GB2325275A

GB2325275A - A device for measuring the quantity of fuel supplied to a fuel injection valve of an internal combustion engine

Info

Publication number: GB2325275A
Application number: GB9809315A
Authority: GB
Inventors: Dieter Handtmann; Juergen Abt; Pawel Drabarek; Walter Bauer
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1997-05-15
Filing date: 1998-05-01
Publication date: 1998-11-18
Anticipated expiration: 2018-05-01
Also published as: FR2763366A1; DE19720333A1; GB2325275B; JPH10318100A; GB9809315D0; FR2763366B1; DE19720333B4

Abstract

A fuel supply system for an i.c. engine comprises a high pressure fuel pump 4, a high pressure storage device 1, eg a common rail, at least one fuel injection valve 10 and a measuring device 17, for measuring the quantity of fuel supplied to the fuel injection valve 10 and which is disposed between the high pressure pump 4 and the high pressure storage device 1, having a measuring piston 20 contained in a cylinder 19 and a sensor 33 for sensing the position of the piston 20 within the cylinder 19. First and second chambers 22, 24 are formed on either side of the piston 20 between the piston 20 and the cylinder 19, each chamber being connected to the fuel supply 3 by an inlet. The fuel supply 3 to the second cylinder 24 is interrupted by an electrically controlled valve 30 which activates the measuring device 17; the pressure differential between the chambers 22, 24 causes the piston 20 to be displaced and discharge fuel from the second chamber 24 to the high pressure storage device 1 to replace fuel used by one of the injection valves 10. By measuring the displacement of the piston 10 the quantity of fuel supplied can be calculated and used as a control signal by an engine regulator 14.

Description

2325275

1 DESCRIPTION METHOD OF MEASURING FUEL, WHICH IS SUPPLIED TO FUELINJECTION VALVES FOR INJECTION INTO AN INTERNAL COMBUSTION ENGINE AND A FUEL-INJECTION SYSTEM FOR THE PURPOSE OF HYMEMENTING THE METHOD

The present invention relates to fuel-injection systems and concerns a method of measuring fuel supplied to fuel injection valves for injection into an internal combustion engine and which is available in a highpressure fuel storage device which is supplied by a high-pressure fuel pump, by means of a measuring device which comprises a measuring piston, which is displaceable in a measuring cylinder by means of incoming fuel, and comprises a sensor device which ascertains the position of the measuring piston.

Such a method is used in a method disclosed in DE-A-29 09 233, wherein a measuring device for measuring fuel which is supplied to fuel injection valves for injection into an internal combustion engine is disposed between a high-pressure fuel storage device and electrically controlled injection valves. This device has the disadvantage that at the most with such a measuring device two injection valves can be monitored and that the quantity of fuel supplied to the fuel injection valves is measured constantly during the operation of the internal combustion engine. This has an adverse effect on the serviceable life of the measuring device and on the other hand involves considerable expense in order to control each injection process by means of the 2 measurement signal of the measuring device.

In accordance with a first aspect of the present invention, the measuring device is disposed between the high-pressure fuel pump and the highpressure fuel storage device and for the purpose of measuring the injection quantities and/or injection curves of the injection processes the supply of fuel to be measured is switched on or switched off to interrupt the measuring process.

In contrast to the known method, the method in accordance with the present invention has the advantage that a control signal, which can be evaluated by the regulating device, is only received during specific conditions of the internal combustion engine, in which conditions the operating state is approximately constant. In an advantageous manner only a single measuring device is provided for all injection valves, in that the supply of fuel to the high-pressure fuel storage device is ascertained, representative of the quantities which are drawn off therefrom and are injected by way of the fuel injection valves for injection purposes. During normal operation the measuring process is switched off, which has a substantially positive effect on the serviceable life of the measuring device.

In an advantageous embodiment the measuring device is switched on or off by virtue of a part of the fuel line bypassing the measuring device being opened or closed, by means of which the measuring device can be switched into the fuel flow or separated therefrom. As a consequence an uninterrupted flow of fuel in the fuel line between the high-pressure ftiel pump and the highpressure ftiel storage device is possible after switching off the measuring 3 device. In an advantageous manner the measuring is performed in such a manner that even during the maximum fuel injection supply rate the piston does not reach the stop and thus a precise measuring result is achieved. Upon completion of the measuring process or prior to a possible stop of the piston towards the side of the high-pressure fuel storage device the measuring process is interrupted in that the fuel line is reopened.

In an advantageous manner, the injection quantity signal is used as a control signal for a regulating device of an internal combustion engine, wherein for example values stored therein are corrected or monitored for the full load injection quantity. It is also possible to perform a control process in other operating ranges by means of ascertaining in accordance with the invention the injection quantities. If a predetermined fuel flow is exceeded, as a result, for example of a malfunction of an injection valve, then in an advantageous manner the supply to the high-pressure fuel storage device is interrupted. In an advantageous manner in the case of the fuel injection system for the purpose of implementing the method defined above the fuel line is interrupted by means of an electrically controlled valve. In one embodiment, in an advantageous manner a reduction in diameter is provided in the fuel line, for example, a Venturi tube, and with the aid of the pressure drop which occurs at this site, the flow, which is issuing from the reduction in diameter, is further directed to the inlet-side chamber, producing a differential pressure which influences the measuring piston and which is able to return the piston into its starting position as the measuring device is switched off during 4 the interruptions in the measuring process.

In a further advantaaeous embodiment the restoring force is produced by a spring. The spring is supported on a stop which is formed as a movable piston and is provided on the outlet side, which stop can be displaced against the force of a biassed spring. In an advantageous manner this stop can comprise a sealing surface by means of which as the piston is displaced upon a predetermined displacement force of the measuring piston being exceeded a through-passage in the fuel line is closed and the further passage of fuel is prevented.

In an advantageous manner, the measuring piston is provided with a sealing surface which in an end position of the measuring piston on its one stop towards the side of the high-pressure fuel storage device cooperates with a valve seat, so that no further fuel can flow via the cylinder to the high-pressure fuel storage device.

In an advantageous manner, for the purpose of measuring the position of the piston in the cylinder an optical sensor ascertains a surface structure of the piston in the form of a reflection grid. Moreover, in a particularly advantageous manner, a damping element is provided, by means of which the pressure fluctuations in the system can be eliminated so that the piston of the measuring device can indicate the desired measured value without being falsified by these fluctuations. As a further security, such a damping element is also provided in advance of each injection valve, so that the fluctuating behaviour of the hydraulic system is also effectively counteracted here in order to achieve an extremely precise measurement result of the measuring device.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which:- Figure 1 shows the diagrammatic illustration of a fuel-injection system comprising the measuring device for the purpose of implementing the method in accordance with the invention; Figure 2 shows a different embodiment of measuring device in accordance with Figure 1; and Figure 3 a damping element for inserting into the connection between the high-pressure fuel pump and the high-pressure fuel storage device or between the high-pressure fuel storage device and the injection valve.

A so-called Common Rail system or injection storage system consists of a high-pressure fuel storage device 1, which is supplied by way of a pressure line 3 from a high-pressure fuel pump 4 with a fuel which has been brought up to a high injection pressure. The high-pressure fuel pump 4 draws off fuel from a fuel storage container 8 by way of a suction line 5, where appropriate a preliminary delivery pump 6 and a filter 7. The high-pressure fuel supplied to the high-pressure fuel storage device is ready for injection and to this end pressure supply lines 9 branch off from the high-pressure fuel storage device and lead in each case to an injection valve 10. The connection from the high pressure pump to a fuel injection valve respectively can be regarded as a fuel line which consists of individual parts, the pressure line 3, the high-pressure fuel storage device 1 and the pressure supply lines 9. The fuel is injected by 6 way of these injection valves controlled in an electrical manner by way of control lines 11, which receive control signals from an electrical regulating device 14, also called control device. This control device also controls the operation of the high-pressure fuel pump 4, e.g. in response to the fuel pressure in the high-pressure fliel storage device which is ascertained by an pressure sensor 15. Depending upon the opening times of the injection valves the quantity of injected fuel changes at a specific level of this pressure in the high-pressure fuel storage device. Mainly this pressure sensor serves to maintain the operating pressure and to ensure that the maximum permissible pressure in the high-pressure fuel storage device is not exceeded. Accordingly the high-pressure fuel delivery pump 4 can be operated either a. variable rotational speed or variable delivering quantities. For the purpose ot monitoring the injection process, in particular for ascertaining the individL.... injection quantities of the injection valves, a measuring device 17 is provided, which is likewise controlled by the control device 14 and whose measuring activities can be switched on and off.

The measuring device consists of a measuring cylinder 19, within which a measuring piston 20 is disposed in a displaceable manner. The said measuring piston is adjacent with its first end face 21 to a first pressure chamber 22 in the closed measuring cylinder and with its second end face 23 to a second pressure chamber 24 at the other end of the measuring cylinder. In the first pressure chamber 22 there is provided an inlet 25 which connects the first pressure chamber with an upstream part of the fuel line in the present 7 exemplified embodiment with the pressure line 3. The second pressure chamber 24 is on the other hand connected to the same with a part lying downstream of the connection of the inlet 25 with the fuel line. An intermediate part 26 of the fuel line lies between the branching of the inlet 25 from the fuel line and the second pressure chamber, in which intermediate part is disposed an electrically controlled valve 30, which can be for example a solenoid valve but also a Piezo valve. The intermediate part 26 issues into the measuring cylinder 19 by way of a connection piece 29 and continues from there as a fuel line via an outlet 27 out of the measuring cylinder 19. Owing to its position, the first pressure chamber 22 is described as the inlet-side, upstream pressure chamber, it is connected to the upstream part of the fuel line and the second pressure chamber 24 is described as the outlet-side, downstream pressure chamber, it is connected to the downstream part of the fuel line. The fuel line leads from the outlet 27 by way of a damper 29 into the high-pressure fuel storage device 1.

When the valve 30 is in the opened state, the through-flow between the high-pressure pump and the high-pressure fuel storage device can occur unhindered. The measuring device 17 lies in parallel with the intermediate part 26 of the fuel line and the measuring piston is not exposed to any of this displacing differential pressure. However, if the electrically controlled valve 30 is closed, then fuel delivered from the high-pressure fuel pump flows into the first pressure chamber 22, where it displaces the measuring piston 20 from a stop 31 in the direction of the second pressure chamber 24 from which by 8 virtue of the movement of the measuring piston 20 fuel is delivered into the high-pressure fuel storage device 1 by way of the outlet 27.

The function of the measuring piston is switched on and off by virtue of the electrically controlled valve 30 being closed or opened respectively by way of several rotations of the internal combustion engine. When the measuring device 17 is switched on, the displacement path of the measuring piston 20 is scanned by a high-resolution path sensor 33, which functions in a non-contact manner, and stored in the control device 14 as a control signal. The injection quantities and injection curves of the individual fuel injection valves are then determined and allocated by means of the signal processors from this path-time function which has the form of a step curve. Preferably, a high-resolution optical path sensor is used which measures in an absolute or incremental manner. To this end, the piston comprises for example a special surface structure 43 which is scanned by means of an optical sensor 33. A rotation preventing device 34 ensures the surface structure is allocated to the path sensor. This surface structure can be, for example, a reflection grid. In an advantageous manner, this measuring process is performed in each case when the internal combustion engine is in a quasi stationary state. As a consequence, a series of injection processes can be ascertained, which produce in total a measurement result which is as precise as possible. It is also possible during such a stationary phase of the operation to compare the settings of the various fuel injection valves with each other and make relevant corrections.

9 In the example illustrated, the inlet 25 branches off from the fuel line within a Venturi tube 32, whereby in the case of an open valve 30 and fuel flowing in the pressure chamber 22 the pressure produced is reduced with respect to the pressure chamber 24, as a result of which the measuring piston 20 is returned to its stop 31 during the interruptions in the measuring process, without requiring a restoring spring. This increases the measuring accuracy during the measuring process since the process is not influenced by the resilient constant of a restoring spring. The measuring piston 20 is formed preferably as a floating, well running piston.

Moreover, in order to increase the measuring accuracy of the measuring device the damping element 28 is provided and comprises restricting through-passages having the function of a hydraulic low pass, so that fluctuations in the high-pressure system, which are produced by virtue of the pressure relief in the high-pressure fuel storage device 1 during the injection processes and in the build up of pressure again during the interruptions in the injection process, are decoupled towards the side of the measuring device 17. Such a damping element is illustrated in Figure 3. In this case a small tube 35 is provided, which comprises on its one end a clamping flange 36 which is clamped in a sealing manner in a connection fitting in the line between the measuring device 17 and the high-pressure fuel storage device 1, wherein the small tube 35 is received into the connection line. The small tube has a blind bore 38 which issues from the flange 36 and from which in turn lead off in a radial manner restrictor bores 39 which are offset with respect to each other in an advantageous manner, so that pressure fluctuations are eliminated by way of this through-passage. The fuel flowing from the high-pressure fuel pump on the side of the clamping flange 36 exits by way of the restrictor bores 38 to the side of the high-pressure fuel storage device. Such an insertion part, as illustrated in Figure 3, can also be inserted into each of the fuel injection lines as an insertion part 28' in order to dampen any fluctuations occurring there.

Whereas in the case of the exemplified embodiment as shown in Figure 1, the measuring device 17 has a differential pressure for restoring purposes, which returns the measuring piston 20 to its stop 31 during the interruptions in the measuring process, the measuring device in accordance with Figure 2 is provided with a restoring spring 42. As in the case of the exemplified embodiment as shown in Figure 1, the measuring piston 20 is disposed in the measuring cylinder 19 in a displaceable manner, wherein it comprises the stop 31 towards the first pressure chamber 22. In this case the measuring piston also has the surface structure 43 described with reference to Figure 1 and in turn the sensor 33 in the form of an optical sensor is provided. Alternatively, the path can also be measured using an electromagnetic sensor, an inductive sensor or a capacitive sensor.

The restoring spring 42 provided in this case is mounted in a blind bore 45 of the measuring piston 20', is supported on its one side therein and on its opposite side is supported on a displaceable stop 46 in the form of a piston which is introduced on the high-pressure storage device side into the cylinder 1T. This stop 46 is influenced by a compression spring 48, which is 11 supported on the housing of the measuring cylinder 19 and is stronger than the spring 42, and held by said spring against a stop 49. The piston is displaceable in the cylinder and comprises in addition through-going bores 50, wherein it is.guaranteed that identical pressure prevails constantly in the two chambers adjacent to said piston, into [sic] the second pressure chamber 24' and in an end chamber 52 lying to the side of the outlet 2T, into which end chamber the connection piece issues and from which end chamber the outlet 27' leads off.

This piston-shaped stop 46 comprises moreover a valve spigot 54 which cooperates with a valve seat 55 which encompasses the outlet orifice of the outlet 27' from the end chamber 52.

If as a result of a malfunction on the part of the high-pressure fuel storage device or on the part of an excessively large amount of fuel being drawn off from the fuel injection valves, then in the case of a closed valve 30 the measuring piston 20' after coming to rest against the end surface of the stop is further displaced together with the stop 46 against the force of the compression spring 48, so that finally the valve spigot 54 closes the outlet 2T. This is a safety function, so that in the event of a malfunction the fuel injection valves do not continue to inject high quantities, which could cause an internal combustion engine to race (overspeed) or become damaged.

This embodiment in accordance with the invention as already described above renders it possible in an advantageous manner using a single measuring device to measure the successive fuel injection quantities of the individual 12 injection valves and the measuring device in addition also provides a safety function in the event of damage occurring on the high-pressure fuel side. The measurement signal variables emitted by the measuring device can be processed in numerous ways by virtue of the control device 14, on the one hand for the purpose of balancing the injection valves, on the other hand for metering the injection quantities and finally for controlling the long-time drifts of the injection quantities of each individual fuel injection valve.

OR?q5CT25 13

Claims

1 - A method of measuring fuel which is supplied to fuel injection valves for injection into an internal combustion engine and which is available in a high-pressure fuel storage device which is supplied by a high- pressure fuel pump, by means of a measuring device which comprises a measuring piston, which is displaceable in a measuring cylinder by means of incoming fuel, and comprises a sensor device which ascertains the position of the measuring piston, wherein the measuring device is disposed between the high-pressure fuel pump and the high-pressure fuel storage device and, for the purpose of measuring the injection quantities andlor injection curves of the injection processes, the supply of fuel to be measured is switched on or switched off to interrupt the measuring process.

2. A method according to claim 1, wherein the measuring process is only implemented if the internal combustion engine is operated in a quasi stationary state.

3. A method according to claim 1 or 2, wherein for the purpose of interrupting the measuring process by means of the measuring device the fuel flowing from the high-pressure fuel pump is directed by way of a part of the fuel line passing the measuring device and for the purpose of switching on the measuring device the part of the fuel line passing the measuring device is blocked.

4. A method according to claim 3, wherein the measuring process is 14 interrupted before the measuring piston arrives at the stop lying to the side of the high-pressure fuel storage device.

5. A method according to claim 4, wherein the injection quantity measuring signal acts as a control signal for a regulating device of the internal combustion engine.

6. A method according to any of claims 1 to 5, wherein when the measuring device is switched on, the fuel supply is interrupted if a predetermined fuel flow is exceeded.

7. A fuel injection system for internal combustion engines comprising a high-pressure fuel storage device which is supplied with fuel from a highpressure fuel pump for storing pressurized fuel, an electrically controlled fuel injection valve which is supplied with fuel from the highpressure fuel storage device and comprising a monitoring device for the purpose of monitoring the quantity of fuel supplied to the fuel injection valve from the high-pressure pump by way of a fuel line by means of a measuring device which comprises a measuring cylinder which on the one hand is connected to a part of the fuel line lying upstream of the measuring device and on the other hand to a part of the fuel line lying downstream of the measuring device between the highpressure fuel pump and injection valve and in which measuring cylinder is disposed a measuring piston which can be displaced between stops and which is adjacent with its end face in the measuring cylinder to a chamber lying upstream on the inlet side and with its other end face is adjacent to a chamber which lies downstream on the outlet side and comprising a sensor device by means of which the position of the measuring piston within the measuring cylinder can be ascertained in a non-contact manner, for the purpose of implement one of the methods in accordance with claim 1 to 5, wherein the inlet-side chamber of the measuring cylinder is connected by way of an inlet to the part of the fuel line lying upstream and the outlet-side chamber is connected to the part of the fuel line lying downstream between which and the part of the fuel line connecting the inlet lies an intermediate part as a passingby part of the fuel line, in which is disposed an electrically controlled valve which can be closed for the purpose of switching on the measuring device.

8. A fuel injection system according to claim 7, wherein the fuel line at the junction of the inlet is formed in such a manner that the fuel flow produces a negative pressure which is effective in the inlet-side chamber, preferably as a Venturi tube.

9. A fuel injection system according to claim 7 or 8, wherein the measuring piston is influenced by a restoring force by means of which it is urged towards the side of the inlet-side chamber.

10. A fuel injection system according to claim 9, wherein the restoring force is provided by means of the negative pressure at the junction of the inlet.

11. A fuel injection system according to claim 9, wherein the restoring force is provided by means of a spring which is supported between the measuring cylinder and the measuring piston.

12. A fuel injection system according to claim 11, wherein the spring is supported against a stop which is formed as a piston which is movable in the 16 measuring cylinder and can be displaced against a biassing spring.

13. A fuel injection system according to claim 12, wherein the displaceable piston comprises a sealing surface with which it can be moved onto a valve seat which encompasses the downstream part of the fuel line during a displacement movement after the biassing force of the biassing spring has been exceeded.

14. A fuel injection system according to any of the aforementioned claims, wherein the monitoring device is disposed between the high-pressure fuel pump and the high-pressure fuel storage device.

15. A fuel injection system according to claim 7, wherein an optical sensor is provided as a sensor device which ascertains a surface structure of the measuring piston in the form of a reflection grid.

16. A fuel injection system according to any of claims 7 to 15, wherein a damping element is disposed betweenihe monitoring device and the highpressure storage device.

17. A fuel injection system according to claim 16, wherein the damping element is formed from a tubular insert comprising a plurality of restrictor bores issuing from a blind bore.

18. A fuel injection system according to claim 17, wherein in addition a damping element is disposed in each case between the high-pressure storage device and each injection valve.

19. A method of measuring fuel substantially as hereinbefore described with reference to the accompanying drawings.

17

20. A fuel injection system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.