Diffuser device with swiveling, downforce-generating output body in the flow path and vehicle with diffuser device

Abstract

Diffuser device (12) for a motor vehicle (10), comprising a diffuser channel (24) extending along a virtual channel path (KB) through which flow can occur in a flow direction (S) and having at least one channel boundary surface (26) curved about a diffuser curvature axis (D), wherein the diffuser curvature axis (D) forms an angle with the channel path (KB), and comprising a drive body (34) which is pivotable about a pivot axis (P) which forms an angle with the channel path (KB) between two operating positions, wherein the drive body (34) has a shape in a section plane orthogonal to the pivot axis (P) that generates drive when flowing towards it,wherein in an activation operating position a leading edge (52) of the output body (34) located closer to the upstream longitudinal end (31) of the diffuser channel (24) has a greater distance from the curved channel boundary surface (26) than in an inactivation operating position different from the activation operating position, characterized in that the pivot axis (P) runs outside the output body (34).

Description

The present invention relates to a diffuser device for a motor vehicle, comprising a diffuser duct which extends along a virtual duct path and through which flow can take place in a flow direction and has at least one duct limiting surface which is curved about a diffuser curvature axis, wherein the curvature axis encloses an angle with the duct path, and comprising an output body which can be pivoted between two operating positions about a pivot axis which encloses an angle with the duct path, preferably a right angle, wherein the output body has a shape which generates output when there is an inflow in a sectional plane orthogonal to the pivot axis, wherein in an activation operating position a front edge of the output body, which front edge is situated closer to the upstream longitudinal end of the diffuser duct, is at a greater distance from the curved duct limiting surface than in an inactivation operating position which is different from the activation operating position.Such a diffuser device is known from DE 10 2013 105 843 A1. The known diffuser device arranged in the rear region of a motor vehicle has a profile body designed with a wing profile shape as the output body, which is initially movable in translation away from the vehicle floor and towards the same, and which is rotatable about an axis of rotation extending in the transverse direction of the vehicle in the extended position moved away from the vehicle floor. The airfoil profile produces aerodynamic drag upon inflow. In this way, by translationally approaching the vehicle floor and removing it, the output element can be deactivated or activated in its effect. In the extended position, the aerodynamic effect of the diffuser device can be varied by rotating the output member about its axis of rotation. In this case, the diffuser device is adjusted together with the output body between a position of maximum output and a position of minimum air resistance in the region of the diffuser device.Diffuser devices are also known in which the curvature of the curved channel limiting surface, which is substantially responsible for the desired output effect of a diffuser device, is variable, up to the forming of the channel limiting surface as a planar channel limiting surface. Such a diffuser device with a variably curved channel limiting surface is known, for example, on the vehicle type 918 of the manufacturer Porsche as a front diffuser device. By the described change of the curvature of the curved channel boundary surface, the diffuser device can be switched on and off as it were.A disadvantage of the solution known from DE 10 2013 105 843 A1 is the complex kinematics, which requires a translatory and a rotatory drive device. Due to these complex kinematics, the known diffuser device can only be used, as described in DE 10 2013 105 843 A1, in the rear region of a vehicle, where sufficient installation space is available for accommodating the required drive devices.The solution of the switchable front diffuser device known from Porsch 918 has the disadvantages of the forces of high magnitude for switching on and switching off the known diffuser device, since the change of the curvature of the curved channel boundary surface takes place in at least one direction counter to the output force generated by the diffuser device, so that the movement drive for the change of the curvature must be able to overcome the output force in addition to the material elasticity of the component having the curved channel boundary surface.It is the object of the present invention to further develop the diffusor device mentioned at the beginning in such a way that it can be used at any desired locations of a motor vehicle.This object is achieved by the present invention with the diffusor device mentioned at the beginning, in which the pivot axis additionally runs outside the driven body.By arranging the pivot axis outside the output body, not only does the output body move rotationally in the diffuser channel, but is also moved translationally along a circular path defined by the distance of the pivot axis from the output body. Thus, the output element can be changed not only with regard to its angle of incidence with respect to the air flow in the diffuser duct, but the location of its arrangement in the diffuser duct can also be changed upstream and downstream within certain limits. In order to ensure that the driven body is arranged in the diffuser duct in each of its two operating positions mentioned, the pivot axis is preferably oriented orthogonally to the duct path.A single drive is thus sufficient for the adjustment of the driven body between the aforementioned operating positions, which are preferably end positions of the driven body. The displacement of the output member between the aforementioned operating positions is also not effected counter to the output force generated by the diffusor device, so that the drive forces and moments required for displacing the output member in the diffusor channel make a drive of small dimensions sufficient.Usually, the diffuser axis of curvature, when viewing the diffuser device in a state operatively arranged in a vehicle, runs parallel to the pitch axis of the vehicle, i.e. parallel to a planar and horizontal reference underlying surface on which the vehicle stands. The curved channel boundary surface extends at its upstream longitudinal end substantially parallel to the vehicle floor surrounding it and curves away from the reference background in the flow direction. By means of the solution proposed in the present case, the output element can be arranged closer to the upstream longitudinal end of the diffuser duct in the inactive operating position and thus prevent an air flow as early as possible along the section of the duct boundary surface curving away from the reference background.Likewise, in the activation operating position, the output body can be arranged in a curved section of the channel limiting surface, where it can exert a stronger effect than in a less strongly curved region or in a region nearly parallel to the reference background near the upstream end of the diffuser channel.Preferably, therefore, the driven body is located closer to the upstream end of the diffuser duct in the inactive operating position than in the active operating position. Likewise preferably, the output body is located closer to the downstream end of the diffuser duct than to the upstream end thereof in the activation operating position.In the activation operating position, the output effect of the diffuser device is greater in amount than in the inactive operating position, in which the output body preferably virtually neutralizes the output effect of the diffuser device.The choice of the position of the pivot axis is a compromise between a maximum rotational change in position of the output body when the pivot axis runs through the output body and a maximum translatory displacement of the output body when the pivot axis is at an infinite distance from the output body. Both cases are only theoretical limit cases which are not encompassed by the present application.Even if it can in principle be sufficient for the pivot axis to be at such a small distance from the output body that the pivot axis passes through the diffuser duct, an advantageously large translatory displacement of the output body within the diffuser duct can be achieved with a still sufficient rotational change in position by the pivot axis running outside the diffuser duct. Such a construction also facilitates the attachment of the pivot drive of the output member, which can then be conveniently arranged outside the diffuser duct at a distance from the vehicle floor and thus at a distance from the curved duct boundary surface.It should be clarified at this point that the output element is arranged in the diffuser duct in both said operating positions, that is to say when the vehicle is moving, an air stream flows against it.In principle, an adjustment of the output member between its aforementioned operating positions can also be effected with only one drive along a complicated movement path, for example by means of a transmission and by movement guidance by a slotted guide path. A preferably simple and thus cost-effective solution, which enables switching of the diffuser device between a neutralized or at least minimal output effect and a maximal output effect, can be achieved in that the pivot mobility of the output body about the pivot axis is the only relative mobility of the output body relative to the diffuser channel.In order to be able to neutralize the output effect of the diffuser device to the greatest possible extent in the inactive operating position, it is advantageous if the output body is brought as close as possible to the curved channel boundary surface with its longitudinal end region situated closer to the upstream longitudinal end of the diffuser channel, for example to a gap dimension of less than 3 mm. Particularly preferably, the output body in the inactive operating position abuts with its longitudinal end region, which is situated closer to the upstream longitudinal end of the diffuser duct, on the curved duct boundary surface. This not only ensures lower holding forces than in the presence of a gap and thus a flow of flow air around the output member It additionally ensures, without additional components, an inactive operating position defined by a mechanical stop, which facilitates the control of the drive or makes at least one separate mechanical movement stop unnecessary.In principle, different configurations are conceivable, on the basis of which the output body produces aerodynamic output when there is an incident flow. For example, an output element with a planar inflow surface, which is set relative to the inflow about an adjustment axis orthogonal to the inflow direction, can already aerodynamically generate an output. Likewise, a driven body with an inflow surface which has flowed against during operation and which is curved about an axis of curvature orthogonal to the inflow direction can aerodynamically produce a driven element. The inflow body is preferably a profile body with an airfoil profile producing aerodynamic output as the shape mentioned at the beginning. In order to achieve the greatest possible output effect with a predetermined inflow, an inflowing air flow flows around the output body, which is preferably designed as a profiled body with a wing profile, in the activation operating position.Due to its shape which produces aerodynamic output when incoming flow, preferably an airfoil shape, the output body preferably has an overpressure side with an overpressure surface wall which is shorter in the flow direction and a negative pressure side which is opposite the overpressure side with a negative pressure surface wall which is longer in the flow direction between its front edge which is closer to the upstream longitudinal end of the diffuser duct and its rear edge which is closer to the downstream longitudinal end of the diffuser duct. According to a flow dynamic theory, air flows along the longer negative pressure side at a higher speed than along the shorter positive pressure side, for which reason the static air pressure is higher on the positive pressure side than on the negative pressure side. In order to achieve the largest possible output in terms of amount by the output body in cooperation with the diffuser device, its overpressure side preferably faces the curved channel limiting surface.In the activation operating position, at least a major part of the overpressure surface wall advantageously extends in a fluid-mechanical and fluid-dynamic manner parallel to the portion of the curved channel boundary surface situated opposite the overpressure surface wall at a distance. Thus, a channel section with a substantially constant flow cross section is defined between the driven body and the channel limiting surface, which can contribute to a particularly low-vortex flow in the region of the driven body.Advantageously, the diffuser device is not only designed to generate output, but rather to direct the air flowing through the diffuser device on the outlet side, i.e. at the downstream longitudinal end of the diffuser device, in a desired direction, for example in order to use the air flow previously used for generating an output after the outlet from the diffuser device for convective cooling of vehicle parts. For this purpose, according to an advantageous development of the present diffuser device, two side limiting surfaces can protrude from the curved channel limiting surface at a distance from one another, wherein at least one side limiting surface is curved about a side curvature axis, wherein the side curvature axis encloses an angle with the diffuser curvature axis. Preferably, the side curvature axis encloses a right angle with the diffuser curvature axis. The diffuser curvature axis and the side curvature axis do not have to intersect, but can be skew.It should also be noted that each axis of curvature of the diffuser axis of curvature and the side axis of curvature may be located at different locations for different portions of the channel boundary surface and the side boundary surface, respectively, such as when the curvature of a surface changes along its course in the flow direction.For the most efficient possible change of location and position of the output body relative to the channel limiting surface, it is advantageous if the pivot axis encloses an angle of less than 10° with the diffuser curvature axis. Preferably, the pivot axis is parallel to the diffuser curvature axis. Therefore, the longitudinal end of the output body, which is situated closer to the upstream longitudinal end of the diffuser duct, is preferably also parallel to the duct boundary surface, so that it can physically bear against the duct boundary surface along its entire length to be measured parallel to the pivot axis.The present invention likewise relates to a motor vehicle having a diffuser device as described and further developed above, wherein, in order to produce an output which is as large as possible, the flow direction through the diffuser duct predominantly runs in the vehicle longitudinal direction. Because of the curved course of at least the channel delimiting surface, the flow direction will locally also have directional components which are different from the vehicle longitudinal direction.Nevertheless, the diffuser device is initially subjected to flow in the longitudinal direction of the vehicle and this flow in the longitudinal direction of the vehicle is determining for the effect of the diffuser device over a large part of its extent. Preferably, the diffuser device is arranged as a front diffuser device in a region of the vehicle underbody situated in front of and next to a front wheel. The arrangement as a front diffuser device is possible due to the need for only a single drive and due to the relatively low drive forces required.In the above-mentioned preferred embodiment with a curved side limiting surface, a flow outlet from the diffuser device to the front wheel can take place, in particular to a brake system arranged on the front wheel, in an advantageous utilization of the air flow flowing through the diffuser device during operation. Thus, the air flow can convectively cool a brake disk after generating a desired output.The present invention is explained in more detail below with reference to the attached drawings. It represents: FIG. 1 shows a roughly schematic bottom view of a vehicle according to the invention with a diffuser device according to the invention, wherein the output body is in the inactive operating position, FIG. 2 is a roughly schematic bottom view of FIG. 1, with the driven body in the activation operating position, FIG. 3 is a roughly schematic side view of the diffuser device of FIG. 1 in the inactive operating position, and FIG. 4 shows a roughly schematic side view of the diffuser device of FIG. 2 in the activation operating position.FIG. 1 shows a roughly schematic bottom view of a vehicle 10 according to the invention, which has a diffuser device 12 according to the invention as well. More specifically, the vehicle 10 includes two diffuser devices 12, each of which is associated with a respective front wheel 14.A typical vehicle coordinate system comprising a roll axis Ro extending parallel to the vehicle longitudinal direction, a yaw axis Gi extending parallel to the vehicle height direction and a pitch axis Ni extending in the vehicle transverse direction is illustrated in FIGS. 1 to 4.The arrangement of the diffuser devices 12 is mirror image with respect to a plane of symmetry containing the roll axis Ro and the yaw axis Gi, which is a vertical longitudinal median plane of the vehicle 10. Each of the diffuser devices 12 is disposed in an area 16 relative to the closest front wheel 14 that is located forward of the front wheel 14 as well as at least partially closer to the longitudinal center plane of the vehicle 10 than the front wheel 14.Because of the mirror symmetry condition described above, it suffices to describe only one of the diffuser devices 12 in detail below. Under the mirror symmetry condition mentioned, the description thereof also applies to the respective other diffuser device 12.The vehicle 10 stands on a planar support base BU, which is the reference base (see FIGS. 3 and 4 ) and which extends parallel to the vehicle base 18 but which bears tangentially at the locations 22 of the front wheels 14 projecting furthest from the vehicle body 20 from the vehicle base 18 and is not illustrated in FIGS. 1 and 2.The diffuser device 12 defines a diffuser passage 24 running substantially along the roll axis Ro, which is bounded along the yaw axis Gi to the vehicle body 20 by a curved passage boundary surface 26. The channel delimiting surface 26 is curved about a diffuser curvature axis D running parallel to the pitch axis Ni, namely in such a way that it curves away from the reference background along the flow direction S along which the diffuser channel 24 is flowed through.The diffuser duct 24 is bounded in the direction of the pitch axis Ni by an inner side boundary surface 28 towards the longitudinal central plane and away from the longitudinal central plane by an outer side boundary surface 30 lying opposite the inner side boundary surface. For better clarity, the side boundary surfaces 28 and 30 are provided with reference numerals only on those diffuser devices 12 on which they can also actually be seen. The inner side boundary surface 28 is curved about a side curvature axis B orthogonal to the diffuser curvature axis D and parallel to the yaw axis Gi in order to allow air flowing into the diffuser duct 24 at the upstream longitudinal end 31 and flowing through the diffuser duct 24 to flow out towards the associated front wheel 14 at the downstream longitudinal end 32. In this way, the air flow leaving the diffuser duct 24 can convectively cool, at least in sections, the front wheel 14 and / or a brake system accommodated therein.In the diffuser duct 24, an output body 34 is accommodated in a pivotable manner relative to the diffuser duct 24.In FIG. 1, the output body 34 is shown in its inactive operating position, whereas in FIG. 2 it is shown in its active operating position. The two operating positions are end positions of the output member 34, beyond which it cannot be moved in the intended diffusor operation.FIG. 3 shows the diffuser device of FIG. 1 in a lateral view along the pitch axis Ni with a view to the inner side boundary surface 28. The diffuser curvature axis D is orthogonal to the plane of the drawing of FIG. 3 ; it is shown in FIG. 3 closer to the channel boundary surface 26 than would be indicated by the curvature of the channel boundary surface 26. Likewise, in FIG. 3, the reference background is shown in dashed lines as a plane orthogonal to the plane of the drawing in FIG. 3 and is provided with the reference symbol BU. The reference background BU is also drawn closer to the diffuser device 12 than corresponds to the actual distance.The output member 34 is pivotable about a pivot axis P parallel to the pitch axis Ni between the aforementioned operating positions. The pivotability about the pivot axis P is the only relative mobility of the output body 34 relative to the channel limiting surface 26 in the intended diffuser operation.The output body 34 is driven by a rotary drive 46 for pivoting movement about the pivot axis P. The rotary drive 46 is advantageously located on the side of the channel limiting surface 26 or of the component having the channel limiting surface 26 facing away from the reference background BU. The rotary drive 46 is thus shielded from the reference background BU by the component having the channel limiting surface 26 or by the vehicle floor 18. A web 48 connects the output body 34 to an output shaft 50 of the rotary drive 46. To achieve greater stability, a web 48 is formed on each of the two longitudinal ends of the output body 34, so that the output body 34 is connected in a rocking manner to the output shaft 50 of the rotary drive 46.The output body 34 has a leading edge 52 located closer to the upstream longitudinal end 31 of the diffuser duct 24 and a trailing edge 54 located closer to the downstream longitudinal end 32. The output body 34 has a profile shape which produces aerodynamic output when there is an inflow in sectional planes orthogonal to the pivot axis P. In the exemplary embodiment, this is shown by way of example as a wing shape with an overpressure side 56 and an opposite underpressure side 58. The positive pressure side 56 is formed by a connecting surface 60 which connects the front edge 52 to the rear edge 54. The low pressure side 58 is formed by an opposite connecting surface 62, which likewise connects the leading edge 52 to the trailing edge 54, but which has a greater length in the flow direction S. The greater length is achieved by a pronounced convex curvature of the connecting surface 62. The connecting surface 60 of the overpressure side 56 is preferably formed slightly concave.In the inactive operating position shown in FIG. 3, the front edge 52 of the output body 34 abuts the curved channel limiting surface 26, so that air flowing along the channel limiting surface 26 does not completely flow through the diffuser channel 24, but rather reaches the negative pressure side 58 of the output body 34 and is deflected by it. The incoming air flows along the driven body 34 to the rear edge 54 and breaks off there. It then continues to flow in the free jet substantially parallel to the rolling axis Ro. An exemplary flow path 64, shown in dotted lines, shows an approximate path of the air flow along the diffuser device 12 when the output member 34 is in the inactive operating position, as shown in FIG. 3. The diffuser device 12 does not then generate any appreciable output, which is its actual purpose, but does not generate any appreciable air resistance, which is otherwise the consequence or side effect of the output generated by the diffuser device 12.In driving situations in which output or additional output is not required by the diffuser device 12, the output body 34 is adjusted into the inactive operating position in which the vehicle 10 can be moved without additional air resistance caused by the diffuser device 12.However, when the diffuser device 12 is intended to generate the greatest possible output, for example in sports driving at high speed, for example on a track, the output body 34 is moved by the rotary drive 46 into the activation operating position shown in FIGS. 2 and 4, into which the diffuser device 12 is activated to generate an output.The output body 34 is then located away from the convex side of the curved channel boundary surface 26 forming a gap 66. In the activation operating position, the connecting wall 60 on the overpressure side 56 of the output body 34 runs parallel to the section of the channel limiting surface 26 opposite it across the gap 66.In the activation operating position, air can flow along the curved channel boundary surface 26, whereby the diffuser device 12 can generate an output force as intended. The flow filament 64 in Figure 4 indicates this.In addition, air flows around the output body 34 in the activation operating position, for which reason it forms a force directed from the overpressure side 56 toward the underpressure side 58, which force, via the webs 48, is transmitted to the vehicle 10, increases the output force generated by the diffuser device 12 in terms of amount. The flow thread 68 in FIG. 4 indicates, together with the flow thread 64, the flow around both sides of the driven body 34.The flow thread 64 in FIG. 4 runs along a virtual channel path KB, along which the diffuser channel 24 extends.

Claims

Diffuser device (12) for a motor vehicle (10), comprising a diffuser duct (24) which extends along a virtual duct path (KB) and can be flowed through in a flow direction (S) and has at least one duct delimiting surface (26) which is curved about a diffuser curvature axis (D), wherein the diffuser curvature axis (D) encloses an angle with the duct path (KB), and comprising an output body (34) which can be pivoted between two operating positions about a pivot axis (P) which encloses an angle with the duct path (KB), wherein the output body (34) has a shape which generates output when there is inflow in a sectional plane which is orthogonal to the pivot axis (P), wherein, in an activation operating position, a front edge (52) of the driven body (34), which front edge is situated closer to the upstream longitudinal end (31) of the diffuser duct (24), is at a greater distance from the curved duct delimiting surface (26) than in an deactivation operating position different from the activation operating position, characterized in that the pivot axis (P) extends outside the driven body (34).Diffuser device (10) according to claim 1, characterised in that the pivot axis (P) extends outside the diffuser duct (24).Diffuser device (10) according to Claim 1 or 2, characterized in that the pivot mobility of the output body (34) about the pivot axis (P) is the only relative mobility of the output body (40) relative to the diffuser duct (24).Diffuser device (10) according to one of the preceding claims, characterized in that the output body (34), in the inactive operating position, bears with its longitudinal end region situated closer to the upstream longitudinal end (31) of the diffuser duct (24) against the curved duct boundary surface (26).Diffuser device (10) according to one of the preceding claims, characterized in that the driven body (34), as a profile body, has, on account of its shape which produces aerodynamic output when incoming flow, in particular its aerofoil profile which produces aerodynamic output when incoming flow, between its front edge (52) which is situated closer to the upstream longitudinal end (31) of the diffuser duct (24) and its rear edge (54) which is situated closer to the downstream longitudinal end (32) of the diffuser duct (24), an overpressure side (56) with an overpressure surface wall (60) which is shorter in the flow direction (S) and a negative pressure side (58) which is opposite the overpressure side (56) and has a negative pressure surface wall (62) which is longer in the flow direction (S), wherein the overpressure side (56) faces the curved duct delimiting surface (26).Diffuser device (10) according to claim 5, characterised in that at least a major part of the overpressure surface wall (60) in the activation operating position runs parallel to the section of the curved channel limiting surface (26) lying opposite the overpressure surface wall (60) at a distance.Diffuser device (10) according to one of the preceding claims, characterized in that two side limiting surfaces (28, 30) protrude from the curved channel limiting surface (26) at a distance from one another, wherein at least one side limiting surface (28) is curved about a side curvature axis (B), wherein the side curvature axis (B) encloses an angle with the diffuser curvature axis (D).Diffuser device (10) according to one of the preceding claims, characterized in that the pivot axis (P) encloses an angle of less than 10° with the diffuser curvature axis (D), preferably parallel to the diffuser curvature axis (D).Motor vehicle (10) having a diffuser device (10) according to one of the preceding claims, characterized in that the flow direction (S) runs predominantly in the vehicle longitudinal direction (Ro), wherein the diffuser device (12) is arranged as a front diffuser device in a region (16) of the vehicle underbody (18) situated in front of and next to a front wheel (14).Motor vehicle according to Claim 9, wherein the diffuser device (10) is designed according to Claim 7, characterized in that a flow outlet takes place from the diffuser device (12) towards the front wheel (14), in particular towards a brake system arranged on the front wheel (14).

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