Title: Semi-active shock absorber control system
Abstract: A semi-active control methodology is provided for a spring/mass system, for example a real-time adjustable shock absorber system. The methodology includes defining a plurality of operating zones based on system parameters and user-definable or preset inputs. The methodology also includes processing to account for non-inertial spring/mass system response and multidimensional forces acting on the system, and an acceleration hedge calculation to accurately define system operation at extrema of travel. The methodology is generally directed at producing a plurality of valve control signals, selecting among the valve control signals, and applying the selected control signal to the valve in a closed-loop feedback system to adjust the energy in the spring/mass system.
Patent Number: 6,904,344 Issued on 06/07/2005 to LaPlante, et al.
| Inventors:
|
LaPlante; John A. (Willington, CT);
Larkins; William T. (Manchester, NH)
|
| Assignee:
|
ActiveShock, Inc. (Manchester, NH)
|
| Appl. No.:
|
838680 |
| Filed:
|
May 4, 2004 |
| Current U.S. Class: |
701/37; 280/5.5; 701/38 |
| Intern'l Class: |
G06F 007/00; B60G017/00; B60G023/00 |
| Field of Search: |
701/37,38
280/55,551.5,551.4
|
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| 5559700 | Sep., 1996 | Majeed et al.
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| 5682968 | Nov., 1997 | Boichot et al.
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| 5692587 | Dec., 1997 | Fratini, Jr.
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| 5712783 | Jan., 1998 | Catanzarite.
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| 5732370 | Mar., 1998 | Boyle et al.
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| 5828970 | Oct., 1998 | Kimura et al.
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| 5862894 | Jan., 1999 | Boichot et al.
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| 5890081 | Mar., 1999 | Sasaki.
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| 5897130 | Apr., 1999 | Majeed et al.
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| 5908456 | Jun., 1999 | Wahlers.
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| 5975508 | Nov., 1999 | Beard.
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| 6049746 | Apr., 2000 | Southward et al.
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| 6070681 | Jun., 2000 | Catanzarite et al.
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| 6097999 | Aug., 2000 | Shal et al.
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| 6112866 | Sep., 2000 | Boichot et al.
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| 6226581 | May., 2001 | Reimann et al.
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| |
| 6604751 | Aug., 2003 | Fox.
| |
Primary Examiner: Beaulieu; Yonel
Attorney, Agent or Firm: Grossman Tucker Perreault & Pfleger, PLLC
Goverment Interests
The U.S. Government has a paid-up license in this invention and the right in
limited circumstances to require the patent owner to license others on reasonable
terms as provided for by the terms of Contract Number USZA22-02-P-0024 awarded
by the Department of Defense.
Parent Case Text
This application is a continuation application under 37 CFR § 1.53(b) of
application Ser. No. 10/341,129 filed Jan. 13, 2003, now U.S. Pat. No. 6,732,033,
which claims priority to U.S. Provisional Application Ser. No. 60/347,662, filed
Jan. 11, 2002, both of which are incorporated herein by reference.
Claims
1. A shock absorber controller for generating a target control signal to adjust
the energy in a spring mass system, said spring mass system comprising at least
two masses, a spring coupled between said masses and a controllable damper, said
shock absorber controller comprising:
a plurality of inputs configured to receive input signals representing parameters
selected from the group consisting of a relative position of said masses, a relative
velocity of said masses, accelerations of said masses, a spring constant of said
spring mass system, a mass of at least one said masses, a critically damped coefficient
of said spring mass system, an upper force threshold for a critically damped force
in said spring mass system, and an endstop position of said spring mass system;
a first processor configured to determine if said spring mass system is compressing
or expanding based on at least said relative velocity of said masses with respect
to one another;
at least second and third processors configured to generate control signals to
control said controllable damper in said spring mass system in response to at least
one of said input signals; and
a fourth processor configured to select one of said control signals based on
said spring mass system compressing or expanding and based on a comparison of said
control signals and configured to generate a target control signal based on said
selected signal, said target signal being proportional to a desired energy in said
spring mass system.
2. The shock absorber controller of claim 1 wherein said second processor is
configured to generate a control signal based on at least said relative velocity
of said masses and proportional to a damping force to be applied to said spring
mass system, and wherein said third processor is configured to generate a control
signal to preposition said spring mass system based on said relative position of
said masses, said relative velocity of said masses and an acceleration of at least
one of said masses.
3. The shock absorber controller of claim 1 wherein said first processor includes
a quadrant determination processor configured to generate a quadrant signal representative
of a quadrant of operation for said spring mass system based on said relative position
and said relative velocity of said masses.
4. The shock absorber controller of claim 1 wherein said second processor includes
an inertial endstop processor configured to generate an inertial endstop force
signal based on at least said relative velocity and a relative position of said
masses with respect to one another, wherein said endstop signal is proportional
to an acceleration that allows one of said masses to arrive at a position of minimum
travel at approximately zero velocity.
5. The shock absorber controller of claim 4 further comprising a non-inertial
endstop processor configured to calculate an absolute velocity and an absolute
displacement of said masses with respect to one another, wherein said inertial
endstop signal is modified by adding said absolute velocity and said absolute displacement.
6. The shock absorber controller of claim 4 wherein said third processor includes
a critically damped processor configured to generate a critical damping force signal
proportional to a critical damping force of said spring mass system based on said
relative velocity, said spring constant, said critically damped coefficient, and
said mass of one of said masses.
7. The shock absorber controller of claim 6 further comprising a pitch and roll
processor configured to measure acceleration of at least one of said two masses
in the x and/or y direction, wherein said critically damped coefficient is modified
based on said measured acceleration.
8. The shock absorber controller of claim 4 wherein said third processor includes
a prepositioning processor configured to generate at least one prepositioning signal
to preposition said spring mass system based on said relative position, said relative
velocity and an acceleration of at least one of said masses.
9. The shock absorber controller of claim 4 further comprising an acceleration
hedge processor configured to generate an acceleration hedge signal proportional
to the addition of acceleration or force of a first one of said masses to that
of the target acceleration or force of a second one of said masses to drive the
average acceleration or force of the second mass to approximately equal the actual
acceleration or force of the first mass, wherein said fourth processor is configured
to add said acceleration hedge signal to said selected signal.
10. The shock absorber controller of claim 1 further comprising a processor configured
to derive said relative velocity from said relative position.
11. A shock absorber controller for generating a target control signal to adjust
energy in a spring mass system, said shock absorber controller comprising:
inputs configured to receive system parameter signals from said spring mass system
and to receive a comfort force signal proportional to an upper force threshold
for a critical damping force;
a determination processor configured to determine if said spring mass system
is compressing or expanding;
an endstop processor configured to generate an endstop force signal proportional
to an endstop damping force;
a critically damped processor configured to generate a damped force signal proportional
to said critical damping force; and
a selection logic processor configured to select one of said endstop force signal,
said damped force signal, or said comfort force signal based on said spring mass
system compressing or expanding and based on a comparison of said force signals
and to generate a target control signal based on said selected signal, said target
signal being proportional to a desired energy in said spring mass system.
12. The shock absorber controller of claim 11 wherein said endstop force signal
is based on at least a relative velocity and a relative position of masses in said
spring mass system and is proportional to an acceleration that allows one of said
masses to arrive at a position of minimum travel at approximately zero velocity.
13. The shock absorber of claim 12 further comprising a non-inertial endstop
processor configured to calculate an absolute velocity and an absolute displacement
of said masses with respect to one another, wherein said inertial endstop signal
is modified by adding said absolute velocity and said absolute displacement.
14. The shock absorber controller of claim 11 wherein said damped force signal
is based on a relative velocity of masses in said spring mass system, a spring
constant of said spring mass system, a critically damped coefficient of said spring
mass system, and a mass of one of said masses.
15. The shock absorber controller of claim 14 further comprising a pitch and
roll processor configured to measure acceleration of said spring mass system in
the x and/or y direction, wherein said critically damped coefficient is modified
based on said measured acceleration.
16. The shock absorber controller of claim 11 further comprising a prepositioning
processor configured to generate at least one prepositioning signal to preposition
said spring mass system based on a relative position of masses in said spring mass
system, a relative velocity of said masses in said spring mass system, and an acceleration
of at least one of said masses, and wherein said selection logic processor is configured
to select said prepositioning signal based on said spring mass system compressing
or expanding and based on a comparison of said control signals.
17. The shock absorber controller of claim 11 further comprising an acceleration
hedge processor configured to generate an acceleration hedge signal, wherein said
selection logic processor is configured to add said acceleration hedge signal to
said selected signal.
18. The shock absorber controller of claim 11 wherein said determination processor
is a quadrant determination processor configured to generate a quadrant signal
representative of a quadrant of operation for said spring mass system based on
a relative position and a relative velocity of masses in said spring mass system.
19. The shock absorber controller of claim 11 wherein said target control signal
is a target acceleration signal.
20. The shock absorber controller of claim 11 wherein said system parameter signals
represent a relative position of masses in said spring mass system and accelerations
of said masses in said spring mass system.
21. The shock absorber controller of claim 20 further comprising a processor
configured to derive a relative velocity of said masses from said relative position.
22. A shock absorber control system for adjusting energy in a spring mass system
comprising at least two masses, a spring between said masses, and a controllable
valve, said shock absorber control system comprising:
sensors for measuring system parameters in said spring mass system including
at least a relative position of said masses;
a controller configured to receive said system parameters, to generate a plurality
of control signals based on said system parameters, and to generate a target control
signal based on a selected one of said control signals, said target control signal
being proportional to a desired energy in said spring mass system; and
a valve controller configured to control said valve in said spring mass system
in response to said target control signal such that said control system operates
as a feedback control loop.
23. The shock absorber control system of claim 22 wherein said sensors comprise
a relative position sensor for measuring said relative position and accelerometers
for measuring an acceleration of each of said masses.
24. The shock absorber control system of claim 22 wherein said controller comprises
a first processor configured to determine if said spring mass system is compressing
or expanding based on at least a relative velocity of said masses with respect
to one another.
25. The shock absorber control system of claim 24 wherein said controller comprises:
at least second and third processors configured to generate said control signals
to control said controllable valve in said spring mass system; and
a selection logic processor configured to select one of said control signals
based on said spring mass system compressing or expanding and based on a comparison
of said control signals and configured to generate a target control signal based
on said selected control signal, said target control signal being proportional
to a desired energy in said spring mass system.
26. The shock absorber control system of claim 22 wherein said controller comprises
a processor configured to derive a relative velocity of said masses from said relative position.
27. The shock absorber control system of claim 22 wherein said controller comprises
a processor configured to generate at least one prepositioning control signal to
preposition said masses, said prepositioning control signal being based on at least
said relative position of said masses, a relative velocity of said masses, and
an acceleration of at least one of said masses.
28. The shock absorber control system of claim 22 wherein said controller comprises
a processor configured to generate at least one force control signal to apply a
damping force to said spring mass system, said force control signal being based
on at least said relative position of said masses.
29. The shock absorber control system of claim 22 wherein said controller comprises
a processor configured to generate an acceleration hedge signal proportional to
the addition of acceleration or force of a first one of said masses to that of
the target acceleration or force of a second one of said masses to drive the average
acceleration or force of the second mass to approximately equal the actual acceleration
or force of the first mass, wherein said controller is configured to add said acceleration
hedge signal to said selected signal.
30. The shock absorber control system of claim 22 wherein said target control
signal is a target acceleration signal proportional.
31. A controller for generating a target control signal to adjust the energy
in a spring mass system comprising at least two masses, a spring coupled between
said masses, and a controllable valve, said selection logic processor comprising:
means for receiving a quadrant signal, an endstop force signal, a critical damping
force signal, a comfort force signal, a valve prepositioning signal, and an acceleration
hedge signal;
means for selecting one of said endstop force signal, said critical damping force
signal, said comfort force signal, or said valve prepositioning signal based on
said quadrant signal and a comparison of said endstop force signal, said critical
damping force signal, and said comfort force signal; and
means for adding said acceleration hedge signal to a selected one of said endstop
force signal, said critical damping force signal, or said comfort force signal.
32. A controller for generating a target inertial and non-inertial energy control
signal in a spring/mass shock absorber system comprising two masses coupled together
by a spring having a controllable valve to adjust the energy in said system, said
controller comprising:
an inertial endstop processor configured to generate an endstop signal based
on the relative velocity and relative position of said two masses, said inertial
endstop signal comprising a signal that is proportional to the minimum acceleration
necessary for one of said masses to arrive at a position of maximum or minimum
travel at approximately zero velocity;
a non-inertial endstop processor configured to modify said endstop signal with
a signal indicative of the absolute velocity and the absolute displacement of said
masses with respect to one another; and
a selection processor configured to determine if said endstop signal should be
designated as a target control signal for said controllable valve based on the
relative velocity of said masses.
33. A controller for generating a target multidimensional damped energy control
signal in a spring/mass shock absorber system comprising two masses coupled together
by a spring having a controllable valve to adjust the energy in said system, said
controller comprising:
a critically damped processor configured to generate a damped signal based on
a spring force constant, said damped signal comprising a signal proportional to
a damped trajectory of at least one of said masses in the z direction, wherein
said damped signal is multiplied by a critically damped coefficient;
a pitch and roll processor configured to modify said critically damped coefficient
based on a measured acceleration of at least one of said two masses in the x and/or
y direction; and
a selection logic processor configured to determine if said damped signal should
be designated as a target control signal for said controllable valve.
34. A controller for generating a target direct valve control signal in a spring/mass
shock absorber system comprising two masses coupled together by a spring and a
controllable valve to adjust the energy in said system, said controller comprising:
a valve prepositioning processor configured to generate a first valve prepositioning
signal to bias said valve so that the system anticipates an impulse acceleration
that will occur to the system and to generate a second valve prepositioning signal
to bias the valve at approximately the open position to allow the mass to freely
move apart within the constraints of the system; and
a selection logic processor configured to select between said first or second
valve prepositioning signals to be designated as a target control signal for said
controllable valve.
35. A controller for modifying a valve control signal with an acceleration hedge
control signal in a spring/mass shock absorber system comprising two masses coupled
together by a spring having a controllable valve to adjust the energy in said system,
said controller comprising:
processors configured to generate a plurality of valve control signals based
on the relative velocity of said masses;
an acceleration hedge processor configured to generate an acceleration hedge
signal proportional to the addition of the acceleration or force of a first one
the masses to that of the second one mass to drive the average acceleration or
force of the second mass to approximately equal the actual acceleration or force
of the first mass; and
a selection logic processor configured to add said acceleration hedge signal
to a selected one of said valve control signals.
Description
1. FIELD OF THE INVENTION
The present invention relates to a controller and control methodology for a semi-active
shock absorber. More particularly, the present invention relates to a system and
method of controlling the relative motion between two masses, using a suspension
that includes a shock absorber or damper. The system and method can be applied
to a number of types of systems such as the primary suspension on a vehicle, which
isolates the mass of the chassis from the motion of the wheels as they run over
rough terrain or a truck, or boat seat that is isolated from the movements of the
cab or hull. The present invention has general applicability to any system that
has a vibration isolation mechanism that isolates the sprung mass from movements
of the unsprung mass such as engine mounts, machinery mounts or other typical applications
for isolation mounts.
2. BACKGROUND OF THE INVENTION
Suspensions and isolation mounts generally fall into one of the following
categories: passive, active or semi-active. Passive mounts usually include a passive
spring and passive damper and can be tuned to provide very good isolation for a
given set of conditions such as fixed masses and constant frequency disturbance
into the unsprung mass. However if the mass changes due to increased payload, or
the input frequency changes due to a change in speed over the ground, the isolation
performance is degraded and often results in very large shock loads when the system
hits the ends of travel, usually referred to as "topping" or "bottoming" the suspension.
Active suspensions are able to provide much better isolation over a wider
range of conditions than a purely passive system. They can read a variety of sensors,
then process the information to provide an optimal target force between the two
masses at any time, given the power limits of the actuators and support systems.
In addition, they are capable of adding energy to the system whereas passive and
semi-active systems can only subtract energy. Active suspensions have not gained
wide acceptance due to high cost and complexity as well as the demand for high
power from the vehicles prime mover. In the case of off-road vehicles with long
travel suspensions moving over rough terrain, the power draw of the suspension
is prohibitive and reduces the maximum acceleration of the vehicle.
Semi-active suspensions are generally less costly and complex than fully
active systems while retaining most of the performance advantages. They use the
passive spring from conventional suspensions and add a controllable damper as well
as the sensors and microprocessor required to allow the damper force to be controlled
in real time. The damper can still only subtract energy from the system, however
it can provide any level of damping that is demanded by the control method, rather
than being governed by the fixed velocity/force laws that are characteristic of
passive dampers.
There are a number of control methods that have been developed for semi-active
suspensions, starting with "skyhook" method described by Karnopp, et al., "Vibration
Control Using Semi-active Force Generator," ASME Paper No. 73DET-123, May 1974,
and U.S. Pat. No. 3,807,678. This method attempts to make the damper exert a force
which is proportional to the absolute velocity of the sprung mass, rather than
the relative velocity between the two masses. Hence the term skyhook since the
mass is treated as though it is referenced to the inertial coordinate system rather
than the ground. While this method can yield very good isolation over bumps that
are smaller than the amount of compression travel in the system, larger bumps cause
the suspension to bottom out resulting in a large shock load being transmitted
into the sprung mass.
Another method has been developed to deal with the bottoming and topping
problem called the "end stop" method. In end stop mode, the microprocessor calculates
the minimum force required to decelerate the sprung mass and prevent the suspension
from bottoming. While this is effective in preventing the high shock loads from
being transmitted into the sprung mass, it results in excessive suspension movement
over smaller bumps. This can be very disconcerting to the operator because it prevents
him from having a good "feel" for the behavior and handling of the vehicle.
There have also been attempts to combine several methods and assign relative
weightings or develop rules that govern the use of alternate methods under certain
circumstances. Most of these efforts have been aimed at isolation efficiency as
the overall goal or metric of relative merit. However there are other factors that
are important in suspension systems such as transient force distribution that can
influence handling and vehicle control, as well as subjective factors such as operator
comfort and confidence.
SUMMARY OF THE INVENTION
The present invention solves the shortcomings of the prior art with a set of
rules that will result in a practical semi-active suspension control method.
In one aspect, the present invention includes a method for determining if a shock
absorber system is compressing and for generating a target control signal for shock
absorber system comprising two masses coupled together by a spring having a controllable
valve to adjust the energy in said system. The method includes the step of determining
if the spring/mass system is compressing in a z direction by determining the current
velocity of the masses with respect to one another. The method also includes the
step of generating an inertial endstop signal based on the relative velocity and
the relative position of said masses, the inertial endstop signal is proportional
to the minimum acceleration necessary for one of the masses to arrive at a position
of minimum travel at approximately zero velocity. The method also includes the
step of generating a damped signal based on a spring force constant, the critically
damped signal is proportional to a critically damped trajectory of at least one
of the masses, and generating a comfort signal defined as an upper force threshold
for said critically damped signal. The method selects one of the signals as a target
signal to control said valve and thereby adjust the energy in the spring/mass system.
In another aspect, the present invention includes a method for determining if
a shock absorber system is expanding and for generating a target control signal
for shock absorber system comprising two masses coupled together by a spring an
having a controllable valve to adjust the energy in the system. The method includes
the steps of determining if the spring mass system is expanding in a z direction
by determining the current velocity of the masses with respect to one another;
generating an inertial endstop signal based on the relative velocity of the masses,
the inertial endstop signal is proportional to the minimum acceleration necessary
for one of the masses to arrive at a position of maximum travel at approximately
zero velocity; and generating a damped signal based on a spring force constant,
the damped signal is proportional to a damped trajectory of at least one of the
masses. The method also includes the steps of generating a first valve prepositioning
signal proportional to the valve position that permits one of the masses to freefall
away from the other mass; and generating a second valve prepositioning signal proportional
to the valve position that permits one of the masses to controllably expand away
from the other mass. The method selects one of these signals as a target signal
to control said valve and thereby adjust the energy in the spring/mass system.
In still another aspect, the present invention provides a method for generating
a target inertial and non-inertial energy control signal in a spring/mass shock
absorber system comprising two masses coupled together by a spring having a controllable
valve to adjust the energy in said system. The method includes the steps of: generating
an endstop signal based on the relative velocity and relative position of the two
masses, the inertial endstop signal is proportional to the minimum acceleration
necessary for one of the masses to arrive at a position of maximum or minimum travel
at approximately zero velocity. The method modifies the endstop signal with a signal
indicative of the absolute velocity and the absolute displacement of the masses
with respect to one another. The method also determines if the endstop signal should
be designated as a target control signal for the controllable valve based on the
relative velocity of said masses.
In yet other aspects, the present invention provides a method for generating a
target multidimensional damped energy control signal in a spring/mass shock absorber
system comprising two masses coupled together by a spring having a controllable
valve to adjust the energy in said system. The method includes the steps of: generating
a damped signal based on a spring force constant, the damped signal is proportional
to a damped trajectory of at least one of the masses in the z direction; defining
a critically damped coefficient; and multiplying the damped signal by the critically
damped coefficient. The method further includes the steps of calculating measuring
the acceleration of at least one of said two masses in the x and/or y direction,
and modifying the critically damped coefficient based on the measured acceleration
of at least one of said two masses in the x and/or y direction. The method also
determines if the damped signal should be designated as a target control signal
for the controllable valve.
Another aspect of the present invention provides a method for generating
a target direct valve control signal in a spring/mass shock absorber system comprising
two masses coupled together by a spring having a controllable valve to adjust the
energy in the system. The method includes the steps of generating a valve propositioning
signal based on the relative position and relative velocity of the masses, the
valve prepositioning signal is proportional to a predefined amount of prepositioning
for the valve so that the energy of the spring assumes a predefined quantity; aind
determining if the valve propositioning signal should be designated as a target
control signal for the controllable valve based on the relative velocity of said masses.
The present invention also provides a method for modifying a valve control signal
with an acceleration hedge control signal in a spring/mass shock absorber system
comprising two masses coupled together by a spring having a controllable valve
to adjust the energy in said system. The method includes the steps of generating
a plurality of valve control signals based on the relative velocity of the masses
and generating an acceleration hedge signal proportional to the addition of the
acceleration or force of a first one the masses to that of the second one of the
masses to drive the average acceleration or force of the second mass to approximately
equal the actual acceleration or force of the first mass. The acceleration hedge
signal is added to a selected one of said valve control signals.
It will be appreciated by those skilled in the art that although the following
Detailed Description will proceed with reference being made to preferred embodiments,
the present invention is not intended to be limited to these embodiments. It should
be understood from the outset that the present invention shall make use of the
terms "methods" or "modular processors", and the such terms shall be construed
broadly as encompassing one or more program processes, data structures, source
code, program code, etc., and/or other stored data on one or more conventional
general purpose and/or proprietary processors, that may include memory storage
means (e.g. RAM, ROM) and storage devices (e.g. computer-readable memory, disk
array, direct access storage). Alternatively, or additionally, such methods or
modular processors may be implemented using custom and/or off-the-shelf circuit
components arranged in a manner well-understood in the art to achieve the functionality
stated herein.
Other features and advantages of the present invention will become apparent
as the following Detailed Description proceeds, and upon reference to the Drawings,
wherein like numerals depict like parts, and wherein:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a representation of a mass/spring system, where relative motion of
the two masses is controlled by a spring and damper;
FIGS. 2A and 2B are space diagrams of the relative position and velocity of
the two masses of the mass/spring system;
FIG. 3 is a collection of exemplary constant deceleration trajectory curves
generated by the system controller of the present invention;
FIGS. 4A and 4B are a collection of critically damped and underdamped trajectories,
respectively, as representing a force generated by the system controller of the
present invention;
FIG. 5 is an exemplary flow chart of the force selection processor utilized
by the spring/mass system controller of the present invention;
FIG. 6 is an exemplary block diagram of the spring/mass system controller of
the present invention;
FIG. 7 is an exemplary system-level control loop of the present invention;
FIG. 8 is another exemplary system-level control loop of the present invention;
FIG. 9 is another exemplary system-level control loop of the present invention,
FIG. 10A is an exemplary spring/mass system response curve in the force-velocity
space (F-V) when the system is controlled in a manner according to the principles
set forth herein; and
FIG. 10B is another exemplary spring/mass system response curve in the force-velocity
space (F-V) when the system is controlled in a manner according to the principles
set forth herein.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
Before describing the present invention in detail, the following definitions
shall be used throughout the Detailed Description.
Definitions
Sprung Mass (SM)—A sprung mass, in the case of a car it would be
the car chassis, in the case of a truck seat, it would be the seat and passenger.
Unsprung Mass (USM)— An unsprung mass, in the case of a car it would
be the wheel; in the case of a truck seat it would be the truck.
Relative Position (Xrel)— means the position of the sprung mass (SM)
and the unsprung mass (USM) relative to one another.
Relative Velocity (Vrel)— means the velocity of the SM and USM relative
to one another.
Bump Stop—Position of physical constraint that limits the minimum
possible relative position of the masses.
Droop Stop—Position of physical constraint that limits the maximum
possible relative position of the masses.
Endstop—means either the droop stop or bump stop or both.
Xend—is a constant for a given system and represent the endstop position.
K—spring force constant.
Fcomfort—an upper force threshold for the critically damped force.
Fcomfort is a user-defined or preset force variable, and is generally provided
to provide a smoother system response than Fcritical.
Fthresh—a force that slows the USM when the system is in freefall
so that the USM goes to the droop stop position at zero velocity. Fthresh is a
user-definable or preset force where an increase in Fthresh brings the USM to the
droop stop more quickly. 0 Gs is an object not being accelerated at all in the
Z direction, perpendicular to the surface of the earth.
-1 Gs is an object in free-fall in the Z direction, perpendicular to the surface
of the earth.
Overview
As an overview, the present invention provides a method for defining various
operating
zones within the characteristic velocity/position control space and a means of
smoothly transitioning between a number of methods as the suspension moves between
zones. In addition, the invention can mimic an inertially controlled shock absorber
valve. This enables it to discern whether the sprung or unsprung mass is moving
and select appropriate damping forces. In other words, it can tell if the vehicle
chassis is moving up, or the suspension and wheel is moving down. If the chassis
is moving, then the suspension will try to damp out the movement. When the suspension
is moving down, and the chassis is experiencing -1 gs, it is usually because the
vehicle is airborne or crossing a large hole and the suspension will allow the
wheel to droop in order to have maximum travel available for the landing or the
next bump. On the other hand, if the chassis is still seeing 0 g, the obstacle
is a pothole, then the system would not let wheel drop nearly as fast in this case.
The invention minimizes the number of sensor readings and subsequent calculations
required to identify the target control parameter. This will help to decrease the
control loop execution time and keep the control bandwidth high, even with inexpensive microprocessors.
One goal of this invention is to produce a practical suspension control system
with good performance in all aspects of vehicle or system dynamics, not just vibration
isolation. It will accomplish this by providing a simple intuitive set of rules
for adjusting the transition threshold between operating zones that is easy to
adjust for different applications or operator preferences. The end result will
be excellent isolation when large inputs to the unsprung mass are experienced without
sacrificing stability and operator feel during normal operation.
FIG. 1 depicts a typical mass/spring system
10. The system
10
includes an unsprung mass USM
12 and a sprung mass SM
14 coupled
together via a spring
16. A damper
18 is provided to control the
energy of the system in a manner according to the present invention. The damper
18 is generalized in the description herein as a valve, as such valves are
well understood in the art. The valve can be, for example, a mechanical, electromechanical,
controllably viscous fluid (electrorheological or magnetorheological fluid type),
or any other controllable valve as is known in the art.
The system also includes a plurality of sensors to generate some of the variables
used by the spring/mass controller, described below. In the exemplary embodiment,
accelerometers
20 and
22 are used to monitor the acceleration of
each of the SM and USM, respectively. Each accelerometer outputs a signal proportional
to the acceleration of the masses. Also, a relative position sensor
26 is
provided to generate a signal proportional to the relative position of the masses
with respect to one another in the z direction. Additionally, a force or pressure
sensor
24 may be included that directly measures the combined force of the
shock absorber and spring (although not a requirement). Other sensors may be provided,
for example, accelerometers in the x and y directions, or pressures sensors within
the shock absorber. The particulars of the sensors are not important for an understanding
of the present invention. Rather, any type of sensor known in the art may be employed
to generate signals proportional to acceleration and position.
Controller
FIG. 6 depicts a block diagram of the spring force (or acceleration) controller
50 of the present invention. The controller
50 includes a plurality
of sensor and user-defined inputs, and generates a target acceleration or force
that is utilized to set the damper to adjust the energy of the spring/mass system.
The controller
50 includes a plurality of modular processors
52,
54,
56,
5S,
60,
62 and
64 to generate
a plurality of control signals that are utilized by the valve to control the spring/mass
system
10. For example, the control signals may include force or acceleration
or direct valve control signals. The controller
50 also includes selection
logic processor
66 that includes the set of predefined miles to select a
target acceleration or force based on the relative position and relative velocity
of the spring/mass system
10. The output of the selection logic processor
66 is a target control signal proportional to a desired energy in the spring/mass
system, as may be represented by acceleration, force or velocity. The following
detailed description shall assume that the control signal is a target acceleration
signal, Atarget, but it should be understood this signal may be generalized as
a target control signal. Atarget is signal that is used to control the valve to
thereby adjust the energy of the system.
The controller of this exemplary embodiment is directed at generating a target
force or acceleration signal based on a set of predefined rules for controlling
the energy in the system defined by the masses and the spring. Of course, the controller
may be adapted to control the unsprung mass or sprung mass independently. The following
detailed description of the controller
50 will discuss the generation of
various force and acceleration signals. Since the masses in the system are known,
these quantities may be used interchangeably. Likewise, it may be desirable to
produce velocity signals instead of force or acceleration signals, and such a modification
is equally contemplated herein by integrating acceleration.
If the modular processors are embodied as executable code running on a processor,
then the controller
50 of the present invention may also include analog
to digital circuitry to convert the analog input signals to a digital value. Such
A/D converters may be selected to have a bit depth and/or sampling frequency to
generate digital signals of a desired resolution. Alternatively, those skilled
in the art will recognize numerous circuit component implementations for the modular
processors to achieve the desired output signals, based on the mathematical formulations
described herein. It should be further noted that the controller
50 may
include processors to derivate or integrate one or more of the input signals to
achieve a desired function. For example, as shown in FIG. 6, a d/dt processor may
be included to derive Vrel from Xrel. Each of the components of the exemplary controller
50 is described below.
Quadrant Determination Processor
60
One of the modular processors of the controller
50 includes a quadrant
determination processor
60. This processor determines the relative position
and velocity of the two masses, and determines the quadrant of operation for the
sprung mass. Referring now to FIGS. 2A and 2B the operational areas of the controller
50 can be roughly mapped out on a 2 dimensional coordinate system in which
the x-axis is the relative displacement between the sprung and unsprung masses
and the y-axis is the relative velocity of the sprung and unsprung masses. The
0,0 point is designated as ride height with no movement of the sprung or unsprung masses.
The third quadrant is compression where velocity is negative and the position
is heading towards a "bottomed out" condition. The second quadrant is also where
the spring is under compression, but returning to ride height. The fourth quadrant
is similar to the third quadrant, except the spring is expanding and the position
is heading toward a "topped out" condition. The first quadrant is similar to the
fourth quadrant but returning to ride height. The quadrant determination process
uses Xrel and Vrel as inputs, and generates a quadrant signal
61 indicative
of the quadrant the system is operating in.
Inertial Endstop Processor
52 and Non-Inertial Endstop Processor
54
Inertial endstop processor
52 uses Xrel, Vrel and Xend to produce
a constant acceleration (or force) signal, Fendstop
53, that is proportional
to the minimum acceleration necessary to arrive at the endstop at zero velocity
(For example, along a deceleration trajectory depicted in FIG.
3). The force
profile that produces the minimum peak force is a constant force. Given a mass
of M, an initial velocity of vo, and an initial position of xo, the kinetic energy is:
To reduce that energy evenly, work must be performed over a distance equal to
the distance to the endstop via a constant force.
Solving for F produces:
##EQU1##
Dividing both sides by the mass produces the acceleration on the left hand
side.
##EQU2##
This equation states a couple of facts.
To determine the constant acceleration necessary to just touch the endstop, the
inputs are current velocity, current position and endstop position (bump stop and
droop stop), no system parameters such as the spring constant or mass are necessary.
Because velocity and position are always changing, this calculation may be performed
at a speed for a desired resolution, e.g. every control cycle.
FIG. 3 depicts exemplary constant deceleration curves which may be generated
by the inertial endstop calculation. The velocity as a function of position for
a constant acceleration is a square root function. Since vo and xo are the current
location and Xend is the endstop location, none of the values depend on system
parameters that are changeable relative to the system. In the exemplary embodiment,
therefore, the inertial endstop calculation can be implemented with a table look-up
or other hard coded method to optimize for code space or execution time.
The inertial endstop processor calculation operates on the assumption that the
unsprung mass has come to rest via an impulse force, and thus, there is no absolute
velocity of the pair moving together. Neglecting this absolute velocity and the
absolute displacement that comes with it may cause the inertial endstop method
to be unprepared for some hard landings in which the force imparted in the vertical
direction upon the unsprung mass is not an impulse.
Two examples would be a boat landing on a wave or a vehicle landing on a slope
that is falling away. In those cases, a pure inertial endstop method would recognize
the need to apply a force higher than the fractional critically damped force much
later than is desirable and generate a large peak force to make up for the earlier underestimate.
To improve upon this, the exemplary controller
50 may also include a non-inertial
endstop processor
54. Essentially, the non-inertial endstop processor
54
anticipates these larger bumps by keeping track of the absolute velocity of the
mass pair. Thus when heading towards bottomed out, even when close to topped out,
a non-inertial endstop calculation can determine if an endstop method needs to
be applied even sooner.
This method starts with a base assumption that the acceleration of the unsprung
mass will be constant at the currently measured or estimated value until it reaches
zero velocity. The inputs to this process are Vrel and the acceleration of the
unsprung mass Ausm. In that case, the distant traveled by the mass pair will be:
##EQU3##
The preceding equation being a result of similar derivation of the above inertial
endstop process
52.
Then the endstop method takes as inputs a modified initial velocity that includes
Vboth and a modified displacement over which the force must be applied.
The initial velocity is:
The displacement over which the force must be applied is:
Where ΔX is calculated as above and the (X-X
end) is the calculation
of the distance of the relative displacement from the end stop.
The non-inertial endstop process
54 produces Vboth and delta X, and inputs
these values into the process for the inertial endstop
52. Thus a modified
and larger delta X and a modified and larger V can be plugged into the inertial
endstop force processor
52 to determine the necessary force in a non-inertial
reference. That is, when the unsprung does not come to rest suddenly but more slowly
over time. This process may be included to help the inertial endstop processor
recognize that the large speed built up during the free-fall must be dissipated
sooner but that it has the entire modified delta X over which to apply the force.
This modifies the Fendstop signal
53 to include these quantities.
Critically Damped Processor
56 and Pitch and Roll Processor
58
The controller
50 may also include a processor
56 that generates
a critical force (or acceleration) Fcritical
57 to return to ride height
(0,0) along a path that is some predetermined fraction, of critically damped. The
inputs to the critically damped processor
56 include K (spring force constant),
the mass of the sprung mass (MS), the relative velocity of the masses Vrel, and
a desired critically damped coefficient ξ.
To calculate that force, one starts with the equation of motion of system comprising
a spring and a linear damper:
Dividing both sides by the mass:
##EQU4##
Since for a mass-spring system the square root of K/M equals ω
o,
which is the resonant frequency, and (B/M) equals the damping coefficient, gamma,
which equals 2*ξ*ω:
Thus the critical damping force (or acceleration) can be calculated by measuring
the relative displacement from ride height and the relative velo
