Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
1998-08-25
2002-06-25
Miller, Carl S. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
Reexamination Certificate
active
06408823
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fuel injection control device for engines with a common-rail type fuel injection system which stores in a common rail a fuel pressurized to a predetermined pressure by a fuel pump and injects the stored fuel from injectors into combustion chambers.
2. Description of the Prior Art
As for the fuel injection control in engines, a common-rail type fuel injection system has been known which provides a high injection pressure and performs optimum control on injection characteristics, such as fuel injection timing and the amount of fuel injected, according to the operating condition of the engine. The common-rail type fuel injection system is a fuel injection system that stores in the common rail a fuel pressurized to a predetermined pressure by a pump and then injects the stored fuel from injectors into corresponding combustion chambers. To ensure that the pressurized fuel will be injected from each injector under optimum injection conditions according to the engine operating conditions, a controller controls the fuel pressure in the common rail and the operation of control valves for the injectors according to the operating conditions of the engine.
The conventional common-rail type fuel injection system will be described by referring to FIG.
11
. The fuel is supplied to individual injectors
1
from a common rail
2
through branch pipes
3
that form a part of the fuel passage. The fuel, which was pumped by a feed pump
6
from a fuel tank
4
through a filter
5
and pressurized to a predetermined pressure, is delivered to a fuel pump
8
through a fuel pipe
7
. The fuel pump
8
may, for example, be a so-called plunger type fuel supply pump driven by the engine which raises the fuel pressure to a high pressure determined by the operating condition of the engine and delivers the pressurized fuel through a fuel pipe
9
to the common rail
2
. The fuel is then stored temporarily in the common rail
2
at the elevated pressure, from which it is supplied to individual injectors
1
. Normally there are provided two or more injectors
1
corresponding in number to cylinders in the engine (or according to the type of engine). These injectors
1
are controlled by a controller
12
to inject fuel supplied from the common rail
2
into the corresponding combustion chambers in optimum amounts and at optimum timings. Because the pressure at which the fuel is injected from the injectors
1
is equal to the pressure of the fuel stored in the common rail
2
, the injection pressure is controlled by controlling the fuel pressure in the common rail
2
.
The fuel flowing from the feed pump
6
into the fuel pump
8
is controlled by a flow control valve
10
. Of the fuel supplied from the branch pipes
3
to the injectors
1
, the fuel that was not used for injection into the combustion chambers is returned to the fuel tank
4
through a return pipe
11
. The controller
12
as an electronic control unit (ECU) is supplied with information on the engine operating condition from various sensors, which include: engine cylinder determination and crank angle sensors for detecting an engine revolution speed Ne, determining the cylinders into which the fuel needs to be injected and calculating the injection timing; an accelerator opening sensor for detecting the accelerator control input Acc such as an accelerator depression; a water temperature sensor for detecting the cooling water temperature; and an intake pipe inner pressure sensor for detecting the inner pressure of the intake pipe. The controller
12
, based on these signals, controls the fuel injection characteristics of the injectors
1
, i.e., the fuel injection timing and the amount of fuel to be injected (injection pressure and injection period) so that the operation characteristics such as engine output, exhaust gas and mileage will become optimum for the current engine operating condition. The common rail
2
is provided with a pressure sensor
13
which detects the fuel pressure in the common rail
2
and sends the detection signal to the controller
12
. Once the fuel is injected from the injectors
1
, the fuel in the common rail
2
is consumed reducing the pressure in the common rail
2
. The controller
12
controls the flow control valve
10
to regulate the amount of fuel delivered by the fuel pump
8
to the common rail
2
so as to maintain the fuel pressure in the common rail
2
at a preset pressure.
An example of the conventional fuel injection control device for internal combustion engines is disclosed in Japanese Patent Laid-Open No. 50649/1988. This fuel injection control device for internal combustion engines comprises a common rail of a certain volume, a fuel supply pump to deliver fuel to the common rail through the fuel supply passage, fuel injection valves to inject fuel supplied to the common rail into the combustion chambers, a flow regulating valve to regulate the amount of fuel flowing from the fuel tank to the fuel supply pump, a pressure detection means to detect a common rail pressure, an operating condition detection means to detect the operating condition of the internal combustion engine, a pressure setting means to set a target pressure of the common rail based on the result of detection by the operating condition detection means, and a pressure control means to control the flow regulating valve according to the result of detection by the pressure detection means and also control the common rail pressure to the target pressure.
With the fuel injection control device for internal combustion engines disclosed in the above official gazette, a flow control valve for controlling the fuel flow from the fuel tank is installed at the suction side of the fuel supply pump that supplies a high-pressure fuel to the fuel injection valves through the fuel supply passage including the common rail. The flow control valve is controlled by the pressure control means to eliminate the deviation between the target fuel pressure in the fuel supply passage, which is set according to the result of detection by the engine operating condition detection means, and the actual fuel pressure in the fuel supply passage. The control of fuel flow performed by the flow control valve is done by changing the cross section of the fuel passage or by controlling the duty ratio to change the valve opening time. When the actual fuel pressure in the fuel supply passage is detected to be higher than the target fuel pressure by more than a predetermined threshold range, the flow control valve performs control to reduce the fuel flow to the fuel supply pump. This in turn reduces the fuel flow delivered by the fuel supply pump to the common rail, resulting in an immediate reduction in the fuel pressure in the pressure accumulation chamber.
The fuel supply pump used in the above fuel injection control device has a stationary shaft fixedly supported in a pump casing, a rotor turning around the stationary shaft, and a ring rotatably supported on the pump casing through a bearing. The rotor has many radial pistons arranged radially therein and shoes inserted between each radial piston and the ring that rotate with the radial pistons. The stationary shaft is formed with a suction port communicating with the flow regulating valve and a delivery port communicating with the common rail. As the rotor turns, the cylinder chambers in which each radial piston reciprocates are brought into communication with the suction port and the delivery port alternately. The alternate communication is synchronized with radially outward or inward displacement of the radial pistons causing the fuel to be discharged from the delivery port.
How the common rail pressure changes is shown at the common rail pressure P in the graph of FIG.
1
. The graph of
FIG. 1
represents a four-cylinder engine with a one-to-one correspondence between each pump chamber and the injector of each cylinder into which the fuel is to be injected. The cylinder determination sensor generates a cylinder determinat
Nishitou Masaaki
Takahashi Susumu
Browdy and Neimark
Isuzu Motors Limited
Miller Carl S.
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