METHOD FOR CONTROLLING CAM SHAFT IN ENGINE

A method for controlling a cam shaft in an engine, may include determining whether a current phase angle of a cam shaft relative to a crank shaft exceeds a predetermined reference range set for determining abnormality of alignment of the cam shaft relative to the crank shaft (S10); when it is determined that the current phase angle exceeds the reference range, determining a control error phase angle which is a difference between the current phase angle and a learned phase angle recently learned as a normal value within the reference range (S20); and controlling an actuator to adjust a phase of the cam shaft and to compensate for an error, taking into account the control error phase angle determined in the determining S20 (S30).

DETAILED DESCRIPTION

Referring toFIGS. 2 and 3, a method for controlling a cam shaft in an engine according to an exemplary embodiment of the present invention includes: determining, by a controller, whether a current phase angle ⊖_curr of a cam shaft relative to a crank shaft exceeds a predetermined reference range of ⊖_thrsh_lo to ⊖_thrsh_hi set for determining abnormality of alignment of the cam shaft relative to the crank shaft (S10), if it is determined that the current phase angle exceeds the reference range, calculating, by the controller, a control error phase angle ω_err to be compensated for from a difference between the current phase angle ⊖_curr and a learned phase angle ⊖_earn recently learned as a normal value within the reference range (S20), and controlling, by the controller, an actuator so that it adjusts the phase of the cam shaft so as to compensate for the error, taking into account the control error phase angle calculated in the calculating S20(S30).

In addition, the method includes: if it is determined that the current phase angle exceeds the reference range as a result of the determining of abnormality S10, accumulating, by the controller, at least one of the count and time of a failure (S15), and determining, by the controller, whether the accumulated failure count C_fail exceeds a predetermined threshold value C_thrsh, and if, so, recording a fail code and lighting Check Engine light (S40). The controlling of the actuator S30is consistently carried out even after the determining of accumulated fail count S40.

That is, the controller controlling an engine receives a current phase angle of a cam shaft relative to a crank shaft in real time to carry out the determining of abnormality S10, and, depending on the result, controls the actuator taking into account a control error phase angle calculated in the calculating S20. By doing so, abnormality of alignment of the cam shaft is actually detected, and thus the actuator is controlled such that it corrects the control error phase angle not only during but also after failure is ascertained in the determining of accumulated fail count S40as far as possible. Accordingly, the engine may normally operate and be protected from malfunction or damage.

The method further includes, after the calculating S20and before the controlling S30, if the control error phase angle ω_err calculated in the calculating S20is greater than the maximum phase angle ω_max adjustable by the actuator, setting, by the controller, the control error phase angle to be limited to the maximum phase angle adjustable by the actuator (S25).

This is because an error beyond the maximum phase angle adjustable by the actuator cannot be compensated for in any case. The maximum phase angle is determined based on hardware limitations such as whether the actuator is of a hydraulic or electric motor type, or how wide range the actuator has.

In the controlling S30, the actuator is controlled with a control target phase angle ω_target obtained by adding the control error phase angle ω_err to a mapping phase angle ω_map, which is obtained by adding control correction phase angles ω_corr according to signals from the sensors representing the operating environment of an engine to a control base phase angle ω_base, i.e., base control value for the phase angle of the cam shaft.

In existing variable valve timing systems, an actuator is controlled with a mapping phase angle ω_map obtained by adding a control correction phase angle ω_corr to a control base phase angle ω_base, such that control is made based on the default control base phase angle, together with the control correction phase angle reflecting internal and external factors of current engine operating environment. In contrast, in the exemplary embodiments of the present invention, the control error phase angle ω_err obtained as described above is further reflected to determine the control target phase angle ω_target, and control is made according to the control target phase angle ω_target. Accordingly, as can be seen fromFIG. 3, if the engine is not operated normally as shown in the left hand but is operated abnormally as shown in the middle, the actuator is controlled according to the control target phase angle as shown in the right hand, so that appropriate timings for opening or closing valves actually necessary for the operating condition of the engine is ensured.

For your information,FIG. 3symbolically illustrates the operation of the present invention using the conceptual relation between the phase angle of an actuator and the phase angle of a cam shaft connected to the actuator.

The predetermined threshold value C_thrsh used for comparing the accumulated fail count is set to be a level not influenced by noise such that noise generated during the transition periods due to rapid changes in operating conditions of an engine does not affect determination, and thus failure is more accurately determined.

That is, the reference value may be determined when designing based on many experiments so that erroneous determination may be prevented due to electric noise which may be generated during transition periods in which rapid changes in operating conditions of an engine are made, such as start-up of the engine, or sudden acceleration or deceleration.

Further, the predetermined reference range, which is set for determining whether or not the alignment of the cam shaft relative to the crank shaft is normal, may be set to be a smaller range than the phase difference which may occur when a teeth of a timing chain connecting the crank shaft and the cam shaft of the engine is moved to the next position.

In other words, although the current phase angle of the cam shaft relative to the crank shaft may be changed at any time due to various factors such as the assembly tolerance of an engine, output error of a crank shaft or cam shaft sensor, slack of a timing chain or belt, the size of such changes is normally so small that it is distinguishable from the size of the phase angle occurring when at least one teeth of the timing chain is moved to the next position, and, therefore, the reference range may be set within the smaller range than the phase difference in the above situation.

Needless to say, the reference range represents that the current phase angle is not normal, and is determined when designing based on experiments and analyses, which is marked as ⊖_thrsh_lo to ⊖_thrsh_hi inFIG. 2.

By configuring an engine control system operating an actuator according to the method described above, the actuator is controlled so that it consistently corrects errors even when the alignment of a cam shaft is deviated, such that engine may be operated substantially normally and the engine may be protected from malfunction or damage consistently.

The rest of the parts ofFIG. 2, which have not been described above, illustrates the followings: if the current phase angle of the cam shaft is determined to be a normal level within the reference range in the determining of abnormality S10, a learned phase angle ⊖_learn is updated with the current phase angle S11, the learned phase angle is stored in a non-volatile memory when the engine is turned off S12, this data is fetched when the engine is started up S13, and this data is used in the calculating S20.

As stated above, according to an exemplary embodiment of the present invention, in an engine having a variable valve timing system, an actuator is controlled so that, even if it is determined that alignment of the cam shaft relative to a crank shaft is abnormal, it allows the engine to operate normally as far as possible, such that malfunction of the engine can be prevented and the operability of the engine can be improved.