U.S. patent application number 09/848697 was filed with the patent office on 2001-11-01 for method for adjusting the gain applied to a seat suspension control signal.
This patent application is currently assigned to Lord Corporation. Invention is credited to St. Clair, Kenneth A..
Application Number | 20010035600 09/848697 |
Document ID | / |
Family ID | 22746966 |
Filed Date | 2001-11-01 |
United States Patent
Application |
20010035600 |
Kind Code |
A1 |
St. Clair, Kenneth A. |
November 1, 2001 |
Method for adjusting the gain applied to a seat suspension control
signal
Abstract
In a seat suspension system, a method for adjusting the gain
applied to a control signal to accommodate for large variations in
rider weight and input severity and thereby provide rider comfort
over a wider range of conditions than is possible with fixed gains
or tunings. The method of the present invention is adaptable to
changes in system operating conditions.
Inventors: |
St. Clair, Kenneth A.;
(Raleigh, NC) |
Correspondence
Address: |
Michael M. Gnibus
111 Lord Drive
P.O. Box 8012
Cary
NC
27512-8012
US
|
Assignee: |
Lord Corporation
|
Family ID: |
22746966 |
Appl. No.: |
09/848697 |
Filed: |
May 3, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60201709 |
May 3, 2000 |
|
|
|
Current U.S.
Class: |
267/131 ;
267/136 |
Current CPC
Class: |
B60G 2800/162 20130101;
B60G 2600/14 20130101; B60N 2/0224 20130101; B60N 2/501 20130101;
B60G 2400/252 20130101; B60N 2/544 20130101; B60G 17/01933
20130101; B60G 2200/345 20130101; B60G 17/018 20130101; B60N 2/548
20130101; B60G 2600/02 20130101; B60N 2/522 20130101; B60G 2600/124
20130101; B60G 2600/17 20130101; B60G 2400/60 20130101; B60G
2800/702 20130101; B60G 2600/1877 20130101; B60G 2500/30 20130101;
B60N 2/508 20130101; B60N 2/0244 20130101; B60N 2/505 20130101;
B60N 2/502 20130101; B60G 2800/164 20130101; B60N 2/525 20130101;
B60G 2600/604 20130101 |
Class at
Publication: |
267/131 ;
267/136 |
International
Class: |
F16F 007/00 |
Claims
I claim:
1. In a seat suspension system having a means for sensing the
relative seat position of the seat and means for controlling the
movement of the seat, a method for controlling the movement of the
seat, the method comprising the steps of: (a) obtaining a leveled
seat height; (b) obtaining a relative seat position from the
sensing means; (c) determining the difference between the leveled
seat height and the relative seat position; (d) calculating the
position power based on the difference calculated in step (c); (e)
determining the relative seat velocity; (f) multiplying the
position power with a gain factor; and (g) multiplying the value of
step (f) with the relative seat velocity to obtain a control
signal.
2. The method as claimed in claim 1 wherein the method comprises
the further step of squaring the difference determined in step (c)
before step (d).
3. The method as claimed in claim 2 wherein the squared difference
determined in step (c) is passed through a low pass filter.
4. The method as claimed in claim 3 wherein the method comprises
the further steps of determining if the relative velocity of the
seat is greater than zero.
5. The method as claimed in claim 4 wherein if the relative seat
velocity is greater than zero, the method comprising the additional
step of setting a first filter factor equal to a value.
6. The method as claimed in claim 5 wherein a first time constant
is set equal to approximately 0.6 sec.
7. The method as claimed in claim 4 wherein if the relative seat
velocity is not greater than zero, the method comprising the
additional step of setting a second filter factor equal to a
value.
8. The method as claimed in claim 7 wherein a second time constant
is set equal to approximately 1.6 sec.
9. The method as claimed in claim 3 wherein the output of the low
pass filter is set equal to current position power.
10. The method of claim 3 comprising the additional step of
determining if the current position power is less than a
predetermined minimum position power.
11. The method of claim 3 comprising the additional step of
determining if the current position power is greater than a
predetermined maximum position power.
12. The method as claimed in claim 10 wherein if the current
position power is less than a predetermined minimum position power,
the method comprising the additional step of setting the current
position power equal to the predetermined minimum position
power.
13. The method as claimed in claim 11 wherein if the current
position power is greater than a predetermined maximum position
power, the method comprising the additional step of setting the
current position power equal to the predetermined maximum position
power.
Description
CROSS REFERENCE
[0001] This application claims the benefit of Provisional
Application Serial No. 60/201,709 filed May 3, 2000.
FIELD OF THE INVENTION
[0002] The invention generally relates to a method for controlling
a means for controlling displacement of a suspended seat, and more
particularly the invention relates to a method for controlling a
damper in a suspended seat system by calculating the positional
power of the system and using the calculated positional power value
as a basis for tuning the system operating parameters.
BACKGROUND OF THE INVENTION
[0003] In a semi-active seat suspension system the displacement of
the seat is controlled by a damper which may be comprised of a
damper that includes a volume of a field responsive material such
as magnetorheological (MR) material or a servo valve controlled
damper, etc. The field responsive material and servo valve
controlled dampers serve to quickly modify the motion control
forces supplied by the damper or other motion control means in a
seat suspension system. During operation of the system, as
required, a signal is sent to the damper to modify the supplied
damping. Frequently, when large magnitude non-typical inputs are
experienced a gain value is applied to the control signal to
rapidly increase the magnitude of the control signal transmitted to
the damper and significantly increase the damping forces.
[0004] In prior art seat suspension control systems the gain values
applied to system control signals or tunings are fixed for a
semi-active seat suspension system. The fixed gain and tuning
values are established based on the seat manufacturer, the typical
seat occupant weights and inputs that are most frequently
experienced when the suspension system is used in the its
associated field, for example in busses or trucks. The shortcoming
associated with systems that apply fixed gain and tuning values to
control signals is that such fixed systems frequently can not
sufficiently prevent endstop collisions when either non-typical
inputs are imparted on the system or when a seat occupant has a
weight that is outside of the tuned weight range.
[0005] The foregoing illustrates limitations known to exist in
present devices and methods. Thus, it is apparent that it would be
advantageous to provide an alternative directed to providing
variable gain values to a control signal. Accordingly, a suitable
alternative is provided including features more fully disclosed
hereinafter.
SUMMARY OF THE INVENTION
[0006] In one aspect of the invention this is accomplished by
providing a method for adjusting the gain applied to a control
signal to accommodate for large variations in rider weight and/or
input severity and thereby provide rider comfort over a wider range
of conditions than is possible with fixed gains or tunings. The
method of the present invention is adaptable to changes in system
operating conditions.
[0007] In another aspect of the invention the method of the present
invention serves as a displacement regulator that tends to cause
the seat displacement to be constant regardless of the weight of
the rider or the magnitude of the input displacements.
[0008] In yet another aspect of the invention, the method causes
the suspension system damper to produce low magnitude control
forces during low severity inputs and low rider weights.
[0009] Another useful feature of the system is that as the severity
of the inputs increases the normal phase lag between the suspended
seat input and the output motions found in passively damped seats
is reduced. This has the effect of coupling the driver more
strongly to the vehicle controls (steering, brake, etc.) making it
easier to control the vehicle in question during large vibratory
inputs.
[0010] The foregoing and other aspects will become apparent from
the following detailed description of the invention when considered
in conjunction with the accompanying drawing Figures.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
[0011] FIGS. 1a, 1b, and 1c are schematic representations of a seat
suspension system that utilizes the semi-active control system of
the present invention to limit endstop collisions.
[0012] FIG. 2 is a schematic representation of the method for
calculating the positional power value for a given seat height.
[0013] FIG. 3 is a schematic representation of how the calculated
positional power value is used to scale the control signal.
[0014] FIG. 4 is a schematic representation of a low pass filter
that is used to smooth the calculated positional power signal.
[0015] FIG. 5 is a detailed schematic representation of the low
pass filter of FIG. 4.
DETAILED DESCRIPTION
[0016] Now turning to the drawings wherein like parts are referred
to by the same numbers in the several views, the present invention
method most generally relates to a method for adjusting the gain
factor applied to control signals in semi-active seat suspensions
and the method is represented generally in flowchart
representations of FIGS. 2-5. The method of the present invention
serves as one means for limiting endstop collisions. As referred to
hereinafter the term endstop shall refer to the end of permissible
seat displacement. FIGS. 1a, 1b and 1c schematically illustrate a
typical seat suspension system 10 adapted for use in combination
with the control method of the present invention where the seat is
shown at different heights. The present invention, senses the
relative seat position which might be a truck seat for example, and
adjusts the gain factor applied to the damper control signal by a
factor of a position power valve based on the deviation of the
relative seat height from the leveled height value. The method of
the present invention serves to greatly decrease travel to the
endstop limits and thereby provides a more comfortable ride to the
driver or passenger occupying seat 12.
[0017] The seat 12 includes a mechanical multibar linkage 14 with
first and second links 21 and 22 shown in FIGS. 1a-c. The linkage
is shown in FIGS. 1a-c is shown in two-dimensions for illustrative
purpose, and it should be understood that the linkage includes
additional members not shown in the Figures. The linkage 14 is
exemplary and it should also be understood that the linkage may be
comprised of any suitable means for movably joining the seat and
suspension system. The links 21 and 22 include respective fixed
location ends 15 and 16 typically rotatably fixed at the back of
the seat, and linearly moveable ends 17 and 18 at the front of the
seat. See FIGS. 1a-1c. The linearly movable ends of links move in a
fixed linear path or track 23 and 24 and the rotatable ends 15 and
16 are fixed by a conventional connection that permits the ends 15
and 16 to be rotatable displaced. A pivotal connection 20 joins the
links 21 and 22 and other members (not shown) comprising the
linkage 14. The mechanical linkage is of conventional design well
known to one skilled in the art and therefore further description
of the linkage is not required.
[0018] A spring 60 is conventionally coupled to the mechanical
linkage 14 at a suitable location and the spring serves to adjust
the leveled height of the seat. The spring may be any suitable well
known spring such as a mechanical coil spring or an air spring. The
leveled seat height is the height that the seat assumes when it is
unaffected or substantially unaffected by vibratory disturbances.
The leveled seat height is selected by the rider for comfort, ease
of reaching vehicle controls such as the steering wheel, brake,
clutch and throttle pedal and also personal preference dictates the
ultimate leveled seat height. The leveled height is controlled by
increasing or decreasing the force supplied by spring 60 by
respectively decreasing or increasing the spring height. The change
in height may be effected in a number of ways such as by
mechanically adjusting the coil spring endpoints or by releasing
air from or introducing air into the air spring.
[0019] A conventional position sensor 30 is connected to link 21
and serves to sense the position of the link 21, and the position
sensor is electrically connected to controller 70 which in turn is
connected to conventional magnetorheological (MR) damper 40. The
damper 40 is connected to link 22. The damper 40 may contain any
suitable field responsive material including magnetorheological
(MR) fluid as indicated. The damper serves to control the
displacement of the seat during operation. The electrical signals
are supplied to the damper during system operation to provide
damping sufficient to prevent the system from reaching the maximum
and minimum endstop limits. The damper 40 may be comprised of any
suitable controllable damper such as a servo valve controlled
damper for example.
[0020] A conventional microprocessor based controller 70 for
processing the sensor signals and actuating the method of the
present invention may be located in the same control housing as
sensor 30 as shown in FIGS. 1a, 1b, and 1c. The controller is
electrically connected to the memory 50. However the controller and
sensor may be discrete components that are not collocated in the
same housing. The control method of the present invention operates
using conventional microprocessor based technology well known to
one skilled in the art and therefore further detailed description
of the microprocessor technology is not required.
[0021] The damper 40 serves to control the displacement of the seat
during operation. The electrical signals are supplied to the damper
during system operation to provide damping sufficient to prevent
the system from reaching the maximum and minimum endstop limits 90
and 91.
[0022] Now turning to the control method of the present invention
shown in FIGS. 2-5, the method provides a means for varying the
gain applied to a damper control signal based on operating
conditions. In this way, the method of the present invention serves
to limit endstop collisions when the system inputs are greater than
typical inputs and also when a person of greater than average
weight is occupying seat 12. The method of the present invention
can be integrated into a well-known seat suspension control routine
that controls typical inputs and riders of average weights. For
example, the method of the present invention could be integrated
into the routine disclosed in U.S. Pat. No. 5,276,622 for "System
for Reducing Suspension Endstop Collisions". In this way, a prior
art control routine that includes the method of the present
invention would provide damping control over a wider range of
system inputs and rider weights.
[0023] As shown in FIG. 3, the control method produces control
signal 308 that is the product of a position power value 200,
velocity gain 305 and the absolute relative velocity of the seat
304. In Step 302 of routine 300 the value of the relative seat
position is obtained from sensor 30 and the change in relative
position of the seat 12 over time is calculated in Step 303. The
value calculated in Step 303 represents the relative seat velocity.
The absolute velocity of the relative seat velocity is taken in
Step 304. In Step 307 of routine 300 the absolute value of the seat
velocity is multiplied by the product of position power calculated
in Routine 200 and the relative velocity gain 305. Steps 200 and
305 will be described in greater detail hereinbelow.
[0024] Specifically, turning to FIG. 2, the positional power which
is a function of the seat movement is calculated in the manner
shown schematically in routine 200. In Step 201 the leveled seat
height or simply leveled height is computed. The leveled seat
height value is stored in controller memory 50 and approximates the
height of the suspended seat 12 with the rider sitting in the seat
and without system vibratory input. The leveled seat height is set
by the seat occupant at the height that allows for easy access to
the steering wheel, clutch and brake pedals, and the shifter knob,
personal preference etc. During operation the leveled seat height
may be computed in Step 201 using any suitable well known digital
or analog low pass filtering technique.
[0025] In Step 202 the value of the leveled seat height is
subtracted from the present relative seat position obtained from
sensor 30 in Step 302. The relative seat height is the distance
between the seat top and the floor of the bus, truck or other
vehicle, and the relative seat position moves during use. The
difference between the relative seat position and the leveled seat
height calculated in Step 202 is squared in Step 203. Although
squaring the difference obtained in Step 202 is disclosed, it
should be understood that the difference could be raised to any
suitable power in Step 203.
[0026] The squared difference is transmitted to a low pass filter
in Step 204. The filter Step 204 is represented in the flowchart
representation of FIG. 4. The squared difference passed through the
conventional low pass filter initially comprises a signal 100 of
varying amplitudes as shown schematically as the input to FIG. 4.
The filtering Step 204 serves to smooth or flatten the variable
amplitude control signal 100 so that it more closely represents a
DC-like signal. The low pass filter may be any suitable means for
filtering specific nonrequired signal frequencies from the signal.
Other types of low pass filters may be used and such filters are
known to one skilled in the relevant art and therefore further
descriptions of such other types of low pass filters are not
required.
[0027] Returning now to the description of the present low pass
filter of the present invention, the low pass filtering Step 204 is
shown in greater schematic detail in FIG. 4. In Step 205 the signal
calculated in Step 203 is passed to the filtering routine 204.
Routine 204 stores the previous low pass filter output value in
Step 223 and in Step 206 the difference between the previous low
pass filter output and the input signal of Step 205 is
calculated.
[0028] In Step 208 the difference calculated in Step 206 is
multiplied by a filter factor determined in Step 207. The routine
of Step 207 is illustrated in greater detail in the flowchart
representation of Step 207 in FIG. 5. Turning to FIG. 5, the
relative velocity calculated in Step 303 is utilized in Routine
207. In Step 209 a determination is made if the relative velocity
value is greater than zero. If the relative velocity is greater
than zero and therefore is increasing, in Step 210 the method
selects a first filter factor identified as A in Step 210. The
first selected filter factor provides a time constant equal to 0.6
sec. If the relative velocity is not greater than zero and is
therefore decreasing, the method selects a second filter factor
identified as B in Step 211. The second selected filter factor
provides a time constant equal to 1.6 sec. The first and second
time constants may be equal to any suitable values for a particular
application. Proper selection of the filter constants is critical
to proper functioning of the method of the present invention. The
time constant represents the time required to reach 67% of a step
change to input in Step 205. Although variable time constants are
shown and described in the preferred embodiment of the invention it
should be understood that the time constant could comprise a single
constant value that is applied regardless of an increase or
decrease in seat velocity.
[0029] The filter factors are summed in Step 212, and the filter
factor is used in Step 207 of Routine 204. In Step 208, the filter
factor 212 is multiplied by low pass filter output difference of
Step 206, and in Step 213 the product of Step 208 and the Step 205
inputs to the low pass filter are summed. The summed value of Step
213 is sent to routine 200 and is the current position power value
in Step 215. This intermediate or current position power may be
referred to herein by the abbreviation PP.
[0030] Steps 216 and 217 of the current method ensure that the
calculated position power value does not exceed the upper and lower
limits before the calculated position power value is supplied to
the main control algorithm 300 to adjust the gain and ultimately
the control signal to be sent to damper 40. By Steps 216 and 217 of
the method of the present invention, the control signal will never
be reduced to zero or will not get undesirably large. In Step 216
the routine determines if the current PP value is less than the
predetermined minimum value 219 for position power. If the current
value of PP is greater than the minimum position power value, then
the routine proceeds to Step 217 wherein it is determined if the PP
value is greater than a predetermined maximum value 221 for
position power. If the current value of PP is not greater than the
predetermined maximum position power value, the routine proceeds to
Step 218 wherein the value of position power is set equal to the
current value of PP.
[0031] If in Step 216 it is determined that the current PP value is
less than the minimum predetermined position power 219 value stored
in memory 50, then the minimum position power value is obtained
from memory is Step 219 and then in Step 220 the current value of
PP is set equal to the predetermined minimum position power value.
If in Step 217 it is determined that the current PP value is
greater than the maximum predetermined position power value 221
stored in memory 50, then the maximum position power value is
obtained from memory is Step 221 and then in Step 222 the current
value of PP is set equal to the predetermined maximum position
power value. Then the current value of PP calculated in either Step
220 or 222 is set equal to the final Position Power in Step 218 and
this value used as the Position Power value in routine 300.
[0032] The PP value calculated by routine 200 is supplied to the
main control routine 300 in Step 218. The calculated PP value is
then used to scale the control signal gain. The relative velocity
gain value is a constant that is stored in memory 50. In Step 306,
the gain factor retrieved in Step 305 is multiplied with the PP
value of Step 218 and then in Step 307 the product of Step 306 is
in turn multiplied by the absolute value of the relative seat
velocity taken in Step 304. The product of Step 307 is then either
sent to control damper 40 or may be sent to a main control
algorithm where signal 308 could be combined with with other
control signal components before the control signal is sent to the
damper 40.
[0033] Thus by the control method of the present invention the
deviation from the leveled seat height is used to scale the gain
factor and adjust the damping force to limit endstop collisions and
maintain rider comfort.
[0034] While I have illustrated and described a preferred
embodiment of my invention, it should be understood that this is
capable of modification, and I therefore do not wish to be limited
to the precise details set forth, but desire to avail myself of
such changes and alterations as fall within the purview of the
following claims.
* * * * *