Internal-combustion engines – Combustion chamber means having fuel injection only – Using multiple injectors or injections
Reexamination Certificate
2001-11-30
2002-10-01
Miller, Carl S. (Department: 3747)
Internal-combustion engines
Combustion chamber means having fuel injection only
Using multiple injectors or injections
C123S447000, C123S496000
Reexamination Certificate
active
06457453
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an accumulator fuel-injection apparatus.
BACKGROUND ART
An accumulator fuel-injection apparatus is known which stably supplies respective cylinders of a diesel engine with high-pressure fuel stored in an accumulator to improve engine performance in a broad operating region. Even with a fuel-injection apparatus of this type, an abrupt explosion combustion takes place in the initial stage of combustion, causing noisy engine operation and increased NOx in exhaust gas, if the fuel injection rate immediately after the start of fuel injection is too high or if the quantity of fuel injected in an ignition delay period is too large.
As a countermeasure against such a problem, auxiliary injection can be performed prior to main injection in each fuel injection cycle. This shortens the ignition delay period, realizing a reduction in an amount of fuel injected in the ignition delay period by the main injection, whereby the abrupt combustion is prevented to reduce the engine noise and the NOx emission. In case that the fuel-injection apparatus is configured to perform high-pressure injection from the beginning of the main injection following the auxiliary injection, however a satisfactory reduction in noise and NOx emission cannot be always achieved. To attain the ignition-delay reducing effect, a minimum required quantity of fuel should be injected in the auxiliary injection. In order to reduce the fuel injection quantity to the required minimum in the fuel-injection apparatus of a type performing the auxiliary injection at a relatively high injection pressure, the auxiliary injection period must be shortened. This requires high control accuracy. If the required control accuracy is not attained, the fuel injection quantity in the auxiliary injection becomes too small or too large, so that the intended effects of the auxiliary injection may not be achieved, resulting in degraded exhaust gas and fuel economy.
As another means of reducing engine noise and NOx emission, an accumulator fuel-injection apparatus has been proposed that injects fuel at a lower fuel injection rate in the initial stage of fuel injection in each fuel injection cycle. Byway of example, the proposed apparatus has a low-pressure accumulator for storing low-pressure fuel, a high-pressure accumulator for storing high-pressure fuel, a selector valve for selectively communicating the low- or high-pressure accumulator with an injector (fuel injection nozzle) to switch injection rate, and an on-off valve for permitting/preventing communication between a control chamber of the injector and a fuel tank to control injection start/end timings.
An accumulator fuel-injection apparatus of this kind, such as for example an apparatus disclosed in International Publication No. WO98/09068, is designed to control opening/closing timings of an on-off valve for injection timing control and of a selector valve for injection rate switching, so as to carry out only main injection or both main injection and auxiliary injection in each fuel-injection cycle. In addition, there is disclosed a technique of performing low-pressure injection in the initial stage of the main injection followed by high-pressure injection.
In connection with the present invention, the apparatus disclosed in the above publication can perform low-pressure auxiliary injection for a short time, and start main injection when a predetermined period of time has elapsed after completion of the auxiliary injection. Low-pressure injection is carried out in the initial stage of the main injection, and then high-pressure injection is carried out over the remaining period.
Specifically, by closing the on-off valve for injection timing control and the selector valve for injection rate switching, a fuel passage connecting the selector valve and a fuel chamber of the injector is filled with low-pressure fuel and a control chamber of the injector communicated with the fuel passage is supplied with the low-pressure fuel, whereby the injector is maintained in a valve-closing state. When the auxiliary-injection start timing is reached, the on-off valve is opened to discharge the fuel in the control chamber to the fuel tank, whereby the injector is opened to make low-pressure auxiliary injection, and the on-off valve is closed when the auxiliary injection period has elapsed. When a predetermined period of time has elapsed after completion of the auxiliary injection so that the main-injection start timing is reached, the on-off valve is opened again to start low-pressure main injection, and the selector valve is opened in the course of main injection so that high-pressure fuel supplied from the high-pressure accumulator is injected through the nozzle, thereby effecting high-pressure injection.
By conducting the low-pressure auxiliary injection and the main injection including low- and high-pressure injections in each fuel injection cycle as described above, the fuel economy and exhaust-gas characteristic of the engine can be improved. However, there is a demand for further improvement in fuel economy and exhaust-gas characteristic.
DISCLOSURE OF THE INVENTION
The object of the present invention is to provide an accumulator fuel-injection apparatus capable of establishing a proper injection pressure in the initial stage of main injection following low-pressure auxiliary injection, to thereby further improve fuel economy and exhaust-gas characteristic.
In order to attain the above object, an accumulator fuel-injection apparatus according to the present invention comprises a first accumulator for storing high-pressure fuel; a control valve for controlling discharge of the high-pressure fuel stored in the first accumulator toward a downstream-side of a fuel passage; a second accumulator, communicated with the fuel passage on the downstream of the control valve, for storing low-pressure fuel; and fuel control means for opening the control valve for a short time between auxiliary short injection and main injection, for opening the control valve in the course of the main injection, and then closing the control valve in conformity with completion of the main injection, while the auxiliary short injection and the main injection are carried out in this order with an interval through a fuel injection nozzle communicated with the fuel passage.
Desirably, the fuel control means establishes an intermediate pressure in the fuel passage on the downstream-side of the control valve in the initial stage of the main injection, the intermediate pressure being higher than the pressure of the low-pressure fuel in the second accumulator and lower than the pressure of the high-pressure fuel in the first accumulator.
With the accumulator fuel-injection apparatus of the present invention, when the control valve is opened for a short time after completion of the low-pressure auxiliary injection, the fuel passage is supplied with high-pressure fuel from the first accumulator for a short time, so that the fuel pressure in the fuel passage becomes higher than an auxiliary-injection pressure. In the initial stage of the main injection effected through the fuel injection nozzle, therefore, fuel is injected at a pressure higher than the auxiliary-injection pressure, desirably at an intermediate pressure higher than the auxiliary-injection pressure and lower than the pressure of the high-pressure fuel. When the control valve is opened in the course of the main injection, the high-pressure fuel is supplied through the fuel passage to the fuel injection nozzle, so that high-pressure injection is performed.
By injecting fuel in the initial stage of the main injection following the low-pressure auxiliary injection, at a pressure higher than the auxiliary-injection pressure, desirably at an intermediate pressure higher than the auxiliary-injection pressure and lower than the pressure of the high-pressure fuel, the fuel injection quantity in the initial stage of the main injection increases as compared with the case where low-pressure injection is performed in the initial stage of
Kohketsu Susumu
Kotooka Seijiro
Tanabe Keiki
Miller Carl S.
Mitsubishi Jidosha Kogyo Kabushiki Kaisha
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