Patent Publication Number: US-6668772-B2

Title: Linear actuator apparatus and actuating control method

Description:
BACKGROUND OF THE INVENTION 
     1) Field of the Invention 
     The present invention relates to improving the speed of linear reciprocating movement of a load, the energy efficiency, and durability of a liner actuator apparatus. The load is, for example, an inlet valve, an exhaust valve, or a fuel injection valve of an automobile gasoline engine. 
     2) Description of the Related Art 
     A prior art linear actuator apparatus is disclosed in, for example, Japanese Patent Application Laid-Open No. 2000-199411. This linear actuator apparatus is used as an actuating apparatus that linearly reciprocates to open or close the inlet valve or the exhaust valve of the automobile gasoline engine. 
     The configuration of this prior art linear actuator apparatus will be explained in detail below. The linear actuator has an actuating unit. The actuating unit includes a magnetic path member comprising a magnetic flux generator equipped with an electromagnetic coil by winding to generate a magnetic flux; and a magnetic field forming section that has at least two pole shoes to form at least one magnetic field region by distributing the magnetic flux. The linear actuator further has a magnetizing member fitted to a mover and having two magnetized surfaces having a different magnetic polarity from each other; an electric current supply unit that supplies a driving current having a magnetism corresponding to either the outward direction or the inward direction of the first mover, to the electromagnetic coil; and a valve stem and a valve element integral with the mover. 
     The linear actuator apparatus operates as explained below. When the current is not supplied to the electromagnetic coil, the valve element is located at a predetermined position (reference position). When a direct current flowing in a predetermined direction is supplied to the electromagnetic coil, the valve element moves in the predetermined direction and is located at an open position, corresponding to the size of the magnetic flux density. Further, when a direct current flowing in a direction opposite to the predetermined direction is supplied to the electromagnetic coil, the valve element moves in a direction opposite to the predetermined direction and is located at a closed position, corresponding to the size of the magnetic flux density. 
     SUMMARY OF THE INVENTION 
     The present invention relates to an improvement in the linear actuator apparatus. 
     The linear actuator apparatus, which linearly reciprocate a load, according to one aspect of the present invention has a first linear actuator including a first mover capable of linearly reciprocating in a first direction and a second direction, the first mover being connected to the load; a second linear actuator including a second mover capable of linearly reciprocating in the first direction and the second direction, the second mover being equipped with an accumulator; and a connecting unit that connects the first mover and the second mover so as to be able to move relative to each other linearly in the first direction and the second direction. The shift of the first mover is larger than that of the second mover. Moreover, the accumulator has a structure such that the accumulator accumulates energy by the shift of the second mover in one of the first direction and the second direction, and shifts the second mover in other one of the first direction and the second direction by discharging the accumulated energy, and the first mover and the second mover have an abutting surface, respectively, which abuts against each other when the accumulator accumulates or discharges energy, to thereby transmit energy to each other via the accumulator. 
     The linear actuator apparatus, which linearly reciprocate a load, according to an another aspect of the present invention has a first linear actuator including a first mover capable of linearly reciprocating in a first direction and a second direction, the first mover being connected to the load; a second linear actuator including a second mover capable of linearly reciprocating in the first direction and the second direction, the second mover being equipped with an accumulator; and a connecting unit that connects the first mover and the second mover so as to be able to move relative to each other linearly in the first direction and the second direction. The shift of the first mover is larger than that of the second mover. Moreover, the accumulator includes a first accumulator having a structure such that it accumulates energy by the shift of the second mover in the first direction due to the operation of the second linear actuator, and shifts the second mover in the second direction by discharging the energy accumulated by the operation of the second linear actuator; and a second accumulator having a structure such that it accumulates energy by the shift of the second mover in the second direction due to the operation of the second linear actuator, and shifts the second mover in the first direction by discharging the energy accumulated by the operation of the second linear actuator. In addition, the first mover and the second mover respectively include a first abutting surface that abuts against each other when the second mover shifts in the second direction due to the discharge of energy by the first accumulator, to transmit the energy discharged from the first accumulator to the load; and a second abutting surface that abuts against each other when the second mover shifts in the first direction due to the discharge of energy by the second accumulator, to transmit the energy discharged from the second accumulator to the load. 
     The actuating control method according to still another aspect of the present invention is realized on the linear actuator apparatuses according to the above-mentioned aspects of the present invention and comprises, at the time of startup, actuating the second linear actuator to shift the second mover in one of the first direction and the second direction and actuating the first linear actuator to shift the first mover in the same direction in which the second linear actuator is actuated. 
     The actuating control method according to still another aspect of the present invention is realized on the linear actuator apparatuses according to the above-mentioned aspects of the present invention and comprises damping the shift of the first mover by the action of the accumulator for accumulating the energy and by controlling the actuation of the second linear actuator. 
     These and other objects, features and advantages of the present invention are specifically set forth in or will become apparent from the following detailed descriptions of the invention when read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross section of relevant parts of a linear actuator apparatus according to an embodiment of the present invention. 
     FIG. 2 is a cross section, in a different direction as compared to that of FIG. 1, of relevant parts of the linear actuator apparatus according to the present invention. 
     FIG. 3 is a cross section, in a different direction as compared to that of FIG. 1, of relevant parts of the linear actuator apparatus according to the present invention. 
     FIG. 4 is a cross section taken along line IV—IV in FIG.  3 . 
     FIG. 5 is a cross section that shows the initial state in FIG.  3 . 
     FIG. 6 is a cross section that shows the closed holding state in FIG.  3 . 
     FIG. 7 is a cross section that shows the open operation state in FIG.  3 . 
     FIG. 8 is a cross section that shows the open holding state in FIG.  3 . 
     FIG. 9 is a cross section that shows the closed operation state in FIG.  3 . 
     FIG. 10 is an explanatory diagram that shows the working waveform of a timing signal, charging of a first coil, charging of a second coil, target current of an electromagnetic coil, stroke of a second mover, and stroke of a first mover. 
    
    
     DETAILED DESCRIPTIONS 
     Exemplary embodiment(s) of the linear actuator apparatus and the actuating control method, according to the present invention, is explained, with reference to the accompanying drawings. The linear actuator apparatus according to this embodiment is used, for example, as an actuating apparatus that linearly reciprocates, that is, opens or closes an inlet valve of an automobile gasoline engine. However, the present invention is not limited to the embodiment. FIGS. 1 to  10  shows the linear actuator apparatus according to the embodiment(s) of the present invention. 
     Explanation of Overall Structure 
     In FIG. 1, reference sign  1  denotes a cylinder head in an automobile gasoline engine. A combustion chamber  2 , an inlet path  3 , and an exhaust path  4  are respectively provided in the cylinder head  1 . An inlet port  5  is provided between the combustion chamber  2  and the inlet path  3 , and an exhaust port  6  is provided between the combustion chamber  2  and the exhaust path  4 . 
     An inlet valve  7  and an exhaust valve  8  are respectively equipped in the cylinder head  1 , so that opening and closing movement is possible. Further, the linear actuator apparatus  9  according to the embodiment and a cam mechanism  10  are also equipped in the cylinder head  1 , respectively. 
     The inlet valve  7  is connected to the linear actuator apparatus  9 . The inlet valve  7  shifts to open or close the inlet port  5 , by the actuating control of the linear actuator apparatus  9 . In other words, the inlet valve  7  is a direct-acting valve, whose  1  opening and closing movement is directly controlled by the linear actuator apparatus  9 . 
     On the other hand, the exhaust valve  8  is connected to the cam mechanism  10 . The exhaust valve  8  opens and closes the exhaust port  6  by the opening and closing movement due to the rotation of a cam in the cam mechanism  10 . The cam mechanism  10  is constructed such that the cam rotates synchronously with the rotation of a crank-shaft (not shown) in the automobile gasoline engine. 
     The linear actuator apparatus  9  comprises a first linear actuator  11 , a second linear actuator  12 , and a connecting unit  13 . The first linear actuator  11  and the second linear actuator  12  are respectively a linear actuator of an electromagnet type. 
     Explanation of the First Linear Actuator  11   
     As the first linear actuator  11 , for example, one described in Japanese Patent Application Laid-Open No. 2000-199411 is used. As shown in FIG.  2  and FIG. 3, the first linear actuator  11  has a holder  14 . The holder  14  holds the first mover  15  so as to be able to linearly reciprocate, that is, so as to enable opening and closing movement. In the figure, “arrow open” indicates the opening direction, that is, the outward direction, and “arrow close” indicates the closing direction, that is, the inward direction. 
     Two fixed holes (through holes) are provided in the first mover  15 , with a space therebetween in the opening and closing direction. Two magnets  16  and  17  are respectively fixed to the two fixed holes. The both sides of the two magnets  16  and  17  are substantially on the same plane with the both sides of the first mover  15 . The both sides of the two magnets  16  and  17  are respectively formed by magnetization on two magnetized surfaces having a different polarity from each other. In other words, as shown in FIG. 3, the left magnetized surface of the first magnet  16  is magnetized in the N pole, the right magnetized surface of the first magnet  16  is magnetized in the S pole, the left magnetized surface of the second magnet  17  is magnetized in the S pole, and the right magnetized surface of the second magnet  17  is magnetized in the N pole. 
     A first yoke  18  in a C-shape, a core  19 , and a second yoke  20  in a plate form are respectively fixed on the holder  14 . The two magnets  16  and  17  in the first mover  15  are arranged so as to enable opening and closing movement, between the first yoke  18 , the core  19 , and the second yoke  20 , respectively. 
     Three pole shoes  21 ,  22 , and  23  are respectively arranged on the both sides of the first yoke  18  and the core  19 , in the opening and closing direction of the first mover  15 . A current supply unit (not shown) is electrically connected to the electromagnetic coil  24 . 
     The core  19  forms a magnetic flux generator equipped with the electromagnetic coil  24  by winding to generate a magnetic flux. The vicinity of the pole shoes  21  and  23 , and the vicinity of the pole shoes  22  and  23  form two magnetic field regions. The first yoke  18  has at least two pole shoes (in this example, three pole shoes  21 ,  22 ,  23 ), to distribute the magnetic flux, and constitutes a magnetic field forming section, which forms at least one (in this example, two) magnetic field region. The second yoke  20  constitutes a magnetic path member. The two magnets  16  and  17  constitute a magnetizing member provided corresponding to the two magnetic field regions. 
     Two inlet valves  7  as the load are connected to one end of the first mover  15 . The inlet valve  7  comprises a valve shaft  25 , and a valve element  26  formed integrally at one end of the valve shaft  25 . The other end of the valve shaft  25  is fixed to one end of the first mover  15 . 
     When the electric current is not supplied to the electromagnetic coil  24 , as shown in FIG. 5, the valve element  26  is located at a predetermined position (reference position, in the initial state). When a direct current flowing in a predetermined direction is supplied to the electromagnetic coil  24 , the valve element  26  moves in the opening direction, corresponding to the magnitude of the magnetic flux density. Further, when a direct current flowing in a direction opposite to the predetermined direction is supplied to the electromagnetic coil  24 , the valve element  26  moves in the closing direction, corresponding to the size of the magnetic flux density. The size of the direct current to be supplied is substantially in proportion to the size of a driving force at the time of shifting the first mover  15  (and the inlet valve  7 ) so as to open or close. 
     Explanation of the Second Linear Actuator  12   
     As shown in FIG.  2  and FIG. 3, a second mover  27  is equipped in the second linear actuator  12 , so as to enable the opening and closing movement in the same direction as that of the first mover  15 . The second mover  27  comprises a rod  28 , and an armature  29  integrally formed with the rod  28  in the intermediate thereof. 
     The second linear actuator  12  comprises a first solenoid  30  and a second solenoid  31 . The first solenoid  30  comprises a first core  32  and a first coil  34  wound on the first core  32 , and the second solenoid  31  comprises a second core  33  and a second coil  35  wound on the second core  33 . The armature  29  of the second mover  27  is arranged between the first solenoid  30  and the second solenoid  31 , so as to enable the opening and closing movement. 
     The first solenoid  30  is excited by energizing the first coil  34 , to shift the second mover  27  (the first mover  15  and the inlet valve  7 ) in the closing direction, and allows the second mover  27  (the first mover  15  and the inlet valve  7 ) to be held at the shifted closing position. The first solenoid  30  is demagnetized by de-energizing the first coil  34 , to release the holding state of the second mover  27  (the first mover  15  and the inlet valve  7 ) at the closing position. 
     On the other hand, the second solenoid  31  is excited by energizing the second coil  35 , to shift the second mover  27  (the first mover  15  and the inlet valve  7 ) in the opening direction, and allows the second mover  27  (the first mover  15  and the inlet valve  7 ) to be held at the shifted opening position. The second solenoid  31  is demagnetized by de-energizing the second coil  35 , to release the holding state of the second mover  27  (the first mover  15  and the inlet valve  7 ) at the opening position. 
     An accumulator  36  is equipped on the second mover  27 . The accumulator  36  has a casing  37  having a hollow cylindrical shape with one end (lower end) being open, and the other end (upper end) being closed. The lower end of the casing  37  is fixed on the second core  33 . A middle casing  38  in a hollow cylindrical shape is fixed in the casing  37 , with the opposite ends being open. A partition board  39  is integrally formed in the intermediate of the middle casing  38 . 
     As shown in FIG. 4, the partition board  39  is provided with a cruciate hole  40 . On the other hand, a cruciate push plate  41  is fixed at one end of the rod  28  of the second mover  27 . The push plate  41  can pass through the hole  40 . 
     A first spring  42  as a first accumulator is arranged between the upper end of the casing  37  and the partition board  39 . A second spring  43  as a second accumulator is arranged between the second core  33  and the partition board  39 . 
     The first spring  42  is for accumulating energy by compression due to the shift of the second mover  27  (the first mover  15  and the inlet valve  7 ) in the closing direction, and for shifting the second mover  27  (the first mover  15  and the inlet valve  7 ) in the opening direction by discharging the energy by expansion. The second spring  43  is for accumulating energy by compression due to the shift of the second mover  27  (the first mover  15  and the inlet valve  7 ) in the opening direction, and for shifting the second mover  27  (the first mover  15  and the inlet valve  7 ) in the closing direction by discharging the energy by expansion. 
     The cross section of the wire of the first spring  42  and the second spring  43  is elliptic, as shown in FIGS. 1 to  3 . The cross section of the wire of the springs  42  and  43  may be circular, as shown in FIGS. 5 to  9 . 
     Explanation of the Connecting Unit  13   
     The other end of the first mover  15  and the other end of the first mover  27  are connected to each other via the connecting unit  13 , so as to be able to move relative to each other in the opening and closing direction. In other words, as shown in FIG. 2, an engagement hole  45  having a large inner size and a through groove  46  having a small inner size are respectively provided at the other end of the first mover  15 . An engagement protrusion  47  having a large external size and a penetrating portion  48  having a small external size are respectively provided at the other end of the rod  28  of the second mover  27 . The engagement protrusion  47  is engaged in the engagement hole  45  so as to be able to move in the opening and closing direction. Similarly, the penetrating portion  48  penetrates through the through groove  46  so as to be able to move in the opening and closing direction. 
     As shown in FIGS. 5 to  9 , the first mover  15  can shift for opening and closing with respect to the holder  14 , between the position where first stoppers  49  and  50  abut against each other (see FIG. 6) and the position where second stoppers  51  and  52  abut against each other (see FIG.  8 ). The second mover  27  can shift for opening and closing with respect to the second linear actuator  12 , between the position where the armature  29  abuts against the first solenoid  30  (see FIG. 6) and the position where the armature  29  abuts against the second solenoid  31  (see FIG.  8 ). 
     The shift of the first mover  15  is a distance T 1  between the second stoppers  51  and  52  (see FIG. 6) in the state that the first stoppers  49  and  50  abut against each other, or a distance T 1  (see FIG. 8) between the first stoppers  49  and  50  (see FIG. 6) in the state that the second stoppers  51  and  52  abut against each other. The shift of the second mover  27  is a distance T 2  between the armature  29  and the second solenoid  31  (see FIG. 6) in the state that the armature  29  abuts against the first solenoid  30 , or a distance T 2  (see FIG. 8) between the armature  29  and the first solenoid  30  (see FIG. 6) in the state that the armature  29  abuts against the second solenoid  31 . 
     The shift T 1  of the first mover  15  is larger than the shift T 2  of the second mover  27 . In this example, the shift T 1  of the first mover  15  is 6 mm, and the shift T 2  of the second mover  27  is 4 mm. As a result, the other end of the first mover  15  and the other end of the second mover  27  can move relative to each other in the opening and closing direction in the connecting unit  13 , by a difference of the shifts T 1 −T 2 =2 mm. 
     The other end of the first mover  15  and the other end of the second mover  27  have, respectively, a first abutting surface  53  and a second abutting surface  54 . As shown, in FIG. 7, the first abutting surface  53  comprises one inner face (lower face) of the engagement hole  45 , and one side (lower face) of the engagement protrusion  47 . The second abutting surface  54  comprises, as shown in FIG. 9, the other inner face (upper face) of the engagement hole  45 , and the other side (upper face) of the engagement protrusion  47 . 
     The first abutting surface  53 , that is, the lower face of the engagement hole  45  and the lower face of the engagement protrusion  47  abut against each other, when the second mover  27  shifts in the opening direction due to discharge of the energy by the first spring  42 , to transmit the energy discharged by the first spring  42  to the inlet valve  7 . The second abutting surface  54 , that is, the upper face of the engagement hole  45  and the upper face of the engagement protrusion  47  abut against each other, when the second mover  27  shifts in the closing direction due to discharge of the energy by the second spring  43 , to transmit the energy discharged by the second spring  43  to the inlet valve  7 . 
     The linear actuator apparatus  9  according to the embodiment has such a configuration, and the operation thereof is explained with reference to FIGS. 5 to  10 . 
     Explanation of the Initial State 
     The initial state is, as shown in FIG.  5  and FIG. 10, a state in which the electric current is not supplied to the first coil  34  and the second coil  35 , that is, in FIG. 10, (B) a state in which charging of electricity to the first coil  34  is OFF, and (C) charging of electricity to the second coil  35  is OFF. As a result, the first solenoid  30  and the second solenoid  31  are not magnetized, that is, in the state of being de-magnetized. 
     On the other hand, the upper and lower surfaces of the push plate  41  of the second mover  27  are respectively pressed by the first spring  42  and the second spring  43 , which have a uniform spring force. As a result, the armature  29  of the second mover  27  is located in the intermediate position between the first solenoid  30  and the second solenoid  31 . In other words, the armature  29  of the second mover  27  is located at a position where the stroke of the second mover  27  is 0, in FIG. 10 (see (E)). 
     Further, the initial state is a state in which an electric current is not supplied to the electromagnetic coil  24 , that is, a state in which the target current of the electromagnetic coil  24  is 0 in FIG. 10 (see (D)). As a result, the first mover  15  is located at a predetermined position, that is, at a position of +2 mm of the stroke of the first mover  15  in FIG. 10 (see (F)). The valve element  26  of the inlet valve  7  integral with the first mover  15  is in a state of half open. 
     Further, the lower face of the engagement hole  45  of the first abutting surface  53  abuts against the lower face of the engagement protrusion  47 . 
     Explanation of Startup, Closing Operation, and Holding Closed State 
     At the time of startup, when the timing signal in FIG. 10 (see (A)) is turned ON, the first coil  34  in the first solenoid  30  is energized. In other words, charging of electricity to the first coil  34  is turned ON. Further, the electromagnetic coil  24  is energized to the closed side. In other words, the target current of the electromagnetic coil  24  becomes negative. 
     As a result, as shown in FIG. 6, the first mover  15  shifts in the closing direction and stops, because the first stoppers  49  and  50  abut against each other. The second mover  27  also shifts in the closing direction and stops, because the first solenoid  30  absorbs the armature  29 . Further, the second mover  27  shifts in the closing direction so that the upper face of the push plate  41  presses the first spring  42 , and the first spring  42  is compressed to accumulate energy. 
     In other words, the stroke of the second mover  27  shifts from 0 to −2 (closing operation in FIG.  10 ). Further, the stroke of the first mover  15  shifts from +2 to 0 (closing operation in FIG.  10 ). As shown in FIG. 6, the valve element  26  closes the inlet port  5 . 
     When the closed state is obtained through the startup and the closing operation, the amount of electric current to be supplied to the electromagnetic coil  24  is reduced. In other words, the target current of the electromagnetic coil  24  is brought close from a negative value to 0. As a result, the first mover  15  is retained, and the state in which the valve element  26  closes the inlet port  5  is retained (holding closed state in FIG.  10 ). In this closed state, the amount of electric current to be supplied to the electromagnetic coil  34  may be reduced than that at the time of startup (starting current), so as to hold the second mover  27  by this small current (holding current). 
     In the closed state, the inlet valve  7  can be lifted via the first mover  15 , by the distance 2 mm of the relative movement in the connecting unit  13 . As a result, the idling control method (Japanese Patent Application No. 2001-036795) can be executed. 
     Explanation of Opening Operation, Opening of Brake, and Holding Open State 
     When the timing signal is changed from ON to OFF, the opening operation shown in FIG. 10 starts. In other words, charging of electricity to the first coil  34  is changed from ON to OFF. The compressed first spring  42  then expands, to discharge the accumulated energy. The energy is transmitted to the first mover  15  through the second mover  27  and the first abutting surface  53 . As a result, the first mover  15  is energized in the opening direction. 
     At the same time, the target current of the electromagnetic coil  24  is changed from a negative value close to 0 to a positive value. The second mover  27  and the first mover  15  then initially shift integrally in the opening direction (the opening operation in FIG.  10 ). In other words, the stroke of the second mover  27  changes from −2 to 0, and the stroke of the first mover  15  changes from 0 to +2. 
     As shown in FIG. 7, when the lower face of the push plate  41  abuts against the second spring  43 , opening of brake in FIG. 10 starts. That is, the target current of the electromagnetic coil  24  changes from positive to negative. Further, the lower face of the push plate  41  presses the second spring  43 , to compress the second spring  43 , so as to accumulate energy. The opening of brake starts to act, to decelerate the shift of the second mover  27  in the opening direction, so that the first mover  15  precedes the second mover  27  in the opening direction. 
     As a result, the lower face of the engagement hole  45  is away from the lower face of the engagement protrusion  47 , on the first abutting surface  53 . In other words, the stroke of the second mover  27  changes from 0 to +2, and the stroke of the first mover  15  changes from +2 to +6. In opening the brake, the target current of the electromagnetic coil  24  is changed from positive to negative. 
     The upper face of the engagement protrusion  47  of the decelerated second mover  27  then abuts against the upper face of the engagement hole  45  in the preceding first mover  15 . In other words, as shown in FIG. 8, the second abutting surface  54  abuts to fully open the inlet valve  7 . The first mover  15  stops due to abutting of the second stoppers  51  and  52  on each other. At this time, the second coil  35  is changed from OFF to ON. The amount of electric current to be supplied to the electromagnetic coil  24  is reduced. In other words, the target current of the electromagnetic coil  24  is changed from a negative value to a positive value close to 0. 
     As a result, the second solenoid  31  absorbs the lower face of the armature  29 , and the fully opened state of the inlet valve  7  is held (holding open state in FIG.  10 ). The shift speed of the first mover  15  (inlet valve  7 ) in the opening direction at the time of fully opening the inlet valve  7  can be adjusted, by adjusting the current to the second coil  35 . 
     Explanation of Closing Operation, Closing of Brake, and Holding Closed State 
     When the timing signal is changed from OFF to ON, the closing operation shown in FIG. 10 starts. In other words, charging of electricity to the second coil  35  is changed from ON to OFF. The compressed second spring  43  then expands, to discharge the accumulated energy. The energy is transmitted to the first mover  15  through the second mover  27  and the second abutting surface  54 . As a result, the first mover  15  is energized in the closing direction. 
     At the same time, the target current of the electromagnetic coil  24  is changed from a positive value close to 0 to a negative value. The second mover  27  and the first mover  15  then initially shift integrally in the closing direction (the closing operation in FIG.  10 ). In other words, the stroke of the second mover  27  changes from +2 to 0, and the stroke of the first mover  15  changes from +6 to +4. 
     As shown in FIG. 9, when the upper face of the push plate  41  abuts against the first spring  42 , closing of brake in FIG. 10 starts. That is, the target current of the electromagnetic coil  24  changes from negative to positive. Further, the upper face of the push plate  41  presses the first spring  42 , to compress the first spring  42 , so as to accumulate energy. The closing of brake starts to act, to decelerate the shift of the second mover  27  in the closing direction, so that the first mover  15  precedes the second mover  27  in the closing direction. 
     As a result, the upper face of the engagement hole  45  is away from the upper face of the engagement protrusion  47  on the second abutting surface  54 . In other words, the stroke of the second mover  27  changes from 0 to −2, and the stroke of the first mover  15  changes from +4 to 0. In closing the brake, the target current of the electromagnetic coil  24  is changed from negative to positive. 
     The lower face of the engagement protrusion  47  of the decelerated second mover  27  then abuts against the lower face of the engagement hole  45  in the preceding first mover  15 . In other words, as shown in FIG. 6, the first abutting surface  53  abuts to fully close the inlet valve  7 . The first mover  15  stops due to abutting of the first stoppers  49  and  50  on each other. At this time, the first coil  34  is changed from OFF to ON. The amount of electric current to be supplied to the electromagnetic coil  24  is reduced. In other words, the target current of the electromagnetic coil  24  is changed from a negative value to a positive value close to 0. 
     As a result, the first solenoid  30  absorbs the upper face of the armature  29 , and the fully closed state of the inlet valve  7  is held (holding open state in FIG.  10 ). The shift speed of the first mover  15  (inlet valve  7 ) in the closing direction at the time of fully closing the inlet valve  7  can be adjusted, by adjusting the current to the first coil  34 . 
     Thereafter, the opening operation, opening of brake, holding open state, the closing operation, closing of brake, and holding closed state are repeated, to thereby open and close the inlet valve  7  based on the predetermined time. In the action, charging of the electricity to the first coil  34  is turned ON at the time of starting holding closed state, but as shown in the chain line in FIG. 10, it may be at the time of starting the closing operation. Further, charging of the electricity to the second coil  35  is turned ON at the time of starting holding open state, but as shown in the chain line in FIG. 10, it may be at the time of starting the opening operation. 
     Explanation of an Example Other Than the Embodiment 
     The embodiment explains a configuration that works at the time of shifting in the opposite directions, that is, at the time of shifting of the inlet valve  7  in the opening direction (outward direction) and at the time of shifting thereof in the closing direction (inward direction). However, it is not limited to this configuration. The configuration may be such that the linear actuator apparatus may work at the time of shifting only in one direction, that is, at the time of shifting the load in the opening direction (outward direction) or at the time of shifting thereof in the closing direction (inward direction). In this case, as the spring, either the first spring  42  or the second spring  43  is necessary. For example, when there is the upper first spring  42 , only a simple stopper instead of the lower second spring  43  can accelerate the shift of the inlet valve  7  in the opening direction, and can reduce the impact at the time of sitting of the inlet valve  7 . 
     It is mentioned above that the second linear actuator  12  comprises the first solenoid  30  and the second solenoid  31 , but it is not limited to this. The second linear actuator  12  may comprise a linear actuator other than the first solenoid  30  and the second solenoid  31 . 
     It is mentioned above that the first spring  42  and the second spring  43  function as the first accumulator and the second accumulator. However, the accumulators may be realized with components other than the springs. Further, it is mentioned above that the first spring  42  and the second spring  43  are compression springs, but the springs could be a tension spring. 
     It is mentioned above that the linear actuator apparatus described in Japanese Patent Application Laid-Open No. 2000-199411 is used as the first linear actuator  11 . However, a linear actuator apparatus other than the one described in Japanese Patent Application Laid-Open No. 2000-199411 may be used. 
     In the embodiment, the inlet valve  7  is used as the load, but in the present invention, the load may be one other than the inlet valve  7 , for example, an exhaust valve or a fuel injection valve of the engine, or the like. 
     As is obvious from the description, according to the present invention, the accumulator efficiently accumulates or discharges the kinetic energy of the first mover and the second mover, thereby enabling a shift of the load at a high speed. After the load has started the shift, it is not necessary to supply the electric current to the second linear actuator at all times, and hence an increase of the driving energy can be suppressed. Since the accumulator can use the accumulated energy for the buffer action, the durability of the linear actuator and the load can be improved. Further, since the first mover and the second mover are connected so as to enable a relative movement thereof, and the shift of the first mover is made larger than that of the second mover, the kinetic energy can be superposed when the first mover and the second mover start to shift. Therefore, such a shift of the mover is made possible that a single linear actuator cannot handle with regard to the speed of response. As a result, the linear reciprocating movement of the load can be accelerated, and there is the effect that a linear actuator apparatus and an actuating control method, which improve the energy efficiency and the durability, can be obtained. 
     Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.