EP2659124B1 - Pressure store device for a fuel injection system - Google Patents

Description

State of the art

The invention relates to a pressure storage device for a fuel injection system, comprising a housing in which a closure body limits a storage space which is expandable from a low pressure level prevailing therein to a high pressure level prevailing therein by moving the closure body.

Known fuel injection systems of internal combustion engines or internal combustion engines, in particular gasoline engines, operate as so-called direct injection (DI) with injection pressures of up to 200 bar. The pressure is generated by means of a pump, in particular a high-pressure pump, which is in particular mechanically driven by the internal combustion engine by means of a camshaft. The pump has a pressure chamber which is compressible by means of a piston in order to convey fuel from the pressure chamber into a pressure region, in particular a high-pressure region, from where the fuel is injected. An electromechanical, in particular electromagnetic quantity control valve controls the amount of fuel delivered by the high-pressure pump per delivery stroke into the high-pressure region, to a so-called rail. Together with a high pressure signal measured by a high-pressure sensor, an engine control unit regulates the pressure in the pressure range to the desired level by means of the quantity control valve. For example, for the general state of the art US20080178846 A1 and DE10350941 A1 ,

Disclosure of the invention

According to the invention, an accumulator device for a fuel injection system, with a housing in which a closure body defines a storage space, which is expandable from a low pressure level prevailing therein to a high pressure level prevailing therein by moving the closure body. A first sealing element and a second sealing element are provided such that at low pressure level the first sealing element and at high pressure level, the second sealing element acts fluid-tight. The fluid-sealing effect results in cooperation with the closure body.

According to the invention, an accumulator device or a pressure accumulator is provided with a seal by means of a first and a second sealing element. In addition, the pressure storage device is designed with a movable closure body, which optionally interacts with one of the two sealing elements fluid-tight. The closure body moves between the two sealing positions within the pressure storage device, thereby allowing the expansion or compression of an associated storage space. At the same time, such a seal closes the storage space separately, especially in those two positions in which the closure body interacts with the sealing elements.

The closure body moves in dependence on the pressure level in the storage space and increases or decreases while the storage space. This allows fuel to be cached in memory space. By moving the closure body pressure oscillations are further reduced in the high pressure area, which relieves the remaining high pressure components.

The sealing elements at the same time provide for an additional seal when the closure body occupies certain positions or positions. These are preferably those layers in which the closure body remains for a long time. As a result, only small pressure losses occur over these periods. Such an accumulator device is preferably used to maintain a minimum pressure in the high pressure region of a fuel injection system.

When the engine is running, at least the high pressure level prevails in the high-pressure region and thus at the pressure-storage device. The system pressure is usually even above the high pressure level of the pressure storage device. This Pressure level is kept low leakage because the closure body cooperates with the second sealing element.

When switching off the engine, although the pressure drops to the low pressure level, wherein the closure body initially bears against any separate sealing element and correspondingly has a slightly larger leakage than on the second sealing element. However, this leakage is tolerable, because the closure body can reach relatively quickly in that position in which prevails in the storage space, the low pressure level. In this case, the closure body seals the high-pressure region in a fluid-tight manner again at the first sealing element.

Thus, an accumulator device is provided with the pressure drops, especially when large amounts of fuel injection, are avoided in the high pressure area. This makes it possible to use a comparatively small-volume rail in the high-pressure range.

At the same time, the present invention provides a particularly cost-effective pressure accumulator, without high demands on the fit between the closure body and a surrounding housing.

The solution according to the invention is in contrast to accumulators whose closure body is designed as a membrane. A membrane has the disadvantage that it can become permeable or leaky over its lifetime and it has a certain residual permeability. Especially when used with fuel, which is an aggressive acting on many materials fluid, this behavior of a membrane may be detrimental. The pressure accumulator device according to the invention does not have this disadvantage, it is inexpensive to manufacture and sufficiently dense over the entire life.

The first sealing element and / or the second sealing element are preferably arranged in the housing such that at least one of the sealing elements forms a stop for the closure body. By means of such a system of the closure body on the first and / or second sealing element, the seal is additionally supported by a pressing of the closure body to the sealing elements. The sealing elements are preferably designed elastically. A seal during existence of the high pressure level (high-pressure operation) is thus preferably made possible by the abutment of the closure body on the second sealing element. This results in a particularly low leakage during this operation with high system pressure

A seal during existence of the low pressure level (standstill) is preferably made possible by contact of the closure body on the first sealing element.

In order to allow a quick pressure build-up, especially during warm start, the combination with a small rail is an advantageous solution in particular. Undesirable pressure drops, which can occur with a small rail, are avoided by the pressure accumulator.

The displacement of the closure body is thereby limited by at least one sealing element, preferably by both sealing elements. The stop of the closure body thus also provides a defined positioning or position of the closure body and thus limits the change in volume of the storage space.

The housing is preferably designed with a cylinder in which the closure body is slidably mounted as a piston. The shape of the closure body or the piston is preferably adapted to the inner shape of the housing. This creates a defined guiding situation for the closure body and a high degree of sealing, also during the movement of the closure body from one sealing element to the other.

Basically, it is desirable that the cross-sectional area of the closure body and that of the housing are designed approximately equal. As a result, the closure body acts as a partition in the housing, which separates the storage chamber in the housing. In this case, the pressure from the high-pressure region is applied to the end face of the closure body, in particular of the piston. The desired accumulator function can advantageously be influenced by a defined design of the front side in terms of their size and shape.

Further, a spring element is preferably provided, with which the closure body is biased in the direction of the storage space. The closure body is biased in the direction of a reduction of the storage space and thus in the direction of the high pressure area. The pressure in the high pressure area acts against this resilient bias. If the closure body at low pressure level in its rest position, it rests against the first sealing element and is at the same time pressed against this sealing element by means of the spring element. The spring element assists the sealing, since its biasing force acts on the first sealing element.

In addition, the spring element acts as a counterforce during the pressure storage at the pressure storage device and leads to a slow retreat of the closure body, while the pressure rises in the high pressure region. In this case, the spring element acts as a counterforce until the closure body comes to rest on the second stop, in particular the second sealing element.

The spring element is preferably an elastic element, a spring, in particular a spiral spring or a gas space. Depending on the design of the spring (spring rate, material, dimensioning) can be adjusted to the closure body whose contact pressure.

The housing is preferably separated from the closure body into two spaces, of which a first space forms the storage space. The housing is adapted to be fluidly connected to the high pressure area of an associated fuel injection system, and the second space is adapted to be fluidly connected to the low pressure area of an associated fuel injection system to remove the leakage from the high pressure area. On the one hand the high pressure from the high pressure region of the fuel injection system and on the other hand, the low pressure from the low pressure region acts on the closure body. The low-pressure region is preferably connected to the second space via a throttle. Thus, an advantageous vibration damping of the closure body and at the same time a force support for the resilient bias of the closure body and thus desired pressure build-up or pressure hold in the high pressure area is achieved

The sealing elements are preferably arranged on the inner circumferential surface of the housing. The sealing elements are then easy to arrange and to hold stationary. This causes a good sealing effect when applying the designed in particular as a piston closure body to the correspondingly positioned sealing elements.

Particularly preferably, the sealing elements are designed annular. The ring shape is inexpensive to manufacture, especially as a classic O-ring. In this case, the annular shape surrounds the inlet or outlet of the pressure storage device. The sealing element rings of this type are thus designed as a complete seal. The ring shape preferably extends radially outward near the piston circumference. This results in a large sealing surface, wherein only relatively small sealing forces are necessary for sealing. The ring shape of the sealing elements can be made relatively easily by injection molding or extrusion.

The closure body is preferably in the applied state on at least one of the sealing elements with an edge region. This results in an improved seal by penetration of the edge region of the closure body in the preferably elastic sealing element.

Preferably, there is further provided a pump of a fuel injection system in which an accumulator means as described above is integrated. The pump thus represents a particularly compact design and a separate tubing to the low pressure system can be avoided.

Further, as mentioned, the pressure accumulating device described above is preferably used in a fuel injection system. While in fuel systems without accumulator and especially at low rail volumes due to the cold start (eg - 30 ° C) very large injection quantity required and increasing in the cold modulus of elasticity of the fuel rail pressure would greatly reduce the pressure accumulator such a large Pressure drop through its fuel storage function.

During cold start, at low pump speed, after pressurizing to system pressure above the upper pressure level of the accumulator, fuel injection occurs. so first the pressure drops to the upper pressure level. The further removal by the injection is nachgefördert by the fuel contained in the accumulator amount of fuel. The pressure then only drops by the equivalent change in force due to the piston stroke during the return of fuel from the pressure accumulator.

The storage function only works with large injection quantities if the pressure would fall below the upper pressure level and thus could lead to disadvantages in atomization and mixture preparation. The pressure accumulator thus compensates disadvantages, such as an otherwise strong pressure drop of a small volume rail, and allows the use of inexpensive small rails. When combining the pressure accumulator with a small rail volume, there are no disadvantages in the pressure build-up time.

The internal combustion engine is rotated in particular with starter speed until the system pressure is built up by the pump. Preferably, the storage volume between the lower and the upper stop is less than the amount that can promote the pump by a stroke. Therefore, the accumulator is filled in a maximum of one delivery stroke. Below and above the two pressure levels of the pressure accumulator, the pressure increase is very fast due to the low rail volume.

Due to the sealing elements or gaskets according to the invention no extreme demands on the piston gap between the piston and the housing must be made, which can only by consuming or expensive measures such. B. an exact pairing of piston and housing or cylinder could be realized.

When the engine stops, ie after the pump has been pumped out, the system pressure slowly drops due to the sum of all leaks in the high-pressure system. The pressure is initially above the upper pressure level, so that the pressure accumulator due to the upper sealing element or the upper seal provides no significant contribution to the total leakage and thus to pressure reduction. Nevertheless, after a certain time, the upper pressure level is undershot, so that the piston no longer seals and increased leakage occurs over the piston gap. This causes the pressure to drop slightly faster, but only to the lower limit. The lower Sealing elements or the lower stop prevents rapid complete pressure reduction. In the lower stop in particular the piston clearance between piston and housing or cylinder has no effect on the total leakage and thus the further pressure drop.

The seal at the upper stop ensures that, especially in modern start / stop systems, which require a quick restart of the internal combustion engine, a sufficiently high rail pressure during startup is present.

The seal in the lower stop ensures that even after longer shutdown periods, ie not only in start / stop mode, there is still a certain minimum pressure and in the high pressure system neither air nor fuel vapor can form in the postheating phase, which makes a safe start difficult ( Hot / warm start).

Optionally, an accumulator device with only one sealing element or a seal is conceivable, so only a seal at the top or only at the bottom stop. The functionality of the pressure storage device is then possibly slightly lower, but this can be justified by lower costs.

Fig. 1

einen hydraulischen Schaltplan eines Kraftstoffeinspritzsystems ohne Druckspeicherung gemäß dem Stand der Technik und

Fig. 2

einen hydraulischen Schaltplan eines Kraftstoffeinspritzsystems mit einer erfindungsgemäßen Druckspeichervorrichtung.

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 hydraulic circuit diagram of a fuel injection system without pressure storage according to the prior art and

Fig. 2

a hydraulic circuit diagram of a fuel injection system with an accumulator device according to the invention.

In Fig. 1 a fuel injection system 10 is shown with a pump 12. In the case of the fuel injection systems 10, the region on the suction side of the pump 12 is referred to as the low-pressure region and the region on the pressure-side of the pump 12 as the pressure region or high-pressure region.

In the low-pressure region, fuel is pumped from a tank 14 through an electric fuel pump 16 at a pressure of about 5 bar through a fuel filter 18 to a line 20. A pressure relief valve 22 may direct fuel from the fuel pump 16 back into the tank 14. On line 16, a low pressure damper 24 is arranged.

In line 20, the amount of fuel that is delivered to the pump 12 is regulated by a quantity control valve 26. The pump 12 increases the pressure of this fuel up to about 200 bar, wherein the fuel is conveyed through a Raildrossel 44 in a rail 28. This high pressure defines the already mentioned high-pressure region on the pressure side of the pump 12. From the rail 28, the fuel can be injected via injection valves 30 into an internal combustion engine 32.

The pressure generated by the pump 12 is partly too high for the desired injection, depending on the operating state of the internal combustion engine 32. Therefore, this overpressure of the pump 12 is derived from the high pressure area in the pump 12. For this purpose, on the pressure side of the pump 12 branches off from the high-pressure region from a return line 34, which leads back into the delivery chamber of the pump 12. A check valve 36 mounted on the pressure side of the pump 12 forms the outlet valve of the pump 12. The check valve 36 only opens at a certain pressure level and prevents fuel from flowing in the opposite direction to its delivery direction. Another, arranged in the return line 34 check valve 38 ensures as a pressure relief valve that only fuel is returned under pressure in the pump 12. Also, this check valve 38 opens only from a certain higher pressure level in the flow direction to the low pressure area.

In addition, as mentioned, in the low-pressure region, the amount of fuel delivered to the pump 12 can be metered by the quantity control valve 26, so that ideally the pump 12 does not generate excessive overpressure at all. The pumped amount of fuel is regulated via a comparatively complex electromechanical system. On rail 28, a high pressure sensor 40 measures the pressure applied there. A controller 42 receives the information regarding the rail pressure from the high pressure sensor 40 and processes it. According to the programming of the control unit 42, the quantity control valve 26 is adjusted. Thus, the quantity control valve 26 regulates the per delivery stroke of the pump 12 supplied Amount of fuel due to the occurring and measured in the rail 24 fuel pressure.

In Fig. 2 an inventive fuel injection system 10 is shown in which the fuel is also first pumped into the line 20 of the low pressure area.

On the pressure side of the pump 12, in the pressure range or high pressure region, a check valve 36 is arranged. The check valve 36 opens only from a certain pressure level and prevents fuel can flow opposite to the conveying direction. Subsequently, the fuel is due to the pump pressure of the pump 12, promoted by the Raildrossel 44, in the rail 28. From there, the fuel reaches the injection valves 30 and is also injected into the engine 32.

On the pressure side behind the pump 12 or between the pump 12 and the rail 28, the high-pressure region is coupled to an accumulator 48. The pressure storage device 48 comprises a housing 50, in which a closure body 52 is biased against the high pressure area with a spring element 54, preferably in the form of a helical spring. Alternatively, a bias of the closure body by means of gas pressure is possible. The closure body 52 is designed in the form of a piston and arranged movable or displaceable in the housing 50. In this case, the closure body 52 delimits a storage space 56.

The storage space 56 is expandable or compressible or can be increased or decreased in volume when the closure body 52 is displaced due to the action of force against its bias in the housing 50. This variability of the volume of the storage space 56 enables a pressure storage function, which will be described later in more detail.

In addition, a first sealing element 58 and a second sealing element 60 are arranged in the housing 50. Viewed in the longitudinal direction of the housing 50, the first sealing element 58 is based on Fig. 2 below the closure body 52 in the storage space 56. The second sealing element 60 is located above the closure body 52 in a space 62 in which the spring element 54 is arranged.

The two sealing elements 58, 60 form a lower and an upper stop for the sliding closure body 52. The sealing elements 58, 60 are annular and arranged on the inner surface of the shell of the case cylindrical housing 50. The ring shape of the same elastic sealing elements 58, 60 is easy to implement. They can be produced relatively easily by injection molding or extrusion.

The pump 12 according to Fig. 2 If the pressure in the high-pressure region exceeds the lower pressure level of the pressure accumulator 48 due to the pump delivery, then the closure body 52 is pushed back and the volume of the storage space 56 increases. The fuel can thus escape in the storage space 56 and limits in this way the pressure increase in the high-pressure region. Usually, the pressure at the pump 12 on the pressure side is at least about 40 bar. The spring element 54 is designed such that it yields at this pressure of about 40 bar or a spring force corresponding to this pressure (lower pressure level). The upper pressure level of the pressure accumulator 48 is designed so that it is just below the usual pressure range at which the injection is operated in normal operation, for example about 50 bar. This ensures that no elevated leakage occurs at injection pressures above approx. 50 bar.

The storage space 56 is configured to receive an amount of fuel needed for cold start injection. If the pressure ceases due to a cold start injection in the storage space 56, the closure body 52 moves back in the direction of its initial position on the first sealing element 58, thus pushing fuel behind and thus preventing an excessive pressure drop.

Between the closure body 52 and the housing 50, leakage occurs due to a sliding seal 64 formed there. Since the fuel from the high-pressure region normally presses against the closure body 52 in the storage space 56, the leakage which occurs at the sliding seal 64, in the space 62nd dissipated. This space 62 is coupled by means of a line 66 to the low pressure area. On the line 66 is a throttle 68, which is designed in the present case by means of a diaphragm. The function of this line and throttle arrangement is that the movement of the closure body 52 is damped, for example, to avoid natural oscillations of the mass-spring system (closure body 52, spring element 54).

The design according to Fig. 2 can also be used with sub-aspects of the design according to Fig. 1 be combined. Thus, in particular in the design according to Fig. 2 a quantity control valve 26 may be provided. Further, the check valve 38 may be replaced by the pressure storage device 48. Furthermore, the according to Fig. 2 electrically driven pump 12 by a according to Fig. 1 mechanically driven pump 12 to be replaced.

Claims (10)

1. Pressure accumulator device for a fuel injection system, having a housing (50) in which a closure body (52) delimits an accumulator chamber (56) which can be expanded from a low pressure level prevailing therein to a high pressure level prevailing therein by way of movement of the closure body (52),
   characterized in that a first sealing element (58) and a second sealing element (60) can be abutted against alternately by the closure body (52), wherein, selectively as a function of the pressure in the accumulator chamber (56), the first sealing element (58) has a fluid-sealing action in the presence of a low pressure level and the second sealing element (60) has a fluid-sealing action in the presence of a high pressure level.
2. Pressure accumulator device according to Claim 1,
   characterized in that the first sealing element (58) and/or the second sealing element (60) are arranged in the housing (50) such that at least one of the sealing elements (58, 60) forms an abutment for the closure body (52).
3. Pressure accumulator device according to Claim 1 or 2,
   characterized in that the housing (50) is formed with a cylinder in which the closure body (52), in the form of a piston, is mounted in displaceable fashion.
4. Pressure accumulator device according to one of Claims 1 to 3,
   characterized in that a spring element (54) is provided by means of which the closure body (52) is preloaded in the direction of the accumulator chamber (56).
5. Pressure accumulator device according to one of Claims 1 to 4,
   characterized in that the housing (50) is divided by the closure body (52) into two chambers, of which a first chamber (56) forms the accumulator chamber and is designed to be connected in fluid-conducting fashion to the high-pressure region of an associated fuel injection system, and the second chamber (62) is designed to be connected in fluid-conducting fashion to the low-pressure region of an associated fuel injection system.
6. Pressure accumulator device according to one of Claims 1 to 5,
   characterized in that the sealing elements (58, 60) are arranged on the inner shell surface of the housing (50).
7. Pressure accumulator device according to one of Claims 1 to 6,
   characterized in that the sealing elements (58, 60) are of annular form.
8. Pressure accumulator device according to one of Claims 1 to 7,
   characterized in that the closure body (52) bears by way of an edge region against at least one of the sealing elements (58, 60) when in an abutting state.
9. Pump for a fuel injection system, in which pump there is integrated a pressure accumulator device according to one of Claims 1 to 8.
10. Use of a pressure accumulator device according to one of Claims 1 to 8 in a fuel injection system.

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