Mechanically fully variable valve train for a gas exchange valve of an internal combustion engine

Abstract

A fully variable mechanical valve train for a gas exchange valve (12) of an internal combustion engine, comprising a pivot lever (8) and a roller rocker arm (1) for actuating the gas exchange valve (12) and for mechanical valve lift adjustment, characterized in that the roller rocker arm (1) has three rollers (2, 5, 11), wherein a first roller (2) has roller contact with an adjusting shaft (3) and a cam (4) of a valve lash compensating element and a second roller (5) has roller contact with a plate-shaped valve closing element (6) which is mounted in a spring plate (7) of the gas exchange valve (12), and wherein the three rollers (2, 5, 11) of the roller rocker arm (1) are made of hardened steel.wherein the roller rocker arm (1) is not hardened and the second roller (5) of the roller rocker arm (1), which runs on the plate-shaped valve closing element (6), is provided with a sliding or rolling bearing and the hardened first roller (2) is provided with a rolling bearing, wherein the pivoting lever (8) has a working cam on which a third roller (11) of the roller rocker arm (1) acts such that, when the adjusting shaft (3) is rotated, the pivoting lever (8) moves the roller rocker arm (1) in the cam (4) in such a way that the valve stroke (13) of the gas exchange valve (12) is provided to be fully variably adjustable over a larger range.

Description

[0001] The invention relates to a mechanically fully variable valve train for a gas exchange valve of an internal combustion engine according to the preamble of patent claim 1.

[0002] Mechanically fully variable valve trains for reducing fuel consumption are known from the state of the art for use in internal combustion engines. In these valve lift characteristics, the geometry of the guide track, the contour of the adjusting shaft, and the working curve of the rocker arm are used to actuate the two intake valves of a 4-valve engine with different lift curves. The valve lift-opening characteristics of the known mechanically fully variable valve trains, as described in DE 101 40 635 A1, are determined by the shape of the working curve, the shape of the guide track, the contour of the adjusting shaft, and the shape of the camshaft lobe. The lift characteristics are therefore predetermined by the working curve, the lift ratios, and the maximum valve acceleration at full lift. This leads to relatively low valve accelerations during partial lifts and thus to low filling ratios.Since the partial strokes are used at low engine speeds, the maximum acceleration during partial strokes is not utilized by these systems. The working curve, which corresponds to the contour, determines the height and opening time of the opening and closing ramps. Since the length of the opening time of the closing ramp is further shortened or reduced in height by the lever transmission, very high manufacturing accuracy is required, which is associated with high costs. Furthermore, these valve train devices introduce an additional rocker arm which moves in a machine-fixed, circular arc-shaped guide path. The circular arc must have a radius such that when the valve lift is adjusted, the gas exchange valve is not opened in the base circle phase, i.e. when the internal combustion engine is ignited.If the gas exchange valve were to be opened during this phase, the efficiency of the internal combustion engine would be greatly reduced, so that an intermediate lever performs an almost purely rotary movement around an adjustment bar. Furthermore, DE 10 2013 013 913 A1 discloses a valve control for a gas exchange valve of an internal combustion engine, in which reliable valve lift adjustment is ensured up to high engine speeds, with low energy requirements for maintaining and adjusting the valve lift, in that the rocker arm and the cam follower lever have curved control surfaces and the rocker arm rests with a first control surface on a machine-side guide element and with a second control surface on a valve element.Due to the coordinated radii of curvature of the control surfaces of the cam follower lever and the rocker arm, the gas exchange valve is not opened during the compression and working phases of the internal combustion engine when the valve lift is adjusted, while the cam follower lever rests on the circular base circle section of the cam of the camshaft.

[0003] Furthermore, DE 10 2014 013 664 A1 discloses a valve train device for independent, fully variable opening time adjustment of the gas exchange valves of an internal combustion engine, in which a rocker arm is supported on a contour of an adjusting shaft and is guided by a roller through a contour of a camshaft and by a roller in a stationary contour of a guide, so that, in interaction with a contour of the rocker arm, a transverse movement in the z-direction is impressed and a gas exchange valve is opened, so that the opening acceleration of the gas exchange valve increases only in the partial load range. DE 2008 047 480 A1 describes a variable-stroke valve train for a cylinder head of an internal combustion engine, with a pivoting lever that has only one roller element with a pivot point, for support on an eccentric shaft and for support on a guide track of a guide.The pivot lever for stroke adjustment can be pivoted between the support points by a cam of a camshaft against a spring force, and the pivot point can be moved parallel to the guide track by the eccentric shaft for stroke height adjustment. WO 2008 / 050817 A1 also describes a variable-stroke valve train for an internal combustion engine with a pivot lever and a roller, in which forces are introduced into a support element by the rocker arm on the guide and torsion shaft sides. WO 87 / 07323 A1 discloses a variable-stroke valve train for an internal combustion engine with a rocker arm with two rollers for articulated connection to the corresponding other transmission elements.Furthermore, an internal combustion engine which uses an internal combustion engine as a braking means is known from US 7 984 705 B2, in which, as also described in DE 10 2014 013 664 A1, the gas exchange valve is opened via the cam lobes on the base circle.

[0004] Based on this prior art, the invention is based on the object of reducing the costs of mechanically fully variable valve trains, further minimizing friction in mechanically fully variable valve trains and, by simplifying the mechanics, also simplifying the manufacture of a mechanically fully variable valve train, combined with a reduction in the holding torques and the adjustment torques of the actuating shaft.

[0005] This object is achieved according to the invention with a mechanically fully variable valve train for a gas exchange valve of an internal combustion engine in that a roller rocker arm has three rollers, a first roller having contact with an actuating shaft and a link of a valve lash adjuster element and a second roller having contact with a valve closing element which is mounted in a spring plate of a gas exchange valve, a pivoting lever having a working curve on which a third roller of the roller rocker arm acts in such a way that when a valve stroke is adjusted, the gas exchange valve opens in a fully variable manner and when the actuating shaft rotates, the roller rocker arm is simultaneously moved in the link and thus adjusts the valve stroke of the gas exchange valve in a fully variable manner.

[0006] The fact that in this design of the mechanically fully variable valve train, the three rollers of the roller rocker arm are made primarily of hardened steel, and the roller rocker arm itself does not require hardening, significantly simplifies the manufacturing process. The design according to the invention also has the advantage of reducing gas exchange losses through throttle-free load control, as well as fuel consumption. Furthermore, variable engine braking can be achieved by first reducing the exhaust valve lift of one exhaust valve and closing the second exhaust valve at higher braking torques.

[0007] Due to the second roller of the roller rocker arm, which runs on the valve closing element and is supported by plain or roller bearings, the friction can be further reduced compared to known mechanically fully variable valve trains, since roller rocker arms known from the prior art have to be hardened since they are in contact with the gate and the plate-shaped valve closing element.

[0008] Because the control shaft in the mechanically fully variable valve train according to the invention is in contact with both the gate and the roller rocker arm, the holding torques of the control shaft and, at the same time, the adjustment torques can be reduced. When the pivoting lever is actuated or deflected, the roller rocker arm rotates around the pivot point of the first roller. Since the first roller of the roller rocker arm is mounted by a rolling bearing, friction is also reduced compared to fully variable valve trains.

[0009] It is advantageous that the pivot lever is mounted so that it can rotate around a fixed axis and is deflected several times by cam lobes of a camshaft which are arranged on a base circle.

[0010] The pivoting lever is designed to move the roller rocker arm in the gate when the control shaft rotates, allowing the valve lift of the gas exchange valve to be fully adjustable over a wider range, for example, at least from 0 to 11 mm. The gas exchange valve is opened several times via the cam lobes on the base circle.

[0011] A further advantage of the mechanically fully variable valve train according to the invention is that the exhaust gas temperature is increased by approximately 100°C through internal residual gas recirculation with a second event (a second opening of the gas exchange valve). This allows the catalyst to heat up more quickly during warm-up, protects the exhaust gas recirculation cooler from fouling, and maintains the catalyst temperature during particulate filter regeneration at idle and at low loads. Since the opening of the gas exchange valve on the intake and exhaust sides is detrimental to full load, the opening duration of the second event must be fully variable or at least deactivatable.

[0012] A second event on an intake valve can thus control the in-cylinder flow and adjust it depending on load and engine speed, so that the valve lift in a fully variable valve train can be changed very quickly from combustion cycle to combustion cycle. This allows the internal residual gas control to be increased very quickly during vehicle acceleration, thus reducing NO x - emissions are reduced.

[0013] With a second event on the exhaust side, the residual gas is very effectively recirculated in an engine with throttle-free load control, e.g., a diesel engine. This internal residual gas recirculation allows the NO to be reduced by rapidly changing the opening time of the gas exchange valve during transient operation (vehicle acceleration). x-Raw emissions and AddBlu consumption are reduced. Controlling the residual gas quantity with a second event reduces fuel consumption with optimized opening timing. If the residual gas is only recirculated via an exhaust valve with a second event, there is no increase in the amount of particulate matter.

[0014] A preferred further development is seen in the fact that with this mechanically fully variable valve train the exhaust gas recirculation cooler is protected against sooting and at the same time can be built much smaller, so that the cooling effort is lower and fuel consumption is better.

[0015] The invention is explained in more detail below using an embodiment shown schematically in a drawing.

[0016] It shows: Fig. 1 an embodiment of a mechanically fully variable valve train.

[0017] In the mechanically fully variable valve train for a gas exchange valve of an internal combustion engine according to Fig. 1 with a mechanically adjustable valve lift adjustment, the gas exchange losses can be reduced through throttle-free load control and fuel consumption.

[0018] The mechanically fully variable valve train has a roller rocker arm 1 with multiple rollers. In the exemplary embodiment with three rollers 2, 5, 11, a first roller 2 is in contact with an actuating shaft 3 and a gate 4 of a hydraulic valve lash adjuster. Because the actuating shaft 3 is in contact with the gate 4 and the roller rocker arm 1, the holding torques of the actuating shaft 3 and, at the same time, the adjustment torques can be reduced. A second roller 5 of the roller rocker arm 1 is in contact with a plate-shaped valve closing element 6 of a gas exchange valve 12. The plate-shaped valve closing element 6 is mounted in a spring plate 7 of the valve train.A pivoting lever 8 is mounted for rotation about a fixed axis 9 and has a working curve 10, on which a third roller 11 of the roller rocker arm 1 acts in such a way that when a valve lift 13 is adjusted, the gas exchange valve 12 opens fully variably. When the actuating shaft 3 rotates, the pivoting lever 8 simultaneously moves the roller rocker arm 1 in the gate 4, thus allowing a valve lift 13 of the gas exchange valve 12 to be fully variably adjusted, for example, from 0 to 11 mm or more. The simultaneous contact of the actuating shaft 3 with the gate 4 of the valve closing element 6 and with the roller rocker arm 1 allows the holding torques of the actuating shaft 3 and, at the same time, the adjustment torques to be reduced. The pivot lever 8 is deflected by a camshaft 14, which has, for example, two, three or four cam lobes 15 on the base circle, and the gas exchange valve 12 is opened several times, preferably three times, via the cam lobes 15 on the base circle.The mechanically fully variable valve train according to the invention also allows the exhaust gas temperature to be increased by approximately 100°C through internal residual gas recirculation with a second event. This allows the catalyst to heat up more quickly during warm-up, protects the exhaust gas recirculation cooler from sooting, and maintains the catalyst temperature during particulate filter regeneration at idle and at low loads. Since the opening of the gas exchange valve on the intake and exhaust sides is detrimental to full load, the opening duration of the second event must be fully variable or at least deactivatable. List of reference symbols 1 roller rocker arm 2 first roller of the roller rocker arm 3 Control shaft 4 backdrop 5 second roller of the roller rocker arm 6 plate-shaped valve closing element 7 spring plates 8 swivel levers 9 fixed axis of the pivot lever 10 Working curve of the pivot lever 11 third roller of the roller rocker arm 12 Gas exchange valve 13 Valve lift 14 Camshaft 15 cam elevation

Claims

[1] Mechanically fully variable valve train for a gas exchange valve (12) of an internal combustion engine, with a pivoting lever (8) and a roller rocker arm (1) for actuating the gas exchange valve (12) and for mechanical valve lift adjustment, characterized bythat the roller rocker arm (1) has three rollers (2, 5, 11), wherein a first roller (2) has a rolling contact with an actuating shaft (3) and a link (4) of a valve clearance compensation element and a second roller (5) has a rolling contact with a plate-shaped valve closing element (6) which is mounted in a spring plate (7) of the gas exchange valve (12), and wherein the three rollers (2, 5, 11) of the roller rocker arm (1) are made of hardened steel, wherein the roller rocker arm (1) is not hardened and the second roller (5) of the roller rocker arm (1) running on the plate-shaped valve closing element (6) is provided with sliding or roller bearings and the hardened first roller (2) is provided with roller bearings, wherein the pivot lever (8) has a working curve on which a third roller (11) of the roller rocker arm (1) acts in such a way thatthat the pivoting lever (8) moves the roller rocker arm (1) in the slotted guide (4) when the actuating shaft (3) rotates, so that the valve stroke (13) of the gas exchange valve (12) is fully adjustable over a larger range. [2] Valve train according to claim 1, characterized by that the roller rocker arm (1) has a roller contact with the actuating shaft (3) as well as with the link (4) of the valve clearance compensation element via the roller-bearing hardened roller (2), and thus the friction during the valve stroke movement and the holding torques of the actuating shaft (3) and at the same time the adjustment torques can be reduced.

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