DE10218736A1 - Diesel engine regulation method detects combustion pressure for calculation of effective engine torque used for regulation of at least one engine operating parameter - Google Patents

Abstract

The regulation method detects the combustion chamber pressure within an engine cylinder (2) in dependence on the crank angle of the crankshaft (4) controlling the movement of the reciprocating piston (3), with derivation of a corresponding engine torque, combined with the angular velocity of the crankshaft for providing the effective engine torque, used for regulation of at least one operating parameter of the engine (1). An Independent claim for a regulating device for a diesel engine is also included.

Description

The present invention relates to a method and an apparatus for controlling a Internal combustion engine, for example a diesel engine, depending on that in the individual combustion chambers or cylinders of the internal combustion engine detected combustion chamber pressure.

For a particularly optimal emission control of an internal combustion engine, for. B. one supercharged diesel engine, is the exact knowledge of as large a number as possible Operating parameters of the engine system are of crucial importance. Such one Operating parameters are the effective, for example, in an internal combustion engine Engine torque, d. H. that actually transmitted to the crankshaft of the internal combustion engine and thus torque available on the clutch of a corresponding motor vehicle, which corresponds to the actual driver request. The effective engine torque differs from that indicated in the internal combustion engine by the combustion Motor torque due to a negative torque loss, which in addition to friction losses such. B. on the pistons and crank mechanism of the internal combustion engine also drive torques of all Auxiliary or belt drive connected consumers (e.g. for the operation of the Air conditioning compressor, the injection pumps, the servo pump, the alternator etc. of the Motor vehicle) includes.

DE 197 49 815 A1 describes an engine management system for an internal combustion engine known, by detecting the combustion chamber pressure in each cylinder or combustion chamber of the internal combustion engine depending on the crank angle in each Engine torque indexed combustion chamber determined and for the torque control of the Motor vehicle is used.

In engine control units of conventional engine management systems, characteristic maps are used for this filed, which motor torque data required for torque control include. By accessing these maps, depending on the appropriate settings detected or ascertained indicated appropriate engine torque Operating parameters of the internal combustion engine, e.g. B. the amount of fuel injected or the ignition timing, etc., for the best possible torque control of the Internal combustion engine are made.

However, the conventional engine management systems do not record the previously mentioned instantaneous effective engine torque. In particular, in Characteristic maps of the type described above only relatively imprecise mean torque values used and the actual behavior of the internal combustion engine is not or only insufficient considered. The effective engine torque and also the one previously mentioned Torque loss does not play a role in conventional motor control loops.

The present invention is therefore based on the object of a method and a To propose a device for regulating an internal combustion engine, the effective Engine torque can be taken into account. The method or the device according to the invention preferably also a determination of Torque loss by which the effective motor torque differs from that in the Internal combustion engine by combustion indicated engine torque, enable.

This object is achieved by a method with the features of Claim 1 and a device with the features of claim 11 solved. The Sub-claims each define preferred and advantageous embodiments of the present invention.

According to the invention, the determination is used to effectively control an internal combustion engine the effective engine torque occurring on the crankshaft of the internal combustion engine proposed. For this purpose, the one occurring in a combustion chamber of the internal combustion engine Combustion chamber pressure as a function of the crank angle recorded and the indexed from it Engine torque derived in the combustion chamber. From the indicated engine torque and the The angular velocity of the crankshaft can then be derived from the effective engine torque be, in particular the torque loss of the internal combustion engine can be determined and used for diagnostic purposes.

An indexed medium pressure value can also be used as an intermediate variable from the combustion chamber pressure data derived and for controlling the internal combustion engine, for example to improve the Idling.

With the help of the invention is improved by using new control variables Regulation of the internal combustion engine possible, which in turn leads to an improvement in Comfort, emissions and fuel consumption. Furthermore The invention enables combustion chamber-based control loops and a combustion chamber-based one Engine management.

The present invention is described in more detail below with reference to the accompanying drawing Explained with reference to a preferred embodiment. The only one shows Figure a simplified representation to explain the cylinder or Combustion chamber pressure detection in an internal combustion engine according to the present invention.

In the figure, a cylinder or combustion chamber 2 or the corresponding cylinder housing of an internal combustion engine 1 , for example a diesel engine, is shown. A piston 3 located in the combustion chamber 2 is driven via a crankshaft 4 of the internal combustion engine 1 . If, for example, it is assumed that the internal combustion engine works with four cycles, the crankshaft 4 and the piston 3 reach the so-called top dead center OT and the bottom dead center UT exactly twice within one working cycle, which corresponds to two complete revolutions of the crankshaft 4 . In automotive engineering, the angles of rotation φ of the crankshaft 4 are specified in degrees crank angle (° KW).

In the exemplary embodiment shown, a pressure sensor 5 is arranged in the region of the cylinder head or the cylinder head gasket, with the aid of which the combustion chamber pressure occurring in the combustion chamber 2 during operation of the internal combustion engine 1 can be detected. For this purpose, the pressure sensor 5 comprises, for example, a measuring membrane, which is expanded or deformed differently depending on the combustion chamber pressure prevailing in the combustion chamber, the extent of the expansion or deformation of this measurement membrane as a measure of the combustion chamber pressure currently prevailing in the combustion chamber 2 Control unit 7 is evaluated.

The combustion chamber pressure prevailing in this way in the combustion chamber 2 is related to the instantaneous position of the crankshaft 4 , ie to the instantaneous angle of rotation φ of the crankshaft 4 . For this purpose, a crankshaft sensor 6 is provided, which continuously detects the current position of the crankshaft 4 and feeds it to the control unit 7 . In this way, the control unit 7 can determine the course of the combustion chamber pressure as a function of the angle of rotation φ of the crankshaft 4 .

There is an assignment for a large number of the numerical evaluations proposed here of the combustion chamber or cylinder pressure currently recorded to the combustion chamber volume required. The basic principles are explained below.

The total stroke volume V _{H of} the internal combustion engine is defined as a function of the combustion chamber stroke volume V _h and the number of cylinders or combustion chambers z as follows:

V _H = V _h .z. (1)

The compression volume V _{C of} each combustion chamber is linked to the stroke volume of the respective combustion chamber via the compression ratio ε as follows:

The instantaneous combustion chamber volume V (φ) results from the crank angle-dependent piston travel χ (φ) (measured from top dead center OT) and the piston area A _k , where r denotes the radius of the crankshaft 4 :

When considering the single figure, the following geometric relationships can be determined, l denoting the length of the connecting rod connecting the piston 3 to the crankshaft 4 and β the connecting rod angle as shown in the figure:

r.sin (φ) = l.sin (β)

l ² = (l.cos (β)) ² + (l.sin (β)) ²

χ (φ) = r. (1 - cos (φ)) + l. (1 - cos (φ)) (4)

With the definition of the so-called pushrod ratio λ _S = r / l, the piston travel (based on the top dead center OT) results in:

The combustion chamber volume V (φ) is therefore dependent on the stroke function

Deriving the lifting function


allows the calculation of the change in the combustion chamber volume depending on the crank angle as follows:


Building on the principles described above, the relationships relevant in the context of the present invention for determining the effective engine torque and the lost torque of the internal combustion engine will be explained below.

The effective efficiency of the combustion process η _e is defined by the conversion of the energy Q _B stored in the fuel into a useful work W _e available on the crankshaft 4 . With the so-called lower heating value H _{u of} the fuel and the fuel mass m _k , the following relationship thus results:

The high-pressure process in the respective combustion chamber or cylinder 2 of the internal combustion engine 1 can be observed with the aid of the aforementioned combustion chamber pressure measurement. The mechanical losses (mechanical efficiency η _m ) can thus be separated from the internal losses (internal efficiency η _i ). With the indicated or internal work W _{i, the} following applies to the effective efficiency of the combustion process:

From the 1st law of thermodynamics, the following differential equation results for the energy balance of the system:

dW _i + dQ _W + dQ _B + dH _E + dH _A + dH _B = dU. (11)

The term dW _i describes the volume change work and is defined in accordance with the relationship dW _i = -p.dV by the combustion chamber pressure p and the volume change dV.

The term dQ _W describes the wall heat energy extracted from the system, and the term dQ _B describes the converted fuel energy or the combustion process of the injected fuel.

With dH _E is the enthalpy change of the mass flowing into the system, with dH _A the enthalpy change of the outflowing mass, and with dH _B the enthalpy change of the injected fuel.

The term dU finally describes the change in the internal energy of the system.

Equation (11) is the basis for the energetic assessment of the processes taking place in a combustion chamber 2 of the internal combustion engine 1 . The heat change in the working gas observed in the combustion chamber pressure p results in the heating curve dQ _H as the sum of the converted fuel energy dQ _B and the negative wall heat energy dQ _W :

dQ _H = dQ _B + dQ _W. (12)

In internal combustion engines, the mean pressure p _m in a combustion chamber corresponds to the work W of a work cycle based on the corresponding stroke volume V _h :

The effective specific work resulting from a combustion can be taken from the crankshaft 4 of the internal combustion engine 1 and expressed in the form of the effective mean pressure p _me , the effective engine torque M _e or the effective power P _e . This effective specific work corresponds to the difference between the specific internal work, expressed by the indicated mean pressure p _mi , the indicated engine torque M _i or the indicated power P _i , and the specific mechanical loss work (loss or friction mean pressure p _mv , loss torque M _v , Power loss P _v ). The mechanical efficiency η _m links the effective and induced quantities as follows:

From equation (14) it can be seen that the previously mentioned mean pressures, moments and Work or services can be converted into each other.

The indicated mean pressure p _mi can be determined directly from the combustion chamber pressure measured with the aid of the pressure sensor 5 . It is derived from the volume change work and characterizes the energy conversion of the working gas in the respective combustion chamber:

The indicated mean pressure p _mi thus corresponds to the volume change work related to the respective stroke volume V _h .

The indicated work corresponds to the area enclosed by the characteristic curve in the respective pV diagram. In four-stroke engines, it is divided into a high-pressure and a gas exchange component. The indicated mean pressure p _{mi_HD of} the high pressure _phase can be used as a parameter for the combustion of the individual combustion chambers and is defined between the two bottom dead centers UT of the crank path as a function of the measured combustion chamber pressure p as follows:

The indicated medium pressure p _{mi_HD of} the high pressure _phase is preferably selected for the regulation and control of the internal combustion engine 1 , since it physically describes the internal work of each combustion chamber 2 .

The internal efficiency η _i describes the quality of combustion, since it compares the fuel energy Q _{B used} with the indicated energy W _i :

The torque M of the internal combustion engine 1 is proportional to the average pressure ≙ of the internal combustion engine (averaged between the individual combustion chambers or cylinders 2 ):

M ~ V _H. ≙. (18)

The indexed engine torque is a conversion of the indexed work into a (virtual) moment (see equation (18) with the index i). The current indicated engine torque of a combustion chamber can be determined approximately as follows:

The current indicated engine torque can be calculated from the continuous observation of the indicated work according to equation (19) by superimposing the curves of all z combustion chambers:

Because the function


for the numerical determination of the indicated mean pressure by the control unit 7 anyway, the determination of the maximum and minimum indicated engine torque and their crank angle positions φ _Mimax , φ _Mimin only represent an insignificant additional effort.

The indicated engine torque is linked to the engine speed via a differential equation of the crank mechanism described in, for example, "Calculation of the combustion chamber pressure curve from crankshaft angular velocity of internal combustion engines", Fehrenbach H., progress reports VDI series 6, energy generation No. 255, VDI publishing house Düsseldorf, 1991, in this regard, reference is expressly made to the statements in this publication. As described, the (momentary) indicated engine torque can be derived from the combustion chamber pressure with a resolution of 1 ° KW. Furthermore, the crankshaft angular velocity is also available with a temporal resolution of 1 ° KW. Thus, the input and output variables of the model of the crank mechanism described in this publication are available, and the effective engine torque M _e (φ) and the loss torque M _V (φ) can be determined therefrom, since the following relationship applies according to this differential equation:

The derivation of the expressions for J and J 'can also be found in the publication described above. In connection with the present invention, it is only important that the right side of equation (21) is known as a function of the angular velocity of the cube shaft, so that if M _i (φ) is also derived from the combustion chamber pressure as described above, the loss torque M _v (φ) and the effective engine torque M _e (φ) can be concluded.

As has already been mentioned, the loss torque M _v (φ) relates to the negative work due to friction losses on the respective piston and crank mechanism, as well as torque losses due to consumers of the respective motor vehicle also driven via the crankshaft, such as the air conditioning compressor, the injection pumps and the servo pump , the alternator etc., back. The following relationship applies between the individual moments:

M _e (φ) = M _i (φ) + M _v (φ) ∧ M _v (φ) <0. (22)

In the operating state "idle" / "engine disengaged", the effective engine torque is zero. Therefore, the loss torque can be determined in this operating state from the above relationships and as a function of the indicated engine torque derived from the combustion chamber pressure. Alternatively or additionally, the drag torque specific to the cylinder or combustion chamber can also be determined via the medium pressure values. The following relationship applies between the medium pressure values:

p _ms = p _{mi_HD} - p _me . (23)

The drag torque can be determined from equation (18) from the drag medium pressure p _ms .

With the help of the additionally obtained information described above, in particular the effective engine torque M _e , the loss torque M _v and the indicated mean pressure p _mi , the existing control loops of the engine management system can be improved, since this additional information flows into the control or regulation of the internal combustion engine can. Certain manipulated variables, e.g. B. the fuel injection quantity, the start of fuel delivery or the fuel injection curve can be changed, for example in the form of a cylinder-specific combustion start or torque control, in such a way that the parameters extracted from the combustion chamber pressure are achieved. In particular, regulation takes place on the basis of the combustion actually taking place in the respective combustion chamber.

In particular, the idling of the internal combustion engine can be improved. At the bottom Speed range, the smooth running of the internal combustion engine can also be improved. It cylinder-specific setpoints for the indicated medium pressure can be specified, if different torque or friction losses for the individual cylinders or Combustion chambers are determined in order to obtain a cylinder-specific control. By recording the (cylinder-specific) indexed mean pressure, an absolute Measure of the torque generated in the combustion in the respective cylinder, so that in combination with a high-resolution crank angle marking very precise and effective cylinder-specific control loops can be created.

With the effective engine torque, a model size of high quality stands for the first time Driving behavior functions "idle", "bucking damping" etc. are available. The effective one As previously described, engine torque is recorded and resolved crank angle can also other components or participants in the drive train, e.g. B. the transmission or the ancillary units can be made available for control.

The fact that in the differential equation of the crank mechanism described above, which the basis for determining the loss torque and the effective torque of the Combustion engine represents, based on the determination of the indicated engine torque in In principle, depending on the combustion chamber pressure, both the input and the Output variables are known, the can in known operating conditions Speed information also for checking the correctness of the pressure sensors of the individual Combustion chambers of the internal combustion engine are used.

The idle control and the bucking damping of the internal combustion engine can by Identification of the parameters of this differential equation adapted in a further step so these parameters are no longer in a lengthy process for different operating conditions must be applied.

With the torque loss, a model size is available, with the aid of which the friction and other losses in the engine can be monitored individually for diagnostic purposes and can be reacted to in a suitable manner. REFERENCE SIGN LIST 1 internal combustion engine
2 cylinder housings
3 pistons
4 crankshaft
5 pressure sensor
6 crankshaft sensor
7 control unit
8 injection valve
OT top dead center
UT bottom dead center
φ crank angle
β connecting rod angle
l connecting rod length
r crankshaft radius

Claims (12)

1. A method for controlling an internal combustion engine, the combustion chamber pressure occurring in a combustion chamber ( 2 ) of the internal combustion engine ( 1 ) as a result of a combustion process being detected as a function of a crank angle (φ) of a crankshaft ( 4 ) of the internal combustion engine ( 1 ) and at least for the control an operating parameter of the internal combustion engine ( 1 ) is used, characterized in that an engine torque indicated by the combustion process in the combustion chamber ( 2 ) is derived from the combustion chamber pressure, and that an engine torque and an angular velocity of the crankshaft ( 4 ) result from the combustion Effective engine torque occurring on the crankshaft ( 4 ) is derived and used to control the at least one operating parameter of the internal combustion engine ( 1 ). 2. The method according to claim 1, characterized in that an indexed mean pressure is derived from the combustion chamber pressure and is used for the control of the internal combustion engine ( 1 ). 3. The method according to claim 2, characterized in that the indicated average pressure for a high pressure phase in the combustion chamber is derived from the combustion chamber pressure and used for the control of the internal combustion engine ( 1 ). 4. The method according to claim 3, characterized in that the indicated mean pressure p _{mi_HD is determined} as a function of the combustion chamber pressure p and a displacement V _{h of} a piston ( 3 ) of the internal combustion engine ( 1 ) located in the combustion chamber ( 2 ) as follows:


5. The method according to any one of claims 2-4, characterized in that the indicated engine torque is derived from the indicated medium pressure. 6. The method according to any one of claims 2-5, characterized in that an idling behavior of the internal combustion engine ( 1 ) is regulated in dependence on the indicated medium pressure. 7. The method according to any one of claims 1-4, characterized in that the indicated engine torque M _i as a function of the crank angle φ of the crankshaft ( 4 ) from the combustion chamber pressure p and a volume V of the combustion chamber ( 2 ) according to the relationship


is derived. 8. The method according to any one of the preceding claims, characterized in that in an idle operating state or a decoupled operating state of the internal combustion engine ( 1 ) from the indicated engine torque and the angular velocity of the crankshaft ( 4 ) a loss torque of the internal combustion engine ( 1 ) is derived, and that the effective engine torque is determined from the indicated engine torque and the loss torque. 9. The method according to claim 8, characterized in that the torque loss is used to diagnose a faulty state of the internal combustion engine ( 1 ). 10. The method according to any one of the preceding claims, characterized in that the method for a plurality of combustion chambers ( 2 ) of the internal combustion engine ( 1 ) is carried out specific to the combustion chamber. 11. Device for regulating an internal combustion engine,
with crank angle detection means ( 6 ) for detecting a crank angle (φ) of a crankshaft ( 4 ) of the internal combustion engine,
with combustion chamber pressure detection means ( 5 ) for detecting the combustion chamber pressure occurring in a combustion chamber ( 2 ) of the internal combustion engine ( 1 ), and
with a control device ( 7 ) for controlling at least one operating parameter of the internal combustion engine ( 1 ) as a function of the combustion chamber pressure detected by the combustion chamber pressure detection means ( 7 ) and the crank angle (φ) detected by the crank angle detection means ( 6 ),
characterized,
that the control device ( 7 ) is designed in such a way that it derives an engine torque indicated by the combustion process in the combustion chamber ( 2 ) from the combustion chamber pressure in order to derive an engine torque from the indexed engine torque and an angular velocity of the crankshaft ( 4 ) due to the combustion on the crankshaft ( 4 ) to derive the effective engine torque that occurs and to use it to regulate the at least one operating parameter of the internal combustion engine ( 1 ). 12. The device according to claim 11, characterized in that the control device ( 7 ) for controlling the internal combustion engine ( 1 ) is designed according to the method according to any one of claims 1-10.