Abstract:
A variable valve timing device delivers rotation of a crankshaft to a first camshaft, and to a second camshaft through the first camshaft. First and second variable valve timing units change phases of the first and second camshafts, respectively. A crankshaft sensor senses angle changes of the crankshaft. A camshaft sensor senses angle changes of the second camshaft. A control portion controls the phase of the second camshaft by controlling the second variable valve timing unit, or controls the phases of both camshafts by controlling the first variable valve timing unit, according to signals from the crankshaft sensor and the camshaft sensor. Also, a control method for such a device. One of several possible modes is selected. Target phases of the camshafts corresponding to an operation of an engine are determined. Phases of the first camshaft and/or the second camshaft are controlled according to the selected mode.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to, and the benefit of, Korean Patent Application No. 10-2007-0118033, filed in the Korean Intellectual Property Office on Nov. 19, 2007, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    (a) Field of the Invention 
         [0003]    The present invention relates to a variable valve timing device and a control method for the same. 
         [0004]    (b) Description of the Related Art 
         [0005]    A typical combustion chamber of an automotive engine is provided with an intake valve for supplying the air/fuel mixture and an exhaust valve for expelling the burned gas. The intake and exhaust valves are opened and closed by a valve lift apparatus connected to a crankshaft. 
         [0006]    A conventional valve lift apparatus has a fixed valve lift amount due to a fixed cam shape. Therefore, it is impossible to adjust the amount of a gas that is being introduced or exhausted. 
         [0007]    If the valve lift apparatus is designed for low driving speeds the valve open time and amount are not sufficient for high speeds. On the other hand, if the valve lift apparatus is designed for high speeds, the opposite is true. 
         [0008]    One proposed system to improve efficiency in high and low driving speeds includes cams that have different profiles. At high speeds, a high lift cam that has a high lift profile and increases opening angles of valves is used, and at low speeds, a low lift cam that has low lift profile and decreases opening angles of valves is used. 
         [0009]    Another proposed system includes a camshaft timing gear provided with a variable valve timing unit in front of an intake valve camshaft, that changes phase angles of the cams without changing opening/closing valve timing. 
         [0010]    However, a variable valve device that uses a variable valve timing unit controls only a phase angle of an intake valve, so efficient control of valve timing is difficult. Alternatively, variable valve timing units must be provided with camshaft phase sensors at both intake and exhaust camshafts. Controlling such a unit is very complicated. 
         [0011]    The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
       SUMMARY OF THE INVENTION 
       [0012]    A variable valve timing device delivers rotation of a crankshaft to a first camshaft, and to a second camshaft through the first camshaft. A first variable valve timing unit changes a phase of the first camshaft. A second variable valve timing unit changes a phase of the second camshaft. A crankshaft sensor senses angle changes of the crankshaft. A camshaft sensor senses angle changes of the second camshaft. A control portion controls the phase of the second camshaft by controlling the second variable valve timing unit, or controls the phases of both camshafts by controlling the first variable valve timing unit, according to signals from the crankshaft sensor and the camshaft sensor. 
         [0013]    The first camshaft may be an exhaust camshaft and the second camshaft may be an intake camshaft. Alternatively, the first camshaft may be an intake camshaft and the second camshaft may be an exhaust camshaft. 
         [0014]    The control portion may select one of several possible modes, and control the camshafts according to the selected mode. The modes may be: a first mode in which the phase of the second camshaft is retarded and the phases of both camshafts are adjusted by adjusting the phase of the first camshaft, a second mode in which the phase of the second camshaft is advanced and the phases of both camshafts are adjusted by adjusting the phase of the first camshaft, a third mode in which the phase of the first camshaft is advanced and the phase of the second camshaft is adjusted, and a fourth mode in which the phase of the first camshaft is retarded and the phase of the second camshaft is adjusted. 
         [0015]    A control method for a variable valve timing device that delivers rotation of a crankshaft to a first camshaft, and to a second camshaft through the first camshaft, is also disclosed. One of several possible modes is selected. Target phases of the first camshaft and the second camshaft corresponding to an operation of an engine are determined. Phases of the first camshaft and/or the second camshaft are controlled according to the selected mode. The modes include: a first mode in which the phase of the first camshaft is retarded and the phases of both camshafts are adjusted, a second mode in which the phase of the second camshaft is advanced and the phases of both camshafts are adjusted, a third mode in which the phase of the first camshaft is advanced and the phase of the second camshaft is adjusted, and a fourth mode in which the phase or the first camshaft is retarded and the phase of the second camshaft is adjusted. 
         [0016]    The first and second modes may include detecting an actual phase of the second camshaft and calculating an actual phase of the first camshaft based on the actual phase of the second camshaft. The third and fourth modes may include detecting an actual phase of the second camshaft. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a perspective view of a variable valve timing device according to an exemplary embodiment of the present invention. 
           [0018]      FIG. 2  illustrates a control principle regarding phases of an intake camshaft and an exhaust camshaft of a variable valve timing device according to an exemplary embodiment of the present invention. 
           [0019]      FIG. 3  is a block diagram showing a variable valve timing device according to an exemplary embodiment of the present invention. 
           [0020]      FIG. 4  is a flow chart of a control method of a variable valve timing device according to an exemplary embodiment of the present invention. 
           [0021]      FIG. 5A  is a flow chart of a control method of a first mode of a variable valve timing device according to an exemplary embodiment of the present invention. 
           [0022]      FIG. 5B  is a flow chart of a control method of a second mode of a variable valve timing device according to an exemplary embodiment of the present invention. 
           [0023]      FIG. 5C  is a now chart of a control method of a third mode of a variable valve timing device according to an exemplary embodiment of the present invention. 
           [0024]      FIG. 5D  is a flow chart of a control method of a fourth mode of a variable valve timing device according to an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0025]    An exemplary embodiment the present invention will be described more fully hereinafter with reference to the accompanying drawings. 
         [0026]    As shown in  FIG. 1 , in a variable valve timing device according to an exemplary embodiment of the present invention, rotation of a crankshaft  10  is transferred to a first camshaft  40  by a first power delivery portion  30 , and rotation of the first camshaft  40  is transferred to a second camshaft  60  by a second power delivery portion  50 . 
         [0027]    A first variable valve timing unit  45  and a second variable valve timing unit  65  are provided to the first camshaft  40  and the second camshaft  60 , respectively. 
         [0028]    A crankshaft sensor  20  detects phase angle changes of the crankshaft  10 . A camshaft sensor  70  detects phase angle changes of the second camshaft  60 . 
         [0029]    Referring to  FIG. 3 , a control portion  100  controls the first and second variable valve timing units  45 ,  65 . The control portion  100  receives signals of phase angle changes from the crankshaft sensor  20  and the camshaft sensor  70 . 
         [0030]    An engine speed sensor  110  detects an operational state of an engine and transmits a signal to the control portion  100 . In addition to the engine speed sensor  110 , other conditions of operational state of the vehicle may be detected by other state detectors (not shown). 
         [0031]    A memory  120  communicates with the control portion  100  and transmits data to the control portion  100  for operation. 
         [0032]    Referring to  FIGS. 1-2 , if the phase angle of the first camshaft  40  is changed by the first variable valve timing unit  45 , the phase angle of the second camshaft  60  also changes, due to the rotation of first camshaft  40  being transferred to the second camshaft  60  by the second power delivery portion  50 . 
         [0033]    However, the converse is not true. That is, the phase angle of the second camshaft  60  can change without changing the phase angle of the first camshaft  40 . 
         [0034]    In the example illustrated in  FIG. 2 , the first camshaft  40  is an exhaust camshaft and the second camshaft  60  is an intake camshaft, but the present invention is not limited thereto. 
         [0035]    Opening and closing timing of the camshafts is controlled by selectively using four control modes. 
         [0036]    Referring to  FIG. 2 ,  FIG. 4 , and  FIG. 5 , in the first mode, the phase of the intake camshaft  60  is retarded, and the phase of the intake camshaft  60  and the exhaust camshaft  40  are simultaneously adjusted by adjusting the phase of the exhaust camshaft  40 . 
         [0037]    In the second mode, the phase of the intake camshaft  60  is advanced, and the phases of the camshafts  40 ,  60  are simultaneously adjusted by adjusting the phase of the exhaust camshaft  40 . 
         [0038]    In the third mode, the phase of the exhaust camshaft  40  is advanced, and the phase of the intake camshaft  60  is adjusted. 
         [0039]    In the fourth mode, the phase of the exhaust camshaft  40  is retarded, and the phase of the intake camshaft  60  is adjusted. 
         [0040]    The retarded phase and the advanced phase may be maximally retarded and maximally advanced phases, respectively. These are relative amounts that can be set in camshafts of the first variable valve timing unit  45  and the second variable valve timing unit  65 , and that can be variable according to the kind of engine. 
         [0041]    Referring to  FIG. 2 , in the first mode, the phases of the exhaust camshaft  40  and the intake camshaft  60  are simultaneously controlled from “A” to “B”. 
         [0042]    A phase change ratio of the intake camshaft  60  is determined according to the second power delivery portion  50 . The phase change ratio can be changed according to required performance. 
         [0043]    In the third mode, the phase of the exhaust camshaft  40  is advanced, and the phase of the intake camshaft  60  is changed from “A” to “C”. 
         [0044]    In the second mode, the phases of the exhaust camshaft  40  and the intake camshaft  60  are simultaneously controlled from “C” to “D”. 
         [0045]    In the fourth node the phase of the exhaust camshaft  40  is retarded, and the phase of the intake camshaft  60  is changed from “B” to “D”. 
         [0046]    Typically, when a vehicle stalls, an exhaust valve is fixed to a retarded phase and an intake valve is fixed to an advanced phase, so it is preferred that a starting control mode is the first mode as shown in  FIG. 4 , but the present invention is not limited thereto. 
         [0047]    Hereinafter, a method for determining phase of each camshaft will be explained. 
         [0048]    In the first mode, a phase of the intake camshaft  60  is detected by the camshaft sensor  70 , and the detected phase is determined to be a present phase of the intake camshaft  60 . 
         [0049]    A phase of the exhaust camshaft  40  is determined by subtracting a first predetermined phase from the phase of the intake camshaft  60 . The first predetermined phase is a difference between the phase of the exhaust camshaft  40  and the phase of the intake camshaft  60  when the phase of the exhaust camshaft  40  is the retarded phase and the phase of the intake camshaft  60  is the advanced phase. 
         [0050]    In the second mode, a phase of the intake camshaft  60  is detected by the camshaft sensor  70 , and the detected phase is determined to be a present phase of the intake camshaft  60 . Further, a phase of the exhaust camshaft  40  is determined by subtracting a second predetermined phase from the phase of the intake camshaft  60 . 
         [0051]    The second predetermined phase is a difference between the phase of the exhaust camshaft  40  and the phase of the intake camshaft  60  when the phase of the exhaust camshaft  40  is the advanced phase and the phase of the intake camshaft  60  is the advanced phase. 
         [0052]    In the third mode, a phase of the intake camshaft  60  is detected and the detected phase is determined to be a present phase of the intake camshaft  60 , and a phase of the exhaust camshaft  40  is determined to be the advanced phase. 
         [0053]    In the fourth mode, a phase of the intake camshaft  60  is detected and the detected phase is determined to be a present phase of the intake camshaft  60 , and a phase of the exhaust camshaft  40  is determined to be the retarded phase. 
         [0054]    The first predetermined phase and the second predetermined phase are saved in the memory  120 , and are used when the control portion  100  determines a control mode. Also, an engine operation condition can be saved in the memory  120  and used for controlling. 
         [0055]    The control portion  100  using signals from each or the sensors  20 ,  70 , and  110  and operation conditions to determine a target phase corresponding to the operation conditions of an engine, and controls phases of the intake camshaft  60  and the exhaust camshaft  40 . 
         [0056]    The control steps can be achieved using a target phase that is saved in the memory corresponding to an operation condition of an engine. 
         [0057]    Referring to  FIG. 4  and  FIG. 5 , a phase of the camshaft is controlled by the first mode (S 410 ) when the engine is turned on. 
         [0058]    An operation condition of an engine is detected (S 420 ), and control steps stop when the engine is not operated (S 460 ) or control steps go ahead when the engine is operated. 
         [0059]    The control portion  100  determines a control mode according to an operation condition of the engine (S 440 ), and controls a phase of the camshaft according to the determined control mode (S 450 ). 
         [0060]    The operation condition is then detected again (S 420 ) and the control continues. 
         [0061]    In  FIG. 5 , control charts are shown for each control mode. 
         [0062]    In the first control node, as shown in  FIG. 5A , the first mode starts (S 510 ), a phase of the intake camshaft  60  is detected (S 512 ), and a phase of the exhaust camshaft  40  is determined by a difference between a phase of the intake camshaft  60  and a phase of the first predetermined phase (S 514 ). The control portion  100  determines a target phase according to data in the memory  120  and detected operation conditions (S 516 ). A phase of the intake camshaft  60  is fixed to the retarded phase, and a phase of the exhaust camshaft  40  is controlled on the basis of the target phase (S 518 ). 
         [0063]    In the second mode, as shown in  FIG. 5B , the second mode starts (S 520 ), a phase of the intake camshaft  60  is detected (S 522 ), and a phase of the exhaust camshaft  40  is determined by a difference between a phase of the intake camshaft  60  and a phase of the second predetermined phase (S 524 ). The control portion  100  determines a target phase according to data in the memory  120  and detected operation conditions (S 526 ). A phase of the intake camshaft  60  is fixed to the advanced phase and a phase of the exhaust camshaft  40  is controlled on the basis of the target phase (S 528 ). 
         [0064]    In the third mode, as shown in  FIG. 5C , the third mode starts (S 530 ), and a phase of the intake camshaft  60  is detected (S 5532 ). The control portion  100  determines a target phase according to data in the memory  120  and detected operation conditions (S 534 ). A phase of the exhaust camshaft  40  is fixed to the advanced phase, and a phase of the intake camshaft  60  is controlled on the basis of the target phase (S 536 ). 
         [0065]    In the fourth mode, as shown in  FIG. 5D , the fourth mode starts (S 540 ), and a phase of the intake camshaft  60  is detected (S 542 ). The control portion  100  determines a target phase according to data in the memory  120  and detected operation conditions (S 544 ). A phase of the exhaust camshaft  40  is fixed to the retarded phase, and a phase of the intake camshaft  60  is controlled on the basis of the target phase (S 546 ). 
         [0066]    The exemplary variable valve timing device and control method can control the phases of the intake camshaft  60  and the exhaust camshaft  40  so that control response speed is fast and malfunctions can be prevented. The control is achieved with one camshaft sensor so that the number of elements, production cost, and maintenance are reduced. 
         [0067]    While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.