Abstract:
In order to provide a fuel pump in which a piston spring arrangement can be made of inexpensive material, knocking noises of a piston are reduced, and components related to the piston are protected against breakdown, a piston-following spring is provided between a fuel pump body and the piston to lower the piston in response to the rotation of an eccentric cam. A pumping member-moving spring is provided between the fuel pump body and a pin connected to a pumping member, and lowers the pumping member when the piston is moved down. The downward movements of the piston and the pumping member are caused by the springs, so that these springs can be made of inexpensive materials, and enable the piston to reliably follow the eccentric cam.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a fuel pump to be actuated by engine power.  
           [0003]    2. Description of Related Art  
           [0004]    Japanese Laid-Open Publication No. 2000-282994 discloses a prior art fuel pump which utilizes rotation of an eccentric cam by an engine by converting the rotation of the eccentric cam into reciprocating motion of a piston. FIG. 6 of the accompanying drawings shows such a fuel pump  10 , and FIG. 7 shows a detailed cross section of essential parts of the fuel pump shown in FIG. 6. The fuel pump  10  includes a bottom body part  14  which is fixedly attached to a cylinder head cover  12  of an engine, a top body part  16  mounted on the bottom body part  14 , a cover  18  on the top body part  16 , and a piston  20  reciprocally mounted in the bottom body part  14 . As shown in FIG. 6, the cover  18  is positioned on top of the top body part  16 , and the bottom body part  14  is mounted under the top body part  16 .  
           [0005]    The fuel pump  10  is to be arranged with a rotary shaft  22  positioned below the piston  20  and having an eccentric cam  24 . The shaft  22  is rotated by engine power, and the eccentric cam  24  is positioned at a tip of the piston  20 . A piston spring  26  is provided between the piston  20  and the bottom body part  14 , and urges the piston  20  toward the eccentric cam  24  so the piston remains in contact with the eccentric cam  24 . The piston  20  thus vertically reciprocates in the bottom body part  14  in response to the rotation of the eccentric cam  24 .  
           [0006]    A diaphragm assembly  30  is coupled to the piston  20 , and includes a diaphragm  28  and a rod  32  coupled to the diaphragm  28 . An engagement member  36  has an elongated hole  34  along an axis thereof, and is fixedly attached to a tip of the rod  32 . Further, a pin  38  is fixedly attached to the piston  20 , and fits in the elongated hole  34  of the engagement member  36 .  
           [0007]    The diaphragm  28  is sandwiched between the bottom body part  14  and the top body part  16 , and a seal such as a gasket is sandwiched between the top body part  16  and the cover  18 . In this state, the bottom body part  14 , the top body part  16  and the cover  18  are fixed together using a bolt  42 . A pump chamber  44  is defined by the top body part  16  and the diaphragm  28 , and is present near the top body part  16 . A diaphragm spring  46  is provided between the bottom body part  14  and the diaphragm  28  in order to continuously urge the diaphragm  28  toward the pump chamber  44  (i.e. toward a pump chamber pressurizing position).  
           [0008]    An intake chamber  48  and a discharge chamber  50  are independently defined by the top body part  16  and the seal  40 . An intake path  52  is formed in the top body part  16  in order to connect the intake chamber  48  to the pump chamber  44 , and the intake path is opened and closed by an intake (one-way) valve  54 . Further, the top body part  16  has a discharge path  56  formed therein in order to connect the discharge chamber  48  to the pump chamber  44 . The discharge path  56  is opened and closed by a discharge (one-way) valve  58 .  
           [0009]    In the fuel pump  10 , the piston  20  vertically reciprocates in response to the rotation of the eccentric cam  24  fixedly attached around the shaft  22 . When both the piston  20  and the diaphragm  28  are moved downward as shown in FIG. 6, the discharge valve  58  closes the discharge path  56 . At the same time, the intake valve  54  is opened, so that fuel is introduced into the pump chamber  44  from the intake chamber  48  via the intake path  52 . Thereafter, when the piston  20  and the diaphragm  28  move upward, the intake valve  54  closes the intake path  52 , and the discharge valve  58  opens the discharge path  56 , so that the fuel is introduced into the discharge chamber  50  from the pump chamber  44 .  
           [0010]    The piston spring  26  must be sufficiently strong so as to maintain the piston  20  continuously in contact with the eccentric cam  24  so that the piston  20  reliably follows the rotating eccentric cam  24 . The piston spring  26  is required for the downward movement of the diaphragm  28  toward a depressurizing position to effect a fuel intake action, and thus must have sufficient strength to overcome the resilient biasing force of the diaphragm spring  46  which resists the downward movement of the diaphragm  28 . Further, the larger the diaphragm  28 , the stronger must be the resiliency of the piston spring  26 . Still further, the more resilient the piston spring  26  must be, the more expensive of a material is generally required to form the piston spring, which inevitably makes the piston spring more expensive.  
           [0011]    If the piston spring  26  is weakened, the piston  20  will sometimes fail to follow the eccentric cam  24 . In such a case, undesirable noises may be caused due to improper interaction between the piston  20  and the eccentric cam  24 . When the piston spring  26  is strengthened in order to overcome this problem, the pin  38  fixedly attached to the piston  20  may strike against the engagement member  36  fixedly attached to the rod  32 , thereby causing significant shocks and perhaps large knocking noises. Such striking contact will cause damage to the pin  38  at the contact point, as well as to the diaphragm  28  and components adjacent the rod  32 .  
         SUMMARY OF THE INVENTION  
         [0012]    In order to overcome the foregoing problems of the related art, the present invention is intended to provide a fuel pump which does not require expensive material for a piston spring, reduces knocking noises and protects components near colliding portions against damage.  
           [0013]    According to the invention, there is provided a fuel pump for pumping fuel in response to rotation of an eccentric cam, the fuel pump comprising: a fuel pump body having a pump chamber; a pumping member movably provided at the pump chamber for pressurizing and depressurizing the pump chamber, the pumping member being movable between a first pumping member position and a second pumping member position; a piston movably mounted to the fuel pump body and being arranged to be operably engaged with the eccentric cam for movement between first and second ends of a piston stroke, the piston being operably coupled to the pumping member so that the pumping member is caused to move toward the first pumping member position due to the piston moving toward the first end of the piston stroke, and toward the second pumping member position due to the piston moving toward the second end of the piston stroke; a piston-following spring operably engaged with the piston to urge the piston toward the first end of the piston stroke; and a pumping member-moving spring operably engaged with the pumping member to urge the pumping member toward the first pumping member position.  
           [0014]    The fuel pump further includes a pumping member spring mechanism urging the pumping member toward the second pumping member position, and the pumping member preferably comprises a diaphragm.  
           [0015]    The fuel pump body comprises a first fuel pump body part, and a second fuel pump body part secured to the first fuel pump body part; and the diaphragm is sandwiched between the first and second fuel pump body parts.  
           [0016]    The fuel pump further preferably includes a first engagement member coupled to the diaphragm; a second engagement member provided at the piston and being arranged for engagement with the first engagement member; and a plate member positioned between the first engagement member and the pump member-moving spring so as to be urged by the pump member-moving spring toward the first engagement member. The second engagement member is engageable with the first engagement member to limit an amount of movement of the first engagement member relative to the piston. Further, a rod preferably couples the first engagement member to the pumping member; the first engagement member comprises a pin fixed to the rod; and the second engagement member comprises an elongated groove provided in the piston, the pin being movably engaged in the elongated groove. The plate member is preferably an annular plate disposed about the rod and between the pin and the pumping member-moving spring. The pumping member-moving spring and the piston-following spring are preferably disposed one within the other and about the rod.  
           [0017]    In the preferred form of the invention, the fuel pump body has defined therein the pump chamber, an intake chamber and a discharge chamber; the pump chamber is bounded by the pumping member; the intake chamber is connected to the pump chamber via a first one-way valve; and the discharge chamber is connected to the pump chamber via a second one-way valve. The first one-way valve allows flow in a direction from the intake chamber to the pump chamber; and the second one-way valve allows flow in a direction from the pump chamber to the discharge chamber. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a cross section of a fuel pump according to one embodiment of the invention.  
         [0019]    [0019]FIG. 2 is a cross section of essential parts of the fuel pump shown in FIG. 1.  
         [0020]    [0020]FIG. 3 is a cross section of a portion of the fuel pump of FIG. 1 showing a piston in a raised state.  
         [0021]    [0021]FIG. 4 is similar to FIG. 3, but further showing a diaphragm in a raised state.  
         [0022]    [0022]FIG. 5 is similar to FIG. 3, but showing the piston in a lowered state.  
         [0023]    [0023]FIG. 6 is a cross section of a prior art fuel pump.  
         [0024]    [0024]FIG. 7 is a cross section of essential parts of the fuel pump of FIG. 6. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]    The present application is based on Japanese Application 2000-401707 filed Dec. 28, 2000, which is hereby incorporated by reference.  
         [0026]    The invention will be described with reference to the accompanying drawings.  
         [0027]    [0027]FIG. 1 is a cross section of a fuel pump  60  according to a preferred embodiment of the invention. FIG. 2 is a cross section of essential parts of the fuel pump  60 . In these drawings, parts corresponding to those in FIG. 6 are denoted by corresponding reference numerals. The fuel pump  60  uses a diaphragm-lowering (or pump member-moving) spring  62  and a piston following-spring  64  in place of the piston spring  26  used in the pump shown in FIG. 6. Similarly to the fuel pump  10  of FIG. 6, the fuel pump  60  includes a fuel pump body comprising a bottom body part  14  and a top body part  16 , a pumping member such as the illustrated diaphragm  28 , a rod  32 , a pump chamber  44 , an intake chamber  48  and a discharge chamber  50 , and is to be arranged adjacent an eccentric cam  24  secured to a rotary shaft  22 . The fuel pump  60  includes a cylindrical piston  70  reciprocally mounted to the fuel pump body for movement between an extended position and a retracted position at opposite ends of a piston stroke. The present discussion assumes that the fuel pump is oriented so that the top body part  16 , the bottom body part  14 , the piston  70  and the eccentric cam  24  are arranged top down in this order as shown in FIG. 1. However, the fuel pump can be oriented in any direction, and further, these components may be assembled in other suitable arrangements.  
         [0028]    The diaphragm-lowering spring  62  is provided around the rod  32  and is coaxial with the rod  32 . Further, the piston-following spring  64  is provided around the diaphragm-lowering spring  62 . A pin  66  as a first engagement member is fixedly attached to a tip of the rod  32 , and an annular plate  68  is attached around the rod  32  in order to come into contact with the pin  66 . The diaphragm-lowering spring  62  has one end thereof kept in contact with the bottom body part  14  and the other end thereof kept in contact with the annular plate  68 . The diaphragm-lowering spring  62  normally maintains the annular plate  68  in contact with the pin  66 .  
         [0029]    In the fuel pump  60 , the cylindrical piston  70  has a closed end  72 , which is arranged to be in contact with the eccentric cam  24 , and an annular open end  74  which is contacted by one end of the piston-following spring  64 . The piston-following spring  64  has the other end thereof kept in contact with the bottom body part  14 , so that the piston  70  is continuously urged toward the eccentric cam  24 .  
         [0030]    The piston  70  has an annular step  76  projecting radially inwardly with respect to the open end  74 . The annular plate  68  is sized so as to contact against the annular step  76 , such that the annular plate  68  is kept from moving toward the closed end  72  of the piston  70  beyond the annular step  76 . Further, the piston  70  has a groove  78  elongated in the moving direction of the piston  70 , and the groove  78  serves as a second engagement member. The pin  66  fixedly attached to the rod  32  is fitted in the groove  78 . Engagement of the pin  66  with the groove  78  limits the range of movement of the pin  66  (and thus the rod  32  and diaphragm  28 ) relative to the piston  70 .  
         [0031]    According to this embodiment, the fuel pump  60  includes both the diaphragm-lowering spring  62  and the piston-following spring  64 . The piston-following spring  64  urges the piston  70  downward (toward the eccentric cam  24 ) while the diaphragm-lowering spring  62  urges the diaphragm  28  downward (toward the eccentric cam  24 ) via the annular plate  68 , pin  66  and rod  32 . A diaphragm (or pumping member) spring  46  urges the diaphragm  28  upward.  
         [0032]    The operation of the fuel pump will be described hereinafter. Referring to FIG. 1, when the piston  70  is moved furthest toward the eccentric cam  24  (i.e. to its most extended position), the diaphragm  28  is in a lowered state. In this state, the diaphragm-lowering spring  62  urges the annular plate  68  into contact with the pin  66  and the annular step  76 , such that pin  66  is positioned slightly below the lengthwise center of the groove  78 .  
         [0033]    As the eccentric cam  24  starts rotating from the state shown in FIG. 1, the piston  70  is raised (see FIG. 3), and the piston-following spring  64  and the diaphragm-lowering spring  62  are compressed. In this state, the annular plate  68  in contact with the annular step  76  is also raised together with the piston  70  while both the rod  32  and the diaphragm  28  are not raised, so that the annular plate  68  moves away from the pin  66 . The pin  66  comes close to the bottom of the groove  78  in response to the upward movement of the piston  70 . With the diaphragm-lowering spring compressed due to the upward movement of the piston  70 , the diaphragm spring  46  is freed to expand and move the diaphragm, as well as the rod  32 , upward. Since discharge of the fuel from the pump chamber  44  to a discharge chamber  50  requires the fuel to flow through a discharge path  56  via a discharge valve (e.g. a one-way valve)  58 , there is a discharge resistance, and this discharge resistance causes the diaphragm  28  to initially remain at a lowered (extended) position as shown in FIG. 1 when the piston  70  is raised to a certain level.  
         [0034]    When the piston  70  is raised to near the top of its piston stroke, the compressed diaphragm spring  46  begins to expand, and raises the diaphragm  28  (see FIG. 4). The pin  66  fixedly attached to the rod  32  comes into contact with the annular plate  68  as the diaphragm  28  and the rod  32  are raised.  
         [0035]    As the eccentric cam  24  continues rotating from the state shown in FIG. 4, the piston-following spring  64  moves the piston  70  downward. At the beginning of the downward movement of the piston  70 , the diaphragm  28  initially remains at a raised position (shown in FIG. 5) due to upward urging by the diaphragm spring  46  and an intake resistance of the fuel due to the intake of fuel from an intake chamber  48  to the pump chamber  44  requiring the fuel to flow through an intake path  52  via an intake valve (e.g. a one-way valve)  54 . In other words, both the rod  32  and the pin  66  initially remain at raised positions, so that the annular plate  68  is kept spaced above the annular step  76  by the pin  66 .  
         [0036]    Thereafter, when the piston  70  moves down to its lowest (extended) position, the diaphragm-lowering spring  62  lowers the diaphragm  28  via the annular plate  68 , and the pin  66  and the rod  32  against the resilient force of the diaphragm spring  46  and the intake resistance of the fuel. Therefore, the fuel pump  60  returns to the state shown in FIG. 1, thus completing one cycle of the fuel pump  60 .  
         [0037]    According to the invention, the piston  70  is moved downward by the piston-following spring  64 , and the diaphragm  28  is moved downward by the diaphragm-lowering spring  62 . In short, the piston  70  and the diaphragm  28  are lowered using separate springs. This enables the piston-following spring  64  and the diaphragm-lowering spring  62  to have relatively mild resiliencies compared with the piston spring  26  used in the fuel pump  10  shown in FIG. 6.  
         [0038]    Further, the diaphragm-lowering spring  62  is not in direct contact with the pin  66  but is in contact with the pin  66  via the annular plate  68 , so that force of the diaphragm-lowering spring  62  can be uniformly applied to the pin  66 .  
         [0039]    Since the present invention uses the two springs to lower the piston and the diaphragm instead of the one spring used in the prior art shown in FIG. 6, the forces required for lowering the piston and the diaphragm are provided by the two springs, thereby allowing the springs to be made of relatively inexpensive material, and reducing the cost of the springs.  
         [0040]    Further, since the downward movement of the piston and that of the pumping member (e.g. diaphragm) are independent according to the present invention, the piston can reliably follow the eccentric cam thereby preventing undesirable noises which may otherwise be caused by the piston following the eccentric cam in an inferior manner.  
         [0041]    Still further, the diaphragm is lowered in a delayed manner after the piston starts moving downward, thereby improving the durability of the diaphragm, the pin and other components. In addition, with the arrangement of the present invention the fuel is introduced at a moderate speed, and this is effective to increase a discharge amount of the fuel.  
         [0042]    Although preferred embodiments of the present invention are described in detail above, the present invention contemplates that many modifications and alternative structures can be utilized. Therefore, the above description is to be taken as exemplary and not in a limiting sense, such that the invention is defined by the metes and bounds of the appended claims.