GB1580510A

GB1580510A - Frictional engagement apparatus

Info

Publication number: GB1580510A
Application number: GB2857379A
Authority: GB
Original assignee: Caterpillar Tractor Co
Current assignee: Caterpillar Inc
Priority date: 1977-04-11
Filing date: 1978-02-03
Publication date: 1980-12-03
Also published as: DE2812852A1; JPS5550216B2; JPS5540389A; FR2387379A1; GB1580509A; JPS53126459A; CA1058099A

Description

( 21) Application No 28573/79

( 62) Divided out of No 1580509 ( 22) Filed 3 Feb 1978 ( 31) Convention Application No 786179 ( 32) Filed 11 April 1977 in ( 33) United States of America (US) ( 44) Complete Specification published 3 Dec 1980 ( 51) INT CL 3 F 16 D 13/38 ( 52) Index at acceptance F 2 C 1 C 3 B 4 1 C 6 ( 72) Inventor JAMES ROBERT STURGES ( 54) FRICTIONAL ENGAGEMENT APPARATUS ( 71) We, CATERPILLAR TRACTOR CO, a corporation organized and existing under the laws of the State of California, United States of America, of 100 N E Adams Street, Peoria, Illinois 61629, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the

following statement:-

The invention relates to a frictional engagement apparatus.

In accordance with the present invention, a frictional engagement apparatus comprises a plate comprising a metallic disc, with an elastomeric material fixed to a face of the disc, the elastomeric material being formed into a plurality of upraised arcuate lands and adjacent arcuate grooves separating adjacent lands, the lands and grooves being generally concentric with the disc, the ratio, R, of the width of a respective land to the sum of the width of the respective land plus the width of a respective adjacent groove falling within a range of between 0 80 and 0 30; and a reaction member having a generally flat surface for engagement with the face of the plate disc, means for propelling the reaction member and elastomeric material covered face of the disc into frictional engagement with one another; and means for supplying a fluid to the elastomeric material covered face of the disc; wherein the width of a land is large compared with the maximum overall variation in flatness of the reaction member surface.

Preferably, the grooves have a substantially smoothly curved crosssection.

An example of a frictional engagement apparatus constructed in accordance with the present invention is illustrated in the accompanying drawings, in which:Figure 1 is a plan view of the plate; Figure 2 illustrates the apparatus partially in section and partially schematically; Figure 3 illustrates, in cross-section, lands of a plate for frictional engagement in accordance with the present invention; and, Figure 4 illustrates graphically a determination of the elastomeric strain limit of an elastomeric material on the plate.

Adverting first to Figure 1, there is illustrated therein a disc 10 made of metal such as steel, the disc 10 having a central plurality of teeth 12 for engagement with a driving member therefor An elastomeric material 14 is affixed to a side 16 of the disc The elastomeric material 14 is formed into a plurality of upraised arcuate lands 18 generally concentric with the disc 10 and a plurality of corresponding arcuate grooves separating adjacent of the lands 18.

In operation, the disc 10 is engaged with a reaction member 22 as by urging the disc towards the reaction member 22 by use of a motor illustrated schematically at 24 which may be driven by a pump 26 or the like The pump 26 can also supply a fluid via a line 28 and a passage 30 to the elastomeric material covered side 16 of the disc 10 and more particularly to the grooves and lands 18 The motor 24 thus serves to force the lands 18 into frictional engagement with the reaction member 22.

It has been discovered that a serious problem exist when an apparatus as just described is utilized In brief, this problem consists of a rupturing along the length of the lands 18 as they are subjected to frictional engagement with the reaction member 22 The present invention particularly relates to the physical relationship between the widths of the lands 18 and the grooves 20 that is necessary to assure that rupturing does not occur.

Figure 3 shows a pair of lands 18 with a groove 20 therebetween It has now been discovered that there is a critical PATENT SPECIFICATION

0 h Z ( 11) 1 580 510 1,580,510 relationship between the width of a land 18 and the sum of the width of said land 18 and the next adjacent groove 20 Thus if one defines the difference between a first side 32 of one land 18 and a first side 32 ' of the next adjacent land 18 as the lead between adjacent lands then the ratio of the width of the land 18 to the lead between adjacent lands, hereinafter referred to as the land to lead ratio is critical in preventing rupture initiation within each one of the lands 18.

Rupture initiation within lands 18 is not a simple phenomenon and has in fact been found to depend upon several factors First, rupture initiation has been found to be dependent upon the nominal pressure at which the disc 10 is pushed against the reaction member 22 Second, the rupture initiation has been found to be dependent upon the speed of rotation of the disc 10 as it contacts the reaction member 22 which in turn determines the temperature to which the elastomeric material 14 is raised by the frictional contact with the reaction member 22 Third, rupture initiation has been found to be dependent upon the spring rate of the particular elastomeric material 14 utilized.

Fourth, rupture initiation has been found to be dependent upon the degree of smoothness of the reaction member 22 where it contacts the lands 18 The overall relationship is relatively complex and if one calculated a strain profile within a land 18 one would obtain a contour diagram generally as shown in Figure 3 wherein the maximum or peak strain would occur in the regional island 34 Further, with a disc 10 having an elastomeric material 14 thereon as illustrated in Figure 2 used against a reaction member 22 it is necessary that a hydraulic fluid such as oil or the like be present upon the lands 18 since a great majority (generally over 90 %) of the clutching or braking force between the lands 18 and the reaction member 22 is taken up in shear of the oil layer therebetween Thus, an upper limit is placed upon the land to lead ratio since if this upper limit is exceeded oil cannot be properly applied to the lands 18 and hence the frictional engagement between the lands 18 and the reaction member 22 will not provide the necessary frictional force through shearing of the oil layer.

Briefly, it has been discovered that if one defines the land to lead ratio as R then 0.80 >R> 0 755-1051 (S/(P+kd)).

In the above equation P equals the engagement pressure expressed in psi applied to engage the elastomeric material covered side of the disc with a reaction member In other words, P is the nominal pressure applied between the disc 10 and the reaction member 22 A variation in the flatness of the generally flat reaction member 22 is d and is normally expressed in inches A linear spring rate constant of the elastomeric material is represented by k and is generally expressed in psi per inch S is equal to the elastic strain limit, expressed as a decimal, of the elastomeric material 14.

The elastic strain limit of the material 14 is determined by testing samples thereof and the results of such testing on one particular material, namely a copolymer of vinylidene fluoride and hexafluoropropylene sold commercially under the trademark Viton by Du Pont is shown in Figure 4 This particular material also included about 36 weight percent carbon black and about 40 weight percent glass fibers A line 36 represents a number of test cycles to which an elastomeric material 14 shaped into lands 18 and grooves 20 and fixed to a disc can be subjected before rupture thereof will occur The elastomeric strain limit is illustrated by a line 38 which indicates that so long as the elastomeric strain limit is not exceeded, then the elastomeric material 14 will not fail even after as many as one million cycles under the fatigue test The fatigue test which was performed comprises using an oscillating load foot of variable force capability to apply a uniform pressure on a representative sample of the moulded friction material in an oil bath at the clutch operating temperature, namely a nominal 2500 F.

It has been found that the above relationship holds especially well and is especially useful when P falls within a range between 100 psi and 800 psi and more preferably within a range between 250 psi and 600 psi It is also preferred that k falls within a range from about 40 psi per inch to about 400 psi per inch and more preferably in a range from about 60 psi per inch to about 120 psi per inch Generally it is preferable that the reaction member 22 be substantially flat and thus it is preferred that d falls within a range between 0 0001 inch and 0 005 inch and more preferably within a range between 0 0005 inch and 0.004 inch Preferably an elastomeric material 14 is chosen so that S falls in a range between 0 05 and 0 20 and more preferably between 0 10 about 0 18 R must fall within a range between 0 8 and 0 3 and more preferably within a range from about 0.75 to about 0 45.

The elastomeric material 14 preferably comprises between 20 % and 50 % by weight of an elastomer which elastomer is preferably a fluoroelastomer such as a copolymer of hexafluoropropylene and vinylidene fluoride but which elastomer can also advantageously be polyacrylate, polyacrylonitrile, silicone, fluorosilicone, polychloroprene, or polyurethane and copolymers and mixtures thereof Said elastomeric material further preferably comprises between 12 % and 40 % of carbon black and between 20 % and 60 %o of glass or ceramic asperite particles 40 per 20 % to % by weight of elastomer, generally uniformly dispersed throughout the elastomer The asperite particles 40 form hard particles in the relatively soft elastomeric material 14 and it is believed that the edges of the asperite particles 40 tend to increase the shear of the hydraulic fluid introduced to the lands 18 thus providing better frictional characteristics thereto.

In the copending parent application No.

Claims

4413/78 Serial No 1580509 we claim a plate

for frictional engagement with a generally flat reaction member, the plate comprising a metallic disc with an elastomeric material fixed to a face of the disc, the elastomeric material being formed into a plurality of upraised arcuate lands and adjacent arcuate grooves, each groove having a substantially smoothly curved crosssection, the grooves separating adjacent lands, the lands and grooves being generally concentric with the disc, and the ratio, R, of the width of a respective land to the sum of the width of the respective land plus the width of a respective adjacent groove falling within a range of between 0 80 and 0.30.

WHAT WE CLAIM IS:1 A frictional engagement apparatus comprising a plate comprising a metallic disc, with an elastomeric material fixed to a face of the disc, the elastomeric material being formed into a plurality of upraised arcuate lands and adjacent arcuate grooves separating adjacent lands, the lands and grooves being generally concentric with the disc, the ratio, R, of the width of a respective land to the sum of the width of the respective land plus the width of a respective adjacent groove falling within a range of between 0 80 and 0 30 and a reaction member having a generally flat surface for engagement with the face of the plate disc, means for propelling the reaction member and elastomeric material covered face of the disc into frictional engagement with one another; and means for supplying a fluid to the elastomeric material covered face of the disc; wherein the width of a land is large compared with the maximum overall variation in flatness of the reaction member surface.
2 An apparatus according to claim 1, wherein the grooves have a substantially smoothly curved cross-section.

For the Applicants:GILL JENNINGS & EVERY, Chartered Patent Agents, 53 to 64, Chancery Lane, London WC 2 A IHN.
3 Printed for Her Majesty's Stationery Office, by the Courier Press, Leamington Spa, 1980 Published by The -Patent Office, 25 Southampton Buildings, London, WC 2 A l AY, from which copies may be obtained.

1,580,510