U.S. patent application number 09/973192 was filed with the patent office on 2002-05-02 for apparatus and method for controlling vehicle behavior.
Invention is credited to Matsuno, Koji.
Application Number | 20020052681 09/973192 |
Document ID | / |
Family ID | 18790880 |
Filed Date | 2002-05-02 |
United States Patent
Application |
20020052681 |
Kind Code |
A1 |
Matsuno, Koji |
May 2, 2002 |
Apparatus and method for controlling vehicle behavior
Abstract
A target yaw rate setting unit of a control characteristics
changing unit computes a first target yaw rate based on the radius
of curvature of a curve. A target yaw rate setting unit of a
braking force control unit computes a second target yaw rate based
on driving conditions. When a cornering decision unit decides a
turning intention, if the absolute value of the first target yaw
rate is larger than the absolute value of the second target yaw
rate, the second target yaw rate is corrected with the first target
yaw rate, and the corrected second target yaw rate is outputted to
a target yaw rate changing unit. A braking force control unit
controls the braking force with the second target yaw rate
corrected.
Inventors: |
Matsuno, Koji; (Tokyo,
JP) |
Correspondence
Address: |
MCGINN & GIBB, PLLC
8321 OLD COURTHOUSE ROAD
SUITE 200
VIENNA
VA
22182-3817
US
|
Family ID: |
18790880 |
Appl. No.: |
09/973192 |
Filed: |
October 10, 2001 |
Current U.S.
Class: |
701/70 ; 701/80;
701/83 |
Current CPC
Class: |
B60W 30/18145 20130101;
B60W 2552/20 20200201; B60W 2540/18 20130101; B60K 17/3462
20130101; B60W 2520/125 20130101; B60W 2720/14 20130101; B60W
2552/30 20200201; B60K 23/0808 20130101; B60T 8/1755 20130101; B60T
2210/24 20130101 |
Class at
Publication: |
701/70 ; 701/80;
701/83 |
International
Class: |
G06F 017/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 11, 2000 |
JP |
P.2000-311042 |
Claims
What is claimed is:
1. A vehicle behavior control apparatus comprising: a road shape
recognizing unit for recognizing the road shape ahead of a vehicle;
a first target yaw rate setting unit for setting a first target yaw
rate on the basis of said road shape; a second target yaw rate
setting unit for setting a second target yaw rate on the basis of
driving conditions of the vehicle; a target yaw rate correcting
unit for correcting said second target yaw rate on the basis of
said first target yaw rate; and a braking force setting unit for
applying a braking force to a selected wheel so that an actual yaw
rate converges into the second target yaw rate corrected by said
target yaw rate correcting unit.
2. The vehicle behavior control apparatus according to claim 1,
further comprising: a turning decision unit for deciding a turning
intention if a steering angle exceeds a presetted value, wherein
said target yaw rate correcting unit corrects said second target
yaw rate gradually toward said first target yaw rate if said
turning decision unit decides the turning intention.
3. A vehicle behavior control apparatus comprising: a road shape
recognizing unit for recognizing the road shape ahead of a vehicle;
a first target yaw rate setting unit for setting a first target yaw
rate on the basis of said road shape; a second target yaw rate
setting unit for setting a second target yaw rate on the basis of
the driving conditions of the vehicle; a target yaw rate correcting
unit for correcting said second target yaw rate on the basis of
said first target yaw rate; and a driving force distribution unit
for setting the driving force distribution to left and right wheels
so that an actual yaw rate converges into the second target yaw
rate corrected by said target yaw rate correcting unit.
4. The vehicle behavior control apparatus according to claim 3,
further comprising: a turning decision unit for deciding a turning
intention if a steering angle exceeds a presetted value, wherein
said target yaw rate correcting unit corrects said second target
yaw rate gradually toward said first target yaw rate if said
turning decision unit decides the turning intention.
5. The vehicle behavior control apparatus according to claim 1,
further comprising: a target lateral acceleration setting unit for
setting a target lateral acceleration on the basis of either the
second target yaw rate corrected by said target yaw rate correcting
unit or the actual yaw rate; and a deceleration control unit for
making a deceleration control if an actual lateral acceleration is
below said target lateral acceleration.
6. The vehicle behavior control apparatus according to claim 3,
further comprising: a target lateral acceleration setting unit for
setting a target lateral acceleration on the basis of either the
second target yaw rate corrected by said target yaw rate correcting
unit or the actual yaw rate; and a deceleration control unit for
making a deceleration control if an actual lateral acceleration is
below said target lateral acceleration.
7. A vehicle behavior control method comprising: recognizing the
road shape ahead of a vehicle; setting a first target yaw rate on
the basis of said road shape; setting a second target yaw rate on
the basis of the driving conditions of the vehicle; correcting said
second target yaw rate on the basis of said first target yaw rate;
and applying a braking force to a selected wheel so that an actual
yaw rate converges into the corrected second target yaw rate.
8. The vehicle behavior control method according to claim 7,
further comprising: deciding a turning intention if a steering
angle exceeds a presetted value, wherein said second target yaw
rate is corrected gradually toward said first target yaw rate if
the turning intention is decided.
9. A vehicle behavior control method comprising: recognizing the
road shape ahead of a vehicle; setting a first target yaw rate on
the basis of said road shape; setting a second target yaw rate on
the basis of the driving conditions of the vehicle; correcting said
second target yaw rate on the basis of said first target yaw rate;
and setting the driving force distribution to left and right wheels
so that an actual yaw rate converges into the corrected second
target yaw rate.
10. The vehicle behavior control method according to claim 9,
further comprising: deciding a turning intention if a steering
angle exceeds a presetted value, wherein said second target yaw
rate is corrected gradually toward said first target yaw rate if
the turning intention is decided.
11. The vehicle behavior control method according to claim 7,
further comprising: setting a target lateral acceleration on the
basis of either the corrected second target yaw rate or the actual
yaw rate; and making a deceleration control if an actual lateral
acceleration is below said target lateral acceleration.
12. The vehicle behavior control method according to claim 9,
further comprising: setting a target lateral acceleration on the
basis of either the corrected second target yaw rate or the actual
yaw rate; and making a deceleration control if an actual lateral
acceleration is below said target lateral acceleration.
Description
BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention relates to a vehicle behavior control
apparatus and a method thereof for applying a braking force to a
predetermined brake wheel on the basis of a set target yaw rate or
for establishing a yaw moment in a vehicle by making a driving
force distribution variable between left and right wheels.
[0002] In recent years, there have been developed/practiced a
variety of vehicle behavior control apparatus for improving a
vehicle behavior and the running performance of a vehicle. In
Japanese Patent Unexamined Publication No. Hei. 2-70561, for
example, there is disclosed a braking force control apparatus which
keeps a stability of the vehicle by comparing an actual yaw rate
and a target yaw rate to control the braking force on the vehicle
in accordance with the comparison result. In Japanese Patent
Unexamined Publication No. Hei. 5-58180, there is disclosed a
left/right driving force distribution control apparatus in which
the target yaw rate is computed on the basis of the vehicle motion
(running) state, and a control signal for distributing the left and
right torques is outputted to a driving force transmission line
while making a feedback to bring the actual yaw rate close to the
target yaw rate, thereby the driving force distribution of an
engine to the right and left side driving force transmission lines
is adjusted so that the vehicle may be turned while moving
according to the target yaw rate.
[0003] As the road surface friction coefficient .mu. drops or as a
vehicle speed rises, however, response of the vehicle drops,
thereby a driver frequently fails to respond sufficiently although
required earlier control. In the prior art, this failure (retard)
in the response may not be sufficed only if the vehicle faithfully
(promptly) corresponds to a steering operation by the driver.
Specifically, the yaw rate feedback to the target yaw rate in the
prior art, which is determined by the vehicle moving state, such as
the steering operation of the driver or the vehicle speed, may
frequently fail to respond sufficiently to actual road
conditions.
SUMMARY OF THE INVENTION
[0004] It is an object to provide a vehicle behavior control
apparatus and a vehicle behavior control method capable of
preventing deviations from lanes or roads due to an improper
operation of a driver without any unnatural feeling, while
reflecting intentions of a driver to the maximum.
[0005] The above-mentioned object can be achieved by the vehicle
behavior control apparatus, according to a first aspect of the
invention, comprising:
[0006] a road shape recognizing unit for recognizing the road shape
ahead of a vehicle;
[0007] a first target yaw rate setting unit for setting a first
target yaw rate on the basis of the road shape;
[0008] a second target yaw rate setting unit for setting a second
target yaw rate on the basis of driving conditions of the
vehicle;
[0009] a target yaw rate correcting unit for correcting the second
target yaw rate on the basis of the first target yaw rate; and
[0010] a braking force setting unit for applying a braking force to
a selected wheel so that an actual yaw rate converges into the
second target yaw rate corrected by the target yaw rate correcting
unit.
[0011] The above-mentioned object can be also achieved by a vehicle
behavior control apparatus, according to a second aspect of the
invention, comprising:
[0012] a road shape recognizing unit for recognizing the road shape
ahead of a vehicle;
[0013] a first target yaw rate setting unit for setting a first
target yaw rate on the basis of the road shape;
[0014] a second target yaw rate setting unit for setting a second
target yaw rate on the basis of driving conditions of the
vehicle;
[0015] a turning decision unit for deciding a turning intention if
a steering angle exceeds a presetted value;
[0016] a target yaw rate correcting unit for correcting the second
target yaw rate gradually toward the first target yaw rate if the
turning decision unit decides the turning intention; and
[0017] a braking force setting unit for applying a braking force to
a selected wheel so that an actual yaw rate converges into the
second target yaw rate corrected by the target yaw rate correcting
unit.
[0018] Further, the above-mentioned object can be achieved by a
vehicle behavior control apparatus, according to a third aspect of
the invention, comprising:
[0019] a road shape recognizing unit for recognizing the road shape
ahead of a vehicle;
[0020] a first target yaw rate setting unit for setting a first
target yaw rate on the basis of the road shape;
[0021] a second target yaw rate setting unit for setting a second
target yaw rate on the basis of driving conditions of the
vehicle;
[0022] a target yaw rate correcting unit for correcting the second
target yaw rate on the basis of the first target yaw rate; and
[0023] a driving force distribution unit for setting the driving
force distribution to left and right wheels so that an actual yaw
rate converges into the second target yaw rate corrected by the
target yaw rate correcting unit.
[0024] Furthermore, the above-mentioned object can be achieved by a
vehicle behavior control apparatus, according to a fourth aspect of
the invention, comprising:
[0025] a road shape recognizing unit for recognizing the road shape
ahead of a vehicle;
[0026] a first target yaw rate setting unit for setting a first
target yaw rate on the basis of the road shape;
[0027] a second target yaw rate setting unit for setting a second
target yaw rate on the basis of driving conditions of the
vehicle;
[0028] a turning decision unit for deciding a turning intention if
a steering angle exceeds a presetted value;
[0029] a target yaw rate correcting unit for correcting the second
target yaw rate gradually toward the first target yaw rate if the
turning decision unit decides the turning intention; and
[0030] a driving force distribution unit for setting the driving
force distribution to left and right wheels so that an actual yaw
rate converges into the second target yaw rate corrected by the
target yaw rate correcting unit.
[0031] The above-mentioned vehicle behavior control apparatus
according to any of from the first aspect to fourth aspect,
preferably further comprises:
[0032] a target lateral acceleration setting unit for setting a
target lateral acceleration on the basis of either the second
target yaw rate corrected by the target yaw rate correcting unit or
the actual yaw rate; and
[0033] a deceleration control unit for making a deceleration
control if the actual lateral acceleration is below the target
lateral acceleration.
[0034] According to the vehicle behavior control apparatus of the
first aspect of the invention, the road shape recognizing unit
recognizes the road shape ahead of the vehicle, and the first
target yaw rate setting unit sets the first target yaw rate on the
basis of the road shape whereas the second target yaw rate setting
unit sets the second target yaw rate on the basis of the driving
conditions of the vehicle. Moreover, the target yaw rate correcting
unit corrects the second target yaw rate on the basis of the first
target yaw rate, and braking force setting unit applies the braking
force to the selected wheel so that the actual yaw rate converges
into the second target yaw rate corrected by the target yaw rate
correcting unit. Thus, the second target yaw rate reflecting the
intention of the driver is corrected with the first target yaw rate
reflecting the actual road shape, and the braking force is
controlled at the corrected target yaw rate. Therefore, it is
possible to prevent the deviation from the lane or the road due to
an improper operation of the driver without any unnatural feeling,
while reflecting the intention of the driver to the maximum.
[0035] According to the vehicle behavior control apparatus of the
second aspect of the invention, the road shape recognizing unit
recognizes the road shape ahead of the vehicle, and the first
target yaw rate setting unit sets the first target yaw rate on the
basis of the road shape whereas the second target yaw rate setting
unit sets the second target yaw rate on the basis of the driving
conditions of the vehicle. Further, the turning decision unit
decides the turning intention if the steering angle exceeds the
presetted value. Moreover, the target yaw rate correcting unit
corrects the second target yaw rate gradually toward the first
target yaw rate if the turning decision unit decides the turning
intention, and the braking force setting unit applies the braking
force to the selected wheel so that the actual yaw rate converges
into the second target yaw rate corrected by the target yaw rate
correcting unit. Thus, the second target yaw rate reflecting the
intention of the driver is corrected with the first target yaw rate
reflecting the actual road shape, and the braking force is
controlled at the corrected second target yaw rate. Therefore, it
is possible to prevent the deviation from the lane or the road due
to an improper operation of the driver without any unnatural
feeling, while reflecting the intention of the driver to the
maximum.
[0036] According to the vehicle behavior control apparatus of the
third aspect of the invention, the road shape recognizing unit
recognizes the road shape ahead of the vehicle, and the first
target yaw rate setting unit sets the first target yaw rate on the
basis of the road shape whereas the second target yaw rate setting
unit sets the second target yaw rate on the basis of the driving
conditions of the vehicle. Moreover, the target yaw rate correcting
unit corrects the second target yaw rate on the basis of the first
target yaw rate, and the driving force distribution unit sets the
driving force distribution to left and right wheels so that the
actual yaw rate converges into the second target yaw rate corrected
by the target yaw rate correcting unit. Thus, the second target yaw
rate reflecting the intention of the driver is corrected with the
first target yaw rate reflecting the actual road shape, and the
braking force is controlled at the corrected second target yaw
rate. Therefore, it is possible to prevent the deviation from the
lane or the road due to an improper operation of the driver without
any unnatural feeling, while reflecting the intention of the driver
to the maximum.
[0037] According to the vehicle behavior control apparatus of the
fourth aspect of the invention, the road shape recognizing unit
recognizes the road shape ahead of the vehicle, and the first
target yaw rate setting unit sets the first target yaw rate on the
basis of the road shape whereas the second target yaw rate setting
unit for setting the second target yaw rate on the basis of the
driving conditions of the vehicle. Further, the turning decision
unit decides the turning intention if the steering angle exceeds a
presetted value. Moreover, the target yaw rate correcting unit
corrects the second target yaw rate gradually toward the first
target yaw rate if the turning decision unit decides the turning
intention, and the driving force distribution unit sets the driving
force distribution to left and right wheels so that the actual yaw
rate converges into the second target yaw rate corrected by the
target yaw rate correcting unit. Thus, the second target yaw rate
reflecting the intention of the driver is corrected with the first
target yaw rate reflecting the actual road shape, and the braking
force is controlled at the corrected second target yaw rate.
Therefore, it is possible to prevent the deviation from the lane or
the road due to an improper operation of the driver without any
unnatural feeling, while reflecting the intention of the driver to
the maximum.
[0038] According to the vehicle behavior control apparatus of any
of from the first aspect to the fourth aspect of the invention, the
target lateral acceleration setting unit sets the target lateral
acceleration on the basis of either the second target yaw rate
corrected by the target yaw rate correcting unit or the actual yaw
rate, and the deceleration control unit makes the deceleration
control if the actual lateral acceleration is below the target
lateral acceleration. In addition to the effects thereof from the
first aspect to the fourth aspect of the invention, it is possible
to prevent the deviation from the lane or road due to the improper
operation of the driver, more reliably.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] FIG. 1 is a schematic diagram for explaining a vehicle
behavior control apparatus in a vehicle according to a first
embodiment of the present invention;
[0040] FIG. 2 is a functional block diagram of the vehicle behavior
control apparatus;
[0041] FIG. 3 is a diagram for explaining how to determine the
radius of curvature of a curve;
[0042] FIG. 4 is a diagram for explaining braking wheel selections
in braking force controls;
[0043] FIG. 5 is a flowchart of a control characteristics changing
routine;
[0044] FIG. 6 is a schematic diagram for explaining the vehicle
behavior control apparatus according to a second embodiment of the
present invention;
[0045] FIG. 7 is the functional block diagram of the vehicle
behavior control apparatus; and
[0046] FIG. 8 is the flow chart of the control characteristics
changing routine.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0047] The embodiments of the present invention will be described
with reference to the accompanying drawings.
[0048] FIGS. 1 to 5 show a first embodiment of the invention. FIG.
1 is a schematic diagram for explaining a vehicle behavior control
apparatus in a vehicle as a whole. FIG. 2 is a functional block
diagram of the vehicle behavior control apparatus. FIG. 3 is a
diagram for explaining how to determine a radius of curvature of a
curve. FIG. 4 is a diagram for explaining braking wheel selections
in braking force controls. FIG. 5 is a flow chart of a control
characteristic changing routine. Here in the first Embodiment, the
present invention is applied to the vehicle which is provided with
a braking force control unit for improving a running stability by
applying a braking force to respective wheels during cornering.
[0049] In FIG. 1, reference numeral 1 designates the vehicle, and
numeral 2 designates an engine, which is arranged in the front
portion of the vehicle. Driving force from the engine 2 is
transmitted from an automatic transmission 3 (including a torque
converter, as shown) at the back of the engine 2 through a
transmission output shaft 3a to a center differential unit 4. Then,
at the center differential unit 4, the driving force is distributed
at a predetermined torque distribution ratio to the front and rear
wheels 15fl, 15fr, 15fl, 15rr.
[0050] The driving force thus distributed from the center
differential unit 4 to the rear wheels 15rl, 15rr is inputted to a
rear wheel final reduction unit 8 through a rear drive shaft 5, a
propeller shaft 6 and a drive pinion 7.
[0051] On the other hand, the driving force thus distributed from
the center differential unit 4 to the front wheels 15fl, 15 fr is
inputted to a front differential unit 12 through a transfer drive
gear 9, a transfer driven gear 10 and a front drive shaft 11. Here,
integrally mounted in a case 13 are the automatic transmission 3,
the center differential unit 4, and the front differential unit
12.
[0052] The driving force inputted to the rear wheel final reduction
unit 8 is transmitted to a left rear wheel 15rl through a rear
wheel left drive shaft 14rl, and to a right rear wheel 15rr through
a rear wheel right drive shaft 14rr. On the other hand, the driving
force inputted to the front differential unit 12 is transmitted to
a left front wheel 15fl through a front wheel left drive shaft
14fl, and to a right front wheel 15fr through a front wheel right
drive shaft 14fr.
[0053] In the back of the case 13, there is disposed the center
differential unit 4. A carrier 16 is rotatably housed in the center
differential unit 4. The transmission output shaft 3a is rotatably
inserted from the front of the carrier 16 into the center
differential unit 4. The rear drive shaft 5 is rotatably inserted
from the back of the carrier 16 into the center differential unit
4.
[0054] A first sun gear 17 having a larger diameter is fixed on the
rear end portion of the transmission output shaft 3a on the input
side. A second sun gear 18 having a smaller diameter is fixed on
the front end portion of the rear drive shaft 5 for the output to
the rear wheels 15rl, 15rr. The first sun gear 17 and the second
sun gear 18 are housed in the carrier 16.
[0055] The first sun gear 17 meshes with a first pinion 19 of a
smaller diameter to form a first gear train. The second sun gear 18
meshes with a second pinion 20 (larger diameter side) to form a
second gear train. The first pinion 19 and the second pinion 20 are
integrated to provide a plurality of pairs (e.g., three pairs) of
pinions which are rotatably borne on the carrier 16. To the front
end of this carrier 16, there is connected the transfer drive gear
9 so that the output power is transmitted from the carrier 16 to
the front wheels 15fl, 15fr.
[0056] In other words, the center differential unit 4 is included
in such a complex planetary gear type without a ring gear that the
driving force from the transmission output shaft 3a is transmitted
to the first sun gear 17 and then is outputted to the rear drive
shaft 5 through the second sun gear 18, and the driving force from
the transmission output shaft 3a is also transmitted from the
carrier 16 to the front drive shaft 11 through the transfer drive
gear 9 and the transfer driven gear 10.
[0057] Moreover, the center differential unit 4 of the complex
planetary gear type is given a differential function by setting
proper tooth numbers of the first and second sun gears 17 and 18
and the first and second pinions 19 and 20 arranged around the
first second sun gears 17 and 18.
[0058] Further, the reference torque distribution can be setted to
a desired distribution (e.g., a larger torque distribution to the
rear wheels 15rl, 15rr) by setting the proper meshing pitch circle
diameters of the first and second sun gears 17 and 18 and the first
and second pinions 19 and 20.
[0059] The first and second sun gears 17 and 18 and the first and
second pinions 19 and 20 are exemplified by helical gears to make
different the helix angles of the first gear train and the second
gear train so that the thrust is left without offsetting the thrust
thereby to establish a frictional torque between the pinion end
faces. The center differential unit 4 has the differential limiting
function by causing the resultant force of the separation and the
tangential load from meshing relations to act on the first and
second pinions 19 and 20 and the surface of the stem of the carrier
for pivoting the first and second pinions 19 and 20, thereby to
establish differential limiting torque function which is
proportional to the input torque.
[0060] Between the carrier 16 and the rear drive shaft 5 of the
center differential unit 4, there is interposed a transfer clutch
21 which adopts the hydraulic multi-disc clutch for making the
driving force distribution between the front and rear wheels 15fl,
15fr, 15rl, 15rr variable. By controlling the applying force of the
transfer clutch 21, the torque distribution between the front and
rear wheels 15fl, 15fr, 15rl, 15rr can be variably controlled
within a range from that of the direct connection of 50:50 for the
4WD to that of the center differential unit 4.
[0061] Numeral 25 designates a brake drive unit of the vehicle 1.
The master cylinder (not shown) connected to a brake pedal operated
by the driver is connected to the brake drive unit 25. As the
driver operates the brake pedal, a brake pressure is introduced by
the master cylinder through the brake drive unit 25 to the
individual wheel cylinders (i.e., a left front-wheel wheel cylinder
26fl, a right front-wheel wheel cylinder 26fr, a left rear-wheel
wheel cylinder 26rl and a right rear-wheel wheel cylinder 26rr) of
the four wheels 15fl, 15fr, 15rl and 15rr so that the four wheels
are braked.
[0062] The brake drive unit 25 is a hydraulic unit which is
equipped with a pressure source, a debooster valve, a booster valve
and so on. The brake drive unit 25 can not only effect the
aforementioned brake operations by the driver but also introduce
the brake pressure freely to the individual wheel cylinders 26fl,
26fr, 26rl and 26rr independently in response to an input signal
from a later-described braking force control unit 40.
[0063] The vehicle 1 is provided with a control characteristics
changing unit 50. The control characteristics changing unit 50 can
correct, if necessary, either a target yaw rate (or a first target
yaw rate) computed by the braking force control unit 40 or a target
deceleration set by the braking force control unit 40.
[0064] The vehicle 1 is also provided with individual sensors for
detecting input parameters, as required for the braking force
control unit 40 and the control characteristics changing unit 50.
Specifically, the wheel speeds of the individual wheels 15fl, 15fr,
15rl and 15rr are detected by wheel speed sensors 31fl, 31fr, 31rl
and 31rr, and a steering angle .theta. H is detected by a steering
angle sensor 32. The detected values are inputted to the braking
force control unit 40 and the control characteristics changing unit
50. An actual yaw rate .gamma. is detected by a yaw rate sensor 33
and is inputted to the braking force control unit 40. An actual
lateral acceleration Gy is detected by a lateral acceleration
sensor 34, and a road shape (e.g., a radius Rn of curvature of a
front curve) in front of the vehicle 1 is detected by a road shape
recognizing unit 35. These detected values are inputted to the
control characteristics changing unit 50.
[0065] Here, the road shape recognizing unit 35 is provided as road
shape recognizing means for determining the curve radius Rn of the
road on the basis of the point data of the road, as inputted from a
navigation device, e.g., the technique disclosed by us in Japanese
Patent Unexamined Publication No. Hei. 11-2528. This method will be
briefly described in the following.
[0066] From the point data inputted from the navigation device,
e.g., three points on the road within the range of about 100 meters
in front are read sequentially (from the vehicle) as a first point
Pn-1, a second point Pn and a third point Pn+1, as illustrated in
FIG. 3. Here, the curve is represented by the point Pn. Therefore,
the individual data are calculated for the curve of a point P1 from
points P0, P1 and P2, for the curve of the point P2 from the points
P1, P2 and P3, ------, and for the curve of the point Pn from the
points Pn-1, Pn and Pn+1.
[0067] In the curve of the point Pn, the distance of the straight
line joining the first point Pn-1 and the second point Pn is
computed on the basis of the positional information of the first
point Pn-1 and the second point Pn, and the distance of the
straight line joining the second point Pn and the third point Pn+1
is computed on the basis of the second point Pn and the third point
Pn+1.
[0068] Then, the straight distance joining the first point Pn-1 and
the second point Pn and the straight distance joining the second
point Pn and the third point Pn+1 are compared to decide which of
them is longer or shorter. As a result, on the basis of the
individual data (including the position and the distance) of the
shorter straight line, the half distance of the shorter straight
distance is computed, and the midpoint position on the shorter
straight line is determined. Here, the shorter straight line is
exemplified by the straight line joining the first point Pn-1 and
the second point Pn, and the midpoint is expressed by Pn-1,n.
[0069] From the individual data (including the position and the
distance) of the longer straight line and the data of the half
distance of the shorter straight distance, on the other hand, a
midpoint equidistance point is determined at the position at a half
distance of the shorter straight distance on the longer straight
line from the second point. Here, the longer straight line is
exemplified by the straight line joining the second point Pn and
the third point Pn+1, and the midpoint equidistance point is
expressed by Pn,n+1.
[0070] On the basis of the positional data of the midpoint Pn-1,n
and the positional data of the midpoint equidistance point Pn,n+1,
moreover, the point of intersection between a straight line
perpendicular at the midpoint Pn-1,n to the shorter straight line
(as expressed by Pn-1 Pn) and a straight line perpendicular at the
midpoint equidistance point Pn,n+1 to the longer straight line (as
expressed by PnPn+1) is determined as a center position. One of the
curves on the road being traveled, so that the curve radius Rn is
computed on the basis of that curve center position. The curve
radius Rn thus computed is further corrected with the road width
information and is inputted to the control characteristics changing
unit 50.
[0071] Next, the structures of the braking force control unit 40
and the control characteristics changing unit 50 will be described
with reference to the functional block diagram of FIG. 2.
[0072] The braking force control unit 40 mainly includes a target
yaw rate setting unit 41, a target yaw rate changing unit 42, a yaw
rate deviation computing unit 43, a target yaw moment setting unit
44, a brake wheel selecting unit 45, a target slip ratio setting
unit 46 and a wheel speed control unit 47. The control
characteristics changing unit 50 mainly includes a cornering
decision unit 51, a target yaw rate setting unit 52, a target yaw
rate change designating unit 53 and a target deceleration setting
unit 54.
[0073] In the target yaw rate setting unit 41 of the braking force
control unit 40, the steering angle .theta. H is inputted from the
steering angle sensor 32, and the wheel speeds of the four wheels
15fl, 15fr, 15rl, 15rr are inputted from the four-wheel wheel speed
sensors 31fl, 31fr, 31rl and 31rr. Then, the target yaw rate
setting unit 41 computes a target yaw rate .gamma.t on the basis of
those driving conditions and outputs signals of the target yaw rate
.gamma.t to the target yaw rate changing unit 42 and the target yaw
rate change designating unit 53 of the control characteristics
changing unit 50. In short, the target yaw rate .gamma.t is
determined as a second target yaw rate, and the target yaw rate
setting unit 41 is provided as second target yaw rate setting
unit.
[0074] Here, the second target yaw rate .gamma.t is computed, for
example, by the following Formula (1):
.gamma.t=(1/(1+A.multidot.V.sup.2)).multidot.(V/L).multidot.(.theta.H/n)
(1)
[0075] wherein: A designates a stability factor indicating the
steering characteristics intrinsic to the vehicle; V designates a
vehicle speed (e.g., an average of the four-wheel vehicle speeds);
L designates a wheel base; and n designates a steering gear
ratio.
[0076] In the target yaw rate changing unit 42, the second target
yaw rate .gamma.t is inputted from the target yaw rate setting unit
41, and a second target yaw rate .gamma.t' corrected is inputted,
if necessary, from the target yaw rate change designating unit 53
of the control characteristics changing unit 50. When the corrected
second target yaw rate .gamma.t' is inputted from the target yaw
rate change designating unit 53, it is changed (or used) as the
second target yaw rate .gamma.t to be used for the braking force
control and is outputted to the yaw rate deviation computing unit
43.
[0077] In the yaw rate deviation computing unit 43, the actual yaw
rate .gamma. is inputted from the yaw rate sensor 33, and the
second target yaw rate .gamma.t is inputted from the target yaw
rate changing unit 42. The yaw rate deviation computing unit 43
computes a yaw rate deviation .DELTA. .gamma. from the following
Formula (2) and outputs it to the target yaw moment setting unit
44:
.DELTA..gamma.=.gamma.-.gamma.t (2)
[0078] In the target yaw moment setting unit 44, the yaw rate
deviation .DELTA..gamma. is inputted from the yaw rate deviation
computing unit 43. The target yaw moment setting unit 44 computes a
target yaw moment Mz(t) from the following Formula (3) and outputs
the target yaw moment Mz(t) signals to the brake wheel selecting
unit 45 and the target slip ratio setting unit 46:
Mz(t)-k3.multidot..DELTA..gamma. (3)
[0079] wherein k3 designates a control gain.
[0080] The brake wheel selecting unit 45 decides the turning
direction of the vehicle in terms of the actual yaw rate .gamma.
from the yaw rate sensor 33. Then, the selecting unit 45 selects
the turning inner rear wheel as the brake force applying wheel, to
which the braking force is applied, when the target yaw moment
Mz(t) calculated by the target yaw moment setting unit 44 is in the
same direction as the turning direction. When the target yaw moment
Mz(t) is in the opposite direction to the turning direction, the
selecting unit 45 selects the turning outer front wheel as the
wheel, to which the braking force is applied. These combinations in
the brake wheel selecting unit 45 are set as follows. Here, both
the actual yaw rate .gamma. and the target yaw moment Mz(t) are
signed by "+" in the leftward turning direction and by "-" in the
rightward turning direction. In order to decide the straight
running state of the vehicle, letter .epsilon. is set as the
positive value which is determined about zero in advance by
experiments or computations. In order to decide that the target yaw
moment Mz(t) is about zero at the turning time, the value
.epsilon.Mz is set to the positive value of about zero determined
in advance by experiments or computations.
[0081] (Case 1): .gamma.>.epsilon. and Mz(t)>.epsilon.Mz, and
leftward turning in understeer left rear wheel braked;
[0082] (Case 2): .gamma.>.epsilon. and Mz(t)<-.epsilon.Mz,
and leftward turning in oversteer right front wheel braked;
[0083] (Case 3): .gamma.<.epsilon. and Mz(t)>.epsilon.Mz, and
rightward turning in oversteer left front wheel braked;
[0084] (Case 4): .gamma.<.epsilon. and Mz(t)<-.epsilon.Mz and
rightward turning in understeer right rear wheel braked; and
[0085] (Case 5): generally straight run with
.vertline..gamma..vertline..l- toreq..epsilon., or turning with
.vertline.Mz(t).vertline..ltoreq.Mz, no braking with no brake wheel
selected (FIG. 4).
[0086] In the target slip ratio setting unit 46, the selection
result of the brake wheel is inputted from the brake wheel
selecting unit 45, and the target yaw moment Mz(t) is inputted from
the target yaw moment setting unit 44. Further, a target
deceleration Gxt is inputted in the target slip ratio setting unit
46, if necessary, from the target deceleration setting unit 54 of
the control characteristics changing unit 50.
[0087] A target slip ratio .lambda.t is computed by the following
Formula (4) and is outputted to the vehicle speed control unit
47:
.lambda.t=Ft/Kb (4)
[0088] wherein: Kb designate a braking stiffness, as obtained from
the relations of the braking force to the slip ratio of the tire;
and Ft designates a target braking force. The target braking force
Ft is computed by the following Formula (5) for a tread d:
Ft-Mz(t)/(d/2) (5)
[0089] When the target deceleration Gxt is inputted from the target
deceleration setting unit 54 of the control characteristics
changing unit 50, the target slip ratio setting unit 46 corrects
the target slip ratio .lambda.t, as expressed by the following
formulas (10) and (11) by using the target deceleration Gxt, and
outputs the signals of the target deceleration Gxt to the wheel
speed control unit 47:
Target Braking Force Ftf of Front
Wheel=(1/2).multidot.Cbf.multidot.m.mult- idot.Gxt (6)
Target Braking Force Ftr of Rear
Wheel=(1/2).multidot.(1-Cbf).multidot.m.m- ultidot.Gxt (7)
[0090] wherein Cbf designates a front/rear braking force
distribution ratio (0 to 1), and m designates a vehicle mass.
Target Slip Ratio Correction .DELTA..lambda.f of Front Wheel=Ftf/Kb
(8)
Target Slip Ratio Correction .DELTA..lambda.r of Rear Wheel=Ftr/Kb
(9)
Corrected Front Wheel Target Slip Ratio
.lambda.tr'=.lambda.t+.lambda..DEL- TA.f (10)
Corrected Rear Wheel Target Slip Ratio
.lambda.tr'=.lambda.t+.DELTA..lambd- a.r (11)
[0091] In the wheel speed control unit 47, the wheel speeds of the
four wheels 15fl, 15fr, 15rl, 15rr are inputted from the four-wheel
wheel speed sensors 31fl, 31fr, 31rl and 31rr, and either the
target slip ratio .lambda.t of the selected brake wheel or the
corrected target slip ratios .lambda.tf' and .lambda.tr' of the
front and rear wheels 15fl, 15fr, 15rl, 15rr are inputted from the
target slip ratio setting unit 46. The wheel speed control unit 47
converts the braking force, as necessary for achieving those target
slip ratios, and outputs thereof to the brake drive unit 25.
[0092] In the control characteristics changing unit 50, the
cornering decision unit 51 receives the steering angle .theta. H
from the steering angle sensor 32 and decides whether or not the
steering angle .theta. H is more than a presetted value .theta. Hc.
The setted value .theta. Hc is a value for deciding whether or not
the driver has a will for cornering. When the steering angle
.theta. H is equal to or more than the set value .theta. Hc, it is
decided that the driver has the cornering will. When the steering
angle .theta. H is smaller than the set value .theta. Hc, it is
decided that the driver has no cornering will. The decision result
is outputted to the target yaw rate change designating unit 53. In
short, the cornering decision unit 51 is provided as a turning
decision unit.
[0093] In the target yaw rate setting unit 52, the wheel speeds of
the four wheels 15fl, 15fr, 15rl, 15rr are inputted from the
four-wheel wheel speed sensors 31fl, 31fr, 31rl and 31rr, and the
curve radius Rn is inputted from the road shape recognizing unit
35. The target yaw rate setting unit 52 computes a target yaw rate
.gamma.c by the following Formula (12) and outputs thereof to the
target yaw rate change designating unit 53. In other words, the
target yaw rate .gamma.c is determined as the first target yaw
rate, and the target yaw rate setting unit 52 is provided first
target yaw rate setting unit.
.gamma.c=V/Rn (12)
[0094] In the target yaw rate change designating unit 53, the
result (in terms of a flag, for example) of the cornering decision
is inputted from the cornering decision unit 51, the first target
yaw rate .gamma.c is inputted from the target yaw rate setting unit
52, and the second target yaw rate .gamma.t is inputted from the
target yaw rate setting unit 41 of the braking force control unit
40. When it is decided that the driver has the cornering will, the
first target yaw rate .gamma.c and the second target yaw rate
.gamma.t are compared in their absolute values. When the absolute
value .vertline..gamma.c.vertline. of the first target yaw rate
.gamma.c is larger than the absolute value
.vertline..gamma.t.vertline. of the second target yaw rate
.gamma.t, the increasing/decreasing correction is made to bring the
second target yaw rate .gamma.t closer to the first target yaw rate
.gamma.c, and the corrected second target yaw rate .gamma.t' is
outputted to the target yaw rate changing unit 42 of the braking
force control unit 40. In short, the target yaw rate change
designating unit 53 is provided as a target yaw rate correcting
unit.
[0095] Here, the second target yaw rate .gamma.t is corrected with
the first target yaw rate .gamma.c, as specified by the following
Formula (13):
.gamma.t'=.kappa.1.multidot..gamma.t+(1-.kappa.1).multidot..gamma.c
(13)
[0096] The constant .kappa.1 for weighing the second target yaw
rate .gamma.t determined from the driving conditions of the driver
and the first target yaw rate .gamma.c determined from the curve in
front of the vehicle 1 is determined as 0<.kappa.1<1 by
reflecting the driving operation of the driver. At this time, the
constant .kappa.1 may be gradually setted from 1 as the correction
starts (or may be gradually set to the first target yaw rate
.gamma.c). When the deviation between the second target yaw rate
.gamma.t and the first target yaw rate .gamma.c is smaller than the
presetted value, the constant .kappa.1 may be gradually increased
to 1. When the information (e.g., the curve radius Rn) necessary
for the control cannot be obtained or when the driver makes the
steering apparently different from the road shape so that the
deviation between the second target yaw rate .gamma.t and the first
target yaw rate .gamma.c exceeds a predetermined upper limit, the
constant .kappa.1 maybe gradually increased to 1 so as to prevent
any abrupt change in the vehicle behavior.
[0097] In the target deceleration setting unit 54, the wheel speeds
of the four wheels 15fl, 15fr, 15rl, 15rr are inputted from the
four-wheel wheel speed sensors 31fl, 31fr, 31rl and 31rr, the
actual lateral acceleration Gy is inputted from the lateral
acceleration sensor 34, and the corrected second target yaw rate
.gamma.t' is inputted from the target yaw rate change designating
unit 53. The target deceleration setting unit 54 computes a target
lateral acceleration Gyt by the following Formula (14). When the
actual lateral acceleration Gy is smaller than the computed target
lateral acceleration Gyt, it is decided that a sufficient control
is not made only by the braking force control unit 40, and the
target deceleration Gxt is computed by the following Formula (15)
and is outputted to the target slip ratio setting unit 46 of the
braking force control unit 40.
Gyt=.gamma.t'.multidot.V (14)
Gxt=.kappa.2.multidot.(.vertline.Gyt.vertline.-.vertline.Gy.vertline.)
(15)
[0098] wherein .kappa.2 is 0<.kappa.2.ltoreq.1 and a coefficient
for setting the deceleration according to the shortage of the
actual lateral acceleration Gy. Here, the coefficient .kappa.2 may
be brought closer to 1 or returned to 0 by deciding the driver will
or by comparing the second target yaw rate .gamma.t and the first
target yaw rate .gamma.c. On a low friction coefficient .mu. road,
for example, the actual lateral acceleration Gy may be extremely
smaller than the target deceleration Gxt, but the coefficient
.kappa.2 is then set smaller than 1. The target lateral
acceleration Gyt of the formula (14) may be computed by using the
actual yaw rate .gamma.:
Gyt=.gamma..multidot.V (14)
[0099] Thus, the target deceleration setting unit 54 has functions
as target lateral acceleration setting unit and deceleration
control unit. The braking force setting unit has the target yaw
rate changing unit 42, the yaw rate deviation computing unit 43,
the target yaw moment setting unit 44, the brake wheel selecting
unit 45, the target slip ratio setting unit 46 and the wheel speed
control unit 47 of the braking force control unit 40.
[0100] Next, FIG. 5 is a flow chart showing a control
characteristics changing routine to be executed in the control
characteristics changing unit 50. First of all, at Step (as will be
abbreviated into "S") 101, the necessary parameters are read in,
and the routine advances to S102, at which the first target yaw
rate .gamma.c based on the curve radius Rn is computed in the
target yaw rate setting unit 52 by the Formula (12).
[0101] Then, the routine advances to S103, at which it is decided
in the cornering decision unit 51 whether or not the steering angle
.theta.H is equal to or larger than the presetted value .theta.Hc.
If the steering angle .theta.H is equal to the set value .theta.Hc,
it is decided that the driver has the cornering will, and the
routine advances to S104. If the steering angle .theta.H is smaller
than the set value .theta.Hc, it is decided that the driver does
not have the cornering will, and the operations leave the
program.
[0102] If the routine decides the cornering will at S103 and
advances to S104, the routine reads the second target yaw rate
.gamma.t based on the driving conditions computed at the target yaw
rate setting unit 41 of the braking force control unit 40, and
advances to S105.
[0103] At S105, the first target yaw rate .gamma.c and the second
target yaw rate .gamma.t are compared in their absolute values. If
the absolute value .vertline..gamma.c.vertline. of the first target
yaw rate .gamma.c is larger than the absolute value .gamma.t of the
second target yaw rate .gamma.t, it is decided that the operation
amount of the driver shorts for turning the actual road shape
(curve), and the routine advances to S106. If the absolute value
.vertline..gamma.c.vertline. of the first target yaw rate .gamma.c
is no more than the absolute value .vertline..gamma.t.vertline. of
the second target yaw rate .gamma.t, it is decided that the
operation amount of the driver is enough, and the routine leaves
the program.
[0104] If the routine decides it at S105 that the operation of the
driver shorts for turning the curve and advances to S106, the
second target yaw rate .gamma.t is corrected by the Formula (13) to
increase/decrease to the first target yaw rate .gamma.c, and the
routine advances to S107, at which this corrected second target yaw
rate .gamma.t' is outputted to the target yaw rate changing unit 42
of the braking force control unit 40. In short, the operations of
S104 to S107 are done (executed) at the target yaw rate designating
unit 53.
[0105] After that, the routine advances to S108, at which the
target lateral acceleration Gyt is computed by the Formula (14) on
the basis of the corrected second target yaw rate .gamma.t', and
the routine further advances to S109.
[0106] At S109, the absolute value .vertline.Gyt.vertline. of the
target lateral acceleration Gyt and the absolute value
.vertline.Gy.vertline. of the actual lateral acceleration Gy are
compared. If the absolute value .vertline.Gyt.vertline. of the
target lateral acceleration Gyt is larger than the absolute value
.vertline.Gy.vertline. of the actual lateral acceleration Gy, it is
decided that a sufficient control is not made only by the braking
force control unit 40, and the routine advances to S110, at which
the target deceleration Gxt is computed by the Formula (15). At
S111, the target deceleration Gxt is outputted to the target slip
ratio setting unit 46, and the routine leaves the program. If it is
decided at S109 that the absolute value .vertline.Gyt.vertline. of
the target lateral acceleration Gyt is equal to or less than the
absolute value .vertline.Gy.vertline. of the actual lateral
acceleration Gy, on the other hand, the routine leaves the program
without any further operation. In short, the operations of S108 to
S111 are done (executed) at the target deceleration setting unit
54.
[0107] Thus, according to the first embodiment, the first target
yaw rate .gamma.c based on the curve radius Rn and the second
target yaw rate .gamma.t based on the driving conditions are
compared. If the absolute value .vertline..gamma.c.vertline. of the
first target yaw rate .gamma.c is larger than the absolute value
.vertline..gamma.t.vertline. of the second target yaw rate
.gamma.t, it is decided that the operation of the driver is
insufficient, and the control is made to approach the first target
yaw rate .gamma.c. Therefore, the deviation from the lane or the
road due to an improper operation of the driver can be prevented
without any unnatural feeling by reflecting the intention of the
driver to the maximum.
[0108] At this time, the absolute value .vertline.Gyt.vertline. of
the target lateral acceleration Gyt and the absolute value
.vertline.Gy.vertline. of the actual lateral acceleration Gy are
compared. If the absolute value .vertline.Gyt.vertline. of the
target lateral acceleration Gyt is larger than the absolute value
.vertline.Gy.vertline. of the actual lateral acceleration Gy, it is
decided that a sufficient control is not made only by the braking
force control unit 40, and the target slip ratio .lambda.t of the
braking force control unit 40 is corrected. Therefore, it is
possible to prevent the deviation from the lane or the road due to
the improper operation of the driver more reliably.
[0109] Next, FIGS. 6 to 8 show a second embodiment of the
invention. FIG. 6 is a schematic diagram for explaining the vehicle
behavior control apparatus in the vehicle 1 as a whole. FIG. 7 is a
functional block diagram of the vehicle behavior control apparatus.
FIG. 8 is a flow chart of a control characteristic changing
routine. Here, the second embodiment is provided with a left/right
driving force distribution control unit for controlling the
left/right driving force distribution of the rear wheels during a
cornering thereby to improve the running stability. The correction
of the target yaw rate by the control characteristics changing unit
is done (performed) on the left/right driving force distribution
control unit. The change in the target deceleration Gxt is done
like the foregoing first embodiment on the braking force control
unit. The portions similar to those of the first embodiment will
not be described by designating thereof by the common reference
numerals.
[0110] As shown in FIG. 6, the rear wheel final reduction unit 8
has a differential function and a power distribution function
between the rear left and right wheels 15rl, 15rr. The rear wheel
final reduction unit 8 includes: a bevel gear type differential
mechanism unit 81; a gear mechanism unit 82 of three trains of
gears; and two sets of clutch mechanism units 83 for making
variable the driving force distribution between the left and right
rear wheels 15rl, 15rr. The components are integrally housed in a
differential carrier 84.
[0111] The drive pinion 7 meshes with a final gear 86 mounted on an
outer circumference (periphery) of a differential case 85 of the
differential unit 81 thereby to transmit the driving force
distributed on the rear wheel side from the center differential
unit 4.
[0112] The differential unit 81 has a differential pinion (or bevel
gear) 88 borne rotatably on a pinion shaft 87 fixed in the
differential case 85, and left and right side gears (or bevel
gears) 89L and 89R meshing with the differential pinion 88 in the
differential case 85. In the differential case 85, the side gears
89L and 89R, respectively, are fixed to ends of the rear wheel left
and right drive shafts 14rl and 14rr.
[0113] Specifically, the differential unit 81 has the differential
case 85 which is rotated on the common axes of the side gears 89L
and 89R by the rotation of the drive pinion 7 thereby to effect the
differential rotations between the rear left and right wheels 15rl,
15rr by the gear mechanism in the differential case 85.
[0114] The gear mechanism unit 82 is divided into the left and
right sides of the differential mechanism unit 81. A first gear
82z1 is fixed on the rear wheel left driveshaft 14rl whereas a
second gear 82z2 and a third gear 82z3 are fixed on the rear wheel
right drive shaft 14rr. These first, second and third gears 82z1,
82z2 and 82z3 are arranged on the common axis of the rotation.
[0115] The first, second and third gears 82z1, 82z2 and 82z3 mesh
with fourth, fifth and sixth gears 82z4, 82z5 and 82z6 arranged on
the common rotational axis. Among which, the fourth gear 82z4 is
fixed on the left wheel side end portion of a torque bypass shaft
90 which is arranged on the rotational axe of the fourth, fifth and
sixth gears 82z4, 82z5 and 82z6.
[0116] At the right wheel side end portion of the torque bypass
shaft 90, there is formed a right side transfer clutch 83a of the
clutch unit 83 for executing the power distribution between the
rear left and right wheels 15rl, 15rr. The torque bypass shaft 90
can be freely connected through the right side transfer clutch 83a
(as the torque bypass shaft 90 is located on the clutch hub side
whereas the stem side of the sixth gear 82z6 is located on the
clutch drum side) to the stem of the sixth gear 82z6 arranged on
the left side of the right side transfer clutch 83a.
[0117] At a position of the torque bypass shaft 90 between the
differential mechanism unit 81 and the fifth gear 82z5, moreover,
there is disposed a left side transfer clutch 83b of the clutch
unit 83. The torque bypass shaft 90 can be freely connected through
the left side transfer clutch 83b (as the torque bypass shaft 90 is
located on the clutch hub side whereas the stem side of the fifth
gear 82z5 is located on the clutch drum side) to the stem of the
fifth gear 82z5 arranged on the right side of the left side
transfer clutch 83b.
[0118] The first, second, third, fourth, fifth and sixth gears
82z1, 82z2, 82z3, 82z4, 82z5 and 82z6 are setted to have teeth
numbers z1, z2, z3, z4, z5 and z6 of 82, 78, 86, 46, 50 and 42,
respectively. With respect to the gear train ((z4/z1)=0.56) of the
first and fourth gears 82z1 and 82z4, the gear train ((z5/z2)=0.64)
of the second and fifth gears 82z2 and 82z5 is an accelerating one,
and the gear train ((z6/z3)=0.49) of the third and sixth gears 82z3
and 82z6 is a decelerating one.
[0119] When both of the right and left side transfer clutches 83a
and 83b are not operatively connected, therefore, the driving force
from the drive pinion 7 is equally distributed through the
differential unit 81 between the rear wheel left and right drive
shafts 14rl and 14rr. When the right side transfer clutch 83a is
operatively connected, however, the driving force distributed to
the rear right drive shaft 14rr is partially returned to the
differential case 85 through the third gear 82z3, the sixth gear
82z6, the right side transfer clutch 83a, the torque bypass shaft
90, the fourth gear 82z4 and the first gear 82z1 sequentially in
the recited order. As a result, the torque distribution to the left
rear wheel 15rl is increased to improve the rightward turnability
of the vehicle 1 for an ordinary frictional road surface .mu..
[0120] When the left side transfer clutch 83b is operatively
connected, on the contrary, the driving force transmitted from the
drive pinion 7 to the differential case 85 is partially bypassed to
the rear right drive shaft 14rr through the first gear 82zl, the
fourth gear 82z4, the torque bypass shaft 90, the left side
transfer clutch 83b, the fifth clutch 82z5 and the second gear 82z2
sequentially in the recited order so that the torque distribution
to the right rear wheel 15rr is enlarged to improve the leftward
turnability of the vehicle 1 for the ordinary frictional road
surface .mu..
[0121] The right and left side transfer clutches 83a and 83b are
connected to a transfer clutch drive unit 27 with a hydraulic
circuit having a plurality of solenoid valves, so that the clutches
83a and 83b are released/applied with the oil pressure which is
established by the transfer clutch drive unit 27. Moreover, control
signals (or output signals for the individual solenoid valves) for
driving the transfer clutch drive unit 27 are outputted from a
left/right driving force distribution control unit 70.
[0122] The target yaw rate .gamma.t (or the second target yaw rate)
to be used for the left/right driving force distribution unit 70 is
corrected and setted, if necessary, by the control characteristics
changing unit 50. A braking force control unit 60 is so connected
that the lateral acceleration is exclusively corrected by the
control characteristics changing unit 50.
[0123] The vehicle 1 is provided with individual sensors for
detecting the input parameters necessary for the control
characteristics changing unit 50, the braking force control unit 60
and the left/right driving force distribution unit 70, and is
connected with other control units so that the necessary data are
inputted thereto. Specifically, the wheel speeds of the individual
wheels 15fl, 15fr, 15rl and 15rr are detected by the wheel speed
sensors 31fl, 31fr, 31rl and 31rr, and the steering angle .theta.H
is detected by the steering angle sensor 32. The detected values
are inputted to the control characteristics changing unit 50, the
braking force control unit 60 and the left/right driving force
distribution unit 70. The actual yaw rate .gamma. is detected by
the yaw rate sensor 33 and is inputted to the braking force control
unit 60 and the left/right driving force distribution unit 70.
Moreover, the actual lateral acceleration Gy is detected by the
lateral acceleration sensor 34 and is inputted to the control
characteristics changing unit 50 and the left/right driving force
distribution unit 70. The road shape (e.g., the curve radius Rn) is
detected by the road shape recognizing unit 35 and is inputted to
the control characteristics changing unit 50. The longitudinal
acceleration Gx is detected by the longitudinal acceleration sensor
36 and is inputted to the left/right driving force distribution
unit 70. With the left/right driving force distribution unit 70,
there are connected an engine control unit 37 for controlling the
engine 2 generally (e.g., controls of a fuel injection rate
control, an ignition time and so on), and a transmission control
unit 38 for the shift control of the automatic transmission 3 and
the transfer control of the transfer clutch 21. Thus, to the
left/right driving force distribution unit 70, there are inputted:
an engine output torque Te from the engine control unit 37; a
transmission gear ratio Gt from the transmission control unit 38;
and a torque distribution ration Ctc (0 to 1) by the center
differential unit 4.
[0124] Next, the structures of the control characteristics changing
unit 50, the braking force control unit 60 and the left/right
driving force distribution unit 70 will be described with reference
to the functional block diagram of FIG. 7.
[0125] The control characteristics changing unit 50 of the second
embodiment has a similar structure to that of the foregoing first
embodiment except that the changing unit 50 receives the second
target yaw rate .gamma.t, as inputted to the target yaw rate change
designating unit 53, from a target yaw rate setting unit 71 of the
left/right driving force distribution unit 70, and the unit 50
outputs the corrected second target yaw rate .gamma.t' to a target
yaw rate changing unit 72 of the left/right driving force
distribution unit 70. The target deceleration Gxt of the target
deceleration setting unit 54 is outputted to the target slip ratio
setting unit 46 of the braking force control unit 60.
[0126] The braking force control unit 60 determines the target yaw
moment Mz(t) with the deviation between the second target yaw rate
.gamma.t and the actual yaw rate .gamma., and controls the braking
force on the basis of the target yaw moment Mz(t). The second
target yaw rate .gamma.t is not corrected by the control
characteristics changing unit 50. Therefore, the target yaw rate
changing unit 42 is omitted from the structure.
[0127] Moreover, the left/right driving force distribution unit 70
includes the target yaw rate setting unit 71, the target yaw rate
changing unit 72, a yaw rate deviation computing unit 73, a target
yaw moment setting unit 74, a grounding load response control unit
75 and a transfer torque changing unit 76.
[0128] Here, the target yaw rate setting unit 71, the target yaw
rate changing unit 72, the yaw rate deviation computing unit 73 and
the target yaw moment setting unit 74 correspond to the target yaw
rate setting unit 41, the target yaw rate changing unit 42, the yaw
rate deviation computing unit 43 and the target yaw rate setting
unit 44 of the braking force control unit 40 in the first
embodiment.
[0129] Specifically, the target yaw rate setting unit 71 receives
the steering angle .theta.H from the steering angle sensor 32 and
the wheel speeds of the four wheels 15fl, 158fr, 15rl, 15rr from
the four-wheel wheel speed sensors 31fl, 31fr, 31rl and 31rr. Then
the target yaw rate setting unit 71 computes the second target yaw
rate .gamma.t on the basis of those driving conditions by the
Formula (1) and outputs the signal to the target yaw rate changing
unit 72 and the target yaw rate designating unit 53 of the control
characteristics changing unit 50.
[0130] In the target yaw rate changing unit 72, the second target
yaw rate .gamma.t is inputted from the target yaw rate setting unit
71, and the corrected second target yaw rate .gamma.t' is inputted,
if necessary, from the target yaw rate change designating unit 53
of the control characteristics changing unit 50. When the corrected
second target yaw rate .gamma.t' is inputted from the target yaw
rate change designating unit 53, the target yaw rate changing unit
72 changes the corrected second target yaw rate .gamma.t' as the
second target yaw rate .gamma.t for correcting the transfer torque,
and outputs the signal to the yaw rate deviation computing unit
73.
[0131] This yaw rate deviation computing unit 73 receives the
actual yaw rate .gamma. from the yaw rate sensor 33 and the second
target yaw rate .gamma.t from the target yaw rate changing unit 72.
Then, the raw rate deviation computing unit 73 computes the yaw
rate deviation .DELTA..gamma. by the Formula (2) and outputs it to
the target yaw moment setting unit 74.
[0132] This target yaw moment setting unit 74 receives the yaw rate
deviation .DELTA..gamma. from the yaw rate deviation computing unit
73, and computes the target yaw moment Mz(t) by the Formula (3) and
outputs the signal to the transfer torque changing unit 76.
[0133] The grounding load response control unit 75 receives the
actual lateral acceleration Gy from the lateral acceleration sensor
34, the longitudinal acceleration Gx from the longitudinal
acceleration sensor 36, the engine torque Te from the engine
control unit 37, the transmission gear ratio Gt from the
transmission control unit 38, and the torque distribution ratio Ctc
(0 to 1) by the center differential unit 4. Then, the grounding
load response control unit 75 computes a rear-wheel left/right
grounding load distribution Xr by the following Formula (19).
Moreover, the grounding load response control unit 75 computes a
transfer torque Ttrf by the following Formula (21) on the basis of
the rear-wheel left/right grounding load distribution Xr, and
outputs the signal to the transfer torque changing unit 76.
[0134] Specifically:
Longitudinal Load Movement
.DELTA.Fzx=(1/2).multidot.m.multidot.Gx.multido- t.(h/L) (16)
Rear Axle Left/Right Load Movement
.DELTA.Fzyr=Ckr.multidot.m.multidot..ve-
rtline.Gy.vertline..multidot.(h/d) (17)
Grounding Load Fzi of Rear Axle Turning Inner
Race=Fzr0+.DELTA.Fzx-.DELTA.- Fzyr (18)
Xr=Fzi/(2(Fzr0+.DELTA.Fzx)) (19)
[0135] wherein: h designates the height of center of gravity; Ckr
designate a roll rigidity sharing ratio (0 to 1) of the rear axle;
d designates a tread; and Fzr0 designate a rear wheel load at a
standstill.
[0136] If the final gear ratio is designated by Gf, the total drive
torque Tr of the rear axle is expressed by:
Tr=Te.multidot.Gt.multidot.(1-Ctc).multidot.Gf (20)
[0137] Hence, the following Formula is obtained:
Ttrf=Tr.multidot.(0.5-Xr) (21)
[0138] The transfer torque changing unit 76 receives the transfer
torque Ttrf from the grounding load response control unit 75 and
the target yaw moment Mz(t) from the target yaw moment setting unit
74. The transfer torque changing unit 76 computes a transfer torque
correction .DELTA.Ttrf from the following Formula (22) so that the
unit 26 controls the transfer clutch drive unit 27 with a transfer
torque Ttrf' (=Ttrf+.DELTA.Ttrf) corrected.
.DELTA.Ttrf=Mz(t)/(d.multidot.Rt) (22)
[0139] wherein Rt designates a tire diameter.
[0140] Thus, in this second embodiment: the road shape recognizing
unit 35 is constituted as a road shape recognizing unit; the
cornering decision unit 51 as a turning decision unit; the target
yaw rate setting unit 52 as a first target yaw rate setting unit;
the target yaw rate setting unit 71 as a second target yaw rate
setting unit; and the target yaw rate change designating unit 53 as
a target yaw rate correcting unit. The target yaw rate changing
unit 72, the yaw rate deviation computing unit 73, the target yaw
moment setting unit 74, the grounding load response control unit 75
and the transfer torque changing unit 76 has the left/right driving
force distribution setting unit, and the target deceleration
setting unit 54 has the functions of target lateral acceleration
setting unit and deceleration control unit.
[0141] Next, FIG. 8 is a flow chart showing a control
characteristics changing routine to be executed in the control
characteristics changing unit 50. First of all, at S101, the
necessary parameters are read in, and the routine advances to S102,
at which the first target yaw rate .gamma.c based on the curve
radius Rn is computed in the target yaw rate setting unit 52 by the
Formula (12). Then, the routine advances to S103, at which it is
decided in the cornering decision unit 51 whether or not the
steering angle .theta.H is equal to or larger than the presetted
value .theta.Hc.
[0142] If the steering angle .theta.H is equal to the set value
.theta.Hc, it is decided that the driver has the cornering will,
and the routine advances to S201. If the steering angle .theta.H is
smaller than the setted value .theta.Hc, it is decided that the
driver does not have the will for cornering, and the operations
leave the program.
[0143] If the routine decides the cornering will at S103 and
advances to S201, it reads the second target yaw rate .gamma.t
based on the driving conditions computed at the target yaw rate
setting unit 71 of the left/right driving force distribution unit
70, and advances to S105.
[0144] At S105, the first target yaw rate .gamma.c and the second
target yaw rate .gamma.t are compared in the absolute values. If
the absolute value .vertline..gamma.c.vertline. of the first target
yaw rate .gamma.c is larger than the absolute value
.vertline..gamma.t.vertline. of the second target yaw rate
.gamma.t, it is decided that the operation of the driver shorts
thereof for the actual road shape, and the routine advances to
S106. If the absolute value .vertline..gamma.c.vertline. of the
first target yaw rate .gamma.c is no more than the absolute value
.vertline..gamma.t.vertline. of the second target yaw rate
.gamma.t, it is decided that the operation of the driver is enough,
and the routine leaves the program.
[0145] If the routine decides at S105 that the operation of the
driver shorts thereof for the actual road shape and advances to
S106, the second target yaw rate .gamma.t is corrected by the
Formula (13) to increase/decrease to the first target yaw rate
.gamma.c, and the routine advances to S202, at which the corrected
second target yaw rate .gamma.t is outputted to the target yaw rate
changing unit 72 of the left/right driving force distribution unit
70. In short, the operations of S201, S105, S106 and S202 are done
(performed) at the target yaw rate designating unit 53.
[0146] After that, the routine advances to S108, at which the
target lateral acceleration Gyt is computed by the Formula (14) on
the basis of the corrected second target yaw rate .gamma.t', and
the routine further advances to S109.
[0147] At S109, the absolute value .vertline.Gyt.vertline. of the
target lateral acceleration Gyt and the absolute value
.vertline.Gy.vertline. of the actual lateral acceleration Gy are
compared. If the absolute value .vertline.Gyt.vertline.0 of the
target lateral acceleration Gyt is larger than the absolute value
.vertline.Gy.vertline. of the actual lateral acceleration Gy, it is
decided that a sufficient control is not made only by the
left/right driving force distribution unit 70, and the routine
advances to S110, at which the target deceleration Gxt is computed
by the Formula (15). At S111, this target deceleration Gxt is
outputted to the target slip ratio setting unit 46, and the routine
leaves the program. If it is decided at S109 that the absolute
value .vertline.Gyt.vertline. of the target lateral acceleration
Gyt is equal to or less than the absolute value
.vertline.Gy.vertline. of the actual lateral acceleration Gy, on
the other hand, the routine leaves the program without any further
operation. In short, the operations of S108 to S111 are done
(executed) at the target deceleration setting unit 54.
[0148] Thus, according to the second embodiment, compared are the
first target yaw rate .gamma.c based on the curve radius Rn and the
second target yaw rate .gamma.t based on the driving conditions. If
the absolute value .vertline..gamma.c.vertline. of the first target
yaw rate .gamma.c is larger than the absolute value
.vertline..gamma.t.vertline. of the second target yaw rate
.gamma.t, it is decided that the operation of the driver is
insufficient, and the control is made to approach the first target
yaw rate .gamma.c. Therefore, the deviation from the lane or the
road due to an improper operation of the driver can be prevented
without any unnatural feeling by reflecting the intention of the
driver to the maximum.
[0149] At this time, the absolute value .vertline.Gyt.vertline. of
the target lateral acceleration Gyt and the absolute value
.vertline.Gy.vertline. of the actual lateral acceleration Gy are
compared. If the absolute value .vertline.Gyt.vertline. of the
target lateral acceleration Gyt is larger than the absolute value
.vertline.Gy.vertline. of the actual lateral acceleration Gy, it is
decided that a sufficient control is not made only by the
left/right driving force distribution unit 70, and corrected is the
target slip ratio .lambda.t of the braking force control unit 60.
Therefore, it is possible to prevent the deviation from the lane or
the road due to the improper operation of the driver more
reliably.
[0150] According to the present invention, as has been described
hereinbefore, the deviation from the lane or the road due to the
improper operation of the driver can be prevented without any
unnatural feeling by reflecting the intention of the driver to the
maximum.
[0151] While the presently preferred embodiments of the present
invention have been shown and described, it is to be understood
that the disclosures are for the purpose of illustration and that
various changes and modifications may be made without departing
from the scope of the invention as set forth in the appended
claims.
* * * * *