EP2659127B1 - Pressure switching valve for a fuel injection system of an internal combustion engine - Google Patents

Description

State of the art

The invention relates to a pressure-switching valve for a fuel injection system of an internal combustion engine, in particular a gasoline engine, with a cylinder in which a closure body for selectively closing an inlet is movable, and in which the closure body is provided with a first effective surface on the hydraulic pressure acts to open the inlet. Furthermore, the invention relates to a fuel injection system with such a pressure-switching valve.

Such a fuel injection system comprises a high-pressure area (rail) and a low-pressure area to which fuel is supplied from a tank, preferably by means of a low-pressure pump, through lines. The high-pressure area is additionally preceded by a high-pressure pump, which increases the pressure of the fuel for direct injection or high-pressure injection to preferably up to approximately 200 bar. The fuel thus passes through the low-pressure pump first to the high-pressure pump, which additionally increases the pressure of the fuel. For adjusting the delivery rate of the pump is usually a quantity control valve, which makes it possible to regulate the pressure generated by the high-pressure pump; by allowing fuel to flow back from the pump delivery chamber to the low-pressure region as a valve. Alternatively, an electromagnetic pressure control valve may be provided on the rail, which allows the fuel to flow from the rail back to the low-pressure region.

Well-known direct injections in gasoline engines operate with injection pressures of up to 200 bar. The pressure is regulated depending on operating point in the range 40 to 200 bar. Background of the art in high pressure generation are systems having a piston pump mechanically driven by the internal combustion engine, a mass control valve, and a high pressure sensor. The flow rate of the pump is changed via the menu control valve. Together With the measured high-pressure signal, the engine control unit regulates the pressure to the desired level. The control of the injection valves is based on the measured pressure signal.

Out DE 10 2005 022 661 A1 a fluid pump or high-pressure fuel pump for an internal combustion engine with a pressure-switching valve is known, which is associated with a delivery chamber of the fluid pump and a low-pressure inlet. Furthermore, at least one valve device is provided there. The pressure-switching valve can block a connection between the delivery chamber and the low-pressure inlet during a suction phase of the fluid pump. The pressure-switching valve should comprise at least one second valve device, which is connected in parallel with the first valve device. The use of two different and parallel valve devices, however, leads to a complex construction.

Further pressure switching valves are out of the WO 2004/048770 A1 and the DE 10 2008 059638 A1 known.

Disclosure of the invention

According to the invention, there is provided a pressure control valve for a fuel injection system of an internal combustion engine, comprising a cylinder in which a closure body is movable for selectively closing an inlet and the closure body is provided with a first effective area to the hydraulic pressure to open the inlet acts. The closure body also has a second active surface, which is designed to be larger than the first active surface.

The pressure switch valve operates as follows: First, the closure body closes the inlet until a pressure has risen to a pressure value p1 at the first effective area. The pressure value p1 and the force thus achieved at the first effective area is just so great that the closure body is displaced by the pressure then acting on the first effective area and thus the inlet is opened.

This fuel or fuel can flow through the inlet in the pressure-switching valve. The flowing fuel now acts on the second effective area, which is larger than the first effective area. Due to this difference in the size of the effective areas, the pressure at the inlet drops to a pressure value p2, wherein the Pressure value p2 is less than the pressure value p1. Depending on the size ratio of the first and the second effective area, the pressure value p2 can be substantially smaller than the pressure value p1.

By the proposed design of a particularly preferred piston-shaped closure body with two different sized active surfaces, it is achieved that the high-pressure fuel initially acts on the smaller effective surface and opens the closure body, but immediately thereafter flows through the pressure-switching valve or its cylinder and the Detects larger effective area, so that the valve is easily pushed further and the fuel is fed back with only slight overpressure in the low pressure area.

According to the invention thus a pressure-switching valve is provided which has a very simple structure. Compared to known systems advantageously a more expensive electrical control is avoided because the problem is solved mechanically. This eliminates therefore also an otherwise required wiring of electrical components. A dependence on a control unit or the electric power amplifiers is eliminated. With the invention, a fuel injection system with a stand-alone, independent of a controller control can be realized.

Furthermore omitted by the invention further components in the fuel injection system. Additional high pressure sensors are no longer needed. Consequently, it is a cost effective system.

It is additionally advantageous that the power loss of the high pressure pump is small by this type of pressure control. Because of the second, larger effective surface area of the closure body, the residual delivery of the piston stroke of the fuel quantity not required back into the low-pressure region or the closure body stroke is more easily possible. Thus, the drive torque at the cam gear, which is required for the residual promotion of the high-pressure pump, correspondingly lower.

Another advantage of such a system is that the high pressure in the pump delivery chamber drops immediately after opening the valve and only with slight overpressure is promoted back to the low pressure range, so that the fuel heats up only slightly. This reduces the power loss.

On the cylinder, an outlet is also advantageously provided, which optionally closes the closure body. The closure body releases this outlet or outlet opening as soon as it has been pushed back a certain distance from its rest position or its position closing the inlet. Through the outlet then the fuel afflicted with pressure flows out of the pressure-switching valve again. As a result, the pressure in the pressure switching valve decreases as explained, and the counterforce acting on the closure body becomes stronger than the force that the pressure of the fuel can exert on the second effective area. Thus, the closure body moves back in the direction of its rest position and closes the outlet and thus the pressure-switching valve again.

The closure body is advantageously biased by a spring or a spring element resiliently against the inlet. In this way, comes from the resilient bias a contact pressure on the preferably designed as a piston closure body. This contact pressure acts counter to the force of the fuel, which acts on the first or second active surface. By a suitable choice of preferably to be arranged in the cylinder spring itself thus the pressure levels at which the pressure-switching valve opens and closes are selected.

Alternatively or additionally, in the pressure switching valve according to the invention the closure body is resiliently biased by means of fluid pressure against the inlet. In particular, a pressurized gas is used as the fluid. The use of such a fluid also gives the closure body a dampening effect. This improves the vibration behavior of the closure body and thus the regulation of the fuel pressure.

According to a further development, the cylinder has a pressure chamber, which seals the closure body. The closure body is preferably designed as a piston or a membrane, which spatially separates the pressure chamber within the cylinder. On the basis of the spatial separation within the cylinder is made possible that different pressures occur in the pressure-switching valve. Thus, in the pressure chamber in addition to the spring force of the fluid pressure for closing abut the pressure-switching valve, while in the remaining region of the cylinder, the pressure or overpressure of the fuel is applied.

According to a further development, the cylinder has an inlet space into which the inlet leads. In addition, a line leads from the inlet space to said pressure chamber. Constructed in this way, a pressure equalization takes place in the pressure switching valve. This pressure compensation influences the damping effect of the fluid of the spring-biased closure body in the pressure chamber. Due to the pressure compensation, damage can be preventively prevented if, for example, pressure fluctuations occur, which could briefly cause strong pressure surges.

With the first effective surface of the closure body, the inlet is preferably closed and this closure is designed in the form of a seat valve with a valve seat. This is a structurally simple and effective way to close the pressure switching valve and open. In seat valves, which are known as poppet valves, the closure body is plate-shaped and is seated with its edge on the inlet opening so that it is closed and sealed.

According to a further development, the second active surface of the closure body is formed on a piston which acts together with the cylinder as a slide valve or forms a slide valve. The additional use of the closure body or piston as a slide valve, also known as a piston valve, the fuel pressure can be controlled improved. Although the use of a slide valve to regulate pressures is common, however, in the present form, the closure body is designed to function as a gate valve as well as a seat valve.

Finally, the invention also provides for a use of the pressure switching valve according to the invention in a fuel injection system of a pump, in which the pump has a pumping space, which is connected by means of a first line to the inlet of the pressure switching valve. In addition, in this case a second line is provided, which leads into the pumping space, and a third line, the connects one or the outlet of the pressure switching valve to the second line.

A pressure switching valve used in this way is able to regulate the overpressure occurring in a pump or high-pressure pump so that no impermissible overpressure is applied to the injection valves and can not damage them. When the target pressure is exceeded, the pressure-switching valve returns the fuel at low pressure back into the fuel circuit before the high-pressure pump, i. in the low pressure or inlet region of the high pressure pump.

Fig. 1

ein Schaubild eines Ausführungsbeispiels eines Kraftstoffeinspritzsystems gemäß dem Stand der Technik,

Fig. 2

ein Schaubild eines Ausführungsbeispiels eines Kraftstoffeinspritzsystems gemäß der Erfindung und

Fig. 3

das Detail III aus Fig. 2.

An exemplary embodiment of the solution according to the invention will be explained in more detail below with reference to the attached schematic drawings. It shows:

Fig. 1

a diagram of an embodiment of a fuel injection system according to the prior art,

Fig. 2

a diagram of an embodiment of a fuel injection system according to the invention and

Fig. 3

the detail III off Fig. 2 ,

In Fig. 1 a fuel injection system 10 is illustrated according to the prior art, in which from a tank 12 by means of an electric fuel pump or low pressure pump 14 liquid fuel at about 5 bar pressure is conveyed into a conduit 16. The line 16 serves as a supply line to a low pressure region 18 and a high pressure region 20 of the fuel injection system 10. For high pressure generation, a pump 22, which is mechanically driven by a cam drive from an internal combustion engine used. This generates the required pressure for the high-pressure region 20, which then rests in a rail 24. By high-pressure injection valves 26, the fuel from the rail 24 finally reaches the internal combustion engine.

To control and regulate the flow rate, which the pump 22 discharges into the high-pressure region 20, there are several options available. By a pressure-switching valve 28, a possible, generated by the pump 22 overpressure can be regulated. For this purpose, the fuel pressure applied to the rail 24 is determined by a high-pressure sensor 30. This value is sent to a controller 32 passed, which in turn can control the pressure-switching valve 28. Together with the measured high pressure signal of the high pressure sensor 30, the controller 32 regulates the pressure to the desired level. This is necessary, inter alia, because excessive overpressure could cause damage to the fuel injection system 10.

Furthermore, in Fig. 1 to see a low-pressure damper 34, the task of which is to dampen the pressure pulsations in the low-pressure region 18. These pulsations can be caused in particular by a return of fuel from the pump 22 back into the low-pressure region 18.

In Fig. 2 and Fig. 3 will be a similar fuel injection system 10, as in Fig. 1 shown. However, this has been dispensed with an electronic pressure control. Instead, an inventive pressure-switching valve 28 is provided on the fuel injection system 10 according to these figures. Incidentally, the fuel injection system 10 differs according to Fig. 2 and Fig. 3 by an additional securing mechanism 38 in the form of a so-called rupture disk 40 or a mechanical pressure relief valve.

The pressure-switching valve 28 is installed in a cylinder 42 as a housing. In the cylinder 42 is a closure body 44 of the piston mold or a piston-shaped configuration. One of the end faces of the piston-shaped closure body 44 has a stepped design and has two differently sized effective surfaces 48 and 50 in the direction of an inlet 46 formed on the front side of the cylinder 42. Of these active surfaces, the active surface 48 is formed in the center of the closure body 44 as a circular disk and smaller in its surface extent than the active surface 50, which is to be found on a further recessed circular ring disk.

The closure body 44 is biased by a spring 52 in the direction of the inlet 46, so that it can selectively close or open the inlet 46 with its active surface 48. When closing, the first active surface 48 corresponds to the inlet 46 in order to seal it as well as possible. For this purpose, the first active surface 48 and the inlet 46 are designed as a so-called seat valve or poppet valve.

On the cylinder 42, an outlet 54 is provided on the lateral surface thereof to deliver fuel from pressure-switching valve 28 to the low-pressure region 18. This outlet 54 can be optionally closed by the closure body 44. Depending on the pressure or force acting on the closure body 44, this shifts axially in the cylinder 42 and thereby can open or close the outlet 54.

In the cylinder 42 substantially two spaces bounded by the closure body 44 are formed. A pressure chamber 56, in which the spring 52 is arranged, which urges the closure body 44 in the direction of the inlet 46, and an inlet space 58, in which the pressurized fuel flows through the inlet 46 and from which the fuel through the outlet 54th can also flow out of the pressure-switching valve 28 again. The two spaces 56 and 58 are thus sealed by the closure body 44 against each other and spatially separated.

A line 60 leads from the outlet 54 to the pressure chamber 56 and thus provides a pressure equalization between the low pressure region 18 and the pressure chamber 56 ago. In the pressure chamber 56, therefore, at least the low pressure prevails, which also urges the closure body 44 in the direction of the inlet 46. Therefore, the spring 52 can be equipped with comparatively low spring force and be correspondingly small and lightweight.

The pump 22 is mechanical, usually driven by a camshaft. It generates in a pump chamber 62 that pressure which it discharges into the line 20. At the same time a line 64 is connected to the pump chamber 62, which leads to the inlet 46 of the pressure-switching valve 28. The outlet 54 of the pressure switching valve 28 is connected by means of a line 66 to the low-pressure region 18. Fuel under pressure can thus be discharged from the pumping chamber 62 into the conduit 64, through the pressure-switching valve 28 and through the conduit 66 into the low-pressure region 18.

As soon as the high-pressure pump 22 of the fuel injection system 10 generates an overpressure to be dissipated, this is present through the line 64 at the inlet 46 of the pressure-switching valve 28. At the inlet 46 of the pressure-switching valve 28 is thus at a pressure on the first, the inlet occlusive active surface 48th the piston-shaped closure body 44 acts. Since the piston-shaped closure body 44 is urged only resiliently against the inlet 46, this retracts as soon as the pressure force on the first active surface 48 is greater than the contact pressure of the closure body 44 of the spring 52 and the pressure chamber 56.

In this case, the inlet 46 is released and fuel first flows into the inlet space 58 of the pressure switching valve 28. Then, the fuel and its pressure is distributed to the second, larger active surface 50 of the closure body 44. This results in a larger pressure force on the closure body 44 and it can easily be displaced further axially in the cylinder 42.

After a short time, the closure body 44 releases the outlet 54 or opens it. The fuel now flows through the outlet 54 in the direction of the low-pressure region 18.

The pressure during closing of the inlet 46 is much lower than that required to open the inlet 46. Due to the second, larger active surface 50, the closure body 44 can be displaced axially in the cylinder 42 with less hydraulic pressure than through the smaller first active surface 48.

The pump 22 can therefore reduce its overpressure particularly quickly and, after the beginning of the discharge, that is, after the opening of the inlet 46, it must only convey against a comparatively low pressure. The pump 22 therefore has a lower power loss, which is created by the release of pressure at the pressure-switching valve 28.

In case of failure, malfunction or other failure of the pressure balance by means of the pressure switching valve 28 is for the fuel injection system 10, a further backup in the form of rupture disk 40. The rupture disks 40 helps in particular in the case that the pump 22 generates an overpressure, which can not be compensated by the pressure switching valve 28. Alternatively, instead of the rupture disk, a pressure relief valve may be provided. This can also reduce a pressure increase in the so-called hot soak. Then this overpressure enters the high-pressure region 20, which is connected to the low-pressure region 18 through a line 68. On or in the line 68, the rupture disk 40 or the pressure limiting valve is arranged. The rupture disk 40 has such a material nature and shape that it breaks or bursts if a certain overpressure rests against it. In this case, the previously closed by the rupture disk 40 line 68 is released, so that the fuel from the high-pressure region 20, can pass through the line 68, in the low-pressure region 18.

The fuse in the conduit 68, which in this example is realized by a rupture disk 40, may also be designed by other means, such as another valve or a material with predetermined breaking point.

One way to compact design of the fuel injection system 10 and the pressure-switching valve 28 is that the pressure-switching valve 28 is integrated into the pump 22 and in particular in the housing. In particular, the pressure-switching valve 28 may be integrated in the region above the pump chamber 62 of the pump 22 in a pump housing. This integral design reduces space requirements and weight.

The principle of the present invention thus lies in the fact that the fuel pump has a pump chamber 62 or delivery chamber with a hydraulically controllable pressure-switching valve 28 or pressure-switching valve connected thereto. The pressure-switching valve 28 is configured so that when, during a pressure stroke, the pump-space pressure reaches a pressure value p1, the pressure-switching valve 28 opens. Immediately thereafter, the pressure-switching valve 28 drops the pump-space pressure to a pressure value p2, the pressure value p2 being smaller than the pressure value p1.

Depending on the ratio of the size of the second effective area to the size of the first effective area, the pressure value p2 can be substantially smaller than the pressure value p1.

As soon as the thereby hydraulically controllable pressure switching valve 28 opens in the course of a pressure stroke, the pump chamber pressure remains at the lower pressure value p2 during the entire rest of the pressure stroke. The pressure-switching valve 28 closes again when the pump space pressure drops below the pressure value p2, which is below normal circumstances again only the case when the pump 22 passes from the compression stroke in the suction stroke.

The advantage of the pump 22 with such a two-stage pressure switching valve 28 over a pump with a pressure control valve with only one pressure value is a lower dissipation when operating the pump. The advantage of the pump 22 with the two-stage pressure-switching valve 28 with respect to a pump with an electrically controllable quantity control valve is in particular in a lower manufacturing cost.

Claims (9)

1. Fuel injection system having a pump (22) which has a pump chamber (62) in which said pump generates a pressure, said pressure being discharged by the pump via a check valve into a line (20) of the high-pressure region, and having a pressure switching valve (28) with a cylinder (42) in which a closure body (44) for selectively closing an inlet (46) is movable, wherein the closure body (44) is equipped with a first effective surface (48) at the inlet (46), on which first effective surface the hydraulic pressure of the pump chamber (62) acts via a first line (64) so as to open the inlet (46), and the pressure of said pump chamber acts, at the opened-up inlet (46), on a second effective surface (50) of the closure body (44), said second effective surface being larger than the first effective surface (48), and the closure body (44), when displaced further, opens up the outlet (54) into the low-pressure region (18), wherein the first line (64) is connected to the pump chamber (62), and the first line (64) leads to the inlet (46) of the pressure switching valve (28).
2. Fuel injection system according to Claim 1, characterized in that an outlet (54) is provided on the cylinder (42), and the closure body (44) can selectively close off the outlet (54).
3. Fuel injection system according to Claim 1 or 2, characterized in that the closure body (44) is resiliently preloaded against the inlet (46).
4. Fuel injection system according to Claim 3, characterized in that the closure body (44) is resiliently preloaded against the inlet (46) by way of fluid pressure.
5. Fuel injection system according to Claim 1 to 4, characterized in that the cylinder (42) has a pressure chamber (56) which is sealed off by the closure body (44).
6. Fuel injection system according to Claim 5, characterized in that the cylinder (42) has an inlet chamber (58) into which the inlet (46) issues, and a line (60) leads from the inlet chamber (58) to the pressure chamber (56).
7. Fuel injection system according to Claim 1 to 6, characterized in that the inlet (46) can be closed off, in the manner of a valve seat, by the first effective surface (48) of the closure body (44).
8. Fuel injection system according to Claim 1 to 7, characterized in that the closure body (44) is in the form of a piston which, together with the cylinder (42), forms a slide valve.
9. Fuel injection system according to Claim 1 to 8, characterized in that a second line (16) is provided which leads into the pump chamber (62), and a third line (66) connects a or the outlet (54) of the pressure switching valve (28) to the second line (16).

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