Information
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Patent Grant
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6234128
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Patent Number
6,234,128
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Date Filed
Monday, March 13, 200024 years ago
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Date Issued
Tuesday, May 22, 200123 years ago
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Inventors
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Original Assignees
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Examiners
Agents
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CPC
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US Classifications
Field of Search
US
- 123 17917
- 123 447
- 123 456
- 123 514
- 123 1799
- 123 17912
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International Classifications
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Abstract
A fuel system has a pump which supplies fuel under pressure to a fuel rail for distribution by fuel injectors to the cylinders of an engine. A fuel accumulator, having a volume greater than the volume of fuel required to start the engine, is disposed in fluid communication with the fuel rail to supply a charge of fuel thereto during engine start-up at a pressure level sufficient to cause fuel atomization within the cylinder. The fuel in the accumulator is stored at the ambient pressure. A spring force or a solenoid force is applied to the fuel in the accumulator such that the fuel is ejected into the fuel rail at the required pressure level. A check valve is positioned to prevent fuel flow from the fuel rail to the pump during the initial discharge from the accumulator. The accumulator is refilled by fuel from the pump during normal operation and the fuel therein is reduced to ambient pressure when the engine operation is discontinued.
Description
TECHNICAL FIELD
This invention relates to fuel injection systems and more particularly to a system for providing a volume of fuel to the fuel injectors at engine start-up.
BACKGROUND OF THE INVENTION
Internal combustion engines utilize many types of fuel injection such as manifold injection, port injection and direct injection. Direct injection engines have a fuel feed system that injects fuel directly into the combustion chamber of the engine. Direct injection engines employ high pressure fuel systems in order to more fully atomize the fuel in the combustion chamber. At start-up of the engine, it is desirable to have the operating pressure of the fuel system be at a sufficient level to achieve proper atomization to sustain low emission levels. It generally requires a number of engine revolutions before the fuel system attains the desired pressure level. This delays the engine start-up.
To alleviate this condition, it has been proposed to install a passive high pressure accumulator to the fuel system such that fuel is stored at the desired pressure between engine shut-off and the next engine start-up. These systems have two drawbacks. The storage of high pressure fuel is undesirable and the accumulators often “leak down” between shut-down and start-up, if the period is long, thereby defeating the purpose of the accumulator.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved direct injection fuel system having an accumulator.
In one aspect of the present invention, an accumulator stores fuel at a low pressure between engine shut-down and engine start-up. In another aspect of the present invention, the fuel stored in the accumulator is delivered to the fuel injectors at a high pressure at engine start-up. In yet another aspect of the present invention, a stored force is applied to the fuel in the accumulator to eject the fuel therefrom and rapidly pressurize the fuel system at the injectors. In still another aspect of the present invention, a spring-loaded piston is employed to force the fuel from the accumulator during engine start-up.
In yet still another aspect of the present invention, the accumulator is filled and the spring-loaded piston is reset by the pressurized fuel supplied from a fuel pump during engine operation. In a further aspect of the present invention, a solenoid-actuated piston is employed to provide the force used to expel the fuel from the accumulator. In a yet further aspect of the present invention, a pressure-on-demand system is provided to assist rapid engine starting by producing a high pressure fuel charge, from low pressure accumulator stored fuel, to the fuel injectors of the engine only at the beginning of the engine-starting operation but prior to pressurized fuel from the normal fuel injection pump becoming available.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a schematic representation of a portion of a fuel injection system incorporating one embodiment of the invention.
FIG. 2
is a schematic representation of a portion of a fuel injection system incorporating another embodiment of the invention.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
A portion of a fuel system
10
is shown in FIG.
1
. The fuel system includes a high pressure fuel pump
12
, a plurality of fuel injectors
14
and an accumulator
16
. The pump
12
and fuel injectors
14
are conventional fuel system components. The pump
12
, when operating, will deliver pressurized fuel in the range of 1 to 150 megapascals (Mpa). The injectors
14
are operated by the vehicle electrical system as controlled by the engine electronic control mechanism, not shown, in a well-known manner.
The accumulator
16
has a housing
18
in which is slidably disposed a piston
20
. The housing
18
and piston
20
cooperate to form an expansible fuel accumulator chamber
22
and an expansible spring chamber
24
. A piston rod
26
extends from the piston
20
to a catch member
28
which is outboard of the housing
18
. A spring
30
, trapped between the housing
18
and the piston
20
in the spring chamber
24
, surrounds the piston rod
26
. The piston
20
and the spring
30
are shown in a latched condition in which a force is stored in the spring
30
.
The catch member
28
is held in the latched condition by a latch member
32
. The latch member
32
is pivotally mounted on a pin
34
. The latch
32
has a latch finger
36
at one end
38
and a control point
40
at the other end
42
. The latch finger
36
engages the catch member
28
to hold the piston
20
in the latched condition. The control point
40
is operatively connected with a solenoid assembly
44
through a rod
46
. The operation of the solenoid assembly
44
is controlled in a conventional manner by the vehicle electrical system such that the solenoid assembly is energized at engine start-up and de-energized after engine state-up.
The pump
12
is in fluid communication with a fuel rail
48
through a passage
50
and a conventional check valve
52
. The fuel rail
48
supplies pressurized fuel to the injectors
14
. The fuel rail
48
is also in fluid communication with the fuel accumulator chamber
22
. The volume of the chamber
22
is greater than the volume of fuel required to start the engine. The housing
18
is in fluid communication through a fuel pressure regulator valve
54
which is in fluid communication with a fuel tank or reservoir
56
through a fuel return passage
58
. The spring chamber
24
is also in fluid communication with the fuel return passage
58
through an exhaust or vent port
60
.
Assuming that the engine has been started previously, the chamber
22
will be full of fuel and the latch
32
will hold the piston
20
in the position shown. When the operator engages the start circuit, the solenoid
44
will actuate the latch member
32
to release the piston
20
and the spring
30
will urge the piston
20
rightward, as viewed in FIG.
1
. The piston
20
, under the influence of the spring
30
, will force the fuel from chamber
22
into the fuel rail
48
at a rate required to feed the engine during start-up. Since the volume of the chamber
22
is greater than the volume of fuel required to state the engine, the accumulator will continue to supply fuel to the fuel rail
48
until the pump
12
is operable. The force stored in the spring
30
will determine the pressure of the fuel delivered to the fuel rail
48
during start-up. The amount of fuel ejected from the fuel accumulator will depend on the number of rotational cycles the engine undergoes prior to the pressure output of the pump
12
reaching the normal operating range. The spring
30
is designed to produce a pressure level in the fuel that is equal to or greater than the minimum pressure required to atomize the fuel as it is injected into the engine cylinders. The minimum pressure requirement will depend on the engine; for example, a diesel engine may have a higher requirement than a spark ignition engine.
The pump
12
is started simultaneously with the release of the piston
20
; however, a brief period of time is required for the pump
12
to raise the pressure level of the fuel system into the operating range. This time period can be sufficient to permit several revolutions of the engine prior to ignition. With the present invention, the fuel rail
48
is fully charged and the engine cylinders receive the proper fuel/air mixture to support combustion. The check valve
52
prevents the fuel in the fuel rail
48
from flowing toward the pump
12
and simultaneously insures that the pump pressure is sufficient to overcome the pressure of the fuel in the fuel rail
48
.
When the pump
12
generates the required pressure level, the check valve
52
will admit fuel from the pump
12
into the fuel rail
48
. Since the normal operating pressure of the pump
12
is greater than the load supportable by the spring, the piston will be urged leftward in the chamber
22
against the spring
30
. When the catch member
28
abuts the latch finger
36
, the latch member
32
will pivot clockwise about the pin
34
. When the catch member
28
has moved leftward sufficiently to clear the end
38
, a low force tension spring
62
will pivot the latch member
32
counterclockwise, thereby holding the piston
20
in the spring-loaded position shown.
The regulator valve
54
will be placed in fluid communication with the chamber
22
and the fuel rail
48
to control the output pressure of the pump
12
when the piston has moved to the spring-loaded position shown. When the engine is shut down, the regulator valve is operated to reduce the pressure in the fuel rail
48
and chamber
22
to ambient pressure by returning any excess fuel to the tank
56
. The fuel system is then prepared for the next engine start-up. The fuel stored in the chamber
22
is at a pressure level substantially equal to the pressure level in the fuel tank
56
.
A fuel system
10
A, shown in
FIG. 2
, includes the fuel pump
12
, check valve
52
, fuel rail
48
, regulator valve
54
and a fuel accumulator
64
. The fuel rail
48
distributes fuel to the injectors
14
in a well-known manner. The accumulator
64
includes a housing
66
, a solenoid
68
and a piston
70
. A return passage
74
connects the area between the left end of the piston
70
and the housing
66
with the fuel tank
56
to ensure that any fuel leaking past the piston
70
does not interfere with the leftward movement of the piston
70
. The piston
70
is slidably disposed in the housing
66
and cooperates therewith to form a fuel accumulator chamber
72
that is in fluid communication with the fuel rail
48
. The solenoid
68
is disposed circumjacent a portion of the housing
66
such that, when energized, the solenoid
68
will urge the piston
70
rightward in the housing
66
, thereby reducing the volume of the chamber
72
. As described above for the fuel system
10
A, the volume of the chamber
72
is greater than the volume of fuel required to start the engine.
When the operator places the ignition circuit in the start mode, the regulator valve
54
is conditioned to control the fuel pressure in the fuel rail
48
within the desired operating range and the solenoid
68
is energized. The solenoid will force the piston rightward, thereby ejecting the fuel in the chamber
72
into the fuel rail
48
to raise the pressure level therein to at least the minimum required for atomization of the fuel as it is injected into the engine cylinders through the injectors
14
. The pump
12
is also operated at this time, but, as described above, the output pressure thereof will take a small amount of time to develop to the required level. However, the fuel expelled from the chamber
72
will permit the injectors to supply fuel at the proper pressure level to the cylinders of the engine. The check valve
52
prevents back flow of fuel from the fuel rail
48
to the pump
12
prior to the pump output pressure reaching the required level. At engine start or when the pump output pressure level is within the required range, the solenoid is de-energized and the excess fuel from the pump
12
will force the piston to the position shown and the chamber
72
will be filled with fuel. The regulator valve
54
will control the pressure in the fuel rail
48
during engine operation and will permit the pressure level in both the fuel rail
48
and the chamber
72
to be reduced to the ambient pressure of the fuel tank
56
.
Claims
- 1. A fuel system for a direct injection engine comprising:a fuel pump; a fuel rail disposed in fluid communication with said pump; a fuel accumulator disposed in fluid communication with said fuel rail including means for forcing fuel from said accumulator into said fuel rail during engine start-up, said accumulator storing fuel at an ambient pressure level between engine shut down and engine restart; said means for forcing fuel from said accumulator comprising a spring positioned between an accumulator housing and a piston; latching means for holding said piston in a spring loaded position during normal engine operation and; means for releasing said latching means during engine start-up and said spring urging said piston to force fuel from said accumulator into said fuel rail during engine start-up.
- 2. A fuel system for a direct injection engine comprising:a fuel pump; a fuel rail disposed in fluid communication with said pump; a fuel accumulator disposed in fluid communication with said fuel rail including means for forcing fuel from said accumulator into said fuel rail during engine start-up, said accumulator storing fuel at an ambient pressure level between engine shut down and engine restart; said means for forcing fuel from said accumulator comprising a solenoid disposed circumjacent said housing and being selectively energizable to urge said piston to expel fuel from said accumulator chamber.
- 3. A fuel system for a direct injection engine comprising:a fuel pump; a fuel rail disposed in fluid communication with said pump; a fuel accumulator disposed in fluid communication with said fuel rail including means for forcing fuel from said accumulator into said fuel rail during engine start-up, said accumulator storing fuel at an ambient pressure level between engine shut down and engine restart; said means for forcing fuel from said accumulator comprising a spring positioned between an accumulator housing and a piston, and latching means for holding said piston in a spring loaded position during normal engine operation.
- 4. The fuel system for a direct injection engine defined in claim 1 further comprising:a fuel pressure in said fuel rail resetting said piston to said spring-loaded position during normal engine operation when fuel is being supplied by said pump.
US Referenced Citations (17)