Lock-up clutch for a hydrodynamic torque converter

Details Lock-up clutch for a hydrodynamic torque converter Lock-up clutch for a hydrodynamic torque converter

2002-06-05

2004-06-01

Rodríguez, Saúl (Department: 3681)

192 clutches and power-stop control

Vortex-flow drive and clutch

Including drive-lockup clutch

C192S10700R, C192S113360

Reexamination Certificate

active

06742637

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention pertains to a lock-up clutch with at least one friction area on a first converter component, which can be shifted into working connection with at least one opposing friction area on a second converter component by an engaging movement, or which can be separated from this opposing friction area by a disengaging movement in the direction opposite that of the engaging movement.
2. Description of the Related Art
U.S. Pat. No. 5,215,173 discloses a lock-up clutch for a hydrodynamic torque converter with a piston, which, as shown in
FIGS. 1 and 2
, carries a friction lining on the side facing a converter cover; the side of this lining which faces away from the piston serves as a friction area. The piston can be moved toward the converter cover to engage the lock-up clutch or away from it to disengage the clutch. As soon as the friction area of the friction lining makes contact with the converter cover, the corresponding contact surface of the latter serves as the opposing friction area. The piston serves as the first converter component, and the converter cover serves as the second converter component of the lock-up clutch.
As soon as the friction lining of the piston comes into contact with the converter cover the rotational movement of the converter housing around its rotational axis is no longer transmitted to the transmission input shaft via a hydrodynamic circuit with an impeller, a turbine wheel, and a stator; instead, the movement is transmitted directly to the shaft by means of the lock-up clutch.
The use of a lock-up clutch may be advantageous from the standpoint of energy efficiency, but in this operating state the lock-up clutch should be used to damp the torsional vibrations which may have been introduced along with the torque. For this reason, the piston of the lock-up clutch is connected by a torsional vibration damper to the transmission input shaft; the torsional vibration damper has stored-energy elements to absorb elastically the torsional vibrations. In designs of lock-up clutches without torsional vibration dampers, such as that shown in
FIGS. 3 and 4
of the same Offenlegungsschrift, however, the pressure which presses the piston against the converter cover is reduced so that the piston can make a desirable slipping movement. Although this slippage may serve effectively to damp the introduced torsional vibrations, it allows in return a considerable amount of heat to build up in the friction area and in the opposing friction area. This principle of lock-up clutch operation with controlled slippage can be realized both with a so-called single-WK (single torque circuit) design according to
FIGS. 1 and 2
and also with a double-WK design according to
FIGS. 3 and 4
, these two designs differing from each other only with respect to the number of friction linings. In the case of the double-WK design, however, the friction linings are preferably attached nonrotatably but with freedom of axial movement to a clutch disk located axially between the converter cover and the piston.
Regardless of the number of friction linings and accordingly of the number of friction areas and opposing friction areas, the previously mentioned buildup of heat caused by slippage makes it necessary to take measures to ensure that this heat can be carried away as quickly as possible from the working area of the lock-up clutch. In U.S. Pat. No. 5,215,173, this is done by thermal conduction through the metal as a result of the temperature gradient which exists between the origination point of the heat and the other areas of the hydrodynamic torque converter through which hydraulic fluid is flowing. When large amounts of frictional work are performed, however, this type of cooling is no longer sufficient, which means that the friction linings will become overheated and that the hydraulic fluid passing over them will deteriorate.
U.S. Pat. No. 5,575,363 discloses an elaboration in this regard. FIGS. 14-17 in particular show systems of grooves either in the friction linings or at least in one of the two converter components, i.e., in the converter cover or in the piston. These grooves make it possible for hydraulic fluid to flow from the radially outer area toward the radially inner area. As shown in
FIG. 1
of this patent, the hydraulic fluid can be carried away through channels provided for the purpose to the rotational center of the hydrodynamic torque converter and thus conveyed out of the converter circuit. The disadvantage, however, is that the grooves offer relatively high resistance to the flow of the fluid; this can be caused, first, by comparatively small flow cross sections of the grooves and, second, by long travel distances in the grooves. A high pressure difference must therefore be built up so that a sufficiently high volume flow rate of hydraulic fluid through the grooves can be obtained in spite of the previously mentioned high flow resistance. As a result, lifting forces which try to lift the piston also develop axially between the converter cover and the piston, and to counteract them it is necessary to apply higher contact pressures. Precisely when high torques are being transmitted, therefore, a considerable amount of energy must be expended to maintain this cooling process.
It is also extremely difficult to lay out the flow cross sections and the lengths of these grooves in such a way that the precise pressure difference required to force the hydraulic fluid through them is obtained. An advantageous solution to this problem is described in U.S. Pat. No. 5,732,804, according to which the length of the grooves is reduced and their cross sections are made relatively large. At least one throttle point is provided, which can be used to adjust the volume flow rate. This throttle point preferably passes through at least one of the friction linings in the axial direction. But even this solution with its advantageous engineering design still provides only a limited cooling action.
Systems of grooves in the friction lining have also become known in which each individual groove has both its inflow and its outflow points on the same radial side of the friction lining, whereas the friction lining also has a friction area radially outside these grooves. This radially outer friction area is closed in the circumferential direction and is intended to prevent a possible pressure-induced leak-through of hydraulic fluid from the radially outer area inward toward the radially inner area. This design of a groove system, shown by way of example in U.S. Pat. No. 4,986,397, may indeed reduce any tendency of the piston to be lifted from the converter cover assigned to it when the pressure of the fluid flowing through the grooves builds up, but on the other hand it suffers from the disadvantage that the flow through each individual groove occurs exclusively by reason of shear forces in the hydraulic fluid, these shear forces being caused by the relative velocity between the limiting surfaces. The conveyed volume flow rate is therefore low, and, in addition, some of the hot hydraulic fluid forced out of the groove which precedes in the circumferential direction is taken up again by the groove which follows in the circumferential direction. The cooling effect which can be achieved is thus correspondingly low.
SUMMARY OF THE INVENTION
The invention is based on the task of designing the friction area of the lock-up clutch of a hydrodynamic torque converter in such a way that a highly effective cooling action can be obtained in the friction area while good energy efficiency is provided at the same time.
This task is accomplished according to the invention by providing a pump on at least one of the converter components, the pump acting in the friction area or in the opposing friction area, namely, a pump with a geometric design which allows it to generate a pressure gradient, it is possible to force the flow of hydraulic fluid through at least one predetermined section, of the friction area and/or of the opposing friction area.
Thus the p

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