GB2231620A

GB2231620A - Apparatus for determining the time curve of the fuel quantity emerging from a fuel injection nozzle of an air- compressing fuel-injected internal combustion engine

Info

Publication number: GB2231620A
Application number: GB9011189A
Authority: GB
Inventors: Karl-Heinz Hoffmann; Ralf Decker; Gerd Huber
Original assignee: Daimler Benz AG
Current assignee: Daimler Benz AG
Priority date: 1989-05-19
Filing date: 1990-05-18
Publication date: 1990-11-21
Anticipated expiration: 2010-05-18
Also published as: GB2231620B; DE3916418A1; FR2647207B1; DE3916418C2; IT1240455B; IT9047981A0; IT9047981A1; FR2647207A1; GB9011189D0

Description

:2:3 1 Cs: -2 (2) 1 Apparatus for determining the time curve of the fuel

auantity emerging from a fuel injection nozzle of an air-compressing fuel-injected internal combustion engine The invention relates to an apparatus for determining the time curve of the fuel quantity emerging from a fuel injection nozzle of an air- compressing fuelinjected internal combustion engine having a liquidfilled measuring tube which is connected to the'injection nozzle and in the course of which there is provided a device for setting a predetermined pressure in the measuring tube and a device for damping pressure waves running through the liquid.

In an apparatus of this kind already known from 11Motortechnische Zeitschrift,t MTZ 25/7 (1964), page 268 - 282, provision is made to set the pressure in the measuring tube via a first throttle valve.In order to damp the pressure waves reflected at the throttle valve (reduction in cross-section) after injection has occurred, which pressure waves would falsify the measurement result, by the beginning of the next injection, an additional throttle valve, in which the reflected pressure wave is additionally damped as it moves backwards and forwards due to an increased wall friction in this region, is provided in the measuring tube, even before the throttle valve for pressure setting. However, this measuring apparatus has the disadvantage that separate and expensive matching of the two throttle valves to one another is necessary for each operating point of the internal combustion engine if the disturbing influence of reflected pressure waves on the measurement result is to be prevented.

The present invention seeks therefore to create an apparatus with which a simple and disturbance-free determination of the time curve of the fuel injection quantity in each operating point of the internal 2 combustion engine is possible.

According to the present invention there is provided apparatus for determining the time curve of the fuel quantity emerging from a fuel injection nozzle of an air-compressing fuel-injected internal combustion engine, having a liquid-filled measuring tube which is connected to the injection nozzle and in the course of which there is provided a device for setting a predetermined pressure in the measuring tube and a device f or damping pressure waves running through the liquid, wherein the device for damping the pressure waves is a tube bundle comprising a plurality of damping tubes of small cross-section, the sum of the individual crosssections of the damping tubes being at least approximately equal to the cross-section of the measuring tube and the pressure-setting device is a pressure regulator provided downstream of the tube bundle.

By virtue of the fact that there is no restriction in cross-section in the transition into the damping tube bundle, there is no reflection at this point of the pressure wave initiated by the injection procedure. At the end of the measuring tube, in contrast, pressure wave reflection at the pressure regulator still occurs. However, this pressure wave now moving backwards and forwards undergoes very pronounced damping as it passes through the tube bundle comprising a large number of individual tubes of small cross-section, more specifically because, due to an increased surface area in this region, there is an increased wall friction. Since the pressure wave has already passed through the tube bundle before it reaches the cross-section-closing or cross-section- restricting pressure regulator, reflection of an already damped pressure wave is all that occurs anyway at the end of the tube. The pressure regulator arranged downstream of the tube bundle guarantees that the predetermined static pressure in the measuring tube cannot be exceeded in any operating point of the internal combustion engine. Bef ore a pressure rise above the i 3 predetermined static pressure can occur after an injection procedure, a correspondingly small quantity of the measuring tube liquid flows out at the pressure regulator. It is thereby guaranteed in the apparatus according to the invention that the contents of the measuring tube have come completely to rest by the beginning of the subsequent injection, in whatever operating point (load and speed) the injection curve is determined. Expensive matching or adjustment of the pressure-setting device and of the device for damping reflected pressure waves or pressure waves running through the measuring tube liquid to the respective operating point is thus no longer necessary.

A pressure regulator of simple construction may be provided if the pressure regulator is a diaphragm valve subjected to gas pressure, which opens above a predetermined static pressure in the measuring tube and is otherwise closed, and in this case, the diaphragm valve prferably has two chambers, which are separated by a diaphragm and of which the first chamber is connected to the measuring tube and to an outlet pipe, the crosssection of the outlet pipe being controllable via the diaphragm, and the second chamber is subjected to a pressure corresponding to the predetermined static pressure.

Since the relationship between the injection rate and the pressure curve is dependent, inter alia, on the density of the contents of the measuring tube and on the speed of sound in the contents of the measuring tube and these two variables, in turn, are temperature-dependent, an additional improvement of measurement accuracy can be achieved if a device for holding constant the temperature of the measuring tube and of the tube bundle is provided.

The holding constant of the temperature of the measuring tube furthermore prevents additional reflections out of the measuring tube due to given thermal stratifications (density differences).

An embodiment of an apparatus according to the 4 invention will now be described by way of example with reference to the accompanying drawing.

Reference 1 indicates a fuel injection nozzle of a diesel internal combustion engine, via which, starting from a high-pressure injection pump not illustrated in the drawing, the fuel is introduced into the combustion chamber of the internal combustion engine. To determine the time curve of the fuel injection quantity of individual injections, the injection nozzle 1 is removed from the cylinder head of the internal combustion engine and connected to a measuring tube 2, which is filled with diesel fuel. In the course of this measuring tube 2 there is arranged a tube bundle 4 comprising 11 damping tubes 3. The inside diameter of each damping tube is 1.5 mm. The cross-section of the measuring tube 2 is here equal to the sum of the cross-sections of the individual damping tubes 3. Downstream of the tube bundle 4, the measuring tube 2 is connected to a pressure regulator 5 designed as a diaphragm valve. The diaphragm valve.5 comprises a housing 6 which delimits two chambers 8 and 9 separated from one another by a diaphragm 7. The first chamber 8 is connected to the measuring tube 2. Branching of f f rom this first chamber 8 there is furthermore an outlet pipe 10, the cross-section of which can be controlled by the diaphragm 7 in such a way that whenever the pressure in the f irst chamber 8 is greater than in the second chamber 9, the outlet pipe 10 is opened and in the event that the pressure in the second chamber 9 is greater than that in the first chamber 8, the outlet pipe 10 remains closed by the diaphragm 7. In this arrangement, the second chamber 9 is connected to a freely adjustable gas pressure source which is, however, not visible in the drawing. Any desired static pressure can thus be set in the measuring tube 2 via the pressure regulator 5. A plurality of strain gauges 11, connected to one another in a suitable manner. via which the expansion of the measuring tube caused by a passing pressure wave after an injection procedure, or an k r, electrical signal corresponding to this variable, is acquired, are secured on the outer wall of the measuring tube 2, being distributed over its circumference in the region of the connection to the fuel injection nozzle 1. This signal is f ed via the measured-value line 12 to an electronic control or evaluation unit 13.

To increase the measurement accuracy, the entire measuring tube 2, including the damping tube bundle 4, is placed in a liquid bath, not illustrated in the drawing for reasons of clarity, the temperature of which is held constant.

If an injection now takes place' via the injection nozzle 1, a pressure wave is produced which runs through the measuring tube liquid. The time curve of this pressure wave is directly proportional to the time curve of the fuel injection quantity. Since this pressure wave now causes a corresponding tube expansion over time, the signal transmitted to the control unit 13 via the strain gauges 11 and the measured-value line 12 corresponds exactly to the time curve of the fuel injection quantity. Af ter appropriate evaluation in the electronic control unit 13 (taking into account of the proportionality constants) this curve is output via a suitable output unit, e.g. an oscilloscope 19. The area underneath the curve 20 here represents the total injection quantity of an injection procedure.

The injection curve is integrated internally in the electronic control unit 13 and can be displayed as the total- or part-injection quantity. In addition, fluctuations of the injection quantity from cycle to cycle are displayed. The electronic control unit 13 furthermore outputs a deflection voltage, constant in terms of the angle, with which a consideration of an angular range independently of the rotational speed is possible on the oscilloscope.

The pressure wave progresses further through the liquid in the measuring tube and finally reaches the damping tube bundle 4 according to the invention. Since 6 there is no reduction in cross-section at the transition into the tube bundle 4 (cross-section of the measuring tube 2 = sum of the individual cross-sections of the damping tubes 3), there is also no ref lection of the pressure wave at this point. However, the relatively large surface area in the tube bundle 4 causes increased friction, with the result that the pressure wave is strongly damped even during the f irst pass through the tube bundle 4. The already damped pressure wave now emerging from the tube bundle 4 is now reflected at the pressure regulator 5. If, due to the pressure wave, the pressure in the measuring tube 2 briefly rises above the predetermined value, the diaphragm 7 lifts off from the outlet pipe 10 and liquid flows off until the outlet pipe 10 is closed again by the diaphragm 7, i.e. until the pressure in the measuring tube 2 or in the chamber 8 again lies just below the pressure prevailing in chamber 9. The pressure wave reflected by the pressure regulator 5 now passes back through the tube bundle 4 and in the process undergoes renewed damping. The pressure wave is finally reflected at the injection nozzle 1 again and once more progresses towards the tube bundle 4. Due to the increased friction in the tube bundle 4, the last residual ripple in the pipe system is also damped after only a short time, it thus always being guaranteed that the contents of the measuring tube have come completely to rest by the beginning of the following injection. Falsification of the measurement result due to any superimposition on the actual pressure wave by a residual ripple of preceding injections still present in the pipe system is thereby excluded. This applies both to injections in rapid succession, as in the case of high speeds of the internal combustion engine, and to large injection quantities, as in the case of a high load on the internal combustion engine.

It is not absolutely essential for chamber 9 of the pressure regulator 5 to be connected to a controllable pressure source; it can also be hermetically sealed.

1 7 However, it is only possible to regulate the static pressure in the measuring tube to a certain value in this way.

Instead of by means of strain gauges, the pressure curve in the measuring tube can also be determined with the aid of a piezoelectric pressure sensor connected to the liquid in the measuring tube via a measuring bore.

To reduce the overall length, it is expedient to design the pipe system comprising measuring tube and tube bundle as a tube spiral with a plurality of tube turns.

1 8

Claims

1. Apparatus f or determining the time curve of the fuel quantity emerging from a fuel injection nozzle of an air-compressing fuel-injected internal combustion engine, having a liquid-filled measuring tube which is connected to the injection nozzle and in the course of which there is provided a device for setting a predetermined pressure in the measuring tube and a device f or damping pressure waves running through the liquid, wherein the device for damping the pressure waves is a tube bundle comprising a plurality of damping tubes of small cross-section, the sum of the individual cross-sections of the damping tubes being at least approximately equal to the cross-section of the measuring tube and the pressure-setting device is a pressure regulator provided downstream of the tube bundle.

2. Apparatus according to Claim 1, wherein the pressure regulator is a diaphragm valve subjected to gas pressure, which opens above a predetermined static pressure in the measuring tube and is otherwise closed.

3. Apparatus according to Claim 2, wherein the diaphragm valve has two chambers, which are separated by a diaphragm and of which the f irst chamber is connected to the measuring tube and to an outlet pipe, the crosssection of the outlet pipe being controllable via the diaphragm, and the second chamber is subjected to a pressure corresponding to the predetermined static pressure.

4. Apparatus according to Claim 3, wherein the second chamber is connected to a controllable pressure source.

9

5. Apparatus acccording to any one of Claims 1 to 4, wherein a device for holding constant the temperature of the measuring tube and of the tube bundle is provided.

6. Apparatus according to any one of Claims 1 to 5, wherein the damping tube bundle comprises 11 individual tubes each having an inside diameter of 1.5 mm.

7. Apparatus for determining the time curve of the fuel quantity emerging from a fuel injection nozzle of an air-compressing fuel-injected internal combustion engine, substantially as described herein with reference to, and as illustrated in, the accompanying drawings.

Published1990 at The Pa.tentOfflee.S',ateRoase.66 71 High Holborn Lon Sales BranCh, St Mary Cray,. dor-WC1R4TP Further copies maybe obtained from The Patent 0Mce. OrPington, Rent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent, Con. 1187