U.S. patent application number 11/020490 was filed with the patent office on 2005-05-12 for active seat suspension control system.
Invention is credited to Bremner, Ronald Dean.
Application Number | 20050098399 11/020490 |
Document ID | / |
Family ID | 32229720 |
Filed Date | 2005-05-12 |
United States Patent
Application |
20050098399 |
Kind Code |
A1 |
Bremner, Ronald Dean |
May 12, 2005 |
Active seat suspension control system
Abstract
A suspension system supports a seat with respect to a base
mounted on a frame of a vehicle. The system includes a hydraulic
actuator coupled between the seat and the base. A single
accelerometer is attached to the base and generates a base
acceleration signal in response to motion of the base. A control
unit actively controls the hydraulic actuator as a function of the
base acceleration signal. The control unit generates a base
velocity signal by integrating the base acceleration signal,
generates a seat position signal representing a position of the
seat relative to the base, generates a seat position error signal
representing a difference between a desired position and the seat
position signal, and generates a command signal as a function of
the velocity signal and of the position error signal. The control
unit controls the actuator by applying the command signal
thereto.
Inventors: |
Bremner, Ronald Dean; (Cedar
Falls, IA) |
Correspondence
Address: |
c/o Deere & Company
One John Deere Place
Moline
IL
61265-8098
US
|
Family ID: |
32229720 |
Appl. No.: |
11/020490 |
Filed: |
December 22, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11020490 |
Dec 22, 2004 |
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10293787 |
Nov 13, 2002 |
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Current U.S.
Class: |
188/266 |
Current CPC
Class: |
B60N 2/0232 20130101;
B60N 2/505 20130101; B60N 2/002 20130101; B60N 2/501 20130101; B60N
2/502 20130101; B60N 2/0244 20130101; B60N 2/525 20130101; B60R
21/01554 20141001; B60N 2/508 20130101; B60N 2/527 20130101 |
Class at
Publication: |
188/266 |
International
Class: |
F16F 009/12 |
Claims
1. An active suspension system for supporting a seat on a base of a
vehicle, comprising: an actuator coupled between the seat and the
base for moving the seat relative to the base; only a single
accelerometer, said single accelerometer being attached directly to
the base and generating only a single base acceleration signal in
response to vertical motion of the base; and a control unit which
converts only the single base acceleration signal into a control
signal, and actively controls the actuator as a function of the
control signal.
2. The suspension system of claim 1, wherein: the control unit
generates a base velocity signal by integrating the base
acceleration signal; the control unit generates a seat position
signal representing a position of the seat relative to the base;
the control unit generates a seat position error signal
representing a difference between a desired position and the seat
position signal; the control unit generates the control signal as a
function of the base velocity signal and of the position error
signal; and the control unit controls the actuator by applying the
control signal thereto.
3. (canceled)
4. The suspension system of claim 1, wherein: the control unit and
the actuator cooperate so that the velocity of the actuator will be
proportional to a magnitude of the control signal.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to a seat suspension system which
isolates a vehicle seat from vibrations.
[0002] Passive suspension systems, such as for a vehicle seat, are
known. For example, John Deere production 6000, 7000, 8000 and 9000
Series tractors have passive seat suspension systems which include
a hydraulic shock absorber in parallel with an air bag.
[0003] Active suspension systems are known which include an
electro-hydraulically controlled actuator working in parallel with
a resilient device, such as a spring. For example, U.S. Pat. No.
4,363,377 (Van Gerpen), issued Dec. 14, 1982, discloses an active
seat suspension system with a hydraulic actuator in parallel with a
spring. A control system controls fluid communication to the
actuator in response to a seat position signal, a stiffness
control, a seat height control and a gain control. U.S. Pat. No.
6,000,703 (Schubert et al.), issued Dec. 14, 1999, discloses an
active cab or seat suspension control system with a hydraulic
actuator in parallel with a pneumatic air spring or air bag. U.S.
Pat. No. 6,371,459, issued to Applicant's assignee, describes an
active seat suspension system wherein an accelerometer is attached
to the seat. However, with an accelerometer attached to the seat,
the system cannot respond until an acceleration of the seat occurs
and is sensed. Also, such an accelerometer must be connected to
wires or cables which are constantly being flexed and which require
special care in routing.
[0004] A system for controlling the pitch of a truck cab is
described in U.S. Pat. No. 5,044,455 (Tecco et al.), issued 3 Sep.
1991. However, this system requires at least front and back
acceleration sensors in order to generate cab or frame pitch
acceleration signals. Furthermore, such a system cannot control
simple vertical acceleration of the cab relative to the frame, it
can only control pitch or pivotal acceleration.
SUMMARY
[0005] Accordingly, an object of this invention is to provide an
active seat suspension system which does not require an
accelerometer attached to the seat.
[0006] This and other objects are achieved by the present
invention, wherein an active suspension system for supporting a
mass, such as a seat supported on a base which is fixed to a frame
of a vehicle, includes a hydraulic actuator coupled between the
seat and the base and a control system which actively controls the
hydraulic actuator. The control system actively controls the
hydraulic actuator as a function of a seat position error signal,
and an acceleration signal generated by an acceleration sensor
which is attached to the seat base.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a simplified schematic diagram of a seat
suspension system according to the present invention; and
[0008] FIG. 2 is a logic flow diagram illustrating an algorithm
performed by the electronic control unit of FIG. 1; and
[0009] FIG. 3 is a schematic block diagram illustrating the seat
suspension system of FIG. 1.
DETAILED DESCRIPTION
[0010] Referring to FIG. 1, an active seat suspension system 10
includes a seat 12 supported by scissors linkage 14 above a seat
base 16 which is fixed relative to a frame 15 of a vehicle. Also
coupled between the seat 12 and the base 16 are a hydraulic piston
or actuator 18. A servo device such as a hydraulic circuit or valve
unit 22 controls fluid communication between the actuator 18, a
pump 24 and a reservoir or sump 26. The valve unit 22 and the
actuator 18 cooperate so that the velocity of the actuator 18 will
be proportional to the magnitude of the signal applied to the input
of the valve unit 22.
[0011] A single accelerometer 32, such as a commercially available
silicon capacitive variation transducer, is attached to the seat
base 16, and generates an acceleration signal representing the
simple vertical acceleration of the base 16. A seat position sensor
34, such as a ratio-metric, rotary Hall-effect transducer, is
coupled to the linkage 14. An electronic control unit (ECU) 36
receives signals from sensors 32 and 34, from a manually operable
control 38 which generates a position command signal. In response
to these inputs, the ECU 36 provides a valve command or control
signal to the valve unit 22.
[0012] An air bag 40 may also be coupled between the seat 12 and
the base 16. The air bag 40 may be controlled by an electronically
controlled air compressor 42 and an electronically controlled vent
valve 44, both controlled by the ECU 36 as described in U.S. Pat.
No. 6,371,459, which is incorporated by reference herein.
[0013] The ECU 36 executes an algorithm 200 represented by FIG. 2.
Conversion of this flow chart into a standard language for
implementing the algorithm described by the flow chart in a digital
computer or microprocessor, will be evident to one with ordinary
skill in the art.
[0014] At step 200 various constants for the accelerometer 32, the
seat height sensor 34, a velocity compensation parameter, a valve
command, gain, offset and filtering, are initialized and stored in
non-volatile memory (not shown) in the ECU 36.
[0015] Step 204 causes the algorithm to wait for an interrupt
signal which occurs at regular time intervals, such as every 4
milliseconds, for example. The interrupt interval is preferably
based upon processor capability and hardware requirements. Step 206
performs maintenance functions, such as incrementing counters (not
shown) which are used to determine when filtering and other
routines should be run.
[0016] If it is the appropriate time to recalculate averages, step
208 directs the algorithm to step 210, else to step 212.
[0017] Step 210 calculates an average of the accelerometer signal
and adjusts the constants based on the response of the cylinder 18
to the valve command signal to compensate for drift of the
accelerometer and to compensate for variations in cylinder
response. The constants may also be adjusted to compensate for
variations of voltage, hydraulic pressure and other parameters.
[0018] Step 212 inputs data from the accelerometer 32 and position
sensor 34. If desired, other data may be received, such as voltage,
hydraulic pressure, etc.
[0019] Step 214 calculates the velocity of the seat base 16 by
integrating the signal from accelerometer 32 for the most recent
time interval.
[0020] Step 216 performs various filtering functions, such as
filtering the seat base velocity value because the valve 22 cannot
respond to high frequencies, and canceling low frequencies. Seat
position, cylinder velocity, voltage and hydraulic pressure signals
could also be filtered. Such filtering may be accomplished via
software filters in algorithm 200 or by analog filters (not shown)
or a combination thereof.
[0021] Step 218 calculates a seat Position_Error value by
subtracting the position command from the sensed seat position.
[0022] Step 220 generates the valve command according to this
equation:
VALVE COMMAND=Filtered seat base
Velocity.times.K.sub.--V.sub.--CMD+K2.sub-
.--V.sub.--CMD+Position_Error.times.K.sub.--Pos,
[0023] where K_V_CMD is predetermined valve command constant,
K2_V_CMD is a valve command offset constant, and K_Pos is gain
constant.
[0024] The resulting system operates to limit vibration of seat 12
with the accelerometer 32 attached to the seat base 16, not the
seat 12. With this algorithm the command sent to the valve 22 is
not based on a complicated equation which attempts to cancel
acceleration. Instead, the system determines the velocity caused by
the acceleration and then cancels most of that velocity. The above
described algorithm is simple for the ECU to execute, thus
providing a rapid response and minimal acceleration of the seat. It
is not possible to cancel all of the seat velocity, as that would
require that the seat stay at the same height, relative to the
center of the earth.
[0025] The constants can be adjusted adaptively if the cylinder 18
does not respond in a linear manner to the command, if different
cylinders have different responses, or if these responses vary over
time. In other words, if the response of cylinder 18 to velocity
commands is slower or faster than desired, the constants could be
changed to achieve the desired response. If the gain of the valve
vs. cylinder velocity command is non-linear, or varies with seat
position, then a table of constants, or an equation relating
response to command could be stored in a memory of the ECU 36.
[0026] This control system could be implemented through the use of
an analog controller, or a hybrid circuit (combination of analog
and digital controller), although an analog system would be more
difficult to make adaptive. Referring to FIG. 3, a position error
signal is generated by a difference unit 100 which receives a
desired seat height signal from operator control 38 and the seat
height signal from sensor 34. The position error is multiplied by
Kpos and applied to summing unit 104. An integrator 102 converts
the base acceleration signal from sensor 32 into a base velocity
signal. The velocity signal is multiplied by Kv_cmd and applied to
summing unit 104. The valve command offset K2_V_cmd is also applied
to summing unit 104. The output of summing unit 104 is applied to
an input of valve unit 22 ??? which in turn controls the velocity
of actuator or cylinder 18.
[0027] While the present invention has been described in
conjunction with a specific embodiment, it is understood that many
alternatives, modifications and variations will be apparent to
those skilled in the art in light of the foregoing description.
Accordingly, this invention is intended to embrace all such
alternatives, modifications and variations which fall within the
spirit and scope of the appended claims.
* * * * *