Internal-combustion engines – Charge forming device – With fuel pump
Reexamination Certificate
2002-02-13
2004-03-16
Moulis, Thomas N. (Department: 3747)
Internal-combustion engines
Charge forming device
With fuel pump
C123S090180, C123S387000
Reexamination Certificate
active
06705297
ABSTRACT:
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 di
Akiyama Kiyokazu
Nakashima Tatsushi
Saito Kimitaka
Takeda Keiso
Moulis Thomas N.
Oliff & Berridg,e PLC
Toyota Jidosha & Kabushiki Kaisha
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