WO2010049203A1

WO2010049203A1 - High-pressure fuel pump for an internal combustion engine

Info

Publication number: WO2010049203A1
Application number: PCT/EP2009/061724
Authority: WO
Inventors: Bernd Schroeder; Berthold Pfuhl
Original assignee: Robert Bosch Gmbh
Priority date: 2008-10-28
Filing date: 2009-09-10
Publication date: 2010-05-06
Also published as: KR20110074892A; CN102197213A; EP2344750A1; DE102008043237A1

Abstract

The invention relates to a high-pressure fuel pump (10) for an internal combustion engine (9) with direct injection, comprising a low-pressure region (12) and a quantity control device (28). The quantity control device (28) comprises a control valve that is arranged upstream from an inlet valve (22) of the high-pressure fuel pump (10) and has a first control position and at least one second control position which differ in the flow-restriction effect thereof.

Description

description

title

High-pressure fuel pump for an internal combustion engine

State of the art

The invention relates to a high-pressure fuel pump for a direct injection internal combustion engine according to the preamble of claim 1. In addition, the invention relates to a method for operating a high-pressure fuel pump for a

Internal combustion engine with direct injection, a control and / or regulating device and a computer program according to the preamble of the corresponding independent patent claim.

Today's fuel systems for internal combustion engines with direct injection usually have a quantity-controlled high-pressure fuel pump in an input range (low pressure range), wherein the volume control is essentially carried out by a speed-synchronous operation of an intake valve of the high-pressure fuel pump. This allows a very precise quantity control. The switching times of the quantity control valves used for this purpose are very short due to the speed-synchronous control. Furthermore, a pressure sensor in a high pressure range is used for flow control. A control and / or regulating device compares an actual pressure with a desired pressure in the high-pressure region and, if necessary, corrects the control for the quantity control valve.

From EP 0 299 337 A2, EP 0 837 986 B1, EP 0 974 008 Bl and DE 196 12 413 Al devices for controlling the fuel pressure are already known. From DE 103 27 411 Al a pressure relief valve for a high-pressure fuel pump is known.

Disclosure of the invention The object of the invention is to provide or further develop a fuel high-pressure pump for an internal combustion engine of the type mentioned, which works reliably and is compact. In addition, the fuel high-pressure pump should be inexpensive.

The object is achieved by a high-pressure fuel pump for an internal combustion engine with the features of claim 1, and with a method for operating a high-pressure fuel pump for an internal combustion engine, a control and / or regulating device and a computer program according to the features of the respective independent patent claim , Features which are important for the invention can also be found in the following description and in the drawing, wherein the features, both alone and in different combinations, can be important for the invention without any explicit reference being made thereto. Advantageous developments can be found in the subclaims.

By the invention, the fuel system is considerably simplified and inexpensive. In the simplest case, a quantity control device with two switching positions is sufficient for this purpose. The two switch positions usually represent a partial delivery position with weakened, more throttled fuel mass flow and a full delivery position with a substantially unimpeded or unthrottled fuel mass flow. The realization of more than two stages, for example, for a fuel delivery of a small amount, a middle subset and a full load amount is possible if necessary. A control of the switch valve is done by a simple design control loop, which causes a switchover depending on an easily determinable operating size from the field of high-pressure fuel pump. So it only has to be recognized whether in the more throttling switch position, a flow rate of fuel is still sufficient or whether it must be switched to a less throttling switching position. On the other hand, it must be recognized in the less strong throttling switching position that the delivery rate of fuel at partial delivery is sufficient for the current operation and thus can be switched to the more throttling switching position. These decisions can be made in an easy to configure and thus inexpensive control and / or regulating device.

It is proposed that the switching valve comprises an electromagnetic actuator. The actuation of the switching valve via an actuator of an electromagnet is a reliable and inexpensive solution. In this case, the switching valve for each direction of movement to be associated with an electromagnet; but it can also be only an electromagnet when switching against a spring force of a spring After switching off, the spring force returns the actuator to its original position. In a quantity control device with two switching positions, this solution is particularly advantageous. Since the switching can be carried out comparatively slowly, there are only low demands on the switching time, which can be sufficiently solved via the switching valve with solenoid. Thus, both the switching valve and an associated electric power amplifier can be relatively simple. This is also cost-cutting and saves installation space. Since the switching takes place only sporadically with low switching speed, the noise due to switching is low.

It is also proposed that the switching valve in the unactuated state is in the switching position with the lowest throttle effect. For example. may occur in case of failure, an interruption of the control line to the switching valve. Even a failure of the power amplifier in a control unit is possible. In these cases of error, a control of the switching valve is no longer possible, it is "unactuated" or "de-energized". Due to the measure according to the invention, despite such a fault, an (emergency) operation of the internal combustion engine is still possible.

Alternatively, it is proposed that the switching valve in the unactuated state is in a switching position with increased throttle effect. Is there a focus in operating the

High-pressure fuel pump on a consumption optimization in the internal combustion engine, so in addition to the mechanical drive line of the high pressure pump and the electrical power of the switching valve must be considered in the error described above. If the internal combustion engine is primarily operated at partial load (and this is predominantly the case with an average driving style), the energy consumption can be reduced by the proposed measure.

In addition, it is proposed that the throttling effect in a switching position is designed so that it allows a volume flow of about 10-20% of the maximum volume flow. The interpretation of the throttle effect in the partial delivery position should be such that the drive power of the high-pressure fuel pump for a given operating cycle in total is minimal. For motor vehicles can z. B. an MVEG cycle (European Driving Cycle for emission and consumption measurements on chassis dynamometers) are based. According to this cycle, only about 10 to 20 percent of the maximum flow rate of the high-pressure pump is needed on average and thus represents a dimensioning optimum. By said design of the throttle effect, a large part of the operating time of the internal combustion engine can be optimally covered in this switching position. It is also advantageous if the high-pressure fuel pump comprises a pressure regulating valve which connects a high-pressure region of the high-pressure fuel pump to a low-pressure region of the high-pressure fuel pump and can thus maintain the pressure in the high-pressure region at least substantially constant. In normal operation, in both positions of the switching valve, the delivery rate of the high-pressure pump may be greater than the quantity requirement of the internal combustion engine. To avoid damage from the high-pressure fuel pump and in particular to a fuel rail, the excess amount of fuel is returned by the proposed pressure control valve from the high pressure area in the low pressure area. The pressure in the

Fuel manifold thus depends essentially on an opening pressure of the pressure control valve.

In addition, it is proposed that the pressure control valve works purely mechanically / hydraulically, preferably a check valve. This is a particularly inexpensive, but effectively working solution, since a pressure sensor and an evaluation of the pressure sensor signals in a control and / or regulating device can be dispensed with. It is also proposed that the control of the switching valve by a signal of a pressure sensor, which detects a pressure prevailing in the high pressure region and / or a driving time of at least one injection valve depends. In the event of a pressure drop in the high-pressure region of the high-pressure fuel pump, an actual activation time of the injection valve must be extended in order to be able to inject the quantity of fuel required for optimal combustion of a fuel / air mixture into a combustion chamber of an internal combustion engine. If the pressure in the high pressure range rises, the ACTUAL activation time is shortened accordingly. The activation time can thus be regarded as a parameter for the pressure in the high-pressure range. Exceeding a predetermined upper or lower limit value of the activation time (S 0 LL activation time) is thus an indication of the changeover, which has the effect that in the low-pressure region the delivery rate of fuel is matched to the investigations in the high-pressure range. The control time is a known operating variable in the control and / or regulating device and can be easily evaluated. Thereby, a switching time for the switching valve can be determined easily and without much effort. However, the pressure in the high pressure range can also be determined by a sensor and then compared in the control and / or regulating device with an upper and lower pressure limit.

In addition, it is proposed that the actuation of the switching valve depends on a pump speed, a prefeed pressure and / or a fuel temperature. The Evaluation of these operating variables enables even more precise switching of the switching valve, saving energy and reducing fuel and emissions.

Brief description of the figures

An embodiment of the invention will be explained by way of example with reference to FIGS. Show it:

FIG. 1 is a schematic representation of a fuel system according to the invention;

injection;

Figure 2 is a schematic representation of the switching valve of Figure 1; and

3 shows a flowchart of the method according to the invention.

Detailed description

Figure 1 shows a schematic representation of a fuel system 8 for a

Internal combustion engine 9 with a high-pressure fuel pump 10. The fuel system 8 is, as will be explained, divided into a low-pressure region 12 shown on the left in FIG. 1 and a high-pressure region 14 shown on the right. A pre-feed pump 16 arranged in the low-pressure region 12 pumps fuel from a fuel reservoir 18 via a low-pressure line 20 with a prefeed pressure to an inlet connection 22 of the high-pressure fuel pump 10. In the high-pressure fuel pump 10, a filter 24 and a pressure damper 26 are arranged in the low-pressure region 12. The pressure damper 26 dampens pulsations arising in the high-pressure fuel pump 10 on the low-pressure side and ensures a high delivery rate even with high numbers of rotations and cams.

Via a switching valve 28 and subsequently an inlet valve 30, the fuel is sucked into a working chamber 32 of the high-pressure fuel pump 10. The switching valve 28 will be described later in detail. The volume of the working space 32 depends on the position of a pump piston 34 in a pump cylinder 36. During one

Downward movement of the pump piston 34, the working space 32 is increased, whereby fuel is sucked. During the upward movement of the pump piston 34, the fuel is highly compressed and via an outlet valve 38 and a for High-pressure region 14 belonging outlet port 40 via a high pressure line 42 further promoted in a rail 44. To the rail 44 injection valves 46 are connected, which inject the fuel directly into combustion chambers 48 of the internal combustion engine 9.

Since in a normal operation, the delivery rate of the high-pressure fuel pump 10 may be greater than the amount of fuel injected by the Einspitzventilen 46, the unneeded amount of fuel from the high pressure region 14 via a pressure control or pressure relief valve 50 is returned to the low pressure region 12. The pressure relief valve 50 may, for example, be designed as a check valve. The pressure in the high-pressure accumulator 44 then essentially corresponds to the opening pressure of the pressure-limiting valve 50. The pressure-limiting valve 50 is connected via a high-pressure line 52 to the high-pressure region 14 and via a low-pressure line 54 to the low-pressure region 12. Pulsations also occur in the high-pressure region 14, in particular when single-cylinder pumps are used, with multi-cylinder pumps also being used, but generating pulsations to a lesser extent. The pulsations affect the pressure control function negatively. For decoupling, a throttle 56 can be arranged hydraulically before (upstream) the pressure limiting valve 50, whereby the pulsations before the pressure limiting valve 50 are damped.

The pump piston 34 is driven by a cam 58 which is of the

Internal combustion engine 9 is driven - for example via a cam or crankshaft (not shown). The cam 58 may also be part of the cam or crankshaft. A sealing of the pump piston 34 to the cam 58 via a sealing element 60. A piston leakage, which arises in the gap between the pump piston 34 and the pump cylinder 36 is returned via a return line 62 in the low pressure region 12.

A control unit 64 controls the switching function of the switching valve 28 via a control line 66. Furthermore, the injection valves 46 are controlled via control lines 68 (in FIG. 1, only one line 68 is shown for the sake of simplicity). The

Internal combustion engine 9 further comprises a speed sensor 70, which detects the rotational speed of a crankshaft, not shown, and a temperature sensor 72, which detects an operating temperature of the internal combustion engine, such as a cylinder head temperature or a cooling water temperature. A computer program for performing the control of the switching valve 28 is stored on a storage medium 74 located in the control unit 64. The detailed construction and the function of the switching valve 28 will be explained in more detail with FIG. On the left side, the switching valve 28 is shown in a switching position "partial funding", on the right side in a switching position "full promotion". The switching valve 28 essentially comprises an actuator 76, which moves a switching element 78, and a spring element 80. The actuator 76 may be formed, for example, as an electromagnet or at least electromagnetically operated and operate in the energized state against the spring element 80. The switching element 78 has in Figure 2 in a lower region on a passage with a throttle 82 for the partial conveying. In addition, a passage 84 is arranged in FIG. 2 for a substantially uninfluenced full delivery.

As a parameter for the identification of the need for switching the switching valve 28, a drive time for the actuation of the injection valves 46 is used. It could also be used by a sensor, not shown, pressure in the rail 44. In the event of a pressure drop in the high-pressure region 14 of the high-pressure fuel pump 10, an actual activation time of the injection valve 46 must be extended in order to be able to inject the quantity of fuel required for optimal combustion of a fuel / air mixture into the combustion chamber 48 of the internal combustion engine 9. With a pressure increase in the high-pressure region 14, the actual activation time is shortened accordingly. Exceeding a predetermined upper or lower limit of the drive time (target drive time) is thus an indication of the changeover, which causes the

Flow rate of fuel in the low pressure range is adapted to the conditions in the high pressure range.

FIG. 3 shows a flowchart with the sequence of the method, in particular the method for adapting a switching time of the switching valve. The method is implemented in a computer program that runs in the control unit. In the query 100 it is determined whether the switching valve 28 is working in partial funding (switching position 82). If this is the case, an increase in a fuel quantity requirement in the high-pressure fuel pump 10 is detected in 110, for example, the actual activation times of the injection valves 46 are detected and evaluated. In 120 it is queried whether the current ACTUAL activation time has exceeded a predetermined upper DESIRED limit value. If this is the case, then in 130 the switching valve 28 is switched to full delivery (switching position 84). If this is not the case, then the next actual activation times are compared with the setpoint limit value.

If it is ascertained in the query 100 that the switching valve 28 is already operating in full delivery (shift position 84), a reduction in the fuel quantity requirement in the high-pressure fuel pump 10 is detected in FIG. 140, again by Detecting and evaluating the actual activation times of the injection valves 46. In 150 it is queried whether the current actual activation time has fallen below a predetermined lower setpoint limit value. If this is the case, then in 160 the switching valve 28 is switched to partial conveying (switching position 82). If this is not the case, then the next actual activation times are compared with the setpoint limit value. After a changeover, the switching time is stored in the control unit 64 at 170. When determining the switching time, influences of further operating variables, such as an engine speed, a prefeed pressure and a fuel temperature, are taken into account in the computer program of the control unit 64. Additional, further operating variables which influence the pressure in the high-pressure region 14 or the fuel quantity requirement are quite conceivable and can be taken into account in further exemplary embodiments.

In order to determine whether the high-pressure fuel pump 10, if the switching valve is in the switching position 82 (partial funding), promotes sufficient fuel, and the actual power or the actual torque or its course and / or an actual speed be evaluated. If a drop in performance is detected, and if, due to a suitable evaluation, this power loss can be attributed to inadequate fuel delivery, this can be used as a switchover criterion to full delivery (shift position 84).

Claims

claims

A high pressure fuel pump (10) for a direct injection internal combustion engine (9) having a low pressure area (12) and a quantity control means (28), characterized in that the quantity control means (28) comprises a switching valve located upstream of an inlet valve (22 ) of the high-pressure fuel pump (10) is arranged and has a first switching position and at least one second switching position, wherein the switching positions differ in their throttle effect.

2. High-pressure fuel pump (10) according to claim 1, characterized in that the switching valve (28) comprises an electromagnetic actuator (76).

3. High-pressure fuel pump (10) according to any one of claims 1 or 2, characterized in that the switching valve (28) is in the unactuated state in the switching position with the lowest throttle effect.

4. high-pressure fuel pump (10) according to any one of claims 1 or 2, characterized in that the switching valve (28) in the unactuated state in a switching position with increased throttle effect.

5. high-pressure fuel pump (10) according to any one of the preceding claims, characterized in that the throttle effect is designed in a switching position so that it allows a flow rate of about 10-20% of the maximum flow rate.

6. high-pressure fuel pump (10) according to any one of the preceding claims, characterized in that it comprises a pressure control valve (50) having a high-pressure region (14) of the high-pressure fuel pump (10) with a low-pressure region (12) of the high-pressure fuel pump ( 10) connects and so can keep the pressure in the high pressure region (14) at least substantially constant.

7. High-pressure fuel pump (10) according to claim 6, characterized in that the pressure regulating valve (50) operates purely mechanically / hydraulically, preferably a check valve.

8. A method for operating a high pressure fuel pump (10) according to any one of the preceding claims, characterized in that the control of the switching valve (28) by a signal of a pressure sensor, which detects a pressure prevailing in the high pressure region and / or a driving time of at least one injection valve (46) depends.

9. The method according to claim 8, characterized in that the switching valve (28) is switched from a more throttling switching position into a less strongly throttling switching position when the actuation time of the injection valve (46) exceeds a limit value.

10. The method according to any one of claims 8 or 9, characterized in that the actuation of the switching valve (28) depends on a pump speed, a prefeed pressure and / or a fuel temperature.

Control and / or regulating device (64) for a high-pressure fuel pump (10), characterized in that it is programmed for use in a method according to one of claims 8 to 10.

12. Computer program, characterized in that it is programmed for use in a method according to one of claims 8 to 10.