An actuator device for a sliding cam system, having at least one sliding cam and having an engagement pin which projects out of a housing, wherein the housing can be fastened to a component of a cylinder head or to the cylinder head of an internal combustion engine, and the engagement pin can be placed in contact with at least one groove of the sliding cam system, which groove has at least one ejection ramp, and wherein the engagement pin has, within the housing, a permanent holding magnet and, adjoining the latter, is a controlling stationary coil core which can be magnetized by an electrical coil, and the engagement pin is spring-loaded in the direction of the sliding cam.
A generic actuator of said type is known from DE-102 40 774 A1. Proceeding from the retracted, inner position of the engagement pin, an activation of the engagement pin is realized through energization of the coil, as a result of which a magnetic field is generated which opposes the field of the permanent holding magnet and displaces the latter. The displacement of the field results in a reduced holding force between the permanent holding magnet and the coil core, such that the magnetic field generated by the coil and the force of the spring acting on the engagement pin causes a deployment of the engagement pin, such that the latter engages into the groove of the sliding cam and, as desired, effects a displacement of the sliding cam.
The return movement of the engagement pin into its inner end position is initiated by the ejection ramp, the aim of which is to move the engagement pin away from the sliding cam counter to the force of the spring to such an extent, and with such an acceleration, that the engagement pin, when the coil is deenergized, is held fixed by the permanent holding magnet and the magnetic field thereof on the coil core.
A problem of this generic design is that, depending on the tolerances of the actuator radially with respect to the sliding cam, the movement and acceleration of the engagement pin by the ejection ramp is not sufficient to ensure that the engagement pin reaches the inner position and is stabilized counter to the force of the spring by the permanent holding magnet.
Furthermore, there is the problem that, in the case of sliding cam systems with three or more sliding cams, at least two engagement pins must be provided. Here, a small spacing of the engagement pins is demanded, said spacing being predefined by the spacing of the gas exchange valves, the spacing of the cylinders of the internal combustion engine and the number of sliding cams. As a result of the small spacing, the design of the actuator described in the prior art is no longer capable of moving and holding the engagement pin with sufficient speed and force.
It is therefore an object of the invention to improve an actuator having features described in the introduction in such a way that greater tolerances can be accommodated, and also a desired small spacing of the engagement pins to one another can be ensured.
The object of the invention is achieved in that, at least at that end region of the engagement pin which faces toward the sliding cam, there is installed an actuating device which is active in the region in which the ejection ramp runs out at the high circle, which actuating device generates an auxiliary force on the engagement pin in the direction of the housing.
The actuating device generates, in addition to the force introduced by the ejection ramp, an auxiliary force by means of which the engagement pin reliably reaches the inner end position. As a result, the tolerances arising during the installation of the electrically actuable device have no significant influence on the actuation of the engagement pin, such that the tolerances need not be kept particularly small. Furthermore, the dimensions of the parts installed in the housing, in particular of the permanent holding magnet on the engagement pin, can be kept smaller, such that it is also possible to realize a smaller spacing of the engagement pins to one another.
In one advantageous embodiment of the invention, it is provided that the engagement pin has, on its end facing toward the sliding cam, an opening in which there is displaceably arranged an actuating element which is loaded in the direction of the sliding cam by means of a restoring spring. Here, the position and the travel of the actuating element and the force of the spring are dimensioned such that the actuating element is compressed in particular in the region of the ejection ramp, but lengthens and is supported against the ejection ramp at the end of the latter, as a result of which the restoring spring of the actuating element exerts such a force on the engagement pin that the latter overcomes the remaining stroke and passes reliably into its inner end position.
In a further embodiment of the invention, it is provided that the actuating element on the engagement pin is in the form of a ball which is installed in a bore of the engagement pin with the associated spring, and that the bore has a constriction at its end in order to ensure that the ball is securely held so as to be prevented from falling out. The constriction may be realized by means of calking of the edge of the bore.
In an alternative embodiment of the invention, it is proposed that the engagement pin has, on its end facing toward the sliding cam, and the throw-off ramp has, in the region in which it runs out at the high circle, respectively one permanent magnet and one permanent counter-magnet, and in that said permanent magnets are installed with opposite poles directed toward one another.
By means of said embodiment of the invention, it is achieved that the repelling magnetic forces of the permanent magnet and of the permanent counter-magnet generate, in the end region of the throw-off ramp, such a force that the engagement pin overcomes the remaining stroke generated inter alia in the case of unfavourable tolerances, and reliably moves into its end position.
It is furthermore expedient for the permanent holding magnet on the engagement pin within the housing to be surrounded by a holding cap or a holding plate which is fastened to the engagement pin in order to securely fix the permanent holding magnet to the engagement pin.
For further explanation of the invention, reference is made to the drawings, which illustrate exemplary embodiments of the invention in simplified form and in which:
Here, the ball 15 protrudes so far that, at least in the region of the ejection ramp 4, said ball is pushed into the bore 13 counter to the force of the restoring spring 14 such that the restoring spring stores force, and the restoring spring, at the end of the ejection ramp, relaxes and accelerates the engagement pin 9 with such intensity that the latter reliably passes into the inner end position.
As a result, as can be seen from
In the exemplary embodiments of
As can furthermore be seen from
In
The ends of the engagement pins 9 are designed correspondingly to the embodiments of the invention described above and are equipped with permanent magnets 16 or balls 15.
Number | Date | Country | Kind |
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102010024030.3 | Jun 2010 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2011/056295 | 4/20/2011 | WO | 00 | 12/28/2012 |