Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Indication or control of braking – acceleration – or deceleration
Reexamination Certificate
1998-06-29
2001-11-27
Nguyen, Tan (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Indication or control of braking, acceleration, or deceleration
C701S080000, C180S197000
Reexamination Certificate
active
06324461
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a road surface condition estimating apparatus for estimating the condition of a road surface on which a vehicle is running, and more specifically to a road surface condition estimating apparatus which is provided with a correlation among a plurality of wheel motion amounts expressing a road surface &mgr; characteristic for each road surface condition, and which estimates and outputs the road surface condition on the basis of the correlation.
The present invention also relates to a variation reduction processing apparatus and more specifically to a variation reduction processing apparatus which can be applied to a road surface condition estimating apparatus, an ABS (anti-lock braking system) apparatus, a driving force controlling apparatus, and the like, and to a road surface condition estimating apparatus to which the variation reduction processing apparatus is applied.
2. Description of the Related Art
Conventionally, an anti-lock brake control device has been proposed wherein, immediately prior to a vehicle's wheel shifting to a locked up state when the coefficient of friction &mgr; between the wheel and the road surface surpasses a peak value of &mgr;, (hereinafter referred to as “a peak &mgr;” or “a peak &mgr; value”) this device can prevent the vehicle's wheels from being locked up by reducing the braking torque acting on the wheel and by controlling the coefficient of friction &mgr; to follow this peak value.
Meanwhile, when a vehicle is running at a certain speed and the brakes are applied, then the vehicle's wheels slip on the road surface. It is known that the coefficient of friction &mgr; between the wheels and the road surface varies, as is shown in
FIG. 21
in relation to the slip ratio &lgr; expressed in formula (1) below.
&lgr;=(
V−V
w
)/
V
(1)
in which V is vehicle speed (conversion into an angular speed) and V
w
is a wheel speed, and accordingly (V−V
w
) corresponds to a slip speed &Dgr;v.
As shown in
FIG. 21
, in this &mgr;-&lgr; characteristic, the coefficient of friction &mgr; reaches the peak value at a certain slip speed (the area A
2
in FIG.
21
).
In Japanese Patent Application Laid-Open (JP-A) No. 1-249559, there has been proposed the following anti-lock brake controlling apparatus. The anti-lock brake controlling apparatus computes the slip ratio from the approximate vehicle speed and the detected wheel speed using the formula (1). The anti-lock brake controlling apparatus controls the braking force in such a manner that the computed slip ratio substantially coincides with a reference slip ratio (a slip ratio giving the peak &mgr;) which has been previously set at a fixed value. Accordingly, the coefficient of friction &mgr; is continually controlled at the peak &mgr; value.
However, the slip ratio at which the coefficient of friction &mgr; reaches the peak &mgr; value varies in accordance with the road surface condition (the type of road surface on which the vehicle is running and the condition thereof) . Accordingly, when performing follow-up control according to the fixed reference slip ratio as in the prior art described in the publication mentioned above, the stopping distance may become too long depending on the road surface, or else the brakes may be controlled so that the coefficient of friction &mgr; goes over the peak &mgr; value, whereby there is the concern that the wheels may lock.
In order to solve this drawback, it is necessary to estimate the road surface condition and change the reference slip ratio in accordance with the estimated road surface condition. However, in the conventional art, there is no technique for accurately estimating the road surface condition.
SUMMARY OF THE INVENTION
In view of the facts mentioned above, an object of the present invention is to provide a road surface condition estimating apparatus for accurately estimating a road surface condition.
In order to achieve the object mentioned above, in accordance with a first invention of the present invention, there is provided a road surface condition estimating apparatus provided with a correlation among a plurality of wheel motion amounts expressing the characteristic of a coefficient of friction &mgr; between a wheel and a road surface with respect to a slip speed for each road surface condition, comprising:
memory means for storing a gradient of the coefficient of friction &mgr; with respect to the slip speed or a physical amount relating to said gradient as one of the wheel motion amounts expressing said correlation; and
road surface condition estimating means for estimating and outputting a road surface condition on the basis of comparison between a converted value of the wheel motion amount for each road surface condition obtained by respectively converting at least one of detected values of the plurality of wheel motion amounts in accordance with said stored correlation and a detected value of the same amount as said wheel motion amount.
In this case, a characteristic of the coefficient of friction &mgr; between the wheel and the road surface with respect to the slip speed &Dgr;v corresponds to a &Dgr;v−&mgr; characteristic expressed in
FIG. 17
, for example, and includes all the other equivalent characteristics (hereinafter, referred to as “road surface &mgr; characteristic”). As the characteristic equivalent to the &Dgr;v−&mgr; characteristic, for example, there are a characteristic shown in FIG.
21
and expressed by a slip ratio in place of the slip speed, a characteristic expressed by a braking force relating to &mgr; (&mgr;W: W is a wheel load) and a braking torque (&mgr;Wr: r is an effective radius of the wheel) in place of the coefficient of friction &mgr;, and the like. The road surface &mgr; characteristic varies corresponding to the road surface condition as shown in FIG.
2
A.
Further, the wheel motion amount corresponds to a physical amount relating to the wheel motion, which is necessary for expressing the road surface &mgr; characteristic, for example, there are vehicle speed, a wheel speed, a wheel deceleration (or acceleration), a slip speed, a braking force, a braking torque, a braking pressure (a wheel cylinder pressure) and the like as well as the physical amounts expressing slipperiness of the wheel such as a gradient of the road surface &mgr; with respect to the slip ratio, a gradient of the braking torque with respect to the slip speed, and the like.
These wheel motion amounts are selected in such a manner as to necessarily and sufficiently express the road surface &mgr; characteristic respectively becoming a fixed relation for each road surface condition, and accordingly, the correlation between the wheel motion amounts directly or indirectly expresses the road surface &mgr; characteristic for each road surface condition.
For example, the road surface &mgr; characteristic in
FIG. 2A
can be at first expressed for each road surface condition by the correlation between the braking force P
c
as another wheel motion amount and the slip ratio &lgr;, as shown in FIG.
2
B. Then, the road surface &mgr; characteristic in
FIG. 2A
can be necessarily and sufficiently expressed by the braking force P
c
, the vehicle speed and the gradient G
d
of the road surface &mgr; as a three-dimensional characteristic for each road surface condition, as shown in
FIG. 2C
, considering the fact that the gradient G
d
of the road surface &mgr; with respect to the slip ratio &lgr;, as well as the &mgr; value, has a peculiar value for each road surface condition in
FIG. 2A
, and using the relation in FIG.
2
B.
In this case, since the slip ratio &lgr; can be expressed by the vehicle speed and the wheel speed, in the case of using the braking force as one of the wheel motion amounts, another wheel motion amount is required, so that in an embodiment shown in
FIG. 2C
, the vehicle speed is employed.
In
FIG. 2C
, the three-dimensional characteristic is expressed by the relation between the braking force and the
Asano Katsuhiro
Ono Eiichi
Sugai Masaru
Umeno Takaji
Yamaguchi Hiroyuki
Kabushiki Kaisha Toyota Chuo Kenkyusho
Nguyen Tan
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Tran Dalena
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