Pressure accumulator device for a motor vehicle fuel injection system, and method for operating a pressure accumulator device of said type

Abstract

An electrically driven solenoid coupled to a spring-operated valve, regulates pressure in an accumulator by opening when a predefined threshold pressure in a pressure accumulator is exceeded. The solenoid provides an assistive force to a spring-closed valve, reducing the amount of pressure required to open the valve responsive to the amount of current provided to the solenoid. The threshold pressure at which the valve opens is thus determined by the amount of current provided to the solenoid. Increasing the current decreases the threshold pressure; decreasing the current increases the threshold pressure.

Claims

1. A method for operating a pressure accumulator device for a motor vehicle fuel injection system, the method comprising: applying fuel at a high pressure, to a pressure accumulator, by a fuel pump; removing pressure from the accumulator by a controllable, pressure reduction valve, the controllable pressure reduction valve comprising a solenoid-operated valve, configured to open responsive to an applied pressure, the applied pressure at which the solenoid-operated valve opens being determined by an amount of current provided to a solenoid coil of the solenoid-operated valve; automatically opening the pressure reduction valve in the event of a predetermined threshold pressure in the pressure accumulator being exceeded; checking pressure regulation of the pressure accumulator, comprising increasing the threshold pressure of the pressure reduction valve, determining whether fluid pressure in the pressure accumulator changes following increasing the threshold pressure of the pressure reduction valve, and determining whether a fault exists in the pressure regulation of the pressure accumulator based upon determining whether the fluid pressure in the pressure accumulator changes, wherein determining whether a fault exists determines a fault selected from the group comprising the pressure accumulator exceeding the predetermined threshold pressure thereof, and at least one of a leak and inefficient operation of the fuel pump existing; and prior to checking the pressure regulation of the pressure accumulator, monitoring the fluid pressure in the pressure accumulator; comparing the monitored pressure with a predetermined setpoint pressure; and comparing a difference between the fluid pressure and the setpoint pressure with a difference threshold value, wherein the checking of the pressure regulation of the pressure accumulator is performed responsive to the differential threshold value being exceeded.

2. The method of claim 1, wherein determining whether a fault exists comprises inferring pressure in the accumulator exceeding the predetermined threshold pressure in the pressure accumulator if the fluid pressure in the pressure accumulator increases following the increase in the threshold pressure of the pressure reduction valve.

3. The method of claim 1, wherein determining whether a fault exists comprises determining the at least one of a leak and inefficient operation of the fuel pump exists if the increase in the threshold pressure of the pressure reduction valve is not followed by a pressure increase in the fluid pressure in the accumulator.

4. The method of claim 3, wherein the pressure reduction valve is controlled by energizing the solenoid coil to generate a magnetic field that exerts magnetic force on an armature of the solenoid, said armature exerting force on a closure element of the pressure reduction valve, a magnitude of the force exerted on the closure element being determined by the magnetic field whereby the threshold pressure for automatic opening of the pressure reduction valve is controlled by controlling current flowing though the solenoid coil.

5. The method of claim 4, wherein the solenoid coil is energized during the operation of the pressure accumulator, and increasing the threshold pressure of the pressure reduction valve comprises switching off the current in the solenoid coil.

6. The method of claim 5, wherein a mechanical force of a spring acts to bias the closure element to a closed position and force is exerted on the closure element in the opening direction by the solenoid armature when the solenoid coil is energized.

7. The method of claim 6, further comprising initially determining an amount of current of the solenoid coil required to overcome a spring force from the spring and other mechanical resistance to opening the pressure reduction valve at atmospheric pressure, and following initially determining an amount of the current, determining a current difference in accordance with an intended threshold pressure and subtracting the current difference from the amount of current, a result of the subtracting being a current for energizing the solenoid coil during operation of the pressure accumulator.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The invention is shown by means of an illustrative embodiment in figures of a drawing and explained below. In the drawings:

(2) FIG. 1 shows a schematic illustration of a pressure accumulator device;

(3) FIG. 2 shows a schematic illustration of a pressure reduction valve;

(4) FIG. 3 shows a diagram which shows the setting of the balance current for compensating the spring force of the pressure reduction valve;

(5) FIG. 4 shows a diagram which illustrates the pressure characteristic in the pressure accumulator depending on various fault events; and

(6) FIG. 5 shows a schematic illustration of the method sequence according to the invention.

DETAILED DESCRIPTION

(7) FIG. 1 shows a high-pressure injection system for a four-cylinder internal combustion engine, which is not shown specifically. The injection system has a pressure accumulator 1, which is connected to four injectors 2, 3, 4, 5. The individual injectors 2, 3, 4, 5 each have injection valves, which are indicated only schematically in FIG. 1.

(8) The pressure accumulator 1 is fed with a fuel from a fuel reservoir 7 by means of a high-pressure pump 6 at a high pressure in the region of several hundred bar to a few thousand bar. The fuel is fed to the high-pressure pump 6 via a fuel line 8 and a filter 9. Regulation of the hydraulic pressure in the high-pressure reservoir 1 takes place in a manner not shown specifically in greater detail by regulating the fuel quantity fed to the high-pressure pump on the low-pressure side.

(9) In order to allow better regulation of the pressure in the pressure accumulator, especially in situations of a falling fuel demand, a pressure reduction valve 10 which connects the pressure accumulator 1 to the low-pressure system, in particular the fuel reservoir 7, is provided. When the pressure reduction valve is open, the pressure in the pressure accumulator 1 can thus be reduced efficiently and quickly.

(10) The pressure reduction valve 10 and an element which controls the fuel supply to the high-pressure pump 6 are advantageously connected, together with a pressure sensor 25 linked to the interior of the pressure accumulator 1, to a common regulating device 11.

(11) FIG. 2 shows the construction of the pressure reduction valve 10 schematically and by way of example. In this case, the pressure accumulator is shown on the left-hand side with the reference sign 1 and is connected to an opening 12 of the pressure reduction valve 10. The opening 12 can be closed by means of a closure element 13. The closure element 13 is connected to a solenoid armature 14 of a solenoid drive, wherein the solenoid armature 14 interacts as part of the solenoid drive with a solenoid coil 15 surrounding it. In the state of rest, i.e. when the solenoid coil 15 is not being supplied with a current, the solenoid armature 14 and, with the latter, the closure element 13 is pressed against the valve seat on the opening 12 by means of a spring 16, which is guided in a spring guide 17, and by means of the correspondingly acting spring force 27, and the pressure reduction valve is thus closed against the hydraulic pressure 26 in the pressure accumulator 1. Thus, no fuel can emerge from the pressure accumulator 1.

(12) If the solenoid coil 15 is supplied with a sufficiently strong electric signal, with the result that a high current flows, the armature 14 is pulled into the coil 15, and the closure element 13 is thus moved away from the opening 12 against the force of the spring 16. Fuel can then be discharged from the pressure accumulator 1 through the opening 12 into the valve chamber 18 and, from there, via the outflow line 19, into the fuel reservoir 7. It is advantageous if the pressure reduction valve 10 is designed in such a way that it can be operated as a digital valve. This means that the valve is operated essentially only in an open position and in a closed position, wherein the opening 12 can be closed and opened very quickly by the movement of the closure element 13.

(13) The fact that the forces acting on the armature 14 from the solenoid drive counteract the spring force 27 can be exploited in order to set the current for the operation of the solenoid drive for continuous operation in such a way that both individual instances of scatter in the spring constants and other production and assembly tolerances are compensated. For this purpose, the pressure reduction valve can first of all be calibrated under atmospheric conditions, i.e. when the pressure accumulator and also the fluid reservoir 7 are under atmospheric pressure, or when both sides of the pressure reduction valve are under the same pressure other than atmospheric pressure. For this purpose, the current is experimentally set in such a way that the magnetic force on the closure element 13 just overcomes the spring force 27.

(14) A certain amount of current is then subtracted from the current thus determined through the solenoid coil, with the result that the pressure reduction valve is initially held closed with a reduced force. The subtracted amount of current is chosen so that the pressure reduction valve opens only when a certain hydraulic force 26, which corresponds to a threshold pressure of the valve, is added by the hydraulic force in the pressure accumulator 1 to the force of the solenoid drive.

(15) The aim of this setting is to enable the pressure reduction valve to open automatically, e.g. at a threshold pressure of 2200 bar in the pressure accumulator 1, if the threshold pressure is 3000 bar without energization of the solenoid coil for instance.

(16) The amount of current which has to be subtracted from the initially determined current at which the magnetic force and the spring force balance out in the valve can be found in a reference table stored in a regulating device 11, for example. However, the amount of current can also be determined by means of an advantageously linear characteristic depending on the desired triggering/threshold pressure of the valve.

(17) For better operation of the pressure reduction valve 10, a restriction 30 is provided in the region of the opening 12 of the valve on the side of the high-pressure accumulator 1. The flow resistance through the restriction 30 is significantly greater than the flow resistance of the opened pressure reduction valve 10. The effect of opening and closing processes of the pressure reduction valve is thereby reduced, and therefore the pressure reduction valve approaches the ideal form of the digital valve. FIG. 3 shows the process of setting the pressure reduction valve schematically in a diagram.

(18) In the lower part of the diagram, the time t is plotted on the horizontal axis, and the current in the solenoid coil 15 is plotted on the vertical axis. The current is increased over the time from t.sub.0 up to the current I.sub.1, which is achieved at time t.sub.1. The current I.sub.1 refers to the current at which the spring force of the compression spring and additional mechanical resistances are balanced out by the magnetic driving force of the solenoid armature and the solenoid coil in the pressure reduction valve when both sides are under atmospheric pressure, and the valve opens. This current I.sub.1 is first of all recorded. After this, the current can be increased further, wherein the valve remains open. At time t.sub.2, it is assumed that the pressure accumulator 1 is put under high pressure. During operation, the pressure reduction valve is now closed again, and then the current is set to the value I.sub.2, which is obtained from the determined current I.sub.1 by subtracting a certain amount of current, which depends on the desired threshold pressure of the valve. At this current I.sub.2, the valve can then be operated continuously.

(19) In the upper part of the diagram in FIG. 3, the time t is plotted on the horizontal axis at the same scale as in the lower part, while the opening path s of the closure element 13 of the pressure reduction valve is shown there on the vertical axis. It can be seen that, initially, at time t=0, the valve is closed and is held closed by the spring force. While the current in the solenoid drive is increased over time, the magnetic force grows until it balances out the spring force at time t.sub.1 and opens the valve, this being shown in the upper part of the diagram in FIG. 3 by the path s.sub.1 traveled by the valve tappet/closure element 13. The valve closes when, at time t.sub.2, the current is lowered from the current above I.sub.1 to 0. The pressure reduction valve remains closed for as long as the pressure prevailing in the pressure accumulator is below the desired threshold pressure. If the current I.sub.2 continues to be applied in the solenoid drive of the valve, the closure element 13 closes the opening 12 by means of the force of the spring 17 until the pressure in the pressure accumulator 1 rises above the threshold value again.

(20) In FIG. 4, the time characteristic is plotted on the horizontal axis, while currents, on the one hand, and pressure characteristics, on the other hand, are plotted on the vertical axis. First of all, a pressure characteristic in the pressure accumulator is illustrated in the setpoint pressure curve 31, which begins with a first pressure p.sub.1 and a horizontal pressure characteristic. In this phase, the pressure p.sub.1 prevails in the pressure accumulator 1, and the pressure reduction valve 10 is not energized. From time t.sub.4 onward, the pressure reduction valve 10 is, on the one hand, energized with the setpoint current, which sets the desired threshold pressure of, for example, 2200 bar at the pressure reduction valve. The pressure demand on the pressure accumulator rises in the course of time, and the pressure is increased there, this being shown by the linear rise in the pressure up to time t.sub.5. Normally, a horizontal pressure characteristic, i.e. the maintenance of a constant pressure in the pressure accumulator, is ensured as soon as the setpoint pressure has been set, which can correspond at the maximum to the threshold pressure of the pressure reduction valve, wherein this pressure is at p.sub.4 in the example shown in FIG. 4.

(21) In the absence of faults, this pressure is ensured by the regulation of the high-pressure pump 6, and therefore the pressure reduction valve 10 does not intervene and can remain closed.

(22) If there is a fault in the system, the desired pressure p.sub.4 is often not reached. It can be seen from the example curves 32 (first fault curve) and 33 (second fault curve) that the pressure in the pressure accumulator reaches a lower value than envisaged, namely pressure level p.sub.3 or p.sub.2. However, it is often difficult to identify the reason for the faulty behavior of the pressure regulating system. By means of the method according to the invention, a greater insight as to the cause of the fault can be obtained by switching off the current to the pressure reduction valve. If there is subsequently a pressure rise when the current is switched off at time t.sub.6, for example, as illustrated by means of the first fault curve 32, this indicates that the pressure reduction valve was closed by switching off the current and that consequently it was open before the current was switched off. This indicates that the pressure in the pressure accumulator 1 was too high and was automatically reduced by the pressure reduction valve. This observation suggests that the pressure regulation is faulty and that the system is under an excess system pressure.

(23) If the pressure characteristic in accordance with the second fault curve 33 is obtained after switching off the pressure reduction valve, it is evident that the valve position has not been changed by switching off the current to the pressure reduction valve. Since the threshold pressure is raised by switching off the current, this allows the conclusion that the applicable threshold pressure had not been reached even before the current was switched off and the valve was thus closed. The pressure level p.sub.3 established in accordance with the second fault curve 33 then has nothing to do with an excess pressure in the system but is very probably attributable to leaks and/or inefficient operation of the high-pressure pump. It is thus possible, by means of the method according to the invention, to perform fault discrimination in the pressure regulating system of the pressure accumulator by switching off the current to the pressure reduction valve.

(24) The method described for operating the pressure accumulator with a controllable pressure reduction valve will once again be briefly outlined with reference to FIG. 5. In a first method step 35, the pressure reduction valve 10 on the pressure accumulator 1 is operated, wherein the pressure accumulator 1 is under atmospheric pressure, as is the fluid reservoir 7. In a second method step 36, a current which just leads to the opening of the valve and which thus cancels out the spring force of the valve and compensates for all tolerances and the additional forces caused thereby is then set at the pressure reduction valve.

(25) In a third step 37, an amount of current which is subtracted from the current required to compensate the mechanical tolerances and the spring force is determined from the current level determined in the second step 36 and from the desired threshold pressure of the pressure reduction valve. In a fourth step 38, the current determined in the third step 37 for continuous energization of the pressure reduction valve 10 is set during the operation of the pressure accumulator.

(26) If the need arises to check the pressure regulation in the system, either in the context of a regular periodic check or the suspicion of a malfunction arises due to a certain deviant behavior or a sensor indication, the current to the pressure reduction valve 10 is switched off in the fifth step 39 and, in the sixth step 40, the development of the measured pressure is detected. In the seventh step 41, fault discrimination and fault determination are carried out on the basis of the analysis of the pressure behavior.