Electromagnetic actuator

An electromagnetic actuator includes a fixed core supported by a bottom wall of a housing, a movable core arranged opposite to the fixed core via an air gap to drive the movable member, and coil assembly supported by the housing to surround both the cores, wherein the movable member and the movable core are connected by connecting means for adjusting the air gap between the fixed core and the movable core, and wherein an adjustment operating hole through which the connecting means is adjusted is provided on the fixed core so as to be opened outside the bottom wall of the housing. Thus, it is possible to freely adjust the air gap between the fixed core and the movable core without preparing several types of connecting members.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electromagnetic actuator having: a fixed core supported by a bottom wall of a housing made of magnetic material; a movable core arranged opposite to the fixed core via an air gap to drive a movable member; and coil assembly comprising a bobbin supported by the housing to surround the fixed and movable cores, and a coil wound around the bobbin.

2. Description of the Related Art

Such an electromagnetic actuator is already known as disclosed in, for example, Japanese Patent Application Laid-Open No. 2001-1765.

In the electromagnetic actuator, characteristics of the movable member concerning thrust and displacement are dependent on an initial air gap between attracted surfaces of the fixed and movable cores, but the 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 air gap has been adjusted by replacing the coupling member.

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

The present invention has been achieved in view of the above-described circumstances, and has an object to provide a low-priced electromagnetic actuator capable of freely adjusting an air gap between fixed and movable cores without preparing various types of coupling members.

In order to achieve the above-described object, according to a first feature of the present invention, there is provided an electromagnetic actuator comprising: a fixed core supported by a bottom wall of a housing made of magnetic material; a movable core arranged opposite to the fixed core via an air gap to drive a movable member; and a coil assembly comprising a bobbin supported by the housing to surround the fixed and movable cores, and a coil wound around the bobbin, wherein the movable member and the movable core are coupled by coupling means for adjusting the air gap between the fixed core and the movable core, and wherein an adjustment operating hole through which the coupling means is adjusted is provided on the fixed core so as to be opened outside the bottom wall of the housing.

With the first feature, by operating the coupling means, it is possible to freely adjust an air gap between the fixed core and the movable core, thereby imparting a desired vibration isolation characteristic to an active type vibration isolating support system. Therefore, the air gap is easily adjusted, and moreover there is no need for preparing various types of components having different dimensions in order to adjust the air gap, whereby the cost can be reduced. Moreover, since the coupling means is operated through the adjustment operating hole of the fixed core which is opened outside the housing, it is possible to accurately adjust the air gap without regard to assembly errors in each part after the completion of assembly of the actuator, thereby easily providing a high-quality actuator.

In addition to the first feature, according to a second feature of the present invention, the fixed core is integrally formed with a positioning shaft in which the adjustment operating hole is opened on an outer end surface and with a flange-shaped first yoke which protrudes from the outer periphery of the fixed core to be arranged opposite to one end surface of the coil assembly; the positioning shaft is fitted and fixed into a positioning hole provided at the bottom wall of the housing; the first yoke is brought into close contact with an inner surface of the bottom wall to surround the movable core; and a second yoke arranged opposite to the other end surface of the coil assembly is continuously provided to the housing.

With the second feature, although the fixed core becomes hollow because it has the adjustment operating hole, a positioning shaft integral with the fixed core is fitted and fixed to the positioning hole in the bottom wall of the housing, and the flange-shaped first yoke is brought into close contact with the bottom wall, whereby the fixed core is firmly reinforced to become capable of withstanding an abutting shock which the fixed core receives from the movable core and suffers no position shift. Moreover, the first yoke effectively increases magnetic paths around the coil assembly in cooperation with the housing and the second yoke, thereby increasing the attracting force between the fixed and movable core.

Further, in addition to the second feature, according to a third feature of the present invention, the bobbin is continuously provided with a coil cover which covers the outer periphery of the coil to seal the coil to the bobbin; the housing is arranged so that its bottom wall faces downward; and between the first yoke and the other end surfaces of the bobbin and the coil cover, there is interposed an elastic plate which water tightly comes into close contact with their opposite surfaces.

With the third feature, by elastically holding the coil assembly on the housing through use of the elastic plate, it is possible to enhance its vibration resistance. Moreover, even when water accumulated in the bottom part of the housing, the coil is waterproofed by the elastic plate, thereby greatly contributing to improvement in durability of the coil.

Further, in addition to the first feature, according to a fourth feature of the present invention, the fixed core is integrally formed with a flange-shaped first yoke which protrudes from an outer periphery of the fixed core to be arranged opposite to one end surface of the coil assembly and which is supported on the bottom wall of the housing; a second yoke which surrounds the movable core and is arranged opposite to the other end surface of the coil assembly is fixed to the housing; a tube-shaped bearing member which slidably supports the movable core is slidably fitted in the second yoke; and a set spring is provided in a compressed state between the second yoke and an outward flange which is formed at a lower end of the bearing member and which is supported on the first yoke, thereby biasing the outward flange toward the first yoke.

With the fourth feature, a stable operation of the movable core can be secured by the bearing member. Moreover, with very simple structure in which a set spring is provided in a compressed state between the outward flange of the bearing member and the second yoke, the bearing member can be installed at a fixed position, whereby no high precision is needed for the installation and the cost can be reduced.

Also, according to a fifth feature of the present invention, there is provided an electromagnetic actuator comprising: a fixed core supported by a bottom wall of a housing made of magnetic material; a movable core arranged opposite to the fixed core via an air gap to drive the movable member; a coil assembly comprising a bobbin supported by the housing to surround the fixed and movable cores, and a coil wound around the bobbin; and a tube-shaped bearing member disposed inside the coil assembly to slidably support the movable core, wherein a first yoke for holding the coil assembly in corporation with the bottom wall is continuously provided to the housing; wherein the bearing member is slidably fitted in the first yoke; wherein a supporting portion for supporting an outward flange formed at one end of the bearing member is provided on the bottom wall; and wherein a set spring for biasing the outward flange toward the supporting portion is provided in a compressed state between the outward flange and the first yoke.

With the fifth feature, since the set spring of the bearing member is arranged on the outer periphery side of the bearing member, even if abrasion powder is produced between the set spring and a portion against which the set spring abuts under pressure, it is possible to prevent the abrasion powder from entering the bearing member, thereby securing smooth sliding of the movable core. Also, since a repulsion force of the set spring is supported on the first yoke continuing to the housing and is not exerted on the movable core, it is possible to prevent any loss of an effective attracting force between the fixed and movable cores due to the repulsion force of the set spring, thereby improving the output performance of the movable core.

Also, in addition to the fifth feature, according to a sixth feature of the present invention, the fixed core is integrally formed with a positioning shaft fitted and fixed in a positioning hole provided on the bottom wall and with a second yoke which comes into close contact with an inner surface of the bottom wall and opposes to the first yoke with the coil assembly sandwiched therebetween, and the second yoke constitutes the supporting portion.

With the sixth feature, the fixed core is reinforced by fitting and fixing the positioning shaft integral therewith in the positioning hole in the bottom wall of the housing and by bringing the second yoke into close contact with the bottom wall. Therefore, the fixed core is capable of withstanding an abutting shock which the fixed core receives from the movable core, and further the fixed core suffers no position shift. Moreover, the second yoke is capable of effectively increasing magnetic paths around the coil assembly in cooperation with the housing and the first yoke, thereby increasing the attracting force between the fixed and movable cores.

Also, according to a seventh feature of the present invention, there is provided an electromagnetic actuator comprising: a fixed core supported by a bottom wall of a housing made of magnetic material; a movable core arranged opposite to the fixed core via an air gap to drive a movable member; and a coil assembly comprising a bobbin supported by the housing to surround the fixed and movable cores, and a coil wound around the bobbin, wherein a small strut for insert-connecting a proximal end of a coupler terminal is integrally formed on one end surface of the bobbin; wherein an outgoing line of the coil wound around the small strut is connected to the coupler terminal; and wherein on a coil cover molded on an outer periphery of the coil and the bobbin so as to seal the coil to the bobbin, there are integrally formed a coupler for holding the coupler terminal to protrude outward in a radial direction of the coil assembly and a protruded portion for enveloping the small strut to protrude from an end surface of the coil cover.

With the seventh feature, by molding the coil cover on the outer periphery of the coil and the bobbin so as to seal the coil to the bobbin, water resistance of the coil can be enhanced.

Moreover, since the coupler for holding the coupler terminal to protrude outward in the radial direction is integrally formed on the coil cover, both the lead wire to be connected to the coil and a coupler holder for supporting the coupler become unnecessary, so that the number of components and assembling steps are reduced and the cost can be reduced.

Also, a small strut for insert-connecting a proximal end portion of a coupler terminal is integrally formed on one end surface of the bobbin; an outgoing line of the coil wound around the small strut is connected to the coupler terminal; and a protruded portion for enveloping the small strut to protrude from an end surface of the coil cover is formed integrally with the coil cover together with the coupler. Therefore, by winding the outgoing line of the coil around the small strut, it is possible to mold the coil cover, the coupler and the protruded portion, while reliably preventing the outgoing line from loosening.

Also, in addition to the seventh feature, according to an eighth feature of the present invention, the coupler is exposed to the outside through an aperture provided from the peripheral wall of the housing to the bottom wall, and the protruded portion is arranged within the aperture so as to be adjacent to the bottom wall.

With the eighth feature, the actuator can be constructed compactly without the need for providing any accommodating space for the protruded portion in the housing, and without overhanging the protruded portion over the outer surface of the housing.

The connecting means corresponds to a connecting bolt55, an adjustment nut56and a set spring57in an embodiment of the present invention to be described later. Also, the first yoke and the second yoke correspond to an upper yoke35and a lower yoke36respectively.

The above-mentioned 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.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the preferred embodiments of the present invention will be described by reference to the attached drawings.

First, a first embodiment of the present invention shown inFIG. 1toFIG. 4will be described. InFIG. 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.

The active type vibration isolating support system M has actually axisymmetric structure with respect to an axis L, and has a plate-shaped installation bracket11to be connected to the engine E; an inner tube12welded to this installation bracket11; an outer tube13which is coaxially arranged around an outer periphery of this inner tube12; and a first elastic body14made of thick rubber or the like to be vulcanized and bonded onto conical surfaces of these inner tube12and outer tube13which oppose to each other. Below this first elastic body14, there are arranged a first orifice formation member15, a second orifice formation member16and a third orifice formation member17, which are arranged vertically and made integral with one another.

The first orifice formation member15is shaped like a disk, and has an aperture15bat a center thereof. The second orifice formation member16is annular, having a gutter-shaped cross section, the upper surface of which has been opened, and is integrally joined with the first orifice formation member15so that the opened upper surface is closed by the first orifice formation member15. The third orifice formation member17is 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 member16so that the opened upper surface is closed by the second orifice formation member16. Outer peripheral portions of the first and second orifice formation members15,16are superimposed on to be made integral with each other, and are fixed to an annular crimping fixed portion13acontinuously provided below the outer tube13.

On an inner peripheral surface of the third orifice formation member17, an outer peripheral surface of the annular second elastic body18made of rubber or the like is vulcanized and bonded. On the inner peripheral surface of this second elastic body18, there is vulcanized and bonded a first cap member19with the lower surface opened, arranged on the axis L. In this first cap member19, a second cap member23and a movable member20are fixed by press-fitting in order. The second cap member23has 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 diaphragm22arranged below the second elastic body18. On the outer periphery of this diaphragm22, a ring member21is vulcanized and bonded, and this ring member21is fixed to the crimping fixed portion13atogether with the outer peripheral portions of the first and second orifice formation members15,16. Because of deflection of the second elastic body18and the diaphragm22, the movable member20is capable of moving up and down together with the first and second cap members19,23.

Thus, between the first elastic body14and the second elastic body18, a first liquid chamber24, in which liquid is sealed, is defined, and between the second elastic body18and the diaphragm22, a second liquid chamber25, in which liquid is likewise sealed, is defined. These first and second liquid chambers24,25communicate with each other via an upper orifice26and a lower orifice27formed by the first to third orifice formation members15to17.

The upper orifice26is defined over a little less than one round thereof between the first and second orifice formation members15,16(SeeFIG. 2), and a partition wall26afor constituting opposite end walls of the upper orifice26is welded between the first and second orifice formation members15,16. The upper orifice26communicates with the first liquid chamber24via a through-hole15ain the first orifice formation member15on one side of the partition wall26a, and communicates with the lower orifice27via a through-hole16ain the second orifice formation member16on the other side of the partition wall26a.

The lower orifice27is defined over a little less than one round thereof between the second and third orifice formation members16,17(SeeFIG. 3), and a partition wall27afor constituting both end walls of the lower orifice27is welded between the first and second orifice formation members15,16. The upper orifice26communicates with the upper orifice26via the through-hole16aon one side of the partition wall27a, and communicates with the second liquid chamber25via a through-hole17aof the third orifice formation member17on the other side of the partition wall27a. Therefore, the first and second liquid chambers24,25are caused to communicate with each other via the upper and lower orifices26,27which have been connected with each other in series.

To the crimping fixed portion13a, a tube-shaped bracket28is 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 bracket28and the outer tube13constitute a supporting casing C of the active type vibration isolating support system M.

To the tube-shaped bracket28, an actuator supporting member30is fixed, and the electromagnetic actuator31for driving the movable member20is supported by this actuator supporting member30.

InFIG. 4, the actuator31has a closed-end tube-shaped housing32made of magnetic material, the upper surface of which has been opened, and a flange32aformed at the upper end thereof is fixed to the actuator supporting member30. The housing32is magnetic material, within which there are installed the fixed core33, the coil assembly34and the upper yoke35in order. The fixed core33has an attracted surface33ain an upper part thereof, a positioning shaft33bprotruding on an underside thereof, and a stepped collar-shaped lower yoke36formed at the outer periphery. The lower yoke36is brought into close contact with the bottom wall32bof the housing32so that the positioning shaft33bis pressed into the positioning hole37in the bottom wall32b. Thus, the fixed core33is fixed to the housing32.

The coil assembly34has a bobbin38made of synthetic resin to be arranged at the outer periphery of the fixed core33, and a coil39to be wound around this bobbin38. On the outer periphery of the lower flange of the bobbin38, a small strut38aprotruding downward is projectingly provided. During molding of this small strut38a, a proximal end portion of the coupler terminal40is insert-connected to the small strut38a. Around the small strut38a, an outgoing line39aof the coil39is wound, the tip end of which is connected to the coupler terminal40by means of soldering, electric welding or the like.

After the outgoing line39ais connected to the coupler terminal40, in order to seal the coil39to the bobbin38, a tube-shaped coil cover41which comes into close contact from the upper and lower end surfaces of the bobbin38to the outer peripheral surface of the coil39is injection-molded using synthetic resin. On that occasion, on this coil cover41, there are integrally formed a coupler42for holding the coupler terminal40to protrude outward in the radial direction of the cover41, and a protruded portion42afor enveloping the outgoing line39afrom the small strut38ato protrude on the lower end surface of the cover41. This coupler42is arranged so as to expose outside the housing32through an aperture43provided from the bottom wall32bof the housing32to the peripheral wall (SeeFIGS. 5 and 6). The protruded portion42ais arranged within the aperture43so as to be adjacent to the bottom wall32bof the housing32.

On the upper end surface of the coil assembly34, particularly on the upper end surface of the coil cover41, there is mounted an annular sealing member45. Also, on the lower end surface of the coil assembly34, particularly on the lower end surfaces of the bobbin38and the coil cover41, a plurality of sealing convex ridges46,46which surround the fixed core33for concentrically lining up are integrally formed. Between their lower end surfaces and thin outer peripheral portion36aof the lower yoke36, there is interposed an elastic plate47. This elastic plate47is molded with elastic material such as NBR or silicone rubber.

The upper yoke35is fixed to the inner peripheral surface of the housing32by press-fitting in order to press and hold the coil assembly34toward the lower yoke36. With the fixing, the sealing member41and the elastic plate47are compressed, whereby the coil assembly34is elastically supported without looseness between the upper yoke35and the lower yoke36, so that vibration resistance of the coil assembly34and water resistance of the coil39are improved. Particularly, since the sealing convex ridges46,46of the bobbin38and the coil cover41on the lower end surface cut into the upper surface of the elastic plate47to further reliably seal the elastic plate47, when rain water or washing water enters the aperture43from the outside to accumulate at the bottom of the housing32, even if contact between the coil cover41, and the coil39and the bobbin38is insufficient, it is possible to reliably prevent water from entering the inner periphery side of the bobbin38, to say nothing of entering the coil39side.

On the inner peripheral surface of a cylindrical portion35ato be arranged on the inner periphery of the bobbin38of the upper yoke35, a thin tube-shaped bearing member50is slidably fitted. At the upper end of this bearing member50, an inwardly-facing flange50apointing inwardly in the radial direction is integrally formed, while at the lower end thereof, an outwardly-facing flange50bpointing outwardly in the radial direction is integrally formed. The outwardly-facing flange50bis superimposed on the thick inner peripheral portion36bof the lower yoke36through the annular elastic plate51, and between this outwardly-facing flange50band the fixed core33, a set spring52made of coil spring is provided in a compressed state, whereby the bearing member50is elastically held on the lower yoke36for vibration isolation.

Also, when the movable core53descends on the fixed core33side, the elastic plate51also serves as a descending stopper for the movable core53, which receives the lower end of the movable core53as a cushion in order to avoid collision between both cores33,53and defines a descending limit thereof.

Slidably fitted to the bearing member50is the movable core53having an attracted surface53aopposed to an attracted surface33aof the fixed core33through the air gap2. The upper end of a connecting bolt55which loosely penetrates a comparatively large-diameter through-hole54opened at the central part of this movable core53is threadably attached to the movable member20. At the lower end portion of the connecting bolt55, an adjustment nut56of the movable core53for supporting the lower end surface around the through-hole54is threadedly engaged. On that occasion, the set spring57for holding the movable core53at a supporting position by the adjustment nut56is provided between the movable member20and the movable core53in a compressed state. Thus, the movable core53is elastically interposed between the set spring57and an adjustment nut56threadedly engaged with the connecting bolt55made integral with the movable member20. On the upper end surface of the adjustment nut56held in press contact with the movable core53, a radial ventilating groove58communicating with the through-hole54is 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.

Thus, if a threaded position of the adjustment nut56with the connecting bolt55is advanced and retreated, up and down positions of the movable core53, that is, the air gap g between attracted surfaces33aand53aof the movable core53and the fixed core33can be adjusted by corporation with the set spring57. An adjustment position of the adjustment nut56is threadedly engaged with and tightly fastened from below by the adjustment nut56, and is fixed by a lock screw59.

As shown inFIGS. 7 and 8, a threaded portion of the connecting bolt55has a normal right-hand thread, whereas in the threaded portion of the lock screw59, a left-hand thread is formed. Therefore, if in a state in which the adjustment nut56is held at a predetermined adjustment position by a tool, the lock screw59is fastened in by another tool, torque of the lock screw59is transmitted to the connecting bolt55through friction so that the connecting bolt55is drawn in on the lock screw59side. Therefore, it is possible to reliably lock at the adjustment position of the adjustment nut56.

At the central portion of the fixed core33, an adjustment operating hole60for allowing the adjustment nut56to go in and out is provided, and by means of a tool inserted into this adjustment operating hole60, the lock screw59and the adjustment nut56are adapted able to be operated. The adjustment operating hole60is composed of a threaded hole60aand a fitting hole60chaving a diameter larger than that of the threaded hole60a, continuing to the lower end of the threaded hole60athrough an annular shoulder portion60b. On the other hand, a peg body61closing the adjustment operating hole60is shaped like a bottomed tube with its upper end opened, and has a threaded tube61ato be threadedly engaged with the threaded hole60awhile receiving the adjustment nut56, a collar portion61bto be fitted in a fitting hole60c, and a bottom portion61c. On the outer periphery of the collar portion61b, there is mounted a sealing member64which comes into close contact with the inner peripheral surface of the fitting hole60c. At the underside of the bottom portion61c, there is formed a polygonal tool engaging projection62.

Until the collar portion61bfitted in the fitting hole60cabuts against the shoulder portion60b, the threaded tube61ais threadedly engaged with and tightly fastened to the threaded hole60a, whereby the adjustment operating hole60can be closed water tightly by the peg body61.

On the upper surface of the bottom portion61cof this peg body61, the elastic plate63is bonded, and the bottom portion61creceives the lower end of the adjustment nut56through this elastic plate63as a cushion to define a descending limit of the movable member20. However, when the adjustment nut56abuts against the bottom portion61cof the peg body61, the movable member20further descends while the movable member20compresses the set spring57after the movable core53reaches the above-described descending limit by descending of the movable member20.

Within the bearing member50, each of attracted surfaces33a,53aof the fixed core33and the movable core53which 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 surface53aof the movable core53surrounds the attracted surface33aof the fixed core33. Therefore, even in the fixed core33and the movable core53within the bearing member50, each having a comparatively small diameter within the bearing member50, it is possible to acquire a comparatively strong attraction force and a comparatively long stroke of the movable core53.

Moreover, since the attracted surface53aof the movable core53is to be formed on the inner peripheral surface side of the core53, a supporting span of the movable core53by the bearing member50can be secured sufficiently long irrespective of the attracted surface53a, and stable ascent and descent of the movable core53can be ensured. In this case, it is effective in acquiring further stable, smooth ascent and descent of the movable core53that the outer peripheral surface of the movable core53is formed with a low friction material layer made of Teflon or the like.

The set spring57is made of coil spring, and by fitting it to a large-diameter portion55aat the base of the connecting bolt55, the set spring57is arranged concentrically with the connecting bolt55. Also, between this set spring57and the movable core53, there is interposed an annular spring seat65made of steel plate in order to prevent the movable core53from wearing. This spring seat65has inner and outer concentric positioning tubular portions66,67which stand up along the inner peripheral surface and outer peripheral surface of the set spring57from the inner peripheral edge portion and outer peripheral edge portion, and the outside positioning tubular portion67is formed longer than the inside positioning tubular portion66. In order to facilitate insertion of the set spring57between these positioning tubular portions66,67, there are formed funnel portions66a,67aat the upper end portions of the positioning tubular portions66,67. Also, on at least one of abutted surfaces in which this spring seat65and the movable core53oppose to each other, a low friction material layer of Teflon or the like is formed to thereby make sliding property of the spring seat65to the movable core53excellent.

Referring toFIG. 1, to a coil39of the actuator31, an electronic control unit U is connected through a coupler42, 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.

Next, the description will be made of an operation of this embodiment.

When the actuator31of the active type vibration isolating support system M is in a non-operating state, although the first and second liquid chambers24,25which communicate with each other through the upper and lower orifices26,27are kept at the same pressure, since a pressure receiving area in the fist liquid chamber24of the first cap member19connected to the movable member20is larger than a pressure receiving area in the second liquid chamber25, a downward load obtained by multiplying the difference in area by pressure in the first liquid chamber24is exerted on the movable member20. When a balance is established between the load and a repulsion force of the second elastic body18against it, the movable member20comes to a halt, forming a predetermined initial air gap g between adsorption surfaces33a,53aof the fixed core33and the movable core53.

When shake vibration of low frequency occurs in the engine E during running of an automobile, the first elastic body14is deformed because of a load inputted from the engine E to change capacity of the first liquid chamber24. Then, the liquid goes and comes between the first and second liquid chambers24,25which communicate with each other through the upper and lower orifices26,27. When the capacity of the first liquid chamber24is enlarged and reduced, the capacity of the second liquid chamber25is reduced and enlarged accordingly, and the variations in capacity of this second liquid chamber25are absorbed by elastic deformation of a diaphragm22. At this time, since shapes and dimensions of the upper and lower orifices26,27and spring constant of the first elastic body14have 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.

In such a shake vibration domain of low frequency of the engine E, the actuator31is kept in a non-operating state.

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 orifices26,27which connect the first and second liquid chambers24,25enters a stick state, so that the engine E becomes unable to exhibit a vibration isolating function. In such a case, the actuator31is driven to exhibit the vibration isolating function.

In other words, the electronic control unit U controls energizing to a coil39of the actuator31on 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 chamber24is reduced due to the downward deformation of the first elastic body14to raise the liquid pressure, the coil39is energized to attract the movable core53on the fixed core33side. As a result, the movable core53descends while deforming the second elastic body18so that the capacity of the first liquid chamber24is enlarged, whereby it is possible to restrict the rise in pressure in the chamber24, 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.

On the other hand, when the engine E is displaced upward and the capacity of the first liquid chamber24is enlarged to raise the pressure in the chamber24, the coil39is demagnetized to release the movable core53. As a result, the movable core53rises due to the repulsion force of the second elastic body18so that the capacity of the first liquid chamber24is reduced, whereby it is possible to restrict the drop in pressure in the chamber24, 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.

During such an operation, when with an excessive increase in the downward load from the engine E to the first elastic body14, the pressure in the fist liquid chamber24is abruptly increased to apply the excessive downward load to the movable member20, the movable member20first descends the movable core53to its descent limit, that is, until the lower end surface of the core53is abutted against the elastic plate51on the thick inner peripheral portion36bof the lower yoke36. Thereafter, the set spring57is compressed and becomes deformed so that the adjustment nut56is moved away from the underside of the movable core53, whereby the movable member20is allowed to further move toward the fixed core33side. Accordingly, by causing the set spring57to absorb the excessive load of the movable member20, it is possible to prevent mutual contact between the fixed core33and the movable core53, and the excessive load acting on the movable core53and the elastic plate51, and to secure their durability.

Thus, if after the movable core53reaches the descent limit, the movable member20descends by a predetermined amount, the adjustment nut56will abut against a bottom portion61cof the peg body61fixed to the fixed core33through the elastic plate63to restrict any excessive increase in the load on the set spring57, thereby preventing any increase in over-load on the fixed core33and the movable core53.

Characteristics in thrust and displacement of the movable member20of the active type vibration isolating support system M are dependent on an initial air gap g between attracted surfaces33a,53aof the fixed core33and the movable cores33,53in a non-operating state of the actuator31. 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 body18to the movable core53. In such a case, a threaded position of the adjustment nut56with respect to the connecting bolt55is advanced and retreated as described above, whereby the initial air gap g can be adjusted properly and easily. Therefore, by energizing the coil39, it becomes possible to impart predetermined thrust and displacement to the movable member20with high precision, to thereby improve the performance of the active type vibration isolating support system M.

Also, if plural types of active type vibration isolating support systems M having different initial air gaps g between the fixed core33and the movable cores33,53are prepared by operating the adjustment nut56, 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.

Moreover, since the adjustment nut56is operated through the adjustment operating hole60of the fixed core33opened outside the housing32, 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.

Although the fixed core33becomes hollow because it has the adjustment operating hole60, the positioning shaft33bintegral therewith is pressed into the positioning hole37in the bottom wall32bof the housing32and the flange-shaped lower yoke36is brought into close contact with the bottom wall32b, whereby the fixed core33is firmly reinforced, and even if it receives an abutting shock from the movable core53, is capable of withstanding the shock sufficiently and besides causes no position shift. Moreover, since the lower yoke36effectively increases magnetic paths around the coil assembly34in cooperation with the housing32and the upper yoke35, the attracting force between the fixed and movable cores33,53can be increased.

On the other hand, an ascent limit of the movable core53is defined by its upper end abutting against an inward flange50aof the bearing member50. When the movable core53abuts against the inward flange50ashockingly, the impulse force is transmitted to the set spring52through the bearing member50and the outward flange50b, to be absorbed by the elasticity of the set spring52. Therefore, the set spring52also serves as an impulse absorbing member which protects the movable core53and the bearing member50from the impulse force.

Since the movable core53is elastically held on the adjustment nut56by the set spring57and an adequate play is provided between the inner surface of the through-hole54in the movable core53and the connecting bolt55, the movable core53and the connecting bolt55are 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 member20, it is possible to prevent the movable core53from inclining for maintaining a good sliding relationship with the bearing member50by means of the oscillation of the connecting bolt55. In this case, with the oscillation of the connecting bolt55, the set spring57moves sideways more or less, however, between this set spring57and the movable core53, there is interposed a spring seat65for holding the lower end portion of the set spring57, and yet, on an abutted surface between the spring seat65and the movable core53, there is formed a low friction material layer. Thus, the spring seat65smoothly slides on the upper surface of the movable core53along with the set spring57, thereby effectively suppressing production of abrasion powder from the movable core53. 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 member50and the movable core53to hinder the movement of the movable core53.

With very simple structure in which a set spring52is provided in a compressed state between the outward flange50bat the lower end of the bearing member50and the upper yoke35, the bearing member50is installed at a fixed position on the lower yoke36. Therefore, no high precision is needed for the installation, and the cost can be reduced. Moreover, since the set spring52is to be arranged on the outer periphery side of the bearing member50, even if friction powder occurs between this set spring52and a portion against which the set spring52presses, it is possible to prevent the friction powder from entering the bearing member50. Particularly since between the outward flange50band the lower yoke36, there is interposed an elastic plate51which is brought into close contact with them, it is possible to reliably prevent the friction powder from entering the bearing member50by the elastic plate51, and the bearing member50is capable of exhibiting excellent guidance property for the movable core53over a long period of time.

Also, since a repulsion force of the set spring52is supported by the upper yoke35continuing to the housing32and is not exerted on the movable core53, it is possible to prevent loss of an effective attracting force between the fixed and movable cores33,53due to the repulsion force of the set spring52, thereby improving the output performance of the movable core53.

In the coil assembly34, since there is molded a coil cover41which is brought into close contact with outer peripheral surfaces of the coil39and the bobbin38so as to seal the coil39to the bobbin38, it is possible to enhance water resistance of the coil39. Moreover, since on the coil cover41, there has been integrally formed a coupler42for holding the coupler terminal40to protrude outward in the radial direction, there is no need for a lead wire to be connected to the coil39and 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.

Also, on one end surface of the bobbin38, there is integrally formed a small strut38afor insert-connecting a proximal end portion of the coupler terminal40; around this small strut38a, there is wound an outgoing line39aof the coil39to be connected to the coupler terminal40; and thereafter, a protruded portion42afor enveloping the small strut38aand the outgoing line39ato protrude from the lower end surface of the coil cover41is integrally formed with the coil cover41together with the coupler42. Therefore, the outgoing line39aof the coil39is wound around the small strut38a, whereby it is possible to mold the coil cover41, the coupler42and the protruded portion42awhile reliably preventing the outgoing line39afrom loosening.

When the coupler42is further exposed to the outside through an aperture43provided from the peripheral wall of the housing32over to the bottom wall32b, the protruded portion42ais arranged at the aperture43so as to be adjacent to the bottom wall32b. Therefore, there is no need for the provision of accommodation space for the protruded portion42ain the housing32, and the protruded portion42aneeds not be overhung over the outer surface of the housing32, whereby the actuator31can be made compact.

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 member20and the connecting bolt55are integrated by forming them as separate members and threadably connecting together, but the members20,55may be integrally constructed from the same material. Also, the fitted portion between the positioning shaft33bof the fixed core33and the positioning hole37in the bottom wall32bof the housing32may be fixed by welding instead of press-fitting.