AN IMPROVED COUPLING FOR LOCOMOTIVES AND TENDERS
Year: 1884

page_text: I LORENTZ ALBERT GROTH, K.G.V. Civil Engineer and Managing Director of
the Universal Inventors and Patentees Financial Company Limited 30 Finsbury
Pavement London EC in the County of Middlesex do hereby declare the nature
of said invention for AN IMPROVED COUPLING FOR LOCOMOTIVES AND TENDERS
a communication to me from abroad by Wilhelm Hartmann of Berlin in the
German Empire to be as follows:-
Two railway carriages assume their best position on a curve when the centres
of their fore and hind axles lay over the centre line of the road In this case the
positions of the axles are secants to the circular curve and the ideal longitudinal
axes of both carriages cut each other in a point the position of which in relation to
the axles of each carriage is easily discovered geometrically This point is called
the theoretical point of intersection.
Every correctly arranged coupling between a locomotive and its tender should
allow of such a relative motion between those two carriages that the longitudinal
axes of both constantly cut one another in the theoretical point of intersection or
in points close thereto.
The coupling forming the subject of this invention is correctly arranged, and is
of the following character:
From a given point in the longitudinal axis of the locomotive a coupling bar
extends to a given point in the longitudinal axis of the tender, which coupling
bar can turn on a bolt on the locomotive and on the tonder.
The longitudinal axis of the tender is formed of a complete prism, it is placed in
a hollow prism taken as the fixed theoretical point of intersection on the locomotive
and which hollow prism surrounds the longitudinal axis of the tender, and is
further moveable round a vertical axis passing through the theoretical point of
intersection.
By means of the device described a definite relative motion between the
locomotive and the tender is effected.
The relative motion which the separate members of a piece of mechanism make
amongst themselves can be shown geometrically by the movement of two curves,
one of which remains stationary, and the other rolls on the stationary one,

page_text: These curves are called polepaths (" Pohlbahnen"). They produce exactly the
saine motion between two bodies as a definite mechanism.
In the before described coupling for locomotives and tenders the Polepaths are
so placed that they both touch in the theoretical point of intersection when the
longitudinal axes of both carriages lay in a straight line.
These polepaths are very complicated curves, & instead of them their circles of
curvature can be taken for the middle position of locomotives and tenders.
The motion between a locomotive and tender is thus defined by two circles, the
peripheries of which, in the case of the locomotive and tender standing in a straight
line, pass through the theoretical point of intersection. The centres of the circles
lay on the longitudinal axes. One circle being fixed to the locomotive, and the
other to the tender.
If the locomotive is stationary, and the tender moves, the circle belonging to the
tender rolls on the circle which is connected to the locomotive.
The two circles are therefore related to one another in exactly the same way as
the pitch circles of two toothed wheels.
The two circles, the diameters of which are defined from fixed rules, are applied
as moveable or fixed tooth-like buffers between the platforms of locomotives and
tenders, and with the first described coupling-bar they force the two carriages to
perform their proper relative motions. By this arrangement in most cases the
buffers can be made as rollers so that the friction between the buffers is reduced.
The two circles are also used in the following way.
In the motion of the tender against the locomotive every point of the tender
describes a cycloid the form of which is dependant upon the size and position of
the two fundamental circles.
Several points are now taken as coupling points on the tender, and the radii of
curvature of the cycloids described from these points are calculated, the centres
of curvature are used as coupling points on the locomotive, and the radii of curva-
ture are formed into coupling-bars. By this means couplings are produced which
effect the same relative motion between the locomotive and tender as the two
fundamental circles.
The tractive power of the locomotive is led from a given point in the longi-
tudinal axis thereof to a given point in the longitudinal axis of the tonder, or from
the centre of gravity of the locomotive to the centre of gravity of the tender.
-By-both-the-described-couplings, which-may-be-combined-together-in various
ways a definite relative motion between the locomotive and the tender is produced,
any other motion is excluded, and the dangerous rolling motion of the locomotive
is removed.

page_text: I LORENTZ ALBERT GROTH K.G.V. Civil Engineer and Managing Director of
the Universal Inventors and Patentees Financial Company Limited 30 Finsbury
Pavement London E.C. do hereby declare the nature of said invention for
" AN
IMPROVED COUPLING FOR LOCOMOTIVES AND TENDERS" a communication to me
from abroad by Wilhelm Hartmann of Berlin in the German Empire and in what
manner the same is to be performed to be particularly described and ascertained in
and by the following statement:—
Two railway carriages, Locomotive and tender, assume their best position on a
curve when the centres of their fore and hind axles lay over the centre line of the
road In this case the position of the axles are secants to the circular curve and
the ideal longitudinal axes of both carriages cut each other in a point the position
of which in relation to the axles of each carriage is easily discovered geometrically
This point is called the theoretical point of intersection.
Every correctly arranged coupling between a Locomotive and its tender should
allow of such a relative motion between those two carriages that the longitudinal
axes of both constantly cut one another in the theoretical point of intersection or
in points close thereto.
The coupling forming the subject of this invention is correctly arranged and is of
the following character.
From a given point in the longitudinal axis of the locomotive a coupling bar
extends to a given point in the longitudinal axis of the tender which coupling bar
can turn on a bolt on the locomotive and on the tender The longitudinal axis of
the tender may be formed of a complete prism placed in a hollow prisin placed at
the fixed theoretical point of intersection on the locomotive and which hollow
prism surrounds the longitudinal axis of the tender and is further moveable round
a vertical axis passing through the theoretical point of intersection By means of
the device described a definite relative motion between the locomotive and tender
is effected.
The relative motion which the separate members of a piece of mechanism make
amongst themselves can be shown geometrically by the movement of two curves
one of which remains stationary and the other rolls on the stationary one These
curves are called "Pole paths' They produce exactly the same motion between
two bodies as a definite mechanism.
""
"
In the above described coupling for locomotives and tenders the "Polepaths"
are so placed that they both touch in the theoretical point of intersection when the
longitudinal axes of both carriages lay in a straight line These "polepaths" are
very complicated curves and instead of them their circles of curvature can be
taken for the middle position of locomotives and tenders,
The motion between a locomotive and tender is thus defined by two circles, the
peripheries of which, in the case of the locomotive and tender standing in a straight
line, pass through the theoretical point of intersection. The centres of the circles
lay on the longitudinal axes One circle being fixed to the locomotive and the
other to the tender.
If the locomotive is stationary and the tender moves the circle bolonging to the
tender rolls on the circle which is connected to the locomotive The two circles
are therefore related to one another in exactly the same way as the pitch circle of
two toothed wheels.
-

page_text: The two circles the diameters of which are defined from fixed rules are applied
as moveable or fixed tooth like profiles between the platforms of locomotives and
tenders and with the first described coupling bar they force the two carriages to
perform their proper relative motions.
The two circles are also used in the following way: In the motion of the tender
against the locomotive every point of the tender describes a cycloid the form of
which is dependent upon the size and position of the two fundamental circles
Several points are now taken as coupling points on the tender and the radii of
curvature of the cycloids described from these points are calculated, the centres of
curvature are used as coupling points on the locomotive and the radii of curvature
are formed into coupling bars. By these means couplings are produced which
effect practically the same relative motion between the locomotive and tender as
the two fundamental circles.
The tractive power of the locomotive is led from a given point in the longitudinal
axis thereof to a given point in the longitudinal axis of the tender or from the
centre of gravity of the locomotive to the centre of gravity of the tender.
As above stated the most favourable position which two railway carriages
(locomotive and tender) connected together can assume in passing round curves is
that in which the middle of the front and rear axle lays in an imaginary cylindrical
surface co-inciding with the centre line of the road and standing normal to the
-plane of the road In this position the distance of the axles projected on to the
plane of the road are secants to the circular curve and as the distance from the rear
axle of the locomotive to the front axle of the tender measured on the imaginary
longitudinal axes of the two carriages even for the sharpest curves can be taken
as constant the longitudinal axes LL and TT Fig 1 of the two carriages always
cut one another in one and the same point I of either the locomotives or tender
longitudinal axis This theoretical point of intersection is therefore in every position
which the locomotive and tender assume with relation to each other..
The fundamental point for both the carriages to be comprised in the moving
system and its position with relation to any other point for instance the middlo
point of the axles is found by simple geometrical relations between the distance of
the axles Therefore if the aforesaid condition as to the correct position of the
two carriages (ia to remain fulfilled) the relative-motion which the tender-executes-
in relation to the locomotive in going round curves consists in a pure circular
motion round the theoretical point of intersection F whilst rotation round any
other point must have as a consequence the undermentioned faults.
As the rolling or reeling motion of the locomotive consists of oscillations round
the vertical axis of its centre of gravity the same can be reduced by forcing the
engine by suitably constructing it to swing round another vertical axis As however
only such an axis can be accepted as passes through the theoretical point of
intersection F any other than this will not admit of the correct placing as above-
mentioned of both carriages in curves that is to say there occur pressures between
the tyres of the wheels and the permanent way which contribute materially to the
rapid wear of both parts and which often becomes powerful enough to occasion the
displacement of the one of the carriages.
A simple bolt connection coupling and others of similar kind for example going
through the point F would fulfill the required object that however is not frequently
employed on account of considerations of construction In most cases another
point for instance the point o Fig 1 laying further back must be chosen and then
in order to obtain the most correct possible placing of the two carriages the
connection the tender must also be made moveable Thereby however the loco-
motive, in relation to its irregular motion, is again almost completely isolated from
the tender for there enter into action for the reduction of the said irregular
movements only the tension of the draw bar O P.
It is not absolutely necessary that the relative movements of both carriages
should consist of a pure circular movement round the theoretical point of inter-
section any other suitable movement approaching to that of the circular movement

page_text: can take place between the two carriages if the same is only of such a kind that
the longitudinal axes of the locomotive and tender cut each other in points which
are as close as possible to the theoretical points of intersection.
"
The principle here set forth, namely substitution for the pure circular motion of
one approximating to it or what is the same thing substitution for the infinitely
small "polepaths" forming the basis of the pure circular motion of the "polepaths"
of finite (up to infinite) size is used in the construction of the described coupling
in the following way.
The angle which the longitudinal axos of the locomotive and tender form with
each other on the sharpest curves amounts at the most to about 6° If we imagine
the position of the two carriages on the curve produced by the turning of the
tender in relation to the locomotive the coupling point p describes a circle round o
while at the same time it ought to describe a circle round the theoretical point of
intersection F This is not possible! If we grant what is fully allowable in small
amplitudes that the imaginary longitudinal axis of the tender moves through the
point F taken as a fixed point on the longitudinal axis of the locomotive an
approximation to a required relative motion is attained by the use of known gear
the nature of which is determined from the following considerations.
In Figs 1 and 2 0 F is rigid and immoveable on the locomotive crank O P, as a
coupling rod turns round o (couple) and T T and P F must always go through the
point F (connecting rod) in ordor that the movement should take place correctly.
This mechanism is however nothing but a moveable crank link, or common coupling
Any other crank gear can however be used according to the position of the
connections in substitution for the relative motion as for instance Fig 3 shows
the reverse of Fig 2 Figs 4 and 5 also show two other cases of the normal thrust
crank gear and finally any suitable crossed crank gear Fig 6.
If the thrust bar T T in Fig 2 were formed bodily as a solid prism and a
corresponding hollow prism capable of turning on a centre were arranged at F a
perfectly correct coupling would be produced As however the point F generally
lays in a very unfavourable position, frequently indeed is not accessibl at all and
on the other hand the solid formation of the longitudinal axis of the tender is
attended with special practical difficulties one is lod to produce approximately the
same constrained or check motion by crank driven mechanism such as the gear
above named.
"
The rotating crank gear is specially shown in Fig 2 together with its "polepaths"
which latter are evidently only the graphic representation of the law of inotion
residing in the gear.
As all points of the tender must obey the law of motion required by the gearing
they pass through somewhat complicated curvos corresponding to the form of the
polepaths which curves are proved by their respective equations to be curves of at
least the fourth order.
The same movement which the gearing produces can also be produced by the
rolling of the two polepaths on one another when they are solid formed and are
furnished with teeth and as for the small angle between the locomotive and tender
only the pieces of the polepaths corresponding to the co-axial positions of the
imaginary longitudinal axes of the locomotive and tender require to be taken into
consideration and as for these can be substituted with sufficient accuracy their
respective circles of curvature as closed mathematical forms the relative motion
between locomotive and tender can be carried out by the rolling of two circles the
diameters of which are in the proportion of 1 to 2.
Fig 8 shows the practical employment of the case shown in Fig 2 where the
theoretical point of intersection F is in front of the coupling point o The smaller
circle belongs to the locomotive while the larger, fixed to the tender hovers as it
were round the first Every part of the tender consequently describes a common
cardioide. If now the centre of curvature for the cardioide described from the
arbitrarily chosen point B for the co axial position of the two systems is sought
and it be carried out on the locomotive as also at B on the tender with bolts and

page_text: both are connected by the coupling rod B M whereby a motion can be produced
sufficiently similar to that produced by the rolling of the two circles within certain
limits The construction is then repeated symmetrically for the point B.
Although by this an exceedingly closed kinematic chain is formed there is
present notwithstanding a power of movement within the required limits without
any pressure or tension arising in the bar as the small play always present between
the bolts and the inner walls of the eyes of the coupling rod even in the very best
workmanship suffices to make the deviation of the circular. movement from the
required curved movement (cardioidal motion) harmless.
The correct connection of two points B B¹ of the tender with two points M M¹
of the locomotive suffices to bring about a perfect checked movement nevertheless
from practical considerations it is desirable to employ at least three bars because
not only is the wear and tear of bars and bolts thereby lessened but the whole of
the spare or safety coupling apparatus is contained in the principle coupling Even
a whole row of points of the tender may be so connected with the locomotive that
the tender accomplishes an approximate circular movement round the point F
within the required limits without its being necessary in all cases to attain an
absolutely circular movement.
Fig 10 shows the employment of five coupling bars and in this case the place
of the centre of curvature is so chosen that all the coupling bars are of the same
length.
If however as is often the case in passenger locomotives the point F lies behind
the coupling point o Fig 7 the construction remains the same but the outward
appearance is somewhat modified this is represented at Fig 11 Here again the
smaller of the two circles belongs to the locomotive and the larger to the tender
only the centres of curvature MI M' fall outside of F As in the former case there
can also be employed in this two or more coupling bars the lengths of which are
either equal or unequal to each other.
Finally however the same checked movement can also be attained by applying
profiles between the tender and locomotive. Fig 12 for example a profile applied
on the tender which profile can assume any suitable outline and a body connected
fast with the locomotive, when the first is given the second can be found by using
the two circles of curvature as pitch circles with the help of the general theory of
tooth gearing.
Fig 12 shows two such profile pieces in the special case as parts of the general
point toothings which can evidently be applied by corresponding formation of their
outlines at suitable places Also by the employment of profile pieces an accumu-
lation of draw bars can be arranged so that if it appears necessary the action of
the draw bar OP can be assisted by one or more others. The spring shown in
Fig 12 can be employed in all the arrangements hereinbefore represented.
The view heretofore taken is a limited one in spite of the new couplings
thereby attained as the coupling bar OP (couple) is employed in all the previously
described constructions of the coupling gear All the couplings shown in sheet 1
have the disadvantage that by reason of their arrangement the resistance of
the train acts on the hinder end of the locomotive at a certain point whereby a
component is produced in the position of the curves of the two carriages which tends
to turn the locomotive so that the already jeopardized outer front wheel of the
locomotive is pressed still more against the outer rail.
An ideal coupling will not however increase this inconvenience but will tend to
reduce where possible and for this purpose must be so arranged that it transmits
the tractive force from a point of the longitudinal axis of the locomotive laying at
a suitable distance towards the front (for example from the centre of gravity or still
Letter from a point laying in front thereof) to a pri perly chosen point of the longi-
tudinal axis of the tender and thereby allows of the turning of the two carriages
round the theoretical point of intersection only (or points in the immediate neigh-
bourhood thereof).

page_text: Figs 13 and 16 show diagrammatically and exaggerated two such couplings
LL shows the longitudinal axis of the locomotive TT that of the tender OP the
draw bar and F the theoretical point of intersection in which the longitudinal axis
of the tender and locomotive are arranged so as to adjust or dislocate themselves
to one another on the grounds already discussed In both cases this adjustment or
dislocation which on the sharpest curves does not reach 10 millimetres is indicated
by an ideal prism guide.
As the pair of prism arranged at F is not in a condition to transmit the traction
this can only take place through the draw bar OP If the predominant tension W
in the said draw bar is resolved at its point of application into two tensions ono in
the direction of the longitudinal axis of the locomotive and the other normal thereto
there arises in the latter the lateral forces V which forms with the distance M of
its point of application O from the centre of gravity a movement which seeks to
turn the locomotive so that the outer front wheel is drawn away from the outer
rail.
The rolling of the locomotive cannot follow without the tender being drawn in
sympathy as the prism guide at the point F can transmit this resultant movement
normally and effectively to the longitudinal axis.
As is apparent without further description these couplings are practically not so
easy to carry out as those shown diagrammatically in Figs 2 to 7 But as these
couplings kinematically defined are nothing but rotating crank loops it is possible
by means of the before described process to derive from them practical arrange-
ments which fulful the same object as the gear can be replaced by their polepaths
and these again with sufficient exactitude for the small angle of deviation by their
circles of curvature for the co axial positions of both systems.
In Figs 13 and 16 are shown the parts of the polo paths to be taken into
consideration as well as their circles of curvature From further theoretical
considerations it is found that it is quite immaterial from which of the two the
gear is designed from the circles of curvature of the polepaths of the gear Fig 13
taken as polepaths, are for the co axial positions of both systems momentarily the
secondary polepaths of the circles of curvature of the gearing polepaths Fig 16
taken as primary polepaths and vice versa.
The circles of curvature rolling on one another approach very nearly the proper
pure circular motion they could be formed solid and when furnished with teeth
serve as a coupling.
That construction would however possess the fault of being most difficult to
carry out practically.
As however according to the proportions of the gearing employed the two circles
lay in such a way that every point of the tender describes when in motion either
an ellipse or a cardioide it is possible to define the radii of curvature for the
conaxial position of the system from any chosen points of the described paths of
the tender and to form these radii of curvature as radius rods or links (the tender
to be regarded as the principal radius rod or link.
The two couplings Figs 14 and 17 show the practical application of this pro-
cedure wherein it is again left entirely to the discretion of the constructor whether
two or more radius rods shall be employed. It is however recommended to connect
three points of the tender by radius rods with three points of the locomotive in
order to reduce wear in the rods and to enable the safety coupling apparatus to be
dispensed with.
Fig 14 shows specially the case (mostly present in goods locomotives) where the
radius rods or links lay inside the two circles of curvature ("polepaths") whilst in
Fig 17 (present in passenger locomotives) the radius rods or links lay outside these.
circles. In both cases the points A A' A² in the motion of the tender in relation
to the locomotive (or what is similar thereto in the rolling of the smaller circle
fixed to the tender in the larger circle which belongs to the locomotive) describe
ellipses the centres of curvature of which for, the conaxial position are the
points M M and Mª All the points are formed as bolts the first named A.A¹

page_text: and A' are connected with the tender and the last named M M and M2 with the
locomotive Between each two pair of points are applied the radius links or
rods A M, A¹ M², A² M² The contradictory position which these connecting devices
occupy with reference to a known proposition of the science of motion is redeemed
by the use of the imperfections or faults of workmanship because the circles which
the points A A¹ and As for example describe by means of the radius rods or links
differ so little from the exact eliptic arc they should trace that within the required
limits and having regard to the above mentioned imperfections of workmanship no
sort of strains can arise from these deviations.
According to the position of bolts M M' and M' paired with the locomotive and
corresponding to their motion relative to the tender there must be applied to the
connecting members belonging to the tender (a plate in Fig 14, a bow in Fig 17)
parts as shown in Fig 14 for the bolt M and in Fig 17 for all three bolts.
It is obvious that the form of the parts drawing the train as also of the radius
rods or links and the number of the latter for two points depends entirely upon the
nature of the connections and that it is in the power of the constructor to produce
the mobility of the couplings in a vertical direction reduced or smaller joints
("Hook's ") (as in Fig 8. 12. 14. 15 and 19. 20) or by combinations of these with
pairs of cylinders (as in Fig 17 and 18).
Finally it is also possible to bring about in these couplings the same checked
motion by combinations of radius rods or links with any suitable profiles instead of
by radius rods or links alone for a body connected with the locomotive encloses.
any suitable profile for instance one connected with the tender by the rolling of the
two circles If therefore the position and outline of one of the two profiles is given
the definite pieces for the other are found by the aid of the theory of tooth
gearing The member of the tender drawing the train must however be connected
with the locomotive by radius rods or links because as was mentioned above the
draw bar OP (Figs 13 and 16) must be replaced by suitable arrangements The
profiles are only substitutions for the ideal pair of prisms.
Fige-19-to-22-show-both characteristic-cases-of-this-kind-of-coupling-as-to-which-
it may be further remarked that the position number and outline of the profiles
can be chosen entirely in conformity with the purpose So likewise it must be
-left to the invention of the constructor whether the train member is to be connected
to the tender by two bolts as in Fig 19 or by one bolt as in Fig 21.
If we imagine for the couplings shown in Fig 8 for example that the motion is
conveyed by the help of two bars B M, B M, every part of the tender must obey
the law of motion of such four cylinder chains and the point P of the tender
therefore describes in relation to the locomotive the dotted curve I. It appears
from this that if the point P is connected with O by a coupling bar the motion of
the two systems within certain limits is secured and O must be the centre of
curvature of the point path described from P for the co axial position of both
systems which is actually the case If we now extend the same reasoning to the
case in which O is coupled with P, and B with M, B¹ describes the dash dotted
path II and it is the centre of curvature for the same in the middle position of
the system M The point B being constrained by the rods B' M¹ and OP describes
the dash dotted path I I which lays symmetrically with the former in reference to
the centre line.
If the motion is reversed (that is to say if the tender is held fast and the
locomotive moves) the same reasoning is employed the point O being constrained
by the rods B M and B¹ M describes the curve I and P is its centre of curvature
for the middle position whilst the points M and M' constrained by the rods B¹ M¹
and OP or BM and O P describe the curves Q and Q¹ Fig 2⚫respectively the
centres of curvature of which are B and B¹ respectively.
The calculations for each of the couplings Figs 8–12. 14. 17 to 22 is made as
follows
Let & represent the distance apart of the axles of the locomotive.

page_text: D
To construct the couplings Figs 14 and 16 the parts A A¹ and A' are chosen on
the tender (or a prolongation thorcof) and the centre of curvature M M¹ and M' of
the elliptic arcs described from A A¹ and A' are calculated by the differential
calculus.
In the same way are found the lengths A¹ M' and A³ M³ in Figs 19 and 21 while
the outlines of the profiles shown in the same figures (which profiles may also be
constructed as rollers) are calculated as before by the rules for tooth gearing.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed I declare that what
I claim is:
1. The connection of the locomotive and tender by means of two or more open
or crossed coupling bars O P, B M, B M¹ and so forth (see Figs 8 to 11 of the
drawings) the lengths and positions of which coupling bars are fixed in the manner
hereinbefore described so that the movement of one of the crank gears (see Figs 1
to 7) takes place between the two adjacent carriages whereby it is immaterial
whether the lengths of the bars are equal to each other or unequal.
2. The connection of the locomotive and tender by means of one or more draw
bars O P et cetera Fig 12 as herein befored described assisted by by the profile pieces
a abb adapted to one another, the dependence of which one another is secured by
the circle of curvature of the pole paths of one of the crank goars Figs 1 to 7
without regard to the position and number of the profile pieces or the manner of
outlining the same.
3. The connection of the locomotive and tender by means of two or more radius
rods or links A M, A¹ M¹, A² M³ and so forth (see Figs 14 and 17) the lengths and
positions of which are fixed in the manner hereinbefore described so that the
movement of one of the crank gears (Fig 13 to 16) takes place between the two
adjacent carriages whereby it is immaterial whether the lengths of the radius rods
or links are equal to one another or unequal,

page_text: 4. The connection of the locomotive and tender by means of one or more radius
rods or links A¹ M¹, A' M' and so forth (see Figs 19 and 21) as herein before
described assisted by the profile pieces a abb adapted to one another the
dependence of which on one another is secured by the circles of curvature of the
polepaths of one of the crank gears (see Figs 13 and 16) without regard to the
inanner of outlining or to the position and number of the profile pieces.
Dated this 9th day of January 1884-
=