RU2773789C2 - Method for braking internal combustion engine - Google Patents

Abstract

FIELD: car industry.

SUBSTANCE: invention can be used in internal combustion engines. A method for braking internal combustion engine (10), in particular a four-stroke internal combustion engine, is proposed. The method includes partial opening of at least one outlet valve (16) of at least one cylinder (12) of internal combustion engine (10) on compression stroke of internal combustion engine (10). The method includes retention of at least one outlet valve (16) in partially open state on working stroke of internal combustion engine (10), following the compression stroke, and on exhaust stroke of internal combustion engine (10), following the working stroke. The method includes closing of at least one partially opened outlet valve (16) in the end of exhaust stroke or on induction stroke of internal combustion engine (10), following the exhaust stroke.

EFFECT: possibility of preferable, in particular in the area of the exhaust stroke, achievement of dynamic change of pressure in a cylinder, and optimization of engine braking effect depending on engine rotations.

13 cl, 2 dwg

Description

The invention relates to a method for braking an internal combustion engine and to a vehicle with a variable valve drive, which makes it possible to implement such a method.

In DE 3922884 A1, a similar method is described, which involves obtaining, in engine braking mode, a decompression that enhances the effect of engine braking, along with closing the retaining valve in the exhaust tract due to the fact that the exhaust valves (inlet valves unchanged) are partially opened due to intervention in the valve timing mechanism of the internal combustion engine in each case on the compression stroke and thus the air drawn into the cylinder during the intake stroke is vented into the exhaust tract with a reduced compression ratio. Additionally, the exhaust valves are fully opened normally on the exhaust stroke, in this case with almost no decompression effect.

Examples of other methods for braking an internal combustion engine are described in DE 102015016 526 A1, DE 102005033 163 A1, DE 19649174 A1 and US 4,592,319 A.

This disclosure of the essence of the invention is, in particular, an additional embodiment of the method described in DE 102013019183 A1 for controlling the effect of engine braking. In particular, DE 102013019183 A1 discloses a method for controlling the braking effect of a valve-controlled internal combustion engine, in particular a four-stroke internal combustion engine for vehicles, in which, in addition to boosting the exhaust gases in the exhaust pipeline, by closing the boost valve, decompression is created due to partial, in particular, irregular opening of at least one exhaust valve per cylinder of an internal combustion engine. At least one exhaust valve opens, overlapping if necessary, on the compression and exhaust strokes. To enhance the engine braking effect, at least one exhaust valve or at least one of the exhaust valves is opened by a predetermined stroke and/or by a value smaller than the normal valve stroke in each case in the TDC (top dead center) region of the pistons between the compression and power strokes, and between the exhaust and intake strokes.

A disadvantage of the method known from DE 102013019183 A1 may be the fact that at low engine speeds, due to gas compression during the exhaust stroke, an undesirable activation of the engine operation can occur when, for example, not all cylinders are operating in the engine braking mode. This activation of the engine can lead to unwanted vibrations in the transmission.

Thus, the object of the present invention is to provide an improved method for braking an internal combustion engine.

The task is achieved by the method and vehicle according to the independent claims. Preferred additional embodiments of the invention are listed in the dependent claims and in the description.

The braking method of an internal combustion engine is particularly suitable for a four-stroke internal combustion engine. The method includes partial opening of at least one exhaust valve of at least one cylinder of the internal combustion engine on the compression stroke of the internal combustion engine. The method involves holding at least one exhaust valve in a partially open state on the next stroke of the internal combustion engine after the compression stroke and on the exhaust stroke of the internal combustion engine following the stroke of the power stroke. The method involves closing at least one partially open exhaust valve at the end (in the TDC region) of the exhaust stroke or on the intake stroke of the internal combustion engine following the exhaust stroke.

The method most advantageously exploits the dynamics of the gas exiting the combustion chambers of an internal combustion engine through the exhaust valves. Partial opening of the exhaust valve on the power and exhaust strokes results in very different cylinder pressure changes on the power and exhaust strokes regardless of engine speed. This makes it possible to set different desired changes in cylinder pressure for different engine speeds and thus engine braking effects. In particular, at low speeds, only compression and decompression in the region of the compression stroke can occur. At higher RPMs, in contrast, the first compression and first decompression may occur on the compression stroke, and the second compression and second decompression on the exhaust stroke. In this way, it is possible to avoid, in particular, the disadvantage mentioned at the outset of the undesirable activation of the engine at low speeds due to compression followed by decompression during the exhaust stroke. This effect is achieved by constantly providing, by partially opening the exhaust valve, the same flow section, however, at low speeds, the gas has more time to exit than at high speeds.

In particular, at least one exhaust valve may be provided upstream of the exhaust path of the internal combustion engine.

In a most preferred further embodiment of the invention, at least one exhaust valve is partially opened so that at some internal combustion engine speed below the internal combustion engine speed limit, compression in the corresponding cylinder on the exhaust stroke is essentially not occurring. In particular, the flow cross-section given by the partial opening of at least one exhaust valve can be set in such a way that at speeds below the limit value, essentially no compression occurs and thus no engine braking effect due to compression in the respective cylinder. on the release stroke. In other words, the flow cross section is sufficient to expel gas through a partially open exhaust valve at a relatively low piston speed at low engine speeds, basically without compression in the cylinder.

In a preferred further embodiment of the invention, at least one exhaust valve is partially opened so that at some internal combustion engine speed above the internal combustion engine speed limit, compression occurs in the corresponding cylinder on the exhaust stroke. In particular, the flow cross section given by the partial opening of at least one exhaust valve can be set in such a way that at revolutions above the limit value, compression occurs and thus an engine braking effect is present in the corresponding cylinder on the exhaust stroke. This allows you to achieve the desired effect of engine braking at high speeds above the limit value. In other words, the flow section has such parameters that at a relatively high piston speed at high engine speeds, it is impossible to push gas through a partially open exhaust valve without increasing the pressure in the cylinder.

In one of the embodiments of the invention, the compression ratio in the corresponding cylinder on the exhaust stroke increases with the increase in the speed of the internal combustion engine above the limit value.

In one of the embodiments of the invention, the speed limit is in the range from 1000 to 1700 rpm, in particular in the range from 1200 to 1500 rpm.

In particular, the rpm limit can be chosen such that the rpm range below the limit is the range in which the aforementioned negative activation of engine operation due to exhaust compression could occur.

In one of the embodiments of the invention, when at least one exhaust valve is partially opened, at least one exhaust valve opens to a height of from 5 to 30% of the maximum valve travel. Alternatively or additionally, at partial opening, at least one outlet valve opens by an amount in the range of 0.5 to 3 mm.

In another embodiment of the invention, the maximum valve travel is in the range of 10 to 16 mm.

In one embodiment of the invention, the partial opening of at least one exhaust valve on the compression stroke begins in the range from 60 to 100° of the crank angle until reaching TDC (top dead center of the stroke of the piston of the corresponding cylinder). Thus, the gas in the combustion chamber is first compressed and only at the end of the compression stroke is pushed into the exhaust tract through the at least one partially open exhaust valve to obtain a decompression effect.

In another embodiment of the invention, the closing of at least one exhaust valve begins at the end of the exhaust stroke or on the intake stroke in the region between TDC (top dead center of the piston stroke of the corresponding cylinder) and 30° of the crankshaft angle after TDC. Thus, the gas that enters during the power stroke from the exhaust tract back into the combustion chamber, depending on the engine speed on the exhaust stroke, is either pushed directly into the exhaust tract through at least one partially open exhaust valve, or at higher speeds, first at least at least partially compressed and only then pushed out through at least one partially open exhaust valve. Thus, at higher revolutions on the exhaust stroke, further compression of the gas in the combustion chamber can occur, followed by decompression of the compressed gas into the exhaust tract, which enhances the effect of engine braking in accordance with the described method.

In particular, the closing of at least one exhaust valve may intersect with the opening of at least one intake valve.

In one exemplary embodiment of the invention, holding the exhaust valve open during the power stroke and the exhaust stroke maintains a constant stroke height of at least one exhaust valve. From a control point of view, this can be realized in a particularly simple way, for example, by means of a constant camshaft lobe height.

In a preferred embodiment of the invention, each cylinder has two exhaust valves and only one of the two exhaust valves is partially opened on the power stroke and held partially open on the exhaust stroke, and closed at the end of the exhaust stroke or intake stroke. Additionally, the second exhaust valve may be closed on the compression stroke, power stroke, exhaust stroke, and intake stroke. This will reduce the stresses on the variable valve actuator associated with the exhaust valves, since, in particular, only one of the exhaust valves of each cylinder is forced to open against the pressure in the combustion chamber on the compression stroke.

In another embodiment of the invention, the method further includes opening at least one intake valve of at least one cylinder on the intake stroke and holding the at least one intake valve closed on the compression stroke, power stroke and exhaust stroke. Thus, in the braking mode of the internal combustion engine, the intake valves can be actuated as in normal operation. Thanks to this, it is not necessary to change the intake valve drive for the engine braking mode. As in normal mode, in engine braking mode, the intake valves are used to direct air from the internal combustion engine's air supply system into the combustion chambers on the intake stroke.

In particular, the method may further include closing a check valve located downstream of at least one exhaust valve on the compression stroke and/or the exhaust stroke. The check valve may preferably be located in the exhaust path.

This invention also relates to a variable valve actuator for an internal combustion engine. The variable valve actuator can in particular be in the form of a position-adjustable cam system. The adjustable valve actuator is designed to implement the method in accordance with the description provided here.

Additionally, the disclosure of this invention relates to a vehicle, in particular, to a utility vehicle (for example, a bus or a truck), with an internal combustion engine equipped with a variable valve actuator as described herein.

It is also possible to apply the method described here to passenger cars, high power engines, off-road vehicles, stationary engines, marine engines, and the like.

The preferred embodiments and features of the invention described above can be combined with each other in any combination. Other details and advantages of this invention are described below with reference to the accompanying drawings. They show:

Fig. 1 Schematic representation of an internal combustion engine cylinder; and

Fig. 2 Valve timing diagram for a four-stroke internal combustion engine.

In FIG. 1 shows a cylinder 12 of an internal combustion engine 10. The internal combustion engine 10 is a four-stroke internal combustion engine, specifically a four-stroke diesel internal combustion engine or a four-stroke gasoline internal combustion engine. Preferably, the internal combustion engine 10 is part of a utility vehicle, such as a truck or bus, and is used to drive the utility vehicle.

Cylinder 12 includes at least one intake valve 14, at least one exhaust valve 16, one combustion chamber 18, and one piston 20.

At least one intake valve 14 connects the combustion chamber 18 to the air supply system of the internal combustion engine 10 to deliver combustion air to the combustion chamber 18. At least one exhaust valve 16 connects the combustion chamber 18 to the exhaust path of the internal combustion engine 10 to remove exhaust gases. For example, each of several cylinders 12 may be provided with two intake valves 14 and two exhaust valves 16.

The at least one exhaust valve 16 may be actuated by a variable valve actuator 22. The variable valve actuator 22 may be in the form of a variable position cam system, for example. The variable position cam system may include at least one cam base with at least two cams. The base for the cams can be installed on the camshaft without the possibility of rotation and with the possibility of displacement along the axis. At least one valve of the gas distribution mechanism is actuated depending on the axial position of the base for the cams relative to different cams of the base. It is also possible that if there are several exhaust valves 16 in each cylinder 12, these exhaust valves 16 of the corresponding cylinder can be actuated differently.

The piston 20 is installed in the cylinder 12 in a known manner with the possibility of reciprocating motion and is connected to the crankshaft 24.

In FIG. 2 is an example of a valve timing diagram showing the actuation of intake valves 14 and exhaust valves 16 of FIG. 1 in the braking mode of the internal combustion engine 10.

Curve A, indicated by a dotted line, shows the stroke of the intake valves 14 as a function of the angle of rotation of the crankshaft 24. Curve B, indicated by a dashed line, shows the stroke of the exhaust valve 16 as a function of the angle of rotation of the crankshaft 24. Curve C, indicated by a solid line, shows the pressure in the combustion chamber 18 in the depending on the angle of rotation of the crankshaft 24 at low engine speeds. The dashed line curve D shows the pressure in the combustion chamber 18 as a function of the angle of rotation of the crankshaft 24 at high engine speeds.

Curves A-D are plotted over a 720° crankshaft rotation (CR) characteristic of a four-stroke engine, with the left axis of the graph representing cylinder pressure in bar and the right axis representing valve travel in mm.

According to curve A, the inlet valves 14 open in the engine braking mode in the same way as in the normal mode on the intake stroke. On the next control cycle, the inlet valves 14 are closed.

In the engine braking mode, the exhaust valves 16 operate differently than in the normal (normal) mode, that is, the exhaust valves 16 are open only on the exhaust stroke. For example, for each cylinder 12 of an internal combustion engine, two exhaust valves 16 may be provided, one of which is held in the fully closed position during engine braking, and the second operates in accordance with curve B.

According to curve B, exhaust valve 16 partially opens in the range of approximately 60 to 100 degrees of rotation KB to top dead center, i.e. before the end of the compression stroke. The exhaust valve 16 is then partially held open for a period of approximately 360° of rotation KB during the power and exhaust strokes. The partially open exhaust valve 16 on the exhaust stroke closes again and remains closed until the next opening on the compression stroke.

According to curve B, the exhaust valve 16 opens only partially. Partial opening can correspond to a valve stroke height in the range of 0.5 to 3 mm. In contrast, the maximum stroke (typical stroke) of the exhaust valve 16 can be from about 10 mm for small internal combustion engines 10 to about 16 mm for very large internal combustion engines 10 used in utility vehicles.

Due to the only partial opening of the exhaust valve 16 according to curve B, it is possible to obtain different pressure dynamics in the combustion chamber 18 at different speeds of the combustion engine 10 .

According to curve C, at low speeds of the internal combustion engine 10, for example up to about 1200 rpm, there is no compression in the combustion chamber 18 on the exhaust stroke. The reason for this is the flow area resulting from the partial opening of the exhaust valve 16. At low speeds of the piston 20, this flow area is sufficient to release the gas in the combustion chamber 18 from the combustion chamber 18 through the partially open exhaust valve 16 without pressurizing. Curve C relates, for example, to the evolution of cylinder pressure at a combustion engine speed of approximately 600 rpm.

On the contrary, according to curve D, at high speeds of the internal combustion engine 10, for example in the range from 1200 to 1500 rpm, compression occurs in the combustion chamber 18 during the exhaust stroke. Due to the increase in engine speed, the speed of the piston 20 also increases and the volume flow through the partially opened exhaust valve 16 also increases. Instead, a second compression occurs before the piston reaches top dead center at the end of the exhaust stroke. During the second compression, the energy is dissipated by the still open exhaust valve 16 and braking power is generated. In particular, the work done in compression brakes the piston 20, resulting in the braking of the internal combustion engine 10 in the engine braking mode. Curve D relates, for example, to the evolution of pressure in a cylinder at an internal combustion engine speed of about 2600 rpm.

Both curves C and D represent the first compression in the combustion chamber 18 on the compression stroke, since the exhaust valve 16 only opens at the end of the compression stroke. As a result of the opening of the exhaust valve 16, the compressed gas is decompressed into the exhaust path, in which, for example, a boost valve is closed at this moment. The compressive work applied by the piston 20, in turn, brakes the internal combustion engine 10. Due to the higher speed of the piston 20 according to curve D, at higher engine speeds, there is more compression in the combustion chamber 18 and thus the braking effect is enhanced compared to the same process at low speeds according to curve C.

During the power stroke, the pressure in the cylinder along curves C and D is low, and due to the backpressure of the exhaust gases in the exhaust tract, air can enter the combustion chamber 18 through the partially open exhaust valve 16.

As a result, at low engine speeds below the limit value, which can be in the range, for example, from 1200 to 1500 rpm, according to curve C, only the gas is compressed in the combustion chamber 18 and the compressed gas is decompressed into the exhaust tract. A single compression-decompression cycle occurs on the compression stroke. At high engine speeds above the limit value on the same curve (curve B) for the same exhaust valve 16 according to curve D, the gas is double compressed in the combustion chamber 18 and the compressed gas is decompressed into the exhaust path through the partially open exhaust valve 16. On the one hand, on the compression stroke, the first compression occurs, followed by decompression. Additionally, on the exhaust stroke, a second compression occurs, followed by decompression.

The transition between curves C and D takes place continuously as the speed of the internal combustion engine 10 increases.

Thus, the invention makes it possible, in the most advantageous manner, to obtain a strong braking effect (curve D) by means of the same valve timing profile for the exhaust valve 16 at high speeds of the internal combustion engine 10 by double compression-decompression. At low speeds, a (small) braking effect is also achieved due to a single compression-decompression (curve C), while the activation of the engine is prevented or at least reduced due to the rejection of the second compression-decompression. Thus, the method automatically adapts to environmental conditions (engine speed), so that additional external control intervention is not required.

The present invention is not limited to the preferred embodiments that have been described above. Moreover, many variations and modifications are possible, which will also use the idea of this invention, and therefore such variations will be included in the scope of legal protection. In particular, this invention claims to protect the subject matter and features of the dependent claims, regardless of reference to the respective claims. In particular, the features of the dependent claims are disclosed independently of all the features of the independent claim 1 and, for example, regardless of the features relating to the partial opening of at least one exhaust valve on the compression stroke, holding at least one exhaust valve in a partially open state on the power stroke and/or exhaust stroke and/or closing of at least one partial open exhaust valve at the end of the exhaust stroke or on the intake stroke according to independent claim 1 of the claims.

Position number list

10 Internal combustion engine

12 Cylinder

14 intake valve

16 Exhaust valve

18 Combustion chamber

20 Piston

22 Variable valve actuator

24 Crankshaft

A Intake valve control curve

B Exhaust valve control curve

C Dynamics of pressure change in the cylinder at low engine speeds

D Cylinder pressure dynamics at high engine speeds

Claims (29)

1. A method for braking an internal combustion engine (10), in particular a four-stroke internal combustion engine, comprising partial opening of at least one exhaust valve (16) of at least one cylinder (12) of the internal combustion engine (10) on the compression stroke of the internal combustion engine (10); holding at least one exhaust valve (16) in a partially open state on the next stroke of the combustion engine (10) after the compression stroke and on the exhaust stroke of the internal combustion engine (10) following the stroke of the stroke; and closing at least one partially open exhaust valve (16) at the end of the exhaust stroke or on the intake stroke of the internal combustion engine (10) following the exhaust stroke; in which at least one exhaust valve (16) is partially opened so that at a speed of the internal combustion engine (10) below the speed limit of the internal combustion engine (10), compression in the corresponding cylinder (12) on the exhaust stroke basically does not occur ; and in which the limit value of revolutions is in the range from 1000 to 1700 rpm, in particular in the range from 1200 to 1500 rpm. 2. The method according to claim 1, in which at least one exhaust valve (16) is partially opened so that at a speed of the internal combustion engine (10) above the limit value of the speed of the internal combustion engine (10), compression occurs in the corresponding cylinder (12) on the exhaust stroke. 3. The method according to claim 2, in which the compression in the corresponding cylinder (12) increases with the increase in the revolutions of the internal combustion engine (10) on the exhaust stroke above the revolution limit value. 4. A method according to any one of the preceding claims, wherein when at least one exhaust valve (16) is partially opened, at least one exhaust valve (16) opens to a height of 5 to 30% of the maximum valve travel; and/or at partial opening, at least one outlet valve (16) opens by 0.5 to 3 mm. 5. The method according to claim 4, wherein the maximum valve travel is in the range of 10 to 16 mm. 6. A method according to any one of the preceding claims, wherein partial opening of at least one exhaust valve (16) on the compression stroke begins in the range from 60 to 100° of the angle of rotation of the crankshaft until TDC is reached. 7. A method according to any one of the preceding claims, wherein closing of at least one exhaust valve (16) at the end of the exhaust stroke or on the intake stroke begins in the range from TDC to 30° of the crankshaft angle after reaching TDC. 8. A method according to any one of the preceding claims, wherein while holding the exhaust valve (16) open during the power stroke and the exhaust stroke, the stroke height of at least one exhaust valve (16) is unchanged. 9. A method according to any one of the preceding claims, wherein each cylinder (12) contains two exhaust valves (16), one of which opens partially on the power stroke and is kept partially open on the exhaust stroke, and closes at the end of the exhaust stroke or on the intake stroke. 10. The method according to claim 9, in which the second exhaust valve (16) is closed on the compression stroke, power stroke, exhaust stroke and intake stroke. 11. The method according to any one of the preceding claims, which further comprises opening at least one intake valve (14) of at least one cylinder (12) on the intake stroke and holding at least one intake valve (14) closed on the compression stroke, power stroke and exhaust stroke. 12. A variable valve actuator (22), in particular a variable position cam system for an internal combustion engine (10), in which the variable valve actuator (22) is configured to implement the method according to any one of the preceding claims. 13. A vehicle, in particular a utility vehicle, with an internal combustion engine (10), including a variable valve drive according to claim 12.

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