internal combustion engine

Abstract

internal combustion engine (8) comprising a camshaft (1) which drives at least one inlet valve (5) with which a fluid inlet in a cylinder (9) of the internal combustion engine (8) can be controlled, - wherein the camshaft (1) comprises at least one cam (2), - wherein the cam (2) has at least a valve opening elevation (7) and a control projection (3,4), - wherein the valve opening lift (7) is arranged to open the inlet valve (5) to a maximum stroke, - wherein the inlet valve (5) is open at least during part of a compression movement of a piston (6) of the internal combustion engine (8) associated with the inlet valve (5) in order to decompress the cylinder (9), - wherein the inlet valve (5) can be controlled by the camshaft (1) via a variable valve timing system, and - wherein the variable valve control allows the valve lift of the inlet valve (5) to be adjusted, - wherein by adjusting the valve lift of the intake valve (5) the operation of the internal combustion engine (8) can be switched between depending on a speed of the internal combustion engine (8) ◯ an operation with early closing of the inlet valve (5) at high speeds, and ◯ an operation with late closing of the inlet valve (5) after the bottom dead center of the piston (6) at low speeds, - characterized by the fact that ◯ the operation with early closing of the inlet valve (5) before a bottom dead center of the piston (6) is adjustable by a small valve lift, and ◯ the operation with late closing of the inlet valve (5) is adjustable by a large valve lift.

Description

[0001] The present invention relates to an internal combustion engine. In particular, the internal combustion engine has an adapted camshaft with which the starting behavior of the internal combustion engine is optimized.

[0002] It is known from the prior art to actuate valves for internal combustion engines using camshafts. Variable valve trains are also known from the prior art for influencing valve timing. Document DD 152 832 A5 describes a method and a device for selectively changing the compression ratio in internal combustion engines. The compression ratio is varied via an intake valve control. Document US 2002 / 0148 426 A1 describes a small four-cylinder engine incorporating a compression relief mechanism to facilitate cranking the four-cylinder engine.

[0003] When an internal combustion engine is started from a standstill, all pistons in all cylinders must perform compression work sequentially. This leads, however, to undesirable vibrations and adverse starting behavior.

[0004] Modern internal combustion engines feature variable valve timing (VVT) actuators that adjust the camshaft position. This allows for cylinder decompression through very late intake valve timing. However, this also results in very late locking positions of the VVT ​​actuators. Under all operating conditions, the engine cannot be started in this configuration. Hydraulic VVT actuators can only be used after pressure has built up by the oil pump, meaning adjustment while the engine is stationary is not possible.

[0005] The invention is therefore based on the objective of enabling the starting of an internal combustion engine under all operating conditions.

[0006] The problem is solved by the features of claim 1. The problem is therefore solved in particular by an internal combustion engine with adjustable cylinder decompression. The internal combustion engine comprises a camshaft that drives at least one intake valve, with which a fluid intake in a cylinder can be controlled. The camshaft has at least one cam. The intake valve of the internal combustion engine can be driven by the at least one cam. For this purpose, the cam has a valve opening elevation that opens the intake valve up to a maximum valve lift. At those points where the cam does not have the valve opening elevation, the intake valve remains closed. According to the invention, the cam has at least one control projection. The control projection is, in particular, present in addition to the valve opening elevation. Advantageously, the control projection is ground onto the cam profile.With the valve timing advance, the intake valve remains open at least during part of the compression stroke of the piston associated with that intake valve in the internal combustion engine. This allows for variable decompression of the cylinder. Decompression, in this context, means that there is less air present in the cylinder than the maximum amount that can be drawn in. This reduced air volume within the cylinder decreases the compression work required by the piston during a compression stroke. As a result, the internal combustion engine offers optimal starting performance.

[0007] The internal combustion engine features variable valve timing. The intake valve is actuated by the camshaft via this variable valve timing system. This system allows for adjustment of the intake valve lift. Specifically, the timing advance on the cam is designed such that the intake valve remains open only at large valve lifts, even when the cylinder piston is at least at bottom dead center. At small valve lifts, the intake valve is closed when the piston is at bottom dead center. Thus, the influence of the timing advance can be adjusted by varying the valve lift.

[0008] The internal combustion engine allows for a change in operation between operation with early intake valve closing before the piston reaches bottom dead center and operation with late intake valve closing after the piston reaches bottom dead center. At low engine speeds, the engine can be operated with late-closing intake valves, while at high engine speeds, the operation switches to early-closing intake valves. This is achieved with the internal combustion engine according to the invention by using large valve lifts at low engine speeds, allowing the timing advance to take effect. At high engine speeds, small valve lifts are used, so the effect of the timing advance diminishes or is no longer present.

[0009] The dependent claims contain preferred further developments of the invention.

[0010] Advantageously, the control projection keeps the intake valve open during the compression stroke of the piston associated with the intake valve. Thus, the intake valve remains open at least until the piston, after reaching bottom dead center, begins its compression stroke. This means that the intake valve remains open for at least part of the compression stroke. Due to the valve opening during the compression stroke, decompression occurs. The shape of the control projection allows for adjustment of the opening time and therefore the degree of decompression.

[0011] In a preferred embodiment of the invention, the maximum valve opening lift of the cam is present at a cam angle between 170° and 190°, particularly at 180°. This maximum valve opening lift enables a maximum valve lift. The control projection is located in a region with a cam angle between 200° and 270°. According to the invention, a deviation of up to 5% is permissible for all angle specifications. Thus, the control projection is located in a region on the camshaft where the intake valve undergoes a closing phase. This means that the valve opening lift and the control projection advantageously overlap. It is also advantageously provided that the control projection is located in a region with a cam angle between 90° and 160°. Again, according to the invention, a deviation of up to 5% is permissible.Particularly preferred is a control projection with the aforementioned cam angle, wherein the two control projections are arranged symmetrically around the valve opening elevation.

[0012] Preferably, the valve lift comprises an additional projection. This additional projection causes the intake valve, driven by the camshaft, to open again. This reopening preferably occurs during the intake valve's closing phase. The closing phase is preferably triggered by the shape of the valve opening projection and the valve lift. In particular, the reopening occurs when the piston associated with the intake valve has reached bottom dead center. This reopening therefore enables cylinder decompression.

[0013] Alternatively or additionally, the valve relief includes a thickening. This thickening delays the closing process of the intake valve driven by the camshaft. Again, the closing process preferably occurs due to the shape of the valve opening lift. The delay extends, in particular, beyond the bottom dead center of the piston associated with the intake valve. Thus, the intake valve remains open for part of the piston's compression stroke, thereby enabling cylinder decompression.

[0014] In particular, the influence can be continuously adjusted between maximum at large valve openings and minimum at small valve openings. Preferably, the internal combustion engine features camshaft adjustment, implemented primarily by phase adjusters. This camshaft adjustment allows for varying the point at which the intake valve closes. Thus, even with small valve lifts, the intake valve does not necessarily have to be closed when the piston is at bottom dead center. By varying the valve lift, the degree of decompression can be adjusted.

[0015] In particular, it is continuously possible to switch between operation with early closing of the intake valve before bottom dead center of the piston of the cylinder and operation with late closing of the intake valve after bottom dead center of the piston of the cylinder.

[0016] Finally, the invention relates to a method for controlling an intake valve of an internal combustion engine. It is provided that the intake valve remains open at least during part of the compression stroke of a piston associated with the intake valve within a cylinder. Thus, decompression of the cylinder preferably takes place.

[0017] Preferably, the method is carried out by performing a re-opening movement of the inlet valve during a closing operation. This re-opening movement occurs particularly when the piston associated with the inlet valve has reached bottom dead center. The decompression can be adjusted by the length and / or magnitude of this re-opening movement.

[0018] According to the invention, the method is carried out in such a way that the closing of the inlet valve is delayed. This delay is achieved by keeping the inlet valve open until the piston associated with the inlet valve reaches bottom dead center. Thus, the closing necessarily occurs only during a compression stroke of the piston.

[0019] Further details, features and advantages of the invention will become apparent from the following description and the figures. These show: Fig. 1 a schematic representation of a camshaft of an internal combustion engine according to a first embodiment of the invention, Fig. 2 a schematic representation of a camshaft of an internal combustion engine according to a second embodiment of the invention, Fig. 3 a schematic representation of the internal combustion engine with a camshaft according to the first embodiment, Fig. 4 a schematic representation of the path of a valve opening when an inlet valve is actuated by the camshaft according to the first embodiment, and Fig. 5 a schematic representation of the course of a valve opening when an inlet valve is actuated by the camshaft according to the second embodiment.

[0020] Fig. Figure 1 schematically shows a camshaft 1 of an internal combustion engine 8 (cf. Fig. 3) according to a first embodiment of the invention. The camshaft 1 serves to drive intake valves 5 of the internal combustion engine 8. In Fig. Figure 1 shows a cam 2 of the camshaft 1. The cam 2 comprises a base circle area and a valve opening lift 7, which results in a maximum lift of the intake valve 5. A maximum of the valve opening lift 7, which causes a maximum lift of the intake valve 5, is located at a cam angle 100° between 170° and 190°, in particular at 180°.

[0021] The cam 2 also has an additional projection 3. The additional projection 3 is preferably arranged in a region with a cam angle 100° between 200° and 270°. Thus, the intake valve 5 is reopened by the additional projection 3. This reopening occurs particularly when a piston associated with the intake valve 5 has reached bottom dead center. Therefore, the additional projection enables decompression of a cylinder associated with the cam 2. This decompression is adjustable by the shape and height of the additional projection 3.

[0022] The intake valve 5 is actuated by an adjustable valve train, which can be installed between the intake valve 5 and camshaft 1. The adjustable valve train allows for setting the lift that the intake valve 5 should execute at a given camshaft 1 position. This also allows for adjusting the effect of the additional lift 3. Thus, by reducing the valve lift, the effect of the additional lift 3 can be reduced. In this way, the decompression of cylinder 9 can be adjusted.

[0023] One effect of the supplementary survey 3 is in Fig. 4 shown. Fig. Figure 4 shows a Cartesian coordinate system, where the abscissa represents the cam angle 100° and the ordinate represents the valve lift of the intake valve 5. The coordinate system shows a first curve 10 and a second curve 20. In the first curve 10, a maximum valve lift of one millimeter is achieved. In the second curve 20, a maximum valve lift of three millimeters is achieved. The adjustable valve train allows the valve lift of the intake valve 5 to be set to achieve the curves shown in the first curve 10 or the second curve 20. It is evident that the additional elevation 3 has no effect on the first curve 10 or the second curve 20.

[0024] Furthermore, a third curve 30 and a fourth curve 40 are shown in the coordinate system. The third curve 30 and the fourth curve 40 represent a valve lift profile as known from the prior art. Thus, the third curve 30 would result if a maximum valve lift of six millimeters were set for a camshaft 1 without additional lift 3. The same applies analogously to the fourth curve 40 if a maximum valve lift of ten millimeters were set.

[0025] Furthermore, in Fig. Figure 4 shows a first supplementary lift curve 50 and a second supplementary lift curve 60. The first supplementary lift curve 50 represents the valve lift profile of the intake valve 5 when a maximum valve lift of six millimeters is set using the camshaft 1 according to the first embodiment. Similarly, the second supplementary lift curve 60 shows the valve lift profile at a maximum valve lift of ten millimeters.

[0026] In particular, a comparison of the first additional elevation curve 50 with the corresponding third curve 30, as well as the second additional elevation curve 60 with the corresponding fourth curve 40, reveals the effect of the additional elevation. This results in a renewed opening movement of the intake valve 5, thereby enabling decompression of the cylinder. Specifically, this renewed opening movement of the intake valve 5 occurs during a compression movement of a piston 6 (see figure 5). Fig. 3).

[0027] Fig. Figure 2 schematically shows a camshaft 1 of an internal combustion engine 8 according to a second embodiment of the invention. In contrast to the first embodiment, a thickening 4 is present on the camshaft 1 instead of the additional ridge 3. The thickening 4 causes a delay in the reduction of the thickness of the maximum ridge 7, so that the closing process of an intake valve 5 driven by the camshaft 1 is delayed.

[0028] Analogous to the first embodiment, the maximum of the valve opening elevation 7 is located at a cam angle 100 of 180°. The thickening 4 extends over a range with a cam angle 100 between 200° and 270°.

[0029] One effect of thickening 4 is in Fig. 5 shown. Fig. 5 shows a diagram analogous to Fig. 4. Also, the first turn is 10, the second turn 20, the third turn 30 and the fourth turn 40 as in Fig. Figure 4 shows that, again, the thickening 4 has no effect on the valve lift of the inlet valve 5 in the first curve 10 and in the second curve 20.

[0030] If a maximum valve lift of six millimeters is set for camshaft 1 according to the second embodiment, a first thickening curve 70 results. If, on the other hand, a valve lift of ten millimeters is set, a second thickening curve 80 results. By comparing the first thickening curve 70 with the corresponding third curve 30 and by comparing the second thickening curve 80 with the corresponding fourth curve 40, the effect of the thickening 4 becomes apparent.

[0031] It can thus be seen that the closing process of the inlet valve 5 is not interrupted by a renewed opening movement, as in the first embodiment, but rather delayed. This delayed closing allows for decompression of the cylinder 9. In particular, the delayed closing occurs via the bottom dead center of a piston 6 (cf. Fig. 3) outwards instead.

[0032] Fig. Figure 3 schematically shows an internal combustion engine 8. The internal combustion engine 8 comprises a camshaft 1 according to the first embodiment of the invention. Alternatively, the internal combustion engine 8 can also comprise the camshaft 1 according to the second embodiment.

[0033] The camshaft 1 serves to drive an intake valve 5. The intake valve 5 is driven by a variable valve timing system (not shown). The intake valve 5 controls a fluid intake of the internal combustion engine 8. Thus, the intake valve 5 is an intake valve of the internal combustion engine 8.

[0034] The internal combustion engine 8 further comprises a piston 6, which is guided in a cylinder 9. The piston 6 is movable between top dead center and bottom dead center and, in particular, performs the strokes of a gasoline engine. Due to the additional elevation 3 or the thickening 4 of the cam 2, the intake valve 5 is also open, in particular, when the piston 6 is in a compression stroke. Thus, decompression of the cylinder 9 takes place.

[0035] The degree of decompression in cylinder 9 is adjustable via the variable valve train. Thus, in the Fig. 4 and Fig.Figure 5 shows that the effect of the additional lift 3 or the thickening 4 is no longer present at small valve lifts. Thus, by reducing the lift of the intake valve 5 by means of the variable valve train, the influence of the additional lift 3 or the thickening 4 can be reduced. The internal combustion engine 8 can therefore be used either in operation with early closing of the intake valve 5 before the bottom dead center of the piston 6 or in operation with late closing of the intake valve 5 after the bottom dead center of the piston 6.

[0036] In particular, cylinder 9 decompression occurs when the intake valve 5 remains open after the piston 6 reaches bottom dead center. This also prevents compression of the entire cylinder 9 when starting the internal combustion engine 8. Thus, the internal combustion engine 8 exhibits optimal starting behavior.

[0037] If the lift of the inlet valve 5 is reduced, the inlet valve 5 will close independently of the additional lift 3 and the thickening 4 until the piston 6 reaches its bottom dead center. Decompression is therefore avoided.

[0038] Furthermore, the additional lift 3 or the thickening 4 allows the internal combustion engine 8 to be switched between operation with early closing of the intake valve 5 before the bottom dead center of the piston 6 and operation with late closing of the intake valve 5 after the bottom dead center of the piston 6. The operation with late closing, which is advantageous at low engine speeds, is made possible by adjusting the valve lift at low engine speeds such that the additional lift 3 or the thickening 4 takes effect, thus keeping the intake valve 5 open beyond the bottom dead center of the piston 6. At high engine speeds, the engine can then be switched to operation with early closing.The internal combustion engine 8 thus resolves the long-standing conflict of objectives in the design of the internal combustion engine 8, in particular the valve train, between operation with early closing of the intake valve 5 and late closing of the intake valve 5 by surprisingly simple means. Reference symbol list: 1 camshaft 2 cams 3 Additional survey 4 Thickening 5 valve 6 pistons 7 Valve opening elevation 8 Internal combustion engine 9 cylinders 10 first curve 20 second curve 30 third curve 40 fourth turn 100 cam angle

Claims

[1] Internal combustion engine (8) comprising a camshaft (1) which drives at least one inlet valve (5) with which a fluid inlet in a cylinder (9) of the internal combustion engine (8) can be controlled, - wherein the camshaft (1) comprises at least one cam (2), - wherein the cam (2) has at least a valve opening elevation (7) and a control projection (3,4), - wherein the valve opening lift (7) is arranged to open the inlet valve (5) to a maximum stroke, - wherein the inlet valve (5) is open at least during part of a compression movement of a piston (6) of the internal combustion engine (8) associated with the inlet valve (5) in order to decompress the cylinder (9), - wherein the inlet valve (5) can be controlled by the camshaft (1) via a variable valve timing system, and - wherein the variable valve control allows the valve lift of the inlet valve (5) to be adjusted, - wherein by adjusting the valve lift of the intake valve (5) the operation of the internal combustion engine (8) can be switched between depending on a speed of the internal combustion engine (8) ◯ an operation with early closing of the inlet valve (5) at high speeds, and ◯ an operation with late closing of the inlet valve (5) after the bottom dead center of the piston (6) at low speeds, - characterized by , that ◯ the operation with early closing of the inlet valve (5) before a bottom dead center of the piston (6) is adjustable by a small valve lift, and ◯ the operation with late closing of the inlet valve (5) is adjustable by a large valve lift. [2] Internal combustion engine (8) according to claim 1, characterized by, that the inlet valve (5) is open during a compression movement of the piston (6) associated with the inlet valve (5) due to the control projection (3, 4). [3] Internal combustion engine (8) according to any one of the preceding claims, characterized by , that a maximum of the valve opening elevation (7) is present at a cam angle (100) between 170° and 190° and the control advantage (3, 4) extends over a range with a cam angle (100) between 200° and 270°. [4] Internal combustion engine (8) according to claim 3, characterized by , that a further tax advantage extends over a range with a cam angle (100) between 90° and 160°. [5] Internal combustion engine (8) according to any one of the preceding claims, characterized by, that the control projection (3, 4) has an additional elevation (3), wherein the additional elevation (3) is designed to interrupt a closing process of the inlet valve (5) by a renewed opening movement of the inlet valve (5) driven by the camshaft (1). [6] Internal combustion engine (8) according to any one of the preceding claims, characterized by , that the control projection (3, 4) has a thickening (4), wherein the thickening (4) delays a closing process of the inlet valve (5) driven by the camshaft (1) until beyond a bottom dead center of the piston (6) associated with the inlet valve (5). [7] Internal combustion engine (8) according to any one of the preceding claims, characterized by, that by adjusting the valve lift of the intake valve (5) the operation of the internal combustion engine (8) can be continuously changed between operation with early closing of the intake valve (5) before a bottom dead center of an associated piston (6) and operation with late closing of the intake valve (5) after the bottom dead center of the piston (6). [8] Method for controlling an inlet valve (5) of an internal combustion engine (8), wherein the inlet valve (5) remains open at least during part of a compression movement of a piston (6) associated with the inlet valve (5) within a cylinder (9) of the internal combustion engine (8) in order to decompress the cylinder (9), wherein a valve lift of the inlet valve (5) of the internal combustion engine (8) is set in order to switch between operating modes of the internal combustion engine (8) depending on a rotational speed of the internal combustion engine (8). - early closing at high speeds, and - a late closing at low engine speeds, in which the closing of the inlet valve (5) is delayed until after the bottom dead center of the piston (6), - characterized by , that o a small valve lift is set for early closing, in which the inlet valve (5) is closed before bottom dead center of the piston (6), and a large valve stroke is set for late closing. [9] Method according to claim 8, characterized by , that a closing process of the inlet valve (5) is interrupted by a renewed opening movement of the inlet valve (5).

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