Abstract:
A high pressure fuel pump with improved lubrication characteristics includes a plunger configured to pressurize fuel supplied to a high pressure chamber formed within a housing at a high pressure to discharge the fuel while being lifted and dropped in the high pressure chamber within the housing, a tappet body configured to support a lower end of the plunger, a cam configured to lift and drop the plunger while rotating, and a roller configured to be installed in a roller shoe pressed in a lower portion of the tappet body and rotate in a state of being in contact with the cam, the fuel supplied to the high pressure chamber passes the roller shoe through at least one lubrication passage and is supplied to a contact area between the roller and the cam or a contact area between the roller shoe and the roller.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority of Korean Patent Application Number 10-2012-0098123 filed Sep. 5, 2012, the entire contents of which application is incorporated herein for all purposes by this reference 
     BACKGROUND OF INVENTION 
     1. Field of Invention 
     The present invention relates to a high pressure fuel pump applied to a common rail system of a diesel engine; and, particularly, to a high pressure fuel pump of which an inner portion is formed with a lubrication passage in which fuel flows to allow components in the high pressure fuel pump to be lubricated, thereby having improved lubrication characteristics. 
     2. Description of Related Art 
     A common rail system mounted to a diesel engine is provided with a high pressure fuel pump into which fuel primarily pressurized by a low pressure fuel pump is introduced from a fuel tank and from which the introduced fuel is discharged by being secondarily pressurized at a high pressure of 2000 bar or more. 
     A schematic structure of such a high pressure fuel pump is described with reference to  FIG. 1 . The high pressure fuel pump includes a housing  110  having an inlet  111  and an outlet  112 , a cam shaft  120  which is rotatably provided within the housing  110  and formed with a cam  121 , a plunger  130  which is lifted by rotation of the cam shaft  120  to pressurize the fuel, a tappet body  131  to support a lower end of the plunger  130 , and a roller  142  provided between the tappet body  131  and the cam  121 . 
     When the cam shaft  120  rotates, the plunger  130  pressurizes the fuel, which is introduced into a high pressure chamber formed within the housing  110  through the inlet  111 , at a high pressure to discharge the fuel to the outlet  112  while being lifted and dropped along at least one cam  121  formed around the cam shaft  120 . 
     In this case, the roller  142  is mounted to a roller shoe  141  pressed in the tappet body  131  and is maintained in a state of contact with the cam  121  during the rotation of the cam shaft  120 , to thereby reduce friction between the cam  121  and the roller shoe  141 . 
     However, the roller  142  is always in contact with the cam  121  by the tappet body  131  supported by a spring  132 , and moreover is inserted in a state of keeping a certain clearance with the roller shoe  141 . 
     According to the structure of the high pressure fuel pump  100  of the related art, the fuel serving as a lubricant is not sufficiently supplied to a clearance between the roller  142  and the roller shoe  141  indicated by “A” in  FIGS. 2 and 3  in which the roller  142  comes into contact with the roller shoe  141  and a contact portion between the roller  142  and the cam  121  indicated by “B” in  FIGS. 2 and 3 , thereby not causing smooth lubrication action. That is, the roller  142  is in surface contact with the roller shoe  141  on a portion indicated by “A”, and the roller  142  is in line contact with the cam  121  on a portion indicated by “B”. Accordingly, there is a problem in that the roller  142 , the roller shoe  141 , or the cam  121  is worn out or burned on the contact surface between the roller  142  and the roller shoe  141  and on the contact portion between the roller  142  and the cam  121  depending on these operations. 
     Therefore, the fuel serving as a lubricant needs to be sufficiently supplied in order to reduce friction on the contact surface and the contact portion. If the lubrication is abnormal, the cam  121  of the cam shaft  120 , the roller  142 , and the roller shoe  141  are worn out. Moreover, in the worst case, a fatal failure such as burning of the high pressure fuel pump  100  is caused. 
     In particular, the roller  142  mounted within the roller shoe  141  is kept at a minimal clearance. Hence, in a case where the lubrication is not smooth, abrasion between the roller  142  and the roller shoe  141  may be immediately caused. 
     The information disclosed in this Background 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. 
     SUMMARY OF INVENTION 
     Various aspects of the present invention provide for a high pressure fuel pump having improved lubrication characteristics which forms a plurality of lubrication passages through which fuel is supplied to a tappet body and a roller shoe so that the fuel serving as a lubricant may be sufficiently supplied around a roller installed to come into contact with a cam of a rotating cam shaft in the high pressure fuel pump. 
     Various aspects of the present invention provide for a high pressure fuel pump having improved lubrication characteristics includes a plunger configured to pressurize fuel supplied to a high pressure chamber formed within a housing at a high pressure to discharge the fuel while being lifted and dropped in the high pressure chamber within the housing, a tappet body configured to support a lower end of the plunger, a cam configured to lift and drop the plunger while rotating, and a roller configured to be installed in a roller shoe pressed in a lower portion of the tappet body and rotate in a state of being in contact with the cam, the fuel supplied to the high pressure chamber passes the roller shoe through at least one lubrication passage and is supplied to a contact portion between the roller and the cam, a contact surface between the roller shoe and the roller, or the contact portion and the contact surface. 
     The lubrication passage may be formed of a communication hole which is formed by removing a partial section of a tappet body inner flange formed toward a center of the tappet body in an inner side surface of the tappet body, and a clearance formed between an outer side surface of the roller shoe which is located downward of the communication hole and fitted into a lower portion of the tappet body inner flange and the inner side surface of the tappet body, and the fuel may be supplied to the contact portion between the roller and the cam through the communication hole and the clearance. 
     The communication hole may be plural in number. 
     The communication holes may be formed at intervals of 180 degrees and formed in a direction perpendicular to a longitudinal direction of the roller. 
     An oil supply groove may be formed to be recessed at a portion in which the inner side surface of the tappet body abuts against the tappet body inner flange. 
     The lubrication passage may be formed of a roller shoe through hole which is formed to be penetrated in an upward and downward direction of the roller shoe, thereby allowing the fuel to be supplied from upward to downward of the roller shoe, and the fuel may be supplied to the contact surface between the roller and the roller shoe through the roller shoe through hole. 
     The roller shoe through hole may be formed from an upper surface of the roller shoe up to the contact surface between the roller shoe and the roller pressed in an inner portion of the roller shoe. 
     The roller shoe through hole may be one or more. 
     The roller shoe through hole may be arranged in a longitudinal direction of the roller. 
     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, which together serve to explain certain principles of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cutaway perspective view illustrating a structure of a high pressure fuel pump in accordance with the related art. 
         FIGS. 2 and 3  are a cutaway perspective view and a cross-sectional view illustrating a drive area in the high pressure fuel pump in accordance with the related art. 
         FIG. 4  is a plane view illustrating an assembly of a tappet body, a roller shoe, and a roller applied to an exemplary high pressure fuel pump having improved lubrication characteristics in accordance with the present invention. 
         FIG. 5  is a cross-sectional view taken along line  5 - 5  in  FIG. 4  for explaining a lubrication passage in the high pressure fuel pump having improved lubrication characteristics in accordance with the present invention. 
         FIG. 6  is a cross-sectional view taken along line  6 - 6  in  FIG. 4  for explaining another lubrication passage in the high pressure fuel pump having improved lubrication characteristics in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     A high pressure fuel pump having improved lubrication characteristics in accordance with various embodiments of the present invention has a structure similar to the high pressure pump described in the related art. In the high pressure fuel pump, fuel supplied to a high pressure chamber passes a roller shoe  41  through at least one lubrication passage and is supplied to a contact portion between a roller  42  and a cam  121  and a contact surface between the roller shoe  41  and the roller  42 . 
     As shown in  FIG. 4 , the lubrication passage is a communication hole  51  through which the fuel supplied to the high pressure chamber formed within a housing  110  of the high pressure fuel pump  100  is supplied to the contact portion between the roller  42  and the cam  121  or a roller shoe through hole  52  through which the fuel is supplied to the contact surface between the roller shoe  41  and the roller  42 . 
     As shown in  FIG. 5 , the lubrication passage may be a passage through which the fuel serving as a lubricant passes through opposite side surface of the roller shoe  41  to be supplied to the contact portion between the roller  42  and the cam  121 . 
     An inner peripheral surface of a tappet body  31  is formed with a tappet body inner flange  31   a  so that a spring seat  131   a  to support a lower end of a spring  132  may be installed. The tappet body inner flange  31   a  is formed in a band shape which protrudes toward a center of the tappet body  31  in the inner peripheral surface of the tappet body  31 . The communication hole  51  is formed through which the fuel may easily move in an upward and downward direction of the tappet body inner flange  31   a  by removing a portion of the tappet body inner flange  31   a.    
     The communication hole  51  is plural in number. Particularly, the communication hole  51  is two in number. In this case, the two communication holes  51  may be arranged at intervals of 180 degrees, and may be formed in a direction perpendicular to a longitudinal direction of the roller  42 . 
     A clearance is formed between the inner peripheral surface of the tappet body  31  and an outer peripheral surface of the roller shoe  41 . Since the clearance is formed between the inner peripheral surface of the tappet body  31  and the outer peripheral surface of the roller shoe  41 , the fuel supplied to an upper portion of the tappet body  31  may be supplied to a lower portion of the tappet body  31  through the communication holes  51 . Thus, the supplied fuel serves as a lubricant and is supplied to the contact portion between the roller  42  and the cam  121 . 
     Here, in order for the fuel to be smoothly supplied to the communication holes  51 , each oil supply groove  31   b  may be formed at a portion in which the inner peripheral surface of the tappet body  31  meets the tappet body inner flange  31   a , particularly, an upper surface side thereof. 
     Accordingly, as shown in  FIG. 5 , the fuel supplied to the upper portion of the tappet body  31  is supplied to the contact portion between the roller  42  and the cam  121  by the communication holes  51  formed by removing partial sections of the tappet body inner flange  31   a  and the clearance formed between the outer peripheral surface of the roller shoe  41  and the inner peripheral surface of the tappet body  31 , such that the fuel is supplied between the roller  42  and the cam  121  and friction is reduced during contact thereof. 
     Meanwhile, the lubrication passage may be a roller shoe through hole  52  which is formed in an upward and downward direction of the roller shoe  41 , that is, in an operation direction of a plunger  130 . 
     As shown in  FIG. 6 , the roller shoe through hole  52  through which the fuel is moved is formed to be penetrated in an upward and downward direction in an inner portion of the roller shoe  41 . The roller shoe  41  is pressed in an inner portion of the tappet body  31 , the roller  42  is rotatably installed in the inner portion of the roller shoe  41  through bearings  43 , and a lower portion of the roller  42  is exposed to come into contact with the cam  121 . Here, the fuel supplied to the high pressure chamber is supplied from an upper portion of the roller shoe  41  through the roller shoe through hole  52  formed in the roller shoe  41  to the contact surface between the roller shoe  41  and the roller  42 , such that the fuel may perform lubrication action between the roller shoe  41  and the roller  42 . 
     The roller shoe through hole  52  may be at least one or plural in number in the roller shoe  41 . 
     In this case, the plural roller shoe through holes  52  are arranged in the longitudinal direction of the roller  42  installed in the roller shoe  41 . The roller  42  is formed in a cylindrical shape and is mounted to the roller shoe  41 . Therefore, the plurality of roller shoe through holes  52  are formed to be arranged in the longitudinal direction of the roller  42  so that the fuel may be supplied in the longitudinal direction of the roller  42 . 
     As above, the fuel serving as a lubricant is supplied by bypassing or passing through the roller shoe  41  or via all of the two paths. 
     According to the operation of the fuel pump, the fuel is directly supplied to the contact portion between the roller  42  and the cam  121  by passing through the clearance between the tappet body  31  and the roller shoe  41  through the communication hole  51  which is one lubrication passage, or the fuel is also supplied between the roller  42  and the roller shoe  41  through the roller shoe through hole  52  which is another lubrication passage. Therefore, lubrication characteristics may be improved at a friction area, to thereby solve a problem due to abrasion of the friction area. 
     In the high pressure fuel pump  100  of the related art, the fuel is supplied only by the clearances between the respective components without the passage through which the fuel is easily moved in the upward and downward direction. Accordingly, the lubrication is not smoothly made at the contact areas such as areas between the roller and the cam and between the roller and the roller shoe, thereby causing abrasion or a burning phenomenon as occasion demands. 
     However, in the above described embodiments, the fuel is sufficiently supplied to the friction area through the plural lubrication passages and is fully filled to serve as a lubricant, thereby improving lubrication characteristics. 
     In accordance with a high pressure fuel pump having improved lubrication characteristics according to various embodiments of the present invention, fuel flows from an upper portion of a tappet body through a plurality of lubrication passages to a lower portion of the tappet body and is sufficiently supplied around a roller which is a rotating component, thereby allowing lubrication characteristics to be improved by the sufficiently supplied fuel during the operation of the roller. That is, the fuel is sufficiently supplied to a contact portion between the roller and a cam and a contact surface between the roller and a roller shoe, thereby allowing the lubrication characteristics to be improved between the roller and the cam and between the roller and the roller shoe. 
     In addition, by improvement in the lubrication characteristics of the roller, the fuel serving as a lubricant is sufficiently supplied to drive areas during the operation of the high pressure fuel pump, namely, contact areas of the roller, the roller shoe, and the cam of the cam shaft. As a result, malfunction of the high pressure fuel pump due to incomplete lubrication action may be prevented in advance. 
     Furthermore, the passage to supply the fuel is divided into two parts and the fuel is directly supplied to the contact area between the roller and the cam and the contact area between the roller and the roller shoe, thereby achieving smooth lubrication characteristics. 
     For convenience in explanation and accurate definition in the appended claims, the terms upper or lower, and etc. 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.