Patent Application
20060151929
The present invention relates in general to a bush type mounting devices, especially fluid-filled cylindrical elastic mount for damping or isolating vibrations based on flows of a non-compressible fluid contained therein. More particularly, the present invention is concerned with such a fluid-filled elastic mount which is capable of internal damping decoupling for small amplitudes.
Bush type hydraulically damped mounting devices are known. These can be cylindrical elastic vibration damping mount members interposed between two members of a vibration system, for flexibly connecting these two members. Usually, the anchor part for one part of the vibrating machinery is in the form of a hollow sleeve with the other anchor part in the form of a rod or tube extending approximately centrally and coaxially of the sleeve. Resilient walls then join the sleeve and the tube and usually define two chambers connected by a passage way. The chambers are filled with hydraulic fluid, and the movement of the fluid from one chamber to the other through the passageway damps the vibration of the parts of the machinery attached to the respective anchor points. See for example, U.S. Pat. No. 4,771,990 and U.S. Pat. No. 5,044,813 and Japanese Patent Application No. 61-206838(A).
This type of cylindrical elastic mount can be made relatively compact and small-sized, and can be readily designed for a comparatively reduced amount of relative radial displacement between the inner and outer sleeves upon application of even an excessively large vibrational load. For these reasons, the cylindrical elastic mount has been widely used as an engine mount, a differential gear mount and a suspension bushing for automotive vehicles.
In addition to inertial damping of vibrations having a high amplitude, e.g. greater than 0.5 mm, and low frequency, e.g. about 4-15 Hz., it is desirable to provide for damping decoupling for vibrations having a low amplitude, e.g. less than 0.5 mm, and high frequency, e.g. about 8-30 Hz.
In U.S. Pat. No. 4,690,389 to West, a fluid-filled elastic mount, a non-compressible fluid filling the fluid chambers is forced to flow through an orifice passage, based on relative pressure changes in the fluid chambers which occur when a vibrational load is applied between the inner and outer sleeves The fluid-filled elastic mount which damps or isolates the applied vibrations based on the resonance of the fluid mass flow through the orifice passage is more effective than the elastic mount which relies on only the elasticity of the elastic body for damping the vibrations. In this fluid-filled cylindrical elastic mount, an improvement in the vibration damping/isolating function based on the resonance of the fluid is provided with respect to only the vibrations whose frequencies are in the neighborhood of the frequency to which the orifice passage is tuned. For instance, the orifice passage may be tuned to effectively provide a high damping effect with respect to relatively low-frequency vibrations based on the fluid resonance. In this case, the orifice passage operates as if it were substantially closed when the frequency of the input vibration is higher than the tuned frequency of the orifice passage. Accordingly, the elastic mount exhibits an excessively high dynamic spring constant, i.e., considerably lowered vibration isolating or damping effect, with respect to the input vibration having a relatively high frequency.
Muramatsu et al, U.S. Pat. No. 5,098,072, teaches a fluid-filled elastic mount including an elastic body interposed between an inner and an outer sleeve, a pressure-receiving chamber disposed between the two sleeves, a first and a second equilibrium chambers partially defined by respective flexible diaphragms for absorbing pressure chambers in the two equilibrium chambers: a first and a second air chamber corresponding to the first and second equilibrium chambers, for permitting elastic deformation of the respective diaphragms; and a first and a second orifice passage for fluid communication between the pressure-receiving and the first and the second equilibrium chambers. The second orifice passage has a ratio of its cross sectional area to its circumferential length, which is higher than that of the first orifice passage. The elastic mount further includes a pressure control device connected to the second air chamber for changing a pressure in the second air chamber. This pressure control device includes a switch device which is operable between a first position for communication of the second air chamber with a first pressure and a second position for communication of the second air chamber with a second pressure higher than the first pressure, so that the fluid flows only through the first orifice passage when the switch device is placed in the first position, and through the second orifice passage when the switch device is placed in the second position.
Strand, U.S. Pat. No. 5,286,011, teaches a bush type mounting device having outer and intermediate sleeves, an inner metal portion and a rubber spring between the inner metal and the intermediate sleeve. The device has an inertial damping channel in an annular space between the outer sleeve and the intermediate sleeve. Damping decoupling is provided by a decoupling pneumatic chamber which extends radially outward from the intermediate sleeve in close association with a holding device.
The present invention is the result of the discovery that the dynamic spring rate and damping of a fluid filled hydrobushing can be managed using a pneumatic control. The bush type mounting device includes an outer sleeve; an intermediate sleeve, radially inward from said outer sleeve defining an annular space; an inner portion radially inward from said intermediate sleeve; a spring material bonded to an outer surface of the inner metal and to an inner surface of said intermediate sleeve diametrically located to provide said device with a main fluid chamber and at least two additional fluid chambers, each containing a fluid and said main chamber being fluidly connected to the first fluid chamber and said first chamber is fluidly connected to the second fluid chamber; an inertial damping channel molded in the annular space connecting the main and said second fluid chamber; and a coupling/decoupling means to alternately couple and at least partially decouple the vibration damping action of the fluid flow through the damping channel, where the coupling/decoupling means includes a flexible extensible elastomeric diaphragm sealingly attached to the intermediate sleeve to create an air chamber, the diaphragm being deflectable into the first fluid chamber a distance relative to the pressure differential between the fluid pressure in the main fluid chamber and the air pressure in the air chamber, one surface of the diaphragm facing the fluid chamber and the opposite surface thereof defining said air chamber, the intermediate sleeve having a port extending through the wall thereof and to permit the flow of air in and out of the air chamber, and a means to control the flow of air through the port in and out of the air chamber to effect pressure changes within the cavity and thereby change the amount of deflection of the diaphragm.
The drawings illustrate a bush type mounting device shown generally at 10 having an outer sleeve 12, an intermediate sleeve 14 having radially outward flanges 18 located radially inward from the outer sleeve 12 to define an annular space 15. Radially inward from the intermediate sleeve 14 is the inner metal portion 16 which can have an aperture 11 through it for attaching the mount, or mounting bolts (not shown) in place of the aperture may be attached for affixing the mount. A rubber spring 19 is bonded between an outer surface of the inner metal 16 and an inner surface of the intermediate sleeve 14 and provides a main fluid chamber 20, a first fluid chamber 21 and a second fluid chamber 22. The first fluid chamber 21, has a diaphragm 23 in it which forms a first air chamber 24, while the second fluid chamber 22 also has a diaphragm 25 which forms a second air chamber 26. Both of the air chambers are bonded to the inner metal 14 and have convex shapes which allow for diaphragm expansion into the fluid chambers, as will be explained in further detail hereinafter.
The device is completely filled with an incompressible fluid, such as a hydraulic fluid, and inertial damping is provided by the narrow channel 27 which is comprised of two circumferential grooves axially outward of the chambers, each with an opening to one of the chambers and a crossover axial groove 28 diametrically opposite the decoupling pneumatic chamber. The flow pattern in the damping channel 27 is illustrated in
The sleeves and the inner metal are generally made of metal. However, it is contemplated that they could be made of engineering thermoplastic. The decoupling pneumatic chamber and the holding means can be made of either metal or thermoplastic. It is preferred that the decoupler pneumatic chamber be made of a thermoplastic, for example, nylon, while the diaphragm will be made of an elastomeric or rubbery material.
Decoupling is provided by pneumatic control of the flow of the fluid to the first fluid chamber and between the main fluid chamber, the inertial damping channel, and the second fluid chamber. During operation of the mounting device, the compression of the spring material will cause the fluid to pumped from the main fluid chamber and in situations where the vibrations are of a relatively low amplitude, the first air chamber will be inflated and prevents flow into the first fluid chamber so that the incompressible fluid will passing through the inertial damping channel. Under conditions of relatively high amplitude, the first air chamber will be collapsed and the fluid will pass into the first fluid chamber in order to dampen the vibration.
In order to accommodate the fluid flow, the second air chamber 26 formed by diaphragm 25 in second fluid chamber 22 is vented to the air by vent line 32. When the fluid flow into the first fluid chamber is restricted because the decoupler resists the collapse of diaphragm 23 and air chamber 24, then diaphragm 25 will collapse from the fluid pressure in fluid chamber 22 and the air in chamber 26 will be vented to the atmosphere via vent line 32. The pressure in diaphragm 23 in first fluid chamber 21 is controlled via decoupler unit 40. Decoupler unit 40 to is in fluid communication with air chamber 24 via an inlet/outlet port 42 which is connected to a tube 44 extending through the wall of intermediate sleeve 14 and to a solenoid valve 62.
The solenoid valve 62 is in turn connected through a tube 64 to another solenoid valve 66. The solenoid valve 62 is presently shown in position to provide open communication between the cavity 24 and the solenoid valve 66 which is presently shown as vented to the outside atmosphere through a large orifice 68.
The solenoid valve 62 also has an off position and a position where the cavity 24 is put in communication with a tube 70 leading to a check valve 72. The solenoid valve 66 also has an off position and a position where the tube 64 is put in communication with a small or restricted orifice 74. The small orifice 74 is sized to provide an optimum level of damping for a specific engine/body/driving condition combination. The amount of damping obtained varies inversely with the size of the orifice.
In operation, when the engine mount 12 is mounted on a vehicle (not shown), the interior of the mount 12 is filled with a sufficient amount of liquid so that when vibration occurs and is imparted through the spring member 19, liquid can be pumped back and forth between the main liquid chamber 20 and the secondary chambers 21 and 22 through the damping channel 27, thereby providing damping of the vibration. In order to have full damping, the decoupler must be disengaged. To accomplish this, the solenoid valve 62 is moved to the position where the cavity 24 is in communication with the check valve 72. As the vibration deflects the diaphragm 23 inwardly into the cavity 24, air is ejected through the check valve 72 but cannot return to the cavity 24. As a result of the vibration, the air is rapidly pumped out of the cavity until the diaphragm 23 is drawn completely against the wall of the cavity 24, as shown in
To provide partial decoupling, the solenoid 62 is moved to the position shown in
While in
The foregoing embodiments of the present invention have been presented for the purposes of illustration and description. These descriptions and embodiments are not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above disclosure. The embodiments were chosen and described in order to best explain the principle of the invention and its practical applications to thereby enable others skilled in the art to best utilize the invention in its various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the invention be defined by the following claims.
