In the prior art, automatic transmission, particularly for motor vehicles, comprise planetary gear sets shifted by means of friction and shifting elements such as clutches and brakes and usually have one starting element, such as a hydrodynamic converter or a fluid clutch, optionally provided with a lock-up clutch and subject to a slip effect.
Such a transmission results from EP 0 434 525 A1. It essentially comprises one drive shaft and one driven shaft disposed parallel with each other, one double planetary gear set disposed concentrically with the driven shaft and five shifting elements in the form of three clutches and two brakes, the optional locking of which by pairs determines the different gear ratios between the drive shaft and the driven shaft. This transmission has a front-mounted range change set and two power paths so that six forward gears are obtained by selective engagement by pairs of the five shifting elements.
Here two clutches are needed in the first power path for transmitting the torque from the front-mounted range change set to two elements of the double planetary gear set. These are situated in the power flow direction essential downstream of the front-mounted range change set in the direction of the double planetary gear set. In the second power path, one other clutch is provided which loosely connects it with another element of the double planetary gear set. The clutches are arranged here so that the internal disc carrier constitutes the output.
In addition, the U.S. Pat. No. 6,139,463 publication has disclosed a compact multiple stage transmission of a planetary design, particularly for motor vehicles, which has two planetary gear sets and one front-mounted range change set, the same as three clutches and two brakes. In this known multiple stage transmission, two clutches C-1 and C-3 are provided in a first power path for transmitting the torque from the front-mounted range change set to the two planetary gear sets. The external disc carrier or the cylinder or piston and pressure compensation side of the clutch C-3 is here connected with a first brake B-1. Besides, the internal disc carrier of the third clutch C-3 is connected with the cylinder or piston and pressure compensation side of the first clutch C-1, the internal disc carrier of the first clutch C-1 is located on the output side and connected with a sun gear of the third planetary gear set.
From the Applicant's DE 199 49 507 A1 is further known a multiple stage transmission where two non-shiftable front-mounted range change sets are provided on the drive shaft which, on the output side, produce two rotational speeds which, together with the rotational speed of the drive shaft, are optionally shiftable by selective engaging of the used shifting elements, to a shiftable double planetary gear set acting upon the driven shaft in a manner such that to change over from one gear to the next sequential higher or lower gear of the two specifically actuated shifting elements, respectively, only one shifting element has to be engaged or disengaged.
From DE 199 12 480 A1 is known an automatically shiftable motor vehicle transmission having three spider planetary gear sets, the same as three brakes and two clutches, for shifting six forward gears and one reverse gear and having one drive shaft and one driven shaft. The automatically shiftable motor vehicle transmission is designed so that the drive shaft is directly connected with the sun gear of the second planetary gear set and the drive shaft is connectable, via the first clutch, with the sun gear of the first planetary gear set and/or via the second clutch with the spider of the first planetary gear set. Additionally or alternatively, the sun gear of the first planetary gear set is connectable, via the first brake, with the housing of the transmission and/or the spider of the first planetary gear set with the housing, via the second brake, and/or the sun gear of the third planetary gear set with the housing via the third brake.
DE 102 13 820 A1 has also disclosed a multiple stage automatic transmission comprising one first input path T1 of a first reduction ratio; one input path T2 which has a higher reduction ratio than said input path T1; one planetary gear set having four elements, said four elements being one first element, one second element, one third element and one fourth element in the sequence of elements in a rotational speed diagram; one clutch C-2 which transmits rotation of the input path T2 to the first element S3; and clutch C-1 which transmits the rotation from the input path T2 to the fourth element S2; one clutch C-4 which transmits rotation from the input path T1 to the first element; one clutch C-3 which transmits rotation from the input path T1 to the second element C-3; one brake B-1 which creates engagement of the fourth element; one brake B-2 which creates engagement of the second element; and one output element coupled with the third element R3.
With the scope of the Applicant's DE 101 15 983 A1 is described a multiple stage transmission having one drive shaft connected with a front-mounted range change set, one driven shaft connected with a rear-mounted range change set and having a maximum of seven shifting elements by the optional shifting of which at least seven forward gears can be shifting without group shift. The front-mounted range change set is formed by a front-mounted planetary gear set or a maximum of two non-shiftable front-mounted planetary gear sets coupled with the front-mounted planetary gear set, the rear-mounted range change set is designed as a two-spider-four shaft transmission with two shiftable rear-mounted range change sets and four free shafts. The first free shaft of said two-spider-four shaft transmission is connected with the first shifting element, the second free shaft with the second and third shifting elements, the third free shaft with the fourth and fifth shifting elements and the fourth free shaft is connected with the driven shaft. For a multiple stage transmission with a total of six shifting elements, the invention additionally proposes to connect the third free shaft or the first free shaft of the rear-mounted range change set with a sixth shifting element. For a multiple stage transmission having a total of seven shifting elements, the invention proposes connecting the third free shaft additionally with a shift shifting element D′ and the first free shaft additionally with a seventh shifting element.
Within the scope of the Applicant's DE 101 15 987 has been described a multiple stage transmission having at least seven gears. Said transmission, together with the drive shaft and the driven shaft, comprises one non-shiftable front-mounted range change set and one shiftable rear-mounted range change set in the form of a two-spider-four shaft transmission. The front-mounted range change set comprises one first planetary gear set which, together with the input rotational speed of the drive shaft, offers a second rotational speed which can optionally be shifted to a rear-mounted range change set. The rear-mounted range change set consists of two shiftable planetary gear sets which, with the six shifting elements, can shift at least seven gears, with two power paths being formed. At the same time, group shifts are always advantageously prevented during each shifting operation. One 9-gear multiple stage transmission has further become known from DE 29 36 969; it comprises eight shifting elements and four gear sets.
Automatically shiftable vehicle transmissions of a planetary design have already generally been widely described in the prior art and are subject to permanent developments and improvement. Said transmissions thus must have a sufficient number of forward gears, the same as one reverse gear and a ratio very well suited for motor vehicles with a high total spread and favorable ratio ranges. They must also make possible a high starting ratio in a forward direction and contain a direct gear, the same is adequate for use both in passenger and in commercial vehicles. In addition, said transmission must have low construction cost, especially require a low number of shifting elements and prevent double shifts in a sequential shifting mode so that in case of shiftings in defined gear groups only one shifting element is changed.
The problem on which this invention is based is to propose a multiple stage transmission of the type mentioned above in which the construction cost is optimized and, in addition, the efficiency degree is improved in the main drive gears with regard to towing and gearing losses. Besides, low torque must act on the shifting elements and planetary gear sets in the inventive multiple stage transmission, the same as the rotational speeds of the shafts, shifting elements and planetary gear sets are to be kept as low as possible. The number of gears, the same as the transmission spread must also be increased so that eight forward gears and at least one reverse gear can be advantageously implemented. Besides, the inventive transmission must be adequate for any design of the vehicle, especially for a front-transverse arrangement.