EP2649320B1 - Fuel delivery system of an internal combustion engine, comprising a rotary pump - Google Patents

Description

State of the art

The invention relates to a fuel delivery system according to the preamble of claim 1.

From the market known fuel systems of internal combustion engines, for example, for gasoline engines, which work with a direct injection of fuel, injection pressures of for example 200 bar are required. Frequently, the required fuel pressure is regulated as a function of an operating state of the internal combustion engine, for example in a range of 40 bar to 200 bar.

For this purpose, it is known to use for generating the required fuel pressure, a piston pump which is mechanically driven by the internal combustion engine. A pressure sensing high pressure sensor and a quantity control valve controlling the amount of fuel may be used to control the pressure. This is done with the cooperation of a control and / or regulating device ("control unit") of the internal combustion engine. The control of the cylinder-specific injection valves takes place as a function of the respectively determined by the high pressure sensor fuel pressure.

Further, it is possible to control the fuel pressure mechanically without the use of a high pressure sensor. This is known from the prior art in connection with mechanically operating injection systems.

The valve-controlled piston pumps typically used for high-pressure generation are manufactured comparatively complex. In addition, generate Single-piston pumps often high pressure pulsations on the high and low pressure side.

An alternative way of fuel delivery is the use of rotary pumps, which generate comparatively low pressure pulsations with respect to piston pumps. In order to generate the required amount of fuel for pressure build-up and injection at a start of the internal combustion engine, these pumps must often be performed oversized. The fuel pumped too much at higher speeds is returned to the low pressure area of the fuel delivery system.

Furthermore, it is known to control vane pumps by means of a pressure-controlled change in the eccentricity as required, so that the amount of fuel returned to the low-pressure region can at least be reduced.

However, many of the simpler demand control methods used with piston pumps fail with rotary pumps because they are inherently forced. In rotary pumps, the inlet and outlet quantities are less determined by a respective pressure, but are essentially dependent on the geometry of the so-called "control" - ie the inlet sections and outlet sections - the rotary pump.

Patent publications in this field are, for example, the EP 1 927 754 A1 , the US 4,102,606 A , the US Pat. No. 6,086,337 A as well as the US 2009/196772 A1 ,

Disclosure of the invention

The problem underlying the invention is solved by a fuel delivery system according to claim 1. Advantageous developments are specified in subclaims. For the invention important features can be found also in the following description and in the drawings, the features both alone and in different combinations may be important for the invention, without being explicitly referred to again.

The fuel delivery system according to the invention has the advantage that the generation of a high fuel pressure by means of a suction-throttled rotary pump can be controlled as needed at least in sections and / or stepwise, whereby the operating noise and pressure pulsations of the suction-throttled rotary pump can be minimized. Thus, the capacity can be easily throttled according to a particular need. In addition, the fuel delivery system according to the invention is inexpensive to produce.

It is contemplated that rotary pumps are generally oversized to produce sufficient fuel pressure even at low engine speeds. It makes use of the invention that the promotion of the fuel - depending on the speed and / or the operating state of the internal combustion engine - can also be done without a continuous over the entire range of the required flow rate control. For example, it may already be sufficient, after the start or cold start of the internal combustion engine, to limit the effective displacement volume of the rotary pump in a stepped manner. The limitation of the displacement volume is done in at least indirect dependence on the Saugdrosselung.

According to the invention, the suction-throttled rotary pump comprises at least two outlet sections located one behind the other and viewed in the direction of rotation, wherein at least one outlet section viewed in the direction of rotation can be hydraulically switched on or off depending on the degree of suction throttling. This makes it possible, depending on the respective fuel requirements, to influence the delivery rate of the rotary pump by means of a comparatively simple switching valve, in spite of suction throttling favorable and quiet operating behavior of the rotary pump.

In one embodiment of the fuel delivery system is seen between on the one hand the front outlet section and on the other hand one in the direction of rotation rear outlet portion and the high-pressure region, a first check valve arranged which blocks to the front outlet portion. Thus, a promotion of fuel is basically possible over both outlet sections. However, if the inlet-side valve device is active, the rotary pump thus operates with suction throttling, the pressure in the front outlet section remains low and therefore separated from the high-pressure region (and also from the rear outlet section). This results in a simple and inexpensive control. Furthermore, it is also possible to provide more than two outlet sections which, depending on the specific embodiment, are hydraulically connected to the high-pressure area either directly or via a further non-return valve respectively from which they can be separated. As a result, the effective displacement volume of the rotary pump can be set even finer or limited.

The fuel delivery system is inexpensive to produce when the rotary pump is a planetary rotor pump. Planetary rotor pumps are also particularly suitable for the application according to the invention in technical terms.

Furthermore, it is provided that the controllable valve device is controlled electrically or mechanically / hydraulically. In the case of an electrical control, the valve can be controlled, for example, by the control and / or regulating device of the internal combustion engine, as a result of which the operation of the rotary pump or the level of the fuel pressure generated can be controlled particularly well. In the case of a mechanical / hydraulic control, the valve device can be controlled, for example, by the pressure prevailing in the high-pressure region, so that regulation of the fuel pressure is possible solely from locally present variables.

A further embodiment of the fuel delivery system provides that the outlet sections are dimensioned and arranged such that at full delivery each outlet section conveys approximately half of a total displacement volume. The front outlet section (and thus the full drive line of the rotary pump) is then needed only during takeoff to quickly build up and maintain the rail pressure. During normal operation, with a fuel demand that is at most half of the starting fuel demand, the first check valve remains against closed, because due to the suction throttling is achieved that the displacement chambers are filled in the rule, a maximum of half. If suction throttles are so strong that the displacement chambers are less than half full (or, for example, not filled), the full load quantity is maximally dissipated and the backflow rate (and thus also the pressure pulsations) is significantly reduced. Possible leaks are included. The dimensioning takes place via the respective geometry of the - in this case two - outlet sections, which are also referred to as "pressure kidneys". The connection or disconnection takes place automatically by the first check valve as a function of the prevailing between the front and the rear outlet section pressure difference, which in turn depends on the scope of Saugdrosselung. It is understood that the outlet sections can also have any other geometry than "kidney-shaped" or "sickle-shaped".

Alternatively, it is provided that the outlet sections are dimensioned and arranged in such a way that in full delivery via the front outlet section approximately 75 percent of the total displacement volume is delivered. As a result, the rotary pump has a particularly low power loss, in particular during operating states with little or no fuel delivery (for example, overrun operation). Therefore, little heat must be dissipated to the environment from the rotary pump. In an upper part-load range or at full load or pressure build-up at the start of the internal combustion engine, when the maximum amount of fuel is conveyed, then there may be an increased backflow instead. The generated power loss can be sufficiently dissipated as a result of the higher fuel delivery, the resulting pulsations can be tolerated or compensated, and the pump noise is covered by the higher operating noise of the engine.

A further embodiment of the fuel delivery system provides that a cross section of the front outlet section has approximately the size of a displacement chamber of the rotary pump. This can be particularly advantageous when the rotary pump has a comparatively small number of displacement chambers. The front outlet section is designed such that essentially only one displacement chamber at a time can promote the first check valve. Thus, the delivery rate of the rotary pump can be controlled steplessly, at least in regions, according to a quantity of fuel to be delivered in each case.

In yet another embodiment, it is provided that the controllable valve device is arranged between the inlet section and the front outlet section. The controllable valve device assumes the task of a quantity control valve. In turn, may be arranged in addition between the front and the rear outlet portion, the first check valve, which can lock to the front outlet portion. With this arrangement, a controlled hydraulic bypass is provided which can recirculate a portion of the amount of fuel delivered from the front exhaust section into the intake section as needed. In this case, the flow cross-section of the quantity control valve can be continuously, stepped or preferably changed switching.

According to the invention, provision is made for a second spring-loaded check valve to be arranged between the inlet section and the rear outlet section, viewed in the direction of rotation, which blocks the rear outlet section. The second check valve has the task, in the case of a possible stoppage of the internal combustion engine and / or the rotary pump to perform an upper pressure limit, for example, if the fuel expands as a result of heating. In addition, may be promoted back into the inlet section by the second check valve possibly too much subsidized amount of fuel. The second check valve has a comparatively high triggering pressure.

Furthermore, it is proposed in this context that the controllable valve device has a hysteresis, such that an opening pressure is greater, preferably approximately twice as large as a closing pressure. This ensures that the maximum flow rate is only provided if it is really necessary to maintain rail pressure.

Figur 1

ein vereinfachtes Schema eines Kraftstoffsystems und eines darin angeordneten Kraftstofffördersystems einer Brennkraftmaschine;

Figur 2

eine erste Ausführungsform des Kraftstofffördersystems von Figur 1;

Figur 3

eine andere Ausführungsform des Kraftstofffördersystems; und

Figur 4

eine weitere Ausführungsform des Kraftstofffördersystems.

Hereinafter, exemplary embodiments of the invention will be explained with reference to the drawings. In the drawing show:

FIG. 1

a simplified schematic of a fuel system and disposed therein a fuel delivery system of an internal combustion engine;

FIG. 2

a first embodiment of the fuel delivery system of FIG. 1 ;

FIG. 3

another embodiment of the fuel delivery system; and

FIG. 4

another embodiment of the fuel delivery system.

The same reference numerals are used for functionally equivalent elements and sizes in all figures, even in different embodiments.

The FIG. 1 shows a greatly simplified scheme of a fuel system 10 of an internal combustion engine, not shown here. In the drawing from left to right, a fuel tank 12 is connected via a low pressure line 14 to a fuel delivery system 16. The region upstream of the fuel delivery system 16 corresponds to a low-pressure region 17. Furthermore, a high-pressure accumulator 20 ("common rail") is connected to the fuel delivery system 16 via a high-pressure line 18. The fuel delivery system 16 includes a rotary pump 22, which may be controlled by a control and / or regulating device 24 of the internal combustion engine. The region downstream of the fuel delivery system 16 corresponds to a high-pressure region 25.

In operation, the rotary pump 22 conveys fuel from the fuel tank 12 into the high-pressure accumulator 20. Starting from this, fuel can be injected by means of injection valves into combustion chambers of the internal combustion engine.

The FIG. 2 1 shows a first embodiment of the fuel delivery system 16 and the high-pressure accumulator 20. In the present case, the fuel delivery system 16 comprises the approximately in the middle region of the drawing shown rotary pump 22 to the high-pressure accumulator 20 toward a first check valve 28 to the low pressure region 17 through a second check valve 30 and a controllable valve device 32nd , which is controllable via an electromagnet 33. The rotary pump 22 is in the present case designed as a planetary rotor pump, which has a radially symmetrical outer housing section 26, an inner gear 36 arranged on a hub 34, and eight planetary gears 38 arranged radially symmetrically in the housing section 26 on a circle (not shown). The internal gear 36 has seven teeth 37 and a circumferential fine toothing (without reference numerals). The planetary gears 38 have a complementary fine toothing.

A rotary arrow 39 indicates the direction of rotation of the hub 34 during operation. Radial between the internal gear 36 and the housing portion 26 and the planetary gears 38 are Verdrängerräume 40, which are only partially identified by their reference numerals, each formed with different sizes and geometries whose volume with the rotational movement of the internal gear first and then decreases again , In the upper portion in the drawing, the rotary pump 22 has an inlet portion 42 (\ "inlet kidney \"), and in the lower portion, a rotationally-directional outlet portion 44 and a rearward outlet portion 46 (\ "exhaust kidney \"). The inlet section 42 and the outlet sections 44 and 46 at least partially cover the displacement chambers 40 and are correspondingly fluidically connected to the displacement chambers 40.

The in the drawing of FIG. 2 shown cross sections of the inlet portion 42 and the front outlet portion 44 and the rear outlet portion 46 each have an approximately kidney-shaped or crescent-shaped geometry. The kidneys or sickles are aligned approximately tangentially to the rotational movement.

The kidney of the inlet section 42 extends in about one third of a circumference and widening in the direction of rotation steadily to about 200 percent of the initial width. The kidney of the front outlet portion 44 extends approximately one-eighth of a circumference and widens in the direction of rotation abruptly to about 200 percent of the initial width. The kidney of the rearward outlet portion 46 extends approximately three sixteenths of a circumference and narrows steadily in the direction of rotation to about 50 percent of the original width.

The first check valve 28 is hydraulically connected via a fluid line 48 to the front outlet portion 44, and via a fluid line 50 to the rear outlet portion 46 and to the fuel reservoir 20, that the first check valve 28 to the front outlet portion 44 toward can lock. The second check valve 30 is hydraulically connected via a fluid line 52 to the inlet section 42 and the outlet of the controllable valve device 32, and via a fluid line 54 to the rear outlet section 46, that the second check valve 30 to the rear outlet section 46th can lock out. Furthermore, the controllable valve device 32 is arranged between the low-pressure line 14 and the fluid line 52.

In operation, the internal gear 36 rotates in the direction of the rotary arrow 39 eccentric to the circle on which the planet gears 38 are arranged. By means of the fine toothing, the seven teeth 37 of the internal gear 36 can mesh with the eight planetary gears 38, wherein the meshing of the internal gear 36 and the eccentricity of the hub 34 is characterized by a kind of "submerged" beating. The immersion movements of the teeth 37 in the interspaces of the planet gears 38 are carried out one after the other and thus time-dependent and location-dependent.

The planet gears 38 rotate in associated recesses of the housing portion 26, wherein the recesses each have the shape of a circle segment. In the present case, a segment height determining the circle segment is greater than the circle radius. The openings of the recesses are directed radially inwardly on the internal gear 36.

Due to the rotational movement of the internal gear 36, the displacement chambers 40 are continuously displaced in the direction of rotation, wherein the displacement chambers 40 in the region of the inlet portion 42 steadily initially larger and then smaller again in the region of the outlet sections 44 and 46. Corresponding to the cross sections of the inlet section 42, the front outlet section 44, and the rear outlet section 46, fuel can thereby be conveyed. In this case, the fuel is sucked by the rotary pump 22 via the inlet portion 42, transported in the direction of rotation, and - depending on the position of Valve means 32 - discharged via both outlet sections 44 and 46 or only via the rear outlet section 46 to the high-pressure accumulator 20 out.

The second check valve 30 may limit the fuel pressure prevailing in the rear outlet section 46 and has a correspondingly high release pressure. Thus, in the event of a fault in the fuel system 10 or in the event of a possible increase in the fuel pressure when the internal combustion engine is stopped (fuel heating), excess fuel can be conducted back to the inlet section 42. The second check valve 30 thus has the function of a pressure relief valve.

The amount of fuel to be delivered by the rotary pump 22 can be metered via the controllable valve device 32. This results in a so-called "suction throttling", wherein the controllable valve device 32 is controlled by the control and / or regulating device 24 by means of the electromagnet 33 as a function of the pressure prevailing in the high-pressure accumulator 20 fuel pressure. For this purpose, among other things, a pressure sensor (not shown) is provided on the high-pressure accumulator 20. Thus, the fuel pressure can for example be continuously adapted to a current operating state of the internal combustion engine and thus regulated.

Alternatively, the controllable valve device 32 may be hydraulically controlled by the fuel pressure of the high-pressure accumulator 20 and thus the fuel pressure may be regulated to a generally fixed value. Optionally, this can be done by means of an additional "Druckabsteuerfunktion". This is in the drawing of FIG. 2 but not shown.

In the present case, the cross-sections of the front outlet section 44 and the rear outlet section 46 are dimensioned so that during so-called "full delivery" of the fuel delivery system 16, each outlet section 44 and 46 delivers approximately half of a displacement volume. With full delivery - the valve device 32 is thus complete and always open - the displacement chambers 40 are completely filled with fuel via the inlet section. As the displacement chambers 40 become smaller, the fuel firstly flows into the fuel reservoir 20 via the front outlet section 44 and the opening check valve 28 and then via the rear outlet section 46 pressed. Such a full promotion takes place, for example, when starting the internal combustion engine for rapid pressure build-up in the fuel reservoir 20.

In a partial delivery, the valve device 32 is activated, thus allowing only a filling of the displacement chambers 40 with liquid fuel of, for example, about 50%. At the end of the filling process, therefore, there is a comparatively low pressure in a displacement chamber, so that it is filled with fuel and fuel vapor. If such a displacement chamber 40 now reaches the region of the front outlet section 44, despite the interim volume reduction of the displacement chamber 40, the pressure prevailing therein is insufficient to open the check valve 28. Only the further volume reduction creates such a pressure that the fuel can be pressed into the fuel reservoir 20 via the rear outlet section 46. If less than half the amount of full funding is promoted, so at most one of the full funding corresponding heat output must be removed from the rotary pump 22, and also remains over the second check valve 30 in the inlet portion 42 guided back fuel amount is relatively small. As a result, pulsations of the fuel pressure can be significantly reduced.

An alternative dimensioning of the cross sections of the front outlet section 44 and the rear outlet section 46 envisages that when the rotary pump 22 is fully conveyed, the front outlet section 44 promotes approximately 75 percent of the displacement volume. This can be a suitable design, for example, if much more fuel is required to start the internal combustion engine than in normal operation.

It can be seen that the outlet sections 44 and 46 in the present case are designed such that the cross section of the front outlet section 44 has approximately the size of the displacement chamber 40. As a result, pressure pulsations of the fuel can be kept relatively small. Pressure pulsations can generally arise when a partially filled displacement chamber 40 is connected to one of the outlet sections 44 and 46, with which a displacement chamber 40 leading in the direction of rotation and already conveying is connected.

The FIG. 3 shows another embodiment of the fuel delivery system 16, in turn supplemented with the high-pressure accumulator 20. The basic structure and some basic function correspond to those of the device of FIG. 2 , so that in the following only the differences in the differently arranged controllable valve device 32 will be described.

In the fuel delivery system 16 of FIG. 3 For example, the front outlet section 44 is hydraulically connected to the inlet section 42 via a fluid line 56, the controllable valve device 32 and a fluid line 58. Depending on the state of the controllable valve device 32 and the respective hydraulic pressure, fuel may flow from the front outlet section 44 back to the inlet section 42. Furthermore, the low-pressure line 14 is hydraulically connected via the fluid line 52 directly to the inlet section 42.

In addition, the controllable valve device 32 of the FIG. 3 a hysteresis, such that an opening pressure is considerably greater than a closing pressure. In the present case, the opening pressure is twice as great as the closing pressure. The controllable valve device 32 thus opens when the opening pressure is exceeded, and closes when the closing pressure has fallen below. The opening and closing pressure can be removed, for example, in the fuel reservoir 20, so it can be the rail pressure. If, for example, after the opening pressure has been exceeded, the controllable valve device 32 opens, it remains open even when the fuel pressure subsequently drops only comparatively little, as long as the closing pressure is not undershot. The same applies vice versa when falling below the closing pressure.

In FIG. 3 is the task of the second check valve 30 with respect to FIG. 2 extended. The second check valve 30 acts in the fuel delivery system 16 of FIG. 3 not only as a pressure relief valve - for example, in the event of a fault - but can also promote a too much pumped amount of fuel from the rear outlet section 46 back into the inlet section 42. As a result of the control achieved by the controllable valve device 32, the amount of fuel flowing through the second check valve 30 is generally comparatively small.

During a cold start of the internal combustion engine, the controllable valve device 32 is initially blocked. The rotary pump 22 delivers fuel into the high-pressure accumulator 20 and continuously builds up fuel pressure there. As long as the fuel pressure in the high-pressure accumulator 20 is still so small that the first check valve 28 can open, the front outlet section 44 and the rear outlet section 46 convey fuel into the high-pressure accumulator 20. The delivery rate of the rotary pump 22 is thus maximal.

After a cold start, the controllable valve device 32 is opened by means of the electromagnet 33 so that fuel can flow from the front outlet section 44 to the inlet section 42. Thus, the normal operation of the internal combustion engine or the fuel delivery system 16 is reached and the controllable valve device 32 remains open as long as the fuel pressure does not fall below the closing pressure. Due to the comparatively low pressure in the outlet section 44, the first check valve 28 remains locked, it is conveyed only via the rear outlet section 46.

As an alternative to the control by the electromagnet 33, the controllable valve device 32 can be controlled hydraulically or mechanically by the fuel pressure of the high-pressure accumulator 20. This is in the FIG. 3 but not shown.

Furthermore, it is possible to carry out the rotary pump 22 with more than just two outlet sections 44 and 46. In this case, the outlet sections may optionally be connected hydraulically to the high-pressure accumulator 20 directly (such as outlet section 46) or via a check valve (such as outlet section 44).

The rotary pump 22 facing the terminals of the fluid lines 48, 50, 52, 54, 56 and 58 are in the drawing of Figures 2 and 3 each marked by a dot. It is understood that the points merely show the hydraulic assignment, but not the exact geometric positions of the respective ports.

Furthermore, it is understood that the embodiment of the FIG. 3 with all variants of the embodiment of FIG. 2 can be combined.

FIG. 4 shows a further embodiment of the fuel delivery system 16. In the present case, the inlet portion 42 of the rotary pump 22 via the fluid line 52 and a mechanical throttle 60 is connected to the low-pressure region 17. The second check valve 30 is connected between the fluid line 52 and the high pressure accumulator 20, wherein the second check valve 30 can block the high pressure accumulator 20 back.

Furthermore, the rear outlet portion 46 is connected via a third check valve 62 to the high-pressure line 18 and the high-pressure accumulator 20, such that the third check valve 62 to the rear outlet portion 46 can lock out. Complementary in the FIG. 4 drawn a reservoir 64, which can accommodate any leaks of the fuel. The fuel delivery system 16 of the FIG. 4 has the advantage that a possible backflow from the high-pressure accumulator 20 to the rotary pump 22 is prevented. In addition, an operating noise of the rotary pump 22 can be reduced.

Claims (7)

1. Fuel delivery system (16) of an internal combustion engine, having a rotary pump (22) which pumps fuel from a low-pressure region (17) into a high-pressure region (25), wherein the rotary pump (22) has at least one low-pressure-side inlet section (42) and at least one high-pressure-side outlet section (44, 46), and having a controllable valve device (32) which is arranged between the low-pressure-side inlet section (42) and low-pressure region (17) and which serves for controlling the delivered fuel flow, characterized in that the rotary pump (22) comprises at least two outlet sections (44, 46) which are situated one behind the other as viewed in the direction of rotation and which are separated from one another, and in that at least one front outlet section (44) as viewed in the direction of rotation can be hydraulically activated or deactivated, and in that, between the inlet section (42) and a rear outlet section (46) as viewed in the direction of rotation, there is arranged a second spring-loaded check valve (30) which blocks in the direction of the rear outlet section (46).
2. Fuel delivery system (16) according to Claim 1, characterized in that a first check valve (28) is arranged between, at one side, the front outlet section (44) and, at the other side, a rear outlet section (46) as viewed in the direction of rotation and the high-pressure region (25), which first check valve blocks in the direction of the front outlet section (44).
3. Fuel delivery system (16) according to at least one of the preceding claims, characterized in that the rotary pump (22) is a planetary rotor pump.
4. Fuel delivery system (16) according to at least one of the preceding claims, characterized in that the controllable valve device (32) is electrically or mechanically/hydraulically controlled.
5. Fuel delivery system (16) according to at least one of the preceding claims, characterized in that the outlet sections (44, 46) are dimensioned and arranged such that, under full delivery conditions, approximately half of a total displacement volume is delivered via each outlet section (44, 46).
6. Fuel delivery system (16) according to one of Claims 1 to 4, characterized in that the outlet sections (44, 46) are dimensioned and arranged such that, under full delivery conditions, approximately 75% of the total displacement volume is delivered via the front outlet section (44).
7. Fuel delivery system (16) according to at least one of the preceding claims, characterized in that a cross section of the front outlet section (44) has approximately the size of a displacement volume (40) of the rotary pump (22).

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