U.S. patent application number 09/731732 was filed with the patent office on 2001-06-14 for method for alarming decrease in tire air-pressure and apparatus used therefor.
Invention is credited to Oshiro, Yuji, Yanase, Minao.
Application Number | 20010003437 09/731732 |
Document ID | / |
Family ID | 26579193 |
Filed Date | 2001-06-14 |
United States Patent
Application |
20010003437 |
Kind Code |
A1 |
Oshiro, Yuji ; et
al. |
June 14, 2001 |
Method for alarming decrease in tire air-pressure and apparatus
used therefor
Abstract
A method for alarming decrease in tire air-pressure for judging
a decrease in internal pressure of a tire attached to a
four-wheeled vehicle and for accordingly generating alarm. A
threshold for judging decompression is set to be larger immediately
after switching an ignition key ON when compared to a threshold for
the vehicle in a normal running condition, and decompression is
judged in a decompression judging time which is shorter than a time
for the vehicle in a normal running condition. The threshold for
judging decompression and the decompression judging time are
returned to those for the normal running condition of the vehicle
in case no decompression is judged. An apparatus used for the
method is also disclosed. It is possible to detect a condition in
which a large decompressed condition exists at an early stage
before starting running so that it is possible to improve the
accuracy of detecting decompression.
Inventors: |
Oshiro, Yuji; (Kobe-shi,
JP) ; Yanase, Minao; (Kobe-shi, JP) |
Correspondence
Address: |
BIRCH, STEWART, KOLASCH & BIRCH, LLP
P.O. Box 747
Falls Church
VA
22040-0747
US
|
Family ID: |
26579193 |
Appl. No.: |
09/731732 |
Filed: |
December 8, 2000 |
Current U.S.
Class: |
340/444 ;
340/442; 73/146.2 |
Current CPC
Class: |
B60C 23/061
20130101 |
Class at
Publication: |
340/444 ;
340/442; 73/146.2 |
International
Class: |
B60C 023/00; B60C
023/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 9, 1999 |
JP |
350426/1999 |
Sep 20, 2000 |
JP |
285419/2000 |
Claims
What is claimed is:
1. A method for alarming decrease in tire air-pressure for judging
a decrease in internal pressure of a tire attached to a
four-wheeled vehicle and for accordingly generating alarm, wherein
a threshold for judging decompression is set to be larger
immediately after switching an ignition key ON when compared to a
threshold for the vehicle in a normal running condition,
decompression is judged in a decompression judging time which is
shorter than a time for the vehicle in a normal running condition,
and the threshold for judging decompression and the decompression
judging time are returned to those for the normal running condition
of the vehicle in case no decompression is judged.
2. An apparatus for alarming decrease in tire air-pressure for
alarming decrease in tire air-pressure for judging a decrease in
internal pressure of a tire attached to a four-wheeled vehicle and
for accordingly generating alarm, comprising a velocity detecting
means for detecting a velocity signal of respective tires, a
judging means for performing calculating processes of a
decompression judgement value for comparing a difference of two
diagonal sums of rotational information of front wheel tires and
rotational information of rear wheel tires based on rotational
information obtained from the velocity signals detected by the
velocity detecting means, an initial judging means for setting a
threshold for judging decompression to be larger immediately after
switching an ignition key ON when compared to a threshold for the
vehicle in a normal running condition and judging decompression in
a decompression judging time which is shorter than a time for the
vehicle in a normal running condition, and a returning means for
returning the threshold for judging decompression and the
decompression judging time to those for the normal running
condition of the vehicle in case no decompression is judged.
3. A method for alarming decrease in tire air-pressure for judging
a decrease in internal pressure of a tire attached to a
four-wheeled vehicle and for accordingly generating alarm,
comprising the steps of setting a threshold for judging
decompression to be larger immediately after switching an ignition
key ON when compared to a threshold for the vehicle in a normal
running condition and judging decompression in a decompression
judging time which is shorter than a time for the vehicle in a
normal running condition; judging whether the vehicle is running on
a bad road while a decompressed condition is judged during the
short decompression judging time; and increasing a number of data
used for judging decompression than compared to a number of data
which might be incorporated during the short decompression judging
time in case it is judged that the vehicle is running on a bad
road.
4. An apparatus for alarming decrease in tire air-pressure for
alarming decrease in tire air-pressure for judging a decrease in
internal pressure of a tire attached to a four-wheeled vehicle and
for accordingly generating alarm, comprising a velocity detecting
means for detecting a velocity signal of respective tires, a
judging means for performing calculating processes of a
decompression judging value for comparing a difference of two
diagonal sums of rotational information of front wheel tires and
rotational information of rear wheel tires based on rotational
information obtained from the velocity signals detected by the
velocity detecting means, an initial judging means for setting a
threshold for judging decompression to be larger immediately after
switching an ignition key ON when compared to a threshold for the
vehicle in a normal running condition and judging decompression in
a decompression judging time which is shorter than a time for the
vehicle in a normal running condition, a bad road judging means for
judging whether the vehicle is running on a bad road while a
decompressed condition is judged during the short decompression
judging time, and a data updating means for increasing a number of
data used for judging decompression than compared to a number of
data which might be incorporated during the short decompression
judging time in case it is judged that the vehicle is running on a
bad road.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a method for alarming
decrease in tire air-pressure and an apparatus used therefor. More
particularly, it relates to a method for alarming decrease in tire
air-pressure and an apparatus used therefor wherein a threshold for
judging a decompressed condition and a setting for a time required
for judging the decompressed condition are varied prior and after
start of driving to thereby improve the accuracy of detecting a
decompressed condition.
[0002] While one possible factor causing decrease in internal
pressure of a tire is minute leakage of air from between rubber
molecules of the tire, it is mostly the case that decreases in
internal pressure are caused through damages of tire units, rims or
tire valves which are component members of tires. Speeds at which
internal pressures are decreased caused by a nail piercing through
a tire, which is the most occurring factor, have so far been
reported upon performing various experiments.
[0003] JAF MATE, June 1995 edition includes a report of results
about experiments performed for testing air-pressure decreasing
speeds in case of blowouts of tires caused through nails. According
to this article, a tire with a normal internal pressure of 2.1
kgf/cm.sup.2 (2.06.times.10.sup.4 Pa) was used, and the internal
pressure decreased only to 1.95 kgf/cm.sup.2 (1.91.times.10.sup.4
Pa) (decrease of approximately 7%) upon elapse of as much as 5
hours in case the nail remained in the tire. Also in case the nail
was removed, the internal pressure decreased to only 1.90
kgf/cm.sup.2 (1.86.times.10.sup.4 Pa)(decrease of approximately
10%) after elapse of 1 hour and to only 1.65 kgf/ cm.sup.2
(1.62.times.10.sup.4 Pa)(decrease of approximately 21%) after
elapse of 5 hours.
[0004] On the other hand, it was found that the air-pressure
remained at 2.60 kgf/cm.sup.2 (2.55.times.10.sup.4 Pa) after
driving for 2 hours under a condition where a nail having a
diameter of 3.1 mm and a length of 65 mm was pierced through a
tread block portion of a tire having a tire size of 215/70R15 and a
normal internal pressure of 2.60 kgf/cm.sup.2 (2.55.times.10.sup.4
Pa). When measuring the internal pressure of the tire when the
vehicle was halting at an interval of 15 seconds after removing
this nail, the internal pressure decreased to 1.90 kgf/cm.sup.2
(1.86.times.10.sup.4 Pa)(decrease by approximately 27%) after
elapse of 60 seconds and to 1.35 kgf/cm.sup.2 (1.32.times.10.sup.4
Pa)(decrease by approximately 48%) after elapse of 120 seconds.
These results indicate remarkably faster internal pressure
decreasing speeds than compared to the test of JAF.
[0005] While there is presently no clear definition as to a degree
of decrease in internal pressure at which the vehicle becomes
dangerous, it will at least not become impossible to drive owing to
the damage of the tire although cornering performances will become
inferior when the decrease in internal pressure is approximately
40%. Thus, by setting this degree of compression as a target value,
it will be possible to inform the driver of danger caused through a
decrease in internal pressure of a tire if it would be possible to
detect a decrease in air-pressure within a time of 60 seconds
although the air-pressure decreasing speed is fast as illustrated
in FIG. 5.
[0006] However, since decreases in internal pressure of a tire will
progress not only during driving but also during halting,
decompression might gradually progresses over night upon parking
one's vehicle without knowing that a blowout has occurred during
driving to find out on the next morning that the tire is largely
decompressed when starting driving.
[0007] In the case of a vehicle which had not been moved for a long
time, tires might be largely decompressed owing to natural
decompression when starting driving of the vehicle.
[0008] On the other hand, according to conventional methods for
estimating decompression of a tire based on revolution velocities
of tires (see, for instance, Japanese Unexamined Patent Publication
No. 305011/1988), a decrease in tire air-pressure cannot be
detected unless the tires are rotating, that is, unless the vehicle
is running so that it might take several tens of seconds for
detecting decompression even if the degree of decompression is
large.
[0009] The present invention has been made in view of these facts,
and it is an object thereof to provide a method for alarming
decrease in tire air-pressure and an apparatus used therefor with
which it is possible to detect a largely decompressed condition
before start of running to thereby improve the accuracy of
detecting decompression. It should be noted that a
"before-start-of-running" condition indicates a condition prior to
throwing of a power source of the apparatus, which is generally a
condition prior to turning an ignition switch ON.
SUMMARY OF THE INVENTION
[0010] In accordance with the present invention, there is provided
a method for alarming decrease in tire air-pressure for judging a
decrease in internal pressure of a tire attached to a four-wheeled
vehicle and for accordingly generating alarm, wherein a threshold
for judging decompression is set to be larger immediately after
switching an ignition key ON when compared to a threshold for the
vehicle in a normal running condition, decompression is judged in a
decompression judging time which is shorter than a time for the
vehicle in a normal running condition, and the threshold for
judging decompression and the decompression judging time are
returned to those for the normal running condition of the vehicle
in case no decompression is judged.
[0011] In accordance with the present invention, there is also
provided an apparatus for alarming decrease in tire air-pressure
for alarming decrease in tire air-pressure for judging a decrease
in internal pressure of a tire attached to a four-wheeled vehicle
and for accordingly generating alarm, comprising a velocity
detecting means for detecting a velocity signal of respective
tires, a judging means for performing calculating processes of a
decompression judgement value for comparing a difference of two
diagonal sums of rotational information of front wheel tires and
rotational information of rear wheel tires based on rotational
information obtained from the velocity signals detected by the
velocity detecting means, an initial judging means for setting a
threshold for judging decompression to be larger immediately after
switching an ignition key ON when compared to a threshold for the
vehicle in a normal running condition and judging decompression in
a decompression judging time which is shorter than a time for the
vehicle in a normal running condition, and a returning means for
returning the threshold for judging decompression and the
decompression judging time to those for the normal running
condition of the vehicle in case no decompression is judged.
[0012] In accordance with the present invention, there is further
provided a method for alarming decrease in tire air-pressure for
judging a decrease in internal pressure of a tire attached to a
four-wheeled vehicle and for accordingly generating alarm,
comprising the steps of setting a threshold for judging
decompression to be larger immediately after switching an ignition
key ON when compared to a threshold for the vehicle in a normal
running condition and judging decompression in a decompression
judging time which is shorter than a time for the vehicle in a
normal running condition; judging whether the vehicle is running on
a bad road while a decompressed condition is judged during the
short decompression judging time; and increasing a number of data
used for judging decompression than compared to a number of data
which might be incorporated during the short decompression judging
time in case it is judged that the vehicle is running on a bad
road.
[0013] In accordance with the present invention, there is yet
further provided an apparatus for alarming decrease in tire
air-pressure for alarming decrease in tire air-pressure for judging
a decrease in internal pressure of a tire attached to a
four-wheeled vehicle and for accordingly generating alarm,
comprising a velocity detecting means for detecting a velocity
signal of respective tires, a judging means for performing
calculating processes of a decompression judging value for
comparing a difference of two diagonal sums of rotational
information of front wheel tires and rotational information of rear
wheel tires based on rotational information obtained from the
velocity signals detected by the velocity detecting means, an
initial judging means for setting a threshold for judging
decompression to be larger immediately after switching an ignition
key ON when compared to a threshold for the vehicle in a normal
running condition and judging decompression in a decompression
judging time which is shorter than a time for the vehicle in a
normal running condition, a bad road judging means for judging
whether the vehicle is running on a bad road while a decompressed
condition is judged during the short decompression judging time,
and a data updating means for increasing a number of data used for
judging decompression than compared to a number of data which might
be incorporated during the short decompression judging time in case
it is judged that the vehicle is running on a bad road.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a block diagram illustrating an embodiment of an
apparatus for alarming decrease in tire air-pressure according to
the present invention;
[0015] FIG. 2 is a block diagram illustrating electric arrangements
of the apparatus for alarming decrease in tire air-pressure of FIG.
1;
[0016] FIG. 3 is a flowchart related to one method of the present
invention;
[0017] FIG. 4 is a flowchart related to another method of the
present invention; and
[0018] FIG. 5 is a view illustrating one example of decrease in
air-pressure of a tire.
DETAILED DESCRIPTION
[0019] A method for alarming decrease in tire air-pressure and an
apparatus used therefor according to the present invention will now
be explained based on the accompanying drawings.
[0020] As shown in FIG. 1, the apparatus for alarming decrease in
air-pressure according to an embodiment of the present invention is
for detecting whether an air-pressure of any of four wheels
W.sub.1, W.sub.2, W.sub.3 and W.sub.4 attached to a four-wheeled
vehicle has decreased or not, and comprises wheel velocity sensors
1, which are normal velocity detecting means, that are respectively
arranged in connection with each of the tires W.sub.1, W.sub.2,
W.sub.3 and W.sub.4. Outputs of the wheel velocity sensors 1 are
supplied to a control unit 2. To the control unit 2, there are
connected a display means 3 composed of liquid crystal display
devices, plasma display devices, or CRT for informing a tire
W.sub.i of which air-pressure has decreased, and an initializing
switch 4 which might be operated by the driver.
[0021] The control unit 2 comprises an I/O interface 2a required
for sending/receiving signals to/from an external device, a CPU 2b
which functions as a center of calculation, a ROM 2c which stores a
control operation program for the CPU 2b, and a RAM 2d into which
data are temporally written and are read out therefrom when the CPU
2b performs control operations. The judging means, initial judging
means and the returning means in the present embodiment are
included in the control unit 2.
[0022] Each vehicle velocity sensor 1 outputs a pulse signal
corresponding to the number of revolution of the tire W.sub.i
(hereinafter referred to as "wheel velocity pulse"). The CPU 2b
calculates a rotational angular velocity F.sub.i for each tire
W.sub.i at a specified sampling period .DELTA.T (sec), for
instance, each .DELTA.T=1 second, based on the wheel velocity pulse
output from the wheel velocity sensor 1.
[0023] Since tires W.sub.i are manufactured to include variations
(initial differences) within specifications, it is not always the
case that effective rolling radii of respective tires W.sub.i
(values obtained by dividing a distance which has been traveled
through a single rotation with 2 .pi.) are identical even though
all of the tires W.sub.i are at normal internal pressure. Thus, the
rotational angular velocity F.sub.i for each tire W.sub.i will be
varied. In order to cancel such variations owing to initial
differences, a corrected rotational angular velocity F1.sub.i is
calculated. More particularly, the following corrections are
made:
[0024] F1.sub.1=F.sub.1
[0025] F1.sub.2=mF.sub.2
[0026] F1.sub.3=F.sub.3
[0027] F1.sub.4=nF.sub.4
[0028] The correction coefficients m, n are obtained by calculating
a rotational angular velocity F.sub.i under a condition, for
instance, that the vehicle is performing straight-ahead running and
obtained as m=F.sub.1/F.sub.2 and n=F.sub.3/F.sub.4 based on the
calculated rotational angular velocity F.sub.i.
[0029] Based on the above F1.sub.1, velocity V of the vehicle
(V.sub.i/4) or lateral directional acceleration (lateral G) is
obtained.
[0030] A decompression judgement value (DEL) for detecting decrease
in air-pressure of tire W.sub.i is for comparing a difference
between two diagonal sums of, for instance, the front wheel tires
and rear wheel tires, and is obtained from the following equation
(1) which is a ratio of a value obtained by subtracting a sum of
signals of one pair of diagonally located wheels from a sum of
signals of the other pair of diagonally located wheels to an
average value of the two sums: 1 DEL = 2 .times. { ( V 1 + V 4 ) -
( V 2 + V 3 ) } V 1 + V 2 + V 3 + V 4 .times. 100 ( % ) ( 1 )
[0031] In case a running test is performed using a vehicle to which
one tire is attached with its internal pressure (air-pressure)
being decreased by 30% from the normal internal pressure in a
normal running condition for the vehicle, the calculated
decompression judgement value is approximately 0.18%.
[0032] A calculated decompression judgement value with a lower
limit being a partial decompression of the tire (8.3%) based on
this test result is approximately 0.05% while a calculated
decompression judgement value with an upper limit being a complete
decompression of the tire (100%) is approximately 0.6%.
[0033] Thus, it was conventionally the case that decompression was
indicated upon detecting decompression for 60 seconds and in case
the decompression judgement value was larger than 0.05% and smaller
than 0.6%.
[0034] However, the present embodiment is so arranged that a
threshold for judging decompression is set to be larger immediately
after an ignition key is turned ON than compared to a threshold for
a normal running condition of the vehicle, e.g. to a value
corresponding to 50% decompression and a length of time for data on
rotational information which are used for judgement is set to be
shorter than a time for a normal running condition of the vehicle,
e.g. to 5 seconds so as to enable early detection of decompression
also when the internal pressure (air-pressure) of the tire has
largely decompressed from the normal internal pressure.
[0035] In case no decompression is judged during this process, the
threshold for judging decompression is set to be a normal
threshold, e.g. value corresponding to 30% decompression, and the
length of time for data used for the judgement is set to be a
normal length, e.g. 60 seconds.
[0036] The present invention will now be explained based on
embodiments while the present invention is not limited to these
embodiments alone.
EMBODIMENT 1
[0037] A Mercedes Benz of A Class type (tire size: 195/50R15) was
used as a vehicle for running, wherein tests were performed with an
air-pressure for a right rear tire being set to 0.5 bar and
air-pressures for the remaining left rear tire and right and left
front tires being set to normal air-pressure of 2.2 bar (Test 1)
and wherein the air-pressure for the right rear tire was changed to
1.0 bar (Test 2). A sampling time for revolution velocities of the
wheels was set to be 1 second.
[0038] Based on data for 60 seconds (60 data) similarly to a
conventional method for detection (Steps S1, S2 and S3), judgement
was performed (Steps S5, S8) with the threshold for judging
decompression being set to the normal threshold (value
corresponding to 30% decompression) (Step S4) with respect to Test
1 and Test 2 as illustrated in FIG. 3. The time required for
performing detection of decompression by using this method for
detection was 74 seconds for Test 1 and 76 seconds for Test 2.
[0039] Thereafter, judgement was performed (Steps S5, S8) with the
threshold for judging decompression being set to the normal
threshold (value corresponding to 50% decompression) (Step S7)
based on data for 5 seconds (5 data) (Step S6) in accordance with
the method for detection of the present invention with respect to
Test 1 and Test 2. The time required for performing detection of
decompression by using the method for detection according to the
present invention was 31 seconds for Test 1 and 28 seconds for Test
2.
[0040] It is obvious from these test results that the time required
for performing detection of decompression could be remarkably
reduced when employing the method for detection according to the
present invention.
[0041] In the present embodiment, it is possible to detect
decompression by using a decompression judging method which usually
takes several tens of seconds to approximately 60 seconds in case
judgement is made immediately after the ignition key is turned ON
and no large decompression is present. However, a method in which
judgement is performed in a short time by using the large threshold
is apt to cause possibilities of variations in judged values owing
to disturbance factors such as slip, acceleration/deceleration or
cornering since the length of time for data used for the judgement
is 5 seconds and thus short. Thus, by limiting such an opportunity
of judgement to be performed only immediately after turning the
ignition ON, it is possible to prevent an alarm (erroneous alarm)
from being generated though the tire is in a normal internal
pressure condition.
[0042] Another embodiment of the present invention will now be
explained. In the above embodiment, the threshold for judging
decompression is set to be larger immediately after the ignition
key is turned ON than compared to a threshold of a normal running
condition for the vehicle, for instance, to be a value
corresponding to 50% decompression, and the length of time for data
on rotational information which are used for judgement is set to be
shorter than a time for a normal running condition of the vehicle,
e.g. to 5 seconds so as to enable early detection of decompression
also when the internal pressure (air-pressure) of the tire has
largely decompressed from the normal internal pressure. In case the
sampling time for the revolution velocities of the wheels is set to
be 1 second, the number of data used for judging decompression will
be 5.
[0043] In case no decompression is judged during this process, the
threshold for judging decompression is set to be a normal
threshold, e.g. value corresponding to 30% decompression, and the
length of time for data used for the judgement is set to be a
normal length, e.g. 60 seconds. The number of data used for judging
decompression will at this time be 30.
[0044] In this manner, it is possible to perform judgement of
decompression by fixing the number of effective data N which are
employed for judging decompression immediately after the ignition
key is turned ON to 5. However, since all data are incorporated
without rejecting data obtained when running on a bad road which
might cause erroneous alarming of decompression, there might be
happened a decompressed condition is erroneously judged even though
the tire is in a normal internal pressure condition with data as
few as 5.
[0045] Thus, the present embodiment is so arranged that a value
increased by 1 to the initial value, for instance, 5 data, is set
to be N each time it is judeged that the vehicle is running on a
bad road. With this arrangement, the number of effective data is
increased for judging decompression depending on degrees of running
on a bad road. The judging means, initializing judging means, bad
road judging means and data updating means of the present
embodiment are incorporated in the control unit 2.
[0046] A "bad road" indicates a split .mu. road, a gravel road or
the like. It should be noted that a split .mu. road is a road
surface with different friction coefficients .mu. for road surfaces
of right and left tires, wherein, for instance, a right-hand side
is an asphalt road surface while a left-hand side is a grass road
surface. A method for judging that the vehicle is running on a bad
road might be a method for judging a bad road in case an amount of
change in differences in respective slip rates of the vehicle on
the right and left that can be obtained from the wheel speeds. A
degree for running on a bad road indicates a number of judging a
bad road condition upon performing judgement of a bad road
condition every second.
[0047] It should be noted that in increasing the amount of
effective data for judging decompression, in case the number
increases excessively, it will become impossible to judge
decompression immediately after the ignition is turned ON so that
measures are taken, for example, to set an upper limit to 10.
EMBODIMENT 2 and COMPARATIVE EXAMPLE 1
[0048] A Volkswagen Golf of 1,600 cc (tire size: 175/80R14 88H) was
employed as a vehicle for running on a road partially including bad
roads with tires of normal air-pressure. At this time, the bad road
was a split .mu. road (road surfaces of asphalt and grass) and the
sampling time for the revolution velocity of the wheels was set to
1 second.
[0049] Judgement of decompression was conducted by employing a
normal method for judgement in which judgement is performed based
on data of 60 seconds (60 data) as illustrated in FIG. 4 (Steps S11
to S17) and a method for judgement for judging a condition where
the vehicle is running on a bad road (Steps S11 to S13, S18 to S23
and S16 to S17) (Comparative Example 1 and Embodiment 2).
[0050] More particularly, the number of effective data N was set to
5 (Step S11) whereupon judgement was performed (Steps S16, S17)
based on data of 60 seconds (60 data) (Step S12, S13, S14) with the
threshold for judging decompression being set to be the normal
threshold (value corresponding to 30% decompression)(Step S15).
[0051] Thereafter, in another method for judgement of the present
invention, in case it is detected that the vehicle is running on a
bad road (Step S18) while a decompressed condition is being judged
based on data of 5 seconds (5 data) (Steps S11 to S13), a value for
the number of data used for judging decompression increased from N
by 1 (N+1) is set to be N (Step S19) and it is then judged whether
this number N has reached 10 or not (Step S20). If it is judged
that the number of effective data has reached 10, an average of
these data N=10 is set to be a judgement value (Steps S21, S22) and
the threshold is set to be a value corresponding to 50%
decompression (Step S23). Thereafter, decompression was judged
using the judgement value and the value corresponding to 50%
decompression (Steps S16, S17).
[0052] In Comparative Example 1, judgement of decompression of a
tire could not be detected early and erroneous alarms were
generated owing to a condition running on a bad road. In Embodiment
2, it was possible to judge decompression of a tire early, and
since data which have been erroneously incorporated when running on
a bad road were averaged by a number of 10, which is more than 5,
no erroneous alarms were generated.
[0053] According to the present embodiment, in case it is judged
that no large decompression has occurred immediately after turning
the ignition key ON, it is possible to detect decompression through
normal judgement of decompression requiring several tens of seconds
to approximately 60 seconds. However, the method in which judgement
is performed in a short time using the large threshold is apt to
cause possibilities of variations in judgement values owing to
disturbance factors such as slip, acceleration/deceleration or
cornering since the length of time for data used for the judgement
is 5 seconds and thus short. Thus, by limiting such an opportunity
of judgement to be performed only immediately after turning the
ignition ON, it is possible to prevent an alarm (erroneous alarm)
from being generated though the tire is in a normal internal
pressure condition.
[0054] As explained so far, the present invention is capable of
detecting a condition in which a large decompressed condition
exists at an early stage before starting running so that it is
possible to improve the accuracy of detecting decompression.
[0055] It is further possible to judge decompression of a tire
early and to further prevent erroneous judgement during a condition
in which the vehicle is running on a bad road.
* * * * *