U.S. patent application number 10/534096 was filed with the patent office on 2006-09-14 for method and device for stabilizing a vehicle combination.
This patent application is currently assigned to Continental Teves AG & CO. oHG. Invention is credited to Jurgen Krober, Dirk Waldbauer, Dirk Waldbauer.
Application Number | 20060204347 10/534096 |
Document ID | / |
Family ID | 32308518 |
Filed Date | 2006-09-14 |
United States Patent
Application |
20060204347 |
Kind Code |
A1 |
Waldbauer; Dirk ; et
al. |
September 14, 2006 |
Method and device for stabilizing a vehicle combination
Abstract
Method and Device for Stabilizing a Car-Trailer Combination A
method and device for stabilizing a car-trailer combination,
including a towing vehicle and a trailer moved by the towing
vehicle, is disclosed. The rolling motions of the towing vehicle
are monitored and measures that stabilize driving are preformed
upon detection of an actual or expected unstable driving condition
of the towing vehicle or the car-trailer combination. In order to
insure a proper intervention, the yaw velocity of the towing
vehicle or the car-trailer combination is detected and the measures
that stabilize driving conditions are controlled dependent upon the
detected yaw velocity.
Inventors: |
Waldbauer; Dirk; (Eppstein,
DE) ; Krober; Jurgen; (Winningen, DE) |
Correspondence
Address: |
CONTINENTAL TEVES, INC.
ONE CONTINENTAL DRIVE
AUBURN HILLLS
MI
48326-1581
US
|
Assignee: |
Continental Teves AG & CO.
oHG
|
Family ID: |
32308518 |
Appl. No.: |
10/534096 |
Filed: |
November 7, 2003 |
PCT Filed: |
November 7, 2003 |
PCT NO: |
PCT/EP03/50802 |
371 Date: |
March 17, 2006 |
Current U.S.
Class: |
410/156 |
Current CPC
Class: |
B60T 7/20 20130101; B60T
8/1708 20130101; B60T 8/248 20130101; B60T 2230/06 20130101; B60T
8/1755 20130101 |
Class at
Publication: |
410/156 |
International
Class: |
B61D 45/00 20060101
B61D045/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 8, 2002 |
DE |
102 52 510.2 |
Claims
1-17. (canceled)
18. A method for stabilizing a car-trailer combination, including a
towing vehicle and a trailer moved by the towing vehicle, the
method comprising: monitoring rolling motions of the towing vehicle
including yaw velocity of the vehicle; detecting an actual or
expected unstable driving condition of the towing vehicle or the
car-trailer combination; and performing measures to stabilize the
driving condition, wherein the measures that stabilize driving are
controlled dependent on a differential value that is produced from
the monitored yaw velocity and a model-based yaw velocity and
evaluated according to criteria indicative of an unstable driving
performance.
19. The method according to claim 18 further comprising:
determining a frequency and an amplitude of each half wave of the
differential value; comparing the determined frequency and
amplitude with stored values; and evaluating the rolling motion of
the car-trailer combination dependent on the result of the
comparison.
20. The method according to claim 19, the frequency is determined
from zero crossings and a time between two zero crossings of the
differential value.
21. The method according to claim 19 further comprising: counting a
number of the half waves of the differential value, where the
amplitude of each half wave reaches or exceeds a threshold value,
and where each positive and negative half wave of the determined
frequency lies within a band defined by a top and a bottom
threshold value; and initiating measures that stabilize driving
when a threshold value representative of a number of half waves is
reached or exceeded.
22. The method according to claim 21, wherein the threshold value
representative of a number of half waves is determined in
dependence on the frequency.
23. The method according to claim 22, wherein at low frequencies,
the threshold value is reached or exceeded with a smaller number of
half waves than is the case at a high frequency.
24. The method according to claim 22, wherein the threshold value
of each half wave representative of the amplitude is determined at
least in dependence on quantities that represent the velocity of
the towing vehicle or the car-trailer combination or the
trailer.
25. The method according to claim 24, wherein with quantities
describing a high speed, the threshold value is reached or exceeded
at lower amplitudes than with quantities describing a low
speed.
26. The method according to claim 21, wherein only a consecutive
number of half waves of the differential value is counted, where
the amplitude of each half wave reaches or exceeds an entry
threshold value, and in that the measures that stabilize driving
are terminated when values reach or fall below only one exit
threshold value ranging below the entry threshold value.
27. The method according to claim 18, wherein data is produced from
a variation of the differential value.
28. The method according to claim 18, wherein the differential
value is weighted with a value, which is produced in dependence on
a steering angle velocity or a steering angle acceleration or the
model-based yaw rate.
29. The method according to claim 18, wherein lateral acceleration
is detected and the variation of the lateral acceleration is
evaluated according to criteria which allow checking plausibility
of the data obtained from the variation of the differential value
and being assessed according to criteria indicative of an unstable
driving performance.
30. The method according to claim 29, wherein a maximum and minimum
values of the lateral acceleration and temporal distances of the
maximum and minimum are determined, a frequency is determined and
the determined frequency is compared with the frequency of the
differential value.
31. The method according to claim 29 further comprising:
discontinuing the measures that stabilize driving when at least one
of the following conditions is satisfied: a frequency of a lateral
signal, in particular the lateral acceleration, and/or the
differential value reaches or exceeds or, respectively, falls below
a top or a bottom threshold value; a frequency of the lateral
signal changes in relation to the frequency of the differential
value towards a top or a bottom limit value; an absolute value of
an average value of the lateral signal exceeds a threshold value.
an amplitude of the lateral signal decreases with a high gradient;
and a difference between the maximum and minimum values of the
lateral signal lies in a narrow band.
32. The method according to claim 29, wherein a phase shift between
the lateral acceleration and the differential value is determined
and evaluated according to criteria that permit defining driving
situations.
33. The method according to claim 32, wherein the measures that
stabilize driving are discontinued or the method is terminated,
respectively, when a threshold value indicative of a great phase
shift is exceeded.
34. A device for stabilizing a car-trailer combination, including a
towing vehicle and a trailer moved by the towing vehicle, wherein
the towing vehicle is monitored in terms of rolling motions and
measures that stabilize driving are taken upon the detection of an
actual or expected unstable driving performance of the towing
vehicle or the car-trailer combination, the device comprising: a
driving stability control having at least a yaw rate sensor for
sensing the yaw velocity and a vehicle model for producing a
reference yaw velocity; a determining unit for determining a
differential value from the yaw velocity and the reference yaw
velocity; and a control unit controlling measures that stabilize
driving dependent on data being obtained from the variation of the
differential value and evaluated according to criteria indicative
of an unstable driving performance.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method and a device for
stabilizing a car-trailer combination, including a towing vehicle
and a trailer moved by the towing vehicle, wherein the towing
vehicle is monitored in terms of rolling motions and measures that
stabilize driving are taken upon the detection of an actual or
expected unstable driving performance of the towing vehicle or the
car-trailer combination.
BACKGROUND OF THE INVENTION
[0002] The present method aims at detecting and controlling the
instabilities of car-trailer combinations (motor vehicle with
trailer), especially of combinations consisting of a passenger car,
pickup truck or sport-utility vehicle and any trailers desired, in
particular caravans, before driving conditions are encountered
during which the driver can no longer maintain control of the
vehicle. These unstable conditions involve the rolling motions
known with car-trailer combinations and the anti-phase build-up
process between the towing vehicle and the trailer as well as
imminent roll-over conditions at too high lateral accelerations
caused by obstacle avoidance maneuvers, lane changes, side wind,
road irregularities and/or hasty steering maneuver requests by the
driver.
[0003] Depending on the driving speed, the oscillations can decay,
remain constant, or increase (undamped oscillation). When the
oscillations remain constant, the car-trailer combination has
reached the critical velocity. Above this speed threshold a
car-trailer combination is unstable, below said threshold it is
stable, that means, possible oscillations die out.
[0004] The magnitude of this critical speed depends on the geometry
data, the tire rigidities, the weight and the distribution of
weight of the towing vehicle and the trailer. Further, the critical
speed is lower in a braked driving maneuver than at constant
travel. In turn, it is higher during accelerated driving than at
constant travel.
[0005] Corresponding methods and devices are known in various
designs (DE 199 53 413 A1, DE 199 13 342 A1, DE 197 42 707 A1, DE
100 34 222 A1, DE 199 64 048 A1).
[0006] DE 197 42 707 C2 discloses a device for damping rolling
motions for at least one trailer towed by a towing vehicle, wherein
the angular velocity of the trailer about the instantaneous center
of rotation or the articulated angle about the instantaneous center
of rotation is sensed and differentiated and taken into
consideration for controlling the wheel brakes of the trailer.
Acceleration sensors at different locations are used as sensors for
the angular velocity. DE 199 64 048 A1 also provides a lateral
acceleration sensor or a yaw rate sensor by means of which the
rolling motion is determined. After the signal is evaluated, a
periodic yawing torque shall be applied to the vehicle. DE 100 34
222 A1 determines a time for a braking intervention correct in
phase, being realized in dependence on the quantity of frequency
and the phase magnitude of the rolling motion.
[0007] In addition, it is known from EP 0 765 787 B1 to take
measures that decelerate driving when the amplitude of a vehicle
quantity related to transverse dynamics and swinging within a
frequency range exceeds a predetermined limit value and when a
steering motion quantity does not exceed a predetermined threshold.
In this case, likewise the lateral acceleration and/or the yaw
velocity (yaw rate) is taken into consideration as a vehicle
quantity measured on the vehicle.
[0008] In doing so, it is necessary to monitor the steering angle
with respect to a predetermined threshold in order to take the
measures that decelerate the vehicle only when the steering angle
is as constant as possible.
[0009] Hence, the stabilization strategy of all design variants can
be summarized as follows: [0010] Detection of the rolling motion by
evaluating the sensor data, with all sensors being favorably
accommodated in the towing vehicle or the trailer; [0011] When an
unstable situation is detected, the vehicle is slowed down by
reducing the engine torque and building up pressure in the wheel
brakes of the towing vehicle; [0012] Additionally or alternatively
a torque about the vertical axis of the towing vehicle is applied,
said torque counteracting the force transmitted from the trailer to
the towing vehicle and, thus, damping the oscillation.
[0013] The detection of the rolling motion of a car-trailer
combination is mainly based on the fact that the yaw rate or
lateral acceleration shows an almost sinusoidal variation, the
frequency of which lies in a typical band, without the driver
performing corresponding steering movements that would cause the
observed variation of lateral quantities. It is problematic with
this detection strategy that there are still other maneuvers
generating similar variations of signals. Thus, sprung-mass
vibrations may be produced, e.g. during cornering with a constant
steering angle, which also induce sinusoidal variations of lateral
quantities. Another possibility of obtaining such variations of
lateral quantities is to drive over rough roadways, in particular
wavy road sections, especially bumps on alternating sides.
SUMMARY OF THE INVENTION
[0014] An object of the invention is to provide a method and a
device permitting the reliable detection of unstable driving
performance.
[0015] According to the invention, this object is achieved in that
the yaw velocity is detected and measures that stabilize driving
are controlled dependent on a differential value that is produced
from the detected yaw velocity and a model-based yaw velocity and
evaluated according to criteria indicative of an unstable driving
performance.
[0016] Advantageously, the method allows for reliably detecting
snaking car-trailer combinations, in particular passenger
car/trailer combinations. In this method, a differential value
.DELTA.{dot over (.psi.)} is generated from the measured yaw rate
and the model-based reference yaw rate, which value is
representative of the deviation of the vehicle from the track
predetermined by the steering wheel position. Because this
differential value represents only the deviation from the desired
track, monitoring the differential value ensures the judgment of
oscillations independently of a curved track passed e.g. due to a
steering angle. Preferably, the differential value is filtered in a
low-pass filter in order to cut off signal peaks triggered by the
detection of coefficients of friction. Spurious detections and,
thus, faulty control activations are avoided in addition. The
method and the device favorably require only a sensor system
provided in an Electronic Stability Program (ESP) driving stability
control.
[0017] In this arrangement, an actuating signal for an electric
motor of a hydraulic pump producing a brake pressure and, hence,
actuating the wheel brake of the towing vehicle or the trailer is
generated by way of the data measured by a yaw rate sensor, derived
in an ESP driving dynamics control operation and logically combined
with the ESP control strategy. In this data the data of a motor
vehicle can be included. It is possible alternatively or
additionally to drive an actuator of an overriding steering system.
By applying equal or different brake pressure to one wheel of
preferably the towing vehicle or to all wheels of the towing
vehicle corresponding to an ESP control strategy, it is possible to
correct the instabilities of the car-trailer combination detected
by sensors and to reduce the possibly existing excessive transverse
dynamics of the car-trailer combination by reducing the vehicle
speed and/or the lateral forces at one wheel by means of increased
brake pressure and/or the increase in the longitudinal forces.
[0018] It is favorable that the frequency and the amplitude of each
half wave of the differential value is determined, compared to
stored values, and the rolling motion of the car-trailer
combination is evaluated in dependence on the result of the
comparison.
[0019] Advantageously, the oscillation frequency of the car-trailer
combination is achieved in that the frequency is determined from
the zero crossings and the time between two zero crossings of the
yaw velocity.
[0020] The condition for detecting a snaking, unstable car-trailer
combination is favorably satisfied by the following steps: counting
the number of the half waves of the differential value where the
amplitude of each half wave reaches or exceeds a threshold value,
counting each positive and negative half wave of the determined
frequency when each positive and negative half wave lies within a
band defined by a top and a bottom threshold value, and comparing
the value of the half waves counted with a threshold value
representative of a number of half waves, and measures that
stabilize driving are initiated when the threshold value is reached
or exceeded. It is favorably arranged so that the conditions are
continuously satisfied and the half waves are serially counted in
order that the threshold value representative of a number of half
waves is reached or exceeded, respectively. The threshold value
representative of a number of half waves can favorably be
determined in dependence on the frequency, and at low frequencies,
the threshold value is reached or exceeded with a smaller number of
half waves than is the case at a high frequency.
[0021] Further, it is advantageous that the threshold value of each
half wave representative of the amplitude is determined at least in
dependence on quantities that represent the velocity of the towing
vehicle or the car-trailer combination or the trailer. It is
arranged for that with quantities describing a high speed, the
threshold value is reached or exceeded at lower amplitudes than is
the case with quantities describing a low speed.
[0022] To avoid constant activation and deactivation of the
controller (ESP driving stability controller), only a consecutive
number of half waves of the yaw velocity are counted where the
amplitude of each half wave reaches or exceeds an entry threshold
value, and the measures that stabilize driving are terminated when
values reach or fall below only one exit threshold value ranging
below the entry threshold value.
[0023] In a preferred embodiment of the invention, the data is
produced from the variation of the differential value. The
model-based yaw velocity is calculated in a vehicle model that is a
component of an ESP driving stability control in a favorable
manner. In the vehicle model, in particular the single-track model,
the model yaw rate is generally produced from the steering angle,
the lateral acceleration and the vehicle speed (vehicle reference
speed).
[0024] Surprisingly, it has been shown that during rapid changes of
the steering angle, i.e. at high steering angle speeds, deviations
in the vehicle model are generated which cause a signal variation
that is confusable with the monitored signal variation when the
car-trailer combination is snaking. It is assumed that these
deviations are due to the reaction times of the signal generation,
on the one hand, and the retarded vehicle reaction, on the other
hand. To avoid these faulty detections, provisions are made to
ensure that the differential value is weighted with a value, in
particular a factor, which is produced in dependence on the
steering angle velocity or the steering angle acceleration or
preferably the model deviation or deviation of the reference yaw
rate, respectively. The reason is that it has been found out that
the model yaw rate deviation or the model yaw rate speed,
respectively, is most appropriate for filtering the differential
value because the vehicle speed vRef and the steering angle
velocity {dot over (.delta.)} go into said value.
[0025] In a particularly favorable embodiment of the method, the
lateral acceleration is detected and the variation of the lateral
acceleration is evaluated according to criteria which allow
checking the plausibility of the data obtained from the variation
of the differential value and being assessed according to criteria
indicative of an unstable driving performance.
[0026] Plausibility is checked by way of finding out the maximum
and minimum values of the lateral acceleration and their temporal
distances, by determining the frequency and comparing it with the
frequency of the differential value.
[0027] Plausibility is additionally checked and the method is
terminated or the measures that stabilize driving are discontinued
when at least one of the following conditions is satisfied: [0028]
the frequency of a lateral signal or a transverse quantity, such as
the lateral acceleration and/or the differential value reaches or
exceeds or, respectively, falls below a top or a bottom threshold
value; [0029] the frequency of the lateral signal changes in
relation to the frequency of the differential value towards a top
or a bottom limit value; [0030] the absolute value of the average
value of the lateral signal exceeds a threshold value; [0031] the
amplitude of the lateral signal decreases with a high gradient;
and/or [0032] the difference between the maximum and minimum values
of the lateral signal lies in a narrow band.
[0033] As the phase shift is small in snaking car-trailer
combinations, it is favorably arranged so that the phase shift
between the lateral acceleration and the differential value is
determined and evaluated according to criteria that permit
determining driving situations.
[0034] It is favorable that the measures that stabilize driving are
discontinued or the method is terminated, respectively, when a
threshold value indicative of a great phase shift is exceeded.
[0035] Further, an object of the invention relates to a device for
stabilizing a car-trailer combination, including an ESP driving
stability control, with a yaw rate sensor for sensing the yaw
velocity and a vehicle model for producing a reference yaw
velocity, with a determining unit determining a differential value
from the yaw velocity and the reference yaw velocity, with a
control unit controlling measures that stabilize driving in
dependence on data being obtained from the variation of the
differential value and evaluated according to criteria indicative
of an unstable driving performance.
[0036] An embodiment of the invention is illustrated in the
accompanying drawings and described in more detail in the
following.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] In the drawings,
[0038] FIG. 1 shows a vehicle with an ESP control system.
[0039] FIG. 2 shows the variation of signals of the differential
value of the snaking towing vehicle.
[0040] FIG. 3 shows the signals of a snaking towing vehicle.
[0041] FIG. 4 is a simplified flow chart showing the control.
[0042] FIG. 5 is a simplified wiring diagram for calculating the
differential value .DELTA.{dot over (.psi.)}.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0043] Before the actual method is referred to, FIG. 3 shall be
used to schematically explain the signal variation of the
oscillation of the yaw rate (dash-dot), of the steering angle
(dash-dash), and the differential value of measured yaw rate and
model or reference yaw rate in dependence on a slalom maneuver or
the slalom-like avoidance of obstacles, respectively. The signal
variation a) shows a sinusoidal variation of the yaw rate {dot over
(.psi.)} and the differential value .DELTA.{dot over (.psi.)} of
model yaw rate and measured yaw rate without the driver steering.
Without a corresponding steering angle variation, the variation of
the yaw rate and the differential value of measured yaw rate and
model-based yaw rate are almost equal.
[0044] FIG. 3b) shows the signal variation that is e.g. produced in
a slalom maneuver when the oscillation is generated by the steering
angle variation alone, where the vehicle can follow the driving
performance of the driver illustrated in the vehicle model. In this
case, the differential value at issue is zero because no deviation
between measured yaw rate and model-based yaw rate is determined.
The vehicle follows the steering angle predefined by the
driver.
[0045] FIG. 3c) shows the signal variation in dynamic slalom
maneuvers. Herein the oscillation is generated alone by the
steering angle variation due to the rapid steering angle changes,
i.e. at high steering angle velocities. The sinusoidal variation of
the differential value is generally based on the fact that the
vehicle can no longer follow the vehicle model. That means, the
model yaw rate determined in the vehicle model is no longer
identical with the measured yaw rate because the vehicle is no
longer able to instantaneously comply with the dynamic steering
angle variations.
[0046] FIG. 1 shows a vehicle with an ESP control system, brake
system, sensor system, and communication provisions. The four
wheels have been assigned reference numerals 15, 16, 20, 21. One
wheel sensor 22, 23, 24, 25 is provided at each of the wheels 15,
16, 20, 21. The signals are sent to an electronic control unit 28
determining from the wheel rotational speeds the vehicle speed v by
way of predetermined criteria. Further, a yaw rate sensor 26, a
lateral acceleration sensor 27, and a steering angle sensor 29 are
connected to the electronic control unit 28. Further, each wheel
includes an individually actuatable wheel brake 30, 31, 32, 33. The
brakes are hydraulically operated and receive pressurized hydraulic
fluid by way of hydraulic lines 34, 35, 36, 37. The brake pressure
is adjusted by way of a valve block 38, said valve block being
actuated irrespective of the driver by way of electric signals
produced in the electronic control unit 28. The driver can
introduce brake pressure into the hydraulic lines by way of a
master cylinder actuated by a brake pedal. Pressure sensors P are
used to sense the driver's braking request are provided in the
master cylinder or the hydraulic lines, respectively. The
electronic control unit is connected to the engine control device
by way of an interface (CAN).
[0047] It is possible to provide a statement about the respective
driving situation and, thus, to realize an activated or deactivated
control situation by way of a determination of the entry and exit
conditions by means of the ESP control system with brake system,
sensor system, and communication provisions that includes the
following pieces of equipment: [0048] Four wheel speed sensors
[0049] pressure sensor (brake pressure in master cylinder
p.sub.main) [0050] Lateral acceleration sensor (lateral
acceleration signal a.sub.actual, lateral inclination angle
.alpha.) [0051] Yaw rate sensor ({dot over (.PSI.)}) [0052]
Steering wheel angle sensor (steering angle .delta., steering angle
velocity {dot over (.delta.)}) [0053] Individually controllable
wheel brakes [0054] Hydraulic unit (HCU) [0055] Electronic control
unit (ECU).
[0056] This renders possible one main component of the method for
stabilizing car-trailer combinations, i.e. the detection of driving
situations, while the other main component, i.e. the interaction
with the braking system, also makes use of the essential components
of the driving stability control.
[0057] A conventional ESP intervention is used to produce an
additional torque by purposeful interventions at the individual
brakes of a vehicle, said torque adapting the actually measured yaw
angle variation per unit of time (actual yaw rate {dot over
(.PSI.)}.sub.actual) of a vehicle to the yaw angle variation per
unit of time (reference or model or nominal yaw rate {dot over
(.PSI.)}.sub.no min al, respectively) influenced by the driver. In
this arrangement, the input quantities which result from the track
desired by the driver are sent to a vehicle model circuit which, by
way of the prior-art single track model or any other driving model,
determines a model yaw rate ({dot over (.PSI.)}.sub.no min al) from
these input quantities and from parameters being characteristic of
the driving performance of the vehicle, but also from quantities
predefined by distinctive features of the ambience. Said model yaw
rate is compared to the measured actual yaw rate ({dot over
(.PSI.)}.sub.actual). The difference between the model yaw rate and
the actual yaw rate (.DELTA.{dot over (.PSI.)}) is converted by
means of a so-called yaw torque controller into an additional yaw
torque M.sub.G which represents the input quantity of a
distribution logic.
[0058] Distribution logic, in turn, determines the brake pressure
to be applied to the individual brakes, possibly in dependence on a
braking request of the driver demanding a defined brake pressure at
the wheel brakes. The purpose of the brake pressure is to produce
an additional torque at the vehicle in addition to the desired
brake effect, as the case may be, said torque supporting the
driving performance of the vehicle in the direction of the steering
request of the driver.
[0059] FIG. 5 schematically shows that part of the ECU 28 wherein
the differential value .DELTA.{dot over (.psi.)} is calculated. ECU
28 includes a vehicle model 50 for producing a model yaw rate. At
least the steering angle and the vehicle speed vRef are sent to the
vehicle model 50. Further data, which can be included in the model,
are the lateral acceleration, the measured yaw rate and a
coefficient of friction determined in a coefficient-of-friction and
situation detection unit. The model yaw rate is produced from the
input signals in the model. In the determining unit 51, the model
yaw rate is compared with the yaw rate sensed by the yaw rate
sensor 26, and the differential value is determined from the yaw
rate and the model yaw rate. The differential value .DELTA.{dot
over (.psi.)}/dt is weighted by a factor produced in dependence on
the model yaw rate change and is filtered in filter 52. The factor
.noteq.0 prevents the spurious detection that has been described
with respect to FIG. 3c).
[0060] FIG. 2 exhibits the signal variation of the differential
value of a snaking towing vehicle.
[0061] As a first component of the detection, the method comprises
a module for analyzing the variation of the difference of the
model/actual yaw rate .DELTA.{dot over (.psi.)}. The model detects
zero crossings 60, 61 of the differential value between the model
yaw rate and the measured yaw rate, said differential value to be
taken into account for the analysis, and determines the time
between two zero crossings. The oscillation frequency is thereby
obtained. A half wave is recognized as valid only if the determined
frequency lies within a typical band (roughly 0.5-1.5 hertz).
Further, a half wave is valid only if the amplitude between two
zero crossings has exceeded a defined threshold. The number of the
valid half waves is counted. When the number of the valid half
waves exceeds a threshold value, the differential value condition
for detecting a snaking car-trailer combination is satisfied.
[0062] Steering movements of the driver are considered directly in
the detection signal by way of monitoring the difference between
the model yaw rate and the measured yaw rate. When the driver e.g.
carries out a slalom maneuver at a low vehicle speed with a low
steering angle velocity, admittedly, the measured yaw rate shows a
variation from which a snaking car-trailer combination could be
concluded. However, the model yaw rate shows the same variation in
the slalom maneuver so that the difference signal is almost zero
and a spurious detection is ruled out. Thus, spurious detections
caused by slalom maneuvers are thus avoided due to this embodiment
of the method. In addition, this method simplifies detecting
snaking car-trailer combinations in a curve.
[0063] During cornering, the yaw rate is given an offset so that
the oscillation no longer swings about the zero point but about
this offset. This fact renders detection more difficult. If,
however, the difference between the model yaw rate and the measured
yaw rate (yaw velocity) is used, this offset will be compensated.
The detection signal will thus always swing about zero.
[0064] Another especially favorable embodiment of the method
provides that the deviation between actual yaw rate and model yaw
rate is additionally weighted by a factor that is calculated in
response to the model yaw rate speed. The quicker the model yaw
rate change is, the smaller the factor becomes, which is, however,
always >0. Said factor is multiplied by the differential value
or differential value signal so that a low differential value is
the result in the event of a quick change of the model yaw rate.
Thus, detection is only allowed in the presence of extreme
oscillations, but is avoided in other cases. It is thereby taken
into account that with rapid steering movements the vehicle is no
longer able to follow the vehicle model so that the difference
between the model yaw rate and the measured yaw rate shows a signal
variation that would cause spurious detections.
[0065] In another especially favorable embodiment of the method,
the number of the demanded half waves depends on the frequency of
the oscillation. The more half waves are demanded, the more
reliable the detection of spurious detections becomes. With low
frequencies, however, it will possibly last too long until an
intervention can take place when great numbers of half waves are
demanded. It is, therefore, favorable to intervene already at low
frequencies when small numbers of half waves prevail, yet to demand
more half waves at high frequencies.
[0066] In another especially favorable embodiment of the method,
the demanded oscillation amplitudes are speed-responsive.
Oscillations are more critical at high speeds than at low speeds.
Therefore, detection takes place already at low differential value
oscillations when the car-trailer combination runs at high speed,
while the threshold is raised at low speeds.
[0067] In still another especially favorable embodiment of the
method, separate entry and exit thresholds are provided for the
differential value amplitudes. An intervention takes place only
when the yaw rate exceeds the high threshold. Thereafter, the
intervention will only be terminated when values drop below a lower
exit threshold. This will ensure that there is a defined
intervention and will prevent that the controller is constantly
activated and deactivated again.
[0068] As a second component of the detection, the method comprises
a module for analyzing the lateral acceleration variation. Maximums
and minimums of the signal are determined. The frequency can be
determined from the distances in time between maximums and
minimums. The frequency must roughly correspond to the frequency of
the differential value signal. The position of the maximums and
minimums of the lateral acceleration signal is compared with the
position of the maximums and minimums of the differential value
signal. The phase shift between differential value and lateral
acceleration can be calculated therefrom. The phase position during
driving on rough roadways is different from the phase position
during driving with snaking car-trailer combinations. The phase
shift is small with snaking car-trailer combinations. This
criterion is examined, and the detection of a snaking car-trailer
combination is forbidden in the event of a too great phase
shift.
[0069] In another especially favorable embodiment of the method,
spurious control activations are prevented by way of several
additional plausibility tests of the lateral signals. The following
signal variations are untypical with snaking car-trailer
combinations and, therefore, cause prevention or stop of
interventions: [0070] The frequency of the lateral signals is
obviously changing (becomes significantly lower or higher). [0071]
The frequency of the lateral signals lies outside the typical
frequency band. [0072] The amplitude of the lateral signals is
significantly decreasing. [0073] The difference of the maximums and
minimums of the lateral signal variations is small. [0074] The
absolute value of the average value of the lateral acceleration is
too high (extreme cornering maneuver; snaking car-trailer
combinations are not plausible in such maneuvers).
[0075] FIG. 4 shows a simplified view of the logical processes of
the control:
[0076] Starting from the yaw rate difference 41 (.DELTA.{dot over
(.psi.)}) between the model yaw rate and the measured yaw rate
determined in the ESP vehicle model (see e.g. the driving stability
control according to FIGS. 1 and 2 and their description in DE 195
15 056 which shall be part of this application), the differential
value 41 is filtered in step 40. This means that the differential
value 41 undergoes low-pass filtering so that extreme peaks will
not occur. Step 42 comprises the search for half waves in the input
signal, which are analyzed by way of two zero crossings, one
maximum, a minimum amplitude and a defined initial gradient. It is
polled in lozenge 43 whether the half wave was detected. If this is
not the case, switch-back to step 42 is made and the search for
half waves is continued. If the half wave was detected by way of
the previous criteria, it is checked in terms of its validity in
lozenge 44. To this end, the following criteria are polled: [0077]
The maximum of the half wave must exceed a defined value. [0078]
The distance of the zero crossings (half wave length) must be in
the significant frequency range. [0079] The hysteresis band must be
left after a defined time. [0080] Starting with the second wave
found: [0081] The half wave length must be identical with the
previous one. [0082] The average value of the lateral acceleration
must not be higher than a defined value. [0083] The lateral
acceleration must have the same sign at the time of the maximum of
the half wave. [0084] The lateral acceleration must have a half
wave of roughly the same duration. [0085] The model yaw rate must
have the same sign at the time of the maximum of the half wave.
[0086] The model yaw rate must be smaller than the vehicle yaw rate
by a certain amount.
[0087] If all of these criteria are satisfied, the half wave is
valid, and the half wave counter is incremented in step 45. In the
case of a significant amplitude decrease (current amplitude is only
X% of the previous amplitude), the counter will not be incremented
but maintains its value, what can lead to a later entry into the
control. If not all the criteria are satisfied, the half wave
counter is reset to zero in step 48. It is found out in lozenge 46
whether N half waves are detected. This will trigger a deceleration
control of the vehicle in step 47.
[0088] The criteria allow a control during cornering and even
during steering movements of the driver.
* * * * *