GB2214576A - Lip seal device - Google Patents

Abstract

A lip seal device for sealing the gap between a housing (1) and a rotary shaft (2) comprises a case (4) surrounding the rotary shaft (2), a lip seal (6) attached inside the case (4), support means (7) for holding the lip seal (6) at its outer circumferential portion and seal means (5) located on the outside circumferential surface of the case (4). The inner circumferential portion of the lip seal (6) is curved towards the sealed fluid. The lip seal (6) includes a sealing surface (10) provided with an annular groove (9) extending continuously in the circumferential direction of the rotary shaft (2) so that the sealing surface (10) has a first (10a) and second (10b) sealing portion. The contact pressure of the first sealing portion (10a) on the rotary shaft (2) is lower than the contact pressure of the second sealing portion (10b) on the rotary shaft (2). …<IMAGE>…

Description

-1 2214576 Lip Seal Device The present invention relates to a lip seal

device having a lip seal in sliding contact with a rotary shaft.

A lip seal device comprising a case surrounding a rotatably supported rotary shaft and a lip seal whose inner circumferential portion is curved toward a sealed fluid and is in sliding contact with the outside circumferential surface of the rotary shaft has been well known A similar lip seal device having a lip seal whose sealing surface on a rotary shaft is provided with a spiral groove is disclosed in US-A- 38)71 ''6 and US-A-3929341 The sealing performance of the latter lip sealing device having a spiral groove is better during the rotation of the rotary shaft than that of the former lip seal device not having such a spiral groove On the other hand, the sealing performance of the latter lip seal device having a spiral groove is much worse during the stoappage of the rotation of the rotary shaft than that of the former lip seal device not having a spiral groove.

Another lip seal device having a lip seal whose sealing surface on the rotary shaft include one or two annular grooves is disclosed in JP-A-55-30542.

According to this invention a lip sealing device for sealing the gap between a housing and a rotary shaft comprises 2 - a case surrounding said rotary shaft; a lip seal attached inside said case; support means for holding said lip seal on at least the outer circumferential portion thereof; and seal means located on the outside circumferential surface of said case; the inner circumferential portion of said lip seal being curved toward a sealed fluid, wherein said lip seal comprises a sealing surface in sliding contact with the outside circumferential surface of said rotary shaft, said sealing surface having an annular groove extending continuously in the circumferential direction of said rotary shaft so that said sealing surface has a first sealing portion in front of said annular groove and a second sealing portion in the rear of said annular groove; the contact pressure of said first sealing portion on said rotary shaft being lower than that of said second sealing portion on said rotary shaft.

-3 Since the thickness of the lip seal of the lip seal device having the annular groove extending continuously in the circumferential direction of the rotary shaft is smaller at the annular groove than at the other portion of the lip seal, the portion having the annular groove is easier to be deformed by the pressure of a sealed fluid Therefore, the portion of the sealing surface of the lip seal at each side of the annular groove is in tighter contact with the outside circumferential surface of the rotary shaft.

Since the annular groove extends continuously in the circumferential direction of the rotary shaft, the contact portions of the lip seal on the outside circumferential surface of the rotary shaft also extend continuously in the circumferential direction of the rotary shaft As the two annular contact portions are obtained by providing the single annular groove, a double sealing effect is produced For that reason, the sealing performance of the lip seal device is better than that of a conventional lip seal device both during the rotation of the rotary shaft and during the stoppage of the rotation.

Further, since the contact force of the portion of the sealing surface of the lip seal in front of the annular groove on the rotary shaft is weaker than that of the other portion of the sealing surface of the lip seal behind the annular groove on the rotary shaft, the high sealing performance of the lip seal device can be maintained for a long period of time If the contact force of the portion of the sealing surface of the lip seal in front of the annular groove on the rotary shaft, were substantially equal to or stronger than that of the other portion of the sealing surface of the lip seal behind the annular groove on the rotary shaft, a relatively good sealing effect would be produced by the front portion of the sealing surface However, this would reduce the leaking of the sealed fluid to the rear portion of the sealing surface resulting in insufficient lubrication of the rear portion The rear portion of the sealing surface would become deteriorated an thereby destroy the sealing function thereof Therefore, only the front portion of the sealing surface would effectively seal the fluid As a result, the above-mentioned double sealing effect would not be produced.

In the present invention, the contact force of the front portion of the sealing surface of the lip seal on the rotary shaft is weaker than that of the rear portion of the sealing surface on the rotary shaft Thus, an appropriate quantity of the sealed fluid leaks along the front portion so as to be supplied to the rear portion and - thereby prevent the wear of the rear portion to maintain the sealing function of the rear portion good for a long period of time In addition, since the contact force of the rear portion of the sealing surface on the rotary shaft is stronger than that of the front portion of the sealing surface on the rotary shaft, the improved double sealing effect is maintained for a long period of time.

In the lip seal device wherein the contact force of the second lip seal on the rotary shaft is weaker than that of the first lip seal on the rotary shaft, a sufficient sealing function is provided by the second lip seal; the sliding contact resistance of the second lip seal to the rotation of the rotary shaft is lower than that in a conventional lip seal device; and the life of the second lip seal is longer than that of the conventional lip seal device.

Particular examples of lip seal devices in accordance with this invention will now be described with reference to the accompanying drawings; in which:- FIG 1 shows a sectional view of a lip seal device which is an embodiment of the present invention; FIG 2 shows an enlarged view of a major part of the lip seal device; RFIG 3 shows a sectional view of another major part of the lip seal device; FIG 4 shows a sectional view of a lip seal device which is another embodiment of the present invention; FIG 5 shows an enlarged view of a major part of the lip seal device shown in FIG 4; FIG 6 shows a sectional view of a lip seal device which is still another embodiment of the present invention; FIG 7 shows a graph indicating the results of a test in which the leaked quantity of a sealed fluid was measured as to the lip seal device shown in FIG.

4, and conventional lip seal devices; FIG 8 shows a sectional view of a lip seal device which is still another embodiment of the present invention; and FIG 9 shows a view of a major part of the lip seal device used for explaining an example of the present invention Embodiments of the present invention are hereafter described in detail with reference to the drawings attached hereto.

FIG 1 shows a sectional view of a lip seal device which is one embodiment of the subject invention The lip seal device comprises a cylindrical case 2 fitted in the hole la of a housing 1, and first lip seal 3 and second lip seal 4 whose outer circumferential portions are attached to the 7 case The inner circumferential portions of the first and second lip seals 3 and 4 are curved toward a sealed fluid, or leftward (as to FIG 1), in the axial direction of a rotary shaft 5 extending through the case 2 Accordingly, the inner circumferential portions are put in sliding contact with the outside circumferential surface of the rotary shaft by the elasticity of the lip seals and the pressure of the sealed fluid to seal the outside circumferential surface of the rotary shaft.

The first lip seal 3, which is a left-hand lip seal (as to FIG 1) located at the side of the sealed fluid, has an annular groove 3 a provided in the sliding contact surface of the first lip seal and extending continuously in the circumferential direction of the rotary shaft The sliding contact surface consists of a first sealing surface 6 a, at the left (as to FIG 1) of the annular groove, or in front of the annular groove, and a second sealing surface 6 b, at the right (as to FIG 1) of the annular groove, or behind the annular groove The cross section of the annular groove 3 a is shaped as a semicircle slightly deformed toward the sealed fluid, as shown in FIG 2 The corner of the joint 7 a of the first sealing surface 6 a and the annular groove 3 a is made nearly rectangular so that the corner is 8 - as sharp Ps possible The joint 7 b of the second sealing surface 6 b and the annular groove 3 a is shaped as a smooth curved surface.

A procedure, such as appropriately setting the width, depth and the position of the annular groove 3 a, is followed so that the contact force Pf of the first sealing surface 6 a on the rotary shaft 5 is set to be weaker than that Pr of the second sealing surface 6 b on the rotary shaft One example of setting the width, depth and the position of the annular groove 3 a, etc will be described referring to Fig 9.

Example

In the case where the lip seal 3 is lmm in thickness, a) the width (D) of the annular groove 3 a = 0 7 mm.

b) the depth of the groove = 0 35 mm.

c) the length ( 1) between the front end of the lip seal and the front end of the groove = 0 7 mm.

d) the length between the rear end of the lip seal and the real end of the lip contact surface = 1 0 mm.

e) the length between the front end of the lip seal and the rear end of the lip contact surface = 2 4 mm.

f) the length between the rear end of the lip contact surface and the rear end of the lip seal = 2 6 mm.

g) the length between the front end of the lip seal and the rear end of the lip seal = about 5 mm.

h) the length of the first sealing portion = 0 5 mm.

i) the length of the second sealing portion 1 0 mm.

j) the material of the lip seal is fluoroplastics.

9 - In this case, the ratio of the depth of the groove to the thickness t of the lip seal is 50 to 5 7, preferibly 60 to 10 %, more preferably to 20 %, and most preferably 45 to 30 % In the above example, the ratio is set to 35 %.

In the case where the thickness of the lip seal is set to be 1, the width of the groove is 0 1 to 1 6, preferably 0 2 to 1 2, more preferably 0.4 to 1 0, and most preferably 0 6 to 0 9 In the example, the width is set to be 0 7.

The curved portion extending from the rear end of the lip contact surface to the rear end of the lip seal contributes contact pressure to the second sealing portion However, when the length to the front end of the lip seal is too long, no effective contact pressure is obtainable For this reason, the length from the front end of the lip seal to the rear end of the lip contact surface is preferably set to be a value smaller than twice as long as the length from the rear end of the lip seal contact surface to the rear end of the lip seal In the example, the former is set to be 0 9 times as long as the latter Further, the length from the front end of the lip seal to the front end of the groove is different from that of the first sealing portion because the front end of the lip seal rises 0 2 mm.

The contact force P 2 of the second lip seal 4 on the rotary shaft 5 is set to be weaker than that Pf of the first sealing surface 6 a on the rotary shaft, by making the inside diameter of the second lip seal larger than that of the first lip seal 3 in a free state before the lip seals are fitted on the rotary shaft.

The cylindrical case 2 has a large-diameter portion 2 a and a smalldiameter portion 2 b The outside diameter of the large-diameter portion 2 a is set to be smaller by a prescribed quantity than the inside diameter of the housing 1 so that the case 2 can be loosely fitted with a prescribed - clearance C in the hole la of the housing The left-hand end (as to Fig 1) of the small-diameter portion 2 b is bent outwardly in the radial direction of the lip seal device so that a flange 2 c is formed An annular groove 10 is defined on the outside circumferential surface of the case 2 by the flange, the small-diameter portion 2 b and a wall 2 d located between the small- diameter portion 2 b and the large-diameter portion 2 a A sealing member 11 made of an O-ring is fitted in the annular groove 10 The annular groove could be provided in the housing.

When the case 2 is fitted with the clearance C in the hole la of the housing 1, the sealing member 11 is press-fitted in the hole to fix the case in the housing so that the sealed fluid present at the left (as to FIG 1) of the case is prevented from leaking rightwardly through the clearance C At that time, the center line of the sealing member 11 and that of the annular groove 3 a are located in a vertical plane perpendicularly intersecting the axis of the rotary shaft 5.

The right-hand end (as to FIG 1) of the large-diameter portion 2 a is bent inwardly in the radial direction of the lip seal device so that a crimped portion 2 e is formed Engaging surfaces 2 f and 2 g facing each other in the axial direction of the lip seal device are constituted by the wall 2 d and the crimped portion 2 e, respectively Between the engaging surfaces 2 f and 2 g, a plate 12, the first lip seal 3, a sealing member 14 embedded with a rigid plate 13 such as a metal washer, the second lip 11 - seal 4 and a plate 15 are interposed in that order from the wall 2 d and pinch-held together side by side in the axial direction of the lip seal device.

The plate 12 is made of a metal so that the outside diameter thereof is smaller by a prescribed quantity than the inside diameter of the large-diameter portion 2 a A projection 3 b formed on the outside circumferential portion of the first tip seal 3 and extending toward the sealed fluid is engaged on the outside circumferential surface of the plate 12 to prevent the first lip seal from com' ng off The inner circumferential portion of the plate 12 is curved toward the sealed fluid, or leftward (as to FIG 1), in the axial direction of the seal lip device so that a cylindrical portion 12 a is formed at the inner circumferential edge of the plate If the inner circumferential portion of the plate 12 were only curved in the form of the truncated cone toward the sealed surface, the edge of the type of the truncated-cone-shaped portion of the plate would likely damage the first lip seal 3 at the time of assembly, conveyance or the like of the lip seal device However, according to the subject invention since the cylindrical portion 12 a is formed at the inner circumferential edge of the plate 12, the edge is prevented from damaging the first lip seal 3.

12 - FIG 3 shows the state of the sealing member 14 not yet disposed in the lip seal device The sealing member 14 is made of an elastic material such as rubber so that an annular projection 14 a extending outwardly in the radial direction of the lip seal device is formed on a part of the outside circumferential surface of the sealing member to surely seal the boundary between the case 2 and the sealing member Both the sides of the sealing member 14 are provided with annular grooves 14 b and 14 c so that the annular grooves absorb the elastic deformation of the annular projection 14 a when the sealing member is fitted in the case 2 and pinch-held by the engaging surfaces 2 f and 2 g.

The outer circumferential portion of the first lip seal 3 is provided with an annular groove 3 c opposite the projection 3 b so that the annular groove also absorbs the elastic deformation of the annular projection 14 a of the sealing member 14 when the sealing member is fitted in the case 2 and pinch-held by the engaging surfaces 2 f and 2 g The projection 3 b and the annular groove 3 c can be simultaneously made by deforming the outer circumferential portion of the first lip seal 3 through extrusion in the axial direction thereof.

13 - The inside circumferential surface of the sealing member 14 is a curved surface 14 d along the sealed-fluid-side curved surface of the second lip seal 4 so as to prevent the inner circumferential portion of the second lip seal from being displaced leftward (as to FIG 1) more than a necessary quantity The inner circumferential edge of the second lip seal 4 contacts the first lip seal 3 to support the first lip seal.

The plate 15, located at the end of the case 2 opposite the sealed fluid, is made of a metal and shaped as a dish so that the central portion of the plate is provided with a projection 15 a extending rightwardly (as to FIG 1) and a recess 15 b having a prescribed form is provided on the central portion opposite the projection, to increase the rigidity of the plate The right-hand side of the projection 15 a and that of the crimped portion 2 e of the case 2 are located in the same plane and simultaneously put in contact with the wall surface lb of the housing 1.

The gap T between the inside circumferential surface of the plate 15 and the outside circumferential surface of the rotary shaft 5 is set to be so small as to prevent the inner circumferential portion of the second lip seal 4 from accidentally being turned back rightward (as to FIG 1).

14 - The plate 15 may be made of a flat metal sheet wherein the recess is formed by the pressure exerted on the plate by the crimping of the crimped portion 2 e In this manner, the right side (as to Fig 1) of the plate can be located in the same plane as that of the caulked portion 2 e of the case.

When the plate 12, the first lip seal 3, the sealing member 14, the second lip seal 4 and the plate 15 are pinch-held by the engaging surfaces 2 f and 2 g, the outer circumferential portion of the sealing member 14 made of the elastic material such as rubber is deformed inwardly in the radial direction of the lip seal device to expand the inner circumferential portion of the sealing member and thereby push and deform the lip seals 3 and 4 in the axial direction of the lip seal device Since the plate 12, located at the side of the sealed fluid, has the cylindrical portion 12 a near the axis of the plate, the rigidity of the plate is high so that the inner circumferential portion of the sealing member 14 is expanded in the direction opposing the sealed fluid If the plate 15 located at the end of the case 2 opposite the sealed fluid were simply shaped as a flat sheet, the central portion of the plate would be conically protruding due to the expansion of the inner circumferential portion of the sealing - member 14 through the action of the second lip seal 4.

Since the degree of the protrusion of the central portion of the plate 15 would vary fromr device to device, the conditions on the contact of the second lip seal and the rotary shaft 5 would fluctuate resulting in inconsistent contact of the rotary shaft 5 and the first lip seal 3 located in contact with the second lip seal, to deteriorate the sealing performance of the lip seal device.

According to the subject invention, the central portion of the plate 15 has the projection 15 a extending in the direction reverse to the sealed fluid and has the recess 15 b having the prescribed is form and located opposite the projection Therefore, the rigidity of the plate is increased and the elastic deformation of the sealing member 14 is restricted to a substantially constant quantity As a result, the conditions on the contact of the rotary shaft 5 and the lip seals 3 and 4 are restricted to substantially constant levels so that a constant and sure sealing effect is provided.

The right-hand side of the projection 15 a of the plate 15 and the crimped portion 2 e of the case 2 simultaneously contact the wall surface lb of the housing 1, as mentioned above Therefore, although 16 - the case 2 is fitted with the prescribed clearance C in the hole la of the housing 1, the case is fixed more stablely than that of a lip seal device in which only the right-hand side of the crimped portion of the case contacts the wall surface of the housing.

Since the sealing surface of the first lip seal 3 is provided with the annular groove 3 a, the thickness of the portion of the first lip seal at the annular groove is reduced to make the portion easier to deform by the pressure of the sealed fluid For that reason, both-the joints 7 a and 7 b of the annular groove 3 a have higher pressure contact with the outside circumferential surface of the rotary shaft Therefore, the contact portion of joints 7 a and 7 b on the outside circumferential surface of the rotary shaft are in the shape of a line and belt, respectively, extending continuously in the circumferential direction of the rotary shaft The two annular contact parts are thus obtained by providing the single annular groove 3 a, to produce a double sealing effect.

When the rotary shaft 5 is rotated, the front part of the first sealing surface 6 a tends to slightly separate outwardly from the outside circumferential surface of the rotary shaft 5 because the contact force Pf of the first sealing surface on 17 - the rotary shaft is set to be relatively weak If the joint 7 a were shaped as a smooth curved surface, the line of contact between the contact portion of joint 7 a and the rotary shaft extending circumferentially therearound is more likely to fluctuate in the axial direction of the rotary shaft.

Thus, the line of contact would tend to resemble a "warped" circle, rather than a "pure" circle.

Therefore, the contact portion would be more likely to become discontinuous in the circumferential direction of the rotary shaft resulting in excess leakage.

However, according to the subject invention, since the corner of the joint 7 a is as sharp as possible and in contact with the outside circumferential surface of the rotary shaft 5, the positions of the circumferential contact portion of the joint 7 a is less likely to fluctuate along the axial length of the shaft Therefore, the contact portion of the joint 7 a maintains a continuous line of contact along the circumference of the rotary shaft 5 to suppress the leakage of the sealed fluid.

In other words, the quantity of the sealed fluid which leaks into the annular groove 3 a along the first sealing surface 6 a can be appropriately regulated in terms of the magnitude of the contact 18 force Pf of the first sealing surface 6 a and the sharpness of the corner of the joint 7 a.

If the corner of the joint 7 b located behind the other joint 7 a were sharp, it would be desirable from a viewpoint of the prevention of leakage of the sealed fluid However, the effect of lubrication by the sealed fluid would be reduced thereby resulting in premature deterioration of the second sealing surface 6 b For that reason, the joint 7 b is shaped as a smooth curved surface to introduce the sealed fluid as a lubricant to the second sealing surface 6 b to lubricate it well.

Since the contact force Pf of the first sealing surface 6 a on the rotary shaft 5 is weaker than that Pr of the second sealing surface 6 b on the rotary shaft, an appropriate quantity of the sealing fluid is allowed to leak along the first sealing surface so as to supply the second sealing surface with lubricating fluid As a result, the wear of the second sealing surface 6 b is prevented to thereby maintain an affective sealing action for a long period of time Since the contact force Pr of the second sealing surface 6 b on the rotary shaft 5 is relatively strong, the sealing action of the second sealing surface is sufficient for a long period of time As: a result, the above-mentioned high double 19 - sealing effect is maintained for a long period of time As very little sealed fluid is supplied as lubricant to the second lip seal 4, the contact force P 2 of the second lip seal on the rotary shaft 5 is the weakest so as to prevent the second lip seal from being worn.

Although the cross section of the annular groove 3 a is shaped as the semicircle slightly deformed toward the sealed fluid, in the above-described embodiment, the present invention is not confined thereto but may be otherwise embodied so that the cross section of the annular groove is shaped as a simple semicircle, a semicircle slightly deformed in the direction reverse to the sealed fluid, or the like.

The center line of the sealing member 11 and that of the annular groove 3 a of the first lip seal are located in the vertical plane perpendicularly intersecting the axis of the rotary shaft 5.

Therefore, the case 2 is prevented form being swung during the rotation of the rotary shaft 5 When the rotary shaft 5 is being rotated, the large-diameter portion 2 a of the case 2 supporting the lip seals 3 and 4 at the outer circumferential portions thereof is displaced in the radial direction of the lip seal device due to the whirl, deflection or the like of - the rotary shaft If the annular groove 10 and the sealing member 11 were located at the right-hand side (as to FIG 1) of the large-diameter portion 2 a of the case 2, the case would be swung and tilted about the sealing member due to the whirl, deflection or the like of the rotary shaft 5 at the time of the rotation thereof Therefore, the lip seals 3 and 4 would become misaligned thereby displacing the positions of the contact portions of the sealing surfaces 6 a and 6 b in the axial direction of the rotary shaft As a result, the contact portions of the sealing surfaces 6 a and 6 b would become likely to extend discontinuous in the circumferential direction of the rotary shaft 5 to deteriorate the sealing performance of the lip seal device.

However, according to the subject invention, since the center line of the sealing member 11 and that of the annular groove 3 a of the first lip seal 3 are located in the vertical plane perpendicularly intersecting the axis of the rotary shaft 5, the swing and tilt of the case 2 are prevented even if the case is displaced in the radial direction of the rotary shaft due to the whirl, deflection or the like thereof The misalignment of the lip seals 3 and 4 is thus prevented to thereby maintain the contact portions of the sealing surfaces 6 a and 6 b 21 - continuous in the circumferential direction of the rotary shaft 5, to prevent the deterioration of the sealing performance of the lip seal device.

However, the center line of the sealing member 11 and that of the annular groove 3 a of the first lip seal 3 do not need to be exactly located in the vertical plane perpendicularly intersecting the axis of the rotary shaft S What is necessary in that respect is that the contact surfaces of the sealing member 11 and the housing 1 or those of the sealing member 11 and the-case 2, and the contact surfaces of the rotary shaft 5 and the sealing surfaces 6 a and 6 b of the first lip seal 3, having the strong contact force on the rotary shaft, are partially overlapped with each other in the axial direction of the rotary shaft.

FIG 4 shows a lip seal device which is another embodiment and has only one lip seal 6 The contact force Pf of a first sealing surface l Oa in front of the annular groove 9 of the lip seal 6, on the rotary shaft 5, is set to be weaker than that Pr of a second sealing surface l Ob behind the annular groove, on the rotary shaft A rotary shaft 2 is rotatably supported and extends through the stepped hole la of a housing 1 The lip seal device 3 seals the gap between the inside circumferential surface of the 22 - housing 1 and the outside circumferential surface of the rotary shaft 2 The lip seal device 3 comprises four members including a case 4 made of a metal, a sealing member 5 made of rubber or synthetic resin, the lip seal 6 made of rubber or synthetic resin, and a spacer 7 made of a metal.

The case 4 is annular shaped so that it surrounds the rotary shaft 2 The cross section of the case 4 comprises an inner axial portion 4 a located in an inner position and extending in the axial direction of the case, a first radial portion 4 b extending outwardly from the right-hand end (as to FIG 4) of the inner axial portion in the radial direction of the case, an outer axial portion 4 c extending from the radial outer end of the first radial portion in parallel with the inner axial outside it, and a second radial portion 4 d extending inwardly from the left-hand end (as to FIG.

4) of the outer axial portion in the radial direction. The cross section of the case is shaped nearly as a rectangular ring cut

at the radially inner left-hand corner thereof.

Before the lip seal 6 and the spacer 7 are assembled in the lip seal device 3, the outer axial portion 4 c and second radial portion 4 d of the case extend in the same axial direction as each other.

After the lip seal 6 and the spacer 7 are assembled 23 - in the lip seal device 3, the second radial portion 4 d of the case 4 is bent inwardly the radial direction thereof so that the case is shaped nearly as the rectangular ring cut at the radially inner left-hand corner thereof.

The sealing member 5 is integrally attached to the case 4 by vulcanization or adhesion, and covers the outside circumferential surface of the outer axial portion 4 c, the side surface of the first radial portion 4 b and the inside circumferential surface of the inner axial portion 4 a continuously.

The sealing member 5 fills a case opening 8 surrounded by the inner axial portion 4 a, the first radial portion 4 b and the outer axial portion 4 c, and continuously covers the inside circumferential surface of the outer axial portion 4 c and the inside surface of the second axial portion 4 d The left-hand end of the portion of the sealing member 5, which fills the case opening 8, constitutes a support surface 5 a The outer circumferential portion of the lip seal 6 is pinch-held at both the sides thereof by the support surface 5 a and the spacer 7 in such a manner that the outer circumferential portion is oriented in the radial direction of the lip seal device 3 The spacer 7 is supported at the left-hand side thereof by the second radial portion 4 d bent 24 - inwardly in the radial direction of the lip seal device 3.

A part of the support surface 5 a supporting the lip seal 6 is provided with a projection 5 b extending toward the lip seal 6 outside the inner axial portion 4 a of the case 4 with regard to the radial direction of the lip seal device 3 and continuing in the circumferential direction of the device The support surface is also provided with an annular groove Sc adjacent to the projection and located outside thereto with regard to the radial direction of the device When the outer circumferential portion of the lip seal 6 is pinch-held by the support surface a and the spacer 7, the projection 5 b of the sealing member 5 is smoothly and elastically deformed more than the other portion of the support surface 5 a while being displaced into the annular groove Sc.

For that reason, even if the elasticity of the sealing member 5 decreases due to the aging thereof, the contact of the projection 5 b and the lip seal 6 is kept sufficient to prevent the sealed fluid from leaking between the spacer 7 and the left-hand side of the lip seal 6 and between the right-hand side of the lip seal and the support surface 5 a of the sealing member for a long period of time.

- The lip seal 6 is pinch-held by the spacer 7 and the left-hand side of the inner axial portion 4 a of the case 4 inside the projection 5 b of the sealing member 5 with regard to the radial direction of the lip seal device 3 Therefore, the pinch-holding is maintained in prescribed state even if the sealing member ages For that reason, the pinch-holding force on the lip seal 6 is prevented from decreasing due to the aging of the sealing member S so that the lip seal does not rotate with the rotation of the rotary shaft 2.

Since the lip seal 6 is pinch-held by the spacer 7 and the left-hand end of the inner axial portion 4 a of the case 4, the firmly pinch-held position of the lip seal can be located nearest the rotary shaft 2 or, to be specific, at the innermost edge of the spacer For that reason, the curved portion of the lip seal 6 is prevented from becoming deformed and from displacing the sealing surface of the lip seal on the rotary shaft 2 in the axial direction thereof.

In addition, the sealing surface will not experience premature wear resulting in a shortened life of the lip seal as contrasted to lip seal device wherein a lip seal is pinch-held outside the middle portion of a spacer with regard to the radial direction of the lip seal device.

26 - Since the thickness of the sealing member 5 at the left-hand end (as to FIG 4) of the inner axial portion 4 a of the case 4 is as small as O 1 to 0 5 mm, the pinch-holding force on the lip seal 6 does not substantially decrease even if the sealing member ages Besides, the small-thickness portion of the sealing member S prevents the lip seal 6 from being damaged by the left-hand end of the inner axial portion 4 a made of a metal The portion of the sealing member 5, which covers the outside circumferential surface of the outer axial portion 4 c of the case 4, is provided with a plurality of annular projections 5 d located at prescribed intervals and each extending continuously in the circumferential direction of the lip seal device 3.

The annular projections 5 d are press-fitted on the inside circumferential surface of the housing to keep the sealing member 5 and the housing liquid-tight to each other.

The inner circumferential portion of the lip seal 6 is curved toward the sealed fluid or leftward (as to FIG 4), and the right-hand side of the bent inner circumferential portion is put in elastic contact with the outside circumferential surface of the rotary shaft 2 by the elasticity of the lip seal 6 so that the sealed fluid present on the left-hand 27 - side of the lip seal is prevented from leaking to the atmosphere present on the right-hand side of the lip seal The sealing surface of the lip seal 6 on the rotary shaft 2 is provided with an annular groove 9 extending continuously in the circumferential direction of the rotary shaft Therefore, the sealing surface consists of a first sealing surface a, between the annular groove and the sealed fluid, and a second sealing surface l Ob, between the annular groove and the atmosphere The first sealing surface i O a is made smoother than the second sealing surface l Ob.

The cross section of the annular groove is shaped as a semicircle slightly deformed toward the sealed surface, as shown in FIG 5 The corner of the joint 9 a of the annular groove 9 and the first sealing surface i O a is made nearly rectangular so that the corner is as sharp as possible The joint 9 b of the annular groove 9 and the second sealing surface l Ob is shaped as a smooth curved surface.

Since the sealing surface of the lip seal 6 is provided with the annular groove 9, the thickness of the portion of the lip seal at the annular groove is reduced to make the portion easier to deform by the pressure of the sealed fluid As a result, the joints 9 a and 9 b of the annular groove 9 have higher 28 - pressure contact with the outside circumferential surface of the rotary shaft 2 Therefore, the contact portion of joints 9 a and 9 b on the outside circumferential surface of the rotary shaft are in the shape of a line and belt, respectively, extending continuously in the circumferential direction of the rotary shaft The two annular contact portions are thus obtained by providing the single annular groove, to produce a double sealing effect.

When the rotary shaft 2 is rotated, the first sealing surface i O a tends to slightly separate outwardly from the outside circumferential surface of the rotary shaft If the joint 9 a were shaped as a smooth curved surface, the line of contact between the contact portion of joint 9 a and the rotary shaft extending circumferentially therearound would likely fluctuate in the axial direction of the rotary shaft.

Thus, the line of contact would tend to resemble a "warped" circle, rather than a "pure" circle For that reason, the contact portion would be likely to become discontinuous in the circumferential direction of the rotary shaft resulting in excess leakage.

However, according to the subject invention joint 9 a is as sharp as possible and in contact with the outside circumferential surface of the rotary shaft 2 Therefore, the position of the 29 - circumferential contact portion is less likely to fluctuate along the axial length of the shaft Thus, the contact portion of the joint 9 a maintains a continuous line of contact along the circumference of the rotary shaft 2 to suppress the leaking of the sealed fluid.

The joint 9 b is located outside the other joint 9 a with regard to the axial direction of the rotary shaft 2, and the continuous circumferential contact portion of the joint 9 b can be maintained better than that of the other joint 9 a If the corner of the joint 9 b were sharp, it would be desirable from a viewpoint of preventing leakage However, the sealed fluid could not be expected to perform lubrication.

For that reason, the life of the joint 9 b would be shortened According to the subject invention, since the joint 9 b is shaped as a smooth curved surface, the sealed fluid is introduced as a lubricant to the second sealing surface l Ob to lubricate it well.

Since the first sealing surface l Oa is made smoother than the second sealing surface l Ob, the first sealing surface conforms with the outside circumferential surface of the rotary shaft 2 better than the second sealing surface before the rotary shaft is initially rotated after the installation of the lip seal device 3 in the housing 1 Therefore, - the first sealing surface of higher smoothness performs a sure sealing action.

When the rotary shaft 2 is rotated for the first time after the installation of the lip seal device 3 in the housing 1, the less smooth second sealing surface l Ob quickly conforms to the outside circumferential surface of the rotary shaft due to the initial wear of the second sealing surface thereon Subsequently, the second sealing surface l Ob is in greater conformity with the outside circumferential surface of the rotary shaft than the first sealing surface i O a when the formation of the rotary shaft is stopped The first sealing surface l Oa of higher smoothness undergoes little initial wear due to the rotation of the rotary shaft 2 and therefore persistently tends to maintain the initial state thereof and does not readily conform to the outside circumferential surface of the rotary shaft.

Therefore, the second sealing surface l Ob seals more effectively than the first sealing surface after the rotary shaft has been rotating for a period of time In contrast, the first sealing surface l Oa provides good sealing action during the initial stage when the second sealing surface is relatively rough.

FIG 6 shows a lip seal device 13 which is still another embodiment and has a first lip seal 16 A and a 31 - second lip seal 16 B The inner circumferential portions of the first and the second lip seals 16 A and 16 B are curved toward a sealed fluid and in sliding contact with the outside circumferential surface of a rotary shaft 12 The first lip seal 16 A located at the side of the sealed fluid is provided with an annular groove 19 of substantially the same constitution as the preceding embodiments A first sealing surface 20 a is provided at the left-hand side (as to FIG 6) of the annular groove 19, and a second sealing surface 20 b is provided at the right-hand side of the annular groove.

A cylindrical case 14 surrounding the first and the second lip seals 16 A and 16 B at the outer circumferential portions thereof has a large-diameter portion 14 a, a small-diameter portion 14 b and a wall 14 c located therebetween The left-hand end (as to FIG 6) of the case 14 is bent outwardly in the radial direction of the lip seal device 13 so that an annular groove 25 is defined on the outside circumferential surface of the case A sealing member 26 is fitted in the annular groove 25 to seal the boundary between the case 14 and a housing 11.

The right-hand end (as to FIG 6) of the large-diameter portion 14 a is bent inwardly in the radial direction of the lip seal device 13 so that a 32 - crimped portion 14 d is formed Between the wall 14 c and the crimped portion 14 d, a plate 27, the first lip seal 16 A, a sealing member 29 embedded with a rigid plate 28 such as a metal washer, the second lip seal 16 B and a plate 30 are pinch-held together in that order from the wall.

The plate 27 is made of a metal so that the outside diameter thereof is smaller by a prescribed quantity than the inside diameter of the large-diameter portion 14 a of the case 14 A projection 16 Aa provided on the outer circumferential portion of the first lip seal 16 A and extending toward the sealed fluid is engaged on the outside circumferential surface of the plate 27 to prevent the first lip seal from coming off The outer circumferential portion of the first lip seal 16 A is provided with an annular notch 16 Ab opposite the projection 16 Aa so that the annular notch absorbs the elastic deformation of the rubber-made sealing member 29 when the sealing member is fitted in the case 14.

The inside circumferential surface of the sealing member 29 is a curved surface 29 a extending along the sealed-fluid-side curved surface of the second lip seal 16 B so as to prevent the inner circumferential portion of the second lip seal from being displaced leftward (as to FIG 6) in the axial direction of the lip seal device 13 more than a necessary quantity This keeps the inner circumferential portion of the second lip seal from being overlapped with the first lip seal 16 A more than a necessary quantity.

The plate 30 located at the right-hand end (as to FIG 6) of the case 14 is made of metal and shaped as a simple washer The gap t' between the inside circumferential surface of the plate and the outside circumferential surface of the rotary shaft 12 is set to be small as to prevent the inner circumferential portion of the second lip seal 16 B from accidentally being bent back rightwardly (as to FIG 6).

It will be easily understood that the annular groove 19 of the first lip seal 16 A produces the same effect as those in the preceding embodiments.

The effect of the present invention is now described with reference to FIG 7 showing the results of a test on the lip seal device 3 shown in FIG 4, and conventional lip seal devices A and B for comparison The conventional lip seal device A was the same as the lip seal device 3 of FIG 4 except that the sealing surface of a lip seal 6 had no annular groove The other conventional lip seal device B was the same as the lip seal device 3 of FIG 4 except that the sealing surface of the lip seal 6 had no annular groove but had a spiral groove extending in such a direction that a sealed fluid having leaked to the sealing surface was returned by the rotation of a rotary shaft 2 In the test, each of the lip seal devices 3, A and B was installed in a compressor of the swash plate type, and the leaked quantity of the sealed fluid was measured After the rotary shaft of the compressor had been continuously rotated at the rate of 4,500 rpm for 24 hours with the inlet pressure and outlet pressure of the compressor set at 1 5 to 2 5 kg/cm 2 and 13 to 18 kg/cm 2, respectively, the rotary shaft was continuously stopped for 24 hours The cycle of such rotation and stoppage was repeated four times, at each of which the total leaked quantity of the sealed fluid during the rotation and stoppage were measured.

As shown in FIG 7, the leaked quantity of the sealed fluid as to the lip seal device 3 of FIG 4 was smaller than that of the sealed fluid as to the conventional lip seal devices A and B, both during the rotation and during the stoppage Therefore, the lip seal device 3 had better sealing performance than the conventional lip seal devices A and B. Further, the sealing performance of the lip seal devices which were the above-described embodiments of the present invention was measured in the same test - where the thickness of each of the lip seals 6 and 16 A of the devices was set at 1 mm and the distance between the inner edge of each lip seal and each of the annular grooves 9 and 19 was changed in a range from 0 3 mm to 1 1 mm The sealing performance tended to improve as the distance was increased The same measurement was performed with regard to the width D of each of the annular grooves 9 and 19 as the width was changed in a range from 0 2 mm to 1 2 mm The sealing performance tended to improve as the width D was increased.

FIG 8 shows a lip seal device which is still another embodiment A first lip seal 3 and a second lip seal 4 are made of the same material such as a material obtained by adding 15 % of graphite by weight to polytetrafluoroethylene, and the inside diameter D 2 of the second lip seal is made larger than that D 1 of the first lip seal in a free state before the lip seals are put in actual use, so that the contact force of the second lip seal on a rotary shaft 5 is weaker than that of the first lip seal on the rotary shaft A sealed fluid is sealed by the first lip seal 3 and a sealing member 16 Since the inner circumferential portion of the first lip seal 3 is in contact with a rotary shaft 5 by the sufficient contact force, the sealed fluid is prevented from 36 - leaking along the boundary between the first lip seal and the rotary shaft A very small quantity of the sealed fluid having leaked between the first lip seal 3 and the sealing member 16 is sealed by the second lip seal 4 Although the second lip seal 4 is in contact with the rotary shaft 5 by the weaker contact force than the first lip seal 3, the second lip seal prevents the very small quantity of the sealed fluid from leaking along the second lip seal, because the pressure of the sealed fluid having leaked along the first lip seal is low.

Since the contact force of the second lip seal 4 on the rotary shaft, 5 is set to be weaker than that of the first lip seal 3 on the rotary shaft as mentioned above, the sliding contact resistance of the second lip seal to the rotation of the rotary shaft is lower than that in a conventional device although the sealing performance of the second lip seal is sufficient Further, the life of the second lip seal 4 is increased because of the weaker contact force thereof on the rotary shaft 5.

In this embodiment, the inside diameter D 2 of the second lip seal 4 is made larger than D 1 of the first lip seal 3 in the free state before being put in actual use, so that the contact force of the second lip seal on the rotary shaft 5 is weaker than 37 - that of the first lip seal on the rotary shaft.

However, the present invention is not confined thereto but may be otherwise embodied so as to make the second lip seal of a more flexible material than the first lip seal to render the contact force of the second lip seal on the rotary shaft 5 weaker than that of the first lip seal on the rotary shaft For example, the first lip seal 3 may be made of a material obtained by adding 15 % of graphite by weight to polytetrafluoroethylene, and the second lip seal 4 may be made of a material obtained by adding 5 to % of graphite by weight to polytetrafluoroethylene, to render the second lip seal more flexible than the first lip seal.

38 -

Claims (11)

1 A lip seal device for sealing the gap between a housing and a rotary shaft, comprising:

a case surrounding said rotary shaft; a lip seal attached inside said case; support means for holding said lip seal on at least the outer circumferential portion thereof; and seal means located on the outside circumferential surface of said case; the inner circumferential portion of said lip seal being curved toward a sealed fluid, wherein said lip seal comprises a sealing surface in sliding contact with the outside circumferential surface of said rotary shaft, said sealing surface having an annular groove extending continuously in the circumferential direction of said rotary shaft so that said sealing surface has a first sealing portion in front of said annular groove and a second sealing portion in the rear of said annular groove; the contact pressure of said first sealing portion on said rotary shaft being lower than that of said second sealing portion on said rotary shaft.

2 A lip seal device according to claim 1, wherein the roughness of said first sealing portion of 39 - said sealing surface is lower than that of said second sealing portion thereof.

3 A lip seal device according to claim 1 or 2, wherein the length of said sealing surface in the axial direction thereof is smaller for said first sealing portion than said second sealing portion.

4 A lip seal device according to any preceding claim, wherein the cross section of said annular groove is shaped nearly as a semicircle.

5 A lip seal device according to claims 1 to 3, wherein the part of the cross-sectional outline of said annular groove which rises from said first sealing portion of said sealing surface forms a sharp edge with the surface of said shaft, and the other part of said cross-sectional outline which rises from said second sealing portion of said sealing surface forms a smooth interface with the surface of said shaft.

6 A lip seal device according to any preceding claim, wherein the peak of said contact pressure of said second sealing portion on said rotary shaft is near said annular groove.

7 A lip seal device according to any preceding claim, further comprising a second lip seal, said second lip seal being located further from said sealed fluid than said first lip seal; the inner circumferential portion of said second lip seal being curved toward - said sealed fluid and having a sealing surface in sliding contact with the outside circumferential surface of said rotary shaft, wherein said sealing surface of said second lip seal constitutes a third sealing portion.

8 A lip seal device according to claim 7, wherein the contact pressure of said first sealing portion on said rotary shaft is set to be lower than that of said second sealing portion on said rotary shaft, and wherein the contact pressure of said third sealing portion on-said rotary shaft is set to be lower than that of said first sealing portion on said rotary shaft.

9 A lip seal device according to claim 7, 8 or 9, wherein the length of said first sealing portion is smaller than the length of said third sealing portion, and the length of said third sealing portion is smaller than the length of said second sealing portion in the axial direction of said sealing surface.

10 A lip seal device according to claim 7 or 8, wherein said second lip is located so that a curved portion of the inner circumferential surface of said first lip at the side opposite to the side of said sealed fluid is in contact with the inner circumferential edge of said second lip to prevent 41 - said first sealing portion from moving in the axial direction thereof.

11 A lip sealing device constructed substantially as described with reference to the accompanying drawings.

Published 1989 at The Patent Office, State House, 66,71 High Holborn, London WC 11 4 TP Further copies maybe obtainedfrom The Patent Office.

Sales Branch, St Mary Cray, Orpington Kent BR 5 3RD Printed by Multiplex techniqcues ltd, St Mary Cray, Kent, Con 1/87