Abstract:
A continuously variable valve actuation (CVVA) system may include a driving cam rotated by a driving force transmitted from a crankshaft, and a driven cam pressed by the driving cam to be rotated around a first end thereof serving as a rotational axle of the driven cam, wherein the driven cam has a cam face at a second end thereof so as to press and open a valve when rotated, and wherein a vertical distance between the rotational axis of the first end of the driven cam and a rotational axis of the driving cam is configured to be adjusted by moving a position of the rotational axis of the first end of the driven cam.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority to Korean Patent Application Number 10-2008-0123665 filed Dec. 5, 2008, the entire contents of which application is incorporated herein for all purposes by this reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to continuously variable valve actuation (CVVA) system and, more particularly, to a CVVA system in which the lift time, the lift distance and the duration of a valve can be simultaneously varied depending on various conditions of an engine, particularly the low-speed/high-speed operating range of an engine. 
     2. Description of Related Art 
     As for an engine, a camshaft is rotated by a rotating force transmitted from a crankshaft, and an intake valve and an exhaust valve reciprocate up and down with regular timing by cams of the camshaft. Thereby, intake air is supplied to a combustion chamber, and combustion gas is exhausted. In this process, a fuel-air mixture is compressed and exploded to generate power. 
     At this time, a device that can continuously vary the lift distance of a valve according to an operating speed of the engine is called a continuous variable valve actuation (CVVA) system. 
     Hereinafter, a conventional CVVA system will be described in detail with reference to the attached drawings. 
       FIG. 1  is a schematic side view illustrating the configuration of a conventional CVVA system. 
     As illustrated in  FIG. 1 , the conventional CVVA system includes a driving cam  4  installed on a camshaft  2 , a swing arm  12  swinging in contact with the driving cam  4 , a driving arm  19  driving a valve  5  in cooperation with the swing arm  12 , a variable arm  13  causing the driving arm  19  to pivot around a swing axle of the swing arm  12 , an actuator driving the variable arm  13 , and a cam means installed between the swing arm  12  and the driving arm  19 . 
     The swing arm  12  and the variable arm  13  are supported on a common control shaft  10  so as to allow relative motion. The driving arm  19  is connected to the variable arm  13  at the base end thereof, and has a driving portion  20  driving a rocker arm  6  at the leading end thereof. Further, the cam means includes a cam face  15  formed on the swing arm  12 , and a cam follower  22  supported on an intermediate portion of the driving arm  19 , and is configured to change an initial position of the driving arm  19  with respect to the swing arm  12  by pivoting of the driving arm  19 . 
     According to the aforementioned configuration of the conventional CVVA system, when the driving cam  4  is rotated in the counterclockwise direction at the position illustrated in  FIG. 1 , the end (particularly, the right-hand end) of the swing arm  12  rotates to move toward the driving arm  19 . When the end of the swing arm  12  comes into contact with the driving arm  19 , the rocker arm  6  is pressed, and thus the valve  5  is opened. 
     At this time, when the variable arm  13  is rotated in the counterclockwise direction at the position illustrated in  FIG. 1 , the intermediate portion of the driving arm  19  comes into contact with the rocker arm  6 , and thus gets near the end of the swing arm  12 . In this state, when the driving cam  4  is rotated, the end of the swing arm  12  presses the driving arm  19  earlier, so that the valve  5  has an earlier lift time and thus a longer lift distance. 
     Thus, the conventional CVVA system illustrated in  FIG. 1  has an advantage in that the lift time and distance of the valve can be regulated depending on the speed of the engine. 
     However, the conventional CVVA system essentially requires the constituent parts of the swing arm  12 , driving arm  19 , variable arm  13 , actuator  11 , etc. in order to transmit the force of the driving cam  4  to the valve  5 , so that the configuration thereof is complicated and the manufacturing costs thereof is increased. 
     The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art. 
     BRIEF SUMMARY OF THE INVENTION 
     Various aspects of the present invention are directed to provide a continuously variable valve actuation (CVVA) system which can simultaneously vary the lift time and the lift distance of a valve and has a simple structure. 
     In an aspect of the present invention, a continuously variable valve actuation system may include a driving cam rotated by a driving force transmitted from a crankshaft, and a driven cam pressed by the driving cam to be rotated around a first end thereof serving as a rotational axle of the driven cam, wherein the driven cam has a cam face at a second end thereof so as to press and open a valve when rotated, and wherein a vertical distance between the rotational axis of the first end of the driven cam and a rotational axis of the driving cam is configured to be adjusted by moving a position of the rotational axis of the first end of the driven cam. 
     The cam face may include a high lift section where the driven cam allows the valve to move more than a preset distance when rotated around the first end thereof, and a low lift section where the driven cam allows the valve to move down less than the preset distance when rotated around the first end thereof, wherein the high lift section has a midpoint farther from the rotational axle of the driven cam than that of the low lift section toward the driving cam. 
     In another aspect of the present invention, the continuously variable valve actuation system may further include an actuator configured to press the first end of the driven cam for adjusting a height of the first end of the driven cam such that the cam face contacting the valve is limited to one of the high lift section and the low lift section regardless of an rotational angle of the driven cam. 
     In further another aspect of the present invention, the continuously variable valve may further include a bracket wherein the driven cam includes a slide stub protruding from the rotational axle thereof and is slidably inserted into a slot formed on the bracket so as to limit a range within which a height of the driven cam is adjusted. 
     The driven cam may include a roller at a portion thereof which comes into contact with the driving cam. 
     The cam face may be curved inwards, and an upper end of the valve may be curved outwards at a part thereof which comes into contact with the cam face. 
     In another aspect of the present invention, the continuously variable valve actuation system may further include a contact block formed an upper portion of the valve, wherein the cam face is curved inwards and an upper end of the contact bracket is curved outwards at a part thereof which comes into contact with the cam face. 
     According to embodiments of the present invention, the lift time and distance of the valve can be simultaneously varied with neither a separate rocker arm for pressing the valve nor a separate variable cam for regulating the lift time of the valve, and thus the CVVA system has a very simple structure and reduces manufacturing costs. 
     The methods and apparatuses of the present invention have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description of the Invention, which together serve to explain certain principles of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side view illustrating the configuration of a continuously variable valve actuation (CVVA) system of the prior art. 
         FIG. 2  is a front perspective view illustrating an exemplary CVVA system according to the present invention. 
         FIG. 3  is a rear perspective view illustrating the exemplary CVVA system according to the present invention. 
         FIG. 4  is a side elevation view illustrating a driven cam in the exemplary CVVA system according to the present invention. 
         FIGS. 5 and 6  are elevation side views illustrating a low lift in the exemplary CVVA system according to the present invention. 
         FIGS. 7 and 8  are side elevation views illustrating a high lift in the exemplary CVVA system according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims. 
       FIG. 2  is a front perspective view illustrating a continuously variable valve actuator (CVVA) system according to various embodiments of the present invention.  FIG. 3  is a rear perspective view illustrating the exemplary CVVA system according to the present invention.  FIG. 4  is a side elevation view illustrating a driven cam in the exemplary CVVA system according to the present invention. 
     According to various embodiments of the present invention, the CVVA system includes a driving cam  200  rotated by a driving force transmitted from a crankshaft  100 , and a driven cam  400  pressed by the driving cam  200  to be rotated around one end thereof serving as a rotational axle. The driven cam  400  has a cam face  410  at the other end thereof so as to press and open a valve  300  when rotated. Thus, as illustrated in  FIG. 2  when the crankshaft  100  is rotated in the clockwise direction, the driving cam fixedly coupled to the crankshaft  100  is also rotated in the clockwise direction. When the driving cam  200  rotates to bring the lobe thereof into contact with the driven cam  400 , the driven cam  400  is rotated in the counterclockwise direction around one end thereof (right-hand side of  FIG. 2 ), serving as a rotational axle, and the cam face  410  of the driven cam  400  which is located at the other end thereof (left-hand side of  FIG. 2 ) slides on the top surface of the contact block  310 , and thus lowers a contact block  310  provided to the upper end of the valve  300 . As the contact block  310  is lowered, the valve  300  is opened. 
     At this time, the driven cam  400  is characterized by regulating a lift distance of the valve  300  (i.e. a distance by which the valve  300  is pushed in a downward direction when opened) and a lift time of the valve  300  according to the position of the rotational axle thereof, and directly pressing the upper end of the valve  300  in a downward direction when pivoted by the driving cam  200  to thereby open the valve  300 . 
     In detail, the conventional CVVA system as illustrated in  FIG. 1  is configured so that a driving force of the driving cam  4  is transmitted to the valve  5  through the swing arm  12 , variable arm  13 , driving arm  19  and rocker arm  6  in turn. In contrast, the CVVA system according to various embodiments may be configured so that a driving force of the driving cam  200  is directly transmitted to the valve  300  through the driven cam  400 . In this manner, since the CVVA system according various embodiments has a very simple configuration, it has an advantage in that it can be manufactured easily and inexpensively. Further, since the CVVA system may employ the single driven cam  400  as the constituent part for transmitting the driving force of the driving cam  200 , it can more stably transmit the driving force of the driving cam  200  and reduce a possibility of malfunction. 
     Here, the cam face  410  of the driven cam  400  has two sections that slide on the upper end of the valve  300  to thereby press the valve  300  in a downward direction when the driven cam  400  is rotated. The two sections include a high lift section H where the driven cam  400  allows the valve  300  to move down more than a preset distance when rotated around the rotational axle, i.e. one end, thereof, and a low lift section L where the driven cam  400  allows the valve  300  to move down less than a preset distance when rotated around the rotational axle, i.e. one end, thereof, as illustrated in  FIG. 4 . 
     Since the high lift section H is farther from the rotational axle of the driven cam  400  than the low lift section L, particularly since the midpoint of the high lift section H is farther from the rotational axle of the driven cam  400  than that of the low lift section L, the valve  300  is farther lowered when the high lift section H of the cam face  410  pushes the upper end of the valve  300 , as compared to when the low lift section L of the cam face  410  pushes the upper end of the valve  300 . 
     In this manner, the structure and principle in which the lowering distance of the valve  300  is varied depending on the height of the rotational axle of the driven cam  400  will be described below in detail with reference to  FIGS. 5 through 8 . 
     Further, according to various embodiments of the present invention, the CVVA system further includes an actuator  600  adjusting the height of one end of the driven cam  400  such that the cam face  410  of the driven cam  400  which comes into contact with the valve  300  is limited to the high lift section H or the low lift section L. 
     The actuator  600  is configured to be raised or lowered by a driving means such as a motor controlled by an electronic control unit (ECU) of the vehicle in contact with the bottom of one end of the driven cam  400 . When the actuator  600  is raised, one end of the driven cam  400  is pushed and raised by the actuator  600 . In contrast, when the actuator  600  is lowered, one end of the driven cam  400  is also lowered. 
     In detail, when one end of the driven cam  400  is raised by upward movement of the actuator  600 , only the high lift section H of the cam face  410  comes into contact with the contact block  310  of the valve  300 , so that the lowering distance of the valve  300  is increased. In contrast, when one end of the driven cam  400  is lowered by downward movement of the actuator  600 , only the low lift section L of the cam face  410  comes into contact with the contact block  310  of the valve  300 , so that the lowering distance of the valve  300  is reduced. 
     At this time, when the rotational axle of the driven cam  400  is too excessively raised or lowered, the cam face  410  of the driven cam  400  is separated from the contact block  310  of the valve  300 , so that the valve  300  may be abnormally raised or lowered. For this reason, the driven cam  400  has a slide stub  430  protruding from the rotational axle thereof, and a bracket  500  for guiding direction and distance where the slide stub  430  moves is additionally installed. 
     The bracket  500  is provided with a slot  510  into which the slide stub  430  is slidably inserted. The slide stub  430  can move only within a length of the slot  510 , so that the cam face  410  of the driven cam  400  is always kept in contact with the contact block  310 . 
     Further, when the driving cam  200  is configured to slide on a certain part of the driven cam  400 , at least one of the driving cam  200  and the driven cam  400  is worn out at its contact part, so that a rotational angle of the driven cam  400  may be changed. 
     Thus, the driven cam  400  is preferably provided with a roller  420  at the contact part with the driving cam  200 . In this manner, since the roller  420  is installed on the driven cam  400 , the roller  420  is rotated together when the driving cam  200  is rotated. As such, no wear occurs between the driving cam  200  and the roller  420 , so that the rotational angle of the driven cam  400  is kept constant. 
     Further, in order to allow the cam face  410  to be kept in stable contact with the contact block  310  when the driven cam  400  is rotated, the cam face  410  of the driven cam  400  is preferably curved inwards, while the contact block  310  of the valve  300  is preferably curved outwards. In various embodiments, although the valve  300  is configured so that the contact block  310  thereof comes into contact with the cam face  410  of the driven cam  400 , the valve  300  may be configured so that the upper end of the stem thereof comes into direct contact with the cam face  410  without the contact block  310 . 
       FIGS. 5 and 6  are side elevation views illustrating a low lift in the CVVA system according to various embodiments of the present invention, and  FIGS. 7 and 8  are side elevation views illustrating a high lift in the exemplary CVVA system according to the present invention. 
     In the case in which a short lift distance of the valve  300  is required, the actuator  600  and one end of the driven cam  400  are lowered (see  FIG. 3 ), and thus the slide stub  430  of the driven cam  400  is located on a lower side of the slot  510 , as illustrated in  FIG. 5 . 
     When the driving cam  200  is rotated at the position illustrated in  FIG. 5 , the lobe of the driving cam  200  comes into contact with the roller  420 . At this time, the driven cam  400  is rotated around the slide stub  430  thereof in the counterclockwise direction, and thus the cam face  410  of the driven cam  400  lowers the contact block  310  of the valve  300 . 
     At this time, only the low lift section L of the cam face  410  comes into contact with the contact block  310  regardless of the rotational angle of the driven cam  400 , so that the valve  300  is no longer lowered at the position illustrated in  FIG. 6 . 
     In contrast, in the case in which a long lift distance of the valve  300  is required, the actuator  600  and one end of the driven cam  400  are raised, and thus the slide stub  430  of the driven cam  400  is located on the upper side of the slot  510 , as illustrated in  FIG. 7 . At this time, the roller  420  of the driven cam  400  is also raised from the position illustrated in  FIG. 5 . As such, when the driving cam  200  is rotated, the lobe of the driving cam  200  comes into contact with the roller  420  earlier. Thus, when the driving cam  200  is rotated in the clockwise direction at the position illustrated in  FIG. 7 , the driven cam  400  is rotated around the slide stub  430  thereof more than the position illustrated in  FIG. 6 , and the valve  300  is farther lowered, as illustrated in  FIG. 8 . In other words, the high lift section H of the cam face  410  of the driven cam  400  comes into contact with the contact block  310 , so that the valve  300  is lowered more than the position illustrated in  FIG. 6 . 
     As described above, the CVVA system can regulate the lift distance of the valve  300  only by raising or lowering one side of the driven cam  400 . Further, the CVVA system can advance or postpone the lift time of the valve by properly machining the profile of the cam face  410 . This profile of the cam face  410  can be variously modified depending on a shape, a mounting position, etc. of each constituent part, and so a detailed description thereof will be omitted. 
     For convenience in explanation and accurate definition in the appended claims, the terms “upper”, and “downwards” are used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures. 
     The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.