DE102011105545B4 - Method for determining a combustion chamber filling of an internal combustion engine of a vehicle and control device for the internal combustion engine - Google Patents

Abstract

Method for determining a combustion chamber charge of an internal combustion engine (401) comprising at least a first cylinder and a second cylinder or three cylinders (105), the first cylinder being in front of the second cylinder in a firing order of the internal combustion engine (401), the method comprising :- Determining a change in an angular velocity (φ̇) of a crankshaft (109) of the internal combustion engine (401) during a compression stroke of the internal combustion engine (401), and- determining the combustion chamber charge (mZyl) as a function of the change in angular velocity (φ̇) during the compression stroke , characterized by, - determining a combustion pressure (202) of the first cylinder, - determining the combustion chamber charge (mZyl) of the second cylinder as a function of the change in angular velocity (φ̇) during the compression stroke of the second cylinder, the determination of the combustion pressure (202) comprising :- detecting a fuel quantity injected into the first cylinder,- detecting an ignition point of the fuel quantity injected into the first cylinder, and- determining a combustion process (202) as a function of the detected ignition point and the detected injected fuel quantity.

Description

The present invention relates to a method for determining a combustion chamber filling of an internal combustion engine and a corresponding control device and a vehicle with an internal combustion engine and the control device.

In order to reduce fuel consumption and emissions from an internal combustion engine, it is desirable to know the states and parameters of the internal combustion engine as precisely as possible, for example in order to optimally set an injection time and an injection quantity of fuel and an ignition process. Various methods for determining parameters, states and variables of an internal combustion engine during operation are therefore known in the prior art.

The DE 195 29 708 C1 relates, for example, to a method and a device for determining a relative compression of an internal combustion engine. The relative compression is determined from a measured alternating component of a current of an electric starter motor with the fuel supply suppressed.

From the DE 39 33 947 C1 a method for determining a combustion pressure in reciprocating piston engines is known. In the method, measurements of accelerations on crankshaft bearings are carried out. The recorded acceleration values can be evaluated for online control, with numerous control variables (filling, mixture, injection and ignition timing, etc.) being derivable from the pressure-proportional acceleration curve.

The DE 10 2004 044 214 A1 relates to a cross connecting rod crank drive. Provided that the crankshaft rotates evenly, heat exchange on the cylinder walls can be determined as a function of the heat transfer value between the working gas and the cylinder walls, the area surrounding the working gases, which depends on the angle of rotation, and the temperature difference between the working gas and the cylinder walls.

The publications are supplemented DE 44 43 517 B4 , DE 102 27 466 B4 , DE 197 53 969 B4 , DE 10 2008 001 376 A1 and the publication by Jeschke J.: "Conception and testing of a cylinder pressure-based engine management system for passenger car diesel engines", Otto von Guericke University Magdeburg, Magdeburg: 2002, dissertation - chap. 8.2.1. called.

Another important parameter of an internal combustion engine is the filling of the combustion chamber. The filling of the combustion chamber can be determined, for example, with an air mass sensor, a so-called hot-film anemometer (HFM). A heated body is used, which gives off energy to the surrounding air. The amount of heat emitted depends on the air flow and can be used as a measured variable. However, the determination via an HFM only measures the inflowing fresh gas mass and, due to its mounting position, usually supplies a signal that is greatly delayed in relation to the actual combustion chamber state. Gas masses from exhaust gas recirculation are also not recorded using the HFM. Furthermore, it is possible to determine the filling of the combustion chamber via an intake manifold pressure sensor, which is closer to the combustion chamber and is therefore more dynamic. With the help of the intake manifold pressure sensor, a combustion chamber filling is determined from the intake manifold pressure, whereby influences from an intervention between the intake manifold and the combustion chamber, such as a fully variable valve train, cannot be taken into account. Furthermore, the combustion chamber charge can be derived from a cylinder pressure sensor mounted in the combustion chamber and thus from the pressure in the combustion chamber. However, at least one expensive cylinder pressure sensor is required for this.

The object of the present invention is therefore to provide a charge determination close to the combustion chamber that is dynamic, i.e. reacts quickly, and takes into account influences outside of the combustion chamber, such as exhaust gas recirculation or a fully variable valve train or an effect of, for example, a throttle valve or swirl flap. In addition, the combustion chamber filling determination should be able to be implemented cost-effectively and reliably.

According to the present invention, this object is achieved by a method for determining a combustion chamber filling of an internal combustion engine according to claim 1, a control device for an internal combustion engine according to claim 5 and a vehicle according to claim 6. The dependent claims define preferred and advantageous embodiments of the invention.

According to the present invention, a method for determining a combustion chamber filling of an internal combustion engine is provided. In the method, a change in the angular velocity of a crankshaft of the internal combustion engine is determined during a compression stroke of the internal combustion engine, and the filling of the combustion chamber is determined as a function of the change in angular velocity during the compression stroke. The filling is thus determined by determining the change in the angular velocity of the crankshaft of the internal combustion engine. Alternatively, a change in the angular velocity of a camshaft or another rotating unit of the internal combustion engine, which rotates in response to the crankshaft of the internal combustion engine. Acceleration and deceleration of the crankshaft is proportional to a change in force acting on a piston of the internal combustion engine, since the piston and crankshaft are mechanically connected to one another via the connecting rod. The pressure in the combustion chamber creates a force on the piston, which is pushed towards top dead center (TDC) during the compression phase. This creates a moment on the crankshaft. The force that drives the piston in the direction of top dead center (e.g. from the inertia of the flywheel mass of the internal combustion engine and the gas force due to the ignition of other cylinders in the internal combustion engine) is opposed to the gas force that acts on the piston due to the compression of the gas mass in the combustion chamber. The same applies to the torques on the crankshaft. Since the gas force depends on the pressure and this depends on the filling of the combustion chamber, the counterforce on the piston in the upward movement and the associated counter-torque on the crankshaft also depend on the filling of the combustion chamber. The delay in the angular velocity of the crankshaft can thus be used as a measure of the filling of the combustion chamber, and the filling of the combustion chamber can be determined reliably and cost-effectively.

Since the combustion chamber filling is recorded directly on the internal combustion engine via the angular velocity of the crankshaft, the method also works reliably in internal combustion engines with variable valve trains and variable flaps, such as throttle flaps or swirl flaps. A high-resolution speed signal is required to determine the change in the angular velocity of the crankshaft. Sensors for detecting such high-resolution speed signals are commonly used in today's internal combustion engines and are therefore available at low cost. The high-resolution speed signal can be evaluated in the engine control unit, for example, and therefore requires no additional components or costs.

According to one specific embodiment, the charge in the combustion chamber is determined by determining the course of compression as a function of the change in angular velocity during the compression stroke and by determining the charge in the combustion chamber as a function of the course of compression. Thus, the compression pressure in the cylinder, which is also known as the drag curve, is determined from the change in angular velocity. The compression line is thus modeled, from which the charge in the combustion chamber can be derived.

The internal combustion engine includes one, two or three cylinders. The internal combustion engine preferably works according to the four-stroke principle and thus has an ignition interval of 240° (three-cylinder engine), 360° (two-cylinder engine) or 720° (single-cylinder engine). To determine the filling of the combustion chamber, for example, the second half of the drag curve can be considered, for example a crankshaft angle range of 90° before top dead center of the cylinder up to the start of fuel injection into the cylinder (in the case of a diesel engine) or ignition in the cylinder ( in a petrol engine). With an ignition interval of at least 240°, overlapping with repercussions from previous combustion can be avoided. It is therefore not necessary to filter out the influence of a preceding combustion process with an ignition interval of at least 240°, as a result of which the reliability of the method can be increased and the determination of the filling in the combustion chamber can be carried out easily. The method can still be used with shorter ignition intervals, for example in engines with four or more cylinders, but the effects of the combustion pressure of a preceding cylinder in the ignition sequence must be filtered out. For this purpose, for example, a combustion pressure of a first cylinder, which is in front of a second cylinder in the firing sequence of the internal combustion engine, can be determined. The combustion chamber charge of the second cylinder is then determined as a function of the change in angular velocity during the compression stroke of the second cylinder and the combustion pressure of the first cylinder.

The combustion pressure of the first cylinder is determined by detecting an amount of fuel injected into the first cylinder and an ignition timing of the amount of fuel injected into the first cylinder. A combustion process can be determined as a function of the ignition point and the injected fuel quantity, on the basis of which the combustion pressure can be determined.

According to a further embodiment, the crankshaft is coupled to a power take-off point via a vibration-decoupled coupling. The vibration-decoupled coupling can take place, for example, with a dual-mass flywheel in the vehicle. As a result, repercussions of the power consumption point on the angular velocity of the crankshaft can be reduced and the accuracy of the method can thus be increased.

According to the present invention, there is further provided a control device for an internal combustion engine. The control device includes an input for receiving a signal indicative of an angular velocity of a crankshaft of the internal combustion engine. The control device is able to determine a change in the angular velocity during a compression stroke of the internal combustion engine as a function of the signal and to determine the combustion chamber charge as a function of the change in angular velocity during the compression stroke. The control device can also be designed to carry out the method described above and therefore also includes the advantages described above.

Finally, according to the present invention, a vehicle is provided which includes an internal combustion engine and a control device as described above. The internal combustion engine includes a rotation angle sensor for detecting an angular velocity of a crankshaft of the internal combustion engine, and the input of the control device is coupled to the rotation angle sensor. Therefore, the vehicle also includes the advantages described above.

• 1 zeigt schematisch einen Kompressionsvorgang eines Zylinders einer Brennkraftmaschine und eine Bestimmung einer Brennraumfüllung aus einer Veränderung einer Winkelgeschwindigkeit einer Kurbelwelle der Brennkraftmaschine gemäß einer Ausführungsform der vorliegenden Erfindung.
• 2 zeigt einen Zylindergasmomentverlauf für eine Brennkraftmaschine mit einem Zündabstand von 180°.
• 3 zeigt einen Zylindergasmomentverlauf für eine Brennkraftmaschine mit einem Zündabstand von 240°.
• 4 zeigt ein Fahrzeug mit einer Steuervorrichtung gemäß einer Ausführungsform der vorliegenden Erfindung.

The present invention will be explained in detail below with reference to the drawings.

• 1 shows schematically a compression process of a cylinder of an internal combustion engine and a determination of a combustion chamber charge from a change in angular velocity of a crankshaft of the internal combustion engine according to an embodiment of the present invention.
• 2 shows a cylinder gas torque curve for an internal combustion engine with an ignition interval of 180°.
• 3 shows a cylinder gas torque curve for an internal combustion engine with an ignition interval of 240°.
• 4 12 shows a vehicle having a control device according to an embodiment of the present invention.

1 shows three states 101-103 of a cylinder 105 of an internal combustion engine during a compression process, a so-called compression stroke. Furthermore, in 1 a state 104 of the cylinder at the beginning of a power stroke of the cylinder 105 is shown.

A piston 106 is arranged in the cylinder 105 and is connected to a crankshaft 109 via a connecting rod 108 . When the crankshaft 109 rotates, the piston 106 moves up and down in the cylinder 105 and thereby reduces or increases a volume 107 in the cylinder 105.

In the state 101 the piston 106 is in an upward movement, ie the volume 107 is reduced. This creates an overpressure in the volume 107, as a result of which a force F _gas acts on the piston in the opposite direction to its movement. The force F _gas causes a moment M _gas on the crankshaft 109 . A moment M, which is brought about, for example, from the inertia of a flywheel mass and a gas force when another cylinder is fired, causes a force F, which drives the piston 106 upwards. In state 102, the piston 106 has moved further up and the crankshaft 109 has rotated further in the direction of arrow φ. In state 103, the piston 106 has reached its top dead center. The force F _gas caused by the compression of the gas trapped in the volume 107 increases from state 101 to state 103 as shown by the number of arrows. Then, in state 104, a fuel is injected and ignited, whereby the piston 106 is accelerated downward and the crankshaft 109 is further rotated in the direction of the arrow φ. In state 104, the moment of flywheel mass M and gas moment M _gas act in the same direction.

wobei k₃ eine vorbestimmte Konstante und V_Zyl das Volumen des Brennraums 107 ist. Bis zum Einspritzzeitpunkt t_l sind, wie aus 1 ersichtlich ist, die Winkelgeschwindigkeit φ̇, die Gaskraft F_Gas und der Zylinderdruck p_Zyl proportional zueinander. Somit gilt: $$m_{Zyl}\sim \dot{\phi }\cdot V_{Zyl}$$

In the diagrams of 1 the angular velocity φ̇, the gas force F _gas , the pressure in the cylinder p _cyl and a mass in the cylinder m _cyl , a so-called combustion chamber filling, are shown over time. Injection and ignition take place at time t ₁ , as shown in state 104 . During the compression phase, the pressure p _Zyl as well as the force F _Gas acting on the piston 106 increases continuously in terms of absolute value. As a result, the angular velocity φ̇ of the crankshaft is continuously reduced. The mass M _cyl in the volume 107 remains constant up to the injection time point t ₁ , since this is a closed volume. Due to the ideal gas equation, the following essentially applies in the combustion chamber 107: $${\text{m}}_{\text{cyl}}=\text{k}3\cdot {\text{p}}_{\text{cyl}}\cdot {\text{V}}_{\text{cyl}}$$

where k ₃ is a predetermined constant and V _cyl is the volume of combustion chamber 107 . Up to the injection point t _l , how off 1 it can be seen that the angular velocity φ̇, the gas force F _gas and the cylinder pressure p _cyl are proportional to each other. Thus: $$m_{Zyl}\sim \dot{\phi }\cdot V_{Zyl}$$

The volume V _cyl can be determined depending on the crankshaft angle φ and the geometry of the cylinder 105 . The angular velocity φ̇ of the crankshaft 109 can, for example Using a crankshaft sensor are detected with high resolution, so that a change in the angular velocity φ̇ can be determined during the compression stroke of the internal combustion engine as a function of a signal from the crankshaft angle sensor. Based on the previously shown proportionality between the mass in the cylinder m _cyl , ie the combustion chamber charge, and the product of the combustion chamber volume V _cyl and the angular velocity φ̇, the combustion chamber charge can thus be determined.

How out 1 As can be seen, a compression characteristic of the cylinder 105 can also be derived from the change in the angular velocity φ̇, since the angular velocity φ̇ changes proportionally to the cylinder pressure p _cyl .

2 shows a curve of a cylinder gas torque of four cylinders in a four-cylinder four-stroke engine. For example, curve 201 shows a cylinder gas moment due to a first cylinder, curve 202 a cylinder gas moment due to a second cylinder, curve 203 a cylinder gas moment due to a third cylinder and curve 204 a gas moment due to a fourth cylinder. How out 2 As can be seen, the gas moments of two consecutive cylinders are superimposed. A combustion characteristic of the second cylinder is substantially in the range of 180° to 360° crankshaft angle. A compression characteristic of the third cylinder also runs essentially in the crankshaft angle range from 180° to 360°. The corresponding cylinder gas moments are therefore superimposed in this area. In order to determine a combustion chamber charge for, for example, the third cylinder from a change in the angular velocity of the crankshaft angle in the range from 270° to 360°, the influence on the combustion characteristic of the second cylinder in the crankshaft angle range from 270° to 360° must therefore be taken into account. This can be achieved, for example, by determining a combustion pressure of the second cylinder and filtering out an effect of the combustion pressure.

3 shows a cylinder gas torque curve of cylinders of an internal combustion engine which works according to the four-stroke principle and has an ignition interval of 240°, ie the internal combustion engine has three cylinders. A curve 301 shows the profile of a cylinder gas torque of the first cylinder and a curve 302 shows the cylinder gas torque profile of a second cylinder. A curve 303 partially shows the course of a cylinder gas torque of the third cylinder. A first cylinder combustion feature is in the crankshaft angle range of approximately 180° to 360°. A compression feature of the second cylinder is in the crank angle range of approximately 240° to 420°. As for determining the charge in the combustion chamber, as with reference to 1 previously described, mainly a crankshaft angle range from 90° before top dead center to top dead center is considered, the crankshaft angle range from 330° to 420° is considered to determine the combustion chamber charge for the second cylinder. This area will look like 3 as can be seen, is essentially unaffected by the combustion characteristic of the first cylinder. Therefore, filtering out the combustion attribute of the preceding cylinder is not required. The method described above for determining the charge in the combustion chamber is therefore suitable for engines with one, two or three cylinders. In internal combustion engines with more cylinders, ie with firing intervals of less than 240°, the effect of the combustion pressure of the preceding cylinder in the firing order must be filtered out.

• - eine hohe Verdichtung, da der Zylinderdruck in der Kompressionsphase dann proportional höher ist;
• - ein später Verbrennungsbeginn, da dadurch ein großes Intervall im Bereich hoher Zylinderdrücke betrachtet werden kann;
• - eine hohe Zylinderfüllung, da der Zylinderdruck in der Kompressionsphase dann höher ist;
• - eine niedrige Zylinderzahl, da dadurch die Störgrößen aus der Verbrennung anderer Zylinder klein sind; und
• - eine geringe Rückwirkung vom Antriebsstrang oder eine systematisch bekannte Rückwirkung des Antriebsstrangs, um Rückwirkungen des Antriebsstrangs auf die Winkelgeschwindigkeit der Kurbelwelle berücksichtigen zu können.

The following boundary conditions can contribute to improving the method described above:

• - a high compression, since the cylinder pressure is then proportionally higher in the compression phase;
• - A late start of combustion, as this allows a large interval in the range of high cylinder pressures to be considered;
• - a high cylinder filling, since the cylinder pressure is then higher in the compression phase;
• - a low number of cylinders, as this means that the disturbance variables from the combustion of other cylinders are small; and
• - A small feedback from the drive train or a systematically known feedback from the drive train in order to be able to take into account reactions from the drive train on the angular velocity of the crankshaft.

4 shows a vehicle 400 with an internal combustion engine 401 and a control device 402. The internal combustion engine 401 includes three cylinders 105, which work on a common crankshaft 109, as in connection with 1 was described. A high-resolution rotational angle sensor 403 is attached to the crankshaft 109 and provides a high-resolution crankshaft angle signal for the control device 402 . Control device 402 is coupled to crankshaft angle sensor 403 via an input 404 . The control device 402 can, for example, be part of a motor electronics of the internal combustion engine 401 or a separate control device. The controller 402 is for performing the related 1 described method for determining the filling of the combustion chamber in the cylinders 105 of the internal combustion engine 401 as a function of a change in the angular velocity of the crankshaft during a compression stroke of the corresponding cylinder 105.

In order to keep the influence of the drive train on the crankshaft 109 low and thereby improve the accuracy and reliability of the method according to the invention, the control device 402 can use a method in which the influence of the vehicle drive train on the gear used, which is in a transmission between the internal combustion engine 401 and drive wheels of the vehicle 400 is inserted, taken into account. In addition, the internal combustion engine 401 in the vehicle 400 can also be used as a so-called range extender, ie the internal combustion engine 401 does not drive the drive wheels of the vehicle 400 directly, but is coupled to an electrical generator which supplies electrical energy for an electrical drive of the vehicle 400 provides. Because how related to 1 as described above, the combustion chamber filling is determined from variables within internal combustion engine 401, the method is particularly suitable for internal combustion engines with variabilities in valve control, exhaust gas recirculation and swirl flaps.

Claims (6)

Method for determining a combustion chamber charge of an internal combustion engine (401) comprising at least a first cylinder and a second cylinder or three cylinders (105), the first cylinder being in front of the second cylinder in a firing order of the internal combustion engine (401), the method comprising : - Determining a change in an angular velocity (φ̇) of a crankshaft (109) of the internal combustion engine (401) during a compression stroke of the internal combustion engine (401), and - Determining the combustion chamber charge (m _Zyl ) as a function of the change in angular velocity (φ̇) during the Compression stroke, characterized by - determining a combustion pressure (202) of the first cylinder, - determining the combustion chamber charge (m _Zyl ) of the second cylinder as a function of the change in angular velocity (φ̇) during the compression stroke of the second cylinder, the determination of the combustion pressure (202 ) comprises: - detecting a fuel quantity injected into the first cylinder, - detecting an ignition timing of the fuel quantity injected into the first cylinder, and - determining a combustion process (202) as a function of the detected ignition timing and the detected injected fuel quantity. procedure after claim 1 , wherein the determination of the combustion chamber charge (m _Zyl ) as a function of the change in angular velocity (φ̇) during the compression stroke comprises: - determining a compression curve (p _Zyl ) as a function of the change in angular velocity (φ̇) during the compression stroke, and - determining the combustion chamber charge (m _cyl ) as a function of the compression curve (p _cyl ). Method according to one of the preceding claims, wherein the determination of the combustion chamber charge (m _Zyl ) as a function of the change in angular velocity (φ̇) during the compression stroke comprises: - Determining the combustion chamber charge (m _Zyl ) of a cylinder (105) as a function of the change in angular velocity (φ̇) during the compression stroke of the cylinder (105) in a crankshaft angle range of 90° before a top dead center of the cylinder (105) up to a start (t _l ) of fuel injection into the cylinder (105). A method according to any one of the preceding claims, further comprising: - Coupling the crankshaft (109) to a power take-off point via a vibration-decoupled coupling. Control device for an internal combustion engine, the control device (402) comprising an input (404) for receiving a signal which indicates an angular velocity (φ̇) of a crankshaft (109) of the internal combustion engine (401), the control device (402) being designed the procedure with the characteristics of Claims 1 until 4 to execute. Vehicle comprising: - an internal combustion engine (401) which includes a rotation angle sensor (403) for detecting an angular velocity (φ̇) of a crankshaft (109) of the internal combustion engine (401), and - a control device (402). claim 5 , wherein the input (404) of the control device (402) is coupled to the rotation angle sensor (403).

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