U.S. patent application number 09/885128 was filed with the patent office on 2002-01-31 for method for alarming decrease in tire air-pressure and apparatus used therefor.
Invention is credited to Sugisawa, Toshifumi.
Application Number | 20020011929 09/885128 |
Document ID | / |
Family ID | 26594357 |
Filed Date | 2002-01-31 |
United States Patent
Application |
20020011929 |
Kind Code |
A1 |
Sugisawa, Toshifumi |
January 31, 2002 |
Method for alarming decrease in tire air-pressure and apparatus
used therefor
Abstract
An apparatus for alarming decrease in tire air-pressure based on
rotational information obtained from tires, comprising a rotational
information detecting means for detecting rotational information of
each tire, a steering angle detecting means, a memory means for
storing the rotational information of each tire and the steering
angle, a turning radius calculating and processing means, a judged
value calculating and processing means, and a correction means for
correcting the turning radius. It is possible to obtain an accurate
turning radius also in case any tire of the following wheels is
decompressed by correcting the turning radius obtained on the basis
of rotational information by using the steering angle information,
thereby the DEL value might be obtained in a more accurate manner
than compared to conventional arrangements.
Inventors: |
Sugisawa, Toshifumi;
(Kobe-shi, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
26594357 |
Appl. No.: |
09/885128 |
Filed: |
June 21, 2001 |
Current U.S.
Class: |
340/444 ;
340/442 |
Current CPC
Class: |
B60C 23/061
20130101 |
Class at
Publication: |
340/444 ;
340/442 |
International
Class: |
B60C 023/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 21, 2000 |
JP |
2000-186129 |
Jun 30, 2000 |
JP |
2000-199106 |
Claims
What is claimed is:
1. An apparatus for alarming decrease in tire air-pressure based on
rotational information obtained from tires attached to a
four-wheeled vehicle, comprising: a rotational information
detecting means for detecting rotational information of each tire;
a steering angle detecting means for detecting a steering angle; a
memory means for storing the rotational information of each tire
and the steering angle; a turning radius calculating and processing
means for calculating a turning radius based on the rotational
information of each tire; a judged value calculating and processing
means for calculating a judged value based on the rotational
information of each tire; and a correction means for correcting the
turning radius in case it has been determined by the steering angle
detecting means that the vehicle is in a straight-ahead driving
condition though the driving condition of the vehicle is a turning
condition when being based on the turning radius obtained on the
basis of the rotational information.
2. An apparatus for alarming decrease in tire air-pressure based on
rotational information obtained from tires attached to a
four-wheeled vehicle, comprising: a rotational information
detecting means for detecting rotational information of each tire;
a steering angle detecting means for detecting a steering angle; a
memory means for storing the rotational information of each tire
and the steering angle; a turning radius calculating and processing
means for calculating a turning radius based on the rotational
information of each tire; a correction means for correcting the
turning radius in case it has been determined by the steering angle
detecting means that the vehicle is in a straight-ahead driving
condition though the driving condition of the vehicle is a turning
condition when being based on the turning radius obtained on the
basis of the rotational information; and a decompression
determining means for determining a decompressed condition of a
tire in case a correction coefficient for the turning radius as
obtained by the correction means is not less than a threshold.
3. The apparatus of claim 2, wherein the threshold is an integrated
value in a predetermined time.
4. A method for alarming decrease in tire air-pressure based on
rotational information obtained from tires attached to a
four-wheeled vehicle, comprising the steps of: detecting rotational
information of each tire; detecting a steering angle; storing the
rotational information of each tire and the steering angle;
calculating a reciprocal of a turning radius based on the
rotational information of each tire; calculating a judged value
based on the rotational information of each tire; and correcting,
when performing correction of the judged value for decompressed
condition due to cornering, the turning radius in case it has been
determined on the basis of the steering angle that the vehicle is
in a straight-ahead driving condition though the driving condition
of the vehicle is a turning condition when being based on the
turning radius obtained on the basis of the rotational
information.
5. A method for alarming decrease in tire air-pressure based on
rotational information obtained from tires attached to a
four-wheeled vehicle, comprising the steps of: detecting rotational
information of each tire; detecting a steering angle; storing the
rotational information of each tire and the steering angle;
calculating a turning radius based on the rotational information of
each tire; correcting the turning radius in case it has been
determined on the basis of the steering angle that the vehicle is
in a straight-ahead driving condition though the driving condition
of the vehicle is a turning condition when being based on the
turning radius obtained on the basis of the rotational information;
and determining a decompressed condition of a tire in case a
correction coefficient for the turning radius as obtained during
the correction process is not less than a threshold.
6. The method of claim 5, wherein the threshold is an integrated
value in a predetermined time.
7. An apparatus for alarming decrease in tire air-pressure based on
rotational information obtained from tires attached to a
four-wheeled vehicle, comprising: a rotational information
detecting means for detecting rotational information of each tire;
a memory means for storing the rotational information of each tire;
a calculating and processing means for calculating a judged value
based on the rotational information of each tire; and a judged
value correcting means for correcting the judged value based on a
lateral acceleration obtained through a lateral acceleration sensor
provided in the vehicle.
8. An apparatus for alarming decrease in tire air-pressure based on
rotational information obtained from tires attached to a
four-wheeled vehicle, comprising: a rotational information
detecting means for detecting rotational information of each tire;
a memory means for storing the rotational information of each tire;
a calculating and processing means for calculating a judged value
based on the rotational information of each tire; and a judged
value correcting means for correcting the judged value based on a
lateral acceleration obtained on a basis of values of a yaw rate
sensor provided in the vehicle.
9. A method for alarming decrease in tire air-pressure based on
rotational information obtained from tires attached to a
four-wheeled vehicle, comprising the steps of: detecting rotational
information of each tire; storing the rotational information of
each tire; calculating a judged value based on the rotational
information of each tire; and correcting the judged value based on
a lateral acceleration obtained through a lateral acceleration
sensor provided in the vehicle.
10. A method for alarming decrease in tire air-pressure based on
rotational information obtained from tires attached to a
four-wheeled vehicle, comprising the steps of: detecting rotational
information of each tire; storing the rotational information of
each tire; calculating a judged value based on the rotational
information of each tire; and correcting the judged value based on
a lateral acceleration obtained on a basis of values of a yaw rate
sensor provided in the vehicle.
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 with which it is
possible to accurately perform cornering correction and to improve
the accuracy of detecting a decompressed condition of a tire.
[0002] A conventional apparatus for detecting decrease in tire
air-pressure (DWS system) determines a decompressed condition of a
tire based on information of four ABS wheel speed sensors. In case
a vehicle performs cornering, the load will be shifted to the
outside owing to the effect of lateral acceleration. Since the
respective longitudinal load and slip ratio of the right and left
tires are different at that time, it is impossible to determine a
decompressed condition. In order to cope with problem, a
conventional DWS performs cornering correction by obtaining a
cornering radius (turning radius) based on a wheel speed ratio of
the inner and outer following wheels (which are the rear wheels in
the case of a FF vehicle and the front wheels in the case of a FR
vehicle) and calculating an amount of change in longitudinal load
and an amount of change in slip ratio accompanying the shift of
load on the basis of the obtained value.
[0003] However, while a difference in rotation of the right and
left following wheels will be caused as a result of a decompressed
condition of either following wheel, it cannot be immediately
determined whether this difference in rotation is due to a
decompressed tire or merely due to cornering. Since it is rarely
the case that cornering movements will last for longer than several
tens of seconds when driving on a public road, wheel ratios of
right and left following and driving wheels are obtained for
approximately one minute and a decompressed condition of the
following tire is determined in case a difference between these
values exceeds a specified value.
[0004] It will therefore take approximately one minute for
determining whether the difference in rotation is due to cornering
or the difference in rotation is due to a decompressed tire when
determining a decompressed condition of the tire. Though very rare,
it might happen that malfunctions in performing determination occur
in the case of certain values for the longitudinal load or slip
ratio, and erroneous alarm might be issued upon determining that
the difference in rotation is due to cornering though actually due
to a decompressed tire or vice versa, determining a decompressed
condition of the tire though the vehicle is actually performing
cornering.
[0005] The present invention has been made in view of these facts,
and it is an object of the present invention to provide a method
for alarming decrease in tire air-pressure and an apparatus used
therefor which is capable of accurately performing cornering
correction and to improve the accuracy of detecting a decompressed
condition.
SUMMARY OF THE INVENTION
[0006] In accordance with a first aspect of the present invention,
there is provided an apparatus for alarming decrease in tire
air-pressure based on rotational information obtained from tires
attached to a four-wheeled vehicle, comprising: a rotational
information detecting means for detecting rotational information of
each tire; a steering angle detecting means for detecting a
steering angle; a memory means for storing the rotational
information of each tire and the steering angle; a turning radius
calculating and processing means for calculating a turning radius
based on the rotational information of each tire; a judged value
calculating and processing means for calculating a judged value
based on the rotational information of each tire; and a correction
means for correcting the turning radius in case it has been
determined by the steering angle detecting means that the vehicle
is in a straight-ahead driving condition though the driving
condition of the vehicle is a turning condition when being based on
the turning radius obtained on the basis of the rotational
information.
[0007] In accordance with a second aspect of the present invention,
there is provided an apparatus for alarming decrease in tire
air-pressure based on rotational information obtained from tires
attached to a four-wheeled vehicle, comprising: a rotational
information detecting means for detecting rotational information of
each tire; a steering angle detecting means for detecting a
steering angle; a memory means for storing the rotational
information of each tire and the steering angle; a turning radius
calculating and processing means for calculating a turning radius
based on the rotational information of each tire; a correction
means for correcting the turning radius in case it has been
determined by the steering angle detecting means that the vehicle
is in a straight-ahead driving condition though the driving
condition of the vehicle is a turning condition when being based on
the turning radius obtained on the basis of the rotational
information; and a decompression determining means for determining
a decompressed condition of a tire in case a correction coefficient
for the turning radius as obtained by the correction means is not
less than a threshold.
[0008] In accordance with a third aspect of the present invention,
there is provided a method for alarming decrease in tire
air-pressure based on rotational information obtained from tires
attached to a four-wheeled vehicle, comprising the steps of;
detecting rotational information of each tire; detecting a steering
angle; storing the rotational information of each tire and the
steering angle; calculating a reciprocal of a turning radius based
on the rotational information of each tire; calculating a judged
value based on the rotational information of each tire; and
correcting, when performing correction of the judged value for
decompressed condition due to cornering, the turning radius in case
it has been determined on the basis of the steering angle that the
vehicle is in a straight-ahead driving condition though the driving
condition of the vehicle is a turning condition when being based on
the turning radius obtained on the basis of the rotational
information.
[0009] In accordance with a fourth aspect of the present invention,
there is provided a method for alarming decrease in tire
air-pressure based on rotational information obtained from tires
attached to a four-wheeled vehicle, comprising the steps of:
detecting rotational information of each tire; detecting a steering
angle; storing the rotational information of each tire and the
steering angle; calculating a turning radius based on the
rotational information of each tire; correcting the turning radius
in case it has been determined on the basis of the steering angle
that the vehicle is in a straight-ahead driving condition though
the driving condition of the vehicle is a turning condition when
being based on the turning radius obtained on the basis of the
rotational information; and determining a decompressed condition of
a tire in case a correction coefficient for the turning radius as
obtained during the correction process is not less than a
threshold.
[0010] In accordance with a fifth aspect of the present invention,
there is provided an apparatus for alarming decrease in tire
air-pressure based on rotational information obtained from tires
attached to a four-wheeled vehicle, comprising: a rotational
information detecting means for detecting rotational information of
each tire; a memory means for storing the rotational information of
each tire; a calculating and processing means for calculating a
judged value based on the rotational information of each tire; and
a judged value correcting means for correcting the judged value
based on a lateral acceleration obtained through a lateral
acceleration sensor provided in the vehicle.
[0011] In accordance with a sixth aspect of the present invention,
there is provided an apparatus for alarming decrease in tire
air-pressure based on rotational information obtained from tires
attached to a four-wheeled vehicle, comprising: a rotational
information detecting means for detecting rotational information of
each tire; a memory means for storing the rotational information of
each tire; a calculating and processing means for calculating a
judged value based on the rotational information of each tire; and
a judged value correcting means for correcting the judged value
based on a lateral acceleration obtained on a basis of values of a
yaw rate sensor provided in the vehicle.
[0012] In accordance with a seventh aspect of the present
invention, there is provided a method for alarming decrease in tire
air-pressure based on rotational information obtained from tires
attached to a four-wheeled vehicle, comprising the steps of:
detecting rotational information of each tire; storing the
rotational information of each tire; calculating a judged value
based on the rotational information of each tire; and correcting
the judged value based on a lateral acceleration obtained through a
lateral acceleration sensor provided in the vehicle.
[0013] In accordance with a eighth aspect of the present invention,
there is provided a method for alarming decrease in tire
air-pressure based on rotational information obtained from tires
attached to a four-wheeled vehicle, comprising the steps of:
detecting rotational information of each tire; storing the
rotational information of each tire; calculating a judged value
based on the rotational information of each tire; and correcting
the judged value based on a lateral acceleration obtained on a
basis of values of a yaw rate sensor provided in the vehicle.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a block diagram illustrating one 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 the present invention;
[0017] FIG. 4 is diagram illustrating correction of judged values
(DEL);
[0018] FIG. 5 is another flowchart related to the present
invention; and
[0019] FIG. 6 is a block diagram illustrating Embodiment 3 of the
apparatus for alarming decrease in tire air-pressure according to
the present invention.
DETAILED DESCRIPTION
Embodiment 1
[0020] 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.
[0021] As shown in FIG. 1, the apparatus for alarming decrease in
air-pressure according to Embodiment 1 of the present invention is
for detecting whether an air-pressure of any of four wheels FL, FR,
RL and RR (W.sub.i, i=1 to 4, 1: front left tire, 2: front right
tire, 3:rear left tire, and 4:rear right tire) attached to a
four-wheeled vehicle has decreased or not, and comprises ordinary
rotational information detecting means 1 respectively arranged in
connection with each of the tires W.sub.i and a steering angle
detecting means S for detecting a steering angle of the wheels.
[0022] The rotational information detecting means 1 might be a
wheel speed sensor for generating rotational pulse by using an
electromagnetic pickup or similar device to obtain wheel speeds
(rotational speeds) on the basis of the number of pulses, or an
angular velocity sensor including those in which electricity is
generated by utilizing rotation such as a dynamo to obtain the
wheel speed on the basis of the voltage thereof. The steering angle
detecting means S might be an ordinary steering angle sensor.
Outputs of the rotational information detecting means 1 and the
steering angle detecting means are supplied to a control unit 2
such as an ABS. To the control unit 2, there are connected a
display means 3 composed of liquid crystal display elements, plasma
display elements, or CRT for informing a tire W.sub.i of which
air-pressure has decreased, and an initialization switch 4 which
might be operated by the driver.
[0023] The control unit 2 comprises, as shown in FIG. 2, 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 turning radius calculating and processing means, judged value
calculating and processing means and turning radius correcting
means in the present Embodiment 1 are included in the control unit
2.
[0024] Each rotational information detecting means 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 1.
[0025] 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:
[0026] F1.sub.1=F.sub.1
[0027] F1.sub.2=mF.sub.2
[0028] F1.sub.3=F.sub.3
[0029] F1.sub.4=nF.sub.4
[0030] 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.
[0031] Based on the above F1.sub.i, speed V of the vehicle is
obtained using the following equation.
V=(V1+V2+V3+V4)/4
[0032] Here, V(i): wheel speed of the tire (m/sec)
[0033] i: 1=front left tire, 2=front right tire, 3=rear left tire,
and 4=rear right tire.
[0034] A decompression judged 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. { ( V1 + V4 ) - ( V2 + V3 ) } V1 + V2 +
V3 + V4 .times. 100 ( % ) ( 1 )
[0035] Since lateral G is generated towards the outside of the
corner in case the vehicle is performing cornering, a larger load
is applied on the outer tires while the load applied on the inner
tires will decrease. The amount of shift in load at this time is
proportional to the lateral G which has been generated through
cornering. The radius of rotation of the tires will also be changed
through the shift in load, and this amount of change is also
substantially proportional to the amount of shift in load.
[0036] The amount of change in the radius of rotation of the tires
might thus be given as a linear expression of the lateral G.
[0037] On the other hand, slip of the driving wheels will increase
in accordance with a decrease in load of the tires. Thus, slip of
the driving tires outside of the corner will decrease while the
slip inside thereof increases. The average slip amount of the right
and left tires owing to cornering being substantially identical and
the amount of shift in slip rate being further proportional to the
amount of shift in load, the amount of shift in slip rate might be
considered to be substantially proportional to the average slip
amount.
[0038] Thus, variable components of the DEL values owing to lateral
G might be given by the following equation (2) based on the linear
expression for the lateral G and the linear expression for the
average slip rate.
Variable component of DEL=lateral G.times.(constant
1+DFR.times.constant 2) (2)
[0039] Here, though the constant 1 is a primary coefficient of the
lateral G affected by the shift in load, it is expressed as a
difference in influence of rotating radius between the front and
rear by the shift in load since the amount of shift in load is not
identical for the front and rear shafts.
[0040] The corrected DEL (cornering correction) might thus be given
by the following equation (3).
Corrected DEL=DEL-lateral G.times.(constant 1+DFR.times.constant 2)
(3)
[0041] It should be noted that DFR denotes a slip rate of the
driving wheels that is obtained by
(V1+V2) /(V3+V4)-1
[0042] in the case of FF (front engine/front drive) and FF based
4WD vehicles and by
(V3+V4)/(V1+V2)-1
[0043] in the case of FR (front engine/rear drive) vehicles.
[0044] The lateral G (lateral acceleration G) might be given by
equation (4) based on the balance thereof with centrifugal force at
the time of turning the vehicle.
Lateral G=V.sup.2/R/9.8 (4)
[0045] The reciprocal (RECPR) of the turning radius R of the
vehicle in the above equation (4) can be obtained from the
following equation (5) in the case of a FF driving vehicle.
RECPR={(V3-V4)/(V3+V4).times.RT.sub.WD}/(1+4.times.V2.times.constant3/(2.t-
imes.9.8.times.RT.sub.WD)) (5)
[0046] Here, RT.sub.WD denotes a tread width (m) of the rear
wheels.
[0047] The constant 1, constant 2 and constant 3 in the above
equation (3) and equation (5) can be obtained through calculation
in the control unit based on the lateral G, DEL and DFR,
respectively which are obtained on the basis of wheel speed
obtained by the speed sensor of the vehicle while the vehicle is
running on a corner with the tires being at normal internal
pressure. Since variations will occur in the constants 1 to 3
depending on the values of the lateral G and the DFR, it is
preferable to utilize mean values of the respective variations.
[0048] The reason why the RECPR is calculated on the basis of the
rear wheels is that the following wheels are less affected by the
driving. The effects of cornering can be decreased to a remarkable
extent by using equation (5). However, it is a premise of equation
(5) that the rear wheels are at normal internal pressure. Thus, in
case the rear wheels should be decompressed, the calculated turning
radius might be wrong so as to cause malfunctions. In another case
in which two wheels on either the right or left side are
decompressed, no determination can be made using the DEL of
equation (1). This is because the value of DEL of equation (1) will
not change in case the two wheels on, for instance, the left side
are decompressed since the wheel speed V1 and the wheel speed V3
will increase by substantially the same degree.
[0049] The present invention is thus arranged that information
obtained by the steering angle detecting means are considered and
if it is judged on the basis of these information that the vehicle
is in a straight-ahead running condition, the value for the RECPR
is considered to be an error as long as the value of the RECPR
obtained by equation (5) is not 0, and the RECPR is corrected
accordingly. That is, a wheel speed for the wheels is first
detected by the rotational information detecting means and
corrected thereafter as illustrated in FIG. 3 (Steps S1 and S2).
Then, the RECPR is calculated by using equation (5) and stored
(Step S3). Information which are obtained from the steering angle
detecting means, e.g. steering angle information from the steering
angle detecting means are converted into digital information of 256
levels and it is accordingly determined whether these information
are in the range of 126 to 129 (that is, whether the vehicle is in
a straight-ahead running condition) (Step S4). If it can be
determined that the vehicle is in a straight-ahead running
condition and the RECPR is c (rear number)(Step S5), it is
determined that this value c is an error due to decompression of a
tire and correction is performed to satisfy corrected RECPR
=RECPR-c as illustrated in FIGS. 3 and 4 (Step SS).
[0050] Thereafter, lateral G is calculated by using equation (4)
which is an ordinary step (Step S10) and in case one of the
following six conditions is satisfied, a reject process is
performed so as not to use the same for calculating the DEL for
eliminating degradation in accuracy of the vehicle speed
information or eliminating erroneous alarm through disturbances
(Step S11).
[0051] (1) When the vehicle is running at a low speed of not more
than 15 km/h in which the accuracy of the sensor is degraded; (2)
When the vehicle is running at a turning radius R of not more than
30 m in which no cornering correction might be performed; (3) When
the vehicle is running at a lateral G of not less than 0.2 g in
which no cornering correction might be performed; (4) When the
vehicle is running at a vertical G of not less than 0.1 g which is
a rapidly accelerating or rapidly decelerating condition; (5) When
the vehicle is running on a bad road such as a gravel road or on a
snowy road; and (6) While the brake is actuated.
[0052] Thereafter, the value for the DEL is calculated based on
equation (1) and this value for the DEL is accordingly corrected
based on equation (3) by using the value for the lateral G and the
corrected RECPR (Steps S12 and 13). The value for the corrected DEL
is integrated and it is determined whether these values have been
accumulated for e.g. five times (Steps S14 and S15).
[0053] While it is possible to determine decompression of a tire
based on the corrected DEL according to the present invention,
variations in data are decreased in Embodiment 1 without decreasing
the number of data by performing moving average of data of DEL of
large variations which have been obtained during one sampling
period, and for further improving the accuracy of determination,
these DEL values are averaged per each sampling period, e.g. every
five seconds (Step S16). By further performing moving average of
the past twelve data of the average values obtained every five
seconds (Step S17), determination of decompression is performed by
using this value of moving average (Step S18).
Embodiment 2
[0054] Determination of a decompressed condition of a tire can also
be performed according to the present invention on the basis of the
value c in a step following the Step S5 as illustrated in FIG. 5.
That is, in case it is determined that the vehicle is in a
straight-ahead running condition from the steering angle detected
by the steering angle detecting means (Step S4), the result of
calculation RECPR=c is integrated (Steps S5 and S6). After
determining whether integration of c has been performed for e.g.
ten times within a specified period (Step S7), in case an absolute
value of the integrated value of c (amount of increase) upon
performing integration for ten times is not less than a threshold,
e.g. 0.02, it might be determined that a tire is in a decompressed
condition (Step S8). The integrated value for c is then initialized
(Step S9). It should be noted that while the threshold is set to be
the integrated value within a specified period in the present
Embodiment 2, it is also possible to set the threshold to be a
specified value, for instance, 0.002, without performing
integration.
[0055] In determining decompression of a tire, it is also possible
to calculate the RECPR not only from the following wheels but also
from the driving wheels. Such calculation might be made by using
the following equation (6), similar to the equation (5).
RECPR2={(VEL1-VEL2)/(VEL1+VEL2).times.FT.sub.WD}/(1+4.times.V.sup.2.times.-
constant 4/ (2.times.9.8.times.FT.sub.WD) (6)
[0056] Here, FT.sub.WD denotes a tread width (m) of the front tires
and the constant 4 might be obtained through running tests.
[0057] Correction is then performed to satisfy corrected
RECPR2=RECPR2-c2 similar to the above method, and in case an
absolute value of c2 (real number) is not less than a specified
threshold or in case an absolute value of an integrated value
(amount of increase) of c2 within a specified period is not less
than a specified threshold, it is determined that a tire is in a
decompressed condition.
[0058] The present invention will now be explained on the basis of
examples while it should be noted that the present is not limited
to these examples.
EXAMPLE 1
[0059] A domestic FF vehicle of 1,600 cc was employed to which
summer tires (size of tire: 185/65R14) were attached. The vehicle
was provided with a wheel speed sensor and a steering angle sensor
such that rotational information of the four wheels and steering
angle information could be stored in a personal computer. The
steering angle information from the steering angle sensor was
stored in the personal computer as digital information of 256
levels ranging from 0 (full steering to the left) to 255 (full
steering to the right) wherein average values per each second were
stored. In case of this vehicle, it was considered that the vehicle
was in a straight-ahead running condition when these values were in
the range of 126 to 129.
[0060] The tire air-pressure of the rear right wheel of the vehicle
was then decompressed by 50% and the vehicle was made to run a test
course of which turning radius R of a left curve was known to be
150 m and 110 m, respectively.
COMPARATIVE EXAMPLE 1
[0061] The vehicle was made to run the same test course as Example
1 with a conventional DWS system being mounted thereon. Only the
wheel speed of the four wheels was calculated by using the personal
computer without performing the steps in the range H in FIGS. 3 and
5.
[0062] It was found that an accurate RECPR could be calculated in
Example 1 by calculating the reciprocal of the turning radius RECPR
(1/400) based on the turning radius 400 m obtained from the
following wheels at the time of straight-ahead running, obtaining
the straight-ahead running condition from the steering angle
sensor, and correcting the RECPR (reciprocal of the turning radius)
accordingly.
[0063] Since the turning radius R obtained from the following
wheels at the time of straight-ahead running was 400 m (the RECPR
was 1/400=0.0025) and the calculated turning radius R was tighter
than the threshold turning radius R of 500 m (the RECPR being
1/500=0.002), a decompressed condition was determined and alarm was
issued accordingly.
[0064] In contrast thereto, an erroneous turning radius was
calculated in Comparative Example 1 although the vehicle performed
running in the same manner, and no alarm was issued.
EXAMPLE 2
[0065] Tires of the left front wheel and the left rear wheel of the
vehicle as used in the above Example 1 were respectively
decompressed by 50% and the vehicle was made to run within the
city. Processes similar to those of Example 1 were performed
thereafter.
COMPARATIVE EXAMPLE 2
[0066] The vehicle was made to run within the same city as in
Example 2 with a conventional DWS system being mounted thereon.
Only the wheel speed of the four wheels was calculated by using the
personal computer without performing the steps in the range H in
FIGS. 3 and 5.
[0067] An alarm was issued in Example 2 since both the corrected
coefficients c and c2 of the RECPR of the following wheels and the
RECPR2 of the driving wheels exceeded their thresholds.
[0068] In contrast thereto, no changes were seen in the judged
value (DEL value) in Comparative Example 2 so that no alarm was
issued.
EMBODIMENT 3
[0069] Embodiment 3 of the present invention will now be explained.
In Embodiment 3, the apparatus is provided with normal rotational
information detecting means each provided in relation with each
tire W.sub.i and with a lateral acceleration (lateral G) sensor SS
for detecting acceleration in lateral directions of the vehicle. A
positive value is defined in case this lateral G acts on the left
side with respect to a moving direction. The lateral G sensor SS
might be a piezoelectric or strain gauge type acceleration
converter. It should be noted that it is alternatively possible to
employ a yaw rate sensor instead of the lateral G sensor for
obtaining the lateral G on the basis of values obtained by this
sensor. In case a system for controlling spinning movements or
similar during running for the purpose of stabilizing the posture
of the vehicle is provided as it is the case with some of the
currently available vehicles, it is possible to use an acceleration
sensor or yaw rate sensor mounted on the vehicle. The calculating
processing means and judged value correcting means of the present
Embodiment 3 are included in the control unit 2.
[0070] According to the present Embodiment 3, the accuracy of the
DWS can be improved on the basis of lateral G obtained by the
lateral G sensor and it is thus possible to detect decompression of
a tire in a more rapid manner.
[0071] The constant 1 and constant 2 of the above equation (3) of
Embodiment 3 might be obtained by calculating the vehicle speed
obtained by the speed sensor of the vehicle, the lateral G obtained
by the lateral G sensor, the DEL and the DFR while making the
vehicle run on a curve with the tires being at normal internal
pressure.
[0072] That is, (1) the vehicle is made to run in a neutral range
(at which time DFR=0 is satisfied) and a constant 1 with which the
corrected DEL becomes zero, e.g. 0.179 is calculated on the basis
of the DEL and the lateral G at this time.
[0073] Then, (2) the vehicle is made to run at a constant speed in
the driving range, and a constant 2 with which the corrected DEL
becomes zero, e.g. 129.02 is calculated on the basis of the DEL,
lateral G and DFR.
[0074] It should be noted that since the constants 1 and 2 vary
depending on the values of the lateral G and DFR, it is preferable
to employ mean values of the respective variations.
[0075] The present invention will now be explained with reference
to an example while the present invention is not limited to this
example.
EXAMPLE 3
[0076] A domestic 3,000 cc FF vehicle was provided and mounted with
a lateral G sensor on a central portion of the vehicle body which
was connected to a personal computer. Values of the lateral G were
thus arranged to be stored on software within the personal
computer. In this manner, the wheel speed of the four wheels and
values of the lateral G sensor could directly be stored and
reflected in the equation (3) for performing cornering
correction.
[0077] The vehicle was made to run under the following five
conditions on a public mountain road, on a course made to perform
stationary turns and on a test course.
[0078] 1: normal internal pressure
[0079] 2: tire air-pressure of front left tire decompressed by
30%
[0080] 3: tire air-pressure of front right tire decompressed by
40%
[0081] 4: tire air-pressure of rear left tire decompressed by
30%
[0082] 5: tire air-pressure of rear right tire decompressed by
40%
COMPARATIVE EXAMPLE 3
[0083] Only the wheel speed of the four wheels was calculated by
using a conventional DWS system, and the lateral G was obtained by
using the following equation (4) calculated from the vehicle speed
of the following wheels.
Lateral G=V.sup.2/R/9.8 (4)
[0084] According to the results of the Example 3 and the
Comparative Example 3, all of the decompressed conditions could be
detected in the Example 3 while decompression could not be detected
for the front left tire decompressed by 30% when performing
stationary turning in Comparative Example 3.
[0085] As explained so far, since the present invention is so
arranged to obtain an accurate turning radius also in case any tire
of the following wheels is decompressed by correcting the turning
radius obtained on the basis of rotational information by using the
steering angle information, the DEL value might be obtained in a
more accurate manner than compared to conventional arrangements. It
is further possible to detect decompression and issue alarm also in
case both tires on either side of the right and left wheels are
simultaneously in a decompressed condition.
[0086] Moreover, using the threshold for the turning radius
obtained on the basis of rotational information, a decompressed
condition of a tire can be determined also in case any tire of the
following wheels or the driving wheels is decompressed.
[0087] By obtaining the lateral G which is required for cornering
correction not through the rotational information detecting means
but from a lateral G sensor or a yaw rate sensor, cornering
correction might be performed in an accurate manner without being
affected by a decompressed condition of a tire. It is accordingly
possible to improve the accuracy of detecting decompression of a
tire.
* * * * *