阅读说明：本技术 用于凸轮轴定位校准的方法和系统 (Method and system for camshaft positioning calibration ) 是由 J·达尔格伦 S·杜耐特 于 2019-05-28 设计创作，主要内容包括：本发明涉及一种用于生成凸轮轴特征的方法,该凸轮轴特征用于燃烧发动机(100)中包括的凸轮轴(110,118)的凸轮轴定位校准。凸轮轴适于使阀门(109,120)打开和关闭通向燃烧发动机的汽缸容积(102)的开口。燃烧发动机还包括适于从外部环境接收空气的进气缓冲罐(204)。进气缓冲罐与燃烧发动机的汽缸容积流体连通,以用于提供空气与喷射到汽缸中的燃料混合。(The invention relates to a method for generating a camshaft characterization for camshaft positioning calibration of a camshaft (110, 118) comprised in a combustion engine (100). The camshaft is adapted to having the valves (109, 120) open and close openings to a cylinder volume (102) of the combustion engine. The combustion engine further comprises an intake buffer tank (204) adapted to receive air from an external environment. An intake buffer tank is in fluid communication with a cylinder volume of the combustion engine for providing air for mixing with fuel injected into the cylinder.)

1. A method for generating a camshaft signature for camshaft positioning calibration of a camshaft (110, 118) comprised in a combustion engine (100) adapted to have valves (109, 120) opening and closing openings to a cylinder volume (102) of the combustion engine, the combustion engine further comprising an intake buffer tank (204) adapted to receive air from an external environment, the intake buffer tank being in fluid communication with the cylinder volume of the combustion engine for providing air to be mixed with fuel injected into a cylinder, wherein the method comprises:

-operating (S102) the combustion engine at a predetermined rotational speed;

-providing (S104) a constant gas flow into the inlet buffer tank;

-measuring (S106) a set of camshaft positions and a set of pressure values indicative of the pressure in the intake buffer tank while the camshaft is rotating and the gas flow into the intake buffer tank is kept constant; and

-providing (S108) a camshaft characteristic comprising the set of camshaft positions and the set of pressure values.

2. The method of claim 1, wherein the camshaft is adapted to control one of an intake port control valve (208) and an exhaust port control valve (214) of the combustion engine.

3. The method of claim 1 or 2, wherein the camshaft characteristic comprises a timing relationship between the set of camshaft positions and the set of pressure values.

4. The method according to any one of the preceding claims, characterized in that it comprises:

-operating the combustion engine at a predetermined further rotational speed;

-measuring another set of camshaft positions and another set of pressure values indicative of the pressure in the intake buffer tank while the camshaft is rotating and the gas flow into the intake buffer tank is kept constant; and

-providing a camshaft characteristic comprising the further set of camshaft positions and the further set of pressure values in relation to the further rotational speed of the combustion engine.

5. A method according to any one of the preceding claims, in which the combustion engine comprises a first camshaft adapted to control inlet control valves of the combustion engine and a second camshaft adapted to control exhaust port control valves of the combustion engine, the method comprising:

-measuring a set of camshaft positions of the first camshaft and a set of camshaft positions of the second camshaft as the camshafts rotate, and measuring a set of pressure values indicative of the pressure in the intake buffer tank as the camshafts rotate and the gas flow into the intake buffer tank remains constant; and

-providing a camshaft characteristic comprising a set of camshaft positions of the first camshaft and a set of camshaft positions of the second camshaft and the set of pressure values.

6. The method of any of the preceding claims, wherein the camshaft characteristics include a timing relationship between each of a set of camshaft positions of the first camshaft and a set of camshaft positions of the second camshaft and the set of pressure values, and a timing relationship between a set of camshaft positions of the first camshaft and a set of camshaft positions of the second camshaft.

7. The method of any one of the preceding claims, comprising storing the camshaft characteristic in a memory.

8. A method for calibrating a camshaft position of a camshaft of a combustion engine, the camshaft being adapted to control a valve to open and close an opening to a cylinder volume of the combustion engine, the combustion engine further comprising an intake buffer tank adapted to receive air from an external environment, the intake buffer tank being in fluid communication with the cylinder volume of the combustion engine for providing air to be mixed with fuel injected into a cylinder, wherein the method comprises:

-retrieving (S202) a camshaft feature indicative of a camshaft positioning calibration;

-operating (S204) the combustion engine at a predetermined rotational speed;

-providing (S206) a constant gas flow into the inlet buffer tank;

-measuring (S208) a set of camshaft positions and a set of pressure values indicative of the pressure in the intake buffer tank, while the camshaft is rotating and the gas flow into the intake buffer tank is kept constant;

-comparing (S210) the set of camshaft positions and the set of pressure values with the camshaft characteristic; and

-providing (S212) an instruction indicating a result of the comparison.

9. The method of claim 8, wherein the method comprises:

-adjusting the camshaft position in accordance with the command.

10. The method according to claim 8 or 9, characterized in that the method comprises:

-determining (S216) a pressure deviation between at least one pressure value of the camshaft characteristic and at least one measured pressure value of a set of measured pressure values of at least one respective camshaft position, and

-adjusting (S218) the camshaft position until the pressure deviation is below a threshold pressure deviation.

11. The method of claim 10, wherein the camshaft position is adjusted to minimize the pressure bias.

12. a camshaft positioning system for camshaft positioning of a camshaft comprised in a combustion engine, the camshaft (110; 118) being adapted to have a valve (208; 214) opening and closing an opening to a cylinder volume of the combustion engine, the combustion engine further comprising an intake buffer tank adapted to receive air from an external environment, the intake buffer tank being in fluid communication with the cylinder volume (102) of the combustion engine for providing air to be mixed with fuel injected into a cylinder, the system comprising a control unit configured to:

-controlling the combustion engine (100) to operate at a predetermined rotational speed;

-controlling an inlet damper (205) to provide a constant air flow into the inlet buffer tank;

-measuring a set of camshaft positions and a set of pressure values indicative of the pressure in the intake buffer tank while the camshaft is rotating and the gas flow into the intake buffer tank is kept constant; and

-providing a camshaft characteristic (402; 404; 406; 408; 410; 420; 422) comprising the set of camshaft positions and the set of pressure values.

13. The camshaft positioning system of claim 12 wherein the control unit is configured to execute a camshaft calibration procedure comprising:

-retrieving a camshaft feature indicative of a camshaft positioning calibration;

-controlling the combustion engine to run at a predetermined rotational speed;

-controlling an inlet flow conditioner (205) to provide a constant flow of gas into the inlet buffer tank;

-measuring a set of camshaft positions and a set of pressure values indicative of the pressure in the intake buffer tank while the camshaft is rotating and the gas flow into the intake buffer tank is kept constant;

-comparing the set of camshaft positions and the set of pressure values with the camshaft characteristic; and

-providing an instruction indicating a result of the comparison.

14. a camshaft positioning system as claimed in claim 12 or 13 comprising a memory for storing the camshaft characteristics.

15. A camshaft positioning system as claimed in any one of claims 12 to 14 wherein the combustion engine is configured to provide propulsion to a vehicle.

Technical Field

The invention relates to a method for camshaft positioning calibration and a corresponding camshaft positioning system.

Background

camshafts are common in combustion engines and are used to control various valves in the combustion engine. The camshaft comprises a shaft and at least one, usually several cams arranged on the shaft. When the shaft rotates, the cam moves about the axis of rotation of the shaft and causes the valve to open or close depending on the rotational position of the camshaft.

By careful design and accurate positioning of the camshaft, high accuracy timing control of the valve can be achieved. One valve is typically arranged to control the flow of an air/fuel mixture into a cylinder of the combustion engine and the other valve is typically arranged to control the exhaust gas emission from the cylinder. The crankshaft controls the stroke of the pistons in the cylinders according to the combustion cycle of the engine. Therefore, it is very important that the timing relationship between the crankshaft and the camshaft is accurate. Poor timing of the camshaft results in higher fuel consumption and increased exhaust emissions to the environment.

Furthermore, although the timing of the camshaft is calibrated during the production of the vehicle, it is difficult to accurately recover the originally calibrated camshaft positioning.

Accordingly, there is a need for improved camshaft positioning calibration.

Disclosure of Invention

In view of the above, it is an object of the present invention to provide an improved camshaft positioning calibration, which allows camshaft positioning calibration of a single camshaft.

According to a first aspect of the invention, a method is provided for generating a camshaft signature (camshaft signature) for camshaft positioning calibration of a camshaft comprised in a combustion engine, the camshaft being adapted for having a valve opening and closing an opening to a cylinder volume of the combustion engine, the combustion engine further comprising an intake buffer tank adapted for receiving air from an external environment, the intake buffer tank being in fluid communication with the cylinder volume of the combustion engine for providing air for mixing with fuel injected into the cylinder, wherein the method comprises: operating the combustion engine at a predetermined rotational speed; providing a constant gas flow into an inlet buffer tank; measuring a set of camshaft positions and a set of pressure values indicative of pressure in the intake buffer tank while the camshaft is rotating and the airflow into the intake buffer tank is held constant; and providing a camshaft characteristic including the set of camshaft positions and the set of pressure values.

The invention is based on the realization that the camshaft position is related to the pressure in the inlet buffer vessel. The camshaft position is directly related to the valve position, in other words, the degree to which the valve is open.

when the valve opens or closes the opening to the cylinder volume, the fluid communication between the intake buffer tank and the cylinder volume changes, whereby the measurable pressure in the intake buffer tank also changes. Thus, the position of the camshaft may be correlated to the measurable pressure in the intake buffer tank. In this manner, the camshaft features provide a "fingerprint" for a single camshaft. Thus, the camshaft characteristics may be considered unique to a particular camshaft in its engine.

The camshaft characteristics may be stored in memory and used for subsequent camshaft positioning.

the flow of air into the intake buffer tank is kept constant so that a measurable pressure change in the intake buffer tank is caused by the opening or closing of the valve due to the rotation of the camshaft.

the rotation of the camshaft is performed in a controlled manner, i.e. at a controlled speed, so that the position of the camshaft can be measured.

The position of the camshaft refers to the rotational position of the camshaft relative to a predetermined reference position. The rotational position may be provided as a relative rotational angle to the reference position.

The pressure value may be provided as a pressure difference value with respect to a pressure at a predetermined reference position of the camshaft. The predetermined position of the camshaft may be defined as zero degrees of rotation.

The predetermined rotational speed may be set by specifying an engine RPM (revolutions per minute). The rotational speed of the vehicle is kept constant, so that it can be ensured that the operating temperature of the engine is relatively constant during the generation of the camshaft characteristic. Maintaining a constant operating temperature reduces the effect of temperature fluctuations on the measured pressure in the intake valve.

In an embodiment, the camshaft may be adapted to control one of an intake port control valve and an exhaust port control valve of the combustion engine.

The camshaft characteristics may also include a timing relationship between a set of camshaft positions and a set of pressure values. In other words, the camshaft characterization may include an associated timing of camshaft positions and pressure values to provide a more accurate camshaft characterization.

according to an embodiment, the method may comprise operating the combustion engine at a predetermined further rotational speed; measuring another set of camshaft positions and another set of pressure values indicative of pressure in the intake buffer tank while the camshaft is rotating and the airflow into the intake buffer tank is held constant; and providing a camshaft characteristic comprising the further set of camshaft positions and the further set of pressure values in relation to a further rotational speed of the combustion engine.

Thus, the camshaft characteristics may advantageously include camshaft positions and pressure values measured at more than one engine speed. In this case, the camshaft features may be considered to comprise a set of partial camshaft features: a first partial camshaft characteristic at a first rotational speed and a second partial camshaft characteristic at a second rotational speed.

According to an embodiment, the combustion engine may comprise a first camshaft adapted to control an intake port control valve of the combustion engine and a second camshaft adapted to control an exhaust port control valve of the combustion engine, the method may comprise: measuring a set of camshaft positions of the first camshaft and a set of camshaft positions of the second camshaft as the camshafts rotate, and measuring a set of pressure values indicative of pressure in the intake buffer tank as the camshafts rotate and the airflow into the intake buffer tank remains constant; and providing a camshaft characteristic comprising a plurality of sets of camshaft positions and the set of pressure values. Thus, the camshaft features may include camshaft positions and pressure values for more than one camshaft, thereby enabling provision of camshaft features for positioning calibration of more than one camshaft.

In the above case, the camshaft characteristics may include a timing relationship between each of the plurality of sets of camshaft positions and a set of pressure values, and a timing relationship between the plurality of sets of camshaft positions.

According to a second aspect of the invention, there is provided a method for calibrating a camshaft position of a camshaft of a combustion engine, the camshaft being adapted to control a valve to open and close an opening to a cylinder volume of the combustion engine, the combustion engine further comprising an intake buffer tank adapted to receive air from an external environment, the intake buffer tank being in fluid communication with the cylinder volume of the combustion engine for providing air to be mixed with fuel injected into the cylinder, wherein the method comprises: retrieving camshaft features indicative of camshaft positioning calibration; operating the combustion engine at a predetermined rotational speed; providing a constant gas flow into an inlet buffer tank; measuring a set of camshaft positions and a set of pressure values indicative of pressure in the intake buffer tank while the camshaft is rotating and the airflow into the intake buffer tank is held constant; the set of camshaft positions and the set of pressure values are compared to a camshaft characteristic and a command indicative of a result of the comparison is provided.

The invention is therefore also based on the realization that an accurate adjustment of the camshaft is achieved using the provided camshaft features. This adjustment may be performed after production of the vehicle, for example, at a shop, by first retrieving the stored camshaft characteristics from a memory, which may be included in the vehicle or stored on a server.

The camshaft position may be adjusted according to the provided command.

for example, in some embodiments, the adjustment may be provided by: a pressure deviation between at least one pressure value of the camshaft characteristic and at least one measured pressure value of a set of measured pressure values of at least one respective camshaft position is determined, and the camshaft position is adjusted until the pressure deviation is below a threshold pressure deviation. Thus, by being able to correlate camshaft position with pressure deviation, a relatively direct but accurate control of camshaft position adjustment is provided. Camshaft position adjustment may be performed while the engine is running.

The camshaft position may be adjusted to minimize pressure deviations. In this way, it is ensured that the camshaft position is as close as possible to the position indicated by the camshaft characteristics.

this second aspect of the invention provides similar advantages as discussed above in relation to the previous aspect of the invention.

according to a third aspect of the invention, there is provided a camshaft positioning system for camshaft positioning of a camshaft comprised in a combustion engine, the camshaft being adapted to have a valve opening and closing an opening to a cylinder volume of the combustion engine, the combustion engine further comprising an intake buffer tank adapted to receive air from an external environment, the intake buffer tank being in fluid communication with the cylinder volume of the combustion engine for providing air for mixing with fuel injected into the cylinder, the system comprising a control unit configured to: controlling the combustion engine to operate at a predetermined rotational speed; controlling an air inlet valve to provide a constant air flow into an air inlet buffer tank; measuring a set of camshaft positions and a set of pressure values indicative of pressure in the intake buffer tank while the camshaft is rotating and the airflow into the intake buffer tank is held constant; and providing a camshaft characteristic including the set of camshaft positions and the set of pressure values.

In an embodiment, the control unit may be configured to perform a camshaft calibration procedure comprising: retrieving camshaft features indicative of camshaft positioning calibration; operating the combustion engine at a predetermined speed and operating temperature; providing a constant gas flow into an inlet buffer tank; measuring a set of camshaft positions and a set of pressure values indicative of pressure in the intake buffer tank while the camshaft is rotating and the airflow into the intake buffer tank is held constant; the set of camshaft positions and the set of pressure values are compared to the camshaft characteristic and an instruction indicative of a result of the comparison is provided.

The system may include a memory for storing camshaft characteristics.

The combustion engine may be configured to provide propulsion to the vehicle.

other features and advantages of the invention will become apparent when studying the appended claims and the following description. It will be appreciated by a person skilled in the art that different features of the invention can be combined to form embodiments other than those described below without departing from the scope of the invention.

drawings

These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing exemplary embodiments of the invention, wherein:

FIG. 1 conceptually illustrates a combustion engine having a crankshaft and a camshaft;

FIG. 2 schematically illustrates an embodiment of the present invention;

figure 3a schematically shows the rotational position of the cam;

FIG. 3b schematically shows a timing diagram of the intake cam and the exhaust cam;

FIG. 4a conceptually illustrates a camshaft feature;

FIG. 4b conceptually illustrates a camshaft feature;

FIG. 5 is a flow chart of method steps according to an embodiment of the present invention;

FIG. 6 is a flow chart of method steps according to an embodiment of the present invention; and

FIG. 7 is a flow chart of additional method steps according to an embodiment of the present invention.

Detailed Description

In this detailed description, various embodiments of systems and methods according to the present invention are described. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person. Like numbers refer to like elements throughout.

FIG. 1 conceptually illustrates an exemplary combustion engine 100 of a vehicle. The combustion engine includes a plurality of cylinders (not shown) and a plurality of pistons 104. A respective piston 104 is provided in each cylinder. The piston 104 is forced to move in the corresponding cylinder by igniting the fuel in the cylinder volume. The stroke motion of the pistons in the cylinders is transferred to a crankshaft 108 for transmitting propulsive power to a driveline (not shown) of a vehicle including the combustion engine 100.

Further, to allow air to mix with the fuel in the cylinder volume, the valve 109 (only one of several valves is numbered) is configured to open an air inlet to the cylinder volume at timed intervals. This timing is provided by a linking mechanism 111 (so-called "timing belt"), the linking mechanism 111 being configured to rotate the first camshaft 110 about the axis of rotation 112 so that the cams 114 of the camshaft 110 open and close the first valves 109 in a synchronized manner with respect to the rotation of the crankshaft, and thus with respect to the stroke of the pistons 104.

further, the second camshaft 118 is configured to open and close a second valve 120 (only one valve is numbered). Timing of the operation of the second valve 120 is also provided by the coupling mechanism 111. Thus, the coupling mechanism is configured to rotate the second camshaft 118 about the rotational axis 115 such that the cams 116 of the second camshaft 118 open and close the second valve 120 in a synchronized manner relative to the rotation of the crankshaft 108, and thus relative to the stroke of the piston 104.

The second valve 120 controls the flow of exhaust gas from the cylinder volume in a manner that is synchronized with the rotation of the crankshaft 108, and thus synchronized with respect to the stroke of the piston 104. The timing relationship between the opening and closing of valves 109 and 120 will be described further below.

Figure 2 conceptually illustrates an intake and exhaust port system of a combustion engine. Specifically, FIG. 2 schematically illustrates an intake buffer tank 204 adapted to receive air from an external environment via a compressor 206 and an intake damper 205, the intake damper 205 configured to regulate airflow into the intake buffer tank 204 and to measure airflow into the intake buffer tank 204. Compressor 206 provides pressurized air to intake buffer tank 204 via intake damper 205. The compressor 206 may receive air from the external environment through an air intake (not shown).

further, a pressure sensor (not shown) is provided to measure the pressure in the intake buffer tank 204. The pressure sensor(s) may be a manifold pressure sensor (MAP sensor) located in the intake buffer tank 204. Additionally, in some possible embodiments, a temperature sensor is provided to measure the temperature of the air in the intake buffer tank 204. This may be advantageous to determine that excessive temperature fluctuations occur in the intake air.

the intake buffer tank 204 is in fluid communication with the cylinder volume 102 via an intake port control valve 208. The cam 210 of the camshaft is adapted to open and close the spring-loaded valve by rotation of the camshaft, as described with reference to fig. 1.

Further, the exhaust buffer tank 212 is adapted to receive exhaust gas from the cylinder volume 102 via an exhaust port control valve 214. The cams 216 of the second camshaft are adapted to open and close the spring-loaded valves 216 by rotation of the camshaft, as described with reference to fig. 1.

Some of the exhaust gas is circulated back through an exhaust gas recirculation cooler 218 and an exhaust gas recirculation valve 220 to mix with air from the intake buffer tank 204 before entering the cylinder volume via the intake port control valve 208. Thus, the intake surge tank 204 and the exhaust surge tank 212 are in fluid communication with each other.

the intake and exhaust port systems may include other components, such as backpressure valves (backpressure valves) and pressure regulators on the exhaust side of the cylinders. These components are known per se to the person skilled in the art.

In an embodiment of the present invention, the air flow into the intake buffer tank 204 is provided at a constant air flow through the control of the intake damper 205 when the combustion engine is operating at a predetermined operating speed (e.g., RPM), relatively constant operating temperature.

The camshaft, including the respective cams 210 and 216, rotates, and the camshaft position sensor measures the position of the camshaft relative to a reference position. The camshaft position is usually given by the angle of rotation relative to a reference position and can be measured by a cam sensor (not shown), which is known per se to the person skilled in the art and can be realized by means of an inductive sensor sensing a magnet attached to the camshaft, a hall effect sensor sensing the magnetic field from the magnet, or an AC coupled sensor sensing the magnetic field influenced by the rotation of the camshaft.

As the camshaft rotates, the cams 210 and 216 cause the respective valves 208, 214 to open and close the respective openings to the cylinder volume 102. The opening and closing of each valve causes a pressure change in the intake buffer tank 204. When measuring the position of the camshaft, a pressure value indicating a pressure change is measured at the same time.

the camshaft characteristics include a set of camshaft positions and a set of pressure values for at least one camshaft.

Accordingly, a camshaft positioning system for camshaft positioning of a camshaft may include a control unit configured to control a combustion engine to operate at a predetermined rotational speed and operating temperature. The control unit may control the inlet damper 205 to provide a constant airflow into the inlet surge tank 204. Further, when the camshaft is rotating and the airflow into the intake buffer tank 204 is kept constant, the control unit uses the cam sensor to measure a set of camshaft positions and uses the pressure sensor to measure a set of pressure values indicative of the pressure in the intake buffer tank. The control unit may then provide a camshaft characteristic including the set of camshaft positions and the set of pressure values.

fig. 3a schematically shows an exemplary rotational position of the cam 301. The cam 301 is rotated by an angle a relative to the reference position. The rotation angle alpha may represent a camshaft position. Several reference positions are possible and the reference position shown in fig. 3a is shown for exemplary purposes only.

The cam diagram shown in fig. 3b depicts the angular position of the cam controlling the intake valve and the angular position of the cam controlling the exhaust valve. Generally, the structure of a camshaft includes a cylindrical shaft having a cam in the shape of a lobe (lobe) extending transversely to the shaft. The cam is configured to convert rotational motion of the shaft into translational motion that controls the reciprocating motion of the valve. The configuration of the cam results in the position of the valve being depicted as a graph as shown in fig. 3.

The lobes represented by curve 302 describe the valve positions of the exhaust valves and the lobes represented by curve 304 describe the valve positions of the intake valves, each caused by a corresponding camshaft rotation. When the cam represented by lobe 302 is in a position that causes exhaust valve lift to exceed level 308, the exhaust valve is fully open to allow exhaust gas to be expelled from the cylinder volume. Similarly, when the cam represented by lobe 304 is in a position where the intake valve lift exceeds level 308, the intake valve is fully open to allow air to enter the cylinder volume.

In addition, the overlap 310 between the lobes 302 and 304 provides a brief duration in which the intake and exhaust ports are at least partially simultaneously open. Thus, this is another supplement to the pressure change in the intake buffer tank 204 caused by the opening and closing of each valve.

Thus, since the valve motion of the intake valve 210 and the exhaust valve 216 is controlled directly or indirectly (through other linkages) by the structure of the cams of the camshaft, the pressure conditions in the intake buffer tank 204 will also be influenced by the structure of the camshaft, and the design of any other linkages associated with controlling the valves 210 and 216 via the camshaft. The camshaft and valves (and other coupling mechanisms) are subject to manufacturing and assembly tolerances, which means that each combustion engine is unique. For this reason, the camshaft features may be generated when the combustion engine is manufactured and the camshaft position is initially configured.

thus, a set of pressure values and associated camshaft position values serve as a camshaft characteristic. Such camshaft characteristics may be determined at the time of manufacture of the vehicle combustion engine. Camshaft characteristics may be stored. Subsequently, camshaft features may be retrieved and used for camshaft recalibration.

Fig. 4a shows a set of camshaft features 402, 404, 406, 408, 410 of a combustion engine, respectively with respect to different engine rpm, 1000rpm, 2000rpm, 3000rpm, 4000rpm, 4500 rpm. The camshaft feature of FIG. 4a is shown for exemplary purposes as a camshaft responsible for controlling the exhaust port control valve (see valve 214 in FIG. 2). The camshaft characteristics include a set of camshaft positions of the camshaft and a set of pressure values (y-axis) indicative of a pressure differential in the intake buffer tank at a zero degree angular position relative to the camshaft for the respective camshaft position. In other words, the pressure value is provided as a pressure difference with respect to the pressure at a predetermined reference position of the camshaft (i.e., at a zero degree rotational position).

Fig. 4b shows another pair of camshaft features 420 and 422 for a combustion engine with respect to different rpm, 1500rpm and 2500rpm, respectively. The camshaft feature of fig. 4b is shown for exemplary purposes as a camshaft for use in charge of controlling the intake port control valve (see valve 208 in fig. 2). The camshaft characteristics include a set of camshaft positions of the camshaft and a set of pressure values (y-axis) indicative of a pressure differential in the intake buffer tank at a zero degree angular position relative to the camshaft for the respective camshaft position.

Fig. 5 shows a flow chart of method steps according to an exemplary embodiment. In a first step S102, the combustion engine is operated at a predetermined rotational speed. Subsequently, in step S104, a constant flow of air is provided into the intake buffer tank. In step S106, a set of camshaft positions and a set of pressure values indicative of the pressure in the intake buffer tank are measured while the camshaft is rotating and the airflow into the intake buffer tank is kept constant. In step S108, a camshaft characteristic is provided that includes the set of camshaft positions and the set of pressure values.

Fig. 6 shows a flow chart of method steps according to an exemplary embodiment. In step S202, camshaft features indicative of camshaft positioning calibration are retrieved. Next, in step S204, the combustion engine is operated at a predetermined rotation speed. In step S206, a constant flow of air is provided into the intake buffer tank. In step S208, a set of camshaft positions and a set of pressure values indicative of the pressure in the intake buffer tank are measured while the camshaft is rotating and the airflow into the intake buffer tank is kept constant. In step S210, the set of camshaft positions and the set of pressure values are compared to the camshaft characteristics. In step S212, an instruction indicating the result of the comparison is provided.

Fig. 7 shows a flowchart of method steps according to an exemplary embodiment. The camshaft position may be adjusted according to the command provided in step S212 of fig. 6. The adjustment may be determined by first determining (S216) a pressure deviation between at least one pressure value of the camshaft characteristic and at least one measured pressure value of a set of measured pressure values of at least one respective camshaft position. In step S218, the camshaft position is adjusted until the pressure deviation is below the threshold pressure deviation. Preferably, the pressure deviation is minimized.

The adjustment of the camshaft position is performed while the engine is running.

the control functions of the present disclosure may be implemented using an existing computer processor, or by a special purpose computer processor incorporated for an appropriate system, for this or another purpose, or by a hardwired system. Embodiments within the scope of the present disclosure include program products comprising machine-readable media for executing or having machine-executable instructions or data structures stored thereon. Such machine-readable media can be any available media that can be accessed by a general purpose or special purpose computer or other machine with a processor. By way of example, such machine-readable media can comprise RAM, ROM, EPROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to execute or store desired program code (in the form of machine-executable instructions or data structures) and which can be accessed by a general purpose or special purpose computer or other machine with a processor. When information is transferred or provided over a network or another communications connection (either hardwired, wireless, or a combination of hardwired or wireless) to a machine, the machine properly views the connection as a machine-readable medium. Thus, any such connection is properly termed a machine-readable medium. Combinations of the above are also included within the scope of machine-readable media. Machine-executable instructions comprise, for example, instructions and data which cause a general purpose computer, special purpose computer, or special purpose processing machines to perform a certain function or group of functions.

Although the figures may show the order, the order of the steps may be different than that depicted. And two or more steps may be performed simultaneously or partially simultaneously. Such variations will depend on the software and hardware systems chosen and on designer choice. All such variations are within the scope of the present disclosure. Likewise, a software implementation could be accomplished with standard programming techniques using rule based logic and other logic to accomplish the various connection steps, processing steps, comparison steps and decision steps.

The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims shall not be construed as limiting the scope.