GB2368401A

GB2368401A - A measuring device for the volumetric measurement of injection quantities

Info

Publication number: GB2368401A
Application number: GB0122673A
Authority: GB
Inventors: Gerd Schmutzler; Dietmar Schorr
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2000-09-20
Filing date: 2001-09-20
Publication date: 2002-05-01
Anticipated expiration: 2021-09-20
Also published as: DE10046572B4; GB0122673D0; DE10046572A1; GB2368401B

Abstract

A device for the volumetric measurement of injection quantities, in which an injection nozzle 3 injects a fluid into a measuring chamber 4 which comprises a metering piston 5, driven, with a gas tight seal, in the measuring chamber 4, and a valve 8 for emptying the measuring chamber 4. As a measure of the injection quantity, the displacement path of the metering piston 5 in the measuring chamber 4 is recorded based in the injection. In a drainage conduit 12 between the measuring chamber 4 and the valve 8 there is disposed a throttling mechanism 13 which ensures improved emptying of the measuring chamber 4. The throttling mechanism 13 consists of a multiplicity of feed-through openings 14 which can be in the form of a diffuser.

Description

1 2368401

Description

Measuring device for measuring injection quantities The present invention relates to a device for the volumetric measurement of injection quantities From DE 39 16 419 C 2 a device of this type is known in which fuel is injected through an injection nozzle into a measuring chamber A gas-pressure- loaded metering piston, which is connected via a lifting rod to an inductive displacement pickup, is driven in the measuring chamber The injection quantity in each case is recorded by measuring the displacement of the piston.

The measuring chamber is emptied via a plate-type filter by means of an electromagnetically actuated valve The valve is spring-tension-loaded The cross-section of the opening of the valve is determined by the balance of forces of spring and electromagnet Since the operating pressure of the injection nozzle varies, the spring tension has to be adjusted by regulating the spring bias in accordance with the operating pressure Operating phases with small injection quantities therefore produce relatively small opening strokes of the valve and consequently small flow apertures This promotes the possibility of a malfunction because owing to the small opening aperture there is a high risk that dirt in the fuel will produce a valve leak as a result of dirt particles becoming jammed in the opening aperture.

Against this, the object of the invention is to make available an improved device for measuring an injection quantity, which device will in particular overcome the drawbacks specified above in emptying the measuring chamber.

In order to achieve this object, a device for measuring an injection quantity is proposed, said device having the features set out in Claim 1.

Accordingly, in a device according to the invention for the volumetric measurement of injection quantities, a throttling mechanism is disposed between the measuring chamber and the valve Through the installation of a throttling mechanism, essentially the same back-pressure will advantageously act constantly on the valve, irrespective of the operating condition The bias of the valve spring consequently does not have to be adjusted to match different operating conditions The throttling mechanism thus makes it possible that, in order to open, the valve will execute the (same) maximum opening stroke even under differing operating conditions, i e the valve will be opened fully In particular, even under operating conditions with small injection quantities, the opening aperture of the opened valve is designed on the basis of the maximum opening stroke to be sufficiently large for blockages to be prevented effectively.

Advantageous embodiments of the invention follow from the subclaims.

In an advantageous embodiment of the invention, the throttling mechanism comprises a multiplicity of feed-through openings, as a result of which the flow behaviour of the fluid on flowing out of the chamber is improved The multiplicity of feed-through openings increases the functional reliability, since the risk of a possible blockage as a result of dirt particles is spread over many openings For a constant throttling effect, the number of feed-through openings has to be increased as the diameters of the individual feed-through openings decrease A filtering effect with regard to dirt particles can thus additionally be achieved through the number and diameter of feed-through openings in the throttling mechanism.

In an advantageous embodiment of the invention, the feed-through openings in the throttling mechanism are fashioned in the form of a diffuser Such a dispersed arrangement of the feed-through openings in the throttling mechanism reduces a tendency to become blocked In addition, the volume of the measuring chamber can in this way be kept small, thereby improving the dynamics of the device.

In a practical development of the invention, the feed-through openings are designed such that the steepness of the characteristic emptying curve of the measuring chamber enables it to be operated with injection quantities at the upper limit and with operating pressure at the lower limit Such an embodiment improves operational reliability since the design of the throttling mechanism also covers operating behaviour in the extreme range With regard to the emptying of the measuring chamber, the most unfavourable case involves minimal operating pressures at maximum injection volumes.

In an advantageous embodiment of the invention, the valve exhibits in the open position an opening aperture which is larger than the diameter of the individual feed-through openings Malfunctions through a valve leak as a result of dirt particles becoming jammed in the opening aperture are avoided since suitably large dirt particles are unable even to pass through the feed-through openings.

The throttling mechanism functions in an advantageous way as a filter for the opening aperture.

In a preferred embodiment of the device according to the invention, a piezo actuator is provided for actuating the valve The use of piezo actuators ensures short switching times and high actuating forces The opening time and opening width of the valve can in this way be specified precisely.

In a further advantageous embodiment of the invention, there is provision for the measuring chamber to be emptied by a one-off or multiple opening of the s valve Depending on the operating point, the emptying process can be controlled in terms of the duration and number of valve openings In this way, the same emptying time can be achieved for each operating point As well as avoiding over-emptying, this can increase the frequency of injection events.

Further advantages and embodiments of the invention follow from the description and accompanying drawing.

The features specified above and the features yet to be described below can of course, without departing from the scope of the present invention, be used not only in the combination indicated in each case but also in other combinations or in isolation.

The invention is illustrated by means of an embodiment in the drawings and is described in detail below with reference to the drawings, in which Figure 1 shows a schematic representation of a measuring device according to the invention in sectional view and Figure 2 shows two metering-piston displacement-time diagrams which illustrate the emptying of the measuring chamber over time.

Figure 1 shows a device 1 according to the invention for the volumetric measurement of injection quantities The device 1 comprises an injection mechanism 2, a measurement chamber 4, in which a metering piston 5 is driven, sealed gastight, and a valve 8 for emptying the measuring chamber 4.

As an injection mechanism, there is provided an injection valve 2, the injection nozzle 3 of which injects a quantity of fluid into the measuring chamber 4 The metering piston 5 in the measuring chamber 4 is of a gas-pressure-loaded design, whereby for example nitrogen is used as the inserted gas 7 When the injection quantity is injected or measured, the valve 8 is closed Consequently, the injection of the fluid quantity into the measuring chamber 4 causes a displacement of the metering piston 5 in the measuring chamber 4 which on account of the back-pressure from the nitrogen takes place at constant pressure in the measuring chamber 4 The displacement of the metering piston represents here a measure of the fluid quantity injected To determine the displacement of the metering piston, a lifting rod 6 is attached to the metering piston 5, the lifting rod transferring the movement of the metering piston 5 to, for example, an inductive displacement pickup.

In order to be able to move the metering piston 5 back to the start position for a further measurement, the fluid has to be removed from the measuring chamber 4 A conduit 12 and the valve 8 are provided for emptying the measuring chamber 4 for this purpose.

The valve 8 is preferably designed as an outwardly opening ball or plugtype valve, through which the clearance volume is kept as small as possible A valve mushroom 9 is pressed via a spring 11 against a valve seat 10 Since the valve 8 in accordance with the invention is actuated with a maximum lift each time it is opened, the valve 8 exhibits a relatively large opening aperture when in the open position By reason of the large opening aperture, small switching times of the valve 8 must reliably be implemented in order to ensure that the measuring device 1 functions reliably A piezo actuator 15, combining high displacement force and short switching times, will therefore preferably be used to actuate the valve 8.

To close the valve 8, the piezo actuator 15 is driven electrically such that through its longitudinal extension the spring 11 is pressed, countering the pressure of the measuring chamber, against the valve seat 10, and the measuring chamber 4 is closed To open the valve 8, the power supply to the piezo actuator 15 is cut As a result, the space taken up by the spring 11 is enlarged and the spring tension of the spring 11 thereby reduced such that even the minimum operating pressure of the measuring chamber 4 is sufficient to lift the valve mushroom 9 from the valve seat 10 and to clear an opening aperture for the fluid to flow out The valve 8 and the piezo actuator 15 may, however, also be designed such that the valve 8 is opened by supplying power to the piezo actuator 15.

As shown in Figure 2, the measuring chamber 4 can be emptied by a one-off or multiple opening of the valve 8 Diagrams a) and b) plot respectively the injection quantity and the displacement of the piston over time in milliseconds.

Diagram a) illustrates a multiple opening of the valve 8 and diagram b) a one- off opening of the valve 8 to empty the measuring chamber In both diagrams, the section A-B shows the injection of the fluid into the measuring chamber 4 and the section B-C the measured-value recording of the injection quantity.

Section C-D illustrates the emptying of the measuring chamber 4 through a multiple or one-off opening of the valve 8.

Through multiple opening of the valve 8, the emptying process can be controlled advantageously by means of the duration and number of valve openings, such that the emptying is achieved in the same emptying time depending on the operating point As a result, the frequency of injection events can be increased and overt-emptying of the measuring chamber 4 avoided.

With reference again to Figure 1, there is disposed according to the invention in the drainage conduit 12 between measuring chamber 4 and valve 8 a throttle 13 via which the fluid flows out from the measuring chamber 4 The throttle 13 is constructed of a multiplicity of feed-through openings 14 which, for -7 example, are designed as drill holes or are produced through electrochemical etching The throttle coefficient and the individual feed-through openings acting in combination are designed such that it remains possible to operate with maximum injection quantities and minimum operating pressure The diameter of the individual feed-through openings 14 is chosen so that this diameter is smaller than the planned opening aperture of the valve 8 when open In this way, the throttle 13 also performs, in addition to the throttling effect, a filtering function, filtering out dirt particles in the fluid which could block the opening aperture of the valve 8 In order to counter a tendency of the throttle 13 to become blocked, the feed-through openings 14 provided are of a diffuser type, i.e dispersed in the throttle 13.

The device according to the invention for the volumetric measurement of injection quantities achieves an improvement in the emptying of the measuring chamber In addition to variable control of the emptying process, the functional reliability in particular of the device is raised since a valve leak as a result of a blockage in the opening aperture of the valve is prevented effectively.

Claims

1 Device for the volumetric measurement of injection quantities, said device having an injection nozzle ( 2) which injects a fluid into a measuring chamber ( 4) which comprises a metering piston ( 5), driven, with a tight seal, in the measuring chamber ( 4) and a valve ( 8) for emptying the measuring chamber ( 5), whereby the injection quantity is recorded by calculating a displacement path of the metering piston ( 5) based on the injection, characterised in that a throttling mechanism ( 13) is disposed between the measuring chamber ( 4) and the valve ( 8).

2 Device according to Claim 1, characterised in that the throttling mechanism ( 13) comprises a multiplicity of feed-through openings ( 14).

3 Device according to Claim 1 or 2, characterised in that the feedthrough openings ( 14) are arranged in the throttling mechanism ( 13) in the form of a diffuser.

4 Device according to at least one of Claims 1 to 3, characterised in that the feed-through openings ( 14) are designed such that the steepness of the characteristic emptying curve of the measuring chamber ( 4) enables it to be operated with injection quantities at the upper limit and with operating pressure at the lower limit.

Device according to at least one of Claims 1 to 4, characterised in that the valve ( 8) exhibits in the open position an opening aperture which is larger than the diameter of the feed-through openings ( 14).

6 Device according to at least one of Claims 1 to 5, characterised in that a piezo actuator ( 15) is provided for actuating the valve ( 8).

7 Device according to at least one of Claims 1 to 6, characterised in that the emptying of the measuring chamber ( 4) is effected by means of a one-off or multiple opening of the valve ( 8).