1. Field of the Invention
The present invention relates to a clutch unit that includes at least one wet clutch that is cooled by a cooling fluid like, e.g., oil, that flows over the friction surfaces. The present invention particularly relates to a clutch unit that includes at least one multidisc clutch having input discs and output discs that are disposed behind one another in an axial direction, wherein a coolant flows between the discs at least when the multidisc clutch is open. The present invention furthermore relates to a clutch unit that includes at least two clutches, in particular multidisc clutches.
2. Description of the Related Art
Multidisc clutch units are disclosed in German published patent application Nos. DE 10 2004 061 020 A1, DE 10 2004 029 145 A1, and DE 10 2004 016 061 A1.
In such clutch units, typically the heat generated through friction at the discs has to be removed by a coolant. For that purpose, the clutches are cooled by oil in most applications. The oil has to be introduced into the clutches and has to be pumped out from the clutches again after the cooling process, in order to be cooled itself, in turn, in a cooler. Thereafter, it can be fed back into the coolant loop.
The quantity of cooling oil supplied to the clutches can be controlled according to the driving condition of the vehicle. While driving, a minimum coolant volume flow can be provided, in order to remove the heat generated by the slippage control of at least one of the clutches. During clutch operation, a large volume flow can be provided, since a rather large amount of heat is thus generated. During synchronization, the volume flow of cooling oil can be reduced to zero, in order to avoid a residual drag moment at the clutch discs. The largest volume flow is required during so-called stall. Thus, the entire engine power is dissipated by the clutch as heat.
Systems that use a separate oil cooler are state of the art. The hot oil is pumped out of the clutch and run into an oil container, or into the transmission sump. From there, the oil is pumped out by a separate pump and fed back to the clutch through an oil cooler.
It is an object of the present invention to provide a cooling device, which facilitates improved cooling of wet clutches. The clutch device in accordance with the present invention should furthermore only require little installation space, and it should preferably be possible to integrate it into the clutch unit. Furthermore, the clutch device in accordance with the present invention should have high efficiency and should be producible in a cost effective manner.