Planetary gear stage and electric drive system

Abstract

Planetary transmission stage (13) with a sun gear (11), with a planet carrier (8) rotatably arranged about a main axis of rotation (HA) and associated planet gears (10) and with a ring gear (12), wherein the planet carrier (8) has a web (32) and planet gear bolts (9) connected in a rotationally fixed manner to the web (32), wherein one of the planet gears (10) is rotatably mounted on one of the planet gear bolts (9), wherein the planet carrier (8) is designed as a one-piece forged part, characterized in that a web eyelet (34) is provided which is welded to the planetary gear bolts (9) on a side facing away from the web (32), wherein planetary gear bearing devices (33) are provided, wherein in each case one of the planetary gear bearing devices (33) is arranged coaxially to one of the planetary gear bolts (9), wherein the web eyelet (34) has first web eyelet rings (35), wherein in each case one of the first web eyelet rings (35) is arranged coaxially to one of the planetary gear bolts (9), wherein in each case one first web eyelet ring (35) is arranged radially inside and axially overlapping the respective planetary gear bearing device (33) with respect to a planetary gear rotation axis (PA) of the planet gear (10) of the associated planetary gear bolt (9), wherein a second planet carrier bearing (44) is provided, which is arranged coaxially to the main axis of rotation (HA) and which radially supports the web (34) directly opposite a second housing ring (45), wherein the second planet carrier bearing (44) is arranged radially inside a second bridge ring (38) and radially outside the second housing ring (45), wherein the first bridge eyeglass rings (35) and the second bridge eyeglass ring (38) are formed in axially opposite directions on the bridge eyeglass (34).

Description

The invention relates to a planetary transmission stage of the type defined in more detail in the preamble of claim 1.Planetary transmission stages, which can be used, for example, in an electric drive system for a motor vehicle, are known from the prior art. Purely by way of example, reference may be made here to DE 10 2019 114 139 B3, which shows a motor vehicle transmission for coupling an electric machine to a drive train.With regard to the planetary transmission ratio stage itself, reference can also be made to DE 10 2018 211 491 A1. There, an arrangement for mounting an output shaft designed as a carrier shaft of a planetary gear set is described. The construction shows a very complex planet carrier made up of numerous components and bearing elements for axial support and a nail bearing formed separately therefrom for radial support. The construction is extremely complex in production and is accordingly expensive and difficult to assemble.DE 10 2009 037 005 A1 and DE 195 36 177 C2 each show a planetary transmission stage in which a planetary carrier, which has a web and planetary gear bolts, is formed in one piece and as a forged part.JP S61-17 562 U, DE 10 2019 218 440 A1, DE 10 2019 109 616 A1, DE 10 2019 123 264 A1, DE 10 2017 114 480 A1 and DE 10 2016 208 827 A1 each show further relevant prior art for forming planetary carriers.The object of the present invention is to specify an improved planetary transmission stage and an improved electric drive system having such a planetary transmission stage.According to the invention, this object is achieved by a planetary transmission stage having the features in claim 1, and here in particular in the characterizing part of claim 1. An electric drive system for a motor vehicle having the features in claim 10 also achieves the object. Advantageous embodiments and further developments of the planetary transmission ratio stage according to the invention are evident from the dependent claims dependent on the main claim.The planetary transmission stage comprises a sun wheel, a planet carrier with associated planet wheels and a ring gear, wherein sun wheel, planet carrier and ring gear are arranged rotatably about a main axis of rotation and thus all coaxially thereto. The planet carrier itself has a carrier and planet wheel pins connected to the carrier in a rotationally fixed manner, wherein the individual planet wheels are rotatably mounted on this planet wheel pin. A special feature already known from the prior art lies in the region of the planetary carrier. This is formed as a one-piece forged part which comprises both the web and the planetary gear bolts. Such a forged part allows high mechanical strengths with good mullability and is preferable as a one-piece component.According to the invention, a pair of web frames is provided which is welded to the planet wheel bolts on a side facing away from the web. In this particularly advantageous embodiment, the one-piece construction of the forged part is thus completed by a pair of web frames at the opposite end of the planetary gear bolts. These bridge pieces are welded to the planet wheel bolts in order to thus easily and efficiently complete the construction of the planet carrier.Furthermore, it is provided according to the invention that planetary gear bearing devices are used, which are each arranged coaxially to one of the planetary gear pins, wherein the pair of planet gears has first planet gear rings, wherein in each case one of the first planet gear rings is arranged coaxially to one of the planetary gear pins. The respective one first web-type planet ring is arranged radially inside and axially overlapping the respective planetary gear bearing device with respect to a planetary gear rotational axis of the planetary gear of the associated planetary gear bolt. The planet wheel bearings or the planet wheels with their planet wheel bearing devices are thus located between the web on the one side of the planet wheel bolts and the web frame on the other side of the planet wheel bolts, which in the region of the planet wheel bolts respectively has the first web frame ring. The terms coaxial, radial and axial refer here in the context illustrated here to the planetary wheel rotational axis of the planetary wheel.Furthermore, according to the invention, a second planet carrier bearing is provided, which is arranged coaxially to the main axis of rotation. This second planetary carrier bearing supports the web frame directly, i.e. radially with respect to a second housing ring without further elements in between. Furthermore, it is provided according to the invention that this second planet carrier bearing is arranged radially inside a second planet carrier ring and radially outside the second housing ring. The bridge frame is thus supported on the second housing ring from the outside, as viewed in the radial direction, via the bearing.Furthermore, it is provided according to the invention that the first planet carrier rings, which are designed for cooperation with the planet gear bolts, and the second planet carrier ring, which is designed for cooperation with the planet carrier bearing, are designed in axially different directions with respect to an axial center of the planet carrier. The first Web-type spectacle rings therefore project beyond a central plane of the Web-type spectacle, for example, in the one axial direction, in particular in the direction of the planetary gear bolts, while the second Web-type spectacle ring projects beyond the central plane of the Web-type spectacle in the axial direction in the opposite axial direction, that is to say the direction facing away from the Web of the planetary carrier.According to a very advantageous development thereof, it can be provided that a weld seam for welding pair of planet gear pins and planet gear bolts is arranged in each case between the first planet gear ring and the planet gear bolt. The bridge ring, which provides a sufficiently thick material, can thus be welded to the planetary gear bolt in a simple and efficient manner.The planet carrier has a first axial contact surface which is designed to secure one of the planet gear bearing devices axially in a first direction. Furthermore, in this advantageous embodiment, it can be provided that the first web-type Brill rings each have a second axial contact surface which is designed to secure one of the planetary gear bearing devices axially in a second direction. The planetary gear bearing device is thus secured between a contact surface of the planetary gear carrier, for example in the region of the carrier and / or of the respective planetary gear bolt, on the one hand, and the second axial contact surface in the region of the carrier frame, on the other hand. Preferably, the planetary gear bearing devices can now be pushed together with the planetary gears onto the planetary gear bolts and secured with the pair of flange pins. If the pair of planet carriers is pressed onto the planet carrier or planet carrier with a certain compressive force, the required prestress of the planet carrier bearing devices can be achieved. In this state of the planetary bearing devices pretensioned with the correct bearing tension, the welding of the bridge frame to the planetary gear bolt then takes place. This is extremely simple and efficient and enables a planet carrier with few components that is cost-effective to produce and easy to install.A further very advantageous embodiment of the planetary transmission stage according to the invention provides, furthermore, that a first planet carrier bearing is arranged radially inside a carrier ring of the planet carrier and radially outside a first housing ring arranged coaxially to the main axis of rotation. The terms coaxial, axial and radial now therefore refer here to the axis of rotation of the planet carrier, which is simultaneously the main axis of rotation of the planetary transmission stage.The planetary bearing devices can be realized basically in different ways. They can be designed, for example, as slide bearings or roller bearings. In this case, for example, a single roller bearing for each of the planetary gears on the corresponding planetary gear pin is a suitable solution with optimized friction behavior. According to a very advantageous development of the planetary transmission ratio stage according to the invention, however, it can now also be provided that each of the planetary gear bearing devices has two bearings between the respective planetary gear bolt and the respective planetary gear. Such a configuration with two bearings allows supporting the planetary gears at a distance in the axial direction. Preferably, the two bearings can be designed in the form of angular ball bearings which are formed spaced apart in the axial direction between the respective planetary gear bolts and the respective planetary gear. By means of two such angular ball bearings, an ideal bearing with both axial and radial support in the respective bearing can be implemented.According to an extraordinarily favorable development of the above-mentioned variant of the planetary carrier bearings as well as of this variant of the invention, it can be further provided that the two pairs of angular ball bearings are arranged in an O-arrangement with respect to their rotational axis. The bearings of each pair are installed in such a way that the pressure lines of the two angular ball bearings rotating about the same axis of rotation run outwards, so that their points of intersection with the respective axis of rotation are arranged at a greater distance in the axial direction than the bearings themselves. This construction is typically referred to as an O-arrangement and here allows a mounting with ideal support.The electric drive system according to the invention for a motor vehicle now comprises an electric machine having a rotor and an output shaft which is connected, for example, to a directly driven wheel or an axle transmission, such as, for example, a differential. Furthermore, in the electric drive system for the motor vehicle, a planetary transmission stage is provided in one of the above-described design variants. In this case, the rotor of the electric machine is connected or connectable to the sun wheel in a torque-transmitting manner. The ring gear is connected or connectable to a housing in a rotationally fixed manner. A rotationally fixed connection in the sense of the invention is understood to mean the connection of two coaxial elements in such a way that they rotate at the same angular speed. The planet carrier itself now forms the output and is connected to the output shaft in a rotationally fixed manner. All in all, the use of the planetary transmission stage with the particularly efficient planetary carrier thus results in a compact construction of such an electric drive system for a motor vehicle that is simple and thus cost-effective in terms of production and assembly.The electric drive system is preferably designed to drive exactly one wheel of the motor vehicle, so that an electrically driven axle of the motor vehicle preferably has two electric drive systems according to the invention, which are arranged mirror-symmetrically to one another.Further advantageous embodiments of the planetary transmission ratio stage and of the electric drive system for a motor vehicle also result from the exemplary embodiments which are described in more detail below with reference to the figures.The following are shown: FIG. 1 is a schematic illustration of an electric drive system for a motor vehicle in an embodiment according to the invention; FIG. 2 shows a sectional illustration of a detail from the electric drive system with a conversion of the planetary transmission ratio stage according to the invention; and FIG. 3 shows a schematic three-dimensional illustration of a planetary transmission ratio stage according to the invention with a view to a pair of planet carriers of a planetary carrier.In the illustration of FIG. 1, an electric drive system 1 is schematically illustrated. It has an electric machine 2, which is preferably designed here as an axial flow machine. This comprises a stator 30, which is arranged rotationally fixedly with respect to a housing 5, and a two-part rotor 3, which is connected rotationally fixedly to a rotor shaft 4. The rotor shaft 4 forms an input shaft into a planetary transmission stage 13 and is connected in a rotationally fixed manner to a sun wheel 11. The planetary transmission stage 13 also comprises a ring gear 12, which is connected to the housing 5 in a rotationally fixed manner. A planet carrier 8 is connected in a rotationally fixed manner to an output shaft 18 which discharges power from the electric drive system 1, as is represented by the output designated by 7 and indicated by an arrow in the illustration of FIG. 1.The illustration in FIG. 2 shows a sectional illustration of the electric drive system 1 in a detail. The rotor 3, of which only the half lying to the right in the electric machine 2 or to the right of the stator 30 is correspondingly shown here, is mounted with respect to a housing 5 via a rolling bearing 6. It is connected in a rotationally fixed manner to the rotor shaft 4, which is embodied in multiple parts. The rotor shaft 4 is supported indirectly via the rolling bearing 6, designed as a spherical bearing, of the rotor 3 and is also supported on the housing via a needle bearing 28. On a side of the planetary transmission stage 13 facing away from the electric machine 2 in an axial direction a, the output 7 is schematically shown with respect to a wheel of the motor vehicle or an axle transmission-e.g. a differential. This output 7 is connected via the output shaft 18 by means of a spline toothing designated with 19 in a rotationally fixed manner to a planetary gear carrier 8 as the output element of the planetary transmission stage 13.The planetary carrier 8 has planetary gear pins 9 directed in the axial direction a in the direction of the electric machine 2. Planetary gears 10, of which two can be seen here, are each mounted on the planetary gear pin 9 via a planetary gear bearing device 33, which is here each designed in the form of two angular ball bearings 33.1 and 33.2. A sun wheel 11 meshes radially on the inside with the planetary wheels 10, which sun wheel is formed by a toothing of the rotor shaft 4. A ring gear 12 supplements this construction to form the planetary transmission stage 13 for converting the torque between the rotor 3 and the output 7.The planet carrier 8 thus comprises the planet wheel bolts 9 and a web 32, wherein the planet wheel bolts 9 are connected to the web 32 in a rotationally fixed and axially fixed manner. In the exemplary embodiment shown here, the planet gears 10 are mounted onto the planet gear bolts 9 together with the two angular ball bearings 33.1 and 33.2, which together form the planet gear bearing device 33. Alternatively, a single roller bearing could also be provided, for example.The planet carrier 8 consisting of the web 32 and the planet gear bolt 9 is preferably designed as a one-piece forged part. After the planetary gears 10 and the planetary gear bearing devices 33, here in the form of the two angular ball bearings 33.1, 33.2, have been placed on the side of the planetary gear wheels 9 facing away from the web 32, a pair of web frames 34 are now placed. In the region of the respective planet wheel pin 9, this pair of planet wheel pins 34 has a first respective planet wheel ring 35 which comes to lie between the planet wheel pin 9 and an inner ring of the angular ball bearing 33.2 facing the pair of planet wheel pins 34 in the radial direction r, with respect to a planet wheel rotational axis PA of the planet wheel 10. The other angular ball bearing 33.1 bears in the axial direction a against a first axial contact surface 36, which is formed on the planetary gear bolt 9 or by the web 32 of the planetary carrier 8. In the region of the bridge 34, a second axial contact surface 29 is accordingly formed for the inner ring of the second angular contact ball bearing 33.2. After the planetary gears 10 with the two angular ball bearings 33.1, 33.2 have been plugged on, a prestress can now be applied to the planetary gear bearing device 33 by pressing the multi-bar frame 34 onto the planetary carrier 8. As a result, the angular ball bearings 33.1, 33.2 can be brought to the required bearing prestress. Once this state has been reached, a continuous or discontinuous weld seam 37 running around the circumference of the planetary gear bolt 9 or of the first polygonal ring 35 is placed between the pair of polygonal ribs 34, and here in particular between the first polygonal ring 35 and the planetary gear bolt 9. This weld seam 37 now ensures that the planet carrier 8 together with the planet gears 10 and their planet gear bearing device 33 is completed by the web frame 34. The construction is very simple and can be mounted ideally in the sense of the required bearing prestress by pressing on the bridge frame 34 before welding, in order to thus extremely efficiently complete the central construction of the planetary transmission stage 13.The two angular contact ball bearings 33.1, 33.2 of the planetary gear bearing device 33 are designed in such a way that the pressure lines d 1 of the one angular contact ball bearing 33.1, which are drawn in the lower half of FIG. 2, and the pressure lines d 2 of the other angular contact ball bearing 33.2 intersect the planetary gear rotational axis PA of the planetary gear 10 drawn in the bottom, at a distance x which is greater than the distance of the two angular contact ball bearings 33.1 and 33.2 in the axial direction a. This structure is usually also referred to as an O-arrangement.For its mounting, the planet carrier 8 itself now has a first carrier ring 39 which is arranged coaxially with the main axis of rotation HA and is arranged in the radial direction r outside a first housing ring 40 which is likewise arranged coaxially with the main axis of rotation HA. Between the first carrier ring 39 of the planetary carrier 8 and the first housing ring 40 of the housing 5 there is an angular ball bearing 14.1 as a first planetary carrier bearing 41 The angular ball bearing 14.1 in this case supports both axial and radial forces, for which purpose a first axial surface 42 and an adjustment disk 43 are provided on the web side and an adjustment disk 43 is provided on the housing side, wherein the adjustment disk 43 is in turn supported on an axial surface, not designated in more detail, of a housing cover 5.1 of the housing 5. As a second planet carrier bearing 44, an angular ball bearing 14.2 is likewise provided, which is arranged in the radial direction between a second housing ring 45 and the second planet carrier ring 38, which here is simultaneously designed as a second carrier ring for the mounting of the planet carrier 8. The planet carrier bearing 44 is supported on the web-plane side on a second axial surface 46. On the side of the housing, the support is effected on an axial surface of the second housing ring 45, which surface is not designated in more detail here.The two angular contact ball bearings 14.1, 14.2 as first and second planet carrier bearings 41, 44 are now arranged in an O-arrangement, this time with respect to the main axis of rotation HA, just like the two angular contact ball bearings 33.1 and 33.2 of the planetary gear bearing device 33. This also means here that the pressure lines D 1 of the first angular contact ball bearing 14.1 and D 2 of the second angular contact ball bearing 14.2 intersect the main axis of rotation HA at a distance denoted here by y which is greater than the distance between the bearings themselves in the same axial direction a. The main axis of rotation HA is the common axis of rotation of the sun gear 11, the planet carrier 8 and the ring gear 12.In the illustration of FIG. 3, the planetary transmission stage 13 can be seen once again in a schematic 3D illustration. For simplification, the illustration of the toothings has been omitted. FIG. 3 shows the ring gear 12 on the outside as a ring, in which three planetary gears 10 rotate in the exemplary embodiment shown here. The planet gears 10 largely cover the planet carrier 8 or its web 32 to be seen. On these are arranged the planetary gear pins 9, on which the planetary gears 10 are mounted accordingly. The majority of the structure is thereby visually concealed by the bridge grooves 34, which are welded to the planetary gear pin 9 via the welded seams 37 in the region of the first bridge groove rings 35 which cannot be explicitly seen here, since they project inward. The second bridge ring 38 can be seen centrally in the region of the bridge 34, via which the planet carrier 8 is mounted on one of its axial sides. In the center of the structure in the illustration of FIG. 3, the sun gear 11 and the rotor shaft 4 can also be seen in analogy to the illustration in FIG. 2.The mounting of the planetary transmission stage 13 as a whole is now designed such that the planetary gear bearing device 33 is arranged in the axial direction between the two planetary carrier bearings 41, 44. As already mentioned above, the sun gear 11 is mounted accordingly via the rotor shaft 4 and thus via the bearing 6 and the needle bearing 28 indicated in the region of the second housing ring 45. A further bearing can be embodied in the region of the second half of the rotor 3 on the other side of the electric machine 2 in the axial direction a, which is no longer shown here.As already indicated, the housing 5 consists of the housing cover 5.1 and a section 5.2, which is designated as the lower housing part and is embodied as such in one piece. The entire structure is now assembled from the side of the housing cover 5.1 by first introducing the electric machine 2 and fixing its stator 30 accordingly, for example, via the indicated screw connection 31. Subsequently, the parts of the planetary transmission stage 13 are introduced with the planet carrier 8 already completed in advance, comprising the carrier 32, planetary gears 10 and carrier glasses 34. The bearing prestress within the planetary bearing devices 33 is already set by pressing on and welding the web frames 34. The bearing prestress for the two planet carrier bearings 41, 44 can be adjusted accordingly during assembly via the adjusting disk 43, since the second housing ring 45 is formed in the housing lower part 5.2 and the first housing ring 40 in the housing cover 5.1. By means of a suitable setting disk 43, the bearing prestress can thus be set when fixing the housing cover 5.1, for example by means of the screw connections 47 indicated with the housing lower part 5.2 of the housing 5.The output shaft 18 can then, as has already been mentioned above, be coupled rotationally fixedly to the planet carrier 8 via the spline shaft toothing 19, so that, for example, a single wheel or an axle transmission, such as in particular a differential of a motor vehicle, is electrically driven via the output 7.List of reference characters1 Electric drive system 2 Electric machine 3 Rotor 4 Rotor shaft 5 Housing 5.1 Housing cover 5.2 Housing lower part 6 Bearing (of the rotor) 7 Output 8 Planet carrier 9 Planetary gear bolt 10 Planetary gears 11 Sun gear 12 Ring gear 13 Planetary transmission stage 14.1 Angular ball bearing of the first planet carrier bearing 14.2 Angular ball bearing of the second planet carrier bearing 18 Output shaft 19 Spline toothing 28 Needle bearings 29 Second axial contact surface on the web frame 30 Stator 31 Screw connection of the stator 32 Web 33 Planetary gear bearing device 33.1 Angular ball bearing 33.2 Angular ball bearing 34 Web frame 35 First web frame ring 36 First axial contact surface on planetary gear bolt 37 Weld seam 38 Second web frame ring 39 First carrier ring 40 First housing ring 41 First planet carrier bearing 42 First axial surface on the web 43 Setting ring 44 Second planet carrier bearing 45 second housing ring 46 second axial surface of the pair of ribs 47 screw connections of the housing cover a axial direction D 1, D 2 pressure lines d 1, d 2 pressure lines HA main axis of rotation PA planetary gear axis of rotation r radial direction X distance y distance

Claims

Planetary transmission stage (13) having a sun wheel (11), having a planet carrier (8) arranged rotatably about a main axis of rotation (HA) and associated planet wheels (10), and having a ring gear (12), wherein the planet carrier (8) has a web (32) and planet wheel pins (9) connected in a rotationally fixed manner to the web (32), wherein in each case one of the planet wheels (10) is rotatably mounted on one of the planet wheel pins (9), wherein the planet carrier (8) is formed as a one-piece forged part, characterized in that there is provided web glasses (34) which are each welded to the planet wheel pins (9) on a side facing away from the web (32), wherein planet wheel bearing devices (33) are provided, wherein in each case one of the planet wheel bearing devices (33) is arranged coaxially with respect to one of the planet wheel pins (9), wherein the web glasses (34) have first web glasses rings (35), wherein one of the first planet carrier rings (35) is arranged coaxially with respect to one of the planet wheel pins (9), wherein the one first planet carrier ring (35) is arranged radially inside and axially overlapping with respect to the respective planet wheel bearing device (33) with respect to a planet wheel rotational axis (PA) of the planet wheel (10) of the associated planet wheel pin (9), wherein a second planet carrier bearing (44) is provided, which is arranged coaxially with respect to the main rotational axis (HA), and which radially supports the planet carrier (34) directly with respect to a second housing ring (45), wherein the second planet carrier bearing (44) is arranged radially inside a second planet carrier ring (38) and radially outside the second housing ring (45), wherein the first planet carrier rings (35) and the second planet carrier ring (38) are formed on the planet carrier (34) in axially opposite directions.Planetary transmission stage (13) according to Claim 1, characterized in that a weld seam (37) for the welding of web glasses (34) and planetary wheel bolts (9) is arranged in each case between the first web glasses ring (35) and the planetary wheel bolt (9).Planetary transmission stage (13) according to Claim 1 or 2, characterized in that the planet carrier (8) has in each case a first axial contact surface (36) which is designed in order in each case to axially secure one of the planet wheel bearing devices (33) in a first direction.Planetary transmission stage (13) according to Claim 3, characterized in that the first Web-type Transmission Rings (35) each have a second axial contact surface (29) which is designed to secure in each case one of the planetary gear bearing devices (33) axially in a second direction.Planetary transmission stage (13) according to one of the preceding claims, characterized in that a first planet carrier bearing (41) is arranged radially inside a first carrier ring (39) of the planet carrier (8) and radially outside a first housing ring (40) arranged coaxially with the main axis of rotation (HA).Planetary transmission stage (13) according to Claim 5, characterized in that the first planet carrier bearing (41) has a first angular ball bearing (14.1) and the second planet carrier bearing (44) has a second angular ball bearing (14.2).Planetary transmission stage (13) according to one of the preceding claims, characterized in that each of the planetary gear bearing devices (33) has two bearings (33.1, 33.2) between the respective planetary gear bolt (9) and the respective planetary gear (10).Planetary transmission stage (13) according to Claim 7, characterized in that the two bearings are designed in the form of two angular ball bearings (33.1, 33.2), which are arranged spaced apart in the axial direction (a) between the respective planetary wheel bolt (9) and the respective planetary wheel (10).Planetary transmission stage (13) according to Claim 6 and / or 8, characterized in that at least one of the two pairs of angular ball bearings (33.1, 33.2; 14.1, 14.2) of the planetary gears (10) and / or of the planetary carrier (8) is arranged in an O arrangement with respect to their respective axis of rotation (PA; HA).Electric drive system (1) for a motor vehicle, having an electric machine (2) which has a rotor (3), having an output shaft (18) and having a planetary transmission stage (13) according to one of the preceding claims, characterized in that the rotor (3) is or can be connected to the sun wheel (11) in a torque-transmitting manner, the ring gear (12) is or can be connected to a housing (5) in a rotationally fixed manner, and the planet carrier (8) is connected to the output shaft (18) in a rotationally fixed manner.

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