Patent Publication Number: US-6705297-B2

Title: Fuel pump for an internal combustion engine

Description:
INCORPORATED BY REFERENCE 
     The disclosure of Japanese Patent Application No. 2001-049047 filed on Feb. 23, 2001, including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     This invention relates to a fuel pump for an internal combustion engine. 
     2. Description of Related Art 
     Fuel pumps for internal combustion engines have been widely utilized as a system for supplying fuel with high pressure for a direct-injection internal combustion engine in a cylinder. According to this type of fuel pump, fuel is generally transmitted under pressure by a lifting movement of a plunger in a cylinder of a pump. The lifting movement of the plunger is produced corresponding to a movement of a cam. 
     FIG. 7 illustrates a schematically sectional view of one example of conventional fuel pumps for internal combustion engines. According to a fuel pump  100 , fuel is introduced from a fuel supply port  107  and is pressurized by the lifting movement of a plunger  102  in a chamber  101  defined in a cylinder  106  at the center of the pump. The pressurized fuel is then discharged from a fuel discharging port  108 . That is, the plunger  102  inserted in the cylinder  106  is provided with a tappet  109  at a bottom portion of the plunger  102 . The plunger  102  is normally biased by a spring in a direction of a cam  103 . 
     Corresponding to an initial start of the internal combustion engine (engine), fuel is introduced into the chamber  101  in the cylinder  106 . An electromagnetic valve  105  serving as a fuel introducing valve is hence closed. A rotation of the internal combustion engine, i.e. a rotation of a crankshaft, is transmitted to a camshaft  104  via a power transmitting mechanism. The cam  103  then comes into contact with the tappet  109  and is rotatably driven. The cam  103  is formed to have a fixed sectional shape (cam profile) with a few (1 to 3) circular projecting portions, i.e. projections. Therefore, the lifting movement of the plunger  102  is produced when the projections of the cam  103  come into contact with the tappet  109  and push the tappet  109  upward. The volume of the chamber  101  is hence decreased and fuel is pressurized and discharged. The cam  103  is further rotated and the projections of the cam  103  are separated from the tappet  109 . The plunger  102  is then returned to the cam  103  by the spring so that the volume of the chamber  101  is increased. In this case, the fuel introducing valve  105  is opened and new fuel is introduced into the chamber  101 . 
     Fuel is transmitted with pressure by repeating the above-described cycle. However, according to the conventional fuel pump for the internal combustion engine, a sufficient amount of discharged fuel could not probably be ensured for obtaining fuel pressure (injection pressure) required by the internal combustion engine especially when the engine is rotated at a low speed, for example when the engine is initially started. 
     That is, a lift amount by the lifting movement of the plunger is fixed. A frequency of the lifting movements of the plunger, i.e. the number of strokes per unit of time, is determined by the rotation speed of the engine (r.p.m.). Therefore, when the engine is rotated at a low speed, for example when the engine is initially started, an amount of discharged fuel per unit of time is decreased. Further, when the engine is rotated at a low speed, for example when the engine is initially started, a compressing cycle by the plunger requires a long time. Therefore, the amount of fuel leaked from a clearance between the plunger and the cylinder is increased so that an actual amount of discharged fuel per stroke is decreased. Further, a required amount of fuel injected at a cold start is from two to four times as large as the required amount of fuel injected under the vehicle being normally running. 
     As a result, the conventional fuel pump for the internal combustion engine may have a problem in that a good performance can not obtained at starting because a desirable fuel injection can not be ensured when the engine is initially started. 
     SUMMARY OF THE INVENTION 
     Considering the above-described problem, according to the invention, an amount of discharged fuel is increased to obtain a required fuel pressure (injection pressure) when an engine is rotated at a low speed, for example when the engine is initially started. Further, a fuel pump for an internal combustion engine is provided for varying the amount of discharged fuel amount to improve the starting performance. 
     A fuel pump for an internal combustion engine according to one of the embodiments of the invention transmits fuel with pressure by a lifting movement of a plunger that is caused to lift by a movement of a cam connected to a camshaft. The fuel pump for the internal combustion engine is provided with a lift amount changing mechanism that changes a lift amount of the plunger caused by the cam. 
     Since this type of fuel pump for the internal combustion engine is provided with a lift amount changing mechanism, the lift amount of the plunger caused by the cam can be varied. Therefore, an amount of discharged fuel per stroke of the plunger is changed and is not determined based only upon a rotation speed of the engine. Therefore, a control of the amount of discharged fuel of the pump can be performed as required. Accordingly, required fuel pressure (injection pressure) can be obtained by increasing the amount of discharged fuel even when the engine is rotated at a low speed, for example when the engine is initially started, so that a starting performance can be improved. 
     A fuel pump for an internal combustion engine of one of the other embodiments of the invention transmits fuel with pressure by a lifting movement of a plunger that is caused to lift by a movement of a cam connected to a camshaft. The fuel pump for the internal combustion engine is provided with a lift number changing mechanism that changes the number of the lifting movements of the plunger that occur per rotation of the internal combustion engine. 
     Since this type of fuel pump for the internal combustion engine is provided with the lift number changing mechanism, the number of the lifting movements of the plunger that occur per rotation of the internal combustion engine can be varied. Therefore, the amount of discharged fuel per rotation of the internal combustion engine is changed and is not determined only based upon the rotation speed of the engine. Therefore, a control of the amount of discharged fuel of the pump can be performed as required. Accordingly required fuel pressure (injection pressure) can be obtained by increasing the amount of discharged fuel even when the engine is rotated at a low speed, for example when the engine is initially started, to improve a starting performance. 
     Further, a fuel pump for an internal combustion engine according to one of the other embodiments of the invention transmits fuel with pressure by a lifting movement of a plunger that is caused to lift by a movement of a cam connected to a camshaft. The fuel pump for the internal combustion engine is provided with a speed changing mechanism that changes a rotation speed of the internal combustion engine, transmits the changed rotation speed to the camshaft, and changes a speed change ratio between the rotation speed of the internal combustion engine and a rotation speed of the camshaft. 
     Since this type of fuel pump for the internal combustion engine is provided with the speed changing mechanism, the number of the lifting movements of the plunger per rotation of the internal combustion engine can be changed by this speed changing mechanism. Therefore, the amount of discharged fuel per rotation of the internal combustion engine is changed and is not determined only based upon the rotation speed of the engine. Accordingly, a control of the amount of discharged fuel of the pump can be performed as required. Therefore, required fuel pressure (injection pressure) can be obtained by increasing the amount of discharged fuel even when the engine is rotated at a low speed, for example when the engine is initially started, to improve a starting performance. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above mentioned and other objects, features, advantages, technical and industrial significance of this invention will be better understood by reading the following detailed description of the preferred embodiments of the invention, when considered in connection with the accompanying drawings, in which: 
     FIG. 1 is a sectional view schematically illustrating a structure of a fuel pump for an internal combustion engine according to a first embodiment of the invention; 
     FIGS. 2 a - 2   c  are enlarged views of a cam portion of the fuel pump for the internal combustion engine illustrated in FIG. 1, wherein FIG. 2 a  is a side view, FIG. 2 b  is a sectional view taken along line  2 — 2  in FIG. 2 a , and FIG. 2 c  is a sectional view taken along line  3 — 3  in FIG. 2 a;    
     FIGS. 3 a - 3   c  are enlarged views of a cam portion of a fuel pump for an internal combustion engine according to a second embodiment of the invention, wherein FIG. 3 a  is a side view, FIG. 3 b  is a sectional view taken along line  2 — 2  in FIG. 3 a , and FIG. 3 c  is a sectional view taken along line  3 — 3  in FIG. 3 a;    
     FIGS. 4 a - 4   d  are enlarged views of a modified example of the cam portion of the fuel pump for the internal combustion engine according to the second embodiment of the invention, wherein FIG. 4 a  is a side view, FIG. 4 b  is a sectional view taken along line  2 — 2  in FIG. 4 a , FIG. 4 c  is a sectional view taken along line  3 — 3  in FIG. 4 a , and FIG. 4 d  is a sectional view taken along line  4 — 4  in FIG. 4 a;    
     FIG. 5 is a sectional view of another modified example of the cam portion of the fuel pump for the internal combustion engine according to the second embodiment of the invention; 
     FIG. 6 is a sectional view schematically illustrating a structure of a fuel pump for an internal combustion engine according to a third embodiment of the invention; and 
     FIG. 7 is a sectional view schematically illustrating a structure of a conventional fuel pump for an internal combustion engine. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings. In the drawings, identical or similar elements will be denoted with the same reference numerals. 
     FIG. 1 is a schematically sectional view of a fuel pump  200  of a first embodiment of a fuel pump for an internal combustion engine for discharging variable amount of fuel according to the invention. In the fuel pump  200  according to the first embodiment, a basic principle to transmit fuel with pressure by a lifting movement of a plunger corresponding to a movement of a cam is the same as a conventional fuel pump  100  illustrated in FIG.  7 . Therefore, the fuel pump  200  according to the first embodiment is formed of the same basic structure as the conventional fuel pump  100 . That is, the fuel pump  200  according to the first embodiment is provided with a cam  203  mounted on a camshaft  204 , a tappet  209  engaged with the cam  203 , a plunger  102  having the tappet  209  at one end portion thereof, a cylinder  106  receiving the plunger  102  therein, and a chamber  101  defined in the cylinder  106 . The fuel pump  200  is further provided with a fuel supply port  107 , a fuel discharge port  108  both of which are connected to the chamber  101 , and an electromagnetic valve  105 . The electromagnetic valve  105  is disposed halfway in a passage connecting the fuel supply port  107  and the chamber  101  and serves as a fuel introducing valve. The plunger  102  and the tappet  209  engaged with the plunger  102  are biased by a spring (not shown) in a direction of the cam  203 . The cam  203  is rotatably driven by a rotation of an engine transmitted to the camshaft  204 , i.e. a rotation of a crankshaft transmitted to the camshaft  204 . 
     According to the first embodiment, the tappet  209  is pushed upward corresponding to the rotation of the cam  203  so that a lift movement of the plunger  102  is performed in the cylinder  106 . Therefore, fuel is transmitted with pressure in the same manner as the conventional fuel pump  100 . A cam  103  of the conventional fuel pump  100  has an even (i.e. a constant) cam profile (in any section) along an axial direction of a camshaft  104 . To the contrary, the cam  203  has an uneven profile along the axial direction of the camshaft  204 . In particular, the cam  203  has a cam profile in which heights (dimensions) of a projection are varied as illustrated in FIGS. 2 a ,  2   b , and  2   c.    
     According to the above-described cam shape, the lift amount of the plunger  102  can be varied corresponding to the movement of the cam  203  along the axial direction of the camshaft  204 . Therefore, the amount of discharged fuel can be varied. That is, when the cam  203  is moved so that a high portion of the projection is engaged with the tappet  209 , the lift amount becomes larger and the amount of discharged fuel is increased. To the contrary, when the cam is moved so that a low portion of the projection is engaged with the tappet  209 , the lift amount becomes smaller and the amount of discharged fuel can be decreased. According to an arrangement structure illustrated in FIG. 1, when the cam  203  is moved to the right side, the amount of discharged fuel is increased. When the cam  203  is moved to the left side, the amount of discharged fuel is decreased. An engaging portion of the tappet  209  with the cam  203  according to the first embodiment does not prevent the cam  203  from moving in the axial direction of the camshaft  204  and is formed to follow a surface of the rotatable cam  203 . 
     Further, according to the first embodiment, the fuel pump  200  is provided with a cam moving apparatus  215  as being schematically illustrated in FIG.  1 . The cam moving apparatus  215  moves the cam  203  along the axial direction of the camshaft  204  corresponding to a fuel pressure in a fluid discharging side passage  206  of the fuel pump  200 . The cam moving apparatus  215  is in a form of a housing structure having a movable wall  202 . An inner space of the housing is connected to the fuel discharging side passage  206  of the fuel pump  200 . The camshaft  204  is rotatably connected to the movable wall  202 . The movable wall  202  is biased by a spring  205  in a direction to decrease the volume of the inner space of the housing. According to the arrangement structure illustrated in FIG. 1, when the fuel pressure in the fuel discharging side passage  206  is increased, the movable wall  202  is moved to the left side in FIG. 1 by the fuel pressure overcoming a spring force. The cam  203  is then moved to the left side. On the other hand, when the fuel pressure in the fuel discharging side passage  206  of the fuel pump  200  is decreased, the movable wall  202  is moved to the right side in FIG. 1 by the spring force overcoming the fuel pressure. The cam  203  is then moved to the right side. 
     As being fully described above, according to the fuel pump  200  of the first embodiment of the invention illustrated in FIG. 1, when the fuel pressure in the fuel discharging side passage  206  of the fuel pump  200  is low, the cam  203  is moved to the right side and the amount of discharged fuel is increased. When the fuel pressure in the fuel discharging side passage  206  of the fuel pump  200  is high, the cam  203  is moved to the left side and the amount of discharged fuel is decreased. That is, according to the above-described structure, a control of the amount of discharged fuel can be performed corresponding to the fuel pressure only by adding a simple structure without using a sensor, an actuator and the like. 
     According to the above described structure, when the fuel pressure is low, for example when the engine is initially started, the cam  203  is moved to the right side in FIG.  1  and the lift amount of the plunger  102  is increased so that the amount of discharged fuel is increased. On the other hand, when the fuel pressure is sufficiently high, for example when the vehicle is normally running, the cam  203  is moved to the left side in FIG.  1  and the lift amount of the plunger  102  is decreased so that excessive fuel is not discharged. 
     Next, a fuel pump for an internal combustion engine according to a second embodiment of the invention will be described. An entire structure of the fuel pump according to the second embodiment is the same as the fuel pump  200  according to the first embodiment illustrated in FIG. 1, yet a cam shape is not the same. More specifically, a cam  210  according to the second embodiment has a cam profile in which the number of projections is varied as illustrated in FIGS. 3 a ,  3   b , and  3   c.    
     According to the above described cam shape, the number of the lifting movements of the plunger  102  per rotation of the camshaft  204  can be varied corresponding to the movement of the cam  210  along the axial direction of the camshaft  204 . Therefore, the amount of discharged fuel can be varied. That is, the number of the lifting movements is increased and the amount of discharged fuel is increased when the cam  210  is moved for engaging the tappet  209  with a many projections portion. On the other hand, the number of the lifting movements is decreased and the amount of discharged fuel is decreased when the cam  210  is moved for engaging the tappet  209  with a less projections portion. 
     According to the arrangement structure illustrated in FIG. 3 a , the amount of discharged fuel is increased when the cam  210  is moved to the right side, and the amount of discharged fuel is decreased when the cam  210  is moved to the left side. Herein, the camshaft  204  is applied with the rotation of the crankshaft, i.e. the rotation of the engine at a constant speed change ratio, to be rotatably driven. Therefore, to change the number of the lifting movements of the plunger  102  per rotation of the camshaft  204  means to change the number of the lifting movements of the plunger  102  per rotation of the internal combustion engine. 
     According to the second embodiment, since the apparatus for moving the cam  210  along the axial direction of the camshaft  204  corresponding to the fuel pressure in the fuel discharging side passage of the fuel pump according to the first embodiment illustrated in FIG. 1 is provided, the control of the amount of discharged fuel is performed corresponding to the fuel pressure in the fuel discharging side passage of the fuel pump in the same manner as the first embodiment when the cam  210  is mounted on the camshaft  204  in a proper direction. That is, according to the fuel pump illustrated in FIG. 1, with the cam  203  replaced by the cam  210  placed in a direction illustrated in FIG. 3 a , the cam  210  is moved to the right side in FIG.  1  and the number of the lifting movements of the plunger  102  is increased when the fuel pressure is low, for example when the engine is initially started. On the other hand, the cam  210  is moved to the left side in FIG.  1  and the number of the lifting movements of the plunger  102  is decreased when the fuel pressure has been sufficiently high, for example when the vehicle is normally running. Therefore, excessive fuel pressure is not discharged. 
     According to the second embodiment, the cam  210  was described. The cam  210  described above has two cam profile portions; one is a cam profile portion with three projections illustrated in FIG. 3 b  and the other one is a cam profile portion with two projections illustrated in FIG. 3 c . However, the number of projections of the cam profile can be freely selected as desired. Further, the number of portions having different projections can be freely selected as desired. FIGS. 4 a  through  4   d  illustrate a cam  220  according to a modified example of the invention. The cam  220  includes three cam profiles. The first one is a cam profile with three projections, the second one is a cam profile with two projections, and the third one is a cam profile with a single projection. When the cam  220  includes a cam profile with four projections or more than that, the cam  220  can not be rotated with a point in contact with the tappet. Therefore, as illustrated in FIG. 5, another disc cam  240  is required to be disposed between a cam  230  and a tappet  235  as being illustrated in FIG.  5 . 
     Next, a fuel pump  700  for an internal combustion engine according to a third embodiment is described. A structure of the fuel pump  700  according to the third embodiment is substantially the same as the aforementioned conventional fuel pump except for an apparatus for transmitting the rotation of the internal combustion engine, the rotation of a crankshaft  705  to a camshaft  701 . As described above, according to the conventional fuel pump, the rotation of the crankshaft is generally transmitted to the camshaft via a belt and the like. If that is the case, a speed change ratio between the crankshaft rotation speed and the camshaft rotation speed is fixed. Therefore, a frequency of the lifting movements of the plunger of the fuel pump is determined only by the rotation speed of the crankshaft, i.e. by the rotation speed of the engine. The amount of discharged fuel is also determined only by the rotation speed of the engine. On the other hand, according to the third embodiment, the rotation of the crankshaft  705  is transmitted to the camshaft  701  via a speed changing mechanism  702 . Therefore, the speed changing mechanism  702  can change the speed change ratio between the rotation speed of the crankshaft and the rotation speed of the camshaft. 
     The speed changing mechanism  702  according to the third embodiment is provided with a driving pulley  707  disposed on the crankshaft  705  and a driven pulley  709  disposed on the camshaft  701 , and a speed changing belt  704 . The speed changing belt  704  is arranged for transmitting rotation between the pulleys  707  and  709 . The speed changing mechanism  702  according to the third embodiment is further provided with a belt moving apparatus  715 . The belt moving apparatus  715  according to the third embodiment moves the speed changing belt  704  along an axial direction of the camshaft  701 . According to the third embodiment, the belt moving apparatus  715  moves the speed changing belt  704  along the axial direction of the camshaft  701  corresponding to the fuel pressure in the fuel discharging side passage  706 . 
     The driving pulley  707  and the driven pulley  709  respectively have a sectional diameter gradually increasing or decreasing along the rotation axis. Both of the pulleys  707  and  709  are in the form of a cone without a cone tip. As illustrated in FIG. 6, a large diameter portion of the pulley  707  and a small diameter portion of the pulley  709  are arranged to face in one direction. On the other hand, a small diameter portion of the pulley  707  and a large diameter portion of the pulley  709  are arranged to face in the other direction. The speed changing belt  704  is arranged on an inclined side surface of each pulley  707  and  709 . 
     According to the above-described structure, when the speed changing belt  704  is moved along the axial direction of the camshaft  701  per rotation of the crankshaft of the internal combustion engine, the rotating number of the camshaft  701 , i.e. a rotating number of a cam  711  per rotation of the crankshaft of the internal combustion engine can be changed. Therefore, the lifting number of the plunger  102  can be changed and the amount of discharged fuel can be changed. That is, according to the arrangement structure illustrated in FIG. 6, when the speed changing belt  704  is moved to the right side in FIG. 6, the large diameter portion of the driving pulley  707  and the small diameter portion of the driven pulley  709  are connected by the speed changing belt  704 . Therefore, the speed change ratio is changed to increase the rotation speed of the camshaft  701 . As a result, the lifting number of the plunger  102  is increased and the amount of discharged fuel is increased. On the other hand, when the speed changing belt  704  is moved to the left side in FIG. 6, the small diameter portion of the driving pulley  707  and the large diameter portion of the driven pulley  709  are connected by the speed changing belt  704 . Therefore, the speed change ratio is changed to decrease the rotation speed of the camshaft  701 . As a result, the lifting number of the plunger  102  is decreased and the amount of discharged fuel is decreased. 
     As described above, according to the third embodiment, the belt moving apparatus  715  is provided for moving the speed changing belt  704  along the axial direction of the camshaft  701  corresponding to the fuel pressure in the fuel discharging side passage  706 . Therefore, the above-described control of the amount of discharged fuel is performed corresponding to the fuel pressure in the fuel discharging side passage  706 . A basic structure of the belt moving apparatus  715  according to the third embodiment is the same as the cam moving apparatus  215  for moving the cam along the axial direction of the camshaft corresponding to the fuel pressure in the fuel discharging side passage of the fuel pump described for the first and second embodiments of the invention. However, a movable wall  703  of the belt moving apparatus  715  is connected to a transmitting means  712  for transmitting a displacement of the movable wall  703  to the speed changing belt  704  instead of being connected to the camshaft. 
     As fully described above, according to the fuel pump  700  of the third embodiment of the invention illustrated in FIG. 6, when the fuel pressure in the fuel discharging side passage  706  of the fuel pump  700  is low, the speed changing belt  704  is moved to the right side in FIG.  6  and the amount of discharged fuel is increased. When the fuel pressure in the fuel discharging side passage  706  of the fuel pump  700  is high, the speed changing belt  704  is moved to the left side in FIG.  6  and the amount of discharged fuel is decreased. 
     According to the above-described structure, when the fuel pressure is low, for example, when the engine is initially started, the amount of discharged fuel is increased. On the other hand, when the fuel pressure is sufficiently high, for example when the vehicle has been normally running, excessive fuel is not discharged. 
     As fully described above, according to the third embodiment, a mounting direction of the driving pulley  707  and the driven pulley  709  is determined considering a moving direction of the belt moving apparatus  715  against a change of the fuel pressure in the fuel discharging side passage. 
     Further, if desired, the control of the amount of discharged fuel can be performed by combining a lift amount changing apparatus for changing the lift amount of the plunger according to the first embodiment and a lifting number changing apparatus for changing the lifting number according to the second embodiment. 
     While the invention had been described with reference to preferred embodiments thereof, it is to be understood that the invention is not limited to the preferred embodiments or constructions. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the preferred embodiments are shown in various combinations and configurations, which are exemplary, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the invention.