CA1098054A - Friction brake - Google Patents

Abstract

FRICTION BRAKE
Abstract of the Disclosure The present invention relates to a friction brake for a wheel which has a hub and is mounted for rotation about a central axis on an axle spindle. The brake is of the type which includes a housing mounted on an inward portion of the spindle to encircle the hub for sealed engagement therewith to define a sealed annular chamber about the hub and the spindle. A pair of disc units are coaxially aligned with the axis and with each other and are mounted within the chamber for movement along the axis. A first disc unit of the pair is non-rotatable and mounted relative to the housing and a second disc unit of the pair is rotatable and mounted relative to the hub. The first disc unit includes an outer disc and an inner disc with the remainder of the pair of disc units axially disposed therebetween. An annular brake acutating unit is mounted within the chamber in alignment with the pair of disc units for selective application of force to the inner disc as the outer disc makes contact with an interior wall of the housing. At least three cylindrical devices are mounted to the housing to extend in an axial direction into the chamber at generally equally circumferentially spaced locations about the inner disc and the outer disc.
Each of the devices has a biasing unit mounted thereon which make contact with the inner and the outer discs tending to increase the distance therebetween. A disc retainer is mounted on the device to produce a predeter-mined frictional contact therebetween which is greater than a maximum force generated by the biasing units. A
unit is provided for engaging the inner disc with the disc retainer to allow limited axial movement of the inner disc without causing the disc retainer to move along the device.
The actuating unit is capable of supplying sufficient force to the inner disc to overcome the predetermined frictional contact and the maximum force to position the disc retainer on the device to establish the location of the limited axial movement of the inner disc within the chamber.

Description

This is a division of Canadian patent application Serial No. 309,769 which was filed on 22 August 1978.
Background oE the Invention Field of the Invention. This invention relates to a -friction brake and, more particularly, to such a brake which includes a plurality of discs and is hydraulically cooled.
Description of the_Prior Art. There have heretofore been provided a number of friction brakes which utilize a plurality of discs and provide hydraulic oil for cooling the brake such as those disclosed in United States Patents

2,823,770; 3,580,369; and 3,~84,708. Although brakes of this type include a number oE configurations and have been successfully utilized to provide reliable braking of a wheel mounted on an axlet there continues to exist a need for such brakes which are more reliable, easier to install and more accessible for repair.
Summary oE the Invention In accordan~e with an aspect of the invention there is provided an improved friction brake for a wheel which has a hub and is mounted for rotation about a central axis on an axle spindle, said brake being of the type which includes a housing mounted on an inward portion o~ said spindle to encircle said hub for sealed engagement therewith to define a sealed annular chamber about said hub and said spindle, a pair of disc means coaxially ali~ned with said axis and with each other and mounted within said chamber for movement along said axis, a first disc means of said pair being non-rotatable and mounted relative to said housing and a second disc means of said pair being rotatable and mounted relative to said hub, said first disc means including an outer disc and an inner disc with the remainder of said pair of disc means axial~y disposed therebetween, annular brake actua-ting means mounted within said chamber in alignment with said pair of disc means for selective application of force to said inner disc as said outer disc makes contact with an interior wall of said housing to produce frictional contact between said pair of disc means, said improvement comprising: at least three cylindrical devices mounted to said housing to extend in an axial direction into said chamber at generally equally circumferentially spaced locations about said inner disc and said outer disc; each of said devices having biasing means mounted thereon which make contact with said inner and said outer discs tending to increase the distance therebetween; a disc retainer mounted on said device to produce a predetermined frictional contact therebetween which is greater than a maximum Eorce generated by said biasing means; means for en~aging said inner disc with said disc retainer to allow limi-ted axial movement of said inner disc without causing said disc retainer to move along said device; and said actuating means being capable of supplying sufficient ~0 force to said inner disc to overcome said predetermined frictional contact and said maximum force to position said disc re~ainer on said device to establish the location of - said 1imited axial movement of said inner disc within said chamber.
It is, therefore, an ob~ect o~ this invention to provide a reliable friction brake which employs a plurality o~ hydraulically cooled discs and includes Eeatures which provide means for initial testing of various components thereof and for ease of assembl~.
It is also an object to provide a friction brake o - the type described which can be more readily and inexpensively repaired should it be required.
These and other objects of the invention are provided in a preferred embodiment thereof which includes a friction brake for a wheel which has a hub and is mounted for rotation around a central axis on an axle spindle. A

backing plate is mounted about an inward portion of the spindle~ An annular hydraulic cylinder is removably secured to the backing plate and has a generally L-shaped cross section to provide a first cylindrical surface thereon adjacent the backing plate whlch has a predeter-mined diameter. A second cylindrical surface on the cylinder is remote from the backing plate and concentric with the Eirst surface and includes a diameter which is different from the predetermined diameter. An annular piston has an L-shaped cross section which is oppositely Griented with respect to the cylinder to be slidably received therein. A third surface on the piston is aligned with the first cylindrical surface and a fourth surface on the piston is aligned with the second cylindrical surface for respective sealed, sliding engagement therebetween. The piston and the cylinder define an operating chamber therebetween. There is provided means for selectively supplying hydraulic fluid to and removing it from the operating chamber to selectively position the piston relative to the cylinder.
A housing is mounted to the backing plate for sealed encirclement of the hub to define a cvoling fluid chamber. Non-rotating disc means are mounted relative to the housing for movement along the axis and rotating disc means are mounted relative to the hub for movement along the axis. The di~c means are located within the cooling fluid chamber and are aligned with each other and between the housing and the piston for ~rictional contact ~; therebetween for braking the wheel when the piston is positioned toward the housing.
Brief Description of the Drawin~s The present invention taken in conjunction with the invention described in Canadian patent application Serial No. 309,769 filed 22 August 1978 will be described in detail hereinbelow with the aid of the accompanying drawings, in which~
Figure l is a sectional side view o~ the preferred em-bodiment of the invention as generally seen along the line 1-1 in Figure 2~

Figure 2 is an elevated side view of the embodiment shown in Figure 1.

DescriPtion of the Preferred Embodiment As seen in Figures 1 and 2, a friction brake 10 is adapted to be installed on a spindle 12 of an axle to provide braking for a wheel 14 which is mounted for rotation about the spindle 12 and an axis 13 thereof. The wheel 14 includes a hub 16 and, in the preferred embodiment, is of the type which is driven by a drive axle 18 extending through the spindle 12. ~owever, it should be clear that the present invention can be employed just as effectively in a configuration wherein the wheel is mounted for free rotation about an axle.

The brake 10 is generally of the type which includes a hydraulic actuating means which is clesigned to apply pressure to a plurality of disc brakes which are continuously cooled by a hydraulic cooling system. A first set of the discs is non-rotatably supported relative to`the axle and a second set of discs, each of which is disposed between adjacent discs of the first set, is mounted for rotation with the wheel. When the operator desires to stop rotation of the wheel, hydraulic oil is provided to the hydraulic actuating means which, in turn, applies a force to the plurality of discs creating sufficient friction therebetween to stop rotation of the wheel about the axle.

The preferred brake 10 includes a backing plate 20 which extends generally perpendicular to the axis 13 and is mounted about an axially inward portion of the spindle 12.
Specifically, in the preferred embodiment, the backing plate 20 is mounted by a plurality of bolts 22 to a flanged portion 24 of the spindle 12. However, it should be clear that a similar backing plate could be welded to the spindle or mounted thereon by any other suitable means.

The backing plate 20 generally provides support for the remainder of the brake 10 and includes openings therethrough for hydraulic ac~uating oil and hydraulic oil which is directed through the brake for cooling of the discs. The actuating means 26 of the preferred brake 10 includes an annular cylinder 28 and an annular piston 30 which piston 30 is mounted for movement in an axial direction when the brakes are applied.

The annular cylinder 28 has a generally L~shaped cross section and is mounted with its base 32 against the backing plate 20. The cylinder 2~ is preferably mounted with four bolts 34 each of which extend through an opening 36 of the backing plate 20 and include a spring washer 38 which abuts the surface 40 of the backing plate 20. The significance of this configuration will be discussed further hereinbelow.

The annular cylinder 28 includes a pair of generally cylindrical surfaces 42, 44 which are respectively on a foot portion 43 and a leg portion 45 of the L-shaped cylinder 28 and are coa~ially aligned with the axis 13. The diameter of the cylindrical surface 42 is less than the diameter of the cylindrical surface 40 and, accordingly, the annular cylinder 28 includes a radially extending surface 46 there~etween.

The piston 3Q similarly is annular 2nd includes an L-shaped cross section having a foot portion 48 and a leg portion 50. However, the piston 30 is oppositely disposed from the cylinder 28 so that the foot portion 48 is generally aligned with and overlies the leg portion 45 of the cylinder and the leg portion 50 overlies and is generally aligned with the foot portion 43 of the cylinder. A generally cylindrical surface 52 of the leg portion 50 has an effective diameter atching the diameter of the surface 42 and a generally cylindrical surface 54 of the foot portion 48 has an effective diameter matching the diameter of the surface 44 o~ the cylinder. Piston sealing rings 56 are provided between each of the matching surfaces 52 and 42 and 54 and 46 to insure that the hydraulic chamber 58 between the cylinder 28 and piston 30 is effectively sealed. The introduction of hydraulic oil to the chamber 58 will thus cause the piston 30 to move in a direction as shown by the arrow A for the introduction of force to the discs.

As thus described, the generai configuration o~ the backing plate 20, cylinder 28 and piston 30 are similar to the configuration shown in United States Patent 3,832,770.
However, significantly, the configuration shown therein discloses that the cylinder should be integrally orrned as a portion of the backing plate rather than their being provided as separate elements~ The configuration of the present invention has the advantage of providing a separate cylinder-piston configuration which can be readily tested prior to installation remote from the spindle to insure its proper operation. This feat-lre is o~ particular advantage if after extensive use of the brake it is found that wear of the cylinder and/or piston requires one or both elements to be remachined or replaced. Accordingly, repair or replacement of the actuating means 26 can be accomplished without removal of the backing plate 20 or any need for its replace~ent due to failure of another element.

Furthert mounting the cylinder 28 to the backing plate 20 by bolts 34 which include a spring washer 38 allows the actuating means 26 to operate efficiently even if the backing plate 20 is subjected to slight distortions or warping during the operation of the axle. Distortion in the backing plate 20 will not be directly transmitted to the cylinder 28 which might impair braking efficiency.

The preferred actuating means 26 is also provided another feature not found in United States Patent 2,832,770 which is intended to improve its reliability. It is possible because of the large diameter of the piston-cylinder configuration for shock, vibration or other outside forces to act on the piston 30 to cause it to become cocked within the cylinder 28 so that it is no longer axially aligned with the axis 130 If the generally`mating cylindrical surfaces of the piston and the cylinder are provided with minimum clearance therebetween, it would be possible for the piston to become jammed within the cylinder, possibly impairing actuation. Therefore, the surfaces 52 and 54 of the annular piston 30, while having been previously described as generally cylindrical to match the adjacent surfaces of the cylinder 2~3, are in fact provided with a cross section which is slightly curved away from the adjacent surfaces of the cylinder 28 at opposite sides of each of the piston sealing rings 56. The surfaces S2 and 54 thus provide sufficient clearance between the piston 30 and the cylinder 28 to insure proper movement of the oiston 30 by the introduction of hydraulic fluid through the fitting 60 to the chamber 58 since there would be no binding between the piston 30 and the cylinder 28. In other words, the primary "contact"
between the piston 30 and Ihe cylinder 28 will remain at the sealing rings 56 throughout operation of the brake 10 even if some cocking of the piston were to exist prior to actuation of the bra~e. It should be noted that this feature might also be employed on piston-cylinder configurations such as those shown in United States Patents 3,580,369 and 3,584,708.

During initial installation of the brake 10, the backing plate 20, cylinder 28 and piston 30 are initially assembled and installed on the spindle 12 as described hereinaboveO To complete the formation of the bra~e 10, an outer 'nousing 62 and two sets of discs 64 and 66 are initially assembled on the hub 16. The outer housing 62 is adapted to be bolted by a plurality of bolts 68 to .the backing ~late 20 for sealed engagement therewith to gene.rally define a pair of chambers 70 and 72 therebetween which receive hydraulic fluid for cooling o:E the brake during operation. In the ~referred embodiment, cooling hydraulics are provided through an opening 73 in the backing plate 20 to provide the oil to the chamber 72 and cause il to flow around and through the discs o4 and 66 into the cl-amber 70. An outlet opening 71 is also provided through the backing plate 20 to allow the hydraulic oil ot exit from the chamber 70 to be returned to the hydraulic cooling system ~not shown) for eventual return to the chamber 72. ~It should be understood that the brake 10 might include an entirely self--~3-contained hydraulic cooling system which would have no external components. Movement of the discs would cause sufficient flow between the chambers 70 and 72 to adequately cool them to improve their efficiency during braking. To insure that the brake 10 is effectively sealed and that the cooling fluid is retained therein in either type of cooling system, seals 74 and 76 are respectively installed ~etween the outer housing 62 and the hu~ 16 and between the hub 1& and the spindle 12.

The plurality of friction discs 64 are disposed about the hub 16 in general alignment with the actuating means 26 and include a plurality of grooves 78 therein which mate with the bolts 68 to allow axial movement thereof but to prevent their rotation relative to the spindle 1~. The plurality of discs 66 are mounted directly to the hub 16 by having an interior diameter which is splined to match a splined region 80 of the hub 16 so that the discs 66 will rotate therewith about the a~is 13. Adjacent discs from the set of discs 64 and 66 are separated by a single disc from the other set to provide an array of alternating discs from each set. While the preferred embodiment therefore includes a plurality of discs as described hereinabove, it should be kept in mind that an e~fective brake can be provided which includes only one stationary disc and one rotating ~isc which are mounted for axial movement to produce friction therebetween upon movement o the actuating means 26.

Accordingly, as mentioned above, during initial installation the outer housing 62 is generally mounted about the hub 16 and the individual discs ~4 and 66 are a]ternatively positioned about the hub 16 prior to installation of the bolts 68. I~ has been found that this form of installation is preferred over a form of installation which might include full assembly of the brake 10 on the spindle 12 prior to mounting of the wheel 14 on the spindle 12 as appears would be required by the installations shown in United States Patents 3,580,369 and 3,584,70~ if a backing plate were to be permanently secured to the spindle. Mounting the wheel 14 on the spindle 12 with the brake 10 installed would be very difficult because of trouble which would be encountered when trying to align the discs 66 with the splined region 80. While this alignment problem is eliminated by generally mounting the above mentioned portions of the brake 10 on the hub 16, there still exists the problem of insuring that the discs ~6, which will generally hold the other elements in position, will remain on the splined region 80 as the outer housing 62 is being brought into contact with the backing plate 20 for final assembly. Accordingly, a circumferential groove 82 is formed in the splined region 80 and is adapted to receive a locking wire 8~ therein after the discs 66 are properly positioned on the hub 16. The locking wire 84 is simply wrapped about the hub 16 with its terminal ends twisted together to insure that it will not be dislodged from the groove 82. The wire 8Ll and groove 82 have no function other than during inst~llation and do not affect brake operation after the brake 10 is fully installed.

To further facilitate installation of the brake 10, one feature thereof includes the addition of ribs 85 to the interior of the housing 62. The ribs 85 generally extend axially toward the backing plate 20 and are located between the bolts 68. Although the installation instructions would specify the a~ount of torquing force to be applied to the bolts 68, it has been found that exceeding these limits could provide sufficient stress to the housing 62 to warp or deform it from its desired position relative the backing plate 20.
Therefore, the ribs 85 provide additional resistance to this type of deflection, even if the recommended limits are exceeded during instal.lation, to insure that the desired diMensions are maintained for proper operation of the bra~e 10 .

As thus explained, one forM of the brake 10 could be provided by simply including the elements described hereinabove. It would be possible to effectively prevent rotation of the wheel 1~ about the spindle 12 by the introducti`on of hydraulic fluid to the actuating means 26.

~3~
-~ --10--The resulting movement of the piston 30 in the ~irection A
would generate a force between the discs 6a and 66 as they are enkrapped between the piston 30 and the outer housing 620 The friction therebetween would be sufficient to stop rotation of the wheel 14 and would be generally uniform at all portions of the discs 64 and 66 even if the contact area on the outer housing 62 were not exactly perpendicular to the axis 13.
Since the preferred piston 30 includes curved surfaces 52 and 54, it would be able to apply proper braking force to the discs even if slightly tilted to conform to the angle of the contact area. Relieving the pressure within the actuating means 26 would allow the piston 30 to be repositioned away from the discs to again allow wheel rotation.

However, in the preferred installation, a s~lf-adjusting feature is provided in the form of a slack adjuster 86 which determines the relative spacing of the discs 64 during normal operation of the wheel 14 prior to ac:tuation of the brake. The slack adjuster 86 includes, in the preferred embodiment, three equally circumferentially spaced bolt elements 87 whlch are mounted to the outer housing 62 and adapted to extend therethrough into the chamber 72~ Each bolt ~7, only one of which will be described since they all function in an identical manner, has an inward portion 88 thereof which has a uniform and continuous cylindrical surface and receives thereon a wa5her 90, a spring 92, a spring retainer 94 and a di,c retainer 96. The washer, spring and spring retainer are free to move axially along the inward portion 88. However, the disc retainer 96 is a spring loaded collar device wnich is adapted for frictional enegagement with the portion 88, requiring in the preferred embodiment about 100 pounds force to overcome friction to allow it to slide along the partion 88. The outermost disc 64 includes a peripheral groove 98 therein adapted to partially encircle the portion 88 for abutting contact with the washer 90. The innermost disc 64 is 35 provided with a groove 100 at its outer periphery which is adapted to be received within a slot 102 in the disc retainer 96. The combined slot and sroove confisuration insures that there is s`ufficient engagement between the inner disc 64 and the disc retainer 96 throughout brake operation; in other words, to insure that slight radial movement of the disc relative the disc retainer 96 will not interfere with their engagement during bra.ke operation. Additionally, the inner disc 64 is provided sufficient surface area about the disc retainer 96 to provide adequate contact for the spring retainer 94 to prevent it from being ansularly displaced relative to the bolt 87..

Therefore, during operation of the slack adjuster 86 relative position is maintained between the inner and outer discs 64 by the combined action of the washer 90, spring 92 and the spring retainer 94 to cause them to be separated until the inner disc 6'1 makes abutting contact with the inner wall of the slot 102 of the disc retainer 96. The maxi~u~ Lorce exerted by the spring 92 is about 50-60 pounds so that there is insufficient force produced to cause the disc retainer 96 ~o slide along the portion 88. During brake operation, the piston 30 will be caused to move toward the discs 64 to make initial contact with the inward disc 64. The hydraulic actuating force is quite sufficient to easily overcome the force cxeated by the spring 92 so that the inner disc 64 is moved axially within the slot 102 as the spring retainer 94 compresses the spring 92. If no adjustment is required, axial force will be applied to the brake to generate frictional force and to prevent rotation of the hub 16. Release of the brakes will allow the spring 92 to reposition the inner disc 64 within the slot 102 as shown in Figure 1.

However, should there exist sufficient wear to the discs 66 or the discs 64, actuation would begin as described above, but full contact between the discs would not be possible prior to the inner disc 64 making contact with the outer wall of the slot 102. Continued movement of the piston 30 would easily overcome frictional engagement between the disc retainer 96 and the portion 88 so that the disc retainer 96 would be axially repositioned at that location which would allow contact between the discs. Release of the brake would again allow the spring to reposition the inner disc 6~ against the inner wall of the slot 102 preventing it from returning to its initial position. As a result, the movement of the disc retainer 96 along the portion 88 will establish the limiting positions for the inner disc 64 to prevent excessive movement of the disc during brake operation. Therefore, during normal operation the maximum movement of the inner disc 64 would be that distance required to move from one side of the slot 102 to the other side thereof.

While there has been shown and described hereinabove the preferred embodiment of the invention, it will now be obvious to those skilled in the art that changes and modifications may be made therein without departing from the claimed invention.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
An improved friction brake for a wheel which has a hub and is mounted for rotation about a central axis on an axle spindle, said brake being of the type which includes a housing mounted on an inward portion of said spindle to encircle said hub for sealed engagement therewith to define a sealed annular chamber about said hub and said spindle, a pair of disc means coaxially aligned with said axis and with each other and mounted within said chamber for movement along said axis, a first disc means of said pair being non-rotatable and mounted relative to said housing and a second disc means of said pair being rotatable and mounted relative to said hub, said first disc means including an outer disc and an inner disc with the remainder of said pair of disc means axially disposed therebetween, annular brake actuating means mounted within said chamber in alignment with said pair of disc means for selective application of force to said inner disc as said outer disc makes contact with an interior wall of said housing to produce frictional contact between said pair of disc means, said improvement comprising:
at least three cylindrical devices mounted to said housing to extend in an axial direction into said chamber at generally equally circumferentially spaced locations about said inner disc and said outer disc;
each of said devices having biasing means mounted thereon which make contact with said inner and said outer discs tending to increase the distance therebetween;
a disc retainer mounted on said device to produce a predetermined frictional contact therebetween which is greater than a maximum force generated by said biasing means;
means for engaging said inner disc with said disc retainer to allow limited axial movement of said inner disc without causing said disc retainer to move along said device; and said actuating means being capable of supplying sufficient force to said inner disc to overcome said predetermined frictional contact and said maximum force to position said disc retainer on said device to establish the location of said limited axial movement of said inner disc within said chamber.