Tire pressure drop alarming apparatus

This invention is concerned with a tire pressure drop alarming apparatus for signaling an abnormal pressure drop of a pneumatic tire by transforming the pressure drop into an electric signal. The apparatus comprises a resonating circuit including a resonance coil and a resonance condenser and includes a retaining body made of metal. The retaining body includes a bottom plate portion interposed between and separating the resonance coil from a vertical portion of a rim flange in such a way that the vertical portion of the rim flange can prevent effects imparting characteristics of the resonance coil, and a side plate portion integrally connected with the base plate portion to be interposed connected with the base plate portion to be interposed between and separating the resonance coil from the parallel portion of the rim flange in such a way that a parallel portion of the rim flange can prevent effects imparting characteristics of the resonance coil, the retaining body being attached to the rim flange with the base plate portion and the side plate portion not deformed.

FIELD OF THE INVENTION 
This invention relates to a tire pressure drop alarming apparatus for 
signaling an abnormal pressure drop of a pneumatic tire by transforming 
the pressure drop into an electric signal. 
BACKGROUND OF THE INVENTION 
Conventionally, there have been proposed a wide variety of tire pressure 
drop alarming apparatuses for signaling an abnormal pressure drop for a 
pneumatic tire. One type of apparatus comprises a resonator attached to 
the outerside of a rim flange of a wheel rim which includes a vertical 
portion substantially perpendicular to a rotational axis of the tire and a 
parallel portion integrally formed with the radially outer end of the 
vertical portion and in parallel with the rotational axis of the tire. In 
general, there are many different rim flange forms of the wheel rim 
depending upon its kind and not produced accurately on the basis of 
Japanese Industrial Standards so that if the conventional resonator is 
attached to the rim flange, the characteristic such as resonance frequency 
and sensitivity Q of the resonator receives effects from the rim flange 
and is thus fluctuated depending upon its position. In this instance, it 
is impossible for the resonator to receive magnetic energy from an 
oscillation coil provided on a body of a car so that the alarming 
apparatus can not alarm the abnormal pressure drop if it occurs. On the 
other hand, the resonator attached with a usual balance weight is easily 
separated from the outside wall of the wheel rim owing to deflection of 
the tire, vibration of the wheel rim, and centrifugal force acting on the 
resonator while the car is moving, or otherwise suddenly scattered at an 
extremely high accelation speed so that it is extremely dangerous for 
adjacent cars and human bodies. 
It is therefore an object of the present invention to provide a tire 
pressure drop alarming apparatus which can retain a constantly stable 
characteristic of a resonator to be attached to a wheel rim regardless of 
the different kinds of the wheel rim and the attachment position to the 
wheel rim of the resonator. 
It is another object of the present invention to provide a tire pressure 
drop alarming apparatus wherein the resonator is firmly attached to the 
outside of the rim flange to prevent dangers caused by separation and 
scattering of the resonator from the rim flange. 
The above and other ojects, features and advantages of the present 
invention will become clear from the following particular description of 
the invention and the appended claims, taken in conjunction with the 
accompanying drawings which show by way of example a preferred embodiment 
of the present invention.

Referring now to the drawings and in particular to FIGS. 1 and 2, the 
reference numeral 1 generally designates a wheel rim for automobiles which 
has a rim 2 at its radially outer end. The rim 2 comprises a cylindrical 
flat base portion 3, a pair of bead seats 4 provided at the axially outer 
ends of the flat base portion 3, and a pair of rim flanges 5 each 
connected to the axially outer end of the bead seat 4. Each rim flange 5 
has a vertical portion 5a substantially vertical to a rotational axis of a 
tire 6 and a parallel portion 5b connected at the radially outer end of 
the vertical portion 5a in substantially parallel relation to the 
rotational axis of the tire 6. The tire 6 cross-sectioned in a toroidal 
form is attached to the wheel rim 1 with its bead portions 7 seated on the 
bead seats 4 of the rim 2. The reference numeral 8 indicates a back plate 
which is securely mounted on a body frame not shown and has an axially 
outer end face securely supporting a radially inner end portion of a 
curved arm 9. On the radially outer end portion of the arm 9 is securely 
mounted an oscillator, generally indicated at 11, which has an oscillation 
coil 10 opposing the vertical portion 5a of the rim flange 5 and an 
oscillating condenser accommodated therein but not shown so that the 
oscillation coil 10 may oscillate a magnetic energy. The reference numeral 
12 represents an indicator which is provided on a car dashboard to be 
connected with the oscillator 11 through a cable 13 and is adapted to 
house a signal processing circuit therein. A pair of retainers 14 and 14' 
are particularly shown in FIGS. 3 and 4, each having a hook 15 at its 
radially outer end. The retainers 14 and 14' are attached to the parallel 
portion 5b of the rim flange 5 to be positioned at the radially outwardly 
of the rim flange 5 and immediately below the parallel portion 5b in such 
a manner that the hooks 15 of the retainers 14 and 14' are in engagement 
with the parallel portion 5b of the rim flange 5 to surround and tightly 
fit the parallel portion 5b of the rim flange 5. Each of the retainers 14 
and 14' has at its radially inner end portion a flat base portion 16 
connected with the hook 15 and formed to extend along the axially outer 
face profile of the vertical portion 5a of the rim flange 5. At the 
radially outer ends of the flat base portion 16 are formed a pair of 
turnup portions 17 and 17' which are disposed at and integrally formed 
with both sides of the flat base portion 16 to be brought into engagement 
with the radially inner face of the parallel portion 5b of the rim flange 
5 for preventing the retainers 14 and 14' from being easily removed out of 
the rim flange 5 when the retainers 14 and 14' are attached to the rim 
flange 5. Each of the retainers 14 and 14' has at its radially inner end 
portion a pair of spaced gird portions 18 and 18' extending axially 
inwardly of the tire 6 from the radially inner end portion of the flat 
base portion 16 to protect pipes, hereinafter particularly described, from 
being damaged when the wheel rim 1 is under rotation as well as to protect 
an assembly of the tire 6 and the wheel rim 1 from being damaged when the 
assembly is assembled into the wheel body. 
With reference to FIGS. 5, 6 and 7, there is shown a retaining plate 19, 
made of metal, which has longitudinally outer end portions formed with 
slots 20 and 20'. As particularly illustrated in FIG. 2, a bolt 21 is 
inserted into each of the slots 20 and 20' and passing through the flat 
base portion 16 to be in threaded relation with a nut 22, so that the 
retaining plate 19 is attached to the retainers 14 and 14' to be disposed 
at the axially outwardly of the vertical portion 5a and immediately below 
the parallel portion 5b. With the movements of the retainers 14, 14' and 
the bolts 21 along the slots 20 and 20' of the retaining plate 19, the 
retaining plate 19 can be adjusted to be in tight contact with the 
radially inner face of the rim flange 5. The retaining plate 19 has at its 
longitudinally intermediate portion a flat base plate portion 23 which 
extends along the axially outer face profile of the vertical portion 5a of 
the rim flange 5. A side plate portion 24 is integrally connected to the 
radially outer end of the base plate portion 23 to be inclined at an 
obtuse angle with respect to the base plate portion 23 and to extend along 
the radially inner face profile of the parallel portion 5b of the rim 
flange 5. A standing portion 25 is integrally connected with the radially 
inner end of the base plate portion 23 to extend vertically with respect 
to the base plate portion 23. In the standing portion 25 is formed a pair 
of slots 26 and 26' spaced apart from each other in the longitudinal 
direction of the retaining plate 19. The foregoing retainers 14, 14' and 
the retaining plate 19 constitute as a whole a retaining body generally 
denoted by the reference numeral 27 in the present invention. 
Referring again to FIGS. 1 and 2, the reference numeral 28 indicates a case 
made of a synthetic resin and housed in a space defined by the base plate 
portion 23, the side plate portion 24 and the standing portion 25 of the 
retaining plate 19. A resonance coil 29 is embeded in the case 28 to be 
disposed at a position separated from the vertical portion 5a of the rim 
flange 5 by the base plate portion 23 of the retaining plate 19 and 
separated from the parallel portion 5b of the rim flange 5 by the side 
plate portion 24 of the retaining plate 19. The cross-sectional contour of 
the resonance coil 29 cross-sectioned in a plane perpendicular to the 
rotational axis of the tire 6 is formed in an elongated circular shape 
having a length measured in the radial direction of the tire 6 shorter 
than that measured in the circumferential direction of the tire 6 as shown 
in FIG. 2. It is therefore to be understood that the base plate portion 23 
of the retaining plate 19 is interposed between the vertical portion 5a of 
the rim flange 5 and the resonance coil 29, and that the side plate 
portion 24 of the retaining plate 19 is interposed between the parallel 
portion 5b of the rim flange 5 and the resonance coil 29. A pair of 
detection switches 30 and 30' are embeded in the case 28 to permit the 
resonance coil 29 to be interposed therebetween, and respectively have at 
their radially inner ends hollow threaded shafts 31 and 31' which are 
adapted to project out of the case 28 and extend throughout the slots 26 
and 26', respectively. Pipes 32 and 32' are connected at their one ends 
with the hollow threaded shafts 31 and 31', and the pipes 32, 32' and the 
case 28 are retained by the retaining plate 19 in such a way that nuts 33 
and 33', which are respectively threadedly engaged with the hollow 
threaded shafts 31 and 31', and the case 28 tightly receive the standing 
portion 25 of the retaining plate 19 therebetween. The one end portions of 
the pipes 32 and 32' are protected from being damaged by the gird portions 
18 and 18' of the retainers 14 and 14', respectively as has been 
described. The pipes 32 and 32' are connected at their other ends with the 
inner chambers so that the inner pressures of the two tires 6 can be 
introduced to the detection switches 30 and 30'. In the case 28 is embeded 
a resonance condenser 34 which is electrically connected with the 
resonance coil 29 and the detection switches 30, 30'. The above-mentioned 
resonance coil 29, the detection switches 30, 30' and the resonance 
condenser 34 constitute as a whole a resonance circuit generally indicated 
at 35. 
The operation of the apparatus of the present invention thus constructed 
above will now be described hereinlater. 
In order to attach the resonator according to the present invention to the 
wheel rim 1, the retainers 14 and 14' are firstly required to be attached 
to the rim flange 5 of the wheel rim 1. At this time, the flat base 
portions 16 are not deformed although the hooks 15 are somewhat deformed. 
The retaining plate 19 is then attached to the retainers 14 and 14' by 
means of the bolts 21 and the nuts 22. At this time, the base plate 
portion 23 and the side plate portion 24 of the retaining plate 19 are not 
deformed since the retaining plate 19 is attached to the flat base 
portions 16 of the retainers 14 and 14'. The case 28 connected with the 
pipes 32 and 32' is then retained by the retaining body 27. At this time, 
the resonance coil 29 is spaced at a predetermined distance from the base 
plate portion 23 and the side plate portion 24 of the retaining plate 19, 
with the result that the resonance coil 29 receives a predetermined effect 
from the base plate portion 23 and the side plate portion 24 of the 
retaining plate 19, thereby causing the characteristic, i.e., resonance 
frequency and sensitivity Q of the resonance coil 29 to be made stable at 
a constant value. That is to say, the resonance coil 29 is protected from 
the effect given to its characteristic from the vertical portion 5a and 
the parallel portion 5b of the rim flange 5 by means of the base plate 
portion 23 and the side plate portion 24 of the retaining plate 19, while 
the resonance coil 29 is given a predetermined effect from the base plate 
portion 23 and the side plate portion 24 of the retaining plate 19. It 
will therefore be understood that a stable characteristic of the resonator 
can be obtained even if the resonator will be attached to any kinds of 
wheel rim, or even if the resonator will be attached to any positions of 
the wheel rims having different shapes. When a normal tire pressure is 
filled in the automobile tire 6 running with such a resonator, the 
detection switches 30 and 30' are not operated and the magnetic energy 
from the oscillation coil 10 is imparted to the resonance coil 29 only one 
time at every time when the resonance coil 29 faces the oscillation coil 
10 at every revolution of the tire 6. At this time, the indicator 12 is 
not operated. When the tire pressure is then abnormally varied, i.e., 
dropped from the normal pressure level by some reason such as puncture, 
the pressure drop variation is transmitted to the detection switches 30 
and 30' by way of the pipes 32 and 32' to operate the detection switches 
30 and 30'. As a consequence, the resonance coil 29 can not receive the 
magnetic energy from the oscillation coil 10 and the pressure drop of the 
tire is then transformed into an electrical signal to operate the 
indicator 12 so that a driver can perceive an alarm from the indicator 12. 
According to the present invention, the retainers 14 and 14' may be 
integrally formed with the retaining plate 19. The retainers 14 and 14' 
are not necessarily needed in the present invention, wherein a pair of 
protrusions are required to be formed on the outer surface of the vertical 
portion of the rim flange and each to have a threaded bore into which a 
bolt is inserted, thereby causing the retaining plate to be attached to 
the wheel rim. Where there has been described in the above embodiment 
about a pair of detection switches which can detect abnormal pressure 
drops of a pair of tires, only one detection switch may be provided to 
detect an abnormal pressure drop of only one tire according to the present 
invention. 
Secondly, embodiments of a grasping device of the present invention will 
now be described hereinafter with reference to the drawings wherein same 
parts or elements as mentioned above are given same reference numerals to 
avoid tedious description. 
FIGS. 8, 9a, 9b and 10 particularly show a grasping device, generally 
indicated at 36, which is made of a flexible metal and is formed in 
substantial T-shape in an expanded state as shown in full lines of FIGS. 
9a and 9b. The grasping device 36 comprises a first grip end portion 37 
formed at its one end portion and inserted into and turned up at a tube 
valve bore or slot 38 to partially surround an inner edge 41 of the tube 
valve bore 38 as shown in full lines of FIG. 8 and phantom lines of FIGS. 
9a and 9b. The tube valve bore 38 is formed in the flat base portion 3 of 
the rim 2 to extend axially of the tire 6, and the first grip end portion 
37 is interposed between the rim 2 and a flap 40, the latter of which is 
disposed between a tire tube 39 and the rim 2. The grasping device 36 
further comprises an intermediate flat portion 42 which is integrally 
connected with the first grip end portion 37 to extend axially of the tire 
6 along the inner periphery of the rim 2. At the intermediate flat portion 
42 are two pairs of spaced pipe grasping projections 43, 43', 44 and 44', 
the former two of which are adapted to grasp the pipe 32 and the latter 
two of which are adapted to grasp the pipe 32' as shown in FIGS. 10 and 
11. To the outer face of the intermediate flat portion 42 opposite to the 
rim 2 is attached a square bar 45 to extend along the intermediate flat 
portion 42. The height of the square bar 45, i.e., the length of the 
square bar 45 measured in the radial direction of the tire 6 is at least 
substantially identical to or somewhat larger than the diameter of the 
pipes 32 and 32' which are adapted to extend along the side walls of the 
square bar 45. It is therefore possible to protect the pipes 32 and 32' 
from being damaged by parts of the vehicle body upon assembling of the 
tire to the vehicle and by stones upon running of the car. 
As shown in FIG. 8, a leg 47 having a slit 46 is formed to extend 
downwardly at the lower end, i.e., radially inner end of the base plate 
portion 23 of the retaining plate 19. The grasping device 36 further 
comprises a second grip end portion 48 formed at the other end portion 
thereof to be inserted into the slit 46 of the leg 47 and to be turned up 
as shown in FIGS. 8, 9a and 9b. It is therefore to be understood that such 
attachment of the second grip end portion to the slit 46 of the leg 47 
causes the case 28 and the retaining plate 19 to be fixedly supported by 
the rim flange 5 axially outwardly of the vertical portion 5a of the rim 
flange 5 and below the parallel portion 5b of the rim flange 5. 
There are shown in FIG. 12 pipe grasping members 49 and 50 which may be 
provided on a square bar 51 to surround and grasp the pipes 32 and 32' in 
cooperation with the pipe grasping projections 43 and 44 according to the 
present invention. FIG. 13 shows pipe grasping members 52 and 53 which may 
be provided on a square bar 54 to support the pipes 32 and 32' in 
cooperation with the pipe grasping projections 43 and 44 according to the 
present invention. 
Where there has been disclosed a grasping device 36 for use in a tire 
pressure drop alarming apparatus of double tires, the grasping device 36 
may be used for a tire pressure drop alarming apparatus for a single tire 
in such a way that a pipe grasping member 55 is formed at one side of the 
intermediate flat portion 42 as shown in FIGS. 14a, 14b and 15 according 
to the present invention. 
The square bar 45 may be omitted from the intermediate flat portion 42 as 
shown in FIGS. 16a, 16b and 16 if not necessary according to the present 
invention.