Endless belt power transmission systems or components – Means for adjusting belt tension or for shifting belt,... – Guide roll mounted for movement of its axis along arcuate...
Reexamination Certificate
2002-05-08
2003-12-09
Charles, Marcus (Department: 3682)
Endless belt power transmission systems or components
Means for adjusting belt tension or for shifting belt,...
Guide roll mounted for movement of its axis along arcuate...
C474S112000
Reexamination Certificate
active
06659896
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention concerns a tensioning device for traction means, especially toothed belts, as they are used, for example, in toothed belt drives of motor vehicles. The present invention furthermore concerns a process for installation of, in particular, a prestressed tensioning device for traction means.
2. Description of Related Art
From U.S. Pat. No. 4,832,665, for example, a tensioning device for toothed belts is known where a tensioning roller is pivoted on an eccentric. The eccentric is arranged pivotably on a carrier which is flange-mounted on a motor by means of a screw. A spiral spring arranged on the eccentric is supported on the one hand on the motor and on the other on the eccentric such that the eccentric with the tensioning roller is sprung against the toothed belt. With this tensioning device, a locking pin is provided which keeps the tension spring in a prestressed arrangement prior to starting up. After flange-mounting the tensioning device to the motor, the locking pin is withdrawn so that the eccentric is sprung under the force of the tension spring against the toothed belt. The toothed belt can wind around the toothed drive pulleys of the crank shaft and the camshafts. It is important that a jumping of the toothed belt over the teeth of the toothed drive pulleys is prevented, since otherwise the control times are altered in an undesirable manner so that a total failure of the internal combustion machine can result. In order to avoid a jumping of the toothed belt, with the tensioning device in accordance with U.S. Pat. No. 4,832,665, a freewheel is arranged between the bolt mentioned and the eccentric. When in the strand of the toothed belt, with which the tensioning roller interacts, excessively high strand tension arises, the eccentric is swivelled against the force of the tension spring. The grip roller freewheel engages in this direction so that an undesirably high deflection of the eccentric out of the belt drive is prevented. As soon as excessively high strand tension has built up, the tensioning roller exerts spring force against the toothed belt so that the required tension is maintained in the strand. In this way, a jumping of the toothed belt is avoided. The freewheel accordingly here takes over the function of a stopper which restricts the swivelling angle of the tensioning arm. With this tensioning device, the expensive construction of the stopper is nonetheless disadvantageous, which requires the freewheel as well as a damping fluid in order to make possible a deflection of the eccentric out of the belt drive.
A so-called double eccentric tensioner is known from DE 40 15 028 A1 which includes an adjusting eccentric and a working eccentric. During installation on the motor block, the tensioning device is at first loosely screwed with bolts passed through an eccentrically arranged fastening bore hole. The tensioning device is swung against the belt with an adjusting tool inserted into a hexagonal recess. When this is stressed, a reaction force acts upon the tensioning device. With further swivelling, the spiral spring is stressed and the installation tool swivelled. The swivelling process is continued until notches provided on the flange and a plastic disk are covered. In this situation, a projection is situated in the middle of a recess of the swivelling area of the tensioning arm. The bolt is screwed fast in this presetting. These double eccentric strainers have the disadvantage that when the adjusting eccentric is swivelled too far for the presetting, the one notch wanders past the other notch. If now the adjusting eccentric is swivelled back until the two notches are aligned with each other, the projection is no longer situated in the center of the recess mentioned, but rather somewhat displaced from it. The reason for this displacement is an internal friction which arises between the machine parts during presetting. In this case, the stopper which is formed by the projection and the recess, has another position so that the swivelling region of the tensioning arm is altered. A hysteresis effect takes place. In practice, this can lead to considerable problems, since first strand tension forces deviate from their predetermined values and secondly because the swivelling range is no longer adjusted to the behavior of the traction means drive.
SUMMARY
The object of the present invention is therefore to provide a tensioning device which is simply constructed and the starting of which is reliably possible.
With the invention, a tensioning device for traction means, especially a toothed belt, is proposed which is provided with a tensioning arm on which a tensioning roller is rotably arranged, and which is furthermore provided with a stopper which restricts a pivoting angle of the tensioning arm, whereby a detachable locking device is provided by which the tensioning arm and the stopper are locked into a position provided for the stopper for joint swiveling.
With the tensioning device of the invention, additional machine elements, as for example free wheels, can be dispensed with. Furthermore, it is assured that any friction possibly arising between parts to be adjusted has no influence on the trouble-free position of the stopper, because due to the locking, no relative motion between tensioning arm and stopper takes place during installation. If the tensioning device is installed in a toothed belt drive, a tension spring can press the tensioning arm against the toothed belt, whereby the tensioning arm swivels together with the stopper. This swiveling motion ends when an equilibrium of forces between strand tension, the force of friction and tension spring force is established. In this situation, the stopper is fixed, and the locking described is relieved so that a further operation-conditioned swiveling of the tensioning arm takes place independently of the stopper. The position of the stopper is now coordinated with the toothed belt drive. Faulty adjustments, especially due to the hysteresis effect, are ruled out because the stopper is only swivelled in the direction of the belt, and because the stopper is moved together with the tensioning arm.
The tensioning arm and the stopper can both be provided in any given case with at least one arrangement which are provided for striking against each other, whereby the arrangements are set at a distance from each other if the tensioning arm and the stopper are locked with each other. This distance is precisely dimensioned such that after installing the tensioning device, the swiveling angle of the tensioning arm is brought out of its middle position (which at least generally agrees with the position after concluding installation) and against the tensioning force of the tension spring on the toothed belt drive. If the excessive strand tension causes a strong deflection of the tensioning arm against the spring force of the tension spring as a consequence, this deflection is stopped in time by the stopper or by the striking of the arrangements on each other. As soon as the strand tension has diminished, the tensioning arm immediately springs under the spring force of the tension spring against the toothed belt so that a jumping of the toothed belt is reliably prevented.
An especially simple and economical tensioning device provides that the tensioning arm is pivotably located on a carrier, whereby a tension spring is supported on the one side on the carrier and on the other on the tensioning arm. This arrangement makes a prestressing of the tension spring possible. If the tensioning arm, the stopper and the carrier are lockable with each other by means of the locking device, the following advantages result: First the locking can take place in an arrangement in which the tension spring is prestressed, and secondly a defined angle between stopper and tensioning arm can already be adjusted in advance.
An especially simple locking device provides a pin which engages for locking in openings of the elements to be locked whereby the pin can be brought out of engagement with the
Miko Josef
Stief Hermann
Charles Marcus
INA-Schaeffler KG
Volpe and Koenig P.C.
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