Compound engines are tending to come more and more into use, inasmuch
as they present many advantages over other kinds, especially as regards
the saving they effect in fuel, and their great regularity, due to the
adjusting of the cranks at right angles.
It is not surprising, then, to see our large manufacturers, who desire
to maintain a reputation, seeking to create new types based upon this
principle. But, in multiplying the parts, as is done in these motors,
the engine is rendered more complicated, and the cost of installation
is increased. Hence the difficulty of placing these motors,
notwithstanding the saving in fuel that is gained by employing them.
Messrs. Bietrix & Co., of St. Etienne, however, have devised a type in
which these two inconveniences seem to have been in a great measure
overcome, and which we illustrate in the annexed engraving.
[Illustration: COMBINED VERTICAL AND HORIZONTAL COMPOUND STEAM ENGINE.]
_Description of the Engine._--The engine as a whole is represented in
longitudinal elevation in Fig. 1, in plan in Fig. 2, and in side view
in Fig. 3. Fig. 4 shows the condenser in transverse section.
The motor consists of a small vertical cylinder, A, and of a large
horizontal one, C, both projecting over a strong hollow frame, B, which
connects them and carries the guides, _g g'_, and the pillow block,
P, of the driving shaft, _p_. The condenser, D, is in a line with the
large cylinder, and the piston, D², of its pump is mounted upon the
prolongation, _d'_, of the piston rod, _a_, of the cylinder, C. The
expansion gear is controlled by the regulator, and the admission may
vary from 1/19 to 1/85. Steam is admitted into the small cylinder
through the pipe, _s_, and its entrance may be regulated at will by
acting upon the hand wheel, _s'_, which controls the maneuvering
rod, _s²_. After expanding, the steam, in escaping from the smaller
cylinder, passes through the pipe, _r_, into the feed-water heater, R,
and then acts in the larger cylinder, _c_, in order to pass afterward
to the condenser, D, through the pipe, _d_.
The frame, B, is in two parts, the vertical part being adjusted by
keys upon the horizontal one, and strong bolts concurring with such a
coupling to make the whole strong and solid. This frame carries plane
slide bars, _g g'_, with beveled counter guides.
The pistons are of the Swedish type, of hollow iron, with steel rods.
The segments are of cast iron. The horizontal connecting rod, M', is
connected directly with the crank pin, _m_, but the vertical one is
fixed to the head of the former, as may be seen in Figs. 3, 8, and 9.
The bearing of the horizontal connecting rod is in three parts, each
having an anti-frictional bushing, and their play being regulated by
bolts, _m²_. Friction being slight in the bearing of the vertical
rod, M, inasmuch as the latter's axis has but a short travel at
each revolution of the driving shaft, it is not provided with an
anti-frictional bushing.
_The Small Cylinder_ (Figs. 5 and 6).--The small cylinder is shown
in detail in Figs. 5 and 6, the valve box cover being removed in the
latter. The diameter of this cylinder is 380 millimeters, the stroke
of the piston is 650 millimeters, and the thickness of the sides is
25 millimeters. It is provided with a steam jacket; and the two ports
are 45 millimeters in width by 200 in length. The exhaust is effected
through an orifice 84 millimeters in diameter.
The distribution is a variable one, according to the Meyer system, the
expansion being caused to vary automatically in the small cylinder, by
means of a regulator, so as to proportion the motive to the resistant
power.
The distributing slide valve, _t_, contains two steam inlets, whose
orifices facing the cylinder are formed by two horizontal, parallel
rectangles, while the inlets debouch toward the opposite surface (in
contact, consequently, with the expansion slide valve, _t'_), according
to two parallelograms, whose larger sides are oblique, and form between
them a sharp angle, as may be seen in Fig. 6. These inlet conduits are
therefore out of true. The slide-valve, _t_, is moved by an eccentric,
E.
The expansion slide-valve, _t'_, has the form of a trapezium, whose two
like sides are parallel with the inclined openings in the slide-valve,
_t_. It is held by a piece, _q_, which carries it along in its backward
and forward motion, but does not prevent it from being moved in a
horizontal direction under the action of the regulator. This piece,
_q_, is keyed upon a rod, _q'_, which is itself jointed at its lower
extremity with the rod, _e'_, of a second eccentric, E', which causes
its vertical motion.
The backs of the valve, _t_, and the piece, _q_, are provided with
grooves, which are designed for giving passage to the steam, the
pressure of which on these surfaces partially balances that that it
exerts in an opposite direction.
_Automatic Regulation_ (Figs 5 and 6).--The upper part of the rod,
_e'_, carries a cam, _f_, that plays freely between two connecting
rods, _f¹_, and the travel of which is limited by two rollers, _f²_
and _f³_, situated between the rods, _f_, which latter are themselves
suspended from a rod, F. The latter slides in a support, F², which
serves likewise as a guide to the rods, _q'_ and _t²_, of the
slide-valves, and which is fixed upon a projection cast in a piece with
the frame, B, and is suspended from the short arm of a bent lever, F',
whose longer arm carries a roller that runs in a vertical groove, _t³_,
in the back of the expansion slide-valve. The lower extremity of the
connecting rods, _f'_, is connected with the sleeve of the regulator,
Q, by a lever, _f^{4}_, and a bent lever, Q'. This latter revolves on
an axis passing through its elbow and mounted at the extremity of a
projection that is cast in a piece with the support of the regulator.
This bent lever is prolonged beyond the sleeve, and carries suspended
from its extremity a small piston-rod that plays in a dash pot, Q³, and
limits the too abrupt motions of the apparatus. The regulator is driven
by a belt and through the intermedium of the bevel pinions, _u_.
It is easy now to understand the purpose and the _modus operandi_ of
the mechanism that permits the regulator to act upon the expansion
gear. When running normally the connecting-rods, _f'_, occupy a
vertical position, and the rollers, _f²_ and _f³_, are placed exactly
at the two extremities of the travel of the cam, _f_.
When the velocity exceeds the normal, the sleeve of the regulator rises
and the lever, Q', tips to the right and forces the rods, _f'_, to
oscillate in the same direction around their upper joint. After that,
the lower roller, _f²_, being situated on the line of travel of the
convex part of the cam, will be carried along by the latter and cause
an oscillation to the right of the bent lever, F. The piece, _t'_,
will then be pushed back in such a way as to partially close the inlet
orifices of the slide-valve, _t_, and, as the steam will thereupon
enter into less quantity, the engine will quickly resume its normal
velocity. If the velocity becomes less that the normal the action will
be just the opposite of that just described.
_The Large Cylinder_ (Figs. 1 and 2).--The two eccentrics, E and E',
which control the distributing gear of the small cylinder, A, actuate
at the same time that of the large one, C, through two rods, _e²_ and
_e³_; such distribution is also effected by means of a sliding-plate
valve. The two steam ports are 45 millimeters and the exhaust port 84
millimeters in diameter.
The large cylinder is 650 millimeters in diameter, and 930 in length.
The stroke of the piston is 650 millimeters.
_The Feed-Water Heater_ (Figs. 1 and 2).--The exhaust from the small
cylinder enters the heater through a pipe, _r_, 140 millimeters
in diameter. This feed-water heater consists of a large cast iron
cylinder, 400 millimeters in internal diameter, and 1.15 meters in
length, connected with the pipe, _r_, on the one hand, and with the
cylinder, C, on the other, by means of two couplings, R' and R². In
its interior are arranged 60 copper tubes, of 29 millimeters internal,
and 31½ millimeters external diameter. These tubes are fixed at their
extremities into two circular supports that are riveted to the interior
of the cylinder. The exhaust from the small cylinder passes into these
tubes, around which circulates steam coming directly from the boiler
through the tube, _r'_, and escapes toward the bottom, with the
condensed water, through the tube, _r²_. The heater is surrounded with
a 2 mm. plate iron jacket.
A communication, _r³_, with a valve-cock, R³, permits of the
introduction, into the large cylinder, of the steam from the heater.
The exhaust steam from the large cylinder goes directly to the
condenser, but there is likewise provided a pipe through which it may
make its exit into the open air, in case, for example, the condenser
needs repairing or there is a failure of water.
_The Condenser_ (Figs. 1, 2, and 4).--The condenser is represented,
half in section and half in external view and in elevation in Fig. 1,
and in plan in Fig. 2; Fig. 4 is a transverse view of it. It consists
of a large cast iron chest, D, bolted by means of its flanged base to
a masonry support. This chest is cast in a piece with a pump chamber,
D', in which works a piston mounted on the prolongation, _d'_, of the
piston-rod of the cylinder, C. The diameter of this piston is 210
millimeters, and its stroke is 650. The condensing jet, whose flow is
regulated by the cock, _d²_, is brought into contact with the steam by
a rose, _d³_, which divides it into small drops.
The pump is a double acting one. Its valves are of rubber, and the
passage-way allowed the water is, in each of them, in section, one-half
that of the piston. The rod, _d'_, slides in a stuffing-box, with
metallic lining, which is shown in Fig. 10.
_Lubrication._--The lubrication of the crank-pin presents some
peculiarities. Two stationary cups, _z_, are placed at the upper
part of the guides, as seen in Fig. 3. These distribute their oil,
drop by drop, into two reservoirs, _z'_, fixed to the upper axis
of the vertical connecting-rod. Two small brass tubes, resting
against the connecting-rod, lead the lubricator into cavities in the
head of the horizontal connecting-rod, M'. One of these cavities
corresponds to the crank-pin and the other to the lower axis of the
vertical connecting-rod. The lubrication of the cylinders is effected
automatically by means of a Consolin apparatus (Fig. 1), based upon the
condensation of the steam and upon the difference between the density
of the oil and condensed water.
_Diagram of Distribution_ (Fig. 11).--We shall first examine that
which relates to the small cylinder. The eccentric of the distributing
slide-valves is adjusted to 123° with respect to the crank, and that
of the expansion slide-valves to 170°, that is to say, so that the
angles of advance are respectively 55 and 57 millimeters for these two
cylinders.
Let us trace two axes, _o x_ and _o y_, at right angles, and a
semi-circumference of any radius whatever, _o m_, which shall represent
the travel of the crank-pin. Let us draw the line, _o_ A, making with
_o y_ an angle of advance of 33°, and the length of which is equal to
the eccentricity of the distributing slide-valve, say 55 millimeters,
and let us describe a circumference on this length taken as a diameter.
Let us trace in the same way the line, _o_ B, making with _o y_
an angle of advance of 80°, and let us describe upon this line a
circumference equal in diameter to the eccentricity of the distributing
slide-valve, say 57 millimeters.
Finally, let us trace points, _o_ and _c_, as centers of arcs of
circles having respectively for radii the distance between the centers
of the circumferences just mentioned and the eccentricity of the
expansion slide-valve. These two arcs will intersect each other at a
point, _c²_, which is thus the fourth angle of a parallelogram whose
other angles are the points, _c_, _c'_, and _o_. From the point, _c²_,
as a center let us describe a circle passing through _o_.
In short, we obtain three circles that are such that the vector
radii, starting from the point, _o_, and limited at the said circles,
represent, for the first, the deviations to the right of the
distributing slide-valve beginning at the middle of its travel, the
second the deviations of the expansion slide-valve, and the third the
relative deviations of the distributing with respect to the expansion
slide-valve.
Let us complete the diagram by describing, from the point, _o_, as
a center, circumferences having for respective radii the length, _o
e_, of the external overlap of the distributing slide-valve, and the
lengths, _o i_ and _o i'_, corresponding to the minimum and maximum
of the interval between one of the edges of the expansion slide-valve
and the external edge of the corresponding inlet orifice of the
distributing slide-valve, when the axes of these two valves coincide.
These radii have the values: _o e_ = 25 mm.; _o i_ = 8 mm.; and _o i'_
= 42 mm. Let us now prolong the radii, _o d_, _o d'_, _o d²_, and _o
f_, until they meet the crank circle, and let us then project these
points of intersection upon a line, M M', parallel with _o x_, and we
shall have all the elements that are necessary to study the different
phases of the distribution in the small cylinder.
Let us complete this diagram in such a way as to study also the
distribution in the large cylinder:
In this cylinder the distribution cannot be modified, that is to say,
the active length of the expansion slide-valve is invariable. The
interval comprised between one of the edges of this valve and the
internal edge of the corresponding inlet orifice is equal, then, to 28
mm. when the axes of the two valves coincide.
Let us describe, from _o_ as a center, a circle having this length for
a radius, and let us again project the intersections of the radius,
_o k_, with the crank circle upon a parallel at M M'. The external
overlap, being the same as in the small cylinder, say 25 millimeters,
the circle, _o e_, already traced for the distribution in the small
cylinder, will serve for the distribution in the large one. Let us join
its intersection with the circle, _c_, and the center, _o_, and let us
trace also the circle of the internal overlap and the radii, _o g_, and
_o h_, and we shall have all the elements of the distribution.
_Advantages of the Engine._--The engine that we have just described
presents all the advantages possessed by horizontal motors and double
cylinder vertical ones without their many inconveniences. It, in fact,
takes up less space than the former, while it possesses more stability
than the latter. Its operation is as regular as that of an engine
having two cranks adjusted at right angles.
The cranked shaft, a costly member of an engine, and one whose duration
is always uncertain, despite the care that has been taken in making it,
is here done away with.
The kind of distribution adopted is well adapted to the great
variations in expansion, and, notwithstanding the two superposed
slide-valves in each cylinder, two eccentrics suffice to operate them.
The regulator, thanks to the mechanism that connects it with the
expansion plate, is freed from all exaggerated resistance, the
eccentric rod alone supporting the entire stress. The regulator is
consequently very sensitive, and is capable of giving a coefficient of
regularity which is more than sufficient in most cases. The condenser,
with its wide apertures, is capable of operating with great speed
without shock.
We may add to this that the engine is simple and compact; the number
of parts is few, and all can be easily got at; the bearings are long,
and the wear is consequently reduced; the dimensions of the steam
ports are wide and permit of great velocities being reached without
counter-pressures; the mode of lubrication has been well studied, and
requires but little attention on the part of the engine man; and,
finally, the cylinder jackets and the superheating of the steam after
it has begun to expand make this an economical motor aside from all the
advantages that we have enumerated.--_Publication Industrielle._
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