Differential Pulley Blocks.
Year: 1888

page_text: Differential Pulley Blocks.
We, WILLIAM WOOD, foreman fitter, and THOMAS WRIGHTSON, Engineer, both of
the Teesdale Iron Works, South Stockton-on-Tees, in the County of York, do hereby
declare the nature of this invention and in what manner the same is to bo
performed, to be particularly described and ascertained in and by the following
statement:
Our Invention has reference to pulley blocks in which the power to raise and lower
weights is obtained from tho combined action of two wheels or pulloys which carry
the lifting chains, and which are forced round in opposite directions by the rolling
motion of a pinion which engages with the internally geared teeth of both lifting
whoels, and is mounted on an eccentric round which it is free to revolve, the eccentric
being secured to or forming part of a spindle, the axis of which coincides with the
axis of rotation of the lifting wheels.
Our invention can also be similarly applied to pulley blocks in which only one
lifting wheel is employed which is forced round by the same means as two lifting
wheels which are combined together, namely, by the rolling motion of a pinion which
in this case gears into the single lifting wheel and a corresponding fixed circle of
internally geared teeth, which serves as the equivalent for the circle of internally
geared teeth in the second lifting wheel.
Pulley blocks constructed with this combination of moving parts are capable of
being geared so that a suspended load is prevented from running down by the pinion
automatically interlocking the lifting wheels, the balance of forces by which the
interlock is effected and maintained being more or less stable according as the distance
between the teeth of the pinion in contact with those of the lifting wheels is greater
or less.
The object of our invention is to render the position or motion of the pinion
adjustable relatively to the lifting wheels by varying the throw of the eccentric as
required, whether the object in view is to compensate for the wearing down of the
said eccentric, or to adjust the interlock between the pinion and the lifting wheels so
as to obtain a greater or less tendency in the pulley block to automatically sustain the
load attached to the lifting chains as required.

page_text: And in order that our invention may be fully understood and readily carried into
effect, we will now proceed to describe the same and for that purpose shall refer to
the accompanying drawings, which illustrato a pulley block constructed to work with
an arrangement or combination of moving parts to which our invention is especially
applicable. Figures 1 and 2 are sectional views showing the internal construction of
the pulley block, Figure 2 being taken on line X X of Figure 1.
A A² are the lifting wheels which are forced round in the opposite directions
indicated by arrows by the pinion B, which is mounted on the eccentric C, round
which it is free to revolve on its own axis, D is the main spindle of the block to which
the eccentric C is secured, and which passes through the axis of the lifting
wheels AA; Figure 2 illustrates more particularly the pinion and lifting wheels when
interlocked in the effort of sustaining a suspended load. In this position the teeth b¹³
of the pinion B are engaged respectively with the tooth a' of the wheel A' and the
tooth a² of the wheel A³, which are thus acted upon at the points of contact with
equal force in opposite directions; when two or more pinion teeth intervene between
the points of contact as in the case, this distance between these points of contact is
great enough to afford a margin of stability in the balance of forces sufficiently
reliable to effectually resist the tendency of the weight to run down.
Pulley blocks are constructed to automatically interlock in this manner when it is
of great importance to be able to leave the load suspended in any position, but for
some purposes for which these pulley blocks are employed, such as for raising or
lowering weights, where speed and facility of manipulation are of more consideration
than the sustaining of the load automatically, the position of the pinion B should be
adjusted relatively to the lifting wheels A' A², by reducing the throw of the eccentric C
so as to allow the pinion B to recede towards the centre or axis of its motion until the
teeth get clear of the teeth a' a², and the positions of contact between the
interlocked teeth of the pinion B and lifting wheels A¹ A² are moved nearer together,
as for instance, to bring the teeth 636 of the pinion B into contact with the teeth a³ a
respectively of the lifting wheels, that is, with only one pinion tooth intervening
between the interlocked teeth, in which case the tendency of the lifting wheels to
remain interlocked by the pinion is less, and consequently less resistance is offered to
the operation of changing the load from a state of rest to a state of motion whether
for raising or lowering.
It is found in practice that when the pinion B has been originally geared into the
lifting wheels A¹ A2, as for instance, to interlock between the teeth a¹ 6' and a² 62 in
the manner herein before described, that the eccentric c wears down principally at the
part e, which is most remote from the axis of the eccentric, and is obviously most
exposed to the friction to be overcome in actuating the pinion B, and that consequently
the pinion recedes towards the centre or axis of its motion until the teeth b₁6² get
clear of the teeth a' a', and the points of contact are moved nearer together, as for
instance, to the teeth as and 63, a and b, with the result that a pulley block which
was fitted together to be thoroughly reliable to automatically sustain a suspended load
in course of time ceases to be so until the throw of its eccentric is re-adjusted, or if
the pinion was originally adjusted to interlock the lifting wheels with the points of
contact between the teeth a³, 63, a, b, that is with a fine margin of stability in the
balance of forces for effecting and maintaining the interlock, that as the eccentric
becomes worn down the interlocking teeth get clear altogether and the pinion becomes
incapable of interlocking the lifting wheels for the purpose of sustaining a suspended
load.
In order to enable the position and motion of the pinion to be adjustable at will
relatively to the lifting wheels for the purposes before mentioned, in the place of the
eccentric at present in use of which the sheave or disc is in one piece and which
consequently cannot be readily adjusted, we substitute an eccentric in which the
part 2, which is the part most exposed to the wear and friction of actuating the
pinion B, is formed as a separate part of the eccentric so that the throw of the eccentric
may be increased or reduced at will by the insertion of liners, packing pieces, or
other equivalent means between the parts c¹ c² of the eccentric; this may be effected

page_text: in various ways, as for instance, by employing set screws or keys, or by providing a
recess in the part 2 to receive the tongue or projection f on the part c², the liner or
packing required being first inserted and by being enclosed is effectnally retained in
position. The travel or rolling motion of the pinion B can then be adjusted
relatively to the lifting wheels A A² at any time, and the nature of the interlock
between the pinion and the lifting wheels readily adapted to the particular purpose
for which each pulley block is intended. .
In pulley blocks constructed with only one lifting wheel with a fixed circle of
internally geared teeth provided instead of the second lifting wheel, the tendency of
the pinion to antomatically interlock the lifting wheel depends. upon the same
condition of adjustment as already described with reference to pulley blocks
constructed with two lifting wheels, and it is therefore obvious that such pulley
blocks can be adjusted or re-adjusted in the same way as in the case of pulley blocks
constructed with.two lifting wheels in the manner illustrated in the accompanying
drawings.
:
Having now described the nature of our invention and in what way the same may
be carried into effect, what we claim in the internal mechanism of pulley blocks of the
kind herein referred to is:-
The means of rendering the travel or rolling motion of the pinion adjustable
relatively to the lifting wheels into which it is geared by mounting on an eccentric
constructed in separate parts whereby the throw of the said eccentric can be varied at
will, substantially in the manner and for the purpose as herein before described with
reference to the accompanying drawings.
1000