EP1913255A1

EP1913255A1 - Fuel supply system, especially for an internal combustion engine

Info

Publication number: EP1913255A1
Application number: EP06763329A
Authority: EP
Inventors: Bernd Schroeder
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2005-07-19
Filing date: 2006-05-29
Publication date: 2008-04-23
Anticipated expiration: 2026-05-29
Also published as: US7527035B2; WO2007009829A1; DE102005033638A1; JP2009501867A; CN101223353A; DE502006004328D1; EP1913255B1; US20080184969A1

Abstract

A fuel supply system comprises a piston pump (6) having a working chamber (104) and an adjustable throttle device (20), arranged upstream of the working chamber (104) and adapted to modify the flow of fuel supplied to the working chamber (104). The invention is characterized in that the throttle device (20), in the closed position, allows a leakage volume to arrive at the working chamber (104). The piston pump (6) comprises a leakage pump device (113) which supplies at least a part of the leakage volume from the working chamber (104) to a low-pressure zone (8) located upstream of the throttle device (20).

Description

Fuel delivery device, in particular for an internal combustion engine

State of the art

The invention relates to a fuel delivery device, in particular for an internal combustion engine, according to the preamble of claim 1.

DE 10220 281 A1 describes a fuel system for an internal combustion engine, in which

Fuel is conveyed from a prefeed pump to a high-pressure pump and from there into a high-pressure fuel rail. To this several injectors are connected, which inject the fuel directly into combustion chambers of the internal combustion engine. The flow rate of the mechanically driven by the engine high pressure pump is effected by a fluidically upstream throttle device. To limit the production effort, is the

Throttle device designed so that it even in completely closed state through a certain amount of leakage of fuel. This is returned to a low-pressure region via a zero-delivery line, in which a zero-feed throttle is present, so it does not reach the actual piston pump.

The present invention has the object, a fuel delivery device of the type mentioned in such a way that it builds as simple as possible.

This object is achieved by a fuel delivery device with the features of claim 1. Advantageous developments are specified in subclaims. Advantages of the invention

In the case of the fuel delivery device according to the invention, it is expressly permitted that the leakage quantity of fuel passed by the throttle device reaches into the working space of the piston pump. Thus can be dispensed with the previously required Nullforderleitung and arranged therein Nullforderdrossel, which greatly simplifies the construction of the fuel delivery device according to the invention. This also saves costs.

In order nevertheless to ensure that, for example, in overrun operation of an internal combustion engine, for which the fuel delivery device is provided, no fuel from the piston pump, according to the invention a special leakage pump means is provided by the leakage amount at least partially from the working space to an upstream of the Throttle device located low pressure range is conveyed away. This may for example be immediately upstream of an inlet valve of the piston pump, so that the fuel delivery device is very compact and additional long lines are not required.

If the return of the leakage amount flows upstream of a filter, abrasion generated during operation of the piston pump is reliably kept away from the piston pump, the throttle device and other valve device, which improves the service life and reliability of the fuel delivery device according to the invention.

Particularly simple and with little additional effort, the leakage pump device can be realized by the pump piston of the piston pump itself and the guide gap between the pump piston and the pump housing. One reaching the workroom

Leakage amount is simply removed in this case by the pressure difference between the working space and the drive side of the pump piston. In this case, a good efficiency of the fuel delivery device is maintained when the guide gap is formed so that when the throttle device is closed, just the leakage amount of the throttle device is conveyed back to the low pressure area.

The fuel delivery device usually conveys into a high-pressure space, for example a high-pressure rail. To easily in certain operating situations one To allow pressure reduction in this high-pressure chamber, this can be connected via a fluidically parallel to an outlet valve of the piston pump throttle with the working space of the piston pump. In this way, it is possible to dispense with a separate pressure relief valve on the high-pressure chamber, which further simplifies or reduces the construction and the corresponding costs of the fuel delivery device according to the invention.

For a reliable operation of the fuel delivery device according to the invention, it makes sense if the opening differential pressure of an inlet valve of the piston pump is at least about 1 bar, since in this case the formation of fuel vapor due to pressure pulsations during operation of the piston pump between the throttle device and the inlet valve is prevented.

The leakage amount is kept low overall by a control opening is not present at the throttle valve but at the throttle body at a throttle device with a throttle slide. The guide gap between throttle slide and throttle housing should be less than or equal to the guide gap between pump piston and pump housing. Typical values are 4 or 7 μm.

In order to avoid unnecessary pressure build-up in the high-pressure chamber, the leakage quantity of the throttle device should be smaller than the fuel requirement of an internal combustion engine when idling, ie if only a minimal amount of fuel is injected into the combustion chambers of the Brennkrafhnaschine.

drawings

Hereinafter, particularly preferred embodiments of the present invention will be explained with reference to the accompanying drawings. In the drawing show:

FIG. 1 is a schematic representation of a first exemplary embodiment of a fuel

Conveyor and a Brennkraftmaschine; - A -

Figure 2 is an enlarged view of a portion of the fuel delivery device of Figure 1;

Figure 3 is a diagram in which a pressure difference across a pump piston of the conveyor of Figure 1, a piston stroke and a leakage amount of a

Throttle device are applied over the angle of a drive shaft;

Figure 4 is a view similar to Figure 1 of an alternative embodiment of a

Fuel-conveying device; and

Figure 5 is an enlarged view of a portion of the fuel conveyor of

FIG. 4.

Description of the embodiments

In FIG. 1, a first embodiment of a fuel delivery device bears the reference numeral 1 as a whole. It comprises a fuel reservoir 2 from which a prefeed pump 3 conveys the fuel via a line 4 to a high-pressure pump unit 10. This includes a throttle device 20 and a high-pressure piston pump 6. The throttle device 20 is fluidly arranged between the prefeed pump 3 and the high-pressure piston pump 6, and it regulates the low pressure side, the flow rate of the high-pressure piston pump 6. The latter is in the present embodiment via a cam 30th driven, which in turn is mechanically driven in a manner not shown in Figure 1 by an internal combustion engine 7, for example, from the cam or crankshaft. The cam 30 may also be part of the cam or crankshaft.

The high-pressure piston pump 6 compresses the fuel supplied to a relatively high pressure and delivers it via a line 5 in a high-pressure chamber 40. In this, the fuel is stored under high pressure, it is also "high-pressure accumulator" or

Called "Rail". To the high-pressure chamber 40, a plurality of injectors 41 are connected, which inject the fuel directly into each associated combustion chambers 42. The pressure prevailing in the high-pressure chamber 40 is detected by a pressure sensor 43. The speed of a not shown crankshaft of the engine 7 is detected by a speed sensor 44, a temperature of the engine 7 via a temperature sensor 45. A control and regulating device 46 controls or regulates inter alia the operation of the throttle device 20, wherein in the control or Control the signals of the sensors 43, 44 and 45, and possibly also other sensors, flow. A computer program for controlling the throttle device is stored on a storage medium 47 of the control and regulating device 46.

Reference is now made to Figure 2, in which the high-pressure pump unit 10 is shown enlarged. Upstream of the throttle device 20, a filter 101 is disposed in the high-pressure pump unit 10 and a pressure damper 102 is arranged in a channel 8 belonging to a low-pressure region. By the latter, pulsations of the high-pressure piston pump 6 are to be damped, for example, in the line 4. Furthermore, he should ensure a high degree of delivery of the high-pressure piston pump 6, even at high rotation and cam numbers.

The throttle device 20 comprises a cylindrical throttle slide 201 and a cylindrical throttle housing 202. The throttle slide 201 is actuated by an electromagnetic actuator 203, against which the throttle slide 201 is acted upon by a compression spring 204. The throttle valve 201 has a smaller diameter portion (not numbered) through which an inlet space 205 is formed between the throttle valve 201 and the throttle body 202. At the throttle slide 201, a circumferential control edge 206 is present, which cooperates with control openings 207 formed on the throttle housing 202. Via a connection 208, these lead to the high-pressure piston pump 6. Between the throttle slide 201 and the throttle housing 202, a guide gap 209 is present.

The high-pressure piston pump 6 in turn comprises an inlet valve 103, via which the fuel can pass from the connection 208 of the throttle device 20 to a working space 104 which is formed between a pump piston 105 and a pump housing 106. The pump piston 105 is connected to a drive space in which the cam 30 is disposed via a

Piston seal 107 sealed. From the working space 104 to the high pressure chamber 40, the fuel passes through an outlet valve 108. Parallel to this, but with opposite opening direction is between the working space 104 and high-pressure chamber 40 a Pressure relief valve 109 is arranged. This is closed during normal operation of the fuel conveyor 1.

Fluidic parallel to the throttle device 20 and the high-pressure piston pump 6, a bypass valve 110 is still arranged in the high-pressure pump unit 10, which connects the high-pressure chamber 40 with the located between the filter 101 and pressure damper 102 channel 8 and opens to the high-pressure chamber 40. This bypass valve 110 is closed during normal operation. In the event of a fault, for example, when the throttle device 20 is stuck in the closed position, however, fuel can pass into the high-pressure chamber 40 via this bypass valve 110, so that at least the pressure generated by the prefeed pump 3 prevails therein, which allows a certain emergency operation of the internal combustion engine 7.

Between the pump piston 105 and the pump housing 106, a guide gap 111 is present. Immediately before the piston seal 107 branches from the guide gap 111 from a leakage line 112, which leads to the low pressure region 8 immediately upstream of the filter 101. The mouth of the leakage line 112 is therefore covered by the pump piston 105, whereas the coming of the inlet valve 103 into the working space 104 and the outgoing from the working space 104 to the outlet valve 108 mouth of the pump piston 105 are always free.

In normal operation, the prefeed pump 3 generates a prefeed pressure in the amount of about 6 bar. Depending on the position of the throttle slide 201 of the throttle device 20 and depending on the corresponding coverage of the control edge 206 with the Steueröfihungen 207 passes more or less fuel to the high-pressure piston pump 6. During the suction phase, the fuel is sucked into the working space 104 via the inlet valve 103. Depending on the throttling, more or less steam is produced in the working space 104. In this way, the delivery rate of the high-pressure piston pump 6 is set to the high-pressure chamber 40. It should be noted that in the present embodiment, the throttle device 20 is "normally closed", which means that the throttle slide 201 is pressed in the closed position with electroless electromagnetic actuator 203 of the compression spring 204. In order to avoid the formation of fuel vapor between the port 208 and the intake valve 103, its opening differential pressure is about 1 bar. When using diesel fuel that has a different vapor pressure, the opening differential pressure can also be significantly smaller. Even in the closed position of the throttle device 20, however, fuel can pass through the guide gap 209 between throttle slide 201 and throttle housing 202 and on via the inlet valve 103 in the working space 104 of the high-pressure piston pump 6. In order nevertheless to prevent the pressure in the working space 104 from reaching a level at which the outlet valve 108 opens and fuel enters the high-pressure space 40, this quantity of fuel, also referred to as "leakage quantity", from the working space 104 is removed from the working space 104 via a leakage pump 113 conveyed away.

In the present exemplary embodiment, this leakage pump device 113 is formed simply by the pump piston 105 and the guide gap 111 between pump piston 105 and pump housing 106. This is in fact dimensioned so that in a delivery stroke of the pump piston 105 just reached when the throttle device 20 into the working space 104 leakage fuel quantity due to the pressure difference between the working space 104 and the prevailing directly before the piston seal 107 prefeed over the

Leakage line 112 is conveyed away. Functionally, the previously known "zero-feed throttle" is thus formed by the guide gap 111.

In this way, a zero promotion of the high pressure piston pump 6 can be reliably realized. Such is desirable, for example, when the internal combustion engine 7, which serves to drive a motor vehicle, is in a coasting operation, in which the cam 30 is driven, but no fuel reaches the combustion chambers 42 via the injectors 41. In order to avoid an undesirable increase in pressure in the high-pressure chamber 40 in such a case, and to be able to dispense with a separate pressure relief device, it must be ensured that the delivery of fuel through the high-pressure piston pump 6 can be completely prevented. This is also possible with a throttle device 20, which is not completely closed in the closed state, thanks to the provided leakage pump device 113.

For this purpose, it is necessary, the guide gap 209 of the throttle device 20 and the

Guide gap 111 of the high-pressure piston pump 6 to match so that the leaked by the throttle device 20 leakage amount is pumped back by means of the pumping movement of the pump piston 105 via the guide gap 111, without being in the Working space 104 of the opening pressure of the exhaust valve 108 is reached at a very specific pressure in the high-pressure chamber 40. This very specific pressure in the high-pressure chamber 40 can be, for example, a pressure at which the injectors 41 can still inject the fuel safely into the combustion chambers 42. FIG. 2 shows the course of the leakage flow through arrows 114.

The functional principle of the leakage pump device 113 can also be seen from the diagram of FIG. It can be seen that in each case in the region of the top dead center of the pump piston 105 (the stroke of the pump piston 105 is represented by the curve 115) in the working space 104, a "pressure mountain" is formed (curve 116). A zero promotion of the high pressure piston pump 6 is present when the maximum pressure of this pressure mountain is at most equal to the current pressure in the high pressure chamber 40. This is only guaranteed if the total amount of leakage that is passed by the throttle device 20, from the leakage pump 113th is dissipated. Otherwise, the pressure in the working space 104 would increase with each cycle of the high-pressure piston pump 6 until the outlet valve 108 finally opens.

The amount of leakage discharged from the leakage pump device 113 via the guide gap 111 is represented by the curve 117. It can be seen that, in the case of the high pressure prevailing in the region of top dead center, a relatively large amount of leakage passes through the guide gap 111 and is discharged from the leakage line 112. Outside the top

However, dead center of the pump piston 105 prevails in the working space 104 partly a lower pressure than in the channel or low pressure region 8, so that even a certain, but very small amount of fuel flows back through the guide gap 111 into the working space 104. A typical vote is that the guide gap 111 has a value of 7 microns, the guide gap 209, however, has a value of 4 microns.

In order to realize operating conditions of the internal combustion engine 7, in which a reduced pressure is desired in the high pressure chamber 40, for example, at idle, the leakage amount of the throttle device 20 should be smaller than the fuel demand of the engine 7 in the idle. This is due to the fact that at such a low pressure in the high pressure chamber 40, the outlet valve 108 opens even at a correspondingly low pressure, so that the maximum pressure in the working chamber 104 also corresponds at most to the reduced pressure in the high pressure chamber 40. With such a However, the reduced pressure also decreases the pressure difference across the guide gap 111, which reduces the "delivery rate" of the leakage pump device 113. Optionally, due to this reduction of the pressure difference across the guide gap 111, even the entire amount of leakage transmitted from the throttle device 20 could be delivered from the high pressure piston pump 6 to the high pressure space 40. Therefore, as stated, this leakage quantity should at most correspond to the fuel demand of the engine 7 when idling.

The pressure in the high-pressure chamber 40 can be lowered by injecting more fuel from the injectors 41 into the combustion chambers 42 than by the fuel delivery device 1 into the high-pressure chamber 40. This can be adjusted by means of the throttle device 20. It is understood that the maximum pressure in the high-pressure chamber 40, which adjusts itself in the overrun mode of the internal combustion engine 7, should in principle not be greater than a pressure at which the injectors 41 are still working reliably. If such a lowering of the pressure in the high-pressure chamber 40 is not possible, this must be compensated by a correspondingly changed control of the injectors 41.

In the event of a fault, for example, if the throttle device 20 is stuck in the open state, the pressure in the high pressure chamber 40 is limited by the pressure relief valve 109 to a certain maximum value.

Incidentally, it should be noted that in the particularly advantageous embodiment described above, the guide gap 111 operates as a flow restrictor between the working space 104 and the leakage line 112. Conceivable, but not shown, but is also that the leakage line branches off directly from the working space 104 and in her a separate flow restrictor is present, which takes over the hydraulic function of the guide gap 111. However, if the guide gap 111 operates as a flow restrictor, this has the advantage that a variable throttling action can be realized which is lowest at bottom dead center of the pump piston 105 and greatest at top dead center.

An alternative embodiment of a fuel delivery device 1 is shown in FIGS. 4 and 5. In this carry such elements and areas, which equivalent functions to elements and areas described in connection with Figures 1 to 3 Embodiment, have the same reference numerals. They are not explained again in detail.

In the case of the fuel delivery device 1 shown in FIGS. 4 and 5, the delivery rate of the prefeed pump 3 can be adjusted. In this way, the pressure in the line 4 and in the

Low pressure range 8 can be set according to a desired form. For this purpose, the prefeed pump 3 is controlled by the control and regulating device 46. This has the advantage that the prefeed pump 3 is always operated with the lowest possible power. On the other hand, an adjustable pre-pressure has the advantage that the control sensitivity of the throttle device 20 is improved. The pressure difference at the throttle device 20 can be adjusted optimally with adjustable admission pressure as a function of load and speed of the internal combustion engine 7. In addition, an increased fuel temperature or a higher vapor pressure can be compensated.

A variable pre-pressure can also be used to reduce the amount of leakage

Throttle device 20 and thus the self-adjusting high pressure in the high pressure chamber 40 to control or regulate. If, for example, the intake pressure is lowered in the overrun mode of the internal combustion engine 7, the leakage quantity of the throttle device 20 is also reduced, since the pressure difference at the guide gap 209 decreases to the same extent. With smaller leakage amount at the guide gap 209 of the throttle device 20 is in overrun the

Internal combustion engine 7 also a lower pressure in the high-pressure chamber 40 a. Conversely, this means that with an adjustable form the requirements for the throttle device 20 can be reduced in terms of control sensitivity and allowable leakage amount. Thus, e.g. the guide gap 209 are increased, whereby the production is simplified.

Another difference between the exemplary embodiment of a fuel delivery device 1 shown in FIGS. 4 and 5 and the previous exemplary embodiment is that a flow throttle 118 is arranged parallel to the outlet valve 108. This allows a "passive" pressure reduction in the high-pressure chamber 40. In overrun the

Internal combustion engine 7 or when stopped internal combustion engine 7 can be reduced in this way via the flow restrictor 118 and the guide gap 111 of the high pressure piston pump 6, the pressure in the high pressure chamber 40 to the pressure prevailing in the low pressure region 8 pressure. In particular, in the overrun mode of the internal combustion engine 7, the pressure in the high-pressure chamber 40 can be lowered to a desired value and regulated by means of the variable admission pressure so that it is ideal for resuming the injection of the injectors 41.

Should it be in the overrun mode of the internal combustion engine 7 to an unsteady suction of

Leakage amount come, which is passed by the throttle device 20, because the vapor pressure between port 208 and inlet valve 103 is exceeded, thus a threatening step-like increase in the pressure prevailing in the high-pressure chamber 40 through the throttle 118 is avoided.

In an exemplary embodiment which is not illustrated, the fuel delivery device comprises a high-pressure piston pump with a plurality of pump pistons and work spaces arranged fluidically parallel to one another. Also in this case, the metering of the fuel can take place via a throttle device. When designing the guide gaps, however, the guide gaps of all pump pistons must be taken into account.

Claims

claims

First fuel conveyor (1), in particular for an internal combustion engine (7), with a piston pump (6) having a working space (104), and with an adjustable throttle device

(20), which is arranged upstream of the working space (104) and can change the flow of fuel to the working space (104), characterized in that the throttle device (20) in the closed state, a leakage amount in the working space (104), and that the piston pump (6) has a leakage pump device (113) which conveys the leakage quantity at least partially from the working space (104) to a low-pressure region (8) located upstream of the throttle device (20).

2. Fuel delivery device (1) according to claim 1, characterized in that the leakage pump device (113) comprises a pump piston (105) of the piston pump (6) and a throttle channel (111), the working space (104) with the low-pressure region (8 ) connects.

3. Fuel delivery device (1) according to claim 2, characterized in that the throttle channel is formed by a guide gap (111) between the pump piston (105) and a pump housing (106).

4. Fuel delivery device (1) according to claim 3, characterized in that the guide gap (111) is formed so that when the throttle device (20) just the

Leakage amount of the throttle device (20) to the low pressure region (8) is fed back.

5. Fuel conveyor (1) according to one of the preceding claims, characterized in that a high-pressure chamber (40) into which the piston pump (6) via an outlet valve (108) promotes, with the working space (104) of the piston pump (6). is connected via a to the outlet valve (108) fluidically parallel throttle (118).

6. Fuel delivery device (1) according to one of the preceding claims, characterized in that the Öffiiungsdifferenzdruck a fluidically between the throttle device (20) and the working space (104) arranged inlet valve (103) is approximately 1 bar.

7. Fuel delivery device (1) according to one of the preceding claims, characterized in that the throttle device (20) comprises a throttle slide (201) which is guided in a throttle housing (202), and that at least one control opening (207) of the throttle device (20) is provided in the throttle body (202).

8. Fuel delivery device (1) according to claims 3 and 7, characterized in that a guide gap (209) between throttle slide (201) and throttle housing (202) is smaller than or equal to the guide gap (111) between the pump piston (105 ) and pump housing (106).

9. Fuel delivery device (1) according to claim 8, characterized in that the guide gap (209) between throttle slide (201) and throttle housing (202) about 4μm and the guide gap (111) between the pump piston (105) and pump housing (106) approximately 7μm is large.

10. Fuel conveyor (1) according to one of the preceding claims, characterized in that the leakage quantity is smaller than the fuel requires an internal combustion engine (7) at idle, which is fed by the fuel delivery device (1) at least indirectly.

11. Fuel delivery device (1) according to one of the preceding claims, characterized in that it comprises a filter (101), and that the leakage quantity is conveyed to an area upstream of the filter (101).

12. Fuel delivery device according to one of the preceding claims, characterized in that it comprises a plurality of fluidically parallel pump pistons and work spaces.