Shaft coupling with axial alignment

Details Shaft coupling with axial alignment Shaft coupling with axial alignment

1998-08-31

2001-03-20

Browne, Lynne H. (Department: 3629)

Joints and connections

Interfitted members

Diametric end slot is joint component

C403S375000, C403S383000, C464S086000

Reexamination Certificate

active

06203238

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a shaft coupling which connects two shafts to transmit torque, wherein one shaft end has at least one recess and/or one projection, and the other cooperating shaft end has at least one projection and/or one recess and these are coupled.
Shaft couplings of this type are known. For example, one type is formed by a bar which projects from one shaft end, in particular the front end, and which engages in a corresponding groove in the front end of the other shaft. A positive lock of this type transmits torques from a driving shaft to a driven shaft. However, these shaft couplings operate fault free only when the two shafts are satisfactorily aligned. To achieve this, centering pins and bores have been provided on the housing parts that accommodate the shafts. However, this merely aligns the housing parts.
For example, this principle is used in motor vehicles, where vacuum pumps are aligned with the aid of centering pins on the cylinder head or on the engine block of an internal combustion engine. If faulty positioning or axial offset occurs on account of mounting errors and/or tolerances between the shaft and the housing, the shaft coupling may be very quickly damaged or destroyed. This happens because the bar of one shaft, which engages in the groove in the other shaft, jams. The drive to the pump may stall. An attempt to prevent this comprises allowing a specific clearance between the bars and the corresponding grooves. However, upon faulty positioning of the shafts, such play promotes so-called edge bearing. Impermissibly high area stresses or edge pressures occur, and these may rapidly wear or even destroy the shaft coupling. To counteract this, the load bearing surfaces of the bars and of the grooves are designed spherical. For spherical surfaces, flattening of the points of contact takes place under compressive forces. In excessively high compressive forces, this effect, known as “Hertzian stress”, causes flattening and plastic deformation of the bar or groove.
Furthermore, the prior art suggests compensating for axial offset or angular misalignment of the shafts by interposing an articulated coupling. Such a coupling may comprise elastic articulated shafts, cardan joints or a generally known Oldham coupling. However, production of such couplings has proven to be costly. Furthermore, the overall length and weight of the overall arrangement are increased by a coupling placed onto the shaft ends. In addition, it is disadvantageous here that, in modern motor vehicle engines, particularly on the cam shaft, relatively high angular accelerations occur, which have the effect of extremely loading the ancillary units driven by the camshaft. As a result of the play in the coupling, the angular accelerations which act on the shafts of the ancillary units may even be increased by a factor of 2 to 4.
Prior art measures are not aimed at avoiding faulty positioning of the shafts, but merely at compensating for its occurrence. This leads to the disadvantages already discussed.
SUMMARY OF THE INVENTION
It is therefore the object of the invention to provide a shaft coupling in which the shafts are aligned.
This object is achieved with a shaft coupling having following the features. A shaft coupling for connecting two shaft ends to transmit torque includes one shaft end having a recess or a projection and the other shaft end also having a recess or a projection. Where there is a recess in one shaft end and a projection on the other shaft end, the projection projects into the recess. The projection and the recess may each have cooperating flat sidewalls.
A centering device on at least one shaft end cooperates with at least one mating centering device on the other shaft end for axially aligning the shaft ends. These may comprise a cylinder or pin at one shaft end and a correspondingly shaped and sized pin receiving recess on the other shaft end, which are in addition to the torque transmitting projection and recess.
The centering devices directly align the shafts. This also avoids faulty positioning, particularly axial offset. This shaft coupling, therefore, reduces the overall length and the weight of a pump unit and also may reduce production costs.
In a preferred embodiment, one centering device is a projection and the mating centering device is a recess that accommodates the projection. As a result, during mounting, a pump shaft can be plugged in a positive locking manner and essentially without play into the drive shaft (camshaft of an internal combustion engine). Correspondingly shaped and sized circular cylindrical design of the recess and of the projection is preferred.
In a particularly preferred embodiment, at least one of the centering device, the mating centering device and/or the connecting element have, at least in some areas, applied material and/or have at least one projection. Applied elastic material on at least one centering device enables secure attachment between the centering devices. The applied material is, for example, a layer that is applied in some areas and, in particular, is realized in the form of a web or webs or as knobs which project. Alternatively, the applied material may be formed by a plug-in part, in particular by a ring on the coupling element. This advantageously achieves the situation where, during the mounting of the shafts, they can be aligned flush. Further, the applied material allows slight play between the shafts during the operation of the pump, since the material or the projection can be deformed or worn away under the action of compressive forces and/or temperature. It is particularly advantageous that, although a very precise alignment of the shafts is carried out during mounting, during operation, play that may occur between the shafts due to thermal distortion is nevertheless reliably compensated for between the recesses and/or projections on the shaft ends.
In a preferred embodiment, the connecting element between two recesses at the shaft ends comprises a pin. Alternatively, a sleeve may be used instead of the pin. However, it is then preferable for the centering device and the mating centering device to be a circularly cylindrical projection.
In a design variant, both the centering device on one shaft end and the mating centering device on the other shaft end are circular cylindrical recesses. The two shaft ends are connected by a connecting element, e.g., a pin, which couples the shafts.
In this further embodiment, the pin does not have material applied, but it is plugged without play into both of the centering device recesses so that there is preferably slight pressure on the pin at both recesses. Such a connecting element may have a predertermined fracture point which fractures in the event of a corresponding axial offset or alignment error. This likewise advantageously ensures that the shaft of the pump is precisely aligned with the driving shaft at the time it is mounted, but that during the pump operation, an axial offset can in turn be compensated for by the recess and/or the projection on the shaft ends.
Other objects and features of the invention are explained below with reference to the drawings.


REFERENCES:
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patent: 767844 (1953-01-01), None
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patent: 1577804 (1980-10-01), None
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Great Britain Search Report dated Feb. 9, 1999.

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