EP1614894B1 - Common-Rail Fuel Injection System with Pressure Wave Damping Means - Google Patents

Abstract

The system has a hydraulic circuit comprising a distributor (16), and chambers (17, 19) in communication with the distributor through corresponding check valves (18, 20). The chambers communicate with each other through a balancing conduit (21). The chambers are connected near a fuel injection orifice and have a volume between 200 cubic millimeters to 600 cubic millimeters, where a wall of one of the chambers is elastic.

Description

The present invention relates to a common-rail injection device for a motor vehicle engine, with a system for damping pressure waves in a hydraulic circuit.

In so-called "common rail" or "common rail" injection systems (diesel, gasoline or any other fuel), each injection generates, in the high-pressure fuel system, pressure waves responsible for interactions between the injections . These interactions result in poor control of the amount of fuel introduced into the cylinder, thus making it very difficult to develop the engines during the development phases, and causing changes in their behavior during the life of the engine.

This problem is more and more critical with the appearance of multiple injections allowed by the new injection systems, consisting of cutting an injection into several smaller injections.

It is proposed in the document EP 1 217 202 to include in the feed circuit of an injector a choke creating a pressure drop in the fuel flow. This pressure drop makes it possible to damp the pressure oscillations at the injector, and therefore to have a pressure that is closer to the supply pressure more quickly after a first injection.

However, the addition of a restriction in the hydraulic circuit limits the pressure actually available to the injector, especially for high flow rates.

It is therefore an object of the invention to provide a device for damping fuel supply pressure oscillations of an injector, without limiting said pressure, even for high flow rates.

With this objective in view, the subject of the invention is a common-rail fuel injection system for a heat engine comprising an injector connected by a supply tube to a common rail, a hydraulic circuit extending from the common rail. to an orifice of the injector, through the feed tube. The injection system further comprises a first chamber in communication with the hydraulic circuit via a first non-return valve passing in the direction from the first chamber, and a second chamber in communication with the hydraulic circuit. via a second non-return valve passing in the direction towards the second chamber, the two chambers being in communication with each other via a balancing duct.

The chambers thus constitute, because of the compressibility of the fuel, fuel reserves under pressure. When opening the injector, the pressure in the hydraulic circuit drops. This decrease is offset by the fuel stored in the first chamber, which can supply the hydraulic circuit through the first check valve. The pressure drop generated thus has a decreased amplitude.

When the pressure in the hydraulic circuit rises, the first non-return valve closes and the second non-return valve opens to allow fuel to enter the second chamber, which further reduces the amplitude of the pressure rise. The balancing pipe balances the pressures in the chambers before the next injection. Thanks to the system according to the invention, the pressure oscillations in the hydraulic circuit are damped more rapidly without creating pressure drops in the supply of the injector.

Advantageously, the chambers are connected as close as possible to the fuel injection orifice. The fuel exchanges are thus closer to the source of the fuel. pressure oscillations, which limits the pressure variations in the rest of the hydraulic circuit.

Preferably, the chambers have a volume of between 200 and 600 mm ³ . The inventor has found that this volume is optimal for most current injectors, the chambers being large enough to have a compression or expansion of the fuel capacity, and small enough to be integrated near the injection port.

The balancing duct has for example a diameter of 50 microns. This diameter is adapted to balance the pressures in the chambers between two injections. The diameter can be increased if there are elastic walls for the chambers.

According to an improvement, at least one of the walls of at least one of the chambers is elastic. In this case, the compressibility of the fuel is seconded by the elastic variation of the volume of the chamber. The volume of the chamber can be reduced by keeping the same fuel efficiency or fuel efficiency.

• la figure 1 est une vue schématique d'un système d'injection conforme à l'invention ;
• la figure 2 est une vue d'un injecteur de la figure 1 en coupe longitudinale selon la ligne II-II de la figure 3 ;
• la figure 3 est une vue en coupe selon la ligne III-III de la figure 2 ;
• la figure 4 est une vue du détail IV de la figure 3 ;
• la figure 5 est un diagramme temporel d'évolution de la pression du carburant en différents endroits de l'injecteur de la figure 2.

The invention will be better understood and other features and advantages will appear on reading the description which follows, the description referring to the appended drawings among which:

• the figure 1 is a schematic view of an injection system according to the invention;
• the figure 2 is a view of an injector from the figure 1 in longitudinal section along the line II-II of the figure 3 ;
• the figure 3 is a sectional view along line III-III of the figure 2 ;
• the figure 4 is a detail view IV of the figure 3 ;
• the figure 5 is a time chart of evolution of the fuel pressure in different places of the injector of the figure 2 .

The injection system according to the invention, as represented on the figure 1 is, for example, a common rail system for a Diesel engine fueled with diesel fuel. Such a system comprises a common rail 10 fed with fuel under pressure, an injector 11 per cylinder of the engine, or four injectors 11 in the example shown. Each injector 11 is connected to the common rail 10 by a feed tube 12. A hydraulic circuit extends from the common rail 10 to an injection port 13 at the end of the injector 11 through the feed tube 12 for channeling the fuel to be injected into a cylinder, not shown.

The Figures 2 to 4 detail one of the injectors 11. The feed tube, not shown in these figures, is connected against an end face 14 of the injector 11. An internal channel 15 extends from the end face 14 to the injection port 13, through a distributor 16, to form a part of the hydraulic circuit. A needle, not shown, makes it possible to close or open on command the hydraulic circuit downstream of the distributor 16.

According to the invention, the injector 11 comprises a first chamber 17 in communication with the distributor 16 via a first non-return valve 18 passing in the direction from the first chamber 17, and a second chamber 19 in communication with the distributor 16 via a second non-return valve 20 passing in the direction towards the second chamber 19. The two chambers 17, 19 are in communication with each other via a balancing duct 21 whose diameter is 50 μm. Each non-return valve comprises a ball 22 held in abutment against a frustoconical seat 23 by a spring 24.

The figure 5 shows the evolution over time of the pressures in different places of the hydraulic circuit. The curve 30 represents the pressure in the distributor 16 in the absence of the chambers, while the curve 31 represents the pressure in the distributor in the presence of the chambers 17, 19. The curve 32 represents the pressure in the first chamber 17 and curve 33 represents the pressure in the second chamber 19.

When the hydraulic circuit is closed, and the common rail 10 is supplied with fuel under pressure, for example at 1000 bar, the same pressure prevails throughout the hydraulic circuit and in the chambers 17, 19. At the time of injection, that is to say, the opening of the hydraulic circuit by the needle, the pressure drops in the hydraulic circuit, and in particular in the distributor 16, as shown by the curves 30 and 31 of the figure 5 . A differential pressure then exists between the chambers 17, 19 and the distributor 16. The first nonreturn valve 18 then opens to allow fuel to flow into the first chamber 17 to the distributor 16, which partially compensates for the fall. This is shown by the level of the cusp 300 of the curve 30, which is below the level of the cusp point 310 of the curve 31.

When the pressure rises in the distributor 16, beyond the pressure level in the first chamber 17, the first non-return valve 18 closes. Then when the pressure in the distributor 16 rises above the pressure level in the second chamber 19, the second non-return valve 20 opens to accept fuel and thus limit the pressure rise in the distributor 16, and therefore in the hydraulic circuit, as shown by the level of the cusp point 311 of the curve 31. After the closing of the first non-return valve 18, the pressure in the first chamber 17 tends to gradually return towards the level of the pressure in the second chamber 19, by the passage of fuel through the balancing duct 21.

During subsequent oscillations of pressure, the second non-return valve 20 opens when the pressure in the distributor 16 exceeds that in the second chamber 19 and closes during the pressure drop. When the second valve 20 is closed, the pressure in the second chamber drops due to the passage of fuel to the first chamber 17 via the balancing duct 21.

The invention is not limited to the example which has just been described by way of example. The invention also applies to an engine operating with another fuel. The chambers may be placed at another point in the hydraulic circuit, between the common rail 10 and the injection port 13. The balancing duct may be made by a larger duct, but with a calibrated restriction such that a diaphragm or Venturi.

Claims (4)

1. Common-rail fuel injection system for a combustion engine comprising an injector (11) connected by a supply tube (12) to a common rail (10), a hydraulic circuit running from the common rail (10) to an orifice (13) of the injector, via the supply tube (12),
   characterized in that the hydraulic circuit comprises a splitter (16), the system further comprising a first chamber (17) in communication with the splitter (16) via a first non-return valve (18) that allows flow in the direction from the first chamber (17), and a second chamber (19) in communication with the splitter (16) via a second non-return valve (20) that allows flow in the direction towards the second chamber (19), the two chambers (17, 19) being in communication with one another via an equalizing duct (21).
2. Injection system according to Claim 1, in which the chambers (17, 19) have a volume of between 200 and 600 mm³.
3. Injection system according to Claim 1, in which the equalizing duct (21) has a diameter of 50 µm.
4. Injection system according to Claim 1, in which at least one of the walls of at least one of the chambers (17, 19) is elastic.

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