Patent Publication Number: US-6216653-B1

Title: Electromagnetic valve actuator for a valve of an engine

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to electromagnetic valve actuators which may be used for actuating a cylinder valve, for example, of an internal combustion engine of vehicles, by mainly using an electromagnetic force. 
     Such electromagnetic valve actuators have been disclosed in U.S. Pat. Nos. 5,799,630 and 4,779,582. The former of the conventional techniques includes a disk-like armature fixed to an intake valve of an engine, and valve-closing and valve-opening electromagnets that attract the armature for moving the intake valve to the closed and full open positions. There are provided a valve-closing spring for biasing the armature in such a direction as to move the intake valve toward the closed position and a valve-opening spring for biasing the armature in such a direction as to move the intake valve toward the full open position. Each electromagnet is connected to an electronic control unit that controls an energizing current for the electromagnet depending on operating conditions of the engine. The intake valve is operated to move to the closed and full open positions and held therein by association of the spring forces of the springs and the attractive forces of the electromagnets alternately energized. The latter of the conventional techniques includes a housing made of a magnetic material, an armature connected with an intake valve of an engine and moveably disposed within the housing, and a pair of compressed springs biasing the armature for retaining the valve in a neutral position between closed and full open positions of the valve. The armature has an H-shape and includes a sleeve portion extending along the center axis of the armature. A pair of electromagnets are disposed in such a manner that the armature is interposed therebetween. An annular permanent magnet is provided for holding the armature in the respective closed and full open position. The electromagnets include upper and lower cores having lower and upper faces opposed to the sleeve portion of the armature. The electromagnets include upper and lower coils that are wound around the cores and disposed on upper and lower faces of the permanent magnet, respectively. When the valve is placed in the respective closed and full open position, each coil is activated with a current therethrough to cancel the magnetic field of the permanent magnetic pole and allow the spring to move the valve member toward the other position. Thus, the motion of the valve is shifted by alternate energization of the coils. 
     However, in the actuator described in the former, upon the valve being moved between the closed and full open positions, the electromagnets are alternately activated with a current to attract the armature against the spring force of the springs. The valve is held in the closed or full open position by continuous energization of the electromagnet. This causes an increased consumption of electrical energy, resulting in undesirable increase in engine load and fuel consumption. In the actuator of the latter, the coils of the electromagnets are not connected in series and independently cooperate with the corresponding core to generate an opposing magnetic field relative to the magnetic field of the permanent magnet upon being energized for the cancellation of the magnetic field of the permanent magnet. The magnetic circuit is formed in which the magnetic flux passes through the core, the housing, the north pole of the permanent magnet and the south pole thereof, and the armature and returns to the core. The magnetic flux of the electromagnet thus passes through the permanent magnet in the direction reverse to the magnetic flux of the permanent magnet. Therefore, the permanent magnet is influenced by the opposing magnetic field relative to the permanent magnet and thus tends to be demagnetized. This will lead to considerable reduction of the durability of the permanent magnet. Further, since resistance in the magnetic circuit will be increased due to the passage of the magnetic flux through the permanent magnet in the reverse direction, the electric energy consumption required for the cancellation of the magnetic field of the permanent magnet will become greater. 
     SUMMARY OF THE INVENTION 
     The present invention contemplates solving the above-mentioned problems of the conventional actuator. 
     It is an object of the present invention to provide an electromagnetic valve actuator capable of reducing electric energy consumption of the electromagnets and preventing a permanent magnet from being demagnetized due to the influence of the opposing magnetic field, serving for increasing the durability of the permanent magnet. 
     According to one aspect of the present invention, there is provided an apparatus for actuating a cylinder valve of an engine, the cylinder valve having a closed position, a full open position and a neutral position between the closed and full open positions, the apparatus comprising: 
     an armature moveable in a direction of an axis, said armature including a sleeve portion extending in the axial direction and a disk portion connected with an inner periphery of the sleeve portion and adapted to be fixed to the cylinder valve; 
     a pair of springs biasing the armature toward a valve-neutral position corresponding to the neutral position of the cylinder valve; 
     a pair of electromagnets attracting the armature for moving the cylinder valve to the closed and full open positions, said electromagnets being disposed in an axially opposed relation to the armature, said electromagnets including a pair of axially spaced magnetic cores; and 
     a permanent magnet retaining the armature for holding the cylinder valve in the closed and full open positions; 
     wherein the sleeve portion of the armature cooperates with the permanent magnet to define a first air gap radially extending therebetween and cooperates with each of the magnetic cores to define a second air gap radially extending therebetween, and the disk portion of the armature cooperates with each of the magnetic cores to define a third air gap axially extending therebetween and variable with the axial motion of the armature. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a vertical section of a preferred embodiment of an electromagnetic valve actuator according to the present invention; 
     FIGS. 2A and 2B are views similar to FIG. 1 but respectively showing the electromagnetic valve actuator in different operating states in which an intake valve is placed in the closed position and the full open position; 
     FIG. 3 is a diagram showing characteristic curves of a permanent magnet, electromagnets and springs; and 
     FIG. 4 illustrates timing diagrams of valve lift of the intake valve and coil current of the electromagnets. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1,  2 A and  2 B illustrate the embodiment of an electromagnetic valve actuator according to the present invention, which is applied to an intake valve of an engine and may also be used with an exhaust valve of the engine. 
     Referring now to FIG. 1, the actuator includes an electromagnetically actuating mechanism  24  for actuating an intake valve  23  of a vehicle engine, a permanent magnet  32  retaining the intake valve  23  in a closed position thereof and a full open position thereof, and a valve-closing spring  25  and a valve-opening spring  26  that are adapted for biasing the intake valve  23  toward a neutral position between the closed and full open positions. FIG. 1 shows the intake valve  23  placed in the neutral position. The intake valve  23  is so configured as to open and close an open end of an intake port  22  formed in a cylinder head  21 . The open end of the intake port  22  is exposed to a combustion chamber. The intake valve  23  includes a valve head  23   a  engageable with an annular valve seat  22   a  provided at the open end of the intake port  22 . The intake valve  23  is engaged with the valve seat  22   a  in the closed position and disengaged therefrom in the full open position. The intake valve  23  also includes a valve stem  23   b  formed integrally with the valve head  23   a  and extending upwardly from the center of an upper surface of the valve head  23   a.  The valve stem  23   b  is slidably moved within a slide hole  21   a  formed in the cylinder head  21 . 
     The electromagnetically actuating mechanism  24  includes a generally cylindrical housing  28  fixed to the cylinder head  21  through fastening bolts  27 , an armature  29  disposed within the housing  28  so as to be moveable in a direction of a center axis X, and a pair of valve-closing and valve-opening electromagnets  30  and  31  attracting the armature  29  for moving the intake valve  23  to the closed and full open positions. The valve-closing electromagnet  30  and the valve-opening electromagnet  31  are disposed in an axially opposed and spaced relation to the armature  29 . 
     The housing  28  includes a pair of generally cylindrical lower and upper housing halves  33  and  34  made of a magnetic material. The lower and upper housing halves  33  and  34  are connected together at opposed outer peripheral flanges thereof by using fastening bolts  35 . The lower and upper housing halves  33  and  34  have substantially same structure. The lower housing half  33  includes a bottom wall and an inner sleeve  33   a  extending upwardly from a central portion of the bottom wall. The inner sleeve  33   a  has an upper radial flange  33   b  extending radially outwardly from an upper end portion of the inner sleeve  33   a.  The inner sleeve  33   a  with the upper radial flange  33   b  forms a reverse L-shape shown in FIG.  1  and cooperates with the bottom wall to define a cylindrical bore  33   c.  The upper housing half  34  includes a top wall and an inner sleeve  34   a  extending downwardly from a central portion of the top wall. The inner sleeve  34   a  has a lower radial flange  34   b  extending radially outwardly from a lower and portion of the inner sleeve  34   a.  The inner sleeve  34   a  with the lower radial flange  34   b  forms an L-shape shown in FIG.  1  and cooperates with the top wall to define a cylindrical bore  34   c  substantially axially aligned with the bore  33   c.  Through the bores  33   c  and  34   c,  an upper portion of the valve stem  23   b  is received moveably in the axial direction. A cover  35  is disposed on the top wall to close the bore  34   c.    
     The permanent magnet  32  is secured to an inner circumferential surface of a middle portion of the housing  28  in which the lower and upper housing halves  33  and  34  are connected together. The permanent magnet  32  is arranged in a radially outwardly spaced relation to the inner sleeves  33   a  and  34   a  of the lower and upper housing halves  33  and  34 . There is a suitable radial space between the permanent magnet  32  and the inner sleeves  33   a  and  34   a , in which a portion of the armature  29  is disposed as explained later. The permanent magnet  32  has a cylindrical shape and a north magnetic pole N at an inner circumferential portion thereof and a south magnetic pole S at an outer circumferential portion thereof. The cylindrical permanent magnet  32  is increased in an axial length, i.e., in an inner circumferential area opposed to the armature  29 , so as to sufficiently attract the armature  29 . In this embodiment, the axial length of the permanent magnet  32  is greater than an entire axial length of the armature  29 . 
     The armature  29  is disposed coaxially with the intake valve  23  and moveable together therewith upwardly and downwardly along the center axis X. The armature  29  has an H-shaped cross section shown in FIG.  1 . The armature  29  includes a disk portion  29   a  and a sleeve portion  29   b  connected with an outer incumferential periphery of the disk portion  29   a  and integrally formed with the disk portion  29   a.  The disk portion  29   a  is fixed to a threaded upper end of the valve stem  23   b  by a nut  36  for the unitary motion with the intake valve  23 . The disk portion  29   a  extends in a direction perpendicular to the center axis X and is disposed within an axial space S defined between the radial flange  34   b  of the inner sleeve  34   a  of the upper housing half  34  and the radial flange  33   b  of the inner sleeve  33   a  of the lower housing half  33 . The disk portion  29   a  has an upper end face opposed to a lower axial end face  34   d  of the radial flange  34   b  with an axial air gap  44   a  and a lower end face opposed to an upper axial end face  33   d  of the radial flange  33   b  with an axial air gap  44   b . The axial air gaps  44   a  and  44   b  are variable as the armature  29  moves along the center axis X, as explained in detail later. The sleeve portion  29   b  extends from the junction with the disk portion  29   a  in two opposing axial directions. The sleeve portion  29   b  is disposed in the radial space between the permanent magnet  32  and the radial flanges  33   b  and  34   b  of the inner sleeves  33   a  and  34   a.  The sleeve portion  29 b has an outer circumferential surface opposed to an inner circumferential surface  32   a  of the permanent magnet  32  with a slight radial air gap  42 . The outer circumferential surface of the sleeve portion  29   b  is entirely effective to be attracted by the permanent magnet  32  in the valve-neutral position, shown in FIG. 1, of the armature  29 . The sleeve portion  29   b  has an inner circumferential surface  29   c  opposed to outer circumferential surfaces of the radial flanges  33   b  and  34   b  with radial air gaps  43 . The radial air gaps  43  are disposed on the upper and lower sides of the disk portion  29   a,  respectively. Preferably, the radial air gaps  43  may be set at such a large value as to effectively reduce leakage of the magnetic flux of the electromagnets  30  and  31 . 
     The valve-closing electromagnet  30  includes a magnetic core formed by the inner sleeve  34   a  of the upper housing half  34  and a coil  30   a  wound around an outer circumferential surface of the magnetic core. The magnetic core includes opposed pole piece portions formed by the lower and upper end portions of the inner sleeve  34   a , respectively. The valve-opening electromagnet  31  includes a magnetic core formed by the inner sleeve  33   a  of the lower housing half  33  and a coil  31   a  wound around an outer circumferential surface of the magnetic core. The magnetic core includes opposed pole piece portions formed by the upper and lower end portions of the inner sleeve  33   a , respectively. The coils  30   a  and  31   a  are connected in series and turned around the corresponding magnetic cores  34   a  and  33   a  in a same direction. One terminal end  37   a  of the coil  30   a  is connected with a terminal end  37   b  of the coil  31   a.  The other terminal ends  38   a  and  38   b  of the respective coils  30   a  and  31   a  are connected to a power source  40  and a controller  41  via an amplifier  39 . 
     The controller  41  is programmed to determine an operating condition of the engine depending on signal outputs from detectors and develops a control signal for activating the coils  30   a  and  31   a  with an electric current. The detectors include a crank angle sensor  50  detecting the number of engine revolution and a temperature sensor  52  detecting temperatures of the electromagnets  30  and  31 , and also may include an airflow meter. The controller  41  may be constituted by a microcomputer including microprocessor unit (MPU), input ports, output ports, read-only memory (ROM) for storing the control program, random access memory (RAM) for temporary data storage, and a conventional data bus. 
     The valve-closing spring  25  is installed in a compressed state within the bore  33   c  of the inner sleeve  33   a  of the lower housing half  33  and biases the armature  29  upwardly. Specifically, the valve-closing spring  25  has a lower end portion supported on an upper face of the cylinder head  21  and an upper end portion supported on a central portion of the lower end face of the disk portion  29   a  of the armature  29 . The valve-opening spring  26  is installed in a compressed state within the bore  34   c  of the inner sleeve  34   a  of the upper housing half  34  and biases the armature  29  downwardly. Specifically, the valve-opening spring  26  has a lower end portion supported on a central portion of the upper end face of the disk portion  29   a  and an upper end portion supported on a rearside face of the cover  35 . Setting loads of the valve-closing and valve-opening springs  25  and  26  are the same. The valve-closing and valve-opening springs  25  and  26  associate with each other to hold the armature  29  in a valve-neutral position, shown in FIG. 1, corresponding to the neutral position of the valve  23  when the coils  30   a  and  31   a  of the electromagnets  30  and  31  are not activated with an electric current. 
     An operation of the electromagnetic valve actuator will be explained hereinafter. 
     When the engine is stopped and the coils  30   a  and  31   a  of the valve-closing and valve-opening electromagnets  30  and  31  are not activated with an electric current, the armature  29  is placed in the valve-neutral position shown in FIG.  1 . In this condition, the upper axial air gap  44   a  between the disk portion  29   a  of the armature  29  and the radial flange  34   b  of the inner sleeve  34   a  of the upper housing half  34  is equal to the lower axial air gap  44   b  between the disk portion  29   a  and the radial flange  33   b  of the inner sleeve  33   a  of the lower housing half  33 . Densities of the magnetic fluxes of the permanent magnet  32  respectively extending toward the electromagnets  30  and  31  are equivalent. 
     Next, the engine starts and the coils  30   a  and  31   a  of the electromagnets  30  and  31  are activated with an electric current in such a direction that a south magnetic pole S is generated at the lower end portion of the inner sleeve  34   a  of the upper housing half  34  and a north magnetic pole N is generated at the upper end portion of the inner sleeve  33   a  of the lower housing half  33 . Namely, the lower end portion with the radial flange  34   b,  of the inner sleeve  34   a  acts as the south magnetic pole piece portion S of the electromagnet  30  and the upper end portion with the radial flange  33   b,  of the inner sleeve  33   a  acts as the north magnetic pole piece portion N of the electromagnet  31 . Thus, the lower pole piece portion of the electromagnet  30  and the upper pole piece portion of the electromagnet  31  have the opposing polarities S and N upon activating the serially-connected coils  30   a  and  31   a  wound in the same direction. In this condition, the density of the magnetic flux extending from the magnetic pole N of the permanent magnet  32  through the disk portion  29   a  of the armature  29  toward the S pole piece portion of the electromagnet  30  is larger, while the density of the magnetic flux extending from the magnetic pole N of the permanent magnet  32  through the disk portion  29   a  of the armature  29  toward the N pole piece portion of the electromagnet  31  is smaller. The armature  29  is attracted toward the S pole piece portion of the electromagnet  30  by the larger flux density. The armature  29  is then moved from the valve-neutral position to the valve-closing position against the spring force of the spring  26 . As the armature  29  moves from the valve-neutral position toward the valve-closing position, the axial air gap  44   a  on the electromagnet  30  side becomes smaller while the axial air gap  44   b  on the electromagnet  31  side becomes greater. The intake valve  23  is upwardly moved with the armature  29  from the neutral position and placed in the closed position shown in FIG. 2A with the engagement of the valve head  23   a  with the valve seat  22   a.  The coils  30   a  and  31   a  are then instantly de-energized. Even in this condition where the coils  30   a  and  31   a  are de-energized, the intake valve  23  can be retained in the closed position by the attraction of the permanent magnet  32  relative to the armature  29 . In the closed position of the intake valve  23 , there is generated a magnetic flux circuit as indicated by arrow in FIG.  2 A. Although only the right half of the magnetic flux circuit is shown in FIG. 2A for simple illustration, the left half thereof is similar to the right half. In the magnetic flux circuit, the magnetic flux extending from the magnetic pole N of the permanent magnet  32  passes through the radial air gap  42 , the disk portion  29   a  of the armature  29 , the smaller axial air gap  44   a  on the electromagnet  30  side, the lower end portion of the magnetic core  34   a  of the electromagnet  30  and the top wall and outer circumferential wall of the upper housing half  34 , and enters the magnetic pole S of the permanent magnet  32 . 
     Subsequently, for moving the intake valve  23  from the closed position to the full open position, the coils  30   a  and  31   a  are activated with a reverse electric current flowing in a direction opposite to the above-described direction. By the activation of the coils  30   a  and  31   a  with the reverse electric current, the magnetic pole N is generated at the lower end portion of the inner sleeve  34   a  of the upper housing half  34  and the magnetic pole S is generated at the upper end portion of the inner sleeve  33   a  of the lower housing half  33 . Namely, conversely to the above-explained case of energization for moving the intake valve  23  to the closed position, the lower pole piece portion of the electromagnet  30  has the magnetic pole N and the upper pole piece portion of the electromagnet  31  has the magnetic pole S. The density of the magnetic flux extending from the magnetic pole N of the permanent magnet  32  toward the S pole piece portion of the electromagnet  31  becomes larger, while the density of the magnetic flux extending from the magnetic pole N of the permanent magnet  32  toward the N pole piece portion of the electromagnet  30  becomes smaller. In this state, there is generated a magnetic flux circuit in which the magnetic flux extending from the magnetic pole N of the permanent magnet  32  passes through the radial air gap  42 , the disk portion  29   a  of the armature  29 , the axial air gap  44   b  on the electromagnet  31  side, the S pole piece portion of the electromagnet  31 , the bottom wall and the outer circumferential wall of the lower housing half  33  and enters the magnetic pole S of the permanent magnet  32 . Substantially no or less amount of the magnetic flux passes through the permanent magnet  32  in a direction opposed to the magnetic flux of the permanent magnet  32 . Thus, the permanent magnet  32  is prevented from being influenced by an undesired opposing magnetic field relative thereto which causes demagnetization thereof, upon energizing the coils  30   a  and  31   a  in the reverse direction. The armature  29  is attracted toward the S pole piece portion of the electromagnet  31 . The armature  29  is moved toward the valve-neutral position with the assistance of the spring force of the spring  26  and then attractively moved to the valve-opening position, shown in FIG. 2B, against the spring force of the spring  25 . Upon the motion of the armature  29  toward the valve-opening position, the axial air gap  44   b  on the electromagnet  31  side becomes smaller, while the axial air gap  44   a  on the electromagnet  30  side becomes greater. The variable axial air gap  44   a  and  44   b  are set in such a manner as to be smaller than the radial air gap  43  when the armature  29  is placed in the respective valve-closing and valve-opening positions as shown in FIGS. 2A and 2B. The intake valve  23  is downwardly moved with the armature  29  through the neutral position to the full open position in the disengagement of the vale head  23   a  from the valve seat  22   a.  The coils  30   a  and  31   a  are instantly de-energized. Even in this state, the intake valve  23  can be held in the full open position by the attraction of the permanent magnet  32  relative to the armature  29 . In the full open position of the intake valve  23 , there is generated a magnetic flux circuit indicated by arrow in FIG. 2B, in which the magnetic flux extending from the magnetic pole N of the permanent magnet  32  passes through the radial air gap  42 , the disk portion  29   a  of the armature  29 , the smaller axial air gap  44   b  on the electromagnet  31  side, the upper end portion of the magnetic core  33   a  of the electromagnet  31 , the bottom wall and the outer circumferential wall of the lower housing half  33 , and enters the magnetic pole S of the permanent magnet  32 . 
     FIG. 3 illustrates characteristic curves of the permanent magnet  32 , the electromagnets  30  and  31  and the springs  25  and  26 , which are exhibited upon shifting the intake valve  23  between the closed and full open positions. In FIG. 3, the permanent magnet  32  creates the attraction Fm as indicated by curves  100 , exerted on the armature  29  against the spring forces  112  and  110  of the springs  26  and  25 . When the intake valve  23  is in the respective closed and full open positions, the attraction Fm of the permanent magnet  32  overcomes the combined spring force Fs, as indicated by line  114 , of the springs  25  and  26 . When the coils  30   a  and  31   a  of the electromagnets  30  and  31  are activated with the reverse electric current for shifting the intake valve  32  between the closed and full open positions, the repulsion FR, as indicated by curve  102 , of the armature  29  is generated. Namely, in the case of activation of the coils  30   a  and  31   a  with the reverse current for shifting the intake valve  32  from one of the closed and full open positions to the other thereof, the combined force of the combined spring force Fs and the repulsion FR of the armature  29  overcomes the attraction Fm of the permanent magnet  32  to eliminate the retention of the armature  29  by the permanent magnet  32 . The intake valve  23  is thus urged to move from one of the closed and full open positions toward the other thereof. 
     Referring now to FIG. 4, a relationship between the activation of the coils  30   a  and  31   a  of the electromagnets  30  and  31  and the closing and opening motion of the intake valve  23  is explained. When activating the coils  30   a  and  31   a  with a coil current C 1  shown in FIG. 4, for shifting the intake valve  23  from the closed position to the full open position, the intake valve  23  is moved from the closed position to the full open position owing to the spring force of the spring  26  and the attractive force of the electromagnet  31 . Immediately after that, the energization of the coils  30   a  and  31   a  is stopped but the intake valve  23  is retained in the full open position as indicated by valve lift curve in FIG. 4, by the attraction of the permanent magnet  32 . Likewise, when activating the coils  30   a  and  31   a  with a coil current C 2  shown in FIG. 4, the intake valve  23  is moved from the full open position to the closed position in a manner reverse to that described above. 
     With the arrangement of the permanent magnet  32 , it is not necessary to continuously supply an electric current to the coils  30   a  and  31   a  of the electromagnets  30  and  31  in order to attractively hold the armature  29  in the valve-closing and valve-opening positions. This also serves for reducing the electric power consumption. 
     Further, when the direction of the energization of the electromagnets  30  and  31  is reversed for moving the intake valve  23  from one of the closed position and the full open position to the other thereof, the armature  29  is attracted by the magnetic field of one of the electromagnets  30  and  31  which is the same as the magnetic field of the permanent magnet  32 . Namely, the magnetic flux of the one of the electromagnets  30  and  31  is substantially prevented from passing through the permanent magnet  32  in the direction opposed to the direction of the magnetic flux of the permanent magnet  32 . Thus, the permanent magnet  32  can be prevented from being influenced by the undesired opposing magnetic field relative to the magnetic field thereof and thus be effectively avoided from being demagnetized. This results in improving the durability of the permanent magnet  32 . 
     Furthermore, since, upon the energization of the electromagnets  30  and  31  in the reverse direction, the magnetic flux is substantially prevented from passing through the permanent magnet  32  in the direction opposed to the magnetic flux of the permanent magnet  32 , the reluctance in the magnetic flux circuit formed thereupon can be reduced. This causes reduction of the electric current supplied to the coils  30   a  and  31   a  required upon the energization thereof in the reverse direction. This can contemplate to reduction in power consumption. 
     Further, since the coils  30   a  and  31   a  of the electromagnets  30  and  31  are connected in series and wound in the same direction, the attractive force of one of the electromagnets  30  and  31  is exerted on the armature  29  with the assistance of the spring force of one of the springs  25  and  26  which is associated with the one of the electromagnets  30  and  31  upon the energization for shifting the intake valve  23  between the closed and open positions. This can improve the response motion of the armature  29 . 
     Although the invention has been described above by reference to a certain embodiment of the invention, the invention is not limited to the embodiment described above. Modifications and variations of the embodiment described above will occur to those skilled in the art, in light of the above teachings. The scope of the invention is defined with reference to the following claims.