GB2328750A

GB2328750A - A method for testing an internal combustion engine for leak-tightness

Info

Publication number: GB2328750A
Application number: GB9817798A
Authority: GB
Inventors: Peter Gulla; Martin Hoppenstedt
Original assignee: Daimler Benz AG
Current assignee: Daimler Benz AG
Priority date: 1997-08-26
Filing date: 1998-08-14
Publication date: 1999-03-03
Anticipated expiration: 2018-08-14
Also published as: GB2328750B; FR2767922B1; ITRM980550A1; IT1302439B1; ITRM980550A0; FR2767922A1; GB9817798D0; DE19737064A1

Abstract

In a method for testing an internal combustion (IC) engine for leak-tightness, the heat arising at a leak due to the exit of a pressurized liquid from a system is detected using thermal imaging cameras or thermocouples. The thermal imaging cameras (or thermocouples) may be placed in an array so as to monitor the pressure connection points of the IC engine. A highly volatile medium may also be introduced in a sealing gap/length of the engine and will evaporate if contact with pressurized fuel is made i.e. when a leak is present.

Description

Method for testing a highly pressurized liquid in a fuel-injection system for leak-tightness The invention relates to a method and a device for testing a highly pressurized liquid in a fuel-injection system of an internal combustion engine for leaktightness.

DE 37 13 255 Al discloses a method for testing closed containers for leak-tightness. A motor-vehicle luggage compartment is mentioned therein as an example for a container. The container or luggage compartment is unpressurized and in the interior a gas is produced which is of a temperature lying clearly below the ambient temperature of the container. A thermal-image detecting device is provided outside the container, which device detects container leaks by the gases which emerge and are essentially below the ambient temperature. Infrared cameras, for example, are proposed for this device.

WO 96/30748 describes a method for detecting irregularities in a container, leakage points being recognised by pressure or temperature differences at the container wall.

DE 33 05 005 c2 discloses a method and a device for determining the temperature distribution along a length of a pipeline, the intention being for the temperature distribution to be determined with the aid of one or more thermocouples or thermistors arranged equidistantly along the length. Infrared cameras are likewise proposed for this purpose.

GB 1 480 173 describes a method in which valve leakages in a piston pump are recognised by a temperature increase of the defective valve. However, the temperature increase here relates to frictional heat which is caused by a liquid backflow in the defective valve.

For the technical background of leak tests reference should also be made to the publications JP 08247885 A, JP 2-287135 (A) and JP 2-78927 (A).

In systems which are under high pressure, as is the case for fuel-injection systems of over 1000 bar, a leak-tightness test is particularly important since a very high pressure is consistently present at all of the sealing points or sealing connections.

Leakage points which in conventional systems or at low pressures can still be rgard: as leakproof, have, however, to be recognised with great precision in high-pressure systems of this type.

To this end it is known to determine the leak-tightness of a motor-vehicle injection system by measuring a drop in pressure. The system is pressurized for this purpose and then the speed at which the pressure drops is observed. Since, customarily, an injection system inevitably contains leakage points at certain points, for example at the nozzle/control-piston device, a certain drop in pressure cannot be avoided. This means that this system of measuring the drop in pressure, which is known in practice, is relatively inexact since critical leakage points may under some circumstances be missed in the overall drop in pressure.

As an alternative to this, it is known in practice to undertake visual tests.

However, in this case, a leak is only recognised if the emerging fuel has filled all of the cavities and emerges from the screw connection. In the case of relatively small leaks, this may sometimes take a very long time. This means that this method is likewise very inexact and cannot be automated very successfully.

The present invention therefore seeks to provide a method and a device for testing a fuel in highly pressurized liquid in a fuel-injection system of an internal combustion engine for leak-tightness, it being possible, by means of the method and device, to detect any leaks which may be present in the system very precisely and, above all, also very rapidly using relatively simple measures.

According to the present invention there is provided a method for testing a highly pressurized liquid in a fuel-injection system of an internal combustion engine for leak-tightness, by detecting the heat arising at a leak and caused by removal of pressure from the liquid, which is pressurized in the system, when it emerges from a leakage point.

The invention also provides apparatus for carrying out the method.

The invention uses the knowledge that a highly pressurized liquid, as is the case with fuel in a fuel-injection system, becomes considerably heated, depending on the difference in pressure when pressure is removed as the liquid emerges at a leakage point. This effect is used according to the invention such that the heating up which arises is recognised or detected by measuring technology. For this purpose, it is merely required to provide appropriate measuring devices at those points at which a leakage may occur, or to allow these points to be monitored by measuring devices.

These measuring devices may be, for example, thermal-imaging cameras and/or thermocouples which are known per se and immediately recognise abnormal temperature increes as a leak.

Points which are inaccessible or are only accessible with difficulty may be recognised by means of a highly volatile medium which can be fed separately from the outside into the sealing gap. If there is a leak at the sealing gap, the emerging fuel heats and evaporates the highly volatile medium and is itself heated in the process. The evaporation rate can then correspondingly be perceived via the formation of streaks.

This advantageously means that there does not have to be such a long wait until the sealing gap is completely filled by fuel and its emergence can then be detected.

This method is particularly suitable especially for detecting leaks at injectors since the latter are generally accessible only with difficulty.

The method according to the invention and a device for this, as is described in Claims 5 to 8, can be used when installed both for testing individual parts of a high-pressure system and for testing the high-pressure system in its entirety.

In the following text, preferred embodiments of the invention are illustrated in principle by reference to the drawing. In the drawing: Fig. 1 shows a schematic, perspective representation of a fuel-injection system of an internal combustion engine with thermal-imaging cameras; Fig. 2 shows a schematic, perspective representation of a fuel-injection system of an internal combustion engine with thermocouples; and Fig. 3 shows a section through an injector of the fuel-injection system represented in Figures 1 and 2.

The invention is described below using a fuel-injection system of a motor vehicle as an example, however, it is of course suitable in principle also for testing other systems which are under a similarly high pressure.

As essential components a fuel-injection system has a high-pressure pump 1 from which a fuel feed line 2 leads to a fuel distributor 3. Individual branch lines 4 lead from the fuel distributor 3 to injectors 5. In the exemplary embodiment, four injectors 5 are provided with corresponding, individual branch lines 4. The injection system has high-pressure connections 6, which are especially at risk of leakage, at the connection of the feed line 2 to the high-pressure pump 1 and the fuel distributor 3, and also further high-pressure connections 6 at the connection between the fuel distributor 3 and the branch lines 4, and also between the branch lines 4 and the injectors 5 associated in each case with them. Such high-pressure connections are generally provided with union nuts at which a leak may occur if not properly fitted.

To monitor the system, in particular the high-pressure connections 6, the embodiment according to Fig. 1 provides one or more thermal-imaging cameras 7 distributed around the system.

A single thermal-imaging camera 7 may be sufficient for the monitoring, depending on the quality of the thermal-imaging cameras 7 and their resolution capacity and the size of the system.

If the system or individual parts of it is/are tested before they are fitted in a motor vehicle, the arrangement to be tested is generally guided past a thermalimaging camera 7, the points to be tested being successively detected by the thermalimaging camera(s) 7.

If a test is not provided until installation or preassembly has taken place, thermal-imaging cameras 7 are to be appropriately distributed around the system.

Instead of a leak test using thermal-imaging cameras 7, according to Fig.

2 thermocouples 8 may be provided as an alternative or else in combination with thermal-imaging cameras. In this case, thermocouples 8 are placed or arranged on the pressure connections 6 or in the immediate vicinity of the pressure connections 6, which thermocouples are elastically connected to a fastening device in the form of a fastening bar 10 via bars 9 in the manner of leaf springs. The bars 9 in the manner of leaf springs cause the thermocouples 8 to be elastically, and hence securely pressed onto the points to be measured, namely the high-pressure connections 6. Via the bars 9 in the manner of leaf springs and the fastening device 10, it is also possible for pulses or signals, which occur in the event of a leak in the thermocouples 8 which are being heated, to be passed on via control lines (not shown) to an evaluation of the temperature-measurement data.

The method according to the invention and the device according to Figures 1 and 2 can also be combined for automatic sorting with leaky parts being eliminated.

When thermal-imaging cameras 7 are used, the temperature increases which arise as a result of a leakage and which in the case of fuel in an injection system may amount to 70 K, for example, can be detected at the points under investigation by differences in brightness on or in the thermal-imaging cameras 7. This process can also be automated using image evaluation algorithms.

For points which are difficult to get access to and in which there may, for example, also be relatively long sealing gaps or sealing lengths, as is the case, for example, in injectors 5, a further method can be undertaken as an alternative or in addition to test for leak-tightness with the aid of a highly volatile medium. This method is represented in principle in Fig. 3. The injector 5 has an injector body 11 in whose interior an injection nozzle 12 is situated. The injector 5 is positioned in a cylinder-head cover 15 by a claw 13 and a claw-type fastening screw 15. Via connecting holes (not shown) the injection nozzle 12 receives fuel which is under high pressure and which it is intended to inject at the lower end into a combustion chamber of an internal combustion engine (likewise not shown). A sealing disc 16 is provided in the lower region to mat;e a seal between the injection nozzle 12 and the injector body 11. In the event of a leak, fuel can rise upwards in a gap 17 between the injection nozzle 12 and the injector body 11 surrounding the latter and can emerge at this point. However, this may last a relatively long time depending on the size of the leak. In order to much more rapidly detect a leak at this point, a highly volatile medium is poured from above or from the outside into the gap 17 and spreads downwards in the gap as far as the sealing disc 16. If a leak is present in the region of the sealing disc 16 and fuel under high pressure correspondingly emerges from the injection nozzle 12, the latter heats up considerably as pressure is removed to take it to atmospheric pressure. This heating is able to evaporate the highly volatile medium and the evaporation rate can be correspondingly detected at the exit from the gap 17 by the thermal-imaging camera 17 via the formation of streaks 18.

Claims

1. A method for testing a highly pressurized liquid in a fuel-injection system of an internal combustion engine for leak-tightness, by detecting the heat arising at a leak and caused by removal of pressure from the liquid, which is pressurized in the system, when it emerges from a leakage point.

2. A method according to Claim 1, wherein the leak is detected by one or more thermal-imaging cameras.

3. A method according to Claim 1, wherein the leak is detected by thermocouples.

4. A method according to any one of Claims 1 to 3, wherein a highly volatile medium is introduced into a sealing gap to test it, the medium evaporating when heated by the liquid which appears.

5. A device for carrying out the method according to any one of Claims 1 to 4, wherein one or more thermal-imaging cameras are provided around the system to monitor pressure connection points.

6. A device for carrying out the method according to any one of Claims 1 to 4, wherein one or more thermocouples are provided at pressure connection points of the system to monitor the leak-tightness.

7. A device according to Claim 5 or 6 for monitoring an injection system of an internal combustion engine, having a high-pressure pump, a fuel feed line to a fuel distributor, and having branch lines leading from the fuel distributor to injectors, wherein thermal-imaging cameras and/or thermocouples are provided to monitor pressure connection points of the fuel feed line to the fuel distributor, the branch lines and the injectors.

8. A device according to Claim 7, wherein the thermocouples bear against the pressure connections or are in the vicinity of them, and are fastened to a fastening device via spring-efastic elements.

9. A method for testing a highly pressurized liquid in a fuel-injection system of an internal common engine for leak-tightness, substantially as described herein with reference to and as illustrated in the accompanying drawings.

10. Apparatus adapted for carrying out the method of claim 9.