Camshaft adjuster and method for operating a camshaft adjuster

Abstract

A method for operating a camshaft adjuster, which includes an adjusting transmission with an input shaft, an output shaft connected in a non-rotatable manner with a camshaft, and an adjusting shaft, whereby the adjusting shaft is driven by an actuator, characterized by the fact that the actuator drives the adjusting shaft by overcoming a torque that is dependent on its angular position.

Claims

1. A camshaft adjuster, comprising: an adjusting transmission, comprising: an input shaft; a camshaft; and, an output shaft non-rotatably connected to said camshaft; and, an adjusting shaft, wherein an actuator drives said adjusting shaft by overcoming a torque that is dependent on an angular position of said adjusting shaft.

2. The camshaft adjuster as recited in claim 1, wherein said torque transmitted by said actuator to said adjusting shaft fluctuates periodically, whereby a cycle of fluctuations of said torque extends for less than half a revolution of said adjusting shaft.

3. The camshaft adjuster as recited in claim 2, wherein for a full revolution of said adjusting shaft of the adjusting transmission when load-free, said torque acting between said actuator and said adjusting shaft goes through at least two minima and maxima.

4. The camshaft adjuster as recited in claim 1, wherein during an adjustment said torque has an alternating sign and acts in a same direction between said actuator and said adjusting shaft.

5. The camshaft adjuster as recited in claim 1, wherein a difference between a maximum torque acting between said actuator and said adjusting shaft and a minimum torque acting between said actuator and said adjusting shaft corresponds to at least 20% of an average torque acting between said actuator and said adjusting shaft.

6. A camshaft adjuster, comprising: an adjusting transmission, comprising, an input shaft; a camshaft; and, an output shaft non-rotatably connected to said camshaft; an adjusting shaft, wherein a plurality of positions of said output shaft allow said output shaft to be adjustable with a torque that is incremental in a first direction and a second direction; and, an actuator operatively arranged to transfer an angle-dependent variable torque to said adjusting shaft.

7. The camshaft adjuster as recited in claim 6, wherein said adjusting transmission is a shaft transmission.

8. The camshaft adjuster as recited in claim 7, wherein said adjusting transmission further comprises a rolling bearing with an even number of rolling elements.

9. The camshaft adjuster as recited in claim 8, wherein said rolling bearing of said adjusting transmission has a varying geometrical design along a respective circumference.

10. The camshaft adjuster as recited in claim 6, wherein said plurality of positions of said output shaft are locking positions in which said output shaft remains without torque from said actuator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Various embodiments are disclosed, by way of example only, with reference to the accompanying drawings in which corresponding reference symbols indicate corresponding parts, in which:

(2) FIG. 1 is a schematic view of a first example embodiment of a camshaft adjuster with a shaft transmission;

(3) FIG. 2 is a schematic view of a second example embodiment of a camshaft adjuster with a shaft transmission;

(4) FIG. 3 is a front partial view of a rolling bearing for a shaft transmission;

(5) FIG. 4 is an enlarged detail view of the rolling bearing shown in FIG. 3;

(6) FIG. 5 is an example embodiment of a rolling bearing for a shaft transmission of a camshaft adjuster; and,

(7) FIG. 6 is a graph of a torque curve in an adjusting shaft during the activation of a camshaft adjuster.

DETAILED DESCRIPTION

(8) At the outset, it should be appreciated that like drawing numbers on different drawing views identify identical, or functionally similar, structural elements of the disclosure. It is to be understood that the disclosure as claimed is not limited to the disclosed aspects.

(9) Furthermore, it is understood that this disclosure is not limited to the particular methodology, materials and modifications described and as such may, of course, vary. It is also understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to limit the scope of the present disclosure.

(10) Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. It should be understood that any methods, devices or materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure.

(11) Parts principally corresponding to each other or parts with the same effect are marked with the same reference sign in all the figures.

(12) FIGS. 1 and 2 show, greatly simplified, an embodiment of a suitable electrically driven camshaft adjuster 1 for use in an internal combustion machine, particularly in a gasoline spark ignition engine, with regard to its principal function on the state-of-the-art referenced at the outset.

(13) Camshaft adjuster 1 includes adjusting transmission 2 as well as actuator 3, namely an electric motor, whereby in the design examples coupling 4 is inserted between actuator 3 and adjusting transmission 2. Adjusting transmission 2 is designed as a shaft transmission in the design example as per FIG. 1 as well as in the design example as per FIG. 2. In both cases chain sprocket 5 serves as a drive element of camshaft adjuster 1, whereas output shaft 6 of adjusting transmission 2 is firmly connected to a camshaft that is not depicted in the figures. In place of chain sprocket 5, in case of a belt driven camshaft, there could be a belt pulley. Internal input gear 7 is connected to chain sprocket 5, which constitutes input shaft 7 of adjusting transmission 2. Adjusting shaft 8, as a third shaft of adjusting transmission 2, can be driven by actuator 3 over coupling 4. As long as adjusting shaft 8 rotates with the rpm of input shaft 7, output shaft 6 also rotates with this rpm.

(14) The angular relation between the camshaft and the crankshaft of the internal combustion machine in this operating status remains unchanged. An adjustment of the camshaft takes place when actuator 3 drives adjusting shaft 8 with an rpm that is different from the rpm of chain sprocket 5. In each of the embodiments included in FIG. 1 and FIG. 2, adjusting transmission 2 involves a high ratio transmission, so that a change of the angular relation between adjusting shaft 8 and input shaft 7 by a particular amount leads to a change of the angular relation between input shaft 7 and chain sprocket 5 on the one hand and output shaft 6 on the other by a much smaller amount.

(15) Adjusting shaft 8 is meant for the activation of wave generator 9. Wave generator 9 includes rolling bearing 10, which is elliptically shaped (not shown in FIGS. 1 and 2). Here, there is inner ring 11 of rolling bearing 10 that is elliptically shaped, while a relatively thin walled outer ring 12 adjusts itself to the shape of inner ring 11. Balls roll as rolling elements 13 between inner ring 11 and outer ring 12.

(16) In the design of the first embodiment of adjusting transmission 2 according to FIG. 1, spur gear 14 is directly on outer ring 12, which is likewise deformable and has the same width measured in the axial direction as outer ring 12.

(17) The external tooth arrangement of spur gear 14 meshes with the inner tooth arrangement of internal input gear 7, whereby this barely takes up half the width of spur gear 14. The inner tooth arrangement of spur gear 14 and of internal input gear 7, engage into each other only at two places oriented at 180 from each other, in the upper and lower area of adjusting transmission 2. In all remaining angular areas spur gear 14 is lifted from internal input gear 7 because of the elliptical shape of rolling bearing 10.

(18) Similarly, spur gear 14 acts together with internal output gear 15 which is arranged with a small clearance axially near internal input gear 7 and is also toothed on the inside. Due to the difference in the number of teeth of internal input gear 7 and internal output gear 15, internal output gear 15 is slightly staggered in relation to internal input gear 7 after one full revolution of inner ring 11. As an example, the number of teeth of internal input gear 7 differs from those of internal output gear 15 by two. Internal output gear 15 is firmly connected to output shaft 6.

(19) The second embodiment shown in FIG. 2 with regard to the basic kinematics corresponds to the first embodiment shown in FIG. 1, whereby in the second embodiment, in place for spur gear 14 and internal output gear 15, a single pot shaped output gear 16 which is connected to output shaft 6 is provided. Output gear 16 has outer tooth arrangement that meshes with the inner tooth arrangement of internal input gear 7, the number of teeth of which differs slightly from the number of teeth of the inner tooth arrangement of internal input gear 7, for instance by two. Output gear 16, at least in the region of the toothing, is elastic enough to be deformed by wave generator 9.

(20) FIG. 3 shows rolling bearing 10 in different states, which can be used as components of wave generator 9 in both the first and second embodiments. A main direction of loading HR in which a force acts on rolling bearing 10 is symbolized by an arrow pointing in the radial direction. The direction of rotation of inner ring 11 that is driven by actuator 3 is indicated by an arrow pointing in the circumferential direction. In the left arrangement of rolling bearing 10 in FIG. 3, there is a flow of force from internal input gear 7 to inner ring 11 straight through rolling element 13. A deformation of thin walled outer ring 12 which is pressed directly on rolling element 13 through the tooth arrangement of internal input gear 7, is practically not possible in this arrangement.

(21) In the right arrangement of rolling bearing 10 in FIG. 3, inner ring 11 is rotated so much that the force acting in the main direction of loading HR is directed midway between two neighboring rolling elements 13. Because of the thin walled construction of outer ring 12, it is deformed in the relevant region, as indicated in FIG. 4 by a dashed line. The loading zone of outer ring 12 in which the deformation is intended is marked BZ. The deflection of outer ring 12 in loading zone BZ, as long as this lies between two rolling elements 13, creates a locking effect of adjusting transmission 2. Since output shaft 6 of the camshaft adjuster rotates several times slower than adjusting shaft 8 and adjusting shaft 8 can already take up multiple locking positions, namely a number corresponding to the number of rolling elements 13, output shaft 6 can be locked extremely fine.

(22) FIG. 5 is an example embodiment of rolling bearing 10 of adjusting transmission 2 which can also be used in both the first and second embodiment of the camshaft adjuster 1. Hereby, a locking effect of rolling bearing 10 is created by a non-round design of inner ring 11. Inner ring 11 has a number of flat spots 17 on its circumference equal to the number corresponding to rolling elements 13, on which the surface of inner ring 11, based on the basic cylindrical form, is recessed by depth t. Depth t is between 0.2% and 20% of the rolling element diameter marked as dk. Furthermore in FIG. 5, cage 18 meant as a guide for rolling element 13 can be seen. In an example embodiment rolling elements 13 are balls. Alternatively, needles or cylindrical rollers can be used as rolling elements for the rolling bearings.

(23) FIG. 6 is a graph indicating the progression of the torque acting in adjusting shaft 8 during the activation of camshaft adjuster 1. The torque graph of FIG. 6 applies to the embodiments of rolling bearing 10 shown in FIGS. 3 and 4 as well as to the embodiment shown in FIG. 5. Depicted is the dependence of the torque, referred to as acting torque ME acting in adjusting shaft 8, on its angular position, whereby angle marked as in the diagram in FIG. 6 covers several cycles of fluctuating torque. As in FIG. 6, activating torque MB progresses approximately sinusoidal; a mean activating torque is designated MB_av, a minimal activating torque MB_min and a maximal activating torque MB_max. The minima of the curve plotted in FIG. 6 correspond to the depicted status of rolling bearing 10 shown in FIG. 4. Output shaft 6 as well as input shaft 7, are in a preferential position in which they can be held with minimal expenditure of energy by actuator 3.

(24) In general, the co-relation between torque MB acting on input shaft 7 and output torque designated MA acting on output shaft 6 can be described as follows:
MB()=MA/(i_BAeta())
where i_BA is designated as the transmission ratio of adjusting transmission 2 and transmission factor eta which is dependent on angle . The angle dependent fluctuation of transmission factor eta reflects in the oscillating curve depicted in FIG. 5. For a transmission whose transmission properties are not dependent on the angular position of the input and output shafts, it would be appropriate to replace eta () with an efficiency factor that is not dependent on the angle. In the case of adjusting transmission 2 of camshaft adjuster 1, the mean value of transmission factor eta averaged over all angles is greater than 0.5. Adjusting transmission 2 must therefore not be classified as a self-locking transmission.

(25) If the curve, plotted as a function of angle of adjusting shaft 8, describing an approximately harmonic oscillation, which specifies activating torque MB required for rotating adjusting shaft 8 in deviation from FIG. 6 into the negative region, then this indicates that adjusting shaft 8 is drawn automatically into the preferential positions, whereby the average activating torque MB_av is positive also in this case. An energization of actuator 3 in this arrangement is only required for adjusting output shaft 6 connected to the camshaft, from one locking point into another. The number of locking points or preferential positions results from the number of revolutions required for adjusting output shaft 6 from one end-stop to a second end-stop, multiplied by the number of rolling elements 13 of rolling bearing 10.

(26) If the transmission ratio i_BA is, for example, 90 and the rotation angle between the end-stops of output shaft 6 is exactly 60, i.e. one sixth of a full revolution, then adjusting shaft 8 must be rotated by 90/6=15 rotations to go from one end-stop to the second end-stop. If rolling bearing 10 of wave generator 9, as drawn in FIG. 3, has eighteen rolling elements 13, whereby between two neighboring rolling elements 13 there is always a preferential position of adjusting shaft 8, then there are during the 15 revolutions in all 1518 =270 preferential positions that distribute themselves uniformly over the said 60 wide adjusting region of output shaft 6.

(27) It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.

REFERENCE NUMBERS LIST

(28) BZ Load zone dk Rolling element diameter eta Transmission factor HR Main direction of loading i_BA Transmission ratio MA Output torque MB Activating torque, torque MB_av Average activating torque MB_min Minimum activating torque MB_max Maximum activating torque t Depth Angle 1 Camshaft adjuster 2 Adjusting transmission 3 Actuator 4 Coupling 5 Chain sprocket 6 Output shaft 7 Input shaft, internal input gear 8 Adjusting shaft 9 Wave generator 10 Rolling bearing 11 Inner ring 12 Outer ring 13 Rolling element 14 Spur gear 15 Internal output gear 16 Output gear 17 Flat spot 18 Cage