Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle subsystem or accessory control
Reexamination Certificate
1999-06-17
2001-10-30
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle subsystem or accessory control
C701S036000, C701S038000, C280S005501, C280S005504, C280S005512, C280S005515
Reexamination Certificate
active
06311110
ABSTRACT:
FIELD OF INVENTION
The present invention relates generally to semi-active suspension control systems and, more particularly, to an adaptive off-state control method for such suspension systems.
BACKGROUND OF THE INVENTION
Reduction of transmitted mechanical energy in the form of shock and vibration between a mass and a support, such as a vehicle body (a sprung mass) and a vehicle wheel (an unsprung mass), is a problem of considerable importance in suspension systems, cab suspensions, seat suspensions and also in the support of sensitive equipment and payloads. Such isolation systems for reducing the transmittal of shock and vibratory energy between a mass and a support are typically disposed between a mass and the support.
For purposes of this invention, prior art isolation systems will be considered as passive, active, and semi-active. Passive isolation devices such as springs or spring-damper combinations as used in most automobiles have a performance that is strictly a function of their inherent structural characteristics. Although such passive devices provide effective isolation in a certain frequency range, they are subject to amplified excitation in passing through their natural or resonant frequency range. This frequency range is determined by the spring rate of the spring and the isolated mass. Because a passive device is subject to amplified excitation at its resonant frequency, harmful effects such as damage to the isolated mass or to the passive device may occur. Further, some passive isolation systems provide adequate control of the sprung mass at the natural frequency of the suspension while imposing far too much damping force between the interconnected members at higher frequencies. Thus, the selection of damping and the amount thereof is a design compromise when using a passive device.
Active isolation systems employ an external power source, which supplies energy in a controlled manner to counteract vibrational forces and to reduce their transmission. Such active isolation systems are advantageous in that they can generate forces as a function of the vibratory condition to be controlled. However, such active systems require a large auxiliary power source and typically require additional equipment such as pumps, motors, and servo-valves, which are may not be sufficiently responsive at high operating frequencies due to the limitations of such equipment to rapidly respond to control signals. Moreover, such active systems tend to be costly and require large amounts of power to operate.
A semi-active system has the inherent limitation that it can generally only produce forces opposing motion of the supported mass; it cannot generate force in the direction of motion. Thus, the term “semi-active” refers to control systems that are limited to removing energy from a system. However, semi-active systems are capable of performance nearly equivalent to that of active systems when operated in accordance with a suitable primary control method and, more particularly, control methods which emulate a so-called “Skyhook” damper such as described in Karnopp, D.C. et al., “Vibration Control Using Semi-active Force Generators,” ASME Paper No. 73-DET-122 (June 1974). Semi-active dampers and various control methods for them are disclosed in Karnopp, U.S. Pat. No. 3,807,678; Miller et al., U.S. Pat. Nos. 4,821,849, 4,838,392 and 4,898,264; Boone, U.S. Pat. No. 4,936,425; and Ivers, U.S. Pat. No. 4,887,699 all owned by the assignee of the present invention.
Semi-active dampers may be either of the “on/off” type, the “orifice setting” type, or the “force controlled” type. An “on/off” semi-active damper is switched according to a suitable control method between “off” and “on” damping states. In the “on-state” the so-called damping coefficient of the damper is of a preselected, relatively high magnitude. For purposes of this invention the term “damping coefficient” means the relationship of the damping force generated by the damper to the relative velocity across the damper, which relationship is not necessarily linear. In its “off-state” the damping coefficient of the damper is approximately zero or of some relatively low magnitude.
An orifice-setting semi-active damper is also switched during operation between an “off-state”, wherein the damping coefficient is approximately zero or of some relatively low magnitude, and an “on-state”. However, when an orifice-setting semi-active damper is in its “on-state,” the damping coefficient thereof normally is changed between a large (theoretically infinite) number of different magnitudes. The magnitude of the damping coefficient is typically determined by the diameter setting of the valve orifice of the damper.
A “force controlled” damper, in theory, is capable of creating any desired dissipative force in the “on-state” independent of the relative velocity across the damper. This is in contrast to the above described “on/off” and “orifice setting” dampers in which the “on-state” damping force depends on the relative velocity across the damper. A force-controlled damper can either be realized by use of feedback control, or by use of pressure controlled valves. In the “off-state” the force-controlled damper will command the valve to the full-open position in which the damping coefficient is approximately zero or some relatively low value.
Although semi-active suspension systems provide substantial performance advantages over other types of systems, they are known to have problems when subjected to large, abrupt input disturbances, i.e., such as those encountered on rough terrain. Excessive suspension motions and travel can result in uncomfortable or damaging force inputs to the suspension system when the suspension reaches its end of travel (either a compressed or extended condition) so as to impact the mechanical end stops of the suspension. End-stop collisions result in degraded isolation by the suspension by significantly increasing the root-mean-square (RMS) accelerations thereof. Therefore, it should be recognized that such end-stop collisions detract from ride comfort, and place undue stress on system components thereby shortening their longevity.
Semi-active isolation systems employing a above-mentioned “Skyhook” control method or a derivative thereof, as described hereinafter in further detail, tend to increase the average range of suspension deflection to provide “smoother” ride characteristics, but under certain conditions, may actually increase the incidence of suspension end-stop collisions. This tendency is discussed in Miller, “Tuning Passive, Semi-active and Fully Active Suspension Systems,” Proceedings of the 27th CDC of IEEE, Vol. 3, 1988 and in Ivers et al., “Experimental Comparison of Passive, On/Off Semi-active and Continuous Semi-active Suspensions,” SAE Paper No. 892484, Dec. 7, 1989.
Of course, the incidence of suspension end-stop collisions can be reduced and even eliminated by utilizing a damper with a sufficiently high damping coefficient. However, this would defeat the performance advantages of semi-active control by unnecessarily limiting the range of suspension deflection for the given range of motion of the suspension and degrading the isolation of the vehicle.
A technical solution for reducing the incidence and severity of suspension end-stop collisions in semi-active isolation systems without degrading their performance is disclosed in Miller, et al., U.S. Pat. No. 5,276,622. In the ('622) patent a method and apparatus controls the operation of an isolation system having an adjustable damper interconnecting relatively movable members. The method and apparatus attenuate the transmission of forces therebetween in which relative movement of the members is restricted beyond a certain limit by one or more end stops. The conditions of operation of the isolation system are monitored by sensors to produce data indicative of relative displacement, relative velocity, acceleration or other conditions. Damper control signals are provided to the damper to adjust the damping characteristics thereof, as determined by the data
Ivers Douglas E.
St. Clair Kenneth A.
Broadhead Brian J.
Cuchlinski Jr. William A.
Gnibus Michael M.
Lord Corporation
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