Description Title of Invention: TORQUE CONVERTER

Technical Field

[0001] The present invention relates to a torque converter that varies transmission torque by causing a friction material provided on the outer peripheral side of one face of a lockup clutch to be in any of an unlocked state in which the friction material is separated from the inner face of the front wall of a casing coupled to pump impellers, a state in which the friction material is in sliding contact with the inner face of the front wall of the casing, and a locked state in which the friction material is pressed against the inner face of the front wall of the casing so that sliding does not occur.

[0002] Note that as long as the torque converter of the present invention is configured so as to include a lock-up clutch, the inclusion or exclusion of a configuration having a torque amplification effect is irrelevant. Background Art

[0003] In recent years, there has been a trend towards incorporating a lock-up clutch in a torque converter of an automatic transmission included in a vehicle such as an automobile (e.g., see Patent Literature 1 to 5).

[0004] With such a torque converter, by causing the friction material of the lock-up clutch to be in a locked state of being forcibly pressed against the inner face of the casing, it is possible to eliminate a loss in the torque capacity that is transmitted from the output shaft of the internal combustion engine coupled to the casing to the input shaft of the automatic transmission via the lock-up clutch.

[0005] In the locked state, frictional heat is generated between the friction material and the casing. A rise in temperature readily occurs due to the frictional heat, particularly in the case in which the size of the friction material is reduced as much as possible in order to achieve a small size and light weight. Patent Literature 1 to 3, for example, have been proposed in order to prevent such a rise in temperature.

[0006] Firstly, in the conventional example according to Patent Literature 1, the friction face of the friction material is provided with a spiral groove, thus causing oil to flow in the spiral groove when the lock-up clutch is locked. The oil that enters the groove flows from the torque converter chamber to the lock-up oil chamber.

[0007] In the conventional example according to Patent Literature 2, the friction face of the friction material is provided with outer grooves that extend from one part of the outer peripheral side to another part of the outer peripheral side and inner grooves that extend from one part of the inner peripheral side to another part of the inner peripheral side, thus causing oil to enter these grooves when the lock-up clutch is locked. Oil from the torque converter chamber enters these grooves and is returned to the same torque converter chamber.

[0008] In the conventional example according to Patent Literature 3, the friction face of the friction material is provided with grooves that extend from the outer peripheral side and stop partway in the radial direction, and the end of the groove on the inner peripheral side is provided with a hole that penetrates in the thickness direction of the friction material, thus causing oil to enter the grooves when the lock-up clutch is locked. Oil from the torque converter chamber enters these grooves and is returned to the same torque converter chamber.

[0009] In these conventional examples, cooling is intended to be performed by supplying oil to areas of contact between the friction material and the casing during the locked state. However, although it is necessary to increase the frictional resistance at the areas of contact to securely obtain bonding force when the lock-up clutch is locked, there is concern that the bonding force will decrease when, for example, an oil film is formed in the areas of contact due to oil entering the grooves as described above.

[0010] With torque converters that include a lock-up clutch such as are described above, in addition to causing the friction material of the lock-up clutch to lock with the inner face of the casing, it is also known that slip control or flex lock-up control are performed in which the friction material of the lock-up clutch is caused to be in sliding contact with the inner face of the casing (e.g., see Patent Literature 4 and 5).

[0011] When the friction material is caused to be in the sliding contact state, a rise in temperature readily occurs due to frictional heat in the areas of sliding contact between the friction material and the member with which it is in contact, and the durability of the friction material readily decreases.

[0012] In the conventional example according to Patent Literature 4, the friction face of the friction material (corresponding to the friction lining 7) is provided with indentations (grooves 8 and 8') that extend from one part of the inner peripheral side to another part of the inner peripheral side, or indentations (grooves 8 and 8' that extend from one part of the outer peripheral side to another part of the outer peripheral side. As a result, when the lock-up clutch (corresponding to the pressure piston) is in the sliding contact state, oil is caused to flow in the indentations, thus cooling the areas of sliding contact, and when the lock-up clutch is locked, oil is prevented from flowing in the indentations, thus avoiding a reduction in bonding force during the locked state (during the pressurization state). In the conventional example according to Patent Literature 4, during both the sliding contact state and the locked state, the friction material of the lock-up clutch is in planar contact with the inner face of the front wall of the casing (corresponding to the housing 6).

[0013] In the conventional example according to Patent Literature 5, the friction material of the lock-up clutch and a friction material of the casing are both provided with grooves that extend along the radial direction at several places on the circumference. As a result, during slip control in which the two friction materials are relatively rotating, oil flows between the grooves of the two friction materials when the grooves align to be in communication with each other, and the flow of the oil is blocked when the grooves are not aligned with each other. Citation List

Patent Literature

[0014] PTL 1: JP H06-42606A PTL 2: JP 2000-329212A PTL 3: JP 2000-337475 A PTL 4: JP 2003-529724A PTL 5: JP 2008-185 IOOA Summary of Invention Technical Problem

[0015] Paragraph 0020 of Patent Literature 4 discloses that in this conventional example, both ends of each indentation (grooves 8 and 8') connect to either the low-pressure chamber or the high-pressure chamber, that is to say, they connect to the same pressure chamber, and therefore a pressure difference does not occur between the two ends of each indentation (grooves 8 and 8'). For this reason, even if oil enters the indentations (grooves 8 and 8') when the lock-up clutch is in the sliding contact state, it can hardly be thought that the oil is flowing. As a result, in the case of the conventional example according to Patent Literature 4, it must be said that there is almost no expectation of the oil having a cooling effect on the faces in sliding contact.

[0016] In the conventional example according to Patent Literature 5, while the lock-up clutch is in the sliding contact state (in the slip lock-up state), it is thought that oil flows from the outer peripheral side to the inner peripheral side via the grooves only when the grooves of one of the friction materials align with the grooves of the other friction material in the circumferential direction to be in communication with each other, and the flow of oil between the grooves is blocked when the grooves are not aligned with each other. In other words, oil flow is allowed only intermittently during the sliding contact state, and when the speed of relative rotation is high, it is thought that even oil flow is allowed, oil flow does not readily occur. Accordingly, in the case of the conventional example according to Patent Literature 5 as well, it must be said that there is almost no expectation of the oil having a cooling effect on the faces in sliding contact.

[0017] For reference, JP H07-208577A discloses providing the friction material (friction lining) of the lock-up clutch with grooves, thus causing the outer peripheral side and the inner peripheral side to be in communication with each other. While the lock-up clutch is in the locked state, the grooves constantly supply oil between the friction material and the member with which it is in contact. For this reason, as the oil flows from the outer peripheral side of the friction material to the inner peripheral side, the pressure difference between the outer peripheral side and the inner peripheral side decreases, and there is concern that the locked state cannot be securely maintained. In view of this, in this conventional example, a narrowed part is provided in part of the grooves in order to suppress the reduction in the pressure difference, but a coun- termeasure for addressing such a failure in the locked state is necessary, and performing processing for the grooves is troublesome.

[0018] In view of this situation, an object of the present invention is to enable an improvement in durability and operating reliability in a torque converter that includes a lock-up clutch. Solution to Problem

[0019] A torque converter according to the present invention is a torque converter, transmission torque being variable by causing a friction material provided on an outer peripheral side of one face of a lock-up clutch to be in any of an unlocked state of being separated from an inner face of a front wall of a casing coupled to a pump impeller, a state (sliding contact state) of being in sliding contact with the inner face of the front wall of the casing, and a locked state of being in pressure contact with the inner face of the front wall of the casing so as to not slide, and a friction face of the friction material being provided with a groove in which, in the sliding contact state, a continuous flow of oil from a torque converter chamber to a lock-up oil chamber is allowed, and in the locked state, the flow of oil is obstructed.

[0020] Note that the torque converter chamber is the space between a turbine runner and the lock-up clutch in the internal space of the casing, and the lock-up oil chamber is an opposing space between the inner face of the front wall of the casing and the lock-up clutch.

[0021] According to this configuration, in the sliding contact state in which the temperature readily rises due to frictional heat, oil continuously flows from the outer peripheral side of the friction material to the inner peripheral side through the groove, thus enabling constantly cooling the areas of sliding contact with new oil.

[0022] Originally, in the sliding contact state, due to the fact that internal pressure in the torque converter chamber is higher than the internal pressure in the lock-up oil chamber, the continuous flow of oil through the groove is smooth, and cooling is efficiently performed with oil that is always new. Furthermore, although causing the oil to flow through groove in this way is accompanied by a slight reduction in pressure in the torque converter chamber, the state in which the oil is flowing is the sliding contact state to begin with, and therefore the reduction in pressure is not an obstacle in performing control for the sliding contact state.

[0023] However, in the locked state, due to the fact that the flow of oil through the groove is blocked, there is no reduction in the pressure in the torque converter chamber, and the locked state can be securely maintained.

[0024] Note that in the locked state, frictional heat is not continuously generated between the inner face of the front wall of the casing and the friction material of the lock-up clutch since they are integrally joined such that sliding does not occur, and therefore cooling by the oil is not necessary.

[0025] Preferably, the groove is provided in an area from an outer peripheral edge of the friction material to partway in a radial direction of the friction material, in the sliding contact state, an outer peripheral side end of the groove is open to the torque converter chamber, and an inner peripheral side end of the groove is open to the lock-up oil chamber, and in the locked state, the inner peripheral side end of the groove is obstructed by an area of pressure contact between the inner face of the front wall of the casing and the friction material.

[0026] In this configuration, the form of the groove is specified. According to this specification, it is clear that in the sliding contact state, the outer peripheral side end of the groove is open to the torque converter chamber, the inner peripheral side end of the groove is open to the lock-up oil chamber, and the oil in the torque converter chamber flows into the lock-up oil chamber. It is also clear that in the locked state, the inner peripheral side end of the groove is obstructed, and the flow of oil is blocked.

[0027] Preferably, the groove is shaped as a straight line along a line that extends in the radial direction from a rotation center of the lock-up clutch, or is shaped as a straight line that is tilted with respect to the line that extends in the radial direction.

[0028] In this configuration, the form of the groove is specified so as to be simple.

According to this specification, it is clear that processing for forming the groove in the friction material can be performed simply. In other words, such a groove can be simply obtained by performing cutting or performing pressing by press molding.

[0029] Preferably, the groove is provided at a plurality of positions equidistantly on a circumference (along the outer peripheral edge) of the friction material.

[0030] According to this configuration, compared with the case of a single groove, much more oil can be supplied to the areas of sliding contact through the grooves in the sliding contact state, thus enabling uniformly cooling the friction material and the casing without variations in the circumference direction, and improving the cooling effect. [0031] Preferably, in the sliding contact state, the lock-up clutch is elastically deformed to an orientation in which at least an outer peripheral side area is tilted, and in the locked state, the lock-up clutch is elastically deformed to an orientation in which at least the outer peripheral side area is substantially parallel with the inner face of the front wall of the casing, the friction material is provided with a tapered chamfer in the outer peripheral area on the friction face, in which a thickness gradually decreases outwardly in the radial direction, and in the sliding contact state, the tapered chamfer of the friction material is in planar contact with the inner face of the front wall, and in the locked state, the tapered chamfer of the friction material is separated from the inner face of the front wall.

[0032] In this configuration, the operation mode of the lock-up clutch is specified.

According to this specification, when the lock-up clutch is tilted in the oblique orientation in the sliding contact state, the tapered chamfer of the friction material is in planar contact with the inner face of the front wall of the casing. Accordingly, in the sliding contact state, the torque capacity that is to be transmitted from the casing to the lock-up clutch side can be increased as much as possible.

[0033] Preferably, in the configuration in which the friction material is provided with the tapered chamfer, the inner peripheral side end of the groove is provided at a predetermined position crossing over to a flat face side from the tapered chamfer side of the friction material.

[0034] Here, the form of the grooves is specified based on the assumption of the configuration in which the friction material is provided with the tapered chamfer. According to this specification, it is clear that in the sliding contact state, the outer peripheral side end of the groove is open to the torque converter chamber, the inner peripheral side end of the groove is open to the lock-up oil chamber, and the oil in the torque converter chamber flows into the lock-up oil chamber, and furthermore, it is clear that in the locked state, the inner peripheral side end of the groove is obstructed, and the flow of oil is blocked.

Advantageous Effects of Invention

[0035] According to the present invention, in a torque converter including a lock-up clutch, when a lock-up clutch is in a sliding contact state in which the temperature readily rises due to frictional heat, a friction material of the lock-up clutch and the inner face of the front wall of a casing with which the friction material is in contact can be efficiently cooled with use of oil for operating the lock-up clutch. Furthermore, when the lock-up clutch is in a locked state, superfluous oil is prevented from entering areas of contact between the friction material of the lock-up clutch and the inner face of the front wall of the casing, thereby enabling securely maintaining the locked state. [0036] Accordingly, the present invention can contribute to an improvement in the durability and the operating reliability of a torque converter. Brief Description of Drawings

[0037] [fig. l]Fig. 1 is a diagram showing a schematic configuration of an example of a torque converter according to the present invention.

[fig.2]Fig. 2 is a front view of a friction material of a lock-up clutch shown in Fig. 1.

[fig.3]Fig. 3 is a perspective view of the friction material of the lock-up clutch shown in Fig. 2.

[fig.4]Fig. 4 is an enlarged view of part of Fig. 1, and shows an unlocked state of the lock-up clutch.

[fig.5]Fig. 5 is an enlarged view of part of Fig. 1, and shows a sliding contact state of the lock-up clutch.

[fig.6] Fig. 6 is an enlarged view of part of Fig. 1, and shows a locked state of the lockup clutch.

[fig.7]Fig. 7 is a front view showing part of a sliding contact area of the friction material of the lock-up clutch in Fig. 5.

[fig.8]Fig. 8 is a front view showing part of a contact area of the friction material of the lock-up clutch in Fig. 6.

[fig.9]Fig. 9 is a front view of a friction material of a lock-up clutch in another example of the present invention.

[fig.10] Fig. 10 is a front view of a friction material of a lock-up clutch in yet another example of the present invention.

[fig.1 l]Fig. 11 is a diagram showing an unlocked state of a lock-up clutch in still another example of the present invention.

[fig.12] Fig. 12 is a diagram showing a sliding contact state of the lock-up clutch in Fig.

11.

[fig.13]Fig. 13 is a diagram showing a locked state of the lock-up clutch in Fig. 11.

[fig.14] Fig. 14 is a diagram showing an unlocked state of a lock-up clutch in still yet another example of the present invention.

Description of Embodiments [0038] Below is a detailed description of preferred examples for realizing the present invention with reference to the attached drawings.

Example 1

[0039] Figs. 1 to 8 show one example of the present invention. First a schematic configuration related to a torque converter of Example 1 of the present invention will be described with reference to Fig. 1. [0040] A torque converter 3 is provided between an internal combustion engine 1 and an automatic transmission 2, and transmits torque generated by the internal combustion engine 1 to the automatic transmission 2 via oil (ATF: Automatic Transmission Fluid) that is a fluid filling the interior of the torque converter 3.

[0041] A pump impeller 4 that is coupled to a crank shaft (output shaft) Ia of the internal combustion engine 1, and a turbine runner 5 that is coupled to an input shaft 2a of the automatic transmission 2 are disposed so as to oppose each other in the torque converter 3. Also, a stator 6 is rotatably provided between the pump impeller 4 and the turbine runner 5 via a one-way clutch 7.

[0042] To briefly describe the operation of the torque converter 3, when the pump impeller 4 rotates along with the rotation of the crank shaft Ia of the internal combustion engine 1, oil flows in the torque converter 3, and this flow of oil applies rotational torque to the turbine runner 5, thus rotationally driving the input shaft 2a of the automatic transmission 2.

[0043] The torque converter 3 is also equipped with a lock-up clutch 8. The lock-up clutch 8 is disposed in the internal space of a casing 10, and is integrally and rotatably coupled to the input shaft 2a of the automatic transmission 2.

[0044] The casing 10 is configured from a casing shell 11 that is formed integrally with the pump impeller 4, and a front cover 12.

[0045] A predetermined gap 14 is provided between an outer casing wall 12a of the front cover 12 and a tubular curved piece 8 a formed on the outer periphery of the lock-up clutch 8. The gap 14 is provided so as to enable part of the oil in a torque converter chamber 15 to move toward a lock-up oil chamber 16 due to the flow of oil caused by the rotation of the pump impeller 4.

[0046] The torque converter chamber 15 is the space between the turbine runner 5 and the lock-up clutch 8 in the internal space of the casing 10, and the lock-up oil chamber 16 is an opposing space between the lock-up clutch 8 and the inner face of the front wall of the front cover 12 of the casing 10.

[0047] A friction material 21 is provided integrally in an outer peripheral side area of one face of the lock-up clutch 8.

[0048] The friction material 21 is formed so as to be disc-shaped, and the outer peripheral side area of the friction face of the friction material 21 is provided with a tapered chamfer 22 such that the thickness gradually decreases outwardly in the radial direction. The friction material 21 is provided with grooves 23 at several places (e.g., 3 places) at equidistant intervals on the circumference (along the outer peripheral edge) of the friction material 21.

[0049] Each of the grooves 23 is formed in the shape of a straight line along a line (Ll, L2, or L3) that extends in the radial direction from a rotation center O of the lock-up clutch 8. For each of the grooves 23, the outer peripheral side end is free at the outer pe- ripheral edge of the friction material 21, and the inner peripheral side end is provided at a predetermined position that crosses over to a flat face 24 side from the tapered chamfer 22 side of the friction material 21.

[0050] Although described in detail later, each of the grooves 23 is an oil channel that allows oil to flow from the torque converter chamber 15 to the lock-up oil chamber 16 when the tapered chamfer 22 of the friction material 21 is in sliding contact with the front cover 12. The depth and total length of each of the grooves 23 is therefore set appropriately in accordance with a required oil flow amount.

[0051] The following describes a basic operation of the lock-up clutch 8.

[0052] The lock-up clutch 8 operates according to a pressure difference between a torque converter apply pressure PA and a torque converter release pressure PR shown in Fig. 1.

[0053] Firstly, if a certain condition for operating the lock-up clutch 8 is not satisfied, that is to say, if PR>=PA, the lock-up clutch 8 remains in an unlocked state in which the orientation of the lock-up clutch is substantially unchanged in a natural state, and the friction material 21 of the lock-up clutch 8 is separated from the front cover 12, as shown in Fig. 4.

[0054] Note that the certain condition is set to a desired condition depending on the torque converter 3 itself or the relationship with the traveling condition of the vehicle in which the torque converter 3 is mounted. For example, the condition may be determined based on the traveling speed of the vehicle, and giving consideration to yet other conditions as well, the flow of the oil is controlled via an appropriate control apparatus or the like (not shown), and the lock-up clutch 8 is caused to be in the unlocked state, a locked state, or a sliding contact state. Note that the sliding contact state is, as is generally known, a state in which slip control or flex lock-up control is performed with respect to the lock-up clutch 8.

[0055] However, when the certain condition for operating the lock-up clutch 8 is satisfied, that is to say, when PR<PA, the lock-up clutch 8 elastically deforms toward the front cover 12 due to being subjected to the pressure of oil from the torque converter chamber 15, and the friction material 21 of the lock-up clutch 8 is pressed against the inner face of the front wall of the front cover 12.

[0056] Note that, at this time, depending on the magnitude of the oil pressure to which the lock-up clutch 8 is subjected, the contact state that the friction material 21 is in with respect to the front cover 12 is either the sliding contact state as shown in Fig. 5, or a complete pressure contact state (locked state) as shown in Fig. 6.

[0057] Here, in the example in which the lock-up clutch 8 is in the sliding contact state, as shown in Fig. 5, the lock-up clutch 8 elastically deforms into an oblique orientation, the tapered chamfer 22 on the outer peripheral side of the friction material 21 comes into planar sliding contact with the inner face of the front wall of the front cover 12, and the flat face 24 of the friction material 21 is separated from the front cover 12.

[0058] In the sliding contact state, as shown in Fig. 7, the opening of each of the grooves 23 provided in the friction material 21 is obstructed by the front cover 12, the outer peripheral side end of each of the grooves 23 is open to the torque converter chamber 15, and the inner peripheral side end of each of the grooves 23 is open to the lock-up oil chamber 16.

[0059] Moreover, in the sliding contact state, due to the fact that the torque converter chamber 15 and the lock-up oil chamber 16 are substantially isolated, the internal pressure of the torque converter chamber 15 is higher than the internal pressure of the lock-up oil chamber 16.

[0060] Due to this pressure difference, oil in the torque converter chamber 15 flows to the lock-up oil chamber 16 through the grooves 23 that are in the state described above.

[0061] While the oil is flowing in this way, the friction material 21 and the front cover 12 are appropriately relatively rotating and are in sliding contact, and therefore due to the sliding contact, the oil in the grooves 23 is drawn onto the faces of the front cover 12 and the friction material 21 that are in sliding contact. Accordingly, an oil film is stably formed on the faces that are sliding contact, and the faces in sliding contact are cooled, thus suppressing a rise in the temperature of the friction material 21 and the front cover 12.

[0062] Furthermore, in the example in which the lock-up clutch 8 is locked, as shown in Fig. 6, the friction material 21 of the lock-up clutch 8 is firmly pressed against the inner face of the front cover 12 such that the flat face 24 of the friction material 21 and the inner face of the front wall of the front cover 12 are in close contact, and the tapered chamfer 23 of the friction material 21 is separated from the inner face of the front wall of the front cover 12. Accordingly, the lock-up clutch 8 becomes integrated with the front cover 12 due to the frictional force between the flat face 24 of the friction material 21 and the front cover 12, and the lock-up clutch 8 integrally rotates along with the front cover 12.

[0063] In this state, as shown in Fig. 8, since the tapered chamfer 23 of the friction material 21 and the inner face of the front wall of the front cover 12 are separated from each other, the opening of each of the grooves 23 provided in the friction material 21 is exposed to the torque converter chamber 15, and the inner peripheral side end of each of the grooves 23 is obstructed by the front cover 12. Accordingly, the torque converter chamber 15 and the lock-up oil chamber 16 are completely isolated from each other.

[0064] In this state in which the grooves 23 are obstructed, the oil in the torque converter chamber 15 no longer flows to the lock-up oil chamber 16, and accordingly, the pressure difference between the torque converter chamber 15 and the lock-up oil chamber 16 is maintained at a certain value without decreasing. For this reason, the load for pressing the lock-up clutch 8 against the front cover 12 can be maintained at a certain value or greater, thus enabling securely maintaining the locked state.

[0065] As described above, according to the present example in which a characteristic feature of the present invention has been applied, when the lock-up clutch 8 is in the sliding contact state, that is to say, during slip control, the friction material 21 and the front cover 12 with which it is in sliding contact can be efficiently cooled by oil. Furthermore, when the lock-up clutch 8 is locked, a reduction in the pressure difference between the torque converter chamber 15 and the lock-up oil chamber 16 is prevented, and the flow of oil into areas between the flat face 24 of the friction material 21 and the front cover 12 that are in pressure contact and are immobile with respect to each other is prevented, thus enabling securely maintaining the locked state.

[0066] Particularly, in the present example, since the grooves 23 are formed equidistantly at several places on the circumference (along the outer peripheral edge) of the friction material 21, the amount of oil that is supplied to the areas of sliding contact during slip control can be increased as much as possible, which is advantageous in that the friction material 21 and the front cover 12 are cooled uniformly and without variations in the circumference direction.

[0067] Note that the present invention can be embodied in various other forms without departing from the spirit or relevant characteristic features of the present invention. Accordingly, the example described above is nothing more than exemplary in every respect, and should not be interpreted as limiting the present invention. The scope of the present invention is disclosed in the claims, and should not be restricted in any way to the body of the description. Furthermore, the present invention also encompasses all variations and modifications that fall within a scope equivalent to the scope of the claims. In other words, the present invention is not limited to only the above example, but rather can be modified or applied in any way that falls within the scope of the claims or a scope equivalent to the scope of the claims. Examples of variations and modifications are described below.

[0068] (1) The disposed number, disposition position, and disposition orientation of the grooves 23 provided in the friction material 21 of the lock-up clutch 8 described in the above example are not limited in any particular way, and can be modified appropriately.

[0069] For example, the present invention also includes cases in which the disposition orientation of the grooves 23 is as shown in Fig. 9 and Fig. 10.

[0070] Firstly, in the example shown in Fig. 9, the grooves 23 are formed in an orientation that is tilted at a predetermined angle "theta" with respect to the straight lines Ll, L2, and L3 that extend in the radial direction from the rotation center O of the lock-up clutch 8. Note that symbol character is described as alphabetical characters as shown below in this specification. Alphabetical character "theta" corresponds to symbol character

"θ".

[0071] In the case of such grooves 23, if the rotation direction of the lock-up clutch 8 is specified to be, for example, the clockwise direction shown in Fig. 9 (the solid line arrows), the grooves 23 are so-called "against the grain". Conversely, if the rotation direction of the lock-up clutch 8 is specified to be, for example, the counter clockwise direction shown in Fig. 9 (the broken line arrows), the grooves 23 are so-called "with the grain".

[0072] These grooves 23 that have a tilted orientation can have a longer total length than the case in the example shown in Fig. 2, and therefore the cooling effect is improved since, for example, a larger amount of oil is supplied to the faces of the friction material 21 and the front cover 12 that are in sliding contact, and an oil film is readily formed on the faces in sliding contact.

[0073] Also, in the example shown in Fig. 10, a groove 23 is formed in the shape of a straight line that connects two separated points X and Y on the outer circumference of the friction material 21, and is parallel to a tangent line L4 that is tangent to a central position Z on the outer circumference of the friction material 21 that is central with respect to the two points. Two or more of this groove 23 can be disposed.

[0074] In this case, the area on one end side and the area on the other end side of the groove

23 are located in the tapered chamfer 22, and the middle area is located in the flat face

24 of the friction material 21.

[0075] In view of this, assuming that the lock-up clutch 8 is in the sliding contact state, that is to say, during slip control, the openings in the areas in the two end areas of the groove 23 provided in the friction material 21 are obstructed by the front cover 12, the two ends of the groove 23 are open to the torque converter chamber 15 in the internal space of the casing 10, and the opening in the middle area of the groove 23 is open to the lock-up oil chamber 16 between the front cover 12 and the lock-up clutch 8.

[0076] However, due to the fact that the torque converter chamber 15 and the lock-up oil chamber 16 are in a substantially non-communicative state, the internal pressure of the torque converter chamber 15 is higher than the internal pressure of the lock-up oil chamber 16.

[0077] In accordance with the above, due to the pressure difference between in the two chambers 15 and 16, the oil in the torque converter chamber 15 flows into the groove 23 from the two ends thereof, and flows out from the middle area of the groove 23 to the lock-up oil chamber 16. Thus, oil is supplied to the faces of the friction material 21 and the front cover 12 that are in sliding contact, and the friction material 21 and the front cover 12 are cooled.

[0078] This groove 23 that is shaped as a long straight line can also have a longer total length than the case in the example shown in Fig. 2, and therefore the cooling effect is improved since, for example, a larger amount of oil is supplied to the faces of the friction material 21 and the front cover 12 that are in sliding contact, and an oil film is readily formed in the faces in sliding contact.

[0079] (2) Although the grooves 23 provided in the friction material 21 of the lock-up clutch 8 in the above example are shaped as a straight line in a planar view, the grooves 23 can also have an appropriately curved configuration in the planar view. The form of this curve is arbitrary.

[0080] (3) The tapered chamfer 22 may be omitted from the friction material 21 of the lockup clutch 8 in the above example.

[0081] In this case, for example, after transitioning from the unlocked state of the lock-up clutch 8 shown in Fig. 11 to the execution of slip control as shown in Fig. 12, the outer peripheral side area of the friction material 21 is in sliding contact with the front cover 12, and the oil in the torque converter chamber 15 flows into the lock-up oil chamber 16 through the grooves 23.

[0082] However, as shown in Fig. 13, when the entire face of the friction material 21 is in the locked state of being in pressure contact with the front cover 12, the entire opening of the groove 23 as well as the inner peripheral side end thereof are obstructed by the front cover 12, and the oil in the torque converter chamber 15 no longer flows into the lock-up oil chamber 16.

[0083] Note that although the grooves 23 can be formed to a depth that is a point partway in the thickness direction of the friction material 21 as shown in Fig. 11, it is also possible to provide the grooves 23 such that, for example, they penetrate from one side face of the friction material 21 to the other side face as shown in Fig. 14.

[0084] (4) Although the above example is described using the example of the torque converter 3 of the automatic transmission 2 mounted in a vehicle such as an automobile, the present invention can also be applied to a torque converter of an automatic transmission mounted in a device other than a vehicle.

[0085] (5) Although the above example is described using the example of the torque converter 3 that has a torque amplification effect, the present invention is applicable even in the case of, for example, a configuration that does not have a torque amplification effect, such as a torque converter that does not include the stator 6, as long as the lock-up clutch 8 is included. For reference, a torque converter that does not have a torque amplification effect is called, for example, a fluid coupling or a hydraulic transmission apparatus. [0086] Note that this application claims priority rights based on JP 2008-294300A filed in

Japan on November 18, 2008. The entire content thereof is hereby incorporated by reference in this application.

Industrial Applicability [0087] The present invention is applicable to a torque converter having a configuration that includes a lock-up clutch.

Reference Signs List [0088] 1 internal combustion engine

Ia crank shaft (output shaft) of internal combustion engine

2 automatic transmission

2a input shaft of automatic transmission

3 torque converter

4 pump impeller

5 turbine runner 8 lock-up clutch

10 casing

11 casing shell

12 front cover

15 torque converter chamber in internal space of casing

16 lock-up oil chamber between front cover and lock-up clutch

21 friction material

22 tapered chamfer of friction material

23 groove in friction material

24 flat face of friction material