Method and device for controlling an internal combustion engine

Disclosed is an internal combustion engine comprising a first and a second cylinder line, each of which is provided with a camshaft for the gas intake valves and the gas discharge valves as well as a mechanism for adjusting a valve overlap between the gas intake valves and the gas discharge vales. A lambda controller whose manipulated variable acts upon an actuator that is allocated to the respective cylinder line is associated with each cylinder line. Values of the manipulated controller variables are detected as non-valve-overlapping values of the two cylinder lines in an operating situation in which the valve overlap is so small that the same does not influence the manipulated controller variables while values of the manipulated controller variables are detected as valve-overlapping values of the two cylinder lines in another operating situation in which the valve overlap is so great that the same influences the manipulated controller variables. A corrective value is determined for the adjusting mechanism assigned to the first cylinder line and/or a corrective value is determined for the adjusting mechanism assigned to the second cylinder line in accordance with the valve-overlapping values and non-valve-overlapping values of the two cylinder lines. The adjusting mechanisms of the two cylinder lines are triggered according to the corrective values assigned thereto.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage Application of International Application No. PCT/EP2005/054596, filed Sep. 15, 2005, which designates the United States of America, and claims priority to German Application No. 10 2004 048 704.9 filed Oct. 6, 2004, the contents of which are hereby incorporated by reference in their entirety

FIELD OF INVENTION

The invention relates to a method and device for controlling an internal combustion engine.

BACKGROUND OF INVENTION

The performance and efficiency requirements for internal combustion engines are becoming increasingly stringent. At the same time, strict statutory provisions require pollutant emissions to be kept low. To this end it is known that internal combustion engines can be provided with adjustment facilities to set a valve overlap between the gas intake valves and gas discharge valves. It is thus possible to increase the torque produced overall by the internal combustion engine and reduce emissions. A valve overlap is the angle range—expressed as the crankshaft angle or camshaft angle—during which both the respective gas intake valve and the respective gas discharge valve enable a corresponding intake or discharge of the cylinder.

Internal combustion engines are also known, with which the individual cylinders are disposed in two lines. Such internal combustion engines are also known as V-engines. With such V-engines three cylinders are for example disposed on one cylinder line and a further three cylinders on a further cylinder line. In addition to low-emission operation and the high level of torque, which should be produced by such internal combustion engines, it is also a challenge to configure such internal combustion engines in such a manner that user-friendly operation is possible.

SUMMARY OF INVENTION

An object of the invention is to create a method and device for controlling an internal combustion engine with two cylinder lines, each allowing user-friendly operation of the internal combustion engine.

The object is achieved by the features of the independent claims. Advantageous embodiments of the invention are characterized in the subclaims.

According to a first aspect the invention is characterized by a method and a corresponding device for controlling an internal combustion engine with a first and second cylinder line, each having one camshaft for gas intake valves and a further camshaft for gas discharge valves of the cylinders assigned to the respective cylinder line. The cylinder lines also each have an adjustment facility to set a valve overlap between the gas intake valves and gas discharge valves. A lambda controller, the manipulated controller variable of which acts on at least one actuator, which is assigned to the respective cylinder line, is assigned to each cylinder line. In at least one operating situation, in which the valve overlap is so small that it has no influence on the manipulated controller variables, values of the manipulated controller variables are detected as non-valve-overlap values of the first and second cylinder lines. In this context no influence means that the valve overlap has a negligible influence on the manipulated controller variables. In at least one further operating situation, in which the valve overlap is so great that it has an influence on the manipulated controller variables, values of the manipulated controller variables are detected as valve-overlap values of the first and second cylinder lines. In this context influence of the valve overlap on the manipulated controller variables means that an undesirably incorrect valve overlap has a relevant influence on the manipulated controller variable and therefore results in an undesirable change in the air mass in the respective cylinders of the respective cylinder line.

A correction value for the adjustment facility assigned to the first cylinder line is determined as a function of the valve-overlap values and non-valve-overlap values of the first and second cylinder lines. Additionally or alternatively a correction value is determined for the adjustment facility assigned to the second cylinder line, similarly as a function of the valve-overlap values and non-valve-overlap values of the first and second cylinder lines. The adjustment facilities of the first and/or second cylinder line are then activated as a function of the correction values assigned to them. The actuators are in particular the injection valves assigned to the respective cylinder line but the actuators can also be other actuators, such as a pulse charging valve.

The invention makes use of the knowledge that the adjustment facility, a generally present transmitter unit between the crankshaft of the internal combustion engine and the respective camshafts and generally present sensor systems for detecting the respective angles of the crankshafts or camshafts are subject to mounting tolerances, changes in their characteristics during operation of the internal combustion engine, etc. Such inaccuracies can be configured differently in respect of the first and second cylinder lines. This can result in different air masses in the cylinders of the first cylinder line on the one hand and the cylinders of the second cylinder line on the other hand. This in turn means that the torques, transmitted by the combustion of an air/fuel mixture in the respective cylinders to the crankshaft, can differ from cylinder line to cylinder line. This means that the internal combustion engine runs in a manner that is not smooth or user-friendly. According to the invention such inaccuracies are identified based on the manipulated controller variables of the respective lambda controllers. Taking account of values of the manipulated controller variables as non-valve-overlap values of the first and second cylinder lines in the operating situation, in which the valve overlap is so small that it has no influence on the manipulated controller variables, ensures that other influencing variables, which impact on the manipulated controller variables, are compensated for and are therefore not ascribed incorrectly to inaccuracies in the area of the actual setting of the valve overlap. The correction value(s) can then be determined in an appropriate manner such that alignment of the valve overlap actually set by way of the cylinders of the first cylinder bank and the second cylinder bank takes place and the air masses flowing into the respective cylinders are therefore also aligned. This results in a high level of torque uniformity between the cylinder lines and thus to very user-friendly running of the internal combustion engine. The manipulated controller variables of the respective lambda controllers are also thus used. Such internal combustion engines, when operated with petrol, are generally fitted with lambda controllers. The manipulated controller variables are therefore available anyway as calculation variables in a corresponding device for controlling the internal combustion engine.

According to a second aspect, the invention is characterized by a method and a corresponding device for controlling an internal combustion engine with a first and second cylinder line, each having one camshaft for the gas intake valves and one for the gas discharge valves of the cylinders assigned to the respective cylinder line. The first and second cylinder lines also each have an adjustment facility to set a valve overlap between the gas intake valves and gas discharge valves. In contrast to the first aspect of the invention, in at least one operating situation, in which the valve overlap is so small that it has no influence on the torque, which is transmitted by the combustion of the air/fuel mixture in the cylinders to the crankshaft, values of a variable, which is representative of the torque generated by the first cylinder line and on the other hand by the second cylinder line, are detected as non-valve-overlap values of the first and second cylinder lines. Also in at least one further operating situation, in which the valve overlap is so great that it has an influence on the torque, which is transmitted by the combustion of the air/fuel mixture in the cylinders to the crankshaft, values of the variables, which are representative of the torque generated by the first cylinder line and on the other hand by the second cylinder line, are detected as valve-overlap values of the first and second cylinder lines. It is also thus possible to equalize the torques generated by the respective cylinder lines in a simple manner.

In an advantageous embodiment of the invention, detection of the non-valve-overlap values and valve-overlap values is started, when the manipulated controller variables of the first and second cylinder lines differ from each other by a predetermined lambda threshold value. It is thus possible to keep the computation outlay low overall, whilst still achieving good equalization of the torques produced by the respective cylinder lines over the operating life of the internal combustion engine with suitable selection of the lambda threshold value.

According to a further advantageous embodiment of the invention, detection of the valve-overlap values and non-valve-overlap values is started, when the values of the variable, which is representative of the torque generated by the first cylinder line and on the other hand by the second cylinder line, differ from each other by a predetermined torque threshold value. It is thus possible to keep the computation outlay low overall, whilst still achieving good equalization of the torques produced by the respective cylinder lines with suitable selection of the lambda threshold value.

According to a further advantageous embodiment of the invention the variable, which is representative of the torque generated by the first cylinder line and on the other hand by the second cylinder line, is selected as a rotational speed gradient. This has the advantage that it is simple to determine and the rotational speed is detected anyway for other control purposes.

According to a further advantageous embodiment of the invention, correction values are calculated as a function of mean valve-overlap values and non-valve-overlap values, which are averaged over a predetermined number of valve-overlap values or non-valve-overlap values or are valve-overlap values or non-valve-overlap values detected during a predetermined time period. This allows more accurate correction.

According to a further advantageous embodiment of the invention, correction of the activation of the adjustment facility or adjustment facilities takes place in an adaptive manner.

Elements with the same structure or function are marked with the same reference characters in all the figures.

DETAILED DESCRIPTION OF INVENTION

An internal combustion engine (FIG. 1) has an intake tract1, an engine block2, a cylinder head3and an exhaust gas tract4. The exhaust gas tract1preferably has at least one throttle valve5, also at least one manifold6and an intake pipe7, which leads to a cylinder Z1via an intake duct into the engine block2. The engine block2also has a crankshaft, which is coupled via a connecting rod10to the piston of the cylinder Z1.

The cylinder head3has a valve gear mechanism with a gas intake valve12, a gas discharge valve13and valve drives14,15.

The internal combustion engine has a number of cylinders Z1to Z8. The cylinders Z1to Z4are assigned to a first cylinder line ZB1, while cylinders Z5to Z8are assigned to a second cylinder line ZB2(FIG. 2). A camshaft18ais assigned to the gas intake valves12assigned to the cylinders Z1to Z4of the first cylinder line. A camshaft18bis assigned to the gas discharge valves13assigned to the cylinders of the first cylinder line ZB1. The camshafts18aand18bare coupled mechanically to the crankshaft8, with an adjustment facility19connected mechanically in between, being used to set a valve overlap VO between the camshafts18aand18b. To this end phase angles of either both or just one of the camshafts18aand18bare adjusted in relation to the crankshaft8by means of the adjustment facility.

To clarify the concept of phase angle,FIG. 3shows the pattern of a signal detected by means of a crankshaft angle sensor36plotted over the crankshaft angle CRK and by way of a comparison signals detected by corresponding camshaft angle sensors. The phase angle is defined by an angle, for example the crankshaft angle between two reference marks, one on the crankshaft and the other on the respective camshaft18a,18b, in relation to an absolute position of the camshaft or crankshaft.FIG. 3shows this by way of example based on the reference mark REF_CRK and the reference mark REF_CAM1on the camshaft18aor the reference mark REF_CAM2on the camshaft18b. The reference mark REF_CRK on the crankshaft8is defined by a falling tooth flank toward a gap in a toothed crankshaft angle sensor wheel. The reference mark REF_CAM1and the reference mark REF_CAM2of the camshaft18aand18bare respectively defined by corresponding tooth flanks of camshaft sensors21a,21b. An adjustment of the respective phase angle is shown inFIG. 3with a broken line.

A camshaft18cis assigned to the gas intake valves12of the cylinders Z5to Z8of the second cylinder line ZB2. A camshaft18dis assigned to the gas discharge valves13of the cylinders Z5to Z8of the second cylinder line ZB2. The camshafts18cand18dare coupled mechanically to the crankshaft like the camshafts18aand18band a valve overlap VO of the gas intake valves and the gas discharge valves12,13of the cylinders Z5to Z8of the second cylinder line ZB2can also be set here by means of an adjustment facility20.

It is not necessary to be able to adjust the phase angle of both of the camshafts18ato18dassigned to a cylinder line ZB1, ZB2in each instance. The valve overlap VO can also be set by means of just one adjustable camshaft18ato18din each instance.

The cylinder head3also comprises an injection valve22and a spark plug23. Alternatively the injection valve22can be disposed in the intake pipe7.

A control device25is provided, to which sensors are assigned, which detect different measured variables and in each instance determine the value of the measured variable. The control device25determines manipulated variables as a function of at least one measured variable and these manipulated variables are then converted to one or more actuating signals to control the actuators by means of corresponding actuating drives. The control device25can also be referred to as a device for controlling the internal combustion engine.

The sensors are a pedal position sensor26, which detects the position of an accelerator pedal27, an air mass sensor28, which detects an air mass flow upstream of the throttle valve5, at least one but preferably two throttle valve position sensors30, which detect the opening angle of the respective throttle valve5, a first temperature sensor32, which detects an intake air temperature, at least one intake pipe pressure sensor34, which detects an intake pipe pressure in the manifold6, a crankshaft angle sensor36, which detects the crankshaft angle CRK, to which a rotational speed N is then also assigned. A second temperature sensor38detects a coolant temperature. At least one camshaft angle sensor39is also provided, which detects a camshaft angle. However a number of camshaft angle sensors can also be present, it being possible in some instances to assign a camshaft angle sensor to each camshaft. An exhaust gas probe42,43is also assigned to each cylinder line ZB1, ZB2, to detect the residual oxygen content of the exhaust gas, its measurement signals being characteristic of the air/fuel ratio in the cylinders Z1to Z4of the first cylinder line ZB1or in the cylinders Z5to Z8of the second cylinder line ZB2.

Any sub-set of the said sensors or even additional sensors can be present, depending on the embodiment of the invention.

Actuators are for example the throttle valve, the gas intake and gas discharge valves, a pulse charging valve, a valve lift adjustment facility, the injection valve22or the spark plug23. Corresponding actuators are also assigned to the cylinders Z2to Z8. The description of the cylinder Z1is simply by way of example for all the cylinders Z1to Z8.

A separate lambda controller46,47is assigned to the control device for each cylinder line ZB1, ZB2. The lambda controller46,47determines a respective manipulated controller variable LAM_FAC1, LAM_FAC2as a function of the measurement signal of the respective exhaust gas probe42,43and a setpoint value of the air/fuel ratio, said manipulated controller variable LAM_FAC1, LAM_FAC2then being used for example to change the fuel mass to be metered to the cylinders either of the first cylinder line ZB1or the second cylinder line ZB2by way of the respective injection valves22, to set the required setpoint value of the air/fuel ratio. The lambda controller46,47can be configured for example as a PI or PII2D controller or as another suitable controller46,47known to the person skilled in the art.

A program for controlling the internal combustion engine in a first embodiment (seeFIGS. 4 and 5) is stored in the control device25and can be executed during operation of the internal combustion engine. The program is started in a step S1.

The program is preferably started in step S1, when the difference between the manipulated controller variables LAM_FAC1, LAM_FAC2is greater than an appropriately selected lambda threshold value THD_LAM. It is then verified in a step S2, whether the current valve overlap VO is greater than a predetermined first threshold value THD1. The valve overlap VO is preferably predetermined as identical for the cylinders Z1-Z8of both cylinder lines ZB1, ZB2.

If the condition of step S2is satisfied, in a step S4the manipulated controller variable LAM_FAC1is assigned to a first non-valve-overlap value NVOV1. A field is preferably assigned in the control device25to the first non-valve-overlap value NVOV1, which is assigned to the first cylinder line ZB1, so that a number of such first non-valve-overlap overlap values NVOV1can be buffered. The first counter CTR1given in square brackets designates the respective position within the vector.

In a subsequent step S6the manipulated controller variable LAM_FAC2is assigned to a second non-valve-overlap value NVOV2, which is assigned to the second cylinder line ZB2. A corresponding vector is provided here too, in order to be able to buffer a number of second non-valve-overlap values NVOV2, which are assigned to the second cylinder line ZB2.

The first counter CTR1is incremented in a step S8.

If however the condition of step S2is not satisfied, in a step S10it is verified whether the valve overlap VO is greater than a second threshold value THD2. The first and second threshold values THD1, THD2are predetermined in an appropriate manner and for example determined beforehand by means of corresponding tests. The first threshold value THD1is selected such that, as long as the valve overlap VO is less than it, the valve overlap VO is so small that it has no or only a negligible influence on the manipulated controller variables, if it differs from the required valve overlap VO to be set. In contrast the second threshold value THD2is selected such that when it is exceeded by the valve overlap VO, the valve overlap VO is so great that it has an influence on the manipulated controller variable LAM_FAC1, LAM_FAC2.

If the condition of step S10is not satisfied, processing is resumed again in step S2, in some instances after a predetermined waiting period or a predetermined crankshaft angle. If however the condition of step S10is satisfied, in a step S12the value of the manipulated controller variable LAM_FAC1is assigned to a first valve-overlap value VOV1. The first valve-overlap value VOV1is thus assigned to the cylinders Z1to Z4of the first cylinder line ZB1. A vector is provided here too in the computation unit of the control device25or in a storage unit of said control device25, to buffer a number of such values, and a counter CTR2designates the storage location within the vector.

In a step S14a second valve-overlap value VOV2is assigned the current value of the manipulated controller variable LAM_FAC2. The second valve-overlap value VOV2is thus assigned to the second cylinder line ZB2. A corresponding vector is provided here too, to buffer a number of values.

A counter CTR2is then incremented in a subsequent step S14.

It is then verified in a step S18, whether both the first counter CTR1and the second counter CTR2exceed a maximum value CTR_MAX, which is predetermined in an appropriate manner. If not, processing is resumed in step S2, in some instances after the predetermined waiting period or after the predetermined crankshaft angle.

If however the condition of step S18is satisfied, in a step S20a mean first non-valve-overlap value NVOV1_M is determined according to the relationship set out in step S20. Mean second non-valve-overlap values NVOV2_M and first and second mean valve-overlap values VOV1_M, VOV2_M are determined correspondingly in the subsequent steps S22to S26.

Processing then continues in a step following the logic point A. This is step S28, in which a first correction value CORI and a second correction value COR2are determined as a function of the mean first and second non-valve-overlap values NVOV1_M, NVOV2_M and the mean first and second valve-overlap values VOV1_M, VOV2M. This can be done for example by means of a predetermined analytical function or preferably by way of a characteristic field with appropriate data input. Such a characteristic field is for example determined beforehand by means of tests on an engine test bed or simulations and stored in the control device25.

In a step S30actuating signals SG1, SG2to control the adjustment facilities19,20are corrected as a function of the first or second correction values COR1, COR2, to align the air masses in the respective cylinders for a set valve overlap VO. Alternatively only one of the correction values COR1, COR2may be determined, and therefore only the corresponding actuating signal SG1or SG2is corrected, similarly to align the air masses in the respective cylinders of the first and second cylinder lines.

The program is then either terminated or in some instances alternatively also resumed in step S2. The first or second correction value COR1, COR2is preferably also adjusted in an adaptive manner.

A second embodiment of the program is described in more detail with reference to the flow diagram inFIG. 6. The program is started in a step S32.

The program is preferably started in step S32, when the values of a variable, which is representative of the torque generated by the first cylinder line ZB1and on the other hand by the second cylinder line ZB2, differ from each other by a predetermined torque threshold value THD_TQ. Such a variable can be a rotational speed gradient for example or even a detected torque.

Steps S34to S58then correspond analogously to steps S2to S26. N_GRD1are rotational speed gradients, which are assigned to the cylinders Z1-Z4of the first cylinder line ZB1. N_GRD2are rotational speed gradients, which are assigned to the cylinders Z5-Z8of the second cylinder line ZB2.