The invention relates to a valve train of an internal combustion engine with a four-cylinder in-line arrangement and variable-stroke actuation of the gas exchange valves. The valve train comprises a first camshaft having a carrier shaft and precisely two first cam pieces, which are arranged for conjoint rotation thereon and so as to be movable between at least two axial positions and which each actuate the intake or exhaust valves of two adjacent engine cylinders by at least two first groups of adjacent cams having different lobes.
A sliding cam valve train of this kind, in which the gas exchange valves of two adjacent engine cylinders are actuated by a common cam piece, is known from DE 10 2005 006 489 A1 and DE 10 2009 016 902 A1. A prerequisite for the reduction achieved here in the complexity of the camshaft is the adequate size of the common base circle angle of all the cams of a cam piece since only this angular range is available for the shifting thereof in operation. Consequently, in-line four-cylinder engines (R4) having two overhead camshafts (DOHC) and the standard ignition sequence 1-3-4-2, in particular, are suitable for this purpose.
As part of the continued tightening of the emission regulations, there is now also an R4 engine with a sliding cam valve train and cylinder shutdown in production—see Motortechnische Zeitschrift MTZ March 2012: “Der 1,4-L-TSI-Ottomotor mit Zylinderabschaltung” (“The 1.4-l TSI spark-ignition engine with cylinder shutdown”).
It is the object of the invention to specify the variability of the stroke of a valve train of the type noted at the outset with a view to further reducing emissions from internal combustion engines in the various operating modes thereof.
This object is achieved by one or more features of the invention. According to this, the valve train should have a second camshaft, which comprises a carrier shaft and precisely two second cam pieces, which are arranged for conjoint rotation thereon and so as to be movable between at least two axial positions and which each actuate the respective other intake or exhaust valves of just one engine cylinder by at least one second group of adjacent cams having different lobes. In this case, the lobes of simultaneously actuating cams of the first cam groups are supposed to be different and to include a zero stroke and the second cam groups are each supposed to include a cam having a zero stroke in order to stop the intake and exhaust valves of the two engine cylinders, the exhaust and intake valves of which are actuated by the second cam pieces.
As a result, a DOHC sliding cam valve train for an R4 engine is obtained which has just four cam pieces and which, on the one hand, can be operated in the cylinder shutdown mode and the intake or exhaust valves of which, for the engine cylinders that cannot be shut down, are operated with two different cam lobes.
Further features of the invention will become apparent from the following description and from the drawings, in which two illustrative embodiments of a valve train according to the invention are shown. Unless otherwise mentioned, features or components which are the same or functionally the same are provided with the same reference numbers here. In the drawings:
The invention will be explained starting with
The intake shaft 8 is made up of the externally toothed carrier shaft 1 and two first cam pieces 10 and 11, which are mounted for conjoint rotation and so as to be axially movable between three positions on the carrier shaft by the internal toothing of said cam pieces. One first cam piece 10 actuates the intake valves of the two engine cylinders I and II, and the other first cam piece 11 actuates the intake valves of the two engine cylinders III and IV. Each of these cam pieces has four first groups, each comprising three adjacent inlet cams having different lobes. The Roman numeral in the designation I-1 to IV-2 of the intake- and exhaust-side cam groups refers to the respective engine cylinder, and the Arabic numeral in said designation refers to the first or second valve of said engine cylinder, each opening with the same lobe. The slotted guide tracks 5 and 6 of axially opposite orientation, into each of which one of two actuating pins engages in order to be able to move the first cam pieces into each of the three axial positions, extend between two adjacent cam groups of each engine cylinder.
The exhaust shaft 9 is made up of the externally toothed carrier shaft 1 and two second cam pieces 12 and 13, which are mounted for conjoint rotation and axial movement between two positions on the carrier shaft by means of the internal toothing of said cam pieces. One cam piece 12 actuates the exhaust valves of engine cylinder I and the other second cam piece 13 actuates the exhaust valves of the engine cylinder IV. Each of these cam pieces has two second cam groups I-1, I-2 and IV-1, IV-2, each having two adjacent exhaust cams with different lobes. Unlike the axially movable cam pieces, the exhaust cam pairs II-1, II-2 and III-1, III-2 of engine cylinders II and III, respectively, are joined firmly to the carrier shaft. The slotted guide tracks 5 and 6 arranged between the two cam groups intersect, and therefore only one actuating pin is required in each case to move these cam pieces into the two axial positions.
The qualitative size of the individual cam lobes and the three corresponding operating modes A to C of the internal combustion engine are listed in the form of a table in
Mode B: starting from mode C, movement of the first and second cam pieces 10, 11 and 12, 13, respectively, by one axial position (to the right into position M in
Mode A: starting from mode B, a further movement of the first cam pieces 10, 11 by one axial position (to the right into position R in
The second valve train according to the invention, as shown in
Alternative embodiments (not shown) of the inventions can be:
stopping engine cylinders II and III instead of I and IV in the cylinder shutdown mode
in the figures, the first camshaft is the exhaust shaft, and the second camshaft is the intake shaft
cam pieces having other known slotted guide tracks
both camshafts have a stroke which is variable in either three stages or just two stages.
1 carrier shaft
2 cam piece
3 end pivot follower
4 gas exchange valve
5 slotted guide track
6 slotted guide track
7 actuating pin
8 first camshaft, intake shaft
8 second camshaft, exhaust shaft
10 first cam piece
11 first cam piece
12 second cam piece
13 second cam piece
Number | Date | Country | Kind |
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10 2013 222 820.1 | Nov 2013 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/DE2014/200617 | 11/4/2014 | WO | 00 |