Seal mechanism and electric actuator having seal mechanism

Abstract

Provided is a seal mechanism that reduces a grease bleeding amount while suppressing an increase in sliding resistance with a simple configuration. A seal mechanism of a rod 1 of an electric actuator 100 filled with grease 10 is characterized by comprising: a double lip wiper 6 arranged on one side of the rod 1, and a single lip wiper 7 arranged at a certain distance from the double lip wiper 6 in the longitudinal direction of the rod 1, wherein the double lip wiper 6 reduces intrusion of dust from the outside and the outflow of the internal lubricant, only one single lip wiper 7 is provided to the rod cover 5 through which the rod 1 is inserted, and has a lip part 7a extending toward the inside filled with the lubricant, and the lip part 7a reduces the outflow of the internal lubricant.

Description

Sealing mechanism and electric actuator having sealing mechanism

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

[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 of these seals during operation (hereinafter referred to as grease seepage), a common approach has been to add additional seals to the interior.

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

[0004] Japanese Patent Application Laid-Open No. 2006-226455

[0005] In the seal structure disclosed in Patent Document 1, adding a seal to prevent grease seepage complicates the structure, which may 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 has a simple configuration and that reduces the amount of grease seeping while suppressing an increase in sliding resistance.

[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 fixed distance 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 lubricant, and the lip portion reduces the outflow of the lubricant from the inside.

[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.

[0009] 1 is a cross-sectional view showing an electric actuator 100 of the present invention. (A) A partial cross-sectional view showing the arrangement of a sealing mechanism of an embodiment. (B) A partial cross-sectional view showing the arrangement of a rod seal 60 of a conventional example. (A) A schematic diagram showing oil film formation by the single lip wiper 7 of the embodiment when the rod is extended in direction A. (B) A schematic diagram showing oil film formation by the rod seal 60 of a conventional example. (A) A schematic diagram showing oil film formation by the single lip wiper 7 of the embodiment when the rod is retracted in direction B. (B) A schematic diagram showing oil film formation by the rod seal 60 of a conventional example. (A) A cross-sectional view in the longitudinal direction showing the shape of the double lip wiper 6. (B) A cross-sectional view showing the shape of the single lip wiper 7. (A) A basic configuration including one double lip wiper 6 is shown. (B) A conventional configuration including a conventional rod seal 60 is shown. (C) A configuration including a double lip wiper 6 and a single lip wiper 7 is shown.

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The present invention will be described in detail below with reference to the accompanying drawings, in which: Fig. 1 is a cross-sectional view showing an electric actuator 100 (actuator) according to the present invention; Fig. 1 will be used to describe the electric actuator 100 according to the present invention.

[0011] The electric actuator 100 of the present invention comprises an electric motor formed by a magnet M and a coil C, a rotary nut 2 (nut) that is driven to rotate by the electric motor, a rod 1 that threads onto the rotary nut 2, a double lip wiper 6 (first seal) and a single lip wiper 7 (second seal), and a housing 4. 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 rotary 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 within 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 current is applied to the coil C, the rotating nut 2 functions as the shaft of the electric motor, generating rotational motion. The rotational motion of the electric motor rotates the rotating nut 2, and the rod 1 threads onto the rotating nut 2, converting the rotational motion into reciprocating motion, causing the rod 1 to reciprocate. That is, the male threaded portion 1a of the rod 1 threads onto the female threaded portion 2a of the rotating nut 2, and the male threaded portion 1a receives this rotational motion, converting the rotational motion into translational motion (reciprocating motion). The rod 1 is held so as not to rotate outside the electric actuator 100. The interior of the electric actuator 100 is filled with grease 10 (lubricant), which lubricates the mechanism. In particular, grease 10 is filled between the female threaded portion 2a of the rotating nut 2 and the male threaded portion 1a of the rod 1 to improve lubrication. The grease 10 is mainly sealed inside the rotating nut 2, but is also present in part in the space in front of the single lip wiper 7. Note that not all of the space is filled with 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 grease 10 is low (approximately 0.1 MPa at most). 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 is included in the housing 4. The rod 1 passes 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 (the atmosphere side) of the rod 1. The annular single-lip wiper 7 has a lip portion 7a (see FIG. 5(B)). Only one annular single-lip wiper 7 is disposed inside the rod cover 5, separated by a certain distance in the longitudinal direction of the rod 1 from the double-lip wiper 6, with the lip portion 7a facing inward on the side opposite the atmosphere side. The lip portion 7a faces the male thread portion 1a of the rod 1 and extends toward the interior, which is filled with grease 10. A bushing 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 bushing 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 6a of the double lip wiper 6 reduces the intrusion of external debris, dust, etc., and the second lip 6b reduces the outflow of the grease 10 inside. The lip 7a of the single lip wiper 7 reduces the outflow (amount of seepage) of the grease 10 filled inside by a sealing mechanism described in the following examples. Furthermore, since only one single lip wiper 7 is provided, an increase in the sliding resistance of the rod 1 is suppressed. According to the embodiment, an actuator having a sealing mechanism that suppresses an increase in sliding resistance and reduces the amount of grease seepage can be provided. The single lip wiper 7 is a type of seal commonly referred to as a dust seal, wiper seal, or scraper seal, and is typically used to prevent the intrusion of external debris and dust. Therefore, while it is not common to use a single lip wiper 7 for leak prevention like a rod seal, in the present invention, by using only one single lip wiper 7 facing backward on the rod, it is possible to significantly reduce grease seepage without increasing sliding resistance.

[0015] (Example) Next, a sealing mechanism according to an example embodiment provided in the electric actuator 100 of the present invention 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 that constitute the sealing mechanism of the example 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 internally 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 to the interior, as shown in FIG. 2(B). The rod seal 60 utilizes the repulsive force of an O-ring 70 disposed on the outside of the rod seal 60 in the radial direction of the rod 1, resulting in high sliding resistance even when only one rod seal 60 is used. Furthermore, test results described below show that the rod seal 60 alone is not effective enough in reducing grease seepage. Therefore, if an additional rod seal 61 and O-ring 71 are placed to improve sealing performance, the sliding resistance caused by the multiple seals increases, which reduces the mechanical efficiency of the electric actuator 100.

[0017] In this embodiment, as shown in FIG. 2A, a single inward-facing lip wiper 7 (or a seal of a similar shape) is added to the interior. This configuration, with the lip portion 7a facing inward and the single lip wiper 7 provided inside the device, is unprecedented. Furthermore, under conditions where the internal grease 10 is at a low pressure of about 0.1 MPa, the inward-facing single lip wiper 7 provides a greater effect in reducing grease seepage than the rod seal 60, and also reduces the increase in sliding resistance. Furthermore, the inward-facing single lip wiper 7 does not require multiple wipers, simplifying the seal configuration and saving space.

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

[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: viscosity of fluid, V: operating speed of rod 1, dp: contact surface pressure, dx: seal influence length, Wa = dp / dx: gradient of contact surface pressure dp in the dx direction, the oil film thickness h is expressed by the following formula.

[0020]

[0021] From equation (1), the conditions under which the oil film thickness h is thick and the amount of grease seeping increases are as follows: - High fluid viscosity η - Fast operating speed V - Low contact surface pressure dp - Long seal influence length dx If the product of the operating speed V of the rod 1 and the viscosity η of the fluid (grease 10) is constant, it can be said that only the ratio of the contact surface pressure dp to the seal influence length dx (i.e., the slope Wa of the contact surface pressure dp) affects the amount of grease seeping.

[0022] FIG. 3A is a schematic diagram of oil film formation when the rod 1 is moved in direction A (first direction) when the single lip wiper 7 of the embodiment is installed. FIG. 3B is a schematic diagram of oil film formation when the rod 1 is moved in direction A when the conventional rod seal 60 is installed. Note that the oil film in the drawing is enlarged for ease of understanding. As shown in FIG. 3A, when the single lip wiper 7 is installed with the lip portion 7a facing the interior filled with grease 10, the gradient Wa of the contact surface pressure dp at the lip portion 7a becomes large, and according to Equation (1), the oil film thickness h becomes thinner. In contrast, as shown in FIG. 3B, when the rod seal 60 is installed, 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 compared to the single lip wiper 7 shown in FIG. 3A.

[0023] As shown in Figure 3A, when the rod 1 moves in the direction A, the contact pressure dp of the single lip wiper 7 is significantly smaller than that of the rod seal 60. Furthermore, the seal tip of the lip portion 7a is generally at an angle slightly larger than a right angle to the rod 1, which tends to shorten the seal influence length dx, significantly increasing the slope Wa of the contact pressure dp and resulting in a very thin oil film thickness h. The rod seal 60 also utilizes the repulsive force of the O-ring 70 located on the outside of the rod seal 60, resulting in a large contact pressure dp. Furthermore, because 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 slope Wa of the contact pressure dp is small, and a thicker oil film thickness h is generated compared to the single lip wiper 7.

[0024] FIG. 4A is a schematic diagram of oil film formation when the rod 1 is retracted in direction B (second direction) when the single-lip wiper 7 of the embodiment is installed. FIG. 4B is a schematic diagram of oil film formation when the rod 1 is retracted in direction B when the conventional rod seal 60 is installed. Note that the oil film in the drawing is enlarged for ease of understanding. Grease 11 indicates residual grease when the rod 1 is retracted in direction B. As shown in FIG. 4A, when the single-lip wiper 7 is installed with its lip portion 7a facing the interior filled with grease 10, the slope Wa of the contact pressure dp becomes smaller, and according to equation (1), the oil film thickness h becomes thicker. In contrast, as shown in FIG. 4B, when the rod seal 60 is installed, the slope Wa of the contact pressure dp becomes larger, and the oil film thickness h becomes thinner.

[0025] 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 seeping outward, arranging the single lip wiper 7 with the lip portion 7a facing inward is advantageous over the arrangement of the conventional rod seal 60.

[0026] Rod seals 60 are not normally used alone, but are generally used in tandem, with several arranged along the longitudinal axis of the 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 subsequent rod seal 61 or wiper seal, as shown in Figure 2(B). In contrast, the shape of the lip portion 7a of the single lip wiper 7 generally functions to prevent external dirt, oil, and moisture from entering the interior, but in the electric actuator 100 using grease 10, there is no particular problem with using it as a seal because almost no pressure is generated inside the actuator.

[0027] As shown in Figure 4(A), when the rod 1 is retracted in direction B, the seal contact pressure dp is the same as when the rod 1 is extended in direction A (see Figure 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 when the rod 1 is extended in direction A. 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, 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,

[0028] When the rod seal 60 moves in direction A to extend the rod 1, it is necessary to generate a certain amount of oil film thickness h (corresponding to grease seepage) to lubricate the rod seal 61 at the subsequent stage. However, when the rod 1 moves in direction B to retract the rod 1, the seal influence length dx is lengthened to recover the grease seepage, making it easier to recover the grease seepage.

[0029] As described above, the lip portion 7a of the single lip wiper 7 functions to prevent external dirt, oil, or moisture from entering the interior, but in order to function to allow grease and oil from the interior to escape to the exterior, 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 block grease, thereby providing an appropriate amount of grease to the double lip wiper 6 and also having the effect of reducing wear on the double lip wiper 6.

[0030] In the present invention, the wiper added to the interior is not limited to a single lip wiper 7. If the shape of the lip portion 7a viewed from the interior has a larger angle (shorter seal-influence length dx) than the shape viewed from the exterior, the effect of reducing grease seepage can be achieved. Furthermore, if the lip shape viewed from the exterior is gentler (larger seal-influence length dx), the effect of returning the seepage to the interior can be achieved, further reducing grease seepage. Furthermore, 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.

[0031] FIG. 5A 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. 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. 5B 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 substantially rectangular main body portion 7b and a lip portion 7a extending in the longitudinal direction from the main body portion 7b. The lip portion 7a is connected to the main body portion 7b.

[0032] In the radial direction of the rod 1, the main body portion 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 major 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 major axis direction. A clearance C (C>0) is secured between the main body portion 7b and the rod 1.

[0033] Next, the grease seepage reduction effect will be described with reference to test results. Table 1 shows the simulated sliding resistance values ​​(theoretical values) for each seal configuration shown in Figures 6(A) to 6(C). Figure 6(A) shows a basic configuration including a double-lip wiper 6 with a dust lip on the outside (atmosphere side). Figure 6(B) shows a conventional configuration including a double-lip wiper 6 on the outside and a rod seal 60 biased by an O-ring 70 on the inside. Figure 6(C) shows an example configuration including a double-lip wiper 6 on the outside and a single-lip wiper 7 on the inside. As shown in Table 1, the sliding resistance for the basic configuration is set to 1.0, and each value is calculated as a relative value. The conventional configuration (with the rod seal 60 added) had a sliding resistance of 3.0, while the example configuration (with the single-lip wiper 7 added) had a sliding resistance of 1.1, demonstrating that an increase in sliding resistance can be suppressed.

[0034] Table 2 shows the results of a comparison of the amount of grease seepage and sliding resistance between the basic configuration (FIG. 6(A)) and the configuration of the example (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 example compared to the basic configuration, with almost no increase in sliding resistance observed.

[0035] Furthermore, 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 in 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 installed, but as shown in Table 1, this is not practical because there is a risk of the sliding resistance increasing significantly.

[0036] 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.

[0037] 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.

[0038]

[0039]

[0040]

[0041] This application claims priority from Japanese Patent Application No. 2023-137263, filed on August 25, 2023, the contents of which are incorporated herein by reference.

[0042] DESCRIPTION OF SYMBOLS 1 Rod 2 Rotating nut (nut) 5 Rod cover (housing) 6 Double lip wiper (first seal) 7 Single lip wiper (second seal) 7a Lip portion 7b Main body portion 10 Grease (lubricant) 100 Electric actuator (actuator) A Protruding direction (first direction) B Retracting direction (second direction) dp Contact surface pressure dx Seal influence length Wa Inclination of contact surface pressure α First angle β Second angle

Claims

1. 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 fixed distance 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 configured to extend toward the interior filled with the lubricant, and the lip portion reduces the outflow of the lubricant from the inside.

2. The seal mechanism according to claim 1, characterized in that in a cross section taken along the longitudinal direction, the second seal has a body portion having a generally rectangular shape, and the lip portion of the second seal extends from the body portion along the longitudinal direction.

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

4. A sealing mechanism as described in claim 1, characterized in that the tip of the lip portion that abuts against the rod has a first angle and a second angle with respect to the longitudinal direction, and the first angle is larger than the second angle.

5. A sealing mechanism as described in claim 1, characterized in that the gradient of the contact pressure of the lip portion of the second seal in the major axis direction when the rod is driven in a first direction is greater than the gradient of the contact pressure of the lip portion in the major axis direction when the rod is driven in a second direction.

6. The sealing mechanism according to claim 1, wherein the actuator is driven reciprocally by an electric current.

7. 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. The seal mechanism according to claim 1, characterized in that a bush or an oilless bearing is provided between the first seal and the second seal.

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

10. An actuator comprising: a sealing mechanism as claimed in any one of claims 1 to 9; a rod; a nut; and an electric motor, wherein the nut rotates due to the rotational motion of the electric motor, and the rod screwed into the nut reciprocates.

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