DE19606054C2 - Valve train of an internal combustion engine - Google Patents

Description

The invention relates to a valve train of an internal combustion engine according to the type of Claims 1 and 2.

Such a valve train is known for example from US-A-5,031,583. The Inlet camshaft for actuating the gas exchange valves is in this valve train relative to the shaft driving them relatively rotatable, which in the End positions of the twisting process an early and a late valve opening phase is set. In addition, the valve lift is at least one gas exchange valve variable. For this purpose, this gas exchange valve is operated via a three-part rocker arm acted upon by a cam with two different lift curves becomes. The three individual elements of the rocker arm are via a coupling element can be coupled or uncoupled from one another, as a result of which in the respective switching positions different valve strokes can be carried out. With such a valve train the valve phase and valve lift are adjustable. Specific assignments of the different valve opening phases and / or different valve strokes Load and / or speed of the internal combustion engine are not in this document refer to.

From US-A-5,081,971 a valve train is also known with which in dependence different valve strokes are adjustable from the speed of the internal combustion engine. This valve train is also equipped with a multi-part rocker arm for each Actuation of a gas exchange valve provided with a cam different lifting heights interacts. Notes on control or on This is a concrete circuit diagram depending on the speed and load Documentation not to be removed either.  

In US 4,873,949 a valve train is also described in which the Camshaft for shifting the valve opening phase with a Adjustment mechanism is provided, by which it is opposite the driving shaft is relatively rotatable. By hydraulic action on the front of the Camshaft adjustment mechanism is shifting the Valve opening phase related to early valve opening or late valve opening possible to a neutral position. In addition to the possibility of phase adjustment the valve lift of the gas exchange valve is variable. To do this is between the actuating Cam of the camshaft and the valve plate of the gas exchange valve one Arranged pressure chamber which can be acted upon or filled with hydraulic medium, which the lifting movement generated by the cam on the gas exchange valve transmits. A control valve is connected to this pressure chamber Dependence on load and speed of the internal combustion engine the pressure chamber is relieved, so that the lifting movement generated by the cam is not on the Gas exchange valve is transmitted. Such a valve lift variation after The lost-motion principle is very complex, however, since it is at least one for each cylinder Internal combustion engine requires a valve controlling the pressure in the pressure chamber. In addition, such a valve train builds very high to cover the entire Cam generated stroke or part of the stroke, between cam and valve seat to be able to record.

In contrast, it is the object of the invention to provide a valve train for a To improve the internal combustion engine so that extensive influence on the Control times of the valve train with structurally simple means and if possible small space is possible. In addition to the component and installation space especially the control engineering structure of the valve train as effective and just be set up. Such a valve train should in particular be able to to influence the combustion process of the internal combustion engine so that especially in the partial load range of the internal combustion engine Consumption improvements can be achieved without this resulting in the idle range and  In particular in the full load range, drops in the power or torque curve result.

This object is achieved with the characterizing features of Claims 1 and 2 solved. Characterized in that the stroke transmission between cams and gas exchange valve a stroke transmission element with two couplable Lifting elements is used with different cam cam curves interact and releasably with a sliding coupling element are connectable, a variation of the stroke is possible in a simple manner. It can Such a stroke variation can be made possible with a very low overall height. In addition, such stroke transmission elements in hydraulic Operation can be summarized in a hydraulic circuit that clearly with can be operated with less effort. So especially at Multi-cylinder engines are dispensed with a large number of switching valves, since the Stroke transmission elements of several cylinders via a common control valve are acted upon. Particularly favorable consumption and emission values for one Internal combustion engine with such a valve train arise when in Partial load range within a medium speed range, the intake valves in one early valve opening phase and at the same time the valve strokes and Opening times of the intake valves in a lower load range are small and at Switched over to a predetermined load limit to large valve strokes will.

Such a valve train is particularly space-saving if that Stroke transmission element in the manner of a tappet with two concentric ones Lifting elements is constructed. Such a valve train can be relatively small Expenditures replace a conventional valve train with bucket tappets. Is becoming Adjustment of the valve opening phase selected an adjustment unit between the Inlet camshaft and an exhaust camshaft driving them is arranged, the exhaust camshaft being driven by the crankshaft of the internal combustion engine  a drive is possible, which is compared to phase adjusters based on the principle of the axial adjuster needs less overall length. It also has a Such phase adjustment mechanism advantages in engines with two rows of cylinders those in the camshaft drive due to the lower number of cylinders and thus connected cam position and firing order considerable torque fluctuations or Torque loads occur.

By using such a valve train for at least two intake valves the stroke transmission elements can be shared by a common Control valve are applied, so that a control valve without additional effort Improvement of the combustion process is possible. There are targeted measures possible to generate a swirl or swirl by, for example, the two Intake valves in one or both stroke transmission modes with different Lift curves are operated.

Especially when the two intake valves of a cylinder are in the partial load range low valve strokes are operated and these valve strokes are different, there is a targeted swirl-like swirling, through which the combustion process can be influenced and improved.

With such a valve train can be done with relatively little mechanical effort with simple control engineering effort and also low Cost of control components (hydraulic pressure supply, control valves, etc.) one achieve significant improvements in consumption and emissions in the partial load range without that compared to internal combustion engines without this facility performance or Torque losses in the full load range occur. By appropriate coordination  here, too, there are significant reductions in consumption and emissions possible.

Further advantages and advantageous developments of the invention result from the Subclaims and the description. An embodiment of the invention is in the following description and drawing explained in more detail. The latter shows in

Fig. 1 is a schematic representation of the valve drive of a cylinder of an internal combustion engine,

Fig. 2 shows a section through a constructed as a cup tappet stroke-transmission member,

Fig. 3 shows a section through a tensioning and adjusting device for varying the valve opening phase and

Fig. 4 is a switching map of the valve train, in which the different operating modes of the valve train are plotted as a function of speed and load of the internal combustion engine.

The valve train of a cylinder of an internal combustion engine (not shown in detail) in FIG. 1 has two gas exchange valves 1 , which are each actuated by the cams 3 of a camshaft 4 via a stroke transmission element designed as a tappet 2 . Each plunger 2 is inserted into a bore 5 of a cylinder head 6 and is supported by a compression spring 7 . The valves 2 (gas exchange valves) comprise a valve plate 9 which interacts with a valve seat 8 of the cylinder head 6 and a valve stem 10 which is provided with a valve spring plate 11 . A valve spring 12 , which holds the valve 2 in the closed position, is arranged between the valve spring plate 11 and the cylinder head 6 . The compression spring 7 is also supported on the opposite side on the valve spring plate 11 .

The stroke transmission element (plunger 2 ) shown in FIG. 2 has two concentric cup elements 13 , 14 (lifting elements), each of which cooperate with different cam areas (partial cams) 15 to 17 of the respective cam 3 . The two outer cam areas 15 and 17 of a cam 3 are of identical design, ie they have the same lifting height and phase position. These cam areas 15 and 17 interact with the outer ( 13 ) of the two cup elements ( 13 , 14 ). The central cam region 16 has a lower lifting height than the two outer cam regions 15 and 17 and interacts with the inner cup element 14 . This is together with the valve stem 10 of a gas exchange valve 1 via a known hydraulic valve lash compensation element (HVA) 18 . The two cup elements 13 and 14 are each approximately cup-shaped and each have a bore 21 , 22 in the area of their bottoms 19 , 20 , which are aligned with one another in the working position shown in FIG. 2 and described in more detail below. The bore 21 in the outer cup element 13 is closed on its outer sides by inserts 23 and 24 . The insert 23 delimits a hydraulically pressurizable pressure chamber 25 , which is closed on the other side by a displaceable piston 26 . This piston 26 bears against a coupling element 27 located in the bore 22 , the opposite end face of which bears against a second piston 28 which is acted upon by a compression spring 29 which is supported on the insert 24 . Hydraulic actuation of the pressure chamber 25 via a control valve (not shown) from the oil circuit of the internal combustion engine, which is also not shown in detail, displaces the piston 26 in the working position of the tappet shown in FIG. 2 in the direction of the inner cup element 14 . This movement is counteracted by the action of the compression spring 29 , which acts on the first piston 26 via the second piston 28 and the coupling element 27 . When the pressure chamber 25 is acted upon appropriately, the piston 26 is displaced such that it is located over part of its length within the bore 21 and partly within the bore 22 in the inner cup element. As a result, the coupling element 27 is adjusted so that it is located partly within the bore 22 in the inner cup element 14 and partly within the outer cup element 13 . In this switching position of the coupling element, the two cup elements 13 , 14 are coupled to one another, ie both cup elements have the same stroke, so that the larger stroke of the two outer cam regions 15 and 17 is transmitted to the stem 10 of the gas exchange valve 1 . If the pressure in the pressure chamber 25 is reduced by appropriate control of the control valve so that the piston 26 , the coupling element 27 and the second piston 28 are moved back by the action of the compression spring 29 in their working position shown in FIG. 2, the two cup elements 13 and 14 freely movable against each other. In this switching position, only the lifting movement caused by the central partial cam 16 is transmitted via the inner cup element 13 to the valve stem 10 of the gas exchange valve 1 . The outer cup element 13 follows the stroke of the two outer partial cams 15 and 17 . However, this movement of the outer cup element takes place without influencing the freely movable inner cup element 14 . Such a tappet element is known per se and is described, for example, in patent application DE 195 46 437.

In order to ensure a correct switching course, the coupling element 27 interacts with a locking element 30 , which in this exemplary embodiment is guided in the bottom 20 of the inner cup element 14 . This locking element engages in one of two side by side locking grooves 31 , 32 on the coupling element and only releases its movement when it can be raised so far that it can dip into a groove 33 in the immediate cam area. This ensures that a displacement of the coupling element regardless of the pressurization of the pressure chamber 25 is only possible when the cam 3 is in a defined rotational position. This mechanical triggering ensures that a displacement of the coupling element can only take place if the cam / the partial cams are in cooperation with the tappet in the base circle phase and if a sufficiently large camshaft angle of rotation range is available for the displacement. This can ensure that incorrect switching is avoided and several or all switchable gas exchange valves can be controlled via a common control valve, since the adjustment takes place only as a function of the rotational position of the camshaft or of the respective cam.

The crankshaft 34 of the internal combustion engine shown in FIG. 3 is connected to a toothed belt or a chain 35 with an exhaust camshaft 36 which actuates the exhaust valves. This exhaust camshaft 36 is connected via an endless drive designed as a chain 37 to the camshaft 4 controlling the intake valves. A hydraulic tensioning device 40 is arranged between the load strand 38 and the lost strand 39 of the chain 37 , each of which engages on the inside of the chain 37 . This tensioning device consists of a hollow outer hydraulic piston 41 and an inner, likewise hollow hydraulic piston 42 which is longitudinally guided therein. A compression spring 43 is clamped in the cavity between the two hydraulic pistons. The outer hydraulic piston 41 can be displaced between two end positions by appropriate pressurization via a second control valve, also not shown in detail. Depending on the switching position of the switching valve, not shown, either the end face 44 of the outer piston 41 or the annular surface 45 thereof is pressurized. This displacement of the outer hydraulic piston 41 between the lost drum and the load belt of the chain 37 causes the camshaft 4 to be rotated relative to the exhaust camshaft 36 . If the hydraulic piston 41 is adjusted to its lower end position in the arrangement shown in FIG. 3, this results in an early valve opening phase, and when the hydraulic piston is moved into its upper end position, a later valve opening phase results. The structure and mode of operation of such a phase adjuster is known per se and is described for example in DE 40 06 910 C1.

By combining such a phase adjustment device (hydraulic tensioning device 40 ) according to FIG. 3 with a switchable plunger element according to FIG. 2, four different operating states of the valve train can be switched:
Operating state A: early valve opening phase and small valve lift,
Operating state B: early valve opening phase and large valve lift,
Operating state C: late valve opening phase and small valve lift,
Operating state D: late valve opening phase and large valve lift.

A particularly economical and yet efficient operation of an internal combustion engine is obtained if the internal combustion engine is operated as a function of speed and load in one of the four operating points A to D using the map shown in FIG. 4. The rotational position of the exhaust camshaft 36 is fixed relative to the crankshaft 34 driving it and the intake camshaft 4 is phase-shiftable relative to it in its rotational position. The intake valves 1 actuated by the intake camshaft 4 are actuated via the switchable tappets 2 by the divided cams 3 , each with two different lift curves.

This map shows the different operating states of the internal combustion engine or the valve train depending on speed and load. It has been shown that the greatest potential for reducing consumption when operating such Internal combustion engine in the optimization of partial load consumption through optimized Combustion, reduction of gas exchange losses and lowering the mechanical power loss. By designing the valve stroke accordingly of the inlet valves and by appropriate channel geometry of the inlet channels is one targeted charge movement adjustable. However, it has been shown that at external charge generation through asymmetry of the reduced intake valve lifts (low valve lift) or tumble generation through appropriate channel design individually or in combination, they can also reduce consumption Effects can occur. Significant consumption advantages in the partial load range are at reduced valve lift by reducing the valve opening forces and thus reduced friction fluid pressure reached. The reduction in valve lift leads to a Reduction of the drive torque of the valve train. Because at low speeds the Internal combustion engine mechanical losses up to 50% due to drive losses Valve drive caused, is therefore a particularly in the partial load range to achieve a significant reduction in consumption. However, these benefits are brought about by Generation of a charge movement with reduced and / or different Valve elevations at least partially compensated. Too much valve lift reduction can, despite a significant reduction in valve opening forces due to Charge exchange losses worsen the effective Fuel consumption.

In the part-load range, it has been shown that particularly favorable consumption can be achieved if, in the case of four-valve engines with two intake valves per cylinder, the two intake valves are operated symmetrically in the part-load range with a valve lift reduction to approximately 30% of the full-load valve lift. A further improvement in consumption can be achieved by simultaneously adjusting the intake camshaft early. At the same time, due to the relatively large overlap areas of the intake and exhaust valve opening phases and the associated internal exhaust gas recirculation, significant improvements in NO _x emissions are achieved. The improved mixture preparation by heating due to the increased residual gas content also reduces the raw HC emissions. The internal exhaust gas recirculation also leads to a reduction in gas exchange losses and contributes to an improvement in effective consumption.

At low speeds (n <n1) to almost full load (pm, max) the Internal combustion engine operated with a late valve opening phase and small valve strokes (Operating state C). The middle map area most frequently used in practice with a comparatively low load (low mean pressures pm, pm <pm1) is below a limit speed n2 with early valve opening phase and small valve strokes covered (operating state A). Very high loads (pm <pm1) or high speeds an upper speed limit (n <n2) with a large valve lift and earlier Valve opening phase operated (operating phase B). Above a specified upper Limit speed (n <n3), the engine is independent of the load condition in Operating state D (late valve opening phase and large valve lift) operated.

Claims (9)

1. valve train of an internal combustion engine with at least one gas exchange valve ( 1 ) per cylinder,
with an inlet camshaft ( 4 ) which actuates the gas exchange valves and which can be rotated relatively to shift the valve opening phase in relation to the shaft driving it,
whereby an early and a late valve opening phase is set in the end positions of the twisting process,
with stroke transmission elements ( 2 ) between the cams ( 3 ) of the intake camshaft and the gas exchange valves,
with means ( 13 , 14 , 27 ) for changing the valve stroke of the gas exchange valve, at least one gas exchange valve per cylinder interacting with a cam ( 3 ) with at least two stroke curves ( 15 , 16 , 17 ),
the stroke transmission element of this gas exchange valve has two stroke elements ( 13 , 14 ), each of which cooperates with different cam lift curves, and the stroke elements can be detachably connected to one another by means of a displaceable coupling element ( 27 ),
characterized by
that an early valve opening phase is set as a function of load pm and speed d of the internal combustion engine in the middle speed range,
that in this speed range at low to medium load, the inlet valves interact with the stroke curves for small valve strokes, and
that in this speed range when a predetermined load is exceeded, a switchover to the stroke curves for large valve strokes takes place. 2. Valve train of an internal combustion engine with at least one gas exchange valve ( 1 ) per cylinder, with a camshaft ( 4 ) actuating the gas exchange valves, which can be rotated relatively to shift the valve opening phase relative to the shaft driving it, with stroke transmission elements ( 2 ) between the cams ( 3 ) the camshaft and the gas exchange valves, and with means ( 13 , 14 , 27 ) for changing the valve lift of the gas exchange valve,
at least one gas exchange valve per cylinder cooperating with a cam ( 3 ) with at least two lift curves ( 15 , 16 , 17 ),
the stroke transmission element of this gas exchange valve has two stroke elements ( 13 , 14 ), each of which cooperates with different cam lift curves, and the stroke elements can be detachably connected to one another by means of a displaceable coupling element ( 27 ),
characterized,
that the stroke transmission element ( 2 ) is constructed in the manner of a bucket tappet with two concentric lifting elements ( 13 , 14 ), and
that the inlet camshaft ( 4 ) is connected via a chain drive ( 37 ) to a second camshaft ( 36 ) for actuating the exhaust valves, which in turn is driven by the crankshaft ( 34 ) of the internal combustion engine, and that in this chain drive a tensioning and adjusting device ( 40 ) is arranged. 3. Valve train according to claim 1 or 2, characterized in that at least two intake valves ( 1 ) are provided per cylinder, and that each intake valve cooperates with a cam ( 3 ) with at least two different stroke curves ( 15 , 16 , 17 ). 4. Valve train according to claim 3, characterized in that the cams ( 3 ) have a first stroke curve ( 15 , 17 ) for large valve lift and a second stroke curve ( 16 ) for small valve lift, and that the lift curves for low valve lift of the at least two one Cams assigned to cylinders are different. 5. Valve train according to one of claims 1, 3 or 4, characterized in that the stroke transmission element ( 2 ) is constructed in the manner of a tappet with two concentric lifting elements ( 13 , 14 ). 6. Valve train according to one of claims 1, 3 to 5, characterized in that the inlet camshaft ( 4 ) is connected via a chain drive ( 37 ) to a second camshaft ( 36 ) for actuating the exhaust valves, which in turn is supported by the crankshaft ( 34 ) the internal combustion engine is driven, and that a tensioning and adjusting device ( 40 ) is arranged in this chain drive. 7. Valve train according to one of claims 2 to 6, in which pm depending on the load and speed d of the internal combustion engine, the valve opening phases by rotating the Inlet camshaft are displaceable relative to the shaft driving them and in the End positions of the twisting process an early and a late valve opening phase are set, characterized in that in the medium speed range early valve opening phase is set in this speed range at lower up to medium load the inlet valves with the stroke curves for small valve strokes cooperate, and that in this speed range when a given load a switchover to the stroke curves for large valve strokes takes place. 8. Valve train according to one of the preceding claims, characterized in that if a predetermined upper speed is exceeded, regardless of the load condition the intake valves operated with a large valve lift in the late valve opening phase will. 9. Valve train according to one of the preceding claims, characterized in that below a predetermined lower speed, the intake valves within a Load range of the internal combustion engine that extends close to the maximum load, be operated with low valve strokes in the late valve opening phase.