Patent Publication Number: US-2019195337-A1

Title: Camshaft unit for vehicle

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2017-0177869, filed Dec. 22, 2017, which is incorporated herein by reference in its entirety. 
     FIELD 
     The present disclosure relates to a camshaft unit for a vehicle. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Generally, valves opening and closing a combustion chamber of an engine generating power at an appropriate timing are opened and closed by a valve opening and closing mechanism connected to a crank shaft, and the engine is divided into a single overhead camshaft (hereinafter, referred to as an SOHC) engine and a double overhead camshaft (hereinafter, referred to as a DOHC) engine. In the SOHC engine, all the valves are opened by a single camshaft, and in the DOHC engine, intake and exhaust valves are opened by two camshafts, respectively, depending on a manner of driving the valves. 
     The DOHC engine has a complicated structure in order to operate two intake valves and two exhaust valves per cylinder, generates large noise, and consumes a larger amount of power in order to drive the respective valves as compared with the SOHC engine. However, in the DOHC engine, the two intake valves and the two exhaust valves are installed in each cylinder and are simultaneously operated by a camshaft for intake and a camshaft for exhaust, respectively, such that intake performance and exhaust performance in the combustion chamber may be improved. 
     In the DOHC engine as described above, one of the camshafts (i.e., a camshaft for either intake or exhaust) directly transfers power, while the other camshaft receives the power transferred from the one camshaft. To this end, an inter-cam driving system uses a gear. However, the inter-cam driving system has a limitation in reducing rattle noise inevitably generated by a backlash, which is a clearance between a driving gear and a driven gear, by improving engagement between teeth, due to engagement characteristics. 
     Therefore, the inter-cam driving system uses a cam gear and a scissors gear, which are backlash compensation gears using scissors spring force, in order to reduce the backlash generated between toothed gears. 
     A camshaft unit for a vehicle used in the related art will be described in detail with reference to  FIG. 1 . The camshaft unit  101  for a vehicle includes a camshaft  110  having a cam  115  formed on a circumference thereof, a cam gear  120  and a scissors gear  130  shaft-coupled to one end of the camshaft  110  and relatively rotated with a scissors spring  135  interposed therebetween, and a wave spring  140 , a scissors washer  145 , and a snap ring  150  sequentially assembled so that the scissors gear  130  is closely adhered to the cam gear  120  in order to hold the scissors gear  130  and the cam gear  120  together in an axial direction. 
     A hub  121  to which the camshaft  110  is to be coupled protrudes from the center of the cam gear  120 , and a pin  122  that is to be coupled to the scissors gear  130  is formed on a plate surface of the cam gear  120 . 
     The scissors gear  130  is maintained in a state in which it is always in contact with the cam gear  120  fixed to the camshaft  110  by elastic force of the scissors spring  135 , such that a backlash becomes “0”, and thus, rattle noise is not generated during driving. In this case, a coupling portion  131  into which the hub  121  of the cam gear  120  is inserted and coupled is provided at the center of the scissors gear  130 , and a pin  132  for fixing the scissors spring  135  is formed on a plate surface of the scissors gear  130 . 
     The wave spring  140  has a wave shape, is closely adhered to an inner surface of the coupling portion  131 , and presses the scissors gear  130  toward the cam gear  120  in the axial direction. 
     The scissors washer  145  is coupled to the inner surface of the coupling portion  131 , and serves to closely adhere the scissors gear  130  toward the cam gear  120  in the axial direction together with the wave spring  140 . 
     The snap ring  150  serves to fix the wave spring  140  and the scissors washer  145  so that the wave spring  140  and the scissors washer  145  coupled to the coupling portion  131  are not separated from the camshaft  110 . 
     However, in the camshaft unit  101  for a vehicle according to the related art, many components are assembled to the camshaft  110 , such that an assembling man-hour is increased, thereby increasing a manufacturing cost. 
     The contents described as the related art have been provided only to assist in understanding the background of the present disclosure and should not be considered as corresponding to the related art known to those having ordinary skill in the art. 
     SUMMARY 
     The present disclosure provides a camshaft unit of a vehicle which utilizes reduced number of components to lower a manufacturing cost. 
     In one form of the present disclosure, a camshaft unit for a vehicle includes: a cam gear shaft-coupled to one end of a camshaft; a scissors gear disposed on a first side of the cam gear while having the camshaft as a concentric axis and configured to rotate relatively to the cam gear; a coil spring provided between the cam gear and the scissors gear, and having a first end fixed to a first side surface of the cam gear and a second end fixed to a second side surface of the scissors gear; and a snap ring installed in a groove formed in a first side surface of the scissors gear and configured to inhibit separation of the scissors gear in an axial direction. The coil spring is configured to transfer a torque of the cam gear to the scissors gear depending on rotation of the cam gear. 
     In one form, the coil spring is configured to provide elastic force in a rotation direction to the scissors gear so that the scissors gear is rotated by the cam gear, and configured to provide elastic force in the axial direction to the scissors gear so as to inhibit the scissors gear from being separated by a relative motion between the cam gear and the scissors gear. 
     A hub may protrude from a central portion of the cam gear toward the scissors gear so that the camshaft is coupled thereto, the hub may be inserted into a coupling portion of the scissors gear in which the groove is formed, and the coil spring may be formed to surround an outer peripheral surface of the hub. 
     Dowel pins may be disposed between a surface of the cam gear and a surface of the scissors gear, and the surfaces of the cam gear and the scissors gear face to each other and are provided with at least one dowel pin of the dowel pins, and the first and second ends the coil spring may be bent in a radial direction from a winding direction of the coil spring and be caught by and fixed to the dowel pins, respectively. 
     The dowel pins may be provided between both ends (i.e., the first and second ends) of the coil spring, and the coil spring may be provided to transfer elastic force in a direction in which both ends of the coil spring become close to each other. 
     In one form, a protruding portion is respectively integrally formed on a surface of the cam gear and the scissors gear, and the surfaces of the cam gear and the scissors gear face to each other, and the first and second ends of the coil spring may be bent in a radial direction and be caught by and fixed to the protruding portions, respectively. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which: 
         FIG. 1  is an exploded perspective view illustrating a camshaft unit for a vehicle in the related art; 
         FIG. 2  is an exploded perspective view illustrating a camshaft unit for a vehicle in one form of the present disclosure; and 
         FIG. 3  is a side view of  FIG. 2  illustrating a cam gear assembled with a coil spring. 
     
    
    
     The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
       FIG. 2  is an exploded perspective view illustrating a camshaft unit for a vehicle in one form of the present disclosure. 
     Referring to  FIG. 2 , the camshaft unit for a vehicle may include a cam gear  20  shaft-coupled to one end of a camshaft  10 ; a scissors gear  40  disposed on one side of the cam gear  20  while having the camshaft  10  as a concentric axis and configured to rotate relative to the cam gear  20 ; a coil spring  30  provided between the cam gear  20  and the scissors gear  40 ; and a snap ring  50  installed in a groove  44  formed in one side surface of the scissors gear  40  and preventing separation of the scissors gear  40  in an axial direction. The scissors gear  40  has one end fixed to one side surface of the cam gear  20  and the other end fixed to the other side surface of the scissors gear  40 , and thus transfers a torque of the cam gear  20  to the scissors gear  40  while being elastically restored depending on rotation of the cam gear  20   
     The cam gear  20  is directly connected to the camshaft  10 , but the scissors gear  40  is not directly connected to the camshaft  10 . The scissors gear  40  is connected only to the cam gear  20  via the coil spring  30 , and the cam gear  20  and scissors gear  40  rotate around a concentric axis. 
     Therefore, the scissors gear  40  serves to remove a backlash of a gear while being relatively rotated with respect to the cam gear  20 . 
     The coil spring  30  connects the cam gear  20  and the scissors gear  40  to each other, and may be deformed by the torque of the cam gear  20  and then transfer the torque to the scissors gear  40  while being elastically restored, thereby allowing the scissors gear  40  to be relatively rotated with respect to the cam gear  20 . 
     The coil spring  30  is extended in a coil shape from one end thereof in a length direction and arrives at the other end thereof. 
     Due to such a shape, the coil shape  30  may provide elastic force in a rotation direction to the scissors gear  40  so that the scissors gear  40  is relatively rotated by the rotation of the cam gear  20 , and may provide elastic force in the axial direction to the scissors gear  40  so as to inhibit or prevent the scissors gear  40  from being separated by a relative motion between the cam gear  20  and the scissors gear  40  in the axial direction. 
     In detail, a hub  24  protrudes from a central portion of the cam gear  20  toward the scissors gear  40  so that the camshaft  10  is coupled thereto. The hub  24  is inserted into a coupling portion  44  of the scissors gear  40  in which the groove  44  is formed, and the coil spring  30  is formed to surround an outer peripheral surface of the hub  24 . 
     That is, the camshaft  10  is coupled to the hub  24  to be directly connected to the cam gear  20 , and the hub  24  of the cam gear  20  is inserted into the coupling portion  44  of the scissors gear  40 . 
     The coil spring  30  has a shape in which it surrounds the outer peripheral surface of the hub  24  to provide the elastic force in the rotation direction and provide the elastic force in the axial direction. 
     For example, one end of the coil spring  30  is fixed to one side surface of the cam gear  20 , and the other end of the coil spring  30  is fixed to the other side surface of the scissors gear  40 . Therefore, when the cam gear  20  is rotated in one direction, one end of the coil spring  30  is rotated in one direction together with the cam gear  20 . 
     Here, since the coil spring  30  is formed of an elastic material, one end of the coil spring is first rotated in one direction, and an entire shape of the coil spring  30  is rotated in one direction with a fine time difference by elastic force restoring the coil spring  30  to its original shape. 
     Due to an action of the force described above, the scissors gear  40  is relatively rotated with a fine time difference with respect to the rotation of the cam gear  20  to remove the backlash, which is a clearance between a driving gear and a driven gear, thereby reducing or preventing generation of rattle noise. The coil spring substitutes for an existing scissors spring. 
     In addition, the coil spring  30  transfers the elastic force in the axial direction, and is basically formed at a thickness at which the cam gear  20  and the scissors gear  40  are formed while having an appropriate distance therebetween. 
     For example, in the case in which force by which the scissors gear  40  becomes close to the cam gear  20  while being relatively rotated is generated, since both ends of the coil springs  30  are fixed to the cam gear  20  and the scissors gear  40 , respectively, the coil spring  30  is compressed, and may then apply the elastic force preventing the scissors gear  40  from being separated from its original position to the scissors gear  40  while being stretched by restoring force. 
     On the other hand, in the case in which force by which the scissors gear  40  becomes distant from the cam gear  20  while being relatively rotated is generated, since both ends of the coil springs  30  are fixed to the cam gear  20  and the scissors gear  40 , respectively, the coil spring  30  is stretched, and then may prevent separation of the scissors gear  40  while being again compressed by restoring force. Therefore, the coil spring  30  may substitute for a role of an existing wave spring. 
     In one form of the present disclosure as illustrated in  FIG. 2 , dowel pins  22   a  and  42   a  are coupled, respectively, to surfaces of the cam gear  20  and the scissors gear  40  facing each other, and one end and the other end the coil spring  30  in a winding direction may be bent in a radial direction and be caught by and fixed to the dowel pins  22   a  and  42   a , respectively. 
     In this case, the dowel pins  22   a  and  42   a  may be provided between both ends of the coil spring  30 , and the coil spring  30  may be provided to transfer the elastic force in a direction in which both ends of the coil spring  30  become close to each other. 
     When the cam gear  20 , the coil spring  30 , and the scissors gear  40  are assembled to each other, a separate assembling pin is inserted into the cam gear  20 , and one end and the other end of the coil spring  30  are caught by the dowel pin  22   a  and the assembling pin, respectively, in a state in which the coil spring  30  is stretched so that both ends of the coil spring  30  become distant from each other. In this case, the assembling pin is inserted into a point more distant from the dowel pin  22   a  of the cam gear  20  as compared with the dowel pin  42   a  of the scissors gear  40 . 
     Then, the scissors gear  40  is disposed to face the coil spring  30 , and the assembling pin is then removed to allow the other end of the coil spring  30  to be caught by the dowel pin  42   a  of the scissors gear  40 , thereby completing the assembling of the cam gear  20 , the coil spring  30 , and the scissors gear  40 . 
     Therefore, elastic restoring force may continuously act in a direction in which both ends of the coil spring  30  become close to each other. 
     That is, the coil spring  30  is fixed by a simple connection relationship between the cam gear  20  and the scissors gear  40 , and transfers power to the scissors gear  40  so that the scissors gear  40  is relatively rotated depending on the rotation of the cam gear  20 , thereby making it possible to remove the backlash between the driving gear and the driven gear. 
     Here, the dowel pins  22   a  and  42   a  are inserted into and fastened to insertion holes drilled in the cam gear  20  and the coil spring  30 , respectively, to be coupled to the respective gears. 
       FIG. 3  is a side view illustrating a form in which a cam gear and a coil spring of  FIG. 2  are coupled to each other. 
     In another example of the present disclosure as illustrated in  FIG. 3 , the cam gear  20  and the scissors gear  40  are manufactured so that protruding portions  22   b  and  42   b  are formed integrally with the cam gear  20  and the scissors gear  40 , respectively, on surfaces of the cam gear  20  and the scissors gear  40  facing each other, and one end and the other end the coil spring  30  in a winding direction may be bent in a radial direction and be caught by and fixed to the protruding portions  22   b  and  42   b , respectively. 
     The protruding portions  22   b  and  42   b  are provided between both ends of the coil spring  30 , and both ends of the coil spring  30  receive elastic force in a direction in which they become close to each other. 
     In this case, a process of manufacturing and assembling a separate dowel pin is omitted, and the protruding portions  22   b  and  42   b  are processed to be formed integrally with the cam gear  20  and the scissors gear  40 , respectively, when the cam gear  20  and the scissors gear  40  are molded, such that a time and a cost required for manufacturing and assembling a separate component may be reduced. 
     According to the camshaft unit for a vehicle having the structure as described above, a manufacturing cost, a volume, and a weight of the camshaft unit for a vehicle may be reduced as the reduced number of internal components are used. 
     Although the present disclosure has been shown and described with respect to specific forms, it will be apparent to those having ordinary skill in the art that the present disclosure may be variously modified and altered without departing from the spirit and scope of the present disclosure.