Method and device for operating a pressure reservoir, in particular for common rail injection systems in automobile engineering

Abstract

A method and to a device for operating a pressure reservoir, where during a compression phase in a pump chamber, a pump periodically increases the pressure of a fluid located therein, and by means of a discharge valve controlled by differential pressure fluid under high pressure is allowed to be introduced from the pump chamber into the pressure reservoir. During a decompression phase following a compression phase, fluid from a fluid reservoir is introduced into the pump chamber by means of a controllable intake valve. In order to be able also to operate the pressure reservoir without a high pressure measurement directly in the pressure reservoir, the fluid pressure in the pressure reservoir is ascertained by means of a pressure determination in the pump chamber. The pressure determination takes place indirectly, monitoring of the intake valve in the decompression phase.

Claims

1. A method for operating a pressure accumulator, in which method a pump periodically, during a compression phase in a pump chamber, increases the pressure of a fluid situated therein, and fluid at high pressure is admitted from the pump chamber into the pressure accumulator by way of a differential-pressure-controlled discharge valve, and in which method, during a decompression phase following a compression phase, fluid is admitted from a fluid reservoir into the pump chamber by way of a controllable intake valve, the method comprising the steps of: determining the fluid pressure in the pressure accumulator by way of a pressure determination in the pump chamber; and measuring the pressure in the pump chamber at a time between the closure of the discharge valve and the subsequent admission of fluid into the pump chamber.

2. The method as claimed in claim 1, wherein measuring the pressure in the pump chamber comprises the steps of determining the pressure in the pump chamber at the time of the opening of the intake valve, in particular by way of a determination of a position of a pump piston at said time of the opening of the intake valve.

3. The method as claimed in one of claims 2, further comprising the steps of determining the pressure in the pump chamber at the closing time of the discharge valve in the preceding compression phase from the time of the opening of the intake valve, in particular from the time difference between the opening time of the intake valve and the time of the maximum compression of the pump.

4. The method as claimed in claim 3, further comprising the step of determining the position of the pump piston, which delimits the pump chamber, at the opening time of the intake valve, in particular taking into consideration the pump speed.

5. The method as claimed in claim 4, further comprising the step of determining a compression ratio from the position of the pump piston at the opening time of the intake valve.

6. The method as claimed in claim 5, further comprising the step of controlling the intake valve electromagnetically by way of a current flowing through a magnet coil and by way of an armature that is driven by the field of the magnet coil.

7. The method as claimed in claim 6, further comprising the step of monitoring the current flowing through the magnet coil is with regard to the current intensity.

8. The method as claimed in claim 7, wherein monitoring the current flowing through the magnetic coil comprises detecting a current signal generated in the magnet coil by an opening movement of the intake valve and of the armature, wherein the method further comprises the step of assigning the opening time of the intake valve based on the current signal detected.

9. The method as claimed in claim 8, further comprising the step of pushing the intake valve into the open position with a defined force by way of a preload spring.

10. A device for generating a fluid pressure in a pressure accumulator, comprising: a pump which has a pump chamber delimited by a driveable pump piston, the pump chamber being connectable at one side to the pressure accumulator by way of a differential-pressure-controlled discharge valve and at the other side to a fluid reservoir by way of a controllable intake valve; an actuating device which controls the intake valve by way of an energizable magnet coil and by way of an armature that can be driven by the field of the magnet coil; and a measurement device which monitors the current flowing through the magnet coil with regard to the current intensity and which detects a current signal generated by a movement of the armature in the field of the magnet coil, the device assigning an opening time of the intake valve to a time of the detected current signal, determining pressure in the pump chamber at the opening time of the intake valve, and determining pressure in the pressure accumulator based upon the determined pressure in the pump chamber.

11. A method for operating a pressure accumulator, comprising: periodically, during a compression phase in a pump chamber, increasing the pressure of a fluid situated therein; admitting fluid at high pressure from the pump chamber into the pressure accumulator by way of a differential-pressure-controlled discharge valve; during a decompression phase following a compression phase, providing fluid from a fluid reservoir to the pump chamber by way of a controllable intake valve; and determining pressure in the pump chamber and determining fluid pressure in the pressure accumulator based upon the determined pressure in the pump chamber, wherein the pump comprises a pump piston, and the method further comprises determining a position of the pump piston at a time of opening of the intake valve, and determining pressure in the pump chamber is based upon the determined position of the pump piston.

12. The method of claim 11, further comprising determining the pressure in the pump chamber at a time of closing of the discharge valve in a preceding compression phase from a time difference between an opening time of the intake valve and a time of a maximum compression of the pump.

13. The method of claim 11, wherein the pump piston delimits the pump chamber, and the method further comprises determining the position of the pump piston at an opening time of the intake valve, based in part upon a speed of the pump piston.

14. The method of claim 13, further comprising determining a compression ratio from the position of the pump piston at the opening time of the intake valve.

15. The method of claim 11, wherein the intake valve comprises a magnetic coil and an armature that is driven by a field of the magnetic coil, and the method further comprises controlling the intake valve using a current flowing through the magnetic coil, detecting a current generated in the magnet coil as corresponding to an opening movement of the intake valve, and assigning an opening time of the intake valve to the detected current, wherein determining pressure in the pump chamber is performed at the opening time of the intake valve.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

(2) FIG. 1 schematically shows an overview of a device according to the invention for generating a fluid pressure in a pressure accumulator;

(3) FIG. 2 shows two typical current intensity profiles of the current through the magnet coil by way of which the intake valve is controlled;

(4) FIG. 3 shows the profile of the pump cycle, plotted versus the time, together with an illustration of the current profile in the magnet coil, which actuates the intake valve by way of an armature; and

(5) FIG. 4 shows a method flow diagram for the determination of the pressure in the pressure accumulator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(6) The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

(7) FIG. 1 schematically shows a pressure accumulator 1, which may be formed for example by a common-rail pressure accumulator in a fuel injection system of a vehicle. On the lower part of the pressure accumulator 1 there are illustrated outlets 2, 3, where injection valves are commonly arranged. For the sake of clarity, these have been omitted in the present drawing.

(8) The device according to the invention is provided for providing fluid, in the present case that is to say a liquid in the form of fuel, in the pressure accumulator, or delivering said liquid into the pressure accumulator, at high pressure, typically several hundred bar. For this purpose, a pump chamber 4 is provided which is delimited in the fluid inlet region by a first wall 6, in the fluid outlet region by a second wall 7, and additionally by a pump piston 5.

(9) The first wall 6 has an opening 6a through which fluid can flow from a fluid reservoir 8 into the pump chamber 4. The opening 6a can be closed by way of a first closure body 9, for example in the form of a cone, so as to form an intake valve such that no fluid can flow through the opening 6a. For this purpose, by way of a first compression spring 11, the first closure body 9 is pushed away from the edge of the opening 6a which forms a valve seat, that is to say the spring 11 acts in an opening direction of the valve. The spring 11 may, contrary to the simplified illustration in FIG. 1, act on the plunger 13 outside the pump chamber, for example in the region of the magnet coil 15.

(10) Since the pressure in the fluid reservoir 8 is normally low, in particular lower than that in the pump chamber 4, for example is at atmospheric pressure, it is necessary, during a compression phase, for the valve 6a, 9, 11 which closes the first wall 6 to be actuated or activated in order to be closed. For this purpose, the valve plunger 13 is provided which can pull the closure body 9 against the opening 6a and against the valve seat. The valve plunger 13 is connected to a magnet armature 14, which moves in the field of the magnet coil 15 and which can be driven by virtue of the magnet coil 15 being energized. The magnet coil 15 can thus have a current applied to it such that the valve 6a, 9, 11 is closed. For this purpose, a force must be applied by way of the magnet coil 15 and the armature 14 which is high enough that the spring force and possibly the differential pressure between the pump chamber 4 and the fluid reservoir 8 are overcome. The plunger 13 may be separate from the closure body 9 or may in particular be connected integrally to said closure body. The spring on the closure body 9 is illustrated merely symbolically, and may be connected to the plunger outside the pump chamber, for example within the magnet coil.

(11) The current through the magnet coil is provided by way of a current source 16 and is monitored by way of a current measurement unit 17. From the current flowing through the magnet coil 15, it is possible to determine the magnetic force acting on the plunger 13 and thus on the closure body 9.

(12) The pump piston 5 in the pump chamber 4, or more precisely on the boundary surface of the pump chamber 4, is driven in cyclic fashion by way of a drive connecting rod 18 and a drive arm 19 of a pump motor 20. The solid lines in FIG. 1 indicate the pump piston approximately at the point of maximum compression in the pump chamber 4, that is to say in the furthest upwardly situated position in FIG. 1. From there, the pump piston 5 is, with an increase in size of the pump chamber 4, that is to say during a decompression process, pulled into the lower position shown by dashed lines, and is moved cyclically upward again from there in order to run through a further compression.

(13) The fuel flows into the pump chamber during the entire downward movement (starting from the opening of the intake valve) of the piston. The valve 6a, 9, 11 is open when deenergized, and fluid can flow from the fluid reservoir 8 into the pump chamber 4. At the same time, the valve which connects the pump chamber 4 to the pressure accumulator 1, and which is formed substantially by the opening 7a, the second closure body 10 and the second compression spring 12, is closed. The constantly high pressure in the pressure accumulator 1 pushes the closure body 10 against the opening 7a in the second wall 7 and thus prevents the fluid from flowing out of the pressure accumulator 1 into the pump chamber and vice versa.

(14) During the course of the upward movement of the pump piston 5 in the pump chamber 4, the valve 6a, 9, 13, 14 is closed by energization of the coil 15, and the pump chamber 4 is closed off on all sides for a period of time. The pressure can increase as far as an upper extreme position of the piston 5, wherein, at a certain time, such a high pressure is reached in the pump chamber 4 that the closure body 10 is pushed away from the opening 7a in the second wall 7 counter to the force of the second compression spring 12, and the pressure accumulator 1 is connected to the pump chamber 4. For this purpose, fluid can flow over from the pump chamber 4 into the pressure accumulator 1, and thus, in the case of a common-rail pressure accumulator, fuel can be replenished. When the pressure has equalized between the pump chamber 4 and the pressure accumulator 1, and when the pump piston 5 moves downward, initiating a decompression process, the closure body 10 is pushed against the opening 7a again, and the fluid that has been introduced into the pressure accumulator 1 remains there.

(15) Normally, the current through the magnet coil 15 is controlled such that, as a result of the closing time of the valve 6a, 9, 11, 13, the fluid v, 13 that has moved from the fluid accumulator 8 through the valve into the pump chamber 4 during the suction phase assumes a precisely defined volume in the pump chamber. Following the compression, during an equalization movement of the compressed medium from the pump chamber 4 into the pressure accumulator 1, pressure equalization between the 2 chambers is achieved. In the subsequent decompression phase (pressure accumulator 1 already closed by valve 7a, 10, 12), the medium that has already been previously compressed must be decompressed to a lower pressure in the fluid accumulator 8 in order to permit a subsequent drawing-in of new medium. Only then will the valve 6a, 9, 13b be able to open. To make it possible for the valve movement to be detected and evaluated during said opening process, it is normally the case that a low current is passed through the magnet coil 15, which low current is not enough to cause an actuation of the valve. Said current, and the reaction of a movement of the magnet armature on the current, can be detected by measurement, and it is thus possible for the time of the valve opening to be inferred. Depending on what pressure, reached as a result of the compression phase, has to be decompressed, an earlier or later valve opening is evident in the current profile. The time of the valve opening may be set in relation to the cyclic movement of the pump piston or of the pump motor. If the pressure in the pressure accumulator 1 falls, it is tendentially necessary for more fluid to be replenished, and, during the subsequent decompression phase, the valve 6a, 9, 11 opens at an earlier time than in the presence of a relatively high pressure in the pressure chamber. The time of the valve opening thus makes it possible to indirectly determine the pressure in the pressure chamber 1.

(16) Normally, the pressure build-up and the replenishment of fluid in the pressure accumulator are subject to regulation, wherein the monitored pressure in the pressure accumulator 1 serves as a setpoint variable. Said pressure is normally monitored by way of a high-pressure sensor 21 in the pressure accumulator. If a high-pressure sensor 21 of said type fails, or if it is the intention for said high-pressure sensor to be temporarily not used, or if said high-pressure sensor is temporarily not usable, then it is possible by way of the method according to the invention for the pressure in the pressure accumulator 1 to be determined by way of an indirect measurement of the pressure in the pump chamber 4.

(17) In FIG. 2, it is schematically illustrated that the current I through the magnet coil 15, measured by way of the current measurement unit 17, varies over time. In the upper curve 22, upon an actuation of the magnet coil 15, an increase of the current intensity is illustrated in the time range 23. After passing through a maximum, the current falls asymptotically owing to the induction action, wherein the magnetic field action in the coil remains constant. At the time t.sub.2, the pressure in the pump chamber 4 has fallen to such an extent that the spring force acting on the plunger 13 can effect a movement of the closure body 9 counter to the differential pressure. Thus, at the time t.sub.2, the plunger 13 moves, and it is thus also the case that the magnet armature 14 moves in the field of the magnet coil 15. This gives rise to an inductive reaction on the current, which is manifest in a bend 24 in the current curve, and which can thus also be verified by monitoring of the current intensity in a monitoring device 36, which is also connected to the pump motor. Through a detection of a bend point of said type, it is thus possible to identify the time t.sub.2 at which the force acting on the closure body 9 in the opening direction exceeds the closure force of the valve exerted by the differential pressure.

(18) In the lower region of FIG. 2, there is illustrated a further current curve 25 which shows a corresponding, slightly different current signal in the form of a low current maximum, on the basis of which it can be verified that, in this case, at the time t.sub.1, the magnet armature 14 together with the plunger 13 has begun its opening movement.

(19) The amplitude of the movement of the pump piston 5 is illustrated schematically by the curve 26 in the lower region of FIG. 3. The upper arcs of the sinusoidal curve show the states in which the pump piston 5 moves upward during the course of a reduction in size of the pump chamber 4 in FIG. 1 and effects a compression. Thus, in the diagram, the curve 26 begins in a phase of maximum compression. At the time t.sub.3, the piston 5 moves downward during the course of a decompression, and the pressure falls initially until the time t.sub.4. At the time t.sub.4, the piston has reached a position in which, in the illustrated example, the pressure in the pump chamber 4 has fallen to such an extent that the valve 6a, 9, 11 opens to the fluid reservoir 8. The intake time period of the intake valve is denoted by 27 in the diagram of FIG. 3, and extends until t.sub.5. In the time period 27, it is thus the case that fluid can flow over from the fluid reservoir 8 into the pump chamber 4.

(20) After the pump piston 5 has passed through its bottom dead center and has begun an upward movement again, at the time t.sub.5, the valve 6a, 9, 13 is closed and the pump chamber is closed on all sides, and thus the compression phase is initiated. The curve 26 rises, and the pressure in the pump chamber 4 is increased. When a maximum pressure is reached at the time t.sub.6, the valve 7a, 10, 12 between the pump chamber 4 and the pressure accumulator 1 opens, and, over an opening time 28, fluid at high pressure can flow from the pump chamber into the pressure accumulator 1.

(21) The upper region of the diagram of FIG. 3 illustrates a cyclic current profile which represents the current intensity through the magnet coil 15. In the region of the decompression movement of the pump piston 5 after the time t.sub.3, the current through the magnet coil is increased slightly for the purposes of better detecting a valve movement. At the time t.sub.4, the pressure prevailing in the fluid reservoir 8 approximately corresponds to the already-decompressed pressure in the pump chamber 4, and the valve 6a, 9, 13 (intake valve) subsequently opens with magnetic force assistance. This is evident from the current rise 29 that is generated as a result of induction during a movement of the magnet armature, which current rise can be used as a signal for acknowledgement of the valve opening. After the opening time 27 of the intake valve has been run through, the current through the magnet coil 15 can be shut off. At the time t.sub.5, the magnetic valve has a so-called closing pulse 50 applied to it, which closes the valve 6a, 9, 13 (intake valve) and thus initiates the compression phase. In the diagram, the opening process is shown for a second time in the region of the curve 30, with the corresponding current signal 31, at the time t.sub.8.

(22) From the detected valve opening times t.sub.4, t.sub.8 in the cycle of the pump movement 26 relating to the respectively preceding TDC (top dead center) of the pump, it is possible in each case to determine the time at which the pressure in the pump chamber has been depleted again after the preceding compression phase. The pressure at the end of the compression phase can be determined by way of a previously known correlation, which is for example stored in a memory device, between valve opening time and pressure. The compression ratio in the pump chamber between the position of the pump piston reached at the time t.sub.4, t.sub.8 and the maximally advanced position of the pump piston, at which maximum compression is attained, is also known. It is thus possible to infer the pressure in the region of maximum compression, which, owing to the opening of the valve 7a, 10, 12 in said time range, corresponds precisely to the pressure in the pressure accumulator 1. This may be realized in each case by calculation of the compression ratio; it is however also possible to realize a correlation list of times t.sub.4, t.sub.8 at which an opening of the intake valve begins and corresponding maximum pressures in the pump chamber obtained by way of a calibration measurement.

(23) FIG. 4 schematically shows the sequence of the method according to the invention in a flow diagram, wherein a first step 32 indicates the identification of a current signal 29, 31 including the identification of the time of the current signal. In the second step 33, said time is set in relation to the profile of the pump piston movement, such that, from the known time of the current signal, it is possible to calculate the position at which the valve 6a, 9, 13 (intake valve) opens. From the known time of the TDC (top dead center) of the pump and that of the valve opening, determined by way of the measurable current rise (e.g. 29 and 30), it is possible to infer in the third step 34 the duration of the decompression phase, and thus the pressure that previously prevailed in the pump chamber 4 and in the pressure accumulator 1 that communicates therewith. From this, by way of the known pump parameters, in particular the distance covered by the pump piston to the maximum position, or by way of the known volume ratios in the position in which the pump piston is situated when the intake valve opens, on the one hand, and at the time of the maximum compression, on the other hand, it is possible for the ratio of the pressures at the time of the opening of the intake valve, on the one hand, and at the time of the closure of the discharge valve 7a, 10, 12, on the other hand, and thus the pressure in the pump chamber and in the pressure accumulator upon the closure of the discharge valve, to be calculated. This is performed in a fourth calculation step 35.

(24) The method composed of the steps 32 to 35 may for example be performed immediately as soon as it is detected that a pressure sensor in the pressure accumulator is defective. Furthermore, the method with the steps 32 to 35 may, for the purposes of calibrating the method according to the invention, be performed in parallel with a pressure measurement by way of a high-pressure sensor in the pressure accumulator.

(25) The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.