Bridging clutch for a torque converter, which includes an axial freewheel clutch

Abstract

A lock-up clutch (100) for a torque converter (10), wherein the lock-up clutch (100) comprises: a piston (106) containing a first wedge surface (140); and a support (12b) for supporting the piston (106), wherein the piston (106) is displaceable along the support (12b) in a first axial direction to cause the lock-up clutch (100) to engage; and a wedge (132) which includes a second wedge surface (138), wherein the wedge (132) is axially displaceable along the support (12b), the first wedge surface (140) is arranged and configured with respect to the second wedge surface (138) such that the contact between the first wedge surface (140) and the second wedge surface (138) limits an axial movement of the piston (106) in a second axial direction which is opposite to the first axial direction, wherein the piston (106) includes a stop surface (144) which contacts a further surface (142) of the wedge (132),wherein the stop surface (144) is configured to contact the further surface (142) of the wedge (132) when the piston (106) is displaced in the first axial direction to cause the bridging clutch to engage, wherein the piston (106) includes a groove (134) formed in a surface thereof, the groove (134) being defined by the stop surface (144) and an inclined surface forming the first wedge surface (140), wherein the wedge (132) is a conical ring held on the support (12b) in the groove (134), wherein the groove (134) is formed in an inner circumferential surface (106a) of the piston (106) and the conical ring is held on an outer circumferential surface (122a) of the support (12b), and wherein the piston (106) has a radially extending section (114), which is configured to contact a clutch disc and includes an axially extending section (116),which extends axially from a first end of the radially extending section (114), wherein the inner circumferential surface (106a) in which the groove (134) is formed is located at a second end of the radially extending section (114).

Description

The present disclosure relates generally to torque converters and in particular to lock-up clutches of torque converters. BACKGROUND OF THE INVENTION US patent 7,913,585 discloses a dual clutch that includes an axial clutch. US patent application 2015 / 0233431 A1 and US patent 8,292,055 disclose concentric slave cylinders that include axial clutches. Publications DE 198 22 665 A1 , DE 100 05 506 A1 , US 5 749 451 A , US 2015 / 0 233 431 A1 and DE 10 2013 213 183 A1 show further known state of the art. BRIEF SUMMARY OF THE INVENTION A bridging clutch for a torque converter with the features of claim 1 is provided. A torque converter is also provided. The torque converter includes the lock-up clutch and a damper assembly configured to transfer torque from the lock-up clutch to a transmission input shaft when the lock-up clutch is engaged. BRIEF DESCRIPTION OF THE DRAWINGS The present invention is described below with reference to the following drawings, wherein: Fig. 1 schematically shows a side cross-sectional view of a torque converter according to an embodiment of the present invention; and Fig. 2 schematically shows an enlarged view of an axial freewheel clutch of the torque converter shown in Fig. 1 with a first and a second wedge of the axial freewheel clutch in contact with each other; and Fig. 3 schematically shows an enlarged view of the axial freewheel clutch of the torque converter shown in Fig. 1, wherein the first and the second wedge are separated from each other. DETAILED DESCRIPTION The disclosure provides an embodiment of a piston for a lock-up clutch for a torque converter, comprising an axial freewheel clutch on a groove formed in the piston and extending around its circumference. The clutch consists of a small conical ring and a complementary groove in the piston, the clutch angles being selected such that displacement of the piston from the clutch disc is limited when the clutch is disengaged. In other words, the inclined surfaces form a wedge to prevent axial displacement of the piston and improve the controllability of the lock-up clutch. Fig. 1 shows a side cross-sectional view of a torque converter 10 according to an embodiment of the present invention. The torque converter 10 is rotatable about a central axis 11 and comprises a front cover 12, which is connected to the crankshaft of an internal combustion engine, and a rear cover 14, which forms a housing 16 for an impeller or a pump 18. The front cover 12 includes a cup-shaped section 12a, which is connected to a rear cover 14, and a hub section 12b, which includes a guide 12c for alignment with the crankshaft. The torque converter 10 also includes a turbine 20, which is arranged opposite the impeller 18, and a damper assembly 22, which is attached to the turbine 20. Furthermore, the torque converter 10 includes a stator 26 axially between the impeller 18 and the turbine 20 and a freewheel clutch 24, which holds the stator 26.The turbine 20 contains a plurality of blades 28, which are mounted on a rounded section 30 of the turbine 20 on a side of the turbine 20 facing the rear cover. Furthermore, the turbine 20 includes a radially inner extension 34 that projects radially inwards from the rounded section 30. On a side of the turbine 20 facing the front cover, this extension is connected to the damper assembly 22. The damper assembly 22 comprises two cover plates 36, 38, which axially hold an inner set of springs 40 between them, the cover plate 36 facing the turbine being riveted to the turbine 20 by a plurality of circumferentially spaced rivets 42. The damper assembly 22 further comprises a centrifugal vibration damper 44 at a radially outer end 46 of the cover plate 36 and a drive flange 48, which is arranged axially between the cover plates 36, 38. The drive flange 48 includes a drive hub 50 at a radially inner end thereof, which has a toothed profile 52 on its inner circumferential surface, serving for rotationally fixed connection to a drive shaft 54 ​​of the gearbox.The drive hub 50 is equipped with a multitude of seals on its outer circumferential surfaces, including a first seal 56 for sealing a first circumferential surface 58 against an inner circumferential surface 60 of a stator hub 62, a second seal 64 for sealing a second outer circumferential surface 66 of the drive hub 50 against a first inner circumferential surface 68 of the hub section 12b of the front cover, and a third seal 70 for sealing a third outer circumferential surface 72 of the drive hub 50 against a second inner circumferential surface 74 of the hub section 12 of the front cover. The first seal 56 is provided on an axial side of the drive hub 50 facing the rear cover, and the third seals 64 and 70 are provided on an axial side of the drive hub 50 facing the front cover.The second outer circumferential surface 66 of the drive hub 50 is located radially outside the third outer circumferential surface 72, so that the axial side of the drive hub 50 facing the front cover contains two steps 50a, 50b. The cover plates 36, 38 transmit torque from the turbine 20 via springs 40 to the drive flange 48. The drive flange 48, in turn, drives the drive shaft 54 ​​of the gearbox. Furthermore, the drive flange 48 includes slots 76 extending around its circumference for receiving the springs 40. Radially outside the springs 40, the cover plates 36, 38 are riveted together by a plurality of rivets 78 spaced apart around the circumference. The rivets 78 project through the cover plates 36, 38 into spaces on the circumference formed between outer tongues 80 extending from a radially outer end of the drive flange 48. A radially outer end 82 of the cover plate 38 forms a spring receptacle 84 for holding a set of radially outer springs 86. The spring receptacle 84 includes a rounded section 88 that follows an outline of approximately half the outer circumference of the springs 86.Another disc 90 of the damper assembly 22 includes a radially extending lower part 92, which is riveted to the side of the cover plate 38 facing the front cover by rivets 94. The disc 90 also includes axial end stops 96 for springs 86, which extend radially outward from the lower part 92 into circumferential spaces between the springs 86 within the spring receptacle 84. Each end stop 96 comprises a radially extending section 96a extending from the lower part 92 and an axially extending section 96b extending from a radially outer end of the radially extending section 96a. Furthermore, the disc 90 includes projections 98 that are radially offset around the circumference within the end stops 96 relative to those extending axially from the lower part 92. The torque converter 10 also includes a lock-up clutch 100, which is formed by an axially inner surface 102 of the front cover 12, a clutch disc 104, and a piston 106. The clutch disc 104 includes a radially extending engagement section 108, which has friction material 110a, 110b on its two axial surfaces. A first friction material 110a is configured to contact the axially inner surface 102, and a second friction material 110b is configured to contact the piston 106. Furthermore, the clutch disc 104 includes drive projections 112 at a radially outer end, which extend into circumferential gaps between the springs 86. Projections 98 of the disc 90 extend into spaces in the circumferential direction on a radially inner edge 112a of the projections 112, which are intended to prevent the clutch disc 104 from tilting. The piston 106 comprises a radially extending engagement section 114 for engaging the friction material 110b and an axially extending section 116 extending axially from a radially outer end of the engagement section 114. A hub section 12b is configured as a support for the piston 106, the hub section 12b being axially fixed and the piston 106 being axially displaceable with respect to the hub section 12b. The piston 106 is equipped with a radially inner seal 118a, which is held in a groove of the piston 106 on an inner circumferential surface 106a of the engagement section 114, and a radially outer seal 118b, which is provided in a groove of a first radial extension 120 of the hub section 12b on an inner circumferential surface 106b of the axially extending section 116.Seal 118a rests against the outer circumferential surface 122a of a second radial extension 122 of the hub section 12b, and seal 118b rests against an outer circumferential surface 120a of the first radial extension 120. The first and second radial extensions 120, 122 are radially fixed in position within the torque converter 10, and the piston 106 is displaceable along the seals 118a, 118b with respect to the first and second extensions 120, 122. The seals 118a, 118b ensure that a side of the first radial extension 120 facing the front cover, a side of the second radial extension 122 facing the rear cover and a side of the piston 106 facing the rear cover enclose a first pressure area 124a which is supplied with a fluid by a first pressure channel 126a formed in the hub section 12b.A second pressure region 124b is formed by an axially inner surface 102 of the front cover 12, a side of the second radial extension 122 facing the front cover, the side of the piston 106 facing the front cover, and the clutch disc 104. The second pressure region 124b is supplied with fluid via a second pressure channel 126b formed in the hub section 12b. The third seal 70 on the drive hub 50 seals the fluid entering the first pressure channel 126a against the fluid entering the second pressure channel 126b, and the second seal 64 on the drive hub 50 seals the fluid entering the second pressure channel 126b against a region on a side of the first radial extension 120 facing the rear cover. In the first pressure area 124a, a leaf spring 128 is provided, which elastically connects the piston 106 to the first extension 120. The leaf spring 128 extends axially between the side of the piston 106 facing the rear cover and the side of the first radial extension 120 facing the front cover, and pushes the piston 106 away from the clutch disc 104 towards the first radial extension. If the pressure in the first pressure area 124a is greater than the pressure in the second pressure area 124b by an amount sufficient to overcome the preload of the leaf spring 128, the bridging clutch 100 is locked by the piston 106 by engaging in the friction material 110b of the clutch disc 104 and enclosing the clutch disc 104 between the surface 102 of the front cover 12 and the piston 106, so that the drive flange 48 is connected to the front cover 12 in a rotationally fixed manner via the damper assembly 22. When the pressure in the second pressure area 124b and the force generated by the leaf spring 128 together form a force that is greater than the force exerted by the pressure in the first pressure area 124a, the bridging clutch 100 is released, so that the drive flange 48 is driven by the turbine 20 and the fluid flow between the impeller 18 and the turbine 20. To ensure controlled disengagement throughout the entire service life of the coupling 120, the piston 106 is equipped with an axial freewheel coupling 130. The coupling 120 comprises a first wedge surface 140, formed by a groove 134 in an inner circumferential surface 106a of the piston 106, and a second wedge surface 138, formed by a wedge in the form of a conical ring 132, which is attached to the outer circumferential surface 122a of the second radial extension 122. The conical ring 132 is provided in the groove 134 before the piston 106 is placed on the hub section 12b. According to an alternative embodiment, the conical ring 132 can be provided on the outer circumferential surface 120a of the first radial extension 120, and the groove 134 can be formed in the inner circumferential surface 106b of the piston 106. According to preferred embodiments, the conical part is made of a compliant material such as a soft metal, e.g.Formed from bronze or rubber. Fig. 2 shows an enlarged cross-sectional view of the axial freewheel clutch 130, in which the first and second wedges are in contact. The conical ring 132 includes an inner circumferential surface 136, which is flush with the outer circumferential surface 122a of the second radial extension 122 and the inclined wedge surface 138, which in this embodiment is frustoconical and abuts a complementary inclined wedge surface 140 of the groove 134. The inclined wedge surfaces 138, 140 are inclined at an acute angle α with respect to the central axis 11 (Fig. 1), with the inner circumferential surface 136 extending parallel to the central axis 11. Accordingly, the inclined wedge surfaces 138, 140 are also inclined at the acute angle α with respect to the inner circumferential surface 136. Furthermore, the conical ring 132 contains a radially extending surface 142, which extends from the inner circumferential surface 136 to the oblique wedge surface 138.The coupling angles α are chosen such that the displacement of the piston 106 (Fig. 1) from the clutch disc 104 (Fig. 1) is limited. That is, the inclined surfaces 138, 140 form a wedge, which prevents axial displacement of the piston 106 beyond a predetermined distance when the clutch 120 is disengaged, thus improving the controllability of the clutch. The groove 134 also includes a radially extending stop surface 144, which extends radially inward from the inclined wedge surface 140 to the inner circumferential surface 106a. When the clutch 100 (Fig. 1) is disengaged, the wedge surfaces 138, 140 engage, and the radially extending surface 142 is axially separated from the radially extending stop surface 144 by a distance X equal to the gap of the clutch 100.When the coupling 100 is locked, the wedge surfaces 138, 140 are spaced apart from each other, and the radially extending surface 142 rests against the radially extending stop surface 144, see Fig. 3 . It was mentioned above, with reference to Figures 1, 2 to 3, that the purpose of the conical ring 132 is to ensure a controlled gap between the piston 106 and the clutch disc 104 throughout the entire service life of the clutch 120. That is to say, the conical ring 132 ensures the axial distance X traveled by the piston 106 during disengagement throughout the entire service life of the clutch 120, even if the friction material 110a, 110b becomes thinner due to wear. After the torque converter 10 is assembled, the conical ring 132 is too far from the axially inner surface 102 of the front cover 12 and from the clutch disc 104, i.e., too far to the right in the views of Fig. 1, Fig. 2 to Fig. 3, and the axial surface of the piston 106 facing the front cover is too far from the axially inner surface 102 of the front cover 12.This can pose a problem because, when the piston 106 is actuated, the pressurized oil used to axially displace the piston 106 can flow through a gap formed between the piston 106 and the clutch disc 104, thus increasing the time required to build up pressure and consequently delaying the engagement of the clutch. However, during the first actuation cycle of the piston 106, the stop surface 144 of the piston 106 presses the radially extending surface 142 of the conical ring 132 axially against the clutch disc 104 and the axially inner surface 102 of the front cover 12, i.e., to the left in the views of Figs. 1, 2 to 3. When the piston 106 is now separated and moves axially away from the clutch disc 104 and the axially inner surface 102 of the front cover 12, the conical ring 132 prevents the piston 106 from moving too far away from the clutch disc 104 and the axially inner surface 102 of the front cover 12, i.e.The conical ring 132 limits the stroke of the piston 106 to ensure a narrow gap between the piston 106 and the friction material 110b. The contact between the wedge surfaces 138, 140 wedges the conical ring 132 between the wedge surface 140 of the piston 106 and the outer circumferential surface 122a of the second radial extension 122 of the hub section 12b, thus preventing the conical ring 132 from moving axially further away from the clutch disc 104 and the axially inner surface 102 of the front cover 12, i.e., to the right in the views of Fig. 1, Fig. 2 to Fig. 3. In other words, the conical ring is clamped radially towards the hub section 12b. As the friction surfaces 110a, 110b wear, the piston 106, through contact between the stop surface 144 of the piston 106 and the radially extending surface 142 of the conical ring 132 during the actuation cycles of the piston 106, and through contact between the wedge surfaces 138, 140 during the disengagement cycles of the piston 106, moves the conical ring further towards the clutch disc 104 and the axially inner surface 102 of the front cover 12, i.e., to the left in the views of Fig. 1, Fig. 2 to Fig. 3, and keeps the stroke X of the piston 106 unchanged.Since the piston 106 restores the position of the conical ring 132, a very tight tolerance can be maintained, as only the relationship between the wedge surface 140 and the stop surface 144 of the piston 106 and the relationship between the wedge surface 138 and the radially extending surface 142 of the conical ring 132 need to be taken into account. According to other embodiments, the wedge can also be formed by strips or segments of a material instead of by the conical ring 132. In the preceding description, the invention has been described with reference to certain exemplary embodiments and examples thereof. However, it is clear that various modifications and changes can be made to these without deviating from the broader essence and scope of protection of the invention, which are set forth in the following claims. Accordingly, the description and the drawings are not to be regarded as a limitation, but rather as an illustration.

Claims

A lock-up clutch (100) for a torque converter (10), wherein the lock-up clutch (100) comprises: a piston (106) containing a first wedge surface (140); and a support (12b) for supporting the piston (106), wherein the piston (106) is displaceable along the support (12b) in a first axial direction to cause the lock-up clutch (100) to engage; and a wedge (132) which includes a second wedge surface (138), wherein the wedge (132) is axially displaceable along the support (12b), the first wedge surface (140) is arranged and configured with respect to the second wedge surface (138) such that the contact between the first wedge surface (140) and the second wedge surface (138) limits an axial movement of the piston (106) in a second axial direction which is opposite to the first axial direction, wherein the piston (106) includes a stop surface (144) which contacts a further surface (142) of the wedge (132),wherein the stop surface (144) is configured to contact the further surface (142) of the wedge (132) when the piston (106) is displaced in the first axial direction to cause the bridging clutch to engage, wherein the piston (106) includes a groove (134) formed in a surface thereof, the groove (134) being defined by the stop surface (144) and an inclined surface forming the first wedge surface (140), wherein the wedge (132) is a conical ring held on the support (12b) in the groove (134), wherein the groove (134) is formed in an inner circumferential surface (106a) of the piston (106) and the conical ring is held on an outer circumferential surface (122a) of the support (12b), and wherein the piston (106) has a radially extending section (114), which is configured to contact a clutch disc and includes an axially extending section (116),which extends axially from a first end of the radially extending section (114), wherein the inner circumferential surface (106a) in which the groove (134) is formed is located at a second end of the radially extending section (114). Bridging coupling (100) according to claim 1, which further comprises a seal (118a) between the second end of the radially extending section (114) and the outer circumferential surface (122a) of the holder (12b). A lock-up clutch (100) according to claim 1, further comprising an axially inner surface (102) of the front cover (12) of a torque converter (10) and a clutch disc (104) which is axially enclosed between the axially inner surface and the piston (106), wherein the piston (106) is axially displaceable in the first direction to press the clutch disc (104) against the axially inner surface (102) and thus cause the lock-up clutch (100) to engage, wherein the first wedge surface (140) is arranged and configured with respect to the second wedge surface (138) such that the contact between the first wedge surface (140) and the second wedge surface (138) limits axial movement of the piston (106) away from the clutch disc (104). Bridging clutch (100) according to claim 1, which further comprises a leaf spring (128) connected to the piston (106) which preloads the piston (106) in the second axial direction. Bridging clutch (100) according to claim 1, wherein the holder (12b) is a hub section of the front cover (12). Bridging clutch (100) according to claim 5, wherein the hub section of the front cover (12) includes a first radial extension (120) and a second radial extension (122) and the piston (106) is displaceable along the first radial extension (120) and the second radial extension (122). Torque converter (10) comprising: the lock-up clutch (100) according to claim 1; a damper assembly (22) configured to transmit torque from the lock-up clutch (100) to a drive shaft (54) of the transmission when the lock-up clutch (100) is locked.

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