Abstract:
A method and apparatus for testing and filling hydraulic assemblies such as a hydraulic clutch control assembly for a motor vehicle. A conduit is placed in communication with a pressure chamber of the assembly; air is sucked out of the pressure chamber through the conduit while a series of pressure readings are taken in the conduit indicative of the gradually declining pressure within the pressure chamber; the pressure readings are utilized to generate a vacuum signature; the vacuum signature is compared to a stored vacuum signature corresponding to an acceptable hydraulic assembly; the hydraulic assembly is accepted or rejected based on the match between the generated vacuum signature and the stored vacuum signature; assuming that the assembly is accepted, liquid is supplied through the conduit to gradually fill the pressure chamber of the assembly while taking a series of pressure readings indicative of the pressure in the chamber during the fill process; the fill pressure readings are utilized to generate a fill signature; the fill signature is compared to a stored fill signature corresponding to an acceptable assembly; and the assembly is rejected or accepted based on the correspondence between the generated fill signature and the stored fill signature.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to hydraulic apparatus in general and more particularly to a hydraulic control apparatus comprising a hydraulic master cylinder and a hydraulic slave cylinder for operating a mechanism remotely located from the master cylinder [the hydraulic control apparatus being prefilled with hydraulic fluid and pretested prior to shipment to a motor vehicle manufacturer for installation in a motor vehicle]. 
     It is known to prefill with hydraulic fluid a motor vehicle clutch control apparatus comprising a master cylinder, a reservoir of hydraulic fluid and a slave cylinder for operating the throw out bearing of a mechanical diaphragm spring clutch. Such prefilled hydraulic control apparatus are shown, for example, in U.S. Pat. Nos. 4,407,125, 4,599,860, 4,503,678, 4,506,507, 4,959,960, and 4,993,259, all assigned to the assignee of the present invention. 
     As is well known, prefilling with hydraulic fluid and pretesting hydraulic apparatus for operating motor vehicle mechanisms such as mechanical clutches presents the many advantages, for the motor vehicle manufacturer, of receiving a fully assembled mechanism comprising all of the components filled with hydraulic fluid and pretested for proper operation ready to install on a motor vehicle on the assembly line without requiring that the components be installed, separately connected by way of a flexible conduit, and filled after installation with hydraulic fluid while being purged of any atmospheric air contained in the apparatus. 
     Fast, efficient and accurate prefilling and testing of the hydraulic apparatus is critical to the commercialization of such prefilled controlled apparatus. Various filling and testing methods are disclosed in the above-identified patents assigned to applicant&#39;s assignee. 
     Specifically, in U.S. Pat. No. 4,407,125, liquid is supplied through the open top of the reservoir until the liquid bleeds out of a bleed port in the slave cylinder whereupon the filling is terminated. 
     In U.S. Pat. Nos. 4,506,507 and 4,503,678, a port is provided in a side wall of the reservoir, vacuum is applied to the system through the port to evacuate the system, liquid is introduced into the system through the port, and the port is thereafter sealed with a plug which serves to allow flow of hydraulic fluid out of the reservoir upon excess pressure but prevents reverse flow. 
     In U.S. Pat. No. 4,959,960, the apparatus is filled by the use of a filling head which is fitted into the open top of the reservoir and which includes a nozzle portion having an exterior surface enclosing a volume which approximates the volume of the diaphragm so that, following filling of the apparatus, removal of the filling head, and reinsertion of the diaphragm, the apparatus is automatically placed in the totally filled condition. In U.S. Pat. No. 4,993,259, the system is closed to substantially preclude escape of hydraulic fluid from the cylinder bore through the conduit means, a predetermined force is applied to the piston to urge the piston to move in the cylinder bore, and the magnitude of the movement of the piston in the cylinder bore in response to the predetermined force is measured to determine the acceptability or unacceptability of the unit under test. 
     Whereas the filling and testing methods disclosed in these patents have proven to be generally satisfactory, there continues to be a need to improve the apparatus and methodology of filling and testing to provide more reliable, less expensive, and faster filling and testing. 
     SUMMARY OF THE INVENTION 
     This invention is directed to the provision of improved method and apparatus for testing the integrity of a fluid pressure apparatus. 
     More specifically, this invention is directed to the provision of improved method and apparatus for filling, and testing the integrity of, a fluid pressure apparatus. 
     Yet more specifically, this invention is directed to the provision of an improved method and apparatus for prefilling  filling and testing a hydraulic control apparatus. 
     The invention methodology relates to the testing and filling of a fluid pressure apparatus having a fluid pressure chamber. For example, the fluid pressure apparatus may comprise a hydraulic control apparatus including a slave cylinder; a conduit connected to one end of the inlet port and the slave cylinder; a master cylinder connected at its discharge port to the other end of the conduit; and a reservoir assembly associated with the master cylinder. 
     According to the invention, the mass of the fluid in the chamber of the fluid pressure apparatus is gradually varied; the pressure in the chamber is noted at successive times as the mass is varied, whereby to generate successive pressure reading readings; a signature is created from the pressure reading readings; and the signature is compared to a known stored signature of a satisfactory apparatus. This methodology provides a convenient means of readily determining the integrity of the apparatus under test. 
     According to one aspect of the invention methodology, the step of gradually varying the mass of fluid in the chamber comprises evacuating air from the chamber to gradually reduce the pressure in the chamber. This evacuation step, which precedes the filling step, is thus utilized to test the integrity of the apparatus. 
     According to another aspect of the invention methodology, the step of gradually varying the mass of fluid in the chamber comprises gradually filling the chamber with a fluid. According to this aspect of the invention methodology, the filling step, following the evacuating step, is utilized to provide a further determination with respect to the integrity of the apparatus. 
     According to a more specific aspect of the invention methodology, the step of gradually varying the mass of fluid in the chamber comprises evacuating air from the chamber to gradually reduce the pressure in the chamber, and thereafter filling the chamber with a fluid; the step of noting the pressure in the chamber at successive times comprises noting the pressure in the chamber at successive times as the chamber is evacuated and thereafter noting the pressure in the chamber at successive times as the chamber is filled; the step of creating a signature from the pressure readings comprises creating a vacuum signature as the chamber is evacuated and creating a fill signature as the chamber is thereafter filled; and the step of comparing the signature to a known storage signature comprises comparing the vacuum signature to a known stored vacuum signature and thereafter comparing the fill signature to a second known stored fill signature. The invention methodology may be applied to various types of fluid pressure systems and apparatus both prefilled and postfilled. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of the invention test apparatus; 
     FIG. 2 is a perspective somewhat diagrammatic view of the invention test apparatus; 
     FIGS. 3 and 4 are vacuum and pressure signatures, respectively, generated by the invention test apparatus; and 
     FIG. 5 is a detail view of an encoder utilized in the invention test apparatus. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The invention test apparatus  10  is intended for use in filling, and testing the integrity of a fluid pressure apparatus having a fluid pressure chamber. For example, test apparatus  10  may be utilized to fill and test hydraulic control apparatus or assembly  12 . 
     Hydraulic apparatus  12  includes a master cylinder  14  including a housing  16 , a reservoir  18 , a piston  20 , and a push rod  22 ; a slave cylinder  24  including a housing  26 , a piston  28 , and a push rod  30 ; and a conduit  32  interconnecting the discharge end  14 a of the master cylinder with the intake end  24 a of the slave cylinder. Apparatus  12  may comprise, for example, a clutch control apparatus for a motor vehicle in which the apparatus is supplied to a motor vehicle manufactured in prefilled and pretested form so that the clutch control apparatus is ready for use simply by connecting the push rod  22  to the clutch pedal of the motor vehicle and associating the push rod  30  with a control lever for the clutch throw out bearing. 
     Test apparatus  10  includes a fixture  34 , an evacuate/fill conduit  36  including a trap  36 a; an evacuation system  38 , a fill system  40 , a scavenge system  42 , and an evaluation system  44 . 
     Fixture  34  is configured to hold the housing  16  of master cylinder  14  so as to preclude movement of the master cylinder during the test procedure. 
     Evacuate/fill conduit  36  includes a free or distal end  36 b communicating with reservoir  18  and another end  36 c. 
     Evacuation system  38  includes a conduit  46 , a conduit  48  connecting with conduit  46  and with the other end  36 c of conduit  36 , a pair of solenoid valves  50  and  52  interposed serially in conduit  46 , a vacuum pump  54  communicating with the distal end of conduit  46 , and a trap  56  interposed between solenoid valve  52  and vacuum pump  54 . 
     Fill system  40  includes an oil cylinder  58  including a piston  60 , an air cylinder  62  including a piston  64 , a connecting rod  66  connecting pistons  60  and  64 , a linear incremental optical encoder  68  including a sensor  70  mounted on connecting rod  66  and a fixed optical bar  71  positioned in a gap  70 a of the sensor, a conduit  72  communicating with one end of the oil cylinder, a conduit  74  extending between conduit  72  and one end of conduit  48 , a solenoid valve  76  in conduit  74 , a check valve  78  in conduit  48 , a conduit  79  connecting with the upper end of conduit  72 , and a solenoid valve  80  interposed in conduit  79 . 
     Scavenge system  42  includes a conduit  81  connected to the other end of conduit  48 , a solenoid valve  82  interposed in conduit  81 , and a scavenge pump  84  connected to the distal or free end  81 a of conduit  81 . 
     Evaluation system  44  includes a transducer  84 , an A/D converter  87 , a clock  88 , a signature generator  90 , a computer  92 , a comparator  94 , a printer  96 , and leads  98 ,  100 ,  102 ,  104 ,  106 ,  108 ,  110  and  112 . 
     Transducer  86  may take any of several well known forms and, for example, may comprise a unit available from DCT Instruments of Columbus, Ohio, as Part No. PTG15VB. Transducer  86  includes a probe  86 a communicating with test/fill conduit  36  and operative to sense the pressure in the conduit  36  at all times. Transducer  86  functions in known manner to convert the pressure signal sensed by the probe  86 a to an output analog electrical signal on lead  98  having a magnitude proportioned to the magnitude of the sensed pressure signal. 
     A/D convertor  87  receives the analog signal on lead  98  and converts the analog signal in known manner to a corresponding digital signal for further transmission on lead  111 . 
     Clock  88  is of known form and functions to emit a clocking or time pulsed signal at selected periodic intervals. 
     Signature generator  90  functions to generate a first signature  114  comprising an evacuation or vacuum signature and a second signature  116  comprising a pressure or fill signature  116 . 
     Comparator  94  functions to store signatures corresponding to known satisfactory apparatus  12  and, specifically, stores a first vacuum signature  118  corresponding generally to signature  114  and a second fill signature  120  corresponding generally to fill signature  116 . Signatures  118  and  120  are stored in computer  92  by testing a plurality of known satisfactory apparatus  12  to generate satisfactory evacuate and fill signatures. 
     Comparator  94  receives signatures  114 / 116  from generator  90  on lead  106  and signatures  118 / 120  from computer  92  on lead  110 , compares the respective signatures and make decisions with respect to the acceptability or unacceptability of the apparatus under test based on the extent to which the signatures generated by generator  90  correspond to the stored signatures in computer  92 . A light console  122  on comparator  94  includes a yellow light  122 a indicating that a test is in progress, a green light  122 b indicating that the unit under test is satisfactory, and a red light  122 c indicating that the unit under test is unsatisfactory. 
     Printer  96  communicates with comparator  94  via lead  108  and functions, upon a signal from comparator  94 , to print a detachable label  124  for securement to the defective apparatus. Specifically, when the comparator  94  determines that an apparatus under test is unsatisfactory it generates a signal via lead  108  for transmission to printer  96  whereupon the printer functions to print out a label  124  for securement to the failed apparatus. The information generated by comparator  94  with respect to each failed unit includes not only the fact that the unit has failed but also the specific nature of the defect causing the failure. Label  124  generated by printer  96  embodies a number or letter code identifying the specific defect of the apparatus. 
     OPERATION 
     In the operation of the invention test apparatus, control apparatus or assembly  12  is received at the test apparatus  10  following assembly of the control assembly  12  in known manner on a production line basis. As each control assembly  12  is received at the test station, the master cylinder  14  of the assembly is fixedly secured in the fixture  34 , the distal end  36 b of evacuate/fill conduit  36  is inserted into the reservoir of the master cylinder, and the push rod  30  of the slave cylinder is held in a contracted position by the utilization of, for example, a shipping strap  126 . 
     With valves  76  and  82  closed and valves  50  and  52  open, vacuum pump  54  is actuated so as to begin to suck air out of the apparatus  12  via conduits  46 ,  48  and  36 . As the air is sucked out of the pressure chambers of the apparatus  12  the pressure in the conduit drops gradually and this pressure is constantly sensed by transducer  86  so that transducer  86  generates a continuous but gradually dropping analog electrical signal on lead  98  for transmittal to A/D convertor  87  where the analog signal on line  98  is converted to a corresponding digital signal whereafter the digital signal is mixed with a clock signal on line  102  and the combined signal is fed to generator  90  to generate vacuum signature  114 , best seen in FIG.  3 . 
     In overview, signature  114  comprises a plot of pressure versus time, begins at approximately atmospheric or 14.7 psi, and gradually drops as air is exhausted from the pressure chambers of the apparatus  12 , reaching a final value of approximately 0.002 psi after a time lapse of for example 12 seconds. 
     Critical and telltale points on the signature curve include the shape of the entry knee  114 a, the location of the outgassing blip  114 b (indicating the release of volatiles or air trapped in pores of the cylinders under test), the slope of the signature line in the region  114 c, and the specific location of the diffusion point  114 d (the point at which there is no longer enough pressure in the system to push air out). The vacuum signature is transmitted in progress by lead  106  to comparator  94  and the comparable portion of the stored vacuum signal  118  in the computer  92  is gradually and simultaneously transmitted via lead  110  to the comparator  94  so that the instantaneous and progressively developing signature from the assembly under test and the stored signature of a proper assembly are gradually and simultaneously displayed and compared. 
     Although a decision with respect to the acceptability or unacceptability of the assembly under test may be deferred until the full signature has been developed and compared to the full stored signature, it is preferable, in the interest of saving time and money, to compare the two signatures at a plurality of points marking the respective conclusion of local graph sections such, for example, as the graph sections A, B, C and D seen in FIG.  3 . 
     Thus the instantaneously generated signature and the stored signature may be compared at the end of graph section A after approximately three seconds of test. If the comparison reveals a discrepancy indicative of a defect, the test is immediately aborted and the test assembly is rejected. The operator is apprised of the rejection by illumination of the red light  122 c on the light console  122  and the operator is precluded from releasing the master cylinder  14  from the test fixture  34  until he has performed an act, such as pressing a button or moving a lever, to indicate that he has noticed the red light and has therefore noticed that the unit under test is defective. At the same time that the defect is noted by the comparison taking place in the comparator  94 , a signal is transmitted from the comparator to the printer, indicating that a defect has been noted and indicating the precise nature of the defect, and the printer  95  thereupon prints a label  124  indicating by letter or by number the nature of the defect, which label may be detached by the operator and positioned on the defective assembly to facilitate repair of the assembly for subsequent retesting. 
     If the comparison of sections A of the instantaneous and stored signatures does not reveal a defect, the test is continued and proceeds through section B. At the conclusion of section B, an instantaneous and stored signature are again compared, and a decision is again made with the acceptability or unacceptability of the assembly. This section by section comparison procedure continues until the test has proceeded through all four sections whereupon, assuming that the test assembly has passed at each comparison at the end of each section, the green light  122 B is illuminated to apprise the operator that the assembly has passed the vacuum test. At such time as the test assembly is determined to have a defect, the exact nature of the defect may then be ascertained utilizing a lookup table incorporated in the comparator and/or the computer. 
     Defects that may be identified utilizing signature section A include gross part leaks and blocked or skived tubes or connectors. Defects that may be identified utilizing signature section B include reversed seals in the master cylinder, damaged seals in the master cylinder, missing or wrong components in the master cylinder, defective or damaged pistons in the master cylinder, center feed problems, blocked or skived tubes, fine leaks in the master cylinder, or scratched bores in the master or slave cylinder. Defects that may be identified utilizing signature section C include fine leaks in the slave cylinder and damaged connector seals. Defects that may be identified utilizing signature section D include unknown abnormalities or anomalies and out of tolerance parts. 
     Once the vacuum test has been completed, and assuming that the test has not been aborted by the detection of a defect in the assembly under test, valves  50  and  52  are closed, valve  76  is opened, and air under pressure is delivered to air cylinder  62  via conduit  128  to move the piston  64  forwardly and thereby move the piston  60  of the oil cylinder forwardly to eject hydraulic fluid out of the oil cylinder. The oil leaving the oil cylinder flows through conduit  72 , conduit  74 , valve  76 , conduit  48 , and check valve  78  to conduit  36  and thereafter into the reservoir  18  to begin filling the pressure chambers of the assembly under test. 
     As the hydraulic fluid flows through conduit  36  into the unit under test, transducer  86  continues to sense the pressure in the conduit  36  and continues to generate an analog signal on lead  98  for transmittal to A/D convertor  87  and transmittal via lead  111  and  104  to generator  90 . This signal is mixed with a digital signal on lead  112  from encoder  68  generated by movement of the sensor  70  with connecting rod  66  relative to fixed optical bar  71  as pistons  60  and  54  continue to move forwardly. Specifically, optical bar  71  includes a plurality of equally, linearly spaced slits  71 a; sensor  70  includes a diode  70 b and a light detector  70 c positioned on opposite sides of gap  70 a; and the digital signal on lead  112  from encoder  68  is generated every time a beam is completed across the gap  70 a between diode  70 b and detector  70 c by virtue of alignment of the diode and detector with a slit  71 a. The fill signature developed during the fill cycle is seen in FIG.  4  and comprises a plot of pressure versus pulses of the encoder, which are indicative of the position of piston  60  of fill cylinder  58 . 
     With respect to the fill signature, the analog signal generated by transducer  86  is read periodically in response to triggering from the encoder  68 . Specifically, encoder  68  triggers A/D converter  87  to take a reading from transducer  86  every time the encoder ends a unit of movement as sensed by the alignment of the diode/detector  70 b,  70 c of the sensor with a slit  71 a in the optical bar. The plot seen in FIG. 4 therefore includes a plurality of points generated at the end of each unit of linear movement of the connecting rod  66  as determined by the movement of sensor  70  with respect to bar  71 . The pressure sensed by the transducer  86  during the course of the fill cycle ranges from essentially zero pressure during the initial portion of the cycle to approximately 35 psi as the maximum pressure in the cycle. 
     Notable and significant points on the fill signature  116  include a flat introductory portion  116 a indicating the filling of the conduits leading to the assembly under test; a blip  116 b indicating filling of the reservoir of the master cylinder; a steep slope portion  116 c indicating movement of the oil through the orifice extending between the reservoir and the bore of the master cylinder; a blip  116 d indicating the start of the filling of the master cylinder; a dwell portion  116 e indicating continued filling of the master cylinder; a blip  116 f indicating the beginning of the filling of the conduit  32 ; a steep slope portion  116 g indicating the continued filling of the conduit; a blip  116 h indicating the start of the filling of the slave cylinder; a plateau portion  116 i indicating continued filling of the slave cylinder; and a blip  116 j indicating the end of the fill cycle, whereafter the pressure falls off sharply and returns essentially to atmospheric. 
     As with the vacuum signature, comparison of the stored full signature  120  to the instantaneously generated fill signature  116  may be delayed until the fill cycle has been completed but, preferably, comparisons are made at the end of each of a plurality of signature sections A, B and C and the test is aborted at such time as any one of these comparisons indicates a defect. 
     At such time as the comparator identifies a defect, either at the conclusion of any one of the sections A, B, or C or at the conclusion of the entire fill cycle, the comparator sends a signal to the printer  96  (to print a label  124  bearing a letter or number identifying the nature of the defect for attachment to the defective assembly under test) and causes the illumination of red light  122 C (to apprise the operator that the assembly under test has failed and require the operator to perform a predetermined manual acknowledging operation prior to release of the assembly under test by fixture  34 ). 
     Defects that may be identified utilizing fill signature section A include system integrity, improper reservoir, improper supply hose, reversed or damaged master cylinder seals, center feed problems, missing or improper master cylinder components, and blocked or skived tubes or master cylinder end connectors. 
     Defects that may be identified utilizing fill signature Section B include improper conduit between master cylinder and slave cylinder, blocked or skived conduits or slave cylinder end connector, and improper connectors. 
     Defects that may be identified utilizing fill signature section C include improper slave cylinder, reverse seal in the slave cylinder, damaged or defective seal in the slave cylinder, damaged or defective piston in the slave cylinder, and missing or improper components. 
     Once the fill cycle has been completed, valve  76  is closed, valves  80  and  82  are opened, scavenge pump  84  is actuated, and the pressurized air supply to air cylinder  62  via conduits  128  is reversed. Reversing of the pressurized air supply to air cylinder  62  causes piston  60  to retreat in air cylinder  58 ; opening of valve  80  allows make-up oil to flow through conduit  79  and  72  to fill in the oil cylinder behind the retreating piston; and the actuation of the scavenge pump in conjunction with the opening of valve  82  allows the scavenge pump to suck residual oil in the system out of the system in preparation for the next test cycle. 
     If a defect is noted at the end of any of the sections A, B, C or D of the vacuum signature or at the end of any of the sections A, B or C of the fill signature, the test is immediately terminated. The operator is apprised of the failure by virtue of illumination of the red light  122 c, and the operator, after acknowledging recognition of the failure by a suitable manual act, releases the master cylinder from the fixture  34  and places the failed apparatus  12  on a conveyor line leading to a rebuild station. 
     At the rebuild station the operator notes the label on the failed unit and specifically notes the specific letter or number code on the label indicating the specific defect in the unit, whereby to aid the repair person in the repair procedure. Following repair of the unit, the unit is placed again on the main conveyor line leading to the test/fill station where the unit is again tested and filled, and hopefully, passed on for shipment. 
     In overview, it is intended that the initial vacuum test detect the vast majority of the defective units while the units are still in a dry and therefore reusable condition, and that the subsequent pressure test detect those few defective units that were not detected by the vacuum test so that only a small percentage of the defective units that are ultimately detected comprise wet units that must be discarded. 
     The invention method and apparatus will be seen to provide many important advantages. Specifically, as compared to other systems employed by the assignee of the present invention for testing and filling, the test is quicker and, in fact, reduces the total evacuate and fill time by approximately 50%; the apparatus required to perform the testing is smaller and therefore takes up less space on the floor of the manufacturing and testing facilities; the test is more accurate since it involves a double test wherein the vast majority of the defective units are detected in the vacuum test and the remaining defective units are detected in the following fill test; since the vast majority of the defective units are detected in the vacuum test before they have been filled, only a few of the defective units are detected after filling and therefore only a few of the defective units have to be discarded; the system can be used to find and eliminate problems in the overall procedure rather than to simply detect bad units and as such provides a means of refining and improving the assembly process rather than simply a means of eliminating bad units resulting from the assembly process; and the fixturing required to hold the units under test is greatly improved and specifically is smaller, simpler, lends itself to modular fixturing, and provides easier loading of the units into the fixtures. 
     Although a preferred embodiment of the invention has been illustrated and described in detail it will apparent that various changes may be made in the disclosed embodiment without departing from the scope or spirit of the invention. For example, although the invention has been illustrated and described for purposes of clarity utilizing an item of comparator hardware to perform the comparison between the instantaneous signatures and the stored signatures, it will be understood that in actual practice the comparison between the instantaneous signatures and the stored signatures may be accomplished in known manner utilizing software. 
     Further, although the invention has been described with respect to the testing of a hydraulic unit including a master cylinder, a slave cylinder, and an interconnecting conduit, the system is equally applicable to the testing of master cylinder units per se with or without a quick connect coupling as well as slave cylinder units per se with or without a quick connect coupling. 
     Further, although the invention has been herein described with respect to a test facility at the end of the production line for the hydraulic unit to be tested and filled, the method of the invention may also be applied to systems (such as clutch or brake systems) that have already been incorporated into a motor vehicle in a dry condition as part of the overall motor vehicle assembly process in which case the invention method is used to test and fill the dry units in situ on the vehicle. 
     In broad overview, the present invention is applicable to the testing and filling of any fluid pressure apparatus having a fluid pressure chamber.