Apparatus for alarming of tire deflation

An apparatus for alarming of tire deflation is provided in which reliability of an alarm is raised by a manner of alarming slightly when tire deflation is small and detection accuracy of a deflation detection mechanism is small, while alarming largely when tire deflation is large and deflation is detected with large accuracy. The apparatus comprises deflation detection means for detecting tire deflation; vehicle speed detection means for detecting a speed of a vehicle; and alarm means for deciding an alarm level depending on a detected tire deflation and a detected vehicle speed, and providing an alarm at the decided alarm level.

BACKGROUND OF THE INVENTION 
The present invention relates to an apparatus for alarming of tire 
deflation and, more particularly, to an apparatus for alarming of tire 
deflation in which, in order to raise reliability of an alarm occurrence, 
an alarm is given slightly when detection accuracy of a mechanism for 
detecting tire deflation is low while the alarm is given largely when 
detection accuracy becomes higher with an advance of deflation. 
Furthermore, taking it into consideration that critical speeds to cause a 
burst differ from each other depending upon a degree of tire deflation, 
the present invention relates to an apparatus for alarming of tire 
deflation in which the alarm is given larger according to an increase in a 
vehicle speed. 
Safe and comfortable travel can be provided by keeping pressures of tires 
on a vehicle at values indicated to each vehicle. However, deflation of a 
tire occurs occasionally from an external damage of the tire and an 
incomplete maintenance, which would seriously influence safety as well as 
comfortableness of driving. So, various kinds of apparatuses for detecting 
tire deflation and alarming a driver have been devised and marketed, but 
the apparatuses have not yet spread widely because of a difficulty in a 
compatibility of cost and reliability. 
In particular, with respect to timing for an alarm and reliability thereof, 
there exists a problem that it is very difficult to determine how far 
deflation should proceed before an alarm is given, since a dangerous 
degree of deflation depends on a vehicle speed. In other words, if the 
alarm is scheduled to be given at a small degree of deflation, there is a 
large merit in respect of sure security of safety. Slight deflation is, 
however, difficult to detect and an easy alarm occurrence causes driver 
uneasiness and repeated easy alarm occurrences have a possibility that a 
driver passes over the very alarm in the truly dangerous case. On the 
other hand, if the alarm is scheduled not to be given until deflation 
proceeds significantly to be detected with certainty, reliability of the 
alarm becomes large while there exists a problem that the alarm would get 
too late in the case of a high speed driving. 
In view of the foregoing, it is an object of the present invention to 
provide an apparatus for alarming of tire deflation in which reliability 
of an alarm is raised by a manner of alarming slightly when tire deflation 
is small and detection accuracy of a mechanism of detecting deflation is 
low, while alarming largely when the tire deflation becomes large and is 
detected with high accuracy. 
In addition, it is also an object of the present invention to provide a 
reliable apparatus for alarming of tire deflation in which, by operating 
an alarm mechanism with a vehicle speed measuring device and alarming more 
largely with an increase of vehicle speed, a balance is well kept between 
an alarm level and a danger of a real nature and a balance is well kept 
accuracy of an alarm, a degree of emergency of the alarm and uneasiness 
given to a driver by the alarm. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, there is provided an apparatus 
for alarming of tire deflation comprising deflation detection means for 
detecting tire deflation; vehicle speed detection means for detecting a 
speed of a vehicle; and alarm means for deciding an alarm level depending 
on a detected tire deflation and a detected vehicle speed, and providing 
an alarm at the decided alarm level. 
The apparatus for alarming of tire deflation of the present invention does 
not alarm unconditionally when a tire reaches to a particular deflation, 
but alarms depending on a degree of deflation in accordance with accuracy 
of a deflation detection mechanism. The apparatus alarms according to a 
level of a vehicle speed since critical speeds at which a tire might cause 
a burst differ from each other. 
For example, in the case of an alarm device using a sound, the higher a 
level of deflation becomes, the louder sound the device alarms under a 
constant speed, while the higher a level of a vehicle speed becomes, the 
louder sound the device alarms under a constant level of deflation.

DETAILED DESCRIPTION 
An apparatus for alarming tire deflation of the present invention will be 
explained with reference to the attached drawing. 
FIG. 1 is a representation of an embodiment of an apparatus for alarming of 
tire deflation of the present invention. As shown in FIG. 1, the apparatus 
of the present invention comprises four deflation detection mechanisms 1 
for measuring tire deflation, a speed measuring device 2 for detecting a 
speed of a vehicle, an alarm mechanism 3 for deciding an alarm level and a 
speaker/light-indicator 4. A deflation detection mechanism 1 is provided 
on each wheel of the vehicle. 
As for a deflation detection mechanism for measuring tire deflation, there 
are two types of detecting tire pressure directly and indirectly. As the 
type of detecting directly, there has been known, for example, a mechanism 
wherein a pressure sensor capable of generating a signal in proportion to 
a tire pressure is embedded in a tire wheel to transmit the signal to a 
vehicle body in the form of radio wave or with the use of electromagnetic 
induction. On the other hand, in the type of detecting indirectly, there 
is detected other physical quantity than tire pressure which varies in 
proportion to change of tire pressure. For example, there can be detected 
a load radius (distance between a road surface and a center of a tire) by 
means of a non-contact displacement gauge; a difference in tire rotational 
speed between a normal pressure tire and a deflated tire by means of a 
rotational pulse generator or tachometer; a bulge or rising of a sidewall 
of a tire by means of a non-contact displacement gauge; and a resonance 
frequency of a tire by means of an acceleration sensor. The measured 
values are changed into electrical signals which are transmitted to a 
vehicle body in the form of radio wave or with the use of electromagnetic 
induction. 
Since the type of detecting directly is, however, so complicated in a 
mechanism, that it is liable to be expensive. On the other hand, the type 
of detecting indirectly can produce a system very economically by 
utilizing, for example, an ABS sensor equipped to a vehicle. It is, 
therefore, preferable to use the latter indirect detection type. 
As for a speed measuring device 2, there can be used a speed indicator of a 
vehicle, a wheel speed sensor attached to ABS, or a non-contact laser 
speedmeter. 
The alarm mechanism 3 includes, an arithmetic and logic unit 
(microcomputer) and a table which is prepared beforehand, an example 
thereof is shown in FIG. 2 mentioned below. 
Based on a signal from the deflation detection mechanism 1 which is 
proportional to a tire deflation, the arithmetic and logic unit calculates 
a tire deflation level. Simultaneously, the arithmetic and logic unit 
decides a vehicle speed based on a signal from the speed measuring device 
2. 
Based on the obtained vehicle speed and tire deflation level, the 
arithmetic and logic unit then decides an alarm level in accordance with 
the table in the alarm mechanism 3 and transmits a signal in proportion to 
the decided alarm level to the speaker/light-indicator 4. 
FIG. 2 is a representation of an example of alarm level for alarming tire 
deflation of the present invention, which shows a relationship between 
vehicle speed level and deflation, and alarm level. In the present 
specification, "deflation level" means a percentage of a deflated portion 
to a total normal pressure of a tire, and "alarm level" means a level of 
emergency perceived to a man, for example, a level of a loudness of a 
sound in the case of an alarm using a sound. 
As shown in FIG. 2, in an apparatus for alarming tire deflation of the 
present invention, an alarm level becomes higher with increase of a 
deflation level under a constant vehicle speed, while the alarm level 
becomes higher with increase of a vehicle speed increases under a constant 
deflation level. A method for determining an alarm level in FIG. 2 is 
explained as follows. 
A line of 100% of an alarm level is decided as a critical line for a tire 
to cause a burst. When the alarm level exceeds a line of 100%, it is not 
strange for a tire to cause a burst any time. 
A lower limit of detection, which is not particularly limited in the 
present invention, is usually set at -15% (deflation of 0.3 kg/cm.sup.2 in 
the case of normal pressure of 2 kg/cm.sup.2). To measure deflation 
smaller than 15% deflation is difficult and lowers detection precision 
(detection accuracy) since pressure and rotational frequency of a tire 
fluctuates under the influence of a temperature, an applying condition, 
precision on pressure control of the tire and so on. Further, detection of 
such small deflation is meaningless, taking it into consideration that 
such small deflation scarcely becomes a problem in so far as safety. 
However, even if the deflation level is only about -15%, a tire generates 
heat when a vehicle speed increases, and the tire is in danger of causing 
a burst when the vehicle speed exceeds 240 km/h. Therefore, a point on a 
segment corresponding to an alarm level of 100% is firstly plotted against 
a critical speed of 240 km/h at a detection lower limit for deflation, 
i.e. -15%. This is regarded as a point A. Secondly, if the deflation level 
is -75% (deflation of 1.5 kg/cm.sup.2 in the case of normal pressure of 2 
kg/cm.sup.2), the tire is in danger of causing a burst when the vehicle 
speed exceeds 80 km/h. This is regarded as a point B. Thirdly, if the 
deflation level exceeds -80%, since the tire is much in danger of causing 
a burst and departure from a rim and an alarm is required to be given as 
soon as possible, the alarm level is set at 100% at a vehicle speed of 0 
km/h. The point of an alarm level of -80% at the vehicle speed of 0 km/h 
is regarded as a point C, then this point C is connected to the point B 
and further connected to the point of A. This is regarded as a segment 
indicating the alarm level of 100%. This is the minimum line to maintain 
safety. 
Next, lines which decrease 10 by 10% in an alarm level are drawn on the 
basis of the segment AB corresponding to the alarm level of 100%. At this 
time, the point D corresponding to a deflation level of -15% and a vehicle 
speed of 40 km/h is regarded as a point of an alarm level of 0%, and the 
segment from the point A to the point D is divided into 10 parts, and then 
segments are drawn from each dividing point parallel to the segment AB. 
Because a tire is not in danger of causing a burst under a vehicle speed 
of not more than 40 km/h in the case of a deflation level of -15%, and 
therefore the alarm level becomes 0%. Alarm levels of the segments are set 
at 90%, 80% . . . , in turn from the nearest to the segment AB. 
The operation of an apparatus for alarming of tire deflation of the present 
invention is explained subsequently. For example, let it be supposed that 
air pressure began to decrease because of some accident when driving the 
vehicle at a constant speed of 80 km/h on an expressway. At first, when a 
deflation level is between 0 and -15%, an alarm is not given, because the 
risk of causing a burst does not exist for such deflation as long as a 
vehicle speed is not so high, and because there are some cases where 
deflation does not occur actually since detection accuracy of deflation 
detection mechanism is low to such a degree of the deflation. 
When the deflation level reaches -15%, the alarm level becomes abruptly 20% 
because of driving at a high speed of 80 km/h. The alarm begins, however, 
to sound softly since the detection accuracy is not yet so high. As the 
deflation level gradually becomes higher and the detection accuracy also 
becomes higher, the alarm level also becomes higher. The volume of the 
alarm increases in the way that the alarm level becomes 40% and 80% 
respectively when the deflation level becomes -30% and -60%. At last, when 
the deflation level reaches to -75% (air pressure of only 0.5 kg/cm.sup.2 
remaining in the case of normal air pressure of 2 kg/cm.sup.2), the alarm 
level becomes 100% and the volume is the largest and the urgency given to 
a driver reaches the highest. So, the driver can immediately slow down the 
vehicle speed or so, and occasionally can act for avoiding a danger, for 
example, stop driving to wait for a maintenance service. 
When the deflation level is -30% (air pressure of 1.4 kg/cm.sup.2 in the 
case of normal air pressure of 2 kg/cm.sup.2), the alarm level is 0% at a 
vehicle speed of 0 km/h but increases gradually according to the increase 
in the vehicle speed. Then, the alarm level becomes 20%, 40%, 60% and 100% 
respectively when the vehicle speed becomes 40 km/h, 80 km/h, 120 km/h and 
200 km/h. So, the driver can avoid a danger beforehand, since the driver 
can follow the volume of the alarm, continue to drive at a vehicle speed 
of around 40 km/h with a smaller volume of the alarm and find a gasoline 
station or so to have an air pressure check. 
Though the alarm level is presented by the magnitude of volume (loudness) 
in the above explanation, since the alarm level is a magnitude of an 
impact given to a driver, the way of alarming in the present invention is 
not particularly limited. That is, the alarm level can be presented by an 
interval of voices as well as a volume when the alarm is given in a voice, 
and by a variation of brightness or color of a lamp and by frequency of 
on-and-off when an on-and-off lamp is utilized, and the combinations of 
these are also available. 
As has been described, since the alarm level is set depending upon 
detection accuracy of the deflation detection mechanism in the tire 
deflation alarm apparatus of the present invention, a driver can correctly 
avoid a danger as required without unnecessarily feeling uneasy. 
Since critical speeds for causing a burst differ from each other depending 
upon the deflation levels, the alarm level is, by measuring both a 
deflation level and a vehicle speed, set higher with the increase in the 
deflation level in the case of a constant vehicle speed, or with the 
increase in the vehicle speed in the case of a constant deflation level. 
Since the alarm is well timed to a degree of a danger in a real drive, the 
driver can correctly decide whether to slow down or stop immediately. 
Thus, the apparatus can alarm with high reliablity without giving the 
driver unnecessary unease. 
While only certain presently preferred embodiments have been described in 
detail, as will be apparent with those familiar with the art, certain 
changes and modifications can be made without departing from the spirit 
and scope of the invention as defined by the following claims.