Internal-combustion engines – Charge forming device – With fuel pump
Reexamination Certificate
2003-03-05
2004-09-07
Moulis, Thomas N. (Department: 3747)
Internal-combustion engines
Charge forming device
With fuel pump
C123S509000, C123S19800E
Reexamination Certificate
active
06786206
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fuel pump drive system.
2. Description of the Related Art
A common rail type fuel injection system for injection of fuel to an engine has been known as a system which can enhance an injection pressure and which optimally controls injection conditions such as fuel injection rate and timings depending upon operational status of the engine.
FIG. 1
is a block diagram typically and schematically showing such common rail type fuel injection system in which fuel in a fuel tank
1
is pressurized by a fuel pump
2
in the form of for example a plunger type variable displacement high-pressure pump.
This fuel pump
2
is driven by an engine output to pressurize the fuel into a required pressure and deliver the same via a fuel conduit
3
to a common rail
4
where the fuel is accumulated in pressurized state.
The fuel pump
2
is provided with a valve means
5
which controls fuel discharge rate to maintain the fuel in the common rail
4
to a predetermined pressure. Relieved fuel from the pump
2
is returned by a return conduit
6
to the tank
1
.
The fuel in the common rail
4
is delivered via delivery conduits
7
to a plurality of injectors
8
each for each cylinder of the engine to inject the fuel into the respective cylinders; part of the fuel delivered via the conduits
7
to the injectors
8
that has failed to be consumed for injection into the cylinders is returned via a return conduit
9
to the tank
1
.
Reference numeral
10
denotes an engine-control computer or ECU (electronic control unit) which receives, for detection of operational status of the engine, various signals such as a cylinder discriminating signal
11
from an engine cylinder discriminating sensor, a crank angle signal
12
from a crank angle sensor for sensing phase difference relative to for example a top dead center (TDC), an accelerator opening signal
13
from an accelerator opening sensor (engine load sensor) for sensing a pressurized amount of an accelerator pedal and an engine revolution speed signal
14
from an engine revolution speed sensor.
The common rail
4
is provided with a pressure sensor
15
which detects pressure in the common rail
4
. A pressure signal
16
from the sensor
15
is also inputted to the electronic control unit
10
.
On the basis of these signals, the electronic control unit
10
issues injection commands
18
to electromagnetic valves
17
of the injectors
8
to optimize the engine output in line with the operational status, thereby optimally controlling fuel injection conditions, i.e., fuel injection rate and timings (injection starting and ending timings).
The pressure in the common rail
4
, which may be lowered due to consumption of the fuel in the rail
4
through injection by the injectors
8
, is controlled by the electronic control unit
10
to a required fuel injection pressure depending upon the operational status of the engine. More specifically, the unit
10
issues a pressure control command
20
to an electromagnetic valve
19
of the discharge rate control valve means
5
of the fuel pump
2
to control the discharge rate of the fuel pump
2
, thereby controlling the pressure in the common rail
4
.
Injection starting and ending timings of the fuel are controlled such that phase difference from a predetermined crank angle (for example, that of TDC) is calculated by the crank angle sensor on the basis of which the electronic control unit
10
issues command pulses (the injection commands
18
) to establish drive current to the electromagnetic valves
17
of the injectors
8
so as to inject the fuel over a predetermined period in terms of the crank angle signal
12
.
In the common rail type fuel injection system thus constructed, the fuel pump
2
is engine driven by torque transmitted from a crankshaft via a gear train with the revolution ratio of the engine to the fuel pump
2
being two-to-one (i.e., two revolutions of the engine per revolution of the fuel pump) as traditional with respect to the timings of the conventional mechanical fuel injection systems; this will needlessly involve increase in capacity of the fuel pump
2
irrespective of the fact that such revolution ratio has no substantive meanings or advantages in the common rail type fuel injection system.
That is to say, in a mechanical fuel injection system where fuel discharge timing of the fuel pump
2
is mechanically made accordant with fuel injection timing for a four cycle engine, the revolution ratio of the engine to the fuel pump must be two-to-one to attain two revolutions of the engine per injection in the respective cylinders whereas such revolution ratio of two-to-one has no specific meanings or needs in a common rail type fuel injection system where the fuel from the fuel pump
2
is accumulated in the common rail
4
in pressurized state and the fuel injection in the respective cylinders is electronically controlled.
In view of the above, the inventors thought of an engine with a common rail type fuel injection system where revolution ratio of the engine to a fuel pump is set to one-to-one, which allows reduced fuel discharge rate per revolution of the fuel pump and thus allows the fuel pump to be smaller-sized, leading to improvement in mountability of the engine to a vehicle.
However, there are problems in this respect. As shown in
FIG. 2
, in a conventional gear train G for transmission of torque from a crankshaft
21
to the fuel pump
2
, rotation or revolution of the crank shaft
21
integral with the crank gear
22
causes a larger main idler
23
in mesh with the gear
22
to rotate integrally with a smaller main idler
24
; then, an air compressor gear
25
in mesh with the idler
24
is rotated integrally with a drive shaft
26
which serves to drive not only the fuel pump
2
but also an air compressor
27
(see FIG.
4
). Therefore, if the revolution ratio of two-to-one as shown in
FIG. 2
is to be changed into one-to-one, then, as shown in
FIG. 3
, the air compressor gear
25
must be in mesh with the larger main idler
23
having gear teeth twice in number as great as that of the smaller main idler
24
, which will involve substantial displacement of an axis of the air compressor gear
25
. As a result, a flywheel housing
28
which is to accommodate such gear train G must be inevitably changed in shape, resulting in significant increase in cost.
More specifically, as shown in
FIG. 4
with reference to the structure shown in
FIG. 2
, the flywheel housing
28
is integrally formed with an accommodation space S for the gear train G which is partly defined by a bracket
28
a
of the housing
28
. The bracket
28
a
is formed with a gear through hole
29
through which the air compressor gear
25
is passed to the space S with the air compressor
27
being fitted together with the fuel pump
2
to the bracket
28
a
; thus, arrangement of the air compressor gear
25
in a position shown in
FIG. 3
utterly away from its original or conventional position will necessitate a new flywheel housing
28
with its gear through hole
29
being formed thereon in a different position. The flywheel housing
28
itself is an expensive and larger-sized part and is of various kinds such that dozens of alternative flywheel housings are usually stocked. Therefore, innovation of such housing with conventional stocks being reserved will lead to vast increase in cost from viewpoints of not only manufacture but also storage.
BRIEF SUMMARY OF THE INVENTION
The present invention was made in view of the above and has its object to set revolution ratio of an engine to a fuel pump to one-to-one without involving vast increase in cost, thereby allowing a fuel pump to be smaller-sized.
The invention is directed to a fuel pump drive system for engine driving a fuel pump by torque transmitted from a crankshaft via a gear train, comprising a conventional flywheel housing with a gear through hole opened to a gear train accommodation space and adapted to receive a conventional input gear as an element
Ishikawa Hideyuki
Koga Ryuuichi
Hino Motors Ltd.
Moulis Thomas N.
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