U.S. patent application number 11/064734 was filed with the patent office on 2005-06-30 for method and device for recognizing cornering and for stabilizing a vehicle in case of over-steered cornering.
This patent application is currently assigned to Continental Teves AG & Co. oHG. Invention is credited to Batistic, Ivica, Schmidt, Holger.
Application Number | 20050143892 11/064734 |
Document ID | / |
Family ID | 27512629 |
Filed Date | 2005-06-30 |
United States Patent
Application |
20050143892 |
Kind Code |
A1 |
Batistic, Ivica ; et
al. |
June 30, 2005 |
Method and device for recognizing cornering and for stabilizing a
vehicle in case of over-steered cornering
Abstract
Methods and devices for detecting cornering and in particular
over-steered cornering, as well as a method and a device for
stabilizing a vehicle in case of an over-steered cornering maneuver
are described. The detection can be carried out with reference to
wheel slip values and/or transverse acceleration values. The
stabilization is carried out upon detection of the over-steered
cornering maneuver by means of suitable interventions in the brake
system.
Inventors: |
Batistic, Ivica;
(Wettenberg, DE) ; Schmidt, Holger; (Frankfurt
A.m., DE) |
Correspondence
Address: |
HONIGMAN MILLER SCHWARTZ AND COHN LLP
32270 TELEGRAPH RD
SUITE 225
BINGHAM FARMS
MI
48025-2457
US
|
Assignee: |
Continental Teves AG & Co.
oHG
|
Family ID: |
27512629 |
Appl. No.: |
11/064734 |
Filed: |
February 24, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11064734 |
Feb 24, 2005 |
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10437681 |
May 14, 2003 |
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6865469 |
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10437681 |
May 14, 2003 |
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09601704 |
Sep 21, 2000 |
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6580995 |
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09601704 |
Sep 21, 2000 |
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PCT/EP99/00689 |
Feb 3, 1999 |
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Current U.S.
Class: |
701/82 ;
701/72 |
Current CPC
Class: |
B60G 2800/016 20130101;
G01B 21/22 20130101; B60G 17/0195 20130101; B60G 17/0162 20130101;
B60G 2800/244 20130101; B60G 2204/11 20130101; B60G 2800/92
20130101; B60G 2400/104 20130101; B60G 2800/97 20130101; B60G
2400/208 20130101; B60G 2800/91 20130101; B60G 2800/70 20130101;
B60T 8/1755 20130101 |
Class at
Publication: |
701/082 ;
701/072 |
International
Class: |
G05D 001/00; B62D
007/09 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 7, 1998 |
DE |
198 04 953.6 |
Feb 7, 1998 |
DE |
198 04 941.2 |
Feb 7, 1998 |
DE |
198 04 956.0 |
Mar 14, 1998 |
DE |
198 11 149.5 |
Jul 20, 1998 |
DE |
198 32 484.7 |
Claims
1-59. (canceled)
60. Method for detecting an over-steered cornering maneuver of a
vehicle, comprising the steps of: determining of the wheel speeds
of several wheels and determining vehicle condition values,
detecting over-steered cornering with reference to one or more of
the determined vehicle condition values, wherein cornering is
detected, if the following condition is met: Sh-Sv>a, wherein Sh
is a value describing the vehicle condition, which has been
determined with reference to at least one vehicle condition value,
Sv being a value describing the vehicle condition, which has been
determined with reference to at least one vehicle condition value,
selecting reduction of the brake pressures or corresponding nominal
values on the wheels located towards the inside of the curve,
increasing the driving moment on the rear axle, changing the
response thresholds of braking assistance functions, wherein the
vehicle condition values are transverse acceleration for a front
and a rear axle of the vehicle.
61. Method according to claim 60, wherein the vehicle condition
values are transverse acceleration for a front and a rear axle of
the vehicle.
62. Method according to claim 61, further including detecting a
brake event.
63. Method according to claim 61, wherein an over-steered cornering
maneuver is detected, if the following condition is met:
Aqha-Aqva>b, Aqha being the transverse acceleration on the rear
axle, Aqva being the transverse acceleration on the front axle, and
b being a safety value.
64. Method according to claim 63, wherein the values that are used
as slip values or transverse acceleration values are averaged with
respect to time or integrated, whereby the averaging or integration
is carried out over a minimum period of time.
65. Method according to claim 64, wherein the minimum period of
time is between 250 and 500 ms.
66. Method according to claim 61, wherein the transverse
acceleration Aq of an axle is determined with reference to the
formula Aq=((Vr+Vl)(Vr-Vl))/(2d) Vr being the wheel speed of the
right wheel on this axle, Vl being the wheel speed of the left
wheel on this axle, and d being the track on this axle.
67. Method according to claim 61, wherein the curve direction is
determined by comparing the slip values or wheel speed values of at
least one left wheel with the values of at least one right wheel,
considering preferably the wheels of the non-driven axle.
68. Device for detecting an over-steered cornering, comprising: a
first detecting device for detecting the wheel speeds of several
wheels, and a second detecting device for detecting the vehicle
condition, and a third detecting device for detecting over-steered
cornering with reference to several of the determined vehicle
condition values, wherein the third detection device detects
over-steered cornering, if the following condition is met:
Sh-Sv>a Sh being a value describing the vehicle condition which
has been determined with reference to at least one vehicle
condition value, Sv being a value describing the vehicle condition
which has been determined with reference to at least one vehicle
condition value, and a being a safety value, a device for
selectively reducing the brake pressures or the corresponding
nominal values on the wheels located towards the inner side of the
curve, a device for increasing the driving moment of the rear axle,
a device for changing a response threshold of a braking assistance
function, wherein the vehicle condition values are transverse
acceleration for a front and a rear axle of the vehicle.
69. Device according to claim 68, further including an interrupting
device which interrupts the detection of over-steered cornering, if
a brake intervenes.
70. Device according to claim 68, wherein said third detecting
device detects over-steered cornering, if the following condition
is met: Aqha-Aqva>b Aqha being the transverse acceleration on
the rear axle, Aqva being the transverse acceleration on the front
axle, and b being a safety value.
71. Device according to claim 70, further including a device which
produces an average value or an integral value used as wheel speed
values or slip values, the averaging or integration being carried
out over a minimum period of time.
72. Device according to claim 71, wherein the minimum period of
time is between 250 and 500 ms.
73. Device according to claim 68, wherein said second detecting
device determines the transverse acceleration of Aq of the center
of the axle with reference to the formula Aq=((Vr-Vl)(Vr-Vl))/(2d)
Vr being the wheel speed of the right wheel on this axle, Vl being
the wheel speed of the left wheel on this axle, and d being the
track on this axle.
74. Device according to claim 68, wherein the direction of the
curve is determined by comparing the slip values or wheel speed
values of at least one left wheel with those of at least one right
wheel.
75. Device according to claim 68, further including a selection
device for selecting the output of the second detecting device, if
relatively low transverse accelerations or wheel slip values are
determined, and failing this selecting the output of the third
detecting device.
76. Device according to claim 68, further including a device for
producing a test value according to one or several transverse
acceleration values or one or several wheel slip values, the test
value being compared with a threshold value.
Description
RELATED APPLICATIONS
[0001] The present application is a divisional patent application
of U.S. Ser. No. 10/437,681, filed May 14, 2003, now U.S. Pat. No.
______, issued ______, which is a divisional patent application of
U.S. Pat. No. 6,580,995 issued Jun. 17, 2003.
TECHNICAL FIELD
[0002] The present invention relates to a method and a device for
recognizing cornering, especially over-steered cornering, and for
stabilizing a vehicle in case of over-steered cornering.
BACKGROUND OF THE INVENTION
[0003] A cornering maneuver can be recognized by different sensors,
for example, steering angle sensors or transverse acceleration
sensors, but the additional expenditure for the sensors also
increases the expenditure for the cabling, the costs and the
failure probability. Thus, there are applications in which it is
desirable that cornering be detected without additional sensors. By
the way, it is often difficult to recognize over-steered cornering,
which is understood as a cornering maneuver in which the vehicle
turns into a curve around its vertical axis to an extent exceeding
the extent that would be necessary or, more generally speaking, in
which a vehicle drives to the outer side of the curve with its
tail. In the extreme case, we are talking about a swerving car in
the broadest sense of the word. The present invention considers in
particular also the extreme cases in which an over-steering exists
only to a relatively small extent, for example, at the beginning of
the vehicle's swerving. It is difficult to recognize an
over-steered cornering maneuver just in these cases so that the
over-steered behavior is increasing slowly until finally the
vehicle is completely unstable. Conventional methods for
recognizing over-steered cornering are not very useful due to the
limited transverse dynamics in the limit range, so that the
response thresholds for stabilizing interventions are not reached.
Thus, a stabilizing brake intervention, which in principle would be
possible, is omitted due to the lacking or delayed recognition of
the over-steered cornering maneuver.
SUMMARY OF THE INVENTION
[0004] It is the object of the present invention to provide methods
and devices for recognizing cornering, especially over-steered
cornering, as well as for stabilizing a vehicle during an unstable
cornering maneuver, which are sensitive, reliable and manage
without additional expenditure for sensors, if necessary.
[0005] Before describing single embodiments of the invention, basic
relations of a vehicle in which the present invention can be
applied are illustrated with regard to FIG. 1 and FIG. 2. FIG. 1
schematically shows a vehicle. Reference numerals 101 to 104 are
the wheels of the vehicle, reference numeral 101 being the left
front wheel, reference numeral 102 the right front wheel, reference
numeral 103 the right rear wheel and reference numeral 104 the left
rear wheel. Reference numeral 105 is the front axle, reference
numeral 106 the rear axle. Reference numerals 111 to 114 are the
wheel sensors detecting the wheel speed of the single wheels,
particularly the rotating speed. Reference numerals 121 to 124
symbolize the wheel brakes. The output signals of the wheel sensors
111 to 114 are transmitted to a control 130. Furthermore, the
control can also receive signals of additional sensors 115 to 117.
In addition, the control 130 produces output signals 131 with which
the longitudinal dynamics and/or the transverse dynamics of the
vehicle can be influenced. Thus, they produce in particular signals
for the wheel brakes 121 to 124 in order to adjust the brake
pressure. In addition, signals can be produced which influence the
driving torque and, if necessary, also the automatic
transmission.
[0006] If a vehicle drives around a corner transverse forces (with
regard to the longitudinal axis of the vehicle) have to be produced
counteracting on the one hand to the centrifugal force resulting
from cornering, and on the other hand to the moment of inertia of
the vehicle itself during steering. The wheels transmit these
forces to the vehicle. If the vehicle is stable the transverse
forces resulting from this process can be transmitted by means of
the static friction between roadway and tire. If the vehicle is
unstable and in particular if it is over-steered, the transverse
forces that are actually necessary are bigger than the forces that
can be transmitted due to the static friction between roadway and
wheels.
[0007] FIG. 2 describes the case that might appear in an
over-steered left-hand curve. In FIG. 2, the left front wheel is
shown. The same reference numerals as in FIG. 1 indicate the same
components. Reference numeral 111 is the wheel sensor, reference
numeral 111a is a marking disc which follows the wheel 101 and
helps determining the rotating speed of the wheel 101. The speed of
the wheel (and vehicle as described below) on the roadway is marked
Vf. It is not oriented parallel to the wheel plane (vertical to the
wheel axis) but extends at an angle, .alpha., to the wheel plane.
FIG. 2 shows the case of a wheel that is not braked. In this case,
it can be assumed that the speed of the wheel in the wheel plane
(vertical to the wheel axis) corresponds to the speed component of
the wheel on the roadway (because the wheel can freely roll). As a
result, the vehicle speed, Vf, can be determined from the vectorial
addition of the longitudinal component, Vl, and the transverse
component, Vq. More specifically, if there is a difference between
the vehicle speed Vf and the longitudinal component, Vl (detected
by the wheel sensors), then the difference can be attributed to a
transverse component, Vq. This is valid both for the vectorial
approach as also for the approach by the absolute amount.
[0008] Furthermore, it was established that during each cornering
(i.e. ultimately also if a cornering maneuver is considered as
stable) there is a transverse component--even if it is small--so
that during each cornering, whether stable or over-steered, a
transverse component is produced. Thus, a speed difference between
the vehicle speed, Vf, and the longitudinal component, Vl (slip).
The slip (difference between vehicle speed, Vf, and longitudinal
component, Vl, or the difference between their absolute amounts)
can be produced on different wheels, according to the driving
situation.
[0009] According to the present invention, cornering is determined
with reference to several slip values on several vehicle wheels.
Also, an over-steered cornering maneuver can be determined with
reference to several slip values on several vehicle wheels.
According to the present invention, over-steered cornering can also
be determined with reference to the transverse accelerations of the
vehicle axles. According to another aspect of the present
invention, over-steered cornering can be determined in a
particularly reliable way if the determination based on the wheel
slip values and the determination based on the transverse
accelerations of the axles are combined with each other. If
over-steered cornering has been detected, according to the present
invention one or more measures supporting stability can be
taken.
[0010] In the following single embodiments of the invention are
described on the basis of the figures, whereby:
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 shows schematically a vehicle in which the invention
can be applied,
[0012] FIG. 2 shows a representation illustrating physical
relationships,
[0013] FIG. 3 shows an embodiment of a device for detecting a
cornering maneuver,
[0014] FIG. 4 shows a device for detecting over-steered
cornering,
[0015] FIG. 5 shows another device for detecting over-steered
cornering,
[0016] FIG. 6 shows another device for detecting over-steered
cornering, and
[0017] FIG. 7 shows the qualitative development of different
values.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] FIG. 3 shows a device for detecting a cornering maneuver.
The same reference numerals as in FIG. 1 indicate the same
components. Reference numerals 111 to 114 are the wheel sensors
that are designed in a block-type manner, but are, in fact,
foreseen for each single wheel. They also correspond to a first
detecting device.
[0019] Reference numerals 302a to 302d is a second detecting device
with which the slip value is determined, preferably for all the
wheels of the vehicle. It is the second detecting device that
preferably receives a signal designating the vehicle speed, Vf. The
signal representing the vehicle speed, Vf, is preferably determined
and made available by a third detection device 303. The device may
be another sensor or even a more complex elaboration device
determining a signal, for example from the signals of the wheel
sensors 111 to 114 by means of suitable strategies.
[0020] In the second detecting device 302a to 302d, the difference
between the vehicle speed and the wheel speed can be determined for
the single wheels so that the slip values for each wheel can be
output.
[0021] Furthermore, suitable pre-processing or post-processing of
the signals 301 can be foreseen. In general, the wheel sensors 111
to 114 provide a more or less high-frequency sequence of pulses.
This can be processed in such a way that a (preferably digital)
signal is generated which directly characterizes the wheel speed.
In addition, filter functions can be implemented to possibly filter
faults and fluctuations. For example, the averaging or integration
over a certain period of time may be foreseen. Observation periods
between 250 and 500 ms, and preferably between 280 and 350 ms, have
resulted advantageous for the averaging or integration. The signal
processing 301 can be foreseen at suitable points in the signal
flow. Thus, for example, the signals coming from the wheel sensors
111 to 114 can be processed or filtered. In addition, the output
signals of the second detecting device can be processed in such a
way, as indicated by the dashed box below 302a.
[0022] Reference numeral 300 is a first detection device
recognizing cornering with reference to several, preferably to all
of the determined slip values. If a cornering maneuver is
recognized, the device can output signals 304 that are received and
further processed by other components/braking functions 305. The
signals 304 are preferably shaped in such a way that the three
cases "curve left", "curve right", no "curve" can be distinguished.
The first detection device 300, as well as the other
components/braking functions 305, can further receive signals that
are shown or not shown to be necessary for realization by signal
processing. In the Figure, the reception of the external sensor
signals 115 to 117 is represented. In addition, the wheel speed
signals and other internal signals can be received.
[0023] The first detection device 300 recognizes a left curve, if
one or more of the following conditions are met:
Shl-S0.gtoreq.Shr-S0,
Svl-S0>0
Svr-S0=0,
[0024] and recognizes a right curve, if one or more of the
following conditions are met at the same time:
Shr-S0.gtoreq.Shl-S0,
Svr-S0>0
Svl-S0=0,
[0025] Shl is the slip on the left-hand rear wheel, Shr is the slip
on the right-hand rear wheel, Svl is the slip on the left-hand
front wheel, Svr is the slip on the right-hand front wheel and S0
is a slip correction value.
[0026] The first condition with one of the two conditions mentioned
afterwards is preferably used for the left-hand or right-hand curve
in order to recognize cornering in one direction. All three
conditions are also preferably used for recognizing cornering in
respectively one direction.
[0027] As already mentioned, the above mentioned conditions can be
examined by means of integrated and averaged slip values with
respect to time. It is in particular desirable that for detecting a
left-hand curve, the integration period for the slip on the
left-hand rear wheel is longer than the integration period
mentioned above. The same applies with regard to the slip on the
right-hand rear wheel for detecting a right-hand curve.
[0028] The slip correction value, S0, is a correction value
eliminating small errors. For example, it can be determined as a
fraction of the vehicle speed, Vf, and/or according to the
transverse acceleration, Aq. The slip correction value, S0, is
preferably between 0.1% and 1% of the vehicle speed, Vf, and also
preferably between 0.4% and 0.6% of the vehicle speed, Vf. The slip
correction value, S0, can also depend on the transverse speed, Aq,
as shown in FIG. 7, in a qualitative manner (S0 decreases with
increasing Aq). Furthermore, it is pointed out, that S0 does not
have to be the same, identical value for all the wheels or all the
conditions. Rather, different slip correction values S0 can be used
for different values or different conditions. In this case, a
single variable was used only in order to simplify the
representation.
[0029] If averaged/integrated values are used for examining the
above mentioned conditions, the slip correction value, S0, has to
be adjusted in a suitable manner or to be included in the
averaging/integration. Thus, the respective integral value
considered would not only be defined by means of the considered
slip value, but by means of the difference between slip value and
slip correction value.
[0030] The first detection device 300 can consider a left-hand
curve as completed, if one or both of the following conditions are
met:
Shl-S0<Shr-S0
Shl-S0=0
[0031] and consider a right-hand curve as completed, if at least
one of the following conditions is met:
Shr-S0<Shl-S0
Shr-S0=0
[0032] The considered values are defined as illustrated above.
[0033] The application of a slip correction value leads to the fact
that only major values can lead to a detection. The comparison of
the wheels of an axle, preferably of the axle which is not driven,
that is used for detecting the curve is based on the finding that
the wheel located toward the inner side of the curve shows slip
values greater than or equal to the slip values of the wheel
located toward the outer side of the curve. The other conditions
serve for excluding disturbing conditions.
[0034] The curve recognition described above is preferably realized
only if the vehicle is not braked. In this case, it is assured that
the slip values that have been determined are those of a wheel
rolling freely and are not falsified by the slip due to
interventions of the brake. If the slip values are compared by
axle, in general the slip values of the wheels on the non-driven
axle are preferably used because in this case there can be no
falsifications due to the slip produced by the vehicle drive.
[0035] With the method described above and the device suitable for
realizing the method, it is possible to determine a curve in a
reliable manner without having to use a steering angle sensor, yaw
rate sensor or transverse speed sensor. The detection result output
by the signal lines 304 of the first detection device 300 is
transmitted to other components/braking functions 305 that can be
braking functions in the broadest sense of the word, for example,
ABS, braking assistance functions, or the like.
[0036] With regard to FIG. 4, a method for detecting over-steered
cornering is described in a device for realizing the method.
Identical reference numerals as in FIG. 3 indicate identical
components with the same functions that are not described again in
order to eliminate repetitions.
[0037] FIG. 4 shows a second detection device 400 detecting
over-steered cornering with relation to several of the determined
slip values. It can output signals 304 being formed as shown in
FIG. 3. In other components/braking functions 305 of the control
130, the signals 304 can be considered in a suitable manner.
[0038] The second detection device 400 can detect over-steered
cornering, if the condition
Sh-Sv>a
[0039] is met, whereby Sh is a value describing the slip behavior
on the rear axle, Sv is a value describing the slip behavior on the
front axle and the value, a, is a safety value.
[0040] Sh can be determined with relation to at least one slip
value, preferably with respect to the slip values of both wheels on
the rear axle, for example, as an average value. The same applies
analogously to the value Sv.
[0041] Over-steered cornering can be detected as completed, if at
least the first, preferably more or all of the following conditions
are met:
Sh-Sv<s
Sh-Sv>-s
Sha<Sva.
[0042] Sh and Sv are defined as above, Sha and Sva are the slip
values of the front and rear wheels on the outside,
respectively.
[0043] The condition used for detecting over-steered cornering is
based on the finding that in case of over-steered cornering, the
slip behavior of the rear axle due to different influences is
bigger than that of the front axle, for example, reflected by the
average slip of the wheels on this axle.
[0044] In order to exclude incorrect detections, the safety value,
a, is introduced. Then an over-steered cornering is detected only
if there is a major difference between the slip behavior on both
axles. The safety value, a, can be a constant or determined
according to the vehicle speed and/or according to the calculated
or measured transverse acceleration, Aq. FIGS. 7b and 7c show the
qualitative dependences for the safety value, a. Based on a lowest
limit value for transverse acceleration, Aq, equal to 0, the safety
value, a, may increase along with the transverse acceleration, Aq.
In addition, the safety value, a, can decrease with increasing
vehicle speed, Vf, towards a limit value.
[0045] The conditions for detecting, if an over-steered cornering
maneuver is completed, are chosen in such a way that slip
differences between front and rear axles that fall within a certain
range, defined by a threshold value, s, are no longer considered as
an over-steered cornering maneuver. The threshold value, s, can be
determined according to the vehicle speed, Vf, and amounts to
values from 0.5% to 1% of the vehicle speed, Vf. The safety value,
a, and the threshold value, s, are chosen with regard to each other
in such a way that the result is a hysteresis-type behavior with
regard to detecting an over-steered cornering maneuver.
[0046] The direction of the curves can be determined by other
conditions, for example, by means of the device described in FIG. 3
or by a suitable sensor.
[0047] In FIG. 4, reference numerals 401 and 402 are devices for
producing the average value with which the average of the slip
values on the front axle or on the rear axle is determined. The
difference is produced in device 403. In device 405, the difference
is compared with the safety value, a, or the threshold value, s,
whereby the safety value, a, and the threshold value, s, are
determined in device 404 according to further operating states.
[0048] The method described in FIG. 4 can be interrupted if the
brake intervenes. In case of brake interventions, it is also
possible to carry out the conditions above for detecting the
over-steered cornering with reference to the slip values of the
front and rear wheels located towards the outside of the curve. The
value describing the slip behavior of an axle is no longer the
average value, but a value based on the slip behavior of the wheel
located towards the outside of the curve. This procedure is based
on the finding that due to the rolling moment of the vehicle around
its longitudinal axis in a curve, the wheels located towards the
outside of the curve are stressed in a more intensive manner, and
thus are subjected to a lower amount of slip due to the braking
maneuver, therefore rarely presenting disturbed signals for the
detection of the over-steered cornering according to the present
invention. In an alternative embodiment of FIG. 4, the wheel speeds
also can be used directly because the subtraction of the vehicle
reference speed from the wheel speeds is eliminated in the
difference 403. Therefore, the production of wheel slip values is
only necessary to the extent that it is needed by other components
or functions. Otherwise, it can be omitted.
[0049] The detection of over-steered cornering described above is
based on the finding that the axial speed component Vq which is not
detected increases according to Vq=Vf.multidot.sin .alpha. with
increasing king pin inclination of the wheel (.alpha. in FIG. 2),
while the longitudinal component Vl according to Vl=Vf.multidot.cos
.alpha. detected in the wheel plane declines. Thus, the slip, for
example, the difference (in absolute values) resulting between the
vehicle speed Vf and the longitudinal component Vl is a measure for
the king pin inclination so that it can be used for evaluating the
over-steering behavior.
[0050] Up to now, the detection of an over-steered cornering
maneuver has been described with reference to the slip values of
the vehicle wheels, but instead of the slip values, the wheel speed
values can also be used for the examination.
[0051] With regard to FIG. 5, another embodiment for determining
over-steered cornering is described. The same reference numerals as
in FIG. 3 indicate the same components that are not described for
brevity.
[0052] The over-steered cornering maneuver of a vehicle can also be
determined based on the transverse accelerations of the vehicle's
axles, the transverse acceleration being the acceleration
approximately in the direction of the radius of the curve, and
thus, also approximately in the direction of the axle. The
transverse acceleration, Aq, can be determined in approximation by
equating the formula for the centrifugal force
(F=m.multidot.v.sup.2/r) with the general formula for the force on
a mass which is to be accelerated (F=m.multidot.a). Thus, results
Aq=v.sup.2/r. Based on a more precise consideration of the
geometric relations in a curve, the transverse acceleration on an
axle can be expressed by
Aq=((Vr+Vl)(Vr-Vl))/(2d),
[0053] whereby, Vr is the wheel speed of the right wheel on the
axle, Vl is the wheel speed of the left wheel on said axle and the
value, d, is the track on the axle. Thus, the transverse
acceleration on the axle can be determined with reference to the
wheel speeds on the axle, the center of the axle being the
mathematically exact point of the determined transverse
acceleration, which is a useful hypothesis for the purpose of the
detection procedure that has to be described.
[0054] Furthermore, the finding is used that in case of an
over-steered driving behavior, the transverse acceleration on the
rear axle is generally bigger than the transverse acceleration on
the front axle.
[0055] Thus, the over-steered driving behavior can be determined by
comparing the transverse acceleration of the rear axle with the
transverse acceleration of the front axle. Over-steered cornering
can be detected, for example, if the condition
Aqha-Aqva>b
[0056] is met, Aqha is the transverse acceleration on the rear
axle, Aqva is the transverse acceleration on the front axle and the
value, b, is a safety value.
[0057] The safety value, b, is introduced into the conditions in
order to separate accidental small deviations resulting from
detecting inaccuracies, because these should not lead to the
detection of an over-steered cornering. The safety value, b, can be
in the range between 5% and 10% of the determined transverse
accelerations Aq, but at least between 0.1 g and 0.2 g. FIG. 7d
shows qualitatively the possible development of the safety value,
b.
[0058] FIG. 5 shows a fourth detection device 501, 502 with which
the transverse accelerations for the front and rear axles can be
determined. These values are transmitted to the third detection
device 500 that carries out the comparison, for example, based on
the condition mentioned above. The signals 304 can be output as
described above as a result of the detection. The determined
transverse accelerations are preferably compared according to their
absolute value. The direction of the curve can be determined by
suitable further conditions or, for example, also by the method or
the device according to FIG. 3. A sensor may be used too.
[0059] As already mentioned above, a suitable signal processing may
be carried out at the beginning and/or for intermediate results,
for example the determined transverse accelerations, in order to
detect the over-steered cornering maneuver according to the present
invention. In FIG. 5, this is again indicated by reference numeral
301, whereby the indicated devices can be foreseen individually or
in combination with each other.
[0060] The determination of over-steered cornering based on the
transverse acceleration is particularly suitable for cornering with
high transverse dynamics, that is, with high transverse
acceleration. In this case, the transverse acceleration can, on the
one hand, be calculated with a satisfactory accuracy. On the other
hand, problems may arise due to the wheel slips when over-steered
cornering is detected.
[0061] FIG. 6 shows an embodiment according to the present
invention, in which the detections according to FIG. 4 and FIG. 5
are combined with one another, and represents the second detection
device 400 of FIG. 4 detecting over-steered cornering with
reference to the wheel slips and the third detection device 500 of
FIG. 5 detecting over-steered cornering with reference to the
transverse accelerations of the vehicle axles. The same components
as in the corresponding position in FIG. 4 are located above the
second detection device 400. The same applies analogously for the
components above the third detection device 500. Resources that are
required by both devices, for example, signal processors, do not
need to be provided twice, but can be used in common.
[0062] Generally, the detection result of one of the two detection
devices can be preferred or chosen. For this reason, a selection
device 600 is foreseen choosing and transmitting either the
detection result of the second detection device 400 or the
detection result of the third detection device 500. The selection
may be carried out according to further operating states of the
vehicle. In particular, in case of a relatively low transverse
acceleration or also in case of relatively small wheel slip values,
the detection of the over-steered cornering with regard to the
wheel slip values may be preferred or chosen. In the case of higher
transverse accelerations or higher wheel slip values, the detection
of over-steered cornering with reference to the transverse
accelerations may be preferred.
[0063] FIG. 6 shows a device 604 producing a test value, the test
value being produced according to the operating states of the
vehicle mentioned above, and in particular according to the
transverse accelerations and/or according to the wheel slips. In a
comparison device 601 of the selection device 600, the test value
can be compared with a threshold value. Based on the comparison,
for example, the second detection device 400 or the third detection
device 500 can be chosen. FIG. 6 shows the commutators 602, 603
choosing either two outputs at a time of the one or the other
detection device and transmitting them, as described above, to the
other components/brake functions 305.
[0064] The detection by combination of the methods described with
reference to FIG. 6, as based on FIGS. 4 and 5, has the advantage
that well adjusted detection procedures are chosen for single
operative states of the vehicle. On the one hand, this permits the
detection of over-steered cornering in a reliable manner, but on
the other hand to avoid error detections in a reliable manner.
[0065] If over-steered cornering has been detected, as described
above, different measures may be taken individually or in
combination with each other.
[0066] A curve-outward moment acting around the vertical axis of
the vehicle may be generated by reducing or building up the brake
pressure with less force/speed (gradient) or a nominal value on one
or more of the wheels located on the inner side of the curve. Then,
the brake force on the wheel located on the outside of the vehicle
increases so that also the curve-outward moment increases (or a
curve-inward turning moment declines). This counteracts to the
over-steering tendency (acting curve-inwardly).
[0067] The increase of the driving moment when towing the vehicle
has a similar effect, especially on the rear axle. This also has a
stabilizing influence counteracting the over-steering tendency.
[0068] Finally, it is possible to change in general the reaction
thresholds for assistance functions. Subject to the fact whether
the braking assistance functions have a positive or negative effect
on over-steered cornering, the corresponding reaction thresholds
may be reduced or increased so that the single functions are more
sensitive or less sensitive. This helps inducing favorable
influences from higher braking assistance functions and avoiding
unfavorable influences.
[0069] The intervention possibilities described above may be
carried out in the other components/braking functions 305 according
to the signals 304. They influence the output signals 131 that
influence the driving behavior of the vehicle.
* * * * *