Tire deflation warning system

Apparatus for the detection of vehicular tire deflation is disclosed. The apparatus generally comprises a post member adapted to be mounted at its proximal and to a vehicle's undercarriage so that its distal end can engage a road surface when the distance between the vehicle and the road surface decreases due to deflation of the tire.

FIELD OF THE INVENTION 
The present invention relates to transporting, in particular to vehicle 
warning devices, and can be used in motor vehicles provided with 
pneumatically inflated tires. 
More particularly the invention relates to systems for detection, 
monitoring and alerting of reduction in the air pressure in the 
road-engaging tires of a vehicle which is riding along the roadway. 
BACKGROUND OF THE INVENTION 
In most cases early detection of slow leaks and development of the deflated 
condition in the tire of a moving vehicle to a large extent depends on the 
personal ability of the driver to feel minor changes in the vehicle riding 
qualities resulting from a loss of pressure in the tire. 
The driver is usually aware of deflation only after the pressure in the 
tire is already lost to such an extent that changes in the vehicle riding 
qualities are accompanied by difficulties in vehicle control, which might 
even cause a safety hazard. 
There are also other undesirable consequences of the deflated condition of 
a tire, e.g., excessive flexing and heating of the tire followed by its 
rapid wear and often irreparable damage. 
This situation becomes especially critical in the case of heavy trucks with 
multiple tires, or truck tractors with articulated vehicles liked towed 
trailers or platforms, in that there are many specific factors relating to 
such vehicles which make working conditions particularly unfavorable for 
early detection of minor changes in vehicle behaviour, i.e., at the very 
beginning of deflation. 
Among the factors which prevent the driver's timely detection of deflation 
development should be mentioned: increased level of noise and vibrations 
during riding, distance disposition of the truck tractor and the towed 
vehicle, excessive loads on the front axle caused by the front drive 
assembly absorbing changes in vehicle behaviour before they are felt by 
the driver, etc. 
There are numerous known systems which have been designed to solve the 
above problem and which are intended to warn the driver about the low 
pressure condition in pneumatic tires of a travelling vehicle. 
These systems can generally be divided into two types: 
1) those including a sensing means directly mounted on the rotating tire 
and able to detect changes in the tire caused by deflation, e.g., 
generation of excessive heat or deficient pressure in the tire. An 
appropriate signal, generated by a sensing means informs the driver of 
these changes. 
2) those including a feeler member which touches the ground when the 
distance between the vehicle and the road surface is reduced due to the 
deflated condition of the tire, and then activates an appropriate 
signal-producing means which warns the driver. 
A description of the systems relating to the first type can be found, for 
example, in Saint's U.S. Pat. No. 4,970,491 and in Wang's U.S. Pat. No. 
5,001,457. 
The system disclosed in Saint includes a transmitter, coupled with the 
valve stem of each vehicle tire, which senses a respective low pressure 
condition of the tire, and which transmits an appropriate signal, 
accordingly activating an alerting means. 
The system described in Wang consists of a plurality of pressure gauges, 
each respectively attached to pneumatic tires and each pressure gauge 
transmitting a signal to the appropriate alarm circuit when a certain tire 
is deflated below a predetermined nominal pressure. 
There are some inherent disadvantages related to this type of warning 
systems, in general, and with those disclosed in the above patents, in 
particular. Among these disadvantages one can mention insufficient 
reliability associated with the possibility of the sensing means affixed 
to the rotating tire to be damaged due to centrifugal forces acting upon 
it. Another disadvantage which can be referred to this type of warning 
system is the inconvenience in maintenance due to the necessity of 
dismantling the sensing means from the deflated tire and remounting it on 
a new one each time replacement of a deflated tire takes place. 
The present invention relates to the second type of warning system referred 
to above, which is based on utilization of a feeler member and its contact 
with the ground to generate an alarm signal. Descriptions of such a system 
can be found in Clothier's U.S. Pat. No. 4,075,602 and Sweet's U.S. Pat. 
No. 5,032,822. 
The low tire alarm system disclosed in Clothier's patent includes a feeling 
member extended in a downward position and mounted on a shaft in the 
vicinity of each tire, and pivot movement of said member is possible with 
respect to the shaft. 
The feeler member is normally situated above ground level when the 
associated vehicle tire is in a normally inflated condition. However, when 
there is a low pressure condition in one or more of the ground-engaging 
tires, contact is made between the feeler member and the ground surface. 
The feeler member is forced by the forward moving vehicle to pivot about 
the shaft, and this causes the electrical circuit to light the lamp which 
warns the driver that a low pressure condition exists in one of the 
vehicle tires. 
The tire deflation warning system specified in Sweet's patent utilizes a 
device which is attached to the wheel axle of a vehicle, adjacent to each 
pneumatically inflated tire at a fixed distance from the underlying road 
surface. This device employs a vertically disposed post-like feeler 
member, its lower extremity adapted to contact the road surface when the 
distance between the road surface and wheel axle is reduced due to tire 
deflation. When the post touches the road surface, it is forced upward, 
thus causing contact to be made with an electrical switch, which in turn 
activates a signal-producing means in the driver's cabin. 
One of the disadvantages associated with the systems referred to above is 
that the feeler member employed in them is made rigid, in order to ensure 
proper activation of the signal-producing means when this feeler member 
touches the road surface. 
Since this rigid feeler member is mounted under the wheel axle and extends 
relatively far downward toward the ground, there is a danger that it might 
easily be damaged by obstacles which protrude above the ground, and which 
are high enough to collide with its lower extremity. 
Collision might happen even before deflation starts and the feeler member 
touches the ground. A similar situation might happen when the vehicle 
returns from the low road side to the main road. 
Another disadvantage of known warning systems lies in the fact that in 
these systems the distance between the lower extremity of the feeler 
member and the road surface depends not only on the tire condition, but is 
also influenced by the loading condition of the undercarriage. This factor 
is especially pronounced in heavy trucks, truck tractors, towed trailers 
and platforms, in which said distance might be reduced by 3,5-7 
centimeters in loaded condition, as compared to not loaded condition. 
The above consideration requires reservation of additional space between 
the feeler member and the road surface in order to ensure that they will 
not touch when the vehicle is loaded, and there is still no tire 
deflation. An inevitable consequence of this requirement is the 
possibility that deflation in the tire will be detected only after 
significant loss of pressure. 
Still another disadvantage associated with known lower pressure warning 
systems relates to the fact that they only alert with regard to deflation 
but are not able to predict tire behaviour after deflation is detected. 
In conclusion, it should be emphasized that despite the fact that the above 
problem of deflation detection in vehicle tires has been known since the 
very beginning of the introduction of pneumatically inflated tires, it is 
still a vital one and there is still a need for a new, reliable, 
convenient and economical system, which will ensure the early detection of 
deflation, its monitoring and timely warning to the driver when this 
condition might become hazardous. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide a system for detection, 
monitoring and warning of loss of pressure in the tire of a moving 
vehicle, in which the above-mentioned drawbacks are sufficiently reduced 
or overcome. 
In particular, the first object of the present invention is to provide a 
simple, reliable and economical system for early detection of tire 
pressure loss, while this system is not connected to the tire itself and 
can be mounted on the wheel axle adjacent to the road without being 
limited to the space between the axle and the road surface. 
The second object of the present invention is to provide a system in which 
the danger of its damage due to collision of the feeler member with 
obstacles protruding above the road surface is reduced. 
The third object of the present innovation is to provide a system in which 
timely detection of tire deflation is ensured in its earliest stage, 
irrespective of the loading condition of the vehicle. 
Still another object of the present invention is to provide a new system 
which ensures early detection of tire deflation, monitoring of current 
tire condition, and warning to the driver of possible tire behaviour. 
The above and other objects and advantages of the present invention can be 
achieved in accordance with the following combination of its essential 
features: 
a system for detection, monitoring and warning of reduction in the air 
pressure in a wheel tire of a traveling vehicle, provided with at least 
one pneumatically inflated tire, when said tire engages the road surface, 
consisting of: 
a means for mounting of said system on the axle of the wheel, preferably 
adjacent to the undercarriage of a vehicle at a certain distance between 
the axle and the road surface corresponding to the normally inflated 
condition of the tire, 
associated with said means and downwardly extending from it, a post adapted 
to contact the road surface by its lower extremity when said distance is 
reduced, for example, due to deflation of the tire, 
sensing means, interacting with said post and adapted to detect when said 
post contacts the road surface 
switching means, controllable by said sensing means, and 
signal producing means adapted to be activated upon on or off condition of 
said switching means and to inform the driver about deflation in the tire, 
characterized in that 
at least part of said post is made resiliently bendable as to be able to 
bow in any direction when it contacts the road surface while being dragged 
by the moving vehicle, when said distance is sufficiently reduced and to 
return to its initial configuration after said distance is, at least 
partially, restored; said sensing means is adapted to detect a condition 
when the post is dragged; the system comprises a timing means, counting 
time interval between each consequent off- and on-condition of said 
switching means, which corresponds respectively to dragged/non-dragged 
condition of the post and said timing means is adapted to activate said 
signal producing means, when said time interval exceeds preset value. 
According to one of the preferred embodiments, said switching means is of 
the normally closed type electric on/off switch. 
In accordance with another preferred embodiment substantially for use in 
heavy trucks or trailing vehicles, said means for mounting and fixing of 
said system comprises a height compensation unit which interacts with the 
undercarriage of the vehicle, and adapts to keep a predetermined distance 
between the lower extremity of said post and the road surface, 
irrespective of the load condition of the undercarriage. 
In accordance with still another embodiment, said height compensation unit 
is formed as a pantograph, and said post is mounted on one of the levers 
of said pantograph, while the opposite lever of said pantograph is adapted 
to contact the undercarriage of the vehicle. 
In a further preferred embodiment, said height compensation unit is formed 
as two-toothed bars meshing with a pinion and said post is adapted to 
contact said first toothed bar, while said second toothed bar is adapted 
to contact said undercarriage. 
Furthermore, in another preferred embodiment substantially for use in 
non-heavy vehicles, said mounting means comprises a body portion embracing 
said wheel axle, and a neck portion formed integrally with the upper 
extremity of said post; a recess is provided between the post and the neck 
portion so as to ensure pivot movement of said post with respect to the 
neck portion while opening said recess, when the lower extremity of said 
post contacts the road surface and is dragged by the moving vehicle and 
said sensing means is located in said recess with possibility to detect 
its opening. 
The present invention, in its various embodiments, has only been summarized 
briefly. 
For better understanding of the present invention as well as of its 
advantages, reference will now be made to the following description of its 
embodiments, combined with accompanying drawings.

DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENTS 
Referring to FIG. 1 the warning system, according to the present invention, 
includes a mounting means formed as a fixture 1, provided with a clamp, 
embracing an axle housing 2 of the wheel (not shown) as to be rigidly 
fixed on it. The system is mounted along the axle, preferably in the 
vicinity of the vehicle wheel, engaging the road surface 4, when the 
vehicle is travelling. 
A further description refers to the warning system arranged for use with 
one tire; however, it should be understood that for detection and warning 
of deflation in the remaining tires, similar systems can be installed to 
operate independently. 
According to the embodiment shown in FIG. 1 and preferably intended for use 
in heavy vehicles, the system is provided with a height compensation unit, 
formed as a pantograph, the lever arms 5,5' of which are installed with 
possibility for movement about axes 6,6' with respect to fixture 1. 
The significance and principle of operation of the height compensation unit 
will be explained in detail later on. 
Lever arm 7 of the pantograph is provided with a retention collar 8, which 
carries spacer rod 9, which extends towards the undercarriage 10 of the 
vehicle. The degree of extension of the rod 9 from the collar 8 can be 
adjusted and fixed by a pair of set screws 11, so as to ensure contact 
with the undercarriage. An additional means for ensuring contact between 
the space rod and the undercarriage can also be provided; for example, 
spring 12, connecting axes 6 with lever arm 7 thus urging rod 9 to move 
towards the undercarriage. 
Lever arm 13 of the pantograph is located opposite lever arm 7 and carries 
a retention bushing 14 for mounting of the feeler member. This feeler 
member is formed as an elongated post 15, the upper extremity 16 of which 
is installed inside the bushing 14, allowing for longitudinal movement and 
then rigid fixation in the bushing 14 by a pair of set screws 17. The post 
15 extends from the bushing 14 downward toward the ground and is provided 
at its distal extremity 18 with a contact member 19. The upper extremity 
16 of the post is mounted in the bushing in such a manner that in the 
normally inflated condition of the tire 3, a certain distance L is 
provided between its distal extremity and the road surface. Once there is 
deflation in the tire 3 the axle housing 2 sinks downward, together with a 
fixture 1 and the pantograph, carrying the post, until the contact member 
19 touches the ground. 
One of the embodiments of said contact member is presented in FIG. 1, where 
this member is shown as a wheel rotatively contacting the road surface and 
adapted to rotate about the longitudinal axes of the post. 
Alternative embodiments of the contact member 19 are also possible, for 
example, as a spherical tip, shoe or pad made of a wear-resistant material 
and attached to the distal extremity of the post. The post is made at 
least partially resiliently bendable so as to ensure that at least in its 
downward extending from the bushing portion, it is able to bow in any 
direction, when its distal extremity touches the road surface and is 
dragged due to the movement of the vehicle. Resiliency of the post ensures 
that this portion becomes straight again when the distance L between the 
contact member and the road surface is at least partly restored. 
As can be seen on FIG. 3b the bent configuration of the post 15' referred 
to above corresponds to the deflated condition in the tire 3', while the 
normally inflated condition of the tire 3 and straight configuration of 
the downward extending portion of the post are shown in FIG. 3a. 
In order to ensure resilient bending, the post can be formed as a thin wall 
tube made of metallic material, or it can be formed as a solid rod made of 
appropriate plastic material with appropriate elastic properties. 
The distance L can be adjusted by loosening screws 17, moving the upper 
extremity 16 of the post along the bushing 14, and then retightening 
screws 17. 
Reference will now be made to FIGS. 2 and 4, in which it is shown that an 
T-shaped bracket 20 is attached by its upper section 20' to the post. 
The bracket extends along the post and carries a sensing means 21, mounted 
on it with the aid of screwed washers 21', 21". Disc 22 is mounted on the 
post in opposite relation to the sensing means 21, so as to provide for 
initial distance Dn corresponding to the straight configuration of the 
post. Once the post bows with respect to its upper extremity 16, fixed in 
the bushing 14, distance Dn changes to Dd, as shown on FIG. 4b. Sensing 
means 21 is adapted to detect this change and to generate the appropriate 
signal in the wiring, W1, W2, connecting sensing means with switching 
means D1 of electrical schematics shown in FIG. 5. The wiring preferably 
includes a pair of wire conductors W1, W2, but can also include only one 
wire conductor and the vehicle body as a second conductor. 
Sensing means 21 can be of any appropriate type, suitable for the above 
purpose, for example, magnetic, inductive or capacitor sensor. Material 
for disc 22 is to be chosen in accordance with the particular type of 
sensor employed. 
The lower section of bracket 20 is preferably provided with magnets 24', 
24", associating with oppositely located metallic bands 25', 25" on the 
post. Magnets 24'24" are adapted to attract metallic bands 25', 25" and 
thus to retain the post in its initial disposition at a distance Do from 
sensing means 21, when the extending portion of the post is straight. By 
virtue of magnets 24', 25" and metallic bands 25', 25", retention of the 
post in this position is ensured despite the inevitable shocks and 
vibrations during vehicle travel. 
Now reference will be made to FIG. 5 which shows the electrical schematic 
with the several switching means and alarms employed in the present 
invention. This schematic is preferably mounted on the instruments board 
in the driver's compartment and preferably includes a main on/off switch 
D1, auxiliary switches R1 and T1, relay R, resetable timing means T and 
signal producing means, including audible and visible arms, S and L. 
The schematic is wired with a source of energy, for example, vehicle 
battery (not shown) supplying operating voltage V to its components. The 
main switch D1 is of the normally closed type and is controlled by a 
signal, generated in sensing means 21. 
By virtue of providing the main switch D1 as a normally closed type, it is 
always ensured that the signal-producing means will be activated and warn 
the driver in the event of a malfunction in the system, caused, e.g., by 
accidentally broken wiring, or the like. The alarms can also be outfitted 
with separate on/off toggle switches, providing for the separate turning 
on and turning off of each of them. 
Besides the above-mentioned signal-producing means which warn the driver of 
the current deflated condition of the tire, additional means can also be 
provided, which inform the driver of current pressure in the tire and 
evaluated time interval remaining since detection of deflated condition in 
the tire until compulsory replacement of the tire. This means comprises an 
additional timer T2 connected with alarms, computing means C and 
displaying means DP and DT for displaying messages advising the driver of 
current tire pressure and remaining time interval until replacement of the 
tire. 
The significance and principle of operation of the height compensation unit 
will now be explained with reference to FIGS. 6a,b. FIGS. 6a,b 
correspondingly refer to the normally inflated condition in the tire 3, 
when the vehicle is not loaded (FIG. 6a) and loaded (FIG. 6b). 
The undercarriage 10 of the not loaded vehicle or platform is spaced from 
the axle housing 2 by a distance A, while the axle housing is spaced from 
the road surface 4 by a distance B. The axle housing carries a fixture 1 
with a pantograph. The arm 7 of the pantograph is provided with a space 
bar 9, interacting with the undercarriage, while the opposite arm 13 of 
the pantograph carries post 15, contact member 19 being mounted on its 
distal extremity. 
In normally inflated condition the distance between the contact member and 
the road surface is L. After the vehicle is loaded, the undercarriage 
springingly sinks down under the weight of cargo at a distance A1 (see 
FIG. 6b), and therefore the distance A shortens to A2=A-A1. 
The weight of the cargo is transferred via suspension (not shown) to the 
axle housing 2, compresses the tire, and thus the axle housing goes down 
together with the fixture, pantograph, and post at a distance B1. As a 
result of this the distance B shortens to B2=B-B1. Were it not a 
pantograph, the shortening of distance B would reduce distance L and a 
situation could arise where the contact member touches the ground when 
there is still no deflation in the tire. 
By virtue of a space rod 9, fixed on the lever arm 7 and interacting with 
the undercarriage, lowering of the undercarriage at distance A1 causes 
pivoting of the pantograph lever arms 5,5' about axes 6,6' with respect to 
fixture 1. This pivoting action results in lifting of the opposite lever 
arm 13 together with the post mounted on it, and therefore the possibility 
is provided to compensate for changes in the distance between the post and 
road surface and to ensure that this distance will always be kept equal to 
L irrespective of whether the vehicle is loaded or not. 
The height at which the post will be lifted and therefore the degree of 
height compensation, is governed by the lever rule and depends on the 
location of axes 6,6' with respect to the lever arm. In order to achieve a 
different degree of compensation, as might be required by a particular 
type of vehicle, by the weight of its load, by the pressure in the tires 
and by the condition of its suspension, a series of apertures 35,35' on 
lever arms 5,5' for axes 6,6', can be provided. 
An alternative embodiment of the height compensation unit as presented in 
FIG. 8, can be employed in the system according to the present invention. 
The height compensation unit according to this embodiment comprises two 
bars 90,90', assembled in housing 60, carried by fixture member 1', which 
is mounted on axle housing 2. As can be seen on FIG. 8 these bars are 
assembled in such a manner that it is ensured that bar 90 contacts the 
undercarriage, while bar 90' contacts the post. 
Each of these bars is provided with a toothed section, and a pinion 80 is 
provided, mounted in the same housing 60 between toothed sections of these 
bars as to ensure their meshing and transfer linear movement of one bar to 
the other in reversed direction. 
In order to ensure reliable contact between bars and undercarriage and the 
post, respectively, coil springs 120,120' are provided. Spring 120 urges 
bar 90 to be lifted up to contact the undercarriage and spring 120' urges 
bar 90' to be lowered to contact with the upper extremity 16 of the post 
15. 
The advantage of this embodiment lies in its compact design and therefore 
possibility for mounting on vehicles, where the axle housing is occupied 
by other accessories and there is no room for mounting of a pantograph. 
As can be seen from the above explanation by virtue of providing a height 
compensation unit, it is ensured that the distance between the contact 
member of the post and the road surface is independent of the position of 
the undercarriage, and therefore, it can be kept minimal as to be 
influenced solely by small changes in the tire pressure in the early 
stages of deflation. 
At the same time, due to the fact that the post is made resiliently 
bendable, there is minimized danger of its damage during possible 
collision with obstacles protruding from the ground. 
Reference should now be made to FIGS. 7a,b which explain the principle of 
operation of the warning system according to the present invention. 
On FIG. 7a a sequence of events is presented from left to right, showing 
how a normally inflated tire 3, traveling along the roadway 4, overcomes 
an obstacle 50, protruding from the road. 
When the vehicle is loaded by weight F, the axle housing is in its lowest 
position at a distance X from the road level; however, the post is 
adjusted so as to ensure that it does not come into contact with the road 
surface. The post has a straight configuration, and therefore there is no 
signal in the sensing means, switching means D1 is closed relay R is 
inoperative and there is no activation of timing means T and signal 
producing means L,R. 
The wheel, provided with a tire 3 is shown in the left section of FIG. 7a, 
being in its initial position before meeting obstacle 50 on the roadway. 
The tire rises up along the obstacle, and then descends, when the obstacle 
is passed. The potential energy accumulated by the tired depends on the 
height of the obstacle and weight of the vehicle. This energy, being more 
than pressure in the tire, causes elastic compression of the tire when it 
engages the ground again and therefore the resulting distance X1 between 
the axle and the ground becomes less than before the obstacle. Due to the 
shortening of this distance the post touches the road surface, and being 
dragged by the moving vehicle, becomes bent as shown at 15' in the middle 
section of FIG. 7a. Bending of the post generates the appropriate signal 
in the sensing means 21, which opens switching means D1, and causes 
engaging of relay R, which closes switch R1 and activates the timing means 
T. 
Compression of the tire loads to its jumping up and restoring of the 
distance X between the axle housing and the ground. The period of time 
needed for restoration of this distance is Tn. 
When this distance is restored, the post disengages the ground and returns 
to its straight configuration, as shown at 15 on the right section of FIG. 
7a. Straightening of the post terminates generation of the signal, by 
sensing means 21, and causes switching of means D1 to its normally closed 
position while immobilizing the relay, opening contact R1 and thus 
disactivating the timing means T. 
On the left section of FIG. 7b, a deflated tire 3' is shown approaching the 
same road obstacle 50. The initial distance between the axle housing 2 and 
the tire is X. After the obstacle is passed, and the tire again engages 
the road, it becomes compressed more than in the previous case due to 
reduced pressure in the deflated tire (see middle section of FIG. 7b). 
Therefore, the distance between the axle housing and road surface reduces 
to X2&gt;X1. 
If deflation in the tire is only in its early stages, the remaining 
pressure will be sufficient to jump the tire up until the distance X2 is 
restored to X, and the post again becomes straight, as is shown at 15 on 
the right section of FIG. 7b. However, it should be understood that the 
period of time Td until this distance is restored will last longer than 
Tn. Timing means T can be programmed, and time interval Tn, corresponding 
to normally inflated condition of the tire, can be preset as to be 
compared with actual time being counted by timer T. If this actual count 
time becomes longer than the preset value, timing means T immediately 
closes contact T1 and signal producing means L and S are activated to warn 
the driver about the current condition of the tire. 
The period of time needed for restoration of said distance from X1 or X2 to 
X, generally depends on several factors, e.g., pressure in the tire, road 
conditions, speed of travel, weight of cargo, etc. Nevertheless, it was 
empirically found that in the warning system according to the present 
invention, utilizing a resiliently bendable post, the dominant factor 
determining restoration time is the tire pressure. In particular, it was 
observed that even reduction of pressure, at approximately 10% from its 
nominal value, could be detected early because this was accompanied by 
tripling of restoration time. 
Such reduction of pressure usually refers to a very early stage of 
deflation which is hardly visible; however, performance of the tire is 
still sufficient for riding and its replacement is not compulsory. 
Therefore, according to the present invention, there is provided the 
possibility for timely detection of deflation, which is one of the main 
advantages of the warning system, compared to known systems, in which the 
distance between the post and the road surface must be kept much longer 
and the warning signal be generated only after sufficient deflation has 
already taken place. 
The time interval Tn can be used as a preset value for timing means T and 
be taken as a reference, corresponding to nominal pressure in the tire. 
Once deflated condition in the tire is timely detected and reduction of 
its pressure is in progress, there is a change in the frequency of warning 
signals, as generated in alarms L,S. This fact can be used for monitoring 
of current tire behaviour in terms of pressure and prediction of time 
interval remaining until this pressure is reduced to such a level that 
driving becomes unsafe. 
For this purpose an additional timing means T2, associated with alarms L,S 
and connected with computing means C, can be used. The computing means C 
can be programmed to calculate current pressure with reference to nominal 
pressure, as well as rate of its change in accordance with current 
frequency of warning signals, and time remaining until it drops to an 
unacceptable level. This information can be displayed by a pressure 
displaying means DP and a time displaying means DT, advising the driver 
when the tire must be replaced. 
As can clearly be seen, since deflation has been detected, the possibility 
of monitoring the current condition of the tire and predicting of its 
future behaviour, presents an additional advantage of the present system, 
unachievable in known systems. 
With reference to FIGS. 9a, b, c further embodiment of the warning system 
according to the present invention will be explained. 
This embodiment relates preferably to light-weight vehicles, in which the 
distance between the post and the road surface is much less influenced by 
the loading condition of the undercarriage and therefore, there a height 
compensation system might not be needed. 
A normally inflated tire 30 of a light-weight car engaging the ground 40 is 
shown in FIG. 9a. The upper extremity 160 of the resiliently bendable post 
150 is formed integrally with the mounting means 100, made of the same 
material and assembled on the axle housing 2, for example, with the aid of 
clamp 80. An elongated recess 140 is provided between the post and 
mounting means, dividing it on the main body portion 70 which is adjacent 
to the axle housing and a neck portion 170, which is adjacent to the upper 
extremity 160 of the post. 
The post extends downward and is provided at its distal extremity with a 
bent section 190, which in normally inflated tire condition is separated 
from the ground by a distance L. When the tire is deflated, section 190 
contacts the road surface and the post is dragged by the moving vehicle. 
By virtue of recess 140 the post resiliently pivots with respect to the 
neck portion 170 while opening recess 140, as is shown on FIG. 9b,c. 
Sensing means 200 is located in said recess so as to detect its opening and 
generate the appropriate signal in wiring W1, W2 thus controlling 
condition of normally closed switching means D1. 
The rest of the system components, according to this particular embodiment 
as well as of its functioning, is similar to that described above. 
The present invention should not be limited to the above preferred 
embodiments and it should be understood that changes and modifications can 
be made by one ordinarily skilled in the art, without deviation of the 
scope of the invention, as will be defined below in the appended claims.