Improvements in Marine Steam Engines.
Year: 1895

page_text: Complete Specification Left, 25th Jan., 1896-Accepted, 29th Feb., 1896
PROVISIONAL DI EGIPTUATION.
Improvements in Marine Steam Engines.
We, MARK HEATON ROBINSON, and MATTHEW HENRY PHINEAS RIALL
SANKEY, both of Ferry Works, Thames Ditton, in the County of Surrey,
Engineers, do hereby declare the nature of this invention to be as follows:-
The objects of this invention are to avoid vibration and to allow the engines to
work conveniently and economically at half power.
The causes of vibration in engines of ordinary construction, in which the cylinders
lie upon the same side of the crank shaft, are two. Firstly, the change of the
momentum of each piston and line of moving parts when near the top of the stroke,
in comparison with the momentum of the same parts when near the change of
bottom of the stroke, due to the different rates of acceleration and retardation in
those respective parts of the stroke caused by the varying angle of the connecting
rods. This, under ordinary circumstances, is the most important source of vibration,
its tendency being to alternately lift and depress the whole of the engine upon its
foundation. Secondly, the other cause of vibration is due to the unbalanced couple
existing between the pistons and other heavy moving parts, in a direction parallel
with the crank-shaft, which gives the engine a tendency to tilt as a whole,
endways.
The latter cause of vibration can be eliminated by well understood methods; for
instance, in a three-crank engine, having cranks of equal throw, if the centre crank
is placed at 180° from the other two cranks, and if the two outer lines of moving
parts are made equal in weight to each other, and collectively equal in weight to
the centre line of moving parts, then the tilting action aforesaid will be entirely
eliminated, provided the bearings be carried upon a sufficiently rigid bed-plate to
resist deformation. Generally this cause of vibration can be eliminated in any
engine by arranging its moving weights symmetrically to each other, reckoning
from a central position upon the crank-shaft to each end outwards, it being observed
that the balance required is of moments of forces and not necessarily of weights of
parts; thus, the longitudinal distance of any moving part from the centre line of
the engine, the weight of the part, and its velocity (due to length of crank throw)
are all elements in determining momentum.
It is also well known, and can be mathematically demonstrated, that in an engine
with three cranks at 120° apart, or, with four cranks at 90° apart, vibration due
to the cause first above described is practically eliminated, provided the ratio of
the length of the several connecting-rods to their respective crauks is the same,
and that the moments of forces existing in the several lines of moving parts
(compounded of their weight and velocity) are equal.
Such a three-crank or four-crank engine as is last described is not however of a
kind in which the tilting action due to the unbalanced couple can be eliminated,
the equal angles of the cranks being a condition essential to the absence of vibration
of the first kind. Thus a four-crank engine, having equal crank throws, similar
connecting rods, and moving parts of equal weight, will be free from vibration of
the first kind if the cranks are at equal angles, namely 90° apart; or it may be
freed from vibration of the second kind by putting the two central cranks in the
same position, and the two outer cranks diametrically opposite to them. There is,
however, no way in which a three-crank or four-crank engine driven by connecting-
rods can be freed simultaneously from both kinds of vibration.

page_text: The minimum number of cranks with which freedom from vibration of the first
kind can be obtained is three.
According to this invention we apply these considerations to marine engines in
such manner that when working at full power the engines are free from vibration
and can readily have some of the cylinders disconnected so that they will work
economically and conveniently at a diminished power.
The engine has six cranks and a single crank shaft the latter being divided into
two parts (each with three cranks)" connected together by a coupling. The
cylinders are connected together and are also connected by diagonal bracing to the
bed plate so that the whole structure forms a continuous longitudinal girder.
When it is desired to work at half power the two parts of the shafts are disconnected
and the three after cylinders only are used. The cranks on each part are 120°
apart and are so arranged that when the parts are coupled together the first
cranks, the second cranks and the third cranks respectively of the two parts
(counting from the coupling) are in the same positions. To ensure this it is
convenient to make the coupling in such a manner that the parts can only be
connected when in their proper relative positions.
The distribution of the steam to the cylinders and the pressures employed in
each may be varied in any convenient manuer but a convenient arrangement is
for the two sets of three cylinders each to constitute a triple-expansion engine
complete in itself.
Whatever may be the arrangement however if as above explained all the cranks
have the same throw then the pistons, connecting rods and other moving parts
belonging to the various cylinders must all be of the same weight or if the throws
are different then the weights of the parts must be varied so that their changes of
momentum remain the same and the ratio of the length of the connecting rod to
the throw of the crank must be the same for each cylinder.
In place of having three cylinders and cranks for each part of the crank shaft,
four may be employed but the cranks of each part must make equal angles to each
other and the other conditions set forth above must be observed.
Dated this 25th day of March 1895.
MARK H. ROBINSON.
M. H. P. R. SANKEY.
Improvements in Marine Steam Engines.
We, MARK HEATON ROBINSON, and MATTHEW HENRY PHINEAS RIALL
SANKEY, both of Ferry Works, Thames Ditton, in the County of Surrey,
Engineers, do hereby declare the nature of this invention and in what manner
the same is to be performed to be particularly described and ascertained in and
by the following statement:-
The objects of this invention are to avoid vibration and to allow the engines to
work conveniently and economically at half power.
The causes of vibration in engines of ordinary construction, in which the
cylinders lie upon the same side of the crank shaft, are two. Firstly the difference
between the rate of change of the momentum of each piston and line of moving
parts when near the top of the stroke, in comparison with the rate of change of
momentum of the same parts when near the bottom of the stroke, due to the
different rates of acceleration and retardation in those respective parts of the
stroke caused by the varying angle of the connecting rods. This, under ordinary
circumstances, is the most important source of vibration, its tendency being to
alternately lift and depress the whole of the engine upon its foundation. Secondly,
the other cause of vibration is due to the unbalanced couple existing between the

page_text: pistons and other heavy moving parts in a direction parallel with the crank-shaft,
which gives the engine a tendency to tilt as a whole, end ways.
The latter cause of vibration can be eliminated by well understood methods;
for instance, in a three-crank engine, having cranks of equal throw, if the centre
crank is placed at 180° from the other two cranks, and if the two outer lines of
moving parts are made equal in weight to each other, and collectively equal in
weight to the centre line of moving parts, then the tilting action aforesaid will be
entirely eliminated, provided the bearings be carried upon a sufficiently rigid
bed-plate to resist deformation. Generally this cause of vibration
eliminated in any engine by arranging its moving weights symmetrically to each
other, reckoning from a central position upon the crank-shaft to each end outwards,
it being observed that the balance required is of moments of forces, and not
necessarily of weights of parts; thus, the longitudinal distance of any moving part
from the centre line of the engine, the weight of the part, and its velocity
(due to the length of crank throw) are all elements in determining momentum.
can be
It is also well-known, and can be mathematically demonstrated, that in an engine
with three cranks at 120° apart, or with four cranks at 90° apart, vibration due
to the cause first above described is practically eliminated, provided the ratio of
the length of the several connecting rods to their respective cranks is the same,
and that the moments of forces existing in the several lines of moving parts
(compounded of their weight and velocity) are equal.
Such a three-crank or four-crank engine as is last described is not however of
a kind in which the tilting action due to the unbalanced couple can be eliminated,
the equal angles of the cranks being a condition essential to the absence of
vibration of the first kind. Thus a four-crank engine, having equal crank throws,
similar connecting rods, and moving parts of equal weight, will be free from
vibration of the first kind if the cranks are at equal augles, namely, 90° apart; or
it may be freed from vibration of the second kind by putting the two central
cranks in the same position, and the two outer cranks diametrically opposite to
them. There is, however, no way in which a three-crank or four-crank engine
driven by connecting-rods can be freed simultaneously from both kinds of
vibration.
The minimum number of cranks with which freedom from vibration of the first
kind can be obtained is three.
According to this invention we apply these considerations to marine engines in
such manner that when working at full power the engines are free from vibration
of either kind described, and can readily have some of the cylinders disconnected
so that they will work economically and conveniently at a diminished power.
The engine has six cranks and a single crank shaft, the latter being divided
into two parts (each with three cranks) connected together by a coupling. The
cylinders are connected together, and are also connected by diagonal bracing to the
bed plate, so that the whole structure forms a continuous girder in the direction of
the longitudinal axis of the engine. When it is desired to work at half power
the two parts of the shaft are disconnected, and the three after cylinders only are
used. The cranks on each part are 120° apart and are so arranged that when the
parts are coupled together the first cranks, the second cranks and the third cranks
respectively of the two parts (counting from the coupling between them) are in
the same positions. To ensure this it is convenient to make the coupling in such
a manner that the parts can only be connected when in their proper relative
positions.
The distribution of the steam to the cylinders and the pressures employed in
each may be varied in any convenient manner, but a convenient arrangement is for
each set of three cylinders to constitute a triple-expansion engine complete
in itself.
Whatever may be the arrangement of cylinders or steam distribution, if as above
explained all the cranks have the same throw then the pistons, connecting rods
and other moving parts belonging to the various cylinders must all be of the same

page_text: weight, or if the throws are different then the weights of the parts must be
varied so that their changes of momentum remain the same, and the ratio of
the length of the connecting rod to the throw of the crank must be the same
for each cylinder.
In place of having three cylinders and cranks for each part of the crank shaft,
four may be employed but the cranks of each part must make equal angles to
each other and the other conditions set forth above must be observed.
Figure 1 shews the crank shaft of a marine engine free from vibration either
vertically or fore-&-aft as regards the movement of the main pistons and working
parts including the valves. There are six cranks in two groups, A. B. C and A'B'C',
with a coupling D between, the latter being so arranged that the two parts of
the shaft will only go together when each of the pairs A and A, B and B¹,
C and C¹ are in the same plane, and in the angular positions shewn in Figure 2.
The three cranks of each group are at equal angular distances apart, viz., 120°, and
each group belongs to an independent triple-expansion engine; or there may be
two groups of four cranks cacb, arranged at equal angles of 90° from each other,
as in Figure 3. As the crank-throws are assumed to be equal, the lines of moving
parts must be, as nearly as possible, of equal weight, and the connecting rods must
be of equal lengths. When it is desired to proceed at half-power, the forward
engine A B C is disconnected; A, B, C then forms an engine free from the
tendency to alternately lift and depress itself (causing vertical vibration) but
subject to a rocking tendency fore-and-aft. This latter may be disregarded, as
the engine framing is of a very rigid kind, and has a length corresponding with
six cylinders, that is, with twice its own natural length; morcover, at this time the
power is only half the maximum at most, and the piston speed less than when all
six cylinders are used. When both engines are running, then, as neither has a
tendency to vertical vibration the two collectively are equally free from it, while
the rocking tendency of each separate engine is nullified by the engines endeavouring
to rock from and towards each other symmetrically-a tendency which produces
no effect owing to the longitudinal stiffness of the engine as a whole.
The several lines of valves are arranged on exactly the same principle, the
angular positions of the eccentrics a and a, b and b', c and c', being the same, while
all the lines of valves weigh the same, have the same stroke, and are symmetrically
placed with regard to the coupling D.
The angular positions of the valves are indicated in Figures 2 and 3.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed we declare that what we
claim is :-
1. The combination of two engines, each separately free from the tendency to
vibration in a vertical plane having their crank shafts in a line with each other
and capable of being so connected that the two engines together are also free
from any tendency to rock end ways substantially as described.
2. Marine engines substantially as described and shown in the drawings.
Dated this 23rd day of January 1896.
MARK H. ROBINSON.
M. H. P. RIALL SANKEY.