Press-in method

Abstract

To provide a press-in method which is press-fitted and fixed without occurrence of a damage such as galling on a press fitted surface.SOLUTION: A press-in method that press-fits a press-in object 1 into a press fitted object 2 by a specified quantity T through push-in of a punch 11 comprises: a push-in step which pushes-in the press-in object 1 by a part t of the specified quantity; and a retreat step which retreats the punch 11 in a direction of separating from the press fitted object 2. The push-in step and the retreat step are repeated several times until push-in amount of the press-in object 1 with respect to the press fitted object 2 reaches the specified quantity T.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a press-fitting method. [Background technology]

[0002] For example, oil seals are commonly used to seal between a drive shaft such as an engine crankshaft and a fixed side such as a housing, in order to prevent oil leakage from the inside.

[0003] This type of oil seal is usually annular overall and is composed of a seal lip that is located relatively radially inward and can slide against the shaft portion as described above, and a seal retainer that is located relatively radially outward and formed integrally with the seal lip.By fixing this seal retainer to a fixed side such as a housing, the oil seal is installed in a state where the shaft portion and the seal lip can slide against each other (see, for example, Patent Document 1 and Patent Document 2).

[0004] Although bolting and welding are known methods for fixing this type of oil seal to a housing, etc., press-fitting is often used to reduce work time and costs. For example, Patent Document 1 below proposes a method for fixing a seal retainer at a predetermined axial position of the housing by press-fitting the outer peripheral surface of the seal retainer into the inner peripheral surface of the housing. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5761784 [Patent Document 2] Patent No. 7254554 Summary of the Invention [Problem to be solved by the invention]

[0006] The above-mentioned press-fitting of the seal retainer is performed by, for example, using a punch to press the seal retainer into the inner periphery of the housing. The press-fitting margin (interference) is set to an appropriate size so as to ensure the required fixing strength of the oil seal (seal retainer). In this type of oil seal, the surface layer of the seal retainer, including the outer peripheral surface, may be integrally formed from the same rubber or elastomer as the seal lip. Therefore, depending on the size of the press-fitting margin, damage (cracks or tears) called galling may occur in the surface layer of the seal retainer, which is made of rubber or elastomer. Such damage may result in oil leakage.

[0007] In view of the above circumstances, the technical problem to be solved in this specification is to achieve press-fitting and fixation without causing damage such as galling to the press-fitted surface. [Means for solving the problem]

[0008] The above-mentioned problems are solved by a press-fitting method according to the present invention, which is a method for press-fitting a press-fitting object into a press-received object by a predetermined amount by pressing a punch, and is characterized by comprising a press-fitting step of press-fitting the press-fitting object by a portion of the predetermined amount and a retracting step of retracting the punch in a direction away from the press-received object, and is characterized by alternately repeating the press-fitting step and the retracting step until the amount of press-fitting of the press-fitting object into the press-received object reaches the predetermined amount.

[0009] The inventors focused on the conventional practice of pressing a press-fitting object into a press-received object by a single continuous pushing operation, and have therefore divided the process into multiple repeated push-fitting operations. Furthermore, after each push-fitting operation (each push-fitting step), the punch is temporarily retracted away from the press-fitting object. Generally, in this type of push-fitting operation, the push-fit load (the reaction force the punch receives from the press-fitting object) tends to increase as the push-fitting progresses. However, by retracting the punch after each small push-fitting operation, as in the present invention, it has been found that the increase in the push-fitting load during the next push-fitting operation can be suppressed. It is believed that the retraction of the punch causes elastic deformation of the press-fitting object in the push-back direction, thereby releasing shear strain generated inside the press-fitting object during the push-fitting operation (the reason for the suppression of the increase in the push-fitting load). Therefore, the press-fitting method according to the present invention can reduce the load acting on the press-fitting object and prevent damage, including galling. Therefore, while the press-fitted object is firmly fixed to the object being press-fitted, the tight contact state achieved by the press-fitting is ensured, and the desired performance that should be achieved by the press-fitting (preventing oil leakage in the case of an oil seal) can be achieved.

[0010] In the press-fitting method according to the present invention, the punch may be retracted to a position where the punch and the press-fit object are separated in the retracting step.

[0011] It has been found that the greater the distance the punch is retracted after the press-fitting operation, the better from the viewpoint of suppressing the press-fitting load. Furthermore, because the release of shear strain generated in the press-fitted object by the press-fitting operation contributes to suppressing the press-fitting load, it is preferable to retract the punch until the load received from the punch becomes zero. For these reasons, by retracting the punch to a position where the punch and the press-fitted object are separated, it is possible to maximize the effect of suppressing the press-fitting load.

[0012] In the press-fitting method according to the present invention, the punch may be driven to advance and retreat by a servo cylinder.

[0013] With a servo cylinder, it is possible to accurately control the drive amount in extremely fine units (for example, on the order of submillimeters). By driving the punch forward and backward with a servo cylinder, it is possible to accurately control the amount of punch push-in, i.e., the amount of press-fitting per operation, in extremely fine units. Therefore, with this configuration, it is possible to maximize the effect of suppressing the press-fitting load.

[0014] In the press-fitting method according to the present invention, the servo cylinder may be configured to be able to measure a reaction force acting on the punch from the object to be press-fitted.

[0015] In this way, by using a servo cylinder having a reaction force measurement function, it is possible to perform the press-fitting operation while monitoring the press-fitting load. This makes it possible to more reliably implement the press-fitting method according to the present invention. Furthermore, since the press-fitting load (reaction force from the press-fitted object) can be measured even when the punch is retracted, it is possible to easily and automatically retract the punch to a position where the punch and the press-fitted object are separated, for example.

[0016] As described above, the press-fitting method according to the present invention can achieve strong press-fitting while suppressing the press-fitting load. Therefore, even if the press-fitting object is an oil seal, for example, where at least the surface layer of the press-fitting object that comes into contact with the object being press-fitted is made of rubber or elastomer, it is possible to suppress damage caused by press-fitting and achieve a strong press-fitting and good adhesion state. [Effects of the Invention]

[0017] As described above, according to the press-fitting method of the present invention, it is possible to achieve press-fitting and fixation without causing damage such as galling to the press-fitted surface. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a diagram showing the overall configuration of an apparatus for carrying out a press-fitting method according to an embodiment of the present invention. [Figure 2]2 is a flowchart showing the flow of a press-fitting method using the device shown in FIG. 1. [Figure 3] 10A and 10B are diagrams conceptually showing the operation of the punch in a press-fitting step and a retreating step. [Figure 4] FIG. 10 is a diagram showing a state in which a predetermined amount of press-fitted material has been press-fitted. [Figure 5] 3 is a graph schematically showing the relationship between the stroke position of the punch and the press-fitting load when the press-fitting method is carried out according to the flow shown in FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, the details of a press-fitting method according to one embodiment of the present invention will be described with reference to the drawings.

[0020] 1 shows the overall configuration of an apparatus (press-fitting apparatus 10) for carrying out a press-fitting method according to one embodiment of the present invention. This press-fitting apparatus 10 includes a punch 11 for pressing in an object to be press-fitted 1, a holding member (first holding member) 12 for holding an object to be press-fitted 2 in a predetermined position, a driving device 13 for driving the punch 11 back and forth, and a control device 14 for controlling the driving device 13.

[0021] In this embodiment, the press-fit object 1 is an oil seal, and the object to be press-fitted 2 is, for example, a metal housing. In this case, although detailed structural illustrations are omitted, the oil seal has a seal lip that can slide against the shaft on its inner periphery, and an annular seal retainer with the seal lip provided radially inward. The seal retainer is composed of a metal core and a covering that covers the core. The covering is formed, for example, from rubber or elastomer and is integral with the seal lip. The covering has a surface layer that includes the outer circumferential surface that comes into contact with the object to be press-fitted during press-fitting.

[0022] Furthermore, when the press-fit object 1 is an oil seal, a cylindrical second holding member 15 is disposed on the outer periphery of the punch 11, and the outer periphery of the press-fit object 1, which is an oil seal (i.e., the outer periphery of a seal retainer), is held by the lower end of this second holding member 15. In this case, the second holding member 15 is supported by, for example, the punch 11 or a support member (not shown) for the punch 11 via an elastic body. Therefore, the second holding member 15 and the punch 11 move together, and after the second holding member 15 comes into contact with the first holding member 12, only the punch 11 can move in the press-fit direction (downward in FIG. 1) (see FIG. 3(a) described below).

[0023] The punch 11 moves along the press-fitting direction and can be inserted into the inner periphery of the press-fit object 2 held by the first holding member 12 (see FIG. 3(a)). In this embodiment, before the start of press-fitting, the press-fit object 1 is held by the second holding member 15 in a state of contact with the end face 11a of the punch 11 (see FIG. 1), and can move integrally with the punch 11.

[0024] The first holding member 12 is capable of holding the object to be pressed in 2 so that the central axis of the object to be pressed in 1 held by the second holding member 15 coincides with the central axis of the object to be pressed in 2 (see FIG. 1).

[0025] The driving device 13 drives the punch 11 so that it can move back and forth (stroke) along the press-fitting direction, and is configured to be able to stop the punch 11 at a predetermined stroke position. In this embodiment, the driving device 13 is configured with a servo cylinder, and is capable of precisely controlling the stroke position of the punch 11 (for example, on the order of submillimeters). Also, in this embodiment, the driving device 13 has a built-in load measuring device such as a load cell, and is able to measure the magnitude of the reaction force acting on the punch 11 as the press-fitting load.

[0026] The control device 14 is capable of controlling the driving of the punch 11 by the drive device 13, and is configured to alternately perform a press-in operation in which the punch 11 is advanced in the press-in direction (downward in FIG. 1) to press-in the press-in object 1 by a fixed amount, and a retreat operation in which the punch 11 is retreated in a direction away from the press-in object 2 (upward in FIG. 1). In this case, the control device 14 is configured to alternately repeat the above-mentioned advance operation and retreat operation of the punch 11 N times until the amount of press-in of the press-in object 1 into the press-in object 2 reaches a predetermined amount.

[0027] Here, when the press-fit amount t per press-fitting operation (corresponding to the above-mentioned constant amount) is set to a constant value, the relationship T = t × N holds between the total press-fit amount T (corresponding to the above-mentioned predetermined amount) and the press-fit amount t per operation. In principle, the press-fit amount t per operation can be any value, but if it is too large, it becomes difficult to fully enjoy the effect of the press-fitting method according to the present invention (the effect of suppressing the press-fit load). From this perspective, for example, the press-fit amount t per operation is preferably 10% or less of the total press-fit amount T, more preferably 5% or less, and even more preferably 2.5% or less.

[0028] Furthermore, the amount of movement per retraction (retraction amount b) can also be set to any value, in principle. For example, from the viewpoint of maximizing the effect of suppressing the press-fit load described below, it is preferable to set the retraction amount b to be larger than the press-fit amount t per retraction, and it is preferable to set the retraction amount b to a value that allows the punch 11 to be retracted to a position where the punch 11 and the press-fit object 1 are completely separated. Whether the punch 11 and the press-fit object 1 are completely separated can be easily determined based on the magnitude of the press-fit load measured by a load measuring device provided in the drive device 13 (determined by whether the press-fit load is substantially zero).

[0029] Hereinafter, the details of the press-fitting method using the press-fitting device 10 having the above configuration will be described in detail with reference to the flowchart shown in FIG.

[0030] First, as shown in Fig. 1, with the press-fitting object 1 held by the second holding member 15 and the object to be press-fitted 2 held by the first holding member 12, the punch 11 is lowered by the driving device 13 to start the operation of pressing the press-fitting object 1 into the object to be press-fitted 2 (step S1 in Fig. 2, the press-fitting step according to the present invention). In this case, for example, the value of the reaction force (press-fitting load) when the press-fitting object 1 is held by the second holding member 15 is set to zero. Also, the stroke position of the punch 11 at the point when the value of the reaction force starts to increase is set to the press-fitting start position P0 (the starting point for calculating the press-fit amount).

[0031] Then, the control device 14 continues the downward movement (press-fitting operation) of the punch 11 while monitoring the value of the reaction force (press-fitting load) acting on the punch 11, and when it detects that the punch 11 has advanced a predetermined press-fitting amount t from the press-fitting start position P0 (step S2 in Figure 2, the state shown in Figure 3(a)), it ends the press-fitting operation by the punch 11 and starts the retreating movement of the punch 11 (step S3 in Figure 2, the retreating step according to the present invention).

[0032] Then, when it is detected that the punch 11 has been retracted by a predetermined retraction amount b from the end position P1 of the previous press-fitting operation (the position shown in FIG. 3(a)) (step S4 in FIG. 2, the state shown in FIG. 3(b)), the control device 14 terminates the retraction operation of the punch 11 and lowers the punch 11 again to start the press-fitting operation of the press-fit object 1 (step S1 in FIG. 2). Note that in this embodiment, the magnitude of the retraction amount b is set so that the punch 11 retracts to a position where the punch 11 and the press-fit object 1 are separated, in other words, so that the value of the reaction force (press-fitting load) being measured temporarily becomes zero (see FIG. 3(b) and the turn-back position below the solid line in FIG. 5, which will be described later).

[0033] As described above, the punch 11 is repeatedly lowered and raised (retracted) while the press-fit object 1 is pressed in by a predetermined press-fit amount t at a time (the state shown in FIGS. 3(c) and 3(d)). When the sum of the press-fit amounts reaches the total press-fit amount T, in other words, when it is detected that the punch 11 has advanced in the press-fit direction from the press-fit start position P0 by the total press-fit amount T (step S5 in FIG. 2, the state shown in FIG. 4), the punch 11 is largely retracted, completing the press-fitting operation. Note that, as in this embodiment, when the magnitude of the press-fit amount t per operation is set (controlled) so that T = t × N holds between the press-fit amount per operation t, the total press-fit amount T, and the number of press-fit operations (press-fit steps) N, the completion of the press-fitting operation may be determined in step S5 based on whether the press-fitting operation by the punch 11 has been performed N times.

[0034] Next, the effects of the press-fitting method according to this embodiment will be described with reference to FIG. 5. In FIG. 5, the solid line indicates the relationship between the stroke position of the punch 11 and the press-fit load acting as a reaction force on the punch 11, which is obtained when the press-fitting method according to this embodiment is carried out. Furthermore, the dashed line indicates the relationship between the stroke position of the punch 11 and the reaction force (press-fit load) acting on the punch 11, which is obtained when the press-fitting object 1 is pressed into the press-fit object 2 by a total press-fit amount T in a single press-fitting operation. These graphs reveal that, in both the conventional press-fitting method and the press-fitting method according to this embodiment, the press-fit load tends to increase as the press-fitting of the press-fitting object 1 by the punch 11 progresses (as the press-fit amount increases).

[0035] On the other hand, differences can be seen in the slope of each graph, i.e., the rate of increase in the press-fit load relative to the press-fit amount. When the conventional press-fitting method is implemented, the rate of increase in the press-fit load relative to the press-fit amount as the press-fitting progresses is relatively large, whereas when the press-fitting method according to this embodiment is implemented, the rate of increase in the press-fit load relative to the press-fit amount (particularly the gradient of the upward-sloping straight line portion) is generally relatively small. Therefore, with the press-fitting method according to this embodiment, the press-fit load L1 (maximum load) at the time when a predetermined amount (total press-fit amount T) of the press-fit object 1 is press-fitted into the press-fit object 2 is smaller than the press-fit load L2 at the time when a predetermined amount of the press-fit object 1 is press-fitted with the conventional press-fitting method.

[0036] As described above, in the press-fitting method according to this embodiment, the press-fitting operation of the press-fitting object 1 into the press-fitted object 2 is repeated multiple times, and after each press-fitting operation (each press-fitting step), the punch 11 is temporarily retracted in a direction away from the press-fitted object 2. By gradually allowing the press-fitting object 1 to elastically recover in the push-back direction, an increase in the press-fitting load (and thus the maximum load L1) during the immediately following press-fitting operation can be suppressed. Therefore, the press-fitting method according to this embodiment reduces the load acting on the press-fitting object 1, preventing damage such as galling. Therefore, while the press-fitting object 1 is firmly press-fitted and fixed to the press-fitted object 2, a tight contact state due to the press-fitting is ensured, enabling the desired performance that should be achieved by the press-fitting (preventing oil leakage when the press-fitting object 1 is an oil seal as in this embodiment) to be exhibited.

[0037] Although one embodiment of the present invention has been described above, the press-fitting method according to the present invention can also adopt configurations other than those described above within the scope of the gist of the method.

[0038] For example, in the above embodiment, the press-fit amount t during each press-fit operation (press-fit step) is set to a constant value, but of course this is not limited to this. For example, although not shown in the drawings, the press-fit amount t may be increased as the number of repetitions of the press-fit operation increases. Alternatively, the press-fit amount t during each press-fit operation may be increased or decreased for each press-fit operation. In short, the magnitude of the press-fit amount t during each press-fit operation can be set arbitrarily, as long as the press-fit load (maximum load) is suppressed when the sum of the press-fit amounts t reaches a predetermined amount (total press-fit amount T).

[0039] There is also no particular limitation on the press-fitting speed, but if it is too fast, the effect of suppressing the press-fitting load will be reduced, and if it is too slow, it will result in an increase in the cycle time for the press-fitting operation. Therefore, it is desirable to take both of these factors into consideration and set the press-fitting speed to an appropriate value.

[0040] In addition, in this embodiment, the case where the retraction amount b per retraction operation is set to be larger than the press-fit amount t per press-fit operation has been exemplified, but of course, the present invention is not limited to this. As long as the desired effect of reducing the press-fit load can be obtained, the retraction amount b per operation may be set to be equal to or smaller than the press-fit amount t per operation.

[0041] In the above explanation, the press-fitting method according to the present invention is applied to the case where an oil seal as the press-fitting object 1 is press-fitted into a housing as the press-fitted object 2, but the application of the present invention is not limited to this. It goes without saying that the present invention can be applied widely and generally, regardless of the shape, material, or press-fitting mode of the press-fitting object 1 or the press-fitted object 2. [Explanation of symbols]

[0042] 1 Press-fit 2. Press-fit object 10 Press-fitting device 11 Punch 11a End face 12 First holding member 13 Drive unit 14 Control device 15 Second holding member b Retraction amount per time L1, L2 press-fit load (maximum load) P0 Press-fit start position t Injection volume per injection T Total injection volume

Claims

1. A method for pressing an object into a target object by a predetermined amount by pressing a punch, comprising: a press-fitting step of press-fitting the press-fit object by a portion of the predetermined amount; a retraction step of retracting the punch in a direction away from the object to be pressed in, the press-fitting step and the retracting step are alternately repeated until the amount of the press-fitting object into the object to be press-fitted reaches the predetermined amount.

2. The press-fitting method according to claim 1 , wherein in the retracting step, the punch is retracted to a position where the punch and the press-fit object are separated from each other.

3. 3. The press-fitting method according to claim 1, wherein at least a surface layer portion of the press-fitting object that comes into contact with the object to be press-fitted is made of rubber or elastomer.

Images