Tire air pressure detection device for detecting air...

Details Tire air pressure detection device for detecting air... Tire air pressure detection device for detecting air...

2002-10-04

2004-07-27

Pope, Daryl (Department: 2632)

Communications: electrical

Land vehicle alarms or indicators

Internal alarm or indicator responsive to a condition of the...

C340S442000, C340S443000, C340S671000, C340S672000, C073S146000, C073S146200

Reexamination Certificate

active

06768418

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a device for detecting tire air pressure based on a vehicle speed signal.
DESCRIPTION OF THE RELATED ART
JP-A-H7-125512 discloses a conventional tire air pressure detection device. The tire air pressure device can detect an accurate tire air pressure by removing the effect of tread-lift. Tread-lift is a phenomenon wherein a dynamic rolling radius of a tire in which tire air pressure has decreased becomes approximately the same as that of a tire in which tire air pressure has not decreased because the radius of tire increases due to a centrifugal force.
When the dynamic rolling radius of the tire increases due to the effect of tread-lift, a determination value for determining tire air pressure decrease is erroneously determined because the dynamic rolling radius of the tire in which tire air pressure has decreased becomes approximately the same as that of a tire of which tire air pressure has not decreased. That is, the determination value for determining tire air pressure decrease varies to close that of a determination value of the tire of which tire air pressure has not decreased. As a result, tire air pressure is not detected accurately.
Accordingly, in JP-A-H7-125512, an air pressure detection device checks a relationship between vehicle speed correlating with the centrifugal force and a determination value for determining the tire air pressure (e.g., a rotational status value), and stores the relationship in memory. Thus, the determination value is compensated for with respect to vehicle speed based on the stored relationship, and therefore tire air pressure is detected accurately.
However, a degree of the effect of the tread-lift also varies with respect to the tire air pressure. For example, a relationship between the tire air pressure and the effect of the tread-lift is shown in FIG.
22
. As tire air pressure decreases, the dynamic rolling radius due to the effect of tread-lift also increases. Incidentally, the dynamic rolling radius &Dgr;R is expressed in, for example, &Dgr;R=10
(−1.97−1.31)
×V
(0.735p−1.147)
, where tire air pressure is P(kfg/cm
2
) and a vehicle speed is V(km/h).
Therefore, although the effect of tread-lift is not generated when tire air pressures of four wheels are identical, it is generated when one of the tire air pressures of the four wheels significantly decreases. As a result, if the determination value is compensated for as mentioned above when the tire air pressures of four wheels are identical, non-uniformity of the determination value increases.
JP-A-H10-100624 also discloses a conventional tire air pressure detection device. The tire air pressure device detects a decrease in tire air pressure based on wheel speed variation D and a front and rear wheel speed ratio &bgr;. The wheel speed variation D and the front and rear wheel speed ratio &bgr; are expressed as follows, where V
FR
corresponds to front right wheel speed, V
FL
corresponds to front left wheel speed, V
RR
corresponds to rear right wheel speed and V
RL
corresponds to rear left wheel speed.
D
=
V
FR
V
FL
-
V
RR
V
RL
(
1
)
β
=
V
FR
+
V
FL
V
RR
+
V
RL
(
2
)
The wheel speed variation D represents a rotational status value calculated based on wheel speeds of four vehicle wheels. For example, the wheel speed variation D is a variable defined as a difference of wheel speed ratios of each pair of wheels located diagonally from each other, and increases or decreases when the tire air pressures of some of the vehicle wheels decrease. The front and rear wheel speed ratio &bgr; is a tire slip status value that denotes a degree of slip status of driven wheels caused by transmitted driving forces. For example, the smaller the front and rear wheel speed ratio &bgr; is, the higher the slip of one (or both) of the driven wheels is.
The wheel speed variation D increases or decreases when the tire air pressures of some of the vehicle wheels decreases below a standard value, and it is zero when each tire air pressure of each tire equals the standard value. Therefore, the tire pressure decrease is detected based on the wheel speed variation D.
However, regarding, for example, a rear wheel drive vehicle, when the tire air pressure of the rear right wheel corresponding to one of the driven wheels decreases below the standard value, the other driven wheel tends to slip easier than the rear right wheel because a ground contact area of the rear right wheel increases and resistance force for suppressing the slip increases even if the diameter of the rear right wheel decreases due to the tire air pressure decrease. Accordingly, the wheel speed variation D varies based on the degree of slip status of the wheels.
Thus, as shown in
FIG. 23
, a regression line is calculated based on a relationship of the front and rear wheel speed ratio &bgr; and the wheel speed variation D using a minimum square calculation methodology. An ideal value of the wheel speed variation D is then calculated by compensating for the wheel speed variation D (or an average D
AVE
). An ideal value of the wheel speed variation D is a value of the wheel speed variation D if the slip does not occur when the front and rear wheel speed ratio &bgr; is 1. Thus, the effect of the slip of the driven wheels is removed, and therefore the tire air pressure decrease can accurately be detected.
However, the wheel speed variation D varies based on the effect of the tread-lift as well as the slip of the driven wheels. Referring to
FIG. 24
, a calculation result of the wheel speed variation D is plotted using white circles (◯) separately from black circles (&Circlesolid;) that indicates a wheel speed variation D when the effect of the tread-lift is not generated. Therefore, the accuracy of the calculation of the wheel speed variation D decreases, and therefore the warning pressure varies.
Further, if vehicle speed is high during the tire air pressure is decreasing, an accurate wheel speed variation D may not be obtained and therefore the tire air pressure decrease cannot be detected accurately.
For example, in the above-mentioned related device (JP-A-H10-100624), the wheel speed variation D under an ideal driven status is calculated based on the regression line. A difference (±D′sh) between the wheel speed variation D under the ideal driven status and a predetermined reference value (D′
AVE
std) is defined as a determination value for determining the tire air pressure decrease. Then, the tire air pressure decrease is determined when the determination value exceeds a warning threshold. In this case, as shown in
FIG. 25
, the higher the vehicle speed is, the smaller the determination value is. That is, it is difficult to determine the tire air pressure decrease because the determination value is small. As a result, the tire air pressure decrease cannot be detected accurately.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a tire air pressure detection device that is capable of obviating the above problems.
It is another object of the present invention to provide the tire air pressure detection device that is capable of increasing the accuracy of the rotational status value even if an effect of tread-lift is generated.
It is another object of the present invention to provide the tire air pressure detection device that is capable of obviating warning pressure non-uniformity.
A tire air pressure detection device of the present invention includes a warning anticipation timing calculating portion for anticipating a warning timing at which the tire air pressure decrease detecting portion will detect the tire air pressure decrease based on the rotational status value compensated for by a rotational status value compensating portion. A tire air pressure decrease detecting portion detects a decrease in tire air pressure when a clocked determination time reaches the warning anticipation timing anticipated by the warning anticipation timing calculating portion.
Accordingly, the driver is warned of the

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