Patent Publication Number: US-2002008341-A1

Title: Hydraulic vibration isolator

Description:
BACKGROUND OF THE INVENTION  
       [0001] The present invention relates to a hydraulic vibration isolator, and more particularly to a hydraulic vibration isolator with a vibrator which has an oscillating piston installed in a communication passage formed between a main chamber and an auxiliary chamber and driven by a rotary actuator. The vibrator is operated at a particular frequency to vibrate a liquid in the main chamber to change a dynamic spring constant of the vibration isolator for a vibration input of that particular frequency.  
       [0002] Among vibration isolators, an automotive engine mount in particular must be able to cope with a wide range of vibration frequencies because the engine as a driving source is operated under a variety of circumstances from an idling state to a maximum revolution speed. To deal with a plurality of these conditions, a hydraulic vibration isolator has already been in use, which has a liquid chamber therein and a vibrator, comprising an oscillating piston for instance, for vibrating the liquid in the liquid chamber at a particular frequency. The conventional hydraulic vibration isolator, however, depends primarily on a negative pressure, such as a suction pressure in the engine, to drive the vibrator. This conventional vibration isolator has drawbacks that the operation of the oscillating piston is difficult to control and that it is difficult to obtain a sufficiently large force generated by the vibrator.  
       [0003] To solve the problems mentioned above, a hydraulic vibration isolator has been proposed which employs an electromagnetic rotary actuator as a drive source for the vibrator. This vibration isolator is described in Japanese Patent Application No. 11-244217, commonly assigned and corresponding to Japanese Patent Unexamined Publication No. 2001-65629 and copending U.S. patent application Ser. No. 652,214, the latter being incorporated herein by reference.  
       [0004] The vibrator of Japanese Patent Application No. 11-244217, as shown in FIG. 9, is installed in a communication passage  50  connecting a main chamber  20  and an auxiliary chamber  30  and mainly comprises an oscillating piston  10 . In the vibrator of this construction, to increase a vibrating force acting on the liquid in the main chamber  20  requires increasing a pressure receiving area of the oscillating piston  10 . This in turn requires increasing the capacity of a motor or actuator  40  for driving the oscillating piston  10 . In this vibrator, a shaft  110 , attached with the oscillating piston  10  and a permanent magnet  450  constituting the actuator  40 , is supported at its ends by ball bearings  120 ,  130 . Further, the shaft  110  is also provided with an oil seal  150  near the bearing  130  on the actuator  40  side for sealing the liquid from the liquid chambers  20 ,  30 . The shaft  110  is subjected to a frictional force of the oil seal  150  at all times. As a result, also to deal with this frictional force (friction loss), the output of the actuator  40  needs to be made large, resulting in an increase in the overall size of the hydraulic vibration isolator.  
       BRIEF SUMMARY OF THE INVENTION  
       [0005] In light of the above, an object of the present invention is to provide a hydraulic vibration isolator that supports the shaft with a bearing system having a small frictional loss and which does not need to use the oil seal described above.  
       [0006] The hydraulic vibration isolator according to this invention has a first connecting or linking member adapted to be mounted to a vibrating body side, a second connecting or linking member adapted to be mounted to a member on a car body side,, an insulator installed between the first and second linking members to isolate vibrations from the vibrating body, a main chamber defined by a chamber wall and sealed with a liquid or incompressible fluid, the chamber wall being partly formed by a part of the insulator, an auxiliary chamber defined by a chamber wall and communicating with the main chamber through an orifice, the chamber wall being partly formed by a diaphragm, a partition member separating the main chamber and the auxiliary chamber from each other, a communication passage passing through the partition member to allow the liquid to flow between the main chamber and the auxiliary chamber, and a vibrator for vibrating the liquid in the main chamber at a predetermined frequency. The vibrator includes an oscillating piston installed in the communication passage, an electromagnetic rotary actuator to drive the oscillating piston at a predetermined frequency, and a rotating shaft connecting the oscillating piston with the rotary actuator. The rotary actuator has a permanent magnet making up a part of the rotary actuator and mounted to the rotating shaft. This hydraulic vibration isolator is characterized in that the oscillating piston and the rotating shaft are supported by a bearing portion and a holding portion, that the bearing portion includes a planar bearing and a journal portion engaging the planar bearing, that the journal portion is so formed as to introduce the liquid between the planar bearing and the journal portion, and that the holding portion is provided on the side of one end portion of the rotating shaft to hold the one end portion rotatably.  
       [0007] With this construction, the rotating shaft on which the oscillating piston is mounted is rotatably supported with a small frictional resistance, which in turn reduces the frictional loss during the operation of the oscillating piston. To describe in more detail, the planar bearing forming the main part of the rotating shaft support portion is supplied a liquid, which performs a function of a lubricating oil, to form a lubricating oil film around the journal portion. This reduces the frictional loss of the rotating shaft.  
       [0008] Another aspect of the present invention provides a hydraulic vibration isolator which, in addition to the construction described above, has iron pieces provided around the permanent magnet and offset from the permanent magnet in the axial direction of the rotating shaft by a predetermined distance to produce a magnetic force acting between the permanent magnet and the iron pieces to force the rotating shaft toward the holding portion side.  
       [0009] In this construction, when the electromagnetic rotary actuator is operated, i.e., the coil is energized by the electric current flowing through it, the magnetic force thus generated moves the permanent magnet and the rotating shaft mounted with the permanent magnet in the axial direction of the rotating shaft toward the line contact portion. As a result, the rotating shaft is more reliably supported at the line contact portion (holding portion), making the operation of the rotating shaft and the oscillating piston smooth.  
       [0010] Still another aspect of the present invention provides a hydraulic vibration isolator which is characterized in that, in addition to the construction described first, the permanent magnet is; mounted to the rotating shaft by a mechanical fastening device without using an adhesive. With this mounting structure of the permanent magnet, there is no need for an oil seal for sealing a liquid. This achieves a further reduction in the frictional loss of the rotating shaft.  
       [0011] The holding portion preferably includes the line contact portion formed in a plane perpendicular to the axis of the rotating shaft. This construction can reduce the frictional loss of the holding portion, realizing a further reduction in the overall frictional loss of the rotating shaft support portion.  
       [0012] The line contact portion preferably includes one of two combinations, the two combinations comprising a combination of a spherical portion provided at a front end portion of the rotating shaft and a conical surface provided on the partition member side to engage the spherical portion and a combination of a conical portion formed at a front end side of the rotating shaft and a rotation defining raised surface, the rotation defining raised surface being provided on the partition member side, formed of a rotation defining surface of a raised curved portion, and adapted to engage the conical portion. With this construction, the line contact portion can be formed in a simple engagement structure of the spherical portion or raised surface portion and the conical surface. Not only does this structure reduce the frictional force but the overall construction can also be simplified.  
       [0013] The journal portion is advantageously provided on the rotating shaft and the outer surface of the rotating shaft at the journal portion is formed with a recess to introduce the liquid. With this construction, the liquid having the function of a lubricating oil is introduced into the recess to form a lubricating oil film between the journal and the planar bearing. The frictional loss of the rotating shaft is therefore reduced.  
       [0014] Alternatively, the outer surface of the rotating shaft at the journal portion may be formed with a spiral groove to introduce the liquid. With this construction, the liquid with the lubricating function is interposed between the journal portion and the planar bearing, thereby reducing the frictional loss of the journal portion, i.e., the rotating shaft, as with the case of the recess.  
       [0015] Alternatively, the outer surface of the rotating shaft at the journal portion may be surface-textured to introduce the liquid between the outer surface of the rotating shaft and the planar bearing, or its surface roughness may be increased. This construction can minimize the frictional loss of the rotating shaft, as with the case of the recess and the spiral groove. That is, the liquid with the lubricating function exists at all times between the journal portion of the rotating shaft and the planar bearing that supports the journal portion, thereby reducing the frictional loss of the journal portion. 
     
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
     [0016] These and other features and advantages of the present invention will be more apparent from the following description when taken in conjunction with the accompanying drawings, in which:  
     [0017]FIG. 1 is a vertical cross section showing an overall construction of the hydraulic vibration isolator as one embodiment of the invention;  
     [0018]FIG. 2 illustrates a first example of a bearing portion of the vibration isolator of FIG. 1 according to the invention;  
     [0019]FIG. 3 illustrates a second example of the bearing portion of the vibration isolator of FIG. 1 according to the invention;  
     [0020]FIG. 4 illustrates a third example of the bearing portion of the vibration isolator of FIG. 1 according to the invention;  
     [0021]FIG. 5 is an exploded perspective view showing how the permanent magnet of the vibrator is assembled;  
     [0022]FIG. 6 is a vertical cross section showing an overall construction of the hydraulic vibration isolator as another embodiment of the invention using a line contact portion of another structure;  
     [0023]FIG. 7 is a cross section showing another example of the line contact portion in the vibration isolator of FIG. 1 according to the invention;  
     [0024]FIG. 8 is a cross section showing another construction of the permanent magnet and its associated components in the vibration isolator of FIG. 1 or FIG. 6 according to the invention; and  
     [0025]FIG. 9 is a vertical cross section showing an overall construction of a conventional vibration isolator. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0026] Embodiments of the hydraulic vibration isolator according to the present invention will be described by referring to FIGS. 1 through 8.  
     [0027] The vibration isolators according to the embodiments of this invention each basically include, as shown in FIG. 1 or FIG. 6, a first connecting or linking member  91  mounted on a vibrating body side; a second connecting or linking member  95  mounted to a member on a car body side; an insulator  8  installed between the first linking member  91  and the second linking member  95  to isolate vibrations from the vibrating body; a main chamber  6  and an auxiliary chamber  7 , both provided in series with the insulator  8  and sealed with a liquid or incompressible fluid; a partition member  3  separating the main chamber  6  and the auxiliary chamber  7  from each other; an orifice  5  connecting the main chamber  6  and the auxiliary chamber  7  to allow the liquid to flow between the two chambers; and a diaphragm  4  forming a part of a wall of the auxiliary chamber  7  to seal the chamber from the atmosphere. The vibration isolators also have a communication passage  31  passing through the partition member  3  and a vibrator  1  to vibrate the liquid in the main chamber  6  at a particular frequency. The vibrator  1  mainly comprises an oscillating piston  11  arranged in the communication passage  31  and also has an electromagnetic rotary actuator  2  to drive the oscillating piston  11 . An antifreeze is used as the liquid sealed in the vibration isolator.  
     [0028] In addition to the oscillating piston  11 , the vibrator  1  has a rotating shaft  15  provided in the communication passage  31 . The rotating shaft  15  is connected to the electromagnetic rotary actuator  2 . The oscillating piston  11  is mounted to the rotating shaft  15  and projects radially outwardly. The oscillating piston  11  is fan-shaped in cross section to conform to the communication passage  31  and is formed integral with the rotating shaft  15 . The rotating shaft  15  is rotatably supported at a line contact portion  35  on the front end side of the rotating shaft and at a bearing portion  33  on the rotary actuator side, as shown in FIG. 1. The line contact portion  35  comprises a conical portion  156  at the end of the rotating shaft  15  and a rotation defining raised surface  356  that engages the conical portion  156 . The bearing portion  33  comprises a journal portion  151  formed on a part of the rotating shaft  1 ! 5  and a planar bearing  331  that engages the journal portion  151 .  
     [0029] In more concrete terms, the conical portion  156  may be provided by a cap  16  which encloses and is secured to a front end  157  of the rotating shaft  15 , as shown in FIG. 7. The cap  16  is made from a metal such as brass. Alternatively, the conical portion  156  may also be made by plating brass over the surface of the front end  157 . The receiving side which engages and is in line contact with the conical portion  156  has the rotation defining raised surface  356  that is formed by rotating a raised curved portion with a predetermined curvature about an axis of the rotating shaft  15 , as shown in FIG. 1 and FIG. 7.  
     [0030] Alternatively, as shown in the embodiment of FIG. 6, the holding portion or line contact portion  35  may be constructed of a spherical face portion  155  provided on the rotating shaft  15  side and a conical face  355  on the receiving portion side formed in the partition member  3 . In that case, the spherical face portion  155  is formed by driving or embedding a steel ball of a predetermined size into the front end portion of the rotating shaft  15 .  
     [0031] Next, the detailed construction of the bearing portion  33  will be described by referring to FIGS.  2  to  4 . FIG. 2 shows a recessed portion  152  as an oil retaining portion formed in the outer surface of the journal portion  151 . The recessed portion  152  may be provided in plural numbers on the circumferential surface. What is required is that the journal portion  151  retains a liquid to form a lubricating film over its outer surface. FIG. 3 shows another example of the journal portion  151  that has a spiral groove  153  as an oil retaining portion formed in its outer surface. Shown in FIG. 4 is still another example of the journal portion  151  which is formed with a pattern  154  on its outer surface consisting of innumerable fine depressions and protrusions. Rather than forming such a pattern  154  or performing surface texturing, the surface roughness of the journal portion  151  may be increased to produce an effect similar to that of the surface texturing. The essential requirement is that innumerable fine depressions and protrusions are formed on the outer surface of the journal portion  151  as by surface texturing to form a large number of oil retaining portions between the journal portion  151  and the planar bearing  331  that engages it, thus forming a lubricating film on the bearing portion  33 .  
     [0032] The electromagnetic rotary actuator  2  for driving the rotating shaft  15  and the oscillating piston  11  at a predetermined frequency basically comprises, as shown in FIG. 1 and FIG. 6, a cylindrical permanent magnet  21  attached to one end of the rotating shaft  15  and a coil  28  for rotating the permanent magnet  21  at a predetermined frequency. The coil  28  is provided around the permanent magnet  21  to oscillate it. In this embodiment the permanent magnet  21  is mechanically secured to one end portion of the rotating shaft  15 . That is, the permanent magnet  21  is mounted without an adhesive. Thus, if the liquid present around the oscillating piston  11  seeps into the area of the permanent magnet  21 , no particular problem arises and there is no need to provide an oil (seal around the rotating shaft  15  to prevent infiltration of the liquid. Hence, the frictional loss around the rotating shaft  15  can be kept low.  
     [0033] Now, the mechanical fixing of the permanent magnet  21  will be explained in detail. As shown in FIG. 5, the rotating shaft  15  has at its front end a stepped portion  158  and a narrow-diameter support portion  159  extending forwardly beyond the stepped portion. A front end of the narrow-diameter support portion  159  is provided with an external thread portion  19 . The external thread portion  19  is D-shaped in lateral cross section when viewed from the front. A disklike plate  24  is sleeved over the narrow-diameter support portion  159  until it engages the stepped portion  158 . Then, a ring-shaped leaf spring  25  is also sleeved over the support portion  159  so it engages the plate  24 . The leaf spring  25  has a function of fixing the permanent magnet  21  to be attached later in the axial direction of the rotating shaft  15 . Next, a cylindrical magnetic iron spacer  22  is attached over the support portion  159 . To the outside of this spacer  22  is attached a cylindrical hollow permanent magnet  21 . Then, a rotation prevention plate  23  is placed in contact with the end of the permanent magnet  21 . Finally, a nut  29  is screwed over the external thread portion  19  at the front end of the rotating shaft  15  projecting from the rotation prevention plate  23  and is then tightened.  
     [0034] In this way, the permanent magnet  21  is secured to the support portion  159  at one end of the rotating shaft  15  by the aforementioned mechanical fastening means. The permanent magnet  21  has a recessed portion  211  formed on one side facing the rotation prevention plate  23 , and the rotation prevention plate  23  has a raised portion  231  formed on one side contacting the permanent magnet  21  to engage the recessed portion  211  of the permanent magnet  21 . An opening  239  in the rotation prevention plate  23  is D-shaped in cross section so that it can fitted over the external thread portion  19  which has a similar D-shaped cross section. Hence, when the nut  29  is fastened, the permanent magnet  21  is held immovable with respect to the external thread portion  19  of the support portion  159  through the rotation prevention plate  23 . The permanent magnet  21  is now prevented from being turned.  
     [0035] Iron pieces  27  of a predetermined shape may be arranged at equal intervals around the permanent magnet  21 , as shown in FIG. 8. These iron pieces  27  are offset from the permanent magnet  21  by a predetermined distance (E) in the axial direction of the rotating shaft  15 . With this arrangement,-when the electromagnetic rotary actuator  2  is operated, i.e., when the coil  28  is energized by the current flowing through it, the permanent magnet  21  and the rotating shaft  15  are pushed in the axial direction toward the line contact portion  35 , i.e., in the direction of arrow F of FIG. 8. This makes the supporting of the rotating shaft  15  by the line contact portion or holding portion  35  in FIG. 1 and FIG. 6 more reliable, allowing the rotating shaft  15  and the oscillating piston  11  to operate smoothly. The elements  27  are not limited solely to the iron pieces but may be made of any other magnetic material which is attracted by a magnetic force of the permanent magnet  21 .  
     [0036] Next, the operation of the vibration isolator of the above construction shown in FIG. 1 or FIG. 6 will be explained. As already described, the vibrator  1  for oscillating the liquid in the main chamber  6  is provided in the partition member  3  that separates the main chamber  6  and the auxiliary chamber  7  from each other. The oscillating piston  11  of the vibrator  1  is driven at a predetermined frequency by the electromagnetic rotary actuator  2 . When the input vibration is an engine idling vibration, for example, the oscillating piston  11  of the vibrator  1  is operated by the electromagnetic rotary actuator  2 . The vibrator  1  applies vibrations to the liquid on the main chamber side of the partition member  3  to vibrate the liquid in the main chamber  6  and thereby absorb a pressure increase of the liquid in the main chamber  6  caused by the engine idling vibration transferred through the insulator  8 . As a result, the dynamic spring constant of a spring system formed by the hydraulic vibration isolator decreases, thus absorbing and isolating the engine idling vibration.  
     [0037] In this series of operations of the hydraulic vibration isolator of this invention, because the rotating shaft  15  mounted with the oscillating piston  11  is supported by the line contact portion  35  with a small frictional resistance and by the bearing portion  33  with an excellent lubricating performance, the frictional loss of the rotating shaft  15  during the operation of the oscillating piston  11  can be kept low. Hence, the output of the rotary actuator  2  can be extracted efficiently. In addition, the isolator of the embodiment above uses no adhesive in mounting the permanent magnet  21  making up the rotary actuator  2 , so that the infiltration of the liquid into the area of the permanent magnet  21  does not pose any problem, making it unnecessary to provide a sealing means such as oil seal around the rotating shaft  15 . This in turn can keep the frictional loss of the rotating shaft  15  low and extract the output of the rotary actuator  2  efficiently. As a result, it is possible to use a small rotary actuator  2 , leading to a reduction in size and weight of the hydraulic vibration isolator.  
     [0038] The bearing portion  33  has a construction, as shown in FIG. 2 to FIG. 4, in which the liquid is introduced between the journal portion  1 ! 51  and the planar bearing  331  to form a lubricating film of the liquid. This construction enhances the Lubricating function of the bearing portion  33 , suppressing the frictional loss of the rotating shaft  15 .  
     [0039] As described above, with the construction of this invention, driving the vibrator at a predetermined frequency can reduce the dynamic spring constant of the spring system of the hydraulic vibration isolator for a vibration input such as engine idling vibration as required, thus absorbing and isolating the engine idling vibration.  
     [0040] Further, because the rotating shaft of the vibrator is supported by the line contact portion with a small friction resistance and by the bearing portion with an excellent lubricating performance, the frictional loss of the rotating shaft during the operation of the oscillating piston can be minimized. This in turn allows the output of the rotary actuator to be extracted efficiently, leading to a reduction in size and weight of the hydraulic vibration isolator.  
     [0041] Further, because the permanent magnet of the rotary actuator is mounted without using adhesive, there is no need to provide a sealing means around the rotating shaft. This minimizes the frictional loss of the rotating shaft, which also ensures efficient extraction of the output of the rotary actuator. This in turn allows the use of a small rotary actuator, reducing the size and weight of the hydraulic vibration isolator. Further, the simplified construction of the bearing portion and its associated components with no sealing means such as oil seal used can reduce the manufacturing cost of the vibration isolator.