Spring devices – Vehicle – Comprising compressible fluid
Reexamination Certificate
2001-07-20
2004-02-24
Lavinder, Jack (Department: 3683)
Spring devices
Vehicle
Comprising compressible fluid
C188S322180
Reexamination Certificate
active
06695294
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a controlled equilibrium device, and more specifically the invention relates to a controlled equilibrium device that provides active relative position control between first and second members where the controlled equilibrium device comprises a first spring rate applied when the device is below a threshold displacement value, a second spring rate applied when the device is above a threshold displacement value and integral damping for controlling the device displacement.
BACKGROUND OF THE INVENTION
Conventional passive isolators and mounts include elastomeric or other resilient members producing a support stiffness that limits, for a particular environment or application, the transmission of vibratory disturbances and displacements across the isolator. If the input excitation frequencies are well above the suspension resonance, then good isolation can be achieved without undue difficulty. However, often there are also large inputs with frequencies near the suspension resonance, which amplifies the excitation. There may be insufficient damping in the conventional passive isolators to control motion at resonance. In such case, the well known isolators with resilient members typically comprise a trade-off between low or “soft” spring rates suitable for effectively limiting the transmission of high frequency vibratory inputs, and high or “hard” spring rates suitable for limiting the relative motion across the isolator caused by low frequency inputs. If the spring rate is too hard, excessive high frequency vibration will be transmitted. If the spring rate is too soft, low frequency inputs will produce excessive strain in the resilient members causing durability problems. In addition, if the spring rate is too soft, low frequency inputs will produce damaging collisions between the suspended device and adjacent devices, due to the large relative displacements. Conventional passive isolators may incorporate progressive stiffness such that the mounts snub near end-of-travel for large, low-frequency input excitations. This is only a slight improvement, since isolation will be degraded for all times at the higher stiffness, and contacting the snubbers typically results in a jolt with resulting decreased passenger comfort or reduced life for suspended components. For the soft spring rate, conventional passive isolators must accommodate a large static deflection, which causes increased size, weight and cost, which are undesirable. If the static load size and location varies, the resulting static deflection also varies, which increases difficulty for connecting to adjacent unsuspended devices and precludes maintaining a level platform which reduces passenger comfort such as in truck cabs.
The above risk of excessive strain in the resilient member may be decreased by increasing the size of the rubber elements, thereby not increasing the strain even as the displacement is increased. However, the increased size will result in greater size, weight and cost, which are undesirable. The above risk of damaging collisions may be decreased by utilizing increased damping, particularly at resonance. However, elastomers typically have low damping values, and those with high damping have reduced durability and higher compression set, which in turn increases the static deflection which is undesirable as discussed above. Adding external damping, for example hydraulic shock absorbers, may help but at increased complexity and cost. Even if the size of the rubber elements and damping could be increased without added size, weight and cost, the resulting system would still have the aforementioned difficulties with snubbing and load leveling.
An alternative to the conventional passive isolator is the conventional passive air-suspension with separate load-leveling valve and hydraulic damper. The air-suspension provides a soft suspension for good isolation of high frequency inputs. The load leveling valve limits the static deflection thereby reducing strain in the suspension. This system effectively provides a high spring rate at very low, quasi-static response frequencies, and a soft spring rate at all other frequencies. The load leveling for a conventional passive air-suspension typically includes a “dead band” wherein the valve is not actuated for high frequency, low amplitude vibrations, thereby minimizing power consumption. The hydraulic damper allows greater damping than the conventional passive isolator and thus limits motion near resonance. However, hydraulic dampers are velocity-sensitive devices, and thus provide no damping at very low, quasi-static response frequencies. Thus the conventional passive air-suspension with separate load-leveling valve and hydraulic damper are particularly ill-suited for applications wherein high damping at very low frequency, quasi-static roll and pitch are important for driver comfort and perceived safety, such as in a four-point-soft cab suspensions. In addition, the load leveling provided by a conventional passive air-suspension responds too slowly to react to anything but quasi-static inputs. Thus, the load leveling provided by a conventional passive air-suspension cannot reduce the time spent near end of travel at the snubbers with resulting reduced performance as discussed above. If the reciprocal of the response time is the “break frequency”, then the “break frequency” must be less than the resonance frequency to maintain stability. For this system, adding damping allows a faster stable response time. By carefully tuning and controlling damping, the response time can be optimized and controlled in a stable manner, thereby providing “fast load leveling”. Fast load leveling further improves the vibration isolation, since it optimally reduces the amount of time near the “end of travel” where the high stiffness of the snubbing reduces the isolation. However, the hydraulic dampers used in a conventional passive air-suspension are not easily controlled since they are sensitive to temperature and prone to leakage. It is therefore desirable to integrate the air-suspension and leveling valve into a single device with carefully tuned, well controlled damping. In addition, integrating the air-suspension, load-leveling valve and damping into a single device reduces system complexity, eliminates device support bracketry and thereby reduces system size, weight and cost.
Another means for canceling noise and vibration across a broadband of frequencies is through the use of active mounts such as those described in U.S. Pat. Nos. 5,526,2292 and 5,845,236 both assigned to Lord Corporation. Such active devices use actuators to cancel the force that is transmitted through the mount. In effect, active mounts are very soft at relatively high vibration frequencies and reasonably stiff at low frequencies to control relative motion. Active mounts provide suitable vibration control however active mounts are quite expensive and conventional active mounts and systems require complex electronic control systems and methods.
Control equilibrium devices or CEM's are typically soft mounts that include a load leveling feature which makes the mount stiffer at low frequencies and soft at high frequencies. One such CEM is disclosed in United Kingdom Patent Number 2,298,021 for “Improved Vibration Isolator” issued and assigned to Barry Controls Limited. As shown in the
FIGS. 2 and 4
of the '021 reference, the vibration isolator generally comprises a core assembly movably suspended within a housing by a resilient member and a valve arrangement such that when the core assembly reaches a predetermined point of deflection, the valve arrangement causes fluid to flow into the core to apply a force tending to return the core assembly to the equilibrium position.
In the '021 reference the core assembly translates freely through the housing until it contacts or is snubbed by the housing. No damping is provided except the low-level damping in the elastomeric members, which as discussed above for conventional passive isolators, may be insufficient to c
Alteri Russell E.
Hildebrand Stephen F.
Ivers Douglas E.
Janowski Michael D.
Jensen William S.
Lavinder Jack
Lord Corporation
Murphy III Edward F.
Nguyen Xuan Lan
LandOfFree
Controlled equilibrium device with displacement dependent... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Controlled equilibrium device with displacement dependent..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Controlled equilibrium device with displacement dependent... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3310633