Bottom bracket gearbox for a bicycle, bottom bracket, and bicycle

Abstract

Bottom bracket gearbox for a bicycle, with at least four shifting elements, a first planetary gear set (PS1) and a second planetary gear set (PS2), characterized in that a bridge of the first planetary gear set (PS1) is non-rotatably connected to a sun gear of the second planetary gear set (PS2) and that a ring gear of the first planetary gear set (PS1) is non-rotatably connected to a bridge of the second planetary gear set (PS2).

Description

The invention relates to a bottom bracket transmission for a bicycle, having at least four shift elements, a first planetary set and a second planetary set.The invention also relates to a bottom bracket bearing with such a transmission. The invention furthermore relates to a bicycle with the bottom bracket or the transmission.A plurality of transmissions are known from the prior art. For example, US 2011 / 0 177 911 A1 discloses a transmission that has three planetary transmissions connected in series with one another with a transmission ratio of low speed. The transmission has a total of seven gear planes, including numerous stepped planets, so that the transmission is of complex construction and thus the construction outlay for the assembly of the transmission is very high.DE 197 45 419 A1 discloses a multi-speed transmission hub having three clutch elements and two connected planetary gear stages connected in series. The sun gear of the first planetary gear stage is fixedly connected to the hub axle.DE 843 783 B discloses an epicyclic change gear mechanism which consists of two epicyclic gear sets which are arranged one behind the other in the direction of power flow and which serve for producing a direct gear and can be used in such a way that the transmission ratio of the other can be changed by one epicyclic gear set.CN 1 05 711 728 A discloses a multi-speed bicycle transmission with two planetary gear stages connected in series for increasing the speed, in which different transmission ratios can be realized by combined control of the sun gears via Bowden cable or by reversing.DE 10 2010 004 552 A1 discloses a device for driving a bicycle, in which a plurality of planetary gear sets can be connected by at least two shiftable clutches in order to realize eight transmission stages.The object of the invention is therefore to specify a transmission which has a low construction outlay.This is achieved by the subject matter having the features of the independent claims. Advantageous further developments are evident from the dependent claims.The bottom bracket transmission according to the invention is characterized in that a carrier of the first planetary set is connected in a rotationally fixed manner to a sun wheel of the second planetary set, and in that a ring gear of the first planetary set is connected in a rotationally fixed manner to a carrier of the second planetary set.The bottom bracket transmission according to the invention has the advantage that a 4-gear transmission can be provided which does not require stepped planets. The transmission has a simple structure and the assembly of the transmission can be carried out quickly. The transmission according to the invention also has the advantage that it is suitable for a bicycle application, in particular in connection with a front-mounted or rear-mounted group described in more detail belowIn a particular embodiment, an input shaft of the transmission can be operatively connectable to the first planetary set and / or operatively connectable to the second planetary set. In particular, the drive shaft can be connected in a rotationally fixed manner to the carrier of the second planetary set by means of a first shift element of the at least four shift elements. In addition, the drive shaft can be connected in a rotationally fixed manner to the carrier of the first planetary set and / or the sun gear of the second planetary set by means of a second shift element of the at least four shift elements.A shaft is not exclusively understood to mean a machine element, for example a cylindrical, rotatably mounted machine element, for transmitting torques, but rather is also understood to mean general connecting elements which connect individual components or elements to one another, in particular connecting elements which connect a plurality of elements to one another in a rotationally fixed manner.The first planetary set and / or the second planetary set can be designed as minus planetary sets. As a result, the transmission has good efficiency. In addition, the planetary sets can have the same stationary transmission ratio. This provides the advantage that many identical parts can be used, which reduces the costs of the transmission.A minus planetary gear set corresponds to a planetary gear set having a carrier on which the planetary gears are rotatably supported, a sun gear and a ring gear, wherein the toothing of at least one of the planetary gears meshes with both the toothing of the sun gear and the toothing of the ring gear, whereby the ring gear and the sun gear rotate in the opposite direction when the sun gear rotates with the carrier fixed.The sun gear of the first planetary gear set can be connected to a transmission housing in a rotationally fixed manner by means of a third shift element of the at least four shift elements. The carrier of the first planetary gear set can be connected to the transmission housing in a rotationally fixed manner by means of a fourth shift element of the at least four shift elements. The ring gear of the second planetary gear set can be connected to the output shaft of the transmission in a rotationally fixed manner.The transmission housing can be a component of a bottom bracket housing, i.e. it can be embodied integrally with the bottom bracket housing. Alternatively, the transmission housing can be configured separately from the bottom bracket housing and, in the assembled state of the transmission, can be arranged in a cavity of the bottom bracket housing. The transmission housing can be designed and arranged in such a way that it does not rotate during operation of the transmission, but is stationary.The transmission can have exactly four shift elements. The first shifting element can be designed as a clutch or freewheel. The second shifting element can be designed as a clutch. The execution of the shift elements as freewheels in each case offers the advantage that no shifting actuation has to be provided. The third and fourth shift elements can each be designed as a brake.The drive shaft can be connected to a pedal bearing crankshaft in a rotationally fixed manner. In this embodiment, the output shaft can be connected in a rotationally fixed manner to a traction means carrier, such as a sprocket wheel or a belt wheel. When the transmission is used in the bicycle, a torque applied to the traction means carrier can be transmitted to a rear wheel by means of a traction means, such as a chain or a belt.As a result, a transmission having exactly four gears is realized. The four gears can be provided by exactly two planetary sets and / or exactly four shift elements. A first gear can be a direct gear, i.e. have a transmission ratio of 1. The remaining gears can have a transmission ratio to speed, i.e. a transmission ratio of less than 1.In a particular embodiment, the transmission can have a third planetary set, which is operatively connected or operatively connectable to the first planetary set and / or to the second planetary set. The third planetary set can be connected upstream or downstream of the first and second planetary sets in terms of drive technology. The third planetary set can be a minus planetary set.In this case, an element of the third planetary set can be connected in a rotationally fixed manner to another element of the third planetary set by means of a fifth shift element. When the fifth shift element is closed, the third planetary gear set is locked, i.e., has a transmission ratio of 1. A ring gear of the third planetary gear set can be connected to a transmission housing in a rotationally fixed manner by means of a sixth shift element.It is very particularly advantageous if the fifth shift element is arranged in such a way that a ring gear of the third planetary set can be connected in a rotationally fixed manner to a sun gear of the third planetary set by means of the fifth shift element. Such an arrangement has the advantage that a low supporting moment is to be applied by the fifth shifting element. Alternatively, it is of course possible for the fifth shift element to be arranged in such a way that the carrier of the third planetary set can be connected to the sun gear of the third planetary set or to the ring gear of the third planetary set in a rotationally fixed manner.In one embodiment, the third planetary set can be connected in drive-wise upstream of the first and second planetary sets during traction operation, i.e. form a front-mounted group. The first and second planetary gear sets, the input shaft, the output shaft and the four switching elements constitute a main group in this embodiment. A carrier of the third planetary gear set can be connected to the pedal bearing crankshaft in a rotationally fixed manner by means of a further drive shaft. In addition, a sun gear of the third planetary gear set can be connected to the drive shaft in a rotationally fixed manner. In this embodiment, the output shaft can be connected to a traction means carrier in a rotationally fixed manner.Alternatively, an embodiment is possible in which the third planetary set is drive-connected downstream of the first and second planetary sets during traction operation, i.e. forms a rear-mounted group. The first and second planetary gear sets, the input shaft, the output shaft and the four switching elements constitute a main group in this embodiment. The carrier of the third planetary set can be connected to the output shaft in a rotationally fixed manner and / or the sun gear of the third planetary set can be connected to a further output shaft in a rotationally fixed manner. In this embodiment, the drive shaft can be connected to the pedal bearing crankshaft in a rotationally fixed manner.The front-mounted group or rear-mounted group can provide exactly two gears and / or have exactly two shift elements, namely the fifth and sixth shift elements. In this case, a first gear can be a direct gear and a second gear can have a transmission ratio to speed. The front-mounted group or rear-mounted group can have exactly one planetary set, namely the third planetary set. The third planetary set does not have a stepped planetary gear. Moreover, the front-mounted or rear-mounted group provides a four-fold gear jump. The main group has approximately geometrically stepped gear jumps, for example in the range from 1.24 to 1.31.Regardless of whether the transmission has the front-mounted group or the rear-mounted group in addition to the main group, all variants result in the same transmission range, i.e. the function of the transmission is overall the same for all variants. Differences exist in the occurring speed and torque ratios at the individual planetary gear sets. Since, on the one hand, the front-mounted or rear-mounted group and, on the other hand, the main group have the direct gear as the first gear, the torque load is similar in both variants. Greater differences result in the rotational speeds since the planetary gear sets located further back in the power flow are operated with an already higher input rotational speed in some gears.The shift elements used in the transmission, such as clutches or brakes, can be designed to be positive-locking or frictional. If the above-mentioned shift elements are designed as freewheels, it is advantageous that, on the one hand, the main group and / or, on the other hand, the front-mounted group or rear-mounted group does not block, in order to prevent the transmission from blocking when the direction of rotation is reversed at the drive input or at the drive output. This can be realized in that the sixth shifting element of the front-mounted or rear-mounted group and / or the third and fourth shifting elements of the main group are designed as a one-way brake, such as a switchable freewheel brake.As a result, by coupling the main group providing four speeds with a front-mounted or rear-mounted group each providing two speeds, an 8-speed transmission can be realized. The transmission is advantageous since eight gears can be realized with exactly three planetary sets, so that the transmission has a short overall length. In addition, the transmission has suitable values for the stationary transmission ratios, so that the planetary gear sets can have a small diameter. A further advantage is that exactly three shifting elements can be designed as brakes. A further shift element can be designed as a clutch and the remaining shift elements can be designed as freewheels. This is advantageous since at least one, in particular exactly four, actuators must be present for actuating the three shift elements designed as a brake and the clutch.In a very particular embodiment, the transmission can have an electric machine which is operatively connected or operatively connectable to the output shaft or the further output shaft. The electric machine can be connected downstream of the first and / or second and / or third planetary set in terms of drive technology. The drive-related subsequent connection of the electric machine offers the advantage that the planetary sets are not loaded with the torque provided by the electric machine. The electric machine also has the advantage that it can assist the cyclist during the driving operation. As a result, a fine gear step is not necessary, since muscle power has a low significance for the drive because of the electric machine.The electric machine consists at least of a rotationally fixed stator and a rotatably mounted rotor and is configured in motor operation to convert electrical energy into mechanical energy in the form of rotational speed and torque, and in generator operation to convert mechanical energy into electrical energy in the form of current and voltage.The electric machine can be arranged offset, in particular in the radial direction, with respect to a central axis of the transmission and / or of the pedal bearing crankshaft. In particular, a central axis of the electric machine can run parallel to a central axis of the transmission. This offers the advantage that the electric machine can be arranged in a region of the transmission in which sufficient space is available for receiving the electric machine. Moreover, an inner diameter of the electric machine may be freely selected, since the non-transmission bottom bracket crankshaft does not pass through the electric machine.The connection of the electric machine to the output shaft or further output shaft can be effected by means of a chain drive and / or belt drive and / or a spur gear transmission and / or a transmission gear. In addition, a freewheel can be arranged in the force flow between the electric machine and the output shaft or the further output shaft. The freewheel offers the advantage that, during operation without an electric machine, no losses are caused by the corotating rotor of the electric machine.A pedal bearing with the transmission according to the invention is very particularly advantageous, wherein the drive shaft or the further drive shaft is connected to the pedal bearing crankshaft in a rotationally fixed manner. The bottom bracket can have a bottom bracket housing, wherein the transmission is arranged in a cavity of the bottom bracket housing. The transmission can be modular. Therefore, the gear as a whole can be inserted into or removed from the cavity. A bicycle with the transmission or the bottom bracket is very particularly advantageous.The subject matter of the invention is schematically illustrated in the figures and is described below with reference to the figures, wherein elements that are the same or have the same effect are usually provided with the same reference numerals. The following shows: FIG. 1 : shows a schematic illustration of the transmission according to a first exemplary embodiment, FIG. 2 : a shift matrix of the transmission shown in FIG. 1, FIG. 3 : shows a schematic illustration of the transmission according to a second exemplary embodiment, FIG. 4 : shows a schematic illustration of the transmission according to the invention according to a third exemplary embodiment, FIG. 5 shows a table with values for the stationary transmission ratio of the planetary gear sets, FIG. 6 : shows a shift matrix of the transmissions according to the invention shown in FIGS. 3 and 4.The transmission according to the first exemplary embodiment shown in FIG. 1 is designed rotationally symmetrical with respect to a pedal bearing crankshaft 4, only the upper half of the transmission being shown.The transmission has four shift elements, namely a first shift element S 1, a second shift element S 2, a third shift element S 3 and a fourth shift element S 4. In addition, the transmission has a first planetary gear set PS 1 and a second planetary gear set PS 2. A carrier of the first planetary set PS 1 is connected in a rotationally fixed manner to a sun gear of the second planetary set PS 2, and a ring gear of the first planetary set PS 1 is connected in a rotationally fixed manner to a carrier of the second planetary set PS 2. In addition, the carrier of the first planetary set PS 3 can be connected to a transmission housing 2 in a rotationally fixed manner by means of the fourth shift element S 4. A sun gear of the first planetary gear set PS 1 is connectable to a transmission housing 2 in a rotationally fixed manner by means of one of the third shift elements S 3.A sun gear of the second planetary gear set PS 2 is connectable to the drive shaft 1 in a rotationally fixed manner by means of the second shift element S 2. A carrier of the second planetary gear set PS 2 is connectable to the drive shaft 1 in a rotationally fixed manner by means of the first shift element S 1. A ring gear of the second planetary gear set PS 2 is connected to the output shaft 3 in a rotationally fixed manner.The first planetary set PS 1 and the second planetary set PS 2 are arranged coaxially with respect to one another and / or with respect to the bottom bracket crankshaft 4. Furthermore, the output shaft 3 is arranged coaxially with the pedal crank shaft 4. The first and second shift elements S 1, S 2 are each designed as clutches. The third and fourth shifting elements S 3, S 4 are each designed as brakes.The transmission is arranged in a cavity of a bottom bracket housing 8. The transmission shown in FIG. 1 forms a main group HG which, as can be seen from FIGS. 3 and 4, is operatively connected to further range groups.The first planetary set PS 1 can have a stationary transmission ratio of -1.6. The second planetary set PS2 can likewise have a stationary transmission ratio of -1.6. The stationary transmission ratio corresponds in the minus planetary gear set to the negative tooth number ratio of ring gear to sun.FIG. 2 shows a shift matrix for the transmission shown in FIG. 1. The symbol "X" identifies the shift elements which are closed at the respective gear. Moreover, FIG. 2 shows the values for the transmission ratio "i" between the input shaft 1 and the output shaft 3. In the further gears, a transmission takes place to speed. The shift elements are actuated by a suitable actuator system.FIG. 3 shows a transmission according to a second exemplary embodiment. The transmission differs from the transmission shown in FIG. 1 in that the transmission has a third planetary set PS 3, which forms a rear-mounted group, which is connected downstream of the main group HG in terms of drive technology. In particular, the third planetary set PS 3 is connected downstream of the first planetary set PS 1 and the second planetary set PS 2 in terms of drive engineering, when considering a force flow from the bottom bracket crankshaft 4 to the output shaft 3 during traction operation.The third planetary set PS 3 is disposed coaxially with the first planetary set PS 1 and the second planetary set PS 2. The third planetary set PS 3 has a fifth shifting element S 5, by means of which a ring gear of the third planetary set PS 3 can be connected to a sun gear of the third planetary set PS 3 in a rotationally fixed manner. In addition, the third planetary set PS 3 has a sixth shift element S 6, by means of which the ring gear of the third planetary set PS 3 can be connected to the transmission housing 2 in a rotationally fixed manner. The fifth shifting element S 5 is designed as a clutch and the sixth shifting element S 6 is designed as a brake.The carrier of the third planetary gear set PS 3 is connected to the output shaft 3 in a rotationally fixed manner. The sun gear of the third planetary gear set PS 3 is connected to a further output shaft 6 in a rotationally fixed manner. A traction means carrier, not shown in the figures, is connected to the further output shaft 6 in a rotationally fixed manner.FIG. 4 shows a transmission according to a third exemplary embodiment. The transmission shown in FIG. 4 differs from the transmission shown in FIG. 3 in that the third planetary gear set PS 3 does not form a rear-shift group NG but a front-shift group VG. This means that the third planetary set PS 3 is connected in front of the main group HG in terms of drive engineering, when considering the force flow from the bottom bracket crankshaft 4 to the output shaft 3 during traction operation.The carrier of the third planetary gear set PS 3 is connected in a rotationally fixed manner to the pedal crank shaft 4 by means of a further drive shaft 5. The sun gear of the third planetary gear set PS 3 is connected to the input shaft 1 in a rotationally fixed manner. The output shaft 3 of the transmission is connected to a traction means carrier, not shown.A further difference of the illustrated transmission is that the transmission has an electric machine 7 which is operatively connected to the output shaft 3, as is illustrated by the dashed line. The connection of the electric machine 7 to the output shaft 6 can be effected via a superposition gear, a spur gear, a chain drive and / or a belt drive, wherein the connection is not shown in FIG. 4. The coupling of the electric machine 7 takes place to the ring gear of the third planetary gear set PS 3.The electric machine 7 is not designed rotationally symmetrically with respect to the bottom bracket crankshaft 4. In particular, the electric machine 7 is arranged offset in the radial direction with respect to the pedal crank shaft 4. In this case, the electric machine 7, the main transmission HG and the preshift transmission VG are arranged within the bottom bracket housing 8.A further difference is that the transmission has a torque sensor 9, by means of which the torque transmitted from the pedal crank shaft 2 to the drive shaft 1 can be measured. The torque sensor 9 can be disk-shaped. Of course, a different embodiment and / or arrangement of the torque sensor 9 is also possible.FIG. 5 shows a table with values for the stationary transmission ratios of the three planetary gear sets. As can be seen from the table, all three planetary gear sets have the same stationary transmission ratio at the level of -1.61.FIG. 6 shows a shift matrix for the transmissions shown in FIGS. 3 and 4. The symbol "x" indicates that the switching element is closed. In the case that the switching element is designed as a free-wheeling device, the symbol "x" means that the free-wheeling device is blocked. In addition, FIG. 6 shows the transmission ratio "i" of the individual gears between the pedal crank shaft 4 and the traction mechanism carrier. The table also shows the gear jump "phi" between two successive gears.The stationary transmission ratios and gear jumps listed in the tables apply for the case where all planetary gear sets have the same stationary transmission ratio. Thus, many identical parts can be used. If different stationary transmission ratios are selected, more harmonic stationary transmission ratios can be achieved.Reference numerals denote reference numerals1 Input shaft 2 Transmission housing 3 Output shaft 4 Bottom bracket crankshaft 5 Further input shaft 6 Further output shaft 7 Electric machine 8 Bottom bracket housing 9 Torque sensor S 1 First shift element S 2 Second shift element S 3 Third shift element S 4 Fourth shift element S 5 Fifth shift element S 6 Sixth shift element HG Main group NG Rear-mounted group VG Front-mounted group PS 1 First planetary set PS 2 Second planetary set PS 3 Third planetary set

Claims

Bottom bracket transmission for a bicycle, having at least four shift elements, a first planetary set (PS1) and a second planetary set (PS2), characterized in that a carrier of the first planetary set (PS1) is connected in a rotationally fixed manner to a sun wheel of the second planetary set (PS2), and in that a ring gear of the first planetary set (PS1) is connected in a rotationally fixed manner to a carrier of the second planetary set (PS2).Pedal transmission according to Claim 1, characterized bya drive shaft (1) which can be operatively connected a. to the first planetary set (PS1) and / or operatively connected to the second planetary set (PS2) and / or which can be connected in a rotationally fixed manner b. by means of a first shift element (S1) to the carrier of the second planetary set (PS2) and / or which can be connected in a rotationally fixed manner c. by means of a second shift element (S2) to the carrier of the first planetary set (PS1) and / or to the sun gear of the second planetary set (PS2).Pedal bearing transmission according to Claim 1 or 2, characterized in that a. the sun wheel of the first planetary set (PS1) can be connected to a transmission housing (2) in a rotationally fixed manner by means of a third shift element (S3), and / or in that b. the carrier of the first planetary set (PS1) can be connected to a transmission housing (2) in a rotationally fixed manner by means of a fourth shift element (S4).Bottom bracket transmission according to one of Claims 1 to 3, characterized in that the ring gear of the second planetary set (PS2) is connected in a rotationally fixed manner to an output shaft (3) of the transmission.Bottom bracket transmission according to one of Claims 2 to 4, characterized in that the drive shaft (1) can be connected to the bottom bracket crankshaft (4) in a rotationally fixed manner.Bottom bracket transmission according to one of Claims 1 to 5, characterized bya third planetary set (PS3) which is operatively connected or operatively connectable to the first planetary set (PS1) and / or to the second planetary set (PS2).Pedal bearing transmission according to Claim 6, characterized in that an element of the third planetary set (PS3) can be connected in a rotationally fixed manner to another element of the third planetary set (PS3) by means of a fifth shift element (S5).Pedal bearing transmission according to Claim 6 or 7, characterized in that a ring gear of the third planetary set (PS3) can be connected to a transmission housing (2) in a rotationally fixed manner by means of a sixth shift element (S6).Bottom bracket transmission according to one of Claims 6 to 8, insofar as the claim refers back to one of Claims 2 to 4, characterized in that a web of the third planetary set (PS3) can be connected to the bottom bracket crankshaft (4) in a rotationally fixed manner by means of a further drive shaft (5), and a sun wheel of the third planetary set (PS3) is connected to the drive shaft (1) in a rotationally fixed manner.Pedal bearing transmission according to one of Claims 6 to 8, characterized in that a carrier of the third planetary set (PS3) is connected to the output shaft (3) in a rotationally fixed manner, and a sun wheel of the third planetary set (PS3) is connected to a further output shaft (6) in a rotationally fixed manner.Bottom bracket transmission according to one of Claims 1 to 10, characterized byan electric machine (7) which is connected, for example, downstream of the first planetary set (PS1) and / or the second planetary set (PS2) and / or the third planetary set (PS3) in terms of drive technology and / or which is operatively connected or operatively connectable, for example, to the output shaft (3) or the further output shaft (6).Bottom bracket bearing with a bottom bracket bearing transmission according to one of Claims 1 to 11, wherein the drive shaft (1) or further drive shaft (5) is connected to the bottom bracket bearing crankshaft (4) in a rotationally fixed manner.Bottom bracket bearing according to claim 12, wherein the bottom bracket bearing has a bottom bracket bearing housing (8) and the bottom bracket bearing transmission is arranged in a cavity of the bottom bracket bearing housing (8).A bicycle having a bottom bracket transmission according to any one of claims 1 to 11 or the bottom bracket according to claim 12 or 13.

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