192 clutches and power-stop control – Vortex-flow drive and clutch – With additional drive or clutch
Reexamination Certificate
2000-10-02
2002-04-30
Marmor, Charles A (Department: 3681)
192 clutches and power-stop control
Vortex-flow drive and clutch
With additional drive or clutch
C192S048900, C192S057000
Reexamination Certificate
active
06378675
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is directed to a clutch device for connecting a motor vehicle drive with a multiple-speed transmission via at least two friction clutches which are connected with associated shift transmission input shafts by respective driven sides such that the clutches can be engaged or disengaged independently of one another.
2. Description of the Related Art
A clutch device of this kind is known, for example, from EP 0 931 951 A1. The clutch device serves to connect the drive of a motor vehicle with a multiple-speed transmission via two friction clutches which are preferably automatically actuated, a clutch release system being associated with each of these friction clutches so that the two friction clutches can be engaged or disengaged independently from one another. One of the friction clutches is arranged on a central transmission input shaft so as to be fixed with respect to rotation relative to it, while the other friction clutch engages at a second transmission input shaft so as to be fixed with respect to rotation relative to it, this second transmission input shaft, constructed as a hollow shaft, enclosing the central transmission input shaft. Clutch devices of this type, which are known in technical circles as “double clutches”, particularly when combined with a multiple-speed shift transmission, offer the possibility of carrying out shifting processes between two respective gear ratio speeds of the transmission without interruption of tractive forces.
The laid open application cited above addresses not only the advantages of such a clutch device, but also indicates the actual problem, albeit only indirectly: It is stated, for example, that both clutch disks can be acted upon jointly during particularly difficult starting processes. Such starting processes occur, for example, when the accelerator pedal is deflected to the region of its stop, while the motor vehicle is kept essentially stationary at the same time by applying the maximum braking force until the clutch has reached its optimal transmission point which, when exceeded, would cause the drive to stall. If the braking action is canceled at this time, the vehicle is started with maximum acceleration. While starting processes of this kind are common primarily in car racing, they may be required particularly in motor vehicles with a relatively weak engine under extreme starting conditions, for example, when starting on an obstruction. This results in high slippage which brings about extensive development of heat. Consequently, not only is there the problem that this heat must be carried away from the area of extension of the friction clutch, but increased wear of the friction clutches must also be taken into account. Further, heating of this kind leads to changes in the coefficient of friction at the friction clutches so that the control of the two release mechanisms, and therefore of the two friction clutches relative to one another, can be appreciably impaired. This is incompatible with a problem-free torque transmission in shifting processes in the shift transmission without interruption of tractive force and without jerking during shifting. Specifically, as a result of inaccuracies in functional matching of the two friction clutches relative to one another caused by heat, a torque ratio not intended in the shifting process is applied to the two transmission input shafts, which can lead to shifting processes in the shift transmission under load. This can overtax the synchronization in the shift transmission so that, aside from the disadvantages with respect to efficiency, the shift transmission can be damaged to the point of complete failure.
Also problematic in clutch devices of this kind are starting processes which are either carried out in opposition to an inclination, wherein the motor vehicle must be prevented from rolling backward, or which are used when parking at the lowest possible speed for precise positioning of the motor vehicle in a parking space. The first operating state mentioned above is referred to in technical circles as “hill-holding”, the latter operating state is referred to as “creeping”. Both starting processes have in common that the friction clutch is operated, sometimes without actuation of the accelerator, over longer period of time with slippage. Although the torques to be transmitted in such starting processes lie well below those in the operating condition described above, an intensive heating of the friction clutches can occur, resulting in the problems detailed above.
Gear-shifting strategies and shifting processes for double-clutch transmissions based on the aimed for adjustment of clutch slip have been suggested (German reference DE 196 31 983 C1) with consequent generation of friction heat. Depending on driving behavior, overheating problems of the type mentioned above cannot be ruled out.
The risk of intensive overheating exists not only in a dry friction clutch, but can also occur in so-called “wet” friction clutches, preferably in the form of a disk or plate clutch which is arranged within a viscous medium such as hydraulic fluid. In this connection, reference is had to German reference DE 198 00 490 A1, for example, in which two plate clutches are arranged in viscous medium, one being provided for forward driving and the other for driving in reverse. The object of German reference DE 198 00 490 A1 is adequate cooling of wet friction clutches of this type, the viscous medium being utilized for this purpose. However, in spite of the liquid cooling, heating of the friction clutches constitutes a considerable problem because, on the one hand, the viscous medium overheats when flowing through flow passages in the form of channels usually provided in friction surfaces of the friction clutch and can accordingly be destroyed and, on the other hand, due to the building up of an opposing pressure between the friction surfaces of two adjacent plates with intensive flow through these grooves, capacity of the friction clutch to transmit torque is reduced and the problem of overheating is therefore exacerbated due to increased slippage. Particularly in plate clutches, this problem can result in that the friction surfaces can no longer separate from one another completely after a disengaging process and, consequently, considerable drag torques can sometimes reach the shift transmission because one of the friction clutches is already closed, while the other has not yet completely opened.
SUMMARY OF THE INVENTION
It is the object of the invention to construct a clutch device in such a way that an intensive heating is prevented in the area of the friction clutches even under unfavorable operating conditions such as in problematic starting processes in a motor vehicle.
This object is met according to the invention by producing an operative connection between one of the friction clutches and a hydrodynamic clutch, the latter can be activated as a substitute for the friction clutch that is in a working connection with the hydraulic clutch during difficult starting processes such as, for example, when overcoming obstacles, when starting on hills using the “hill-holder” function and when “creeping” for parking the motor vehicle in a narrow parking space. In this respect, the hydrodynamic clutch is advantageous in a two-fold sense: first, while starting processes with a hydrodynamic clutch, even under full load, lead to a temporally limited relative movement of the driving member—usually formed by an impeller wheel—with respect to the driven member having a turbine wheel and therefore result in losses for reasons pertaining to flow, the heat development occurring in this connection remains within strict boundaries, especially since the transmission of torques in hydrodynamic clutches of this type entails a comparatively high volume flow of viscous medium circulating between the impeller wheel and turbine wheel. As soon as the turbine wheel has almost reached the rotational speed of the impeller wheel, the hydrodynamic clutch operates wit
Kundermann Wolfgang
Sudau Jörg
Cohen & Pontani, Lieberman & Pavane
Mannesmann Sachs AG
Marmor Charles A
Rodríguez Saúl
LandOfFree
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