Seal mechanism and electric actuator having the same

Abstract

To provide a seal mechanism which enables reduction of an amount of exuded grease while inhibiting increase of slide resistance with a simple structure.SOLUTION: A seal mechanism of a rod 1 of an electric actuator 100 filled with grease 10 includes: a double lip wiper 6 disposed at one side of the rod 1; and a single lip wiper 7 which is disposed spaced a predetermined distance apart from the double lip wiper 6 in a longitudinal direction of the rod 1. The double lip wiper 6 reduces dust entering from the outside and outflow of a lubricant. Only one single lip wiper 7 is provided at a rod cover 5 into which the rod 1 is inserted and has a lip part 7a extending toward the inside filled with the lubricant. The lip part 7a reduces leakage of the lubricant therein.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a sealing mechanism and an electric actuator having a sealing mechanism. [Background technology]

[0002] In some reciprocating electric actuators filled with grease, multiple seals are placed between the rod (moving part) and the housing (fixed part).To reduce the phenomenon of grease seeping out from these seals during operation (hereinafter referred to as grease seepage), it has been common to add additional seals to the inside.

[0003] For example, paragraph 0058 of Patent Document 1 discloses that durability is improved by preventing the second scraper from scraping out the lubricant, grease, etc. filled inside to the outside, thereby maintaining the lubricating function for a long period of time. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2006-226455 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the seal structure disclosed in Patent Document 1, adding a seal as a measure against grease seepage would complicate the structure, which could result in increased sliding resistance and reduced mechanical efficiency as an actuator.

[0006] An object of the present invention is to provide a sealing mechanism that reduces the amount of grease seeping while suppressing an increase in sliding resistance with a simple configuration. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides a sealing mechanism for an actuator rod filled with lubricant, comprising a first seal arranged on one side of the rod and a second seal arranged a certain distance away from the first seal in the longitudinal direction of the rod, wherein the first seal reduces the intrusion of dust from the outside and the outflow of the lubricant from the inside, and the second seal is provided alone in a housing through which the rod passes, and has a lip portion extending toward the interior filled with the lubricant, and the lip portion reduces the outflow of the lubricant from the inside. Effect of the Invention

[0008] According to the present invention, it is possible to provide a sealing mechanism that reduces the amount of grease seeping while suppressing an increase in sliding resistance with a simple configuration. [Brief description of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing an electric actuator 100 of the present invention. [Diagram 2] 1A is a partial cross-sectional view showing the arrangement of the seal mechanism of the embodiment, and FIG. 1B is a partial cross-sectional view showing the arrangement of a rod seal 60 of a conventional example. [Diagram 3] 1A is a schematic diagram showing the formation of an oil film by the single lip wiper 7 of the embodiment when the rod is projected in the direction A. FIG. 1B is a schematic diagram showing the formation of an oil film by the rod seal 60 of the conventional example. [Figure 4] 1A is a schematic diagram showing the formation of an oil film by the single lip wiper 7 of the embodiment when the rod is retracted in a direction B. FIG. 1B is a schematic diagram showing the formation of an oil film by the rod seal 60 of the conventional example. [Diagram 5] 1A is a cross-sectional view taken along the major axis, showing the shape of a double lip wiper 6. FIG. 1B is a cross-sectional view taken along the major axis, showing the shape of a single lip wiper 7. [Figure 6](A) shows a basic configuration equipped with one double lip wiper 6. (B) shows a conventional configuration equipped with a conventional rod seal 60. (C) shows a configuration equipped with a double lip wiper 6 and a single lip wiper 7. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. Fig. 1 is a cross-sectional view showing an electric actuator 100 (actuator) of the present invention. The electric actuator 100 of the present invention will be described with reference to Fig. 1.

[0011] The electric actuator 100 of the present invention is composed of an electric motor formed of a magnet M and a coil C, a rotating nut 2 (nut) that is rotated by the electric motor, a rod 1 that screws into the rotating nut 2, a double lip wiper 6 (first seal) and a single lip wiper 7 (second seal), a housing 4, etc. The electric actuator 100 is an actuator that is electrically driven to reciprocate, in that the rod 1 is driven to reciprocate when the electric motor rotates the rotating nut 2. A driven member is fixed to the tip of the rod 1, and the reciprocating motion of the rod 1 causes the driven member to reciprocate.

[0012] The rotating nut 2 is held inside the housing 4 via a rotating bearing 3. A magnet M is attached to the outer peripheral surface of the rotating nut 2, and when a current is applied to the coil C, the rotating nut 2 functions as the shaft of the electric motor, generating a rotational motion. The rotating nut 2 rotates due to the rotational motion of the electric motor, and the rod 1 is screwed into the rotating nut 2, converting the rotational motion into a reciprocating motion, and the rod 1 reciprocates. That is, the male threaded portion 1a provided on the rod 1 is screwed into the female threaded portion 2a provided on the rotating nut 2, and the male threaded portion 1a receives the rotational motion, converting the rotational motion into a translational motion (reciprocating motion). The rod 1 is held so as not to rotate outside the electric actuator 100. The inside of the electric actuator 100 is filled with grease 10 (lubricant), and the mechanism is lubricated by the grease 10. In particular, the grease 10 is filled between the female threaded portion 2a provided on the rotating nut 2 and the male threaded portion 1a of the rod 1 to improve the lubrication state. The grease 10 is mainly enclosed inside the rotating nut 2, but is also partially present in the space in front of the single lip wiper 7. Note that not all of the space is filled with the grease 10, and air is also present. The application of the present invention is limited to cases where the pressure in the area filled with the grease 10 is low (approximately a maximum of 0.1 MPa as a guideline). Furthermore, the embodiment is not limited to the rotating nut 2, and may be an electric actuator that uses a mechanism that converts rotation into linear motion by threading a ball screw or the like.

[0013] A rod cover 5 is attached to the end of the housing 4, and the rod cover 5 is included in the housing 4. The rod 1 is inserted through the rod cover 5 and extends outside the rod cover 5. The annular double lip wiper 6 has a first lip portion 6a and a second lip portion 6b (see FIG. 5(A)), and is disposed at the end of the rod cover 5 with the first lip portion 6a facing one side (atmospheric side) of the rod 1. The annular single lip wiper 7 has a lip portion 7a (see FIG. 5(B)), and is disposed inside the rod cover 5, with the lip portion 7a facing inward on the opposite side to the atmospheric side, at a certain distance from the double lip wiper 6 in the longitudinal direction of the rod 1. The lip portion 7a faces the male thread portion 1a of the rod 1, and is configured to extend toward the inside filled with grease 10. A bush 8a is disposed between the double lip wiper 6 and the single lip wiper 7, but an oilless bearing may be provided instead of the bush 8a. The single lip wiper 7 may be disposed inside the rod cover 5 by a collar 8b. A bellows cover 9 may be provided to cover the portion of the rod 1 exposed from the rod cover 5.

[0014] When the rod 1 of the electric actuator 100 of the present invention reciprocates, the first lip portion 6a of the double lip wiper 6 reduces the intrusion of dirt, dust, etc. from the outside, and the second lip portion 6b reduces the outflow of the grease 10 inside. The lip portion 7a of the single lip wiper 7 reduces the outflow (seepage) of the grease 10 filled inside by a sealing mechanism of an embodiment described later. Furthermore, since only one single lip wiper 7 is arranged, an increase in the sliding resistance of the rod 1 is suppressed. According to the embodiment, it is possible to provide an actuator having a sealing mechanism that suppresses an increase in sliding resistance and reduces the amount of grease seepage. The single lip wiper 7 is a type of seal generally called a dust seal, wiper seal, or scraper seal, and is usually used for the purpose of preventing the intrusion of dirt and dust from the outside. Therefore, it is not common to use the single lip wiper 7 to prevent leakage like a rod seal, but in the present invention, by using only one single lip wiper 7 in the reverse direction on the rod, it is possible to obtain an effect of significantly reducing grease seepage without increasing sliding resistance.

[0015] (Example) Next, a sealing mechanism according to an embodiment of the present invention provided in the electric actuator 100 will be described. Fig. 2(A) is a partial cross-sectional view showing the arrangement of the double lip wiper 6 and single lip wiper 7, which are the sealing mechanism according to the embodiment. Fig. 2(B) is a partial cross-sectional view showing the arrangement of a rod seal 60 according to a conventional example. The advantages of the configuration of the present invention over a configuration in which a rod seal 60 used in a general hydraulic cylinder or the like is added to the inside will be explained using the sealing theory described below.

[0016] A conventional method for reducing grease seepage from the seal portion is to add a rod seal 60 inside as shown in FIG. 2(B). The rod seal 60 is in the radial direction of the rod 1 and utilizes the repulsive force of the O-ring 70 arranged on the outside of the rod seal 60, so even if only one rod seal 60 is used, the sliding resistance is large. In addition, the test results described below show that the rod seal 60 alone is not sufficient in reducing grease seepage. Therefore, if an additional rod seal 61 and O-ring 71 are arranged to improve the sealing performance, the sliding resistance due to the multiple seals increases, which causes a decrease in the mechanical efficiency of the electric actuator 100.

[0017] In the embodiment, as shown in FIG. 2(A), one inward-facing single lip wiper 7 (or a seal of a similar shape) is added inside. This configuration in which the lip portion 7a faces inward and the single lip wiper 7 is provided inside the device is not conventional. Under conditions where the internal grease 10 is at a low pressure of about 0.1 MPa, the inward-facing single lip wiper 7 has a greater effect of reducing grease seepage than the rod seal 60, and the increase in sliding resistance is also smaller. Furthermore, in the case of the inward-facing single lip wiper 7, there is no need to provide multiple wipers, and the seal configuration is simple and space-saving.

[0018] Next, using sealing theory, the advantage of adding the single lip wiper 7 of the embodiment to the rod 1 of the electric actuator 100 over adding a rod seal 60 used in general hydraulic cylinders, etc., in reducing grease seepage will be explained.

[0019] The amount of grease seeping out is expressed by the oil film thickness h in seal theory, and the thicker the oil film thickness h, the greater the amount of grease seeping out. Where: η: Fluid viscosity V: Rod 1 movement speed dp: contact pressure dx: Seal impact length Wa=dp / dx: Inclination of contact pressure dp in the dx direction Then, the oil film thickness h is expressed by the following formula.

number

[0020] FIG. 3(A) is a schematic diagram of oil film formation when the rod 1 is projected in the direction A (first direction) when the single lip wiper 7 of the embodiment is arranged. FIG. 3(B) is a schematic diagram of oil film formation when the rod 1 is projected in the direction A when the conventional rod seal 60 is arranged. The oil film in the drawing is drawn enlarged for easy understanding. As shown in FIG. 3(A), when the single lip wiper 7 is arranged with the lip portion 7a facing the inside filled with grease 10, it can be seen that the gradient Wa of the contact surface pressure dp at the lip portion 7a becomes large, and the oil film thickness h becomes thinner according to formula (1). In contrast, as shown in FIG. 3(B), when the rod seal 60 is arranged, it can be seen that the gradient Wa of the contact surface pressure dp at the seal portion, which is the contact point between the rod seal 60 and the rod 1, becomes small, and the oil film thickness h becomes thicker than that of the single lip wiper 7 shown in FIG. 3(A).

[0021] As shown in FIG. 3(A), in the operation in the direction A in which the rod 1 protrudes, the contact pressure dp of the single lip wiper 7 is considerably smaller than the contact pressure dp of the rod seal 60. In addition, the seal tip of the lip portion 7a is generally at an angle slightly larger than a right angle with respect to the rod 1, so the seal influence length dx tends to be short, the gradient Wa of the contact pressure dp becomes extremely large, and the oil film thickness h becomes very thin. In addition, the rod seal 60 uses the repulsive force of the O-ring 70 arranged on the outside of the rod seal 60, so the contact pressure dp is large. Furthermore, since the seal portion, which is the contact point between the rod seal 60 and the rod 1, has a certain angle and length, the seal influence length dx is long, the gradient Wa of the contact pressure dp becomes small, and a thicker oil film thickness h is generated compared to the single lip wiper 7.

[0022] FIG. 4(A) is a schematic diagram of oil film formation when the rod 1 is retracted in the direction B (second direction) when the single lip wiper 7 of the embodiment is arranged. FIG. 4(B) is a schematic diagram of oil film formation when the rod 1 is retracted in the direction B when the conventional rod seal 60 is arranged. The oil film in the drawing is drawn enlarged for easy understanding. Grease 11 indicates the residual grease when the rod 1 is retracted in the direction B. As shown in FIG. 4(A), when the single lip wiper 7 is arranged with the lip portion 7a facing the inside filled with grease 10, it can be seen that the gradient Wa of the contact pressure dp becomes small, and the oil film thickness h becomes thicker according to formula (1). In contrast, as shown in FIG. 4(B), when the rod seal 60 is arranged, it can be seen that the gradient Wa of the contact pressure dp becomes large, and the oil film thickness h becomes thinner.

[0023] From the above, it can be seen that when the single lip wiper 7 is arranged with the lip portion 7a facing inward inside an interior filled with grease 10, the grease 10 inside is less likely to move outward, and conversely, the remaining grease 11 is more likely to be drawn inward. On the other hand, when the rod seal 60 is arranged inside, it can be seen that the grease 10 inside is relatively more likely to move outward, and conversely, the remaining grease 11 is more difficult to draw inward. In other words, for the purpose of reducing grease seepage to the outside, arranging the single lip wiper 7 with the lip portion 7a facing inward is advantageous over the arrangement of the conventional rod seal 60.

[0024] Rod seals 60 are not usually used alone, but are generally used in tandem, with several arranged along the longitudinal axis of rod 1, or in combination with a wiper seal. For this reason, it is necessary to generate a certain amount of oil film to lubricate the rear rod seal 61 or wiper seal as shown in Fig. 2(B). In contrast, the shape of the lip portion 7a of the single lip wiper 7 generally functions to prevent foreign matter, oil, and moisture from the outside from entering the inside, but in the electric actuator 100 using grease 10, there is almost no problem in using it as a seal because almost no pressure is generated inside the actuator.

[0025] As shown in Fig. 4(A), in the operation in direction B in which the rod 1 is retracted, the seal contact pressure dp is the same as in the operation in direction A in which the rod 1 is protruding (see Fig. 3(A)). However, the seal influence length dx is long for both the rod seal 60 and the single lip wiper 7, and the oil film thickness h generated is larger than in the operation in direction A in which the rod 1 is protruding. In other words, the gradient Wa of the contact pressure in the major axis direction of the lip portion 7a of the single lip wiper 7 when the rod 1 is driven in direction A in which the rod 1 is protruding is larger than the gradient Wa of the contact pressure in the major axis direction of the lip portion 7a when the rod 1 is driven in direction B in which the rod 1 is retracted.

[0026] When the rod seal 60 moves in direction A to project the rod 1, it is necessary to generate a relatively thick oil film thickness h (corresponding to grease seepage) to lubricate the downstream rod seal 61. However, when the rod 1 moves in direction B to retract the rod 1, the seal influence length dx is made longer to collect the grease seepage, making it easier to collect the grease seepage.

[0027] As described above, the lip portion 7a of the single lip wiper 7 functions to prevent dirt, oil, or moisture from the outside from entering the inside, but in order to function not to prevent grease and oil from the inside from escaping to the outside, the seal influence length dx is long, similar to the configuration that collects seepage from the rod seal 60. In other words, as described above, the single lip wiper 7 does not completely stop the grease, so it provides an appropriate amount of grease to the double lip wiper 6, and also has the effect of reducing wear of the double lip wiper 6.

[0028] In the present invention, the wiper added to the inside is not limited to a single lip wiper 7, and if the shape of the lip portion 7a seen from the inside has a larger angle (seal influence length dx is short) than the shape seen from the outside, the effect of reducing grease seepage can be obtained. Furthermore, if the lip shape seen from the outside is gentle (seal influence length dx is large), the effect of returning the seepage to the inside can be obtained, making it possible to further reduce grease seepage. In addition, the contact surface pressure dp of the seal only needs to be about the same as that of a general dust seal, and even if multiple seals are installed, the increase in sliding resistance is small.

[0029] FIG. 5(A) is a cross-sectional view in the longitudinal direction showing the shape of the double lip wiper 6. The double lip wiper 6 has a first lip portion 6a and a second lip portion 6b, and a recess 6c is provided between the first lip portion 6a and the second lip portion 6b, and the recess 6c fits into the rod cover 5. The first lip portion 6a is located on the atmospheric side, and the second lip portion 6b is located on the inner side. FIG. 5(B) is a cross-sectional view in the longitudinal direction showing the shape of the single lip wiper 7. The single lip wiper 7 has a body portion 7b having a substantially rectangular shape, and a lip portion 7a extending from the body portion 7b in the longitudinal direction. The lip portion 7a is connected to the body portion 7b.

[0030] In the radial direction of the rod 1, the main body 7b is disposed inside the rod cover 5 and does not abut against the rod 1, while the lip portion 7a abuts against the rod 1. The tip of the lip portion 7a that abuts against the rod 1 has a first angle α and a second angle β with respect to the long axis direction, and the first angle α is larger than the second angle β. The first angle α may be an angle smaller than a right angle with respect to the long axis direction. A clearance C (C>0) is secured between the main body 7b and the rod 1.

[0031] Next, the effect of reducing grease seepage will be described with reference to the test results. Table 1 shows the simulation values ​​(theoretical values) of the sliding resistance in each seal configuration shown in Fig. 6(A) to (C). Fig. 6(A) shows a basic configuration having one double lip wiper 6 with a dust lip on the outside (atmosphere side), Fig. 6(B) shows a conventional configuration having a double lip wiper 6 on the outside and one rod seal 60 biased by an O-ring 70 on the inside, and Fig. 6(C) shows a configuration of an embodiment having a double lip wiper 6 on the outside and one single lip wiper 7 added on the inside. As shown in Table 1, the sliding resistance in the basic configuration is set to 1.0, and each numerical value is calculated as a relative value. The sliding resistance is 3.0 in the conventional configuration (rod seal 60 is added), but the sliding resistance is 1.1 in the configuration of the embodiment (single lip wiper 7 is added), and it can be seen that the increase in sliding resistance can be suppressed.

[0032] Table 2 shows the results of comparing the amount of grease seepage and sliding resistance of the basic configuration (FIG. 6(A)) and the configuration of the embodiment (single lip wiper 7 added, FIG. 6(C)) under certain test conditions, using the electric actuator 100. Note that the value for the basic configuration is set to 1.00 and each value is calculated as a relative value. Although there is some variation in the test results, it can be seen that the amount of grease seepage is reduced by about 90% in the configuration of the embodiment compared to the basic configuration, while there is almost no increase in sliding resistance.

[0033] Additionally, although the test conditions are different from those in Table 2, Table 3 shows the results of comparing the amount of grease seepage in the basic configuration and the conventional configuration. As with Table 2, the basic configuration is set to 1.00 and each value is calculated as a relative value. It can be seen that at least in the conventional configuration (one rod seal 60 added), there is no reduction in the amount of grease seepage. It is expected that the amount of grease seepage will be reduced if multiple rod seals 60 are arranged, but as shown in Table 1, this is not practical as there is a risk of a significant increase in sliding resistance.

[0034] According to the embodiment, it is possible to provide a sealing mechanism that reduces the amount of grease seeping while suppressing an increase in sliding resistance with a simple configuration.

[0035] Although the preferred embodiments and application examples of the present invention have been described above, the present invention is not limited to these embodiments and application examples, and various modifications and changes are possible within the scope of the gist of the present invention.

[0036] [Table 1]

[0037] [Table 2]

[0038] [Table 3] [Explanation of symbols]

[0039] 1 Rod 2 Rotating Nut (Nut) 5 Rod cover (housing) 6 Double lip wiper (first seal) 7 Single Lip Wiper (Second Seal) 7a Lip 7b Main body 10 Grease (lubricant) 100 Electric actuator (actuator) A Protruding direction (first direction) B Retract direction (second direction) dp Contact pressure dx Seal impact length Wa Contact pressure gradient α First angle β Second angle

Claims

1. In a sealing mechanism for an actuator rod filled with a lubricant, a first seal disposed on one side of the rod; a second seal disposed a fixed distance from the first seal in a longitudinal direction of the rod; The first seal reduces the intrusion of dust from the outside and the outflow of the lubricant from the inside, the second seal is provided in a housing through which the rod passes, and has a lip portion configured to extend toward the inside filled with the lubricant; A sealing mechanism, wherein the lip portion reduces loss of the lubricant therein.

2. In cross section along the longitudinal axis, the second seal has a body portion that is generally rectangular in shape; The seal arrangement of claim 1 , wherein the lip portion of the second seal extends from the body portion along the longitudinal axis.

3. 3. The seal mechanism according to claim 2, wherein the main body portion is disposed in the housing and does not abut against the rod in a radial direction of the rod, and the lip portion abuts against the rod.

4. 2. The sealing mechanism according to claim 1, wherein a tip portion of the lip portion that abuts against the rod has a first angle and a second angle with respect to the longitudinal axis direction, the first angle being larger than the second angle.

5. 2. The sealing mechanism according to claim 1, wherein a gradient of the contact pressure of the lip portion of the second seal in the longitudinal direction when the rod is driven in a first direction is greater than a gradient of the contact pressure of the lip portion in the longitudinal direction when the rod is driven in a second direction.

6. The sealing mechanism according to claim 1 , wherein the actuator is electrically driven to reciprocate.

7. 2. The seal mechanism according to claim 1, wherein the pressure in the region filled with the lubricant is a maximum of about 0.1 MPa.

8. 2. The seal mechanism according to claim 1, wherein a bush or an oilless bearing is provided between the first seal and the second seal.

9. 2. The seal mechanism according to claim 1, wherein the lubricant is filled between the rod and a nut that engages with the rod.

10. A sealing mechanism according to any one of claims 1 to 9; Rod and Nut and and an electric motor. An actuator, characterized in that the nut rotates due to the rotational motion of the electric motor, and the rod screwed into the nut reciprocates.

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