The present invention relates to an apparatus for controlled inflation
af pneumatic tires. In order to effect a reasonably rapid inflation of a tire it
is necessary to make use of a source of pressurized air, in which the air pressure
is rather much higher than aimed at in the tire, and for that reason, as well known,
it is impossible with ordinary equipment to measure the tire pressure during the
inflation. If a manometer is arranged in connection with the inflation hose it
is necessary to stop the inflation from time to time and keep an inflation pause,
during which the air pressure is equalized in the tire and hose system to enable
a steady and true reading of the meter. In repair shops it frequently happens that
a repaired or newly mounted tire should be inflated from ambient pressure e.g.
to 2 bars, and even with the use of an inflation air pressure of some 8 bars the
operation takes a considerable time, both for the actual inflation and for the
required inflation or measuring pauses.
Such pauses are not required as long as the operator can feel that
the tire has not yet become stiff, but once the tire is felt stiff there is still
a considerable inflation to be carried out, and the operator cannot feel on the
tire whether the correct higher pressure has been attained nor whether perhaps
a much higher pressure is built up, even to a degree of explosion danger. Such
danger should be avoided by all means, and it is particularly important, therefore,
that the operator makes use of several measuring pauses, particularly towards the
end of the inflation operation. On the other hand, these several pauses account
for a large part of the duration of the inflation work.
As disclosed in my US Patent No. 4.510.979 it is possible to design
an inflation apparatus which will automatically take care of a correct inflation
by providing for the necessary measuring pauses in connection with the use of
a contact manometer, whereby the operator need not attend to the inflation process
once the apparatus has been started, but of course such an apparatus is relatively
expensive, and it still requires a relatively long total inflation time for each
tire, i.e. it has a correspondingly limited capacity.
It is the purpose of this invention to provide an apparatus which
is capable of inflating tires with a high capacity, i.e. relatively fast for each
single tire, without the operator having to attend to the process, and without
the apparatus being complicated in any way.
The invention is based on the finding that in practice all or at
least the vast majority of tires and tire tubes produced by different manufacturers
throughout the world are highly similar with respect to air throughflow characteristics
of their air nipples. The outer diameter and the threading of the nipples are chosen
according to an international standard for cooperation with standard inflating
auxiliaries, but so far there has been no need for any standard with respect to
the interior dimensioning of the nipples, except that the nipples should be provided
with a valve cone acting as a check valve and having an actuator portion operable
to be depressed by a central stub on a standard inflating connector head at the
end of an inflation hose, such that it is possible to effect even a de-inflation
from outside, or rather so as to enable a deinflation by a depression of the actuator
portion by any relevant instrument or tool.
For readjusting the tire pressure it is common practice that the
said valve cone is left in the inflation nipple, but for the total inflation of
a repaired or newly monted tire it is common pratice to remove the valve cone insert
in order to essentially increase the flowthrough capacity of the nipple such that
the inflation may take place as rapidly as possible. Once the inflation is completed
it is then necessary to demount the inflating connector head of the inflation
hose and remount the cone unit the nipple, whereby it is in practice unavoidable
that some air escapes from the tire. However, it is generally desired or prescribed
that a repaired or newly mounted tire should be initially inflated to a pressure
somewhat above the desired operational pressure such that the tire and its mounting
is suitable tested by an overpressure, and if this over-inflation is driven up
to some 3,5 bars as prescribed, then the air escape by the said remounting of the
valve cone will be connected, by way of experience, with a pressure drop to a
value very close to the desired operational pressure. Thus, it is sufficient to
thereafter carry out a fine manually controlled adjustment of the final tire pressure,
which can be done in few seconds.
Even with the valve cones inserted or removed, respectively, the
flowthrough capacities of the different nipples are very much alike, and according
to recent developments tires are now marketed, in which the valve cone is not retractable.
Such tires, therefore, when inflated to the said overpressure, should be bleeded
to the operational pressure by actuation of the valve cone, again with suitable
pauses for control measuring.
According to the invention the said finding with respect to practically
all current tire nipples having equal through-flow charactistics, irrespective of
the tire dimensions, is utilised in the design of an inflation apparatus having
a timer controlled valve and an associated timer, which may be preset in accordance
with the volume of the tire to be inflated from ambient pressure, such that a tire
of that particular size, with the use of a source of compressed air of a given
pressure, will be inflated through an individual period of time which is just long
enough to secure the attainment of the desired tire pressure. This could well
be the operative pressure, but in connection with repairs or new mountings it will
normally be the said test overpressure.
Due to the said equality there is a practically linear connection
between the required inflation time and the volume of the tire generally for different
tires even from different manufactures of tires or tire tubes, and when the said
timer is properly adjusted to the volume, therefore, the inflation to the correct
end pressure will thus be achievable in one uninterrupted blow, without any measuring
pauses at all. Many experiments have shown that a remarkable inflation accuracy
is obtainable in this manner, and at least for an inflation to the said overpressure
it is not even necessary to make any control measurement, because the accuracy
requirements are here not very high.
The inflation to the said overpressure applies to tires born with
and without inserted valve cones. It has been found that there is a tight relationship
between these conditions such that the said timer may still be preset in accordance
with the volume of the tire to suit one of the conditions and then adjusted by
a constant factor to suit the other condition. The inflation of a tire "with valve
cone" will require an inflation time which is between 50 and 60% longer than for
a tire "without valve cone", irrespective of the tire volume, and in practice,
therefore, the apparatus may be provided with one read-in unit for the tire volume
and one selector referring to the actual tire being "with or without valve cone".
It should be mentioned that the said constant relation between the
tire volume and the required inflation time will of course not apply to all thinkable
tires, but what is relevant here is the majority of tires of ordinary passenger
cars. For the tire of heavy trucks or other groups of special vehicles the said
relation may be different and thus require another adjustment of the inflation
For the treatment of tires "with valve cone" it is a special circumstance
that upon the inflation to the said overpressure the tire will be conveniently
bleedable to the operational pressure through the same hose, through which the
tire has been inflated, the connector portion of this hose having a connector head
including a stub member for depressing the valve cone. The primary finding of
the invention as to the equal characteristics of the different nipples, even "with
cones", resulted in the assumption that also the required bleeding could be controlled
on a pure time basis, without requiring several control measurements. Many experiments
have shown that this assumption is true, such that in case of a tire "with valve
cone" the tire may first be inflated to the required overpressure and thereafter
be bleeded to the required operational pressure all based on a time controlled
inflation and bleeding procedure. It has been found that the inflation and bleeding
accuracy is hereby high enough to secure a final result which is indeed very near
to the required operational pressure, such that the final pressure will need none
or only one or a few control measurements in order to be adjusted correctly.
It has been found that in practice it is possible to design the inflation
apparatus as a standard for use with a compressor producing an air pressure of
10 bars, this pressure being used widely as a pressure standard. However, as there
is a well defined relation between the compressor pressure and the inflation time,
the apparatus may well be provided with an adjustment button enabling the apparatus
to be adjusted to some deviating inlet pressure.
In the following the invention is described in more detail with reference
to the drawing, in which:
- Fig. 1 is a schematic diagram of an apparatus according to the invention, while
- Fig. 2 is a view of a lay-out of the front panel of the apparatus.
The apparatus according to fig. 1 comprises a housing having an inlet
stub 4 for pressurized air from an external compressor and an outlet stub 6 for
an inflator hose 8 for connection with the air nipple 10 of a tire 12. Inside the
housing 2 the inlet stub 4 is connected with a pipe 14 having a branch pipe 16
leading to a manually operated three-way valve 18, through which the pipe 16 continues
in a pipe 20, which communicates with a pipe 22 connected with the outlet stub
6. The pipe 14 is connected to another three-way valve 24, which is normally closed,
and to a pipe 26 leading to a pressure gauge 28.
As long as the valve 24 is closed the apparatus thus described will
constitute a conventional controlled inflation apparatus, in which the valve 18
is operable to furnish compressed air to the hose 8 through the pipes 16,20 and
22. The schematically indicated valve member of the valve 18 has three positions
18a, 18b and 18c, of which 18a is a closed position, while 18b is an open position
interconnecting the pipes 16 and 20. 18c is a bleeding position, in which the pipe
20 is connected with an open stub 34 on the valve 18. Thus, in position 18b of
the valve member the tire is inflatable, while it is bleedable in position 18c.
For the present invention a major component is the valve 24, which
is controllable by a timer 38 so as to cause the tire 12 to be inflated to a desired
overpressure without any measuring pauses at all. The valve member of this valve
has three positions, viz. a closed position a, an open inflation position
b, in which the pipe 14 is connected with the hose 8, and an open bleeding
position c, in which the hose 8 is connected with the atmosphere through
a stub 40.
The timer 38 is preset according to the volume of the tire to be
inflated. The volume may be read into a unit 42, which is connected with the timer
38 through a selector 44 to be set in accordance with the tire or tube nipple
being "with/without cone". In the position "with cone" of this selector a resistor
or another relevant unit 46 will be actuated to cause the timer to be adjusted
to a time interval longer than the time preset with selector 44 in "without cone"
position. In the latter case, when a start actuator 48 is operated, the timer 38
as connected with the valve 24 through a control wire 50 will actuate this vale
to open in position b during the preset time and thereafter to close again.
Hereby the tire is inflated to the desired or prescribed overpressure.
When the over-inflated tire has been inspected more or less the operator
will remove the hose 8 from the nipple 10 and immediately insert the valve cone
into the nipple, and by the associated outslip of air from the tire the pressure
therein will drop to about the required final pressure. Thereafter the hose 8 may
be mounted on the nipple 10 again, whereby the mouth piece of the hose, designated
9, will depress the cone and make it possible for the operator to adjust the pressure
finally by means of the manually operable valve 18.
If the tire nipple is "with cone" the actuation signal to the valve
24 through the wire 50 will have increased duration, such that the required overpressure
will be attained anyhow. When the inflation is stopped a signal from the timer
38 is passed to a delay unit 52 serving to start a bleed timer 54 with the associated
desired delay. Also this timer 54 has been preset in accordance with the setting
of the units 42 and 44, though only with the selector 44 in the "with cone" position,
viz. so as to be set to a timing required for the tire to be bleeded from the
attained overpressure to the desired final pressure. The timer 54, through a wire
56, actuates the valve 24 to open into position c, whereby the desired
bleeding is achieved through the stub 40, inasfar as the said cone is steadily
depressed by the mouthpiece 9 of the hose 8. When the apparatus has been proberly
calibrated and the inlet air pressure on the stub 4 is kept constant the automatically
obtained final pressure will often be so close to the desired final pressure that
further adjustment by means of the manually operated valve 18 will not be necessary,
but otherwise it will be easy to finely adjust the final pressure by means of that
valve before the hose 8 is removed from the nipple 10.
Particularly the tires "with cone" will be inflatable to the desired
overpressure and then bleedable to the desired final pressure while they are housed
inside a safety cage as shown schematically at 58 in fig. 1. Thus, the operator
may ascertain that the tire is able to witstand the overpressure without coming
close to the tire while it is overpressurized. This will amount to an important
safety measure, because in some cases the overpressure results in a tire explosion
which may be extremely dangerous to any nearby person.
Fig. 2 illustrates a possible layout of the front panel of an apparatus
operating according to the description of fig. 1. The manual valve 18 is represented
by two press buttons 18′b and 18′c, which are usable for inflation
and bleeding, respectively, though as already known these two buttons may be combined
as a single button operable to effect the two functions by respective degress
of depression. The selector 44 comprises press buttons 44a and 44b for the required
selection between "with cone" and "without cone". The pressure gauge 28 is illustrated
as a pointer manometer having fixed indications for 2 or 3 bars. The starter button
is represented at 48, and 42 designates the tire volume setting unit, which is
shown to comprise two turnable buttons 60 and 62 for the reading in of the width
and the diameter of the tire, respectively, whereby the combined setting of associated
potentiometers will represent the volume of the tire, such as desclosed in the
said earlier US- Patent No. 4.510.979, without even the volume itself being known.
If it is prescribed that the tire volume is read into the unit 42
before any of the buttons 44a or 44b is actuated, then the function of the starter
button 48 may be taken over by each of the buttons 44a and 44b, whereby the button
48 may be avoided.
It will be appreciated that an apparatus according to the invention
should not necessarily be able to perform all of the functions discussed above,
since already the automatic full-flow or uninterrupted inflation of the tire to
the desired or prescribed overpressure will constitute an important contribution,based
on a volume conditioned time control of the inflation, and the design of the apparatus
may be correspondingly simplified.
An important factor, of course, is the inlet pressure of the compressed
air on the inlet stub 4. While an inlet pressure of ten bars is a widely used standard
the actual inlet pressure could well sometimes deviate from the standard, and
in such cases, of course, the apparatus should be correspondingly calibrated, either
with respect to a throttling of the airflow or a general adjustment of the timing
response of the timer/timers 38,54 to the setting of the unit/units 42,44. A throttling
of the air flow may be obtained in various manners, e.g. with the use of different
insert plugs for insertion into the inlet stub 4 for adaption of the apparatus
to different inlet air pressures. Another possibility is to measure the air flow
through the hose 8 with the hose end piece in a free condition and to adjust a
control valve (not shown) in the pipe 14 to a setting, at which the flow corresponds
to the standard flow as produced by a pressure source of 10 bars. Thereafter a
few empiric adjustments may be made. Also, the pressure gauge 28 may be used as
a guide for the adjustment of such a valve, when the air is exhausted freely through
the mouth piece 9 or through a calibration nozzle inserted therein; if the apparatus
is preadapted to an inlet pressure of ten bars the gauge 28 will respond to the
air outlet through such a nozzle by a well defined reading when the inlet pressure
is ten bars, and the control valve may be adjusted to effect this reading when
the inlet pressure differs from the ten bars.
The apparatus, of course, could be combined with an air compressor
and thus be preadapted closely to the pressure thereof.
According to a preferred arangement however, there is mounted adjacent
the inlet 4, before or after the branch pipe 16, a pressure reduction valve 64
of the pressure regulating type, which is set to some suitable standard, preferably
8 bars, somewhat lower than the pressure supplied from the compressor. Commonly
the supplied pressure will fluctuate, e.g. between 9 and 11 bars, and with an
automatically stabilized pressure at e.g. 8 bars on the main valve 24 the achievable
inflation accuracy by the time controlled operation of the valve is surprisingly
By way of example, with the use of an inflation pressure of 8 bars
as controlled by a pressure regulating valve 60 the following inflation times have
been found to be required:
- 1) Tire "without cone", inflation to overpressure 3,5 bars:
Tire 165×13&sec; : Inflation time
Tire 195×14&sec; : Inflation time
- 2) Tire "with cone", inflation to overpressure 3,5 bars and subsequent automatic
deflation to 2 bars:
Tire 165×13&sec; : Inflation time
22.secs, delay (by unit 52) 0,5-1 sec.for enabling reading of gauge 28 at rest,
subsequent bleeding time 15,0 secs.
Tire 195×14&sec; : Inflation time
31 secs., delay 0,5-1-sec., bleeding time 28 secs.
The accuracy has been found to be better than 0,2 bar.
With the relative very rapid operation og the device the device is
well suited to be arranged in line with a tire changing or mounting machine, which
cannot normally operate that fast.
In some countries such as Italy the inflation pressure is prescribed
to af maximum less than the said 8 bars, although the tires are normally guaranteed
to resist at least 10 bars. In such cases, of course, the pressure regulator 64
as well as the timer 38 should be adjusted accordingly.
It has been found practical to provide the device with a calibration
button 66, fig. 2, by means of which an associated potentiometer may finely adjust
the operation of the timer 38 and even the timer 54 when required. There may be
some tolerance deviations in the volumes af tires of equal nominal volume, and
if a whole series af truly similar tires is to be handled it is convenient to adjust
the calibration button 66 if it is found that the first tire is not indflated
fully correctly. The button should be reset before the handling of a new series