192 clutches and power-stop control – Clutches – Plural clutch-assemblage
Reexamination Certificate
2002-07-15
2004-04-20
Lorence, Richard M. (Department: 3861)
192 clutches and power-stop control
Clutches
Plural clutch-assemblage
C192S11000B
Reexamination Certificate
active
06722483
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a twin clutch, in particular an actively closing, dry friction clutch device disposed within a transmission housing and intended for a twin clutch transmission of a motor vehicle having an internal combustion engine, a crankshaft, and two transmission input shafts which are each connected to a separate friction clutch and can selectively be connected to the crankshaft via a clutch housing.
Twin clutch transmissions have been known for quite a long time and are preferably used in motor vehicles. A twin clutch transmission generally has two coaxially disposed transmission input shafts which are in each case assigned a separate friction clutch and a group of gear steps, i.e. gear speeds. The one group of gears generally includes odd numbered gears (first gear, third gear, etc.) and the reverse gear, while the other group includes even numbered gears (second gear, fourth gears, etc.). In a twin clutch transmission configured in such a manner, a shifting operation, i.e. a shifting from an active source gear into a next-higher or next-lower target gear, initially includes shifting into the target gear, which can take place, for example, via a corresponding shifting sleeve and a synchronized gear shift clutch assigned to a gearwheel of the target gear, and a subsequent, overlapped opening of the friction clutch assigned to the transmission input shaft of the source gear, and closing of the friction clutch assigned to the transmission input shaft of the target gear. Except during shifting operations, the transfer of force thus takes place in each case alternately via one of the two transmission input shafts.
A substantial advantage of the twin clutch transmission over a conventional stepped variable-speed transmission is that the shifting operations are performed substantially without interrupting the tractive force. This improves the acceleration in tractive operation and also improves the deceleration ability in overrun operation. Moreover, the driving comfort is improved because abrupt changes in acceleration are largely eliminated and because noise due to load changes caused by load backlashes between components of the drivetrain are largely avoided.
A considerable mechanical effort is necessary in the case of the manual actuation of two engine clutches and the shifting of two gears that are simultaneously applied for a given time. Therefore, twin clutch transmissions are generally configured as automated transmissions. In other words, the actuation of the engine clutches and the shifting of the gears take place via associated auxiliary drives which can be configured such that they can be actuated electro-magnetically, by an electric motor, by a pressure medium, for example hydraulically, or in another manner.
Conventional twin clutch transmissions use two oil-cooled multidisk clutches for starting up and shifting. The oil cooling has the disadvantage that, inter alia, a pump is required for this purpose and that the internal combustion engine must drive this pump continuously. Since this pump simultaneously also constitutes the oil pressure supply of the transmission control, it has to be configured, on the one hand, for a high volumetric flow of oil for the cooling, but, on the other hand, also for a high pressure for activating the transmission. Oil pumps of this type represent a constant power loss and thereby reduce the overall efficiency of the transmission and of the drivetrain.
Dry clutches result in a substantial improvement with regard to the efficiency. They do not require an active cooling and therefore do not require a pump that is designed for a high volumetric flow. The actuation energy for clutches of this type can be provided directly by electric motors or through the use of a hydraulic unit having an electrically operated pump.
However, the disadvantage of dry clutches in the form as previously used in the case of manual transmissions or automated transmissions (ASG: Automated Shifted Gearbox) is that the actuating force for disengaging (opening) the clutch is transferred, via the clutch, onto the crankshaft and has to be absorbed by the crankshaft, more specifically by the axial bearing of the crankcase. This axial bearing is a hydrodynamically lubricated sliding bearing which operates always or at least predominantly in the “mixed film lubrication range” due to the generally prevailing conditions with regard to rotational speed, load and configuration of the bearing. This mixed film lubrication or mixed friction firstly results in an increased torque loss at this point, but secondly also induces additional wear of the engine bearings.
In conventional drivetrains having manual transmissions this situation does not cause a real problem. The clutches are configured such that they open actively. Axial forces are only produced here if the driver declutches, i.e. actuates the clutch. However, this circumstance only occurs during a gear shift, when the vehicle is at a standstill (for example at traffic lights) or else during starting. The frequency of this occurrence in comparison with the overall service life of the vehicle is so low that no additional, impermissible wear can occur as a result. The reason for this conventional manner of construction is the expedient installation. The clutch is first screwed to the crankshaft on the finished engine and subsequently the transmission is connected to the engine.
In contrast, in automatic transmissions or in twin clutch transmissions having wet clutches, the clutch is a direct component of the transmission. The installation of the clutches (the converter) takes place within the framework of the installation of the transmission. An advantage of this method is that the transmission forms together with the clutches an independent unit that can be pre-checked. The installation in the vehicle manufacturing plant is considerably simplified and the risk of additional installation errors is substantially reduced.
While, as explained above, the axial force loading of the engine bearings does not, because of the small load duration, constitute an impermissible stress of manual transmissions, in the case of automated manual transmissions and in the case of twin clutch transmissions having dry friction clutches it really does lead to difficulties. The reason for this is that in the case of transmissions of this type it is expedient not to completely close the clutch. Instead, it is better to operate the clutch either with only a small over-capacity (the company LUK uses the term “torque tracking”) or with a small slip (“microslip”).
Both methods have the advantage that short-term torque surges are not transferred to the drive unit, but rather can be dissipated by a short-term slipping of the clutch. Moreover, in the case of twin clutch transmissions, the operation with a microslip has further advantages which considerably improve the quality of the gear shifting.
An additional difference between manual transmissions and twin clutch transmissions is the fact that in the case of manually operated shifting mechanisms, as explained, the clutches are configured as actively opening clutches while, in the case of twin clutch transmissions, they are generally configured as actively closing clutches, for safety reasons.
The necessity for a permanent activation of the clutches therefore leads, in the case of dry clutches of a conventional type, to an axial force being continuously transferred to the engine bearings. The disengaging bearings or clutch release bearings are likewise subjected to severe stress. The consequence is increased wear. Moreover, in the case of actively closing clutches, the frictional losses on the axial bearing of the crankshaft can lead to an increase in fuel consumption.
German Utility Model No. DE 91 14 528 U1 discloses a wet twin clutch which is provided within a transmission housing. The twin clutch has two oil-cooled multidisk clutches, the inner disks of which are connected to a common carrier and the outer disks of which are connected i
Becker Volker
Damm Ansgar
Kruse Georg
Lutz Wolf-Rüdiger
Schade Frank
Beck Manfred
Greenberg Lawrence A.
Lorence Richard M.
Stemer Werner H.
Volkswagen AG
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