Abstract:
A gauge for measuring the geometry of a fluid passage in a workpiece at precise gauge points in the passage. The gauge includes a probe with an internal gas flow passage extending to a calibrated orifice or port in the probe. Pressure developed in the gas passage when the orifice is at each gauge point is detected whereby the geometry of the passage is established.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     A precision air gauge for measuring the geometry of fluid passages in a fuel injector. 
     2. Background Art 
     In the manufacture of fuel injectors, particularly fuel injectors for diesel engines, precision machining of plunger bores, control valve openings, fluid passages and other physical features of an injector pump body or an injector valve body are required. An example of a known injector with precision machined pressure distribution passages may be seen, for example, by referring to U.S. patent application Ser. No. 09/245,106, filed Jan. 29, 1999, which is owned by the assignee of the present invention. That injector, which is commonly referred to as a unit pump, includes an injector pump plunger mounted for reciprocation in a cylindrical bore in a pump body. The bore and the plunger define a pumping chamber, which is pressurized during a fuel injection event as the plunger is stroked by a cam follower driven by an engine camshaft. A control valve body, formed integrally with the pump body, includes a control valve opening that receives a control valve. The control valve opening is in communication with the pumping chamber and with a high pressure distribution circuit that communicates with an injection nozzle formed in a nozzle body. 
     In the manufacture of a unit pump of this kind, high pressure precision machined passages are required for connecting the pumping chamber with the control valve chamber and for connecting high pressure regions of the assembly to the injection nozzle. Dimensional control of the passages during precision machining of an injector of this kind is critical. 
     We are aware of prior art air gauges for measuring the quality and dimensions of a machined opening or a fluid passage wherein air pressure is introduced to the opening or the passage through an orifice in the air gauge. The characteristics of the machined opening or the passage can be detected by measuring the air pressure developed at the gauge orifice as a gauge probe is inserted into the passage or into the machined opening. The magnitude of that pressure can be used as an input signal for a pressure sensor to determine variations in the dimensions of the opening or the passage. For example, U.S. Pat. No. 4,704,896 discloses a probe that can be inserted into a drilled, blind opening or passage to detect whether the opening or the passage has internal threads. 
     Another example of a known air gauge using a probe to measure the characteristics of a machined opening is disclosed in U.S. Pat. No. 3,667,284. That measuring gauge includes a tapered bore with multiple radial jets that communicate with a central air passage. By measuring the back pressure developed at each jet, an operator can determine whether the opening is properly tapered. An equal back pressure at each jet position will indicate that the bore is properly tapered. If the bore is not properly tapered, the back pressure readings will vary. 
     Air gauges of the kind disclosed in prior art teachings are not practical for obtaining precision readings of the physical characteristics of a fluid pressure passage at precise gauge points. Attempts to use such air gauges to measure the characteristics of a fluid passage at precise depths using a trial-and-error technique generally are unacceptable and not practical for use in a high volume injector manufacturing environment. If an attempt is made to precisely control the depth of the probe using externally mounted gauge blocks, for example, the measurement routine becomes too complex to use on a shop floor in a high-volume manufacturing operation. Further, the results would not be precise enough to meet desired quality standards. 
     SUMMARY OF THE INVENTION 
     In the manufacture of an injector of the kind disclosed in the previously identified pending patent application, a long precision-machined passage must be drilled in an injector pump or control valve body to provide fluid communication between the control valve chamber and the source of high injection pressure at the pumping chamber. Following the precision drilling operation, the open end of the passage must be plugged to seal the passage against leakage during operation. For this purpose, it is preferred to use a pin, which is inserted into the passage following the machining operation. The pin can be formed with a shape memory alloy (SMA) and inserted in the opening with minimal pressure (for example, finger pressure). The pin then can be heated so that it will expand to provide a permanent seal. To be effective, the dimensions of the opening must be precise. For this reason, close dimensional tolerances at specified gauge points are required by quality control standards. 
     The air gauge of the invention includes a probe that can be inserted into a machined fluid pressure passage in the pump or control valve body. The probe extends from a probe body that receives a sleeve secured to the body at a fixed position with respect to the probe. A depth control bushing, according to one embodiment of the invention, is secured to one end of the sleeve by a lost-motion connection that will permit relative movement between the bushing and the sleeve. 
     A spring is located between the bushing and the probe body so that the probe body normally is biased against a first stop established by the lost motion connection. When the probe is inserted in the passage, a first gauge point is established when the bushing engages a stop surface on the pump or control valve body. The sleeve then can be moved to advance the probe within the passage until a second stop on the sleeve engages a stop surface on the bushing. In this way, two precise gauge points are established in the opening, and air pressure measurements are taken at each point. By comparing the measurements, it can be determined whether a desired degree of taper in the passage is present following the machining operation. Further, out-of-roundness of the passage and deviations in diameter for the passage can also be detected. These characteristics of the pressure passage, particularly measurements of the taper of the passage, can readily be obtained with the required precision and with repeatable inspection results. 
     In an alternate embodiment of the gauge of the invention, a stop surface on the bushing engages a stop surface on the probe body when the probe is advanced from the first gauge point to the second gauge point. 
     According to still another alternate embodiment of the invention, multiple positions of the probe relative to the bushing are established by a detent mechanism rather than by engageable stop surfaces on the bushing and the sleeve. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic representation, partly in cross-section, of a unit pump fuel injector for an internal combustion engine, such as a diesel engine; 
     FIG. 2 is an enlarged cross-sectional view of the outer end of a drilled pressure distribution passage in the injector shown in FIG. 1; 
     FIG. 3 is a cross-sectional view of a bushing that forms a part of the gauge of the invention; 
     FIG. 4 is a cross-sectional view of a sleeve that is assembled on the probe body of the invention; 
     FIG. 5 is a side elevation view of the structure of FIG. 4; 
     FIG. 6 is a cross-sectional overall assembly view of the air gauge assembly of the invention; and 
     FIG. 7 is an alternate gauge construction embodying the invention. 
     FIG. 8 is another alternate gauge construction embodying the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 is a schematic representation of a unit pump fuel injector for a diesel engine. It comprises a fuel injection nozzle tip  10  with nozzle orifices  12 . Nozzle tip  10  is adapted to be mounted in a combustion chamber of an internal combustion engine. The nozzle tip  10  is part of a nozzle body located within a nozzle nut  14 , which in turn is secured by a threaded connection to the lower end of a pump body  16 . A plunger bore or opening  18  in the pump body  16  receives a pump plunger  20 . A pressure chamber (not shown in FIG. 1) is defined by the plunger opening  18  and the lower end of the plunger. A cam follower  22 , supported within guide sleeve  24 , is reciprocated in known fashion by a camshaft and cam follower assembly (not shown). 
     Plunger spring  26  urges the cam follower and the plunger  20  in an upward direction. It is seated on spring seat  28  formed on the pump body  16 . 
     A valve body  30 , which in the assembly of FIG. 1 is formed integrally with the pump body  16 , defines a valve chamber  32 . Control valve  34  received in the valve chamber  32  is connected to an actuator armature  36  for an actuator generally shown at  38 . A cross-passage  40  connects the high-pressure pumping chamber at the end of the plunger  20  with the control valve chamber  32 . The control valve  34  controls the degree of communication between passage  40  and the low pressure return circuit shown in part at  42 . 
     The valve  34  includes a valve land  44 , which is closed against a valve seat on the valve body  30  when the armature  36  is drawn in an upward direction by actuator  38 , as viewed in FIG.  1 . Actuator  38  is energized by a solenoid that is under the control of an electronic engine controller in known fashion. 
     A control valve spring  46  normally urges the valve  34  to an open position, thereby normally depressurizing passage  40  at intervals between high-pressure pulses for each injection event. 
     The passage  40  will be described in more particular detail with reference to FIG.  2 . The outward end of the passage  40  is sealed by a closure pin  48 . 
     The pin  48  is preferably formed of shaped memory alloy (SMA) material, which has known expansion characteristics when heated. It can be inserted using minimal pressure following drilling of the passage  40 . The pin then can be heated to expand the alloy, thereby forming a permanent seal that will resist leakage from the high-pressure passage  40 . 
     FIG. 1 shows the passage  40  at the left side of the plunger  20 . The cross-sectional view of FIG. 2 is oriented to show the passage  40  at the right-hand side of the plunger  20 . 
     The cross-sectional view of FIG. 2 shows the pump body and the valve body. The passage  40  is only partly visible in FIG. 2, but it communicates with the high-pressure pumping chamber at the lower end of the plunger in plunger opening  18 . 
     FIG. 2 shows an end part of passage  40  that extends to the exterior of the housing  30 , as shown at  54 . The valve body  30  is machined with a flat, precisely controlled surface at  54  against which the end of the probe of the invention is engageable, as will be explained subsequently. 
     The end of the passage  40 , as seen in FIG. 2, has two precision gauge points identified by reference numerals  56  and  58 . These gauge points in one working embodiment of the invention are spaced apart by 5 mm. The distance between gauge point  58  and the precision machine surface  54  in one working embodiment is 2.5 mm. The total distance from the surface  54  to gauge point  56  is 7.5 mm. By precisely measuring the dimensions of the passage  40  at gauge points  56  and  58 , the taper of the passage  40  can be determined precisely. Further, if the passage  40  exhibits out-of-roundness, that also can be detected at each gauge point. 
     Precision dimensional measurements at each of the gauge points are made using the measurement probe assembly of FIGS. 3,  4 ,  5  and  6 . The assembly includes a bushing shown in FIG. 3 at  60 . The bushing is generally cylindrical, as indicated, and has a reduced diameter nose portion or collar portion  62  with a precisely machined end surface  64 . The bushing  60  has a central opening  66 , which receives the end of a probe that will be described with reference to FIG.  6 . 
     A spring chamber  68  is coaxially aligned with opening  66 . A probe body chamber  70  of larger diameter than the diameter of opening  68  receives a probe body. A tapped opening  72  is formed at the right-hand end of the bushing, as shown at  72 . This receives a stop element, as will be described with reference to FIG.  6 . 
     A stop sleeve  74  for the probe assembly of the invention is shown in FIGS. 4 and 5. It includes a large diameter portion  76  and a smaller diameter portion  78 . A threaded opening  80  is formed in the large diameter portion to receive a set screw, as will be described with reference to FIG.  6 . The smaller diameter portion  78  has an elongated slot  82 . A precision machined shoulder  84  is formed at the interface of the large diameter portion  76  and the smaller diameter portion  78 . Similarly, the end surface of the bushing, seen in FIGS. 3 and 6 at  86 , is precisely machined so that when the probe is assembled, the travel of the probe within the passage  40  is controlled, shoulder  84  being engageable with the end surface  86 . 
     As seen in FIG. 6, a probe  90  has an end that can be inserted in the opening  40  following a drilling operation and following a machining operation to precisely establish flatness of surface  54  on the valve body  30 . The probe  90 , which extends through opening  66  in bushing  60 , includes a probe body  92  of larger diameter, as seen in FIG.  6 . Probe body  92  is received within a central opening formed in the sleeve  74 . It is held fast within the sleeve  74  by a set screw  94  in threaded opening  80 . Reduced diameter portion  78  of sleeve  74  is received in the open end of bushing  60 . A stop screw  95  is received in opening  72  in the large diameter portion of the bushing  60 . Stop screw  95  is received in slot  82  formed in the sleeve  74 . This prevents rotation of the probe with respect to the bushing while allowing movement of the probe in an axial direction with respect to the bushing  60 . 
     The probe  90  and the probe body  92  are formed with an internal air pressure flow passage  100 . Although it is contemplated that shop air normally available in a manufacturing facility can be used to pressurize passage  100 , other gases under pressure could be used if that is desired. 
     Passage  100  extends to a fitting  102  to facilitate attachment with an air line schematically shown at  104 . A column gauge and pressure transducer of conventional design is connected to the air line  104 , as shown at  106 . The measured pressure in line  104  is observed by means of a suitable readout device  108 . 
     The end of the probe  90  has an air flow port or metering orifice  110 , which connects the air flow passage  100  with the interior of the pressure passage to be measured, such as the passage  40  previously described. During operation, the probe end  90  is inserted into the passage  40  until the end surface  64  of the bushing  60  engages surface  54  on the valve body. At that point, the orifice  110  is located precisely at gauge point  58  seen in FIG. 2. A back pressure is developed because of the flow restriction provided by the clearance between the probe end  90  and the walls of the passage  40 . As the sleeve  74  is advanced, the probe  90  will advance farther into the passage  40  until the orifice  110  is precisely located at gauge point  56 , seen in FIG.  2 . At that point, another reading of the back pressure in passage  100  is obtained and recorded by the transducer  106  and the readout device  108 . When both readings are obtained, the end of probe  90  can be withdrawn and used in a subsequent inspection procedure for another injector part. 
     The travel of the probe relative to the surface  54  is controlled by the spacing between the shoulder  84  of the sleeve  74  and the end surface  86  of the bushing. In a working embodiment of the invention, that distance can be 5 mm, which is precisely the distance between the gauge points  56  and  58 . 
     The probe is advanced within the bushing  60  against the opposing force of spring  112 , which is seated on a shoulder  114  of the probe body  92 . 
     FIG. 7 shows an alternate gauge construction embodying the invention. It has elements that correspond to elements of FIG. 6, and its mode of operation is essentially the same as the mode of operation of the gauge of FIG.  6 . Elements in FIG. 7 that have counterpart elements in FIG. 6 are identified by similar reference numerals, although prime notations are added. 
     The gauge of FIG. 7 includes an adjustable nose  62 ′ that is threadably received in a threaded opening in bushing  60 ′. The nose can be locked securely in place after it is properly adjusted relative to bushing  60 ′. Jam nut  62 ″ is used for that purpose. 
     The left end of the nose  62 ′ engages machined surface  54  on the valve body  30  as the end of probe  90 ′ is inserted in the passage  40  to be measured. The right end of the nose  62 ′ serves as a shoulder for spring  112 ′. The spring  112 ′ is seated on shoulder  114 ′ of the probe body  92 ′. A desired preload for the spring  112 ′ then can be established. 
     The bushing  60 ′ has a shoulder  60 ″ that is engaged by shoulder  114 ′ when the spring is compressed. The distance between shoulder  114 ′ and shoulder  60 ″ may be the same as the spacing between shoulder  84  and end surface  86  of FIG. 6 (i.e., 5 mm). The distance between orifice  110 ′ and the end of nose  62 ′ may be the same as the spacing between orifice  110  and the end surface  64  of FIG. 6 (i.e., 2.5 mm). 
     As in the case of the design of FIG. 6, the probe of FIG. 7 has an internal gas flow passage (not shown) which communicates with orifice  110 ′. 
     The probe body  92 ′ is received in a handle  74 ′, which may be knurled if that is desired. Stop screw  95 ′ is threaded into probe body  92 ′ rather than into the bushing as in the case of the FIG. 6 version. It extends through a slot  82 ′ in bushing  60 ′. 
     FIG. 8 is another alternate construction having elements with features common to the construction of FIG.  6 . The common elements are identified with the same reference numerals used in FIG. 6, but prime notations are added. 
     In the construction of FIG. 8, sleeve  74 ″ is held fast on probe body  92 ″ by set screw  94 ′ in threaded opening  80 ′ in sleeve  74 ″. Sleeve  74 ″ is slotted at  82 ″. Bushing  62 ′″ is provided with a threaded opening  72 ′ which receives screw  95 ″. Slot  82 ″ receives screw  95 ″ so rotary motion of bushing  60 ′″ relative to probe body  92 ″ is avoided. 
     The axial position of the bushing  60 ′″ relative to the probe  90 ″ is defined by a detent mechanism generally shown at  116 . The detent mechanism comprises a spring loaded plunger  118  in an externally threaded detent cage  120 , which is secured in a threaded opening in bushing  60 ′″. Plunger  118  registers with any one of multiple detent recesses  122  in sleeve portion  78 ′. 
     In the embodiment of FIG. 8, multiple gauge points at which measurements are taken are determined by the spacing of detent recesses  122 . As in the case of the embodiments of FIGS. 6 and 7, the end surface  64 ′ on collar portion  62 ′″ is brought into engagement with surface  54  when a measurement is made. The bushing  60 ′″ can be adjusted from one detent position to another relative to the probe body as multiple measurements are made at the gauge points in passage  40  defined by the spacing of detent recesses  122 . 
     Having described one embodiment of the invention, it will be apparent to persons skilled in the art that modifications may be made without departing from the scope of the invention. All such modifications and improvements thereof are intended to be covered by the following claims.