One-piece, force-locking compensating coupling made from plastic

The compensating coupling presented here can inexpensively be produced by injection moulding. Both axial and radial shifts as well as angular errors can be compensated for to a significant extent. In contrast to conventional plastic couplings, higher torques can be transferred. Its connection to the respective shafts is realized by an innovative clamping hub that secures the required traction.

Challenge

Production of multi-piece couplings is expensive and time-consuming. There are one-piece compensating couplings that can be produced inexpensively, however these are only suitable for low tourques. Especially the connection to the shaft can be a critical point. For the coupling to be able to transfer a high as possible tourque, the connection to the shaft has to offer the needed traction. Thus, there is a lack for inexpensive plastic compensating couplings with an appropriate shaft-coupling for medium tourques.

Our Solution

Fig. 1: One-piece compensating coupling according to design (II). (Source: Prof. Dr. Sven Lippardt)

The Figure on the right, illustrates the newly designed plastic coupling (Fig. 1). This one-piece design can easily be produced by injection moulding (s. Fig. 2 B).
Alternately placed rigid discs that are connected by thin-walled and flexible compensating elements allow for compensation of both axial and radial shifts as well as angular errors. Particular significance lies in the form of the compensating elements. In contrast to conventional coil springs, the incline of the coil spring is not constant, but they rather bend towards the discs. Thus allowing for simultaneous transmission of torques and compensation of relatively large misalignment.
Two types of construction are useful:
(I) Two rigid discs connected by flexible compensating elements. This design builds extremely compact, however it is only suitable for compensation of axial shifts and angular errors.
(II) Between the two end discs, multiple intermediate discs, that are themselves connected to the compensating elements, can be integrated. Such designs can in addition also compensate for radial shifts.

A friction-free transmission of tourques to the shaft, can for this coupling easily be realized by a clamping hub in combination with a contact element, for example a coating that increases the friction coefficient (s. Fig. 2 A).

Fig. 2: A) Clamping hub (1) that consists of a clamp (2) that eccentricly fits on the coupling body (4) and is tightened by a screw (3) to clamp onto the shaft. A coated contact element (5) increases the friction coefficient. B) Production of a compensating coupling by injection molding using three mold tools (7) that comprise shapes for the interspaces. (Source: Prof. Dr. Sven Lippardt)

Advantages

compensation for large misalignments
transmission of unusually high tourques for plastic couplings
production via injection moulding possible
other production methods applicable (machining, additive technologies)
modular design: one size clamp for different sizes of couplings

Applications

Transmission of medium tourques for which conventional plastic couplings are not suitable, but metal couplings would be overbuild.

Development Status

CAD-Drawings are available and injection moulding tools have been designed. Transmittable tourques have been determined by flexural strength tests with test rods and simulations of the coupling under load by the finite-elemente-method (see table).

Patent Status

Disclosed patent applications:
   German patent application: DE102017113075A1
    International patent application: WO2018228910A1
    Another patent application has been filed.

Applicant:
Ostfalia University of Applied Sciences – University Braunschweig/Wolfenbüttel

Contact

Dr. Tilmann Götze
Patent Manager Physics & Technology
E-Mail: tgoetze(at)sciencebridge.de
Tel.: +49 (0) 551 30 724 159
Reference: CPA-2017-FHBW and CPA-2108-FHBW
www.sciencebridge.de