GB2152173A - Shaft coupling - Google Patents

Abstract

A shaft coupling for radially misaligned shafts, comprising two members such as discs 1A, 2A connected to respective shafts, each having at least three pivot elements 3, 6 equally circumferentially disposed on a circle concentric with the rotational axis of the respective member, and a number of arm members 4 each having a connection to a respective pivot element 3 of one member, a corresponding pivot element 6 of the other member, and to the other arm members (connection 5.) One of the connections for each arm member is a pivotal connection only, and the other connections provide for pivoting and sliding movement longitudinally of the respective arm member. <IMAGE>

Description

SPECIFICATION Shaft coupling This invention relates to a coupling for establishing a torque tramsmitting connection between two shafts or other rotary elements (hereinafter termed shafts) which may be radially misaligned.

One form of known coupling for radially misaligned shafts is the Oldham coupling. The shafts have discs which face one another, having grooves extending across their faces angularly displaced at 90 degress to one another, and there is an intermediate disc having walls on opposite faces, engaging in the grooves. When the coupling is in use, the intermediate disc undergoes an eccentric motion at twice the rotational speed of the shafts.

This gives an out-of-balance condition, rendering the coupling unsuitable for high speeds. A further disadvantage of such a coupling is that friction losses are high, as a result of sliding of the walls of the intermediate disc in the grooves of the discs on the shafts.

A further known type of shaft coupling utilises an intermediate disc, connected to discs on the shafts by at least three coupling members, in the form of arms, respectively.

Each arm is pivotally connected to one of the .shaft discs and to the intermediate disc, the arms being uniformly circumferentially arranged. In such a coupling, known as a Schmidt coupling, the intermediate disc occupies a defined position in which it rotates about its own axis, provided the shafts are radially misaligned. If the shafts are aligned, or only very slightly misaligned, the intermediate disc assumes an undefined position in which it may carry out an undesirable radial movement. Therefore the coupling is not suitable for all possible alignment conditions of the shafts.

It is the object of the present invention to provide a shaft coupling able to accommodate radial misalignment between two shafts but which is still usable if the shafts are aligned. It is a further object of the invention to provide a coupling which does not cause an out-ofbalance situation to arise if the shafts coupled are radially misaligned. Desirably, the coupling should be compact and able to accommodate a relatively high degree of radial misalignment.

According to the invention, we provide a coupling for radially misaligned shafts, comprising two members, preferably discs, connected repsectiveiy to said shafts and each having at least three pivot elements equally circumferentially disposed on a circle concentric with the rotational axis of the respective member, and a number of arm members each connected to a pivot element of one member, a corresponding pivot element of the other member and to the other arm members, one of said connections for each arm member being a pivotal connection only and the other connections thereof providing for pivoting and sliding movement longitudinally of the arm member.

In a coupling according to the invention, the position of the centre of mass of the assembly of arm members is independent of the angle of rotation, if rotation occurs with the shafts misaligned radially. Thus there is no out of balance condition when in use in the misaligned state. A further advantage of the coupling according to the invention is that if the shafts are aligned with one another, the centre of mass of the arm members lies at the rotational axis of the shafts, assuring balanced operation. The coupling is thus suitable for use in a situation where the state of alignment of the shafts to be coupled varies. A further advantage of the coupling is that it is relatively short in the axial direction.

Each of said arm members may include at least one elongate aperture extending longitudinally thereof, through which an element extends to provide said pivoting and sliding connection. The diameter of the element extending through the aperture is preferably substantially equal to the inside width of the aperture, for clearance free guiding thereof. If the pivoting and sliding connections are together on each arm member, two elements may extend through a single longitudinally extending aperture in the arm member of correspondingly greater length.

The pivotal connection for each arm member may be substantially at the centre of each arm member, in which case the pivoting and sliding connections are at the ends of each arm member, or the pivotal connection may be at or adjacent an end of each arm member, with the sliding and pivoting connections adjacent to one another.

The embodiment in which the pivotal and sliding connections are at the ends of the arm members is particularly suitable for greater radial offsets between the shaft.

The pivotal, and pivotal and sliding joints of the coupling may include roller or needle roller bearings, in order to reduce friction and wear caused by the rotary and sliding movements occurring at such connections.

The invention will now be described by way of example with reference to the accompanying drawings, of which Figure 1 is a side view, partly in section, of one embodiment of coupling according to the invention; Figure 2 is 3 section on the line ll-ll of Fig.

1; Figure 3 shows diagrammatically the arrangement of arm members of the coupling of Figs. 1 8 2; Figure 4 is a view corresponding to Fig. 3 showing a different embodiment of the invention; Figure 5 is another view corresponding to Fig. 3 showing yet another embodiment of the invention; Referring firstly to Fig. 1 of the drawings, the coupling there illustrated provides a torque transmitting connection between shafts 1, 2. The input shaft 1 is provided with a member in the form of a disc 1 a. Disc 1 a, and the output shaft 2 has a disc 2a whose diameter is greater than that of disc la is provided with three uniformly circumferentially spaced axially extending pivot elements in the form of bolts 3. Similarly, disc 2a is provided with three circumferentially spaced bolts 6.The bolts 3, 6 are attached to their respective discs by screws as shown at 9 in Fig. 1 for one of the bolts 6. The bolts 3, 6 have shoulders 3a, 6a of different axial lengths.

The torque transmitting connection is provided between the discs 1 a, 2a by three arm members 4, which are disposed generally radially. Each arm member has a bore 4b susbstantially at the centre thereof, through which a respective one of the bolts 3 on disc la extends. A washer 7 and retaining ring 8 at the end of each bolt 3 secures the respective arm member 4 thereto, for pivotal movement. Each of the arm members 4 has an elongate aperture 4a adjacent to its outermost end, extending longitudinally of the arm member. This receives a respective one of the bolts 6 on the disc 2a. Again, a washer 7 and retaining ring 8 secures the arm member to the bolt 6 for sliding and pivotal movement.

At their radially innermost ends, the arm members 4 are connected together by a bolt 5, again with a washer 7 and retaining ring 8, extending through elongate apertures 4c in the arm members. Thus, the arm members are connected here for pivotal movement and sliding movement longitudinally of each respective arm member. It will be appreciated that the differences in lengths of the shoulders 3a, 6a on the bolts 3, 6 respectively are dependent on the thicknesses of the arm members 4.

The arrangement of the arm members 4, and the sliding and pivotal connections thereon means that torque can be transmitted between the discs 1 a, 2a if the rotary axes thereof are not in alignment with one another.

In the misaligned condition, the centre of mass of the assembly of arm members is represented by the bolt 5, which does not move as the coupling rotates and therefore the coupling remains in rotary balance. If the shafts are aligned, the bolt 5 lies on the common axis of rotation of the shafts.

Fig. 3 shows diagrammatically the arrangement of the arm members and the sliding and pivotal connections thereon, for the embodiment of Figs. 1 and 2. An alternative embodiment is shown in Fig. 4, in which the arm members 4 are connected to one another at their radially innermost ends by a pivotal connection at bolt 5. Bolts 3, 6 are connected to the arm members for sliding and pivotal movement, in a common elongate aperture 4ac in each arm member.

In the embodiment of Fig. 5 shows yet another embodiment of the invention, in which bolts 6 are connected to the arm members for pivotal movememnt only, extending through apertures 4b therein. Bolts 3, and the common connecting bolt 5, are connected to the arm members for sliding and pivotal movement extending through elongate apertures 4ac therein.

In all the embodiments described, roller or needle roller bearings may be incorporated at the bolts 3, 5, 6 where they engage the arm members to reduce friction and wear.

Claims (8)

1. A coupling for radially misaligned shafts comprising two members connected respectively to said shafts and each having at least three pivot elements equally circumferentially disposed on a circle concentric with the rotational axis of the respective member, and a number of arm members each connected to a pivot element of one member, a corresponding pivot element of the other member, and to the other arm members, one of said connections for each arm member being a pivotal connection only and the other connections providing for pivoting and sliding movement longitudinally of the arm member.

2. A coupling according to claim 1 wherein each of said arm members includes at least one elongate aperture extending longitudinally thereof through which an element extends to provide said pivoting and sliding connection.

3. A coupling according to claim 1 or claim 2 wherein said pivotal connection is substantially at the centre of each arm member.

4. A coupling according to claim 1 or claim 2 wherein said pivotal connection is at or adjacent to an end of each arm member.

5. A coupling according to claim 3 or claim 4 wherein said pivotal connection is established with a respective one of said pivot elements on one of said members connected to a shaft.

6. A coupling according to claim 3 or claim 4 wherein said pivotal connection is the connection of the arm members to one another.

7. A coupling according to any one of the preceding claims including roller bearing elements at said pivotal and sliding connections.

8. A coupling substantially as hereinbefore described with reference to Figs. 1, 2 and 3, or Fig. 4, or Fig. 5 of the accompanying drawings.