This application is the U.S. National Phase of PCT Application No. PCT/DE2018/100264 filed on Mar. 23, 2018 which claims priority to DE 10 2017 106 350.1 filed on Mar. 24, 2017, the entire disclosures of which are incorporated by reference herein.
This disclosure relates to a valve timing gear of an internal combustion engine having variable-lift gas exchange valves, comprising:
Here each displacement groove axially defines part or all of the outlet area by way of only one groove wall, that on which the actuator pin in engagement with the displacement area positively accelerates the cam piece into the present displacement direction.
As is generally known, a so-called sliding-cam valve gear is a variable-lift gas exchange valve timing gear of an internal combustion engine, the variable lift of which is produced by the axial displacement of a cam piece with cams of different lobe lifts on a rotationally driving carrier shaft. Here the associated gas exchange valve is selectively actuated by one of the cams of a cam group according to the axial position of the cam piece on the carrier shaft. The cam piece is displaced by means of actuator pins, which engage alternately in an axial link of the cam piece with two axially opposed displacement grooves and displace the (rotating) cam piece between the axial positions according to the axial path of the displacement grooves.
The displacement grooves are situated next to the cams, so that the length of the cam piece depends on the width of the cam group, i.e. the number and width of the individual cams, and on the width of the axial link.
DE 10 2004 024 219 A1 of generic type discloses a cam piece having an axial link, which is of relatively narrow construction in that a part of the displacement groove in the outlet area is axially defined by only one groove wall.
The object of the present disclosure is to specify a valve timing gear of the generic type having a cam piece, the overall dimensions of which lengthwise are further reduced, making it suitable even for small internal combustion engines with relatively little overall axial space available for the cam piece.
According to the disclosure this object is achieved in that the width of the displacement grooves in their outlet area is smaller than the diameter of the actuator pins. The further reduction in the overall space taken up by the axial link compared to the prior art cited is therefore achieved in that each displacement groove in the part of the outlet area that is axially open with only one defining groove wall is narrower than the diameter of the actuator pin.
This means, on the one hand, that in the axially open outlet area of the displacement grooves, that groove wall on which the (inactive) cam piece is supported by the actuator pin under negative acceleration, i.e. decelerating in the displacement direction, is partially or completely eliminated. Since any adjoining residual wall thickness of the axial link is also eliminated along with this groove wall, the reduction in the length of the axial link is twice this residual wall thickness. Since, on the other hand, the outlet areas are narrower by a differential amount than the diameter of the actuator pins, there is an additional reduction in the length of the axial link of twice this differential amount.
In this design development, the function of the non-existent groove walls in this area in retarding the cam piece is substantially assumed by an already necessary detent, which locks the cam piece in the respective axial position relative to the carrier shaft and slows it during the process of engagement. As an addition or alternative, the cam piece may be slowed by a camshaft bearing, which serves as stop for the cam piece.
In a development of the disclosure, the cam piece should have two cam groups, which axially adjoin both sides of the (centrally interposed) axial link. Such a cam piece is typical for valve timing gears in which the carrier shaft is supported not between the two inlet or exhaust valves of a cylinder, but between the cylinders of the internal combustion engine.
In addition, the displacement grooves may each have a inlet area preceding the displacement area in the direction of rotation of the cam. In this case the inlet area has a radius of the groove base decreasing in the direction of rotation of the cam, the displacement area has a constant radius of the groove base, and the outlet area has a radius of the groove base increasing in the direction of rotation of the cam. The axial distance of the outlet areas is greater than the axial distance of the inlet areas. In the case of the aforementioned central axial link this diverging axial path of the displacement grooves means that in the outlet areas the actuator pins axially overlap with the cams rotating there. This affords the option of transporting the actuator pin, still extended towards the displacement groove after each displacement operation of the cam piece, back into the actuator by means of the then passing cam lobe.
Further features of the disclosure emerge from the following description and from the figures showing two exemplary embodiments. Unless otherwise stated, the same or functionally equivalent features or components are here provided with the same reference numerals. In the drawings:
The disclosure will be explained with reference to
The displacement of each of the cam pieces 3 on the carrier shaft 2 required for activation of the respective cam 4 or 5 as a function of the operating point is undertaken via an axial link with helical displacement grooves 10 and 11, which run circumferentially on both ends of the cam piece 3. Depending on the current axial position of the cam piece 3, a cylindrical actuator pin 12 or 13 of an actuator (not shown), fixed to the cylinder head, engages in each of the displacement grooves 10 and 11, which run in opposite axial directions corresponding to their opposing displacement directions, according to the direction of the arrow indicated, and displaces the cam piece 3 rotating with the carrier shaft 2 into the other axial position. With a groove base 14 and opposing groove walls 15 and 16, the displacement grooves 10, 11 each have a U-shaped cross section over their entire circumferential extent.
The cam pieces 3 are locked to the carrier shaft 2 in both axial positions. This is achieved by means of a known detent device, not visible here. This is usually in each instance a spring-loaded ball in a transverse bore of the carrier shaft 2, which engages in axial adjacent inside grooves in the cam piece 3.
The first exemplary embodiment of a cam piece 3′ according to the disclosure represented in
The overall space remaining for the axial link between the cam groups axially adjacent thereto on both sides results from the spacing of the currently active cam 4 or 5, identical to the spacing between the inlet or exhaust valves, and the width of the cams 4 and 5. The cam width at the same time is instrumental in determining the axial rise of each displacement groove 10′ and 11′. Since in internal combustion engines with a relatively small cylinder bore the valve spacing is correspondingly small and the cams 4, 5 have a mechanically determined minimum width, the overall space available for an axial link with fully circumferential U-shaped displacement grooves 10, 11 according to
Compared with the known axial link according to
The reduced width w of the axial link compared to known axial links results from the fact the displacement grooves 10′ and 11′, at least in the area of the outlet areas 19, are virtually cut off axially to such a degree that the displacement grooves 10′, 11′ axially define part or all of their outlet areas 19 solely by way of the closest adjacent groove walls 15′ and that there the width s of the displacement grooves 10′, 11′ is smaller than the diameter d of the cylindrical actuator pins 12, 13. In the present exemplary embodiment all of the outlet areas 19 and part of the displacement areas 18, that is to say in the transitional area to the outlet areas 19, are axially defined solely by way of the groove walls 15′. This fact is illustrated in
The axial overlapping of the engaged actuator pins 12, 13 with the cams 4 and 5 is not harmful if the actuator pin 12, 13 is transported out of the rotational area of the cam lobe by the actuator and/or by the groove base 14 radially rising in the direction of rotation of the cam, before a collision with the rotating cams 4, 5. Alternatively a cam collision may even be desirable if the lobe of the rotating cam 4, 5 transports the actuator pin 12 or 13 out of the cam rotational area in a controlled manner, i.e. with a mechanically acceptable load stress.
The partial absence of the groove walls 16′ exercising negative acceleration, i.e. retarding the cam piece 3′ in the current displacement direction is compensated for by the aforementioned detent device, which retards the cam piece 3′ until it engages in its new axial position. Alternatively or in addition to this, the cam piece 3′ may also strike against the adjacent camshaft bearings, if necessary, with hydraulic or mechanical impact damping.
In the figures:
In the inlet area 17 the radius of the groove base 14 decreases in the direction of rotation of the cam indicated, from the high circle radius r-H to the groove base radius r-V, which in the displacement area 18 is constant and smaller than the cam base circle radius r-G. In the outlet area 19 the groove base radius increases from r-V back to the high circle radius r-H.
The relationship r-H>r-G applies, moreover, because the actuator pins 12 and 13 axially overlapping with the cams 4 and 5 respectively in the outlet area 19 must have radial free travel relative to the cams 4 and 5 by the time the relative position of the incipient overlap is reached. The high circle radius r-H is thereby always greater than the cam base circle radius r-G.
The second exemplary embodiment of a cam piece 3″ according to the disclosure similarly represented in
Number | Date | Country | Kind |
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10 2017 106 350.1 | Mar 2017 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/DE2018/100264 | 3/23/2018 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2018/171843 | 9/27/2018 | WO | A |
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Number | Date | Country | |
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20200271025 A1 | Aug 2020 | US |