Patent Publication Number: US-2005133321-A1

Title: Automotive stabilizer incorporated with suspension system

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates in general to automotive stabilizers and more particularly to the automotive stabilizers of a type that is incorporated with a suspension system to provide the vehicle with a stabilized driving behavior.  
      2. Description of the Related Art  
      In independent suspension systems of wheeled motor vehicles, stabilizers are widely used for providing the vehicles with a stabilizing effect during turning and cornering. Most stabilizers are of a type that, for controlling rolling of the vehicle body at turning and cornering, uses practically a torsional rigidity of an antisway or torsion bar. However, due to the nature of the stabilizers of such type, when the vehicle is running straightly on a bumpy road, the relative displacement (or motion) of right and left suspension arms is restricted and thus the impact absorption effect of the suspension system itself becomes lowered, which deteriorates the drivability of the vehicle.  
      In view of the undesirability of the stabilizers of such type, Japanese Laid-open Patent Application (Tokkaihei) 5-32115 proposes to make the rolling restricting function of the stabilizer ON/OFF selectively in accordance with a running condition of the vehicle.  
      In order to clarify the task of the present invention, the stabilizer of the publication will be briefly discussed with reference to  FIGS. 12, 13  and  14  of the accompanying drawings.  
      As is seen from  FIG. 12 , the stabilizer of the publication generally comprises an antisway bar  102  that extends transversely relative to a vehicle body and an ON/OFF switch mechanism  103  that switches ON/OFF operation of antisway bar  102 . Antisway bar  102  comprises a pair of arm portions  106  and  107  and a torsion portion  108  extending between arm portions  106 . Torsion portion  108  is supported by the vehicle body through a bracket (not shown) that has a rubber bush installed therein. Arm portion  106  is pivotally connected to a con&#39;rod  140  through a coupling  141 , and con&#39;rod  140  is vertically movably connected to a lower arm  109  of the suspension structure through ON/OFF switch mechanism  103 . The other arm portion  107  is connected to the other lower arm. To assume ON condition, ON/OFF switch mechanism  103  fixes con&#39;rod  140  to lower arm  109 , and to assume OFF condition, the switch mechanism  103  releases con&#39;rod from lower arm  109 .  
      As is seen from  FIGS. 13 and 14 , ON/OFF switch mechanism  103  comprises a pair of recesses  155  and  156  formed in diametrically opposed portions of a generally middle part  157  of con&#39;rod  140 . ON/OFF switch mechanism  103  further comprises a pair of lock pieces  171  and  172  that are selectively engaged and disengaged with and from recesses  155  and  156  of con&#39;rod  140 . The selective engagement/disengagement of lock pieces  171  and  172  is controlled by a drive mechanism  180 . That is, when, due to work of drive mechanism  180 , lock pieces  171  and  172  are brought into engagement with recesses  155  and  156 , a vertical movement of con&#39;rod  140  relative to lower arm  109  (see  FIG. 12 ) is prevented thereby to induce ON condition of the switch mechanism  103 , while, when lock pieces  171  and  172  are disengaged from recesses  155  and  156 , the vertical movement of con&#39;rod  140  is permitted thereby to induce OFF condition of switch mechanism  103 .  
     SUMMARY OF THE INVENTION  
      However, due to its inherent construction, even the stabilizer of the publication has some drawbacks which are as follows.  
      That is, even when ON condition is needed by switch mechanism  103  under turning or cornering of the associated motor vehicle, such ON condition is not practically established if the position of recesses  155  and  156  of con&#39;rod  140  does not coincide with that of lock pieces  171  and  172 . Furthermore, even if such position coincidence is nearly made due to the sloped construction of recesses  155  and  156 , a greater force is needed by drive mechanism  180  to achieve a tight connection between lock pieces  171  and  172  and recesses  155  and  156 , which causes increase in cost and size of drive mechanism  180 .  
      Accordingly, it is an object of the present invention to provide an automotive stabilizer incorporated with a suspension system, which is free of the above-mentioned drawbacks.  
      According to the present invention, there is provided an automotive stabilizer incorporated with a suspension system, which can assuredly control the rolling restricting function thereof in ON/OFF manner even under turning or cornering of an associated motor vehicle.  
      According to the present invention, there is further provided an automotive stabilizer incorporated with a suspension system, which can effect the control of the rolling restricting function with a compact drive means.  
      In accordance with a first aspect of the present invention, there is provided an automotive stabilizer incorporated with a suspension system, which comprises an antisway bar adapted to extend transversely relative to a vehicle body, the antisway bar including a pair of arm portions and a torsion portion extending between the arm portions; a pivot member pivotally connected to a junction portion between the torsion portion and selected one of the arm portions; a link lever extending from the pivot member; a cylinder device including a cylindrical case and a piston slidably received in the cylindrical case, the cylindrical case being connected to one of the selected arm portion and the link lever and the piston being connected to the other of the selected arm portion and the link lever; and a control system that restricts the movement of the piston in the cylindrical case when actuated.  
      In accordance with a second aspect of the present invention, there is provided an automotive stabilizer incorporated with a suspension system, which comprises an antisway bar adapted to extend transversely relative to a vehicle body, the antisway bar including a pair of arm portions and a torsion portion extending between the arm portions; a pivot member pivotally connected to a junction portion between the torsion portion and selected one of the arm portions; a link lever extending from the pivot member; a cylinder device including a cylindrical case, a piston slidably received in the cylindrical case and a piston rod extending from the piston to the outside of the cylindrical case, the cylindrical case having therein first and second work chambers that are isolated by the piston; a first pivot member through which the cylindrical case of the cylinder device is pivotally connected to a part of the selected arm portion; a second pivot member through which the piston rod is pivotally connected to the link lever; and an ON/OFF switch circuit that is able to selectively provide an opening condition to communicate the first and second work chambers and a closed condition to isolate the first and second work chambers.  
      In accordance with a third aspect of the present invention, there is provided an automotive stabilizer incorporated with a suspension system, which comprises an antisway bar adapted to extend transversely relative to a vehicle body, the antisway bar including a pair of arm portions and a torsion portion extending between the arm portions; a pivot member pivotally connected to a junction portion between the torsion portion and selected one of the arm portions; a link lever extending from the pivot member; a cylinder device including a cylindrical case, a piston slidably received in the cylindrical case and a piston rod extending from the piston to the outside of the cylindrical case, the cylindrical case having therein first and second work chambers that are isolated by the piston; an outer cylindrical case slidably disposed on the cylindrical case to define between a third work chamber; an accumulator; a first pivot member through which the outer cylindrical case is pivotally connected to a part of the selected arm portion; a second pivot member through which the piston rod is pivotally connected to the link lever; and an electromagnetic control valve unit that is able to provide three operation conditions which are a first condition wherein the first and second work chambers are connected and the third work chamber and the accumulator are disconnected, a second condition wherein the first and second word chambers are disconnected and the third work chamber and the accumulator are connected, and a third condition wherein the first and second work chambers are disconnected and the third work chamber and the accumulator are disconnected. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic view of an automotive stabilizer incorporated with a suspension system, which is a first embodiment of the present invention;  
       FIGS. 2A, 2B  and  2 C are schematic views taken from the direction of the arrow “F” of  FIG. 1 , showing various operation conditions of the stabilizer of the first embodiment;  
       FIGS. 3A, 3B  and  3 C are additional schematic views taken from the direction of the arrow “F” of  FIG. 1 , showing also operation conditions of the stabilizer of the first embodiment;  
       FIG. 4  is a schematic view of a control system employed in the stabilizer of the first embodiment, which includes a cylinder device and an electromagnetic ON/OFF valve;  
       FIG. 5  is a view similar to  FIG. 4 , but showing an control system employed in a stabilizer of a second embodiment of the present invention;  
       FIG. 6  is a view similar to  FIG. 4 , but showing a control system employed in a stabilizer of a third embodiment of the present invention;  
       FIG. 7  is a partial view of a cylinder device employed in the control system of  FIG. 6 , showing the detail of a structure through which an end of a coil spring is connected to a piston;  
       FIGS. 8A, 8B  and  8 C are partial views of a cylinder device employed in the control system of  FIG. 6 , showing the detail of another structure through which the end of the coil spring is connected to the piston;  
       FIG. 9  is a view similar to  FIG. 4 , but showing a control system employed in a stabilizer of a fourth embodiment of the present invention;  
       FIG. 10  is a view similar to  FIG. 4 , but showing a control system employed in a stabilizer of a fifth embodiment of the present invention;  
       FIGS. 11A, 11B  and  11 C are sectional views of a control valve unit employed in the stabilizer of the fifth embodiment, showing different operation conditions thereof respectively;  
       FIG. 12  is a perspective view of a stabilizer of a related art employed in an automotive suspension system;  
       FIG. 13  is an exploded view of an ON/OFF switch mechanism employed in the stabilizer of the related art; and  
       FIG. 14  is a sectional view of the ON/OFF switch mechanism of the stabilizer of the related art. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
      In the following, various embodiments of the present invention will be described in detail with reference to the accompanying drawings.  
      For ease of understanding, various directional terms, such as, right, left, upper, lower, rightward and the like are used in the following description. However, such terms are to be understood with respect to a drawing or drawings on which corresponding part or portion is shown.  
      Referring to FIGS.  1  to  4  of the drawings, particularly  FIG. 1 , there is schematically shown an automotive stabilizer  100  incorporated with a suspension system, which is a first embodiment of the present invention.  
      As is seen from  FIG. 1 , automotive stabilizer  100  comprises an antisway bar “AS” that extends transversely relative to an associated motor vehicle. Antisway bar “AS” includes axially opposed arm portions  2  and  3  and a torsion portion  4  extending between arm portions  2  and  3 .  
      Torsion portion  4  is pivotally supported by a body of the associated motor vehicle through brackets (not shown) that have rubber bushes  17  and  18  installed therein, and arm portions  2  and  3  are connected to lower arms (not shown) of the suspension system.  
      At a junction part between torsion portion  4  and arm portion  3 , there is provided a pivotal bearing  7  from which a link lever  5  extends to a cylinder device  6 A. As shown, between link lever  5  and arm portion  3 , there extends the cylinder device  6 A, thereby to constitute a so-called link mechanism.  
      That is, arm portion  3  is integrally connected to torsion portion  4  in a manner to pivot about the junction part between torsion portion  4  and arm portion  3  in an imaginary plane that is perpendicular to an axis of torsion portion  4 .  
      In the link mechanism, cylinder device  6 A comprises a cylindrical case  8  and a piston  11  slidably received in case  8 . Case  8  is equipped at one end thereof with a bracket  9  by which a shaft  12  is pivotally held. Shaft  12  is equipped with a lever  10  of which leading end is fixed to arm portion  3 . Thus, one end of case  8  is pivotally connected to arm portion  3 . A piston rod  13  extending from piston  11  is pivotally connected to link lever  5  through a pivot member  14 . With this arrangement, arm portion  3  is pivotal about the axis of torsion portion  4  in the imaginary plane, as is mentioned hereinabove.  
      The interior of cylindrical case  8  is divided by piston  11  into first and second work chambers  15  and  16  which are positioned at the sides of bracket  9  and pivot member  14  respectively.  
      As will be described in detail hereinafter, first and second work chambers  15  and  16  are connected through a control system.  
      When, in operation, the vehicle is subjected to a rolling due to running on a corner, the paired arm portions  2  and  3  produce therebetween a relative displacement (or motion) in a direction about the axis of torsion portion  4 . However, in the present invention, even if such relative displacement is present, the rolling restricting function of the stabilizer  100  can be controlled is ON or OFF by the Control system irrespective of the degree of relative displacement. That is, if the rolling restricting function is not needed by the stabilizer  100 , the Control system is tuned to assume an open condition. With this, two chambers  15  and  16  become communicated to induce a free flow of hydraulic fluid between two chambers  15  and  16 . Thus, piston  11  of cylinder device  6 A is permitted to move freely thereby allowing both torsion portion  4  and arm portion  3  to make a relative pivoting therebetween. While, if the rolling restricting function is needed by stabilizer  100 , the Control system is turned to assume a close condition. With this, two chambers  15  and  16  become isolated from one another to interrupt the free flow of the fluid between two chambers  15  and  16 , and thus the free movement of piston  11  of cylinder device  6 A is suppressed. Under this condition, an effective length of cylinder device  6 A, that is, the length from the pivot shaft  12  to pivot member  14  becomes fixed, and thus, due to the fixed condition of cylinder device  6 A, the pivotal connection between torsion portion  4  and arm portion  3  through pivotal bearing  7  is suppressed any longer. That is, the rolling restricting function of the stabilizer  100  becomes ON.  
      The above-mentioned operation will be clarified when referring to the illustrations of  FIGS. 2A, 2B  and  2 C. These drawings are views taken from the direction of the arrow “F” of  FIG. 1 .  
       FIG. 2A  shows a condition wherein both arm portion  2  and arm portion  3  are in their normal positions,  FIG. 2B  shows a condition wherein arm portion  2  and arm portion  3  are both displaced in the same direction in a clockwise direction, and  FIG. 2C  shows a condition wherein both arm portion  2  and arm portion  3  are both displaced in the same direction in a counterclockwise direction.  
      In all of the conditions shown by these drawings, there is produced no relative displacement about the axis of torsion portion  4  between arm portion  2  and arm portion  3 , and thus, there is produced no relative displacement between case  8  of cylinder device  6 A and piston  11  of the same. Accordingly, irrespective of ON/OFF operation of the Control system, the stabilizer  100  does not exhibit the rolling restricting function.  
       FIGS. 3A, 3B  and  3 C are also views taken from the direction of the arrow “F” of  FIG. 1 .  
       FIG. 3A  shows a condition wherein both arm portion  2  and arm portion  3  are in their normal positions,  FIG. 3B  shows a condition wherein arm portion  3  is displaced in a clockwise direction about the axis of torsion portion  4  and the other arm portion  2  is in its normal position, and  FIG. 3C  shows a condition wherein arm portion  3  is displaced in a counterclockwise direction about the axis of torsion portion  4  and the other arm  2  is in its normal position.  
      In the condition of  FIG. 3A , there is produced no relative displacement about the axis of torsion portion  4  between arm portion  2  and arm portion  3 , and thus, there is produced no relative displacement between case  8  of cylinder device  6 A and piston  11  of the same. Accordingly, irrespective of ON/OFF operation of the control system, the stabilizer does not exhibit the rolling restricting function.  
      In the conditions of  FIGS. 3B and 3C , there is produced a relative displacement about the axis of torsion portion  4  between arm portion  2  and arm portion  3 . That is, under cornering of the associated motor vehicle, the Control system is closed to make the rolling restricting function ON for restraining such relative displacement. While, when the vehicle is running straightly on a bumpy road, the control system is opened to make the rolling restricting function OFF for permitting such relative displacement.  
      The control system incorporated with cylinder device  6 A is shown in  FIG. 4 .  
      As is described hereinabove, cylinder device  6 A generally comprises cylindrical case  8 , piston  11  slidably received in case  8  through an oil seal  17 , piston rod  13  connected to piston  11  to move therewith.  
      As shown, due to provision of piston  11 , the interior of case  8  is divided into first and second work chambers  15  and  16 . For the reason which will become apparent hereinafter, case  8  is formed with an opening  15 a exposed to first work chamber  15 .  
      Piston rod  13  has an upper portion that extends upward through an opening of an upper lid  19  fixed to case  8 . For sealing piston rod  13  relative to upper lid  19 , an oil seal  20  is provided by the opening of the lid  19 , as shown. Piston rod  13  has further a lower portion that extends downward through an opening of a bottom wall  21  of case  9 . An oil seal  22  is provided by the opening of the bottom wall  21 . Bracket  9  is secured to bottom wall  21  through bolts  27 .  
      As shown, piston rod  13  is formed with an axially extending passage  26  that has first and second openings  26 a and  26 b. In the illustrated condition, first opening  26 a is exposed to the outside of cylindrical case  8  and second opening  26   b  is exposed to second work chamber  16  of case  8 .  
      First and second work chambers  15  and  16  are connected through the control system which comprises a first passage  23  that extends from opening  15   a , an electromagnetic ON/OFF valve  24  that has the other end of first passage  23  connected thereto, a second passage  25  that extends from the ON/OFF valve  24  to first opening  26   a  of passage  26  of piston rod  13 . Thus, when piston rod  13  takes the illustrated position and ON/OFF valve  24  takes an open position (not the illustrated position), the two work chambers  15  and  16  are connected thereby smoothing movement of piston rod  13  in case  8 .  
      That is, as is understood from the circuit of  FIG. 4 , even when, due to rolling of the associated motor vehicle, there is produced a relative displacement between the two arm portions  2  and  3  (see  FIG. 1 ) about the axis of torsion portion  4  of antisway bar “AS”, the rolling restricting function of stabilizer  100  can be made ON or OFF by electromagnetic ON/OFF valve  24  at will irrespective of the degree of the relative displacement.  
      When ON/OFF valve  24  is opened, the hydraulic fluid in cylinder device  6 A is permitted to flow freely between two work chambers  15  and  16  through the open circuit, and thus piston  11  is permitted to move freely in case  8  of cylinder device  6 A. In this condition, torsion portion  4  and arm portion  3  of antisway bar “AS” are permitted to make a relative pivoting. That is, in this condition, the rolling restricting function of stabilizer  100  is OFF.  
      While, when ON/OFF valve  24  is closed, the flow of the fluid between two work chambers  15  and  16  is suppressed and thus movement of piston  11  in case  8  of cylinder device  6 A is suppressed. Under this condition, torsion portion  4  and arm portion  3  of antisway bar “AS” are prevented from making the relative pivoting. That is, in this condition, the rolling restricting function of stabilizer  100  is ON.  
      It is to be noted that ON/OFF valve  24  has a so-called fail safe function. That is, when, due to some unexpected trouble, the electromagnet of valve  24  fails to be energized, valve  24  is forced to take the close position by the force of a biasing spring. That is, in such case, the rolling restricting function of stabilizer  100  is ON.  
      Referring to  FIG. 5 , there is shown a control system that is employed in a second embodiment  200  of the present invention.  
      That is, in the control system employed in the second embodiment  200 , case  8  of cylinder device  8 B has an opening  15   a  through which first work chamber  15  is connected to second passage  25  and an opening  16 a through which second work chamber  16  is connected to first passage  23 . That is, first and second work chambers  15  and  16  are connected through first and second passages  23  and  24  and ON/OFF valve  24 , directly.  
      Since operation of this switch circuit is substantially the same as that of the above-mentioned first embodiment  100  of  FIG. 4 , explanation of the operation will be omitted.  
      Referring to  FIG. 6 , there is shown a control system that is employed in a third embodiment  300  of the present invention.  
      As will be understood as the description proceeds, in this third embodiment  300 , the rolling restricting function of stabilizer can be controlled to Low and High modes.  
      Since the switch circuit employed in this third embodiment  300  is similar to that of the above-mentioned first embodiment  100 , only parts and portions which are different from those of the first embodiment  100  will be described in detail in the following. Substantially same parts and portions as those of the first embodiment  100  are denoted by the same numerals.  
      As is seen from  FIG. 6 , within first work chamber  15 , there is installed a coil spring  28  that extends between upper lid  19  and piston  11 . That is, upper and lower ends of coil spring  28  are fixed to upper lid  19  and piston  11  respectively.  
      More specifically, upper end of coil spring  28  has a straight threaded bolt part  29  passing through an opening of upper lid  19 , and lower end of coil spring  28  has a straight threaded bolt part  30  passing through an opening of piston  11 . The upper and lower threaded bolt parts  29  and  30  are engaged with respective nuts  33  for achieving the connection thereof with upper lid  19  and piston  11 , as shown.  
      The detail of such bolt-and-nut connection will be well understood from  FIG. 7  that shows the detail of the connection between the bolt part  30  and piston  11 . As shown, an oil seal  31  and a spring seat  32  are further used for such connection.  
      Due to provision of coil spring  28  installed in the above-mentioned manner, piston  11  can be biased toward upper lid  19  or bottom wall  21  depending on the position of piston  11 . That is, when first work chamber  15  is fed with hydraulic fluid, piston  11  is forced to move downward toward bottom wall  21  expanding coil spring  28 . Thus, in this case, coil spring  28  functions to bias piston  11  upward toward upper lid  19 , while when second work chamber  16  is fed with the fluid, piston  11  is forced to move upward toward upper lid  19  compressing coil spring  28 . Thus, in this case, coil spring  28  functions to bias piston  11  downward toward bottom wall  21 .  
       FIGS. 8A, 8B  and  8 C show another way of connecting coil spring  28  to upper lid  19  or piston  11 . As is seen from these drawings, each turned end portion  28   a  of coil spring  28  is shaped to have a flat base surface that is perpendicular to an axis of coil spring  28 . The turned end portion has three cut recesses  28   b  for neatly receiving arm portions of respective clamps  34  that are secured to piston  11  (or upper lid  19 ) through respective bolts  70 .  
      If desired, coil spring  28  may be installed in second work chamber  16  not in first work chamber  15 , and furthermore, if desired, respective coil springs  28  may be installed in first and second work chambers  15  and  16 .  
      As is understood from the circuit of  FIG. 6 , even when, due to rolling of the associated motor vehicle, there is produce a relative displacement between the two arm portions  2  and  3  (see  FIG. 1 ) about the axis of torsion portion  4  of antisway bar “AS”, the rolling restricting function of stabilizer  300  can be controlled to Low or High mode at will by electromagnetic ON/OFF valve  24  irrespective of the degree of the relative displacement.  
      When ON/OFF valve  24  is opened, the hydraulic fluid is permitted to flow freely between two work chambers  15  and  16  through the open circuit, and thus piston  11  is permitted to move freely in case  8  of cylinder device  6 C. In this condition, torsion portion  4  and arm portion  3  of antisway bar “AS” are permitted to make a relative pivoting through coil spring  28  and link lever  5 . Under this condition, a resistance induced by the relative displacement between torsion portion  4  and arm portion  3  is a tandem combination of a resistance induced by the torsional rigidity of torsion portion  4  and a resistance induced by coil spring  28  through link lever  5  about the axis of torsion portion  4 , and thus, the resistance induced by the relative displacement between torsion portion  4  and arm portion  3  is smaller than a resistance induced by only the torsional rigidity of torsion portion  4 . Thus, under this condition, the rolling restricting function of stabilizer  300  is controlled to Low mode.  
      While, when ON/OFF valve  24  is closed, the flow of the fluid between two work chambers  15  and  16  is suppressed and thus movement of piston  11  in case  8  of cylinder device  6 C is suppressed. Under this condition, torsion portion  4  and arm portion  3  of antisway bar “AS” are prevented from making the relative pivoting, and thus, the rolling restricting function of stabilizer  300  is controlled to High mode.  
      In the arrangement of the third embodiment  300  of  FIG. 6 , a high drive stability of an associated motor vehicle is obtained especially when the vehicle is subjected to a sharp steering to avoid an obstruction on the road and then subjected to a counter-steering for recovering the posture of the vehicle. During this, a marked centrifugal force is applied to the vehicle body. That is, if switching from Low mode to High mode is made timely during such steering of the vehicle, a high and much effective rolling restricting operation is exhibited by the stabilizer.  
      It is to be noted that the control system of  FIG. 6  has a fail-safe function. That is, when, due to some unexpected trouble, the electromagnet of valve  24  fails to operate, valve  24  is forced to take the close position by the force of a biasing spring. Thus, in such case, the rolling restriction function of stabilizer  300  takes High mode. Of course, a reversed operation viz., Low mode may be adopted in such unexpected trouble. That is, in this case, valve  24  is forced to take the open position by the force of the biasing spring.  
      Referring to  FIG. 9 , there is shown a control system that is employed in a fourth embodiment  400  of the present invention.  
      Also in this fourth embodiment  400 , the rolling restricting function of stabilizer can be controlled to Low and High modes.  
      Since the switch circuit of the fourth embodiment  400  is similar to that of the second embodiment  200  of  FIG. 5 , only parts or portions which are different from those of the second embodiment  200  will be described in detail in the following. Substantially same parts and portions as those of the second embodiment  200  are denoted by the same numerals.  
      As is seen from  FIG. 9 , within first work chamber  15  of cylinder device  6 D, there is installed a coil spring  28  of which upper and lower ends are connected to upper lid  19  and piston  11  in the above-mentioned manner.  
      Since operation of this switch circuit is substantially the same as that of the above-mentioned third embodiment  300  of  FIG. 6 , explanation of the operation will be omitted.  
      Referring to  FIGS. 10, 11A ,  11 B and  11 C, particularly  FIG. 10 , there is shown a control system that is employed in a fifth embodiment  500  of the present invention.  
      As will be understood as the description proceeds, in this fifth embodiment  500 , the rolling restricting function of stabilizer can be controlled to Off, Low and High modes.  
      Since the switch circuit employed in the fifth embodiment  500  is similar to that of the above-mentioned third embodiment  300  of  FIG. 6 , only parts and portions which are different from those of the third embodiment  300  will be described in detail in the following. Substantially same parts and portions as those of the third embodiment  300  are denoted by the same numerals.  
      As is seen from  FIG. 10 , an outer cylindrical case  35  is further provided in which cylindrical case  8  is slidably received. For achieving a hermetical sealing between two cases  8  and  35 , an oil seal  39  is provided to an upper part of outer case  35 , and for achieving a smoothed axial movement of case  8  relative to outer case  35 , a slide bearing  40  is provided to outer case  35 .  
      Due to the telescopic connection between two cases  8  and  35 , there is produced a third work chamber  36  through which the lower portion of piston rod  13  passes. As shown, third work chamber  36  is defined between bottom wall  21  of cylindrical case  8  and a bottom wall  41  of outer case  35 . Bottom wall  41  is formed with an opening through which the lower portion of piston rod  13  passes downward. For assuring a sealing between piston rod  13  and bottom wall  41 , an oil seal  42  is provided to the bottom wall  41 , as shown. Bracket  9  is secured to bottom wall  41  through bolts  27 . Outer core  35  is formed with an opening  36   a  exposed to third work chamber  36 .  
      In place of electromagnetic ON/OFF valve  24  employed in the above-mentioned first, second, third and fourth embodiments  100 ,  200 ,  300  and  400 , an electromagnetic control valve unit  38  is employed in this fifth embodiment  500 .  
      This control valve unit  38  has four ports, which are a port “A” to which opening  15   a  of first work chamber  15  is connected through first passage  23 , a port “B” to which first opening  26   a  passage  26  of piston rod  13  is connected through second passage  25 , a port “C” to which opening  36   a  of third work chamber  36  is connected through a third passage  43  and a port “D” to which an accumulator  37  is connected through a fourth passage  44 . As will be clarified as the description proceeds, third work chamber  36  and accumulator  37  are connected through third passage  43 , port “C”, a selectable passage defined by control valve unit  38 , port “D” and fourth passage  44 .  
      The detail of electromagnetic control valve unit  38  is shown in  FIG. 11A .  
      As shown, valve unit  38  generally comprises a cylindrical case  47 , a spool  48  slidably received in case  47 , two reaction springs  49  and  50  for biasing spool  48  toward a balanced position and an electromagnetic actuator  51  for moving spool  48  against the biasing force of reaction springs  49  and  50  when energized.  
      Cylindrical case  47  has therein an elongate bore including equally spaced four (viz., first, second, third and fourth) grooves  52 ,  53 ,  54  and  55  that are merged with ports “A” “B”, “C” and “D” respectively.  
      Spool  48  has first, second and third lands  56 A,  56 B and  56 C and is biased by the two (viz., first and second) reaction springs  49  and  50  to have a neutral position as shown by  FIG. 11A . That is, in this neutral position, ports “A” and “B” are connected, and ports “C” and “D” are disconnected.  
      When actuator  51  is energized in a first manner, spool  48  is moved rightward to take a rightmost position as shown in FIG.  11 B against the force of spring  50 . In this case, ports “A” and “B” are disconnected and ports “C” and “D” are connected, as shown.  
      While, when actuator  51  is energized in a second manner, spool  48  is moved leftward to take a leftmost position as shown in  Fig. 11C  against the force of spring  49 . In this case, ports “A” and “B” are disconnected and ports “C” and “D” are also disconnected.  
      Even when there is produced a relative displacement between arm portions  2  and  3  about the axis of torsion portion  4  (see  FIG. 1 ) because of rolling of the associated motor vehicle, the rolling restricting function of stabilizer  500  can be controlled to Off, Low or High mode by suitably operating the control system of  FIG. 10 , which will be clarified from the following description.  
      When, upon energization of actuator  51  in the first manner, valve unit  38  assumes the condition of  FIG. 11B , first and second work chambers  15  and  16  (see  FIG. 10 ) are disconnected suppressing free flow of the hydraulic fluid therebetween, and third work chamber  36  is connected to accumulator  37  permitting free flow of the hydraulic fluid therebetween. In this case, piston  11  is suppressed from making a free movement in case  8  of cylinder device  6 E and case  8  is permitted to make a free movement in outer case  35 . Thus, torsion portion  4  and arm portion  3  of antisway bar “AS” are permitted to make a relative pivoting. That is, in this condition, the rolling restricting function of stabilizer  500  has Off mode.  
      While, due to de-energization of actuator  51 , valve unit  38  assumes the condition of  FIG. 11A , first and second work chambers  15  and  16  (see  FIG. 10 ) are connected permitting free flow of the hydraulic fluid therebetween, and third work chamber  36  is isolated from accumulator  37  suppressing free low of the hydraulic fluid therebetween. In this case, piston  11  is permitted to make a free movement in case  8  of cylinder device  6 E and case  8  is suppressed from making a free movement in outer case  35 . Under this condition, pivotal connection between torsion portion  4  and arm portion  3  is made through coil spring  28  and link lever  5 . Thus, in this case, a resistance induced by the relative displacement between torsion portion  4  and arm portion  3  is a tandem combination of a resistance induced by the torsional rigidity of torsion portion  4  and a resistance induced by coil spring  28  through link lever  5  about the axis of torsion portion  4 , and thus, the resistance induced by the relative displacement between torsion portion  4  and arm portion  3  is smaller than a resistance induced by only the torsional rigidity of torsion portion  4 . Thus, under this condition, the rolling restricting function of stabilizer  500  has Low mode.  
      While, upon energization of actuator  51  in the second manner, valve unit  38  assumes the condition of  FIG. 11C , first and second work chambers  15  and  16  (see  FIG. 10 ) are disconnected suppressing free flow of the hydraulic fluid therebetween, and third work chamber  36  is isolated from accumulator  37  suppressing free flow of the hydraulic fluid therebetween. In this case, piston  11  is suppressed from making a free movement in case  8  of cylinder device  6 E and case  8  is suppressed from making a free movement in outer case  35 . Thus, the actual length of cylinder device  6 E becomes fixed, and thus, torsion portion  4  and arm portion  3  are prevented from making a relative pivoting through link lever  5 . That is, in this condition, the rolling restricting function of stabilizer  500  has High mode.  
      Thus, in stabilizer  500  of the third embodiment, not only ON/OFF switching for the rolling restricting function that is needed when an associated motor vehicle runs on bumpy/paved road, but also switching between Low and High modes for the rolling restricting function is achieved.  
      In the following, modifications will be briefly described.  
      If desired, additional work chamber, that is, a fourth work chamber may be provided. In this case, further mode can be provided in addition to the above-mentioned Off, Low and High modes.  
      If desired, coil springs may be installed in second and third work chambers  16  and  36 . In this case, the Off, Low and High modes of the rolling restricting function are much finely controlled. By suitably selecting the spring constant of each coil spring, much desired control for the rolling restricting function is achieved.  
      If desired, the control system may be applied also to a junction portion between torsion portion  4  and the other arm portion  2 . In this case, it is preferable to employ different types of cylinder devices for respective switch circuits.  
      If desired, a steered angle detecting means may be provided for detecting a steered angle of steered road wheels. That is, in accordance with information signal from the detecting means, ON/OFF valve  24  or control valve unit  38  is controlled. In this modification, ON/OFF section for the rolling restricting function or Off, Low and High mode selection for the function can be controlled in accordance the steered angle of the steered road wheels. Furthermore, in accordance with the surface condition of the road and running condition of the vehicle, the rolling restricting function can be automatically controlled.  
      In first, second, third and fourth embodiments  100 ,  200 ,  300  and  400 , electromagnetic ON/OFF valve  24  is used as an element of the ON/Off switch circuit. If desired, in place of such valve  24 , a valve that can take a half-open position or continuously changeable positions may be used. When such valve is used, the following advantageous operation is expected. That is, when, with the two arm portions  2  and  3  showing a relative displacement, Off instruction is applied to the rolling restricting function, the rolling restricting function is gradually changed to Off mode, which suppresses a sudden change of posture of the associated motor vehicle.  
      If desired, passages  23 ,  25   43  and  44  or some of them may have orifices. Under flowing of the hydraulic fluid in the passages, a damping force is produced by stabilizer. Thus, when, with two arm portions  2  and  3  showing a relative displacement, the rolling restricting function is turned OFF, movement of piston  11  of cylinder device is slowed and thus sudden change of posture of the vehicle is suppressed.  
      If desired, in place of the above-mentioned cylinder devices  6 A to  6 E, other types of cylinder devices may be used so long as they has means for controlling the actual length.  
      The entire contents of Japanese Patent Application 2003-419688 filed Dec. 17, 2003 are incorporated herein by reference.  
      Although the invention has been described above with reference to the embodiments of the invention, the invention is not limited to such embodiments as described above. Various modifications and variations of such embodiments may be carried out by those skilled in the art, in light of the above description.