WO2011042273A1 - Actuator for an internal combustion engine - Google Patents

Abstract

Known electromagnetic actuators comprising permanent magnets often have the disadvantage that returning the tappet is often not possible solely by way of permanent magnetic forces, when a distance of over 1 mm between the armature and core must be overcome. According to the invention, an actuator is proposed, in which the permanent magnet (32) is arranged in a stationary manner within the electromagnetic circuit (4) and means (34, 40) are designed for focusing axial magnetic field lines on the permanent magnetic circuit (8).

Description

 DESCRIPTION

Actuator for an internal combustion engine

The invention relates to an actuator for an internal combustion engine with an actuator consisting of an electromagnetic circuit having a coil, a fixed core, a movable armature and a yoke, a plunger which is actuated via the electromagnetic circuit and which is connected to the armature and a permanent magnetic circuit consisting of the yoke, the core, the armature and a permanent magnet which holds the armature in a holding end position in the de-energized state of the electromagnetic circuit.

Such actuators are used for example for adjusting sliding cam contours on which different lifting profiles are formed and which are arranged displaceably on a camshaft. The actuator engages in a groove of the sliding cam. After the axial adjustment resulting therefrom, the actuating element is normally passively returned to its starting position via a lifting contour of the groove.

Such an actuator is known for example from WO 03/021612 AI. The actuator of the electromagnetic actuator described herein is formed by a plunger which is engageable with the sliding cam groove. The adjusting device has a permanent magnet, which is firmly connected to the plunger and is held by its magnetic force, the plunger in its retracted position. By driving an electromagnet, the field of the permanent magnet is so far weakened that the holding force is lower as a force which is exerted in the extension direction of the plunger via a spring element on the plunger, so that the plunger is moved into the groove. By a lifting contour of the plunger is moved back to its original position.

In addition to these actuators with an electromagnet and a plunger communicating therewith, it is also known, for example from DE 10 2007 028 600 A1, to arrange a plurality of adjusting elements in a common housing.

In the mentioned actuators, however, there is the problem that the permanent magnet shocks and thus mechanical forces is exposed, which can lead to demagnetization and thus the loss of holding power. In addition, in the known actuators has the disadvantage that the passive return of the plunger is not always working, since no sufficient force can be applied to bridge the distance between the armature plate and the rest of the permanent magnetic circuit. Due to the always necessary for the installation of such an actuator for camshaft adjustment tolerances, however, a tightening of the plunger must be ensured in its Halteendposition already at a distance of about 1 mm. Furthermore, in the known actuators, a relatively large mass must be accelerated upon actuation. It is therefore the object to provide an actuator in which without actuation of the solenoid is already ensured that the armature plate and thus the plunger is already pulled at a greater distance from the rest of the permanent magnetic circuit in its retracted position. At the same time a too large and thus not solvable about an electromagnet normal size adhesive force in the final position must be prevented. In addition, a mechanical load on the permanent magnet should be avoided as much as possible. A long Lifetime of the actuator with the lowest possible power consumption should be achieved.

This object is achieved by the characterizing part of the main claim. Characterized in that the permanent magnet is arranged stationary within the electromagnetic circuit and means for concentrating axial magnetic field lines are formed on the permanent magnetic circuit, the force acting in the direction of movement of the plunger permanent magnet force is increased, whereby the plunger is already attracted at a greater distance from the rest permanent magnetic circuit. In addition, a mechanical load of the permanent magnet due to shocks, so that its functionality is ensured over a long period of time. The mass to be moved is very small, so that no high actuating forces must be applied.

Preferably, as means for concentrating axial magnetic field lines, the permanent magnet is arranged axially between the core and the yoke, and the core and the permanent magnet are arranged radially spaced from the yoke. Due to the axial arrangement of the permanent magnet, a mechanical impact load is excluded. Due to the radial distance between the magnet or the core and the yoke, a violation of magnetic field lines in the radial direction in the permanent magnetic circuit is avoided. Thus, a bundling of axial magnetic field lines takes place, since the magnetic field can continue only in this direction. This leads to an increased magnetic force in the axial direction, ie in the direction of movement of the plunger with a constant large magnet.

In an advantageous embodiment, the armature has a radially extending armature plate. This serves to close the magnetic circuits, wherein the permanent magnetic circuit can be closed only in the holding position. In an advantageous embodiment of the invention, the means for concentrating the magnetic field lines are formed by a yoke axially extending in the direction of the armature plate extension reduced thickness, which surrounds the armature plate at least partially radially in the Halteendstellung. In this extension, the magnetic field lines are correspondingly bundled out of the yoke. Due to the small thickness of the extension, the field lines also mainly have an axial direction. Accordingly, this focused field acts on the anchor plate already when the anchor plate is still at a distance to its support point, since depending on the height of the extension and the magnetic force acts on the extension on the anchor plate, so that a corresponding distance to the support surface are overcome can.

Preferably, the anchor has a cavity in its interior. As a result, the weight of the armature is reduced so that inertial forces and thus required holding and adjusting forces decrease and faster actuation is possible.

In a further embodiment, the means for focusing the magnetic field lines are formed by an axially extending in the direction of the armature portion of the core, which projects into the holding end position in the cavity of the armature. This arrangement has substantially the same effect as the axially extending projection on the yoke. Here, too, field lines are bundled in the axial direction and guided into areas that reduce an axial distance between the parts of the magnetic circuit to exert a force from the armature, even at an distance of about 1mm from the holding end position, in the direction of its holding end position emotional. In a further embodiment, a spring element is arranged in the cavity of the armature, which rests against a stop formed in the interior of the armature and against the core. Compared In addition to known designs, not only the moving mass but also the required axial space can be reduced as a result.

Preferably, the anchor plate is spaced apart from the yoke in the holding end position. Accordingly, a gap in the magnetic circuit is maintained in the retracted end position. Through this gap, the holding force of the permanent magnet is reduced so that a release of the armature plate with a conventional electromagnet remains possible. The otherwise very high magnetic forces are thus reduced to use smaller electromagnet or a lower amperage to release the holding power can.

In an alternative or further embodiment, the armature is arranged in the holding end position at a distance from the core. This also reduces the holding force of the permanent magnet in the same way.

In an advantageous embodiment of the invention, the diameter of the permanent magnet is greater than the free diameter in the interior of the bobbin and the permanent magnet is arranged on the end facing away from the plunger of the coil. Thus, strong relatively large-sized permanent magnets can be used with which sufficient attraction forces can be achieved even at spaced portions of the magnetic circuit. Preferably, a support surface for the armature plate is formed in the housing in its second end position, wherein in the support surface at least one additional permanent magnet is arranged. Thus, an additional holding force can be generated in the second end position, the magnetic field is also available for bearing feedback.

Preferably, a non-contact sensor is arranged in a housing of the actuator, via which a changing with movement of the armature plate magnetic field is detected. This field change causes a different output signal of the sensor whose size is a measure of the position of the plunger. Thus, a precise bearing feedback is possible. Depending on the sensor used, both changing field line directions and strengths can be used for position measurement. The movable anchor plate generates a field change during their movement.

In a particularly advantageous embodiment, two adjusting elements are arranged side by side in the housing. In this case, to adjust a sliding cam, the first adjusting element to move the cam in a first direction and the second actuator to move the cam in the opposite direction. Accordingly, an actuation only one of the actuating elements is necessary and desired. Their arrangement in a common housing simplifies assembly and reduces the required space.

In a further embodiment, the non-contact sensor is arranged on an axis of symmetry of the two control elements in the housing, which is operatively connected to two actuators, each actuator is associated with an additional permanent magnet, wherein the two permanent magnets are polarized opposite to the sensor operatively connected. Due to the position of the sensor, it is thus possible to detect the position of both control elements with only one sensor due to the different direction of the field lines. Accordingly, the number of components used is reduced compared to known designs.

There is thus provided an actuator which can apply a sufficient force to tighten the plunger from a distance of about 1mm to the end position. Nevertheless, the holding force in this end position remains such that a release by means of a normal electromagnet remains possible. Several such control elements can be arranged in a common housing and their position by means of a common position sensor can be detected. The actuator according to the invention requires only a small space due to its small size. It has a high durability due to the low mechanical load of the permanent magnet.

Two embodiments of actuators according to the invention are shown in the figures and will be described below.

Figure 1 shows a side view of an actuating element of an actuator according to the invention in a sectional view.

Figure 2 shows a side view of an actuator according to the invention with two to Figure 1 alternatively executed actuators in a sectional view.

FIG. 3 schematically shows a top view of an arrangement of a sensor for an actuator according to the invention according to FIG. 2.

The actuator 2 shown in Figure 1 of an actuator according to the invention consists of an electromagnetic circuit 4, a plunger 6 which is actuated via the electromagnetic circuit 4 and a permanent magnetic circuit 8 for generating a holding force in a holding end position of the plunger. 6

The electromagnetic circuit 4 has a coil 10 which is surrounded by a yoke 12 and in the interior of which an axially movable armature 14 is arranged, which is fixedly connected to the plunger 6 so that it is moved with movement of the armature 14. The armature 14 is designed as a hollow cylinder, from which an armature plate 16 extends radially outwardly and which has a recess 18 in which the plunger 6 is fixed by welding. In the cavity 20 of the armature 14, a spring element 22 is arranged in the form of a helical spring, which faces with its first end against a paragraph 24 shown only in Figure 2 the armature 14 or the plunger 6 is supported and supported with its second end against a core 26 which is arranged in the present embodiment in a bobbin 28.

The outer diameter of the armature 14 moves with play within a coil carrier 28. The guide of the plunger 6 takes place in a again only in Figure 2 shown guide housing part 30 which radially surrounds the plunger 6 in the axial direction.

The permanent magnetic circuit 8 consists of a permanent magnet 32, which is arranged axially between the core 26 and a radially extending portion of the yoke 12 and radially inside of the coil carrier 28, and the yoke 12, the armature 14 and the core 26th

The core 26 has three sections axially one behind the other. A first axially extending portion 34 has a cylindrical shape with a shoulder, so that two cylinders axially behind each other arise, and protrudes into the hollow cylindrical armature 14, wherein the outer diameter of the portion 34 in the region of the larger portion is slightly smaller than the inner diameter of the Cavity 20. At this cylindrical portion 34 is followed by a second cylindrical portion 36 of larger diameter, which has substantially the same diameter as the armature 14. There follows a third portion 38 which has a diameter growing in the opposite direction to the plunger until this diameter corresponds to the diameter of the permanent magnet 32. The entire core 26, the permanent magnet 32 and the armature 14 are surrounded by the bobbin 28 made of plastic. The bobbin 28 thus extends in the opposite direction to the plunger axially over the coil 10 away until the axially delimiting portion of the yoke 12. In this case, by the coil support 28, the radial distance between the core 26th or the permanent magnet 32 and the axially extending yoke 12 held so large that a violation of magnetic field lines is avoided as completely as possible, whereby a bundling of the existing magnetic forces is achieved.

Furthermore, a radially inwardly extending portion is formed on the yoke 12 at the end facing the plunger, which serves as a conclusion. From this section extends axially in the direction of the anchor plate 16, an annular extension 40 which surrounds the armature plate 16 radially in the holding position.

The operation of the constructively described in the foregoing actuator is described below with reference to an application of the actuator for sliding cam adjustment.

In its initial position, which corresponds to the retracted position or the holding end position of the plunger 6, the armature 14 bears against the core 26 with its first axial end. In this position, the armature 14 and thus the plunger 6 is held by the permanent magnetic circuit 8 whose field lines from the permanent magnet 32 via the yoke 12 in the armature plate 16 and the armature 14 and back over the core 26 to the opposite pole of the permanent magnet 32. It is accordingly a closed magnetic field, which exerts a holding force on the armature 14 which is greater than a spring force acting in the opposite direction, which exerts the spring element 22 on the armature 14. The existing holding force is particularly dependent on existing gaps in the permanent magnetic circuit 8. Since the holding force in such an actuator without column is very large, the axially extending portion of the armature 14 is formed slightly longer than the distance between the support surface of the armature 14th at the core 26 and the lower edge of the yoke 12 without the annular extension 40. This results in a gap 42 between the radially inwardly extending portion the yoke 12 and the anchor plate 16 in the holding end position. Alternatively, it would be possible to leave a distance between the core 26 and the armature 14 in the holding end position by the armature plate 16 abuts the yoke 12 before the armature 14 reaches the core 26.

If now one of the sliding cams on a camshaft to be actuated, the plunger 6 must be moved to an extended state. For this purpose, a magnetic field is generated by the electromagnetic circuit 4, which acts counter to the magnetic field 8 of the permanent magnet. This leads to a weakening of the force acting between the armature 14 and the core 26 holding force until finally the spring force is greater than the holding force, whereby the armature 14 is released from the core 26. It follows under the action of the spring force, a movement of the armature 14 and thus the plunger 6, in which they move from the core 26 in its second extended end position. For this purpose, no electromagnetic force is required in this embodiment. In this second end position of the plunger 6 is held by the spring force and a permanent magnetic force generated by one or more additional permanent magnets 45 which are arranged in the region of a support surface 48 of the housing 44 or in the present embodiment shown in FIG 2 in the guide housing part 30, on which the armature plate 16 rests in its extended position, as shown only in Figure 3. These interact with a non-contact sensor 46, by means of which the contact of the armature plate 16 can be seen in a known manner.

The plunger 6 slides in this state with its pointing out of the actuator end in a groove of the sliding cam and moves it to the desired position. These grooves are formed so that at the end of the rotation of the plunger 6 is actively raised by a survey of the groove, so that the plunger 6 and the armature 14 are moved in the direction of the holding end position. In this use of the actuator, the stroke of the groove is made slightly smaller than the stroke This is due to installation tolerances required, otherwise there would be a risk of jamming of the camshaft. However, the existing gap in this position must be bridged in order to hold the armature 14 in its final position, if possible without having to activate the electromagnetic circuit 4. Accordingly, the magnetic force necessary for this purpose should be applied by the permanent magnetic circuit 8. For this purpose, it is necessary to generate permanent magnetic magnetic lines acting in the axial direction already at a distance of about 1 mm between the armature 14 and the core 26.

This purpose is served by the axially extending projection, from which permanent magnetic field lines extend in the direction of armature plate 16, which have a large axially acting component and the armature 16 extending paragraph 34, from which permanent magnetic field lines in the direction of the armature 16th extend. In this case, there is a high magnetic force, in particular in the region of the extension 40, since the permanently magnetic, axially extending field lines are bundled in the thin extension 40. Accordingly, a high attraction force is generated, by means of which the spring force can be overcome already about 1 mm before reaching the end stop. Thus, there is an extremely low power consumption, since a current is only required to trigger the adjustment of the holding end position. In addition, it can be seen that there is no mechanical stress on the permanent magnet 32 because the movement of the armature 14 does not act on the fixed magnet 32.

As an additional measure for bundling the permanent magnetic axially acting field lines is the axially extending portion 34 of the core 26. The entire field lines of the permanent magnet 32 are formed by the narrowing in the direction of the armature 14 of the form Kerns 26 bundled, so that here too high axial magnetic forces between the core 26 and the armature 14 occur.

The actuator shown in Figure 2 differs from that shown in Figure 1 in particular in that two adjusting elements 2a, 2b are arranged side by side in a common housing 44, wherein the first actuator 2a is shown in its second end position and the second actuator 2b in his Holding end position is shown. Furthermore, the core 26 extends over the entire axial length of the bobbin 28, so that the armature plate 16 serves to close the magnetic circuits 4, 8. In this embodiment also extends an extension 40 from the yoke 12 in the direction of the anchor plate 16. In addition, a cylindrical portion 34 of the core 26 extends into the cavity 20 of the armature. The gap 42 is formed in this embodiment between the armature plate 16 and the core 26 in the holding end position, while the armature plate rests against the yoke 12.

Another difference is the arrangement of the spring element in the plunger 6 instead of in the armature 14. The operation is identical to that described above.

From Figure 3, a possibility for the arrangement of the non-contact magnetic sensor 46 is additionally apparent. This is arranged on an axis of symmetry 50 between the two adjusting elements 2a, 2b. This arrangement has the advantage that both adjusting elements 2a, 2b can be monitored via the magnetic sensor 46 or their position can be detected. For holding in the end position here serve four small bar magnets 45 in the guide housing part 30, in the region of the stop of the armature plate 16, wherein it is important to ensure that each closest to the sensor 46 permanent magnet 45a of the first control element 2a opposite polarity to the nearest permanent magnet 45b of the second control element 2b. As a result, due to the output signal of the sensor 46 is a distinction between the two actuators 2a, 2b possible. By this arrangement, four different signals for the four approachable positions of the actuator, so that a clear assignment of the signal to the position of the actuator is possible.

It becomes clear that the described actuator has a low power consumption as well as a high service life due to the low mechanical load of the magnet. A possible release without too large to be applied actuating forces is also ensured as a sufficient tightening force by the permanent magnetic circuit before reaching the holding end position. A holding force and a bearing feedback even with two actuators in a housing is ensured with only one sensor and prevents unwanted loosening. Furthermore, there is good electromagnetic compatibility.

It should be clear that design changes of the described embodiments in the scope of the main claim are conceivable and a use of such an actuator in other areas is possible. For example, it would be possible to create an attractive force for achieving the holding end position by energizing the coil. For this purpose, the current direction in comparison to the release of the actuating element from the holding end position would be reversed. This would lead to a permanent magnetic field amplifying field and thus also support a return of the armature to the starting position. Furthermore, different constructive forms can be developed to reinforce or weaken existing permanent and electromagnetic fields.

Claims

 P A T E N T A N S P R E C H E Actuator for an internal combustion engine with an actuator consisting of: an electromagnetic circuit having a coil, a fixed core, a movable armature and a yoke, a plunger which is actuatable via the electromagnetic circuit and which is connected to the armature, and a permanent magnetic circuit consisting of the yoke, the core, the armature and a permanent magnet which holds the armature in a holding end position in the de-energized state of the electromagnetic circuit, characterized in that the permanent magnet (32) is arranged stationarily within the electromagnetic circuit (4) and means (34, 40) for concentrating axial magnetic field lines are formed on the permanent magnetic circuit (8). Actuator for an internal combustion engine according to claim 1, characterized in that as means for concentrating axial magnetic field lines, the permanent magnet (32) is disposed axially between the core (26) and the yoke (12) and the core (26) and the permanent magnet (32) are radially spaced from the yoke (12). Actuator for an internal combustion engine according to claim 1 or 2, characterized in that the armature (14) has a radially extending armature plate (16). 4. Actuator for an internal combustion engine according to claim 3, characterized in that  the means for concentrating the magnetic field lines are formed by an extension (40) of reduced thickness extending axially in the direction of the armature plate (16) and at least partially radially surrounding the armature plate (16) in the holding end position. 5. Actuator for an internal combustion engine according to one of the preceding claims,  characterized in that  the armature (14) has a cavity (20) in its interior. 6. Actuator for an internal combustion engine according to claim 5,  characterized in that  the means for concentrating the magnetic field lines are formed by a section (34) of the core (26) extending axially in the direction of the armature (14), which in the holding end position projects into the cavity (20) of the armature (14). 7. Actuator for an internal combustion engine according to one of claims 5 or 6,  characterized in that  in the cavity (20) of the armature (14) a spring element (22) is arranged, which abuts against a in the interior of the armature (14) or the plunger (6) formed shoulder (24) and against the core (26). 8. Actuator for an internal combustion engine according to one of the preceding claims,  characterized in that the anchor plate (16) in the holding end position spaced from the yoke (12) is arranged. 9. Actuator for an internal combustion engine according to one of the preceding claims,  characterized in that  the armature (14) in the holding end position spaced from the core (26) is arranged. 10. Actuator for an internal combustion engine according to one of the preceding claims,  characterized in that  the diameter of the permanent magnet (32) is greater than the free diameter in the interior of the coil carrier (28) and the permanent magnet (32) is arranged at the end of the coil (10) facing away from the plunger (6). 11. Actuator for an internal combustion engine according to one of the preceding claims,  characterized in that  in the housing (44) has a bearing surface (48) for the armature plate (16) is formed in its second end position, wherein in the support surface (48) at least one additional permanent magnet (45) is formed. 12. Actuator for an internal combustion engine according to one of the preceding claims,  characterized in that a non-contact sensor (46) is arranged in a housing (44) of the actuator, via which a magnetic field changing with movement of the armature (14) can be detected. 13. Actuator for an internal combustion engine according to one of the preceding claims,  characterized in that  two adjusting elements (2a, 2b) are arranged side by side in the housing (44). 14. Actuator for an internal combustion engine according to claim 12,  characterized in that  on an axis of symmetry (50) of the two adjusting elements (2a, 2b) in the housing (44) of the non-contact sensor (46) is arranged, which is operatively connected to the two adjusting elements (2a, 2b), each control element (2a, 2b) each one additional permanent magnet (45a, 45b) is associated, wherein the two permanent magnets (45a, 45b) opposite polarized with the sensor (46) are operatively connected.