JP2007192366A - Frictional engaging device of vehicular automatic transmission - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a frictional engaging device of a vehicular automatic transmission superior in responsiveness of hydraulic pressure by bleeding air in a piston hydraulic chamber without causing leakage of a hydraulic fluid when supplying the hydraulic pressure. <P>SOLUTION: A piston 72 is positioned on the support wall 36a side at the beginning of supplying the hydraulic fluid in the hydraulic chamber 76, and at this time, since a ventilation passage 90 is positioned over a rubber member 88, air in the hydraulic chamber 76 is exhausted via a ventilation passage 90. Afterwards, when the piston 72 advances to the frictional engaging element 66 side, since the ventilation passage 90 is positioned in the hydraulic chamber 76 on the support wall 36a side more than the rubber member 88, the hydraulic pressure in the hydraulic chamber 76 can be held without leaking the hydraulic fluid. As a result, hydraulic pressure reduction in the hydraulic chamber 76 is prevented, and the deterioration in controllability caused by the hydraulic pressure reduction in the hydraulic chamber 76 can be prevented. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a friction engagement device provided in an automatic transmission for a vehicle, and more particularly to an air vent structure that accumulates in a piston hydraulic chamber to which hydraulic pressure that is a drive source of the friction engagement device is supplied.

  A frictional engagement device for an automatic transmission for a vehicle includes a frictional engagement element that connects members when pressed, a piston that presses the frictional engagement element, and hydraulic oil that is a driving source of the piston. A piston hydraulic chamber to be supplied and a return spring that urges the piston in a direction in which the piston does not press the friction engagement element are mainly provided. Here, when hydraulic oil is supplied to the piston hydraulic chamber, the hydraulic pressure advances the piston and presses the friction engagement element. When the frictional engagement elements are engaged with each other by this pressing, the members that support the respective friction plates are connected to rotate or stop rotating integrally.

  The hydraulic control device for controlling the hydraulic pressure of the friction engagement device in the vehicle automatic transmission is generally disposed below the vehicle automatic transmission, and the piston hydraulic chamber and the piston are disposed above the hydraulic control device. It is easy to stay in the piston hydraulic chamber disposed above. In particular, when the hydraulic circuit is long, air is unlikely to escape from the drain port of the hydraulic circuit, and is likely to accumulate in the hydraulic circuit. When air accumulates in the piston hydraulic chamber, when the hydraulic pressure is supplied into the piston hydraulic chamber, the hydraulic pressure performs the work of compressing the air, resulting in a response delay corresponding to the work, which is indicated by a broken line as shown in FIG. With respect to the hydraulic pressure command value by the hydraulic control device, the actual hydraulic pressure value indicated by a solid line has a waveform that cannot be followed quickly and has a delay. Accordingly, there is a problem that the engagement of the friction engagement element is delayed and the controllability of the friction engagement device is deteriorated.

  With respect to this problem, Patent Document 1 discloses a technique for providing an air vent hole that is always open in the piston hydraulic chamber and discharging the air accumulated in the piston hydraulic chamber.

JP-A-11-141661

  By the way, the air vent hole of Patent Document 1 has a complicated structure, and the air vent hole is always opened, so that there is a problem that hydraulic oil leaks from the air vent hole and the hydraulic pressure is lowered. There is a problem that this decrease in hydraulic pressure leads to deterioration in controllability of the friction engagement device.

  The present invention has been made against the background of the above circumstances. The object of the present invention is to provide a frictional engagement device for an automatic transmission for a vehicle. It is an object of the present invention to provide a frictional engagement device for an automatic transmission for a vehicle that has good hydraulic response due to the loss of the pressure.

  In order to achieve the above object, the gist of the invention according to claim 1 is that (a) a piston fitted in a cylinder hole formed in a cylinder member so as to be slidable in the axial direction is provided. And a friction engagement device of an automatic transmission for a vehicle for advancing in an axial direction and pressing a friction plate by supplying hydraulic pressure to a piston hydraulic chamber formed in the cylinder hole by the cylinder member. (B) One of the cylinder member and the piston is provided with a seal member that seals a gap between the wall surface of the cylinder hole and the piston, and (c) the other of the cylinder member and the piston is provided. (D) The air vent oil passage is positioned across the seal member when the piston is located on the retracted side, and When tonnes is advanced, it characterized in that it is is positioned in the piston pressure chamber of the retraction side of the sealing member.

  According to a second aspect of the present invention, there is provided a vehicular automatic transmission friction engagement device according to the first aspect, wherein the air vent oil passage is provided at an upper end portion of the piston hydraulic chamber. It is characterized by.

  According to a third aspect of the present invention, there is provided a vehicular automatic transmission friction engagement device according to the second aspect, wherein the cylinder hole is an annular cylinder hole, and the piston is an annular piston. The seal member is provided at a rear end portion of the annular piston, and the air vent oil passage is provided on a wall surface on an outer peripheral side of the annular cylinder hole.

  According to a fourth aspect of the present invention, there is provided a friction engagement device for an automatic transmission for a vehicle according to any one of the first to third aspects, wherein a flow section of the air vent oil passage is the piston. It is characterized by being formed sufficiently smaller than the flow section of the oil passage for supplying hydraulic pressure to the hydraulic chamber.

  According to the friction engagement device for an automatic transmission for a vehicle according to the first aspect of the present invention, when the hydraulic pressure is initially supplied to the piston hydraulic pressure chamber, the piston is located on the backward side, and at this time, the air vent oil passage is sealed. Since it is located across the members, the air in the piston hydraulic chamber is discharged through the air vent oil passage. Thereafter, when the piston moves forward in the direction of pressing the friction plate, the air vent oil passage is positioned in the piston hydraulic chamber on the backward side of the seal member, so that the hydraulic oil does not leak and maintains the hydraulic pressure in the piston hydraulic chamber. be able to. As a result, a decrease in the hydraulic pressure in the piston hydraulic chamber can be prevented, and a deterioration in controllability of the friction engagement device associated with a decrease in the hydraulic pressure in the piston hydraulic chamber can be prevented.

  According to the friction engagement device for an automatic transmission for a vehicle of the invention according to claim 2, since the air vent oil passage is provided at the upper end portion of the piston hydraulic chamber, air is efficiently discharged, The controllability of the friction engagement device is further improved.

  According to a friction engagement device for an automatic transmission for a vehicle according to a third aspect of the present invention, the seal member is provided at a rear end portion of an annular piston, and the air vent oil passage is formed in the annular cylinder hole. By being provided on the outer peripheral wall surface, the air vent oil passage is disposed at the uppermost position of the piston hydraulic chamber, so that air is discharged most efficiently and the controllability of the friction engagement device is further improved. The

  According to the friction engagement device for an automatic transmission for a vehicle according to the fourth aspect of the present invention, the flow cross section of the air vent oil passage is sufficiently larger than the flow cross section of the oil passage supplying hydraulic pressure to the piston hydraulic chamber. Therefore, the friction engagement device can function with little change in hydraulic pressure due to the air vent oil passage.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a skeleton diagram illustrating a vehicle drive device 10 to which the present invention is applied. The vehicle drive device 10 is suitably employed in an FF (front engine / front drive) type vehicle, and includes an engine 12 as a driving source for traveling. The output of the engine 12 composed of an internal combustion engine is output to the left and right drive wheels via a torque converter 14 that functions as a fluid transmission device, a vehicle automatic transmission 16, a differential gear device (not shown), a pair of axles, and the like. It is to be transmitted.

  The torque converter 14 is connected to a transmission case 36 via a pump impeller 14p connected to a crankshaft of the engine 12, a turbine impeller 14t connected to an input shaft 32 of the automatic transmission 16, and a one-way clutch. The stator impeller 14s is provided to transmit power via a fluid. A lockup clutch 38 is provided between the pump impeller 14p and the turbine impeller 14t. When the lockup clutch 38 is engaged, the pump impeller 14p and the turbine impeller 14t are integrated. It can be rotated to.

  The vehicular automatic transmission 16 includes a first transmission unit 24 mainly composed of a single pinion type first planetary gear unit 22, a single pinion type second planetary gear unit 26, and a double pinion type third planetary unit. A second transmission unit 30 mainly composed of the gear device 28 is provided on the coaxial line, and the rotation of the input shaft 32 is shifted and output from the output gear 34. The input shaft 32 corresponds to an input member, is a turbine shaft that is rotated integrally with the turbine impeller 14t of the torque converter 14, and the output gear 34 corresponds to an output member. The right and left drive wheels are driven to rotate by meshing with the differential gear device via a shaft or directly. The vehicle automatic transmission 16 and the torque converter 14 are substantially symmetrical with respect to the center line, and the lower half of the center line is omitted in FIG.

  The first planetary gear unit 22 constituting the first transmission unit 24 includes three rotating elements, a sun gear S1, a carrier CA1, and a ring gear R1, and the sun gear S1 is connected to the input shaft 32 for rotational driving. And the ring gear R1 is selectively connected to the transmission case 36, which is a non-rotating member, via the third brake B3, whereby the carrier CA1 is rotated at a reduced speed with respect to the input shaft 32 as an intermediate output member. Output. Further, the second planetary gear device 26 and the third planetary gear device 28 constituting the second transmission unit 30 are partially connected to each other to constitute four rotating elements RM1 to RM4. Specifically, the first rotating element RM1 is configured by the sun gear S3 of the third planetary gear device 28, and the ring gear R2 of the second planetary gear device 26 and the ring gear R3 of the third planetary gear device 28 are connected to each other to perform the second rotation. The element RM2 is configured, and the carrier CA2 of the second planetary gear unit 26 and the carrier CA3 of the third planetary gear unit 28 are coupled to each other to form a third rotating element RM3. A four-rotation element RM4 is configured. In the second planetary gear device 26 and the third planetary gear device 28, the carrier CA2 and the carrier CA3 are constituted by a common member, the ring gear R2 and the ring gear R3 are constituted by a common member, and The pinion gear of the two planetary gear unit 26 is a Ravigneaux type planetary gear train that also serves as the second pinion gear of the third planetary gear unit 28.

  The first rotation element RM1 (sun gear S3) is selectively connected to the transmission case 36 by the brake B1 and stopped rotating, and the second rotation element RM2 (ring gears R2, R3) is selectively transmitted by the second brake B2. The fourth rotation element RM4 (sun gear S2) is selectively connected to the input shaft 32 via the first clutch C1, and the second rotation element RM2 (ring gears R2, R3) is connected to the case 36 and stopped. Is selectively connected to the input shaft 32 via the second clutch C2, and the first rotating element RM1 (sun gear S3) is connected to the carrier CA1 of the first planetary gear unit 22 which is an intermediate output member, and the third rotating element RM3 (carriers CA2, CA3) is integrally connected to the output gear 34 to output rotation. Each of the first to third brakes B1 to B3, the first clutch C1, and the second clutch C2 is a multi-plate hydraulic friction engagement device that is frictionally engaged by a hydraulic cylinder. By switching the release state, each of the six forward speeds and one reverse speed is established.

  The operation table of FIG. 2 collectively shows the relationship between the operation states of the clutch and the brake and the respective shift stages, and “◯” represents engagement. In the vehicle automatic transmission 16 according to the present embodiment, a forward six-stage multi-speed transmission is achieved by engaging any two of the two clutches C1 and C2 and the three brakes B1 to B3.

  FIG. 3 is a sectional view showing a part of the vehicle automatic transmission 16 to which the present invention is applied. In the vehicle automatic transmission 16, a plurality of planetary gear devices and friction engagement devices are disposed around the input shaft 32 in a mission case 36 that is a non-rotating member. The input shaft 32 is connected to the engine via a torque converter (not shown) and is rotated integrally.

  The input shaft 32 includes a first shaft 42 connected to a torque converter (not shown) and a second shaft 44 that is spline-fitted to the first shaft 42. A first intermediate shaft 46 that is rotatable relative to the shaft 44 is provided.

  A flange portion 42 a extending in the radial direction is provided at the shaft end portion of the first shaft 42. The sun gear S1 of the first planetary gear device 22 is connected to the outer peripheral edge of the flange portion 42a by welding, and is rotated integrally with the first shaft 42. The carrier CA1 of the first planetary gear device 22 is spline-fitted to the outer peripheral portion of the first intermediate shaft 46. The ring gear R1 of the first planetary gear unit 22 includes a gear portion 48 having meshing teeth on the inner peripheral surface, and a drum portion connected to the gear portion 48 at one end portion of the gear portion 48 and having a slightly larger diameter than the gear portion 48. 50. A spline portion 52 is formed on the outer peripheral surface of the drum portion 50. Further, an outer peripheral portion of a disc-shaped restricting plate 54 that restricts the movement of the ring gear R1 in the axial direction is fixed to the inner peripheral surface of the drum portion 50. Thrust bearings 55 are interposed between one side surface of the inner peripheral portion of the restriction plate 54 and the carrier CA1 and between the other side surface and a fastening nut 62 described later.

  A second intermediate shaft 56 connected to a carrier CA3 (not shown in FIG. 3) of the third planetary gear device 28 and rotatably supported is provided on the outer peripheral side of the first intermediate shaft 46. An output gear 34 that is spline-fitted to the outer peripheral portion of the second intermediate shaft 56 and rotatably supported on the inner peripheral wall of the support wall 36a that protrudes from the outer periphery of the transmission case 36 to the inner peripheral side via a bearing 58 is provided. It has been. The output gear 34 has a cylindrical cylindrical portion 34a whose inner peripheral portion is spline fitted to the second intermediate shaft 56 and whose outer peripheral portion is supported by a bearing 58, and the first planetary gear unit 22 side of the cylindrical portion 34a. And a gear portion 34b extending in the radial direction from the end portion and having gear teeth on the outer peripheral edge thereof. Further, a fastening nut 62 is screwed onto an end portion of the second intermediate shaft 56 on the first planetary gear device 22 side to prevent the output gear 34 from moving to the first planetary gear device 22 side.

  A friction engagement element 66 that is a constituent member of the friction engagement device 64 that functions as the brake B3 is disposed on the outer peripheral side of the ring gear R1 of the first planetary gear device 22. The friction engagement element 66 is formed between a plurality of inward friction plates 68 that are spline-fitted to the inner peripheral side of the mission case 36 so as not to be relatively rotatable and movable in the axial direction, and the plurality of inward friction plates 68. And a plurality of outward friction plates 70 fitted to the spline portion 52 of the drum portion 50 of the ring gear R1. Note that the inward friction plate 68 and the outward friction plate 70 of the present embodiment correspond to the friction plate of the present invention.

  The frictional engagement device 64 includes the frictional engagement element 66, an annular piston 72 for pressing the frictional engagement element 66, and a dish that urges the piston 72 in a direction to isolate it from the frictional engagement element 66. A spring 74 and a hydraulic chamber 76 to which hydraulic oil for driving the piston 72 is supplied are provided. Note that the hydraulic chamber 76 of this embodiment corresponds to the piston hydraulic chamber of the present invention.

  The piston 72 includes a cylindrical cylindrical portion 78 that is positioned on the radially outer side of the gear portion 34b of the output gear 34, a flange portion 80 that is provided at the end of each of the friction plates 68 and 70 of the cylindrical portion 78, a cylindrical portion The bottom portion 82 is provided at the other end of the portion 78. The flange portion 80 protrudes substantially perpendicular to the cylindrical portion 78 and radially outward. The bottom portion 82 has an annular shape protruding substantially vertically and radially inward with respect to the cylindrical portion 78. The bottom portion 82 slides in the axial direction in an annular annular hole 84 formed on the side surface of the support wall 36a. It is movably fitted. The disc spring 74 has an outer peripheral end brought into contact with the outer peripheral portion of the bottom portion 82 of the piston 72, and an inner peripheral end of the disc spring 74 in order to prevent the disc spring 74 from moving to the first planetary gear unit 22 side. It is made to contact | abut to the snap ring 86 fitted by. The hydraulic chamber 76 is annularly formed between an annular hole 84 formed in the support wall 36 a and a bottom portion 82 of the piston 72 fitted in the annular hole 84. In addition, a rubber member 88 for sealing is attached to the hydraulic chamber 76 side of the bottom portion 82 of the piston 72 so that a gap between the wall surface of the annular hole 84 and the bottom portion 84 of the piston 72 that slides on the wall surface is provided. Sealing is performed to prevent leakage of hydraulic oil from the hydraulic chamber 76. The support wall 36a of this embodiment corresponds to the cylinder member of the present invention, the annular hole 84 corresponds to the cylinder hole of the present invention, and the rubber member 88 corresponds to the seal member of the present invention. .

  A wall surface 84 a on the outer peripheral side of the annular hole 84 is provided with a ventilation path 90 parallel to the axis. 4 and 5 are enlarged cross-sectional views for explaining the air passage 90. 4 shows a state in which the piston 72 is positioned on the support wall 36a side (retreat side in the present invention) by the disc spring 74. FIG. Shows a state of being advanced to the friction engagement element 66 side (the forward side in the present invention). In FIG. 4, the piston 72 does not press the frictional engagement element 66, and in this state, the air passage 90 is positioned across the rubber member 88, thereby the hydraulic chamber 76 and the external space 92. Are communicated by the air passage 90. Further, when this ventilation path 90 is viewed from the direction of arrow A, it is formed in a semicircular shape on the outer peripheral wall surface 84a of the annular hole 84 formed in the support wall 36a as shown in FIG. The position of the passage 90 is located at the upper end of the hydraulic chamber 76. On the other hand, in FIG. 5, the piston 72 advances toward the friction engagement element 66 and presses the friction engagement element 66. In this state, the air passage 90 is positioned in the hydraulic chamber 76, and the hydraulic pressure is increased. The chamber 76 and the external space 92 are blocked by a rubber member 88. Further, the flow cross section of the air passage 90 is formed sufficiently smaller than the flow cross section of the oil passage 93 that supplies hydraulic pressure to the hydraulic chamber 76 shown in FIG. In addition, the ventilation path 90 of a present Example respond | corresponds to the air bleeding oil path of this invention.

  In the friction engagement device 64 configured as described above, when the hydraulic oil is supplied to the hydraulic chamber 76, the piston 72 is opposed to the friction engagement element 66 side against the urging force of the disc spring 74 by the hydraulic pressure of the hydraulic oil. When the inward friction plate 68 and the outward friction plate 70 are engaged by the flange portion 80 of the piston 72 pressing the friction engagement element 66, the ring gear R1 is connected to the transmission case 36 and stops rotating. Be made. Here, when the hydraulic pressure begins to be supplied to the hydraulic chamber 76, the piston 72 is advanced by the hydraulic pressure, and the air in the hydraulic chamber 76 is moved by the hydraulic oil through the air passage 90 as shown by the arrow in FIG. It is discharged to the external space 92 through. Next, when all the air in the hydraulic chamber 76 is exhausted and the hydraulic chamber 76 is filled with the hydraulic oil, the hydraulic chamber 76 is sealed by the rubber member 88 as shown in FIG. Leakage is prevented.

  FIG. 7 is a graph showing the response of an actual hydraulic pressure value indicated by a solid line to a hydraulic pressure command value by a hydraulic control device (not shown) indicated by a broken line in the present embodiment. Here, the horizontal axis indicates time, and the vertical axis indicates the hydraulic pressure value. In the present embodiment, the actual hydraulic pressure value indicated by the solid line quickly follows the hydraulic pressure command value indicated by the broken line, and the friction engagement in which the air passage 90 shown in FIG. 9 described above is not formed. Responsiveness is improved compared to the device. This indicates that the air in the hydraulic chamber 76 is discharged by supplying the hydraulic oil, and the work of compressing the air in the hydraulic chamber 76 is omitted.

  As described above, according to the above-described embodiment, when the hydraulic oil is initially supplied into the hydraulic chamber 76, the piston 72 is positioned on the support wall 36a side, and at this time, the air passage 90 straddles the rubber member 88. Therefore, the air in the hydraulic chamber 76 is exhausted through the air passage 90. Thereafter, when the piston 72 moves forward to the friction engagement element 66 side, the air passage 90 is positioned in the hydraulic chamber 76 on the support wall 36a side with respect to the rubber member 88. The hydraulic pressure can be maintained. As a result, a decrease in the hydraulic pressure in the hydraulic chamber 76 is prevented, and deterioration of the controllability of the friction engagement device due to a decrease in the hydraulic pressure in the hydraulic chamber 76 can be prevented.

  Further, according to the above-described embodiment, since the air passage 90 is provided at the upper end portion of the hydraulic chamber 76, the air is efficiently discharged, and the controllability of the hydraulic pressure is further improved.

  Further, according to the above-described embodiment, the rubber member 88 is provided on the hydraulic chamber 76 side of the annular piston 72, and the ventilation path 90 is provided on the outer peripheral wall surface 84 a of the annular annular hole 84. Since 90 is disposed at the uppermost position of the hydraulic chamber 76, air is discharged most efficiently, and the controllability of the hydraulic pressure is further improved.

  In addition, according to the above-described embodiment, the flow cross section of the air passage 90 is formed sufficiently smaller than the flow cross section of the oil passage 93 that supplies the hydraulic pressure to the hydraulic chamber 76, so that the friction engagement device 64 is ventilated. It is possible to function with almost no change in hydraulic pressure due to the passage 90.

  Further, according to the above-described embodiment, the friction engagement device 64 has a simple structure only by providing the air passage 90, and it is only necessary to add a process of providing the air passage 90, so that it is necessary to increase the number of parts. Therefore, a practical friction engagement device 64 is obtained.

  Next, another embodiment of the present invention will be described. In the following description, parts common to those in the above-described embodiment are denoted by the same reference numerals and description thereof is omitted.

  8 is obtained by fitting an O-ring 94 to the piston 72 instead of the rubber member 88 attached to the piston 72 in FIG. In this embodiment, the O-ring 94 corresponds to the seal member of the present invention. Also in this embodiment, the O-ring 94 performs the same function as the rubber member 88. When the piston 72 is located on the side of the support wall 36a indicated by the solid line, the hydraulic chamber 76 and the external space 92 communicate with each other through the air passage 90. When the hydraulic oil is supplied into the hydraulic chamber 76 and the piston 72 is moved to the position indicated by the broken line, the hydraulic chamber 76 and the external space 92 are blocked by the O-ring 94, and the hydraulic oil leaks. Be blocked. As a result, the same effect as in the above-described embodiment can be obtained, and the same characteristics as in FIG. 7 can be obtained.

  As mentioned above, although the Example of this invention was described in detail based on drawing, this invention is applied also in another aspect.

  For example, in the above-described embodiment, the vehicle drive device 10 is an FF type vehicle, but is not particularly limited to an FF type vehicle, and the present invention is applied to other types of vehicles such as an FR type vehicle. Can do.

  In the above-described embodiments, the present invention is applied to the brake device, but is not particularly limited, and can be applied to a clutch device.

  In the above-described embodiment, the cross section of the air passage 90 is formed in a semicircular shape as shown in FIG. 6, but these shapes are not particularly limited and can be freely changed. .

  In the above-described embodiment, the rubber member 88 is attached to the piston 72 and the ventilation path 90 is formed in the support wall 36a. However, the ventilation path 90 is formed in the piston 72 and the annular hole 84 of the support wall 36a is formed. Alternatively, the rubber member 88 can be attached to the surface.

  The above description is only an embodiment, and the present invention can be implemented in variously modified and improved forms based on the knowledge of those skilled in the art.

1 is a skeleton diagram illustrating a vehicle drive device to which the present invention is applied. FIG. 2 is a diagram illustrating engagement of a clutch and a brake for establishing each gear position of the vehicle automatic transmission of FIG. 1. It is sectional drawing which shows a part of automatic transmission for vehicles with which this invention was applied. It is an expanded sectional view for demonstrating the structure of the ventilation path of FIG. It is another expanded sectional view for demonstrating a structure of the ventilation path of FIG. It is the arrow line view which looked at the ventilation path of FIG. 4 from the arrow A direction. It is a chart which shows the responsiveness of the oil pressure command value of this example, and an actual oil pressure value. It is an expanded sectional view for demonstrating the ventilation path which is the other Example of this invention. It is a chart which shows the responsiveness of the oil pressure command value and actual oil pressure value of the conventional friction engagement device.

Explanation of symbols

  16: Automatic transmission 36a: Support wall (cylinder member) 64: Friction engagement device 68: Inward friction plate (friction plate) 70: Outward friction plate (friction plate) 72: Piston 76: Hydraulic chamber (piston hydraulic chamber) 84: Annular hole (cylinder hole) 88: Rubber member (sealing member) 90: Air passage (air venting oil passage) 93: Oil passage 94: O-ring (sealing member)

Claims (4)

By supplying a hydraulic pressure to a piston hydraulic chamber formed in the cylinder hole by the piston and the cylinder member, a piston fitted into the cylinder hole formed in the cylinder member so as to be slidable in the axial direction is provided. A friction engagement device for an automatic transmission for a vehicle for advancing in a central direction to press a friction plate,
One of the cylinder member and the piston is provided with a seal member that seals a gap between a wall surface of the cylinder hole and the piston,
An air vent oil passage is provided on the other of the cylinder member and the piston,
The air vent oil passage is positioned across the seal member when the piston is positioned on the retreat side, and when the piston moves forward, the air vent oil passage is located in the piston hydraulic chamber on the retreat side with respect to the seal member. A friction engagement device for an automatic transmission for a vehicle, wherein the friction engagement device is positioned.   The friction engagement device for an automatic transmission for a vehicle according to claim 1, wherein the air vent oil passage is provided at an upper end portion of the piston hydraulic chamber.   The cylinder hole is an annular cylinder hole, the piston is an annular piston, the seal member is provided at a rear end portion of the annular piston, and the air vent oil passage is formed on the annular cylinder hole. The friction engagement device for an automatic transmission for a vehicle according to claim 2, wherein the friction engagement device is provided on a wall surface on an outer peripheral side. The vehicle according to any one of claims 1 to 3, wherein a flow cross section of the air vent oil passage is formed sufficiently smaller than a flow cross section of an oil passage supplying hydraulic pressure to the piston hydraulic chamber. Friction engagement device for automatic transmission.

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