Page 187 - The Tribology Handbook

Self-synchronising clutches B5

Helical I I
splines I
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Figure 5.2 A high power semi-rigid clutch in the disengaged and engaged position

Clutches of this type, as shown in Figure 5.2, have typical a clutch acts like a spacer flexible coupling. A spacer
dimensions and weights as shown in Table 5.1. clutch of this type is shown in Figure 5.3.
The clutch can also be designed to accept changes in
axial length, as may be necessary due to the thermal
Table 5. I Typical dimensions and weights of expansion of a generator system.
s ynchronising self shifting clutches In dual drive systems one driver can be stopped and
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Torque B wt maintenance can be carried out on that machine whilst the
capacrQ A driven machine continues to run, driven by the other
driver. To ensure the safety of operators the input side of
40 kNm 360 mm 375 mm 150 kg the clutch must be held stationary by a maintenance lock
60 330 440 210 which can be mounted within the clutch casing.
100 290 510 280 Clutches can be fitted with an internal thrust bearing
160 370 600 420 between the input and output sides so that the clutch is a
380 580 840 1125 fixed length and positions the output machine from the
1000 720 1000 2750 input or vice versa. Such a bearing is usually only
subjected to high thrust forces when the clutch is engaged
If there is misalignment between the input and output and in this condition there is no relative rotation across the
sides of the clutch (e.g: when a clutch is installed between bearing so it has a high thrust capacity.
separate machines such as a fan and a steam turbine) the Clutches can be fitted with a lock so that once engaged
clutch must be designed to accept this misalignment. Such and locked they do not disengage and hence can transmit
reverse torque (e.g. in a marine reversing drive). The lock
requires a control system to lock and unlock the c!utch and
INPUT TEETH CLUTCHTEETH
this is normally arranged through a hydraulic servo
interlinked with the plant control system. The lock can be
preselected before clutch engagement so that the clutch
locks immediately it engages.
The clutches can be fitted with a lock-out so that when
selected the clutch will not engage (e.g. in a ship where an
engine must be tested without driving the propeller). The
lock-out again requires a control system.
Clutches can be arranged so that they only engage at
high speeds for example in a steam turbine generator
where the steam turbine must turn slowly forward for
Figure 5.3 A spacer clutch which can also act as a cooling without engaging the clutch and turning the
flexible coupling between two shafts generator.
B5.2