VIBRATION ISOLATING DEVICES

Abstract: A vibration isolating device comprises a main vibration-­ absorbing body provided with a hollow chamber (37) containing a vibration-damping liquid, and a plurality of partition members (18, 12) each provided with a restricted passage (38, 64) to divide the hollow chamber into at least three small liquid chambers (37A, 37B, 37C). In this device, one of the partition members (18) is provided with a restricted passage (38) having a sectional area larger than that of the restricted passage (64) formed in the other remaining partition member (12).

Description: This invention relates to a vibration isolating device for damping vibrations from a vibration source. A vibration isolating device, generally called a rubber vibration isolator, is used, for example, as an engine mount for automobile vehicles, whereby vibrations from an internal-combustion engine are absorbed so as not to be transmitted to a vehicle chassis. As a vibration isolating device of this type, there has been proposed a vibration isolating device comprising two vibration-damping liquid chambers separated by a partition member provided with a restricted passage, in which vibrations from a vibration source are absorbed by a flow resistance subjected to the liquid when the vibration is transmitted to the one chamber to thereby allow the liquid to flow from the one chamber to the other through the restricted passage. In this device, not only is the vibration transmitting force lowered as far as possible at various vibration frequencies, but also the damping force is developed at a frequency range of 10-20 Hz corresponding to the vibration from the engine. In the conventional engine mount, however, it is very difficult to absorb vibrations of particular frequency other than the engine vibration. That is, when the vibration input to the engine mount is a high frequency, the amplitude is small which renders the restricted passage into a clogged state, so that the pressure inside the liquid chamber rises to increase the dynamic spring constant. As a result, the vibration transmitting rate is undesirably raised to adversely affect the ride comfort of the vehicle. As a countermeasure for overcoming the latter problem, there has also been proposed a vibration isolating device capable of absorbing high-frequency vibrations, but is not yet sufficient to damp the high-frequency vibrations. Therefore, it is strongly demanded to develop a vibration isolating device capable of damping vibrations at a wider frequency range. Attention is also drawn to the disclosures of GB-A-2041485 and FR-A-2415241, which shows a device having all the features of the first part of the independent claim. With the foregoing in mind, the present invention aims to provide a vibration isolating device which can effectively prevent the transmission of vibrations to a vehicle chassis by not only generating a damping force against a low frequency vibration but also suppressing a dynamic factor to not more than 1.5 times with the resonance of the damping liquid against vibrations of a higher frequency range.. The present invention provides a vibration isolating device, comprising a main vibration-absorbing body provided with a hollow chamber containing a vibration-damping liquid therein, the said hollow chamber containing the vibration-damping liquid being divided into first, second and third small liquid chambers by two partition members, wherein one of the partition members is provided with a first restricted passage having a sufficiently large diameter, and the other partition member comprises a plate material having a ceiling part and is provided with a second restricted passage having a small diameter, and wherein the said second chamber which is disposed between the said two partition members has a part of the wall thereof deformable to relieve the pressure in said chamber, characterized in that the said restricted passage extends substantially parallel with respect to the said ceiling part of the said plate material so as to have a long axial length, the numerical value of said axial length of the said second restricted passage measured in centimeters being more than 5 times the numerical value of the sectional area thereof represented by square centimeters, and in that the wall of the third liquid chamber opposite to the said other partition member is comprised by a diaphragm. The invention will be described with reference to the accompanying drawings, wherein: Fig. 1 is an exploded perspective view of a lower partition member especially used in the vibration isolating device of the invention according to Fig. 7; Figs. 2 to 4 are sectional views of first to third embodiments of the vibration isolating device according to the invention, respectively; Fig. 5 is graph showing a relation between frequency and dynamic factor in the devices of Figs. 2, 3 and 4; Figs. 6a and 6b are graphs showing dynamic factor and tan δ with respect to frequency in the device of Fig. 4, respectively; Fig. 7 is a sectional view of a fourth embodiment of the vibration isolating device according to the invention, respectively; Figs. 8 and 9 are graphs showing tan δ and dynamic factor with respect to frequency in the device of Fig. 7, respectively; and Figs. 10 and 11 are sectional views of other embodiments of the partition member used in the invention, respectively. Like parts are designated by like numerals throughout the different figures of the drawings. In Fig. 2 is sectionally shown a first embodiment of the vibration isolating device according to the invention. This vibration isolating device is used as an engine mount for automobile vehicle. The vibration isolating device comprises a hollow bottom cylinder 10, to the inside of which at its axially middle position is clamped an outer peripheral portion of a ring plate 12. Further, a lower diaphragm 14 is clamped at its outer peripheral portion between the ring plate 12 and a step portion 10A of the cylinder 10 formed just beneath the ring plate 12 and forms an air chamber 16 together with a bottom plate 10B of the cylinder 10. This air chamber 16 may be communicated with an exterior through a hole formed in the bottom plate 10B. The upper end portion of the bottom cylinder 10 is fixed to a lower end portion of a joint cylinder 20 through an upper partition member 18. The upper end portion of the joint cylinder 20 is enlarged upward, to which is bonded a rubber member 22 as a vibration-absorbing main body by vulcanization. In this case, other elastomeric materials may be used instead of the rubber member 22. The upper end portion of the rubber member 22 is bonded by vulcanization to a base plate 24 provided with a fitting bolt 26. The base plate 24 is used for carrying an engine (not shown), wherein the engine is fixed to the base plate 24 through the fitting bolt 26. A flange 28 is protruded outward from the lower end portion of the joint cylinder 20 and provided with plural fitting bolts 30 for fixing a vehicle chassis (not shown). A closed space is defined as a liquid chamber by the bottom cylinder 10, lower diaphragm 14, joint cylinder 20, rubber member 22 and base plate 24 and filled with a vibration-damping liquid such as water or the like. The upper partition member 18 divides the closed space into an upper liquid chamber 37A and a middle liquid chamber 37B. Both the liquid chambers are communicated with each other through a cylindrical hole 18A formed in the center of the partition member 18 as a restricted passage. The ring plate 12 clamped together with the lower diaphragm 14 to the bottom cylinder 10 serves as a lower partition member and comprises a central upheaved portion composed of a cylindrical part 58 and a ceiling part 60, which divides the closed space into the middle liquid chamber 37B and a lower liquid chamber 37C. Thus, the closed space is divided into the upper liquid chamber 37A, middle liquid chamber 37B and lower liquid chamber 37C by the upper partition member 18 and the lower partition member 12. As shown in Fig. 1, the ring plate 12 is formed by lapping and fixing two plate materials 56 and 62. The plate material 56 is a hat-shaped body provided with the cylindrical part 58 and the ceiling part 60 and made, for example, by deep drawing of a disc metal sheet. To a recess bottom of the plate material 56 is fixed the plate material 62 of an annular metal sheet provided at its outer peripheral portion with a ring-like depression 63. In this way, a restricted passage or an orifice 64 is formed between the plate material 56 and the plate material 62, and communicated with the middle liquid chamber 37B through an opening 66 formed in the ceiling part 60 of the plate material 56 on the one hand and with the lower liquid chamber 37C through an opening 68 formed in the plate material 62 on the other hand. In this illustrated embodiment, the partition member 18 provided with the cylindrical hole 18A is disposed at a side of vibration source or near the base plate 24. Further, the orifice 64 is small in the diameter and long in the axial length as compared with the cylindrical hole 38. (The numerical value of the axial length of the orifice 64 measured in centimeters is more than 5 times the numerical value of the sectional area thereof represented by square centimeters). The operation of the vibration isolating device of Fig. 2 will be described below. The flange 28 is mounted on the vehicle chassis and fixed thereto through the fitting bolts 30, while the engine for automobile vehicle is fixed to the base plate 24 through the fitting bolt 26. In the mounting of the engine, the dead weight of the engine is applied to the base plate 24 to increase the pressure inside the upper liquid chamber 37A. Such an increase of the pressure is transmitted to the middle liquid chamber 37B through the cylindrical hole 38 and further to the lower liquid chamber 37C through the orifice 64, whereby the lower diaphragm 14 is displaced toward a direction of contracting the air chamber 16. In the working of the engine, vibrations generated from the engine are transmitted to the device through the base 24. Of course, the rubber member 22 can absorb the vibration owing to its damping function based on the internal friction. In case of a low vibration frequency, for example, when vibrations have a frequency range of 5-20 Hz and an amplitude of ±0.5-1.0 mm, the vibration-damping effect is further enhanced by the viscosity resistance caused in the flowing of the liquid through the restricted passage having a long axial length and a small sectional area or the orifice 64. In this case, the cylindrical hole 18A hardly develops the vibration-damping action because it has a large sectional area. Particularly, the vibration-damping effect against vibrations of low frequency and large amplitude is large because the orifice 64 is a C-shaped, long restricted passage defined between the plate material 56 and the plate material 62. Moreover, the axial length of the orifice 64 may optionally be adjusted by changing a relative angle between the openings 66 and 68 in the fixing of the plate material 62 to the plate material 56 by welding or the like. In case of a high vibration frequency, for example, when vibrations have a frequency range of more than 20 Hz and a slight amplitude, there is a possibility that the orifice 64 becomes a clogged state. In this case, the cylindrical hole 18A does not produce the clogging owing to its large sectional area, so that the liquid inside the device produces a liquid column resonance, whereby specified high frequency vibrations are appropriately absorbed in accordance with the shape and size of the cylindrical hole 18A. In the illustrated embodiment, the bottom cylinder 10 may be made from a metal or a flexible elastomer. As the bottom cylinder is rendered flexible, the resonance frequency produced in the cylindrical hole 18A and the orifice 64 becomes lower, from which a proper resonance frequency can be selected. The size of the first restricted passage in the partition member 18 preferably meets the following requirements. Assuming that the volume of the upper liquid chamber 37A is changed by A cm³ when the rubber member 22 is bent by 1 cm under the application of the engine dead weight, if the upper liquid chamber 37A has an effective diameter of D₀ cm and an effective sectional area of π (D₀/2)² and the restricted passage has a length of L cm and a diameter of D cm, it is required to satisfy D/D₀ of not less than 1/3 and the numerical value of L/D² of not more than 1/3. When D/D₀ is less than 1/3, the restricted passage is apt to produce the clogging at the high vibration frequency. Further, when L/D² is more than 1/3, the reduction of dynamic factor occurs at low vibration frequency. The term "dynamic factor" used herein means a ratio of dynamic spring constant to static spring constant. When the size of the restricted passage satisfies the above requirements, a low dynamic factor can be obtained at a high frequency range of 100-200 Hz. If there is plotted a relation between the frequency and the dynamic factor in a vibration isolating device of the invention, and a relation between the frequency and the loss factor (tan δ) in the same device, it can be understood that a large vibration-damping force can be obtained at an arbitrary frequency. In a modification of the vibration isolating device according to the invention, a rubber member (not shown) having a hardness larger than that of the rubber member 22 is secured at its one end to an upper surface of the base plate 24 and at the other end to a fitting plate (not shown) for an engine provided with the fitting bolt 26. Moreover, the bottom plate 10B can be provided at its outer bottom surface with a fitting bolt (not shown). By means of said rubber member, the building-up of the dynamic factor in the liquid column resonance can be made low. Moreover, the rubber member may also be disposed at the side of the bottom cylinder 10. In the embodiment of the vibration isolating device according to the invention, shown in Fig. 2, the plate material 56 constituting a part of the partition member 12 is provided at the center of the ceiling portion 60 with a circular hole 60A for receiving a movable disc body 72. This movable disc body 72 is provided at its outer peripheral edge with a flange 74 of ⊐-shape in section and is possible to move in up and down direction by a slight amount (about 0.1-0.05 mm) with respect to the peripheral edge of the circular hole 60A, whereby the pressure increase can be suppressed under high frequency vibrations. The fitting position of the movable disc body 72 is not restricted as far as it is existent between the middle liquid chamber 37B and the lower liquid chamber 37C. In Fig. 3 is shown a second embodiment of the vibration isolating device according to the invention, which is a further modification of the device shown in Fig. 2. In this case, the partition member 12 is formed by clamping an annular plate 56A between the bottom cylinder 10 and the bottom plate 10B thereof and inserting the plate material 56 provided at its outer peripheral edge with a flange 74 of ⊐-shape in section into a hole of the annular plate 56A. Thus, it is possible to slightly move the plate material 56 in up and down direction with respect to the annular plate 56A and hence the bottom cylinder 10, whereby there can be obtained the same effect as in the device of Fig. 2. In Fig. 4 is shown a third embodiment of the vibration isolating device according to the invention, which is a modification of the device shown in Fig. 2. That is, a rubber membrane 76 is fixed to a peripheral edge of the circular hole 60A formed in the central portion of the ceiling portion 60 instead of the movable disc body 72. In this case, wire cords or the like are embedded in the rubber membrane 76 to restrict the moving quantity of the membrane 76. Thus, the rubber membrane 76 plays the same role as the movable disc body 72. Fig. 5 shows the relation between the frequency and the dynamic factor in the devices of Figs. 2, 3 and 4. Fig. 6a and 6b show experimental results in the device of Fig. 4. In this experiment, the upper liquid chamber 37A is filled with 70 cc of an anti-freezing liquid, each of the middle and lower liquid chambers 37B, 37C is filled with 30 cc of an anti-freezing liquid, the air chamber 16 is filled with 70 cc of air, the rubber member has a dynamic spring constant of 120 kgf/cm and tan δ (loss factor) of 0.1, and the bottom cylinder 10 is an elastomer having the same volume elasticity as that of the rubber member and a dynamic spring constant of 220 kgf/cm. Further, the opening 18A has a diameter of 4 cm and a length of 0.5 cm and the orifice 64 has a diameter of 0.8 cm and a length of 5.0 cm. In the device having the above dimensions, tan δ can be made large against vibrations having a frequency of 10-15 Hz and an amplitude of ±1 mm as shown in Figs. 6a and 6b. Further, since the device has the rubber membrane 76 as a movable member, there is no building-up of the dynamic spring constant against vibrations having a frequency of about 10 Hz and a small amplitude of about ±0.05 mm and tan δ is not produced at a frequency of about 10 Hz. And also, the dynamic spring constant can considerably be reduced at a frequency of 100-180 Hz due to the presence of the opening 18A. In a further modification of the vibration isolating device according to the invention, a ring member (not shown) can be embedded in the rubber member 22 to adjust the elastic force of the rubber member 22. In a still further modification of the vibration isolating device according to the invention, a regulating plate (not shown) can be integrally fixed to the top surface of the base plate 24 and extends outward therefrom. The outer peripheral portion of the regulating plate is bent downward at a right angle to form a regulation part. An annular rubber stopper is secured to the inner surface of the regulation part and is opposite to a rubber member fixed to the outer peripheral surface of the joint cylinder 20. In this embodiment, therefore, the movement of the base plate 24 in the lateral direction can be restricted. In Fig. 7 is shown a fourth embodiment of the vibration isolating device according to the invention, wherein the ring plate 12 composed of the two plate materials 56 and 62 as shown in Fig. 1 is clamped at its outer periphery between a ring plate member 12A and the lower diaphragm 14 in the middle portion of the bottom cylinder 10; and also the partition member 18 composed of two plate materials 90 and 92 is clamped at its outer periphery between a ring plate member 98 and the joint cylinder 20, to form an orifice 88 similarly to the orifice 64, which orifice 88 communicates with the chambers 37A and 37B through openings 94 and 96 respectively. Further, a cylindrical diaphragm 32 is bonded by vulcanization at its upper and lower end portions to the ring plate members 98 and 12A, whereby an air chamber 34 is formed between the cylindrical diaphragm 32 and the bottom cylinder 10. In this case the air chamber 34 may be communicated with an exterior through a hole formed in the bottom cylinder 10. Fig. 8 shows the relation between the frequency and the loss factor (tan δ) of the device shown in Fig. 7, wherein a characteristic curve 100 is the case against vibrations having a low frequency and a large amplitude and a characteristic curve 102 is the case against vibrations having a high frequency and a small amplitude. Furthermore, Fig. 9 shows the relation between the frequency and the dynamic factor of the device shown in Fig. 7, wherein a characteristic curve 104 is the case against vibrations having a low frequency and a large amplitude and a characteristic curve 106 is the case against vibrations having a high frequency and a small amplitude. In Figs. 8 and 9, the characteristics 100 and 104 are achieved by the orifice 64, while the characteristics 102 and 106 are achieved by the orifice 88. A characteristic 108 shown by dotted lines in Fig. 9 shows the relation between the frequency and the dynamic factor when only the orifice 64 is provided in the device of Fig. 7. In Fig. 10 is shown a modification of the restricted passage of the partition member 18, wherein the partition member 18 is a hat-shaped body of a plate material 110 and a flat plate 114 is disposed in a recess portion of the plate material 110 through a pin 112 fixed to the center of the ceiling part of the plate material 110. Further, a plurality of small circular holes 116 are formed in the ceiling part around the pin 112 in correspondence with the flat plate 114. Thus, the upper liquid chamber 37A is communicated with the middle liquid chamber 37B through a restricted passage 118 defined between the ceiling part of the plate material 110 having holes 116 and the flat plate 114. In Fig. 11 is shown another modification of the restricted passage of the partition member 18, wherein a hollow cylindrical body 120 is fixed to the inner peripheral surface of that portion of the partition member 18 which forms the cylindrical hole 38. Therefore, the inside of the cylindrical body 120 defines a restricted passage 122. In the embodiments of Figs. 10 and 11, vibrations having a high frequency and a small amplitude can be absorbed by the liquid column resonance through the restricted passage 118 or 122. Moreover, the vibration frequency to be absorbed can be adjusted by optionally changing the size of such a restricted passage. Although all of the above illustrated embodiments have been described with respect to the small three liquid chambers divided by two partition members, the invention is applicable to the vibration isolating devices having four or more small liquid chambers. In the latter case, a restricted passage having a largest sectional area among restricted passages communicating the liquid chambers with each other is disposed near the side of vibration source. As mentioned above, according to the invention, the hollow chamber in the main vibration-absorbing body composed mainly of the elastomeric material is filled with a vibration-damping liquid and divided into at least three liquid chambers by plural restricted passages, and a first restricted passage among these restricted passages has a diameter larger than that of the remaining restricted passages, so that vibrations over a wide frequency range can be damped effectively. Further, the size of the restricted passage can be adequately changed in accordance with the vibration frequency to be absorbed.

Claims: A vibration isolating device, comprising a main vibration-absorbing body provided with a hollow chamber (37) containing a vibration-damping liquid therein, the said hollow chamber containing the vibration-damping liquid being divided into first, second and third small liquid chambers (37A,37B,37C) by two partition members (18; 12), wherein one of the partition members (18) is provided with a first restricted passage having a sufficiently large diameter, and the other partition member (12) comprises a plate material (56) having a ceiling part (60) and is provided with a second restricted passage (64) having a small diameter, and wherein the said second chamber (37B) which is disposed between the said two partition members (18;12) has a part of the wall thereof deformable to relieve the pressure in said chamber, characterized in that the said restricted passage (64) extends substantially parallel with respect to the said ceiling part (60) of the said plate material (56) so as to have a long axial length, the numerical value of said axial length of the said second restricted passage (64) measured in centimeters being more than 5 times the numerical value of the sectional area thereof represented by square centimeters, and in that the wall of the third liquid chamber (37C) opposite to the said other partition member (12) is comprised by a diaphragm (14). A vibration isolating device as claimed in Claim 1, characterized in that the said first restricted passage (38) satisfies the following relationships: D/D₀ is not less than 1/3, and the numerical value of L/D² is not more than 1/3 in which D is the diameter of the said first restricted passage (38), L is the length of the said first restricted passage and D₀ is the effective diameter of a liquid chamber (37A) located above the said first restricted passage, all of D, L and D o being measured in centimeters. A vibration isolating device as claimed in Claim 1 or 2, characterized in that a part of the said side wall of the said second chamber (37B) extending between the said two partitions is formed of a deformable material (32). A vibration isolating device as claimed in Claim 1 or 2, characterized in that at least a part (72, 12) of the said other partition member (12) is floatably disposed between the said second and third liquid chambers (37B, 37C). A vibration isolating device as claimed in Claim 1 or 2, characterized in that a rubber membrane (76) is fixed to a peripheral edge of a circular hole (60A) formed in the central portion of the ceiling portion (60) of the said other partition member (12). A vibration isolating device as claimed in any of claims 1 to 5, characterized in that the said restricted passage (64) extends in a single plane with respect to the said ceiling part (60).

Inventors: USHIJIMA, TAKAO, YAMAZAKI, HARUMICHI
Applicants: BRIDGESTONE CORPORATION
Application year: 1984
Main classification: F16F13
IPC codes: F16F13