JP7576016B2 - Wet Friction Materials - Google Patents

Description

The present invention relates to a wet friction material. More specifically, the present invention relates to a wet friction material that is used in the presence of a lubricating oil and that can be incorporated into wet clutches, wet brakes, and the like.

2. Description of the Related Art Conventionally, wet clutches and wet brakes using wet friction materials have been used for torque transmission, braking, etc. For example, in automatic transmissions of automobiles and the like, wet friction materials are used in wet hydraulic clutches.
A wet clutch has multiple wet friction materials and multiple separator plates arranged alternately with a small clearance between them, and is structured to transmit or not transmit torque by pressing the two together when in operation or when idling. In addition, lubricating oil is supplied into the clutch to reduce friction of the wet friction materials during this pressing and separating process and to absorb frictional heat caused by friction.
When the clutch is idling, the wet friction material and the separator plate rotate relative to each other while being separated from each other. However, due to the viscosity of the lubricating oil, the wet friction material and the separator plate may rotate together, and it is known that a torque called drag torque is generated at that time. This drag torque consumes unnecessary energy when the clutch is idling, so it is desired to reduce it as a measure for reducing fuel consumption, which has been rapidly progressing in recent years. The following Patent Documents 1 and 2 are known as techniques for reducing this drag torque.

JP 2005-282648 A JP 2001-295859 A

Patent Document 1 discloses a wet friction material in which, for oil grooves formed by the gaps between segment pieces, oil grooves whose inner peripheral opening or middle portion expand in a symmetrical shape and oil grooves whose width from the inner peripheral opening to the outer peripheral opening are mixed in a predetermined ratio. It is disclosed that the adoption of this wet friction material can provide a sufficient drag torque reduction effect even in areas where there is a large amount of lubricating oil or where the lubricating oil is difficult to remove.
Patent Document 2 discloses a wet friction material in which at least one of the opposing end faces of two adjacent segment pieces has a notch cut into the inside at an inner peripheral end and/or middle part of the opposing end face, and an oil groove defined by the two opposing end faces has a wide portion with a wide groove width at an inner peripheral opening and/or middle part by the notch. It is disclosed that the use of this wet friction material can provide a wet friction material having a segment piece shape that is excellent in cooling performance and can reduce drag torque.
As disclosed in the above-mentioned Patent Documents 1 and 2, there are various approaches to reducing drag torque, and drag torque reduction is attempted by selecting an optimal form in response to a wide variety of product requirements. For this reason, as a measure to reduce fuel consumption, which has been strongly demanded in recent years, more forms of drag torque reduction are required to meet a wide variety of product requirements.

The present invention was made in consideration of the above problems, and aims to provide a wet friction material that achieves a reduction in drag torque in a form different from conventional methods.

The present invention is as follows.
The invention described in claim 1 is a wet friction material including a core plate having a flat ring shape and a friction portion arranged in a ring shape on a main surface of the core plate,
The friction portion includes a plurality of segment pieces and a plurality of oil grooves formed between the segment pieces,
The segment piece is provided with a first piece having a shape in which the upper left and upper right corners of a substantially rectangular piece are cut off into a substantially triangular shape, and the lower left and lower right corners are cut off into a substantially rectangular shape.
The invention described in claim 2 is characterized in that, in the invention described in claim 1, the segment piece further includes a second piece having a shape in which the upper left and upper right corners of a roughly rectangular piece are cut off into roughly triangular shapes, and the lower left and lower right corners are cut off into roughly triangular shapes.
The invention described in claim 3 is characterized in that, in the invention described in claim 2, the first pieces and the second pieces, the same number as or a different number than the first pieces, are arranged alternately in the circumferential direction of the core plate in the friction portion.
The invention described in claim 4 is characterized in that in the invention described in claim 3, the first pieces and the second pieces are arranged alternately one by one in the circumferential direction of the core plate.
The invention described in claim 5 is the invention described in claim 3, wherein a plurality of the first pieces successively arranged in a circumferential direction of the core plate form a first piece group,
The second pieces are arranged in a circumferential direction of the core plate to form a second piece group,
The first piece group and the second piece group are alternately arranged in the circumferential direction of the core plate.
The invention described in claim 6 is summarized as being related to any one of the inventions described in claims 1 to 5, in that the number of the first pieces is 10% or more and 90% or less of the total number of the segment pieces.
According to a seventh aspect of the present invention, in the wet friction material according to any one of the first to sixth aspects, when the wet friction material is rotated in a circumferential direction around the center of the ring shape of the core plate as a rotation center in the presence of a lubricating oil,
The first piece has a shape in which a dam portion that causes lubricating oil to run up onto the surface of the friction portion is formed at a portion where the lower left and right corners are cut out in an approximately rectangular shape.
The invention described in claim 8 is the invention described in claim 7, wherein, when the maximum left-right length of the first piece is W _P1 and the left-right length of the portion cut out into an approximately rectangular shape is W _D1 , then 0.08≦W _D1 /W _P1 ≦0.34.
The invention described in claim 9 is the invention described in claim 7 or 8, wherein, when the maximum length of the first piece in the up-down direction is _HP1 and the length of the portion cut out in an approximately rectangular shape is _HD1 , 0.07≦H _D1 /H _P1 ≦0.4.

The wet friction material of the present invention has a different structure than conventional materials, which makes it possible to reduce drag torque.

1A and 1B are an overall plan view and a partially enlarged perspective view showing a wet friction material according to an embodiment; FIG. 2 is a plan view showing a first piece of the embodiment. 13A to 13D are plan views showing a first piece according to another embodiment. FIG. 4 is a plan view showing a second piece of the embodiment. 13A to 13D are plan views showing a second piece according to another embodiment. FIG. 2 is a partially enlarged plan view showing the wet friction material of the embodiment (Example 1). FIG. 11 is a partially enlarged plan view showing a combination of segment pieces in another embodiment (Example 2). FIG. 11 is a partially enlarged plan view showing a segment piece in a different combination. FIG. 11 is a partially enlarged plan view showing a segment piece in a different combination. FIG. 11 is a partially enlarged plan view showing a segment piece in a different combination. FIG. 13 is a partially enlarged plan view showing a combination of segment pieces of a comparative product (Comparative Example 1). 1 is a graph showing the correlation between drag torque and rotation speed obtained by using the wet friction materials of Examples 1 and 2 and Comparative Example 1.

The present invention will now be described with reference to the drawings.
The matters shown here are illustrative and are for illustrative purposes of the embodiments of the present invention, and are described for the purpose of providing what is believed to be the most effective and easy-to-understand explanation of the principles and conceptual features of the present invention. In this respect, it is not intended to show structural details of the present invention beyond a certain extent that are necessary for a fundamental understanding of the present invention, and the description in conjunction with the drawings will make it clear to those skilled in the art how some forms of the present invention are actually embodied.

In addition, when describing the planar shape of each part in this specification, the description will be given assuming that it is placed at the 12 o'clock position on the watch face. That is, for example, when describing a segment piece, the description will be given assuming that the segment piece is placed at the 12 o'clock position on the watch face.
Thus, for a given segment piece, "right" means the direction from the 9 o'clock position to the 3 o'clock position on the clock face, "left" means the direction from the 3 o'clock position to the 9 o'clock position on the clock face, and "up" means the direction from the 6 o'clock position to the 12 o'clock position on the clock face, and "down" means the direction from the 12 o'clock position to the 6 o'clock position on the clock face.

The wet friction material 10 of the present invention includes a core plate 11 having a flat ring shape, and a friction portion 12 arranged in a ring shape on a main surface 111 of the core plate 11 .
The friction portion 12 includes a plurality of segment pieces 13 and a plurality of oil grooves 14 formed between the segment pieces.
The wet friction material 10 of the present invention is characterized in that the segment piece 13 includes a first piece 131 having a shape in which the upper left and upper right corners of a substantially rectangular piece are cut off in a substantially triangular shape and the lower left and lower right corners are cut off in a substantially rectangular shape (see FIGS. 1 and 6 to 10).

The wet friction material 10 of the present invention may further include, as the segment piece 13, a second piece 132 having a shape in which the upper left and upper right corners of a substantially rectangular piece are cut out into a substantially triangular shape and the lower left and lower right corners are cut out into a substantially triangular shape (see FIGS. 1, 6, and 8 to 10).
Furthermore, the wet friction material 10 of the present invention may be configured such that, in the friction portion 12, first pieces 131 and second pieces 132, the number of which is the same as or different from the number of the first pieces 131, are alternately disposed in the circumferential direction of the core plate 11 (see FIGS. 1, 6, and 8 to 10).

[1] Core Plate The core plate 11 has a flat ring shape as shown in Fig. 1. That is, the plate has an annular shape with a hole in the center.
The center of the ring shape of the core plate 11 is the center of rotation P. The core plate 11 has a main surface 111 to which the segment pieces 13 are joined and on which the friction portion 12 is formed.
The main surface 111 may be provided on only one surface of the core plate 11 or on both surfaces of the core plate 11. In other words, the friction portion 12 may be formed on only one surface of the core plate 11 or on both surfaces of the core plate 11.

The core plate 11 may have other necessary configurations in addition to the main surface 111. Examples of the other configurations include engagement teeth. The engagement teeth may be provided by protruding from the inner peripheral surface or the outer peripheral surface of the core plate 11.
1, the wet friction material 10 may have engagement teeth 113 protruding from an outer circumferential surface 112. The engagement teeth 113 are arranged so as to be able to mesh with a spline that is arranged so as to surround the wet friction material 10 from the outside.

The size of the core plate 11 is not limited, and the correlation between the outer diameter and the inner diameter is not limited, but for example, if the outer diameter is _R1 (if the engagement teeth 113 are present, the outer periphery diameter based on the outer periphery surface 112 excluding the engagement teeth 113) and the inner diameter is _R2 (inner periphery diameter), the ratio _R1 / _R2 can be 1≦ _R1 / _R2 ≦10, 1.05≦ _R1 / _R2 ≦5, or 1.1≦ _R1 / _R2 ≦3.
If the thickness of the core plate 11 is D (mm), the thickness D is not limited, but can be, for example, 0.1≦D(mm)≦10 mm, 0.3≦D(mm)≦7, or 0.5≦D(mm)≦5.
The core plate 11 may be formed from any material, but examples of materials that can be used include various carbon steels (S35C, S55C, etc.), cold-rolled steel plates (SPCC, SPCCT, etc.), and low-carbon high-tensile steels (NCH780, etc.).

[2] Friction portion As shown in Fig. 1, the friction portion 12 includes a segment piece 13 and an oil groove 14. Specifically, the friction portion 12 is formed by arranging a plurality of segment pieces 13 in a ring shape with the oil groove 14 interposed therebetween.
The friction portion 12 has a function of adjusting the degree of interlocking between the wet friction material 10 and an adjacent counter member (such as a separator plate) depending on the degree of contact between the wet friction material 10 and the counter member.
That is, the wet friction material 10 has a braking function (braking function) and a torque transmission function with respect to the mating material.
The friction portion 12 may have the same shape on the front main surface 111 and the back main surface 111 of the core plate 11, or may have different shapes.

(1) Segment Piece The segment piece 13 constitutes the friction portion 12, and its surface serves as a friction surface.
The segment pieces 13 define oil grooves 14 between adjacent segment pieces 13. That is, the shape of the oil grooves 14 is determined by the outer shape of the segment pieces 13 and the arrangement of the segment pieces 13.
The number of segment pieces 13 arranged on one main surface 111 of the core plate 11 is not limited, but may be, for example, 10 to 100. This number is preferably 15 to 90, more preferably 20 to 80, and particularly preferably 25 to 60.

The configuration of the segment piece 13 is not limited, and for example, a paper body containing base fiber and filler material solidified with a curable resin can be used.
As the base fiber, various synthetic fibers, regenerated fibers, inorganic fibers, natural fibers, etc. can be used. Specifically, cellulose fibers (pulp), acrylic fibers, aramid fibers, etc. are preferred.
Further, as the filler, cashew dust as a friction modifier, graphite and/or molybdenum disulfide as a solid lubricant, diatomaceous earth as an extender pigment, etc. can be used. These may be used alone or in combination of two or more. Furthermore, as the thermosetting resin, phenol resin and/or its modified resin can be used.
In addition, the segment piece 13 is usually joined and fixed to the main surface 111 of the core plate 11, but the method of joining the segment piece 13 to the core plate 11 is not limited, and methods such as thermal fusion, adhesion (gluing) via an adhesive, etc. can be used.

The wet friction material 10 includes a first piece 131 as the segment piece 13 .
As shown in FIG. 1 , the wet friction material 10 may further include a second piece 132 as the segment piece 13 .
The first piece 131 and the second piece 132 will be described below.

(1-1) First Piece The first piece 131 is a segment piece having a shape obtained by cutting the upper left and upper right corners of an approximately rectangular piece into an approximately triangular shape and cutting the lower left and lower right corners into an approximately rectangular shape, as shown in FIG. 2 .
That is, the first piece 131 is a segment piece having a first upper cut-out portion 131A where the upper left and upper right corners are cut out in an approximately triangular shape, and a first lower cut-out portion 131B where the lower left and lower right corners are cut out in an approximately rectangular shape.
The first piece 131 can also be said to be a roughly T-shaped segment piece having first upper cutouts 131A at the upper left and upper right, and first lower cutouts 131B at the lower left and lower right.

The detailed shape of first piece 131 is not particularly limited as long as it has a shape including first upper cutout portion 131A and first lower cutout portion 131B.
The first piece 131 may have, for example, an upper side 131C and a lower side 131D that are curved, specifically, curved upwardly so that the curvature corresponds to the distance from the center of rotation P.
In order to make the groove width of the oil groove 14 formed between adjacent segment pieces of the first piece 131 approximately constant, for example, the left and right side edges 131E of the first piece 131 can be inclined so that the center of rotation P is located on the extension line of the inclined side edges 131E.
The first piece 131 may have chamfered corners.

In FIG. 2, the first upper cutouts 131A are the same size on the left and right, and the first lower cutouts 131B are the same size on the left and right.
The first upper cutout 131A does not need to be the same size on the left and right sides, and may be different sizes on the left and right sides.
The first lower cutout portion 131B does not necessarily have to be the same size on the left and right, and may be different sizes on the left and right.

Moreover, the first piece 131 can be formed, for example, into a shape as shown in FIGS.
The first piece 131 shown in FIG. 3A has a shape that is wider in the left-right direction than the shape shown in FIG.
The first piece 131 shown in FIG. 3(b) has a shape in which a first lower cutout 131B is larger than the shape shown in FIG.
The first piece 131 shown in FIG. 3(c) has a laterally asymmetrical shape as compared to the shape shown in FIG. 2, by changing the sizes of the left and right first lower cutouts 131B.
The first piece 131 shown in FIG. 3D has a shape in which the left and right first upper cutouts 131A are larger than the shape shown in FIG.

In the first piece 131, the size of the first lower cutout 131B is not limited, but if the maximum length of the first piece in the left-right direction is W _P1 and the length of the first lower cutout 131B in the left-right direction is W _D1 , then 0.08≦W _D1 /W _P1 ≦0.34 can be satisfied. Within this range, an excellent drag torque reduction effect can be obtained.
W _D1 /W _P1 may further be set to 0.1≦W _D1 /W _P1 ≦0.3, and may further be set to 0.15≦W _D1 /W _P1 ≦0.25.

Specifically, the lower limit of the length W _D1 of the first lower cutout portion 131B in the left-right direction can be set to 1 mm or more. The lower limit of W _D1 can be set to 1.7 mm or more, and can further be set to 2.5 mm or more.
The upper limit of W _D1 can be set to 3.5 mm or less. The upper limit of W _D1 can be set to 3.2 mm or less, and further can be set to 3 mm or less.

In the first piece 131, the size of the first lower cutout 131B is not limited, but if the maximum length in the vertical direction of the first piece is H _P1 and the length in the vertical direction of the first lower cutout 131B is H _D1 , then 0.07≦H _D1 /H _P1 ≦0.4 can be satisfied. Within this range, an excellent drag torque reduction effect can be obtained.
H _D1 /H _P1 may further be set to 0.1≦H _D1 /H _P1 ≦0.35, and may further be set to 0.15≦H _D1 /H _P1 ≦0.3.

Specifically, the lower limit of the length H _D1 of the first lower cutout portion 131B in the up-down direction can be set to 1 mm or more. The lower limit of H _D1 can be set to 2 mm or more, and can further be set to 3 mm or more.
The upper limit of H _D1 can be set to 5 mm or less. The upper limit of W _D1 can be set to 4.5 mm or less, and further can be set to 4 mm or less.

In the first piece 131, the size of the first upper cutout 131A is not limited, but when the cut angle with respect to the side edge 131E is θ ₁ , it can be set to 20 degrees≦θ ₁ ≦60 degrees. Within this range, an excellent drag torque reduction effect can be obtained.
θ ₁ may further be set to 30 degrees≦θ ₁ ≦55 degrees, and may further be set to 40 degrees≦θ ₁ ≦50 degrees.

In the first piece 131, the size of the first upper cutout 131A is not limited, but if the maximum length of the first piece in the up-down direction is H _P1 and the length of the first upper cutout 131A in the up-down direction is H _U1 , then 0.07≦H _U1 /H _P1 ≦0.4 can be satisfied. Within this range, an excellent drag torque reduction effect can be obtained.
H _U1 /H _P1 may further be set to 0.1≦W _U1 /W _P1 ≦0.35, and may further be set to 0.2≦H _U1 /H _P1 ≦0.3.

Specifically, the lower limit of the length H _U1 of the first upper cutout 131A in the up-down direction can be set to 1 mm or more. The lower limit of H _U1 can be set to 1.5 mm or more, and can further be set to 2 mm or more.
The upper limit of H _U1 can be set to 5 mm or less. The upper limit of H _U1 can be set to 4.5 mm or less, and further set to 4 mm or less.

(1-2) Second Piece The second piece 132 is a segment piece having a shape obtained by cutting out the upper left and upper right corners of an approximately rectangular piece into approximately triangular shapes, and cutting out the lower left and lower right corners into approximately triangular shapes, as shown in FIG.
That is, the second piece 132 is a segment piece having a shape including a second upper cutout portion 132A where the upper left and upper right corners are cut out in an approximately triangular shape, and a second lower cutout portion 132B where the lower left and lower right corners are cut out in an approximately triangular shape.
The second piece 132 can also be said to be a roughly octagonal segment piece having second upper cutouts 132A at the upper left and upper right and second lower cutouts 131B at the lower left and lower right.

The detailed shape of second piece 132 is not particularly limited as long as it has a shape including second upper cutout portion 132A and second lower cutout portion 132B.
The second piece 132 may have, for example, an upper side 132C and a lower side 132D that are curved, specifically, curved upwardly so that the curvature corresponds to the distance from the center of rotation P.
In order to make the groove width of the oil groove 14 formed between adjacent segment pieces approximately constant, the second piece 132 can be shaped, for example, so that the left and right side edges 132E are inclined so that the center of rotation P is located on the extension line of the inclined side edges 132E.
The second piece 132 may have chamfered corners.

In FIG. 4, the second upper cutouts 132A are the same size on the left and right, and the second lower cutouts 132B are the same size on the left and right.
The second upper cutout 132A does not need to be the same size on the left and right sides, and may be different sizes on the left and right sides.
The second lower cutout portion 132B does not need to be the same size on the left and right sides, and may be different sizes on the left and right sides.

Moreover, the second piece 132 can be formed, for example, into a shape as shown in FIGS.
The second piece 132 shown in FIG. 5A has a shape that is wider in the left-right direction than the shape shown in FIG.
The second piece 132 shown in FIG. 5(b) has a shape in which a second lower cutout 132B is larger than the shape shown in FIG.
The second piece 132 shown in FIG. 5(c) has a laterally asymmetrical shape as compared to the shape shown in FIG. 4, by changing the sizes of the left and right second lower cutouts 132B.
The second piece 132 shown in FIG. 5(d) has a shape in which the left and right second upper cutouts 132A are larger than the shape shown in FIG.

In the second piece 132, the size of the second lower cutout 132B is not limited, but if the maximum length of the second piece in the left-right direction is W _P2 and the length of the second lower cutout 132B in the left-right direction is W _D2 , then 0.08≦W _D2 /W _P2 ≦0.45 can be satisfied. Within this range, a suitable drag torque reduction effect can be obtained.
W _D2 /W _P2 may further be set to 0.1≦W _D2 /W _P2 ≦0.4, and may further be set to 0.15≦W _D2 /W _P2 ≦0.3.

Specifically, the lower limit of the length W _D2 of the second lower cutout portion 132B in the left-right direction can be set to 1 mm or more. The lower limit of W _D2 can be set to 1.7 mm or more, and can further be set to 2.5 mm or more.
The upper limit of W _D2 can be set to 5 mm or less. The upper limit of W _D2 can further be set to 4 mm or less, and further can be set to 3.5 mm or less.

In the second piece 132, the size of the second lower cutout 132B is not limited, but if the maximum length of the second piece in the vertical direction is H _P2 and the length of the second lower cutout 132B in the vertical direction is H _D2 , then 0.07≦H _D2 /H _P2 ≦0.4 can be satisfied. Within this range, a favorable drag torque reduction effect can be obtained.
H _D2 /H _P2 may further be set to 0.1≦H _D2 /H _P2 ≦0.35, and may further be set to 0.15≦H _D2 /H _P2 ≦0.3.

Specifically, the lower limit of the length H _D2 of the second lower cutout portion 132B in the up-down direction can be set to 1 mm or more. The lower limit of H _D2 can be set to 2 mm or more, and can further be set to 3 mm or more.
The upper limit of H _D2 can be set to 5 mm or less. The upper limit of W _D2 can be set to 4.5 mm or less, and further can be set to 4 mm or less.

In the second piece 132, the size of the second upper cutout 132A is not limited, but when the cut angle with respect to the side edge 132E is _θ2 , it can be set to 20 degrees≦ _θ2 ≦60 degrees. Within this range, a suitable drag torque reduction effect can be obtained.
θ ₂ may further be in the range of 30 degrees≦θ ₁ ≦55 degrees, and may further be in the range of 40 degrees≦θ ₂ ≦50 degrees.

In the second piece 132, the size of the second upper cutout 132A is not limited, but if the maximum length of the second piece in the up-down direction is H _P2 and the length of the second upper cutout 132A in the up-down direction is H _U2 , then 0.07≦H _U2 /H _P2 ≦0.4 can be satisfied. Within this range, a favorable drag torque reduction effect can be obtained.
H _U2 /H _P2 may further be set to 0.1≦W _U2 /W _P2 ≦0.35, and may further be set to 0.2≦H _U2 /H _P2 ≦0.3.

Specifically, the lower limit of the length H _U2 of the second upper cutout 132A in the up-down direction can be set to 1 mm or more. The lower limit of H _U2 can be set to 1.5 mm or more, and can further be set to 2 mm or more.
The upper limit of H _U2 can be set to 5 mm or less. The upper limit of H _U2 can be set to 4.5 mm or less, and further set to 4 mm or less.

(1-3) Regarding the First Piece and the Second Piece The maximum width W _p1 of the first piece 131 and the maximum width W _p2 of the second piece 132 may be different, but are preferably the same.
If they are the same, the shape of the oil grooves 14 formed between the segment pieces can be made uniform, and the variation in shape can be suppressed, thereby achieving a satisfactory reduction in drag torque.

The left-right lengths W _D1 and W _D2 and the up-down lengths H _D1 and H _D2 of the first lower cutout 131B of the first piece 131 and the second lower cutout 132B of the second piece 132 may be different, but it is preferable that they are the same.
If they are the same, the shape of the oil grooves 14 formed between the segment pieces can be made uniform, and the variation in shape can be suppressed, thereby achieving a satisfactory reduction in drag torque.

The cut angles _θ1 and _θ2 and the vertical lengths H _U1 and H _U2 of the first upper cutout 131A of the first piece 131 and the second upper cutout 132A of the second piece 132 may be different, but are preferably the same.
If they are the same, the shape of the oil grooves 14 formed between the segment pieces can be made uniform, and the variation in shape can be suppressed, thereby achieving a satisfactory reduction in drag torque.

(2) Oil Groove The oil groove 14 is a groove that serves as a passage for lubricating oil and is formed as a gap between the two segment pieces 13 when the two segment pieces 13 are disposed apart from each other.
As shown in FIG. 6, in the wet friction material 10, the segment pieces 13 are disposed spaced apart from one another, and each segment piece 13 has an oil groove 14 as a gap therebetween.
That is, the oil groove 14 is a through groove that penetrates the wet friction material 10 from the inner periphery side to the outer periphery side.

The oil groove 14 can function as a guide for discharging the lubricating oil supplied from the inner circumferential side of the wet friction material 10 toward the outer circumferential side.
The oil grooves 14 are arranged on the main surface 111 of the core plate 11 in a number corresponding to the number of the segment pieces 13 .
When all the segment pieces 13 are spaced apart, the number of oil grooves 14 is the same as the number of the segment pieces 13 .

When only the first piece 131 or the first piece 131 and the second piece 132 are used as the segment piece 13, the oil groove 14 has an oil reservoir groove 141 at the end on the inner circumferential side of the wet friction material 10 (see FIG. 6 ).
That is, the oil groove 14 formed between adjacent first pieces 131 has a widened area between the first lower cutouts 131B, and this area becomes an oil reservoir groove 141.
Furthermore, since the second piece 132 has a second lower cut-out portion 132B, the oil groove 14 formed between adjacent second pieces 132 and the oil groove 14 formed between adjacent first piece 131 and second piece 132 also have a shape having an oil reservoir groove 141.

The oil groove 14 having the oil reservoir groove 141 is shaped such that the widened oil reservoir groove 141 is followed by a narrow oil groove 14, so that the flow of lubricating oil from the oil reservoir groove 141 toward the outer periphery of the core plate 11 is suppressed, thereby allowing the lubricating oil to be stored in the oil reservoir groove 141.
The lubricating oil stored in the oil reservoir groove 141 climbs over the segment pieces 13 and onto the surface of the friction portion 12 due to centrifugal force or the like caused by the rotation of the wet friction material 10 .
Therefore, the oil groove 14 having the oil reservoir groove 141 has the effect of promoting the lubricating oil to run up onto the surface of the friction portion 12 .

When only the first piece 131 or the first piece 131 and the second piece 132 are used as the segment piece 13, the oil groove 14 has an oil drain groove 142 at the end on the outer circumferential side of the wet friction material 10 (see FIG. 6 ).
That is, the oil groove 14 formed between adjacent first pieces 131 has a widened area between the first upper cutout portions 131A, and this area becomes the oil drain groove 142.
Furthermore, since the second piece 132 has a second upper cut-out portion 132A, the oil groove 14 formed between adjacent second pieces 132 and the oil groove 14 formed between adjacent first piece 131 and second piece 132 also have a shape having an oil drain groove 142.

The oil groove 14 having the oil drain groove 142 has a shape in which the narrow oil groove 14 is followed by the widened oil drain groove 142, so that the discharge of the lubricating oil from the oil drain groove 142 which is widely open toward the outer periphery of the core plate 11 is promoted, thereby enabling the lubricating oil to be actively discharged.
Therefore, the oil groove 14 having the oil drain groove 142 has the effect of suppressing the retention of lubricating oil on the surface of the friction portion 12 and promoting the discharge of the lubricating oil to the outer periphery of the core plate 11.

The size of the oil groove 14 is not limited, but for example, the width _D1 of the oil groove 14 other than the oil reservoir groove 141 and the oil drain groove 142 is preferably 0.1 mm or more and 10 mm or less, more preferably 0.2 mm or more and 7 mm or less, and particularly preferably 0.5 mm or more and 5 mm or less.
The maximum width _D2 of the oil reservoir groove 141 is, for example, preferably 2.5 mm or more and 13 mm or less, more preferably 4 mm or more and 12 mm or less, and particularly preferably 5 mm or more and 10 mm or less.
The maximum width _D3 of the oil drain groove 142 is, for example, preferably 2.5 mm or more and 23 mm or less, more preferably 4 mm or more and 17 mm or less, and particularly preferably 5 mm or more and 10 mm or less.

(3) Combination of Segment Pieces As shown in Fig. 7, the segment piece 13 may be made of only one type of first piece 131 (see Fig. 7), but it is preferable to use two types of the first piece 131 and the second piece 132 in combination (see Figs. 1, 8, 9, and 10). When the two types of the first piece 131 and the second piece 132 are used in combination, an excellent drag torque reduction effect can be obtained.
The segment piece 13 may have a shape other than the two shapes of the first piece 131 and the second piece 132 .

When the segment pieces 13 are used in combination of two types, a first piece 131 and a second piece 132, it is preferable that a predetermined number of first pieces 131 and an equal or different number of second pieces 132 as the first pieces are arranged alternately in the circumferential direction of the core plate 11.
As an example of such a combination of segment pieces 13, as shown in FIG. 8, there is a combination in which one first piece 131 and one second piece 132, the same number as the first piece 131, are alternately arranged one by one in the circumferential direction of the core plate 11.
Alternatively, as shown in Figure 9, a combination can be used in which five first pieces 131 and one second piece 132, which is an odd number of the first pieces 131, are arranged alternately in the circumferential direction of the core plate 11.

When combining a plurality of first pieces 131 and a plurality of second pieces 132, it is preferable that a plurality of first pieces 131 that are consecutive in the circumferential direction of the core plate 11 form a first piece group 13A, and a plurality of second pieces 132 that are consecutive in the circumferential direction of the core plate 11 form a second piece group 13B, and that the first piece group 13A and the second piece group 13B are arranged alternately in the circumferential direction of the core plate 11.
1, three first pieces 131 arranged consecutively in the circumferential direction of the core plate 11 form a first piece group 13A, and two second pieces 132, an odd number of which is different from the first pieces, are arranged consecutively in the circumferential direction of the core plate 11 to form a second piece group 13B. The first piece group 13A and the second piece group 13B are alternately disposed in the circumferential direction of the core plate 11.
10 , two of the first pieces 131 that are consecutive in the circumferential direction of the core plate 11 form a first piece group 13A, and two of the second pieces 132 that are the same number as the first pieces 131 form a second piece group 13B that are consecutive in the circumferential direction of the core plate 11. The first piece group 13A and the second piece group 13B are alternately disposed in the circumferential direction of the core plate 11.

When the segment piece 13 is used in combination with the first piece 131 and a piece other than the first piece 131, such as the second piece 132, it is preferable that the number of the first pieces 131 be 10% or more and 90% or less of the total number of the segment pieces 13.
Furthermore, when the segment pieces 13 are used in combination of two types, the first pieces 131 and the second pieces 132, it is preferable that the number of the first pieces 131 is 50% or more and 90% or less of the total number of the segment pieces 13. That is, when the two types, the first pieces 131 and the second pieces 132, are used in combination, the first pieces 131 and the second pieces 132 may be the same in number, but by having more first pieces 131 than second pieces 132, drag torque reduction can be achieved satisfactorily.

[3] Reduction in Drag Torque (1) Climbing Effect This will be described assuming that the wet friction material 10 is rotated in the counterclockwise direction, for example, as shown in FIG. 1 , with the center of the ring shape of the core plate 11 as the center of rotation P in the presence of a lubricating oil.
The lubricating oil is supplied to the wet friction material 10 from the inner periphery side of the core plate 11 , and is discharged to the outer periphery side of the core plate 11 through the oil groove 14 by the centrifugal force of the wet friction material 10 .
In detail, the lubricating oil flows from the inner side of the core plate 11 into the oil reservoir groove 141 at the inner end of the oil groove 14, passes through the oil groove 14, and is discharged from the oil drain groove 142 at the outer end of the oil groove 14 to the outer side of the core plate 11.

The oil reservoir groove 141 is defined and formed by the first lower cutout portion 131B, i.e., the portion of the first piece 131 where the lower left and right corners are cut out in an approximately rectangular shape, and the flow path in the oil groove 14 from after passing through the oil reservoir groove 141 to the oil drain groove 142 is narrower than the flow path of the oil reservoir groove 141.
As a result, the lubricating oil flowing into the oil reservoir groove 141 is temporarily blocked from flowing from the inner side to the outer side of the core plate 11 by the inner surface of the first lower cutout portion 131B, which becomes the dam portion 131F, and the oil is stored in the oil reservoir groove 141.
When the amount of lubricating oil stored in the oil reservoir groove 141 reaches a level sufficient to overcome the dam portion 131F, the oil overflows from the oil reservoir groove 141 and climbs up onto the surface of the friction portion 12 (see the thick arrow in FIG. 1).

In other words, the shape of the first piece 131 is such that the dam portion 131F that causes the lubricating oil to run up onto the surface of the friction portion 12 is formed in the first lower cutout portion 131B.
The lubricating oil that has been pushed up onto the surface of the friction portion 12 by this dam portion 131F is subjected to centrifugal force and moves on the first piece 131 toward the outer periphery in the opposite direction to the rotational direction of the wet friction material 10 (clockwise) (see the thick arrow in FIG. 1).
The lubricating oil moving on the first piece 131 reaches the oil drain groove 142 defined by the first upper cut-out portion 131A, flows into this oil drain groove 142, and is discharged from the oil drain groove 142 to the outer circumferential side of the wet friction material 10.

When the lubricating oil moves over the first piece 131 , it forms an oil film on the surface of the first piece 131 .
This oil film is formed by a necessary and sufficient amount of lubricating oil to maintain lubrication between the wet friction material 10 and the mating material (e.g., a separator plate) by the lubricating oil quickly spreading from the oil reservoir groove 141 to the oil drain groove 142.
In other words, the first piece 131 has a dam portion 131F formed in the first lower cut-out portion 131B and is shaped to have the first upper cut-out portion 131A, thereby providing a riding-up effect that causes the lubricating oil to ride up onto the surface of the friction portion 12 and be discharged.
Due to this riding effect, the amount of lubricating oil present between the wet friction material 10 and the mating material (e.g., a separator plate) is kept to a necessary and sufficient amount to maintain lubrication, and co-rotation of the wet friction material 10 and the mating material is suppressed, thereby achieving a reduction in drag torque.

(2) Effect of Combination of First Piece 131 and Second Piece 132 A wet friction material 10 using a combination of the first piece 131 and the second piece 132 will be described.
The second piece 132 has a shape having a second lower cut-out portion 132B and a second upper cut-out portion 132A, and, similar to the first piece 131, has the above-mentioned riding-up effect of causing the lubricating oil to ride up onto the surface of the friction portion 12 and be discharged (see the thin arrow in Figure 1).

When comparing the first lower cutout 131B of the first piece 131 with the second lower cutout 132B of the second piece 132, if the left-right lengths W _D1 and W _D2 and the up-down lengths H _D1 and H _D2 are approximately the same, the area of the first lower cutout 131B is larger than the area of the second lower cutout 132B in a planar view. Therefore, in the oil reservoir groove 141, the first lower cutout 131B can store a larger amount of lubricating oil than the second lower cutout 132B, and can cause a larger amount of lubricating oil to run up onto the surface of the friction portion 12.
In other words, both the first piece 131 and the second piece 132 have a riding effect, but the riding effect of the first piece 131 is stronger than that of the second piece 132 because it can cause a greater amount of lubricating oil to ride up onto the surface of the friction portion 12 (see the thick arrow in Figure 1).
In addition, the riding effect of the second piece 132 is weaker than that of the first piece 131 (see the thin arrow in FIG. 1).

When the first piece 131 (first piece group 13A) and the second piece 132 (second piece group 13B) are arranged alternately in the circumferential direction of the core plate 11, the wet friction material 10 can have both a portion where the riding-up effect of the first piece 131 is strong and a portion where the riding-up effect of the second piece 132 is weak.
In other words, when the wet friction material 10 uses both the first piece 131 and the second piece 132 as the segment pieces 13, it is possible to create uneven strengths in the ride-up effect.

The drag torque occurs when a wet friction material and a counter material (e.g., a separator plate), which are separated from each other and rotate relative to each other, rotate together with the lubricating oil present around them as an intermediate.
Therefore, in order to reduce the drag torque, it is preferable to suppress the co-rotation of the wet friction material and the mating material by utilizing the rotation difference between the wet friction material and the mating material, which are rotating relative to each other, by peeling the mating material off the wet friction material, or by shearing the lubricating oil present around both of them, particularly in the outer periphery where the co-rotation force is large.

As described above, the wet friction material 10 using both the first piece 131 and the second piece 132 can form unevenness in the strength of the riding-up effect. In this wet friction material 10, with regard to the amount of lubricating oil that rides up from the oil reservoir groove 141 onto the surface of the friction portion 12, there are many portions where the riding-up effect is strong and few portions where the riding-up effect is weak.
In the area where the riding effect is weak, the amount of lubricating oil riding on the surface of the friction portion 12 is small, and the amount of lubricating oil that serves as an intermediate between the friction portion 12 and the counter material is small, so that the counter material can be easily peeled off from the wet friction material even with a weak force (rotational torque) due to the rotational difference in the relative rotation. When the counter material is peeled off from the wet friction material in the area where the riding effect is weak, the counter material is also easily peeled off from the wet friction material in the area where the riding effect is strong.
Therefore, in comparison with a wet friction material in which the ride-on effect is uniform overall, the wet friction material 10 using both the first piece 131 and the second piece 132 can obtain a so-called peeling effect in which the opposing material can be easily peeled off from the wet friction material by utilizing the rotational difference in the relative rotation, by intentionally forming unevenness in the strength of the ride-on effect.

Furthermore, in the wet friction material 10 in which unevenness in the strength of the riding-up effect is formed, with regard to the amount of lubricating oil that moves from the surface of the friction portion 12 to the oil drain groove 142, there are many portions where the riding-up effect is strong and few portions where the riding-up effect is weak.
In the area where the riding effect is weak, the amount of lubricating oil discharged from the oil drain groove 142 to the outer periphery is small. Therefore, the resistance required to shear the lubricating oil in the outer periphery of the wet friction material 10 is small, and the lubricating oil can be sheared even with a weak force (rotational torque) due to the rotational difference in the relative rotation.
Therefore, in comparison with a wet friction material in which the ride-on effect is uniform overall, the wet friction material 10 using both the first piece 131 and the second piece 132 has unevenness in the strength of the ride-on effect, which makes it possible to suppress the shear resistance of the lubricating oil in the outer circumferential portion.

As described above, the wet friction material 10 using both the first piece 131 and the second piece 132 can intentionally provide uneven strength of the ride-on effect.
The wet friction material 10, in which the strength of the riding effect is intentionally varied, can obtain a peeling effect against the counter material and can suppress the shear resistance of the lubricating oil at the outer periphery.
The wet friction material 10, in which the strength of the riding effect is intentionally varied by the peeling effect and the suppression of the shear resistance of the lubricating oil, can achieve an excellent reduction in drag torque.

The present invention will be described below with reference to examples, without citing any description common to the respective examples.
[1] Preparation of wet friction material [Example 1]
A wet friction material 10 (see FIG. 1 ) of the first embodiment includes a core plate 11 and friction portions 12 arranged on main surfaces 111 of the core plate 11 (both the front main surface 111 and the back main surface 111 ).
The friction portion 12 includes a plurality of segment pieces 13 and oil grooves 14 formed between the segment pieces 13 .
The wet friction material 10 includes, as the segment pieces 13, a plurality of first pieces 131 and a plurality of second pieces 132. The total number of the segment pieces 13 is 45. Of these segment pieces 13, 27 are the first pieces 131 and 18 are the second pieces 132.
Three of the first pieces 131 are consecutive in the circumferential direction of the core plate 11 to form a first piece group 13A, and two of the second pieces 132 are consecutive in the circumferential direction of the core plate 11 to form a second piece group 13B.
The first piece group 13A and the second piece group 13B are arranged alternately in the circumferential direction of the core plate 11.

Regarding the first piece 131, if the maximum length in the left-right direction is W _P1 and the length of the first lower cutout 131B in the left-right direction is W _D1 , then W _D1 /W _P1 = 0.18, and W _D1 = 2 mm. Also, if the maximum length in the up-down direction is H _P1 and the length of the first lower cutout 131B in the up-down direction is H _D1 , then H _D1 /H _P1 = 0.36, and H _D1 = 4.5 mm.
Regarding the second piece 132, if the left-right length of the second lower cutout 132B is W _D2 , then W _D2 = W _D1 = 2 mm, and if the up-down length of the second lower cutout 132B is H _D2 , then H _D2 = H _D1 = 4.5 mm.

The segment pieces 13 are made by impregnating a paper body obtained by papermaking a fiber base material such as pulp and aramid fiber, a friction modifier such as cashew dust, and a filler such as diatomaceous earth with a thermosetting resin (resin binder) and then heating and curing the paper body. The segment pieces 13 are joined to both the front and back main surfaces of the core plate 11 by applying pressure and heat.
The core plate 11 is made of NCH780 and has gear-shaped engagement teeth 113 on its outer periphery. The outer diameter of the core plate 11 (the diameter defined by the outer periphery of the core plate 11 excluding the engagement teeth 113) is 176 mm, and the inner diameter of the core plate 11 is 148.4 mm.

[Example 2]
The wet friction material 10 of the second embodiment (see FIG. 7) includes only first pieces 131 as the segment pieces 13, and the total number of the first pieces 131 is 45. Apart from this difference, the wet friction material 10 is similar to the wet friction material 1 of the first embodiment.

[Comparative Example 1]
The wet friction material 10 of Comparative Example 1 (see FIG. 11) includes only the second pieces 132 as the segment pieces 13, and the total number of the second pieces 132 is 45. Apart from this difference, the wet friction material 10 is similar to the wet friction material 1 of Example 1.

[2] Correlation between drag torque and rotation speed Four pieces of each of the wet friction materials of Examples 1 and 2 and Comparative Example 1 in [1] above were used to measure drag torque at rotation speeds of 500-3000 rpm using an SAE friction tester under the following test conditions. The obtained results are shown in the graph of FIG.
It should be noted that FIG. 12 indicates that the drag torque increases toward the upper side of the vertical axis.

(1) Test Conditions Automatic transmission lubricating oil ("ATF" is a registered trademark of Idemitsu Kosan Co., Ltd., but hereinafter referred to as "ATF" regardless of the registered trademark) was used. Four test wet friction materials were set in an environment of an oil temperature of 80°C, an ATF oil amount of 0.5 L/min (axial lubrication), and a pack clearance of 0.20 mm/sheet for the spacing of the wet friction materials. The rotation speed was changed from 500 to 3000 rpm, and the drag torque (N·m) was measured at six points of 500 rpm, 1000 rpm, 1500 rpm, 2000 rpm, 2500 rpm, and 3000 rpm. The measurement time was 15 seconds/each rotation, and the number of repetitions was 5 times.

(2) Effects of Test Examples From the results in FIG. 12, it is understood that in all of the wet friction materials of the Examples, the drag torque is reduced compared to the Comparative Example.
That is, compared to Comparative Example 1 in which only the second piece 132 was provided as the segment piece 13, Examples 1 and 2 showed a significant reduction in drag torque in the entire range of 500 to 3000 rpm.
Furthermore, compared to Example 2 in which only the first piece 131 is provided as the segment piece 13, Example 1 in which both the first piece 131 and the second piece 132 are provided achieved an even more significant reduction in drag torque in the entire range from 500 to 3000 rpm.
In particular, in Example 1, excellent drag torque reduction was achieved in the range of 500 to 1000 rpm, and it is believed that the drag torque reduction achieved by using the first piece 131 and the second piece 132 in combination is advantageous in the range of smaller relative rotation speeds.

The present invention is not limited to the specific examples shown above, and various modifications may be made within the scope of the present invention depending on the purpose and application.

The wet friction material of the present invention is not particularly limited in its use, and is widely used in, for example, automobiles (four-wheeled automobiles, two-wheeled automobiles, etc.), railway vehicles, ships, airplanes, etc. Among these, as an automobile product, it is preferably used in an automatic transmission (AT). The present wet friction material may be used in a transmission in one sheet or in multiple sheets, but it is preferable to use multiple sheets. The more sheets of the present wet friction material are used in one transmission, the greater the cumulative effect can be obtained. In other words, drag torque can be reduced more effectively in a wet multi-plate clutch that uses a large number of sheets of wet friction material.

10: wet friction material; 11: core plate; P: rotation center; 111: main surface; 112: outer circumferential surface; 113: engaging teeth;
12: friction portion, 13: segment piece, 13A: first piece group, 13B: second piece group,
131; first piece, 131A; first upper cutout, 131B; first lower cutout, 131C; upper edge, 131D; lower edge, 131E; side edge, 131F; dam portion,
132; second piece, 132A; second upper cutout, 132B; second lower cutout, 132C; upper edge, 132D; lower edge, 132E; side edge,
14; Oil groove, 141; Oil sump groove, 142; Oil drain groove.

Claims (6)

A wet friction material comprising a flat ring-shaped core plate and a friction portion arranged in a ring shape on a main surface of the core plate,
The friction portion includes a plurality of segment pieces and a plurality of oil grooves formed between the segment pieces,
Assuming that the segment piece is placed at the 12 o'clock position on the clock face, "right" means the direction from the 9 o'clock position to the 3 o'clock position on the clock face, "left" means the direction from the 3 o'clock position to the 9 o'clock position on the clock face, "up" means the direction from the 6 o'clock position to the 12 o'clock position on the clock face, and "down" means the direction from the 12 o'clock position to the 6 o'clock position on the clock face,
The segment pieces include:
a first piece having a shape in which the upper left and upper right corners of a substantially rectangular piece are cut off into a substantially triangular shape and the lower left and lower right corners are cut off into a substantially rectangular shape ;
a second piece having a shape in which the upper left and upper right corners of the substantially rectangular piece are cut off into a substantially triangular shape and the lower left and lower right corners are cut off into a substantially triangular shape ,
The friction portion is provided with the first pieces and the same number of the second pieces as the first pieces,
The wet friction material is characterized in that the first pieces and the second pieces are alternately arranged one by one in the circumferential direction of the core plate . A wet friction material comprising a flat ring-shaped core plate and a friction portion arranged in a ring shape on a main surface of the core plate,
The friction portion includes a plurality of segment pieces and a plurality of oil grooves formed between the segment pieces,
Assuming that the segment piece is placed at the 12 o'clock position on the clock face, "right" means the direction from the 9 o'clock position to the 3 o'clock position on the clock face, "left" means the direction from the 3 o'clock position to the 9 o'clock position on the clock face, "up" means the direction from the 6 o'clock position to the 12 o'clock position on the clock face, and "down" means the direction from the 12 o'clock position to the 6 o'clock position on the clock face,
The segment pieces include:
a first piece having a shape in which the upper left and upper right corners of a substantially rectangular piece are cut off into a substantially triangular shape and the lower left and lower right corners are cut off into a substantially rectangular shape ;
a second piece having a shape in which the upper left and upper right corners of the substantially rectangular piece are cut off into a substantially triangular shape and the lower left and lower right corners are cut off into a substantially triangular shape ,
The friction portion includes the first pieces and the second pieces, the number of which is equal to or different from the number of the first pieces ,
The first pieces are arranged in a circumferential direction of the core plate to form a first piece group,
The second pieces are arranged in a circumferential direction of the core plate to form a second piece group,
The wet friction material is characterized in that the first piece group and the second piece group are alternately disposed in a circumferential direction of the core plate . 3. The wet friction material according to claim 2 , wherein the number of the first pieces is 10% or more and 90% or less of the total number of the segment pieces. When the wet friction material is rotated in a circumferential direction around the center of the ring shape of the core plate in the presence of a lubricating oil,
3. The wet friction material according to claim 1, wherein the first piece has a shape in which a dam portion that causes lubricating oil to run up onto a surface of the friction portion is formed in a region where a lower left corner and a lower right corner are cut out in a substantially rectangular shape. 5. The wet friction material according to claim 4 , wherein, with respect to the length of the portion remaining as the segment piece, when the maximum length in the left-right direction of the first piece is W _P1 and the length in the left- right direction of the portion cut out into a substantially rectangular shape is W _D1 , the relationship is 0.08≦W _D1 /W _P1 ≦0.34. 6. The wet friction material according to claim 4 or 5, wherein, with respect to the length of the portion remaining as the segment piece, when the maximum length in the up-down direction of the first piece is defined as _Hp1 and the length in the up- down direction of the portion cut out into a substantially rectangular shape is defined as _Hd1 , 0.07≦ _Hd1 / _Hp1 ≦0.4 is satisfied.

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