The invention pertains to a torsional vibration damper on a bridging clutch of a hydrodynamic clutch arrangement.
A torsional vibration damper of this type is known from, for example, U.S. Pat. No. 7,073,646. The hydrodynamic clutch arrangement, realized in the form of a torque converter, is designed with a bridging clutch. The side of the clutch piston facing the clutch housing is provided with a friction surface, by means of which the piston can be brought into frictional connection by way of an intermediate plate with an opposing friction surface on the clutch housing. The bridging clutch establishes a working connection between the clutch housing, which is attached nonrotatably to a drive such as the crankshaft of an internal combustion engine, and the torsional vibration damper. That is, the connection is established between the clutch housing and a drive-side transmission element of the torsional vibration damper, this transmission element being attached nonrotatably but with freedom of axial movement to the intermediate plate. The drive-side transmission element cooperates with energy-storage devices of a drive-side energy-storage group and with cover plates serving as an intermediate transmission element to form a drive-side damping device. The cover plates, which are a certain axial distance apart, for their own part cooperate with energy-storage devices of a takeoff-side energy-storage group and with a takeoff-side transmission element to form a takeoff-side damping device. This is connected nonrotatably to a takeoff-side component such as a gearbox input shaft.
When considered as a free vibration system with a hydrodynamic clutch arrangement, the drive train of a motor vehicle can be broken down roughly into six masses. The drive with a pump wheel represents the first mass, the turbine wheel the second mass, the gearbox input shaft the third mass, the universal shaft and the differential the fourth mass, the wheels the fifth mass, and the vehicle as a whole the sixth mass. In the case of a free vibration system with n=six masses, it is known that there will be n−1 eigenfrequencies, i.e., 5 eigenfrequencies, the first of which pertains to the rotation of the overall vibration system and is unimportant with respect to the damping of vibrations. The rotational speeds at which the eigenfrequencies are excited depend on the number of cylinders of the drive, which is designed as an internal combustion engine. FIG. 2 shows a logarithmic plot of the amplitude-frequency curve at the turbine wheel of a hydrodynamic clutch arrangement.
In the effort to minimize fuel consumption, there is a trend toward closing the bridging clutch even at very low speeds to minimize the losses in the hydrodynamic circuit caused by slippage. For the bridging clutch, this means that it is closed at a frequency which may indeed be above the first and second eigenfrequencies EF1 and EF2 but still below the third and fourth eigenfrequencies EF3 and EF4. Whereas the first two eigenfrequencies EF1 and EF2 in the hydrodynamic circuit of the hydrodynamic clutch arrangement can be damped, the drive train can be excited to generate undesirable noise on passage through the third and fourth eigenfrequencies EF3 and EF4. The third eigenfrequency EF3 in particular can have very large amplitudes.
To return to U.S. Pat. No. 7,073,646, the torsional vibration damper according to FIG. 1, for example, has two damping devices, where the drive-side device is connected nonrotatably to the intermediate plate as a component of the bridging clutch, and where the takeoff-side damping device is connected nonrotatably to the gearbox input shaft as a takeoff-side component of the hydrodynamic clutch arrangement. The turbine wheel, functioning effectively as a mass element between the two damping devices, is connected to the intermediate transmission element.
Because of the way in which the turbine wheel is connected, the drive-side damping device acts as a torsional vibration damper (TD) of the type referred to in professional circles as a “standard TD” and, taken in itself, would make available the damping curve shown in FIG. 3. In the case of the amplitude-frequency curve at the turbine wheel of a hydrodynamic clutch arrangement shown schematically as a logarithmic plot in FIG. 2, a standard TD would lower both the amplitude of the third eigenfrequency EF3 and the amplitude of the fourth eigenfrequency EF4. For the third eigenfrequency EF3, however, the obvious elevation in rotational irregularity in the speed range around 1,500 rpm would remain, as can be seen in FIG. 3.
Because, in the case of the torsional vibration damper according to U.S. Pat. No. 7,073,646, the takeoff-side damping device and its takeoff-side transmission element are able to rotate relative to the turbine wheel attached to the intermediate transmission element, the takeoff-side damping device acts as a torsional vibration damper of the type called in professional circles a “turbine torsion damper” or “TTD”, which, taken in itself, would result in the damping curve shown in FIG. 3, in which the elevation in rotational irregularity resulting from the third eigenfrequency EF3 is shifted to a range of around 1,000 rpm and therefore would cause very little trouble in the normal rpm range.
In contrast to the preceding discussion, the torsional vibration damper according to U.S. Pat. No. 7,073,646, called in professional circles a “two-damper converter” or TDC, is designed with a standard TD as a damping device on the drive side, which reduces the eigenfrequencies EF3 and EF4, and with a TTD as a damping device on the takeoff-side, which shifts the eigenfrequency EF3, which is the troublesome one, to a lower speed at which it generates little if any perceptible noise. The damping curve shown in FIG. 3 can thus be achieved with a TDC.
A damping curve of this type is desirable for modern vehicles, so that they can be operated with a completely engaged bridging clutch even in the lower partial load range relevant to fuel economy without thus making it necessary to accept disadvantages in the form of annoying vibrations or noise. To the extent that the bridging clutch is to be closed even at speeds as low as 1,000 rpm, however, even the damping curve provided by a TDC can still prove insufficient.
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