Abstract:
A method for controlling the drive of an actuator of an active vibration isolation support system is provided in which one cycle of the actuator moving a movable member out and back is divided into a plurality of micro time regions, a voltage applied to the actuator is duty-controlled in each micro time region, and the duty ratio in at least the last micro time region is set to 0%. As a result, the current passing through the actuator can be made 0 in the final stage of the out and back movement cycle before the movable member moves back to the original position. This can minimize the current passing when the movable member moves back to its original position at the end of the cycle, thus suppressing the needless generation of heat in a coil of the actuator. Therefore, it is possible to prevent an increase in the electrical resistance of the coil which would otherwise hinder the achievement of a required value of current, and to prevent thermal damage to equipment surrounding the coil.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a method for controlling the drive of an actuator of an active vibration isolation support system that includes an elastic body receiving a load from a vibrating body, a liquid chamber having a wall of which at least a part is formed from the elastic body, a movable member that moves out and back to change the capacity of the liquid chamber in a cycle, and an actuator that receives supply of current to generate an electromagnetic force for moving the movable member out. 
   2. Description of the Relevant Art 
   In order to move the movable member of this type of active vibration isolation support system out and back in response to a vibration frequency of an engine, a voltage is cyclically applied to the actuator. As shown in  FIG. 6 , the movable member moves out due to an electromagnetic force generated by a coil upon applying a rectangular voltage pulse to the actuator in the first half of one cycle of the out and back movement of the movable member, and the movable member moves back due to the elastic force of a return spring by stopping the application of the voltage to the actuator in the second half of the cycle. Therefore, it is possible to reduce the vibration of the engine by alternately switching on and off the voltage applied to the actuator to make the movable member move out and back. 
   As shown in  FIG. 6 , even if a rectangular voltage pulse is cyclically applied to the actuator of the active vibration isolation support system, since the current passing through the actuator changes in a sawtooth waveform with a time lag, the current might not become zero within a period when the voltage to the actuator is switched off. This might cause the generation of heat in the coil of the actuator, thus raising its temperature to increase its electrical resistance, so that a required value of current might not be obtained, and equipment surrounding the coil might be thermally damaged. 
   SUMMARY OF THE INVENTION 
   The present invention has been achieved in view of the above-mentioned circumstances, and it is an object of the present invention to minimize the generation of heat in an actuator of an active vibration isolation support system. 
   In order to achieve this object, in accordance with a first aspect of the present invention, there is provided a method for controlling the drive of an actuator of an active vibration isolation support system that includes an elastic body receiving a load from a vibrating body, a liquid chamber having a wall of which at least a part is formed from the elastic body, a movable member that moves out and back to change the capacity of the liquid chamber in a cycle, and an actuator that receives a supply of current to generate an electromagnetic force for moving the movable member out, the method including the step of controlling the current supplied to the actuator such that the current passing through the actuator becomes zero at least when the movable member has moved back. 
   In accordance with this arrangement, the current passing through the actuator is controlled to become zero when the reciprocally movable member moves back to its original position after being moved out by the electromagnetic force generated by a current supplied to the actuator. Therefore, the current can be minimized when the actuator is stopped and the movable member moves back, thereby suppressing needless generation of heat in the actuator. 
   Furthermore, in accordance with a second aspect of the present invention, in addition to the first aspect, there is provided a method for controlling the drive of an actuator of an active vibration isolation support system wherein it further includes the steps of: setting a large number of consecutive micro time regions in the cycle; and carrying out duty control of the voltage that is applied to the actuator in each of the micro time regions. 
   In accordance with this arrangement, since the voltage applied to the actuator is duty-controlled in each of the large number of consecutive micro time regions set in a cycle of out and back movement of the movable member, the current passing through the actuator when the movable member has moved back can reliably be made zero. 
   An engine E of an embodiment corresponds to the vibrating body of the present invention, a first elastic body  14  of the embodiment corresponds to the elastic body of the present invention, and a first liquid chamber  24  of the embodiment corresponds to the liquid chamber of the present invention. 
   The above-mentioned object, other objects, characteristics, and advantages of the present invention will become apparent from an explanation of a preferred embodiment that will be described in detail below by reference to the attached drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  to  FIG. 5  illustrate one embodiment of the present invention. 
       FIG. 1  is a longitudinal cross sectional view of an active vibration isolation support system. 
       FIG. 2  is a cross sectional view along line  2 — 2  in  FIG. 1 . 
       FIG. 3  is a cross sectional view along line  3 — 3  in  FIG. 1 . 
       FIG. 4  is an enlarged view of an essential part of  FIG. 1 . 
       FIG. 5  is a diagram showing a method for controlling an actuator. 
       FIG. 6  is a diagram showing a conventional method for controlling an actuator. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   An active vibration isolation support system M shown in  FIGS. 1 to 4  is provided for elastically supporting an engine E on a vehicle body frame F of an automobile. The system is controlled by an electronic control unit U to which are connected an engine rotational speed sensor Sa for detecting the engine rotational speed, a load sensor Sb for detecting the load that is input to the active vibration isolation support system M, an acceleration sensor Sc for detecting the acceleration acting on the engine E, and a lift sensor Sd for detecting the amount of lift of a movable member  20  of an actuator  29 , which will be described below. 
   The active vibration isolation support system M has a structure that is substantially symmetrical with respect to an axis L. The system includes an inner tube  12  that is welded to a plate-shaped mounting bracket  11  joined to the engine E, and an outer tube  13  that is disposed coaxially around the inner tube  12 . The inner tube  12  and the outer tube  13  are bonded by vulcanization bonding to the upper end and lower end respectively of a first elastic body  14  made of a thick rubber. A disc-shaped first orifice-forming member  15  having an aperture  15   b  in its center, an annular second orifice-forming member  16  having a U-shaped cross section open at the top, and a third orifice-forming member  17  similarly having a U-shaped cross section open at the top, are welded into a single unit. The outer peripheries of the first orifice-forming member  15  and the second orifice-forming member  16  are superimposed and fixed in a crimping part  13   a  provided in a lower part of the outer tube  13 . 
   The outer periphery of a second elastic body  18  made of a rubber membrane is fixed by vulcanization bonding to the inner periphery of the third orifice-forming member  17 . A cap  19  that is fixed by vulcanization bonding to the inner periphery of the second elastic body  18  is press-fitted and fixed onto a movable member  20  that is disposed on the axis L in a vertically movable manner. A ring  21  is fixed in the crimping part  13   a  of the outer tube  13 . The outer periphery of a diaphragm  22  is fixed to the ring  21  by vulcanization bonding. A cap  23  is fixed by vulcanization bonding to the inner periphery of the diaphragm  22 , and press-fitted and fixed onto the movable member  20 . 
   A first liquid chamber  24  within which a liquid is sealed, is defined between the first elastic body  14  and the second elastic body  18 . A second liquid chamber  25  within which a liquid is sealed, is defined between the second elastic body  18  and the diaphragm  22 . The first liquid chamber  24  and the second liquid chamber  25  communicate with each other via an upper orifice  26  and a lower orifice  27  that are formed from the first to third orifice-forming members  15 ,  16  and  17 . 
   The upper orifice  26  is an annular passage formed between the first orifice-forming member  15  and the second orifice-forming member  16 . A through hole  15   a  is formed in the first orifice-forming member  15  on one side of a partition  26   a  provided in a part of the upper orifice  26 . A through hole  16   a  is formed in the second orifice-forming member  16  on the other side of the partition  26   a . The upper orifice  26  is therefore formed along an almost complete circumference from the through hole  15   a  of the first orifice-forming member  15  to the through hole  16   a  of the second orifice-forming member  16  (see  FIG. 2 ). 
   The lower orifice  27  is an annular passage formed between the second orifice-forming member  16  and the third orifice-forming member  17 . The through hole  16   a  is formed in the second orifice-forming member  16  on one side of a partition  27   a  provided in a part of the lower orifice  27 . A through hole  17   a  is formed in the third orifice-forming member  17  on the other side of the partition  27   a . The lower orifice  27  is therefore formed along an almost complete circumference from the through hole  16   a  of the second orifice-forming member  16  to the through hole  17   a  of the third orifice-forming member  17  (see  FIG. 3 ). 
   That is, the first liquid chamber  24  and the second liquid chamber  25  communicate with each other via the upper orifice  26  and the lower orifice  27  that are connected to each other in tandem. 
   Fixed in the crimping part  13   a  of the outer tube  13  is an annular mounting bracket  28  for fixing the active vibration isolation support system M to the vehicle body frame F. Welded to the lower face of the mounting bracket  28  is an actuator housing  30  forming an outer shell of the actuator  29  for driving the movable member  20 . 
   A yoke  32  is fixed to the actuator housing  30 . An annular coil  34  wound around a bobbin  33  is housed in a space surrounded by the actuator housing  30  and the yoke  32 . A bottomed-cylinder-shaped bearing  36  is inserted from below into a tubular part  32   a  of the yoke  32 , the tubular part  32   a  being fitted in the inner periphery of the annular coil  34 , and is positioned by a retaining part  36   a  at the lower end of the bearing  36  being engaged with the lower end of the yoke  32 . A disc-shaped armature  38  that faces the upper face of the coil  34  is slidably supported on the inner periphery of the actuator housing  30 , and a step  38   a  formed on the inner periphery of the armature  38  engages with the upper end of the bearing  36 . The armature  38  is forced upward by a dish spring  42  that is disposed between the armature  38  and the upper face of the coil  34 , and is positioned by being engaged with a retaining part  30   a  provided on the actuator housing  30 . 
   A cylindrical slider  43  is slidably fitted in the inner periphery of the bearing  36 . A shaft  20   a  extending downward from the movable member  20  runs loosely through the upper base of the bearing  36  and is connected to a boss  44  that is fixed to the interior of the slider  43 . A coil spring  41  is positioned between the upper base of the bearing  36  and the slider  43 , whereby the bearing  36  is forced upward by the coil spring  41  and the slider  43  is forced downward. 
   A lift sensor Sd provided beneath the actuator  29  includes a sensor housing  45  that is fixed to the lower end of the actuator housing  30 . A sensor rod  47  is slidably supported in a guide member  46  that is fixed to the interior of the sensor housing  45 , and forced upward by means of a coil spring  48  which is disposed between the sensor rod  47  and the base of the sensor housing  45 , so as to be in contact with the boss  44  of the slider  43 . A contact point  50  that is fixed to the sensor rod  47  is in contact with a resistor  49  that is fixed to the interior of the sensor housing  45 . The electrical resistance between the lower end of the resistor  49  and the contact point  50  is input into the electronic control unit U via a connector  51 . Since the lift of the movable member  20  is equal to the travel of the contact point  50 , the lift of the movable member  20  can be detected based on the electrical resistance. 
   When the coil  34  of the actuator  29  is in a demagnetized state, the coil spring  41  applies a downward elastic force to the slider  43  slidably supported in the bearing  36 , the coil spring  48  applies an upward elastic force thereto via the sensor rod  47  and the boss  44 , so that the slider  43  comes to rest at a position where the elastic forces of the two coil springs  41  and  48  are in balance. When the coil  34  is energized in the above-mentioned state so as to draw the armature  38  downward, the step  38   a  pushes and slides the bearing  36  downward thus compressing the coil spring  41 . As a result, the elastic force of the coil spring  41  increases to lower the slider  43 , and the movable member  20  that is connected to the slider  43  via the boss  44  and the shaft  20   a  therefore descends, so that the second elastic body  18  connected to the movable member  20  deforms downward to increase the capacity of the first liquid chamber  24 . Conversely, when the coil  34  is demagnetized, the movable member  20  rises, the second elastic body  18  deforms upward, and the capacity of the first liquid chamber  24  decreases. 
   When a low frequency engine shake vibration occurs while the automobile is traveling, a load that is input from the engine E deforms the first elastic body  14  thus changing the capacity of the first liquid chamber  24 , so that the liquid travels to-and-fro between the first liquid chamber  24  and the second liquid chamber  25 , which are connected to each other via the upper orifice  26  and the lower orifice  27 . When the capacity of the first liquid chamber  24  increases and decreases, the capacity of the second liquid chamber  25  decreases and increases accordingly, and this change in the capacity of the second liquid chamber  25  is absorbed by elastic deformation of the diaphragm  22 . Since the shapes and dimensions of the upper orifice  26  and the lower orifice  27  as well as the spring constant of the first elastic body  14  are set so that a high spring constant and a high attenuation force can be obtained in a region including the above-mentioned frequency of the engine shake vibration, the vibration that is transmitted from the engine E to the vehicle body frame F can be effectively reduced. 
   In the above-mentioned frequency region of engine shake vibration, the actuator  29  is maintained in a non-operational state. 
   When vibration occurs having a frequency higher than that of the above-mentioned engine shake vibration, that is, when idling vibration or muffled sound vibration due to rotation of a crankshaft of the engine E occurs, since the liquid within the upper orifice  26  and the lower orifice  27  that provide communication between the first liquid chamber  24  and the second liquid chamber  25  becomes stationary and cannot exhibit the vibration isolation function, the actuator  29  is operated so as to exhibit the vibration isolation function. 
   The electronic control unit U controls the application of current to the coil  34  of the actuator  29  based on signals from the engine rotational speed sensor Sa, the load sensor Sb, the acceleration sensor Sc and the lift sensor Sd. More specifically, when the engine E is biased downward due to the vibration and thus the capacity of the first liquid chamber  24  decreases to increase the liquid pressure, the armature  38  is drawn in by energizing the coil  34 . As a result, the armature  38  moves downward together with the movable member  20  while compressing the coil spring  41 , thus deforming downward the second elastic body  18  that is connected along its inner periphery to the movable member  20 . The capacity of the first liquid chamber  24  thereby increases to suppress the increase in the liquid pressure, so that the active vibration isolation support system M generates an active support force to prevent transmission of the downward load from the engine E to the vehicle body frame F. 
   Conversely, when the engine E is biased upward due to the vibration and thus the capacity of the first liquid chamber  24  increases to decrease the liquid pressure, the drawing-in of the armature  38  is canceled by demagnetizing the coil  34 . As a result, the armature  38  moves upward together with the movable member  20  due to the elastic force of the coil spring  41 , thus deforming upward the second elastic body  18  that is connected along its inner periphery to the movable member  20 . The capacity of the first liquid chamber  24  thereby decreases to suppress the decrease in the liquid pressure, so that the active vibration isolation support system M generates an active support force to prevent transmission of the upward load from the engine E to the vehicle body frame F. 
   The electronic control unit U compares the actual lift of the movable member  20  that has been detected by the lift sensor Sd with a target lift thereof that has been calculated based on outputs from the engine rotational speed sensor Sa, the load sensor Sb, and the acceleration sensor Sc, and the operation of the actuator  29  is feedback-controlled so that a deviation converges to 0. 
   As shown in  FIG. 5 , when the target lift of the actuator  29  is in a sinusoidal waveform having a fixed period, a large number of consecutive micro time regions are set in the fixed period, and duty control of the voltage that is applied to the actuator  29  is carried out in each of the micro time regions. In the present embodiment, 12 micro time regions together form one cycle for the lift of the actuator  29 , and duty control of the voltage that is applied to the actuator  29  is carried out individually in each of the 12 micro time regions. 
   More specifically, the duty ratios of the 12 micro time regions are decreased gradually from 100% such that the duty ratios of the last two micro time regions are set at 0%. As a result, the lift of the actuator  29  can be obtained as a sinusoidal wave form with 12 micro time regions in one cycle. Decreasing the number of consecutive micro time regions whose duty ratios change with a defined pattern from the above number of  12 , shortens the cycle of the lift. Conversely, increasing the number of consecutive micro time regions, lengthens the cycle of the lift. Furthermore, changing the pattern of the duty ratios of a plurality of micro time regions forming one cycle in various ways, controls the waveform of the lift of the actuator  29  as desired. 
   Unlike the conventional example explained by reference to  FIG. 6 , in the present embodiment, the current becomes zero at the end of one cycle of the lift of the actuator  29  (that is, one cycle of moving out and back of the movable member  20 ), and thus generation of heat in the coil  34  of the actuator  29  can be minimized, thereby preventing the electrical resistance of the coil  34  from increasing to hinder the achievement of a required value of current, and preventing thermal damage to equipment surrounding the coil  34 . 
   In order to make the current zero in the final stage of moving back of the movable member  20  that is moved out and back by the actuator  29 , since the current cannot be made zero instantly by setting the duty ratio of the micro time region to 0%, it is necessary to gradually decrease the duty ratios of a plurality of preceding micro time regions toward 0%. That is, in order to make the current zero in the final stage of moving back of the movable member  20 , it is necessary to totally control the duty ratios of the plurality of micro time regions in conjunction with each other. 
   An embodiment of the present invention has been described in detail above, but the present invention can be modified in a variety of ways without departing from the spirit and scope of the invention. 
   The active vibration isolation support system M supporting the engine E of the automobile is illustrated as one example in the embodiment, but the active vibration isolation support system of the present invention can be applied to the support of other vibrating bodies such as a machine tool.