Gear device, camshaft adjuster having the gear device, and internal combustion engine

Abstract

The invention relates to a gear device for a motor vehicle, as is used, for example, for adjusting a camshaft in a combustion engine in order to influence the phase angle between crankshaft and camshaft. Such gear devices have to be constructed compactly and also have to have high resistance to wear, in particular upon reaching end stops during adjustment of the phase angle. For this purpose, the gear device has hydraulic end stop damping by the drive unit and the output unit having communicating cavities.

Claims

1. A gear device for an electric camshaft adjuster, the gear device comprising: a drive unit, an output unit disposed radially inside of the drive unit, an electric adjustment unit configured to adjust a phase position of the output unit in relation to the drive unit, a rotary plain bearing defined by an inner peripheral surface of the drive unit and an outer peripheral surface of the output unit, a first projection and a second projection arranged on the drive unit so as to extend radially inward, a third projection arranged on the output unit so as to extend radially outward between the first projection and the second projection, a first cavity defined by the drive unit and the output unit between the first projection and the third projection, a second cavity defined by the drive unit and the output unit between the second projection and the third projection, and an overflow path connecting the first cavity to the second cavity, wherein the overflow path is formed on the drive unit between the first projection and the second projection, or the overflow path extends across the third projection, wherein the output unit is configured to rotate in relation to the drive unit between (i) a first end stop phase position in which the third projection contacts the first projection in a first rotational direction, and (ii) a second end stop phase position in a second rotational direction, and wherein the overflow path is configured to enable hydraulic fluid to flow from the first cavity to the second cavity so as to dampen an impact between the drive unit and the output unit when the electric adjustment unit adjusts the phase position to the first end stop phase position.

2. The gear device according to claim 1, wherein a cross-sectional area of the overflow path is narrowed when the first end stop phase position is reached.

3. The gear device according to claim 2, wherein the cross-sectional area of the overflow path is narrowed via one of the inner or outer peripheral surfaces.

4. The gear device according to claim 1, wherein the overflow path is closed before the first end stop phase position is reached.

5. The gear device according to claim 1, wherein a cross-sectional area of a first end of the overflow path is different from a cross-sectional area of a second end of the overflow path.

6. The gear device according to claim 1, wherein the overflow path is formed via a sintering process.

7. The gear device according to claim 1, further comprising one or more sealing elements configured to seal the first and second cavities.

8. An internal combustion engine comprising the gear device for the electric camshaft adjuster according to claim 1, wherein the hydraulic fluid is engine oil of the internal combustion engine.

9. The gear device according to claim 1, wherein the gear device is a strain wave gear.

10. The gear device according to claim 9, wherein the drive unit is a ring gear.

11. An electric camshaft adjuster, comprising: a strain wave gear device including: a ring gear, an output unit disposed radially inside of the ring gear, an electric adjustment unit configured to adjust a rotary position of the output unit relative to the ring gear, a rotary plain bearing defined by an inner peripheral surface of the ring gear and an outer peripheral surface of the output unit, a first projection and a second projection arranged on the ring gear so as to extend radially inward, a third projection arranged on the output unit so as to extend radially outward between the first projection and the second projection, a first cavity defined by the ring gear and the output unit between the first projection and the third projection, a second cavity defined by the ring gear and the output unit between the second projection and the third projection, and a depression defining an overflow path formed on the ring gear between the first projection and the second projection so as to connect the first cavity to the second cavity, wherein the output unit is configured to rotate in relation to the ring gear between (i) a first end stop phase position in which the third projection contacts the first projection in a first rotational direction, and (ii) a second end stop phase position in a second rotational direction, and wherein the depression is configured to enable a flow of fluid from the first cavity to the second cavity so as to dampen an impact between the ring gear and the output unit when the electric adjustment unit adjusts the phase position to the first end stop phase position.

12. The electric camshaft adjuster according to claim 11, wherein the depression extends circumferentially on the ring gear.

13. The electric camshaft adjuster according to claim 11, wherein the overflow path is closed before the first end stop phase position is reached by the third projection.

14. The electric camshaft adjuster according to claim 11, wherein the depression is formed via a sintering process of the ring gear.

15. The electric camshaft adjuster according to claim 11, wherein the depression is formed on an axial surface of the ring gear.

16. An electric camshaft adjuster, comprising: a strain wave gear device including: a ring gear, an output unit disposed radially inside of the ring gear, an electric adjustment unit configured to adjust a rotary position of the output unit relative to the ring gear, a rotary plain bearing defined by an inner peripheral surface of the ring gear and an outer peripheral surface of the output unit, a first projection and a second projection arranged on the ring gear so as to extend radially inward, a third projection arranged on the output unit so as to extend radially outward between the first projection and the second projection, a first cavity defined by the ring gear and the output unit between the first projection and the third projection, a second cavity defined by the ring gear and the output unit between the second projection and the third projection, and a depression defining an overflow path extending across the third projection so as to connect the first cavity to the second cavity, wherein the output unit is configured to rotate in relation to the ring gear between (i) a first end stop phase position in which the third projection contacts the first projection in a first rotational direction, and (ii) a second end stop phase position in a second rotational direction, and wherein the depression is configured to enable a flow of fluid from the first cavity to the second cavity so as to dampen an impact between the ring gear and the output unit when the electric adjustment unit adjusts the phase position to the first end stop phase position.

17. The electric camshaft adjuster according to claim 16, wherein the depression is arranged on an axial surface of the output unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The disclosure is explained below using exemplary embodiments. In the figures:

(2) FIG. 1a shows a side view of a schematic representation of a left half of a gear device according to the disclosure,

(3) FIG. 1b shows a detailed view of the gear device from FIG. 1a from a right half of the gear device that is not shown in FIG. 1a,

(4) FIG. 2a shows a side view of a schematic representation of a right half of a gear device according to the disclosure, and

(5) FIG. 2b shows a detailed view of the gear device from FIG. 2a.

DETAILED DESCRIPTION

(6) A strain wave gear is designed as a gear device 101 for adjusting a camshaft (not shown) and has a drive unit in the form of a drive wheel 103 and an output unit in the form of an output wheel 105, which are arranged one inside the other with the same axis of rotation.

(7) The drive wheel 103 has an external toothing 104, which serves to accommodate a toothed belt (not shown). The gear device 101 in an internal combustion engine can be driven by means of this toothed belt. For this purpose, the toothed belt is connected to the crankshaft of the internal combustion engine and transmitted in such a way that the drive wheel 103 is driven at half the crankshaft speed.

(8) The output wheel 105 has an internal toothing 106 in which an adjustment unit 107 engages and is thus connected to the output wheel 105. Furthermore, the output wheel 105 is connected in a torque-proof manner to the camshaft of the internal combustion engine, so that the camshaft rotates, depending on the engine speed, together with the gear device 101 at half the crankshaft speed.

(9) In the example shown, the adjustment unit 107 is a strain wave gear, but this is not detailed. The adjustment unit 107 influences a phase adjustment angle 129, which is defined about the common axis of rotation of the drive wheel 103 and the output wheel 105 and describes the rotation of the drive wheel 103 against the output wheel 105 about this axis.

(10) By adjusting the phase adjustment angle 129, the phase angle of the camshaft in relation to the crankshaft can now be adjusted within specified limits while the internal combustion engine is running with the transmission ratio between the crankshaft and the gear device 101 remaining the same and thus also a linearly dependent speed of the camshaft in relation to the crankshaft.

(11) A plain bearing is formed between an inner lateral surface 109 of the drive wheel 103 and an outer lateral surface 111 of the output wheel 105, which enables the output wheel 105 to rotate without issues within the drive wheel 103.

(12) Stop cams 113 are formed within the drive wheel 103 on the inner lateral surface 109 and stop cams 114 are formed in the area of the outer lateral surface 111 of the output wheel 105, which are applied at regular intervals along the respective circumference and thus form a segmentation which interlocks between the drive wheel 103 and the output wheel 105.

(13) The phase adjustment angle 129 is mechanically limited by means of this segmentation by the stop cams 113 and the stop cams 114. The representation shows a left end position of the output wheel 105 within the drive wheel 103. The output wheel 105 can be rotated within the drive wheel 103 through the full phase adjustment angle 129 between two adjacent stop cams 113.

(14) Cavities are formed between the stop cams 113 within the segmentation of the drive wheel 103 and are separated from one another by the stop cams 114 of the output wheel. First cavities 115 and second cavities 117 each form a hydraulic active unit having a stop cam 114, which is filled with the engine oil of the internal combustion engine as the hydraulic medium.

(15) The gear device is sealed laterally against the escape of oil, i.e., from the direction of the side surfaces 123 and 124 and from a side facing away (not shown) by means of further components. These components can be cover discs, for example, or components of the adjustment unit 107. Sealing against the escape of oil then takes place by means of O-rings arranged between these components and the side surfaces 123 and 124.

(16) For the functional description of two configurations below, it should be mentioned that in the operating state shown, the first cavity 115 is enlarged to its full extent and the second cavity 117 is reduced to a size close to zero by reaching the respective end stop between the stop cam 113 and the stop cam 114. At this point, only a minimal oil film remains between the stop cam 113 and the stop cam 114, which cannot be represented.

(17) In a first embodiment, a channel 121 or overflow path is introduced within the stop cam 114 in the output wheel 105. This channel 121 is formed as a depression from a side surface 124 of the output wheel 105 and can therefore be easily produced by means of milling or in a sinter metallurgical process. In the present case, the drive wheel 103 and the output wheel 105 have been produced in such a sinter metallurgical process.

(18) A respective input side 125 and a respective output side 127 of the channels 121 are designed differently in such a way that the channels 121 have a larger cross-section on the input side 125 than on the output side 127.

(19) The input side 125 and the output side 127 are arranged in such a way that a respective first cavity 115 and a respective second cavity 117 can be completely freed of oil through the respective channel 121 when a correspondingly assigned end stop of the output wheel 105 within the drive wheel 103 is reached.

(20) If a phase adjustment between the drive wheel 103 and the output wheel 105 is now carried out by means of the adjustment unit 107, this must take place as uniformly and quickly as possible for smooth engine operation of the internal combustion engine and for a consistently high power output. On the other hand, too rapid an adjustment with the stop cams 114 hitting the stop cams 113 leads to high wear or even breakage of the stop cams 113 or 114 with the destruction of the functionality of the strain wave gear 101.

(21) The function between a first cavity 115 and a second cavity 117 within an active unit is described. Of course, this description can be used for any active unit made up of first cavities 115 and second cavities 117. In total, the functional behavior of the strain wave gear then results from the superimposed function of a plurality of active units.

(22) The oil, which is enclosed in the first cavity 115, prevents rotation of the output wheel 105 relative to the drive wheel 103 by means of the stop cam 114. If a rotation is now initiated by means of the adjustment unit 107, the oil must flow through the channel 121 in the stop cam 114 and experiences increased resistance here. The size of this resistance is influenced by the cross-section of the input side 125, the cross-section of the output side 127 and the cross-section of the channel 121 itself.

(23) If the output wheel 105 now reaches its end stop within the drive gear 103, the rest of the oil that is still present in a cavity 115 or 117 between the stop cam 114 and the stop cam 113 in the thickness direction of the strain wave gear is pressed out of this cavity. As a result of this process, when the end stop is reached, the adjustment process is dampened so that a damage to the strain wave gear 101 is reliably avoided.

(24) In a second (alternative) embodiment of a strain wave gear 101, a channel 222 or overflow path is introduced within the side surface 123 in the drive wheel 103. This channel is formed as a depression from the side surface 123 of the drive wheel 103 and can therefore be easily produced by means of milling or in a sinter metallurgical process. In the present case, the drive wheel 103 and the output wheel 105 have been produced in such a sinter metallurgical process.

(25) A respective input side 226 and a respective output side 228 of the channels 222 are designed differently in such a way that the channels 222 have a larger cross-section on the input side 226 than on the output side 228.

(26) The input side 226 and the output side 228 are arranged in such a way that a respective first cavity 115 and a respective second cavity 117 can be completely freed of oil through the respective channel 222 when a correspondingly associated end stop of the output wheel 105 within the input wheel 103 is reached up to an angle of about 3 in the direction of rotation before reaching the final end stop because the oil can flow freely between the cavities through the channel 222. For the remaining 3, an oil cushion forms in the remaining cavity 117, which additionally dampens the end stop.

(27) If a phase adjustment between the drive wheel 103 and the output wheel 105 is now carried out by means of the adjustment unit 107, this must take place as uniformly and quickly as possible for smooth engine operation of the internal combustion engine and for a consistently high power output. On the other hand, too rapid an adjustment with the stop cams 114 hitting the stop cams 113 leads to high wear or even breakage of the stop cams 113 or 114 with the destruction of the functionality of the strain wave gear 101.

(28) Again, the function between a first cavity 115 and a second cavity 117 within an active unit is described. Of course, this description can also be used for the second embodiment for each active unit made up of first cavities 115 and second cavities 117. In total, the functional behavior of the strain wave gear then results from the superimposed function of a plurality of active units.

(29) The oil, which is enclosed in the first cavity 115, prevents rotation of the output wheel 105 relative to the drive wheel 103 by means of the stop cam 114. If a rotation is now initiated by means of the adjustment unit 107, the oil must flow through the channel 222 in the side surface 123 and experiences increased resistance here. The magnitude of this resistance is influenced by the cross-section of the input side 226, the cross-section of the output side 228 and the cross-section of the channel 222 itself.

(30) If the output wheel 105 now reaches a position of approx. 3 before its mechanical end stop within the drive wheel 103, then the rest of the oil which is still present in the thickness direction of the strain wave gear 101 between the stop cam 113 and the stop cam 114 in a cavity 115 or 117 is not immediately pressed out of this cavity by the position of the input side 226 or the output side 228, depending on the direction of rotation, but remains as a cushion-like residual quantity initially in the corresponding cavity 115, 117. As a result of this process, the adjustment process is dampened before the end stop is reached, which means that damage to the strain wave gear 101 is avoided even more reliably and for more extreme operating states or incorrect activations, and softer adjustment behavior for the camshaft is also achieved.

LIST OF REFERENCE SYMBOLS

(31) 101 Gear device, strain wave gear 103 Drive unit, drive wheel 104 Outer toothing 105 Output unit, output wheel 106 Inner toothing 107 Adjustment unit 109 Inner lateral surface 111 Outer lateral surface 113 First stop element 114 Second stop element 115 First cavity 117 Second cavity 121 Overflow path, channel 123 Side face 124 Side face 125 Input side 127 Output side 129 Phase adjustment angle 222 Overflow path, channel 226 Input side 228 Output side 229 Phase adjustment angle