Clutch or Brake System for a Heavy Duty Vehicle

Heretofore clutch and brake systems for heavy duty vehicles have been beset with one or more of the following shortcomings, which are described primarily in the context of a brake system but have like application to clutch systems as well which is apparent to those skilled in the art:

a) there is an inordinate amount of thermal expansion of the brake drum during the braking mode due to heat transfer from the brake shoe resulting in an undesirable and unsafe brake fading condition; b) where disc brakes are utilized in the system, the heat generated during the braking mode is transferred to the hydroscopic brake fluid causing the latter to boil producing gas bubbles entrapped within the system thereby seriously affecting the responsiveness of the disc brake shoes to the travel of the brake pedal; c) severe stress and fatigue are created within the liner and shoe due to the differential in the coefficient of thermal expansion between the liner and shoe; d) excessive wear of the liner occurs because of the mode of attachment of the liner to the shoe; e) there is ineffective noise and temperature shielding from the shoe; f) the system embodies an inordinate number of component parts some of which are of costly and complex design; and g) servicing of the system is a costly, difficult, time consuming and labor intensive operation.

An improved clutch or brake system has been provided which readily avoids the aforenoted shortcomings of the prior systems.

The improved system may be utilized in a variety of vehicles.

Because of the extensive contact area which exists between the carrier member and the molded liner assembled therewith, the improved system is possessed of superior shear strength in the plane of stress induced during the braking mode.

The improved system utilizes a thermal shield, which is positioned between the shoe and the carrier member/liner assembly prior to the assembly being secured to the shoe; thereby, in addition to the enhanced static, dynamic and fatigue strength properties of the system, highly desirable temperature and noise shielding from the brake shoe itself results during the braking mode.

Further and additional advantages and virtues possessed by the improved system will become apparent from the description, accompanying drawings and appended claims.

In accordance with one embodiment of the invention an improved clutch or brake system is provided which includes a shoe having a first coefficient of thermal expansion; a moldable friction liner aligned with a surface of the shoe; and a carrier member backing and being assembled with the liner. The carrier member/liner assembly is possessed of a second coefficient of thermal expansion. The assembly is attached to the shoe surface for limited relative adjustment with respect thereto so as to compensate for any differential in thermal expansions which might occur between the shoe and carrier member/liner assembly during the braking mode and thus relieve potential stress buildup within the system.

For a more complete understanding of the invention reference is made to the drawings wherein:

FIG. 1 is a fragmentary perspective view of one embodiment of the improved system removed from a heavy duty vehicle.

FIG. 2 is similar to FIG. 1 but showing the system components in exploded relation.

FIG. 3 is an enlarged top view of the carrier member shown in FIG. 2 and with the shanks of the attaching rivets in phantom lines.

FIGS. 4 and 5 are enlarged fragmentary sectional views taken respectively along lines 4--4 and 5--5 of FIG. 3.

FIG. 6 is an enlarged fragmentary sectional view taken along line 6--6 of FIG. 3 and showing the carrier member assembled with the molded brake liner.

Referring now to the drawings and more particularly to FIGS. 1 and 2 an improved clutch or brake system 10 is shown which is adapted for use on heavy duty vehicles including automobiles, trucks, aircraft, buses, recreation vehicles and the like. The system 10 is capable of being utilized with either disc or drum type brakes which are either hydraulically or pneumatically actuated. The system 10 as illustrated includes a shoe 11 formed of a durable metal or a high strength composite material. The shape and size of the shoe will depend upon the type and operating capabilities of the vehicle on which the system is to be installed. The shoe 11 has an exposed surface 11a to which a liner assembly 12 is attached by a plurality of rivets 13; see FIG. 2. The shoe is possessed of a first coefficient of thermal expansion.

The liner assembly 12 is provided with an apertured carrier member 14, sometimes referred to as an attachment plate. The carrier member is formed of a relatively thin gauge metal (e.g., 18ga to 22ga) and has a peripheral configuration akin to that of the shoe exposed surface. The member 14 is provided with a plurality of elongate apertures 15 arranged in substantially end to end relation and forming three generally parallel rows I, II and III; except, at opposite ends wherein a transversely extending elongate aperture 15a and a rivet hole R are formed. Each elongate aperture 15 has rounded ends 15b and is delimited by a continuous flange F which flares away from the shoe exposed surface 11; see FIGS. 4 and 5, and penetrates a short distance into the back side 16a of the liner 16 of a friction material, which is molded thereto; see FIG. 6. While the flared flanges F present a low profile there is nevertheless a strong bond established between the carrier member 14 and the liner 16 because during molding of the liner, portions thereof flow through the elongate apertures 15 and 15a and form keys K which interlock with the flared surfaces of the apertures when the friction material hardens; see FIG. 6. Because of the number, location and shape of the apertures 15 and 15a there is extensive contact area between member 14 and liner 16; thus, resulting in the liner assembly 12 being possessed of superior shear strength in the plane of stress induced during the braking mode. The shear strength is limited only by the method of attachment of the assembly to the shoe exposed surface.

As seen in FIG. 3, carrier member 14 is provided with a plurality of rivet holes R which are arranged in a predetermined pattern. The pattern corresponds to the pattern of rivet holes RR formed in shoe 11; see FIG. 2. The size and shape of holes RR correspond substantially to the cross-sectional configuration of the shanks 13a of the rivets. The size and shape of holes R, on the other hand, are oversized relative to the rivet shanks so as to permit limited relative movement between carrier member/liner assembly 12 and shoe 11 during the braking mode. Due to a differential in the coefficients of thermal expansion between the assembly 12 and shoe 11, the limited relative movement permitted by the oversized holes R compensated for such differential and thus, avoids undesirable induced stress and fatigue buildup within the components.

Another serious problem which previously existed in many prior art systems related to inadequate shielding of the noise and heat generated at the interface between the shoe and liner during the braking mode. This thermal problem frequently created a serious and unsafe condition known as "brake fading". Such condition occurs normally in a drum-type braking system wherein the heat generated during the braking mode is transmitted to the drum itself causing the later to expand thus, necessitating greater force being applied to the brake pedal in order to actuate the shoe to a required braking relation with the drum. A similar situation oftentimes occurs in prior disc-type braking systems wherein a hydroscopic braking fluid is employed as a means for actuating the braking discs. In such a situation the brake fluid is heated to a boiling state by the heat generated during the braking mode. When boiling of the brake fluid occurs, air bubbles become entrapped within the system thereby rendering the actuation of the discs less responsive to the distance of travel of the brake pedal.

Besides the problems caused by the heat generated during the braking mode, there is also the problem of noise created in prior braking systems when in the braking mode.

The improved system 10 resolves both the heat and noise problems by the utilization of a layer 17 of a thermal/acoustic barrier material (e.g., silicone impregnated compressed Kaolin fiber) which remains stable under varying operating condition. Layer 17 may be in the form of a pad per se or in the form of a thin pad sandwiched between two thin metal sheets, not shown. In either case, the layer 17 is positioned between the exposed surface 11a of the shoe and the underside of the carrier member/liner assembly 12. Layer 17 preferably covers the entire shoe surface 11a and is provided with at least the same number of rivet holes as provided in the shoe.

The arrangement and configuration of the apertures 15 and 15a and the rivet holes R in the carrier member 14 may vary from that shown without adversely affecting the scope of the disclosed invention. Under any circumstances it is important that the apertures not materially weaken the strength and durability of the carrier member. Furthermore, the flanges F delimiting the apertures must provide maximum contact area between the carrier member and the liner molded thereto and at the same time provide a low profile. The improved system embodies a minimum number of component parts, is easy to manufacture and install, and effectively overcomes the aforenoted serious problems besetting prior systems of this general type.