Patent Publication Number: US-6661219-B2

Title: Apparatus having an electromagnetic actuator including an armature and at least one inductive element connected to the armature for determining the position of the armature

Description:
FIELD OF THE INVENTION 
     The invention relates to an apparatus having an electromagnetic actuator. 
     BACKGROUND INFORMATION 
     An actuator of this type for operating an inlet or exhaust valve of an internal combustion engine is described in Japanese Published Patent Application No. 07 224 624. The electromagnetic actuator includes two electromagnets, an opening magnet and a closing magnet, between the pole surfaces of which an armature is arranged such that it can be moved coaxially with respect to a valve axis. The armature acts on a valve stem of the inlet or exhaust valve. Furthermore, a prestressed spring mechanism acts on the inlet or exhaust valve via the armature. Two prestressed compression springs are used as the spring mechanism, of which an upper compression spring loads the inlet or exhaust valve in the opening direction, and a lower compression spring loads the inlet or exhaust valve in the closing direction. When the electromagnets are not energized, the armature is held in an equilibrium position between the electromagnets, by the compression springs and valve springs. 
     In addition to an operating coil, the electromagnets each have a measurement coil. The measurement coils are arranged in the radially inner region of the operating coils. The position of the armature between the electromagnets influences the inductance of the measurement coils, by which the position of the armature can be deduced from the detected inductance values of the measurement coils. The inductance decreases in a highly non-linear manner with the distance between the armature and the measurement coils, and the measurement coils are subject to strong magnetic fields from the operating coils during operation. 
     Furthermore, an electromagnetic actuator for operating an inlet or exhaust valve in an internal combustion engine and having a pivoting armature is described in German Published Patent Application No. 196 28 860, which pivoting armature is mounted between two electromagnets such that it can pivot about one axis. 
     It is an object of the present invention to provide an apparatus having an actuator for operating an actuating element, in which the position of the armature and/or of the actuating element may be detected as accurately as possible and over a wide range during operation of the actuator. 
     SUMMARY 
     The above and other beneficial objects of the present invention are achieved by providing an apparatus as described herein. 
     The present invention relates to an apparatus having an electromagnetic actuator for operating an actuating element, in particular an inlet or exhaust valve of an internal combustion engine, which includes an electromagnetic unit via which an armature which is mounted such that it may move and is operatively connected to the actuating element may be moved, and having a measurement apparatus which has at least one inductive measurement element at least for detecting a position of the armature, and in particular having a spring mechanism which acts on the actuating element. 
     At least one inductive measurement element may be firmly connected to the armature. The inductive measurement element, which is firmly connected to the armature and is thus moved with the armature, allows any dead band to be reduced, in which no measurement signal, or only an inaccurate, weak measurement signal, may be detected during operation. In contrast to an inductive measurement element which is attached to an electromagnet in the electromagnetic unit, the measurement element which is attached to the armature is not continuously subjected to a strong magnetic field, but moves into and out of the magnetic fields of the electromagnets, by which a large measurement signal, which may be evaluated well, may be detected at an early stage before the armature meets a pole surface of the electromagnets. Advantageous open and closed-loop control of the armature movement may be achieved on the basis of a small dead band. Furthermore, a measurement element which moves with the armature allows the position of the armature with respect to two electromagnets that are at a distance from one another to be detected, without having to attach an inductive measurement element to each electromagnet. If, in addition to the inductive measurement element which is firmly connected to the armature, at least one additional inductive measurement element is attached to the electromagnetic unit, so that at least two measurement signals may be detected, this results in a particularly accurate measurement, e.g., because correction values may be determined. 
     In order to achieve a measurement signal which is as large as possible and may be detected and evaluated well, the measurement element which is firmly connected to the armature is formed by a measurement coil, e.g., by a measurement coil having a number of turns. 
     The inductive measurement element may be at least partially fitted in the armature. The measurement element may be arranged such that it is protected against external influences, and any reduction in a contact area of the armature may be avoided, with the physical volume remaining unchanged. If, furthermore, the measurement element is fitted in the armature during production, for example, during a casting process, this furthermore allows attachment parts, assembly effort and costs to be avoided. However, it is also possible for the measurement element, which is in the form of a measurement coil, to be wound onto the armature, and this may be achieved in a physically simple manner. Furthermore, all the positively locking, force-fitting and/or integral-material connections are possible, for example, bonded joints, soldered joints, etc. 
     The measurement element may be arranged on one surface of the armature so that, when the armature meets a pole surface of the electromagnetic unit, the armature enters a recess in the pole surface, in which a winding of the electromagnetic unit is fitted. There is no need for any additional recesses or additional physical space. 
     The data detected by the measurement element may be transmitted via various data transmission devices from the moving armature to a receiving unit which is firmly connected to a housing, for example, by radio, infrared, sliding contacts, etc. However, if the armature is mounted such that it may pivot, this makes it possible to transmit data in a physically simple manner via a pivoting shaft of the armature, e.g., via data lines. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal cross-sectional view through an electromagnetic actuator. 
     FIG. 2 is a cross-sectional view of the electromagnetic actuator illustrated in FIG. 1 taken along the line II—II. 
     FIG. 3 is a longitudinal cross-sectional view of an electromagnetic actuator having a pivoting armature. 
     FIG. 4 is a cross-sectional view of the electromagnetic armature illustrated in FIG. 3 taken along the line IV—IV. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates a detail of an internal combustion engine in a motor vehicle, having a reciprocating piston  19 , which is guided in a cylinder block  18 , and a cylinder head  20  which ends at the cylinder block  18 . A valve drive with an electromagnetic actuator for operating an inlet or exhaust valve  21  is arranged in the cylinder head  20 . 
     The actuator includes an electromagnetic unit  16  with a first opening magnet  23 , which acts in the opening direction  22 , and a second closing magnet  25 , which acts in the closing direction  24 , and between which an armature  12  is arranged such that it may be moved coaxially. The armature  12  acts via an armature shaft  27 , which is guided in an armature shaft guide  26 , and via a hydraulic play compensation element  28  on a valve stem  29 , which is guided in a valve guide  30  in the cylinder head  20 . 
     Furthermore, a spring mechanism  31  acts on the valve stem  29  and includes an upper valve spring  32 , which acts in the opening direction  22 , and a lower valve spring  33 , which acts in the closing direction  24 . The valve spring  33 , which acts in the closing direction  24 , is arranged in a spring area  34 , which is incorporated in the cylinder head  20 , on the side of the opening magnet  23  facing the inlet or exhaust valve  21 , is supported via a ring  35  on the cylinder head  20 , and acts via a spring contact  36  in the closing direction  24  on the valve stem  29 . 
     The valve spring  32  which acts in the opening direction  22  is arranged on the side of the closing magnet  25  facing away from the inlet or exhaust valve  21  and is supported at an end facing away from the inlet or exhaust valve  21  on a cover  37  which is mounted on the cylinder head  20  and acts with an end, which faces the inlet or exhaust valve  21 , via a spring contact  38  on a spring tappet  39 , which is guided via a guide  40  in the closing magnet  25  and one end face of which, which points in the direction of the inlet or exhaust valve  21 , acts on an end face of the armature shaft  27 . 
     In order to draw the armature  12  out of its equilibrium position between the electromagnets  23 ,  25  when starting the internal combustion engine, either the closing magnet  25  or the opening magnet  23  is briefly overenergized, or the armature  12  is caused to oscillate at its resonant frequency  30  by an oscillation-formation routine. 
     When the inlet or exhaust valve  21  is in the closed position, the armature  12  rests on a pole surface of the closing magnet  25 , through which current is passing, and is held by it. The closing magnet  25  further prestresses the valve spring  32  which acts in the opening direction  22 . 
     In order to open the inlet or exhaust valve  21 , the closing magnet  25  is switched off, and the opening magnet  23  is switched on. The valve spring  32  which acts in the opening direction  22  accelerates the armature  12  beyond the equilibrium position, so that it is attracted by the opening magnet  23 , and the valve spring  33  which acts in the closing direction is further prestressed. The armature  12  strikes a pole surface of the opening magnet  23  and is held by it. In order to close the inlet or exhaust valve  21 , the opening magnet  23  is switched off, and the closing magnet  25  is switched on. The valve spring  33  which acts in the closing direction  24  accelerates the armature  12  beyond the equilibrium position towards the closing magnet  25 . The armature  12  is attracted by the closing magnet  25 , strikes the pole surface of the closing magnet  25  and is held by it. 
     In order to allow the movement of the armature  12  to be controlled with an open or closed loop, its position, speed and acceleration are, according to the present invention, detected via inductive measurement elements  10 ,  14  which are in the form of measurement coils having a number of turns. One of the measurement elements  10  is introduced into the armature  12  such that it is firmly connected to it, and the other measurement element  14  is mounted on that side of the guide  40  for the spring tappet  39  in the closing magnet  25  which faces the inlet or exhaust valve  21 , next to the pole surface of this closing magnet  25 . The data detected by the measurement element  14  which is arranged in the closing magnet  25  are transmitted via data lines, and the data detected by the measurement element  10  which is arranged in the armature  12  are transmitted via four transmitters  42 , which are distributed uniformly over the circumference of the armature  12 , via infrared to a receiving and evaluation unit  41  as illustrated in FIGS. 1 and 2. 
     FIG. 3 illustrates an alternative electromagnetic actuator for operating an inlet or exhaust valve  43  of an internal combustion engine. The actuator includes an electromagnetic unit  17  with two electromagnets  44 ,  45 , an opening magnet  44  and a closing magnet  45 . Each of the electromagnets  44 ,  45  includes a solenoid coil  67 ,  68 , which is wound on a coil former, and a coil core  69 ,  70  with two yoke limbs, the end faces of which form pole surfaces. A pivoting armature  13  is mounted between the pole surfaces such that it may pivot in both directions about one axis. The pivoting armature  13  acts via a projection  72 , which is integrally formed on it, and via a valve stem  48  on the inlet or exhaust valve  43  as illustrated in FIGS. 3 and 4. The valve stem  48  is mounted, such that it may be moved axially, via a stem driver  49  in a cylinder head  50  of the internal combustion engine. 
     Furthermore, the actuator includes a spring mechanism with two prestressed valve springs  51 ,  52 , e.g., with a valve spring  51  which is in the form of a torsion rod spring and acts in the opening direction  53 , and with a valve spring  52 , which is in the form of a helical compression spring and acts in the closing direction  54 . 
     The pivoting armature  13  is firmly welded to a hollow pivoting shaft  55  as illustrated in FIG.  4 . The pivoting shaft  55  is mounted in a first bearing point  56  via first sliding bearing  57  on a bearing bolt  58  in a first housing wall  58  of an actuator housing  60  and is mounted in a second bearing point  61  via a second sliding bearing  62  on the torsion rod spring in a second housing wall  63  of the actuator housing  60 . The torsion rod spring is connected at one end to the housing wall  63  such that it may not rotate and acts on the inlet or exhaust valve  43  via a separating wall  64 , which is arranged in the pivoting shaft  55  such that it may not rotate, via the pivoting shaft  55 , via the pivoting armature  13 , and via the valve stem  43 . 
     The helical compression spring is supported via a first spring mounting  65  on the cylinder head  50  and acts on the inlet or exhaust valve  43  via a second spring mounting  66  and via the valve stem  48  as illustrated in FIG.  3 . When the electromagnets  44 ,  45  are not energized, the pivoting armature  13  is held by the valve springs  51 ,  52  in an equilibrium position between the pole surfaces of the electromagnets  23 ,  25 . The actuator is started in a corresponding manner to the actuator illustrated in FIGS. 1 and 2. 
     In order to allow the movement of the pivoting armature  13  to be controlled by an open loop or closed loop, its position, speed and acceleration are detected, according to the present invention, via inductive measurement elements  11 ,  15  in the form of measurement coils having a number of turns. The one measurement element  11  is wound onto the pivoting armature  13 , and the other measurement element  15  is mounted in the closing magnet  45 , on a side of the solenoid coil  68  facing the inlet or exhaust valve  43 . 
     The data detected by the measurement element  15  which is arranged in the closing magnet  45  are transmitted via data lines, and the data which are detected by the measurement element  11  which is wound on the armature  12  are transmitted via a data line  71  to a receiving and evaluation unit  73 . The data line  71  is routed from the measurement element  11  through a hole  46 , which extends in the direction of movement of the pivoting armature  13 , and through a hole  47 , which extends at right angles to the movement direction, in the pivoting armature  13  into the hollow pivoting shaft  55 , from where the data line  71  is routed through a hole  74  in the bearing bolt  58  to the receiving and evaluation unit  73 . 
     When the pivoting armature  13  strikes the pole surface of the closing magnet  45 , the measurement element  11  passes between the yoke limbs of the closing magnet  45 , and when the pivoting armature  13  strikes the pole surface of the opening magnet  44 , the measurement element  11  passes between the yoke limbs of the opening magnet  44 .