U.S. patent application number 10/133477 was filed with the patent office on 2002-10-31 for electrically adjustable semiactive damper control.
Invention is credited to Grotendorst, Jorg, Sommer, Stefan, Stiller, Alexander.
Application Number | 20020161498 10/133477 |
Document ID | / |
Family ID | 7683092 |
Filed Date | 2002-10-31 |
United States Patent
Application |
20020161498 |
Kind Code |
A1 |
Stiller, Alexander ; et
al. |
October 31, 2002 |
Electrically adjustable semiactive damper control
Abstract
One or several vibration dampers of a vehicle suspension have a
damping force arrangement wherein a control signal is computed
within the actuating range in accordance with a standard control
method for adjusting the damper characteristic. The drive of a
damper adjustable in accordance with this invention is so improved
that body movements (notwithstanding a harder adjusted damping for
critical driving situations) are substantially suppressed as early
as possible. In specific driving situations, the adjusting range of
the damper force is changed in that the upper limit of the
adjusting range is raised or lowered and/or the lower limit of the
adjusting range is raised or lowered. A soft damper setting takes
place preferably in dependence upon signals which announce or
display a change of the vehicle longitudinal deceleration or
vehicle transverse acceleration.
Inventors: |
Stiller, Alexander;
(Garbsen, DE) ; Sommer, Stefan; (Garbsen, DE)
; Grotendorst, Jorg; (Garbsen, DE) |
Correspondence
Address: |
Walter Ottesen
Patent Attorney
P.O. Box 4026
Gaithersburg
MD
20885-4026
US
|
Family ID: |
7683092 |
Appl. No.: |
10/133477 |
Filed: |
April 29, 2002 |
Current U.S.
Class: |
701/37 ;
280/5.515 |
Current CPC
Class: |
B60G 2800/162 20130101;
B60G 17/04 20130101; B60G 2400/208 20130101; B60G 2800/18 20130101;
B60G 2400/60 20130101; B60G 2400/821 20130101; B60G 17/08 20130101;
F16F 9/46 20130101; B60G 2400/104 20130101; B60G 2400/204 20130101;
B60G 2600/02 20130101; B60G 2500/10 20130101; B60G 2600/184
20130101; B60G 2400/518 20130101; B60G 2400/106 20130101 |
Class at
Publication: |
701/37 ;
280/5.515 |
International
Class: |
B60G 023/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 27, 2001 |
DE |
101 20 918.5 |
Claims
What is claimed is:
1. A method for controlling the damping force for at least one
vibration damper of a vehicle wheel suspension of a vehicle, the
method comprising the steps of: providing a damper for generating a
damper force and said damper having a damper characteristic
adjustable within an adjusting range for the damping force
delimited by upper and lower limit values; detecting a first signal
representing the vertical velocity at a part of said vehicle
chassis as a suspended mass; detecting a second signal representing
the vertical velocity of the unsuspended wheel mass; computing an
input control signal based on said first and second signals for
adjusting said damper characteristic within said adjusting range in
accordance with a standard control process; discretely or
continuously adjusting said damping characteristic to said input
control signal; and, changing said adjusting range in specific
driving situations so as to cause one or both of said upper and
lower limits to be raised or lowered.
2. The method of claim 1, comprising the further step of limiting a
damper soft setting in dependence on signals which indicate a
change of vehicle longitudinal deceleration.
3. The method of claim 1, comprising the further step of limiting a
damper soft setting in dependence upon signals which indicate a
change of the vehicle transverse acceleration.
4. The method of claim 1, comprising the further step of limiting a
damper hard setting when detecting large roadway unevenness
utilizing adaptive algorithmic circuits or self-learning units.
5. The method of claim 1, said vehicle having a vehicle body and
said method comprising the further step of permitting a damper hard
adjustment in dependence upon the body velocity so as to cause a
widening of the adjusting range in the direction of a damper
hardening and so as to cause a narrowing of the adjusting range in
the direction of a damper hardening.
6. The method of claim 1, comprising the further step of narrowing
said adjustment range in a direction of a damper hardening with a
permanent priority relative to limiting in the direction of a
damper soft setting.
7. The method of claim 1, comprising the further step of limiting
an actuating variable in a direction of a soft damper adjustment
when determining a defect in the control algorithm.
8. The method of claim 1, comprising the further step of adapting
the adjusting range to a specific driving situation.
9. The method of claim 8, wherein the adaptation of said adjusting
range always takes p lac e when said specific driving situation is
announced .
10. The method of claim 1, wherein said standard control process is
the skyhook process.
11. An arrangement for controlling the damping force for at least
one vibration damper of a vehicle wheel suspension of a vehicle,
the arrangement comprising: a damper for generating a damper force
and said damper having a damper characteristic adjustable within an
adjusting range for the damping force delimited by upper and lower
limit values; means for detecting a first signal representing the
vertical velocity at a part of said vehicle chassis as a suspended
mass; means for detecting a second signal representing the vertical
velocity of the unsuspended wheel mass; means for computing an
input control signal based on said first and second signals for
adjusting said damper characteristic within said adjusting range in
accordance with a standard control method; a damping force unit for
discretely or continuously adjusting said damping characteristic to
said input control signal; and, means for changing said adjusting
range in specific driving situations so as to cause one or both of
said upper and lower limits to be raised or lowered.
12. The arrangement of claim 11, further comprising means for
limiting a damper soft setting in dependence on signals which
indicate a change of vehicle longitudinal deceleration.
13. The arrangement of claim 11, further comprising means for
limiting a damper soft setting in dependence upon signals which
indicate a change of the vehicle transverse acceleration.
14. The arrangement of claim 11, further comprising means for
limiting a damper hard setting when detecting large roadway
unevenness utilizing adaptive algorithmic circuits or self-learning
units.
15. The arrangement of claim 11, said vehicle having a vehicle body
and said arrangement further comprising means for making a hard
damper setting in dependence upon the body velocity so as to cause
a widening of the adjusting range in the direction of a damper
hardening and so as to cause a narrowing of the adjusting range in
the direction of a damper hardening.
16. The arrangement of claim 11, further comprising means for
narrowing said adjustment range in a direction of a damper
hardening with a permanent priority relative to limiting in the
direction of a damper soft setting.
17. The arrangement of claim 11, further comprising means for
limiting an actuating variable in a direction of a soft damper
adjustment when determining a defect in the control algorithm.
18. The arrangement of claim 11, further comprising means for
adapting the adjusting range to a specific driving situation.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a method and an arrangement for
controlling (open loop or closed loop) the damping force for at
least one vibration damper of a vehicle wheel suspension.
BACKGROUND OF THE INVENTION
[0002] For reasons of driving safety, it is desirable to undertake
the electric control of a vehicle damper in such a manner that the
driving safety remains ensured even when there is a failure of the
damper control because of a defect in the control unit or in the
case of a fault with the current supply. This greater driving
safety is more likely provided with a harder damping than with a
softer damping. For this reason, the control should basically be so
designed that the harder damping characteristic becomes effective
when there is a fault of the control; whereas, the damping by means
of the electric control reacts softer and therefore with greater
comfort.
[0003] It is known to control semiactive dampers in accordance with
the skyhook method. In the skyhook method, a desired damping force
is computed which is proportional to the body velocity. In
electrically adjustable dampers, a desired current is computed (in
general, with an inverse damping characteristic field) from the
desired damping force and the determined damping velocity and, with
this desired current, an electrical valve changes the damping force
in the damper. Because of the characteristic of a passive damper,
only the least damaging damping force (the smallest possible
damping) is adjusted when there are mutually opposite signs of
damping velocity and required damping force.
[0004] The parameters of the skyhook controller (especially the
proportional coefficient with which the vehicle body velocity is
evaluated) or, more generally, the parameters of a characteristic
field with which the body velocity is evaluated, are optimized
usually with respect to the following: a low body excitation, low
wheel load fluctuations and additional subjective criteria such as
vehicle handling based on the evaluation of many vehicle maneuvers
and these parameters are fixedly adjusted. For a fixed adjustment,
a compromise must always be made between the driving comfort and
the vehicle handling characteristics. A significant quality
advantage is obtained when the control system recognizes specific
driving maneuvers wherein the basic matching of the dampers is not
used but (adapted in correspondence to the specific driving
maneuver) the optimal damping is adjusted in a targeted manner. In
the literature, this is done, for example, by changing the
proportional coefficient of the body velocity.
[0005] The skyhook controller has the disadvantage that the damping
force is continuously switched between hard and soft in dependence
upon the damper velocity. This can, for example, lead to unwanted
acoustic problems. A further disadvantage of the skyhook controller
is that the damper automatically adjusts to "soft" when the body
velocity is not present. This can lead to unwanted velocity
movements (for example, at high vehicle speeds or braking and/or
steering maneuvers) and therefore to a deterioration of the driving
comfort.
[0006] The skyhook method is disclosed, for example, in German
Patent 4,135,525 and German patent publication 4,115,061.
SUMMARY OF THE INVENTION
[0007] It is an object of the invention to so improve the driving
of a damper, which is adjustable in accordance with a standard
control method, especially the skyhook method, so that unwantedly
occurring body movements in the above-mentioned driving situations
are suppressed as early as possible and as much as possible.
[0008] The method of the invention is for controlling the damping
force for at least one vibration damper of a vehicle wheel
suspension of a vehicle. The method includes the steps of:
providing a damper for generating a damper force and the damper
having a damper characteristic adjustable within an adjusting range
for the damping force delimited by upper and lower limit values;
detecting a first signal representing the vertical velocity at a
part of the vehicle chassis as a suspended mass; detecting a second
signal representing the vertical velocity of the unsuspended wheel
mass; computing an input control signal based on the first and
second signals for adjusting the damper characteristic within the
adjusting range in accordance with a standard control process;
discretely or continuously adjusting the damping characteristic to
the input control signal; and, changing the adjusting range in
specific driving situations so as to cause one or both of the upper
and lower limits to be raised or lowered.
[0009] According to the method of the invention, this does not take
place only via a reduction of the control in the manner that the
maximum value of the actuating variable is reduced in especially
previously defined driving situations and the minimum value of the
actuating variable in increased; instead, and in accordance with
the invention, a narrowing as well as a widening of the adjusting
range is detected. In this way, the situation is taken into account
for the driving conditions in which the vehicle body velocity is
zero, the dampers of the vehicle are adjusted to soft (and
therefore an adjusting range of zero is adjusted) and, starting
from this driving condition, the adjusting range is widened when a
body acceleration is indicated because of the driving condition.
Furthermore, with the invention, the possibility is provided that a
wide actuating range is narrowed.
[0010] The basic idea of the invention is that the adjusting range
of the damper is adapted to the specific driving situation and
already then when this driving situation is announced, for example,
with the actuation of the brake pedal.
[0011] The damping forces, which are generated by the skyhook
algorithm in dependence upon the body and damper velocities, are
changed via the above changeability of the actuating range of the
skyhook algorithm in dependence upon these signals. The damping
forces are changed within the technical capability of the
particular damper for the duration of the critical driving
situation with respect to a possible soft setting or a possible
hard setting.
[0012] In accordance with a preferred embodiment, the changeability
of the maximum value and/or minimum value is coupled to driving
dynamic variables, that is, a change of the control range can be
coupled to certain pregiven vehicle measured variables.
[0013] Signals, which announce or indicate a change of the vehicle
longitudinal deceleration, are, for example: changes of the brake
pressure, changes of the brake light signal, driver command torque,
engine drive torque or accelerator pedal position.
[0014] Signals which announce or indicate a change of the vehicle
transverse acceleration are, for example: changes of the measured
transverse acceleration or the transverse acceleration computed
from the steering angle and the vehicle speed.
[0015] When determining whether action is required via the control
electronics, which are connected to the corresponding sensors, the
adjusting variables can be adjusted in the direction of a damping
hard adjustment or a damping soft adjustment depending upon
weighting. The adjustment is gradual or time delayed, that is, the
adjustment is not abrupt.
[0016] With the aid of limiting the adjusting range in accordance
with the invention, a significantly improved damping of the vehicle
velocity is provided especially for acceleration operations in the
longitudinal and transverse directions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The invention will now be described with reference to the
drawings wherein:
[0018] FIG. 1 is a diagram providing a schematic illustration of a
wheel suspension;
[0019] FIG. 2 is a force/velocity diagram;
[0020] FIG. 3 is a block diagram showing the damping adjustment in
accordance with the invention;
[0021] FIG. 4 is a damper force diagram in accordance with the
state of the art; and,
[0022] FIG. 5 is a damper force diagram in accordance with the
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION
[0023] The basic idea of the skyhook method is the assumption that
the vehicle body is damped relative to a reference point (skyhook)
independent of the vehicle. From this, an idealized damping force
is provided by:
F.sub.Sky=v.sub.A*k.sub.Sky
[0024] wherein:
[0025] F.sub.Sky=skyhook damping force,
[0026] v.sub.A=body velocity; and,
[0027] k.sub.sky=damping coefficient.
[0028] The above cannot be realized because, on the one hand, such
an independent reference point is not given and, on the other hand,
the damper is connected to the wheel and chassis in most vehicles
and, for this reason, the damper can only influence the relative
speed of wheel to body. In semiactive dampers, the damping force is
adjusted between k.sub.min and k.sub.max via the damping
coefficient, for example, electrically or pneumatically. The
damping force results from the damper velocity and the adjusted
damping coefficient (see characteristic field). The practical
application of the skyhook method is mostly that, when
F.sub.Sky and v.sub.D=dx.sub.A/dt-dx.sub.R/dt
[0029] have the same sign, the ideal skyhook force is set as:
F.sub.D=v.sub.A*k.sub.Sky
[0030] and when
F.sub.Sky and v.sub.D=dx.sub.A/dt-dx.sub.R/dt
[0031] do not have the same sign, that damping force is adjusted
which comes closest to the skyhook value:
F.sub.D=v.sub.A*k.sub.min.
[0032] The block diagram of FIG. 3 shows an embodiment of the
damper electronics of the invention. The sensors (not shown), which
are required for the determination of the longitudinal and
transverse accelerations and for the determination of roadway
unevenness, are arranged on the circuit at the input end. The data
(actual values), which are supplied by the sensors, are compared to
pregiven desired values. If the actual values exceed the pregiven
desired values, then (because of an inverse damping characteristic
field) the current for actuating an electronic valve, which acts on
the damper, is reduced whereby the damping characteristic is
shifted in the direction "hard".
[0033] In contrast, the damping force adjustment with respect to
the sensor responsible for recognizing the state of the roadway
functions differently. If the sensed street unevenness exceeds a
pregiven limit value, then a gradual amplified or even maximum
current i is applied to the electromagnetic valve, which means a
reduction of the damper force F.sub.D.
[0034] The actuator referred to herein can, for example, be
electromagnetic valves or pneumatically actuated valves. What is
significant for the invention is influencing the damping force in
dependence upon the particular driving situation with the aid of
the control method according to the invention and with the
arrangement according to the invention for carrying out the method
of the invention.
[0035] From the diagram of FIG. 4 it can be seen that there is
always a switching back and forth of the damping force between the
limit values, which are technically possible, that is, minimum and
maximum.
[0036] According to the invention, the upper limit as well as the
lower limit can be changed (FIG. 5). With this, there is not only a
changeability of the control range but also the particular absolute
amount of the damping force can be adjusted. The basic state is
given with the minimum damping (soft). For specific driving
situations, the adjusting range of the damping is expanded. This
can take place in dependence upon the vehicle speed, for example,
for a speed range of 60 to 130 km/h and preferably a range of 90 to
110 km/h. Essential to the invention is the change of the damping
force adjusting range in each case.
[0037] It is understood that the foregoing description is that of
the preferred embodiments of the invention and that various changes
and modifications may be made thereto without departing from the
spirit and scope of the invention as defined in the appended
claims.
* * * * *