Abstract:
An active type vibration isolating support system includes: an elastic body for elastically supporting a vibratory body; a liquid chamber to be defined by the elastic body; a movable member for changing capacity of the liquid chamber; and an actuator for driving the movable member. The actuator has: a fixed core; a movable core coupled to the movable member for being arranged opposite to the fixed core via an air gap; and a coil for generating an electromagnetic attracting force between the fixed and movable cores. The movable member and the movable core are coupled together through coupling units capable of adjusting the air gap. Thus, without preparing several types of coupling members, it is possible to obtain a desired vibration isolating characteristic by freely adjusting the air gap between the fixed core and the movable core.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to improvement of an active type vibration isolating support system comprising: an elastic body for elastically supporting a vibratory body on a supporting system; a liquid chamber which is defined by this elastic body and in which liquid is sealed; a movable member for changing capacity of this liquid chamber; and an actuator for driving this movable member, the system being electromagnetically constructed with the actuator equipped with: a fixed core which is supported by the supporting system; a movable core which is coupled to the movable member and is arranged opposite to this fixed core; and a coil for generating an electromagnetic attracting force between these fixed and movable cores.  
         [0003]     2. Description of the Related Art  
         [0004]     Such an active type vibration isolating support system is already known as disclosed in, for example, Japanese Patent Application Laid-Open No. 2001-1765.  
         [0005]     In the active type vibration isolating support system, characteristics of the movable member concerning thrust and displacement are dependent on an initial air gap between attracted surfaces of those fixed and movable cores of the actuator, but the above-described initial air gap may not be within the tolerance due to accumulated manufacturing errors of each part of the actuator. In the conventional one, for such an occasion, several types of coupling members with different length for coupling the movable member to the movable core have been prepared in advance and the above-described air gap has been adjusted by replacing the coupling member.  
         [0006]     However, such adjustment means for air gaps requires several types of coupling members, and moreover, takes time and efforts in the replacement operation, so that the cost is inevitably increased.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention has been achieved in view of the above-described circumstances, and has an object to provide a low-priced active type vibration isolating support system capable of easily obtaining a desired vibration isolating characteristic without preparing several types of coupling members, by freely adjusting rendering an air gap between a fixed core and a movable core.  
         [0008]     In order to achieve the above-described object, according to the present invention, there is provided an active type vibration isolating support system comprising: an elastic body for elastically supporting a vibratory body on a supporting system; a liquid chamber defined by this elastic body, in which liquid is sealed; a movable member for changing capacity of this liquid chamber; and an electromagnetic actuator for driving this movable member, wherein the actuator is equipped with: a fixed core to be supported on the supporting system; a movable core to be coupled to the movable member, for being arranged opposite to this fixed core via an air gap; a coil for generating an electromagnetic attracting force between these fixed and movable cores; and a coupling device for coupling the movable member to the movable core so as to be able to adjust the air gap between the fixed core and the movable core.  
         [0009]     With this feature, by operating the coupling device, it is possible to freely adjust the air gap between the fixed core and the movable core to impart a desired vibration isolating characteristic to the active type vibration isolating support system. Therefore, it is easy to adjust the air gap, and besides, it becomes unnecessary to prepare plural types of components having different dimensions in order to adjust the air gap, whereby the cost can be reduced.  
         [0010]     Also, according to another feature of the present invention, there is provided an active type vibration isolating support system, comprising: an elastic body for elastically supporting a vibratory body on a supporting system; a liquid chamber defined by this elastic body, in which liquid is sealed; a movable member for changing capacity of this liquid chamber; and an electromagnetic actuator for driving this movable member, wherein the actuator is equipped with: a fixed core to be supported by the supporting system; a movable core to be coupled to the movable member for being arranged opposite to this fixed core via a conical tube-shaped air gap; a coil for generating an electromagnetic attracting force between these fixed and movable cores; a coupling device coupled to the movable member to penetrate the movable core in the axial direction so as to be relatively movable to support a fixed core-side end surface of the movable core; a set spring provided between the movable member and the movable core in a compressed state, for biasing the movable core toward a supporting portion of the coupling device; and a stopper member which even after the movable core has reached a limit of movement on the fixed core side, enables moving toward the fixed core side while the movable member compresses the set spring, and in order to restrict compression and deformation of the set spring in a predetermined amount or more, limits an amount of movement of the movable member after the movable core reaches the limit of movement.  
         [0011]     With this another feature, when the movable member receives excessive pressure in the liquid chamber and the movable core reaches the limit of movement toward the fixed core side, the set spring is compressed and becomes deformed, the supporting portion of the coupling means is moved away from the movable core, and the movable member is allowed to further move toward the fixed core side. Therefore, the excessive load of the movable member is absorbed by the set spring to prevent an operation of an over-load on the fixed core and the movable core, so that their durability can be secured.  
         [0012]     Also, since an amount of movement of the movable member after the movable core reaches the limit of movement is restricted by a stopper member, it is possible to restrict an excessive increase in the load at the set spring, thereby preventing an increase in over-load on the fixed core and the movable core.  
         [0013]     The supporting system includes the casing C and the body frame F in the embodiments of the present invention to be described later, the vibratory body includes the engine E, the elastic body includes the first elastic body  14 , the coupling device includes the coupling bolt  55  and the adjustment nut  56 , and the stopper member includes the peg body  61 .  
         [0014]     The above-described object, other objects, characteristics, and advantages of the present invention will become apparent from an explanation of a preferred embodiment, which will be described in detail below by reference to the attached drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  is a longitudinal section showing an active type vibration isolating support system according to a first embodiment of the present invention.  
         [0016]      FIG. 2  is a sectional view taken on line  2 - 2  in  FIG. 1 .  
         [0017]      FIG. 3  is a sectional view taken on line  3 - 3  in  FIG. 1 .  
         [0018]      FIG. 4  is an enlarged view showing a part  4  in  FIG. 1 .  
         [0019]      FIG. 5  is a view taken from arrow  5  in  FIG. 4 .  
         [0020]      FIG. 6  is a view taken from arrow  6  in  FIG. 4 .  
         [0021]      FIG. 7  is a perspective view showing an adjustment nut in  FIG. 4 .  
         [0022]      FIG. 8  is a longitudinal section of an exploded side view showing the adjustment nut, a connecting bolt and a lock screw.  
         [0023]      FIG. 9  shows a second embodiment of the present invention similar to  FIG. 4 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]     Hereinafter, the preferred embodiments of the present invention will be described by reference to the attached drawings.  
         [0025]     First, a first embodiment of the present invention shown in  FIG. 1  to  FIG. 4  will be described. In  FIG. 1 , an active type vibration isolating support system M is, in order to elastically support the engine E on the body frame F in an automobile, interposed therebetween.  
         [0026]     The active type vibration isolating support system M has actually axisymmetric structure with respect to an axis L, and has a plate-shaped installation bracket  11  to be connected to the engine E; an inner tube  12  welded to this installation bracket  11 ; an outer tube  13  which is coaxially arranged around an outer periphery of this inner tube  12 ; and a first elastic body  14  made of thick rubber or the like to be vulcanized and bonded onto conical surfaces of these inner tube  12  and outer tube  13  which oppose to each other. Below this first elastic body  14 , there are arranged a first orifice formation member  15 , a second orifice formation member  16  and a third orifice formation member  17 , which are arranged vertically and made integral with one another.  
         [0027]     The first orifice formation member  15  is shaped like a disk, and has an aperture  15   b  at a center thereof. The second orifice formation member  16  is annular, having a gutter-shaped cross section, the upper surface of which has been opened, and is integrally joined with the first orifice formation member  15  so that the opened upper surface is closed by the first orifice formation member  15 . The third orifice formation member  17  is also annular, having a gutter-shaped cross section, the upper surface of which has been opened, and is integrally joined with the second orifice formation member  16  so that the opened upper surface is closed by the second orifice formation member  16 . Outer peripheral portions of the first and second orifice formation members  15 ,  16  are superimposed on to be made integral with each other, and are fixed to an annular crimping fixed portion  13   a  continuously provided below the outer tube  13 .  
         [0028]     On an inner peripheral surface of the third orifice formation member  17 , an outer peripheral surface of the annular second elastic body  18  made of rubber or the like is vulcanized and bonded. On the inner peripheral surface of this second elastic body  18 , there is vulcanized and bonded a first cap member  19  with the lower surface opened, arranged on the axis L. In this first cap member  19 , a second cap member  23  and a movable member  20  are fixed by press-fitting in order. The second cap member  23  has its lower end portion protruding toward a lower place of the first cap member  19 . On the outer peripheral surface of this protruded portion, there is vulcanized and bonded an inner peripheral end portion of a diaphragm  22  arranged below the second elastic body  18 . On the outer periphery of this diaphragm  22 , a ring member  21  is vulcanized and bonded, and this ring member  21  is fixed to the crimping fixed portion  13   a  together with the outer peripheral portions of the first and second orifice formation members  15 ,  16 . Because of deflection of the second elastic body  18  and the diaphragm  22 , the movable member  20  is capable of moving up and down together with the first and second cap members  19 ,  23 .  
         [0029]     Thus, between the first elastic body  14  and the second elastic body  18 , a first liquid chamber  24 , in which liquid is sealed, is defined, and between the second elastic body  18  and the diaphragm  22 , a second liquid chamber  25 , in which liquid is likewise sealed, is defined. These first and second liquid chambers  24 ,  25  communicate with each other via an upper orifice  26  and a lower orifice  27  formed by the first to third orifice formation members  15  to  17 .  
         [0030]     The upper orifice  26  is defined over a little less than one round thereof between the first and second orifice formation members  15 ,  16  (See  FIG. 2 ), and a partition wall  26   a  for constituting opposite end walls of the upper orifice  26  is welded between the first and second orifice formation members  15 ,  16 . The upper orifice  26  communicates with the first liquid chamber  24  via a through-hole  15   a  in the first orifice formation member  15  on one side of the partition wall  26   a,  and communicates with the lower orifice  27  via a through-hole  16   a  in the second orifice formation member  16  on the other side of the partition wall  26   a.    
         [0031]     The lower orifice  27  is defined over a little less than one round thereof between the second and third orifice formation members  16 ,  17  (See  FIG. 3 ), and a partition wall  27   a  for constituting both end walls of the lower orifice  27  is welded between the first and second orifice formation members  15 ,  16 . The upper orifice  26  communicates with the upper orifice  26  via the through-hole  16   a  on one side of the partition wall  27   a,  and communicates with the second liquid chamber  25  via a through-hole  17   a  of the third orifice formation member  17  on the other side of the partition wall  27   a.  Therefore, the first and second liquid chambers  24 ,  25  are caused to communicate with each other via the upper and lower orifices  26 ,  27  which have been connected with each other in series.  
         [0032]     To the crimping fixed portion  13   a,  a tube-shaped bracket  28  is also fixed, and this is fixed to the body frame F, whereby the active type vibration isolating support system M is installed to the body frame F. This tube-shaped bracket  28  and the outer tube  13  constitute a supporting casing C of the active type vibration isolating support system M.  
         [0033]     To the tube-shaped bracket  28 , an actuator supporting member  30  is fixed, and the electromagnetic actuator  31  for driving the movable member  20  is supported by this actuator supporting member  30 .  
         [0034]     In  FIG. 4 , the actuator  31  has a closed-end tube-shaped housing  32  made of magnetic material, the upper surface of which has been opened, and a flange  32   a  formed at the upper end thereof is fixed to the actuator supporting member  30 . The housing  32  is magnetic material, within which there are installed the fixed core  33 , the coil assembly  34  and the upper yoke  35  in order. The fixed core  33  has an attracted surface  33   a  in an upper part thereof, a positioning shaft  33   b  protruding on an underside thereof, and a stepped collar-shaped lower yoke  36  formed at the outer periphery. The lower yoke  36  is brought into close contact with the bottom wall  32   b  of the housing  32  so that the positioning shaft  33   b  is pressed into the positioning hole  37  in the bottom wall  32   b.  Thus, the fixed core  33  is fixed to the housing  32 .  
         [0035]     The coil assembly  34  has a bobbin  38  made of synthetic resin to be arranged at the outer periphery of the fixed core  33 , and a coil  39  to be wound around this bobbin  38 . On the outer periphery of the lower flange of the bobbin  38 , a small strut  38   a  protruding downward is projectingly provided. During molding of this small strut  38   a,  a proximal end portion of the coupler terminal  40  is insert-connected to the small strut  38   a.  Around the small strut  38   a,  an outgoing line  39   a  of the coil  39  is wound, the tip end of which is connected to the coupler terminal  40  by means of soldering, electric welding or the like.  
         [0036]     After the outgoing line  39   a  is connected to the coupler terminal  40 , in order to seal the coil  39  to the bobbin  38 , a tube-shaped coil cover  41  which comes into close contact from the upper and lower end surfaces of the bobbin  38  to the outer peripheral surface of the coil  39  is injection-molded using synthetic resin. On that occasion, on this coil cover  41 , there are integrally formed a coupler  42  for holding the coupler terminal  40  to protrude outward in the radial direction of the cover  41 , and a protruded portion  42   a  for enveloping the outgoing line  39   a  from the small strut  38   a  to protrude on the lower end surface of the cover  41 . This coupler  42  is arranged so as to expose outside the housing  32  through an aperture  43  provided from the bottom wall  32   b  of the housing  32  to the peripheral wall (See  FIGS. 5 and 6 ). The protruded portion  42   a  is arranged within the aperture  43  so as to be adjacent to the bottom wall  32   b  of the housing  32 .  
         [0037]     On the upper end surface of the coil assembly  34 , particularly on the upper end surface of the coil cover  41 , there is mounted an annular sealing member  45 . Also, on the lower end surface of the coil assembly  34 , particularly on the lower end surfaces of the bobbin  38  and the coil cover  41 , a plurality of sealing convex ridges  46 ,  46  which surround the fixed core  33  for concentrically lining up are integrally formed. Between their lower end surfaces and thin outer peripheral portion  36   a  of the lower yoke  36 , there is interposed an elastic plate  47 . This elastic plate  47  is molded with elastic material such as NBR or silicone rubber.  
         [0038]     The upper yoke  35  is fixed to the inner peripheral surface of the housing  32  by press-fitting in order to press and hold the coil assembly  34  toward the lower yoke  36 . With the fixing, the sealing member  41  and the elastic plate  47  are compressed, whereby the coil assembly  34  is elastically supported without looseness between the upper yoke  35  and the lower yoke  36 , so that vibration resistance of the coil assembly  34  and water resistance of the coil  39  are improved. Particularly, since the sealing convex ridges  46 ,  46  of the bobbin  38  and the coil cover  41  on the lower end surface cut into the upper surface of the elastic plate  47  to further reliably seal the elastic plate  47 , when rain water or washing water enters the aperture  43  from the outside to accumulate at the bottom of the housing  32 , even if contact between the coil cover  41 , and the coil  39  and the bobbin  38  is insufficient, it is possible to reliably prevent water from entering the inner periphery side of the bobbin  38 , to say nothing of entering the coil  39  side.  
         [0039]     On the inner peripheral surface of a cylindrical portion  35   a  to be arranged on the inner periphery of the bobbin  38  of the upper yoke  35 , a thin tube-shaped bearing member  50  is slidably fitted. At the upper end of this bearing member  50 , an inwardly-facing flange  50   a  pointing inwardly in the radial direction is integrally formed, while at the lower end thereof, an outwardly-facing flange  50   b  pointing outwardly in the radial direction is integrally formed. The outwardly-facing flange  50   b  is superimposed on the thick inner peripheral portion  36   b  of the lower yoke  36  through the annular elastic plate  51 , and between this outwardly-facing flange  50   b  and the fixed core  33 , a set spring  52  made of coil spring is provided in a compressed state, whereby the bearing member  50  is elastically held on the lower yoke  36  for vibration isolation.  
         [0040]     Also, when the movable core  53  descends on the fixed core  33  side, the elastic plate  51  also serves as a descending stopper for the movable core  53 , which receives the lower end of the movable core  53  as a cushion in order to avoid collision between both cores  33 ,  53  and defines a descending limit thereof.  
         [0041]     Slidably fitted to the bearing member  50  is the movable core  53  having an attracted surface  53   a  opposed to an attracted surface  33   a  of the fixed core  33  through the air gap g. The upper end of a connecting bolt  55  which loosely penetrates a comparatively large-diameter through-hole  54  opened at the central part of this movable core  53  is threadably attached to the movable member  20 . At the lower end portion of the connecting bolt  55 , an adjustment nut  56  of the movable core  53  for supporting the lower end surface around the through-hole  54  is threadedly engaged. On that occasion, the set spring  57  for holding the movable core  53  at a supporting position by the adjustment nut  56  is provided between the movable member  20  and the movable core  53  in a compressed state. Thus, the movable core  53  is elastically interposed between the set spring  57  and an adjustment nut  56  threadedly engaged with the connecting bolt  55  made integral with the movable member  20 . On the upper end surface of the adjustment nut  56  held in press contact with the movable core  53 , a radial ventilating groove  58  communicating with the through-hole  54  is formed in such a manner that when the movable core is moving up and down, air can be smoothly circulated in space above and below it.  
         [0042]     Thus, if a threaded position of the adjustment nut  56  with the connecting bolt  55  is advanced and retreated, up and down positions of the movable core  53 , that is, the air gap g between attracted surfaces  33   a  and  53   a  of the movable core  53  and the fixed core  33  can be adjusted by corporation with the set spring  57 . An adjustment position of the adjustment nut  56  is threadedly engaged with and tightly fastened from below by the adjustment nut  56 , and is fixed by a lock screw  59 .  
         [0043]     As shown in  FIGS. 7 and 8 , a threaded portion of the connecting bolt  55  has a normal right-hand thread, whereas in the threaded portion of the lock screw  59 , a left-hand thread is formed. Therefore, if in a state in which the adjustment nut  56  is held at a predetermined adjustment position by a tool, the lock screw  59  is fastened in by another tool, torque of the lock screw  59  is transmitted to the connecting bolt  55  through friction so that the connecting bolt  55  is drawn in on the lock screw  59  side. Therefore, it is possible to reliably lock at the adjustment position of the adjustment nut  56 .  
         [0044]     At the central portion of the fixed core  33 , an adjustment operating hole  60  for allowing the adjustment nut  56  to go in and out is provided, and by means of a tool inserted into this adjustment operating hole  60 , the lock screw  59  and the adjustment nut  56  are adapted able to be operated. The adjustment operating hole  60  is composed of a threaded hole  60   a  and a fitting hole  60   c  having a diameter larger than that of the threaded hole  60   a,  continuing to the lower end of the threaded hole  60   a  through an annular shoulder portion  60   b.  On the other hand, a peg body  61  closing the adjustment operating hole  60  is shaped like a bottomed tube with its upper end opened, and has a threaded tube  61   a  to be threadedly engaged with the threaded hole  60   a  while receiving the adjustment nut  56 , a collar portion  61   b  to be fitted in a fitting hole  60   c,  and a bottom portion  61   c.  On the outer periphery of the collar portion  61   b,  there is mounted a sealing member  64  which comes into close contact with the inner peripheral surface of the fitting hole  60   c.  At the underside of the bottom portion  61   c,  there is formed a polygonal tool engaging projection  62 .  
         [0045]     Until the collar portion  61   b  fitted in the fitting hole  60   c  abuts against the shoulder portion  60   b,  the threaded tube  61   a  is threadedly engaged with and tightly fastened to the threaded hole  60   a,  whereby the adjustment operating hole  60  can be closed watertightly by the peg body  61 .  
         [0046]     On the upper surface of the bottom portion  61   c  of this peg body  61 , the elastic plate  63  is bonded, and the bottom portion  61   c  receives the lower end of the adjustment nut  56  through this elastic plate  63  as a cushion to define a descending limit of the movable member  20 . However, when the adjustment nut  56  abuts against the bottom portion  61   c  of the peg body  61 , the movable member  20  further descends while the movable member  20  compresses the set spring  57  after the movable core  53  reaches the above-described descending limit by descending of the movable member  20 .  
         [0047]     Within the bearing member  50 , each of attracted surfaces  33   a,    53   a  of the fixed core  33  and the movable core  53  which oppose to each other is formed in a conical surface so as to define a conical tube-shaped air gap g therebetween, and is arranged so that the attracted surface  53   a  of the movable core  53  surrounds the attracted surface  33   a  of the fixed core  33 . Therefore, even in the fixed core  33  and the movable core  53  within the bearing member  50 , each having a comparatively small diameter within the bearing member  50 , it is possible to acquire a comparatively strong attraction force and a comparatively long stroke of the movable core  53 .  
         [0048]     Moreover, since the attracted surface  53   a  of the movable core  53  is to be formed on the inner peripheral surface side of the core  53 , a supporting span of the movable core  53  by the bearing member  50  can be secured sufficiently long irrespective of the attracted surface  53   a,  and stable ascent and descent of the movable core  53  can be ensured. In this case, it is effective in acquiring further stable, smooth ascent and descent of the movable core  53  that the outer peripheral surface of the movable core  53  is formed with a low friction material layer made of Teflon or the like.  
         [0049]     The set spring  57  is made of coil spring, and by fitting it to a large-diameter portion  55   a  at the base of the connecting bolt  55 , the set spring  57  is arranged concentrically with the connecting bolt  55 . Also, between this set spring  57  and the movable core  53 , there is interposed an annular spring seat  65  made of steel plate in order to prevent the movable core  53  from wearing. This spring seat  65  has inner and outer concentric positioning tubular portions  66 ,  67  which stand up along the inner peripheral surface and outer peripheral surface of the set spring  57  from the inner peripheral edge portion and outer peripheral edge portion, and the outside positioning tubular portion  67  is formed longer than the inside positioning tubular portion  66 . In order to facilitate insertion of the set spring  57  between these positioning tubular portions  66 ,  67 , there are formed funnel portions  66   a,    67   a  at the upper end portions of the positioning tubular portions  66 ,  67 . Also, on at least one of abutted surfaces in which this spring seat  65  and the movable core  53  oppose to each other, a low friction material layer of Teflon or the like is formed to thereby make sliding property of the spring seat  65  to the movable core  53  excellent.  
         [0050]     Referring to  FIG. 1 , to a coil  39  of the actuator  31 , an electronic control unit U is connected through a coupler  42 , and to this electronic control unit U, there is inputted each detection signal of a rotation speed sensor Sa for detecting engine rotation speed, a load sensor Sb for detecting a load to be inputted into an active type vibration isolating support system M, and an acceleration sensor Sc for detecting acceleration that is exerted on an engine E.  
         [0051]     Next, the description will be made of an operation of this embodiment.  
         [0052]     When the actuator  31  of the active type vibration isolating support system M is in a non-operating state, although the first and second liquid chambers  24 ,  25  which communicate with each other through the upper and lower orifices  26 ,  27  are kept at the same pressure, since a pressure receiving area in the fist liquid chamber  24  of the first cap member  19  connected to the movable member  20  is larger than a pressure receiving area in the second liquid chamber  25 , a downward load obtained by multiplying the difference in area by pressure in the first liquid chamber  24  is exerted on the movable member  20 . When a balance is established between the load and a repulsion force of the second elastic body  18  against it, the movable member  20  comes to a halt, forming a predetermined initial air gap g between adsorption surfaces  33   a,    53   a  of the fixed core  33  and the movable core  53 .  
         [0053]     When shake vibration of low frequency occurs in the engine E during running of an automobile, the first elastic body  14  is deformed because of a load inputted from the engine E to change capacity of the first liquid chamber  24 . Then, the liquid goes and comes between the first and second liquid chambers  24 ,  25  which communicate with each other through the upper and lower orifices  26 ,  27 . When the capacity of the first liquid chamber  24  is enlarged and reduced, the capacity of the second liquid chamber  25  is reduced and enlarged accordingly, and the variations in capacity of this second liquid chamber  25  are absorbed by elastic deformation of a diaphragm  22 . At this time, since shapes and dimensions of the upper and lower orifices  26 ,  27  and spring constant of the first elastic body  14  have been set so as to show high spring constant and a high attenuation force in a frequency domain of the shake vibration, vibration to be transmitted from the engine E to the body frame F can be effectively reduced.  
         [0054]     In such a shake vibration domain of low frequency of the engine E, the actuator  31  is kept in a non-operating state.  
         [0055]     When vibration of a frequency higher than the shake vibration, that is, idle vibration or booming noise vibration that occurs during idling of the engine E occurs, liquid within the upper and lower orifices  26 ,  27  which connect the first and second liquid chambers  24 ,  25  enters a stick state, so that the engine E becomes unable to exhibit a vibration isolating function. In such a case, the actuator  31  is driven to exhibit the vibration isolating function.  
         [0056]     In other words, the electronic control unit U controls energizing to a coil  39  of the actuator  31  on the basis of a detection signal inputted from the engine rotation speed sensor Sa, the load sensor Sb, the acceleration sensor Sc and the like. Specifically, when the engine E leans is displaced downward because of vibration and the capacity of the first liquid chamber  24  is reduced due to the downward deformation of the first elastic body  14  to raise the liquid pressure, the coil  39  is energized to attract the movable core  53  on the fixed core  33  side. As a result, the movable core  53  descends while deforming the second elastic body  18  so that the capacity of the first liquid chamber  24  is enlarged, whereby it is possible to restrict the rise in pressure in the chamber  24 , and after all, the active type vibration isolating support system M generates an active supporting force for preventing the downward load from the engine E to the body frame F from being transmitted.  
         [0057]     On the other hand, when the engine E is displaced upward and the capacity of the first liquid chamber  24  is enlarged to raise the pressure in the chamber  24 , the coil  39  is demagnetized to release the movable core  53 . As a result, the movable core  53  rises due to the repulsion force of the second elastic body  18  so that the capacity of the first liquid chamber  24  is reduced, whereby it is possible to restrict the drop in pressure in the chamber  24 , and after all, the active type vibration isolating support system M generates an active supporting force for preventing the upward load from the engine E to the body frame F from being transmitted.  
         [0058]     During such an operation, when with an excessive increase in the downward load from the engine E to the first elastic body  14 , the pressure in the fist liquid chamber  24  is abruptly increased to apply the excessive downward load to the movable member  20 , the movable member  20  first descends the movable core  53  to its descent limit, that is, until the lower end surface of the core  53  is abutted against the elastic plate  51  on the thick inner peripheral portion  36   b  of the lower yoke  36 . Thereafter, the set spring  57  is compressed and becomes deformed so that the adjustment nut  56  is moved away from the underside of the movable core  53 , whereby the movable member  20  is allowed to further move toward the fixed core  33  side. Accordingly, by causing the set spring  57  to absorb the excessive load of the movable member  20 , it is possible to prevent mutual contact between the fixed core  33  and the movable core  53 , and the excessive load acting on the movable core  53  and the elastic plate  51 , and to secure their durability.  
         [0059]     Thus, if after the movable core  53  reaches the descent limit, the movable member  20  descends by a predetermined amount, the adjustment nut  56  will abut against a bottom portion  61   c  of the peg body  61  fixed to the fixed core  33  through the elastic plate  63  to restrict any excessive increase in the load on the set spring  57 , thereby preventing any increase in over-load on the fixed core  33  and the movable core  53 .  
         [0060]     Characteristics in thrust and displacement of the movable member  20  of the active type vibration isolating support system M are dependent on an initial air gap g between attracted surfaces  33   a,    53   a  of the fixed core  33  and the movable cores  33 ,  53  in a non-operating state of the actuator  31 . However, the initial air gap g may not be within the tolerance due to accumulated manufacturing errors of each portion from the installation area of the second elastic body  18  to the movable core  53 . In such a case, a threaded position of the adjustment nut  56  with respect to the connecting bolt  55  is advanced and retreated as described above, whereby the initial air gap g can be adjusted properly and easily. Therefore, by energizing the coil  39 , it becomes possible to impart predetermined thrust and displacement to the movable member  20  with high precision, to thereby improve the performance of the active type vibration isolating support system M.  
         [0061]     Also, if plural types of active type vibration isolating support systems M having different initial air gaps g between the fixed core  33  and the movable cores  33 ,  53  are prepared by operating the adjustment nut  56 , it will be possible to easily obtain active type vibration isolating support systems M having characteristics corresponding to plural car models, thereby contributing to reduction of cost.  
         [0062]     Moreover, since the adjustment nut  56  is operated through the adjustment operating hole  60  of the fixed core  33  opened outside the housing  32 , the initial air gap g can be accurately adjusted without regard to assembly errors in each portion after the completion of assembly of the active type vibration isolating support system M.  
         [0063]     Although the fixed core  33  becomes hollow because it has the adjustment operating hole  60 , the positioning shaft  33   b  integral therewith is pressed into the positioning hole  37  in the bottom wall  32   b  of the housing  32  and the flange-shaped lower yoke  36  is brought into close contact with the bottom wall  32   b,  whereby the fixed core  33  is firmly reinforced, and even if it receives an abutting shock from the movable core  53 , is capable of withstanding the shock sufficiently and besides causes no position shift. Moreover, since the lower yoke  36  effectively increases magnetic paths around the coil assembly  34  in cooperation with the housing  32  and the upper yoke  35 , the attracting force between the fixed and movable cores  33 ,  53  can be increased.  
         [0064]     On the other hand, an ascent limit of the movable core  53  is defined by its upper end abutting against an inward flange  50   a  of the bearing member  50 . When the movable core  53  abuts against the inward flange  50   a  shockingly, the impulse force is transmitted to the set spring  52  through the bearing member  50  and the outward flange  50   b,  to be absorbed by the elasticity of the set spring  52 . Therefore, the set spring  52  also serves as an impulse absorbing member which protects the movable core  53  and the bearing member  50  from the impulse force.  
         [0065]     Since the movable core  53  is elastically held on the adjustment nut  56  by the set spring  57  and an adequate play is provided between the inner surface of the through-hole  54  in the movable core  53  and the connecting bolt  55 , the movable core  53  and the connecting bolt  55  are capable of relatively oscillating. Therefore, when during an operation of the active type vibration isolating support system M, a load in an inclined direction is applied to the movable member  20 , it is possible to prevent the movable core  53  from inclining for maintaining a good sliding relationship with the bearing member  50  by means of the oscillation of the connecting bolt  55 . In this case, with the oscillation of the connecting bolt  55 , the set spring  57  moves sideways more or less, however, between this set spring  57  and the movable core  53 , there is interposed a spring seat  65  for holding the lower end portion of the set spring  57 , and yet, on an abutted surface between the spring seat  65  and the movable core  53 , there is formed a low friction material layer. Thus, the spring seat  65  smoothly slides on the upper surface of the movable core  53  along with the set spring  57 , thereby effectively suppressing production of abrasion powder from the movable core  53 . Therefore, it is possible to prevent trouble resulting from the abrasion powder, in such a case where the abrasion powder enters sliding portions of the bearing member  50  and the movable core  53  to hinder the movement of the movable core  53 .  
         [0066]     With very simple structure in which a set spring  52  is provided in a compressed state between the outward flange  50   b  at the lower end of the bearing member  50  and the upper yoke  35 , the bearing member  50  is installed at a fixed position on the lower yoke  36 . Therefore, no high precision is needed for the installation, and the cost can be reduced. Moreover, since the set spring  52  is to be arranged on the outer periphery side of the bearing member  50 , even if friction powder occurs between this set spring  52  and a portion against which the set spring  52  presses, it is possible to prevent the friction powder from entering the bearing member  50 . Particularly since between the outward flange  50   b  and the lower yoke  36 , there is interposed an elastic plate  51  which is brought into close contact with them, it is possible to reliably prevent the friction powder from entering the bearing member  50  by the elastic plate  51 , and the bearing member  50  is capable of exhibiting excellent guidance property for the movable core  53  over a long period of time.  
         [0067]     Also, since a repulsion force of the set spring  52  is supported by the upper yoke  35  continuing to the housing  32  and is not exerted on the movable core  53 , it is possible to prevent loss of an effective attracting force between the fixed and movable cores  33 ,  53  due to the repulsion force of the set spring  52 , thereby improving the output performance of the movable core  53 .  
         [0068]     In the coil assembly  34 , since there is molded a coil cover  41  which is brought into close contact with outer peripheral surfaces of the coil  39  and the bobbin  38  so as to seal the coil  39  to the bobbin  38 , it is possible to enhance water resistance of the coil  39 . Moreover, since on the coil cover  41 , there has been integrally formed a coupler  42  for holding the coupler terminal  40  to protrude outward in the radial direction, there is no need for a lead wire to be connected to the coil  39  and a coupler holder for supporting the coupler, so that a number of components and assembly man-hour are reduced, and the cost can be reduced.  
         [0069]     Also, on one end surface of the bobbin  38 , there is integrally formed a small strut  38   a  for insert-connecting a proximal end portion of the coupler terminal  40 ; around this small strut  38   a,  there is wound an outgoing line  39   a  of the coil  39  to be connected to the coupler terminal  40 ; and thereafter, a protruded portion  42   a  for enveloping the small strut  38   a  and the outgoing line  39   a  to protrude from the lower end surface of the coil cover  41  is integrally formed with the coil cover  41  together with the coupler  42 . Therefore, the outgoing line  39   a  of the coil  39  is wound around the small strut  38   a,  whereby it is possible to mold the coil cover  41 , the coupler  42  and the protruded portion  42   a  while reliably preventing the outgoing line  39   a  from loosening.  
         [0070]     When the coupler  42  is further exposed to the outside through an aperture  43  provided from the peripheral wall of the housing  32  over to the bottom wall  32   b,  the protruded portion  42   a  is arranged at the aperture  43  so as to be adjacent to the bottom wall  32   b.  Therefore, there is no need for the provision of accommodation space for the protruded portion  42   a  in the housing  32 , and the protruded portion  42   a  needs not be overhung over the outer surface of the housing  32 , whereby the actuator  31  can be made compact.  
         [0071]     Next, the description will be made of a second embodiment of the present invention shown in  FIG. 9 .  
         [0072]     This second embodiment is different from the first embodiment in closed structure of an adjustment operating hole  60  of the fixed core  33 . More specifically, the adjustment operating hole  60  is constructed by lining fitted holes  60   c  having a large diameter to the lower end of the simple through-hole  60   a  having no thread via an annular shoulder portion  60   b,  and the inner peripheral surface of the fitted hole  60   c  is provided with an annular restraining groove  58 . On the other hand, a peg body  61  corresponds to one obtained by cutting off the threaded tube  61   a  from the peg body  61  of the first embodiment. In the fitted hole  60   c,  a collar portion  61   b  of the peg body  61  is fitted via a sealing member  64 , and between this collar portion  61   b  and the shoulder portion  60   b  at the upper end of the fitted hole  60   c,  there is interposed an elastic member  72  such as a wave washer. Thus, in a state in which the elastic member  72  has been compressed by the peg body  61 , a stopper ring  71  for supporting the underside of the peg body  61  is engaged with the restraining groove  58 .  
         [0073]     With the above-described structure having no threaded tube  61   a,  the peg body  61  can be downsized by an amount corresponding to the threaded tube  61   a  of the peg body  61  in the first embodiment, and on installing to the adjustment operating hole  60 , since the need to rotate the peg body  61  can be circumvented, this is advantageous to maintain the durability of the sealing member  64 .  
         [0074]     Since the other components in the structure are the same as those of the first embodiment, portions corresponding to those of the first embodiment in  FIG. 9  are designated by the same reference numerals, and description thereof will be omitted.  
         [0075]     The present invention is not limited to the above-described embodiment, but it is possible to change the design in various ways without departing from the gist of the invention. For example, in the above-described embodiments, the movable member  20  and the connecting bolt  55  are integrated by forming them as separate members and threadably connecting together, but the members  20 ,  55  may be integrally constructed from the same material. Also, the fitted portion between the positioning shaft  33   b  of the fixed core  33  and the positioning hole  37  in the bottom wall  32   b  of the housing  32  may be fixed by welding instead of press-fitting.