Internal Combustion Engine for a Motor Vehicle, Having a Control Unit for Aligning a Camshaft and Method for Operating Such an Internal Combustion Engine

Abstract

An internal combustion engine for a motor vehicle includes a crankshaft, a camshaft, a cylinder, a piston movably disposed in the cylinder and coupled to the crankshaft for driving the crankshaft, a first gas exchange valve which is assigned to the cylinder, a first valve clearance compensation device, where via the first valve clearance compensation device the first gas exchange valve is displaceable between a first open position and a first closed position by a first cam of the camshaft, and a control unit. The control unit is configured to align the camshaft such that the first valve clearance compensation device is pressure-loaded in the idle state of the crankshaft by a plateau area assigned to the first cam to hold the first gas exchange valve in the first open position.

Claims

1.-6. (canceled)

7. An internal combustion engine for a motor vehicle, comprising: a crankshaft; a camshaft; a cylinder; a piston movably disposed in the cylinder and coupled to the crankshaft for driving the crankshaft; a first gas exchange valve which is assigned to the cylinder; a first valve clearance compensation device, wherein via the first valve clearance compensation device the first gas exchange valve is displaceable between a first open position and a first closed position by a first cam of the camshaft; and a control unit which is configured to align the camshaft, at least during a change of state of the crankshaft from an operating state in which the crankshaft rotates to an idle state in which the crankshaft is stationary, such that the first valve clearance compensation device is pressure-loaded in the idle state by a plateau area assigned to the first cam to hold the first gas exchange valve in the first open position.

8. The internal combustion engine according to claim 7, wherein the control unit is configured to align the camshaft such that the first valve clearance compensation device at least substantially abuts a central section of the plateau area in the idle state.

9. The internal combustion engine according to claim 7 further comprising: a second gas exchange valve which is assigned to the cylinder; and a second valve clearance compensation device, wherein via the second valve clearance compensation device the second gas exchange valve is displaceable between a second open position and a second closed position by a second cam of the camshaft.

10. The internal combustion engine according to claim 9, wherein the second valve clearance compensation device is in stroke-free contact with the second cam while the first valve clearance compensation device is pressure-loaded by the plateau area in the idle state and the first gas exchange valve is held in the first open position.

11. The internal combustion engine according to claim 9, wherein the second gas exchange valve is actuatable by the second cam using the second valve clearance compensation device such that a decompression of the cylinder can be effected.

12. A method for operating the internal combustion engine for a motor vehicle according to claim 7, comprising the step of: aligning the camshaft by the control unit, at least during the change of state of the crankshaft from the operating state in which the crankshaft rotates to the idle state in which the crankshaft is stationary, such that the first valve clearance compensation device is pressure-loaded in the idle state by the plateau area assigned to the first cam to hold the first gas exchange valve in the first open position.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1 is a diagram which shows a valve stroke course of a first gas exchange valve as well as a second gas exchange valve over a crank angle course of a crankshaft of an internal combustion engine, wherein the first gas exchange valve and the second gas exchange vale are assigned to a first cylinder of the internal combustion engine;

[0025] FIG. 2 is a further diagram which shows the respective valve stroke course of the first and second gas exchange valve and a respective mass of air flowing into the first cylinder and air flowing out via the crank angle course of the crankshaft during a charge exchange at a rotational speed of the crankshaft of less than 500 rpm;

[0026] FIG. 3 is a further diagram which shows a speed of the air flowing into the first cylinder and the air flowing out via the crank angle course of the crankshaft during charge exchange at a rotational speed of the crankshaft of less than 500 rpm;

[0027] FIG. 4 is a further diagram which shows the respective valve stroke course of the first and second gas exchange valve and the respective masses of air flowing into the first cylinder and air flowing out via the crank angle course of the crankshaft during the charge exchange at a rotational speed of the crankshaft of greater than or equal to 500 rpm; and

[0028] FIG. 5 is a further diagram which shows the speed of the air flowing into the first cylinder and the air flowing out via the crank angle course of the crankshaft during charge exchange at the rotational speed of the crankshaft of greater than or equal to 500 rpm.

DETAILED DESCRIPTION OF THE DRAWINGS

[0029] FIGS. 1 to 5 serve to illustrate an operation of an internal combustion engine not depicted in more detail here for a motor vehicle also not depicted in more detail here. The internal combustion engine comprises a crankshaft, a camshaft, a first cylinder in which a first piston of the internal combustion engine coupled to the crankshaft for driving the latter is moveably accommodated, a first gas exchange valve which is assigned to the first cylinder, a hydraulic, first valve clearance compensation device via which the first gas exchange valve can be displaced between a first open position and a first closed position by means of a first cam of the camshaft.

[0030] In addition, the internal combustion engine comprises a control unit which is set up to align the camshaft, at least during a change of state of the crankshaft from an operating state in which the crankshaft rotates to a rest state in which the crankshaft is stationary, in such a way that the first valve clearance compensation device is pressure-loaded in the idle state by means of a plateau area 11 assigned to the first cam, and thus the first gas exchange valve is held in the first open position. The first cam is designed as a plateau cam.

[0031] The control unit is set up to align the camshaft in such a way that the first valve clearance compensation device at least substantially abuts a central section 13 of the plateau area 11 in the idle state of the crankshaft.

[0032] In addition, the internal combustion engine comprises a second gas exchange valve, which is assigned to the first cylinder, and a hydraulic, second valve clearance compensation device, via which the second gas exchange valve can be displaced between a second open position and a second closed position by means of a second cam of the camshaft.

[0033] The second valve clearance compensation device is in stroke-free contact with the second cam, while the first valve clearance compensation device is pressure-loaded by means of the plateau area 11 in the idle state, and thus the first gas exchange valve is held in the first open position. The second gas exchange valve can be actuated by means of the second cam using the second valve clearance compensation device in such a way that a decompression of the first cylinder can be effected. The second cam is designed as a decompression cam.

[0034] The internal combustion engine is designed in this case to perform a so-called “direct start” with particularly low effort, i.e., to start the internal combustion engine solely by combustion energy and thus to accelerate the crankshaft from the idle state to the operating state solely by combustion energy. Furthermore, the internal combustion engine is suitable for a conventional start by means of a starter or an electric motor, for example. The internal combustion engine according to the invention is particularly suitable for starting a hybrid motor vehicle without load.

[0035] In order to carry out the start and in particular the direct start, i.e., the starter-free acceleration (acceleration without starter) of the crankshaft of the internal combustion engine from the idle state to the operating state, the crankshaft is shifted from the operating state to the idle state before the direct start, and in doing so, is stopped by means of the control unit in a position (crankshaft position) in relation to the first cam (“plateau cam”) in such a way that a valve actuation (rocker arm, drag lever, cup tappet etc.) is shut down approximately in the center or in a central section 13 of the plateau area 11 and thus in a plateau zone of the plateau area 11, where it results in a constant stroke 10 of the first gas exchange valve. In FIG. 1, this is the case in a crank angle range between approximately 435° KW and 500° KW (crank angle). A corresponding valve stroke course 12 in the combustion operation is plotted as a dashed line in a diagram in FIG. 1, which shows the valve stroke h.sub.V over the crank angle ° KW. The valve stroke course has a corresponding plateau area 11 with its central section 13. The first open position of the first gas exchange valve is substantially between the gas exchange OT (GWOT) at about 360° KW and shortly after the bottom dead centre (BDC) at about 570° KW. In this way, the first gas exchange valve, which is designed as the first inlet valve of the first cylinder, is opened (in the first open position) when the internal combustion engine is shut down (idle state of the crankshaft), and thus compresses the first valve clearance compensation device (first HVA), i.e., in other words pressure-loads it, whereby the first HVA is out of operation. This means that, after the internal combustion engine has been shut down, a valve stroke of the first gas exchange valve is smaller than the stroke 10 by the amount of the compressed first valve clearance compensation device. This does not pose a problem for starting the internal combustion engine in the form of direct starting, since the first inlet valve remains wide open during the intake stroke despite compressed first HVA.

[0036] Furthermore, by shutting down the internal combustion engine in such a way that the first HVA is depressed (pressure-loaded) by the plateau area 11 and thus the first gas exchange valve is held in the first open position, no compression-related torque is introduced via the camshaft into the crank drive and thus the crankshaft, especially as the first gas exchange valve does not act or press on any flank of the first cam via the valve actuation. Overall, any backward or forward swinging of the crankshaft of the internal combustion engine during shutdown can be avoided and a defined position of the camshaft and the crankshaft can be assumed.

[0037] The valve actuation of the first gas exchange valve resulting from the kinematic coupling of the camshaft or the first cam and the first HVA supports the starting (direct start) of the internal combustion engine, i.e., the acceleration of the crankshaft from its idle state at the transition from the plateau area 11 to a falling flank of the first cam, such that the acceleration of the crankshaft can take place with an introduction of a torque via the camshaft to the crankshaft and accordingly the starting of the internal combustion engine can be designed to be particularly low-effort.

[0038] The second gas exchange valve, which is designed as a second inlet valve assigned to the first cylinder, is still closed when the internal combustion engine is shut down, since the second inlet valve is only opened between 570 and 630° KW and closed between 630° KW and 690° KW by means of the second cam designed as a “decompression cam”. As can be seen in FIG. 1 by means of a valve stroke course 14 assigned to the second inlet valve, a second open position can substantially occur between 600° KW and 675° KW. The second open position of the second gas exchange valve only occurs in the first closed position of the first gas exchange valve. The first open position of the first gas exchange valve occurs in the second closed position of the second gas exchange valve.

[0039] The second inlet valve opens for the decompression in the compaction cycle, i.e., when the first piston is located between its bottom dead canter (BDC) at 540° KW and its top ignition dead centre (TDC) at 720° KW, as is also shown in FIG. 1. The hydraulic, second valve clearance compensation device (second HVA) of the second inlet valve is therefore unloaded when the internal combustion engine is switched off and therefore in operation when the internal combustion engine is restarted (direct start), especially since no engine oil has been previously forced out of the hydraulic, second HVA, which allows the decompression of the (compressing) first cylinder to take place during start/restart of the internal combustion engine.

[0040] By way of example, if the internal combustion engine is designed as a 4-cylinder engine having an ignition sequence 1-3-4-2 (first cylinder-third cylinder-fourth cylinder-second cylinder), the decompression cam (second cam) of the cylinder “2” (second cylinder) acts on the second inlet valve of this cylinder “2”, since the ignition distance is 180° KW and thus the plateau area 11 of the first cam (“plateau cam”) for the first inlet valve of the cylinder “1” and the decompression cams (second cam) of the second inlet valve of the cylinder “2” coincide. Thus, the first inlet valve of the cylinder “1” is opened (in the first open position) when the internal combustion engine is switched off by the plateau area 11 of the “plateau cam” and is fired when the internal combustion engine is (directly) started, whereby ignitable fuel-air mixture contained in the first cylinder (cylinder “1”) is ignited, while in cylinder “2” (which is ignited in the fourth position in the ignition sequence and thus the last of the four cylinders to be ignited), the corresponding decompression cam acts on the second inlet valve of the cylinder “2”. However, the negative influence of the compressed, second HVA for this second inlet valve of the cylinder “2” is negligible for the direct start of the internal combustion engine, since there is a residual stroke of this second inlet valve (i.e., there is a decompression effect), and the cylinder “2” has already been at least partially decompressed when the internal combustion engine is switched off.

[0041] If the internal combustion engine is designed as a 6-cylinder engine, for example, this problem does not arise, since in this case, the ignition distance (between the total of 6 cylinders) is 120° KW, and thus the “filling cam” of the first cylinder and the “decompression cam” of the second cylinder coincide.

[0042] After the internal combustion engine has been started, i.e., in other words the camshaft from the idle state into the operating state, the inlet-side valve train is switched over, for example, when the rotational speed of the internal combustion engine is in the range of 1000 rpm. In doing so, the first cam and simultaneously the second cam are switched over to third and fourth cams respectively arranged in parallel to the two cams, resulting in an inlet valve stroke course 16 of the first gas exchange valve and the second gas exchange valve, which is illustrated in FIG. 1 by a solid line.

[0043] An exhaust-side valve train assigned to the first cylinder remains unaffected, which can be seen in an exhaust valve stroke course 18 shown in FIG. 1.

[0044] The inlet-side valve train can be operated by means of a so-called “Camtronic system”, for example, and thus the valve stroke course 12, 14 and/or the inlet valve stroke course 16 can be varied. Different inlet-side cams are provided for the first and second inlet valve in a starting or decompression mode with a plateau cam (with its valve stroke course 12) and a decompression cam (with its valve stroke course 14) and, for example, two identical cams without respective plateau or decompression areas for the normal combustion operation. By way of example, the two third and fourth cams arranged next to a plateau cam and a decompression cam are designed as filling cams and each have the valve stroke course 16.

[0045] FIGS. 2 to 5 show the respective first and second open positions and the corresponding first and second closing positions of the first gas exchange valve and the second gas exchange valve with the respective opening and closing times of the respective inlet valve stroke courses 12 and 14.

[0046] FIGS. 2 to 5 serve to illustrate that the plateau cam in conjunction with the decompression cam can cause changed flow behaviour compared to decompression devices previously known from the prior art.

[0047] On the respective axes of the diagrams shown in FIG. 2 to FIG. 5, in addition to the valve stroke h.sub.v and the crank angle ° KW, the integrated mass flow of fresh air in kg, as well as the speed—expressed by the Mach number Ma—of the gas (air) flowing during charge exchange, are also specified. In the case of previously common strokes of decompression devices, gas exchange valves were opened in each case to such an extent that there was no or only a slight influence on the flow of the charge of the first cylinder exiting the combustion chamber.

[0048] With corresponding decompression strokes by means of the second cam, decompression can be performed at low rotational speeds (less than 500 rpm, see FIG. 2), as expressed by the valve stroke course 14. An integrated mass flow 24 is depicted with a solid line, as generated by the valve stroke course 12 of the plateau cam. The first gas exchange valve is moved from its first closed position to its first open position, after which the mass flow 24 increases from zero to a positive value of zero, different from zero. Subsequently, the first gas exchange valve is moved back into its first closed position. During the first closed position of the first gas exchange valve, the second gas exchange valve is moved from its second closed position to its second open position, after which a mass flow 26 is generated by the valve stroke course 14 of the decompression cam, with a negative value different from zero. Subsequently, the second gas exchange valve is then moved back to its second closed position. As depicted by the dotted line, a negative integrated mass flow 26 exits the cylinder again via the second gas exchange valve. The total mass of fresh air remaining in the cylinder is the sum of the two mass flows 24 and 26 after the open position of the second gas exchange valve in its second closed position. As can be seen in FIG. 3, the valve stroke course 12 of the first gas exchange valve has a speed course 20 of the inflowing fresh air. During decompression (valve stroke course 14) by means of the second cam, the Mach number 1 of the air flowing out of the cylinder is not reached (course 22). At higher rotational speeds (greater than 500 rpm), the decompression effect decreases and compression is carried out in the first cylinder to such an extent that ignition is possible. As can be seen in FIG. 4, the inflowing fresh air (mass flow 24) has a similar course as in FIG. 2. However, the mass flow 26 of the air flowing out of the cylinder (decompression) generated by the valve stroke lift 14 significantly decreases. The fresh air remaining in the cylinder increases, such that a sufficient compression is achieved for a combustion of fuel in the first cylinder, whereby fuel injected into the first cylinder can ignite and combust. As can be seen in FIG. 5, the valve stroke course 12 of the first gas exchange valve has, at higher rotational speeds, a speed profile 20 of inflowing fresh air which is higher than at low rotational speeds (FIG. 3). During decompression (valve stroke course 14) by means of the second cam, the Mach number 1 is exceeded (course 22). In this case, the flow is blocked during decompression due to the super critical speed itself and the mass flow 26 of outflowing fresh air via the second gas exchange valve of the first cylinder decreases with the same valve stroke course 14. The integrated mass flows 24 shown in FIGS. 2 and 4 do not change significantly in the example shown at rotational speeds in the range of 500 rpm.

[0049] The internal combustion engine according to the invention and the method according to the invention ensure that a decompression effect is also present after longer standstill periods of the internal combustion engine.

LIST OF REFERENCE CHARACTERS

[0050] 10 stroke [0051] 11 plateau area [0052] 12 valve stroke course [0053] 13 central section [0054] 14 valve stroke course [0055] 16 inlet valve stroke course [0056] 18 exhaust valve stroke course [0057] 20 speed [0058] 22 speed [0059] 24 mass flow [0060] 26 mass flow