Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
2000-01-13
2001-02-20
Miller, Carl S. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C123S299000
Reexamination Certificate
active
06189509
ABSTRACT:
The present invention relates to a fuel injection device for Diesel engines equipped with pulsating injection pumps, this device comprising, per piston, at least one injector receiving a calibrated injector needle designed to inject calibrated fuel jets into the combustion chamber of said piston, a high pressure supply conduit for the fuel and a low pressure fuel return conduit.
BACKGROUND OF THE INVENTION
Specifications for developing Diesel engines are constantly changing. This technical constraint is mainly linked to the fields of environment and economy such as the emissions pollutants (nitrogen oxides, hydrocarbons, particles, etc.), the noise made by the engine or fuel consumption. The requirements in terms of optimizing the combustion environment to take into account these evolutions in specifications require a particular effort regarding the injection process. The ideal injection which would make it possible to obtain a pollution-free combustion would be achieved if:
1. the start of fuel inlet is performed at low flow rate so as to not mix too much fuel with the air from the combustion chamber during the ignition time, the injected flow constantly increases so that the combustion fully accompanies the start of expansion associated with movement of the piston in the engine's cylinder,
2. the fuel pressure is important to obtain proper pulverization and consequently good mixing of the fuel with the air,
3. the end of the injection is clear-cut to limit the insufficiently pulverized fuel inlet and reduce combustion trails as much as possible.
In practice, conventional strategies generally used are for example
increasing the compression ratio,
reducing the injection advance,
increasing injection pressures.
These strategies aim to compress the main combustion period into a shorter period of time which is better located at the start of the pressure reduction. Despite everything, the combustion performance remains very sensitive to the details of form of the law on fuel inlet in the combustion chamber.
In standard injection devices using a pulsating pump, the injection pump, by delivering the fuel, makes the pressure increase progressively in the pump's volumes, the conduits and the injector. This progressive increase takes place before and then during the injection period. After the pump has stopped delivering, the injection ends with the effect of the depressurization of these same volumes, the injector needle being solely controlled by a basic return device comprising one or several springs.
The advantage of these injection devices relates to the injection start which, in this case, is relatively moderate and, consequently, favorable to items 1 and 2 mentioned above, unless one needs too high a cutting-in pressure for the injector.
On the other hand, the major drawback is that the injector only closes when the pressure has become much lower than the cutting-in pressure. As a result, the end of the injection is not efficient and generates combustion trails, bringing about emissions of soot and penalizing efficiency.
In so-called “Common-Rail” constant pressure injection devices, the high-pressure pump feeds all the injectors at a virtually constant and adjustable pressure to adjust the inlet rate and the pulverization of fuel. The opening and the closing of each injector are controlled by one electrovalve, which makes it possible to adjust the injection advance and the quantity injected, in accordance with certain examples of embodiment described in publications FR-A-2 016 477, U.S. Pat. No. 4,545,352, DE-C-42 36 882, DE-A-44 06 901 and U.S. Pat. No. 4,249,497.
The advantage of these injection devices is the flexibility of the potential adjustments and especially the very good end of injection by controlled closing, which is favorable to items 3 and 4 above.
Nevertheless, the major drawback lies in the fact that at the start of the injection, the injected flow very quickly reaches the maximum flow, which is detrimental to items 1 and 2 above. It is possible to neutralize the effect on the ignition deflagration (item 1) by using the pre-injection, but there is little chance of making the law of fuel inlet (item 2) progressive.
SUMMARY OF THE INVENTION
The aim of the present invention is to provide an effective solution to improve the performance of conventional injection devices using a pulsating pump in order to effectively fulfil increasingly stringent requirements and notably by providing
a more moderate injection start than with conventional devices, favorable to item 1 mentioned above, with the possibility of performing a pre-injection,
an injection pressure which increases during the whole injection period, favorable to item 2 above,
an end of injection which is as clear-cut as with constant pressure devices, favorable to item 4 above,
an adjustable injection advance.
This aim is achieved by an injection device such as the one defined in the preamble and characterized in that it comprises a device for controlling the opening and the closing of the injector needle, this device comprising a discharge circuit connecting the supply conduit and the return conduit for the fuel, this circuit being controlled by an electrovalve and comprising, upstream from the electrovalve, a relief valve provided with calibrated orifice, this valve communicating both with the said electrovalve and a discharge orifice arranged on the return conduit and being designed to ensure that both the start of the injection is progressive and that this injection closes quickly by diverting the flow of fuel not injected towards said discharge orifice which, when depressurizing the supply conduit, generates a closing pressure on the injector needle.
In one embodiment of the invention, the control device can comprise a calibrated flap arranged upstream or downstream from the electrovalve, this flap being designed to keep the injection device at a required pressure level between two injections.
Generally speaking, the discharge circuit is independent of the high-pressure fuel injection circuit during the injection cycle, the relief valve and the electrovalve being closed.
Depending on the case, the closing pressure can be applied directly on the injector needle or by means of a piston.
In one alternative embodiment, the control device can comprise a delay orifice arranged downstream from the calibrated orifice and designed to delay the opening of the relief valve so as to bring about the momentary opening of the injector needle to perform a pre-injection of fuel.
Depending on the embodiments chosen, the calibrated orifice can be incorporated into the relief valve. Likewise, the valve orifices, flap and electrovalve of the control device can be partially or totally incorporated into the unit bearing the injector.
In one fuel injection device comprising several injectors for the same Diesel engine, the return fuel conduits for each injector can be advantageously connected to one another to a joint return tunnel. This joint return tunnel can be fixed to a calibrated return valve designed to maintain a required level of pressure in said return conduits for each injector.
Likewise, the first discharge circuits can be connected to one another by a joint control tunnel, which can also be fixed to a calibrated control valve designed to maintain a required level of pressure in said discharge circuits for each injector.
In some embodiments, the joint return tunnel and the joint control tunnel can be connected to one another by a calibrated control valve.
REFERENCES:
patent: 4249497 (1981-02-01), Eheim et al.
patent: 4440132 (1984-04-01), Terada et al.
patent: 4545352 (1985-10-01), Jourde et al.
patent: 4741478 (1988-05-01), Teerman et al.
patent: 5626119 (1997-05-01), Timms
patent: 5647316 (1997-07-01), Hellen et al.
patent: 5664545 (1997-09-01), Kato et al.
patent: 5740775 (1998-04-01), Suzuki et al.
patent: 5771865 (1998-06-01), Ishida
patent: 42 36 882 (1994-04-01), None
patent: 42 40 517 (1994-06-01), None
patent: 44 06 901 (1995-09-01), None
patent: 2 016 477 (1970-05-01), None
patent: 2 752 268 (19
Cummins Wartsila S.A.
Davis and Bujold
Miller Carl S.
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