Friction plate for wet-type multiplate clutch

A friction plate for a wet-type multiplate clutch provided with a core plate and friction linings fixed on opposite sides of the core plate, respectively. Each of the friction linings is formed such that at a section thereof located on a side radially inner than a radial center line thereof, the friction lining has a thickness that gradually increases from an inner circumferential portion of the section toward an outer circumferential portion of the section.

FIELD OF THE INVENTION

This invention relates to a friction plate for a wet-type multiplate clutch useful in an automatic transmission, friction device or the like. It is to be noted that the term “fragmentary sector” as used herein means a geometric figure bounded by two radii and the included arc of a larger circle without a geometric figure bounded by two radii and the included arc of a smaller circle, in which the larger and smaller circles are concentric with each other and the former radii and the latter radii overlap with each other, respectively.

DESCRIPTION OF THE BACKGROUND

To improve the fuel economy of automobiles, there is an outstanding demand for a reduction in the idling drag of wet-type multiplate clutches for use in automatic transmissions or the like. With a view to meeting this demand, it has been a conventional practice to form spiral grooves, outer-end-closed grooves or the like on the surfaces of friction linings in a clutch such that under a centrifugal force, a force which pulls off a counterpart member is produced at the surface of each friction lining to reduce a drag torque in a stable state during idling.

FIG. 1is a cross-sectional view illustrating the fundamental construction of a wet-type multiplate clutch. Separator plates3are connected through splines to spline grooves51on a drum5, while friction plates4which are arranged opposite the separator plates3are connected through splines to spline grooves82on a hub8. Upon engagement of the clutch, a piston9is pressed under a hydraulic pressure toward the right-hand side as viewed in the drawing so that the separator plates3and friction plates4are pressed as engagement members against a flange2and a snap ring1. As a consequence, a torque is transmitted from the drum5to the hub8. Designated at numeral81are lubrication holes arranged in the hub8.

The friction plates4are each provided with a core plate41in the form of a metal disc and friction linings7fixed on opposite sides of the core plate41, respectively. As mentioned above, the friction linings are each provided on a surface thereof with various oil passages or oil grooves so that owing to the production of a hydraulic pressure under a centrifugal force, forces which press the friction surfaces act to achieve a reduction in drag torque upon idling and a prompt release upon disengagement of the clutch.

With friction plates of the conventional construction, a large oil amount leads to a reduction in the coefficient of friction under the influence of pressure-producing grooves upon engagement of a clutch so that, while the engaging torque remains small, the engagement progresses and the torque abruptly increases at the end of braking time. Such a large oil amount, therefore, becomes a cause of a shift shock. It may, therefore, be contemplated to make the pressure-producing grooves smaller in an attempt to obtain adequate friction characteristics. This, however, leads to a reduction in the force at friction surfaces, said force serving to pull off the counterpart members during idling, thereby bringing about an increase in idling drag.

Substantial difficulties have been encountered in designing grooves such that they can achieve both a reduction in idling drag and adequate friction characteristics.

SUMMARY OF THE INVENTION

To resolve the above-described problems, the present invention provides, in one aspect thereof, a friction plate for a wet-type multiplate clutch, said friction plate being provided with a core plate and friction linings fixed on opposite sides of the core plate, respectively, wherein each of the friction linings is formed such that at a section thereof located on a side radially inner than a radial center line thereof, the friction lining has a thickness that gradually increases from an inner circumferential portion of the section toward an outer circumferential portion of the section.

In another aspect of the present invention, there is also provided a friction plate for a wet-type multiplate clutch, said friction plate being provided with a core plate and friction linings fixed on opposite sides of the core plate, respectively, wherein the friction linings are each segmented into fragmentary sectors, the fragmentary sectors are bonded on its corresponding side of the core plate, a predetermined plural number of the fragmentary sectors are each formed such that at a section thereof located on a side radially inner than a radial center line of the corresponding friction lining, the fragmentary sector has a thickness that gradually increases from an inner circumferential portion thereof toward an outer circumferential portion thereof, and the remaining ones of the radial friction lining segments have a uniform thickness.

Owing to the above-described constructions of the present invention, the present invention has made it possible to achieve both stable friction characteristics and a reduction in a drag upon idling.

FIG. 9shows one example of characteristics of engaging torque, in which engaging torque (N·m) is plotted along the ordinate while braking time is plotted along the abscissa. An alternate long and short dash line indicates the braking time versus engaging toque characteristics of friction plates of the conventional construction. It is appreciated that, when the oil amount is increased to reduce the idling drag, the torque is small at the beginning but abruptly increases in the last stage to develop a shift shock. On the other hand, the invention construction the braking time versus engaging toque characteristics of which are indicated by a solid line are appreciated to show stable friction characteristics throughout the engagement.

In the present invention, the friction linings on each friction plate are each formed such that at a section thereof located on a side radially inner than a radial center line thereof, the friction lining has a thickness that gradually increases from an inner circumferential portion of the section toward an outer circumferential portion of the section. Each of the friction linings can define a planar, curved or stepped surface at the section. Further, the section and a remaining section of each friction lining can be made of materials having different compression characteristics, respectively.

Referring first toFIG. 2, a friction lining7fixed on a core plate41of a friction plate4(seeFIG. 1), the entire radial width of said friction lining being indicated by letter A, is formed such that at an annular section70located on a side radially inner than a radial center line of the friction lining7, the friction lining7has a thickness that gradually increases from an inner circumferential portion of the annular section70toward an outer circumferential portion of the annular section70. It is to be noted that in each ofFIG. 2and the subsequent figures except forFIGS. 7 and 9, numeral41indicates a core plate and numeral42designates splines on an inner circumference of the core plate.

FIG. 3throughFIG. 6show friction plates according to the first to fourth embodiments of the present invention as viewed in cross-section along line C-C inFIG. 2. In the first embodiment depicted inFIG. 3, an annular section corresponding to the annular section70inFIG. 2defines a planar surface71with the thickness of said annular section gradually increasing from its inner circumferential portion toward its outer circumferential portion.

In the second embodiment shown inFIG. 4, the annular section defines a curved surface72, and in the third embodiment illustrated inFIG. 5, the annular section defines a stepped surface73. In the fourth embodiment illustrated inFIG. 6, an annular section74, which corresponds to the annular section70inFIG. 2, and a remaining section of a friction lining7are made of materials having different compression characteristics, respectively. The surfaces72,73and the surface71shown inFIG. 3define a radially inner section of the friction lining7, inward from a radial center line of the friction lining7, which has a thickness that gradually increases from an inner circumferential portion of said inner section toward an outer circumferential portion of said section. A radially outer section of the friction lining7, outer to the radial center line and having a uniform thickness is also shown in the drawings.

Referring back toFIG. 2, the radial width B of the annular section70the thickness of which gradually increases may desirably meet the following inequality: B<A/2 (A: the entire radial width of the friction lining7). With a view to ensuring an adequate flow and distribution of oil, radial oilways75can be arranged at suitable angular intervals in the direction of the circumference of the friction lining7as shown inFIG. 7. These radial oilways75can be formed on the friction lining7by either molding or cutting. As an alternative, as illustrated inFIG. 7, a friction lining can be segmented into fragmentary sectors7A. These fragmentary sectors7A can then be bonded on its corresponding side of a core plate41with angular intervals left therebetween such that oilways75are formed.

Reference is next had toFIG. 8. Instead of forming the section70, the thickness of which gradually increases from its inner circumferential portion toward its outer circumferential portion, over the entire circumference of the friction lining7of the friction plate4, a predetermined plural number of such fragmentary sectors,7AC, are each formed such that at a section thereof located on a side radially inner than a radial center line of the corresponding friction lining, the fragmentary sector has a thickness that gradually increases from an inner circumferential portion thereof toward an outer circumferential portion thereof, and the remaining ones of the fragmentary sectors,7AD, have a uniform thickness. Also as shown inFIG. 8, lubrication holes81of a hub8can be arranged in registration with the fragmentary sectors7AC, each of which includes a section70having a thickness that gradually increases from an inner circumferential portion thereof toward an outer circumferential portion thereof.

The friction linings on the friction plate according to the present invention are each formed such that at the section thereof located on the side radially inner than the radial center line thereof, the friction lining has a thickness that gradually increases from the inner circumferential portion of the section toward the outer circumferential portion of the section. It is, therefore, possible to reduce the drag torque upon idling even when an oil amount is controlled as desired, and further, to achieve both of the maintenance of stable friction characteristics upon engagement and a reduction in idling drag. Accordingly, a wet-type multiplate clutch making use of friction plates according to the present invention is suited for use in an automatic transmission, friction device or the like.

This application claims the priority of Japanese Patent Application 2004-293241 filed Oct. 6, 2004, which is incorporated herein by reference.