Rotor balancing devices

The rotor balancing device disclosed herein comprises a cylindrical cup-shaped housing for mounting in a hollow rotor to be balanced having a central pivot on which two bushes are mounted. Two bob weights are connected by tension springs or other restraining devices to the two respective bushes to rotate about a pivot within the housing wall. The inner side of the housing wall and/or the weights have a coating of a contact or thermally activated adhesive. The restraining force of the tension springs is such that when the shaft in which the balancing device is mounted is rotated to a speed between natural frequencies of the vibration of the shaft and is nearer the lower frequency (i.e. in a mass controlled state) so that the weights in the balancing device assume positions in which any out-of-balance in the shaft is counter balanced by the weights, the springs are extended sufficiently to allow the weights to contact the inner side of the housing and are secured thereto permanently by the adhesive to balance the shaft permanently.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to rotor balancing devices and is particularly 
although not exclusively applicable to balancing devices for motor vehicle 
propeller shafts. 
2. Description of the Prior Art 
U.K. Patent No. 832048 discloses an automtic balancing device comprising a 
housing having an annular cavity filled with a dampening fluid, for 
example oil or ethylene glycol. Within the dampening fluid, rolling bodies 
are arranged to be freely movable. Should an unbalance occur in the rotary 
body during operation thereof, the rolling bodies will roll around the 
annular cavity and will assume, under the action of the components of 
force set up by the unbalance, positions in which they compensate for the 
out of balance. The specification also discloses the use of a solid but 
low melting point damping medium which can render the balls substantially 
immovable when cold, for example during a starting period or during any 
other phase of operation. The damping medium may be melted either by 
friction occurring during operation of the rotating body or by external 
heating. 
The disadvantage with the device having a damping fluid described above is 
that the rolling bodies will tend to move out of their balancing positions 
when the device is at rest so that the device will always be out of 
balance when it is started from rest and will not be in balance until it 
has been rotated above its resonant frequency speed. 
The disadvantage with the device having a low melting point damping medium 
described above is that heating of the damping medium causing it to melt 
and allowing the rolling bodies to move will occur in use of the device so 
that when the bodies can move out of the balancing positions if the device 
is not rotating just above its resonant frequency speed and the bodies 
could then act to increase the out of balance of the device. 
It is an object therefore of the present invention to provide a method and 
means for balancing a rotor in which the rotor, once balanced, remains 
permanently balanced. 
The applicants co-pending U.S. Pat. Appliction Ser. No. 625242, pending in 
Group 230 discloses a rotor balancing arrangement in which a rotor to be 
balanced has an annular cavity containing two balls free to roll around 
the cavity. An initially inert heat sensitive adhesive is coated around 
the cavity and the rotor is rotated to a speed just have its first 
resonant frequency vibration so that the balls take up balancing positions 
in the cavity counter-balancing the out-of-balance of the shaft. The 
adhesive is then activated by an external heat source to lock the balls in 
the balancing position so that the shaft is permanently balanced. In the 
latter arrangement balls are required which are free to rotate around the 
inner surface of the annular cavity until they reach the balancing 
position and it is an object of the present invention to provide an 
arrangement which avoids the rolling of weights around the annular cavity. 
SUMMARY OF THE INVENTION 
The invention provides a rotor balancing device comprising a plurality of 
weights, means for each weight to mount the weights both for rotation 
about the rotor axis and for radial movement with respect to the axis, the 
arrangement being such that the weights are prevented from moving into 
axial alignment with each other along the rotor axis, and means to secure 
the weights in fixed positions against both radial and rotational movement 
with respect to the rotor whereby the weights can be allowed to assume 
positions to counter balance any out-of-balance in the shaft when the 
shaft is rotated to a balancing speed in which it is between natural 
frequencies of vibration and is nearer the lower frequency (i.e. is in a 
mass controlled state) and can then be locked in said positions 
permanently to balance the shaft.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring firstly to FIG. 1 of the drawings there is shown a vehicle 
propeller shaft 10 which comprises a hollow tube in which a balancing 
device indicated at 11 is mounted. The balancing device comprises a 
cup-shaped housing 12 comprising a flat circular base 13 and a cylinder 
peripheral wall 14 which engages with an interference fit in the tubular 
propeller shaft. The base 13 has an upstanding pivot 15 concentric with 
the wall 14 on which two cylindrical bushes 16 are rotatably mounted. Two 
"bob" weights 17 are mounted to rotate with the bushes 16 by tension 
springs 18 respectively. The outer surface of each "bob" weight 17 has a 
coating of contact adhesive 19 and the inner surface of the housing 14 has 
a frictional surface 20 or vice versa. The weights 17 are arranged so that 
their paths just overlap to prevent the weights moving into axial 
alignment of each other. 
The propeller shaft is rotated to a balancing speed in which the shaft is 
between natural frequencies of vibration and is nearer the lower frequency 
(i.e. is in a mass controlled state) and this causes the "bob" weights 17 
to move into position which counterbalance any out of balance in the 
shaft. The springs 18 are selected so that at that speed, the centrifugal 
force acting on the weights is sufficient to draw the weights outwardly 
into engagement with the inner surface of the housing wall and the weights 
are then secured in those positions by the contact adhesive. Thus when the 
shaft slows down, the weights remain in the counterbalancing positions and 
the shaft is balanced for all speeds. 
FIG. 2 shows a modification in which each tension spring 18 is replaced by 
a compression spring 21 and each weight 17 is retained against outward 
movement into engagement with the outer wall of the housing by a 
restraining thread 22 connected between the weights 17 and its respective 
bearing 16 which is arranged to snap, extend or tobe fused by electrical 
means when the propeller shaft reaches said balancing speed. 
In the arrangement shown in FIG. 3, the thread 22 is retained and the 
compression spring 21 is replaced by a locking device which is connected 
between the "bob" weights 17 and its bearing 16 which permits the "bob" 
weight to move radially outwardly into engagement with the housing 
peripheral wall but prevents return of the "bob" weight. In the example 
shown the locking device comprises an over-centre linkage 23. 
FIG. 4 shows a similar arrangement to that of FIG. 1 except that the "bob" 
weights 17 are pivotally mounted on swing arms 24 connected to the 
respective bearings 16 to swing in planes containing the pivot axis and 
the tension springs 18 are provided to prevent outward pivoting of the 
"bob" weights until said balancing speed is reached. In this case the 
outer wall 14 of the housing has an inwardly projecting V-section annulus 
25 which is provided on either flank thereof with contact adhesive or 
frictional surface for engagement with the frictional surfaces or contact 
adhesive on the "bob" weights 17 as described earlier. 
FIG. 5 shows a further construction in which the bearings 16 are axially 
slidable along the pivot and the "bob" weights 17 have contact adhesive on 
the sides thereof adjacent the base 13 of the housing and the base 13 has 
an upstanding shoulder 26 provided with a frictional face 27. 
Alternatively the contact adhesive could be provided on the shoulder 26 
and the frictional faces provided on the weights 17. A spring 28 
restrained by a severable thread 28a is provided for moving the bearings 
16 towards the bottom face of the housing 13. When the shaft reaches said 
balancing speed and the thread is severed and the bearings are moved 
axially of the pivot to secure the weights to the shoulder in 
counterbalancing positions as described earlier. 
In FIG. 6, each "bob" weight 17 is connected to it bearing 16 by a 
frictional telescopic strut 28 and the outer face of the "bob" weight 17 
has a layer of contact adhesive and the peripheral wall 14 of the housing 
has a frictional surface or vice versa as described with respect to FIG. 
1. The frictional telescopic arm is arranged to release the "bob" weight 
17 when the propeller shaft reaches the balancing speed and the "bob" 
weights 17 move into counterbalancing positions as described earlier and 
are then secured to the wall of the housing by the contact adhesive to 
balance permanently the shaft. In a modification of the arrangement shown 
in FIG. 6 the outer face of the "face" weights 17 and the wall 14 of the 
housing are provided with axially extending splines which prevent the 
weights moving circumferentialy around the housing and the telescopic 
struts 28 prevent the weights from moving inwardly of the wall of the 
housing so that the weights are locked permanently in their 
counterbalancing positions. 
It will be appreciated that many modifications may be made to the above 
described embodiments without departing from the scope of the invention. 
For example, the contact adhesive used could be replaced by a thermally 
activated adhesive in which case an external heating source is provided 
for activating the adhesive when the weights have assumed counterbalancing 
positions. 
The contact or thermally activated adhesive could be on corresponding 
engaging faces of the weights and the housing or where means are provided 
for opposing inward movement of each weight the adhesive or splines could 
be replaced with suitable interengaging frictional surfaces on the weights 
and the housing.