# Patent

## Title
Multi step transmission

## Abstract

The multi step transmission comprising gear sets (P1, P2, P3, P4), eight shafts and six shift elements. The sun gear of set (P1) couples the drive shaft, the carrier of set (P1) couples shaft (3) which couples a housing via brake (03), the drive shaft via clutch (13) and shaft (5) via clutch (35). Shaft (5) couples the ring gear of set (P2), to the sun gears of sets (P3, P4), and the drive shaft couples, via clutch (18), shaft (8) that couples the carrier of set (P4). Shaft (6) couples the ring gear of set (P1) and, via clutch (67), shaft (7) that couples the carrier of set (P2). The sun gear of set (P2) couples the housing. The ring gear of set (P3) couples shaft (4) that couples the housing via brake (04). The output shaft couples the ring gear and carrier of sets (P4, P3) respectively.

## Background
This application claims priority from German patent application Ser. No. 10 2009 028 715.9 filed Aug. 20, 2009.
FIELD OF THE INVENTION
The present invention relates to a multi step transmission of a planetary design, in particular an automatic transmission for a motor vehicle
BACKGROUND OF THE INVENTION
According to the prior art, automatic transmissions, particularly for motor vehicles, comprise planetary gear sets that are shifted using friction elements or shift elements such as clutches and brakes, and typically are connected to a start-up element, such as a hydrodynamic torque converter or a fluid coupling, that is subject to a slip effect and is provided optionally with a lock-up clutch.
Such an automatic transmission is known, for example, from the applicant's DE 199 49 507 A1, according to which two non-shiftable front-mounted gear sets are provided on the drive shaft and generate two rotational speeds on the output side, which, in addition to the rotational speed of the drive shaft, can be selectively meshed with a shiftable double planetary gear set acting on the output shaft by selective engagement of the shift elements such that only one of the two currently actuated shift elements must be engaged or disengaged to shift from one gear to the next higher or lower gear.
By using five shift elements, seven forward gears are obtained; by using six shift elements, nine or ten forward gears are obtained.
Furthermore, patent DE 102 13 820 A1 makes known a multi-speed automatic transmission with eight forward gears and one reverse gear, which comprises a first input path T1 of a first transmission ratio; an input path T2 that has a higher transmission ratio than that of input path T1; a Ravigneaux type planetary gear set with four elements, namely, a first element, a second element, a third element and a fourth element in the sequence of elements in a rotational speed diagram; a clutch C-2 which transfers rotation of the input path T2 to the first element S3; a clutch C-1, which transfers rotation from the input path T2 to the fourth element S2; a clutch C-4, which transfers rotation from the input path T1 to the first element; a clutch C-3, which transfers rotation from the input path T1 to the second element C3; a brake B-1, which produces meshing of the fourth element; a brake B-2, which produces meshing of the second element; and an output element that is coupled to the third element S3.
Furthermore, a nine-speed multi step transmission is known from DE 29 36 969 A1; it comprises eight shift elements and four gear sets, wherein one gear set serves as a front-mounted gear set and the main gearing includes a Simpson set and a further gear set serving as reverse gearing.
Further multi step transmissions are known, for example, from the applicant's DE 102005010210 A1 and DE 102006006637 A1.
Automatically shiftable vehicle transmissions, of planetary design, are already generally described numerous times in the prior art and are continually undergoing further development and improvement. These transmissions should have a relatively simple design, in particular requiring a low number of shift elements, and minimize the need for double shifting when sequential shifting is performed, thereby ensuring that only one shift element is ever switched when shifting is performed in defined groups of gears.
The applicant's document, DE 102008000428.3 which is not yet published, discloses a multi step transmission of a planetary design that includes an input shaft and an output shaft which are disposed in a housing. The known transmission includes at least four planetary gear sets which are designated, in the following, as the first, second, third, and fourth planetary gear set, at least eight rotatable shafts which are designated in the following as the drive shaft, output shaft, third, fourth, fifth, sixth, seventh, and eighth shaft, and at least six shift elements comprising brakes and clutches, whose selective engagement produces different transmission ratios between the input shaft and the output shaft, such that preferably nine forward gears and one reverse gear can be realized.
The first and second planetary gear sets, which are preferably designed as minus planetary gear sets, form a shiftable front-mounted gear set, wherein the third and fourth planetary gear sets form a main gear set.
In the known multi step transmission, the carriers of the first and second planetary gear sets are coupled together via the fourth shaft which is connected to an element of the main gear set, the ring gear of the first planetary gear set is coupled to the sun gear of the second planetary gear set via the eighth shaft, which is detachably connectable to the drive shaft via the first clutch, and the sun gear of the first planetary gear set can be coupled to a housing of the transmission by means of the third shaft, via a first brake, and is detachably connectable to the drive shaft via a second clutch, wherein the ring gear of the second planetary gear set can be coupled to a housing of the transmission by means of the fifth shaft via a second brake. In addition, the seventh shaft is constantly connected to at least one element of the main gear set, and can be coupled to a housing of the transmission via a third brake, wherein the sixth shaft is constantly connected to at least one further element of the main gear set and is detachably connectable to the drive shaft, via a third clutch; the output shaft is constantly connected at least to one further element of the main gear set.
In the known transmission, the fourth shaft is preferably constantly connected to the ring gear of the third planetary gear set, the sixth shaft is constantly connected to the ring gear of the fourth planetary gear set and to the carrier of the third planetary gear set, and is detachably connectable to the drive shaft via the third clutch. Furthermore, the seventh shaft is constantly connected to the sun gears of the third and fourth planetary gear sets, and can be coupled to a housing of the transmission via the third brake. In this case, the output drive is produced via the output shaft that is constantly connected to the carrier of the fourth planetary gear set. Furthermore, the third and fourth planetary gear sets can be combined or reduced to a Ravigneaux set having a common carrier and a common ring gear.
SUMMARY OF THE INVENTION
The object of the present invention is to propose a multi step transmission of the initially described type, which has nine forward gears and at least one reverse gear having a sufficient transmission ratio, in which the design complexity and the overall size, in particular the overall length and the weight, are optimized, and in which efficiency is improved with respect to drag losses and gearing losses. In addition, in the multi step transmission according to the invention, minimal support moments should act on the shift elements. The transmission, according to the invention, should be particularly suited for a front transverse installation.
Accordingly, a multi step transmission, according to the invention, of a planetary design is proposed which has an input shaft and an output shaft which are disposed in a housing. In addition, there are provided at least four planetary gear sets which are designated, in the following, as the first, second, third, and fourth planetary gear sets, eight rotatable shafts which are designated, in the following, as the drive shaft, output shaft, third, fourth, fifth, sixth, seventh, and eighth shafts, and at least six shift elements comprising brakes and clutches, whose selected engagement produces different transmission ratios between the drive shaft and the output shaft, such that preferably nine forward gears and one reverse gear can be realized.
The planetary gear sets, viewed axially, are disposed in the sequence of first planetary gear set, second planetary gear set, third planetary gear set, fourth planetary gear set, and are preferably designed as minus planetary gear sets.
As is well known, a simple minus planetary gear set comprises a sun gear, a ring gear, and a carrier on which the planetary gears are rotatably supported, the planetary gears meshing with the sun gear and the ring gear. As a result, when the carrier is fixed, the ring gear has a direction of rotation that is opposite that of the sun gear. In contrast, a simple plus planetary gear set comprises a sun gear, a ring gear and a carrier, on which inner and outer planet gears are rotatably supported, wherein all inner planet gears mesh with the sun gear and all outer planet gears mesh with the ring gear, wherein each inner planet gear meshes with only one outer planet gear. As a result, when the carrier is fixed, the ring gear has the same direction of rotation as the sun gear.
According to a preferred embodiment of the invention, the sun gear of the first planetary gear set is connected to the drive shaft, the carrier of the first planetary gear set is connected to the third shaft which can be coupled to a housing of the transmission via a first brake and is detachably connected to the fifth shaft via a second clutch, the fifth shaft is connected to the ring gear of the second planetary gear set, to the sun gear of the third planetary gear set, and to the sun gear of the fourth planetary gear set, and the drive shaft is detachably connected, via a third clutch, to the eighth shaft that is connected to the carrier of the fourth planetary gear set.
Furthermore, the ring gear of the first planetary gear set is connected to the sixth shaft which is detachably connected via a fourth clutch to the seventh shaft that is connected to the carrier of the second planetary gear set, the ring gear of the third planetary gear set is connected to the fourth shaft which can be coupled to a housing of the transmission via a second brake, the sun gear of the second planetary gear set is coupled to a housing of the transmission, and the output shaft is connected to the carrier of the third planetary gear set and the ring gear of the fourth planetary gear set.
It is provided that the first planetary gear set can be locked (blocked) by engaging a first clutch, wherein the first clutch is preferably designed as a clutch that detachably connects the third shaft to the drive shaft, or as a clutch that detachably connects the third shaft to the sixth shaft.
The embodiment of the multi step transmission, according to the invention, results in transmission ratios that are particularly suitable for passenger vehicles, and in a greater overall gear ratio of the multi step transmission, thereby improving driving smoothness and significantly reducing fuel consumption.
Furthermore, design complexity is significantly reduced with the multi step transmission, according to the invention, due to a low number of shift elements. Using the multi step transmission according to the invention, it is advantageously possible to perform a start-up using a hydrodynamic converter, an external start-up clutch, or any other suitable external start-up element. It is also conceivable to perform a start-up using a start-up element integrated in the transmission. Preferably, a shift element that is actuated in the first forward gear and in the reverse gear is suitable.
Moreover, the multi step transmission, according to the invention, results in good efficiency in the main drive gears with respect to drag losses and gearing losses.
Furthermore, low moments are present in the shift elements and in the planetary gear sets of the multi step transmission, thereby advantageously reducing wear in the multi step transmission. In addition, the low moments make it possible to utilize correspondingly low dimensions, thereby reducing the necessary installation space and related costs. Furthermore, the rotational speeds of the shafts, shift elements, and planetary gear sets are low.
In addition, the transmission, according to the invention, is designed to allow adaptability to different drive train embodiments in terms of power flow direction and spatial aspects.



BRIEF DESCRIPTION OF THE DRAWINGS
The invention is described in greater detail in the following, as an example, with reference to the attached figures. They show:
FIG. 1: a schematic view of a first preferred embodiment of a multi step transmission according to the invention;
FIG. 2: a schematic view of a second preferred embodiment of a multi step transmission according to the invention;
FIG. 3: an example of a shift pattern for a multi step transmission according to FIG. 1; and
FIG. 4: an example of a shift pattern for a multi step transmission according to FIG. 2.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a multi step transmission, according to the invention, which has a drive shaft 1, an output shaft 2, and four planetary gear sets P1, P2, P3 and P4 which are disposed in a housing G. Planetary gear sets P1, P2, P3 and P4, in the example shown in FIG. 1, are designed as minus planetary gear sets. According to the invention, at least one planetary gear set can be implemented as a plus planetary gear set if the carrier and ring gear connection are exchanged and, simultaneously, the value of the stationary transmission ratio is increased by 1 in comparison to the embodiment as a minus planetary gear set.
In the embodiment shown, the planetary gear sets, viewed axially, are disposed in the sequence P1, P2, P3 and P4.
As shown in FIG. 1, six shift elements are provided, namely, two brakes, 03, 04 and four clutches 13, 35, 18 and 67. The spatial disposition of the shift elements can be arbitrary, and is limited only by the dimensions of the outer design. The clutches and the brakes of the transmission are preferably implemented as friction shift elements or lamellar shift elements.
Selective shifting of nine forward gears and one reverse gear can be realized using these shift elements. The multi step transmission, according to the invention, has a total of eight rotatable shafts, namely, the shafts 1, 2, 3, 4, 5, 6, 7 and 8, wherein the drive shaft is the first shaft, and the output shaft is the second shaft of the transmission.
According to the invention, it is provided that the sun gear of the first planetary gear set P1 is connected to the drive shaft 1 of the multi step transmission in FIG. 1, wherein the carrier of the first planetary gear set P1 is connected to the third shaft 3 which can be coupled via a first brake 03 to a housing G of the transmission, and is detachably connectable via a first clutch 13 to the drive shaft 1, and via a second clutch 35 to the fifth shaft 5. By engaging the first clutch 13, the first planetary gear set P1 can be locked (blocked) by coupling the sun gear to the carrier.
As shown in FIG. 1, the fifth shaft 5 is connected to the ring gear of the second planetary gear set P2, to the sun gear of the third planetary gear set P3, and to the sun gear of the fourth planetary gear set P4, wherein the drive shaft 1 is detachably connected, via a third clutch, to the eighth shaft 8 that is connected to the carrier of the fourth planetary gear set P4.
According to the invention, the ring gear of the first planetary gear P1 set is connected to the sixth shaft 6 which is detachably connected, via a fourth clutch 67, to the seventh shaft 7 that is connected to the carrier of the second planetary gear set P2, wherein the ring gear of the third planetary gear set P3 is connected to the fourth shaft 4 which can be coupled to a housing G of the transmission via a second brake 04, and wherein the sun gear of the second planetary gear set P2 is coupled to a housing G of the transmission (shaft 0); the output shaft 2 is connected to the ring gear of the fourth planetary gear set P4 and to the carrier of the third planetary gear set P3.
According to the invention, the first clutch 13 and second clutch 35, viewed axially, can be disposed between the first and second planetary gear set P1, P2, the fourth clutch 67, viewed axially, is preferably disposed between the second and the third planetary gear set P2, P3, and wherein the third clutch 18, viewed axially in the power flow direction in the traction mode, can be disposed after the fourth planetary gear set P4.
The embodiment shown in FIG. 2 differs from the embodiment in FIG. 1 in that the first clutch is designed as a clutch 36 via which the third shaft 3 is detachably connectable to the sixth shaft 6 thereby enabling the first planetary gear set P1 to be locked (blocked) by coupling the carrier of the first planetary gear set P1 to the ring gear of the first planetary gear set P1.
FIG. 3 shows an example of a shift pattern of a multi step transmission according to FIG. 1. Three shift elements are engaged for every gear. The shift pattern shows, as examples, the particular transmission ratios i of the individual gear steps, and, to be determined therefrom, the gear increments or step changes phi to the next higher gear, wherein the value 9.005 is the transmission ratio spread.
Typical values for the stationary transmission ratios of the planetary gear sets P1, P2, P3 and P4 implemented as minus planetary gear sets are −1.953, −2.191, −2.235 and −2.404, respectively. FIG. 3 shows that double shifting or group shifting is avoided when shifting sequentially since two adjacent gear steps share two shift elements. It is also shown that a large transmission ratio spread is attained with small gear increments.
The first forward gear is attained by engaging the second brake 04 and the second and fourth clutches 35, 67; the second forward gear is attained by engaging the second brake 04 and the first and second clutches 13, 35; the third forward gear is attained by engaging the second brake 04 and the first and fourth clutches 13, 67; the fourth forward gear is attained by engaging the second brake 04 and the third and fourth clutches 18, 67; the fifth forward gear is attained by engaging the first, third and fourth clutches 13, 18, 67; the sixth forward gear, which is preferably implemented as a direct gear, is attained by engaging the first, second and third clutches 13, 35, 18; the seventh forward gear is attained by engaging the second, third and fourth clutches 35, 18, 67; the eighth forward gear is attained by engaging the first brake 03 and the second and third clutches 35, 18; and the ninth forward gear is attained by engaging the first brake 03 and the third and fourth clutches 18, 67, wherein the reverse gear is attained by engaging the first and second brakes 03, 04 and the fourth clutch 67.
Since the second brake 04 and the fourth clutch 67 are engaged in the first forward gear and in the reverse gear, these shift elements can be used as start-up elements.
For the case in which, according to the embodiment depicted in FIG. 2, the first clutch is designed as a clutch 36 via which the third shaft 3 can be detachably connected to the sixth shaft 6, the fourth gear, in contrast to the shift pattern shown in FIG. 3, is attained by engaging the second brake 04 and first and third clutches 36, 18 as illustrated in FIG. 4; the transmission ratio spread in this instance is 9.007.
According to the invention, different gear increments can also result from the same gear pattern depending on the shift logic, thereby making it possible to realize an application-specific or vehicle-specific variation.
According to the invention, it is possible to provide additional freewheels at each suitable location of the multi stepped transmission, for example, between a shaft and the housing, or possibly to connect two shafts.
According to the invention, an axle differential and/or a distributor differential can be disposed on the drive side or on the output side.
Within the scope of an advantageous development, the drive shaft 1 can be separated from a drive motor, as needed, by a clutch element, wherein a hydrodynamic converter, a hydraulic clutch, a dry start-up clutch, a wet start-up clutch, a magnetic powder clutch, or a centrifugal clutch can be used as the clutch element. It is also possible to dispose such a start-up element in the power flow direction after the transmission wherein, in this case, the drive shaft 1 is continuously connected to the crankshaft of the engine.
The multi step transmission, according to the invention, also makes it possible to situate a torsional-vibration damper between the engine and the transmission.
Within the scope of a further, not represented embodiment of the invention, a wear-free brake, for instance, a hydraulic or electric retarder or the like, can be disposed on each shaft, preferably on the drive shaft 1 or the output shaft 2, which is of special significance for use in commercial vehicles in particular. Furthermore, a power take-off drive can be provided on each shaft, preferably on the drive shaft 1 or the output shaft 2, for driving additional assemblies.
The friction shift elements that are used can be designed as power shiftable clutches or brakes. In particular, force locking clutches or brakes can be used, for instance, lamellar clutches, band brakes, and/or cone clutches.
A further advantage of the multi step transmission presented here is that an electric machine can be attached to each shaft as a generator and/or as an additional drive machine.
Obviously, any structural embodiment, in particular any spatial disposition of the planetary gear sets and the shift elements individually and relative to each other, and insofar as it is technically expedient, falls under the scope of protection of the present claims, without influencing the function of the transmission as specified in the claims, even if these embodiments are not explicitly represented in the figures or in the description.
REFERENCE CHARACTERS


    1 first shaft, drive shaft
    2 second shaft, output shaft
    3 third shaft
    4 fourth shaft
    5 fifth shaft
    6 sixth shaft
    7 seventh shaft
    8 eighth shaft
    03 first brake
    04 second brake
    13 first clutch
    18 third clutch
    35 second clutch
    36 first clutch
    67 fourth clutch
    P1 first planetary gear set
    P2 second planetary gear set
    P3 third planetary gear set
    P4 fourth planetary gear set
    i transmission ratio
    phi gear increment
    G housing

## Claims

1. A multi step transmission of a planetary design for an automatic transmission for a motor vehicle, the multi-step transmission comprising:
a drive shaft (1);
an output shaft (2);
first, second, third and fourth planetary gear sets (P1, P2, P3, P4) which are disposed in a housing (G); and
a rotatable third shaft (3), a rotatable fourth shaft (4), a rotatable fifth shaft (5), a rotatable sixth shaft (6), a rotatable seventh shaft (7) and a rotatable eighth shaft (8) and at least six shift elements (03, 04, 13, 18, 35, 36, 67), comprising first and second brakes (03, 04) and first, second, third and fourth clutches (13, 18, 35, 36, 67) whose selected engagement produces different transmission ratios between the drive shaft (1) and the output shaft (2) so that nine forward gears and a reverse gear can be achieved;
wherein a sun gear of the first planetary gear set (P1) is connected to the drive shaft (1);
a carrier of the first planetary gear set (P1) is directly connected to the third shaft (3) which is connectable to the housing (G) of the transmission, via the first brake (03);
the third shaft (3) is directly connected to the second clutch (35), and the second clutch (35) is directly connected to the fifth shaft (5) so that third shaft (3) is detachably connectable, via the second clutch (35), to the fifth shaft (5);
the fifth shaft (5) is directly connected to a ring gear of the second planetary gear set (P2), to a sun gear of the third planetary gear set (P3) and to a sun gear of the fourth planetary gear set (P4);
the drive shaft (1) is detachably connectable, via the third clutch (18), to the eighth shaft (8) that is connected a carrier of the fourth planetary gear set (P4);
the sixth shaft (6) is connected to a ring gear of the first planetary gear set (P1) and is detachably connectable, via the fourth clutch (67), to the seventh shaft (7) that is connected to a carrier of the second planetary gear set (P2);
a sun gear of the second planetary gear set (P2) is coupled to the housing (G) of the transmission;
a ring gear of the third planetary gear set (P3) is connected to the fourth shaft (4) which is connectable to the housing (G) of the transmission, via the second brake (04);
the output shaft (2) is connected to a ring gear of the fourth planetary gear set (P4) and to a carrier of the third planetary gear set (P3), and
the first planetary gear set (P1) can be locked by engagement of the first clutch (13 or 36) such that, when locked, the sun gear, the planet carrier and the ring gear of the first planetary gear set (P1) all rotate together in unison with one another.

2. The multi step transmission according to claim 1, wherein the first, the second, the third and the fourth planetary gear sets (P1, P2, P3, P4) are minus planetary gear sets.

3. The multi step transmission according to claim 1, wherein the first clutch (13 or 36) one of detachably connects the third shaft (3) to the drive shaft (1), and
detachably connects the third shaft (3) to the sixth shaft (6).

4. The multi step transmission according to claim 3, wherein a first forward gear is attained by engagement of the second brake (04) and the second and fourth clutch (35, 67);
a second forward gear is attained by engagement of the second brake (04) and the first and the second clutches (13 or 36, 35);
a third forward gear is attained by engagement of the second brake (04) and the first and the fourth clutch (13 or 36, 67);
a fifth forward gear is attained by engagement of the first, the third and the fourth clutch (13 or 36, 18, 67);
a sixth forward gear is attained by engagement of the first, the second and the third clutched (13 or 36, 35, 18);
a seventh forward gear is attained by engagement of the second, the third and the fourth clutches (35, 18, 67);
an eighth forward gear is attained by engagement of the first brake (03) and the second and the third clutches (35, 18),
a ninth forward gear is attained by engagement of the first brake (03) and the third and the fourth clutched (18, 67),
the reverse gear is attained by engagement of the first and the second brakes (03, 04) and the fourth clutch (67),
when the first clutch (13) detachably connects the third shaft (3) to the drive shaft (1), a fourth forward gear is attained by engagement of the second brake (04) and the third and the fourth clutches (18, 67), and
when the first clutch (36) detachably connects the third shaft (3) to the sixth shaft (6), the fourth forward gear is attained by engagement of the second brake (04) and the first and the third clutches (36, 18).