Abstract:
In an active vibration isolation support system, a movable member is connected to an armature (movable core) of an actuator and moved out and back by the armature, the armature is housed in a sealed space, and a pressure of the sealed space is maintained at substantially atmospheric pressure by a flexible bag that is disposed within the sealed space and communicates with the atmosphere via a through hole formed in a wall defining the sealed space. Therefore, while preventing dust and water from entering the sealed space to prevent malfunction of the armature, a change of pressure is prevented in the sealed space to maintain a neutral position of the movable member, thereby controlling vibration of the movable member with a good precision.

Description:
RELATED APPLICATION DATA  
       [0001]     The present invention claims priority under 35 USC 119 based on Japanese patent application No. 2005-249926, filed on Aug. 30, 2005. The subject matter of this priority document is incorporated in its entirety by reference herein.  
       BACKGROUND OF INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an active vibration isolation support system comprising: an elastic body that receives a load from a vibrating body; a liquid chamber having a wall of which at least a part is formed from the elastic body; an actuator that moves out and back by receiving a supply of current according to a vibrational state of the vibrating body; and a movable member that is operated by an armature of the actuator so as to change a capacity of the liquid chamber; at least the armature of the actuator being housed in a sealed space that is cut off from the atmosphere, and the movable member facing the sealed space.  
         [0004]     2. Description of Related Art  
         [0005]     Such an active vibration isolation support system is known from, for example, Japanese Patent Application Laid-open No. 2004-293601. In this active vibration isolation support system, a space in which an armature of an actuator moves out and back is sealed, thereby preventing malfunction of the armature due to the entrance of dust or water.  
         [0006]     However, in this conventional system, the armature of the actuator is disposed in the sealed space, which is sealed so that dust or water does not enter, and a part of a wall defining the sealed space is formed from a movable member that moves out and back by being connected to the armature. As a result, the pressure of the sealed space changes according to the ambient temperature or heat generated by the actuator itself Therefore, the movable member receives a resistance when it moves in a direction in which the difference between the pressure of the sealed space and the atmospheric pressure increases, and its neutral position rises. In addition, the movable member receives an urging force when it moves in a direction in which the difference between the pressure of the sealed space and the atmospheric pressure decreases, and its neutral position falls. As a result, a clearance beneath the armature changes, and thus a driving force generated by the actuator changes, leading to a problem that it becomes difficult to control vibration of the movable member with a good precision.  
       SUMMARY  
       [0007]     The present invention has been accomplished under the above circumstances, and it is an object thereof to provide an active vibration isolation support system in which a neutral position of an armature of an actuator does not change according to a change in pressure of a sealed space housing the armature, while preventing dust and water from entering the sealed space.  
         [0008]     In order to achieve the above object, according to a first feature of the present invention, there is provided an active vibration isolation support system comprising: an elastic body that receives a load from a vibrating body; a liquid chamber having a wall of which at least a part is formed from the elastic body; an actuator that moves out and back by receiving a supply of current according to a vibrational state of the vibrating body; and a movable member that is operated by an armature of the actuator so as to change a capacity of the liquid chamber; at least the armature of the actuator being housed in a sealed space that is cut off from the atmosphere, and the movable member facing the sealed space, wherein a pressure cushioning member is provided for maintaining a pressure of the sealed space at substantially atmospheric pressure.  
         [0009]     With the first feature, the pressure of the sealed space, which houses the armature of the actuator that makes the movable member of the active vibration isolation support system move out and back and which the movable member connected to the armature faces, is maintained at substantially atmospheric pressure by the pressure cushioning member. Therefore, it is possible to stabilize the neutral positions of the armature and the movable member by preventing the pressure of the sealed space from varying, while preventing malfunction of the armature by preventing dust or water from entering the sealed space, thereby performing control of the movable member by the actuator with a good precision.  
         [0010]     According to a second feature of the present invention, in addition to the first feature, the pressure cushioning member comprises a flexible bag that is disposed within the sealed space and communicates with the atmosphere via a through hole formed in a wall defining the sealed space.  
         [0011]     With the second feature, the pressure cushioning member comprises the flexible bag which is disposed within the sealed space and communicates with the atmosphere via the through hole formed in the wall defining the sealed space. Therefore, it is possible to maintain the pressure of the sealed space at substantially atmospheric pressure by expansion and contraction of the flexible bag which communicates with the atmosphere, even if the capacity of the sealed space changes as a result of the armature of the actuator making the movable member move out and back.  
         [0012]     According to a third feature of the present invention, in addition to the first feature, the pressure cushioning member comprises a flexible bag that is disposed within the sealed space and communicates with the liquid chamber via a through hole formed in a wall defining the sealed space.  
         [0013]     With the third feature, the pressure cushioning member comprises the flexible bag, which is disposed within the sealed space and communicates with the liquid chamber via the through hole formed in the wall defining the sealed space. Therefore, it is possible to maintain the pressure of the sealed space at substantially atmospheric pressure by expansion and contraction of the flexible bag which communicates with the liquid chamber at substantially atmospheric pressure, even if the capacity of the sealed space changes as a result of the armature of the actuator making the movable member move out and back.  
         [0014]     A first elastic body  19  of an embodiment corresponds to the elastic body of the present invention, first and second liquid chambers  30  and  31  of the embodiment correspond to the liquid chamber of the present invention, a movable core  54  of the embodiment corresponds to the armature of the present invention, and bags  64  and  65  of the embodiment correspond to the pressure cushioning member of the present invention.  
         [0015]     The above-mentioned object, other objects, characteristics, and advantages of the present invention will become apparent from preferred embodiments that will be described in detail below by reference to the attached drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  to  FIG. 4  show a first embodiment of the present invention, wherein  
         [0017]      FIG. 1  is a vertical sectional view of an active vibration isolation support system;  
         [0018]      FIG. 2  is an enlarged view of part  2  in  FIG. 1  showing the flexible bag disposed in the sealed space and in communication with the atmosphere via a through hole formed in the actuator housing wall;  
         [0019]      FIG. 3  is a diagram for explaining a method of fixing the bag of  FIG. 2  within the sealed space; and  
         [0020]      FIG. 4  is a flow chart for explaining the operation of the active vibration isolation support system.  
         [0021]      FIG. 5  and  FIG. 6  show a second embodiment of the present invention, wherein;  
         [0022]      FIG. 5  is a diagram corresponding to  FIG. 2  showing the flexible bag disposed in the sealed space and in communication with the liquid chamber via a through hole formed in the wall defining the sealed space; and  
         [0023]      FIG. 6  is a diagram for explaining a method of fixing the bag of  FIG. 5  within the sealed space. 
     
    
     DETAILED DESCRIPTION  
       [0024]     Selected illustrative embodiments of the invention will now be described in some detail, with reference to the drawings. It should be understood that only structures considered necessary for clarifying the present invention are described herein. Other conventional structures, and those of ancillary and auxiliary components of the system, are assumed to be known and understood by those skilled in the art.  
         [0025]     Referring to  FIG. 1  and  FIG. 2 , an active vibration isolation support system M (active control mount) for elastically supporting an automobile engine in a vehicle body frame has a structure that is substantially symmetrical with respect to an axis L. In the active vibration isolation support system M, between a flange portion  11   a  at the lower end of a substantially cylindrical upper housing  11  and a flange portion  12   a  at the upper end of a substantially cylindrical lower housing  12 , a flange portion  13   a  on the outer periphery of an upwardly opening substantially cup-shaped actuator case  13 , an outer peripheral portion of an annular first elastic body support ring  14 , and an outer peripheral portion of an annular second elastic body support ring  15  are superimposed and joined by crimping. In this process, an annular floating rubber member  17  is disposed between an upper part of the actuator case  13  and an inner face of the second elastic body support ring  15 .  
         [0026]     Joined by vulcanization bonding to the first elastic body support ring  14  and a first elastic body support boss  18  disposed on the axis L, are the lower end and the upper end of a first elastic body  19  made of a thick rubber. A diaphragm support boss  20  is fixed to an upper face of the first elastic body support boss  18  by a bolt  21 . An outer peripheral portion of a diaphragm  22 , whose inner peripheral portion is joined by vulcanization bonding to the diaphragm support boss  20 , is joined by vulcanization bonding to the upper housing  11 . An engine mounting portion  20   a  integrally formed on an upper face of the diaphragm support boss  20  is fixed to the engine (unillustrated). A vehicle body mounting portion  12   b  at the lower end of the lower housing  12  is fixed to the vehicle body frame (unillustrated).  
         [0027]     A flange portion  23   a  at the lower end of a stopper member  23  is joined by bolts  24  and nuts  25  to a flange portion  11   b  at the upper end of the upper housing  11 . The engine mounting portion  20   a  projectingly provided on the upper face of the diaphragm support boss  20  faces a stopper rubber member  26  attached to an upper inner face of the stopper member  23  so that the engine mounting portion  20   a  can abut against the stopper rubber member  26 . When a large load is input to the active vibration isolation support system M, the engine mounting portion  20   a  abuts against the stopper rubber member  26 , thereby suppressing excessive displacement of the engine.  
         [0028]     An outer peripheral portion of a second elastic body  27 , made of a membranous rubber, is joined by vulcanization bonding to the second elastic body support ring  15 . A movable member  28  is embedded in and joined by vulcanization bonding to a central portion of the second elastic body  27 . A disc-shaped partition member  29  is fixed between an upper face of the second elastic body support ring  15  and the outer peripheral portion of the first elastic body  19 . A first liquid chamber  30  defined by the partition member  29  and the first elastic body  19 , and a second liquid chamber  31  defined by the partition member  29  and the second elastic body  27 , communicate with each other via a through hole  29   a  formed in the middle of the partition member  29 .  
         [0029]     An annular through passage  32  is formed between the first elastic body support ring  14  and the upper housing  11 . One end of the through passage  32  communicates with the first liquid chamber  30  via a through hole  33 , and the other end of the through passage  32  communicates via a through hole  34  with a third liquid chamber  35  defined by the first elastic body  19  and the diaphragm  22 .  
         [0030]     The structure of an actuator  41  for driving the movable member  28  is now described.  
         [0031]     Mounted within the actuator case  13  in sequence from the bottom to the top are a stationary core  42 , a coil assembly  43 , and a yoke  44 . The coil assembly  43  is formed from a bobbinless coil  46  disposed between the stationary core  42  and the yoke  44 , and a coil cover  47  covering the outer periphery of the bobbinless coil  46 . The coil cover  47  is formed integrally with a connector  48  running through openings  13   b  and  12   c  formed in the actuator case  13  and the lower housing  12  and extending outward. A seal  49  is disposed between an upper face of the coil cover  47  and a lower face of the yoke  44 . A seal  50  is disposed between a lower face of the bobbinless coil  46  and an upper face of the stationary core  42 .  
         [0032]     A thin cylindrical bearing member  51  is fitted, in a vertically slidable manner, into an inner peripheral face of a cylindrical portion  44   a  of the yoke  44 . An upper flange  51   a  and a lower flange  51   b  are formed at the upper end and the lower end respectively of the bearing member  51 , the upper flange  51   a  being bent radially inward, the lower flange  51   b  being bent radially outward. A set spring  52  is disposed in a compressed state between the lower flange  51   b  and the lower end of the cylindrical portion  44   a  of the yoke  44 . The bearing member  51  is supported by the yoke  44  by the lower flange  51   b  being pressed against the upper face of the stationary core  42  via an elastic body  53  by means of the elastic force of the set spring  52 .  
         [0033]     A substantially cylindrical movable core  54  is fitted, in a vertically slidable manner, into an inner peripheral face of the bearing member  51 . A rod  55 , extending downward from the center of the movable member  28 , runs loosely through the center of the movable core  54 , and a nut  56  is tightened around the lower end of the rod  55 . A set spring  58  is disposed in a compressed state between a spring seat  57  provided on an upper face of the movable core  54  and a lower face of the movable member  28 . The movable core  54  is fixed by being pressed against the nut  56  by means of the elastic force of the set spring  58 . In this state, the lower face of the movable core  54  and the upper face of the stationary core  42  face each other across a conical air gap g. The rod  55  and the nut  56  are loosely fitted into an opening  42   a  formed in the center of the stationary core  42 , and the lower end of this opening  42   a  is blocked by a plug  60  via a seal  59 . The seals  49 ,  50  and  59  can prevent water or dust from entering a sealed space  61  in the actuator  41  via the openings  13   b ,  12   c  and  42   a  formed in the actuator case  13 , the lower housing  12  and the stationary core  42 .  
         [0034]     Outer peripheral edges of an annular bag  64  having a U-shaped section are joined by vulcanization bonding to an upper ring  62  and a lower ring  63 , each of which are formed so as to have an L-shaped section. The upper ring  62  and the lower ring  63  are fixed by being interposed between a second elastic body support ring  15  and a yoke  44 . A cut-out  63   a  is formed in one area of the upper edge of the lower ring  63  which is in intimate contact with the lower edge of the upper ring  62 . The cut-out  63   a  faces a through hole  13   c  formed in the actuator case  13 . Therefore, the interior of the bag  64 , which is an elastic body disposed within a sealed space  61 , is cut off from the sealed space  61 , and communicates with the atmosphere via the cut-out  63   a  of the lower ring  63  and the through hole  13   c  of the actuator case  13 .  
         [0035]     As shown in  FIG. 3 , the upper ring  62  and the lower ring  63 , to which the bag  64  is joined by vulcanization bonding, are fixed within the actuator case  13  by being press-fitted into an inner peripheral face of the actuator case  13 .  
         [0036]     Returning to  FIG. 1 , an electronic control unit U, to which is connected a crank pulse sensor Sa for detecting a crank pulse that is outputted accompanying rotation of a crankshaft of the engine, controls the supply of current to the actuator  41  of the active vibration isolation support system M. The crank pulse of the engine is outputted 24 times per revolution of the crankshaft, that is, once every 15° of the crank angle.  
         [0037]     The operation of the first embodiment of the present invention having the above-mentioned arrangement are now described.  
         [0038]     When low frequency engine shake vibration occurs while the automobile is traveling, the first elastic body  19  is deformed by a load input from the engine via the diaphragm support boss  20  and the first elastic body support boss  18 , thus changing the capacity of the first liquid chamber  30 , so that a liquid moves to and fro between the first liquid chamber  30  and the third liquid chamber  35  via the through passage  32 . When the capacity of the first liquid chamber  30  increases/decreases, the capacity of the third liquid chamber  35  decreases/increases correspondingly, and this change in the capacity of the third liquid chamber  35  is absorbed by elastic deformation of the diaphragm  22 . The shape and the dimensions of the through passage  32  and the spring constant of the first elastic body  19  are set so that a low spring constant and high attenuation force are exhibited in the frequency region of the engine shake vibration. Therefore, it is possible to effectively suppress the vibration transmitted from the engine to the vehicle body frame.  
         [0039]     In the frequency region of the engine shake vibration, the actuator  41  is maintained in a non-operating state.  
         [0040]     When there is vibration having a higher frequency than that of the above-mentioned engine shake vibration, that is, vibration during idling or vibration during cylinder cut-off due to rotation of the engine crankshaft, the liquid within the through passage  32  providing communication between the first liquid chamber  30  and the third liquid chamber  35  becomes stationary and a vibration isolation function cannot be exhibited; the actuator  41  is therefore driven to exhibit a vibration isolation function.  
         [0041]     In order to operate the actuator  41  of the active vibration isolation support system M to exhibit the vibration isolation function, the electronic control unit U controls the supply of current to the bobbinless coil  46  based on a signal from the crank pulse sensor Sa.  
         [0042]     That is, in the flow chart of  FIG. 4 , firstly in step S 1 , crank pulses output from the crank pulse sensor Sa every 15° of crank angle are read in. In step S 2 , the crank pulses thus read in are compared with a reference crank pulse (TDC signal of a specified cylinder) so as to calculate a time interval between the crank pulses. In step S 3 , a crank angular velocity ω is calculated by dividing the 15° crank angle by the time interval between the crank pulses. In step S 4 , a crank angular acceleration dω/dt is calculated by differentiating the crank angular velocity ω with respect to time. In step S 5 , a torque Tq around the engine crankshaft is calculated from 
 
 Tq=I×dω/dt,  
 
 where I is the moment of inertia around the engine crankshaft. This torque Tq becomes 0 if it is assumed that the crankshaft rotates at a constant angular velocity ω, but in an expansion stroke the angular velocity ω increases by acceleration of a piston, and in a compression stroke the angular velocity ω decreases by deceleration of the piston, thus generating a crank angular acceleration dω/dt; as a result a torque Tq that is proportional to the crank angular acceleration dω/dt is generated. 
 
         [0043]     In step S 6 , a maximum value and a minimum value of two successive torque values are determined. In step S 7 , amplitude at the position of the active vibration isolation support system M supporting the engine is calculated as the difference between the maximum value and the minimum value of the torque, that is, a torque variation. In step S 8 , a duty waveform and timing (phase) of current applied to the bobbinless coil  46  of the actuator  41  are determined.  
         [0044]     Thus, when the engine moves downward relative to the vehicle body frame and the first elastic body  19  is deformed downwardly thereby decreasing the capacity of the first liquid chamber  30 , energizing the bobbinless coil  46  of the actuator  41  with matching timing allows the movable core  54  to move downward toward the stationary core  42  by means of the attractive force generated in the air gap g, and the second elastic body  27  is deformed downwardly by being drawn by the movable member  28  connected to the movable core  54  via the rod  55 . As a result, the capacity of the second liquid chamber  31  increases, so that the liquid in the first liquid chamber  30  which is compressed by the load from the engine, passes through the through hole  29   a  of the partition member  29  and flows into the second liquid chamber  31 , thereby reducing the load transmitted from the engine to the vehicle body frame.  
         [0045]     Subsequently, when the engine moves upward relative to the vehicle body frame and the first elastic body  19  is deformed upwardly thereby increasing the capacity of the first liquid chamber  30 , de-energizing the bobbinless coil  46  of the actuator  41  with matching timing allows the attractive force generated in the air gap g to disappear and the movable core  54  to move freely, so that the second elastic body  27  that has been deformed downwardly recovers upwardly by its own elastic recovery force. As a result, the capacity of the second liquid chamber  31  decreases, and the liquid in the second liquid chamber  31  passes through the through hole  29   a  of the partition member  29  and flows into the first liquid chamber  30 , thereby allowing the engine to move upward relative to the vehicle body frame.  
         [0046]     In this way, by energizing and de-energizing the bobbinless coil  46  of the actuator  41  according to the cycle of vibration of the engine, it is possible to generate an active damping force that prevents vibration of the engine from being transmitted to the vehicle body frame.  
         [0047]     As described above, since the sealed space  61  is cut off from the outside and sealed, it is possible to reliably prevent dust or water from entering the sealed space  61 . Thus, it is possible to prevent malfunction due to dust or water becoming attached to sliding portions between the movable core  54  and the bearing member  51  disposed in the sealed space  61 .  
         [0048]     Furthermore, since the movable member  28  and the second elastic body  27  face the sealed space  61 , when the pressure of the sealed space  61  becomes higher than atmospheric pressure as a result of an increase in the ambient temperature or heat generation in the actuator  41  itself, the second elastic body  27  is deformed upward so as to raise the neutral position of the movable member  28 , and as a result an air gap g beneath the movable core  54  increases and the attractive force of the actuator  41  decreases. In contrast, when the ambient temperature decreases and the pressure of the sealed space  61  becomes lower than atmospheric pressure, the second elastic body  27  is deformed downward so as to lower the neutral position of the movable member  28 , and as a result the air gap g beneath the movable core  54  decreases and the attractive force of the actuator  41  increases.  
         [0049]     In this way, if the neutral positions of the second elastic body  27  and the movable member  28  change due to a variation in the pressure of the sealed space  61 , there is a problem that the precision is degraded in controlling the amplitude of the movable member  28  by the actuator  41 .  
         [0050]     However, in this embodiment, when the pressure of the sealed space  61  is going to increase, the bag  64 , which communicates with the atmosphere via the through hole  13   c , contracts so as to suppress an increase in the pressure of the sealed space  61 ; whereas when the pressure of the sealed space  61  is going to decrease, the bag  64 , which communicates with the atmosphere, expands so as to suppress a decrease in the pressure of the sealed space  61 . That is, the pressure of the sealed space  61  is always maintained at substantially atmospheric pressure. As a result, it is possible to prevent degradation in the precision in controlling the amplitude of the movable member  28  due to variation in the pressure of the sealed space  61 , and to enhance the vibration isolating effect of the active vibration isolation support system M.  
         [0051]      FIG. 5  and  FIG. 6  show a second embodiment of the present invention wherein  FIG. 5  is a diagram corresponding to  FIG. 2 , and  FIG. 6  is a diagram for explaining a method of fixing the bag of  FIG. 5  within the sealed space.  
         [0052]     Although the bag  64  of the first embodiment communicates with the atmosphere via the through hole  13   c , a bag  65  of the second embodiment communicates with a first liquid chamber  30 . That is, the bag  65 , which is integrally joined by vulcanization bonding to a ring  66 , is press-fitted from below into the inner periphery of a second elastic body support ring  15 , and fixed by being interposed between a yoke  44  which is assembled from below and the second elastic body support ring  15 . The internal space of the bag  65  and the first liquid chamber  30  communicate with each other via a through hole  67  running through the bag  65 , the second elastic body support ring  15 , and a partition member  29 .  
         [0053]     The interior of the through hole  67  and the bag  65  are filled with a liquid of the first liquid chamber  30 . Since the first liquid chamber  30  communicates with a third liquid chamber  35  which is defined by an easily deformable diaphragm  22 , the first liquid chamber  30  is maintained at substantially atmospheric pressure, and therefore the interior of the bag  65  is maintained at substantially atmospheric pressure. With this arrangement, even if the movable member  28  and the second elastic body  27  move up and down accompanying operation of the actuator  41  and thus the capacity of a sealed space  61  changes, it is possible to absorb the change in the capacity by expansion and contraction of the bag  65  having an elasticity, and to maintain the pressure of the sealed space  61  at substantially atmospheric pressure. As a result, it is possible to prevent degradation in the precision in controlling the amplitude of the movable member  28  due to variation in the pressure of the sealed space  61 , and to enhance the vibration isolating effect of the active vibration isolation support system M.  
         [0054]     Although the embodiments of the present invention have been described above, various modifications in design can be made thereto without deviating from the subject matter of the present invention.  
         [0055]     For example, in the embodiments, the pressure cushioning member comprises the bag  64  or  65  which is filled with air at atmospheric pressure or a liquid at atmospheric pressure, but the pressure cushioning member may comprise fine through holes which provide communication between the sealed space  61  and the atmosphere without allowing dust or water to pass therethrough.