Improvements in or relating to Devices for Inflating Pneumatic Tyres.
Year: 1894

page_text: Date of Application, 16th Aug.. 1894--Accepted, 22nd Sept., 1894
COMPLETE SPECIFICATION.
Improvements in or relating to Devices for Inflating Pneumatic
Tyres.
A communication from RUDOLPH HOFFMANN, Wheelwright, of Krauschutz,
near Elsterwerda, Empire of Germany.
I, ALFRED JULIUS BOULT of 323 High Holborn in the County of Middlesex,
Chartered Patent Agent, 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 :-
This invention relates to apparatus acting automatically during the rotation of a
wheel to maintain or increase the air-pressure in a pneumatic tyre.
The apparatus consists essentially of an air-pump applied to and used in
connection with wheel-tyres and provided with a safety-valve, whereby, through
the compression of the tyre, during rotation, owing to the weight of the wheel, air
is forced into the tyre when insufficiently inflated until a certain tension is
established. The working of the air-pump ceases as soon as the pressure within
the wheel-tyre equals that of a spring actuating the piston to drive it forwards;
thereby excessive pressure-strain on the tyre is prevented. The action of this
device is so energetic, that a journey may be commenced with slack or loosely
inflated tyres, and nevertheless, after a short distance has been covered, the tyres
will have become fully inflated. The apparatus, however, not only has the
advantage that it provides for the right pressure being maintained in the tyres
without any co-operation on the part of the rider, but also its use is associated
with the further and greater advantage that the wheel can be provided with a
safety valve. Hitherto there has been a fear (arising from the risk of a prejudicial
loss of pressure) of applying a safety-valve to a pneumatic tyre, although, in view
of the frequent bursting of the tyre, through great heat, such a precaution would
be very beneficial; but with this new appliance, on the contrary, a safety-valve
can now be fearlessly employed, because it at all times speedily compensates for
any sudden loss of pressure.
The invention is illustrated, by way of example in the accompanying drawings,
which show two principal arrangements thereof, differing from each other in point
of construction but having all essential characteristics in common.
The first of these now to be explained is shown in Figs. 1, 2 and 3.
Figure 1 is an elevation of the device as applied to a cycle;
Figure 2 a vertical cross section of the wheel-tyre and device;
Figure 3 a longitudinal vertical section of Figure 1.
The body A of the device which is herein described as the cylinder or barrel of
a piston air-pump, is like all known inflation or non-return valves hitherto used for
pneumatic tyres, secured radially to the inner side of the wheel-rim B (in the usual
way) which
perforated for the purpose; it is actually only a little larger than
the valves in use (the scale of the drawings being 2 to 1 i.e. twice the natural size).
A is carried by the screwed nipple A' which passes through the inner wall of the
pneumatic tyre C and through the wheel-rim B and by means of suitable washers,
packings and a screw-nut tightly presses the two together and makes an air-tight
joint.
The piston a travels within the body A as in a cylinder, which is bored out for
the purpose, and provided with a flexible bucket or cup 6 which, when the device is
inoperative, closes the boring and, in conjunction therewith forms the pressure
valve of the air-pump. The piston rod is jointed to the piston head a, and consists

page_text: of two parts c and d, both partly tubular in form, and having their tubular
portions arranged to slide one within the other. By means of this contrary slide-
motion of these two parts, a helical spring e is subjected to more or less
compression, which as the spring is strong under normal conditions ensures the
maintenance of the sliding parts cd in their position of greatest extension, or their
restoration thereto, when displaced; this movement however is limited by an
arrangement of slots in c and studs in d. This spring device which ordinarily
when the entire apparatus is operative, is not itself called into action, is designed
to prevent fracture or distortion under exceptionally extensive piston strokes or
unexpected shocks. Such abnormal movements of the piston may occur whenever
that point of the pneumatic tyre which is diametrically opposite to the apparatus,
runs over any projecting stone or other irregularity in or on the road surface etc.
If in such case the piston were driven too far forward the part d of the piston rod
would be driven inwards in the part c, and the spring e would be compressed so as
to absorb the shock.
The inner part d (forming the outer extremity) of the piston rod e terminates in
a rounded bulb-shaped head projecting into the hollow of the pneumatic tyre,
opposite to a boss or thickened part f of the inner wall of the pneumatic tube as
shown in the drawings, but which may be formed in the outer or protecting cover
of the tyre at that place. Secured to cat near its upper end and to the lower
extremity of A' the helical spring g tends to draw the piston a radially outwards
against the air pressure prevailing within the pneumatic tube C. Inside and close
by g the helical central springe working in the hollow of the piston rod between
the parts e and d, co-operates therewith and with the jointed connection between c
and a (previously mentioned) to establish an elastic cushion between the fixed
nipple A' and the movable piston a i.e. the pneumatic tube and the plunger piston
of the air pump.
At the outer end of the pump barrel A is located the inspiration or suction
valve; and on the other side of the piston the bent pipe D is secured to the pump
barrel and fitted with the safety valve i.
The working of the above described apparatus proceeds as follows;-
On a journey as is well known that portion of the periphery of the pneumatic
tyre which runs over the ground (.e. the tread) becomes more or less flattened,
even to the extent of half its thickness, in spite of the air pressure within the
pneumatic tube. This of course would take place at fone such peripheral point.
Thereupon the boss f being pushed inwards communicating the movement by the
piston rod d-c to the piston a which is thrust inwards towards the centre within
the barrel A. The suction valve is thereby closed and the air above the piston
is thus cut off from the outer atmospheric air and compressed until its pressure
overcomes the pressure within the pneumatic tyre acting on the other side of the
piston a, when the flexible bucket b yields so that the compressed air in A passes
through to the other side of a until the equilibrium is restored. At the commence-
ment of the return under the influence of the reaction of the spring g the bucket b
is forced back against the piston head a and the outlet being closed the augmented
volume of air in the outer chamber of A (i.e. relatively to the axis of the wheel)
is forced outwards into the pneumatic tyre C, while simultaneously the partial
vacuum created in the (radially) inner chamber of A draws in fresh air from the
outside through the suction valve h. Seeing that the outward stroke of the piston
is produced by the superior reactionary pressure of the spring g it will cease so
soon as the latter pressure and the antagonistic air-pressure in the pneumatic tyre
are brought into equilibrium by the increase of the latter and the increase of the
former, and the piston will then remain stationary in its outermost position (in
relation to the axis of the wheel) until relaxation in C and the flattening inwards
offcause the latter to again act on the piston and drive it inwards, when the same
cycle of operations is repeated.
Thus by means of the spring g which can be made of any desired strength the
maximum pressure within the pneumatic tyre can be determined and limited. On

page_text: the other hand the safety valve i serves to release any temporary over-pressure in
the pneumatic tyre caused e.g. in exceptional cases, such as high temperature.
The modification illustrated in Figure 4 in a longitudinal section corresponding
to that shown in Figure 3 has the advantage in comparison with that just described
of minimising all prejudicial waste of space between the spring controlled working
parts in the pump barrel; and further the piston rod is formed all in one piece
without a sliding or oscillating joint, which is advantageous on account of the small
dimensions of the piston rod in any such apparatus, which is a cause of difficulty in
the production and manipulation of two such sliding hollow parts as previously
described.
In this modification as in the preceding example the pump barrel A which differs
only in form from that previously described, is secured to the wheel-rim B and
pneumatic tyre C by means of a screwed nipple A' &c. The piston rod d however
consists of a solid rod whereof the outer bulb shaped end or head as before rests
upon the boss or thickened part f of the pneumatic tyre; while its inner end is
screwed into the outer end of the socket piece k whose opposite end is provided
with a female screw into which is screwed the socket of the disc forming the
piston. The main helical spring g whereby the piston is controlled, in this case lies
entirely within the pump barrel A and encircles k. It is secured as shown by
means of its lowest coil being enlarged in size and confined between the sleeve g¹
and the dished disc 92 which are secured to A. by a screwed double joint cap which
being also screwed on the outer end of the nipple A¹ firmly connects A to A¹
i.e. the apparatus to the tyre; at its inner end which is somewhat contracted in
diameter, the helical spring k is held fast between the piston disc and the socket
piece forming the screwed connection between those two parts as above explained,
and which at the same time secure the metal disc or washer and the leather
disc against . The socket of this piston disc screwing into k has its hollow
continued, in conical shape, through the disc itself to the upper surface thereof,
forming a conical seat for the spring-controlled ball-valve m kept on its seat by the
spring ; the socket itself forming the valve-chamber, from which the air taken
in through the valve (on the inward stroke of the piston) finds its way to the
pneumatic tyre through the radial passages k¹ in the socket-piece k, the outer part
of A, passages in the outer end of the socket piece k and the nipple A¹. The
suction valve h at the free end of A is also formed as a spring-controlled valve
similar to m.
A piece of fine gauze or equivalent n covering the outside of the
valve h (but within the protecting cap) protects it against the entrance of dust.
Between these valves h and m the pump barrel is fitted with a duplicate or false
end (or piston) O which is held in the normal position as shown, by the com-
paratively strong spring p. The disc o like the piston disc l, is provided with a
leather disc, a metal disc, and a ball-valve g; its position is so selected that under
normal conditions and a regular working of the invention, the piston I approaches
quite close to o or even pushes it slightly backward: there is therefore no space
prejudicially wasted in the cylinder or pump barrel A. Should the piston however
suddenly chance to make an abnormally large stroke, the yielding of the spring p
would allow of the increased displacement of O and absorb the shock of impact.
In this manner although the piston rod is solid and unyielding, all risk of fracture
or distortion of the parts is avoided.
In this modification also the safety-valve is different in form as shown at D-i on
the drawing; the bend-pipe D of Figures 1 and 3 being dispensed with in favour
of a small, flat sheet-metal cap; wherein the valve closing device assumes the form
of a flat disc or plate i carried by a spring arm i¹ which is adjustable by means of a
set-screw so as to vary the pressure on the safety-valve at will.
Having now particularly described and ascertained the nature of the said inven-
tion as communicated to me by my foreign correspondent, and in what manner the
same is to be performed I declare that what I claim is ;-
1. An apparatus for increasing and regulating the air pressure within a

page_text: pneumatic tyre during the rotation of the wheel comprising a piston air-pump such
as A A secured to the wheel-rim (B) in communication with the pneumatic
tyre (C) and provided at the inner end with an aspiration or suction valve h. and
having its piston (a or 1) provided with a valve (b or m) whereof the piston
rod (c-d or d) projects into the hollow pneumatic tyre and rests against the tyre
so that it and the piston are moved radially inwards (towards the axis of the wheel
against the antagonistic pressure of a spring 9 opposed to the air pressure in the
pneumatic tyre until equilibrium is established between the latter and the pressure
of the spring substantially as described and illustrated in the accompanying
drawings.
2. In apparatus such as described in Claim 1 a piston rod consisting of two
movable parts such as c sliding one within the other against the pressure of a
spring (e) substantially as described and illustrated in the accompanying
drawings.
3. In apparatus such as described in Claim 1 a double or false cylinder end such
as o in the pump-barrel (A) provided with a valve q and controlling spring which
double or false cylinder end when the apparatus is working in a regular manner
excludes any wasteful and therefore prejudicial space by separating it from the
working part of the pump barrel while yielding under abnormal conditions such as
a sudden prolongation of the piston stroke substantially as described and illustrated
in the accompanying drawings.
4. The combination with apparatus such as described in Claim 1 of a safety
valve (D-) on the pump barrel (A) substantially as described and illustrated in
the accompanying drawings.
5. The combination and arrangement of parts constituting the complete
pneumatic tyre inflating device substantially as described and illustrated in
Figures 12 and 3 of the accompanying drawings.
6. The combination and arrangement of parts constituting the complete
pneumatic tyre inflating device substantially as described and illustrated in
Figure 4 of the accompanying drawings.
Dated this 16th day of August 1894.
W. P. THOMPSON & BOULT,
Agents for the Applicant.