Measuring and testing – Tire – tread or roadway
Reexamination Certificate
2001-10-15
2003-11-04
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Tire, tread or roadway
Reexamination Certificate
active
06640623
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to a road surface state estimating device and, more particularly, to a road surface state estimating device (a device for estimating the state of a road surface) that estimates a physical quantity representing a road surface state such as a braking force gradient and a driving force gradient in a low slip region including a steady traveling (running) region.
2. Description of the Related Art
Japanese Patent Application Laid-Open (JP-A) No. 2000-118375 discloses an ABS device for estimating a braking torque gradient (obtained by a braking force gradient being multiplied with a square of a wheel effective radius) from a wheel speed signal, and maximizing braking force by controlling the estimated braking torque gradient to coincide with a target value near zero. In this device, the braking torque gradient is estimated on the basis of a wheel deceleration motion model represented by the following Equation (1), whereby the braking torque gradient, therefore, the braking force gradient can be accurately estimated in a limit braking region where a wheel deceleration motion is dominant.
ν
¨
w
=
-
kR
c
2
J
ν
.
w
+
w
(
1
)
where &ngr;
w
represents a wheel speed (m/s); w represents a road surface disturbance; k represents a braking force gradient (Ns/m); R
C
represents an effective radius of the tire (m); and J represents moment of inertia of a vehicle.
However, in a low slip region where the braking force gradient is relatively large, the wheel deceleration motion is affected by a suspension longitudinal resonance, which is a resonance generated at near 15 Hz, and a tire rotation resonance, which is a resonance generated at near 40 Hz. Therefore, there is a problem in that it is not possible to accurately estimate the braking force gradient in the low slip region by the technique in which the braking torque gradient is estimated on the basis of the Equation (1).
Japanese Patent Application Laid-Open (JP-A) No. 11-78843 discloses a wheel state estimating device, wherein a braking force gradient is estimated on the basis of a tire rotation vibration model. By noting that resonance characteristics of the tire rotation vibration become sharper as the braking force gradient becomes larger, a damping coefficient of the tire rotation vibration is identified to estimate the braking force gradient.
However, in a case of braking in which the braking force gradient becomes small, because wheel deceleration motion becomes dominant, tire rotation vibration is not generated. Therefore, in the prior art described above, there is a problem in that the braking force gradient cannot be estimated in a case of braking in which tire rotation vibration is not generated.
SUMMARY OF THE PRESENT INVENTION
The present invention has been conceived to solve the above problem. It is an object of the present invention to provide a road surface state estimating device which estimates a physical quantity representing a road surface state such as a braking force gradient, a driving force gradient and a road surface &mgr; gradient in a low slip region including a steady travelling (running) region.
Principles of the present invention will now be described. As shown in
FIG. 1
, a wheel resonance system can be represented by a dynamic model in which torsional spring elements
14
and
16
of a tire, having respective spring constants K
1
and K
2
, are interposed between a rim
10
and a belt
12
and in which a suspension element, in which a spring element
18
having a spring constant K
3
is connected in parallel with a damper
20
, is interposed between the rim
10
and a vehicle body. In this model, a disturbance from the road surface (road surface disturbance) is transmitted from the belt
12
through the spring elements
14
and
16
to the rim
10
, to affect a wheel speed &ohgr;, and is transmitted to the vehicle body through the suspension element.
Description will now be given of relation between the braking force gradient and a wheel speed frequency characteristic quantity representing following frequency of transmission characteristics from a road surface disturbance to the wheel speed, using a fifth order full wheel model, in which a first order wheel decelerating motion, second order longitudinal direction suspension resonance, and second order tire rotation resonance are integrated. The braking force gradient is represented, as shown in
FIG. 2
, by a gradient of a tangent of a curve representing a relationship between a braking force and a slip speed (or slip rate).
FIG. 3
is a gain diagram showing frequency responses from a road surface disturbance to the wheel speed for ranges from a limit braking range to a low slip range where there is some margin for tire characteristics (i.e., for ranges from a range at which the braking force gradient is 300 Ns/m to a range at which the braking force gradient is 10000 Ns/m). That is, the diagram shows the relationship between frequency and gain of amplitude of the wheel speed with respect to amplitude of the road surface disturbance.
The wheel speed frequency characteristics in
FIG. 3
indicate that, for the range where the braking force gradient is relatively small, such as near the limit of friction force between a tire and a road, the gain is large in a low frequency range and is small in a high frequency range. Namely, for the range where the braking force gradient is relatively small, the wheel speed frequency characteristic quantity, which represents a difference between the gain in the low frequency range and the gain in the high frequency range, is large.
In contrast, the gain in the low frequency range for the range where the braking force gradient is relatively large, such as a steady traveling region, is much smaller compared to that for the range where the braking force gradient is relatively small, in the wheel speed frequency characteristics. Further, in the high frequency range, the gain for the range where the braking force gradient is relatively large is not much smaller than the gain for the range where the braking force gradient is relatively small due to the influence of rotational resonance of the tire (near 40 Hz) being generated. Therefore, for the range where the braking force gradient is relatively large, the wheel speed frequency characteristic quantity is small. Also, a wheel speed frequency characteristic quantity, which represents a difference between a vibration level of a wheel speed signal in the low frequency range and a vibration level of a wheel speed signal in the high frequency range, changes similarly to the wheel speed frequency characteristic quantity which represents the difference between the low frequency range gain and the high frequency range gain.
It is apparent from the above that the wheel speed frequency characteristic quantity which represents the difference between the low frequency range gain and the high frequency range gain, or the wheel speed frequency characteristic quantity which represents the difference between the wheel speed signal vibration level in the low frequency range and the wheel speed signal vibration level in the high frequency range, decreases as the braking force gradient increases. Utilizing this characteristic, the braking force gradient can be estimated from the wheel speed frequency characteristic quantity.
Referring to the frequency band near 40 Hz in
FIG. 3
at which rotational resonance of the tire occurs, the greater the braking force gradient, the sharper the peak waveform of rotational resonance of the tire. Further, as the braking force gradient becomes greater, the overall frequency characteristics of the peak waveform move to a higher frequency range.
Namely, if the wheel characteristics is approximated to a first-order lag model, it can be understood that a break point frequency becomes higher as the braking force gradient becomes greater, as shown in FIG.
6
. It is therefore possible to estimate the braking force gradient from the wheel speed frequency characteristi
Ono Eiichi
Sawada Mamoru
Sugai Masaru
Tanaka Akira
Umeno Takaji
Dickens C.
Lefkowitz Edward
Toyota Jidosha & Kabushiki Kaisha
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