Vehicle manufacturing methods

Abstract

The objective is to provide a vehicle manufacturing method that can shorten the total cycle time (total working time) related to tightening nuts. [Solution] A tightening system is prepared to perform the tightening of the nut 57 by transporting the workpiece, before the nut 57 is fastened to the pinion gear 51, in the order of seating device 2, first tightening device 3, and second tightening device 4. The nut 57 is seated on the first bearing 54 in seating device 2. The workpiece after the nut 57 is seated is transported to first tightening device 3. Either first tightening device 3 or second tightening device 4 performs a series of basic steps in order: preliminary tightening, in which the nut 57 is rotated at a predetermined rotation angle; final tightening, in which the nut 57 is fastened with a predetermined torque; and preload measurement, in which the preload, which is the initial load on the nut 57 after final tightening, is measured.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a vehicle equipped with a pinion gear for transmitting driving force.

Background Art

[0002] In vehicles such as automobiles, as a mechanism for transmitting the rotational driving force generated by a driving source such as an engine to the wheels, a propeller shaft extending in the vehicle longitudinal direction, a front wheel shaft and a rear wheel shaft extending in the vehicle width direction, and gear devices such as a transfer gear and a rear differential gear are mounted on the vehicle.

[0003] A rear differential gear (hereinafter abbreviated as rear diff) includes a drive pinion (driving-side pinion gear) connected to the propeller shaft and a ring gear connected to the rear wheel shaft in a case called a differential carrier in order to transmit the rotational driving force transmitted from the propeller shaft to the rear wheel shaft orthogonal to the propeller shaft.

[0004] In the process of fixing and tightening the drive pinion to the differential carrier of the rear diff with a lock nut, after tightening by controlling the tightening angle, the preload, which is the initial load of the lock nut after tightening, is measured. If it is within the specified value range, it is transferred to the next process, but several tightening adjustments may be involved to make the preload fall within the specified value.

[0005] Therefore, due to the relationship between the cycle time and the conveyor line, two tightening devices are provided in series, and by performing re-tightening and re-measurement of the preload with the tightening device on the downstream side of the conveyor line, the working efficiency is improved.

[0006] As a conventional technology that improves the transport line to enhance work efficiency, for example, as described in Patent Document 1, there is a transport device that moves substrates between areas arranged in mutually orthogonal first and second transport directions and allows the substrates to wait in either area as needed. This transport device allows substrates to overtake, bypass, and reverse, thereby reducing congestion of substrates within the substrate transport device. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2001-315960 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] However, as mentioned above, in the manufacturing of vehicles, in the process of tightening the lock nut onto the drive pinion, the order in which the drive pinions are transported must be maintained in order to maintain the combination of the drive pinion and the ring gear in the next process after the lock nut tightening process, and there is a constraint that the drive pinion cannot overtake the previous drive pinion.

[0009] Furthermore, as mentioned above, the lock nut may require several adjustments and tightening to ensure the preload is within the specified range. Therefore, the total tightening time varies each time depending on the number of adjustments. Consequently, in a series process with two tightening devices installed in series as described above, splitting the process at a specific step results in waiting time for tightening in either the preceding or succeeding step, leading to a longer cycle time and posing a problem.

[0010] This invention has been made in view of the above circumstances, and aims to provide a vehicle manufacturing method that can shorten the total cycle time (total working time) related to tightening nuts. [Means for solving the problem]

[0011] To solve the above problem, the present invention provides a method for manufacturing a vehicle equipped with a pinion gear that transmits driving force generated by a drive source and a ring gear that meshes with the pinion gear, wherein the vehicle comprises: the pinion gear having a shaft portion; a first bearing at the tip end and a second bearing at the rear end of the shaft portion that are fitted onto the shaft portion and rotatably support the pinion gear; a distance piece sandwiched between the first bearing and the second bearing; and a nut that, when fastened to a male threaded portion formed on the shaft portion, seats on the first bearing and presses the first bearing, the second bearing and the distance piece. A vehicle equipped with a nut, wherein a tightening system is prepared to perform the nut tightening work by transporting the workpiece in the unit before the tightening of the nut is completed to a seating device, a first tightening device, and a second tightening device in that order, and the nut is screwed onto the male thread portion of the shaft portion with the seating device and seated on the first bearing, the workpiece after the nut is seated is transported to the first tightening device, and either the first tightening device or the second tightening device performs a series of basic steps in which the nut is rotated at a predetermined rotation angle for preliminary tightening, the nut is tightened with a predetermined torque for final tightening, and preload measurement is performed to measure the preload, which is the initial load on the nut after final tightening.

[0012] The pinion gear that transmits the driving force of the vehicle's power source cannot overtake the workpiece containing the pinion gear due to the compatibility of the meshing between the pinion gear and the ring gear it is paired with. Therefore, with a workpiece containing a pinion gear, multiple workpieces are fed in sequence, and the actions necessary to tighten the nuts on the pinion gear must be processed one by one (takt processing).

[0013] Therefore, in order to shorten the cycle time for tightening nuts, it is important to minimize idle time, especially for the second tightening device, which is the furthest downstream of the series of seating devices, first tightening devices, and second tightening devices.

[0014] From this perspective, the above manufacturing method features the following characteristics: First, the time-consuming process of seating the nuts is completed in advance using a seating device. Then, a series of basic processes—preliminary tightening, final tightening, and preload measurement—are performed using either the first or second tightening device. This minimizes downtime between the first and second tightening devices. As a result, the time available for performing the basic processes on both the first and second tightening devices increases, thus shortening the total cycle time (total working time) for nut tightening.

[0015] In the above-described method for manufacturing a vehicle, when the workpiece is present in the second fastening device, it is preferable to perform a series of basic steps of preliminary fastening, final fastening, and preload measurement in the first fastening device. When the workpiece is not present in the second fastening device, it is preferable to send the workpiece from the first fastening device to the second fastening device and perform a series of basic steps of preliminary fastening, final fastening, and preload measurement in the second fastening device.

[0016] The above manufacturing method makes it possible to reliably reduce the idle time of the second clamping device, and reliably increase the time available for executing the basic process in both the first and second clamping devices. As a result, it becomes possible to reliably shorten the total cycle time.

[0017] In the above-described method for manufacturing a vehicle, the first and second fastening devices are capable of performing adjustment steps, such as re-tightening the nut and re-measuring the preload, if the preload measured in the preload measurement in the basic process is outside the specified value and therefore unsatisfactory. If, after the first fastening device has completed the basic process for the workpiece, the second fastening device continues the adjustment step for the preceding workpiece for more than a predetermined set time from the start of the adjustment step, it is preferable to have the workpiece after the basic process is completed in the first fastening device wait in the first fastening device until the adjustment step for the preceding workpiece in the second fastening device is completed.

[0018] In the above manufacturing method, the controller of the clamping system can determine whether the adjustment process for the preceding workpiece in the second clamping device is nearing completion or still ongoing. This allows the workpiece after the basic process is completed in the first clamping device to be temporarily held in the first clamping device. As a result, even if there is an adjustment process after the basic process, the overall cycle time can be stabilized.

[0019] In the above-described method for manufacturing a vehicle, it is preferable that the set time is shorter than the average time required for the re-preload measurement in the adjustment step of the second tightening device, and that after the set time has elapsed, a determination standby timer is activated to cause the workpiece to wait in the first tightening device within a predetermined waiting time.

[0020] In the above manufacturing method, when the judgment standby timer is activated, the first tightening device holds the workpiece in a predetermined waiting time. If the preload measurement of the preceding workpiece fails in the second tightening device, the second tightening device performs an adjustment process. However, it is also possible to perform the adjustment process in the first tightening device in parallel. As a result, it becomes possible to perform the adjustment process in both the first and second tightening devices, improving the efficiency of tightening nuts on continuously transported workpieces.

[0021] In the above-described method for manufacturing a vehicle, it is preferable that the determination standby timer stops when the re-preload measurement in the adjustment step of the second tightening device is completed.

[0022] When the preload measurement for the adjustment process in the second tightening device is completed, the judgment standby timer stops. This allows the tightening system controller to accurately determine that the adjustment process is in progress in the second tightening device before the judgment standby timer stops. As a result, the adjustment process in the first tightening device can be reliably performed in parallel with the adjustment process in the second tightening device, further improving the efficiency of tightening nuts on continuously transported workpieces.

[0023] In the above-described method for manufacturing a vehicle, it is preferable that the pinion gear during the tightening operation of the nut by the first tightening device is conveyed to the second tightening device behind the preceding pinion gear without overtaking the preceding pinion gear during the tightening operation of the nut by the second tightening device.

[0024] In the above manufacturing method, since the pinion gear among the workpieces is not caused to overtake the preceding pinion gear, the workpieces can be conveyed from the first tightening device to the second tightening device in a state where the combination of the pinion gear and the ring gear in each workpiece matches.

Advantages of the Invention

[0025] As described above, according to the method for manufacturing a vehicle of the present invention, the total tact time (total working time) related to the tightening of the nut can be shortened.

Brief Description of the Drawings

[0026] [Figure 1] It is a perspective view showing an engine of an automobile to which the method for manufacturing a vehicle according to an embodiment of the present invention is applied and a driving force transmission system from the engine to a front wheel shaft and a rear wheel shaft. [Figure 2] It is a cross-sectional view of the rear differential gear in FIG. 1. [Figure 3] It is a manufacturing process explanatory view showing the flow of workpieces in the method for manufacturing a vehicle according to an embodiment of the present invention and an outline of operations executed by a seating device, a first tightening device, and a second tightening device. [Figure 4] It is a system configuration diagram of a tightening system used in the method for manufacturing a vehicle according to an embodiment of the present invention. [Figure 5] It is a front view showing an example of the configuration of the first tightening device and the second tightening device. [Figure 6] It is a cross-sectional explanatory view showing a state where the nut-side socket in FIG. 5 is fitted to the nut and the pinion-side socket is fitted to the spline on the tip side of the drive pinion. [Figure 7]This flowchart shows a method for manufacturing a vehicle according to an embodiment of the present invention, and is a flowchart of the steps when the second clamping device in the first half and second half is empty. [Figure 8] This is a flowchart of a vehicle manufacturing method according to an embodiment of the present invention, showing the steps in the latter half when the second tightening device is not available. [Figure 9] This diagram illustrates the operation of the seating device, the first tightening device, and the second tightening device when a series of workpieces are continuously supplied to the tightening system shown in Figure 4, and each workpiece is tightened once as a re-tightening. [Figure 10] This is a process diagram illustrating the operation of the seating device, the first tightening device, and the second tightening device when a series of workpieces are continuously supplied to the tightening system shown in Figure 4, and each workpiece is tightened twice as a re-tightening. [Figure 11] This diagram illustrates the operation of the seating device, the first tightening device, and the second tightening device when a series of workpieces are continuously supplied to the tightening system shown in Figure 4, and each workpiece is tightened three times as a re-tightening step. [Modes for carrying out the invention]

[0027] Hereinafter, a method for manufacturing a vehicle according to an embodiment of the present invention will be described in detail with reference to the drawings.

[0028] (Vehicle configuration) As shown in Figure 1, the vehicle to which the manufacturing method of the present invention is applied is an automobile equipped with an engine 101 as a drive source, comprising: a transmission 102 that changes the rotational driving force generated by the engine 101 to convert it into a predetermined rotational speed and torque; a pair of front wheel shafts 103 that extend in the vehicle width direction and are connected to front wheels (not shown) and to which the rotational driving force changed by the transmission 102 is transmitted via a clutch (not shown); a transfer case 104 that transmits the rotational driving force from the front wheel shafts 103 to a propeller shaft 105 with the direction changed at a right angle; a pair of rear wheel shafts 107 that extend in the vehicle width direction behind the propeller shaft 105 and are connected to rear wheels (not shown); and a rear differential gear 106 (hereinafter abbreviated as rear differential 106) that transmits the rotational driving force from the propeller shaft 105 to the rear wheel shafts 107 with the direction changed at a right angle.

[0029] Furthermore, the vehicles to which the manufacturing method of the present invention is applied may be not only gasoline or diesel vehicles equipped with an engine 101 as a drive source, but also electric vehicles (EVs) equipped with a motor, or hybrid vehicles equipped with both an engine and a motor.

[0030] The transfer case 104 is equipped with a ring gear (not shown) connected to the front wheel shaft 103 and a pinion gear (not shown) connected to the propeller shaft 105 and meshing with the ring gear, thereby enabling the transmission of rotational driving force from the front wheel shaft 103 to the propeller shaft 105 with a 90-degree change in direction.

[0031] (Rear differential configuration 106) The rear differential 106 is equipped with a ring gear 52 (see Figure 2) connected to the rear wheel shaft 107 and a drive pinion 51 (see Figure 2) connected to the propeller shaft 105 and meshing with the ring gear 52, thereby enabling the transmission of rotational driving force from the propeller shaft 105 to the rear wheel shaft 10107 with a 90-degree change in direction.

[0032] The rear differential 106, as shown in Figure 2, comprises a differential carrier 53 which serves as a case (divisible into a first part 53a and a second part 53b), a drive pinion 51 which is a drive-side pinion gear housed in the first part 53a of the differential carrier 53, and components attached to the drive pinion 51, including a first bearing 54, a second bearing 55, a distance piece 56, and a nut 57.

[0033] This unit, consisting of the first part 53a of the differential carrier 53, the drive pinion 51, the first bearing 54, the second bearing 55, the distance piece 56, and the nut 57, corresponds to the workpiece W (see Figures 5-6) before the tightening of the nut 57, which will be described later.

[0034] Furthermore, the rear differential 106 includes a ring gear 52 housed in the second portion 53b of the differential carrier 53 that meshes with the drive pinion 51, a pair of shaft connectors 61 connected to a pair of rear wheel shafts 107 (see Figure 1), a pair of side gears 62 connected to the opposing ends of the pair of shaft connectors 61, and a pair of pinion gears 63 that mesh with the pair of side gears 62. One of the pair of shaft connectors 61 is connected to the ring gear 52.

[0035] The drive pinion 51 has a bevel tooth portion 51a and a shaft portion 51b. The shaft portion 51b has a spline 51c and an external thread portion 51d formed on it, starting from the tip side.

[0036] The first bearing 54 and the second bearing 55 are fitted side by side on the front end (farthest from the bevel teeth 51a) and rear end of the shaft portion 51b to rotatably support the drive pinion 51. The first bearing 54 and the second bearing 55 are made of ball bearings or the like and have a ring-shaped inner race that is in close contact with the shaft portion 51b, a ring-shaped outer race that has a larger diameter than the inner race, and a plurality of balls that are rotatably inserted between the inner race and the outer race. The outer race is fitted to the inner surface of the first portion 53a of the differential carrier 53.

[0037] The distance piece 56 is a cylindrical metal body that is inserted into the shaft portion 51b and sandwiched between the first bearing 54 and the second bearing 55.

[0038] The nut 57 has an internal threaded portion 57a, and by fastening it to the external threaded portion 51d formed on the shaft portion 51b, it seats on the first bearing 54 and presses the first bearing 54, the second bearing 55, and the distance piece 56 in the axial direction. The distance piece 56 is crushed in the axial direction by the pressing force from the nut 57 (it is crushed in a shape that bulges outward as shown in Figure 2).

[0039] In the rear differential 106 configured as described above, the rotational driving force transmitted to the drive pinion 51 connected to the propeller shaft 105 (see Figure 1) is transmitted to the ring gear 52, which has teeth 52a that mesh with the bevel teeth 51a of the drive pinion 51, after changing direction at a right angle. The rotational driving force transmitted to the ring gear 52 is transmitted to one of the pair of shaft connection parts 61 and to the other of the pair of shaft connection parts 61 via the pair of side gears 62 and the pair of pinion gears 63. This allows rotational driving force to be transmitted to the pair of rear wheel shafts 107 connected to the pair of shaft connection parts 61. Furthermore, if a difference in rotational angle occurs between the pair of rear wheel shafts 107 when the direction of the vehicle is changed while the vehicle is in motion, the pair of pinion gears 63 that mesh with the pair of side gears 62 rotate in opposite directions to absorb the difference in rotational angle between the pair of rear wheel shafts 107. In this way, the rear differential 106 can function as a differential.

[0040] (Basic steps for tightening nut 57) When manufacturing the rear differential 106 configured as described above, the nut 57 is screwed onto the male threaded portion 51d of the drive pinion 51 and seated on the inner race of the first bearing 54, and the first bearing 54, the second bearing 55, and the distance piece 56 are pressed together and tightened to the specified torque.

[0041] To shorten the total cycle time (total working time) for this nut tightening operation, the vehicle manufacturing method of this embodiment prepares a tightening system 1 equipped with a seating device 2, a first tightening device 3, a second tightening device 4, and a controller 5 (see Figure 4) that controls these devices 2 to 4. (The timer 6 for judgment standby provided in the controller 5 in Figure 4 will be explained later.) In other words, a tightening system 1 is prepared to perform the tightening of the nuts 57 by transporting the workpiece W (see Figures 5-6) of the rear differential 106 (first part 53a of the differential carrier 53, drive pinion 51, first bearing 54, second bearing 55, distance piece 56, and nut 57) in the order of seating device 2, first tightening device 3, and second tightening device 4 as shown in Figure 3, before the tightening of the nuts 57 is completed.

[0042] In this tightening system 1, the workpiece W before the nut 57 is tightened is transported in the order of seating device 2, first tightening device 3, and second tightening device 4. That is, the drive pinion 51 that is tightening the nut 57 in the first tightening device 3 does not overtake the preceding drive pinion 51 that is tightening the nut 57 in the second tightening device 4, but is transported to the second tightening device 4 after the preceding drive pinion 51.

[0043] In the seating device 2, the nut 57 is screwed onto the male threaded portion 51d of the shaft portion 51b of the drive pinion 51 to seat it on the first bearing 54. Specifically, the seating surface of the nut 57 is brought into contact with the inner race (the inner portion fitted to the shaft portion 51b) of the first bearing 54 with a predetermined torque.

[0044] The seating device 2 is equipped with a nut tightening section 7 and a torque measuring section 8, as shown in Figure 4, for performing the seating operation.

[0045] In the tightening system 1, the workpiece W after the nut 57 has been seated is transported to the first tightening device 3 by a transport mechanism (not shown).

[0046] Then, while observing the availability of the second tightening device 4, a series of basic steps are performed in order to minimize downtime using either the first tightening device 3 or the second tightening device 4: preliminary tightening, in which the nut 57 is rotated at a predetermined rotation angle; final tightening, in which the nut 57 is fastened to a predetermined torque; and preload measurement, in which the preload, which is the initial load on the nut 57 after final tightening (i.e., the rotational resistance until the nut 57 or drive pinion 51 starts to rotate).

[0047] (Configuration of the first tightening device 3 and the second tightening device 4) The first tightening device 3 and the second tightening device 4 each have the same basic configuration for performing the above-mentioned basic processes (preliminary tightening, final tightening, and preload measurement), and each includes a nut tightening section 9, a rotation angle measuring section 10 for measuring the rotation angle of the nut 57, and a torque measuring section 11 for measuring the tightening torque of the nut 57.

[0048] The nut tightening section 9 includes a pinion rotating section 12 that rotates the drive pinion 51 and a nut reversing section 13 that reverses the rotation of the nut 57, so that the nut 57 can be properly tightened to the shaft portion 51b of the drive pinion 51 without axial wobble.

[0049] As an example of a specific configuration, the first tightening device 3 and the second tightening device 4, as shown in Figures 5-6, include a nut-side socket 31 that fits onto the nut 57 to prevent the nut 57 from rotating during preload measurement, a pinion-side socket 32 ​​that fits onto the spline 51c at the upper end of the drive pinion 51, a tightening nut runner 33, a pair of upper and lower reduction gears 34, a tightening nut runner release cylinder 35, a gear release cylinder 36, a preload measuring nut runner 37, an electromagnetic clutch 38, a loop-shaped belt 39, a pallet 40 on which the workpiece W is mounted, a pallet transport unit 41 that moves the pallet 40 horizontally, and a lifting cylinder 42 that raises and lowers the pallet 40 below the sockets 31 and 32.

[0050] As shown in Figure 6, the nut-side socket 31 is a cylindrical member having internal teeth 31a, and the internal teeth 31a can be fitted into the nut 57. Similarly, the pinion-side socket 32 ​​is a cylindrical member having internal teeth 32a, and the internal teeth 32a can be fitted into the spline 51c at the upper end of the drive pinion 51.

[0051] The tightening nut runner 33 is connected to the pinion-side socket 32 ​​and rotates to rotate the drive pinion 51 during preliminary and final tightening, thereby applying a fastening force (corresponding to the pinion rotation section 12 in Figure 4). The pair of upper and lower reduction gears 34 are connected to the tightening nut runner 33 and reverse the rotation of the nut-side socket 31 during preliminary and final tightening (corresponding to the nut reversal section 13 in Figure 4). The tightening nut runner disconnection cylinder 35 disconnects the tightening nut runner 33 from the pinion-side socket 32 ​​during preload measurement. The gear disconnection cylinder 36 disconnects the pair of upper and lower reduction gears 34 from each other during preload measurement. The preload measuring nut runner 37 rotates the pinion-side socket 32 ​​during preload measurement (with the nut-side socket 31 and nut 57 stationary) and measures the rotational resistance of the pinion-side socket 32 ​​as the preload (corresponding to the torque measurement section 11 in Figure 4). The electromagnetic clutch 38 connects the preload measuring nut runner 37 to the belt 39 during preload measurement. The loop-shaped belt 39 connects the preload measuring nut runner 37 and the pinion-side socket 32 ​​in a torque-transmitting manner. The tightening nut runner 33 also has the function of the rotation angle measuring unit 10 shown in Figure 4, which rotates the drive pinion 51 and measures its rotation angle.

[0052] (Operation of seating device 2, first tightening device 3, and second tightening device 4) In the fastening system 1 configured as described above, the following operations are performed in each of the seating device 2, the first fastening device 3, and the second fastening device 4, as shown in Figure 3.

[0053] <Seating device 2> The nut 57 is seated, and the workpiece W is sent to the first tightening device 3.

[0054] <First clamping device 3> (1) If the second clamping device 4 is available, the workpiece W is sent to the second clamping device 4. (2) If there is a workpiece W preceding the second tightening device 4, the basic processes of preliminary tightening, final tightening, and preload measurement are performed. (3) If the preload measurement results indicate that further tightening is necessary, the additional adjustment steps will be to tighten (or loosen) the bolts and perform another preload measurement. (4) After the preload measurement in (2) and (3) above, wait until the preload measurement of the second tightening device 4 is completed. After waiting, if the second tightening device 4 is available, send the workpiece to the second tightening device. If it is not available, tighten if necessary (otherwise wait until it becomes available).

[0055] <Second tightening device 4> (1) When a workpiece W arrives after all processing (preliminary tightening, final tightening, preload measurement, and confirmation that no further tightening is necessary) has been completed in the first tightening device 3, it is passed directly through the second tightening device 4. (2) When an unprocessed workpiece W arrives, perform preliminary tightening, final tightening, and preload measurement. (If necessary, perform retightening and preload measurement again.) (3) If a workpiece W that requires further tightening is found based on the preload measurement results of the first tightening device 3, the workpiece is further tightened and the preload measurement is performed again.

[0056] As described above, the first tightening device 3 and the second tightening device 4 of this embodiment are capable of performing adjustment steps, such as re-tightening the nut 57 and re-measuring the preload, respectively, when the preload measured in the preload measurement in the basic process falls outside the specified value and is deemed unacceptable.

[0057] If, after the basic process for workpiece W is completed in the first tightening device 3, the adjustment process (retightening and re-preload measurement) for the preceding workpiece W in the second tightening device 4 continues beyond a predetermined set time T1 (see Figures 10-11), the workpiece W after the basic process is completed in the first tightening device 3 is kept in the first tightening device 3 until the adjustment process for the preceding workpiece W in the second tightening device 4 is completed. This stabilizes the overall cycle time even when there is an adjustment process after the basic process.

[0058] The set time T1 is measured using the timer 6 for the controller 5 in Figure 4, or another timer.

[0059] Furthermore, the set time T1 is set to be shorter than the average time required for the re-preload measurement in the adjustment process at the second tightening device 4. After the set time T1 has elapsed, the timer 6 for judgment waiting in the controller 5 is activated, and the workpiece W is made to wait in the first tightening device 3 within a predetermined waiting time T2. This makes it possible to perform the adjustment process at both the first tightening device 3 and the second tightening device 4.

[0060] Furthermore, the timer 6 for judgment standby stops when the re-preload measurement in the adjustment process of the second tightening device 4 is completed. This ensures that the adjustment process in the first tightening device 3 is reliably executed in parallel with the adjustment process in the second tightening device 4.

[0061] (Explanation of the flowchart) The operation procedure for tightening the nut 57 in the above embodiment is carried out in the steps shown in the flowcharts in Figures 7 and 8.

[0062] First, in step S1 of Figure 7, the seating device 2 seats the nut 57 of the workpiece W.

[0063] Next, in step S2, the workpiece W is moved to the first clamping device 3. The movement of the workpiece W is performed by the conveying device of the clamping system 1 (for example, the pallet conveying unit 41 in Figure 5), a handling robot, or by an operator.

[0064] Next, in step S3, the controller 5 determines whether there is a workpiece W preceding the second clamping device 4.

[0065] <If there is no preceding work W> If there is no preceding workpiece W (the result is NO in step S3), the process proceeds to step S16, and the workpiece W is moved to the second clamping device 4.

[0066] Next, in step S17, the second tightening device 4 performs the basic processes of preliminary tightening, final tightening, and preload measurement of the workpiece W.

[0067] Next, in step S18, the controller 5 determines from the preload measurement results whether it is necessary to tighten (or loosen) the bolts (i.e., whether an adjustment process is necessary).

[0068] If retightening (or loosening) is necessary (if step S18 is YES, i.e., if the preload measurement fails), proceed to step S19, where the adjustment process involves retightening (or loosening) and performing another preload measurement. Then return to step S18.

[0069] On the other hand, if there is no need to further tighten (or loosen) the bolt (if step S18 is NO, or if the preload measurement is successful), the tightening process for this workpiece W is terminated.

[0070] <If there is a preceding work W> If there is a preceding workpiece W (if YES in step S3), proceed to step S4 in Figure 8, where the first tightening device 3 performs the basic processes of preliminary tightening, final tightening, and preload measurement of the workpiece W.

[0071] Next, in step S5, the controller 5 determines from the preload measurement results whether it is necessary to tighten (or loosen) the bolts (i.e., whether an adjustment process is necessary).

[0072] If further tightening (or loosening) is necessary (if step S5 is YES, i.e., the preload measurement is unsuccessful), proceed to step S6 to determine if the preceding workpiece W is still in the second tightening device 4.

[0073] If the preceding workpiece W is not in the second clamping device 4 (if step S6 is NO), the process proceeds to step S11, where the workpiece W is moved to the second clamping device 4. In step S12, as in steps S19 and S18 above, the second clamping device 4 performs an adjustment process, which is to tighten (or loosen) the workpiece again and to measure the preload again. In step S13, if the result of the second preload measurement is unsatisfactory, the process returns to step S12. If it is satisfactory, the clamping operation on the workpiece W is completed.

[0074] On the other hand, if the preceding workpiece W is still in the second clamping device 4 (if step S6 is YES), the process proceeds to step S7. In step S7, the first clamping device 3 is made to wait for a timer operation time T2 (i.e., waiting time) which is set time T1 after the start of preload measurement of the preceding workpiece W in the second clamping device 4 (see T1 (set value) and T2 in Figures 9-11).

[0075] Next, after the timer operation time T2 of step S7 has elapsed, step S8 determines whether the work on the preceding workpiece W by the second clamping device 4 has been completed.

[0076] If the work on the preceding workpiece W at the second tightening device 4 is not completed (if step S8 is NO), the process proceeds to step S9, where the first tightening device 3 performs an adjustment process, which involves further tightening (or loosening) and another preload measurement. After that, the process returns to step S5 to determine the preload measurement result.

[0077] If the work on the preceding workpiece W at the second clamping device 4 is completed (if step S8 is YES), the second clamping device 4 will soon be free, so the process proceeds to step S10, and the first clamping device 3 waits until there are no more preceding workpieces W at the second clamping device 4. After that, steps S11 to S13 above, which relate to the processing at the second clamping device 4, are executed.

[0078] Furthermore, if in step S5 above there is no need to further tighten (or loosen) the first tightening device 3 (i.e., if step S5 is NO, i.e., the preload measurement is successful), the process proceeds to step S14, and the first tightening device 3 waits until there are no more workpieces W ahead of the second tightening device 4. After that, the process proceeds to step S15, where the successful workpiece W is moved to the second tightening device 4, and the tightening operation on this workpiece W is completed by allowing it to pass through the second tightening device 4 without further processing.

[0079] (Explanation of tightening and waiting) The tightening (or loosening) process described above in the adjustment procedure is usually performed several times (about 1 to 3 times). If the tightening and preload measurement of the later workpiece can be performed in parallel while the preceding workpiece is being tightened and the preload measurement is being performed again, the total cycle time (total working time) can be shortened even with the adjustment procedure. Therefore, when the preload measurement of the preceding workpiece is about to be completed, the parallel processing described above can be made possible by waiting until the preload measurement of the later workpiece or the preload measurement of the later workpiece is completed.

[0080] Therefore, referring to the time charts in Figures 9-11, we will explain in more detail the waiting period for the workpiece after retightening 1 to 3 times.

[0081] Figures 9-11 are process diagrams illustrating the operation of the seating device 2, the first tightening device 3, and the second tightening device 4 when a series of workpieces W are continuously supplied to the tightening system 1 in Figure 4, and each workpiece W is subjected to retightening 1 to 3 times.

[0082] In Figures 9-11, in order to investigate the waiting time of the subsequent workpieces W, all workpieces W are seated using the seating device 2, and the basic processes of preliminary tightening, final tightening, and preload measurement are performed using the first tightening device 3.

[0083] Furthermore, the abbreviations in Figures 9-11 are as follows: "Temporary": temporary tightening, "Main": final tightening, "Pre": preload measurement, "Increase": further tightening or loosening, "Transport": transport to the next stage, "Up" or "Rise": raise the workpiece and connect it to the sockets 31 and 32 (see Figures 5-6), and "Down" or "Descend": lower the workpiece and move it away from the sockets 31 and 32.

[0084] In the time chart for one tightening cycle in Figure 9, a series of workpieces W supplied continuously are all moved to the second tightening device 4 after preload measurement by the first tightening device 3, where one tightening cycle and another preload measurement are performed as adjustment steps.

[0085] As shown in Figure 9, the timer 6 is activated after a set time T1 (set value) from the start of the preload measurement again by the second tightening device 4 for the preceding workpiece W, and a waiting time T2 is measured. However, the preload measurement of the subsequent workpiece W is not finished during the waiting time T2. Therefore, in the time chart for one tightening cycle in Figure 9, the subsequent workpiece W does not need to wait after the preload measurement, as the preceding workpiece W has been removed from the second tightening device 4 and is no longer there. Therefore, the subsequent workpiece W can move to the second tightening device 4 for tightening and another preload measurement.

[0086] Next, in the time chart for the two tightening cycles in Figure 10, all of the continuously supplied workpieces W move to the second tightening device 4 after the preload measurement at the first tightening device 3, where they undergo two tightening cycles and two more preload measurements, which are adjustment processes.

[0087] As shown in Figure 10, the timer 6 is activated after a set time T1 (set value) from the start of the second preload measurement for the preceding workpiece W in the second tightening device 4 to measure a waiting time T2. During the waiting time T2, the preload measurement of the subsequent workpiece W is completed, so the subsequent workpiece W waits in the first tightening device 3 until the second preload measurement of the preceding workpiece W is completed. As a result, in the time chart of the two retightenings in Figure 10, the adjustment process of the preceding workpiece W, which consists of two retightenings and two re-preload measurements, is performed in parallel with the basic process of the subsequent workpiece W, which consists of preliminary tightening, final tightening, and preload measurement. This makes it possible to sequentially perform the basic process of preliminary tightening, final tightening, and preload measurement in the first tightening device 3 and the adjustment process of two retightenings and two re-preload measurements in the second tightening device 4 for a series of continuously supplied workpieces W without interruption.

[0088] Next, in the time chart for the three tightening cycles in Figure 11, a series of workpieces W that are continuously supplied alternately repeat two patterns after the preload measurement (first preload measurement) in the basic process of the first tightening device 3. These patterns are: the first pattern, which involves moving to the second tightening device 4 to perform all three adjustment cycles of tightening and three more preload measurements; and the second pattern, which involves performing one adjustment cycle of tightening and one more preload measurement before moving to the second tightening device 4 to perform the remaining two tightening cycles and two more preload measurements.

[0089] As shown in Figure 11, the timer 6 is activated after a set time T1 (set value) from the start of all 1st to 3rd re-preload measurements for the preceding workpiece W in the first pattern, and a waiting time T2 is measured. At this point, during the second waiting time T2, the preload measurement of the basic process for the subsequent workpiece W (the first preload measurement) is completed, so the subsequent workpiece W in the second pattern waits in the first clamping device 3 until the second re-preload measurement of the preceding workpiece W is completed.

[0090] As a result, in the time chart for three tightening cycles shown in Figure 11, while the adjustment process for the preceding workpiece W in the first pattern, which consists of three tightening cycles and three re-preload measurements, is being performed, the basic process for the subsequent workpiece W in the second pattern, which consists of preliminary tightening, final tightening, preload measurement, and adjustment process, which consists of one tightening cycle and one re-preload measurement, can be performed in parallel.

[0091] Furthermore, as described above, after the second pattern workpiece W has already completed one retightening and another preload measurement at the first tightening device 3, it proceeds to the second tightening device 4 to perform the remaining two retightenings and two more preload measurements. Subsequently, the first pattern workpiece W undergoes the basic processes of preliminary tightening, final tightening, and preload measurement at the first tightening device 3, and then waits until the second pattern workpiece W has completed its two more preload measurements. This allows subsequent first pattern workpieces W to move back to the second tightening device 4 and complete all of the adjustment processes: three retightenings and three more preload measurements.

[0092] Therefore, even in the case of the time chart for three tightening cycles shown in Figure 11, it is possible to sequentially and smoothly process a series of workpieces W that are continuously supplied, alternating between the first pattern (three tightening cycles with the second tightening device 4) and the second pattern (one tightening cycle with the first tightening device 3 and two tightening cycles with the second tightening device 4).

[0093] (Features of this embodiment) (1) The manufacturing method of the vehicle in this embodiment prepares a tightening system 1 that performs the tightening of the nut 57 by transporting the workpiece W, before the nut 57 is fastened, in the order of seating device 2, first tightening device 3, and second tightening device 4. The seating device 2 screws the nut 57 onto the male thread portion 51d of the shaft portion 51b and seats it on the first bearing 54. The workpiece W, after the nut 57 has been seated, is transported to the first tightening device 3.

[0094] Then, while observing the availability of the second tightening device 4, a series of basic steps are performed in order to minimize downtime, using either the first tightening device 3 or the second tightening device 4: preliminary tightening, in which the nut 57 is rotated at a predetermined rotation angle; final tightening, in which the nut 57 is fastened to a predetermined torque; and preload measurement, in which the preload, which is the initial load on the nut 57 after final tightening.

[0095] The drive pinion 51, which transmits the driving force of the vehicle's engine 101, cannot overtake the workpiece W containing the drive pinion 51 due to the compatibility of its meshing with the ring gear 52 that it is paired with. Therefore, the workpiece W containing the drive pinion 51 must advance the multiple workpieces W that are fed in succession and process the necessary actions for tightening the nut 57 onto the drive pinion 51 one by one (takt processing).

[0096] Therefore, in order to shorten the cycle time for tightening the nut 57, it is important to minimize the idle time of the second tightening device 4, which is the furthest downstream of the series of seating devices 2, first tightening device 3, and second tightening device 4.

[0097] From this perspective, the above manufacturing method features the first step of pre-setting the time-consuming nut 57 using the seating device 2. Then, while monitoring the availability of the second tightening device 4, a series of basic processes—preliminary tightening, final tightening, and preload measurement—are performed using either the first tightening device 3 or the second tightening device 4. This minimizes idle time for both the first and second tightening devices 3 and 4. As a result, the time available for performing the basic processes on both the first and second tightening devices increases, thus shortening the total cycle time (total working time) for tightening the nut 57.

[0098] (2) In the vehicle manufacturing method of this embodiment, when a workpiece W is present in the second fastening device 4, the first fastening device 3 performs a series of basic steps including preliminary fastening, final fastening, and preload measurement. When there is no workpiece W in the second fastening device 4, the workpiece W is sent from the first fastening device 3 to the second fastening device 4, and the second fastening device 4 performs a series of basic steps including preliminary fastening, final fastening, and preload measurement.

[0099] This makes it possible to significantly reduce the idle time of the second tightening device 4, and to significantly increase the time available for executing the basic process at both the first tightening device 3 and the second tightening device 4. As a result, it becomes possible to significantly shorten the total cycle time.

[0100] (3) In the vehicle manufacturing method of this embodiment, the first tightening device 3 and the second tightening device 4 are capable of performing adjustment steps, respectively, in which the preload measured in the preload measurement in the basic process falls outside the specified value and is deemed unacceptable, by re-tightening the nut 57 and re-measuring the preload.

[0101] If, after the basic process for the workpiece W is completed in the first clamping device 3, the adjustment process for the preceding workpiece W in the second clamping device 4 continues beyond a predetermined set time T1 from the start of the work, the workpiece W after the basic process is completed in the first clamping device 3 is kept in the first clamping device 3 until the adjustment process for the preceding workpiece W in the second clamping device 4 is completed.

[0102] In the above manufacturing method, the controller 5 of the tightening system 1 or the operator can determine whether the adjustment process for the preceding workpiece W in the second tightening device 4 is about to finish or is still ongoing. This makes it possible to temporarily place the workpiece W after the basic process is completed in the first tightening device 3. This allows for stabilization of the overall cycle time even when there is an adjustment process after the basic process.

[0103] (4) In the vehicle manufacturing method of this embodiment, the set time T1 is set to be shorter than the average time required for the re-preload measurement in the adjustment process of the second tightening device 4. After the set time T1 has passed, the timer 6 for judgment waiting is activated, and the workpiece W is placed in the first tightening device 3 to wait for a predetermined waiting period.

[0104] In the above manufacturing method, when the timer 6 for judgment waiting is activated, the first tightening device 3 keeps the workpiece W waiting for a predetermined waiting time. If the preload measurement of the preceding workpiece W in the second tightening device 4 fails, the second tightening device 4 performs an adjustment process. However, in parallel, the first tightening device 3 can also perform the adjustment process. As a result, the adjustment process can be performed in both the first tightening device 3 and the second tightening device 4, improving the efficiency of tightening the nuts 57 of the continuously transported workpieces W.

[0105] (5) In the vehicle manufacturing method of this embodiment, the timer 6 for judgment waiting stops when the re-preload measurement in the adjustment process of the second tightening device 4 is completed.

[0106] When the preload measurement for the adjustment process in the second tightening device 4 is completed, the timer 6 for judgment standby stops. This allows the controller 5 of the tightening system 1 or the operator to accurately determine that the adjustment process is being performed in the second tightening device 4 before the timer 6 stops. As a result, the adjustment process in the first tightening device 3 can be reliably performed in parallel with the adjustment process in the second tightening device 4, further improving the work efficiency of tightening the nuts 57 of the continuously transported workpieces W.

[0107] (6) In the vehicle manufacturing method of this embodiment, the drive pinion 51 that is tightening the nut 57 in the first tightening device 3 does not overtake the preceding drive pinion 51 that is tightening the nut 57 in the second tightening device 4, but is transported to the second tightening device 4 after the preceding drive pinion 51.

[0108] In the above manufacturing method, no drive pinion 51 of the workpiece W overtakes a preceding drive pinion 51, so that the workpiece W can be transported from the first clamping device 3 to the second clamping device 4 with the combination of drive pinion 51 and ring gear 52 of each workpiece W matching.

[0109] (modified version) In the above-described manufacturing method, the fastening of a nut 57 to the drive pinion 51 of the rear differential was used as an example, but the present invention is not limited to this and can also be applied to fastening a nut to the pinion gear in the transfer case 104 shown in Figure 1. [Explanation of Symbols]

[0110] 1. Tightening System 2. Seating device 3. First tightening device 4. Second tightening device 5 Controllers 6 Timer 51 Drive pinion (pinion gear) 52 Ring Gear 54 First bearing 55 Second bearing 56 Distance Piece 57 Nut 101 Engine (power source) 106 Rear Differential Gear (Rear Differential)

Claims

1. A method for manufacturing a vehicle comprising a pinion gear that transmits driving force generated by a drive source and a ring gear that meshes with the pinion gear, The vehicle is a vehicle comprising a unit having a pinion gear having a shaft portion, a first bearing at the tip end and a second bearing at the rear end of the shaft portion fitted onto the shaft portion and supporting the pinion gear rotatably, a distance piece sandwiched between the first bearing and the second bearing, and a nut that, when fastened to a male threaded portion formed on the shaft portion, seats on the first bearing and presses the first bearing, the second bearing and the distance piece, A tightening system is prepared to perform the tightening of the nuts by transporting the workpiece in the unit before the tightening of the nuts is completed through a seating device, a first tightening device, and a second tightening device in that order. The seating device is used to screw the nut onto the male thread portion of the shaft and seat it on the first bearing. The workpiece after the nut has been seated is transported to the first tightening device. Either the first or second tightening device performs a series of basic steps in which the nut is rotated at a predetermined angle, the nut is tightened to a predetermined torque, and the preload is measured to determine the initial load on the nut after the final tightening. A method for manufacturing a vehicle characterized by the following:

2. In the method for manufacturing a vehicle according to claim 1, When the workpiece is in the second clamping device, the first clamping device performs a series of basic steps: preliminary tightening, final tightening, and preload measurement. When there is no workpiece in the second clamping device, the workpiece is sent from the first clamping device to the second clamping device, and the second clamping device performs a series of basic processes including preliminary tightening, final tightening, and preload measurement. A method for manufacturing a vehicle characterized by the following:

3. In the method for manufacturing a vehicle according to claim 1, The first and second tightening devices are capable of performing adjustment steps, respectively, to re-tighten the nut and re-measure the preload if the preload measured in the preload measurement in the basic process falls outside the specified value and is therefore unacceptable. If, after the first clamping device has completed the basic process for the workpiece, the second clamping device continues the adjustment process for the preceding workpiece for a longer period than a predetermined set time from the start of the adjustment process, the first clamping device will hold the workpiece for which the basic process has been completed in the first clamping device until the adjustment process for the preceding workpiece in the second clamping device is completed. A method for manufacturing a vehicle characterized by the following:

4. In the vehicle manufacturing method described in claim 3, The setting time is shorter than the average time required for the re-preload measurement in the adjustment step of the second tightening device. Once the aforementioned set time has elapsed, the judgment standby timer is activated, causing the workpiece to wait in the first clamping device for a predetermined waiting period. A method for manufacturing a vehicle characterized by the following:

5. In the vehicle manufacturing method described in claim 4, A method for manufacturing a vehicle, characterized in that the determination standby timer stops when the re-preload measurement in the adjustment step in the second tightening device is completed.

6. In the method for manufacturing a vehicle according to any one of claims 1 to 5, The pinion gear being used to tighten the nut in the first tightening device is transported to the second tightening device after the preceding pinion gear, without overtaking the preceding pinion gear being used to tighten the nut in the second tightening device. A method for manufacturing a vehicle characterized by the following:

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