WO2004027250A1

WO2004027250A1 - Fuel injection unit for internal combustion engines

Info

Publication number: WO2004027250A1
Application number: PCT/DE2003/000878
Authority: WO
Inventors: Achim Koehler; Sascha Ambrock
Original assignee: Robert Bosch Gmbh
Priority date: 2002-09-13
Filing date: 2003-03-18
Publication date: 2004-04-01
Also published as: DE10242591A1

Abstract

A fuel injection unit, in particular, a common rail fuel injection unit is disclosed, whereby possible leakage amounts from a measuring unit (37) are drained into a second throttle (28) on the pressure side of the high pressure fuel pump (17).

Description

Fuel injection system for internal combustion engines

State of the art

The invention relates to a fuel injection system for an internal combustion engine, in particular a common-rail fuel injection system, with a high-pressure fuel pump with at least one pump element and with a pre-feed pump, the Vorförderpu pumping fuel from a tank to the suction side of the pump element (s) and with the pre-feed pump delivered fuel amount is passed through a metering unit to the high-pressure fuel pump.

Under unfavorable circumstances, it can happen with these fuel injection systems that an undesirable pressure builds up on the pressure side of the high-pressure fuel pump. This can, for example

Internal combustion engine occur if the metering unit is not 100% tight. The amount of leakage flowing through the metering unit is put under high pressure in the high-pressure fuel pump and leads to an undesirable one Rise in rail pressure. If the control unit detects one. strong deviation between the target rail pressure and the actual rail pressure. B. an emergency driving program can be activated. This emergency driving program can, for example, switch off the internal combustion engine by the

Protect the fuel injection system from damage caused by impermissibly high pressures in the rail.

Advantages of the invention

In a fuel injection system according to the invention for an internal combustion engine, in particular for a common-rail fuel injection system, with a control unit, with. a high-pressure fuel pump, with at least one pump element and with a prefeed pump, the

Pre-feed pump conveys fuel from a tank to the suction side of the pump element (s) and the amount of fuel delivered by the pre-feed pump is passed through a metering unit to the pump element (s) between the pressure side

High-pressure fuel pump and a low-pressure area of the fuel injection system means for discharging a leak.

These means for discharging a leak can effectively prevent the undesirable build-up of pressure when the internal combustion engine is in overrun mode and thus ensure that the internal combustion engine is not switched off.

The means according to the invention for discharging a leak can be designed as an orifice or throttle. The following is related to. the invention uses only the term "choke". However, we always mean both Chokes as well as orifices.

In an advantageous variant of the invention, the means for discharging a leak are designed as a 2-way flow control valve, so that the amount of leakage is independent of that on the pressure side of the

High pressure fuel pump pressure is kept almost constant and thus that of the

High pressure fuel pump work to be performed is minimized.

In a particularly advantageous embodiment of the invention, the flow through the 2-way flow control valve is electrically adjustable, so that the 2-way flow control valve according to the invention is controlled by a control unit

Fuel injection system can be controlled and thus the operating behavior of the 'fuel injection system according to the invention is further improved.

In this embodiment of the invention

The fuel injection system can also optimize the control concept of the fuel injection system if there is no coasting operation as follows:

The delivery rate of the

High-pressure fuel pump specified depending on the operating point of the internal combustion engine. The pressure prevailing in the common rail can then be adjusted very precisely and sensitively by means of the electrically controllable 2-way flow control valve, so that the quality of the pressure control in the pressure range of the fuel injection system according to the invention is further improved by suitable control of the 2-way flow control valve. This leads to improved operating, consumption and Emission behavior of the internal combustion engine and can be realized without additional technical and financial effort. It has proven to be advantageous if the 2-way flow control valve according to the invention can discharge a flow rate between 0.1 l / h to 50 l / h.

Alternatively, the 2-way flow control valve can also be designed as a hydraulically controlled valve and a control piston guided in a housing with a

Have measuring throttle, wherein the hydraulic forces acting on the control piston are absorbed by a compression spring, which is supported at one end against the control piston and at the other end against the housing, and wherein the control piston has a control edge which the

Control throttle more or less closes depending on the hydraulic forces acting on the control piston.

Alternatively, the control piston can have a control needle instead of a control edge, which closes the control throttle more or less depending on the hydraulic forces acting on the control piston.

Both embodiments have in common that the amount of leakage is kept constant almost independently of the pressure prevailing on the pressure side of the high-pressure fuel pump, and thus the energy losses resulting from the removal of the amount of leakage from the high-pressure area of the fuel injection system according to the invention are minimized.

It has also proven to be advantageous if the Measuring throttle is arranged upstream of the control throttle.

In a further addition to the invention, the control piston is brought into contact with a paragraph fixed to the housing by the compression spring in the unpressurized state and closes the paragraph, so that the 2-stage flow control valve according to the invention only opens when a certain pressure is reached and thus the pressure builds up the commissioning of the fuel injection system according to the invention is improved.

If the shoulder covers part of an end face of the control piston which is pressurized by fuel, the pressure above which the 2-way flow control valve according to the invention opens can be increased further.

Depending on the space available, the means for discharging a leak can be arranged on the common rail or the high-pressure fuel pump of the fuel injection system according to the invention.

Further advantages and advantageous refinements of the invention can be found in the following drawing and its description.

drawing

Show it:

Figure 1 shows an embodiment of a fuel injection system according to the invention and

Figures 2 to 4 embodiments of adjustable chokes according to the invention.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS An exemplary embodiment of a common rail injection system according to the invention is shown schematically in FIG. A prefeed pump 1 draws fuel (not shown) from a tank 5 via an inlet line 3. The fuel is filtered in a filter 7.

The prefeed pump 1 can be designed, for example, as a gear pump and has a first pressure relief valve 11. On the suction side, the pre-feed pump 1 is throttled by a first throttle 13. A print page 15 of the

Pre-feed pump 1 supplies a high-pressure fuel pump 17 with fuel. The high-pressure fuel pump 17 is designed as a radial piston pump with three pump elements 19 and drives the prefeed pump 1. A suction valve 21 is provided on the suction side of the pump elements 19. A check valve 23 is provided on the pressure side of the pump elements 19, which prevents the fuel under high pressure, which was pumped into a common rail 25 by the pump elements 19, from flowing back into the pump elements 19. A pressure sensor 26 is provided on the common rail 25 and is used for pressure control.

The high-pressure lines of the fuel injection system are shown in FIGS. 1 and 2 with thick lines, while the areas of the fuel injection system under low pressure are shown with thin lines. The common rail 25 supplies one or more in FIG. 1 not injectors illustrated with fuel via a respective high pressure line 27. An adjustable choke 28 can, if required, the pressure side of the high-pressure fuel pump 17 with a return line 29 connected via the return line 29 and a leakage line ^'31, the leakage and the control quantities of the injector or injectors, not shown in returned the tank 5.

The high-pressure fuel pump 17 is supplied by the prefeed pump 1 on the one hand via a fuel line 33 with fuel for the pump elements 19 and on the other hand via a supply line 35 with fuel for lubrication.

A 'metering unit 37 is arranged in the fuel line 33 and, together with the adjustable throttle 28, takes over the delivery rate control of the high-pressure fuel pump 17 and the pressure control of the Com on-Rail 25. The control concept is described in more detail below. The fuel line 33 opens into a

Distribution line 39 via which the pump elements 19 are supplied with fuel.

For removing leaks from the pump elements 19 and the one used to lubricate the high-pressure fuel pump 17

Fuel, one or more leakage lines 41 are provided, each with a third throttle 43. The leakage lines 41 open into the return line 29.

A check valve 45 and a fourth throttle 47 are provided in the supply line 35. A vent throttle 49 is provided upstream of the fourth throttle 47 and establishes a hydraulic connection between the supply line 35 and the return line. The Vent throttle 49 facilitates the restarting of the fuel injection system when the tank 5 has been run empty.

In push mode, i.e. For example, when driving a motor vehicle downhill, no fuel is to flow into the pump elements 19 and no fuel is to be injected into the combustion chambers of the internal combustion engine by the injectors (not shown). Since the metering unit 37 does not seal tightly in this operating state under unfavorable circumstances, fuel can reach the pump elements 19 via the fuel line 33 and the distribution line 39. As a result, without suitable remedial measures, a pressure would build up on the suction side of the pump elements 19 which is so great that the pump elements 19 open the suction valves 21 and suck in fuel during the suction stroke. This would have the consequence that the pressure in the common rail 25 rises inadmissibly.

In order to prevent this, the adjustable second throttle 28 is provided, which together with the metering unit 37 prevents the impermissible pressure build-up described above. The second throttle 28 allows fuel to flow from the pressure side of the pump elements 19 into the low-pressure region of the fuel injection system. The outflow of fuel through the second throttle 28 prevents the above-mentioned build-up of pressure on the pressure side of the pump elements 19 in push mode due to the leakage of the metering unit 37.

2a and b, a first embodiment of an adjustable throttle according to the invention in the form of a 2-way flow control valve 51 is shown schematically. The 2-way flow control valve 51 has a high pressure connection 53 , which is hydraulically connected, for example, to the common rail 25 or the pressure side of the high-pressure fuel pump 17 (see FIG. 1). The high-pressure connection 53 opens into a housing 55 of the 2-way flow control valve 51, in which a control piston 57 is guided with a measuring throttle 59.

The control piston 57 divides the interior of the housing 55 into a first part 61 and a second part 63. The first part 61 has the same pressure as on the pressure side of the high-pressure fuel pump 17 and in the common rail 25 (see FIG. 1), while in second part 63 there is a lower pressure. The pressure reduction takes place in the control throttle 59 when the fuel under high pressure flows from the first part 61 through the control throttle 59 into the second part 63 of the interior of the housing 55.

Because of the pressure difference between the first part 61 and the second part 63 of the interior of the housing 55, a hydraulic force acts on the control piston 57, which in the position shown in FIG. 2 presses it to the left against a compression spring 65. The compression spring 65 thus absorbs the hydraulic forces acting on the control piston 57.

A leakage discharge 67 starts from the second part 63 of the interior of the housing 55. The leakage discharge 61 is with the low pressure area of the fuel injection system (see FIG. 1) _. hydraulically connected. In the position of the control piston 57 shown in FIG. 2a, the control piston 57 releases the entire cross section of the leakage discharge 67. This is due to the fact that the pressure in the first part 61 or in the high-pressure connection 53 is comparatively low. When the pressure in the high-pressure connection 53 increases, the amount of leakage that flows through the measuring throttle 59 increases. As a result, the hydraulic force acting on the control piston 57 also increases and moves the control piston 57 further to the left in the position shown in FIG. 2b. As a result, a control edge 69 partially closes the leakage discharge 67, which leads to an increase in the flow resistance within the 2-way flow control valve 51. This limits the amount of leakage that flows from the high-pressure connection 53 into the leakage discharge 67. By a suitable dimensioning of the metering orifice 59, the spring stiffness of the compression spring 65 and the opening cross section of the leakage discharge 67, the leaks of can ^'ge, which according to the invention by the 2-way flow control valve flows 51, even if the pressure during operation of the fuel injection system can be kept almost constant Common Rail 25 is undergoing major changes.

FIG. 3 shows a further exemplary embodiment of a 2-way flow control valve 51 according to the invention. The same components are provided with the same reference symbols and the same applies with regard to FIGS. 2a and b accordingly. In this embodiment, the control edge 69 of the control piston 57 together with the

Leakage discharge 67 a control throttle 71, the cross section of which depends on the position of the control piston 57 relative to the leakage discharge 67.

In contrast to the exemplary embodiment according to FIGS. 2a and b, the control piston 57 rests on a shoulder 73 in the housing. The shoulder 73 closes the measuring throttle 59 in the control piston 57, so that in the state shown in FIG. 3 there is no leakage from the high-pressure connection 53 into the Leakage discharge 57 can reach. The compression spring 65 ensures that the control piston 57 is in contact with the shoulder 71. Only when there is such a high pressure in the first part 61 of the interior of the housing 55 that the pressure on the part of the housing not covered by the shoulder 73

End face 75 of the control piston 57 acting hydraulic force is greater than the contact pressure of the compression spring 65, the control piston 57 moves away from the shoulder 71. In the position of the 2-way flow control valve shown in FIG. 3, the control piston 57 then moves downward.

As soon as the control piston 57 is no longer in contact with the shoulder 71, fuel can flow from the first part 61 of the interior of the housing via the second part 63 thereof into the leakage discharge 67. From this moment on, the control behavior of the 2-way flow control valve according to the invention according to FIG. 3 is the same as that of the exemplary embodiment according to FIGS. 2a and b. Paragraph 71 therefore makes it possible to close the 2-way flow control valve 51 until a minimum pressure is reached.

4 shows a third exemplary embodiment of a 2-way flow control valve according to the invention. The main difference is that the control piston 57 does not have a control edge, but a control cone 75 which interacts with a sealing seat 77 in the housing 55. In this exemplary embodiment, the control throttle 71 is formed by the control cone 75 and the sealing seat 77. When the control piston 57 rests on the sealing seat 77, the 2-way flow control valve 51 according to the invention is closed. The same applies to the position of the control piston 57 shown in FIG. 4, in which it is pressed by the compression spring 65 against the stop 73 is and the stop 73 closes the measuring throttle 59 in the control piston 57.

5 shows the operating behavior of the 2-way flow control valves according to FIGS. 3 and 4 shown in diagram form. The pressure P _Rall in the common rail 25 or in the high-pressure connection 53 is plotted on the abscissa, while the flow rate Q per unit of time [1 / h] is plotted on the ordinate. Below a minimum pressure P _Ε . _n , the control piston 57 is still in contact with the

Stop 73 so that the amount of leakage Q is equal to 0 in this area. When the minimum pressure P _{min is reached} , the control piston 57 lifts off the shoulder 73 and fuel flows from the high-pressure connection 53 into the leakage discharge 67. After a maximum has been reached, the leakage quantity Q. drops rapidly with increasing pressure, which is due to the characteristic of the control throttle 71 is.

When a maximum pressure P is reached. closes the control piston 57 the leakage discharge 67, so that the

Flow through the 2-way flow control valve 51 is prevented. As a rule, the 2-way flow control valve will be designed in such a way that the minimum pressure P _{min is} slightly less than the minimum pressure of the injectors (not shown) of the fuel injection system and that the maximum pressure P _mav is selected so that when the internal combustion engine is in overrun, it is also below In the most unfavorable circumstances, the leakage quantities that occur are safely discharged and, during normal operation of the internal combustion engine, the 2-way flow control valve according to the invention closes again, if possible, at low pressures P _^ .., since the efficiency of the fuel injection system increases when the leakage discharge 67 is closed.

Claims

Expectations

1. Fuel injection system for an internal combustion engine, in particular a common rail fuel injection system, with a high-pressure fuel pump (17), with at least one pump element (19) and with a prefeed pump (1), the prefeed pump (1) fuel from a tank (5) to the suction side of the pump element (s) (19) and the quantity of fuel delivered by the prefeed pump (1) is passed through a metering unit (37) to the pump element (s) (19), characterized in that between the pressure side of the high-pressure fuel pump (17) and a low pressure area of the fuel injection system are provided with means for discharging a leak (28, 51).

2. Fuel injection system according to claim 1, characterized in that the means for discharging a leak are designed as an orifice or throttle (28)

3. Fuel injection system according to claim 1, characterized in that the means for discharging a leak are designed as a 2-way flow control valve (51).

4 .. Fuel injection system according to one of claims 1 to 3, characterized in that the flow through the throttle (28) or the 2-way flow control valve (28, 51) is electrically adjustable.

5. Fuel injection system according to claim 3, characterized in that the 2-way flow valve (51) has a control piston (57) guided in a housing (55), that a measuring throttle (59) is provided in the control piston (57), that a control throttle (71) cooperating with the control piston (57) is provided in the housing (51), that the hydraulic forces acting on the control piston (57) are generated by a compression spring (65), which at one end opposes the control piston (57) and supported at the other end against the housing (51), and that the control piston (57) has a control edge (69) which more or less closes the control throttle (71) as a function of the hydraulic forces acting on the control piston (57).

6. Fuel injection system according to claim 3, characterized in that the 2-way flow valve (28) has a control piston (57) guided in a housing (51), that a measuring throttle (59) is provided in the control piston (57) A control throttle (67) is provided in the housing (51) so that the hydraulic forces acting on the control piston (57) are supported by a compression spring (65), which is supported at one end against the control piston (57) and at the other end against the housing (51) , and that the control piston () has a control cone (77) which closes the control throttle (67) more or less depending on the hydraulic forces acting on the control piston (57).

7. Fuel injection system according to claim 5 or 6, characterized in that the measuring throttle (57) is arranged upstream of the control throttle (71).

8. Fuel injection system according to one of claims 5 to 7, characterized in that the control piston (57) from the compression spring (65) in the depressurized state is brought into abutment with a shoulder (73) fixed to the housing, and that the shoulder (73) Measuring throttle () closes.

9. The fuel injection system according to claim 8, characterized in that the shoulder (73) covers part of an end face (75) of the control piston (57) which is acted upon by pressurized fuel.

10. Fuel injection system according to one of the preceding claims, characterized in that the means for discharging a leak (28, 51) on the common rail (25) or the high-pressure fuel pump (17) are arranged.