EP1312791A2 - High pressure fuel pump with vented membrane accumulator - Google Patents

Abstract

The first compartment (39) is hydraulically-connected with a fuel return line (45).

Description

State of the art

The invention relates to a high pressure fuel pump for an internal combustion engine, with at least one Pump element, with a fuel supply, with a High-pressure line, the pump element being fuel promotes the fuel supply in the high pressure line, and with a membrane accumulator, the membrane accumulator one has a first subspace and a second subspace are separated from each other by a membrane, and wherein the second compartment with the pressure of the fuel feed is applied.

In this high-pressure fuel pump, for example in common rail injection systems Otto engines with direct petrol injection is used, the Membrane accumulators, those that occur during operation To dampen pressure surges in the fuel supply and a Sufficient supply of fuel to the delivery area during the suction stroke of the pump element or elements guarantee.

The flow control of this high pressure fuel pump takes place via a volume control valve, which to this Purpose of a hydraulic connection between the delivery room of the pump element and the fuel supply can. When this connection is made, it promotes Pump element no longer in the high pressure line; rather in the fuel supply. By regulating the Piston pump is the degree of utilization of the High pressure fuel pump improves because the Work consumption of the pump element is greatly reduced if this only against the low pressure in the fuel supply Must do work.

When the quantity control valve is opened, the Fuel supply suddenly with a pressure surge acted upon, the considerable mechanical Injection system stresses. Around At least partially reducing pressure surges is a Membrane accumulator with a diffusion-tight and in a row the hard membrane provided in the fuel supply.

During the suction stroke of the pump element occurs in Fuel supply a dynamic pressure drop, which the Danger of vapor bubble formation and cavitation with it brings. The pressure drop in the fuel supply occurs because for a short time the one sucked in by the piston pump Amount of fuel is greater than that of one Low pressure pump pumped into the fuel supply Fuel quantity; or because the liquid in the Inlet line must be accelerated. In this Operating state, the diaphragm accumulator keeps the pressure in Fuel inlet at least partially upright, so that the undesirable vapor bubble formation is effectively suppressed.

If the membrane accumulator, for example due to the break the membrane that has become ineffective are bypass and Fuel supply full of the above pressure peaks exposed to damage sooner or later leads. In addition, without the membrane memory during Suction strokes of the piston pump cause cavitation, resulting in their Damage.

The invention has for its object a High pressure fuel pump for an internal combustion engine with a small diaphragm accumulator with a good one To provide damping behavior,

This task is for a high pressure fuel pump an internal combustion engine, with at least one Pump element, with a fuel supply, with a High pressure line, the piston pump fuel from the Supports fuel supply to the high pressure line, and with a membrane accumulator, the membrane accumulator one has a first subspace and a second subspace are separated from each other by a membrane, and wherein the second compartment with the pressure of the fuel feed is acted upon, in that the first subspace is hydraulically connected to the fuel return.

Advantages of the invention

Through the hydraulic connection of the first part and Fuel return can use a soft membrane with which large strokes can be achieved. Such Membranes according to the invention can be made of rubber, the opposite Fuel that is not diffusion-tight can be produced. Membranes according to the prior art, which are diffusion-tight are very hard, so a large diameter of the membrane accumulator is necessary to achieve the necessary Absorb damping volume.

The connection according to the invention between the first subspace and fuel return allows the removal of the by soft and well damping membrane diffusing Fuel in the fuel return.

In addition, the hydraulic according to the invention Connection ensures that even if the Membrane no fuel can get into the environment. Finally, the solution according to the invention is very simple feasible and can also be done without major changes already existing mass-produced High pressure fuel pumps are introduced.

In a variant of the invention it is provided that in the hydraulic connection between the first compartment and Fuel return a throttle and / or an orifice is provided so that the small amount of fuel which diffuses easily through the membrane from the second Subspace can be pushed out.

Functionality increases again, if the flow resistance of the throttle or orifice in Direction from the first part of the room to the fuel return is dimensioned that in the case of a defective membrane in the Fuel inflow clearly compared to the normal state reduced time-averaged pressure in the first subspace so that if the diaphragm accumulator fails, the Internal combustion engine with reduced fuel delivery and consequently also reduced pressures in the High pressure line can continue to be operated. Thus stands the driver one with an inventive High pressure fuel pump equipped vehicle Emergency driving function available, which allows him to to go to the nearest workshop. Because of the reduced Fuel flow and the resulting Power reduction in the internal combustion engine recognizes this Control unit malfunction and can be a Warning device, e.g. a signal light in the Activate the dashboard of the vehicle.

A delivery head of the low-pressure pump of around 4 is usual up to 6 bar. It turned out to be advantageous if the flow resistance of the throttle or orifice is selected in this way is that there is a medium pressure when the membrane is defective of about 1.5 bar in the fuel supply. This On the one hand, pressure differences are sufficiently large to easy to be detected and on the other hand is a Pressure of 1.5 bar in the fuel feed is sufficiently high to to enable an emergency driving function of the vehicle.

The operating behavior of the invention High pressure fuel pump is further improved when the Flow resistance of the throttle or orifice in the direction from the first part of the fuel return is smaller than from Fuel return to the first compartment. At this Design of the throttle or orifice ensures that the removal of fuel from the first compartment only against low flow resistance must occur while the backflow of fuel from the fuel inlet is hindered in the first subspace. As a result it in operation to form vapor bubbles in the first Subspace, which improves the function of the damper.

This effect can be further increased if in the hydraulic connection between the first part and A return valve is provided for fuel return. This check valve must be arranged so that the Backflow of fuel from the fuel inlet into the first subspace is prevented.

In an advantageous embodiment of the invention High pressure fuel pumps are the throttle, the orifice and / or the check valve in a connector arranged, which in a the hydraulic connection between the first compartment and the fuel return Bore in a pump housing of the high pressure fuel pump and / or the membrane accumulator arranged, in particular is pressed.

Further variants of the invention High pressure fuel pump provide that the membrane has at least one elastic rubber layer and / or that the diaphragm accumulator is a spring-loaded Membrane accumulator is. Both variants allow that Design of a particularly good pressure shock absorbing Diaphragm accumulator.

Further advantages and advantageous configurations of the Invention are the drawing, its description and the Removable claims.

drawing

Fig. 1

ein Blockschaltbild eines ersten Ausführungsbeispiels einer Einspritzanlage mit einer erfindungsgemäßen Hochdruckkraftstoffpumpe,

Fig. 2

eine schematische Darstellung eines zweiten Ausführungsbeispiels einer erfindungsgemäßen Hochdruckkraftstoffpumpe,

Fig. 3

Ausführungsbeispiele einer erfindungsgemäßen Drossel und eines erfindungsgemäßen Rückschlagventils und

Fig. 4

eine Schnittdarstellung eines dritten Ausführungsbeispiels einer erfindungsgemäßen Hochdruckkraftstoffpumpe.

Show it:

Fig. 1

2 shows a block diagram of a first exemplary embodiment of an injection system with a high-pressure fuel pump according to the invention,

Fig. 2

2 shows a schematic illustration of a second exemplary embodiment of a high-pressure fuel pump according to the invention,

Fig. 3

Embodiments of a throttle according to the invention and a check valve according to the invention and

Fig. 4

a sectional view of a third embodiment of a high pressure fuel pump according to the invention.

Description of the embodiments

Figure 1 shows a block diagram of a first Embodiment one with an inventive High pressure fuel pump 1 equipped injection system for internal combustion engines. The high pressure fuel pump 1 is via a fuel inlet 3, 3a, 3b with fuel supplied from a tank 5. The fuel is from one electric low pressure fuel pump 7 from the tank 5 in the fuel feed 3 promoted. A low pressure regulator 9 regulates the pressure in the fuel inlet 3 to, for example, 4 up to 6 bar.

The high-pressure fuel pump 1 according to the invention promotes Embodiment shown here via a High-pressure line 11 in a common rail 13, which in turn is connected to injectors 15. On the common rail 13 are a Pressure relief valve 17 and a pressure sensor 19 arranged. 1 are not shown in FIG Control device which regulates and controls the Injection system takes over, signal lines, electrical Utility lines and more.

The high-pressure fuel pump 1 has, for example, at least one Pump element 21 with a piston (not shown) and a cylinder (not shown). The pump element 21 delivers fuel from the fuel inlet 3 into the High pressure line 11. To prevent the fuel from flowing back the high pressure line 11 into the pump element 21 and from the To prevent pump element 21 in the fuel inlet 3b, are an outlet valve 23 in the high pressure line 11 and a Inlet valve 25 is provided in the fuel inlet 3b.

The quantity control of the high pressure fuel pump 1 takes place via a bypass 27, which is not shown Delivery chamber of the pump element 21 and the fuel inlet 3 connects with each other, and one arranged in the bypass 27 Volume control valve 29.

If the quantity control valve 29, as shown in FIG. 1, is open, the pump element 21 does not promote Fuel into the high pressure line 11, but only in the bypass 27.

As soon as the quantity control valve 29 is closed, builds a pressure during the delivery stroke of the pump element 21 in the delivery chamber (not shown) of the pump element 21 and the pump element 21 delivers into the high pressure line 11 as soon as the pressure in the delivery chamber (not shown) is higher than the pressure in the high pressure line 11 behind the exhaust valve 23.

If the quantity control valve 29 during the delivery stroke is opened, the fuel in the bypass 27 and then in the fuel inlet 3 with a pressure surge acts on the pump element 21 upstream components such as tank 5, Low pressure fuel pump 7, low pressure regulator 9 or Connecting elements, not shown, such as. B. Damage the quick connectors of the high pressure fuel pump can.

To reduce these pressure surges, there is 3 in the fuel inlet a membrane accumulator 31 is provided. The membrane accumulator 31, which is only shown schematically here, consists of a Housing 33, the interior of a membrane 35 in two Subspaces is divided. If the membrane 35 is undamaged is, the membrane 35 seals the subspaces liquid-tight against each other. In the first subspace 39 of the housing 33 a compression spring 37 housed against the Membrane 35 and the housing 33 supports. The second room 43 of the housing 33 is connected to the fuel inlet 3 and is filled with fuel. Once the above Pressure surge in the second subspace 43 of the membrane accumulator 31 reached, the compression spring 37 is compressed and thus absorbs the energy contained in the pressure surge.

If the pump element 21 during the suction stroke with high Speed of fuel from the fuel inlet 3 sucked in, this leads to a strong pressure drop in the Fuel inlet 3, 3a and 3b, because the delivery rate of Low pressure fuel pump 7 is not sufficient to this To drive peak demand. While printing in Fuel inlet 3 sinks sufficiently, presses the compression spring 37 the membrane 35 of the membrane accumulator 31 in the direction of second subspace and thus delivers fuel from the Membrane accumulator 31 in the fuel inlet 3. The Membrane accumulator 31 therefore has two functions: it protects the Injection system from harmful pressure peaks and he ensures sufficient fuel flow from the Fuel inlet 3b in the pump element 21 during the Suction stroke.

The leakage amount of the pump element 21 is a Fuel return 45 is returned to the tank 5. Between the first subspace 39 and the fuel return 45 is a connecting line 47 with a throttle 49 available via the fuel (not shown) which diffuses through the membrane 35 into the first subspace 39, can be dissipated. If the membrane 35 during the Suction strokes, as described above, towards the second Moving part 43, throttle 49 throttles the Fuel return flow from the fuel inlet 3 in the first Subspace 39 so strong that the fuel in the first Subspace 39 at least due to the strong negative pressure partially evaporated. So there is in the first part at most one corresponding to the vapor pressure of the fuel Pressure, which in turn gives the elastic properties in the first Partial space improved.

When the diaphragm 35 of the diaphragm accumulator 31 leaks the fuel should also flow into the first compartment 39 and via the connecting line 47 in the Fuel return 45. As a result, the membrane reservoir 31 ineffective and the pressure in the fuel inlet 3 drops far from (for example to 1.5 bar) that the Internal combustion engine only with reduced power and Speed can be operated. This will damage that otherwise due to the pressure peaks when controlling the Flow rate of the pump element would be prevented. Due to the pressure drop in the fuel inlet 3, the Malfunction of the injection system from not shown Control unit recognized and a corresponding emergency driving program to be activated.

In Figure 2 is a second embodiment High-pressure fuel pump according to the invention in sections shown. The same components are the same Provide reference numerals and it applies to the figure 1 said accordingly. In Figure 2 is clearly too recognize that in this embodiment the Pump element 21 from a piston 51 which in a Cylinder bore 53 is made. The Cylinder bore 53 and piston 51 limit one Delivery space 55. Via the inlet valve 25, the Fuel from the fuel inlet 3 into the delivery space 55 arrive when the piston 51 is in the position shown in FIG. 2 shown arrangement moves down. this is the so-called suction stroke.

As soon as the piston 51 is up again in the direction of Inlet valve 25 moves, the volume of the Delivery chamber 55, the inlet valve 25 closes and Fuel is in through the exhaust valve 23 High pressure line 11 pushed out, provided that Volume control valve 29 is closed.

When the piston 51 has enough fuel in it Has promoted high pressure line 11, that will Volume control valve 29 opened. This switch position of the Quantity control valve 29 is shown in Figure 2. By the opened quantity control valve 29 can be that of the piston 51 delivered fuel into the fuel inlet 3 be pushed out. This results in the one already mentioned Pressure surge in the fuel inlet 3, which by the Membrane memory 31 is damped. On the piston 51 is a Ring channel 57 is provided, which of fuel from the Fuel inlet 3 is flowed through. This will make the Piston 51 cooled and lubricated. Via a flow restrictor 59 the fuel from the ring channel 57 in the Fuel return 45 discharged. The amount of leakage from the Pump element 21 is also from a leakage space 61 discharged into the fuel return 45.

In Figure 2 it can be seen that the membrane accumulator 31 Has housing 33. A membrane 35 divides this Internal volume of the housing 33 in a first subspace 39 and a second subspace 43 liquid-tight. The second Partial space 43 is hydraulic with the fuel inlet 3 connected. If there is a pressure surge in fuel inlet 3 occurs, this lifts the membrane 35 against the force of one arranged in the first partial space 39 compression spring 63 and thus relieves this pressure surge. The compression spring 63 supports one end on the diaphragm 35 via a support plate 65 from.

As already with reference to the first embodiment (figure 1), the first subspace 39 is above the throttle 49 and the connecting line 47 with the fuel return 45 hydraulically connected. If through the membrane 35 Fuel from the second subspace 43 into the first subspace 39 diffuses, this fuel can over the Connection line 47 are discharged. The throttle 49 is dimensioned so that these small amounts of fuel, which diffuse through the membrane 35, easily removed can be. On the other hand, the fuel from the Fuel return 45 is not complete in the first Partial flow 39 back when the compression spring 63 during of the suction stroke of the pump element 21, the membrane back in pushes back their starting position. This happens yourself at a very high speed and therefore can the fuel from the fuel return 45 is not in the flow through the throttle 49 at the same speed. It A vapor bubble therefore forms in the first subspace 39. Because of this vapor bubble, the functionality of the Membrane accumulator 31 as a pressure damper despite the Connection line 47 to the fuel return 45 guaranteed. Furthermore, the throttle 49 is closed too dimension that in the case of a defective membrane 35 a reduced pressure level in the fuel supply 3 established. This reduced pressure level of e.g. B. 1.5 bar is sufficient to run emergency operation Ensure internal combustion engine without impermissibly high Pressure surges in the fuel inlet 3 by opening the Volume control valve 29 cause damage during emergency operation on fuel inlet 3 and components associated with it do not arise. this will achieved in that after the error detection by the Diagnostics in the control unit, the system pressure in the common rail is significantly reduced, which in turn leads to lower Pressure surges on the supply line after opening the Volume control valve leads. This also reduces the Maximum engine speed.

In Figure 3, two embodiments are more inventive Diaphragm memory 31 shown in sections. In which The embodiment of Figure 3a is in place of Throttle 49 a check valve 67 is provided. In which 3b is the throttle 49 trained that they have a low flow resistance in the flow direction from the first subspace 39 in the Connection line 49 and vice versa has significantly greater flow resistance. This increased Flow resistance promotes the formation of vapor bubbles in the first subspace 39 during the suction stroke of the pump element 21 (see Figure 2).

In Figure 4 is another embodiment High-pressure fuel pump according to the invention in section shown. In this embodiment, the housing 33 of the diaphragm accumulator 31 executed in two parts. It consists of a cover 33a and a lower part 33b. By Screwing the lid 33a and lower part 33b together Membrane 35 clamped and at the same time the compression spring 63 biased. The connecting line 47 runs partially through the cover 33a and then through a housing 69 the high pressure fuel pump. In an expanded Section 71 of the connecting line 47 is a Connecting part 73 used. In this connection part 73 the throttle 49 is provided. This solution is manufacturing technology and with regard to possible Repairs very cheap. Of course, at all embodiments in place of the throttle 49 Check valve may be provided. The combination of Throttle 49 (see Figure 3b) and check valve 67 (see Figure 3a) is possible and in certain applications also beneficial.

All in the description, the following claims and The features shown in the drawing can be both individually as well as in any combination with each other be essential to the invention.

Claims (10)

High-pressure fuel pump for an internal combustion engine, with at least one pump element (21), with a fuel inlet (3), with a fuel return (45), with a high-pressure line (11), the pump element (21) fuel from the fuel inlet (3) into the high-pressure line (11) conveys, and with a membrane accumulator (31), the membrane accumulator (31) having a first partial space (39) and a second partial space (43), which are separated from one another by a membrane (35), the second partial space ( 43) is acted upon by the pressure of the fuel inlet (3), characterized in that the first partial space (39) is hydraulically connected to a fuel return (45). High-pressure fuel pump according to Claim 1, characterized in that a throttle (49) or an orifice is provided in the hydraulic connection between the first partial space (39) and the fuel return (45). High-pressure fuel pump according to claim 2, characterized in that the flow resistance of the throttle (49) or orifice in the direction from the first subspace (39) to the fuel return (45) is dimensioned such that when the diaphragm (35) is defective in the fuel inlet (3) the normal state sets significantly reduced mean pressure. High-pressure fuel pump according to claim 2 or 3, characterized in that the flow resistance of the throttle (45) or orifice in the direction from the first subspace (39) to the fuel return (45) is smaller than from the fuel return (45) to the first subspace (39). High-pressure fuel pump according to one of the preceding claims, characterized in that a check valve (67) is provided in the hydraulic connection between the first partial space (39) and the fuel return (45). High-pressure fuel pump according to one of claims 2 to 5, characterized in that the throttle (45), the orifice and / or the check valve (67) are arranged in a connecting piece (73), and in that the connecting piece (73) into a hydraulic connection A bore (71) is formed between the first sub-chamber (39) and the fuel return (45) in a pump housing (69) of the high-pressure fuel pump (1) and / or the diaphragm accumulator (31), in particular it is pressed in. High-pressure fuel pump according to one of the preceding claims, characterized in that the membrane (35) has at least one elastic rubber layer. High-pressure fuel pump according to one of the preceding claims, characterized in that the diaphragm accumulator is a spring-loaded diaphragm accumulator (31). High-pressure fuel pump according to one of the preceding claims, characterized in that a connecting line (47) inside the high-pressure fuel pump is connected to the fuel return (45). High-pressure fuel pump according to one of the preceding claims, characterized in that the pressure in a common rail (13) is reduced after the detection of a failure of the diaphragm accumulator.

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