Patent Publication Number: US-2022220906-A1

Title: Valve control apparatus for engine

Description:
BACKGROUND OF THE DISCLOSURE 
     Field of the disclosure 
     The present disclosure relates to a valve control apparatus for controlling opening and closing of an exhaust valve and an intake valve of an engine. 
     Related Art 
     In general, a valve control apparatus for an engine includes a camshaft in which cams for opening and closing an exhaust valve and an intake valve of each cylinder are coupled to one shaft. 
     To describe a four-stroke engine as an example, the engine cycle consists of four piston strokes: intake, compression, explosion, and exhaust. That is, one cycle is completed by two rotations of the crankshaft. In addition, an intake valve and an exhaust valve for each cylinder are mounted on a cylinder head of the engine, and the opening and closing of the intake valve and the exhaust valve is performed by rotation of a camshaft that rotates in conjunction with the crankshaft. At this time, the camshaft rotates by being connected to the crankshaft with the timing chain or the like, and the camshaft rotates once while the crankshaft rotates two times. 
     Therefore, the crankshaft and the camshaft rotate according to the four-stroke cycle operation of each cylinder, and the intake valve and the exhaust valve are opened and closed with the rotation of the camshaft, enabling continuous operation of the engine. 
     Here, a typical camshaft is designed to open the intake valve and the exhaust valve one by one. The intake valve is designed to increase the volumetric efficiency by allowing fresh air to enter the cylinder well and, and the exhaust valve is designed to allow exhaust gas to escape well. 
     Meanwhile, various new technologies are being applied to diesel engines to satisfy the enhancing environmental regulations, and an exhaust gas recirculation (EGR) system and a selective catalytic reduction (SCR) system are mainly used as a method for reducing nitrogen oxides in the exhaust gas. 
     However, when the exhaust gas recirculation system and the selective catalytic reduction system are applied to the engine to reduce the nitrogen oxides in the exhaust gas, there is a limitation that the cost of manufacturing the engine is greatly increased and the structure of the engine is quite complicated. 
     SUMMARY 
     Embodiments of the present disclosure provide a valve control apparatus for an engine capable of improving engine torque, improving fuel economy of the engine, lowering the temperature of engine exhaust gas, and reducing nitrogen oxide emissions, by increasing the volumetric efficiency of an engine cylinder. 
     In an aspect, there is provided a valve control apparatus for an engine that opens and closes an exhaust valve and an intake valve of the engine in conjunction with a crankshaft of the engine. The valve control apparatus for the engine includes an exhaust valve opening and closing device opening and closing the exhaust valve during a first exhaust valve opening period, and an intake valve opening and closing device opening and closing the intake valve during a first intake valve opening period. In addition, the exhaust valve opening and closing device is configured to further open and close the exhaust valve during a second exhaust valve opening period relatively shorter than the first exhaust valve opening period within the first intake valve opening period, and the intake valve opening and closing device is configured to further open and close the intake valve during a second intake valve opening stage relatively shorter than the first intake valve opening period within the first exhaust valve opening period. 
     The valve control apparatus for an engine may further include a camshaft connected to the crankshaft and driven to rotate, the exhaust valve opening and closing device may include an exhaust cam provided on the camshaft, and the intake valve opening and closing device may include an intake cam provided on the camshaft. The exhaust cam may include a first exhaust cam nose for opening and closing the exhaust valve during the first exhaust valve opening period and a second exhaust cam nose for opening and closing the exhaust valve during the second exhaust valve opening period, the intake cam may include a first intake cam nose for opening and closing the intake valve during the first intake valve opening period and a second intake cam nose for opening and closing the intake valve during the second exhaust valve opening period, and the second exhaust cam nose and the second intake cam nose may be formed to have a size relatively smaller than the first exhaust cam nose and the first intake cam nose, respectively. 
     A profile of the exhaust cam may be formed so that a ratio of the second exhaust valve opening period by the second exhaust cam nose of the exhaust cam to the first exhaust valve opening period by the first exhaust cam nose of the exhaust cam is falls within a range of 0.32 to 0.36. 
     A profile of the exhaust cam may be formed so that a ratio of the second intake valve opening period by the second intake cam nose of the intake cam to the first intake valve opening period by the first intake cam nose of the intake cam is falls within a range of 0.34 to 0.38. 
     A piston reciprocating within a cylinder of the engine may be located at a top dead center when a crankshaft rotation angle is 0 degrees, 360 degrees, and 720 degrees, and be located at a bottom dead center when the crankshaft rotation angle is 180 degrees and 540 degrees, and a maximum opening point of the exhaust valve in the second exhaust valve opening period may fall within a range of 487 degrees to 507 degrees based on the crankshaft rotation angle. 
     The first intake valve opening period may fall within a range of 310 degrees to 590 degrees based on the crankshaft rotation angle. 
     A piston reciprocating within a cylinder of the engine may be located at a top dead center when a crankshaft rotation angle is 0 degrees, 360 degrees, and 720 degrees, and be located at a bottom dead center when the crankshaft rotation angle is 180 degrees and 540 degrees, and a maximum opening point of the intake valve in the second intake valve opening period may fall within a range of 216 degrees to 236 degrees based on the crankshaft rotation angle. 
     The first exhaust valve opening period may fall within a range of 120 degrees to 390 degrees based on the crankshaft rotation angle. 
     A maximum lift of the exhaust valve in the second exhaust valve opening period and a maximum lift of the intake valve in the second intake valve opening period may be 0.8 mm or more. 
     According to embodiments of the present disclosure, a valve control apparatus for an engine can improve engine torque, improve fuel economy of the engine, lower the temperature of engine exhaust gas, and reduce nitrogen oxide emissions, by increasing the volumetric efficiency of an engine cylinder. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a valve control apparatus for an engine according to an embodiment of the present disclosure. 
         FIG. 2  is a view illustrating a profile of an intake cam of  FIG. 1 . 
         FIG. 3  is a view illustrating a profile of an exhaust cam of  FIG. 1 . 
         FIG. 4  shows lift diagrams of an intake valve and an exhaust valve operated by the valve control apparatus for the engine of  FIG. 1 . 
         FIG. 5  shows operating states of the intake valve and the exhaust valve at point P 1  of  FIG. 4 . 
         FIG. 6  shows operating states of the intake valve and the exhaust valve at point P 2  of  FIG. 4 . 
         FIG. 7  shows operating states of the intake valve and the exhaust valve at point P 3  of  FIG. 4 . 
         FIG. 8  shows operating states of the intake valve and the exhaust valve at point P 4  of  FIG. 4 . 
         FIG. 9  is a view illustrating a numerical limitation of the profile of the valve control apparatus for the engine of  FIG. 1 . 
         FIG. 10  is a graph showing an experiment result according to an operation of the intake valve when the engine to which the valve control apparatus for the engine of  FIG. 1  is applied is operating in a low speed region. 
         FIG. 11  is a graph showing an experiment result according to an operation of the intake valve when the engine to which the valve control apparatus for the engine of  FIG. 1  is applied is operating in a high speed region. 
         FIG. 12  is a graph showing an experiment result according to an operation of the exhaust valve when the engine to which the valve control apparatus for the engine of  FIG. 1  is applied is operating in a low speed region. 
         FIG. 13  is a graph showing an experiment result according to an operation of the exhaust valve when the engine to which the valve control apparatus for the engine of  FIG. 1  is applied is operating in a high speed region. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art may easily implement the present disclosure. The present disclosure may be implemented in various different forms and is not limited to the embodiments described herein. 
     It is to be noted that drawings are schematic and are not drawn to scale. Relative dimensions and ratios of parts in the drawings are exaggerated or reduced in size for clarity and convenience in the drawings, and any dimensions are merely exemplary and not limiting. In addition, the same reference numerals are used to indicate similar features to the same structure, element, or part appearing in two or more drawings. 
     Embodiments of the present disclosure specifically represent ideal embodiments of the present disclosure. As a result, various variations of the illustration are expected. Accordingly, embodiments are not limited to a specific shape in the illustrated area, and includes, for example, a modification of the shape by manufacturing. 
     Hereinafter, a valve control apparatus  101  for an engine according to an embodiment of the present disclosure will be described with reference to  FIGS. 1 to 13 . The valve control apparatus  101  may control opening and closing of an intake valve  710  and an exhaust valve  720  of the engine. Here, the engine may be a four-stroke diesel engine, and may include a crankshaft. The crankshaft is a device that converts the reciprocating motion of a piston  400  into rotational motion. Since the crankshaft is widely known to those skilled in the art, detailed descriptions of the crankshaft will be omitted. 
     Specifically, in the four-stroke engine, one cycle is completed with four piston strokes: intake, compression, explosion, and exhaust. That is, the piston  400  descends in the intake stroke, the piston  400  rises in the compression stroke, the piston  400  descends in the combustion stroke, and the piston  400  rises in the exhaust stroke. In this way, since the piston  400  reciprocates twice in one cycle, the crankshaft rotates twice. The intake valve  710  and the exhaust valve  720  are mounted on the cylinder head of the engine for each cylinder  500 . The valve control apparatus  101  is for opening and closing the intake valve  710  and the exhaust valve  720  every one cycle, and the valve control apparatus  101  may include an intake valve opening and closing device for opening and closing the intake valve  710  and an exhaust valve opening and closing device for opening and closing the exhaust valve  720 . The intake valve opening and closing device and the exhaust valve opening and closing device may be configured in a mechanical or electronic manner. According to an exemplary embodiment, the electronic intake valve opening and closing device and the exhaust valve opening and closing device may be configured to be connected to the intake valve  710  and the exhaust valve  720 , respectively, to be driven by electromagnetic force, or to open and close the intake valve  710  and the exhaust valve  720  by driving a camshaft  100  to be described later with an electric device, such as an electric motor. Meanwhile, the mechanical intake valve opening and closing device and the exhaust valve opening and closing device may include a camshaft  100  for opening and closing the intake valve  710  and the exhaust valve  720  by rotating in conjunction with the crankshaft of the engine. The camshaft  100  may be provided to open and close the intake valve  710  and the exhaust valve  720  by one rotation per cycle, and connected to the crankshaft through a power transmission means such as a timing chain so as to rotate once as the crankshaft rotates twice. In addition, as the camshaft  100 , one camshaft  100  having a plurality of cams controls the intake valves  710  and the exhaust valves  720 , or a plurality of cams are installed in a distributed manner on a plurality of camshafts  100 , so that the plurality of camshafts  100  may share the control of the opening and closing of the intake valves  710  and the exhaust valves  720 . The electronic valve control apparatus and the mechanical valve control apparatus described above may control an opening and closing timing, period, and valve lift of the intake valve  710  and the exhaust valve  720  in the same degree. Hereinafter, for convenience of understanding, a mechanical valve control apparatus using one camshaft  100 , which can be referred to as a universal structure, will be described as an example. 
     As shown in  FIG. 1 , the camshaft  100  of the valve control apparatus  101  for the engine according to an embodiment of the present disclosure includes an intake cam  200  and an exhaust cam  300 . The intake cam  200  opens and closes the intake valve  710  while rotating, and the exhaust cam  300  opens and closes the exhaust valve  720  while rotating. 
     Specifically, as shown in  FIG. 2 , the intake cam  200  may include a first intake cam nose  210  and a second intake cam nose  220 . The second intake cam nose  220  is formed to have a size relatively smaller than that of the first intake cam nose  210 . In addition, the second intake cam nose  220  is formed on the opposite side of the first intake cam nose  210 , but the second intake cam nose  220  and the first intake cam nose  210  are not necessarily formed at an angle of 180 degrees. 
     The first intake cam nose  210  of the intake cam  200  opens and closes the intake valve  710  during the first intake valve opening period, and the second intake cam nose  220  of the intake cam  200  additionally open and close the intake valve  710  during the second intake valve opening period. At this time, the second intake valve opening period is relatively shorter than the first intake valve opening period. In addition, the second intake valve opening period falls within the first exhaust valve opening period to be described later. That is, the intake valve  710  is opened and closed by the second intake cam nose  220  during the time when the exhaust valve  720  is opened by the first exhaust cam nose  310 . 
     The exhaust cam  300  may include a first exhaust cam nose  310  and a second exhaust cam nose  320 , as shown in  FIG. 3 . The second exhaust cam nose  320  is formed to have a relatively smaller size than that of the first exhaust cam nose  310 . In addition, the second exhaust cam nose  320  is formed on the opposite side of the first exhaust cam nose  310 , but the second exhaust cam nose  320  and the first exhaust cam nose  310  are not necessarily formed at an angle of 180 degrees. 
     The first exhaust cam nose  310  of the exhaust cam  300  opens and closes the exhaust valve  720  during the first exhaust valve opening period, and the second exhaust cam nose  320  of the exhaust cam  300  additionally open and close the exhaust valve  720  during the second exhaust valve opening period. At this time, the second exhaust valve opening period is relatively shorter than the first exhaust valve opening period. In addition, the second exhaust valve opening period falls within the first intake valve opening period described above. That is, the exhaust valve  720  is opened and closed by the second exhaust cam nose  320  during the time when the intake valve  710  is opened by the first intake cam nose  210 . 
     The intake valve  710  may be opened in advance by a preset crank rotation angle before the exhaust valve  720  is closed. The section in which the intake valve  710  and the exhaust valve  720  are simultaneously opened in this way is referred to as an overlap section, and in the present embodiment, the overlap section is formed within the range of 35 degrees to 40 degrees based on the crank rotation angle, and the angle between the point at which the intake valve  710  starts to open and the top dead center of the piston is formed larger than the angle between the point at which the exhaust valve  720  is closed and the top dead center of the piston. Here, the piston top dead center is 360 degrees based on the crank rotation angle. For example, the time point at which the intake valve  710  starts to open for the above-described overlap may be set to be faster than the piston top dead center within the range of 24 degrees to 28 degrees based on the crank rotation angle, and the point at which the exhaust valve  720  is completely closed may be set to be later than the piston top dead center within a range of 10 degrees to 16 degrees based on the crank rotation angle. Accordingly, the intake valve  710  and the exhaust valve  730  may be simultaneously opened in a total of three sections, including simultaneous opening sections in two sections to be described later. 
     Hereinafter, an operating process and effects of the camshaft  100  of the valve control apparatus  101  for the engine according to an embodiment of the present disclosure will be exemplarily described with reference to  FIGS. 4 to 8 . 
       FIG. 4  is a graph showing a timing and degree of opening and closing of the intake valve  710  and the exhaust valve  720  by rotation of the camshaft  100  of the valve control apparatus  101  for the engine.  FIGS. 5 to 8  show opening and closing states of the intake valve  710  and the exhaust valve  720  at points P 1 , P 2 , P 3 , and P 4  of  FIG. 4 , respectively. 
     However, in  FIGS. 5 to 8 , the connection structure between the camshaft  100  of the valve control apparatus  101  for the engine and the intake valve  710  and the exhaust valve  720  is not shown in detail, but it is known to those skilled in the art in a variety of ways. For example, the intake cam  200  and the exhaust cam  300  may directly contact the intake valve  710  and the exhaust valve  720 , respectively, to open and close them. In addition, the intake cam  200  and the exhaust cam  300  may open and close the intake valve  710  and the exhaust valve  720  through mechanisms such as a push rod, a tappet, and a rocker arm. Specifically, the engine may be classified into a side valve (SV) type, an over-head valve (OHV) type, an over-head camshaft (OCC) type, a dual over-head camshaft (DOHC) type, and the like, based on the position of the valve or the camshaft  100  of the valve control apparatus  101  for the engine. In addition, as described above, the valve control apparatus may open and close the valves by using an electronic control method. 
     First, when the exhaust stroke starts while the piston  400  rises, the camshaft  100  of the valve control apparatus  101  for the engine in conjunction with the crankshaft rotates and the first exhaust cam nose  310  of the exhaust cam  300  opens the exhaust valve  720 . Here, the exhaust valve  720  opened by the first exhaust cam nose  310  is opened during the first exhaust valve opening period. 
     Next, at point P 1  of  FIG. 4 , as shown in  FIG. 5 , the intake valve  710  is opened by the second intake cam nose  220  of the intake cam  200  within the first exhaust valve opening period. In this way, when the intake valve  710  is opened during the exhaust stroke, some of the exhaust gas in a combustion chamber of the cylinder  500  is discharged through the intake valve  710 , and the exhaust gas discharged through the intake valve  710  is introduced into the combustion chamber of the cylinder  500  again together with new air in the subsequent intake stroke. In this way, when some of the exhaust gas is discharged through the intake valve  710  in the exhaust stroke and then introduced back into the cylinder  500  in the intake stroke, an effect similar to the exhaust gas recirculation (EGR) system in the related art can be obtained. 
     Then, at point P 2  in  FIG. 4 , as shown in  FIG. 6 , the intake valve  710  is first closed, and the exhaust gas is discharged through the exhaust valve  720  to complete the exhaust stroke. 
     Next, at point P 3  of  FIG. 4 , as shown in  FIG. 7 , when the intake stroke starts while the piston  400  descends, the camshaft  100  of the valve control apparatus  101  for the engine in conjunction with the crankshaft rotates and the first intake cam nose  210  of the intake cam  200  opens the intake valve  710 . Here, the intake valve  710  opened by the first intake cam nose  210  is opened during the first intake valve opening period. In this way, when the intake valve  710  is opened, the exhaust gas discharged through the intake valve  710  in the exhaust stroke is introduced into the combustion chamber of the cylinder together with fresh air. 
     Next, at point P 4  of  FIG. 4 , as shown in  FIG. 8 , the exhaust valve  720  is opened by the second exhaust cam nose  320  of the exhaust cam  300  within the first intake valve opening period. Then, some of the new air introduced into the combustion chamber of the cylinder  500  through the intake valve  710  is immediately discharged through the exhaust valve  720 . Due to this phenomenon, as the residual gas inside the cylinder  500  is reduced, the internal pressure of the cylinder  500  is lowered, and more new air is introduced through the intake valve  710 , accordingly. That is, the volumetric efficiency of the cylinder  500  is improved. In addition, new air that is introduced into the intake valve  710  and immediately exits through exhaust valve  720  has an effect of lowering the overall temperature of the exhaust gas. That is, the temperature of the exhaust gas discharged from the engine can be reduced. 
     With this configuration, the valve control apparatus  101  for the engine according to an embodiment of the present disclosure can improve engine torque, improve fuel economy of the engine, lower the temperature of engine exhaust gas, and reduce nitrogen oxide emissions, by increasing the volumetric efficiency of the cylinder  500 . 
     In particular, it is possible to reduce nitrogen oxide emissions without installing complex equipment to apply an exhaust gas recirculation (EGR) system and a selective catalytic reduction system to the engine. 
     However, when the intake valve  710  is opened during the exhaust stroke, the internal pressure of the cylinder  500  and the pressure on the exhaust valve  720  side have to be higher than the pressure on the intake valve  710  side, and the pressure varies according to the operating conditions of the engine, and thus the opening/closing timing and period of the intake valve  710  has to be determined in consideration of both when the engine is operating in the low speed region and when the engine is operating in the high speed region. 
     In addition, when the exhaust valve  720  is opened during the intake stroke, the opening and closing timing and period of the exhaust valve  720  have to be determined in consideration of the variation in pressure depending on the rotational speed of the engine and the volumetric efficiency of the cylinder  500 . 
     That is, opening the intake valve  710  during the exhaust stroke and opening the exhaust valve  720  during the intake stroke are distinctly different technologies and have different purposes, and thus the simple combination of the two technologies cannot be easily applied. 
     When opening the intake valve  710  during the exhaust stroke and opening the exhaust valve  720  during the intake stroke are simultaneously applied, the performance of the engine may be rather degraded. For example, when the engine is operating in a low speed region, the amount of air filled in the cylinder  500  is rather reduced, and the torque of the engine may be reduced, accordingly. 
     Therefore, the valve control apparatus  101  for the engine according to an embodiment of the present disclosure is made to an optimum value in consideration of all the above-described matters. 
     Hereinafter, profiles of the intake cam  200  and the exhaust cam  300  included in the valve control apparatus  101  for the engine according to an embodiment of the present disclosure will be described with reference to lift diagrams shown in  FIG. 9 . 
     First, the piston  400  reciprocating within the cylinder  500  of the engine to which the valve control apparatus  101  for the engine according to an embodiment of the present disclosure may be located at a top dead center when a crankshaft rotation angle is 0 degrees, 360 degrees, and 720 degrees, and is located at a bottom dead center when the crankshaft rotation angle is 180 degrees and 540 degrees. 
     A first exhaust valve opening period A 1  may fall within a range of 120 degrees to 390 degrees based on the crankshaft rotation angle. As an example, the first exhaust valve opening period A 1  may range from 140 degrees to 375 degrees based on the crankshaft rotation angle. 
     A second exhaust valve opening period A 2  falls within a first intake valve opening period B 1 , but a maximum opening point A 3  of the exhaust valve  720  in the second exhaust valve opening period A 2  may fall within the range of 487 degrees to 507 degrees based on the crankshaft rotation angle. That is, the exhaust valve  720  can be opened to the maximum later than the piston bottom dead center in the first intake valve opening period B 1 . In addition, A profile of the exhaust cam  300  may be formed so that a ratio of the second exhaust valve opening period A 2  by the second exhaust cam nose  320  of the exhaust cam  300  to the first exhaust valve opening period A 1  by the first exhaust cam nose  310  of the exhaust cam  300  is falls within a range of 0.32 to 0.36. 
     The first intake valve opening period B 1  may fall within a range of 310 degrees to 590 degrees based on the crankshaft rotation angle. As an example, the first intake valve opening period B 1  may range from 330 degrees to 580 degrees. 
     A second intake valve opening period B 2  falls within the first exhaust valve opening period A 1 , but a maximum opening point B 3  of the intake valve  710  in the second intake valve opening period B 2  may fall within the range of 216 degrees to 236 degrees based on the crankshaft rotation angle. That is, the intake valve  710  can be opened to the maximum later than the piston bottom dead center in the first exhaust valve opening period A 1 . In addition, a profile of the intake cam  200  may be formed so that a ratio of the second intake valve opening period B 2  by the second intake cam nose  220  of the intake cam  200  to the first intake valve opening period B 1  by the first intake cam nose  210  of the intake cam  200  is falls within a range of 0.34 to 0.38. 
     In addition, profiles of the exhaust cam  300  and the intake cam  400  may be formed so that a maximum lift A 4  of the exhaust valve  720  in the second exhaust valve opening period A 2  and a maximum lift B 4  of the intake valve  710  in the second intake valve opening period B 2  is 0.8 mm or more. 
     In addition, the maximum lift A 4  of the exhaust valve  730  in the second exhaust valve opening period A 2  may be set to 10% or less of the maximum lift B 5  of the intake valve  710 , and the maximum lift B 4  of the intake valve  710  in the second intake valve opening period B 2  may be set to 10% or less of the maximum lift A 5  of the exhaust valve  720 . Meanwhile, the maximum lift A 4  of the exhaust valve  720  in the second exhaust valve opening period A 2  may be formed to be relatively large compared to the maximum lift B 4  of the intake valve  710  in the second intake valve opening period B 2 . Meanwhile, the maximum lift A 4  of the exhaust valve  720  in the second exhaust valve opening period A 2  may be formed to be relatively large within a range of 15% to 25%, compared to the maximum lift B 4  of the intake valve  710  in the second intake valve opening period B 2 . 
     In addition, the maximum lift time A 3  of the exhaust valve  720  in the second exhaust valve opening period A 2  and the maximum lift time B 3  of the intake valve  710  in the second intake valve opening period B 2  may be formed to have a first phase difference T 1  of  260  degrees to 280 degrees based on the crankshaft rotation angle. The maximum lift point of the exhaust valve  720  in the first exhaust valve opening period A 1  and the maximum lift point of the intake valve  710  in the first intake valve opening period B 1  may be formed to have a second phase difference T 2  of 190 degrees to 210 degrees based on the crankshaft rotation angle, and thus the first phase difference T 1  may be formed to be larger than the second phase difference T 2  by 30% or more. In addition, a fourth phase difference T 4  between the maximum lift point A 3  of the exhaust valve  720  and the maximum lift point of the intake valve  710  in the first intake valve opening period B 1  may be formed larger than a third phase difference T 3  between the maximum lift point B 3  of the intake valve  710  and the maximum lift point of the exhaust valve  720  in the first exhaust valve opening period A 1 . As an example, the third phase difference T 3  may be formed from 20 degrees to 28 degrees, and the fourth phase difference T 4  may be formed from 38 degrees to 48 degrees. 
     With the phase differences described above, it is possible to not only help improve the volumetric efficiency of the cylinder and purify exhaust gas, but also prevent machining defects and durability degradation due to interference between the first intake cam nose  210 , the second intake cam nose  220 , the first exhaust cam nose  310 , and the second exhaust cam nose  320  when the camshaft  100  of the valve control apparatus  101  for the engine is machined. 
     Hereinafter, with reference to  FIGS. 10 to 13 , experiment results of an engine to which the valve control apparatus  101  for the engine according to an embodiment of the present disclosure, which is manufactured with the above-described numerical values, is applied will be described. 
     Experimental results were divided into when the engine is operating in the low speed region and when the engine is operating in the high speed region, and again, the intake valve  710  and the exhaust valve  720  are separately displayed. Here, the low speed region and the high speed region may be variously changed depending on the type and performance of the engine. In the present experiment, the low speed region was 800 rpm, and the high speed region was 1800 rpm. 
     Specifically,  FIG. 10  is a graph showing the experimental results by the operation of the intake valve  710  when the engine is operating in the low speed region, and  FIG. 11  a graph showing the experimental results by the operation of the intake valve  710  when the engine is operating in the high speed region. That is,  FIG. 10  shows a change in internal pressure of the cylinder  500 , a change in intake pressure, a change in exhaust pressure, and the degree of opening of the intake valve  710 , when the engine to which the valve control apparatus  101  for the engine according to an embodiment of the present disclosure is applied is operating in the low speed region, and  FIG. 11  shows a change in internal pressure of the cylinder  500 , a change in intake pressure, a change in exhaust pressure, the degree of opening of the intake valve  710  when the engine to which the valve control apparatus  101  for the engine according to an embodiment of the present disclosure is applied is operating in the high speed region. 
     The timing of opening of the intake valve  710  during the exhaust stroke is to be set in a section where the internal pressure of the cylinder  500  and the pressure on the exhaust valve  720  side are higher than the pressure on the intake valve  710  side. 
     Here, the pattern in which the internal pressure of the cylinder  500  fluctuates is different in the high speed region and the low speed region depending on the operating conditions of the engine. In addition, both patterns of fluctuations in the intake pressure and the exhaust pressure may be different. 
     Therefore, the second intake valve opening period B 2  is always to be set in a section in which the internal pressure of the cylinder  500  and the pressure on the exhaust valve  720  side are higher than the pressure on the intake valve  710  side, even if the operating condition of the engine changes. That is, the section in which the intake valve  710  is opened during the exhaust stroke is to be determined in consideration of section S 1  in  FIG. 10  and section S 2  in  FIG. 11 . 
     In conclusion, it can be seen as the optimal condition through  FIGS. 10 and 11  that the maximum opening point B 3  of the intake valve  710  in the second intake valve opening period B 2  falls within the range of 216 degrees to 236 degrees based on the crankshaft rotation angle. 
     In addition,  FIG. 12  is a graph showing the experimental results by the operation of the exhaust valve  720  when the engine is operating in the low speed region, and  FIG. 13  a graph showing the experimental results by the operation of the exhaust valve  720  when the engine is operating in the high speed region. That is,  FIG. 12  shows a change in internal pressure of the cylinder  500 , a change in intake pressure, a change in exhaust pressure, and the degree of opening of the lifted exhaust valve  720 , when the engine to which the valve control apparatus  101  for the engine according to an embodiment of the present disclosure is applied is operating in the low speed region, and  FIG. 11  shows a change in internal pressure of the cylinder  500 , a change in intake pressure, a change in exhaust pressure, the degree of opening of the lifted exhaust valve  720  when the engine to which the valve control apparatus  101  for the engine according to an embodiment of the present disclosure is applied is operating in the high speed region. 
     Due to the characteristics of the engine, the change in the exhaust pressure is relatively large compared to the intake pressure. Therefore, there is a section in which the exhaust pressure is temporarily smaller than the intake pressure and the internal pressure of the cylinder by the fluctuation of the exhaust pressure. That is, the timing of opening the exhaust valve  720  during the intake stroke is to be determined at a point where the internal pressure of the cylinder  500  and the pressure on the intake valve  710  side are higher than the pressure on the exhaust valve  720  side. In this way, some of the new air introduced through the intake valve  710  may be discharged out of the cylinder  500  directly through the exhaust valve  720  due to the pressure difference. 
     Here, the pattern in which the internal pressure of the cylinder  500  fluctuates is different in the high speed region and the low speed region depending on the operating conditions of the engine. In addition, both patterns of fluctuations in the intake pressure and the exhaust pressure may be different. 
     Therefore, the second exhaust valve opening period A 2  is always to be determined at a point where the internal pressure of the cylinder  500  and the pressure on the intake valve  710  side are higher than the pressure on the exhaust valve  720  side, even if the operating condition of the engine changes. That is, the section in which the exhaust valve  720  is opened during the intake stroke is to be determined in consideration of section S 3  in  FIG. 12  and section S 4  in  FIG. 13 . 
     In conclusion, it can be seen as the optimal condition through  FIGS. 12 and 13  that the maximum opening point A 3  of the exhaust valve  720  in the second intake valve opening period A 2  falls within the range of 487 degrees to 507 degrees based on the crankshaft rotation angle. 
     In addition, through the experiment, it was seen that an effect is exhibited when the maximum lift A 4  of the exhaust valve  720  in the second exhaust valve opening period A 2  and the maximum lift B 4  of the intake valve  710  in the second intake valve opening period B 2  is 0.8 mm or more. That is, it could be seen that a significant effect is exhibited that can improve engine torque, improve fuel economy of the engine, lower the temperature of engine exhaust gas, and reduce nitrogen oxide emissions, by increasing the volumetric efficiency of the cylinder  500  by lifting the intake valve  710  and the exhaust valve  720  at least 0.8 mm or more to open them. 
     Although the embodiments of the present disclosure have been described above with reference to the accompanying drawings, it should be understood that those skilled in the art to which the present disclosure pertains can carry out other modifications without changing the technical spirit or essential features thereof. 
     Therefore, the embodiments described above are merely exemplary in all respects and should not be construed to be limited, and it should be understood that the scope of the present disclosure is defined by the following claims and the meanings and ranges of the claims and all modifications and changed forms derived from their equivalents fall within the scope of the present disclosure. 
     INDUSTRIAL AVAILABILITY 
     According to embodiments of the present disclosure, a valve control apparatus for an engine may be used to improve engine torque, improve fuel economy of the engine, lower the temperature of engine exhaust gas, and reduce nitrogen oxide emissions, by increasing the volumetric efficiency of an engine cylinder.