor vehicle 1 and can therefore be arranged not only in a flow-optimized manner but also in a protected manner.The venting line 5 itself can be formed from plastic, in particular from fiber-reinforced plastic, or alternatively also from metal, for example from light metal. In particular, a plastic design is possible without problems in the motor vehicle 1 according to the invention due to the electric drive and the thus missing exhaust pipes on the underbody 10.All in all, a significant reduction of air friction losses of rotating parts in axle housings 2, 2 a, 2 bcan be achieved with the motor vehicle 1 according to the invention, wherein an undesired discharge of oil into the environment can be avoided at the same time on account of the at least one oil separator 6, 6 a, 6 barranged in the venting line 5.

Claims

Motor vehicle (1) having at least one electric motor (3) arranged in an axle housing (2) for driving the motor vehicle (1), characterized - in that a venting line (5) for venting the axle housing (2) by means of reduced pressure is provided, - in that the venting line (5) is connected via at least one oil separator (6) to a reduced-pressure generating device (7) for generating a reduced pressure venting the axle housing (2), and - in that the reduced-pressure generating device (7) is designed as a diffuser (8), in particular as a rear diffuser, or - in that the venting line (5) ends at a vehicle rear or at an underbody (10), or - in that the venting line (5) is incorporated into an underbody (10) of the motor vehicle (1).Motor vehicle (1) according to Claim 1, characterized in that the motor vehicle (1) has a front axle housing (2a) with at least one electric motor (3a) arranged therein and a rear axle housing (2b) with at least one electric motor (3b) arranged therein, both of which are connected to the venting line (5).Motor vehicle (1) according to Claim 2, characterized in that an oil separator (6, 6a, 6b) is arranged in the venting line (5) both in the region of the front axle housing (2, 2a) and in the region of the rear axle housing (2, 2b).Motor vehicle (1) according to one of the preceding claims, characterized in that the venting line (5) is formed from plastic, in particular from fibre-reinforced plastic, or from metal.Motor vehicle (1) according to one of the preceding claims, characterized in that the axle housing (2) is connected to an environment exclusively via the venting line (5).

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