Couplings

Couplings play a fundamental role in transmissions. They ensure to connect the engine with the gearbox on the one hand and, on the other hand, to connect the gearbox with the machine.

The wrong type of coupling or a bad alignment can cause heavy damage to the transmission by inserting additional stresses. On the other hand, the choice of a wrong coupling can be less well adapted to transmissions where alignment errors occur at the input or output shafts. One should also be aware that in some applications the torsional stiffness plays an important role.

1. Stiff couplings

In this category of couplings you can find the following couplings:

  • flange couplings
  • sleeve couplings
  • spline couplings
  • freewheel clutches
  • torque restrictions
  • safety couplings
  • hydraulic clutches

These types don’t allow any alignment error. They are not applicable for shaft connections where one shoud take into account the alignment deviations.

2. Flexible couplings

a. Universal joints
These couplings transfer torques between axes that mutually form an angle.
– Universal joints
b. Flexible couplings
These couplings can to some extent compensate alignment errors between two axes. These couplings can also be divided into two categories.

i) Couplings that compensate alignment errors by sliding of coupling parts

  • The tooth coupling belongs to this group and is widely applied. These are mainly applied in shaft connections with alignment errors and where axial clearance is required.
  • The spherical couplings are mainly applied in three point supports.
  • The chain coupling.

ii) Couplings that compensate alignment errors by folding the coupling parts
These couplings contain foldable diaphragms that are attached between two flanges. They are applied to fast rotating axes and require no lubrication.

  • The metal plate couplings

3. Flexibel couplings

The flexible couplings are applied for partially absorbing colliding loads or vibrations.

  • The bolt coupling belongs to this type and consists of two flanges with driving plate pins with rubber cases. The bolts are fixed in holes with a diametrical clearance from 0.5 upto 1 mm. The elasticity is, however, limited.
  • Claw couplings have better elastic properties.
  • The Falk-Bibby coupling is another type of flexible coupling that captures parallel and angular distortion errors and allows axial displacements. A spring connects the conical external teeth of both flanges.

4. Engagement couplings

This type of coupling compensate no alignment errors or other defects. The following couplings belong to this group:

  • starting couplings
  • electromagnetic couplings
  • magnetic couplings
  • hydraulic engagement torques
  • magnetic couplings
  • pneumatic couplings
  • one-piece friction couplings
  • sheet couplings
  • conical couplings
  • engagement tooth couplings
  • brake couplings
  • safety engagement couplings

All proposed flexible couplings can compensate certain alignment errors, however, these exceptions should be as low as possible in order to ensure the proper functioning of the transmission. The properties and permissible deviations are supplier related and can be found in the relevant catalogues. Below you will find the three main deviations:

Ashoekfout

Shaft angle error

Radiale fout

Radial error

Axiale asverplaatsting

Axial shaft displacement

E
mm
R
mm
A
°
E
mm
R
mm
A
°
E
mm
R
mm
A
°
E
mm
R
mm
A
°
E
mm
R
mm
A
°
E
mm
R
mm
A
°
Membrane coupling
Tooth coupling
Metal spring coupling
Bolt coupling
Claw
coupling
Flexible coupling
30
3
0,1
1,5
40
3
0,14
1,5
50
2
0,25
1
55
3
0,14
1,5
60
2
0,25
1
65
6
0,19
1,5
70
1
0,15
0,12
80
6
0,22
1,5
2
0,2
0,14
85
3
0,4
1
90
2
0,2
0,13
95
2
0,2
0,12
100
1,8
0,1
0,1
6
0,23
1,5
3,2
0,15
0,1
105
3
0,2
0,11
3
0,4
1
111
3,2
0,15
0,1
120
6
1,2
3
3,2
0,15
0,1
3
0,25
0,12
4
0,5
1
125
2,4
0,1
0,1
6
1,4
3
130
3
0,25
0,11
140
3,2
0,2
0,1
3
0,3
0,12
4
0,5
1
145
3
0,2
0,1
150
2,6
0,1
0,1
3,2
0,2
0,1
155
3
0,2
0,1
3
0,3
0,11
160
8
1,6
3
3,2
0,2
0,1
165
4
0,65
1
170
3,2
0,1
0,1
175
3
0,2
0,1
180
8
1,7
3
4
0,35
0,11
190
195
3,8
0,15
0,1
3,2
0,2
0,1
5
0,65
1
200
8
0,9
1,5
3
0,2
0,1
4
0,4
0,11
210
215
4,6
0,15
0,1
3,2
0,2
0,1
220
8
1
1,5
225
5
0,45
0,11
230
6
0,8
1
235
4
0,25
0,1
245
4
0,25
0,1
250
10
1,2
1,5
4,8
0,25
0,1
260
5,2
0,2
0,1
270
4,8
0,25
0,1
6
0,8
1
280
10
1,7
1,5
4
0,25
0,1
295
6,6
0,2
0,1
310
6,4
0,28
0,1
6
1
1
Ashoekfout

Shaft angle error

Radiale fout

Radial error

Axiale asverplaatsting

Axial shaft displacement

E
mm
R
mm
A
°
E
mm
R
mm
A
°
E
mm
R
mm
A
°
E
mm
R
mm
A
°
E
mm
R
mm
A
°
E
mm
R
mm
A
°
Membrane coupling
Tooth coupling
Metal spring coupling
Bolt coupling
Claw
coupling
Flexible coupling
315
4
0,25
0,1
320
13
1,8
1,5
335
7
0,3
0,1
350
6,4
0,28
0,1
355
5
0,3
0,1
360
8
1,1
1
385
6,4
0,28
0,1
5
0,3
0,1
460
490
5
0,3
0,1
510
8
1,6
1
575
6
0,4
0,1
670
6
0,4
0,1
725
6
0,4
0,1
850
7
0,5
0,1
990
7
0,5
0,1
1060
7
0,6
0,1
1220
9
0,75
0,1

PLEASE NOTE

The specified values are guide values and are therefore not binding. For the correct permissible values one should consult the supplier of the appropriate couplings.