METHOD AND DEVICE FOR TIGHTNESS TESTING OF A TEST OBJECT HAVING AT LEAST TWO SEPARATE CHAMBERS

Abstract: A method and a device for tightness testing of two separate chambers (C1, C2) of a test object (T), the two chambers being separated by at least one partition wall, especially in serial production. A possible pressure change in each chamber compared to the pressure in an associated reference container (R1, R2) is measured. Preferably in a first step, the tightness between the chambers (C1, C2) is tested by connecting each chamber to the respective reference container (R1, R2) and applying different, high pressures (TR1, TR2), The chamber (C2) having the lowest pressure and the associated reference container (R2) are disconnected (V5, V5') from each other and connected to a differential pressure sensor (D1) for detecting a possible pressure increase caused by internal leakage. If no internal leakage is detected, each chamber is then tested with respect to a possible external leakage.

Description: "Method and Device for Tightness Testing of a Test Object having at least two Separate Chambers" The invention relates to a method and a device for tightness testing of a test object having at least two seoarate chambe separated by at least one partition wall. In seria-1 production of parts, which have to be pressure tig it is often necessary to test the tightness of each and ever part. It is essential that the testing operation is reliabl and as fast as possible, and preferabl .an automatic testing system is used. Such systems have been developed along vario lines, as described in the Swedish Patent specifications 7313782-0, 7412067-6 and 7506284-4. Thus, the Swedish patent specification 7412067-6 discloses a tightness testing method in which'a test object and a refe¬ rence container are filled with a test fluid at the same pre sure and are connected to each side of a pressure sensitive diaphragm mounted in a differential pressure sensor, the diaphragm being deflected when the pressure falls in the test object due to leakage in the same. hether the test object should be classified as "tight" or "leaking" is a re¬ lative concept in the sense that" a certain leakage can al- ways be detected if a sufficiently high pressure is applied and/or a sufficiently long measuring time is used. In serial production certain s.c. tightness requirements are therefore established, according to which a test object is considered tight if leakage (diaphragm deflection of a certain degree) cannot be detected at a given testing pressure within a pred termined measuring time. The main object of the present invention is to improve this method for test objects having at least two separate chamber separated by at least one partition wall. An example of such objects are internal combustion engines having separate chambers, i.e. chambers for fuel, a lubricant and/or a cool¬ ing medium. The improvement should in the first place invol a reduction of the testing time for each test object without jeopardizing the reliability. According to the invention, this object is achieved by a method and a device, respectively, wherein the tightness between the chambers is tested by applying to the two cham¬ bers different fluid pressures both exceeding or both being below (i.e. both lying on the same side of the ambient press the ambient atmospheric pressure, whereupon the pressure in the chamber having the lowestover-pressure or the highest under-pressure, respectively, is checked with regard to a possible pressure increase or decrease, respectively, indi- eating an internal leakage in the test object. In case of su internal leakage (upon application of over-pressure) the pre sure will rise in the low pressure chamber. The pressure in¬ crease indicates unambiguously that the leakage is internal, and the test operation can be concluded already at this: stag if, on the other hand, no internal leakage is indicated, the test is continued by a tightness test of each chamber with respect to a possible leakage towards the outside, i.e. a s.c. external tightness test. For many types of test objects having at least two chambers, the tightness requirements for internal leakage can be set much lower than for external leakage. Thus, the testing time for the internal tightness test can be made shorter than that of the external tightness test. By the mere making of a parate testing of the internal tightness and, above all, by m i ' ig ' the internal tightness test first and only thereafter, in case no internal leakage is found, completing the testing an external tightness test, the total average testing time per object can be reduced considerably. Thus, the tightness test does not have to be a "bottleneck" in the oroduction. By using a differential pressure sensor, the time needed for each tightness test and, consequently, the total testing time per test object may be further reduced by a controlled change of pressure simulating a slight leakage, either by a controlled pressure increase on the high pressure side or by a controlled pressure reduction, e.g. by means of a well- defined gas-leak, on the low pressure side (high and low pressures here denote the pressures on each side of the dia¬ phragm of the differential pressure sensor) . The invention is described further below with reference to t drawing which is a schematical representation of a tightness testing device. To the right on the drawing, there is a test object T havin two chambers Cl and C2, which are separated from each other a partition wall M. It should be emphasized that the test object T is shown schematically only on the drawing, whereas in reality the test object is normally of a rather complicat configuration.Likewise, the test object may contain three or more chambers mutually separated from each other and each being pressure tight internally towards the other chambers as well as externally towards the environment. The two chambers C1,C2 of the test object T are connected by means of detachable connectors (not shown) and hoses or con¬ duits LI and L2 to a source of pressurized gas (not shown either, but indicated by the arrow PI to the left on the drawing) . In the conduits LI and L2 there are inserted elec- trically controllable cut-off valves VI, V2 and V4, V5, respe tively, as well as pressure regulating valves TRl and TR2, respectively, so that the chambers can be connected to the pressurized gas source, though each with a different fall of pressure in the respective pressure regulating valve TRl, TR2. Between the valves VI and V2, there is connected a branch conduit L3, which in turn communicates, via a hose or condui L5, with a first reference container Rl. Correspondingly, a branch conduit L4 and a conduit L6 are connected between the conduit L2 and a second reference container R2. The reference containers Rl and R2 should each have a volume substantially of the same size as the volume of the chambers Cl and C2, respectively, of the test object T and these con- tainers may consist of the chambers of a test object care¬ fully tested in advance and found tight. On both sides of the branch conduits L3, L4, there are inser ted in each conduit L5 and L6 electrically controllable cut- off valves V2' , V3 and V5' , V6, respectively. By opening the valves V3, V6, the conduits are evacuated so that the pressu ized gas exhausts (arrows P2) into the ambient air or into a recovery tank (in case a pressurized gas other than air or highly purified air is used) . Moreover, in the conduits LI and L2 (between the valves V1,V and V4, V5, respectively) a pressure sensor TVl and TV2, res tively, is connected and arranged to close the valves VI and V4, respectively, when reaching a predetermined pressure. The cut-off valves V5 and V5' are controlled by two parallel connected time relays Tl and T3, which are described more fully below. Between the conduits Ll and L5 a differential pressure senso D2 is connected, which is represented schematically on the drawing and is provided with a diaphragm which is exposed on each side to the pressure in the respective conduit Ll,L5 The deflection of the diaphragm actuates an electrical conta included in series in a circuit containing a time relay T4 and a signal lamp which is lit when the actuated contact clo ses within a time period or measuring time determined_by th relay T4. Correspondingly, two differential pressure sensors D3 and Dl are connected between the conduits L2 and L6 and each adapted to actuate a circuit having a time relay T5, T2, and a signal lamp for indicating a relative pressure red tion in the respective conduit L2, L6. Finally, controlled gas leaks r i.e. throttles S1,S2 and S3, are connected to the conduits Ll, L2 and L6,via electrically trolled cut-off valves V8, V9 and V7. The device also comprises electrical circuits for controllin and actuating the various valves etc., but these circuits ar of a conventional nature and, therefore, they do not need to be described here. The device operates essentially in the following way: From the start, the valves V1,V2,V2' ,V4,V5 and V5' are open, whereas the remaining valves are closed. The conduits Ll, L5, L2 and L6 are thus connected via the pressure regulators TRl, TR2 to the pressurized gas source (arrow PI) , so that the system is filled with gas. When the respective predetermined pressure has been achieved in each partial circuit Ll, Cl, L5, Rl and L2, C2, L6, R2, the pressure sensors TVl and TV2 cause the valves VI and V4 to close. After a stabilizing time, predetermined by the time relay Tl, the valves V5 and V5' will close. Consequently, the partial circuit L2, C2 is separated from the partial circuit L6, R2 and from the partial circuit Ll, Cl, L5, Rl. Thus, one chamber Cl of the test-object is still connected to the corresponding reference container Rl, whereas the other chamber C2 of the test object is completely separated from its associated reference contai¬ ner R2, although the chamber C2 and the container R2 at this stage have exactly the same pressure. When the valves V5, V5' are closed, the valve V7 is opened to the controlled leak S3, and there follows a control measure¬ ment (internal measurement) of the tightness between the cha ber Cl exposed to a relatively high pressure and the chamber C2 exposed to a relatively low pressure. During a time period, predetermined by the time relay T2, a possible pressure increase in the chamber C2 is detected by means of the diaphragm of the differential pressure sen¬ sor Dl. This measuring time period can be kept rather short because a slow, controlled pressure reduction is effected in the circuit L6, R2 by means of the control leak S3. In the event of a leakage exceeding a certain leakage flow (corresponding to the given pressure difference between Cl and C2 and the predetermined measuring time) , the contact co nected to the diaphragm of the pressure sensor Dl closes the associated electrical circuit and lights the signal lamp to indicate internal leakage. In such a case the testing of the test object is concluded and the next test object is tested. If an internal leakage is not detected,the tightness test is continued by testing the tightness of each chamber Cl and C2 in relation to the outside, i.e. an external tightness test. For this purpose, the valves V5 and V5' are opened during a latively short stabilizing time determined by the time relay T3, so as to ensure that the high pressure and low pressure cuits have the same pressure at all points in each circuit. In this connection, the valve V7 and, after the stabilizing time, the valves V2, V2* , V5 and V5* are also closed. During the next following time period determined by the time relay T4, a possible pressure drop in the circuit Ll, Cl is detected by means of the diaphragm of the differential pres¬ sure sensor D2. Simultaneously, during a time period deter- mined by the time relay T5 (thus,both time periods can be started at the samemoment to gain time), a possible pressure EJR! drop in the circuit L2, C2■ is detected by means of the differential pressure sensor D3. A possible leakage (indicat by the respective signal lamp) in each circuit must constitu an external leakage, since these testing measurements have been preceded by an internal tightness test. After a complete testing operation, the valves V2, V2' , V3, V5, V5 ' and V6 are opened to let out the testing pressure, whereupon the test object can be taken out and be replaced b the next one. A number- of modifications can be effected within the scope o the inventive idea. For example, the differential pressure sensors D1-D3 can be replaced by inductive pressure sensors of the kind described in the Swedish Patent specification 7507483-1. Furthermore, the two pressure sensors Dl and D3 can be replaced by only one differential pressure sensor operating in both directions. It is also possible to measure the pressure in the low pres¬ sure chamber C2 by means of an ordinary pressure sensor, i.e by measuring the absolute pressure in the chamber C2, during the internal tightness testing. The essential point is that a possible pressure increase in the low pressure chamber can be detected during the internal tightness testing. As an alternative, vacuum can be used instead of a high pres sure. In that case, reduced pressures substantially below th ambient air pressure are applied in the two chambers Cl and Then, the chamber Cl or C2 having the highest pressure (clo¬ sest to the ambient pressure) is tested with regard to a pos le pressure drop caused by internal leakage to the other chamber. The signal lamps may be replaced or supplemented by other indicators and/or control means, e.g.for automatic control o the entire testing operation. The valves may be controlled in some other way than electrically. Finally, separate pres¬ sure or vacuum sources may be connected to the high pres¬ sure and low pressure circuits, respectively, in which case the pressure regulators TRl and TRl are no longer necessary,

Claims: C L A I M S 1. A method for testing the tightness of two separate chambe (Cl, C2) of a test object (T) , said two chambers being separ by at leastone partition wall, by detecting a possible change of pressure in each chamber during predetermined time period c h a r e c t e r i z e d in that the tightness between the two chambers (C1,C2) is tested by applying to each chamber a gas pressure substantially different from the ambient pressu the gas pressures in the chambers being mutually different b both lying on the same side of said ambient pressure, and in that the pressure in the chamber (C2) having the pressure closest to the ambient pressure is tested with respect to a possible pressure change away from the ambient pressure, sai change being caused by internal leakage. 2. A method as defined in claim 1, c h a r a c t e r i z e d in that the internal tightness test is followed by testing the tightness of each chamber towards the outside, the latte external testing being performed only in case the first, internal test indicates no leakage between the chambers. 3. A method as defined in claim 2, c h a r a c t e r i z e d in that the predetermined time period (T2) for said first, internal tightness test is chosen considerably shorter than the time period (T4,T5) for the external tightness test of each chamber. 4. A method as defined in anyone of claims 1-3, c h r a c¬ t e r i z e d in that the time period for each tightness tes is reduced by a controlled change of pressure (S1-S3) in eac measuring circuit. 5. A method as defined in claim 4, c h a r a c t e r i z e d in that the controlled change of pressure is achieved by means of a well-defined gas leak (S1-S3) in the circuit having the lowest pressure. ^^ j ?.E 6. A device for testing the tightness of two separate chambe (C1,C2) of a test object (T) , said two chambers being sepa¬ rated by at least one partition wall,comprising conduits (L5, L3, Ll, L6, L4, L2) for connection of each of said chambers to a gas source (TRl, TR2) having a pressure dif¬ ferent from the ambient pressure, valve means (VI, V2, V2* , V4, V5, V5') in said conduits, and pressure sensors (D1-D3) for detecting a possible change of pressure in each chamber, c h a r a c t e r i z e d in that said conduits and valve means are arranged in such a way that said two chambers (C1,C2) are connectable to each one of said gas sources (TRl, TR2) for applying gas pressures both being different from the ambient pressure, said gas pressures being mutually different but both lying on the same side of the ambient pre sure, and in that the chamber(C2) having the pressure closes to the ambient pressure is connectable to the associated pressure sensor (Dl) for detecting a possible pressure change away from the ambient pressure, said change being caused by internal leakage. 7. A device as defined in claim 6, c h a r a c t e r i z e d in that said pressure sensor is a differential pressure sensor (Dl) connected between said chamber (C2) and an associated reference container (R2) .

Inventors: BERGSTRAND GUNNAR
Applicants: BERGSTRAND GUNNAR, NOLEK SYSTEM AB
Application year: 1980
Main classification: G01M3
IPC codes: G01M3