Method of detecting defective assembly

Abstract

To provide an assembly failure detection method capable of detecting an assembly failure occurring in an assembly process of press-fitting a small cylinder member into a press-fitted hole of a large cylinder member.SOLUTION: The assembly failure detection method is performed in an assembly process in which the adjusting pipe (small cylindrical member) 60 is press-fitted into the press-fit hole 81 of the connector (large cylindrical member) 80. In the assembling step, the adjustment pipe 60 is press-fitted into the press-fit hole 81 of the connector 80 via the center pin 50 by a pressing load of the electric cylinder (drive device) 40 from a state in which the lower end portion 65 of the adjustment pipe 60 is in contact with the mouth of the press-fit hole 81 in the upper end portion 830 of the connector 80 whose axial direction is vertically installed. The determination device 30 monitors the pressing load of the electric cylinder 40 by a load cell (load sensor) 42, and determines that an assembly failure has occurred when the waveform of the pressing load with respect to the displacement amount of the center pin 50 deviates from a predetermined allowable range.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a method for detecting assembly defects. [Background technology]

[0002] Conventionally, methods for determining an abnormality based on the measurement value of a load sensor have been known. For example, Patent Document 1 discloses a detection method capable of accurately detecting the condition of a seal member when an internal combustion engine injector is inserted into an injector mounting hole in a cylinder head.

[0003] In the measurement step of this detection method, a load sensor is used to measure the insertion load acting on the seal member when the injector for an internal combustion engine is inserted into the injector mounting hole in the cylinder head. In the determination step, when the insertion distance of the injector for an internal combustion engine is within a predetermined range, the occurrence of an abnormality in the seal member is determined based on whether the absolute value of the difference between the maximum and minimum values ​​of the insertion load obtained by the load sensor is within a tolerance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-190201 Summary of the Invention [Problem to be solved by the invention]

[0005] The detection method in Patent Document 1 is implemented during the process of attaching a completed injector to an engine, not during the injector manufacturing process. Furthermore, Patent Document 1 does not mention anything about detecting assembly defects that may occur during the injector manufacturing process.

[0006] In the following, in the assembly process, the injector is installed so that the inlet of the fuel passage opens upward. A cylindrical connector is fixed to the inner wall of the body pipe that forms the fuel passage. A spring that biases the needle in the valve-closing direction is inserted into the bottom of the press-fit hole of the connector. Furthermore, an adjustment pipe is inserted so that its lower end abuts against the opening of the press-fit hole, and then the adjustment pipe is press-fitted into the press-fit hole.

[0007] If the center of the inserted adjusting pipe is misaligned with the center of the connector, the adjusting pipe will scrape the inner wall of the connector's press-fit hole while being pressed in, generating foreign matter. Also, if the amount of oil applied to the adjusting pipe press-fitting portion is insufficient, scratches or dents may occur when the adjusting pipe is pressed in. A detection method that can detect such defective products is needed to prevent them from being sent to subsequent processes.

[0008] If the adjust pipe is considered the "small cylindrical member" and the connector is considered the "large cylindrical member," the above problem is not limited to injectors but can be generalized to the "assembly process of press-fitting a small cylindrical member into a press-fit hole in a large cylindrical member" in any cylindrical product. An object of the present invention is to provide an assembly defect detection method that can detect assembly defects that occur in the assembly process of press-fitting a small cylindrical member into a press-fit hole in a large cylindrical member. [Means for solving the problem]

[0009] The assembly defect detection method according to the present invention is carried out in the assembly process of press-fitting the small tubular member 60 into the press-fit hole 81 of the large tubular member 80. In this assembly process, the small tubular member is press-fitted into the press-fit hole of the large tubular member via the center pin 50 by the pressing load of the drive unit 40, with the small tubular member's lower end 650 abutting against the mouth of the press-fit hole at the upper end 830 of the large tubular member, which is installed vertically in the axial direction.

[0010] The determining device (30) monitors the pressing load of the drive device by the load sensor (42), and determines that an assembly defect has occurred when the waveform of the pressing load relative to the displacement of the center pin falls outside a predetermined allowable range.

[0011] In the present invention, assembly defects that occur during the assembly process of press-fitting a small cylindrical member into a press-fit hole of a large cylindrical member (for example, press-fitting an adjust pipe into a press-fit hole of a connector in the manufacture of an injector) can be detected from the pressure load waveform and prevented from being passed on to subsequent processes. An elastic compression member (for example, a spring) may be housed in the lower part of the press-fit hole of the large cylindrical member.

[0012] Preferably, the drive device is an electric cylinder capable of adjusting the drive load or drive speed. Since the electric cylinder itself can detect the amount of displacement, there is no need to provide a stroke sensor. Furthermore, for example, when a common manufacturing device is used to perform the assembly process of multiple types of products with different press-fit portion dimensions or materials, using an electric cylinder as the drive device makes it possible to precisely adjust the appropriate press-fit load and press-fit speed for each product. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. [Figure 2] A diagram of the first stage of the assembly process. [Figure 3] This figure continues from the top of Figure 2. [Figure 4] A diagram of the second stage of the assembly process. [Figure 5] A diagram of the third stage of the assembly process. [Figure 6] A diagram of the fourth stage of the assembly process. [Figure 7] Enlarged view of part VII in Figure 6. [Figure 8] A diagram of the fifth stage of the assembly process. [Figure 9] 10 is a diagram showing the state of a non-defective pattern in the assembly process. [Figure 10] Graph of pressing load waveform for a non-defective pattern. [Figure 11] FIG. 10 is a diagram showing an example 1 of assembly failure. [Figure 12] FIG. 10 is a diagram of a pressure load waveform for assembly failure example 1. [Figure 13] FIG. 11 is a diagram showing an example 2 of assembly failure. [Figure 14] FIG. 10 is a diagram of a pressure load waveform for assembly failure example 2. [Figure 15] FIG. 10 is a diagram of a pressing load waveform for assembly failure example 3. [Figure 16] FIG. 10 is a diagram of a pressing load waveform for assembly failure example 4. DETAILED DESCRIPTION OF THE INVENTION

[0014] The assembly defect detection method according to the present invention will be described with reference to the drawings. This assembly defect detection method is carried out in an assembly process in which a small cylindrical member is press-fitted into a press-fit hole of a large cylindrical member during the manufacturing process of a certain product. The small cylindrical member is a cylindrical member with a smaller diameter than the large cylindrical member. In this embodiment, the assembly process in which an adjust pipe, which is a "small cylindrical member," is press-fitted into a press-fit hole of a connector, which is a "large cylindrical member," during the manufacturing process of an injector will be described as an example.

[0015] The schematic configuration of an injector 90 will be described with reference to FIG. 1. The injector 90 is mounted on an engine of a vehicle or the like and injects pressurized fuel into a combustion chamber through a nozzle hole. In the following description, the inlet 96 side of a fuel passage 95 will be described as the top and the nozzle hole 99 side as the bottom, following the orientation shown in FIG. 1. The internal components of a housing 91 that forms an outer shell are configured in a cylindrical shape that is approximately coaxial with an axis O. A coil 92 that generates a magnetic field when current is applied is inserted into the bottom of the housing 91. Magnetic members 931 and 933 form a magnetic circuit that transmits the magnetic field of the coil 92.

[0016] A body pipe 94 that forms a fuel passage 95 is provided inside the housing 91. The body pipe 94 is formed by joining, in order from bottom to top, a first magnetic portion 941, a non-magnetic portion 942, and a second magnetic portion 943. Magnetism is transmitted from the magnetic member 931 to the first magnetic portion 941, and magnetism is transmitted from the magnetic member 933 to the second magnetic portion 943.

[0017] Connector 80, which is a "large cylindrical member," is press-fitted and fixed to the inner wall of body pipe 94, spanning non-magnetic portion 942 and second magnetic portion 943. A movable core 87, which is movable by magnetic attraction, is provided below connector 80, which also serves as a fixed core. A valve seat 97, which has a fuel chamber 98 and multiple injection holes 99 (see FIG. 7 for an enlarged view), is provided at the lower end of body pipe 94. A needle 88 connected to movable core 87 moves up and down to open and close the valve portion of valve seat 97.

[0018] A press-fit hole 81 is formed in the center of the connector 80, and a spring 70 serving as an "elastic compression member" is housed in the connector 80, spanning from the bottom of the press-fit hole 81 to the recess of the movable core 87. The spring 70 biases the needle 88 in the valve-closing direction via the movable core 87. An adjustment pipe 60 serving as a "small cylindrical member" is press-fitted into the top of the connector 80, thereby adjusting the set load of the spring 70.

[0019] When the coil 92 is not energized, the needle 88 moves down due to the biasing force of the spring 70, closing the valve portion of the valve seat 97. When the coil 92 is energized, the movable core 87 is attracted to the connector 80, opening the valve portion of the valve seat 97, and the fuel in the fuel passage 95 passes through the passage hole 61 of the adjustment pipe 60, passes through the communication passage in the needle 88, and is injected from the injection hole 99.

[0020] Next, with reference to Figures 2 to 8, an assembly process will be described in which the spring 70 and the adjustment pipe 60 are inserted from above the fuel passage 95, and then the adjustment pipe 60 is press-fit into the press-fit hole 81 of the connector 80. Up until this previous process, the connector 80 has been fixed to the inner wall of the body pipe 94. The filter shown at the fuel passage inlet 96 in Figure 1 has not yet been installed. Figures 2 and 3 show the first stage of the assembly process, and Figures 4, 5, 6, and 8 show the second to fifth stages, respectively. Figure 7 shows an enlarged cross section of the injector 90 in the fourth stage.

[0021] In the manufacturing apparatus 100, a pallet 10 on which an injector 90, which is a workpiece, is placed is transported along a rail (not shown). In addition to a workpiece receiving hole 11, the pallet 10 is formed with a guide shaft 12 extending vertically and a cam 15 having an inclined surface 16 at its upper end. The injector 90 is placed so that its lower portion is received in the workpiece receiving hole 11 and its fuel passage inlet 96 opens upward. The guide shaft 12 guides the descent of the feeding unit 20. The cam 15 moves a cam plate 25 to open a stopper 27.

[0022] The feeding unit 20 includes a unit body 21, a guide bush 22, a holder 23, a cam plate 25, a slider 26, a stopper 27, a feeding guide 28, etc., which are arranged so as to be able to descend as a unit. The guide bush 22 is fitted onto the guide shaft 12 and slides along the guide shaft 12.

[0023] The holder 23 and the insertion guide 28 are arranged coaxially with the axis O of the injector 90. A set hole 24 is formed in the center of the holder 23, and receives the spring 70 on the lower side and the adjust pipe 60 on the upper side. The insertion guide 28 is connected to the lower end of the holder 23, and is inserted into the fuel passage 95 of the workpiece from the second stage onwards. In the first and second stages, the spring 70 and the adjust pipe 60 received in the set hole 24 are prevented from falling into the insertion guide 28 by a stopper 27.

[0024] A center pin 50 supported by a pin guide 45 is provided above the holder 23 and coaxial with the axis O of the injector 90. As shown in FIG. 3, an electric cylinder 40 serving as a "drive device" is also provided above the center pin 50. A load cell 42 serving as a "load sensor" is interposed between the tip of a rod 41 of the electric cylinder 40 and a pin head 51 of the center pin 50. The load cell 42 detects the pressing load that causes the rod 41 of the electric cylinder 40 to extend and lower the center pin 50.

[0025] The electric cylinder 40 is capable of adjusting the driving load or driving speed. It may also have a servo function that performs feedback control to adjust to a target load or target speed during driving. Note that while Fig. 3 shows the overall length of the electric cylinder 40 to represent the full stroke of the rod 41, the overall length of the electric cylinder 40 is not shown in other figures.

[0026] The determination device 30 monitors the displacement of the center pin 50 and the pressing load of the electric cylinder 40 detected by the load cell 42. In this embodiment, the electric cylinder 40 is used as the "drive device," so the driving stroke of the rod 41 can be obtained as the displacement of the center pin 50. The determination device 30 determines whether an assembly defect has occurred based on whether the waveform of the pressing load relative to the displacement of the center pin 50 is within a predetermined allowable range.

[0027] The operation of the manufacturing apparatus 100 will be explained in order from the first stage to the fifth stage. In the first stage, the chuck 19 moves and holds the upper part of the workpiece. At this time, the feeding unit 20 waits in a position where the lower end of the feeding guide 28 is above the workpiece. The spring 70 and the adjustment pipe 60 housed in the set hole 24 of the holder 23 are prevented from falling by the stopper 27. The center pin 50 waits above the holder 23.

[0028] In the second stage, the feeding unit 20 descends to a height where the slider 26 of the cam plate 25 abuts against the inclined surface 16 of the cam 15. The tip of the feeding guide 28 is inserted into the fuel passage 95 of the workpiece. After the second stage, the slider 26 descends along the inclined surface 16, and the stopper 27 begins to open. In the third stage, the slider 26 reaches the bottom of the inclined surface 16, and the stopper 27 completes opening. In the fourth stage, the spring 70 and the adjustment pipe 60 pass from the set hole 24 through the cylindrical hole of the feeding guide 28 and drop into the fuel passage 95 of the workpiece.

[0029] 7 shows the state in which the spring 70 and adjust pipe 60 have fallen into the workpiece. The outer diameter of the spring 70 is smaller than the inner diameter of the press-fit hole 81 of the connector 80. The inserted spring 70 falls to the bottom of the press-fit hole 81 and is held in place with its lower end abutting against the bottom 86 of the recess in the movable core 87.

[0030] The connector 80 has an inner tapered portion 84 formed at the mouth of the press-fit hole 81, the inner diameter of which gradually decreases from an upper end surface 83 toward an inner wall 82 of the press-fit hole 81. The upper end surface 83 and the inner tapered portion 84 are collectively referred to as an upper end portion 830. The adjusting pipe 60 has an outer tapered portion 66 formed therein, the outer diameter of which gradually increases from a lower end surface 65 toward the outer wall 62. The lower end surface 65 and the outer tapered portion 66 are collectively referred to as a lower end portion 650. The outer diameter of the adjusting pipe 60 is formed larger than the inner diameter of the press-fit hole 81 of the connector 80 by the amount of the press-fit allowance.

[0031] When the adjusting pipe 60 is inserted following the spring 70, the lower end 650 of the adjusting pipe 60 comes into contact with the mouth of the press-fit hole 81 at the upper end 830 of the connector 80. If the inserted adjusting pipe 60 falls ideally coaxially with the connector 80, as shown in Figure 7, the outer tapered portion 66 of the adjusting pipe 60 will fit into the inner tapered portion 84 of the connector 80. However, as will be described later, the state shown in Figure 7 does not necessarily occur with all workpieces.

[0032] In the subsequent fifth stage, the rod 41 of the electric cylinder 40 extends, and the center pin 50 descends through the set hole 24 of the holder 23 and the cylindrical hole of the insertion guide 28. Then, after the lower end surface 55 of the center pin 50 abuts against the upper end surface 63 of the adjust pipe 60, the adjust pipe 60 is press-fitted into the press-fit hole 81 of the connector 80 by the pressing load of the electric cylinder 40. While the adjust pipe 60 is being press-fitted into the connector 80, the lower end portion 650 of the adjust pipe 60 abuts against the spring 70, and then the spring 70 is compressed.

[0033] As described above, in this assembly process, spring 70 is inserted into the lower part of press-fit hole 81 of connector 80 from the entrance of fuel passage 95 of the workpiece, which is installed so as to open upward, and further, adjust pipe 60 is inserted so that lower end portion 650 abuts against the opening of press-fit hole 81 of connector 80. Thereafter, center pin 50 is lowered by the pressing load of electric cylinder 40, and adjust pipe 60 is press-fitted into press-fit hole 81 of connector 80.

[0034] Here, let us consider a case where the centers of the spring 70 and adjusting pipe 60 are set misaligned from the center of the workpiece due to misalignment of the pallet 10 (including misalignment of the rails) or misalignment of the workpiece. When the spring 70 and adjusting pipe 60 fall into the workpiece in this state, the outer tapered portion 66 of the adjusting pipe 60 will not fit into the inner tapered portion 84 of the connector 80 and may ride up onto the upper end surface 83. If the center pin 50 is lowered in this state, the adjusting pipe 60 will scrape the inner wall 82 of the press-fit hole 81 as it is pressed in, generating foreign matter.

[0035] Alternatively, scratches or dents may occur when the adjust pipe 60 is press-fit due to an insufficient amount of oil applied. Defects or dents inside the connector 80 cannot be detected externally, and there is a risk that a defective product will be sent to a subsequent process. The assembly defect detection method of this embodiment aims to detect such assembly defects within the process.

[0036] 9 and 10, the state of a non-defective pattern in the assembly process and the pressing load waveform for the non-defective pattern will be described. Below, the horizontal axis of the load waveform diagram represents the displacement of the center pin 50, and the vertical axis represents the load with which the electric cylinder 40 presses the adjust pipe 60 via the center pin 50. The numerical values ​​of the displacement and load are merely examples.

[0037] The thick solid curve in the center of the load waveform diagram is the average load waveform (Ave) of a non-defective product. The displacement amount for the average load waveform is divided into regions P, A, B, and C. Region P is the preload region until the lower end surface 55 of the center pin 50 hits the upper end surface 63 of the adjustment pipe 60, and the load is zero.

[0038] State 1 in Figure 9 corresponds to the boundary between Area P and Area A, where the lower end surface 55 of the center pin 50 abuts against the upper end surface 63 of the adjust pipe 60. At this point, in a non-defective product, the outer tapered portion 66 of the adjust pipe 60 enters the inner tapered portion 84 of the connector 80. State 1 is expressed as "a state in which the lower end 650 of the adjust pipe 60 abuts against the inner tapered portion 84, which is the opening of the press-fit hole 81 at the upper end 830 of the connector 80." As the center pin 50 descends from State 1, the adjust pipe 60 gradually becomes more upright, and the load increases in Area A.

[0039] State 2 corresponds to region B. When the adjust pipe 60 is completely upright, the load required for press-fitting is minimized, and the load temporarily decreases in region B.

[0040] State 3 corresponds to region C. As the adjust pipe 60 is press-fitted, the contact area between the outer wall 62 of the adjust pipe 60 and the inner wall 82 of the connector 80 increases, and the load increases in region C. After that, the lower end 650 of the adjust pipe 60 abuts against the spring 70, and the spring 70 is compressed.

[0041] The dashed two-dot lines drawn above and below the average load waveform are the upper and lower limit distribution waveforms calculated from "Ave (average value) ± 4σ (standard deviation)" of non-defective products. Based on these upper and lower limit distribution waveforms, the broken lines of the upper and lower limit thresholds are defined. The upper limit threshold in the P (preload) region is determined to a constant value by a load that correlates with the defect state of the upper end surface 83 of the connector 80. The lower limit threshold in the P region is determined to a negative constant value. The break points of the upper and lower limit thresholds are defined by virtual lines that offset a specified margin from the upper and lower limit distribution waveforms, respectively. The range between the lower and upper limit thresholds is the "specified tolerance range."

[0042] The determination device 30 monitors the pressing load of the electric cylinder 40 for each workpiece undergoing the assembly process using a load cell 42, and determines that the workpiece is a good product when the waveform of the pressing load relative to the displacement of the center pin 50 is within a predetermined tolerance range. On the other hand, when the waveform of the pressing load is outside the predetermined tolerance range, it determines that an assembly defect has occurred in the workpiece. Next, specific examples of assembly defects will be explained with reference to Figures 11 to 16. In the load waveform diagrams of Figures 12 and 14 to 16, thick dashed lines indicate NG waveforms due to assembly defects.

[0043] (Example 1 of assembly failure) As shown in Figure 11, assembly defect example 1 is a defect in which the adjust pipe 60 is tilted, causing one side of the lower end surface 65 of the adjust pipe 60 to ride up onto the upper end surface 83 of the connector 80. If a pressing load is applied to the center pin 50 in this position, a flaw (or dent) FL1 may occur from the upper end surface 83 of the connector 80 to the inner tapered portion 84 at the point where the adjust pipe 60 hits. In this case, as shown in Figure 12, a spike waveform appears at the end of region P. No abnormalities are observed in the waveform during press-fitting after the adjust pipe 60 is fitted into the correct position.

[0044] (Example 2 of improper assembly) 13, assembly defect example 2 is a defect in which the outer wall 62 of the adjust pipe 60 and the inner wall 82 of the connector 80 scrape against each other due to an insufficient amount of oil applied to the inner wall 82 of the press-fit hole 81, which may result in a scratch (or dent) FL2 on the inner wall 82. In this case, as shown in FIG. 14, the pressing load exceeds the upper limit threshold in the region B to C. Note that a similar waveform will also be produced if the press-fit interference is excessive because the inner diameter of the press-fit hole 81 of the connector 80 is smaller than the tolerance range or the outer diameter of the adjust pipe 60 is larger than the tolerance range.

[0045] (Examples of improper assembly 3 and 4) 15 and 16, we will explain assembly failure examples 3 and 4, in which the pressing load waveform falls below the lower threshold. Assembly failure example 3 is a defect caused by the axial length (Ztp in FIG. 13) of the inner tapered portion 84 of the connector 80 being outside the tolerance range. In this case, as shown in FIG. 15, the rising position of the load waveform is offset to the right side of the figure (the downward side of the center pin 50), and exceeds the lower threshold line.

[0046] In assembly defect example 4, the inner diameter of press-fit hole 81 of connector 80 is larger than the tolerance range, or the outer diameter of adjust pipe 60 is smaller than the tolerance range, resulting in an insufficient press-fit interference. Vibrations and shocks during product operation may loosen adjust pipe 60, changing the valve-closing characteristics of needle 88. In this case, as shown in Figure 16, the pressure load falls below the lower threshold in region C.

[0047] As described above, the assembly defect detection method of this embodiment detects assembly defects that occur in the assembly process of press-fitting the adjust pipe 60 into the press-fit hole 81 of the connector 80 in the manufacture of the injector 90 from the pressure load waveform, and can prevent the defect from being passed on to the subsequent process. The determination device 30 is only required to determine that at least an assembly defect has occurred. All workpieces determined to have an assembly defect may be discarded as is.

[0048] In the manufacturing apparatus 100 of this embodiment, an electric cylinder 40 capable of adjusting the driving load or driving speed is used as the "driving device." Because the electric cylinder 40 itself can detect the amount of displacement, there is no need to provide a stroke sensor. Also, for example, a common manufacturing apparatus 100 may be used to perform the assembly process for multiple types of injectors 90 with different press-fit portion dimensions or materials. If the press-fit portion dimensions or materials differ, the appropriate press-fit load and press-fit speed will also differ. Therefore, by using the electric cylinder 40 as the driving device, it is possible to accurately adjust the appropriate press-fit load and press-fit speed for each product.

[0049] (Other embodiments) (a) The drive device that lowers the center pin 50 is not limited to an electric cylinder; it may be an air cylinder or a hydraulic cylinder, and the displacement of the center pin 50 may be detected by a stroke sensor separate from the cylinder. Furthermore, by providing a flow control valve or the like upstream of the air cylinder or hydraulic cylinder, rough speed adjustment is possible, even if it is not as accurate as an electric cylinder.

[0050] (b) When the waveform of the pressing load is outside a predetermined tolerance, the determination device 30 may not only determine that an assembly defect has occurred, but also classify the estimated defect mode based on the pattern of the waveform abnormality and notify the worker or manager. The destination of the workpiece may be switched for each defect mode, and the workpiece may be separated into workpieces to be discarded and workpieces to be reworked.

[0051] Furthermore, the relationship between various parameters related to the assembly process and the failure mode may be learned by machine learning. Furthermore, if assembly failures (see FIGS. 13 and 14) that are presumed to be caused by an insufficient amount of oil applied occur consecutively, feedback control may be performed to increase the amount of oil applied to the equipment.

[0052] (c) The application of the assembly defect detection method of the present invention is not limited to the process of press-fitting the adjust pipe 60 into the press-fit hole 81 of the connector 80 in the injector 90, but is generally expanded to "the process of press-fitting a small cylindrical member into the press-fit hole of a large cylindrical member" by the pressing load of the drive member. An elastic compression member equivalent to the spring 70 in the above embodiment may be housed in the lower part of the press-fit hole of the large cylindrical member. Generally, as the small cylindrical member is press-fitted into the large cylindrical member, the lower end of the small cylindrical member comes into contact with the elastic compression member, and then the elastic compression member is compressed.

[0053] The present invention is not limited to the above-described embodiment, and can be embodied in various forms without departing from the spirit of the invention. [Explanation of symbols]

[0054] 30...determination device, 40: Electric cylinder (drive device), 42: Load cell (load sensor), 50···Center pin, 60...Adjusting pipe (small cylindrical member), 650...Lower end portion, 70...Spring (elastic compression member), 80: Connector (large cylindrical member), 81: Press-fit hole, 830: Upper end portion.

Claims

1. In an assembly process in which a lower end (650) of a small cylindrical member (60) abuts against the mouth of a press-fit hole (81) at an upper end (830) of a large cylindrical member (80) that is installed with its axial direction vertical, the small cylindrical member is press-fitted into the press-fit hole of the large cylindrical member via a center pin (50) by a pressing load of a drive device (40), The determination device (30) monitors the pressing load of the drive device using a load sensor (42), and determines that an assembly defect has occurred when the waveform of the pressing load relative to the displacement amount of the center pin falls outside a predetermined allowable range.

2. 2. The assembly defect detection method according to claim 1, wherein the driving device is an electric cylinder whose driving load or driving speed is adjustable.

3. An elastic compression member (70) is housed in the lower part of the press-fit hole of the large cylindrical member, 3. A method for detecting assembly defects according to claim 1 or 2, wherein the lower end of the small tubular member abuts against the elastic compression member while the small tubular member is being press-fitted into the large tubular member, and then the elastic compression member is compressed.

4. The large cylindrical member is a connector fixed to the inner wall of a body pipe (94) that forms a fuel passage of the injector (90), the elastic compression member is a spring that biases the needle (88) of the injector in a valve closing direction, the small cylindrical member is an adjustment pipe that adjusts the set load of the spring, The spring is inserted into the lower part of the press-fit hole of the connector from the inlet of the fuel passage that is installed so as to open upward, and the adjust pipe is further inserted so that its lower end abuts against the opening of the press-fit hole of the connector.

4. The assembly defect detection method according to claim 3, which is applied to an assembly step in which the center pin is lowered by a pressing load of the drive device to press-fit the adjust pipe into the press-fit hole of the connector.

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